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Q  P34  .  F59  A  textbook  of  physio 


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A    TEXTBOOK    OF 

PHYSIOLOGY 


BY 

MARTIN    FLACK 

C.B.E.,  M.B.,  B.Ch.(Oxon.) 

RESEARCH    STAFF,    DEPARTMENT    OF    APPLIED    PHYSIOLOGY,    MEDICAL    RESEARCH 

COMMITTEE  ;    LATE    LECTURER    IN    PHYSIOLOGY    AND    CHEMICAL    PATHOLOGY 

LONDON    HOSPITAL    MEDICAL    COLLEGE  ; 

AND 

LEONARD    HILL 

M.B.,  F.R.S. 

DIRECTOR    OF    APPLIED    PHYSIOLOGY    DEPARTMENT    MEDICAL    RESEARCH    COMMITTEE 
LATE    PROFESSOR    IN    PHYSIOLOGY    (LONDON    UNIVERSITY)    LONDON 
HOSPITAL    MEDICAL    COLLEGE 


ILLUSTRATED 


NEW  YORK 
LONGMANS,     GREEN     &     CO. 
LONDON:    EDWARD    ARNOLD 
1919 

[.4//  ri^/its  resefve<i\ 


Printed  in  Great  Britain 


IMIEFACE 

The  preparati(ni  of  this  textbook  was  began  before  the  war  at  a 
time  when  we  were  both  actively  engaged  in  teaching  at  the  London 
Hospital  Medical  College,  and  when  it  war.  considered  that  we  might 
with  advantage  put  together  and  harmonize  the  physiology  we  were 
teaching.  In  order  to  secure  uniformity  of  style,  each  ocction  has 
been  written  in  the  f^.rst  instance  by  the  same  hand,  and  then  finished 
in  its  present  form  by  careful  collaboration  between  the  two  of  us. 

While  physiological  research  has  been  confined  in  many  directions, 
progress  along  certain  lines  has  been  especially  remarkable  since  the 
outbreak  of  war.  We  have  endeavoured  to  take  these  recent  ad- 
vances into  consideration,  before  completing  the  work,  in  spite  of  the 
great  difficulties  under  which  we.  in  common  with  all  jihysiologists, 
have  laboured. 

The  book  has  been  written  with  the  primary  object  of  giving  to 
the  student  in  an  easily  understandable  form  the  fundamental  facts 
and  theories  of  physiology,  bearing  in  mind  the  limitations  necessary 
in  a  student's  textboolc.  We  have  followed  the  example  of  Michael 
Foster,  and  have  avoided  burdening  the  students  memory  with  the 
names  of  authorities.  \\  hen  ready  to  lea^■e  the  narrow  scoi)e  of  a 
textl)0()k  for  the  wide  realms  of  independent  thought,  those  who 
wish  to  extend  their  physiological  knowledge  can  easily  fi.nd  their 
way  into  the  literature  of  research  l)y  means  of  the  various  archives  and 
journals  of  physiology. 

Although  written  primarily  to  meet  the  requirements  of  the 
medical  student,  it  is  hoped  that,  in  view  of  the  ever -increasing 
importance  of  the  proper  application  of  j^hysiology  to  general  medi- 
cine, the  work  may  also  prove  of  value  to  the  general  ])rac -itioner. 

For  the  use  of  illustrations  we  are  indebted  to  Dr.  J.  Barcroft, 
F.R.S.;    Professor   W.   M.  Bavliss,   F.R.S.:  Professor  W.    B.  Canno.i: 


vi  PREP^ACE 

Professor  J.  M.  Cowan;  Professor  V.  Dahlgren ;  Professor  W.  E. 
Dixon,  F.R.S. ;  Dr.  Robert  Hutchison  ;  Professor  A.  Keith,  F.R.S. ; 
Professor  J.  N.  Langley,  F.R.S.;  Dr.  Thomas  Lewis,  F.R.S.;  Dr. 
F.  W.  Mott,  F.R.S.;  Professor  F.  G.  Parsons  and  Professor  William 
Wright;  Dr.  M.  S.  Pemhrey;  Sir  E.  A.  Sharpey  Schafer,  F.R.S.; 
Professor  C.  S.  Sherrington,  F.R.S.;  Sir  J.  Purves  Stewart,  K.C.M.G.; 
Professor  Swale  Vincent;  and  Dr.  A,  D.  Waller,  F.R.S.  Also  to  the 
Editors  of  the  Jovrnal  of  Physiology,  the  Quarterly  Journal  of  Experi- 
mental Physiology,  and  Brain  ;  to  the  Secretary  of  the  Royal  Society; 
and  to  the  following  publishers  for  permission  to  use  such  illustrations: 
Messrs.  Longmans,  Green  and  Co. ;  J.  and  A.  C-hurchill ;  Constable 
and  Co.,  Ltd.;  Macmillan  and  Co.,  Ltd.;  John  Wright  and  Sons,  Ltd.; 
the  .Delegates  of  the  Clarendon  Press;  the  Syndics  of  the  Cambridge 
University  Press;  Yale  L^niversity  Press;  Oxford  Medical  Publications; 

Shaw  and  Sons. 

MARTIN  FLACK. 
LEONARD  HILL. 


CONTEXTS 


BOOK  I.— GENERAL  PHYSlOLOfiY 

CHAl'TER 

I.    BIOLOiUCAL   INTRODUCTION 
ir.    THE   CELL  -  -    "  -      ' 

III.  PHYSICO-CHEMICAL   IXTKODUCTION 

IV.  THE   CHEMICAL   COMPOSITION    OF   THE   BODY 

V.  THE   PROTEINS      ----- 

VL  FATS    AND    LIPOIDS  .  .  -  - 

VIL  THE    CARBOHYDRATES       -  -  -  - 

VIII.  ENZYMES    OR    FERMENTS 


I 

8 
17 
33 
39 
53 
59 
68 


BOOK  II.— THE  BLOOD 


IX.  GENERAL  ACCOUNT  OF  THE  BLOOD 
X.  THE  PLASMA 

XI.  THE  CORPUSCLES  OF  THE  BLOOD 
XII.  THE  CLOTTING  OF  BLOOD 

XIII.  H/EMOLY'SIS    AND    IMMUNITY 

XIV.  THE    TESTS    FOR    BLOOD 


75 

82 
86 
101 
105 
112 


BOOK  III.— THE  CIRCULATION  OF  THE  BODY  FLUIDS 

XV.    THE  MECHANISM    OF    TRANSPORT  -  -  -  -  -115 

XVI.    THE  PHYSIOLOGY    OF    THE    HEART                -----  127 

XVII.    THE  COURSE    OF    THE    CIRCULATION    IN    MAMMALS                '                   -                   -  142 

XVIII.    THE  NUTRITION    OF   THE    HEART                   .                  .                  .                  -                  .  158 

XIX.    THE  CARDIAC    NERVES       -------  171 

XX.    THE  PHYSICAL   FACTORS    OF   THE   CIRCULATION    -                  -                  -                  -  179 

XXI.    THE  ARTERIAL   PRESSURE                 -.-..-  186 

XXn.    THE  EFFECT    OF    POSTURE                ------  194 

XXIII.    THE  VELOCITY    OP    BLOOD-FLOW                     -                   .                   .                   -                   .  203 

XXIV.    THE  PULSE  -  -  -  -  -  -  -  -211 

XXV.    THE  CAPILLARY    CIRCULATION       ------  218 

XXVI.    THE  PRESSURE    AND    VELOCITY    OF    THE    BLOOD    IN    THE    VEINS  -                   -  225 

XXVIL    THE  VASO-MOTOR   NERVES                ------  229 

XXVIII.    THE  CIRCULATION   IX    SPECIAL    PARTS       -----  236 

XXIX.  LY.MPjr    ---------  250 


BOOK  IV.— THE  PHYSIOLOGY  OF  RESPIRATION 

XXX.    GENERAL    ACCOUNT    OF   RESPIRATION         -                  -  -  . 

XXXI.    THE    MECHANIS-^I    OF    RESPIRATION'               -                   -  .  - 

XXXII.    THE    MECHANICS    OF    BREATHING                  -                  .  -  - 

XXXIII.  THE    REGULATION    OF    BREATHING                 -                   -  .  . 

XXXIV.  THE    EFFECTS    OF    EXCESS    OF    CARBON    DIOXIDE 

XXXV.    THE    PRINCIPLES    OF    VENTILATION                .                   .  -  . 

XXXVI.    .METHODS    OF    D  ETEPailNING    RESPIRATORY    EXCHANGE  - 


276 
284 
289 
302 
312 
317 


BOOK  V. -GENERAL  METABOLISM  AND  DIETETICS 

XXXVII.  GENERAL   METABOLISM    AND    DIETETICS   -  -  -  - 

-XXXVIII.  METABOLISM   DURING    STARVATION              -  .  -  . 

X.XXIX.  METABOLISM    UNDER    VARYING    CONDITIONS 

XL.  GENERAL   DIETETICS  ------ 

XLL  THE   CHIEF   FOODSTUFFS                    -                  .  .  -  . 

XLII.  DIET    UNDER    VARIOUS    CONDITIONS             -  .  -  - 

XLIII.  SPECIAL   DIETETIC    .METHODS,    ETC.  -  -  - 

vii 


325 
333 
341 
344 
353 
356 
304 


Vlll 


CONTENTS 


I'.OUK  VI.-THK  rilOCKSSKS  ( )J'  DKiKS'NOM 


(  IIAI'IKI! 

XI.IV.  TIIU    MKIIISMSM     III-    Si:i   KKTION,    ETC.      • 

XLV.  DK;  I'.STION    IN    TlIK    .Mlll'TJl 

Xl.Vl.  DUJKSTION    ]X    THE    STOMACH 

XI.Vll.  DICESTION    IX    THE    SMAI.I.    JXTESTIXE       - 

XI.VIII.  'I'llFC    l,AK(!E    IXTESTINE 

XMX.  THK    .MECHAXICAl,    FA(  'I'OIIS    ol'    DKJ  ES'l  I(  )N 


PAfiE 

3(;7 

:j7I 

■  :{7i) 

:?!)! 

402 
40)) 


BOOK   VII.     SI'KCIAL  .M  KTABOJ.ISMS 

L.  IIIK  ,\l  I'M' \)i()l.lSM    (II-     I'liO'l'KlN      -  -  -  - 

1,1.  THK  .METAJtOI.lSM    OF    CAKBOH  VUKATE      - 

LI  I.  THE  METABOLISM    OF    FAT 

LIU.  THE  METABOLISM    OF    NUCLEIN    -  .  -  - 

I. IV.  THE  Fl'NCTIOXS    OF    THE    LIVER    AM)    SI'LEFX       - 


421 

42() 
43(i 

44:j 

447 


BOOK  Vlll.- THE   FL'NCTIOXS  OF  THK  KIDXKV 


I.V.    THE    LKIXE 
L\I.    T][E    SECl!ETIO\    OF    mUXE 


4.-):5 
47:{ 


BOOK  IX.— THE  FUNCTIONS  OF  THE  SKIN  AND  THE  BODY 
TEMPEBATURE 

LVII.    THE    FLNCTIONS    OF    THE    SKIN      -  -  .  -  - 

LVIIt.    THE    TEMI'EHA'n;i!E    OF    T}IE    HOI)^  .... 


485 

4!)2 


BOOK  X.— THE  FUNCTIONS  OF  TH  F   Dl'ClLESS  (iLANDS 

r.IX.    INTERNAL    SECIIETIONS  ..... 


")0:j 


BOOK  XL— THE  TISSUE  OF  .MOTION 

LX.    THE    MECHANISM    OF    MOVEMENT                       ..-■..  ,-)2.'j 

LXI.    THE    STRUCTURE    AND    PHYSICAL    I'lHIl'EHTlES    OF    .MFS(  i.K                -                   -  .")?0 

LXII.    THE    CONTRACTION    OF    MUSCLE                          .....  .");}<» 

I.XIII.    THE   PRODUCTION    OF   HEAT   AND    THE   (HEMIC  AI.   CHANilES    IN    MT'S(  1,E       -  7l7)-2 

lAIV.     ANIMAL    Ef.ECTIUCITV           .......  ."i,")!) 


BOOK  XU.-THE  NEKV(JUS  SYSTE.M 

LXV.  ']HE    NElltoN  ...... 

LX\1.  THE    PHVSIOLOG'^'    OF    THE    NEKVE-FIBRE 

LXVII.  THE    RECEPTOR    MECHANISMS  -CUTANEOUS    SENSATIONS 

LXVIII.  TASTE    AND    SMELL  .  .  .  .  - 

LXIX.  VISION       ..-.--. 

LXX.  HEARING  ...... 

LXXI.  THE    PROPKIO CEPTn  E    >1E(HANISM 

I.XXII.  THE    SPINAL    (OLD  .  .  .  .  . 

I.XXIII.  THE    HIiAJN  ...... 

LXXIV.  SLEEP        ....... 

LXXV.  SOUND    PRODUCTION    AND    SPEEt  H 

LXXVI.  THE    AUTONO.MIC    NERVOUS    SYSTEM 


;•)()!) 

57!) 
58.5 
593 
59!) 
()4;5 
(i.-4 
(5(52 
685 
735 
73!t 
74S 


BOOK  XIII.— REPRODUCTION 

LXXVII.    OROWTH    AND    REPRODUCTION       - 

INDEX      .----- 


755 

785 


A    TEXTBOOK    OF    PHYSIOLOGY 

BOOK  I 
GENERAL    PHYSIOLOGY 

CHAPTER    I 

BIOLOGICAL  INTRODUCTION 

Living  in  the  stagnant  water  of  most  ditches  is  the  tiny  animalcule 
known  as  the  Amoeba  (Fig.  1).  If  a  drop  of  water  containing  this  little 
•organism  be  placed  on  a  slide  beneath  the  lens  of  a  microscope,  exami- 


lU.V, 


'  6'  .'^■'.''o ■::&>.'/ 
■.•v..°'v'';.-'(5'*'.-i-.-  i 

"•X©.  ''■.■?•  i-:-'   ; 


;*.--. ...  o",  *••; 


"J 


?yr 


n. 


c.v. 


Fig.  1. — Amceba  Proteus,  an  Organism  consisting  of  a  Single  Naked  Cell. 
X  280.     (Redrawn  after  Sedgwick  and  Wilson.) 

iV,  Nucleus;  v).v.,  water- vacuoles;  c.v.,  contractile  vacuole; /.),■.,  food  vacuole. 

nation  shows  that  the  tiny  animal  consists  of  a  mass  of  semi-fluid 
material  known  as  protoplasm.  Scattered  in  this  semi-fluid  mass 
<are  a  number  of  granules;  at  one  spot  theie  is  an  empty  space,  the  con- 
tractile vacuole ;  while  in  the  centre  is  a  round,  more  highly  specialized 

1 


2  A  TEXTBOOK  OF  L>HV810LO(iY 

structure,  the  nucleus.  01)servation  shows  that  the  ania-ha  gradually 
moves  about  in  the  fluid  — here  thrusting  out  one  little  foot-like  mass, 
or  pseudopodium,  there  retracting  another,  and  thus  ju-ogressing. 
If  it  be  touched  in  an}-  way,  the  pseudojiodia  are  withdrawn.  The 
organism  thus  responds  to  a  stimulus,  and  possesses  what  is  termed 
irritability.  Should  there,  perchance,  be  any  food  material  present, 
such  as  algse,  it  may  be  seen  how,  by  means  of  the  pseudopodia,  the 
food  is  surrounded  and  gradually  absorbed  into  the  ])rotoi)lasmic 
mass.  This  food  is  gi-adually  broken  down,  digested,  and  assimilated, 
any  indigestiljle  or  waste  material  being  latet  extruded  from  the 
surface.  From  time  to  time  the  vacuole  contracts,  voiding  by  this 
process  waste  products  of  the  animal's  activity.  Finally,  under 
favourable  circumstances,  the  little  animal  may  be  seen  to  grow,  and 
eventually  divide  into  two  organisms,  thereby  reproducing  itself  (Fig.  2). 


^;i^j 


K_y 


Fig.  2. — Successive  C'hais(ges  exhibited  by  an  Amceba.     (Vcrvvorn  from  "Quain's 
*  Anatomy.") 


The  amoeba  is  a  type  of  what  is  known  as  a  unicellular  organism; 
it  consists  of  but  one  unit  or  cell.  That  one  cell  performs  all  the 
life-processes.  All  organisms,  however,  are  not  so  simjDle  in  structure; 
the  higher  forms  of  life  consist  of  a  great  number  of  cells,  and  are 
therefore  termed  multicelli  lar.  The  multicellular  organisms  have 
been  evolved  from  the  simpler  unicellular  one — in  some  cases  through 
an  almost  infinite  number  of  stages.  Past  history,  or  phylogeny, 
as  shown  by  fossil  remains,  indicates  that,  as  the  ages  passed, 
animals  gradually  became  more  and  more  complex  in  structure. 
Some  of  the  simpler  forms  have  continued  to  exist,  others  have  become 
lost.  So,  too,  of  the  evolved  multicellular  forms — many  continue 
with  us,  but  some  have  passed  away.  The  abilit}"  of  an  organism  to 
maintain  its  life  depends  upon  its  power  to  adapt  itself  to  existing 
conditions — upon  its  being  efticient.  The  multicellular  organism 
developed  its  efficiency  over  the  unicellular  organism  along  two  lines: 


BIOLOGICAL  INTRODUCTION  3 

first,  b}'  forming  a  colony  of  individuals;  secondly,  by  instituting  a 
differentiation  of  cells,  with  a  division  of  labour. 

In  the  first  method,  the  formation  of  a  colony  of  similar  cells, 
the  cells,  like  the  amoeba,  still  carry  out  all  the  life-functions  indi- 
vidually; each  cell  lives  alone.  The  number  of  cells  in  such  a  colon}' 
is  not  limited;  it  is  but  a  group  of  individuals,  not  one  individual. 
Certain  protozoa  and  protophyta  exist  as  colonies.  An  example 
is  Carchesium  (Fig.  3). 

In  a  little  more  advanced  order  of  colonization  the  number  of 
members  of  the  colony  is  limited  and  kept  constant,  death  of  a  member 
being  followed  b}-  replacement.  Such  a  colony  is  generally  ensheathed 
by  a  wall,  so  that  the  cells  have  no  independent  movement.  With 
these  limitations,  each  cell  of  the  colony  performs  its  vital  functions 
independently- .     An  example  of  such  a  colony  is  Gonium  (Fig.  4). 


Fig.  3. — A  Colony  of  Individuals  of  Carchesium,  ATT.iCHED  by  a  Common  Branch- 
ing Stalk,  showing  /,  the  Contractile  Stalk  of  One  Individual.  '  (Reray, 
I'cdrivvn  after  Dahlgron  and  Kepner.) 


In  the  second  method  a  differentiation  of  cells,  with  a  division  of 

labour,  takes  place.     Here  the  colony  becomes  the  individual not  a 

group  of  individuals.  The  members  of  this  group  range  from  a 
simple  multicellular  organism  to  man.  Volvox  globator  (Ficr.  5) 
represents  the  beginning  of  this  type  of  organization.  In  it  certain 
cells  become  differentiated  for  the  main  function  of  life — reproduction 
— each  of  the  other  cells  performing  all  the  other  functions. 

In  the  higher  organizations  certain  cells  become  segregated  and 
form  a  tissue— that  is,  a  group  of  cells  performing  more  or  less  one 
definite  function.  Later  the  differentiated  tissues  become  grouped 
into  organs,  each  having  some  particular  function.  Nevertheless, 
each  cell  remains  a  separate  living  unit,  having  its  own  share  of  work 
to  perform. 

The  developmental  history — ontogeny — of  the  multicellular  organ- 


A  TEXTBOOK  Ol'    PHYSIOLOOY 


1  u;     4. — GoNiirM  Pectokale,   showiisx,   the  Individuals.     (From   Tahlgren  and 
Kepnor,  after  Stern.) 


Fig.  5. — Volvox  Globatoe,  a  Colony  of  Cells  in  which  All  the  Cells  aee  con- 

EINED  TO  THE  SuEFACE  OF  THE  SpHEEE,  LEAVING  A  CaVITY  InTEEIOELY.       (From 

Dahlgren  and  Kepner,  after  J.  H.  Emerton.) 

The  cells  are  united  by  protoplasmic  strands  radiating  from  each  cell.     The  dif- 
ferentiated cells,  or  ova,  are  shaded  dark. 


BIOLOGICAL  INTRODUCTION  5 

isms  confirms  the  evidence  of  the  past  history,  or  phytogeny.  Each 
multicelhilar  organism  develops  from  a  single  fertilized  egg,  or  oosperm. 

The  fertilized  cell  at  first  divides,  and  divides  again  to  form  many 
similar  cells.  These  cells  then  become  differentiated  into  various 
tissues,  which  eventually  become  grouped  to  form  different  organs 
(p.  773).  In  the  course  of  development  a  three-layer  blastoderm 
is  formed. 

From  the  outer  laj'er — ectoderm — chiefl}^  the  epithelial  protective 
and  nervous  tissues  are  developed;  from  the  middle  layer— mesoderm 
— the  supporting  and  muscular  tissues;  from  the  inner — endoderm — 
the  respiratory  and  alimentary  tissues. 

By  the  name  of  epithelium  is  designated  the  tissue  lining  the 
outer  and  inner  surfaces  of  the  body.  Occupying  this  position,  its 
main  function  is  that  of  transferring  material  from  the  surfaces  to 
the  tissues  within.  It  also  plays  a  part  in  protecting  the  underlying 
organs,  and  in  receiving  stimuli  and  transforming  these  into  sensory 
nerve  impulses.  From  it,  also,  the  glandular  structures  of  the  body 
are  developed — e.g.,  salivary  glands,  glands  of  stomach,  intestine,  etc. 

The  supporting  and  connective  tissues  are  developed  to  give 
rigidity  and  tensile  strength  to  protoplasm,  and  thus  enable  the  mul- 
ticellular organism  to  preserve  a  definite  form.  For  these  purposes 
fibres,  plates,  and  such  massive  structures  as  the  bones,  are  formed. 
The  ligamentum  nuchse  of  the  ox  affords  an  excellent  example  of 
tensile  strength,  while  the  shells  of  molluscs  and  cartilaginous  and 
bony  structures  testify  to  the  great  rigidity  which  may  be  developed. 
Cells  of  like  origin  may  also  act  as  a  storehouse  of  food  material — ■ 
e.g.,  fat. 

The  muscular  tissue  has  become  developed,  not  only  to  move  the 
organism  from  place  to  place,  but  also  to  assist  in  the  internal  opera- 
tions of  the  stationary  organism — for  example,  the  heart,  cilia,  etc. 
Its  essential  property  is  the  power  of  contraction. 

By  a  combination  of  thes3  three  tissues,  epithelial,  connective, 
and  muscular,  the  outer  covaring  parts,  or  integument,  of  the  body  is 
formed.  One  of  the  chief  functions  of  this  integumsnt  i^  to  protect 
the  expovsed  outer  parts  of  the  body  from  dangers  to  which  it  is  sub- 
jected, whether  the  animal  live  in  the  water  or  in  the  air.  This  it 
can  do  both  mechanically  and  by  the  production  of  means  of  defence 
— e.g.,  poison.  The  integument  possesses  also  lubricating  and  cleans- 
ing powers.  Sometimes,  too,  it  has  the  power  to  produce  attractive 
or  repulsive  odours,  to  prepare  adhesive  material,  or  to  spin. 

Examples  of  mechanical  protection  are  seen  in  the  stiff  fibres 
developed  by  many  lower  animals — e.g.,  the  turbellarian  worms,  to 
protect  against  undue  pressure ;  the  cuticle  of  the  earthworm ;  the 
carapace  of  the  lobster  and  the  shell  of  the  tortoise;  the  scales  of 
fishes  and  of  birds'  legs;  the  feathers  of  birds  and  the  hair  of  animals; 
the  outer  covering  of  the  human  skin  generally,  and  in  particular  the 
thickened  areas  of  the  palms  of  the  hands  and  soles  of  the  feet. 

Various  examples  of  offensive  protection  may  also  be  given.  Formed 
within  the  cell   are  the  trichocyst  of  paramoecium,  the  rhabdites  or 


C  A  TEXTBOOK  OF  PHYSIOLOGY 

stylets  of  the  turbellarian  worms,  the  stings  of  the  nettle  colls  of  hydra. 
Built  by  ((lis  are  the  stings  of  bees  and  wasps,  the  poison  hairs  in  the 
larva?  of  some  moths,  the  ])()ison  glands  of  some  spiders,  the  stinging 
spine  of  the  weaver-fish  and  of  the  whip-ray,  the  weak  poison  of  the 
]tectoral  fin  of  the  cat-fish,  the  spine  of  the  porcupine,  the  claws  of 
the  higher  animals,  and  the  nail  of  man. 

The  integument  may  provide  lubricating  material  either  all  over 
the  body  surface  or  onl}'  in  special  areas.  The  lubricant  material 
may  at  the  same  time  serve  additional  functions-^for  examjile,  as  a 
preservative  from  water,  as  a  cleanser,  or  as  a  food-gatherer,  and  so 
forth.  The  lubricating  material  may  be  slimy  (mucus),  oily,  or  watery, 
in  nature. 

The  mucus  provided  by  certain  of  the  clams  serves  the  purpose  of 
lubricating,  and  also  of  removing  dust  and  aiding  the  collection  of 
food.  The  slime  produced  by  the  earthworm  serves  the  double  purpose 
of  lubricating  the  animal  and  of  preparing  its  dwelling-place.  The 
mucus  of  the  salivary  glands  of  the  mammal  and  of  the  mucous  cells 
lining  the  alimentary  tract  is  both  lubricant  and  protective. 

The  second  form  of  lubricating  material,  that  of  an  oily  nature, 
is  found  in  the  higher  animals  (birds  and  mammals).  It  is  a  protec- 
tion against  both  the  drying  of  the  skin  and  the  wetting  of  the  feathers, 
hair,  or  skin.  Such  a  material  is  formed  in  the  oil  glands,  b}'  which 
birds  oil  their  feathers,  and  in  the  sebaceous  glands,  by  which  the 
hairs  and  skin  of  mammals  are  kept  greased.  Sometimes  these  oils 
possess  a  distinctive  scent,  either  repulsive  or  agreeable;  such  is  the 
case,  for  example,  in  the  musk  rat,  musk  ox,  and  the  skunk. 

The  watery  (serous)  form  of  secretion  is  comparatively  rare. 
Possibly  the  lachrymal  glands  moistening  the  eyes  of  mammals,  and 
the  sweat  glands  moistening  the  skin,  may  be  grouped  here,  as  well 
as  the  secretion  which  lubricates  surfaces  of  joints,  the  synovial  fluid. 
By  the  evaporation  of  sweat  the  body  is  cooled. 

Among  the  lower  animals  an  extremely  adhesive  fluid  is  sometimes 
l^rodviced,  which  enables  them  with  the  aid  of  a  sucker  or  pad  to  stick 
to  surfaces — e.g.,  that  of  the  head  of  the  leech  and  the  legs  of  beetles. 
In  other  cases  the  adhesive  fliiid  hardens  into  a  thread;  thus  the 
cocoons  are  formed  by  the  spinning  glands  of  the  larvse  of  moths 
(silkworm). 

Many  of  the  lower  animals  also  possess  odour-producing  glands 
— e.g.,  the  skunk;  a  well  known  example  also  is  the  so-called  stink-pot 
turtle.  Other  reptiles — for  example,  the  American  toad  (Bufo) — 
produce  an  extremely  offensive  fluid.  The  secretion  of  Bufo  is  partly 
mucous,  partly  serous,  and  it  is  said  to  be  poisonous.  But  it  is  among 
the  invertebrates  that  this  power  of  producing  offensive  and  attractive 
odours,  as  judged  by  man,  has  been  reduced  to  a  fine  art.  Various 
butterflies  produce  distinctly  j)leasant  odours.  Such  odoriferous 
glands  are  situated  in  various  parts  of  the  body  or  wings. 

But  besides  rendering  themselves  efficient  in  this  direction,  the 
multicellular  organisms  have  developed  other  systems  of  tissues,  well 
adapted  to  meet  the  conditions  under  which  the  animals  live.     With 


BIOLOGICAL  INTRODUCTION  7 

the  division  of  labour  there  is  elaborated  [a)  an  alimentary  system, 
by  which  the  necessary  foodstuffs  are  taken  into  the  organism  and 
reduced  to  a  proper  state  for  absorption;  (6)  a  respiratory  system, 
by  which  the  oxygen  necessary  for  the  cell  processes  is  introduced, 
-and  the  carbon  dioxide  produced  by  these  processes  eliminated; 
(c)  a  transport  and  circulatory  s^^stem,  b}'  which  these  necessaries 
are  conveyed  to  all  the  body  cells  to  supply  their  needs,  and  the 
laroducts  of  cell  activity  conveyed  away  for  excretion  either  by  the 
respiratory  mechanism  or  by  (d)  a  specially  developed  excretory 
.system. 

Finally  there  remain  two  special  systems — the  nervous  and  the 
reproductive.  The  nervous  sj^stem  serves  to  put  the  organism  into 
communication  and  correlation  with  outer  chemical,  physical,  and 
mechanical  conditions.  It  does  this  by  its  receptor,  conductor,  and 
effector  functions.  It  is  irritable,  and  receives  a  stimulus  either 
directly  or  indirectly,  conducts  the  stimulus  as  a  nerve  impulse,  dis- 
charges it  on  some  other  cell  or  cells,  and  the  e  produces  its  effect. 
The  system  is  primarily  intended  for  communication  between  parts 
of  the  body  more  or  less  widely  separated;  in  the  higher  animals  it 
becomes  an  extremely  complicated  system,  and  according  to  its  degree 
of  comj)lexity  and  the  manifold  functions  it  perfo:-ms,  so  is  the 
organism  classed  by  man  in  the  ladder  of  life.  Man,  placed  by  himself 
at  the  top  of  the  ladder,  has  the  most  complicated  and  most  highly 
developed  nervous  system.  To  the  reproductive  system  is  assigned 
the  highly  important  function  of  maintaining  the  particular  species 
of  the  organism.  In  the  multicellular  organism,  the  cells  other  than 
the  reproductive  cells  perish  after  a  longer  or  shorter  period  of  exist- 
ence. But  the  reproductive  cells,  under  appropriate  conditions, 
give  rise  to  fresh  individuals,  thereby  perpetuating  an  unbroken  chain 
of  living  cells. 

Physiology  is  the  science  which  treats  of  the  normal  functions 
of  these  various  systems. 


CHAPTER  II 

THE  CELL 

During  the  latter  part  of  the  seventeenth  century  the  simple  micro- 
scopes of  the  day  demonstrated  that  plants  were  composed  of  small 
box-like  spaces  surrounded  with  a  distinct  wall,  and  filled  with  lic^uid. 
The  name  of  cell  was  given  to  these.  In  1839  Schwann  put  forward 
the  theory  that  the  animal  body  was  built  of  cells.  The  identity  of 
];)rotoplasm  in  all  forms  of  life,  plant  and  animal,  was  established,  and 
the  cell  defined  as  a  nucleated  mass  of  protoplasm.  The  cell  may 
be  regarded  as  a  working  unit  of  protoplasm. 

The  body  of  a  cell  consists  of  a  substance  called  protoplasm  or  cyto- 
plasm (Fig.  6).  In  the  young  living  egg  cell  (such  as  echinoderm  ova), 
the  structure  appears  homogeneous,  like  egg  white;  while  in  older 
cells  it  appears  alveolar  or  reticular.  To  bring  structures  into  view,^ 
and  to  enable  thin  sections  of  organs  to  be  cut,  fixing  and  staining 
reagents  are  used.  The  reagents  which  are  used  to  fix  and  harden 
tissues  for  microscopical  examination,  such  as  alcohol,  a  saturated 
solution  of  mercuric  chloride,  etc.,  coagulate  protoplasm  and  j)roduce 
thread-like  and  granular  precipitates  in  cells  —  artefacts  —  which 
often  produce  appearances  of  structure  not  existing  in  the  living  cells. 
Svich  granules  and  fibres  apjDcar  in  homogeneous  solutions  of  egg  white 
or  peptone  when  treated  with  hardening  reagents.  We  must  not 
draw  conclusions  as  to  cell  structure  without  comparing  the  fixed  with 
the  living  cell.  The  same  method  of  hardening — i.e.,  the  same  chemical 
process — can,  however,  be  justly  used  to  compare  the  structure  of 
normal  with  that  of  abnormal  organs.  Reagents  can  also  be  used 
to  investigate  the  chemistry  of  the  cells ;  to  identify  in  them  by  different 
staining  reactions  fat,  glycogen,  iron,  potassium,  etc.  This  is  a 
valuable  method  of  microscopical  studj\  The  essential  structure  of 
a  living  cell  appears  to  be  a  homogeneous  fluid  material  studded  with 
a  large  number  of  minute  granules  (Fig.  7).  Between  these  two  phases, 
granule  and  fluid,  physico-chemical  changes  take  place  which  manifest 
themselves  in  the  life  of  the  cell.  The  foam  structure  of  protoplasm 
can  be  closely  imitated  by  rubbing  up  oil  with  potash  or  sugar  into  a 
very  finely  divided  paste.  A  drop  of  this  is  jDut  into  a  drop  of  wat^r 
on  a  microscopic  slide.  The  water  is  attracted  h\  the  osmotic  pressure 
of  the  potash  or  sugar  and  produces  the  foam.  Radium  bromide  powder 
dropped  into  a  gelatin  and  broth  medium  produces  cell -like  structures 
which  increase  in  size  and  divide,  multiiDlying,  apparently,  like  a  living 
organism.     The  radium  gives  off  an  emanation,  the  product  of  its. 

8 


THE  CELL 


9 


atomic  energy,  and  this  is  accompanied  by  heat.  The  emanation 
coagulates  the  protein  and  decomposes  water  into  oxygen  and  hydrogen 
producing  the  "  cells,"  really  bubbles  of  gas  surrounded  by  a  coagulum. 
As  the  gaseous  emanation  continues  to  form,  "  cells  "  grow — i.e., 
the  bubbles  bulge  out,  burst,  and  form  new  bubbles.  There  is  no 
production  of  life  in  these  phenomena.  They  are  of  interest  as  show- 
ing ways  in  which  an  alveolar  structure  may  be  formed  in  colloidal 
solutions.     The  atomic  energy  made  evident  to  us  by  radium  may 


ncl. 

yk .  a/.i  _ 


Fig.  0. — Ovum  of  a  Cat  Just  Before  Matueitv.     (Redrawn  from  Dahlgren  and' 

Kepner. ) 

Cm.,  Cell  membrane;  n.m.,  nuclear  membrane;  nd.,  nucleolus;  mics.,  microsomes; 

yk.  al.,  yolk  alveoli. 

possibly  be  a  form  of  energy  of  fundamental  importance  in  living 
matter,  although  the  elements  into  which  livmg  matter  is  decomposed 
are,  as  far  as  we  can  see,  stable.  If  an  unstable  mixture  be  made 
of  two  sterile  colloidal  solvitions  of  opposite  electrical  sign.,  such  as 
fsrric  hydrate  (  +  ve)  and  silicic  acid  (  — ve),  and  be  left  standing, 
growth-like  structures  appear,  simulating  in  outward  appearance  simple 
Hving  protoplasmic  forms. 

The  granules  so  frequently  lodged  in  the  cell  may  be  fat,  pigment, 
glycogen,  or  protein.     The  last  may  stain  either  with  a  dye  possessing 


10 


A  TEXTBOOK  OF  PHYSl()LO(iY 


an  active  acid  radicle — e.g.,  prtassium  chroma' e — or  one  with  an 
active  basic  radicle — e.g.,  rosanilin  acetate.  The  graniile.-i  with 
affinity  for  acid  radicles  are  basic,  those  for  basic  are  acidic  in  nature;' 
still  other  granules  are  neutral  and  stain  with  both  radicles:  the 
names  given  for  these  are  respectively  oxyphil,  basophil,  and 
neutrophil  granules.  The  first  and  last  are  most  common.  A 
constant  element  of  the  cell  is  the  nucleus.  It  consists  of  nuclear 
plasma  and  nuclear  network.  The  form  of  the  nucleus  varies,  but 
corresponds  in  general  to  the  shape  of  the  cell — large  and  round  in 
nerve  cells,  long  and  oval  in  involuntary  muscle  fibres,  irregular  neck- 
lace-shaped in  leucocytes.  Especially  large  nuclei  are  found  in  young 
ova  and  nerve  cells.  The  nuclear  reticulum  consists  of  granules  of 
nuclein,  which  stain  deeply  with  basic  dyes,  and  is  thus  called  chro- 
matin  bv  histo'ogists.     The  basic  affinitv  of  nuclein  is  due  to  the 


Fig.   7. -Yeast  Cells  photographed  by   Ultraviolet  Light  iHRouiiu  Quartz 

LENSE.S.     (Barnard.) 


nucleic  acid  it  contains.  This  substance  is  rich  in  phosphorus,  as 
may  be  shown  by  sjoecial  staining  methods.  The  nuclein  granules  are 
embedded  in  a  less  stainable  network — the  linin.  Embedded  in  the 
nucleoplasm  are  one  or  two  larger  granules  which  do  not  behave  to 
chemical  reagents  in  the  same  way  as  the  nuclein  ;  these  are  called 
nucleoli.  Surrounding  the  resting  nuclevis  is  a  perforated  nuclear 
membrane,  through  which  cell  protoplasm  and  nucleoplasm  are  in 
continuity. 

The  nucleus  seems  to  be  the  mainspring  of  the  cell's  activity. 
Wherever  in  a  cell  growth  is  active,  there  seemingly  is  placed  the 
nucleus  (Fig.  8).    It  controls  the  cell  metabolism  and  its  reproduction. 

In  the  case  of  the  protozoa,  when  the  nucleus  is  separated  off  with 
one  part  of  the  ceil,  that  part  grows;  the  remainder  ceases  to  grow,  and 
dies. 


THE  CELL 


11 


The  complicated  structure  of  protoplasm,  and  the  fact  that  it  is 
constantly  in  a  state  of  flux  and  change,  prevent  its  existence  in  large 
masses  It  must  be  intimately  bathed  Avith  the  fluids  that  feed  and 
cleanse  it.  Hsnce  the  cellular  structure,  and  the  evolution  of  circu- 
latory mechanisms  in  the  higher  multiceJluJar  animals.  Protoplasm, 
in  order  to  live,  must  protect  itself  from  extremes  of  temperature, 
and  from  other  active   physical  or  chemical  changes  which  split  up  its 


Fig.  8. — To  show  the  Migration  of  the  Nucleus  to  the  Point  of  Growth  in 
Plants.     (Redrawn  after  Haberlandt,  from  Wilson's  "  The  Cell,"  etc.) 

A,  Young  epidermal  cell  of  Luziila,  with  central  nucleus  before  thickening  of  the 
membrane  ;  B,  three  epidermal  cells  of  Monstera  during  thickening  of  outer 
wall;  (7,  cell  from  seed  coat  of  ScopuUna  during  thickening  of  the  inner  wall; 
D,  E,  position  of  the  nuclei  during  the  formation  of  branches  in  the  root -hairs 
of  the  pea. 


molecules  into  simpler  (dead)  compounds.  It  must  have  the  food 
necessary  to  keep  up  its  cycle  of  change  served  to  it  in  proper  form. 
Protoplasm,  therefore,  moves,  not  onl}'  to  find  food,  but  to  avoid 
injurious  influences.  Protoplasm  moves  by  effecting  a  redistribution 
of  its  substance,  and  certain  parts  are  especially  set  apart,  so  situated 
as  to  produce  definite  changes  in  the  shape  of  the  living  organism,  and 
so  differentiated  in  structure  as  to  ]ierform  rapid  movements — cilia, 
muscles.     It  is  well  to  remember  that  movement  in  response  to  ex- 


12 


A  TEXTJiOOK  OF  PHYSIOLUCY 


citation  is  by  no  means  confined  to  the  living  world.  Heat  and  mag- 
netism cause  movements  in  inanimate  matter,  and  the  response  of 
living  matter  to  certain  foims  of  excitation  appears  to  be  as  inevitable 
as  the  lengthening  of  an  iron  bar  when  heated.  The  unicellular  animals 
move  either  by  flowing  out  in  one  or  other  direction,  a  part  forming  a 
pseudopodium,  and  the  rest  following,  or  by  means  of  vibratile  lashes, 
the  cilia,  which  are  set  round  the  circumference  of  the  cell  body  or 
at  one  or  othei'  pole.  A  pseudo]X)dium  may  be  imitated  by  a  capillary 
tube  filled  with  mastic  varnish.  This  will  extend  a  pseudopodium 
towards  and  eventually  engulf  a  glass  fibre  wet  with  alcohol.  A 
glass  fibre  covered  with  shellac  is  taken  up  by  a  chloroform  drop 
(Figs.  9a  and  9b). 

Movement  is  excited  by  the  various  chemical  and  physical  forms  of 
energy,  and  may  be  toward  the  source  of  energy  or  against  it — 
positive  or  negative.    The  slime  fiuigus,  Myxomycetes  plasmodium, 


Fig.  9a. — A  Glass  Fibre  Wet  with  Alcohol 
BEiKG  Engulfed  by  a  Pseudopodium  of 
Mastic  Vaknish.     (After  Ehumblcr.) 


Fig.  9b. — A  Glass  Fibre  Coated 
with  Shellac,  taken  up 
by  a  Drop  of  Chloro- 
form.    (After  Rhumbler.) 


forms,  by  the  union  of  many  amoeba-like  cells,  a  sheet  of  protoplasm 
which  spreads  for  many  inches,  over  rotten  woods.  The  plasmodium 
shows  marvellous  veins  in  which  granular  p)rotoplasm  streams,  with 
extraordinary  rhythm,  first  in  one  and  then  in  the  reverse  direction. 
The  Plasmodium  flows  towards  and  over  its  suitable  food,  digesting 
and  absorbmg  as  it  goes.  It  is  attracted  by  certain  chemical  sub- 
stances— positive  chemiotaxis.  It  is  repelled  by  others,  e.g.,  a  trace 
of  Cjuinine,  or  too  concentrated  a  solution  of  salts,  etc. — negative 
chemiotaxis.  Similarly,  paramoecia  or  opalinse  gather  round  a  drop 
of  dilute  acid,  and  are  repelled  bj^  dilute  alkali.  H  -  ions  exert 
a  positive  and  HO  +  ions  a  negative  chemiotaxis.  Paramoecia  exhibit 
positive  galvanotaxis  to  the  negative  pole  of  a  constant  current.  They 
gather  round  this  pole  when  the  current  is  passed  through  the  drop 
of  water  containing  them.  Tadpoles  turn  their  heads  toward  the  anode. 
The}'  avoid  one  end  of  a  trough  if  this  be  heated  to  25°-30°  C,  and  seek 
the  cooler  end — negative  thermotaxis.  They  seek  red  light  and  avoid 
the  blue — phototaxis.     Worms,  earwigs,  etc.,  placed  in  a  box  with  a 


THE  CELL 


13 


cover  half  blue  and  half  red,  and  exposed  to  sunlight,  are  disturbed  by 
blue  light,  and  actively  move  till  they  finalty  come  to  rest  under  the 
red.  This  exciting  effect  of  blue  light  acts  on  the  skin  and  produces 
its  effect  even  in  blind  animals.  It  is  the  most  refrangible  rays  of 
the  spectrum,  the  so-called  viltra-violet  raj^s,  which  have  the  marked 
effect  on  living  matter.  These  rays  produce  in  us  sunburn,  followed 
by  a  protective  pigmentation  of  the  skin.  They  act  as  a  bactericide, 
e.g.,  the  tubercle  bacillus  is  killed  by  light  and  the  powerful  arc  light 
(the  Finsen  light)  is  emploj^ed  to  cure  lupns. 
The  exclusion  of  all  but  red  and  yellow  rays 
from  the  sick-room  is  said  to  prevent  the  sup- 
puration of  the  eruption  in  small-pox  The 
black  man  is  protected  from  the  ultra-violet 
rays  by  his  pigment.  Similar  but  more  ]iowerful 
effects  are  produced  by  mercury  vapour  lamps 
enclosed  in  quartz.  The  light  from  these  lamps 
is  particularly  rich  in  ultra-violet  rays,  since  the 
•spectrum  of  mercury  vapour  contains  many 
bright  lines  in  the  ultra-violet  region  of  the 
spectrum,  and  quartz,  unlike  glass,  is  easily 
transparent  to  the  rays  (Fig.  10). 

As  a  rule  cells  are  small  in  size,  some  few 
thousandths  of  a  millimetre  in  diameter.  Occa- 
sionally—for example,  the  egg  of  a  bird — the 
cell  is  macroscopic  in  size,  owing  to  the  large 
amount  of  vegetative  or  nutritive  cytoplasm 
present. 

The   shape    varies   more   than   the  size.     In 
the    various    tissues    it    becomes    modified    to 
almost  any   shape — flat  discs,  cubes,  hexagons, 
'  rods,  or  branching  forms. 

There  is  an  individuality  of  the  cells  of  the 
multicellular  organism.  Their  power  to  survive 
removal  from  the  body  is  very  great;  thus,  the 
sperm  of  the  drone  is  received  by  the  queen  bee 
in  her  nuptial  flight,  and  remains  active  for  the 
rest  of  her  life  in  the  receptaculum  seminis.  In 
the  cloacal  sac  of  the  female  salamander  the 
sperm  is  retained  active  for  two  years  after 
copulation.  The  bat  is  Aved  in  autumn,  and  be- 
comes pregnant  after  her  winter  sleep.  Living  spermatozoa  have 
been  found  eleven  days  after  excision  in  the  excised  testicles  of  guinea- 
pigs  kept  at  0°  C.  Living  human  spermatozoa  have  been  found  in  the 
uterus  eight  and  a  half  days  after  cohabitation.  The  leucocA'tes  of 
the  frog  showed  amoeboid  movements  after  being  kept  tliree  weeks 
in  a  moist  chamber.  Dog's  blood  kept  ten  days  on  ice  has  been 
successfully  transferred  into  a  dog.  Movement  of  ciliated  cells  has 
been  observed  in  a  tumour  eighteen  days  after  its  removal  from  the  nose. 
Pieces  of  the  mucous  membrane  of  the  frog's  mouth  ])\\t  in  the  dorsal 


:^:^ 


Fig.  10. — Lesions 
produced  by  the 
Ultra  -  Violet 
Rays  acting  upon 
the  Rabbit's  Ear 
screened  by  a 
Piece  of  Black 
Cardbo.^rd,  from 
which  THE  Design 
AND  Letters  were 
Cut  Out.  (After 
V.  Henri.) 


14 


A  TEXTBOOK  OF  PHYSIOLOGY 


lymph  sac  of  the  same  animal  showed  active  cilia  after  five  months 
Pieces  of  hmnan  skin  kept  in  ascitic  fluid  for  at  least  one  week  have 
grown  on  trans])lantation.  The  cornea  of  a  hare  kept  at  0°  C.  has 
survived  nine  to  twelve  days,  and  l)een  successfullj^  transplanted. 
The  excised  heart  of  a  three-months-old  child  has  been  made  to  beat 
twenty  hours  after  death.     In  the  last  few  years  the  survival  of  tissue 


Fig.  U. — Camera  Lucida  Drawixc;  of  Cells  from  the  Heart  of  Rabbit's 
Embryo  (Sevek  to  Eight  Days  Old)  growing  in  Culture  Medium.  (N.  C. 
Lake,  from  Journal  of  Physiology.) 

A.  Main  mass  of  tissue;  B,  degenerate  cells;  C,  inner  columnar  cell;  D,  liquefied 
medium;  A',  protoplasmic  thread;  F,  outer  spindle  cell;  G,  fibrin  network  with 
blood  platelets  at  nodes;  H,  nucleus  showing  chromatin;  /,  tendency  to  striation. 

cells  has  been  extensively  studied,  and  the  question  arises  as  to  whether 
true  cultures  are  obtained.  The  growth  of  nerve  cells  has  been  studied 
in  pieces  of  the  frog  embryo  j^laced  in  clotted  frog's  lymph.  By 
repeatedly  alternating  the  life  of  the  tissue,  first  putting  it  in  a  culture 
medium  and  warmth  and  then  in  Ringer's  solution  and  cold,  pulsating 
pieces  of  heart  muscle  have  baen  kept  for  three  months.     Cell  move- 


THE  CELL  15 

luent  in  cxplanted  tissue  has  been  kinematographically  studied.  Such 
cells  use  the  threads  of  fibrin  of  the  plasma  medium  as  guides  in  their 
wanderings.  While  the  cells  of  explanted  tissues  live  and  multiply, 
it  is  doubtful  how  far  they  show  the  characteristics  of  the  particular 
tissue.^  It  is  said  the  new-formed  cells  take  on  an  indifferent  character, 
and  never  show  the  characteristic  formation  of  the  mother  organ. 
If  true  cultures  of  the  cells'  organs  could  be  obtained,  the  method 
would  lend  itself  admirably  to  the  stud}'  of  histogenesis,  metabolic 
processes,  age  and  death  phenomena  of  cells.  It  has,  however,  been 
claimed  recently  that  contractile  cells  which  must  be  considered 
muscular  have  been  obtained  by  culture  of  the  cells  of  the  heart  of  the 
embryo  ra1)bit  (Fig.  11). 

The  phenomena  of  movement,  irritability,  the  digestion  and  ab- 
sorption of  food,  its  assimilation  and  dissimilation,  the  excretion  of 
waste  materials,  growth  and  reproduction,  are  essentiall}^  those  of 
living  matter.     Phj^siology  is  the  study  of  such  life  processes. 

These  processes  in  part  conform  to  the  laws  of  physics  and  chemistry 
which  have  been  found  to  govern  matter  generally.  Of  much,  how- 
ever, at  present  the  explanation  is  not  clear,  and  to  expess  the  reactions 
of  living  matter  terms  such  as  "  biological  force,"  '"vital  force,"  and 
"  biotic  energy,"  are  often  employed.  The  use  of  such  terms  does  not, 
or  should  not,  indicate  that  there  is  any  deep  and  unfathomable  mystery 
about  life  phenomena  other  than  that  hitherto  insoluble  mystery 
which  enwraps  the  universe,  and  conceals  from  us  the  ultimate  origin 
and  the  nature  of  what  we  choose  to  term  matter  and  energy;  rather, 
it  means  that  the  phj-sico-chemical  laws  governing  matter  have  not 
yst  been  sufficiently  found  out  to  render  clear  the  interpretation  of 
living  processes.  With  each  fresh  advance  in  natural  science  the 
phenomena  of  life  are  being  correlated  with  phenomena  of  non-living 
matter,  and  there  can  be  no  doubt  that  with  a  fuller  knowledge  of 
chemical  and  physical  laws  manj^  of  the  processes  now  labelled  ''  vital  " 
will  be  capable  of  being  grouped  under  these  laws.  To  say  this  does 
not  lessen  the  dignitj^  of  the  conception  of  life;  rather,  it  exalts,  by 
unifying,  our  general  conception  of  the  universe.  A  certain  arrange- 
ment of  matter  acts  as  a  transformer  through  which  the  phenomena 
of  life  become  manifest.  The  universal  source  of  energy,  whatever 
it  may  be,  becomes  transformed  into  the  various  manifestations  of 
energy  which  we  call  life,  including  the  workings  of  Mind.  In  dead 
matter  the  transformations  of  energy  are  otherwise  in  character,  but 
the  play  of  energy  is  no  less  ceaseless  in  character,  no  less  beyond  final 
explanation,  no  less  worthy  of  veneration.  Nothing  is  common  or 
simple  to  him  who  has  really  probed  into  the  secrets  of  Nature. 

The  following  has  been  put  forward  as  a  tentative  sj^eculation 
on  the  origin  of  life : 

The  whole  world  of  living  plants  and  animals  depends  for  its  present 
continuance  upon  the  synthesis  of  organic  compounds  from  inorganic 
by  the  green  colouring  matter  of  the  plant  acting  as  a  transformer  of 
light  energy  into  chemical  energy.  This  present  stats  of  affairs  must 
have  been  evolved  from  something  more  simple  existing  at  the  com- 


13  A  TEXTBOOK  OF  PHYSIOLOGY 

mencement.  For  chloroijliyll,  which  now  acts  as  the  transformer,  is 
itself  one  of  the  most  complex  of  known  organic  substances,  and  could 
not  have  been  the  first  organic  substance  to  be  evolved  from  inorganic 
matter.  In  considering  the  origin  of  life,  therefore,  the  start  must  be 
made  in  a  purely  inorganic  Avorld  without  a  trace  of  organic  matter, 
either  plant  or  animal. 

Recently  it  has  been  shown  that,  when  dilute  solutions  of  colloidal 
ferric  hydroxide,  or  the  corresjionding  uranium  compound,  are  exposed 
to  strong  sunlight,  or  to  the  ultra-violet  Ta,ys  of  .a  quartz  mercury  arc, 
there  are  synthesized  the  same  organic  compounds  which  are  at  present 
formed  as  the  first  stage  in  the  process  of  organic  synthesis  bj^  the  green 
plant — namel}',  formaldehyde  and  formic  acid.  Taking  the  ^  iew  that 
the  earth  arose  from  a  gaseous  nebula,  it  may  be  assumed  that  at  first, 
as  the  planet  cooled  down,  only  elements  were  present,  at  a  lower 
temj)erature  binary  compounds  formed,  next  simple  crystalloidal  salts 
arose.  Then,  by  the  union  of  single  molecules  into  grouj)s  of  fifty  or 
sixty,  large  molecular  colloidal  aggregates  ap2:)eared.  As  these  non- 
diffusible  or  colloidal  aggregates  increased  in  complexity,  they  also 
became  more  delicately  balanced  in  structure  and  labile — that  is  to  say, 
they  were  easily  destroyed  by  sudden  changes  in  environment,  but, 
within  certain  limits,  were  peculiarly  sensitive  to  energy  changes,  and 
could  take  up  energy  in  one  form  and  transform  it  into  another.  These 
labile  colloids  took  up  water  and  carbon  dioxide,  and,  activated  by 
the  sunlight,  produced  the  pimj^lest  organic  structures.  Next  these 
simpler  organic  structures,  reacting  with  themselves,  and  with  nitro- 
genous inorganic  matter,  continued  the  process,  and  built  up  more 
and  more  complex,  and  also  more  labile,  organic  colloids,  until  finally 
these  acquired  the  property  of  transforming  light  energy  into  chemical 
energy.  By  the  continued  action  of  this  "  law  of  molecular  complexity  " 
life  originated.  Such  an  origin  of  life  was  no  fortuitous  accident,  and 
the  same  processes  are  still  guiding  life  onwards  to  higher  evolution 
in  a  progressive  creation. 


CHAPTER  III 

PHYSICO-CHEMICAL  INTRODUCTION 

The  cells  of  the  boch'  are  bathed  in  solutions  containing  Ijoth  col- 
loids and  crystalloids.  The  phenomena  exhibited  by  substances  in 
solutions  are  closely  related  to  those  exhibited  by  gases,  concerning 
which  the  basic  facts  are  better  known.  The  fundamental  gas  laAvs, 
proven  by  experiment,  may  be  grouped,  two  as  physical,  and  one  as 
■chemical,  in  nature. 

The  first  law  is  that  the  volume  occupied  by  a  given  mass  of  gas  varies 
inversely  as  th"  jjressure  to  which  it  is  subjected,  provided  the  temperature 
is  kept  constant  (Boyle's  law).  Experimental  work  has  shown  that  for 
■ordinary  gases  under  ordinary  conditions  Bojle's  law  may  be  taken 
as  accurate. 

The  second  law  is  that  the  volume  occupied  by  a  given  mass  of  gas, 
kept  under  constant  pressure,  increases  as  its  temperature  is  raised,  and 
the  relative  expansion  is  approximately  the  same  for  all  gases  (Gay- 
Lussac's  law).  It  is  found  that  the  volume  of  a  gas  increases  by  ^U, 
of  the  volume  it  occupies  at  0^  C.  for  a  rise  of  1°  C,  always  provided 
the  jjressure  remains  the  same. 

From  these  two  laws  it  can  be  shown  that  the  pressure  exerted  by  a 
given  mass  of  gas  kept  at  constant  volume  increases  with  rising  tem- 
perature in  the  same  proportion  as  the  volume  increases  at  constant 
pressure. 

The  third  law  is  also  associated  with  the  name  of  Gay-Lvissac. 
It  is  the  law  of  volumes.  It  states  that,  when  tivo  gases  combine  with 
each  other  to  form,  a  third  gas,  the  volumes  of  the  reacting  gases  are  in 
simple  ratios  to  one  another  and  O  the  volume  of  the  gaseous  product,  all 
being  measured  at  the  same  temperature  and  pressure — for  example,  one 
volume  of  hydrogen  combines  with  one  volume  of  chlorine  to  form  two 
volumes  of  hydrochloric  acid.  On  one  hypothesis  (Avogadros)  regard- 
ing the  nature  of  gases,  it  is  supposed  that  equal  volumes  of  different 
gases  measured  at  the  same  temperature  and  pressure  contain  the  same 
number  of  molecules  or  ultimate  particles.  The  molecules  are  rot  the 
same  thing  as  the  atoms  of  an  element;  a  molecule  may  contain  one, 
two,  or  more  atoms,  and  the  element  is  univalent,  divalent,  trivalent, 
according  to  the  number  of  atoms  its  molecule  contains. 

Diffusion. — A  characteristic  feature  of  a  gas  is  its  ability  to  occupy 
with  great  rapidity  any  space  afforded  it.  If  two  vessels  containing 
different  gases  at  the  same  pressure  be  put  in  communication  with  each 
other,  the  gases  gradually  mingle,  each  moving  from  places  of  high 
concentration  to  places  of  low  concentration  until  the  partial  pressure 

17  2 


18 


A  TEXTBOOK  OF   PtnSJOLOOY 


of  each  gas  is  the  same  tliiougl.out  and  cquilibiiiun  is  attained.  This 
is  termed  the  process  of  diffusion  of  gases;  it  is  a  molecular  process, 
and  takes  place  independently  of  any  movement  of  gas  as  a  whole  by 
stirring.  Diffusion  is  a  relativel}^  slow  process,  and  the  mixture  of 
gases  is  very  greatly  accelerated  by  stirring — e.g.,  in  the  lungs.  Ex- 
perimentally it  was  found  by  Gr-aham  that  the  velocity  of  "  effusion," 
as  he  termed  it,  of  a  given  volume  of  any  gas  is  inversely  proportional 
to  the  square  root  of  its  density.  His  experiments  consisted  in 
determining  the  times  taken  for  a  given  volume  of  various  gases,  kept 


Fig.  12.— Kydkcgen  Generated  from  a  Kipp"s  Apparatus  is  liberated  in  the 
Neighbourhood  of  the  Porous  Pot.  The  Hydrogen  diffuses  into  the 
Pot  Quicker  than  the  Air  diffuses  out,  so  that  Water  is  forced  up  the 
Tube  out  of  the  Woulffe's  Bottle. 


at  CQUStant  pressvire,  to  pass  through  a  minute  hole  in  a  metal  plate 
into  a  receiver,  which  he  kept  constantly  evacuated.  This  law, 
governing  the  rate  of  diffusion  of  gases,  is  well  shown  by  the  experi- 
ment illustrated  in  Fig.  12. 

Experiments  have  been  made  in  which  the  diffusion  of  a  gas  is 
observed  through  a  tube,  when  the  concentration  of  the  gas  at  one 
end  is  kept  at  zero  or  at  a  constant  low  value.  For  example,  when 
caustic  potash  is  kept  at  the  bottom  of  a  tall  cylinder  full  of  carton 
dioxide,  there  is  a  constant  flow  of  carbon  dioxide  to  the  potash  at 
the  bottom  of  the  cylinder;  the  flow  is  inversel}'  proportional  to  the 


PHYSICO-CHEMICAL  INTRODUCTION  19 

length  of  the  diffusion  cohimn.  The  same  holds  good  for  the  diffusion 
of  water  vapour  into  strong  sul})huric  acid.  If  a  diaphragm  be  placed 
at  the  free  end  of  the  diffusion  column,  it  is  found  that  the  amount  of 
gas  which  diffuses  is  proportional  to  the  diameter  of  the  ajierture,  and 
not  to  its  area.  Another  remarkable  fact  is  that,  if  in  the  diffusion 
tube  a  diaphragm  be  pkiced  containing  many  minute  perforations, 
the  diffusion  flow  is  checked  but  little  or  nil,  each  aperture  in  a  multi- 
perforate  diaphragm  acting  independently  of  the  others. 

It  has  been  found  that  the  assimilation  of  CO.,  by  the  leaf  of  a  plant 
is  due  to  a  similar  process  of  diffusion.  If  the  stomata  or  pores  of  the 
leaf  be  blocked,  no  assimilation  of  CO.^  takes  place.  The  amount  of 
CO.,  entering  the  leaf  depends  on  the  concentration  of  CO^  inside  the 
leaf  and  the  linear  dimensions  of  the  stomata.  It  is  found  experi- 
mentally Avith  leaves  of  Helianthus  that  the  amomit  of  CO^  taken  in  is 
but  a  fraction  of  the  amount  calculated  for  the  leaf  as  a  mult iperf orate 
septum.  This  is  because  the  gas,  having  sntered  the  stomata,  has 
to  pass  into  solution  in  the  leaf  fluid —a  relatively  slow  process  as 
compared  with  gaseous  diffusion. 

This  brings  us  to  the  next  point — the  passage  of  gases  into  solution 
in  water.  The  power  of  v\ater  to  dissolve  a  gas  varies  markedly  with 
the  nature  of  the  gas :  the  solubility  of  the  same  gas  in  the  water  also 
varies  with  the  temjieratiu'e  and  the  pressure  at  which  the  absorption 
is  taking  place,  and  with  the  concentration  of  other  substances  in 
solution  in  the  water.  In  regard  to  temi^erature,  the  solubility  di- 
minishes as  the  temperature  rises.  The  solution  of  the  gases  of  the 
atmosphere  in  fat,  on  the  othov  hand ,  is  independent  of  the  temperature. 
In  regard  to  pressure,  it  is  found  that  the  quantity  of  gas  dissolved, 
either  by  weight  or  A'olume,  at  normal  temperature  and  pressure 
(N  T.P.)  in  a  given  volume  of  water  at  a  given  temperature  is  directty 
proportional  to  the  pressure;  thus,  by  doubling  the  pressure  twice  as 
much  gas  passes  into  solution  (Henry's  law). 

The  definite  relationship  between  the  gas  and  the  absorbing  fluid 
is  sometimes  termed  the  "  absorption  coefficient  " — that  is,  the  volume 
of  gas  reduced  to  N.T.P.  which  is  taken  up  b}'  that  volume  of  the 
fluid  under  the  normal  pressiue  of  one  atmosphere.  In  the  following 
table  the  absorption  coefficients  are  given  for  oxygen,  nitrogen,  and 
CO.,,  in  v/ater. 


"emp. 

Oxi/jen. 

X  itro'jiii. 

Carbon  Diox\de. 

{\° 

0-0  iS9 

0  0230 

1-713 

10= 

0-0380 

o-oior. 

1-101 

20" 

()-0310 

0-01(34 

0-S7S 

30^ 

()-02(i2 

0  0138 

0-G65 

40" 

0UJ31 

0-01  IS 

0-520 

The  table  shows  that  the  absorption  coefficient  of  nitrogen  in  water 
at  30°  is  0  0138 — that  is  to  say,  one  c.c.  of  water  at  30°  C.  absorbs  at 
atmospheric  pressure  00138  c.c.  of  nitrogen  measured  at  N.T.P. 
It  also  shows  that  oxygen  is  more  soluble  than  nitrogen,  and  CO.,  more 
soluble  than  either.  Fat  dissolves  between  five  and  six  times  as  much 
of  these  gases  as  water. 


20  A  TEXTBOOK  OF  PHY,SrOL()(;Y 

Diffusion  oJ  Gas  through  a  Liquid  Film. — The  solululitv  of  a  gas 
is  important  iu  (U-tt'iiiiiiiing  the  })a.ssage  of  a  gas  through  a  watery 
fihn.  It  is  found  that  the  velocity  of  its  diffusion  is  directly  ])ro- 
portional  to  the  absorption  coefficient  of  a  gas  in  water.  It  is 
also  found  that,  other  things  being  equal,  the  amount  of  gas  passing 
from  the  ])lace  of  high  ])ressure  through  a  Avatery  film  to  the  ]ilace  of  low 
pressure  is  proportional  to  the  difference  in  pressure  of  the  gas  on  the 
two  sides  of  the  film.  The  importance  of  the  first  factor  may  be 
demonstrated  as  follows:  A  piece  of  pig  s  bladder  is  tied  over  one  end 
of  a  short  wide  tube.  The  other  end  of  the  tube'is  closed  by  a  rubber 
cork  through  which  is  passed  a  narrow  glass  tube,  which  passes  to  a 
manometer  containing  coloured  water  or  to  some  other  mechanism 
for  recording  change  in  pressure.  The  membrane  is  now  impregnated 
with  water;  it  is  important  to  note  that  membrarics  dried  in  air  are 
almost  if  not  quite  impermeable  to  such  gases  as  carbon  dioxide 
and  oxygen.  A  beaker  containing  a  gas  is  then  inverted  over  the 
tube  carrying  the  membrane.  If  the  gas  be  hydrogen,  no  movement 
of  fluid  is  recorded  bj"  the  manometer.  On  the  other  hand,  with  a  very 
soluble  gas  such  as  ammonia,  a  rise  of  pressure  is  shown  in  a  short  time. 

The  exchange  of  oxygen  and  carbon  dioxide  in  aquatic  plants 
depends  upon  the  power  of  the  water  to  dissolve  these  gases,  and  on 
the  diffusion  of  the  dissolved  gases  through  the  membrane  of  the 
plant,  which  is  impregnated  with  water.  If  the  medium  in  which 
the  plant  lives  be  freed  from  air,  the  plant  dies.  The  process  of  the 
diffusion  through  the  walls  of  submerged  plants  has  been  shown  to 
follow  the  laws  cited  aljove;  the  gaseous  interchange  is  therefore  a 
slow  process.  On  this  account  the  oxygen  and  carbon  dioxide  liber- 
ated in  the  assimilatory  and  respirator}'  processes  of  the  plant  are 
stored  in  intercellular  sjoaces  and  kept  for  future  use.  This  is  particu- 
larly the  case  in  the  parts  of  aquatic  plants  Avhich  are  embedded  in  the 
mud  at  the  bottom  of  the  water.  Fiwther,  since  oxygen  and  carbon 
dioxide  are  more  soluble  in  water  at  low  temperatures,  the  facilities 
for  gaseous  interchange  are  greater  at  these  temperatures,  and  it  is 
known  that  marine  plants  such  as  algae  flourish  more  abundantly  in 
the  Arctic  than  in  warmer  waters. 

In  dealing  with  the  gaseous  interchange  in  the  process  of  respiration, 
we  shall  have  to  discuss  whether  this  takes  place  according  to  the 
principles  regulating  the  diffusion  of  gases  across  a  liquid  film. 

Solubility  of  Gases  in  Salt  Solutions. — In  general,  the  more  con- 
centrated a  salt  solution,  the  less  soluble  a  gas  in  it.  Thus,  while 
1  c.c.  of  pure  water  at  25°  C.  dissolves  0  0308  c.c.  of  oxygen,  1  c.c.  of 
a  ??  sohition  of  NaCl  dissolves  but  0-0262  c.c.  of  this  gas,  a  N 
solution*  00223  c.c.  a  2  N  sohition  00158  c.c.  We  shall  see 
that  the  absorption  of  oxygen  by  the  blood,  which  contains 
salts   in   solution,  is  not   a  physical  j)rocess;   for.  instead  of  taking 

*  A  normal  solution  (N  solution)  is  made  by  dissolving  the  molecular  weight  in 

N  .  ,  . 

grammes  of  NaCl  in  1  litre  of  water.    ^  denotes  a  halt'  norm."!l  solution,  2  N  a  twice 

normal  soluiion,  and  so  on. 


PHYSICO-CHEMICAL  IXTRODUCTION 


21 


--b 


u]_)  a  lessened  amount  of  oxygen  compared  with  water,  it  is  capable 
<jf  taking  up  far  more,  the  absorption  of  oxygen  of  blood  as  a 
whole  not  being  a  purely  physical,  but  mainl_\'  a  chemical,  process. 
Besides  salts,  acids,  bases,  and  soluble  substances  like  cane-sugar,- 
have  a  similar  effect  in  lowering  the  solubility  of  gases.  Recent 
study  has  demonstrated  the  fact  that  the  relative  effect  on  the 
solubility'  of  gases  of  different  salts  is  nearly  independent  of  the 
gas  employed.  Therefore  the  diminished  solvent  po^er  of  a  salt 
solution  as  compared  to  water  is  mainly  determined, 
not  by  the  nature  of  the  gas,  but  by  some  factor  in 
the  relationship  of  the  water  to  the  salt.  It  has  also 
been  suggested  that  the  lowered  solvent  power  is  due 
to  hydration  of  the  dissolved  salt,  and  thus  some  of 
the  water  is  no  longer  free  to  absorb  the  gas. 

The  process  of  diffusion  is  not  confined  to  gases. 
Solutions  exhibit  the  phenomenon  of  diffusion.  If 
Mater  be  carefidly  added  to  a  strong  blue  solution  of 
copper  sulphate  with  as  little  mixing  as  possible,  a 
process  of  diffusion  begins  Avhich  does  not  cease  until 
the  salt  concentration  is  the  same  thjoughout  the 
liquid,  and  the  Avhole  liquid  coloiired  blue.  Naturally 
the  process  takes  time,  the  rate  of  movement  being 
much  less  than  in  the  case  of  gaseous  diffusion.  By 
])lacing  a  graduated  tube  on  top  of  the  vessel  the 
rate  of  diffusion  may  be  roughly  measured  (Fig.  13). 
Just  as  with  a  gas.  the  movement  may  be  regarded 
as  due  to  the  pressure  of  the  dissolved  substance;  the 
molecules  are  said  to  be  driven  from  a  place  of  high 
concentration  to  one  of  low  concentration  inider  the 
influence  of  osmotic  pressure. 

To  measure  such  pressure  it  is  necessary-  to  have  a 
membrane  which  Aviil  allow  free  passage  to  the  solvent, 
but  not  to  the  substance:  it  must  be  ■"semi-perme- 
able," as  it  is  termed.  Then  \\'ith  pure  ^^'at^r  on  one 
side  of  the  membrane,  and  a  \\atery  solution  of  a  sub- 
stance— e.g.,  sugar — on  the  other,  since  diffusion  of 
the  dissolved  substance  is  barred,  the  sj^stem  seeks 
to  get  into  equilibrium,  as  far  as  possible,  by  water 
passing  through  the  membrane  to  the  solution.  Such 
a  membrane  may  be  formed  by  fdling  a  porous  vessel 
of  iniglazed  porcelain,  which  has  been  well  soaked 
in  water,  Mith  a  solution  of  copper  sulphate  (2-5  grains  ]:er  litre), 
and  introducing  it  into  a  solution  of  jiotassium  fcrrocyanide  (2-1 
grains  per  litre).  The  salts  diffuse  into  the  porcelain,  and,  meeting 
in  the  interior,  form  a  filmy  deposit  of  copper  ferrocyanidc.  Aftei- 
standing  a  considerable  time,  the  pot  is  taken  out.  thoroughly 
washed,  and  soaked  in  water.  Or  a  similar  membrane  may  be  formed 
by  taking  a  glass  tube  about  1  centimetre  in  diameter,  one  end  of 
which   has   been  di|)|  cd  in  gelatin  to  which  a  little  potassium  diehro- 


FiG.     13.  —  To 
Demoxstrate 

DiFFU.SKIN      IN 

Liquids. 

The  flask  /;  and 
the  .superim- 
posed grr.du- 
ated  tubcrt  are 
ti  1 1  e  d  with 
water.  Some 
crystals  of  cop- 
per sulphate 
are  intro- 
duced. The 
diffusion  of  the 
blue  salt  can 
be  seen  and  the 
rate  measured 
in  t  he  cali- 
brated tub:-. 


22  A  TEXTBOOK  OF  Pll VSIOl.OGV 

mate  has  been  added.  The  j;olatiii  forms  a  liliii  over  the  end  of  tl\e 
tube,  which  is  allowed  to  dry  in  the  light,  it  is  then  soaked  in  water 
to  reuio\e  the  dichrouiate.  Copper  sulphate  is  now  ]>laced  in  the  tube, 
which  is  then  immersed  in  potassium  ferrocyanide.  By  this  means 
a  brown  film  of  copper  ferrocyanide  becomes  deposited  in  the  almost 
colourless  gelatin,  and  a  membrane  is  obtained  which  is  good  for  demon- 
stration purposes.  The  membrane  of  cop]:;er  ferrocyanide  has  been 
found  to  be  impermeable  to  substances  such  as  cane-sugar  and  dex- 
trosCj  but  permeable  to  water.  It  is  therefore  semi-];erme.ible  in 
regard  to  water  and  such  substances  in  solution.  -  This  can  be  demon- 
strated by  filling  the  vessel  bearing  the  mciubrane  with  cane-sugar 
solution,  and  cementing  into  it  a  rubber  cork  carrying  a  long  glass  tube. 
On  immersing  the  pot  in  a  vessel  of  water,  liquid  is  seen  to  rise  in  the 
glass  tube,  and  it  attains  a  considerable  height  if  the  membrane  be 
sufficiently  well  made  and  strong.  Eventually  the  height  of  the 
column  balances  the  pressure,  which  is  tending  to  force  the  water  in, 
thereb}''  giving  a  measure  of  the  driving  force,  which,  although  opposite 
to  it  in  direction,  is  equivalent  to  the  osmotic  pressure  of  the  substance 
in  solution. 

In  the  animal  and  plant  world  we  meet  A\'ith  many  such  semi- 
permeable membranes.  Such  a  one  is  that  covering  peas,  beans,  or 
barley  grains.  If  the  last  be  placed  in  an  aqueous  solution  of  sul- 
phuric acid,  the  water  penetrates  the  grain,  which  swells  in  consequence 
and  increases  76  per  cent,  of  its  weight.  Sulphuric  acid  does  not 
penetrate,  as  is  shown  by  the  fact  that  the  blue  pigment  in  the  aleurone 
granules  inside  the  grain  is  not  changed  red,  as  it  would  be  if  the  acid 
penetrated  the  grain.  When  the  covering  of  the  grain  is  broken,  the 
change  cf  colour  at  once  takes  place. 

Instead  of  the  acid,  a  salt  such  as  sodium  chloride  might  be  used. 
The  amount  of  water  absorbed  by  the  seeds  wall  then  depend  upon 
the  concentration  of  the  salt  in  the  water,  since  there  is  noAv  competi- 
tion between  the  seed  and  the  salt  for  the  water.  Thus,  the  increase 
of  weight  of  the  seeds  with  a  2  per  cent,  solution  of  sodium  chloride 
is  aboiit  40  per  cent. ;  with  a  saturated  solution  it  is  but  14  per  cent. 
The  phenomenon  is,  however,  not  one  of  osmosis  only,  the  process 
known  as  imbibition  also  comes  into  play.  This  comparative  im- 
permeability of  the  outer  coat  of  seeds  is  recognized  by  agriculturists; 
otherwise  such  poisons  as  copper  sulphate  could  not  be  used  to  destroy 
fungus  spores  upon  the  seeds  Avithout  killing  the  seeds  themselves. 

Much  study  has  been  devoted  to  the  phenomena  of  osmosis.  It 
has  already  been  stated  that,  if  the  force  of  attraction  between  solvent 
and  solution  be  measured,  the  osmotic  pressure  of  the  solution  is 
measured  at  the  same  time.  The  exact  nature  of  this  force  is  not  yet 
completely  understood,  but  it  has  been  shown  that  it  is  governed  by 
certain  fundamental  laws  closelj^  allied  to  those  already  given  for  gases. 
Thus,  it  is  found  that  the  osmotic  'pressure  exerted  by  a  given  quantity 
of  the  dissolved  substance  is  inversely  jnoportional  to  the  volume  of  the 
solution  [e.g.,  Boyle's  law).  In  other  words,  the  osmotic  pressure  of 
a  solution  is  proportional  to  the  concentration  of  the  dissolved  sub- 


PHYSICO-CHEMICAL  INTRODUCTION  23 

«t?.nce.  In  regard  to  temperature,  it  appears  to  be  true,  allowing  for 
ex)Derinieti.tal  difficulties,  that  the  osmotic  pressure  of  a  solution  is  pro- 
portional to  the  absolute  temperature  {e.g.,  Gay-Lussac's  law  for  gases). 
Also  it  is  true  for  dilute  solutions  {e.g.,  of  sugar)  that  the  osmotic  x>res- 
si'.re  is  e^ual  to  the  pressure  ivhich  the  molecular  concentration  of  the 
substance  would  exert  if  it  were  in  the  gaseous  state  at  the  same  tempera- 
ture, and  occ^^pied  the  same  volume  as  the  solution. 

If  two  solutions  of  different  osmotic  pressure  be  separated  by  a 
semi-permeable  membrane,  osmotic  exchange  of  water  will  take  place 
until  the  pressures  are  equal  on  the  two  sides  of  the  membrane,  the 
water  passing  from  the  solution  with  the  smaller  osmotic  pressure 
to  that  with  the  greater.  This  can  be  well  shown  by  the  following 
pretty  experiment,  the  success  of  which  depends  upon  choosing  the 
right  strengths  of  solution:  A  little  potassium  ferrooyanide  (nearly 
saturated)  is  slowly  run  from  a  narrow  glass  tube  the  end  of  which  dips 
below  a  solution  of  copper  sulphate  (a  gramme-molecular  solution)* 
contained  in  a  tall  glass  jar.  As  the  ferrocyanide  runs  out,  a  filmy  bag 
of  copper  ferrocyanide  is  formed  at  the  end  of  the  tube.  When  the 
bag  is  about  1  to  2  cm.  in  diameter,  a  slight  jerk  will  disengage  it, 
and  it  will  sink  slowly  to  the  bottom  of  the  vessel.  Its  rontent 
having  a  greater  osmotic  pressure,  water  will  entor  the  bag  and 
gradual^  distend  it.  The  density  of  the  bag  is  thus  gradually  diminished, 
and  eventualh^  becomes  less  than  that  of  the  surrounding  copper 
sulphate  solution,  when  the  bag  rises  spontaneously  to  the  top  of  the 
jar.  The  experiment  may  be  varied  by  fitting  the  top  of  the  narrow 
glass  tube,  containing  the  ferrocyanide  solution,  with  a  piece  of  rubber 
tubing,  and  pushing  a  drop  of  ferrocyanide  out  by  closing  this  tubing 
with  a  chp-  When  the  glass  tube  is  now  lowered  into  the  copper 
sulphate,  a  hanging  membrane  is  formed  at  its  bottom.  Water  passes 
into  the  ferrocj^anide,  and  the  copper  sulphate,  concentrating  in  the 
immediate  neighbourhood  of  the  membra,ne,  becomes  denser  than 
the  rest  of  the  solution  and  sinks.  This  can  be  easily  seen  by  the 
naked  eye,  owing  to  the  difference  in  refractive  power  of  the  denser 
solution.  If  the  experiment  be  reversed,  and  dilute  feiro?yanide,  in  a 
tube  with  an  upturned  end,  be  placed  in  strong  copper  sulphate 
solution,  the  copper  sulphate  in  the  neighbourhood  of  the  membrane 
is  diluted,  and  a  steady  ascending  stream  of  the  diluted  liquid  can 
be  seen. 

Interesting  experiments  on  osmosis  have  been  done  Avith  plants. 
For  example,  in  the  epidermis  of  the  leaf  of  the  plant  Tradcscantia 
discolor  the  fluid  coloured  contents  of  the  cells  are  normally  in  close 
contact  with  the  rigid  cell  wall,  which  behaves  as  a  semi -permeable 
membrane  (Fig.  l-',  ^).  If  it  be  immersed  in  a  solution  containing 
0-22  of  a  gramme-molecule  of  cane-sugar  per  litre,  the  coloured  contents 
detach  themselves  from  the  wall  at  one  or  more  places.  '"  Plas- 
molysis,"  ao  it  is  termed,  has  taken  place  (Fig.  14,  B).  Owing  to  the 
withdrawal  of  water,  there  has  been  a  decrease  in  the  bulk  of  the  cell 

*  The  molecular  weight  in  grammas  dissolved  in  1  litre. 


24 


A  TEXTBOOK  OF  PHYSIOLOGY 


contents.  The  solutidii  of  cane-sugar  has  ther(>forc  a  greater  osmotic- 
pressure  than  the  cell  saj);  it  is  termed  a  hypertonic  solution.  If. 
instead  of  sugar,  another  substance,  such  as  potassium  nitrate  (I 
gramme-molecule  per  litre),  be  used,  the  solution  formed  is  so  strongly 
hypertonic  that  the  plasmolysis  is  very  marked  (Fig.  14,  C). 

Plasmolysis  may  also  be  readily  demonstrated  by  taking  shavings 
fVoui  a  beetroot,  carefully  washing  these  and  immersing  them  for 
a  time  in  5  per  cent,  sodium  chloride.  The  appearance  under  the 
microscope  before  and  after  is  very  characteristic.  The  red  corpuscles 
of  the  blood  behave  in  a  similar  manner.  The  delicate  membrane 
surrounding  the  corpuscle  is  j^ermeable  to  water,  but  impermeable 
to  many  dissolved  substances.  In  this  case,  however,  there  is  no  rigid 
cell  wall  foi  mii-g  the  outer  membrane.  If,  therefore,  water  passes 
into  such  a  cell,  it  A\ill  first  swell  up,  and  then  burst,  thus  allowing  the 
contained  red  pigment  to  escape,  a  process  known  as  the  laking  of 


Fiu.  14. — To  .SHOW  THK  Effect  of  Plasmolysis  in  Tradesca.vtia  Dlscolor. 

(After  Dc  Vries.) 

h.  Cell  wall;  /,-.  nucleus;  r(.  plastids;  .s.  stream  lines  in  protojilasni;  y;,  ])iot()]ilast. 


blood,  or  haemolysis.  A  solution  fiom  which  water  passes  into  the 
corpuscles  is  known  as  hypotonic.  A  solution  from  which  water 
passes  in  and  out  of  the  corpuscle  in  equal  amounts  is  known  as 
isotonic.  The  concentration  of  sodium  chloride  required  to  form  a 
sohition  isotonic  with  nearly  all  mammalian  bloods  is  0-9  per  cent.;  a 
solution  of  this  concentrat.'on  is  terjned  '"  physiological  saline  '"  or 
"  physiological  salt  '"  solution. 

Hypertonic  solutions  diminish  the  volume  of  the  corpuscle  owing 
to  water  passing  out  of  them.  It  is  suggested  that  this  passing  out  of 
fluid  from  living  cells  as  the  result  of  the  action  of  hypertonic  solu- 
tions may  affect  the  activity  of  such  cells.  Thus,  it  is  possible  that 
in  many  plant  cells  the  formation  of  stai-ch  from  sugar  onl}'  takes, 
place  when  the  sugar  concentration  reaches  a  certain  limit.  Indeed, 
it  is  found  that  with  cells  having  a  sugar  concentration  short  of 
this  limit  the  formation  of  starch  can  be  induced  by  i)roducing  i^las- 
molysis  with    a   solution  of  potassium   nitrate;  thi-  by  withdrawing 


physic()-che:mical  introduction 


25 


Avatci  raises  the  concentration  in  the  cell  to  the  minimum  necessary 
for  starch  production. 

It  has  also  been  shown  that  unfertilized  eggs  of  the  sea-urchin 
(Strongylocentrotus  purpuratiis)  m^,}'    be   made   to   develop   parthe- 
nogenetically  by  the  use  of  h^-^jertonic  solutions. 
The  unfertilized  egg   of   the  frog  develops   if   its 
membrane  is  pricked  with  a  needle,  and  its  osmotic 
relation  to  the  surrounding  water  thus  disturbed . 


C=^ 


The  Mode  of  Action  of  a  Semi-Permeable  Mem- 
brane.— .Since  osmosis  plays  an  important  part  in 
the  maintenance  of  equilibrium  between  plant  and 
animal  cells  and  their  surroundings,  it  is  highly 
important  to  know  how  semi-permeable  mem- 
branes act.  From  the  study  of  precipitation 
membranes,  it  appears  to  be  the  size  of  the 
molecular  interstices  which  enables  such  a  mem- 
brane to  differentiate  between  various  substances. 
It  was  at  first  thought  to  act  merely  like  a 
sieve,  but  that  is  not  the  sole  factor.  For 
example,  if  a  glass  tube  with  a  length  of  rubber 
tubing  and  ?.  clamp  at  the  end  be  filled  with 
carbon  dioxide,  the  rubber  then  clamped,  and  the 
glass  tube  cpiickly  placed  in  a  vertical  position  in 
a  beaker  of  water,  the  carbon  dioxide  will  gradu- 
ally diffuse  out  through  the  rubber  and  the  water 
rise  in  the  glass  tube  (Fig.  15).  Rubber  is  per- 
meable to  carbon  dioxide  but  not  to  oxygen  and 
nitrogen.  Further,  when  methyl  alcohol  and  ether 
are  separated  b}'  a  membrane  of  pig's  bladder,  th  re 
is  an  osmotic  flow  from  the  alcohol  to  the  ether. 
If,  however,  the  two  fluids  be  separated  by  vul- 
canized rubber,  osmosis  takes  place  in  the  opposite  -^^  carbon  dioxide 
.lirection.  This  is  because  the  pig's  bl.ckler  TniZltS:t 
absorbs  ten  times  as  much  alcohol  as  ether, 
whereas  rubber  absorbs  one  hundred  times  as 
much  ether  as  alcohol.  Therefore  the  compara- 
tive permeability  or  imperin^abilit}'  to  different 
substances  of  a  non-living  semi-jiermeable  mem- 
brane depends,  also,  on  its  power  to  dissolve 
or  absorb  them.  Experiments  on  living  membranes,  made  chiefl}^ 
on  plants,  tend  to  show  that  it  is  a  selective  absorption  on  the  part 
of  the  membrane  which  determines  the  ability  or  inability'  of  a  sub- 
stance lo  enter  the  cell.  The  permeable  substances  have  been  found 
by  experiment  to  be  generally  soluble  in  fatty  oils;  the  plasmatic 
membrane  of  the  cells,  therefore,  probably  consists  of  some  such 
substance;  indeed,  it  is  claimed  that  cell  walls  are  rich  in  lecithin  and 
cholesterin — both  bodies  of  a  lipoid  nature.  xAs  evidence  of  this 
it    is    found  that  the   basic    aniline    dyes,  which    readily    permeate 


Fig.     15. — To     show 

THE      PeIXCIPLE     OF 

THE      Semi-Perme- 
able Membrane. 


the  top,  water  rises 
from  the  beaker, 
owing  to 
ability  of 
diffuse  in 
the  rubber. 


the    in- 

air    to 

through 


26  A  TEXTBOOK  OF  PHVSrOLOGY 

the  cell,  are  dissolved  by  solutions  of  cholesterin  aiul  of  lecithin, 
whereas  sulphone  dyes,  to  which  the  cells  are  impermeable,  are 
but  sparingly  soluble  in  these  media.  This  hypothesis  of  the 
lipoid  nature  of  cell  membranes  is  widely  accepted  at  the  present 
day,  but  it  is  not  altogether  satisfactory,  and  has  been  subjected 
to  adverse  criticism.  It  fails,  for  instance,  to  cx])lain  reasonably 
wh}'  cells  arc  so  readily  permeable  to  water.  It  is  also  stated  that 
there  are  dyes  readily  soluble  in  these  lipoids  which  are  quite  incapable 
of  penetrating  into  the  living  cell;  while  there  are  also  dyes  insoluble 
in  cholesterin  which  readily  pass  through  the  plasmatic  membrane 
of  the  cell.  Moreover,  certain  inorganic  salts  insoluble  in  fat 
penetrate  into  the  cell.  The  sap  in  the  plant,  for  instance,  supjjlies 
salts  by  some  means  to  the  cells. 

From  a  physiological  point  of  view,  then,  a  purely  physical  theory 
of  permeability  is  not  altogether  adequate.  The  red  corpuscle  is 
rich  in  potassimn  and  phosphate,  yet  the  medium  (plasma)  in  which 
it  floats  is  j^oor  in  these  substances,  but  rich  in  sodium  and  chlo- 
ride, in  which  the  corpuscle  is  poor.  Yet,  as  the  cell  receives  its 
nutriment  from  the  plasma,  the  membrane  of  the  corpuscle  cannot 
be  wholty  impermeable  to  potassium  salts.  If  this  be  so,  their  retention 
in  the  cell  is  opposed  to  osmotic  force.  Apparently  there  is  some 
specific  intervention  of  the  membrane  or  some  special  affinity  of  the 
cell  substance  for  potassium  salts.  So,  too,  in  the  case  of  the  bodily 
secretions.  We  shall  see  that  it  is  difHcult  to  understand,  for  instance, 
how  urea  can  be  passed  by  purely  osmotic  agency  from  the  blood, 
in  which  it  is  in  weak  concentration,  to  the  urine,  where  its  concen- 
tration is  much  greater.  There  appears,  therefore,  to  be  a  physio- 
logical as  well  as  a  physical  permeability  of  the  cell.  This  is  further 
shown  by  the  following  interesting  experiments :  If  tadpoles  be  im- 
mersed in  a  5  to  6  per  cent,  solution  of  cane-sugar  they  are  unaffected. 
If  they  be  transferred  to  an  8  per  cent  sohition,  they  shrink,  owing 
to  loss  of  water.  But  immersion  in  a  solution  less  than  6  jDer  cent, 
(hypotonic)  is  not  followed  by  an  intake  of  water  and  swelling  of  the 
tadpoles,  as  might  be  expected.  Therefore  the  epithelial  membranes 
of  the  tadj)ole  are  apparently  permeable  to  water  in  one  direction  only. 
A  bag  made  of  toad's  lung,  if  placed  in  effervescing  soda  water,  rapidly 
fills  with  gas  and  floats.  If,  however,  the  lung  be  titrncd  inside  out, 
it  does  not  fill  with  gas.  The  experiment  succeeds  no  less  if  the  lung 
in  each  case  is  filled  with  water.  Each  cell  must  be  regarded  as  the 
seat  of  active  chemical  action,  where  concentrations  of  dissolved 
substances  are  con^itantl}^  altering.  Other  phenomena,  e.g.,  imbibi- 
tion, T)lay  an  iinportant  part. 

The  direct  determination  of  the  osmotic  pressure  of  a  solution  is  a 
matter  of  difficulty.  Therefore  it  is  usual  to  ascertain  it  by  some 
indirect  method — by  other  properties  of  solutions  quantitatively  related 
to  osmosic  pressure — such  as  the  lowering  of  the  vapour  pressure 
of  the  solvent  when  the  dissolved  substance  is  non-volatile,  or  the 
raising  of  the  boiling-point  of  the  solvent.  The  method,  however, 
most  generally  employed  for  physiological  solutions  is  the  lowering 


PHYSICO-CHEMICAL  INTRODUCTION 


27 


of  the  freezing-point  of  the  solvent.  The  extent  to  which  the  freezing- 
point  of  a  solution  is  lower  than  that  of  the  solvent  is  proportional 
to  the  concentration  of  the  dissolved  substance. 


—The  appar- 
Beckniann's 


V 


Determination  of  the  Lowering  of  the  Freezing-Point 

atus  generall}^  emplo3'cd  for  this  purpose  is  known  xw 

(Fig.  16).     It  consists  of  a  tube,  A ,  placed  in  a 

jacket,  B,  provided  with  a  special  thermom- 
eter, D,  and  a  platinum  or  nickel  wire  stirrer. 

The  jacket  B  fits  into  a  metal  plate  which 

covers  a  thick  glass  jar,  C,  also  provided  with 

a   stirrer.     When   the   experiment   is   to    be 

made,  this  jar  is  filled  with  a  freezing  mixture, 

Avhich  will  give  a  temperature  about  2-3°  below 

the   F.P.    of   the   solvent.     A  known  weight 

(10-20  c.c.)  of  the  solvent  is  placed  in  A,  and 

its  cork  carrying  the  thermometer  and  stirrer 

inserted.     The  temperature  of  A  is  first  low^- 

ered   by  placing  it  in  the  freezing  mixture; 

but  as  the  freezing-point  is  approached  it  is 

fitted  into  the  jacket  B  and  stirred  regularl}^ 

so    that    a    steady    fall    of    temperature    is 

assured.      The     thermometer     is     carefully- 

watched;   after  p.  time   the   merciu^y  ceases 

to   fall,    then    suddenly    rises    and    remains 

stationary  for  a  moment  before  starting  to  fall 

again.     The  point  risen  to  gives  the  F.P.  of 

the  solvent  for  pure  v'ater,  0°  C.     A  known 

weight  (1-2  gms.)  of  the  solute  (the  body  to 

be  dissolved)  is  noAv  introduced  through  the 

side-tube,  and  after  it  has  dissolved  the  F.P 

is  again  determined  in  a  similar  manner.     It 

is  well  not  to  cool  too  rapidly  or  too  much; 

the  thermometer  should  not  rise  more  than 

0-4°  to  0-5°  C.  to  its  final  position,  otherwise 

the  operation  must  be  repeated.     Excessive 

supercooling  causes  the  separation  of  a  con- 
siderable quantity  of  the  solid  solvent  when 

freezing  occurs,  and  this  makes  an  appreci- 
able   increase    in    the    concentration-  of   the 

solution.      The    freezing-point    method     has 

been     extensively     used    in    studN^ng     the 

osmotic   pressure  of    the  blood  in   different 
the     urine     in    patho- 

man.  It  has  been  shown  tliat  the  F.P.  of 
invertebrate  marine  animals  is  the  same  as 
which  they  liv3;  they  are  incapable  of  preserv- 
ing any  difference  of  osmotic  pressure;  if  the  osmotic  pressure  of 
the  w^ater  be  varied,  that  of  the  bod}'  fluids  varies  also.     But  in  the 


Fig.  10. — Beckmann's   Ap- 
paratus   FOR    DETERJirS- 

iNG  THE   Depression  of 
Freezing-Point. 


animals,    and     also 
logical   conditions  in 
the    bod}^    fluids    of 
that  of  tlie  water  in 


28  A  TEXTBOOK  OF  PHY8IOLO(;^• 

case  of  many  aquatic  vertebrates  this  i.s  not  the  case,  the  blood 
luider  ordinary  conditions  has  a  different  osmotic  pressure  to  the 
medium  in  which  the  animal  lives,  and  is  but  shghtly  altered  by 
variations  in  the  medium.  This  is  true,  for  instance,  of  the  tclecstean 
fishes;  the  blood  <^»f  the  clasmobranchs.  on  the  other  hand,  varies  in 
osmotic  pressure  with  that  of  the  surrounding  sea-water. 

It  was  stated  above  that  the  lowering  of  the  osmotic  jiressure  of 
a  solution  is  proportional  to  the  concentration  of  the  dissolved  sub- 
stance. Although  this  is  true,  it  is  found  that  there  are  very  many 
substances,  such  as  sodimn  chloride,  for  example,  which  yield,  by  the 
method  of  the  lowering  of  the  F.P..  a  molecular  weight  quite  incon- 
sistent with  the  formula?  accepted  for  them.  The  osmotic  activity 
of  these  bodies  points  to  an  abnormally  large  number  of  dissolved 
units  in  their  solutions.  This  is  explained  b^'  the  view  that  acids, 
bases,  and  salts,  in  aqueous  solution  become  dissociated  to  a  greater 
or  less  extent  into  j^ositively  and  negatively  charged  particles  or  ions. 
These  ions  increase  the  number  of  nnits  present  in  the  solution,  and 
endow  it  with  an  enhanced  osmotic  activity.  Sodium  chloride,  for 
example,  when  dissolved  in  Avater  splits  to  a  large  extent  into  positively' 

charged  sodium  ions,  Na,  and  into  negatively  charged  chlorine  ions, 

CI.     Hydrochloric  acid  splits  into  H  and  C"l.  caustic  j^otash  into  K 

and  OH,  potassium  nitrate  into  K  and  NO.,.  One  molecule,  it  Avill 
be  seen,  produces  but  two  ions.  The  ""  ionic  '""  hypothesis  furnishes 
an  adequate  explanation  of  the  abnormal  osmotic  influence  exerted 
by  such  bodies  'n  aqueouj  solution.  It  also  explains  intel- 
ligibh"  the  behaviour  of  various  solutions  to  the  passage  of  an 
electric  current.  It  is  known  that  the  solutions  of  the  bodies  which 
give  an  abnormal  effect  in  lo^^ering  the  F.P.  of  water  ako  conduct 
an  electric  current:  they  are  electrolytes.  When  two  electrodes,  one 
charged  j^ositively  and  the  other  negatively,  are  placed  in  such  fjolu- 
tions,  according  to  this  hy};othesis  an  attractive  force  is  exerted 
upon  the  ions  of  opposite  signs.  Thus,  the  positively  charged  ions 
move  towards  the  negative  electrode,  and  the  negatively  charged  to 
the  positive  electrode :  the  undissociated  neutral  molecules,  remaining 
unaffected  and  exhibiting  no  tendency  to  move  in  either  direction, 
play  no  part  in  the  transport  of  electi'icity  through  ^he  solution. 
The  efficiency,  therefore,  of  a  given  quantit}'  of  a  salt  to  conduct  an 
electric  current  depends  upon  the  extent  of  dissociation  of  that  salt. 
It  is  found  by  experiment  that  the  amount  of  dissociation,  and  there- 
fore the  condu.ctivity.  increases  as  the  .solutions  of  the  salts  become 
less  concentrated. 

In  the  body  fluids  there  are  some  substrnccs  in  solution  which  are 
electrolytes,  and  will  therefore  conduct  electricit}- ;  others  which  are 
non-electrolytes,  and  will  not  conduct  electricit3\  The  fluids  conduct 
according  to  the  amount  of  the  electrolytes  present.  Thus,  blood- 
serum  has  a  conductivity  of  about  the  same  as  that  of  a  0-8  per 
cent,  sodium  chloride  solution.     When  the  non-conducting  corpuscles 


PHYSICO-CHEMICAL  INTRODUCTION 


21) 


of  the  blood  are  present,  as  in  Avhippeil   blood,   the   conductivity  is 
reduced  to  about  half. 

We  shall  see  how  various  ions  are  supposed  to  play  important  parts 
ill  the  body  functions.  For  example,  the  excised  muscles  remain  contrac- 
tile and  the  heart  beats  when  bathed  with  a  solution  containing  a  certain 
concentration  of  sodium,  potassium,  and  calcium  ions.  The  hydrogen 
(H)  and  the  hydroxyl  (OH)  ions  also  are  important.  These  when  com- 
bined yield  a  molecule  of  water.  The  free  H  ion  in  aqueous  solution 
possesses  the  ])roperty  of  endowing  a  substance  with  acidity — e.g., 

4- 

HCl  (H  and  CI):  the  OH  ion,  on  the  other  hand,  gives  alkalinity — 

e.g.,  caustic  potash  (K  and  OH).     Various  reactions  will  only  take 

place    when    a    free    H    ion    is    present — for   example,    the    splitting 

of  cane-sugar  into  dextrose  and  levulose — and  it 

is  found  that  the  rate  of    this  change  depends 

upon  the  concentration  of  the  H  ions.     So,  too, 

it  is  suggested  that  the  free  H  ion  in  the  blood 

plays  a  part  in  exciting   the  respiratory   centre 

and   determining   inspiration.      The   immunizing 

properties    of    the    blood  are  closeh'    connected 

with  the  concentration  of  H  ions. 

Crystalloids  and  Colloids. — Thus  far  attention 
has  been  jjaid  only  to  such  characteristics  as  the 
osmotic  activity  and  the  conduction  of  the  electric 
current  by  various  bodies.  Another  distinction 
between  substances  may  now  be  ]3ointed  out — 

that  is.  the  readiness  with  which  they  crystallize  ^"^''-  17. —To  show 
from  water;  and  those  which  crystallize  readily 
— e.g.,  sodium  chloride,  sugar — also  diffuse  readily 
through  animal  membranes,  and  are  known  as 
crystalloids.  Those  which  crystallize  with  diffi- 
culty, or  not  at  all,  are  characterized  by  low 
diffusive  power  or  absolute  inability  to  pass 
through  animal  or  vegetable  membranes.  Such 
bodies  are  termed  colloids,  from  the  gummy  nature  of  many 
bodies  belonging  to  the  group — e.g..  gums,  starches,  etc. 

This  difference  may  be  demonstrated  by  placing  a  mixture  of  a 
colloid  and  crystalloid  in  a  tube  of  ])arehment,  and  ]ilacing  the  tube 
in  distilled  water — e.g.,  a  solution  containing  the  red  ])igment  of  blood 
(haemoglobin)  and  sodium  chloride.  The  litemoglobin  does  not  pass 
through  the  membrane,  and  the  water  outside  remains  uncoloured. 
But  a  test  for  chloride  shows  the  presence  of  this  in  the  water  after 
a  short  time  (Fig.  17). 

Some  crystalloids  are  electrolytes  and  ionize;  others  are  non- 
electrolytes  and  do  not  ionize.  All,  however,  form  true  solutions  in 
water.  In  contradistinction  to  the  last  property  of  these  bodies,  we 
have  a  group  of  substances  which  are  quite  insoluble  in  water  when 
in  bulk,  but  which,  if  finely  divided  by  mechanical  means,  can  be 


TALLOID,       BUT       XOT 

OF  .4.  Colloid. 

The  hiBiiioglobin  in  the 
parchment  tube  does 
not  diffuse  out,  the 
chloride  does. 


30  A  TEXTBOOK  OF  PHYSIOLOGY 

suspended  in  Widcr  in  such  a  manner  a.s  to  l)e  evenly  distributed 
throughout  the  Ihiid  with  but  little  tendency  to  settle  out  or  aggre- 
gate together.  8uch  sul)stances  form  suspensions  or  emulsions.  They 
are  non-diffusible,  refract  light,  exert  no  osmotic  pressure,  do  not 
conduct  electricity,  and  contain  particles  visible  under  the  microscope. 
Between  these  two  extremes  comes  the  group  of  bodies  classed  at  the 
present  time  as  colloids,  some  a])pr(v;\chiiig  more  nearl}^  the  crystalloids, 
some  more  nearly  the  suspensions.  But  for  the  most  part  colloids 
possess  characteristics  which  clearly  differentiate  them  from  crystal- 
loids.    These  characteristics  may  be  enumerated  as  follows: 

They  are  generally  amorphous  in  form;  some,  however,  can  be 
made  to  crystallize  luider  appropriate  conditions.  Although  giving 
a  homogeneous  solution  when  seen  beneath  the  microscope  with 
ordinary  illumination,  yet  if  a  beam  of  light  be  passed  through  the 
solution  particles  become  visible,  or,  rather,  halos  surrounding  these, 
owing  to  the  dispersion  of  light  waves  from  the  surfaces  of  the  particles 
suspended  in  the  solution,  just  the  same  as  a  ray  of  light  becomerj 
visible  on  passing  into  a  dusty  room.  This  is  known  as  "  Tyndall's 
phenomenon."  The  particles  arc  too  small,  but  the  halos  surrounding 
them  are  large  enough,  to  be  seen  under  the  microscope.  Since  colloids 
are  not  far  removed  from  suspensions,  relatively  slight  changes  suffice 
to  aggregate  the  particles  and  throw  them  out  of  solution.  If  the 
colloid,  thus  thrown  out,  can  again  be  dissolved  in  the  solvent,  it  is 
said  to  be  precipitated;  often,  however,  it  cannot  be  rediseolved,  and 
it  is  then  said  to  be  coagulated.  Agencies  which  produce  aggregation 
or  agglutination  are  a  rise  of  temperature,  and  the  adding  of  large 
quantities  of  neutral  salts,  a  process  known  as  "  salting  out." 

The  suspenrjion  of  the  colloid  particles  in  the  solvent  depends  on  the 
particles  carrying  an  electrical  charge  and  their  mutual  repulsion. 
Any  factor  which  reduces  this  charge  tends  to  aggregate  the  particles. 
Colloidal  suspensions,  like  those  of  colloidal  gold,  are  at  once  thrown 
out  by  the  electrical  discharge  of  the  particles — labile  colloids.  In  the 
case  of  colloidal  emulsions  there  is  a  relation  between  the  molecules 
and  the  solvent,  and  the  particles  are  less  easily  thrown  out — stabile 
colloids. 

In  colloidal  solutions  the  size  of  the  particles,  roughly,  is  between 
the  limits  of  microscopical  vision  (0-1  fi)  and  ultra-microscopical  vision 
(0-001  ju)-  Above  the  limit  we  have  suspensions,  and  below  it  we 
approach  the  true  molecular  solutions.  The  :;u.rfc.cc  of  the  particles 
plays  a  great  ])art  in  the  chemistry  of  the  colloids.  The  minute  sub- 
division causes  an  enormous  increase  in  surface.  Supi:ose  a  cubic 
centimetre  of  gold  be  subdivided  into  particles  with  a  side  of  0  001  ^t 
the  little  cubes  (10^^  in  number)  Avoidd  have  a  total  surface  of  600 
square  metres,  roughly  equal  to  a  surface  measuring  25  yards  by 
25  yards.  All  surfaces  have  the  jiower  of  adsorption — e.g.,  charcoal 
adsorbs  gases,  colouring  matters;  fire-clay  adsorbs  coal-gas  in  such 
a  way  that  intense  incandescence  with  very  perfect  combustion  is 
brought  about  in  the  surface  of  the  brick  when  coal-gas  is  forced 
through  it  and  lighted;  platinum  black  adsorbs  and  brings  about  the 


PHYSICO-CHEMICAL  INTRODUCTION  31 

union  of  hydrogen  and  oxj'gen.  The  adsorptive  power  of  colloids  is 
very  great  owing  to  their  fine  particulate  condition  and  enormous 
surface,  and  this  plays  a  great  part  in  the  chemistry  and  physics  of 
living  cells. 

Most  colloids  are  held  back  bj'  very  fine  filters.  Thus,  the  colloids 
of  blood-plasma  can  be  separated  by  the  use  of  a  porcelain  filter  candle 
which  has  Ijeen  soaked  in  a  solution  of  gelatin.  The  water  and 
salts  can  be  pressed  through  such  a  filter.  Colloids  are  indiffusible 
through  animal  or  vegetable  membranes.  The  membranes  themselves 
are  colloids,  and,  since  colloids  do  not  readily  dissolve  in  colloids, 
it  is  clear  they  will  diffuse  but  little  through  each  other.  Crystalloids, 
on  the  other  hand,  as  we  have  seen,  diffuse  readily;  they  are  generally 
soluble  in  colloids.  This  difference  in  property  can  be  well  demon- 
strated by  placing  a  stick  of  agar  jelly  (colloid)  in  some  ammoniated 
copper  sulphate  .solution  (crystalloid),  and  another  in  some  Prussian 
blue  solution  (colloid).  It  will  be  found  that  the  blue  copper  solution 
penetrates  readily,  the  Prussian  blue  not  at  all.  Colloids  also  appear 
to  influence  physico-chemical  processes  but  little.  Crystalloids  will 
diffuse  almost  as  readily  from  colloids  as  from  water.  So,  too,  chemical 
processes  take  place  in  colloidal  solution  almost  as  if  colloids  were 
absent.  Advantage  is  taken  of  these  properties  in  the  body.  A 
crystalloid,  when  not  linked  or  adsorbed  to  a  colloid,  will  wander 
freely  and  diffuse  away  from  a  cell;  a  colloid  will  remain  where 
it  is  formed.  Thus,  we  find  that  the  crystalloid  dextrose  is  con- 
verted in  the  liver  hito  the  colloid  glycogen  for  storage  j^urposes, 
but  to  escape  from  the  liver  cell  the  glycogen  is  converted  again 
to  the  crystalloid  dextrose.  The  osmotic  pressure  exerted  by 
colloids  is  very  small  or  nil.  It  is  believed  that  when  absolutely  pure 
and  free  from  traces  of  crystalloids  colloids  exert  no  osmotic  pressure. 
Also  they  depress  the  freezing-point  of  a  solution  but  little.  Increasing 
the  amoimt  of  egg  albumin  in  water  from  14  to  44  per  cent,  causes 
l)ut  an  alteration  of  freezing-point  from  0-02"  to  0-06°  C.  Since,  also, 
lolloids  ionize  Init  little,  they  conduct  electricity  but  little.  On  the 
passage  of  an  electric  current  through  a  colloidal  solution,  however, 
the  particles  of  most  colloidal  solutions  tend  to  move  in  the  electric  field ; 
cataphoresis,  as  the  phenomenon  is  termed.  This  j^robably  depends  upon 
the  existence  of  a  high  surface  tension  in  colloids.  Surface  tension  may 
be  described  as  the  force  with  which  a  fluid  strives  to  reduce  its  free 
surface  to  a  minimiim.  When,  therefore,  we  sjaeak  of  the  lowering 
of  the  surface  tension  of  a  fluid,  we  mean  that  the  force  tending  to 
reduce  its  free  .surface  is  weakened,  so  that  the  free  surface  increases. 
The  formation  of  emulsions  is  due  to  such  a  lowering  of  the  surface 
tension.  Water  and  oil  will  not  mix,  the  oil  floating  on  the  surface 
of  the  water,  owing  to  the  high  sm-face  tension  of  the  oil.  If,  how- 
ever, some  sf)a])  he  added  to  the  water,  the  big  oil  drop  is  seen  to  break 
down  gradually  into  a  number  of  smaller. 

Imbibition, — Most  of  the  organic  colloids  exhibit  the  proj^erty  of 
taking  up  fluid  without  chemical  change.  This  is  the  phenomenon 
of  imbibition.     For  example,   dry  gelatin    brought    in  contact  with 


32  A  TEXTBOOK  OF  PHY8lOLO(;Y 

Avater  swells  greatly  and  becomes  a  jelly,  liuhihition  j)lays  a  great 
part  in  the  vital  phenomena  of  cells.  Each  cell  has  a  normal  water 
content,  which,  however,  may  vary  within  certain  limits  according 
to  the  tissue.  Withdrawal  of  water  below  the  normal  limits  impairs 
the  cell  processes,  which  are  either  suspended  for  the  time  being,  as 
in  the  case  of  the  spores  of  bacteria,  or  altogether  destroyed.  With- 
drawal of  15  jjcr  cent,  of  water  ra]iidly  from  a  frog,  or  of  33  per  cent, 
slowly,  stops  all  its  cell  activities.  If,  however,  the  amount  of  water 
in  a  cell  rises  above  its  normal  upper  limit,  its  activities  are  also  im- 
paired; it  becomes  water-laden  and  boggy,  ^r,  to  use  the  scientific 
term,  "  oedematous."  The  power  of  a  cell  to  regulate  its  water  con- 
tent is  largely  due  to  the  iihenomenon  of  ''  ini])ibilion."  Tn  this 
phenomenon,  perhaps  the  electrical  charge,  and  repulsion  of  the 
particles,  of  the  colloids  of  the  cells  are  chiefly  concerned,  and  exert 
the  pull  which  draws  the  water  into  the  cell.  The  process  is  different 
from  osmosis,  since  the  addition  of  certain  salts  to  the  colloid,  instead 
of  aiding  the  passage  of  water,  tends  to  hinder  it.  Electrolj'tes, 
which  favour  the  aggregation  of  a  colloid,  oppose  the  imbibition  of 
water  by  it,  and  vice  versa.  The  cells — e.g.,  secreting  cells  of  glands — 
are  confined  b}"  more  or  less  rigid  membranes,  and  the  force  of  imbibi- 
tion may  be  used  to  do  work  such  as  secretion.  When  a  tissue  becomes 
oedematous,  the  normal  imbibition  power  of  the  tissues  is  altered; 
for  example,  owing  to  an  alteration  of  the  reaction  of  the  tissues  in 
an  acid  direction,  the  proteins  of  the  cell  exert  increased  imbibitory 
power,  and  thus  become  "oedematous"  or  "water-logged."  Thus, 
the  dead  eye  of  an  ox  placed  in  faintly  acid  water  becomes  tensely 
swollen.  Such  swelling  is  hindered  by  the  addition  of  sodium  citrate. 
So,  too,  if  the  hind-leg  of  a  frog  be  ligatured  so  that  the  blood-supply 
is  cut  off,  and  the  animal  placed  in  water,  the  ligatured  hind-limb 
swells  up  to  three  or  four  times  the  normal  size.  If  placed  in  a  dry 
vessel,  the  limb  decreases  in  size,  almost  drying  u])  If  removed  from 
the  body  and  placed  in  water,  it  swells  up  again  to  a  great  size. 

The  muscles  of  a  frog  swell  when  exj^osed  to  a  pressure  of  water 
over  350  atmospheres,  and  lose  their  contractile  power.  This  may 
return  if  the  excess  of  water  is  at  once  dried  off.  Exposure  to  such 
pressures  kills  all  terrestrial  and  shallow-Avater  life,  except  that  of 
spore-bearing  bacteria,  by  a  kind  of  water  coagulation.  The  bacteria 
are  protected  by  their  tough  membrane.  The  deep  sea  fishes  which 
live  at  depths  of  two  miles  or  more  must  be  immune  to  such  water- 
pressures. 


CHAPTER  IV 
THE  CHEMICAL  COMPOSITION  OF  THE  BODY 

A  CONSIDEBA-BLE  iminljcr  of  the  elements  have  been  detected  on 
anaI3^sis  of  the  dead  bodies  of  the  various  forms  of  hfe  found  on  the  earth, 
but  the  number  com])osing  the  bodily  structure  of  the  higher  animals 
is  strikingl}'  few.  The  chief  of  these  are  carbon  (C),  hydrogen  (H), 
nitrogen  (N),  oxygen  (O),  phosphorus  (P),  sulphur  (S),  chlorine  (CI) 
so:]ium  (Na),  potassium  (K),  calcium  (Ca),  magnesium  (Mg),  and 
iron  (Fe).  Others,  such  as  iodine,  boron,  and  fluorine,  are  found  in 
minute  traces.  The  elements  contained  in  the  above  list  occur  chiefly 
in  combination;  some,  however,  such  as  nitrogen  and  oxygen,  are 
dissolved  in  the  body  fluids. 

The  chief  chemical  compounds  which  are  obtained  on  dissociation 
of  the  bod}^  may  be  grouped  as  (1)  water,  (2)  inorganic  compounds, 
(3)  organic  compounds. 

Water  is  a  constituent  part  of  all  tissues  of  the  animal  body, 
the  water  content  varying  according  to  the  nature  and  function 
of  the  tissue  from  50  to  90  per  cent.  The  chief  exceptions  are 
the  enamel  and  cement  of  the  teeth,  which  contain  0-2  per  cent, 
and  10  j)er  cent,  respectively'.  Adipose  tissue  contains  29  to 
30  per  cent,  water,  the  brain  90  per  cent.,  skin  72  per  cent.,  muscles 
76  per  cent.,  lungs  79  per  cent.,  heart  79-5  per  cent.,  and  the 
lens  of  the  eye  98-7  per  cent.  The  percentage  in  the  body  fluids 
ranges  from  79  per  cent,  in  blood  to  99-5  per  cent,  in  sweat  and 
.saliva. 

Inorganic  Compounds. — These  are  chlorides,  phosphates,  carbon- 
ates, and  sulphates.  The  chlorides  are  found  chiefly  as  sodium 
chloride.  This  salt  may  be  extracted  from  all  tissues  and  fluids. 
More  rarely  found  are  the  chlorides  of  potassium  and 
r.mmonium. 

The  phosphates  are  also  ^^'idel3'  distributed,  calcium  and  mag- 
nesium phosphate  occurring  particularly  in  .bone,  of  which  the  ash 
contains  respectively  85  to  90  of  the  former  and  1-5  to  1-9  per  cent, 
of  the  latter  sal;.  Soluble  phosphates  are  also  found  in  nearly  all 
the  tissues  and  body  fluid.;. 

The  soluble  carbonates  and  bicarbonates  of  the  alkalies,  sodium 
and  potassium,  occur  chiefly  in  the  body  fluids,  helping  to  confer 
uj)on  these  a  slightly  alkaline  reaction  to  litmu.-i.  Insoluble  car- 
bonates occur  in  bone. 

33  3 


34  A  TEXTBOOK  OF  PHYSIOLOGY 

The  sulphates  do  not  occur  in  any  large  quantity,  but  the  alkaline 
sulphates  are  regular  constituents  of  the  chief  body  fluids. 

A  little  fluorine  occurs  combined  as  calcium  fluoride  in  the  teeth 
;uk1  bones. 

Among  the  inorganic  bodies  must  also  be  classed  hydrochloric 
acid,  which  occurs  in  the  secretion  of  the  stomach,  and  carbon  dioxide, 
present  in  the  blood  and  body  fluids  as  well  as  in  the  expired 
air. 

Organic  Compounds. — These  are  compounds  of  carbon  with  hydro- 
gen, oxygen,  and  in  some  cases  nitrogen.  Phosphorus,  sulphur,  iron, 
chlorine,  iodine,  may  also  enter  into  the  composition  of  the  various 
organic  compounds,  of  which  there  are  three  chief  grouj)s,  proteins, 
fats  and  lipoids,  and  carbohydrates.  In  addition  there  are  the  pro- 
ducts of  the  breaking  down  of  these  bodies  within  the  organism. 

The  carbon  atom  is  tetravalent-^that  is  to  say,  it  can  combine 
with  four  atoms  of  another  element  (for  example,  hydrogen)  to 
form  such  a  body  as  CH^,  which  is  methane,  or  marsh-gas.  Another 
fundamental  proj^erty  of  the  carbon  atom  is  that  it  can  unite  with 
other  carbon  atoms  to  form  a  chain  or  a  ring,  thus  giving  rise  to 
the  possibility  of  a  large  number  of  very  complicated  bodies,  the 
molecides  of  which  are  imited  together  through  the  carbon  atoms 
contained  in  them.  There  arc-  also  rings  composed  of  carbon  and 
nitrogen. 

1.  Starting  from  methane,  CH^,  by  the  addition  of  one  atom  of 
oxygen, 

H      H  H    OH 

C         +0=  c 

H     H  H     H 

IMcthano  Methyl  alcohol 

we  obtain  an  alcohol,  methyl  alcohol,  HCH^OH,  which,  as  it  contains 
the  group  CHgOH,  is  termed  a  primary  alcohol.  If  we  start  from 
propane,  CHgCH.jCH^,  the  compound  two  above  methane  in  the 
chain. 

CH3 

I 
CH, 

I 
CH3 

Propane 

the  f  ormula5  show  that  it  is  possible  to  obtain  two  monatomic  alcohols 
(alcohols  containing  one  OH  group) :  one  the  primary  alcohol  (primary 
propyl  alcohol,  as  it  is  termed),  containing  the  group  CH^OH;  the 
other  with  the  group  CHOH  characteristic  of  a  so-called  secondary 
i  Icohol — secondary  propyl  alcohol. 


CH,,OH 

CH, 

CH, 

1 

CHOH 

1 

CH3 

CH3 

•imary  propyl 
alcohol 

Secondary  propyl 
alcohol 

THE  CHEMICAL  COMPOSITION  OF  THE  BODY 


35 


But  it  is  possible  to  obtain  (if  the  carbon  chain  be  long  enough) 
diatomic,  triatoraic,  hexatomic  alcohols.     For  example,  from  propane: 


CH3 

I 
CH, 

I 
CH3 

Propane 


CH2OH 

1 

CHOH 
CH3 

A  diatomic 
alcohol 


CH2OH 

CHOH 
CHoOH 

Triatomic  alcohol 
(glycerine) 


2.  If,  instead  of  one  atom  of  oxj^gen,  two  atoms  are  linked  on  to 
methane, 

H       OH 


H     OH 

\ 
C 

/ 

H     OH 


C 
H       lOH 


H 


\ 
C  -O 

H 

Formaldehyde 


water  sj^hts  off,  leaving  a  body  containing  the  group  =  CO  which  is 
designated  as  the  carbonyl  group. 

Thus,  from  propane  it  is  possible  to  obtain  by  oxidation: 


CH, 


CH., 

I    " 
CH> 

Propane 


0 

c 
I  ^ 

CH, 
CH3 

Propaldehyde 


CH. 


C  =  0 


CH3 

Acetone 


Bodies  containing  the  characteristic  grouping  CHO  are  known 
as  aldehydes ;  those  Avith  the  grouj)ing  C  =  0  are  termed  ketones. 
Generally  aldehj'des  and  ketones  are  obtained  bj'  oxidation  of 
alcohols,  primary  alcohols  yielding  aldehydes,  secondary  alcohols 
yielding  ketones. 

Thus: 


0 

CH20H 

c 

CHoOH 

H 

CHOH 

CHOH 

1 

C=0 

CH2OH 

Glycerine 

( 

Glyce 
(0 

:^H20H 

rine  aldehyde 
vcyaldehydo) 

( 

Die 

(0 

:^H20H 

xyacetone 
^yketone) 

30  A  TEXTBOOK  OF  PHYSIOLOGY 

3.  If  three  molecules  of  oxygen  be  introduced  into  methane,  water 
iigain  splits  off: 

HO       OH  OH 

\  ,  / 

C  -^H-C  orH.COOH 

:  \. 

H  OH ,  0 

Formic  acid 

A  body  containing  the  characteristic  gTQup  COOH  is  obtained. 
This  is  called  the  carboxyl  group ;  its  possession  confers  acid  properties 

CHs'. 
upon  the  bodies  containing  it.     From  ethane,     |         it  is  possible  to 

CH3 

obtain  either  one  or  two  carboxjd  groups  bj'  oxidation : 

CH3         CH3         COOH 
CH3  COOH        COOH   . 

Ethane  Acetic   acid  Oxalic   acid 

(a  monocarboxylic  (a  dicarboxylic 

acid )  acid ) 

A  body  containing  one  COOH,  such  as  acetic  acid  above,  is  known 
as  a  monocarboxylic  acid;  a  body  containing  two  such  groups,  like 
oxalic  acid,  is  known  as  a  dicarboxylic  acid.  In  general  acids  are 
obtained  by  the  oxidation  of  alcohols,  aldehydes,  ketones: 

CH3.CH2.OH  +00=  CH3.COOH  +  H2O 

Ethyl  alcohol  Acetic  acid 

2CH3.CH,.CHO  +0^=  2CH3.CH0.COOH 

Pro})aldehyde  Propionic  acid 

CH3.CO.CH3  +  2O0  =  CH3COOH  +  CO.,  +  H2O 

Acetone  Acetic  acid 

In  the  group  of  bodies  known  as  amino-acids,  one  of  the  valencies 

of  the  carbon  atom  is  satisfied  h\  the  amino  group  NHg,  instead  of 

with  hydrogen: 

CH3  CH,NH2 

I     ■  I     " 

COOH  COOH 

Acetic  acid  Monamino-acetic  acid 

(glycin) 

Just  as  there  exist  many  acids  of  which  acetic  acid  is  the  first  of  the 
chain,  so  there  exist  many  amino-acids  of  which  glycin  is  the  simplest. 
By  introducing  two  amino  groups  into  the  acid  molecule,  bodies 
known  as  diamino-acids  are  obtained. 

4.  If  four  molecules  of  oxygen  be  introduced  into  methane,  tAvo 


THE  CHEMICAL  COMPOSITION  OF  THE  BODY  37 

molecules  of  water  split  off,   leaving  carbon  dioxide,  COg,   the  end 
product  of  oxidation  of  carbon  compounds  in  the  body. 


HO 


IHO 


/ 


CI 


OIH. 


;0H 


=  2H,0+COo 


The  tendency  of  the  carbon  molecule  to  form  rings  has  been  men- 
tioned ;  the  chief  of  these  is  the  so-called  benzene  or  carbocyclic  ring,, 
which  is  represented  as  six  carbon  atoms  hnked  together  thus : 


or 


Benzene  itself  is  CgH,.,  an  atom  of  hydrogen  being  linked  on  "to 
each  carbon  atom.  Starting  from  benzene,  it  is  possible  to  obtain  a 
large  nmnber  of  compounds,  so-called  aromatic  compounds,  a  few  of 
which,  such  as  phenylalanin  and  tyrosin,  enter  into  the  construction 
of  some  of  the  body  compoiuids. 

Or  carbon  may  be  linked  with  nitrogen  to  form  a  ring  thus : 


C- 


C 


C 


c 


or 


N 


H 


N 

I 
H 


Four  carbon  atoms  linked  to  an=:NH  or  imino  group  give  the 
pyirhol  ring. 

In  other  bodies  the  benzene  and  pyrrhol  rings  are  found  combined 
together,  yielding  a  compound  ring  found  in  such  bodies  as  tryptophan, 
indol,  and  skatol.     The  ring  may  be  represented  thus: 

H 


H 


KH 


38  A  TEXTBOOK  OF  PHYSIOLOCJY 

A  combination  of  four  carbon  atoms  vvitii  two  nitrogen  atoms  yields 
a  ring  known  as  the  pyrimidin  ring: 

N     CH 

I  I 
HC     CH 

II  I' 
N— CH 

Another  ring  which  occurs  is — 

HC— NH 

i  CH 

HC N 

known  as  the  iminazol  ring.     This  is  found  in  the  body  histidin. 

A  combination  of  the  pyrimidin  Avith  the  iminazol  ring  yields  the 
important  nucleus  or  ring  known  as  the  purin  ring.  The  different 
positions  in  this  nucleus  have  been  numbered,  and  it  may  be  repre- 
sented thus: 

N,  -  C, 

C2     5C-N, 

'^      ':  .  C, 

N3-C4-N, 

Each  of  these  rings  will  be  referred  to  A\heu  dealing  with  com- 
pounds or  groups  of  bodies  containing  them. 


CHAPTER  V 
THE    PROTEINS 

Section  I. 

The  proteins  form  a  group  which  i.s  to  be  regarded  as  the  most  im- 
portant of  all  orgajiic  compounds.  They  are  obtained  from  all  dead 
cells,  and  are  intimately  connected  with  the  life  of  the  cell,  for  without 
them  as  foo:lstuffs  the  cells  cannot  live.  Tiiey  are  bodies  of  biological 
origin;  so  far  no  effort  to  make  them  in  the  laboratory  has  been  suc- 
cessful. Most  of  the  members  of  this  group  are  amor23hous  bodies 
of  high  molecular  weight.  The  protein  molecule  is  made  up  of  the 
elements  carbon,  h3'drogen,  nitrogen,  oxygen,  and  sulphur.  The 
amounts  of  these  elements  vary  considerably  in  different  proteins,  as 
can  be  seen  from  the  following  table: 

Prolein.  G.  H.  N.  O.  S. 

1-25 


FibrinD^en  ..  .52-93  ..  090  ..  Ilr66  ..  •22-06 

Serum  albumin  ..  .>2-()8  ..  7-10  ..  15-93  ..  21-96 

Serum  trlobulin  .  .  .-)2-71  . .  7-01  .  .  15-85  . .  23-32 

Keratin      ..  ..  50-G5  ..  &'M  ..  17-14  ..  -20-85 

Elastin       ..  ..  54-32  ..  (v99  ..  16-75  ..  21-94 

<i-latin       ..  ..  49-83  ..  6-80  ..  17-97  ..  2.vl3 


1-90 
1-11 
5-00 

0-70 


The  nitrogen  and  the  sulphur  are  usually  combined  in  two  ways — 
loosely  and  firmly.  The  loosely  combined  portions  of  nitrogen  can 
be  split  off  from  the  molecule,  as  ammonia,  by  heating  with  caustic 
alkali.  The  looseh'  combined  sulphur  may  be  demonstrated  by  heating 
with  basic  lead  acetate  and  alkali  when  the  black  coloration  due  to 
formation  of  lead  sulphide  occurs.  All  proteins  when  heated  give 
a  smell  of  burnt  feathers,  due  to  the  evolution  of  ammonia,  pyridine, 
and  other  bodies. 

The  Constitution  of  Protein. 

The  constitution  of  protein  is  exceedingly  complex.     The  calcu- 
lated formulae  for  some  jiroteins  are  as  follows: 

Egg  albumin           .  .  C^gg  . .  H.^g,;  .  .  Njg  . .  O78  . .  S2 

Serum  alljumui      .  .  ('45^  .  .  H^-q  . .  N^^^  .  .  Oi4o  . .  S2 

Hemoglobin  (horse)  QgQ  . .  HiQgg  . .  N^io  ■  •  O241  -  •  ^2 

Htemoglobin  (dog)  C7-5  . .  Hun  ■  ■  ^i9i  •  -  ^2U  -  •  ^2 

This  complex  constitution  has  been  recently  studied  in  two  ways: 
(1)  by  working  out  the  products  of  the  breaking  down  (the  hj'droh'sis) 
of  different  proteins;  (2)  by  endeavouring  to  link  together  simple 
cleavage  products,  and  thereby  produce  some  form  of  protein. 


40  A  TEXTBOOK  OF  PHYSIOLOGY 

111  tlie  process  of  hydrolysis,  water  at  first  enters  into  the  molecule, 
which  then  breaks  into  smaller  molecules.  The  first  products  are 
known  as  proteoses,  the  next  as  peptones,  both  of  which  groups 
retain  many  protein  characters.  The  peptones  are  further  split 
into  groups  of  amino-acids  known  as  polypeptides,  and  finally  these 
grou])s  are  broken  down  into  the  individual  amino-acids — organic 
acids  in  which  an  atom  of  hydrogen  has  been  rejDlaced  by  an  NH^ 
group. 

The  chief  products  formed  as  the  result  of  protein  h3'drolj'sis  may 
be  grouped  as  follows : 

Group  I. — Monamino-acids  (containing  one  NH.,  group): 

(a)  Monocarboxylic   (containing  one  COOH  group),   the  chief 

of  these  being  glycin,  alanin,  t^erin,  valin,  leucin. 
(6)  Dicarboxylic    (containing    two    COOH    groups),    the    chief 
being  aspartic  acid  and  glutaminic  acid. 

Group  II. — "  Ringed  "  amino-acids,  containing — 

(a)  The  benzene  ring,  such  as  phenyl  alanin,  tyrosin. 
(6)  Heterocyclic  rings,  such  as  proline,  oxyprolinc,  tryptophan, 
and  histidin. 

Group  III. — Diamino-acids  (containing  tAvo  NH^  groups). 

In  this  group  are  contained  the  two  "  hexone  bases  "  lysin,  arginiii. 
With  these  cystin,  a  sulphurized  diamino-acid,  may  be  classed. 
Other  constituents  arc  : 

(a)  Pyrimidin  bases,  cytosin,  thymin,  and  uracil. 
(6)  Purin  bases,  adenin  and  guanin. 

The  chief  of  these  bodies  will  now  be  considered  in  a  little  more 
detail. 

Glycin  is  a  monamino-acetic  acid,  GH^NH.^COOH.  Hippuric 
acid  is  its  benzoyl  compound  C^^H^CO.NH.CH^COOH.  Glycin  is 
also  compoimded  with  cholalic  acid,  and  forms  ;  odium  glycocholate, 
one  of  the  salts  of  the  bile. 

Alanin  is  the  amino-acid  of  the  next  acid  above  acetic,  namely, 
propionic,  C^H-COOH.  Its  formula,  therefore,  is  C.H^NH^.COOH 
(8-amino-propionic  acid). 

Serin  is  oxy-alanin  (oxy-amino-propionic  acid),  CH„OH.0H. 
NHCOOH. 

Valin  is  amino-valerianic  acid, 

ch!  /  ch.ch.nh^cooh. 

Leucin,  CgH^pNH^.COOH,  is  the  a-amino-acid  of  caproic  acid, 
CgHjjCOOH.  It  crystallizes  readily  as  sj^herules,  is  widespread,  and 
present  normally  in  the  pancreas,  thymus,  thyroid,  spleen,  brain,  liver, 
kidneys,  and  salivary  glands. 


THE  PROTEINS  41 

Aspartic  acid,  C2H3NH2(COOH).,,  is  amino-succinic  acid: 

NH, 

I 
CH.COOH 

I 
CH.COOH 

It  is  not  present  in  large  amounts  among  the  protein  products  of 
decomposition.  Asparagin,  the  amide  of  this  acid,  however,  is  very 
widely  distributed  in  the  vegetable  kingdom. 

Glutaminic  acid,  C3H3NH,(COOH),,  is  amino-gkitaminic  acid: 

NH, 

CH.COOH 

1 

CH, 

CH,COOH 

is  especially  abundant  in  the  proteins  of  seeds,  although  it  occurs  in 
all  the  proteins  yet  examined,  with  the  exception  of  protamines. 

Phenyl  alanin  is  alanin  in  which  a  further  atom  of  hydrogen  has 
been  replaced  by  the  phenyl  group  (CpHj).  Its  formula,  therefore, 
is  C^H^.CH.NH^.COOH  (phenyl-a-amino-propionic  acid),  or  more 
graphically : 


CH2CH.NH2COOH 

Tyrosin  contains  instead  of  the  phenyl  group  the  oxyphenyl 
group  CyH^OH.  It  is  p -oxyphenyl -a -amino -propionic  acid. 
C,H3(CeH^0H)NH,C000,  or  graphically: 

OH 


CH^CHNH^COOH 

It  crystallizes  easily  in  fine  needles,  and  with  leucin  was  the  first 
product  of  protein  h3-drolysis  isolated.  Millon's  reaction  is  due  to  its 
presence. 

Adrenalin,  the  active  substance  of  the  suprarenal  gland,  has  the 
formula 

OHf'     '^CHCOHj.CH^NCHg 

OH 


42  A  TEXTBOOK  OF  PHYSIOLOGY 

and  is  supposed  to  have  its  origin  from  tyrosin.  Animal  pigments 
such  as  melanin  are  formed  from  tyrosin  l>y  the  action  of  a  ferment, 
tyrosinase.  Kresol  and  ])hen()l  are  formed  out  of  ])henyl  alanin  and 
tyrosin  in  the  colon  by  bacterial  decomposition,  and  are  excreted  as 
*'  ethereal  sul])hates  "  in  the  urine. 

Tryptophan,   ^uHj.^NgO^,  is  /-indol-amino-pro])ionic    acid;   it    con 
tains   a  heterocyclic  ring  formed  of  the   fusion  of  the   benzene   and 
pyrrhol  rings.     Its  formula  is — 

C.CH.C  H(NH,)COOH 

"cH 


NH 

It  is  the  mother-substance  of  indol  and  skatol.     It  is  responsible  foi" 
the  giyoxyhc  reaction  (see  later). 

Prolin  is  ^a-pyrrolidin  carboxylic  acid,  C^HgNO.,,  or  graphically: 

H,C CH., 

I  1 

H,C        CH.COOH 

NH 

It  has  been  found  in  both  animal  and  vegetable  proteins. 

Oxyproline  is  oxy-pyrrolidin  carboxylic  acid,  and  was  first  obtained 
by  the  hydrolysis  of  casein  and  gelatin. 

Arginin,  lysin,  and  histidin,  each  contain  six  molecules  of  carbon, 
and  being  of  a  basic  nature,  were  formerly  classified  together  as  the 
"■  hexone  bases." 

Lysin  is  a-diamino-caproic  acid;   leucin  is  monamino-caproic  acid. 

The  formula  of  lysin  is  CH,(NHJ.(CH,)3CH<^^^^jj 

By  putrefaction  of  Ij^sin  i^entamethylendiamin  (cadaverin)  is  produced, 
while  tctramethylendiamin  (putrescin)  is  formed  from  ornithin. 

Arginin  is  a  guanidine  derivative  of  ornithin,  which  is  u-S-di- 
amino-valerianic  acid,  C4H_(NHJ^C00H.  It  has  basic  properties, 
and  reacts  strongly  to  litmus.     Its  formula  is — 

(NH)C—NH.(CH2)3— CH.COOH 

I  I 

NH^  NH^ 

Histidin  is  not  a  true  diamino-acid ;  it  is  a  diazine  derivative.  It 
is  amino-imidazol-propionic  acid,  and  has  the  formula 


THE  PROTEINS  43 

CH— NH 

CH 

/ 

C N' 

I 
CHo 

I 
CH(NH,) 

COOH 

From  the  fact  that  these  three  bodies  (especially  argnin)  occur 
largely  in  the  simplest  proteins  known  (protamines),  and  appear  to 
be  among  the  very  last  bodies  split  off  by  hydrolysis  from  more 
complex  proteins,  it  has  been  thought  that  they  form  the  central 
nucleus  of  protein. 

Cystin  is  notable  for  the  amount  of  sulphur  which  it  contains.  It 
is  di-amino-di-thio-lactylic  acid : 

CH.,S SCH, 

I     "  1       " 

CHNH.,    CHNHo 

I  "     1  " 

COOH      COOH 

It  is  found  largely  in  the  keratin  of  Jiair,  horn,  nails,  and  hoofs.  It 
crystallizes  in  colourless  hexagonal  plates. 

The  pyrimidin  and  pur  in  bases  are  obtained  chiefly  from  the  group 
of  proteins  known  as  nucleoproteins,  and  are  more  fully  discussed  later 

When  protein  is  subjected  to  hydrolysis  by  the  digestive  juices, 
it  is  parti}'  converted  by  the  action  of  the  acid  or  alkali  present  into 
?.  derivative  of  protein  known  as  metaprotein.  A  considerable  amount 
of  ammonia  is  also  split  off.  The  hydrolysis  of  protein  may  be  repre- 
sented as  follows  : 

Protein ^  Metaprotein 


' 

Proteoses 
Peptones 
Polypeptides 

-4/ 

Amino  acids 

1 

Group  7.  A 

Group  /.B 

4^                           xl- 
Group  II. A         Group  II.b 

(Monamino 

Monocar- 

box  ylic ) 

Glycin 

Alanin 

(ilonamino 
dicarboxylic) 
Aspartic  acid 
Glutamic  acid 

(Bonzene  ring)    (Other rings) 
Phenyl  alanin     Prolin 
Tyrosin                Oxyprolin 
Tryptophan 
Histidin 

Serin 
Valin 

L^uoin 

Group  HI 
(I)iamino 

acids) 
Lysin 
Arginin 
C3^stin 


(Other  con- 
stituents 
Pyrimidin  bases 
Purin  bodies 
Carbohydrate, 
etc. 


44 


A  TEXTBOOK  OF  J'HV.SIOLOGY 


111  the  following  table  will  be  seen  the  varying  yields  of  the  different 
amino  aeids  obtained  from  1(10  jn^rts  of  varions  jjroteins,  after  complete 
hydrolysis  with  iiych-oehloric  or  snl])huric  acid.  Tyrosin  and  cystin 
are  separated  by  crystallization,  after  neutralizing  and  concentrating 
the  liquid.  The  diamino  acids — arginin,  lysin,  and  the  allied  body 
histidin — are  separated  from  the  rest  of  the  products  by  being  pre- 
cipitated by  phosphotungstic  acid  in  acid  solution.  Try])tophan  is 
separated  by  })reci])itation  by  mercuric  sulphate  in  the  presence  of 
5  per  cent,  sulphuric  acid  after  ti-yptic  digestion.  The  othei-  amintt 
acids  are  separated  after  hydrol3'sis  of  protein  by  hydrochloric  acid 
by  fiactional  distillation  of  their  ethereal  salts  under  greatly  reduced 
pressure.  It  will  be  noticed  that  the  figures  given  do  not  by  anj^  means 
add  up  to  100  per  cent.  This  is  due  to  the  occurrence  of  some  in- 
evitable loss  in  the  method  of  separation,  and  to  the  fact  that,  doubt- 
lees,  all  the  components  of  protein  have  not  yet  been  isolated. 


Globulin 

Caseiuo- 

Glob  in 

! 

Gliadin 

! 

1  Keratin 

Edestin 
(Jrom 
i   H  cmp- 
{    Seed). 

'  Fibroin 

I'Jnd  Products. 

(Horse 

gen 
(Cow's 

31  ilk). 

of 

[from 

'  (Sheep' s- 

1    [from 

\Seruni). 

Horse. 

Wheat). 

Wool). 

j    Silk). 

Group  I. a: 

' 

Glycin 

3() 

— 

— 

0-8 

0-G 

3-8 

i     3G-0 

Alanin 

2-1 

!•(» 

4-2 

2-() 

4-4 

3-G 

24-0 

Serin 

0-4 

(:)-4 

0-G 

0-1 

1       0-1 

0-2 

,       1-6 

Valin 

— 

1-0 

— 

— . 

1       2-8 

1-0 

Leucin 

j     18-0 

10-2 

30-0 

G-0 

!      11-4 

21-0 

1-6 

Group  I.b: 

j 

Aspartic  acid 

1      2-G 

1-2 

4-4 

1-2 

2-4 

4-6 

0-2 

Glutamic  acic 

ij      9-0 

11-0 

1-8 

3G-() 

13-0 

14-0 

— 

Group  II. a: 

I 

Phenyl  alanir 

11      3-8 

3-2 

4-2 

2-G 

. 

2-4 

l-G 

Tyrosin 

1      2-2 

4-4 

1-G 

2-G 

— 

2-1 

ll-« 

Group  II. b: 

Prolin 

,      2-8 

3-2 

2-0 

9-0 

2-0 

2-0 

Oxyprolin 

;            

— 

— 

— 





Tryptophan 



1-4 

— 

1-0 



1-4 



Histidin 

i      2-1 

2-6 

12-0 

— 

0-6 

0-G 

O-l 

Group  III. : 

Lysin 

i      '^'  ^ 

5-8 

4-4 





1-0 



Arginin 

i 

4-8 

?yi 

3-4 



14-0 

1-0 

Cystin 

0-8 

0-1 

0-3 

0-4 

Ammonia 
.'j-l; 

Large 

7-2 

0-2 

Absence 

Yields 

Large 

Absence 

Large 

Largo 

of 

also 

amount 

amount  of 

of  phenyl! 

amount 

amounts 

arginin  j 

diamino - 

of 

glutamic 

alanin 

of  leucin. 

of glycin, 

Character- 

trioxy- 

leucin. 

acid. 

and 

glutamic 

alanin. 

istics 

dodecamic  ' 

histidin, 

ammonia ; 

tyrosin ; ' 

acid, 

and 

icid  0-75; 

lysin 

absence 

large 

arginin 

tyrosin 

absence  of 

of  lysin 

amount 

' 

glycin; 

and       ' 

)f  cystin; 

large 

histidin 

smaU 

amount 

j 

amount  ; 

^ 

of  lysin 

c 

)f  glyc'n  ' 

THE  PROTEINS  45 

As  a  result  of  this  hydro  lytic  method  of  procedure,  we  now  know 
that  the  proteins  differ  greatly  in  composition;  for  example,  the 
protein  of  the  spleen  is  different  from  that  of  the  thymus  or  of  the 
pancreas.  Further,  the  protein  of  the  same  tissue  differs  in  animals 
of  different  species — e.g.,  the  serum  albumin  of  the  blood  of  one  animal 
has  a  different  constitution  to  the  serum  albumin  of  an  animal  of 
another  species;  the  same  is  true  of  the  chief  protein  (caseinogen)  of 
milk.  We  can  understand,  therefore,  why  it  is  that  the  proteins  of 
the  food  have  to  be  broken  down  into  such  numerous  end  products 
in  the  digestive  tract;  of  these  end  products  those  are  selected 
which  are  of  value  in  building  up  the  animal's  own  particular  forms 
of  protein,  forms  which  differ  in  various  parts  of  the  body  and 
differ  from  the  protein  ingested.  It  is  only  by  a  yevy  complete  hydro- 
lysis that  the  particular  valuable  end  products  can  be  obtained 
free  from  products  of  lesser  value  (see  also  under  Digestion). 

The  results  of  the  second  procedure,  the  synthetic,  have  been 
highly  interesting.  Starting  with  a  simple  end  product  such  as 
glycm,  two  of  its  molecules  have  been  combined  together,  forming  a 
dipeptide,  glycyl-glycin,  with  the  elimination  of  water,  thus: 

OH    1    H 
NH,CH2C0    I    NHCH^COOH  =--  NHaCHaCO.NHCH.^COOH  +  H^O 

Glycin  4-  Glycin  Glycyl-glycin  +  Water 

Tlie  addition  of  another  molecide  forms  a  tripeptide,  and  so  on  until 
polypeptides  are  formed.     Penta-glycl-glycin,  for  example,  is — 

NH2CH2CO(NHCH3CO)  4NHCH2COOH 

Not  only  has  gtycin  been  combined  with  glycin ;  other  end 
products,  such  as  alanin,  leucin.  tyrosin,  have  been  combined  together. 
An  example  of  such  is  the  polypeptide  (do-dekapeptide)  leucyl-deka- 
glycyl-glycin: 


(NHCH.,CO)io      I      NHCH.COOH 

Glvcyl  (Hycin 


C,H9CH(NH2)CO 

Lcucjd 

By  many  such  operations  polypeptides  have  been  obtained,  which, 
if  not  actually  having  the  same  composition,  have  many  resemblances 
to  peptones. 

Section  II. 
The  Physical  and  Chemical   Properties  of  Proteins. 

The  proteins  possess  certain  well-marked  physical  and  chemical 
properties. 

1.  All  proteins,  with  the  exception  of  a  few  vegetable  proteins, 
are  insoluble  in  alcohol  and  ether.  They  vary  as  to  theh  solubility 
in  water,  the  more  common  proteins  (albumins  and  globulins)  being 
either  soluble  in  water  (albumins)  or  soluble  in  weak  saline  solutions 
(globulins). 


46  A  TKXTBOOK  OF  PHYSIOLOGY 

2.  The  solution  given  by  them,  however,  is  colloid;',!,  and  therefore 
will  not  diffuse  through  animal  membranes  or  parchment  paper.  In 
this  they  are  xnilike  crystalloids,  such  as  inorganic  salts,  which  readily 
diffuse  through  such  membranes. 

3.  Most  of  the  so-called  native  proteins  (al})umins  and  globulins) 
coagulate  when  their  solutions  are  heated,  different  proteins  coagu- 
lating at  different  temperatures,  varying  usually  from  SO""  C.  to  78''  ('. 
A  faint  degree  of  acidity  and  the  presence  of  much  neutral  salt  aids 
this  process. 

Heat  coagulation  is  probably  brought  about  first  by  the  interacli.n  of  protein  and 
water  :  a  hydrolytic  product,  metaprotein,  is  produced  (dcnaturation);  secondly  by 
agglutination  and  separation.  A  certain  increase  of  acidity  or  alkalinity  favours 
denaturation,  but  opi)oses  agglutination.     The  reverse  is  true  for  neutral  salts. 

Protein  does  not  form  a  true  solution;  its  particles  are  suspended  in  the 
solvent,  and  carry  an  electrical  charge.  Any  factor  which  reduces  this  charge  tends 
to  bring  about  agglutination,  cither  precipitation,  which  is  reversible  on  dialyzing 
away  the  reagent,  or  coagulation.  The  particles  are  no  longer  electrically  repelled, 
and  run  together  under  the  influence  of  gi'avity.  In  the  case  of  proteins,  which 
have  amphoteric  properties,  the  charge  of  the  particle  is  positive  when  the  fluid  is 
acid,  and  negative  when  the  fluid  is  alkaline.  When  a  neutral  salt  is  added,  the 
agglutinating  ion  is  that  which  carries  a  charge  opposite  in  sign  to  that  of  the  par- 
ticle. The  agglutinating  power  increases  with  the  valency.  Thus  an  acid  solution  of 
protein  is  precipitated  by  negative  ions,  for  the  particles  of  protein  have  positive 
oharges;  the  potassium  salt  of  citric  acid  (trivalent)  is  much  more  effective  than 
the  potassium  salt  of  sulphuric  acid  (divalent),  and  this  more  than  the  potassium  salt 
of  hydrochloric  acid  (univalent).  An  alkaline  solution  of  protein  is  agglutinated  by 
positive  io;  s;  cerium  chloride  (trivalent)  is  more  efficient  than  barium  chloride 
(divalent),  and  this  Tiiore  than  sodium  chloride  (monovalent). 

4.  Most  proteins  are  uncrystallizable.  Some  j^roteins,  however, 
can  be  fairly  easily  crystallized,  especially  certain  vegetable  proteins, 
such  as  those  of  hemp-seed  (edestin)  or  of  the  Brazil  nut  (excelsin). 

5.  Almost  all  proteins  turn  polarized  light  to  the  left.  Haemo- 
globin is  an  exception. 

6.  Certain  well-marked  colour  reactions  are  given  by  the  majority 
of  proteins,  all  of  which  give  valuable  information  as  to  the  constitu- 
tion of  the  protein  molecule.  One  such  reaction — namely,  the 
biuret — is  characteristic ;  a  body  that  does  not  give  this  is  not  classed 
as  a  protein.     The  most  important  of  these  reactions  are — 

{a)  The  biuret.  A  violet  or  rose-pink  colour  with  copper  sulphate 
and  caustic  potash  denotes  the  presence  of  two  or  more  CO — NH — 
linkages.     All  proteins  give  this  reaction. 

(b)  The  xanthoproteic.  With  nitric  acid  a  white  curd  turning 
yellow  on  heating,  and  orange  on  addition  of  ammonia,  denotes  the 
presence  of  the  benzene  ring  in  the  protein  molecule.  Proteins 
yielding  the  ringed  amino-acids  give  this  reaction. 

(c)  Millon's — with  a  mixture  of  mercuric  and  mercurous  nitrates, 
a  white  precipitate  turning  brick  red  on  heating — signifies  the  presence 
of  a  benzene  ring  with  m\  hydroxyl  group  attached — in  other  words, 
the  phenolic  group.     Proteins  containing  tyrosin  give  this  test. 

{d)  Hopkins's  modification  of  Adamkiewicz's  reaction. 
The  reaction  signifies  the  presence  of  tryptophan  in  the  protein 
molecule.     Acetic  acid,  containing  glyoxylic  acid  as  an  impurity,  is 


THE  PROTEINS  47 

added  to  protein,  and  then  a  little  strong  sulphuric  acid  carefully; 
a  violet  ring  is  developed  at  the  jiniction  of  the  fluids. 

(e)  Proteins  containing  a  carbohydrate  moiety  yield  Molisch's 
test.  A  purple  colour  over  green  is  developed  when  a-naphthol  and 
sulphuric  acid  are  added  to  the  protein. 

(/)  Proteins  containing  loosely  combined  sulphur  yield  with  lead 
acetate  and  caustic  alkali  a  black  precipitate  of  lead  sulphide. 

(g)  Many  proteins  are  jjrecipitated  ("  salted  out  ")  from  solution  by 
the  addition  of  neutral  salts,  such  as  ammonium  sulphate,  magnesium 
sulphate,  sodium  chloride,  in  varjang  concentrations.  Such  precipi- 
tates are  again  soluble  in  the  original  solvents. 

(h)  Proteins  are  coagulated — that  is,  thrown  down  as  a  precipitate 
no  longer  soluble  in  the  original  solvent — b.y  mechanical  agitation, 
addition  of  the  salts  of  heavy  metals,  mineral  acids  and  many  other 
acids,  such  as  tannic,  picric,  etc. 

All  proteins  do  not  necessarily  give  all  the  above  reactions.  It  is 
perhaps  somewhat  difficult  to  define  a  protein.  Most  of  them  may 
be  defined  as  bodies  of  biological  origin  insoluble  in  alcohol  and 
giving  the  biuret  test.  (All  these  properties  should  be  studied  in 
connection  with  the  experiments  given  in  Practical  Physiology). 


Section  III. 

The  Classification  of  Proteins. 

The  following  classification  has  been  adopted;  it  is  based  partly 
upon  the  results  of  chemical  investigation,  and  f)artly  upon  such 
physical  properties  as  solubility,  salting  out,  etc.  It  cannot  be  regarded 
as  complete. 

1.  Protamines.    . 

2.  Histones. 

3.  Albumins. 

4.  (iJlobulins. 

5.  Phosphoproteins. 

6.  Scleroproteins. 

7.  Compound  proteins. 

The  protamines  are  held  to  be  the  simplest  proteins  known.  They 
occur  combined  with  nucleic  acid  in  the  spermatozoa  of  certain  fishes 
such  as  the  salmon,  sturgeon,  mackerel,  and  herring.  Sturin,  from 
the  sturgeon,  has  the  formula  C.^^H^gNj^O. ;  salmin  (salmon)  and 
clupein  (herring)  have  the  formula  Cg^H^.N^-Og.  They  are  difficult  to 
obtain  in  a  state  of  purity.  Upon  hydrolysis  they  yield  large  amounts 
of  the  hexone  bases,  arginin,  lysin,  and  histidin,  esjiecially  arginin. 

The  histones  occur  mainly  in  combination.  They  are  more  com- 
plex than  the  protamines,  and  are  coagulable  by  heat,  soluble  in 
dilute  acid,  and  precipitated  from  water}'  solution  by  ammonia.  The 
best  known  is  globin  split  off  from  the  heemoglobin  of  the  blood ."=\'^ 


48  A  TEXTBOOK  OF  PHYSIOLOGY 

The  albumins,  of  which  serum  al])unun,  lactalbiimin,  and  egg 
albumin,  uie  examples,  are  soluble  in  distilled  water  and  in  saline, 
but  not  in  saturated  solutions  of  ammonium  sulphate  and  anhydrous 

Rcdium  sul])hate. 

The  globulins,  on  the  other  hand,  are  insolu})le  in  distilled  water 
and  in  saturated  solutions  of  all  neutral  salts.  Furthermore,  they 
are  insoluble  in  half-saturated  solutions  of  ammonium  sulphate  and 
anhj'drous  sodium  sulphate.  They  are  soluble  in  weak  saline  solutions. 
The  most  important  are  serimi  globulins,  egg  globulin,  the  myosinogen 
of  muscle,  and  the  fibrinogen  of  blood. 

The  phosphoproteins  derive  their  name  from  the  large  amount  of 
l^hosphorus  which  they  contain.  Phosphorus  is  easily  split  off  by 
prolonged  treatment  with  1  per  cent,  caustic  soda  at  37°  C,  a  fact 
which  distinguishes  the  phosphoproteins  from  nucleoproteins.  They 
differ,  too,  from  the  latter  in  containing  no  purin  bodies.  They 
resemble  the  globulins  in  many  of  their  properties,  but  the}^  are  not 
coagulable  by  heat.  The  chief  members  of  the  groups  are  the  case- 
inogen  of  milk  and  the  vitellin  of  egg  yolk. 

The  scleroproteins  com2:)rise  a  heterogeneous  group  of  proteins 
formerly  known  as  the  albuminoids.  They  are  obtained  mainly  from 
the  "  hard  "  or  supporting  structures  of  the  body.  Among  the  better 
known  are  collagen,  from  white  fibrous  tissue,  and  its  hydride  gelatin. 
Gelatin  is  remarkable  in  yielding  little  or  no  aromatic  bodies  on  de- 
composition. Keratin,  charactcrizxl  bj'  containing  a  large  amount 
of  sulphur,  occurs  in  the  skin  and  its  appendages,  such  as  hair  and 
horn.     Elastin  is  found  in  elastic  tissue,  ossein  in  bone. 

The  compound  proteins  consist  of  proteins  to  which  groups  other 
than  protein  are  united  to  form  a  complex  molecule.  The  groujjs 
usually  classified  are — (1)  chromoproteins,  (2)  glucoproteins,  (3)  nucleo- 
proteins. Some  authorities  add  lecitho-protein.s — that  is,  compounds 
of  lecithin  and  protein  (see  Lecithin). 

The  chromoproteins,  as  their  name  signifies,  are  the  coloured 
proteins,  the  chief  member  being  haemoglobin,  a  compound  of  a 
globin,  and  an  iron-containing  portion,  heematin. 

The  glucoprotains  contain  a  carbohydrate  nucleus  attached  to 
the  protein.  Several  proteins  not  contained  in  this  class,  such  as 
egg  albumin  and  nucleoprotein,  contain  carbohydrate,  but  not  in 
such  large  amoixnts.  The  chief  members  of  this  class  are  the  mucins. 
The  carbohydrate  in  them  is  usually  glucosamine,  of  which  there  is 
often  as  much  as  30  per  cent.  When  glucoprotein  is  treated  Avith 
dilute  mineral  acid,  a  sugar  is  split  off  which  gives  the  "  reducing  " 
tests  for  sugar,  but  will  not  ferment  with  yeast. 

The  nucleoproteins  form  the  chief  constituent  of  the  nuclei  of  cells. 
They  consist  of  protein  in  combination  with  nuclein,  itself  a  compound 
of  protein  with  nucleic  acid.  There  are  several  nucleic  acids.  The 
simplest  (so-called  guanylic  acid),  found  in  the  pancreas,  yields,  on 
decomposition,  phosphoric  acid,  guanin,  and  a  pentose;  nucleic  acid 
proper  yields  the  purin  bodies,  guanin  and  adenin,  a  hexose,  and 


THE  PROTEINS 


49 


pyrimidin  bases,  especially  cytosin.     The  following  scheme  shows  the 
relationship  of  nuclein: 

Nucleoprotein 
(digested  with  pepsin) 


Nuclein  (brown  sediment  decomposed 
~  ~~  by  acid  alcohol) 


4/ 

Peptone 
(goes  into  solution) 


Acid  melfiprofi.in  (in  solution) 


Nucleic  acid  (white 
precipitate)  heated  in  clo'-'cd  tube  with  HCl 


\lr  \1/  \U 

Purin  bodies  Garhohjdrate  Phosphoric  acid 

adenin,  guanin)      (pentose  or  hexose) 


Pyrimidin  bases 
(especially  eytosia) 


The  chief  of  the  pyi'imidin  bases  is  cytosin — amino-oxyiDyrimidin 
CjH^N^O,  graphically  expressed : 

HN— CNH 

II       II 
OC     CH 


N=CH 
Uracil  is  diox3rpyrimidin,  C^H^NoO.,, 

HN— CO 

I       I 
OC     CH 

I       II 
HN— CH 

Thymin  is  methyl  uracil,  CsHgNgO^, 

HN— CO 

I      I 
OC    C.CH3 

I    II 

HN— CH 

The  Purin  Bases  are  perhaps  the  most  important  cleav^age 
products  of  nucleoprotein,  distinguishing  it  from  phosphoprotcin, 
which  does  not  contain  them.  They  are  all  compounds  of  the  hypo- 
thetical purin  ring  (see  p.  3!- ), 

The  two  immediate  products  of  hydrolysis  are  adenin  and  guanin. 
These  are  in  close  relationship  with  the  bases  hypoxanthin  and 
xanthin  and  with  uric  acid. 


50  A  TEXTBOOK  OF  PHYSIOLOGY 

Adeniii  is  6-amiiio-purin,  CjHyN^NH^,  the  amino  grouping  ])oing 
ill  the  ()  position  of  the  purin  ring.     (jlr<'])hically  expressed  it  is 

N=C.NH., 


^CH 


HC     C— NH. 

II      II 

N_C— N- 

Oiianin,  C-H3N4O.,,  is  2-amino-6-oxypurin,  or 


HN— CO 

NH, 

CH 


H2N.C    C— NH 


N— C— N^ 
Besides  being  fonnd  as  a  product  of  hydrolysis  of  nucleoprotein, 
it  is  found  in  small  quantity  in  muscles  and  also  in  the  scales  of  fishes 
Hypoxanthin,  C^H^N^O,  is  6-oxypurin,  or 

HN CO 

I  1 

HC        C— NH 

II  II  t'H 

N C— N 

It  is  obtained  from  adenin  by  "  deaminization,"  the  replacement 
of  the  NH.,  group  by  an  atom  of  oxygen.  This  takes  place  in  the  body 
as  the  result  of  the  action  of  an  enzyme  known  as  adenase : 

C5H3N4NH2  +  H.O  =  C5H4N4O  +  NH3. 

Hypoxanthin  is  also  found  in  the  muscles.  It  is  abundant  in  the 
sperm  of  certain  fishes,  such  as  the  salmon  and  the  carp.  It  also 
occurs  in  snuxll  quantities  in  bone  marrow,  in  milk,  and  in  urine. 

Xanthin,  C^H^N^O^,  is  2,  6,  dioxypurin,  or 

HN— CO 

I        I 
OC      C— NH 

I       II  CH 

NH— C— N 

It  bears  the  same  relationship  to  guanin  as  hypoxanthin  does  to 
adenin.  In  the  body  the  enzyme  guanase  converts  guanin  into  xanthin. 
Oxidizing  enzymes  also  possess  the  power  of  converting  hypoxanthin 
to  xanthin  by  adding  on  an  atom  of  oxygen. 

Uric  acid  is  trioxypurin;  its  chemical  relationshij3s  are  discussed 
fully  later  (see  p.  458). 

Derived  Proteins :  Acid  and  Alkali  Metaprotein  may  be  pre- 
pared by  treating  a  solution  of  egg  A\'hite  with  a  little  dilute  acid 
(10  per  cent.  HCl)  or  dilute  alkali  at  body  temperature  for  five  minutes, 
and  then  heating  uj^  to  the  boiling-point.  The  metaprotein  thus 
formed  differs  from  the  original  egg  albumin  in  not  being  coagulated 
by  heat  while  in  the  acid  or  alkaline  solution,  and  in  being  precipitated 
(salted  out)  by  half-saturation  with  ammonium  sulphate  (see  table 


THE  PROTEINS 


51 


below).  Acid  metaprotein  may  be  changed  into  alkali  metaprotein, 
but  the  reverse  change  cannot  take  place,  since  the  alkali  splits  off 
some  of  the  loosely  combined  nitrogen  and  siili)hur.  If  alkali  meta- 
protein be  prepared  by  the  action  of  strong  alkali  on  egg  white,  a 
substance  known  as  '"  Lieberkuhn's  jelly  "  is  formed.  Acid  meta- 
protein is  formed  in  peptic,  alkali  metaprotein  in  tryptic,  digestion. 

Proteoses  and  Peptones. — These  occur  in  the  first  stages  of  protein 
cleavage  (see  table  I xlo\\),  and  are  more  fully  dealt  with  under  Diges- 
tion (p.  386). 

The  proteoses  are  usueJl}'  divided  into  i^rimary  and  secondary. 
They  are  not  coagulated  by  heat,  are  very  slightly  diffusible, 
give  a  pink  colour  with  the  biuret  test,  and  a  white  j^recipitate 
with  salicyl-sulphonic  acid,  which  disap23ears  on  heating  and  reappears 
on  cooling.  Primary  proteoses  (except  a  form  known  as  hetero- 
protecse)  are  salted  out  by  half-saturation  with  ammonium  sulphate, 
secondary  proteoses  by  full  saturation  (see  table  bcljw,  also  p.  3h'6). 

Peptones  are  characterized  by  their  read}^  diffusibility  through 
parchment  membranes.  They  also  give  a  characteristic  pink  colour 
with  the  biuret  test.  They  are  not  coagulated  by  heat,  and  are  not 
precipitated  by  nitric  or  salicyl-sul])honic  acid.  They  are  preci])itated 
by  alcohol  and  picric  acid. 


Protein. 

Solii- 
hility. 

Diffusi- 
bility. 

Action 

of 
Heat. 

Biuret 
Test. 

11 

Is' 

Salting  out  with 
+         MgSOJull  Satu- 
ration. 

Globulin 

Saline 

Nil 

Coagu- 

Violet 

Half 

lated 

Albumin 

Water 

Nil 

Coagu- 
lated 

Violet 

Full 

- 

Primary 

Water 

Slight 

Not 

Pink 

Half 

-1- 

proteoses 

coagu- 
lated 

Secondary 

Water 

Slight 

Not 

Pink 

Full 

_ 

proteoses 

coagu- 
lated 

Peptones 

Water 

Consider- 
able 

Not 
coagu- 
lated 

Pink 

Not 

' 

Acid 

Acid 

Not 

Half 

-1- 

metaprotein 

coagu- 
lated 

Alkali 

AlkaU 

Not 

Half 

+ 

metaprotein 

coagu- 
lated 

Caseinogen 

Weak 
a  kali 

Nil 

Not 
coagu- 
lated 

Violet 

Half 

-h 

Nitric  or 
Sal  icy  I 

Sill  pho- 
nic 
Acids. 


Action  of 
Alcohol. 


Pp.  insol.  Ppt'd,  then 

on  coagu- 

hcating         lated 
Pp.  insol.  Ppt'd,  then 


on 
heating 
Pp.  sol. 

on 
heating 
Pp.  sol. 

on 
heating 
No  pp. 


coagu- 
lated 
Ppt'd 


Ppt'd 


Not  ppt'd 


Ppt'c 


52 


A  TEXTBOOK  OF  PHYSIOLOGY 


CoLOiTK  Tests  for  Proteins. 


Name. 


Biuret  (Rose's 

or  Piotrowski's 

tost). 

Xanthoproteic 


Millon's 


Adamliiewicz's 
or  Hopkins's 
(glyoxylic) 

Lead  sulphide 
test 


Molisch's  test 


Procedure- 


Result. 


KOHandCuSO^ 


Add  HN0:5 


Add  mixture  of 
mercuric  and 
mercurous 

nitrates 

Glacial  acetic  and 
H2SO4 

Lead  acetate 
+  KOH 


a-Naphthol  and 
H2SO4 


Violet  or 
pink  colour 


White  pp., 

yellow  on 

heating, 

orange  with 
ammonia 

White  pp., 
brick  red 
on  heating 


Violet  ring 


Black  colour 

on  heating, 

due  to 

formation  of 

lead  sulphide 

Purple  ring 


Significance. 


Two  CONH  groups  linked 
toofether 


Presence  of  benzene  ring 


Presence  of  hydroxybenzene 
ring 


Presence  of  tryptophan 
Presence  of  sulphur 


Presence  of  carbohydrate 
group  attached  to  protein 


CHAPTER  VI 
FATS  AND  LIPOIDS 

Section  I. 

Neutral  Fats  and  Fatty  Acids. — Fats  occur  widely  distributed  in 

the  plant  and  animal  kingdom.     In  the  former  they  occur  in  seeds, 

roots,  and  fruits;  in  the  latter  in  varying  quantities  in  all  tissues,  but 

particularly  in  the  adijjose  tissue,  bone  marrow,  and  milk.     Neutral 

fats  are  compounds  of  the  fatty  acids  with  the   triatomic  alcohol, 

glycerine.     They  are  generally  j^ellowish  in  colour  or  colourless,  and 

when  pure  have  neither   odour  nor  smell.     They  have  the  general 

formula : 

CH2— O— CO— R 

I 
CH— 0— CO— R 

I 

CH.— 0— CO— R 

— where  R,  the  fatty  acid  radical,  usually  stands  for  palmitic,  stearic, 
or  oleic  acid.  Of  these,  palmitic  and  stearic  are  saturated  acids,  and 
have  the  general  formula  CnHg^  ^^COOH,  n  being  17  in  stearic  acid, 
CJ-H35COOH,  and  15  in  palmitic  acid,  C15H33COOH.  Oleic  acid, 
C1.H33COOH,  is  unsaturated,  and  therefore  possesses  the  power  of 
decolorizing  dilute  bromine-water  and  of  combining  with  iodine. 
This  latter  propertj^  is  used  to  determine  the  amount  of  olein  present  in 
the  ordinary  fats,  which  are  mixtures  of  varying  proportions  of  olein, 
stearin,  and  palmitin.  The  melting-point  of  fat  also  varies  according 
to  the  relative  amounts  of  these  fats  present.  Olein  is  fluid  at  ordinary 
temperature,  melting  at  -5°  C;  whereas  palmitin  melts  at  45°  C, 
and  stearin  at  about  56°  C.  The  Huid  nature  of  fat  at  body  tempera- 
ture is  therefore  due  to  the  amount  of  olein  which  it  contains.  Butyrin 
occurs  in  the  fat  of  milk. 

When  a  liquid  fat  is  shaken  with  soap,  mucilage,  or  egg  albumin, 
it  becomes  finely  divided,  or  "  emulsified."  Rancid  fat  emulsifies  on 
addition  of  alkali  far  more  easily  than  neutral  fat,  because  soap  is 
formed  from  the  alkali,  free  fatty  acid  being  present,  and  the  soap 
renders  emulsification  easier.  Hence  the  fact  that  fat  is  rendered 
faintl}^  rancid  in  the  stomach  is  of  importance.  Emulsification  is  a 
physical  change;  the  minute  subdivision  hastens  the  chemical  change 
of  fat. 

By  hydrolysis  of  fat,  glycerine  and  fatty  acid  are  produced.  This 
process  is  known  as  saponification,  and  can  be  brought  about  by  such 
agencies  as  superheated  steam,    boiling  with   alkali,   long-continued 

53 


54  A  TEXTBOOK  OF  PHYSIOLOGY 

contact  with  air  (oxygen  is  taken  up  and  rancid  oil  produced),  the 
action  of  fat-sphtting  enzymes  or  Hpases. 
The  reaction  can  be  represented  thus: 

C3H,(OCj,H3,CO)3  +  3H.0  =  C3H3(OH)3  +  3Cj,H3,COOH 

Palmitin  GlyccMinc  i'almitic  acid 

In  true  saponification  the  fatty  acid  formed  combines  with  the 
alkali  present  to  form  a  soap : 

t^isHs^COOH  +NaHO=  Ci^HgiCGONa  +  H2O 

Soap 

Fats  from  different  species  of  animals  vary  in  composition,  and 
fats  from  different  parts  of  the  same  animal  have  \'arying  composition 
depending  upon  the  combination  of  individual  fats  which  form  the 
mixed  fat  of  any  part.  From  the  liver,  for  example,  fatty  acids, 
more  unsaturated  than  oleic  and  belonging  to  the  linolic  and  linolenic 
series,  have  been  isolated.  Milk  fat  is  characterized  by  its  yield  of 
butyric,  caproic,  caprylic,  and  other  volatile  fatty  acids.  From 
kidney  fat  an  acid  known  as  carnaubic  acid  has  been  isolated. 

Stearin,  CH20Ci8H3,0 
CH0Ci8H350 
CH,0C,A50 

occurs  generally  in  animal  fat,  but  is  found  also  in  certain  vegetable 
fats.  It  is  the  hardest  and  most  insoluble  of  the  three  common 
fats.  Its  melting-point  when  pure  is  55°  C,  but  as  obtained  from 
the  tissues  about  63°  C. 

Stearic  acid,  the  acid  of  stearin,  crystallizes  in  long  rhombic  plates, 
and  crystals  of  it  may  sometimes  be  seen  in  a  melted  rancid  fat  after 
it  has  solidified. 

Palmitin,  CIl.,OC^Ji^^O 

CHbCieH.^iO 

CH,OCi,H,iO 

occurs  largely  in  human  fat.  Its  melting-point  is  about  50°  C. 
Palmitic  acid  crystallizes  as  fine  needles. 

Olein,  CH2OC18H33O 
CH0Ci,H3,0 
CH,OCi8H3,0 

is  verj^  widespread,  being  found  in  most  animal  and  vegetable 
fats.  At  ordinary  temioeraturc  it  is  liquid,  solidifying  at  -  G°  C, 
and  acts  as  a  solvent  for  the  stearin  and  palmitin  of  ordinary 
fat.  The  melting-point  of  a  fat,  its  iodine  value,  and  staining 
properties  with  osmic  acid,  depend  upon  the  amount  of  oleic  acid 
present. 

The  fatty  acids  may  be  obtained  from  neutral  fats  by  treating 
with  dilute  mineral  acid,  when  the  fatty  acid  will  collect  as  an  oily 


FATS  AND  LIPOIDS  55 

scum  upon  the  top  of  the  fluid.     Fatty  acids  in  appearance  closely 
resemble  neutral  fats,  being  generally  almost  colourless. 

Fatty  acids  may  be  distinguished  from  neutral  fats — 
.  1.  By  their  reaction.  This  is  usually  tested  as  follows:  Some 
alcoholic  phenolphthalein  solution  is  added  to  alcohol,  and  one  drop 
of  weak  alkali  (1  per  cent,  sodium  carbonate)  added.  The  addition 
of  neutral  fats  will  not  discharge  the  red  colour  thus  produced,  fatty 
acids  will. 

2.  Fatty  acids  dissolve  in  cold  sodium  carbonate  to  form  a  soap; 
neutral  fat  is  insoluble  in  cold  sodium  carbonate. 

3.  The  acrolein  test.  The  acrolein  is  derived  from  glycerine. 
Neutral  fats  therefore  give  this  test,  fatty  acids  do  not.  To  ]ierform 
the  test,  the  substance  is  mixed  with  acid  potassium  suli^hate  (KHSOJ 
by  grinding  in  a  mortar.  Upon  heating  the  mixture  acrolein  is  evolved, 
if  the  test  is  positive,  and  may  be  recognized  by  its  acrid  smell  and  by 
the  fact  that  it  blackens  a  })iece  of  paper  dipped  in  an  ammoniacal 
solution  of  silver  nitrate. 

It  is  important  to  be  able  to  distinguish  different  forms  of  fat. 
The  chief  chemical  methods  emplo3'cd  are — 

1.  Melting-point.  This  varies  with  different  animals.  Mutton  fat, 
44°  to  51°  C,  is  generally  higher  than  pig  fat,  36°  to  46°  C. 

2.  Specific  gravity.  Some  melted  fats  will  float  in  alcohol  at  room 
temperature;  others  will  not.  For  example,  margarine,  which  often 
contains  light  vegetable  oils,  will  float,  pure  butter  will  sink. 

3.  Acid  value.     The  amount  of  free  fatty  acid  contained  in  the  fat. 

4.  Iodine  value.  The  percentage  amount  of  iodine  absorbed  by 
a  weighed,  quantity  of  fat.  This  depends  upon  the  amount  of  un- 
saturated fatty  acids  present,  such  as  olein. 

5.  The  amount  of  volatile  fatty  acids  present  (Reichert-Meissl  value). 
Obtained  by  saponifying  the  melted  fat  with  alcoholic  potash,  and 
treating  the  soap  thus  obtained  with  sxdphuric  acid.  Volatile  fatty 
acids  will  distil  off.  These  are  collected  in  standard  ^^^  alkali,  and 
their  amount  determined  by  titration.  Pure  butter  has  a  much 
higher  value  in  volatile  acids  than  has  margarine. 

Soaps  are  the  compounds  of  fatty  acid  and  a  base.  When  the 
base  is  sodium,  ordinary  washing  soap  is  obtained :  when  it  is  ])otassiinn. 
"  soft  "  soap  is  produced.  Those  are  soluble  in  water,  f.  'ming 
a  "  soapy  "  colloidal  solution.  They  are  "'  salted  out  '"  b\-  full  satura- 
tion with  ammonium  sulphate.  With  solutions  of  calcium  or  mag- 
nesium salts  they  yield  a  dense  white  2)recipitate ;  this  accounts  for 
the  dithculty,  familiar  to  everyone,  of  washing  with  a  ""  hcird  "  water. 

When  boiled  with  a  mineral  acid  (20  per  cent.  sul})huric),  the  fatty 
acid  is  displaced  from  combination,  and  collects  at  the  top  as  a  Avhitc 
scum  or  oily  fluid. 

If  lead  acetate  be  added  to  a  soap  solution,  a  white  ]n-ecipitatc  of 
lead  soap  (lead  plaster)  is  obtained. 


56  A  TEXTBOOK  OF  PHYSIOLOGY 

Section  II. 
Lipoids. — Uudcr  this  uanie  are  grouped  a  number  of  fat-like  (lijjoid) 
bodies,  rebciubliiig  fat  mainly  in  their  common  sohibiHty  in  certain 
solvents.  They  occur  in  the  protoplasm  of  all  cells,  and  are  probably 
bodies  of  wide  biological  significance.  They  are  particularly  abundant 
in  nervous  tissue.     They  may  be  classified  as  follows : 

I.  The  Phosphatides — bodies  containing  carbon,  hydrogen,  oxygen, 
nitrogen,  and  phosphorus. 

II.  The  Galactosides — bodies  containing  carbon,  hydrogen,  oxygen 
and  nitrogen. 

III.  The  Cholesterols — bodies  containing  carbon,  hjalrogen,  and 
oxygen. 

I.  The  PoHriPitATiDEs  are  all  compounds  of  the  triatomic  alcohol 
glycerine,  to  which  a  fatty  acid,  phosphoric  acid,  and  a  nitrogenous 
base  are  attached.  The  chief  members  of  this  group  are  the  lecithins. 
The  members  may  be  classified  according  to  the  proportion  of  nitrogen 
to  phosphorus  in  their  molecule : 

Monamino-monophosphatides :  lecithins,  cephalin. 

IN  IP 

Monaniino-diphosphatides :  cuorin. 

IN  2P 

Diamino-monoj^hosphatides :  sphingomyelin,  jecorin. 

2N  IP 

Diamino-diphosphatides,  etc. 

2N  2P,  etc. 

Triamino-monophosphatides :  carnaubin,  obtained  from  kidney 
fat,  belongs  to  this  group,  but  yields  no  phosphoric  acid. 

The  action  of  narcotics  and  of  chloroform  and  ether  has  been 
attributed  to  the  solubility  of  these  substances  in  the  phosphatides  of 
the  nerve  cells.  In  the  reactions  of  specific  cell  poisons,  toxins  such 
as  snake  poison,  and  ha^molysins,  lecithin  may  take  an  active  part. 
So,  too,  in  the  action  of  ferments.  Cholesterol,  on  the  other  hand, 
may  act  as  an  antibody,  precipitating  ferments,  and  neutralizing  the 
action  of  snake  venom. 

The  Lecithins.  The  lecithins  are  the  most  important  members 
of  this  group  of  phosphatides,  and  also,  perhaps,  the  most  important 
of  lipoids.  They  are  present  in  all  the  cells  of  the  body,  and  are 
particularly  plentiful  in  the  envelope  of  red  blood -corpuscles,  in 
nervous  tissue,  bone  marrow,  liver,  and  bile. 

The  lecithins  probably  play  an  important  part  in  the  metabolism 
of  the  cells,  forming  easily  dissociable  compounds  with  sugars,  pro- 
teins, etc.,  and  helping  in  the  transport  of  these  substances  in  the  body 
fluids.  The  fact  that  each  tissue  has  its  specific  lipoid  helps  to  endow 
that  tissue  with  it;i  specific  function.  In  the  nervous  tissues  these 
substances  arc  of  paramount  importance,  and  on  extensive  degenera- 
tion of  nervous  tissue  the  body  becomes  poorer  in  kcithhis. 


FATS  AND  LIPOIDS  57 

Lecithins  differ  from  fats  in  containing  nitrogen  and  phosphorus. 
Two  of  the  hydroxyl  groups  of  the  glycerine  radical  are  combined 
with  fatt}^  acids,  the  remaining  one  being  linked  to  phosphoric  acid  in 
conjunction  with  an  ammonium  base,  chohn.  The  structural  formula 
of  lecithin  is,  therefore — 


/  CH,OCi,H35CO| 
CHOC17H35CO  f 


Stearic  acid 
Glycerine 

OH 
[  CR^— 0— P— 0 

^  0-N=  (CH3)3 

Phosphoric  \ 

Acid  CH.,— CH.OH 

Cholin 

Pure  lecithin  has  a  waxy  appearance;  it  is  soluble  in  alcohol  and 
chloroform,  less  soluble  in  ether.  When  mixed  with  water  and  viewed 
under  the  microscope,  it  gives  out  peculiar  processes  which  remind 
one  of  the  pseudopodia  of  an  amoeba.  There  are  various  lecithins, 
which  differ  according  to  the  fatty  acid  combined  with  the  molecule. 

Like  the  fats,  the  lecithins  can  be  hydrolyzed.  When  saponified 
they  yield  fatty  acid,  glycerophosphoric  acid,  and  cholin: 


C4iH9oNP09  +  3H20  = 

=  2{C,sR,,0,)  +c,}i,-po,+c,ii,,m, 

Lecithin 

Stearic              Glycero-             Cholin 

acid              phosphoric 

acid 

Lecithin  is  split  up  by  cell  ferments,  and  phosphatides  may  be 
rebuilt  in  the  laboratory  of  the  cell. 

Cholin — trimethyloxyethylammonium  hydrate — 

OH 

(CH3)3N- 

CH2.CH2OH 

— is  closely  related  to  the  alkaloid  muscarin.  Methylamines  are  among 
the  products  of  bacterial  decomposition  of  lecithins.  Neurln,  which 
contains  one  molecule  of  Avater  less  than  cholin,  is  a  very  poisonous 
product,  and  may  be  the  cause  of  "ptomain"  poisoning.  ChoUn  pro- 
duces a  marked  fall  of  blood-pressure  when  injected  into  the  blood.  It 
is  said  that  cholin  occurs  in  the  blood  and  spinal  fluid  when  nervous  tissue 
is  undergoing  degeneration,  and  can  be  isolated  as  yellow  octahedral 
crystals  by  adding  platinum  chloride  to  an  alcoholic  extract  of  the 
fluids.  These  crystals  differ  from  similar  ones  obtained  by  the  inter- 
action of  potassium  chloride  (also  present  in  b'ooi)  with  platinum 
chloride,  in  that  thej^  become  changed  when  treated  with  a  strong  solu- 
tion of  potassium  iodide  to  dark  brown  plates.  The  claim  that  choHn 
can  be  demonstrated  in  these  fluids  has  not  met  with  general  acceptance. 
II.  The  GALACT031DE5. — These  bodies  occur  largely  in  the  body 
known  as  protagon,   obtained  from  the  brain  tissue.     They  are  so 


58  A  TEXTBOOK  OF  PHYSIOLOGY 

(•all(!(l  hecaii.so  ii])on  hydrolysis  they  yield  the  reducing  sugar  galactose, 
ill  addition  they  also  yield  a  base  known  as  sphingosiii,  and  an  acid 
of  a  fatty  acid  nature.  The  two  chief  members  of  this  group  are 
cerebrin,  or  ])hrenosin.  and  kerasin. 

TTT.  The  Cholesterols. — Cholesterol,  C^.H,.OH,  chemically  s])eak- 
ing  belongs  to  quite  a  different  series  of  t)odies.  It  contains  neither 
nitrogen  nor  phosphorus,  and  is  prol)ably  a  monatomic  alcohol  of  the 
terpcne  series.  Bodies  of  this  series  are  common  in  plants,  examples 
being  camphor  and  turpentine.  The  following  formula  has  been 
suggested : 

(CH,)^  -  OH— CH^— CH^— Ci.H.,  — CH  =  CH, 

CH,        CH, 

CH(OH) 

It  occurs  in  all  the  cells  and  fluids  of  the  body  in  small  quantities, 
but  particularly  in  nervous  tissue  and  in  the  envelope  of  the  red  blood- 
corpuscles.  It  is  also  present  in  the  bile,  from  which  in  catarrhal 
states  of  the  bile-ducts  it  may  sometimes  separate,  forming  biliary  calcvdi. 

Cholesterol  is  probably  not  merely  a  waste  product  as  it  was  once 
deemed  to  be.  As  stated  above,  it  hinders  the  action  of  ferments  and 
also  that  of  certain  poisons,  such  as  snake  venom  and  saponin,  upon 
the  red  blood-corpuscles. 

It  is  sometimes  found  as  an  ester  in  the  liver  and  plasma  in  com- 
bination with  a  fatty  acid  such  as  oleic,  palmitic,  or  stearic.  It  occurs 
also  in  the  suprarenal  capsules  in  this  form. 

Cholesterol  is  soluble  in  ether,  chloroform,  and  warm  alcohol.  Its 
solutions  are  dextrorotatory.  From  these  it  crystallizes  in  charac- 
teristic colourless  transparent  plates,  each  with  a  small  piece  knocked 
out  of  the  corner.  It  is  insoluble  in  water,  dilute  acids,  or  alkalies. 
The  most  general  tests  for  cholesterol  are— 

1.  A  red  coloiu'  results  when  concentrated  sidphuric  acid  is 
added  to  a  chloroform  solution  of  cholesterol.     (Salkowski's  test.) 

2.  A  play  of  colours,  red,  blue,  green,  is  obtained  when  the 
same  acid  is  added  to  a  solution  of  cholesterol  in  acetic  anhydride. 
(Liebermann's  test.) 

Isocholesterol,  a  body  similar  to  cholesterol  in  most  respects,  is 
found  in  sebum.  It  differs  from  cholesterol  in  not  giving  Salkowski's 
test,  and  in  being  levorotatory  in  solution. 

Phytocholesterol  is  the  special  name  ajiplicd  to  the  cholesterols 
of  plants,  from  ^hich  animal  cholesterols  are  probably  derived. 

Cephalin  is  found  largely  in  both  the  Avhite  and  grey  matter  of 
nervous  t  issues.    It  is  soluble  in  ether  and  chloroform,  but  not  in  alcohol . 

Sphingomyelin  is  found  in  protagon,  and  also  in  the  suprarenal 
capsules. 

Jecorin  is  found  in  the  liver.  It  is  probably  a  combination  of  a 
phosjjhatide  and  a  sugar. 


CHAPTER  VII 
THE  CARBOHYDRATES 

These  important  foodstuffs  occur  abundantly  in  the  vegetable 
kingdom,  and  are  also  found  in  small  quantities  in  the  animal  kingdom, 
either  in  the  free  state  or  combined  with  proteins.  As  a  group  the 
carbohydrates  form  one  of  the  chief  energy-producers  or  foods. 

As  their  name  implies,  they  are  composed  of  carbon,  hydrogen, 
and  oxygen,  the  latter  elements  being  j^resent  in  the  proportion  found 
in  water  (2  :  1).  Their  general  formula  is  C^^^H.^ifin-  It  was  at  one 
time  thought  that  carbohydrates  were  bodies  containing  six  atoms 
of  carbon  or  some  multiple  thereof.  This  is  now  known  not  to  be  the 
case;  indeed,  the  most  recent  classification  of  the  simplest  members 
of  the  group  is  according  to  the  number  of  carbon  atoms  contained 
in  the  molecule;  those,  for  example,  containing  three  atoms  being 
termed  trioses,  those  with  five  atoms  pentoses,  those  with  six  atoms 
hexoses,  and  so  on.  It  must  not  be  thought  that  all  bodies  containing 
C,  H,  0,  with  the  hydrogen  and  oxygen  in  the  proportion  of  water, 
are  contained  in  the  group  of  carbohydrates;  for  example,  C.^H^Oa 
is  the  empirical  formula  for  acetic  acid,  CgHgOg  that  of  lactic  acid. 

Nevertheless,  the  definition  holds  for  the  most  part,  and  the  best- 
known  members  of  the  series  do  contain  six  molecides  of  carbon  or 
some  multiple  of  six.     These  are  generally  grouped  as  follows: 

1.  The  monosaccharides — CV.HjoOr, 

2.  The  disaccharides— Ci.Ho.O,"'! 

3.  The  polysaccharides — (CpHjoOg)^ 


Section  I 

The  Monosaccharides. — The  chief  monosaccharides  of  physio- 
logical importance  arc  the  hexoses,  dextrose,  levulose,  and  galactose. 
Each  has  the  em})irical  formula  C,.Hi._,0,,.  Dextrose  is  the  aldehyde  of 
the  hexatomic  alcohol  sorbite;  levulose  is  the  ketone  of  the  hexatomic 
alcohol  mannite;  galactose  is  the  aldehyde  of  another  hexatomic; 
alcohol,  dulcite.  Each  alcohol  has  the  formula  C,.H^(OH)|..  The 
structural  formula  of  these  sugars  mav  be  represented  as  given  on 
p.  60. 

Levulose  differs  from  the  other  t^o  in  being  a  ketone;  dextrose 
and  galactose  differ  from  each  other  and  from  their  many  isomers 
in  the  position  of  the  so-called  as}  inmetric  carbon  atoms.     All  bodies 

59 


CO 


A  TEXTBOOK  OF  PHYSIOLOGY 


like  the  above,  which  rotate  the  phiiie  of  pohirized  hght,  contain  one 
or  more  asymmetric  atoms. 


COH 

I 
HCOH 

HOCH 

I 
HCOH 

1 
HCOH 


CH2OH 

Dextrose 


CH.OH 

CO 

I 

HCOH 

I 
HOCH 

1 
HOCH 

CH2OH 

Lovulosc 


COH 

I 
HCOH 

I 
HOCH 

I 
HOCH 

HCOH 

CH2OH 

Galactose 


The  waves  of  light,  moving  onwards,  vibrate  in  every  plane.  When  they  pass 
through  a  quartz  plate  they  are  plane  polarized,  and  vibrate  only  in  one  plane.  A 
.stretched  string  can  be  plucked  and  made  to  A'ibrate  from  side  to  side,  or  from 
above  down,  or  in  any  other  plane.  If  the  string  passes  through  a  vertical  slit, 
it  can  onlj'  be  made  to  vibrate  in  the  above-down  direction;  it  is,  so  to  speak, 
jjlane  polarized.  The  quartz  plate  has  a  similar  effect  on  light.  If  two  quartz 
plates  are  arranged  so  that  the  light  must  pass  through  both,  then  the  light  polarized 
by  the  first  plate  can  pass  through  the  second  if  this  be  placed  with  its  optical  axis 
in  the  same  relation  as  that  of  the  first  plate.  If  the  second  plate  is  turned  at  right 
angles  to  the  first  plate,  the  light  polarized  by  the  first  plate  cannot  pass  the  second. 
If  a  solution  which  rotates  polarized  light  is  placed  in  a  tube  between  the  two  quanz 
plates,  its  efiect  on  the  rotation  of  the  second  quartz  plate  can  be  determined.  Special 
instruments  called  polarimc  '^ers  are  contrived  for  measuring  the  effect  of  solutions 
on  the  rotation  of  polarized  light,  and  so  arriving  at  the  strength  of  the  solutions, 
e.g.,  of  sugar. 

The  various  groups  may  be  arranged  in  a  figure  round  an 
asymmetric  carbon  atom  so  that  one  arrangement  corresponds  to 
dextrorotation,  another  to  levorotation.  The  two  figures  cannot  be 
superimposed  so  that  the  same  two  groups  coincide.  In  this  respect 
it  is  interesting  to  note  that  Pasteur  found  that  racemic  acid,  which 
has  holohedral  crystals,  and  is  neutral  in  its  action  to  polarized 
light,  could  be  decomposed  into  dextrorotatory  and  levorotatory 
tartaric  acids  with  hemihedral  crystals.  Of  these  crystals,  those 
which  were  right-sided  gave  dextrorotation,  those  which  were  left- 
sided  gave  levorotation.  By  growing  Penicillium  glaucum  upon 
racemic  acid,  the  dextrorotatory  portion  of  ordinary  tartaric  acid  is 
destroyed  and  the  levorotatorj^  acid  is  left. 

The  monosaccharides  are  colourless  cr3'stalline  bodies  (with  a 
sweetish  taste)  readily  soluble  in  water,  with  difficulty  soluble  in 
alcohol,  and  insoluble  in  ether.  They  possess  the  property  of  depositing 
metallic  silver  from  ammoniacal  silver  solutions,  cuprous  oxide  from 
alkaline  coj)per  solutions,  and  bismuth  suboxide  from  alkaline  bismuth 
solutions.  This  property  is  of  especial  value  as  a  test.  The  chief 
tests  are  the  following : 

1.  Moore's  test.  Upon  heating  with  one  quarter  of  its  volume  of 
strong  caustic  potash  or  soda,  the  solution  becomes  yellow,  then  brown, 


THE  CARBOHYDRATES  61 

due  to  the  formation  of  caramel  and  levulinic  acid;  a  faint  odour  of 
caramel  is  also  produced. 

2.  Trommer's  test.  A  mixture  of  weak  copper  sulphate  and 
potassium  hydrate  yields,  on  heating  with  the  sugar  solution,  a  red 
precipitate  of  cuprous  oxide.  At  first  cupric  hydrate  is  formed  by 
the  interaction  of  the  alkali  and  the  copper  sulphate;  this  hydrate  is 
then  reduced  to  cuprous  hydrate,  with  the  formation  of  acid.  The 
cuprous  hydrate  on  further  heating  loses  water,  forming  cuprous 
oxide. 

1 .  CuSO^  +  2K0H  =  Cu(OH).,  +  K0SO4 

Copper       Caustic         Cupric     Potassium 
siilpliato       potash        hydrate      sulj)hate 

2 .  2Cu(OH)2  +  RCHO  =  Cu2(OH)2  +  R.COOH  +  H2O 

Cupric         Aldehyde        Cuprous  Acid  and  water 

hydrate  lij^drato 

3.  Cu,(OH)+H20  =  Cu20 

The  above  only  takes  place  when  the  amount  of  copper  solution  is 
neither  too  little  nor  too  much.  Excess  of  copper  salt  leads  to  the 
formation  of  brown  cupric  hydrate,  which  spoils  the  test. 

3.  Fehling's  test.  For  this  reason  the  excess  of  copper  salt  is 
generally  held  in  solution  by  the  addition  of  Rochelle  salt  (sodium 
potassium  tartrate)  in  definite  proportion  to  the  alkali  and  copper 
salt.  This  is  known  as  Fehling's  solution.*  When  freshly  prepared 
it  is  unaltered  by  boiling.  It  is  reduced  by  all  the  sugars  except 
cane-sugar.  Unfortunately,  it  is  also  reduced  by  other  bodies,  such 
as  uric  acid,  creatinin,  glycuronic  acid,  etc. 

4.  Nylander's  test.  This  disadvantage  does  not  pertain  so  much  to 
the  salts  of  bismuth.  The  solution  most  generally  employed  is  Nylander's 
solution. f  Upon  boiling  for  a  few  minutes  with  a  sugar,  the  solution 
goes  yellowish-brown  to  black,  and  finally  deposits  a  precipitate  of 
metallic  bismuth.  Glycuronic  acid  gives  this  test;  uric  acid  and 
creatinin  do  not. 

5.  Barfoed's  test.  An  acid  solution  of  cupric  acetate  gives  a  red 
precipitate  with  the  monosaccharides. 

6.  Phenylhydrazine  test.  This  test  consists  in  heating  about  10  c.c. 
of  the  sugar  solution  in  a  test-tube  on  a  water-bath  with  phenyl- 
hydrazine  hydrochloride  and  sodium  acetate — as  much  as  will  cover 
a  threepenny-piece  of  the  former,  and  a  sixpenny-piece  of  the  latter. 
After  about  thirty  minutes  a  yellow  crystalline  precipitate  settles  out 
which  looks  like  yellow  sheaves  under  the  microscope. 

The  osazones  yielded  by  dextrose  and  levulose  are  the  same;  that 
of  galactose  is  the  same  in  appearance,  but  differs  in  melting-point 
(see  table,  p.  04). 

Of  the  disaccharides,  cane-sugar  does  not  yield  an  osazone;  until 

*  Fehling's  solution  =  Copper  sulphate  3-l*30  grammes,  NaOH  50-60,  Rochelle 
salt  173  grammes,  per  litre  of  water. 

t  Nylander's  solution  ==  Bismuth  subnitra to  20  grammes,  Rochelle  salt  40  grammes, 
dissolved  in  1,000  c.e.  of  8  per  cent.  NaOH. 


,  62  A  TEXTBOOK  OF  PHYSIOLOGY 

it  becomes  inverted;  lactose  yields  distinctive  crystalline  rosettes, 
which  are  better  obtained  if  a  little  free  acetic  acid  be  also  added  to 
the  sugar  solution;  maltose  yields  an  osazone,  so  soluble  that  it  does 
not  appear  until  the  solution  is  cooled. 

7.  Molisch's  test.  All  carbohydrates  yield  with  a-naphthol  and 
sulphuric  acid  a  purple  colour.  The  greenish  colour  which  is  also 
present  forms  no  part  of  the  test.  The  test  is  ver}^  sensitive;  carbo- 
hydrates linked  to  proteins  yield  it. 

8.  The  Fermentation  test.  This  is  a  very  useful  test  for  aiding  in 
distinguishing  the  different  sugars.  The  sugar- solution  is  introduced 
with  a  small  piece  of  brewer's  yeast  into  a  Southall's  urometer  (see 
p.  4r)8),  and  placed  in  an  incubator  at  37"  C.  The  production 
of  carbon  dioxide  gas  indicates  fermentation.  A  control  tube  of 
3^east  and  water  should  yield  no  gas. 

9.  The  Polarimetric  test.  This  consists  in  determining  the  rotation 
power  of  a  solution  of  known  strength  of  the  sugar.  In  the  case  of 
disaccharides  the  rotatory  power  is  determined  before  and  after 
inversion  with  acid.  Each  disaccharide  behaves  differently  on  hydro- 
lysis (see  table,  p.  64). 

Dextrose  (also  termed  glucose  and  grape-sugar)  occurs  abundantly 
as  such  in  the  grape,  in  other  sweet  fruits,  seeds  and  roots,  and  honey ; 
it  is  more  often  found  in  conjunction  with  levulose.  It  is  formed  by 
boiling  starches  and  dextrins  with  dilute  sulphuric  acid,  the  syrupy 
sugar  thus  formed  being  largely  em])loyed  in  beer,  jam,  and  sweet 
making.  Occasionally  arsenical  impurities  in  the  common  sulphuric 
acid  (oil  of  vitriol)  used  in  this  process  have  led  to  cases  of  arsenical 
poisoning.  It  is  also  produced  from  starch  by  hydrolytic  changes  in 
the  alimentary  tract.  Dextrose  is  the  sugar  found  in  the  blood  and 
muscles  (1  per  1,000  parts),  being  an  important  source  of  energy  to  the 
latter.  Under  normal  conditions  only  the  merest  trace  occurs  in  the 
urine.  In  the  body  it  is  converted  into  and  stored  as  animal  starch 
or  glycogen.     The  specific  power  of  rotation  of  glucose  is  +  52-6. 

Levulose  (fructose)  occurs  widely  in  conjunction  with  dextrose  in 
fruits,  and  also  in  hone}'.  It  is  generally  obtained  as  the  result  of 
the  splitting  up  of  cane-sugar.  It  may  occur  in  the  urine.  It  is 
readily  soluble  in  water,  but  not  in  cold  alcohol.  Its  levorotatory 
power  is  about  —  93.  It  gives  the  usual  reducing  tests,  and  ferments 
readily  with  yeast.  Its  osazone  is  similar  to  that  of  dextrose,  the 
melting-point  being  204°  C.  The  characteristic  test  for  levulose  is 
known  as  Seliwanoff's  test.  When  one  part  of  HCl  in  two  parts  of 
water,  in  which  a  few  crystals  of  resorcin  have  been  dissolved,  is 
added  to  levulose,  a  deep  cherry-red  colour  results. 

Galactose  is  obtained  by  the  splitting  of  lactose  (milk-sugar).  It 
is  also  obtained  when  certain  lipoids  (galactosides)  are  split  by  weak 
mineral  acids.  It  is  less  soluble  in  water  than  dextrose.  It  gives  the 
reducing  tests.  Its  osazone  melts  at  196°  to  197°  C.  It  turns  the 
plane  of  polarized  light  to  the  right,  its  rotatory  power  being  -f  81. 
With  yeast  it  ferments  but  slowly.     Upon  oxidation  with  nitric  acid 


THE  CARBOHYDRATES  63 

it  3uekls  first  galactonic  and  then  mucic  acid;  the  latter,  being  in- 
soluble, separates  out  as  crystals. 

The  Pentoses,  CgH^^Og,  occur  as  the  complex  carbohj'drates  of 
the  vegetable  world,  known  as  pentosans.  They  also  occur  in  the 
constitution  of  certain  nucleoproteins  of  the  animal  kingdom  (see 
p.  49).  They  are  of  interest  as  occurring  in  human  urine  in  the  rare 
anomaly  of  metabolism  known  as  pentosuria. 

Glyeuronic  acid,  C,.HjqO., 

CHO 

(CH0H)4 

I 
COOH, 

is  a  derivative  of  dextrose.  It  is  found  as  a  combined  acid  in  the 
blood,  bile,  and  urine.  It  gives  the  same  reduction  tests  as  dextrose, 
and  also  the  special  pentose  reactions  (q.v.).  The  osazone,  which 
resembles  glucosazone,  is  difficult  to  obtain.  With  bromphenylhy- 
drazine  hydrochloride  a  gh'curonate  is  formed  characterized  by  its 
insolubilit}^  in  alcohol.  Glj'curonic  acid  itseH  is  dextrorotator}',  but 
its  compounds  are  levorotatory. 

Glucosamine,  CgHjgNOj, 

CH,OH 

1     ■ 
(CH0H)3 

CHNH, 

1 
COH, 

also  called  chitosamine,  is  most  readily  prepared  from  ehitin  {e.g., 
decalcified  lobster  shells)  by  the  action  of  strong  hydrochloric  acid. 
It  is  an  amino  sugar,  and  has  been  obtained  from  glucoproteins  (mucins) 
and  other  proteins.  Glucosamine  has  reducing  properties  similar  to 
dextrose,  yields  the  same  osazone,  but  is  not  fermentable. 

Sectiok  II. 

The  Disaccharides  (Ci-iHooO^^).  —  The  disaccharides  cane-sugar, 
maltose,  and  lactose,  are  to  be  regarded  as  the  combination  of  two 
molecules  of  monosaccharides  with  the  elimination  of  a  molecule  of 

C12II22O11  +  H3O  =  CgHioOg  +  CgHi^Ofi 

Cane-sugar -f- water  =  dextrose-H  levulose 
Maltose  -|-  water=dextrose-l-  dextrose 
Lactose  -h  water  =  dextrose  +  galactose 

Each  disaccharide  is  readily  split  by  boiling  with  Aveak  mineral 
acid  into  its  component  monosaccharides.     Cane-sugar  may  also  be 


04 


A  TEXTBOOK  OE  rHYSIOLiXlY 


split  by  weak  organic  acids  such  as  citric  and  tartaric.  This  process, 
one  of  hydrolysis,  is  sometimes  termed  inversion  owing  to  the  fact  that 
cane-sugar  before  hydrotysis  is  dextrorotatory,  but  after  hydrolysis 
is  levorotatory.  In  the  case  of  maltose  and  lactose  the  term  is  also 
employed,  but  no  inversion  of  polarized  light  takes  place  on  hydrolysis ; 
maltose  gives  a  considerable  fall,  lactose  a  slight  rise,  in  rotating 
power  after  "  inversion." 

None  of  the  disaccharides  yields  Barfoed's  test. 

Cane-sugar,  or  saccharose,  occurs  widely  in  the  plant  world,  very 
abundantly  in  the  sugar-cane  and  the  sugar-beet.  It  jDossesses  a 
distinctly  sweet  taste,  is  easily  soluble  in  water,  but  with  difficulty  in 
alcohol.  Its  rotator}^  power  is  60-5  before,  and  -  20  after,  inversion. 
In  other  resjaects  it  gives  few  positive  tests.  It  does  not  give 
Moore's  test  nor  the  ordinary  reducing  tests.  It  gives  no  osazone. 
It  does  not  ferment  with  yeast  mitil  inverted. 


The  Reactions  op  Monosaccharides  and  Disaccharides. 


Dextrose. 

Levidose. 

Galactose. 

Maltose. 

Lactose. 

;     Cane- 
Sugar. 

Moore's  test 
(KOH) 

+ 

+ 

+ 

-t- 

-f- 

- 

Trommer's  test 
(CUSO4+  KOH) 

+ 

-1- 

-1- 

-Fve 

33% 

weaker 

than  D. 

-Fve 
26-50/, 
weaker 
than  D. 

Fehling's  test 

(CuS04+K0H-f- 

Rochelle  salt) 

-1- 

+ 

-1- 

+ 

+ 

— 

Nylander's  test 

(bismuth  sub- 

nitratt  +  KOH-t- 

Rochelle  salt) 

+ 

+ 

+ 

-1- 

i 

-1- 

Barfoed's  test  (acid 
cupric  acetate) 

-f- 

+ 

-f 

- 

- 

- 

Phenylhydrazine 

test  (Osazone 
crystals  formed) 

Long  thin 
needles 
M.P.  204 

Long  thin 
needles 
M.P.  204 

Long  thin 
needles 
M.P.  186 

Short 

thick 

needles 

;M.P.  206 

YeUow 
rosettes 
M.P,  201 

Rotary  power  on 
polarized  light 

-1-52-7 

-93 

-1-81 

+  137 

-t-52-5 

+  66-5 

Effect  of  hydro- 
lysis on  rotary 
power 

— 

— 

— 

Marked 
fall 

Slight 
rise 

Inverted 

to  20 
to  the  left 

Yeast  fermentation 
test 

Marked 

Marked 

Very 
little 

Marked 

Nil 

Marked 

after 
inversion 

Solubility  in  alco- 
hol; cane-sugar  =1 

— 

+ 

—       1 

Insol. 

1 

THE  CARBOHYDRATES  65 

Maltose  is  produced  as  the  result  of  hydrolytic  changes  either  by 
the  action  of  acids  or  of  enzymes  upon  starch.  It  is  readily  soluble 
in  water,  and  fairly  soluble  in  alcohol.  Its  solutions  are  dextro- 
rotatory: [ajjj  =  137-139.  It  ferments  readily  with  yeast.  It  gives 
the  same  reduction  tests  as  dextrose,  with  the  exception  of  Barfoed's. 
The  osazone  is  difficult  to  prepare,  requiring  warming  for  as  long  as 
one  and  a  half  hours.  The  crystals  are  characteristic  in  shape, 
being  coarser  than  those  of  dextrososazone.  Their  melting-point 
is  205°. 

Lactose  is  the  characteristic  animal  sugar,  being  found  only  in 
milk,  and  occasionally  in  the  urine  of  pregnant  women.  It  dissolves 
fairly  readily  in  water,  has  a  faint  sweetish  taste,  and  is  insoluble 
in  alcohol.  Its  solutions  are  dextrorotatory,  and  [aj^  =  52-5.  With 
the  exception  of  Barfoed's  it  gives  all  the  reduction  tests.  Its 
osazone  forms  characteristic  rosettes,  and  has  a  melting-point 
of  201°  C.  With  nitric  acid  it  yields  mucic  acid  crystals.  It  is  not 
fermentable  with  pure  j^east,  but  it  undergoes  alcoholic  fermentation 
with  the  "  kephir"'  fungus.  With  this  fiingus  an  alcoholic  drink  is 
prepared  chiefly  from  mare's  and  camel's  milk. 


Section  III. 

The  Polysaccharides. — This  group  includes  the  more  complex 
■carbohydrates,  such  as  the  dextrins  and  vegetable  gums,  starches  and 
celluloses.  They  are  characterized  by  the  large  size  of  their  molecule, 
being  tlierefore  colloidal  in  nature. 

The  Celluloses  (C^H^qO.)??-. — Plant  cellulose  is  in  reality  a  mixture 
of  celluloses.  These  bodies  are  insoluble  in  hot  or  cold  water, 
alcohol,  ether,  and  dilute  acids  or  alkalies.  They  are  soluble, 
Jiowever,  in  ammoniacal  copper  oxide  solution  (Schweitzer's  re- 
agent), from  which  they  are  precipitated  by  acids.  When  acted 
upon  with  strong  sulphuric  acid,  cellulose  yields  a  substance  known 
as  amyloid,  which  gives  a  blue  colour  with  iodine  solution;  by  pro- 
longed treatment  dextrose  is  produced.  By  the  action  of  strong 
nitric  acid,  explosives  (nitro-celluloses)  such  as  gun-cotton  are 
produced. 

In  the  intestinal  tract,  particularly  of  herbivora,  the  enzyme  known 
as  cytase  partially  decomposes  cellulose. 

The  Starches  (C^-Hj^oO^)/?-  are  a  reserve  food  of  wide  distil 
bution  in  the  vegetable  kingdom,  being  stored  as  grains  shaped  in 
various  forms  in  seeds  (the  cereals),  tubers  (potatoes),  etc.  As  a 
commercial  product  starch  is  a  white  amorphous  powder  without  taste 
or  smell,  insoluble  in  cold  water,  but  jdelding  an  emulsion  with 
hot  water.  A  starch  emulsion  is  best  made  by  mixing  starch  to  a 
paste  in  the  cold,  and  gradually  stirring  this  into  boiling  water,  a  well- 
known  domestic  process.  By  the  action  of  the  boiling  water  the  starch 
grains  are  made  to  swell  up  and  break,  and  the  starch  i«  eon  verted 


m 


A  TEXTliOOK  OF  PflYSTOLOCY 


from  the  variety  known  as  in.solii))le  starch  into  sohible  starch.  The 
sohition  yields  a  characteristic  bhie  colour  with  iodine  solution,  which, 
if  sufficient  starch  be  present,  disappears  on  heating,  and  reappears 
on  cooling.  2-5  to  4-G  j^er  cent,  solutions  exhibit  a  rotatory  power  of 
about  +202.  Starch  gives  neither  Moore's  nor  Trommer's  test,  and 
none  of  the  other  reduction  tests.  It  does  not  ferment  with  yeast. 
Upon  boiling  witli  dilute  acid,  or  under  the  action  of  the  grouji  of 
enzymes  known  as  diastases,  it  is  split  first  into  dextrins  and  then 
into  sugars,  maltose  being  formed  as  the  result  of  enzyme  action, 
dextrose  by  the  action  of  the  acids.  Starches  are  "  salted  out  "  by 
half-saturation  with  ammonium  sulphate.  They  are  also  precipitated 
from  their  solutions  by  50  to  55  jier  cent,  alcohol.  In  some  plants, 
such  as  the  tubers  of  the  dahlia,  a  special  variety  of  starch  known 
as  inulin  occurs.  It  forms  an  amorphous  white  powder,  differing 
from  ordinary  starch  in  giving  a  yellow  colour  with  iodine  solution, 
and  yielding  levulose  on  h3^drolysis  with  acid.  Diastatic  enzjmies  have 
little  or  no  effect  on  this  body. 

Glycogen,  or  animal  starch,  found  chiefly  in  the  liver  of  animals,  is 
obtained  as  a  white  amorphous  powder  soluble  to  an  opalescent  solu- 
tion in  water.  It  gives  a  mahogany  brown  colour  with  iodine,  is  pre- 
cipitated from  solution  by  60  per  cent,  alcohol  and  basic  lead  acetate. 


Characterlstic  Reactions  of  Polysaccharides. 


Starch. 

Glycogen. 

Eryihrodextrin. 

Achroodextrin. 

Moore's  test 

- 

- 

Reduction  fests: 
Trommer,  etc. 

~ 

— 

- 

- 

Ditto  after 
hydrolysis 

+ 

+ 

+ 

+ 

S  olubility  in 
water 

Opalescent ; 

sol.  in 

hot  water 

Opalescent 

solution  in 

cold 

Clear  solution 
in  cold 

Clear  solution 
in  cold 

Solubility  in 
alcohol 

Insol. 

Precipitated 
by  60% 

Precipitated  by 
80%-85% 

Precipitated  by 
90% 

Iodine  solution 

Blue 

Mahogany 
brown 

Red 

No  colour 

Salting  out  with 
Am^SOi 

Half- 
saturation 

Full 

Full 

Not  salted 
out 

Basic  lead 
acetate 

Precipitated 

Precipitated 

Not  precipitated 

Not  precipitated 

Dextrins  (C'^HjqO-)?^. — These  are  the  first  products  of    the  hydro- 
lysis of  starches  produced  by  the  action  of  weak  acids  or  of  starch- 


THE  CARBOHYDRATES  07 

splitting  enzymes.  Commercial  dextrin  is  a  sweetish,  sticky  amorphous 
powder.  It  probably  consists  of  many  dextrins,  of  which  two  may 
be  mentioned — erythrodextrin  and  achroodextrin.  It  often  contains 
some  reducing  sugar. 

Erythrodextrin,  or  "red  dextrin,"  as  its  name  imi^lies,  is  so  called 
because  it  yields  a  port-wine  colour  with  iodine  solution.  It  is 
regarded  as  the  first  product  of  the  hydrolysis  of  soluble  starch.  It  is 
distinguished  from  glycogen  by  giving  a  clear  solution  in  hot  water, 
and  requiring  80  to  85  per  cent,  alcohol  to  precipitate  it  from  solution. 
It  is  also  not  precipitated  by  basic  lead  acetate  solutions.  It  requires 
full  saturation  with  ammonium  suljjhate  to  salt  it  out  (see  table,  p.  00). 

Achroodextrin,  or  ''  colourless  "  dextrin,  gets  its  name  because  it 
giv^es  no  colour  with  iodine  solution.  It  occurs  at  a  later  stage  in  the 
hydrolysis  of  starch;  being  of  smaller  molecular  weight,  90  })er  cent, 
alcohol  is  required  to  precipitate  it  from  solution.  The  dextrins  when 
pure  do  not  give  Moore's  test,  Trommer's,  or  other  reduction  tests; 
these  are  only  given  after  hydrolysis  to  sugars  has  taken  place. 


CHAPTER  VllI 

ENZYMES  OR  FERMENTS 

The  chemist  recognizes  a  class  of  bodies  of  far-reaching  action 
called  catalysts.  A  catalyst  is  a  substance  which  by  its  presence 
hastens  a  chemical  reaction.  A  catalyst  cannot  start  a  reaction. 
Chemical  eqviilibrivim  depends  on  the  laws  of  chemical  dynamics, 
on  the  nature  of  the  reacting  substances,  their  active  mass  or 
concenti'ation,  and  external  conditions  such  as  temperature,  pressure, 
etc.  A  catalyst  cannot  alter  the  equilibrium  of  forces,  or  the  final 
transformation  of  energy  due  to  a  reaction.  It  can  only,  so  to  speak, 
oil  the  wheels  of  the  machine.  When  dry  hydrogen  and  oxygen  gas 
are  mixed,  they  combine  to  form  water,  but  with  such  slowness  that 
the  reaction  2H2  +  02^21120  escapes  observation.  Finely  divided 
platinum  acts  as  a  catalyst,  and  enormouslj^  accelerates  this  reaction. 
The  catalysts  may  accelerate  a  reversible  reaction  in  either  direction. 
Thus,  in  the  common  type  of  reaction. 

Acid  and  alcohol  ;^  ester  and  water, 

the  acid  ester  in  the  presence  of  a  great  excess  of  water  can  almost 
wholly  be  split  into  acid  and  alcohol,  while  in  strong  concentration 
most  of  the  acid  and  alcohol  goes  to  form  the  ester.  The  same  catalyst 
can  accelerate  this  reaction  in  either  direction  according  to  the  condi- 
tions. 

Enzymes  (ev  (vfjiyj,  in  yeast)  or  ferments,  are  bodies  which  act  like 
catalysts,  and  have  the  power  of  accelerating  the  rate  of  hydrolysis 
of  certain  substances  or  substrates.  Probably  all  the  reactions  which 
take  place  within  living  cells,  or  are  produced  in  digests  by  the 
secretions  of  the  cells,  are  aceelerated  b}'  enzymes.  It  is  the  accelera- 
tion of  any  reaction  which  makes  it  manifest  and  effectual,  for  the 
transformation  of  energy  produced  by  the  reaction  is  concentrated  in 
a  short  space  of  time.  It  was  from  the  action  of  yeast  that  the 
term  "  fermentation  "  arose.  The  yeast  sets  the  must  in  a  fer- 
ment; it  froths  and  bubbles.  When  the  action  of  digestive  juiees 
came  to  be  studied,  it  was  seen  to  be  of  the  same  ferment  nature,  and 
a  distinction  came  to  be  made  between  "organized"  and  "unor- 
ganized "  ferments.  An  organized  ferment  was  the  living  cell,  such 
as  yeast,  which  brought  about  fermentation  by  the  metabolism 
involved  in  its  growth  and  multiplication.  The  unorganized  ferment 
was  contained  in  the  juice  secreted  from  a  cell,  and  acted  on  a  substrate 
at  a  distance  from  that  cell — e.g.,  saliva  acting  on  starch  in  the  momtk 
and  stomach. 

68 


ENZYMES  OR  FERMENTS  69 

It  was  thought  that  onty  the  living  yeast  organism  could  bring 
about  this  characteristic  fermentation;  after  many  attempts,  how- 
ever, a  juice  was  expressed  from  the  yeast  cell  which  fermented  no 
less  well  than  the  hving  organism;  thus  the  distinction  between  the 
two  kinds  of  ferments  disappeared,  and  the  term  "  organized  ferment  " 
became  unnecessary. 

When  the  action  of  enzj^mes,  like  those  of  yeast,  is  normally  effected 
within  the  cell,  the  enzymes  are  grouped  as  "intracellular''  enzymes, 
or  endoenzymes;  those  which  act  when  discharged  from  the  cell  are 
classed  as  "  extracellular  "  enzymes,  or  exoenzymes.  Under  this 
latter  group  are  placed  the  enzymes  concerned  in  the  processes  of 
digestion.  There  are  granules  of  a  precursor,  or  zymogen,  stored 
within  the  cells  of  the  secreting  glands  of  the  stomach,  pancreas,  etc., 
and  these  are  discharged  in  response  to  certain  definite  stimuli.  The 
precursors  when  discharged  require  to  be  "  activated  " — i.e.,  turned 
into  the  active  enzyme  by  the  presence  of  some  other  body.  Prob- 
ably all  enzymes  require  the  presence  of  a  "  co -enzyme  "  before 
they  manifest  their  full  activitj".  Thus  yeast  juice  can  be  squeezed 
through  a  porcelain  filter  candle  impregnated  with  gelatin  by  a 
pressure  of  300  atmosiDheres ;  the  expressed  juice  is  found  to  have 
no  enzymic  action  until  mixed  with  phosphates,  and  some  other 
substance  that  is  diffusible  and  not  destroyed  by  boiling,  which  is 
left  behind  in  the  cell  residues  on  the  filter.  These  act  as  co-enzyme 
to  the  expressed  juice.  The  "  intracellular  "  enzymes  are  concerned 
intimately  with  processes  of  metabolism.  If  a  piece  of  liver  be  kept 
under  aseptic  conditions,  it  will  be  found  that  the  longer  it  is  kept 
the  less  nitrogen  it  contains  in  the  form  of  protein,  the  more  in  the 
form  of  products  of  protein  disintegration.  Thus,  of  the  nitrogenous 
substances  in  some  fresh  liver,  90-4  per  cent,  were  found  to  be  in- 
soluble and  9-6  per  cent,  soluble  in  water.  After  keeping  mider 
aseptic  conditions  for  twenty  days,  39-4  per  cent,  of  the  nitrogenous 
compounds  were  found  to  be  insoluble,  and  60-6  soluble.  Similar 
results  have  been  obtained  on  keeping  other  organs,  such  as  the 
spleen,  th^'mus,  kidney.  The  products  of  tliis  self-digestion,  or 
'■  autolysis,"  appear  to  be  the  same  as  those  of  ordinary  intestinal 
digestion,  but  the  different  stages  have  not  yet  been  worked  ovit. 
Autoh'sis  takes  place  in  an}^  part  of  the  living  organism  Avhen  the 
blood-supply  is  shut  off  from  it.  Thus,  if  an  artery  be  blocked  by  a 
thrombus,  and  the  blood-supply  cut  off  fiom  part  of  the  brain,  it  is 
found  that  the  central  part  softens  and  undergoes  autolysis.  The 
same  occurs  in  a  part  of  the  liver  if  the  circulation  be  cut  off  from  it. 
The  chief  circumstance  favouring  this  change  appears  to  be  the  in- 
creased acidity  of  the  cell  juice  produced  by  want  of  oxygen.  The 
peripheral  parts  do  not  undergo  the  same  degree  of  autolysis,  owing 
to  the  diffusion  into  them  of  oxygen  and  alkaline  fluid  from  the  neigh- 
bouring cells.  Such  changes  take  place  anj^where  in  the  bod}'  as  the 
result  of  thrombosis  or  infarction.  Autolysis  also  occurs  in  the  living 
organism  in  acute  yellow  atrophy  of  the  liver,  in  phosphorus-poisoning, 
and  in  certain  acute  fevers.     The  products  of  this  digestion  can  in 


70  A  TEXTBOOK  OF  PHYSIOLOGY 

such  cases  be  detected  in  the  urine.  It  is  sn|)])osed  that  there  are 
intracellular  enzymes  normally  contained  within  the  tissues;  these 
enzymes,  under  the  varying  conditions  of  life,  build  up  and  break 
down  the  tissues  according  to  the  need  of  that  tissue  and  of  the  body 
as  a  whole.  Under  adverse  circumstances,  such  as  the  shutting  off  of 
the  blood-supply  or  the  presence  of  toxins  and  poisons,  the  action 
jnay  ]iroceed  mainly  in  the  direction  of  disintegration. 

Besides  the  enzyme  concerned  with  the  cell  proteins,  we  have 
evidence  of  enzymes  acting  upon  carbohydrates  and  fats.  A  striking 
example  is  the  enzyme  glycogenase,  which  forms  glycogen  from  the 
dextrose  brought  to  the  liver  cells,  and  as  occasion  needs  reconverts 
this  glycogen  into  dextrose.  There  are  intracellular  enzymes  con- 
cerned in  the  formation  of  urea,  uric  acid,  etc.  From  the  liver  alone 
at  least  fifteen  enzymes  have  been  isolated,  which  shows  the  great 
importance  of  the  intracellular  enzymes  in  the  metabolic  processes  of 
the  body. 

Whether  enzymes  be  extracellular  or  intracellular,  they  have  the 
following  well-marked  properties : 

1.  Enzymes  perform  their  action  best  at  an  ojotimum  temperature. 
For  the  enzymes  of  our  body  this  is  37°  C,  the  body  temiDerature.  Cold 
inihibits  their  action,  but  does  not  kill  them,  even  when  they  are 
subjected  (as  has  been  the  case  with  some  unicellular  organisms)  to 
the  great  cold  produced  by  evaporation  of  liquid  air.  Warming 
above  the  temperature  of  the  body  tends  to  inhibit,  while  temperatures 
varying  from  55°  C.  to  70°  C.  destroy  their  action  altogether. 

2.  They  have  an  optinnnn  medium  in  which  they  act.  This  is 
usually  faintly  alkaline  (to  litmus),  and  corresponds  in  the  case  of 
intracellular  enzymes  to  the  reaction  of  the  body  tissue  fluids.  The 
pepsin  contamed  in  gastric  juice  acts  best  in  an  acid  medium;  others 
apparently  work  best  in  a  neutral  medium.  The  enzymes  of  some 
micro-organisms  work  best  in  the  absence  of  free  oxygen,  and  are 
termed  "  anaerobic,"  in  contradistinction  to  the  enzymes  reqviiring 
free  oxygen  for  their  activity,  which  are  called  "'aerobic." 

3.  They  are  specific  in  action.  Enzymes  are  classified  according 
to  the  substrate  upon  which  they  act.  There  are,  for  example,  pro- 
teolytic (protein-splitting),  lipolj'tic  (fat-splitting),  amylolytic  (starch- 
splitting),  sucrolytic  (sugar-sjilitting)  enzymes,  as  well  as  several  others. 
It  is  found  that  the  proteolytic  act  only  on  protein,  the  starch-splitting 
only  upon  starch,  and  so  forth. 

Nevertheless,  the  active  powers  of  some  enzymes,  which  are  secreted 
together,  correspond  so  closely  (for  examj^le,  j^epsin  and  rennin)  that 
the  double  action  may  be  manifestations  of  one  parent  substance.  We 
may  regard  the  parent  substance  as  having  different  groups  of  ''  side- 
chains  "  attached  to  it,  one  group  of  side-chains  acting  as  jiepsin,  the 
other  as  rennin.  This  idea  is  even  more  applicable  where  the  sphere 
of  action  of  some  of  them  appears  to  be  so  limited  that  it  is  difficult 
to  conceive  of  the  existence  of  a  separate  enzyme  for  each  action. 

Proteolytic  (Protein-splitting)  are  pepsin,  trypsin,  and  erepsin. 
Pepsin    is    the    active    proteol3?tic    enzyme   of    the  stomach,   tryj)sin 


ENZYMES  OR  FERMENTS  71 

•of  the  ]}aiicreas.  Erepsin  occurs  in  the  succns  entericus,  in  the 
intestinal  mucous  membrane,  and  in  the  tissues  generally.  The 
main  action  of  these  enz^'mes  (explained  more  full}'  later)  may  be 
^ynopsized  thus: 

Pepsin  Trypsin  Erepsin  _ 

•  •  Protein  •  -^ 

Proteoses 

Peptones  ' 


Polypeptides 

I 
\\^  Amino  acids 


Erepsin  (V) 


Lipolytic   (Fat-splitting)  lipase   or    steapsin  occur    particularly  in 
the  gastric  juice,  pancreatic  juice,  and  the  bloocl: 


Neutral  fat 


1/  ::j 

Fatty  acid  Glycerine 

Amylolytic  (Starch-splitting) — sometimes  known  as  the  diastases. 
The  chief  are  the  ptyalin  of  the  saliva,  which  acts  on  boiled  or  soluble 
starch,  and  amylopsin  of  the  pancreatic  juice,  which  can  act  on  un- 
boiled starch. 

Amj'lopsin 
Starch  « 

Ptyalin  \j/ 

•  Soluble  starch 

Erythrodextrin 

Achroodextrin 

^  Maltose 

The  glycogenase  of  the  liver  ma}^  iDerhajDS  be  included  in  this 
group;  it  converts  glycogen  through  similar  stages  to  maltose. 

Sucrolytic  (Sugar-splitting). — These  enzymes  split  the  disaccharide 
sugar  into  monosaccharides.  They  occur  chiefly  in  the  succus  enteri- 
•  cus;  their  action  may  be  expressed  graphically  as  follows: 

Maltase  Lactase  Invertase 

Maltose  Lactose  Cane-sugar 


\l/  \lr  \!/  \U  4/  "nI/ 

Dextrose     Dextrose  Dextrose     Galactose  Dextrose     Levulose 


72  A  TEXTBOOK  OF  PHYSIOLOGY 

De-aminizing. — A  grou})  of  euzyincs  which  remove  the  NH.^  group- 
from  bodies,  substituting  therefor  an  OH  grou])  and  forming  ammonia. 
—e.g. : 

(1)  CH3CH.NH.,.C00H  +  H^O  =  CH3CHOH.COOH  +  NH3 

Alanin  Water  Lactic  acid  Ammonia 

(2)  C5H3N4.NH,  +  H,()  --  C.H^NjO  +  NH., 

Ack'iiin  Hypoxaiithiii  Ammonia 

Coagulative. — In  this  grou])  are  included  '"  rennin,"  which  helps 
to  bring  about  the  clotting  of  milk,  and  '"  thrombin,'"  \\'hich  is  believed 
to  play  a  part  in  the  coagulation  of  the  blood.  These  actions  are 
by  no  means  identical;  for  whereas  the  product  of  the  rennin  action 
is  still  soluble,  that  of  the  thrombin  action  is  insoluble: 


Rennin 

Thrombin 

Caseinogen 

I'ibrinogen 

1 

Soluble  casein 

1 
Fibrin  (insoluble) 

4.  The  action  of  enzymes  is  inhibited  by  the  accumulation  of 
the  products  of  activity.  This  is  best  seen  in  test-tube  experi- 
ments. In  the  body  such  products  are  constantly  being  removed 
by  absorption. 

5.  They  are  reversible  in  action.  This  has  been  shown  to  be  true 
for  a  great  number  of  enzymes,  not  yet  for  all.  Reversible  action  wa& 
first  shown  with  the  sugar-splitting  enzyme  maltase.  This  enzyme 
usually  splits  maltose  into  two  molecules  of  dextrose.  In  a  test-tube 
experiment  only  a  certain  amount  of  maltose  is  converted  into  dex- 
trose, the  accumulating  dextrose  tending  to  stop  the  action.  A  point 
of  equilibrium  is  therefore  reached  when  there  is  present  as  the  result 
of  the  enzymic  action  a  certain  amount  of  maltose  and  a  certain 
amount  of  dextrose.  If  more  maltose  be  added,  the  action  goes  on 
until  the  same  proportion  is  reached.  If  dextrose  be  added,  the  enzyme 
reconverts  some  of  the  dextrose  to  maltose  until  the  same  point  of 
equilibrium  is  again  reached. 

Another  example  is  the  enzyme  (lipase)  which,  according  to  the 
conditions,  breaks  ethyl  butyrate  down  into  ethyl  alcohol  and  butyric 
acid,  or  builds  up  ethyl  butyrate  from  these  bodies. 

C3H-COOC2H,=  C3H,C00H  +G,H50H 

Ethyl  butyrate        Butyric  acid      Ethyl  alcohol 

<-  

— ^ 

This  reversible  action  is  particularlj^  important  in  the  case  of  intra- 
cellular enzymes  ;  with  varying  conditions  of  the  blood  and  tissue 
fluids  the  cells  of  the  body  may  at  one  time  act  in  a  building-up 
(anabolic),  and  at  another  time  act  in  a  breaking-down  (katabolic), 
direction. 


ENZYMES  OR  FERMENTS  75 

6.  They  are  inhibited  by  the  action  of  antiseptics  and  disuifectants 
and  kindred  bodies.  This  statement  is  true  for  the  enzymes  found 
in  the  body,  but  not  for  all  enzymes. 

7.  They  are  carried  do\\ii  from  solution  by  flocculent  precipitates. 
For  this  reason  it  is  difficult  to  say  whether  enzymes  are  protein  in 
nature  or  only  carried  down  by  the  precipitated  protein.  Most  enzymes 
are  apparently  closely  associated  with  protein,  although  it  is  claimed 
that  some  have  been  prepared  which  do  not  give  the  protein  tests. 
They  are  colloidal  in  nature  and  indiffusible,  and  readih'  taken  up  by 
finely  divided  substances,  such  as  kaolin,  alumin,  etc.  In  general 
they  are  soluble  in  dilute  glycerine,  sodium  chloride  solution,  and 
dilute  alcohol  and  water. 

8.  (a)  They  are  precipitated  from  solution  by  alcohol  and  am- 
monium sulphate. 

(6)  The  precipitate  on  redissolving  in  water  again  manifests 
enzymic  characteristics.  These  facts  (6,  7,  8)  show  the  intimate 
relationship  that  enzymes  bear  to  other  products  of  cell  activity — e.g., 
bacterial  toxins,  h9emol3'sins,  and  such  bodies. 

9.  By  the  presence  of  an  enzj'me  a  chemical  action  is  accelerated 
without  the  enzyme  itself  being  used  up  in  the  final  reaction.  One 
part  of  invertase  can  hydrolyze  100,000  parts  of  cane-sugar;  one  part 
of  rennin  acts  on  200,000  parts  of  caseinogen.  It  is  not  possible  to 
saj^  whether  an  enzyme  combines  in  any  intermediate  stage  of  the 
reaction.  This  is  sometimes  the  case  in  other  forms  of  catalytic 
action. 

10.  It  was  originally  believed  that  the  rate  of  action  of  enzymic 
activit}'  was  proportional  to  the  square  root  of  the  amount  of 
enzyme  present.  Recent  investigations  with  more  delicate  methods 
tend  to  show  that  for  most  enzymes  the  intensity-  of  action  is 
almost  directly  proportional  to  the  concentration  of  enzyme 
])resent. 

11.  The  action  of  an  enzyme  may  be  hindered  or  stopped  by  the 
presence  of  a  body  known  as  an  anti-enzyme.  The  exact  manner  in 
which  these  work  is  not  sufficiently  well  known.  Anti-rennin  may  be 
produced  in  the  blood  by  the  injection  of  rennin.  The  alimentarj^ 
tract  is  believed  to  contain  anti-enzymes  which  prevent  the  digestive 
enz3'me  from  attacking  it.  Intestinal  worms  also  contain  anti- 
enzymes  for  the  usual  ferments  of  the  digestive  tract.  Administra- 
tion of  an  enzyme  for  which  the  worms  {e.g.,  tape-worms)  have 
no  anti-enzyme  {e.g.,  papain)  brings  about,  their  partial  diges- 
tion, so  that  their  removal  from  the  body  by  a  purge  then  becomes 
eas}'. 

All  the  above-mentioned  enzymes  belong  to  a  class  the  mode  of 
action  of  which  is  hydrolytic.  Besides  these  there  exists  in  the  body 
a  group  of  enzymes,  "  the  oxidases,"  which  plays  a  great  part  in  the 
oxidative  processes  of  the  body.  These  are  generally  divided  into 
two  groups:  the  primary,  or  direct  oxidases,  which  can  transfer  oxygen 
directh'  to  other  bodies;  the  indirect,  or  peroxidases,  which  transfer 
oxygen  only  in  the  presence  of  a  peroxide,  from  which  they  set  the 


74  A  TEXTBOOK  OF  PHYSIOLOGY 

oxygen  free  and  then  transfer  it  to  the  body  to  be  oxidized.  An 
example  of  oxidizing  action  occurring  in  the  body  is  the  following: 

C5H4N4O  +  0  -  C5H4N4O0  +  O  =  C5H4N4O3 

Hypoxaiithin  Xanthin  Uric  acid 

The  oxidases  give  a  blue  colour  with  tincture  of  guaiacuni  alone,  the 
peroxidases  with  tincture  of  guaiacum  in  the  j^resence  of  peroxides. 

According  to  recent  investigations,  it  is  claimed  that  oxidases 
are  in  reality  a  mixture  of  ox^'genases,  bodies  containing  iron  and 
manganese,  and  peroxidases.  The  oxygenase  in  the  process  of 
oxidation  is  believed  to  take  up  molecular  oxygen  and  become 
converted  into  peroxide.  This  peroxide  is  then  activated  by  the 
peroxidases,  and  has  a  great  oxidizing  power. 

It  is  i^ossible  that  certain  of  the  reductions  taking  jilace  in  the 
body  may  be  ascribed  to  the  i^resence  of  enzymes  known  as  "  re- 
ductases." More  light  is  required  on  this  subject;  some  of  the 
eductions  in  the  body  are  apparently  not  of  an  enzymic  nature. 


BOOK    II 

CHAPTER    IX 

THE  BLOOD 

All  the  cells  of  a  multicellular  organism  are  engaged  in  building-up 
(anabolic)  and  breaking-down  (katabolic)  processes.  In  the  unicellular 
these  processes  are  performed  by  a  direct  interchange  between  the 
single  cell  and  the  surrounding  medium,  but  in  the  higher  organiza- 
tions special  fluid  tissues — the  blood  and  the  lymph  —  have  been 
evolved,  which  circulate  in  order  to  supply  the  requisite  conditions 
for  these  metabolic  processes.  The  functions  of  the  blood  may  be 
summarized  as  follows: 

1.  To  act  as  the  medium  of  absorption  and  exchange  between 
the  alimentary  canal,  the  lungs,  and  the  tissues,  and  to  supj^ly  the 
sources  of  energy  (food,  oxygen)  to  the  tissues  for  metabolic 
purposes. 

2.  To  supply  to  the  tissues  a  medium  consisting  of  water,  colloids 
and  electrolytes  (inorganic  salts)  of  a  concentration  and  osmotic 
pressure  kept  constant  within  narrow  limits,  in  which  they  are  able 
to  carry  oiit  their  vital  processes. 

3.  To  convey  from  one  organ  to  another  the  internal  secretions 
and  the  hormones  (chemical  messengers),  which  regulate  the  activity 
of  the  organs. 

4.  To  convey  the  products  of  katabolism  from  the  tissues  to  the 
organs  of  excretion,  the  lungs  and  kidneys. 

5.  To  endow  the  body  with  a  mechanism  protective  against  harmful 
micro-organisms. 

6.  In  the  higher  animals  to  distribute  and  help  to  regulate  the 
heat  of  the  body. 

7.  By  its  power  of  clotting  to  seal  up  wounds  and  prevent  serious 
loss  of  blood  or  tissue  lymph. 

The  blood  is  a  thick,  viscous  liquid,  with  a  saltish  taste  and  a 
peculiar  faint  odour.  When  viewed  under  the  microscope  it  is  seen 
to  consist  of  a  transparent  liquid,  the  l>lood-plasma,  in  which  float  a 
number  of  formed  bodies,  the  red  and  pale  corpuscles  of  the  blood. 
According  to  some  authorities,  there  is  a  third  solid  component — the 
blood-platelets. 

75 


76  A  TEXTBOOK  OF  PHYSIOLOGY 

The  Colour  of  vertebrate  blood  varies  from  a  bright  red  in  the 
blood  of  the  arteries  to  a  deep  purple-red  in  the  veins.  It  is  due  to 
a  pigment — haemoglobin — which  is  contained  within  the  red  corpuscles 
of  the  blood  and  acts  as  the  carrier  of  oxygen.  The  blood  of  inverte- 
brates and  coidatcs  may  be  either  colourless  or  possess  one  of  a  variety 
of  colours.  Haemoglobin  occurs  in  solution  in  the  plasma  of  many  o.f 
the  worms  and  lower  Crustacea.  The  echinoderms  also  possess  a  red 
pigment  in  their  blood  (echinochrom).  Some  Crustacea  have  a  blue 
pigment — haemocyanin — which  contains  copper  and  is  in  solution  in 
the  blood.  It  is  blue  in  the  arterial  blood,  when  combined  with 
oxygen,  and  colourless  in  venous  blood — i.e.,  when  deoxygenated. 
Its  combining  power  for  oxj'gen  is  only  about  one-fourth  that  of 
haemoglobin.  Some  worms  contain  a  green  pigment  (chlorocruorin) ; 
others  a  red  pigment  (haemoerythrin).  Certain  molluscs  and  tunicates 
possess  colourless  blood  and  yet  have  substances  in  it  capable  of  com- 
bining with  oxygen  and  transporting  it  to  the  tissues  (achroglobin). 

The  Specific  Gravity  of  the  blood  of  man  varies  between  1055  and 
1060.  The  red  corpuscles  have  a  specific  gravity  of  1 080  and  the  plasma 
one  of  1030.  The  specific  gravity  is  usually  obtained  by  the  fol- 
lowing method.  By  means  of  a  pipette  a  drop  of  blood  is  placed  in 
the  middle  of  a  mixture  of  benzol  (sp.  gr.  0-88)  and  chloroform  (sp.  gr. 
1-485).  The  mixture  has  a  specific  gravity  approaching  that  of  blood. 
If  the  blood-drop  falls,  more  chloroform  is  added;  if  it  rises,  more 
benzol — until  a  condition  is  obtained  when  the  corpuscle  remains 
suspended  in  the  mixture.  The  specific  gravity  of  the  mixture  is 
now  taken  with  the  hydrometer.  The  operation  must  be  quickly 
performed  (1  to  2  minutes),  otherwise  the  specific  gravity  of  the  blood 
alters  owing  to  diffusion  taking  place  between  the  blood  and  the 
liquids.  The  specific  gravity  is  infiuenced  by  the  number  of  corpuscles 
and  the  amount  of  haemoglobin.  It  is  high  in  the  new-born  (1066). 
It  sinks  in  starvation,  after  haemorrhage,  in  anaemias,  and  in  diseases  of 
the  kidney,  etc. 

Specific  Gravity  of  Blood. 

Man 1056-1061       Rabbit  1042-1062 

Woman  1053-1061       Of  serum        1030-1042 

Dog 1060  Of  red  corpuscles      ..  ..      1080-1085 

The  specific  gravity  varies  with  the  age  and  sex;  it  is  diminished 
after  eating  and  increased  by  exercise.  It  gradually  falls  during  the 
day  and  rises  during  the  night. 

Reaction. — The  reaction  of  a  fluid  depends  upon  the  number  of 
free  hydrogen  (H)  ions  in  it,  which  give  an  acid  reaction  relative  to 
the  number  of  free  hydroxyl  (OH)  ions,  which  give  a  basic  or  alkaline 
reaction. 

Blood  is  almost  neutral  in  reaction  as  determined  by  the  electrical 
method.  Its  reaction  to  litmus  is  slightly  alkaline.  This  is  because 
litmus  acts  as  a  weak  acid,  and,  displacing  carbonic  acid  gas  from  its 
combination  in  the  blood  (carbonate),  combines  with  the  base  and  turns 


THE  BLOOD  77 

blue — the  alkaline  reaction.  To  phenolphthalein  blood  is  neutral,  for 
this  reagent  cannot  decompose  the  carbonates.  Blood  can  take  up 
a  certain  amount  of  acid  before  it  begins  to  react  acid.  This  is 
because  it  contains  carbonates  ("  buffer  salts  ")  and  proteins  which 
combine  with  the  acid.  It  is  for  this  reason  that  it  is  difficult  to  ascer- 
tain the  reaction  of  the  blood  by  chemical  means.  Titrating  with  acid, 
fhe  amount  of  neutralizable  alkalinity  is  obtained,  alkali  being  liberated 
in  the  process  from  the  proteins  and  by  dissociation  of  the  carbonates 
(NagCOg,  NaHCOg)  and  the  phosphates  (NagHPOJ.  This  neutrahzable 
alkali  usually  equals  350  to  400  milligrammes  NaHO  per  100  c.c. 
But  the  real  alkalinity,  as  measiired  by  the  electrical  method,  is  due 
to  free  OH  ions,  and  these  are  usually  present  in  a  concentration 
little  greater  than  in  water.     Na^COg  in  aqueous  solution  is  dissociated, 

+  = 

more  or  less,  into  the  ions  2Na  and  CO3.     8ome  of  the  CO3  ions  com- 

+  _  -  - 

bine  with  H  ions  of  the  dissociated  water,  forming  HCO^,  and  HO  ions 
are  thus  set  free  to  produce  the  alkaline  reaction.     On  adding  acid 

these  HO  ions  are  removed,  and,  the  equilibrium  being  disturbed, 
more  Na.^COg  is  dissociated,  and  this  goes  on  until  all  the  Na.^COg  is 
dissociated.  The  alkali  existing  as  salts,  carbonates,  and  phosphates, 
is  knoAvn  as  diffusible  alkali;  that  combined  with  protein  is  termed 
non-diffusible  alkali.  As  the  corpuscles  are  richer  in  diffusible  alkali 
than  the  plasma,  the  number  of  corpuscles  modifies  the  amount 
of  neutralizable  alkali. 

On  passing  carbon  dioxide  gas  through  blood,  the  loose  combination 
between  alkali  and  protein  of  both  the  plasma  and  corpuscles  is  split 
up,  and  sodium  carbonate  partly  formed.  CO3  ions  pass  from  the 
corpuscles  into  the  plasma,  and  CI  ions  from  the  plasma  into  the 
corpuscles,  and  as  the  sodium  carbonate  in  the  plasma  is  increased,  so 
is  the  neutralizable  alkalinity. 

It  is  very  difficult  to  affect  the  reaction  of  the  blood  by  swallowing 
acids.  Two  drachms  of  official  hydrochloric  acid  taken  with  food 
have  no  effect  upon  the  reaction  of  the  blood,  because  the  acid  com- 
bines with  the  ])roteins  of  the  food,  etc.;  two  drachms  of  tartaric  acid, 
on  the  other  hand,  may  diminish  the  neutralizable  alkahnity.  These 
acids  combine  with  the  bases  and  form  salts  which  are  little  disso- 
ciated. 

Acids  entering  the  blood  are  neutralized  by  combination  with 
ammonia,  a  product  of  protein  katabolism,  or  by  union  with  bases  of 
the  carbonates,  carbonic  acid  being  expired.  Alkalies  are  neutralized 
b}^  the  carbonic  acid  produced  in  the  body.  The  blood  is  thus  kept 
neutral  while  the  amount  of  acid  or  alkali  passing  into  it  varies 
considerably.  Muscular  exertion  diminishes  the  titration  alkalinity 
owing  to  the  production  of  lactic  acid.  The  concentration  of  the 
H  ions  in  the  blood  regulates  the  activity  of  the  respiratory  centrsf; 
lactic  acid  and  carbonic  acid  are  both  produced  on  exertion,  and  their 
eumulative  effect  produces  dyspnoea.  The  '"  buffer  salts  "'  help  to 
regulate  this. 


7S  A  TEXTBOOK  OF  PHYSIOLOGY 

The  Amount  of  Blood. — This  varies  according  to  the  method  by 
which  it  is  determined  and  for  different  animals.  The  following  table 
gives  some  of  the  results  which  have  been  obtained : 

■iv-is  of  body-weight 


Dog  . . 

jV   of  body-weight 

Pig     .. 

Guinea-pig  .  . 

A- 

Bird 

Rabbit 

'.'■        "^                        ',', 

Frog 

Cat   . . 

^i^ 

Man 

Horse 

Tr.                       »> 

New-born  child 

It  is  stated  in  man  to  vary  from  3|  to  4  litres. 

The  old  method  (that  of  Welcker)  of  obtaining  the  amount  of 
blood  of  an  animal  was  (1)  to  bleed  the  animal  into  a  weighed  flask, 
(2)  remove  all  traces  of  blood  by  perfusing  the  vessels  thoroughly 
with  water,  (3)  chopping  up  the  body  with  the  exception  of  the  in- 
testines and  washing  the  choppings  in  water.-  The  washings  are 
measured  and  the  amount  of  blood  in  them  gauged  by  determining 
the  amount  of  haemoglobin — by  finding  how  much  the  blood  must 
be  diluted  to  correspond  in  depth  of  tint  to  that  of  the  washings. 
This  method  is  not  very  exact,  since  during  the  death  from  haemorrhage 
the  tissue  fluids  pass  into  the  blood,  giving  too  high  a  result. 

In  man  the  amount  has  been  ascertained  by  the  carbon  monoxide 
method.  In  this  method  the  subject  breathes,  through  a  tin  of  soda 
lime  to  absorb  exhaled  CO,,  in  and  out  of  a  bag  containing  a  known 
volume  of  carbon  monoxide  mixed  with  a  sufficiency  of  oxygen. 
Carbon  monoxide  has  a  strong  affinity  for  haemoglobin,  and 
combine?  with  this,  displacing  oxygen.  After  sufficient  time  for 
the  whole  of  the  CO  to  be  absorbed  a  sample  of  the  subject's 
l)lood  is  taken  and  the  percentage  saturation  of  the  blood  with  carbon 
monoxide  determined.  The  carbon  monoxide  gives  the  blood,  suit- 
ably diluted,  a  pink  colour,  and  the  determination  is  effected  by 
comparing  the  tint  of  (1)  the  sample,  with  (2)  a  sample  of  the  subject's 
normal  blood,  (3)  a  sample  of  the  subject's  blood  saturated  with  CO, 
all  three  samples  being  diluted  1  in  200.  A  standard  carmine  solution 
is  added  to  (1)  and  (2)  till  the  tint  of  each  equals  that  of  (3).  Suppose 
twice  as  much  carmine  has  to  be  added  to  (2)  as  to  (1),  then  (1)  is 
half  saturated  with  CO.  The  amovnit  of  O,  or  CO  which  can 
combine  with  100  c.c.  of  the  subject's  blood  is  found  by  the  use  of  the 
Haldane-Gowers  hsemoglobinometer.  The  amount  of  CO  absorbed 
is  known,  and  thus,  if  it  be  found  that  blood  is  25  per  cent,  saturated 
and  the  person  has  absorbed  150  e.c.  of  CO,  it  is  obvious  that  all  the 
blood  will  require  600  c.c.  of  CO  to  saturate  it.  If  it  is  found  that 
100  c.c.  of  the  blood  are  satiirated  by  20  c.c.  of  carbon  monoxide  or 

oxygen,  the  total  volume  of  the  blood  is  --        =3,000  c.c,  etc. 

,     j&     '  20 

By  this  method  the  amount  of  blood  in  man  is  reckoned  to  be 
about  -L  of  the  l)ody  weight  (^L  for  fat  men).  Generally  speaking, 
this  method  gives  a  lower  value  than  the  other,  and  there  has  been  a 
considerable  amount  of  discussion  recently  as  to  the  accuracy  of  the 
CO  method.     CO  is  taken  nj)  by  the  haemoglobin  in* the  muscles;  the 


'THE  BLOOD 


79 


amount  of  this  seems  to  increase  with  age,  even  equalhng  5  or  6  per  cent, 
of  the  whole  Hb  content  of  the  bod3^  This  is  a  som'ce  of  error.  The 
more  muscular  animals  with  darker  flesh  have  more  Hb  in  their 
•muscles — e.g.,  hare  more  than  rabbit,  duck  than  fowl.  It  is  claimed 
by  authorities  who  have  made  careful  experiments  by  the  "bleeding 
method  that  this  is  really  the  more  exact,  and  that  the  quantity  of 
blood  in  an  animal  bears  a  definite  relationship  to  the  amount  of  the 
bod}^  surface.  Thes-e  observers  used  oxygenated  Locke's  fluid  to 
wash  out  the  circulator}^  system,  and  so  avoided  the  transference  of 
tissue  fluid  into  the  blood.  B  =  W«/j. — ^where  B  is  the  blood- volume 
in  cubic  centimetres,  W  the  weight  of  the  body  in  grammes,  nO-10-0-12, 
and  h  a  constant  (calculated  from  experiments)  determined  for  each 
species  of  animal.  The  body  surface  is  usually  calculated  from  the 
body  weight  by  the  formula  S=A-.Wf  (0-70 -0-72  is  more  accurate 


6    3.    6    9    12  is  18  21Z4  27'36'-'--'-'---'-0"V  ^  ^    12   15  18 
Atcent  T.O.C.=  Total  Oxygen  Capacity.  ^^^^ 

Fig.  18. — Effect  of  High  Altitude  (.in  Blood.     (Dreyer  and  Walker.) 

than  ^).  The  smaller  and  lighter  animals,  which  have  a  relatively 
greater  body  surface  than  the  heavier  ones,  have  also  a  relatively 
greater  blood-volume.  This  agrees  with  their  relative  rates  of  body 
heat  loss  and  metabolism,  and  also  with  the  sectional  areas  of  their 
tracheae  and  aortae  and  weight  of  heart  muscle.  A  wild-rabbit  con- 
tains 25  per  cent,  less  blood  and  25  per  cent,  more  haemoglobin  in  its 
blood  than  a  tame  rabbit  of  the  same  weight.  A  wild-hare  contains 
double  the  blood-volume,  30  per  cent,  more  haemoglobin,  and  three 
times  more  heart  muscle  than  a  wild-rabbit  of  the  same  weight.  No 
doubt  the  same  kind  of  difference  exists  between  an  athlete  and 
sedentary  worker. 

In  travellers  to  high  altitudes  the  blood  becomes  concentrated 
and  the  oxygen  capacit}^  increased  (Fig.  18).  The  concentration 
happens  in  the  first  day  or  two,  and  is  due  to  withdrawal  of  plasma. 
After  some  weeks  the  number  of  corpuscles  and  the  total  amount  of 


80  A  TEXTBOOK  OF  PHYSIOLOGY 

haemoglobin  are  found  increased  by  the  new  formation  of  corpuscles 
in  the  red  marrow.  In  rabbits  taken  from  Basle  (740  millimetres 
barometric  pressure)  to  St.  Moritz  (620  millimetres)  the  total  haemo- 
globin increased  12  per  cent,  and  the  blood-volume  decreased  11  per 
cent.  The  increase  in  the  percentage  of  haemoglobin  Avas  12  per  cent. 
Thus  the  body  compensated  for  the  attenuation  of  the  air  and  lowered 
partial  pressure  of  oxygen. 

Cooling  or  bandaging  a  limb  concentrates  the  blood  therein.  The 
breathing  of  an  excess  of  COg  and  the  taking  of  amyl  nitrite  dilutes, 
of  chloral  hydrate  concentrates,  the  blood. 

The  Osmotic  Pressure. — The  osmotic  pressure  of  the  whole  blood 
is  measured  by  the  depression  of  the  freezing-point.  Generally 
/\  =  -0-56°  C.  for  human  blood,  but  varies  from  -0-51°  C.  to 
—  0-62°  C.  with,  the  diet  and  amount  of  fluid  ingested.  If  the 
products  of  metabolism  increase  in  the  blood,  owing  to  the  fact 
that  they  are  not  properly  eliminated  by  the  kidneys,  ^  may  be 
increased.  According  to  some  observers,  if  /^  constantly  equals  or 
exceeds  —0-58°  C.  it  is  a  sign  that  both  kidneys  are  diseased. 

The  Electrical  Conductivity  o£  the  Blood. — As  the  blood-plasma 
contains  inorganic  salts  (electrolytes)  in  solution,  it  has  the  jDroperty 
of  conducting  an  electric  current.  Defibrinated  blood  is  generally 
employed  for  this  measurement.  The  conductivity  varies  with  the 
relative  proportion  of  corpuscles  and  serum — being  low  with  many 
corpuscles  and  less  serum,  high  with  relatively  few  corpuscles  and 
much  serum.  In  cases  of  anaemia  the  conductivity  is  greatly  increased. 
The  corpuscles,  owing  to  their  colloid  nature,  lessen  the  conductivity. 

Viscosity. — Blood  compared  to  water  is  relatively  a  viscous  fluid. 
Its  viscosity  maj^  be  determined  by  allowing  blood  to  flow  under  a 
definite  pressure  through  a  capillary  tube  of  known  dimensions,  and 
measuring  the  outflow  in  a  given  time  Taking  the  viscosity  of  water 
as  1,  that  of  the  blood  of  man  is  5-1 ;  that  of  dog,  4-7  ;  that  of  the  cat,  4-2. 
Viscosity  generally  varies  in  the  same  direction  as  the  specific  gravity. 
Sweating  increases  it;  increased  temperature,  on  the  other  hand, 
diminishes  it. 

In  the  condition  known  as  polycythaemia  the  viscosity  may 
become  9  or  10  times  that  of  water.  In  this  condition  the  red  blood- 
corpuscles  are  greatl}^  increased  in  number  in  proportion  to  the  plasma, 
reaching  as  many  as  11,000.000  per  c.  mm.  On  the  other  hand,  in  the 
form  of  anaemia  known  as  chlorosis  or  ""  green  sickness,"  because  of  the 
greenish  look  of  the  patient,  the  plasma  is  greatl}'  increased  in  amount, 
so  that  the  corpuscles  are  relatively  diminished,  and  the  viscosity  of 
the  blood  is  also  nu;ch  diminished,  often  to  just  over  2.  The  flow  of 
the  blood  is  so  controlled  by  the  va  so -mot  or  system  that  slight  altera- 
tions in  viscosity  are  of  little  if  any  account. 

Analysis. — The  most  accurate  analyses  of  the  blood  have  been 
<lone  upon  that  of  animals;  the  following  table  shows  the  quantitative 
composition  of  the  blood  in  the  ox,  horse,  and  man : 


THE  BLOOD 


81 


. . 

Ox  Blood. 

Horse  Blood.         Human  [ 

Man). 

Cor- 
puscles 
325-5. 

Serum 
674-5. 

Cor- 
puscles 
397-7. 

Sx '  rli. 

Serum 
486-98. 

Water 

192-65 

616-25 

245-87 

551-14  1   349-69 

439-02 

Solids 

132-85 

58-25 

153-84 

51-15       163-33 

47-96 

Hffiuioglobin 

103-10 

— 

125-8 

"             '   \ 

— 

Protein 

2(»-S9 

48-90 

20-05 

4-2-65     1     — 

— 

Sugar 

— 

0-708 

— . 

0-90  1 

- 

— 

Organic       ^ 

substances 

Cholesterin 

MO 

0-83o 

0-26 

0-31 

— 

Lecithin 
Fat 

1-22 

1-129 
0-625 

1-93 

1-05 
0-50 

y  159-59 

43-82 

Fatty  acid 

— 

0-02 

0-36 

— 

• — 

Phosphoric  acid 

0-017 

0-0089 

0-05 

0-01 

3-74 

4-14 

as  nuclein 

Soda 

0-726 

2-908 

— 

2-62 

0-24 

1-66 

Potash 

0-235 

0-17] 

1-32 

0-15 

1-59 

0-15 

Iron  oxide 

0-544 

— 

0-59 

— . 

— 

— 

Inorganic 

Lime 

— 

0-08 

— 

0-07 

— 

— 

substances 

Magnesia 

0-005 

0-03 

0-04 

0-03 

■    

— 

Chlorine 

0-59 

2-48 

0-18 

2-20 

0-90 

1-72 

Phosphoric  acid 

0-239 

0-164 

0-98 

0-15 

— 

— 

.Inorganic  P2O5 

0-114 

0-057 

0-76 

0-05 

— 

CHAPTER  X 
THE    PLASMA 

The  plasma  in  which  the  blood-corpuscles  float  is  like  the  middle- 
man, and  barters  between  the  tissues.  Its  composition  summarizes 
the  building-up  and  breaking-down  processes  of  the  body.  It  carries 
the  necessary  nutriment  from  the  alhnentary  tract  to  the  tissues, 
and  foodstuffs  to  and  from  the  food  depots  of  the  body.  It  carries 
also  the  necessary  water  and  salts  to  the  tissues,  thereby  surrounding 
them  with  a  medium  in  which  they  can  carry  out  their  activities. 
Protoplasm  yields  70  to  90  per  cent,  of  water,  and  this  proportion 
has  to  be  maintained,  or  damage,  and  eventually  death,  ensue. 

The  electrolytes  in  solution  are  of  the  greatest  importance,  as  de- 
jnonstrated  by  the  fact  that  a  frog's  heart  beats  for  da3^s  in  a  solution 
containing  potassium,  sodium,  and  calcium  salts  in  the  proportion 
contained  in  blood.  If,  however,  there  be  too  much  soluble  calcium 
salts  j^resent,  the  heart  ceases  to  beat,  stopping  tightly  contracted  in 
the  state  known  as  systole.  If  too  much  solul)le  potassium  salt  be 
present,  the  heart  stops  beating  in  a  flabby,  relaxed  condition  known 
as  diastole.  The  mammalian  heart  may  beat  for  days  in  the  same 
solution  if  it  is  warmed  to  body  temperature  and  oxygenated  by 
bubbling  oxygen  gas  through  it. 

The  unfertilized  eggs  of  sea-urchins  and  other  animals  can  be 
made  to  develop  into  larvse  by  altering  the  concentration  of  certain 
electrolytes  in  the  sea-water.  It  is  possible  that  some  of  the  conditions 
of  ill-health  and  disease  may  be  due  to  an  altered  relationship  of  the 
salts  of  the  plasma,  disturbing  the  vital  processes.  At  present  it  is  not 
possible  for  us  to  investigate  this  i^roportion  of  salts;  it  is  apt  to  be 
little  considered  or  even  overlooked  altogether.  Salts  are  constantlj'' 
leaving  the  body  in  the  urine,  and  unless  they  are  replaced  in 
the  proper  amount  salt  starvation  occurs.  An  animal  deprived 
of  salts  dies  just  as  soon  as  an  animal  cut  off  from  food.  Besides 
the  waste  products  formed  in  the  different  organs  as  a  result  of 
their  activity,  the  plasma  may  receive  from  certain  tissues  special 
substances  which  have  been  elaborated  by  them.  Such  bodies  are 
the  so-called  internal  secretions.  They  play  a  great  part  in 
regulating  the  various  functions  of  the  body.  Sometimes,  too,  a 
special  messenger,  or  "  hormone,"  is  added  to  the  plasma.  For 
example,  blood  leaving  the  upper  part  of  the  small  intestine  during 
digestion  takes  away  in  the  plasma  a  messenger,  or  hormone,  named 
secretin.     The  secretin  on  reaching  the  pancreas  in  the  course  of  the 

82 


THE  PLASMA  83 

circulation,  delivers,  so  to  speak,  a  message  that  more  pancreatic 
juice  is  required;  the  pancreas  is  thrown  into  a  state  of  activity 
and  secretes  the  necessary  juice.  Another  example  is  furnished  by  the 
Ovary.  When  the  mother  becomes  pregnant,  the  corpus  luteum  in 
the  ovary  elaborates  a  hormone  which,  passing  into  the  maternal  cir- 
culation, causes  the  large  development  of  mammary  tissue  which  takes 
place  previoiis  to  the  birth  of  the  ,young.  It  has  also  been  suggested 
that  the  embryo  elaborates  a  hormone  which,  passing  into  the  maternal 
blood,  further  stimulates  the  growth  of  the  mammary  gland.  After 
birth  this  hormone  no  longer  circulates,  since  its  source  is  removed;  the 
breast  tissue  is  no  longer  built  up,  but,  on  the  contrary,  the  lack  of 
hormone  leads  to  a  breaking  down  of  this  proliferated  tissue  with  the 
formation  of  the  first  milk  necessary  to  the  young  which  have  been 
born. 

It  is  questionable  whether  the  plasma  contains  enzymes.  It  has 
no  sugar-destroying  ferment,  but  probably  contains  a  lij)ase,  which 
plays  a  part  in  the  fat  metabolism  of  the  bod}^ 

The  plasma  is  greatly  concerned  with  the  defences  of  the  body 
against  poisonous  substances  or  living  intruders.  It  provides  a  medium 
in  which  the  white  corpuscles  live,  and  one  of  their  functions  is  to 
migrate  to  the  scene  of  attack  and,  if  possible,  repel  or  kill  invading 
bacteria.  But  besides  the  leucocytes  there  are  in  the  blood  defensive 
substances  known  as  antitoxins,  immune  bodies.  These  enable  the 
body  either  actively  to  neutralize,  or  in  other  ways  to  render  ineffec- 
tive, the  harmful  substances  which  may  effect  an  entrance. 

Plasma  may  be  most  readily  obtained  by  receiving  horse's  blood 
into  a  cooled  vessel  and  allowing  it  to  stand.  The  corpuscles  sink 
and  the  plasma  comes  to  the  top.  Blood  which  has  been  kept  from 
clotting  by  the  addition  of  neutral  salts  may  be  centrifuged;  ''  salted  " 
plasma  is  thus  obtained.  Sodium  citrate  or  potassium  oxalate  may  be 
employed  to  decalcify  the  blood  and  prevent  clotting. 

The  plasma  must  be  regarded  as  a  living  tissue.  It  is  always  to 
be  borne  in  mind  that  the  substances,  considered  below,  obtained  by 
submitting  to  analysis  living  tissues,  are  dead  products.  The  con- 
stitution of  the  living  protoplasm  is  a  complex  the  nature  of  which 
is  only  surmised. 

The  Proteins. — On  analj^sis  7  to  8  per  cent,  of  proteins  are  obtained; 
these  can  be  separated  into  three  by  the  method  of  salting  out — 
fibrinogen,  serum  globulin,  and  serum  albumin.  The  amount  of 
fibrinogen  is  very  small,  0-2  to  0-7  per  cent.  Present  in  blood-plasma, 
but  not  in  the  serum,  it  is  this  protein  which  is  concerned  in  the  process 
of  clotting. 

Serum  globulin  is  precipitated  by  half -saturation  with  ammonium 
sulphate  or  full  saturation  with  magnesium  sulphate.  Serum  albumin 
requires  full  saturation  with  ammonium  sulphate.  Fibrinogen  is 
thrown  down  by  half-saturation  with  sodium  chloride. 

Serum  globulin  is  soluble  in  dilute  saline  solutions,  but  not  in 
distilled  water.     It  is  therefore  precipitated  from  solution  when  the 


84  A  TEXTBOOK  OF  PHYSIOLOGY 

salt  is  removed  by  dialysis,  or  by  great  dilution  with  water.  It 
eoagulates  at  69°  C.  to  75"  C,  and  has  a  levorotatory  power  of  —  47-8°. 
It  is  possible  that  it  is  not  one  single  body,  since  by  differences  in 
solubility  and  precipitability  two  bodies  have  been  obtained — euglob- 
ulin,  easily  precipitated  by  28  to  30  per  cent,  of  ammonium  sulphate; 
and  pseudo-globulin,  requiring  36  to  44  volumes  per  cent,  of  this  salt. 
According  to  some  observers,  after  coagulation  has  taken  place 
there  is  found  in  the  serum  a  fibrin  globulin  which  is  formed  as  a  pro- 
duct when  fibrinogen  is  converted  into  fibrin.  It  is  apparently  almost 
identical  with  fibrinogen. 

Filrinogen  is  a  body  of  the  globulin  type,  coagulated  by  heat 
at  about  56"  C.  It  is  precipitated  from  solution  by  half-satura- 
tion with  sodium  chloride.  The  precipitate  may  be  redissolved  in 
dilute  saline,  and  the  solut'on  thus  obtained  clotted  at  37°  C.  by  the 
addition  of  a  trace  of  blood-serum.  This  experiment  is  important  to 
the  theory  of  the  clotting  of  blood. 

Serum  albumin  is  a  body  soluble  in  water  and  not  precipitated  from 
solution  by  magnesium  sulphate.  Its  coagulation  temperature  varies 
according  to  the  amount  of  salt  present  in  the  solution.  Dissolved 
in  distilled  water  it  coagulated  at  about  50°  C. ;  with  salts  present  in 
the  solution  the  temperature  of  coagulation  is  higher.  When  a  solu- 
tion of  serum  albumin  almost  saturated  with  ammonium  sulphate  is 
allowed  to  concentrate  by  standing,  crystals  of  a  compound  of  albumin 
with  the  salt  fall  out. 

The  source  of  the  proteins  yielded  by  plaf^ma  is  not  known.  The 
yield  of  fibrinogen  is  said  to  depend  on  the  liver.  Blood,  the  circu- 
lation of  which  is  confined  to  the  heart  and  lungs,  loses  its  property 
of  coagulability,  whereas  blood  circulated  through  the  liver  has  an 
increased  coagulative  power.  According  to  one  theory  of  protein 
metabolism  (q.v.),  the  blood-proteins  are  formed  out  of  the  protein 
products  of  digestion  at  the  time  of  the  passage  of  these  through  the 
intestinal  wall  into  the  blood. 

The  amount  of  protein  yielded  by  the  plasma  is  said  to  vary  in 
certain  diseased  conditions.  In  cases  of  infection,  such  as  pneumonia, 
it  is  increased,  particularly  the  fibrinogen  moiety.  Globulins  are  said 
to  be  increased  relatively  to  the  albumin  (the  so-called  "  protein 
quotient  ")  in  parenchymatous  nephritis.  The  normal  proportion  is 
4-^-  :  3  in  man.  It  varies  in  different  animals.  The  plasma  of  cold- 
blooded animals  chiefly  yields  globulins.  In  the  regeneration  of  the 
plasma  after  haemorrhage  the  albumin  is  formed  first,  and  afterwards 
the  globulin.  Closely  allied  to  the  globulin  portion  of  the  blood  are 
the  protective  substances,  such  as  antitoxins,  haemolysins,  bacterio- 
lysins,  precipitins,  etc.  Some  observers  state  that  proteoses, 
peptones,  and  amino-acids,  are  to  be  found  in  the  blood.  This, 
however,  is  strenuously  contested  by  others. 

Lipoids. — Fat  in  a  very  finely  emulsified  form  and  soaps  are  found 
in  the  blood.  The  amount  in  normal  human  blood  varies  according 
to  the  diet,  being  increased  by  the  taking  of  milk  or  other  fat.     It 


THE  PLASMA  85 

varies  normalh-  from  1-8  to  0-85  per  cent.     In  the  pregnant  animal 
the  fat  content  of  the  plasma  is  much  increased. 

The  Hpoids  lecithin  and  cholesterin  are  also  present  in  the  plasma, 
and  probabh'  play  a  conside  able  part  in  the  protective  mechanisms 
of  the  body,  as  well  as  furnishing  a  supplj"  of  these  bodies  to  the  other 
tissues. 

Carbohydrate. — Dextrose  is  normally  present  ;  the  percentage 
found  varies  from  0-06  to  0-1.  If  the  content  is  raised  above  the  latter 
figure,  the  excess  is  excreted  in  the  urine.  It  is  a  question  whether 
the  dextrose  is  free  in  solution  or  looseh'  combined  with  the  proteins ; 
a  small  amount  of  it  is  combined  with  lecithin  to  form  a  substance 
known  as  jecorin.  The  presence  of  glycuronic  acid  has  been  demon- 
strated in  the  serum.  It  is  usually  combined  as  comjDound  glycuron- 
ates.  It  has  been  recently  shown  that  the  red  corpuscles  contain 
sugar. 

The  salts  obtained  from  plasma  form  1  to  2  per  cent,  of  its  weight, 
and  are  chiefly  sodium  chloride,  with  traces  of  calcium,  potassium, 
and  magnesium  chloride  and  phosphate. 

The  straw-3-ellow  colouring  matter  of  the  plasma  can  be  extracted 
with  amjd  al  ohol,  and  is  called  lipochrome. 

The  gases  of  the  plasma  will  be  dealt  with  later. 

The  plasma  contains  various  antienzymes,  immune  bodies,  com- 
plement, etc.,  the  presence  of  which  is  detected  by  biological  tests. 

The  chief  products  of  katabolism  of  the  various  foodstuffs,  presence 
of  which  has  been  demonstrated  in  the  plasma,  are  urea  (0-02  to 
O'l  per  cent.),  uric  acid,  creatin,  creatinin,  and  traces  of  ammonia. 
While  it  is  cj[uestioned  whether  amino-acids  are  normal  constituents 
of  plasma,  they  are  undoubtedly  present  when  any  organ  or  tissue  is 
digesting  itself  (autolysis),  as  in  phosphorus  poisoning,  acute  yellow 
atrophy  of  the  liver,  etc.  They  then  make  their  appearance  in  the 
urine. 

The  plasma  under  diverse  conditions  is  found  to  have  a  most 
striking  consistencj^  in  composition.  Thus,  after  the  intravenous 
injection  of  water  or  salt  solution  the  bloocl  is  rapidly  brought  to 
the  normal  composition.  The  tissues  give  or  take  from  the  blood, 
the  glands  secrete  and  kidne3^s  excrete  for  this  purpose.  Even  during 
starvation  its  composition  is  maintained. 


CHAPTER  XI 
THE  CORPUSCLES  OF  THE  BLOOD 

The  Red  Blood-Corpuscles. — The  red  blood-corpuscles,  or  erythro- 
cytes, are  the  elements  to  \\'hich  is -due  the  red  colour  of  the  blood  of 
all  the  vertebrate  animals  except  Amphioxus,  which  has  colourless 
blood.  They  were  first  seen  in  human  blood  by  Leuwenhoek  in  1673. 
They  had  been  previously  seen  in  frog's  blood  by  Swammerdam  in 
1658. 

Human  red  blood-corpuscles  are  non-nucleated  biconcave  discs 
having  a  diameter  of  about  1  to  8  u.  Two  views  are  held  as  to  their 
structure.  According  to  one  view  they  are  to  be  regarded  as  capsules 
containing  the  red  pigment,  hsemoglobin  (Hb) — probably  in  a  special 
colloidal  state.  The  amount  of  the  j)igment  is  so  great  that  it  could 
not  be  in  solution.  A  red  corpuscle  contains  32-05  per  cent.  Hb,  and 
only  63-21  per  cent,  water,  and  so  strong  a  solution  of  Hb  cannot  be 
made.  The  other  view  regards  them  as  consisting  of  a  stroma  or 
network  in  which  the  pigment  is  enmeshed.  In  either  case  the  outer 
surrounding  structure  is  protein  in  nature,  richly  impregnated  with 
lecithin  and  cholesterin.  It  has  been  suggested,  but  not  proven,  that 
these  lipoid  bodies  stand  guard  over  the  corpuscles,  and  determine 
what  substances  may  pass  into  the  corpuscles  and  what  may  not. 

The  form  of  the  red  corpuscle  varies  in  different  species.  Man 
and  the  other  mammalia,  with  the  exception  of  the  camelidse  (camel, 
llama,  etc.),  have  non-nucleated  biconcave  discs.  Camels  have  long 
non-nucleated  ellij)tical  corpuscles.  Birds,  reptiles,  fish,  have  elliptical 
nucleated  corpuscles.  The  number  to  each  cubic  milhmetre  varies 
in  general  with  the  size — the  larger  the  corpuscle,  the  smaller  the 
number  per  cubic  millimetre.  The  following  table  shows  the  size 
and  number  per  cubic  centimetre  in  various  animals : 


Proteus  anguinus 
Frog 
Chaffinch 
Mail      . . 
Goat     . . 
Llama  . . 


No.  per  c.mm. 


30,000 

404,000 

3,(500,000 

5,000,000 

9,500,000 

14,000,000 


The  corpuscles  are  endowed  with  elasticity,  and  alter  their  shape 
in    passing    through    the    capillaries.     The    red   corpuscles   represent 

88 


THE  CORPUSCLES  OF  THE  BLOOD 


87 


35  to  40  per  cent,  of  the  weight  of  the  blood.  This  can  be  ascer- 
tained bj'  centrifnging  blood  in  a  fine  graduated  capillar}*  tube  known 
as  a  hsematocrit.  If  done  with  a  very  rapid  centrifuge,  fresh  blood 
may  be  used ;  otherwise  oxalated  or  citrated  blood  is  employed. 
The  number  of  corpuscles  is  greatly  reduced  in  anaemia.  Normally 
there  are  5,000,000  to  5,500.000  per  cubic  millimetre  in  man's  blood, 
4,500,000  to  5,000,000  in  woman's  blood  (15  to  25  billions  in  the 
whole  blood  of  a  man  with  a  surface  of  1.000  to  1,700  square  metres). 
The  number  per  c.mm.  varies  from  time  to  time;  it  is  stated  to  be 
diminished  after  drinking  much  fluid  and  during  pregnancy,  increased 
after  profuse  sweating,  after  exercise,  after  hot  and  cold  baths,  in 
the  blood  of  the  new-born,  and  in  venous  stasis. 

At  high  altitudes  the  number  of  the  corpuscles  and  the  Hb  content 
of  the  body  is  increased  (see  Fig.  18). 


Fic.  10. — The  Thoma-Zeiss  H.^macytometer. 


,  The  red  corpuscles  undergo  various  changes  in  shape  Avhen  sub- 
mitted to  the  action  of  different  substances.  Distilled  water  causes 
them  to  swell  and  burst  {cf.  Haemolysis) ;  strong  salt  solution  (hyper- 
tonic) causes  them  to  shrink  and  crinkle,  or  crenate;  tannic  acid  causes 
the  haemoglobin  to  leave  the  envelope  and  appear  as  a  dot  outside. 
When  blood  is  shed,  the  red  corpuscles  show  a  tendency  to  run  together 
mto  rolls  like  piles  of  coins. 

Enumeration  o£  Red  Corpuscles. — This  is  done  by  an  apparatus 
known  as  a  haemacytometer.  The  form  generall}^  employed  is  that 
shown  in  Fig.  19.  The  apparatus  consists  of  (1)  two  graduated  mixing 
pipettes,  labelled  101  and  11  respectively;  (2)  a  specially  constructed 
counting  chamber.  A  small  disc  of  glass  (B)  and  a  thicker  plate  of 
glass  (D)  are  affixed  to  a  glass  slide  so  as  to  form  a  platform  (B)  sur- 
rounded by  a  well.  When  a  cover-glass  is  placed  over  this  plat- 
form, a  fine  film-like  space  of  known  thickness  is  left  between  the 
platform  and  the  cover-glass.  The  platform  is  ruled  in  squares, 
each  Jl^J  of  a  sqx;are  millimetre  (C  in  Fig.). 

For  counting  red  corpuscles  the  pipette  labelled  101  is  employed. 
Blood  is  sucked  up  to  the  mark  1,  and  then  quickly  diluting  fluid  up 


88 


A  TEXTBOOK  OF  PHYSIOLOGY 


to  the  mark  101,  and  the  mixture  well  shaken.  For  diluting  normal 
saline  3  per  cent,  f^odium  chloride,  or  Haj^em's  solution,*  may  be  used. 
For  counting  fcoth  forms  of  corpuscles,  Sherrington's  or  Toison'sf 
fluid  may  he  employed.  These  contain  a  dye  (methylene  blue  or 
methyl  violet)  which  stains  the  pale  cells  and  enables  them  to  be  counted 
more  readily. 

After  a  thorough  shaking  the  first  few  drops  of  fluid  are  rejected, 
and  then  a  drop  of  the  mixture  is  placed  upon  the  platform  and  mounted 
with  a  cover-glass.  Any  excess  of  fluid  runs  into  the  surrounding 
well.  Care  is  taken  that  there  is  not  sufficient  fluid  to  fill  the  well, 
otherwise  the  film  beneath  the  cover-glass  is  altered  in  thickness  and 
the  result  vitiated.  The  scale  on  the  platform  is  focussed,  and  the 
cells  in  a  square  and  those  lying  on  two  of  its  adjoining  sides  are 
counted.  Usually  40  to  100  squares  are  counted.  Each  square  is 
-1-  of  a  square  millimetre  in  area,  and  the  depth  of  the  cell  is  0-1  milli- 
metre. Over  each  square,  therefore,  lies  j^Vo  "^^^^i^  millimetre  of  the 
diluted  blood.  On  multiplying  by  4,000  the  average  number  of  cor- 
liuscles  found  in  each  square,  and  again  by  100,  because  of  the  dilution, 
the  number  in  1  cubic  millimetre  of  und  luted  blood  is  obtained.  For 
example,  12x4,000x100=4,800,000,  about  the  average  number  in 
man's  blood. 

The  Origin  of  the  Red  Corpuscle. — The  origin  of  the  red  corpuscle 
varies  with  the  stage  of  existence. 

1.  In  early  foetal  life  the  nucleated  red  corpuscles  are  first  formed 
from  the  mesoderm  where  ever  the  formation  of  capillary  vessels  is 
taking  place  (Fig.  20). 

y^^^  ^-^^^^^^>     .  erythrocyte 

uasoform.  cell — '■ — *'*#^— -^:ir>~vW    (5)  '/S^  , ,     , 
,      L,    X  ->w  ----^^-,^^}^^^ii^z/^ — blood  ues. 

hypoblast ^^^00^^"^^^^: 

Fig.  20. — Section  across  Yolk  Sac  showing  Bloodvessels  and  Nucleated  Red 
Blood -Corpuscles  forming  in  its  Mesoblastic  Layer.     (Keith,  after  Selenka.) 


The  cells  (angioblasts)  in  the  region  where  a  capillary  is  to  be 
formed  unite  together  to  form  a  syncytium  (a  fusion  of  cells).  Their 
nuclei  divide  at  some  places  faster  than  others,  so  that  an  accumula- 
tion of  colourless  cells  (primitive  hsemoblasts)  is  formed  at  certain 
points.  These  cells  become  coloured  by  the  formation  of  haemoglobin 
within  them,  and  form  the  primitive  coloured  cells  of  the  blood — ^the 
so-called  primitive  erythroblasts.  A  hoUowing-out  process  now  takes 
place  at  the  enlargements,  and  the  newly  formed  corpuscles  float  in 
a  clear  fluid  in  the  cavities  thus  made,  the  whole  forming  so-called 

*  Hayem's  solution  consists  of:  Mercuric  chloride,  0-5  gramme;  sodium  sulphate^. 
5  grammes;  sodium  chloride,  1  gramme;  distilled  water,  200  c.c. 

t  Toison's  solution  is:  Methyl  violet,  0-025  gramme;  sodium  chloride,  1  gramriae;. 
sodium  sulphate,  8  grammes;  glycerine,  30  c.c. ;  distilled  water,  IfiO  c.c. 

Sherrington's  fluid  is:  Methylene  blue,  0-1  gramme;  sodium  chloride,  1-2  grammes; 
neutral  potassium  oxalate,  1'2  grammes;  distilled  water,  800  c.c. 


THE  CORPUSCLES  OF  THE  BLOOD         89 

blood-islands.  The  spaces  between  the  blood-islands  is  next  exca- 
vated, some  of  the  angioblasts  becoming  converted  into  blood-cor- 
puscles, others  forming  the  cells  of  the  capillary  wall.  This  process 
goes  on  until  the  circulation  is  established  and  capillary  formation  is 
complete.  The  blood-cells  thus  formed  multiply  within  the  vessels. 
Later  on,  when  the  circulation  is  established,  large  blood-cells  (megalo- 
blasts),  derived  from  the  primitive  hsemoblasts,  also  make  their 
appearance  in  the  blood.  From  the  megaloblasts  are  derived  smaller 
normoblasts,  which  lose  their  nuclei  and  become  converted  into  the 
erythrocji^es  similar  to  those  of  the  adult. 

By  some  authorities  it  is  held  that  hsemoblast  cells  also  give  rise 
to  lymj)hoblasts,  from  which  lymphocj'tes  are  developed,  and  possibly 
leucocytes;  also  to  myeloblasts,  from  which  myelocytes  and  leucocj'tes 
are  develoiDcd.  All  the  first  blood-corpuscles  according  to  this  scheme 
have  a  common  mesoblastic  parent  cell,  the  hsemoblast. 

HiEMOBLAST 


Primitive       Megaloblast     Lymphoblast  Myeloblast 

Erythroblast  |  |  "   | 

Normoblast     Lymphocyte  Eosinophil     Neutrophil     Basophil 

I  (large  and  small)  myelocyte     myelocyte     myelocyte 

Primitive  Erythroblast     Leucocyte  ?  Eosinophil     Neutrophil     Basophil 

Erythrocyte  |                 (neutrophil)  leucocyte       leucocyte      leucocyte 

"^ , '       Erythrocyte    — -,. ^ , — — ■' 

Mesoderm       ^ , — -        Lymph  Red  marrow 

of  foetus  Red  marrow          glands 

The  red  corpuscles  are  formed  in  mid-fcetal  life  to  a  certain  extent, 
and  in  late  foetal  life  to  a  large  extent,  in  the  liver,  spleen,  connective 
tissue,  and  red  bone  marrow;  but  in  the  last  few  weeks  of  foetal  life 
the  red  bone  marrow  becomes  almost  the  sole  source.  The  cells  arising 
from  the  bone  marrow  are  non-nucleated. 

In  the  human  embryo  at  the  fourth  week  only  nucleated  cells  are 
present;  in  the  fourth  month  they  form  about  25  per  cent,  of  the 
whole,  while  at  full  time  but  few  nucleated  corpuscles  are  found. 

2.  After  birth  the  red  bone  marrow  is  the  sole  source  of  the  red 
blood-corpuscles.  Here  nucleated  erythroblasts  are  always  to  be 
found,  derived  from  mega'oblasts  and  normoblasts.  When  extensive 
destruction  of  the  corpuscles  is  taking  place,  this  erythroblastic  tissue 
shows  signs  of  great  activity,  and  in  times  of  great  need  the  nucleated 
red  cells  of  the  marrow  may  pass  into  the  blood. 

Generall}^  however,  the  erythroblasts  multiply  by  cell  division; 
these  cells  then  exclude  or  absorb  their  nucleus,  and  pass  into  the 
circulation  as  non-nucleated  er}i:hroc3'tes. 

Function. — The  great  function  of  the  red  corpuscles  is  to  carry 
oxygen  to  the  tissues.  This  it  does  by  virtue  of  the  haematin  portion 
of  its  haemoglobin.  This  function  is  destroyed  on  taking  blood  from 
an  animal,  defibrinating  it,  and  heating  it  to  56°  C.  On  injecting 
into  the  animal  the  blood  which  has  been  thus  warmed,  the  corpuscles 


<)J  A  TEXTBOOK  OF  PHYSIOLOGY 

are  immediately  dissolved.  On  the  other  hand,  blood  kept  at  0°  for 
several  days  (three  to  four)  can  be  reinjected  into  an  animal  and  still 
functionate.  Haemoglobin  plays  a  considerable  part  in  the  transport 
of  carbon  dioxide  from  the  tissues  to  the  lungs.  It  has  a  specifir 
capacity  for  absorloing  Cavbou  dioxide. 

The  Fate  of  the  Red  Blood-Corpuscles. — It  is  not  po.ssible  to  say 
how  long  the  red  corpuscle  circulates  before  it  is  destroyed,  j^ossibly 
three  to  four  weeks.  After  some  such  time  the  corpuscle  is  probably 
destroyed  in  the  spleen,  the  liberated  hsemoglobin  passing  to  the  liver 
to  be  disintegrated  there.  From  it  the  iron-free  bile-pigments  bilirubin 
and  biliverdin  are  formed,  the. iron  being  stored  in  the  liver. 

This  iron  can  be  stained  blue  by  treating  sections  of  the  liver 
with  potassium  ferrocyanide  and  hydrochloric  acid,  or  black  by  a 
pure  solution  of  haematoxylin. 

The  iron  in  the  liver  is  greatly  increased  in  conditions  in  which  a 
large  destruction  of  red  corpuscles  takes  place.  It  has  been  suggested 
that  the  spleen  regulates  the  iron  metabolism  of  the  body;  and  it  is 
possible  that  some  of  the  destruction  of  red  corjjuscles  takes  place 
there,  accompanied  by  the  formation  of  pigment  and  the  storage  of 
iron  in  the  sjDlenic  cells.  It  is  sujjposed  that  the  stored  iron  is  again 
used  to  form  haemoglobin. 

Chemistry  of  the  Red  Corpuscle. — The  framework,  or  stroma, 
consists  of  protein  and  lipoids,  ^\•ithin  which  are  the  salts,  notably 
salts  of  potassium,  and  the  haemoglobin  (see  table,  p.  81). 

The  pigment  hsemoglobin  forms  90  per  cent,  of  the  corpuscle.  It 
is  one  of  the  compound  proteins,  a  chromoprotein  consisting  of  an 
iron-containing  portion  (hsematin)  and  a  protein  portion  (globin); 
the  latter  is  a  histone. 

Haemoglobin,  as  other  proteins,  varies  in  composition  in  different 
animals. 


C. 

1 
H. 

\ 
7-25      1 

.V. 

.S'. 
0-447 

Fe. 
0-400 

0. 

Ox 

54-66 

17-70 

19-54 

Horse    . . 

51-15 

6-76 

17-94 

0-390 

0-335 

23-43 

Dog       .. 

54-57 

7-22 

16-38 

O-.'idS 

0-336 

20-93 

Pig        .. 

34-71 

7-38 

17-43 

0-479 

0-399 

19-60 

Its  percentage  composition  is  approximately — 

C  54-71;  H  7-.38;  N  17-43;  S  0-79;  Fe  0-399;  0  19-602. 

Hsemoglobin  is  readily  soluble  in  water;  coagidated  by  heat  to 
a  brown  coagulum;  dextrorotatory  to  polarized  light.  It  can  be 
obtained  in  crystalline  form,  but  more  readily  from  some  bloods 
than  others.  It  is  easily  obtained  from  the  blood  of  the  rat  after 
the  addition  of  distilled  water.  In  the  guinea-pig's  blood  haemolysis 
is    first    produced    by   the   addition   of    chloroform    or  ether.     Upon 


THE  CORPUSCLES  OF  THE  BLOOD  91 

evaporation  the  chloroform  or  ether  extract  deposits  crystals  of 
oxy  haemoglobin. 

Crystals  are  readily  obtained  from  the  blood  of  the  squirrel,  rabbit, 
and  also  from  the  mouse  and  rodents  generally ;  less  readily  from 
man,  horse,  cat,  birds,  and  fishes.  It  is  a  more  difficult  matter  to 
obtain  crj'stals  from  the  blood  of  the  sheep,  ox,  and  pig. 

The  crj'stals  vary  in  size  and  shape  according  to  the  animal  from 
which  they  are  prepared  (Fig.  21).  Those  from  the  rat  are  needle- 
shaped,  resembling  those  from  human  blood;  from  the  guinea-pig 
they  are  quadrilateral  prisms;  from  the  squirrel,  hexagonal  plates. 

The  rosy  colour  and  plump  look  of  health  is  due  to  a  plentiful 
supph'  of  well-oxj^genated  blood  in  the  face.  The  great  function  of 
the  red  corpuscle  is  to  carry  oxygen,  and  the  most  characteristic 
property  of  the  pigment  liijemogiobin  is  its  power  to  form  a  loose 
chemical  combination  with  oxygen.     The  body  thus  formed  is  termed 


Fi5.  21. — Crystals  of  Oxyh.5:jio:!Lobix  fro:.i  Horse's  Elood. 

oxyhgemoglobin,  and  it  is  to  this  body  that  the  bright  red  colour  of 
arterial  blood  is  due.  If  arterial  blood,  diluted,  let  us  say,  with  water 
to  1  in  500,  is  examined  with  the  spectroscope,  two  absorption  bands 
are  seen  in  the  yellow  and  the  green  between  the  lines  D  and  E  (Fig.  22). 
The  addition  of  a  reducing  substance,  such  as  ammonium  sulphide,  to 
this  solution  displaces  the  oxygen  from  the  oxy haemoglobin.  The 
solution,  now  changed  to  a  purplish  colour,  gives  the  spectrum  of 
hsemoglobin;  one  broad  but  less  dark  band  is  seen  between  D  and  E 
(Fig.  22). 

Carboxyhsemoglobin. — Blood  exposed  to  coal-gas  or  carbon  mon- 
oxide gives  a  spectrum  resembling  OHb,  but  the  solution  of  COHb 
is  markedly  pinker  in  colour,  and  is  not  reduced  by  the  addition  of 
ammonium  sulphide.  This  serves  to  distinguish  the  two.  When  a 
solution  of  carboxyhsemoglobin  is  greatly  diluted,  it  remains  pink, 
while  that  of  oxyhaemoglobin  diluted  to  the  same  extent  becomes 
yellowish-green . 


92  A  TEXTBOOK  OF  PHYSIOLOGY 

The  presence  of  CO  in  coal-gas  and  in  after-damp  in  mines  is  a 
frcqiicnt  cause  of  death.  CO  has  about  150  times  as  great  an  affinitj'^ 
for  Hb  as  O^,  and  thus  it  comes  about  that,  if  a  man  breathes  long 
euoiighan  atmosphere  containing  0-1  percent.  CO,  half  the  oxygen  will 
be  displaced  from  his  V)lood.  The  haemoglobin  of  the  blood  becomes 
combined  to  form  COHb,  insufficient  oxygen  is  now  carried  to  the 
tissues,  and  death  from  oxygen  want  ensues.  It  is  therefore  dangerous 
to  breathe  an  atmosphere  containing  more  than  0-05  per  cent.  CO  is 
without  colour  or  smell,  and  its  presence  cannot  be  sensed.  The  want 
of  oxj'gen  gives  little  warning,  and  a  man  breathing  CO  may  lose 
consciousness  unwitting  of  his  danger.  A  small  vertebrate,  such  as 
a  bird  or  mouse,  is  affected  much  sooner  than  a  man,  and  it  is  a  wise 
precaution  to  send  a  cage  bird  with  an  exploring  party  into  a  mine 
where  "  after-damp  "  exists.  Ordinary  illuminating  gas  contains 
about  5  per  cent,  of  carbon  monoxide,  and  water-gas,  used  in  some 
towns,  as  much  as  30  to  40  per  cent.  CO  poisoning  in  such  towns 
has  accounted  for  even  1  per  cent,  of  all  the  deaths.  Seventy-five 
per  cent,  saturation  of  the  haemoglobin  with  CO  causes  dizziness  and 
palpitation  on  exertion;  the  heart  fails  to  keep  up  the  extra  circula- 
tion required  then.  Brain-power  is  greatly  diminished  although  the 
subjects  do  not  know  it.  In  deaths  from  house  on  fire  the  people 
are  as  a  rule  rendered  unconscious  by  CO  poisoning  before  they  arc 
burnt.  The  bodies  of  men  killed  by  CO  poisoning  have  a  pink  colour, 
due  to  the  COHb  formed. 

Nitroxyhsempglobin  (NOHb)  also  has  a  spectrum  resembling  the 
above,  but  the  two  bands,  although  in  approximately  the  same  posi- 
tion, are  not  by  any  means  so  clear-cut;  the  shading  appears  "  woolly." 
NOHb  is  not  reduced  bj^  ammonium  sulphide.  It  is  prepared  bj' 
adding  a  solution  of  ammonia  to  the  blood,  and  then  passing  nitric 
oxide  gas  through  the  solution.  It  is  formed  in  the  blood  by  the  action 
of  the  nitrites — e.g.,  amyl  nitrite  or  such  bodies  as  nitro-benzol. 
Methsemoglobin  is  first  formed,  and  afterwards  nitroxyhaimoglobin. 

For  cases  of  partial  j^ioisoning  by  carbon  monoxide  or  nitrites  the 
correct  treatment  is  to  place  the  j)atient  in  an  atmosphere  of  oxygen, 
preferably  under  pressure,  so  that  the  Hb  which  is  uncombined  may 
have  an  ample  supply  of  oxygen  to  draAv  upon,  and  more  oxygen  may 
become  dissolved  in  the  plasma  of  the  blood  owing  to  its  increased 
partial  pressure.  At  a  pressure  of  oxygen  of  two  atmospheres  about 
2-5  per  cent,  of  oxygen  is  dissolved  in  the  plasma,  and  this  is  enough 
to  maintain  life  in  the  presence  of  any  percentage  of  CO.  A  mouse 
poisoned  by  CO,  and  rendered  moribund,  revives  in  two  atmospheres 
of  oxygen,  and  tumbles  over  again  when  the  pressure  is  lowered  to 
atmospheric  pressure.  The  resuscitation  and  swooning  of  the  mouse 
maj^  be  repeated. 

NOHb  is  even  more  stable  than  COHb.  It  can  be  distinguished 
from  COHb  by  giving  a  bright  red  coagulum  on  boiling,  whereas 
COHb  gives  a  brownish  one.  The  difference  in  colour  is  approximately 
that  between  the  outer  red  ring  of  salt  beef  and  the  inner  brown  zone. 
In  this  case  the  haemoglobin  in  the  muscle  has  formed  NOHb  owins: 


THE  CORPUSCLES  OF  THE  BLOOD 


93 


to  bacterial  decomposition  in  the  presence  of  the  sahpetre  used  in 
the  process  of  preservation. 

Metheemoglobin    (MetHb). — Oxj-haemoglobin    is   frequently    repre- 
sented  by   the   formula   HbC      ;    methaemoglobin    by    the    formula 

Hb^    ,  although  the  correctness  of  the  latter  has  been  questioned. 

It  is  formed  in  the  stale  blood,  and  may  be  prepared  by  adding  to 
a  solution  of  Hb  a  few  drops  of  a  fresh-made  solution  of  potassium 


Osyhaimoglobin 


Hiemoglobin 
(reduced) 


Carboxyhitmo- 
glubin 


Acid  hiematin 


Alkaline  hsematin 


Reduced  alkaline 
h»niatin  or  h;i- 
mochroiuogen 


Methfemoglobic 


Acid  Haem  itop or- 
phj-iia 


Wave    kngths    in 


Fig.  22. — Ilood  hPECTEv.     (Waller.) 


ferric3-anide.  The  loosely  combined  oxygen  of  the  OHb  is  turned 
out,  and  the  Hb  then  combines  in  a  more  stable  form  with  an  equal 
amount  of  oxygen  taken  up  from  the  decomposition  of  bicarbonates 
in  the  blood,  a  chemical  reaction  taking  place  in  which  the  ferric^anide 
is  reduced  to  ferroc3'anide. 


0 


^ 


0 


Hb      I  -F4Xa3{reCy,.)-h4NaHC03=02+Hb' 

O  0 

+  4Na,(FeCy6)  +4C0.,  -f-2HoO 


94  A  TEXTBOOK  OF  PHYSIOLOGY 

Oil  this  reaction  depends  the  chemical  method  of  determining  the 
amount  of  loosely  combined  oxgyen  in  the  blood. 

The  solution  of  MetHb  is  greenish-brown  in  colour.  The  spectrum 
of  this  solution  suitably"  diluted  shows,  in  addition  to  the  two  bands 
characteristic  of  OHb,  another  band  in  the  red  near  the  line  C.  These 
three  bands  are  well  marked  and  of  almost  equal  intensity.  The  O^ 
in  methajmoglobin  is  not  yielded  to  the  vacuum  pump,  and  is  not 
available  for  respiratory  jDurposes.  By  treatment,  however,  with 
ammonium  sulphide  MetHb  can  be  easily  reduced  to  Hb,  which  in 
turn  can  be  converted  again  to  OHb  by  shaking  well  in  air.  MetHb 
is  sometimes  passed  in  the  urine  after  the  administration  of  excessive 
doses  of  potassium  chlorate,  and  antipyretics  such  as  phenacetin, 
antifibrin,  etc.  It  is  formed  when  the  red  corpuscles  are  hsemolyzed 
and  a  considerable  amount  of  Hb  is  set  free  in  the  blood-stream. 
The  condition  is  known  as  methaemoglobinuria.  The  deep  brown 
colour  gives  the  urine  a  peculiar  look.  The  spectroscopic  test  serves 
to  identify  it. 

Haemoglobin  is  split  into  globin  and  haematin  by  the  action 
of  heat,  acids  and  alkalies,  etc.,  and  there  are  a  number  of  derivatives 
of  hsematin  which  give  characteristic  spectra. 

Chief  of  these  are  acid  haematin,  alkaline  hsematin,  reduced  alkaline 
hsematin  (hsemochromogen),  and  hsematoporphyrin  (iron-free  hsematin). 

Acid  Hsematin  is  readily  prepared  by  shaking  up  a  small  amount 
of  defibrinated  blood  with  a  few  drops  of  20  per  cent,  acetic  acid, 
and  then  suitably  diluting  the  mixture  with  60  per  cent,  alcohol.  It 
forms  a  brownish  solution,  giving  a  well-marked  absorption  band  in 
the  red  near  the  line  C,  nearer  than  the  similar  band  of  MetHb. 
Sometimes  two  bands  are  seen  between  D  and  E,  but  they  are  feeble, 
and  not  of  the  same  intensity  as  the  band  in  the  red.  Acid  hsematin 
cannot  be  reduced  to  Hb  by  the  action  of  ammonium  sulphide. 
This  serves  to  distinguish  acid  hsematin  from  methsemoglobin. 

Alkaline  Haematin  is  prepared  similarly  by  shaking  up  a  small 
amount  of  defibrinated  blood  with  20  per  cent,  potash  and  diluting 
with  weak  alcohol.  It  gives  one  broad  absorption  band  between 
C  and  T>,  which  is  in  contrast  to  the  band  of  Hb  between  D  and  E. 

Reduced  Alkaline  Hsematin  (Hsemochromogen). — This  gives  an 
extremely  characteristic  spectrum  in  suitable  dilutions ;  one  very  dark 
band  between  D  and  E  and  another  less  dark  band  between  E  and  b.  It 
is  only  the  spectrum  which  has  a  band  in  this  postion.  Hsemo- 
chromogen is  prejoared  by  adding  potash  to  the  solution  of  blood, 
or  dissolving  an  old  dried  blood-stain  in  potash,  and  reducing  it  by 
ammonium  sulphide.  As  it  can  be  prepared  from  old  blood-stains, 
it  affords  us  a  test  for  blood  of  great  medico-legal  value.  A  solution 
of  hsemochromogen  and  globin,  if  mixed  and  allowed  to  stand,  will 
reunite  and  form  hsemoglobin. 

Acid  Hsematoporphyrin.  —  By  the  addition  of  acid  to  hsemo- 
chromogen the  iron  is  spUt  off  from  the  compound  with  the  production 


THE  CORPUSCLES  OF  THE  BLOOD         95 

of  acid  hsematoporphyrin.  It  can  be  prepared  by  treating  a  drop 
of  defibrinated  blood  with  a  small  amount  of  strong  suli^huric 
acid,  shaking  well,  and  diluting  the  resultant  mixture  with  more 
concentrated  acid  until  the  mixture  is  suflficiently  diluted  to  be  viewed 
through  the  spectroscope.  The  spectrum  presents  two  bands:  one 
narrow,  just  to  the  red  side  of  the  line  D;  another  broader,  between 
D  and  E. 

The  sulphuric  acid  splits  haemoglobin  into  its  constituents 
hsematin  and  globin;  the  hsematin  is  then  deprived  of  its  iron  with  the 
formation  of  hsematoporphj^rin. 

Alkaline  hsematoporphj'rin  is  produced  in  a  similar  manner  to 
the  acid,  but  very  strong  alkali  is  used.  Alkaline  hsematin  is  first 
formed,  but  this  is  subsequently  broken  down  to  iron-free  alkaline 
hsematin  or  alkaline  hsematoporphyrin.  The  spectrum  of  this  body 
presents  four  bands — a  narrow  band  between  C  and  D,  two  between 
D  and  E,  and  a  broad  band  between  E  and  F. 

Hsematoporphyrin  may  occur  in  the  urine  after  such  drugs  as 
svilphonal  have  been  taken,  and  is  usually  of  the  alkaline  variety. 
The  formula  for  hsematoporphyrin  is  CigH^gXoOg.  It  is  closely  related 
to  the  pigment  bilirubin  ,of  the  bile,  which  has  the  same  empirical 
formula. 

If  a  solution  of  a  copper  salt  in  ammonia  be  added  to  hsematopor- 
ph^Tin,  turacin  is  formed — a  pigment  found  in  the  red  feathers  of 
certain  birds  (plantain-eaters).  The  important  pigment  of  plants, 
chlorophjdl,  is  a  near  ally.  If  treated  with  caustic  jootash  at  190°  C, 
it  yields  a  body  phylloporph3'rin,  CigH^gNjO.  Both  hsematoporphyrin 
and  iDhylloporphjTin  yield  on  reduction  a  bod}'  called  hsemopjrrol. 
It  has  been  suggested  that  hsemoglobin  is  synthesized  out  of  the  chloro- 
phjdl  eaten  in  the  food. 

From  hsematin,  bj'  the  action  of  acids,  hsematoporphjrin  and  a 
body  termed  mesoporphyrin  are  obtained.  B3'  reduction  of  haema 
toporphj*rin,  hsemopyrrol  (CgH^gN)  is  obtained,  and  by  oxidation  and 
treatment  with  caustic  potash  methylethylmaleic  acid  anhydride 
(CgHgOj).  Both  these  bodies  can  also  be  obtained  by  the  splitting 
of  chlorophyll. 

Oxyhaeraoglobin 

Haematin 

Haematoporphyrin 


Mesoporphyrin  Hsemopyrrol  (CgHjgN) 

Methylethylmaleic  acid 
anhydride  (C^HgOs) 

The  pigments  of  the  bile  (bilirubin  and  biliverdin),  the  pigments 
of  the  fseces  (stercobilin),  one  of  the  pigments  of  the  urine  (urobilin),  are 
derivatives  of  hsematin,  and,  like  hsematoporphyrin,  contain  no  iron. 


96 


A  TEXTBOOK  OF  PHYSIOLOGY 


In  old  blood-clots,  flat,  lozciige-shaped  crystals,  of  a  bright  red 
colour,  are  often  found.  This  is  an  iron-free  derivative  of  hsemoglobin, 
isomeric  with  bilirubin,  and  called  hsematoidin. 

Besides  the  derivatives  which  have  been  studied  with  the  spectro- 
scope, there  is  another  derivative  of  haematin — haeniin,  which  is  identi- 
fied by  the  rhombic  form  and  Inown  colour  of  its  crystals.  Haemin 
is  the  hydrochloride  of  hsematin,  and  is  prepared  by  heating  blood 
with  glacial  acetic  acid. 

The  Estimation  of  Hsemoglobin. — By  estimating  the  haemoglobin 
in  the  blood  we  can  measure  the  oxygen-carrying  power,  and  make 
comparative  tests  of  the  blood  in  cases  of  anaemia,  etc.  The  measure- 
ment is  made  by  the  use  of  an  instrument  known  as  the  haemoglobin- 
ometer.  In  this  country,  apparatus  shown  in  Fig.  23  is  chiefly 
employed.     This  contains  a  sealed  tube  (D)  containing  coal-gas  and 


Fig.  23. — Haldane-Gowers'  H^emoglobinometer. 


a  standard  solution  of  human  blood  (1  in  200);  the  haemoglobin, 
being  combined  with  CO,  makes  the  solution  a  stable  one.  A 
small  quantity  (up  to  mark  20  or  so)  of  distilled  water  (carried  in  a 
bottle  (^4)  furnished  with  a  pij^ette  stopper)  is  placed  in  the  graduated 
tube  C.  Blood  is  taken  from  the  patient,  either  from  the  finger-tip 
or  the  lobe  of  the  ear,  and  sucked  up  into  the  pipette  B  to  the  mark  20, 
and  then  carefully  added  to  the  water  in  the  graduated  tube.  The 
distilled  water  lakes  the  blood,  and  a  solution  of  oxyheemoglobin  is 
formed.  This  is  converted  into  COHb  b}^  passing  coal-gas  into  the 
tube  and  shaking  it  with  the  solution.  Or  the  distilled  water  in  the 
bottle  A  may  be  previously  saturated  with  CO  by  bubbling  coal-gas 
through  it.  All  that  now  remains  is  to  dilute  carefully  the  solution 
of  COHb  with  water  until  it  is  of  the  same  tint  as  the  standard 
tube  when  compared  against  a  white  background.  The  percentage 
of  Hb  is  registered  by  the  graduations  in  the  tube.     The  standard  is 


THE  CORPUSCLES  OF  THE  BLOOD  97 

made  from  ox-blood  which  had  the  power  to  combine  with  18^  vohimes 
of  oxygen  when  shaken  with  air.  Blood  of  the  same  strength  as  this 
can  coml)ine  with  the  same  amount  of  oxygen. 

■  Taking  the  percentage  of  haMiioglobin  in  man  as  100,  woman  nor- 
mally has  90  per  cent.,  children  85  per  cent.  The  new-born  infant 
has  a  high  percentage,  140  per  cent.,  which  quickly  decreases  in  the 
first  few  months  of  life  to  just  bolow  normal.  The  effect  of  altitude 
has  been  mentioned. 

The  Pale  Corpuscles. — The  pale  corpuscles  of  the  blood  have  been 
variously  classified.  At  present  the  best  classification  appears  to 
be  that  based  upon  their  supposed  origin  and  their  staining  properties. 
According  to  the  origin,  the  pale  corpuscles  may  be  divided  into  leuco- 
cytes (amoeboid  cells),  arising  in  the  bone  marrow  and  passing  primarily 
into  the  blood — essentially,  therefore,  blood-corpuscles;  lymphocytes, 
probably  non-amoeboid  or  but  faintly  amoeboid  cells,  arising  in 
lymphoid  tissue  and  passing  primarily  into  the  lymph — essentially 
lymph-corpuscles. 

By  staining  reactions  the  leucocytes  are  classified  under  three 
headings : 

Neutrophil. 

Eosinophil,  or  acidophil. 

Basophil. 

The  lymphocytes  are  divided  into  two  groups — the  large  and  the 
small.  The  various  staining  properties  can  be  seen  in  a  well-made 
blood-film,  which  can  be  prepared  as  follows: 

Two  clean  slides  are  taken  with  well-cut  edges.  The  slide  upon 
which  the  film  is  to  be  made  is  gently  rubbed  with  fine  emery-paper 
to  give  it  a  very  slightly  roughened  surface.  The  edge  of  the  other 
slide  is  applied  to  a  small  drop  of  blood  obtained  by  pricking  the  finger; 
this  edge  is  applied  to  the  roughened  slide  at  an  angle  of  45  degrees, 
and  by  a  sweeping  movement  the  blood  is  lightly  and  evenly  spread 
over  the  roughened  surface.  To  this  film  Leishman's  stain  is  added ;  it 
consists  of  equimolecular  weights  of  methylene  blue  and  eosin  dissolved 
in  methyl  alcohol,  and  is  a  fixing  agent  by  virtue  of  the  methyl  alcohol. 
After  fixing  for  thirty  seconds  the  stain  is  diluted  with  water,  1  :  2, 
when  it  assumes  a  pinkish  tint  and  acts  as  a  stain.  The  film  is  stained 
for  about  five  minutes,  and  is  then  washed  with  distilled  water.  It  is 
finally  dried  wdth  blotting-paper.  The  methylene  blue  acts  as  a  basic 
dye  because  the  base  in  this  salt  is  the  active  group,  and  it  reacts 
with  nucleic  acid  in  the  nucleo-protein  of  the  cell.  Eosin  is  an  acid 
dj^e  because  the  acid  in  this  salt  is  the  active  group,  and  it  reacts 
with  the  basic  substances  of  the  cell. 

Stained  in  this  way  the  neutrophil  corpuscles  appear  two  and  a 
half  times  as  wide  as  a  red  corpuscle,  with  a  fragmented  nucleus  stained 
blue  and  the  fragments  joined  together  with  faintly  stained  pieces  of 
chromatin.  For  this  reason  it  is  called  polymorphonuclear.  With 
the  magnification  of  a  '.  objective  small  pinkish  granules  may  be  just 
visible;  these  are  well  seen  with  an  oil-immersion  (J,)  lens. 

7 


98  A  TEXTBOOK  OF  PHYSIOLOGY 

The  eosinophil  corpuscles  are  also  polymorphomiclear,  ))ut  their 
big  I'ed  granules  are  easily  seen  under  the  ,1  objective. 

The  rare  basophil  cell  (sometimes  called  a  mast  cell)  has  large 
blue  granules. 

In  numbers  the  pale  corpuscles  vary  from  5,000  to  S, ()()()  ])er  cubic 
millimetre.  If  they  are  much  above  this  number,  the  condition  of 
leucocytosis  is  said  to  exist;  below  that,  of  leucoj^enia. 

A  differential  blood-count  of  the  pale  corpuscles  {i.e.,  the  relative 
percentage  of  each  corpuscle)  of  a  film  shows  that  there  is  in  normal 
blood  visually  75  per  cent,  leucocytes  and  25  per  cent,  lymphocytes. 
The  leucocytes  are  divided  as  follows:  Neutrophils  71  to  73  per 
cent.,  eosinophils  2  to  4  per  cent.,  basophils  0-5  per  cent,  or 
less.  Morbid  conditions  which  cause  large  numbers  of  basophils  to 
appear  in  the  blood  are  extremely  serious,  and  for  this  reason  they 
have  been  termed  "  the  harbingers  of  death."  Of  the  25  per  cent, 
of  lymphocytes,  normally  23  per  cent,  are  small,  2  per  cent, 
large ;  these  numbers  vary  slightly,  but  any  large  variation  is  regarded 
as  pathological. 

In  the  horse  the  nimiber  of  leucocytes  per  cubic  millimetre  of  blood 
is  8,000  to  11,000;  in  the  ox,  7,000"to  9,000;  goat,  9,000  to  12,000; 
sheep,  9,000;  pig,  16,000. 

The  proportion  of  leucocytes  to  lymphocytes  also  differs,  lympho- 
cytes forming  30  per  cent,  of  the  total  in  the  j)ig,  30  to  40  per  cent, 
in  the  horse,  25  to  35  per  cent,  in  the  ox. 

The  Origin  oJ  the  Pale  Corpuscles. — Although,  as  stated  above,  it 
is  generally  held  that  the  leucocytes  and  lymphocytes  have  a  separate 
origin,  especially  in  adult  life,  the  leucocytes  arising  from  myelocytes 
in  the  bone  marrow,  and  the  lymphoc3rtes  from  lymphatic  tissue, 
there  are  some  authorities  who  believe  that  in  foetal  life  the  haemo- 
blast  affords  an  origin  for  all  the  other  forms  of  corpuscles  (see 
table,  p.  89). 

The  Functions  of  the  Pale  Corpuscles. — The  leucocytes  by  virtue 
of  their  amoeboid  or  pseudopodial  movements  can  surround  particles 
of  foreign  material  and  take  them  into  their  substance.  For 
this  reason  they  are  termed  phagocytes.  By  virtue  of  their  phago- 
cytic action  the  leucocytes  play  a  great  part  in  defending  the  bod}^ 
from  the  onslaught  of  invading  microbes,  emigrating  from  the  vessels 
for  the  purpose  (Fig.  24).  They  also  probably  play  a  part  in  forming 
the  protective  substances  of  the  plasma,  such  as  antigen,  complement, 
and  opsonin  (see  p.  109).  When  blood  is  shed,  these  corpuscles  help 
to  produce  the  clotting  of  blood. 

The  lymphocytes  play  a  part  in  the  absorption  of  fat,  and 
possibly  in  uric  acid  metabolism. 

Enumeration  of  White  Corpuscles. — The  pale  corpuscles  may  be 
counted  by  the  Thoma-Zeiss  instrument.  In  this  case  the  pipette 
giving  the  smaller  dilution  1  in  10  (labelled  11)  is  used.  The  usual 
diluting  fluid  contains  0-3  per  cent,  acetic  acid  tinted  with  methyl 
green.     The  weak  acid  destroys  the  red  corpuscles,  and  the  methyl 


THE  CORPUSCLES  OF  THE  BLOOD 


99 


green  tints  the  nuclei  of  the  pale  corpuscles,  rendering  counting  easier. 
The  process  of  effecting  the  required  dilution  and  placing  it  on  the 
slide  is  the  same  as  that  described  for  the  red  corpuscle. 

The  pale  may  be  counted  at  the  same  time  as  the  red  corpuscles  if 
Toison's  or  Sherrington's  fluid  is  used. 

Leucocytosis. — An  increase  in  the  number  of  pale  corpuscles  occurs 
physiologically  during  digestion,  especially  after  meals  rich  in  proteins 
and  fat ;  after  muscular  exercise ;  in  pregnant  and  parturient  women ; 
and  in  the  new-born  child.  The  neutrophil  cells  are  increased  in  a 
number  of  pathological  conditions,  in  acute  infections  such  as  supj^u- 
ration,  pneumonia,  diphtheria,  erysipelas,  etc.  In  the  condition  known 
as  leuksemia,  either  the  levxcocytes  or  the  lymphocytes  may  be  greatly 
increased,  according  as  the  marrow  or  lymph  glands  are  the  seat  of 
disease.     Sometimes,  although  the  total  number  is  not  much  increased, 


Fig.  21. — Emigration  of  Leucocytks.     (From  Waller's  "Human  Physiology.") 

Vc;Sjls  of  the  inferior  surface  of  the  frog's  tongue  as  they  appear  after  the  escape 
of  the  corpuscles,  filled  with  stationary  blood,  deformecl  and  indented  at  the 
points  of  escape,  near  which  the  corpuscles  are  generally  found.  (After  Waller, 
Phil.  Mag.,  1840,  "Microscopic  Observations  on  the  Perforation  of  the  Capillaries 
by  the  Corpuscles  of  the  Blood.") 


the  proportion  of  eosinophil  corpuscles  is  increased.  This  occurs  in 
cases  infected  with  the  parasites  trichina  or  anchylostomum,  in  asthma, 
and  certain  skin  diseases. 

Leucopenia  occurs  after  exposure  to  X  rays  and  injections  of 
cholin.  In  certain  infections  such  as  typhoid  the  pale  corpuscles  are 
said  to  be  diminished. 

Blood-Platelets. — The  so-called  blood-platelets,  or  thi'ombocytes, 
are  bodies  of  doubtful  origin.  Opinions  vary  as  to  their  character 
and  nature.     According  to  one  group  of  observers  thej'  are  to  be 


A  TEXTBOOK  OF  PHYSIOLOGY 

looked  upon  as  a  third  kind  of  l^lood-corpuscle;  according  to  the 
others  they  are  but  artefacts.  A  great  diversity  of  opinion  exists 
among  the  supporters  of  the  view  that  they  are  a  true  corpuscle. 
They  are  variously  stated  to  be  amceboid  and  non-amoeboid ;  nucleated 
and  non-nucleated.  Their  diameter  is  2-3  ^^.  They  are  best  seen  if  a 
drop  of  blood  is  received  on  to  a  block  of  paraffin  wax  and  placed  in  a 
rrmist  chamber.  The  blood  does  not  coagidate  when  thus  received 
on  wax.  At  the  end  of  twenty  minutes  most  of  the  red  cor])UScles 
have  sunk  to  the  bottom  of  the  drop.  The  platelets,  being  lightest, 
remain  at  the  top  of  the  drop,  and,  if  this  be  gently  removed,  large 
numbers  of  platelets  will  be  seen. 

Platelets  increase  in  number  after  the  blood  is  shed.  In  a  well- 
made  blood-film  few  or  no  platelets  are  seen.  If,  however,  the  blood 
is  allowed  to  stay  on  the  slide  some  time  before  being  drawn  into  a 
film,  it  will  be  found  that  many  bodies  which  might  be  termed  blood- 
platelets  are  visible. 

It  seems  probable  that  they  are  to  Ije  looked  upon  as  artefacts, 
and  may  be  grouped  into  four  categories: 

1.  Platelets  containing  haemoglobin. 

2.  Platelets  containing  no  haemoglobin. 

3.  Platelets  with  an  inner  body. 

4.  Platelets  without  an  inner  body. 

In  normal  blood  there  exist  few,  if  any,  platelets,  and  such  as 
exist  are  generally  clumped  together.  They  separate  from  the 
plasma  owing  to  contact  with  foreign  bodies,  and  in  part  owing  to 
the  lowering  of  temperature.  The  addition  of  so-called  fixing  and 
indifferent  fluids  may  produce  enormous  numbers  of  them,  the  number 
varying  for  different  fluids.  On  adding  a  metaphosphate  solution  to 
blocd  the  platelets  appear  suddenly,  and  belong  to  the  amoeboid  tyj)e; 
when  a  solution  of  potassium  oxalate  is  used,  they  are  at  first  of  this 
type,  but  afterwards  appear  as  pin-like  and  tailed  bodies;  subse- 
quently small  bodies  are  extruded  from  the  red  corpuscles.  These 
bodies  stain  differently,  and  resemble  bodies  which  form  in  coagulating 
blood  after  the  administration  of  certain  poisons.  It  is  possible  that 
a  few  platelets  of  this  type  may  exist  in  normal  blood.  The  exact 
source  of  origin  is  not  known;  they  may  arise  from  the  fragmentation 
of  red  corpuscles,  possibly  the  fragmentation  of  jDale  corpuscles,  but 
generally  are  regarded  as  fine  deposits  of  the  blood-proteins.  When 
first  discovered  they  were  regarded  as  young  red  corpuscles,  after- 
wards they  were  thought  to  be  young  white  corpuscles;  both  views 
are  now  known  to  be  wrong. 

Recently  a  compromise  between  the  divergent  views  has  been 
suggested,  and  the  platelets  grouped  into  "  platelets  " — true  cori:»uscles, 
which  are  believed  to  play  some  part  in  the  coagulation  of  the 
blood,  and  "blood-dust"  protein  granules  of  about  1^,  known  as 
hsemoconea.  "  Blood-dust  "  is  insoluble  in  alcohol  or  ether,  and  is  not 
blackened  by  osmic  acid.  Some  regard  it  as  formed  of  the  extruded 
granules  of  the  i)ale  corpuscles. 


CHAPTER  XII 
THE  CLOTTING  OF  BLOOD 

If  the  blood  be  allowed  to  flow  freely  from  a  wound,  the  flow 
gradually  lessens  as  the  blood  becomes  more  viscid,  and  at  length 
ceases,  a  clot,  or  coagulum,  being  formed  at  the  site  of  injury.  , 

As  a  rule  the  blood  coming  from  clean-cut  wounds  clots  less  readily 
than  that  from  jagged  wounds.  Washing  and  cleaning  a  wound 
prolongs  the  bleeding;  on  the  other  hand,  contact  of  the  wound  with 
a  foreign  body  such  as  a  piece  of  rag  or  of  cotton-wool  quickens  its 
arrest. 

The  clot  serves  a  double  purpose — it  plugs  the  bleeding-points, 
and  so  prevents  the  loss  of  precious  blood,  and  it  forms  a  protection 
against  the  entry  of  harmful  organisms  into  the  blood-stream.  If 
the  blood  be  received  as  it  is  shed  into  a  perfectly  clean  vessel  and 
put  aside  to  clot  in  a  quiet  place,  it  will  be  found  that  the  jelly-like 
coagulum  is  at  first  so  solid  that  the  vessel  can  be  turned  upside  clown, 
and  considerable  force  is  required  to  disengage  the  clot  from  the  vessel. 
The  clot  gradually  shrinks  in  size  and  squeezes  out  drops  of  a  clear, 
almost  colourless,  fluid  known  as  the  serum.  The  shrinkage  slowly 
continues  until  at  last  there  remains  a  shrunken  dark  red  clot  at  the 
bottom  of  the  vessel  and  a  quantit}^  of  clear  straw-coloured  serum 
above  it.  If  the  blood  be  horse's  or  cat's  blood,  an  upper  yellowish 
layer  is  also  formed,  known  as  the  "  buffy  coat."  This  consists  of 
the  pale  corpuscles  which  are  lighter  and  romain  on  top,  the  heavier 
red  corpuscles  quickly  settling  down  to  the  bottom  in  the  blood  of 
these  animals. 

Coagulation  of  the  blood  may  be  retarded  in  various  ways.  The 
best-known  methods  are  the  following: 

(i.)  Cold,  by  receiving  blood  into  a  vessel  placed  on  ice. 

(ii.)  Contact  with  the  wall  of  the  bloodvesjcl.  If  a  large  vein — 
for  example,  the  jugular  vein  of  the  horse — be  ligatured  in  two  places, 
and  the  tube  of  blood  thus  formed  be  excised  and  hung  up,  the  cor- 
puscles will  sink  to  the  bottom,  leaving  the  unclotted  plasma  above. 

(iii.)  Receiving  the  blood  into  a  smooth  vessel  smeared  with  oil. 

(iv.)  Addition  to  the  blood  of  neutral  salts  such  as  magnesium  or 
sodium  sulphate. 

(v.)  Addition  to  the  blood  of  a  soluble  oxalate,  citrate,  or  fluoride. 

(vi.)  Addition  of  a  body  (hirudin)  obtained  b}'  extracting  the  heads 
of  leeches.  Certain  snake  poisons  and  bacterial  toxins  also  stop 
coagulation. 

101 


102  A  TEXTBOOK  01^^  PHYSIOLOGY 

(vii.)  By  injecting  into  an  animal  before  killing  it  certain  substances 
such  as  commercial  peptone,  soap  solution,  or,  very  slowly,  a  weak 
alkaline  solution  of  nucleoprotein. 

(viii.)  The  addition  of  acids,  alkalies,  ammonia  sugar  solution, 
glycerine,  or  much  Avater. 

Clotting  may  be  facilitated,  on  the  other  hand — 
(i.)  By  keeping  the  temperature  that  of  the  body, 
(ii.)  By  injuring  the  wall  of  the  containing  bloodvessel, 
(iii.)  By  receiving  on  to  a  rough  surface  to  which  the  blood  adheres; 
by  beating  it  with  twigs  or  shaking  it  with  glass  beads.     The  addition 
of  finely  powdered  carbon  or  platinum  black  also  quickens  coagulation, 
(iv.)  By  adding  serum  or  blood-clot. 

(v.)  By  adding  saline  extract  of  lymphatic  glands  and  other  tissues, 
(vi.)  Possibly  by  the  addition  of  soluble  calcium  salts. 
The  explanation  of  all  the  above  facts  in  regard  to  the  clotting  of 
blood  is  a  matter  of  great  difficulty.     Opinions  strongly  at  variance 
are  held  in  regard  to  the  exact  processes  which  take  place. 

The  following  seem  to  be  the  certain  facts  about  the  clotting  of 
blood,  whatever  may  be  the  interpretation  of  the  same : 

(i.)  When  blood  clots  the  protein  of  the  plasma  known  as  fibrinogen 
is  involved  and  becomes  converted  either  partially  or  wholly  into  a 
solid  body  known  as  fibrin.  This  is  shown  by  the  experiment  that 
fibrinogen  may  be  precipitated  from  plasma,  redissolved  in  saline, 
and  clotted  at  37°  C,  by  the  addition  of  a  trace  of  blood-serum  or  a 
watery  extract  of  serum  proteins  coagulated  by  alcohol. 

(ii.)  Calcium  ions  are  necessary  for  the  process.  Thus,  the  addition 
to  blood,  as  it  is  shed,  of  a  soluble  oxalate  or  fluoride  which  precipitates 
the  calcium  ions,  or  of  a  soluble  citrate  which  prevents  their  dissocia- 
tion, stops  the  coagulation  of  the  blood. 

(iii.)  Calcium  ions  take  part  in  an  intermediate  and  not  in  the 
final  process,  since  a  calcium-free  solution  of  fibrinogen  may  be  clotted 
by  the  addition  of  calcium-free  blood-serum — i.e.,  blood  which  has 
already  clotted. 

(iv.)  Tissue  juice  has  the  property  of  greatly  accelerating  the 
process  of  clotting.  Bird's  blood  straight  from  the  vessel  does  not 
clot;  if  tissue  extract  be  added,  the  blood  clots  almost  at  once.  The 
addition  of  lymph  from  a  blister  accelerates  the  clotting  of  human 
blood. 

(v.)  Adhesion  between  the  blood  and  a  foreign  substance  gives 
an  impidse  towards  coagulation,  while  lack  of  such  adhesion  prevents 
the  blood  from  clotting. 

The  explanation  given  of  the  above  facts  is  that  blood,  flowing  from 
a  wound,  becomes  mixed  with  the  tissue  fluids  in  the  cut,  and  the 
blood  with  the  tissue  fluid  in  the  presence  of  calcium  ions  forms  an 
enzyme  known  as  thrombin  from  a  forerunner  present  in  the  blood, 
known  as  thrombogen  or  prothrombin,  which  is  probably  derived 
from  the  white  corpuscles  and  blood-platelets.  It  is  only  when  tissue 
juices  and  calcium  ions  are  present  that  this  enzyme  formation  takes 
I  lace.      This  explains  why  a  jagged  wound  clots  more  readily  than 


THE  CLOTTING  OF  BLOOD  103 

a  clean  cut,  and  why,  when  calcium  ions  arc  withdra^Mi  from  the 
blood  b}^  the  addition  of  a  solul^le  oxalate  or  citrate,  the  blood  will 
not  clot.  The  enzyme  thrombin  thus  formed  then  acts  upon  the 
fibrinogen  of  the  plasma  and  transforms  it  into  so.id  fibrin,  which 
entangles  the  red  corpuscles  and  forms  the  blood -c'ot. 
The  process  may  be  represented  as  follows : 

Thrombokinase  (from  Free  Ca  ion  Prothrombin  or  thrombogen 

tissue  fluid,  possiblj^        (I'r^m  plasma]      (from  white  corpuscles,  blood-platelets) 
also  white  corpuscles)  ^  _^— -^ 


Thrombin Fibrixogen 

(enzyme)  (soluble  protein  of  j)lasma) 

-I 

Fibrin 

(insoluble  protein  or  clot 

entangling  red  corpuscles) 

In  accordance  with  the  above  view  of  enzymic  action  it  is  supposed 
that  oxalate,  fluoride,  and  citrate,  prevent  the  formation  of  the  enzyme 
b}'  withdrawing  calcium  ions,  and  that  fluoride  also  destroys  throm- 
bokinase. Hirudin  is  believed  to  be  an  antithrombin.  Cobra  poison 
is  held  somehow  to  interfere  with  the  action  of  thrombokinase. 
Roughened  surfaces,  etc.,  break  down  white  corpuscles  and  provide 
•points  d'appui  from  which  the  enzyme  can  act.  Cold  inhibits  enzymic 
activity;  on  the  other  hand  body  temperature  hastens  it.  Oil  and 
smooth  surfaces  deprive  the  enzyme  of  points  for  action. 

Coagulation  Time,  tested  in  a  Glass  Vessel  at  Room  Temperature. 

Man 2  to  6    minutes      Ox 8  to  10  minutes 

Dog 1  to  8  „  Pig 10  to  15 

Sheep  .,  ..       4  to  8  „  Horse  ..  ..      15  to  30         ,, 

According  to  the  above  view  the  tissue  extract  has  only  an  indirect 
action  on  clotting;  other  authorities  believe  that  the  tissue  juices 
have  a  direct  clotting  action.  Recently  it  has  been  suggested  that 
thrombin  results  from  the  interaction  of  two  substances,  cytozyme 
and  serozyme.  The  former  is  said  to  be  present  in  tissue  cells  and 
blood-platelets,  and  is  not  destroyed  by  heating  to  100°  C,  while  the 
latter  is  present  in  serum  and  is  destroyed  by  heat  at  56°  C.  Vt-ry 
little  serozyme  is  srid  to  be  in  plasma,  and  its  origin  is  unknown. 

According  to  another  view  of  clotting,  thrombin  and  its  antibod}', 
antithrombin,  are  present  in  the  blood.  When  blood  is  shed  the 
tissue  fluid  combines  with  the  anti-thrombin,  leaving  the  thrombin 
free  to  convert  fibrinogen  into  fibrin. 

According  to  still  another  view,  thrombin  does  not  bring  about 
clotting,  but  is  a  body  produced  as  the  result  of  clotting.  Upon  this 
view  the  bodies  which  take  part  in  the  clotting  are  fibrinogen, 
thrombogen,  thrombokinase  (sometimes  called  thrombozyme),  and 
calcium    salts.     When   blood   is  shed  the  three  colloids — fibrinogen, 


104  A  TEXTBOOK  OF  PHY8IOLO0Y 

lluomliooc-n  and  lluoinliokiiiiisc — become  in  a  state  of  unstable 
e(|uilibrhnn,  and  unite  together  to  form  fibrin  and  thrombin.  The 
presence  of  calcium  ions  is  necessary  for  this  to  take  place.  The 
projiortion  of  fibrin  produced,  compared  to  thrombin,  varies  according 
to  the  proportion  of  the  three  colloids  taking  part  in  the  process. 
The  exciting  cause  of  this  unstable  equilibrium  may  be  any  of  the 
j)hysical  or  chemical  agents  known  to  facilitate  clotting,  such  as 
contact  with  the  walls  of  a  glass  vessel,  tissue  extracts,  and  so 
forth. 

Haemophilia. — This  is  a  disease  characterized'by  the  great  tendency 
to  severe  bleedings  in  those  afflicted  with  it;  hence  these  are  known 
as  "  bleeders."  The  characteristic  bleedings  are  into  joints,  and 
subcutaneous  haemorrhages  following  slight  injuries  or  strains.  It  is 
an  hereditary  disease,  confined  to  the  male  sex;  women  transmit  the 
disease,  bvit  never  suffer  from  it.  The  cause  of  the  condition  is  not 
known;  it  has  been  wrongly  attributed  to  abnormal  thinness  or  brittle- 
ness.  of  the  vessel  wall.  The  most  generally  accepted  view  is  that 
some  agent  (thrombokinase)  is  missing  from  the  tissue  fluids,  so  that 
these  do  not  cause  the  blood  to  clot.  This  view  accords  with  the 
fact  that  certain  tissues  of  a  bleeder  mav'  bleed,  and  not  others;  and 
that  tissues  may  bleed  at  certain  times,  and  not  at  other  times. 
The  condition  is  very  rare.  Genealogical  trees,  showing  male  bleeders 
and  tranauission  through  females,  have  been  constructed  from  records 
going  back  to  many  generations. 


CHAPTER  XIII 

HiEMOLYSIS  AND  IMMUNITY 

Haemolysis. — If  small  amounts  of  blood  be  taken  in  two  test- 
tubes  and  diluted  with  physiological  saline  (0-8  per  cent.  NaCl 
solution)  and  with  distilled  water  respectively,  it  will  be  seen  that 
there  is  a  marked  difference  betAveen  the  red  fluid  contained  in 
the  two  tubes.  The  blood  diluted  w^ith  physiological  saline  is  red 
and  opaque;  that  distilled  with  distilled  water  is  red  and  clear.  The 
blood  has  become  "  laked,"  or  haemolyzed,  by  the  water.  By  means 
of  the  change  to  a  clear  red  solution  it  is  easy  to  say  when  haemolysis 
has  taken  place.  Very  slight  traces  of  haemolysis  may  be  detected 
in  the  upper  layers  of  the  tube  when  the  corpuscles  have  sunk  to  the 
bottom.  By  haemolysis  is  understood  the  process  in  which  a  red 
corpuscle  is  damaged  so  that  the  haemoglobin  contained  within 
passes  into  the  surrounding  fluid.  Heemolj'sis  or  laking  is  always 
due  to  injury  of  the  stroma  or  envelope  of  the  red  corpuscle,  and  may 
be  induced  b}'  a  number  of  means: 

(a)  Physical. 
(6)  Chemical. 

(c)  Foreign  sera. 

(d)  Bacterial  toxins. 

(e)  Vegetable  poisons. 

(/)  Animal  poisons  such  as  snake  venoms. 

Physical. — Tlie  addition  of  phj'siological  saline  to  blood  does  not 
cause  laking  because  it  contains  salt  (NaCl)  in  about  the  same  concen- 
tration as  that  of  the  salts  in  the  plasma.  There  is  therefore  no  great 
interchange  of  Avater  between  the  added  fi^iid  and  the  red  corpuscles. 
The  addition  of  distilled  water  causes  laking  because  it  contains  no 
salts  in  solution.  The  red  corpuscles  of  the  blood  contain  inorganic 
salts  in  the  ionized  state.  When  the  distilled  water  is  added  to  the 
blood,  water  passes  into  the  red  corpuscles,  until  there  is  produced 
an  ec[ual  concentration  of  ions  on  either  side  of  the  cor2)uscular  en- 
velope. The  water  passing  in  greatly  distends  the  corpuscle  and 
eventually  ruptures  the  envelope.  The  pigment  contained  in  the 
corpuscle  then  passes  into  the  surrounding  medium,  and.  becoming 
dissolved  in  it,  forms  the  clear  red  solution  characteristic  of  haemoh'sis. 
The  membrane  of  the  corpuscle  forms  a  semi-permeable  membrane 
which  is  easily  permeated  by  the  Avater  but  does  not  alloAv  the  salts 
to  pass  out.    Alternate  freezing  and  thawing  also  damage  the  envelope 

105 


J  Of)  A  TEXTBOOK  OF  PHVSTOLOCIY 

owing  to  water  being  separated  as  ice  in  the  process  of  freezing. 
Electrical  currents  of  high  potential  may  also  disintegrate  the 
corpuscles. 

Chemical.^Many  chemical  bodies,  such  as  arseniuretted  hydrogen, 
nitro-benzol,  nitro-glycerine,  nitrites,  guaiacol,  saj)onin,  jjyrogallol, 
acetanilide,  and  ammoniinn  salts,  produce  laking.  Others,  such  as 
sugar  and  sodiuni  chloride,  do  not;  these  cannot  permeate  the  corpus- 
cular envelope.  While  urea  and  ammonium  chloride  permeate  the 
corpuscles  readily,  a  solution  of  urea  in  isotonic  solution  of  sodium 
chloride  does  not  lake  the  corpuscles,  although  ammonium  chloride 
does.  A  solution  of  ether  in  distilled  water  produces  laking.  It  is 
suggested  that  the  permeability  of  the  corpuscles  is  controlled  by  the 
cholesterin  and  lecithin  in  the  stroma  as  solvents  of  lecithin  and 
cholesterin  i^roduce  laking — for  example,  chloroform,  ether,  bile  salts, 
and  amyl  alcohol;  but  the  majority  of  hajmolytic  agents,  both  inor- 
ganic and  organic,  are  not  solvents  of  these  lipoids. 

Haemolysis  by  Foreign  Sera. — If  a  few  drops  of  the  blood  of  a 
man  be  mixed  with  the  serum  of  a  rabbit  in  a  test-tube,  it  will  be  found 
that  the  solution,  red  and  opaque  to  begin  with,  becomes  after  a  time 
transj^arent,  showing  that  haemolysis  has  taken  place.  This  property 
is  increased  by  immunizing  the  rabbit  against  the  foreign  red  corpuscles. 
The  injection  of  a  very  small  dose  of  foreign  corpuscles  is  sufficient  to 
raise  the  haemolytic  power  of  the  serum.  For  example,  0-125  gramme 
of  ox  blood,  injected  intravenously  in  the  rabbit,  produces  a  hsemo- 
lysin  which  specifically  acts  on  ox  corpuscles,  so  that  rapid  laking 
takes  place  when  the  rabbit's  serum  is  mixed  with  ox  corpuscles  but 
not  when  mixed  with  any  other  animal's  corpuscles. 

The  explanation  given  for  this  phenomenon  is  the  same  as  for  bacteriolysis  (see 
p.  109).  Sera,  and  especially  imunized  sera,  have  po^er  to  destroy  bacteria.  There 
are  concerned  two  substances  in  the  serum:  (1)  an  amboceptor,  which  is  increased  by 
immunization,  and  (2)  a  complement,  which  is  present  in  fresh  normal  serum  and  is 
destroyed  by  heating  to  55°  C.  Very  little  is  known  as  to  the  chemical  properties  or 
mode  of  action  of  these  bodies.  The  action  takes  place  quickest  at  a  little  above  body 
temperature.  If  the  ox  corpuscles  and  rabbit's  serum  are  mixed  at  0°  C,  there  is  no 
haemolytic  action,  because  the  complement  cannot  act  at  this  temperature,  but  the 
amboceptor  combines  with  the  corpuscles  and  can  be  removed  with  these  from  the 
serum.  After  separation  by  the  centrifuge  the  corijuscles  can  be  washed  in  isotonic 
salt  solution,  to  remove  all  traces  of  the  rabbit's  serum,  separated  by  the  centrifuge 
again,  and  then  mixed  with  normal  serum  and  warmed  to  body  temperature.  Laking 
then  takes  place  because  the  complement  alone  is  wanted  to  complete  the  reaction,  and 
this  is  present  in  any  fresh  normal  serum. 

Haemagglutinins,  similar  to  the  agglutinins  which  are  produced  to  antagonize 
bacteria,  can  also  be  obtained  by  the  injection  of  foreign  blood  into  an  animal.  These 
cause  the  red  corpuscles  to  run  together,  or  agglutinate.  Some  sera  contain  no  hsemo- 
lysins,  only  agglutinins;  others  contain  hsemolysins  and  no  agglutinins.  The  two 
bodies,  however,  usually  exist  side  Ijy  side,  sometimes  the  action  of  one  being  more 
marked,  sometimes  the  action  of  the  other.  In  agglutination  the  surface  tension  is 
altered;  the  lecithin  and  cholesterin  constituents  of  the  stroma  are  supposed  to  take 
a  part. 

The  haemolytic  action  of  eel's  serum  is  exceptional.  If  as  little  as  O'l  c.c.  of  eel's 
serum  per  kilo  of  body  weight  is  injected  into  a  rabbit,  it  dies  in  two  or  three  minutes. 
This  serum  differs  from  other  sera  insomuch  as  heating  to  54°  C.  destroys  its  action, 
which  is  not  restored  by  the  addition  of  complement. 


H.^MOLYSTS  AND  IIVCVIUNITY  107 

Bacterial  Hsemolysins. — Certain  pathogenic  bacteria — e.g..  Bacillus  pyocyaneus 
and  staphylococcus  (the  organism  of  boils) — produce  agglutinins  for  human  corpuscles. 
Sometimes  these  play  a  part  in  the  formation  of  emboli.  The  corpuscles  may  bo 
clumped  together,  mixed  with  the  infecting  bacteria,  and  carried  by  the  circulation 
'to  another  part  and  so  spread  the  mischief.  Haemolysis  occurs  in  the  blood  during 
an  attack  of  blood-poisoning  (septicsemia).  The  best-known  bacterial  hsemolysins  are 
those  produced  bj-  the  bacteria  of  tetanus  (lockjaw)  and  of  typhoid,  and  the  staphj^- 
lococcus  and  streptococcus.  They  are  known  as  totano-lysin,  typho-lysin,  etc. 
Their  action  is  due  to  direct  combination  with  the  cell  without  the  aid  of  an  inter- 
mediary (amboceptor).  They  are  therefore  comparable  to  toxins,  which  unite  directly 
with  the  red  corpuscles  and  destroj'  them. 

Hsemolysis  produced  by  Vegetable  Poisons. — Some  vegetable  poisons,  crotin 
(croton-oil  seed)  and  plialein  (Pltallu-i  impitdictis,  a  fungus),  have  a  very  marked 
haemolytic  action,  and  others,  ricin  (castor-oil  bean)  and  abrin  (jequirity  bean),  agglu- 
tinate,' but  produce  little  hannolysis.  Immunity  can  be  established  against  these 
bodies  and  antibodies  produced.  Against  another  group  of  vegetable  poisons  no 
antibodies  are  produced.  In  this  are  included  saponin,  cyclanin  from  cyclamen, 
solanin  from  the  green  potato,  helveUic  acid  from  a  species  of  mushroom  {Helrdla 
esctdenta).  Saponin  produces  hsemolysis  in  1  :  100,000.  These  poisons  differ  alto- 
gether from  bacterial  toxins,  being  resistant  to  heat,  and  having  no  resemblance  to 
proteins.  They  are  related  to  glucosides.  The  action  of  saponin  is  prevented  by 
the  presence  of  an  excess  of  cholesterin  in  the  blood  ;  haemolysis  is  probably  caused 
by  the  cholesterin  portion  of  the  stroma  linking  the  poison  to  the  corpuscles.  The 
toxicity  of  these  substances  is  not  in  anj^  way  proportional  to  their  hsemotytic 
powers',  their  chief  effect  being  paralysis  of  the  heart  and  injury  to  the  central 
nervous  system. 

Haemolysis  by  Snake  Venoms. — The  salivary  secretion  of  certain  snakes — cobra, 
rattlesnake,  copperhead — causes  agglutination  of  the  red  corpuscles,  and  in  some 
cases  also  induces  hsemolysis.  The  snakes  secrete  in  their  saliva  an  amboceptor,  and 
the  person  bitten  provides  the  complement.  An  animal  can  be  immunized  agamst 
snake  venom  so  that  it  comes  to  withstand  many  times  the  lethal  dose.  An  "  anti- 
venin  "  is  produced  which,  bj-  linking  on  to  the  amboceptor  in  the  snake  venom,  pre- 
vents its  union  with  the  red  corpuscle. 

The  hsemolj-sins  can  be  dried  at  a  cool  temperature  without  losing  potency,  are 
destroj^ed  by  acids  and  alkalies,  and  inhibited  in  their  action  by  salts.  Introduced 
by  the  stomach  they  have  no  action.  In  health  but  little  haemolysis  takes  place  apart 
from  the  destruction  of  effete  corpuscles.  In  fevers  haeiliolysis  may  be  produced 
by  bacterial  toxins.  It  is  suggested  that  certain  anaemias  may  be  due  to  haemolysins 
formed  by  parasitic  inhabitants  of  the  alimentary  tract.  If  more  than  a  small  amount 
of  haemoglobin  is  set  free  in  solution  in  the  plasma,  it  escapes  in  the  urine,  giving  rise 
to  the  condition  known  as  haemoglobinuria.  In  some  rare  cases  haemoglobinuria 
foUows  exposure  to  cold — e.g.,  it  occurs  in  some  persons  after  putting  the  hands  in 
iced  water. 

Immunity. — Besides  the  substances  which  can  be  isolated  by 
chemical  means,  weighed,  and  anatyzed,  there  are  manj^  and  subtle 
properties  possessed  by  the  plasma,  such  as  its  immunizing  powers, 
which  can  only  be  detected  by  the  newly-discovered  biological  tests. 
These  tests  depend  on  the  reaction  of  living  substances,  and  are  of 
the  most  extraordinary  delicacy.  On  these  properties  of  the  plasma 
depend  the  immunity  of  the  organism  against  infective  diseases  and 
certain  toxins  of  animal  or  vegetable  origin.  The  immunizing  sub- 
stances are  quite  specific  for  each  bacterium  or  toxin.  It  is  known 
that  man  is  immune  to  certain  infective  diseases  which  affect  other 
animals.  For  example,  he  is  immune  to  swine  fever.  This  is  termed 
natural  immunity.  It  is  also  known  that  a  second  attack  of  whooping- 
cough,  measles,  smallpox,  etc.,  is  rare.  He  who  has  suffered  once 
has  an  acquired  immunity.     Such  acquired  immunity  may  be  estab- 


K)S  A  TEXTBOOK  OF  PHYSIOLOGY 

lislu'd  agaitisl  xarious  ioi'Dis  of  poisons,  vcgetabk'  or  animal,  hnt  in 
])articular  against  bacteria  and  tlie  ])oisons  they  elaborat{\  which  are 
known  as  toxins.  Two  forms  of  ijnnninity,  then,  may  be  acquired — 
one,  which  is  the  better  understood,  deals  with  the  toxins,  the  second 
deals  with  the  bacteria  themselves.  In  dealing  with  toxins  the  body 
has  the  ])()wer  to  elaborate  a  group  of  substances  which  are  known 
as  antitoxins.  If  at  appropriate  intervals  and  in  ap])ropriate  doses  an 
aninud's  body  be  injected  either  (1)  with  one  of  the  poisons  or  toxins, 
p.oduced  in  nutrient  media  by  the  growth  of  such  bacteria  as  the  bacilli 
of  diphtheria,  tetanus  (lockjaw),  or  (2)  withr  vegetable  proteins  of  a 
poisonous  nature,  such  as  abrin  (jecj[uirity  bean)  and  ricin  (castor- 
oil  bean),  or  (3)  Avith  an  animal  poison,  such  as  the  venoms  of 
different  forms  of  snakes,  scorpions,  bees,  wasps,  and  spiders,  a 
sj)ecific  antitoxin  negativing  the  action  of  each  of  these  poisons  is 
produced  in  the  blood. 

It  his  been  postulated  that  the  living  protoplasm  consists  of  a  central  living  nucleus 
and  numerous  side  chains,  or  receptors,  w  liich  are  attached  to  this.  To  each  of  these 
one  or  other  function  is  allotted — above  all,  the  absorption  of  nourishment.  The  side 
chains,  or  receptors,  form  complexes  of  atoms  in  the  molecules  of  the  protoplasm 
which,  owing  to  their  chemical  structure,  are  able  to  combine  or  link  up  with  other 
substances — for  example,  nutritive  material,  or  toxit  s.  The  receptors  combine  with 
certain  groups  of  atoms  of  these  substances  which,  owing  to  their  combining  powers, 
^are  termed  haptophoric  groupa,  or  h:)p';ophors.  The  combination  between  these 
haptoi^hors  of  the  nutritive  material,  or  of  the  toxins  with  the  rcceiators  of  the  cells, 
which  have  an  affinity  for  them,  is  necessary  before  either  the  nutriment  or  the  toxin 
can  have  its  effect  on  the  cell.  If  when  a  toxin  gains  entrance  within  the  organism 
it  finds  no  receptors  of  a  structural  substance  to  link  with  it,  it  can  exert  no  poisonous 
effect,  and  the  organism  is  naturally  immune  to  that  toxin.  Besides  the  haptophoric 
group  the  toxin  possesses  a  grou])  which  has  the  poisonous  effect.  This  is  the  toxi- 
phoric  groui^,  or  tjxoplior.  We  may  sujijiose  that  a  nutritive  group  linking  itself 
to  the  central  chemical  nucleus  of  the  cell  help?  to  maintain  the  lability  of  the  mole- 
cular complex  which  manifests  the  phenonuna  of  life,  while  a  toxic  group  either 
arrests  the  lability  or  shatters  the  molecular  structure  of  this  nucleus. 

The  toxophor  is  harmless  unless  anchored  on  to  the  cell  by  the  haptophor. 
Just  as  a  lock  cannot  be  opened  unless  the  person,  the  active  agent,  has  the  key. 
Evidence  has  been  obtainecl  which  makes  it  likely  that  these  two  groups  do  exist, 
and  that  the  toxin  may  lose  its  poisonous  properties  without  losing  its  power  of  uniting 
to  the  cells;  thus,  in  the  case  of  tetanus  toxin  it  has  been  ,'hown  that  treatment  with 
carbon  disulphide  destroj'S  the  poisonous  property  of  the  toxin,  but  not  its  power 
to  evoke  the  production  of  antitoxin.  The  haptophoric  group  remain;  linked  with 
the  body  tissue  cells,  and  produce;  antitoxins  by  stimulating  the  production  of  re- 
ceptors. Such  a  modified  toxin  is  called  a  toxoid.  Antitoxin;  are  cell-receptors 
which  combine  with  the  haptophorous  grouji  of  the  toxin  and  render  it  harmless. 
These  cell-receptors  are  produced  in  great  numbers,  and  set  free  in  the  blood  by  the 
action  of  a  toxoid,  or  by  repeated  small  and  non-lethal  injections  of  a  toxin.  The 
union  of  the  haptophoric  groups  with  the  cell-receptors  stimulates  an  increased  pro- 
duction of  these  cell-receptors  which  are  secreted  into  the  blood.  Anti  oxic  sera  are 
thus  produced  by  the  injection  of  toxoids  or  non-lethal  doses  of  toxins.  It  is 
suggested  that  the  linkage  of  a  chemical  group  with  a  particular  side  chain  of  a  cell 
evokes  the  production  of  other  side  chains  of  a  similar  configuration,  and  the  jDroduction 
of  these  may  be  stimulated  to  such  an  extent  that  they  escape  from  the  cell  into  the 
blood  and  endow  this  with  antitoxic  power.  The  receptors  (antitoxin)  Uberated 
by  any  mammal  immunized  against  a  given  toxin  are  apparently  the  same;  thus, 
the  antidiphtheritic  toxic  serum  of  horse,  sheep,  or  goat  will,  if  injected,  neutralize  the 
diphtheria  toxin  in  another  animal — as,  for  example,  the  guinea-pig  or  man.  But 
each  antitoxin  is  specific  and  will  neutralize  the  toxin  which  produces  it  and  no  other; 
antidiphtheritic  serum,  for  example,  would  be  of  no  use  if  employed  as  the  curative 
agent  for  the  toxin  of  tetanus.  Every  lock,  so  to  speak,  must  have  its  own  key,  and  if 
the  man  has  not  the  right  key  he  cannot  open  the  door.     In  this  comparison  the  man 


HEMOLYSIS  AND  IMMUNITY  109 

is  the  toxin,  the  key  the  haptoph(n-,  tlie  lock  the  receptor.  If  the  man  happened 
to  have  left  his  key  fitted  in  a  loose  lock  he  would  not  be  able  to  open  his  door  on 
reaching  home.  So  the  toxins  meeting  the  loose  receptors  in  the  blood  (antitoxin) 
become  bound  to  these  and  cannot  attack  the  cells.  The  neutralization  of  the  toxin 
by' the  antitoxin  can  be  demonstrated  in  vitro.  It  is  stated  to  be  a  chemical  process 
taking  place  in  definite  proportions  with  the  liberation  of  a  small  amount  of  heat. 
Neither  toxin  nor  antitoxin  is  destroyed  in  the  process;  they  are  simply  linked  to- 
gether, and  in  some  cases,  at  any  rate,  can  be  separated  again  by  appropriate  means. 
The  reaction  is  accelerated  by  warmth,  slowed  by  cold,  and  occurs  more  rapidly  in 
strong  than  in  weak  solutions. 

The  chemical  nature  of  the  antitoxin  is  unknown.  It  is  closely  related  to  serum 
globulin,  being  carried  down  when  this  is  precipitated,  but  is  not  necessarily  pi'otein, 
although  its  general  pro])erties  are  those  of  a  colloid.  Unlike  an  enzyme,  it  is  not 
carried  down  by  an  indifferent  precipitatj.  A  toxin  seems  to  be  a  simpler  body 
than  an  antitoxin,  for  in  the  case  of  the  haemolysis  produced  by  the  Megatherium 
bacillus,  the  toxin  can  be  pressed  through  a  porcelain  filter  impregnated  with  gelatin, 
while  the  antitoxin  cannot  pass  it.  Toxic  effects  are  sometimes  produced  by  the 
injection  of  antitoxic  sera.  These  effects  must  not  be  ascribed  to  the  antitoxins,  but 
to  other  bodies  contained  in  the  foreign  serum  which  is  injected. 

There  are  many  bacteria  which  do  not  liberate  soluble  toxins  into  the  plasma, 
but  have  endotoxins  which  accumulate  within  them,  and  only  become  liberated 
when  the  bacteria  are  disintegrated.  The  body  elaborates  no  antitoxins  for 
such  as  these.  Under  this  class  come  cholera  and  typhoid  bacilli.  If  an  animal 
be  injected  with  appropriate  doses  of  typhoid  bacilli,  alive  or  dead  (the  bacterial 
vaccines  prepared  for  man  are  sterilized  by  heat),  the  blood  acquires  bactericidal 
j)roperties  which  are  specific  for  the  typhoid  bacillus.  It  is  then  found  to  contain 
an  agglutinin  which  causes  the  bacilli  to  stick  together  or  agglutinate,  and,  if  motile, 
to  become  motionless.  This  is  seen  to  take  place  when  a  drop  of  serum  is  mixed 
with  a  drop  of  culture  fluid  containing  living  typhoid  bacilli.  Further,  it  contains 
an  opsonin  which  renders  the  bacilli  more  "tasty,"  so  that  they  are  eaten  or 
destroyed  by  the  white  leucocytes,  known  as  phagocytes.  In  some  cases  the  plasma 
also  acquires  anti-enzymes  which  counteract  the  action  of  the  enzymes  contained 
in  the  bacteria.  The  plasma  natui'ally  contains  anti-enzymes  which  neutralize 
the  enzymes  in  the  body,  such  as  thrombin,  pepsin,  etc.  Lastly,  by  virtue  of 
precipitins  it  obtains  the  power  of  precipitating  the  bacterial  proteins.  All  these 
reactions  arc  specific  against  the  bacteria  injected,  and  are  quite  distinct  from  each 
other. 

The  mode  of  action  of  bactericidal  serum  is  different  to  that  of  antitoxic  serum. 
If  a  bactericidal  serum — for  example,  a  serum  taken  from  an  animal  which  has  re- 
ceived repeated  injections  of  non-lethal  doses  of  cholera  vibrios — be  heated  to  55'^  C. 
for  fifteen  minutes,  it  is  found  to  have  lost  its  power  of  destroying  these  bacteria. 
Vet  if  now  inactive  normal  serum  be  added  to  this  inactivated  heated  serum,  it  again 
becomes  bactericidal.  By  the  process  of  immunization  the  blood  has  obtained  some 
new  substance  not  destroyed  by  heating  to  55'  C,  which  is  unable  by  itself  to  kill 
bacteria,  but  is  able  to  do  so  when  associated  with  another  body,  which  is  contained 
in  normal  serum  and  is  destroyed  by  heating  to  55°  C.  Just  as  is  the  case  with  hsemo- 
lytic  sera,  there  are  two  bodies  concerned  in  this  process  of  bacterial  immunity — 
the  one  devolop:nl  during  immunization  and  not  destroyed  by  55°  C,  the  immune 
body,  or  amboc:p'.or,  the  other  present  in  normal  serum  and  susceptible  to  heat — 
the  complemsiit.  Any  protein  which  provokes  the  production  of  an  haemolj-sin, 
antitoxin,  antivenin,  precipitin,  immune  body,  etc.,  is  called  an  UTlt'gDi?.  The  action 
of  the  immune  body  and  complement  is  explained  on  the  supposition  that  the  immune 
body  is  a  haptophor  which  unites  the  bacteria  to  the  complement.  The  complement 
takes  on  the  role  of  toxin  (toxic  to  the  bacteria).  The  immune  body  differs  from 
antitoxin  in  having  two  affinities — one  for  the  bacteria  and  one  for  the  complement; 
for  this  reason  the  immune  body  is  termed  amb  coptor.  There  are  some  sera  which 
naturally  possess  amboceptors  apart  from  any  process  of  immunization.  The  term 
immune  body  is  reserved  for  amboceptors  produced  by  immunization. 

The  Immune  Sody. — The  immune  bodj'  is  apparently  formed  in  all  the  tissizes  of 
the  body,  particularly  the  connective  tissues.  It  is  not  destroyed  by  temperatures 
which  are  fatal  to  the  complement  Thus,  twenty  hours'  heating  at  (iO"  C.  scarcely 
injures  it,  but  at  lU(t  ('.  it  is  destroyed  almost  at  once.  It  is  resistant  to  putrefaction, 
and  has  been  ke])t  for  as  long  as  eight  years.  It  seems  to  be  closely  associated  with, 
or  absorbed  to,  the  serum  globulins,  and  on  this  account  is  not  dialyzable. 


110  A  TEXTBOOK  OF  PHYSIOLOGY 

The  Complement  is  believed  to  be  tlie  actual  destroying  agent.  It  is  not  increased 
in  tlic  blood  during  the  process  of  immunization,  and  thus  it  comes  about  in  some 
cases  that  there  is  not  sufficient  comjjlcment  for  all  the  immune  substances  whose 
action  it  is  sought  to  demonstrate.  A  sufficiency  can  be  provided  by  the  addition 
t)f  normal  serum.  The  origin  of  the  complement  is  not  known.  The  leucocytes 
and  the  tissues  may  each  play  a  part  in  providing  it.  The  complement  is  easily 
destroyed  by  heating  to  5(5°  C.  While  its  chemical  nature  is  quite  unknown,  it  is  worth 
noting  that  in  the  ease  of  snake  venom  the  phosphorized  fat,  lecitliin,  plays  the  part 
of,  or  is  associated  with,  the  complement. 

The  Deviation  of  the  Complement. — When  serum  containing  a  specific  immune 
body  is  inactivated  (has  its  complement  destroyed)  by  heat  and  mixed  with  the 
antigen  used  in  its  ])roduction,  a  combination  takes  plajoe  between  the  two,  and  the 
antigen  is  then  said  to  be  sensitized.  However,  no  visible  effect  is  apparent  until 
complement  contained  in  fresh  serum,  usually  that  of  a  guinea-pig,  is  added.  The 
complement  combines  with  the  sensitized  antigen,  and  may  produce  a  visible  effect 
(e.g.,  haemolysis).  It  should  be  noted  that  an  antigen  can  only  be  sensitized  by  its 
specific  immune  body,  and  that  complement  can  only  combine  with  the  antigen  when 
linked  to  the  specific  immune  body;  thus,  the  combination,  or  fixation,  of  the  com- 
plement can  be  made  a  test  for  the  presence  of  a  specific  immune  body.  The  test 
is  very  delicate  and  of  great  diagnostic  value,  and  is  carried  out  in  the  following  way : 

A  rabbit  is  immunized  against  sheep's  blood-corpuscles.  Its  serum  is  obtained, 
heated  to  56°  C,  and  kept  in  sealed  capsules.  This  serum  will  hajmolyze  sheep's 
corpuscles  if  a  certain  minimal  amount  of  normal  serum  of  a  guinea-pig  is  added. 
The  minimal  amount  is  determined  by  experiment.  All  is  now  ready  for  testing  the 
blood,  say,  of  a  man  susi^ected  to  be  infected  with  typhoid  bacilli.  Serum  is  obtained 
from  this  man  and  heated  to  56°  C.  to  destroy  the  complement  in  it.  It  is  then  mixed 
with  typhoid  bacilli  and  the  minimal  amount  of  normal  guinea-pig  serum  added. 
The  mixture  is  kept  at  body  temperature,  and  time  enough  allowed  for  the  specific 
immune  body  (if  present)  to  fix  the  complement  and  antigen  (the  typhoid  bacilli). 
It  is  then  added  to  a  mixture  of  sheep's  corpuscles  and  the  heated  rabbit's  serum. 
Haemolysis  will  not  take  place  if  the  complement  has  been  fixed  in  the  first  stage  of  the 
test,  since  none  will  be  left  to  combine  with  the  sensitized  sheep's  corpuscles;  and  in 
such  a  case  it  is  clear  that  the  suspected  serum  did  in  fact  contain  typhoid  immune 
bodies.  If  haemolysis  does  take  place,  the  complement  could  not  have  been  fixed 
in  the  first  stage,  and  thus  the  suspected  serum  was  not  from  a  case  of  typhoid. 

Opsonins. — -These  are  specific  substances  in  the  serum  which  act  on  bacteria  in 
such  a  way  as  to  make  the  phagocytes  ingest  them.  Their  presence  is  demonstrated 
thus :  Blood  is  collected  and  allowed  to  clot.  The  white  corpuscles  are  separated  from 
the  serum  by  means  of  the  centrifuge.  The  serum  is  pij^etted  off,  and  the  corpuscles 
mixed  with  physiological  salt  solution,  and  again  separated  by  the  centrifuge.  This 
procedure  washes  the  corpuscles  free  from  serum.  Bacteria  are  mixed  with  the 
washed  corpuscles  and  the  mixture  kept  at  body  temperature  for  ten  minutes.  A 
film  is  then  made,  stained,  and  the  average  number  of  bacteria  ingested  by  the  phago- 
cytes counted.  A  similar  experiment  is  performed,  only  in  this  case  the  serum  is 
allowed  to  act  on  the  bacteria.  The  phagocytes  ingest  many  bacteria  which  have  been 
first  acted  on  by  the  serum,  and  very  few  of  those  which  have  not  been  so  treated. 
Thus,  the  serum  contains  opsonin  which  prej^ares  the  dish  for  the  leucocytes  to  ingest. 
Opsonins  exist  in  the  normal  blood  of  many  animals,  and  aie  increased  in  amount 
by  the  process  of  immunization — by  vaccination  with  dead  bacteria.  The  opsonins 
in  the  serum  of  one  animal  are  able  to  act  on  the  bacteria,  so  that  they  are  ingested  by 
the  phagocytes  taken  from  another  animal.  Their  chemical  nature  is  not  known. 
They  are  of  the  utmost  importance  in  furthering  the  defence  of  the  body  by  the 
phagocytes. 

Agglutinins, — These  are  bodies  possessing  the  property  of  clumping  bacteria. 
The  bacteria  themselves  are  not  greatly  damaged  by  the  process,  but  it  tends  to  pre- 
vent the  dissemination  of  the  organisms,  and  it  may  in  some  way  favour  phagocytosis. 
The  nature  of  the  change  thus  brought  about  in  the  bacteria  is  not  well  known,  but 
their  colloidal  nature  is  probably  altered  by  changes  in  surface  tension.  Agglutinins 
can  be  prepared  against  almost  all  bacteria.  Their  place  of  formation  is  not  known. 
They  have  been  demonstrated  in  the  blood  and  to  a  less  extent  in  the  milk.  Attached 
in  some  way  to  the  globulin  in  the  plasma,  they  cannot  be  separated  from  it.  They 
are  destroyed  by  heat;  the  temperature  of  destructidh  varies  for  different  agglutinins. 
As  in  all  processes  of  a  like  nature  the  concentration  of  the  electrolytes  in  solution 
affects  their  action. 


HAEMOLYSIS  AND  IMMUNITY  111 

Precipitins. — These  bodies  are  present  in  the  blood  of  an  immunized  animal, 
and  produce  a  precipitation  of  the  soluble  bacterial  proteins  if  added  to  a  filtrate  of 
the  culture  used  for  immunizing  the  animal.  Their  action  is  specific.  Precipitins 
can  be  produced  bj'  the  injection  of  any  protein,  provided  that  the  protein  is 
foreign.  It  is  useless  to  try  and  immunize  a  rabbit  against  rabbit's  serum,  and 
it  is  better  not  to  employ  closely  related  specie?,  such  as  rabbit  and  guinea-pig.  As 
the  result  of  the  injection  of  horse's  serum  into  a  rabbit  a  precipitin  is  obtained  in 
tlie  rabbit's  serum  which  precipitates  the  proteins  in  the  serum  of  the  horse  and  of 
no  other  animal.  Similarly,  as  the  result  of  the  injection  of  cow's  milk  a  precipitin 
is  obtained  which  precipitates  only  the  proteins  of  cow's  milk  and  not  those  of  the 
milk  of  any  other  animal.  The  specific  action  of  precipitins  shows  us  that  the  structure 
of  the  homologous  proteins  varies  in  different  animals.  Only  by  the  injection  of 
foreign  proteins  can  precipitins  be  produced,  and  the  power  of  the  proteins  to 
produce  precipitins  is  lost  when  they  become  split  up  into  peptones.  Fats  and 
carbohj^irates  cannot  produce  precipitins.  The  precipitation  test  can  only  be  made 
outside  the  body.  If  serum  containing  precipitins  be  injected  intravenously,  it  does 
not  cause  precipitation,  but  provokes  an  increase  in  the  number  of  leucocytes.  The 
material  obtained  from  a  mummy  five  thousand  j^ears  old  gave  the  j^recipitin 
reaction  for  man. 

The  action  of  precipitms  is  modified  by  the  concenti-ation  of  electrolytes.  A 
precipitin  has  two  linkages:  one  the  haptophor,  which  links  on  to  the  protein,  and 
another  linkage  (destroyed  by  heating  to  60°  C),  which  induces  the  change  bringing 
about  the  precipitation  of  the  protein. 

The  precipitin  appears  in  the  blood  about  six  days  after  the  first  injection  of 
protein  has  been  made.  Following  each  subsequent  injection  it  disappears  for  a  time, 
and  then  appears  again.  When  the  injections  are  finished,  the  precipitin  quickly 
disappears  from  the  blood,  its  fate  is  not  known,  and  it  cannot  be  detected  in  the  urine. 
The  source  of  precipitins  is  not  known.  As  an  increased  number  of  leucocytes 
(leucocytosis)  follows  each  injection,  it  has  been  thought  that  these  produce  the 
precipitins. 

The  precipitins  are  attaclied  to  the  globulins  in  the  plasma  and  cannot  be  separated 
from  them. 

Cytotoxins. — By  the  injection  of  animals'  cells,  bodies  called  cytotoxins  are  pro- 
duced in  the  blood.  These  are  capable  of  destroying  the  foreign  cells  injected.  Red 
corpuscles,  leucocytes,  spermatozoa,  kidnej-  substance,  stomach,  thyroid,  and  nervous 
tissues,  have  all  yielded  specific  cytotoxms,  and  so-called  erythrolytic,  nephrolytic, 
and  other  "  lytic  "  sera  have  been  produced.  Small  gastric  ulcers  have  been  caused 
by  injecting  the  blood  of  one  animal  immunized  against  the  injections  of  the  mucous 
membrane  of  the  stomach  of  another  species  of  animal.  The  red  corjjuscles  afford 
the  best  material  for  stud3dng  this  phenomenon  (c/.  Haemolysis,  p.  105). 

Hypersusceptibility,  Anaphylaxis. — Some  peojile  are  extraordinarily  sensitive 
to  the  ingestion  of  certain  nutritive  material  such  as  crab  flesh,  strawberries,  egg  white. 
They  are  made  sick  by  eating  one  or  other  of  these  things,  or  suffer  from  the  eruption 
of  a  nettle-rash,  the  result  of  a  disturbance  of  the  equilibrium  between  the  osmotic 
pressure  of  the  tissues  and  tissue  lymph,  whicli  in  its  turn  is  due  to  the  toxic  effect 
whicli  the  ingested  material  has  on  the  tissue  metabolism.  Similarily,  sensitivity 
may  be  produced  by  injection  of  a  small  dose  of  a  foreign  protein — e.g.,  of  horse  serum; 
the  sensitivity  is  so  increased  that  a  second  dose  of  the  same  serum,  containing  perhaps 
little  more  than  a  millionth  of  a  gramme  of  protein,  may  produce  the  severest  sj^mptoms 
of  intoxication  and  even  death.  The  hypersusceptibility  or  hypersensitivity  thus 
induced  is  termed  anaphylaxis.  The  initial  cause  of  the  symptoms  seems  to  be  con- 
striction of  the  bronchial  tubes  and  obstruction  of  the  airway  and  a  great  fall  in  the 
blood-pressure,  accompanied  by  congestion  and  even  haemorrhages  in  the  mucous 
membranes  of  the  bowels.  Convulsions,  follow  the  consequent  anaemia  of  the  brain. 
If  the  animal  recover,  it  is  immune  to  further  injections  of  this  serum.  The  sensi- 
tivity lasts  a  very  long  time.  Anaphylaxis  has  been  the  cause  of  alarming  symptoms 
in  man  in  certain  eases  where  a  second  dose  of  antitoxic  serum  has  been  given  after 
an  interval  of  time.  (In  some  10  per  cent,  of  normal  individuals  a  single  injection 
of  antitoxic  serum  is  followed  by  similar  though  less  severe  symptoms.)  Anaphy- 
laxis may  be  regarded  as  the  opposite  to  immunity. 


OH AFTER  XIV 
THE  TESTS  FOR  BLOOD 

t'ROM  what  has  gone  before  we  may  now  grou])  the  chief  tests  for 
blood.  These  may  be  divided  into  ( 1 )  microscopical,  (2)  spectroscopical, 
(3)  chemical,  (4)  biological. 

Microscopical. — By  the  use  of  the  microscope  the  size  and  shape 
Oi  the  corpviscles  can  be  ascertained  (see  p.  EG).  Reptilian,  birds',  or 
camel's  blood  can  be  distinguished  from  that  of  the  domestic  animals 
or  man.  The  method  is  of  no  service  in  distnginshing  between  the 
com m oner  ma mmals . 

Spectroscopical. — The  preparation  of  spectra  of  hsemochromogen, 
hsematoporphyrin,  and  acid  hsematin,  are  useful  in  indicating  the 
presence  of  blood  (see  p.  94).  In  old  blood-stains  the  haemoglobin 
is  broken  down  to  hsematin. 

Chemical. — Under  this  heading  we  may  include  {a)  the  preparation 
of  hsemin  crystals,  (6)  the  guaiacum  test  for  blood. 

Preparat:c7i  of  Hoemin  Crystals. — Some  of  the  suspected  deposit  is 
taken  and  placed  upon  a  slide  with  a  crystal  of  common  salt  or  sodium 
iodide.  Acetic  acid  is  added  sufihciently  to  float  the  cover-slip. 
Warmth  is  then  applied  until  bubbles  begin  to  rise  beneath  the  cover- 
slip.  The  slide  is  then  removed  from  the  flame  to  cool,  and  the  pro- 
cess is  repeated  three  or  four  times.  Great  heat  must  not  be  used. 
Upon  examination  beneath  the  microscope,  chocolate  rhombic  crystals 
of  hsemin  (hsematin  chloride  or  haematin  iodide)  will  be  seen  (Fig.  25). 

The  Cuaiacum  Test  for  Blood  is  usually  employed  in  testing 
for  blood  in  urine,  stomach  contents,  and  other  body  fluids.  If  to 
the  boiled  suspected  solution  a  drop  of  tincture  of  guaiacum  be  added, 
then  a  few  drops  of  ozonic  ether,  and  the  reddish  guaiacum  turns  to 
a  blue  colour,  it  signifies  blood.  The  ro:.ct:on  depends  on  the  iron 
combined  in  the  haemoglobin.  The  enzymes  known  as  oxidases  give 
the  test,  and  therefore  a  positive  result  is  sometimes  obtained  with 
such  body  fluids  as  milk  and  saliva,  and  with  the  juices  of  vegetables, 
apple,  pineapple,  potato,  which  sometimes  leave  a  brown  stain  re- 
sembling stale  blood.  As  the  oxidases  are  destroyed  by  heat  a  solu- 
tion suspected  to  contain  blood  should  be  boiled  before  it  is  tested. 
If  this  condition  is  complied  wdth,  a  positive  reaction  may  be  taken 
to  indicate  blood.  If  the  test  is  negative,  blood  is  certainly  absent. 
Instead  of  ozonic  ether,  hydrogen  joeroxide  or  old  oil  of  turpentine 
can  be  used.  Various  tests  have  been  devised  using  bodies  other 
than  guaiacum  resin.     Such  bodies  are — aloin,  bcnzidin,  and  the  leuco 

112 


THE  TESTS  FOR  BLOOD 


113 


base   of  malachite  green  and  of  phenolphthalein.     The  last-named 
body  is  stated  to  be  extremely  sensitive. 


Fi ;.  2.:\— H  i:MiN  Crystals,     x  1,500. 


Biological. — The  biological  te?t  depends  upon  the  fact  that  the 
serum  of  an  animal  injected  with  foreign  corpuscles  develops  the  power 
of  precipitating,  aggkitinating,  and  dissolving  corpuscles  similar  to 
those  injected,  but  not  those  of  other  species  of  animals.  A  rabbit  is 
injected  with  2  to  3  c.c.  of  human  serum  at  intervals  during  four 
days,  until  10  to  15  c.c.  have  been  injected.  After  one  to  two  weeks 
the  animal  is  bled,  the  serum  collected  and  placed  in  sterile  tubes,  and 
used  as  needed.  This  serum  is  mixed  with  the  suspected  blood,  which 
is  dissolved  or  suspended  in  isotonic  salt  solution  in  the  proportion  of 
1  :  100;  the  mixture  is  placed  at  37°  C.  If  the  blood  be  human,  a 
turbidity  is  produced,  changing  within  three  hoiirs  to  a  flocculent 
precipitate.  The  blood  of  closely  allied  species,  such  as  the  other 
Primat'CS — e.g.,  chimpanzee — may  give  a  slight  precipitate.  The  test 
has  been  used  to  detect  human  blood  in  medico-legal  cases,  and  to  con- 
firm the  supposed  consanguinity  of  different  species  of  animals.  It  shows 
the  near  relation  of  man  to  the  gorilla,  the  ourang,  and  the  chimpanzee. 

8 


BOOK    III 
THE   CIRCULATION   OF   THE    BODY   FLUIDS 

CHAPTER  XV 
THE  MECHANISM  OF  TRANSPORT 

The  unicellular  organism  floating  in  a  nutritive  water}'  fluid 
lives  by  exchange  between  its  body  and  the  surrounding  medium. 
In  the  multicellular  organism  the  deeper  parts  become  too  far 
removed  from  the  siu-face  for  a  rapid  exchange  of  material  to  take 
place,  and  devices  such  as  infolding  are  evolved,  which  lead  the 
medium  into  the  inner  recesses  of  the  bod}'. 

With  the  higher  organization  brought  about  by  evolution,  a  limit 
soon  became  set  to  such  infolding,  which  interfered  with  the  differenti- 
ation of  structure  and  division  of  labour  necessary  to  render  the 
organism  efficient  in  the  struggle  for  existence.  Hence,  there  came 
about  the  development  of  a  body  cavity,  or  coelom,  filled  with  an 
internal  medium,  which,  as  blood  or  lymph,  was  at  first  made  tO' 
circulate  by  the  general  movements  of  the  bodj-.  Later  was  evolved 
a  special  pump — the  heart,  or  several  hearts — and  a  system  of  vascular 
tubes,  at  first  partly  and  then  conipletel}-  closed.  By  the  aid  of 
these  the  internal  medium  could  be  driven  with  greater  swiftness 
and  insure  the  better  nourishment  of  every  part.  The  internal  tissue 
of  a  Turbellarian  worm,  for  example,  is  a  loose  aggregate  of  cells,  differ- 
entiated to  a  slight  extent  in  structure  and  no  doubt  in  function, 
comiected  by  strands  of  protoj^lasm.  Between  the  cells  are  inter- 
cellular clefts,  which  are  connected  with  larger  channels  which 
extend  through  the  body,  and  act  as  circulatory  channels.  These 
clefts  and  channels  are  filled  with  a  fluid  which  carries  the  food  and 
oxygen  supply  to,  and  the  waste  products  from  the  internal  tissues, 
and  in  every  way  acts  as  a  simple  blood.  A  to-and-fro  movement 
takes  place  as  a  result  of  the  movements  of  the  animal.  The  meso- 
dermal ceUs  in  contact  with  the  primitive  channels  become  differ- 
entiated in  part  into  tissues,  which  form  waUs  to  these  spaces.  The 
primary  circulation  spaces  become  specialized  into  continuous  channels 
which  run  the  length  of  the  body.  The  blood  is  driven  to  and  fro 
in  this  body  cavity,  or  coelom,  by  the  movements  of  the  muscles  of 
the  body,  and,  so  propelled,  bathes  the  respiratory  tissues,  the  wall 
of  the  gut,  the  nephridia  and  other  structures. 

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In  the  mollusca  we  find  definite  blood-channels,  the  larger  of  which, 
in  the  cephalopods,  have  well-developed  muscular  walls,  and  act  as 
])umiDs  driving  by  Avavc-like  contractions  the  contained  fluid  before 
them. 

In  the  lobster  there  is  developed  a  heart.  It  is  endowed  with  a 
rhythmic  activity  of  its  own,  and  forces  the  blood  through  a  sj^stem 
of  larger  vessels — the  arteries — to  smaller  frailer  vessels — the  capil- 
laries^ — and  thence  to  open  spaces  between  the  masses  of  connective 
tissue — the  lacunse.  From  these  lacunse  the  blood  is  returned  to 
the  heart  by  another  system  of  channels — the  veins. 

In  insects  the  circulatory  mechanism  is  simple.  A  dorsal  pump — 
the  heart^forces  the  blood  through  a  vessel  which  runs  in  the 
median  line  from  one  end  of  the  body  to  the  other  into  large  sinuses 
and  spaces;  from  these  it  is  returned  to  the  heart.  In  the  limbs 
are  placed  accessory  hearts,  which  force  the  blood  to  their 
extremities. 

In  the  vertebrates  the  evolution  of  the  circulatory  system  is  carried 
to  the  highest  point.  Blood  is  pumped  from  a  well-differentiated 
strong  muscular  heart,  by  means  of  an  arterial  system  with  well- 
marked  muscular  and  clastic  walls,  into  a  capillary  system  the  walls 
of  which  are  formed  by  a  single  layer  of  endothelium.  The  lacunar 
system  still  persists  in  part,  for  in  certain  organs,  such  as  the  spleen, 
the  capillaries  are  not  closed  vessels,  but  open  into  the  tissue  spaces. 
From  the  capillaries  the  blood  is  returned  by  Itirger  channels — thi.; 
veins — to  the  heart. 

In  Amphioxus  the  blood  vascular  sj'stem  is  still  of  the  primitive 
lacunar  type  This  lowest  vertebrate  possesses  two  hearts — a  dorsal 
heart,  driving  arterial  blood  to  the  system,  and  a  ventral  one,  which 
is  termed  the  "'  respiratory  heart,"'  sending  blood  to  the  gills.  In 
fishes  the  heart  is  single,  and  essentially  respiratory  in  function, 
propelling  blood  to  the  giUs,  thence  to  the  aorta  and  to  the  system 
generally,  and  back  again  to  the  heart. 

In  the  amphibia  there  are  two  auricles  and  one  ventricle ;  in  reptiles 
two  auricles  and  a  partial  separation  of  the  ventricle  into  two.  It  is 
only  in  the  birds  and  mammalia  that  the  two  systems  become  quite 
distinct — two  auricles  and  two  ventricles — the  right  auricle  and 
ventricle  forming  the  respiratory  system,  the  left  auricle  and  ventricle 
the  systemic.  This  evolution  has,  however,  been  carried  out  on 
quite  a  different  plan  in  the  two  hearts,  the  bird's  heart  differing  in 
many  points  from  the  mammalian. 

In  man  the  heart  is  about  equal  in  size  to  a  closed  fist,  measuring 
about  5  inches  long,  3-|  inches  wide,  and  weighing  in  the  adult  about 
300  grammes,  or  0-46  per  cent,  of  the  body  weight.  In  the  new-born 
baby  it  weighs  about  24  grammes,  0-76  per  cent,  of  the  body  weight. 
The  average  weight  of  the  male  and  female  heart  is  almost  the  same. 
The  volume  is  estimated  by  filling  the  cavities  with  wax,  to  be  100  to 
130  c.c.  for  each  auricle,  and  150  to  200  c.c.  for  each  ventricle. 

The  auricles  have  much  thinner  walls  than  the  ventricles.  The 
muscle  of  the  auricles  consists  of  a  circular  layer  common  to  both, 


THE  MECHANISM  OF  TRANSPORT  117 

and  a  deeper  layer  separate  for  each  chamber.  The  auric ulo- ventri- 
cular ring  consists  of  connective  tissue  separating  the  muscle  of  the 
auricles  from  that  of  ventricles  except  at  one  spot  on  the  septiim  (see 
p.  121,  the  A.-V.  bundle),  and  possibly  at  the  right  lateral  external 
margni. 

The  right  auricle  is  more  or  less  quadrilateral  in  shape,  being 
prolonged  in  the  upper  corner  to  an  ear-like  process — the  right  auricular 
appendix.  Into  it  the  superior  and  inferior  vense  cavse  open.  At 
the  junction  of  the  superior  vena  cava  and  auricle  is  situated  a  small 
mass  of  tissue  known  as  the  "  sinu-auricular  node." 

The  right  ventricle  forms  the  chief  part  of  the  anterior  surface 
of  the  heart.  It  communicates  with  the  right  auricle  and  with  the 
pulmonary  artery.     At  the  entrance  from  auricle  to   ventricle  are 

'st  arch 

2ncl  arch 
uentral  aorta 


conus  arteriosus 


prim,  uentriciei .  /      \prim.  auricle 


sinus  uenosus 


vit  vein^^'''^  ^"^uit  ueir, 

Fig.  26. — ^The  Primitive  Divisions  of  the  Embryonic  Heart.     (Keith.) 

situated  the  tricuspid  valves,  while  the  entrance  to  the  pulmonary 
artery  is  guarded  by  thin  watch-pocket-like  valves — ^the  semilunar 
valves. 

The  left  auricle  is  situated  posteriorly.  It  likewise  possesses  an 
appendix.  Into  it  the  four  pulmonary  veins  open.  The  left  auricle 
communicates  with  the  left  ventricle,  the  orifice  being  guarded  by  the 
two  flapped  bicuspid  or  mitral  valves. 

The  left  ventricle  forms  the  chief  part  of  the  posterior  surface, 
and  also  the  apex  of  the  heart.  It  forms  the  chief  muscular  mass  of 
the  heart,  the  wall  being  in  places  i  inch  in  thickness.  It  com- 
municates with  the  left  auricle  and  with  the  aorta.  At  the  orifice  of 
the  aorta  are  situated  delicate  semilunar  or  watch-pocket  valves. 
Opposite  the  cusps  are  bulgings  of  the  aortic  wall — the  sinuses  of 
Valsalva.     From  the  anterior  one  arises  the  right  coronary  artery, 


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A  TEXTBOOK  OF  PHYSIOLOGY 


and  from  the  left  posterior  the  left  coronary  artery.     These  vessels 
supply  the  heart  muscle. 

Various  accounts  are  given  of  the  arrangement  of  the  musculature 
of  the  ventricles.  Internally,  the  muscular  fibres  are  thrown  into 
columns — the  colunnue  carna?  and  the  papillary  muscles.  The  super- 
ficial fibres  take  origin  from  the  auriculo-ventricular  ring,  and  wind 
.spirally  about  the  heart,  to  end  in  the  papillary  muscles,  or  pass  up 
in  the  septum  to  the  ring  again  on  the  inner  surface  of  the  heart. 
The  middle  layers,  which  form  the  bulk  of  the  tissue,  consist  of  bundles 
of  fibres  running  more  or  less  circularly  round  the  ventricles. 


Fig.  27. — Generalized  Tvpe  of  Vertebrate  Heart.     (Keith.) 

a,  Sinus  venosus  and  veins;  b,  auricular  canal;  c,  auricle;  d,  ventricle;  e,  bulbus  cordis; 
/,  aorta;  1-1,  sinu-auricular  junction  and  venous  valves;  2-2,  canalo-auricular 
junction;  3-3,  auricular  ]iart  of  auricle;  4-4,  invaginated  part  of  auricle; 
5,  balbo-ventricular  junction. 


By  the  study  of  the  primitive  type  of  vertebrate  heart  a  clear 
concej)t  has  been  gained  not  only  of  anatomical  arrangement,  but  of 
the  function  of  certain  parts  in  the  more  highly  developed  mam- 
malian heart. 

The  heart  develops  as  a  tul:)e  (Fig.  26),  and  the  auricle  is  regarded 
as  a  dorsal  expansion  of  this  tube,  and  the  ventricle  as  a  ventral 
expansion. 

The  diagram  (Fig.  27)  represents  the  general  type  of  a  primitive 
vertebrate  heart.  The  cardiac  tube  begins  at  {a)  and  ends  at  (/). 
Dorsally  is  placed  the  expansion  (c),  the  auricle,  while  {d)  represents 
the  ventricular  outgrowth.  Such  a  heart  may  be  said  to  consist  of  five 
chambers.     At  the  venous  end  (a)  the  sinus  venosus  is  formed    by 


THE  MECHANISM  OF  TRANSPORT  110 

the  junction  of  the  two   great  veins.      The  blood  enters  the  heart, 
and  the  wave  of  contraction  begins  here. 

Chamber  (6)  represents  the  original  cardiac  tube  from  which  the 
auricle  has  grown  out  dorsally.  It  is  known  as  the  "  auricular  canal," 
and  may  be  subdivided  into  three  parts:  {A)  the  part  of  the  cardiac 
tube  antecedent  to,  and  opposite,  the  outgrowth  of  the  auricle  (2-2) — 
generally  termed  the  "  basal  part  ";  {B)  the  part  which  comes  after 
the  outgrowth  of  the  auricle  and  before  the  downgrowth  of  the  ven- 
tricle (3-3) — the  ■■  auricular  ring  ";  {€■)  a  part  (4-4)  which  has  become 
invaginated  into  the  ventricle.  The  ventricle  is  represented  by  (d), 
while  (e)  at  the  arterial  end  of  the  cardiac  tubs  represents  the  chamber 
known  as  the  "  bulbus  cordis." 


Fig.  28. — Right  Auricle  seen  from  thk  Side.     (Keith  a-.id  Flack.) 

it,  Su]ierior  vena  cava;  b,  appendix;  S.-A.,  sinu-auricular  node;  c,  vestibule  of  left 
auricle;  /,  union  in  sulcus  terminalis  of  two  branch  arteries  arising  from  right 
coronary  artery;  </,  another  anastomosing  branch  from  right  coronary  arterv; 
/,  inferior  vena  cava;  /,  aorta. 

In  such  a  heart  the  flow  through  the  organ  is  directed  by  four 
sets  of  valves:  (1)  Placed  between  the  sinus  and  auricular  canal  (the 
venous  valves);  (2)  at  the  auricular  ring  at  the  entrance  to  the  ven- 
tricle; (3)  and  (4)  at  either  end  of  the  bulbus  cordis. 

The  two  auricles  of  the  mammahan  heart  are  formed  by  a  fusion 
of  the  musculature  of  three  parts  of  the  primitive  vertebrate  heart — 
the  sinus,  the  auricular  canal,  and  the  primitive  auricle. 

The  two  ventricles  are  developed  side  by  side  from  the  ventral 
wall  of  the  primitive  tube,  an  infolding  of  the  walls  fusing  to  form 
the  interventricular  septum. 

The  bulbus  cordis  comes  to  be  represented  by  the  infundibular 
part  of  the  right  ventricle. 

In  the  mammalian  heart  the  sinus  venosus,  with  the  venous  valves, 
has  almost  disap])eared.  Its  most  important  remnant  is  a  small 
mass  of  tissue  at  the  junction  of  the  superior  vena  cava  and  the  auricle 
(Fig.  28) — the  sinu-auricular  node. 

In  the  human  heart  the  sinu-auricular  node  is  about  the  size  of 


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a  grain  of  wheat.  It  has  a  special  blood-supply,  and  here  the  nerves 
of  the  heart  form  an  intimate  contact  with  the  musculature.  Micro- 
scoijically,  it  consists  of  pale  cardiac  muscle  fibres,  with  which  the 
nerve  fibres  appear  to  become  actually  continuous.  This  tissue,, 
apparently  intermediate  in  nature  between  muscle  and  nerve,  is 
characteristic  of  the  sinu-auricular  and  auricido-ventricular  nodes, 
and  is  termed  "  nodal  tissue."'  The  nodal  tissue  becomes  less  in 
amount  and  more  concentrated  in  position  as  one  passes  from  the  lower 
to  the  higher  type  of  heart.  With  the  increasing  specialization  of 
the  organ  the  extra-cardiac  nerves  enter  into-a  more  direct  relation- 
ship with  the  cardiac  musculature ;  the  heart  to  a  certain  extent  loses 
its  independence,  and  becomes  more  a  part  of  the  general  organization. 


Tig.  29. — A,  Sinu-Aukiculae  Ju^T:TION  in  Human  Heart;  B,  Sintt- Auricular. 
Junction  in  Turtle's  Heart.  The  Figures  represent  Corresponding 
Parts  in  the  Two  Hearts.     (Keith  and  Flack.) 

1,  Musculature  of  superior  vena  cava  or  sinus  in  A,  of  sinus  venosus  in  B  ; 
2,  artery  and  surrounding  nodal  tissue  at  sinu-auricular  junction;  3,  position  of 
venous  valve  in  A.  In  B,  3  indicates  junction  of  musculature  of  sinus  and 
auricle  in  the  venous  valve;  4,  auricular  muscle,  differs  from  sinus  musculature 
in  both  A  and  B  in  having  a  very  slight  endocardial  covering;  5,  subepicardial 
tissue;  6,  connective  tissue  between  sinus  and  auricle. 


The  auricular  canal  has  also  become  profoundly  modified,  owing 
to  the  development  of  two  auricles  instead  of  one.  The  basal  part 
is  represented  chiefly  by  the  interauricular  septum. 

Similarly,  the  development  of  tW'O  ventricles  by  the  downgrowth 
of  an  interventricular  septum  has  brought  about  a  rearrangement  of 
the  auricular  ring  and  the  invaginated  portion  of  the  auricular  canal. 
Most  of  the  auricular  ring  has  become  indistinguishable  from  the  rest 
of  the  auricular  tissue,  but  at  the  base  of  the  interauricular  sept'.m 
there  is  found  a  mass  of  "  nodal  "  tissue,  known  as  the  auriculo- 
ventricular  or  A.-V.  node  (3,  Fig.  30). 


THE  MECHANISM  OF  TRANSPORT 


121 


The  invaginated  portion  has  become  greatly  reduced  in  amount, 
and  instead  of  extending  into  the  ventricles  all  round  the  A.-V.  groove,^ 
as  it  was  in  the  primitive  type  of  heart,  it  is  represented  by  a  small 
•muscular  band  of  fibres  arising  from  the  A.-V.  node,  and  passing  into 
the  ventricles — the  auriculo-ventricular  bundle. 

It  consists  essentially  of  four  portions:  The  A.-V.  node,  the  main 
bundle,  the  septal  divisions,  the  terminal  ramifications. 

These  parts  can  be  made  out  more  easily  in  some  hearts  than 
other.  In  the  hearts  of  the  sheep  and  ox  it  is  easy,  owing  to  the 
paleness  of  its  fibres,  to  dissect  out  the  whole  bundle.  In  these  hearts, 
the  fibres  constituting  the  bundle  present  a  greater  contrast  to  the 
musculature  of  the  heart. 


Fig.  30. — Right  Auricle  and  Ventricle  of  Calf.     (Keith  and  Flack.) 

1,  Central  cartilage;  2,  main  A.-V.  b:in:lle;  3,  A.-V.  node;  i,  right  septal  division  of 
•A.-V.  bundle;  5,  moderator  band;  8,  orifice  of  coronary  sinus.  . 


The  auriculo-ventricular  node  lies  at  the  base  of  the  interauricular 
septum  on  the  right  side,  below  and  to  the  right  of  the  coronary  smus. 
It  is  in  close  muscular  connection  with  the  interauricular  septum, 
and  thus  indirectly  with  the  sinu-auricular  node. 

The  main  bundle,  arising  from  the  A.-V.  node  (Fig.  30),  rides  along 
the  top  of  the  interventricular  septum  below  the  pars  membranacea  septi 
— a  spot  easily  found  in  the  human  heart  by  holding  the  organ  up  to 
the  hght  after  opening  the  chamber.  It  then  divides  into  the  right 
and  left  septal  divisions  for  the  right  and  left  ventricle  respectively. 
The  right  baiid  is  cord-like,  and  is  somewhat  embedded  in  the  septum, 
becoming  superficial  as  it  approaches  the  septal  group  of  the  musculi 
papillares.  The  left  bundle  is  subendocardial  throughout  its  course  to  the 
septal  musculi  papillares,  and  has  the  form  of  a  delicate  ribbon  of  fibres. 

The  terminal  ramifications  may  be  said  to  arise  from  these  groups 
of  septal  musculi  papillares.  Starting  from  these,  they  run  in  the 
"  moderator  band  "  on  the  right  side,  and  in  several  small  bands  on 
the  left  side,  passing  as  delicate  trabeculse  to  fuse  with  the  ventricular 
musculature. 


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On  niicroscojiic  cxaniinalion  there  may  be  seen  (1)  the  branched 
network  of  cells  in  the  A.-V.  node,  (2)  the  large  pale  cells  of  the  main 
bundle,  (3)  the  i^ecnliar  Purkinje  cells  constituting  the  septal  divisions 
and  the  terminal  ramifications.  In  the  human  heart  the  different 
portions  of  the  l)uu<lle  are  not  so  easily  recognized,  but  with  practice 
it  can  be  identified  both  macroscopically  and  microscopically.  It  is 
interesting  to  note  that  the  invaginated  portion  of  the  auricular  canal 
(the  A.-V.  bundle)  has  persisted  in  the  part  of  the  primitive  cardiac  tube 
which  has  been  least  disturbed  by  the  development  of  the  two  ventricles. 

There  possibly  exists  another  muscular  connection  between  right 
aiu'icle  and  right  ventricle  in  the  right  lateral  external  part  of  the 
A.-V.  groove. 


Fig.  31. — Left  Ventricle  of  Calf.     (Keith  and  Flack.) 

1,  Left  septal  division  of  A.-V.  bundle;  2-3,  subaortic  musculature  divided  to  show 
passage  of  bundle  from  right  side  of  heart;  4-5,  branches  of  left  septal  division 
passing  to  6,  moderator  bands  containing  prolongations  of  bundle  to  fuse  with 
musculature  of  heart  wall;  9,  left  auricle;  10,  aorta;  11,  12,  aortic  valves; 
13,  pulmonary  artery. 

In  the  heart  of  the  bird,  which  contains  no  sinu-auricular  node 
and  no  muscular  bundle  in  the  position  of  the  A.-V.  bundle,  a  similar 
muscular  connection  has  been  found  in  the  posterior  aspect  of  the 
A.-V.  groove  in  the  region  of  the  left  superior  vena  cava. 

Microscopic  Anatomy. — The  vertebrate  heart-muscle  consists  of 
fibres,  which  in  their  turn  are  composed  of  fibrils,  or  sarcostyles  and 
sarcoplasm.  Nuclei  are  situated  at  regular  intervals  in  the  fibres, 
and  are  surrounded  by  a  small  mass  of  granular  protoplasm — the 
sarcoplasm.  Running  out  from  the  central  sarcoplasm  to  the  periphery 
between  the  fibrils  there  is  a  very  delicate  protoplasmic  membrane — 


THE  MECHANISM  OF  TRANSPORT 


123 


the  sarcolemma — often  richlj'  impregnated  with  fine  granules.  The 
sarcoplasm  and  nuclei  represent  the  remains  of  the  primitive  cells 
(myoblasts)  from  which  the  heart  is  developed;  the  fusion  of  these 
•forms  a  syncytium  in  which  the  fibrils  develop.  These  are  the  true 
contractile  elements  of  the  muscle  fibres.  They  are  somewhat  pris- 
matic in  shape,  and  lie  in  bundles  at  the  periphery  of  the  fibre,  the 
centre  being  occupied  by  the  nucleus  and  sarcoplasm.  The  sarcostyles 
exhibit  a  longitudinal  striation  due  to  the  fibrils,  and  sometimes  a 
transverse  striation  due  to  the  presence  of  singly  and  doubly  refractile 
substances  alternate!}^  placed  within  the  fibrils  (Fig.  32). 


Fig.  32. — Muscular  Network  of  Normal  Heart  of  Adult  Man.     (Przewoski.) 

a.  Septum;  b,  fibrils  passing  through  thickenings  in  fibre;  c,  nuclei  of  cells;  d,  short 
segment  without  nucleus.     (From  "  Quain's  Anatomy."') 


There  is  an  intimate  fusion  between  neighbouring  fibres;  a  number 
of  fibrils  from  one  fibre  pass  into  a  neighbouring  fibre. 

At  intervals  transverse  lines  appear  in  the  fibres.  Some  think 
these  are  caused  by  a  local  thickening  of  the  fibre  produced  by  the 
process  of  death;  others  believe  they  have  some  sjiecial  function  in 
regulating  the  growth  of  the  fibres.  They  are  not  to  be  regarded  as 
a  cement  substance  separating  different  heart  cells. 

The  Nervous  Elements  of  the  Vertebrate  Heart. — The  vertebrate 
heart  is  very  rich  in  nervous  elements — ganglion  cells,  nerve  fibres, 
and  nerve  endings.  There  is  a  very  rich  supply  of  ganglion  cells  in 
the  auricle.     In  the  frog's  heart  they  are  grouped  at  the  sinu-auricular 


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A  TEXTBOOK  i)V  PHYSIOLOGY 


junction  ((J.  1,  Fig.  3o),  uy.on  the  interauriciilar  ,s('[)tuin  (0.  2,  Fig.  33), 
at  the  auriculo-ventiicular  junction  (0.  3,  Fig.  33). 

In  regard  to  the  distribution  of  ganglion  cells  in  the  ventricles,  it 
is  generally  conceded  that  they  exist  in  the  upper  third  of  the  ventricle, 
the  lower  two-thirds  being  regarded  as  ganglion-free. 

The  nerve  endings  in  the  heart  are  both  receptor  and  effector. 
As  regards  the  sensory  nerve  endings  (the  depressor  nerve),  some  ob- 
servers hold  that  they  do  not  supply  the  heart,  but  only  the  aorta; 
others  believe  they  end  as  tree-like  expansions  very  like  those  found 
in  fascia  and  tendon  in  both  the  outer  covering  of  the  heart  (epi- 
cardium)  and  the  lining  membrane  (endocardium). 


Fig.  33. — Inter-Atjeictilar  Septum  and  Ventricle  showing  the  Vagus  Nerves 
AND  Ganglia.     (Hedon.) 

G.  1,  .Sinu-auriculai'  or  Picmak'.s;  G.  2,  septal,  or  v.  Eezold's;  G.  3,  auriculo-ventricular, 

or  Bidder's. 

The  effector  nerve  endings  come  from  both  the  vagus  and  sympa- 
thetic nerves,  and  it  is  stated  that  each  heart  fibre  is  surrounded  by 
a  nervous  network  right  down  to  the  apex. 

Structure  of  the  Bloodvessels. — The  whole  vascular  system  is  lined 
within  by  a  la3'er  of  flattened  cells — the  endothelium.  Each  cell  is 
exceedingly  thin,  and  cemented  to  its  fellows  by  a  wavy  border  of 
an  interstitial  cement  (protoplasm)  substance.  The  endothelium 
affords  a  smooth  surface,  along  which  the  blood  can  flow  with  ease. 
It  rests  on  a  soft,  thin  film  of  connective  tissue,  the  two  together 
forming  the  internal  coat,  or  intima.  Outside  it  there  exists  in  the 
arteries  and  veins  a  middle  and  an  external  coat.  The  middle  coat, 
or  media,  varies  greatly  in  thickness,  and  contains  most  of  the  non- 
striated  muscle-cells,  which  in  the  smaller  arteries  and  arterioles  form 


THE  MECHANISM  OF  TRANSPORT  125 

a  particularly  well-developed  band.  In  the  larger  arteries  a  great 
deal  of  yellow  elastic  tissue,  together  with  some  white,  fibrous 
tissue,  pervades  the  middle  coat.  At  the  inner  and  outer  border  of 
this  coat  the  elastic  fibres  fuse,  to  form  an  internal  and  external 
fenestrated  membrane — a  marked  feature  of  an  artery.  This  coat 
endows  the  arteries  with  lability  (extensibility  and  elasticity)  and 
contractility.  The  outside  coat  consists  mostly  of  white  fibrous  tissue, 
and  not  only  protects  the  arteries,  but  bj'  its  rigidity  prevents  over- 
distension. The  connective  tissue,  hke  the  leather  case  of  a  football, 
allows  extension  of  the  elastic  layers  up  to  a  certain  point,  and 
then  becomes  taut.  In  the  veins  where  the  middle  coat  is  some- 
what thinner  and  contains  less  elastic  tissue,  the  outer  coat  consists 
largeh'  of  muscle-fibres.  There  is  more  white  connective  tissue  in  the 
walls  of  the  veins.  The  valves  of  the  veins  are  formed  of  fibrous 
and  elastic  tissue  covered  with  endothelium.  The  walls  of  the  larger 
bloodvessels  are  supplied  with  blood  through  the  vasa  vasorum. 
As  the  arterioles  branch  into  capidaries  the  muscular  and  elastic 
elements  become  less  and  less,  until  in  the  capillaries  themselves 
there  is  left  only  the  layer  of  endothelium,  suj^ported  by  some  stellate 
connective-tissue  cells.  There  is  some  evidence  that  the  cells  fining 
the  capillaries  can  alter  their  shape,  and  so  contract  the  lumen  of 
these  vessels.  A  phagocytic  action  is  also  ascribed  to  these  cells — 
e.g.,  in  the  liver.  In  early  embryonic  life  these  cells  give  origin  to 
red  corpuscles  (see  j).  SS).  The  capillaries  form  networks,  which 
accommodate  themselves  to  the  structure  of  the  organs — e.g.,  longi- 
tudinal networks  in  muscle,  loops  in  the  papillae  of  the  skin,  close - 
meshed  netAvorks  round  the  alveoli  of  glands,  cells  of  liver,  etc.  In 
the  liver  the  blood  penetrates  into  the  substance  of  the  liver  cells, 
the  capillaries  forming  sinusoids.  In  the  spleen  the  capillaries  open 
into  the  pulp.  The  lumen  of  the  capillaries  can  be  widened  or  narrowed 
by  var3ang  contractility.  As  the  capillaries  join  together  to  form 
the  venules,  muscle  fibres  again  appear  and  coat  the  wall  of  the 
litter.  The  bloodvessels  arc  supplied  Avith  vaso-motor  nerves,  which 
regulate  their  calibre  and  the  supply  of  blood  according  to  the  needs 
of  the  body.  The  nerves  end  in  a  plexus  of  fibrils  among  the  muscle 
fibres.  Ganglion  cells  occupy  the  larger  nodes  of  the  nerve  plexus. 
The  ends  of  a  torn  artery  retract,  coil  up  within  the  external  coat, 
and  so  prevent  haemorrhage.  The  excised  arteries — e.g.,  of  an  ox  or 
sheep — contract  when  mechanicalh'  irritated,  and  remain  capable  of 
contraction  for  some  days  after  excision.  They  maj^  be  relaxed  by 
freezing,  or  by  poisoning  with  a  solution  of  fluoride  of  sodium. 

The  elastic  tssues  of  the  arteries  successfully  withstand  the  strain 
of  the  pulse  some  seventy  times  a  minute  throughout  the  years  of 
a  long  life. 

The  elastic  co-efiicients  of  the  several  layers  of  the  coat  of  an  artery 
increase  from  within  out,  and  thus  great  strength  is  obtained  with 
the  use  of  a  small  amount  of  material.  The  elasticity  of  a  healthy 
artery  is  almost  perfect,  while  the  breaking  strain  both  of  arteries  and 
veins  is  very  great,  and  far  above  that  exerted  by  the  blood-pressure 


126  A  TEXTBOOK  OF  PHYSIOLOGY 

— e.g.,  they  Jiiay  withstcand  an  iiitoual  pressuic  uj)  to  about 
10  atmospheres.  It  has  proved  possible  to  stitch  divided  arteries 
and  veins  together  so  perfectly  that  the  circulation,  can  continue 
through  them.  The  kidneys  have  thus  been  successfully  trans- 
planted from  one  cat  to  another,  and  have  continued  to  functionate 
for  some  thxys.  A  piece  of  artery,  killed  by  immersion  in  formol 
solution,  has  been  intercalated  in  the  aorta  of  an  animal,  and  the 
circulation  has  continued  unimpaired.     It  forms  a  scaffold  for  repair. 

The  heart  is  enclosed  in  a  tough  inextensile  bag — the  pericardium 
— the  functions  of  which  are  to  give  the  he'art  a  smooth  bag  to 
work  in,  moistenetl  with  pericardial  fluid;  to  prevent  misplacement 
and  check  over-dilatation  of  the  heart,  in  jDarticular  during  great 
muscular  efforts.  The  j^ericardium  restrains  the  over-stretching  of 
the  heart  in  just  the  same  way  as  the  leather  cover  of  a  football  stops 
over-distension  of  the  indiarubber  bladder  within  it. 

The  abdominal  organs  and  bloodvessels,  encompassed  by  the 
muscular  wall  of  the  abdomen,  may  be  regarded  as  enclosed  in 
a  sphere  of  muscle.  Above  is  the  dome  of  the  diaphragm,  below 
the  basin-like  levator  ani,  closing  the  outlet  of  the  pelvis;  in 
front  are  the  recti  muscles,  behind  the  quadrati  lumborum  and  the 
spine;  while  the  oblique  and  transverse  muscles  complete  the  wall 
at  either  side.  The  brain  is  enclosed  in  a  rigid  and  unyielding  box 
of  bone— the  cranium;  the  limbs  are  encompassed  by  the  extensile 
and,  in  health,  taut  and  elastic  skin;  while  the  organs,  such  as  the 
salivary  glands  and  kidneys,  possess  a  capsule  which  confines  them 
and  limits  their  expansion. 

The  bloodvessels  are  thus  confined  by  the  walls  and  membranes 
of  the  body  and  influenced  bj'  every  muscular  movement. 

The  heart's  energy  is  spent  in  maintaining  a  pressure  of  blood 
in  the  elastic  arteries,  and  owing  to  the  difference  of  pressure  in  the 
arteries  and  veins,  the  blood  is  kept  flowing  throiigh  the  capillaries 
into  the  veins.  The  movements  of  the  body,  j^articularly  ihosc  of 
respiration,  help  to  return  the  blood  from  the  capillaries  and  veins 
to  the  heart.  In  the  veins,  especially  those  of  the  limbs,  valves  are 
placed  to  direct  the  blood  heart  wards.  The  blood  is  propelled  by  the 
heart,  which  varies  both  in  rate  and  energy  of  beat,  through  muscular 
and  labile  arteries,  delicate  capillaries,  and  muscular  veins — a  system 
which  varies  in  capacity  and  may  alter  in  lability.  This  system  is 
supported  by  the  tissues  which,  by  their  contractility,  elasticity,  and 
secretory  force  modify  their  support  of  the  vascular  system  most 
profoundly.  The  width  of  bed  through  which  the  blood  flows  varies 
greatly  at  dift'erent  parts  of  the  circuit.  The  resistance  offered  to  the 
moving  blood  is  very  much  greater  in  the  capillary-sized  vessels  than 
in  the  large  arteries  and  veins. 

The  problems  of  the  circulation  are  thus  far  from  simple.  They 
resolve  themselves  mainly  into  a  consideration  of  (1)  the  physiology 
of  the  heart;  (2)  the  physical  characters  of  the  circulation;  (3)  the 
control  of  the  heart  and  vessels  by  the  nervous  system. 


CHAPTER  XVI 
THE  PHYSIOLOGY  OF  THE  HEART 

The  Heart  as  a  Muscle. — The  properties  of  the  cardiac  muscle 
may  be  studied  either  on  the  beating  or  on  the  still  heart.  The  excised 
heart  continues  to  beat  for  some  time  outside  the  bod}',  and  has  the 
power  of  rhythmic  automaticity.  The  still  heart  is  obtained  in  the 
mammal  when  the  heart  is  cut  out  from  the  body  and  kept  in  physio- 
logical saline  until  it  ceases  to  beat. 

The  contraction  of  the  heart  is  usually  recorded  by  means  of  a 
lever  which  \u'ites  on  a  smoked  surface  (Fig.  34).     By  this  means  a 


O 


Fig.  34. — Levkr  for   Recording  the  Frog's  Heart.      (Pembrey  ami   Phillips.) 

record  such  as  Fig.  35  is  obtained.  If  an  arrangement  of  two  levers 
be  used,  the  contractions  of  the  auricle  and  ventricle  can  be  separately 
recorded  (Fig.  36)  if  the  heart  be  clamped  at  the  auriculo-ventricular 
groove. 

The  excised  heart  of  the  frog  will  beat  for  days  in  a  moist  chamber. 
The  auricles  and  ventricles  stop  beating  when  a  ligature  is  tied  around 
the  sinu-auricular  junction  (the  first  Stannius'  ligature)  (Fig.  35).  Such  a 
stUled  frog-heart  responds  to  a  single  stimulus — mechanical,  thermal, 
chemical,  or  electrical — by  a  single  beat.  The  electrical  stimulus  is 
generally  chosen,  but  it  is  important  to  note  that  heart-muscle  responds 

127 


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A  TEXTBOOK  OF  PHYSIOLOGY 


Fig.  35.— Con'teaction  of  the  Er^oo's  Heart  Hecoiided  by  the  Suspension 

Method.     (L.  H.) 

The  effect  of  tightening  the  first  Stannius  ligature  at  first  gently  and  then  firmly. 
1     Ihe  curve  should  be  read  from  right  to  left.     The  time  is  marked  in  seconds. 


Fig.  36.— Recoed  of  the  Contraction  of  Auricle  and  Ventricle  (Toad)  by 
THE  Use  of  Clamp  and  Levees.     (L.  H.) 

The  upper  tracing  lathe  auricle,  and  here  the  contraction  is  represented  by  the  down- 
stroke.      The  time  is  marked  in  seconds. 


THE  PHYSIOLOGY  OF  THE  HEART 


129 


to  the  stimuli  characteristic  for  muscle  (ammonia,  dilute  mineral 
acids),  and  not  to  those  for  nerve  (glycerine).  We  see,  then,  that  the 
heart  possesses  the  properties  of  excitability  and  contractility,  and 
that  excitability  (the  power  to  respond  to  a  stimulus  from  without) 
continues  longer  than  the  property  of  rhythmic  automaticity  (the 
power  of  responding  to  the  stimulus  given  from  within). 

Thus  the  heart  of  the  embryo  chick  at  three  days  possesses  great 
rhythmic  automatic  power,  but  little  excitability  to  artificial  stimuli; 
later,  the  rhythmic  automaticity,  especially  that  of  the  ventricles, 
decreases,  while  the  excitability  increases.  The  auricle  becomes 
more  automatic  than  the  ventricle,  the  ventricle  more  excitable  than 
the  auricle. 

The  130 wer  of  contractility  varies  in  different  hearts  and  in 
different  parts  of  the  heart.  It  is  most  marked  in  the  ventricular 
musculature.     The  difference  between  automaticity  and  excitability 


Pig.  37. — Effect  of  increasing  Diastolic  Pressures — that  is,  increasing  tub 
Load — on  the  Isometric  Curve  of  the  Frog's  Heart.     (O.  Frank.) 


is  more  apparent  than  real,  automaticity  depending  on  the  site  of 
■application  and  the  kind  of  stimulus. 

The  contraction  obtained  by  stimulating  cardiac  muscle  resembles 
that  obtai)ied_by  stimulating  ordinary  muscle  (see  Fig.  275).  Just  as 
a  striped  muscle  works  better  with  increasing  load  up  to  a  certain 
point,  so,  too,  the  heart-muscle  contracts  more  powerfully  as  the 
load  is  increased  up  to  a  certain  point,  but  after  that  weakens  and 
stretches  (Fig.  37).  In  severe  muscular  exercise  the  work  of  the 
heart  is  greatly  increased:  contracting  more  often,  it  rests  less.  The 
heart  responds  to  such  strains  by  growing  larger  and  stronger. 

Cardiac  muscle  presents  certain  fundamental  characteristics  which 
are  different  from  those  of  striped  muscle.  Thus,  cardiac  muscle 
responds  to  any  efficient  stimulus  with  a  maximal  contraction,  some- 
times called  the  "  all-or-nothing  law."  Striped  muscle  responds 7t5' 
increasing  stimuli  by  contractions  rising  from  minimal  to  maximal. 
The  difference  is  more  apparent  than  real,  for  probably  only  a  few  of 
the  fibres  of  a  muscle  are  stimulated  by  a  minimal  stimulus,  while  in 
the  syncytium  of  the  heart-muscle  the  stimulus  spreads  everywhere. 

9 


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A  TEXTBOOK  OF  PHYSIOLOGY 


3       C! 


XI 


THE  PHYSIOLOGY  OF  THE  HEART 


131 


If  an  external  stimulus  be  applied  to  the  ventricle  during  the 
period  of  contraction  or  systole  of  the  heart,  it  has  no  effect  for  a 
considerable  period  of  the  sj'stole  (Fig.  38).  The  heart-muscle  is 
said,  therefore,  to  possess  a  refractory  period.      The  varying  excita- 


FlG.     39. — To     ILLUSTRATE     THE    VARYING     EXCITABILITY    OF    A    FROG'S    HeART    AT 

Different  Periods  of  Systole  and  of  Diastole.  (Waller.) 

The  excitability  is  lowest  during  the  first  half  of  systole,  greatest  during  the  second 

half  of  diastole. 

bilit}^  of  the  heart  at  different  periods  of  systole  and  diastole  is  repre- 
sented in  Fig.  39.  If,  however,  the  external  stimulus  be  applied 
towards  the  end  of  systole  and  during  the  period  of  relaxation  of  the 
heart — the  diastole — it  responds  with  a  contraction — an  extra  systole. 


Fig.  40. — Effect  of  Tetanizing  the  Stanniused  He.art.     (L.  H.) 

The  curve  should  be  read  from  left  to  right.     The  time  is  marked  in  seconds.     The 
third  line  shows  the  period  of  stimulation. 

Such  extra  systoles  are  followed  by  a  longer  pause  than  normal— 
the  compensatory  pause.  It  is  nearly  equal  in  length  to  the  normal 
pause  plus  the  amount  cut  off  from  the  previous  pause  by  the 
induction  of  the  extra  systole.      The  heart  therefore   continues   to 


132  A  TEXTBOOK  OF  1>HV8I0L0GY 

make  the  same  number  of  beats  as  visual  in  a  given  time,  in  sjiite 
of  the  induction  of  extra  systoles.  The  length  of  the  compensatory 
paiise  is  due  to  the  refractory  period;  the  im])ulse  (;ausing  the  normal 
contraction  reaches  the  ventricle  at  a  tim(i  when  it  is  in  a  state  of 
systole  induced  by  the  artificial  stimulus.  It  is  therefore  refractory, 
and  the  normal  impulse  has  no  effect.  The  ventricle  is  not  stimu- 
lated again  until  the  next  normal  impulse  arrives,  and  thus  the  pause 
is  produced. 

In  the  case  of  the  frog's  heart,  a  compensatory  pause  does  not 
follow  extra  contractions  ijiduced  by  stimidatibns  of  the  sinus.  Extra 
systoles,  followed  l>y  the  compensatory  pause,  are  produced  by  a 
stimulus  applied  to  some  other  part  of  the  heart — e.g.,  auricle  or 
ventricle.  It  is  assumed,  therefore,  that  the  normal  stimulus  actually 
arises  in  the  sinus. 

This  is  also  true  for  the  mammalian  heart.  Electrical  stimulation 
of  the  sinu-auricular  node  does  not  induce  an  irregularity  of  rhythm, 
but  either  a  slowing  or  a  weakening  of  the  whole  heart,  according  to 
the  intensity  of  the  stimulus. 


immmmmmmmmmmmm 

Pjq.  41. — Normal  Electro-Cardiogram.     (W.  T.  Ritchie,  from  Cowan's  "Diseases 

of  the  Heart.") 

Normal  cardiac  muscle  cannot  be  tetanized  (Fig.  40),  as  it  is 
impossible  to  bring  about  a  true  summation  of  stimuli  in  the  normal 
heart.  In  Fig.  38  it  is  seen  that  a  second  stimulus  applied  towards 
the  end  of  systole  can  only  produce  a  small  amount  of  summation, 
because  it  does  not  act  sufficiently  soon  after  the  first  stimulus  owing 
to  the  refractory  period. 

The  cardiac  muscles  of  certain  invertebrates — for  example,  of  the 
horseshoe  crab,  Limulus — do  not  possess  the  characteristic  properties 
of  the  vertebrate  heart-tissue.  It  possesses  no  refractory  period, 
gives  submaximal  contractions,  and  can  be  tetanized. 

Like  other  forms  of  muscle,  the  heart-muscle  possesses  the  property 
of  tonicity.  The  heart  may  be  tonically  contracted  or  dilated,  and 
by  its  systole  expel  the  blood  from  a  larger  or  a  smaller  cavity.  The 
mammalian  heart  can  be  placed  in  an  instrument  called  the  "  cardio- 
meter "  (Fig.  68),  and  its  volume  recorded  and  the  alterations  of 
tonicity  measured.     The  tonicity  is  influenced  by  the  cardiac  nerves. 

If  the  frog's  ventricle  be  placed  in  a  weak  solution  of  caustic  soda 
(1  in  20,000  of  normal  saline),  it  relaxes  less  and  less  between  the  beats, 


THE  PHYSIOLOGY  OF  THE  HEART  133 

and  eventually  stands  still  in  systole ;  in  lactic  acid  (1  in  10,000  normal 
saline)  the  contractions  become  less  and  less,  and  finally  the  ventricle 
stops  in  a  state  of  complete  relaxation.  The  drugs  digitalis  and 
veratrine  yield  results  similar  to  alkalies,  muscarin  similar  to  that 
of  acids.  Chloroform  lessens,  and  adrenalin  increases,  the  tonicity 
of  the  heart.  After  death  from  chloroform,  the  heart  is  dilated  and 
the  muscle  flabby. 

The  heart  possesses  the  properties  of  rhythmic  automaticity,  of 
starting  a  stimulus.      It  also  possesses  the  property  of  conduction 


fmm  t^'-^ifsHmnH  ^tsrmi^itm  \f^Am»^  ^/Wi^ww^  ^ii^)mim  \ 

Fig.  42. — Electro-Cardiogkam  from  a  Case  of  Complete  Heartblock. 
(W.  T.  Ritchie,  from  Cowan's  "  Diseases  of  the  Heart.") 

The  auricular  rate  is  97,  the  ventricular  rate  38,  per  minute. 

of  an  impulse.  It  is  a  vexed  question  whether  these  properties 
reside  in  the  heart-muscle  itself,  or  in  the  nervous  tissue  abounding 
there,  or  in  the  intermediate  nodal  tissue.  The  electrolytes  in  solution 
in  the  tissue  lymph  are  essential  factors  in  the  maintenance  both  of 
rhythmic  automaticity  and  tonicity*. 

The  Electrical  Change  of  the  Heart. — The  contraction  of  the  heart, 
like  that  of  other  muscle,  is  accompanied  by  an  electrical  change. 
The  part  in  contraction  is  at  different  potential  to  the  part  at  rest. 


pM^ 


Fig.    43. — Electro-Cardiogram  shovving  Regularly    Recurring    Ventricular 
Extra  Systoles.     (W.  T.  Ritchie,  from  Cowan's  "  Diseases  of  the  Heart.") 

Thus,  an  electrical  wave  accomx^anies  the  wave  of  contraction.  This 
is  studied  by  means  of  either  the  capillary  electrometer  or  the  string 
galvanometer.  The  principle  of  the  string  galvanometer  is  that  a 
movable  conductor,  a  very  fine  silvered  glass  thread  or  a  quartz 
fibre,  suspended  between  the  poles  of  a  powerful  electro-magnet  at 
right  angles  to  the  lines  of  force  of  the  magnetic  field,  tends  to  be 
deflected  to  one  or  other  side  according  to  the  direction  of  the  current. 
The  degree  of  deflection  is  directly  proportional  to  the  intensity  of 
the  current  and  to  the  strength  of  the  magnetic  field,  and  inversely 
proportional  to  the  weight  and  tension  of  the  fibre.     The  changes  of 


134  A  TEXTBOOK  OF  PHYSIOLOGY 

potential  attending  the  contraction  of  the  heart  cause  the  lil)re  to 
oscillate;  these  oscillations  are  rcc(,](l((l  on  a  niovinf^  ])hotogra|)hic 
plate.  The  photographic  records  (electro-cardiograms)  obtained  with 
these  instruments  afford  a  most  beautiful  method  of  recording  the 
rhythm  of  normal  and  abnormal  hearts  in  man;  they  can  be  obtained 
by  connecting  right  and  left  hands,  the  right  hand  and  left  foot,  or 
the  left  hand  and  left  foot,  of  a  patient  with  the  instrument  by  means 
of  baths  of  salt  solution  into  which  the  wires  dip.  The  second  varia- 
tion or  "  derivation  ■'  (right  hand  and  left  foot)  is  mo.st  commcmly  em- 
ployed. The  heart  is  placed  obli<[uely  across  the  body,  and  the 
wave  of  contraction  and  accompanying  electrical  wave  begins  in  the 
base,  passes  to  the  apex,  and  thence  to  the  base  again.  The  right  hand 
or  mouth  is  favovrably  placed  as  a  lead  for  indicating  the  electrical 
condition  of  the  base,  and  the  left  hand  or  either  foot  for  that  of  the 
apex.  By  recording  the  electrical  variation,  and  using  in  turn  different 
leads,  favourable  and  unfavouraljle — e.(j.,  mouth  and  left  hand,  and 
mouth  and  right  hand — the  axis  of  the  electrical  current,  and  so  of 
the  heart  in  the  body,  can  be  determined.  By  making  use  of  the 
telephone-wires,  there  have  been  recorded  the  electrical  changes  of 
the  hearts  of  patients  comfortably  seated  or  in  bed  in  a  hospital  a 
mile  away. 

The  normal  electro-cardiogram  is  seen  in  Fig.  41.  P  is  the  deflection 
due  to  auricular  systole;  Q  R  8T  are  deflections  of  ventricular  origin, 
R  representing  ventricular  systole.  Fig.  42  represents  the  condition 
of  heartblock;  the  ventricles  are  seen  to  be  beating  at  a  slower  rate 
than  the  auricles,  and  quite  independent  of  them.  Fig.  43  is  an  electro- 
cardiogram showing  in  the  big  upward  deflection  the  occurrence  at 
regular  intervals  of  a  ventricvdar  extra  systole. 

Tissue  of  Origin  and  Mode  of  Conduction  of  the  Excitatory  Wave. — 
A  long  controversy  has  raged  around  the  question  as  to  the  actual 
tissue  in  w^hich  the  excitatory  wave  of  the  heart  arises  and  by  which 
it  is  conducted.  It  is  to  be  borne  in  mind  that  the  two  questions  are 
really  distinct.  They  are  frequently  confused.  Experiments  which 
bear  on  the  site  of  origin — i.e.,  the  tissue  in  w^hich  the  excitatory 
wave  arises— have  been  quoted  as  evidence  of  the  mode  of  conduction 
of  this  wave,  and  vice  versa.  It  must  be  granted  that,  if  the  excitatory 
wave  be  found  to  arise  in  one  form  of  tissue,  it  is  highly  probable  that 
it  will  also  be  conducted  by  that  tissue,  but  it  is  not  necessarily  the 
case.  It  is  quite  conceivable  that  the  excitatory  wave  may  arise 
in  nerve  and  be  conducted  b}^  muscle,  or  arise  in  muscle  and  be  con- 
ducted by  nerve,  or,  arising  how  it  maj^  the  excitatory  wave  may  be 
conducted  both  by  muscle  and  by  nerve  in  order  that  the  proper 
sequence  of  contraction  may  be  assured.  The  structure  of  the  nodal 
tissues  suggests  that  nerve  structure  there  fuses  into  that  of  muscle. 
It  is  only  recently  that  the  claims  of  the  nodal  tissue  have  been  ad- 
vanced as  the  site  of  origin  of  the  excitatory  wave.  For  several 
years  a  controversy  has  waged  between  those  who  uphold  the  neuro- 
genic and  myogenic  theories.  According  to  the  neurogenic  theory, 
nerve  is  thought  to  be  the  supreme  tissue,  and  it  is  supposed  that  the 


THE  PHYSIOLOGY  OF  THE  HEART  135 

excitatory  Avave  of  the  heart  arises  in  nervous  tissue  within  the  heart, 
and  is  conducted  by  that  tissue.  Those  holding  the  myogenic  doctrine 
state  that  the  wave  has  its  origin  in  heart  muscle  itself,  and  is  pro- 
pagated by  muscle.  In  the  end,  it  seems  likely  to  be  shown  that 
the  pacemaker  of  the  heart  is  a  kind  of  tissue  half  nerve,  half 
muscle. 

Of  the  two  views,  the  neurogenic  is  the  older.  As  the  heart  beats 
in  the  bod}^  after  all  the  nerves  passing  to  the  heart  are  cut,  or  outside 
the  body  when  properly  fed,  it  was  clear  to  the  older  observers  that 
the  nervous  centre  originating  the  heart  impulse  could  not  be  in  the 
brain,  and  therefore  it  was  supposed  to  be  in  the  ganglion  cells  of  the 
heart.  The  fact  that  a  ligature  tied  tightly  round  the  sinu-auricular 
groove  brings  the  auricles  and  ventricles  of  the  frog's  heart  to  a  stand- 
still was  thought  to  indicate  that  the  chief  grouj)  of  ganglion  cells 
concerned  in  the  origin  of  the  excitatory  wave  was  situated  in  that 
region.  A  second  ligature  applied  to  the  A.-V.  groove  (the  second 
Stannius'  ligature)  causes  the  ventricle  to  beat  again,  and  the  neuro- 
genist  ascribed  this  to  the  fact  that  the  ganglia  in  this  region 
are  stimulated  by  such  a  ligature.  Why  one  ligature  should  destroy 
the  action  of  ganglion  cells  and  a  second  similar  ligature  excite  their 
action  is  not  apparent;  but  it  is  said  that,  if  the  A.-V.  ganglia  be  ex- 
tirpated, this  second  ligature  is  ineffective  in  starting  the  ventricle. 
Other  evidence  cited  as  supporting  the  neurogenic  theory  is  the  ex- 
periment of  thrusting  a  needle  into  the  interventricular  septum  of 
the  mammalian  heart.  It  is  said,  that,  if  the  needle  be  inserted  on 
the  left  side  of  the  lower  end  of  the  ujDper  third  of  the  septum,  it 
.produces,  instead  of  a  beat  of  the  ventricles,  a  condition  known  as 
'■  fibrillation." 

Recent  experiments  upon  the  heart  of  the  horseshoe  crab,  L'mulus, 
afford  clear  evidence  of  the  neurogenic  origin  of  the  excitatory  Avave' 
in  this  invertebrate  heart.  The  heart  consists  of  a  tube  10  to  15 
centimetres  long,  divided  into  segments  by  the  successive  origin  of 
the  arteries.  When  the  heart  beats,  all  the  segments  appear  to 
contract  simultaneously,  although  probably  a  rapid  wave  of  con- 
traction passes.  There  are  three  nervous  strands — one  median  and 
two  lateral — which  run  along  the  outer  surface  of  the  heart  and 
anastomose  freely.  The  median  strand  contains  ganglion  cells,  and 
one  especially  large  ganglion.  It  is  easy  to  separate  this  strand  from 
the  heart  without  injury  to  the  muscle.  Its  entire  removal  causes 
cessation  of  the  whole  heart-beat,  while  removal  of  a  portion  causes 
stoppage  in  the  corresponding  segment  of  the  heart. 

As  regards  the  nervous  conduction  of  the  excitatory  wave,  the 
•chief  points  advocated  in  its  favour  are  these: 

1.  It  has  been  asserted  that  a  different  rhythm  in  aiu'icles  and 
ventricles  (allorh\thmia)  can  be  set  up  by  cutting  a  nerve  running 
from  auricle  to  ventricle.     This  is  unconfirmed. 

2.  For  a  long  time  no  muscular  connection  was  known  to  exist 
between  auricles  and  ventricles  in  the  mammalian  heart,  This  piece 
■of  evidence  is  negatived  by  the  discovery  of  the  A.-V.  bundle,  but 


136  A  TEXTBOOK  OF  PHYSIOLOGY 

it  cannot  be  denied  that  this  connection  contains  nerve  fibres — a 
point  insisted  upon  by  the  upholders  of  the  neurogenic  theory. 

3.  If  in  the  heart  of  the  Lhni  lus  a  section  of  the  median  nervous 
strand  be  made,  it  immediately  abolishes  the  synchronism  of  the 
different  segments.  The  parts  on  either  side  of  the  section  continue 
to  beat,  but  no  longer  with  the  same  rhythm.  If  a  section  be  made 
of  the  muscle  of  this  heart,  it  produces  no  effect. 

In  estimating  the  value  of  the  experiments  on  Limulvs  it  must  be 
remembered  that  it  is  an  invertelirate  evolved  in  the  epochs  of 
geological  tinu',  and  that  the  muscle  of  its  heart  seems  more  akin 
to  mammalian  smooth  muscle. 

The  m\'ogenic  theory  is  based  upon  the  following  points : 

I.  The  different  chambers  of  the  heart  beat  with  a  different  rhythm 
when  separated  from  each  other.  There  is  no  differentiation  of  any 
nervous  tissue  of  origin  and  conduction  in  these  chambers,  so  far  as 
is  known,  while  there  is  a  marked  difference  in  the  histological  appear- 
ance of  the  muscle  of  the  different  heart  chambers. 


Fig.  44.— Kabbit's  Heart,  A.-V.  Bundle  Cut,  showing  Effect  of  Stimulation  of 
Right  Vagus  Nerve.     (W.  Cullis  and  E.  M.  Tribe.) 

The  indejendcnt  rhythm  of  aiiricles  and  ventricles  is  scon  at  the  beginning,  but 
particularly  well  at  the  end  of  the  tracing.  The  nerve  acts  upon  th?  auricles  but 
not  ujon  ih?  ventricles. 

2.  The  experiment  in  regard  to  the  A,-V.  ganglia  is  incorrect. 
Excitation  of  the  ganglion  cells  of  this  group  causes  *no  contrac- 
tion. It  is  the  excitation  of  the  muscidature  of  the  auricular 
ring  which  evokes  contraction. 

3.  Isolated  parts  of  the  great  veins  of  cold-blooded  hearts  con- 
taining no  ganglion  cells  beat  automatically.  Thus,  a  jDiece  of  the- 
sinus  of  the  frog  beats  for  four  days,  and  no  less  than  17,0CO  con- 
tractions were  recorded. 

4.  The  apex  of  the  mammalian  heart,  said  to  have  no  nerve  ganglia, 
Avhen  suitably  fed  exhibits  slow  rhythmic  contractions. 

5.  The  embryonic  heart  pulses  before  muscle  and  nerve  have 
become  differentiated  in  it. 

6.  It  is  possible  to  cause  hearts  to  beat  again  several  hours  after 
death.     The   heart  of   a   boy,   dead  of  pneumonia,  was  resuscitated 


rf ,  (M'lvrrriTY 
THE  PHYSIOLOGY  OF  THE  HEART  137 


^  l/C 


006^ 


-00/8 


OO^^ 


J)  &:l 


Figs.  4:5a  and  45b. — A,  Outline  (Three-quarters  Natural  Size)  to  Scale  of 
THE  Right  Surface  of  a  Dog's  Heart,  giving  Time-Readings  of  Intrinsic 
Deflections  of  the  String  Galvanometer  taken  at  a  Number  of  Points. 
B,  Ditto  of  Left  Surface.     (Lewis  and  Rothschild.) 


138  A  TEXTBOOK  OF  PHYSIOLOGY 

twenty-eight  hours  after  death,  the  heart  of  a  eat  after  freezmg  and 
thawing.     Nervous  tissue  dies  quickly. 

7.  Certain  molluscs,  arthropods,  and  tunicates,  have  automatic 
hearts  containing  no  ganglion  cells. 

For  muscular  conduction  of  the  excitatory  wave  there  is  also  a 
considerable  array  of  evidence : 

1.  With  the  discovery  of  the  A.-V.  bundle  there  is  now  no  histo- 
logical reason  against  it;  in  fact,  experiments  upon  this  bundle  show 
that  its  destruction  by  cutting,  ligaturing,  or  clamping,  produce 
allorhythmia — a    different    rhythm    in    auricles    and    ventricles,    the 


Fig.  46. — Figure  showing  T^,  the  Point  of  Peimary  Negativity,  as  studied 
BY  the  String  Galvanometer,  to  Various  Leads  from  Other  Parts  of  the 
Heart.  The  Excitatory  Wave  therefore  starts  from  T^.  T  are  Leads 
FROM  T.5;nia,  S  prom  Sinus,  A  from  Auricle.     (T.  Lewis.) 

auricles  beating  considerably  quicker  than  the  ventricles  (Fig.  44). 
By  gradual  compression  of  the  bundle,  varying  degrees  of  arhythmia 
can  be  produced  before  this  allorhythmia  is  brought  about.  Recent 
work  Avith  the  string  galvanometer  has  showTi  that  the  excitatory 
wave  follows  the  course  of  the  A.-V.  bundle.  The  impulse  reaches 
the  inside  of  the  ventricular  wall  where  the  A.-V.  bundle  arborizes 
before  it  reaches  the  outer  surface.  It  also  reaches  the  outer  surface 
in  the  neighbourhood  of  the  moderator  band  before  it  reaches  parts 
of  the  ventricular  wall  nearer  the  A.-V.  groove  (Fig.  45). 

Clinically,  disease  of  the  A.-V.  bundle  leads  to  an  allorhythmia — 
Stokes-Adams'  disease  or  heartblock  (Fig.  42).  Whether  allo- 
rhythmia induced  by  absolute  destruction  of  the  A.-V.  bundle  ever 


THE  PHYSIOLOGY  OF  THE  HEART  139 

passes  off,  and  the  ventricles  again  come  to  follow  the  lead  of  the 
auricles,  is  a  point  requiring  further  investigation. 

2.  The  auricular  and  ventricular  muscle  can  be  cut  in  zigzag 
fashion,  and  yet  the  muscular  impulse  still  passes,  provided  the 
muscular  bridges  are  of  sufficient  breadth. 


Fig.  -17. — Showing  (A)  Effect   of   Cold   on  the  Dog's  Sinu-Aukicular  Node 
(Cold  applied  at  F)  and  (B)  on  the  Axtricle.     (M.  F.) 

3.  No   disturbance   of  rhythm   is   brought   about   by   cutting   or 
stimulating  the  nerves  connecting  auricle  and  ventricle. 


Fig.  48. — Showing  Effect  of  Clamping  Sinu-Auricular  Nude  at  A  in  Dog's 
Heart.     No  Stoppage,  but  Slight  Slowing  of  Rhythm.     (M.  F.) 

Tiiiu"  in  seconds, 

4.  In  perfused  hearts,  conduction  may  occur  when  the  nervous 
elements  are  presumably  degenerated. 

5.  The  conduction  of  the  excitatory  wave  can  pass  in  all  directions. 
Reverse  conduction  from  ventricle  to  auricle  can  also  occur.     Thus, 


140 


A  TEXTBOOK  OF  PHYSIOLOGY 


with  a  quick  stimulatioti  of  the  ventricles,  these  may  beat  first,  fol- 
lowed by  the  auricles.  The  rate  of  conduction  of  the  excitatory 
wave  is  said  to  be  in  favour  of  muscular  comhiction. 

It  is  certain  that  the  excitatory  wave  arises  in  the  region  of  the 


[^"■iG.  49. — Showing  Effect  of  Excision  of  Sinu-Auriculak  Node  and  Part  of 
THE  Superior  Vena  Cava  and  Right  Auricle  at  A  in  Rabbit's  Heart.  No 
Stoppage  of  Heart.     (M.  F.) 

great  veins,  and  under  normal  conditions  passes  through  the  auricles 
and  thence  to  the  ventricles.  With  the  discovery  of  the  sinu-auricular 
node  at  the  junction  of  the  superior  vena  cava  with  the  auricle  there 
was  a  tendency  to  regard  this  nodal  tissue  as  the  automatic  tissue  of 
the  heart.     Experimental  evidence  has  shown  that  the  nodal  tissue 


Fig.  50.— Showing  the  Effect  (B)  of  Ligature  of  the  Muscular  Connection 
between  Auricles  and  Ventricles  in  the  Heart  of  the  Chicken.  Heart- 
block  is  induced.     (M.  F.) 

yl  =  Normal  rhythm  before  ligature.     Time  in  seconds. 


possesses  a  high  degree  of  automaticit}-.  The  string  galvanometer  shows 
that  it  is  in  the  sinu-auricular  node  that  the  normal  excitatory  wave 
of  the  heart  arises  (Fig.  46).  Here  alone  can  the  normal  rhythm  of 
the  mammalian  heart  be  modified — e.g.,  by  cold,  which  lessens  the 
frequency  of  the  heart  (Fig.  47),  or  by  mechanical  or  electrical 
stimidation. 

But  elam^nng  or  excision  of  the  sinu-amicular  node  docs  not  stop 


THE  PHYSIOLOGY  OF  THE  HEART  141 

the  normally  beating  heart  (Figs.  48,  49).  In  the  dog  it  causes  a 
slight  slowing,  in  the  rabbit  it  has  no  effect.  Under  these  circum- 
stances, the  electro-cardiogram  shows  that  the  excitatory  wave  now 
arises  in  the  A.-V.  node. 

But  excision  of  the  A.-V.  node  in  the  well-nourished  normal  heart, 
beating  in  situ,  does  not  stop  either  auricles  or  ventricles.  The 
auricles  beat  as  before,  and  the  ventricles  with  a  slow  independent 
rhythm  of  their  own. 

The  nodal  tissue,  therefore,  cannot  be  regarded  as  the  sole  re- 
pository of  the  automaticity  of  the  heart.  It  is  apparently  longer 
lived  than  the  other  parts;  so  that  under  conditions  of  malnutrition 
the  excision  of  the  tissue  may  cause  cessation  of  the  heart-beat.  It 
is  in  the  areas  of  the  nodes  that  the  dying  heart  beats  last,  and  beats 
first  when  restored  by  perfusion. 

Further,  the  bird's  heart,  which  possesses  a  very  high  degree  of 
automaticity,  possesses  no  nodal  tissue. 

In  the  bird's  heart,  heartblock  may  be  induced  by  the  ligature  of 
the  muscular  connection  between  auricles  and  ventricles  (Fig.  50). 
This  connection  does  not  run  in  the  position  of  the  A.-V.  bundle,  but 
posteriorly  in  the  outer  wall  of  the  right  side  of  the  heart.  It  is 
possible  that  there  is  also  a  connection  between  auricles  and  ventricles 
in  the  mammalian  heart  in  this  region,  but  if  there  be,  it  is  not  the 
path  of  the  normal  excitatory  wave  of  the  heart. 

To  sum  up,  it  appears  that  the  evidence  at  present  available 
supports  the  view  that  the  excitatory  wave  of  the  mammalian  heart 
arises  normally  in  the  sinu-aurici;lar  node,  and  spreads  over  the 
auricular  muscle,  and  thence  to  the  ventricles  by  the  musculature  of 
the  A.-V.  bundle.  The  retardation  which  takes  place  in  the  A.-V. 
bundle  causes  the  ventricle  to  beat  at  the  projjer  period  after  the 
auricle.  The  A.-V.  bundle  normally  conducts  the  excitatory  wave 
to  the  different  parts  of  the  ventricles,  so  that  these  parts  contract 
co-ordinately,  and  wring  the  blood  out  of  the  heart. 

Although  the  property  of  rhythmic  automaticitj^  is  highly  developed 
in  the  nodal  tissue,  this  tissue  is  not  to  be  regarded  as  the  only  tissue 
of  the  heart  possessing  automaticity.  The  ordinary  musculature  of 
the  auricles  is  also  endowed  with  this  property,  and  that  of  the  ven- 
tricles to  a  less  degree. 


CHAPTER  XVIT 


THE  COURSE  OF  THE  CIRCULATION  IN  MAMMALS 

The  heart  is  to  be  regarded  as  a  double  organ,  each  half  consisting 
of  an  auricle  and  a  ventricle.  The  right  half  contains  dark  venous 
blood  which  has  been  returned  from  the  body,  and  is  sent  to  the  lungs; 
the  left  heart  contains  the  bright  oxygenated  blood  which  has  been 
returned  from  the  lungs,  and  is  distributed  to  the  body.  There  are 
thus  two  circulations — the  one,  the  pulmonary,  from  the  right  side 

of  the  heart  by  the  pulmonary  artery 
to  the  capillaries  of  the  lungs,  and 
back  to  the  left  heart  by  the  pulmo- 
nary  veins;  the  other,  the  systemic, 
from  the  left  side  of  the  heart  by  the 
aorta  to  the  arteries  and  capillaries 
of  the  body  tissues  and  organs, 
whence  the  blood  returns  by  the  veins 
to  the  right  side  of  the  heart. 

A  schematic  representation  is 
given  of  the  circulatory  system  in 
the  accompanying  diagram  (Fig.  51). 

The  venous  blood  flows  into  the 
right  auricle  (R.A.)  from  the  superior 
and  inferior  venae  cavae,  and  from  the 
right  auricle  into  the  right  ventricle 
through  the  right  auriculo -ventricular 
orifice.  The  right  ventricle  (R.V.) 
driv^es  through  the  pulmonary  artery 
the  blood  received  from  the  right 
auricle.  The  right  auriculo-ventricular 
valve,  or  tricuspid,  and  the  pulmo- 
nary semilunar  valve,  are  represented 
directing  flow  of  blood  in  this  direction. 
From  the  pulmonary  capillaries 
the  blood  returns  by  the  pulmonary  veins  (P.V.)  into  the  left 
auricle  (L.A.),  and  so  through  the  left  auriculo-ventricular  orifice, 
guarded  by  the  mitral  valve,  into  the  left  ventricle  (L.V.).  By  the 
left  ventricle  the  blood  is  driven  through  the  aortic  orifice,  guarded 
by  the  semilunar  valves,  and  is  distributed  to  the  systemic  arteries, 
and  so  to  the  capillaries  of  the  various  organs  and  back  to  the  veins. 
The  muscular  wall  of  the  auricles,  and  that  of  the  right  ventricle, 

142 


'vc.      \      nv. 


Fig.  51. — Diagram  of  Heart  tu 
SHOW  THE  Course  of  the  Blood. 
(M.  S.  Pcmbrey.) 

S.V.G.,  Superior  vena  cava; /. F.C, 
inferior  vena  cava;  R.A.,  right 
auricle;  T.,  tricuspid  valves; 
R.V.,  right  ventricle;  P.,  pulmo- 
nary valves;  P.  A.,  pulmonary 
artery;  P.V.,  pulmonary  vein; 
L.A.,  left  auricle;  M.,  mitral 
valves;  L.V.,  left  ventricle;  a, 
aortic  valves;  A.,  aorta. 


COURSE  OF  CIRCULATION  IN  MAMMALS  143 

are  much  thinner  than  that  of  the  left  ventricle.  This  is  so  because 
the  energy  required  of  the  left  ventricle  must  exceed  that  of  the  right 
%-cntricle,  inasmuch  as  the  resistance  in  the  systemic  system  exceeds 
that  in  the  pulmonary  circuit. 

The  Cardiac  Cycle. — The  changes  in  form  of  the  heart  can  be  studied 
in  an  animal  the  heart  of  which  has  been  exposed  by  opening  the 
thorax  under  an  ansesthetic,  artificial  respiration  being  meanwhile 
maintained,  the  movements  being  recorded  by  levers  writing  on  the 
kymograph ;  or  the  mammalian  heart  may  be  removed  and  fed  with 
warm  oxygenated  nutritive  fluid  (see  p.  159);  or  the  circulation  may 
be  short-circuited  by  what  is  known  as  the  heart-lung  preparation, 
the  blood  still  being  sent  through  the  lungs  of  the  animal  to  keep  it 
oxygenated  (see  p.  163). 

When  the  heart  is  watched  beating  in  full  vigour  and  rapidity, 
it  is  an  impossible  task  to  unravel  by  the  eye  alone  the  sequence 
of  events. 

Harvey,  the  discoverer  of  the  circulation  of  the  blood,  felt  and 
described  this  difficulty  in  his  wTitings: 

'"  When  first  I  gave  my  attention  to  vivisections,  as  a  means  of 
discovering  the  movements  and  uses  of  the  heart,  and  sought  to 
discover  these  from  actual  inspection,  and  not  from  the  Avritings  of 
others,  I  found  the  task  so  truly  arduous,  so  full  of  difficulties,  that 
I  was  almost  tempted  to  think  (with  Fracastorius)  that  the  movement 
of  the  heart  was  only  to  be  comprehended  by  God;  for  I  could  neither 
rightl}^  perceive  at  first  when  the  systole  and  when  the  diastole  took 
place,  nor  when  and  where  dilatation  occurred,  by  reason  of  the 
rapidity  of  the  movements,  which  in  many  animals  is  accomplished 
in  the  twinkling  of  the  eye,  coming  and  going  like  a  flash  of  lightning: 
so  that  the  systole  presented  itself  to  me,  now  from  this  point,  now 
from  that,  the  diastole  the  same;  and  then  everything  was  reversed, 
the  movements  occurring,  as  it  seemed,  variously  and  confiLsedly 
together. 

"  When  the  heart  begins  to  flag,  to  move  more  slowly,  and,  as  it 
were,  to  die,  the  movements  then  become  slower  and  rarer,  the  pauses 
longer,  by  which  it  is  made  much  more  easy  to  perceive  and  unravel 
what  the  movements  really  are,  and  how  they  are  performed. 

'■  In  the  pause,"  Harvey  sslys,  "as  in  death,  the  heart  is  soft, 
flaccid,  exhausted,  lying,  as  it  were,  at  rest.     In  the  movement  and* 
interval  in  which  this  is  accomplished,  three  principal  circumstances 
are  to  be  noted : 

"  1.  That  the  heart  is  excited,  and  rises  upward,  so  that  at  this 
time  it  strikes  against  the  breast,  and  the  pulse  is  felt  externally. 

"  2.  That  it  is  everywhere  contracted,  but  more  especially  towards 
the  sides,  so  that  it  looks  narrower,  relatively  longer,  and  more  drawn 
together. 

"  3.  The  heart,  being  grasped  in  the  hand,  is  felt  to  become  harder 
during  its  action.  Now  this  hardness  proceeds  from  tension,  precisely 
as,  when  the  forearm  is  grasped,  its  tendons  are  perceived  to  become 
tense,  and  resilient  when  the  fingers  are  moved. 


144 


A  TEXTBOOK  OF  PHYSIOLOGY 


■•  4.  Jt  may  further  be  observed  in  fishes  and  the  colder-blooded 
-animals,  such  as  frogs,  serjients,  etc.,  that  the  heart,  when  it  moves, 
becomes  of  a  j)aler  colour;  when  quiescent,  of  a  deeper  red  colour. 

■•  There  is  also  to  be  noticed  in  the  heart  a  certain  obscure  un- 
dulation and  lateral  inclination  in  the  direction  of  the  axis  of  the 
ri^'ht  ventricle,  as  if  twisting  itself  shghtly  in  jDcrforming  its  work." 

Analyzing  the  movements  of  the  chambers  of  the  heart,  Harvey 
•determined  that: 

•'  First  of  all  the  auricle  contracts,  and  in  the  course  of  its  contrac- 
tion forces  the  blood  (which  it  contains  in  ample  quantity  as  the  head 
of  the  veins,  the  storehouse,  and^cistern  of  the  blood)  into  the  ventricle, 
Avhich  being  filled,  the  heart  raises  itself  straightway,  makes  all   its 


I  1       1       1        . 

■f^.   '  'T^ 

Kk 

I  •^B      ^i^V     JiK ' 
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t 

^li 

Fie.  52. — Serial  Photogeaphs  of  the  Perfused  Heart  of  the  Frog,  from   a 
Cinematograph  Film;  Fifteen  Images  per  Second.     (G.  R.  Mines.) 


fibres  tense,  contracts  the  ventricles,  and  performs  a  beat,  by  which 
» beat  it  immediately  sends  the  blood  sujiplied  to  it  by  the  auricle  into 
the  arteries." 

A  cinematograph  record  of  the  movements  of  a  frog's  heart  is 
seen  in  Fig.  52. 

Movements  oJ  the  Heart. — The  movements  of  the  heart  consist  of 
a  period  of  contraction,  which  is  called  the  systole,  and  a  period  of 
relaxation,  the  diastole.  The  two  auricles  contract  at  the  same  time, 
followed  by  the  synchronous  contraction  of  the  ventricles.  Finally, 
there  is  a  period  when  the  whole  heart  is  in  a  state  of  relaxation. 
This  sequence  of  events  is  known  as  the  cardiac  cycle.  Taking 
seventy-five  as  the  average  number  of  heart-beats  per  minute,  each 
cardiac  cycle  will  occupy  0-8  second. 


COURSE  OF  CIRCULATION  IN  MAMMALS 


U5 


-By  some  it  is  believed  that  the  right  auricle  contracts  very  shortly 
before  the  left  auricle,  and  the  left  ventricle  before  the  right  ventricle. 
Of  this  period  of  0-8  second — 

Auricular  S3'stole  occupies  about  0-1  second. 

,,        diastole         ,,  ,,      0'7        „ 

Ventricular  systole        „  ,,      0*3        „ 

,,  diastole       ,,  „      O-o        „ 

The  sequence  and  duration  of  the  events  happening  in  the  heart, 
and  the  pressure  inside  the  heart — the  endocardiac  pressure — are 
studied  by  means  of  an  instrument  termed  the  "  cardiac  sound." 
The  sound — a  two-way  tube — is  pushed  down  the  jugular  vem  until 


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Fig.  53. — Tracings  from  the  Heart  of  a  Horse,  by  Chauveatj  and  Marey. 

The  upper  tracing  is  from  the  right  auricle,  the  middle  from  the  right  ventricle,  and 
the  lowest  from  the  apex  of  the  heart.  The  horizontal  lines  represent  time, 
and  the  vertical  amount  of  pressure.  The  vertical  dotted  lines  mark  coincident 
points  in  the  three  movements.  The  breadth  of  one  of  the  small  squares  repre- 
sents one-tenth  of  a  second.  The  auricular  contraction  is  less  sudden  than 
the  ventricular,  and  lasts  only  a  very  short  time,  as  indicated  by  the  line  a  h. 
The  ventricle,  on  the  other  hand,  contracts  suddenly  and  forcibly  and  remains 
contracted  a  considerable  time,  as  shown  by  the  line  c'  d'  and  by  the  flat  top 
to  the  curve  which  succeeds  d' . 


the  orifice  of  one  tube  lies  in  the  right  ventricle,  and  of  the  other  in 
the  right  auricle.  The  cardiac  orifices  of  the  tubes  are  covered  with 
rubber  membrane,  beneath  which  are  wire  springs  set  to  resist  com- 
pression. The  tubes  are  connected  with  recording  tambours,  which 
AVTite  on  a  moving  drum  covered  with  smoked  paper.  Another 
tambour  may  be  used  to  record  the  cardiac  impulse.  The  aortic 
pulse  curve  may  also  be  recorded  in  other  experiments  simultane- 
ously with  the  left  intraventricular  pressure.  This  is  effected  by 
pushing  the  sound  down  the  carotid,  so  that  one  tube  opened  into  the 
aorta  and  the  other  into  the  left  ventricle.     The  tracings  so  obtained 

10 


140 


A  TEXTBOOK  OF  PHV.SIOl.OOY 


(Fig.  ~)2)  teach  us  the  following  facts:  (1)  The  auricular  contraction 
is  less  siuklcn  than  the  ventricular,  and  lasts  only  a  v^ery  short  time, 
The  ventricle,  on  the  other  hand,  contracts  suddenly  and  forcibly, 
and  remains  contracted  a  considerable  time,  as  shown  respectiv^ely 
by  the  ascent  of  the  curve  and  the  flat  top  of  the  curve  which  succeeds. 

(2)  The  aiiricular  movement  precedes  the  ventricular,  and  the  latter 
coincides  with  the  impulse  of  the  apex  against  the  wall  of  the  chest. 

(3)  The  contraction  of  the  auricle  influences  the  pressure  in  the  ven- 
tricle, as  shown  by  the  small  rise  a'  b',  and  that  of  the  ventricle  influ- 
ences the  pressure  in  the  auricle  somewhat,  as  shown  by  the  wave  c'  d'. 

A  tracing  of  aortic  and  intraventriculFjr  pressure  curves  is  given  in 
Fig.  54.  The  beginning  of  the  aortic  pulse  curve  (I)  obviously  marks 
the  opening  of  the  semilunar  valves,  the  dicrotic  notch  (4)  follows  their 
closure.  The  moment  of  closure  (3)  can  be  ascertained  by  listening  to 
the  second  sound  of  the  heart,  which  occurs  immediately  after  the 
closure,  and  is  produced  by  the  sudden  tension  of  the  closed  valves.     It 


Fig.  54. — Aortic  and  Intraventricular  Pressure  Curves.     (Hiirthle.) 

Time  trace=  j-J^^  sec;  O'l,  period  of  rising  tension;  1-4,  period  of  output;  4,  dicrotic 

notch. 


can  also  be  determined  by  connecting  the  two-way  sound  to  a  differential 
manometer,  and  recording  the  difference  of  pressure  in  the  ventricle 
and  aorta.  The  valves  open  at  the  moment  when  the  ventricular 
pressure  exceeds  the  aortic,  and  close  when  the  aortic  exceeds  the 
ventricular  pressure.  If  the  differential  manometer  be  used,  with, 
one  sound  opening  in  the  right  auricle  and  the  other  in  the  right 
ventricle,  the  tracing  indicates  the  moment  when  the  auriculo-ven- 
tricular  valves  close  and  open. 

The  absence  of  a  mechanism  for  preventing  regurgitation  of  blood 
from  the  auricles  of  birds  and  mammals  is  remarkable,  for  in  fishes,, 
amphibia,  and  reptiles,  this  is  effected  by  valves  guarding  the  sinu- 
aurictilar  junction  (Fig.  2(3).  In  the  warm-blooded  vertebrates,  with  the 
appearance  of  the  diaphragm  and  the  fusion  of  the  sinus  vcnosus  with 
the  right  auricle,  the  venous  cistern  formed  b}^  the  sviperior  and  inferior 
vense  cavse,  the  innominate,  iliac,  hepatic,  and  renal  veins  takes  the 
place  of  the  sinus.     Six  pairs  of  valves  prevent  regurgitation  from  this. 


COURSE  OF  CIRCULATION  IX  MAMMALS 


147 


cistern — viz.,  those  placed  in  the  common  femoral,  the  subclavian, 
and  jugular  veins  (Fig.  55).  The  cistern,  when  filled,  may  hold  some 
400  c.c.  of  blood.  In  the  liver  there  may  be  some  500  c.c.  of  blood. 
This  can  be  expressed  into  the  cistern  by  abdominal  pressure.  In 
the   i^ortal   venous   system,    when  distended,    may   be   held   another 


If-  oiniiich 


f^r-l    IthO 


Fig.  5o. — Diagram  of  the  Venous  Cistern  from  which  the  Heart  is  Filled 

(Keith.) 

The  abdommal  or  infra-diaphragmatic  part  of  the  cistern  is  indicated  in  black;  the 
thoracic  or  supra-diaphragmatic  is  stippled.  The  heart  is  compressed  upwards 
and  backwards  against  its  attachments. 


500  c.c,  which  can  be  expressed  through  the  portal  veins  and  the 
liver  into  the  cistern.  There  is  thus  a  large  volume  of  blood  for  the 
heart  to  draw  upon  during  diastole,  and  this  may  be  of  particular 
value  during  the  performance  of  a  great  muscular  effort.  Respiration 
bj^  the  aspirating  action  of  the  thorax  sucks  this  blood  into  the  heart, 
while  the  inspiratory  descent  of  the  diaphragm  squeezes  the  abdominaf 


14S  A  TEXTBOOK  OF  PHVSIO.LOOY 

contents  and  forces  blood  from  the  liver  and  cistern  into  the  heart. 
These  forces  take  the  place  of  the  sinus  venosus,  and  are  far  more 
efficient.  The  intra-abdominal  pressure  may  be  raised  considerably 
on  bending  or  straining.  Under  such  conditions,  the  pericardium 
protects  the  right  side  of  the  heart  from  being  over-distended  with 
venous  blood. 

With  these  facts  in  view,  we  can  now  describe  the  complete  course 
of  a  cardiac  cycle  (Fig.  56).  We  Avill  start  at  the  moment  when  both 
chambers  of  the  heart  are  in  diastole.  The  blood  pours  from  the  vena 
cava  and  pulmonary  veins  into  the  two  auricles.  These  are  relaxed,  and 
their  cavities  open  into  the  ventricles  by  the  funnel-shaped  apertures 
formed  by  the  dependent  segments  of  the  tricuspid  and  mitral  valves. 
The  blood  passes  freely  through  these  apertures  into  the  ventricles. 
The  small  positive  pressure  which  is  always  present  in  the  venous 
cistern  (aided  by  the  respiratory  forces)  is  at  this  time  filling  both 
chambers  of  the  right  heart,  while  the  positive  pressure  in  the  pul- 
monary veins  is  filling  those  of  the  left  heart.  The  auricular  systole 
now  takes  place.  Their  circular  muscle  bands  compress  the  blood  out 
of  the  auricles  into  the  ventricles,  while  the  longitudinal  bands  aid 
in  this,  and  also  pull  up  the  base  of  the  ventricles  to  meet  the  load  of 
blood  (Fig.  58).  As  the  contraction  starts  from  the  mouths  of  the 
vena  cava,  and  sweeps  towards  the  ventricles,  little  or  no  regurgita- 
tion of  blood  occurs  into  the  venous  cistern  under  normal  conditions, 
but  the  cessation  of  flow  into  the  auricle  during  its  systole  does  produce 
a  slight  rise  of  pressure  in  the  cistern,  which  is  shown  by  the  wave  a 
in  tracings  taken  from  the  jugular  pulse  (see  Fig.  116).  The  function 
of  the  auricles  is  to  rapidly  complete  the  filling  of  the  ventricles,  and 
thereby  slightly  distend  its  walls.  Within  normal  limits,  the  greater 
the  distension  the  more  forcible  the  contraction. 

The  auriculo-ventricular  valves  are  floated  up  and  brought  into 
apposition  by  eddies  set  up  in  the  blood  which  streams  into  the  ven- 
tricles, and  close  without  noise  or  jar  at  the  moment  when  the  intra- 
ventricular pressure  in  the  least  exceeds  that  in  the  auricles.  The  thin, 
moist,  film-like  edges  of  the  tricuspid  and  mitral  valves  of  the  heart 
come  into  perfect  apposition,  and  prevent  all  leakage,  while  the  fibrous 
parts  give  strength  and  support.  Then  follows  ventricular  systole 
{A,  Fig.  56).  The  contraction  of  the  ventricular  musciilature  around 
these  orifices  limits  the  size  of  the  auriculo-ventricular  orifices,  and 
maintains  the  competency  of  the  valves.  By  contracting  synchron- 
ously with  the  muscular  wall  of  the  ventricles,  the  papillary  muscles, 
with  the  aid  of  the  chordae  tendinese,  pull  down  the  diaphragm  formed 
by  the  closed  auriculo-ventricular  valves.  As  these  form  the  floor  of 
the  auricles,  their  cavities  are  thereby  expanded.  At  the  same  time, 
the  papillary  muscles  shorten  the  longitudinal  diameter  of  the  ventricles, 
and  enable  the  valvular  and  muscular  parts  of  the  ventricles  to  approach 
together  and  squeeze  out  the  blood  from  the  ventricles.  By  the 
attachment  of  the  chordae  tendinese  to  the  auriculo-ventricular  valves, 
and  the  action  of  the  papillary  muscles,  the  membranous  diaphragm 
formed  by  the  valves  is  made  to  act  as  part  of  the  muscular  wall  of 


COURSE  OF  CIRCULATION  IN  MAMMALS 


149 


each  ventricle,  and  thus  the  cavity  of  each  comes  to  be  equivalent 
to  a  sphere  surrounded  by  muscle. 

When  the  intraventricular  pressure  rises  the  least  bit  above  that 
in  the  pulmonary  artery  and  aorta  respectively,  the  semilunar  valves 


O.Ssec. 


Fig.  56. — The  Time  Relations  of  the  Impulse,  Intra-Aueicular  and  Ventric- 
ular, AND  Arterial  Pressure  Curves.  (Modified  from  Hiirthle;  L.H.,  from 
AUc bin's  "Manual  of  Medicine.") 

A,  The  beginning  of  ventricular  systole;  B,  tbe  oiDening  of  tbe  semilunar  valves j 
J-J5, period  of  rising  tension;  (7,  the  closure  of  the  semilunar  valves;  A-C,  period 
of  output  (systole);  D,  the  beginning  of  the  dicrotic  wave  on  the  pulse  curve; 
C-E,  period  of  diastole ;  E,  the  beginning  of  the  next  cardiac  cycle.  The  dura- 
tion of  the  first  and  second  sound  of  the  heart  is  marked  below  the  intra-auric- 
ular  pressure  curve.  The  pressures  arc  given  in  mm.  Hg.  The  waves  on 
the  plateau  of  the  ventricular  curve  are  due  to  elastic  vibrations  and  are  partly 
instrumental;  the  first  fall  in  the  curve  of  auricular  pressure  is  produced  by  the 
systolic  output  of  blood ;  the  second  auricular  fall  is  due  to  ventricular  diastole. 
The  high-pressure  pulse  is  anacrotic. 

quietly  open  {B,  Fig.  56)  and  the  blood  is  expelled.  The  elastic  vessels 
are  in  their  turn  expanded  by  the  expulsive  force  of  the  heart,  so  as 
to  receive  the  blood. 

The  outflow  of  blood  from  the  ventricles  is  rapid  at  first.     It 
becomes  slower  as  the  arteries  become  distended  and  the  pressure  of 


150 


A  TEXTBOOK  OF  PHYSIOLOGY 


blood  rises  within  them,  and  ceases  when  the  arterial  pressure  becomes 
equal  to  that  iii  the  ventricles.  As  the  outflow  diminishes,  the  semi- 
lunar pockets  are  filled  by  eddies  of  blood,  and  their  thin,  delicate 
«dges  are  biought  nearer  and  nearer,  until  finally  they  come  into 
apposition.  This  closure,  which  effectually  iDrevents  regurgitation, 
is  effected  without  jar  or  noise  at  the  moment  when  the  outflow  ceases 
and  the  ventricles  begin  to  expand.  The  heart,  as  a  good  ]iuni]) 
should,  works  with  the  least  possible  jar.  During  the  contraction 
of  the  ventricles,  blood  has  been  pouring  from  the  veins  into  the 
auricles;  and  directly  the  ventricular  systolS  ceases,  the  auriculo- 
ventricular  valves  open,  and  the  blood  begins  to  fill  the  expanding 
ventricular  cavities.  For  a  brief  moment  the  ventricles  remain  dilated 
and  at  rest,  then  the  auricles  contract  again,  and  the  cycle  of  changes 
once  more  is  repeated.  During  the  first  period  of  ventricular  systole 
— the   period    of   rising    tension    (A-B,    Fig.    56),    or    "  presphygmic 


A  B 

Tig.  57. — Diagram  of  Right  Side  of  Heaet,  showing  A,  Systole- AiTRif:uLo- 
Ventrictjlar  Valves  Shut,  Chords  Tendine.^  drawn  Tattt,  Semilunar 
Valves  of  Pulmonary  Artery  Open.  B,  Diastole- Auriculo-Ventric- 
ular  Valves  Open,  Blood  entering  from  Auricle  to  Ventricle,  Semi- 
lunar Valves  of  Pulmonary  Artery  Shut. 


interval,"  as  it  is  called — all  the  valves  are  closed,  and  the  ventricle 
is  getting  up  pressure.     This  period  has  been  measured,  and  has  been 
found   to   occupy   about    0-02    to    ()-04  second.     The  second  period 
is  that  of  the  systolic   output    (B-(\   Fig.  56),  and   lasts  about  0-2 
second— that  is,  from  the  moment  when  the  semilunar  valves  open 
to  the  moment  when   they  close.     These  periods  can    be    measured 
on  man  by  taking  simultaneous  records  of  the  pulse  in  the  carotid 
artery   and   of  the    cardiac    impulse   and   sounds.     The  ujjstroke   of 
the    pulse-curve    recorded     from    the    carotid    artery   can    be    taken 
as   marking    the    moment    when    the    semilunar   valves    open,    while 
the    dicrotic   notch    on    the    pulse-curve    marks   their    closure.     The 
second  sound  of  the  heart  occurs  immediately  after  their  closure, 
fnd,  by  listening  to  it,  one  can  note  the  time  of  this  event  on  the 
impulse-curve,  the  upstroke  of  which  marks  the  beginning  of  ven- 
tricular systole.     Thus,  the  presphj'gmic  interval  extends  from  the 


COURSE  OF  CIRCULATION  IN  MAMMALS 


151 


beginning  of  the  upstroke  of  the  impulse-curve  to  the  beginning  of 
the  upstroke  of  the  carotid  pulse-curve.  The  first  sound  of  the  heart 
is  synchronous  with  the  upstroke  of  the  impulse-curve.  A  small  cor- 
rection must  be  made  for  the  delay  in  the  transmission  of  the  pulss 
to  the  carotid  artery.  The  period  of  sj^stolic  output  extends  from  the 
beginning  of  the  upstroke  of  the  2:)ulse-curve  to  the  dicrotic  notch, 
and  the  diastolic  period  from  this  notch  to  the  beginning  of  the  next 
upstroke.  The  relation  of  the  auricular  systole  to  the  ventricular  can 
be  determined  by  simidtaneously  recording  the  pulse  in  the  jugular  vein 
and  carotid  artery.  The  c  wave  in  the  jugular  pulse  is  synchronous 
with  the  upstroke  in  the  carotid  pulse,  and  the  a  wave,  which  precedes 
the  c  wave,  marks  the  auricular  systole  (see  Fig.  116). 

The  intraventricular  pressure  rises  or  falls  during  the  output 
period  according  to  the  state  of  the  peripheral  resistancie.  The 
maximal  systolic  pressure  exerted  by  the  heart  varies  with  the  internal 
tension — that  is,  with  the  degree  of  diastolic  filling  and  obstruction 


SUP:  VEN.-CAV 


/'•.RT:ME.SOCARD 
PERlCARO 

sinus  transv 
v£ncus  mesocaro 
inf:ve:n.cav 

Fi:;.  58. — Heart  pulled  Forwards  to  show  its  Attachment  bv  Arterial  (di) 
AND  Venous  (ce)  Mesccardii.     (Keith.) 


to  outflow.  The  heart-muscle  responds  to  increased  tension  by  a 
greater  output  of  energy,  and  this  it  does  with  little  loss  in  rapidity 
of  action.  By  its  reserve  power  the  heart  may  throw  out  during 
hard  exercise  ten  times  the  volume  of  the  normal  output  per  minute, 
and  may  maintain  its  output  when  the  aortic  pressure  is  even  twice 
its  normal  value. 

The  Movements  of  the  Heart  in  Situ. — The  normal  fulcra  for  the 
movements  of  the  heart  in  the  closed  thorax  are  afforded  through  the 
pericardium  (Fig.  58).  The  pericardium  is  reflected  on  to  the  wall  of  the 
heart  at  the  point  where  the  vena  cava  and  aorta  leave  the  pericardial 
sac.  This  part  of  the  pericardium  gives  a  fixation  point  to  the  auricles, 
being  attached  to  the  roots  of  the  lungs,  and  thereby  to  the  thoracic 
wall,  to  the  diaphragm,  and  to  the  structures  at  the  root  of  the  neck. 
On  opening  the  chest,  the  normal  fulcra  for  the  movements  of  the 
auricles  are  lost,  and  this  renders  it  difficult  to  record  the  exact  move- 
ments of  the  heart.     The  longitudinal  and  circular  muscle  fibres  of 


152 


A  TEXTBOOK  OF  PHYSIOLOGY 


the  ventricles  are  antagonists.  The  circular  fibres,  by  their  con- 
traction, tend  to  lengthen  the  apex-base  diameter.  The  longitudinal 
fibres  resist  this,  and  the  two  together  wring  the  blood  out  of  the 
heart.  The  apex  is  maintained  as  a  fixed  point  by  this  antagonistic 
action,  and  thus  the  longitudinal  fibres  are  enabled  to  expand  the 
auricles  by  ]oulling  down  the  floor  of  these  chambers.  This  action  is 
important,  as  it  contributes  to  the  filling  of  the  auricles  simultaneously 
with  the  emptying  of  the  ventricles.  Tracings  of  the  jiigular  pulse 
give  evidence  of  such  action. 

In  the  case  of  the  auricles,  the  longitudinal  musculi  pectinati  not 
only  help  the  circular  fibres  to  expel  the  blood,  but  draw  up  the  base 
of  the  ventricle  to  meet  its  load  of  blood.     Thus,  the  A.-V.  groove  is 


"^_'  ^- 


FiG.  59. — To  SHOW  THE  Antagonistic  Action  of  the  Musculatuees  of  the  Eight 
Auricle  and  Ventricle.     (Keith.) 

.4,  position  of  A,-V.  groove  at  end  of  auricular  systole;  B,  at  end  of  ventricular  systole. 


l^ulled  up  during  auricular  systole,  and  down  during  ventricular 
systole  {A,  B,  Fig.  59).  The  posterior  and  upper  borders  of  the  left 
auricle  lie  against  the  unyielding  structures  of  the  posterior  medi- 
astinum, the  pidmonary  artery,  and  bronchi,  the  floor  and  anterior 
part  being  in  contact  with  the  base  of  the  ventricle  and  ascending 
aorta  respectively.  The  latter  parts  alone  are  free  to  move  during 
systole.  Thus,  the  left  ventricular  base  is  drawn  up  and  the  aorta 
back  on  auricular  systole. 

Modes  of  Examining  the  Living  Heart. — The  physiologist  or  physi- 
cian has  many  means  at  his  disposal  of  examining  the  heart's 
action.     Its    efficiency    may    be    tested    by    noting    how    much    its 


COURSE  OF  CIRCULATION  IN  MAMMALS 


153 


rate  of  beat  is  increased  b}'  taking  exercise  and  also  how  quickly 
the  normal  rate  of  beat  is  resumed  after  such  exercise.  By  palpa- 
tion, with  the  hand  over  the  region  of  the  heart,  its  stroke,  the 
cardiac  impulse,  can  be  felt;  b}^  percussion,  the  anatomical  limits 
of  the  organ  can  be  defined;  by  auscultation  with  the  ear  directly, 
or  with  use  of  the  stethoscope,  the  sounds  of  the  heart  can  be  heard. 
The  cardiac  impulse  can  be  recorded  by  the  tambour  method  of 
registration;  the  heart -sounds  by  means  of  the  microphone  and 
string  galvanometer;  while  the  volume  and  movements  of  the  heart 
can  be  studied  with  the  help  of  the  Rontgen  rays. 


Mitral 


Tricuspid    ~ 


Fig.  00. — Diagram  showing  Surface  Relations  of  Lungs,  Heart,  and  Cardiac 

Valves.     (Cowan.) 


The  Cardiac  Impulse. — The  impulse  is  caused  b}'  the  sudden  harden- 
ing of  the  muscular  mass  of  the  ventricles  against  the  chest  wall.  It 
coincides  with  the  beginning  of  systole.  The  position  at  which  the 
impulse  is  felt  varies  with  the  position  of  the  bod}'.  Normally,  with  the 
bod}^  in  the  supine  position,  the  impulse  is  visible  in  the  fourth  or  fifth 
intercostal  space  2  inches  below  the  nipple  and  3i  inches  from  the  mid- 
sternal  line  (Fig.  60).  In  rising  to  the  standing  posture,  the  impulse  shifts 
its  position  downwards  and  to  the  left  for  4  to  1  inch.  When  a  man 
rolls  over  on  to  his  right  side,  the  impulse  may  shift  from  3  to  4  inches 
to  the  right,  and  disappear  beneath  the  sternum.  Similarly,  on  rolling 
on  to  the  left  side,  the  impulse  shifts  to  the  left  of  the  nipple  line. 


I"i4  A  TEXTBOOK  OF  PHYSIOLOGY 

The  shifting  is  due  to  the  effeet  of  gravity  on  the  lieart.  In  each 
position  a  different  part  of  the  heart  is  brought  in  close  contact  with 
the  chest  wall.  The  chest  wall  is  driven  out  by  the  systole  only 
where  the  heart -muscle  touches  it;  at  other  places  it  is  slightly  drawn 
in.  This  indrawing  is  believed  to  be  due  to  the  expulsion  of  the  blood 
from  the  thorax  by  the  left  ventricle.  The  thorax  being  a  closed 
cavity,  negative  pressure  is  produced  by  each  systole  when  the 
blood  passes  out  by  the.  arteries  of  the  head,  limbs,  and  abdomen. 
This  vacuum  is  filled  by  (1)  the  drawing  of  air  into  the  lungs;  hence 
the  cardio-pnevnnatic  movement,  which  may  be  detected  by  connecting 
a  water  manometer  with  one  nostril,  and  closing  the  other  nostril; 

(2)  the  drawing  of  venous  blood  into  the  great  veins  and  right  auricle ; 

(3)  the  slight  indrawing  of  the  chest  wall.  The  impulse  may  be  re- 
corded by  placing  a  small  cup  or  receiving  tambour  over  the  spot 
where  it  is  most  evident,  and  connecting  the  inside  of  the  cup  by  a 
tube  to  the  recording  tambour.  The  cup  need  not  be  closed  by  a 
rubber  dam,  for  an  air-tight  junction  can  be  effected  by  pressing  it 
upon  the  skin.  The  stroke  of  the  heart  is  transmitted  as  a  wave  of 
comiDression  to  the  air  within  the  system  of  tambours.  The  recording 
tambour  writes  on  a  drum  moved  by  clockwork,  and  covered  with  a 
smoked  paj^er.  From  the  record  so  obtained  we  can  obtain  informa- 
tion as  to  the  time-relations  of  the  heart-beat,  but  no  accurate  in- 
formation as  to  its  energy  or  amount  of  contraction. 

The  Sounds  of  the  Heart. — When  the  ear  is  apjilied  over  the  cardiac 
region  of  the  chest,  or  a  stethoscope  is  employed,  two  sounds  are 
hoard.  The  first,  heard  most  intensely  near  the  apex,  is  a  didler  and 
longer  sound  than  the  second,  which  is  shorter  and  shar-jDer,  and  is 
heard  best  over  the  base  of  the  heart.  The  syllables  lilb,  dnjip,  express 
fairly  well  the  characters  of  the  two  sounds,  and  the  accent  is  on  lub 
when  the  stethescope  is  over  the  apex — thus,  h'lb-dvj^jJ,  Inb-dujjp, 
lib-duj)}) — and  on  the  second  sound  when  over  the  base — thus,  lub- 
d/'ij)]^.  lub-d'pj),  lub-ditpij. 

The  first  sound  is  caused  by  the  sudden  tension  (1)  of  the  cardiac 
muscle;  (2)  of  the  diaphragms  formed  by  the  closed  auriculo-ventricular 
valves;  (3)  of  the  papillary  muscles  and  chordae  tendinese.  This 
sound  is  heard  in  an  excised  mammalian  heart  empty  of  blood ;  there- 
fore it  is  largely  muscular  in  origin.  It  is  not  heard  in  a  turtle's 
heart,  because  this  contracts  too  slowly. 

When  the  sounds  and  the  contraction  are  recorded  together,  the 
record  shows  that  the  first  sound  begins  about  0-01  second  before  the 
cardiogram  marks  the  beginning  of  the  systole,  and  for  the  first  0-06 
second  of  its  duration  this  sound  is  heard  only  over  the  apex  (Fig.  61). 
Over  the  base  of  the  heart  the  first  sound  is  heard  just  at  the  time 
when  the  semilunar  valves  open  and  the  output  begins.  The  first 
ft,ound  ceases  before  the  ventricular  contraction  is  over,  for  it  is  the 
sudden  tension,  not  the  continiiance,  of  contraction  that  causes  it. 
The  beginning  of  the  second*  sound  marks  the  sudden  tension  of  the 
semilunar  valves,  which  immediately  follows  their  closure. 

For  clinical  purposes  it  is  important    to    bear    in   mind  what  is 


COURSE  OF  CIRCULATION  IN  MAMMALS 


155 


happening  in  the  heart  whilst  one  hstens  to  its  sounds.  During  the 
first  sound  we  have  (1)  contraction  of  the  ventricles,  closure  of  the 
auriculo -ventricular    valves,    and   impulse    of   the    apex    against   the 


m 


Via.  <>1. — Electro-Cakdiosram,  Carotid   Pjlss  CuitvE,   amd   Heart   Sounds  of 

A  Dog.     (T.  ].o.vis.) 

Tho  sounds  are  recorded  ))y  a  microphone  titted  to  a  stethoscope  connected  with 
a  second  st'ino-  sjalvanonioter. 


Fia.  ()2. — Electro-Cardiogram  and  Rough  Aortic  Murmu.i  in  Man.     (T.  Lewis.) 

chest;  (2)  rushing  of  the  blood  into  the  aortic  and  pulmonary  artery, 
and  filling  of  the  auricles.  With  the  second  sound  we  have  closure 
of  the  semilunar  valves  from  the  elastic  recoil  of  the  aorta  and  pul- 


!,-)() 


A  TEXTBOOK  OF  PHYSIOLOGY 


monary  artery,  relaxation  of  the  ventricular  walls,  opening  of  the 
a\n-icnlo-ventricular  valves  so  as  to  allow  the  passage  of  blood  from 


^ 


auricle  to  ventricle,  and  diminished  pressure  of  ajDex  against  chest 
wall.  During  the  long  pause  there  are  taking  place  (1)  gradual  re- 
filling of  the  ventricle  from  the  auricle ;   (2)  contraction  of  the  auricle 


COURSE  OF  CIRCULATION  IN  MAMMALS  157 

so  as  to  entirely  fill  the  ventricle.  The  sound  of  the  tricuspid  valve 
is  heard  loudest  at  the  junction  of  the  fourth  right  costal  cartilage 
with  the  sternum,  that  of  the  mitral  over  the  apex  beat,  that  of  the 
aortic  semilunar  valves  in  the  direction  of  the  aorta,  where  it  comes 
nearest  to  the  surface  at  the  second  right  costal  cartilage — the  pul- 
monary— to  the  left  and  external  to  the  margin  of  the  sternum.  The 
sounds  are  changed  in  character  by  valvular  lesion  (Figs.  62  and  63) 
or  muscular  weakness  of  the  heart,  and  afford  important  signs  to  the 
physician. 

Murmiu-s  are  produced  by  eddies  setting  some  part  of  the  mem- 
branous walls  or  valve  flaps  in  vibration.  Thus,  if  a  fine  instrument 
provided  Avith  a  hook  be  passed  down  the  carotid  into  the  aorta, 
and  the  aortic  valves  are  torn  and  rendered  incompetent,  a  murmur 
results.  Inflammation,  shrinkage,  and  incompetence  of  the  valves 
results  from  rheumatic  and  other  infections. 

If  a  stethoscope  be  placed  over  a  large  artery,  a  murmur  will  be 
heard,  caused  b}"  the  blood  rushing  through  the  vessel  narrowed  by 
the  pressure  of  the  instrument.  The  fluid  escapes  into  a  wider  portion 
of  the  vessel  beyond  the  point  of  pressure,  and  the  sound  is  caused 
by  the  eddies  set  up  there  throwing  the  membranous  wall  of  the  vessel 
into  vibration.  Such  a  sound  is  heard  over  an  aneurism.  The 
placental  bruit  heard  during  pregnancy  is  a  sound  of  this  kind,  arising 
from  pressure  on  the  uterine  arteries.  In  cases  of  insufficient  aortic 
valves  a  double  blowing  murmur  may  be  heard,  the  first  being  due  to 
the  rush  of  blood  into  the  vessel,  and  the  second  by  the  regurgitation 
of  the  blood  back  into  the  ventricle.  These  murmurs  are  produced  by 
eddies  of  blood  setting  the  membranous  parts  into  vibration. 

Occasionally  a  murmur  seems  to  be  produced  by  the  displacement 
of  air  in  the  bronchial  vessels  by  the  beat  of  the  heart,  and  may  simulate 
the  murmur  of  aortic  incompetence.  By  placing  a  stethoscope  over 
the  jugular  vein  on  the  right  side,  and  above  the  collar-bone,  a  murmur 
is  heard — the  bruit  de  diable — particularly  if  the  subject  turn  his  head 
to  the  left.  This  is  held  to  be  due  to  the  vibration  of  the  blood  in  the 
jugular  vein  rushing  from  the  dilated  to  the  contracted  part.  It  is 
more  marked  during  auricular  diastole  and  during  inspiration. 


CHAPTER  XVIII 
THE  NUTRITION  OF  THE  HEART 

In  the  lower  vertebrates,  such  as  the  frog,  the  heart  is  directly 
nourished  by  the  blood  which  fills  the  cavities  in  its  sponge-like  struc- 
ture. In  the  warm-blooded  vertebrates,  there  is  a  special  arrange- 
ment of  coronar\-  vessels.  The  two  coronary  arteries  (right  and  left) 
originate  at  the  root  of  the  aorta  from  bulgings  of  the  aortic  walls — 
the  sinuses  of  Valsalva.  The  sinuses  are  three  in  number,  corre- 
sponding to  the  number  of  cusps  of  the  semilunar  valves.  The 
right  coronary  artery  arises  from  the  anterior  sinus,  the  left  coronary 
artery  from  the  left  posterior  sinus.  Their  branches  penetrate  the 
muscular  substance,  and  end  in  a  rich  plexus  of  capillaries.  From 
these  arise  the  radicles  of  the  coronary  veins,  which  open  into  the 
right  auricle  by  the  coronary  sinus  and  other  small  veins.  These 
openings  are  valved  by  remnants  of  the  primitive  sinus  venosus.  The 
heart,  in  contracting,  exerts  a  greater  pressure  than  that  of  the 
coronary  arteries,  and  so  arrests  the  flow  in  these  during  the  height 
of  systole,  and  squeezes  the  blood  within  the  coronary  capillaries 
and  veins  on  into  the  right  auricle.  On  diastole,  the  coronary  system 
fills  again.  8udden  occlusion — e.g.,  by  the  injection  of  paraffin — of 
any  large  part  of  the  coronary  arteries  produces  irregular  and  inco- 
ordinate contractions — "  fibrillation,"  as  it  is  called — followed  by 
death  of  the  heart.  Degeneration  of  the  coronary  arteries  in  advanced 
life  is  associated  with  a  distressing  form  of  cardiac  illness  known  as 
"  angina  pectoris."'  The  great  anatomist  John  Hunter,  who  died 
after  a  heated  debate,  was  found  by  Jenner  to  have  calcified  coronary 
arteries. 

It  has  long  been  known  that  the  heart  of  the  frog  or  tortoise  can 
be  kept  beating  normally  for  hours  after  removal  from  the  body, 
particularly  if  it  is  provided  with  a  suitable  solution  of  salts.  Ringer 
worked  out  the  necessary  ingredients  of  this  solution  to  be :  sodium 
chloride,  0-7  per  cent.;  potassium  chloride,  0-03  per  cent.;  calcium 
chloride,  0-02")  per  cent. 

The  excised  mammalian  heart  can  be  kept  beating  in  the  same 
way,  provided  the  nutritive  fluid  is  oxygenated  and  the  heart  kej)t 
at  body  temperature.  A  solution  containing  one-third  defibrinated 
blood  and  two-thirds  Ringer's  salt  solution  is  especially  suitable. 
The  beat  of  the  heart  of  a  child  was  restored  thereby  twenty  hours 
after  death  from  pneumonia;  the  excised  heart  of  a  cat  was  kept 
beating   for  four  days;    the  heart   of  a   monkey  was   restored  after 

158 


THE  NUTRITION  OF  THE  HEART  159 

freezing  the  aniinal.  The  nex-ves  of  the  excised  heart  retain  their 
action  for  some  time  if  the  nutritive  flvxid  is  immediately  circulated 
through  the  coronary  arteries.  Thus,  the  heart's  action  can  be  con- 
veniently studied  when  taken  from  the  body  of  a  mammal. 

By  using  defibrinated  blood  mixed  with  the  perfusion  fluid  food 
material  is  brought  to  the  heart.  By  some  it  is  considered  that  the 
serum  albumin  is  the  essential  substance.  In  Locke's  fluid*  dextrose 
is  added  to  the  above  salts,  and  this  forms  an  admirable  perfusion 
fluid.  But  the  heart  will  beat  when  supplied  with  oxygenated  Ringer's 
solution  only :  neither  the  serum  albumin  nor  the  dextrose  appfear  to 
be  necessary.  The  important  factors  are  the  free  ions  of  sodium,  potas- 
sium, and  calcium,  and  certain  concentrations  of  these  appear  to  be 
absolutely  necessary  for  the  rhythmic  automaticity  and  efficient 
working  of  the  heart.  With  increase  of  the  contents  of  the  calcium, 
ions  the  heart  contracts  more  powerfully  (Fig.  64).  If  the  amount 
of  calcium  be  large  the  heart  relaxes  less  and  less  completely,  and 
eventually  stops  in  a  state  of  tonic  contraction. 


Fig.  ()1. — Isolated  Rabbit's  Heart  perfused  with  Locke's  Solutiox.     (Dixon.) 
At  the  arrow  5  mgrm.  of  calcium  chloride  were  given.     Time  in  seconds. 

Excess  of  the  potassium  ions  has  an  oj^ijosite  effect  (Fig.  65).  The  beat 
of  the  heart  becomes  more  and  more  feeble,  and  it  ceases  to  beat  in  a 
state  of  complete  relaxation  (diastole).  Excess  of  the  sodium  ion 
causes  the  beat  of  the  heart  to  become  weaker  and  weaker,  and 
eventually  fail  altogether  (also  in  diastole).  There  is  therefore  an 
antagonism  between  the  calcium  ions  and  those  of  sodium  and 
potassium. 

The  origin  of  the  excitatory  wave  is  intimately  dependent  upon 
interaction  between  these  ions  and  the  colloids  of  the  heart  muscle, 
those  of  calcium  playing  a  prominent  part  in  the  contraction  of  the 
heart,  those  of  potassium  in  its  relaxation. 

If  the  heart  is  treated  with  lactic  acid  until  it  is  brought  to  a 
standstill  in  diastole,  it  can  be  j^artly  restored  by  increasing  the  con- 
centration of  calcium  in  the  Ringer's  solution,  and  completely  restored 

*  Locke's  fluid  is  distilled  water,  100  c.c. ;  sodium  chloride,  0-9  gramme;  potassium 
chloride,  0-042  gramme;  calcium  chloride,  0-04S  gramme;  sodium  bicarbonate,  0-0'? 
gramme;  dextrose,  0''2  gramme.  .   .. 


160  A  TEXTBOOK  OF  PHYSIOLOGY 

by  then  perfusing  with  a  high  concentration  of  iwtassiuni  sahs,  sub- 
sequently washed  out  by  physiological  saline. 

Potassium  itself  may  restore  the  heart  from  a  lactic  acid  diastole, 
but  not  so  completely  as  the  combination  of  calcium  and  potassnim. 
The  fact  that  the  heart  can  be  restored  from  diastole  induced  by 
lactic  acid  by  a  high  concentration  of  ])otassium,  which  is  jxjisonous 


Fig.  65. — Isolated  Rabbit's  Heart  perfused  with  Ringer's  Solution.     (Dixon.) 

In  I., 0*2  per  cent,  potassium  chloride  .added  to  the  fluid.     11.  shows  gradual  recovery 

when  KCl  withdrawn. 

to,  and  induces  complete  relaxation  in,  the  normal  heart,  shows  how 
far  we  are  from  understanding  the  true  part  played  by  these  ions  in 
relation  to  the  antomaticity  of  the  heart. 

The  Diastolic  Filling  of  the  Heart.— In  the  excised  heart  no 
evidence  of  any  suction  power  has  been  observed;  indeed,  the  heart 
will  only  fill  when  supplied  with   blood  under  a   positive  pressure. 


THE  NUTRITION  OF  THE  HEART  K3I 

Similarly,  when  the    thorax  is   opened,  the   heart   cannot   fill    itself 
unless  aided  by  a  positive  pressure  in  the  veins. 

If  the  pressure  in  the  vense  cavse  were  not  positive,  then  negative 
pressure  occurring  in  the  heart  cavities  would  lead  to  a  collapse  of  the 
thin- walled  venae  cavae,  and  not  to  suction  of  blood  from  the  veins. 
In  hydraulic  engineering,  the  efforts  of  engineers  are  directed  towaids 
making  the  water  enter  the  system  without  shock.  If  the  negative 
pressure  had  any  sudden  and  decided  action,  there  would  be  shock 
and  consequent  loss  of  energy. 

The  driving  force  of  the  heart  is  sufficient  by  itself  to  maintain, 
at  any  rate  for  a  time,  and  in  the  horizontal  position  of  the  animal,  a 
circulation  when  the  thorax  is  opened,  artificial  respiration  established, 
and  the  muscles  paralyzed  by  injection  of  curari.  Under  these  con- 
ditions, the  circulation  may  fail  altogether  in  the  vertical  posture 
when  gravity  opposes  the  return  (see  later,  the  effect  of  posture,  p.  11)4). 

Normally,  the  filling  of  the  heart  is  largely  under  the  control  of 
the  respiratory  pump.  In  the  closed  thorax,  the  pressure  is  less  than 
that  of  the  atmosphere  by  that  amount  which  is  required  to  overcome 
the  pulmonary  elasticity  and  expand  the  lungs  to  the  size  of  the  thoracic 
cavity.  In  ordinary  inspiration,  this  pressure  is  equivalent  to  9  mm. 
Hg;  in  the  position  of  the  deepest  inspiration,  it  may  sink  to  30  mm. 
Hg.  On  the  one  hand,  the  extrathoracic  veins  are  under  a  pressure 
made  jjositive  by  the  compressive  action  of  the  skeletal  muscles, 
contraction  of  muscular  walls  of  viscera,  and  the  respiratory 
pump;  on  the  other  hand,  the  intrathoracic  veins  and  the  heart 
are  under  a  slight  negative  pressure,  which  in  inspiration  may 
become  9  to  30  mm.  Hg.  The  venous  blood  is  thus  pressed  and 
aspirated  into  the  heart  from  the  venous  cistern.  Each  descent  of 
the  diaphragm  compresses  the  abdominal  organs,  and  if  in  sequence 
to,  or  synchronously  with,  the  inspiratory  movements  of  the  thorax 
the  abdominal  muscles  be  thrown  into  contraction,  then  the  resijira- 
tory  muscles  act  powerfully  on  the  venous  cistern,  not  only  as  a  suction 
but  also  as  a  force  pump.  To  prevent  overdistension  of  the  right 
heart,  the  breath  is  always  held  when  the  abdominal  muscles  are 
forcibly  contracted — e.g.,  on  straining  at  stool,  or  when  the  abdomen 
is  compressed.  The  pericardium,  too,  supports  the  heart  and  limits 
its  distension.  The  venous  cistern  in  its  turn  is  filled  by  the  force 
of  the  heart-beat  (the  vis  a  tergo),  but  in  particular  by  the  muscular 
jnovements  of  the  limbs  and  viscera  aided  by  the  valvular  action  of 
the  veins.  During  any  violent  exercise,  such  as  running,  the  skeletal 
muscles  alternately  contract  and  expand,  and  a  full  tide  of  blood  flows 
through  the  locomotor  organs.  The  stroke  of  the  heart  is  then  both 
more  energetic  and  more  frequent,  and  the  blood  circulates  with  in- 
creased velocity.  Under  these  conditions,  the  filling  of  the  heart  is 
maintained  by  the  pumping  action  of  the  skeletal  and  respiratory 
muscles.  The  abdominal  wall  is  contracted,  and  the  reserve  of  blood 
is  driven  from  the  splanchnic  vessels  to  fill  the  dilated  vessels  of  the 
lo  3omotor  organs.  At  each  respiration  the  pressure  within  the  thoracic 
cavity  becomes  less  than  that  of  the  atmosj)here,  and  the  blood  is 

11 


162  A  TEXTBOOK  OF  PHYSIOLOGY 

aspirated  from  the  veins  into  the  right  side  of  the  heart  and  lungs ^ 
conversely,  at  each  expiration  the  thoracic  pressure  increases,  and  the 
blood  is  expressed  from  the  lungs  into  the  left  side  of  the  heart.  While 
the  respiratory  pump  at  all  times  renders  important  aid  to  the  cir- 
culation of  the  blood,  its  action  becomes  of  supreme  importance  during 
such  an  exercise  as  running.  The  runner  pants  for  breath,  and  this 
not  onl}'  increases  the  intake  of  oxygen,  but  maintains  the  diastolic 
filling  of  the  heart.  It  is  of  importance  to  grasp  the  fact  that  the 
circulation  of  the  blood  depends  not  only  on  the  heart,  but  on  the 
vigour  of  the  respiration  and  the  activity  of  the  skeletal  muscles. 
Muscular  exercise  is  for  this  reason  a  sine  qua  non  for  the  maintenance 
of  vigorous  mental  and  bodily  health. 

An  experiment  which  throws  light  on  the  filling  of  the  heart  is 
the  following:  A  pressure-bottle  filled  with  oil  is  connected  by  a 
T-piece  with  (1)  an  oil  manometer,  (2)  a  tube  tied  into  the  pericardial 
sac.  So  soon  as  the  jaressure  of  the  oil  is  raised  to  60  to  70  mm. 
oil,  the  arterial  pressure  falls  by  20  to  30  mm.  Hg,  while  the  vena 
cava  pressure  rises  to  about  5  mm.  Hg.  By  a  pressure  of  at  most 
240  to  300  mm.  oil,  the  arterial  pressure  is  brought  to  zero.  By 
no  possible  means  in  the  anajsthetized  animal  can  the  vena  cava 
pressure  rise  beyond  this  pressure,  and  thus  the  heart  is  unable  to 
fill.  The  quantity  of  blood  thrown  into  the  aorta  by  each  contrac- 
tion of  the  left  ventricle  must  correspond  to  that  entering  the  right 
ventricle  during  diastole,  otherwise  the  blood  will  become  congested 
in  the  veins,  and  the  circulation  quickly  come  to  an  end. 

In  the  dog,  either  the  vena  cava  superior,  or  the  vena  cava  inferior 
below  the  liver  may  be  completely  occluded,  and  yet  no  change  of 
pressure  in  arterial  pressure  is  indicated  by  the  arterial  manometer. 
If  on  the  other  hand  the  vena  cava  inferior  between  the  liver  and  the 
heart  be  compressed,  there  occurs  an  immediate  and  marked  descent 
of  the  arterial  pressure.  Thus  a  rabbit,  in  which  the  portal  vein  has 
been  ligatured,  perishes  within  a  few  minutes,  owing  to  the  rapid 
accumulation  of  the  blood  in  the  portal  tributaries.  The  capacity 
of  these  is  so  great  that  they  are  sufficient  to  hold  all  the  blood;  the 
plasmia,  too,  rapidly  leaks  out  of  the  capillaries  when  the  circulation  is 
thus  arrested.  The  filling  of  the  heart  is  thus  enormously  diminished 
while  the  aorta  continues  to  empty  itself  by  its  elastic  reaction  into 
these  veins. 

On  occluding  the  jnilmonary  artery  of  an  animal  the  left  heart 
empties,  and  the  arterial  pressure  falls  towards  zero.  The  pressure 
in  the  vense  cavse  rises,  but  only  by  a  very  few  millimetres  of  Hg. 
If  one  vena  cava  be  half  occluded,  the  venous  pressure  rises  distal  to 
the  obstruction,  but  only  by  a  few  millimetres  of  Hg,  and  for  a  short 
while.  A  few  hours  after  the  pressure  in  the  veins  is  found  to  be 
normal.  It  is  important  to  note  that  the  oedema,  or  dropsy,  which 
follows  such  obstruction,  or  occurs  in  heart  disease,  is  not  caused  by 
transudation  due  to  a  rise  of  venous  pressure,  but  by  nutritive  changes 
in  the  tissues  which  follow  the  obstructed  flow. 

If  the  thorax  of  a  dog  or  cat  be  compressed,  the  arterial  pressure 


THE  NUTRITION  OF  THE  HEART 


1G3 


falls  towards  zero,  owing  to  the  increased  intrathoracic  pressure 
obstructing  the  filling  of  the  heart,  while  the  vena  cava  pressure  rises 
a  few  millimetres  of  Hg  (Fig.  6G).  The  extent  of  the  effect  depends 
greatly  on  the  rigidity  of  the  thorax  and  resisting-power  of  the 
animal.  In  man,  compression  of  the  chest  produces  the  same  result; 
loss  of  consciousness  may  be  induced  and  convulsive  spasms  owing 
to  the  production  of  acute  cerebral  anaemia. 

In  the  fatal  crushes  of  panic-stricken  crowds,  death  is  produced 
by  compression  of  the  thorax  and  circulator}^  failure.  The  women 
and  children  with  collapsible  chests  are  the  first  to  die,  while  the 
men  with  most  rigid  chests  escape.  When  a  person  is  strangled,  or 
the  lar3aix  is  blocked  bj'  some  hard,  impacted 
mass  of  food  too  hastily  swallowed,  death  is 
hastened  by  the  violent  expiratory  spasms, 
which  drive  the  blood  out  of  the  abdominal 
veins  into  the  heart  and  engorge  the  face 
with  venous  blood. 

To  sum  up,  the  heart  is  filled  in  diastole 

by- 

1.  The  contraction  of  the  heart  produc- 
ing a  positive  pressure  in  the  veins  (the 
vis  a  tergo). 

2.  The  action  of  the  respiratory  pump 
creating  a  negative  pressure  in  the  thorax 
and  a  positive  pressure  in  the  abdomen. 

3.  The  contraction  of  the  muscles  of  the 
bod}'  generally  impelling  the  blood  onward 
toward  the  heart. 

4.  Change  of  posture  and  the  action  of 
gravity. 


Fig.  66. — -Compression  of 
THE  Thorax  {A-B).  (Hill 
and  Barnard.) 

Compensitory  effect  of 
poweifiil  inspirations, 
alternating  with  forced 
expiratory  efforts  (glot- 
tis closed).  Aorta  mm. 
Hg,  vena  cava  mm. 
water. 


The  Systolic  Output  and  the  Work  of  the 
Heart. — To  estimate  the  work  of  the  heart, 
it  is  necessary  to  know  the  mean  pressure 
(H),  the  velocity  of  blood  in  the  aorta  (V), 
and  the  volume  of  sj'stolic  output  (Q). 

The  velocity  of  blood  in  the  aorta  may 
be  obtained  by  one  of  the  methods  given 
later  (p.  203). 

Having  obtained  the  velocity  (V),  the  output  can  be  reckoned  if 

the  sectional  area  of  the  aorta  (A)  and  the  time  of  the  cardiac  cycle 

(T)  be  known.     To  calculate  half  the   diameter  of  the  aorta,  thus 

2"^ 
getting  the  radius   (r).      The   sectional  area  (A)  =  :?/•-  (77==    "');    60 


(From  Schiifer's  "Physiology.") 


divided  by  the  number  of  heart-beats  per  minute  gives  T  in  seconds 
Then  Q  =  AVT. 

The  output  of  the  heart  may  be  determined  by  means  of  the  heart- 
lung  preparation  (Fig.  67).  Under  an  anaesthetic,  and  after  injection 
of  hirudin  to  prevent  the  clotting  of  the  blood,  artificial  respiration  is 
established,  and  the  common  carotid  artery,  the  descending  aorta  and 


1G4 


A  TEXTBOOK  OF  PHYSIOLOGY 


the  interior  vena  cava  are  ligatured.  A  cannula,  connected  with 
a  manometer,  M,  is  placed  in  the  innominate  artery.  From  this  the 
blood  is  led  past  the  air  cushion  B,  which  represents  the  elasticity  of 
the  arteries,  to  a  rubber  tube,  R,  in  a  tube,  T.  This  can  be  compressed 
by  the  pump  8  and  jjressure  bottle  A,  and  corresponds  to  the  perijoheral 
resistance.  Thence  the  blood  passes  to  a  vessel,  N,  where  it  is  aerated 
and  thence  siphoned  to  one  where  it  is  warmed,  and  from  there  to  the 
.superior  vena   cava   through  a    cannula  containing  a  thermometer. 


Fig.  G7. — Diagram  of  Apparatus  (described  in  Text)  used  in  the  Heart-Lung 
Preparation.     (Knowlton  and  Starling.) 


The  output  of  the  ventricle  for  a  given  time  may  be  estimated  by 
measuring  the  flow  from  the  bypass  to  the  vessel  N.  If  the  rate  of 
beat  be  known,  the  output  per  beat  is  easily  calculated. 

The  volume  of  output  may  be  estimated  indirectly  by  deter- 
mining (1)  how  much  oxygen  is  absorbed  from  the  inspired 
air  per  minute;  (2)  the  difference  in  the  oxygen  content  of  the 
arterial  and  venous  blood;  (3)  the  number  of  heart-beats.  If 
1,000  c.c.  of  oxygen  are  absorbed  from  the  air  breathed  in  a 
minute,  and  the  arterial  blood  contains  10  per  cent,  more  oxygen 
than  the  venous,  and  the  heart  beats  100  times  per  minute,  then, 
since    10    c.c.    of    oxygen    are    carried    away    by    each    100    c.c.   of 


THE  NUTRITION  OF  THE  HEART  165 

blood,  the  amount  of  blood  necessary  to  carry  away   1,000  c.c.  is 

— ^- —  =10,000.     If  this  be  divided  by  the  beats  per  minute  (100), 

then  the  output  for  each  beat  would  be  100  c.c.  In  man,  the  output 
volume  can  be  determined  by  breathing  in  a  deep  breath  of  air  mixetl 
with  nitrous  oxide — a  very  soluble  gas — holding  the  breath  and  find- 
ing how  much  of  this  gas  is  carried  away  by  the  blood  dviring  a 
given  time,  about  thirty  seconds.  A  sample  of  the  alveolar  air  is 
taken  at  the  beginning  and  at  the  end  of  holding  the  breath,  and  the 
amount  of  air  in  the  lungs  at  the  beginning  and  at  the  end  of  this 
period  is  determined.  From  the  amounts  of  nitrovs  oxide  in  the 
samples  the  amount  of  nitrous  oxide  present  in  the  lungs  at  the 
beginning  and  at  the  end  of  the  experiment  is  known.  This  gives 
the  amount  absorbed  from  the  lung  in  the  time.  Then,  knowing  the 
solubiHty  of  the  gas  (1  c.c.  of  blood  absorbs  0-43  c.c.  of  the  gas),  the 
amount  of  blood  necessary  to  absorb  the  known  amount  from  the 
mean  percentage  of  gas  present  can  be  calculated.  This  divided  by 
the  length  of  time  of  the  experiment  and  the  heart-beats  i)er  minute 
gives  the  output  for  each  beat.  The  output  for  man  is  calculated  to 
be  60  to  100  c.c.  It  is  ten  times  as  great  or  more  during  hard  exercise. 
The  work  of  the  heart  may  be  calculated  from  the  following 
formula : 

W=QH  +  ^^\ 

where  M  =  the  weight  of  the  mass  of  blood  moved,  and  ^=the  acceler- 
ating force  due  to  gravity,  this  =  9-8.  Q  x  H  represents  the 
work    of    each  heart-beat  in  overcoming  the  peripheral   resistance. 

=the   energy   of  the  velocitv   of  the  blood  ejected.     These  two 

must  be  added  together. 

We  may  take  the  output  of  the  left  ventricle  as  100  grammes;  the 
mean  pressure  of  the  aorta  as  110  mm.  Hg.  Since  mercury  is  about 
13-5  times  heavier  than  blood,  this 

=  110  millimetres  x  13-5,  or 
0-110  metre   x  13-5. 

We  have  therefore  in  gramme-metres  of  work : 

W=  100  X  0-110  X  13-5  +  ^^^ 

2  X  9-8 

=  148-5+1-26.3 
=  149-765, 

or,  approximately,  150  gramme-metres  of  work  for  each  contraction 
of  the  left  ventricle.  It  is  clear  that  almost  all  the  work  of  the  heart 
is  spent  in  overcoming  resistance,  and  it  suffices,  for  roughh"  calcu- 
lating the  work,  to  multiply  the  output  by  the  arterial  pressure. 

We  can  say  that  the  work  of  the  left  ventricle  is  equivalent  to 


166 


A  TEXTBOOK  OF  PHYSIOLOGY 


throwing  uji  a  5-ouiice  ball  a  yard  high  seventy  times  a  minute.  The 
right  ventricle,  since  it  contracts  against  considerably  less  pressure, 
has  less  work  to  do.  It  is  generally  considered  as  doing  about  one- 
third  the  work  of  the  left. 

Taking  into  consideration  the  variations  in  pressure  and  f)utput, 
the  hunum  heart  is  estimated  to  perform  about  12,000  to  20,000  kilo- 
gramme-metres of  work  per  day — that  is  to  say,  it  performs  sufficient 
work  to  raise  the  body  weight  through  200  to  300  metres  above  sea- 
level — say  up  a  hill  of  1,000  feet. 

Twenty  thousand  kilogramme-metres  would  be  equivalent  to  50 
calories  out  of  the  total  3,000  calories  which  a  man  takes  in  as  food. 
A  labourer  does  about  150,000  kilogramme-metres  of  external  work  a 
day.  The  work  of  the  heart  is  increased  two  or  three  times  by  muscular 
labour,  and  even  ten  times  by  great  exertion.  When  the  heart  does 
work  it  also  produces  heat,  and  probably  five  times  as  much  heat  as 
work.     It  has  lieen  estimated  that  the  heart  requires  per  diem,  to 


Recorder 


Via.  tiS. — The  Cakdiometek. 


maintain  its  energy,  an  amount  of  solid  food  (water-free)  equal  to  the 
weight  of  solids  in  the  heart  itself — i.e.,  about  60  grammes  of  sugar 
or  protein.  A  relatively  high  jiroportion  of  blood  must  be  circulated 
per  minute  through  the  coronary  arteries  to  maintain  the  vigour  of 
the  heart,  and  its  use  of  oxygen  per  gramme  of  weight  per  minute  is 
high.  Thus,  for  the  whole  body  of  the  dog  there  was  used  0-017  c.c. 
per  gramme  of  tissue  per  minute;  for  the  heart,  0*045  to  0-083;  and 
for  the  active  secretory  glands,  0-07  to  1-0. 

The  volume  of  the  output  of  the  heart  may  be  recorded  by  means 
of  the  cardiometer. 

Various  forms  have  been  devised.  The  most  convenient  consists 
of  a  large  thistle  funnel  covered  with  a  rubber  membrane  in  which 
a  round  hole  of  appropriate  size  has  been  made  with  a  heated  soldering- 
iron  (Fig.  68).  After  the  establishment  of  artificial  resjiiration,  the 
thorax  of  the  animal  is  opened  and  its  heart  inserted  through  the  rubber 
membrane  so  that  this  fits  snugly  to  the  base  of  the  ventricles.  The 
tube  of  the  funnel  is  connected  with  a  piston  recorder.     A  cannula 


THE  NUTRITION  OF  THE  HEART 


167 


is  placed  in  the  carotid  artery,  and  connected  to  a  mercury  valve, 
whereby  the  blood-pressure  can  be  regulated  by  raising  or  sinking  a 
tube  in  mercury,  and  in  which  the  blood  is  also  kept  warm  until  it 
is  returned  to  the  animal  by  the  jugular  vein.  The  circulation  is' 
<?onfined  to  the  heart  and  lungs,  and  the  effect  of  various  conditions 
•on  the  output  studied.  Fig.  69  shows  a  tracing  obtained  by  this 
means. 

Experiments  on  the  output  of  the  heart  show — 

1.  That  within  certain  limits  the  systolic  output  is  independent 
of  the  resistance. 

2.  That  under  favourable  conditions  a  rise  of  resistance  may  in- 
crease the  systolic  output. 


^:yW^^/MM/; 


■  -•'■■'y'..%!':'.i;,,-,:./yr   ' 


|«B«(BWW!SWf*«!PRf»SS»5»  :».'"-*  :•  *« 


■^-~r~t'a1~P'~1Mr-t-r-ir-t-i' 


Pig.  69. — Tr.^cixg  showing  Volume  of  Output  of  Heart.     (Knowlton  and  Starling. ) 

^4,  Volume  of  ventricle;  B,  arterial  pressure;  C,  output  of  left  ventricle  measured; 

D,  time  in  seconds. 


3.  That  with  increasing  jjeripheral  resistance  the  sj'stolic  output 
as  a  rule  decreases. 

4.  That  as  the  arterial  pressure  generally  increases  in  spite  of  the 
diminished  sy.stolic  output,  the  diminution  in  output  per  second  must 
be  proportionately  smaller  than  the  increase  in  resistance. 

The  diminution  of  the  output  per  second  is  usually  shown  most 
strikingly  during  the  rise  of  arterial  jiressure  which  is  occasioned  by 
asphyxia.  In  the  asphyxial  condition  the  heart  muscle  rapidly  fails, 
and  passes  into  paralytic  dilatation;  while  the  output  from  the  ven- 
tricles is  opposed,  the  venous  input  is  increased  by  the  action  of  the 
lespiratory  spasms. 

In  the  first  stage  of  asphyxia  a  large  vascular  area  of  arterioles. 


16S 


A  TEXTBOOK  OF  PHYSIOLOGY 


Fig.  70.— ARTEr.iAL  Pkessvke  ;  Efflct  of  A.sriivxiA.    Animal  Anesthetized  ani> 

CUEARIZED.       (L.  H.) 

At   A   the  artificial  respiration  was  stopped.      The  large  oscillations  are  Traube- 

Hering  curves. 
D-.:ration  in  hundredths 
of  a  second 

]0n 


60 


70 


Pulse-frequencj-  \     50 
per  minute       ) 

FiQ.  71. Duration    of    Systole   and    of    Diastole    with   Different  Pulse- 

Frequencies.     (Waller.) 


THE  NUTRITION  OF  THE  HEART 


im 


such  as  the  si^lanchnic,  is  thrown  into  constriction,  and  the  blood  is 
propelled  from  the  constricting  vessels  into  the  veins,  and  thus  the 
diastolic  filling  of  the  heart  is  increased;  at  the  same  time,  the  velocity 
of  flow  through  the  locomotor  organs  is  accelerated,  owing  to  a  compen- 


!  (Rate  of  Fiilse  : 

prSssuri  of  pulse) 
1           1 

0,- 

Cons 

ur.fpt'ion 

1 

J 

1 

1 

1 
1 

!           '           1 
pressure  \r)f  p-J/sc 

1 

numoer  of  pulse 

beak 

1 
i 

i          1 
1          1 

' 

1 
1 

1 

Time  in  periods  of  20  minutec 


Fig.  72. — Diagkam  showing  the  Relationship  of  Oxygen  Consumption  to  the 
Rate  of  the  Pulse  and  the  Arterial  Pressure.     (Barcroft.) 

satory  dilatation  of  the  vessels  in  these  organs.-  The  heart  accelerates, 
the  systolic  output  increases,  and  the  arterial  pressure  rises  (Fig.  70). 
In  the  second  stage  the  vagal  centre  of  the  spuial  bulb  is  excited  by 
the  high  arterial  pressure,  the  heart  freci[uency  is  lessened,  and  the 


Fig.  73.— Contraction  of  Frog's  Heart,  showing  Accelerator  Effect  of  Weak 
Stimulation    of    Vago-Sympathetic.     (Pembrey  and  Phillips.) 

Tlierc  is  increased  tone  in  the  after-effect. 


output  diminished.  Further,  so  soon  as  the  arterial  pressure  reaches 
a  certain  point,  the  heart  becomes  unequal  to  the  strain  of  emptying 
itself  against  the  resistance;  the  output  then  becomes  imperfect,  the 
residual  blood  increases,  the  left  aiu'icular  pressure  rises,  and  the 
blood  is  congested  in  the  lungs  and  within  the  venous  system. 


170 


A  TEXTBOOK  OF  PHYSIOLOGY 


The  amount  of  work  done  by   the   heart  varies  with  the  pulse 
frequency  per  niimite  (Fig.  71). 


Tahlk  siiowiNri  Duration  of  Systhle  to  Diastolic,  ktc,  with  Different 
Pulse-Frequencies. 


Puhe.- 

Duration  of 

Duration  of 

Frequency 
per  Minute. 

Systole  in  Hun- 

Diastole in  Hun- 

Ratio of  Systole  to 

Hours  of  Work 

dredths  of  a 

dredths  of  a 

Cardiac  Cycle. 

per  Diem. 

Second. 

Second. 

50 

37 

83 

•31 

1-5 

60 

34 

m 

■34 

8^2 

70 

32 

54 

•37 

8^9 

§0 

30 

45 

•40 

9^6 

90 

28 

38 

•42 

10^2 

100 

27 

33 

.45 

10-8 

In  Fig.  71  jDulse-frequencies  per  minute  are  indicated  along  the 
abscissa.  Durations  of  systole  and  of  diastole  are  given  in  hundredths 
of  a  second.  Their  respective  curves  show  that  the  systole  shortens 
by  about  y^^  second  for  each  increase  of  ten  beats  per  minute,  and 
that  the  diastole  shortens  by  about  j\%  second. 


Fig.  74. — Excitation  of  Vago-Sympathetic.     (L.  H.) 

Note  the  after-effect:  a  staircase  augmentation  of  the  heart-beat.  The  stars  indicate 
the  beginning  and  end  of  stimulation.  The  downstroke  represents  contraction. 
The  time  is  marked  in  seconds. 


The  shaded  and  unshaded  portions  represent  resjoective  time  of 
work  and  time  of  rest  at  various  pulse-frequencies. 

The  rate  of  beat  and  the  arterial  pressure  also  influence  the  amount 
of  oxygen  consumption  by  the  heart  muscle.  This  is  well  seen  in  the 
diagram  (Fig.  72). 


CHAPTER  XIX 

THE  CARDIAC  NERVES 

The  vagus  nerve,  when  excited,  slows  or  even  arrests  the  action  of 
the  heart  (Fig.  44).  The  cardio-inhibitory  nerves,  as  they  are  called, 
have  been  found  in  all  classes  of  vertebrates  and  in  many  inverte- 
brates. The  existence  of  nerve  fibres  which,  when  excited,  augment 
and  accelerate  the  beat  of  the  heart  has  also  been  demonstrated. 
These  belong  to  the  sympathetic  nervous  system.  In  the  frog,  the 
two  nerves  run  in  one  triuik — the  vago- sympathetic  nerve — a  variable 
response  to  stimulation  is  therefore  obtained  (Figs.  73,  74).     In  the 


Fig.  75. — Cardiac  Nerves  of  Frog. 


frog,  the  symjDathetic  fibres  come  off  the  ganglion  of  the  third  spinal 
nerve  (first  post-brachial),  and  pass  along  the  sympathetic  trunk  to 
join  the  vagus  nerve  where  its  ganglion  lies  at  the  base  of  the  skull 
(Fig.  75).  In  mammals,  the  accelerator  nerves  arise  from  the  first 
to  the  fifth  thoracic  anterior  spinal  nerve  roots,  the  preganglionic 
fibres  having  their  "cell  .stations"  in  the  first  thoracic  and  inferior 
cervical  ganglia,  whence  they  pass  to  the  heart  partly  in  company 
with  the  cardiac  branches  of  the  vagus,  and  partly  as  separate 
twigs    (Fig.   76).     The  vagus   cardiac   fibres  belong  to   the   cerebral 

171 


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A  TEXTBOOK  OF  PHYSIOLOGY 


autonomic  system.  They  arise  from  a  centre  in  the  medulla  oblongata 
by  the  middle  of  the  lowermost  group  of  vagus  roots,  and  the  pre- 
ganglionic fibres  have  their  cell-stations  in  the  ganglion  cells  of  the 
heart.  These  ganglion  cells  lie  chiefly  in  the  subpericardial  tissue, 
in  the  posterior  wall  of  the  auricles  between  and  around  the  orifices 
of  the  venae  cava^  and  j^ulmonary  veins,  and  between  the  aorta  and 
pulmonary  artery.  The  right  nerve  goes  particularly  to  the^anglion 
cells    in    the    neighbourhooti    of    the    sinu-ain-icular    node,    through 


Fig.  7G. — C'akdiac  Nervks  of  Dog.     (Foster.) 


which  certain  of  the  post-ganglionic  fibres  act.  The  inhibitory 
fibres  run  chiefl}^  in  this  nerve.  The  centre  is  in  tonic  action,  and 
constantly  bridles  the  heart's  action,  and  this  when  the  vagi  are 
divided,  the  frequency  of  the  heart  increases  and  the  blood-pressure 
rises.  During  stimulation  of  the  peripheral  end  of  the  vagus  the 
arterial  pressure  falls  and  the  vena  cava  pressure  rises  (Fig.  77). 
The  vagus  centre  is  reflexly  excited  by  the  inhalation  of  chloroform, 
ammonia,  or  other  vapour  irritant  to  the  air-passages;  also  by 
the  want  of    oxygen    in    the    blood,   as    in    asphyxia.     It    may   be 


THE  CARDIAC  NERVES 


173 


excited  refiexly  by  irritation  of  the  abdominal  nerves — e.g.,  a  blow 
in  the  abdomen — and  by  increased  pressure  in  the  cerebral  vessels. 
The  accelerator  and  augmenting  fibres  likewise  have  their  centre  in 
the  spinal  bulb,  and  this  is  in  tonic  action,  antagonizing  more  or  less 
the  action  of  the  vagal  centre.  The  vagus  nerve,  by  its  action,  pro- 
duces changes  Avhich  result  in  a  dejDression  of  the  excitabilitj%  the 
conductivity,  the  force,  and  the  frequency  of  the  heart.  By  some 
authorities  these  are  believed  to  be  separate  influences,  so  that  the 
vagus  nerves  are  said  to  contain  bathmotropic,  dromotropic,  inotropic, 


,NMNN^ 


Fig.  77. — The  Effect  of  Excitation  of  the  Peripheral  End  of  the  Vagus 
Nerve  upon  the  Blood-Pressure  in  the  Aorta  (Top  Curve)  and  the  Vena 
Cava  (Second  Curve)  in  mm.  Hg  of  a  Curarized  Animal  with  Artificial 
Respiration.     (L.  H.) 

Note  the  inhibition  of  the  heart;  the  great  fall  of  aortic  and  the  insignificant  rise  of 
vena  cava  pressure;  the  escape  of  the  heart  from  the  vagus  action  and  the  after- 
effect on  the  aortic  pressure.  The  time  is  marked  in  seconds,  and  the  signal  line 
shows  the  duration  of  vagus  stimulation. 


and  chronotropic  fibres,  influencing  through  their  nerve  endings  the 
above-mentioned  properties  in  the  order  named.  Possibly,  also,  the 
tonicity  of  the  heart  muscle  is  affected.  The  chronotropic  action, 
slowing  the  frequency  of  the  beat,  is  the  most  characteristic  action. 
The  heart  becomes  dilated  and  engorged  with  blood,  stopping  in 
diastole.  The  right  vagus,  in  which  chronotropic  fibres  chiefly  run, 
probably  manifests  its  action  upon  the  auricles  through  the  sinu- 
auricular  node.  The  left  vagus  is  held  by  those  authorities  who 
believe  in  the  different  kinds  of  fibre  to  contain  chiefly  fibres  other 


174 


A  TEXTBOOK  OF  PHYSIOLOGY 


(i) 


(ii) 


r  r  I  I  I  r  I  M  M  I  I  M  I  M  M  f  I  I  M  (  I  M  N  M  M  I  M  I 


i%l%(^TftTfl'^ 


w¥^IMriM% 


r  I  f  M  I  1 1  I  M  I  I  n  I  n  n  N  M  1 1  (  M  I  N  I  ( r  I  f  M  (  M  r 


(iii) 


1,    'ii.lMl'l   '  ■W"i'»Mll    llii 

*'  'ill  if  iiiiii  ■!>  'i 


I  I  I)   I   I    I   I    I   I    I   I    M   M   I   I   M   I   I   I   (   I   I   M   I 


Fig.  78. — Tracings  (i.)  to  show  and  (ii.)  the  Abolition  of  Effect^ of^  Right 

ACCELERATOE  IN  THE  DOG,  FREEZING  THE  S.-A.  NODE.   THE  ACCELERATOR 

Nerve  was  stimulated  between  the  Strokes,  (iii.)  The  Action  of  Right 
Nerve  beforehand — the  Action  also  returned  after  the  Effects  ^of 
THE  Cold  had  passed  off.  (M.  F.) 


If    ilill  m  'I'lf  'I'll   'I' 


rTTTTTTl'f  I  r  I  I  I  [)(  f  M'l  ?  n  If  /  I  f  '1  [  N  I  f  f  I  f  f  I  11  M  I  I 


Fig.  79. — To  show  the  Action  of  the  Left  Accelerator  in  the  Dog  even  after 

FREEZING    OF    S.-A.    NODE.       (M.    F.) 

The  nerve  stimulated  from  A'-A" ;  freezing  started  at  Z'and  continued  all  the  time. 


THE  CARDIAC  NERVES 


175 


--^^^---'^^^MU^jmwjm/MM^ 


i^''ff'^mm^'yni"rr"ni 


\\\.'VfW^ 


^MfMmmiwmimMi 


iJ'uUlI'dUUiJU 


Fig.  80. — Shows  Effect  uf  Stimulation  of  Vagus  (A)  and  of  Accelerator 
Nerves  (B)  in  Cat's  Heart  with  A.-V.  Bundle  Cut.  (W.  Cullis  and  E.  M. 
Tribe.) 

The  vagus  effect  is  abolished,  but  the  action  of  the  accelerators  persists,  especially  the 

augmentor  effect. 


Tvi.  81. — Shows  the  Effect  of  a  Small  Injection  of  Muscarine  upon  the  Dog's 
Heart    (Ventricle  Upp3h,  Auricle  Lower  Tracing).     (Dixon.) 

The  auricle  was  completely  inhibited  in  diastole.     At  B  atropine  was  injected  into  a 
vein,  r.nd  tlu'  inhibitory  effects  passed  off. 


176 


A  TEXTBOOK  OF  PHYSIOLOGY 


than  chronotropic.  Its  chronotropic  fibres  generally  do  not  pass  to 
the  sinu-auriciilar  node;  perhaps  they  may  pass  to  the  A.-V.  node. 
The  left  nerve  has  been  said  to  act  directly  on  the  ventricles;  it  is 
})robable,  however,  that  the  vagus  nerves  only  manifest  their  action 
indirectly  through  action  upon  the  auricle  (Figs.  44  and  80).  We 
need  not  suppose  different  kinds  of  nerve  endings;  it  is  probable 
that  the  different  results  are  obtained  through  varying  intensity 
of  stimulation  action  upon  the  same  endings.  After  vagal  arrest,  the 
heart  beats  more  forcibly,  owing,  perhaps,  to  the  greater  accumula- 
tion of  contractile  material  dviring  the  period  of  rest. 

The  converse  of  all  these  effects  occurs  on  stimulation   of  the 
accelerator  nerves  (Figs.   78  and  79).     During  stimulation  of  these 


Li    1.0, 


sth..|v;'j. 

Jmm 


Fig.  82. — Dissection^  of  the  Vagus,  the  Depressor,  and  Cervical  Sympathetic 
Nerves  in  the  Rabbit,     (Cyon.) 


nerves  the  heart  beats  more  quickly  and  forcibly,  excitability  and 
conductivity  being  also  increased.  Excitation  of  these  nerves  may 
excite  to  renewed  efforts  an  excised  heart  which  has  just  ceased  to 
beat  owing  to  a  withdrawal  of  the  supply  of  nutritive  solution ;  hence 
it  is  thought  by  some  that  the  accelerator  nerves  tonically  exert  a 
sustaining  influence  on  the  heart.  The  accelerator  nerves  act  directly 
upon  both  auricl  s  and  ventricles  (Figs.  79  and  80). 

The  alkaloid  atropine  paralyzes  the  vagal  nerve  endings  in  the  heart, 
while  nicotine  paralyzes  the  endings  of  the  preganglionic  fibres  in  the 


THE  CARDIAC  NERVES  177 

ganglion  cells.  In  a  frog,  these  differences  can  be  easily  shown. 
-Stimulation  of  the  sinu-auricular  groove  will  produce  an  action  both 
before  and  after  the  application  of  nicotine,  but  not  after  atropine. 
Both  drugs  prevent  the  effect  of  stimulating  the  vagus.  In  mammals, 
a  local  application  of  the  drugs  to  the  sinu-auricular  node  abolishes 
the  mhibitory  action  of  the  vagus.  Muscarin,  obtained  from  poisonous 
fungi,  slows  and  finally  arrests  the  heart  probably  by  acting  upon 
the  vagus  nerve  endings;  atropine  antagonizes  this  action  (Fig.  81). 

A  great  many  of  the  cardiac  vagal  fibres  convey  impulses  to  the 
spmal  bulb  (centripetal),  and  reflexly  influence  the  heart-frequency, 
the  breathing,  and  the  tonus  of  the  bloodvessels.  In  particular, 
certain  fibres,  termed  depressor,  cause  dilatation  of  the  arterioles,  and 
a  fall  of  arterial  pressure,  by  inhibiting  the  tonic  action  of  the  vaso- 
motor centre  in  the  spinal  bulb.  The  depressor  fibres  arise  from  the 
root  of  the  aorta,  and  overdistension  of  this  part  excites  them,  as 


Fig.  83. — Aoktic  Pkessuee.     Excitation  of  Depkessor.     (BayKss.) 

The  drum  was  stopped  in  the  middle  of  the  curve,  and  the  excitation  maintained  for 

seventeen  minutes. 


evidenced  not  only  by  the  above  effect,  but  also  by  the  electrical 
variation  (action  current)  which  has  been  observed  passing  uj)  the 
depressor  nerve.  In  some  animals,  such  as  the  rabbit,  it  is  found  in 
the  neck  as  a  slender  nerve  running  close  to  the  sympathetic.  It 
can  be  recognized  in  the  rabbit  by  the  fact  that  it  joins  the  vagus 
and  its  superior  laryngeal  branch,  dividing  into  two  shortly  before 
its  junction  with  these  (see  Fig.  82).  Stimulation  of  its  peripheral 
end  has  no  effect. 

The  fall  of  blood-pressure  (Fig.  83)  induced  by  excitation  of  the 
depressor  results  chiefly  from  vaso-dilatation  in  the  splanchnic  area. 
After  section  of  the  splanchnics,  this  fall  of  blood-pressure  naturally 
is  not  marked.  Its  action  is  increased  by  the  secretion  of  the  thyroid 
gland,  induced  by  stimulation  of  the  superior  laryngeal  nerves,  or 
by  the  injection  of  thyroid  extract. 

In  the  vagus  nerve  there  are  also  sensory  fibres  which  when  excited 
cause  reflexly  through  the  vasomotor  centre  a  rise  of  pressure  (Fig.  84). 

12 


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A  TEXTBOOK  OF  PHYSIOLOGY 


Sensory  impressions  originating  in  the  heart  do  not  as  a  rule  enter 
into  consciousness.  Carried  by  the  cardiac  nerves  to  the  sympathetic 
gangha,  and  thence  to  the  upper  thoracic  region  of  the  spinal  cord,  they 
come  into  relation  there  with  the  senf-ory  nerves  from  the  pectoral  region, 
u])])cr  limb,  shoulder,  neck,  and  head.  The  impressions  are  not  felt 
in  the  heart,  but  referred  to  these  sensory  cutaneous  nerves  (Fig.  38'} ). 
Thus,  cardiac  pain  is  felt  in  the  chest  wall  and  upper  limbs,  and  par- 
ticularly on  the  left  side.     The  function  of  the  cardiac  nerves  is  ta 


vw.v.,Vvv^^^^^ 


Vu*.y 


"%\M/'' 


iiniiiiiiiiiiiilmiui 


iiniiiiil  iiiiiiii.iiiiii  I  III  mil  I  iiiimiiiiiiii 


Fig.  84. — Aortic  Blood-Pressuke.     (L.  H.) 

A,  Effect  of  exciting  the  central  end  of  vagus.  The  effect  was  depressor.  B,  On 
shifting  up  the  electrodes  to  a  fresh  unexposed  part  of  the  nerve  the  effect  changed 
to  pressor.     The  time  is  marked  in  seconds. 


co-ordinate  the  beat  of  the  heart  with  the  needs  of  the  body,  and  to 
co-ordinate  the  functions  of  other  organs  with  the  needs  of  the  heart. 
For  example,  an  undue  rise  of  arterial  pressure,  induced,  let  us  say, 
by  compression  of  the  abdomen,  excites  the  centre  of  the  vagus,  and 
produces  slowing  of  the  heart  and  a  consequent  lowering  of  arterial 
pressure.  The  heart  of  a  mammal  continues  to  functionate  after  a 
section  of  all  the  branches  of  the  cardiac  plexus  has  been  made,  so 
that  the  nervous  control  and  co-ordination  of  the  heart  are  not  abso- 
lutely essential  to  the  continuance  of  life. 


CHAPTER  XX 

THE  PHYSICAL  FACTORS  OF  THE  CIRCULATION 

Some  of  the  phj-sical  laws  which  govern  the  circulation  may  be 
ilhistrated  ])y  means  of  schemata  made  of  rigid  cyHndrical  tubes. 

Flow  of  Fluid  in  Cylindrical  Tubes. — In  a  cylindrical  tube,  the  fluid 
particles,  flowing"  under  constant  pressure,  move  parallel  with  the 
axis,  but  with  varying  velocity.  In  the  axial  layer  the  velocity  is  at 
its  greatest;  at  the  wall  it  is  almost  nil.  The  wall  is  wet  with  the 
fluid,  and  there  is  friction  between  the  moving  particles  of  fluid.  The 
fluid  may  be  considered  as  consisting  of  an  infinite  number  of  concentric 
cylindrical  surfaces,  which  glide  over  one  another,  and  move  the 
more  rapidly  the  smaller  their  radius.  The  velocity,  which  is  reckoned 
from  the  outflow  per  second  per  sectional  area  of  the  tube,  yields  us 
the  mean  velocity  of  all  these  cylinders  of  fluid.  Poiseuille  has  laid 
down  the  law  that  the  mean  velocity  is  directly  proportional  to  the 
sectional  area  of  the  tube  and  pressure  gradient.  We  can  find  the 
mean  velocity  by  the  product  of  three  factors — sectional  area,  pressure 
gradient,  and  a  constant  coefficient,  which  depends  on  the  viscosity 
or  physico-chemical  nature  of  the  fluid  in  the  conditions  of  experiment. 
This  coefficient  can  be  defined  as  that  mean  velocity  which  a  current 
would  have  with  a  unit  pressure  gradient  in  a  tube  of  unit  sectional 
area. 

The  coefficient  at  one  and  the  same  temperature  varies  for  different 
fluids,  and  is  found  to  be  smaller  in  proportion  to  the  viscosity  of  the 
fluid. 

The  viscosity  of  blood  is  found  to  be  three  and  a  half  to  five  times 
that  of  distilled  Avater.  A  mixture  of  blood  and  water  is  less  viscous 
than  blood.  Thus,  the  velocity  of  the  circulation  is  increased  by  the 
injection  of  Ringer's  solution.  The  viscosity  of  the  blood  is  increased 
when  there  is  great  loss  of  water — e.g.,  in  cholera.  Alterations  in 
viscosity  can  be  compensated  for  by  the  vaso -motor  system,  which 
regulates  the  peripheral  resistance,  and  are  therefore  of  minor  im- 
portance. 

By  experiments  upon  the  flow  of  distilled  water  in  capillary  glass 
tubes,  0-65  to  0-15  millimetre  in  diameter,  Poiseuille  reached  the 
following  conclusions : 

1.  That  the  amount  of  OTitflow  is  proportional  to  the  head  of 
pressure.  . 

2.  That  the  time  spent  in  the  outflow  of  a  certain  volume  of  flmd 

179 


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A  TEXTBOOK  OF  PHYSIOLOGY 


at  a  constant  i)ressure,  if  the  diameter  be  constant,  is  diiectly  pro- 
portional to  tlu^  length  of  the  tube. 

3.  That  with  the  same  head  of  pressure  the  time  spent  in  the 
outflow  of  a  certain  volume  of  fluid  through  equally  long  tubes  is 
inversely  |)roi)orti()nal  1o  the  fourth  power  of  the  diameter. 

The  Flow  in  a  Tube  of  Varying  Diameter. — Since  fluid  is  hicom- 
pressible,  an  equal  amount  must  flow  in  the  unit  of  time  through 
every  section  of  the  tube,  and  thus  the  velocity  in  any  part  of  a  tube 
which  varies  in  diameter  stands  in  inverse  proportion  to  the  sectional 
area.  In  such  a  tube  the  pressure  gradient  is  steepest  in  the  narrowest 
section,  for  there  the  velocity  and  the  friction  is  greatest.  In  two 
sections  of  equal  tliameter  the  pressure  gradient  is  the  same.  Where 
a  wide  section  follows  ujDon  a  narrower,  the  lateral  pressure  may  either 


Fig.  85.— Schema  to  show  the  Velocity  and  Resistance  Heads. 
B,  Pressure  bottle  ;    A,  tube  with  piezometers;  E  F,  Pitot  tubes. 

sink,  remain  unaltered,  or  even  rise.  How  this  can  be  so  is  seen  by 
the  following  considerations:  At  any  point  of  the  tube  the  whole 
pressure  head  (H)  equals  the  sum  of  the  velocity  head  (h^)  and  the 
resistance  head  (h^).  Now  H  decreases  uniformly  along  the  tube, 
and  since,  where  the  tube  widens,  the  velocity  becomes  less,  and  H^ 
suddenly  diminishes,  it  follows  that  /r  increases,  and  it  is  conceivable 
that  h}  in  the  wide  section  may  become  higher  than  h'^  in  the  narrow 
section.  In  other  words,  since  more  of  H  is  spent  in  maintaining 
the  velocity  in  the  narrow  section,  the  lateral  pressure  may  be  lower 
here  than  in  the  succeeding  wide  section. 

The  Flow  in  Branching  Tubes.— When  a  tube  branches  into  a  number 
of  smaller  branches,  and  these  connect  again  into  one  tube,  we  have 
two  opposing  factors  to  consider: 


PHYSICAL  FACTORS  OF  THE  CIRCULATION 


181 


1.  The  increase  of  sectional  area.  The  velocity  is  inversely  pro- 
portional to  the  whole  sectional  area  of  the  branches. 

2.  The  increase  of  resistance,  due  to  the  great  extent  of  surface 
contact  between  the  moving  fluid  and  the  fluid  that  wets  the  walls 
of  the  tubes.  The  resistance  is  proportional  to  the  surface  area, 
nearly  proportional  to  the  square  of  the  velocity,  and  inversely  pro- 
portional to  the  sectional  area.  The  formula  used  by  engineers  for 
what  they  cafl  "skin  fraction"  is  R  =  ^S^;^  where  R  =  resistance ; 
1c,  a  constant;  S,  surface  area;  v,  velocity. 

If  water  flows  from  a  head  of  pressure  through  a  tube  on  which 
stand  a  number  of  vertical  side  tubes,  it  is  found  that,  according  to 


Fig.  86. — Schema  to  show  Effect  of  introducing  Resistance. 


the  degree  that  the  outflow  from  the  tube  is  obstructed,  so  will  the 
water  rise  in  the  side  tubes ;  the  nearer  the  side  tube  to  the  head  of 
pressure,  the  higher  the  fluid  rises  in  it  (Fig.  86). 

This  is  because  water  flowing  through  a  tube  from  a  constant  head 
of  pressure  encounters  a  resistance  occasioned  by  the  friction  of  the 
moving  water  particles  against  each  other  and  against  the  stationary 
layer  that  wets  the  wall  of  the  tube.  Part  of  the  potential  energy  of 
the  head  of  pressure  is  spent  in  endowing  the  fluid  with  kinetic  energy, 
part  in  overcoming  this  resistance.  The  latter  and  greater  part  is 
rubbed  dowai  into  heat.  The  narrower  the  tube  is  made,  the  greater 
the  friction,  until  finally  the  flow  ceases,  the  total  energy  being  then 
insufficient  to  overcome  the  resistance. 

This  is  well  exemplified  by  the  modified  schema  (Fig.  86).  W  is  a 
bottle  containing  coloured  water  connected  to  the  rigid  tube  X,  on  which 


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A  TEXTBOOK  OF  PHYSIOLOGY 


stand  the  vertical  side  tubes  A  to  E.  R  is  a  resistance  introduced  by 
means  of  a  wide  tube  filled  with  f-mall  glass  marbles.  Y  is  a 
rubber  tube  of  equal  calibre  to  A'  leading  to  the  rigid  tube  Z,  similar 
to  X.  The  amount  of  fluid  flowing  to  the  tube  can  be  regulated  by 
the  clami?  K.  Further,  the  fluid  can  flow  from  the  tube  X  to  the 
tube  Z  either  by  Y  when  the  clamp  L  is  shut  and  clamp  L^  open,  or 
by  the  tube  R  when  the  clamp  L^  is  shut  and  clamp  L  is  open. 

When  there  is  a  free  flow  from  W  (K  open),  and  free  communica- 
tion b}^  }'  from  X  to  Z  {L  closed,  L^  ojien),  it  will  be  seen,  according 
to  the  resistance  introduced  by  clamp  M,  the  coloured  fluid  rises  in 
all  the  side  tubes  to  a  nearly  equal  extent,  gradually  decreasing 
irom  A  to  J.  When  the  clamp  L^  is  slightly  closed,  the  fluid  rises 
higher  in  tubes  A  to  E  than  before,  and  faUs  in  tubes  F  to  J.  The 
same  thing  is  seen  if  the  fluid,  instead  of  passing  by  7,  is  sent  through 
i?,  which  better  exemplifies  the  circulation. 


Fig.  87. — Schema  to  show  the  Flow  in  Rigid  and  Elastic  Tubes.     (Marey.) 
The  compressor  should  compress  the  single  tube  not  the  double  tube,  as  figured. 

In  this  schema  the  flow  has  been  through  rigid  tubes.  The  same 
laws  which  have  been  discussed  in  connection  with  rigid  tubes  obtain 
in  elastic  tubes  if  the  flow  of  fluid  be  continuous. 

If  the  inflow  be  intermittent,  in  the  case  of  the  rigid  tube,  the  whole 
column  of  fluid  is  driven  on,  atep  by  step,  by  each  stroke  of  the  pump, 
and  the  outflow  is  intermittent.  In  an  elastic  tube,  on  the  other  hand, 
if  the  resistance  to  the  output  has  been  made  great,  as  by  constricting 
the  orifice,  the  elastic  wall  of  the  tube  is  extended  by  the  input, 
of  the  pump,  and  the  elasticity  of  the  wall  comes  into  play,  and  con- 
tinues the  output  after  the  stroke  of  the  pump  has  ceased,  so  that  the 
flow  becomes  continuous. 

This  is  shown  by  the  schema  (Fig.  87).  Here  the  coloured  water 
flows  from  a  head  of  pressure  through  two  tubes  1  metre  long,  and 
of  the  same  bore;  but  one  tube  is  rigid,  the  other  elastic.  The 
outflow  orifices  are  also  of  the  same  size. 


PHYSICAL  FACTORS  OF  THE  CIRCULATION 


183 


On  rhythmical^  shutting  and  opening  the  compressor,  it  will  be 
found  that  the  outflow  from  the  elastic  tube  is  continuous,  from  the 
rigid  it  is  intermittent.  The  increased  and  continuous  flow  is  due 
to  the  potential  energy  stored  up  in  the  stretched  wall  of  the  elastic  tube. 
The  elastij  tube  also  delivers  more  fluid  per  minute  than  the  former. 

In  the  circulator}^  sj^stem  we  are  concerned  with  a  system  of  elastic 
tubes.  The  conditions  appertaining  in  the  circulation  can  best  be  repre- 
sented, therefore,  by  a  schema  having  elastic  tubes,  such  as  Fig.  88. 

Here  H,  the  bulb  of  a  Higginson  syringe,  represents  the  head  of 
pressure^the  heart.  Two  valves,  representing  the  mitral  and  aortic 
valves,  regulate  the  flow  in  one  direction  only.  Coming  away  from 
the  syringe  is  a  rubber  tube  (about  i  inch  diameter),  which  divides 
into  two  .channels  the  arteries,  leading  (1)  to  two  lamp  glasses  filled 


Co-pillarics 


Fig.  88. — Artificial  Schema. 


with  chopped  rubber  sponge  (the  capillaries),  and  (2)  to  a  rubber  tube 
«hut  with  a  clamp  (the  short  circuit).  This  clamp  represents  the 
muscle  wall  of  the  arterioles.  These  are  connected  with  the  inner 
tube  of  a  bicycle  tyre,  representing  the  capacious  venous  system,  and 
this  in  turn  to  the  Higginson  syringe  again. 

Inserted  in  the  circuit  are  manometers  connected  by  T-pieces  to 
the  artery  and  to  the  vein.  The  whole  system  is  filled  with  water, 
air  being  removed  by  tilting  the  board  to  which  the  schema  is  fixed 
and  working  the  pump,  but  only  so  far  that  the  vein  is  not  distended, 
and  there  is  no  positive  pressure  in  the  system  when  at  rest.  When 
the  screw  clip  (the  arterioles)  is  widely  open,  there  is  little  resistance 
to  flow.  The  outflow  from  the  artery  into  the  vein  then  ceases  during 
diastole,  the  conditions  being  the  same  as  if  the  artery  were  a  rigid  tube. 
The  variations  of  pressure  are  great  both  in  artery  and  veins,  and  both 


184 


A  TEXTBOOK  OF  PHYSIOLOGY 


manometers  are  affected  to  almost  a  like  extent.  On  screwing  up 
the  clip  (increasing  the  resistance  in  the  arterioles),  the  flow  becomes 
less  and  less  intermittent  as  the  resistance  increases,  and  eventually 
becomes  contiivuous.  The  pressure  rises  in  the  arteries,  the  systolic 
and  diastolic  variations  in  pressure  becoming  greath'  reduced.  The 
variations  in  pressure  disappear  from  the  veins.  This  represents  what 
takes  place  in  the  vascular  system. 

The  Elasticity  oi  Arteries.  —  An  artery 
possesses  great  lability,  that  is,  it  is  easily 
distended;  it  has  great  elasticity,  recovering 
its  shape  after  the  distending  force  is  removed. 
The  curves  of  extensibility  and  elasticity  may 
be  worked  out  on  excised  arteries  either  by 
weighing  and  unweighing  a  strip  of  vessel  wall,  or 
by  recording  the  expansion  of  a  short  length  of 
artery  when  submitted  to  a  pressure  of  water. 
Such  curves  vary  according  as  the  artery  is 
relaxed  or  contracted.  The  muscle  in  its  wfll 
alters  the  lability  by  its  contraction  or  relaxa- 
tion (Figs.  89,  i;0). 

The  breaking 
strain  of  a  healthy 
artery  is  very  great. 
In  some  experi- 
ments the  caret  d 
of  a  goat  f.r.ccc^;;;- 
fully  withstood  a 
pressure  of  2.250 
mm.  Hg — that  i.;, 
about  fourteen 
times  the  normal 
blood-pressure.  It 
takes  an  internal 
pressure  of  3,000 
to   8,500    mm.  Hg 

to  rupture  the  carotid  artery  of  a  dog.  In  the  ease  of  the  human  carotid 
the  smallest  rupturing  pressure  was  found  to  be  1,290  mm.  Hg.  The 
larger  arteries  rupture  more  easily  than  the  smaller,  and  thus  the  aorta 
breaks  asunder  at  a  lower  tension  than  the  radial. 

In  the  vascular  sj^stem,  an  area  of  vessels  of  capillary  size  is  placed 
between  the  large  arteries  and  veins.  This  area  opposes  a  great 
resistance  to  flow.  The  effect  of  the  peripheral  resistance,  as  it  is 
called,  is  to  raise  the  pressure  on  the  arterial  side  and  lower  it  on  the 
venous.  The  resistance  to  flow  is  situated  chiefly,  not  in  the  capil- 
laries, but  in  the  small  arteries,  where  the  velocity  is  high.  "  Skin 
friction  " — that  is,  the  friction  of  the  moving  concentric  layers  of 
blood  against  one  another  and  against  the  la^^er  which  wets  the  wall 
of  these  bloodvessels — is  f)roportional  to  the  surface  area  and  to  the 
viscosity  of  the  blood;  is  nearly  proportional  to  the  square  of  the 


Fig.  89. — Elongation  of  Con- 
tracted Aktery,  with  Rise 
OF  Internal  Pressure  (0  to 
300  Mm.  Hg).  Length 
=  Hi    Mm.  (Mac William.) 


Fig.  90. — Elongation 
OF  Relaxed  Artery, 
with  Rise  of  Inter- 
na l  Pressure. 
L  e  N  g.t  h  2 1  Mm. 
(MacWilliam.) 


PHYSICAL  FACTORS  OF  THE  CIRCULATION  185 

velocity  of  flow;  and  is  inversely  proportional  to  the  sectional  area  of 
the  vessels.  Owing  to  the  resistance  to  the  capillary  outflow,  the 
large  arteries  are  expanded  by  each  systolic  output  of  the  heart,  and 
the  elasticity  of  their  walls  comes  into  play,  causing  the  outflow  to 
continue  during  the  succeeding  diastole  of  the  heart.  The  conditions 
are  such  that  the  intermittent  flow  from  the  heart  is  converted  mto 
a  continuous  flow  through  the  capillaries.  If  the  arteries  were  rigid 
tubes,  it  ^\-ould  be  necessary  for  the  heart  to  force  on  the  whole  column 
of  blood  at  one  and  the  same  time;  but,  owing  to  the  elasticity  of  these 
vessels,  the  heart  is  saved  from  such  a  prolonged  and  jarrmg  strain, 
and  can  pass  into  diastolic  rest,  leaving  the  elasticity  of  the  distended 
arteries  to  maintain  the  flow.  Besides  the  saving  of  heart-strain, 
there  is  the  advantage  of  a  greater  outflow  through  elastic  than  through 
rigid  tubes.  As  a  result  of  disease,  the  elastic  tissue  may  degenerate 
and  the  arteries  become  more  rigid. 

The  four  chief  factors  which  co-operate  in  producing  the  conditions 
of  pressure  and  velocity  in  the  vascular  system  are — 

(1)  The  heart-beat; 

(2)  The  peripheral  resistance ; 

(3)  The  elasticity  of  the  arteries; 

(4)  The  quantity  of  blood  in  the  system. 

Suppose  the  body  to  be  in  a  horizontal  position,  and  the  vascular 
system  to  be  brought  to  rest  by,  say,  arrest  of  the  heart.  A  sufficiency 
of  blood  to  distend  it  collects  within  the  venous  cistern.  The  arterial 
system,  owing  to  its  elasticity  and  contractility,  empties.  If  the  heart 
now  begin  to  beat,  blood  is  taken  from  the  venous  system,  and  is 
driven  into  the  arterial  system.  The  arteries  receive  more  blood  than 
escapes  through  the  capillary  vessels,  and  the  arterial  side  of  the 
system  becomes  fllled  until  equilibrium  is  reached,  when  as  much 
blood  escapes  from  the  arterial  into  the  venous  side  per  unit  of  time 
as  is  delivered  into  it  by  the  heart.  The  flow  in  the  capillaries  and 
veins  now  becomes  a  constant  one,  and  if  the  side-pressure  be 
measured,  it  will  be  found  to  fall  from  the  arteries  to  the  capillaries, 
and  from  the  capillaries  to  the  vense  cavse.  In  the  large  arteries 
there  is  a  large  side-pressure  which  rises  and  falls  with  the  pulses 
of  the  heart.  The  pulse-waves  spread  out  over  a  wider  and  wider 
area  as  the  arteries  branch.  They  finally  die  away  in  the  arterioles. 
An  increase  or  decrease  in  the  energy  of  the  heart-beat  will  increase 
or  decrease  respectively  the  velocity  of  flow  and  pressure  of  the 
blood.  An  increase  or  decrease  in  the  total  width  of  the  arterioles 
respectively  will  lessen  or  raise  the  resistance,  increase  or  decrease 
the  velocity,  lower  or  raise  the  blood-pressure.  A  loss  of  blood, 
other  conditions  remaining  the  same,  would  cause  a  decrease  in  pres- 
sure and  velocity.  As  a  matter  of  fact,  even  a  considerable  loss  is 
compensated  for  by  the  adjustability  of  the  vascular  system.  Tissue 
lymph  passes  from  the  tissues  into  the  blood,  and  the  bloodvessels  of 
the  limbs  and  abdomen  constrict,  and  thus  the  pressure  is  kept  up, 
and  an  efficient  circulation  maintained  through  the  brain,  lungs,  and 
coronary  vessels  of  the  heart. 


CHAPTER  XXI 
THE  ARTERIAL  PRESSURE 

The  term  "  blood-}Dressiire  "  is  somewhat  loosely  used.  Generally, 
it  signifies  the  arterial  pressure,  but  it  can  be  equally  well  applied  to 
the  pressure  of  blood  in  the  capillaries  or  in  the  veins.  For  the  sake 
of  accuracy,  it  is  better  to  speak  of  the  arterial  blood-pressure  or  arterial 
pressure,  the  capillary  pressure,  and  the  venous  pressure. 

The  Blood-Pressure. — It  has  long  been  known  that  the  blood  is 
under  different  jiressure  in  the  various  parts  of  the  system.  From 
a  divided  artery  the  blood  flows  out  in  forcible  spurts,  from  a  vein  it 
flows  out  continuously  and  with  little  force.  It  takes  very  little 
pressure  of  the  flngers  to  blanch  the  capillaries  of  the  skin  or  nail-bed, 
to  stop  the  blood-flow  in  the  superficial  veins,  but  an  appreciable 
amount  of  pressure  to  obliterate  the  radial  artery. 


Fig.  91. — Arterial  Cannula. 


Measurement  of  Arterial  Pressure. — Stephen  Hales  (1733)  was  the 
first  to  measure  the  blood-pressure.  He  fastened  a  long  glass  tube 
held  vertically  to  the  femoral  artery  of  a  horse,  using  a  brass  cannula 
and  a  goose's  trachea  as  a  flexible  tube  for  making  connection.  He 
saw  the  arterial  blood  rise  some  6  feet  high  in  the  tube,  and  oscillate 
there  with  each  pulse-beat  and  respiration. 

Later  the  mercurial  manometer  was  adapted  to  the  same 
purpose.  This  consists  of  a  U-shaped  tube  containing  mercury, 
which,  being  13-5  times  heavier  than  blood,  allows  the  manometer 
to  be  brought  to  a  convenient  height.  On  the  top  of  the  mer;ury 
rides    a    float    provided   with  a  writing    style    (see    Fig.   !t2).      The 

186 


THE  ARTERIAL  PRESSURE 


187 


introduction  of  rubber  tubing  for  the  connections  made  the  method 
of  inquiry  comparatively  simple. 

The  method  of  procedure  now  usually  employed  is  as  follows: 
The  artery  of  an  anaesthetized  animal  is  exposed  and  ligatured. 
A  clamp  is  pla:ed  upon  the  artery  nearer  the  heart,  and  the  special- 
shaped  cannula  (Fig.  91)  introduced  between  the  ligatiu-e  and  the 
clamp.  The  cannula  and  tubing  are  filled  with  a  suitable  fluid,* 
to  prevent  coagulation,  from  a  reservoir  (R,  Fig.  92),  raised  to  a 
height  sufficient  to  introduce  a  pressure  about  equal  to  the  antici- 
pated arterial  pressure  of  the  animal.  This  prevents  more  than  a 
trace  of  blood  entering  the  connections. 

The  clamp  is  now  removed  from  the  arterj^  and  the  ])ressure  is 
transmitted  to  the  manometer,  the  style  of  which  can  be  brought  to 


Fig.  92. 


-Arrangement  of  Cannula,  Pressure  Bottle,  and  Mercurial 
Manometer,  for  Recording  Blood-Pressure. 

C,  Cannula;  p,  p^,  clips;  F,  float;  S,  writing  style. 


write  on  a  drum  covered  with  smo':ed  paper,  and  driven  slowly  round 
by  clockwork  or  electric  motor.  By  this  means  tracings  (»f  the  arterial 
blood-pressure  are  obtained,  and  the  influence  upon  the  blood-pressure 
of  various  agents  recorded  and  studied.  For  the  veins,  a  manometer 
filled  with  salt  solution  is  used,  as  mercury  is  too  heavy  a  fluid  to 
record  the  far  slighter  changes  of  venous  pressure.  The  manometer 
may  be  connected  with  a  recording  tambour. 

The  arterial  blood-pressure  record  obtained  with  the  mercurial 
manometer  exhibits  cardiac  and  respiratory  oscillations.  The  method 
gives  us  a  fairly  accurate  record  of  the  mean  pressure,  l)ut  the  mass 
of   the    mercury  causes    such    inertia    that    the    instrument  is  quite 

*  Saturated  magnesium  sulphate  may  be  employed  for  t  he  dog  and  rabbit,  but  not 
for  the  cat.  For  this  animal,  saturated  sodium  sulphate  should  be  used.  A  10  per  cent, 
sodium  citrate  or  0-4  per  cent,  potassium  oxalate  solution  may  also  be  employed  for 
all  animals. 


188 


A  TEXTBOOK  OF  PHYSIOLOCiY 


unable  to  record  faithfully  the  actual  systolic  and  diastolic  varia- 
tions of  pressure.  To  effect  this  record,  delicate  spring  manometers 
of  rapid  action  and  small  inertia  have  been  invented  (Fig.  93).  The 
sphygmoscope  consists  of  the  finger  of  a  rubber  glove  drawn  loosely 


Fiu.  93. — Kurthle'.s  Spring  Manomt."  lr. 


'iit 


ailN' 


Fig.  94. — Sphygmoscope. 


so  as  to  leave  an  air-space  over  the  end  of  a  rubber  cork  and  enclosed 
in  a  glass  tube.  The  finger  stall  acts  as  a  spring  and  the  tube  is 
connected  with  a  recording  tambour  (Fig.  94).     A  mercury  manometer 


Fig.  95. — The  Armlet  Sphygmometer.      (Leonard  Hill.) 

The  arm  is  slipped  through  the  armlet,  and  the  latter  fixed  round  the  upper  arm  by- 
drawing  the  straps  tight.  The  armlet  should  be  placed  at  the  same  level  as  the 
heart.  The  syringe  bulb  is  then  rhythmically  compressed,  while  the  radial  pulse 
is  felt.  The  height  of  the  mercurial  column  is  noted  at  which  the  pulse  just  fails 
to  meet  the  wrist.  The  screw  valve  attached  to  the  syringe  bulb  is  opened,  and 
the  pressure  allowed  to  fall  gradually,  a  reading  being  taken  at  the  moment  when 
the  pulse  again  reaches  the  wrist. 

provided  with  maximum  and  minimum  valves  has  also  been  employed 
to  indicate  the  maximal  systolic  and  minimal  diastolic  pressure. 

For  determining  the  arterial  pressure  in  man,  the  apparatus  used 
is  known  as  a  "  sphygmometer,"  or  "  sphygmomanometer."     This  con- 


THE  ARTERIAL  PRESSURE 


189 


sists  of  an  armlet,  a  rubber  bag  encased  in  soft  leather,  connected  bj 
tubing  and  T-piece  to  a  syringe  bidb  for  raising  the  pressure,  and  a 
mercury  manometer  or  spring  gauge  for  registering  the  same  (Fig.  95). 

After  the  armlet  is  buckled  on,  the  pressure  is  gradua,lly  raised  in 
the  armlet  b}'  means  of  the  syringe.  A  reading  is  taken  when  the 
pulse  in  the  artery  is  obliterated  below  the  armlet  (the  systolic  pressure). 
The  disappearance  and  reappearance  of  the  j)ulse  may  be  felt  with 
the  fingers,  or  heard  by  placing  a  stethoscope  over  the  artery  at  the 
elbow.  When,  as  the  pressure  i.s  relaxed,  the  i^ulse  comes  throiigh 
under  the  armlet,  a  loud  sound  is  heard  sj'nchronous  with  each  systolic 
wave.  As  the  pressure  is  further  relaxed,  the  sound  undergoes 
variation  in  tone,  but  at  a  certain  point  suddenly  diminishes  or  dis- 
appears. If  the  pressure  be  read  at  this  point,  it  denotes  the  diastolic 
pressure.  It  has  been  proved  by  experiments  on  animals  that  the 
sj'stolic  and  diastolic  jwessures,  so  measured,  agree  with  measurements 
made  directly  by  connecting  the  artery-  with  a  spring  manometer. 

The  pocket  sphj'gmometer  shown  in  Fig.  06  consists  of  a  rubber 


J,  J. HICKS    SOLE  MAKER    LONDON.    PATENT. 
Fig.  96. — Leonard  Hill  Pocket  Sphygmometer. 


bag  covered  with  silk,  which  is  tilled  v\'ith  air,  and  connected  by  a  short 
length  of  tube  to  a  manometer.  This  manometer  consists  of  a  gradu- 
ated glass  tube  open  at  one  end.  A  small  hole  is  in  the  side  of  the  tube 
near  this  end.  A  meniscus  of  coloured  t  Ikalinc  water  is  introduced  up 
to  the  side  hole — the  zero  mark  on  the  scale — by  placing  the  open  end 
of  the  tube  in  water.  The  bag  is  now  connected  to  the  gauge,  so  that 
the  side  hole  is  closed  by  the  rubber  tube.  To  take  the  arterifc.l  pres- 
sure the  rubber  bag  is  covered  with  the  hand,  and  pressed  on  the 
radial  artery  until  the  pulse  (felt  beyond)  is  obliterated,  the  height 
to  which  the  meniscus  rises  in  the  manometer  being  read.  This  gives 
the  systolic  pressure  in  the  artery.  The  air  above  the  meniscus  acts 
as  a  spring,  converting  the  instrument  into  a  spring  manometer.  It 
is  graduated  empirically  in  millimetres  of  mercury.*- 

The  systolic  pressure  of  young  men,  taken  in  the  radial  artery 
with  the  arm  at  the  same  level  as  the  heart,  may  be  taken  to  be  about 
100  to  110  mm.  of  Hg.  In  men  of  forty  to  sixty  years  the  systolic 
pressure  is  often  about  140  millimetres,  but  in  some  robust  men  it  is 
no  higher  than  in  youth. 

It  is  very  necessary  to  remember  that  the  blood-pressures,  taken 

*  The  graduation  is  at  sea-level.    A  correction  would  be  necessary  for  high  altitude:). 


19D 


A  TEXTBOOK  OF  PHYSIOLOGY 


in  different  vessels  and  postures,  vary  with  the  hydrostatic  pressure 
of  the  eohnnn  of  blood  which  lies  above  the  point  of  measurement. 
In  the  horizontal  ])osture  the  pressure  is  practically  the  same  in  all 
the  big  arteries.     In  the  standing  position  the  arterial  pressure  in  the 


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arteries  of  the  leg  is  higher  than  in  the  arm  by  the  height  of  the  column 
of  blood  separating  the  two  points  of  measurement  (see  p.  200). 

A  difference  between  arm  and  leg  pressures  in  the  horizontal 
position  can  be  brought  about  in  the  nornipJ  person  by  violent  exercise, 
for  this  increases  the  height  of  the  systolic  wave.     The  leg  arteries, 


THE  ARTERIAL  PRESSURE 


191 


under,  the  above  conditions,  are  less  labile,  and  conduct  the  big  crest 
of  the  wave  better  than  the  arm  arteries.  There  are  other  possible 
factors  at  work  which  cannot  be  discussed  here.  In  cases  of  aortic 
regurgitation  there  is  present  a  well  marked  and  diagnostic  difference 
of  pressure  between  arm  and  leg  in  the  horizontal  position. 

When  the  bag  of  the  sphygmometer  is  applied  to  an  arterj-  (such  as 
the  dorsalis  pedis)  which  lies  upon  bone  unsupported  by  tissues,  a  far 
lower  jDressure  (30-35  mm.  Hg)  than  that  in  the  artery  suffices  to  obliterate 
the  pulse.  Under  these  conditions,  the  artery  is  easily  deformed  from 
the  round  to  the  oval  shape.  This  change  in  shape  occasions  an  in- 
creased resistance  to  the  passage  of  the  pulse-wave,  and  the  force  of 


k  ^j-j^MrU.y^-mu^^' 


A.  ABDOMEN. 


B.  CHEST. 


C.ABOOMEN. 


"^nsp. 

BP.Lme 


D.  CHEST. 


Fig.  98. — Influexce  of  Chest  axd  Abdumi>"al  Beeathixg  ()>•  the  Pulse.     (Lewis.) 


the  pulse  in  consequence  becomes  spent  in  the  labile  arterial  system 
above  the  point  of  deformation.  Where  the  arter}'  is  surrounded  by 
tissues  full  of  circidating  blood,  it  cannot  become  deformed  until  the 
blood-pressure  in  the  vessels  of  the  surrounding  tissues  is  overcome. 
The  pressure  of  the  bag  first  obliterates  the  veins;  the  pressure  then 
rises  in  the  capillaries  and  approximates  to  the  arterial  pressure  as  the 
compression  is  increased.  Finalh\.  the  arterial  pressure  is  overtoj)ped, 
and  then  the  compression  comes  to  act  upon  the  main  artery,  and 
this  being  deformed,  the  pulse  ceases  to  come  through.  This  is  ex- 
emplified in  Fig.  97.  In  A,  with  the  artery  laying  in  a  tube  surrounded 
by  tiuid,  corresponding  to  the  tissues,  the  pressure  recj^uireel  to  drmp 


192  A  TEXTBOOK  OF  PHYSIOLOGY 

down  the  pulse;  just  overto])})e(l  the  arterial  pressure.  When  exposed 
on  a  watchglass,  as  in  B,  the  lumen  became  deforinod  and  the  pulse 
damped  at  a  much  lower  pressure. 

If  the  armlet  be  placed  upon  the  arm,  and  kept  at  a  pressure  a 
little  below  that  of  the  arterial  supply  to  the  arm,  the  limb  gradually 
becomes  congested  and  the  superficial  veins  engorged  with  blood. 
Measurement  of  the  pressure  in  these  superficial  veins  reveals  a  pressure 
approximately  equal  to  that  registered  by  the  manometer  measuring 
the  arterial  joressure.  The  capillaries  of  the  arm,  under  these  condi- 
tions, become  more  and  more  congested;  those  that  were  previously 
empty  gradually  fill.  An  aching  feeling  comes  on,  which  terminates 
the  experiment.  The  experiment  shows  how  many  capillaries  arc 
cmj^ty  under  normal  conditions.  In  active  life  we  are  continually 
moving  our  position,  so  as  to  prevent  continuous  jjressure  on  any 
]:)art  and  further  the  circulation. 

Circumstances  affecting  the  Arterial  Pressure. — The  arterial  pres- 
sure is  raised  during  exertion  by  the  more  forcible  beat  of  the  heart — 
e.g.,  pressures  of  140  to  190  mm.  Hg  have  been  observed  immediately 
after  running  upstairs.  It  rapidly  sinks  to  a  lower  level  than  usual 
after  the  exertion  is  over — e.g.,  90  mm.  Hg — owing  to  the  quieter 
action  of  the  heart  and  the  persistence  of  the  cutaneous  dilatation 
of  the  bloodvessels  which  is  evoked  by  the  rise  of  body  temperature. 
In  athletes,  after  a  long  race,  rectal  temperatures  of  102°  to  105°  F. 
have  been  observed.  Mental  occupation  and  excitement  raises  the 
arterial  pressure.  People  engaged  in  brain  work  have  in  general  a 
higher  pressure  than  people  engaged  in  purely  manual  labour  working 
in  the  same  atmospheric  conditions.  After  meals  there  is  a  rise  in 
l^ressure. 

The  ordinary  statement  that  insj)iration  raises  and  expiration 
lowers  the  blood-pressure  is  only  true  for  an  animal  under  experi- 
mental conditions.  The  effect  of  respiration  on  the  blood-pressure 
is  very  complex.  A  deep  intercostal  breath,  if  not  too  prolonged, 
yields  a  fall,  a  deep  diaphragmatic  inspiration,  a  rise,  of  pressure. 
Forced  breathing  ceaises  a  fall,  while  Valsalva's  experiment,  a  deep 
expiration  with  the  mouth  and  nose  shut,  causes  a  marked  rise  in  the 
arterial  pressure.  The  effects  on  the  pressure  of  different  tj'pes  of 
breathing  in  a  trained  subject  were  as  folloAvs: 


Type  of  Ereathinj.  i     Inspiration. 

Suspended 
Inspiration. 

Expiration. 

Suspended 
Expiration. 

Thoracic                  . .                - 
Abdominal             . .                4 

+ 

+ 

■Jr- 

Records  of  the  pulse  obtained  by  the  suspension  method  (p.  211) 
show  these  results  (Fig.  98).  In  such  records  a  rise  in  the  tracing 
indicates  a  rise  of  pressure,  a  fall  in  the  tracing,  a  fall  of  pressure. 

Increase  in  the  amount  of  fluid  by  transfusion  cannot  raise  the 


THE  ARTERIAL  PRESSURE  193 

pressure  alxive  what  can  be  obtained  with  a  normal  amount  of  blood. 
Similarly,  bleeding  to  the  extent  of  2  to  3  per  cent,  of  the  body  weight 
causes  little  or  no  fall  of  arterial  pressure. 

The  taking  of  alcohol  lowers  the  arterial  pressure.  During  chloro- 
form anaesthesia  the  pressure  falls  (Fig.  104).  During  deep  sleep  the 
pressure  is  lower,  but  not  lower  than  in  the  waking  state  when  the 
body  is  recumbent  and  at  rest.  Immersion  in  a  hot  bath  lowers,  in 
a  cold  bath  raises,  the  pressure. 

The  arterial  pressiu-e  is  considerably  higher  in  warm  than  in  cold 
blooded  animals — at  least  three  times  greater.  The  pressure  is  inde- 
pendent of  the  size  of  the  animal,  and  thus  may  be  as  great  in  the  cat 
as  in  the  horse. 

It  will  thus  be  seen  that  the  maintenance  of  a  mean  arterial  pressure 
of  constant  height  is  the  function  of  the  circulatory  mechanism.  On 
the  one  hand,  we  are  convinced  that  this  object  is  attained  during  life; 
on  the  other  hand,  we  know  that  countless  and  ceaseless  variations. 
are  occurring  in  all  parts  of  the  circulatory  system.  The  whole  system, 
is,  therefore,  so  craftily  built  and  so  delicately  balanced  that  every 
variation  in  one  part  is  compensated  by  a  simultaneous  and  contrary 
variation  in  another  part,  and  thus,  throughout  the  wear  and  tear  of 
life,  the  aortic  pressure  is  kept  at  a  constant  mean  height. 


15 


CHAPTER  XX  IT 


THE  EFFECT  OF  CHANGE  OF  POSTURE  ON  THE 
CIRCULATION 

Thk  circulation  is  «o  contrived  that  it  remains  constant  and 
efficient,  not  only  in  the  horizontal  position,  but  also  when  the  living 
animal  is  ceaselessly  shifting  the  position  of  his  body.  The  hydro- 
static influence  of  gravity  must  have  had  a  most  imj)ortant  bearing 
on  the  evolution  of  the  mechanisms  which  control  the  circulation. 

This  is  well  demonstrated  by  the  following 
model ; 

Suppose  a  closed  and  rigid  tube  filled  with  water 
and  fixed  to  a  board.  When  the  board  is  placed 
in  the  horizontal  joosition,  the  pressure  in  all  parts 
of  the  tube  will  be  the  same.  If  the  board  be 
turned  into  the  vertical  position,  then  the  pressure 
p,  I  ^ — v^.  I  y.  at  the  top  end  will  become  higher  than  the  pressure 
lrn|f\Jl^'](  \\i  at  the  bottom  end  by  the  height  of  the  column  of 
fluid.  The  fluid  will  still  equally  pervade  the  tube 
in  all  its  parts.  This  must  be  so,  because  the  fluid 
is  incompressible,  and  the  tube  is  rigid  and  unyield- 
ing in  structure. 

If  the  rigid  tube  be  now  replaced  by  an  elastic 
tube,  and  this  at  the  j)oints  A  and  B  be  made  to 
expand  into  thin-walled  elastic  bags,  then  the  con- 
ditions become  markedly  different  (Fig.  99).  On 
placing  such  a  model  in  the  vertical  position,  the 
bag  {B)  expands  under  atmospheric  pressure  plus 
the  pressure  of  the  column  of  fluid  [A,  B);  and 
while  the  water  flows  into  B,  A  empties  and  shrinks 
luider  the  atmospheric  pressure. 

If  a  pump,  P,  which  can  work  with  uniformity 
and  maintain  a  constant  circiilation,  })e  placed  in 
such  a  model ;  if  the  outflow  tubes  or  arteries  be  made 
of  small  capacity,  and  labile — that  is,  possessing 
considerable  extensibility,  and  elasticity — and  the  inflow  tubes  or 
veins  be  valved,  and  be  made  of  considerable  capacity  and  slight 
extensibility  and  elasticity ;  and  if  a  sponge  be  inserted  as  a  resistance 
in  the  bags  {A  and  B),  then  many  of  the  conditions  of  the  systemic 
circulation  are  closely  represented  in  the  model.  A  is  now  equivalent 
to  the  capillary  area  of  the  head,  B  to  the  splanchnic  area  of  capillar'es. 
When  the  model  is  placed  in  the  vertical  position  with  the  puni]) 

194 


Fig.  99.  —  Artifi- 
cial Schema  to 
SHOW  Effect  of 
Gravity  on  the 
Circulation. 


THE  EFFECT  OF  CHANGE  OF  POSTURE  195- 

at  work,  owing  to  the  great  disteusibility  of  the  splanchnic  capillaries, 
and  veins  {B),  the  fluid  will  collect  in  B,  and  A  will  cnipt}-.  But  it 
B  is  compressed  by  the  hand  so  as  to  raise  the  fluid  in  the  vein  u]> 
to  the  pump,  then  the  circulation  Avill  recommence. 

The  blood,  owing  to  its  weight,  continually  presses  downwards, 
and  under  the  influence  of  gravity  would  sink  if  the  veins  and  capil- 
laries of  the  lower  parts  were  sufficientlj'  extensile  to  contain  it.  Such 
is  actually'  the  case  in  the  snake  or  eel,  for  the  heart  empties  so  soon 
as  one  of  these  animals  is  immobilized  in  the  vertical  posture.  This 
does  not  occur  in  an  eel  or  snake  immersed  in  water,  for  the  hydro- 
static pressure  of  the  column  of  water  outside  balances  that  of  the 
blood  within.  During  the  evolution  of  man  there  have  been  developed 
special  mechanisms  bj'  Avhicli  the  determination  of  the  blood  to  the 
lower  parts  is  prevented,  and  the  assumption  of  the  erect  posture 
rendered  j)ossible.  The  pericardium,  by  its  attachments,  prevents 
displacement  of  the  heart  as  a  whole,  and  also  supports  the  right  heart 
Avhen  the  weight  of  a  long  column  of  venous  blood  suddenly  bears 
upon  it — as,  for  example,  when  a  man  stands  on  his  head.  The  ab- 
dominal viscera  are  slung  upwards  to  the  spine;  below  they  are  sup- 
ported bj''  the  pelvic  basin  and  the  wall  of  the  abdomen,  the  muscles 
of  which  are  arranged  so  as  to  act  as  a  natural  waistband.  If  tame 
hutch  rabbits,  with  large  patulous  abdomens,  be  suspended  and 
immobilized  in  the  erect  posture,  death  may  result  in  from  fifteen  to 
thirty  minutes,  for  the  circulation  through  the  brain  ceases  and  the 
heart  soon  becomes  emptied  of  blood.  If,  however,  the  capacious 
veins  of  the  abdomen  l^e  confined  by  an  abdominal  bandage,  no  such 
result  occurs. 

In  a  man  6  feet  high  the  hydrostatic  pressure  of  a  column  of 
blood  reaching  from  the  vertex  of  the  head  to  the  sole  of  the  foot  is 
equal  to  140  mm.  Hg.  But  man  is  naturally  provided  v\'ith  an  efficient- 
abdominal  belt,  although  this  is  often  weakened  by  neglect  of 
exercise  and  by  gross  indolent  living.  The  splanchnic  arterioles 
are  maintained  in  tonic  contraction  by  the  vaso-motor  centre,  and 
thus  the  floAv  of  blood  to  the  abdominal  viscera  is  confined  within 
due  limits.  The  veins  of  the  limbs  are  broken  into  short  segments 
by  valves,  and  these  support  the  weight  of  the  blood  in  the  erect 
posture.  The  brain  is  confined  M'ithin  the  rigkl  wall  of  the  skull,  and 
by  this  wall  are  the  cerebral  vessels  supported  and  confined  when  the 
pressure  is  increased  by  the  head-down  posture.  Every  contraction  of 
the  skeletal  muscles  compresses  the  veins  of  the  body  and  limbs,  for 
these  are  confined  beneath  the  taut  and  elastic  skin.  The  pressure 
•of  the  body  agamst  external  objects  has  a  like  result.  Guided  by 
the  valves  of  the  veins,  the  blood  is  b}^  such  means  continually  driven 
upwards  into  the  vense  cava?.  If  the  reader  hangs  one  arm  motionless 
until  the  veins  at  the  back  of  the  hand  become  congested,  and  then 
either  elevates  the  limb  or  forcibly  clenches  the  fist,  he  will  recognize 
the  enormous  influence  which  muscular  exercise  and  continual  change 
of  posture  has  on  the  return  of  blood  to  the  heart.  It  becomes  weari- 
some and  i^oon  impossible  for  a  man  to  stand  motionless.     When  a 


J9() 


A  TEXTBOOK  OF   PHVS10L0(JY 


man  is  crucified — that  is  to  say.  iiiiinobiii/.ed  in  the  erect  posture — 
the  blood  slowly  sinks  to  the  most  dependent  parts,  oedema  and  thirst 
result,  and  finally  death  from  cerebral  anaemia  ensues.  In  man, 
standing  erect,  the  heart  is  situated  above  its  chief  reservoir— the 
abdominal  veins.  The  blood  is  raised  by  the  action  of  the  respiratory 
movements,  which  act  both  as  a  suction  and  as  a  force  pump;  for  the 
blood  is  not  only  aspirated  into  the  right  ventricle  by  the  expansion 


Fig.  100. — To  show  Effect  of  Gravity  upon  the  Circulation  :   Carotid  and 
Superior  Vena  Cava  Pressures  of  Dog.     (L.  H.) 

FD,  Animal  turned  into  feet-down  position  with  cannulse  in  axis  of  rotation.  The 
arterial  pressure  fell  in  fifty  minutes  from  110  mm.  Hg  to  42  mm.  Hg.  From  C 
to  EX  animal  was  immersed  in  a  bath  which  was  deepened  to  chin  at  D.  Note 
increased  effect  of  respiration  on  venous  pressure  after  FD,  and  again  after  bath. 
Note  also  fall  of  pressures  at  FD.  and  compensatory  rise  of  arterial  pressure,  which 
gradually  weakens. 


of  the  thoracic  cavity,  but  is  expressed  from  the  abdomen  by  the 
descent  of  the  diaphragm.  When  a  man  faints  from  fear,  his  miiscular 
system  is  relaxed  and  respiration  inhibited.  The  blood,  in  conse- 
quence, sinks  into  the  abdomen,  the  face  blanches,  and  the  heart 
fails  to  fill.  He  is  resuscitated  either  by  compression  of  the  abdomen 
or  by  being  placed  in  a  head-down  posture.  To  prevent  faintness 
and  drive  the  blood-stream  to  his  brain  and  muscles,  a  soldier  tightens 


THE  EFFECT  OF  CHANGE  OF  POSTURE  197 

his  belt  before  entering  into  action.  Similarly,  men  and  women  with 
lax  abdominal  wall  and  toneless  muscles  take  refuge  in  the  wearing  of 
abdominal  belts.  To  maintain  a  vigorous  circulation  and  digestion, 
it  is  necessary  to  exercise  the  muscles  daily,  particularly  those  of  the 
abdomen. 

.  The  question  may  be  studied  experimentally  by  passing  cannuls& 
•down  the  external  jugular  vein  and  carotid  artery  into  respectively 
the  superior  vena  cava  and  aorta  of  a  dog,  ana?sthetized,  and  placed 
upon  a  specially  constructed  animal  table,  which  is  made  to  tm-n 
romid  an  axis  j^assing  through  the  body  at  the  level  of  the  cannulas. 
Upon  turning  the  table,  any  alteration  in  the  level  of  fluid  in  the 
manometer  tubing  is  thus  avoided.  The  effect  of  changes  of  posture 
are  then  truly  recorded.  On  placing  the  animal  in  the  feet-down 
posture,  the  arterial  and  venous  j^ressures  immediately  fall.  The 
venous  pressure  remains  down  luitil  the  horizontal  posture  is  once 
more  assumed.     The  arterial  pressure  raj^idly  rises  again  to  normal 


Fig.  101. — Aortic  Press-re.     (L.  H.) 

A,  Vertical  feet-down  position  ;  B,  C,  effect  of  abdominal  compression; 
D,  hDrizontal  position. 

{FD:  Fig.  100),  and  often  it  may  be  found  to  rise  above  normal. 
The  respiratory  undulations  are  frequently  intensified  while  the  animal 
is  in  the  feet -down  posture.  If  left  long  in  the  feet-down  position, 
the  compensatory  mechanism  graduallv  fails  and  the  arterial  pres- 
sure falls  (Fig.  100). 

If  the  spinal  cord  be  divided  at  the  level  of  the  first  dorsal  vertebra, 
the  infiuence  of  the  bidbar  centres  on  the  parts  below  the  section  is 
removed.  Abdominal  and  intercostal  respiration  is  paralyzed,  and 
the  breathing  becomes  purely  diaphragmatic.  The  tone  of  the  great 
splanchnic  area  of  arterioles  is  lost,  the  tone  of  the  abdominal  A\all 
is  abolished,  and  thus  the  capacity  of  the  abdominal  vessels  is 
greatly  increased.  The.  total  effect  on  the  animal,  when  lying  in 
the  horizontal  posture,  is  a  considerable  fall  of  arterial  pressiu-e, 
and  a  marked  diminution  of  the  respiratory  undulations  of  pressure. 
If  the  animal  be  now  droiDjied  into  the  vertical  feet-down  posture, 
the  arterial  pressure  falls  rapidh^  and  may  reach  zero;  the  circidation 
is  then  at  an  end.  This  is  so  because  the  great  abdominal  veins  sag 
•out  midcr  the  hj'^drostatic  pressure.     In  them  the  whole  of  the  blood 


1U8  A  TEXTBOOK  OF  PHYSIOLOGY 

collects,  for  it  can  ])ass  rapidly  through  the  dilated  arteiioles;  there 
is  no  mechanism  left  for  filling  the  heart.  Thus  the  heart,  empty  of 
blood,  continues  to  beat  to  no  purpose.  If  the  abdommal  wall 
be  compressed  with  the  hand  (B,  (\  Fig.  lOl).  the  capacity  of  the 
veins  and  si)lanchnic  area  is  reduced,  the  right  heart  is  once  more 
filled  with  blood,  the  arterial  pressure  rises,  and  the  circulation 
is  renewed.  On  taking  off  the  hand,  the  heart  once  more  empties, 
the  arterial  pressure  falls,  and  the  circulation  ceases.  When  the 
animal  is  returned  to  the  horizontal  position,  the  influence  of  gravity 
is  abolished,  and  the  circulation  immediately  becomes  re-established. 
The  effect  of  compression  of  the  abdomen  in  the  horizontal  position 
is  also  evident  (/?,  C,  Fig.  102)  but  slight.  In  the  feet-up  position 
the  aortic  pressure  rises  under  the  influence  of  gravity,  returning 
to  normal  if  compensation  takes  place  or  when  the  horizontal  posi- 
tion is  resumed  (Fig.  102).  Such  experiments  prove  that  in  the 
anaesthetized  animal  there  are  two  chief  compensatory  mechanisms 
by  which  the  hydrostatic  effect  of  gravity  is  overcome — namely,  the 
vaso-motor  mechanism  of  the  arterioles  and  the  respiratory  ];ump. 


Fig.  102. — Aortic  Pbessuee.     (L.  H.) 

A,  Horizontal  position;  B,  C,  abdomen  compressed;  D.  vertical  fect-iip  position; 
£",  i^,  abdomen  compressed;  G,  horizontal. 

It  is  necessary  to  examine  these  separately,  and  estimate  the  relative 
power  of  each. 

The  vaso-motor  tone  of  the  great  splanchnic  area  can  be  easily 
abolished,  without  affection  of  the  respiratory  mechanism,  by 
section  of  the  sjilanchnic  nerves — that  is  to  say,  if  these  nerves  are 
reached  by  a  lumbar  incision,  and  all  interference  with  the  thorax 
or  abdominal  wall  is  avoided. 

As  the  result  of  section  of  the  splanchnic  nerves  in  the  vertical  feet- 
down  posture,  the  arterial  pressure  falls  very  considerably;  but, 
nevertheless,  the  circulation  may  remain  efficient,  on  account  of  the 
action  of  the  respiratory  pump.  A  form  of  respiration  may  be 
evoked  whicli  consists  of  thoracic  inspiratory  aspirations,  combined 
with  powerful  abdominal  compressions.  Thereby  the  diastolic  filling 
of  the  heart  is  maintained,  and  the  velocity  of  flow  through  the 
splanchnic  capillaries  checked.  On  dividing  the  abdominal  wall  by 
a  crucial  incision,  the  support  of  the  abdominal  muscles  is  withdrawn, 
the  splanchnic  vessels  dilate,  and  the  pressure  falls  to  a  further  extent. 
Finally,  on  suddenly  opening  the  thorax,  the  j)ressure  falls  to  zero,. 


THE  EFFECT  OF  CHANGE  OF  POSTURE  199 

and  the  circulation  ceases  (Fig.  103).  By  compression  of  the  abdomen, 
or  by  a  return  to  the  horizontal  posture,  the  circulation  can  be  onoe 
more  renewed. 

This  experiment  shows  that  the  respiratory  pump  can  compensate 
for  the  influence  of  gravity  when  the  vaso-motor  mechanism  is 
paralyzed.  The  respiratory  pump  can  be  paralyzed  by  itself  and 
without  damage  to  the  vaso-motor  meohan'sm  by  the  inject'on  of 
curari.  The  power  of  the  heart  miy  then  be  sufficient  by  itself  to 
maintain  the  circulation  in  the  feet-down  position,  so  long  as  the 
capacity  of  the  abdominal  vessels  is  kept  under  control  bj'  the  vaso- 
motor nerves. 

The  effect  on  the  circulation  of  rendering  the  intrathoracic  pressure 


Fig.  103. — Aortic  Pressuee  :    Morphixized  Dog.     (L.  H.) 

.4,  Vertical  feet -duwn  position,  .>planchnic  nerves  divided  ;  B,  effect  of  compressing 
abdomen  ;  C,  abdominal  wall  divided  ;  D,  thorax  opened. 

positive — e.g.,  by  compression  of  the  thorax — is  that  the  blood  stag- 
nates in  the  abdomen,  and  the  circulation  ceases,  whenever,  by  any 
means,  the  thoracic  pressure  is  rendered  sufficiently  positive  to  over- 
come the  venous  pressure  produced  by  the  driving  power  of  the  heart 
and  the  compressive  action  of  the  abdominal  wall.  Owing  to  the 
influence  of  gravity,  this  state  of  affairs  is  brought  about  more  easily 
in  the  vertical  feet-down  position  than  in  the  horizontal  posture. 
Compensation  for  the  positive  intrathoracic  pressure  is  supplied  by 
firm  compression  of  the  abdomen:  the  heart  then  fills,  and  the 
arterial  pressure  regains  its  normal  level. 

Measurements   of  arterial   pressure   likewise   reveal   the   effect   of 
gravity  upon  the  circulation  in  man.     In  a  normal  man  standing  up- 


200 


A  TEXTBOOK  OF  PHYSlOLOdY 


right  the  pressure  in  the  post-tibial  artery  in  the  leg  is  higher  than  the 
pressure  in  the  brachial  artery  by  the  height  of  the  column  of  blood 
which  reaches  from  one  artery  to  the  other,  about  70  mm.  Hg. 

In  the  horizontal  posture  the  ])ressures  are  the  same.  With  the 
body  in  an  L-^haped  ])osition,  or  in  the  head-down  posture,  there  is 
also  a  difTercnce  in  jiressure  between  arm  and  leg.  These  differences 
are  well  exemplified  in  the  following  figures.  It  will  be  noticed  that 
it  is  the  leg  pressure  which  alters,  not  the  brachial  to  any  great  extent: 


Posture. 


Horizontal 

.Standing 

L-posture,  legs  up 
Vertical,  head  down 


Brachial 

Artery, 

Pressure  in 

Mm.  Hg. 


106 
110 
115 
115 


Posterior 

Tibial 

A  rtery. 

Pressure  in 

Mm.  Hg. 


106 
165 

85 
50 


Difference 
in  Mm.  Hg. 


30 
65 


Difference 
calculated 

Height  of 
Colnmti, 

JromHeig/it 
of  Column 

separating 
Armlets, 

in  Mm. 

Hg. 

in  Cm. 

0 

0 

58 

75-4 

.S3 

44 

63 

82 

In  changes  of  posture,  then,  the  pressure  in  the  brachial  artery — 
that  is,  in  the  root  of  the  aorta — is  maintained  at  practically  a  con- 
stant height  by  the  tone  of  the  splanchnic  arterioles  and  action  of 
the  respiratory  pump.  If  the  splanchnic  arterioles  are  in  an  efficient 
state  of  tone,  and  if  the  abdominal  veins  are  supported  by  the  tone 
of  the  abdominal  wall,  then  the  splanchnic  vessels  will  not  dilate  under 
the  hydrostatic  stress  of  gravity.  The  nervous  mechanism  involved 
is  probably  of  the  simplest  nature,  for  if  the  arterial  pressure  sud- 
denly rise  or  fall  at  the  moment  of  change  in  posture,  the  bulbar 
centres  are  thereby  either  directly  or  reflexly  excited  to  increased  or 
decreased  activit3^  A  sudden  fall  of  arterial  pressure  provokes 
acceleration  of  the  heart,  amplified  respiration,  and  increased  vaso- 
constriction. A  sudden  rise  of  pressure,  on  the  other  hand,  provokes 
a  slow  heart,  shallow  respiration,  and  vaso -dilatation. 

When  the  compensatory  mechanism  is  abolished  by  destruction, 
exhaustion,  or  inhibition  of  the  bulbar  centres,  the  circulation  fails, 
and  becomes  inadequate  to  maintain  life  in  the  vertical  feet-down 
posture.  The  blood  passes  into  the  capacious  reservoirs  of  the  tone- 
less abdominal  veins,  the  heart  empties,  and  the  cerebral  circulation 
ceases.  There  can  be  no  doubt  that  the  control  of  this  compensatory 
mechanism  is  one  of  the  most  important  and  necessary  functions  of 
the  group  of  bulbar  centres — a  function  which  must  have  been  evolved 
to  its  highest  point  as  man  in  his  evolution  assumed  the  erect  posture. 

During  the  course  of  each  daj'  the  compensatory  mechanism 
becomes  exhausted  ;  especially  is  this  so  after  severe  muscular 
exertion.  By  sleep  the  compensatory  power  is  restored.  In  condi- 
tions of  neurasthenia,  weakness  and  exhaustion  after  disease,  shock 
after  severe  injury  or  haemorrhage,  this  i)ower  may  be  almost  entirely 
lost.     In  this  connection  we  must  bear  in  mind  the  supply  of  ad- 


THE  EFFECT  OF  CHANGE  OF  POSrURE 


201 


Fig.  104. — The  Effect  t>F  Aujiini.stkatiun  ijf  Chlukofurm  upon  the  Heart 
Volume  (Cardiometer)  and  Arterial  Pressure  of  a  Decerebrate  Dog  : 
Time  in  Seconds.     (Dixon.) 

3  to  4  per  cent.  Chloroform  administered  during  period  A.  Systole  (downstroke) 
becomes  progressively  weaker  and  cardiac  tonus  is  diminished,  so  that  the  heart 
becomes  distended  with  blood,  only  a  small  proportion  of  which  is  expelled  during 
systole.  The  fall  in  blood-pressure  is  due  to  this  effect;  as  the  cardiac  systole 
improves  the  blood-pressure  rises. 


Fig.  IOo. — Sa.me  as  Fig.  104,  but  nearly  Pure  Ether  administered.     (Dixon. 

The  systolic  contractions  are  weakened,  but  the  effect  is  less  serious  than  with  chloro- 
form, and  the  fall  in  blood -pressure  less. 


202  A  TEXTBOOK  OF   PHYSIOLOGY 

renalin  furnished  by  the  a(h-eiial  «i;laiMls.  Ath-enah'n  maintains  the 
tone  of  the  syni))athetic  S3'stem. 

By  su(I(l(ui  fright  in  the  standing  posture  the  respiration  is  often 
arrested,  th(;  vaso-motor  tone  inhibited,  and  syncope  induced  by  the 
blood  sinking  into  the  abdomen.  Recovery  from  syncope  is  brought 
al:out  by  the  assumption  of  the  horizontal  position  or  compression 
of  the  belly.  When  the  compensatory  mechanism  is  entirely  lost, 
the  circulation  is  only  possible  in  the  recumbent  position,  and  life  is 
at  its  lowest  ebb.  Among  the  anaesthetics  in  common  use,  chlorofoj-ni 
stands  jDrepotent  as  a  drug  which  has  the  power  to  abolish  the  com- 
pensatory mechanism.  Chloroform  causes  cardiac  dilatation  (Fig.  104), 
weakens  the  respiration,  and  makes  flaccid  the  abdominal  muscles. 
The  effects  of  ether  are  not  so  serious  (Fig.  105). 

A  useful  clinical  guide  to  the  condition  of  the  compensatory 
mechanism  in  man  is  afforded  not  only  by  the  pressure  in  the  brachigl 
artery,  but  by  the  rate  of  the  pulse  on  change  of  posture.  If  the  heart 
greatly  accelerates  on  rising  from  the  horizontal  to  the  vertical  position, 
the  mechanism  is  deficient. 


CHAPTER  XXiri 


THE  VELOCITY  OF  BLOOD-FLOW 

The  velocit^'of  the  blood  at  an}'  point  in  a  vessel  may  be  defined 
as  the  length  of  the  column  of  blood  flowing  by  that  point  in  a  second. 
In  the  case  of  a  tube  siipplied  by  a  constant  head  of  pressure,  we  can 
divide  the  tube  and  measure  the  outflow  per  second:  knowing  the 
volume  of  this,  and  the  cross  area  of  the  artery,  v.'e  can  determine 
the  length  of  the  column.  This  kind  of  experiment  cannot  be  done 
■  >n  the  living  animal,  because  the 
opening  of  the  vessel  alters  the 
resistance  to  flow,  and  the  loss  of 
blood  also  changes  the  physiological 
conditions.  To  determine  the  velo- 
city, other  means  must  be  devised. 
One  form  of  instrument  is  called 
the  "  stromuhr  "  (stream-clock), 
(Fig.  106)  consisting  of  two  bulbs 
mounted  on  a  rotating  platform 
pierced  with  two  holes.  One  bulb  is 
tilled  with  oil,  the  other  with  blood. 
The  bulbs  are  connected  together 
by  a  tube  at  their  upper  end,  and 
the  lower  end  of  the  one  full  of  oil  is 
brought  over  one  hole  in  the  rotating 
platform.  The  central  end  of  the 
arter}'  is  connected  to  the  same 
hole  and  the  peripheral  end  to  the 
other,  over  which  stands  the  bulb 
full  of  blood.  The  blood,  being 
allowed  to  flow,  displaces  the  oil  out 
of  the  one  bull)  into  the  other. 
Directly  this  happens,  the  bulbs  are 
rotated,  and  the  one  full  of  oil  is 
again  brought  over  the  central  end 

of  the  artery.  The  number  of  rotations  per  minute  is  counted,  and 
the  volume  of  the  bulb  being  known,  we  obtain  the  volume  of  blood 
that  passes  through  the  instrument  per  minute. 

An  improved  form  of  the  instrument  is  seen  in  Fig.  107. 

In  using  this  instrument,  the  tube   {y^)   is  placed  in  connection 
with    the    central   end,   and   the   tube    (^/.,)   in   connection   with  th& 

203 


Fig.  106. — Thk  Stromuhr. 


204 


A  TEXTBOOK  OF  PHYSIOLOGY 


peripheral  cud  of  the  artery  which  is  under  investigation.  The  whole 
instrument  is  washed  out  with  oil  to  prevent  clotting,  and  filled  with 
defibrinated  blood.  80  soon  as  the  blood  is  allowed  to  flow  from  the 
artery,  the  metal  ball  {b)  is  driven  over  by  the  current  till  it  reaches 
the  end  of  the  cylinder  (a).     The  instrument  is  then  rapidly  rotated 


Fig.   107. — Stromuhr.     (Tigcrstedt.) 

on  the  drum  (k),  so  that  the  position  of  the  entering  and  exit 
tubes  is  le versed.  The  metal  ball  is  now  once  more  driven  by  the 
current  to  the  opposite  end  of  the  cylinder.  This  jDrocedure  is 
repeated  several  times,  and  the  number  of  revolutions  during 
the  period  of  observation  is  noted.      The  capacity  of  the  cylinder 


Fig.    108. — ChAUVEAU's    H.^MODliuMUilETER. 


(a),  minus  the  volume  of  the  ball  (6),  multiplied  by  the  number'of 
Tevolutions,  gives  the  volume  of  blood  which  has  passed  during  the 
period  of  observation ;  and  this  volume,  divided  by  the  time  and  the 
sectional  area  of  the  artery,  gives  the  mean  velocity  per  second.  In 
using  the  stromuhr,  the  mean  velocity  in  an  artery  is  found  to  vary 
greatly.     This,  for  the  most  part,  is  owin^  to  the  variations  of  resist- 


THE  VELOCITY  OF  BLOOD-FLOW 


205 


ance  in  the  peripheral  arterioles.  During  the  operative  procedure,, 
the  blood-How  must  for  a  time  be  cut  off,  and  this  causes  a  temporary 
parah'sis  of  the  arterioles,  which,  passing  off  as  the  circulation  is 
restored,  causes  variations  in  resistance. 

In  another  instrument,  the  hsemodromometer  (Fig.  108),  a  T-tube 
is  inserted  into  the  artery,  in  which  hangs  a  small  pendulum,  the  stem, 
of  the  pendulum  pasing  through  a  rubber  dam,  which  closes  the  vertical 
limb  of  the  tube.  The  pendulum  is  deflected  b}^  the  How,  and  the 
greater  the  velocity,  the  greater  the  deflection.  The  deflection  can 
be  recorded  by  connecting  the  free  end  of  the  pendulum  to  a  tambour 
arrangement.  By  this  instrument  the  variations  of  velocity  during 
systole  and  diastole  of  the  heart  can  be  recorded  and 
measured,  biit  it  can  only  be  used  in  the  vessels  of  large 
animals. 

If  in  a  schema  similar  to  that  given  in  Fig.  85  two  |i— - 
shaped  tubes,  a  and  b  (Pitot's  tubes),  be  inserted,  one  with 
the  elbow  opposing  the  stream,  the  other  with  the  elbow 
in  the  direction  of  the  stream,  the  fluid  will  rise  higher 
in  a  than  in  an  ordinary  side  tube,  and  lower  than  this 
in  b.  This  is  because  the  flowing  stream  exerts  a  push 
on  a  and  a  pull  on  b.  The  amount  of  this  push  and 
pull  varies  with  the  velocity  of  the  stream,  so  that  from 
the  difference  in  the  height  of  the  two  tubes  the  velocity 
can  be  calculated.  In  an  instrument  known  as  the 
photohaematochometer  (Fig.  109)  the  difference  in  height 
is  recorded  by  photography. 

The  velocity  may  also  be  calcidated  b}'  the  electrical 
method,  estimating  the  time  taken  for  the  blood  to  pass 
between  two  points  of  an  artery  when  salt  solution  is 
injected  into  the  circulation  (see  Circulation-time,  j^.  209). 

In  man,  the  quantity  of  blood  which  passes  through 
the  hand  or  foot  has  been  measured  by  plethysmographic  Fig.  109.  — 
means  (Fig.  110)  and  also  deduced  from  the  quantity  pnOTo'^ri 
of  heat  which  the  part  gives  off  to  a  water  calorimeter  matocho- 
in     which     it     is     immersed.       The    flow    in    grammes      meter. 

XT  1 

per  minute  is  obtained  from  the  formula,  Q=  -  ,^~^, '  where  Q 

m(I-i^)   s 

is  the  quantity  of  blood,  H  the  number  of  small  calories  given  off  in 

tn  miniates,  T  the  temperature  of  the  blood  entering  the  hand,  T^  that 

of  the  blood  leaving  the  hand,  and  s  the  specific  heat  of  the  blood 

(0-9°).     T  may  be  taken  as  0-5°  lower  than  the  rectal  temperature, 

and  T^  the  same  as  that  of  the  tepid  water  in  the  calorimeter. 

The  general  relations  of  the  velocity  of  the  blood  in  the  arteries, 
capillaries,  and  veins,  is  expressed  bj'  the  curv^e  shown  in  Fig.  111. 
The  velocity  in  the  large  arteries  may  reach  500  millimetres  per  second 
in  s^^stole,  and  fall  to  150  millimetres  in  diastole.  The  smaller  the 
artery  the  less  is  this  difference,  and  the  more  uniform  the  rate  of 
flow. 

The  velocity  and  pressure  of  the  blood  in  the  aorta  are  dependent 


200 


A  TEXTBOOK  OF  PHYSIOLOGY 


u])()n  the  energy  of  the  heart  and  ii])on  the  ])eri|)h<ial  resistance.     In 
the  hving  animal  these  factors  are  varying  constantly. 

1.  With  the  energy  of  the  heart  constant,  {a)  the  jjcripheral  re- 
sistance may  increase,  so  that  the  pressure  in  the  aorta  becomes  greater 


Sec 


•T 

/ 

/ 

/ 

J 

^ 

-.K- 

a< 

/ 

r-»«' 

u 

_J 

»-M 

J 

c 

urve 

a. 

^ 

^h- 

►Cl»_ 

-=*. 

curve 

c 

J 

/ 

12-   13'    /v'   IS"    d°    I]'  ii°  If  20"  zr   2z'  zi'  2f  «"  zC'  zy  zi'  2^'  io° 

EiG.  110. — Velocity  of  Flow  by  Plethysmogeaphic  Method.     (Hewlett.) 

Observations  on    a    single   individual :    a.  Passing  from  comfort  to  marked  chilli- 
ness; h,  comfort;  c,  passing  from  coolness  to  beginning  perspiration. 


Fiu 


111. — Diagram  showing  General  Relations  of  the  Velocity 3  f  the  Blood 
IN  THE  Arteries,  Capillaries,  and  Veins.     (Fredericq.) 


and  the  velocity  less;  (6)  the  peripheral  resistance  may  decrease,  the 
velocity  becoming  greater  and  the  pressure  less. 

2.  With  the  resistance  constant,  the  energy  of  the  heart  may 
increase  or  decrease,  thereby  increasing  or  decreasing  both  velocity 
and  pressure. 


THE  VELOCITY  OF  BLOOD-FLOW 


207 


3.  If  both  the  energy  of  the  heart  and  the  peripheral  resistance 
increase  proportionate!}',  the  pressure  will  rise,  but  the  velocity  remain 
constant. 

4.  With  an  increase  in  the  energy'  of  the  heart-beat,  and  a  decrease 
in  resistance  proportional  to  the  increase  of  cardiac  energ}^  the  pressure 
will  remain  constant  and  the  velocity  become  greater. 

5.  If  the  energy  of  the  heart  decreases,  but  the  peripheral  resistance 
increases  in  proportion,  again  the  pressure  remains  constant,  but  the 
velocity  becomes  less. 

6.  With  a  decrease  in  heart-beat,  and  a  proportional  decrease  in 
resistance,  the  pressure  falls,  but  the  velocit}^  remains  constant. 

7.  By  virtue  of  the  vaso-motor  mechanism  (see  p.  229),  the  periph- 
eral resistance  may  at  the  same   time  be  increased  in  one    section 


Fig.  112. — Carotid  Ahteky 


Velocity  of  Pressure  Curves. 
and  Lortet.) 


(Chauvcau 


of  the  arterial  system  and  decreased  in  another,  so  that  it  is  possible 
for  the  j)ressure  and  velocity  in  the  aorta  to  remain  constant,  Avhile 
the  velocit}'  is  varying  in  opposite  directions  in  different  parts  of  the 
vascular  system.  The  velocity  in  one  particular  arter}',  therefore,  is 
no  guide  to  the  general  condition  pertaining  in  the  system,  and  such 
velocity  bears  no  absolute  relation  to  the  rate  of  heart-beat  or  general 
arterial  pressure. 

In  the  tracing  (Fig.  112)  are  shown  the  synchronous  records  of 
velocity  (F)  and  of  pressure  (P)  obtained  in  the  carotid  of  the  horse.  It 
will  be  seen  that  the  curve  of  velocity  reaches  its  maximum  before  the 
curve  of  pressure.  This  is  so  because,  as  the  arteries  become  overfilled, 
the  heart  cannot  maintain  the  initial  velocity  of  outj)ut.  By  experiment 
it  was  found  that  the  velocity  in  the  carotid  artery  of  the  horse  reached 
520  millimetres  per  second  during  systole,  while  at  the  time  of  the 
dicrotic  wave  the  velocity  sank  to  220  millimetres  j)er  second,  and  in 
diastole  to  150  millimetres  per  .second.  Continuous  records  of  the 
velocity  curve  afford  a  valuable  means  of  arriving  at  the  volume  of 
blood   flowing  through  the  vascular  area   supplied  by  the  arter^'  in 


2(  8  A  TEXTBOOK  OF  PHYSIOLOGY 

question.     Thus  the  effect  on  the  blood-flow  of  vasomotoria!  excite- 
ment or  functional  activity  can  be  investigated. 

By  means  of  the  th-omograph  it  has  been  sliowti  that,  during 
systole,  the  blood  is  checked  by  the  compressive  action  of  the  cardiac 
muscle  in  its  flow  from  the  aorta  towards  the  coronary  arteries ; 
that  the  velocity  of  flow  in  the  carotid  is  five  or  six  times  greater 
when  a  horse  is  actively  masticating  than  when  at  rest.  The  normal 
velocity  in  the  carotid  artery  during  systole  was  found  to  be  540  milli- 
metres per  second.  After  section  of  the  cervical  sympathetic,  how- 
ever, in  consequence  of  the  peripheral  dilatation,  the  velocity  becomes 
equal  to  750  millimetres  per  second.  After  section  of  the  spinal  cord 
in  the  upper  dorsal  region,  the  velocity  in  the  arterial  system  becomes 
greatly  accelerated  during  systole,  and  greatly  diminished  during 
diastole.  Owing  to  the  lowering  of  the  peripheral  resistance  from 
the  loss  of  vascular  tone,  the  heart  is  able  to  discharge  the  blood  with 
greater  rapidity  into  the  venous  system,  and  in  consequence,  during 
diastole,  the  arterial  system  is  emptied  of  blood  to  a  great  extent.  If 
this  condition  be  pushed  to  an  extreme,  and  the  frequency  of  the  heart 
be  small,  the  blood  becomes  discharged  into  the  veins  intermittently. 
Comparative  records  have  been  obtained  of  the  velocity  of  flow 
in  the  carotid  and  facial  arteries.  At  the  end  of  the  diastole  the 
velocity  is  small  in  the  carotid,  and  relatively  great  in  the  facial 
artery.  In  the  beginning  of  the  systole  the  primary  wave  of  velocity 
rises  rapidly  in  the  carotid,  and  is  proportionately  small  in  the  facial 
artery.  The  secondary  increase  of  velocity,  which  is  produced  by 
the  dicrotic  wave,  is  far  more  evident  on  the  carotid  than  on  the  facial 
curve.  These  results  show  how  the  intermittent  energy  of  the  heart  is 
stored  up  by  the  elasticitj-  of  the  large  arteries,  and  expended  in 
maintaining  a  continuous  flow  through  the  small  arteries. 

The  flow  in  the  large  veins  is  approximately  equal  to  that  in  the 
large  arteries.  In  the  jugular  vein  of  a  dog  the  mean  velocity  was 
found  to  be  225  millimetres,  and  in  the  carotid  260  millimetres,  per 
second.  The  velocity  in  the  capillaries  has  been  measured  by  direct 
observation  with  the  microscope.  It  is  very  small — e.g.,  0-5  to  1  milli- 
metre per  second.  This  variation  of  velocity  in  different  parts  of  the 
vascular  system  is  explained  by  the  difference  in  the  width  of  bed 
through  which  the  stream  flows.  The  vascular  system  may  be  com- 
pared to  a  stream  which,  on  entering  a  field,  is  led  into  a  multitude 
of  irrigation  channels,  the  sum  of  the  cross-sections  of  all  the  channels 
being  far  greater  than  that  of  the  stream.  The  channels  gradually 
unite  together  again,  and  leave  the  field  as  one  stream.  If  the  flow 
proceeds  uniformly  for  any  given  unit  of  time,  the  same  volume  must 
flow  through  Siwy  cross-section  of  the  system.  Thus  the  greatest 
velocity  is  where  the  total  bed  is  narrowest,  and  slowest  where  the  bed 
widens  to  the  dimensions  of  a  lake. 

Any  general  change  in  velocity  at  any  section  of  this  circuit  tells 
both  backwards  and  forwards  on  the  velocity  in  all  other  sections, 
for  the  average  velocity  in  the  arteries,  veins,  and  capillaries,  these 
vessels  being  taken  respectively  as  a  whole,  depends  always  on  the 
relative  areas  of  their  total  cross-sections. 


THE  VELOCITY  OF  BLOOD-FLOW  209 

The  Time  Necessary  Jor  a  Complete  Circulation. — The  blootl,  iji 
leaving  the  heart,  may  take  a  short  cu'cuit  through  the  corouary 
system  of  the  heart,  and  so  back  to  the  right  heart,  or  it  may  take  a 
long  and  devious  course  to  the  toes  and  back,  or  through  the  intestinal 
capillaries,  portal  system,  and  hepatic  capillaries.  It  is  obvious,  then, 
that  the  time  any  two  particles  of  blood  take  to  complete  the 
circuit  may  be  different.  Experiments  have  been  made  to  determine 
how  rapidh'  am'  substance  like  a  poison,  which  enters  the  blood,  may 
be  distributed  over  the  bod}'.  A  salt,  such  as  potassium  ferrocyanide, 
is  injected  into  the  jugular  vein,  and  the  blood  collected  in  successive 
samples  at  seconds  of  time  from  the  opposite  jugular  vein.  These 
samijles  are  tested  for  the  presence  of  the  salt  by  the  addition  of  ferric 
chloride.  A  strong  solution  of  methylene  blue  may  be  injected  into 
the  jugular  vein  of  a  rabbit,  and  the  moment  determined  by  a  stop- 
watch when  the  blue  colour  appears  in  the  carotid  artery. 

By  this  means  the  following  times  were  obtained  in  different 
animals : 

Seconds.  Seconds. 

Squirrel  4-39  Horse  31-.")(» 

Cat         (VeO  Cock  0-17 

Hedgehog         7-61  Duck  10-ti4 

Rabbit  7-79  Goose  10-S(i 

Dog lG-70 

The  length  of  the  circuit  is  found  to  make  little  difference  in  the 
animal  lying  horizontal.  This  is  so  because  the  time  is  chietly  spent 
in  the  passage  of  the  blood,  not  through  the  arteries  and  veins,  l)ut 
through  the  capillaries.  Thus,  the  following  are  mean  results  in  four 
double  determinations : 

.Tugular  to  jugular  (dog)      ..  ..  ..  ..  I G* 32  seconds. 

.Jugular  to  crural  (dog)         ..  ..  ..  ..  18'08        ,, 

If  the  respiratory  movement  of  a  man  be  recorded,  and  he  take  a 
breath  from  a  bag  containuig,  say,  5-0  per  cent,  of  CO.,,  his  breathing 
M'ill  be  augmented  when  the  blood  charged  with  excess  of  CO.,  in  the 
lungs  reaches  the  respiratory  centre  (half  the  circuit).  This  time  can 
be  measured,  and  it  approximately  indicates  the  time  spent  in  the 
blood  travelling  from  the  lungs  to  the  centre. 

The  circulation  time  of  various  organs  may  be  determined  by 
injecting  salt  solution  into  a  vein,  and  observing  with  the  aid  of 
a  Wheatstones  bridge  arrangement  and  galvanometer  the  change  in 
electrical  resistance  which  occurs  in  the  corresponding  artery  when  the 
salt  solution  reaches  it.  The  moment  of  injection  and  that  of  the 
alteration  in  resistance  are  observed  with  a  stop-watch. 

It  has  been  determined  that  the  fastest  travelHng  blood  can 
complete  the  circuit  in  about  the  time  occupied  by  twenty-five  to 
thirty  heart-beats — say  in  twenty  to  thirty  seconds.  This  result 
shows  how  rapidly  methods  must  be  taken  to  prevent  the  absorption 
of  poisons — for  example,  snake-poison.  The  fastest  travelling  blood 
in  the  pulmonary  circuit  occupies  only  about  one-fifth  of  the  time  spen1> 
by  that  in  the  systemic    circuit.     In  animals  of    the    same    species 

14 


210 


A  TEXTBOOK  OF  PHYSIOLOGY 


the  circulation  time  increases  rather  in  proportion  with  the  surface- 
than  the  Aveight.  That  some  of  the  blood  takes  a  very  long  time  to 
return  to  the  heart  is  shown  by  the  long  time  it  takes  to  wash  the 
vascular  system  free  of  blood  by  the  injection  of  salt  solution.  The 
circulation -time  is  shortest  for  the  heart  and  the  retina. 

The  circnilation-time  for  the  stomach  is  relatively  short — equal 
generally  to  about  that  of  the  lungs.  It  is  relativeh"  long  in  the 
kidney,  spleen,  and  liver,  being  much  more  variable  in  these  organs 
than  it  is  in  the  lungs,  more  easily  affected  by  changes  of  external 
temperature — diminished  by  warmth,  increased  by  cold. 

Circulation  Tevies. 


Doo- 


Time 

Weight. 

in  Seconds. 

2-0  kilos 

4-05  (pulmonary) 

11-8      „ 

8-70 

18-2      ., 

. .        10-40 

13-3      „ 

8-40 

13-3      „ 

10-95  (spleen) 

13-3      , 

1.3-30  (kidney) 

CHAPTER  XXIV 

THE  PULSE 

By  the  expulsion  of  the  blood  at  each  systole  the  walls  of  the 
aorta  are  suddenly  distended.  From  the  aorta  a  wave  of  distension 
passes  down  the  walls  of  the  arteries.  This  wave  of  distension  is 
called  the  "  pulse."  As  the  pulse  is  distributed  over  an  ever -widening 
field  its  energy  is  expended  in  dilating  the  elastic  arteries,  and 
disappears  tinally  in  the  arterioles.  From  a  wounded  artery  the  blood 
spurts   in   pulses,  from  a  wounded  vein   it   flows   continuously.     By 


Fig.   113. — The   SrsPE>fsiON   Method    of    using  the   Dudgeon   Sphygmogeaph, 

(Lewis.) 


feeling  two  pulses,  or,  better,  by  placing  tambours  on,  say,  Uie 
carotid  and  radial  arteries,  and  recording  the  two  pulses  synchro- 
nously, it  has  been  found  that  the  pulse  occurs  later  the  farther 
the  seat  of  observation  is  away  from  the  heart.  The  velocity  with 
which  the  pulse-wave  travels  dowii  the  arteries  has  been  determined 
thus.  It  is  about  7  to  8  metres  per  second — twenty  to  thirty  times 
as  fast  as  the  blood  flow.  The  wave-length  of  the  pulse  is  obtained 
by  multiplying  the  duration  of  the  inflow  of  blood  into  the  aorta  by 
the  velocity  of  the  pulse-wave.     It  is  about  3  metres. 

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212 


A  TEXTBOOK  OF  PHYSIOLOGY 


The  examination  of  the  ])nlsc  is  of  great  importance  to  the  physician. 
It  yields  him  information  as  to  the  state  of  the  heart,  the  static  of  the 
arteries,  the  amount  and  variations  of  the  arterial  pressnre. 

The  pulse  may  be  investigated  either  directly  by  the  finger  or, by 
the  aid  of  instruments  known  as  sphygmographs  (Fig.  113).  The  pulse 
is  generally  felt  in  the  radial  at  the  wrist.  i)r(iferably  on  both  sides. 
With  the  linger  the  jjoints  noted  may  be  grouped  into  (a)  those  which 
give  information  concerning  the  heart — e.g.,  the  frequency,  generally 
seventy  to  seventy-five  per  minute  in  man,  regularity  or  irregularity, 
equality  or  inequality  of  the  beats;  (6)  those  which  yield  knowledge 


Fig.  114. — Mackukzie's  PoLYCUAru. 

The  parts  of  the  polygraph  may  be  described  as  follows:  The  body  A,  containing  the 
paper-rolling  and  time-marker  movements;  the  writing  tambours  BB,  with 
supporting  tjar,  Bl ;  wrist  tambour,  C,  with  attachment,  CI,  for  strapping  on 
to  wrist;  paper  roll  bracket,  D;  paper  roll,  Dl ;  cup  receiver,  E;  pens,  FFF. 

about  the  vessel — e.g.,  its  size  and  the'  condition  of  its  wall;  (c)  those 
which  yield  combined  information  of  the  two — the  volume,  force,  and 
tension  of  the  pulse. 

B}'  volume  is  meant  the  amovnit  of  movement  in  the  pulse  during 
the  passage  of  the  pulse-wave;  by  force  is  understood  the  maximum 
pressure  as  felt  by  the  finger  in  the  vessel  during  the  beat;  by  tension 
the  pressure  between  the  beats. 

These  last  data  can  only  be  accurately  measined  by  means  of  the 
sphygmometers  already  described,  for  the  finger  begins  to  flatten  the 
artery  and  stop  the  passage  of  the  pulse-wave  when  exerting  a  pressure 
much  less  than  that  within  the  artery. 

In  a  normal  healthy  pulse  the  beats  are  regular  and  of  equal 
strength.  The  vessel  is  soft  and  pliant,  not  tortuous,  rigid,  or  thick- 
ened. The  force  and  tension  are  moderate — that  is,  they  are  best 
felt  when  a  moderate  degree  of  pressure  is  applied. 


THE  PULSE 


213 


For  recording  the  j^ulse,  an  instrument  such  as  that  shown  in  Fig.  113 
may  be  used.  The  disadvantages  are  that  the  tracings  are  but 
of  short  length  and  that  in  the  ordinary  form,  which  is  strapped 
round  the  wTist,  the  pulse  tracing  is  modified  by  the  effect  of  pressure 
upon  the  venae  comites  of  the  army.  For  this  reason  it  is  better  to 
employ  the  suspension  method  illustrated  in  the  figure,  in  which  the 
pressure  of  the  lever  is  exerted  directly  over  the  radial  artery. 

Of  greater  service  is  the  instrument  knowai  as  the  polygraph 
(Fig.  114).  With  this  mstrument  it  is  possible  to  take  two  tracings 
at  the  same  time,  and  that  of  a  time-marker.  The  usual  combina- 
tion is  a  tracing  of  the  radial  and  venous  pulses. 


Fig.  115. — Diagram  showing  the  Average  Position  of  the  Jugular  Bulb. 

(Keith.) 

a.  The  jugular  point,  25  nun.  from  the  sternal  end  of  the  clavicle  (c);  h,  jugular  bulb, 
behind  sternal  head  of  sterno -mastoid  and  in  front  of  first  stage  of  subclavian 
artery ;  rf,  subclavian  vein ;  e,  sternal  head  of  sterno-mastoid ;/,  superior  vena  cava ; 
(J,  manubrium  sterni . 

Such  simultaneous  graphic  curves  are  valuable,  since  they  record 
information  of  the  time  relations  and  the  nature  of  the  contraction  of 
the  separate  heart  chambers. 

The  Venous  Pulse  in  man  is  best  recorded  by  applying  a  small 
metal  receiver  (3-4  centimetres  diameter,  1  centimetre  deep)  between 
the  two  heads  of  origin  of  the  relaxed  sterno-mastoid  muscle  (Fig.  115), 
and  transmitting  the  pulsations  by  air  to  a  delicate  recording  tambour. 
By  this  means  a  tracing  of  the  Jugular  bulb  is  obtained,  where  it 
lies  a  little  above,  and  about  25  millimetres  external  to,  the  inner 
end  of  the  clavicle.  The  bulb  is  so  called  because  in  the  internal 
jugular  vein  at  this  point  is  a  pair  of  valves,  and  here  a  bulging  of 
the  vessel  takes  place  in  cases  of  impeded  flow  to,  or  of  regurgitation 
from,  the  auricles. 

The  venous  pulse  shows  three  main  elevations  (o.  c,  v).  The  exact 
interpretation  of  some  of  these  factors  is  still  a  matter  of  doubt. 


214  A  TEXTBOOK  OF  PHYSIOL()(.Y 

The  a  wave  is  due  to  the  contraction  of  the  right  auricle.  It 
disappears  Avhen  this  chamber  is  not  beatmg.  and  is  sometimes  re- 
placed by  a  series  of  oscillations  when  the  auricle  is  fibrillating.  Its 
exact  mode  of  origin  and  propagation  is  not  known,  but  it  is  certainly 
synchronous  with,  and  an  indication  of,  auricular  contraction. 
Comparison  of  the  records  in  Fig.  1 10  shows  that  p  precedes  a.  Allow- 
ance must  be  made  for  time  of  propagation. 

The  c  wave  owes  its  origin  to  the  ventricular  systole,  since  it  dis- 
appears when  the  ventricle  ceases  to  beat.  It  has  been  supposed  to 
be  due  to  the  pulsation  of  the  neighbouring  artery,  and  in  many 
instances  this  is  undoubtedly  the  case;  but  it  occurs  also  in  curves 
taken  when  the  arterial  influence  has  been  removed,  and  also  iw  the 
curves  of  interauricular  pressure.     It  is  possibly  due  to  the  bulging 


I      I 
1      I 


Fig.  116. — Simultaneotts  Records  showing  the  Time  Relations  of  Waves  of 
Jugular  Pulse  and  Electrocardiogram.  (AV.  T.  Ritchie,  from  Cowan's 
"  Diseases  of  the  Heart." ) 

P  Precedes  a,  B  precedes  c. 

into  the  auricle  of  the  closed  tricuspid  valve  at  the  onset  of  ventricular 
systole.  The  mode  of  origin  is  under  discussion — both  factors  may  con- 
tribute— \\h\\e  for  clinical  purposes  it  may  be  reckoned  as  synchronous 
with  the  primary  wave  of  the  arterial  jiulse  in  the  neck.  In  Fig.  116 
it  is  seen  that  the  wave  R  of  the  electrocardiogram  precedes  the  wave  c. 

Various  divergent  views  are  held  about  the  origin  of  the  v  wave. 
The  two  views  generally  held  are — (1)  that  it  is  due  to  the  filling  of 
the  auricles  during  ventricular  sj-stole;  (2)  that  it  is  due  to  the  move- 
ment of  the  auriculo-ventricular  groove  at  the  beginning  of  diastole 
(Fig.  off)      Probably  both  factors  contribute. 

The  depressions  on  either  side  of  the  c  wave,  sometimes  called 
X  and  x',  are  really  one  depression  broken  by  the  c  wave.  They  are 
probably  due  to  (1)  the  auricular  relaxation  dependent  upon  the 
inspirator}^  diminution  of  intrapleural  pressure;  (2)  the  expansion  of 
the  auricular  walls  which  results  from  ventricular  systole,  by  the  de- 
pression of  the  diaphragm  formed  at  the  floor  of  the  auricle  by  the 
closed  auriculo-ventricular  valves.  The  first  factor  is  active  only 
during  inspiration. 


THE  PULSE 


215 


The  depression  after  v,  sometimes  termed  the  //  dcpre^r-ioii,  is 
usually  attribiited  to  the  opening  of  the  A.-V.  valves,  and  the  passage 
of  blood  from  auricles  to  ventricles  at  the  beginning  of  .•.■mmon 
diastole. 

The  Arterial  Pulse  Curve.— In  the  arterial  record,  or  sphygmograph, 
the  upstrol^e  corresponds  to  the  systolic  output  of  the  left  ventricle, 
marking  the  openhig  of  the  aortic  valves 
and  the  pouring  of  the  blood  into  the 
arteries. 

The  downstroke  represents  the  time 
during  which  the  valves  are  shut  and 
the  blood  is  flowing  out  of  the  arteries 
into  the  capillaries.  There  are  subsi- 
diary waves  on  the  downstroke.  The 
chief  of  these  is  called  the  "  dicrotic 
wave,"  the  notch  preceding  which  marks 
the  closure  of  the  semilunar  valves 
(c,  Fig.  117).  The  dicrotic  notch  is 
caused  by  the  swing  back  of  the  blood 
towards  the  heart  when  the  outflow 
ceases,  and  the  elastic  rebound  of  the 
blood  from  the  closed  semilunar  valves 
and  root  of  the  aorta  causes  the  dicrotic 
wave.  If  the  aortic  valves  move  back 
1  centimetre  and  the  diameter  of  the 
orifice  of  the  aorta  is  2-6  centimetres, 
then  1-8  centimetres  of  blood  move  back 
towards  the  heart.  It  is  most  manifest 
when  the  systole  is  short  and  sharp,  and 
the  output  of  l)lood  from  the  arterioles 
rapid;  in  other  words,  when  the  heart- 
beat is  strong,  the  systolic  pressure 
high,  and  the  diastolic  pressure  low. 
Its  central  origin  is  proved  b}'  the  fact 
that  it  appears  in  the  carotid  or  brachial 
at  the  same  interval  of  time  after  the 
primary  wave  as  in  the  radial  artery.  A 
smaller  wave,  predicrotic,  ])receding  this 
occxu's  during  the  period  of  output. 
and  sometimes  is  placed  on  the  ascend- 
ing limb  of  the  pulse-curve.  This  occurs 
when  the  peripheral  resistance  is  great, 
and  the  pulse  is  then  termed  anacrotic. 

It  usually  occurs  when  the  outflow  from  the  heart  is  impeded — as, 
for  example,  by  stenosis  of  the  aortic  valves.  By  compression  of  the 
abdominal  aorta  the  carotid  pulse  can  easily  be  made  to  exhibit  an 
anacrotic  wave. 

The    post-dicrotic  waves  are  due  to  secondary  elastic   swings  of 
i:he  big  arteries  followins  the  dicrotic  swinsf.     The  form  of  these  waves 


;ij    ^ 


21G 


A  TEX'rP>()()K  OF  PHYSIOLOGY 


is  modified  !)>>■  the  prestsure  of  ap])lication  of  the  sphygmograph  and 
by  instrumental  errors.  The  pulse  may  be  recorded  by  allowing  an 
artery  to  spurt  upon  a  moving  paper  (Fig.  118). 

As  already  said,  the  pulse  wave  occurs  later,  the  farther  the  place 
of  observation  is  from  the  heart.     This  is  well  seen  in  Fig.  119. 

We  have  no  scale  by  which  we  can  measure  the  blood-pressure 
in  sphygmograph  tracings. 

When  the  arterioles  are  dilated,  or  Avhen  the  capillaries  are  only 
filled  at  each  systole,  the  pulse  may  pass  through  the  arterioles  and 

reach  the  capillaries,  as  may  be  seen  in 
the  pink   of  the  nail  when  the  arm  is 
held   above  the  head  in  cases  of  aortio 
regurgitation. 
IB  The    normal    average    pulse-rate    is 

ijB  72    per    minute,    in    woman    about    80. 

Tall  men  usually  have  a  slower  rate  than 
MB^  short  men.     Individual  variations  from 

I  W  40  to  100  have  been  observed  consistent 

^  *  '  with   health.     Napoleon,    a    short    man, 

had  a  pulse-rate  of  40.  In  the  new-born, 
the  pulse  beats  on  the  average  130  to- 
140  times  a  minute  ;  in  a  one-year-old 
child,  120  to  130;  three  years,  110;  ten 
years,  90;  fifteen  years,  80  to  85.  Active 
muscular  exercise  may  increase  the  pulse- 
rate  to  130.  Nervous  excitement,  extreme 
debility,  and  rise  of  body  temperature, 
also  increase  it  markedly.  The  pulse  is^ 
more  frequent  when  one  stands  than 
when  one  sits  or  lies  down.  In  100  young 
men  of  twenty-seven  years  the  average 
was :  78-9  standing,  70-1  sitting,  66-6  lying. 
In  states  of  debility  this  difference  be- 
tween horizontal  and  erect  postures  may  increase  to  30  to  50  per 
minute.  The  taking  of  food,  especially  hot  food,  increases  the 
frequency;  so  does  smoking  cigarettes. 

The  average  pulse-rates  for  different  ages  is  given  in  the  following; 
table  • 


Fig.    118.— HiEMAUTOGEAM. 

(Landois  and  Stirling.) 


Age, 
in  Years. 

Foetus 

0-1 

1-12 

3-4 

5-9 

9-10 
12-13 
16-17 

19-20 


ilea 
Women 


Pulse-Bate, 
per  Minute. 

135-140 
134 
117 
108 

98 

91 

88 

80 

72 

80 


THE  PULSE 


217 


At  the  third  month  the  infant's  pulse  may  be  faster  than  at  birth, 
owing  to  the  increase  of  muscular  activity. 

Large  animals  have  a  slower  rate  than  small.  The  elephant. has 
a  frequency  of  25  to  30,  the  ox  36  to  40,  the  sheep  60  to  80,  the  dog 


Femoral 


Radial 


Foot 
(plctliysm.) 


Time  in 
i„  second 


Fig.  ll!>.— The  Pulse  Wave  ix  the  Arterial  SYSXEii,     (Waller.) 


100  to  120.  the  rabbit  about  150,  small  birds  and  mice  over  600. 
Li  the  last  the  rate  is  recorded  by  means  of  the  electrical  variation  of 
the  heart. 


CHAPTER  XXV 
THE  CAPILLARY  CIRCULATION 

The  blood  is  brought  into  contact  with  tlie  tissues  through  the? 
endothelial  wall  of  the  capillaries;  this  is  therefore  of  the  greatest- 
tenuity.  Here  takes  place  that  exchange  of  material  which  maintains 
the  combustion  of  the  body — the  lire  of  life.  The  aim  of  the  circu- 
lation is  attained  when  the  arterialized  blood  laden  with  food  material 
and  oxygen  is  driven  into  the  capillaries  of  the  bod}'. 

In  size,  the  capillaries  vary  in  different  organs.  In  the  biain  the 
length  has  been  estimated  to  be  0-7(J9  millimetre  (pons)  and  042  milli- 
metre (optic  thalanuis);  in  the  mucosa  of  the  stomach  0-6  millimetre; 
and  in  the  liver  0-5  to  1  -1  millimetres.  The  diameter  of  the  capillaries 
varies  from  (j-007  to  0-013  millimetre. 

Malpighi  (1661)  first  observed  the  capillary  circulation  under  the 
microscoj^e.  He  examined  the  lung,  the  mesentery,  and  bladder  of  the 
frog.  It  has  since  been  seen  in  many  other  transparent  or  translucent 
parts  of  animals. 

The  Microscopical  Examination  of  the  Circulation. — By  usi)ig  a 
low  power  it  is  possible  to  examine  simultaneously  arteries,  capillaries, 
and  veins  in  the  same  tield.  The  first  thing  which  strikes  the  obserxer 
is  the  different  direction  of  the  stream  in  the  arteries  and  in  the  veins. 
On  account  of  the  reticular  arrangement  of  the  capillaries,  the  direc- 
tion of  the  stream  through  them  is  by  no  means  constant.  There 
may  l)e  a  complete  cessation  of  the  flow  for  a  period  in  a  capillary 
channel,  or  the  direction  of  the  current  may  even  be  reversed  for  a 
longer  or  shorter  time.  The  flow  through  the  arteries  is  by  far  the 
most  rapid.  In  the  veins,  also,  the  stream  is  so  rapid  that  it  is  diffi- 
cult to  catch  the  contour  of  the  corpuscles.  The  stream  is  slower  in 
the  small  veins,  and  in  the  capillaries  the  movement  is,  as  a  rule,  so 
tardy  that  the  individual  corpuscles  can  be  determined  without  any 
difiicultv'.  The  inconstancy  of  the  caj)illary  stream  is  generally  ap- 
parent. If  a  group  of  capillaries  be  kept  for  some  time  under  observa- 
tion, the  blood  is  occasionally  seen  to  hurry  suddenly  through  a  number 
of  these  with  increased  rapidity.  This  continues  for  a  while,  aiid  then 
the  stream  becomes  again  sloAver  and  slower,  till  after  an  interval  it 
resumes  the  quiet  rate  of  flow  which  has  been  maintained  A^ithout 
interruption  in  the  neighbouring  capillaries.  These  variations  depend 
on  alterations  in  the  lumen  of  the  afferent  arteries. 

The  arterial  stream  is  pulsative,  and  each  systole  may  be  recognized 
even  in  very  small  arteries  by  the  rhythmical  acceleration  and  re- 

218 


THE  CAPILLARY  CIRCULATION  219 

tardation  of  the  blood-stream.  Such  a  rhythmical  movement  is 
absent  from  the  capillaries  and  veins  in  a  normal  condition;  the 
stream  is  continuous  in  both.  In  the  arteries  the  core  of  red 
corpuscles  does  not  completely  fill  the  lumen,  but  moves  along  the 
axis  of  the  stream.  To  the  outside  there  lies  a  clear  layer  of  plasma, 
in  which,  when  the  stream  moves  slowly,  white  corpuscles  roll.  In 
the  veins  there  is  also  a  similar  peripheral  plasmatic  layer,  in  which 
the  white  corpuscles  roll  slowlj-  along,  sticking  noAV  and  again  to  the 
wall  of  the  vessels  in  their  course.  In  the  smallest  cai^illaries  the 
plasma  layer  cannot  be  distinguished,  the  red  corpuscles  march  in 
single  file,  and  often  become  distorted  and  bent  as  they  pass.  These 
capillaries  are  invisible  to  the  eye  so  soon  as  corpuscles  cease 
to  pass  tlu^ough  them.  Thus,  in  the  course  of  an  observation, 
capillaries  may  be  seen  to  appear  and  vanish  from  view.  In  the 
angles  of  the  capillary  network,  red  corpuscles  may  be  seen  to  stick 
and  hang  in  the  balance,  bent  round  the  angle,  half  in  one  branch 
and  half  in  another,  until  finally  swept  on  into  the  rush  and  hurry 
of  the  stream. 

The  white  corpuscles  progress  with  a  sIom"  rolling  motion  in  the 
plasmatic  layer.  The  axial  stream  travels  with  the  greatest  velocity, 
and  thus  the  side  of  the  leucocyte  which  lies  at  any  moment  nearer 
the  axis  is  driven  on  with  the  greater  speed;  hence  the  rolling  move- 
ment. The  white  corpuscles  travel  in  the  peripheral  layer,  the  red 
in  the  axial  layer,  for  the  latter  are  the  heavier.  It  is  not,  as  has  been 
supposed,  that  the  white  are  lighter  and  the  red  corpuscles  heavier 
than  the  plasma.     Both  forms  are  of  a  higher  density  than  the  plasma. 

If  particles  of  graphite  and  carmine  be  circulated  through  glass 
capillaries,  the  lighter  carmine  particles  travel  in  the  peripheral  layer. 
When  resin  is  substituted  for  graphite,  the  carmine  travels  in  the 
axis.  If  pus  corpuscles  and  milk  globules  are  circulated,  the  cor- 
puscles occupy  the  axial  stream. 

If  the  resistance  in  the  arterioles  be  lowered  to  a  certain  point,  the 
capillar}^  circulation  remains  no  longer  pulseless.  Tiius,  when  the 
chorda  tympani  nerve  is  stimulated,  the  blood  may  issue  in  pulses 
from  the  vein  of  the  submaxillary  gland.  By  plunging  the  hand  in 
very  hot  water,  the  pulse  may  be  seen  to  reach  even  the  turgid  veins 
on  the  back  of  the  hand.  In  ca.ses  of  aortic  insufficiency,  a  capillar}^ 
pulse  is  readily  obtained  in  any  area  of  congestion  which  is  produced 
by  scratching  the  skin. 

The  effect  of  vaso-dilatation  can  be  observed  under  the  microscope 
— e.g.,  in  the  tongue  of  a  curarized  frog.  On  bnishing  the  tongue 
an  appearance  of  intense  redness  shows  that  arterial  congestion  has 
set  in.  All  the  vessels,  arteries,  capillaries,  and  veins,  are  wide  and 
strongly  distended  with  blood.  Innumerable  capillaries  are  perceptible 
at  a  glance,  where  previous^  a  few  red-coloured  threads  were  toil- 
somely sought  for  ;  and  in  all  these  vessels,  small  and  large,  the  blood 
rushes  on  with  the  greatest  rapidity — so  rapidty  that  even  in  the 
capillaries  the  ej-e  in  vain  strives  to  catch  the  outline  of  a  single 
corpuscle. 


220  A  TEXTBOOK  OF  PHYSIOLOGY 

By  the  application  of  a  piece  of  ice-  to  the  tongue  of  a  frog,  vaso- 
dilatation can  be  converted  into  constriction.  The  arteries  become 
narrow,  the  tongue  pale.  The  eye  has  difficulty  in  finding  any  except 
the  larger  vessels.  Few  capillaries  ap])ear  to  contain  blood,  and 
where  a  considerable  quantity  of  blood  is  still  present,  as  in  the  arteries 
and  veins,  the  flow  is  tardy,  and  even  in  the  arteries  the  individual 
corpuscles  can  now  generally  be  recognized. 

In  a  warm-blooded  animal,  the  results  of  exjiosure  to  an  irritant 
are  much  more  rapidly  established.  After  exposure  of  a  rabbit's 
ear  to  water  at  55^  0.,  the  blood  is  altogether  unable  to  penetrate 
the  arteries.  A  change  has  taken  jilace  in  the  relations  between  the 
blood  and  the  vessel  wall  as  regards  friction  and  adhesiveness,  and 
thus  complete  stasis  of  the  circulation  arises.  If  the  change  be  less 
intense,  the  porosity  of  the  vessel  is  affected,  and  a  quantitative  and 
qualitative  change  in  the  transudation  from  the  capillaries  ensues. 
The  rabbit's  ear  may  be  entirely  separated  from  the  body,  with  excep- 
tion of  the  central  artery  and  vein.  After  section  of  all  the  vaso- 
motor nerves  by  this  means,  vascular  dilatation  is  greatly  increased 
by  rubbing  the  ear,  and  all  the  phenomena  of  inflammation  occur 
after  the  application  of  an  irritant.  We  have  here  to  deal,  not  with  a 
nervous  mechanism,  but  with  a  change  of  the  vessel  wall.  The  circu- 
lation through  the  capillaries  is  possible  only  so  long  as  the  vessel  wall 
is  in  the  normal  physico-chemical  condition  which  characterizes  the 
living  state. 

The  corpuscles  continue  to  move  through  the  capillaries  for  some 
seconds,  or  even  minutes  in  a  few  of  the  capillaries,  after  the  bulbus 
arteriosus  has  been  ligated ;  they  run  faster  on  pressing  or  moving  the 
leg.  Observations  of  this  kind  show  how  immeasurably  slight  a 
difference  of  pressure  is  required  to  produce  a  flow  in  the  capillaries.  On 
clenching  the  fist  the  cajjillaries  of  the  hand  blanch.  By  the  ceaseless 
muscular  movements  and  changes  of  posture  of  the  living  mobile  animal 
the  capillary  pressure  is  kept  in  the  skin  approximately  the  same  as 
the  atmosphere,  for  whenever  the  blood  is  thus  pressed  out  of  them 
into  the  veins  the  pressure  does  not  become  positive  in  the  capillaries 
till  they  fill  agahi. 

In  the  intestinal  wall  the  blood  is  similarly  expressed  by  the 
muscular  contractions  of  the  gut.  In  encapsulated  organs,  such  as  the 
glands,  on  the  other  hand,  the  capillary  pressure  may  rise  with  the 
secretory  pressure  up  towards  the  arterial  pressure.  This  is  the  case 
in  the  salivary  gland  when  the  secretion  is  made  to  take  place 
against  pressure.  Secreting  cells  are  confined  by  limiting  membranes, 
membranae  proprise,  tough  and  homogeneous,  but  of  great  tenuity. 
These  membranes,  Avhile  allowing  the  protoplasm  of  gland  cells 
or  muscle  plasma  to  imbibe  fluid  from  the  capillaries,  limit  the 
expansion  produced  by  intracellular  forces.  Thus  the  salivary 
glands  may  secrete  saliva  at  a  pressure  greater  than  arterial 
pressure,  and  the  blood  continue  to  flow  through  the  gland. 
The  expansion  of  the  alveoli  is  limited,  so  that  it  narrows  and 
does    not    shut     up    the    veins    (see    Fig.    llPc).       The    result    is 


THE  CAPILLARY  CIRCULATION  221 

a  rapid  tiow  of  blood  through  dilated  arteries,  and  almost  rigid 
vessels,  arteries,  capillaries,  and  veins,  all  at  the  fnll  or  nearlj'^  full 
arterial  pressure.  Similarly,  in  an  inflamed  area,  by  the  inhibition 
of  fluid  in  the  damaged  tissue  cells  which  are  confined  by  connective 
tissue,  the  veins  are  compressed  and  narroAved,  and  the  arteries  being 
dilated,  the  capillary  pressure  rises,  and  the  whole  part  throbs  Avith 
the  pulse  and  receives  a  rapid  flow  of  blood.  If  the  swelling  is  too 
great,  strangulation  of  the  circulation  occurs,  and  the  surgeon's  knife 
is  reqviired  to  relieve  tension  and  promote  flow. 

Rate  of  Flow. — The  velocity  of  a  blood-cor]^uscle  in  the  capillai'ies 
of  a  frog's  muscle  has  been  reckoned  to  be  0-28  mm.  per  second.  The 
method  most  conveniently  used  is  to  employ  an  ocular  micrometer,  and 
follow  the  course  of  a  corpuscle  d\iring  a  ]^eiiod  of  time  given  by 
a  clock  beating  one-fifth  seconds.  The  velocity  has  thus  been  found  by 
various  observers  to  be  0-25  to  0-57  millimetre  per  second  in  cold- 
blooded animals. 

B}^  the  entoj^tic  method  the  velocity  in  the  retinal  capillaries  has 
been  calculated  to  be  0-75  millimetre  per  second.  With  suitable 
illumination  of  the  eye  the  corpuscles  are  seen  by  the  subject  on  a 
ground-glass  screen  held  11  to  16  centimetres  from  the  eye.  A 
corpuscle  can  be  followed  20  to  30  millimetres  on  the  screen. 
Knowing  the  distance  of  the  screen  from  the  anterior  nodal  point 
of  the  eye  (A),  the  distance  of  the  retina  from  the  posterior  nodal 
point  (B),  and  the  distance  travelled  by  the  corpuscle  on  the 
screen  (C),  the  real  distance  x  travelled  in  a  given  time  can  be  cal- 
culated. 

BC 
"=  A  • 

As  the  red  corpuscles  travel  in  the  axial  part  of  the  stream,  and  as 
the  mean  velocity  in  any  tube  equals  one-half  the  axial  velocity,  the 
true  mean  velocity  of  flow  is  less  than  the  above.  It  can  be  taken  to 
be  about  15  to  3')  millim3tre3  per  minute,  and  in  the  smallest  capil- 
laries, where  the  flow  is  often  obstructed,  it  is  still  less.  Since  the 
v'elocity  stands  in  inverse  proportion  to  the  sectional  area  at  any 
point  in  a  system  of  tubes,  the  proportional  relationship  of  the  total 
.sectional  area  of  the  capillaries  to  that  of  the  aorta  can  be  reckoned 
if  we  know  the  mean  velocity  in  the  capillaries  and  in  the  aorta.  Thus, 
if  the  mean  velocity  be  taken  as  500  millimetres  per  second  in  the 
aorta,  and  0-5  millimetre  par  second  in  the  capillaries,  the  reUtioa 
is  1  =1,000.  In  man  the  sectional  area  of  the  aorta  is  4-4  square  centi- 
metres. The  total  sectional  area  of  the  capillaries  filled  with  blood 
at  the  thw.  is  thus  equal  to  4,400  square  centimetres.  This  result  is, 
of  course,  only'ai)proximate. 

The  Capillary  Blood-Pressure. — The  measurement  of  the  capillary 
pressure  has  been  attempted  by  placing  a  glass  plate  2-5  to  5  square 
millimetres  in  size  on  the  skin  in  a  suitable  place,  such  as  on  the  last 
jomt  of  the  finger.     From  this  glass  plate  hangs  a  small  scale-pan. 


222  A  TEXTBOOK  OF  PHYSIOLOGY 

On  Ihi.s  weights  are  i)lace(l  until  t\u'  pressure  is  reached  at  which  the 
skin  is  blanched  and  the  capillaries  comi)ressed. 

In  another  inethod  a  small  rubber  bag  with  a  hole  in  the  centie 
is  placed  on  the  skin.  Both  bag  and  skin  are  moistened  with  glycerine, 
and  the  whole  is  covered  with  a  glass  plate  so  held  as  to  make  an  air- 
tight junction.  By  means  of  a  side  tube  air  is  then  blown  into  the 
bag  until  the  skin  blanches,  the  pressure  being  indicated  on  a  man- 
ometer. These  methotls  are  inaccurate,  for  the  horny  layer  of  the  skin 
resists  the  compression. 

The  web  or  mesentery  of  a  frog,  being  laitl  on  a  glass  jDlate,  can 
be  compressed,  while  under  the  microscope,  by  a  thin  transparent 
membrane,  which  forms  the  base  of  a  glass  capsule.  The  latter  is  filled 
with  water,  and  connected  with  a  pressure-bottle  and  manometer. 
By  this  means  it  was  found  that  pressure  of  100  to  loO  mm.  H._,0 
is  suflficient  to  stop  the  circulation  in  the  capillaries  and  veins  of  the 
frogs  web;  in  the  arteries  200  to  250  mm.  K^O.  In  periods  of  a  few- 
minutes  the  pressure  may  vary  20  to  30  mm.  H^O.  On  producing 
vagus  inhibition  of  the  heart  by  striking  the  abdomen,  the  pressure 
sank  to  0,  and  then  rose  again  in  the  veins  to  70  to  100  mm.  H.^0, 
owing  to  venous  congestion.  Temporary  anaemia  of  the  web  caused 
dilatation  of  the  vessels,  and  this  produced  in  its  turn  a  higher  capillary 
pressure. 

Such  methods  necessitate  the  fixation  of  the  jjart,  and  cannot 
be  quickly  performed.  They  obstruct  the  flow  and  therefore  do  not 
give  the  capillary  pressure  laider  normal  conditions. 

If  the  upper  arm  be  constricted,  so  as  to  block  the  venous  exits, 
the  pressure  in  the  cutaneous  veins  of  the  arms  rises  fairly  rapidly 
to  the  static  arterial  pressure.  It  takes  a  long  time  for  the  cajiillaries 
to  all  become  flistended  with  blood.  The  veins  fill  through  the 
wider  channels.  If  we  .«queeze  the  fist  luider  these  conditions,  the 
capillaries  are  emptied  into  the  veins  and  momentarily  blanched,  and 
we  see  that  it  is  possible  to  have  then  a  high  pressure  in  both  arteries 
and  veins,  and  a  low  pressure  in  the  capillaries.  The  distension  of 
the  capillaries  vessels  causes  aching  pain,  and  this  d'scomfort  prevents 
our  keeping  our  limbs  motionless  in  a  dependent  posture,  and  causes 
us  to  move  the  parts  of  the  body,  to  fidget,  and  so  relieve  congestion. 
In  the  brain,  the  capillar}'  venous  pressure  can  be  estimated 
by  finding  the  tension  which  is  sufficient  to  just  compress  the 
brain  as  it  bulges  into  the  trephine  hole.  This  j^ressure  in  the 
horizontal  position  of  the  animal  is  usually  about  10  mm.  Hg.  The 
capillary  pressure  varies  widely  with  changes  in  the  general  venous 
and  arterial  pressures,  and  with  the  position  of  the  animal.  Thus, 
iu  the  brain,  the  pressure  may  fall  below  zero  in  the  vertical  feet-down 
jjosition  (the  fontanelle  of  an  infant  suffering  from  diarrhoea  may 
become  depressed),  and  rise  to  almost  50  mm.  Hg  during  the  height  of 
strychnine  convulsions.  The  intracranial  pressure  (cerebro -spinal 
fluid  pressure),  and  the  cerebral  venous  pressure,  are  one  and  the 
same.  So,  too,  in  the  eyeball  the  intra-ocular  pressure  (aqueous  fluid 
2:»ressure),  and  the  pressure  of  the  veins  within  the  eyeball,  are  the 


THE  C.M'ILLAUY  CIKCIJLATION 


223 


cixp 


Fig.  119a. — Schema  of  Kidney. 

Thi'  renal  L-apsulc  (c)  encloses  the  whole,  including  arteries  («),  capillaries  (cap),^'and 
veins  («),  with  surrounding  Ijniph  sj)ace  {Is).  The  menihrana  propria  (//)/>), 
confines  the  secreting  cells  (.sc).  The  pelvis  [p)  and  ureter,  membrana  propria 
and  capsule,  are  inextensile  beyond  a  certain  degree. 

Fig.  119b. — Schema  of  Eyeball. 

The  rigid  coat  (c)  confines  the  whole.  The  secreting  cells  (.sc)  are  set  on  a  membrana 
propria  (w/>),  and  secrete  the  aqueous  {nq).  There  is  adjustment  of  capillarv- 
venous  to  secreting  pressure  by  latter  acting  on  venous  outlet  (c).  The  flow  of 
blood  through  capillaries  icap)  stops  when  aqueovs  pressure  is  raised  just  about 
arterial  pressure  in  ya). 

Fig.  119c. — Schema  of  Salivary  Glaxd. 
The  alveolus,  with  secreting  cells  (.sc)  and  duct,  ars  surrounded  by  a  membrana  propria 
{mi)),  inextensile  beyond  a  certain  degree.  The  capsule  of  the  gland  (c)  is  also 
inextensile  beyond  a  certain  degree.  The  secretorj-  cells  (.sc)  raise  the  pressure 
of  saliva,  and  the  membrana  propria  {mji)  prevent  strangulation  of  the  circula- 
tion through  capillaries  [cap)  by  limiting  the  expansion  of  the  alveolus.  A 
certain  am.ount  of  expansion  is  permitted,  which,  acting  on  the  vein  (v)  just 
before  its  exit  through  capsule,  raises  the  capillary-venous  pressure.  The 
capillaries  and  vein-  then  become  a  more  rigid  system  of  tubes,  and  the  flow  of 
blood  from  a  to  v  is  accelerated. 


224  A  TEXTBOOK  OJ-^  PHYSIOLOGY 

same.  Tissue  iluid  pressure  and  capillary  pressure  constantly  balance 
each  other. 

The  capillary  pressure  stands  in  far  closer  relationship  to  the  venous 
pressure  than  to  the  arterial  pressure.  Between  an  artery  and  its 
capillaries  lies  the  unknown  and  varying  resistance  of  the  arterioles; 
between  the  capillaries  and  veins  there  is  no  such  resistance. 

Although  often  put  forward,  the  view  is  erroneous,  that  fluid 
filters  through  the  cai)illary  wall  under  the  influence  of  the  capillary 
blood -pressure.  No  measurable  difference  in  pressure  normally  exists 
between  the  capillary  pressure  and  that  of  the  tissue  fluids,  such  as 
the  aqueous  or  cerebro-spinal  fluid.  The  wet  films  of  the  protoplasm 
which  form  the  walls  of  capillaries  cannot  act  as  rigid  sieve-like  struc- 
tures. The  tissue  cells  are  bj-  their  colloidal  structure  endowed  with 
the  power  of  linking  np  or  setting  free  the  crystalloids  l)rought  to  them 
in  solution.  They  are  the  seat  of  play  of  complex  physical  forces, 
such  as  imbibition  and  osmosis,  as  well  as  of  chemical  reaction,  selective 
in  character,  and  dependent  on  the  enzymic  contents  of  the  cells. 
The  cells  control  the  passage  of  fluid  in  one  of  the  other  directions 
in  just  the  same  way  as  do  the  unicellular  organisms,  in  which,  as 
regards  the  secretory  processes,  there  can  be  no  question  of  filtration. 
This  vicAv  is  illustrated  in  Figs  1  KIa,  IUIb,  llOc 

Apart  from  other  experiments  which  tell  against  the  filtration 
hypothesis,  and  quoted  m  their  respective  sections,  there  remains 
the  outstanding  fact  that  in  the  brain  and  eye,  where  measure- 
ments have  been  made,  the  capillarj^-venous  pressure  and  the  tissue- 
fluid  pressure  are  not  measurably  different.  Moreover,  the  membrante 
propiise  are  arranged  to  allow  the  tissue  cells  to  produce  osmotic  and 
secretory  pressures,  not  to  support  the  capillaries  as  rigid  filtering 
membranes.  Leakage  occurs  when  the  skin,  or  capsule  fan  oi-gan,  is 
wounded,  because  capillary  pressure  is  then  no  longer  balanced  by 
tissue  fluid  pressure. 

The  organs  rhythmically  pulse  full  Avith  systole  and  shrink  with 
diastole,  and  the  pulse  furthers  the  flow  of  tissue  lymph  as  well  as 
the  circulation.  Every  muscular  movement,  by  compressive  action 
and  the  action  of  valves  in  veins  and  lymphatics,  aids  the  circulation. 
The  membranse  proprise,  by  limiting  expansion,  allow  secretory  cells 
to  raise  the  pressure  of  the  tissiie  fluid  and  produce,  for  example,  the 
intra-ocular  pressure.  The  capillary-venous  pressure  within  the  eye- 
ball adjusts  itself  to  this  secretory  pressure,  for  the  pressure  must 
just  exceed  the  intra-ocular  pressure  for  the  circulation  to  continue. 


CHAPTER  XXVI 

THE  PRESSURE  AND  VELOCITY  OF  THE  BLOOD  IN 
THE  VEINS 

The  most  striking  difference  between  the  structure  of  an  artery 
and  its  vense  comites  is  a  decrease  of  elastic  tissue  in  the  veins,  together 
with  an  increase  of  white  connective  tissue.  The  veins  are  tubes  with 
muscular  walls,  which  not  only  fall  together,  but  contract  when  empty, 
and  under  slight  pressure  expand  to  their  full  capacity.  Beyond 
this  point,  the  walls,  on  account  of  the  quantity  of  connective  tissue 
entering  into  their  structm'e  can  extend  but  little. 

The  resistance  to  a  breaking-strain  on  the  part  of  the  veins  is  very 
great.  It  requires  a  higher  pressure  to  rupture  a  vein  than  the  cor- 
responding artery. 

If  by  external  compression  the  various  outlets  be  blocked,  the 
pressure  rises  in  the  vein  to  the  full  pressure  in  the  artery.  For  this 
reason  the  veins  must  be  strong  enough  to  bear  any  such  increased 
strain.  There  is,  however,  another  need  for  strength  of  veins,  and 
that  is  that  they  may  be  able  to  bear  the  strain  which  may  arise  from 
external  violence.  The  superficial  veins  are  endowed  with  more 
muscular  and  elastic  tissue  than  those  deeper,  while  those  veins  which 
run  in  the  muscles  and  in  the  bones,  and  are  protected  from  violence 
and  supported  by  firm  structures,  possess  no  muscular  elements. 
When  exposed,  a  superficial  vein  contracts  on  mechanical  stimu- 
lation and  on  cooling,  while  it  may  be  made  to  dilate  on  applying 
warmth. 

Pressure  in  the  Venous  System. — -In  the  active  animal  the  venous 
pressure  varies  according  to  the  hydrostatic  pressure  of  the  column 
of  blood  above  the  point  of  measurement  and  with  the  action  of 
the  muscles  which  express  the  blood  onwards  towards  the  heart. 
In  the  horizontal  position,  when  these  factors  are  almost  elimin- 
ated, the  pressure  in  the  large  veins  is  found  to  be  equal  to  a  few 
centimetres  of  blood,  or  about  5  mm.  Hg.  When  a  cannula  is 
pushed  down  the  jugular  vein  past  the  valve  till  its  opening  lies  in 
the  vena  cava  superior,  the  lateral  pressure  of  this  vein  is  ob- 
tained. It  may  become  negative  during  inspiration.  The  negative 
pressure  which  occurs  in  the  right  auricle  on  each  cardiac  oscillation 
is  estimated  at  —  2  to  —  3  mm.  Hg,  and  may  become  —  5  to  -  8  mm.  Hg 
during  inspiration. 

In  the  sheep,  with  the  animal  in  the  horizontal  posture  and  ini- 

22")  15 


226  A  TEXTBOOK  OF  P>^^^SJ()LOGY 

mobile,  during  normal  quiet  resijiration  tlio  following  venous  j^ressures 
have  been  found: 


Mm. 

llg. 

Mm.  JJg. 

Left  innominate     . . 

— 

0-1 

External  facial 

.     +     3-(» 

Right  jugular 

..      + 

0-2 

Rrachial 

.      +      4-1 

Right  subchivian  . . 

— 

0-1 

Rranch  of  the  brachial     . 

.    +    y-o 

Left  jugular 

. .     — 

0-1 

Crural 

.    +  11-1 

Left  subclavian 

. .      - 

0-G 

It  must  be  clearly  understood  that  these  venous  pressures  are 
only  true  for  the  animal  in  the  horizontal  posture.  They  vary  greatly 
with  the  posture  and  movement  of  the  body. 

The  negative  pressure  in  the  central  veins  is  due  to  the  action 
of  the  heart  and  the  suction  of  the  thoracic  cavity  produced  by 
the  elastic  pull  of  the  lungs.  Owing  to  this  negative  pressure,  when 
a  large  vein  is  opened  in  the  neighbourhood  of  the  thorax,  air  may 
be  sucked  into  the  circulation.  Air  that  has  thus  obtained  an  entry  has 
been  observed  to  pass  right  through  the  pulmonary  circulation  and  to 
enter  the  arteries.  The  danger  of  air  thus  entering  during  surgical 
operations  has  been  recognized.  A  large  amount  of  air  can  be  slowly 
injected  into  a  vein  without  killing  an  animal.  A  rapid  injection, 
such  as  would  be  caused  by  blowing  air  into  the  venous  cannula, 
kills  by  causing  frothing  in  the  heart  and  embolism  in  the  lungs  and 
coronary  arteries.  The  danger  of  embolism  from  the  entry  of  air  is 
much  greater  in  a  small  than  in  a  large  animal,  for  the  smaller  the 
heart  the  less  the  amount  of  air  required  to  hinder  its  action  by 
frothing. 

In  man,  the  venous  pressure  has  been  measured  by  finding  the 
pressure  just  required  to  prevent  a  cutaneous  vein  refilling  after  it 
has  been  emptied  beyond  a  valve.  The  armlet,  or  bag,  of  the  sjihyg- 
mometer  is  j^ressed  upon  a  suitable  vein,  with  the  limb  placed  at  the 
heart  level,  and  the  vein  emptied  by  stroking  the  blood  on  past  the 
next  valve.  The  pressure  of  the  armlet,  or  bag,  is  then  relaxed  till 
the  vein  just  refills,  and  the  pressure  read.  On  immobilizing  the  part 
to  take  such  a  measurement,  the  venous  pressure  rises;  how  quickh' 
depends  on  the  state  of  dilatation  of  the  arterioles  in  the  limb.  It 
is  not  possible  thus  to  measure  the  pres.sure  in  the  normal  conditions. 

Rate  of  Flow  in  the  Veins. — Turning  to  the  question  of  the  velocity 
of  the  venous  flow,  it  is  obvious  that  the  average  input  of  the 
heart  must  equal  the  average  output  per  second  in-  order  that 
the  circulation  may  continue.  If  the  veins  that  enter  the  heart  were 
of  the  same  sectional  area  as  the  arteries  that  leave  it,  then  the  velocity 
would  be  the  same  in  these  A^eins  as  in  the  arteries.  When  the  vense 
cavse  are  filled  with  blood,  the  total  sectional  area  is  found  to  be  con- 
siderably greater  than  that  of  the  aorta.  But,  as  normally  these 
veins  are  not  filled  to  their  capacity,  it  is  probable  that  the  velocity 
of  the  flow  in  them  is  approximately  equal  to  that  of  the  aorta.  The 
velocities  in  the  carotid  artery  and  the  jugular  vein,  or  in  the 
umbilical  artery  and  the  vein  of  sheep's  embrA'o,  have  been  measvtred 
with  the  stromuhr,  and  have  been  found  to  be  almost  the  same. 


PRESSURE  AXD  VELOCITY  OF  BLOOD  I^;  VEINS     227 

The  valves  in  the  veins  allow  the  blood  to  be  forced  only  towards 
the  heart.  The  pumping  action  of  walking  can  be  observed  on  the 
veins  of  the  back  of  the  foot.  After  standing  still  for  a  time,  the 
veins  become  prominent.  The  pressure  is  considerable,  as  can  be 
ganged  from  the  feel.  After  taking  a  few  stej^s,  they  are  emptied, 
squeezed  between  the  .skin  and  muscle. 

Numerous  anastomoses  exist  between  the  veins,  so  that,  if  the 
floAv^  of  blood  be  obstructed  in  one  direction,  it  readily  finds  a  passage 
in  another. 

The  venous  circulation  is  imj)eded  by  (1)  a  lessening  of  the  heart 
power;  (2)  cardiac  valvular  effects,  such  as  incompetence  or  narrowing 
of  the  valvular  orifices;  (3)  obstruction  to  the  filling  of  the  heart,  as 
in  cases  of  pericardial  effusion;  (4)  obstruction  of  the  pulmonary 
circulation,  as  by  coughing  and  by  pleuritic  effusion.  The  results  of 
venous  congestion  are  less  efficient  circulation,  a  duskj^  appearance 
of  the  skin,  a  fall  of  cutaneous  temperature,  and  an  effusion  of  the 
fluid  into  the  tissue  .spaces,  producing  oedema  or  drop.sy.  This  last 
effect  is  not  due,  as  has  been  supposed,  to  increased  capillary  pres- 
sure producing  increased  transudation,  for  no  such  increase  in  venous 
and  capillary  pressure  is  found  under  the  conditions.  It  is  due  to 
the  altered  nutrition  of  the  tissues,  which  results  from  the  deficient 
circulation.  The  products  of  katabolism  which  collect  within  them 
increase  the  osmotic  properties  of  the  tissues. 

If  for  any  reason  the  left  ventricle  fail  to  maintain  its  full  systolic 
output,  it  ceases  to  receive  the  full  auricular  input,  and  in  consequence 
the  i3ulmonary  vessels  congest.  This  tells  back  on  the  right  heart, 
and  the  right  ventricle  is  unable  to  emptj^  itself  into  the  congested 
pulmonary  vessels,  and  this  in  its  turn  leads  to  venous  congestion. 
The  final  result  of  any  obstruction  thus  is  a  pooling  of  the  blood  in 
the  venous  cistern.  D^'spnoea  results  from  cardiac  insufficiency.  It 
is  excited  by  the  increa.sed  venosity  of  the  blood  acting  on  the  respira- 
tory centre.  Both  the  excess  of  carbon  dioxide  and  deficiency  of 
oxygen  increase  the  acidity  of  the  blood,  and  this  excites  the  centre. 
The  increased  respiratory  movements  aid  the  circulation. 

The  vascular  system  is  so  constructed  that  considerable  changes 
of  pressure  may  be  brought  about  on  the  arterial  side  without  any 
(or  scarcely  any)  alteration  of  the  pressures  in  the  venous  or  pulmonary 
sections  of  the  circulatory  system.  A  high-pressure  main  (the  arteries) 
runs  to  all  the  organs,  and  this  is  supplied  with  taps;  for  by  means 
of  the  vaso-motor  nerves,  which  control  the  diameter  of  the  arterioles, 
the  stream  can  be  turned  on  here  or  there  and  any  part  flushed  A^ith 
the  blood,  while  the  supply  to  the  remaining  parts  is  kept  luider  control. 
Normally,  the  sum  of  the  resistances  which  at  any  moment  oppose 
the  oiitflow  through  the  capillaries  is  maintained  at  the  same  value, 
for  the  vascular  S3^stem  is  so  co-ordinated  by  the  nervous  system  that 
the  dilatation  of  the  arterioles  in  any  one  organ  is  compensated  for 
by  constriction  in  another.  Thus  the  arterial  pressure  remains  con- 
stant, except  at  times  of  great  muscular  activity. 

The  great  splanchnic  .system  of  arterioles  acts  as  "  the  re^is^ance 


228  A  TEXTBOOK  OF  PHYSIOLOGY 

box  "  of  the  arterial  system.  By  the  constriction  of  these  arterioles 
during  mental  or  muscular  activity,  the  blood-current  through  the 
abdominal  organs  is  diminished,  and  increased  through  the  brain  and 
muscles;  while  by  dilatation  during  rest  and  digestion  the  contrary 
effect  is  produced.  The  constriction  of  the  splanchnic  vessels  does 
not  sensibly  diminish  the  capacity  of  the  total  vascular  system,  for 
the  veins  relax.  Thus  big  variations  of  arterial  pressure,  brought 
about  by  constriction  or  dilatation  of  the  arterial  system,  produce 
little  or  no  effect  on  the  pressure  in  the  great  veins  or  pulmonary 
circuit.  On  the  other  hand,  the  contraction  of  the  abdominal 
muscles,  as  we  have  seen,  intluences  the  diastolic  or  filling  pressure  of 
the  heart. 

Hsemorrhage  and  Transfusion. — The  circulation  may  be  aided  by 
the  transfusion  of  salt  solution  (0-8  per  cent.)  or  blood  after  severe 
haemorrhage,  or  in  states  of  surgical  shock.  Only  the  blood  of  man 
must  be  used.  The  direct  giving  of  blood  by  connecting  the  radial 
artery  of  a  relation  to  the  median  vein  of  a  patient  has  been  used  as 
a  means  of  effecting  restoration.  Blood  may  be  withdrawn  from  the 
system  slowly  to  the  extent  of  4  per  cent.,  rapidly  to  the  extent  of 
2  per  cent.,  of  the  body  weight  without  lowering  the  arterial  pressure, 
owing  to  the  compensatory  contraction  of  the  anerioles  and  the  rapid 
absorption  from  the  tissues  into  the  blood.  The  beneficial  effects 
of  the  old  treatment  by  bleeding  were  probably  due  to  this  latter 
effect.  The  immune  properties  of  the  blood  may  be  increased  by  the 
passage  of  tissue  juices  into  it.  The  withdrawal  of  the  tissue  lymph 
excites  extreme  thirst  and  a  great  need  for  water  after  severe  haemor- 
rhage. About  75  per  cent,  by  weight  of  the  tissues,  excluding  fat 
and  bone,  consists  of  water.  The  volume  of  tissue  lymj^h  is  unknown, 
but  it  must  be  considerable — perhaps  greater  than  that  of  the  blood. 
The  lymphatics  drain  off  the  excess  of  fluid  which  transudes  from 
the  capillaries,  and  finally  return  it  to  the  vascular  system.  The 
interchange  between  tissue,  blood,  and  lymph,  depends  upon  the 
forces  of  the  living  cells,  which  are  as  yet  far  from  complete  elucidation. 

The  vascular  system  confines  the  red  corpuscles  to  its  channels, 
but  cannot  be  regarded  as  a  closed  system ;  for  the  fluid  of  the  blood- 
plasma  transudes  through  the  capillary  wall  into  the  tissue  spaces, 
and  enters  the  lymphatics.  Thus,  if  large  quantities  of  Ringer's 
solution  be  transfused  into  the  circulatory  system,  it  not  only  collects 
in  the  capacious  reservoirs  of  the  veins  and  capillaries,  especially  in 
the  lungs,  liver,  and  abdominal  organs,  but  in  the  tissue  spaces.  Hence 
the  pressure  in  the  vascular  system  cannot  be  raised  b}^  the  injection 
of  enormous  quantities  of  fluid.  If  the  fluid  part  of  blood  be  increased, 
capillary  transudation  becomes  greater,  and  the  excess  of  fluid  is 
excreted  from  the  kidneys  and  glands  of  the  alimentary  canal.  If 
the  fluid  part  of  the  blood  diminish,  then  fluid  passes  from  the  tissue 
spaces  into  the  blood,  and  the  sensation  of  thirst  arises,  and  more 
drink  is  taken. 


CHAPTER  XXVII 
THE  VASO-MOTOR  NERVES 

The  bloodvessels  are  supplied  with  constrictor  and  dilator  nerve 
fibres  which  regulate  the  size  of  the  vascular  bed  and  the  distribution 
of  the  blood  to  the  various  organs.  The  arteries  may  be  compared 
to  a  high -pressure  main  supplying  a  town.  By  means  of  the  vaso- 
motor nerves  the  arterioles  (the  house  taps)  can  be  opened  or  closed, 
and  the  current  turned  on  to  or  off  any  organ  according  to  its  func- 
tional needs.  If  all  the  arterioles  be  dilated  at  one  and  the  same 
time,  the  aortic  pressure  falls,  and  the  blood,  taking  the  pathways 
of  least  resistance,  gravitates  to  the  most  dependent  parts  of  the 
vascular  system;  just  as,  if  all  the  taps  in  the  town  were  opened  at 
once,  the  pressure  in  the  main  would  fail,  and  only  the  taps  in  the 
lower  parts  of  the  town  would  receive  a  supply.  The  discovery  of 
the  vaso-motor  nerves  is  due  to  Claude  Bernard  (1851).  He  dis- 
covered that  b}'  section  of  the  cervical  sympathetic  nerve  he  could 
make  the  ear  of  a  rabbit  flush,  while  by  stimulation  of  this  nerve  he 
could  make  it  blanch.  He  almost  made  the  further  discovery  that 
stimulation  of  certain  nerves,  such  as  the  chorda  tympani  supplying 
the  salivary  gland,  produces  an  active  dilatation  of  the  bloodvessels. 
The  vaso -constrictor  fibres  issue  in  the  anterior  spinal  roots  (the  white 
rami),  from. the  second  thoracic  to  the  second  lumbar  root,  and  pass 
to  the  sympathetic  chain  of  ganglia.  The  fibres  are  of  small  diameter, 
and  probabl}"  arise  from  cells  situated  in  the  lateral  horn  of  the  grey 
matter  of  the  spinal  cord.  They  each  have  a  cell  station  in  one  or 
other  ganghon,  and  proceed  as  post-ganglionic  fibres  to  the  cervical 
sympathetic,  to  the  mesenteric  nerves,  and  back  as  the  grey  rami  to 
join  the  nerves  of  the  limbs  (Fig.  457). 

Nicotine  paralyzes  ganglion  cell  synapses,  and  by  ap];)lying  this  test 
to  the  various  ganglia  the  cell  stations  of  the  vaso-constrictor  fibres 
supplying  each  organ  have  been  mapped  out.  The  vaso-dilator  fibres 
have  not  so  restricted  an  origin,  for  they  issue  in  the  efferent  roots  in 
all  parts  of  the  neural  axis.  The  two  kinds  of  nerves,  although  antag- 
onistic in  action,  end  in  the  same  terminal  plexus  which  surrounds  the 
vessels.  The  presence  of  vaso-dilator  fibres  in  the  common  nerve  trunks 
is  masked,  on  excitation,  by  the  overpoAvering  action  of  the  vaso-con- 
strictor nerves.  The  latter  are,  hoMever,  more  rapidly  fatigued  than 
the  former,  and  by  this  and  other  means  the  presence  of  vaso-dilator 
fibres  can  be  demonstrated  in  almost  all  parts  of  the  body.  The 
nervi  erigentes  to  the  penis  and  the  chorda  tympani  supplying  the 
salivary  glands  are  the  most  striking  examples  of  vaso-dilator  nerves. 

229 


230 


A  TEXTI3()()K  OF  PHYSIOLOGY 


The  vaso-dilator  nerves  for  the  hmbs  issue  in  the  jwsterior  spinal 
roots.  The  posterior  roots  contain  the  afferent  nerves  (touch,  pain, 
etc.).     The  same  fibres   serve   as   vaso-dilator   fibres.     The   impulses 


Fig.  120. — Diagram  of  a  Plethvsmograph  axd  Piston  PvEcordek. 
The  rubVjer  bands  fasten  the  glass  lid  in  position. 

which  produce  vaso-dilatation  are  termed  '"  antidromic  "  (against 
the  stream).  We  know  that  nerve  fibres  conduct  impulses  indifferently 
in  either  direction,  and  that  the  synai3sis  and  nerve  endings  control 
the  result  of  such  impulses. 


Fig.  121.  — Pithed  Cat:  Carotid  Blood-Pressuke.     (H.  H.  Tale.) 

Upper  curve  shows  effect  of  0025  uiilligrammc  of  adrenalin  before,  lower  curve  of 
0-1  milligramme  of  adrenalin  after,  10  milligrammes  of  crgotoxine. 

Excitation  of  these  posterior  roots  causes  reflexly  a  rise  of  blood - 
pressure,  and  directly  a  vaso-dilatation  in  the  part  the  nerves  supply. 
Thus  it  is  assured  that  the  irritated  or  injured  part  receives  immedi- 
lately  a  greater  supply  of  blood. 


THE  \'ASO-MOTOR  NERVES 


231 


The  vaso-iuotor  centre  exerts  a  tonic  influence  over  the  caUbre 
both  of  the  arterial  and  portal  systems. 

Much  work  has  been  done  to  determine  the  origin  and  exact 
distribution  of  the  vaso-motor  nerves  to  the  various  organs,  and 
the  reflex  conditions  under  which  they  come  normally  into  action^ 
and  our  knowledge,  the  fruits  of  these  inquiries,  has  come  to  a  con- 
dition of  considerable  exactness.  This  knowledge  is  of  great  practical 
importance  to  the  physician,  and  it  has  been  obtained  entirely  by 
experiment  on  living  anaesthetized  animals.  No  dissections  of  the 
dead  animal  could  have  informed  us  of  the  vaso-motor  nerves.     Vaso- 


C.C. 


Fig.  122. 

F,  Depressor;  R,  pressor  afferent  impulses  affecting  the  arteriole  muscle  through  CC, 
vaso -constrictor  centre,  and  through  DC,  vaso-dilator  centre.  Effect  shown  by 
+  and  —  signs.     (Bayliss.) 

motor  effects  can  be  studied  by  (1)  observing  the  flushing  or  blanching 
of  an  organ:  (2)  measuring  the  temperature  of  a  part  or  organ;  (3) 
measuring  the  venoi;s  outflow ;  (4)  recording  the  pressure  in  the  artery 
going  to  and  the  vein  leaving  the  organ;  (5)  observations  on  the 
volume  of  an  organ.  To  make  these  last  observations,  the  organ  is 
enclosed  in  a  suitable  air-tight  box,  or  plethysmograph,  an  opening 
being  contrived  for  the  vessels  of  the  organ  to  pass  through  so  that 
the  circulation  may  continue.  The  box  is  filled  with  air  or  water, 
and  is  connected  with  a  recording  tambour  (Fig.  120). 

The  chief  effects  of  vaso-constriction  are  an  increased  resistance 


232 


A  TEXTBOOK  OF  PHYSIOLOGY 


and  lessened  How  through  an  organ,  diminished  volume  and  tension 
of  the  organ;  the  venous  blood  issues  fiom  it  very  slowly  and  is  darker 
in  colour,  and  the  temperature  of  the  organ  sinks.     If  a  large  area 

be    constrieted,    the    general    arterial 
pressure  rises. 

The  vaso -motor  centre  is  situated 
in  the  spinal  bulb  beneath  the  middle 
of  the  floor  of  the  fourth  ventricle. 
The  tone  of  the  vascular  system  is  not 
disturbed  when  the  great  brain  and 
mid-brain  is  destroyed  as  far  as  the 
region  of  the  pons,  but  as  soon  as  the 
spinal  bulb  is  injured  or  destroyed  the 
arterial  pressure  falls  very  greatly,  and 
the  animal  passes  into  a  condition  of 
j^  surgical  shock  if  kept  alive  by  artificial 
respiration.  Painting  the  floor  of  the 
fourth  ventricle  with  a  local  anaesthetic 
— e.g.,  cocaine — has  the  same  lowering 
effect  on  the  blood-pressure.  Division 
of  the  cervical  spinal  cord  or  of  the 
splanchnic  nerves  lowers  the  blood- 
pressure  greatly.  The  one  lesion  cuts 
off  the  whole  body,  the  other  the 
abdominal  organs,  from  the  tonic  in-- 
///^  fluence    of    the    centre.     The    fall    of 

"  '       pressure  is  due  almost  entirely  to  the 

pooling  of  the  blood  in  the  portal  veins 
and  vena  cava  inferior.  On  the  other 
hand,  electrical  excitation  of  the  lower 
end  of  the  divided  cord  or  splanchnic 
nerves  raises  the  pressure  by  restoring 
the  vascular  tone.  If  an  animal  be 
kept  alive  after  division  of  the  spinal 
cord  in  the  lower  cervical  region,  which 
is  possible,  since  the  phrenics,  the  chief 
C,  Constrictor;  Z>,  dilator  neurones;  ^otor  nerves  of  respiration,  come  off 
^,  muscle  cell  of  arteriole  in  body;  above  this  region,  it  is  found  that  the 
K,  muscle  t-ell  of  arteriole  of  vascular  tone  after  a  time  becomes 
kidney;  E,  anercnt  nerve  oi  the  .         .  i     ,i  t,  •  r      i       i 

kidney  influencing  the  body  restored  and  the  condition  of  shock 
arteriole  through  the  bulbar  passes  awav.  By  iio  second  section 
centres  and  the  kidney  arteriole  ^f  ^jje  spinal  cord  can  the  general 
locally  through  the  spinal  centres.  ,.,.  e     ^       ,,  -,         ii. 

Effect  on  centres  shown  by  +  and  Condition  of  shock  be  reproduced,  but 
-  signs.     (Bayliss.)  a   total   destruction   of  the  cord  once 

more  causes  a  general  loss  of  the 
vascular  tone.  From  the  experimental  result  so  obtained,  it  is 
argued  that  subsidiary  vaso-motor  centres  exist  in  the  spinal  cord, 
and  there  is  evidence  to  show  that  these  centres  may  be  excited  re- 
flexly.     After  the  lumbar  cord  has  been  destroyed,  the  tone  of  the 


Fin.   123. 


THE  VASOMOTOR  NERVES 


233 


vessels  of  the  lower  limbs  is  recovered  in  the  course  of  a  few  days. 
In  this  case  the  recovery  is  attributed  to  the  ganglionic  and  nervous 
structures  which  are  intercalated  between  the  spinal  cord  and  the 
muscular  walls  of  the  bloodvessels.  There  are  thus  three  mechanisms 
of  control:  the  bulbar  centre,  influenced  particularly  by  the  visual, 
auditory,  and  vestibular  nerves ;  the  spinal  centres ;  and  the  peripheral 
ganglionic  structures. 

The  vaso-motor  centre  is  reflexly  excited  by  the  afferent  nerves, 
and  its  ever-varj^ing  tonic  action  is  made  up  of  the  balance  of  the 


Fig.  124. — Showing  the  Effect  of  a  Pleasant  Taste  (+  )  and  of  an  Unpleasant 
Taste  (-)  upon  (1)  the  Volume  of  the  Abdominal  Organs,  (2)  the  Volume 
of  the  Arm,  (3)  the  RESPiR^TiaN. 


pressor  and  depressor  influences  which  thus  reach  it,  and  from  the  quality 
of  the  blood  which  circulates  through  it.  Pressor  effects — i.e.,  those 
causing  increased  constriction  and  rise  of  arterial  pressure — may  be 
produced  by  stimulating  the  central  end  of  almost  any  afferent 
nerve,  and  especially  that  of  a  cutaneous  nerve  (see  Fig.  £4). 
Depressor  effects  are  always  obtained  by  stimulating  the  depressor 
nerve  (Fig.  S3),  and  may  be  obtained  by  stimulating  the  afferent 
nerves  under  special  conditions.  There  seems  to  be  good  evidence 
that,  after  division  of  the  vaso-constrictor  nerves,  dilatation  of  a  limb 
can  be  brought  about  reflexly  by  stimulating  the  depressor  nerve,  and 


234 


A  TEXTBOOK  OF  PHYHIOLOOY 


in  this  case  the  effect  must  be  brought  about  by  active  excitation  of 
the  vaso-dilator  nerves.  It  is  probable  that  there  are  vaso-dilator 
fibres  in  symj)athetic  nerves.  Thus  adrenalin,  which  normally  causes 
a  rise  of  arterial  pressure,  after  a  dose  of  ergotoxine  causes  a  fall 
(Fig.  121).  The  best  explanation  of  this  result  is  that  vaso-dilator 
fibres  are  now  stimulated.  It  seems  probable  that  with  depressor 
reflexes  there  is,  along  with  the  inhibition  of  tone  in  the  vaso-constrictor 
centre,  an  excitation  of  the  vaso-dilator  centre;  and  with  pressor 
reflexes  an  excitation  of  the  vaso-constrictor  centre  and  an  inhibition 
of  the  vaso-dilator  centre  (Fig.  122).     When  an  afferent  nerve  from 


Fig.  125. ^The  Effect  of  the  Suggestion  to  a  Hypnotized  Subject  of  his 
Execution  (-  to  -i- )  upon  (1)  the  Volume  of  the  Abdominal  Organs, 
(2)  the  Volume  of  the  Arm,  (3)  the  Respir.4.tion. 


any  particular  organ — e.g.,  the  kidney  (Fig.  123) — excites  the  usual 
pressor  reflex  on  the  general  blood-pressure,  a  vaso-dilatation  is  pro- 
duced through  spinal  centres  in  the  organ  itself,  thus  ensuring  a 
maximal  blood  supply  to  the  active  organ.  In  these  local  reflexes 
there  is  excitation  of  constrictors  and  inhibition  of  vaso-dilators 
(Fig.  123).  That  these  reflex  vaso-motor  effects  frequently  occur  is 
shown  hy  the  blush  of  shame,  the  blanching  of  the  face  by  fear,  the 
blanching  of  the  skin  by  cold,  and  the  flushing  which  is  produced  by 
heat.  The  rabbit's  ear  blanches  if  its  feet  are  put  into  cold  water. 
In  Fig.  124  are  shown  the  effects  of  pleasant  r.nd  unpleasant  tastes 


THE  VASO-MOTOR  NERVES  235 

upon  the  volume  of  the  abdominal  organs,  the  volume  of  the  ai'm, 
and  the  respiration.  In  like  manner  the  effects  of  the  suggestion 
of  his  execution  to  a  hypnotized  subject  are  recorded  in  Fig.  125. 
The  vaso-motor  mechanism  is  one  of  the  most  important  of  those 
mechanisms  which  control  the  body  heat.  Stimulation  of  the  nasal 
iliucous  membrane  causes  flushing  of  the  vessels  of  the  head,  constric- 
tion elsewhere,  and  a  rise  of  arterial  pressure.  Food  in  the  mouth, 
or  even  the  sight  or  smell  of  food,  causes  dilatation  of  the  vessels  of 
the  salivary  gland.  The  mucous  membrane  of  the  air-passages  flush 
and  secrete  more  actively  when  a  draught  of  cold  air  strikes  the  skin. 
Ice  placed  on  the  abdomen  constricts  not  only  the  vessels  in  the  skin, 
but  those  in  the  kidney.  Many  other  examples  might  be  given  of  the 
control  which  the  vaso-motor  system  exerts,  but  the  above  are  suffi- 
cient to  suggest  the  influence  which  the  physician  can  bring  to  bear 
on  the  blood-su]3ply  of  the  various  organs. 


CHAPTER  XXVIII 

CIRCULATION  IN  SPECIAL  PARTS 

The  Pulmonary  Circulation. — The  pulmonary  artery,  carrying 
venous  blood,  divides  and  subdivides,  and  the  smallest  branches  end 
in  a  plexus  of  capillaries  on  the  walls  of  the  air  cells  of  the  lung.  From 
this  plexus  the  blood  is  drained  by  the  radicles  of  the  four  pulmonary 
veins  which  open  into  the  left  auricle.  The  pressure  in  the  pulmonary 
artery  has  been  found  to  be  12  to  30  mm.  Hg — that  is,  from 
one-third  to  one-sixth  of  the  aortic  pressure;  the  blood  also 
takes  only  one-third  of  the  time  to  complete  the  pulmonary  circuit 
that  it  takes  to  make  the  systemic.  The  four  chief  factors  which 
influence  the  pulmonary  circulation  are — (1)  the  force  and  output  of 
the  right  ventricle;  (2)  the  diastolic  filling  action  of  the  left  auricle 
and  ventricle;  (3)  the  diameter  of  the  pulmonary  capillaries,  which 
varies  with  the  respiratory  expansion  of  the  lungs;  (4)  the  intra- 
thoracic pressure. 

In  inspiration,  the  lungs  are  distended  in  consequence  of  the  greater 
positive  pressure  on  the  inner  surfaces  being  greater  than  the  negative 
pressure  on  their  outer  pleural  surfaces.  The  negative  pressure  in 
the  intrathoracic  cavity  results  from  the  enlargement  of  the  thorax 
by  the  inspiratory  muscles.  When  the  elastic  lungs  are  distended  by 
a  full  inspiration,  they  exert  an  elastic  traction  amounting  to  about 
15  mm.  Hg.  The  heart  and  vessels  within  the  thorax  are  submitted 
to  this  traction — that  is,  to  the  pressure  of  the  atmosphere  minus 
15  mm.  Hg — while  the  vascular  system  of  the  rest  of  the  body  bears 
the  full  atmospheric  pressure.  The  thin-Avalled  aiu'icles  and  veins 
yield  more  to  this  elastic  traction  than  the  thick-walled  ventricles 
and  arteries.  Thus,  inspiration  exerts  a  suction  action  which  furthers 
the  filling  of  the  veins  and  auricles.  This  action  is  assisted  by  the 
positive  pressure  exerted  by  the  descending  diaj)hragm  on  the  con- 
tents of  the  abdomen.  Blood  is  thus  both  pushed  and  sucked  into 
the  heart  in  increased  amount  during  inspiration. 

Experiment  has  shown  that  the  bloodvessels  of  the  lungs  when 
distended  are  wider  than  those  of  collapsed  lungs.  Suppose  an  elastic 
bag  having  minute  tubes  in  its  walls  be  dilated  by  blowing  into  it, 
the  lumina  of  the  tubes  will  be  lessened,  and  the  same  occurs  in  the 
lungs  if  they  are  artificially  inflated  with  air ;  but  if  the  bag  be  placed 
in  a  glass  bottle,  and  the  jDressure  on  its  outer  surface  be  diminished 
by  removing  air  from  the  space  between  the  bag  and  the  side  of  the 
bottle,  the  bag  will  distend  and  the  lumina  of  the  tubes  be  increased. 
Thus,  it  seems  that  inspiration,  by  increasing  the  calibre  of  the  pul- 
monary vessels,  draws  blood  into  the  lungs,  and  the  movements  of 
the  lungs  become  an  effective  force  in  carrying  on  the  pulmonary 

236 


CIRCULATION  IN  SPECIAL  PARTS  237 

circulation.  It  has  been  estimated  that  there  is  about  one-twelfth 
of  the  whole  blood  quantum  in  the  lungs  during  inspiration,  and  one- 
fifteenth  during  expiration.  The  great  degree  of  distensibility  of 
the  pulmonar}'  vessels  allows  of  frequent  adjustments  being  made,  so 
that  within  wide  limits  as  much  blood  in  a  given  time  will  pass  through 
the  puhnonary  as  through  the  systemic  system.  The  limits  of  their 
adjustment  may,  however,  be  exceeded  during  violent  muscular 
exertion.  The  compressive  action  of  the  skeletal  muscles  returns  the 
blood  to  the  venous  cistern,  and  if  more  arrives  than  can  be  trans- 
mitted through  the  lungs  and  oxygenated  in  a  given  time,  the  right 
heart  becomes  engorged,  breathlessness  occurs,  and  signs  of  venous 
congestion  appear  in  the  flushed  face  and  turgid  veins.  The  w^eaker 
the  musculature  of  the  heart,  the  more  likely  is  this  to  occur,  hence 
the  breathlessness  on  exertion  which  characterizes  cardiac  affections. 
Any  oedema  of  the  lung  resulting  from  its  congestion  also  impedes  the 
passage  in  of  oxygen.  Hence  the  benefit  of  oxj-gen  inhalation  in 
strenuous  exercise.  The  training  of  an  athlete  consists  largely  in 
developing  and  adjustmg  his  heart  to  meet  this  strain.  Similarly, 
the  weak  heart  may  be  trained  and  improved  by  carefully  adjusted 
exercise. 

Rhythmic  compression  of  the  thorax  is  the  method  of  resuscita- 
tion from  suffocation,  for  this  not  only  aerates  the  lungs,  but  produces 
a  circulation  of  blood.  B}"  compressmg  the  abdomen  to  fill  the  heart, 
and  then  compressing  the  thorax  to  empty  it,  the  valves  meanwhile 
directing  the  flow,  a  pressure  of  blood  can  be  maintained  in  the  aorta 
even  when  the  heart  has  ceased  to  beat,  and  this  if  patiently  continued 
may  lead  to  renewal  of  the  heart-beat. 

As  regards  the  effect  of  breathing  upon  the  arterial  blood-pressure, 
the  resvilts  are  complex.  It  is  generally  stated  that  inspiration  at 
first  causes  a  fall  and  then  a  rise  of  blood-pressure,  and  that  expiration 
causes  flrst  a  rise  and  then  a  fall.  The  rate  of  the  heart-beat  is  also 
affected  during  these  times,  being,  when  the  vagi  are  intact,  slower 
in  expiration  and  quickened  by  inspiration. 

In  animals  under  deep  ansesthesia  the  inspiratory  rise  is  due  to 
lessened  pressure  in  the  pericardium,  and  the  consequent  increased 
filling  of  the  heart.  It  is  abohshed  b}'  allowing  free  access  of  air  to 
the  pericardial  sac. 

In  man  sphygmographic  tracings,  taken  by  the  suspension  method 
(Fig.  98),  show  that  the  effect  on  the  arterial  pressure  varies  with 
the  type  of  breathing  (see  p.  191). 

A  deep  breath  generally  produces  a  fall,  often  accompanied  by  the 
so-called  pulsus  paradoxus,  an  alteration  in  rhythm  often  considered 
to  have  a  pathological  import,  but  normal  in  sleeping  dogs,  and  of 
occasional  occurrence  in  boys  at  the  time  of  adolescence. 

The  pulmonarj'  circuit  may  be  shut  off  to  a  large  extent  in  animals 
under  artificial  respiration,  with  little  or  no  effect  upon  the  arterial 
blood-pressure.  Ligation  of  the  vessels  of  the  left  lung  produced 
in  eighteen  cases  no  noticeable  effect  on  the  output  of  the  heart  per 
second.     Of  the  other  thirteen,  in  eleven  the  pressure  was  decreased 


238  A  TEXTBOOK  OF  PHYSIOLOGY 

6  to  10  per  cent.,  in  two  18  to  20  per  cent.  The  lungs  and  their 
circulation  in  men  are  arranged  to  meet  a  demand  ten  times  that 
of  the  resting  condition.  A  rise  of  arterial  blood -pressure  is  obtained 
in  Valsalva's  experiment — a  deep  expiration  with  the  nose  shut — and 
is  due  to  the  greatly  increased  abdominal  pressure.  In  this  condition 
and  in  coughing  this  pressure  as  measured  per  rectum  may  rise  as  high 
as  94  mm.  Hg.  In  deep  abdominal  breathing  it  may  rise  to  30  mm. 
Hg,  showing  a  respiratory  variation  of  20  mm.  Hg. 

The  evidence  that  the  pulmonary  arteries  are  controlled  by  vaso- 
motor nerves  is  conflicting.  In  the  intact  animal  it  is  diflicult  to 
determine  whether  a  rise  of  pressure  in  the  pulmonary  artery  is  pro- 
duced really  by  constriction  of  the  j)ulmonary  system  or  by  changes 
in  the  output  of  the  heart;  hence  different  observers  have  reached 
conflicting  conclusions.  When  the  lungs  have  been  sujiplied  with  an 
artificial  circulation  and  a  constant  head  of  pressure,  to  eliminate  the 
action  of  the  heart,  no  diminution  in  outflow  has  been  observed  on 
exciting  the  branches  of  the  vagus  or  sympathetic  nerves  which  supply 
the  lungs. 

The  use  of  adrenalin,  which  causes  vaso-constriction  when  perfused 
through  organs  possessing  vaso-constrictor  nerves,  has  given  con- 
flicting results.  This  is  apparently  due  to  the  fact  that  different 
joreparations  and  compounds  of  adrenalin  have  been  used.  With 
adrenalin  itself  there  is  evidence  of  vaso-constriction;  with  adrenalin 
chloride  there  is  no  evidence  of  such.  The  vaso-constriction  when 
produced  is,  however,  not  of  a  very  marked  character.  Weighing 
the  evidence,  it  would  appear  that  the  pulmonary  vessels  may  possess 
vaso-constrictor  nerves,  but  that  the  action  of  these  is  far  less  marked 
than  that  of  the  nerves  to  other  organs. 

The  Coronary  Circulation. — The  heart  is  supplied  with  blood  from 
the  two  coronary  arteries,  which  arise  from  the  aorta  just  above  the 
semilunar  valves.  The  arteries  supply  both  auricles  and  ventricles, 
and  their  terminal  ramifications  run  deep  into  the  muscle.  The 
heart  becomes  fliished  and  supplied  with  blood  during  each  diastole ; 
with  each  systole  the  heart  pales  and  the  blood  is  expressed  into  the 
right  auricle  through  the  coronarj^  sinus.  To  determine  the  existence 
of  coronary  vaso-constrictor  and  of  vaso-dilator  fibres  is  a  complex 
matter,  since  stimulation  of  the  effector  nerves,  the  vagus  and 
the  sympathetic,  also  affect  the  heart  miiscle.  During  stimvdation 
of  the  vagus  with  the  heart  in  situ,  it  is  claimed  that  a  marked 
vasodilatation  of  the  smaller  arteries  can  be  seen  with  the  aid 
of  a  hand  lens.  On  the  isolated  perfused  heart,  stimulation  of  the 
vagus,  according  to  some  observers,  jaelds  a  diminished  outflow  from 
the  coronary  veins,  evidence  of  vaso-constriction;  stimulation  of  the 
sympathetic,  an  increased  outflow,  evidence  of  vaso-dilatation.  In 
i^erhaps  the  most  trustworthy  of  those  experiments  performed  on 
the  perfused  heart,  neither  vagus  nor  sympathetic  gave  evidence  of 
any  effect  whatsoever  on  the  calibre  of  the  coronary  arteries.  This 
is  confirmed  by  the  fact  that  adrenalin  is  also  without  apparent  effect 
when  perfused  through  the  coronary  vessels. 


CIRCULATION  IN  SPECIAL  PARTS  239 

The  Cerebral  Circulation. — The  circulation  of  the  brain  is  some- 
what peculiar,  since  this  orgaii  is  enclosed  in  a  rigid  bony  covering. 
The  limbs,  glands,  and  viscera,  are  enclosed  in  connective-tissue 
sheaths,  but  can  exjsand  when  the  blood-pressure  rises ;  the  expansion 
of  the  brain,  on  the  other  hand,  is  confined.  The  circulation  in  the 
marrow  of  bones  resembles  that  in  the  brain  and  spinal  cord. 

In  1783,  Alexander  Monro  the  younger  put  forward  the  view  that 
the  quantity  of  blood  within  the  cranium  is  almost  invariable.  "  For 
being  enclosed  in  a  case  of  bone,"  he  writes,  "  the  blood  must  be 
continually  flowing  out  of  the  veins,  that  room  may  be  given  to  the 
blood  which  is  entering  by  the  arteries.  For  as  the  substance  of  the 
brain,  like  that  of  the  other  solids  of  our  body,  is  nearty  incompressible, 
the  quantity  of  blood  within  the  head  must  be  the  same  at  all  times, 
whether  in  health  or  disease,  in  life  or  after  death,  those  cases  only 
excepted  in  which  water  or  other  matter  is  effused  or  secreted  from 
the  bloodvessels;  for  in  these  a  quantity  of  blood  equal  m  bulk  to  the 
effused  matter  will  be  pressed  out  of  the  cranium." 

These  facts  are  confirmed  by  experiment.  If  a  glass  plate  be 
screwed  into  a  trephine  hole,  on  compressing  the  innominate  and 
subclavian  arteries,  the  j)ial  arteries  can  be  seen  to  become  less  in 
size.  The  brain,  however,  does  not  collapse  or  retreat  from  the  glass 
window.  If  the  arteries  empty,  the  veins  fill.  If,  on  the  other  hand, 
the  glass  window  be  faultily  jilaced,  and  allow  leakage  into  the  cranial 
cavity,  air  passes  within,  and  the  brain  collapses  under  atmospheric 
pressure.  This  experiment  proves  that  the  brain  in  the  closed 
cranium  can  by  no  means  completely  empty  itseK  of  blood,  even 
though  the  arterial  pressure  should  fall  to  zero. 

Similarly,  if  an  animal  be  placed  in  the  vertical  feet-down  position, 
and  the  skull  be  trephined,  then,  on  opening  the  dura  mater,  the  brain, 
which  before  was  in  close  apposition  with  that  membrane,  can  be 
seen  collapsing,  as  it  is  emptied  of  blood  by  atmospheric  joressure. 
The  quantity  of  cerebro-spinal  fluid  which  moistens  the  surface  of  the 
brain  is  not  large,  and  the  blood-content  of  the  brain  can  vary  suddenly 
only  to  a  slight  degree  by  displacement  of  the  cerebro-spinal  fluid. 

No  sure  evidence  of  the  condition  of  the  cerebral  circulation  can 
be  drawn  from  examination  of  the  brain  after  death,  for  in  many 
different  ways  the  relative  volume  of  blood  and  the  serous  fluid 
within  the  cranium  may  be  altered  by  post-mortem  changes.  By 
slow  changes  there  can  come  about  more  blood  and  less  tissue  fluid 
and  brain  substance  in  the  skull,  or  less  blood  and  more  brain  sub- 
stance and  fluid.  In  inflammatory  states  brain  substance  may 
undergo  lysis,  and  be  carried  away  by  the  blood-stream,  and  the 
bloodvessels  dilate  and  hold  more  blood.  The  balance  between 
volume  of  brain  substance  and  blood  must  continually  var}^  with  the 
metabolism  of  this  organ. 

The  conditions  affecting  the  cerebral  circulation  may  be  studied 
by  simultaneously  recording  (1)  the  aortic  pressure,  (2)  the  vena  cava 
pressure,  (3)  the  intracranial  pressure,  (4)  the  cerebral  venous  pressure 
— the  cranium  being,  as  in  the  normal  condition,   a  closed  cavity. 


240  A  TEXTBOOK  OF  PHYSIOLOGY 

To  effect  this  tlu^  intracranial  pressure  is  measured  by  means  of 
a  brain-jn-essure  gauge  (Fig.  120),  while  the  cerebral  venous  pressure 
is  obtained  by  screwing  a  cannula  into  the  torcular  Herophili,  a  bony 
cavity  within  the  occiput  of  the  dog.  The  pressure  of  the  cerebro- 
spinal fluid  can  be  measured  by  ti'e])hining  the  atlas,  opening  the  dura 
mater,  screwing  a  tube  into  the  trephine  hole,  and  connecting  this 
tube  with  a  water  manometer. 

By  these  means  the  following  principles  of  the  cerebral  circulation 
have  been  determined : 

When  the  aortic  pressure  rises,  the  expansion  of  cerebral  volume 
can  take  place  only  to  a  certain  limited  amount ;  for  as  soon  as  all  the 
cerebro-spinal  fluid  has  been  driven  out  of  the  cranium,  the  brain  is 
everywhere  in  contact  with  the  rigid  wall  of  the  skull.  Any  further 
exj)ansion  of  the  arteries  can  only  take  place  by  an  equivalent  com- 
pression of  veins,  for  the  semi-fluid  brain  matter  is  incompressible. 
The  reservoirs  of  blood  in  the  veins  will,  therefore,  be  so  far  con- 
stricted, until  the  cerebral  venous  pressure  rises  to  the  pressure  of 
the  brain  against  these  veins.  Thus,  as  the  arterial  pressure  rises,  the 
whole  circulatory  system  of  the  brain  will  assimilate  itself  more  and 


fn  r  riu^Jwwiuii<tVui  ^T,iu»i  lit 


Fig.  126. — Hill's  Cerebral  Pressure  Gauge. 

more  to  a  scheme  of  rigid  tubes.  Thus  the  velocity  of  the  blood-flow 
will  be  increased,  and  the  relative  distribution  of  the  blood  in  the 
arteries,  capillaries,  and  veins,  will  be  changed. 

The  intracranial  pressure  is  in  all  physiological  conditions  the  same 
as  the  cerebral  venous  pressure.  The  intracranial  j)ressure,  or  pres- 
sure of  brain  against  skull  wall,  is,  in  fact,  that  pressure  which  remains 
after  the  force  of  the  heart  has  been  expended  in  driving  the  blood 
through  the  cerebral  arterioles.  It  is  therefore  an  ever-varying 
quantity. 

In  the  normal  conditions,  with  the  animal  in  the  horizontal  posi- 
tion, the  intracranial  pressure  may  approximate  to  about  100  mm.  H,0. 

In  the  spasms  of  strychnine-poisoning  the  intracranial  tension 
may  rise  to  40  to  50  mm.  Hg.  Ths  is  due,  not  only  to  the  rise  of 
arterial  pressure,  but  to  the  rise  of  vena  cava  pressure  produced  by 
general  muscular  spasm. 

The  intracranial  or  cerebral  venous  pressure  varies  directly  with 
changes  in  vena  cava  pressure,  but  only  proportionately  with  those  in 
aortic  pressure.  If  the  torcular  Herophili  be  oioened  in  a  freshly 
killed  animal,  and  the  abdominal  veins  be  compressed,  venous  blood 
can  be  driven  out  of  the  torcular  in  a  continuous  stream.     Between 


CIRCULATION  IN  SPECIAL  PARTS 


2U 


the  vena  cava  and  the  torcular  there  lies  no  appreciable  resistance; 
between  the  aorta  and  the  cerebral  capillaries  or  veins  there  lies  the 
resistance  of  the  arterioles. 

Ever}^  change  in  the  position  of  an  animal,  owing  to  the  influence 
of  gravity  on  the  vascular  system,  affects  the  cerebral  circulation. 
Every  variation  in  respiration  and  every  muscular  movement  is  fol- 
loAved  by  passive  changes  in  the  circulation  of  the  brain.  Compression 
of  the  jugular  veins  or  the  abdomen  causes  a  marked  rise  in  cerebral 
venous  pressure.  The  movements  of  the  muscles  on  the  neck  by 
pressing  on  the  jugular  vein  are  sufficient  to  affect  the  cerebral  circu- 
lation. 


Tig.  127. — To  show  Effect  of  Stimulating  Peripheral  Exd  of  the  Vagus  on 
THE  Cerebral  Pressure. 

A,  Carotid  pressure;  B,  I'ight  auricle;  C,  intracranial  pressure;  D,  torcular  pressure. 


Every  stimulus  that  enters  the  organism  and  affects  the  general 
vaso-motor  centre  produces  a  passive  effect  on  the  cerebral  circulation. 
It  is  by  means  of  the  great  splanchnic  area  that  the  blood-supply  to 
the  brain  is  controlled.  An  anpemia  of  the  spinal  bulb  excites  the 
vaso-motor  centre ;  the  sj)lanchnic  vessels  constrict,  the  blood -pressure 
rises,  and  more  blood  is  driven  through  the  brain.  At  the  same  time 
the  respiratory  centre  is  excited,  and  by  the  increased  action  of  the 
respiratory  pump  more  blood  is  driven  to  the  right  heart,  and  thence 
to  the  brain.  We  have  in  the  vaso-motor  centre  a  protective  mechan- 
ism by  Mhich  blood  can  be  drawn  at  need  from  the  abdomen  and 
supplied   to   the   brain.     At  the   moment   that   excitation   from   the 

16 


242  A  TEXTBOOK  OF  PHY8I0L00Y 

outside  world  demands  cerebral  response,  the  sjilanchnic  area  constricts- 
and  more  blood  is  driven  through  the  brain. 

The  arterial  supply  to  the  brain  is  in  the  lower  animals  ko  super- 
abundant that  in  the  dog  four  of  the  arteries — two  common  carotids 
and  two  vertebrals^ — which  sui)ply  the  brain  can  be  tied  in  the  course 
of  ten  minutes,  and  yet  the  animal  either  at  once,  or  after  a  temporary 
])eriod  of  idiocy  and  paralysis,  completely  recovers.  In  the  monkey, 
on  the  other  hand,  ligation  in  one  operation  of  the  two  carotids  and 
one  vertebral  artery  produces  either  death  in  twenty-four  hours  or 
softening  of  the  great  brain,  accompanied  by  idiocy  and  paralysis 
of  movement  and  sensation.  The  efficiency  of  anastomosis  through 
the  circle  of  Willis  varies  in  different  individuals.  Sudden  com- 
pression of  one  common  carotid  artery  in  some  men  produces  epileptic 
spasm,  and  ligation  of  this  artery  has  been  followed  in  some  by  more 
or  less  temporary  paralysis  on  the  opposite  side  of  the  body ;  in  others 
the  effect  is  nil. 

Whether  the  cerebral  arteries  are  supplied  with  vaso-motor  nerves 
is  very  doubtful.  The  usual  methods  of  investigation  give  no 
evidence  of  these  in  the  brain  of  the  intact  animal.  After 
establishing  an  artificial  circulation  of  the  brain,  the  addition  of 
adrenalin  to  the  nutritive  fluid  is  stated  to  reduce  the  outflow;  and 
it  is  supposed  that  adrenalin  acts  by  stimulating  the  ends  of  the  vaso- 
motor nerves,  rather  than  by  stimulating  the  muscular  coats  of  the 
arteries.  The  veins  of  the  pia  and  dura  mater  have  no  middle  muscular 
coats  and  no  valves.  The  venous  blood  emerges  from  the  skull  in 
man  mainly  through  the  opening  of  the  lateral  sinuses  into  the  internal 
jugular  vein;  there  are  communications  between  the  cavernous  sinuses- 
and  the  ophthahnic  veins  of  the  facial  system,  and  with  the  venous 
plexuses  of  the  spinal  cord.  The  points  of  emergence  of  the  veins 
are  well  protected  from  closure  by  compression.  The  brain  can  regulate 
its  own  blood-supply  by  means  of  the  cardiac  and  vaso-motor  centres. 
Deficient  supply  to  these  centres  excites  increased  frequency  of  the 
heart  and  constriction  of  the  arteries,  especially  those  of  the  great 
splanchnic  area.  Cerebral  excitement  has  the  same  effect,  so  that 
the  active  brain  is  assured  of  a  greater  blood-supply.  As  the  brain 
in  the  processes  of  ideation,  etc.,  acts  as  a  whole,  vaso-motor  nerves 
for  locally  controlling  the  cerebral  circulation  seem  unnecessary. 

The  Circulation  in  the  Head. — The  vaso -constrictor  fibres  for  the 
head  issue  from  the  spinal  cord  by  the  upper  thoracic  anterior  root* 
(1  to  5  in  the  dog),  and  pass  into  the  cervical  sjanpathetic  nerve. 

The  vaso -dilator  supply  to  the  face  and  mouth  also  issues  from 
the  upper  thoracic  roots,  and  passes  up  the  cervical  sympathetic  nerve 
to  the  Gasserian  ganglion,  and  thence  to  the  fifth  nerve.  Some  of 
the  dilator  fibres  issue  directly  from  the  cranial  origin  of  the  fifth 
nerve,  for  stimulation  of  this  nerve  between  the  pons  and  the  Gasserian 
ganglion  flushes  the  face.  Excitation  of  the  lingual  and  glosso- 
phar3'ngeal  nerves  dilates  the  vessels  of  the  tongue,  while  stimulation 
of  the  hypoglossal  nerve  constricts  that  organ.  These  constrictor 
fibres  come  from  the  superior  cervical  sympathetic  ganglion. 


CIRCULATION  IN  SPECIAL  PARTS  243 

The  circulation  in  the  mucous  membrane  of  the  mouth  has  been 
examined  bj'  direct  observation,  while  the  volume  of  the  tongue  can 
be  investigated  with  a  suitable  plethysmograph.  By  observing  the 
effects  of  section  or  excitation  of  the  cervical  and  thoracic  sympathetic 
nerves  during  ophthalmoscopic  examination  of  the  eye  in  the  curarized 
rabbit,  both  vaso-constrictor  and  vaso-dilator  nerves  have  been 
ascribed  to  this  organ,  but  the  evidence  in  support  of  such  nerves 
is  far  from  strong. 

The  Salivary  Glands. — The  vaso-constrictor  fibres  to  the  sub- 
maxillary gland  issue  from  the  first  to  the  second  or  the  second  to  the 
third  thoracic  anterior  roots,  and  pass  up  the  cervical  sympathetic 
nerve.  The  cell  stations  for  these  fibres  lie  in  the  superior  cervical 
ganglion. 

The  vaso-dilator  fibres  to  the  submaxillary  gland  pass  by  way  of 
the  chorda  tympani  from  the  facial  nerve,  and  have  their  cell  stations 
in  contiguity  with  the  gland.  The  vaso-dilator  fibres  to  the  parotid 
gland  issue  from  the  glossopharyngeal  nerve,  and  pass  to  the  gland 
by  way  of  the  auriculo -temporal  nerve.  The  circulation  in  these 
glands  has  been  studied  bj'  placing  a  cannula  in  an  efferent  vein  and 
observing  the  outflow,  or  by  exposing  the  gland  and  directly  inspecting 
its  colour. 

The  Circulation  through  the  Limbs. — By  far  the  greater  quantity 
of  the  blood,  50  to  70  per  cent.,  lies  within  the  roomy  reservoirs  of 
the  abdominal  and  thoracic  organs.  From  thence,  by  means  of  the 
vaso-motor  mechanism,  the  blood  is  distributed  to  the  locomotor 
organs  at  need  in  times  of  activity. 

In  the  organs  of  locomotion,  the  quantit}"  of  blood  during  rest  has 
been  roughly  estimated  to  be  36  per  cent.,  and  during  activity  66  per 
cent.,  of  the  whole  blood  quantum. 

The  blood-flow  from  the  deep  femoral  vein  of  the  dog  during  an 
epileptic  fit  (excited  by  essential  oil  of  absinthe)  is  three  to  five  times 
as  great  as  during  rest.  The  contraction  of  the  muscles  expresses 
the  blood  which  is  within  them  on  into  the  veins. 

Similarly,  massage  greatly  increases  the  flow  of  blood  through  the 
muscles.  Massage  of  a  considerable  muscular  area  produces  a  fall  of 
general  arterial  pressure,  in  consequence  of  the  deviation  of  blood 
into  the  dilated  miiscular  vessels.  This  fall  may  amount  to  one-fifth 
of  the  initial  pressure.     Warmth  also  greatly  increases  the  blood-flow. 

In  the  curarized  animal  the  outflow  from  the  muscular  veins  of 
the  lower  limb  is  increased  on  excitation  of  the  motor  nerves.  Vaso- 
dilator fibres  must  run,  therefore,  in  these  nerves.  On  the  other 
hand,  evidence  of  a  diminished  outflow  on  stimulation  of  the  peripheral 
end  of  the  abdominal  sympathetic  has  been  obtained  in  the  curarized 
dog.  We  must  therefore  admit  the  existence  of  vaso-constrictor 
fibres.     They  are,  however,  but  poorl}-  developed  in  the  muscles. 

At  times  of  great  muscular  effort  a  man  closes  his  glottis,  and  holds 
compressed  his  thorax  and  abdomen.  By  this  means  the  intrathoracic 
and  intra-abdominal  pressures  are  raised,  the  outlet  from  the  veins 


244 


A  TEXTBOOK  OF  PHYSIOLOGY 


of  the  face  and  limbs  impeded.  Hence  the  veins  stand  out  "  knotted  " 
in  a  straining  man,  and  the  pressure  rises  within  them  towards  arterial 
pressure. 

During  a  run  the  rhythmic  movements  help  to  pump  the  blood 
through  the  muscles  and  back  to  the  heart.  The  control  of  the  blood- 
supply  to  the  limbs  has  been  studied  by  the  thermometric  or  plethys- 
mographic  method.     The  temperature  in  the  upper  limb  is  raised  by 


R'-hind  limb 
L'hind  limi 


Kidney       "^r-J 


/■"^Ww' 


Jejunum 


V      / 


^'\^^x^j^,^_^r 


•^^'^^^\r^  ,-    J^f^ 


Wa^-" 


Fem^Art^ 


AvM 


'^%:J^\.F\.t. 


jEccc.  Sc-iatzc 


Fig.  128. — To  show  Effect  of  Excitation  of  the  Superficial  Branch  or  Crur.^l 
Nerve  on  the  Arterial  Pressure  and  on  the  Volume  of  the  Spleen, 
Jejunum,  Kidney,  and  Feet.     (Hallion  and  Fran9ois-Frank.) 


destruction  of  the  first  thoracic  ganglion,  by  section  of  the  brachial 
plexus  or  mid-thoracic  roots.  In  the  hind-limb  a  rise  of  temperature 
occurs  after  dividing  the  sciatic  nerve.  The  vaso-motor  fibres  have 
been  traced  to  the  lower  thoracic  roots.  They  pass  down  the  sympa- 
thetic chain  in  the  lower  lumbar  region.  On  excitation  of  these  vaso- 
motor nerves,  the  greatest  change  of  temperature  is  found  in  the  feet. 
This  is  so  because  the  pad  of  an  animal's  foot  is  free  from  a  furry  coat, 


CIRCULATION  IN  SPECIAL  PARTS  245 

and  thus  forms  one  of  the  more  important  places  for  the  regulation  of 
the  temperature  of  the  bod^-. 

With  the  aid  of  the  plethysraograph,  the  vaso -motor  nerves  of  the 
Hmbs  have  been  minutely  studied.  The  vaso-constrictor  fibres  which 
supply  the  fore-limb  leave  by  the  anterior  roots  from  the  third  to  the 
eleventh  thoracic  nerves.  The  hind-limb  is  supplied  by  fibres  from 
the  eleventh  thoracic  to  the  third  lumbar  nerve. 

By  each  root  the  volume  of  the  whole  limb  is  effected. 

The  chief  outflow  of  constrictor  fibres  occurs  from  the  sixth  dorsal 
to  the  first  lumbar  nerve.  Thus  the  limbs  and  the  abdominal  viscera 
get  their  suppl}^  approximately  from  the  same  part  of  the  spinal  cord. 
The  vaso-motor  mechanism  of  the  limbs  is  not  powerfully  developed. 

By  stimulation  of  a  sensory  nerve  of  a  limb  the  vessels  of  that 
limb  expand,  and  elsewhere  the  vessels  constrict.  Usually,  the  other 
limbs  expand  owing  to  the  passive  dilatation  produced  by  rise  of 
aortic  pressure  which  follows  the  reflex  constriction  of  the  splanchnic 
vessels.  The  reflex  constriction  of  these  limbs  can  be  obtained  after 
section  of  the  splanchnic  nerves. 

The  sympathetic  cell  station  for  the  fibres  of  the  upper  limb  is  the 
stellate  ganglion;  of  the  hind-limb,  the  sixth,  seventh  lumbar,  and 
first  sacral  ganglia.  The  vaso-motor  fibres  to  the  trunk  follow  the 
same  distribution  as  the  pilomotor  fibres. 

The  general  changes  which  take  place  on  exciting  the  central  end 
of  an  afferent  nerve  are  shown  exceedingly  well  in  Fig.  128.  In  this 
there  is  shown  a  simultaneous  record  of — 

1 .  The  pressure  in  the  femoral  artery 

2.  The  volume  of  the  spleen. 

3.  The  volume  of  the  jejunum. 

4.  The  volume  of  the  kidney. 

5.  The  volume  of  the  left  hind-limb. 

6.  The  volume  of  the  right  hind-limb  (innervated). 

On  exciting  the  central  end  of  the  left  sciatic  nerve,  the  arterial 
pressure  rises,  and  the  spleen,  jejunum,  and  kidney,  constrict.  The 
right  foot  is  passively  expanded  by  the  rise  of  arterial  pressure.  There 
next  occurs  a  compensatory  slowing  of  the  heart,  accompanied  by 
active  dilatation  of  the  left  limb.  The  arterial  pressure  then  falls  to 
a  lower  height. 

The  volume  of  the  limbs  depends  both  upon  the  arterial  and  the 
vena  cava  pressure.  If  the  arterial  pressure  and  the  venous  pressure 
rise,  as  on  performing  a  Valsalva  experiment,  then  the  volume  of 
the  limb  increases  greatly.  Here  the  venous  pressure  rises  towards 
the  mean  arterial  pressure,  for  the  outlet  of  the  veins  is  blocked  by 
the  rise  of  intrathoracic  pressure.  If  the  vena  cava  pressure  rises 
while  the  arterial  pressure  falls,  the  two  effects  may  balance  each 
other,  and  the  volume  of  the  limb  remain  constant. 

The  tracing  of  the  limb  volume  shows  all  the  respiratory  and  cardiac 
oscillations.     The  limb  may  expand  most  either  with  expiration  or 


246  A  TEXTBOOK  OF  PHYSIOLOGY 

with  inspiration,  according  as  the  expiratory  ri.se  of  vena  cava  yjres.sure 
or  the  insjiiratory  rise  of  arterial  pressure  has  the  greater  effect. 

During  Traube-Hering  oscillations  of  arterial  pressure,  the  volume 
of  a  limb  follows  the  rise  and  fall  of  aortic  pressure. 

It  has  been  said  that  an  antagonism  exists  between  the  vaso-motor 
mechanisms  of  the  splanchnic  and  locomotor  organs.  Thus,  while 
during  asphyxia  the  splanchnic  vascidar  area  constricts,  the  vessels 
of  the  skin  and  muscles  dilate.  The  dilatation  of  the  latter,  however,  is 
in  all  probability  not  occasioned  by  active  dilatation,  but  is  due  to 
the  overmastering  power  of  the  splanchnic  constrictors.  By  the  rise 
of  aortic  pressure  the  vessels  in  the  remaining  parts  of  the  body  are 
passively  dilated,  and  the  blood-flow  is  thus  increased  through  the 
skin  and  muscles.  That  this  is  so  is  suggested  by  the  fact  that  after 
the  circulation  has,  by  ligation  of  the  thoracic  aorta  and  vena  cava 
inferior,  been  limited  to  the  fore  part  of  the  body,  either  asphyxia 
or  excitation  of  the  vaso-motor  centre  produces  a  slight  rise  of  arterial 
pressure,  owing  to  the  constriction  of  the  vascular  areas  of  the  face 
and  fore-limbs.  Previous  to  the  double  ligation  the  same  excitation 
produces  splanchnic  constriction,  a  great  rise  of  aortic  pressui-e,  and 
dilatation  in  the  face  and  fore-limbs.  Plethysmographic  evidence  of 
constriction  of  the  leg  has  been  obtained  during  asphyxia. 

Whether  the  dilatation  of  the  locomotor  organs  be  active  or  passive 
is  of  no  particular  importance.  The  fact  remains  that  the  splanchnic 
area  forms  the  chief  seat  of  varying  resistance,  and  when  the  splanchnic 
vessels  are  constricted  the  blood  is  driven  with  increased  velocity 
through  the  locomotor  organs,  and  is  determined  from  the  deep  to  the 
superficial  parts  of  the  body. 

The  Portal  Circulation. — The  portal  circulation  is  pecuHar  in  that 
the  blood  passes  through  two  sets  of  capillaries.  Arterial  blood  is 
conveyed  to  the  capillary  networks  of  the  stomach,  spleen,  pancreas, 
and  intestines,  by  branches  of  the  abdominal  aorta.  The  portal  vein 
is  formed  by  the  confluence  of  the  mesenteric  veins  Avith  the  splenic 
vein,  which  together  jdrain  these  capillaries.  The  portal  blood  breaks 
lip  into  a  second  plexus  of  capillaries  within  the  substance  of  the  liver. 
The  hepatic  veins  carry  the  blood  from  this  plexus  into  the  inferior 
vena  cava.  Ligation  of  the  portal  vein  causes  intense  congestion  of 
the  abdomuial  vessels,  and  so  distensile  are  these  that  they  can  hold 
nearly  all  the  blood  in  the  body;  thixs,  the  arterial  j^ressure  quickly 
falls,  and  the  animal  dies  just  as  if  it  had  been  bled  to  death.  The 
portal  circulation  is  largely  maintained  by  the  action  of  the  respiratory 
pump,  the  peristaltic  movements  of  the  intestine,  and  the  rhythmic 
contractions  of  the  spleen;  these  agencies  help  to  drive  the  blood 
through  the  second  set  of  capillaries  in  the  liver.  The  systole  of  the 
heart  may  tell  back  on  the  liver  and  cause  it  to  swell,  for  there  are 
no  valves  between  it  and  the  inferior  vena  cava,  when  there  is 
obstruction  in  the  right  heart  or  pulmonary  circulation.  The 
increased  respiration  which  results  from  muscular  exercise  greatly 
furthers  the  hepatic  circulation,  increasing  at  the  same  time  the  con- 
sumption of  food  material.     Thus  exercise  relieves  the  overfed  man. 


CIRCULATION  IN  SPECIAL  PARTS 


247 


'The  liver  is  so  vascular  and  distensile  that  it  may  hold  oue-quarLer  of 
the  blood  in  the  body. 

The  hepatic  branches  of  the  portal  vein  are  supplied  by  vaso- 
constrictor fibres  issuing  by  the  anterior  roots  from  the  third  to  the 
eleventh  thoracic  nerves. 

Vaso -constrictor  nerves  run  to  the  mesenteric  arteries  in  the 
splanchnic  nerves  from  the  fifth  downwards.  They  have  cell  stations 
in  the  semilunar  ganglia.  The  upper  roots  go  to  the  duodenum  and 
jejunum,  the  lower  to  the  ileum  and  colon.  The  splanchnics  also 
contain  vaso-dilator  fibres.  They  issue  especially  in  the  eleventh  to 
"the  thirteenth  thoracic  roots.     Stimulation  of  these  nerves  gives  a 


Fig.  129. — Aktekial  Pressure  (1)  A^'u  (J>;cometek  TKACI^■G  (2)  of  Kidney 
Volume.     (Bradford.) 

Between  the  points  starred  the  tenth  dorsal  rcot  was  excited.     The  time  is  marked 

in  seconds. 


preliminary  constriction,  followed  by  a  dilatation.  The  usual  effect, 
therefore,  on  the  arterial  pressure,  of  stimulating  the  peripheral  end 
of  the  splanchnic,  is  a  big  rise  followed  by  a  fall  of  pressure. 

The  spleen  is  supplied  through  the  splanchnic  nerves  with  con- 
strictor and  inhibitory  fibres.  The  existence  of  such  has  been  demon- 
strated by  oncometry.  During  digestion  this  organ  shows  rhythmic 
phases  of  expansion  and  contraction  occurring  at  the  rate  of  one  per 
minute.  In  addition,  as  digestion  proceeds,  it  gradually  expands  for 
several  hours,  and  then  returns  slowly  to  its  original  size.  The  spleen 
therefore  acts  as  a  blood-reservoir  in  the  portal  circulation. 

The  Renal  Circulation. — The  circulation  in  the  kidney  is  studied 
with  great  ease  by  the  plethysmographic  method.  A  metal  oncometer 
was  first  used  for  this  purpose.     A  suitable  box  can  be  moulded  with- 


248  A  TEXTBOOK  OF  PHYSIOLOGY 

out  difficulty  out  of  gutta-percha  (Fig.  IllO).  The  kichicy,  having  beeiv 
exposed  by  a  lumbar  incision,  is  drawn  out  of  the  wound  and  placed 
in  the  box.  The  pedicle  of  the  kidney  passes  out  through  a  groove 
in  one  side  of  the  chamber.  The  box  is  closed  by  a  glass  cover,  and 
this  is  made  air-tight  by  a  free  application  of  thick  vaseline.  The  altera- 
tions in  the  volume  of  the  ki(hiey  are  recorded  by  means  of  a  tambour. 
The  tracing  of  renal  volume  follows  exactly  the  curve  of  arterial  pres- 
sure, and  exhibits  both  the  cardiac  and  respiratory  oscillations. 

Excitation  of  the  splanchnic  nerves  jDroduees  constriction  of  the 
kidney.  The  renal  vaso -motor  fibres  to  the  anterior  roots  arise  from 
the  sixth  to  the  thirteenth  thoracic  nerves.  Most  of  the  renal  vaso- 
motor fibres  are  found  in  the  eleventh,  twelfth,  and  thirteenth 
nerves. 

By  reflex  excitation  it  is  more  common  to  obtain  contraction  than 
expansion  of  the  kidney,  but  expansion  is  frequently  witnessed  when 
the  central  ends  of  the  eleventh,  twelfth,  and  thirteenth  posterior 
thoracic  roots  are  stimulated.  Vaso-dilator  fibres  in  the  anterior 
roots  are  evidenced  by  employing  a  slow  rate  of  excitation  (one  per 
second). 

Injections  of  normal  saline,  or  of  a  2  to  3  per  cent,  solution  of 
caffeine  of  soda,  double  the  velocity  of  blood-flow  in  the  renal  artery, 
as  measured  by  the  stromuhr.  This  occurs  after  section  of  the  renal 
nerves.  Hence  the  diuretic  action  of  these  drugs.  If  urea  be  in-  _ 
jected,  it  produces  local  dilatation  of  the  kidney,  while  it  excites  the 
vaso -motor  centre  and  causes  general  vaso -constriction. 

The  Circulation  in  the  Generative  Organs. — Excitation  of  the  first 
and  second  sacral  nerves  in  the  dog  produces  erection  of  the  penis. 
The  existence  has  been  demonstrated  of  a  centre  in  the  lumbar  region 
of  the  cord,  by  means  of  which  erection  can  be  reflexly  excited.  In 
the  rabbit,  monkey,  and  cat,  the  vaso-dilators  run  in  the  second  and 
third  anterior  sacral  roots. 

The  outflow  from  the  vena  pudenda  communis  is  increased  as  much 
as  eight  times  on  excitation  of  the  nervi  erigentes.  The  vaso-con- 
strictor  fibres  issue  from  the  third,  fourth,  and  fifth  lumbar  anterior 
roots. 

The  internal  generative  organs  are  supplied  with  vaso -constrictor- 
nerves  from  the  lumbar  anterior  roots. 

All  the  vaso-constrictor  fibres  to  the  generative  organs  pass  through 
cells  stationed  in  the  inferior  mesenteric  and  sacral  ganglia  of  the 
sympathetic.  The  vaso-dilator  nerves  pass  through  cell  stations  in 
scattered  ganglia  situated  near  these  organs. 

The  Foetal  Circulation.— In  the  mature  foetus,  the  fluid  brought 
from  the  placenta  by  the  foetal  umbihcal  vein  is  partly  conveyed  at 
once  to  the  vena  cava  ascendens  by  means  of  the  ductus  venosus, 
and  partly  flows  through  two  trunks  that  unite  with  the  portal  vein,, 
returning  the  blood  from  the  intestines  into  the  substance  of  the  liver,, 
thence  to  be  carried  back  to  the  vena  cava  by  the  hepatic  vein.  Having 
thus  been  transmitted  through  the  placenta  and  the  liver,  the  blood 


CIRCULATION  IN  SPECIAL  PARTS  249^ 

that  enters  the  vena  cava  is  purely  arterial  in  character;  but,  being 
mixed  in  the  vessels  with  the  venous  blood  returned  fi'om  the  trunk 
and  lower  extremities,  it  loses  this  character  in  some  degree  by  the 
time  it  reaches  the  heart.  In  the  right  auricle,  which  it  then  enters, 
it  would  also  be  mixed  Avith  the  venous  l)lood  brought  down  from  the 
head  and  ui)j)er  extremities  by  the  descendmg  vena  cava,  were  it  not 
that  a  provision  exists  to  impede  (if  it  does  not  entirely  prevent)  any 
further  admixture.  This  consists  in  the  arrangement  of  the  Eustachian 
valve,  which  directs  the  arterial  ciu-rent  (that  flows  upwards  through 
the  ascendmg  vena  cava)  into  the  left  side  of  the  heart,  through  the 
foramen  ovale — an  ojDening  in  the  septum  between  the  auricles — 
whilst  it  directs  the  venous  current  (that  is  beiiig  retm-ned  b}'  the 
superior  vena  cava)  into  the  right  ventricle.  Wiien  the  ventricles 
contract,  the  arterial  blood  contained  in  the  left  is  propelled  into  the 
ascending  aorta,  and  supplies  the  branches  that  proceed  to  the  head 
■and  upper  extremities  before  it  undergoes  any  further  admixture; 
while  the  venous  blood  contained  in  the  right  ventricle  is  forced  into 
the  pulmonary  arter}-,  and  thus  through  the  ductus  arteriosus — 
branching  off  from  the  pulmonary  artery  before  it  passes  to  the  two 
lungs — into  the  descending  aorta,  mingling  with  the  arterial  currents 
which  that  vessel  previously  conveyed,  and  thus  supplying  the  trunk 
and  lower  extremities  with  a  mixed  fluid.  A  portion  of  this  is  con- 
vej^ed  bv  the  umbilical  arteries  to  the  placenta,  in  which  it  undergoes 
the  renovating  influence  of  the  maternal  blood,  and  from  which  it  is 
returned  in  a  state  of  purity.  In  consequence  of  this  arrangement 
the  head  and  upper  extremities  are  svipplied  with  pure  blood  returning 
from  the  placenta,  whilst  the  rest  of  the  body  receives  blood  that  is 
partly  venous.  This  is  probably  the  explanation  of  the  fact  that 
the  head  and  upper  extremities  are  most  developed,  and  from  their 
weight  occupy  the  inferior  position  in  the  uterus.  At  birth  the  course 
of  the  circulation  ixndergoes  changes.  As  soon  as  the  lungs  are  dis- 
tended by  the  first  inspiration,  a  portion  of  the  blood  of  the  pulmonary 
artery  is  diverted  into  them  and  undergoes  aeration;  and,  as  this 
portion  increases  with  the  full  activity  of  the  hmgs,  the  ductus  arteri- 
osus gradually  shrinks,  and  its  cavity  finally  becomes  obliterated. 
At  the  same  time  the  foramen  ovale  is  closed  by  a  valvular  fold,  and 
thus  the  direct  communication  between  the  two  auricles  is  cut  off. 
Wlien  these  changes  have  been  accomplished,  the  circulation,  which 
was  before  carried  on  upon  the  plan  of  that  of  the  higher  reptiles,, 
becomes  that  of  the  complete  warm-blooded  animal,  all  the  blood 
which  has  been  returned  in  a  venous  state  to  the  right  side  of  the  heart 
being  transmitted  through  the  lungs  before  it  can  reach  the  left  side 
or  be  propelled  from  its  arterial  trunks. 

After  birth  the  umbilical  arteries  shrmk  and  close  up,  and  become 
the  lateral  ligaments  of  the  bladder,  while  their  upper  parts  remain 
as  the  superior  vesical  arteries.  The  umbilical  vein  becomes  the 
ligamentum  teres.  The  ductus  venosus  also  shrinks,  and  finally  is 
closed.  The  foramen  ovale  is  closed,  and  the  ductus  arteriosus  shriveU 
and  becomes  the  Ugamentum  arteriosum. 


CHAPTER  XXIX 
LYMPH 

By  means  of  the  circulatory  system  the  blood  is  taken  to  the  great 
network  of  capillaries  which  ramify  in  their  myriads  amid  the  various 
tissues  of  the  body.  Since,  however,  this  blood  capillar}'  system  is 
a  closed  one,  blood  itself  does  not  come  into  actual  contact  with  the 
tissue  cells  themselves.*  These  cells  are  bathed  in  a  fluid — the  tissue 
fluid,  or  lymph — and  it  is  this  fluid  which  finally  takes  to  the  tissues 
the  substances  necessary  for  their  proper  nutrition  and  adequate 
working,  and  takes  from  them  the  products  of  their  activity. 

The  lymphatic  system  is  a  most  extensive  one.  It  consists  of  the 
interstitial  or  lacunar  spaces  Avhich  exist  in  almost  all  parts  of  the 
body;  the  delicate  lymphatic  capillaries;  the  larger  lymphatic  vessels, 
"which  ultimately  unite  to  form  the  thoracic  duct  or  the  right  h'mphatic 
duct ;  the  lymphatic  tissues  of  the  body,  such  as  the  lymphatic  glands ; 
and  the  lymphatic  tissue  incorporated  in  the  spleen,  thymus,  etc. 
The  large  serous  spaces,  such  as  the  peritoneum,  pericardium,  may 
also  be  included  in  this  system. 

For  many  years  past  the  exact  relationship^  between  the  inter- 
stitial spaces  and  the  lymphatic  vessels  has  been  the  subject  of  con- 
siderable discussion.  One  view,  formerly  accorded  almost  general 
acceptation,  is  that  the  interstitial  spaces,  or  lacunae,  communicate 
directly  with  the  delicate  Ijanph  capillaries,  which  in  turn  unite  to 
form  larger  channels  or  lymphatics,  and  ultimately  open  into  the 
venous  system  by  the  thoracic  duct  or  the  right  lymphatic  duct. 

According  to  this  view,  the  tissue  fluids  bathing  the  cells  and 
the  lymph  flowing  from  a  lymphatic  duct  are  one  and  the  same  fluid, 
since  there  is  absolute  continuity  between  the  duct  lumen  and  the 
tissue  spaces.  Another  view,  which  has  recently  gained  much  support, 
is  that  the  interstitial  tissue  spaces  do  not  directly  communicate  with 
the  lymph  capillaries.  The  lymphatic  system,  according  to  this  vie^ , 
is,  as  regards  the  tissue  spaces,  a  closed  system.  It  probably  communi- 
cates by  stomata  with  large  serous  spaces,  such  as  the  peritoneal 
space,  and  possibly  also  with  the  spaces  of  certain  mucosae — e.g.,  the 
bronchial  and  nasal. 

On  this  h>])othesi; .  the  tissue  fluid  of  the  interstitial  spaces  is  dis- 
tinct from  the  lymph  of  the  lymphatic  system.  Little  or  nothing  is 
known  as  to  the  exact  composition  of  such  tissue  fluid ;  it  is  assumed 
to  be  of  much  the  same  composition  as  the  lymph.     This  bathes  the 

*  Except  in  the  spleen  and  liver.  Blood-capillaries,  too,  run  into  the  giant 
ganglion  cells  which  feed  the  electric  organ  in  Malapterurus. 

250 


LYMPH  251 

tissues  with  a  suitable  medium  for  thieir  activities,  and  carries  to  them 
the  food  material  necessar}^  for  such  activities  and  for  repair ;  carrying 
also  bodies  such  as  hormones  or  co-enzymes,  which  stimulate  or  aid 
tissue  activity.  From  the  tissues  it  carries  away  the  products  of 
their  activity — either  synthetic,  such  as  internal  secretions  and  hor- 
rnones,  or  the  katabolic  or  waste  products  resulting  from  such  activity. 
In  regard  to  the  digestive  tract,  the  tissue  fluid  acts  as  a  transport 
fluid  for  the  absorbed  products  of  digestion.  Some  of  these,  such 
as  those  of  protem  and  carbohydrate  digestion,  pass  into  the  blood 
of  the  portal  vein.  The  products  of  fat  digestion,  on  the  other  hand^ 
pass  into  the  closed  lymj^hatic  vessel,  or  lacteal.  They  give  to  the 
lymph  a  milky  appearance,  from  which  the  name  of  these  particular 
lymph  channels  is  derived. 

In  other  parts  of  the  body,  also,  there  is  the  same  quick  transference" 
of  some  bodies  from  the  tissue  fluid  to  the  blood,  and  of  others  to  the 
lymph.  In  discussing  the  processes  of  lymph  formation  (see  later), 
this  point  must  be  borne  in  mind.  For  example,  when  a  salivary 
gland  is  secreting,  we  must  inquire  what  processes  determine  the 
bodies  which  pass  (1)  from  the  gland  to  the  saliva,  (2)  into  the  tissue 
fluid,  (3)  from  the  tissue  fluid  to  the  venous  blood,  (4)  from  the  tissue 
fluid  into  the  lymph  leaving  the  gland. 

The  properties  of  lymph  are  generally  studied  by  collecting  the 
fluid  as  it  flows  from  the  thoracic  duct  of  a  small  mammal,  or  from 
the  main  Ijanphatic  channel  of  each  of  the  varioixs  organs  of  the  larger 
domestic  animals.  For  demonstration  purposes,  a  cannula  is  usually 
placed  in  the  thoracic  duct  of  a  fau'-sized  fasting  dog,  and  a  good  How 
of  lymph  insured  by  the  intravenous  injection  of  commercial  peptone 
solution.  Such  lymph  is  a  viscid,  opalescent  fluid,  faintly  alkaline 
in  reaction,  specific  gravity  1010  to  1020.  The  first  lymph  which 
flows  coagulates  spontaneously,  although  less  quickly  than  blood. 
After  a  time,  however,  owing  to  the  effect  of  the  peptone,  it  becomes 
incoagulable.  Chemically,  it  contains  the  same  constituents  as  blood- 
plasma,  the  diffei-ences  being  quantitative.  It  is  poorer  in  proteins, 
and  richer  in  Avater  and  salts. 

The  lymph  from  different  parts  varies  in  quantitative  composition. 
For  example,  that  from  the  liver  contains  more  solids  than  that  from 
the  limbs.  The  lymph  flowing  from  the  same  organ  also  varies  quan- 
titatively in  composition  according  to  the  degree  of  activity  of  the 
organ.  As  a  result  of  various  analj'ses,  the  composition  of  lym^jh 
may  be  given  somewhat  as  follows : 

Per  Cent. 

Water  93-5- 9.5-8 

Solids  4-2- {■)•.■■> 

Proteins       . .  . .  .  .  . .  .  .  . .  3- .5 — 4*3 

Fats  'i 

^o-'^P.^       I 0-4-0-9 

Lipoids     i 

Dextrose  ) 

Salts  (chiefly  XaCl)  0-7— 0-8 

0)      . .  . .  . .  . .  . .  •  •  • •  traces 

CO.,  '.'.  37—5!  vols. 


252  A  TEXTBOOK  OF  PHYSIOLOGY 

Lymph  also  contains  white  corpuscles  similar  to  those  in  the  blood, 
lymphocytes  jjarticularly  ioredominating. 

The  amount  of  lymph  flowing  from  the  thoracic  duct  in  twenty- 
four  hours  has  been  found  in  human  patients  to  vary  from  1,200  to 
2,280  c.c.  per  day.  Li  a  dog  of  10  kilos,  the  amount  was  640  c.c. 
We  cannot  take  this  as  indicative  of  the  normal  flow,  for  the  escape 
of  lymph  through  a  wound  is  unrestrained  by  the  conditions  which 
pertain  in  the  closed  l)ody. 

The  Processes  concerned  in  the  Formation  of  Lymph. — Consider- 
able divergence  of  opinion  is  manifested  as  to  these ;  a  vast  amount  of 
evidence  has  accumulated  which  is  held  to  support  the  various  views 
entertained  b\'  different  authorities.  From  such  experimental  data 
one  great  fact  emerges — namely,  that  lymph  flow  is  the  concomitant 
of  tissue  activity.     For  example — 

1.  When  the  liver  is  active,  either  as  the  result  of  an  injection  of 
peptone  or  during  the  processes  of  digestion,  there  is  an  increased 
flow  of  lymph  from  the  liver. 

2.  When  the  salivary  gland  is  made  to  secrete  by  stimulation  of 
the  chorda  tympani  nerve  (see  p.  374),  there  is  a  marked  increase  of 
lymph  flow  from  the  gland. 

3.  When  the  pancreas  is  made  to  secrete  as  the  result  of  an  injec- 
tion of  secretin  (see  p.  307),  there  is  similarly  an  increased  flow  of 
lymph  from  that  organ. 

4.  From  the  resting  limbs  there  is  practically  no  flow  of  hanph; 
activity  gives  rise  to  a  well-marked  flow. 

The  two  chief  views  held  in  regard  to  lymph  formation  are  the 
mechanical  and  the  secretory.  The  mechanical  view  holds  that  lymph 
transudes  from  the  blood-capillaries  as  the  result  of  the  processes  of 
filtration  and  osmosis.  A  higher  pressure  is  supposed  to  pertain  in 
the  capillaries  and  cause  filtration.  According  to  the  secretory  view, 
lymph  is  formed  as  the  result  of  cell  activity.  The  cells  actively 
draw  water,  etc.,  from  the  blood-capillaries  into  the  tissue  spaces 
according  to  their  functional  needs. 

The  experimental  evidence  in  regard  to  filtration  consists  chiefly 
of  experiments  in  which  a  rse  of  capillary  pressure  is  induced  as  the 
result  of  partial  or  total  blocking  of  the  venous  circulation.  This 
does  not  occur  under  normal  conditions.  The  result,  also,  is  an  in- 
creased flow  of  lymph,  which  differs  considerably  in  composition  from 
that  flowing  under  normal  circumstances. 

Such  an  experiment  is  the  ligation  of  the  veins  of  a  limb,  which 
causes  an  increased  flow  of  lymph  poorer  in  solids  than  normal  and 
red-coloured,  owing  to  the  presence  of  red  corj^uscles.  Ligation  of 
the  portal  vein  ra  ses  the  pressure  in  the  capillaries  of  the  intestinal 
area,  and  causes  a  marked  increase  of  tymph.  Occlusion  of  the  inferior 
vena  cava  above  the  diaphragm  causes  an  increased  flow  of  lymph 
from  the  liver,  due,  according  to  this  view,  to  the  rise  in  pressure  in 
the  liver  capillaries.  Similarly,  occlusion  of  the  aorta  causes  an  in- 
creased flow  of  lymph  from  the  liver,  the  pressure  in  these  circum- 
stances in  the  inferior  cava  being  slightl}^  raised  or  remaining  unaltered. 


LYMPH  253 

It  has  never  been  shown  that  a  rise  m  capillary  pressure  with  a 
normal  venous  circulation  produces  an  increased  flow  of  lymph.  On 
the  contrary,  experiments  show  that  such  a  rise  of  capillary  pressure 
may  take  place  Avithout  an  increased  flow  of  lymph  necessarily-  re- 
sulting. Reference,  for  example,  has  already  been  made  to  the 
fact  that  stimulation  of  the  chorda  tympani  causes  a  great  floA\' 
of  saliva  accompanied  by  a  marked  floAv  of  Ij^mph  from  the  gland. 
When  the  endings  of  this  secretory  nerve  are  paralyzed  by  atrojiine, 
stimulation  still  produces  a  marked  rise  of  capillary  pressure,  but  no 
salivary  secretion  or  increased  lymph  flow  results.  So,  too,  if  the 
motor  nerves  to  a  limb  be  cut,  and  the  blood-pressure  raised  by  caiising 
a  general  vaso-constriction  of  the  rest  of  the  bodj^  the  quantity  of 
lymph  flowing  from  the  limb  while  performing  passive  rhythmical 
movements  is  not  increased,  but  diminished. 

Differences  in  the  constitution  of  lymph  coming  from  different  parts, 
or  from  the  same  part  at  different  times,  are  attributed  upon  the 
filtration  view  to  an  altered  permeability  of  the  vessel  wall.  The 
exact  reason  for  such  alterations  appears  to  be  due  rather  to  the  different 
forms  of  activity  in  the  various  parts,  and  in  the  same  parts  at  different 
times.  Reasons  for  a  disbelief  in  the  possibility  of  a  filtration  mechan- 
ism within  the  body  are  adduced  in  dealing  Avith  the  capillary  pressure 
(see  p.  223). 

Furthermore,  it  has  been  shown  recently  that  Aenous  stasis  cause!>; 
lymph  formation,  not  by  A'irtue  of  filtration,  but  by  changes  in  the 
tissues  themselves,  due  primarily  to  lack  of  oxj^gen,  causing  the  forma- 
tion of  acid.  With  such  acid  formation,  AA-ater  passes  by  imbibition 
into  the  tissues,  leading,  if  long  continued,  to  oedema.  Such  a  con- 
dition is  pathological,  not  physiological. 

In  regard  to  the  part  played  by  osmosis,  it  may  quite  Avell  be  that 
the  interchange  betAAeen  blood  and  tissues  is  largely  regulated  by  this 
process.  For  example,  the  lymph  formation  attending  tissue  activity 
maA'  possibly  be  explained  by  the  supposition  that  the  products  of 
cell  actiAdty,  being  relatiA'ely  of  small  molecular  AA'eight,  cause  b}^ 
increased  osmotic  pressure  a  floAA'  of  fluid  from  the  blood  into  the 
tissue  spaces. 

The  numerous  experiments  Avhich  haA'e  been  made  of  injecting 
such  crystalloid  bodies  as  sodium  chloride,  dextrose,  urea,  so-called 
lymphagogues,  tend  to  support  the  A'iew  that  osmosis  plaj's  a  part  in 
the  formation  of  lymph.  Certain  recent  experiments,  hoAA^ever,  shoA\' 
that  the  chloride  content  of  the  lymph  may  rise  aboA^e  that  of  the 
blood-serum.  If  this  be  the  case,  then  osmosis  cannot  be  the  AA'hole 
story. 

It  has  also  been  pointed  out  that  each  tissue  or  organ  obtains  its 
•OAAii  special  products  from  the  lymph,  often  in  large  quantities.  TIk^ 
most -quoted  example  is  the  calcium  content  of  milk.  A  coav  may  A'ield 
daily  25  litres  of  milk  containing  42-5  grammes  of  Ca.  As  the  lymph 
of  the  thoracic  duct  contains  but  0-18  per  cent.,  236  litres  of  lymph 
would  be  needed  to  su])]ily  this  calcium  to  the  milk,  assuming  that 
.all  the  calcium  comes  from  the  lymph.     This  is  held  greath'  to  sujjport 


254  A  TEXTBOOK  OF  PHYSIOLOGY 

the  secretory  view,  that  lymph  and  uiilk  are  formed  by  the  special 
activity  of  the  gland  cells.  The  cells  of  each  organ  draw  what  they 
need  from  the  blood. 

The  fact  that  some  bodies  ajjpear  to  be  quickly  transferred  from 
the  tissue  fluid  to  the  venous  blood,  while  others  appear  to  be  passed 
on  into  the  lymphatics,  has  led  to  the  view  that  the  bodies  passed 
into  the  lymphatics  ai-e  toxic,  and  are  taken  to  the  lymphatic  glands 
to  have  this  toxicity  destroyed.  It  has  been  shown  experimentally 
that  tymph  injected  into  the  arterial  system  causes  marked  effects 
upon  the  arterial  pressure  and  rate  of  heart-beat. 

The  Movement  oJ  Lymph. — To  what  factors  is  due  the  flow  of 
hanph  ?  In  the  amphibia  and  fishes  there  are  special  lymph  hearts, 
but  these  are  lacking  in  mammals.  The  lymphatics  have  valves  to 
direct  the  flow,  and  these  valves  have  special  muscle  fibres  arranged 
about  them  which,  it  has  been  suggested,  act  as  a  pumping  mechanism. 
Such  a  claim  has  not  been  substantiated.  The  vessels,  however, 
appear  to  be  innervated  with  constrictor  and  dilator  nerves,  and  it  is 
conceivable,  although  not  proven,  that  alterations  in  the  lumen 
may  aid  the  flow. 

According  to  the  ^neehanical  view,  the  flow  of  lymph  is  maintained 
by  the  filtration  pressure  transmitted  from  the  vis  a  tergo,  the  heart- 
This  point  has  already  been  debated.  The  heart-beat  plays  an  im- 
portant factor  in  pulsing  organs  full  of  blood  with  each  heart-beat. 
This  systolic  filling  squeezes  on  the  lymph  in  the  lymphatics. 

The  chief  factors  in  causing  a  flow  of  lymph  are  the  activities  of 
the  tissues,  muscular  movement,  and  the  resjiiratory  pump. 

The  various  serous  membranes  of  the  body  are  moistened  by  fluids 
which  more  or  less  resemble  lymph  in  composition.  The  amount 
of  protein  in  these  different  fluids  varies  considerably,  although  imder 
normal  circumstances  the  quantity  of  such  fluids  is  in  some  cases 
so  small  that  accurate  analyses  have  not  been  made.  The  composi- 
tion of  the  fluids  is  altered  when  there  is  increased  formation  due  to 
inflammatory  disease,  and  it  is  such  fluids  which  for  the  most  part 
have  been  analyzed. 

The  pericardial  fluid  is  a  somewhat  sticky,  lemon-coloured  fluid, 
which  contains  about  96-1  per  cent,  of  water  and  3-9  per  cent,  of  solids. 
The  chief  solids  are  proteins  (2-8  per  cent.)  and  salts,  mostly  sodium 
chloride  (0-7  per  cent.).  Traces  of  fat,  lecithin,  and  cholesterin,  are  also 
present. 

Pleural  fluid  is  normally  present  in  such  small  amounts  that  analysis 
of  the  healthj'  fluid  has  not  been  made.  The  same  is  true  of  normal 
peritoneal  fluid. 

The  cerebro-spinal  fluid  is  a  thin,  clear  fluid,  characterized  by  its 
low  specific  gravity  (1007  or  1008)  and  its  low  protein  content.  The 
protein  is  of  a  globuhn  nature.  A  small  amount  of  cojojoer -reducing 
substance  is  also  present,  which  is  probably  sugar.  In  disease,  the 
constitution  of  the  fluid  may  be  altered  in  various  Avays.     The  state- 


LYMPH  255 

ment  that  choline  is  present  in  certain  nervous  diseases  has  not  met 
with  general  acceptation.  The  fluid  is  secreted  by  the  cells  of  the 
choroidal  fringes  of  the  brain,  and  absorbed  into  the  cerebral  veins, 
probably  by  way  of  the  Pacchionian  bodies. 

The  aqueous  humour  of  the  eyeball  is  a  clear  fluid,  alkaline  in 
reaction,  of  low  specific  gravity  (1005  to  1008),  and  containing 
normally  but  a  trace  of  protein.  It  is  secreted  by  the  ciUary  pro- 
cesses of  the  eyeball,  and  absorbed  by  the  veins  of  the  iris  and  those 
in  the  angle  of  the  eye. 


BOOK   IV 

CHAPTER  XXX 
RESPIRATION 

One  of  the  mo  it  rem.xrkable  properties  of  living  substance  is  its 
dependence  on  a  supply-  of  ox^'gen.  The  vital  processes  in  the  cell 
substance  by  which  energy  is  set  free  and  food  obtained  depend  on 
this,  and  carbon  dioxide,  the  chief  end  product  of  these  processes, 
must  be  got  rid  of,  as  well  as  a  sufficiency  of  oxygen  obtained.  Many 
kinds  of  bacteria — g.gr.,  tetanus  bacilli — and  parasitic  worms,  which 
live  in  the  intestine,  are  what  are  termed  "  obligate  anaerobes."  They 
secure  their  oxygen  by  decomposition  of  foodstuffs,  and  are  poisoned 
by  free  oxygen.  All  other  bacteria,  the  higher  plants,  and  animals, 
are  aerobes,  and  take  up  free  oxygen  from  the  atmosphere  by  a 
respiratory  process.  Plants  both  excrete  carbon  dioxide  and  assimi- 
late it. 

By  the  aid  of  chlorophyll  energized  by  sunlight,  plants  synthesize 
water  and  carbon  dioxide  into  formic  aldehyde,  which  by  molecular 
condensation  is  converted  into  an  aldose;  hence  arise  sugar  and  starch. 
At  the  same  time  as  this  remarkable  synthesis  goes  on,  the  plant 
protoplasm  uses  up  oxygen  and  produces  carbon  dioxide.  From  the 
nitrates  and  other  salts  absorbed  by  the  rootlets  and  the  aldose  syn- 
thesized in  the  leaves  the  plant  proteins  are  built.  Sunlight  forwards 
this  synthesis,  converting  nitrates  in  watery  solution  into  nitrites, 
An  endDth3rmic  reaction;  the  sugars  and  starch  may  also  be  converted 
into  fat.  The  source  of  the  energy  of  all  these  sjmtheses  in  the  plant 
is  the  sun's  rays.  The  chlorophyll  absorbs  the  light  rays,  and  trans- 
forms them  into  energy  which  is  stored  as  potential  energy  in  the 
proteins,  carbohydrates,  and  fats,  built  by  the  plant.  These  form 
the  foodstuffs  of  bacteria,  moulds,  and  animals,  by  which  they  are 
broken  down  again  into  water,  carbon  dioxide,  salts,  and  simple  com- 
pounds of  nitrogen — -the  materials  for  fresh  plant  synthesis.  So  the 
cycle  of  life  proceeds  (Fig.  130).  The  bacteria  form  the  final  link  in 
the  chain;  some  decompose  dead  animal  and  plant  matter  (denitrify- 
ing bacteria),  while  other  symbiotic  bacteria  help  the  rootlets  of  certain 
plants  (legumes)  to  secure  atmospheric  nitrogen  (nitrifying  bacteria). 
If  it  were  not  for  bacteria,  the  world  would  quickly  become  cumbe-re:! 
up  as  a  charnel  house.  The  circulation  of  nitrogen  in  nature  is  shown 
in  Fig.  131. 

It  has  recently  been  found  that  when  carbon  dioxide  gas  is  passed 

257  17 


258 


A  TEXTBOOK  OF  PHYSIOLOGY 


through  very  dilute  solutions  of  inorganic  colloids  (uranic  or  ferric 
oxide)  in  the  presence  of  sunlight,  the  synthesis  of  formic  aldehyde 
and  acid  is  obtained.  It  has  been  suggested  that  we  have  in  this  a 
possible  first  stage  in  the  evolution  of  organic  material  and  life  pro- 
cesses from  inorganic  matter.  »f 

The  exchange  of  gases  between  the  respiratory  tissue  and  the 
outer  medium  is  known  as  "  external  respiration."  The  process 
whereby  the  exchange  of  these  gases  takes  place  between  the  blood 
and  the  different  jmrts  of  the  body  is  known  as  "  internal,"  or  "  tissue 
respiration,"  Cold-blooded  animals  can  live  for  some  hours  in  an 
atmosphere  of  nitrogen,  and  hibernating  cold-blooded  animals — e.g.y 


Products}  of 
pla-nt  lif,',  H2O 

Proteid.  ^tarch 
FsLt 


Pla.nt 


ucts  of 
riaJ 
Decbm position 
moms.  etc. 


IVATCR     NITRATES 
&    OTHER     SALTS. 

Fig.  130, — ^To  illustrate  the  Cycle  of  Plant,  Animal  and  Bacterial  Life, 
The  arrows  indicate  the  materials  which  each  take  up  and  give  out  to  the'world. 


snails  which  shut  themselves  up  for  the  winter — retain  their  existence 
for  months  without  respiration.  On  the  other  hand,  a  very  active 
respiration  and  rapid  exchange  of  gases  are  necessary  in  the  warm- 
blooded animal,  because  the  rate  of  metabolism  is  very  great,  and 
within  the  body  there  is  no  means  afforded  for  laying  in  a  store  of 
oxygen  sufficient  to  last  more  than  a  minute.  The  carbon  dioxide, 
too,  which  in  normal  concentrations  plays  an  important  part  in 
regulating  body  processes,  when  present  within  the  body  in  excess,, 
has  a  narcotic  poisonous  effect  upon  the  organism. 

The  blood  is  exposed  to  the  air  in  the  lungs  over  a  verj^  extensive 
surface — perhaps  as  much  as  100  square  metres — in  a  film  one  corpuscle 
thick,  and  the  whole  blood  circulates  through  the  lungs  about  once  a 


RESPIRATION 


259 


minute  when  resting,  antl  as  often  as  ten  times  a  minute  during  hard 
muscular  work.  According  to  the  simplest  hypothesis,  and  the  one 
generally  accej^ted,  the  venous  blood,  which  enters  the  pulmonary 
capillaries,  has  a  lower  oxygen  and  higher  carbon  dioxide  concentration 
or  pressure  than  that  in  the  pulmonary  air.  An  exchange  takes  place 
between  the  blood  and  the  pulmonary  tissue  lymph,  and  then  be- 
tween this  fluid  and  the  pulmonary  air,  this  exchange  being  in 
accordance  with  the  physical  laws  which  govern  the  solution  and 
diffusion  of  gases. 


|NtTRATE-N.' 


lURINEl     \       I  FAECES  I         \^  /i_PL^ 

/  a/  ;xx 

EA  PUTRE-  /     IPUTRE-  Y^ 


UREA        I         IPUTRE- I  / 

FERMptTATIONl         |  FACTION  |        / 

•  /  /  /  . 


/ 


I  ^i^>^j<f^ 

|AMMONIA-N.|^ HNITROSOBACTERIaI 


■- ^NITRITE-N.[ 


Fig.   131. — To  illustrate  the  Circulation  of  Nitrogen  in  Nature. 


The  Blood  Gases. — The  presence  of  gases  in  the  blood  was  first 
demonstrated  when  Robert  Boyle  (1636)  placed  blood  under  his 
vacuum  pump  and  made  it  boil.  The  gas  content  of  the  blood  is 
obtained — (1)  by  exposing  the  blood  to  a  vacuum  and  pumping  off 
the  gases;  (2)  by  chemical  means,  whereby  the  different  gases  are 
displaced  chemicallv  from  the  blood. 

Extraction  of  Blood  Gases  by  Means  of  Pump. — The  general  prin- 
ciple of  the  pump,  of  which  many  forms  have  been  devised  for 
the  extraction  of  blood  gases,  is  that  the  blood  is  exposed  to  a 
barometric  vacuum.  A  simple  form  of  pump  is  shown  in  Fig.  132. 
The  pump  consists  of  a  mercury  reservoir  {A),  which  is  connected 
with  a  second  reservoir  {B)  by  means  of  pressure  tubing.  The  upper 
end  of  B  is  closed  by  a  three-way  tap.  By  means  of  this  tap  B  can 
be  put  in  connection  with  either  the  tube  E  leading  to  the  blood- 
receiver  F ,  or  with  the  tube  C  leading  to  the  eudiometer  H.     The 


260 


A  TEXTBOOK  OF  PHYSIOLOGY 


blood-receiver  jf^  is  constructed  of  three  bulbs,  so  as  to  prevent  the 
blood  frothing  over  into  B  during  the  extraction  of  the  gases.  To 
either  end  of  F  is  fixed  a  piece  of  thick,  small-bored  pressure  tubing 
provided  with  a  clip. 

In  using  the  pump,  the  blood-receiver  F  is  placed  in  the  position 
indicated  by  the  dotted  line.  A  is  raised,  and  B  is  put  in  connection 
with  F,  and  F  is  filled  Avith  mercur}'.     The  screw  clip  on  the  rubber 


Fig.   132  — Hill's  Blood-Gas  Pump. 


tube  at  the  upper  end  of  F  is  then  closed,  and  .4  lowered  imtil  F  is 
exhausted,  except  for  2  or  3  c.c.  of  mercury  which  are  purposel}^  left 
within.  The  screw  cHp  on  the  lower  end  of  F  is  next  closed,  and  F  is 
then  detached  from  the  pump  and  weighed.  Blood  is  collected  in 
this  evacuated  receiver,  which  is  then  connected  to  the  apparatus, 
and  the  gases  pumped  off  into  the  eudiometer  H,  where  they  are 
analyzed.  The  amount  of  COg  is  determined  by  introducing  20  per 
cent.  KOH,  the  oxygen  by  introducing  a  solution  of  pyrogallic  acid. 
The  relative  proportions  of  the  gases  are  shown  in  Fig.  133.  The 
remainder  is  nitrogen. 


RESPIRATION 


261 


AvL 


For  very  accurate  work  a  tapless  modification  of  the  Topler 
pump,  is  best  employed  (Fig.  134).  The  general  arrangement  of 
the  parts  is  shown  in  the  figure,  which  is  drawn  to  scale  one- 
tenth  of  the  actual  size.  The  pump  (P),  together  with  the  drying 
apparatus  (D)  and  condenser  (E),  possesses  neither  taps,  nor  mercury, 
nor  rubber  joints,  the  various  parts  being  glass  and  sealed  together 
with  a  blowpipe.  The  blood  is  introduced  into  the  froth-chamber, 
which  is  made  up  of  a  cylindrical  bulb  (C)  and  two  double-walled 
condenser  bulbs  {A),  the  lower  of 
which  terminates  in  a  barometer 
tube  85  centimetres  long  dipping 
below  mercury.  This  part  of  the 
apparatus  is  sealed  on  to  the  con- 
denser at  X.  The  a])paratus  is 
evacuated  in  the  usual  way,  and 
the  height  of  the  mercury  in  the 
vessel  B  adjusted  so  that  the 
barometric  column  just  reaches  the 
entrance  of  the  lower  froth-bubble 
(A).       In    order     to    prevent    the 

-/Vitro^en 


-Oxj/gen 


Carbon 
Dioxide 


Fig.  133. 


Fig.  134.  —  Modification  ok  the 
Topler  Tapless  Pump  for  Accurate 
Blood-Gas  Analysis.  (Buckmaster 
and  Gardner.) 


occlusion  of  air  in  the  mercury,  or  between  the  mercury  and  the  glass, 
after  a  high  vacuum  has  been  produced,  the  tube  AB,  and  also  P, 
is  heated  with  a  Bunseii  burner  almost  to  the  boiling-point  of  mercury. 
The  evacuation  is  then  completed.  It  is  now  advisable  to  allow  the 
jjump  to  stand  for  a  day  or  two,  with  occasional  pumping  before  use. 
A  very  high  vacuum  can  in  this  way  be  obtained.  The  condenser 
must  be  large,  and  as  efficient  as  possible.  The  drying  vessel,  filled 
with  pure  sulphuric  acid,  is  provided  with  a  tube,  the  end  of  which 
can  be  easily  broken,  so  that  it  is  easy  to  refill  with  sulphuric  acid. 


262 


A  TEXTBOOK  OF  PHYSIOLOGY 


After  using  the  pump,  air  is  introduced  up  the  barometer  tube  AB, 
and  the  froth-chambers  cut  from  the  condenser  X.  The  detached 
part  can  then  be  readily  cleaned,  sterilized,  and  resealed  on  the  con- 
denser. 

The  chemical  method  employed  is  one  in  which  oxygen  is  displaced 
from  the  blood  by  the  use  of  potassium  ferricyanide,  and  the  CO,  is 
displaced  by  the  action  of  tartaric  acid.  The  most  convenient  form 
of  apparatus  for  this  purpose  is  that  shown  in  Fig.  135.  The 
oxygen  is  liberated  from  the  hsemoglobin  in  one  of  the  two  bottles. 
The  pressures  in  these  become  unequal,  and  the  difference  in  pressure 
is  indicated  by  the  movement  of  fluid  (clove-oil)  in  the  manometer. 
The  difference  in  the  level  of  the  fluid  surface  on  either  side  is  read, 
and  by  this  means  the  amount  of  oxvgen  liberated  is  determined, 


Fig.   135. — Barcroft's  Differential  Blood-Gas  Apparatus. 


since  a  special  calibration  of  the  instrument  has  been  made,  and  the 
amount  of  oxygen  corresponding  to  a  difference  in  level  is  known. 
By  such  means  it  is  found  that  arterial  blood  has  a  gas  content  some- 
where about  18  c.c.  O2,  44  c.c.  COg,  1  c.c.  N2;  and  venous  12  c.c.  O2, 
50  c.c.  CO2,  1  c.c.  Ng.  The  blood  from  the  veins  varies  widely  in  its 
gas  content  according  to  the  activity  of  the  part  from  which  it  comes. 
Simultaneous  analyses  of  the  blood  going  to  and  coming  from  a  part 
give,  when  the  amount  of  blood  circulating  through  the  part  is 
known,  a  knowledge  of  the  internal  respiration  of  that  part  (see 
later,  p.  320). 

The  gases  in  the  blood  are  in  part  dissolved  according  to  the 
I^hysical  laws  of  absorption,  but  by  far  the  larger  amount  is  in  so- 
called  weak  chemical  combination.  Water  dissolves  gases  accord- 
ing to  the  pressure,  temperature,  and  nature  of  the  gas,  and  the  solu- 
bility is  lessened  by  the  presence  of  salts,  etc.,  in  solution  in  the  water. 


RESPIRATION 


263 


Table  showing  the  Absorption  Coefficients  for  Blood  of  Oxygen,  Nitrojen 

AND  Carbon  Dioxide. 


Oxygen. 


15° 


Water 
Plasma 
Blood 
Corpuscles 


Nitrogen. 


38° 


0-0342  !  0-0237 

0-033  0-023 

0-031     1  0-022 

0-028  0-019 


15° 


38° 


COo 


15° 


0-0179 
0-017 
0-016 
O-OU 


0-0122 
0-012 
0-011 
0-010 


1-019 
0-994 
0-937 
0-825 


38° 


0-555 
0-541 
0-511 
0-450 


By  the  help  of  the  absorption  coefficients  we  can  calculate  the  quan- 
tities of  oxygen,  nitrogen,  and  carbon  dioxide  which  would  be  dissolved 
in  100  c.c.  of  blood  shaken  with  air  at  room  temperature  (15°  C.)  and 
760  millimetres  pressure.  From  a  pressure  of  760  millimetres  that  of 
the  (average)  water  vapour  at  15°  C.  must  be  subtracted — 12-7  milli- 
metres— giving  as  total  pressure  for  the  air  minus  water  vapour: 
760—12-7=747-3    miUimetres.      For  oxygen,  the  partial   pressure  is 

20-92 

-y— ~   of  this  pressure,  20-92  being  the  percentage  of  this  gas  in  the 

atmosphere  measured  under  dry  conditions. 
20-92 
100 

With  this  partial  j^ressure  the  amount  of  oxygen  dissolved  in  100 
of  blood  will  be 

0-031  X  100  X  156-6 


747-3  =  156-6  millimetres. 


760 


0-639 


where  0-031  is  the  coefficient  of  absorption  for  blood  at  15°  C. 

But  in  the  lung  alveoli  the  conditions  are  different.  The  tempera- 
ture is  38°  C. ;  therefore  a  different  coefficient  of  absorption  is  required. 
The  air  is  saturated  with  vapour,  and  the  amount  of  water  vapour  is 
much  increased,  giving  a  partial  pressure  of  49-3  millimetres;  and, 
lastly,  the  chemical  composition  of  the  air,  measured  xmder  dry 
conditions,  is  different  from  that  of  the  atmosjiheric  air.  Here  the 
composition  is,  approximately:  Oxygen,  14  to  15  per  cent.;  nitrogen, 
80  to  80-2  per  cent.;  and  carbon  dioxide  4-8  to  5  per  cent.  Under 
these  conditions,  the  amount  absorbed  by  100  c.c.  of  blood  is — 


(Co- 
efficient) 


(Partial 
pressure) 


Oxygen 


Nitrogen 


Carbon  dioxide 


0-022  X  (100  x^Vyx  (760-49-3) 
760 
0-011  x  80-2  X  (760-49-3) 


760 
0  051  x4-8x  (760-49-3 

7eo 


=  0  309  c.c. 


=  0-825  c.c. 


2-29  c.c. 


264 


A  TEXTBOOK  OF  PHYSIOLOGY 


When  these  values  are  compared  with  the  amounts  of  the  gases- 
obtained  from  the  blood,  it  is  found  that  only  nitrogen  is  in  true 
physical  solution.  Of  the  carbon  dioxide  and  ox^'gen  the  greater  part 
is  in  chemical  condnnation;  yet,  inasmuch  as  considerable  quantities 
of  these  gases  can  be  pumped  from  the  blood,  this  chemical  combination 
is  of  an  easily  dissociable  (weak)  form.  When  the  blood  is  submitted 
to  the  vacuum  pump,  the  gases  do  not  come  off  in  proportion  as  the 
pressure  is  reduced — indeed,  with  the  first  reduction  of  pressure  little 
gas  comes  off — but  when  the  pressure  is  considerably  lowered,  and  the 
blood  warmed,  the  gases  come  off  with  a  rush,  and  the  blood  "  boils  " 
and  froths  in  a  very  striking  way. 

The  oxygen  is  combined  with  the  red  corpuscles,  as  is  shown  b}'  the 
fact  that,  when  the  corpuscles  are  removed  from  the  plasma,  the 
latter  only  takes  up  that  amount  of  oxygen  which  is  dissolved 
in  accordance  with  the  coefficient  of  absorption.  It  is  to  the- 
haemoglobin  of  the  corpuscles  that  the  oxygen  is  looselj"  attached,  and 


A 


40 


100 


Fig. 


136. — A  Series  of  Toxometees  indicating  the  PBESsrEE  cf  Oxygek  to 
WHICH  THE  Blood  is  exposed.     (Barcroft.) 


the  amount  of  oxygen  taken  up  by  the  blood  over  and  above  that 
which  can  be  absorbed  by  purely  physical  means  depends  upon  the 
amount  of  haemoglobin  j^resent. 

Many  experiments  have  been  made  to  ascertain  the  specific  oxygen 
capacity  of  the  blood.  The  earliest  observations  were  made  correctly 
on  the  blood  itself;  then  it  was  thought  better  to  separate  the  haemo- 
globin and,  purifying  this,  determine  its  combining  powers.  From 
the  results  so  obtained  it  was  concluded  that  a  given  amount  of  haemo- 
globin always  combined  with  a  definite  amount  of  oxygen  (1  grm. 
of  Hb  with  1-34  c.c.  of  Oo);  100  c.c.  of  human  blood  contains  about 
12  to  15  grms.  Hb.  1-34  x  14  =  19,  which  is  about  the  percentage  of 
oxygen  found  in  arterial  blood.  Recent  research,  however,  has  shown 
that  the  exact  amount  of  oxygen  depends  upon  a  number  of  factors — 
e.g.,  the  temperature,  concentration  of  salts,  and  of  carbon  dioxide 
in  the  blood.  The  blood  is  exposed  to  an  atmosphere  containing  a 
known  concentration  (pressure)  of  oxygen,  and  thoroughly  shaken 
with  this  (Fig.  136).     It  is  then  withdrawn  without  contact  with  the 


RESPIRATION 


265 


air,  and  the  percentage  of  oxygen  in  it  determined  by  the  vacuum 
pump  or  the  differential  blood  gas  ajDparatus.  Charts  are  thuspre- 
pared  in  which  the  amounts  of  oxj'gen  combined  at  different  pressures 


c^ 


^l 


1^ 


i 


m 
si 


40 


.1 

3 


i 


Fig.  137. 


^  mm.  pressure 

-Cylinders  Spaced  Apart  at  Distances  Proportional  to  thFjPressures 
OF  Oxygen  dissolved  in  Solution.     (A.t  r  Barcroft.) 


are  plotted  in  the  form  of  a  curve  (Fig.  137).  There  has  to  be 
subtracted  from  the  total  volume  of  gas  found  the  amount  which  is 
calculated  to  be  simply  dissolved.  The  following  table  gives  examples 
of  the  results  obtained  for  horse's  blood  at  38°  C: 


Oxygen  in 

C.C. 

calculated  at 

N.T.andP. 

in  100  G.C.  of  Blood. 

Degree  of 

Degree  of 

Oxygen  Pressure 

Saturation 

Dissociation 

Chemically 

Dissolved  in 

per  Cent. 

per  Cent. 

hound. 

Plasma. 

10  mm. 

6-0 

0-020 

30-0 

70-0 

20     „    .. 

12-9 

0-041 

64-7 

35-3 

30     „    .. 

16-3 

0-061 

81-6 

18-4 

40     „    .. 

18-1 

0-081 

90-4 

9-6 

50     „    .. 

19-1 

0-101 

95-4 

4-6 

60     „    .. 

19-5 

0-121 

97-6 

2-4 

70     „    .. 

.  i           19-8 

0-141 

98-8 

1-2 

80     „    .. 

.   i           19-9 

0-162 

99-5 

0-5 

90     „    .. 

19-95 

0-182 

99-8 

0-2 

150 

20-0 

0-303 

100-0 

0-0 

It  is  found  that  above  a  tension  of  oxygen  of  150  millimetres,  corres- 
ponding to  an  atmospheric  pressure  of  760  millimetres,  the  amount 


266 


A  TEXTBOOK  OF  PHYSIOLOGY 


of  oxygen  chemically  combined  increases  inappreciably.  Therefore, 
when  blood  is  shaken  with  air  at  ordinary  atmospheric  pressure,  it 
becomes  practically  saturated  with  oxygen,  and  the  degree  of  satura- 
tion in  the  above  table  is  obtained  by  comparing  the  amount  of  oxygen 
combined  with  the  blood  at  a  given  pressure  of  oxygen  with  the 
amount  combined  when  shaken  with  air  at  atmospheric  pressure. 
By  taking  the  amount  of  oxygen  combined  to  100  c.c.  of  blood  as 
ordinates,  and  the  oxygen  tensions  as  abscissso,  the  curve  of  dissocia- 
tion of  oxyhsemoglobin  is  obtained.  Thus,  by  joining  the  points 
between  the  shaded  portions  of  Fig.  137  a  curve  is  obtained  which 
shows  the  percentage  of  oxyhsemoglobin  of  the  total  haemoglobin  to 
the  concentrations  of  oxygen  dissolvcfl  in  the  fluid  at  all  pressures 
up  to  100  millimetres. 

(00 
90 
80 
70 

60 
50 
40 
30 
20 
10 


0    10  'M       30   40   50   CO   70       80   00   ICO 

Fig.  138. — Oxygen  Dissociation  Curves  of  Human  Blood  exposed  to  0,  3,  20, 
40,  AND  90  Millimetres  COo.     (Barcroft.) 

Ordinate  =  i3ercentage  satuiation;  abscissa  =  oxygen  pressure. 


o. 

^ 

^ 

■= 

// 

<y       / 

^7 

// 

/  /  /  / 

- 

Various  factors  are  found  to  modify  this  dissociation  curve.  Such 
factors  are — 

1.  The  H  ion  concentration  present  in  the  blood.  The  greater 
the  H  ion  concentration,  the  less  the  amount  of  oxygen  which  com- 
bines with  the  blood.  This  is  well  seen  in  conditions  when  there  is 
increased  concentration  of  carbon  dioxide  and  of  lactic  acid  (Fig.  138). 

2.  Solutions  of  haemoglobin  give  quite  different  values  to  those  of 
haemoglobin  undischarged  from  the  corpuscles.  The  haemoglobin  forms 
90  per  cent,  of  the  dried  weight  of  the  corpuscles,  and  much  more  is 
present  than  can  be  in  solution.  It  must  be  held  in  some  peculiar 
colloidal  state. 

3.  The  proportion  of  salts  present  in  the  blood  (Fig.  139). 

4.  The  temperature  (Fig.  140). 


RESPIRATION 


267 


The  manner  in  which  carbon  dioxide  exists  in  the  blood  is  more  diffi- 
cult of  explanation.  Besides  being  dissolved  in  the  watery  plasma  and 
corpuscles,  it  is  believed  that  the  carbon  dioxide  is  in  part  loosely  com- 
bined in  the  blood-plasma  as  a  weak  acid,  attached  to  the  alkali  present 
and   to   the   proteins,  and   also   to    the    red    corpuscles,    particularly 


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40 


50 


70 


Fig.  139. — Effect  of  H.e.moglobin  Solution  and  of  Salts  on  Oxygen 
DISSOCLA.TION  Curve.     (Barcroft.) 

I.  Dissociation  curve  of  hsemoglobin  dissolved  in  water. 
n.  „  „  „  „  „       -T^o  NaCl 

III.  ,.  „  „  „  „       -9%  KCl 

Ordinate  =  percentage  saturation  of  haemoglobin;  abscissa  =  tension  of  oxygen  in 
millimetres  of  mercury.  Rectangle  surrounding  point  =  magnitude  of  experi- 
mental error.     Temperature  37°-38°  C. 


the  protein  jjortion  (the  globin)  of  the  haemoglobin.  Haemoglobin 
consists  of  95  per  cent,  globin  and  5  per  cent,  hsematin;  the 
oxygen  is  attached  to  the  latter,  which  contains  the  iron.  Two  in- 
teresting facts  have  been  shown  in  regard  to  the  chemical  combina- 
tion of  COg  in  the  blood:  first,  that  in  spite  of  the  presence  of  free 
alkali,  blood — but  not  plasma — gives  up  almost  all  it-s  CO.,  to  the 


2G8 


A  TEXTBOOK  OF  PHYSIOLOGY 


vacimm  pump;  and,  secondly,  that  blood  added  to  a  soda  solution 
sets  free  COg  from  it.  The  probable  explanation  is  that  the  blood- 
proteins,  especially  the  hsemoglobin  and  the  serum  globulin,  by  virtue 
ot  their  amphoteric  reaction,  can  act  as  both  acids  and  alkalies.  The 
Ijiiilding-stones  of  proteins,  the  amino-acids,  contain  both  NHg  and 
COOH  groups.  When  the  partial  pressure  of  CO2  is  low,  as  in  the 
lungs,  these  proteins  act  as  weak  acids,  and  turn  out  COg.     On  the  other 


I        \^ " 

; 

^__. 

— . 

. — : — 

1         i  "  ^^"^^ 

/ 

HI 

y^ 

^ 

^- 

- 

/       / 

Vl^ 

^ 

^^ 

(/ 

/                     -- 

V 

■^            \ 

// 

/ 

/ 

\\ 

/ 

\\l 

/ 

W  / 

1  / 

\ , 

20 


30  - 


40  -\—l- 


50 


60 


70 


80 


90 


30 


40 

Fig.   140. 


50  60 

(Barcroft.) 


100 


Dissociation  curves  I.,  11.,  III.,  IV.,  and  V.  correspond  to  16°,  25°,  32°,  38°,  and  4&°^C. 
respectively.  Oxygen  pressure  plotted  horizontally,  perccnta£;e  of  reduced 
haemoglobin  vertically  downwards 


hand,  when  the  CO2  pressure  is  high,  as  in  the  tissues,  it  seems 
probable  that  these  proteins  act  as  alkalies,  and  actually  combine  with 
the  CO2  and  aid  in  its  transport  away  from  the  tissues. 

That  the  corpuscles  help  to  expel  the  CO^  is  shown  by  the  fact 
that  acid  must  be  added  to  plasma  in  order  to  obtain  all  the  CO2 
combined  with  it,  exj^osure  to  a  vacuum  not  being  sufficient  by  itself 
wholly  to  decompose  the  CO2  compounds  in  the  plasma. 


RESPIRATION  2G9 

The  following  was  estimated  to  be  the  distribution  of  CO^  in 
100  CO.  of  arterial  blood,  the  pressure  of  CO2  being  equal  to 
30  mm.  Hg:  Physically  absorbed,  1-9  c.c.  (0-7  c.c.  in  corpuscles); 
as  bicarbonate,  12  c.c;  as  organic  compounds  in  plasma,  11-8  c.c; 
in  htjemoglobin,  about  7-5  c.c;  as  bicarbonate  in  corpuscles,  about 
6-8  c.c— total.  40  c.c. 

The  Pressure  of  the  Gases  in  the  Alveolar  Air,  Blood,  and  Tissues. — 
In  order  that  we  may  discuss  the  processes  by  which  the  interchange 
of  gases  takes  place  between  the  alveolar  air  and  the  blood  in  the 
lungs,  and  between  the  blood  in  the  capillaries  and  the  tissue  fluids, 
it  is  necessary  that  Ave  know  the  pressure  of  the  gases  in  these  various 
parts.  It  is  possible  that  such  an  interchange  is  a  physical  process 
following  well-known  physical  laws ;  on  the  other  hand,  it  is  possible 
that,  owing  to  the  incessant  demand  of  the  tissues  for  oxygen,  and  the 
need  of  freeing  them  from  excess  of  CO2,  that  secretory  processes, 
unexplainable  by  known  physical  laws,  may  play  a  part  in  this  gaseous 
interchange.  Such  a  process  would  be  the  passage  of  a  gas  from  a 
region  of  lower  concentration,  through  a  layer  of  cells  wet  with 
tissue  lymph,  to  a  region  of  higher  concentration.  If  this  took 
place,  it  would  be  fair  to  assume  that  the  intervening  cells  and  the 
blood  were  in  some  way  aiding  the  process  by  virtue  of  their  own 
special  vital  metabolism.  It  might  be  said  that  the  cells  were  actually 
secreting  the  gas  into  the  region  of  higher  concentration,  just  as  the 
kidney  secretes  urea  from  the  blood,  where  it  may  be  1  per  1,000, 
into  the  urine,  where  it  may  be  20  per  1,000. 

Both  views  have  been  advocated,  and  are  still  advocated,  in  regard 
to  the  processes  of  respiration.  One  school  of  thought  believes  that 
all  the  processes  may  be  explained  by  known  physical  laws;  another 
school  holds  that,  under  some  circumstances  at  any  rate,  the  pro- 
cesses of  gaseous  interchange  are  aided  by  active  intervention  on  the 
part  of  the  bod}^  cells,  particularly  those  of  the  alveoli.  To  ascertain 
the  merits  of  these  conflicting  views,  it  is  necessary  to  know  the  partial 
pressure  of  the  gases  concerned  in  this  interchange  in  the  various  parts 
of  the  body,  and  also  to  study  the  accuracy  of  the  methods  by  which 
these  pressures  are  calculated. 

Partial  Pressure  of  Gases  in  the  Blood. — Manj^  experiments  have 
been  made  by  various  researchers  to  determine  exactly  the  partial 
pressure  of  the  gases  in  both  arterial  and  venous  blood.  In  general, 
the  method  employed  has  been  to  bring  the  circulating  blood  into 
contact  with  a  gas  mixture  of  known  composition,  and  by  analysis  at 
the  end  of  the  experiment  to  ascertain  the  composition  of  this  mixture. 
The  blood,  thoroughly  shaken  with  the  mixture,  gets  into  equilibrium 
with  it,  and  the  blood  gases  then  have  th?  same  partial  pressure  as 
those  found  in  the  mixture.  The  instruments  emploj^ed  for  this 
purpose  are  known  as  "  aerotonometers."  The  microtonometer  is 
the  apparatus  now  most  generally  employed.  In  this  apparatus 
(Fig.  141),  a  bubble  of  air  (2)  of  2  millimetres  diameter  is  brought  into 
contact  with  the  blood  coming  from  an  arterj^  or  vein.  The  blood 
enters  by  a  fine  point  (1),  and  keeps  the  bubble  in  constant  movement. 


270 


A  TEXTBOOK  OF  PHYSIOLOGY 


so  that  the  exchange  between  the  air  in  the  bubble  and  the  gases  of 
the  blood  is  a  ra]iid  one.  The  bubble  (2)  can  be  drawn  into  the  fine 
calibrated  tube  (3)  by  means  of  the  screw  piston  (4),  and  measured 
therein.  The  wide  part  of  this  tube  (1)  is  first  filled  with  Ringer's 
solution,  and  the  bubble  introduced  into  it  by  means  of  a  pipette. 
It  is  then  drawn  into  (3),  measured,  and  again  returned  to  (1).  The 
blood  is  now  allowed  to  flow  through  (1)  for  a  few  minutes  by  way 
of  (5)  and  (6).  The  bubble  is  once  more  measured  in  (3),  and  then  (5) 
is  filled  with  potash  solution,  the  bubble  returned  to  (5),  then  to  (3), 
and  again  measured.  Finally,  (1)  is  filled  with  sodium  pyrogallate 
solution,  and  the  manoeuvre  repeated.  Thus  the  percentage  of  COj 
and  O2  is  obtained,  for  the  potash  absorbs  the  COg  and  the  pyro- 
gallate Og.  From  the  percentage  measured  at  atmospheric  pressure 
the  partial  pressures  are  calculated. 


Fio.  141. — Schematic  Representation  of  Krogh's  Mickotonometek. 
Description  in  text. 


The  invasion  coefficient  is  the  amount  of  gas  which  enters  1  square 
centimetre  of  the  surface  in  one  minute  at  atmospheric  pressure.  This 
has  been  measured  in  the  case  of  a  bubble  of  air  by  means  of  the  micro- 
aerotonometer.  The  film  covering  this  bubble  is  comparable  in  tenuity 
to  that  of  the  pulmonary  endothelium. 

A  very  rough  calculation  of  the  invasion  coefficient  sviggests  that  it 
demands  a  difference  of  pressure  on  the  two  sides  of  the  lung  surface 
of  1  nun.  Hg  for  every  100  c.c.  of  oxygen  absorbed  by  the  lung  per 
minute. 


RESPIRATION 


271 


The  results  obtained  by  the  microtononieter  support  the  view 
that  the  exchange  of  gases  in  the  lungs  is  brought  about  by  the  process 
of  diffusion,  and  not  by  active  secretion.  The  oxygen  passes  from 
the  alveolar  air,  where  its  pressure  is  higher,  into  the  arterial  blood, 
where  its  pressure  is  lower.  The  carbon  dioxide  passes  from  the 
venous  blood,  where  its  pressure  is  higher,  into  the  alveolar  air,  where 
its  pressure  is  lower;  and  the  pressure  of  carbon  dioxide  in  the  arterial 
blood  leaving  the  alveolus  is  higher,  or  at  any  rate  not  lower,  than  that 
in  the  alveolar  air. 

There  is  nothing  inherently  improbable  in  the  conception  of  the 
lung  as  a  gas-secreting  organ.    Gas  is  secreted  by  several  aquatic  organ- 


FiG.  142. — Five  Gas-Secreting  Cells  from  the  Gas  Gland  in  the  Svvim-Bladdek 
OF  the  Paradise  Fish  Macropodus  V iridi-auratus.  (Redrawn  after  Reis  and 
Nusbaum  from  Dahlgren  and  Kepner. ) 

b,  Tliickened  distal  border  of  cells  on  the  lumen;  vac,  gas-vacuoles;  ir.,  trophospougia, 
the  organs  concerned  in  the  elaboration  of  gas  from  the  materials  of  the  cell ;  bl.  ca., 
blood  capillary. 


isms  for  the  purpose  of  flotation  (Fig.  142).  The  swim-bladder  of  the 
fish  is  an  organ  developed,  like  the  lung,  as  an  outgrowth  from  the  gut. 
Gas  is  secreted  in  it,  so  as  to  render  the  specific  gravity  of  the  fish 
equal  to  that  of  the  surrounding  water.  In  fish  at  great  depths, 
the  gas  is  compressed  by  even  hvxndreds  of  atmospheres  of  pressure, 
due  to  the  superincumbent  water.  The  fish  secrete  oxygen  gas  against 
this  enormous  pressure,  and  the  swim-bladder  is  immune  to  oxygen- 
poisoning.  If  the  swim-bladder  in  a  codfish  is  punctured,  and  the 
gas  drawn  off,  the  bladder  fills  again;  but  this  does  not  take  place  if 
the  vagus  nerves  be  divided.  Thus  the  secretion  of  the  gas  is  con- 
trolled by  these  nerves.  Some  authorities  have  sought  evidence  that 
the  gaseous  exchange  in  the  lungs  is  not  only  a  process  of  secretion, 
but  one  controlled  by  the  vagus  nerves.  The  function  of  the  swim- 
bladder  is  manifested  by  taking  two  goldfish,  and  fastening  a  piece 
of  cork  to  the  dorsal  fin  of  one,  and  a  piece  of  lead  to  the  ventral  fin 
of  the  other.     Both  are  returned  to  a  tall  jar  of  water,  and  the  one 


272 


A  TEXTBOOK  OF  PHYSIOLOGY 


is  drawn  by  the  cork  to  the  surface,  and  the  other  by  the  lead  to  the 
bottom.  Next  day  they  have  adjusted  their  specific  gravity  by  means 
of  their  swim-bladders,  and  are  swimming  about  easily.  On  removing 
the  lead,  that  fish  irresistibly  floats  to  the  surface;  on  removing  the 
cork,  the  other  one  sinks  to  the  bottom.  Thej^  have  again  to  adjust 
their  SAvim-bladdors.  If  goldfish  in  water  are  placed  in  a  pressure 
chamber,  and  suddenly  compressed,  they  sink  to  the  bottom,  owing 
to  the  shrinkage  of  the  gas  in  the  bladder.     If  a  fish  is  hooked  in  deep 


Piii.  143. — Fish  brought  vp  from  a  Considerable  Depth  with  Swollen  Swim- 
Bladder  PROJECTING  from  Mouth.     (After  Regnard.) 


water,  and  started  on  the  way  up,  the  gas  in  the  bladder  exjjands, 
■and  the  fish  floats  to  the  surface,  and  the  bladder  often  bursts 
(Fig.  143).  There  is  a  glandular  mechanism  in  the  swim-bladder  for 
secreting  gas.  and  another  mechanism  for  absorbing  it. 

Against  the  theory  of  pulmonary  secretion  is  the  fact  that  the 
pulmonary  endothelial  cell  is  a  flattened  structure  entirely  unlike  the 
granular  secreting  cells  typical  of  glands. 

Evidence  in  favour  of  pulmonary  secretion  has  been  sought  by 
a  method  quite  different  to  that  of  the  aerotonometer.  If  blood  is 
shaken  with  air  containing,  say,  0-05  per  cent,  of  carbon  monoxide, 
the  haemoglobin  is  shared  between  the  oxygen  and  carbon  monoxide 


RESPIRATION 


273 


in  proportions  depending  on  their  relative  pressures  and  chemical 
affinity.  Carbon  monoxide  has  an  affinity  about  150  times  as  great 
as  oxygen.  Blood  saturated  M'ith  carbon  monoxide,  and  diluted 
1  in  200  times,  has  a  pink  colour;  the  extent  of  saturation  with  carbon 
monoxide  can  be  estimated  bj^  a  method  depending  on  the  depth  of 
this  colour.  If  three  samples  of  blood  (diluted  1  in  200)  are  taken, 
and  one  is  saturated  with  carbon  monoxide  (shaken  with  coal-gas), 
the  second  parth^  saturated,  and  the  third  not  at  all,  the  colours  of 
the  samples  are  obviously  different.  The  normal  sample  is  straw- 
coloured.  A  standard  solution  of  carmine  can  be  run  in  from  a  pipette, 
and  the  amounts  found  which  will  make  Sample  2  and  Sample  3 
equal  in  pinkness  to  Sample  1 .  From  the  relative  amounts  of  carmine 
used  the  degree  of  saturation  of  Sample  2  is  discovered. 


Fig.  144. — Haldane's  AprARAxrs  for  determining  Oo  Tension  in  Human 

Blood. 

B,  T,  C,  Apparatus  for  br- athing  air  containing  CO  at  measured  concentration; 
M,  mouthpiece;  T',  valves  made  of  pieces  of  intestine;  B,  air-bag  for  controlling 
pressure  during  expiiation;  G,  meter. 


Now,  when  air  containing  0-05  per  cent,  carbon  monoxide  is 
breathed  for  a  sufficient  period  to  allow  the  w^hole  blood  to  get  into 
equilibrium,  the  saturation  with  carbon  monoxide  is  found  to  be  less 
than  that  when  the  blood  is  shaken  with  the  same  mixture  outside 
the  body;  particularly  is  this  the  case  under  conditions  of  oxygen 
want — e.g.,  at  high  altitudes,  partial  asph}xia — when  it  is  suggested 
there  would  be  secretion  of  oxygen  into  the  blood  by  the  lung.  The 
oxygen  pressure  in  the  arterial  blood  raised  by  secretion  is  supposed 
to  antagonize  the  union  of  carbon  monoxide  with  the  haemoglobin. 
However,  other  explanations  havb  been  given  of  this  result.  The 
technique  of  the  method  is  as  follows: 

18 


274 


A  TEXTBOOK  OF  PHYSIOLOGY 


The  subject  inspires  through  the  mouthpiece  31,  and  expires 
through  the  meter  (Fig.  144).  Water  is  allowed  to  nm  from  R  into 
C,  which  contains  pure  CO,  and  disphiccs  this  gas  at  such  a  rate  as  to 
give  a  known  concentration  of  CO  in  the  vohime  of  air,  indicated  by 
the  meter,  which  is  being  breathed.  The  breathing  is  continued  long 
enough  for  the  blood  to  come  into  equilibrium  with  the  partial  pref - 
sure  of  CO  and  0.,  which  is  being  breathed  (the  partial  pressure  of 
O  is  that  of  the  air).  The  finger  is  then  pricked,  and  samples  of  blood 
taken,  and  the  saturation  determined  by  the  carmme  method  given 


^0 

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16 

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15 

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220        30        W       60        3 


20       30       ttO 
Fig.  145. 


50 


P.O       30       W 


Dotted  line  ^pressure  in  the  air  at  bifurcation  of  trachea. 
Solid  line  =  pressure  in  the  blood. 

In  the  upper  j)art  of  the  figure  are  shown  the  pressures  of  oxygen,  in  the  lower  jiart  the 
pressures  of  carbon  dioxide.  Ordinate  pressure  of  oxygen  expressed  in  per- 
centages of  an  atmosphere.     Abscissa  =  time.     (Krogh.) 


above.  A  sample  is  shaken  with  the  air  (contauaing  the  known  per- 
centage of  CO),  which  was  breathed.  If  this  sample  is  found  to  be 
more  saturated  with  CO  than  that  drawn  from  the  finger  durmg  the 
breathing,  the  conclusion  is  drawn  that  the  partial  pre.ssure  of  oxygen 
in  the  blood  in  the  pulmonary  veins  is  higher  than  that  in  the  air. 

The  colorimetric  method  is  liable  to  error ;  moreover,  a  part  of  the 
carbon  monoxide  actually  absorbed  may  leave  the  blood  and  com- ' 
bine  with  haemoglobin  in  the  muscles.     There  is  no  evidence  in  favour 
of  any  of  the  carbon  monoxide  being  destroyed  in  the  body,  error 
does  not  seem  to  arise  from  that  cause. 


RESPIRATION  275 

To  sum  up,  the  differences  of  pressure  of  carbon  dioxide  and  of 
oxygen  found  by  the  microtonometer  in  the  blood  and  at  the  bifurca- 
tion of  the  trachea  support  the  view  of  diffusion  (Fig.  145).  It  is 
estimated  also  that  the  process  of  diffusion  can  carry  oxygen  in 
amounts  sufficient  for  hard  work  through  the  puhnonary  endothelium. 
The  rate  of  diffusion  in  the  lung  is  probably  accelerated  by  the 
chemical  affinity  of  haemoglobin  with  oxj'gen:  we  need  not  therefore 
ascribe  a  secreting  power  to  the  pulmonary  endothelium. 

But  it  is  still  a  question  whether  diffusion  can  cover  the  oxygen 
needs  at  great  altitudes — e.g.,  24,000  feet,  to  which  a  few  climbers 
have  attained. 

Carbon  dioxide  is  about  twenty-five  times  as  soluble  in  water  as 
oxj^gen  is,  hence  it  passes  through  the  alveolar  wall  far  more  easily 
than  oxygen  with  a  given  difference  of  partial  pressiu*e.  A  compara- 
tively slight  increase  in  breathmg,  hy  ventilating  the  lungs,  enormousty 
increases  the  small  difference  in  diffusion  pressvu'e  on  which  the  passage 
of  COg  depends,  but  only  produces  a  slight  proportional  increase  in 
the  diffusion  pressure  which  drives  oxygen  inwards.  Hence,  under 
certain  conditions,  grejTiess  of  the  face,  faintness,  and  danger  from 
heart  failure,  the  signs  of  oxygen-want,  may  arise  when  hypeipnoea 
and  venous  congestion,  the  signs  of  COg  excess,  are  absent. 


CHAPTER  XX  XT 
THE  MECHANISM  OF  RESPIRATION 

In  the  unicellular  organism,  oxygen  is  taken  in  from  the 
surrounding  medium,  and  the  CO2  given  out  through  the  cell  sur- 
face. In  the  more  complex  organisms,  a  special  respiratory  apparatus 
becomes  evolved,  and  two  kinds  of  respiration  are  distinguished: 
external  respiration,  by  which  oxygen  is  taken  from  the  surrounding 
medium  into  the  circulating  transport  fluid — the  blood — and  the  COg 
given  off  from  this  fluid  to  the  medium;  internal  respiration,  by  which 
a  gaseous  interchange  takes  place  between  the  body  fluids  and  the 
various  body  cells,  oxygen  being  taken  to  the  cells,  and  CO,^  removed 
from  them.  Internal  respiration  is  probably  the  same  process  in  all 
forms  of  animals.  External  respiration  differs  with  the  stage  of 
develoiDment,  and  also  with  the  habitat  of  the  animal.  The  lower 
forms  of  invertebrates  usually  breathe  through  the  skin;  the  higher 
forms,  when  living  in  the  water,  by  a  specially  developed  system  of 
gills;  when  land  dwellers,  by  a  special  system  of  branching  tubes 
known  as  "  tracheae,"  which  carry  the  air  diiect  to  the  blood-spaces 
surrounding  the  individual  cells. 

In  low  temperatures,  the  frog  can  breathe  by  its  skin  alone.  In 
man,  1-5  per  cent,  of  the  respiratory  exchange  is  reckoned  to  take 
place  through  the  skin,  and  somewhat  more  on  sweating.  A  small 
amount  of  respiratory  exchange  takes  place  through  air  which  is 
swallowed:  certain  fishes  breathe  by  this  method. 

Among  the  vertebrates,  fishes  have  a  special  system  of  gills,  by 
which  the  gaseous  interchange  between  the  surrounding  water  and 
the  blood  is  effected. 

Amphibians  in  the  larval  stage — e.g.,  the  tadpole — also  possess 
<yills;  but  in  the  adult  animal  these  are  replaced  by  lungs.  In  the 
higher  vertebrates,  after  birth,  external  respiration  is  always  effected 
by  means  of  specially  developed  lungs.  During  development,  how- 
ever— as,  for  example,  in  the  human  foetus — traces  of  the  remains  of 
the  gill  apparatus  can  still  be  seen. 

In  the  higher  organisms,  the  circulatory  mechanism  suffices  for  the 
transport  of  the  gases  to  and  from  the  tissues,  and  various  devices 
have  been  adopted  to  facilitate  the  interchange  between  the  outer 
medium  and  the  respiratory  apparatus.  In  fishes,  the  water  is  taken 
in  through  the  mouth,  passed  over  the  gills,  and  out  by  the  gill-slits; 
in  many  amphibia,  the  air  is  swallowed  into  the  lungs.  In  birds, 
during  rest,  the  movements  of  the  ribs  suffice  to  draw  air  through  the 
lungs  and  in  and  out  of  the  five  large  air-sacs.     The  lungs  are  not 

276 


THE  MECHANISM  OF  RESPIRATION  277 

expanded  with  air,  but  the  t)lood  Ls  pumped  in  and  out  of  them  by 
the  movement  of  the  ribs.  During  flight,  the  wing  movement  insvires 
adequate  respiration.  The  air-sacs  play  a  great  part  in  flight  and 
extend  the  leverage  with  which  the  muscles  act,  at  the  same  time 
keeping  the  body  light.  Opening  the  air-sacs  in  the  resting  bird  causes 
no  upset  of  breathing.  In  the  flying  bird,  an  immediate  dyspnoea 
is  induced,  and  flight  becomes  impossible.  It  has  also  been  shown  that 
for  proper  heat  regulation  of  the  body  the  air-sacs  are  necessar3^ 

In  mammals,  the  gaseous  interchange  is  effected  by  the  movements 
of  the  sternum,  ribs,  and  abdomen,  drawing  air  into  and  expelling  it 
from  the  air-tight  chest,  or  thorax  (see  later,  p.  28i). 

In  man,  the  respiratory  tract  may  be  said  to  consist  of  the  following 
parts : 

1.  The  Nose. — The  respiratory  portion  of  the  nose  consists  of  the 
inferior  meatus  and  the  lower  portion  of  the  superior  meatus.  These 
parts  are  covered  by  a  verj'  vascular  ciliated  nuicous  membrane, 
which  provides  a  mucous  secretion.  Thick  hairs,  or  vibrissse,  project 
into  the  respiratory  airway,  and  guard  the  entrance  against  insects. 
Air  taken  in  through  the  nose  is  warmed  and  moistened,  and,  more 
important  still,  injurious  particles  of  dust  and  bacteria  are  removed 
from  it.  The  mucous  membrane  is  extremely  sensitive  to  changes 
in  the  atmosphere.  When  the  air  playing  round  the  head  is  cool 
and  relatively  dry,  the  mucous  membrane  is  firm  and  moist,  and  a 
good  airway  is  insured;  when  the  air  is  stagnant,  warm,  and  humid, 
the  mucous  membrane  becomes  engorged,  wet  with  secretion,  and 
boggy.  It  is  not  the  cold  outside  atmosphere  of  winter,  but  the 
warm  infected  air  of  crowded  rooms,  which  causes  the  epidemics  of 
'"  cold  in  the  head."  The  nose  also  acts  as  an  accessory  resonating 
chamber  in  speech,  as  the  term  talking  "  through  the  nose  '  testifies. 
To  produce  this  the  airway  through  the  nose  is  greatly  diminished. 

2.  The  Pharynx. — Air  is  conducted  through  the  upper  part  of  the 
pharynx  into  the  larynx.  Its  shape  and  movement  play  a  large  part 
in  determining  the  quality  of  the  voice.  Here  and  in  the  tonsils 
there  is  much  lymphoid  tissue  which  possibly  guards  from  infection 
by  inhaled  bacteria. 

3.  The  Larynx. — This  specialized  part  of  the  respiratory  tract  in 
which  the  voice  is  produced  is  dealt  with  later  (see  p.  739). 

4.  The  Trachea,  or  windpipe,  which  divides  into  the  tAvo  as 
bronchi ;  these  divide  into  smaller  divisions,  known  as  bronchial  tubes, 
which  in  their  turn  divide  into  bronchiales,  ultimately  opening  into 
the  essential  distensible  elements  of  the  lungs,  the  funnel-shaped 
infundibuli,  and  the  alveoli. 

The  trachea  is  provided  wdth  ciliated  epithelium,  and  is  wet  with 
mucus  secreted  by  the  glands  of  its  mucous  membrane.  In  this 
mucus  any  entering  dust  or  bacteria  are  caught,  to  be  carried  upwards 
by  the  ciha  and  away  from  the  lungs.  The  walls  of  the  larger  of 
these  i^assages  (the  trachea  and  bronchi)  are  provided  with  cartilage. 

The  bronchial  tubes  are  supplied  with  smooth  muscle  innervated 


278 


A  TEXTBOOK  OF  PHYSIOLOGY 


by  the  vagus  and  sympathetic  iieives.  During  hard  exercise  the 
capacity  of  the  bronchial  tubes  is  said  by  some  to  increase  in  order 
to  lessen  resistance  and  facilitate  the  rapid  and  great  ventilation  of 
the  lungs.  By  means  of  this  muscle  the  airway  can  certainly  l)e 
increased  or  decreased  so  that  air  may  more  or  less  readily  be 
taken  into  the  lungs  (Fig.  146).  Drugs  also  affect  this  mechanism 
(Figs.  147,  148).     The  muscle  can  control  the  entry  of  air  into  one  or 


Fig.  J46. — Decerebrate  Animal:  Lung  Volume  and  BLOOD-rKESsuRE.  To 
SHOW  Effect  of  Excitation  of  Peripheral  Vagu.s  and  of  Right  Cervical 
Sympathetic.     (Dixon  and  Ransom.) 


other  part  of  the  lung.  There  is  some  evidence  that  all  ])arts  of  the 
lung  are  not  in  action  during  quiet  breathing.  The  muscle  supports 
the  tubes  in  expiratory  effort. 

The  infundibular  sacs  of  the  lung  are  lined  with  flattened  cubical 
eells,  supported  by  a  framework  of  elastic  fibres  and  richly  supplied 
by  bloodvessels.  The  alveoli  are  smaller  terminal  expansions  set  in 
the  funnel-shaped  infundibula. 

Air  Volume. — In  dealing  with  respiration,  certain  terms  are  used 
which  require  defining.  The  volume  of  air  breathed  by  a  person  at 
each  quiet  respiration  is  termed  the  tidal  air.     This  averages,  in  a 


THE  MECHANISM  OF  RESPIRATION 


:27t> 


Fig.  147. 

Upper  curve  shows  lung  volume,  lower  arterial  pressure  of  cat  with  right  vagus  cut. 
At  indication  mark  0*0075  gramme  of  i)ilocarpine  nitrate  injected.  There  is 
constriction  of  the  bronchial  muscles,  which  diminishes  the  amount  of  air  entering 
and  leaving  the  lungs.  The  blood-pressure  falls.  Both  effects  are  due  to  stimu- 
lation of  the  vagus  nerve-endings.     (Brodic  and  Dixon.) 


Fig.  148. 

Upper  curve  represents  the  volume  of  small  lobe  of  lung,  amount  of  air  entering  and 
leaving  lung  shown  respectively  by  up-and-down  strokes.  Lower  curve,  blood- 
pressure.  At  indicated  marks  two  small  doses  of  lobelia  injected  into  a  vein. 
There  is  almost  immediate  dilatation  of  the  bronchioles;  the  rise  in  blood -pressure 
is  a  vaso-motor  effect.     (Brodie  and  Dixon.) 


resting  man,  300  to  500  c.c.  The  amount  of  air  which  can  be  taken 
into  the  kings  by  forced  inspiration  after  a  normal  qviiet  inspiration 
is  the  complemental  air,  averaging  1,500  to  2,000  c.c;  that  which 
•can  by  forced  effort  be  expelled  from  the  lung  after  a  quiet  expiration 


280 


A  TEXTBOOK  OF  PHYSIOLOGY 


is  the  supplemental  air,  also  1,500  to  2,000  c.c.  in  volume. 
three  together  give  the  vital  capacity  of  an  individual. 


These 


Tidal  air    . . 
Complcmental  air 
Supplemental  air 


300-500  c.c. 
1,500-2,000  c.c. 
1,500-2,000  c.c. 


Vital  capacity ■..  ..         3,300-4,500  c.c. 

The  vital  capacity  can  be  measured  by  expiring  to  the  greatest 
extent  after  the  fullest  possible  inspiration  mto  a  spirometer  (Fig.  149)' 
— a  form  of  gasometer.     The  vital  capacity  of  an  individual  can  be 


Fig.  149. — Spiuu-metek. 
T,  Mouth-piece;  M,  manometer;  Cp,  counterpoise;  R,  scale. 

greaty  increased  by  practice.  Some  athletes  (swimmers)  have  a> 
capacity  of  6i  litres.  The  amount  breathed  out  depends  largely  upon 
proper  muscular  co-ordination.  It  also  varies'  with  posture,  being, 
greatest  when  standing,  and  least  when  lying  doAvn. 

The  amount  of  air  left  in  the  lungs  after  the  greatest  expiration 
possible  has  been  taken  is  termed  the  residual  air,  and  measures 
1,500  to  2,000  c.c.  The  expired  tidal  air  comes  from  the  trachea, 
bronchi,  and  alveoli.  It  is  calculated,  of  500  c.c.  expired,  140  to- 
160  c.c.  comes  from  the  trachea  and  bronchi,  forming  the  "  dead- 


THE  MECHANISM  OF  RESPIRATIOX 


281 


space  "  air,  and  the  remainder  from  the  aveoH — true  alveolar  air. 
The  dead-space  air  does  not  undergo  a  respirator}^  exchange. 
In  the  resting  man,  350  c.c.  of  the  total  tidal  air  mixes  with  3,000  to 
4,000  c.c.  in  the  lungs  (supplemental  and  residual  air),  so  that  only 
about  one-tenth  of  the  air  is  changed  at  each  breath;  much  less  in 
shallow  breathing.  In  deep  breathing,  the  complemental  air  is  added 
to  the  tidal,  and  1,660  to  2,360  c.c.  mixes  with  the  air  in  the  kmg^ 
about  one-half  is  changed. 

A  sample  of  alveolar  air  may  be  obtained  by  expiring  deeply 
through  a  piece  of  rubber  tubing  of  about  1  inch  bore  and  4  feet  length 
(Fig.  150).  The  "  dead-space  "  air  is  blown  out  of  the  tube,  and  the 
tube  is  filled  with  alveolar  air.  The  end  of  the  tube  is  closed  with  the 
tongue  or  with  forceps,  and  through  the  T -piece  a  sample  is  drawn 
off  into  a  suitable  sampHng  tube,  which  has  been  previous^  evacuated 


Mouth  pi  zee 


Wi 


SsLmpling  Tube 


Fig.  '  )0. — Apparattts  for  Collection  of  Sample  of  Alveolar  Air. 

and  Priestley.) 


(Haldane 


by  means  of  a  reservoir  fitted  with  a  rubber  tube.  The  sample  may  be 
taken  at  the  end  of  a  normal  expiration  following  an  inspiration,  or 
preferabh'  two  samples  may  be  secured,  the  second  immediately  after 
expiration  following  normal  inspiration.  The  mean  of  the  analyses 
gives  the  normal  alveolar  air. 

Alveolar  air  contains  4-5  to  6  per  cent.  CO.,,  13-5  to  15  per  cent.  Og, 
79  to  80  x>er  cent.  No.  The  CO.,  percentage  in  men  (5  to  6  per  cent.) 
is  generally  a  little  higher  than  in  women  and  children  (4  to  5  per  cent.). 

The  composition  of  ordinary  inspired  air  at  normal  temperature 
and  pressure — 0°  C.  and  760  millimetres — ma}^  be  given  as  follows: 


Oxygen 

Carbon  dioxide 
Nitrogen  *     .  . 
Water  vapour 
Temperature 

Expired  an-: 

Oxygen 

Carbon  dioxide 
Nitrogen  * 
Water  vapour 
Temperature 


20- 9-2  volumes  per  cent. 

0-03-0-04 

.      79-03 

\'ariablo 
Variable 


16-00  per  cent. 
•4-00       „ 
80-00       „ 

Saturated 
37°  C. 


*  Including  0-94  per  cant,  argon. 


282 


A  TEXTBOOK  OF  PHYSIOLOGY 


Expired  air  is  diminished  about  one-fiftieth  in  volume  as  com- 
pared with  the  inspired  air.  This  is  due  to  the  oxygen  combined 
with  products  of  tissue  oxidation  which  passes  out  of  the  body  in 
the  urine.     To  obtain  expired  air  for  analysis,  the  subject  breathes 


M 


B 


Fig.  151. — Haldane's  Gas  Analysis  ArrAKAXUS. 


through  a  mouth-piece,  provided  with  inlet  and  outlet  valves,  inta 
a  large  rubber-lined  canvas  bag.  The  contents  of  the  bag  are 
squeezed  through  a  meter,  and  thus  the  volume  of  expired  air 
measured ;  while  a  sample  is  secured  for  analysis  by  means  of  a  T-piece 
into  an  evacuated  sampling  tube.     If  the  subject  breathe  for,   say. 


THE  MECHANISM  OF  RESPIRATION  283 

ten  minutes,  and  the  number  of  respirations  be  counted,  the  tidal  air 
ean  be  calculated  ;  from  the  analysis  the  respiratory  exchange  can  be 
estimated  as  well  as  the  composition  of  the  expired  air  (see  later,  p.  317). 

One  of  the  best  forms  of  apparatus  for  the  estimation  of  the  gases 
in  inspired  and  expired  air  is  shown  in  Fig.  151. 

The  gas  is  measured  in  the  graduated  gas-burette  .4,  provided 
with  a  three-way  tap.  Surrounding  the  gas-burette  is  a  water-jacket. 
The  whole  is  supported  b}'  a  clamp  and  retort  stand.  The  gas-burette 
is  connected  b}'  pressure  tubing  to  the  levelling  tube  B,  which  is  held 
by  a  spring  clamp  attached  to  the  retort  stand.  A  and  B  contain 
mercury,  and  by  raising  or  lowering  B  gas  can  lie  expelled  from  or 
drawn  into  .4.  One  of  the  connections  of  the  three-waj-  tap  is  used 
for  taking  in  the  sample,  the  other  connects  the  burette  with  an 
absorption  apparatus  arranged  as  in  the  figure. 

The  bulb  E,  filled  with  20  per  cent,  caustic  potash,  absorbs  CO,. 
The  bulb  F,  filled  Avith  alkaline  pyrogallic  acid  solution,  absorbs 
O.,.  Alkali  in  G  and  H  protects  the  p\To  solution  from  the  air.  F  is 
emptied  and  refilled  through  K.  The  tap  on  the  absor])tion  pipette 
places  either  E  or  F  in  connection  with  the  gas-burette.  There  is 
a  control  tube  by  A\hich  alterations  in  temperature  or  barometric 
pressure  during  the  analj'sis  can  be  compensated  for. 

The  sample  of  gas  is  taken  into  the  burette  from  the  sampling 
tube  (Fig.  150),  mercury  being  sucked  into  the  tube  to  take  the  place 
of  the  gas  entering  the  burette.  After  measuring  the  amount  of  the 
sample  it  is  passed  into  E  to  absorb  CO.^.  When  a  constant  reading 
is  obtained,  it  is  passed  into  F  until  all  the  oxygen  is  absorbed. 
To  take  an  example  :  Suppose  the  amoimt  of  gas  taken  in  was 
20-12  c.c.  After  absorption  of  carbon  dioxide  in  E  the  burette 
reading  was  19-06;  after  absorption  of  oxvgen  in  F  it  was  16-01. 

Then  in  20-12  parts  of  the  sample  there  is  20-12- 1906  =  1-06  of 
CO^,  in  100  parts  therefore  there  are — 

1-06x100 

2().|2 —  =  5"22  approx. 

Also  in  20-12  parts  of  the  sample  there  are  19-06- 16-01 -3-05 
parts  of  0-2 . 

In  100  parts  therefore  there  are — 

3-05  X  100 

20-12      ^^"^'^^  approx. 

The  percentage  of  sample,  therefore,  is  5-22  Ci).^;  l"ill  O2. 


CHAPTER  XXXII 

THE  MECHANICS  OF  BREATHING 

To  facilitate  gaseous  interchange,  the  process  of  breathing  or 
ventilation  of  the  kings  takes  place.  In  the  act  of  inspiration  in 
mammals  the  chest  is  expanded,  air  is  drawn  into  the  lungs ;  in 
the  act  of  expiration  the  chest  and  lung  capacity  is  diminished,  and 
air  forced  out  from  the  lungs. 

Anatomical  Considerations. — To  understand  properly  the  move- 
ments concerned  in  the  processes  of  inspiration  and  expiration,  certain 
anatomical  details  in  regard  to  the  bony  framework  and  the  muscula- 
ture of  the  thorax  have  to  be  considered.  The  varying  extensibility 
of  different  parts  of  the  lung  has  also  to  be  borne  in  mind. 

In  the  inspiratory  movement,  the  thorax  is  expanded  in  three 
dimensions.  In  regard  to  the  exact  manner  in  which  these  move- 
ments take  place  there  is  still  some  uncertainty.  The  chief  move- 
ments, ho\\  ever,  may  be  grouped  as — 

1.  The  movements  of  the  diaphragm. 

2.  The  movements  of  the  ribs  and  rib  cartilages. 

Breathing  of  the  abdominal  type,  such  as  occurs  in  man,  is 
chiefly  diaphragmatic;  breathing  of  the  thoracic  t\^e,  such  as  takes 
place  in  corsetted  women,  is  mainly  costal.  Normally,  breathing  is 
a  combination  of  the  two  t_\"pes — sometimes  one,  sometimes  the  other 
prevails. 

The  Action  and  Movements  of  the  Diaphragm. — Separating  the 
thorax  froiii  the  abdomen,  the  diaphragm,  in  its  resting  position,  reaches 
up  to  aboiit  the  fifth  intercostal  space.  The  fleshy  part  of  the  muscle 
lies  close  to  the  ribs,  the  central  dome-like  part  being  mainly  of  a 
tendinous  nature.  There  has  been  considerable  speculation  as  to  the 
exact  nature  of  the  movements  performed  by  the  diaphragm.  The 
view  commonh'  expressed  is  that  the  muscle,  by  its  contraction,  in 
association  with  muscles  which  fix  the  throax,  opens  up  the  angle 
which  it  forms  with  the  thoracic  wall,  thereby  enabling  the  lung 
to  expand  in  a  downward  direction.  In  such  a  movement  the 
central  tendinous  portion  is  supposed  not  to  participate.  After 
contraction,  it  is  assumed  that  the  diaphragm  passively  returns  to 
the  position  of  rest. 

Recent  study  of  the  diaphragmatic  movement  by  means  of  the 
X  rays  has  shown,  however,  that  there  is  a  forward  downward  move- 

28  i 


THE  MECHANICS  OF  BREATHINC4  285 

ment  of   the  whole    diaphragm,    accompanied  by  a  definite    move- 
ment of  the  abdominal  viscera. 

The  diapln-agm  may  be  regarded  as. consisting  of  two  parts:  (1)  The 
spinal,  or  crural,  from  the  spinal  column  and  arcuate  ligaments  to  the 
back  portion  of  the  central  tendon;  (2)  the  costo-sternal,  or  anterior, 
attached  to  the  front  and  sides  of  the  central  tendon,  and  arising  by 
several  digitations  from  the  ribs.  The  arch  of  the  diaphragm  rests 
upon,  and  is  supported  equably  by,  the  abdominal  viscera,  and  is  at 
the  same  time  kept  constantl}"  applied  at  the  circumference  to  the 
inner  wall  of  the  thorax  by  the  negative  intrathoracic  pressm-e.  Thus, 
when  its  two  parts  contract,  it  acts  like  a  true  piston,  moving  in  a 
forward  and  downAvard  direction.  In  quiet,  normal  breathing  the 
amount  of  movement  of  the  right  dome  is  about  i  inch,  that  of  the 
left  dome  and  of  the  central  tendon  somewhat  less. 

The  Movement  o£  the  Ribs. — In  general,  two  movements  of  the  ribs 
are  recognized  as  taking  place  in  insjjiration :  (1)  Round  an  axis  cor- 
responding to  the  spinal  articulation,  increasing  the  back-to-front 
diameter  of  the  thorax;  (2)  round  one  corresponding  to  the  spino- 
sternal  articulation,  increasing  the  diameter  from  side  to  side.  Owing 
to  the  variation  in  size,  shape,  inclination,  and  articulation  of  the  ribs, 
such  an  explanation,  while  essentially  true  in  a  general  sense,  is  im- 
perfect. It  is  better  to  divide  the  ribs  into  two  sets:  (1)  The  upper, 
the  second  rib  to  the  fifth;  (2)  the  lower,  the  sixth  rib  to  the  tenth. 
These  two  sets  differ  in  their  musculature,  in  the  nature  of  their  articu- 
lation and  ligaments,  in  their  shape  and  arrangement,  and  in  their 
movements. 

It  is  better  not  to  regard  the  first  rib  as  one  of  the  costal  series, 
but  to  associate  it  with  the  manubrium  sterni,  with  which  it  performs 
a  special  movement  of  its  own.  The  lowest  two  ribs,  inasmuch  as 
they  are  unattached  in  front^ — '"  floating  " — are  essentially  j^arts  of 
the  abdominal  wall.  Concerned  in  the  resjiiratory  movements,  there- 
fore, are — 

1.  The  first  rib  and  manubrium  sterni. 

2.  The  upper  costal  series  (2-5). 

3.  The  lower  costal  series  (6-10). 

4.  The  floating  ribs  (11,  12). 

The  First  Rib  and  Manubrium  Sterni. — The  first  pair  of  ribs  and 
the  manubrium  sterni  are  intimately  bound  together,  and  form, 
Avith  the  manubrium,  a  lid  or  operculum  to  the  thorax.  Behind  this 
lid  is  articulated  with  the  spinal  column,  in  front  with  the  body  of  the 
sternum,  the  manubrio- sternal  joint  (Fig.  152).  During  inspiration 
there  is  a  slight  upward  movement  of  the  lid,  allowed  by  the  manubrio- 
sternal  joint,  which  causes  an  expansion  of  the  anterior  part  of  the 
apex  of  the  lungs.  This  movement  is  particularly  marked  in  the 
thoracic  tvqje  of  breathing.  To  demonstrate  the  movement  at  the 
manubrio -sternal  joint  small  mirrors  are  fixed  above  and  below  this 
joint,  and  the  movements  of  the  reflected  spots  of  light  observed  on 
a   screen.     During  inspiration  the  spots  diverge,   during  expii-atiou 


286 


A  TEXTBOOK  OF  PHYSI0LO(;V 


they  come  together.  In  people  ^ith  ill-developed  chests  there  is  but 
little  iiiovement  here.  The  posterior  part  of  the  apex  of  the  lung  is 
but  little  affected  by  the  movement  of  the  operculum,  its  expansion 
being  seciu'ed  by  diaphragmatic  breathing. 

The  Movement  of  the  Upper  Ribs. — It  is  on  these  that  most 
of  the  observations  upon  rib  movements  and  the  action  of  the 
intercostal  muscles  have  been  made.  During  inspiration,  both  sets  of 
intercostal  muscles  act  together,  and  draw  up  the  upi)er  ribs  towards  the 
operculum,  which  acts  as  a  fulcrum.  During  expiration,  the  lower  set 
of  ribs  are  fixed,  and  act  as  fulcrum,  and  the  upper  set  are  (h-awn  down 
toward  them  by  the  intercostal  muscles.  This-  view  of  the  action  of 
the  intercostals  is  not  accepted  by  everyone.  There  is  some  experi- 
mental evidence  to  show  that  the  external  intercostal  muscles  act 
during  inspiration.     The  fibres  slant  from  above  downwards  and  for- 

17/  Ce^y.'/eri:.'  ^4 

NecU  of  l^t F^'ib 

Apex  oF  Lung ^^^^^«^^^    ^""    ^'^ 

l^'Rib  (inspir.) .  ^-^^^^^^^^^^rd 

Manub.OnspirJ    -    ^  J^%g^   u^^^V^  "'^ 

Manub.ie.p.)-yL.^  '^^^-^ttS 

Fig.  152. — Diagram  tu  show  Respiratory  Movements  of  the  First  Pair  or  Ribs 
AND  Manubrium  Sterni  and  the  Effect  or  these  Movements  on  the  Expan- 
sion OF  THE  Apex  of  the  Lung.     (Keith.) 


wards,  and.  shortening,  raise  the  ribs.  The  fibres  of  the  internal 
intercostals.  on  the  other  hand,  slant  from  above  downwards  and 
backwards,  and.  shortening,  lower  the  ribs.  The  Uvo,  acting  together, 
make  rigid  the  thoracic  wall.  The  intercartilaginous  fibres  act  with 
the  external  intercostals. 

The  Movement  of  the  Lower  Ribs. — The  purpose  of  the  miovement 
of  the  lower  ribs  is  to  expand  the  lower  lobe  of  the  lung.  The  dia- 
phragm is  .the  chief  muscle  concerned,  aided  by  the  ilio-costalis^  and 
the  external  intercostals,  and  the  interchondral  muscles.  The  an- 
tagonistic muscles  are  the  external  oblique,  the  internal  oblique, 
and  the  trans versalis.  During  inspiration,  owing  to  the  mode  of 
articulation  of  the  ribs,  the  lateral  and  anterior  part  of  each  moves 
outwards  more  than  the  one  above.  At  the  same  time,  the  lower  ribs 
are  raised,  together  with  the  sternum,  so  that  the  net  result  of  the 
lower  rib  movement  is  to  increase  the  transverse  and  back-to-front 


THE  MECHANICS  OF  BREATHING  287 

diameter  of  the  lower  thorax,  and,  with  the  diaphi-agm  moving  down- 
wards, the  vertical  diameter  of  the  whole  cavit>^ 

Inspiration  is  therefore  a  very  complex  act, "and  it  is  owing  to  the 
complicated  nature  of  the  movements  concerned  that  the  lungs  are 
divided   into   lobes.     The   upper  ribs   are   chiefly   concerned   in    the 


Lower  Bord.  (exp 
Louver  Bord. 
Crus  (inspir 

Crus  (expir 


Fig.  153. — Mediastinal  Aspect  of  Right  Luxg  to  show  Respiratory  Movement 
OF  the  Root.     (Keith.) 

The  crus  of  the  diaphragm  is  also  indicated,  and  its  attachment  to  the  root  of  the 
lung  thi-ough  tlie  pericardium.  Arrows  indicate  direction  of  inspiratory  move- 
ment of  various  parts  of  the  lung. 

expansion  of  the  upper  lobes,  the  lower  ribs  in  the  expansion  of  the 
lower  lobes,  the  diaphragm  promoting  the  expansion  of  the  M'hole 

In  the  act  of  inspiration  it  is  also  to  be  noted  that,  owing  to  the 
varjing  degree  of  extensibilit}^  of  the  different  structures  of  the  luno-, 
the  organ  expands  more  in  the  manner  of  a  Japanes3  fan — least  in  the 
neighbourhood  of  the  great  vessels  and  bronchi  (the  root  of  the  lung), 
most  in  the  outermost  zone  just  beneath  the  pleurae  (subplein-al  zone). 


288  A  TEXTBOOK  OF  PHYSIOLOGY 

The  infundibula  also  vary  in  size  in  these  different  zones  of  the  lung, 
being  largest  in  the  subpleural  zone,  and  smallest  at  the  root  of  the 
lung  (Fig.  153). 

The  two  surfaces  which  are  most  expanded  are  the  diaphrag- 
matic and  the  sterno-costal,  or  ventro -lateral.  In  general,  the  apical 
surfaces  remain  almost  stationary.  It  is  only  when  the  lungs  are  well 
ventilated  that  the  parts  most  remote  from  these  surfaces  of  direct 
expansion  are  brought  properly  into  action.  In  peoj)le  of  sedentary 
habits,  therefore,  such  parts  of  the  lung  fall  into  a  condition  of  disuse, 
and  receive  a  poor  supply  of  blood,  with  its  immunizing  properties. 
This  explains  why  phthisis  so  frequently  attacks  the  apex  of  the  lungs 
first. 

tT'!  When  inspiration  becomes  forced,  accessory  muscles,  such  as  the 
scaleni,  sterno-mastoid,  trapezius,  pectoral,  rhomboid,  and  serratus 
anticus  muscles  are  brought  into  play.  The  arms  are  fixed,  so  that 
the  muscles  passing  from  the  thorax  to  the  arms  can  come  into  play 
on  the  thorax.  A  patient  suffering  from  dyspnoea  sits  up,  and  grasps 
the  arms  of  a  chair. 

In  regard  to  expiration,  it  is  often  stated  that  quiet  exinration  is 
brought  about  by  a  passive  collapse  of  the  expanded  liuig,  the  thorax 
following  this  recoil  b}'  virtue  of  its  weight.  It  seems  probable  that 
such  a  process  is  aided  and  made  to  work  smoothly,  even  in  quiet 
expiration,  by  the  contraction  of  the  muscles  antagonistic  to  those 
concerned  in  inspiration.  Such  muscles  are  those  of  the  abdominal 
wall,  and  possibly  the  internal  intercostals. 

In  forced  expiration  many  muscles  are  called  into  pla}^  such  as 
the  serratus  posticus  inferior  and  the  rectus,  obliquus,  and  trans- 
versus  muscles  of  the  abdominal  wall. 


CHAPTER  XXXIII 

THE  REGULATION  OF  BREATHING 

The  movements  of  respiration  are  regulated  by  a  centre  which  has 
been  localized  in  the  medulla  oblongata.  This  localization  has  been 
made  by  watching  the  effects  upon  respiration  of  removal  of  the  brain 
from  above  downwards  and  from  below  upwards.  By  this  means  it 
is  found  that,  when  an  area  of  grey  matter  in  the  floor  of  the  fourth 
ventricle  is  damaged,  all  signs  of  respiratory  movement  completely 
cease.  To  this  centre  run  afferent  nervous  paths  from  various  parts 
of  the  body,  and  also  from  the  higher  nervous  centres;  from  it  pass 

Jmpu/sesC+and-) 
from  cerebral  cortex. 


Impulses  (.-)  from  nostrils. 
Impulses(-or+)from  skin. 
Impulses(-)from  larynx. 


Impulses  from  bn^s  limiting 
excessive  inspiration  ancK?) 
excessive  expiration 


lo  intercostals. 


To  diaphragm. 

To  accessory  muscles 
m  laboured  breathing. 


Vui.   13-i. — Diagram  illustrating  Regulation  <if  Rksiuratiun. 
(+  )  signifies  increased  ln'oalhing;  (  -  )  diminished  or  inhihitod  lircathing. 


efferent  channels  to  the  muscles  concerned  in  breathing.  .Such  fibres 
do  not  pass  directly  from  the  centre  to  these  muscles,  but  form  a 
synapse  with  the  anterio:-  horn  celh  in  the  spinal  coi'd,  from  which 
the  effector  nerves  to  the  muscles  of  respiration  arise.  Thus  the 
diaphragm  is  supplied  by  the  phrenic  nerve,  which  arises  from  the 
third,  fourth,  and  fifth  cervical  nerves;  the  intercostal  miiscles  from 
corresponding  branches  of  the  intercostal  nerves. 

Since  the  movements    of    breathing   persist   after  all  tlie  afferent 

289  10 


200 


A  TEXTBOOK  OF  PHY.SIOLOCiY 


nervou.s  connections  have  been  cut.  and  cease  when  the  circulation  is 
stopped,  it  is  clear  that  the  centre  is  de]3cndent,  in  the  first  place,  for 
its  activity  upon  the  blood  circulating  through  the  centre.  The 
respiratory  centre  mav  be  diagramniatically  re])rcsented  as  follows 
(Fig.  ir,-i): 

The  question  next  arises  as  to  what  is  the  condition  in  the  arterial 
blood  which  calls  the  respiratory  centre  into  action.  Experimentally 
it  can  be  shown  that  blood  which  has  been  shaken  up  with  some 
carbon  dioxide  gas  causes,  when  injected  into  the  peripheral  end  of  the 
vertebral  or  caiotid  artery — that  is,  towards  the  brain — an  immediate 
increa.se  in  the  de^jth  of  the  resjiirator}'  movements  (Fig.  155).  If 
injected  into  the  jugular  vein,  there  may  be  no  effect  upon  the 
respiration;  or  if  there  be  an  effect,  this  will  be  delayed,  and  not  by 


Fig.  155. — An.isthetized  Dcg. 

Upper  tracing,   respiration;  lower  tracing,   blood-jDressure.     The   arrow    marks 
injection  of  20  c.c.  of  COo  and  O2  saturated  blood  into  peripheral  carotid. 


any  means  marked.  When  injected  in  this  manner,  the  excess  of  COo 
may  all  be  eliminated  from  the  blood  during  its  passage  through 
the  lungs.  If  not  all  eliminated,  it  will,  after  fourteen  or  fifteen 
seconds  (the  time  of  the  lesser  circulation),  cause  an  effect  upon  res- 
piration— an  effect  which,  as  shown  by  the  time  of  delay,  is  central  in 
origin  (Fig.  156).  The  carbon  dioxide  of  the  blood,  therefore,  in  some 
way  affects  the  respiratory  movements  centrally  and  not  j)eri])herally. 
Again,  if  blood  to  which  a  little  acid,  such  as  lactic  or  butyric, 
has  been  added  be  injected  towards  the  brain,  the  respiratory  move- 
ments are  likewise  deepened.  Thus,  any  increased  acidity  of  the 
blood  affects  the  centre.  It  will  be  remembered  that  blood,  as  tested 
by  physical  methods,  is  neutral.  The  H  and  HO  ions  balance  one 
another.  Any  excess  of  H  ions  at  once  stimulates  the  respiratory 
centre. 


THE  REGULATIOX  OF  BREATHING  291 

Analyses  of  the  alveolar  air  of  the  lungs  reveal  the  fact  that  an 
individual  normally  so  regulates  his  respiration  that  the  pressure  or 
concentration  of  CO.,  in  the  alveolar  air  is  kept  constant,  varying  in 
different  individuals  from  about  4-5  to  6  per  cent.,  measured  at  normal 
barometric  pressure.  If  the  barometric  pressure  be  increased — as, 
for  example,  by  going  into  compressed  air  or  down  a  mine — the  per- 
centage of  CO.,  in  the  lung  falls  inversely  in  proportion  to  the  increase 
of  barometric' pressure;  if  it  be  decreased,  b}'  going  up  a  mountain, 
the  percentage  of  COg  rises  inversely  in  a  similar  proportion.  The 
partial  pressure  of  CO2  remains  the  same  in  the  lung  in  each  case. 
At  great  altitudes,  where  oxygen-want  comes  into  play,  this  no  longer 
holds  good,  for  the  balance  of  acid  and  base  in  the  blood  is  then  altered 
by  the  excretory  activity  of  the  kidney.  The  CO.^  is  reduced  propor- 
tionately by  increased  pulmonary  ventilation,  so  that  the  total  concen- 
tration of  acid  in  the  blood  remains  the  same.     It  is  clear,  then,  that 


Fig.  loU. — AN.EsiHtTizKD  Dog. 

Upper  tracing,   respiration;  lower  tracing,   blood-pressure.     The   arrow   marks   the 
injection  of  30  c.c.  of  CO.2  and  Oo  saturated  blood  into  the  jugular  vein. 

the  partial  pressure  of  carbon  dioxide  in  the  alveolar  air  and  in  the 
arterial  blood  going  to  the  respiratory  centre  normally  plays  an  im- 
portant part  in  bringing  about  respiration.  The  addition  of  CO2  to 
the  air  breathed  immediately  increases  the  depth  of  breathing — 
unconsciously  when  the  amount  is  small  (1  to  2  per  cent.);  conscious^,, 
with  marked  hyperpnoea,  when  the  amount  is  larger  (3  to  5  j)er  cent.). 
If,  on  the  other  hand,  the  tension  of  CO^  in  the  blood  be  reduced — as, 
for  example,  by  forced  deey)  breathing — this  is  followed  by  a  period 
of  apnoea  (cessation  of  breathing),  until  the  CO^  again  rises  to  a  partial 
pressure  sufficient  to  stimulate  the  centre  again. 

Normally,  the  breathing  movements  of  the  body  are  so  regulated 
that  the  partial  pressure  of  CO.,  in  the  blood  is  kept  almost  constants 
When  much  GOo  is  produced — as,  for  example,  in  hard  muscular  work 
— the  ventilation  of  the  lunss  is  greatlv  increased.     This  increased 


292 


A  TP]XTBOOK  OF  PHYSIOLOGY 


ventilation  is  then  due  in  part  to  the  lactic  acid  formed  within  the 
muscles.     This  increase  in  ventilation  is  seen  from  the  following  table : 


Resting 
Walking     . . 
Running    . . 
Swimming  in  cold  water 
Running  up  and  down  stairs  (greatest  \ 
possible  effort  of  a  noted  swimmer)  / 


Litres 

Besp. 

per  Minute. 

per  Minute. 

6-7 

. .       13-U 

24 

14 

60 

15 

90 

— 

190 


over  60 


It  will  be  seen  that,  with  moderate  exercise,  the  greater  ventilation 
is  brought  about  by  increased  depth  rather  than  increased  frequency. 
The  frequency  of  respiration,  even  the  sensation  of  depth  of  respira- 
tion, is  no  guide  to  the  actual  amount  of  ventilation.     Thus,  when 


'^'^'mmmitl^ 


\^V^vv 


llllllllllllllllllllllllllllllllllllllllllllllllllll 


lllllllllllllllllllllllllllllllllllllllll 


Fig.  157. 

Upper  tracing,  respiration  bj-  diaphragm  slip;  lower  tracing  blood-pressure.  During 
first  period  9*()  per  cent.  CO2  in  air;  during  second  period  10  per  cent.  CO2  with 
33  per  cent.  O2.     Time  every  two  seconds.     (F.  H.  Scott.) 


reclining  on  a  couch  after  a  sea-bathe,  one  has  the  sensation  of  deep 
prolonged  breaths,  and  imagines  a  great  ventilation  of  the  lungs  is 
taking  place.  When  measured,  such  ventilation  may  amount  to  but 
4  to  6  litres  joer  minute.  Frequent  shallow  breathing  may,  in  reality, 
put  but  little  air  into  the  lungs.  Such  breathing  takes  the  air  in  and 
out  of  the  mouth  and  trachea  rather  than  into  the  lung  alveoli. 

It  is,  then,  the  hydrogen  ion  concentration  of  the  arterial  blood 
to  which  the  respiratory  centre  responds.  During  normal  life  and 
health  the  centre  reacts  sharply  to  the  slightest  differences  in  the 
hydrogen  ion  concentration — differences  so  slight  that  they  cannot 
be  demonstrated  by  the  jDresent  methods  of  blood  gas  analysis; 
special  electrical  methods  are  required  to  show  them.  The  regulation 
of  the  hydrogen  ion  concentration  seems  to  depend  chiefly  upon  the 
kidney.     The  hj^drogen    ion  concentration  of  the  urine  alters  enor- 


THE  REGULATION  OF  BREATHING 


293 


mously  under  various  conditions — 25,000  times  as  great  as  the  limit 
within  which  that  of  the  arterial  blood  varies  during  rest.  Smce  an 
increase  of  2  millimetres  of  COj  pressvire  in  the  blood  increases  the 
resting  ventilation  of  the  lungs  by  over  100  per  cent.,  and  yet  causes 
a  scarcely  measurable  alteration  in  the  hydrogen  ion  concentration  of 
the  blood,  it  is  obvious  that  the  sensitivity  of  the  respiratory  centre  is 
extremely  great. 

Any  increase  in  the  percentage  of  oxygen  breathed,  and  of  the 
pressure  of  oxygen  in  the  blood,  does  not  diminish  the  excitability 
of  the  centre  to  CO.,  when  the  breathing  is  normal.  The  breath, 
however,  can  be  held  longer,  and  more  work  can  be  done  while  it  is 
held,  when  the  lungs  are  previouslj'  filled  with  oxygen  than  with  air. 
Athletes  may  rmi  a  quarter  or  half  mile  more  easily  and  quickly  if  they 
breathe  oxygen  before,  and  start  Avith  the  lungs  full  of  oxygen.  Breath- 
ing oxygen  before  and  after  the  race  prevents  stiffness.  The  explana- 
tion is  that  the  greater  oxygen  supply  lessens  the  formation  of  lactic 


Fig.  158. — A^^ESTHETIZED  Dog. 
Upper  tracing,  respiration;  lower  tracing,  blood-pressure;  white  space  =20  seconds. 
Between  the  arrows  (^"^7^4^  was  breathed. 


acid  in  the  muscles.  This  is  proved  by  the  fact  that  lactic  acid  appears 
in  the  urine  which  an  untrained  man  passes  in  the  next  hour  after 
a  hard  run;  but  if  he  wear  a  breathing  apparatus  (such  as  is  used  for 
rescue  work  in  mines,  etc.),  and  breathe  oxygen  during  the  run,  little 
or  no  lactic  acid  appears  in  the  urine.  The  increase  of  acid  concentra- 
tion tells  particularly  against  the  efficiency  of  the  heart  and  skeletal 
muscles.  Forced  breathing  can  be  carried  on  much  longer  and  to  a 
greater  extent  when  oxygen  is  used  instead  of  air,  probably  because 
the  forced  breathing  interferes  with  the  circulation  in  the  brain. 

When  a  very  low  percentage  of  oxygen  is  breathed,  there  results 
marked  hyperpnoea  (Fig.  158),  but  of  less  sudden  onset  than  that 
produced  by  COg.  The  same  is  true  in  animals  when  blood  de- 
ficient in  oxygen  is  injected  into  the  peripheral  carotid  (Fig.  159). 
The  effect  of  oxygen-want  is  not  noticed  until  the  O^  per- 
centage falls  below  14.      On  greater  reductions — e.g.,  to  5  per  cent.— 


294 


A  TEXTBOOK  OF  PHVSfOLOGY 


coTisciou.siiess  may  be  lost  before  the  hyperpiKea  develops.  For 
this  reason  the  effects  of  Avaut  of  oxj-gen  are  particularly  insidious. 
Hence  the  great  danger  of  entering  deoxygenated  air  which  collects  in 
wells,  sewers,  and  unventilated  ]mrts  of  coal-mines — men  are  over- 
come without  warning.  Thus  a  man  exploring  a  cavity  in  the  roof 
of  a  mine  breathed  the  deoxygenated  air  therein,  and  fell  miconscious 
off  a  short  ladder.  Breathing  the  purer  air  on  the  floor,  he  quickly 
recovered,  and,  jumping  up,  knocked  down  the  man  who  held  the 
ladder  "  for  making  him  tumble  off  the  ladder  !" 


Fig.  159. — Am.esthetized  Dog. 

Injection  of  15  c.c.  CO  blood  into  peripheral  carotid.     Upper  tracing,  respiration; 
lower  tracing,  blood-pressure.     Tinle  in  .seconds. 

To  effect  rescues  from  deoxygenated  air,  a  suitable  breathing 
apparatus  must  be  worn.  The  i)resence  of  such  air  can  be  tested  by 
the  use  of  a  cage-bird.  Owing  to  its  rapid  metabohsm,  the  bird  is 
affected  much  more  rapidly  than  a  man. 

In  animals,  it  has  been  shown  that  the  respiratory  centre  responds 
to  changes  in  the  temperature  of  blood  going  to  the  centre.  Warming 
the  blood  in  the  carotics  causes  increased  breathing:  cooling  it  tends 
to  diminish  breathing.  This  mechanism  probably  plays  a  great 
])art  in  those  animals  who  regulate  their  heat  loss  }nainlv  by  respira- 
tion, and  not  by  the  skin.  The  short,  sharp  panting  of  the  dog  is 
characteristic.     vSuch  respiration  is   very  frequent  and  shallow. 

The  respiratory  centre  is  co-ordinated  by  impulse^  which  reach  it 
through  afferent  nervous  channels,  but  considerable  divergence  of 
opinion  exists  as  to  the  amount  these  play  in  the  regulation  of 
respiration  in  man.     Special  acts  are  undoubtedly   due  to  nervous 


THE  REGULATION  OF  BREATHING  295 

stimulation.  Thus,  the  stimulation  of  the  upper  part  of  the  larynx 
by  a  crumb  "  going  the  wrong  way  "  induces  through  the  superior 
laryngeal  nerve  inhibition  of  inspiration,  followed  by  a  fit  of  coughing, 
by  which  the  crumb  is  expelled.  During  swallowing,  respiration  is 
inhibited:  it  is  impossible  to  breathe  and  swallow  at  the  same  time. 
This  is  owing  to  a  reflex  excited  through  the  glosso-pharyngeal  nerve. 
iStimulation  of  the  mucous  membrane  of  the  trachea  and  bronchi 
also  induces  coughing,  excited  reflexly  through  the  vagus  nerve. 
Stimulation  of  the  mucous  membrane  of  the  nose  with  a  mechanical 
irritant  induces  sneezing,  while  a  chemical  irritant,  such  as  an  irre- 
spirable  gas — e.g.,  a  high  percentage  of  COg,  ammonia  vapour, 
chlorine,  sulphur  dioxide — excites  spasm  of  the  glottis. 

Stimulation  of  the  walls  of  the  external  auditory  meatus  with  a 
foreign  body  or  by  a  plug  of  Avax  may  induce  coughing— a  reflex  excited 
through  a  twig  of  the  vagus  nerve  (the  alderman's  or  Arnold's  nerve) 
A  powerful  light  may  excite  sneezing.  The  "  stomach  cough  "  is  due 
to  reflex  irritation  of  the  vagus  nerve  supply  to  the  stomach.  "  Hic- 
cough," caused  by  a  spasmodic  contraction  of  the  diaphragm,  is 
probably  due  to  reflex  stimulation  of  the  centre,  excited,  perhaps, 
by  overdistension  of  the  stomach.  Persistent  hiccough  may  occur  in 
case  of  severe  illness — e.gr.,  carcinoma  of  the  stomach,  large  haemorrhage 
from  the  intestines,  etc. 

The  •'  winding  "  following  a  blow  in  the  pit  of  the  stomach  has 
been  attributed  to  stimulation  of  the  respu-atory  centre  through  the 
splanchnic  nerves.  The  "  knock-out  blow  "  on  the  chin  is  said  to 
jar  the  medulla  oblongata.  A  powerful  electrical  current  passed 
through  the  head  may  temporarily  arrest  the  respiration,  while,  if  it 
pass  through  the  heart,  it  may  throw  this  into  fibrillar  contraction, 
and  so  produce  death. 

The  nerve-supply  of  the  larynx  comes  from  the  superior  and  from 
the  inferior  (recurrent)  larjmgeal  branches  of  the  vagus.  The  superior 
laryngeal  is  the  sensory  nerve  to  its  mucous  membrane,  and  furnishes 
the  effector  supply  to  the  crico-thyroid  muscle.  The  recurrent  laryn- 
geal branch  of  the  vagus  supplies  the  motor  fibres  to  the  other  muscles. 
If  this  nerve  be  compressed  or  cut  on  one  side,  the  voice  is  lost,  because 
the  corresponding  vocal  cord  cannot  be  adducted.  Breathing  is  also 
somewhat  laboured,  because  it  cannot  be  abducted,  so  that,  when 
laryngoscopic  examination  is  made,  the  cord  does  not  move  as  it 
should  to  the  middle  line  on  phonation,  nor  away  from  it  on  inspira- 
tion. When  the  nerve  is  gradually  affected,  the  abductor  muscle, 
the  posterior  crico-arytenoid,  fails  first;  in  deep  ether  ansesthesia 
the-  adductor,  the  lateral  crico-arytenoid,  is  most  affected.  Paralysis 
of  the  superior  laryngeal  nerve,  besides  leading  to  loss  of  sensation, 
causes  hoarseness,  due  to  deficient  tension  of  the  vocal  cords  as  the 
result  of  jDaralysis  of  a  cricothyroid  muscle. 

Any  sudden  and   forcible   stimulation  of  the  skin  modifies  the 
respiratory  act — e.g.,  the  first  plunge  into  a  cold  bath.     It  is  customary 
to  flick  ^\'ith  ^\'et  towels  an  infant  which  does  not  breathe  after  bu-th, 
■or  to  smack  it. 


2116  A  TEX'J  BOOK  OF  PHV81Ui.()(;Y 

Exi30suic  to  a  cold  wind  induces  a  man  to  breathe  more  to 
keep  himself  warm . 

A  yawn  is  a  long,  deep  inspiration  through  the  widely-opened 
mouth;  and  at  the  same  time  the  bod}'  may  be  stretched  in  a  charac- 
teristic way.  This  furthers  the  circulation,  and  increases  the  oxygen, 
supply. 

A  sigh  is  a  long-draMii  inspiration,  followed  by  a  deep  expiration. 

The  Influence  of  the  Vagi. — The  division  of  one  vagus  alone  has 
little  effect  upon  the  respiratory  movements.  After  section  of  both 
vagi,  the  breathing  in  animals,  such  as  the  dog,  cat,  or  rabbit,  becomes 
slower  and  deeper;  inspiration,  normally  the  shorter,  becomes  longer 
than  expiration  (Fig.  160).     The  same  effect  is  obtained  if  the  two 


Normal  resjiiiMlicn 


Attr  Eedio'.i  of  uii 
vagus  the  ficquem ; 
ol  jespiiatioii  is  sumi 
Tiliat  dimiiiisl.od 


After  section  of  liotl. 
vagi  the  fieqiicui  y  <  f 
resi  iration  is  uiuli 
diniiuisLcd 


Excitiition  of  centi:il 
end  of  left  v;ifiis 
:  uue'.erat^s  rcs].i;a;  i.ui 


Time  li:  sec  oi.ds 

Fiu.  1()(». — Influence  or  tue  Vagus  upon  Respikatoky  Movements.      (Waller.) 

vagi  be  cooled  to  3''  C,  a  process  which  eliminates  any  irritative 
effect  of  a  current  of  injury  such  as  might  be  established  bj'  dropping 
a  cut  nerve  into  a  wound. 

When  non-polarizable  electrodes  are  placed  upon  the  vagus  nerve„ 
and  connected  with  a  string  galvanometer,  it  may  be  observed  that 
inflation  of  the  lungs  induces  a  marked  current  of  action,  deflation  a. 
less  marked  one.  In  the  animal  breathing  normally  an  electrical  varia- 
tion in  the  vagr.s  neive  has  been  recorded  synchronously  with  each 
inspiration,  indicating  the  passage  of  a  nerve  impulse  (Fig.  163) .  A  fork" 
cible  collapse  of  the  lung  ako  excites  a  negative  variation  in  the  vagus. 
It  has  been  shown  that  positive  inflation  (blowing  up)  of  the  lungs 
causes  the  diaphragm  to  come  to  a  standstill  in  the  expiratory"  position ; 
negative  ventilation  (sucking  air  out  of  the  lungs),  induces  inspiratory 


THE  REGULATION  OF  BREATHING  297 

standstill  of  the  diaphragm.  These  effects  are  abolished  when  the 
vagi  are  cut.  These  results  are  interpreted  as  showing  that  the  vagus 
nerve  terminates  in  tAvo  sets  of  nerve  endings,  one  set  stimulated  by 
stretching  of  the  lung  during  inspiration — inspiration-inhibiting — the 
other  stinnilated  bj'  collapse  of  the  lung — inspiration-inducing. 

Co-ordinating  the  action  of  all  the  skeletal  muscles  are  "  proprio- 
ceptive fibres,"  through  which  extension  inhibits  flexors,  and  flexion 
inhibits  exteixsors  (see  Fig.  400,  p.  683)-  It  is  most  probable  that 
each    respirator^'    act    should   consist    of   the  action  of    one    set    of 


Fig.  161. — Ixspiratoey  Spasm  of  thk  Diaphragm  pkoduced  bv  Excitation  of  thk 
Vagus  dtjeing  the  Period  shown  by  the  Signal  a,  h.     (Fredericq  and  Nucl.) 

The  down-stroke  represents  inspiration;  the  uj)-stroke  expiration. 

muscles,  and  inhibition  of  the  antagonists,  co-ordinated  by  afferent 
fibres.  The  vagus  nerve  endings  in  the  lungs  would  then  correspond 
to  nerve  endings  in  joints.  The  phrenic  nerves  contain  afferent 
fibres  from,  as  well  as  motor  fibres  to,  the  diaphragm.  The  evidence 
so  far  is  positive  for  the  action  of  onh'  one  set  of  nerve  endings 
— inhibiting  inspiration — and  these  only  when  the  inspiration  is 
large — be3'ond  the  normal  tidal  capacity — but  it  maj^  well  be  that  the 
string  galvanometer  is  not  a  delicate  enough  instrument  to  indicate 
normal  gentle  nerve  impulses.     We   may   conclude   that   while    the 


Fig.  162. — Expiration  Spasm  of  the  Diaphragm  produced  by  Weak 
Stimulation  of  the  Vagus.     (Fredericq  and  Nuel.) 

The  down-stroke  represents  inspiration;  the  up-stroke  expiration.     The  signal  line 
shows  the  duration  ot  stimulation. 

chemical  stimulus  of  acid  in  the  blood  is  alwajs  present  to  induce 
a  new  inspiration,  the  afferent  fibres  to  the  centre  reflexly  make 
the  muscles  work  smoothly  and  with  perfect  co-ordination. 

Stimulation  of  the  central  end  of  the  vagus  nerve  below  the  origin 
of  the  superior  laiyngeal  branch  with  moderate  induction  shocks 
quickens  respiration;  strong  excitation  causes  inspiratory  spasm  and 
may  bring  about  cessation  of  breathing  in  inspiration  (Fig.  161). 
Very  weak  induction  shocks  and  chemical  stimuli — e.g.,  strong  KCl 
solution — bring  about  slowing  of  respiration  or  standstill  in  the 
expiratory  phase  (Fig.  162). 


298 


A  TEXTBOOK  OF  PHYSIOLOGY 


To  sum  1 1]) — 

1.  The  respiratory  centre  is  normally  rhythmically  stimulated  by 
the  hytlrogen  ion  concentration  of  the  blood.  This  ion  concen- 
tration is  kept  constant  both  by  the  expiration  of  carbon  dioxide  and 
b}'  the  action  of  the  kidneys.  The  regulation  is  such  that  the  pressure' 
of  carbon  dioxide  in  the  alveolar  air  is  kept  remarkably  constant. 
Any  alteration  markedly  affects  the  breathing.  An  increase  of  0-22 
per  cent.  (2  to  3  per  cent,  in  inspired  air)  doubles  the  ventilation  of 
the  resting  man;  a  diminution  by  that  amount  causes  a  temporary 
cessation  of  breathing  (apnoea). 

2.  The  response  of  the  respiratory  centre  is  not  modified  under 
normal  conditions  by  the  amount  of  oxygen  in  the  alveolar  air.  When 
the  breath  is  held,  or  when  hard  muscular  work  is  being  performed, 
lactic  acid  is  produced  in  the  muscles  owing  to  lack  of  oxygen.  The 
breathing  of  oxygen  lessens  this  acid  production  and  its  effect  on 
the  respiratory  c&aiie. 


Tig.  163. — Figure  showing  the  Electrical  Changes  in  the  Vagus  Nerve  which 

ACCOMPANY    the    RESPIRATORY    AND    HEART   MOVEMENTS.       (Einthoveil.) 

V,  Electro vagogram ;  p,  respiration  record  (up,  insj^iration  ;  down,  expiration);  c,  ])ulso 

record. 


3.  In  certain  animals,  such  as  dogs,  which  depend  upon  breathing 
ior  the  regulation  of  heat  loss,  the  temperature  of  the  blood  affects 
the  action  of  the  respiratory  centre.  Similarly,  in  a  man  immersed 
in  a  very  hot  bath,  the  breathing  becomes  rapid. 

4.  Afferent  fibres  run  to  the  respiratory  centre  from  the  lungs 
in  the  vagus  nerve.  The  function  of  these  fibres  is  to  co-ordinate  the 
action  of  the  respiratory  centre  with  the  degree  of  distension  or  collapse 
of  the  lungs.  Of  the  two  sets  of  fibres,  those  which  normally  inhibit 
inspiration  are  the  most  generally  active.  B}^  the  action  of  these 
fibres,  waste  of  time  and  muscular  effort  is  saved  in  breathing. 
They  play  no  part  in  exciting  the  normal  rhythmic  activity  of  the 
respiratory  centre. 

5.  The  respiratory  centre  is  also  affected  by  nervous  imjjulses- 
from  other  parts  of  the  body,  which  induce  modifications  of  the 
respiratory  act. 


THE  REGULATION  OF  BREATHING 


!>!)<> 


Hyperpnoea,    Dyspnoea.  —  By 

hyperpnoea,  increased  volunie  of 
breathing  is  designated;  dyspnoea, 
on  the  other  hand,  applies  to  dis- 
tressful breathing.  Both  may  be 
induced  by  the  agencies  which 
excite  the  respiratory  centre  to 
increased  action,  such  as  excess  of 
carbon  dioxide,  Avant  of  oxygen, 
diminished  alkalinity  of  the  blood, 
due  to  acid  formation,  and  rise  in 
the  temperature  of  the  blood  (heat 
dyspnoea).  The  cardiac  dyspnoea 
of  heart  disease  is  chiefly  due  to 
Avant  of  oxygen. 

Apnoea. — The  condition  of  "'  no 
breathing"  is  due  to  a  lack  of 
chemical  stimulation  of  the  respi- 
ratory centres.  It  occurs  after 
forced  breathing  which  washes 
out  carbon  dioxide  from  the  blood 
(Fig.  164).  It  is  claimed  that 
there  exists  also  a  "  vagus  "  apnoea, 
produced  in  animals  by  repeated 
rapid  distension  of  the  liuigs  b}^ 
artificial  means.  By  this  means 
the  inspiration-inhibiting  fibres  of 
the  vagus  are  so  stimulated  that 
apnoea  ensues.  This  apnoea  may 
be  due  to  washing  carbon  dioxide 
out  of  the  l)lood,  but  it  is  more 
difficult  to  obtain  when  the  vagi 
are  cut;  it  is  stated  that  if  the 
ventilation  of  the  lungs  be  made 
with  an  indifferent  gas,  such  as 
hydrogen,  it  is  jDossible  to  obtain 
apnoea,  but  not  after  the  vagi  arc 
cut  (Figs  165,  166).  It  is  very 
doubtful  if  vagus  apnoea  occurs 
in  man,  for  it  has  been  shown  that 
apnoea  cannot  be  produced  if  the 
alveolar  air  percentage  of  CO2  is 
not  reduced  below  the  normal  CO., 
percentage. 

Periodic,  Grouped,  or  Cheyne- 
JStokes  Breathing. — Group  ])reath- 
ing  is  natural  in  young  children 
when  asleep,   and    in   hibernating 


(-i  o 

■A  — 
<      '1. 

s  6 

1^    n  '1 


O  o 


c5      g 


300 


A  TEXTBOOK  OF  PHYSIOLOGY 


animals.  Cheyne-Stokes  breathing  is  a  type  of  breathing  characterized 
by  a  Avaxing  and  waning  of  the  depth  of  the  respiratory  movements 
(Fig.  167).     Starting  from  a  state  of  apnoea,  the  respirations  gradually 


Fig.  165. — Cat,  Vagi  Intact.  Fig.  166. — Same  Cat  as  Fig.  165. 

(F,  H.  Scott.)  Vagi  Divided.     (F.  H.  Scott.) 

Upper  tracing,  thoracic  respiration  re- 
corded by  means  of  tambours;  lower 
tracing,  carotid  blood-pressure.  Period 
of  insufHation  of  lungs  shown  by  rise 
iu  line  of  respiratory  tracing.  , 

become  more  and  more  marked,  reaching  a  maximum  where  the  depth 
is  considerably  deeper  than  normal,  and  then  gradually  decline  again, 
and  cease,  to  be  followed  by  another  period  of  activity.  This  type  of 
breathing  occurs  clinically  in  cases  with  defective  circulation,  renal 


Fig.  167. — Chevxe-Stokes  Respiration. 


disease,  etc.,  and  is  due  to  oxygen- want  in  the  respiratory  centre,  which 
causes  it  to  act  in  a  periodic  manner.  Oxygen -want  causes  a  hyperpnoea 
Avhich  reduces  the  alveolar  percentage  of  COj.     Apnoea  then  results 


THE  REGULATION  OF  BREATHING  301 

until  oxygen  want  again  stimulates  the  centre.  Group  breathing  may 
be  abolished  by  the  giving  of  ox^^gen,  or  breathing  2  to  3  per  cent.  CO.,. 
It  frequently  occurs  at  high  altitudes,  owing  to  the  diminished 
partial  pressure  of  oxygen  in  the  rarefied  atmosphere.  It  can  be 
produced  experiment  all  j'  in  most  people  by  forced  breathing  for  two 
to  three  minutes.  After  the  subsequent  apnoea,  breathing  returns 
for  the  lirst  few  minutes  in  a  periodic  fashion.  If,  however,  the  lungs 
are  filled  with  oxygen  instead  of  air  at  the  end  of  the  forced  breathing, 
the  apnoea  is  of  much  longer  duration,  and  breathing  returns  in  a 
perfectly  regular  manner. 

Under  these  circumstances,  in  addition  to  the  ordinary  respiratory 
oscillations,  rhythmic  variations  of  pressure  frequentl}^  appear  in  the 
tracings  of  arterial  pressure.  These  variations  are  known  as  Traube- 
Hering  curves.  They  can  be  evoked  by  the  injection  of  a  little 
magnesium  sulj)hate  solution  into  the  circulation  of  the  dog  (Fig.  168). 
During  the  asphyxial  rise  of  arterial  pressure  in  the  curarized  dog, 


Fi3.  li)3. — Tkaube-Hering  Cukves  after  Injection  of  Magnesium  Sulphate. 

these  curves  occur,  and  also  after  injection  of  a  large  dose  of  morphia. 
In  conditions  of  ansemia  of  the  bulbar  centres,  produced  either  by 
tying  the  cerebral  arteries,  or  compression  of  the  brain,  and  after 
injection  of  chloroform  into  the  cerebral  arteries,  Traube  curves 
frequently  become  apparent. 

In  periodic  respiration  of  cerebral  origin,  the  waxing  and  waning 
of  the  blood-pressure  seems  to  be  due  to  the  effect  of  the  venous  blood 
on  the  vaso-motor  centre,  rather  than  on  the  heart.  Oxygen -want 
stimulates  the  respiratory  and  vaso-motor  centres  at  the  same  time. 

In  the  case  of  morphia,  the  respiratory  centre  injured  by  morphine 
does  not  react  to  the  acid  ions  in  the  blood  until  these  reach  a  con- 
centration which  injiu'es  the  heart.  The  pieriodic  fall  of  pressure  in 
this  case  is  due  to  an  asphyxia  of  the  heart.  When  the  breathing 
starts,  the  heart  recovers,  and  the  blood-jiressure  rises.  The  breathing 
ceases  once  more  so  soon  as  some  of  the  carbon  dioxide  in  the  blool 
has  been  exhaled. 


CHAPTER  XXXIV 
THE  EFFECTS  OF  EXCESS  OF  CARBON  DIOXIDE 

Breathe])  in  very  high  percentages,  30  per  cent,  and  upwards, 
CO.,  acts  as  an  anaesthetic  and  narcotic.  There  is  first  induced  a 
spasm  of  respiratioti .  then  consciousness  is  lost,  the  respiration  becomes 
quiet,  the  heart-beat  enfeebled,  and  death  ensues  owing  to  the  direct 
action  of  COo  upon  the  heart-muscle.  In  smaller  percentages  00^ 
has  an  excitatory  effect — at  first  upon  the  respiration,  then  upon  the 
circulation  also.  A  .small  increase  of  COg  in  the  air  breathed  in  causes 
a  marked  increase  in  pulmonary  ventilation.  With  an  increase  of 
3  per  cent,  this  becomes  noticeable  to  the  person  breathing;  with 
5  per  cent,  the  hyperpnoea  is  very  marked,  the  respirations  are  quick- 
ened, the  pulse  becomes  quicker  and  fuller;  with  6  per  cent,  there 
begins  to  be  a  retention  of  CO.^  within  the  body,  breathing  is  distressful, 
headache  develops,  ])rofuse  sweating  breaks  out.  The  blood-pressure 
is  greatly  raised,  and  the  pulse  may  be  felt  drumming  in  the  ears. 
Later,  the  mind  becomes  confused,  and  loss  of  consciousness  ensues. 
It  is  possible  for  a  man,  having  filled  his  lungs  with  oxygen,  and  then 
holding  his  breath,  to  run  himself  into  a  state  of  unconsciousness. 
In  such  cases,  as  mtich  as  11  per  cent,  of  C'O.,  is  found  in  the  alveolar 
air.  Athletes  who  run  themseh'CS  out  are  overcome  by  the  excess 
of  acid  in  the  blooi ! . 

Most  deaths  attributed  to  excess  of  carbon  dioxide  are  in  reality  due 
to  oxygen-want.  High  percentages  of  COg  sufficient  to  cause  death 
cause  spasm  ^ »f  the  glottis  and  choking.  Divers  have  often  been  over- 
come by  an  exc(^s,s  owing  to  defective  supply  of  air  in  deep  water. 
At  a  pressure  of,  say,  4  atmospheres  (100  feet)  there  is  four  times 
the  volume  of  air  in  the  helmet,  and  to  ventilate  it  four  times  as 
much  air  must  be  pumped  through  it  as  at  I  atmosphere.  It  has 
not  been  recognized  until  recently  that  the  deeper  the  diver  goes,  the 
more  air  must  be  given  him. 

Effects  of  Deficiency  of  Carbon  Dioxide. — If  carbon  dioxide  be 
washed  out  of  the  body  by  forced  breathing,  the  desire  to  breathe 
disappears  for  a  time,  and  a  condition  of  apnoea  ensues,  which  may 
la.st  as  long  as  two  to  three  minutes,  and  even  longer  (Fig.  164). 
If  oxygen  be  forcibly  breathed,  the  apnoea  may  last  five  to  seven 
minutes,  and  even  nine  minutes.  Forced  breathing  produces  a  curious 
condition  of  spasm  of  the  hand,  sensations  of  "  pins  and  needles  "  in 
the  hands  and  feet,  with  coldness  and  pallor,  and  a  sensation  of  tight- 

302 


THE  EFFECTS  OF  EXCESS  OF  CARBON  DIOXIDE      303 


ness  round  the  head.     The  forced  breathing  of  oxygen  is  unaccom- 
panied by  such  feelings. 

Probably  a  certain  tension  of  CO.,  is  required  in  the  body  fluids 
for  the  proper  carrying  out  of  many  bodily  processes.  If  this  be 
lessened,  such  processes  are  impaired. 

Effects  of  Excess  of  Oxygen. — Breathing  an  excess  of  oxygen  under 
normal  conditions  does  not  cause  increased  oxidation  of  the  bod}-.  The 
body  cannot  be  fanned  Uke  a  fire  into  rapid  combustion.  The  nervous 
system  sets  the  rate  of  activity  of  the  tissues.     When,  however,  hard 


ft 


Fii;.  169. — Section  of  Luxa  showing  Exudation  in  Bronchial  Tube  and  Alveum 
OF  Lung  produced  by  Three  Atmospheres  of  Oxygen.     (Bulloch  and  Hill.) 

muscular  ^^■ork  is  being  performed,  an  excess  of  oxygen  in  the  alveolar 
air  enables  more  work  to  be  done.  This  is  because  it  prevents  the 
formation  of  lactic  acid  in  the  muscles,  and  thus  lessens  the  hyperpnoea, 
Avhieh  renders  work  inelficient,  and  maintains  the  force  of  the  heart. 
High  percentages  of  O2 — e.g.,  3  atmospheres — act  as  an  irritant 
to  the  lungs,  induce  pneumonia  (Fig.  169),  lower  the  metabolism, 
and  cause  convulsions.  Breathing  of  pure  ox3'geii  for  several 
hours  at  ordinary  atmospheric  pressure  does  not  have  any  harmful 
effect,  but  it  causes  pneumonia  if  breathed  continuously  for  a  dav  or 


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A  TEXTBOOK  OF   PH>'SlOLO(JY 


Iavo.     An  atniosphcro  containing  under  70  ])cr  cent,  of  oxygen  can  he 
breathed  witli  impimily  for  any  length  of  time. 

The  Effects  oi  Want  of  Oxygen. — The  s3nnptom.s  produced  vary 
greatly  according  to  the  rate  at  which  such  want  is  produced.  When 
immediate,  as  on  breathing  into  the  lungs  marsh-gas,  nitrogen,  or 
hydrogen,  there  is  rapid  loss  of  consciousness,  followed  by  convul- 
sions (Fig.  170),  with  a  slight  rise  of  blood-j)ressure,  followed  by 
<;cssation  of  respiration,  broken  only  by  occasional  inspiratory  gasps, 
iall  of  blood-pressure,  due  to  vagus  inhibit 'ou.  and  death. 


l^iG.  170. 

Uj)))or  tracing,  respiration  recorded  by  diaphragm  .-lip:  lower  tracing,  carotid  blood- 
pressure.  Time=t\vo  f-cconds.  During  period  indicated  5  per  cent,  oxygen  in 
nitrogen  was  inhaled.     (F.  H.  Scott.) 


A  match  or  candle  will  not  burn  when  there  is  less  than  17  per 
cent,  of  oxygen  in  the  atmosphere,  but  a  man  feels  no  inconvenience 
until  the  oxygen  percentage  falls  below  14  per  cent.  Then  there 
supervenes  a  hyperpnoea  of  gradual  onset,  Avith  a  slight  rise  of  blood- 
pressure,  increased  pulse-rate,  and  marked  cyanosis;  and  when  about 
-6  per  cent,  is  reached,  lois  of  consciousness  quickly  takes  place.  At 
first,  on  breathing  14  to  10  per  cent.  O2,  there  is  a  slight  exaltation. 
The  person  has  tlie  greatest  confidence  in  himself,  and  is  quite  con- 
fident that  he  is  '"  all  there.''  whereas,  in  reality,  his  mental  capacity 
is  greatly  affected.  The  breathing  is  deepened,  but  no  dyspnoea 
is  present.     Then,  at  about  8  per  cent.,  without  warning,  or  possibly 


THE  EFFECTS  OF  EXCESS  OF  CARBON  DIOXIDE     305 

^vith  slight  dyspnoea  or  air-hunger,  consciousness  may  be  lost,  followed 
by  i^aratysis,  or  in  some  cases  the  parah'sis  of  the  muscles,  particularly 
those  of  the  limbs,  may  precede  the  loss  of  consciousness.  Thus,  in 
a  balloon  ascent,  at  29.000  feet,  Coxwell,  although  suddenly  finding 
.himself  jiaralyzed  in  his  limbs,  Avas  able  to  pull  M'ith  his  teeth  the 
safet\'-valve  rope  of  the  balloon,  and  to  save  himself  and  Glaisher. 
In  the  case  of  the  ascent  of  Croce-Spinelli,  Sivel,  and  Tissandier,  the 
aeronauts  were  all  paralyzed  suddenly  before  they  could  breathe 
from  the  oxygen  bags  with  which  they  had  provided  themselves. 
Similar  symptoms  follow  gradual  poisoning  by  carbon  monoxide  or 
€oal-gas.  Miners  display  the  same  lack  of  judgment  when  affected 
by  carbon  monoxide. 


Xormal 
respiration 


1st  stage 
(prolonged 
expiration) 


2nd  stajje 
(exj)iratjry 
eonvulsionsj 


3rd  si  age 
(exhaustion ) 


Time  iu  seconds 


Fig.  171. — Asphyxia  Tracing  :    Rabbit.     (Waller. 
The  line  falls  with  inspiration,  rises  with  expiration. 


In  carbon  monoxide  jjoisoning,  the  lack  of  oxygen  is  brought  about 
by  the  decreased  oxygen-carrying  capacity  of  the  blood,  due  to  the 
iormation  of  COHb.  The  symptoms  begin  to  sho  v  themselves  Avhen 
the  blood  is  one-fourth  saturated.  With  50  per  cent,  saturation,  thf 
mental  sj-mptoms  become  mai-ked.  and  the  slightest  exertion  is  danger- 
ous, since  it  may  bring  on  convulsions  and  death.  It  is  dangerous  to 
breathe  air  containing  as  little  as  0-05  per  cent.  CO,  for  the  affinity 
of  CO  for  Hb  is  about  150  times  that  of  0.,.  There  is  5  to  6  per  cent. 
CO  in  coal-gas,  as  much  as  30  per  cent,  in  water-gas,  3  per  cent,  or 
more  in  after-damp  after  explosions  in  mines.      CO  03curs  in  con- 

•20 


:o6 


A  TEXTBU(JK  OF  PHYSIOLOGY 


lined  places  where  there  is  fuel  burning  with  deficient  oxygen-.su])ply.. 
To  relieve  CO  poisoning,  oxygen  should  be  administered,  and  artificial 
respiration  ])erfornied . 

The  whole  of  the  body  is  very  susceptible  to  a  deficiency  of  oxygen; 
it  leads  to  acid  formation  and  lessened  alkalinity  of  the  tissues. 
Oedema,  cloudy  swelling,  and  fatty  degeneration,  according  to  recent 
research,  are  associated  with  such  diminished  alkalinity.  Lack  of 
oxygen  greatly  affects  the  working  capacitj'  of  the  muscles,  especially 
of  the  heart-muscle.  Irritant  gas  poisons,  by  prtducing  cede n: a  of  the 
lungs,  cause  oxygen-want.  Recoveiy  is  very  slow  or  may  not  occur  after 
prolonged  oxygen-want.  Symptoms  of  oxygen-want  may  also  he 
induced  by  poisons  which  form  methaemoglobin.  Such  poisons  are  the 
chlorates  of  sodium  and  potassium,  nitrites,  and  dinitrobenzene. 


EiG.  172. 

T,  Tracing  of  tb-racic  uiovemcnts;  A,  liacing  of  abdominal  movements.  In  top 
tracing  is  sho-wn  the  respiratory  movements  and  time  (a — oj)  during  which 
hreath  could  be  held  in  Turin.  In  lower  tracing  the  same  at  Monte  Rosa 
(l.')003  feet  above  sea-level).  The  increased  depth  of  respiration  and  inability 
to  hold  the  breath  long  is  well  seen.     (Mosso.) 


Asphyxia  is  caused  by  interference  with  the  ventilation  of  the  lungs. 
It  may  be  produced  by  breathing  an  irrespirable  gas,  as  already 
described,  but  it  may  also  be  produced  by  such  means  as  occlusion  of 
the  trachea  or  opening  the  chest  cavity.  When  studied  experiment- 
alty — as,  for  example,  by  clamping  the  trachea — asphyxia  is  di^•ided 
into  three  stages  (Fig.  171): 

1.  The  stage  of  increasing  dyspnoea. 

2.  The  convulsive  stage. 

3.  The  stage  of  exhaustion. 

When  the  trachea  is  clamped,  the  first  stage  lasts  about  a  minute. 
The  breathing  is  markedly  increased  in  depth,  expiration  being  pro- 


THE  EFFECTS  OF  EXCESS  OF  CARBON  DIOXIDE      307 


Joiiged;  the  heart-beat  is  increased  in  force  and  frequenc}';  the  blood- 
pressure  rises;  the  tongue  in  the  case  of  an  animal,  the  lips  and  face 
also  in  the  case  of  rnan,  darken  to  a  purplish  hue. 

In  the  second  stage,  the  respiration  becomes  violent  and  con- 
vulsive; the  blood-pressure  remains  high,  due  to  the  vaso-constriction 
produced;  the  heart-beats  show  the  sign  of  vagus  inhibition;  the 
duskiness  of  the  mucous  membranes  increases. 

In  the  thh'd  stage,  the  breathing  and  convulsions  practically 
cease;  the  heart  beats  feebly  and  irregularly;  the  blood-j)ressure 
gradually  falls,  and  the  tracing  shows  marked  undulations  of  pressure, 
known  as  the  Traube-Hering  Avaves  (Fig.   lOS).     The  pupils  become 


Liens 


Arc -light 


Microscope 


Frog- 


Screen 


Compressed  air 
cylinder 


Fig.   173. — Diagram  of  Apparatcs  by  which  Eff:;ct  of   Compression  and 
Decompression  is  stjdied  upon  Capillaries  of  Frog's  Web. 


dilated,  the  mucous  membranes  become  pale  and  anaemic,  faeces  and 
urine  may  be  voided.  Post  mortem,  the  right  side  of  the  heart  is 
found  distended  with  blood,  the  left  side  contracted  and  empty.  The 
great  veins  and  the  lungs  are  also  engorged  with  blood. 

Effects  of  Diminished  Atmospheric  Pressure. — Another  train  of 
symptoms  due  to  oxygen-want  is  that  known  as  "  mountain  or  alti- 
tude sickness."  It  effects  aeronauts  as  well  as  mountain-climbers. 
In  their  case,  the  oxygen-want  results  from  the  d;min'shed  atmo- 
sj)heric  pressure,  and  consequent  reduction  in  the  partial  pressure  of 
the  oxygen  in  the  blood.  The  symptoms  are  headache,  nausea, 
distress  in  breathing,  especially  upon  exertion.  Mountain  sickness 
frequently  begins  at  altitudes  of    6,000  to    10,000  feet,   particularly 


308 


A  TEXTBOOK  OF  PHYSIOLOGY 


if  the  ascent  has  been  fairly  rapid  b}^  railwaj^,  so  that  no  adapta- 
tion takes  place  during  the  journey.  It  is  suggested  that  the  oxygen- 
want  leads  the  kidney  to  excrete  more  base  than  acid  from  the  blood, 
and  thus  increasing  the  breathing,  lessens  the  concentration  of  carbon 
dioxide  in  the  blood  and  alveolar  air.  By  lessening  the  concentration 
of  CO,  in  the  alveolar  air,  that  of  oxygen  is  increased. 

The  effect  of  oxygen-want  is  well  seen  in  the  inability  vohnitarily 
to  hold  the  breath  for  any  length  of  time  (Fig.  172).  Acclimatization 
takes  place  in  about  eight  to  ten  days.     This  is  due,   in  the   first 


Fig.  174. — View  of  Chamber  used  for  Study  of  Effects  of  Compression  and 
Decompression  on  Man:  Workman  Inside.     (Hill  and  Greenwood.) 

The  chr^mber  is  fitted  with  electric  belt,  electric  light,  telephone,  observation  window, 
compression  pipe  from  gas-engine,  decompression  tap. 


place,  to  a  concentration  of  the  blood-plasma,  followed  by  an  increased 
formation  of  blood-corpuscles  and  hsemoglobin  (Fig.  18).  Hence 
the  oxygen-carrying  power  of  the  blood  is  increased ;  an  alteration  in 
the  acid  concentration  of  the  plasma  compensates  for  the  diminished 
jjartial  pressure  of  carbon  dioxide. 

On  the  strength  of  determinations  of  the  partial  pressure  of 
oxygen  in  the  blood,  by  the  CO  method  (p.  273),  it  is  asserted 
that  compensation  is  brought  about  by  secretory  activity  of  the  king 
epithelium,  since  the  oxygen-pressure  of  the  arterial  blood  has  been 


THE  EFFECTS  OF  EXCESS  OF  CARBON  DIOXIDE     cOO 

found  to  be  35  millimetres  above  the  oxygen-pressure  in  the  alveolar 
air.     But  there  are  doubts  as  to  the  validity-  of  this  method. 

Airmen  usuallj'  suffer  at  altitudes  from  15,000  to  20,000  feet.  In 
their  case  there  is  no  evidence  of  acclimatization  to  the  effects  of  high 
altitudes.     Administration  of  oxygen  mitigates  these  ill  effects. 


<*» 


Fig.  175. — Air  Bubbles  Set  Free  ix  Vessels  of  Heart  after  Rafid 
Decompression,     (v.  Schrotter.) 

Increased  Atmospheric  Pressure — Caisson  Diseass. — In  contra- 
distinction to  the  effects  of  diminished  barometric  pressure,  increased 
barometric  pressure  in  itself  produces  no  untoward  symptoms.   "  Caisson 


Fi  ;.   176. — To  show  Gas  Bubbles  in  Arteries  and  Veins  of  Intestines  after 
Rapid  Decompression,     (v.  Schr6:ter.) 


disease  "  and  "  diver's  palsy"  result  from  the  effects  of  decompression 
from  a  high  atmospheric  pressure,  not  from  the  compression.     Caissons. 


310  A  TEXTBOOK  OF  PHYSIOLOGY 

are  steel  chaniljers  filled  with  compressed  air,  and  provided  with  air- 
locks, used  for  excavating  tunnels  and  foundations  of  bridges  under 
water.  Divers  are  encased  in  a  dress  into  which  air  is  ]  umped 
at  a  pressure  just  greater  than  that  of  the  superincumbent  water. 

A 


^^'^....^^^ffo%    A 


^"•'■■:^^7 


-'-->-'•-    '*'.^^^-^- 


>/    ^ 


•A 


t,-"^'         .t*^   •/.''  .,i't 


-"'^^i^-*'  » 


It    •      • 


Fig.  177.— -4,  Normal  Kidney  of  Cat;  i?,  Kidney  of  Cat  DEcoJMrr.issLD  Rapidly 
FROM  Eight  Atmospheres  prepared  by'  Same  Method. 

At  a  pressure  of  2  to  3  atmosi)hercs  it  becomes  impossible  to  Avhistle 
or  whisper,  owing  to  the  density  of  the  air.  There  are  no  sensations, 
beyond  this  disability,  to  indicate  the  abnormal  pressure.  The  pressure 
in  the  middle  ear  has  to  be  equalized  by  opening  the  Eustachian 
tube  during  the  rise  of  atmospheric  pressure.     This  can  be  effected 


THE  EFFECTS  OF  EXCESS  OF  CARBON  DIOXIDE     311 

I)y  swallowing,  or  b}'  an  expiratory  effort  made  with  the  mouth  and 
nose  shut. 

The  symptoms  of  sickness  range  from  small  pains  in  the  joints 
and  muscles,  known  as  '"  bends,"  to  sudden  paralyses  or  death.  The 
subject  has  been  thoroughly  studied  experimentally  (Figs.  173,  174)  and 
the  cause  of  the  troiible  is  now  clearly  understood.  At  high  pressures 
the  blood  and  fat  take  up  large  quantities  of  nitrogen  in  simple  physical 
soAition.  When  the  pressure  is  reduced  rapidly,  the  nitrogen  becomes 
freed  in  the  circulation,  and,  becoming  lodged  as  bubbles  of  gas  in 
various  parts  of  the  body,  produces  symptoms  of  varying  severity 
according  to  the  degree  of  damage  and  the  site  of  injury  (see 
Figs.  17.1-178).  Rapid  decompression  is  therefore  the  danger.  The  rate 
of  decompression  must  be  regulated  according  to  the  pressure  and  period 
of  saturation  of  the  body.     A  diver  who  has  been  for  a  short  time  at 


Pig.  178. — ^Xeirotic  Areas  (Pale)  in  Posterior  Columns  of  Spinal  Cord,  frcm 
A  Fatal  Case  of  Compressed  Air  Illness,     (v.  Sehrotter.) 

a  great  depth  may  be  relatively  more  quickly  decompressed  than  a 
man  who  has  been  working  several  hours  in  a  less  pressure.  The 
decompression  is  carried  out  in  stages,  for  it  is  safe  to  allow  a  certain 
amount  of  supersaturation,  as  bubbles  do  not  easily  form  in  the  blood 
— e.g.,  the  diver  ascends  rapidly  from  a  depth  of  100  feet  (4  atmos- 
pheres) to  33  feet  (2  atmospheres),  and  pauses  there  for  some  time, 
meanwhile  exercising  his  muscles  to  accelerate  the  circulation  and 
ventilation  of  the  lungs,  and  so  wash  the  excess  of  dissolved  nitrogen 
out  of  his  bod}'.  He  then  returns  to  the  smface.  For  each  atmos- 
phere of  air  the  water  of  the  body  dissolves  about  0-8  per  cent,  of 
nitrogen.  As  fat  dissolves  five  to  six  times  as  much  nitrogen  as 
water,  there  is  particular  danger  of  bubbles  forming  in  the  nervous 
ti.ssues.     All  fat  men  are  excluded  from  work  in  deep  water. 

The  solution  of  nitrogen  in  the  body  fluids  durmg  compression 
and  the  giving  out  of  the  excess  of  dissolved  nitrogen  dining  decom- 
pression has  b?en  stuelied  on  subjects  who  drank  a  epiart  or  so  of  water 
just  before  entering  the  chamber,  and  collected  samples  of  their  mine 
at  various  stages  of  compression  and  decompression.  The  nitrogen 
dissolved  in  these  samples  was  pumped  out  by  means  of  the  mercurj' 
gas  pump  and  estimated. 


CHAPTER  XXXV 
THE  PRINCIPLES  OF  VENTILATION 

Our  comfort  or  di.scouifort  in  crowded  rooms  and  shut-up  places 
depends  on  the  chemical  purity  of  the  air  only  in  so  far  ?.s  it  afiects 
the  olfactory  sense,  but.  to  a  vast  degree,  on  the  influence  of  the 
temperature,  relative  humidity,  and  the  variations  of  these  qualities 
of  the  air,  which  act  on  the  great  field  of  cutaneous  sensibility.  When 
it  is  stated  that  the  chemical  purity  is  of  little  account,  the  proviso 
is  made  that  the  air  is  only  altered  by  the  presence  of  healthy  human 
beings,  and  is  neither  renclered  poisonous  by  the  escape  of  coal-gas,  or 
other  noxious  trade  product,  nor  deoxygenated  by  the  oxidative  pro- 
cesses of  the  soil,  as  it  is  in  mines,  reference  l^eing  made  only  to  the 
discomfort  and  ill-health  caused  by  the  deficient  ventilation  of,  or 
bad  methods  of  heating,  dwelling-houses,  schools,  factories,  theatres, 
chapels,  etc. 

The  chemical  purity  of  the  air  has  to  be  considered  from  three 
points  of  view- — the  concentration  of  carbon  dioxide,  the  concen- 
tration of  oxj^gen,  the  su]iposed  presence  of  organic  poison  exhaled  in 
the  breath. 

It  is  commonly  supposed  that  any  excess  of  COo  acts  as  a 
poison.  The  truth  of  the  matter  is  quite  otherwise;  for,  Avhat- 
ever  the  percentage  of  CO.,  in  the  atmosphere  may  be,  that  in  the 
pulmonary  air  is  kept  constant,  as  we  have  seen,  at  about  5  per  cent, 
of  an  atmosphere  by  the  action  of  the  respiratory  centre.  It  is  there- 
fore impossible  that  any  excess  of  CO.,  should  enter  into  our  bodies 
when  we  breathe  the  air  of  the  worst -ventilated  room,  in  which  the 
percentage  of  CO.^  assuredly  does  not  rise  above  0-5  per  cent.,  or  at 
the  outside  1  per  cent.  The  only  result  from  breathing  such  an 
excess  of  COg  is  a  slight  and  unnoticeable  increase  in  the  ventilation 
of  the  lungs.  The  increased  ventilation  is  exactly  adjusted  so  as  to 
keep  tl  e  concentration  of  CO.,  in  the  lungs  at  the  normal  5  per  cent, 
of  an  atmosphere. 

At  each  breath  we  re  breathe  into  our  lungs  the  air  in  the 
nose  and  large  air-tubes  (the  dead-space  air),  and  about  one-third 
of  the  air  which  is  inhaled  into  the  lungs  is  "  dead-space  "  air. 
Thus,  no  man  breathes  pure  outside  air  into  his  lungs,  but  air 
contaminated  perhaps  by  one-third  or  (on  deep  breathing)  by  one- 
tenth  with  expired  air.  When  a  child  goes  to  sleep  with  its  head 
partly  buried  under  the  bedclothes,  or  in  a  cradle  with  the  air  con- 
fined  by   curtains,   he   rebreathes  the  expired  air  to  a  still  greater 

312 


THE  PRINCIPLES  OF  VENTILATION  313 

extent,  as  do  all  animals  that  snuggle  together  for  warmth's  sake. 
Not  only  the  newborn  babe  sleeping  against  its  mother's  breast,  but 
pigs  in  a  stye,  young  rabbits,  rats  and  mice  clustered  together  in  their 
nests,  young  chicks  under  the  brooding  hen,  all  alike  may  breathe 
a  higher  percentage  than  that  legally  allowed  in  spinning  mills  or 
Aveaving  sheds.  To  rebreathe  one's  own  breath  is  a  natural  and 
inevitable  performance ;  to  breathe  some  of  the  air  exhaled  by 
another  is  the  common  lot  of  men  who,  like  animals,  have  to  crowd 
together  and  husband  their  heat  in  fighting  the  inclemency  of  the 
temperate  and  Arctic  zones.  By  a  series  of  observations  made  on 
rats  confined  in  cages  with  small  ill-ventilated  sleeping  chambers,  it 
has  been  shown  that  the  temperature  and  humidity  of  the  air — not 
the  carbonic  acid  and  oxygen  concentration  of  the  air — determines 
whether  the  animals  stay  inside  the  sleeping-room  or  come  outside. 
When  the  air  is  cold,  thej^  hke  to  stay  inside,  even  when  the  carbonic 
acid  rises  to  4  per  cent,  or  5  per  cent,  of  an  atmosphere;  when  the 
sleeping  chamber  is  made  too  hot  and  moist,  the}"  come  outside. 

In  breweries,  the  men  who  tend  the  fermentation  vats  work  for 
long  hours  in  concentrations  of  CO^  of  0-5  to  1-5  per  cent.  Such 
men  are  no  less  healthy  and  long-hved  than  those  engaged  in  other 
processes  of  the  brewing  trade. 

The  ox\'gen  in  the  worst-ventilated  schoolroom,  chapel,  or  theatre, 
is  never  lessened  by  more  than  1  per  cent,  of  an  atmosphere.  The 
ventilation  through  chink  and  cranny,  chimney,  door,  and  window, 
and  the  porous  brick  wall,  suffices  to  prevent  a  greater  diminution  of 
the  oxygen  concentration.  In  all  the  noted  health  resorts  of  the 
Swiss  mountains,  such  as  St.  Moritz,  the  concentration  of  oxygen  is 
lessened  considerably  more  than  this.  On  the  high  plateaux  of  the 
Andes  there  are  great  cities:  Potosi,  with  100,000  inhabitants,  is  at 
4,165  metres  (barometric  pressure  about  440  mm.  Hg).  Railways 
and  mines  have  been  built  even  at  altitudes  of  14,000  to  15,000  feet. 
Owing  to  the  nature  of  the  chemical  combination  of  oxj^gen  with 
haemoglobin,  man  can  adjust  himself  to  verj'  great  variations  in 
oxygen  concentration.  At  Potosi,  girls  dance  half  the  night,  and 
toreadors  display  their  skill  in  the  bull-ring.  All  the  evidence  goes 
to  show  that  it  is  only  when  oxygen  is  lowered  below  a  pressure  of 
14  per  cent,  to  15  per  cent,  of  an  atmosphere  that  signs  of  oxygen- 
want  arise.  A  diminution  of  1  per  cent,  of  an  atmosphere  has  not  the 
slightest  effect  on  our  health  or  comfort. 

A  commonly  accepted  hypothesis  is  that  organic  chemical  poisons 
are  exhaled  in  the  breath,  and  that  the  percentage  of  CO.2  is  a 
valuable  guide  as  to  the  concentration  of  these.  It  is  believed 
necessary  to  keep  the  C0.>  below  0-1  per  thousand,  so  that  the 
organic  poisons  may  not  collect  to  a  harmful  extent.  The  evil 
smell  of  crowded  rooms  is  accepted  bj'  most  as  unequivocal  evidence 
of  the  existence  of  organic  chemical  poison  in  the  exhaled  breath. 
This  smell,  however,  is  only  sensed  b}',  and  excites  disgust  in.  one 
who  comes  to  it  from  the  outside  air.  He  who  is  inside,  and  helps 
to  make  the  "  fugg."  is  whoUv  unaware  of  the  sp.me.  and  unaffected 


eo- 


314  A  TEXTBOOK  OF  PHYSIOLOGY 

by  it.  While  wc  naturally  avoid  any  smell  that  excites  disgust  and 
jnits  us  off  our  appetite,  yet  the  offensive  quality  of  the  smell  does 
not  prove  its  poisonous  nature.  On  descending  into  a  sewer,  after 
the  first  ten  minutes  the  nose  ceases  to  smell  the  stench ;  the  air  therein 
is  usually  found  to  be  far  freer  from  bacteria  than  the  air  in  a  school- 
room or  tenement. 

If  we  turn  to  foodstuffs,  we  recognize  that  the  smell  of  alcohol  and 
of  Stilton  or  Camembert  cheese  is  horrible  to  a  child  or  dog,  while  the 
smell  of  putrid  fish — the  meal  of  the  Siberian  native — excites  no  less 
disgust  in  an  e])icure,  who  welcomes  the  cheese.  Among  the  hardiest 
and  healthiest  of  men  are  the  North  .Sea  fishermen,  who  sleep  in  the 
cabins  of  trawlers  reeking  with  fish  and  oil,  and  for  the  sake  of  warmth 
shut  themselves  up  until  the  lamp  may  go  out  from  want  of  oxygen. 
The  stench  of  such  surroundings  may  effectually  put  the  sensitive, 
untrained  brain-Avorker  off  his  appetite,  but  the  robust  health  of  the 
fisherman  proves  that  this  effect  is  nervous  in  origin,  and  not  due  to 
a  chemical  organic  poison  in  the  air. 

The  supposed  existence  of  organic  chemical  poison  in  the  expired 
air  is  based  upon  experiments  in  Avhich  either  the  condensation  water 
obtained  from  the  breath,  or  water  which  was  used  several  times 
over  to  wash  out  the  trachea  of  dogs,  was  injected  into  guinea-pigs 
and  rabbits.  The  water  Avas  injected  subeutaneously  and  in  large 
amounts,  and  produced  signs  of  illness,  collapse,  and  death. 

vSuch  experiments  have  been  repeated  b}^  many  others,  and  with 
negative  results  by  those  whose  methods  of  work  demand  most  respect. 
A  few  confirmatory  results  have  been  obtained  by  methods  of  experi- 
ment which  are  truly  absurd  in  their  conception:  1  to  2  c.c.  of  con- 
densation water  (obtained  by  breathing  for  many  hours  through  a 
cooled  flask)  have  been  injected  into  a  mouse  weighing  13  grammes 
or  so.  This  is  equivalent  to  injecting  5  litres  of  water  into  a  man 
weighing  65  kilos.  Who  would  not  be  made  ill  by  the  injection  of 
about  9  pints  of  cold  water  beneath  his  skin  ?  It  has  been  shoAvn 
that  injections  of  pure  water  alone  in  doses  of  over  1  c.c.  may  make  a 
mouse  ill. 

In  the  washings  of  a  dog's  trachea,  or  the  condensation  fluid  obtained 
from  the  breath,  there  is  bound  to  be  present  traces  of  the  proteins  of 
the  saliva.  A  second  injection  of  such  into  the  same  animal  might 
produce  "anaphylactic  shock"  (see  p.  111).  Experiments  have  been 
published  which  seem  to  show  that  guinea-pigs  can  be  sensitized  by  the 
injection  of  the  condensation  water  of  human  breath,  so  that  anaphy- 
laxis is  produced  in  these  pigs  by  a  subsequent  injection  of  a  trace  of 
human  serum.  Owing  to  the  method  employed,  it  seems  certain  that 
saliva  must  have  contaminated  the  condensation  water.  The  guinea- 
pigs  therefore  became  sensitized  to  human  protein  by  the  injection  of 
the  condensation  water  containing  traces  of  salivary  protein.  Such 
results,  it  is  claimed,  afford  evidence  in  favour  of  the  exhalation  of 
a  volatile  protein — an  organic  chemical  poison.  If  there  were  any- 
thing in  these  claims,  we  should  expect  to  find  rats,  which  dwell  in 
the  same  confined  cage  and  breathe  each  other's  breath,  sensitive  to 


THE  PRINCIPLES  OF  VENTILATION  315 

the  injection  of  a  trace  of  each  other's  protein.  According  to  those 
Avho  study  the  phenomena  of  anaphylaxis,  no  such  sensitivity  can  be 
shown.  If  rats  and  guinea-]iigs  be  confined  together  for  one  or  two 
months  under  the  worst  possible  conditions  of  ventilation,  the  gviinea- 
pigs  subsequently  show  no  signs  of  anaphylactic  symptotus  when 
injected  with  a  smaJl  dose  of  rats  serum. 

It  has  been  claimed  that  if  rabbits  be  arranged  in  a  series  of 
chambers,  with  the  air  led  from  one  chamber  to  another,  so  that 
each  succeeding  chamber  received  the  vitiated  air  from  the  one 
before  it,  the  animals  in  the  end  cage  died ;  but  if  the  air  received 
into  this  cage  were  passed  through  sulphuric  acid  the  rabbits 
remained  alive. 

These  experiments  also  have  been  repeated  with  the  greatest  care 
by  several  workers.  It  has  been  proved  conclusively  that  no  harm 
results  so  long  as  a  sufficient  air-current  is  maintained  to  keep  the 
carbonic  acid  below  a  poisonous  amount.  The  animal  in  the  last 
cage  dies  when  the  COg  reaches  10  to  12  per  cent.  If  the  (-O^  is  kept 
down,  the  animal  in  the  last  cage  puts  on  Aveight  and  thrives  as  Avell 
as  the  animal  in  the  first  cage.  Of  course,  it  is  necessary  in  such 
experiments  to  clean  the  chambers  daily,  and  supply  the  animals  with 
suitable  food  and  bedding. 

A  man  can  live  many  days  in  a  closed  chamber  in  comfort  without 
damage  to  his  health,  having  not  the  slightest  cognizance  of  any  defect 
in  ventilation,  when  the  ventilation  is  so  reduced  that  the  carbonic 
-acid  accumulates  in  the  chamber  up  to  1  per  cent. — that  is  to  say,  so 
long  as  the  air  in  the  chamber  is  kept  cool  and  dry.  Eight  students 
were  enclosed  in  a  small  chamber  holding  about  3  cubic  metres  of 
air,  and  kept  therein  until  the  COo  has  reached  3  to  4  per  cent.,  and 
the  oxygen  has  fallen  to  17  or  16  per  cent.  Unaware  that  the 
oxygen  was  insufficient  to  support  comljustion  they  were  puzzled  to 
find  they  could  not  light  a  cigarette.  The  wet-bulb  temperature 
rose  meanwhile  to  about  85°  F..  the  dry-bulb  a  degree  or  two  higher. 
Their  discomfort  became  great,  but  this  was  relieved  to  an  astonish- 
ing extent  by  putting  on  electric  fans  placed  in  the  roof,  whirling 
the  air  in  the  chamber,  and  so  cooling  their  bodies. 

In  a  crowded  room,  the  air  confined  between  the  bodies  and  clothes 
of  the  people  is  almost  warmed  up  to  body  temperature  and  saturated 
with  moisture,  so  that  cooling  of  the  bod}^  by  radiation,  convection 
by  evaporation,  becomes  almost  impossible.  This  leads  to  sweating, 
wetness,  and  flushing  of  the  skin,  and  a  rise  of  skin  temperature. 
The  blood  is  sent  to  the  skin,  and  stagnates  there  instead  of  passing 
in  ample  volume  through  the  brain  and  viscera.  Hence  arise  the 
feelings  of  discomfort  and  fatigue.  The  fans  in  the  experiment 
mentioned  above  whirled  away  the  blanket  of  stationary  wet  air  round 
their  bodies,  and  brought  to  the  students  the  somewhat  cooler  and 
drier  air  in  the  rest  of  the  chamber,  and  so  relieved  the  heat  stagna- 
tion from  which  they  suffered.  The  relief  became  far  greater  when 
cold  water  was  circiilated  through  a  radiator  placed  in  the  chamber, 
and  so  cooled  the  air  of  the  chamber  about  10^  F. 


316  A  TEXTBOOK  OF  PHY8IOLOCJY 

The  experiments  showed  that  l)reathi]ig  increased  percentages  of 
COg,  and  diminished  oxygen  percentages  of  2  to  3  per  cent.,  had  little- 
effect  in  modifying  the  frequency  of  the  pulse,  while  the  increased 
temperature  and  humidity  of  the  air  had  a  profound  effect.  If  the 
percentage  of  COo  in  the  chamber  were  suddenly  raised  up  to  2  per 
cent.,  the  subjects  inside  were  quite  imaware  of  this.  If  the  air  in  the 
chamber  were  breathed  through  a  tube  by  a  man  standing  outside, 
none  of  the  discomfort,  experienced  by  those  shut  up  inside,  was 
felt.  Similarly,  if  one  of  those  in  the  chamber  breathed  through  a 
tube  the  pure  air  outside,  he  was  not  relieved.  The  cause  of  the 
discomfort  was  thus  proved  to  be  heat  stagnation  due  to  the 
excessive  heat  and  humidity,  and  absence  of  movement  of  the  air. 
The  wet  and  drj'  bulb  thermometers  do  not  indicate  the  degree  of 
this  heat  stagnation;  this  may  be  measured  by  the  katathermometer 
described  later  (see  p.  500). 

The  cooling  power  of  the  atmosphere  exerted  on  the  skin  depends 
far  more  on  its  movement  than  on  its  temperature;  the  air  in  ordinal y 
rooms  with  the  windows  closed  is  so  still  that  the  cooling  power 
approximates  to  that  in  the  tropics  out  of  doors.  The  good  effects  of 
open-air  life  depend  very  largely  on  the  wind  and  its  cooling  power 
stimulating  the  metabolism  of  the  bod}'.  It  has  been  shown  that  Ihe 
will  to  perform  either  mental  or  physical  tasks  is  diminished  by  hot, 
moist  atmospheres,  the  pulse  m  increased  in  frequency,  the  arteiiaL 
blood-pressure  lowered  and  the  appetite  diminished  by  such. 


CHAPTER  XXXVI 

lyrETHODS  FOR   THE  DETERMINATION   OF  THE   RESPIRATORY 

EXCHANGE 

The  respiratory  exchange  can  be  measured  by  collecting  the 
expired  air  in  canvas-rubber  bags.  The  bags  are  large  so  that 
the  air  expired  by  a  resting  man  for  periods  of  half  an  hour  may 
■quite  conveniently  be  collected.     When  it  is  required  to  determine 


i-raSi^es 


Eic 


179. — ^Apparatus  used  for  Determining  the  Total  Respiratory  Change 
IN  Man.     (C.  G.  Douglas.) 


the  exchange  dviring  exercise,  such  as  walking,  running,  swim- 
ming, etc.,  smaller  bags  may  be  used,  and  the  air  of  one  or  two 
minutes'  breathing  collected.  The  subject  of  the  experiment  wears 
a  mouthpiece  fitted  with  inspiratory  and  exjiiratory  valves.  The 
nose    is    closed    by   a    clip.     By   means   of   the   valves,   the   outside 

317 


318 


A  TEXTBOOK  OF  PHYSTOlJXiV 


air  is  iiispirod.  ami    the  cxpiicil    aii'  directed   into  tlic  collectiiifi-  bag 
(Fig.  179). 

The  respiratory  exchange  is  calculated  by  squeezing  tlie  contents 
of  the  bag  through  a  meter,  and  thus  measuring  the  volume  of  the  air 
expired  in  the  given  time,  and  by  determining  the  composition  of 
samples  of  the  expired  air.  For  example,  if  it  be  found  that  a  man 
at  rest  has  breathed  out  on  an  average  7  litres  per  minute,  and  that 
the  expired  air  contains,  say,  4  per  cent,  of  CO.^  and  ir)-S()  per  cent, 
of  Og,  then,  taking  the  percentage  of  O.,  in  the  inspired  air  under  the 
conditions  of  the  ol)servation*  as  20-80,  the  percentage  absorbed  is 

5  (20-80 -15-80).  the  amount  of  O.,  absorbed  ig- =350  c.c.  per 

''  -  100 


minute.     Likewise,  the  amount  of  CO.,  given  out  is 


4  X  7000 
100 


=  280  c.c. 


|)er  minute. 

In  the  case  of  small  animals,  another  method  of  procedure  is  adopted. 
The  volimie  of  CO.2  expired  is  estimated  from  the  weight  of  CO.2  given 
out  by  the  ai\imal.  m  hile  the  oxygen  used  is  arrived  at  by  subtracting 


M        K  A      B      C      \) 

Fig.  180. — Tin:  Haldaxe-Pembrey  Respiration  Aitaratcs. 

the  loss  in  weight  of  the  animal  in  a  given  time  from  the  combined 
weights  of  CO2  and  water  given  off  by  it.  The  apparatus  suitable  for 
a  mouse  or  rat  is  illustrated  in  Fig.  180.  A  beaker  serves  as  animal 
chamber ;  this  is  closcfl  liy  a  cork  and  pierced  by  inlet  and  outlet  tubes  and 
a  thermometer.  The  cork  is  soaked  in  melted  paraffin  before  insertion 
to  secure  air-tighf  closure.  The  beaker  is  generally  placed  in  a  water- 
bath  regulated  to  the  desired  temperature.  Air  is  drawn  into  the 
chamber  through  a  meter  by  means  of  an  aspirator  or  filter  pumj^. 
The  incoming  air  is  freed  from  CO.^  and  water  by  being  drawn  through 
a  bottle  {M)  containing  soda  fime,  and  another  (iV)  containing  pumice 
and  sulphuric  acid.  The  issuing  air  is  led  through  a  pair  of  tubes 
{A,  B)  containmg  sulphuric  acid  and  pumice  to  remove  the  water, 
and  another  pair,  C  containing  soda  lime,  D  containing  sulphuric 
acid  and  pumice.  Tube  C  removes  the  COg,  and  D  catches  the  water 
liberated  from  the  soda  lime.  In  actual  practice,  tubes  C  and  D 
are  du])licated,  as  a  control.  The  duplicates  should  not  change  in 
weight  during  an  experiment.  From  the  increase  in  weight  of  tubes 
A,  B  during  a  given  time  the  weight  of  Avater  given  off  is  obtained; 


¥ov  accurate  wxn-k  these  volumes  must  be  reduced  to  0°  C.  and  TOO  mm. 


DETERMINATION  OF  THE  RESPIRATORY  EXCHANGE     319 

the  increase  of  weight  in  C  and  D  gives  the  weight  of  CO2.  The  loss 
of  weight  in  the  animal  is  obtained  by  weighing  the  animal  in  the 
beaker  before  and  after  experiment.  Then  since  the  molecnlar  weight 
of    a  gas  in   grammer.    measures  22-4  litres   under  normal  condition 

44 

of  temperature  and  pressure,  the  CO.,  in  grammes  x  ^     =  volume  of 

CO2  given  out ;  simihirly,  the  loss  of  weight  of  CO.,  and  water  vapour 
deducted  from  the  loss  of  weight  of  the  animal  gives  the  weight  of 

32 

oxvgen  taken  in;  this  in  grammes  x  :=r2i—r  =  volume  of  oxvgen  taken  in. 
.  e  o  22-4 

Such  a  method  is  not  convenient  for  larger  animals  and  for  man. 
The  respirator}'  exchange  in  such  has  been  investigated  by  placing 
the  animal  in  a  closed  chamber  which  contains  a  known  quantity  of 
air.  This  air  is  circulated,  the  CO2  given  off  being  absorbed  by  caustic 
alkali,  and  oxygen  graduall}'  added  to  replace  that  used  up  and  keep 
the  pressure  constant.  The  oxygen  used  is  known  from  the  amount 
which  has  entered  the  chamber;  the  amount  of  COo  absorbed  is  esti- 
mated by  titrating  the  alkali.  In  some  laboratories,  large  rooms  have 
been  fitted  up  for  the  special  study  of  the  respiratory  exchange  in 
man  under  varying  conditions. 

The  res]:)iratoiy  exchange  is  greatly  increased  by  muscular  A\ork, 
as  the  following  table  shows : 


Subject. 

CO 
per 

2  Output 
Minute. 

vet 

Output 
Minute. 

-M.  F. 
L.  H. 

Resting  on  coucli  after  breakfast 
Quiet  walk  of  225  yards  in  2?  minutes 

(3  miles  per  hour  approximately) 
Riding  bicycle    1   mile  in   4  minutes 

42  seconds     . . 
Resting  on  couch 
Climbing  cliff 
Swimming 

337 

1,06.3 

1,103 

301 

2,438 

3,804 

374 

1,257 

1,218 

345 

2.404 

3,361 

Exposure  to  a  cold  wind  may  double  the  respiratoiy  exchange  of 
the  resting  man;  by  stimulating  him  to  muscular  activity  it  n.ay  do 
much  more  than  this. 

The  Respiratory  Quotient. — The  volume  of  CO2  given  out  divided 
by  the  \olume  of  O^  taken  in  gives  the  respirator}^  quotient: 

CO2  by  volume 


R.Q. 


0..  by  volume 


Thus,   in  the  experiment  on  man,   280  c.c.  of   COg  was   given  out, 

350  c.c.  of  Oo  taken  in. 

280 

TheR.Q..-.= =0-8. 

350 

The  res]iiratory  quotient  varies  according  to  the  nature  of  the  food  being 
oxidized  in  the  bodv.    On  a  mixed  diet  it  is  found  to  be  about  0-85. 


320  A  TEXTBOOK  OF  PHYSIOLOGY 

With  carboh3(lrate  the  quotient  is  1.  The  following  formula 
summarizes  its  decomposition: 

CfiHioO,  +  60.,  =  6C0,  +  6HoO. 
6C0.,_, 

6o; 

In  the  case  of  carbohydrate  there  is  sufficient  oxygen  in  the  mole- 
cule for  the  formation  of  water ;  oxygen  is  only  required  for  the  forma- 
tion of  carbon  dioxide.  In  the  case  of  protein  and  fat  part  of  the 
ox\^gen  taken  in  combines  with  hydrogen  to  form  water;  the  R.Q. 
is  therefore  less  than  1.  With  protein  it  is  about  0-82.  The  following 
formula  has  bsen  suggested  as  summarizing  its  decomposition : 

C->Hii,NiA2S  +  770o-  63C02  +  38HP  +  9CO(NH,),  +  S03. 

Urea 

07  =  77-^^- 

For  fats  undergoing  direct  katabolism  in  the  bo:ly  it  is  found  to 
be  about  0-7.  The  following  formula  summarizes  the  katabolism  of 
olein : 

C3H.(Ci8H330,)3  f  80O.,  =  57CO,  +  52H,0. 

^0^=^..0-7l/ 
O,      SO 

Muscular  work,  although  greatly  increasing  the  respiratory  ex- 
change, may  not  affect  the  respiratory  quotient.  The  respiratory 
c^uotient  of  animals  previous  to  and  during  hibernation  and  during 
starvation  is  referred  to  under  Fat  Metabolism  (pp.  439,  440). 

Internal  or  Tissue  Respiration  denotes  gaseous  interchange  batween 
the  blood  and  tissue  fluids  on  the  one  hand,  and  the  body  cells  on 
the  others.  A  frog  placed  in  nitrogen  continues  to  joroduce  CO2  for 
some  hours,  so  does  a  frog  whose  blood  is  replaced  b}^  physiological 
saline.  Excised  '^  surviving  '"  organs,  artificially  circulated,  continue  to 
use  Oo  and  i>roduce  COo.  The  glow  organ  of  a  glow-worm  glows  only 
in  the  presence  of  oxygen.  These  are  proofs  of  tissue  respiration. 
That  the  living  tissues  have  a  marked  affinity  for  oxygen  can  be 
shown  by  injecting  a  solution  of  methylene  blue  intravenously.  On 
killing  the  animal,  it  is  found  that,  although  the  blood  be  blue,  the 
tissues,  such  as  the  muscles,  are  uncoloured.  Upon  exposing  the 
muscles  to  oxygen,  they  become  blue,  showing  that  the  muscles  have 
reduced  the  methylene  blue,  and  thus  decolorized  it.  Since  methylene 
blue  is  a  fairly  stable  compound,  the  great  affinity  of  the  tissues  is 
well  shown  by  the  experiment.  They  store  up  but  little  combined 
oxygen,  and  the  oxidative  changes  which  occur  in  them  are  supposed 
to  be  due  to  enzymes  known  as  "  oxidases  "  and  "  peroxidases  " 
(see  p.  73).  When  a  tissue  is  active,  much  more  oxygen  is  taken 
from  the  circulating  blood  and  mo.'e  COg  is  given  up  to  the  blood. 
This  gaseous  interchange  can  be  calculated  by  estimating  the  amount 
of  CO2  and  O2  in  the  blood  going  to  and  leaving  the  organ,  and  by 


DETERMINATION  OF  THE  RESPIRATORY  EXCHANGE     321 

measuring  the  blood-flow  through  the  organ  in  a  given  time.  Such 
experiments  have  been  made  upon  the  heart,  muscles,  kidneys, 
salivary  glands,  and  other  tissues. 

In  the  following  table  some  of  the  results  obtained  are  given. 
The  gaseous  interchange  may  be  expressed  either  in  c.c.  per  minute 
or  in  c.c.  per  gramme  of  tissue  substance  per  minute. 


Table  showing  Effect  of  Activity  upon  the  Internal  Respiratory 

Exchange. 


Or-jan. 


Beiting. 


Gas  in  c.c.  per  Min. 

( to  COo 


Artic^. 
Gas  in  c.c.  -per  Min. 

()o  COo 


Salivary  gland 
Salivary  gland 
Panci'eas 
Kidney     . . 


0-32 
0-32 
0-i9 
0-57 


0-20 
0-20 


1-20 
0-93 
1-71 
2-95 


1-58 
0-60 


/Stimulation  of 
-     chorda  tympaai 
Injection  of  secretion 
Active  diuresis 


jSalivary  gland 

Hea.rt 

Intestine 

Liver 


!n<  per  Gnu.  per  Min. 
U-028  — 

0-010  — 

0-00  87  — 

0-00.5  — 

(Fasting  animal.) 


Gas  per  Grin,  per  Min. 
0-052  — 

0-045  — 

0-0194:         — 

0-0.50  — 

(Fed  animal.) 


Injection  adrenalin 
Injection  adrenalin 
Absorption   of    phy- 
siological saline 


The  oxygen  use  of  the  heart  is  reduced  during  vagal  stimulation 
and  increases  after  its  cessation.  The  use  of  ox\^gen  by  the  heart  is 
also  greatly  reduced  Id}^  the  injection  of  chloroform  water  into  the  blood. 

When  the  nerve  of  a  muscle  is  divided,  its  metaboHsm  is  markedly 
decreased;  the  respiratory  quotient  is  practically  unaltered  by  the 
complete  rest  so  induced.  The  oxygen  use  per  minute  per  kilo- 
gramme of  substance  has  been  estimated  as  folloAvs:  Muscle,  4  c.c- 
salivary  gland,  25  c.c;  pancreas,  40  c.c;  intestine,  23  c.c;  kidney, 
26  c.c;  liver,  30  c.c 

Energy  displayed  by  a  contracting  muscle  or  a  secreting  gland  is  not 
in  itself  a  manifestation  of  oxidation  in  the  sense  that  the  Avork  of  an 
internal  combustion  engine  is  a  direct  manifestation  of  the  oxidative 
explosion  in  the  cylinder;  they  are  more  to  be  compared  to  the 
running-down  of  an  alarm  clock.  The  clock  is  wound,  and  at  a  wiven 
moment  the  j^otential  energj'  of  the  spring  is  released.  It  must  then 
be  rewound.  It  is  during  the  jieriod  of  "  rewinding  "  that  oxidation 
is  increased  and  cm  ample  supph^  of  blood  is  required.  There  is  some 
evidence  that  the  pressure  of  oxygen  in  the  tissue-juices  of  glands 
approximates  to  that 'in  the  venous  blood,  while  in  muscle  it  is  almost 
nil.  The  latter,  therefore,  on  any  diminution  of  blood-flow  suffers 
from  oxygen-want. 

The  blood  which  leaves  an  organ  is  waruier,  more  acid,  and 
altered  in  saline  content.     Each  of  these  factors  may  aifl  the  dis- 

21 


322 


A  TEXTBOOK  OF  PHYSIOLOGY 


Fig.  181. — Sylvester's  Method:  Means  of  producing  Inspiration. 


Fig.  181a. — Sylvester's  Method:  Means  of  producing  Expiration. 


Fig.    182. — Schafer's   Method    of    Artificial   Respiration.     (From    Rowland's 
"Hygiene  for  Teachers.") 


DETERMINATION  OF  THE  RESPIRATORY  EXCHANGE    323 

sociation  of  oxyhaemoglobiii.  In  jDarticular,  by  locally  increasing  the 
acid  in  the  blood  within  the  capillaries,  the  hard-working  tissues 
dissociate  oxygen  from  the  oxyhsemoglobin  and  make  the  red  corpuscle 
discharge  its  cargo  of  oxj^gen  with  rapidit3^  At  the  same  time,  by 
increasing  the  general  acidity  of  the  blood,  the  tissues  provoke  the 
respiratory  centre  to  increased  activity.  The  increased  acidity  of  the 
blood  not  only  modifies  the  dissociation  curve  of  oxyhsemoglobin,  but 
is  accompanied  by  a  lower  percentage  of  COo  in  the  alveolar  air,  a 
lower  respiratory  quotient,  and  diminished  power  of  the  hsemoglobin 
to  combine  with  oxygen  in  the  lungs. 

Artificial  Respiration. — In  this  country  two  methods  are  in  vogue. 
In  the  older  method — Sylvester's — the  subject  is  placed  on  his  back, 
with  a  pillow  or  folded  garment  beneath  the  shoulders.  The  tongue 
is  pulled  well  forward,  the  mouth  kept  open.  Inspiration  is  induced 
by  grasping  the  arms  below  the  elbow,  and  gradually  raising  them 
above  the  head  (Fig.  181 ).   Expiration  is  produced  by  bending  the  arms. 


Fig.  1S)3. — Cat:  Record  of  Respiration. 

A,  Chloroform  on  between  the  arrows;  B,  COgon  between  the  arrows;  C,  CO.^  on  again. 

Time  in  seconds. 

and  pressing  them  forcibly  against  the  chest  wall  (Fig.  181a).  These 
operations  should  be  performed  about  twentj^  times  a  minute.  The 
method  has  the  disadvantage  of  being  fatiguing  to  the  operator. 

The  more  recent  method  —  Schiifer's  —  has  largely  overcome 
this  defect.  In  it  the  subject  is  placed  face  downwards,  with  the 
upper  part  of  the  chest  raised  by  a  pillow  or  some  similar  support. 
The  operator  stands  at  the  side  of  the  su^bject  facing  his  head:  then, 
placing  his  hands  on  the  lowest  ribs  on  either  side,  he  slowh'  brings 
the  weight  of  his  body  to  bear  upon  his  own  arms,  and  thus  presses 
upon  the  thorax  of  the  subject,  and  forces  air  out  of  the  lungs.  Then 
he  gradually  relaxes  the  pressure  by  bringing  his  own  bodj^  up  again 
to  a  more  erect  position  without  moving  the  hands  (Fig.  182). 

The  rhythmic  ]iressure  on  the  thorax  helps  to  squeeze  blood  through 
the  heart  and  lungs,  and  it  is  as  important  to  effect  this  as  it  is  to  intro- 
duce air.  The  excitatory  effect  of  CO^  upon  the  respiration  might 
be  made  use  of  in  cases  of  poisoning  due  to  oxygen-want  (carbonic 


324 


A  TEXTBOOK  OF  PHYSIOLOGY 


oxide  and  nitrite,  etc.)  and  in  cases  of  drowning,  suffocation  and 
chloroform  syncope  (Fig.  182).  To  carry  out  the  method  most  effec- 
tively there  would  be  required  an  anaesthetic  mouth-piece  and  rubber 
bag  filled  with  oxygen  in  and  out  of  which  the  operator  has  respired 
several  times.  This  is  then  given  the  patient  to  breathe  while  arti- 
ficial respiration  is  done.  To  respirate  children  artificially  it  is  best 
to  put  mouth  to  mouth  (interposing  a  handkerchief)  and  rhythmically 
blow  11])  the  lungs.     A  hand  placed  on  the  belly  ])revents  the  stomach 


Jt 


it^S^rK* 


I'^iG.  184. 


-IHE  ViVATOR  Apparatus  for  Artificial  Kespiration. 
(Siebe,  Gorman  and  Co.) 


The  api^aratus  consists  of  a  special  pump,  which,  on  the  downstroke,  delivers  oxygen 
from  a  bag  (connected  to  an  oxygen  cylinder)  into  the  inspiratory  tube  of  a 
mask,  which  is  fastened  or  held  tightly  over  the  patient's  nose  and  mouth. 
Having  completed  the  downstroke  and  so  forced  oxygen  into  the  patient's 
lungs,  the  pump  on  its  return  or  upstroke  not  only  sucks  in  a  fresh  supply  of 
oxygen  to  be  deUvered  on  the  next  downstroke,  but  also  opens  a  valve,  which 
is  connected  with  the  expiratory  tube  of  the  mask,  thus  allowing  the  expiratory 
recoil  of  the  expanded  chest  and  lungs  of  the  patient  free  play.  The  valve 
i-emains  open  during  the  upstroke  and  automatically  closes  when  the  stroke  is 
completed.  The  piston  of  the  pumji  then  descends  and  delivers  another  supply 
of  oxygen,  and  so  on. 


being  blo^^al  up,  or  the  gullet  can  be  closed  by  pressing  the  larj^nx 
backwards.  A  pump  has  been  contrived  for  this  pm'joose,  fitted  with 
a  face  mask  (Fig.  184).  The  stroke  of  the  piston  is  arranged  to  open 
a  valve  at  the  end  of  the  inflation  so  as  to  allow  deflation  of  the  lungs 
by  the  elastic  recoil  of  the  thorax.  Such  a  pump  cannot  be  used  to 
suck  air  out  of  the  lungs,  for  suction  causes  the  walls  of  the  small 
bronchial  tubes  to  come  together,  and  does  not  empty  the  alveoli. 


BOOK    V 

CHAPTER  XXXVII 
GENERAL  METABOLISM  AND  DIETETICS 

Metabolism  and  reproduction  are  the  chief  characteristics  of 
living  matter.  Wc  laiow  that  complex  bodies  such  as  proteins,  fats, 
and  carboh3xlrates,  are  constant!}'  taken  into  the  body,  and  that 
each  undergoes  its  own  special  metabolism.  As  the  result  of  these 
reactions  chemical  energy  is  tran.sformed  into  heat  and  m.echanical 
work;  waste  products,  such  as  carbon  dioxide  and  urea  are  formed, 
and  excreted  from  the  body. 

The  study  of  general  metabolism  concerns  the  intake  and  output 
of  energy  b}',  and  the  processes  of  building  up  and  breaking  down 
which  occur  in,  the  body  as  a  whole ;  while  the  study  of  the  special 
metabolisms  deals  with  the  exact  chemical  changes  undergone  by  the 
various  foodstuffs,  and  with  the  localization  of  such  changes  in  the 
body. 

General  Metabolism:  Methods. — The  general  metabohsm  of  a 
man  or  animal  may  be  investigated  by  two  means:  (1)  Directh% 
by  ascertaining  the  heat  value  of  the  foodstuffs  taken  in,  and 
then  measuring  the  heat  given  off,  either  as  such  or  as  work,  the 
work  performed  being  subsequently  calculated  as  heat.  (2)  Indirectly, 
by  drawing  up  a  balance-sheet  between  the  intake  (the  amount  of 
food  and  amount  of  oxygen  taken  in)  and  the  output  (the  amount  of 
the  various  bodies  excreted  in  the  breath,  urine,  fseces,  and  sweat), 
and  from  these  calculating  the  energy  exchange.  Of  these,  the  second 
method  demands  a  less  difficult  technique  and  is  more  generally 
employed.  For  very  exact  work  a  combination  of  the  methods  is 
used . 

The  body  is  to  be  looked  upon  as  a  machine  capable  of  performing 
work  and  liberating  heat.  In  the  living  as  in  the  inanimate  world, 
there  is  no  such  thing  as  a  loss  of  energy.  All  such  apparent  losses 
are  merely  transformations  of  energy,  the  chief  transformation  in 
the  body  being  that  of  the  chemical  energy  of  the  foodstuffs  into 
work  and  heat. 

It  is  not  possible,  however,  to  account  for  the  operations  that  go 
on  in  the  human  machine  on  the  supposition  that  man  is  a  thermo- 
dynamic engine. 


326 


A  TEXTBOOK  OF  PHYSIOLO(JY 


The  unit  by  which  work  is  measured  is  the  kilogramme-metre 
(kgm.).  This  is  the  force  necessary  to  raise  a  kilogramme  vertically 
through  1  metre  from  the  earth's  surface.* 


Fm.  185.— Bomb  Calorimeter.     (Berthelot.) 

-  .  Water  jacket;  B,  water  calorimeter;  C,  bomb;  D,  stirrer  worked  by  motor  G; 
E,  thermometer;  F,  cable  carrying  wires  to  a  and  d. 


The  imit  by  which  heat  is  measured  is  the  Calorie.  This  is  the 
heat  required  to  raise  1  kilogramme  of  water  through  1°  C.  (preferably 
from  20°  C.  to  21°  C).     For  smaller  measurements  the  small  calorie 

*  As  this  force  varies,  owing  to  the  shape  of  the  earth  being  greater  at  the  poles 
than  at  the  equator,  the  unit  known  as  the  "erg"  is  now  employed  in  exact  work. 
This  is  the  force  which  will  impart  to  a  resting  grarame-mass  a  velocity  of  1  centi  - 
metre  per  second.     One  kilogramme-metre  equals  980,000  ergs. 


GENERAL  METABOLISM  AND  DIETETICS  327 

■^ToVio   C^alorie),  or  gramme-calorie,  is  employed;  while  for  the  finest 
work  the  micro  calorie,  or  milligramjiie-calorie,  is  used. 

In  order  to  measure  the  amount  of  heat  retained  or  given  out  by 
a  man,  it  is  necessary  to  know  the  specific  heat  of  his  tissues.  This 
has  been  determined  as  0-8.  A  hibernating  dormouse  weighing 
10  grammes,  and  with  a  body  temperature  of,  say,  4°  C,  when  placed 
in  100  c.c.  of  water  at  0°  C.  until  cooled  to  3°  C.,  does  not  yield  10, 
but  only  8,  calories  to  the  water.  Consequenth^  if  a  70  kgm.  man 
has  his  temperature  raised  1°  C,  he  stores  up  70x0-8=56  calories 
-of  heat. 

The  Intake  of  Energy. — The  combustion  of  each  of  the  foodstuffs 
liberates  a  definite  amount  of  heat,  be  it  l^urnt  inside  or  outside  the 
animal  body.  Exact  m.easixrements  of  the  heat  of  combustion  of  the 
different  constituents  of  the  body  are  obtained  by  means  of  an  instru- 
ment known  as  the  boiib  calorimeter.  The  substance  to  be  burnt  is 
dried,  weighed  end  placed  in  a  strong  steel  bomb,  the  inside  wall  of 
which  is  protected  either  by  thick  enamel  or  platinum.  The  bomb 
is  then  filled  with  oxygen  under  pressure  (20  to  25  atmospheres),  and 
placed  in  a  vessel  (Fig.  185)  containing  a  weighed  quantity  of  water. 
This  water  vessel  contains  a  delicate  thermometer  and  a  stirrer,  D, 
which  can  be  driven  by  a  motor.  It  is  also  carefully  protected  by 
a  jacket  (A) — a  vacuum  jacket  is  best — from  alterations  in  tem- 
perature of  the  surrounding  atmoq^here.  The  temperature  of  the 
Avater  is  carefully  noted,  and  then  the  substance  is  burnt  in  the 
oxygen  by  causing  a  A\ire  with  which  it  is  in  contact  to  glow.  This 
is  effected  by  passing  an  electric  current  through  wires  led  into  the 
bomb.  Combustion  is  ra.pidly  completed  ;  the  temperature  of  the 
Avater  is  raised  thereby,  and  the  rise  noted.  From  this  by  means  of 
appropriate  calculations  allowing  for  the  caloric  capacity  of  the 
apparatus,  etc.,  the  heat  liberated  by  the  combusted  substance  is 
ascertained. 

In  the  calorimeter  all  the  carbon  combined  in  the  molecule  of 
foodstuff  is  converted  to  carbon  dioxide,  the  hj'drogen  to  water,  and 
the  nitrogen  is  freed  as  nitrogen  gas.  In  the  body  the  carbon  mostly 
is  excreted  as  CO.,,  and  the  hydrogen  as  water;  biit  the  whole  of  the 
nitrogen  and  a  small  part  of  the  carbon  and  hydrogen  are  excreted 
combined  in  urea.  u.ric  acid,  creatinin,  etc.  These  bodies  have  a 
considerable  specific  heat  of  combustion;  therefore,  in  estimating  the 
heat  value  of  the  protein  in  the  diet,  it  is  necessary  to  subtract  the 
heat  value  of  the  nitrogenous  excreta  from  the  total  value,  obtained 
on  burning  the  protein  in  the  bomb  calorimeter. 

The  table  on  p.  328  gives  the  combustion  value  of  some  of  the 
chief  substances  met  with  in  the  body,  expressed  in  several 
terms. 

The  Indirect  Method. — The  food  given  is  carefully  weighed,  and  its 
content  in  protein,  fat,  and  carbohydrate,  calculated  from  tables 
giving  the  analytical  composition  of  the  various  foodstuffs. 

In  more  accurate  work  the  amount  of  protein  in  the  diet  may  be 
-estimated   by   determining,   when  the  diet   contains  no  other  nitro- 


828 


A  TEXTBOOK  OF  PHYSIOLOGY 


genous  bodies,  the  total  nitrogen  excreted  in  the  urine,  and  multiplying 
this  by  6-25 — the  average  ratio  of  nitrogen  (16  per  cent.)  to  the  total 
weight  of  protein  (Vk"^  6-25). 


starch 
Dextrose 
Cane-sugar 
Lactose  (water 
Fat  (human) 
Butter  . . 
Caseinogen 
]\Iuscle  protein 
Legumin 
Urea     . . 
Uric  acid 
Hippuric  acid 
Alcohol 
Butyric  acid 


fiee 


Per  Gramme  of 
Substance 
(rj.  cal.). 


41U() 

H743 

3955 

39o2 

!t.l4(t 

!t23u 
5850  (435(1)* 
5()50  (4150)* 
5703  (4-203)* 

•2542 

2750 

5G6S 

7080 

51)40 


Per  Cramme 

Molecid'.r 

Per  Gramme 

Per  Gramme 

Weight  of 

0>  used 

CO2  formed 

Substance 

ig'.cal.). 

{g.  cal.). 

{kg.  cal.). 

C.78-8 

3530 

2572 

(i73-7 

3509 

2552 

1353-t; 

^    3522 

2562 

1351-0 

3520 

25GO 

—    -. 

3353 

4702 

152-5 
402-0 
1014-0 
325-7 
5-22-7 


32!)  I 

2047 

3223 

2902 

32:-)  I 

2909 

3177 

3400 

3208 

2100 

3252 

1281 

3392 

3701 

3207 

2970 

*  The  first  is  bomb  vahie:  the  8L>eond  is  value  for  body  after  subtracting  value  for 
urea  formed,  etc. 

Note  that  column  2  is  kilogramme-calorics,  the  other  columns  gramme-calories. 

Let  us  suppose,  for  example,  that  the  diet  is  calculated  to  contain 
(dry  weight)  125  grammes  of  jn-otein.  500  grammes  of  carbohydrate, 
and  50  grammes  of  fat. 

From  the  chemical  composition  of  each  of  these  foodstuffs  the 
amount  of  carbon  and  nitrogen  is  calculated — 


Protein 
Carbohydrate 
Fat   .." 

Total 


Carbon 

Xilrogen 

Grammes). 

{Grammes) 

02 

20 

200 

. — 

38 

— 

300 


20 


The  energy  value  of  such  a  diet  in  terms  of  heat  is- 


Protein 
Carbohydrate 
Fat     .  ■. 


Calorics. 
125x4-1=   51-2-5 
500x4- 1  =  2050-0 
50x9-3=   '105-0 

3027-5 


The  Output. — Since  protein  is  the  only  body  in  the  above  diet 
which  contains  nitrogen  and  sulphur,  the  amount  of  protein  katab- 
olism  of  the  body  can  be  arrived  at  by  estimating  carefully  the  amount 
of  nitrogen  or  sulphur  combined  in  the  excreta.     The  nitrogen  is  most 

*  For  the  food  digested  and  utilized  the  values  can  be  taken  as  protein  4,  fat  9,. 
c.".rboh5'drate  4. 


GENERAL  METABOLISM  AND  DIETETICS  329 

usually  chosen.  This  occurs  mainh'  in  the  urine,  to  a  small  extent  in 
the  fseces  and  sweat.  The  total  nitrogen  of  the  urine  is  usually'  deter- 
mined by  KjeldahUs  process  (see  p.  455),  and  to  this  1  gramme  of 
nitrogen  is  added — that  is,  the  average  amovint  excreted  in  the  fseces. 
The  nitrogen  of  the  fseces  is  derived  in  part  from  unabsorbed  food, 
and  in  part  from  the  various  secretions  of  the  alimentary  tract.  The 
above  average  has  been  ascertained  by  experiments  upon  animals 
placed  on  a  nitrogen -free  diet.  It  has  to  be  borne  in  mind  that  several 
days  are  required  for  the  elimmation  of  all  the  nitrogen  taken  in  in 
the  case  of  some  protems.  The  nitrogen  is  eliminated  at  varj'ing 
rates  when  different  t\'pes  of  proteins  are  ingested. 

The  ])roportion  of  sulphvir  in  m-ine  to  nitrogen  is  1  :  5-2 — about 
the  same  as  in  protein.  The  determination  of  the  sulphur  excretion 
is  therefore  a  guide  as  to  the  breakmg  down  of  protein  and  a  control 
of  the  nitrogen  determinations.  The  determination  of  the  protein 
metabolized  from  the  sulphur  excretion  has  the  advantage  that  in 
general  the  sulphur  of  the  protein  is  more  quickly  excreted  than  the 
nitrogen,  but  has  the  disadvantage  that,  being  small  in  amoiuit,  the 
experimental  error  is  likely  to  be  greater. 

Protein  yields  a  certain  amount  of  carbon  combined  A\'ith  the 
nitrogen  of  the  urinary  excreta.  It  has  been  determined  that  for 
ever}'  gramme  of  nitrogen  excreted  0-67  gramme  of  carbon  is  excreted. 
This  ratio  is  constant,  so  that  it  is  not  necessary-  to  estimate  the 
proportion  of  carbon  in  the  nitrogenous  bodies  of  the  urine. 

Protein  on  its  oxidation  also  yields  CO2  and  water.  The  COg 
output  is  more  easy  to  estimate  than  the  water  output  of  the  body. 

•  Of  the  carbon  dioxide  excreted  a  small  part  comes  from  protein, 
the  remainder  from  fat  and  carbohydrate.  The  amount  of  carbon 
coming  from  protein  is  found  by  multiplying  the  amount  of  nitrogen 
excreted  b}'  3-3,  since  the  proj)ortion  of  carbon  to  nitrogen  in  protein 
is  3-3  :  1.  Since  the  tissues  contain  far  more  fat  than  carljohydrate, 
any  carbon  retained  in  the  bod}'  is  usually  reckoned  as  fat.  Each 
gramme  of  carbon  represents  1-3  grammes  of  fat,  the  proportion  of 
carbon  to  the  total  weight  of  fat.  A  small  amount  of  carbon  is  lost 
as  fat  in  the  fseces. 

Let  us  suppose  that  with  the  above  intake  the  output  was — 

Carbon.  Nitrogen. 

In  urine  11  (16-5x  0-GT)  l(>-o 

In  faeces  .  .  .  .  .  .  5  l-O 

In  breath         ..  ..  ..       2o4  — 

270  17-5 

There  is  a  retention  in  the  body  of  30  grammes  of  carbon  and 
2-5  grammes  of  nitrogen.  This  nitrogen  =  2-5  x  6-25  =  15-62o  grammes 
of  protein.  In  this  protein  there  is  2-5  x  3-3  =  8-25  grammes  of  carbon; 
so  that  30— 8-25  =  21-75  grammes  of  carbon  is  represented  as  fat.. 
To  estimate  this  as  fat  we  must  multiply  the  carbon  b}'  1-3  (fat 
contains  76  per  cent,  of  carbon),  21-75  x  1-3  =  28-275.     Therefore  on 


330 


A  TEXTBOOK  OF  PHYSIOLOGY 


the  above  diet  lo-625  grammes  of  protein  and  28-275  grammes  of 
fat  were  retained  per  day  in  the  organism.  The  energy  exchange 
can  be  obtained  by  deducting  from  th(^  energy  value  of  the  food 
eaten  the  amount  of  lieat  represented  by  these. 


Protein 
Fat 


Calories. 
15'625x4-l=   64  (ajipioximately) 
28-275  X  9-3  =  263 

327 


Since  3,027-5  were  suppHed,  the  amount  of  energy  liberated  is, 
therefore,  3,027-5  -  327  =  2,700-5  calories. 


Fia.  186. — Horizontal  Section  of  Self-Registering  Calorimeter  for  Experi- 
ments WITH  Small  Animals.     (A.  V.  Hill  r.nd  A.  M.  Hill.) 

F,  F,  F,  F,  Vacuum  between  walls  of  a  cylindrical  Dewar's  flask;  A,  incoming  water 
from  tank;  D,  D,  D,  D,  section  of  lead  tubing  around  outride  of  fiask;  K,  junction 
between  outer  lead  tubing  and  T-piece  E^ :  E^  and  £'.j.  inlet  and  exit  T-pieces 
containing  the  thermopile  T ;  H,  H,  coil  of  lead  tubing  inside  flask;  B,  exit  pipe 
for  water;  G,  self -registering  galvanometer. 


Another  indirect  guide  to  the  energy  liberated  by  the  tissues  under 
varying  conditions  is  the  amount  of  oxygen  absorbed  by  them.  This 
is  a  good  guide  in  successive  comparative  experiments,  since,  provided 
the    quality    and   relative   proportion    of    the    foodstuffs    burnt   are 


GENERAL  METABOLISM  AND  DIETETICS 


331 


approximately  the  same,  it  is  fair  to  assume  that  any  change  in  the 
oxygen  intake,  and  also  in  the  CO2  outiaut,  are  due  to  the  conditions 
of  experiment,  such  as  exposure  to  cold,  warmth,  wind,  etc.  The 
respiratory  exchange  is  therefore  often  used  to  estimate  the  amount 
of  energy  liberated  in  the  tissues. 

It  is  necessar}^  for  very  accurate  work  to  remember  that  different 
foodstuffs  liberate  different  amounts  of  energy  for  the  same  amount 
of  oxygen  absorbed.     Thus,  100  grammes  of  oxygen  will  burn — 


35  grammes  of  fat,  giving  energy  equal  to  325  calories. 
84-4     grammes     of     carbohydrate,     giving    energy    equal 

346  calories. 
74-4  grammes  of  protein,  giving  energy  equal  to  362  calories. 


to 


Given  the  respiratory  quotient  and  total  energy  output  of  the  body, 
calculations  can  be  made  of  the  relative  use  of  glycogen  and  fat  for 
each  litre  of  oxygen  consumed  (see  Respiratory  Quotient,  p.  319). 


Fig.   187. — Figure  of  Respik.atiox  Chamber  for  JIan. 

The  pir  is  drawn  from  the  chamber  l)y  the  rotary  blower  and  pivS.sed  over  vessels 
A — E  back  to  the  chamber.     Oxygen  ma}'  be  added  as  required  from  F. 


The  Direct  Mcthod.—Tius  is  done  by  placing  the  man  or  animal 
in  a  respiration  calorimeter.  In  the  case  of  an  animal  it  is  difficult  to 
estimate  the  exact  amount  of  energy  lost  as  muscular  work;  the 
animal  is  therefore  in  these  direct  observations  kept  as  quiet  as  possible. 
The  forms  of  water  calorimeter  which  were  first  used  have  been  given 
up,  on  account  of  large  experimental  error,  and  replaced  by  some 


:332  A  TEXTBOOK  OF  PHYSIOLOGY 

form  of  air  calorimeter.  In  Fig.  186  is  shown  a  self-registering  appar- 
atus, suitable  for  the  study  of  small  animals.  It  consists  of  a  Dewar's 
flask,  with  the  thermo-electric  junctions  npon  the  inlet  and  exit  water 
tubes.  These  junctions  are  connected  with  a  galvanometer,  the 
deflection  of  which  can  be  registered. 

The  direct  method  is  especially  applicable  to  man,  since  the  amount 
of  Avork  done  can  be  measvired,  and  the  amount  of  heat  lost  and  the 
respiratory  exchange  calculated,  at  the  same  time.  Special  double- 
walled  calorimeters  adequately  furnished  with  bed,  chairs,  etc.,  and 
de\'ices  for  performing  mechanical  work,  have  been  built  in  some 
laboratories.  Within  the  calorimeter  is  a  coil  of  water-pipes,  fitted  with 
special  metal  discs,  which  quickly  takes  up  any'  heat  liberated  in  the 
chamber.  Cool  water  is  made  to  flow  through  this  coil  and  the 
volume  ■  and  temperature  of  the  water  entering  and  leaving  it  is 
accurately  measured,  and  thus  the  heat  output  is  calculated.  Almost 
the  whole  of  the  heat  given  off  by  the  body  is  taken  up  by  the 
circulating  water,  for  any  loss  of  heat  to  the  outside  air  is  checked 
by  maintaining  equality  of  temperature  between  the  inner  and  outer 
walls.  This  is  insured  by  means  of  (1)  thermo-electric  couples  con- 
nected with  a  galvanometer  which  detects  any  inequality ;  (2)  electric 
furnaces;  (3)  water  coils  placed  between  the  outer  and  inner  walls, 
hj  means  of  which  any  difference  in  temperature  is  compensated. 
Adequate  ventilation  is  maintained  by  some  form  of  pump,  and  the 
carbon  dioxide  output  and  oxygen  intake  obtained  after  the  fashion 
already  described  for  determining  the  respiratory  exchange;  pre- 
cautions havv^  to  be  taken  to  secure  the  measurement  of  heat  given 
off  in  the  ventilation  air  (Fig.  187). 

For  the  performance  of  mechanical  work  a  bicycle  is  used;  the 
hind-wheel  is  replaced  by  a  metal  disc  which  revolves  against  a 
strap,  the  tension  of  which  is  measured  by  a  spring  balance.  By 
means  of  friction  the  work  done  is  thus  converted  into  heat.  The 
revolutions  of  the  bicycle  and  the  force  required  to  turn  the  bicycle 
can  be  measured,  and  the  work  calculated  from  these  data. 

How  accurately  such  appliances  can  work  is  shown  by  the  following: 
In  several  series  of  experiments  extending  over  forty -five  daj^s,  the 
measurement  of  the  amount  of  heat  produced  by  the  animal  in  the 
calorimeter  equalled  99-53  per  cent,  of  the  heat  calculated  to  have 
arisen  from  the  combustion  of  food  and  body  tissues. 

The  following  is  an  example  of  a  five-day  experiment  on  a  fasting 
dog  of  4-5  kilos  weight: 

Calculated  indirectlv  from  the  nitrogen  and  carbon  ex- 
creted =  259-3. 
Calculated  directlv  bv  the  calorimeter  method  =  261-0. 


CHAPTER  XXXVIII 

METABOLISM  DURING  STARVATION 

Starvation  may  be  brought  about  by  withholding  all  food- 
stuffs from  the  body,  or  by  withholding  separately  either  proteins, 
water,  or  mineral  salts.  When  all  foodstuffs  are  withheld  from  an 
animal,  and  only  water  given,  the  body  begins  to  live  at  its  own 
expense,  loss  of  weight  ensues,  and  finally  the  animal  dies.  The  time 
of  death  depends  largely  upon  the  state  of  nutrition  at  the  start. 
The  process  of  starvation  is  only  painful  in  the  last  stages.  Profes- 
sional fasters  aj)pear  in  public  from  time  to  time,  going  without  food 
for  as  long  as  forty  days,  with  apparently  but  little  inconvenience  to 
themselves.  From  observations  upon  such,  it  appears  that  the  ratio 
of  metabolism  to  actual  bodj-  weight  alters  but  little  during  starva- 
tion; in  other  words,  the  loss  of  w^eight  and  the  lessening  of  the  meta- 
bolic processes  of  the  body  proceed  together.  At  the  beginning  of 
the  starvation  period,  the  nitrogen  elimination  in  the  urine  quickly 
drops  to  a  fairly  constant  level.  The  drop  is  quicker  the  greater  the 
amount  of  nitrogen  in  the  food  eaten  beforehand.  For  example,  a 
dog  receiving  2,500  grammes  of  meat  daily  excreted  on  the  first  daj' 
of  starvation  60-1  grammes  of  urea;  on  the  fifth  day,  12-3  grammes. 
With  a  moderate  nitrogenous  diet — 1,500  grammes  of  meat — the 
excretion  on  these  days  was  26-5  and  14-8  grammes;  with  a  diet  poor 
in  nitrogen,  13-8  and  12-1  gTammes. 


Day  of 

JIvch  X 

Moderate  N 

Little  y 

Starvation. 

in  Food. 

in  Food. 

in  Food. 

1 

C9-1 

26-5 

13-S 

2 

24-9 

lS-(i 

U-.-) 

n 

12-3 

14-S 

12-1 

8 

10-1 

12-1 

10-7 

From  this  day  onward  the  nitrogen  excretion  remains  more 
or  less  constant  until  just  before  death,  when  there  occurs  a  sudden 
rise.  The  explanation  is  that  the  animal  is  hving  on  a  minimum 
amount  of  its  own  protein,  and  getting  nearly  all  its  energy  for  the 
first  day  or  so  from  its  store  of  carbohydrate,  and  subsequenth^  from 
its  body  fat.  This  conclusion  is  reached  by  measuring  the  heat  loss 
and  by  ascertaining  the  respiratory  quotient,  and  calculating  from 
this  how  much  carbohydrate  and  how  much  fat  are  being  metabolized. 
It  is  possible,  since  starving  animals  and  man  give  a  low  respiratory 
quotient,  that  some  of  this  fat  may  first  be  changed  to  carbohydrate 
and  metabolized  in  this  fashion.     It  is  difficult, however,  to  say  exactly 


334 


A  TEXTBOOK  OF  PHYSIOLOGY 


what  is  causing  the  low  respiratory  quotient  of  the  starving  animal. 
It  may  be  partly  accounted  for  by  the  elimination  of  acetone  bodies 
in  the  urine  (see  p.  4G8).  When  the  store  of  fat  is  exhausted,  the 
protein  consumption  and  the  urea  output  goes  up  and  the  end  is  then 
near. 

During  starvation,  the  urine  becomes  considerably  lessened  in 
amount.  Salts  continue  to  be  excreted,  the  amount  of  sodium 
chloride  being  markedly  decreased,  but  that  of  potassium,  calcium, 
magnesium,  and  phosphates  increased.  This  is  due  to  tissue  destruc- 
tion, especiall}'  of  the  bony  tissues.  Life  persists  at  the  expense  of  what 
may  be  termed  the  less  important  tissues  and  organs,  as  can  be  seen 
from  the  following  table: 


Male  Cat. 


Adipose  tissue  . . 

Spleen    . . 

Liver 

T(!sticles 

Muscles 

Kidneys 

Skin 

Intestine 

Lungs     .  . 

Pancreas 

Bones 

Heart 

Brain 


97  per  cent,  loss  of  weight. 

()7 

.")4 

■id 

31 

■2("> 

•21 

18 

IS 

IT 

11- 


An  outstanding  feature  in  starvation  is  the  manner  in  which  the 
blood,  although  some\\'hat  decreased  in  amount,  is  kept  more  or  less 
constant  in  composition. 

A  similar  principle  applies  to  those  animals  which  undergo  periods 
of  voluntary  abstention  from  food.  Previous  to  such  periods  they 
make  special  provision  by  storing  up  large  supplies.  One  particularly 
interesting  example  is  the  salmon.  While  living  in  the  sea,  the  food- 
supplies  are  taken  in  and  stored  as  j)rotein  and  fat  chiefly  in  the 
tail  muscles  and  the  fat  depots  of  the  body.  During  the  migration 
up-river  to  the  "  spawning-ground,"  which  lasts  several  months,  no 
food  is  taken  in,  and  the  whole  of  the  energy,  spent  in  swimming 
and  in  the  development  of  the  sex  organs,  takes  place  at  the  expense 
of  these  food-supplies. 

Animals  which  hibernate  also  lay  up  a  store  of  food  previous  to 
and  Uve  at  the  expense  of  this  during  the  period  of  hibernation 
(see  pp.  439,  440). 

Lack  of  Water. — The  living  processes  of  protoplasm  are  dependent 
on  its  water  content.  Water  has  been  found  to  form  66  per  cent, 
of  the  entire  body  of  a  well-fed  ox,  57-9  per  cent,  of  a  well-fed 
pig,  and  63-2  per  cent,  of  a  well-fed  sheep.  Since  it  is  contmuously 
leaving  the  body  in  the  urine,  breath,  sweat,  and  other  secretions, 
it  must  be  replaced.  The  amount  of  water  lost  under  average 
conditions  of  temperature  and  humidity  is  about  1-25  per  cent,  of 
body  weight  diu-ing  rest  and  hunger,  1-32  per  cent,  during  rest 
and  average  diet,  and  2-91  per  cent,  during  hard  work  and  average 


METABOLISM  DURING  STARVATION  335 

diet.  Depriving  an  animal  of  water  Avill  kill  it  more  quickty  than 
depriving  it  of  the  dr}^  proximate  j)rinciples  of  the  food. 

Water  is  taken  in  as  such  and  in  combination  with  the  food.  Fresh 
fruit  and  vegetables  have  a  large  water  content.  This  water  iaa,y  be 
contained  in  the  s^'stem  of  water-tubes  of  a  plant,  when  it  is  more  or 
less  pure  water,  or  it  ma}-  be  in  the  form  of  "  sap,"  when  it  is  more 
concentrated  and  contains  mineral  salts  and  organic  bodies  in  addition. 
Lean  meat  contains  about  80  per  cent,  of  water,  so  a  carnivore  almost 
gets  enough  water  in  its  food. 

The  proportion  of  Avater  in  various  vegetables  can  be  seen  in  the 
table  on  p.  349. 

Lack  of  Mineral  Salts. — The  v.ithholding  of  mineral  salts  from  the 
diet  also  brings  about  death  more  quickh*  than  the  withholding  of 
the  proximate  principles.  The  salts  of  the  body  are  partly  in  solution 
and  partly  combined  with  the  organic  substances.  Those  in  solution 
are  of  the  greatest  importance  in  providing  the  proper  medium  for 
the  living  tissues.  When  salts  are  withheld,  those  combined  with  the 
organic  substances  of  the  bod}'  become  free  to  replace  the  salts  in 
solvition,  which  are  lost  in  the  urine. 

The  ions  of  sodium,  potassium,  and  calcium,  must  be  continually 
taken  in  with  the  food,  to  keep  the  proper  relationship  between  these 
bases  in  the  blood,  so  that  the  action  of  the  ion  of  no  one  base  pre- 
dominates. We  knoAv  that  certain  enzj-mic  processes,  such  as  the 
clotting  of  blood  and  milk,  depend  on  the  presence  of  calcium  ions, 
and  that  muscular  contraction  is  affected  b}'  the  concentration  of 
calcium,  sodium,  and  potassium  ions  present  in  the  blood.  When 
calcium  is  withheld  from  the  diet,  the  bones  are  gradualh'  decomposed 
to  replace  the  loss. 

Different  results  follow  the  withholding  of  one  or  other  groups 
of  salts.  Thus,  deprivation  of  chlorides  is  followed  by  marked  symp- 
toms of  inanition.  This  is  due  partly  to  gastric  distiu-bance,  and 
partly  to  the  ascendanc}'  obtained  by  the  potassium  ion,  which  worku 
deleteriously  upon  the  bodily  functions.  When  there  is  a  lack  of 
sodium  salts  as  compared  with  potassium  salts,  or  an  abundance  of 
l^otassium  salts  relative  to  sodium  salts,  such  as  occurs  with  a  vegetable 
diet,  the  potassium  of  the  salts  ingested  is  in  part  replaced  by  sodium 
from  the  body,  and  some  of  the  sodium  salt  so  formed  is  excreted  in 
the  urine.  This  causes  a  loss  of  NaCl  from  the  body,  and  a  supply 
of  NaCl  becomes  imperative.  For  this  reason  many  vegetarian 
animals  wander  miles  to  visit  "  salt-licks  " — lumps  of  crude  rock  salt. 
On  an  animal  diet  sufficient  salts  are  introduced  with  the  food  itself. 
The  desu'e  for  salt  b}'  the  various  human  races  varies  with  the  pre- 
ponderance of  vegetable  food  in  their  diet.  The  peasants  in  France  eat 
four  times  as  much  salt  as  the  town  dwellers ;  the  carnivorous  tribes 
of  men  do  not  know  or  do  not  value  salt.  Rice-eaters  are  an  exception. 
Rice  contains  six  times  less  potassium  than  wheat,  ten  to  twenty 
times  less  than  peas,  twenty  to  thirty  times  less  than  potatoes.  Rice- 
eaters,  like  flesh-eaters,  do  not  require  much  common  salt.  In  the 
Soudan  the  negroes  burn  a  plant  which  yields  an  ash  rich  in  sodium. 


336  A  lEXTlJOUK  OF  PHY.SlULUdY 

and  use  this  for  salt.  During  salt  starvation  the  amount  of  chlorine 
in  the  urine  constantly  decreases,  so  that  eventually  the  excretion  of 
chlorine  may  stop. 

Lack  of  Alkali  Carbonates. — If  the  alkaline  bases  be  withheld,  there 
ensues  an  acid  intoxication  of  the  body,  and  life  thus  endangered. 

Lack  of  Phosphates. — Lack  of  phosphates  may  seriously  impair 
the  bodily  functions.  The  bony  tissues  are  particularly  affected. 
It  is  a  question  as  to  how  far  lack  of  phosphates  affects  the  formation 
Avithin  the  body  of  phosphorized  compounds  such  as  phosphoprotein, 
and  of  phosphorized  fats  such  as  lecithin.  The  available  evidence 
seems  to  show  that  these  bodies  can  be  S3"nthesized  from  organic 
bodies  poor  in  phosphorus  and  inorganic  phosphates. 

Lack  of  Iron. — Iron  is  of  great  importance  to  the  organism,  since 
it  is  contained  in  the  blood-pigment,  haemoglobin,  and  also  in  the 
nuclei  of  cells.  It  is  necessary,  too,  for  the  oxidative  processes 
initiated  by  oxidases.  Lack  of  iron  leads  to  ansemia,  insufficient 
nutrition,  and  eventually  to  death. 

Although  debated,  it  seems  probable  that  iron  may  be  utihzed 
when  ingested  in  either  organic  or  inorganic  form.  Iron  is  introduced 
into  the  body  by  various  foodstuffs.  This  can  be  seen  from  the  fol- 
lowing table,  which  shows  the  amount  of  iron  in  milligrammes  in 
100  grammes  of  dried  substance: 


White  of  eocr  . . 

trace 

Carrots 

S-6 

Rice    . .          . . 

1-2 

Apples 

13 

Wheat  flour  .  . 

1-6 

Cabbage 

17 

Milk 

2-3 

Beef 

17 

Peas   . . 

6-2 

Yolk  of  egg 

. .      10-24 

Potatoes 

6-4 

Spinach 

. .     33-39 

Lack  of  Carbohydrates  and  Fats. — The  result  of  withdrawing  fats 
and  carbohydrates  from  the  diet  depends  on  the  class  of  animal. 
Carnivora  can  live  for  a  long  time  on  a  diet  consisting,  as  nearly  as 
possible,  of  protein  only,  viz.,  lean  meat  freed  from  as  much  fat  as 
possible.  Omnivora  or  herbivora  do  not  appear  to  be  able  to  live  on 
such  a  diet.  The  replacement  of  fat  by  excess  of  carbohydrate  leads 
to  the  retention  of  water  in  the  body.  Fat  starvation  causes  a  form  of 
•dropsy.  The  food  eaten  per  diem  should  contain  at  least  60  grms. 
of  fat. 

Lack  of  Lipoids.  —  There  is  some  evidence  that  these  may  be 
synthesized  in  the  body  out  of  protein  and  carbohydrate.  They  are 
essential,  and  it  is  advisable  that  they  should  be  in  the  diet. 

Lack  of  Vitamines. — The  fresh  foods  contain  certain  active  prin- 
ciples necessary  for  nutrition  and  growth,  which  may  be  removed  by 
the  modern  processes  of  milling  or  canning  food.  If  these  are  in- 
sufificient  nutrition  is  gravely  affected. 

The  first  knowledge  of  the  effect  of  a  deficit  of  these  bodies  wa« 
afforded  by  the  study  of  the  disease  known  as  beri-beri.  It  is  now 
conclusively  shown  that  this  disease  is  due  to  feeding  (as  the  almost 
sole  article  of  diet)  on  "  polished  "  rice — that  is  to  say,  rice  from  which 


METABOLISM  DURING  STARVATION 


33-; 


the  outer  husks  have  been  removed.  Under  these  conditions  pains 
and  weakness  of  the  muscles  in  the  Hmbs  develop,  with  a  lowering 
or  comi^lete  loss  of  sensibility;  often  cedema  also  supervene  3.  and  in 
some  cases  death  rajDidly  ensues.  If  instead  of  polished  rice  the 
whole  rice  be  eaten,  such  symptoms  do  not  develop.  The  addition  of 
the  '■  polishings  "  to  polished  rice  also  prevents  the  onset  of  symp- 
toms. The  proportion  of  cases  of  beri-beri  in  the  Java  prisons  was 
reduced  from  1  in  39  to  1  in  10,000  when  unshelled  rice  was  substituted 


Fig.  188. — To  show  Effect  of  Vitamixe  ox  Xuteitiox.     (Schaumann.) 

A,  Pigeon  fed  on  food  containing  no  vitamine.  unable  to  stand  up;  B,  after  adding 
vitamine  to  food  the  first  day;  C,  the  second  day. 


for  shelled  rice.  In  some  districts  of  the  East  the  disease  has  com- 
pletely disappeared  since  this  substitution  has  been  made.  The 
necessary  substance  is  contained  in  the  subpericarpal  tissue  of  the 
rice;  its  nature  has  not  yet  been  determined.  The  phosjihorized 
organic  bodies  which  are  abundant  in  the  husk  may  be  of  consider- 
able importance  to  the  organism. 

S3'mptoms  similar  to  beri-beri  may  be  induced  in  animals  by  feeding 
them  on  polished  rice ;  these  symptoms  are  almost  immediately  relieved 
when  an  acid  extract  of  the  "  polishings  "  is  added,  after  neutraliza- 
tion, to  the  rice. 


338 


A  TEXTBOOK  OF  PHYSIOLOGY 


Animals — e.g.,  pigeons — fed  upon  polished  rice  gradually  lose 
weight,  develop  nervous  symptoms  al<in  to  beri-beri,  and  die.  Post 
mortem  extensive  changes  are  found  in  the  cells  of  the  central  nervous 
system,  and  inflammatory  changes  in  the  nerve  trunks. 

A  similar  substance  is  included  in  the  husks  and  germ  of  the  wheat 
berr3^  White  flour  made  from  the  wheat  berry  from  which  the  bran 
(the  outer  husk),  the  sharps  (the  under  husk),  and  the  germ  have 
been  removed,  will  not  sup])ort  life  by  itself.  Neither  will  bread  made 
from  it;  while  wholemeal  bread  will. 

The  possession  of  this  substance  accounts  for  the  superiority  of 
'•  standard  "  and  particularly  of  wholemeal  bread  over  '"  white  " 
bread.  By  the  children  of  the  very  poor,  who  live  mainly  on  bread 
and  margarine,  it  is  imperative  that  wholemeal  bread  should  be  eaten. 


Fia.lfe'J.-Tu  .siiuw   iuFECT  OF  ViTAMiNES  ON  Geo'w Til.     (After  C.  Funk.) 
These  chicks  are  of  the  same  age,  the  smaller  fed  on  a  diet  deficient  in  vitamincs. 


The  anti  beri-beri  vitamines  have  been  found  to  occur  in  yeast,  in 
various  vegetables,  and  in  milk;  they  are  not  destro3'ed  by  heating 
to  100°  C,  but  are  destroyed  at  120°  C. 

There  are  also  anti-scorbutic  vitamines,  the  lack  of  which  cause 
scurvy.  These  are  destroyed  easily  by  cooking  or  preserving,  hence 
the  advantage  of  raw  fruit  or  salads  in  the  diet.  Potatoes,  fresh 
vegetables,  oranges,  and  fruit  not  too  ripe  are  rich  in  these  vitamines. 
The  introduction  of  the  potato  has  expelled  scm-vy  from  the  towns. 
Tn  addition  to  the  above  there  is  a  fat-soluble  vitamine  essential  to 
growth  present  in  butter  and  animal  fat  margarine,  but  not  in  vege- 
table oil  margarine  or  lard,  present  also  in  g.een  vegetables  which 
form  the  complete  food  of  an  herbivorous  animal. 


3IETAB0LISM  DURING  STARVATION 


339 


Metabolism  with  Excess  of  Protein. — When  an  animal  excretes  in 
the  urine  daily  the  same  amount  of  nitrogen  as  it  is  receiving  in  the 
diet,  it  is  said  to  be  in  a  state  of  nitrogenous  equilibrium.  If  the 
amount  of  the  nitrogen  taken  in  be  suddenly  increased  (for  example, 
an  animal  is  put  on  to  a  lean  meat  diet),  the  nitrogen  output  goes  up; 
but  at  first  the  amount  of  nitrogen  excreted  lags  b?hind  that  ingested, 


Fig.  189a. 
Qhick  A,  weight  1G2  gms.;  Chick  B,  342  gms.,  are  birds  of  same  age  (81  days).  A  re- 
ceived corn  ghiten  food,  B  received  lactalbunnn  in  addition.  Chicks  C  and  D 
also  (81  day.s  old)  received  corn  gluten  and  cottonseed  flour.  A  gained  52  gnis. 
in  5.")  days :  B.  283  gms.  in  55  days ;  C,  284  gms.  in  53  days ;  D,  322  gms.  in  53  days, 
(Osborne  and  Mendel.) 


SO  that  nitrogen  equilibrium  is  not  attained  for  several  days — • 
generally  three  to  five,  the  time  varying  according  to  the  nature  of  the 
protein  fed.     During  these  days  the  animal  is  storing  up  nitrogen 


3-K)  A  TEXTBOOK  OF  PHYSIOLOGY 

in  the  body,  and  this  store  is  not  again  lost  initil  the  amonnt  of  protein 
in  the  diet  is  reduced. 

When  there  is  a  large  amount  of  protein  in  a  mixed  diet,  the  fat 
katabolism  in  the  body  is  reduced,  so  that  some  of  the  fats,  or  carbo- 
hydrates, in  the  diet  are  not  used,  and  may  be  stored  up  as  fat. 
The  proteins  are  not  all  of  equal  value,  for  some  do  not  contain 
essential  "  building  stones."  Thus,  gelatin  does  not  suffice  as  a  tissue- 
former,  but  can  act  as  a  source  of  energy.  When  fed  with  an  ade- 
quate protein  diet,  gelatin  acts  as  a  protein-sparer.  Fed  during 
.starvation,  gelatin  spares  protein  to  the  extent  of  about  35  per  cent. 
Generally  speaking,  about  one-fifth  of  the  true  protein  nitrogen  can 
be  replaced  by  gelatin  nitrogen.  Gelatin  also  exerts  a  sparing  action 
on  fat  katabolism.  Gelatin,  therefore,  although  insufficient  for  body- 
building, from  the  point  of  view  of  energy  is  quite  a  useful  article  of 
diet.  Gelatin  can  be  made  a  much  more  sufficient  tissue-builder  V)y 
feerling  with  it  those  important  amino-acids,  tyrosin  and  tryptophane, 
which  are  lacking  in  its  constitution.  The  same  holds  good  for  zein, 
r.  protein  obtained  from  maize.  Tlv>  amino-acid  content  of  a  diet 
is  important  in  regard  to  growth  (see  Fig.  189,  A). 

The  Effect  of  Fat. — Fat,  when  added  to  the  diet,  exerts  a  sparing 
effect  upon  the  katabolism  of  protein.  Thus,  Avhen  a  dog  was  fed 
with  1,500  grammes  of  protein,  its  nitrogen  excretion  was  equivalent 
to  the  katabolism  of  1,512  grammes.  On  the  addition  of  150  grammes 
of  fat,  the  nitrogen  excretion  equalled  1,474  grammes  of  protein. 
Carbohydrates  exert  a  like  or  even  greater  sparing  effect  on  proteins. 
The  addition  of  fats  or  carbohydrates  to  a  diet  of  protein,  insufficient 
by  itself,  will  enable  an  animal  to  attain  nitrogenous  equilibrium  and 
even  to  store  protein  in  the  body.  But  the  protein -supply  cannot  be 
taken  below  a  certain  minimum,  a  minimum  which  seems  to  vary 
with  different  foodstuffs.  Thufj  30  grms.  of  protein  suffice  on  a  diet 
of  potatoes,  and  80  grms.  on  a  diet  of  bread.  On  a  diet  largely  consist- 
ing of  potatoes  the  body  can  be  run  on  a  very  low  plane  both  of  energy 
and  protein  value.  For  times  of  scarcity,  then,  the  potato  is  invaluable. 
The  most  virile  races  of  the  world  occupy  cool  climates  and  eat  food- 
stuffs yielding  high  energy,  protein,  and  fat  values — e.g.,  meat  and 
cereals.  Few  people  recjuiring  a  diet  of  3,500  colories  can  digest  with 
comfort  more  than  500  grms.  of  carbohydrates,  while  the  use  of  more 
than  120  grms.  of  protein  is  wasteful.  About  1 ,000  calories  have  then 
to  be  made  up  from  fat.  and  this  means  eating  a  little  over  100  grms. 
Fat  is  easily  digested,  and  does  not  cause  the  rise  in  heat  production 
AA'hich  protein,  and  to  a  lesser  degree  sugar,  does. 


CHAPTER  XXXIX 

METABOLISM  UNDER  VARYING  CONDITIONS 

The  body  requires  a  certain  amount  of  energy  lor  tlie  })erformance 
of  its  functions  during  rest.  This  is  known  as  the  basal  requirement, 
and  is  best  ascertained  by  determining  the  respiratory  exchange  of 
a  person  in  a  state  of  complete  rest  twelve  hours  after  the  last 
meal,  which  should  not  have  been  rich  in  carbohydrate.  Such  a 
state  is  best  obtained  in  bed,  before  rising,  in  the  early  mornmg, 
when  the  surrounding  medium  is  uniform  in  temperature,  the  muscles 
are  well  rested,  and  other  systems  of  the  body,  such  as  the  alimentary 
system,  are  more  or  less  inactive. 


-'^  +  - 


__-;.\i 


^ 


^ 


-frJ-T- 


-U4-^- 
-X— 1-- 
— 2a- 


-i — I — 1— 
I    I    I 
I    I    I 

-r-o— t- 
-h^s-l— 

I     r 


-t- 

:    I 
I    ! 


—-i  I    ! 


-W4-4- 


I     I 


1-V 


---Xi 


FlU.    lyU. — ]^IAGRAM     TO    ILLUSTRATE   THE    RELATION     BETWEEN    VoLUME    OR    WeIGHT 

AND  Surface.     (Waller.) 

The  volumes  are  1,  8,  27  c.cm.;   the  weights  are  1,  8,  27  grammes;  the  surfaces  are 
6,  24,  54  square  cm.;  the  ratio  of  increase  is  1,  4,  9. 


Of  this  basal  requirement  it  is  calculated  that  10  to  20  per  cent, 
of  the  total  energy  is  required  for  the  maintenance  of  the  work  of 
circulation  and  respiration. 

The  Weight  of  the  Body  and  the  Suriace  Area. — The  larger  the 
mass  of  an  animal,  the  greater  its  absolute  energy  requirements,  and 
the  greater  its  absolute  consumption  of  material.  While  this  is  true 
for  the  absolute,  it  is  not  true  for  the  relative  amounts.  The 
smaller  the  animal,  the  relatively  greater  is  its  energy  out])ut.  This 
is  l)ecause,  calculated  per  kilo  body  weight,  small  warm-blooded 
animals  have  a  proportionately  greater  surface  area.  They  have 
therefore  need  of  a  greater  heat  production,  involving  an  increased 
metabolism. 

841 


342 


A  TEXTBOOK  OF  PHY.SiOLOGY 


This  is  seen  in  the  following  table  from  ex])eriments  on  animals 
during  a  period  of  twenty -four  hoius'  hunger: 


Animal. 


Horse 

Pig 

Man 

Dog 

Goose 


Weight  in 

Energy  released  during 
24  Hours'  Starvation. 

Kilos. 

Per  1  Kilo 

Per  1  Cm. 

Body  Weight. 

Surface. 

441 

11-3 

948- 

128 

1!»-I 

1078 

64 

32-1 

1042 

15 

51*5 

1039 

3-5 

GO- 7 

967 

This  rule  holds  for  larger  and  smaller  animals  of  the  same 
species,  as  may  be  seen  from  the  following  figure. 

The  accompanying  table  shows  the  oxygen  use  per  minuta  in  man 
in  the  first  few  years  of  life,  and  again  at  the  age  of  puberty. 


Age, 
Years. 


C 

9 

14 

17 

Adults 

(22-43) 


Weight 
in  Kilos. 


11-5 
18-4 
21-8 
36-1 
44-3 
()6-7 


O2  consumed      O.y  Use  per 
per  Min.,  Kilo  of 

C.G.  Body  Weight. 


Relative  Consumption 
of  Oxygen  to  A  dull 
(Standard=  100). 


112-2 
139-9 
148-0 

188-1 
212-7 
227-9 


0-70 
7-61 
6-79 
5-21 
4-80 
3-41 


Per  Kilo 

of 

Per  Sq.  M. 

Body  Wei 

ght. 

of  Surface. 

285 

160 

223 

145 

199 

137 

152 

125 

140 

123 

100 

100 

The  basal  metabolism  of  man,  measured  under  conditions  of  fast- 
ing and  rest  in  bed,  is  40  calories  per  horn-  per  sq.  metre  of  skin  sur- 
face, 37  for  woman,  50  for  boys  of  12-13  years.  The  formula  used  for 
measm'ing  the  surface  is  A  ^  W  ^'^^^  x  H  O"^^  x  71*84.  A  =  sq.  metres ; 
W  =  weight  in  kilogrammes;  H  =  height  in  centimetres. 

In  young  animals  the  increased  metabolism  may  be  due  in  part  to 
the  actual  processes  of  metabolism  being  more  active  in  the  growing 
than  in  the  adult  animal.  During  the  early  months  of  their  life  infants 
appear  to  be  an  exception  to  the  rule;  their  metabolism  is  much  loAver 
than  it  should  be  as  calculated  from  the  body  surface.  The  infant  is 
kept  warm,  and  sleeps  quietly  most  of  its  time  in  cradle  or  pram. 
This  very  likely  is  not  the  case  with  the  infant  of  the  native  Austra- 
liin  or  Terra  del  Fuegian.  Infants  are  generally  over-coddled,  and 
are  made  more  virile  by  some  exposure  to  cold  and  exercise.  In  old 
age  the  metabolism  is  reduced. 

It  is  doubtful  whether  sex  influences  the  metabolism  in  any  degree. 


METABOLISM  UNDER  VARYING  CONDITIONS         343 

Work. — During  work  the  metabolism  is  increased.  This  is  due 
to  the  increased  activity  of  the  muscles.  Investigation  shows  that 
this  is  mainly  at  the  expense  of  the  fats  and  carbohydi-ate,  and  but 
little  at  the  expense  of  the  proteins,  unless  there  be  a  deficit  of  the 
two  first.  The  respirator}^  exchange  is  greatly  increased  by  muscular 
work  (see  p.  319). 

A  subject  pedalled  a  b'cycle  sixteen  hours  out  of  twenty-four. 
The  whole  energy  expended  =  9,981  calories.  The  energy  of  the  food 
taken  =  5,138  calories.  The  energy  taken  out  of  the  body  substance 
=  4,843  calories.  The  energy  derived  from  tissue  protein  only  =  478 
calories.  As  the  man  was  an  athlete  in  training,  his  muscles  were  not 
overdone,  and  thus  the  protein  metabolism  was  scarcely  increased.  The 
experiment  shows  how  body  fat  may  be  taken  off  by  hard  exercise. 

When  no  muscular  work  is  done,  as  during  the  first  hours  of 
sound  sleep,  the  metabolism  of  the  body  markedly  decreases;  during 
the  waking  hours  it  again  increases.  But  if  th^  individual  keeps  at 
rest  and  protected  from  cold,  there  is  no  increased  metabolism  during 
these  hours. 

External  Temperature. — A  lowering  of  the  external  temperature 
•excites  to  more  muscular  movement,  voluntary  and  involuntary, 
and  thereby  increases  metabolism.  Shivering  helps  to  keep  up  the 
teinperatiu-e.  Exi)o:;ure  to  cold  wind  may  double  the  respkatory 
•exchange,  even  if  the  individual  sits  quiet  in  a  chair  and  does  not  shiver. 

There  is  a  relation  between  the  cooling  power  of  the  atmosphere, 
the  skin  temperature,  and  the  rate  of  metaboHsm.  Thus  the  appetite 
is  increased  at  a  bracing  place. 

The  raising  of  the  body  temperature  increases  the  metabolism. 

Feeding. — The  taking  in  of  food  raises  the  metabolism,  partly  owing 
to  the  mechanical  work  involved  in  digestive  processes,  partly  owing 
to  the  chemical  processes.  With  some  foods  this  may  be  very  great — 
as  much  as  50  per  cent,  of  the  energy  value  of  the  food  taken  in.  For 
instance,  with  a  horse  chewing  hay,  48  per  cent,  of  the  energy  value 
is  used  up  in  the  work  of  mastication  and  digestion,  whereas  but 
19-7  per  cent,  is  so  used  in  the  case  of  oats.  It  has  been  calculated, 
for  the  caloric  value  of  the  food  taken  there  is  expended  in  heat  pro- 
duction duiing  digestion  and  assimilation — 

Fats  . .  . .  . .  . .  . .     about  2|  per  cent. 

Starches        . .  . .  . .  . .  . .  ,,     9         ,, 

Proteins        . .  . .  . .  . .  . .  ,,1"         >> 

Proteins,  having  so  high  "  a  specific  dynamic  energy,"  are  heating, 
thus  more  protein  is  consumed  by  man  in  cold,  and  less  in  tropical 
•climates.  In  the  adaptation  of  an  Englishman  to  a  tropical  climate 
diet  is  of  great  importance.  On  a  diet  of  rice  and  bananas  monkej^s 
.successfully  withstand  exposvn-e  for  hours  to  the  tropical  sun. 


CHAPTER   XL 


DIETETICS 

Briefly  stated,  we  take  in  food — ■ 

1.  To  rebuild  the  living  tissues. 

2.  To  obtain  energy  for  the  biological  processes. 

3.  To  preserve  the    proper  medium  in  which  these  i)ro- 

cesses  can  be  carried  out. 

The  Selection  o£  Foodstuffs. — Hitherto  we  have  spoken  of  proteins. 
tats,  and  car):ohy(hates.  .-oinewhat  as  if  the}'  were  usually  foi  nd 
separately,  as  such,  in  the  food  materials  in  common  use.  This  is  not 
the  case  in  regard  to  the  majority  of  the  commoner  natural  food 
materials.  These  are  mixtures  of  all  three  classes  of  nutrients,  as 
can  be  seen  from  the  following  tables.  Nevertheless,  the  food  materials 
can  be  grouped,  according  to  their  constitution,  into  those  which  are 
mostly  protein,  mostlj-  fat,  mostly  carbohydrate,  or  mostly  water. 
Some  prepared  foodstuffs,  such  as  sugars  and  starches,  or  butter  and 
oils,  are  almost  exclusively  one  class. 


Pro- 

Fat 

Carbo- 

Total 

tein 

Weight 

hydrate 

Weight 

Caloric 

Weight 

in 

Weight 

in 

Value. 

in 

(  rms. 

in 

Grms. 

Gnus. 

Grms. 

Man  (moderate  work).  . 

lis 

50 

500 

674 

£054 

Man  (hard  work) 

14.-. 

100 

450 

695 

3370 

Man  (moderate  work) .  . 

101) 

100 

240 

440 

2324 

Man  (moderate  work) .  . 

130 

40 

550 

720 

3160 

Man  (subsistence  diet) 

o~ 

14 

341 

412 

1760 

Man  (active  labour)      .  . 

1.10 

71 

568 

795 

3G30 

Man  (moderate  work)  .  . 

12.-. 

125 

400 

G50 

3325 

Man  (aged ) 

100 

OS 

350 

518 

2475 

Woman  (mc  derate  worl^) 

<J2 

44 

400 

536 

2425 

Woman  (a.eed)  .  . 

S(.» 

50 

260 

390 

1£C0 

Children  (1-2) 

28 

37 

75 

140 

765 

Children  (2-6) 

5.5 

40 

200 

295 

1420 

Children  (6-15)  .  . 

75 

43 

325 

443 

2040 

In  regard  to  practical  dietetics,  several  important  points  have  to 
be  considered: 

1.  The  amount  and  proportion  of  the  various  foods  which  are  neces- 
sary to  meet  the  physiological  needs  of  the  body  at  different  ages  in  the 
different  sexes,  and  under  various  conditions  of  activitj'  and  environment . 

344 


DIETETICS  345 

2.  The  proper  selection  of  food  materials  to  supph'  such  an  adequate 
diet,  including  the  economic  purchase  of  the  same. 

3.  The  various  methods  of  preparing  food  for  consumption. 

4.  Food  hygiene. 

Much  study  has  been  expended  upon  the  question  of  the  adequate 
dietar}'.  There  is  a  general  consensus  of  expert  opinion  that  all  three 
classes  of  foodstuffs  should  enter  into  the  dietary-  of  man.  the  amount 
and  proportion  of  these  being  regulated  according  to  conditions  of 
age.  sex,  activity,  and  environment.  In  the  table  on  p.  343  are  shown 
a  few  of  the  diets  suggested  by  various  authorities,  the  weights  being 
given  in  the  dry  condition  of  the  foodstiiffs: 

The  chief  point  of  interest  in  the  above  is  the  amount  of  protein 
required  in  the  adequate  diet.  It  is  generally  conceded  that  the 
amount  of  protein  required  is  from  100  to  120  grammes.  The  following 
diets  have  been  suggested  for  temperate  chmates  as  the  residt  of  recent 
^\  ork.     The  values  arc  given  for  food  as  purchased. 


Protein.  Fat.  .     ,    ,'  Calories, 

ay  drat  e. 


Sedentary '  88  108  345  2.501 

Moderate  hard  work 


(125  137  470  33(34 

\116  158  538  3762 


Very  hard  work 


/  145  195  557  4223 

U45  235  666  4954 


The  work  done  hy  an  ordinary  labourer  is  estimated  to  be  100,000 
kg.  metres,  2000  calories  can  be  taken  as  the  maintenance  requirement 
of  the  resting  man.  The  mechanical  equivalent  of  heat — 4-23  kg.  m.= 
1  calorie.  The  efficiency  of  a  man  as  machine  is  taken  as  20  per  cent. 
The  fuel  value  of  the  food  spent  on  work  is  then  about  1200  calories. 

The  peace  dietary  provided  to  the  British  Arnw  is  supplemented 
by  food  bought  for  supper,  and  the  pay  is  now  sufficient  to  enable 
this  to  be  done  ^\■ithout  hardship.  Experience  seems  to  show  that 
the  plan  of  letting  the  men  buy  their  own  supper  works  smoothly, 
and  is  preferred;  it  gives  elasticity  to  the  diet,  and  allows  each  man 
to  select  the  quality  and  amount  of  food  which  suits  him.  The  recruit 
— a  growing  lad— ^requires  more  food,  and  the  Army  Council  have  wisely 
granted  him  a  messing  allowance.  He  usually  buj's  considerable  quanti- 
ties of  cakes.  The  war  rations  of  the  British  Army  in  South  Africa 
may  be  contrasted  with  that  of  Japan  and  Russia  in  Manchuria : 


Protein.  Fat.  /,.,      '  Calorics. 


Injdrate. 


Briti:*li  138  105  528 

.Japanese         158  27  840 

Russian  187  27  775 


3903 
4313 
4891 


34(3 


A  TEXTBOOK  OF  PHYSIOLOGY 


A  little  one,  4,000  calories,  i.s  now  the  amount  of  the  field  service 
ration  of  the  British  Army. 

A  study  of  the  different  dietaries  of  the  world,  selected  by  the 
people  themselves,  shows  that  the  age  and  occupation  markedly 
influence  the  actual  consumption  of  food,  but  that  economic  and  other 
conditions  largely  influence  the  diet  chosen  by  men  doing  the  same 
type  of  work  in  different  countries.  In  the  following  table  (Lang- 
worthy)  the  physiological  availability  of  food  ingested  is  taken  into 
account : 


United  States  (laboiu'er,  moderate  mus- 
cular work) 

United  States  (labourer,  hard  muscular 
work)    . . 

Ireland  (working  man) 

England  (working  man) 

Scotland  (working  man)   . . 

Sweden  (working  man) 

Sweden  (working  man,  hard  work) 

Finland  (working  man)     . . 

Finland  (working  man,  hard  work) 

Northern  Italy  (labourers) 

Southern  Italy  (labourers) 

Japan  (labourers)  .  . 

China  (labourers)  .  . 

Congo  (labourers)  .  . 

United  States  (students) 

Scotland  (students) 

Sweden  (students) 

Finland  (students) 

Japan  (students)    .  . 


Protein 

Ccdori-es  of 

Protein 

Energy 

eaten. 

Total  Diet. 

dige-Ucd. 

utilized. 

100 

3,68.') 

92 

3,425 

177 

6,485 

162 

6,000 

98 

— 

90 

3,107 

89 

— 

82 

2,685 

108 

— 

OO 

3,228 

134 

— 

123 

3,281 

189 

— 

174 

4,557 

114 

— 

105 

3,011 

167 

— 

150 

4,378 

12.5 

— 

115 

3,655 

148 

— 

136 

4,400 

118 

— 

103 

4,415 

91 

— 

83 

3,400 

108 

— 

90 

2,812 

106 

3,560 

98 

3,285 

143 

— 

132 

3,979 

127 

— 

117 

3,032 

157 

— 

144 

3,984 

98 

— 

88 

2,800 

These  confirm  the  results  of  research  as  to  the  amount  of  protein 
required  in  a  diet.  It  is  aj^parent  that,  allowing  for  individual  tastes 
and  characteristics,  100  to  120  grammes  of  protein  should  be  con- 
tained in  the  diet  of  an  average  individual.  Allowance  also  must  be 
made  for  the  fact  that  all  proteins  are  not  of  equal  nutritive  value. 
Reference  has  already  been  made  to  the  great  value  of  protein  bodies, 
like  caseinogen,  containing  aromatic  groupings  such  as  tyrosin 
and  tryptophan,  and  to  the  inefficiency  to  support  life  of  bodies  like 
gelatin,  zein,  hordein,  w^hich  contain  none  or  little  of  such  groupings. 

Recently  it  has  been  suggested  that  a  diet  containing  a  minimum 
of  protein  (about  40  to  50  grammes)  daily  is  better.  It  is  certain  that 
an  excessive  ingestion  of  protein  is  harmful,  especially  when  taken  with 
lack  of  exercise,  but  the  evidence  adduced  in  favour  of  such  a  small 
amount  when  the  individual  is  healthy  and  energetic  is  by  no  means 
convincing.  It  does  not  follow  that  a  minimum  diet  is  an  optimum 
diet,  and  since  we  must  assume  that  the  present  races  are  the  survivors 
of  the  fittest,  there  is  no  reason  to  believe  that  the  ingestion  of  100 
to  120  grammes  of  protein  daily,  as  is  common  to  all  virile  races  of  the 


DIETETICS  347 

world,  is  in  aiw  Avay  harmful,  provided  the  other  ordinary  rules  of 
health  are  attended  to  at  the  same  time. 

It  has  also  been  shown  by  investigations  carried  out  in  Indian  prisons 
that  the  more  virile  races  of  India  c  xt  animal  food  in  which  protein 
figures  largely;  the  less  virile  races,  on  the  other  hand,  exist  mainly- 
on  a  vegetarian  and  small  protein  diet.  By  transferring  members 
of  the  less  virile  tribes  to  a  diet  containing  a  larger  amount  of  protein, 
a  great  improvement  in  physique  was  observed.  It  is  noticeable, 
also,  that  the  children  of  parents  who  have  visited  Europe  are  often 
of  better  physique  than  their  parents.  This  is  probably  because, 
during  the  visit  to  Europe,  their  parents  acquired  the  habit  of  taking 
more  protein  in  the  diet,  and,  consequently,  the  growing  children 
have  received  more  protein,  especially  animal  proteiii.  than  did  their 
parents  when  young.  It  is  quite  jwssible  that  the  small  physique 
of  some  races  is  due  in  part  to  a  lack  of  protein  in  the  diet  of  their 
ancestors.  The  fat  in  animal  food  may  be  of  no  less  imi^ortance. 
The  mighty  Norsemen  were  great  flesh-eaters. 

In  regard  to  the  selection  of  foodstuffs,  the  table-<  on  pp.  347-350 
give  the  analyses  of  the  most  important  groups  of  foodstuffs,  with  their 
approximate  cost.*  Certain  valuable  facts  can  be  gleaned  from  them 
for  the  recommendation  of  dietaries,  especially  to  the  less  well-to-do 
classes.  Thus,  it  will  be  seen  that  the  chief  protein-containing  foods 
are  lean  meat,  fish,  eggs,  cheese,  milk,  legumes  (peas  and  beans), 
certain  nuts  (almond,  brazil,  walnut),  and  the  cereals.  The  chief 
fat-containing  foods  are  butter,  margarine,  fat  pork,  various  vegetable 
oils  (olive),  and  nuts  (almond,  brazil,  cocoanut,  and  walnut).  The 
chief  carbohydrate-containing  foods  are  the  cereal  grains  (wheat, 
barley,  rye,  oats,  etc.),  with  certain  fruits  (banana,  grape,  cherry,  etc.), 
and  the  chestnut.  As  watery  foods  may  be  classed  milk,  fresh  vege- 
tables and  fruits,  fresh  meat,  fish,  and  shellfish.  As  relative Ij^  dry 
foods  may  be  grouped  flours  and  meals,  bread,  biscuits,  dried  fruits, 
nuts,  cured  meats  and  fish,  cheese,  butter,  sugar.  It  is  obvious 
that  the  food  value  of  a  substance  is  to  be  gauged  largely  bj^  the 
amount  and  nature  of  the  dry  matter  it  contains. 

Certain  foodstuffs,  chiefly  natural,  can  in  themselves  supply  all 
the  necessary  proximate  principles  of  food :  grains,  meat,  eggs,  milk, 
cheese,  nuts.  Other  foodstuffs,  chiefl}'  manufactured,  supply  but  one 
kind  of  nutrient — e.g.,  starches  (sago,  tapioca),  sugar,  butter,  lard. 
Vegetable  foodstuff's  (flours,  meals,  oats,  sugar)  are  relatively  cheap, 
animal  foodstuffs  (beef,  mutton,  etc.)  relatively  dear.  In  supph^ing 
extra  calories  it  is  to  be  noted  also  that  carbohydrates  are  relatively 
cheap,  fats  relatively  dear.  The  tables  show,  for  example,  that  one 
shilling  may  purchase  as  flour,  11,646  calories;  as  meat,  2,400  calories; 
as  fish  (large  amount  of  waste),  495  calories. 

In  regard  to  cost,  it  is  a  great  waste  of  money  on  the  part  of  the 
public  to  buy  many  articles  ahead}'  packed  for  them,     ^^^lat  they 

*  These  prices  are  the  average  prices  which  were  in  operation  in  1913-14,  and 
were  obtained  by  visiting  markets  and  shopping  quarters,  especially  those  where  the 
poorer  classes  shop.  Tno  pri^ci  of  foj:l  have  doubled  during  the  war  (see  also 
graph,  p.  361). 


348 


A  '1  KXTIJOOK  OF  PHYSIOLOGY 


gain  ill  some  cases  in  cleanness  they  lose  in  all  case;   in  the  cost  of  the 
packing. 

Man's  vagaries  in  appetite  are  Jio  guide  to  the  nutritive  value  of 
food.  Expensive  foodstuffs  are  not  necessarily  more  nutritious — 
e.g.,  rib  of  lieef  and  brisket,  butter  and  margarine,  salmon  and  herring. 

Table  showing   Compi'SITiox,   Fdoi)   Value,   and   Cost  of   Protein  Foods. 


u 

fe 

S-S 

K>       . 

^ 

•s  « 

S> 

•si 

4 

0? 

1 

a. 

^ 

e 

'■^ 

|4 

t 





—  — 



. — 

—   — 



— 



Fresh  Beef: 

Brisket,  edible  . . 

— 

:)4-(i 

1.V8 

28-5 

— 

0-9 

1,495 

— 



as  bought 

•23-3 

41-t) 

12-0 

22-3 

— 

0-6 

1,165 

6d. 

2,330 

Flank,  edible     . . 



59-3 

19-() 

21-1 



0-9 

1,255 

— 

— 

as  bought 

5*5 

56-1 

18-6 

19-9 

— 

0-8 

1,185 

5id. 

2,400 

Ribs,  edible 



57-0 

17-8 

24-6 

— 

0-9 

1,370 

— 

— 

as  bought 

20-1 

45-3 

14-4 

20-0 

— 

0-7 

1,110 

1/- 

1,110 

Veal (average)  .  . 

— 

70-0 

20-2 

9-0 

— 

1-2 

755 

— 

— 

Mutton: 

Neck,  edible 

— 

::,(rii 

l()-7 

26-3 

— 

1-0 

1,420 

— 

— 

as  bought 

26-4 

41-5 

12-2 

19-6 

— 

0-7 

1,055 

6d. 

2,110 

Leg,  edible 



63-2 

18-7 

17-5 



1-0 

1,085 

— 

— ■ 

as  bought 

17-7 

r)i-9 

15-4 

14-5 

— 

0-8 

900 

lid. 

982 

Pork: 

Flank,  edible     . . 



59-0 

18-5 

22-2 

— 

1-0 

1,280 

— 

— 

as  bought 

18-0 

48-0 

1,5-1 

18-6 

— 

0-7 

1,065 

9d. 

1,420 

Loin,  edible 



48-2 

1.5-7 

36-3 



0-7 

1,825 

— 

— 

Middle,  as  bought 

ll>-7 

38-() 

12-7 

28-9 

— 

0-7 

1,455 

v- 

1,455 

Fowls : 

edible  . . 



(;3-7 

19-3 

16-3 



1-0 

1,04.5 

— 

— 

as  purchased 

2-v;t 

47-1 

13-7 

12-3 

— 

0-7 

775 

3/6 
each. 

— 

Fish: 

Cod  (whole  )odible 

— 

82- (i 

Ki-r) 

0-4 

— 

1-2 

S25 

— 

— 

as  purchased 

52-5 

38-7 

8-4 

0-2 

— 

0-6 

165 

4d. 

495 

Salmon    (whole), 

edible 

— 

04-() 

22-0 

12-8 

— 

1-4 

950 

— 

— 

as  purchased .  . 

34- 'J 

40-9 

15-3 

8-9 

— 

0-9 

660 

2/- 

330 

Turbot  edible    . . 



71-4 

14-8 

14-4 

- — 

1-3 

885 

— 

— 

as  purchased 

47-7 

57-3 

(i-S 

7-5 

— 

0-7 

460 

1/3 

— 

Herring,       fresh, 

edible 



72-.") 

19-. 5 

7-1 

— 

1-5 

C60 

— 

— 

as  purchased 

42-(i 

41-7 

11-2 

3-9 

— 

0-9 

375 

Id.ea. 

— 

Herring,  smoked. 

edible 

— 

34-(i 

3()-9 

1.5-8 

— 

13-2 

1,355 

• — 

— 

as  purchased . . 

44-4 

19-2 

20-. 5 

8-8 

— 

7-4 

750 

Id.ea. 

— 

Shellfish: 

Oysters,  edil>le 

— 

S()-9 

(i-2 

1-2 

3-7 

2-  1 

235 

— 

in  shell,  as  pur- 

chased 

81-4 

1()-1 

1-2 

0-2 

0-7 

0-4 

45 

— 

— 

Lobster,  edible . . 



79-2 

16-4 

1-8 

0-4 

2-2 

390 

— 

— 

as  purchased .  . 

Cl-7 

30-7 

5-9 

0-7 

0-2 

0-8 

140 

— 

— 

Eggs: 

edible  (cooked). . 

— 

73-2 

14-0 

12-0 

— 

0-8 

765 

— 

— 

in  shell,as  bought' 

11-2    1 

(55-0 

12-4 

10-7 

" 

0-7 

680 

1/- 

850 

DIETETICS 


349 


Table  Showing  Cumpo.sition,  Food  Valtte,  a>-d  Cost  of  Proteix 
FooDS  (Continued). 


i 

!^ 

i    «  0 

•«* 

<J 

0 

-S  " 

i.    ■' 

^ 

?4. 

J»  ^ 

0  -^ 

55 

^" 

■J 

1 

y: 

1  f^^ 

3i 

"^ 

^ 

^ 

"^ 

^J 

ll 

§  S 

■^ 

~s 

1        ~o 

Aver 
per  1 

Cheese : 

American  red,  as 

purchased 

— 

2S-(i 

29-(> 

38-3 



3-5 

.  2,165 

Id. 

3,711 

Cheddar,  as  pur- 

1 

chased 



27-4 

27-7 

3()-S 

4-1 

4-0 

2,145 

.7id. 

3,432 

Dutch,    as    pur- 

- 

chased 

— 

35-2 

37-1 

17-7 

— 

lO-O 

1,435 

7id. 

2,296 

Roquefort,    as 

-  --  - 

purchased 

Milt- 

— 

3y-3 

22-0 

29-5 

1-8 

G-8 

1,700 

1/3 

1,360 

Whole,    as    pur- 

chased 

— 

S7-0 

3-3 

4-0 

5-() 

It- 7 

32.-J 

2d. 

p.  pt. 

2,440 

Skimmed 

— 

!)l)-.-) 

3-4 

0-3 

5-1 

0-7 

170 

Id. 

p.  pt. 

— 

Condensed, 

sweetened 

— 

2()-l) 

S-S 

8-3 

54-1 

I-:) 

1,520 

4id. 
p.  tin. 

— 

Beans:  dried 

(4-4) 

12-6 

22-5 

1-8 

59-0 

3- .J 

1,605 

2il. 

9,630 

Peas :  dried 

(4-.-,) 

9-5 

24-G 

1-0 

62-() 

2-9 

1,655 

2il. 

9,930 

Table  showing  Composition,  Food  Value,  and  C^st  of  Fat  Foods. 


Salt  Pork : 

Edible    .. 

— 

17-7 

8-4 

72-2 

— 

3-4 

3,200 

6d. 

6,400 

Belh',    as    pur- 

chased 

8-2 

16-2 

( •  ( 

fi()-2 

— 

3-2 

2,935 

— 

— 

Butter 



11-0 

!•(» 

85-0 

— 

3-0 

3,605 

1/4 

2.704 

Margarine  . . 



9-5 

1-2 

8.3-(t 

— 

6-3 

3,525 

6d. 

7,050 

Cream,      as      pur- 

chased 

— 

74-0 

2-5 

18-5 

4-5 

0-5 

910 

16 

— 

Lard, refined 



— 

— 

100  (t 

— 

— 

4,220 

8d. 

6,330 

Nuts: 

Almond,  edible 

(2-0) 

4-S 

21-(» 

.-)4-9 

17-3 

2-0 

3,030 

3d. 

— 

as  purchased 

45-0 

2' 7 

11-5 

30-2 

9-5 

M 

1,660 

6d. 

3,320 

Brazil,  edible    . . 

— 

5-3 

17-0 

66-8 

7-0 

3-9 

3,265 

— 

— 

as  purchased 

49-6 

2-ti 

8-6 

.33-7 

3-5 

2-0 

1,655 

8d. 

— 

Cocoanut,   pre- 

pared 



3-5 

6-3 

57-4 

31-5 

1-3 

3,125 

— 

— 

Walnut,  edible 

(1-7) 

2-5 

27-6 

.-)t)-3 

11-7 

1-9 

.3,105 

— 

— 

as  purchased .  . 

74-1 

0-6 

7-2 

i4-(; 

3-0 

0-5 

.05 

6d. 

1.710 

Ham: 

Smoked,  medium 

edible 



40-3 

16-3 

38-8 

— 

4-8 

1,940 

— 

— 

as  purchased . . 

13-6 

34-8 

14-2 

33-4 

— 

4-2 

1,675 

1/- 

1,675 

Sausage,  pork 

— 

46-2 

17-4 

32-5 

— 

3-4 

1,695 

lOd. 

— 

Beef  liver,  edible . . 

— 

71-2 

20-7 

4-5 

1-5 

1-6 

605 

— 

— 

as  purchased 

7-3 

65-6 

20-2 

3-1 

2-5 

1-3 

555 

6d. 

1,110 

Sweetbreads,         as 

as  purchased     . . 

— 

70-9 

16-8 

12-1 

— 

1-6 

,     825 

— 

— 

Tripe 

— 

St;- 5 

11-7 

1-2 

(1-2 

0-3 

270 

(id. 

550 

350 


A  TEXTBOOK  OF  PHYSIOLOGY 


Tablk  sjiowiNo  Composition,  Food  Value,  and  Cost  of  Carbohydrate  Foods. 


Wheat  flour : 

Patent      roller,' 

family  grade 
Self-raising 
Wheat  bread,  white 
Wheat  rolls,  white  i 
Wheat  bread,brown' 
Rye  bread 
Biscuits:       Creamt 
crackers  . . ! 

Oatmeal  . . 
Oats  (rolled) 
Rice 

Starch  (tapioca)  . . 
Starch  (sago)  . .! 
Sugar  brown  . .  [ 

Sugar  (granulated)  j 
Honey 

Apples  (dried) 
Currants  (dried)   . . 
Raisins,      as     pur- 
chased   . . 
Figs  (dried) 
Prunes,      as      pur- 
chased 
Chestnuts  (dried):   ' 
edible 
as  purchased     . . 


1 
1 

, 

! 

1 

1^ 

Oh 

1 

1 

•4 
t 

to 

Fuel  Value 
Pound. 

Average  P 
'   per  Pound, 

(0-6) 

12-8 

10-8 

M 

74-8 

0-5 

1,640 

Ifd. 

11,646 

(0-4) 

10-8 

10-2 

1-2 

73-0 

4-8 

1,600 

2d. 

9,600 

(0-5) 

35-6 

9-3 

1-2 

52-7 

,  1-2 

1,205 

— 

— 

(0-6) 

29-2 

8-9 

4-1 

56-7 

1-1 

1,395 

— 

— 

43-6 

5-4 

1-8 

47-1 

2-1 

1,050 

— 

— 

(0-5) 

35-7 

9-0 

0-6 

53-2 

1-5 

1,180 

~ 

— 

(0-6) 

6-8 

9-7 

12-1 

69-7 

1-7 

1,990 

7d. 

3,411 

(0-9) 

7-3 

16-1 

7-2 

67-5 

1-9 

1,860 

2^d. 

— 

(1-3) 

7-7 

16-7 

7-3 

66-2 

2-1 

1,850 

2^d. 

— 

(0-2) 

12-3 

8-0 

0-3 

79-0 

0-4 

1,630 

2^d. 

— 

(0-1) 

11-4 

0-4 

0-1 

88-0 

0-1 

1,650 

4d. 

4,950 

(0-3) 

12-2 

9-0 

0-4 

78-1 

0-3 

1,635 

3d. 

6,540 

— 

. — • 

— 

950 

— 

1,765 

2id. 

-^1 

— 

— 

— 

— 

100-0 

— 

1,860 

2id. 

11,320 

— 

18-2 

0-4 

— 

81-2 

0-2 

1,520 

— 

- — 

28-1 

1-6 

2-2 

66-1 

2-0 

1,350 

— 

— 

17-2 

2-4 

1-7 

74-2 

4-5 

1,495 

5d. 

3,588 

10-0 

13-1 

2-3 

3-0 

68-5 

3-1 

1,445 

7d. 

2,477 

— 

18-8 

4-3 

0-3 

74-2 

2-4  ■ 

1,475 

6d. 

2,950 

15-0 

19-0 

1-8 

— 

62-2 

2-0 

1,190 

5d. 

5-1 
2,856 

(2-7) 

5-9 

10-7 

7-0 

74-2 

1 
2-2 

1,875 

3d.     1 



24-0 

4-5 

8-1 

5-3 

56-4 

1-7    i 

1,425 

'■      1 

— 

Table  ;jHo\vtng  Composition,    Food   Value,  and   Cost   of   Watery  Foods. 


as 


as 


Vegetables : 
Artichokes, 

purchased 
Asparagus, 

purchased 
Beans,  edible    . . 

Fresh     string, 
as  purchased 
Beetroot,  edible 

as  purchased 
Cabbage,  edible 

as  purchased 
Carrots,  edible 

as  purchased 
Cauliflower 
Celery,  edible     . .  | 

as  purchased 
Cucumber,  edible 

as  purchased     { 
Lettuce,  edible . . 

as  purchased     < 
Muslirooras 


(0-8)      79-5 


(0-8) 
(1-9) 

(1-8) 

(M) 
20-0 
(M) 
15-0 
(M) 
20-0 
(1-0) 

20-0 

(0-7) 
15-0 
(0-7) 
15-0 

(0-8) 


94-0 

89-2 

83-0 
87-5 
70-0 
91-5 
77-7 
88-2 
70-6 
92-3 
94-5 
75-6 
95-4 
8M 
94-7 
80-5 
88-1 


2-6    I     0-2       16-7 


1-8 
2-3 

2-1 
1-6 
1-3 
1-6 
1-4 
M 
0-9 
1-8 
M 
0-9 
0-8 
0-7 
1-2 
1-0 
3-5 


0-2 
0-3 


3-3 

7-4 


1-0 

0-7 

0-8 


0-3 

6-9 

0-7 

0-1 

9-7 

M 

0-1 

7-7 

0-9 

0-3 

5-6 

1-0 

0-2 

4-8 

0-9 

0-4 

9-3 

1-0 

0-2 

7-4 

0-9    • 

0-5 

4-7 

0-7 

0-1 

3-3 

1-0 

0-1 

2-6 

0-8 

0-2 

3-1 

0-5 

0-2 

2-6 

0-4 

0-3  : 

2-9 

0-9 

0-2  : 

2-5 

0-8 

0-4 

6-4 

1-2 

365 

105 
195 

180 

215 

170 

145 

125 

210 

160 

140 

85 

70 

80 

70 

90 

75 

210 


Id. 
lOd. 

Id. 
id. 


|d. 
Id. 

Id. 

2d. 

Id. 
8d. 


:  4,380 

126 
4,160 


2,260 

3,000 

1,960 
1,680 

840 

420 

900 
315 


DIETETICS 


?51 


Table  showing  Composition,  Food  Value,  and  Cost  of  Watery  Foods 

{Continued) 


=0 

0^ 

&: 

Protein. 

6s 

t 
1 

Fuel  Value  per 
Pound. 

Average  Price 
per  Pound,  etc.. 

Approx.  Caloric 
Value  for  1/. 

Vegetables  (cont.)  : 

Onions,  edible  . . 

(0-8) 

87-6 

1-6 

0-3 

9-9 

0-6 

225 

— 

— 

as  purchased 

10-0 

78-9 

1-4 

0-3 

8-9 

0-5 

205 

Id. 

2,460 

Peas,green{f  resh ) 

edible 

(1-7) 

74-6 

7-0 

0-5 

16-9 

1-0 

465 

— 

— 

as  purchased . . 

4o-0 

40-8 

3-6 

0-2 

9-8 

0-6 

255 

Hd. 

2,040 

Potatoes     (raw) 

edible 

(0-1) 

78-3 

2-2 

0-1 

18-4 

1-0 

385 

— 

— 

as  purchased . . 

20-0 

62-6 

1-8 

0-1 

14-7 

0-8 

310 

|d. 

4,960 

Rhubarb,  edible 

(1-1) 

94-4 

0-6 

0-7 

3-6 

0-7 

105 

— 

as  purchased . . 

40-0 

56-6 

0-4 

0-4 

2-2 

0-4 

65 

id. 

2,520 

Spinach     (fresh). 

as  purchased . . 

— 

92-3 

2-1 

0-3 

3-2 

2-1 

110 

Ud. 

880 

Tomatoes 

(0-6) 

94-3 

0-9 

0-4 

3-9 

0-5 

105 

4'd. 

315 

Turnips,  edible .  . 

(1-3) 

89-0 

1-3 

0-2 

8-1 

0-8 

185 

— 

— 

as  purchased .  . 

3()-() 

62-7 

0-9 

0-1 

5-7 

0-6 

125 

id. 

3,000 

Fruits : 

Apples,  edible   . . 

(1-2) 

84-6 

0-4 

0-5 

14-2 

0-3 

290 

— 

— 

as  purchased . . 

25-0 

63-3 

0-3 

0-3 

10-8 

0-3 

220 

2d. 

1,320 

Bananas,     Jam- 

aica: edible 

(1-0) 

75-3 

1-3 

0-6 

22-0 

0-8 

460 

— 

— 

as     purchased 

35-0 

48-9 

0-8 

0-4' 

14-3 

0-6 

300 

6d. 

600 

Cherries,  edible 

(0-2) 

80-9 

1-0 

0-8 

16-7 

0-6 

365 

— 

— 

as  purchased 

15-0 

76-8 

0-9 

0-8 

15-9 

0-6 

345 

4d. 

735 

Grapes,  edible  . . 

(4-3) 

77-4 

1-3 

1-6 

19-2 

0-5 

450 

— 

— 

as  purchased 

25-0 

58-0 

1-0 

1-2 

14-4 

0-4 

335 

6d. 

670 

Oranges,  edible 



86-9 

0-8 

0-2 

11-6 

0-5 

240 



— 

as    purchased 

27-0 

63-4 

0-6 

0-1 

8-5 

0-4 

170 

iw. 

1,360 

Pears,  edible 

(2-7) 

84-4 

0-6 

0-5 

14-1 

0-4 

295 

— 

— 

as  purchased 

10-0 

76-0 

0-5 

0-4 

12-7 

0-4 

260 

3d. 

1,040 

Plums,  edible    . . 

— 

78-4 

1-0 

— 

20-1 

0-5 

395 

— 

— 

as  purchased 

3-0 

74-5 

0-9 

— 

19-1 

0-5 

370 

2d. 

2,220 

Raspberries 

(2-9) 

85-8 

1-0 

— 

12-6 

0-6 

255 

5d. 

612 

Strawberries : 

edible 

(1-4) 

90-4 

1-0 

0-6 

7-4 

0-6 

180 

— 

— 

as  purchased . . 

5-0 

85-9 

0-7 

0-6 

7-0 

0-6 

j    175 

4d. 

.325 

Water-melon: 

edible 

— 

92-4 

0-4 

0-2 

6-7 

0-3 

140 

— 

— 

as  purchased .  . 

59-4 

37-5 

0-2 

0-1 

2-7 

0-1 

(>0 

u\. 

1.440 

Animal : 

Milk      .  . 

— 

87-0 

i     3-3 

4-0 

5-0 

0-7 

325 

■ — 

— 

Oysters 

1     — 

86-9 

1 

1     6-2 

1-2 

3-7 

2-0 

235 

1 

1     — 

— 

3r)2 


A  TEXTBOOK  OF  PHYSIOLOGY 


.''ooD  Values  in  Hoiseiiomj  .Mkasdies 


Fond'i  KS  Eattn. 


Dairy :    ^^iH^'     •  •  •  ■     .       • 

Skimmed  and  buttci-  milk. . 

Cream,  thin,  20%    ) 

Cream,  thick,  m^o  J 

Condensed  milk:  sweetened  y 
unsweetened  j 

Butter  

Cheese,  Cream         \ 

Chee  c.  Skim-milk  - 

Cheer,  American  J 

Egi;s,  whole  . . 

Eggs,  yolk     . . 

Eggs,  scrambled 
Meat'and  Fish  (cooked): 

Beef  tea,  clear  soujjs 

Fish,  lean   \  cod,  flounder  . . ) 

Fish,  fat     /shad,  salmon      j 

Meat,    lean  \ 

Meat,  medium  fat     V 

M-  a%  fat  J 

Lamb  chop  (edible  portion) 

Oysters,  medium  size  (raw) 
Cereals  &  Vegetables  (cooked): 

Bread,  white  or  brown 

Vienna  roll    . . 

Crackers  (Uneeda)   .. 

Cereals,  cooked,  moist 

Cereals,  eaten  dry    . . 

Shredded  Wheat 

Gruels,  cereal 

Thickened  or  cream  soups. . 

Macaroni 

Potato,  boiled  or  baked     . . 

Potato,  mashed 

Rice,  boiled  .  . 

Corn,  canned 

Peas,  fresh     .  ■ 

Lima  beans    .  . 

Squash  . . 
Fruits:  Apple,  pear     .. 

Apple  sauce  . . 

Banana 

Orange 

(jrape  fruit    .  . 

Strawberries  . . 

Dried  tigs,  dates,  raisins 

Fruit  jelly,  sweetened 
Desserts:  Custard 

Ice  cream 

Sponge  cake  .  . 

Pudding  (rice,  tapioca,  bread) 
Alcohol  . . 

Whisky,  brandy,  etc.  (50%  ) 

Wines  (8-25«.o ) 
Miscellaneous :  Sugar  . . 

Hone}',  marmalade  . . 

Olive  oil 

Olives 

Almonds,  shelled     .  . 

Cocoa  powders 


Actwd 
Amount. 


8  oz. 

8    .. 


Htmnehold 


Approximate. 


A  "lass 


,,.  /    A  tablespoon 

l()gras.  ' 


20 
10 

15 

50 
15 
40 


Leaping  teasp'n   -[ 

A  pat  or  ball 
i  in.  cube 


One 

Heaping  ta);lesp  n 


5  oz.  A  teacup 

50  gms.  Leaping  tablesjj'n 

(  Medium  slice 

50    „    -,'  5x3x1  in. 


45 
1(1 


40  ., 

7  „ 
40  „ 

5  ,,  ■ 

30  ., 

8  oz. 
8  „ 

25  gms. 

95  ., 

35  „ 

30  „ 

35  „ 

35  „ 

25  „ 

35  „ 

120  „ 

45  „ 

100  ., 

130  „ 

80  ., 

100  „ 

100  „ 

50  „ 

40  „ 

40  „ 

20  „ 

45  „ 

12  „ 
1  oz. 

1  „ 
8  gms. 

10 '  „ 

4  „ 

7  -, 

25  „ 

10  ., 


A  medium 
One 

1  slice,  4  X  4  X  i  in. 
One 

F±eaping  tablesp'n 

One  " 

A  soup  plate 

Heaping  tablesp'n 
One  medium 
Heaping  tablesp'n 


1,  medium  size 

Heaping  tablesp'n 

1,  medium  size 

1, 

One-half  small 

Medium  saueeri'ul 

Heaping  tablesp'n 


Slice 2  x4x-Hn. 
Heaping  tablesp'n 
A  tablespoon 
Small  wineglass 

Heaping  tablesp'n 

A  teaspoon 
1  medium  size 
Heaping  tablesp'n 
Heaping  teaspoon 


Calo-    Pro- 

ries.      tein. 


160 

80 
30 
00 
70 
35 
SO 
65 
''  5 
70 
75 
55 
45 

5-20 

35 

105 

'0 

1.% 

200 

165 

8 

70  I 

115  ! 

30  : 

35 

20 
110  , 

75 
160  , 

25 

90  I 

40 

35  : 

35 
40 
20 
20 
75 
70 

100  : 

70   1 

35 

40 
350 
160 

55 
135 

75 

80 

85 

85 
15-50 

33 

33 

37 

15 
1()5 

50 


\Fni. 


\Carbo- 
hydrnte. 


Gms- 

Gms. 

7-5 

9-5 

7-5 

1-0 

0-5 

3-0 

0-5 

3-0 

2-0 

2-0 

2-0 

2-0 

— 

8-5 

4-0 

5-0 

4-5 

2-5 

4-0 

5-5 

6-5 

5-0 

2-5 

5-0 

4-0 

3-0 

1  •0-4-5 



8-5 

— 

11-0 

6-5 

11-5 

2-5 

11-5 

9-0 

8-5 

18-0 

9-5 

13-5 

1-0 

0-2 

2-3 

0-5 

3-5 

I-O 

0-5 

0-5 

1-0 

— 

0-3 

— 

3-0 

0-5 

2-5 

1-0 

5-5 

4-5 

1-0 

0-5 

2-0 

— 

1-0 

1-0 

1-0 

— 

1-0 

0-5 

2-5 

1-0 

1-0 

— 

0-5 

— 

0-5 

0-5 



0-5 

i-5 

0-5 

1-0 

— 

0-5 

— 

1-0 

0-5 

2-5 

3-0 

0-5 

_.. 

2-5 

0-5 

1-5 

9-0 

1-5 

2-0 

2-0 



2-0 

, 

4-0 

_. 

1-5 

5-0 

13-5 

2-0 

3-0 

CHAPTER  XLI 
THE  CHIEF  FOODSTUFFS 

It  is  necessary  to  consider  a  iew  of  the  commoner  foodstutJs  in 
more  detail. 

Milk. — Cow's  milk  is  a  staple  article  of  diet  for  persons  of  all  ages. 
It  is  to  be  noted  that  milk  is  relatively  a  waterj^  and  therefore  not  a 
cheap,  food.  Fresh  cow's  milk  is  amphoteric  in  reaction,  with  a 
specific  gravity  of  1028  to  1034.  When  skimmed,  the  specific  gravity 
rises  to  1033  to  1037.  A  little  water  added  will  again  reduce  the 
specific  gi'avity,  and  a  little  colouring  matter  will  help  to  cover  up 
the  fraud.  Milk  contains  all  the  necessary  foodstuffs — proteins,  fat, 
lipoids,  carbohydrate,  water,  and  salts.  The  chief  protein  is  case'n- 
ogen,  a  phospho-j^rotein,  notable  for  its  high  content  in  the  ringed 
amino  acids— t^Tosin  and  tryptophane.  A  certain  amount  of  coagu- 
lable  protein — lactalbumin — is  also  present.  Caseinogen  is  clotted  by 
rennet.     When  this  takes  place  outside  the  body,  "  junket  "  is  formed. 

Caseinogen  is  easily  precipitated  from  solution  by  acid.  When 
milk  goes  sour  on  standing,  lactic  acid  is  formed  as  the  result  of  the 
action  of  a  bacillus — B.  lactis — upon  the  sugar  contained  in  milk. 
The  lactic  acid  so  formed  precipitates  the  caseinogen  as  the  "  curds," 
leaving  a  clear  fluid — the  ''  whey."  The  term  "  whey  "  is  often  given 
to  what  is  left  after  caseinogen  has  been  removed  by  any  means. 
When  milk  is  clotted,  a  clear  fluid  exudes  after  a  time — '"  rennet 
whey."  If  caseinogen  be  precipitated  by  acid,  neutral  salts  or 
alcohol,  ■■  acid,"  "  salt,"  or  ''  alcoholic  ""  whey  is  obtained.  Some  whej^s 
— e.g.,  rennet,  acid — contain  lactalbumin:  others  do  not,  the  albumin 
being  removed  with  the  caseinogen — e.g.,  alcoholic  whev. 

The  fats  of  milk  are  carried  down  with  the  caseinogen.  Olein 
forms  the  chief  fat  (43  per  cent.);  palmitin  (33  per  cent.)  and  stearin 
(17  per  cent.)  are  also  present,  together  with  7  per  cent,  of  fats  of  the 
volatile  fatty  acids — butyrin,  caproin,  and  caprj'lin.  It  is  this  con- 
tent of  volatile  fatty  acids  which  aids  to  distinguish  butter  from 
margarine.  The  fats  occur  in  the  form  of  fine  droplets,  each  drop 
of  the  emulsion  b?ing  surrounded  with  a  fine  film  of  caseinogen. 

In  the  whey  are  contained  the  sugar  lactose  and  the  salts.  The 
chief  salt  is  calcium  phosphate;  the  phosphate  of  magnesium  and 
the  chlorides  of  sodium  and  potassium  are  also  present.  Milk  con- 
tains but  little  iron.  The  milk  of  different  animals  varies  in  the 
content  of  the  chief  constituents.  The  differences  between  cow's 
and  human  milk  are  discussed  elsewhere  (see  p.  537).     The  composition 

353  23 


354  A  TEXTBOOK  OF  PHYSIOLOCV 

of  the  milk  of  various  animals  can  be  seen  in  the  following  table  (Konig) 
stated  in  parts  per  1,000  of  milk: 


Water. 
S71-7 

Solids. 

Proteins. 



35-5 

Fat. 

■ 

Sugar. 

Salts. 

Cow 

128-3 

36-9 

48-8 

7-1 

Horse 

9iK)-(; 

99-4 

18-9 

10-9 

66-5 

3-1 

Ass   .  . 

UDO-d 

100-0 

21-0 

13-0 

63-0 

3-0 

Goivt 

869-1 

130-9 

36-9 

4U-9 

44-5 

8-6 

Sheep 

835-0 

165-0 

57-4 

61-4 

39-() 

6-6 

Pig    .. 

8-23-7 

167-3 

60-9' 

64-4 

40-4 

10-6 

Dog  . . 

754-4 

245-6 

99-1 

95-7 

31-9 

7-3 

Cat   . . 

816-3 

183-7 

90-8 

33-3 

49-1 

5.8 

Elephant      . . 

678-5 

i 

321-5 

30-9 

195-7    ■ 

88-5 

6-5 

The  walius's  milk  contains  as  much  as  43  per  cent,  of  fat.  By 
the  action  of  a  special  fungus — the  kephir  finigus — the  lactose  of  milk, 
which  does  not  normally  undergo  alcoholic  fermentation,  ferments 
to  alcohol  (1  to  3  per  cent.),  giving  with  cow's  milk  the  drink  known 
as  kephir,  with  mare's  milk  koumiss.  It  is  a  general  drink  in  Bulgaria 
and  the  Steppes  of  Russia. 

Meat  consists  of  the  muscle  of  animals  and  fat,  with  a  certain 
amount  of  connective  tissue.  Besides  the  visible  fat  in  prime  meat, 
there  is  a  considerable  amount  of  masked  fat  also  in  the  fibres.  The 
muscle  also  contains  various  extractives  and  other  bodies. 

Eggs  are  an  exceedingl}-  valuable  article  of  diet  by  virtue  of  their 
great  digestibilit}-.  The  white  of  the  egg  consists  chiefly  of  egg 
albumin,  Avith  a  small  amount  of  egg  globulin,  and  a  mucus-like 
body — ovo-mucoid.  A  small  amount  of  sugar  {0-5  per  cent.),  and 
traces  of  fats,  lipoids,  and  salts  (0-6  per  cent.),  are  present.  In  the 
yolk  there  is  present  also  the  phospho-protein  vitellin,  fat,  and  the 
colouring  matter  lipochrome. 

The  Cereals — wheat,  barley,  oats,  rye,  rice — are  the  most  wideh" 
used  articles  of  diet.  They  contain  much  starch,  and  have  the  great 
advantage  of  being  cheap.  In  their  husks  are  contained  valuable 
salts  and  vitamines.  Their  proteins,  besides  not  being  so  well  absorbed 
as  animal  proteins,  do  not  contain  such  an  appropriate  assortment 
of  "  bricks"  for  building  animal  tissues  as  do  the  animal  foodstuffs. 
Some  of  the  '■  bricks  " — e.g.,  glutamic  acid — are  present  in  large  quantity, 
and  if  used  for  body-building,  must  be  broken  down  previous  to 
resynthesis.  It  has  been  shown  that  proteins,  such  as  zein  (from 
maize)  and  hordein  (from  barley),  do  not  by  themselves  suffice  to 
give  the  appropriate  nitrogen  to  the  body.  Oatmeal  with  7  p'  r 
cent,  of  fat,  against  1  per  cent,  in  wheat,  is  a  verj'  valuable  article  ot 
diet,  and  should  figure  largely'  in  the  diet  of  all  peoples  inhabiting 
temperate  zones. 

Flour  is  made  from  the  endosperm  of  wheat.  Generally  the  outer 
husk  (bran),  inner  husk  (sharps),  and  the  germ,  are  removed  during 


THE  CHIEF  FOODSTUFFS  355 

the  milling  process,  and  white  flour  is  obtained.  Further,  it  Ls  fre- 
quenth*  bleached  with  acids,  and  white  calcium  salts  added  to  give 
extra  whiteness.  There  is  economic  loss  in  such  bleaching  processes, 
which  are,  if  anything,  injurious  to  the  consumer.  When  milled  Avhole, 
whole-meal  is  obtained;  when  only  the  bran  is  removed,  "  standard  " 
flour  results.  The  chief  protein,  gluten,  globuhn-like  in  nature, 
when  mixed  with  water,  becomes  viscid,  forming  a  dough.  Gluten 
consists  of  two  portions — gliadin,  soluble  in  alcohol;  and  glutinin. 
soluble  in  alkali.  The  viscidity  is  due  to  the  gliadin.  Grains  poor 
in  ghadin — e.g..  rice,  oats — do  not  form  a  dough  when  mixed  with 
Avater. 

Bread. — The  dough  formed  from  flour  is  not  a  suitable  food, 
owing  to  its  iniperviousness  to  the  digestive  juices.  When  made 
pervious  by  aeration,  and  baked,  it  becomes  bread.  This  aeration  is 
performed  by  carbonic  acid  gas  generated  by  the  action  of  the  3'east 
which  is  mixed  with  the  dough,  and  of  a  diastase  already  present  in 
the  flour. 

The  Pulses. — This  group  of  dry  foodstuffs  contain  in  the  dry  state 
a  large  amount  of  protein  and  carbohydrate,  and,  being  cheap,  are 
valuable  as  articles  of  diet.  They  have  the  disadvantage,  however,  that 
their  physiological  availability — the  amount  absorbed  during  diges- 
tion— is  considerably  lower  than  with  the  animal  foodstuffs.  They 
cannot  be  eaten  dr^-,  and  when  mixed  with  water  and  cooked  they 
become  very  bulky  foods.  The  proteins  of  pulses  and  cereals  do  not 
seem  to  be  composed  of  such  suitable  "bricks"  for  building  animal 
tissues  as  are  the  proteins  of  animal  foodstuffs. 

The  Fruits  are  of  value  bj'  reason  of  the  anti-soorbutic  principles, 
the  organic  acids,  salts  and  water  the}"  contain.  Certain  fruits  also 
contain  appreciably  large  quantities  of  sugar.  The  banana,  often 
classed  as  a  fruit,  contains  a  relatively  large  amount  of  nutriment. 

Green  Vegetables  are  of  value  as  introducing  a  small  percentage 
of  food,  with  salts,  vitamines,  and  a  certain  amount  of  cellulose, 
which  stimulates  the  peristaltic  action  of  the  intestines.  The  salts 
of  the  vegetable  acids  are  converted  into  alkaline  carbonates,  and  are 
of  importance  in  regulating  the  acidity  of  the  blood.  The  green 
foodstuffs,  particularh'  spinach,  also  introduce  iron  into  the  body. 
Chlorophyll  is  possibly  a  precursor  of  haemoglobin. 

Potatoes  contain  carbohydrate  and  a  small  amount  of  protein,  but 
this  is  in  a  most  available  form.  They  also  contain  vitamines,  and 
thus  are  of  great  importance  to  town  populations. 


(H AFTER  XLII 

DIET  UNDER  VARIOUS  CONDITIONS 

If  man  had  to  take  his  nutriment  as  one  article  of  diet,  to  get 
the  necessar}-  protein — 15  grammes  of  nitrogen — he  would  require: 
1-J  pounds  of  beef,  or  8  pints  of  milk,  or  3  pounds  of  bread,  or  13  pounds 
of  potatoes,*  or  60  pounds  of  apples.  A  diet  consisting  of  125 
grammes  of  protein,  50  grammes  of  fat,  and  500  grammes  of  carbo- 
hydrate, is  contained  in  approximately  |  pound  prime  lean  meat, 
li  pounds  bread,  2  ounces  butter,  h  pint  milk,  1  pound  potatoes, 
and  1  pound  oatmeal.  The  fat  is  raised  to  100  grammes  in  the  army 
service  ration — i.e.,  for  hard  work  in  the  open  air  of  this  climate. 

Sex  and  Age. — Since  man  is  generally  bigger  than  woman  and 
does  more  muscular  work,  he  requires  the  bigger  intake  of  energy. 
Men  and  women  of  equal  surface  area,  and  performing  equal  work, 
require  the  same  energy  intake.  A  family  of  father,  mother,  and 
four  children  (13,  11,  9,  and  7  years)  is  estimated  to  require  the 
food  of  4-5  men.  Boys  over  13  require  a  full  "man  value" — viz., 
3,400  calories — food  as  purchased,  the  loss  in  cooling  and  absorption 
is  estimated  to  be  10  per  cent.  A  woman  or  girl  over  13  requires  -8 
man  value.  In  old  age  there  is  a  marked  decrease  in  vitality  and 
bodily  activity.  Old  j^eople  therefore  need  not,  and  do  not,  take  in 
the  supply  of  energy  required  in  the  prime  of  life.  Old  bedridden 
people  live  on  a  diet  which  probably  does  not  yield  more  than  1,000 
calories. 

Work. — It  has  already  been  mentioned  how  the  oxygen  consump- 
tion and  CO2  output  are  increased  by  muscular  work.  Not  only  do 
the  muscles  perform  more  mechanical  work,  but  the  bod}'  generally 
is  called  upon  to  do  more  "  physiological  '"  work  to  meet  their 
needs.  Either  protein,  fat,  or  carbohj^drate,  can  yield  the  energy 
required  for  muscular  work,  but  since  such  work  can  be  done  most 
economically  at  the  expense  of  the  last,  a  diet  for  hard  muscular  work 
should  contain  an  ample  supply  of  caibohydrate  with  enough  fat  to 
sustain  the  work  between  meals.  Carbohydrate  is  used  first,  while 
fat,  more  slowly  digested  and  absorbed,  is  used  later. 

Temperament. — Some  people  are  by  temperament  vivacious  and 
active,  others  are  more  phlegmatic  and  quiet.  The  latter  Avill  expend 
less  energy  as  muscular  work  than  the  former,  and  therefore  require 

*  Three  to  four  grammes  of  nitrogen  seem  to  suffice  on  a  potato  diet. 

356 


DIET  UNDER  \'ARIOUS  COXDITIOXS  357 

a   correspondiugh'  less  intake  of  energy  as  food.     If  they  take   as 
much,  they  grow  fat. 

Climate. — Cold  increases  the  activity — i.e.,  the  amount  of  muscular 
work  i^erformed — heat  diminishes  it.  In  cold  climates  there  should 
therefore  be  an  increase  in  the  energy  intake,  particularly  in  the  form 
of  fat,  which,  owing  to  its  high  caloric  value,  is  vevy  heat-giving.  In 
the  tropics,  on  the  other  hand,  food  must  be  cut  down,  particulfaly 
protein  owing  to  its  high  specific  dynamic  energy.  The  diet  of  natives 
in  Singapore  averages  CO  grms.  protein,  35  fat,  and  2£0  carbohydiate. 
with  e.n  energy  value  of  about  1,600  calories. 

The  Nutrition  of  the  Foetus. — During  pregnancy,  the  embr\-o  is 
nourislied  at  the  expense  of  the  mother  through  the  placenta.  It  is 
during  the  last  three  months  of  pregnancy  that  the  great  increase  in 
weight  of  the  foetus  occurs;  at  the  same  time,  the  mother's  oxygen 
use  increases  about  25  per  cent,  above  the  normal.  Calculation  shows, 
however,  that  not  more  than  10  grammes  of  dry  matter  per  day  are 
required  for  adequate  growth  of  the  foetus.  Anah'sis  of  the  full-time 
foetus  shows  that  an  average  child  of  7  pounds  contains  nearly  400 
grammes  of  protein,  300  grammes  of  fat,  and  83  grammes  of  mineral 
ash,  chiefly  calcium  and  phosphoric  acid.  In  regard  to  the  c£uestion 
of  the  diet  of  the  mother,  therefore,  it  is  obvious  that  no  excessive 
demands  are  made  upon  her  in  the  matter  of  food  intake.  Special 
diets  are  not  required  by  the  pregnant  woman.  All  that  is  required 
is  a  slightly  increased  intake  of  simple  protein  and  lime-giving  foods, 
such  as  meat,  milk,  eggs,  cereals,  fruits,  and  vegetables.  The  more 
nearly  a  mother  lives  a  normal  healthy  life,  the  better  it  is  for  the  foetus. 

The  Nutrition  of  the  New-born  Infant. — The  new-born  infant  should 
be  fed,  if  possible,  by  its  mother.     Every  mother  should  do,  and  should 
be  encouraged  to  do,  all  in  her  power  to  suckle  her  own  infant.     The 
mother's  milk  is  best  adapted  to  the  needs  of  the  growing  child.     It  is 
sterile :   it  contains   the    right     kinds    and    proportions    of    protein, 
lecithin,   and  salts.     It  has  been  shown  that  there   is   a   proportion 
between  the  composition  of  the  mother's  milk  and  the  rate  at  which 
the  young  grow.     This  is  especially  marked  in  quickly  growing  animals. 
Thus,  a  puppy  doubles  its  weight  in  eight  days;  its  mother's  milk 
contains  7-1  per  cent,  of  protein  and  1-3  per  cent,  of  ash.     A  child 
takes  six  months  to  double  its  Aveight ;   human  milk  contains   but 
1-5  per  cent,  of  protein  and  0-2  per  cent,  of  ash.     The  lecithin-content 
of  the  mother's  milk  varies  somewhat  with  the  relative  weight  of  the 
brain  to  the  body  weight.     Relatively,  the  larger  the  brain  the  bigger 
the   lecithin-content   of  the   mother's   milk.     In  the   calf  the   brain 
weight  to  body  weight  is  1  :  370;  in  the  puppy,  1  :  30;  in  the  new-born 
child,  1  :  7.     In  proportion,  the  milk  of  the  different  mothers  contains 
lecithin  in  percentage  of  the  total  protein  1-4,  2-11,  and  3-05  respec- 
tiveh'.     It  is  well  adapted  to  the  child's  digestive  powers,  and,  what 
is  also  important,  it  contains  bodies  capable  of  increasing  the  child's 
immunity  to  any  ailments  which  may  befall  it  in  early  life.     This  last 
point  was  proved  by  the  following  ingenious  "'  changeling  ''  experi- 


358  A  TEXTBOOK  OF  PHYSIOLOGY 

ment:  A  male  and  a  female  mouse  were  rendered  immune  to  a  ]ioisou 
(abriii).  Each  was  then  mated  to  a  non-immune  companion.  It  was 
found  that  the  offspring  of  the  immune  male  and  non-immune  female 
possessed  no  immunity  against  the  poison.  On  the  other  hand,  the 
offspring  of  the  non-immune  male  and  of  the  immune  female  possessed 
such  an  immunity,  which  gradually  increased  after  birth,  and  Avas 
therefore  not  derived  solely  from  the  placenta.  The  offspring  were 
then  changed.  The  immune  female  suckled  the  non-immune  young, 
the  non-immune  female  suckled  the  imnume  young.  It  was  found 
that  the  former  soon  acquired  an  immunity,  the  latter  quickly  lost 
their  immunity  to  the  poison. 

Of  the  infant  mortality  mider  one  year,  and  particularly  under 
eight  months,  the  great  proportion  of  deaths — in  some  cities  as  large 
as  170  per  1,000,  over  300  in  Russia — is  among  artificially  fed  babies. 
It  must  be  borne  in  mind  that  such  deaths  are  largely  among  the 
very  poor,  and  the  artificial  food  in  such  cases  is  often  inadequate, 
and  certainly  not  kept  sterile  and  clean.  The  case  against  artificial 
feeding  is  largely  a  case  against  careless  or  ignorant  artificial  feeding. 
With  a  properlj'  prepared  clean  food,  such  as  the  child  can  digest, 
and  eontainmg  the  "building  stones"  suitable  for  its  adequate 
growth,  there  is  every  reason  to  believe  that  the  child  develops,  in 
most  cases,  into  just  as  health}^  a  babe  as  does  the  breast-fed  infant. 
The  introduction  of  dried  milk  has  proved  of  the  greatest  import- 
ance in  lessening  infant  mortality. 

The  mother  shoidd  be  urged  to  suckle  the  child  during  the  first 
months  as  much  for  her  own  sake  as  for  the  child's.  The  act  of  suckling 
exerts  a  tonic  effect  upon  the  uterus.  It  assists  in  stopping  hsenior- 
rhage  from  the  placental  site,  and  helps  to  secure  the  proper  involution 
of  the  uterus. 

The  Secretion  oS  Milk — The  Mechanism  of  Secretion. — During 
pregnancy,  preparation  is  made  for  the  feeding  of  the  young.  The 
mammary  glands  begin  to  increase  in  size — the  engorged  veins  testify 
to  the  activity  taking  place ;  there  is  great  proliferation  of  the  alveolar 
cells  and  duct  epithelium.  This  takes  place  under  the  influence  of 
a  hormone  produced  by  the  corpus  luteum  of  the  mother,  and  possibl}^ 
by  the  foetus  itself.  Nervous  connections  of  the  gland  are  not  essen- 
tial. The  gland  may  be  transplanted  in  the  pregnant  animal,  and  will 
continue  to  proliferate.  After  birth,  the  proliferated  resting  glands 
enter  into  a  state  of  great  secretory  activity,  possibly  owing  to  the 
removal  of  an  inhibitory  influence  from  the  foetus.  The  first  secreted 
fluid  is  known  as  "  colostrum."  This  is  secreted  for  the  first  few  days, 
and  is  then  followed  by  the  supply  of  the  milk  proper.  The  secretion 
is  under  both  nervous  and  chemical  agencies.  The  sucking  efforts  of 
the  offspring  are  a  great  factor  in  producing  a  good  supply  of  milk. 
For  this  reason,  the  new-born  child  should  be  frequently  put  to  the 
breast,  even  though  the  supply  of  food  be  scanty.  It  has  been  shown 
in  animals  that  various  chemical  bodies,  such  as  pituitary  extract  (see 
p.  523),  and  extract  of  the  involuting  uterus,  when  injected,  cause  an 
increased  flow  of  milk.     It  is  stated,  also,  that  in  woman  the  injection 


DIET  UNDER  VARIOUS  CONDITIONS  35^ 

•of  some  of  the  mother's  oami  milk  or  of  a  sterile  solution  of  caseiuogeu 
into  the  buttock  Mill  cause  an  increased  supply  of  milk.  In  medical 
practice,  various  lactagogues  are  employed  to  increase  the  flow  of  milk, 
such  as  extract  of  cotton-seed.  It  is  doubtful  if  the  supply  of  milk 
thus  stimulated  is  adequate  to  the  needs  of  the  child.  It  is 
.probabh'  better  to  supplement  a  deficient  supply  by  careful  artificial 
feeding. 

Milk  is  a  true  secretion.  It  contains  proteins  and  carbohydrate 
not  found  in  the  blood-plasma.  It  contains,  also,  a  proportion  of 
saUs  quite  different  to  those  found  in  the  blood-plasma,  the  proportion 
of  some  salts,  such  as  that  of  calcium,  being  so  great  that  they  could 
not  be  derived  from  the  blood  by  such  processes  as  filtration,  diffusion, 
or  osmosis.  The  phospho-protein  caseinogen  probably  originates 
from  the  cell  protoi^lasm  of  the  mammary  gland  itself,  possibly  by  a 
hydrolysis  of  the  nucleo-protein  of  the  gland,  and  subsequent  synthesis 
to  caseinogen.  The  milk  fat  comes  partly  from  the  fat  of  the  food. 
An  ingested  fat,  such  as  sesame-oil,  may  be  traced  into  the  milk,  but 
only  in  ver}'  small  quantities.  Most  of  the  fat  is  probably  formed  in 
the  gland  by  synthesis  from  the  components  of  the  mammary  gland, 
probably  the  proteins.  It  is  possible,  also,  that  some  is  formed  from 
the  carbohydrate  brought  in  the  blood  to  the  gland. 

The  origin  of  the  mi.k-sugar  is  not  well  known:  possibly  it  is 
formed  by  a  rearrangement  of  the  dextrose  brought  in  the  blood  to 
the  gland.  Certain  drugs  are  secreted  in  the  milk — a  fact  of  import- 
ance to  nursing  mothers.  Compounds  of  morphine,  iodine,  arsenic, 
mercury,  and  iron,  are  among  such. 

The  Composition  of  Human  Milk.— Colostrum,  the  first  secreted 
milk,  has  a  high  specific  gravity— 1040  to  1060.  It  is  richer  than 
ordinary  human  milk  in  coagulable  protein  (albumin),  and  is  yellower 
in  colour.  It  is  rich  in  special  cellular  elements,  known  as  "'  colostrum 
corpuscles." 

Human  21  ilk  is  whitish-blue  in  colour,  with  a  specific  gravity  of 
1026  to  1036.  It  is  amphoteric  in  reaction,  but  has  a  lower  absolute 
alkalinity  and  acidity  than  cow's  milk.  The  caseinogen  of  human 
milk  has  a  shghtly  different  chemical  constitution  to  that  of  cow's 
millv.  It  is  said  by  some  authorities  to  have  a  carbohydrate  moiety 
attached  to  it.  With  rennet,  it  yields  a  far  less  dense  and  uniform 
elot.  The  precipitate  with  weak  acid  is  more  easily  soluble  in  excess. 
This  accounts  for  the  greater  digestibility  of  human  milk.  The  pro- 
portion of  caseinogen  to  lactalbumin  is  smaller  in  human  than  in  cow's 
milk,  being  in  human  milk  2  :  1,  in  cow's  milk  nearly  6:1.  The  fat 
of  human  milk  is  stated  to  be  poorer  in  the  volatile  fatty  acids  than  cow's 
milk.  The  composition  of  human  milk  varies  greatly.  Its  average 
composition  is  probably  respresented  bj'  the  following  figures,  those 
of  cow's  milk  being  given  for  comparison : 


Water. 

Protein. 

Fat. 

Carbohydralc. 

Sails, 

Human    . . 
Cow's 

90-2 
S7-4 

1-5 
.3-4 

3-1 

3-7 

5-0 

4-8 

0-2 
C-7 

3(Hi  A  TEXTBOOK  OF  PHYSIOLOGY 

It  will  he  seen  that,  in  addition  to  the  c|iialitative  differences 
mentioned  aljove,  the  qnantitative  composition  of  hmnan  milk  is 
markedly  different  from  that  of  cow's  milk.  Woman's  milk  is  poorer 
ill  proteins,  richer  in  sugar,  poorer  in  salts.  Human  milk  is  also  richer 
in  lecithin.  In  regard  to  the  salts,  it  is  to  be  noted  also  that  they  are 
present  in  quite  different  proportions  to  those  of  cow's  milk.  The 
following  figure:^  rein-esent  the  content  in  1.0(10  parts  of  mik: 


K./K 

XiiJ). 

VaO. 

MgO. 

FeSh- 

PPh- 

67. 

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0-591 

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(»•()(  13.") 

1-8-2 

0-ns 

It  will  be  seen  that  human  milk  is  much  poorer  (six  times)  in  cal- 
cium salts  and  in  inorganic  phosphorus,  as  well  as  being  generally 
poorer  in  all  salts.  It  is  obvious,  therefore,  that,  besides  being  im- 
possible to  make  cow's  milk  qualitativel}'  like  human  milk,  il  's  quite 
out  of  the  question  to  make  it  quantitatively  the  same.  In  the  past, 
much  has  been  written  about  humanizing  cow's  milk.  To  effect 
such  is  out  of  the  question.  If  the  old  rule  be  followed,  by 
which  it  was  fought  to  bring  about  a  correct  human  proportion 
of  proteins,  fats,  and  carbohydrates,  in  cow's  milk — namely,  to  dilute 
with  water  and  then  add  cream  and  sugar — it  is  obvious  that  the 
proportion  of  salts  is  disregarded.  ''  Humanizing  "  is  therefore  a 
very  rough  process  at  the  best,  and  it  is  never  worth  while  putting  a. 
patient  to  ex]iense  to  buy  so-called  humanized  milk. 

Artificial  Feeding. — Artificial  feeding  is  sometimes  necessar}^  and 
the  question  then  arises  as  to  what  food  an  infant  should  be  given. 
The  principles  to  be  borne  in  mind  in  artificial  feeding  are  that  the 
food  and  receptacles  shall  be  clean,  and  not  teeming  with  micro- 
organisms; and  that  the  food  shall  be  easily  digestible  by  the  child, 
and  contain  the  essential  ""  bricks  ""  necessary  for  its  growth.  Cow's 
milk  is  obviously  the  most  handy  substitute;  as  shown  above,  it 
is  not  possible  to  humanize  it ;  but  it  must  be  acknowledged  that 
some  of  these  attempts  at  humanizing  have  succeeded  in  rendering 
the  cow's  milk  more  easily  digestible  b}^  the  child.  Some  authorities 
recommend  the  addition  of  barley-water,  others  of  sodium  citrate. 
In  the  table  (p.  359)  is  set  forth  a  method  of  feeding  proved  success- 
ful .  It  should  be  noticed  that  there  is  no  need  to  use  expensive 
lactose,  and  if  the  parent  be  too  poor  to  purchase  cream,  a  vegetable 
oil  may  be  used.  The  large  quantity  of  fat  serves  a  double  purpose: 
it  nourishes  the  child,  and  at  the  same  time  ensures  that  the  iniant 
is  not  constipated.  The  addition  of  the  lime-water  insurer;  that  the 
clot  of  casein  is  light  and  easily  digestible. 

Generally  sjjeaking,  the  patent  infant  foods  b}'  no  means  approxi- 
mate to  the  correct  proportions  of  the  constitu3nts  of  human  milk; 
many  contain  starch,  wh'ch  a  very  young  child  cannot  digest.  The 
proteins  are  not  readily  soluble  in  Avater,  and  there  is  also  a  deficiency 
in  fats.  If  milk  is  boiled,  the  anti-scurvy  vitamines  require  to  be 
replaced  by  the  giving  of  orange  or  swede  juice. 


DIET  UNDER  VARIOUS  CONDITIONS 


361 


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362 


A  TEXTBOOK  OF  PHYSIOLOGY 


Weaning.— The  inilk  of  a  mother  begins  to  decrease  in  quantity 
at  the  end  of  the  sixth  or  seventh  month.  It  is  therefore  desirable  that 
the  child  should  be  partially  weaned  at  this  time.  A  further  reason 
is  that  the  mother's  milk  is  deficient  in  iron,  and  this  deficiency  begins 
to  be  felt  about  this  time.  It  has  been  shown  that  the  young  embryo 
has  stored  within  it  sufficient  iron  to  last  it  until  it  can  begin  to  take 
other  food.  Thus,  in  the  case  of  the  rabbit,  the  embryo  has  enough 
iron  stored  until  the  young  animal  begins  to  run  about  and  take  green 
food. 


Fig.   191.— Peotein  keqtjired   fok  Weight  and  Stjeface  at  Difeeeent  Ages. 

(WaUer.) 

W,  TF=Body  weight  in  Idlos  (1  mm.  =  l  kilo);  S,  »S=bod3'  surface  in  square  metres 
(1  cm.=  l  square  metre);  s,  s=body  surface  per  1  kilo  body  weight  in  square 
cms.  (1  cm.  =  l  gramme);  N,  iV^=  protein  per  kilo  body  weight  in  grammes 
(1  cm.  =  l  gramme). 

During  the  period  of  lactation,  the  mother's  dietary  must  be 
liberal  in  the  more  nutritious  foodstuffs.  It  must  be  remembered 
that  she  is  called  upon  to  supply  amounts  varying  from  20  grammes 
on  the  first  day  up  to  about  1,000  gi-ammes  at  the  end  of  the  sixth 
or  seventh  month.  As  far  as  possible,  also,  she  must  be  spared  from 
grief  or  anxiety,  which   seriously  affect  the  nvlk,  causing  digestive 


DIET  UNDER  VARIOUS  CONDITIONS 


363 


disturbances  and  loss  of  weight.  Since  certain  drugs  are  secreted  in 
the  milk,  only  such  medicines  as  are  prescribed  by  a  medical  man 
should  be  taken  by  her.  The  progress  of  an  infant  is  best  judged  by 
a  gain  in  Aveight,  which  should  be  steady — from  4  to  16  ounces  per 
week,  excepting  during  the  first  week  of  life 

Childhood. — It  is  obviously  important  that  the  gi'owing  child  should 
haAc  an  abundant  supply  of  food  material,  especially  protein  and 
such  material  as  is  necessary  for  the  growth  of  the  developing  organism. 
Further,  it  is  to  be  borne  in  mind  that  the  child  is  not  only  growing, 
but  also  that  it  is  a  small  animal,   and    therefore   has  a  relatively 


1400C 


IZOOC 


lOOOC 


800C 


600C 


400  ( 


200C 


Fiu.  191a. — Table  of  Food  Values  sitowixg  Calories  Pukchasable  peh  Penny. 

(Nuel  Pa  ton.) 

greater  surface  area  and  a  corresponding  greater  respiratory  exchange 
(Fig.  190).  Further,  the  child,  when  healthy,  is  always  active  while 
awake.  From  Fig.  191,  it  is  obvioits  that  in  the  first  few  years  of  life, 
and  again  at  the  age  of  puberty,  the  food-supply  should  be  parti- 
cularly liberal. 

In  the  diet  of  a  growing  child,  the  cereals  and  potatoes  should 
figure  largely.  At  first  ground  oats,  later  oatmeal  or  rolled  oats,  are 
of  particular  value,  by  virtue  of  the  large  amount  of  proximate 
principles,  as  well  as  the  large  salt  content.  Milk  in  various  forms, 
eggs,  meat,  fresh  fruit,  should  also  1)e  incorporated  in  the  dietar3^ 


CHAPTER  XLIII 

SPECIAL  DIETETIC  METHODS,  ALCOHOL,  COOKING,  ETC. 

Special  Dietetic  Methods. — Of  these  the  best  known  is  vegetarianism, 
either  '"  true  "'  or  "  false.  "  In  "  true  "  vegetarianism,  no  animal  food 
whatsoever  is  eaten;  in  "  false  "  vegetarianism,  such  animal  ^oods  as 
milk,  cheese,  and  eggs,  are  freely  consumed .  There  is  little  to  be  said 
against  false  vegetarianism,  provided  that  sufficient  of  these  animal 
foodstuffs  are  eaten,  insuring  a  good  supply  of  protein  and  not  too 
much  vegetable  fibre.  The  proteins,  too,  are  such  in  kind  and 
amount  that  putrefaction  in  the  large  intestine  is  not  great.  To  this 
"false"  vegetarianism  owes  its  popularity. 

In  regard  to  "  true  '"  vegetarianism,  there  is  very  little  evidence 
in  support  of  the  main  contentions  of  its  devotees.  It  is  said  that, 
on  anatomical  grounds,  man  is  not  a  carnivorous  animal;  that  meat 
js  therefore  an  imnatiu'al  food,  dangerous  to  health.  Man's  alimentary 
canal  is  very  different  from  that  of  a  rabbit,  with  its  enormous  caecum; 
and  the  monkey,  his  near  relation,  eats  animal  food,  eggs,  insects,  etc., 
as  well  as  nuts  and  fruits.  Granted  that  excessive  ingestion  of  animal 
protein  induces  unwholesome  putrefaction  in  the  large  intestine,  so 
that  toxins  are  formed  deleterious  to  health,  this  was  no  case  against 
a  moderate  intake  of  meat.  The  most  virile  tribes  of  the  world, 
past  or  present,  were  or  are  great  meat-eaters.  Trouble  arises  from 
over-indulgence;  some  meat-eaters,  owing  to  lack  of  exercise,  do  not 
keep  themselves  fit,  and  therefore  do  not  compare  favourably-  with 
vegetarians,  who  keep  themselves  fit.  The  evidence  shows  that  a 
"fit  ■■  meat -eater  is  of  better  physique  and  mental  capacity  than  a 
"fit  "  vegetarian.  True  vegetarianism  has  the  di-sadvantage  of  intro- 
ducing too  much  ballast,  just  as  pure  meat-eating  introduces  too 
little.  Further,  the  physiological  availability  of  such  foodstuffs  is 
considerably  less,  and  the  proteins  are  of  less  value  for  tissue -forming. 
Various  other  special  dietetic  methods  —  "raw  food,"'  '"  purin- 
free,'  "low  protein" — have  their  adherents.  In  these  days  of 
adulteration  and  separation  of  natural  foods  it  is  quite  possible  that 
errors  may  arise  in  man's  diet,  but  it  is  safe  to  conclude  that  if  the 
general  public  devoted  as  much  attention  to  keeping  itself  fit  by  proper 
muscular  exercise  in  the  open  air,  as  it  does  to  the  question  of  diet,  the 
latter  would  cease  to  be  of  such  importance. 

Alcohol.- — When  taken  in  small  quantities,  alcohol  is  burnt  in  the 
human  body,  serving  as  a  source  of  energy.     Thus,  it  has  been  shown 

364 


SPECIAL  DIETETIC  METHODS,  ALCOHOL,  COOKING        3(35 

in  an  experiment  on  man  in  the  respiration  calorimeter  that  the 
addition  of  72  grammes  of  alcohol  (500  calories)  to  a  fixed  diet  exerted 
a  gi'eater  sparing  effect  on  the  protein  of  the  diet  than  did  130  grammes 
of  sugar  (515  calories).  It  is  probable  that  alcohol  in  such  small 
non-toxic  amounts  acts  as  a  carbohydrate-sparer.  It  is  possible,  also, 
that  a  small  amount  of  alcohol  facilitates  digestion.  While  there  is  no 
basis  of  fact  for  the  assertion  that  dire  effects  are  produced  by  the 
taking  of  a  small  amount  of  alcohol  into  the  human  system,  there  is 
great  economic  waste  of  food  in  their  preparation.  Energy  is  dissi- 
pated by  the  process  of  fermentation.  There  is  in  a  gallon  of  beer 
only  one-tenth  of  the  energy  of  the  barley  used  in  its  preparation, 
and,  even  allowing  for  the  food  value  of  the  waste  products  used 
for  feeding  cattle,  there  is  still  a  considerable  loss  of  valuable 
energ}^ 

By  \artue  of  its  quick  absorjation  from  the  stomach,  and  the  ease 
by  which  it  is  combusted,  alcohol  is  of  great  service  in  medicinal  doses 
in  treatment  of  cardiac  failure.  The  feeling  of  warmth  promoted  by 
alcohol  is  due  to  an  increased  blood-flow  in  the  cutaneous  vessels,  so 
that  alcohol,  instead  of  keeping  out  the  cold,  may  tend  to  make  the 
body  lose  more  heat.  "  Wine  is  a  mocker,"'  and  he  who  is  exalted  by 
it  is  a  lenient  critic;  hence  its  reputation  ior  promoting  sociability.  It 
removes  the  consciousness  of  fatigue  and  the  feeling  of  care,  and  makes 
facile  the  play  of  thought  and  speech  by  weakening  the  higher  function 
of  brain-inhibition.  The  subjective  impression  of  mental  capacity, 
exalted  under  the  influence  of  alcohol,  is  unconfirmed  by  test.  Small 
doses  have  no  effect,  larger  ones  diminish  the  fineness  of  control  and 
skill  in  handi-w'ork.  A  man  under  the  influence  of  alcohol  will  make 
more  mistakes  in  type-WTiting  and  in  casting  columns  of  figures. 
Habitual  indulgence  in  alcohol,  by  banishing  the  pressing  sense  of 
dut}^,  makes  a  man  indifferent  to  the  obligations  of  family  and 
national  life.  It  is  the  monotonous,  confined  existence  in  modern 
cities  which  impels  him  to  such  indulgence.  He  who  lives  a  hygienic 
life,  oxygenates  his  tissues  by  outdoor  exercise,  and  thus  keeps  a 
cheerful,  active  mind,  will  need  not  the  '"  wine  which  maketh  glad 
the  heart  of  man,"'  but  the  "  bread  ^^'hich  strengtheneth  man"s 
heart." 


Table  showixCx   Percentage  of  Alcohol  ix  the  Commoner   Spirits, 
WrxE.s,  AND  Beers  (J'ke-War  Ti-me'^). 


Spirits. 
Rum  . . 

Alcohol 
per  Cent.     \ 
. .     43-45       i 

Wines. 
Port    .. 

Alcohol 
per  Cent. 
. .     -25 

Beers. 
English  ale 

Alcohol 

per  Cent. 

5-7 

Brandy 

Wlii-skV 
Gin 

. .     43-45       i 
.  .     40 
. .     35-37 

Sherry 
Champagne 
Hock 
i       Claret 

. .     -21 
.  .      10-15 
. .      10 
. .       9 

Stout      . . 
English  lager 
German  lager 

..      4-7 
..     4-5 
..      3-4 

Tea  and  coffee  owe  their  popularit}'  partly  to  the  alkaloid  caffeine 
— a  methyl-purin — partly  to  the  aromatic  ]irinciples  contained  in 
them.     In  small  do-^es   caffeine   is   stimulating:    in  large  doses  it  is 


366  A  TEXTBOOK  OF  PHYSIOLOGY 

poisonous.  When  prepared  properly — that  is,  when  infused  for 
only  a  few  minutes  and  then  poured  off — tea  is  free  from  injinious 
effects,  but  the  habit  of  taking  strong  tea  every  two  or  three  hours 
of  the  day  is  to  be  condemned  no  less  strongly  than  the  taking  of 
alcohol. 

Cocoa  is  more  of  a  foodstuff,  particularly  if  made  with  milk.  It 
contains  fat  and  a  certain  amount  of  theobromine — an  alkaloid 
closelj^  related  to  caffeine. 

Cooking  of  Food. — This  is  accomplished  bj'  means  of  heat,  either 
moist  or  dry.  Cooking  has  certain  advantages  and  certain  disad- 
vantages, the  former  outweighing  the  latter.  The  chief  disadvantage  in 
cooking  is  that  coagulable  proteins  are  j^ossibly  rendered  more  insoluble 
in  the  digestive  juices,  so  that  their  digestion  takes  longer,  although 
eventually  it  is  just  as  complete.  On  the  other  hand,  cooking  kills 
bacteria  and  other  parasites  such  as  trichinse  and  tape-worms,  which 
may  be  present  in  the  food.  The  connective  tissue  of  meats  is 
rendered  more  soluble,  the  fibres  disintegrated  and  made  easier  for 
mastication,  especially  by  moist  heat.  In  the  cereals,  the  starch 
granules  swell  up  and  rupture  the  cellulose  envelope,  rendering  the 
cell-content  more  accessible  to  the  digestive  juices.  In  vegetables, 
the  woody  fibre  is  also  more  or  less  disintegrated,  the  tissue  rendered 
more  tender,  and  the  cell-contents  more  or  less  liberated.  Dry  heat 
also  converts  a  certain  amount  of  starch  into  dextrin- — e.g.,  as  in  the 
crust  of  bread. 

The  chief  forms  of  cooking  are  boiling,  broiling,  and  roasting. 
The  main  loss  in  cooking  is  water — the  loss  increases  with  the  length  of 
time  of  cooking — in  roasting  a  considerable  quantity  of  fat  (the 
dripping)  is  lost  from  the  joint.  When  boiling  is  employed,  the  liquor 
should  be  used  to  prepare  soup,  otherwise  a  considerable  proportion 
of  proteins,  extractives,  vitamine,  and  salts,  is  lost.  This  is  true 
both  for  meat  and  vegetables.  The  peeling  of  vegetables  greatly 
increases  such  loss.  The  most  economical  forms  of  cooking  are 
broiling  and  \>y  casserole. 

In  the  prejiaration  of  food,  various  flavours  and  condiments  are 
often  added.  When  used  in  moderate  cpxantities,  these,  by  rendering 
the  food  "  toothsome,"  have  the  effect  of  causing  a  "  psychic  '"  flow 
of  gastric  juice,  and  therebj^  promoting  digestion.  On  the  other  hand, 
the  excessive  use  of  condiments  tends  to  upset  the  digestive  apparatus. 
The  appetizing  effects  of  cooking  enhance  the  pleasures  of  the  table, 
but  often  lead  to  overeating,  and  so  to  nutritive  disorders  of  sedentary 
workers.  A  certain  amount  of  uncooked  natural  food  should  be 
eaten,  such  as  fruits  and  salads. 

Meals  should  be  restricted  to  three  a  day,  and  no  food  should 
be  taken  between  meals.  For  the  preservation  of  the  teeth,  it  is 
necessar}'  that  the  mouth  be  kept  free  from  food  for  most  hours  of  the 
day. 


BOOK   VI 

THE   PROCESSES   OF  DIGESTION 

CHAPTER  XLIV 

THE  MECHANISM  OF  THE  SECRETION  AND  ACTIVATION  OF 
THE  DIGESTIVE  FLUIDS 

For  the  proper  digestion  of  the  food,  digestive  juices  are  necessary. 
These  are  provided  either  by  large  compound  glands  which  He  wholly 
outside  the  alimentary  canal,  and  are  connected  to  it  by  ducts,  such  as 
the  salivary  glands,  liver,  and  pancreas;  or  by  glands  which  occur 
in  the  lining  membrane  of  the  alimentary  tract  itself.  These  are 
comparatively  simple  gland  tubes,  and  line  the  whole  of  the  stomach, 
small  and  large  intestine.  The  lining  cells  of  the  alimentary  canal 
also  contribute  to  the  secretion  of  mucus,  which  acts  as  a  lubricant, 
protects  the  mucous  membrane  from  too  high  a  concentration  of 
ingested  material,  and  furthers  the  passage  of  contents  down  the  gut. 

To  understand  rightly  the  processes  concerned  in  the  digestion  of 
food,  it  is  necessary  that  we  stud}' — (1)  the  mechanisms  b}'  which 
the  digestive  fluids  are  provided ;  (2)  the  means  by  which  the 
enzymes  they  contain  are  activated  or  otherwise  rendered  efiicient 
digestive  agents. 

The  proper  preparation  of  foodstuffs  for  digestion,  and  their 
adequate  digestion,  are  matters  of  first  importance  to  the  general 
\\ell-being  of  the  body.  Discomfort  and  local  pain  occur  when  these 
functions  are  temporarily  deranged ;  malnutrition,  anaemia,  depression 
of  spirits,  and  general  ill-health,  follow  chronic  indigestion. 

Digestion  of  the  food  is  necessary,  in  the  first  place,  in  order  to 
convert  the  complex,  colloidal,  non-diffusible,  and  insoluble  protein, 
starch,  and  the  fat,  into  simpler  soluble,  diffusible,  and  non-colloidal 
compounds,  which  are  absorbed  by  the  cells  lining  the  alimentary 
tract.  Secondly,  it  is  necessary  because  some  of  the  component  parts 
of  the  food  material  introduced  into  the  body  are  of  little  or  no  value 
to  the  bodj^ ;  others  are  of  intermediate  value ;  others,  again,  are  so 
precious  that  without  them  the  body  camiot  live.  In  order,  there- 
fore, that  these  components  maj'  be  sorted  according  to  their  true  value, 
it  is  necessary  that  they  be  separated  from  each  other  by  the  hydro^ 
lyzing  action  of  the  digestive  enz3anes. 

367 


368  A  TEXTBOOK  (^F  PHYSIOLOCY 

Generally,  throughout  both  the  vegetable  and  animal  world,  we 
find  foodstuffs  are  taken  into  the  living  cells  in  a  state  of  simple  solu- 
tion, either  alread}^  dissolved  in  water,  or  brought  into  solution  by 
enzymes  and  water  secreted  by  the  cells.  From  the  protozoon  which 
engulfs  its  food  up  to  the  mammal  is  this  true.  True  also  is  it  of  the 
insectivorous  plants,  such  as  the  sundew  and  pitcher-plant  (the 
former  entraj)s  insects  with  nets,  or  the  latter  with  lethal  wells  of 
w^ater);   of  the  yeast  or  bacterium;  and  of  plants  generally. 

The  Mechanism  of  Secretion. — Two  methods  of  calling  forth  secre- 
tion are  employed:  (1)  The  nervous  reflex;  (2)  the  chemical  reflex,  or 
"  hormone  "  mechanism. 

One  or  both  of  these  mechanisms  may  be  used  to  provide  a  juice. 
More  exact  details  are  given  when  each  juice  is  considered  separately. 
Nervous  tissue  has  been  elaborated  for  the  especial  purpose  of 
quick  transference  of  messages  from  one  part  of  the  body  to  another. 
The  nervous  mechanism  is  called  into  pla3'  when  rajiid  secretion  is 
wanted.  The  nervous  mechanism  is  therefore  used  for  the  supply 
of  the  saliva  and  for  the  first  flow  of  the  gastric  juice.  While 
enough  fluid  for  the  immediate  demands  of  the  body  is  provided  by 
the  nervous  mechanism,  the  chemical  mechanism  is  present  to  insure 
the  presence  of  an  adequate  amount  of  digestive  juices  for  the  thorough 
preparation  of  food  and  its  complete  digestion. 

For  the  liberation  of  the  "hormone  reflex,''  either  (1)  the  prod- 
ucts of  the  digestion  brought  about  by  "  nervous  "  flow,  or  (2)  some 
constituent  of  the  juices  so  secreted,  is  concerned  in  calling  forth  this 
"  chemical  "  flow  of  juice.  For  example,  in  the  stomach  we  find  that 
the  presence  of  dextrin  and  peptones — that  is,  the  products  of  a 
salivary  and  gastric  digestion  respectively — liberate  from  the  pyloric 
mucous  membrane  a  body — "  gastrin  " — which  is  absorbed  into  the 
blood,  and,  reaching  the  gastric  glands,  excites  a  further  flow  of  gastric 
juice.  It  may  be  also  that  there  is  something  in  the  saliva  able  to 
bring  this  mechanism  into  action,  for  it  has  been  noticed  that  swallowed 
saliva  ap^Dcars  to  have  the  powder  of  evoking  a  flow  of  gastric  juice. 

The  flow  of  pancreatic  juice  is  also  brought  about  by  a  "'  chemicaJ  " 
reflex — namely,  by  the  liberation  from  the  duodenal  mucous  mem- 
brane of  a  body  termed  "  secretin,"  which  passes  in  the  blood  to  the 
pancreas,  and  stimulates  that  organ  to  activity.  There  is  evidence 
that  the  pancreas  may  also  be  excited  to  secrete  by  impulses  reaching 
it  through  its  nerves.  This,  however,  does  not  appear  to  be  the  normal 
mechanism.  In  the  case  of  secretion  excited  bj^  nervous  mechanisms, 
it  is  probable  that  the  nervous  excitation  of  the  gland  evokes  a  ""  hor- 
mone "  in  the  gland  itself,  which  excites  the  secretion.  For  example, 
an  extract  of  resting  salivary  gland  has  no  effect  when  injected  into 
the  blood,  but  an  extract  of  the  same  gland,  after  stimulation  of  the 
chorda  tympani  nerve,  is  said  to  provoke  secretion  of  saliva  when 
injected. 

The  exact  natm-e  of  the  substance  provoking  the  flow  of  succus 
entericus  is  not  well  known.  Undoubtedly,  the  acidity  of  the  chyme 
entering  the  duodenum  plays  a  most  important  part  as  regards  the 


SECRETIOX  AND  ACTTVATIOX  OF  DIGESTIVE  FLUIDS      369 

provision  of  this  juice  in  the  duodenum.  It  is  suggested  that,  for 
the  other  parts  of  the  small  intestine,  the  absorption  of  the  products 
oi  the  digestion  in  the  parts  above  evokes  a  messenger  which,  absorbed 
into  the  blood,  calls  forth  a  flow  of  appropriate  juice  in  the  regions 
.  lower  down  the  tract. 

The  bile  takes  an  important  share  in  the  preparation  of  the  food 
for  intestinal  digestion — for  example,  in  the  emulsification  of  fats 
and  the  precipitation  of  protein  from  acid  solution.  A  quick  flow 
of  bile  is  therefore  required.  In  animals  where  a  gall-bladder  exists, 
the  first  flow  of  bile  is  probabh*  provided  by  the  contraction  of  the 
gall-bladder,  which  is  excited  by  a  nervous  reflex.  The  reflex  arises 
from  the  stimulus  of  food  passing  the  pjdorus.  A  further  supply  of 
bile  is  provided  from  the  liver  by  the  action  of  "'  secretin."  This 
insures  its  presence  in  the  intestine  in  amounts  adequate  to  the  food 
which  is  arriving  there  to  be  digested.  Possibty,  too,  the  products  of 
digestion  reaching  the  liver  cause  a  further  flow  of  bile.  The  reab- 
sorption  of  bile  salts  from  the  intestine  stimulates  the  liver  to  secretion, 
but  this  is  usualh'  after  the  period  of  active  digestion,  and  the  bile 
secreted  by  this  mechanism  is  generalh*  stored  in  the  gall-bladder, 
there  being  a  correspondingly  active  secretion  to  replenish  the  depleted 
store.     The  following  chart  shows  how  different  juices  are  pro\'ided: 

Juice.  Mechanism. 

Saliva         . .  . .  . .     Nervous  reflex. 

Gastric  juice  ..  ..      (1)  Nervous  reflex. 

(2)  Liberation  of  gastrin  (chemical  reflex). 
Bile  ..  ..  ..     (1)  Probably  nervous  reflex  contraction  of  gafl. bladder. 

(2)  By  secretin  (chemical  reflex). 

(3)  By  products  of  digestion  reaching  liver. 

(4)  By  absorption  of  bile  salts. 
Pancreatic  juice    ..          ..      (1)  By  secretin. 

(2)  Probably  also  by  nervous  reflex. 
Succus  entericus  . .  . .      (1)  By  acid  chjane. 

(2)  By  absorption  of  products  of  digestion. 

We  have,  therefore,  to  bear  these  mechanisms  in  mind  \\hen  thinking 
of  the  digestive  disorders  which  may  possibly  arise.  It  may  well  be 
that  in  some  conditions  the  flow  of  one  or  other  of  these  juices  is  not 
evoked  adequately,  owing  to  a  failure  of  the  pro]ier  stimulus  for  its 
secretion. 

.  The  Activation  of  the  Juices. — In  most  of  the  juices  the  digesting 
agent,  or  enzyme,  is  in  the  form  of  a  precursor,  or  zymogen.  This 
zj'mogen  must  be  converted  into  the  enzyme,  or  "'  activated,"  as  it  is 
termed,  before  it  becomes  potent.  The  enzyme  of  the  saliva — 
"  ptyalin  "" — is  probably  activated  by  the  bacteria  of  the  mouth,  or 
some  other  body  present  in  the  mouth,  since  in  the  horse  it  has  been 
found  that  if  the  saliva  be  collected  aseptically  it  manifests  no  digestive 
action.  It  is  only  when  bacteria  are  allowed  to  enter  the  saliva  that 
the  enzyme  attains  its  digestive  power.  Bacteria  probably  play  a 
similar  and  important  part  in  other  parts  of  the  alimentaiy  tract, 
even  when  specific  activators  of  the  zymogens  are  secreted  there. 

24 


;no  A  TEXTBOOK  OF  PHYSIOLOGY 

The  normal  acti\ator  of  the  gastric  zymogens — joepsinogen  and 
prorennin — is  the  hych'ochloric  acid  (HCl)  of  the  gastric  juice.  It 
has  been  found,  howexer.  that  these  two  zymogens  may  become 
converted  into  the  active  enzymes  in  conditions  where  little  or  no  HCl 
is  being  secreted.  In  such  cases,  the  exact  activator  is  not  known; 
it  is  quite  probable  that  bacteria  play  a  part.  Similarly,  the  normal 
activator  of  the  trypsinogen  of  the  pancreatic  juice  is  a  substance 
known  as  "  enterokinas^e,"  which  is  secreted  in  the  succus  entericus. 
But  it  is  probable  that  an  enzyme — "deuterase"  —  and  calcium 
salts  also  possess  the  power  of  converting  this  zymogen.  The 
other  enzymes  found  in  pancreatic  juice  are  possibly  secret ■^d  as 
zymogens,  but  the  exact  nature  of  their  activating  agent  is  not  known. 
The  same  must  be  said  in  regard  to  the  enzymes  of  the  succus  entericus. 
The  steapsin  of  the  pancreas  reqitires  the  presence  of  bile  salts  to  act 
as  co-enzyme.  The  enzyme  loses  its  digestive  power  if  these  be 
dialyzed  awaj".  It  is  quite  possible  that  in  some  conditions  of  digestive 
disturbance  there  is  an  inadequate  liberation  of  the  enzymes  from  the 
zymogens,  in  others  an  inadequate  secretion  of  the  zymogens.  At 
j^resent,  om-  knowledge  on  these  points  is  fragmentary. 


Juice. 

Proenzyme, 

Activator. 

Saliva 

Ptyalin 

Bacteria 

Gastric 

Pepsinogen 
Prorennin 

Hydrochloric  aci 

Pancreati 

Trypsinogen 

Entcrokinase. 
Calcium  salts. 
Deuterase. 
Bacteria  (?). 

In  regard  to  other  enzymes,  the  present  state  of  knowledge  is  in- 
sufficient for  them  to  be  tabulated. 


CHAPTER  XLV 
DIGESTION  IN  THE  MOUTH 

The  Saliva. — The  saliva  is  secreted  from  three  pairs  of  glands  in 
the  region  of  the  mouth.  These  are  the  parotid,  tlie  submaxillary, 
and  the  sublingual.  It  is  also  secreted  by  other  minute  glands  con- 
tained in  the  buccal  mucous  membrane.  The  character  of  the  saliva 
varies  in  the  different  glands. 

The  parotid  of  man  and  most  animals  yields  a  thin  serous  (albumin- 
ous) saliva,  while  from  the  submaxillary  gland  "  mixed  "'  saliva,  partly 
serous  or  watery,  partly  mucous  or  viscid,  is  usually  obtained ;  in  the 
rabbit,  however,  the  secretion  of  the  submaxillary  glands  is  wholly 
serous.  Saliva  is  a  mixture  of  the  secretions  of  all  these  glands. 
The  parotid  saliva  of  man  is  a  thin,  faintly  alkahne  fluid,  containing 
but  little  protein  and  no  mucus.  Its  specific  gravity  varies  from 
1003  to  1012.  It  contains  a  starch-splitting  enzyme — ptyalin — and 
in  most  cases  a  small  amount  of  potassium  sulphocyanide,  with  a 
variable  small  amount  of  salts  (0-5  to  1-6  per  cent.)  and  gases  in  solu- 
tion (oxygen,  nitrogen,  and  carbon  dioxide).  The  oxygen  in  the  saliva 
is  greater  in  amount  than  that  which  is  dissolved  in  water  when  exposed 
to  the  atmosphere.     The  excess  must  be  secreted  m  the  saliva.  ^  . 

Submaxillary  saliva  varies  according  to  the  exciting  conditions. 
In  man,  the  submaxillary  sahva  is  ordinaril}"  a  clear,  viscid,  alkaline 
secretion,  with  a  specific  gravity  of  1002  to  1005,  and  about  0-3  to 
0-5  per  cent,  of  solids.  It  contains  much  mucin,  traces  of  protein 
and  the  ferment  ptyalin,  potassium  sulphocyanide,  and  inorganic 
salts,  the  chief  of  which  are  the  chlorides  of  sodium  and  potassium, 
the  phosphates  of  calcium  and  magnesium,  and  the  bicarbonate  of 
calcium  and  sodium.  Traces  of  sulphates  are  also  present.  In 
the  dog  two  kinds  of  submaxillary  saliva  are  recognized:  that  pro- 
duced b\'  stimulation  of  the  chorda  ty<mpani  nerve,  known  as^ 
chorda  saliva,  and  that  produced  by  stimulation  of  the  sympathetic 
nerve,  known  as  sympathetic  saliva.  Chorda  saliva  is  the  abundant 
secretion  of  the  gland,  having  a  specific  gravity  of  1003  to  1005.  and 
containing  about  1-2  to  1-4  per  cent,  of  solids.  Sjunpathetic  saliva  is 
very  much  smaller  in  amount,  and  considerabh*  richer  in  solids 
(1-6  to  2-8  per  cent.).     Its  specific  gravity  is  1007  to  1018. 

Sublingual  saliva,  the  most  alkaline  of  the  salivas,  is  transparent, 
viscid  saliva,  comparatively  rich  in  mucin  and  solids.  It  also  contains 
ptyalin  and  potassium  sulphocyanide. 

371 


Per  Cent. 

Per  Cent. 

995-10 

994-10 

4-84 

5-90 

1-02 

2-13 

l-;j4 

1-42 

()-U(i 

0-10 

1-82 

2-19 

o72  A  TEXTBOOK  OF  PHYSIOLOGY 

The  secretion  of  the  buccal  glands  consists  chicfl}-  of  thick  mucus. 

The  mixed  sahva  obtained  from  the  mouth  lias  therefore  a  com- 
bination of  the  properties  of  the  secretions  forming  it.  Its  quanti- 
tative composition  may  be  seen  by  the  following  analysis: 


Water  

Solids 

Mucin 

Soluble  organic  bodies 

Sulphocyanide 

Salts  

It  is  usually  somewhat  turbid,  owing  to  the  presence  of  epithelial 
cells  and  of  food  particles.  Upon  standing,  it  becomes  more  so,  owing 
to  the  deposition  of  calcium  carbonate  and  organic  matter,  which  forms 
the  tartar  deposited  on  teeth. 

In  some  animals,  saliva  contains  an  oxidase  and  maltase.  The 
exact  significance  of  the  potassium  sulphocyanide  is  not  known. 
Smokers  are  said  to  have  more  than  non-smokers.  This  is  very  doubt- 
ful. Its  presence  can  readity  be  detected  by  the  red  colour  obtained 
upon  adding  a  little  HCl  and  some  ferric  chloride  to  the  saliva. 

The  functions  of  the  saliva  are — 

1.  To  act  as  a  solvent  by  virtue  of  the  large  amount  of  water  it 
contains,  and  also  in  part  as  a  solvent  for  the  digested  soluble  nutritive 
substances.  Probably,  saliva  plays  a  larger  j^art  in  this  way  than  is 
usually  believed. 

2.  To  act  as  a  lubricant  by  virtue  of  its  mucus  content,  and  thus 
facilitate  the  act  of  SAvallowing. 

3.  To  act  upon  boiled  starch  as  a  digestive  agent. 

4.  To  aid  taste — dry  substances  cannot  be  tasted — and  indirectl^^ 
through  taste,  to  stimulate  the  flow  of  saliva  and  gastric  juice. 

5.  To  moisten  the  mouth,  and  thereby  aid  articulation;  to  wash 
out  the  mouth,  and  thereby  get  rid  of  noxious,  evil-tasting,  or  poisonous 
substances  ;   to  clean  and  protect  the  teeth  from  decay. 

6.  Possibly,  when  swallowed,  to  act  as  an  excitant  to  the  flow  of 
gastric  juice. 

The  manifold  nature  of  its  functions  accounts  for  the  variation 
found  in  the  composition  of  saliva.  The  nature  of  the  saliva  secreted 
is  adapted  in  the  main  to  that  function  which  is  in  most  demand. 
This  adaptation  depends  upon  three  factors — chemical,  physical,  and 
psj^chic.  Acids  and  evil-smelling  substances  cause  a  great  flow  of 
thin  parotid  saliva;  dry  bread,  cooked  potatoes,  hard-boiled  eggs, 
cavise  a  flow  of  saliva  rich  in  ptyalin,  the  mucus  and  \\ater  content 
varying  according  to  the  dryness ;  sugar  evokes  a  saliva  poor  in  mucin  : 
a  pebble  put  in  the  mouth  evokes  no  secretion,  while  sand  calls  forth 
a  large  flow. 

The  movements  of  chewing  and  si)eaking  excite  the  flow ;  the  hold- 
ing of  food  in  the  mouth  evokes  little  or  no  secretion.  The  sight  of 
food  makes  an  animal's  mouth  "  water  ";  the  sight  of  a  colour  asso- 
ciated with  a  given  food  may  do  this  also.     A  stone  painted  like  a 


DIGEST'IOX  IN  THE  MOUTH  373 

piece  of  meat  will  at  first  evoke  secretion  in  a  dog  until  the  animal 
realizes  it  is  a  frand;  then  it  ceases  to  do  so. 

The  smell  of  food  causes  a  flow  of  saliva,  varying  according  to  the 
appetite.  It  is  particularly  copious  when  the  animal  is  hungry. 
Hearing  a  noise  associated  with  food — e.g.,  the  rattle  of  the  food-plato 
— also  induces  a  salivary  flow. 

The  amount  of  saliva  secreted  while  eating  depends — 

1.  Upon  the  dryness  of  the  food. 

2.  Upon  its  chemical  properties. 

3.  Upon  the  length  and  thoroughness  of  the  act  of  chewing. 

4.  Upon  the  water  intake. 

5.  Whether  accessory  stimulants  be  present,  such  as  mustard  or 
pepper. 

6.  Upon  the  excitability  of  the  nervous  mechanism  of  the  salivar}^ 
glands  themselves. 

The  quantity  of  saliva  generally  varies  from  500  to  1,500  c.c.  per 
day.     Experiments  showed  that  a  girl  secreted  while  chewing — 

150  grammes  of  sugar  . .  .  .  . .  . .  . .  . .  200  c.c.  of  saliva. 

1,200        „         of  milk 200      „ 

200         „  of  bread  126      „ 

700         ,,         of  mixed  diet :  meat,  soup,  potatoes  ..  ..  300      ., 

10         ,,         of  thin  bread  and  butter      . .  . .  . .  . .         2      ,, 

10         „  of  dry  bread   .  .  . .  .  .  . .  . .  .  •        15       „ 

The  Mechanism  of  Secretion. — During  the  process  of  secretion  there 
occur  certain  well-marked  changes  in  the  gland  cells.  In  a  serous 
gland,  prior  to  secretion,  the  cells  are  filled  with  granules  which  stain 
readily,  the  nuclei  of  the  cells  being  almost  obscured  or  appearmg 
at  one  side  as  more  or  less  irregular  masses.  During  secretion,  these 
granules  become  discharged  from  the  cell,  the  nuclei  become  more 
prominent,  while  the  cells  markedly  shrink  in  size. 

In  the  mucous  gland  the  process  is  comparable.  The  resting  cell, 
with  its  large  refractile  granules  and  nuclei  flattened  towards  the  base 
of  the  cell,  is  replaced  after  secretion  by  the  smaller  '"  exhausted  " 
cell,  devoid  of  mucigen  granules,  with  well-marked  spherical  nucleus 
placed  in  the  middle  of  the  cell.  During  the  period  of  rest,  the  cells 
again  elaborate  new  granular  material,  and  pass  into  the  "  restmg 
state." 

The  salivary  secretion  takes  place  under  nervous  influence,  the 
whole  process  being  presided  over  bj^  a  centre  in  the  medulla  oblongata 
(c)  in  the  region  of  the  glosso-pharjmgeal  nucleus.  To  this  centre  come 
impulses  directly  by  various  sensory  nerves,  and  also  indirectly  via 
the  higher  centres  (c  )  of  the  brain  (Fig.  192).  Thus  it  is  that  contact 
of  food  with  the  buccal  mucous  membrane  or  stimulation  of  the  central 
end  of  the  lingual  or  glosso-phar\'ngeal  nerve  gives  rise  to  a  flow  of 
saliva.  Exactly  how  the  sensory  discrimination  and  adaptation  of 
the  flow  of  saliva  are  brought  about  is  not  known.  The  results  show 
that  such  discrimination  is  a  fimctionof  the  lower  subconscious  centres. 
Sight  and  hearing  act  reflexly  through  the  higher  centres;  so  do  past 


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A  TEXTBOOK  OK  IMI VSI ()!.()( JY 


impressions,  such  as  are  aroused  by  Ihiiiking  of  a  favourite  meal. 
This  may  make  the  mouth  water,  especially  in  a  state  of  hiniger. 

The  efferent  nerves  from  the  centre  are  the  auriculo-temporai 
nerv^e  to  the  parotid  gland,  the  chorda  tj^mpani  nerve  to  the  sub- 
maxillary and  the  sublingual  glands.  The  sympathetic  system  also 
gives  a  weak  effector  nerve  to  the  submaxillary  gland  and  sublingual 
gland. 

The  course  of  the  effector  nerves  is  somewhat  complicated.  While 
stimulation  of  the  fifth  nerve  above  the  otic  ganglion  is  without  effect 
upon  the  secretion  of  the  parotid  gland,  stimulation  of  the  ninth  nerve 
as  it  leaves  the  brain  causes  a  flow  of  saliva.  The  effector  fibres 
therefore  pass  from  the  ninth  nerve  to  the  fifth.  They  follow  the 
path  of  Jacobson's  nerve,  and  the  small  superficial  petrosal,  to  the 
otic  ganglion,  which  is  the  cell-station  of  this  nerve. 

-<Merricr'y. 


Parotid  gland 
(by  auricula  ■  tempers  i 
nerve) 


(Buccal 
\  mucous 
{membrane. 

Tongue 


^SubmaxillarLj  gland 
(by  chorda  tympani) 

.■^Sublingual  gland 
(bu  chorda  tumpani 
^    ner/ef 


\  By  vagus  to  stomac.'i 
■\     for  gastricjuice. 

Fig.  192. — Diagram  to  show  Connections  of  the  Nervous  Centre  concerned 
IN  THE  Secretion  of  Saliva  and  Gastric  Juice. 


The  stimulation  of  the  sympathetic  nerve  to  the  parotid  does  not 
effect  a  flow  of  saliva.  It  is  stated,  however,  that  if  the  nerve  be 
stimulated  at  the  same  time  as  Jacobson"s  nerve,  or  the  glosso-pharjn- 
geal,  the  solid  content  of  the  saliva,  particularly  the  organic,  is  con- 
siderably raised. 

In  regard,  to  the  submaxillary  and  sublingual  glands,  it  has  been 
proved  experimentally  that  if  the  lingual  nerve  be  cut  high  up,  reflex 
secretion  of  saliva  still  occurs.  Similarly,  stimulation  of  the  perii:)heral 
end  of  this  nerve,  and  after  it  has  been  cut  high  up,  has  no  effect 
upon  secretion.  On  the  other  hand,  if  the  chorda  tympani  nerve 
be  cut,  reflex  secretion  is  abolished ;  while  stimulation  of  the  peripheral 
end  causes  a  copious  flow  of  watery  saliva.  This  nerve  issues  from 
the  seventh  nerve  as  a  small  branch,  and,  joining  the  lingual  in  the 
lower  part  of  its  course,  runs  with  it  for  a  short  way,  and  then  passes 
to  the  glands.  The  course  of  the  fibres,  however,  is  interrupted  by 
the  interposition  of  ganglia.  The  fibres  to  the  sublingual  gland  end 
in  a  small  ganglion,  known  as  the  "  submaxillary  ganglion  "  (it  ought 
to  be  termed  "sublingual");  the  fibres  to  the  submaxillary  gland 
end  in  a  minute  ganglion  situated  in  the  hilus  of  the  gland.     The  cell 


DIGESTION  IX  THE  MOUTH  375 

stations  are  shown  by  painting  the  gangha  with  nicotine  ;  this 
paralyzes  the  synapses  or  end  terminations  of  the  preganghonic 
fibres  with  the  ganghon  cells. 

There  is  some  discussion  as  to  the  manner  in  which  the  effector 
nerve  acts.  According  to  one  view,  there  are  tAvo  kinds  of  fibres  in 
the  nerve — trophic  fibre?,  which  cause  changes  in  the  granular  material, 
preparing  it  for  its  discharge  from  the  cell;  and  the  secretory  fibres, 
which  bring  about  this  discharge.  Upon  this  view,  the  sympathetic 
nerve  is  mainly  trophic,  the  cranial  (chorda)  nerve  is  mainh'  secretory. 

It  is  more  generally  held,  however,  that  one  kind  of  fibre  causes 
all  the  changes  attendant  on  secretion,  the  difference  between  chorda 
and  sympathetic  saliva  being  due  to  the  difference  in  blood-supply. 
With  the  chorda  stimulation  there  is  a  great  vaso-dilatation,  with 
sympathetic  stimulation  there  is  marked  constriction  of  the  small 
arteries  supplying  the  gland.  Vaso-dilatation  is  probably  also  pro- 
duced localh'  by  the  products  of  metabolism  of  the  gland. 

Tiie  action  of  the  nerv^ous  mechanism  appears  to  be  more  marked 
at  som?  times  than  others.  It  is  more  marked  in  a  state  of  hunger  than 
in  a  state  of  satiety.  It  may  possibly  be  that  the  products  of  digestion 
•or  the  saliva  itself  become  absorbed,  and  affect  the  excitability  of  the 
nervous  mechanism  or  the  cells  of  the  gland. 

A  day  or  two  after  the  chorda  tympani  nerve  has  been  divide:! 
there  begins  a  slow  continuous  secretion  of  saliva,  known  as 
paralytic  sjcretion  which  lasts  from  five  to  six  weeks.  As  the 
nerve  itself  degenerates  in  three  to  five  days,  the  secretion  is 
obviously  due  to  some  local  apparatus  in  the  gland.  If  the  sympathetic 
nerve  be  cut  at  the  same  time,  the  secretion  is  diminished  or  stopped. 
JSTo  paralytic  secretion  follows  secretion  of  the  sympathetic  nerve  by 
itself;  this  produces  little  or  no  observable  effect.  Tne  same  is  true 
in  regard  to  excision  of  the  superior  cervical  ganglion. 

The  characteristic  saliva  of  any  one  gland  may  be  obtained  by 
placing  a  small  glass  camiula  m  the  main  duct,  and  stimulating  the 
■effector  nerve.  The  submaxillary  gland  is  the  one  which  lends  itself 
most  readily  to  this  experiment.  By  such  means  the  true  secretory 
nature  of  the  sahva  can  be  demonstrated.  If  the  cannula  placed  in 
the  submaxillary  duct  be  connected  to  a  manometer,  and  the  pressure 
Avhich  is  produced  in  the  duct  during  stimulation  of  the  chorda  tympani 
be  measured,  it  may  be  found  to  rise  to  twice  the  height  of  the  pressure  of 
the  arterial  blood  supplying  the  gland  (Fig.  1 9,3) .  The  saUvary  secretion 
is  therefore  a  true  secretion.  It  is  not  merely  a  passage  through  into 
the  salivary  ducts  as  the  result  of  pure  mechanical  processes,  such  as 
filtration,  diffusion,  or  osmosis.  Even  with  so  great  a  pressure,  the 
blood  still  flows  through  the  salivary  glands.  This  is  because  the 
blood-capillaries  of  the  gland  are  protected  from  occlusion  by  the 
basement  membranes  which  enclose  the  alveoU  of  the  gland.  These 
membranes,  strengtheiied  by  connective  tissue,  limit  the  expansion 
of  the  alveoli,  just  as  the  leather  case  of  a  football  hmits  the  expansion 
of  the  bladder  M'ithin.  A  certain  amount  of  expansion  is  allowed, 
however — enough  to  narrow  the  veins  within  the  gland,  and  convert  the 


376 


A  TEXTBOOK  OF  PHYSI0L0<;N 


bloodvessels,  arteries,  capillaries,  and  veins,  into  a  more  rigid  system, 
through  which  a  very  rapid  flow  of  blood  takes  place.  Thus,  the  whole 
gland  s\\ells  under  these  conditions,  and  feels  very  tense  to  the  touch. 
If  the  blood-supply  to  the  gland  be  lessened  by  a  moderate  compression 
of  its  arterial  supply,  the  rate  of  secretion  remains  unchanged,  Con- 
sideraMe  compression  decreases  the  amount.     A  sahvary  gland  will 


A^^e^ld.'   Zaro 


SaJivary  Zero 


M'ffKiiilVi 


Arf-Grt^l  Zero 


Salivary  Zero 


Fro,  193. — Tkacings  from  Two  Different  Dogs,  anaesthetized  by  Morphine 
AND  Chloroform,  showing  the  Arterial  (Carotid)  Pressures  and  the 
Secretory  Pressures  of  Saliva  during  Excitation  of  the  Chorda  Tympani 
Nerve.     (From  Froceedbujs  Rcyai  Scciely.) 

With  a  .salivary  prosfriire  of  2-iO  mm.  Hg  and  an  arterial  pressure  of  ISO  n.m.  Hg., 
l)lood  still  flowed  through  the  gland. 


even  secrete  a  few  drojis  when  its  blood-supjoly  is  cut  off — e.g.,  after 
cutting  off  the  head.  Certain  drugs,  such  as  atropine,  paralyze  the 
secretory-  fibres  of  the  gland,  but  not  the  fibres  producing  vaso-dilata- 
tion.  Thus,  when  the  chorda  tympani  nerve  is  stimulated  after 
injection  of  atropine,  a  rapid  blood  flow  and  increased  pressure  is 
obtained  in  the  gland,  but  no  secretion.  An  injection  of  quinine 
hydrochloride  produced  vaso-dilatation  in  the  gland,  but  no  secretion. 


DIGESTIOX  IX  THE  MOUTH  377 

The  total  osmotic  pressure  of  the  blood  is  4,500  mm.  Hg,  whereas 
that  of  the  sahva  is  but  3,000  mm.  Hg. 

During  the  j^rocess  of  secretion  there  is  a  greatly  increased  tissue 
respiration  within  the  gland,  the  amount  of  oxygen  used  up  and  the 
amount  of  carbon  dioxide  given  out  being  markedly  increased. 

Gaseous  Exchange. 

0,  taken  up.  CO.y  Output. 

Resting  gland  ..  ..     0-25  c.c  per  minute.  0-17  c.c.  per  minute. 

Active  gland  ..  ..     0-86       „  „  0-39 

The  blood-flow  may  be  increased  seven  to  ten  times  during  secre- 
tion, and  the  amount  of  hinph  formed  goes  up  markedly. 

From  these  considerations,  the  conclusion  is  reached  that  the  sahva 
is  not  a  filtrate  or  transudate,  but  a  product  of  the  activity  of  the 
gland  cells,  separated  by  forces  which  cannot  at  present  be  grouped 
luider  the  physico-chemical  processes  which  have  been  worked  out  in 
the  laboratory. 

Certain  diffusible  substances  in  the  blood — sugar,  for  example — - 
never  appear  in  the  sahva,  whereas  certain  salts,  if  taken  into  the 
body,  are  picked  out  bj"  the  salivary  glands  and  secreted  in  the  saliva. 
This  is  the  case  with  iodides  and  mercury.  This  fact  must  be  borne 
in  mind  in  prescribing  these  drugs. 

The  secretion  of  iodides  is  sometimes  made  use  of  to  test  the 
absorbing  power  or  motility  of  the  stomach.  Potassium  iodide  is 
given  by  the  mouth,  and  the  time  taken  for  the  appearance  of  iodides 
(tested  for  by  starch  solution  and  chloroform)  in  the  saliva  noted. 
The  rate  of  appearance  varies  with  the  absorptive  power  of  the  stomach 
for  iodides.  It  is  questioned  whether  this  gives  any  guide  for  the 
ordinary  absorptive  power.  To  test  the  motility,  the  iodide  is  given 
in  a  capsule,  which  is  not  digested  by  the  gastric,  but  by  the  pancreatic 
fluid,  and  the  time  taken  until  the  iodide  appears  in  the  saliva.  The 
test  cannot  be  regarded  as  by  am^  means  acciu-ate,  since  its  passage 
out  of  the  stomach  is  rather  a  haphazard  matter;  but  should  the 
iodides  appear  within  two  to  three  hours,  the  motility  of  the  stomachs 
is  regarded  as  normal. 

Heat  is  produced  in  the  gland,  as  is  sho^^^l  by  the  oxygen  use  and 
production  of  carbon  dioxide,  but,  owing  to  the  velocit}'  of  the  circu- 
lation, it  is  not  possible  to  observe  the  difference  in  temperature.  It 
has  been  claimed  that  the  saliva  is  one  or  two  degrees  warmer  than  the 
blood;  but  if  the  bulb  of  a  very  delicate  thermometer  be  introduced 
into  the  aorta  through  the  femoral  arterj',  and  the  bulb  of  another 
thermometer  is  placed  in  the  cannula  attached  to  the  salivary  duct, 
and  this  cannula  be  filled  with  Avater  of  the  same  temperature  as  the 
blood,  then  on  stimulating  the  secretion  no  change  in  temperature  is 
observed.  Electrical  changes  (see  later,  p.  566)  are  also  observed  in 
the  gland.  The  current  of  rest  gives  place  to  a  current  of  action, 
but  the  direction  of  the  current  is  different  according  as  the  chorda 
tympani  or  cervical  sympathetic  is  excited. 


378  A  TEXTBOOK  OF  PHYSIOLOGY 

The  Action  of  the  Ptyalin. — The  enzyme  ptvalin.  wiien  present  in 
the  sahva  of  an  animal,  acts  upon  ])oiled  starch,  and  converts  it  through 
the  stages  of  er^throdextrin  and  achroodextrin  to  maltose.  The  stages 
can  well  be  demonstrated  by  taking  a  series  of  test-tubes  con- 
taining iodine  solution,  and  a  test-tube  containing  some  Fehling's 
solution.  Another  tube  containing  some  starch  solution,  preferably 
at  about  37°  C,  is  taken,  and  some  saliva  placed  in  it.  A  drop  of  this 
mixture,  added  at  once,  gives  with  the  iodine  a  blue  colour;  after 
a  short  time,  the  addition  of  a  drop  to  another  tube  gives  a  red  colour 
(erythrodextrin) ;  later,  no  colour  is  obtained  when  a  drop  of  the 
solution  is  added  to  the  iodine.  A  little  later,  some  of  the  solution 
boiled  with  the  Fehling  solution  will  give  the  reduction  due  to  the 
presence  of  sugar  (maltose).  With  very  active  saliva,  sugar  may 
appear  in  half  to  one  minute. 

The  rate  of  action  of  ptyalin  de]Dends  upon  the  kind  of  starch ; 
also  the  reaction  in  which  it  is  acting.  It  acts  best  in  neutral  or  very 
weak  acid — 0-003  per  cent.  HCl.  It  is  inhibited  by  stronger  acid,  such, 
for  example,  as  0-3  per  cent.  HCl.  Organic  acids  do  not  stop  the  action 
of  ptyalin  until  they  reach  a  strength  about  ten  times  that  of  inorganic 
acids. 

Common  salt  greatly  favours  the  action  of  ptyalin,  making  it 
about  ten  times  as  active.  Other  chlorides  have  a  similar  but  less 
marked  action.     Alkaline  carbonates  hinder  the  action. 

The  action  of  ptyalin  continv;es  in  the  stomach,  digestion  of  poly- 
saccharides proceeding  until  inhibited  by  acid.  This  may  be  as  long 
as  forty-five  minutes.  The  saliva  has  an  immunizing  effect,  protect- 
ing the  teeth  from  deca5^  Mouth-breathing  and  the  habit  of  eating 
too  often  and  too  much  soft  and  sticky  food,  whereb}^  chronic  slight 
derangement  of  the  alimentary  canal  is  induced,  together  contribute  to 
the  deca}'^  of  teeth.  The  decay  is  the  result  of  bacterial  action, 
favoured  by  acid  fermentation  of  food  allowed  to  stick  between  the 
teeth. 


CHAPTER  XLVI 

DIGESTION  IN  THE  STOMACH 

On  anatomical  and  physiological  grounds  this  organ  is  divided 
into  three  divisions — namely: 

1 .  The  fmidus,  or  the  reservoir. 

2.  The  cardia  or  body,  or  the  digestive  chamber. 

3.  The  pylorus,  or  the  churn  or  mill. 

A  schematic  outline  of  the  organ  is  shown  in  Fig.  194.  The 
normal  position  in  man  in  the  vertical  position  is  seen  in  Fig.  195. 
It  is  to  be  noted  that  it  reaches  to  the  umbilicus  (U). 

The  fundus  may  be  regarded  in  animals  as  being  separated  from 
the  cardia  by  an  imaginary"  line  passing  from  the  cardiac  orifice  to 
the  opposite  i)oint  on  the  greater  curvature:  in 
man,  by  the  part  lying  above  the  horizontal  plane 
of  the  cardiac  orifice. 

The  incisura  angularis,  I. A.,  denotes  the  point 
of  demarcation  between  the  body  or  cardia  and 
the  pyloric  portion.   This  portion  itself  is  divisible 
into   two    parts — the    pj^loric   vestibule   and   the 
pyloric    canal.      The   vestibule   lies  between  the 
incisura  angularis  and  the  pj'loric    canal.      The 
canal  is  the  tube-like  portion  of  the  pylorus  Avhich 
leads  from  the  vestibule  to  the  pylori?  sphin:ter.  ^^^-  194.  —  Schematic 
The    stomach   wall    consists  of    three    muscular     Stomach.    (Cannon.) 
coats,   arranged    from  outside   inwards  in  longi- 
tudinal, circular,  and  oblique  fashion.    The  longi-  ^'Cardia;  F,  fundus; 
^     T      1  J-  •>!     ii  r    -1  B,  body;  P,  pylorus; 

tudmal  are  contmuous  with  those  ot    the  oeso-     /j,     incisura    ano-u- 

phagus,  and  radiate  over  the  stomach,  to  end  at  the  laris ;  PO,  pyloric 
pylorus.  The  circular  fibres  completely  invest  canal, 
the  whole  stomach,  being  particularly  well  marked 
in  the  pyloric  portion,  especialh"  at  the  pyloric  sphincter.  They  also 
form  a  well-marked  thickening  at  the  incisura  angularis.  termed  the 
"  transverse  band."  The  oblique  fibres,  starting  as  two  strong  bands 
from  the  left  of  the  cardiac  orifice,  pass  along  the  anterior  part  of  the 
dorsal  and  ventral  surfaces  toA\ards  the  pylorus,  gradually  disappearing 
as  they  go. 

The  structure  of  the  glands  varies  in  the  different  portions  of  the 

379 


380 


A  TEXTBOOK  OF  PHYSIOLOGY 


stoiiuich.  The  glands  of  the  fundus  are  simple  tubules  lined  with  one 
layer  of  cells,  somewhat  similar  to  the  crypts  of  Lieberkiihn  of  the 
smaller  intestine.  The  glands  of  the  cardia  or  body  have  short  ducts 
with  long,  straight  tubules.  In  these  tubules  arc  two  sets  of  cells. 
The  central  or  chief  cells  are  cubical  in  shape,  and  contain  coarse 
granules,  which  are  usually  in  greater  profusion  nearer  the  lumen. 
Lying  in  between  the  central  cells,  and  to  their  outer  side,  are  a  number 
of  large  spheroidal  cells,  known  as  the  "  parietal  "  or  "  oxyntic  " 
(acid-forming)  cells.  Each  of  these  cells  appears  to  be  connected  to 
the  lumen  of  the  gland  by  a  number  of  small  channels  which  pass 
between  the  central  cells. 

In  the  pylorus  the  glands  have  long  ducts,  and  the  secreting  tubules 
are  long;  and  much  branched,  being  often  continued  into  the  submucous 


Fig.  195. — Diagram  showing  the  Position  of  the  Stomaih.     (Hurst.) 
-f'=Fundus;  P.6'.  =  pyloric  canal;  ?7=  umbilicus. 


tissue.  Here,  again,  there  is  only  one  form  of  cell  lining  the  gland, 
corresponding  to  the  central  cells,  but  distinctly  less  granular  in  nature. 
Corresponding  to  these  different  sets  of  glands  we  have,  also,  three 
distinct  kinds  of  secretion  or  juices.  The  secretion  of  the  cardia  is 
neutral  or  faintly  alkaline  in  reaction,  poor  in  salts,  rich  in  mucin, 
and  containing  in  some  animals  (the  pig)  an  amylolytic  and  probably 
a  maltose-splitting  enzyme  (maltase).  The  juice  of  the  fundus  is 
characteristic  in  being  acid  in  reaction.  It  contains  peptic,  rennet, 
and  lipolytic  enzymes.  The  secretion  of  the  pylorus  is  alkaline  in 
reaction,  and  contains  a  small  quantity  of  proteolytic  enzyme,  no 
lipase,  and  much  mucin. 

Gastric  Juice. — The  term  "  gastric  juice  "  is  now  usually  applied 
to   the  funda!   secretion,  which,   in  fact,  must    be  regarded  as   the 


DIGESTION  IN  THE  STOMACH 


381 


characteristic  secretion  of  the  stomach.  It  is  a  matter  of  some 
difficulty  to  obtain  it  pure;  indeed,  there  is  onl}^  one  method — 
namely,  that  of  making  a  gastric  fistula. 

The  older  methods  include — (1)  the  giving  of  ^aerf orated  hollow 
balls  of  lead  which  contain  food  to  birds  of  prey  (the  balls  are  sub- 
sequently vomited  up);  (2)  the  swallowing  of  a  sponge  to  which  a 
string  is  fastened,  whereby  it  is  subsequently  withdrawn  and  squeezed ; 
(3)  killing  of  an  animal  after  giving  some  indigestible  material  to  eat, 
and  collecting  the  juice;  (4)  the  withdrawal  of  the  stomach-contents 
by  the  passage  of  an  oesophageal  tube  three-quarters  of  an  hour  after 
a  test-meal  has  been  eaten.  These  methods  give  only  gastric  contents, 
the  mixed  secretions  plus  the  ingested  food  and  fluid,  and  we  gain 
thereby  no  idea  of  what  constitutes  the  true  gastric  juice. 

The  first  gastric  fistula  studied  Avas  one  accidentally  made  hy  a 
gunshot  wound  upon  a  Canadian,  Alexis  St.  Martin.     Beaumont  took 


c  A 

Fig,  196. — Pawlow"s  Method  of  e.stablishing  a  Gastric  Fistula. 

A,  B,  Incision;  S,  segment  of  stomach  separated  off;  Ji,  abdominal  wall;  e,  mucous 
membrane;  P,  pylorus;  0,  oesophagus;  Rv,  right  vagus  nerve;  L>:,  left  vagus  nerve. 


the  man  into  his  service,  and  published  a  small  book,  the  result  of 
patient  years  of  observation.  A  fistula  has  been  established  in  dogs, 
and  observations  made  by  several  workers.  A  technique  which  leaves 
intact  the  blood  and  nerve  supply  has  been  recenth'  perfected 
(see  Fig.  196). 

In  order  that  no  food  or  saliva  shall  reach  the  stomach,  an  oesoph- 
ageal fistula  is  made  by  bringing  the  oesophagus  out  to  the  side  of 
the  neck,  dividing  it,  and  stitching  both  the  upper  and  the  lower  end 
into  the  wound,  so  as  to  leave  the  orifice  of  each  patent.  Any  food 
or  saliva  passing  down  the  oesophagus  falls  out  from  the  upper  end, 
and  does  not  reach  the  stomach  (sham  feeding).  Through  the  lower 
opening  substances  can  be  introduced  directly  into  the  stomach. 
Tiie  gastric  juice  obtained  in  this  manner  is  a  clean  watery  licjuid; 
its  percentage  composition  varies  in  different  animals. 


382  A  TEXTiiUOK  OF  i'HV8i(JLUGY 


Man.  ]*<"J-  Sheep. 


Water 99-44  U7-:}0  98-6 

Organic  matter,  chw^y  \iei)iii\\        ..          ..          ..  0*S2  l-Tl  0-4 

Inorganic  matter — 

(rt)  Free  hydrochloric  acid          0-2-0-3  0-3((  0-1 

(h)  Chlorides  and  phosphates  of  alkalies  and 

alkaline  earths         (>l-(»-J  (Hiij  i         0-9 


The  specitic  gravity  is  ()-()0l  to  0-OKJ. 

The  special  characteristic  of  this  juice  is  its  acidity.  This  has  four 
main  functions: 

1.  To  kill  ingested  bacteria  in  the  stomach,  and  thus  (a)  inhibit  the 
entry  of  pathogenic  organisms  into  the  body,  and  (h)  prevent  the  early 
2:>utref action  of  the  ingested  food. 

2.  To  facilitate  protein  digestion. 

3.  To  liberate  the  hormone  secretin  from  its  precursor  in  the  duo- 
denal mucous  membrane,  and  thus  excite  the  flow  of  juices  from  the 
pancreas  and  liver. 

4.  To  induce  a  flow  of  intestinal  juice  in  the  duodenum. 

In  regard  to  the  first  function,  it  has  been  shown  that  the  acidity 
of  the  juice  in  guinea-pigs  is  sufficient  to  kill  the  cholera  vibrio  or 
bacillus.  If,  however,  the  gastric  juice  were  first  neutralized,  the 
introduction  of  the  bacilli  killed  the  animals. 

Apart  from  pathogenic  bacteria,  it  is  important  that  bacteria 
which  split  proteins  and  carbohj'drates  be  kept  in  check ;  otherwise 
a  large  jjart  of  the  ingested  food  would  be  wasted. 

Meat  mixed  with  gastric  juice,  or  a  dead  frog  in  a  snake's  stomach, 
will  keep  sweet  and  free  from  putrefaction  for  days. 

A  considerable  amount  of  controversy  has  taken  place  in  regard 
to  the  nature  of  this  acidity.  It  was  at  first  believed  to  be  due  to  lactic 
acid.  That  it  is  due  to  hydrochloric  acid  is  shown  conclusively  by 
the  fact  that  in  an  analysis  of  the  juice  there  are  more  chlorme  atoms 
found  than  can  combine  with  all  the  bases.  How  far  the  acid  is  com- 
bined or  free  in  the  secreted  juice  is  a  matter  of  doiibt.  Most  of  it  is 
probably  not  free  in  the  chemical  sense,  but  so  loosely  combined  that 
it  is  able  to  effect  its  physiological  function.  The  difference  is  shown 
thus:  (1)  A  solution  of  pure  hydrochloric  acid  of  the  same  degree 
of  acidity,  when  heated  quickly,  gives  off  acid  fumes;  gastric  juice 
does  not  until  a  sj'rupy  consistency  of  concentration  is  reached; 
(2)  hydrochloric  acid  of  the  same  acidity  will  transform  starch  into 
dextrins,  gastric  juice  will  not;  (3)  the  inverting  j^ower  of  gastric  juice 
upon  disaccharides  is  not  so  powerful  as  an  equivalent  strength  of 
hydrochloric  acid.  Nevertheless  the  acid  in  the  pure  juice  certainh" 
reacts  acid  to  such  indicators  as  congo-red,  dimethylaminoazobenzol, 
and  therefore  may  be  termed  "  jDhysiologically  "  active.  HCl  is 
freely  dissociated  into  H  and  CI  ions  in  such  dilutions  as  are  found  in 
the  stomach.     Weak  organic  acids,  such  as  lactic  and  butj^ic,  are 


DIGESTION  IX  THE  STOMACH  383 

l>ut  slightly  dissociated.  Hydrochloric  acid  readily  combines  with 
proteins,  and  this  is  known  as  "  combined  acid,"  for  it  dissociates 
very  sHghtly.  Under  these  circumstances,  it  will  not  give  the  reac- 
tions of  free  acid.  Considerable  importance  is  attached  clinically  to 
the  proportion  of  the  free  acid  to  the  combined.  A  small  amount  of 
acidity  may  also  be  due  to  the  presence  of  acid  salts. 

The  Mechanism  of  Secretion. — ^  After  a  period  of  secretion,  the 
granules  of  the  chief  cells  have  greatly  decreased  in  number,  and  the 
colls  have  become  shrmiken.  These  granules  have  given  rise  to  the 
peptic  ferment  of  the  juice,  for  less  ferment  can  be  obtained  from  cells 
poor  in  granules  than  from  those  rich  in  granules. 

The  granules  are  the  precursor  or  zj'mogen.  This  can  be  shown 
as  follows:  Sodium  carbonate  destroys  the  active  enzyme  pepsin. 
Nevertheless,  a  sodium  carbonate  extract  of  the  fundus,  when  rendered 
faintty  acid  with  hydrochloric  acid,  manifests  all  the  digestive  actions 
of  pepsin.  The  precursor  is  not  destroyed  b}^  sodium  carbonate,  and 
the  extract  of  zymogen,  when  rendered  acid  by  HCl,  is  converted  into 
the  enzyme.  If  the  fundus  is  first  treated  with  hydrochloric  acid, 
and  then  with  sodium  carbonate,  no  active  enzyme  is  obtained,  for 
the  zymogen  is  converted  by  the  acid  and  the  enzyme  destroj-ed  by 
the  sodium  carbonate. 

The  parietal  or  oxj'ntic  cells  secrete  the  h^'drochloric  acid,  smce 
the  acidity  only  appears  in  the  jiiice  of  that  portion  of  the  stomach 
where  they  occur.  This  is  not  the  only  example  of  free  mineral  acid 
being  excreted  b}'  glands.  In  a  giant  mollusc,  Dolium,  the  salivary 
glands  secrete  H2S0^  (about  2  per  cent,  solution).  This  juice  effer- 
vesces when  it  falls  on  a  marble  floor.  It  is  strange  that  living  cells 
should  secrete  so  potent  an  acid,  which  is  destructive  to  Ufe.  The 
h3'di'ochloric  acid  is  probably  secreted  in  a  combined  state,  which 
becomes  active  after  secretion. 

The  gastric  juice  is  liberated  by  a  double  mechanism — ^nervous  and 
chemical. 

The  Nervous  Mechanism. — The  gastric  glands  have  a  double  nerve- 
supply  from  the  autonomic  sj'stem:  (1)  the  vagus,  (2)  the  S3"mpathetic. 
It  is  not  easy  to  excite  directly  the  secretory  fibres  to  the  stomach 
and  produce  secretion,  as  can  be  done  in  the  case  of  the  salivary  gland. 
On  the  other  hand,  the  secretion  can  be  excited  reflexly,  the  afferent 
paths  being  the  same  as  those  which  excite  the  secretion  of  saliva. 
The  effect  of  psychic  and  other  stimuli  has  been  fully  studied  by 
means  of  sham  feeding  on  the  dog,  in  which  oesophageal  and  gastric 
Hstulse  have  been  established.  Secretion  results  from — (1)  the  psychic 
element,  (2)  contact  with  buccal  mucous  membrane  and  the  act  of 
mastication,  (3)  the  taste  of  food  (see  Fig.  192).  The  sight  of  food 
causes  a  secretion;  in  a  hungry  dog  this  contmues  for  as  long  as  one 
and  a  half  hours.  If  the  animal  is  then  given  a  sham  meal,  it  is 
found  that  the  amount  of  secretion  obtained  by  the  psychical  stimu- 
lation is  rather  greater  than  that  obtained  by  the  introduction  of 
the  food  into  the  mouth. 


384  A  TEXTBOOK  OF  rHV.SlOLUGY 

The  psychical  secretion,  or  "  appetite  juice,"  may  be  provoked  by 
seeing,  hearing,  by  smeUing  food,  and  in  human  beings  by  memory  alone. 
The  thought  of  food  makes  the  mouth  of  a  hungry  person  "  water," 
and  the  gastric  juice  flow.  "  Digestion  waits  on  appetite  "  is  a  sound 
proverb.  It  is  a  disputed  point  as  to  whether  food,  by  its  presence 
in  the  stomach,  nervously  excites  a  flow  of  juice.  It  is  now  generally 
held  that  such  is  not  the  case,  for  introduction  of  food  through  an 
oesophageal  fistula  into  a  dog's  stomach  while  it  is  sleeping  excites  no 
flow  of  juice.  The  same  is  true  in  the  case  of  man.  The  secretion, 
excited  either  by  the  psychical  reflex  or  by  the  reflex  from  the 
mouth,  is  abolished  by  cutting  the  vagi;  this  points  to  these  nerves 
as  containing  the  efferent  secretory  nerves  to  the  stomach.  Division 
of  both  vagi  may  give  rise  to  absence  of  gastric  movement  and 
disorder  of  digestion;  it  has  been  performed  below  the  diaphragm 
with  little  ill  effect.  The  existence  of  the  second  mechanism  of 
ijroviding  juice  complicates  matters.  It  is  difflcult  to  produce  a 
secretion  of  gastric  juice  by  stimulating  the  peripheral  end  of  the 
vagus  nerve,  owing  to  the  disturbing  action  of  the  nerve  upon  the 
heart.  About  four  days  after  section  of  the  nerve,  when  the 
cardio-inhibitory  fibres  have  degenerated,  stimulation  of  the  peri- 
pheral end  of  the  divided  vagus  excites,  after  a  latent  period  of 
three  to  five  minutes,  a  marked  flow  of  gastric  juice.  It  is  difficult, 
however,  to  explain  the  long  latent  period. 

The  Chemical  Mechanism. — Secretion  is  called  forth  by  the  libera- 
tion of  a  hormone  —  '■gastrin"  —  and  its  absorption  into  the 
blood-stream.  The  ''  gastrin  "  is  stored  in  the  pyloric  mucous  mem- 
brane, and  is  liberated  by  such  bodies  as  dextrins,  maltose,  dextrose, 
peptones ;  in  fact,  the  products  of  digestion  of  a  part  of  the  alimentary 
tract  at  higher  level  than  the  pylorus.  The  products,  when  injected 
into  the  blood  by  themselves,  excite  little  or  no  secretion.  The 
gastrin  is  not  destroyed  by  boiling. 

Variation  of  Composition. — It  is  held  by  some  authorities  that 
the  juice  obtained  by  nervous  excitation  does  not  vary  in  quality, 
whereas  that  secreted  by  the  chemical  mechanism  (local  changes  in 
the  stomach)  shows  marked  variation  in  the  quantity  and  nature  of 
the  juice.  Thus,  the  secretion  is  said  to  be  greatest  in  amount  with 
meat,  the  digestive  power  greatest  with  bread. 

100  grammes  cut  meat  . .  . .  . .  . .        =     300  c.c. 

250        „  milk        =     200  c.c. 

Fats  are  said  to  increase  the  amount  of  pepsin,  starch  to  lessen  it. 
Others  doubt  this  adaptation  of  the  juice  to  the  food  eaten.  The 
amount  of  juice  may  also  vary  with  the  amount  and  character  of  the 
salts  in  the  food,  its  alkalinity  or  acidity.  Thirst,  muscular  exercise, 
and  a  condition  of  plethora,  markedly  infiuence  the  quantity  of  juice 
secreted.  The  introduction  of  food  into  the  ileum  and  into  the  rectum 
excites  a  flow  of  juice;  at  present,  it  is  difficult  to  say  whether  by  the 
nervous  or  chemical  mechanism.  The  effect  of  food  on  the  juice  is 
given  in  the  following  order: 


DIGESTION  IX  THE  STOMACH  3S5 


Degree  of 
Acidity. 

Degree  of 
Digestive  Activity. 

Duration  of  Secretion 
of  J  u  ice. 

Meat 
Milk 
Bread 

Bread 

Meat 

Milk 

Bread, 

Meat 

3Iilk 

The  Digestive  Processes  in  the  Stomach — Peptic  Digestion. — The 
peptic  enzyme  is  proteolytic  in  nature,  and  acts  only  in  acid  medium 
(HCl  0-1  to  0-5  per  cent.);  in  fact,  it  is  probable  that  the  true  digestive 
l^rinciple  is  a  combination — pepsin-hydrochloric  acid.  The  proteui  is 
first  swollen  and  partially  disintegrated  by  the  hydrochloric  acid,  and 
then  acted  upon  b}'  the  pepsin-hydrochloric  acid.  This  can  be  shown 
by  the  following  experiments:  (1)  Coagulated  egg-albumin  soaked  in 
0-3  HCl,  and  then  washed  and  added  to  neutral  pepsin,  is  not  digested; 
(2)  if  the  swelling  of  protein  be  stopped  by  the  jiresence  of  bile,  diges- 
tion is  stoi^ped  or  greatly  hindered. 

The  peptic  ezyme  digests  all  proteins  except  keratin.  Elastin  is 
but  little  attacked.  The  other  proteins,  including  gelatin,  are  easil}' 
digested,  passing  through  the  prelimmary  stages  of  conversion  into 
proteoses,  primary-  and  secondary,  to  peptones  and  pejDtides  (abiuretic 
bodies  not  giving  the  biuret  test).  The  change  is  by  no  means  so 
com^Dlete  as  in  the  case  of  the  pancreatic  enzyme,  tr3'psm.  It  may  be 
represented  as  follows : 

Protein > Acid  metaprotein 


Primary  proteoses  (proto  and  hetero) 
Secondary  proteoses  (A,  B^  C) 
Peptones  (A,  B) 
Peptides  (giving  no  biuret  test). 

The  methods  by  which  the  presence  of  these  bodies  can  be  shown  in 
the  digest  can  be  gathere  I  from  the  table  on  p.  386,  which  embodies 
the  chief  facts  ascertained  by  recent  research.  It  will  be  seen  that 
the  chief  differences  between  them  are  brought  out  by  their  I'elative 
solubility  on  addition  of  a  saturated  solution  o.  ammonium  sulphate, 
salicylsulphonic  acid,  or  alcohol. 

It  has  been  found  that  only  a  smill  percentage  of  protein  is 
converted  into  acid  metaprotein  (fornierh'  called  "  syntoain "). 
Some  of  the  primary  proteoses  are  split  off  earlisr  than  the  others; 
the  same  remark  applies  to  the  secondary  proteoses  and  peptones. 
Therefore,  quite  early  in  the  digestive  pro?ess.  peptones  and  peptides 
make  their  appearance.  Tnis  is  to  be  explaine:!  bv  the  fact  that  these 
bodies  are  not  of  the  same  chemical  composition.  For  example,  hetero- 
proteose  3delds,  on  decomposition,  chiefly  leucin  and  gl3'cin,  -whilst 
proto  proteose  3'ields  much  tv'rosin  and  indol.  Similarly,  with  the 
second a^^y  proteose  <,  one  was  found  to  contain  much  sulphur,  another 


886 


A  TEXTBOOK  OF  PHYSIOJ.OCJY 


but  little;  one  mueh  carbohydrate,  another  but  httle.  Their  chemical 
nature  in  part  determines  the  rate  at  which  these  bodies  are  spUt  off 
from  the  protein  ingested.  Therefore,  early  in  digestion  there  is 
a  beginning  of  the  sorting  out  of  the  special  constituents  of  the 
different  proteins — a  sorting  out  to  enable  the  body  to  choose  the 
portions  of  the  ingested  protein  requisite  for  the  building  of  its  own 
special  proteins.  In  digests  made  in  the  test-tube,  the  maximmn  of 
hetero-  and  proto -proteose  occurs  in  half  an  hour,  and  then  rapidly 
diminishes.  One  form  of  secondary  proteose  (B)  showed  similar 
variations,  A  gave  its  maximum  in  five  to  eight  hours,  C  after  two 
or  three  days,  peptone  in  one  to  two  months.  Of  the  contents  of  a 
dog's  stomach,  after  half  to  six  hours'  digestion  of  cooked  meat, 
90  per  cent,  consisted  of  proteoses,  acid  metaprotein  accounting  for 
the  other  10  per  cent.  The  peptones  and  peptides  are  absorbed  as 
soon  as  they  are  formed  in  the  stomach.  Normally,  this  absorption 
is  from  20  to  30  per  cent,  of  the  protein  eaten.  The  toxin  of 
protein-like  bodies — for  example,  of  tetanus  and  of  snake  venom — 
is  rendered  innocuous  bj'  gastric  digestion. 


Salici/lsul- 

phonic  Acid 

and 

Protun. 

Precipitation 

with 

Solubility 
in  Alcohol. 

Biuret  Test. 

Millon's 
Reaction. 

H\0.^  Tests. 
Precpitate 

Violet 

Native 

Globulins(haU' 

Insoluble 

+ 

saturation ) 

coagulated 

Albumins  (full 

on  boiling 

s;.tin-dcion) 

Acid  niL-ta- 

Half 

— 

Do. 

Do. 

Do. 

protein 

saturation 

Primary 

Half 

Hetero  in- 

Precipitate 

Rose  pink 

Hetero,feebIe ; 

proteose 

saturation 

soluble  in 

soluble  on 

proto,  strong 

(hetero  and 

32% ;  proto- 

boiling, 

proto) 

soluble  in 
80% 

reappearing 
on  cooling 

tSecondary 

Two-thirds 

Partly  in- 

Do. 

Do. 

+ 

proteo.se  A 

saturation 

soluble  in 

70% 

Secondary 

Full  satura- 

Partly insol- 

Do. 

Do. 

One  variety 

proteose  B 

tion 

uble  in  35% ; 

—   ; 

(several 

partly  solu- 

Others' + 

varieties) 

ble  in  80O(, 

Secondary 

Full  satura- 

Soluble in 

Do. 

Do. 



])roteose  C 

tion  plus  acid 
(HSOj 

68-80% 

I^eptoncs 

Not  pre- 

A insoluble 

Not  pre- 

Do. 

— 

cipitated 

in  QQ% : 

cipitated 

B  soluble  in 

Not  pre- 

Do. 

-1- 

96% 

cipitated 

Peptic  digestion  in  the  same  period  does  not  break  down  the 
protein  so  far  as  tryptic  digestion.  The  fact  that  with  prolonged 
gastric  digestion  in  vitro  all  the  end  products  of  tryptic  digestion  are 
formed,  except  the  hexone  bases,  would  seem  to  afford  support  to  the 


DIGESTION  IN  THE  STOMACH  387 

view  that  these  bodies  form  the  central  nucleus  round  which  the  rest 
of  the  protein  molecule  is  built. 

The  Action  of  Rennet. — The  rennet  enzj-me  runs  parallel  in  secre- 
tion to  })epsin.  There  is  a  prorennin  in  the  mucous  membrane,  like 
pepsinogen,  which  is  not  destroyed  by  a  weak  sodium  hydrate  solu- 
tion, and  is  converted  by  hydrochloric  acid ;  but  remiin,  unlike  pepsin, 
can  act  also  in  neutral  and  faintly  alkaline  media.  The  action  of 
rennin  is  upon  the  caseinogen  of  millv.  The  molecule  of  this  soluble 
protein  is  rearranged  by  the  action  of  the  rennin,  so  that  a  body 
called  ■■  soluble  casein  "  is  formed.  Here  the  action  of  the  rennin 
ceases.  This  soluble  casein,  in  the  presence  of  calcium  salts,  forms 
insoluble  casein,  or  the  clot  of  milk. 

(1)  Caseinogen  +  Rennin  =Soluble  casein. 

(2)  Soluble  casein  +  Ca  salts  ==Insoluble  casein,  or  clot. 

Thus,  if  in  a  test-tube  experiment  rennin  be  added  to  some  milk, 
from  which  the  calcium  salts  have  been  removed  by  the  addition  of 
a  soluble  oxalate,  its  action  proceeds  to  stage  (1),  and  no  clot  forms. 
If  after,  say,  fifteen  minutes  the  milk  be  heated  to  100°  C,  the  rennet 
enzyme  is  destroyed.  The  addition  of  calcium  salts  now  causes  the 
clot  to  form,  thus  showing  that  the  rennet  enzyme  is  merely  concerned 
in  the  rearrangement  of  the  molecule,  and  not  in  the  formation  of  the 
insoluble  clot. 

Why  a  rennet  enzyme  should  be  provided  to  clot  milk  is  somewhat 
a  mj'stery,  since  unclottcd  milk  is  digested  by  pepsin  and  trypsin. 
It  is  noteworthy  that  in  plants,  as  well  as  animals,  a  rennet  enzyme 
is  found  running  parallel  in  secretion  with  proteolytic  enzymes.  The 
clotting  may  be  merel}^  a  result  of  the  action  of  the  proteolytic 
enzyme  on  the  protein  caseinogen. 

The  Lipase  of  the  Gastric  Juice. — The  presence  of  a  gastric  lipase 
has  been  established :  at  one  time  it  was  held  to  be  due  to  a  reflux 
of  pancreatic  juice  through  the  pylorus.  It  exerts  its  maximum 
action  in  neutral  or  faintly  acid  medium.  Therefore,  normally  its 
action  in  the  stomach  is  not  at  all  potent.  Nevertheless,  it  is  probably 
important,  inasmuch  as  by  its  action  neutral  fats  will  be  rendered 
slightly  rancid,  and  these  fats,  on  entering  the  small  intestine,  owing 
to  this  rancidity,  will  be  far  more  easily  and  more  finely  emulsified 
than  would  otherwise  be  the  case,  and  their  digestion  thereby  greatly 
facilitated  (see  later,  p.  395). 

The  Action  of  Gastric  Juice  upon  Starches  and  Sugars. — In  some 
animals — e.g..  the  pig — the  starches  will  be  digested  by  the  amy- 
lopsin  of  the  cardiac  juice.  By  the  stomach  of  man  and  the  dog  there 
is  probably  no  amylopsin  secreted.  Nevertheless,  the  fact  must  not 
be  overlooked  that  in  the  cardiac  reservoir  salivar}-  digestion  normalty 
proceeds  for  thirty  to  forty  minutes. 

The  hydrochloric  acid  of  the  gastric  juice  exerts  but  little  or  no 
hydrolyzing   effect    upon   starches,    dextrins,    and    the  disaccharides. 


388  A  TEXTIiOOK  OK   F^HVSIOLOCY 

In  man,  but  not  in  the  dog,  there  is  probably  an  invertase  present 
Avhich  converts  canc-sngar  into  dextrose  and  levulose. 

Why  does  the  Stomach  not  Digest  itself  ? — It  may  be  asked:  "  Why 
does  the  stomach  not  digest  itself  i"  There  are  ])robably  several  con- 
<litions  contributing  to  this;  among  the  chief  reasons  assigned  are 
the  following: 

1 .  Tlie  large  amount  of  mucin  secreted  is  protective  against  the 
secreted  juice. 

2.  The  circulation  of  a  large  amount  of  alkaline  blood  keejjs  the 
cells  of  the  Avail  alkaline  in  reaction. 

The  cells  of  the  Avail  are  living,  and  living  substance  can,  b}'  its 
reactions,  resist  attack,  neutralize  acid,  secrete  antiferment,  etc. 
Any  part  of  the  stomach  Avail  from  Avhich  the  blood-supply  is  cut 
off- — e.g.,  by  thrombosis — is  attacked.  Gastric  ulcers  result  from 
lessened  poAvers  of  resistance.  The  injection  of  gastric  mucous  mem- 
brane of  guinea-pig  into  rabbit  may  cause  a  specific  cytolysin  to  form 
in  the  rabbit's  serum.  Injection  of  this  serum  into  the  guinea-pig 
may  cause  gastric  ulcer.  It  has  been  shoA\'n  that  if  the  hind -leg  of 
a  liA'ing  frog  is  introduced  into  the  stomach  it  is  digested  by  the  gastric 
juice.  Probabty,  acid  first  kills  the  tissue  and  then  digestion  takes 
place.  On  the  other  hand,  the  alkali  of  the  j^ancreatic  juice  is  not 
sufficiently  strong  to  alter  the  structure,  and  so  no  digestion  takes  place. 

Absorption  in  the  Stomach. — The  absorption  of  Avater  from  the 
stomach  is  very  small  in  amount.  This  has  been  shoAvn  to  be  the 
case  by  injecting  a  measured  quantity  through  the  pyloric  orifice, 
keeping  this  orifice  closed,  and  draAving  the  Avater  off  again  after  a 
given  time.  There  is  a  small  but  definite  absorption  of  salts  and  sugar, 
while  the  absorption  of  protein  in  the  form  of  peptides  (abiuretic  bodies) 
amounts  to  20  to  30  per  cent.  The  absorption  of  alcohol  is  rajiid,  and 
bodies  soluble  in  it  are  therefore  Avell  absorbed,  such  as  strychnine 
and  other  drugs. 

The  Examination  oi  Gastric  Contents. — Much  importance  is  attached 
by  some  clinicians  to  the  examination  of  the  gastric  contents  after  a 
test-meal,  Avhich  is  giA'en  in  the  morning  after  fasting  twelve  hours. 
The  meal  usually  consists  of  50  grammes  bread  and  a  little  tea  without 
milk;  it  is  important  that  it  should  be  Avithdrawn  by  the  stomach-tube 
at  a  definite  time  (three-quarters  of  an  hour)  after  the  meal.  It 
should  be  noted  that  the  contents  consist  of — 

1.  The  remnants  of  the  test-meal. 

2.  The  mixed  secretions  of  the  stomach. 

3.  The  SAvalloAved  saliva. 

It  must  be  remembered  that  the  amount  of  secretion  may  vary,  as 
may  also  the  rate  of  emptying  of  the  stomach  and  the  rate  of  absorption. 
For  this  reason  it  is  difficult  from  a  test-meal  alone  to  say  definitely 
Avhat  is — (1)  the  secretory  jjoAver,  (2)  the  motor  poAver,  (3)  the  absorptiA^e 
power  of  the  stomach.  The  chief  points  to  ascertain  about  gastric 
contents  are  the  total  amomit  of  the  acidity  of  its  contents ;  its  nature. 


DIGESTION  IN  THE  STOMACH  380 

whether  hydrochloric  or  some  abnormal  organic  acid,  such  as  lactic,  is 
present;  the  total  acidity-;  whether  the  acid  is  free  or  combined;  and 
how  much  in  each  state.  Man}'  methods  have  been  devised  for  this 
purpose.  Opinion  varies  as  to  whether  it  is  important  for  the  hydro- 
chloric acid  to  be  free.  Apparent!}^  it  matters  little,  from  the  digestive 
point  of  view,  whether  it  is  free  or  combined;  but  in  the  combined 
state  the  protective  power  of  the  free  acid  against  bacteria  is  lacking. 
The  amount  of  free  to  combined  acid  will  depend  upon — 

1.  The  amount  of  secretion. 

2.  The  amount  of  protein  in  the  stomach. 

3.  The  rate  of  emptying. 

4.  The  rate  of  absorption. 

5.  The  amount  of  mixing  of  the  contents. 

For  testing  the  total  acidit}',  the  best  indicators  are  probably 
phenolphthalein  (which  gives  a  slightly  high  reading)  and  rosolic  acid. 
The  amount  of  free  acid  is  obtained  by  the  use  of  such  indicators  as 
congo-red  (turned  blue  by  free  acid),  Giinzburg's  reagent,  dimethyl- 
aminoazobenzol  (Tcipfer's  reagent),  tropseolin  00.  The  amount  of 
the  combined  acid  is  obtained  by  deducting  the  free  from  the  total 
acidity.  An  excellent  method  is  that  known  as  the  method  of  deficit 
and  excess. 

Method  of  Excess. — Ten  c.c.  of  the  contents  are  taken.  If  free  acid 
is  present,  this  is  estimated  b}'  running  in  ^-^  NaOH  until  neutralized, 
and  testing  from  time  to  time  by  removing  a  small  drop  to  congo-red 
paper,  which  is  no  longer  turned  blue  when  the  neutralization  point  is 
reached.  A  few  drops  of  phenolphthalein  are  then  added,  and  the 
acidity  to  this  indicator  measured.  This  amount  gives  the  combined 
acidity,  that  with  congo-red  the  free  acidity,  and  the  two  together 
give  the  total  acidity. 

The  Method  of  Deficit. — If  by  testing  with  congo-red  it  is  found  that 
free  acid  is  absent,  10  c.c.  of  the  contents  are  taken,  and  -^  HCl  added 
until  free  acid  makes  its  appearance  to  congo-red.  The  amount 
added  is  noted,  and  this  gives  the  deficit.  The  sample  is  then 
exactly  neutralized  by  a  corresponding  amount  of  y*^  NaOH,  phenol- 
phthalein added,  and  the  acidity  to  this  indicator  measured,  this  giving 
the  amount  of  the  combined  and  also  the  total  acidity. 

Physiologically  active  HCl  may  also  be  determined  (A)  by  mixing 
the  filtered  gastric  contents  with  excess  of  sodium  bicarbonate,  drying, 
incinerating,  and  determining  the  total  chlorides  in  the  ash  by 
Volhard's  method  (see  Urine,  p.  462).  The  process  is  now  repeated 
without  the  addition  of  sodium  bicarbonate  (B).  In  this  case  only 
the  mineral  chlorides  are  retained  in  the  ash.  A-B  gives  the  physio- 
logically active  HCl. 

The  amount  of  enzyme  may  be  estimated  roughly  by  determining 
the  action  of  the  rennin  present.  The  rennin  is  assumed  to  run  parallel 
with  the  pepsin.  In  several  tubes  5  c.c.  of  milk  and  2-5  c.c.  of  1  per 
cent,  calcium  chloride  are  taken.    To  these  are  added  5  c.c.  of  the  gastric 


390  A  TEXTBOOK  OF  PHYSIOLOGY 

contents  diluted  respectively  10,  20,  40,  80,  160,  and  320.  With  7iornial 
juice,  a  solid  clot  is  obtained  with  (hlutions  of  10,  20,40;  a  dihition  of 
80  gives  a  cheesy  clot,  and  of  160  a  Haky  clot.  This  method  is  of  value 
for  clinical  purposes. 

The  amount  of  pepsin  present  is  most  quickly  and  conveniently 
estimated  by  the  use  of  carmine-stained  fibrin.  It  is  only  an 
approximate  method.  It  depends  upon  the  fact  that,  as  the  fibrin 
becomes  digested,  the  liberated  carmine  stains  the  solution.  There- 
fore, the  deeper  the  tint,  the  greater  the  amount  of  the  enzyme.  The 
exact  amount  of  carmine  set  free  is  gauged  by  comparison  with  an 
artificial  scale  of  solution  of  carmine  of  known  strength,  and  thus  the 
activity  of  the  enzyme  is  estimated. 

Another  method  consists  in  the  digestion  of  coagulated  egg- 
albumin  in  narrow  tubes  of  known  dimensions ;  it  is  only  accurate  for 
very  weak  pepsin  solutions,  since  after  a  certain  amount  of  digestion 
stagnation  ensues.  Recently,  several  accurate  methods  have  been 
introduced.  One  depends  upon  the  fact  that  a  suspension  of  coagu- 
lated egg-white  becomes  quite  clear  under  the  influence  of  pepsin. 
Various  quantities  (0-2  to  1  c.c.)  of  the  enzyme  are  added  to  5  c.c.  of 
this  suspension  and  1  c.c.  of  0-4  per  cent.  HCl,  and  the  time  at  which 
clearing  occurs  noted.  The  egg-white  suspension  is  prepared  by 
rubbing  up  egg-white  in  a  basin  until  it  is  of  uniform  consistence. 
This  is  then  slowly  mixed  and  rubbed  with  water  until  it  is  diluted 
five  times.  After  straining  through  gauze,  the  solution  is  heated  at 
60°  C.  for  twenty  minutes,  and  again  strained.  For  use  this  is  again 
diluted  nine  times. 

The  description  of  the  anatoni}-  and  digestive  processes  already 
given  above  applies  to  man  and  the  carnivora.  In  many  other  animals, 
the  lower  end  of  the  oesophagus  is  dilated  to  form  a  crop,  or  proventri- 
culus,  which  functionates  as  a  reservoir.  In  the  horse  and  pig,  this 
passes  into  the  stomach  without  any  marked  constriction ;  food  there- 
fore passes  easily  from  one  part  to  the  other.  In  ruminants,  the  crop 
is  modified  into  a  large  rumen,  or  paunch,  and  a  small  honeycombed 
reticulum.  The  rumen  acts  as  a  reservoir  for  the  swallowed  food. 
The  function  of  the  reticulum  is  apparently  to  hold  fluid  and  moisten 
the  foodstuffs  in  the  rumen  preparatory  to  the  "  chewing  of  the  cud." 
From  the  rumen,  the  food  is  returned  again  to  the  mouth,  the  cud  is 
cheAved,  and  again  swallowed.  This  time  it  is  passed  through  the 
rumen  into  the  omasum  by  means  of  the  unfolding  of  a  double  fold 
in  the  roof  of  the  rumen.  The  omasum,  sometimes  termed  by  butchers 
"'  the  Bible,"  is  an  organ  containing  many  strong  muscular  leaves. 
These  leaves  are  covered  with  coarse  epithelium,  and  the  organ,  by 
its  movements,  churns  the  food  into  a  proper  consistency  for  entering 
the  rest  of  the  alimentary  tract.  It  yields  no  digestive  secretion. 
The  true  stomach,  with  its  digestive  fluid,  is  the  next  chamber,  and 
is  known  as  the  "  abomasum."  Here  digestion  proceeds,  as  already 
described. 


CHAPTER  XLVII 

DIGESTION  IN  THE  SMALL  INTESTINE 

After  being  churned  to  a  proper  fluid  consistency  in  the  pyloric 
mill,  and  having  attained  to  a  certain  degree  of  acidity,  the  gastric 
contents  little  by  little  are  passed  through  the  pyloric  aperture,  and 
enter  as  a  chyme  the  first  part  of  the  small  intestine.  This  is  the  short, 
horseshoe-shaped  duodenum.  It  is  the  aciditj"  of  the  chyme  in  the 
pylorus  which  excites  the  relaxation  of  the  pyloric  aperture.  On 
reaching  the  duodenum,  the  acidity  of  the  chyme  causes  the  door 
behmd  it  to  shut,  and  prevents  regurgitation  into  the  stomach.  The 
■chyme  contains — 

1.  Such  sugars,  stai'ches,  and  proteins  as  have  not  been  acted 
upon  by  the  salivary  or  peptic  ferments. 

2.  Acid,  free  and  combined. 

3.  Proteoses  and  peptones. 

4.  Rancid  fat. 

On  its  entrance  into  the  duodenum,  a  number  of  important  events 
are  brought  to  pass : 

1.  A  flow  of  bile  is  provoked  from  the  gall-bladder. 

2.  The  acid  contained  in  the  chyme  liberates  from  the  duodenal 
mucous  membrane  the  hormone  ''  secretin,"  which,  circulating  in 
the  blood,  calls  forth  a  flow  of  digestive  juice  from  the  pancreas  and 
a  further  floAV  of  bile  from  the  liver. 

3.  The  presence  of  the  chyme  in  the  intestines,  probably  owing  to 
its  acidity  and  the  nature  of  its  contents,  causes  a  flow  of  succus  enteri- 
cus — the  digestive  fluid  of  the  small  intestine. 

On  these  three  fluids  —  the  bile,  pancreat'c  juice,  and  succus 
«ntericus — depends  the  proper  digestion  of  the  entering  foodstuffs. 

THE  BILE. — This  varies  in  appearance  and  composition  according 
to  its  source.  Bile  from  the  gall-bladder  is  a  ropy,  viscid  substance, 
bitter  to  taste,  faintly  alkaline  in  reaction,  with  a  specific  gravity  from 
1015  to  1040.  Its  colour  in  man  varie.s  from  yellow  to  green.  Bile 
obtained  from  the  liver  before  entering  the  gall-bladder  is  a  clear, 
limpid  fluid  of  low  specific  gravity  (1010).  pale  yellow  in  colour.  In 
the  gall-bladder,  water  is  absorbed  varying  in  amount  according  to 
the  time  of  stay,  and  a  mucous  recretion  is  added.  The  protein  in  this 
secretion  in  most  animals  mainly  consists  of  phospho-protein.  In 
man,  however,  it  is  stated  to  be  true  glyco-protein.  The  difference 
between   the   two  kinds  of  bile  is  shown  in  the  following  analysis: 

391 


392 


A  TEXTBOOK  OF  PHYSlOLOCiY 


/. 

11* 

81) 

'.IT 

14 

!) 

0-9  to  1-8 

3 

0-5 

0-2 

(t-{)6  to  0- 1  f) 

()•.-)  t 

.  l-O 

0-02  to  n-oy 

OvS 

(1-7  to  0-8 

I.,  obtaijied   from  gall-bladder  of  persons  accidentally  killed  while  in 
good  health;  II.,  obtained  from  a  fistula  during  life: 

IX    100    PART.S    OF     RlLK. 

Water 

Solids 

Organic  salts 

Mucin  and  pigment 

Cholesterol    . . 

Lecithin  and  fat 

Inorganic  salts 

The  Organic  Salts. — The  organic  salts  are  the  sodium  salts  of  the 
bile  acids.  These  acids  are  known  as  glycochoHc  (C.^^H^gNOg)  and 
tauroeholic  (C^j-H^^NvSO-).  The  former  is  more  abundant  in  herbivo ra- 
the latter  in  carnivora.  The  bile  acids  are  formed  in  the  liver,  and 
are  compounds  cf  cholic  or  cholalic  acid  with  the  amino-acids 
glycin  and  taurin  respectivel3\  Cholalic  acid  is  probably'  related 
to  cholesterol;  it  contains  two  primary  and  one  secondary  alcoholic 
groupings.  It  is  probable,  also,  that  there  are  several  varieties  of  it, 
and  therefore  several  varieties  of  glycocholic  and  tauroeholic  acids. 
Glycin  is  mon-amino- acetic  acid,  CH2NH2COOH  (see  p.  40).  Tamin  is 
amino-ethyl-sulphonic  acid,  CHo— NHo— OH.,  SO.,  OH,  and  is  derived 
from  cystm,  COOH-CHXH^  CH^'S-SCH,  CHNH.3COOH. 

This  is  converted  h\  reduction  into  cystein,  and  this  by  oxidation 
to  cysteinic  acid,  COOH  CHNH^-CHoSOaOH,  which,  by  the  loss  of 
a  molecule  of  COo,  yields  taurin. 

The  salts  of  the  bile  acids  are  dextro-rotatory,  and  crystallize  in 
fine  needles  or  prisms.  It  is  due  to  their  presence  that  lecithin  and 
cholesterol  are  soluble  in  the  bile.  In  the  intestine,  they  are  decom- 
posed by  bacterial  action  into  their  constituent  parts,  and  mostly- 
reabsorbed,  only  a  small  amount  of  cholalic  acid  being  found  in  the 
faeces.     The  exact  fate  of  the  taurin  is  not  known. 


Sodium  glycocholate 


Glycocholic  acid 


Glvcin 


Reabsorbed 


(holding  cholesterin  in 
solution) 


Cholalic  acid 


Small  amount  with 
cholesterin  in  faeces 


Sodium  taurocholate 


Tauroeholic  ac;d 


Taurin 
Reabsorbed 


Th''  ))ile  salts  can  be  recognized  by  the  fact  that,  when  added  to 

*  The  average  quantity  secreted  in  twenty-four  hours  varies  from  500  to  1,000  c  c. ; 
on  an  averasre  about  750  c.c. 


DIGESTION  IN  THE  SMALL  INTESTINE  393 

cane-sugar  and  strong  sulphuric  acid,  the}'  give  a  purple  colour  (Petten- 
kofer's  test).  This  is  due  to  the  reaction  of  cholalic  acid  with  the 
furfurol  formed  by  the  interaction  of  the  cane-sugar  and  sulphuric 
acid.  An  even  more  delicate  test  depends  upon  the  fact  that  the  bile 
salts  so  lower  the  surface-tension  of  an}'  fluid  containing  them  that 
flowers  of  sulphur  will  no  longer  float  when  sprinkled  on  the  top,  but 
immediately  sinks  to  the  bottom.  The  test  is  a  useful  one  for  showing 
the  presence  of  bile  in  the  urine.     It  is  sometimes  kno\\ai  as  Hay's  test. 

The  bile  salts  endow  the  bile  with  its  powers  of  solution  of  fatty 
acids,  and  of  aiding  the  digestion  and  absorption  of  protein.  The 
property  of  bile  salts  of  precipitating  protein  from  acid  solution  may 
be  used  as  a  test  for  bile  salts.  If  a  solution  of  bile  salts  be  added  to 
a  1  per  cent,  solution  of  Witte's  peptone  acidified  with  acetic  acid, 
a  A\-hite  precipitate  or  milkiness,  due  to  the  precipitated  protein,  is 
produced. 

In  the  shark  and  allied  fishes  there  exists  a  third  group  of  bile 
acids,  rich  m  sulphur,  and  akin  to  ethereal  sulphuric  acid.  These 
bile  acids  yield  sulphuric  acid  on  boiling  with  hydrochloric  acid. 

The  Bile  Pigments. — There  are  several  bile  pigments.  The  chief 
pigments  of  normal  bile  are  bihrubin  and  bihverdin.  By  oxidation, 
derivatives  of  these  pigments  are  formed,  some  of  which  have  been 
isolated  from  gall-stone-s — bilifuscin,  biliprasin,  bilicj^anin,  choleprasin, 
and  choletehn.  Bilirubin  occurs  most  abundantly  in  carnivora, 
bihverdin  in  herbivora.  The  pigments,  however,  are  readily  inter- 
changeable, bihrubin  being  found  in  gall-stones  of  cattle,  and  bih- 
verdin in  the  placenta  of  the  bitch.  Their  presence  can  be  detected 
by  the  addition  of  fummg  nitric  acid  (that  is,  nitric  acid  containing 
nitrous  acid);  there  occurs  a  play  of  colours  due  to  oxidation  deri- 
vatives— green,  blue,  pvirple,  yeUow. 

Bilirubin  may  be  isolated  as  a  reddish  powder  or  as  rhombic 
plates.  It  combines  readily  with  calcium  to  form  an  insoluble  salt, 
and  upon  standing  in  contact  with  air  becomes  oxidized  to  biliverdui. 
It  is  soluble  in  chloroform,  and  in  solution  exhibits  no  absorption  bands 
in  the  spectrum. 

Bihverdin  is  an  amorphous  substance,  insoluble  in  chloroform,  and 
therefore  easily  separated  from  bilirubin.  Bilirubin  appears  to  be 
derived  from  the  disintegration  of  haemoglobin  in  the  liver,  the  iron 
IJortion  of  the  blood-pigment  being  split  off  and  retained  in  the  liver. 
Its  empirical  formula  is  C3.,H3(.N^Og,  that  of  hsematin  is  C.,H.j.,NjO^Fe. 
Bihrubin  has  the  same  empirical  formula  as  haematoidin,  which  occurs 
in  old  blood-clots,  and  hsematoporphyrm,  which  is  sometimes  foimd 
in  urine.  Neither  of  the  latter,  however,  give  Gmelin's  test.  Wlien 
reduced  by  sodium  amalgam,  in  alcoholic  solution,  both  it  and  bili- 
rubin are  converted  into  hydrobilhubin.  Hydrobihi-ubhi  can  also  be 
formed  from  hsematin  or  hsematoporph^-rin  by  the  action  of  more 
powerful  reducing  agents. 

By  still  further  oxidation,  haematinic  acid  (CgHgOj)  is  formed 
from  ])ile  pigments,  haematin,  and  hsematoporph^Tin.  These  facts 
indicate  the  close  relationship  between  htematiu  and  bile  pigments. 


384  A  TEXTBOOK  OF  PHYSIOLOGY 

It  is  from  the  pigment  of  effete  corpuscles  that  the  bile  pigments  are 
formed  in  the  liver.  In  the  intestine,  the  bile  pigments  are  converted 
by  bacteria  into  the  pigment  stercobilin  (similar  to  hydrobilirubin). 
Most  of  this  is  excreted  with  the  faeces,  but  some  is  absorbed  into  the 
|X)rtal  blood,  in  part  to  be  excreted  again  in  the  bile,  in  part  to  give 
rise  to  a  urinary  pigment — urobilin. 

Lecithin  and  cholesterol  have  already  been  dealt  with  (Chapter  VI.). 
These  substances  are  widely  distributed  in  the  tissues,  and  are  of 
great  value  to  the  organism.  They  are  probably  to  be  regarded  both 
as  secretorj^  and  excretory  products  in  the  bile.  It  has  been  found 
that  the  l)ile  of  animals  which  normally  ingest  much  fat — e.g.,  the  polar 
bear — contains  relatively  more  lecithin  (and  probably  other  phos- 
phorus-containing bodies)  than  does  the  bile  of  other  animals.  Lecithin 
and  cholesterol  play  a  part  in  the  digestion  of  fat,  helping  the  bile 
salts  in  the  solution  of  fatty  acids  and  absorption  of  fat. 

The  Inorganic  Salts  are  chiefly  sodium  chloride,  sodium  carbonate, 
and  disodium  hydrogen  phosphate.  There  are  also  salts  of  iron  (iron 
phosphate),  calcium,  and  magnesium.  Manganese  is  also  present  in 
minute  quantity. 

The  Mechanism  oJ  Secretion. — While  the  secretion  of  the  bile  from 
the  liver  is  continuous,  periods  of  greater  and  less  activity  occur. 
Its  entrance  into  the  intestine  is  intermittent.  The  first  increase  in 
flow  is  brought  about  directly  the  food  begins  to  enter  the  duodenum ; 
a  second  maximum  is  reached  about  six  hours  later.  The  bile  secreted 
in  the  periods  between  digestion  is  stored  in  the  gall-bladder.  Some 
animals,  however,  such  as  the  horse,  elephant,  donkey,  mouse,  have 
no  gall-bladder.  The  stimuli  to  the  continuous  secretion  of  bile  are 
at  least  three  in  number — viz.: 

\.  The  hormone  "'  secretin." 

2.  The  products  of  digestion. 

3.  The  reabsorbed  bile  salts. 

The  flow  in  response  to  secretin  is  by  no  means  so  marked  as  that  of 
the  pancreatic  juice.  It  is  stated  that  the  products  of  digestion  modify 
the  amount  of  bile  excreted  considerably,  proteins  exciting  the  biggest 
flow,  fats  somewhat  less,  and  carbohydrates  little,  if  any,  flow.  In- 
jected bile  salts  are  known  to  act  as  cholagogues.  The  constituents 
of  the  bile  salts  reabsorbed  from  the  intestine  probably  play  a  similar 
part,  and  stimulate  an  adequate  secretion  of  bile  to  fill  the  gall-bladder 
in  the  periods  between  active  digestion.  The  gall-bladder  and  the 
excretory  passages  receive  nerve  fibres  from  the  vagus  and  sympathetic 
nerves.  The  sympathetic  are  stated  to  be  inhibitory,  the  vagus  to 
be  motor,  in  nature.  It  is  probablj^'  in  virtue  of  these  latter  fibres 
that  bile  is  ejected  from  the  gall-bladder  in  response  to  jiassage  of  food 
through  the  pyloric  orifice. 

The  Functions  of  Bile. — That  the  secretion  of  bile  is  continuous, 
even  during  starvation,  points  to  the  fact  that  it  is  an  excretion ;  that 
bile  is  poured  into  the  beginning  of  the  digestive  tract,  and  not  into 


DIGESTION  IN  THE  SMALL  INTESTINE  395 

the  end,  points  to  the  fact  that  it  is  a  secretion  \\hich  plays  an  impor- 
tant part  in  the  digestive  processes.  Bile  is  not  an  actual  digesting 
agent,  for  by  itself  it  has  little  or  no  digestive  power.  It  is  true  in 
some  cases  it  contains  an  amylopsin,  but  the  action  of  this  enz3'me 
is  negligible.  Bile  jjlaj's  an  important  part  in  the  preparatory  digestive 
and  absorptive  processes  of  the  small  intestine.  As  its  early  presence 
in  the  duodenum  would  suggest,  bile  is  essentially  "  the  pre])arer  for 
digestion."    The  functions  of  the  bile  ma^^  be  summarized  as  follows: 

1.  The  rancid  fats  in  the  chj^me  are  far  more  efficiently  emidsified 
in  the  presence  of  bile  than  in  the  presence  of  the  alkaline  juices  alone. 

2.  The  undigested  proteins  and  proteoses  are  precipitated  by  the 
bile  from  their  acid  solution,  and  thus  delayed  in  the  digestive 
area  of  the  duodenum ;  if  they  remained  in  solution,  they  might  be 
passed  on  too  quickly;  in  this  state,  too,  they  are  more  easily  assailable 
by  the  digesting  euz^nnes.  since  food  in  a  particulate  form  is  more 
easily  attacked. 

3.  The  digestive  processes  are  helped — (1)  by  the  neutralization 
of  the  acid  in  the  chyme;  (2)  by  activation  of  the  lipoh^tic  (fat- 
splitting)  enzymes  of  the  pancreatic  juice;  (3)  by  all  the  digestive 
enzymes  working  with  greater  rapidity  in  the  presence  of  bile. 

4.  In  the  absorptive  processes,  bile  is  especially  helpful  in 
promoting  the  absorption  of  fat.  When  bile  is  withheld  from  the 
intestine,  much  of  the  fat  eaten  escapes  digestion  and  absorption,  and 
appears  in  the  faeces.  Bile  aids  this  absorption  by  dissolving  fatty 
acids  and  taking  into  solution  insoluble  soaps  of  calcium  and  magne- 
sium formed  in  the  course  of  digestion. 

5.  Bj^  its  propert}^  of  lowering  surface  tension,  bile  enables  the 
substances  to  be  absorbed  to  come  into  more  intimate  contact  with 
the  absorbing  surface. 

6.  Bile  has  been  credited  with  antiseptic  properties.  There  is 
nothing  in  support  of  this  viev/;  in  fact,  special  media  for  the  growth  of 
bacteria  are  sometimes  prepared  containing  it.  The  truth  of  the  matter 
is  this:  Owang  to  the  presence  of  bile,  all  digestive,  and  therefore 
absorptive,  processes  are  quickened,  so  that  the  bacteria  of  the  intestine 
have  little  chance  to  carry  putrefactive  and  fermentative  processes 
beyond  normal  limits.  It  is  the  digestion  and  absorption  of  fats 
"wh'.ch  is  of  particular  importance,  for,  when  fats  are  not  well  digested, 
protein  digestion  is  hindered  by  their  presence,  and  putrefactive  changes 
then  take  place. 

7.  The  chief  excretory  function  of  the  bile  would  seem  to  be  to 
rid  the  organism  of  the  dissolved  cholesterin,  some  of  the  cholalic 
acid,  and  the  bile  pigment. 

THE  PANCREAS  AND  ITS  SECRETION.— The  pancreas  is  a  long, 
narrow  gland  of  the  acino-lulndar  type.  In  man,  its  main  duct  (the 
duct  of  Wirsung)  opens  into  the  duodenum,  together  with  the  common 
bile  duct,  about  8  to  10  centimetres  be^'ond  the  pyloric  orifice.  The 
point  and  mode  of  entry,  however,  varies  in  other  animals.  In  the 
dog,  there  are  two  ducts — the  one  opening  with  the  bile  duct,  the 
other   3   to   5   centimetres  lower    down.     The    latter   is  usually  the 


:m>  A  TEXTBOOK  OF  PHYSIOLOGY 

bigger.  In  the  rabbit,  the  orifice  of  the  ])aiTcreatic  duet  is  consider- 
ably below  that  of  the  bile  (35  centimetres).  The  structure  of  the 
living  gland  can  be  particularly  well  studied  in  this  animal,  since  the 
gland  is  spread  in  the  mesentery  in  a  thin,  transparent  layer  which 
can  be  examined  under  the  microscope.  The  cells  are  seen  to 
resemble  closely  those  of  the  parotid  gland.  Before  secretion,  they 
have  been  observed  to  be  swollen  and  distended  with  granules;  after 
secretion,  the  cells  become  shrunken,  most  of  the  granules  have  dis- 
a])peared.  and  are  only  seen  near  the  lumen. 

In  this  gland,  also,  are  certain  little  aggregations  of  tissue  known 
as  the  "  islets  of  Langerhans.''  The  exact  significance  of  these  has 
been  much  debated.  Some  hold  that  they  a-re  the  secreting  alveoli 
in  an  exhausted  condition.  It  is  now,  however,  generally  conceded 
that  they  represent  the  inclusion  of  another  gland  within  the  pancreas — 
a  gland  which  is  formed  separate  in  certain  fishes.  The  function  of 
these  islets  is  discussed  in  the  chapter  on  internal  secretions  (p.  511). 

The  Pancreatic  Juice  can  be  obtained  by  the  insertion  of  a  cannula 
into  the  duct,  and  making  a  temporary  or  permanent  fistula.  It  is  a 
clear,  slightly  viscid,  strongly  alkaline  fluid.  The  composition  of 
the  juice  varies,  that  secreted  upon  the  establishment  of  a  fistula 
being  as  a  rule  considerably  richer  in  solids  than  that  secreted  some 
days  later. 


Directly  after 

Pancreatic 

Operation. 

Fistula. 

00-08 

97-68 

9-02 

2-3-2 

lt-04 

1-04 

0-88 

0-68 

Water     . . 

Total  solids 

Organic 

Inorganic 

In  cases  where  a  pancreatic  fistula  has  resulted  from  an  operation 
in  man,  the  amount  of  the  secretion  has  been  found  tc  vary  from 
600  to  800  c.c.  per  diem,  and  to  have  a  specific  gravity  of  1007. 

The  organic  constituents  are  due  to  the  enzymes  contained  in  it, 
together  with  some  heat-coagulable  protein.  There  are  also  traces  of 
leucin,  tyrosin.  xanthin,  and  soaps.  The  inorganic  salts  are  mostly 
the  chloride,  carbonate,  and  phos]:)hate  of  sodium.^  The  alkalinity  of 
the  juice  is  due  to  the  two  latter.  In  addition,  there  is  pre.sent  potas- 
sium chloride  and  the  phosphates  of  calcium  and  magnesium. 

This  juice  is  the  most  powerful  digestive  fiuid  of  the  ahmentary 
canal.  It  contains  several  enzymes,  the  best  known  being  the  protein- 
sphtting  (trypsin),  fat-splitting  (steapsin  or  lipase),  starch-.splitting 
(amylopsin).  and  the  rennet  enzyme.  It  is  probable  that  rennin 
and  trypsin  are  to  be  regarded  as  side-chains  of  the  same  bod}-. 
The  other  enzymes  can  apparently  be  separated  from  each  other,  and 
are  stated  to  vary  in.  amount  in  the  juice  according  to  the  nature  of 
the  food.  Thus,  when  the  secretion  on  a  milk  diet  is  compared  with 
that  on  a  bread  diet,  it  is  found  to  contain  half  the  tryptie,  one- 
c|uarter  the  amylolytic,  and  six  times  the  fat-splitting  potency. 
Further  evidence  of  the  independence  of  the  enzymes  is — 


DIGESTION  IN  THE  SMALL  INTESTINE  397 

1.  The  diastase  does  not  appear  in  the  juice  until  a  month  after 
birth,  trypsin  being  present  from  the  start. 

2.  Tryjasin  can  be  precipitated  and  separated  from  the  other 
enzymes  b^'^  addition  of  collodion. 

It  was  at  one  time  stated  that  the  enzymic  content  of  the  juice  was 
not  only  modified  to  meet  the  nature  of  the  food,  but,  if  necessar}^ 
new  enzymes  were  manufactured  to  digest  fresh  articles  of  food  in 
the  diet.  For  example,  on  a  mixed  diet,  the  pancreatic  juice  contains 
no  lactose-splitting  enzyme  (lactase).  It  was  said  that,  with  the 
introduction  of  a  milk  diet,  a  lactase  became  secreted  in  the  pancreatic 
juice.  The  experimental  evidence  is  now  against  this  view,  and  by 
some  workers  the  adaptation  to  the  diet  of  the  enzymic  content  of 
the  juice  is  seriously  called  in  question. 

The  juice  is  said  by  some  to  contain  several  other  enzymes,  in 
particular  a  nuclease  (nucleic-acid-splitting  enzyme).  Traces  of 
erepsin,  maltase,  and  lactase  have  been  found. 


Fig.  197. — To  show  Effect  of  Injection  of  Secretin.     (Bayliss  and  Starling.) 
A,  Blood-pressure;  B,  drops  of  panereatic  juice;  C,  drops  of  l)ile. 

The  Mechanism  of  Secretion. — Reference  has  been  made  to  the 
'■  hormone,"  or  chemical  mechanism  of  secretion.  "  Secretin  "  is 
stored  as  pro -secretin,  especially  in  the  duodenal  mucous  mem- 
brane, and  in  less  amount  in  the  jejunum.  In  the  ileum  there  is 
none. 

To  prepare  it  the  mucous  membrane  is  scraped  from  a  piece  of 
small  intestine,  thoroughly  minced,  and  ground  up  with  sand  in  a 
moT-tar.  Tiie  whole  is  then  treated  with  0-3  per  cent,  hydrochloric 
acid,  and  boiled.  This  coagulates  the  proteins  and  extracts  the 
secretin,  which  is  not  destroyed  by  boiling.  The  clear  fluid  is  filte.'ed 
off,  carefully  neutralized,  and  used  for  intravenous  injection  to  pro- 
voke pancreatic  secretion  (Figs.  197,  198).  Secretin  is  soluble  in 
alcohol  and  ether. 

Not  only  acid,  but  water  and  oil  call  forth,  by  their  i)resence  in 
the  intestine,  a  flow  of  pancreatic  juice.  So  do  such  bodies  as 
pepper,    mustard,    and    alcohol.     Soaps    have    a    particularly  potent 


398 


A  TEXTBOOK  OF  PHYSIOLOGY 


effect,  find  it  is  quite  possible  that  the  profhicts  of  (ligestion  may 
in  some  wa\  modify  the  enz\)nic  content,  soti])s  calling  forth 
steapsin,  dextrins  amylopsin,  peptones  trypsin,  and  so  on. 

It  is  a  question  whether  the  secretion  of  the  pancreatic  juice  may 
be  reflexly  excited  by  a  nervous  mechanism.  Stimulation  of  the  vagus 
causes  a  flow  of  juice  after  a  long  latent  ]ieriod,  ])robably  by  increasing 
the  movements  of  the  stomach  and  the  flow  of  acid  chyme  into  the 
duodenum.  However,  a  secretion  has  been  obtained  when  the  outflow 
of  chyme  from  the  stomach  Avas  prevented,  and  the  chemical  mechanism 
thus  excluded.  In  favour  of  the  nervous  mechanism  is  the  fact  that, 
in  the  dog,  pancreatic  juice  begins  to  flow  one  to  one  and  a  half  minutes 
after  the  ingestion  of  food,  and  before  the  entrance  of  the  gastric 
contents  into  the  duodenun^ 


Fig.  198. — To  .sh<r.v  Action  uf  Aciu  Kxtkact  of  Mlcous  Membkane  of  Duodenum 
(Secretin)  dehydrated  by  Alcohol.     (Bayliss  and  Starling.) 

A.  Blood -pressure;  B,  drops  of  pancreatic  juice. 

The  quantity  of  juice  secreted  varies  in  amount  with  the  nature 
of  the  nourishment.  The  period  at  which  the  maximum  secretion 
occurs  al&o  varies,  as  the  following  figures  show:  meat,  2  hours;  bread, 
a  little  later:  milk,  3  to  4  hours.  These  figures  apply  to  the  dog. 
In  man.  after  a  carbohydrate  meal,  the  maximum  is  reached  between 
3  to  4  hours :  after  meat  and  fat,  4  to  5  hours.  Carbohydrates  produce 
most  secretion,  proteins  somewhat  less,  and  fat  least  of  all. 

The  Activation  of  the  Pancreatic  Enzymes. — Opinion  seems  to 
vary  considerably  about  the  state  in  which  the  steapsin  and  amylopsin 
of  the  juice  are  secreted.  Some  hold  that  they  are  secreted  in  the 
active  state,  others  that  the  pancreas  elaborates  and  secretes  their 
zymogens. 

There  is  no  doubt  about  trypsin:  this  is  secreted  as  trypsinogen. 


DIGESTION  IN  THE  SMALL  INTESTINE  399 

It  seems  probable  the  other  two  are  also  secreted  as  zymogens.  The 
potency  of  freshly  secreted  juice  or  of  a  glycerine  extract  of  fresh 
pancreas  is  feeble.  Treatment  with  dilute  acetic  acid  greatly  increases 
it.  A  glycerine  extract  increases  in  potency  with  keeping,  and  its 
power  is  accelerated  by  dilution  with  a  weak  solution  of  salts,  and 
especially  by  the  addition  of  another  potent  extract.  The  transforma- 
tion of  the  zymogens  of  steapsin  and  amylopsin  (if  transformation  there 
be)  must  be  rapid,  that  of  trjqjsinogen  is  slow.  The  activation  of 
trypsinogen  does  not  normall}*  take  place  until  the  small  intestine  is 
reached.  If  tripsin  were  active  in  the  juice,  it  would  destroy  steapsin 
and  amylopsin.  In  the  intestine,  these  enzymes  are  j)rotected  by  the 
presence  of  the  bile  and  the  proteins  of  the  chyme.  How  the  activa- 
tion of  trypsinogen  is  brought  about  by  enterokinase,  calcium  salts, 
and  probably  bacteria,  has  been  already  mentioned  (p.  370). 

The  Digestive  Action  of  the  Pancreatic  Juice — Tnjpsin. — Most 
proteins  are  readily  hydrolyzed  by  this  enzyme  acting  in  an  alkaline 
medium.  Trypsin,  unlike  pepsin,  does  not  attack  collagen  and 
gelatin.  Like  pejDsin,  it  digests  elastin  but  little,  and  keratin  not  at 
all.  Nucleo-protein  is  sjjlit  into  nucleic  acid  and  a  protein.  In  the 
digestion  of  other  proteins,  little  alkali  metaprotem  is  formed,  and 
digestion  proceeds  so  quickly  that  primary  proteose  is  not  as  a  rule 
found;  the  peptone  stage  is  quickly  reached.  The  peptones  are  hydro- 
lyzed to  polypeptides,  and  these  in  turn  to  amino-acids,  ammonia, 
pyrimidin,  and  pyrollidin  bases.     The  following  table  shows  this: 

Protein -^Alkali  Metaproteln 


Proteoses  (mainh-  secondary) 


Peptones 


Polypeptides 


Amino-Acids  (see  p.  43) 

This   digestion   takes  place   in   stages.     Some   amino-acids,   such   as 
tjTosin.  are  split  off  earlier  than  others. 

Starch  is  digested  by  amylopsin,  passing  to  maltose  through 
the  same  stages  as  in  the  case  of  digestion  by  ptyalin.  The  pan- 
creatic diastase,  however,  exerts  a  considerable  action  upon  unboiled 
starch.     This  is  not  the  case  with  ptyalin  (see  p.  71). 


400  A  TEXTBOOK  OF  PilVSlOLOOY 

Steapsin,  in  the  presence  of  bile,  acts  upon  the  finely  emulsified 
fats,  and  converts  them  into  glycerine  and  fatty  acid  (see  p.  71)- 

Lecithin  is  liydrol\zed  to  glycerine,  fatty  acid,  and  choline.  It 
is  not  clear  what  ])art  rennin  can  play,  as  all  ingested  milk  is  curdled 
in  the  stomach. 

The  nuclease  present  splits  nucleic  acid  into  purin  bodies.  In 
cases  of  pancreatic  disease,  it  is  stated  that,  owing  to  the  absence  of 
trypsin  and  luiclease,  the  cell-nuclei  in  the  food  are  not  disintegrated, 
and  therefore  pancreatic  disorder  can  be  traced  by  examining  the 
fseces  after  a  meal  rich  in  cell  nuclei,  such  as  sweetbreads. 

THE  SUCCUS  ENTERICUS. — This  is  secreted  by  the  tubular 
glands  lining  the  small  intestines,  and  also  by  the  glands  of  Brunner. 
To  obtain  the  juice,  a  piece  of  the  intestine  is  isolated  with  the 
mesentery  intact,  and  the  two  open  ends  are  sewn  into  the  abdominal 
walls — the  severed  ends  of  the  intestine  are  reunited  (Vella's  method), 
or  one  end  only  of  the  isolated  j^iece  of  the  intestine  is  sewn  into  the 
abdominal  wall,  the  other  being  sutured  (Thiry's  method).  Such  fistulae 
have  l)een  established  in  man  by  operations  undertaken  to  relieve 
strangulated  hernia,  etc.  In  either  case,  the  juice  can  be  removed 
from  the  loop  and  tested  in  vitro,  or  food  can  be  introduced  into 
the  loop,  and  afterwards  removed  and  examined. 

Obtained  in  this  way,  the  succus  entericus  is  a  yellowish,  turbid, 
viscid  fluid,  alkaline  in  reaction,  with  a  specific  gravity  of  1007  to  1010, 
and  a  solid  content  of  about  1-5  per  cent.  The  viscidity  is  probably 
due  to  a  body  of  the  nucleo-j)rotein  type,  rather  than  to  a  true  mucin 
(gluco-protein).  It  plays  an  important  part  in  protecting  the  intestine 
and  facilitating  the  movements  of  the  intestinal  contents.  The  juice 
also  contains  a  small  amount  of  serum  albumin  and  globulin,  and 
certain  enzymes — erepsin,  invertase,  maltase,  and  a  feeble  lipase. 
In  animals  taking  milk,  a  lactase  is  also  i:)resent.  In  addition,  it 
contains  enterokinase.  The  chief  salts  are  sodium  chloride  and 
carbonate.  The  glands  of  Brunner  in  the  duodenum  secrete  a  pepsin- 
like enzyme;  also  in  herbivora  a  diastatic  enzyme. 

The  intestinal  secretion  reaches  its  maximum  about  three  hours 
after  food,  continuing  for  six  to  eight  hours.  It  is  greater  in  the 
ixpper  than  in  the  lower  part  of  the  intestine.  It  is  stated  to 
average  in  the  dog  about  100  c.c.  daily,  in  man  from  150  to  800  c.c, 
but  it  is  very  difficult  to  give  accurate  figures. 

The  Mechanism  of  the  Secretion. — The  nnicus  comes  mainly  from 
the  goblet  cells,  the  rest  of  the  secretion  from  the  other  cells  of  the 
glands.  The  granules  of  these  increase  during  rest,  and  diminish 
during  activity.  The  juice  is  secreted  in  the  upper  part  of  the  intes- 
tine in  response  to  the  presence  of  hydrochloric  acid  in  the  gut,  but 
whether  it  is  due  to  the  direct  excitation  of  the  cells  or  to  a  "  hormone  " 
mechanism  is  not  definitely  decided.  In  regard  to  the  secretion  in  the 
lower  part,  it  seems  probable  that  this  is  determined  by  the  absorption 
of  the  products  of  digestion  higher  up,  and  it  may  be  that  it  varies  in 
composition  and  amount  according  to  the  nature  of  the  food  absorbed. 


DIGESTION  IN  THE  SMALL  INTESTINE  401 

It  is  claimed  that  the  absorption  of  intestinal  jnice  itself  ma}'  also  play 
a  part  in  exciting  fm-thev  secietion. 

As  regards  nervous  influence  upon  secretion,  the  evidence  that 
such  exists  is  inconclusive.  The  result  which  follows  division  of  the 
nerves  supplying  an  isolated  portion  of  intestine  is  untrustworthy, 
since  the  large  amount  of  fluid  then  secreted  but  little  resembles  the 
true  juice,  and  is  more  akin  to  lymph.  It  is  a  result  of  the  vasodila- 
tation and  congestion  of  the  looj). 

The  Uses  of  the  Juice.— By  virtue  of  its  mucus,  it  is  protective 
and  lubricatory.  The  enterokinase  plays  an  important  part  in  the 
activation  of  trypsinogen.  Invertase  inverts  cane-sugar  to  dextrose 
and  levulose;  maltase  converts  maltose  into  two  molecules  of  dextrose; 
lactase  converts  lactose  into  dextrose  and  galactose.  The  action  of 
the  lipase  and  diastase  are  similar  to  those  of  pancreatic  juice.  As 
extracts  of  the  intestinal  mucous  membrane  are  distinctly  more 
active  than  the  juice  itself,  it  has  been  suggested  that  the  enzymes 
are  present  as  such  in  the  mucoiis  membrane,  and  may  exert  most 
of  their  action  intracellular! y  during  absorption.  This  applies  par- 
ticularly to  erepsin,  an  enzyme  which  acts  upon  proteoses  and  pep- 
tones, and  converts  them  into  amino-acids  and  ammonia,  tSince 
this  enzyme  occurs  in  all  animal  tissues,  it  may  be  inferred  that 
its  action  is  mainly  intracellular.  It  occurs  in  greatest  amount  in 
the  intestinal  mucous  membrane,  next  in  the  kidnej',  and  then  in 
decreasing  amount  in  the  pancreas,  spleen,  liver,  heart  muscle,  skeletal 
muscle,  and  brain.  The  large  amount  in  the  intestinal  mucous  mem- 
brane indicates  its  important  function  there.  Perhaps,  by  the  reversible 
action  of  which  enzymes  are  capable,  it  brings  about  the  synthesis  of 
the  products  of  protein  digestion  during  their  absorption  through  the 
intestinal  mucous  membrane  (see  later,  p.  424). 

Functions  of  the  Small  Intestine. — The  functions  of  the  small 
intestine  may  be  briefly  reviewed  as  follows:  In  the  upper  part  of  the 
intestine,  into  which  the  digestive  fluids  are  poured,  the  function  is 
essentially  digestive;  in  the  middle  and  lower  parts,  the  function  is 
in  the  main  absorptive.  By  the  time  the  contents  of  the  small  pass 
into  the  large  intestine,  ]>ractically  all  the  foodstuffs  have  been 
absorbed  that  are  going  to  be  absorbed.  Little  or  no  absorption  of 
foodstuffs  takes  place  in  the  large  intestine. 

A  certain  amount  of  fermentation  of  carbohydrate,  as  the  result 
of  bacterial  activity,  may  occur  under  normal  conditions  in  the  small 
intestine,  but  as  a  rule  there  is  no  putrefaction  of  proteins. 


CHAPTER  XLVIII 
THE  LARGE  INTESTINE 

The  Function  of  the  Large  Intestine. — Recently  there  has  been 
Kome  discussion  as  to  whether  the  large  intestine  performs  a 
useful  function.  By  some  surgeons  it  is  regarded  merely  as  a 
sewer-pipe,  in  which,  as  the  result  of  bacterial  action,  the  fer- 
mentation of  carbohydrate  and  the  putrefaction  of  protein  proceed 
apace,  so  that  he  is  to  be  considered  a  happy  man  who  has  rid  himself 
of  such  an  encumbrance  (!).  Such  an  opinion  flies  in  the  face  of 
Nature  and  the  laAvs  of  evolution.  The  trouble  would  appear  to  be 
that  people,  while  clamouring  loudty  for  modern  sanitation,  do  not 
trouble  to  keep  this  "  sewer-pipe  "  in  a  wholesome  condition.  In 
the  large  intestine,  the  greater  part  of  the  ingested  water  is  absorbed 
into  tiie  body.  This  is  curious,  considering  the  disgust  such  feculent 
water  \\ould  give  iis.  It  is  very  doubtful  whether  any  products  of 
digestion  are  absorbed  in  the  large  intestine.  It  was  formerly  believed 
that  protein  digestion  was  continued  in  the  large  intestine,  and  that 
an  appreciable  absorption  of  the  products  was  absorbed  into  the 
system.  Recent  researches  cast  doubt  upon  this  point.  It  may  be 
that  a  small  absorption  of  the  products  of  protein  digestion  takes 
place. 

In  rectal  feeding",  the  nutriment  so  given  is  passed  back  by  reversed 
peristaltic  movements  into  the  small  intestine,  and  there  digested 
and  absorbed.  Within  a  few  minutes  of  giving  an  egg  enema,  the 
yellow  fluid  has  been  seen  pouring  from  a  duodenal  fistula.  . 

The  absorption  of  water  is  of  considerable  importance  to  the  body 
It  is  also  of  great  convenience,  since  it  conduces  to  the  proper  forma- 
tion of  fseces  and  greatly  reduces  their  bulk.  As  the  result  of  extirpa- 
tion of  the  whole  large  intestine  in  a  dog,  it  was  found  that  the  faeces 
passed  each  dsij  were  greatly  increased  in  weight,  and  contained  five 
times  the  normal  amount  of  water.  The  absorption  of  protein  was 
slightly  diminished,  but  not  that  of  carbohydrates  and  fats.  In 
some  waj'  not  at  present  adequately  understood,  the  calcium  and 
phosphatic  metabolism  is  influenced  by  the  large  intestine.  On  a 
herbivorous  diet,  the  amount  of  calcium  excreted  by  the  large 
intestine  and  passed  in  the  faeces  is  considerably  greater  than  on 
an  omnivorous  diet.  On  this  latter  diet,  the  proportion  of  calcium 
passed  in  the  faeces  compared  to  the  urine  is  75  :  25 ;  on  a  herbivorous 
diet,  the  proportion  may  be  95  to  5. 

The  large  intestine  is  the  playground  of  bacteria.  The  contents 
afford  an    ideal   culture    medium.      Its  glands    secrete    an    alkaline 

402 


THE  LARGE  INTESTINE  403 

mucus,  and  little  or  no  oxygen  is  present.  The  conditions  thus 
favour  the  growth  of  anaerobic  organisms,  and  their  action  consists 
of  oxidations  and  reductions,  rather  than  of  hydrolytic  changes, 
such  as  are  occasioned  b}-  enzymes.  Proteins  and  carbohydrates 
are  chiefly  acted  upon,  fats  but  little.  The  action  upon  carbohydrates 
is  often  referred  to  as  fermentation,  that  upon  proteins  as  putre- 
faction. The  same  bacteria  do  not  act  upon  both  kinds  of  food- 
stuffs; indeed,  they  are  antagonistic  to  each  other  to  a  certain 
extent.  The  protein-decomposing  bacteria  are  of  manj^  kinds,  the 
chief  of  \^hich  is  Bacillus  putrificus.  They  are  anaerobes,  working 
in  the  absence  of  oxygen.  The  bacteria  which  act  upon  carbohydrates, 
on  the  other  hand,  are  aerobes,  the  chief  being  B.  coli  and  B.  lactis 
aerogenes. 

Protein  decomposition  leads  to  the  formation  of  such  bodies  as 
sulphuretted  hydrogen,  methyl-mercaptan,  marsh  gas,  ammonia, 
carbon  dioxide,  lower  fatty  acids,  phenyi-acetic  and  phenyl -propionic 
acids,  phenol,  cresol.  indol,  skatol.  The  first-named  bodies  are  generally 
passed  ^je/-  rectum  ;  the  last  four  bodies  are  absorbed  into  the  system, 
and  are  harmful.  If  only  absorbed  in  small  amounts,  they  are  arrested 
in  the  liver,  combined  with  sulphuric  acid,  and  converted  into  the 
ethereal  sulphates  which  are  excreted  in  the  urine.  If  absorbed 
in  larger  amounts,  they  escape  this  action  of  the  liver,  and  there  then 
follows  a  general  feeling  of  unfitness  and  dei^ression,  headache,  and 
various  other  nervous  symptoms,  due  to  alimentary  toxaemia. 

Normally,  there  is  no  formation  in  the  large  gut  of  putrescin  and 
cadaverin,  bodies  which  result  from  protein  decomposition  outside 
the  body.  These  are  only  found  in  special  conditions,  such  as 
dysentery  and  cystinuria.  The  difference  between  enzymic  and 
bacterial  action  upon  protein  can  be  appreciated  by  placing  in  an  incu- 
bator at  37^  C.  two  fiasks  containing  minced  meat  in  alkaline  fluid. 
The  meat  in  one  flask  is  acted  upon  by  trypsin,  bacterial  action  being 
stopped  by  some  toluol;  the  meat  in  the  other  is  acted  upon  by  any 
bacteria  which  happen  to  be  present.  After  two  or  three  days,  the 
flask  containing  the  enzymic  digest  has  a  peculiarly  faint,  but  not 
repulsive,  smell:  the  flask  containing  the  products  of  bacterial  action 
stinks. 

Carbohydrate  fermentation  leads  to  the  formation  of  carbon  dioxide, 
hydrogen,  butyric,  lactic,  and  acetic  acids.  The  two  processes  proceed 
simultaneously  in  different  parts  of  the  intestine.  Generally  speaking, 
carbohydrate  fermentation  leads  to  the  formation  of  a  greater  bulk 
of  gas  of  a  less  impleasant  nature  than  the  smaller  amount  of  gas 
derived  from  j^rotein  decomposition. 

Under  normal  healthy  conditions,  protein  decomposition  does  not 
proceed  to  the  same  extent  as  outside  the  body.  There  is  consider- 
able discussion  as  to  the  reason  of  this.  It  has  already  been  mentioned 
.that  there  is  an  antagonism  between  the  different  kinds  of  bacteria, 
and  the  presence  of  carbohydrate  ma 3"  be  partly  responsible  for  this 
limited  action.  Milk  in  the  diet,  and  especially  milk-sugar — lactose — 
are  said  to  be  particularly  efficient  in  limiting  the  putrefaction  of 


404  A  TEXTB(J()K  OF  rHVSJOJ.OC^Y 

])rotein,  and  this  is  believetl  to  be  due  to  the  fact  that  they  give  play 
to  the  growth  of  antagonistic  lactic  acid  bacilli.  Quite  recently  it 
became  fashionable  to  take  lactic  acid  bacilli  by  the  mouth.  This 
cannot  be  said  to  have  been  very  effective  as  a  cure,  partly,  perhaps, 
because  man\'  of  the  preparations  sold  were  sterile.  At  the  best 
it  substituted  the  lesser  evil — fermentation  of  carbohydrate  for  the 
putrefaction  of  j)rotein. 

The  bacteria  are  killed  off  by  the  action  of  the  healthy  intestinal 
wall;  while  the  contents  swarm  with  bacteria,  the  mucous  membrane 
and  blood  circulating  within  it  are  sterile.  Foreign  Imcteria,  such  as 
vibrios,  appear  to  be  killed  if  introduced  into  the  large  intestine. 

As  the  result  of  bacterial  action,  the  pigment  of  the  faeces — sterco- 
bilin — and  one  of  the  pigments  of  the  urine — urobilin — together  with 
its  precursor  urobilinogen,  are  formed  from  the  bile  pigments.  Bile 
salts  are  also  decomposed  into  cholalic  acid,  and  either  taurin  or 
glycin. '  Cholesterin  becomes  converted  into  an  allied  body — copro- 
.sterin. 

The  fact  that  extensive  bacterial  action  takes  place  in  the  intestine 
does  not  mean  that  it  is  necessarily  harmful ;  indeed,  when  kept  within 
limits,  it  is,  if  anything,  helpful  to  the  body.  A  certain  amount  of 
gas  promotes  the  movements  of  the  large  bowel,  and  assists  the  removal 
of  the  waste  material.  Experiments  have  been  made  to  test  the 
value  of  the  intestinal  flora  to  the  animal.  Guinea-pigs  delivered  by 
Caesarian  section,  breathing  sterile  air,  and  fed  on  sterile  food,  pro- 
gressed as  well  as  the  controls  kept  non-sterile.  Sterile  chicks,  on 
the  other  hand,  did  badl}'  on  sterile  food.  Some  died  in  eighteen 
daj's,  while,  in  about  the  same  tnne  as  a  starving  control,  others 
recovered  when  the  bacteria  of  chicken  faeces  were  added  to  their 
food.  The  guts  of  Arctic  animals,  such  as  the  polar  bear,  are  said  to 
be  almost  sterile.  Herbivorous  animals  obtain  a  great  deal  of  the 
nitrogenous  foodstuffs  from  non-protein  compounds,  especially 
asparagin.  It  is  suggested  that  the  intestinal  bacteria  of  herbivora 
build  up  proteins  which  are  utilized  out  of  these  amides.  Asi:taragin 
camiot  be  utilized  l)y  carnivora.  By  the  bacteria  in  the  capacious 
caecum  of  herbi\'ora  celhdose  is  split  into  glucose,  lactic,  butyric 
acids,  etc.  These  are  absorbed  and  utilized,  and  thus  cellulose,  which 
forms  so  large  a  bulk  of  the  food,  becomes  a  chief  source  of  energy. 
Hydrogen  and  methane  are  also  produced  by  the  bacterial  fermen- 
tation of  cellulose,  and  constitute  a  small  part  of  the  flatus  passed 
from  the  bowel.  A  certain  amount  of  oxygen  is  set  free  and  utilized. 
In  balancing  up  the  metabolism  of  cattle,  these  gaseous  excretions, 
which  leave  the  body  both  by  wa^'  of  bowel  and  lung,  have  to  be  taken 
into  account. 

Protein  putrefaction  is  ahvays  going  on  in  the  large  bowel,  even 
when  no  food  is  being  taken.  The  jDroteins  of  the  secreted  juices  are 
then  decomposed.  It  is  only  when  bacterial  action  is  allowed  to  get. 
beyond  proper  limits  that  it  becomes  harmful.  Excess  of  food  and 
a  sluggish  large  intestine  favoiu-  the  condition.  It  is  obvious  that  no 
more  food,  especially  proteins,  should  be  taken  in  than  can  be  digested 


THE  LARGE  IXTESTIXE  405 

and  absorbed  by  the  small  intestine.  Xo  large  excess  of  digestible 
foodstuffs  should  be  passed,  with  the  juices  capable  of  digesting  them, 
into  the  large  intestine,  for  the  products  of  digestion  cannot  be,  or 
are  not  readily,  absorbed  there.  ^lore  important  still,  the  movements 
of  the  large  intestine  must  be  aided  hy  the  massage  obtained  by  exercise 
of  the  abdominal  muscles,  by  hard  ])liysical  work,  and  deep  breathing. 
The  great  prevalence  of  trouble  in  the  large  intestine  is  due  to  loading 
it  with  excess  food,  and  to  the  development  of  a  sluggish  colon 
by  lack  of  exercise.  Plain  living  and  exercise,  not  the  quack's  pill 
or  the  surgeon's  knife,  are  the  cure  for  the  troubles  which  arise  in 
this  region  of  the  gut.  The  fortunes  of  pill- vendors  are  an  index  of 
the  gluttony  and  sloth  of  man. 
Faeces. — The  faeces  consist  of — ■ 

1.  Indigestible  material,  such  as  keratin  and  cellulose. 

2.  Material  digested  with  difficulty — elastm,  cartilage. 

3.  Superfluous  and  non-absorbed  products  of  digestion — fatty 
acids,  insoluble  soaps,  amino-acids.  purin  bodies  from  nucleo-protein, 
haematin  from  haenioglobin,  toxic  bodies  with  an  aromatic  nucleus. 

4.  Products  of  bacterial  activity — indol,  skatol.  These  are  ab- 
sorbed and  excreted  in  the  urine  as  non-toxic  compounds  of  sulphuric 
and  glycuronic  acids. 

5.  Components  of  digestive  juices  secreted  by  the  alimentary  tract 
— tryjDsin,  diastase,  cholalic  acid,  bile  salts,  lecithm,  stercobilin  from 
bile  pigments,  coprosterin  from  cholesterin. 

6.  Excretion  of  the  intestinal  wall — calcium  and  iron  salts,  epithelial 
cells,  leucocytes. 

7.  Bacteria,  forming  a  large  part  of  the  faeces,  even  half  the  weight. 
The  faeces  are  as  a  rule  alkaline  or  neutral  in  reaction.     The  bulk 

varies  with  the  kind  of  food  and  kind  of  animal.  In  man,  on  a  mixed 
diet,  the  daily  amount  evacuated  is  about  120  to  150  grains,  containing 
30  to  37  grains  of  solids;  on  a  vegetable  diet,  333  grains,  and  75  grains 
of  solids.  The  offensive  smell  is  mostly  due  to  skatol.  The  colour 
varies  according  to  the  food.  Meat  gives  a  dark,  almost  black,  stool; 
large  amounts  of  fat  make  the  faeces  clay-coloured:  much  bread  im- 
parts a  light  colour.  The  breast-fed  infant  passes  motions  of  the 
colour  and  consistency  of  mustard,  acid  in  reaction,  and  inoffeiLsive  in 
smell.  Meconium,  the  dark-greenish  faeces  passed  by  the  newly-born 
child,  are  similarly  acid  in  reaction,  and  inoffensive.  It  consists  of 
cells,  and  remains  of  bile  and  digestive  fluids.  There  is  no  sign  of 
am^  bacterial  action. 

The  chemical  analysis  of  the  faeces  is  not  often  undertaken  in 
clinical  laboratories.  It  affords  valuable  information  in  certain 
conditions . 


CHAPTER  WAX 

THE  MECHANICAL  FACTORS  OF  DIGESTION 

The  mechanical  factor  plays  an  important  part  in  the  processes 
oi  digestion,  and  is  intimately  related  with  the  chemical  factors.  The 
mechanical  factor  insures  the  proper  subdivision  and  mixing  of  the 
food  with  the  digestive  secretions,  exposes  the  products  of  digestion 
to  the  absorptive  surfaces,  propels  them  from  one  region  of  the  gut 
to  another,  and  finally  discharges  the  waste  material  from  the  body. 
It  is  obvious  that  these  processes  must  be  conducted  in  an  orderly 
fashion,  otherwise  the  food  might  either  be  inadequately  digested  or 


Fig.  199. 


-Outlines  of  an  Almost  Instantaneous  Radiograph  of  the  Stomach 
OF  a  Cat  during  Digestion.     (Cannon.) 


0,'Cardia;  P,  pylorus;  at  1,  2,  3,  4,  5,  are  indentations  due  to  peristaltic  waves 
passing  towards  the  pylorus. 


inadequately  absorbed.  The  kind  and  rate  of  movement  in  the  different 
parts  of  the  alimentary  tract  varies,  therefore,  according  to  the  special 
digestive  actions  which  are  being  effected  in  those  parts. 

The  muscles  at  the  beginning  and  at  the  end  of  the  alimentary 
tract  are  under  voluntary  control;  the  rest  of  the  musculature  of  the 
tract,  however,  is  of  the  smooth  variety,  automatic  in  action.  The 
automaticity  is  dependent,  for  the  most  part,  iipon  the  primitive 
nerve  plexus  (Auerbach's)  in  the  w^all  of  the  gut;  it  is  influenced  by 

406 


THE  MECHANICAL  FACTORS  OF  DIGESTION 


407 


impulses  from  the  central  nervous  system.     Some  of  the  movements 
may  be  purely  muscular  in  origin. 

To  study  the  movements,  animals  or  men  are  given  food  mixed 
Avith  bismuth  subnitrate,  or,  better,  with  bismuth  oxychloride.  The 
position  and  movements  of  the  food  is  observed,  by  means  of  the 
,X  rays  and  the  fluorescent  screen,  or  b}^  almost  instantaneous 
radiographs  (Fig.  199)  at  various  intervals  after  the  taking  in  of 
the  food.  Tracings  may  be  taken  upon  tissue  paper  laid  upon  a  piece 
of  lead  glass*  placed  over  the  screen  (Fig.  200).  The  great  advantage 
of  this  method  is  that  the  normal  passage  of  food  through  the  alimen- 
tary tract  can  be  observed  over  a  long  period  of  time,  and  the  charac- 
teristic movements  of  each  part,  their  normal  rate  and  frequency,  be 


Fis.  200. — Tkacixgs  of  the  Shabow  cast  by  the  Stomach  (Cat),  showing  Changes 
IN  the  Shape  of  the  Organ  at  Intervals  of  an  Hour  during  the  Digestion 
OF  A  Meal.     (Cannon.) 


accurately  studied.  The  disadvantage  of  viewing  the  guts  directly 
after  operative  procedures  is  that  the  normal  movements  are  greatly 
interfered  with  thereby,  or  even  abolished.  Nevertheless,  they  can 
to  a  certain  extent  be  studied  by  immersing  the  anaesthetized  animal 
in  a  bath  of  warm  Ringer's  solution,  before  opening  the  abdominal 
wall. 

Movements  of  Mastication. — By  an  up-and-down  movement  of 
the  lower  jaw.  the  food  is  seized  by  the  front  teeth;  by  a  side-to-side 
movement,  it  is  chewed  by  the  back  teeth.  The  tongue  and  cheeks 
assist  in  this  latter  process  by  forcing  the  food  between  the  grinding 

*  The  lead  glass  is  used  to  protect  the  observer  from  the  ill  effects  of  prolonged 
exposure  to  X  rays. 


408 


A  TEXTBOOK  OF  PHYSIOLOGY 


surfaces  until  it  is  thoroughly  chewed.  In  man.  the  duration  of  the 
process  of  chewing  varies  with  the  nature  of  the  food  and  the  tempera- 
ment of  the  individual.  Some  ]^)eople,  generalh'  3'oung,  chew  their 
food  much  less  than  others.  Great  value  is  attached  to  thorough 
mastication  by  some,  but  many  continue  to  bolt  their  food,  as  does 
a  dog,  often  apj^arently  without  harm. 

The  degree  of  chewing  varies  with  the  nature  of  the  food,  a  hard, 
dry  food  requiring  considerably  more  chewing  than  a  soft,  pappj^ 
food.  Generally  speaking,  the  food  is  chewed  for  twenty  to  thirty 
seconds,  and  in  this  time  about  1  to  1^  grammes  of  saliva  may  be 
added  to  a  mass  which  generally  varies  from  3  to  6  grammes.  The 
pressure  exerted  during  chewing  may  be  as  great  as  270  pounds  as 
measured  by  a  sjiring  d^iiamometer.  Such  great  pressures  are.  how- 
ever, not  usually  employed,  since  a  side-to-side  grind  is  more  effective 
than  the  direct  thrust.     Thus,  the  crushing-point  of  cooked  meat  to 


Naso- pharynx 


-  Soft  palate 


_  Oesophagus 


A  B 

Fig.  201.— To  show  the  Mechaxism  of  the  First  Stage  of  Swallowing. 
A,  at  rest;  B.  swallowing. 


a  direct  thrust  varies  from  15  to  80  pounds,  with  a  grinding  move- 
ment but  I  to  2  pounds  pressure  is  required  for  cooked  tongue, 
and  but  40  jDounds  pressm-e  for  tough  beef.  The  softening  effect  of 
saliva  upon  the  pressure  required  in  chewing  is  also  very  marked. 
Soft  crumb  bread,  for  example,  requires  more  than  60  pounds  direct 
pressure,  but  when  softened  with  a  little  saliva  it  can  be  masticated 
with  a  pressure  of  3  pounds.  The  chewing  of  agreeable  foodstuffs  is 
of  value  in  reflexly  promoting  a  flo^^•  of  gastric  juice,  and  perhaps 
causing  a  tonic  contraction  of  the  circular  muscles  of  the  stomach, 
thus  regulating  the  stomach  movements.- 

The  Mechanism  of  Swallowing. — After  a  proper  degree  of  ma.stica- 
tion,  the  food  is  gathered  as  a  bolus  at  the  back  of  the  tongue.  Then 
follows  the  complex  secj[uence  of  events  which  constitute  the  act  of 
swallowing.  Forward  movement  of  the  bolus  is  prevented  by  the 
l^ressure  of  the  tip  and  sides  of  the  tongue  against  the  hard  palate 
and  the  teeth.     It  is  impossible  to  swallow  with  the  tongue  relaxed. 


THE  MECHANICAL  FACTORS  OF  DIGESTIOX         400 

Then,  breathing  being  inhibited,  there  follows  a  short,  sharp  con- 
traction of  the  mylohyoid  and  hyoglossus  mnscles.  The  action  of  the 
mylohyoid  is  to  press  the  tongue  upAvards  against  the  hard  palate, 
that  of  the  hyoglossus  to  pull  it  backwards.  The  result  of  the  com- 
bined action  is  a  piston-like  thrust,  which  propels  the  bolus  into  the 
phar\Tix.  Its  entrance  into  the  naso -pharynx  is  prevented  by  the 
contraction  at  the  same  time  of  the  palato-pharyngeus  and  levator 
palati  muscles.  The  levator  palati  pulls  the  soft  palate  down 
against  the  posterior  pillars  of  the  fauces,  which  are  approximated  by 
the  contraction  of  the  palato-pharnygeus  muscles.  The  bolus  first 
strikes  the  soft  palate,  then  the  back  Avail  of  the  pharynx;  it  next 
passes  between  the  pharyngeal  wall  and  the  epiglottis,  the  oesophagus 
ni  the  meantime  being  kej)t  closed  by  the  pressure  of  the  larynx; 
the  hj^oid  bone  and  the  larynx  are  now  raised,  the  glottis  approximated 
to  the  epiglottis,  the  respiratory  tract  thus  shut  off,  and  the  gullet 
opened ;  so  that  the  bolus,  propelled  by  the  mylohyoid,  glides  into 
the  open  oesophagus  (Fig.  201). 

This  is  the  end  of  the  first  stage  of  deglutition — the  stage  voluntarily 
initiated.  Then  follows  the  second  stage — the  involuntary  stage — 
namely,  the  passage  of  food  down  the  oesophagus  proper  to  the  cardiac 
orifice  of  the  stomach.  In  time  past,  conflicting  opinions  were  held 
as  to  the  relative  importance  of  the  initial  impulse  imparted  in  the 
first  voluntary  stage  and  of  the  peristaltic  action  of  the  oesophagus 
itself.  From  recent  experiment  by  means  of  X  rays,  it  would  appear 
that  this  depends  largely  upon  the  nature  of  the  food,  solids  and 
pappy  foods  being  passed  down  by  the  peristaltic  action  of  the 
oesophagus  itself — liquids,  on  the  other  hand,  passing  quickly  down  by 
the  impetus  given  by  the  j^iston  action  of  the  mylohyoid.  The  rate 
of  the  transmission  in  the  different  parts  of  the  oesophagus  is  variable. 
It  depends  upon  the  nature  of  the  muscle.  Thus,  in  the  goose,  where 
the  muscle  is  smooth,  a  uniform  slow  peristalsis  takes  place.  It  takes 
twelve  seconds  for  a  solid  bolus  to  traverse  15  centimetres  of  gullet. 
In  the  cat,  the  peristalsis  is  rapid  as  far  as  the  heart  level  (4  seconds), 
and  slow  (6  or  7  seconds)  for  the  remainder — less  than  a  third  of  the 
whole  distance.  It  is  at  the  heart  level  that  the  muscle  changes 
from  striated  to  smooth.  In  the  dog,  the  peristalsis  is  quick  through- 
out, the  time  taken  for  a  solid  bolus  being  4  or  5  seconds  from  larynx 
to  cardia.  In  the  dog,  the  whole  oesophagus  is  composed  of  striated 
muscle.  In  both  the  cat  and  dog,  liquids  travel  much  more  quickly 
than  the  solid  or  semi-solid  bolus. 

In  man,  the  lower  end  of  the  oesophagus  is  composed  of  smooth, 
muscle,  and  a  slower  rate  of  peristalsis  is  observed  in  this  region. 
X-ray  observations  upon  man  show  that  solids  and  semi-solids  are 
moved  down  the  oesophagus  by  peristaltic  action,  irrespective  of  the 
position  of  the  body,  and  OAve  practicalh*  nothing  to  the  prelimmary 
impetus,  the  time  required  for  a  AAcll-lubricated  bolus  being  from 
8  to  18  seconds,  for  a  dry  bolus  seA^eral  minutes.  Liquids,  on  the 
other  hand — e.g.,  milk  containing  bismuth — are  shot  rapidly  through, 
the  greater  part  of  the  oesoj)hagus.     In  the  head-down  position,  they 


410 


A  TEXTBOOK  OF  PHYSIOLOGY 


ascend  the  gullet  in  one-third  of  the  time  occvipied  by  solids  in  the 
normal  position  of  the  body. 

The  Nervous  Mechanism  of  Swallowing. — Swallowing  is  a  reflex 
act,  the  nervous  centre  controlling  it  being  situated  in  the  floor  of  the 
fourth  ventricle  in  the  spinal  bulb.  The  afferent  impulses  which 
provoke  the  reflex  arise  in  the  neighbourhood  of  the  pharynx ;  in  the 
dog  and  cat,  chiefly  from  the  posterior  wall  of  the  pharynx, 
opposite  the  opening  from  the  mouth — an  area  supplied  by  the  glosso- 
phar3'ngeal  nerve.  Impulses  also  arise  from  the  upper  part  of  the 
soft  palate,  supplied  by  the  ninth  and  the  second  part  of  the  fifth 
nerves,  and  from  the  base  of  the  epiglottis,  supplied  by  the  superior 
larjTigeal  division  of  the  tenth  nerve. 


Fig.  202. — Diagrams  of  Positio:n  of  Shadow  in  (Esophagus  at  Intervals 
OF  A  Second  after  Swallowing.     (Hurst.) 


In  monkeys,  the  swallowing  reflex  is  most  easily  evoked  in  the  region 
of  the  tonsils ;  in  man,  from  the  back  wall  of  the  pharynx  and  round 
about  the  base  of  the  tongue.  The  abilitj'  to  swallow  depends  upon 
the  presence  of  these  special  sensitive  spots,  as  is  shown  by  the  fact 
that  if  a  sponge  moistened  with  cocaine  be  swallowed,  and  then  pulled 
back  by  means  of  an  attached  thread,  the  power  to  sw^allow  is  lost  for 
a  time.  "NMienever  a  bolus  of  food  or  saliva  is  made  to  stimulate 
one  of  these  sensitive  spots,  sw^allowing  involuntarity  occurs. 

The  chief  efferent  or  effector  paths  are  fibres  running  in  the  hypo- 
glossus  to  the  hyoglossus,  in  the  third  branch  of  the  fifth  to  the  mylo- 
hyoid, in  the  glosso -pharyngeal  and  the  pharyngeal  branches  of  the 
vagus  to  the  muscles  of  the  palate  and  phar3^lx,  and  in  the  vagus 
to  the  oesophagus  itseff.  Stimulation  of  these  fibres  causes  strong 
contraction  of  the  oesophagus;  section  of  both  vagus  nerves  pro:luces 


THE  MECHANICAL  FACTORS  OF  DIGESTION  411 

paralysis.  The  paralysis,  however,  passes  off  after  a  time  in  the  non- 
striated  part  of  the  oesophagus,  which  is  endowed  with  the  property 
of  performing  peristaltic  movements  b}'  virtue  of  its  intrinsic  nervous 
mechanism:  a  secondary-  ""  lower  "  reflex  mechanism,  dependent  upon 
the  nerve  plexuses  in  the  wall  of  the  oesophagus.  By  this 
mechanism,  the  presence  of  the  bolus  in  the  oesophagus  itself  causes 
contractions,  which  push  it  onward  towards  the  stomach.  Nor- 
mally this  mechanism  probably  plays  little  or  no  part,  the  peri- 
staltic movenients  being  controlled  reflexly  through  the  vagus  nerve. 
After  the  oesophagus  has  been  divided  in  an  animal  under  moderate  or 
light  anaesthesia,  a  swallowing  movement  initiated  in  the  upper  seg- 
ment is  followed  by  a  movement  in  the  lower  segment.  The  peri- 
staltic wave  of  the  latter  must  in  this  case  be  excited  and  co-ordmated 
reflexly  through  the  central  nervous  system.  In  deep  anaesthesia,  how- 
ever, this  reflex  proi^agation  of  the  peristaltic  wave  may  be  abolished, 
and  a  wave  of  peristalsis  initiated  in  the  upper  segment  of  a  divided 


^^  V 


¥»i 


Pig.  203. — Tracings  of  the  Shadows  of  the  Contexts  of  the  Stoimach  and 
Intestines  (Cat's)  made  Two  Hours  after  Feeding  {A)  with  Boiled  Leak 
Beef,  (B)  with  Boiled  Rice.     (Cannon.) 

or  Jigated  oesophagus  is  not  passed  beyond  the  point  of  interruption. 
We  conclude,  then,  that  normally  the  contraction  of  the  oesophagus 
is  a  part  of  the  series  of  reflex  nervous  discharges  initiated  in  the 
"  swallowing  centre  "  b}^  the  stimulation  of  the  afferent  fibres. 

The  Movements  of  the  Stomach. — The  movements  of  the  stomach 
are  adapted  to  the  functions  of  its  different  parts.  By  the  X-ray 
method  it  is  seen  that  the  fundus,  or  reservoir,  is  practicaUy  devoid 
of  movement.  It  exerts  a  tonic  grasp  on  its  contents,  which  tend 
to  press  them  onwards  whenever  oj)portunity  arises.  Peristaltic 
waves  arise  from  the  middle  of  the  stomach  (1  to  6,  Fig.  190),  and 
pass  in  succession  towards  the  pylorus.  As  food  becomes  discharged 
into  the  intestine,  the  circular  muscle  becomes  tonically  contracted 
so  as  to  give  a  tubular  form  to  the  middle  region,  along  which 
the  peristaltic  waves  continue  to  pass.  The  contents  of  the  fundus 
are  thus  gradually  passed  into  the  pylorus,  and  eventually  the  shadow 
of  the  fundus  disappears  (5,  6,  7,  Fig.  200).  The  regular,  wave-like 
contractions  which  pass  over  the  pyloric  end  deepen  as  they  go,  and 


412 


A  TEXTBOOK  OF  PHYSIOLOGY 


churn  up  the  food  when  (he  i\vIorie  orifice  is  clo.scd,  and  pass  it  on  to 
the  duodenum  when  the  orifice  is  open. 

These  ehurtiing  movements  are  the  first  movements  noticed  when 
an    animal    is    examined    under    X     rays    after    receiving    a    good 


40 

/, 

f 

7.' 

<n30 

1-1 

// 

^ 

~- 

— 

1 

r 

/ 

a 

■3  20 

d 

8 

10 

k 

,- 

/ 

^ 

^ 

•^ 

/ 

/ 

M 

j 

1 

/ 

/  / 

/ 

,' 

[_^ 

/ 

0      k     1  2     0     >,     1  2  3  4 

^      A  Hours  B 

Ficj.  204. — To  SHOW  Effect  of  Coksistency  of  Food  upon  the  Rate  of  Leaving 
THE  Stomach.     (Cannon.) 

A,  Light  continuous  line  =  potato  of  standard  consistency;  heavy  continuous  line  = 
potato  of  thick  doughy  consistency;  dash  hue  =  thin  gruelly  consistency. 
B,  heavy  line  =  lean  beet  of  standaz'd  consistency;  light  line  =  lean  beef  of  thin 
gruelly  consistency. 

meal.  After  a  short  time,  an  annular  constriction  appears  at  the 
vestibule,  and  passes  slowly  over  the  rest  of  the  pylorus,  being  followed 
by  regular  waves  arising  in  the  same  regic«i.      Then  a  little  later  (two 


i I 

1 f 

1?- 

/      / 
/      ' 

1 

/ 

„/ 


Fig.  205. 

The  continuous  line  shows  the  rate  of 
disappearance  from  the  stomach  of  a 
carbohydrate  meal  (biscuits,  rice,  pota- 
toes) moistened  with  water;  the  dotted 
line  of  a  similar  meal  moistened  with 
1  per  cent.  NaHCO;.  There  is  marked 
retardation  of  the  latter.     (Cannon.) 


33 

• 

20 

• 

• 

1 

10 

1 

/ 

/ 
/ 

/ 

y 

/ 

Hours     ^1  2 

Fig.  20(3. 

The  continuous  line  shows  the  rate  of 
disappearance  of  a  meal  of  protein 
(fibrin,  fowl,  lean  beef);  the  dotted  line 
that  of  same  meal  fed  as  acid  protein. 
(Cannon.) 


to  three  minutes)  the  contractions  which  arise  from  the  middle  of  the 
body  make  their  appearance,  the  amount  of  contraction  becoming 
much  more  marked  when  the  vestibule  is  passed.      These  peristaltic 


THE  MECHANICAL  FACTORS  OF  DIGESTION 


413 


|i|=z 


waves  do  not  pass  into  the  duodenum,  the  muscular  continuity  between 
the  parts  being  interrupted  by  a  ring  of  fibrous  tissue.  The  time  of 
recurrence  of  the  waves  varies  in  different  animals,  and  also  with 
the  nature  of  the  food.  In  cats,  there  are  generally  four  to  six  per 
minute;  in  dogs,  about  four;  in  man,  three.  Fat  diminishes  the 
number  per  minute,  carbohydrate  increases  them. 


40 


,30 


1 20 


10 


0     U     1  2  3  4 

Hours 

Fig.  207. — To  show  RetardiNc^  Effects  of  Fats  upon  Food  leaving 
Stomach.     (Cannon.) 

Light  line  =  curve  of  mashed  potato;  heavy  line  =  curve  of  mutton  fat;  dash  line  = 
curve  of  potato  and  mutton  fat  mixed. 

The  opening  of  the  pyloric  orifice  is  co-ordinated  with  the  acidity 
and  the  consistency  and  nature  (Fig.  204)  of  the  gastric  contents. 
Generally  speaking,  carbohydrates  leave  first,  proteins  next,  and  fats 
last  (Fig.  205).  Carbohydrates  as  a  rule  leave  the  stomach  quickly, 
but  if  fed  with  alkali  their  exit  is  retarded  (Fig.  205).  Feeding  proteins 
with  acid,  on  the  other  hand,  hastens  their  normally  slow  exit 
(Fig.  200).  Fats  retard  the  exit  of  other  foods  (Fig.  207).  When 
the  acid  contents  of  the  stomach  reach   the  duodenum,  the  pyloric 


irrw'W'ii'*riWhP'''WPl^^ 


-J I I L- 


Ficj.  208. — Record  showing  Cessation  of  Rhythmic  Regurgitations  of  Fluid 
FROM  Stomach  into  (Esophagus  after  acidifying  Gastric  Contents  at  A  . 
(Cannon.) 

Upstroke  =  outHo\v,  small  oscillations  due  to  respiration.     Time  in  half-minutes. 


aperture  closes.  Thus,  acid  on  the  p3doric  side  oj^ens,  on  the  duodenal 
side  shuts  the  pyloric  orifice,  the  regulation  probably  depending  on 
a  local  reflex  mechanism. 

The  cardiac  orifice  is  normall}^  kept  shut.  In  the  resting  condition 
of  the  stomach  the  sphincter  resists  a  tension  of  about  25  cm.  of  H2O. 
We  are,  therefore,  not  conscious  of  the  rancid  contents  of  the  stomach. 


414  A  TEXTBOOK  OF  PHYSIOLOGY 

During  digestion,  the  acidity  of  the  contents  causes  the  closure  of  the 
sphincter  to  become  firmer.  When  the  stomach  is  very  full,  and  there 
is  no  acidity  of  the  reservoir  contents,  rhythmic  relaxation  and  contrac- 
tion of  the  cardiac  orifice  may  occur,  with  the  result  that  the  stomach 
contents  are  regurgitated  into  the  oesiophagus.  This  has  been  ex- 
perimentally' demonstrated  on  cats  both    l)y  the  X-ray  method  and 


Fig.  209. — Diagkam  repeesenting  the  Pkocess  of  Rhythmic  .Segmektation. 

(Cannon.) 

Lines  1,  2,  3,  4,  indicate  the  sequence  of  appearance  in  a  single  loop.  The  dotted 
lines  represent  the  regions  of  division.  The  arrows  show  the  relation  of  the 
particles  to  the  segments  they  subsequently  form. 

by  direct  registration  b}'  means  of  a  tambour  placed  in  the  oesophagus. 
The  addition  of  acid  immediately  caused  a  cessation  of  such  move- 
ments (Fig.  20K). 

That   such  a  regurgitation  occurs  in  man  has  been  proved  by  the 
fact  that  lycopodium  s]:ores  swallowed  overnight  in  a  gelatin  capsule 


Fig.  210. — Photograph  of  the  Small  Intestine  segmentikg  its  Contents. 

(Cannon.) 

have  been  fomid  in  the  mouths  of  persons  next  morning,  although 
there  was  no  trace  of  them  in  the  mouth  one  to  two  hours  after  swal- 
lowing. It  is  suggested  that  the  disagreeable  taste  in  the  mouth  and 
the  coated  tongue  of  the  dyspeptic  may  be  due  in  part  to  particles  of 
food  regurgitated  from  the  stomach,  especially  when  there  is  a  de- 
ficiency of  hydrochloric  acid  in  that  organ. 


THE  MECHANICAL  FACTORS  OF  DIGESTION         415 

The  movements  of  the  stomach  and  its  si^hincters  may  be  modified 
by  the  action  of  the  vagus  nerve.  Stimulation  of  the  peripheral  end 
of  the  vagus  nerve  causes  contraction  of  the  cardiac  sphincter,  but 
after  the  intravenous  administration  of  atropine  the  action  of  the 
same  nerve  on  this  sphincter  becomes  inhibitory.  On  vagal  stimula- 
tion, the  tone  of  the  stomach  increases,  and  the  peristaltic  waves 
augment.  In  some  cases  there  may  be  a  preliminary  transitory 
inhibitory  effect.  The  effect  on  the  pyloric  sphincter  is  imcertairi. 
It  is  probably  dependent  upon  the  condition,  at  the  moment  of  stimu- 
lation, of  the  local  nervous  mechanism  which  controls  that  orifice. 
Sometimes  it  opens,  and  sometimes  it  closes.  The  sympathetic  nerve 
is  generally  believed  to  be  inhibitory  to  the  stomach,  but  this  action 
is  ojDen  to  question. 


Fig.  211.— Segmentation  of  the  Small  Intestine  in  Man.     (Hui>t  ) 

Vomiting  is  controlled  by  a  nervous  reflex,  and  can  be  induced 
either  centrally  or  peripherally.  Tickling  the  throat  between  the 
pharynx  and  top  of  the  oesophagus  will  often  induce  it.  The  effector 
fibres  run  in  the  vagus  nerve.  The  cardiac  orifice  is  relaxed,  the  body 
of  the  stomach  rendered  flaccid  and  dilated,  and  the  tone  of  the  pvlorus 
increased.  A  strong  contraction  occurs  at  the  incisura  annularis 
dividing  the  stomach  into  two  separate  portions.  The  stomach 
contents  are  then  voided  by  a  simultaneous  contraction  of  the  dia- 
phragm and  the  muscles  of  the  belly  wall.  As  vomiting  proceeds,  the 
stomach  wall  contracts  down  on  the  remaining  contents;  otherwise 
the  stomach  is  essential^  passive  during  the  act  of  vomiting. 

The  Movements  of  the  Small  Intestine. — On  observin<y  bv  the 
X-ray  method  a  length  of  small  intestine,  it  is  noticed  that  the  first 
movement,  after  food  enters  it,  is  the  sudden  division  of  the  length 
into  a  number  of  small  ovoid  segments  of  almost  equal  size  (Fig.  209). 
A  moment  lat.er,  these  small  segments  themselves  divide  into  two  the 


416 


A  TEXTBOOK  OF  PHYSl()J.O(;Y 


neighbouring  halves  uniting  to  form  imw  segments.  A  moment  later, 
the  process  is  repeated,  and  this  ''  rhythmic  segmentation  "  of  the 
intestinal  contents  proceeds  incessantly  for  about  half  an  hour  at  a 
rate  of  about  twenty-eight  to  thirty  a  mmute.  During  this  period, 
the  position  of  the  food  M'ithin  the  gut  is  but  slightly  changed.  Rhyth- 
mic segmentation  has  been  observed  in  the  cat,  Avhite  rat,  dog,  and 
man.  In  the  rabbit,  a  rhythmic  shifting  of  the  food  to  and  fro  has 
been  observed  (Fig.  210).  Segmentation  of  the  small  intestine  in  man 
is  shown  in  Fig.  211. 

The  effect  of  rhythmic  segmentation  is  to  mix  the  food  in  the  gut 
thoroughly,  bring  it  into  intimate  contact  Avith  the  mucous  membrane, 
and  to  pump  on  the  contents  of  the  capillaries  and  lacteals  carrying 
the  absorbed  foodstuffs.  These  movements  probably  correspond  to 
the  gentle,  swavang,  "  pendulum  "  movements  which  have  been 
observed  by  the  method  of  direct  observation.  The  pendular  move- 
ments" are  accompanied  by  rhythmical  contractions  at  a  rate  of  twelve 


Fig.  212. — Pe^'dhlum  Movements  of  the  Iktestin'e  inhibited  by  Excitation 
OF  the  Splakcknic  Nekve  during  the  Peeiod  marked  by  the  White  Line. 
(Starling.) 


to  thirteen  per  minute.  These  movements  are  not  affected  by  the 
application  of  nicotine  or  cocaine.  The}'  appear,  however,  to  be 
dependent  upon  the  integrity  both  of  the  muscle  and  the  nervous 
plexus,  since  strips  of  the  intestinal  longitudinal  muscle  devoid  of 
an}'  nervous  plexus  do  not  perform  these  movements.  They  are 
inhibited  by  excitation  of  the  splanchnic  nerve  (Fig.  212).  The 
separated  muscle  has  no  refractory  period,  gives  summated  con- 
tractions, can  be  tetanized,  and  gives  no  rhythmic  response  to 
continued  stinndation.  Preparations  of  muscle  with  Auerbach's 
plexvis  attached  possess  a  refractory  period  to  weak  stimulation, 
-cannot  be  summated  or  tetanized,  and  exhibit  rhythmic  contrac- 
tions to  continued  stimulation. 

The  food  is  moved  onward  in  the  intestine  by  means  of  a  peristaltic 
wave,  which  may  be  observed  in  two  forms — (1)  a  slowly  advancing 
contraction  (2  to  3  centimetres  per  minute),  which  moves  the  nutri- 
ment but  a  slight  distance  ("  true  peristalsis  "):  and  (2)  a  swift  move- 


THE  MECHANICAL  FACTORS  OF  DIGESTION  417 

nient,  passing  over  the  entire  length  of  inte-jtine  in  about  a  minute, 
and  tending  to  void  it  of  its  contents  (so-called  "  rushing  peristalsis  "). 
■'  True  peristalsis  "  involves  a  contraction  of  the  gut  above  the 
contents,  and  a  relaxation  below  them  (Fig.  213).  To  study  this,  a  small 
balloon  may  be  introduced  into  the  gut,  and  connected  with  a  recording 
tambour.  The  animal  is  immersed  in  a  bath  of  warm  Ringer's  solution 
before  exposure  of  the  gut.  A  stimulus  applied  locally  above  a  bolus 
introduced  into  the  gut  will  cause  relaxation  of  the  wall  in  the  region 
of  the  bolus,  whereas  pinching  below  the  bolus  induces  a  strong  con- 
traction of  the  gut  upon  the  bolus  itself.  Peristalsis  is  dependent 
upon  the  loaal  nervous  mechanism  of  the  small  intestine,  and  is 
abolished  by  painting  the  wall  with  cocaine  or  nicotine.  It  con- 
tinues, however,  when  all  connections  with  the  central  nervous 
s3\stem  are  destroyed  (Fig.  214). 


Fig.    213.  —  Diagkam    showing    Peei- 
STALTic  Contraction  of  Intestine. 


Fi:i.  21-i.  —  Pho'imkku'Ii  of  a  Peri- 
STAiiTic  Wave  of  Small  Intestine 
pushing  Material  into  the  Colon. 
(Cannon.) 

"Peristaltic  rush"  is  probably  of  the  nature  of  true  peristalsis, 
and  occurs  particularly  when  it  is  necessary  to  rid  the  gut  of  irritating 
substances.  It  is  usually  stated  that  antiperistalsis  does  not  occur 
in  the  small  intostine,  and,  so  far,  has  not  been  observed,  but  clinical 
evidence  points  to  the  fact  that  it  occurs.  For  instance,  nutrient 
enemata  containing  egg  administered  jje/'  rectum  have  been  observed 
shortly  afterwards  flowing  from  a  duodenal  fistula.  In  cases  of 
intestinal  obstruction,  also,  the  vomit  may  become  of  a  faecal  nature 
— .so-called  ''faecal  vomiting." 

The  movements  of  the  small  intestine  are  affected  by  the  vagus 
and  sympathetic  nerves.  Peripheral  stimulation  of  the  vagus  causes 
an  initial  inhibition  of  the  whole  small  gut,  followed  by  increased 
contractions.  Stimulation  of  the  .splanchnic  nerves  causes  inhibition 
of  the  •  movements,  with  relaxation  of  both  muscular  coats.  The 
si^lanchnics  probably  exert  a  tonic  inhibitory  influence,  which  may 
become  excessive  in  abdominal  and  nervous  disorders.  The  time 
usually  occupied  by  the  food  in  traversing  the  22 -i  feet  of  small 
intestine  is  about  six  hours. 

27 


418 


A  TEXTBOOK  OF  PHYSIOLOGY 


The  ileo-colic  sphincter  is  normally  closed,  but  relaxes  before  an 
advancing  peristaltic  wave,  and  admits  the  food  into  the  large  intes- 
tine. Stimulation  of  the  splanchnic  nerve  produces  a  strong  contrac- 
tion of  this  sphincter.     Vagal  stimulation  has  no  effect  on  it. 

The  Movements  o£  the  Large  Intestine. — The  ileo-colic  sphincter 
opens  before  the  wave  of  peristalsis  when  this  reaches  the  terminal 
part  of  the  ileum,  and  the  ileal  contents  are  then  passed  on  into  the 
large  intestine.  The  ilrst  effect  of  their  advent,  observed  by  the 
skiagraph  method,  is  to  bring  about  antiperistaltic  movements  of 
the  ascending  colon.  These  start  from  the  junction  of  the  ascending 
and  transverse  colon,  and  force  the  food  down  into  the  caecum,  the 
ileo-colic  sphincter  being  now  closed.  The  waves  of  antiperistalsis 
occur  at  about  the  same  rate  as  those  of  the  stomach  (five  to  six  a 


Fig.  21">. — Diagram  to  show  the  Hours  which  elapse  after  a  Bismuth  Meal 

BEFORE  the  DIFFERENT  PaRTS  OF  THE  COLON  ARE  REACHED,       (Hurst.) 


minute),  and  the  period  of  antiperistalsis  lasts  on  an  average  about 
four  to  five  minutes,  and  recurs  after  varying  lengths  of  time,  generally 
from  ten  to  fifteen  minutes.  Antiperistalsis  is  the  predominating 
movement  of  the  first  part  of  the  colon.  As  a  result,  the  contents 
are  retained  there  for  a  considerable  time,  generally  about  two  hours, 
and  the  absorption  of  water  is  greatly  facilitated.  It  is  probable  that 
the  arrival  of  new  material  ui  the  large  intestine  pushes  on  the  contents 
beyond  the  antiperistaltic  area,  but  it  is  possible  that  from  time  to 
time  a  wave  of  true  peristalsis  helps  to  push  on  the  contents  into  the 
transverse  colon. 

Thus  far,  true  waves  of  antiperistalsis  have  not  been  observed 
in  man,  but  there  is  reason  to  think  that  such  take  place  in  him  no 
less  than  m  animals.  It  is  known  that  nutrient  enemata  are  quickly 
passed  back  into  the  ascending  colon,  and,  when  large,  may  j)ass 
thence  into  the  small  intestine. 


THE  MECHANICAL  FACTORS  OF  DIGESTION 


419 


As  the  contents  pass  along  the  large  intestine,  they  become  sepa- 
rated into  semi-solid  globular  masses.  In  the  transverse  and  descending 
colon,  antiperistalsis  is  very  slight,  and  the  predominating  movement 
is  a  slow  true  peristalsis. 

The  pelvic  colon  down  to  the  acute  flexure  {P.R.F.,  Fig.  216)  just 
above  the  rectum  is  the  storehouse  of  fseces.  Occasional  long- 
continued  waves  of  contraction  force  the  contents  well  down  into  the 
pelvic  colon,  and  eventually,  by  rendering  the  angle  of  flexure  less 
acute,  force  some  of  the  contents  into  the  rectum.  This  leads  to  a 
desire  to  defjecate.  These  long-drawn  movements  are  subject  to  the 
control  of  a  centre  in  the  lumbar  spinal  cord.  They  are  probably 
evoked  by  distension  of  the  gut  stimulating  the  afferent  nerve- 
endings  in  the  pelvic  nerve.  The  times  taken  for  the  passage  of  food 
through  the  large  intestine  in  man  are  marked  in  hom-s  in  Fig.  215. 


Fig.  216. — Diagram  of  Rectum (Ilur.^t), showing Pelvi-Rectal  Flexure  (P.R.F.); 
F.ECES  IN  GoLO-s  {F.);  Houston's  Valve  (V.H.);  Rectal  Ampulla  {R.A.); 
Levator  Ani  {L.A.);  Internal  Sphincter  {I.S.A.);  External  Sphincter 
(E.S.A.). 


Defsecation. — To  stimulate  the  desire  to  defaecate,  the  distension 
of  the  empty  rectum  by  a  small  amount  of  fseces  is  sufficient  (Fig.  216). 
Such  an  amount  is  normall}'  passed  into  the  rectum  from  the  pelvic 
colon  as  the  result  of  peristaltic  action  refiexly  induced  by  the 
taking  of  food  on  an  empty  stomach.  Hence  the  desire  to  defsecate 
after  breakfast.  The  result  maj^  also  be  brought  about  by  physical 
exercises  and  a  cold  bath,  or  even  by  the  muscular  exercise  involved 
in  dressing. 

That  it  is  the  distension  of  the  rectum,  and  not  the  actual  contact 
of  the  faeces  with  the  rectal  mucous  membrane,  which  leads  to  the 
desire  to  defsecate  has  been  shown  by  inflating  the  rectum  wuth  a 
balloon.  If  the  desire  be  not  obeyed,  the  w^all  of  the  rectum  relaxes, 
the  intrarectal  pressure  falls,  and  the  desire  passes  away,  only  to 
recur  when  the  intrarectal  pressure  is  again  raised  by  the  advent  of 
fseces.     Defaecation  may  sometimes  be  started   by  voluntary  effort. 


420  A  TEXTBOOK  OF  PHYSIOLOGY 

The  glottis  is  closed  after  an  inspiration,  and  the  action  of  the  dia- 
phragm and  the  abdominal  muscles  forces  fseces  past  the  pelvi-rectal 
flexure. 

When  the  desire  to  defsecate  is  obeyed,  the  rectum  is  further  dis- 
tended by  fseces  bj^  raising  the  intra-abdominal  pressure  in  the  above- 
mentioned  fashion.  The  contraction  of  the  diaphragm  after  inspira- 
tion is  the  most  effective  agent  in  raising  the  abdominal  pressure. 
This  is  aided  by  the  crouching  posture  assumed.  The  contraction 
of  the  abdominal  muscles,  the  flexion  of  the  spine,  the  pressure  of 
the  thighs  against  the  belly  wall,  and  the  contraction  of  the  muscles 
of  the  pelvic  floor,  serve  to  sustain  the  increased  abdominal  pressiu'e. 

When  the  rectum  is  sufficiently  distended,  there  ensue  strong 
jjeristaltic  contractions  of  the  whole  colon,  which,  in  conjunction 
with  continued  contraction  of  the  abdommal  muscles  and  the  relaxa- 
tion of  the  anal  sphincters,  force  the  fseces  out,  the  final  expulsion 
being  aided  by  the  contraction  of  the  levator  ani  muscles,  which 
draw  the  anal  canal  upwards,  and  also  constrict  the  lowest  part  of 
the  rectum. 

Although  normally  a  voluntary  process,  defsecation  may  take  place 
in  involuntary^  fashion  when  the  rectum  becomes  sufficiently  distended 
with  fseces.  The  fseces  may  become  hard  and  dry  when  the  voluntary 
aids  to  defsecation  are  lacking,  and  it  may  be  difficult  to  expel  the 
hardened  masses. 

Defsecation  is  stated  to  be  under  the  control  of  a  centre  in  the 
lumbo-sacral  region.  The  effector  nerves  run  to  the  rectum  in  the 
sympathetic  system  by  way  of  the  inferior  mesenteric  ganglion  and  the 
hypogastric  nerves,  and  in  the  pelvic  nerves  (nervi  erigentes)  from 
the  third  sacral  nerve  to  the  inferior  hsemorrhoidal  plexus.  Stimula- 
tion of  both  sets  of  nerves  leads  to  contraction  of  the  rectum.  It  is 
probable,  however,  that  the  jDclvic  nerves  are  the  more  effective,  and 
that  the  hsemorrhoidal  plexus  may  be  regarded  as  a  subordinate 
centre  for  defsecation,  since  a  somewhat  incomplete  reflex  act  of 
defsecation  can  occur  in  the  dog  even  when  the  lumbo-sacral  cord  is 
destroyed.  The  levator  ani  and  the  external  sphincter  muscles  are 
supplied  by  the  fourth  sacral  nerve.  The  action  of  these  muscles, 
controlled  from  the  spinal  centre,  is  essential  for  the  complete  reflex. 
The  lumbosacral  centre  is  under  control  of  excitatory  or  inhibitory 
impulses  from  the  cerebrum,  and  when  this  control  is  withdrawn,  as 
after  division  of  the  spinal  cord,  incontinence  of  fseces  results. 


BOOK    \  11 

CHAPTER  L 

SPECIAL  METABOLISMS 

Absorption. — The  absorption  of  the  foodstuffs  takes  place  cliiefly 
ill  the  small  intestine,  and  particularly  in  the  middle  and  lower  portions. 
Considerable  discussion  has  taken  place  as  to  the  mechanism  of  this 
absorption,  and  at  first,  when  physiological  science  was  young,  such 
comparatively  simple  processes  as  filtration,  diffusion,  and  osmosis, 
were  evoked  to  explam  it.  It  is  now  generally  conceded  that  it  is 
controlled  by  unknown  forces  of  the  hving  cells  lining  this  part  of 
the  alimentary  canal.  The  chief  evidence  iipon  which  this  conclu- 
sion is  based  may  be  summarized  as  follows : 

1.  If  the  mucous  membrane  be  removed  from  a  piece  of  intestine, 
the  absorptive  power  is  abolished. 

2.  Poisoning  the  cells  by  washing  the  mucous  membrane  with 
a  dilute  solution  of  sodium  fluoride,  or  scalding  them,  destroys  the 
absorptive  process. 

3.  The  absorption  of  water  from  the  intestine  takes  place  much 
more  quickly  than  does  diffusion  through  a  dead  membrane. 

4.  The  rate  of  absorption  of  the  products  of  digestion  is  too  rapid 
to  be  explained  by  simpler  physical  processes.  Peptone  is  absorbed 
from  the  intestine  more  readily  than  dextrose;  on  the  other  hand, 
dextrose  diffuses  through  parchment  quicker  than  peptone.  Sodium 
sulphate  is  not  readily  absorbed  from  the  intestine,  yet  it  readily 
diffuses  through  parchment. 

5.  The  absorption  of  water,  saline  and  other  salts  (magnesium 
sulphate)  is  attended  b}-  a  greatlj^  increased  consumption  of  ox3'gen 
b\'  the  intestinal  cells,  showing  that  absorption,  even  of  water,  is  an 
active  process  (see  p.  321). 

6.  The  animal's  own  serum,  identical  in  composition  and  isotonic 
with  the  blood,  is  complet-elj'  absorbed  if  introduced  within  a  loop  of 
intestine. 

7.  Certain  products  of  digestion,  such  as  those  of  fat,  and  probably 
of  protein,  are  altered  during  their  passage  through  the  cells  of  the 
mucous  membrane. 

The  Metabolism  of  Protein. — In  the  intestine  the  protein  is  broken 
down  into  proteoses,  peptones,  polypeptides,  and  amino-acids.     There 

421 


422  A  Tf]XTB()()K  OF  PHYSIOLOGY 

is  considerable  difference  of  ojjinion  as  to  how  far  it  is  necessary  for 
piotein  to  be  broken  down  before  it  can  be  absorbed.  It  depends  to 
a  certain  extent  upon  the  nature  of  the  protein.  Thus,  casein,  edestin, 
acid  metaprotein,  intro(htced  directly  into  the  small  intestine,  are  not 
absorbed  at  all;  egg-albumin,  serum-albumin,  are  absorbed  slightly 
(about  20  per  cent.);  and  alkali  metaprotein  considerably  (70  per 
cent.).  Undoubtedly,  these  proteins  are  considerably  modified,  but 
to  what  degree  is  uncertain,  before  reaching  the  blood.  Proteoses 
and  pei^tones  appear  to  be  readil}^  absorbed  from  the  small  intestine, 
but  it  is  doubtful  whether  they  reach  the  blood  as  such.  When  they 
do,  it  is  only  in  such  minute  cpiantities,  difficult  of  detection,  and  out 
of  all  proportion  with  the  amount  actually  absorbed.  It  is  probable 
that  the  absorbed  proteoses  and  peptones  are  converted  into  amino- 
acids  by  the  cells  of  the  wall  of  the  intestine.  It  is  known  that  the 
cells  of  the  mucous  membrane  are  very  rich  in  erepsin.  It  has  been 
shown  that  proteoses  and  peptones  disappear  from  the  lumen  of  an 
isolated  loop  of  intestine  which  is  perfused  with  defibrinated  blood, 
and  that  no  peptones  can  be  detected  in  the  blood.  The  amino-acids 
formed  as  the  result  of  digestive  processes  within  the  lumen  are 
also  absorbed.  In  this  process  it  is  suggested  the  leucocj^tes  present 
in  the  mucous  membrane  in  some  Avay  play  an  important  part. 

The  question  now  arises,  What  becomes  of  these  amino-acids, 
which  either  pass  into  or  are  formed  within  the  intestinal  wall  ?  It 
is  a  very  complex  one,  and  at  present  by  no  means  fully  eluci- 
dated. 

Before  attempting  to  consider  the  t^^o  main  hypotheses,  it  is  well 
to  grasp  the  general  idea  luiderlying  the  processes  of  protein  meta- 
bolism. The  proteins  of  the  food  are  necessary  to  the  life  of  the 
animal.  Without  a  certain  amount  of  protein  in  the  diet,  the  animal 
slowly  but  surely  dies.  This  jDrotein  is  necessary  for  the  repair  and 
growth  of  tissue  proteins.  Two  points  are  to  be  observed  in  this 
connection:  first,  that  the  animal's  own  proteins,  which  recpiire 
building  afresh,  differ  in  constitution — the  protein  of  the  muscles,  for 
instance,  differs  from  the  protein  of  the  kidney  substance;  secondly, 
the  ingested  proteins,  from  which  these  different  proteins  are  to  be 
replaced,  differ  even  more  widely  in  constitution.  This  is  especially 
the  case  when  the  ingested  protein  is  of  vegetable  origin.  It  is  easily 
understood  that  only  a  portion  of  such  ingested  proteins  may  be 
of  service  to  the  animal  in  rebuilding  its  particular  proteins.  Such 
portion  may  be  considerable  or  inconsiderable,  according  to  the  nature 
of  the  protein  taken  in.  The  process  of  protein  digestion  may  be 
compared  to  house-breaking,  the  process  of  protein  anabolism  to  the 
reconstruction  of  a  number  of  new  houses  from  the  bricks  of  the 
demolished  houses.  Certain  of  the  building-stones  are  of  great 
value  in  rebuilding  the  new  houses,  others  are  of  partial  vahie, 
others  are  of  little  or  no  value  at  all.  In  protein  anabolism,  the 
amino-acids  are  such  building-stones.  Some  are  of  great  value — 
precious — others  appear  to  be  of  lesser  value. 

It  has  been  shown  by  experiment  that  an  animal  can  live  when 


SPECIAL  METABOLISMS  423 

fed  on  the  amino-acid  products  of  a  meat  digest.  If,  however,  it  bo 
fed  on  selected  amino-acids,  it  is  found  that  on  some  it  can  stiU  Hve, 
on  others  it  gradually  starves.  For  example,  the  monamino -acids 
by  themselves  do  not  support  life,  neither  do  the  diamino-acids.  On 
the  other  hand,  the  addition  of  ringed  amino-acids,  such  as  phenyl- 
alanin,  tyrosin,  and  tryptophan,  has  been  found  to  support  life. 
So,  too,  proteins  which  do  not  contain  these  last  amino-acids,  such 
as  gelatin  and  zein,  fail  to  keep  an  animal  alive.  The  addition  of 
ringed  amino-acids  to  such  proteins  renders  them  more  life-supporting. 
From  this  point  of  vicAV,  it  is  interesting  to  note  that  Nature  provides 
the  young  growing  animal  with  a  protein — caseinogen — esjiecially 
rich  in  both  tjTosin  and  tryptophan. 

The  two  hypotheses  held  in  regard  to  the  metabolism  of  protein 
differ  (1)  as  to  the  place  of  selection  of  the  building-stones — the 
amino-acids;  (2)  as  to  the  form  in  which  the  material  for  reconstruc- 
tion is  presented  to  the  tissues. 

According  to  one  view,  the  amino-acids  pass  as  such  into  the  portal 
blood.  It  is  claimed  that  their  j^resence  there  can  be  demonstrated 
by  special  indicators,  such  as  /^-naphtha-sulphonic  acid.  The  gut  of 
the  octopus  is  natural!}^  suspended  in  a  bath  of  blood,  and  amino- 
acids  are  said  to  appear  in  this  blood  when  protein  is  digested  in  the 
gut.  The  absorbed  amino-acids  are  then  taken  in  the  portal  blood 
to  the  liver,  which  controls  their  passage  into  the  general  circulation 
according  to  the  needs  of  the  body.  Each  amino-acid  has  its  own 
special  metabolism. 

It  has  been  shown  that,  if  such  bodies  as  glycin,  alanin,  arginin, 
be  perfused  through  the  isolated  liver,  the  urea  content  of  the  blood 
leaving  the  liver  is  increased.  These  amino-acids  are  only  of  partial 
value  to  the  body.  The  nitrogenous  moiety  contained  in  them  may 
perhaps  be  regarded  as  valueless,  for  it  is  rapidly  excreted.  These 
amino-acids  are  first  deaminized,  the  ammonia  split  off  being 
converted  into  urea,  while  the  non-nitrogenous  moiety  remains. 
There  is  reason  to  suppose  that  this  is  first  converted  into  a  lower 
fatty  acid,  which  then  becomes  converted  into  dextrose,  a  conversion 
of  great  importance  in  carbohydrate  metabolism.  In  the  case  of 
alanin,  for  example,  the  process  may  be  represented  as  follows: 

CH3CH.NH.COOH  +  H.0  -  CH3CHOH.COOH  +  NH, 

Alanin  Lactic  acid 

2CH3CHOH.COOH  ^CeHiaOe 

(CsHgOs)  Dextrose 

The  fate  of  the  monamino-dicarboxjdic  acids,  such  as  aspartic  and 
glutamic  acids,  is  probably  the  same.  The  diamino-acids,  such  as 
arginin  and  lysin,  together  with  the  closely  allied  histidin,  are  probably 
also  broken  down  into  nitrogenous  and  non-nitrogenous  moieties, 
the  nitrogenous  being  mainly  excreted  from  the  body  in  the  form  of 
iirea,  the  non-nitrogenous  part  being  possibly  converted  into  dextrose. 

It  is  not  yet  knoAvn  sufficiently  well  what  exactly  happens  to 


424 


A  TEXTBOOK  OF  PHV.SIOLOGY 


tyrosin  and  tryptophan.  These  are  of  great  vahie  to  the  body,  and 
in  the  liver  they  are  probably  modified  into  a  form  available  for 
the  tissues.  It  is  certain  that  they  are  not  rapidly  destroyed,  and 
their  nitrogenous  moiety  excreted  from  the  l:ody  in  the  form  of 
urea.  If  a  non-nitrogenous  moiety  be  split  off,  it  may  give  rise  to 
dextrose. 

Cystin  (diamino-di-thio-lactic  acid)  is  broken  down  in  the  liver,  the 
sulphur  moiety  giving  rise  in  part  to  taurin  and  in  part  to  inorganic 
sidphates.  It  is  possible  that  the  carbon-containing  lactic  acid  portion 
may  give  rise  to  dextrose. 

The  fate  of  the  other  bodies  is  not  sufficiently  elucidated  to  be 
mentioned  here,  but,  according  to  this  hypothesis,  they  also  each 
undergo  their  own  special  metabolism  in  the  liver.  The  fact  that 
there  occur  certain  inherited  but  very  rare  errors  of  metabolism, 
such  as  alkaptonuria  and  cystinuria,  is  held  to  lend  support  to  the 
hypothesis,  which  may  be  represented  diagrammatically  as  follows; 


Portal, 
Blood  ' 


Aninioiiiuns 
carbonate- 

(and 
carbamate) 


Products  of  Protein   Digest  ion. 


Mouamiao 

nionocar- 

boxylic 

acids, 

glycin, 

alanin, 

leucin 


Liver    >     Urea 


/ 

Urea 


Monamino 

dicar- 

boxylic, 

glutamic, 

aspartic 


\ 


Diamiiio- 
acids, 

arginin, 
lysin 


Dextrose      Urea 


;  Dex- 
trose 


Phenyl 

alanin, 

tyrosin, 

tryptophan 


Prepared 
for  tissues 


Cystin 


Taurin  Inorganic 
and  sulph- 

?  dextrose       ates 


An  objection  to  this  hypothesis  is  that  it  is  not  quite  clear  from 
what  source  the  body  derives  all  the  bricks  necessary  for  the  rebuilding 
of  its  proteins.  In  these  proteins,  amino-acids,  such  as  alanin  and 
gtycin,  are  incorporated,  and  it  is  by  no  means  clear  from  what  source 
such  amino-acids  come. 

According  to  the  second  hypothesis,  the  amino-acids  do  not  pass 
from  the  intestine  into  the  blood.  It  is  said — (1)  that  their  presence 
there  has  never  been  conclusively  demonstrated;  (2)  that  if  the  circu- 
lation be  confined  to  the  intestinal  wall  and  pancreas,  heart,  lungs, 
and  muscles  of  respiration,  the  blood  contains  no  proteoses,  peptones, 
or  amino-acids.  It  is  therefore  held  that  the  amino-acids,  during 
their  passage,  are — (1)  either  synthesized  into  protein,  so-called 
"  plasma  protein  " ;  or  (2)  deaminized.  with  the  formation  of  ammonia. 

The  ''  plasma  protein  ""  is  held  to  be  a  protein  f-o  built  that  all  the 
cells  of  the  body  can  abstract  from  it  just  the  bricks  they  desire  to 
rebuild  their  own  particular  protein.  In  building  up  this  plasma 
protein,  all  the  amino-acids  of  digestion  are  not  used.  Many  are  in 
excess — such,  for  example,  as  glutamic  and  aspartic  acids,  when 
plant  proteins  have  been  ingested.  These  are  deaminized  in  the 
intestinal  wall,  and  the  ammonia  thus  formed  passes  to  the  liver 
as  ammonium   carbonate  or  carbamate,  there    becoming  converted 


SPECIAL  METABOLISMS  425- 

into  urea.  It  may  be  assumed  in  this  case  that  the  non-nitrogenous, 
moiety  formed  as  the  result  of  deaminization  is  taken  to  the  liver, 
being  there  converted  into  dextrose  and,  finally,  in  part  to  glycogen 
(see  next  page). 

In  support  of  this  view,  it  has  been  sho«n  that  a  dog  may  be  fed 
on  digested  protein  (amino -acids),  and  kept  in  nitrogen  equilibrium, 
even  when  its  portal  blood  is  short-circuited  from  the  liver  by  an 
Eck's  fistula  (see  p.  448).  The  blood  coming  from  the  intestine  during 
periods  of  digestion  is  stated  to  be  demonstrably  richer  in  protein  of 
a  globulin  nature. 

This  view  may  be  regarded  as  a  modification  of  older  ones  concern- 
ing protem  metabolism.  According  to  these,  serum  albumin  and 
serum  globulin  were  formed  in  the  intestinal  wall,  and  passed  into  the 
portal  blood.  The  views  differed  as  to  the  subsequent  fate  of  these 
proteins.  According  to  one  view,  all  protein  was  subsequent^  built 
up  into  living  protoplasm  before  it  was  destroyed:  according  to  the 
other,  some  of  the  protein,  called  "  tissue  protein,''  was  built  up  into 
protoplasm ;  the  remainder  was  not  so  built  up,  but  served  as  a  source 
of  energ}^ — the  so-called  ''  circulating  protein."'  The  speed  with  which 
an  increased  intake  of  nitrogen  appears  in  the  urine  as  urea  is  against 
the.  view  that  such  nitrogen  has  been  built  up  into  protoplasm.  On 
the  other  hand,  when  we  consider  the  rapidity  Avith  which  protoplasm 
grows — e.g.,  yeast  multiplying — we  cannot  put  such  a  possibility  out 
of  court.  As  to  whether  any  of  the  protein  formed  in  the  intestinal 
mucous  membrane  acts  solely  as  circulating  protein,  there  is  at 
present  no  evidence. 

Much  more  work  is  required  upon  this  intricate  and  difficult 
subject.  Up  till  now,  there  can  be  said  to  be  no  established  theory 
of  protein  metabolism,  onh'  two  tentative  hypotheses,  of  which  the 
second,  given  above,  appears  the  more  probable — namely,  that  a 
special  plasma  protein  is  s^^lthesized  in  the  intestinal  mucous  mem- 
brane, containing  all  the  necessarj^  bricks  for  the  rebuilding  of  the  tissue- 
proteins.  Excess  of  digested  protein  is  deaminized  in  the  intestinal 
mucous  membrane,  and  the  ammonia  thus  formed  is  short-circuited 
from  the  body  as  urea. 

Protein,  or  the  amino-acids  split  from  it,  increases  the  rate  of 
metabolism  and  heat-production  stimulating  the  cells  of  the  body  to 
activity,  having  a  specific  dynamic  action  greatev  than  carbohydrate^ 
and  much  greater  than  fat.  This  stimulating  action  is  traced  to  oxy- 
or  keto-acids,  the  non-nitrogenous  moiety  of  protein  metabolism. 


CHAPTER  LI 

THE  METABOLISM  OF  CARBOHYDRATE 

The  digestive  processes  reduce  the  carbohydrates  to  the  mono- 
saccharides— dextrose,  levulose,  and  galactose — the  chief  of  which 
is  dextrose,  since  cane-sugar  and  lactose  normally  form  but  an  in- 
significant part  of  the  diet.  Dextrose  is  absorbed  unchanged  into 
the  portal  blood  by  the  activity  of  the  intestinal  cells.  The  portal 
blood  therefore  becomes  charged  with  sugar  above  the  content  nor- 
mally present  in  blood.  The  excess  of  sugar  acts  as  a  stimulus  to  the 
liver,  which  abstracts  the  excess,  so  that  the  blood  leaves  that  organ 
supplied  with  about  0-01  per  cent,  of  sugar — the  normal  content. 
The  diffusible  sugar  retamed  by  the  liver  is  elaborated  into  the 
non-diffusible  colloid  glycogen,  and  stored  as  such.  There  has  been 
much  controversy  as  to  the  ultimate  fate  of  the  glycogen.  The 
generally  accepted  view  is  that  there  is  a  reversible  ferment  action  in 
the  liver.  The  ferment  converts  sugar  into  glycogen  when  the  portal 
blood  comes  laden  with  sugar,  and  glycogen  into  sugar  when  the 
blood  comes  to  the  liver  impoverished  in  sugar. 

(1)  Dextrose  (2)  Dextrose 

t  1  I 

Glycogen  (ilycogen 

/\ 
Fat     Carbohydrate  portion 
of  i^rotein 

Another  view  is  that  glycogen  is  never  again  converted  to  dextrose 
in  life,  but  is  elaborated  into  fat,  or  it  may  possibly  be  combined  to 
the  proteins  as  a  carbohydrate  moiety.  The  balance  of  evidence  is 
in  favour  of  the  first  view. 

The  glycogen  quickly  disappears  from  the  liver  after  death,  and 
dextrose  is  formed.  It  is  also  probable  that  this  j^rocess  takes  place 
in  life,  and  not  only  post-mortem.  There  seems  to  be  good  evidence, 
too,  that  when  blood,  with  a  low  dextrose  content,  is  perfused  through 
the  liver,  it  acquires  dextrose.  It  is  true  that  glycogen  may  give 
rise  to  fat  under  certain  conditions,  but  the  available  evidence  indicates 
that  such  fat,  when  metabolized  within  the  body,  is  again  broken 
down  to  glycogen  and  dextrose  (see  p.  440).  Leaving  the  liver,  the 
dextrose  passes  in  the  blood  to  the  heart,  and  thence  to  the  system 
generally,  to  be  katabolized. 

The  Katabolism  of  Dextrose. — Three  views  are  held  as  to  the  manner 
in  Avhich  dextrose  is  normally  broken  down  within  the  body.      Accord- 

426 


THE  METABOLISM  OF  CARBOHYDRATE  427 

ing  to  one  view — the  least  accepted— sugar  is  broken  down  by  the  body 
in  the  same  way  as  it  is  by  the  yeast  cell — that  is,  through  inter- 
mediary stages  to  alcohol,  and  then  to  carbon  dioxide  and  water. 
There  is  some  proof  of  this  taking  place  in  plants,  but  the  evidence 
for  such  a  katabolism  in  the  animal  tissues  is  scanty. 

According  to  a  second  view,  dextrose  breaks  down  to  glycuronic 
acid,  and  then  to  carbon  dioxide  and  water.  Until  recently,  this 
view  has  received  wide  acceptance.  Gl^^curonic  acid  is  closely  related 
to  dextrose,  and  is  found  in  the  blood  and  in  the  urine. 

All  the  recent  evidence,  however,  tends  to  show  that  dextrose  is 

normally  broken  down  to  lactic  acid,  and  then  to  carbon  dioxide  and 

water.     Tiie  muscles  are  the  chief  seat  of  dextrose  katabolism.     In 

the  absence  of  oxygen,  lactic  acid  is  not  broken  down,  and  may  be 

detected  in  the  urine  and  in   the   sweat — e.g.,  after   hard   muscular 

exercise,  or  when  an  excised  muscle  is  tetanized  in  the  absence  of 

oxygen. 

(1)  Dextrose  (2)  Dextrose  (3)  Dextrose 

I  I  I 

Alcohol  Glycuronic  acid  Lactic  acid 

/\  /\  /\ 

CO.     H.O  COj    H2O  CO2    H.2O 

We  must  now  inquire  with  a  little  more  detail  into — (1)  the  glyco- 
genic function  of  the  liver ;  (2)  the  conditions  necessary  for  the  breaking 
down  of  sugar  in  the  body. 

The  Glycogenic  Function. — By  this  function,  the  supply  of  dextrose 
in  the  blood  is  regulated,  and  kept  at  a  constant  amount  (0-01  per 
cent.)  adequate  to  the  needs  of  the  body.  When  the  supply  of  sugar 
in  the  blood  is  large,  as  at  the  height  of  digestion,  the  dextrose  is 
abstracted  and  stored  as  glycogen;  when  the  supply  of  sugar  in  the 
blood  is  poor,  then  glycogen  is  converted  into  dextrose,  and  passes 
into  the  blood.  Normally,  the  liver  restrains  any  surplus  supply 
of  dextrose  from  reaching  the  systemic  blood,  and  causing  what  is 
termed  a  hypergljjccemia.  When  hypergtycaemia  results,  the  kidneys 
immediately  eliminate  the  excess  sugar,  and  dextrose  appears  in  the 
urine,  forming  the  condition  known  as  glycosuria.  The  efficiency  with 
which  the  liver  performs  this  function  is  judged  by  the  sugar 
content  of  the  blood  and  urine. 

As  a  general  rule,  the  urine  o\\\\  is  tested,  but  in  special  conditions 
the  sugar  content  of  the  blood  is  also  tested,  for  a  small  excess  of  sugar 
may  exist  in  the  blood  Avithout  causing  glycosuria.  Moreover,  all 
glycosurias  are  not  due  to  inefficiency  of  the  liver  and  hyperglyesemia. 
To  estimate  the  amount  of  dextrose,  the  blood  is  laked  and  diluted, 
shaken  with  colloidal  ferric  hydroxide  (dialyzed  iron),  and  then  a 
small  amount  of  sodium  sulphate  added.  By  this  means  the  blood- 
proteins  are  precipitated.  The  sugar  in  the  filtrate  may  then  be 
estimated  Iw  Bertrand's  process  (see  p.  468). 

The  Sources  of  Glycogen — Carbohydrate. — That  glycogen  is  largely 
formed  from  dextrose  may  be  experimental^  proved  by  starving 
a  rabbit,  and  subsequently  feeding  it  with  carrots  —  a  diet  rich  in 


428  A  TEXTBOOK  OF  PHYSIOLOGY 

carbohydrates.  During  starvation,  the  glycogen  content  of  the  Hver 
falls  very  low;  during  feeding  with  abundant  carbohydrate,  the  liver 
content  becomes  very  high — e.g.,  18  per  cent,  of  the  weight  may  be 
glycogen.  As  already  stated,  at  the  height  of  digestion  the  blood 
leaving  the  liver  is  poorer  in  dextrose  than  the  blood  reaching  it. 
Perfusion  experiments  also  show  that  dextrose  is  abstracted  by  the 
liver  from  defibrinated  blood  containing  an  excess  of  this  sugar. 
Levulose  also  gives  rise  to  glycogen;  galactose  gives  but  little. 
Pentoses  do  not  ajjjDcar  to  be  direct  glycogen-formers. 

Protein. — Opinions  differ  widely  as  to  whether  glycogen  arises 
from  proteins.  As  the  result  of  direct  feeding  experiments,  many 
observers  claim  that  feeding  with  proteins  increases  the  amount  of 
glycogen  in  the  liver,  even  when  proteins  are  fed  which  yield  no  carbo- 
hydrate group,  such  as  caseinogen  and  gelatin.  Other  observers 
contend  that  i^roteins  are  glycogen-sparers  rather  than  glycogen- 
formers;  that,  under  such  feeding  conditions,  the  glycogen  content 
of  the  liver  is  increased,  because  dextrose  is  spared  in  the  bod}^  when 
there  is  an  abundance  of  protein  fed.  The  fact  that  glycogen  does 
not  disappear  entirely  from  the  body  even  during  long-continued 
starvation  would  appear  to  indicate  that  proteins  may  serve  as  a 
source  of  glycogen.  The  conversion  of  protein  into  glycogen  probably 
takes  place  by  the  deaminization  of  amino-acids,  the  non-nitrogenous 
moiety  of  such  acids  becoming  converted  into  dextrose,  and  thence 
to  glycogen.  Perfusion  experiments  have  shown  that  glycin,  alanin, 
asparagin,  act  as  precursors  of  glycogen.  It  seems  probable  that 
more  sugar  and  glycogen  arise  from  protein  than  is  generally  recognized. 

Fat. — In  regard  to  the  products  of  the  digestion  of  fat,  there  is 
no  evidence  to  show  that  glycogen  arises  from  the  fatty  acids.  On 
the  other  hand,  there  is  evidence  to  show  that  glycerine  gives  rise  to 
dextrose,  and  may  possibly  give  rise  to  a  small  amount  of  glycogen. 

CH,OH  CH.,OH 

I     "  I    " 

CHOH ^  (CHOH), 

I  I 

CH^OH  CHO 

Glycerine  Dextrose 

It  is  possible,  also,  that  under  certain  conditions  fat  stored  in  the 
liver  becomes  broken  down  to  form  glycogen.  Such  fat,  however, 
has  been  previously  built  up  in  the  organism  from  dextrose  and 
glycogen  (see  p.  440). 

The  glycogenic  function  of  the  liver  is  very  easily  disturbed,  and 
its  continual  disorder  results  in  the  disease  dialDctes. 

The  Influences  affecting  the  Glycogenic  Function — (1)  The  Nervous 
Influence. — First  and  foremost  come  nervous  influences.  Puncture 
of  the  floor  of  the  fourth  ventricle  in  the  middle  line  in  the  region 
between  the  originof  the  eighth  and  tenth  nerves  causes  hyperglycaemia, 
the  disappearance  of  glj-cogen  from  the  liver,  and  the  appearance  for 


THE  METABOLISM  OF  CARBOHYDRATE 


42!) 


the  time  being  of  much  dextrose  in  the  urine.  If  the  animal  has  been 
starved  previous  to  the  puncture,  no  such  riesult  folloAvs.  There  is 
therefore,  supposed  to  be  a  "'  centre  "'  in  this  region  of  the  medulla 
through  which  the  glycogenic  function  of  the  liver  is  controlled.  The 
result  has  been  attributed  b}"  some  authorities  to  the  disturbance  of 
the  circulatory  conditions  of  the  liver,  owing  to  interference  with  the 
vaso-motor  centre.     Such  circulatory  disturbance  possibly  does  plf\y 


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Minutes. 


Fxa.  217. — Curves  showlng  the  Relationship  betweex  the  Goncextratios  of 
Sugar  in  Arterial  Blood,  the  Concextratiox  of  the  Urixe,  and  the  Rate 
OF  Urine  Formation,  following  Stimulation  of  the  Splanchnic  Nerve. 
(MacLeod.) 


a  part,  but  it  is  more  generally  held  that  there  exists  a  true  glycogenic 
centre  apart  from  the  vasomotor  centre.  To  this  centre  run  afferent, 
and  from  it  efferent  paths.  The  afferent  paths  are  not  fully  eluci- 
dated. Interference  with  other  parts  of  the  brain  and  nervous 
sj'stem  may  induce  glycosuria.  Fright  causes  glycosuria  in  a  cat. 
If  the  vagus  nerve  be  cut  in  the  neck,  stimulation  of  the  central  end 
produces  gh^cosuria.  This  experiment  has  been  interpreted  as  showing 
that  the  vagus  contains  afferent  fibres  to  the  glycogenic  centre.  It 
seems  more  probable  ^hat  the  glycosuria  results  from  the  asphyxial 


430  A  TEXTBOOK  OF  PHYSIOLOGY 

condition  wliicli  results  from  the  spasm  of  respiration  induced  by  the 
vagus  stimulation.  The  chief  efferent  fibres  ultimately  reach  the 
splanchnic  nerve.  When  the  splanchnics  are  cut,  puncture  of  the 
medulla  induces  no  glycosuria.  Stimulation  of  the  uncut  splanchnic 
nerves  brings  about  glycosuria  (Fig.  217). 

To  sum  up,  in  the  medulla  is  situated  a  centre  which  regulates 
the  glycogen  metabolism  of  the  liver.  The  vagus  nerve  possibly 
contains  afferent  fibre:;  to  this  centre;  the  splanchnic  nerve  conveys 
efferent  fibres  from  it  to  the  liver.  It  is  possible  that  this  centre  is 
directly  affected  by  the  sugar  content  of  the  blood  supplied  to  it, 
and  that  some  drugs  which  induce  glycosuria  act  directly  upon  the 
centre,  exciting  in  much  the  same  manner  as  a  puncture  does. 

(2)  The  Chemical  Influence. — Adrenalin  plays  a  part  in  the  regula- 
tion of  the  glycogenic  function.  It  has  been  known  for  a  considerable 
\ime  that  injection  of  adrenalin  into  the  blood-stream  causes  glyco- 
suria. This  is  now  attributed  to  the  action  of  adrenalin  upon  the 
endings  of  the  splanchnic  nerves  in  the  liver.  Adrenalin  has  the 
property  of  stimulating  in  the  body  all  the  functions  which  the  sympa- 
thetic nerves  excite.  It  acts  upon  the  so-called  ''  receptive  sub- 
stance," which  occurs  between  the  sympathetic  nerve  fibre  and  the 
effector  tissue. 

We  may  provisionally  conclude  that  the  liver  performs  its  glycogenic 
function — (1)  under  the  influence  of  nervous  impulses  brought  from 
the  glycogenic  centre  by  the  sj)lanchnic  nerves;  (2)  under  the  influence 
of  adrenalin  brought  by  the  blood. 

By  some  authorities  it  is  held  that  the  internal  secretion  of  the 
pancreas  also  plays  a  part  in  regulating  the  glycogenic  function  of 
the  liver.     The  evidence  on  this  point  is  contradictory  in  nature. 

The   Influences   under   which   Sugar   is   Broken  Down.  —  Various 

agencies  have  been  or  are  held  to  intiiKuce  the  splitting  of  dextrose 
in  the  body.  At  one  time,  considerable  weight  was  attached  to  the 
supposed  presence  of  a  glycolytic  ferment  in  the  blood.  Recent 
evidence  indicates  that  the  presence  of  such  an  enzyme  in  the  blood 
is  more  than  doubtful.  At  the  present  time,  great  importance  is 
given  by  many  authorities  to  the  action  of  an  internal  secretion  from 
the  pancreas.  This  internal  secretion  is  believed  to  be  derived  from  the 
"islets  of  Langerhans  "  in  the  pancreas.  Circulating  in  the  blood,  it 
enables  the  tissues,  particularly  the  muscles,  to  break  down  dextrose. 
The  tissue  fluid  obtained  from  a  mixture  of  pancreas  and  muscle  can 
break  down  dextrose;  extract  of  pancreas  by  itself  has  no  such 
action;  that  of  muscle  but  slight  action  on  dextrose.  The  active 
substance  obtained  from  the  pancreas  is  not  an  enzyme.  It  is 
soluble  in  water  and  alcohol,  not  destroj^ed  by  heat,  and  is  believed 
to  activate  the  zymogen  of  a  glycolytic  enzyme  present  in  muscle,  or 
possibly  in  the  leucocytes. 

The  above  statement  has  not  been  accepted  by  all  workers. 

Pancreatic  glycosuria  is  discussed  more  fully  elsewhere.  From 
the  evidence,  we  tentatively  conclude  that  in  the  normal  body  an 
internal  secretion  derived  from  the  pancreas   plays  a  part  in  the 


THE  METABOLISM  OF  CARBOHYDRATE 


431 


breaking  down  of  dextrose  by  the  muscles.  The  parts  possibly  plaj^ed 
by  the  secretions  of  the  suprarenal  and  pancreas  are  sho^\ai  diagram- 
matically  in  Fig.  218. 

Glycosuria. — Dextrose  may  appear  in  the  urine  under  any  of  the 
following  conditions: 

1.  The  liver,  supplied  with  too  much  dextrose,  is  unable  to  deal 
with  it  all,  so  that  an  excess  of  sugar  passes  into  the  blood  and  is 
excreted  by  the  kidnej's. 

2.  The  liver,  over-stimulated,  suddenly  turns  a  large  amount  of 
glycogen  into  dextrose,  floods  the  blood  with  sugar,  and  thus  induces 
glycosuria. 

3.  The  glj'cogenic  function  of  the  liver  remains  normal,  but  the 
power  of  the  body  to  break  down  dextrose  is  diminished,  so  that  the 
sugar  accumulates  in  the  blood,  and  this  leads  to  glycosuria. 

(Sugar  Content) 
Blood 


Adrenal  Secretion 


Liver. 
(Glycogen  Store) 

Fig.  218. — Diagra.m  indicating  Influence  of  Panckeas  and   Sttprarenals  on 
Carbohydrate  Metabolism.     (After  Underhill  and  Fine.) 


4.  There  is  no  excess  of  dextrose  in  the  blood,  but  sugar  forms 
within  the  kidney  substance  itself,  and  is  excreted  in  the  urine. 

5.  The  amomit  of  dextrose  in  the  blood  remains  normal,  but  the 
kidneys  become  more  ''  permeable  "  to  sugar.  Thus  sugar,  which  is 
normally  retahied  in  the  body,  passes  into  the  urine. 

When  glycosuria  occurs,  it  may  be  due  to  one  or  other  or  a 
combination  of  these  conditions.  Glycosuria  may  be  exi:)erimentally 
induced  in  various  waj's,  the  chief  of  which  are  the  following: 

1.  Alimentary  Glycosuria. — This  follows  the  ingestion  of  too  much 
sugar — for  example,  150  to  200  grammes  of  dextrose,  and  considerably 
less  lactose,  levulose,  and  galactose.  Children  sometimes  eat  ^  pound 
or  even  \  pound  of  sweets.  Alimentary  glycosuria  is  due  to  the 
"  flooding  '"  of  the  liver  with  too  much  sugar.  It  is  sometimes  termed 
"■  glycosuria  e  saccharo."     It  may  also  be  produced,  but  more  rarety, 


432  A  TEXTBOOK  OF  PHYSIOLOGY 

by  the  ingestion  of  too  much  starch  (""  glycosuria  e  aniylo  ").  Many 
healthy  members  of  a  German  garrison  were  foinid  to  have  sugar  in 
the  urine  because  too  much  starch  Avas  inchided  in  their  dietary. 
Alimentary  glycosuria  occurs  more  readily  in  some  individuals  than 
others.  Clinicians  differ  as  to  whether  people  in  whom  this  glycosviria 
occurs  easily  are  to  be  regarded  as  physiological  or  pathological. 

2.  Puncture  {Neurogenous)  Olyccsuria  has  been  already  men- 
tioned. It  results  from  the  disturbance  of  the  glycogenic  centre  in  the 
medulla  oblongata  which  controls  the  conversion  of  hepatic  glycogen 
into  sugar.  Clinical  experience  shows  that  a  similar  condition  arises 
from  meningitis  (inflammation  of  the  coverings  of  the  brain),  injuries 
to  the  brain  and  upper  part  of  spinal  cord,, tumours  of  the  brain, 
especially  of  the  fourth  ventricle,  cerebellar  haemorrhage,  and  possibly 
from  psychic  shock,  mental  worry,  and  overwork.  The  increased 
mobilization  of  sugar  in  the  blood  may  be  secondary  to  the  passage 
of  adrenalin  into  the  blood,  and  possibly  the  internal  secretion  of  the 
pituitary  gland.  It  has  been  shown  that  fright  increases  the  output 
of  adrenalin. 

It  is  possible  that  some  of  the  drugs,  such  as  caffein  and  strychnine, 
which  cause  glycosuria,  act  on  the  glycogenic  centre.  Injection  of 
piperine  and  the  giving  of  anaesthetics  cause  glycosuria,  apparently 
due  to  the  dyspnoea  thereby  produced,  for  it  is  abolished  if  oxygen 
be  given  simultaneously.  The  same  holds  true  of  the  glycosuria 
induced  by  the  stimulation  of  the  central  end  of  the  vagus  nerve. 
The  results  may  be  due  to  the  effect  partly  upon  the  centre,  and 
partly  upon  the  perijsheral  nervous  mechanism. 

3.  Pancreatic  Glycosuria. — The  remarkable  discovery  was  made  at 
the  end  of  last  century  that  total  extirpation  of  the  pancreas  results 
in  a  fatal  glycosuria,  while  if  a  small  piece  of  gland  (one-fifth)  be  left 
in  situ,  or  transplanted,  no  glycosuria  results.  The  glycosuria  has 
no  relation,  therefore,  to  the  digestive  secretory  function  of  the  pan- 
creas. Considerable  discussion  has  taken  place  as  to  the  cause  of 
this  glycosuria.  Some  have  contended  that  it  results  from  operative 
damage  done  to  the  splanchnic  nerves  and  symi^athetic  ganglia  in 
the  neighbourhood  of  the  pancreas.  This  view  now  finds  little 
acceptance. 

It  has  been  suggested  by  others  that  after  the  extirpation  of  the 
pancreas  the  liver  more  actively  j)roduces  sugar.  In  an  ordinary 
fasting  animal,  the  liver  loses  more  weight  than  the  rest  of  the  body, 
whereas  in  a  depancreatized  animal  starving  from  glycosuria  (the 
gland  was  removed  in  part  at  first,  followed  by  subsequent  destruc- 
tion of  the  remainder)  the  liver  does  not  lose  weight,  although  the 
total  weight  of  the  animal  diminishes  rapidly. 

The  view  most  generally  accepted.  However,  in  regard  to  pan- 
creatic glycosuria  is  that  there  results  a  diminished  utilization  of 
sugar  by  the  tissues.  Possibly  the  hepatic  control  of  sugar  is 
also  affected.  As  the  simultaneous  injection  of  a  j)ancreatic  extract 
prevents  that  glycosuria  which  follows  injection  of  adrenalin,  it  has 
been  suggested  that  the  internal  secretions  of  the  suprarenals  and 


THE  METABOLISM  OF  CARBOHYDRATE  433 

pancreas  together  control  the  sugar  content  of  the  blood.  There  is 
also  evidence  of  a  mutual  retardation  of  action  effected  between  the 
th\Toids  and  the  pancreas.  Thus,  when  the  pancreas  is  removed, 
there  oscur.s  an  increased  metabolism  of  protein  and  fat,  which  is 
attributed  to  the  unrestrained  activity  of  the  thyroid  and  supra- 
renal glands.  These  conclusions,  if  substantiated,  afford  a  striking 
example  of  the  mutual  interdependence  of  the  various  internal  secre- 
tions of  the  bod}^  (see  later,  p.  503). 

The  fasting  depancreatized  animal  contmues  to  excrete  sugar. 
As  regards  the  source  of  this  sugar,  it  has  been  shown  experimentally 
that  injection  of  such  amino-acids  increased  its  formation.  The 
sugar  may  therefore  be  derived  from  protein  decomposition. 

The  question  of  the  formation  of  sugar  from  tissue  protein  has 

also  been  investigated  by  comparing  the  amount  of  dextrose   (D) 

secreted  in  the  lu'ine  with  the  amount  of  nitrogen  (X)  secreted  as  urea, 

giving  the  so-called  ^-  ratio.     When  a  depancreatized  animal  is   fed 

on  protein  freed  from  all  traces  of  carbohydrate,  both  dextrose  and 

nitrogen  are  increased  in  the  urine,  but  the  ratio  is  not  altered  from 

what  it  was  during  fasting,  which  shows  that  the  dextrose  and  the 

nitrogen  of  the  urine  have  a  common  source.    If  all  the  non-nitrogenous 

moiety  of  protein   were  used  to  form   sugar,  the  ^  ratio  would  be 

about  7.     This  can  be  seen  from  the  following  calculation:  Protein 

contains  on  an  average  52  per  cent,  of  carbon  and  17  per  cent,  of 

2iitrogen;  urea,  CONoH^,  contains  20  per  cent,  of  carbon  and  51  per 

cent,  nitrogen.     If  17  grammes  of  nitrogen  derived  from  100  grammes 

of  protein  are  excreted  as  lu'ea,  the  latter  accounts  for  6^  grammes 

of   carbon.      This    leaves    52-6§  =  45|    grammes    of    carbon    to    be 

accounted  for.     In  the  gramme-molecular  weight  of  sugar.  C^H^gOg — 

180 — there  are  72  grammes  of  carbon.     Therefore,  if  72  grammes  of 

carbon  go  to  form  180  grammes  of  sugar,  4tJ  grammes  of  carbon 

.„  ,         180x45^- 
wiii  form        ^^ 

'*"  ^180x136 

3x72 

^113-3  grammes  of  sugar 

.    D     113-3     _ 
•  •  ^.=  -,_    =  /  nearly. 
jN  1  / 

In  an  animal  suffering  from  pancreatic  glycosuria,  however,  all 
the  carbon  is  not  converted;  a  D  :  X  of  about  3  to  4  being  maintained. 

Dextrose  may  also  be  formed  from  the  glycerine  moiety  of  fats. 
It  has  been  shown  that  in  the  condition  of  pancreatic  glycosuria 
glycerine  ^nelds  an  increase  of  sugar  in  the  urine.  It  is  to  be  concluded, 
then,  that  after  extirpation  or  in  certain  diseased  states  of  the  pancreas 
dextrose  may  appear  in  the  urine,  and  this  sugar  ma}-  be  derived 
from  carbohydrates,  proteins,  and  fats. 

4.  Phloridzin  Glycosuria. — Phloridzin  is  a  glucoside  obtained  from 
the  root  bark  of  cherry  and  apple  trees.  If  it  be  injected  intc  an  animal 
glycosuria   results.     If  it   be   injected   into   one   renal   artery,   sugar 

28 


434  A  TEXTBOOK  OF  PHYSIOLOGY 

api3ear.s  in  the  urine  secreted  by  tliat  kidney  before  it  appears  in  the 
urine  secreted  by  the  other  kidnej-.  If  it  be  mixed  with  defibrinated 
blood  and  perfused  through  an  excised  kidney,  sugar  is  excreted. 
No  hyperglyeaemia  is  induced,  and  no  store  of  glycogen  in  the  liver  is 
requisite.  The  sugar  is  formed  in  the  kidney  inider  the  influence  of 
the  drug.  The  sugar  does  not  come  from  the  drug  itself,  since  phlore- 
tin,  the  jjortion  of  the  alkaloid  which  is  free  from  dextrose,  also  causes 
glycosuria.  Two  sources  of  the  sugar  huxe  been  suggested :  (1)  Glucos- 
amine, the  carbohj'drate-holding  group  attached  to  the  blood-proteins ; 
(2)  amino-acids  formed  within  the  kidney  itself. 

The  amount  of  sugar  is  often  too  large  to  be  accounted  for  wholly 
by  the  first  view.  The  administration,  together  with  the  drug,  of 
alaniu  and  other  allied  amino-acids  causes  an  increased  sugar  excretion. 
The  nitrogen  excretion  of  the  urine  is  also  increased  by  phloridzin, 
the  jj  ratio  being  3-6  after  all  the  hepatic  glycogen  has  been  got  rid 
of  by  fasting. 

5.  Adrenalin  Glycosuria. — The  fact  that  injection  of  adrenalin 
causes  gtycosuria  has  already  been  mentioned.  It  is  believed  that 
adrenalin  normally  aids  the  liver  in  the  performance  of  its  glycogenic 
function  (see  p.  428).  Injection  of  adrenalin  apparent^  increases  the 
conversion  of  glycogen  into  dextrose,  and  thus  floods  the  blood  with 
sugar — a  condition  allied  to  puncture  diabetes.  Adrenalin  causes 
glycosuria  in  starved  animals,  and  also  in  animals  which  have  been 
submitted  to  the  administration  of  phloridzin.  It  is  stated  that 
the  administration  of  adrenalin  in  increasing  doses  causes  a  deposition 
of  glycogen  in  the  liver,  but  not  in  the  muscles,  in  rabbits  from 
whom  all  traces  of  glycogen  had  been  removed  both  by  starvation  and 
doses  of  str3^chnine.  The  convulsions  produced  by  strj^chnine  expend 
the  last  of  the  glycogen.  This  internal  secretion  therefore  plays  an 
important  part  in  the  production  of  glycogen  from  sugar,  of  sugar 
from  gh'cogen,  and  of  sugar  from  proteins. 

6.  Thyroid  and  Parathyroid  Glycosuria. — After  removal  of  both 
the  th\Toid  and  parathyroid  glands,  the  organism  is  said  to  show  a 
diminished  tolerance  to  dextrose.  When  the  th^yroids  alone  are  re- 
moved (see  p.  515  for  a  discussion  of  the  relationship  of  these  glands  to 
each  other),  there  is  no  evidence  of  such  diminished  tolerance.  It 
is  necessary  that  the  parathyroids  be  ali-o  removed.  The  para- 
thyroids apparently  influence  carbohydrate  metabolism  in  such  r. 
way  as  to  prevent  the  accumulation  of  excessive  sugar  within  the 
organism.  The  thyroids  probably  have  a  function  which  is  supple- 
mentary' to  the  action  of  adrenalin.  Taking  away  the  thyroids  has 
been  shown  to  lessen  the  glycosuria  induced  by  a  given  dose  of  ad- 
renalin. Excess  of  thyroid,  on  the  other  hand,  possibly  causes 
glycosuria  bv  bringing  about  a  more  marked  action  of  adrenalin 
(see  p.  505). 

7.  Pituitary  Glycosuria. — It  is  claimed  that  intravenous  or  sub- 
cutaneous injection  of  extracts  of  the  posterior  lobe  of  the  pituitary 
gland  causes  a  glycosuria  in  animals  fed  on  an  ordinary  diet,  and  that 
this  is  due  to  an  internal  secretion  which  lowers  the  utilization  of 


THE  METABOLISM  OF  CARBOHYDRATE  435 

dextrose  in  the  organism.  Conversely,  removal  of  the  posterior  lobe 
is  said  to  endow  animals  with  an  increased  tolerance  to  excessive 
amomits  of  dextrose  (see  later,  p.  522). 

The  interrelation  and  exact  mode  of  action  of  all  these  glands 
requires  far  more  work  before  any  clear  and  dogmatic  statements  can 
be  made  in  regard  to  their  control  of  carbohydrate  metabolism. 

8.  "  Salt  "  Glycosuria. — Glycosuria  follows  the  injection  of  1  per 
cent,  solution  of  sodium  chloride  into  the  blood  of  an  animal.  It  has 
been  suggested  that  the  salt  renders  the  kidnej'  cells  more  permeable 
to  sugar.  On  the  other  hand,  it  is  cj^uite  possible  that  the  ghcogenic 
centre  in  the  medulla  is  affected.  Injection  of  a  soluble  calcium  salt 
(ionized  calcium)  abolishes  the  glycosuria  induced  b}'  the  sodium  ion. 

Diabetes  Mellitus. — In  this  disease,  or  rather  in  the  collection  of 
])athological  conditions  grouped  under  this  name,  the  patient  generally 
passes  much  sugar  in  the  urine.  Cases  maj^  be  described  as  mild 
and  severe.  In  the  mild  cases,  the  gtycosuria  disappears  when  carbo- 
hyckate  is  removed  from  the  diet,  the  trouble  being  due  only  to 
defective  storage  or  oxidation  of  sugar.  In  the  severe  cases,  the 
sugar  cannot  be  thus  removed  from  the  urine.  It  is  probable  that 
the  less  .severe  of  such  cases  derive  sugar  from  protein  onl}',  whereas 
the  more  severe  and  rapidly  fatal  cases  derive  it  from  fats  also.  The 
acetone  bodies  which  often  occur  in  the  urine  of  diabetics  are  dis- 
cussed elsewhere  (Urine,  p.  468).  Under  the  name  diabetes  are  classed 
glycosurias  of  various  origin — neurogenous,  hepatogenous,  pancreatic, 
etc.^ — a  great  number  of  such,  but  by  no  means  all,  being  due  to  some 
defect  in  the  pancreatic  control  of  carbohydrate  metabolism.  For  a 
full  discussion,  textbooks  of  pathology  and  medicine  should  be  con- 
sulted. The  tests  for  sugar  in  urine  are  dealt  with  under  Urine 
(p.  467), 


CHAPTER  Lll 
THE  METABOLISM  OF  FAT 

The  Absorption  of  Fat.  —  Fat  i.s  digested  into  fatty  acids  and 
glycerine,  and  brought  into  solution.  The  preliminary  emulsification 
of  the  fat  facilitates  its  digestion,  not  its  absorption .  The  view  once 
put  forward,  and  now  abandoned,  Avas  that  emulsified  neutral  fat  is 
absorbed  in  the  particulate  form  M'ithout  being  split  into  fatty  acid 
and  glycerine.  The  absorption  of  fats  from  the  intestine  depends 
upon  the  solubility  of  free  fatty  acids  and  soaps  in  the  bile.  The 
bile  salts  increase  the  solubility  of  soaps  in  water ;  they  also  prevent 
its  gelatinization,  and  thereby  greatly  aid  absorption.  The  lecithin  of 
the  bile  also  plaj-s  an  important  part  in  the  solution  of  fatty  acids  and 
soaps.  Fats  of  high  melting-points  are  not  absorbed  so  well  as  fats 
with  low  melting-points;  free  fats  are  better  absorbed  than  those 
enclosed  in  cell  membranes. 

During  absorption  the  dissolved  fatty  acids  and  soaps  pass  into 
the  intestinal  mucous  membrane.  Here,  by  the  activity  of  the  cells, 
they  are  again  synthesized  with  glycerine  into  particles  of  neutral 
fat,  and  these  pass  into  the  lacteals,  which  fill  Avith  a  milky  white 
lymph  known  as  chyle.  The  lacteals  derive  their  name  from  this 
milky  fluid,  and  were  discovered  through  it. 

Leucocytes  aid  the  passage  of  the  synthesized  neutral  fat  into  the 
lacteals.  They  are  to  be  seen  in  sections  of  the  villi  stained  Avith 
osmic  acid,  crowded  with  particles  of  fat.  Hoav  the  particles  are 
handed  on  from  the  columnar  cells  to  the  leucocytes  is  unknoAA^n. 
Not  all  the  fat  eaten  finds  its -way  into  the  lacteals.  The  fate  of  the 
remainder  is  unknoAvn.  It  probably  passes  into  the  blood,  forming 
some  linkage  with  the  protoplasm  of  the  plasma  and  corpuscles. 
The  lacteals,  then,  act  as  an  overflow,  and  protect  the  liver  from 
being  flooded  Avith  fat.  Our  methods  of  anatysis  do  not  allow  us  to 
detect  any  increase  of  fat  in  the  portal  blood,  but  neither  do  they  permit 
us  to  be  sure  of  an  increase  therein  of  sugar  or  amino-acids  during 
digestion.  The  circulation  is  so  rapid  that  an  immeasurably  small 
increase  of  any  of  these  substances  must  suffice  to  carry  them  aAvay. 
About  60  per  cent,  of  the  ingested  fat  is  found  in  the  chyle  as 
neutral  fat,  and  a  small  quantity  (4  to  5  per  cent.)  as  soaps. 

Anabolism  of  Fat. — From  the  lacteals  the  chyle  passes  to  the  recep- 
taculum  chyii,  and  thence  by  the  thoracic  duct  into  the  A^enous  blood. 
During  this  passage  the  neutral  fat  is  again  broken  down  into  soluble 
soaps,  passing  as  such  into  the  blood,  so  that  there  is  no  danger  of  the 

436 


THE  METABOLISM  OF  FAT  437 

fat  plugging  the  small  bloodvessels,  as  would  be  the  case  if  it  were 
in  a  state  of  fine  emulsion.  It  is  also  better  available  for  storage  in 
the  various  fat  depots  of  the  body. 

The  fat  dejjots  of  the  body  are  situated  in  the  subcutaneous  tissue, 
in  the  subperitoneal  tissue,  between  the  muscles,  and  around  various 
organs  of  the  body,  such  as  the  kidney  and  the  eyeball.  The  depots  of 
fat  act  primarity  as  the  storehouses  of  a  food  possessed  of  great  energy 
value.  They  also  protect  the  bodj"  from  heat  loss,  and  act  as  cushions, 
giving  form  and  beauty  to  the  body,  preventing  jarring,  and  giving 
support  to  the  various  organs.  The  haggard  face,  the  chilly  tempera- 
ment, and  the  falling  down  of  the  viscera,  alike  result  from  want  of 
fat.  Fat  is  also  stored  intracellularly  in  other  cells — e.g.,  muscle 
fibres  and  the  liver  cells — beside  those  of  the  true  adipose  tissue, 
much  of  it  in  a  masked  form,  probably  combined  with  protein  or 
other  bodies,  so  that  it  does  not  react  with  fat  .stains. 

The  fat  in  the  various  depots  is  not  always  of  the  same  character. 
It  is  more  fluid  in  some  parts  than  others.  Chemically,  also,  the 
same  difiference  is  found. 

This  is  shown  in  the  following  table: 


„       ^  „.  '    Sp.Gr.at       Melting.  \    l°^''T         Free  Acid.. 

Fat  of  P^.  foo°C.  Point      \  ^"""^^Z^  (See  p.  55.) 

{See  p.  55. )   ^       ^         - 


Back  0-8607  33-8  60-6  0-152 

Kidney 0-8590  4S-2  52-6  0-163 

Omentum  0-858S  U-o  53-1  0-360 


The  fats  of  the  subcutaneous  tissue  are  chiefly  compounds  of 
oleic,  stearic,  and  palmitic  acids.  From  the  fats  of  the  liver,  kidney, 
heart  muscle,  however,  acids  are  found  more  unsaturated  than  oleic, 
belonging  to  the  linoleic  and  linolenic  series. 

The  fat  of  milk  is  also  characterized  by  the  presence,  in  addition 
to  the  ordinary  fats,  of  butjTic  and  other  volatile  fatty  acids.  The 
lower  melting-jjoint  of  the  fat  of  the  pig's  back  may  allow  mobility 
of  the  tissues  there,  exposed  as  they  are  to  the  cool  atmosphere.  The 
melting-point  may  be  adapted  to  keep  the  fat  of  any  part  soft,  but 
not  fluid.  The  melting-point  of  the  subcutaneous  fat  is  altered  by 
covering  the  pig's  back  with  a  sheep's  pelt.  The  fat  stored  within  the 
body  maj' arise  from  three  sources:  (1)  Ingested  fat,  (2)  carbohydrate,. 
(3)  proteins. 

Fat  from  Fat. — That  fat  arises  from  ingested  fat  is  easih'  capable 
of  demonstration.  Nature  makes  experiment  for  us.  It  can  be^ 
shown  that  the  fat  of  the  sea-dolphin  has  a  high  iodine  value  when 
the  fish  it  feeds  on  have  fats  of  a  high  iodine  value.  When  the  fish 
eaten  have  fats  of  a  low  iodine  value,  the  iodine  value  of  the  fat  of 
the  dolphin  falls.  The  fat  of  the  fish-eating  ducks  has  a  high  iodine 
value  (84-8).  that  of  farm  duck  a  lower  value  (58-5).  Horses  fed  on 
oats  have  an  oily  fat  of  a  high  iodine  number  similar  to  that  of  the 


43S  A  TEXTBOOK  OF  PHYSIOLOGY 

oil  contained  in  oats.  The  wild-boar,  when  feeding  on  acorns  and 
beech-nuts,  acquires  a  fat  Avith  properties  akin  to  those  of  the  beech 
and  acorn  oils.  Many  exact  experiments  have  also  been  made  to 
prove  this  point.  An  animal  is  starved  to  reduce  its  fat  as  much  as 
possible,  and  it  is  then  fed  Avith  a  fat  the  properties  of  which,  such 
as  melting;point,  iodine  number,  etc.,  are  known.  In  addition,  the 
iatty  acid  contained  in  the  fat  often  has  its  own  characteristic 
properties.  Such  fats  are  rapeseed  oil,  linseed  oil,  sesame  oil,  coco- 
butter,  etc.  After  feeding  a  starved  dog  or  goose  with  sesame  oil, 
it  was  found  that  the  fat  was  more  oily,  and  the  presence  of  the  sesame 
oil  could  be  demonstrated  in  the  fat  by  shaking  it  Avith  an  equal  Aolume 
of  strong  hydrochloric  acid  and  a  trace  of  a  2  per  cent,  alcoholic  solu- 
tion of  furfurol.  A  purple-red  colour  dcA^eloped  Avhen  sesame  oil 
was  present.  The  foUoAving  figures  show  the  effect  of  feeding  mutton 
fat  and  of  feeding  coco -butter  on  dogs: 


-,  ,^.  Melting-          j   ..                Fatty 

Melting.  p^^^^l^         Iodine            j^J 

Pom  of  Fat  ^nimJa  I'^'^^Tr,,    ^'^^ribe.r. 

>^-  Fat.  ^^'' P- ^^-y  (See  p.  55.) 


Mutton 46-51 

Coco-butter  23-28 

Carbohydrate        . .  . .  . .  — 


The  fed  fat  also  goes  in  part  into  the  milk,  so  that  the  iodine  number 
and  other  properties  of  the  cream  are  altered.  The  characteristic  test 
for  sesame  oil  is  given  by  the  cream  yielded  by  a  cow  fed  wdth 
sesame  oil.  It  is  probably  of  considerable  importance  that  the  right 
fat  should  be  stored  in  order  that  the  body  may  be  kept  hard  and 
in  good  condition.  The  soft  toAvnsman  may  OAve  his  softness  to  the 
quality  of  his  fat  as  Avell  as  to  lack  of  muscular  dcA'^elopment. 

Fat  from  Carbohydrate. — Fat  may  also  arise  from  the  carbohydrate 
taken  in  as  food.  This  is  obv^ious  to  those  engaged  in  fattening  pigs 
or  geese  for  market.  Carbohydrate  is  the  chief  food  given.  It  has 
been  proved  scientifically  by  giA^ing  animals,  after  preliminary  starA^a- 
tion,  a  diet  containing  a  minimum  of  protein  and  much  carbohydrate. 
By  comparing  these  with  controls — e.g.,  animals  taken  from  the 
same  litter — it  can  be  shown  that  the  experimental  animals  put  on 
so  much  fat  that  even  if  it  be  supposed  that  all  the  non-nitrogenous 
moiety  of  the  protein  eaten  AAcre  converted  into  fat,  yet  there  is 
more  fat  to  be  accounted  for;  this  must  haA^e  come  from  the  cai'bo- 
hA^drate  fed. 

EA'idence  in  faA'our  of  the  formation  of  fat  from  carbohj'drate  is 
also  obtained  from  the  respirator}^  quotient  (1)  of  hibernating 
animals  Avhich  are  storing  fat  ^preparatory  to  their  winter  sleep,  (2)  of 
animals  which  are  being  fattened  bA"  forced  feeding  with  large  amounts 
of  carbohydrate — ^for  example,  of  geese  stuffed  to  make  fat  livers 
for  the  preparation  of  jJdte  de  foie  gras.     Under  these  circumstances. 


THE  METABOLISM  OF  FAT  439 

the  respiratory  quotient,  which  for  carbohydrate  is  1,  and  under  1 
for  proteins  and  fats,  rise?  well  above  1 — e.g.,  to  1-3  or  1-4.  At  first 
the  diserej)ancy  was  attributed  to  experimental  error,  but  the  ex- 
planation now  generally  accepted  is  that  carbohydrate  is  being  turned 
into  fat,  and  that  in  the  process  carbon  dioxide  is  liberated,  so  that  the 
respiratory  quotient  is  raised  above  1.  The  following  formula  siim- 
•  niarizes  the  series  of  chemical  changes  which  bring  about  this  result : 

13C«H,,0,  =  C,,H,„,0,  +  23CO,  +  26H,0 

Pat  from  Protein. — -The  question  as  to  the  formation  of  fat  from 
protein  is  a  vexed  one.  It  cannot  be  denied  that  such  a  forma- 
tion is  possible  within  the  organism.  From  the  amino -acids  arising 
from  autolyzed  body  protein  or  from  digested  protein  the  formation 
of  carbohydrate  may  take  place,  and  from  this  carbohydrate  fat  may 
well  be  formed.  From  the  available  evidence  it  would  appear  that, 
although  such  a  formation  is  possible,  the  animal  body  under  normal 
conditions  doss  not  make  use  of  this  power. 

Under  certain  conditions,  however,  such  as  the  development  of 
larvae,  the  formation  after  death  of  a  waxy  body  known  as  adipocere, 
and  possibly  in  some  cases  of  so-called  fatty  degeneration  during 
life,  such  a  transformation  of  amino-acids  into  fat  does  take  place. 
It  has  been  shown,  for  example,  that  some  of  the  higher  non-volatile 
fatty  acids  are  formed  when  the  larvae  of  the  blowfly.  Calliphora,  are 
rubbed  with  Witte's  peptone  into  a  homogeneous  mass.  So,  too,  it 
has  been  shown  that  fl3'-maggots,  estimated  from  controls  to  contain 
a  known  quantity  of  fat,  when  allowed  to  feed  on  blood  of  a  known  fat 
content,  develop  after  a  time  much  more  fat  than  existed  in  them- 
selves and  the  blood  together  at  the  start  of  the  experiment.  Such 
exj)eriments  have  not  been  accepted,  owing  to  the  fact  that  fat  may 
result  in  the  blood  from  bacterial  decomposition.  Recent  researches, 
however,  tend  to  confirm  rather  than  discount  these  results. 

In  regard  to  the  formation  of  adipocere,  this  is  a  wax-like  m'xture 
of  insoluble  soaps,  fatty  acids,  and  ammonia,  which  is  found  in  corpses 
exposed  to  water.  It  is  quite  possible  that  lower  organisms  may  also 
play  a  part  here,  and  its  development  from  the  body  proteins  is  by 
no  means  proved.  Positive  results  have  been  claimed  from  fesding 
experiments,  but  it  has  been  pointed  out  that  the  calculations  giving 
these  were  based  upon  a  wrong  assumption  of  the  proportion  ^vhich 
nitrogen  bears  to  carbon  in  the  meat  fed.  When  the  calculations  are 
corrected,  the  formation  of  fat  from  protein  is  found  to  be  unproven. 
The  evidence  of  the  most  recent  feeding  experiments  is  contradictory, 
some  observers  claiming  that  a  formation  of  fat  from  protein  can  be 
shown,  others  denying  this. 

From  what  has  been  said  above,  we  may  conclude  that  there  exists  in 
omnivora  no  fat  rigidly  characteristic  of  each  t^'pe  of  animal,  for  foreign 
fats  may  be  stored  as  such.  Recent  work,  however,  is  tending  to 
show  that  an  animal's  own  characteristic  fat  is  formed  from  carbo- 
hydrate just  the  same  as  a  plant's  characteristic  fat  or  oil  is  formed 
from  these  bodies.     Different  species  of  animals  form  a  different  fat 


440  A  TEXTBOOK  OF  PHVSTOLOOY 

when  fed  with  the  same  carbohydrate.  The  figures  given  in  the  table 
(p.4c8)  show  that  the  fat  deposited  from  the  carbohydrate  in  the  diet 
differs  considerably  from  that  of  the  same  animal  when  fed  on  other 
fats,  and  ])robably  represents  the  animal's  own  characteristic  fat. 
It  is  this  fat  which  makes  for  a  hard  body  and  physical  fitness. 

The  Katabolism  of  Fat. — Tn  regard  to  the  katabolism  of  fat,  evidence 
is  scanty.  It  is  (piite  probable  that  there  exists  two  different  forms 
of  katabolism — (1)  of  the  ingested  fat  taken:  (2)  of  the  fat  formed 
within  the  animal's  own  body  from  other  bodies.  The  fat  of  the  food 
may  be  regarded  as  a  wanderer.  It  is  formed,  in  the  first  place, 
within  some  plant  or  animal  from  lower  bodies,  and,  unless  used  up 
again  within  the  i:>arent  organism,  it  passes  from  plant  to  animal, 
and  from  animal  to  animal,  until  bmnt  up  and  used  in  the  processes 
of  metabolism.  Such  foreign  fat  is  eventuall,y  burnt  to  carbon  dioxide 
and  water.  The  fatty  acids,  if  saturated,  are  probably  first  broken 
down  to  the  higher  unsaturated  fatty  acids,  and  then  to  the  lower 
unsaturated  fatty  acids,  such  as  ;5-oxybutyric  acid  and  aceto-acetic 
acid,  and  finally  to  COo  and  water. 

Fat 
Glycerine     Saturated  fatty  acid 

! 

Unsaturated  fatty  acids 

/\ 
CO^     HoO 

If,  however,  the^fat  formed  within  the  organism — for  example, 
from  carbohydrate  in  the  time  preparatory  to  hibernation — be  kata- 
bolized — e.g.,  during  hibernation — there  is  good  evidence  to  show 
that  such  fat  is  broken  down  h\  \\a.\  of  carbohydrate  again. 

Fat 

I 
Carbohj'drate 

CO.,     H^O 

The  best  evidence  in  favour  of  this  view  has  been  obtained  from 
the  observation  of  the  respiratory  quotient  of  hibernating  animals. 
Normally,  fat  gives  a  respiratory  quotient  of  0-7  (see  p.  319)-  This 
is  the  lowest  of  the  figures  given  by  the  three  classes  of  foodstuffs. 
In  hibernating  animals,  however,  much  lower  figures  have  been  ob- 
tained—e.g'.,  0-23  for  the  dormouse,  0-5  for  the  hedgehog.  The 
explanation  given  for  these  low  figures  is  that  the  stored  fat  is  being 
converted  into  carbohydrate;  and  since  carbohydrate  contains  more 
oxygen  in  its  molecule,  oxygen  is  used  up  in  the  process,  and  the 
respiratory  quotient  of  the  animal  correspondingly  reduced.  The 
process  may  be  summarized  by  the  folloAving  formula : 

2C2H5(Ci8H330,)3  +  640^  =     leCfiH.aO,     + 1800^  +  8H,0 

Olein  Dextrose 

.    C0.,_18_ 
••    Oo  -64-"^^^ 


THE  METABOLISM  OF  FAT  441 

In  man,  during  starvation,  respiratory  quotients  below  0-7  have 
also  been  observed,  and  it  is  quite  possible  that,  under  these  circum- 
stances, some  fat  is  being  converted  into  carboh3'drates,  and  meta- 
bolized in  that  manner. 

The  Metabolism  of  Lecithin. — Lecithins  are  found  in  all  the  tissues 
of  the  body,  partly  free,  partly  combined  with  protein.  Entering 
largely  into  the  composition  of  the  cell  membrane,  they  are  supposed 
to  control  the  passage  of  bodies  into  the  cell,  in  addition  to  pla3ing 
an  important  part  in  the  chemical  processes  of  the  cell.  The  amomit 
of  lecithin  is  diminished  in  the  body  by  starvation,  and  also  by 
wasting  diseases  and  phosphorus-poisoning. 

Anabolism. — The  various  lecithins  are  probably  continuously 
being  formed  in  the  organism.  From  experiments  made  hy  feeding 
with  foreign  fats,  it  is  found  that  such — e.g.,  linseed  oil — are  not 
built  up  into  the  lecithins  of  the  body.  That  lecithin  is  formed  in 
the  organism  is  shown  hx  the  fact  that  mice  fed  on  a  lecithin-free 
diet  grew  well,  and  brought  forth  young.  It  is  possible  that  each 
animal  has  its  own  characteristic  lecithm,  and  that  the  fatty  acid 
molecules  of  these  are  developed  from  the  carbohj'drate  of  the  diet, 
and  not  from  the  fat.  Lecithin  is  formed  in  green  leaves  ex^iosed 
to  light. 

Katabolism. — When  lecithin  breaks  down,  it  forms  first  of  all 
glycerophosphoric  acid  and  cholin,  and  subsequently  glycerine, 
phosphoric  acid,  and  fatty  acid.  The  phosphoric  acid  is  probabh' 
excreted  in  the  urine  as  phosphates,  and  the  other  bodies  burnt  up 
in  the  organism.  Under  certain  circumstances,  the  lecithin  and  its 
derivatives  may  be  deposited  in  the  cell  as  oily  droplets,  giving  a 
condition  similar  to  that  known  as  "'  fatty  degeneration." 

Fatty  Degeneration. — In  certain  diseases,  and  after  the  application 
of  experimental  methods,  such  as  phosphorus-poisoning,  the  cells 
of  certain  organs  show  on  microscopic  examination  the  presence  of 
fatty  droplets  within  the  cell.  The  nucleus  of  the  cell  may  or  may 
not  be  fragmented.  Such  a  condition  has  been  termed  "  fatty  de- 
generation." Much  experimental  work  has  been  done  to  prove  the 
origm  of  this  fat,  and  also  the  circumstances  which  bring  about  the 
condition.  In  regard  to  the  latter  point,  one  of  the  chief  causes  is 
a  diminished  alkalinity  of  the  cell  fluid.  Fatty  degeneration  takes 
place  in  dying  cell;;. 

In  regard  to  the  source  of  the  fatty  droplets,  the  chief  views  held 
are  these: 

1.  That  the  fat  is  essentially  an  infiltration  into  the  cells  from  the 
fat  depots  of  the  body. 

2.  That  the  fat  is  the  "  masked  "  fat  of  the  cell  which  has  become 
"■  revealed  ""  in  droplet  form — e.g..  that  the  fat  is  fat  which  was  linked 
to  protein,  and  has  become  dissociated  and  visible. 

3.  That  the  fat  has  been  formed  from  carbohydrates  of  the  cell, 
or  from  amino-acids  produced  as  the  result  of  the  autolysis  of  the 
cell  proteins. 


442  A  TEXTBOOK  OF  PHYSIOLOGY 

4.  That  the  fatty  substance  is  derived  from  the  lecithin  of  the  cell. 

5.  That  the  fatty  substance  is  a  compound  of  cholesterin- 
cholesterjd  oleate,  possibly  derived  from  lecithin. 

It  is  quite  possible  that  there  are  various  chemical  bodies  which 
give  rise  to  the  microscopical  apiDcarance  known  as  fatty  degenera- 
tion. It  seems  very  likely,  also,  that  "  fatty  degeneration  "  varies 
in  nature  according  to  the  tissue  in  which  it  is  taking  place. 

Obesity  is  usually  the  outcome  of  excessive  feeding  and  lack  of 
muscular  exercise,  particularly  the  latter.  But  this  is  not  the  only 
cause,  for  some  people  never  become  fat,  however  much  they  eat  or 
however  little  exercise  they  take;  others,  while  eating  little  and  taking 
much  exercise,  show  a  tendency  to  fatness.  The  obesity  of  some  may 
be  associated  with  a  greater  absorption  of  foodstuffs  from  the  ali- 
mentary tract  rather  than  a  greater  intake  of  food;  that  of  others 
is  associated  with  an  inadequate  oxidation  of  the  foodstuffs,  a  peculi- 
arity of  their  metabolism  due,  perhaps,  to  a  deficiency  of  oxidases. 
An  hereditary  tendency  to  fatness  is  often  seen  in  families.  It  is 
well  knoAvn  that  different  breeds  of  cattle  vary  in  the  readiness  with 
which  they  can  be  fattened.  The  amount  of  the  internal  secretions 
of  the  sexual  glands,  and  possibly  also  of  the  thyroid,  may  play  some 
part  in  this  tendency  to  fatness.  Castrated  animals  and  eunuchs 
become  fat.  This  may  only  be  due  to  laziness  developed  as  a  result 
of  the  loss  of  their  sexual  instincts,  but  is  probably  also  due  to  the 
removal  of  some  direct  effect  upon  metabolism.  At  the  menopause, 
many  women  tend  to  put  on  flesh. 

We  know  that  the  secretion  of  the  thyroid  promotes  the  metabolism 
of  protein  and  fat,  so  that  a  deficiency  of  thjToid  secretion  may  be 
a  cause  of  obesity.  Thyroid  extract  is  frequently  given  with  success 
in  obesity,  but  its  effects  have  to  be  carefully  watched.  For  most 
cases,  a  restricted  diet,  mainly  of  protein,  which  of  all  the  foodstuffs 
most  promotes  metabolism,  and  much  exercise,  is  the  best  treatment. 
Fresh  fruit  and  green  vegetables  are  bulky,  and  satisfy  the  desire 
for  a  full  stomach.  They  contain  some  90  per  cent,  of  water.  The 
obese  should  eat  these  and  avoid  concentrated  foods,  such  as  sugar, 
fat,  meat  cooked  with  fat. 

The  truly  obese  man  is  an  unfortunate.  Owing  to  the  large 
amount  of  fat,  he  has  much  weight  to  carry,  he  cannot  easily  lose 
heat,  his  breathing  movements  are  impaired,  so  that  he  readily  becomes 
fatigued,  quickly  gets  out  of  breath,  and  sweats  profusely.  The  dura- 
tion of  life  in  the  obese  is  shortened.  By  giving  a  few  minutes  daily 
to  physical  exercise  of  all  parts  of  the  body,  with  bathing,  massage, 
and  skin  friction,  by  active  exercise  on  holiday,  and  a  wdsety  restricted 
diet  at  all  times,  the  body  can  be  kept  fit  and  the  protuberant  belly 
of  the  middle-aged  citizen  avoided. 


CHAPTER  LIII 


THE  METABOLISM  OF  NUCLEIN 

Xtjclein  linked  on  to  protein  forms  the  compound  body  nucleo- 
protein,  the  chief  protein  constituent  of  the  cell  nucleus.  Little  or 
nothing  is  kno^^^l  as  to  the  building  up  of  nuclein  or  of  nucleo -protein 
within  the  body.  Such  a  synthesis  is  undoubtedly  always  taking 
place,  but  the  exact  nature  of  the  precursors  emploj'ed  in  the  process 
is  not  known.  In  the  adult  body  there  is  no  evidence  to  show  that 
the  purin  bodies  of  the  food  are  used  in  the  process.  In  the  young, 
in  the  early  months  of  growth,  there  takes  place  an  abundant  forma- 
tion of  nuclein,  and  upon  a  food  (milk)  which  contains  practically 
no  nuclein.  During  the  incubation  of  the  hen's  egg,  nucleo -protein 
is  formed  within  the  cells  of  the  embryo  at  the  expense  of  the  food 
yolk,  which  contains  almost  no  nuclein  or  its  derivatives, 

Xuclem  breaks  down  as  follows : 


Nuclease 
of  pancreas 


Nuclein 


Protein 


Nucleic  acid 


Enzymes  of 
tissues 


Turin  bodies         Phosphoric  acid         Carbohydrate         Pyrimidin    V 
adenin  (hexose  or  bases        = 

guanin  pentose)  (chiefly 

cytosin) 

Adenin  and  guanin  are  amino-purins,  being  respectively  amino- 
pm-in  and  amino-oxypiu'in  (c/.  p.  50).  In  some  cases,  guanin  alone 
is  formed.  Probably  the  ingested  nuclein  is  broken  down  by  the 
nuclease  of  the  pancreatic  juice  to  nucleic  acid  and  protein.  The 
nucleic  acid  thus  formed  is  absorbed  into  the  blood,  perhaps  by  the 
action  of  the  pale  corpuscles,  and  taken  to  tissues,  where  it  is  further 
acted  upon,  particularly  in  tissues  such  as  the  spleen,  liver,  and 
thymus,  which  contain  enzj^mes  capable  of  breaking  it  down  into  the 
purin  bodies  adenin  and  guanin,  phosphoric  acid,  carbohydrate  and 
pjrimidin  bases.     The  adenin  and  guanin  thus  formed  are,  by  the 

443 


444  A  TEXTBOOK  OF  PHYSIOLOGY 

action  of  the  enzymes  adenase  and  guanase  present  in  these  tissues, 
convei'ted  by  deamiiiization  into  hypoxanthin  and  xauthin  respec- 
tively (r/.  p."  50) : 

C5H3N4.NH2  +  H2O  =-■  C5H4N4O  +  NH3 

Adenin  Hypoxanthin 

C5H3N4O.NH,  +  H,0  -  CjH.N.O.  +  NH3 

Guanin  Xanthiii 

By  the  action  of  oxidases  also  present  in  the  tissues  the  hj^po- 
xanthin  and  xanthin  are  converted  into  uric  acid  (tri-oxy-purin). 
The  whole  process  may  be  grajDhically  represented  as  follows: 

Adenin  -^         Hypoxanthin 

(by  action  of  adenase)  (+  0  by  oxidase) 

CgHaNj.NH,  C5H4N4O 

(amino  purin)  (mon-oxy-purin) 

I 

i 

Guanin  -^  Xanthin 

(by  action  of  guanase)  (+0  by  oxidase) 

C5H3X4O.NH2  C5H4X4O2 

(amino  oxv-purin)  (di-oxy-purin) 

I 

Uric  Acid 
C5H4N4G3 

(tri-oxy-purin) 

Some  of  the  uric  acid  thus  formed  may  further  be  converted  into 
urea  hy  the  presence  of  a  uricohi;ic  enz3'me.  This  enzyme  occurs  in 
the  liver,  muscles,  and  kidney's,  and  probably  destroys  a  considerable 
amount  of  the  uric  acid  formed  in  the  bodj*.  Indeed,  uric  acid,  even 
when  given  in  the  food,  owing  to  the  presence  of  this  enzyme,  causes 
no  increase  in  the  uric  acid  output  of  the  body. 

Uric  acid  is,  however,  regarded  as  the  chief  end  product  of  nuclein 
and  purin  metabolism.  The  uric  acid  thus  formed  is  taken  to  the 
kidneys  for  excretion,  but  in  what  form  is  not  exactly  known.  Uric 
acid  is  about  iovty  times  more  soluble  in  blood  than  in  distilled  water. 
This  is  not  attributable  to  the  alkalinity  of  the  blood  (which  is  in 
reality  neutral),  since  uric  acid  is  also  much  more  soluble  in  acidified 
blood-serum  than  in  distilled  water.  Probably  uric  acid  is  carried 
in  the  blood  in  combination  with  some  other  organic  body,  and  not, 
as  was  once  generally  sujoposed,  with  sodium  salts  (sodium  urate  and 
soditim  acid  urate).  The  nature  of  the  organic  complex  is  not  known. 
It  is  by  some  supposed  to  be  thyminic  acid,  but  no  such  compound 
has  yet  been  isolated  from  the  blood. 

Experiment  shows  that  the  uric  acid  which  occurs  in  the  urine 
has  two  sources — an  exogenous,  from  the  purins  of  the  food;  an  endo- 
genous, from  the  purins  liberated  by  the  breaking  down  of  the  cell 
nuclei,  and  possibly  also  from  other  bodies.  The  presence  in  the  urine 
of  uric  acid  of  endogenous  origin  is  shown  by  the  fact  that  upon  a 
purin-free  diet  uric  acid  is  excreted  in  the  urine.  The  amount  then 
excreted  is  fairly  constant  for  each  individual.     This  excretion  reaches 


THE  METABOLISM  OF  NUCLEIN  445 

its  maximum  during  the  early  hours  of  the  morning,  and  subsides 
to  a  minimum  towards  evening.  It  is  apparently  unaffected  by  the 
periods  of  digestive  and  metabolic  activity  following  each  meal, 
but  more  uric  acid  is  excreted  after  a  rich  than  after  a  poor, 
nitrogenous,  purin-free  meal.  The  amount  of  uric  acid  is  therefore 
in  some  way  associated  with  the  degree  of  nitrogenous  metabolism 
of  the  body.  The  excess  of  uric  acid  may  be  ascribed — in  part,  at 
least — to  the  increased  functional  activity  of  the  body  cells.  Thus, 
severe  muscular  exercise  is  followed  after  several  horn's  by  a  rise  in 
the  amovmt  of  endogenous  uric  acid  excreted.  Also,  in  diseases  where 
a  large  amount  of  cell  dismtegration  is  taking  place  {e.g.,  leukaemias, 
fevers),  the  output  of  endogenous  uric  acid  is  increased.  It  is  not 
affected  by  the  giving  of  diuretics.  While  endogenous  uric  acid 
undoubtedly  arises  from  the  destruction  of  the  cell  nucleins,  the 
question  remains  as  to  whether  any  can  come  from  other  sources. 
It  is  known  that  there  is  a  large  hx-poxanthin  content  in  muscle,  and 
it  maj'  possibly  be  that  some  uric  acid,  especially  the  increase  after 
muscular  exercise,  comes  from  this  source.  The  amount  of  endogenous 
uric  acid  is  more  than  can  come  from  nuclear  destruction  in  the 
body. 

It  has  been  demonstrated  on  birds  that  perfusion  of  the  liver 
with  ammonia  and  lactic  acid  leads  to  a  formation  of  uric  acid.  There 
is  no  evidence  that  an}^  such  sjTithesis  of  uric  acid  takes  place  in  the 
mammal.  In  birds,  such  a  synthesis  is  homologous  to  the  formation 
of  urea  in  the  liver  of  a  mammal,  and  therefore  it  is  not  to  be  expected 
in  the  latter.  It  must  be  concluded  that  the  exact  source  of  all  the 
endogenous  purin  is  not  known.  The  exogenous  origin  of  uric  acid 
is  proved  by  the  fact  that  it  is  greatly  increased  in  the  urine  by  the 
giving  of  foods  containing  nuclein  or  purin,  especially  foods  rich  in 
nucleo-protein,  such  as  sweetbreads,  and  those  containing  much  hj^jDo- 
xanthin,  such  as  meat  extracts.  All  the  purins  administered  in  the 
food  are  not,  however,  excreted  in  the  urine  as  uric  acid;  some  are 
excreted  as  purins.  The  amount  of  uric  acid  formed  in  the  organism 
varies  with  the  kind  of  purin  fed  and  the  species  of  the  animal  which 
eats  it.  For  example,  in  man,  only  one-half  of  the  hypoxanthin 
administered  as  such  appears  as  uric  acid  in  the  urine,  and  but  one- 
fourth  of  the  purin  in  nuclein  w^hen  that  is  fed.  In  the  dog,  compared 
with  man,  about  ten  times  as  much  purin  disappears  in  its  passage 
through  the  organism;  in  the  rabbit,  about  three  times. 

There  is  doubt  as  to  whether  the  methyl  purins  (caffeine,  theo- 
bromine) lead  to  a  formation  of  uric  acid  in  the  organism,  or  whether 
they  are  secreted  as  purins  in  the  urine. 

One  of  the  symptoms  of  gout  is  a  permanent  increase  in  the  amount 
of  uric  acid  in  the  blood — a  "  uricsemia."  Various  reasons  have  been 
ascribed  as  the  cause  of  this.  At  one  time  it  was  believed  to  be  due 
to  defective  excretion  of  uric  acid  by  the  kidney.  Research  does  not 
lend  much  support  to  this  view,  although  it  is  quite  possible  that  the 
kidney  changes  Avhich  occur  late  in  the  disease  may  to  some  extent 
affect  the  elimination  of  uric  acid  by  the  organ. 


446  A  TEXTBOOK  OF  PHYSIOLOGY 

It  is  suggested  by  some  that  the  chief  factor  in  gout  is  a  defect 
in  the  transport  of  uric  acid;  by  others  it  is  beheved  to  be  due  to 
a  deficient  enzymic  activity,  particularly  of  the  uricolytic  enzyme  ot 
the  body.  Others  believe  that  gout  is  due  to  a  toxni  of  uitestinal 
origin;  yet  again  others  deem  it  to  be  secondary  to  abnormal  carbo- 
hydrate or  fat  metabolism.     The  whole  question  is  sub  judice. 


CHAPTER  LTV 
THE  FUNCTIONS  OF  THE  LIVER  AND  SPLEEN 

The  liver  is  developed  as  a  tubular  outgrowth  from  the  duodenum. 
The  ultimate  endings  of  this  tube  break  up  into  numerous  fine  ducts 
lined  by  ej^ithelial  cells  of  large  size — the  liver  cells.  The  whole 
makes  a  lobulated  gland,  the  lobule  belonging  to  each  branchmg 
duct  being  separated  from  its  neighbour  by  connective  tissue 
(Glisson's  capside).  In  this  interlobular  connective  tissue  run — 
(1)  bile  ducts,  (2)  branches  of  the  portal  vein  (interlobular), 
(3)  branches  of  the  hepatic  artery,  (4)  lymphatic  vessels.  In  (1) 
bile,  in  (4)  lymph  flows  from  the  lobules,  in  (2)  and  (3)  blood 
flows  to  the  lobules.  The  liver  lobule  has  a  large  blood-supply.  The 
hepatic  artery  brings  oxygenated  blood,  and  the  portal  vein  blood 
containing  foodstuffs  which  have  been  absorbed  from  the  alimentary 
canal.  The  capillaries  arising  from  the  artery  and  portal  vein  anastomose 
as  they  radiate  through  the  lobule,  forming  a  network  of  fine  branching 
vessels  (interlobular  branches).  These  unite  in  the  centre  of  the 
lobule  to  form  an  intralobular  vessel,  which  joins  with  others  to  make 
a  sublobular  vein,  the  fusion  of  sublobular  veins  finally  forming  the 
hepatic  vein.  The  large  branches  of  this  gape  open  when  the  liver  is 
cut.  The  bile  canaliculi,  the  first  comemncement  of  the  bile  ducts,  are 
channels  between  the  liver  cells,  and  can  be  demonstrated  by  giving 
Guch  a  dye  as  sulph'ndigotate  of  soda.  This  is  secreted  with  the 
bile,  and  distends  and-stains  the  canaliculi.  They  can  also  be  stained 
by  Golgi's  method. 

The  liver  is  an  organ  of  manifold  functions,  some  of  which  have 
already  been  mentioned  or  dealt  with.  We  propose  in  this  section 
to  group  together  the  various  functions  of  the  organ  in  order  that 
the  scope  of  its  activities  may  be  appreciated. 

1.  The  Formation  and  Excretion  of  Bile. — Within  the  liver  the  bile 
salts  are  synthesized,  and  the  bile  pigments  are  derived  from  the 
haemoglobin  of  effete  blood-corpuscles.  These,  together  with  the  other 
constituents  of  the  bile,  are  secreted  into  the  bile  canaliculi,  and  pass 
thence  into  the  intestine,  there  to  fulfil  the  various  functions  already 
indicated  (see  p.  391). 

2.  The  Glycogenic  Function. — The  liver  acts  as  the  storehouse  of 
the  colloid  glycogen.  This  it  forms  from  the  dextrose  brought  by 
the  portal  vein,  and  under  approjDriate  circumstances  reconverts  it 
into  dextrose  for  use  in  other  parts  of  the  body,  particularly  in  the 

447 


448  A  TEXTBOOK  OF  PHYSIOL(JGY 

muscles  (see  p.  427).  The  liver  probably  also  forms  glycogen  from 
other  bodies,  including  the  non-nitrogenous  moiety  left  over  when 
certain  amino-acids  are  deaminized,  either  in  the  intestinal  mucous 
membrane  or  in  the  liver  itself  (c/.  p.  424), 

3.  Storage  of  Fat. — Although  the  liver  contains  a  certain  per- 
centage of  '■  masked  '"'  fat — that  is,  fat  which  is  not  visible  to  staining 
processes — under  certain  circumstances,  such  as  during  pregnancy 
and  lactation,  the  liver  contains  large  amounts  of  visible  fat,  the 
exact  significance  of  which  is  not  known.  Thus  visible  fat  in  the 
liver,  which  occurs  in  "  fatty  degeneration,"  is  not  always  a  patho- 
logical phenomenon. 

4.  The  Formation  of  Uric  Acid. — The  liver  jiossesses  deaminizing 
enzymes  which  are  capable  of  converting  purin  bodies,  such  as  adenin 
and  guanin,  into  the  oxypurins  hypoxanthin  and  xanthin,  and  also 
oxidizing  enzymes  capable  of  converting  these  bodies  to  uric  acid. 
It  also  in  the  mammal  contains  a  uricotytic  enzyme  which  turns  uric 
acid  into  lu'ea. 

5.  The  Formation  of  Urea.— The  liver  plays  an  important  part  in 
(he  metabolism  of  protein,  jjarticularly  in  the  end  processes  of  this 
metabolism  which  result  in  the  formation  of  urea. 

The  fact  that  urea  is  formed  in  the  liver  can  be  demonstrated  in 
various  ways : 

(1)  Extirpation  of  the  liver  in  the  frog  leads  to  a  diminution  in 
the  amount  of  urea  excreted,  and  an  increase  of  ammonia  bodies  in 
the  excreta. 

(2)  In  birds,  such  as  the  goose,  there  is  a  connecting  vein  between 
the  portal  vein  and  the  inferior  vena  cava.  Ligature  of  the  portal 
vein  on  the  liver  side  of  this  connection  diverts  the  contents  of  the 
portal  system  into  the  inferior  cava.  Under  these  circumstances, 
there  occurs  in  birds  a  marked  diminution  in  the  excreta  of  the  amount 
of  uric  acid,  the  homologue  of  urea  in  the  mammal,  and  a  corresponding 
increase  in  the  amount  of  ammonium  compounds. 

(3)  In  mammals,  a  similar  condition  of  affairs  may  be  brought 
about  by  the  operation  devised  by  Eck,  and  known  as  Eck's  fistula. 
The  operation  consists  in  making  a  communication  between  the  portal 
vein  and  the  inferior  vena  cava.  As  before,  the  portal  vein  is  ligated 
as  it  enters  the  liver,  and  the  portal  circulation  is  thereby  deviated 
from  the  liver.  Under  these  circumstances,  the  amount  of  urea  is 
greatly  decreased  in  the  virine,  the  ammonia  content  being  greatly 
increased.  It  is  generally  stated  that  animals  upon  which  this  experi- 
ment has  been  performed  show  marked  symptoms  of  metabolic  dis- 
turbance, accompanied  by  signs  of  ferocity  and  bad  temper.  This 
apparently  depends  upon  the  nature  of  the  diet  given  after  the  oj)era- 
tion.  Dogs  which  have  had  such  an  experiment  performed  upon 
them,  with  the  hepatic  artery  and  vein  ligated  in  addition,  remain 
for  many  days  after  the  operation  quite  happy  and  docile  so  long  as 
they  were  fed  on  bread  and  milk.  During  this  time  they  were  becom- 
ing progressively  thinner.     Any  form  of  meat  in  the  diet,  however, 


THE  FUNCTIONS  OF  THE  LIVER  AND  SPLEEN        44!) 

immediately  brought  on  signs  of  surliness,  and  eventualh'  induced 
convulsions. 

(4)  In  certain  forms  of  liver  disease  the  amount  of  vu'ea  passed  in 
the  urine  is  markedly  diminished,  the  amovint  of  ammonia  bodies 
being  correspondingly  increased. 

(5)  Perfusion  of  blood-containing  ammonium  carbonate  through 
.  the  liver  of  a  mammal  leads  to  a  marked  increase  in  the  urea  content 

of  the  blood.  This  experiment  was  done  originally  upon  the  liver  of 
a  dog,  but  it  holds  true  for  all  mammals.  According  to  some  autho- 
rities, amino-acids,  such  as  glycin,  alanin,  arginin,  also  lead  to  the 
formation  of  urea  when  perfused  through  the  isolated  liver.  This, 
however,  is  not  accepted  by  all — at  any  rate,  as  a  normal  process. 

L^rea,  therefore,  is  undoubtedly  formed  in  the  liver,  the  main 
precursor  being  compounds  of  ammonia.  These  compounds  are 
particularly  the  carbonate,  which  may  be  graphically  represented  as 

^^  .ONH, 

and  the  carbamate,  Avhich  may  be  figured  as 

^^/ONH^ 

The  change  to  urea  nuiy  probably,  therefore,  be  I'epresented  as 
follows : 

^^\ONHj ^     ^^     NH. >    '-^   .NH, 

Ammonium  carbonate  Ammonium  carbamate  Urei 

Some  of  the  urea  formed  in  the  liver  may  be  derived  from  the 
conversion  of  uric  acid  to  urea.  It  has  been  shown  in  the  laboratory 
that  creatin  may  give  rise  to  urea.  There  is,  however,  no  good 
evidence  to  show  that  such  is  the  case  inside  the  body. 

Most  of  the  urea  formed  in  the  liver  is  derived  from  the  nitrogenous 
part  of  the  food  taken  in — that  is  to  say,  it  is  exogenous  in  origin. 
Alterations  in  the  amoimt  of  nitrogenous  food  cause  similar  fluctua- 
tions in  the  amount  of  mea  in  the  urine  (see  p.  455).  The  view  held 
as  to  the  form  in  which  the  j^reci^rsor  of  urea  reaches  the  liver 
depends  naturall.y  upon  which  hyiDothesis  of  protein  metabolism 
is  put  forward.  According  to  the  first  view  (p.  424),  urea  would 
be  derived  mainly  from  the  amino-acids  brought  to  the  liver  by 
the  portal  blood,  particularly  from  such  amino-acids  as  gh^cin, 
alanin.  leucin.  and  arginin.  According  to  the  other  view,  no  such 
acids  exist  in  the  portal  blood.  The  precur.sor  of  most  of  the  urea 
formed  in  the  liver  would  in  this  case  be  the  ammonia  which  has 
been  broken  off  from  the  excess  amino-acids  during  the  process  of 
their  deaminization  in  the  intestmal  mucous  membrane.  This  is 
transported  to  the  liver  in  the  form  of  the  carbonate  and  carbamate, 
and  converted  into  urea.  Some  urea  might  also  be  formed  from 
excess  amino-acids  left  over  in  the  bloodstream  after  a  tissue  has 

29 


450  A  TEXTBOOK  OF  PHYSIOLOCiV 

taken  from  the  plasma  protein  the  particular  amino-acids  of  which  it 
has  need.  Another  part  of  the  urea  might  also  be  endogenous  in 
origin,  being  formed  in  the  liver  from  the  amino-acids  resulting  from 
the  katabolism  of  protein  in  various  parts  of  the  body. 

The  question  as  to  whether  urea  is  formed  solely  in  the  liver  should 
probably,  despite  views  to  the  contrary,  be  answered  in  the  negative. 
There  is  apparentlj-  a  small  formation  of  urea  from  endogenous  i)re- 
curfcors  in  other  parts  of  the  body,  particularly-  the  muscles.  Per- 
fusion of  the  hind-limbs  of  an  animal  with  defibrinated  blood  leads 
to  an  increase  of'  the  urea  content  in  the  venous  over  the  arterial 
blood.  It  is  correct,  however,  to  say  that  the  main  mass  of  urea 
execreted  from  the  bodj'  is  formed  in  the  liver  from  the  nitrogenous 
moiet}''  of  the  j)rotein  food  taken  in. 

0.  Protective  Function. — Another  important  function  of  the  1  ver 
is  its  i)rotective  function.     This  is  manifested  in  various  ways: 

(1)  The  nocuous  products  of  protein  putrefaction  in  the  large  in- 
testine, such  as  indol,  skatol,  phenol,  tresol,  are  combined  in  the  liver 
with  sulphuric  acid  to  form  the  innocuous  potassium  salt  of  the  acid. 

NH  :C8H6  +  0  =  NH  .CsHsOH 

Indol  Indoxyl 

NH  :C«H,OH  +  SO./  OK  =  ^^  ••CsH,.O.SO,K  +  H,0 

Potassium  Potassium  indoxyl 

aoid  sulphate         Sulphuric  acid  (indican) 

CeH.OH  +  S0,<  OK  =  CsH^.O.SOaK  +  H,0 

Phenol  Potassium  phenol 

Sulphuric  acid 

In  cases  of  excessive  formation  these  bodies  are  combined  v.ith 
glycuronic  acid  also. 

(2)  Drugs,  such  as  chloral,  camphor,  etc.,  are  combined  with 
glycuronic  acid  in  the  liver,  and  rendered  harmless  or  less  harmful. 

(3)  When  acid  formation  is  going  on  within  the  body — for  example, 
the  formation  of  aceto-acetic  acid  and  f/-oxy-but\Tic  acid  during 
starvation,  or  in  pathological  conditions  such  as  diabetes  melliliis— 
the  liver  to  a  certain  extent  negatives  the  ill  effects  of  such  acids  by 
combining  them  with  ammonia,  thereby  markedly  increasing  the 
ammonia  content  of  the  urine. 

(4)  The  liver  possesses  the  property  of  retaining  within  its  cells 
poisonous  minerals,  such  as  phosphorus,  arsenic,  mercurj-.  antimony. 
But  little  is  known  as  to  the  exact  manner  in  which  this  is  accomplished. 

7.  Fibrinogen  Formation, — The  liver  is  possibly  the  organ  in  which 
the  fibrinogen  of  the  blood  arises,  also  antithrombin  when  peptone 
is  injected  into  the  blood;  this,  according  to  the  generally  accepted 
view  of  blood-coagulation,  renders  the  blood  and  lymph  incoagulable 
—the  result  of  such  an  injection. 


THE  FUNCTIONS  OF  THE  LIVER  AND  SPLEEN        451 

8.  Heat  Formation. — The  liver,  by  virtue  of  its  manifold  chemical 
activities,  produces  heat. 

9.  Venous  Reservoir. — Lastly,  the  liver  acts  as  a  venous  reservoir 
interposed  in  the  portal  circulation,  and  bj'  \Trtue  of  this  property 
prevents  overdistension  of  the  right  side  of  the  heart.  The  blood 
within  it  is  expressed  into  the  heart  by  the  action  of  the  diaphragm, 
and  the  vigour  of  the  hepatic  circulation  therefore  depends  very  much 
on  the  vigour  of  respiration  that  is  on  muscular  exercise.  In  cases  of 
failure  of  the  right  side  of  the  heart  the  liver  becomes  greatly  engorged 
with  blood,  and  is  felt  pulsating  below  the  margin  of  the  ribs. 

The  Spleen. — The  exact  nature  of  the  main  function  of  the  spleen 
is  a  matter  of  surmise.  The  gland  can  be  extirpated  from  man  and 
animals  without  ill  effects.  It  is  stated  to  have  been  removed  from 
athletes  in  classical  times,  to  prevent  "  stitch."  It  appears  probable 
that,  after  the  operation,  there  is  a  compensator}'  overgrowth  or 
hAq^ertrophy  of  lymphatic  tissue.  It  has  been  shown  recently  that 
after  extirpation  of  the  spleen  more  iron  is  lost  than  formerlj'  in  the 
urine;  the  spleen  ma}'  therefore  be  the  regulator  of  the  iron  meta- 
bolism of  the  body.  There  is  some  evidence  that  in  the  spleen  the 
effete  red  blood-corpuscles  of  the  bod}^  are  destroyed.  It  is  question- 
able whether  in  adult  life  the  spleen  plays  any  part  in  the  formation 
of  red  corpuscles,  although  it  certainh'  does  so  in  the  foetus.  By 
virtue  of  its  lymphatic  tissue,  the  spleen  gives  origin  to  some  of  the 
lymphocytes  of  the  blood,  and  pla3^s  a  considerable  part  in  the  purin 
metabolism  of  the  body.  During  the  first  hours  following  digestion 
the  spleen  is  swollen  in  size,  acting  like  the  liver  as  a  blood-reservoir 
in  the  portal  circulation.  The  spleen  rh3ii;hmically  contracts.  The 
enlargement  of  the  spleen  in  certain  fevers — e.g.,  malaria,  tyjjhoid — 
shows  that  it,  like  the  lymph  gland,  is  engaged  in  protecting  the  body 
against  bacterial  invasion. 


BOOK    VIII 

THE    FUNCTIONS   OF   THE    KIDNEY 

CHAPTER  LV 
THE  URINE 

The  urine,  continuous^  secreted  by  the  kidneys,  averages  about 
1,500  CO.  (50  ounces)  in  twenty-four  hours.  The  larger  part  of  this 
amount  is  passed  during  the  day,  but  in  certain  diseased  conditions 
more  uiaj^  be  passed  during  the  night.  For  this  reason,  some  clinicians 
have  the  urine  passed  during  the  twenty-four  hours  collected  in  two 
portions.  The  day  urine  is  taken,  say,  from  8.30  a.m.  to  8.30  p.m., 
the  bladder  being  emptied  at  both  these  times.  The  remainder  is  the 
'■  night  urine."  Children  pass  considerabty  less  urine  than  an  adult. 
At  five  years  the  daily  amount  is  about  390  c.c,  at  twelve  3'"ears  about 
830  c.c,  about  fifteen  the  amount  begins  to  approximate  to  that  of 
the  adult. 

As  the  urine  passed  at  difi^erent  times  during  the  day  varies  con- 
siderably in  composition,  it  is  usual  to  take  the  total  urine  of  twenty- 
four  hours  for  purposes  of  chnical  analysis.  Various  factors  modify 
the  amount  passed.  An  increased  secretion  follows  a  large  consump- 
tion of  food  or  drink,  and  exposure  to  cold.  On  the  other  hand,  in- 
gestion of  little  food  or  drink,  exposure  to  heat,  great  muscular  work, 
the  conditions  which  produce  sweating,  lead  to  a  diminished  secretion. 

Normal  urine  is  a  transparent,  limjjid,  watery  fluid,  yellow  in 
colour.  When  shaken  in  a  test-tube,  there  is  a  little  froth,  which 
does  not  last  long.  When  certain  pathological  bodies  are  present, 
particularly  bile  and  protein,  the  urine  is  less  mobile,  and  the  froth 
much  more  marked.  Thus,  the  presence  of  albumin  may  be  indicated 
by  the  froth  on  shaking. 

The  odour  of  healthy  urine  is  described  as  aromatic.  After  stand- 
ing for  some  time,  this  changes  to  an  "  ammoniacal  "  smell,  owing  to 
the  action  of  organisms  {Micrococcus  urece)  which  fall  into  it,  and 
by  their  growth  break  down  the  urea  present,  with  the  liberation 
of  ammonia. 

The  specific  gravity  of  urine,  as  tested  by  the  instrument  known 
as  the  urinometer.  is  on  an  average  1015  to  1025.  These  figures 
apply  to   the   twenty-four-hour  sample ;    for  samples  casualh^  taken 

4r)H 


454  A  TEXTBOOK  OF  PHYSIOLOGY 

it  may  var}'  greatly.  A  urine  may  have  a  specific  gravity  below 
1010  after  much  drinking,  or  as  high  as  1035  after  much  sweating. 
An  abundant  urine  of  low  specific  gravity  is  suggestive  of  some  patho- 
logical condition,  such  as  diabetes  insipidus  or  chronic  renal  disease, 
while  the  passage  of  large  quantities  of  pale  urine  of  high  specific 
gravity  suggests  the  presence  of  sugar  in  the  urine.  If,  on  the  other 
hand,  the  colour  be  high,  some  condition  causing  loss  of  water  from 
the  l)od\-,  such  as  diarrha?a  or  fever,  ma\'  be  present.  The  quantity 
of  the  solids  in  the  urine  per  litre  may  be  roughly  estimated  by 
taking  the  specific  gravity  of  the  urine  at  15°  C,  and  multiplying 
it  by  2-33. 

The  osmotic  pressure,  measured  by  depression  of  freezing-point, 
varies  from    -  0-8°  to  -2-7°  C. 

The  reaction  of  the  urine,  as  tested  by  chemical  indicators,  is 
generally  acid.  To  the  ph3'sical  test  the  urine,  like  the  blood,  is 
neutral  (see  p.  76).  The  acidity  to  Ltmus  is  due  mainly  to  the  acid 
phosphate  of  sodium  (XaH2P04).  When,  however,  urine  is  passed 
during  the  digestion  of  a  meal,  it  is  often  amphoteric  or  alkaline  in 
reaction.  This  is  because  the  acid  phos])hate  in  the  blood  is  con- 
verted into  disodium  phosjohate  (XaoHPO^).  owing  to  the  formation x)f 
the  HCl  of  the  gastric  juice.  The  reaction  of  urine  may  also  be  alka- 
line after  eating  fruits  and  V3getables  containing  organic  acids  (citric, 
malic,  etc.).  These  are  converted  in  the  bodj^  into  alkaline  carbonates, 
which  are  excreted  in  the  urine.  It  is  believed  by  some  authorities 
that  the  acidity  of  the  urine  is  in  part  due  to  the  presence  of  volatile 
organic  acids  in  the  urine.  It  is  stated  that,  if  urine  be  distilled,  the 
2:)art  which  distils  off  is  acid,  owing  to  the  presence  of  such  volatile 
acids. 

For  clinical  purposes,  the  total  acidity,  and  indirectly  the  am- 
monia, of  the  urine  may  be  determined  by  a  method  in  which  the 
acidity  is  first  estimated  by  titrating  Avith  ^^^^  XaHO.  Xeutralized 
formalin  is  then  added.  The  ammonia  of  the  urine  combines  with 
this  to  form  the  neutral  compoiuid  lu'otropine,  setting  free  the 
acids  to  which  the  ammonia  is  combined.  A  second  estimation 
with  f'jj  NaHO  gives  this  acidity,  and  from  it  the  amount  of  nitrogen 
present  as  ammonia  may  be  calculated  by  multiplying  by  00014. 

The  Transparency  and  Colour  of  the  Urine. — Freshly  voided  normal 
urine  is  transparent,  and  possesses  a  ^^ellowish  colour,  the  exact  tint 
■of  Avhich  fluctuates  widely  even  in  health  according  to  the  degree  of 
dilution  and  the  reaction  of  the  urine.  This  colour  is  due  chiefly  to 
the  pigment  urochrome.  Other  pigments — urobilin,  uroerythrin, 
iirorosein — also  occur  in  normal  urine  under  various  conditions. 

Urochrome. — The  origin  of  this  pigment  is  not  known.  It  is 
probablj-  derived  from  protein,  as  it  contains  nitrogen  and  sulphur 
in  its  molecule.  It  yields  no  absorption  bands  when  examined  spectro- 
scopic ally. 

Urobilin  is  not  present  in  freshly  voided  urine,  but  its  chromogen 
is — urobilinogen.  The  darkening  of  urine  on  standing  is  due  to  the 
conversion    of    urobilinogen    into    urobilin.     Urobilin,  when    present, 


THE  URINE  455 

gives  one  broad  absorption  band  in  the  green  between  b  and  F.  The 
urine  containing  it  is  generally  dichroic,  appearing  red  by  transmitted, 
and  green  by  reflected,  light.  If  urobilinogen  be  in  excess,  it  is  found 
that  an  acid  solution  of  dimethjdparaminobenzaldehyde  (2  grammes 
in  100  c.c.  5  per  cent.  HCl),  when  added  to  the  urine,  turns  red  in 
the  cold.  With  normal  urine,  such  a  red  coloxu-  is  only  developed  on 
Leating. 

Ui'oerythrin  confers  a  dark  pink  colour  on  concentrated  urine. 
■Spectroscopically,  it  yields  two  bands,  one  at  E,  the  other  at  F.  They 
are  not  well  defined.     Urorosein  is  an  indol  derivative. 

Composition. — Normal  urine  contains  about  96  per  cent,  of  water 
•and  4  per  cent,  of  solids.  The  chief  organic  boclies  are — Urea,  uric 
acid,  purin  bodie3,  creatinin,  ethereal  sulphates,  neutral  sulphur  com- 
jjounds,  oxalic  acid,  hippuric  acid,  enzjanes,  pigments. 

The  inorganic  solids  are — Chloride  solids  of  sodium  and  potassium, 
sulphates,  phosphates,  carbonates. 

The  Nitrogenous  Constituents. — The  chief  of  these  are  urea,  am- 
monia, uric  acid,  creatinin,  hippuric  acid.  There  are  various  other 
substances  in  small  quantities,  including  the  purin  bases.  These 
vary  in  percentage  according  to  the  intake  of  nitrogenous  food  in  the 
diet.  With  the  exception  of  ci'eatinin,  the  amount  of  these  bodies 
•excreted  falls  as  the  amount  of  the  nitrogen  in  the  diet  is  decreased. 

According  to  the  diet  the  percentage  of  urea  varies  in  relation  to 
the  percentage  of  other  bodies,  particularly  to  the  percentage  of 
ammonia. 

This  is  shown  by  the  following  analyses  of  such  urines: 


Nitrogen-Rich  Diet.  Nitrogen-Poor  Diet. 


Total  nitrogen  excreted 
Urea  N 
Ammonia  N 
Uric  acid  I\   . . 
•Creatinin  N  . . 
Undetermined  N 


Almost  the  whole  of  the  nitrogen  taken  in  the  food  is  excreted  in 
the  urine.  Protein  contains  about  15  per  cent,  of  nitrogen,  and  if  100 
grammes  are  consumed,  about  1  gramme  nitrogen  will  be  passed  in  the 
faeces,  a  trace  in  the  sweat,  and  the  rest  in  the  urine.  B}^  estimating 
the  total  nitrogen  of  the  twenty-four  hours'  urine  the  intake  of  protein 
■can  be  calculated. 

The  Total  Nitrogen  of  the  Urine  is  estimated  by  means  of  Kjeldahl's 
method,  or  one  of  its  modifications.  The  process  is  carried  out  in 
three  stages:  (1)  The  oxidation  of  the  nitrogen  present  in  the  urine  to 
ammonia;  (2)  the  distillation  and  collection  of  this  ammonia  in  a 
standard  acid  solution:  (3)  the  ascertaining  by  titration  of  the  amount 
of  this  ammonia. 


Griii3. 

Grm.s- 

16-8 

3-60 

14-7  (S7-.5 

per  cent.) 

2-20  ((il-7 

i)er  cent.) 

0-49  (3-0 

jj         ) 

0-12  (11-3 

,,          ) 

0-18  (1-1 

»>         ) 

0-09  (  2-5 

,,         ) 

U-58  (3-6 

>'          ) 

0-60  (17-2 

,,         ) 

0-85  (4-0 

) 

0-27  (  7-3 

) 

456  A  TEXTBOOK  OF  PHYSIOLOGY 

111  the  first  part  of  the  process,  a  known  quantity  of  the  mine  is. 
heated  in  a  long-necked,  hard  glass  flask  with  strong  sulphuric  acid, 
and  a  little  of  the  sulphates  of  j)otassium  and  copper  are  added  to 
facilitate  oxidation  by  raising  the  boiling-point  of  the  acid.  The 
ammonia  formed  is  combined  Avith  the  sulphuric  acid  to  form  am- 
monium sulphate.  The  heating  is  continued  until  the  Hind  becomes 
almost  colourless. 

In  the  second  jjart  of  the  process,  the  excess  of  acid  is  neutralized 
by  strong  alkali  (40  per  cent.  NaHO),  an  excess  of  alkali  being  added. 
Then  the  ammonia  is  distilled  over  into  a  standard  acid  solution 
(-j^  H.2SO4)  containing  an  indicator  such  as  methyl  orange.  The  indi- 
cator is  required  to  show  that  there  is  sufficient  acid  present  to 
trap  all  the  ammonia  driven  over. 

In  the  third  part  of  the  process,  the  excess  of  acid  in  the  receiving 
flask  is  ascertained  by  titrating  with  standard  alkali  (j^^  NaHO). 
By  subtracting  this  excess  from  the  amount  of  standard  acid  originally 
taken,  the  amount  of  acid  combined  with  ammonia  is  found.  Multi- 
plying this  amount  by  0-0014,  we  arrive  at  the  amount  of  nitrogen  in 
the  sample  of  urine. 

Urea  is  the  chief  nitrogenous  waste  sub.stance  of  the  mammal. 
Its  formula  is 

/\H 

and  it  maj  be  regarded  as  carbonic  acid  (HoCOg),  or 

^^  \0H 

in  which  the  two  hj'droxyl  groups  (OH)  have  been  replaced  by 
two  amine  (XH^)  groups.  It  has  the  same  empirical  formula  as 
ammonium  cvanate.  from  which  bodv  it  was  first  prepared  bj^ 
Wohler  in  1828— 

CONKH,    ^    ^'^     Nh! 

— the  first  synthesis  of  an  organic  substance  out  of  inorganic  material. 
Carbamic  acid 

XHo 


^^\0H 

may  be  jiresent  in  the  urine  as  a  salt,  for  example  after  experi- 
mentally excluding  the  liver  from  the  circulation.  It  is  apparently 
a  precursor  in  the  svnthesis  of  urea  (see  p.  449). 

Pure  urea  consists  of  colourless  elongated  crystals.  It  is  extremely 
soluble  in  water,  alcohol,  and  acetone,  but  insoluble  in  ether  and 
chloroform.  It  possesses  the  j)roperty  of  dissolving  connective  tissue,, 
and  may  be  used  in  making  teased  preparations — e.g.,  to  isolate 
muscle  fibres.  It  is  also  a  good  solvent  for  uric  acid.  It  combiner 
with  acids  to  form  salts,  such  as  urea  nitrate  and  urea  oxalate 
(Figs.  219,  220). 


THE  URIXE 


45- 


\A^hen  solid  urea  is  heated  in  a  drj"  test-tube,  it  first  melts  and  then 
goes  solid  again.  During  the  process  ammonia  gas  is  given  off,  and 
the  body  known  as  biuret  is  formed,  which,  with  a  little  copper  sulphate 
and  some  caustic  potash,  gives  a  pink  colour. 

2co<^;g2  =.  XH3 + co<^;h, 

A  Ho 

Biuret 

If  still  further  heated,  a  body  known  as  cyanuric  acid  (C3N3H3O3) 
is  formed,  which  does  not  give  the  biuret  test. 

Urea  is  precipitated  from  solution  as  a  dense  white  precipitate  by 
the  addition  of  mercuric  chloride. 

The  presence  of  urea  in  urine  may  be  shown  by  concentrating  the 
urine  by  evaporation  over  a  water-bath,  and  adding  concentrated 
nitric  or  oxalic  acid,  when  crj^stals  of  xn-ea  nitrate  or  oxalate  will  be 


!■"[  ;.  219. — Urea  Xitratk. 


Fig.  220.^Urea  Oxalate. 


deposited.  Crystals  of  urea  may  be  obtained  by  rubbing  the  urea 
nitrate  into  a  paste  with  barium  carbonate — as  a  result,  barium 
nitrate  and  urea  are  formed,  with  the  evolution  of  carbon  dioxide, 
and  then  extracting  with  alcohol,  and  allowing  the  alcohol  to 
evaporate.  Crystals  of  urea  may  also  be  obtained  directly  from 
concentrated  urine  by  extracting  with  acetone,  and  allowing  the 
acetone  to  evaporate.  On  heating  with  acids  under  pressure,  urea  is 
decomposed  into  ammonia  and  carbon  dioxide.  It  is  also  split  thus 
by  the  ferment  urease  present  in  certain  bacteria  and  in  the  soya  bean. 
When  fuming  nitric  acid  is  added  to  urine,  an  evolution  of  carbon 
dioxide  and  nitrogen  takes  place,  owing  to  a  decomposition  of  the  urea, 
as  expressed  liy  the  equation 

C0<^15-  +  2HN0o  =  CO.,  +  2X,  +  3K,0 


458 


A  TEXTBOOK  OF  PHYSIOLOGY 


A  similar  reaction  takes  place  when  sodium  hypobromite  is  added 
to  urine,  but  nitrogen  alone  is  evolved,  the  CO2  remaining  combined 
to  the  alkali  present  in  the  solution. 

CO<5§2  +  SNaBrO  +  2NaH0  =  3NaBr  +  X,  +  3HoO  +  Na.COg. 

Advantage  is  taken  of  this  reaction  for  estimating  the  daily  output 
of  urea.  The  method  is  not  very  exact,  since  nitrogen  is  also  evolved 
from  uric  acid  and  other  bodies  present  in  the  mine.  A  known  amount 
of  urine  is  mixed  with  an  excess  of  the  hypobromite  solution,  and  the 
evolved  nitrogen  collected.  The  apparatus  employed,  such  as  Dupre's, 
is  generally  graduated  in  percentages  of  urea.  With  Southall's  ureo- 
meter  (Fig.  221)  one  c.c.  of  urine  from  a  special  pipette  is  carefully 
injected  below  the  bend  of  the  tube  which  is  filled  with  h3'i3obromite. 
If  no  such  apparatus  be  available,  the  gas  may  be 
collected  over  water  in  a  burette,  and  the  amount 
of  urea  calculated  from  the  fact  that  01  gramme 
of  urea  yields  35-4  c.c.  of  nitrogen. 

A  more  exact  method  of  estimating  urea  in  urine 
is  to  heat  some  of  the  urine  Avith  magnesium  chloride 
and  hydrochloric  acid.  The  urea  under  these  cir- 
cumstances is  broken  down  to  ammonia,  which 
combines  Avith  the  acid  jDresent  to  form  ammonium 
chloride.  The  other  nitrogenous  constituents  of  the 
urine  are  not  affected  in  the  process.  The  amount 
of  ammonia  in  the  ammonium  chloride  thus  formed 
is  then  determined  by  Kjeldahl's  process. 

There  is  little  information  of  clinical  value  to  be 

gained  from  an  estimation  of  the  urea  output  alone. 

What  is  required  is  a  knowledge  of  the  amount  of 

nitrogen  taken  in  the  diet,  and  the  relative  values 

of  the  urea,   creatinine,  ammonia,  etc.,  excreted  in 

pathological  conditions.     Clinical  information  of  this 

character  has  yet  to  be  collected. 

The  precursors  of  urea  and  the  site  of  its  formation  in  the  body 

have  already  been  discussed.     About  25  to  40  grammes  of  urea  are 

excreted  dai.y,  the  amount  varying  according  to  the  diet. 

Uric  Acid  is  the  chief  nitrogenous  waste  product  of  birds  and 
reptiles.  It  occurs  also  in  mammalian  urine  combined  with  alkalies. 
The  empirical  formula  of  uric  acid  is  C.H^N^Og;  it  is  tri-oxy-purin, 
and  the  formula  may  be  graphically  represented  thus: 

HN— CO 


Fig.  221. 
Ueeometer. 


OC      C— NH 


HN— C— N 


CO 


(see  p.  50).     About  0-4  to  0-7  gramme  of  uric  acid  is  excreted  in 
the  human  urine  daily.     It  is  a  dibasic  acid,  and  therefore  forms  two 


THE  URIXE 


459 


classes  of  salts — the  normal  urates  (Xa^f )  and  the  acid  urates  (XaHC). 
The  chief  urates  present  in  the  urine  are  acid  sodium  urate  (C-H.^XaX^O) 
and  normal  sodium  urate  (C-H,Xa.,Xj0.j).  Sometimes  ammonium  urate 
also  occurs.  Urates  are  frequently  deposited  from  concentrated  urme 
as  a  pinkish  deposit  coloured  ])v  uroerythrin.  Such  a  deposit  is 
sokible  on  heating  or  addition  of  alkaU.  Urates  are  sometimes  amor- 
phous, sometimes  erystaUine,  as  ""  thorn  apples,"  fan-shaped  clusters  of 
prismatic  needles  (Fig.  222).  To  obtain  uric  acid  quickly,  a  consider- 
able quantity  of  urine  (about  100  c.c.)  is  taken,  ammonia  added  till 
the  reaction  is  alkaline,  and  then  the  urine  saturated  with  ammonium 
chloride.  Ammonium  urate  is  ]Dreci]3itated.  and  from  this  precipitate 
uric  acid  may  be  obtained  bv  the  addition  of  acid.     If  hydrochloric' 


Fig.  222. — Sjdil'ji  Urate,     x  3.50. 


acid  be  added  to  urine,  and  the  urine  be  left  to  stand  for  twenty-four 
hours,  crystals  of  uric  acid  fall  out,  usually  highly  pigmented  Avith 
urorosein,  and  known  as  the  brick-dust  or  cayenne-pepper  deposit. 
Under  the  microscope,  the  crystals  apjiear  shaped  like  whetstones, 
barrels,  wedges,  rosettes,  and  coloured  reddish-yelloA\'  (Fig.  223). 
Uric  acid  is  sometimes  passed  in  acid  urines,  and  known  as  gravel. 
Stones  formmg  in  the  bladder  and  kidney  are  often  found  to  be  com- 
posed of  uric  acid  or  urates. 

Uric  acid  is  almost  insoluble  in  \\ater.  It  is  lield  in  solution  in  the 
urine  partly  bj'  the  alkaline  phos]jhates.  and  partly  by  the  in-ea 
preiont.  It  is  readily  soluble  in  alkalies.  \Mien  evaporated  with 
nitric  acid,  it  leaves  a  yellowish  residue,  Avhich  turns  purple  on  adding 
ammonia,  and  blue  with  caustic  potash  (the  murexide  test).  Urates 
also  give  this  murexide  test,  which  depends  upon  the  fact  that  a  sub- 
stance— alloxantin — is  formed  from  uric  acid,  and  combines  with 
ammonia  to  form  ammonium  purjiuratc. 


460 


A  TEXTBOOK  OF  PHYSIOLOGY 


A  strong  solution  of  uric  acid  in  alkali  reduces  Fehling's  solution 
on  heating,  but  not  Nylander's  solution  (see  p.  (il).  It  will  also 
reduce  silver  nitrate  in  the  cold.  If  a  drop  of  an  alkaline  uric  acid 
solution  be  placed  on  a  filter-paper,  and  a  drop  of  silver  nitrate 
solution  be  added,  a  blackened  area  of  reduced  silver  results  (Schiff's 
test). 

Uric  acid  is  estimated  quantitatively  by  precipitating  it  as  am- 
monium urate,  as  described  above,  washing  the  precipitate  carefully 
to  remove  all  traces  of  chlorides,  setting  free  the  uric  acid  by  the 
addition  of  sulphuric  acid,  and  titrating  with  a  standard  solution  of 
potassium  permanganate  imtil  the  rose  colour,  which  at  first  dis- 
appears, just  persists. 

Uric  acid  is  both  exogenous  and  endogenous  in  origin  (see  p.  444). 
It  is  increased  by  ingestion  of  bodies  rich  in  nuclei  (sweetbreads,  etc.). 
In  disease,  it  is  increased  when  tissue  destruction  is  going  on,  as  in 


Fig.  223. — Uric  Acid  Crystals.     (8avill. 


leukaemia  and  acute  fevers.  Much  has  been  made  of  uric  acid  as  a 
cause  of  gout.  There  is  no  evidence  to  show  that  its  formation  is 
increased  in  gout.  It  has  no  toxic  properties,  and  there  is  nothing 
to  justify  its  ill  reputation,  or  the  advertisements  of  the  quack  medicine 
vendors.  The  precursors  of  uric  acid  and  the  site  of  formation  have 
already  been  discussed  (p.  444). 

Purin  Bodies. — Hypoxanthin,  adenin,  and  xanthin,  are  present  in 
normal  urine  in  small  amounts.  These  are  supposed  to  be  derived 
from  the  decomposition  of  nucleic  acid.  Methylxanthin  results  from 
the  taking  of  coffee  and  tea  which  contain  caffeine  (tri-methyl- 
xanthin).  and  of  cocoa  which  contains  theobromine  (di-methyl- 
xanthin).  Guanin  is  present  in  the  urine  of  several  of  the  inverte- 
brata. 

Allantoin  is  the  chief  end-product  of  the  metabolism  of  nuclein  in 
some  animals,  and  occurs  in  human  urine  in  traces  and  in  allantoic 


THE  URINE  401 

fluid.     It  is  obtained  on  oxidation  of  uric  acid  by  a  ferment — uricase 
— or'by  oxidising  agents  (ozone,  permanganate  of  potash). 

HN-CO 

OC       C— NH      .,.-     ..  ,  „  n     or^     HN— CO 

I  CO  +  O  +  HoO  =  C0<  I  . ,, . 

HN— C— NH  NH  .  CH.NH.CO.NH2 

It  can  be  synthesized  out  of  glyoxylic  acid  (COOH.CHO)  and  urea,  and 
is  a  diureid  of  glyoxylic  acid. 

Creatinin  (C4H.N3O)  is  excreted  in  the  urine  in  such  a  very  constant 
amount — about  1  gramme  in  twenty-four  hours — that  some  have 
regarded  it  as  a  measure  of  the  nitrogenous  metaboHsm  of  the  tissues 
(endogenous  metabolism).  Creatin,  or  methylguanidin-acetic  acid 
is  found  in  the  muscles,  and  therefore  in  meat  extracts.  On 
heating  with  dihite  HoSO^,  it  passes  into  its  anhydride,  creatinin. 
Creatin  is  excreted  when  the  ])rotein  substance  of  the  body  is  being 
broken  down,  and  occurs  in  the  urine  during  starvation  and  fevers, 
also  during  lactation.  The  creatin  which  is  eaten  in  meat  is  probably 
decomposed  by  the  intestinal  bacteria. 

The  relationship  of  the  creatin  to  the  creatinin  of  the  body  is  a 
matter  of  considerable  complexity.  Contrary  to  what  was  once 
believed,  it  is  probable  that  creatinin  is  the  mother -substance  of 
creatin,  and  not  creatin  of  creatinin.  It  is  possible  that  creatinin 
is  formed  in  the  liver  from  some  product  of  protein  digestion,  and 
that  the  creatin  of  the  muscles  is  built  up  from  the  creatinin  thus 
formed. 

The  presence  of  creatinin  in  the  urine  is  shown  by  adding  a  few 
drops  of  a  saturated  solution  of  picric  acid  and  a  little  20  per  cent, 
solution  of  caustic  potash.  A  transparent  red  colour  is  produced 
(Jaffe's  test).  Sugar  in  the  ra-ine  gives  the  same  colour,  but  deeper 
and  opaque.  Thus,  there  is  no  difficulty  in  distinguishing  between 
the  two. 

Another  test  for  creatinin  is  to  add  a  few  drops  of  a  freshly  pre- 
pared solution  of  sodium  nitroprusside  and  20  per  cent,  solution  of 
caustic  potash  to  the  urine.      A  red  colour  is  /y^ 

produced,  which  disappears   on  heating  or   on         ^3 
the  addition  of  acetic  acid. 

Oxalates   occur  in  the  urine   combined  with     ^.  ^  ^ 
calcium,  and  the  salt  is  normally  kept  in  solu-     '^> 
tion   by   the    acid    sodium    phosphate    present.  ^^ 

When   precijiitated,    it   occurs    as    envelope   or     ^       ^^ 
dumb-bell    shaped    crystals    insoluble  in  acetic  ^^^ 

and  easil}^  soluble  in  hydrochloric  acid  (Fig  224).       IlaVe   Crvstals. 
About  0-017  gramme  of  oxalic  is  excreted  daily.       iSavill.) 
This  is  mainly  derived  from  the   food,  and   is 

increased  by  the  ingestion  of  fruits  and  vegetables,  such  as  rhubarb, 
strawberries,  tomatoes,  spinach,  cabbage.    There  are  cases  of  "  oxa- 


402  A  TEXTBOOK  OF  PHYSIOLOGY 

luriti  "  wlure  the  oxalates  are  precipitated,  but  as  a  rule  are  not 
increased,  in  the  urine.  Such  patients  generally  suffer  from  an  acid 
dyspepsia,  and  have  less  acid  sodium  phosphate  than  usual  in  the 
urine;  hence  the  oxalates  fall  out  of  solution. 

Hippuric  Acid  (0,jHgN403)  occurs  in  human  urine  in  small  quantities 
as  sodium  Jiip|)urate  (J  to  i  gramme  daih').  It  is  much  more  plentiful 
in  the  urine  of  herbivorous  animals,  such  as  the  horse.  It  is  increased 
in  man  by  the  ingestion  of  fruits,  such  as  mulberries  and  cranberries, 
Avhich  contain  aromatic  acids  which  are  oxidized  to  benzoic  acid  in 
the  body,  and  also  by  taking  benzoic  acid  as  a  drug.  Hippuric  acid 
is  of  interest,  >since  its  synthesis  from  benzoic  acid  and  glycin  takes 
place  by  enzymic  action  in  the  kidney  itself.  If  the  kidney  be  perfused 
with  defibrinated  blood  containing  these  two  bodies,  hippuric  acid  is 
formed. 

C,H5C00H  +  CH0NH2COOH  =  CHoNH.COCeHs.COOH  +  HgO. 

Hippuric  acid  separates  as  crystals  from  the  urine  of  the  cow  or 
horse  on  standing  after  the  addition  of  125  grammes  of  ammonium 
sulphate  and  7-5  c.c.  of  concentrated  sulphviric  acid  to  500  c.c.  of  urine. 
The  crj'Stals,  on  evaporation  with  strong  nitric  acid,  form  nitro- 
benzene, with  the  odour  of  oil  of  bitter  almonds. 

Ammonia  generally  appears  in  small  quantities  in  normal  urine, 
its  amount  varying  according  to  the  diet.  When  acids  are  introduced 
into  the  body,  or  acid  formation  takes  place  in  the  organism,  the 
amount  of  ammonia  in  the  urine  is  increased.  The  ammonia  pro- 
vided by  the  liver  neutralizes  the  acids.  This  is  sometimes  the  case 
in  diabetes  mellitus  and  in  eclampsia  of  pregnancy. 

Again,  ammonia  may  be  increased  in  the  urine  when  the  liver, 
the  chief  seat  of  urea  formation,  is  diseased.  Normally,  about  0-7 
gramme  of  ammonia  escapes  conversion  into  urea. 

Chlorides. — The  chief  chloride  is  that  of  sodium  (1  gramme  per 
100  c.c.  urine).  It  is  derived  chiefly  from  the  "  salt  "  of  the  food. 
The  presence  of  chlorides  in  urine  maj^  be  shown  by  addition  of  silver 
nitrate  and  nitric  acid  to  the  urine,  when  a  white  precipitate  is  obtained 
which  is  soluble  in  ammonia.  Without  the  addition  of  nitric  acid, 
the  phosphates  of  the  urine  are  also  precipitated. 

To  estimate  the  chlorides  in  the  urine,  they  are  precipitated  by 
excess  of  standard  silver  nitrate  in  presence  of  nitric  acid.  The  excess 
of  silver  nitrate  is  then  found  by  titrating  with  a  standard  solution  of 
potassium  or  ammotiium  thiocyanate.  using  iron  alum  as  the  indicator 
(Volhard's  method). 

Chlorides  are  diminished  in  amount  in  the  urine  in  many  febrile 
affections,  particularly  pneumonia. 

Sulphates  and  Neutral  Sulphur. — Sulphur  occurs  in  the  urine  in  three 
forms:  (1)  The  inotgaiiic  sulphates;  (2)  the  organic  or  ethereal  sul- 
phates; (3)  neutral  sulphur. 

Inorganic  l^ulyliates  occur  as  the  compounds  of  sodiiun  and  potas- 
sium.    Thej'  are  readily  detected  by  adding  a  solution  of  barium 


THE  URINE  46a 

chloride  and  a  little  hydrochloric  acid  to  the  urine.  A  white  precipitate 
of  barium  sulphate  results.  The  acid  prevents  the  precipitation  of 
phosphates. 

Organic  or  Ethereal  Sulphates  are  compounds  of  sulphuric  acid 
with  such  bodies  as  indol,  skatol,  phenol,  cresol.  Their  presence  may 
be  sho\vn  b}-  precipitating  the  inorganic  sulphates  and  phosphates 
Avith  alkahne  barium  chloride,  filtering,  and  heating  the  filtrate 
almost  to  boiling  with  strong  HCl.  By  this  means  the  organic  sulphates 
are  decomposed,  and  form  a  faint  white  cloud  of  barium  sulphate. 
If  they  are  in  excess,  a  white  precipate  forms. 

"  Neutral  Sulphur  "  is  the  sulphur  present  in  urine,  not  in  the  form 
of  sulphate,  but  as  an  integral  part  of  the  molecule  of  the  organic 
substance— e.^.,  cystin. 

About  2^  grammes  of  sulphuric  acid  (SO3)  are  excreted  daily. 
The  inorganic  sulphates  are  derived  mainly  from  the  protein  katabolism 
of  the  food.  Inorganic  sulphates — e.g.,  Epsom  salts — are  not  ingested 
as  such,  owing  to  their  unpleasant  bitter  taste. 

The  ethereal  sulphates  are  conjugates  of  sulphuric  acid  with  toxic 
bodies  formed  by  putrefaction  of  protein  in  the  intestine,  especiallj^ 
of  the  tyrosin  and  tr;>'ptophan  portions  of  the  molecule.  The  phenol, 
cresol,  indol,  and  skatol,  there  formed  are  absorbed  into  the  portal 
circulation,  and  combined  in  the  liver  with  sulphuric  acid,  and  so 
rendered  harmless. 

Normally,  the  inorganic  sulphates  are  about  ten  to  tAventy  times 
more  abundant  than  the  organic.  The  relative  proportion,  however,  is 
not,  as  has  been  supposed,  a  direct  measure  of  the  putrefactive  pro- 
cesses in  the  intestine.  It  has  been  found  that  this  proportion,  and 
that  of  the  neutral  sulphur,  varies  with  the  amount  of  nitrogen  in  the 
diet,  as  shown  in  the  following  table : 


Nitrogen-Rich  Diet.  Nitrogen -Poor  Diet. 


Volume  of  urine       ..          ..          ..  1,170  c.c.  385  c.c. 

Total  nitrogen           . .          . .          . .  i      16-8  grammes.  3-60  grammes. 

Total  SO;j 3-64        „  0-76 

Inorganic 3-27         .,          (90  %)  0-46         ,.       (60-5  %) 

Organic 0-19         „         (5-2°:)  0-10         .,       (13-2  %> 

Neutral 0-lS        „         (4:-8  %)  0-20         „       (26-3%) 


The  best  guide  to  the  extent  of  the  intestinal  putrefactive  processes 
is  now  believed  to  be  given  by  the  amount  of  indican  present  in  the 
urine.  Indican  is  the  indoxyl-sulphate  of  potassium  formed  from 
the  indoxyl  brought  to  the  liver  in  the  portal  blood  (see  p.  450). 

NH.CgHjOH  +SOo<^g  =  S0.<^^''H6^'  +  H,0. 

Indoxyl  Acid  Ind'can 

potassium 
sulphate 


464 


A  TEXTBOOK  OF   I'H VSlOLOOY 


Indoxyl  is  formed  from  iiidol  (C^H-N)  and  jnobably  in  the  intestinal 
wall  duiing  absorption.  Indol  is  formed  as  the  result  of  bacterial 
action  upon  tryi)tophane. 

The  best  test  for  indican  is  to  add  to  the  mine  some  concentrated 
HCl  containing  a  trace  of  ferric  chloride.  Upon  shaking  with  a  little 
chloroform,  indigo  blue,  or  occasionally  indigo  red,  is  formed. 
Normal  mine  gives  but  a  trace  of  colour,  if  any;  with  excess  of 
indican  the  colour  is  deep. 

Phosphates. — These  are  grouped  as — (1)  alkaline  phosphates  of 
potassium,  sodium,  and  ammonium;  (2)  earthy  phosphates  of  calcium 
and  magnesium.  The  two  grouj)S  occur  in  about  the  ratio  of  3  :  1. 
Phosphoric  acid  forms  three  series  of  salts:  Normal  ])hosphate, 
Na3P04,Ca3(P04)o;  mono-hydrogen  phosphate,  Na,HPO,,Ca2H(P04); 
di-hj^drogen     phosphate,     NaH.,P04,CaH.,(PO4).^.     The     normal     and 


Fig.  225. — Calcium  Carbonate  (fkom  Human  Urine),     x  400. 


mono-hydrogen  phosphates  are  alkaline  to  litmus,  the  di-hydrogen 
to  acid.  The  three  sodium  phosphates  and  the  di-hydrogen  calcium 
phosphate  are  soluble  in  water,  the  other  two  calcium  salts  are  in- 
soluble. The  deposit  of  phosphates  which  sometimes  occurs  is  due 
to  the  earthy  phosphates  being  precipitated  when  the  urine  loses  its 
acid  reaction.  When  CO.,  is  driven  from  urine  by  heating,  such  a 
deposit  of  phosphates  sometimes  occurs.  It  is  distinguished  from  a 
coagulum  of  protein  by  the  fact  that  it  is  readily  soluble  in  acetic 
acid. 

The  earthy  phosphates  yield  a  white  crystalline  precipitate  on  the 
addition  of  ammonia.  The  presence  of  phosphates  generally  may  be 
shown  by  adding  nitric  acid  and  ammonium  molybdate  to  urine. 
Upon  heating  this,  a  yellow  precipitate  is  obtained. 

To  estimate  phosphates  in  the  urine,  some  acid  sodium  acetate 
is  first  added  to  the  urine  to  prevent  the  formation  of  free  nitric  acid 


THE  URINE 


4G5 


from  the  uranium  uitrate  employed  in  the  titration.  The  urine  is  heated 
to  SO''  C,  and  the  phosphates  are  then  precipitated  by  a  standard 
sohition  of  uranium  nitrate.  A  little  powdered  solid  potassium 
ferrocyanide  may  be  added  as  indicator.  This  turns  brown  when  the 
end-point  is  reached.  One  c.c.  of  the  standard  solution  equals 
0-005  gramme  of  phosphoric  acid. 

Xormally,  about  2  to  3  grammes  of  the  phosphoric  ion  (Po^^i) 
are  excreted  daily.  This  is  chiefly  derived  from  the  phosphorus 
compounds  of  the  food,  inorganic  phosphates,  and  organic  phosphorus 
compounds,  such  as  phospho-protein,  nucleo-protein,  and  lecithin. 
A  considerable  proportion  of  the  phosphates  is  excreted  by  the  large 
bowel,  particularly  the  earthy  jihosphates.  The  deposit  of  phosphates 
which  sometimes  occurs  in  the  urine  of  children  is  probably  due  to 
an  excessive  amount  of  calcium  in  the  m'ine  arising  from  defective 
excretion  by  the  large  intestine. 

Carbonates. — These  occur  as  the  carbonate  and  bicarbonate, 
particularh"  of  sodium,  after  the  ingestion  of  organic  acids  in  vegetables 
and  fruits.     A  crystalline  deposit  of  calcium  carbonate  maj^  be  found 

(Fig.  225).     On  addition  of  acid,  the  urine  effervesces  

from  the  evolution  of  carbon  dioxide.  The  urine  of  the 
horse  or  cow  is  normally  alkaline,  and  cloudy  with 
phosphates  and  carbonates. 

Abnormal  Constituents  of  the  Urine. — The  chief 
abnormal  constituents  met  with  in  urine  are  protein, 
sugar,  blood,  and  bile. 


V,   — s 

<  — ♦ 


Proteins. — Various  proteins  may  be  passed  in  the 
urine.  In  the  condition  known  clinically  as  albuminuria 
the  serum  albumin  and  serum  globulin  of  the  blood 
pass  through  the  kidneys  into  the  urine.  The  former  is 
usually  in  larger  amount.  Such  a  urine  always  gives 
an  abundant  froth  on  shaking.  ""  Albumin  "'  in  the 
lu'ine  is  detected  by  the  following  tests,  Avhich  mu.st  be 
applied  to  clear  urine — i.e..  filtered  or  centrifuged  —  if 
necessary:  (1)  The  urine  boiled  after  bemg  faintly 
acidified  with  acetic  acid.  Albummous  urine  gives  a 
coagulum.  (2)  On  the  careful  addition  of  nitric  acid  a 
Avhite  ring  (precipitate)  appears  at  the  junction  of  the 
fluids.     This  ring  does  not  disappear  on  heating. 

Other  tests  mentioned  in  the  section  on  the  proteins 
{p.  46)   may  also    be    u.sed.     It   must    be  remembered, 
however,  that    normal   urine   contams  a  trace   of   protein,  and   the 
tests  employed  should  be  such  as  will  reveal  onh'  an  increase  beyond 
the  normal  amount. 

For  quantitative  clinical  jjurposes,  a  special  form  of  test-tube 
is  used  (Fig.  226).  This  tube  is  filled  with  clear  urine  up  to  the 
mark  U,  and  a  mixture  of  picric  and  cit  ic  acids  up  to  the  mark  R. 
If  albumin  be  present,  a  whitish-j'ellow  precipitate  forms.    On  leaving 

30 


Fig,  226,  — 
E  s  bach's 
Albumixo- 

METEK. 


4GG  A  TEXTBOOK  OF  PHYSIOLOGY 

this  to  stand  for  twenty-four  hours,  the  amount  may  be  read  off  on 
the  graduations  of  the  tube.  The  figures  correspond  to  the  number 
of  grammes  of  albumin  present  per  litre. 

Normal  urine  yields  a  "  mucus  "  on  standing,  which  appears  to 
be  a  mixture  of  nucleo-protein  and  gluco-proteiu.  This  is  derived 
from  the  urinar}-  trnft.  .Tii  catarrhal  conditions  of  this,  the  amount 
of  mucus  may  be  so  much  increased  that  a  condition  known  as  "'  mucin- 
uria  '""  is  met  with.  A  white  precipitate,  insoluble  in  excess,  and 
increased  on  boiling,  is  indicative  of  "  mucin."  The  test  often  succeeds 
better  when  the  urine  is  previously  diluted  to  half  its  strength  with 
\\'ater. 

Another  abnormal  condition  of  the  urine  hometimes  met  with  is 
due  to  the  presence  of  proteoses  in  the  urine.  These  appear  in  the 
urine  when  disintegration  of  tissue  is  going  on  during  an  infective 
disease — e.g.,  in  pneumonia,  when  an  abscess  known  as  empj'ema  is 
forming.  A  special  form  of  proteosuria,  known  as  myelopathic  or 
Bence- Jones  proteosuria,  occurs  with  a  condition  of  diffuse  malignant 
tumour  (sarcoma)  of  the  bone-marrow. 

Proteoses  may  be  distinguished  from  albumin  by  the  fact  that  the 
precipitate  with  nitric  or  salicylsulphonic  acid  disappears  on  heating, 
and  reappears  on  cooling.  The  Bence-Jones  proteose  is  further 
characterized  by  the  fact  that  urine  containing  it  becomes  opaque 
at  a  comparatively  low  temperature  (60°  C),  with  the  formation  of 
a  sticky  coagulum.  If  the  reaction  be  acid,  this  coagidum  disappears 
on  further  heating,  and  reappears  on  cooling.  With  strong  hydro- 
chloric acid  this  proteose  gives  a  sharp  ring,  which  also  disappears 
on  heating  and  reappears  on  cooling. 

Blood. — The  red  corpuscles  or  the  blood-pigment  may  pass  into 
the  urine.  The  former  condition  is  known  as  ''  haematuria,'"  the  latter 
as  "  hsemoglobinuria.""  When  the  urine  contains  but  little  blood, 
it  presents  a  peciiliar  ''  smoky  "  appearance;  with  larger  quantities, 
the  urine  appears  red  or  reddish-brown,  according  to  the  variety  of 
blood-pigment  present.  The  presence  of  blood  is  detected  clinically 
by  making  some  of  the  urine  strongly  alkaline  with  caustic  soda,  and 
boiling.  Should  blood  be  present,  a  reddish-brown  deposit  is  formed, 
"u  ith  greenish  fluid  above.  Various  drugs  taken  by  the  i:)atient,  such 
as  senna,  rhubarb,  may  yield  a  similar  result.  The  "  guaiac  test  " 
(see  p.  112)  also  serves  to  identify  blood.  There  are  certain  fallacies 
in  this  test.  Iodides  in  the  urine  may  give  it;  also  the  presence 
of  saliva,  through  spitting  into  the  pot,  and  pus.  In  hsematuria, 
blood-corpuscles  may  be  detected  in  the  sediment  after  centrifuging 
or  allowing  the  urine  to  stand.  The  spectra  of  oxyhaemoglobin  or 
methsemoglobin  may  be  obtained ;  more  often  the  latter. 

Occasionally,  alkaline  hamatoporphjTin  is  met  with  in  considerable 
quantities  in  the  urine,  giving  it  a  dark,  port-wine  colour.  This  is 
generalh'  due  to  poisoning  by  drugs,  such  as  sulphonal.  Such  a 
urine  will  not  give  the  guaiac  test,  owing  to  the  absence  of  iron  in 
hsematoporphyrin.  To  identif}^  it,  the  pigment  should  be  converted 
into  the  acid  variety  by  the  addition  of  hydrochloric  acid,  and,  if 


THE  URINE  467 

iiecessar}^  extracted  with  amyl  alcohol.     The  spectrum  of  acid  hsema- 
toporphjTin  can  then  be  identified. 

Sugars  in  the  Urine. — The  sugar  which,  under  certain  conditions, 
appears  in  the  mine  is  dextrose  or  glucose.  Rarel}^  levulose,  lactose, 
or  pentose,  may  be  excreted. 

Glycosuria  is  a  symptom  of  the  disease  known  as  diabetes  mellitus. 
It  does  not  follow,  however,  that  every  person  who  is  found  to  have 
dextrose  in  the  urine  has  diabetes,  although  it  is  probable.  Traces 
of  dextrose  occur  in  normal  urine,  but  not  in  sufficient  amount  to  give 
the  tests  for  sugar  as  generally  applied.  Various  other  substances 
in  the  urine,  such  as  glj^curonic  acid,  vu-ic  acid,  creatinin,  phosphates, 
may  give  a  positive  reaction  with  Fehling's  solution,  which  is  the 
test  most  frequently  emploj'ed  for  the  detection  of  dextrose.  This  is 
a  matter  of  considerable  importance,  for  the  presence  of  one  or  other 
of  these  substances  may  lead  to  a  false  diagnosis  of  sugar  in  the  urine, 
a  serious  error,  and  one  which  falls  particularly  hard  on  candidates 
for  life  insurance.  Therefore,  the  tests  for  sugar  in  urine  should 
alwa3's  be  carefully  applied. 

Trommer's  test  is  not  to  be  recommended,  owing  to  the  haphazard 
proportions  of  the  testing  solutions — copper  sulphate  and  potash. 

Fehling's  test  is  best  applied  by  boiling  the  Fehling's  solution  and 
the  urine  in  separate  tubes,  and  then  mixing  the  two.  If  reduction 
occurs  ivithont  further  heating,  it  is  almost  certainly  due  to  the 
presence  of  dextrose  in  the  urine.  Gtycuronic  acid  and  compound 
glycuronates,  uric  acid,  creatinin,  phosphates,  do  not  cause  reduction 
under  these  conditions. 

A  positive  reaction  obtained  with  Nylander's  test  is  strongly  con- 
firmatory, for.  besides  sugar,  only  glycuronic  acid  and  its  compounds 
will  reduce  the  bismuth  salt. 

The  phenyl-hydrazine  test  helps  to  differentiate  sugar,  but  the 
most  certain  test  of  all  is  fermentation  with  j'east.  This  should 
always  be  applied. 

An  approximate  estimate  of  the  amount  of  sugar  present  in  the 
urine  may  be  made  by  taking  the  specific  gravity  of  the  urine  before 
and  after  it  has  been  fermented  with  yeast  for  twenty -foiu^  hours. 
Each  degree  of  specific  gravity  lost  equals  1  grain  of  sugar  per  ounce 
of  urine.  The  quantity  of  sugar  in  the  urine  maj'  be  estimated  in 
various  other  wa_\'s.  The  methods  given  here  are  not  ver}'  exact, 
but  sviffice  for  clinical  work.  The  standard  solution  of  Fehling  is 
generally  used.  A  measured  quantity  of  the  solution  is  taken,  and 
kept  boiling  in  an  open  dish,  while  the  urine,  suitably  diluted,  is 
run  in  from  a  burette  until  the  blue  cupric  solution  is  entirely  reduced 
and  decolorized.  Ten  c.c.  of  Fehling's  solution  are  reduced  b}^ 
0-05  gramme  of  dextrose.  The  unmodified  Fehling's  method  is 
not  to  be  recommended,  owing  to  the  difficulty  of  recognizing  the 
end-point.  The  use  of  an  indicator,  such  as  ferrous  thiocyanate, 
is  helpful.  The  end-point  is  reached  when  a  drop  of  the  solution 
no  longer  turns  a  drop  of  the  indicator  red.     This  shows  that  there  is 


408  A  TEXTBOOK  UF  PHYSIOLOGY 

no  cnpric  salt  left,  for  a  cupric  salt,  when  brought  into  contact  with 
the  ferrous  thiocyanate,  oxidizes  it  to  ferric  thiocyanate,  which  is 
red  in  colour.  A  modified  Fehling's  solution  (Pavy's  solution)  has 
strong  ammonia  added  to  it.  As  this  keeps  the  red  precipitate  of 
cuprous  oxide  in  solution,  the  disappearance  of  the  blue  colour  is 
evident.  The  end-point  is  reached  when  the  solution  becomes  colour- 
less. Pavy's  solution  is  ten  times  less  strong  than  Fehling,  1  c.c. 
being  reduced  by  0-005  gramme  of  dextrose.  The  urine  should 
therefore  be  diluted  more  before  carrying  out  the  test. 

In  another  modification  of  the  test  (GJerrard's),  the  red  deposit 
of  the  Fehling's  solution  is  held  in  solution  by  the  double  cyanide  of 
potassium  and  copper.  Gerrard's  solution  is  mixed  and  boiled  with 
Fehling's  solution.  In  Bertrand's  modification,  the  cuproiis  oxide 
precipitate  produced  by  the  presence  of  the  sugar  is  dissolved  in  a 
solution  of  ferric  sulphate  in  sulphuric  acid.  During  the  process  of 
solution,  an  amount  of  lerrous  salt  becomes  produced,  which  is  equiva- 
lent to  the  amoimt  of  cuprous  oxide.  The  ferrous  salt  is  then 
measured  by  titrating  with  a  standardized  solution  of  potassium 
permanganate.  It  is  the  most  reliable  method  for  estimating  sugar 
in  simple  solutions. 

The  polarimeter  may  also  be  employed  to  estimate  the  amount 
of  sugar  in  urine,  but  it  is  necessary  that  the  urine  be  absolutely  clear, 
and  not  high-coloured.  Protein,  if  present,  and  any  other  levo- 
rotatory  substances,  must  be  removed  before  the  measurement  is  made. 

In  diabetic  urine,  various  volatile  acids,  such  as  /5-oxybutyric 
acid  and  aceto-acetic  acid,  are  wont  to  occur  in  conjunction  with 
acetone.  The  acetone  bodies  are  also  excreted  in  starvation  or  on 
a  diet  of  fat  with  a  limited  amount  of  protein,  in  certain  fevers,  severe 
anaemias,  and  phosphorus-poisoning — conditions  in  which  the  tissues 
are  unable  to  use  glucose.  These  bodies  are  closely  related,  as  their 
formulae  show,  the  bodies  Avith  the  smaller  molecule  being  derived 
from  those  with  the  larger: 

/i-oxybutyric  acid,  CH3.CH0H.CIl.,.C()0H. 
Aceto-acetic  acid,  CHg.CO.CHg.CO^H. 
Acetone,  CH3.CO.CH3. 

They  are  most  probably  derived  from  an  incomplete  breaking 
down  of  amino-acids,  particular^  in  the  liver,  and  are  therefore 
indirectly  derived  from  protein  (see  p.  423).  In  starvation  and  in  the 
last  stages  of  diabetes,  in  diabetic  coma,  they  are  probably  also  derived 
from  the  higher  fatty  acids  of  the  body  fat. 

/3-Oxybutyric  Acid,  a  volatile  acid,  is  levo-rotatory,  and  does  not 
ferment  with  yeast.  No  satisfactory  simple  test  has  been  devised 
for  its  detection  in  urine.  It  generally  occurs  combined  with  am- 
monia, and  an  idea  of  the  amount  of  the  volatile  acids  of  the  urine 
can  be  obtained  by  the  method  already  given  (p.  454). 

Aceto-acetic  Acid  may  be  tested  for  by  adding  ferric  chloride  to  the 
urine.  If  present,  a  red  colour  is  obtained ;  if  small  in  amount,  it  may 
be  first  extracted  with  ether,  to  which  a  little  sulphuric  acid  is  added. 


THE  URINE  469 

Acetone  gives  a  peculiar  fruity  odour  to  the  urine.  It  is  best 
detected  b}-  Rothera's  test.  Ten  c.c.  of  urine  are  saturated  with 
ammonium  sulphate  by  adding  the  solid  salt,  and  a  few  drops  of  a 
solution  of  sodium  nitro-prusside  and  2  to  3  c.c.  of  strong  ammonia- 
added.  On  allowing  to  stand,  a  colour  appears  like  that  of  perman- 
ganate of  potash.  Urine  containing  acetone  will  also  jaeld  the  charac- 
teristic odour  of  iodoform  when  an  alcoholic  solution  of  iodine  and  a, 
little  strong  ammonia  are  added  to  it. 

Levulose. — Levulosuria  by  itself  is  a  rare  condition,  but  levulose 
occurs  in  the  urine  with  dextrose  in  cases  of  "  mixed  mellitu  "ia." 
The  polarimeter  and  the  resorcin  test  are  used  for  its  detection. 

Lactose. — "'  Lactosuria  ""  occurs  sometimes  in  mothers  Avho  are 
suckling  their  children.  The  sugar  may  occur  in  quite  appreciable 
amount  in  the  urine.  The  chief  points  Mhich  aid  in  its  detection  are  these : 
it  reduces  Fehling's  solution;  it  does  not  ferment  with  yeast;  it  yields 
characteristic  small  rosettes  with  the  phenjd-hydrazine  test  (see  p.  65). 
Pentose. — "'  Pentosuria  "  is  a  rare  condition.  It  may  occur  tem- 
porarily as  the  result  of  large  ingestion  of  fruit,  such  as  cherries, 
grapes,  and  plums.  Occasionally,  a  pentose  occurs  in  conjunction 
with  dextrose  in  cases  of  glycosuria.  There  is  a  rare  anomaly  of 
metabolism  in  which  pentose  occurs  regularly  in  the  urine.  8uch  a 
pentosuria  is  accompanied  by  no  morbid  symptoms,  is  probably 
harmless,  and  needs  no  treatment.  The  pentose  in  question  is  usually 
arabinose.  The  low  melting-point  of  the  osazone  (160°  C).  the  non- 
fermentation  with  3'east,  and  Bials  orcin  test,  serve  to  indicate  the 
presence  of  a  pentose  in  the  urine. 

Bile  in  the  Urine. — In  the  condition  known  as  '"  jaundice,''  bile 
appears  in  the  urine.  As  the  result  of  obstruction  of  the  bile-passages^ 
bile  enters  the  lilood.  and  so  reaches  the  urine.  The  bile  pigments 
generally  confer  a  greenish  or  brownish  colour  on  the  urine.  They 
may  be  detected  by  the  play  of  colours  formed  when  fuming  nitric 
acid  is  added  (Gmelin"s  test).  The  presence  of  bile  salts  in  the  urine 
may  be  best  shown  by  Hay"s  sulphur  test.  If  "  flowers  ""  of  sulphur 
are  sprinkled  on  the  surface  of  urine  containing  bile,  the  sulphur  sinks 
readily. 

Alkaptonuria  is  due  to  an  inborn  anomah'  affecting  i^rotein  meta- 
bolism. It  is  of  interest  as  throwing  light  on  the  halfway  stages  of 
protein  decomposition,  for  it  seems  probable  that  the  breaking  down 
of  the  tyrosin  group  is  not  carried  so  far  as  usual,  rather  than  that 
an  abnormal  body  is  formed.  In  the  urine,  homogentisic  acid  (di- 
hydroxji^henylacetic  acid)  is  secreted. 

OH 


ICH,.C00H 
OH 


470 


A  TEXTBOOK  OF  I'HYSIOLOGY 


The  urine  is  natural  in  appearance  when  passed,  but  on  exposure  to 
iiir  gradually  darkens  from  the  surface  downwards,  until  it  ultimately 
becomes  a  deep  brown-black  colour.  Such  a  urine  reduces  Fehling's 
solution,  but  does  not  give  Nylander's  test.  With  Millon's  reagent 
it  gives  a  yellow  precipitate;  the  addition  of  ferric  chloride  drop  by 
drop  causes  a  passing  blue  colour.  It  does  not  ferment  with  yeast, 
nor  rotate  the  plane  of  polarized  light.  After  poisoning  with  carbolic 
acid,  the  urine  may  contain  a  similar  body.  Alka])tonuric  in-ine  may 
be  distinguished  from  one  containing  the  pigment  melanin  by  the 
fact  that  the  latter  does  not  reduce  Fehling's  solution. 

Cystinuria. — Cystin,  di-amino-di-thiolactic  acid  is  the  suljohur- 
holding  product  of  protein  decomposition.  It  is  a  condensation 
derivative  of  molecules  of  cystein  —  thio-amino-propionic  acid. 
Taurin  (of  the  bile  acid — taurocholic  acid)  yields  cystein  on  oxidation. 
It  does  not  normalh^  occur  in  the  urine.     It  is  a  rare  anomaly,  the 


Fig.  227. — Cvstin  Crystals,     x  350. 


result  of  an  inborn  error  of  metabolism.     It  affects  particularly  the 
male  issue  of  the  marriage  of  near  relations,  such  as  first  cousins. 

Cystin  only  occurs  in  acid  urine.  Six-sided  cr3'stals  of  cystin 
(Fig.  227)  may  form  from  the  urine  on  the  addition  of  acetic  acid, 
but  usually  the  urine  yields  a  dejiosit  of  these  crystals.  They  are 
soluble  in  alkali.  If  some  of  the  deposit  be  placed  under  a  cover- 
glass,  and  strong  hydrochloric  acid  added,  delicate  prisms  are  formed 
as  the  acid  reaches  the  crystals.  These  disappear  if  water  be  added. 
Dissolved  in  caustic  potash,  cystin  gives  a  violet  colour  when  fresh 
sodium  nitroprusside  is  added  and  the  solution  warmed.  An  alkaline 
solution  of  cystin  gives  a  black  precipitate  of  lead  sulphide  when  boiled 
with  lead  acetate  solution.  Stones  composed  of  cystin  have  rarely 
been  found  in  the  bladder. 

Urinary  Deposits. — The  deposits  of  normal  urine  vary  in  character, 
according  as  they  are  deposited  from  acid  or  alkaline  urine.  The 
following  occur  in  acid  urine: 


THE  URINE 


471 


1.  Uric  Acid. — These  appear  as  a  "' cayenne -pepper  "  deposit  at 
the  bottom  of  the  specimen,  the  crystals  being  pigmented  with  uro- 
erythrin.  In  shape,  the  crystals  resemble  Avhetstones,  dumb-bells, 
orange  pips,  etc.,  and  are  often  grouped  together  in  rosettes  (Fig.  223) 

2.  AmorpJious  Urates  occur  as  a  brickdust  or  pinkish  deposit. 
The}-  consist  of  masses  of  amorphous  granules  tinted  with  urinary 
pigment.  They  easily  pass  into  solution  when  the  urine  is  warmed 
or  rendered  alkaline. 

3.  Sodium  Urate. — This  occurs  but  seldom  in  adults;  frequently, 
however,  in  the  urine  of  the  newly-born.  In  appearance,  the  crystals 
resemble  the  thorn-a])ple,  little  spheres  with  numerous  spines  radiating 
from  them  (Fig.  222). 

4.  Calcium   O.ralate    occurs    as    characteristic    colovirless,    shining, 
'"  envelope  "  crj-stals  (Fig.  224).     In  reality,  they  are  small  octahedra. 
In   some   cases,   calcium   oxalate   occurs  also   in  dumb-bells  forms. 
They  are  insoluble  in  acetic  acid  and  ammonia,  but  soluble  in  hydro 
chloric  acid. 


Fig.  228. — Triple  Phosphate 
Crystals. 


5:-^  "'^A:^ 


'Jilt 


Fig.  229. — Stellar  Phosphate 
Crystals.     (Savill.) 


Rarely,  deposits  may  occur  in  acid  urine  of — (a)  acid  calcium 
phosphate  (C'aHPO^) — rosettes  of  prisms  or  dumb-bells;  (6)  hippuric 
acid,  especially  after  the  administration  of  benzoic  acid — colour- 
less four-sided  prisms,  insoluble  in  Iwdrochloric  acid,  soluble  in  am- 
monia; [c)  cyst  in — colourless  hexagonal  crystals,  often  thrown  out 
of  solution  b}-  the  addition  of  acetic  acid,  soluble  in  ammonia;  (d)  cones 
of  leucin  and  white  sheaves  of  tATosin. 

In  alkaline  urine,  the  chief  salts  to  be  deposited  are  the  phosphates. 
They  are  all  soluble  in  acetic  acid,  and  the  amount  of  deposit  is  in- 
creased by  bailing.     There  occur — 

1.  (a)  Most  commonly  the  Phosphate  of  Calcium,  "Earthy" 
Phosphate,  Ca3(P0^).,,  generally  as  white  amorphous  granules,  more 
rarely  as  colourless  prismatic  crystals  radiating  in  clusters. 

(b)  Ammonium  Magnesium  Phosphate,  MgXHjPOj,  or  Triple 
Phosphate,  especially  in  urine  which  has  undergone  ammoniacal  fer- 
mentation. In  appearance,  they  resemble  coffin-lids  or  feathery 
stars — ■■  feathery  phosphates  "'  (Fig.  22">). 

2.  Ammonium  Ura'e,  especialh-  in  cases  of  inflammation  of  the 
bladder — "  C3^stitis."'     Small    s]:)hei'ical    cr^-stals    resembling    sodium 


472  A  TEXTBOOK  OF  PHYSIOLOGY 

urate,  usually  associated  Avith  lri|)le  ]ihosphate  crystals  and 
bacteria 

3.  Calcium  Carbonate. — Occasionalh'  in  hinnan  urine,  hut  com- 
monly in  the  urine  of  herhivora.  In  hinnan  urine,  generally  as 
amorphous  gramiles;  more  rarely,  as  in  horse's  urine,  as  dumb-bells 
or  spheres  (Fig.  225).  They  are  easily  soluble,  with  eflPervescence,  in 
acetic  acid. 

In  the  urine  there  may  also  occur  epithelium  from  the  kidney, 
bladder,  and  urinary  passages,  and  in  women  from  the  vagina.  In 
pathological  urine  there  may  occur — 

1.  Red  blood  corpuscles,  either  normal,  swollen,  or  crenated. 

2.  White  corpuscles,  or  ""  pus  "  corpuscles. 

3.  Fatt}"  globules  in  '"  liiDuria." 

4.  Various  forms  of  "'  casts  "  of  the  kidne}'  tubules. 


r'HAPTER  LVT 

THE  SECRETION  OF  URINE 

In  unicellular  organisms  of  low  activit}-  there  is  no  special  structure 
for  the  excretion  of  the  waste  products  of  metabolism;  the  general 
surface  of  the  cell  serves  as  a  medium  for  their  discharge.     In  onc- 


-COLUECTTl/B?; 


!?■'  COWVOL 


COLLECT:  TV/BE. 


UBCTERIC  BUD 


NEPHRrc   Bud 


GROWING  Et.D 
(uretet-ic) 


nephric  Tubule 


Glomerulus 


s^C0LLECT:ru3S;. 
(Urcte)-ic) 


COLLECTING  TUBES 


(B) 


Fro.  230. — Illustratixg  the  Development  of  the  Rexal  Tvbule.     (Keith, 

after  G.  C.  Huber.) 

A,  Growing  end  of  collecting  tubule  with  nephric  bud  attached  to  it.  B,  First  stage 
of  development  of  nephric  bud  into  nephi-ic  tubule.  C\  Fully  developed  renal 
tubule.  The  part  formed  from  the  ureteric  bud  is  represented  in  outline  ;  the 
part  from  nephric  tubule  is  shaded. 


celled  organisms  of  greater  activity  there  exist  special  contractile 
vacuoles,  which  from  time  to  time  expel  from  the  cell  waste  fluid, 
which  may  contain  solid  particles.  In  such  a  fluid  the  presence  of 
uric  acid  has  been  demonstrated. 

47;J 


474  A  TEXTBOOK  OF  PHYSIOLOGY 

In  the  metazoa,  the  taking  \ip  of  waste  products  is  done  by  special- 
ized organs — the  nephridia — which  are  bathed  by  the  body  fluid. 

In  the  verte])rates  there  are  three  stages  of  renal  development. 
First,  the  pronephros  which  represents  a  collection  of  ])riinitive 
nephridia  and  excretes  the  waste  jH-oducts  into  the  crelom.  The 
pronephros  is  represented  bj^  the  kidney  of  fishes.  Secondly,  the 
mesonephros  appears ;  thirdly,  the  metanephros.  The  mesonephros  is 
re])iesentc(l  by  the  kidney  of  the  amphibia,  the  metanephros  by  the 
kidney  of  birds  and  mannnals.  In  the  development  of  the  human 
embryo,  all  three  stages  are  rej)resented,  a  transitory  pronephros  at 
the  third  Aveek,  then  the  mesonephros,  from  which  the  genital  organs 
are  developed,  and  lastly,  the  metanephros  or  permanent  kidney. 
The  last  is  formed  by  the  combination  of  two'elements :  a  nephric  or 
secretory  part,  a  duct  or  excretory  part  (Fig.  230).  The  kidney  is  a 
collection  of  these  elements,  the  whole  being  held  together  by  con- 
nective tissue,  and  compactly  bound  up  in  a  covering  capsule. 

The  Minute  Structure  of  the  Kidney  Tubule. — Each  tubule  starts 
in  the  cortex  of  the  kidney  as  an  expansion — the  capsule  of  BoAvman — 
into  which  dips  a  tuft  of  capillaries — the  glomerulus.  The  wall  of 
the  capsule  is  formed  of  flattened  endothelium,  and  is  involuted  by 
the  tuft  of  the  capillaries.  The  cells  covering  the  glomerulus  form  a 
sjaicj^tium.  The  glomerulus  itself  is  a  lobulated  structure.  The 
endothelium  of  the  ca]3sule  and  other  parts  of  the  renal  tubule  rests 
upon  a  homogeneous  basement  membrane.  The  cajisule  narrows  to 
a  neck,  also  lined  by  flattened  e]:)ithelium,  and  this  passes  into  the 
first  convoluted  tubule.  Here  the  epithelium  consists  of  cubical  granu- 
lar cells,  called,  on  account  of  the  rod-like  disposition  of  the  granules, 
*'  rodded  epithelium."  Leaving  this  convoluted  portion,  the  tubule 
narrows  and  passes  down  into  the  medulla  as  a  long,  straight  limb, 
lined  with  flattened  epithehum — the  descending  loop  oS  Henle.  Turn- 
ing suddenly  ujiAvards,  it  again  passes  into  the  cortex  as  the  ascending 
loop  o£  Henle.  Here  the  epithelium  is  cubical  and  granular.  In  the 
cortex  the  tubule  again  expands  as  the  distal  convoluted  tubule,  Avhere 
the  epithelium  once  more  becomes  "rodded.""  Finalh',  the  tubule 
opens  into  a  collecting  tubule  lined  with  a  more  flattened  epithelium. 
This  conveys  the  urine  to  the  pelvis  of  the  kidney  (Fig.  231a). 

The  Arrangement  of  the  Blood-Supply. — In  the  mammalian  kidney 
the  renal  artery,  after  entering  the  substance  of  the  kidney  at  the 
hilum,  breaks  ujd  in  the  boundary  zone  between  cortex  and  medulla 
into  a  number  of  small  vessels,  which  anastomose  with  each  other, 
and  give  off  branches  both  to  the  cortex  and  to  the  medulla.  Of 
these,  the  arterise  rectse  pass  downwards  into  the  medulla,  and  form 
capillaries  around  the  descending  and  ascending  loops  of  Henle.  The 
main  blood-supply,  however,  j)asses  by  straight  (interlobular)  branches 
into  the  cortical  zone.  These  give  off  on  all  sides  small  branches, 
which  pass  to  the  glomeruli.  From  the  glomeruli  pass  efferent  veins, 
which  are  of  smaller  calibre  than  the  afferent  arteries.  These  veins 
]>artake  of  the  nature  of  a  "  portal  circulation,"  since  from  the  glomeruli 


THE  SECRETION  OF  URINE 


475 


they  pass  among  the  tubules  of  the  cortex,  and  there  again  form  a 
second  capillary  system  which  anastomoses  with  the  capillary  system 


Fig.  "iSlA. — Diagram  of  Course  of  Two 


UiUNiFKKors  Tri'.ULEs.     (Klein.) 

./,  cortex  ;  B,  boiuidaiy  zone  ;  C,  papillary 
zone  of  medulla  :  aa',  supeiKcial  and 
deep  layers  of  cortex  free  from  glome- 
ruli. 


•23lR. — Diagram  of  Distribution 
OF  Bloodvessels  in  Human  Kidney. 
( Ludwig. ) 
ai.  Interlobular  arteries  ;  ri.  interlobular 
veins  ;  g,  glomerulus  ;  cti,  stellate  vein  : 
ar,  vr,  arteria;  and  ven;^  rectte  forming 
bundles  ;  ab,  vb ;  vp,  venous  plexus  in 
the  papillffi. 


of  the  medulla.     Both  systems  then  join  to  form  the  efferent  veins, 
which  anastomose  in   the   boundary  zone,  Avliers^e  larger  veins  run 


476  A  TEXTBOOK   OF   l»HVSlOJ.O(;^' 

to    the   hiluiii    of    tlie    kidney,    and    together    form    the    renal    win 
(Fig.  23lB). 

Such  an  anatomical  arrangement  of  tid)ules  and  blood-.siipply 
suggested  to  Bowman,  who  first  described  it.  in  1840.  that  the 
urine  had  a  double  source  of  origin — glomerular  and  tubular.  He 
suggested  that  the  water  and  salts  of  the  urine  were  filtered  from  the 
blood  in  the  glomeruli,  while  the  organic  constituents  of  the  urine 
were  secreted  by  the  tubules,  especially  by  the  convoluted  portions. 
Ludwig  laid  stress  on  the  vas  efferens  leaving  the  glomerulus  being 
narrower  than  the  vas  afferens,  and  put  forward  the  view  about  the 
same  time  (1844)  that  water  and  crystalloids  of  the  blood  filtered 
through  the  glomeruli,  and  the  urine  was  concentrated  from  this  by 
resorption  in  the  tubules. 

A  controversy  arose  aroimd  these  tAvo  views,  which  resolved  itself 
into  a  question  of  principle.  The  LudAvig  view  was  the  more  mechani- 
cal one.  It  sought  to  minimize  the  unknown  forces  of  the  living 
cells,  and  to  make  the  excretion  of  urine  a  question  of  filtration  through 
the  glomeruli  and  concentration  by  physical  means  in  the  tubules. 
The  adherents  of  the  Bowman  view  attributed  special  selective  activity 
to  the  glomerular  and  tubular  cells.  The  secretion  of  urine,  to  them, 
was  a  vital  function,  and  not  to  be  explained  by  known  physical 
processes,  such  as  filtration  and  osmosis.  The  glomerular  epithelium 
secreted  water  and  salts  (NaCl,  etc.),  the  tubules  the  sjiecific  urinary 
substances  (urea,  etc.)  and  some  water.  The  activity  of  the  kidney 
was  regulated  by  the  amovmt  of  water  and  urinary  substances  in  the 
blood,  and  the  velocity  of  flow  of  the  blood  through  the  kidney.  This 
is  the  view  which  has  steadilj'  gained  supjDort. 

In  the  course  of  the  controversy  two  salient  facts  have  emerged: 
(1)  That  a  concentration  by  resorption  of  dilute  urine  in  the  tubules 
cannot  be  brought  about  by  such  physical  forces  as  osmosis;  (2)  that 
in  the  secretion  of  urine  the  kidney  cells  are  performing  work. 

In  regard  to  the  first  point,  it  soon  became  clear  that  those  physical 
forces  which  had  been  evoked  by  the  Ludwig  school,  such  as  diffusion 
and  osmosis,  could  not  concentrate  the  weak  urine  supposedly  filtered 
through  the  glomerulus.  When  blood  and  urine  are  placed  on  either 
side  of  a  parchment  membrane,  water  passes  b}^  dialysis  from  the 
blood  to  urine.  The  electrolytes  in  normal  urine  are  more  concen- 
trated than  in  the  blood.  In  the  case  of  the  urine  passed  after  drinking 
a  quart  or  two  of  water  the  opposite  condition  pertains.  The  kidney 
Works  either  way  against  osmotic  force.  It  may  secrete  a  urine  Avith  far 
more  salt  than  in  the  blood,  or  a  urine  with  almost  no  salt  in  it  at  all. 
In  regard  to  the  second  point,  it  has  been  demonstrated  that 
during  the  process  of  active  secretion  the  amount  of  oxygen  taken  up 
by  the  kidney  from,  and  the  amount  of  CO.^  given  up  to,  the  blood 
i"s  greatly  increased.     This  is  seen  from  the  following  figures: 


0„  per  minute       .  .          . .          . .  4-35  c.c.  5-58 

CO.j  per  minute 1-88  c.c.  3-93  c.c 

Urine  per  minute             . .          . .  O-Oo  c.c.  l-o3  c.c 

Work  per  minute             ..          ..  327*0  g.cms.  irGl-Og.cn 


c.c. 
c.c. 


g.cm.s. 


THE  SECRETION  OF  URIXE 


The  work  may  be  performed  in  an  excretory  direction  or  in  an 
absorptive  direction.  For  instance,  to  concentrate  through  a  semi- 
permeable membrane  the  urine  from  the  chloride  content  of  the  blood 
(0-38  per  cent.)  to  that  of  normal  urine  (0-8  per  cent.)  requires 
the  expenditure  of  a  large  amount  of  work  on  the  part  of  the  kidney 
cells.  It  would  also  require  a  large  expenditure  of  work  to  separate, 
as  after  large  libations,  a  urine  consisting  of  little  more  than  water. 

The  questions  in  dispute,  then,  at  the  present  time  are  these: 
(1)  Is  the  Avork  of  the  kidney  performed  in  activeh^  secreting  sub- 
stances in  the  glomerulus  and  in  the  tubules  i  or  (2)  is  it  secreting 
in  the  tubules  only  ?  or  (3)  is  the  work  performed  in  concentrating 
urine  in  the  tubules  ?  or  (4)  is  it  concerned  in  all  these  processes  ? 


Oi  - 


005- 


L,s(}, 


Ha^O^.  Rlnqer- Solution. 

Fig.  2.32. 
Line^oxygeii  consumption;  black  aroa  =  urine  excreted.     (Bareroft  and  Straub.) 


Valuable  evidence  has  been  adduced  by  the  study  of  the  action, 
upon  the  internal  respiration  of  the  kidney,  of  various  substances, 
such  as  sodium  chloride,  Ringer's  solution,  urea,  caffeine,  and  sodium 
sulphate — substances  which  stimulate  the  flow  of  urine,  and  act  as 
diuretics.  The  last  three  substances,  when  injected  into  the  blood, 
cause  a  diuresis  which  is  attended  by  a  markedty  increased  absorption 
of  oxygen:  5  per  cent,  sodium  chloride  and  Ringer's  solution,  on  the 
other  hand,  cause  a  diuresis  Avhich  is  unattended  by  any  such  increased 
oxygen  absorption  (Fig.  232).  When  the  kidney  cells  have  been 
poisoned  b}^  mere  iric  chloride,  the  oxAgen  consumption  of  the  kidney 
almost  stops.     Sodium  sulphate  is  then  practically  Avithout  action  in 


478  A  TEXTBOOK  OK  F^HYSIOLOGY 

causing  diuresis;  .sodium  chloride  still  eoatinues  to  do  so.  Also  it  is 
found,  under  these  circumstances,  that  if  the  blood  be  much  diluted 
with  Ringer's  solution,  the  chlorine  content  of  the  mine  closely 
approximates  to  that  of  the  blood. 

From  these  experiments  it  would  seem  that  the  excretion  of  such 
bodies  as  urea  and  sodium  sulphate  call  forth  the  cell  activity  of  the 
kidne}',  while  chlorides  do  not.  Such  experiments,  however,  do  not 
negative  the  view  that  work  may  also  be  spent  in  actively  concen- 
trating the  urine  in  the  tubules. 

The  theoiies  of  Bowman  and  Ludwig  have  been  variously  modified 
as  the  result  of  the  ever-extending  researches  into  the  nature  of  the 
renal  functions.     The  following  are  the  chief  modifications: 

1.  A  modification  of  the  original  view  of  Lildwig.  A  dilute  urine 
containing  all  the  urinary  constituents  is  filtered  through  the  glomeru- 
lus, and  becomes  concentrated  by  cell  activity  during  its  passage 
through  the  urinary  tubules. 

2.  Modifications  of  the  original  view  of  Bowman,  (a)  Water  and 
salts  are  filtered  through  the  glomerulus,  and  the  organic  constituents 
are  actively  added  by  the  tubules.  (6)  The  water  and  salts  are 
actively  secreted  by  the  glomerular  cells,  and  the  organic  substances 
by  the  cells  of  the  tubules. 

3.  A  combination  of  the  above  views — namely,  that  water  and 
salts  are  either  filtered  or  secreted  from  the  blood  in  the  glomeruli, 
and  that  the  tubules  have  a  double  function — (a)  to  add  the  organic 
constituents  of  the  urine  by  cell  activity  in  one  part  of  their  course; 
and  (6)  to  concentrate  the  urine  by  a  similar  agency  in  another  part. 

It  will  be  .seen  at  once  that  research  resoh^es  itself  into  an  inquiry 
into — 

1.  The  function  of  the  glomerulus  and  its  mode  of  action. 

2.  The  functions  of  the  tubules. 

The  Function  of  the  Glomerulus, — Three  points  have  to  be  .settled: 
(1)  Is  a  dilute  urine  filtered  through  the  glomerulus  ?  or  (2)  are  only 
the  Avater  and  salts  of  the  urine  isolated  in  the  glomerulus  ?  and 
(3)  if  so,  is  it  by  a  simple  physical  process,  such  as  filtration,  or  by  an 
active  process  of  cell  secretion  ? 

Those  who  uphold  the  filtration  hypothesis  base  it,  in  the  first 
place,  uj)on  the  arrangement  of  the  bloodvessels  of  the  glomerulus. 
As  measured  in  histological  preparations  of  injected  kidney,  the 
afferent  artery  appears  to  be  of  greater  bore  than  the  efferent  vein. 
It  is  suggested  that  this  develops  a  high  filtration  jiressure  in  the 
capillaries  of  the  glomerulus.  It  is  claimed  that  evidence  of  this  is 
afforded  by  the  results  of  various  expsriments  which  are  directed 
towards  the  increase  of  the  arterial  pressure  within  the  kidney,  either 
by  producing  a  general  rise  of  arterial  pressure  or  a  local  rise  by  causing 
vaso-dilatation  within  the  organ.  Whenever  the  pressure  is  thus 
raised — as,  for  example,  by  stimulation  of  the  sj^inal  cord  after  section 
of  the  renal  nerves,  or  during  the  injection  of  large  amounts  of  fluid, 
Avhich  temporarily  leads  to  a  condition  of  plethora — there  is  an  in- 
creased floAv  of  urine.     When,  however,  the  arterial  pressure  is  lowered, 


THE  SECRETION  OF  URINE  479 

either  locally,  as  b}'  ligature  of  the  renal  artery,  or  generally  by  division 
of  the  spinal  cord  in  the  neck,  then  the  secretion  ceases.  When  the 
arterial  pressure  in  the  renal  artery  is  diminished,  as  by  stimulation 
of  the  spinal  cord  without  previous  section  of  the  renal  nerves,  or  of 
the  splanchnic  nerve,  or  by  haemorrhage,  then  the  flow  of  urine  is 
diminished. 

Such  experiments  undoubtedly  shoM"  that,  the  flow  of  urine  is 
increased,  when  the  renal  arterial  pressure  is  high,  and  diminished 
when  it  is  low.  The  results  may,  however,  be  correlated  with  the  flow 
of  blood  through  the  kidney.  \^'Tien  the  flow  of  blood  is  increased  or 
diminished,  so  also  is  the  secretion  of  urine.  Against  the  filtration 
h}T3othesis  is  the  fact  that  ligature  of  the  renal  vein,  which  certainly 
raises  the  pressure  in  the  renal  capillaries  to  the  full  arterial  pressure, 
not  oul}'  causes  no  increased  flow  of  urine,  but  stops  it  altogether. 
Again,  when  the  renal  artery  is  iigated  for  a  few  minutes,  and  the  liga 
ture  then  removed,  the  floAv  of  urine  does  not  immediately  begin 
again  for  an  hour  or  so,  and,  when  it  does,  the  character  of  the  urine 
is  pathological — it  contains  albumin. 

On  the  filtration  hypothesis,  it  is  assumed  that  F  (the  filtration 
pressure)  =  P  (the  kidney  arterial  pressure)  ~p  (the  glomerular 
pressure ) .     ¥  =  F  —  jJ- 

This  being  the  case,  then,  in  the  condition  of  F  —  {j^  +  p^) — where/*/ 
indicates  a  slight  obstruction  to  the  flow  in  the  ureter,  and  therefore 
a  rise  of  glomerular  pressure,  and  a  consec£uent  diminution  of  the 
filtration  jiressure — there  should  be  a  diminished  flow  of  urine.  This, 
however,  has  been  shown  experimentally  not  to  be  the  case.  Indeed, 
under  these  conditions,  there  is  an  increased  flow  of  urine,  and  if 
phloridzin  is  administered  to  the  animal^  there  is  an  increased  ex- 
cretion of  sugar  as  the  result  of  this  obstruction.  The  obstruction 
stimulates  the  kidney  to  secrete. 

Further,  it  may  be  pointed  out  that,  according  to  the  views  ex- 
pressed in  the  section  on  capillary  pressure,  it  does  not  seem  possible 
for  a  high  filtration  pressure  to  exist  within  the  glomeruli.  The 
pulsatile  force  is  transmitted  to,  and  expands,  all  j)arts  of  the  kidney. 

The  histological  examination  of  the  kidne}-  shows  no  evidence 
of  membranes  so  arranged  as  to  allow  filtration  from  the  capillaries 
into  the  capsules.  There  is  nothing  to  keep  the  membrane  separatmg 
blood  and  urine  open  and  rigid  as  a  filtration  membrane.  The  capsule 
and  tubules  are  surrounded  by  a  membrane,  but  this  is  so  arranged 
as  to  limit  their  expansion  and  allow  the  passage  from  capillary  to 
lumen  of  tubule  bj'  osmotic  or  other  forces  set  up  within  the  tubule 
by  the  active  secretion  of  the  renal  cells.  The  structural  arrange- 
ments point  to  a  pull  of  fluid  from  capillary  to  tubule,  not  to  a  mechani- 
cal push  produced  by  blood-pressure. 

The  process  of  secretion  at  the  glomerulus  must  be  just  as  much 
an  act  of  cell  activity  as  is  the  formation  of  the  corresponding  waste 
fluid  in  unicellular  organisms,  or  in  worms  which  have  their  nephridia 
bathed  in  blood-sinuses — conditions  which  clearly  negative  the 
filtration  hypothesis. 


480  A  TEXTBOOK  OF  PHYSIOLOGY 

Whatever  the  nature  of  the  mechanism  may  be,  tlie  passage  of 
Avater  seems  to  be  carried  out  with  a  minimmn  amount  of  work  on 
the  part  of  the  kidney,  as  is  shown  by  the  fact  that  an  intravenous 
injection  of  5  per  cent,  sodium  chloride  solution  causes  a  diuresis 
imattended  by  any  increased  oxygen  absorption.  The  total  osmotic 
pressure  of  the  blood  is  equal  to  seven  atmospheres,  and  if  water  were 
separated  from  the  blood  through  a  semi -permeable  membrane,  work 
woiild  have  to  be  done  to  overcome  this  pressure.  If  the  water  and  salts 
of  the  blood,  and  not  the  urea,  sugar,  etc.,  were  separated,  the  osmotic 
pressure  overcome  would  be  considerably  higher  than  the  blood- 
pressure.  After  dilution  of  the  blood  with  0-9  per  cent.  NaCl  solution 
to  pro\'t)ke  diuresis,  it  Avas  found  that  the  kidney  secreted  urine  M'hen 
the  blood -pressure  Avas  loAvered  even  to  18  mm.  Hg. 

Water  flows  from  the  ureter  A\hen  circulated  through  the  blood- 
vessels of  the  dead  kidney.  In  contiguity  lie  the  renal  A'essels, 
glomeruli,  and  the  tubules,  and  it  is  probable  that  the  membranes 
which  separate  these  allow  leakage  in  the  poisoned  or  dead  kidney. 
It  becomes  then  an  indifferent  matter  Avhether  the  Avater  takes  the 
channel  of  the  tubules  or  A^enules.  The  kidney  substance  imbibes 
the  water,  becoming  converted,  so  to  speak,  into  a  bog  or  morass. 
When  a  0-75  per  cent,  solution  of  NaCl  is  perfused  through  the  excised 
kidney  of  the  ox,  the  filtrate  varies  very  slightly  from  the  jierfused 
fluid,  and  stoppage  of  the  renal  A^ein  increases  its  amount.  In  the 
living  kidney,  the  stoppage  of  the  renal  A^ein  arrests  the  secretion  of 
urine. 

It  has  been  suggested  that  one  function  of  the  glomerulus  is  to 
act  as  a  pulsating  mechanism  ^^laced  at  the  commencement  of  the 
tubule.  Undoubtedly,  Avith  each  heart -beat  the  ui'ine  is  driven 
forAvard  out  of  the  tubules  into  the  pelvis  of  the  kidne3^  The  whole 
kidney  expands  with  systole  and  shrinks  on  diastole,  and  not  only 
blood  is  expressed  from  the  renal  A^eins,  but  urine  from  the  collecting 
tubules  by  each  systolic  expansion.  The  pulsatile  expansion  of  the 
kidney  is  necessary  for  the  normal  secretion  of  urine. 

The  Nature  of  the  Glomerular  Secretion. — At  the  present  time  it 
is  impossible  to  say  what  is  the  exact  nature  of  the  secretion  of  the 
glomerulus.  Probably  the  mechanism  is  such  that  water  and  salts, 
especially'  chlorides,  pass  through  with  great  ease.  In  cases  Avhere 
by  injury  or  operation  the  tubules  in  the  medulla  haA^e  been  largely 
destroyed,  and  the  glomeruli  in  the  cortex  left  intact,  a  much  more 
Avatery  urine  is  secreted. 

The  proteins  and  the  sugar  of  the  blood  are  held  back,  by  the 
glomerular  membranes,  since  normal  urine  contains  only  traces  of 
these  bodies.  When  the  glomeruli  are  damaged,  these  bodies  may 
pass  through  into  the  urine,  especially  the  blood-proteins.  Direct 
leakage  then  takes  place.  It  is  a  matter  of  doubt  whether  any  of  the 
nitrogenous  constituents  pass  into  the  urine  at  the  glomerulus.  It 
may  be  concluded  that  its  main  function  is  the  separation  of  water 
and  salts. 

In  the  frog,  the  renal  portal  A^ein  is  the  main  blood-supply  of  the 


THE  SECRETION  OF  URIXE  481 

urinary  tubules,  and  ligation  of  this  vein  affects  but  little  the  amount 
of  urine  secreted.  On  the  other  hand,  ligation  of  the  renal  arteries 
which  supply  the  glomeruli  causes  a  cessation  of  the  urinary  flow.  As 
a  small  amount  of  secretion  may  then  be  excited  by  the  injection  of 
a  diuretic,  it  is  concluded  that  the  tubules  can  secrete  some  water. 

The  Secretory  Function  of  the  Tubule. — If  the  kidne\-  tubules  are 
damaged  by  a  poison,  autl  a  solution  of  sodium  chloride  added  to 
the  blood,  the  excess  of  chloride  quickly  passes  into  the  urine.  On 
the  other  hand,  if  urea  is  added  to  the  blood,  it  is  not  excreted. 

This  experiment  indicates  that  the  chief  secretory  function  of  the 
tubules  is  to  add  the  waste  nitrogenous  products  to  the  fluid  separated 
from  the  glomerulus.  Confirmatory  evidence  has  been  obtained  by 
mjecting  into  the  blood  of  an  animal  an  organic  d3'e,  such  as 
indigo-carmine,  which  is  sesreted  in  the  urine.  The  site  of  secretion 
can  only  be  ascertained  after  stopj)nig  the  glomerular  secretion  of 
water.  This  is  effected  b}'  the  fall  of  blood-pressure  Avhich  follows  a 
section  of  the  spinal  cord.  Under  these  circumstances,  the  convoluted 
portions  of  the  tubules  of  the  kidney  are  found  filled  with  pigment 
granules.  In  the  bird,  after  ligation  of  the  ureter,  there  follows  a 
■deposition  of  urates  (which  correspond  to  the  urea  of  the  mammal) 
within  the  cells  of  the  tubules.  Uric  acid  and  its  salts  can  be  stained 
with  silver  nitrate,  and  demonstrated  AA'ithin  the  cells  of  the  tubules, 
the  stain  being  developed  by  a  solution  of  hydro quinone. 

Vacuoles  akin  to  excretory  vacuoles  have  been  described  in  the 
cells  of  the  convoluted  tubules.  These  gradually  grow  in  size,  and 
eventually'  void  their  watery  and  granular  contents  into  the  lumen 
of  the  tubule.  In  thirst}'  animals  fed  on  dry  food  the  cells  fill  up 
most  of  the  lumen,  and  are  full  of  granules.  After  diuresis,  the  cell 
are  shrunken  and  the  lumen  is  wide. 

Resorption  by  the  Renal  Tubules. — The  evidence  so  far  adduced 
in  favour  of  resorption  is  far  from  conclusive.  It  is  claimed  that, 
after  removal  of  the  medulla  of  the  kidney,  there  tends  to  be  secreted 
a  urine  which  is  much  more  Avatery.  It  is  also  claimed  that  such  a 
function  is  indicated  b}'  notable  differences  in  the  rate  of  secretion 
of  two  salts  when  injected  into  the  blood  in  equal  amounts  of  their 
equivalent  solutions — e.g.,  of  NaCl  and  NagSO^.  The  difference  is 
equall}'  well  explained  by  a  selective  secretory  activity.  The  kidney 
has  the  special  function  of  turning  out  from  the  blood  foreign  salts, 
and  of  keeping  constant  the  concentration  of  normal  salts  in  the 
blood. 

"  Pigment  casts  ""  have  been  found  in  the  collecting  tubules  after 
the  injection  of  carmine  into  the  circulation,  and  this  may  point  to 
a  coneentration  of  the  urine,  possibly  in  the  second  convoluted 
tubules.  Onl}'  a  little  carmine  is  to  be  found  in  the  first  convoluted 
tubules,  for  the  glomerular  secretion  of  water  washes  it  on  as  it  is 
secreted  there.  This  is  the  best  evidence  so  far  adduced  in  favour  of 
resorption  within  the  urinary  tubule. 

The  concentration  of  urea  in  the  blood  is  O-o  to  0-6  per  mille, 

31 


482  A  TP:XTB00K  OF  PHYSIOLOGY 

and  30  grammew  of  urea  may  be  secreted  per  diem.  To  effect  this 
by  resorption,  60  litres  would  have  to  be  concentrated  to  2  litres. 
Such  an  active  resorption  is  possible  for  the  amount  of  blood  flowing 
through  the  kidnej^s  is  very  large.  It  has  been  estimated  at  300  to 
600  litres,  and  even  at  1,800  litres,  per  diem — an  amount  ample 
enough  to  allow  resorption  to  play  an  active  part. 

Intravenous  injection  of  concentrated  salt  or  sugar  solution  pro- 
duces diuresis  both  by  exciting  the  renal  cells  and  by  making  the  blood 
more  watery.  The  water  is  drawn  into  the  blood  from  the  tissues, 
and  the  concentration  of  the  blood  thus  rapidly  brought  back  ta 
normal.  The  diuresis  is  not  large  because  the  body  holds  to  its 
water.  The  intravenous  injection  of  isotonic  and  h3q:;otonic  solutions 
both  excites  the  renal  cells  and  accelerates  the  blood-flow  through 
the  kidney;  the  water  thus  introduced  produces  much  diuresis.  Urea 
acts  as  a  powerful  diuretic,  and  causes  vaso-dilatation  of  the  kidnej'. 
Caffeine  likewise,  but  this  acts  when  the  renal  vaso-motor  nerves  are 
destroyed.     Caffeine  causes  little  diuresis  in  thirsty  animals. 

To  sum  up,  the  balance  of  evidence  at  present  available  seems  to 
indicate  that  the  water  and  salt  content  (particularly  chloride)  of  the 
urine  are  secreted  by  the  action  of  the  glomerular  cells,  and  that  the 
organic  constituents  of  the  urine  are  added  by  the  cell  activity  of  the 
tubules.  The  evidence  in  favour  of  a  concentrating  mechanism  in 
the  tubules  is  slight,  but  it  is  most  probable  that  the  urine  is  the 
l)roduct  of  the  give  and  take  of  the  renal  cells,  bathed  as  thej'  are 
by  the  contents  of  the  tubule  on  one  side,  and  by  the  lymph  which 
percolates  from  the  capillaries  on  the  other.  There  are  diuretic 
substances  in  the  blood  which  stimulate  the  kidney  to  secrete,  e.g., 
urea;  and  the  secretory  activity  depends  on  the  amount  of  these 
substances — that  is,  on  their  concentration  and  on  the  volume  of  the 
blood  passing  through  the  kidneys  per  diem.  The  above  view  is 
strengthened  by  the  fact  that  development  ally  the  kidney  has  a 
double  organ — a  secretory  and  an  excretory  part. 

The  Passage  of  Urine  along  the  Ureters. — The  urine  collects  in  the 
pelvis  of  the  kidnej-,  and  passes  thence  down  the  ureters  to  the 
bladder.  The  ureters  are  smooth-muscle  tubes  lined  by  transitional 
epithelium.  The  muscle  is  arranged  in  a  circular  outer  and  a  longi- 
tudinal imier  layer.  It  is  probable  that  ganglion  cells  are  j^resent 
between  the  muscular  layers  throughout  the  entire  length,  but  they 
are  particularly  abundant  in  the  upper  and  lower  thirds. 

Under  the  influence  of  the  secretorj-  pressure,  and  in  the  erect 
man  under  the  influence  of  gravity,  the  urine  j)asses  into  the  begin- 
nings of  the  ureter,  which  then  by  peristaltic  movements  passes  the 
urine  down  into  the  bladder.  These  peristaltic  movements  occur 
regularly  about  everj^  ten  to  twenty  seconds,  being  more  frequent 
the  greater  the  amount  of  urine,  but  the  presence  of  urine  in  the  ureter 
does  not  seem  to  be  necessary  to  evoke  them.  They  proceed  over 
the  ureter  at  a  rate  of  about  20  to  30  millimetres  per  second. 

There  is  some  doubt  as  to  the  exact  nature  of  these  movements. 
It  ^^•as  held  that  they  were  mj'ogenic  in  origin,  because  the  middle 


THE  SECRETIOX  OF  URINE  48S 

third  of  the  ureter  was  believed  to  be  devoid  of  a  local  gaiiglionated 
nervous  mechanism.  Such,  however,  is  now  known  to  exist,  and  it 
is  highh'  i^robable  that  the  smooth  muscle  of  the  ureter  executes^ 
these  rhythmic  peristaltic  movements  by  virtue  of  a  local  nervous^ 
mechanism. 

Although  the  ureters  are  supplied  by  extrmsic  nerves,  the  exact 
action  of  these  is  somewhat  doubtful.  It  is  stated  that  stimulation 
of  the  splanchnic  fibres,  which  reach  the  ureter  through  the  renal 
l^lexus,  produce  acceleration  of  the  upper  end  of  the  ureter,  wliile 
stimulation  of  the  h^-pogastric  nerves  has  a  similar  accelerator}'  effect 
upon  the  lower  end  of  the  ureter. 

The  ureters  enter  the  bladder  obliquel}'  at  the  upper  corners  of 
the  trigone  of  the  bladder.  This  oblique  course  prevents  a  regurgita- 
tion of  urine.  The  orifice  of  the  urethra  is  closed  by  the  thickened 
circular  fibres  at  the  base  of  the  bladder — the  internal  sj)hincter — 
and  bj'  the  voluntary  muscle — the  compressor  urethrae — outside  the 
bladder.  The  urine,  therefore,  gradually'  accumulates  in  the  bladder, 
and  this  gradually  relaxes  to  accommodate  its  load.  The  incoming 
urine  raises  the  pressure  within  the  bladder  up  to  about  15  to  20  c.m. 
of  HgO.  At  this  point  the  desire  to  micturate  usually  manifests  itself, 
and  the  urine  is  voided.  If,  however,  this  be  not  done,  the  bladder 
further  relaxes,  and  the  desire  passes  aAvay  for  the  time  being. 

The  Act  of  Micturition. — During  the  time  that  urine  is  accumu- 
lating within  the  bladder  the  organ  performs  rhythmic  movements. 
As  the  organ  fills,  these  gradually  increase  in  force,  until  some  urine 
is  forced  j^ast  the  internal  sphincter,  and  then  micturition  may  reflexly 
take  place.  This  is  the  case  in  the  decerebrate  or  spinal  animal,  or 
in  the  invoknitary  micturition  of  children  with  weak  control. 
Normalh',  however,  the  reflex  is  curbed,  and  when  there  is  desire  to 
micturate,  the  passage  of  urine  into  the  first  part  of  the  urethra  is 
aided  by  the  voluntary  efforts  of  the  individual.  The  intra-abdominal 
pressure  is  rai.sed  b\'  closing  the  glottis,  so  holding  the  diaphragm 
in  the  inspiratorj'  position,  and  by  contracting  the  muscles  of 
the  abdominal  wall.  The  passage  of  a  few  drops  of  urine  through 
the  internal  sphincter  stimulates  the  sensory  nerve-endings  of  the 
pelvic  nerve.  As  a  result  of  this,  the  sphincter  of  the  bladder  is 
reflexly  inhibited,  while  the  body  of  the  bladder  contracts  dowai  and 
voids  its  contents. 

IVIicturition  is  therefore  a  reflex  act,  the  centre  for  which  is  situated 
in  the  lumbar  spinal  cord.  This  centre  is,  in  the  adult,  imder  the 
control  of  the  will,  but  in  the  new-born  this  is  not  the  case. 
A  baby,  for  the  first  iew  months  of  its  life,  passes  urine  in  response 
to  the  demands  of  the  lower,  and  not  of  the  higher,  reflex  arc.  It 
has  to  be  taught  control.  In  some,  the  nervous  mechanism  concerned 
in  this  reflex  is  overexcitable,  so  that  even  in  adult  life,  when  the 
cerebral  control  is  cut  off,  either  bj^  sleep  or  excitement,  urine  is 
reflexly  voided. 

The  efferent  nerves  concerned  in  the  reflex  are  chiefly  the  pelvic 
nerves.     In   some    animals    the    hypogastric    nerves    are    also    con- 


484  A  TEXTBOOK  OF  J^HV.SIOJ.OGY 

cerned.  As  indicated,  the  action  of  these  nerves  varies  in  different 
animals.  It  is  possible  that  both  are  usually  concerned  in  the  act 
of  micturition,  particularly  in  raising  the  tension  for  the  initial  prt)- 
cess.  The  pelvic  nerves,  when  stimulated  peripherall}^  usually  cause 
a  marked  contraction  of  the  body  of  the  bladder,  and  an  inhibition 
of  the  sphincter  of  the  trigone,  while  the  hypogastrics  cause  an 
inhibition  of  the  wall  of  the  bladder.  The  latter  are  therefore 
mainly  in  action  during  the  accumulation  of  urine  within  the  bladder; 
the  pelvic,  on  the  other  hand,  during  the  voiding  of  the  viscus. 

The  hypogastric  supply  of  the  bladder  affords  an  example  of  what 
is  known  as  an  "  axon-reflex."  If  all  the  nerves  connected  with  the 
inferior  mesenteric  ganglion  be  divided  with  the  exception  of  the 
right  hypogastric  nerve  to  the  bladder,  then  stimulation  of  the  central 
end  of  the  left  hypogastric  nerve  will  cause  a  contraction  of  the  right 
half  of  the  bladder.  The  explanation  is  that  the  preganglionic  fibre 
branches  in  the  ganglion,  one  branch  forming  a  cell  station  with  the 
right  nerve,  another  branch  continuing  in  the  left  nerve  to  the  bladder. 
vStimulation  of  the  left  nerve  therefore  can  influence  the  bladder  through 
the  cell  station  in  the  ganglion. 

The  last  drops  of  urine  are  expelled  from  the  urethra  bj^  the  con- 
tractions of  the  bulbo-cavernosus  (accelerator  urinse)  muscles.  The 
act  of  micturition  can  be  stopped  by  the  contraction  of  the  com- 
pressor urethrse,  but  it  is  difficult  to  do  this  when  the  reflex  is  in  full 
action. 


BOOK  IX 

THE    FUNCTIONS    OF   THE    SKIN    AND    HODY 
TEMPERATURE 


CHAPTER  LVII 

THE  FUNCTIONS  OF  THE  SKIN 

One  function  of  the  skin  is  to  confine  and  support  the  soft  parts 
with  a  strong,  pliable,  elastic  cover,  and  protect  them  from  harm. 
Its  structure  is  adapted  to  these  functions.  The  skin,  by  virtue  of 
its  blood-supph'  and  sweat  glands,  also  plays  a  great  part  in  regu- 
lating the  temperature  of  the  organism,  and  by  virtue  of  special 
nervous  structures  affords  information  of  the  nature  of  the  surround- 
ings in  which  the  organism  finds  itself. 

The  skin,  in  addition,  acts  as  an  organ  of  excretion,  and  to  a 
certain  extent  as  an  organ  of  absorption.  In  some  animals,  the  skin 
serves  a  respiratory  function. 

The  skin  consists  of  two  parts — the  epidermis,  or  outer  skin,  and 
the  cutis  vera  (true  skin),  or  corium.  The  epidermis  consists  of 
stratified  squamous  epithelium,  and  has  no  bloodvessels.  The  most 
external  laj^er  is  known  as  the  stratum  corneum,  or  "  horny  layer." 
Its  cells  are  largely  composed  of  keratin,  and  are  of  a  scaly  nature. 
This  layer  is  particularly  thick  in  the  jDalms  of  the  hand  and  soles 
of  the  feet.  The  next  layer  inwards  is  known  as  the  stratum  lucidum. 
Its  cells  appear  clear  and  free  from  granules.  Within  this  layer  is 
another,  known  as  the  stratum  granulosum.  Its  cells  are  charac- 
terized by  the  presence  of  granules  of  eleidin,  a  substance  which 
stains  deeply  with  hsematoxylin.  Beneath  this  comes  the  deepest 
layer  of  the  epidermis — the  rete  mueosum,  or  stratum  Malpighii  (the 
IMalpighian  layer),  the  cells  of  which  are  not  horny,  but  protoplasmic 
in  nature.  It  is  in  this  layer  that  there  is  dej)osited  the  pigment 
melanin,  which  gives  a  characteristic  black  colour  to  the  skin  of  the 
dark  races.  The  cells  are  in  more  than  one  layer,  those  in  the 
deepest  are  columnar,  those  above  polyhedral  in  shape.  They  multiply 
in  the  deepest  layer,  and  are  gradually  pushed  out,  and  undergo  the 
change  into  horny  matter  as  the  older  layers  are  Avorn  off.  Tissue 
lymph  soaks   between  the  cells,  and  keeps   up  the  transpiration  of 

485 


486 


A  TEXTBOOK  OF  PHYSIOLOCY 


water   from   the   surface.     The  lymph  .'ffords  niHtciial   wliereby  the 
chemical  change  into  keratin  is  effected. 

The  true  skin — dermis,  or  corium — consists  chiefly  of  connective 
tissue.  The  outermost  layer  is  a  dense  fibrous  tissue,  which  is  thrown 
into  multitudes  of  papillae  or  ridges.  Corresponding  to  those  are  the 
patterns,  seen  on  the  surface  of  the  epidermis,  which  cover  the  ridges. 
The  patterns  on  the  finger  tips  are  peculiar  to  each  individual,  and 
afford  finger  prints  for  identification.  This  layer  is  well  supplied 
with  plexuses  of  capillary  vessels,  and  also  contains  some  of  the 
organs  of  sensation,  such  as  Meissner's  corpuscles,  etc.  The  deepest 
layer  of  true  skin  consists  of  fatty  or  adipose  tissue.  Besides  serving 
as  a  fat  dejjot,  it  is  of  importance  in  keeping  the  heat  within  the 


J''iG.  233. — MicKuscoPE,  Low  Poweii.     Section  through  the  Skin. 

A,  Horny  layer  of  cells;  B,  layers  of  soft  growing  cells;  C,  thick  connective-tissue 
coat ;  D,  fat  layer ;  E,  sweat-gland  and  duct ;  F,  hair ;  O,  sebaceous  gland ;  H,  papilla 
of  hair;  J,  small  artery;  K,  muscle  of  hair;  L,  capillaries. 


"body.  Arctic  mammals  are  protected  by  thick  layers  of  blubber. 
It  also  acts  as  a  cushion,  and  gives  softness  of  contour  and  beauty 
■of  form  to  the  body.  In  some  positions — e.g.,  neck,  scrotum — 
plain  muscles  fibres  are  found  in  the  corium.  Connecting  the  two 
layers  of  the  corium  is  a  loose  fibrous-tissue  layer. 

Hair  follicles  are  found  in  all  parts  of  the  skin  of  man,  except  in 
that  of  the  palms  of  the  hand  and  of  the  soles  of  the  feet.  They  are 
developed  from  the  Malpighian  layer,  which  grows  downwards  into 
the  corium.  They  consist  of  various  layers  corresponding  to  the 
epidermis  and  dermis,  the  hairs  growing  up  from  a  layer  of  cells  known 
as  the  hair  bulb.  Smooth  muscle  fibres,  forming  the  pilo-motor 
nerves,  are  attached  to  each  hair  follicle,  and  cause  it  to  stand  erect 


THE  FUNCTIONS  OF  THE  SKIN  487 

when  in  action.  Nerves  end  in  plexuses  within  the  outer  layers  of 
the  follicle.  The  mouths  of  sebaceous  glands  also  open  into  the  upper 
part  of  the  hair  follicles.  These  glands  are  situated  in  the  Malpighian 
layer,  and  are  of  a  comi^oiuid  saccular  form,  and  lined  by  cubical 
■cells. 

The  thick  epidermis  protects  the  underlying  structures  from  the 
ceaseless  frictional  contact  with  the  external  world,  and  wards  off 
wounds  and  invasion  by  pathogenic  organisms. 

The  nails  were  originally  weapons  of  offence,  as  well  as  of 
defence. 

The  hairs  shoot  off  the  rain,  and  keep  the  body  dr\'.  They  also, 
when  touched,  stimulate  organs  of  sensation.  Tne  fur  of  animals 
prevents  loss  of  heat  by  convection.  Man  developed  as  a  tropical  animal, 
with  scanty  hair,  and  endures  the  cold  of  the  temperate  and  Arctic 
■climates  b}"  fashioning  clothes  of  the  hair  of  animals  or  fibres  of 
plants. 

The  fat  of  the  deep  layers  protects  against  heat  loss,  aiid  also 
serves  as  fat  depots  for  the  body  against  times  of  stress  (starva- 
tion). 

The  ceruminous  glands  of  the  ear,  by  the  odour  and  bitter  taste 
of  their  secretion,  are  said  to  prevent  insects  entering  the  external 
ear. 

The  sebaceous  glands,  by  their  secretion — the  sebum — -keep  the 
skin  supple,  and  protect  it  from  the  drying  effects  of  the  atmosphere, 
and  from  the  ill-effects  of  immersion  in  water.  Moreover,  pathogenic 
organisms  cannot  grow  through  this  secretion. 

The  sebum  is  of  a  fatty  or  waxy  nature,  containing  fatt}'  acids, 
which  render  it  acid,  and  iso-cholesterin.  It  is  continuously  secreted 
by  the  sebaceous  glands,  Avhich  occur  mainly  in  the  regions  supplied 
Avith  hair,  the  mouths  of  the  glands  opening  into  the  hair  follicles. 
Tne  secretion  is  squeezed  out  of  the  gland  by  the  contractile  action 
of  the  smooth  muscle  supplying  the  base  of  the  hair  follicle. 

Sweat  Glands. — From  the  stratum  Malpighii  are  developed  sweat 
glands.  These  lie  in  the  deeper  layer  of  the  corium,  and  are  particu- 
larly abundant  in  the  palms,  soles,  forehead,  and  axillae.  There  are 
estimated  to  be  per  square  inch  of  skin: 

Neck,  back^ 

Back                     417 

Buttocks     J 

Chest  and  abdomen       . .          •  •  ^>]}l^_ 

Thigh,  inner  surface       . .          • .  570 

Thigh,  outer  suviace      .  .          . .  554 

The  gland  proper  is  situated  in  the  dermis.  It  consists  of  a  coiled 
tube,  lined  with  a  single  layer  of  secreting  cells,  arranged  upon  a 
basement  membrane,  on  the  inner  side  of  which  lie  some  smooth 
jnuscle  fibres.     The  dusts  are  lined  with  cells  in  the  corium,  and  form 


Forehead  . . 

. .      1,258 

■Cheeks 

548 

Hand,  palm 

. .     2,736 

Hand,  back 

..      1,490 

Foot,  scle 

. .     2,(538 

Foot,  back 

924 

Xeck,  front  and 

sides 

. .      1,303 

488  A  TEXTBOOK  OF  PHYSIOLOGY 

a  spiral  passage  through  the  epidermis,  and  so  reach  the  surface  of 
the  skin. 

The  perspiration,  or  sweat,  is  a  watery  fluid  (99  per  cent,  is  water), 
generally  neutral  or  faintly  alkaline  in  reaction.  The  1  per  cent, 
of  solid.s  is  chiefly  sodium  chloride  and  fatty  bodies,  as  is  seen  from, 
the  following  table: 


Water    . . 

. .     98-88 

Solid.s 

..       1-12 

Salts 

. .       0-57 

Sodium  chloride 

0-22-0-33 

Alkaline    sulphate.s,    ]ihosi)hates, 

lactates, 

and 

potassium  chloride 

0-lS 

Fats,  fatty  acids  and  cholesterol 

0-1] 

Epithelium 

.  .        0-17 

Urea             . .          

.  .       0-08 

Usually  the  excretion  of  urea  by  the  skin  is  negligible,  but  during 
a  day's  march  on  a  ver\'  hot  da}^  as  much  as  12  per  cent,  of  the  total 
nitrogen  outj)ut  ma}-  be  excreted  in  the  sweat.  Sometimes  a  pink  sweat 
is  secreted  in  the  axillae,  coloured,  it  is  said,  by  products  of  putrefaction 
absorbed  from  the  large  intestine. 

The  amount  of  sweat  varies  largety  with  the  temperature  of  the 
surroundings  and  the  heating  of  the  body  by  muscular  work — e.g., 
600  grammes  on  an  ordinar}-,  and  3,000  grammes  on  a  warm  day 
in  which  considerable  exercise  is  taken. 

The  function  of  the  sweat  is  to  moisten  the  skin  and  to  cool  the  bodj- 
by  evaporation.  As  the  evaporation  of  1  gramme  of  water  requires 
540  calories,  we  see  the  cooling  efficiency  of  the  sweating  mechanism. 
A  man  without  sweat  glands  was  only  able  to  work  in  the  hot 
sun  by  wetting  his  shirt  frequent!}-,  and  so  artificially  making  good 
the  absence  of  sweat.  In  a  hot  chamber  his  bod}-  temperature  quickly 
became  febrile.  The  importance  of  the  sweat  as  an  excretion  of 
material  is  little  or  nil. 

Sweating  is  under  the  control  of  the  central  nervous  sj^steni;  the 
centre  is  stated  to  be  situated  in  the  floor  of  the  fourth  ventricle,  and 
is  provoked  by  a  rise  of  temperature  of  the  blood  which  circulates 
through  it.  >Such  a  rise  is  generally  produced  by  muscular  Avork. 
Experimentally  it  can  be  shown  that  the  warming  of  the  carotid 
blood  induces  sweating.  It  may  also  be  stimulated  b}'  increased  con- 
centration of  COo  in  the  blood,  as  in  asphyxia,  and  by  certain  drugs 
known  as  diaphoretics — e.g.,  mori^hine. 

The  centre  is  also  affected  by  afferent  nervous  impulses.  Stimula- 
tion of  the  central  end  of  the  sciatic  nerve  causes  sweating  reflexh'. 
Such  sweating  is  associated  with  a  vaso-constriction  in  the  limb, 
showing  that  the  vaso-dilatation  of  the  skin,  which  generally 
accompanies  sweating,  is  not  a  necessar}-,  although  a  favourable, 
condition. 

The  efferent  channels  for  the  sweat  nerves  run  in  the  .sympathetic 
system,  arising  from  the  thoracic  region  of  the  .spinal  cord  (see  pTcO)- 
Communication  is  established  with  the  .sympathetic  ganglia  by  the 
white  rami  communicantes  of  the  various  nerves.     Leaving  the  ganglia, 


THE  FUNCTIONS  OF  THE  SKIN  481> 

the  grey  rami  commumcantes  establish  connection  with  the  nerves 
supplying  the  skin  of  the  various  parts  of  the  body  (sea  p.  750)- 
After  the  spinal  cord  has  been  divided,  sweating  does  not  take  place 
in  the  parts  below  the  lesion. 

Sweating  is  provoked  in  the  pads  of  a  cat's  foot  on  stimulating 
the  peripheral  end  of  the  sciatic  nerve.  A  few  beads  of  sweat  will 
appear  if  the  nerve  be  stimulated  just  after  amputation  of  the  foot, 
but  its  amount  is  very  scanty  in  tha  absence  of  blood-flow.  The 
secretory  pressure  of  the  sweat,  when  this  is  obstructed,  rises  higher 
than  the  blood-pressure.  Sweating,  therefore,  is  the  result  of  an 
active  secretion,  and  not  a  mere  mechanical  transudation  of  fluid 
from  the  blood.  It  is  accompanied  by  an  electrical  variation  in  the 
skin  current,  as  maj'  be  demonstrated  in  the  pad  of  the  excised  cat's 
foot,  if  this  be  led  off  to  the  galvanometer,  and  the  sciatic  nerve 
excited.  The  nerve-endings  in  the  sweat  glands  may  be  paralj^zed 
by  atropine,  and  stimulated  bj^  pilocarpine  and  physostigmine  applied 
localh\ 

Transpiration  of  water  from  the  bloodvessels  through  the  skin  is 
continually  taking  place.  The  skin  is  thus  kept  supple  and  moist. 
The  loss  of  water  by  transpiration  is  insensible  perspiration,  and  it 
increases  with  the  temperature  of  the  skin.  Sensible  perspiration  is 
produced  by  the  action  of  the  sweat  glands. 

Absorption  by  the  Skin. — For  a  body  to  be  absorbed  by  the  un- 
broken skm,  it  is  necessary'  for  it  either  to  be  of  a  fatty  nature  or  to 
be  administered  in  fat.  Thus,  it  is  stated  that  cod-liver  oil  rubbed 
into  a  weakly  child  serves  as  a  source  of  nutriment.  Mercury  has 
been  administered  in  the  form  of  an  ointment. 

Watery  fluids  are  not  absorbed.  For  such  a  fluid  to  pass  into 
the  tissue  lymph,  it  is  necessary  to  abrade  the  skin,  as  in  vaccination. 
A  foreign  protein  injected  subcutaneoush^  sensitizes  the  body,  so  that 
a  subsequent  injection  of  a  trace  of  the  same  protein  made  a  few 
weeks  later  may  produce  shock,  or  death,  the  phenomena  of  anaphy- 
laxis (see  p.  111).  The  mere  washing  of  the  uninjured  skin  by  the 
solution  of  foreign  protein  has  no  such  effect,  showing  that  none  is 
absorbed. 

The  Respiratory  Function  of  the  Skin. — The  amount  of  CO^  given 
off  by  the  skin  of  man  is  very  small.  It  increases  markedly  during 
sweating,  and  mav  become  two  to  four  times  as  great  as  before.  This 
is  seen  in  the  following  figures  obtained  from  a  naked  man: 


Water  per  Hour.  CO2  per  Hour. 


Temp.  0 

jAir 

29-8= 

35-4° 
38-4° 

C. 
C. 

c. 

c. 

22-2  grammes  0-37  gramme 

50-3        „  0-35 

IOC'S        „  1-04  grammes 

158-S        ,,  1-23 


490 


A  TEXTBOOK  OF  PHYSIOLOGY 


When  clothing  is  Avorn,  the  increased  COg  and  water  output  occurs 
at  a  lower  temperature : 


Temp,  oj Air. 

Water  per  Hour. 

CO2  p(ir  Hour. 

28-9°  C. 
31-8°  C. 
32-7°  C. 
33-4°  C. 

50-S  grammes 
110-1 
119-1 
122-3 

0-33  gramme 

0-30 

0-37 

0-80 

These  observations  were  carried  out  in  still  air  in  a  respiratory 
chamber. 

In  frogs  and  kindred  animals,  the  exchange  is  great  enough  to 
enable  the  animal  to  live  without  lungs.  There  is  a  special  pulmo- 
cutaneous  circidation  for  this  purpose. 

The  Function  of  Pigment. — The  value  of  pigment  in  the  Malj)ighian 
layers  of  the  skin  of  man  is  to  protect  against  the  lethal  cflect  of 
intense  sunlight.  Rays  are  absorbed  by  the  pigment  of  the  skin, 
and  converted  into  heat-rays,  which  in  their  turn  increase  the 
transpiration  of  water  from  the  cutaneous  capillaries,  and  stimulate 
the  cutaneous  nerve -endings,  and  jjrovoke  sweating.  Thus,  the 
energy  of  the  sun  is  sweated  off  the  body  of  the  black  man.  On  the 
other  hand,  rays  penetrate  to  the  blood  of  the  white  man,  and  are 
absorbed  by  the  haemoglobin,  and  there  converted  into  heat-rays. 
Moreover,  the  rays  j^roduce  sunburn  in  the  skin  of  the  white  man, 
resulting  in  joig mentation.  The  white  man,  therefore,  to  keep  whik . 
has  to  wear  clothes  and  to  shelter  himself  from  the  sun,  while  the 
black  man  is  happy  naked.  The  white  man  wears  white  clothes  in 
the  tropics  to  reflect  and  scatter  the  sun's  rays;  also  these,  by 
entangling  air,  lessen  the  loss  of  heat  by  convection  and  evapora- 
tion. Thus,  the  clothed  white  man  cannot  do  field  labour  and  be 
comfortable  in  the  tropics,  and  fans  are  of  the  utmost  necessity  for 
securing  his  comfort  and  efficiencj^  indoors.  The  naked  black  man 
is  physiologically  efficient  for  life  in  the  tropics. 

The  absorption  of  rays  by  the  skin  of  the  negro  is  jDrobably 
the  reason  why  the  photograph  of  the  naked  negro  is  less  distinct 
than  that  of  the  white  man,  from  whose  skin  more  rays  are  reflected. 
The  j)igment  is  not  derived  from  blood-pigment,  but  belongs  to 
a  group  of  bodies  known  as  melanins.  The  pigment  of  the  hair  and 
skin  of  the  negro  has  been  found  to  contain  about  15-5  per  cent,  of 
nitrogen,  3-6  per  cent,  of  sulphur,  and  a  trace  of  iron,  the  pigment  of 
the  hair  containing  less  nitrogen  than  that  of  the  skin.  The  pigment 
is  probably  derived  from  t3Tosin  by  the  action  of  an  oxidase. 

In  addition  to  the  function  of  protection  against  the  uun's  rays, 
})igment  is  used  among  animals  for  various  other  purposes.  Animals, 
such  as  the  Arctic  fox  and  hare,  may  undergo  seasonal  change  of 
colour  for  jarotective  purposes,  changing  a  brown,  soil-colour  summer 
coat  to  a  Avhite,  snow-colour  winter  coat.     The  change  seems  to  be 


THE  FUNCTIOXS  OF  THE  SKIN  491 

more  than  one  of  colour,  for  a  white  rabbit,  or  an  Arctic  hare  in 
its  winter  coat  of  Avhite,  is  immune  to  an  intravenous  injection  of 
nucleo-protein,  which  produces  in  the  pigmented  animal  coagulation 
of  the  blood. 

Pigment  is  used  for  purposes  of  offence  as  well  as  of  defeni-e. 
It  is  particularly  marked  in  reptiles,  amj)hibia,  and  fishes.  Pigmen- 
tation also  plays  a  marked  part  in  the  sexual  relationships  of  some 
animals,  particularh'  of  birds.  The  male  bird  is  decked  in  vivid 
colours,  especially  in  the  springtime  of  active  com'tship.  True 
albinos  are  devoid  of  pigment,  and  their  irises  are  pink  owing  to 
the  reflexion  of  light  from  the  blood  circulating  therein. 


CHAPTER  LVin 
THE  TEMPERATURE  OF  THE  BODY 

Man,  in  common  with  other  mammals,  belongs  to  the  group  of 
warm-blooded  or  homothermic  animals.  In  this  group  the  internal 
temperature  of  the  body,  under  normal  circumstances  of  life,  is  kept 
aj^proximately  constant. 

During  the  katabolic  processes  of  the  body  heat  is  constantly 
evolved,  chiefly  in  the  muscles  and  the  glands.  It  is  estimated  that, 
of  the  1,700  calories  of  heat  produced  per  diem  by  a  man  of  11  stone 
when  fasting  and  resting  quietly  in  bed,  about  1,200  calories  are  pro- 
produced  in  the  muscles,  and  500  in  the  glands.  On  the  other  hand, 
loss  of  heat  is  constantly  occurring  from  the  surface  of  the  body  by 
radiation  and  convection,  and  b}'  the  evaporation  of  sweat.  A  certain 
amount  of  heat  is  also  lost  through  the  lungs.  It  has  been  calculated 
that  an  adult  man  in  a  ;itill  atmosphere  of  medium  temperature  loses 
43-7  per  cent,  of  his  heat  by  radiation,  31  per  cent,  by  convection, 
20-6  per  cent,  by  evaporation  of  sweat,  1-2  per  cent,  in  warming  in- 
spired air,  1-5  per  cent,  in  warming  the  food  and  drink,  1-8  per  cent, 
in  performance  of  external  work.  These  proportions  vary  with  the 
temperature,  as  is  shown  by  the  following  table : 


Extern  II ' 

Total  Heat 

Tempenitiire. 

produced. 

Deg.  C. 

Cal.  per  Kg. 

7-6 

83-5 

15-0 

63-0 

20-0 

53-5 

25-U 

54-2 

30-n. 

56-2 

Loss  hy  Con- 
vection and 

Loss  hy 

Radiation. 

Evaporation. 

Cal. 

Cal. 

71-7 

11-8 

49-0 

14-0 

37-3 

16-2 

37-3 

16-9 

30-0 

2()-2 

As  the  temperature  rises  the  loss  by  convection  and  radiation 
decreases,  and  that  by  evaporation  rises. 

The  Normal  Temperature. — The  normal  temperature  of  man  is 
usually  stated  to  be  98-4°  F.  This  is  the  temperature  as  ascertained 
by  taking  it  in  the  mouth  or  axilla.  This  method  is  liable  to  con- 
siderable error.  A  more  correct  idea  of  the  true  internal  temperature 
may  be  obtained  by  taking  the  temperature  in  the  rectum,  or  b}'  passing 
water  and  holding  the  bulb  of  the  thermometer  in  the  stream  of  urine. 

492 


THE  TEMPERATURE  OF  THE  BODY 


493 


The  rectal  temperature  is  normally  about  99-6°  F.,  the  ''  urhie  "  tem- 
perature about  99°  F. 

Owing  to  the  loss  of  heat  from  the  surface,  the  temperature  of  the 
skin  is  not  so  constant  as  the  internal  temj)erature  of  the  body;  in 
fact,  it  shows  considerable  variation  according  to  the  surrounding 
conditions.     For  example: 


Indoors. 

Ten  Minutes  after 
a  Swim  in  Sea. 

Chest 

. .     30°  C. 

24°  C. 

Cheek 

. .     32i°  C. 

25i°  C. 

Neck 

. .     33°  C. 

31°  C. 

Back  of  hand 

. .     31°  C. 

24i°  C. 

Arm    . . 

..     3]i°C. 

29|°  C. 

Abdomen 

. .     33°  C. 

26|-°  C. 

Leg 

. .     32°  C. 

30J  °  C. 

In  a  cold  wind  the  cheek  temperature  may  be  as  low  as  15^  C.  In 
hot,  moist  atmospheres  the  skin  temperature  rises  up  to  the  internal 
temperature  of  the  bod}'.  Too  much  uniformity  of  skin  temperature 
is  undesirable. 


p. 

7 

8 

9 

10 

11 

12 

1 

2 

3 

i 

5 

6 

7 

8 

9 

10 

11 

12 

1 

2 

3 

4 

5 

6 

7 

0. 

99*6 

37 

37 
37 
37 
37 
37 
36 
36 
36 
36 
36 
36 
36 

56 
W 

W4 

^ 

^ 

S 

^. 

W? 

/ 

\ 

.^ 

^ 

N 

\ 

•^cf 

pit-n 

/ 

\ 

00 

9S-8 

/ 

\ 

11 

AST) 

/ 

\ 

00 

98-4 

/ 

\ 

8Q 

98-2 

/ 

\ 

VR 

<»s-n 

/ 

\ 

67 

07-8 

/ 

\ 

S6 

*)7-6 

y^ 

\ 

44 

fl7-4 

1 

/ 

^^^^ 

fl7-? 

\ 

/ 

99 

Fig.  234. — Daily  Vaki.atiun  of  Temperature  of  Man.     (M.  S.  Pembrey.) 


While  the  rectal  temperature  represents  the  body  temperature, 
that  of  the  mouth  rises  and  falls  with  the  cooling  power  of  the  atmo- 
sphere. It  is  therefore  illusory  to  fix  the  mouth  temperature  at  any 
given  figure.  In  the  Arctic  region,  when  the  outside  temperature 
ranged  from  12°  to  30°  C.  below  zero,  and  that  of  the  engine-room  of 
the  ship  was  37°  C,  the  mouth  temperature  varied  from  34-58°  C.  to 
37-45°  C— i.e.,  5-17°  F.  The  mouth  is  cooled  through  the  floor  of 
the  mouth  rather  than  through  the  inspired  air.  After  drinking  hot 
fluid,  the  mouth  will  give  too  high  a  reading. 

The  temperature  of  man  shows  a  daily  variation  dependent  for 
the  most  part  upon  muscular  activity.  It  rises  during  the  day  to 
a  maximum  about  6  p.m.,  and  falls  during  the  night  to  a  minimum 
about  2.30  to  3  a.m.     Night  work,  depending  largely  upon  its  severity. 


404  A  TEXTBOOK  OF  PHYSIOLOGY 

reverses  or  tends  to  reverse  this  curve.  In  nocturnal  birds  the  tem- 
perature rises  during  the  night,  and  falls  during  the  daj'.  On 
travelling  from  Australia  the  curve  adjusts  itself  as  night  becomes 
day.  The  clergyman,  the  navty,  and  the  sailor,  show  temperature 
curves  which  vary 'with  the  occupations  and  mode  of  life  of  each. 

A  man  resting  in  bed  shows  the  same  variation,  but  not  to  so 
marked  an  extent.  The  diurnal  variation  is  accounted  for  b}^  the 
"  restlessness  "  during  the  day  as  compared  with  the  deep  rest  of 
sleep  during  the  earh'  night  hours.  It  is  more  difficult  to  get  absolute 
rest  in  the  light  and  noise  of  daytime.  Infants,  in  the  first  few  weeks 
of  life,  show  no  marked  variation. 

The  taking  of  food,  especially  if  it  be  warm  or  involve  much  work 
on  the  part  of  the  glands  and  muscle?  cf  mastication,  may  raise  the 
general  temperature  of  the  bodj-  slightly.  It  plays  no  part,  however, 
in  the  production  of  the  daih^  variation,  which  is  approximately  the 
same  whether  a  man  be  taking  food  or  starving. 

Muscular  activity  raises  the  body  temperature.  After  a  three- 
mile  race  the  rectal  temperature  in  a  man  not  in  good  training  was 
as  high  as  105°  F.,  and  did  not  reach  normal  again  until  the  sixth 
hour  after  the  race.  After  a  strenuous  game  of  football,  rectal  tem- 
peratures of  102°  to  103°  F.  are  the  rule.  This  is  owing  to  the  large 
amount  of  heat  liberated  by  the  muscles  during  musciilar  work 
(see  p.  552). 

If  the  subject  be  unsuitably  clothed,  and  do  hard  muscular  work 
in  a  warm,  windless  atmosj)here,  there  may  result  "  heat-stroke." 
Such  a  danger  arises  in  the  marches  of  soldiers  in  close  formation  on 
warm,  windless  days.  This  is  because  the  loss  of  heat  from  the  body 
cannot,  under  these  conditions,  keep  j^ace  with  the  heat  production. 
The  subject,  owing  to  his  clothing  and  the  high  external  temperature, 
cannot  lose  heat  rapidly  enough  bj'  convection  and  sweating.  The 
clothes  entangle  air,  and  keep  it  stationary.  This  air  is  warmed 
and  moistened  by  the  skin,  and  thus  the  body  is  enclosed  in  a  layer 
of  stagnant  humid  air.  In  a  crowd,  too,  the  air  is  confined  between 
the  bodies  of  the  people.  Wind  sweeps  the  stagnant  air  out  of  the 
clothes,  and  by  throwing  off  the  coat  and  opening  the  shirt  we  gain 
relief.  The  clothing  should  be  adapted  to  the  requirements  of  climate 
and  occupation,  not  to  fashion. 

The  highest  temperature  recorded  with  recovery  is  in  a  case  of 
malaria  (45°  C.)  or  113°  F. ;  the  lowest  tem^Derature  with  recovery, 
22-5°  C.  It  has  been  shown  that  rabbits  lowered  to  31°  to  34°  C. 
breathed  more  slowly,  and  could  not  raise  their  temperature  by 
shivering.  At  26°  to  29°  C.  their  nervous  co-ordination  was  damaged, 
and  they  were  easily  hjqDnotized.  At  26°  to  22°  C.  the  arterial  pressure 
began  to  fall ;  stimulation  of  the  skin  provoked  twitches.  At  19°  C. 
the  vital  centres  became  paralyzed,  and  death  ensued.  The  tempera- 
ture in  local  peripheral  parts  may  be  lowered  far  more,  and  these 
parts  recover  from  the  temporary  "  numbness."  Prolonged  and 
excessive  cold  leads  to  local  death  and  gangrene  (frost-bite). 

Generalty  speaking,  the  internal  temperature  of  birds  is  warmer 


THE  TEMPERATURE  OF  THE  BODY  495 

than  mammals,  and  the  temperature  of  small  warm-blooded  animals 
is  in  most  cases  higher  than  that  of  large  ones.  This  can  be  seen 
from  the  following  table : 


Hedgehog 

. .     34-8"-35-5°  C. 

Man,  rectum 

. .     37-2"  (98-96^  F.) 

Dog 

. .     37-5^-39-5°  C.      1 

„     axilla 

.  .     3(v9=  (98-45='  F.) 

Rabbit     . . 

. .     38-3°-39-9°  C.      ! 

„     mouth 

..     30-87°  (98-36°  F.) 

Guinea- pig 

.  .     37-3°-39-5°  C. 

Infants 

.  ,     37-6^ 

Pigeon 

. .     41-0°-42-5°  C. 

The  lower  vertebrata,  such  as  reptiles,  fish,  amphibia,  are  cold- 
blooded— that  is  to  say,  they  maintain  their  bod}-  temperature  scarcely 
above  that  of  the  surrounding  air  or  water.  Fish  may  be  frozen,  and 
recover  if  carefully  thawed.  A  frog  in  winter  becomes  cooled  down, 
and  hibernates;  in  summer  it  is  warmed  up,  and  becomes  active. 
The  mammal,  by  maintaining  a  uniform  body  temperature,  is  active 
in  all  the  seasons.  A  hibernating  mammal  changes  from  warm-  to 
cold-blooded  when  food  becomes  scarce  in  the  winter.  A  hibernatmg 
animal  will  not  allow  itself  to  be  frozen.  It  wakes  up,  and  in  a  short 
while  becomes  warm-blooded. 

In  between  these  two  classes — warm-  and  cold-blooded — come  the 
rarer  egg-laying  marsupial;;  of  Australia,  such  as  Echidna  and  Ornitho- 
rhynchus.  The  power  of  these  animals  to  regulate  their  body  tempera- 
ture at  a  constant  level  is  less  well  developed  than  in  mammals,  but 
their  temperature  in  a  cold  atmosphere  is  always  manj-  degrees 
above  the  surrounding  medium.  For  example,  the  normal  tempera- 
ture of  Echidna  is — 

At  4°  C 25-5°  C. 

At  20°  C 28-6°  C. 

At30°C.         30-9°  C. 

At  3.5°  C 34-8°  C. 

The  Regulation  of  the  Body  Temperature  depends  upon  nervous 
control.  In  young  birds  just  before  hatching,  and  in  prematurely  born 
mammals,  this  mechanism  is  not  working,  they  have  to  be  kept  warm. 
A  child  born  at  the  seventh  month  has  to  be  carefully  wrapped  in 
cotton-wool,  or  even  placed  in  an  incubator.  At  birth  at  full  time, 
on  the  other  hand,  the  heat-regulatmg  mechanism  is  working  in  man, 
and  for  this  reason  so  much  care  need  not  be  taken  to  prevent  heat 
loss.  Some  mammals,  such  as  the  rabbit,  which  is  born  naked,  do 
not  acquire  the  power  of  regulation  until  a  considerable  time  after 
birth.  The  newly-born  guinea-pig,  on  the  other  hand,  is  born  covered 
with  hair,  and  can  regulate  its  temperature.  The  newly  hatched 
chick  can  regulate  its  temperature;  the  naked  young  of  mam'  birds, 
on  the  other  hand,  are  not  able  to  do  so. 

The  evidence  as  to  the  existence  of  a  centre  regulating  the 
temperature  of  the  body  is  conflicting.  It  is  known  that  lesions 
of  the  central  nervous  system  in  certain  regions — e.g.,  the  optic 
thalamus  and  corpus  striatum,  pons,  and  medulla — produce  an  upset 
of  the  power  of  heat  regulation,  but  it  would  not  be  exact  to  describe 
any  one  of  these  sites  as  the  "  heat -regulating  centre  "  of  the  body. 


496  A  TEXTBOOK  OF  PHYSIOLOGY 

The  nervous  sj^stem  regulates  the  body  temperature  iii  two  ways : 
(1)  By  the  control  of  the  sites  of  production — the  muscles  and  the 
large  glands;  (2)  bj^  the  control  of  the  structures  concerned  in  heat 
loss- — the  cutaneous  bloodvessels,  the  sweat  glands,  etc.  That  heat 
is  developed  in  the  muscles  has  been  demonstrated  (see  p.  552).  It 
has  not  been  shown  in  other  organs,  but  the  respiratory  exchange 
in  the  glands  proves  that  heat  is  developed  therein.  The  circulation 
through  a  gland  is  so  rapid  that  the  heat  formed  therein  is  at  once 
distributed  through  the  body;  thus  even  the  most  delicate  thermo- 
meters fail  to  shoAV  that  the  gland  is  hotter  than  the  blood. 

The  Regulation  of  Heat  Production  is  controlled  reflexly  through 
the  sensitivity  of  the  skin  to  changes  of  temperature.  The  sensation 
of  cold  increases  the  tone  and  activity  of  the  muscles;  shivering  in- 
creases muscular  activity  without  displacing  the  layer  of  air  which 
is  in  contact  with,  and  warmed  by,  the  body.  It  may  increase  the 
heat  production  of  a  man  at  rest  from  50  to  90  per  cent.  The  cooling 
of  one  leg  in  a  bath  of  cold  water  may  provoke  local  shivering  in 
that  leg.  Exposure  to  cold  leads  us  voluntarily  to  increase  our 
muscular  movements.  We  move  about,  stamp  our  feet,  and  beat  our 
arms,  in  order  to  keej)  warm. 

A  certain  degree  of  exjoosure  to  cold  is  therefore  valuable.  It 
stimulates  the  tone,  metabolism,  and  activity,  of  the  body,  and  in 
this  lies  the  healthiness  of  open-air  life.  The  activity  of  the  body 
provoked  bj'  cold  leads  to  an  ampler  ventilation  of  the  lungs  and  a 
more  vigorous  circulation  of  the  blood.  By  raising  the  metabolism, 
it  increases  the  appetite  and  better  digestion  of  food,  thus  lessening 
the  bacterial  decomposition  of  food  in  the  large  bowel,  and  preventing 
the  absorption  of  toxic  j^roducts  therefrom.  The  cooling  effect  of  the 
wind  is  far  more  powerful  than  that  of  the  surrounding  temperature, 
and  is  the  most  important  quality  of  open  fresh  air.  It  not  only 
€ools,  but  by  its  varying  stimulation  of  the  skin  prevents  monotony  of 
sensation  and  invigorates.  Ideal  outdoor  conditions  are  the  radiant 
heat  of  the  sun  warming  the  ground  and  thereby  the  feet  and  those 
parts  of  the  body  turned  towards  it,  together  with  a  cooling  wind 
blowing  on  the  face. 

On  the  other  hand,  the  sensation  of  heat  produces  relaxation  of 
the  muscles,  a  lessened  tone  and  activity,  and  diminished  metabolism. 
Too  warm  an  atmosphere — in  particular,  one  that  is  windless  and 
monotonous- — is  therefore  disadvantageous,  on  account  of  its  relaxing 
effect. 

The  Regulation  of  Heat  Loss  is  accomplished  by  the  nervous  control 
of  the  loss  of  heat  from  the  skin  by  radiation,  convection,  and  evapora- 
tion. This  regulation  is  brought  about  through  the  vaso-motor 
oentre  and  the  centre  controlling  sweating.  The  afferent  channels 
concerned  in  the  regulation  of  the  cutane  nis  bood-supply  are  chiefly 
those  from  the  skin.  The  sensation  of  cold  causes  a  constriction  of 
the  cutaneous  bloodvessels,  and  thus  diminishes  the  loss  of  heat. 
On  the  other  hand,  a  sensation  of  warmth  induces  a  flushing  of  the 


THE  TEMPERATURE  OF  THE  BODY 


497 


<3utaneous  vessels,  which  greatly  facilitates  heat  loss  by  convection 
■and  radiation.  Sweating  is  controlled  by  a  centre  in  the  medulla 
which  is  stimulated  reflexly,  or  directly  by  the  temperature  of  the  blood 
passing  through  it.  When  this  temperature  is  raised  by  warming  the 
■carotid  arteries,  visible  beads  or  drops  of  sweat  are  secreted  by  the 
«weat  glands,  and  these,  by  the  cooling  produced  by  their  evaporation, 
greatly  aid  in  the  cooling  of  the  surface  of  the  body.  The  effect 
of  raising  the  external  temperature  upon  the  water  output,  the  heat 
production,  and  the  carbon  dioxide  output  of  the  body  is  seen  in  the 
iiccompanying  charts  (Figs.  235,  236). 


i       i 


Wa'cr  Output       

CO2  Outpi-ct  

SaUiraJtiort  detitit 


..^- 


Fig.  235. — The  Effect  hf  kaisin.;;  the  Exters.ax  Temperatfue  ox  the  Water 
Output  and  Heat  Productiox.  Saturatiox  Defk  it  ixdicates  Relative 
Saturatiox'  of  Air  with  Moisture.     (Rubner.) 


■^ 

VfaOr  Output  of 
fastinq  (lop. 

i          1 

i          i   / 

*> 

<, 

Saturatinn,  deticit 

y. 

/ 

d 

\ 

-^. 

.--- 

-— 

1 



_ 





--^' 







. — 



Tctn 

percL 

ure 

75 


10 


^       ^       ^5       ^      ^ 


Fig.  23(). — The  Effect  of  raising  External  Temperature  ox  Water  and  Carbon 
Dioxide  Output.     (Rubx-ier.) 

The  amount  of  heat  lost  in  the  expired  air  may  also  be  regulated. 
Warming  the  carotid  artery  leads  to  increased  breathing,  and  this 
increases  the  evaporation  of  water  and  heat  loss.  The  loss  of  heat 
by  evaporation  demands  further  consideration. 

The  rate  of  evaporation  from  a  Avet  surface  at  body  temperature 
in  still  air  depends  directly  upon  the  vapour  pressure  of  the  surround 
ing  atmosphere,  and  is  independent  of  either  the  temperature  or 
barometric  pressure  of  the  atmosphere.  The  skin  may  be  regarded  as 
a  porous  wall  backed  by  capillary  vessels,  by  means  of  which  moisture 
is  supplied.  The  capillaries  are  profoundly  affected  by  physical 
conditions  without — e.g.,  constricted  by  cold — and  by  phj'siological 
•conditions  within — e.g.,  flushed  with  wine. 

Simple  diffusion  of  aqueous  vapour  away  from  the  body  would  be 


498  A  TEXTBOOK  OF  PHYSIOLOGY 

I'elatively  a  very  slow  process;  but  as  aqueous  \apour  lias  a  density 
of  onh  0-62.  air  being  taken  as  unity,  and  as  the  cooler  air  of  the 
atmosj)here  is  warmed  and  expanded  by  the  body  heat,  the  body 
itself  sets  uja  convectional  currents  which  greatly  accelerate  the  loss 
of  vapour.  At  32°  F.  saturated  air  holds  l,'^Jth  of  its  weight  of  water 
vapour,  at  59°  F.  J^th,  and  at  86°, F.,  ^Qth..  The  body  warms  up  the 
air  in  contact  with  it,  and  saturates  it  at  skin  temperature.  The  air 
entangled  in  the  clothes  thus  warmed  and  saturated  cannot  escape 
easih^  if  the  atmosphere  is  still.  Wind  carries  away  the  air  as  fast 
as,  or  much  faster  than,  the  skin  M-arms  and  saturates  it.  Thus, 
wind  enormously  increases  the  cooling  of  the  body  surface  both  by 
convection  and  evaporation.  The  skin  resjaonds  to  a  cold  dry  wind 
by  vaso-constriction  and  diminished  transpiration  of  water.  The 
skin  becomes  pale  and  dry.  and  the  heat  loss  is  thus  cut  down.  We 
seek  shelter,  and  put  on  more  clothes.  On  warm,  close  days  the  skin 
becomes  flushed  and  moist,  we  throw  off  clothes,  and  make  use  of  fans. 

Water  vapour  is  a  far  better  conductor  than  dry  air,  and  tin  s 
damp  cold  air  feels  raw  and  chill,  while  dr}^  cold  air  is  pleasant.  Water 
has  240  times  the  thermal  conductivity  and  3,000  times  the  heat  capacity 
of  air.  The  particles  of  cold  or  even  freezing  water  in  a  winter  fog  strike 
the  cold  nerve-endings,  and  by  cooling  these  give  us  an  unpleasant  chilly 
sensation.  The  fog,  by  penetrating  into  our  clothes,  robs  these  of  their 
protecting  value.  The  intensity  of  the  temperature  sense  depends 
on  the  difference  between  the  blood-temj)erature  within  the  cutaneous 
capillaries  and  the  surface  temperature  of  the  skin  without.  The  fog 
gives  us  a  shower  of  cold  particles  of  water,  while  a  cold  dry  wind 
constricts  the  bloodvessels  of  the  skin,  and,  while  having  a  far  greater 
cooling  effect,  dees  not  give  us  the  same  sensation  of  chill. 

Water  vapour,  like  glass,  is  almost  opac{ue  for  the  least  refrangible 
rays — the  infra-red — and  transparent  for  the  middle  luminous  anel 
calorific  radiations.  Thus,  on  a  cloudy  day  the  water  vapour  both 
scatters  and  absorbs  the  dark  heat  rays,  and  less  heat  reaches  the  earth. 
On  tl  e  other  hanel.  clouds  after  a  sunny  day.  just  as  a  glass-house, 
]3revent  the  escape  of  the  dark  heat  rays  from  the  earth,  and  cause 
a  w^arm  night.  On  a  clear  night  these  rays  raeliate  into  space,  anel  the 
earth  cools.  The  transparency  and  eliathermancy  of  the  air  are 
properties  of  the  greatest  importance,  since  living  energj'  is  derived 
from  the  sun's  light  and  heat.  Water  vapour  and  dust  in  the  atmo- 
sphere serve  both  to  soften  the  scorching  power  of  the  sun  and  to 
prevent  the  rapiel  scattering  into  sj^ace  of  the  heat  gained  by  the 
earth. 

The  motive-powers  of  the  atmosphere  are  convection  and  evapora- 
t ion  produced  by  the  sun's  heat .  The  Avinds  arise  from  the  elisi^lacement 
of  the  warm  moist  and  therefore  lighter  air  by  cold  heavier  air,  and  the 
rain  falls  as  the  moist  air  becomes  condensed  in  higher  altitudes  or 
against  colel  lanel  surfaces.  The  beauty  of  earth  anel  sk}^,  the  glories 
of  sunrise  and  sunset,  depenel  upon  the  particles  of  dust  and  vapour 
in  the  atmosphere.  The  particles  reflect  anel  scatter  the  shorter  rays 
and  transmit  the  longer.     At  sunrise  anel  sunset  the  oblique  rays  pass 


THE  TEMPERATURE  OF  THE  BODY  409 

through   a   much  greater  depth   of   atmosphere;   hence   the  greater 
splendour  of  the  colours. 

As  the  temperature  of  the  air  and  surrounding  objects  is  made  to 
approach  that  of  the  body,  loss  by  radiation  and  convection  becomes 
small,  then  nil.  Finally,  as  the  air  temperature  comes  to  exceed 
that  of  the  body,  heat  passes  from  the  air  to  the  body.  The  body, 
however,  does  not  become  heated  so  long  as  the  air  is  dry.  The 
sweat  glands  come  into  action,  and  the  body  heat  continues  to  be  lost 
by  conversion  of  water  into  aqueous  vapour.  The  difficulty  of  main- 
taining the  thermostatic  equilibrium  of  the  body  increases  when  the 
conditions  become  such  that  the  whole  elimination  of  heat  is  by 
evaporation. 

A  man  can  stay  in  a  dry  atmosphere  at  a  temperature  sufficient 
to  cook  his  dinner.  He  can  keep  cool  by  sweating.  He  cannot 
stand  a  water  or  steam  bath  above  bod}^  temperature  without  becom- 
ing overheated.  Immersion  for  a  few  minutes  in  a  bath  at  110°  F. 
raises  the  rectal  temperature  to  103°  F.,  greatly  accelerates  the  breath- 
ing and  pulse,  loA^ers  the  arterial  pressure,  and  flushes  the  skin.  On 
standing  up  suddenly,  a  sense  of  faintness  ensues.  A  cold  shower- 
bath  taken  now  at  once  constricts  the  skin,  slows  the  j)ulse,  raises  the 
blood-pressure,  and  removes  all  sense  of  faintness,  w^hile  the  rectal 
temperature  still  remains  at  103°  F. 

Baths  cold  and  hot  are  a  most  potent  means  of  altering  the  meta- 
bolism both  of  the  skin  and  of  the  whole  body. 

The  amount  of  heat  lost  by  evaporation  is  ver}^  great  under  con- 
ditions of  hot  dry  atmosphere.  Thus,  it  was  estimated  that  10  litres 
of  water  were  lost  from  the  body  during  a  ride  at  a  temperature  of 
45°  C.  in  South  California. 

In  a  dry  hot  atmosphere,  such  as  the  stokehole  of  a  steamer  in 
the  tropics,  the  men  are  kept  cool  by  sweating,  the  forced  draught  of 
air  to  the  furnace  insuring  this.  The  amoiuit  of  drink  required  ma}'  be 
enormous — e.g.,  15  pints  of  water  a  day.  In  certain  factories,  mines,  etc., 
where  the  air  is  warm  and  moist,  it  is  of  great  economic  importance 
to  keep  the  air  in  movement,  or  the  vapour  pressure  down  to  a  level 
commensurate  with  the  performance  of  efficient  work,  and  main- 
tenance of  comfort  and  health.  A  regulation  made  for  weaving- 
sheds  and  spinning-mills  is  that  the  wet-bulb  thermometer  should  not 
be  allowed  to  rise  above  75°  F. 

The  amount  of  water  lost  from  the  bodj-  during  a  march  m.iy  be 
calculated  by  weighing  the  body  before  and  after  the  march,  supposing 
no  food  or  drink  is  taken,  and  no  faeces  or  urine  passed  during  the 
march.  The  weight  of  oxygen  taken  in  balances  approximately  the 
weight  of  carbonic  acid  given  out.  The  water  retained  in  the  clothes 
may  be  estimated  by  weighing  the  clothes  before  and  after  the  march. 
Such  estimations,  coupled  with  those  of  pulse-rate  and  body  tempera- 
ture, have  shown  the  value  to  soldiers  of  opening  or  taking  off  their 
tunics  in  hot  weather.  If  the  evajooration  of  sweat  and  convection 
is  made  easy,  fatigue  and  danger  of  heat-stroke  are  prevented.  It 
has  been  calculated  that  a  resting  soldier  weighing  70  kilogrammes, 


500 


A  TEXTBOOK  OF  J'H VSlOJ.O(;Y 


while  marcliing  with  a  load  of  31  kilogrammes,  produces  7-73  calories 
per  mimito.  or  enough  heat  to  raise  his  l)ody  by  1^  C.  in  8-7  minutes. 
This  shows  the  importance,  then,  of  jn-operly  clothing  the  soldier  for 
marching  in  hot  weather. 

The  thermometer  gives  the  average  temperatuie  of  the  surround- 
ings; it  tells  nothing  as  to  the  rate  of  cooling — the  matter  of  greatest 
importance  to  the  body.  The  katathermometer  has  been  introduced 
to  measiire  this.  This  is  a  large-bulbed  spirit  thermometer  which  is 
warmed  a))o\'e  body  temperature.  The  rate  of  cooling  is  determined 
as  the  meniscus  falls  from  100°  to  95°  F.  with  a  stoj)- 
f\  watch  (Fig.  237).  A  factor  is  determined  for  each 
instrument,  by  means  of  which  is  reckoned  the  rate 
,|  of  cooling  per  sq.  cm.  of  surface  per  second  at  body 

^  temperature.      The  dry-bulb  katathermometer  indi- 

cates the  rate  of  heat  loss  bj'  radiation  and  convec- 
tion, the  wet-bidb  by  radiation,  convection,  and  evap- 
oration. The  difference  betweeii  the  two  gives  the 
rate  of  cooling  by  evaporation.  The  instrument 
shows  the  g]-eat  cooling  effect  of  wind,  and  is  of 
value  in  investigating  the  conditions  of  the  open  air 
and  of  ventilation  in  buildings  (see  p.  31(5). 

Clothes. — The  cutaneous  fat  is  the  natural  garment 

of   the  body.     The   warming   value   of   fat   may   be 

gathered    from    the    fact   that    with    a  temperature 

difference  of  18-2°  C.  a  layer  of  skin,  2  millimetres 

thick,  lets  through  0-00248  calory  per  minute,  whereas 

2  millimetres,  of  skin  ])lus  2  millimetres  of  fat  lets 

through    only   0-00123    calory.     Anointing   the   skin 

with  grease  Avards  off  "  frost-bite  "'  in  those  exposed 

to  cold  and  wet.     The  grease  prevents  the  macera- 

[  ^^f;!      tion  of  the  skin  hy  water.    If  water  soaks  into  the 

%M,i^       skin   its   non-conducting  power  is    greatly  reduced. 

c/fy         ,v/:7         Exposure  to  sea  water  can  be   borne  much    better 

than  fresh  water  because   salt  Avater,  owing  to  its 

Pig.  237.  —  The  isotonic    properties,    does    not    macerate    the    skin. 

K.\TA  Thkkmo-  Channel   swimmers   thickly  cover   their  bodies  Mith 

ducedirom  Phi/,  grease,    and   are    noted    for    the   thickness  of    their 

Trans.        Boi/.  cutaneous  fat.     The  vernix  caseosa  of  the  new-born, 

***'"'■•)  washed  off  by  the  midwife,  is  designed  to  protect  it 

from  wet  and  cold  after  birth. 

Clothes  increase  evaporation  and  lessen  loss  of  heat  b}'  convection 

and  radiation,  in  still  air  io  an  extent  of  47  per  cent.     At  18°  C. 

a  clothed   man  of    74  kilos  lost  79  calories  per  hour  clothed,   and 

124   calories    per   hour  naked.      The    clothes    entangle    and    render 

-stationary  the  air  within  their  cellular  structure  and  between  their 

layers.      The    more    garments    A\e    put    on   over   one  -another,    the 

more  laj^ers  of  entangled  air.     To  keep  us  warin,  the  clothes  must 

prevent  the  wind  sweeping  away  the  entangled  air;   to  keej)  cool, 

the  wind  must  have  free  i>\a.Y.     When  dry,  cellular,  wool,  or  cotton 


THE  TEMPERATURE  OF  THE  BODY  501 

clothes  are  equally  good- — e.g.,  flannel  or  flannelette  of  the  same 
thickness;  but  flannel  prevents  heat  loss  much  better  than  cottoa 
when  wet.  The  wet  cotton  touches  the  skin  while  the  wet  elastic 
hair  fibres  stand  f)fE  and  keep  air  entangled.  Silk  or  cotton  is 
the  coolest  garb  for  summer,  and  flannel  the  best  for  damp,  cold 
weather.  Overclothing  throws  out  of  use  and  weakens  the  natural 
defensive  mechanisms  of  the  body  against  cold.  Man  has  immense 
imiate  powers  of  withstanding  cold,  evolved  in  his  long  struggle  with 
Xature.  Excessive  exposure  to  cold  produces  local  death,  or  death 
of  the  whole  body;  but  if  a  man  survive  exposure — e.g..  after  a 
shipwreck — ho  recovers,  and  does  not  suffer  from  such  ills  as  are 
commonly  attributed  to  -chill.  Darwin  describes  the  inhabitants, 
including  mother  and  baby,  of  Tierra  del  Fuego  standing  in  the  cold 
sleet  naked,  but  greased  with  fish  oil,  and  the}'  haA'e  to  keep  down 
the  population  to  the  food  supply  by  infanticide.  Babies,  especially 
among  the  poorer  classes,  are  generally  overclothed  and  kept  in  too 
warm  and  stagnant  atmospheres  to  the  detriment  of  theii'  vitality. 
This  is  a  cause  of  the  high  mortality  of  infants  in  industrial  towns. 
The  amount  of  clothes  worn  by  individuals  depends  much  on  habit. 
We  can  accustom  ourselves  to  few  or  many  clothes.  The  young  and 
vigorous  want  few  clothes,  while  the  old,  in  whom  the  fires  of  life  are 
weakening,  want  manv. 


BOOK    X 

THE  FLNCTIONS  OF  THE  DUCTLESS  (tLANDS 

CHAPTER  LIX 
INTERNAL  SECRETIONS 

The  metabolism  is  greatly  affected  by  what  are  known  as  the 
"  internal  secretions."  In  certain  glands  there  is  elaborated  material 
which,  instead  of  being  discharged  from  the  glands  by  a  system  of 
ducts  as  an  "  external  "  secretion,  passes  from  the  gland  cells  into 
the  blood  or  lymph  as  an  "  internal  secretion.""  Such  may  come 
from  glands  which  have  no  system  of  ducts — e.g.,  the  th;vToid,  supra- 
renal— or  they  may  come  from  glands  which  are  also  provided  with 
a  system  of  ducts — e.g.,  pancreas,  testes — and  have  therefore  both  an 
"  external  "'  and  an  "  internal  "  secretion. 

Of  late,  researches  have  been  extremely  p/olifie  in  this  branch  of 
jjhysiology.  So  much  is  controversial  that  it  is  only  possible  to 
indicate  what  appear  to  be  the  characteristic  functions  of  each  gland ; 
even  these  cannot  be  stated  in  a  dogmatic  manner. 

With  the  evolution  of  the  multicellular  organism  there  takes  place 
a  differentiation  of  organs  corresponding  to  a  division  of  labour,  and 
an  interworking  of  these  organs  is  established.  It  is  hard  to  say, 
then,  what  are  all  the  functions  of  any  one  organ,  since  an  organ,  in 
jjei-forming  these,  not  only  fulfils  its  own  life,  but  aids  the  functions, 
growth,  and  nutrition  of  the  other  organs  of  the  body.  Thus,  the 
blood  carries  the  heat  developed  in  one  part  from  that  part  to  another, 
and  thereby  affects  the  working  of  the  body;  it  carries  the  hormone^ 
"'  gastrin  "  and  "  secretin,"  which  provoke  secretion  of  digestive  juices; 
it  carries  urea  from  the  liver,  where  it  is  formed,  to  the  kidney,  v\'here 
it  excites  that  organ  to  secretion.  The  muscles  yield  carbonic  acid 
and  other  acids,  which,  going  to  the  respiratory  centre,  control  the 
respiration.  The  action  of  the  secretions  we  are  considering  form 
part  of  this  interworking  system,  and  the  keynote  of  their  action  is 
their  interdependence  on  one  another. 

The  whole  body  is  bathed  internally  ^\ith  tissue  fluid  or  lymph, 
and  it  is  necessary  that  this  fluid  colloidal  complex  contain  ov 
have  linked  to  it  various  salts  in  proper  proportions,  also  a 
number   of    internal    secretions.     The   diminution   or   excess   of   any 


504 


A  TK  XT  HOOK   OF  PH  VSJO!.0(  ;^' 


one  of  these  seeic'ticii-;   will    alter  the  motaboUc  conditions  of  the- 
body.  sf)jn''t iine-<  in  an  aiiaVolie.  somotiTnos  in  a  katabolic  direction. 

_  A  possible  example  of  thia 

■f  interdependence     has    al- 

-|  ready    been    referred    to 

_         E  under  carbohydrate  meta- 

rp         ^  bolisni.      It    is    suggested 

I         2  that  normally  internal  se- 

^         E  eretions  from  the  pancreas. 

c         T.  suprarenal,    thyroid,    and 

f         r-  possibly  other  glands,  help 

'        .£  to  regidate  carbohydrate 

^  metabolism."       When    all 

1  these  are  present  in  cor- 

t  rect   amounts,  the  meta- 

J  holism  proceeds  in  orderly 

f  fashion.      If,  however,  the 

J  _  balance  be  upset — for  ex- 

j-f  ample,  by  too  little  of  the 

~         I  r  pancreatic  secretion  being 

i        ^1  present — then    the    kata- 

I        Z  f^  holism    of    sugar    is    de- 

^-1  ranged.     Too  much  sugar 

i^    ^tS  therefore   accumulates   in 

'.    E_-  the  blood,  and  the  eondi- 

^   ^c  tion  of  glycosuria  results. 

'%  ^-  In  the  development  of 

ZTc  sexual    characteristics     a 

■=  I  balance   between    variou.s 

X  %■  internal  secretions  is  con- 

~.=  cerned — for  examj)le,  the 

Z  ~  testes  or  ovary,  and  the 

.J  suprarenal,    thymus,    and 

\  in  the  female  possibly  the 

7  thyroid  gland.    The  action 

■^  of  these  internal  secretions 

?  has  been  investigated  by 

-§  various  methods,  chief  of 

■-1  which  are  the  extirpation, 

=  transplantation     of      the 

■^  gland,   and    the   in'jection 

=        -^  of  gland  extracts.   Clinical 

I        'Z  cxjierience     has     yielded 

"        -^  valuable  information. 

^  Although     the     exact 

~  extent  of  the  dej^endence 
of  the  action  of  the  various 
internal  secretions   one   on  another  is  to  a  large  extent   conjectural, 

the  fa-^t  that  such  an   interworking  does  take  ])lace  has  been  experi- 


INTERNAL  SECRETIONS  505 

mentally  demonstrated.  The  active  principle  of  the  suprarenal  gland 
— adrenalin — produces  certain  Avell-known  effects ;  for  instance,  it  pro- 
duces a  rise  of  blood-pressm-e. 

From  Fig.  238  it  Avill  be  seen  that,  after  the  nerves  to  the  thyroid 
gland  have  been  stimulated,  the  injection  of  the  same  amount  of 
adrenalin  in  the  same  time  gives  a  greater  rise  of  blood-pressure  than 
it  did  before  the  stimulation  of  these  nerves.  This  is  the  more  re- 
markable, since  a  second  injection  of  adrenalin,  without  stimulation 
of  the  thvroid  nerves,  normally  gives  a  smaller  rise  of  blood-pressure 
than  before.  This  increased  action  of  adrenalin  is  abolished  if  the 
thyroid  be  excised  before  its  nerves  are  stimulated,  but  is  obtained 
when  extracts  of  the  th\Toid  gland  are  injected  into  the  animal  just 
previously  to  the  dose  of  adrenalin. 

These  exjieriments,  then,  give  definite  evidence  of  the  interworking 
of  the  secretions  named,  and  it  is  probable  that  the  other  secretions 
also  interact,  some  in  an  anabolic  and  some  in  a  katabolic  direction. 

The  Organs  of  Generation — Testes. — The  testis  is  generally  regarded 
as  a  "double  ""  gland,  consisting  (1)  of  germinal  cells,  which  form 
the  external  secretion  or  eloment.i  concerned  in  reproduction;  (2)  of 
interstitial  cells,  which  form  an  internal  secretion  intimately  coimected 
with  the  general  metabolism  of  the  body  and  the  acquisition  of  second- 
ary male  characteristics.  The  view  that  the  interstitial  cells  act  as 
a  separate  gland  is  not  accepted  by  all  authorities,  but  the  foUowing^ 
facts  go  to  support  the  view.  It  is  stated  that,  when  the  vasa  deferent  a 
are  tied,  the  germinal  cells  atroj^hy.  but  the  interstitial  cells  persist. 
Exposure  to  X  rays  is  known  to  render  animals  impotent,  but  does 
not  change  their  secondary-  sexual  characteristics.  Histological 
examination  in  such  cases  shows  that  the  generative  cells  are  de- 
stroyed, but  the  interstitial  cells  are  not  damaged. 

The  effects  of  castration  have  long  been  known.  As  a  direct 
local  rcr^ult  the  animal  is  rendered  impotent,  and  the  accessory  sexual 
apparatus  atrophies.  Generally,  the  sexual  development  of  the 
animal  is  arrested;  the  so-called  secondary  sexual  characteristics  are 
not  acquired  (Figs.  239,  240);  the  general  metabolism  is  so  affected 
that  the  animals  tend  to  laziness  and  fatness.  An  excessive  growth  of 
bone  is  also  frequently  brought  about.  These  results  are  due  to  th& 
cutting  off  from  the  bod}-  of  the  internal  secretions  of  the  glands.  It 
makes  no  difference  whether  the  seminal  vesicles  be  left  or  removed. 

The  results  of  transplantation  experiments  show  that  thesecondar}' 
male  characteristics  may  be  developed  by  this  means — e.g.,  the  spurs 
and  comb  of  the  cock,  or  the  large  thumb  of  the  male  frog.  If  the 
testicle  be  transplanted  in  infancy,  no  sj^ermatozoa  develop,  but  the 
gland  becomes  composed  of  large  quantities  of  interstitial  cells,  and 
the  secondary  male  characteristics  are  acquired.  It  is  stated  that 
a  testicle  so  transplanted  into  a  female  tends  to  give  her  body  male 
characteristics. 

The  internal  secretion  of  the  testes  has  been  held  to  exert  marked 
influence  upon  the  general  health  and  mental  and  muscular  activity 
of  the  individual.     It  is  claimed  that  a  substance — spermin  (C-H^jN2)' 


i500 


A  TEXTBOOK  OF  PHYSIOLOGY 


— isolated  from  testicular  extracts,  may  be  used  to  increase  neuro- 
muscular activity  and  lessen  fatigue,  and  Ibui;  be  of  service  in  old 
age,  when  the  testes  are  failing  to  act.  Some  advertised  patent 
medicines  on  the  market  claim  on  untrustworthy  evidence  to  give 
wonderful  rejuvenating  effects.  They  contain  a  certain  amount  of 
extract  of  boar's  testicles. 

Whether  the  general  effect  of  excision  or  transplantation  upon 
metabolism  be  so  great  as  is  supposed  by  some,  it  is  obvious  that 
upon  the  grooving  animal  the  effects  are  far-reaching.  For  instance, 
in  man,  not  only  are  the  secondary  male  characteristics  called  forth 
— e.g.,  the  beard,  the  large  larynx,  etc. — but  the  growth  of  the  skeleton 
is  affected,  so  that  it  is  possible  to  differentiate  between  the  male 
and  female  skeleton.  It  is  probable  that  s'uch  secretions  may  be 
held    partly    responsible    foi    the    different   outlook   of    man   and   of 


Fig.  230. — Herdwick  Ram 

(Normal). 

The  effect  of  castration  on  horn-growth  is  well  seen 


ric.  2-10.     Herdwicx  Wether 

WITHOUT    HORXS    VISIBLE. 


(Marshall.) 


-woman  upon  life,  the  cerebral  processes  differing  according  as  the 
nervous  system  is  bathed  with  testicular  internal  secretion  or  with 
ovarian  internal  secretion. 

The  Prostate  Gland. — It  is  believed  hy  some  that  an  internal 
secretion  of  the  prostate  gland  has  an  important  action  on  the  forma- 
tion and  ejaculation  of  spermatozoa.  There  is,  however,  little  evidence 
for  this  view.  It  is  generally  believed  that  the  prostatic  secretion 
aids  the  movements  of  the  spermatozoa. 

The  Ovary. — The  interstitial  cells  of  the  ovary  play  much  the 
same  part  in  the  female  as  the  interstitial  testicular  cells  in  the  male. 
Extirpation  of  both  ovaries  in  young  girls  prevents  the  onset  of  men- 
struation, and  brings  about  notable  alterations  in  their  appearance. 
When  the  ovaries  are  removed  after  jjuberty,  menstruation  ceases 
and  pregnancy  is  prevented.  There  follow  some  atrophy  of  the 
breasts,  uterus,  and  vagina,  and  a  tendency  to  obesity. 

That  these  effects  are  not  nervous  in  origin,  as  was  once  believed, 
is  shown  by  the  fact  that  transplantation  of  the  ovary  induces  once 


INTERNAL  SECKETIONS 


507 


more  heat,  or  "  oestrus,"'  in  spayed  animals.  Further,  the  injection 
of  extracts  of  ovaries  in  an  oestrus  state,  or  the  grafting  of  such  into 
these  animals,  produces  the  signs  of  heat  in  them.  It  is  also  stated 
that  as  the  result  of  tiansplantation  of  an  ovar}"  into  the  growing 
male  the  teats  and  breasts  become  enlarged,  and  may  even  form  milk. 


■  \^   ■ 
^j'y  -  ■ 


£^ 


^^/^^^ 


Fig.  241. — Section  through  StrpRARENAL  Body  of  Dog  showing  Zones  of  Cortex 
AND  Medulla.     (Swale  Vincent,  drawn  by  Mrs.  Thompson.) 

c,  Capsule;  m.,  medulla;  z.f.,  zona  faseiculata;  z.g.,  zona  glomerulosa;  z.r.,  zona 

reticularis. 


The  corpus  luteum,  into  which  a  Graafian  follicle  develops  after 
discharge  of  the  ovum,  is  believed  to  exert  considerable  influence  by 
jaelding  an  internal  secretion.     This  controls  the  fixation  of  the  ovum 


■■)(IS  A  TEXTBOOK  OF  PHYSIOLOGY 

within  the  uterus,  probably  by  maititainiug  an  increased  metabolism 
of  the  uterus  during  the  earh'  stages  of  pregnane}-.  The  eorpus 
hiteum  also  furnishes,  in  the  initial  stages  of  pregnancy,  an  internal 
secretion  which  stinndates  development  of  the  mammary  gland. 

The  Suprarenal  Bodies. — Each  suprarenal  gland  consist  of  a  cortex 
and  a  mcdidla.  The  cortex,  the  cells  of  which  are  arranged  in  charac- 
teristic colunmar  fashion,  is  derived  from  the  mesoblast  associated 
with  the  urogenital  system,  the  Wolftian  ridge.  The  medulla  is  of 
nervous  origin,  and  its  cells  are  arranged  in  strands  which  enn:esh 
lacunar  veins.  Manj^  of  these  cells  are  characterized  by  their  affinity 
for  chromium  salts,  and  are  therefore  known  as  chromophil  cells. 
Such  chromophil  cells  are  also  found  in  the  ganglia  of  the  sympathetic 


f 


./,^\ 


Fig.  242. — .Skctiox  thkougii  a  Group  of  Chromophil  Cell.s  in^kferior  Cervical 
Ganglion   of  a  Dog.     (Swale   Vincent.) 

nervous  system,  and  in  accessor}-  suprarenal  masses  which  are  often 
found  connected  with  the  abdominal  ganglia  of  this  system  (c/.  Fig.  242). 

Little  is  known  concerning  the  function  of  the  cortex  of  the  supra- 
renal glands,  but  it  has  l;een  suggested  that  it  interacts  with  the  sexual 
glands  influencing  the  acquirement  of  sex  characters.  In  manj-  cases 
of  sexual  precocity  an  abnormal  development  of  the  cortex  of  the 
suprarenal  has  been  found. 

Far  more  evidence  has  been  obtained  as  to  the  function  of  the 
medulla  of  the  sujirarenal.  whicli  appears  to  be  of  great  importance 
to  the  organism.  Addison  long  ago  pointed  out  that  the  fatal  disease 
known  by  his  name  was  ahvays  attended  by.  and  therefore  probably 
due  to,  disease  of  the  suprarenal  glan(3s.  The  disease  is  characterized 
by  these  symptoms:  a  gradual  increasing  muscular  weakness,  bronzing 
of  the  skin,  and  vomiting. 


INTERNAL  SECRETIONS 


501) 


It  has'been  shown  that  extirpation  of  the  suprarenal  glands  almost 
invariably  causes  death.  The  fatal  result  was  at  one  time  attributed 
to  an  accumulation  of  toxic  bodie-;  within  the  organism.     Such  toxic 


Fig.  2-43.— .Showing  Rise  of  BLOOD-niEssrKE  due  to  Release  of  Rkessure  ox 
ScrpRARENAL  Veik.  (Ffom  "  Internal  .Secretions,"  Swale  Vincent.)  (Gardner 
and  Gunn.) 

The  vein  has  been  compressed  for  some  time  and  was  released  at  point  signalled. 


bodies  were  believed  to  be  destroyed  by  the  glands.  It  is  now  known 
that  the  chief  function  of  the  suprarenal  medulla  is  to  furnish  as 
an  internal  secretion  an  active  principle — adrenalin.  Adrenalin,  as 
its  structural  formula  shows — 


OH 


CHOH.CH0NHCH3 

_ — is  An  aromatic  bod}-  nearly  allied  to  t^Tosin,  and  is  probably  derived 
from  t^Tosin. 

The  best-known  function  of  adrenalin  is  its  power  to  induce  con- 
striction of  the  smooth  muscle  of  the  arterioles,  'and  thereby  cause  a 
rise  of  arterial  pressure  (Fig.  238,  a,  b).  The  supply  of  adrenalin  to 
the  blood  is  under  the  control  of  the  splanchnic  nerves.  If  these  be 
stimulated  the  arterial  pressure  is  raised,  but  not  after  extirpation  of 
the  suprarenals  (Fig.  245). 

This  is  only  one  of  the  functions  of  adren  iliu,  for  an  intravenous 
injection  of  adrenalin  acts  upon  all  smooth  muscle  supplied  by  the 


no 


A  TEXTBOOK  OF  PHYSIOLOGY 


sympathetic  system,  and  in  every  case  produces  the  same  eflfects  as  does 
excitation  of  the  sympathetic  nerves  (see  Figs.  240,  247).  It  is  probable 
that   (his  action  is   manifested  throucrh  the  "  receptive  substance  " 


Fig.  2-iA. — Thxc'Im:  .sikaving  Kffixt  on  Carotid  Pressure  of  Ax.esthetized 
Dog  bv  Intravenous  Injection  at  Signal  of  an  Extract  from  the  Chromo- 
riiiL  Bodies  of  Three  Dogs. 


165.       '%y. 


84- 


l-'iG.  245.— Pithed  Animal.     (T.  K.  Elliott.) 

A  Effect  of  stimulation  of  both  splanchnic  nerves;  118  mm.  Hg  rise  of  pressure. 
B,  Ditto,  after  removal  of  intestines;  48  mm.  rise  of  pressure.  C,  Ditto,  after 
removal  of  suprarenals;  no  rite  of  pressure. 


uhich  eifects  the  union  between  the  sympathetic  nerve  fibre  and  the 
smooth  muscle.  This  receptive  substance  depends  for  its  action  upon 
the  integrity  of  the  muscle  rather  than  upon  the  integrity  of  the  nerve 


INTERNAL  SECRETIONS 


ill 


fibre,  as  is  shown  by  the  fact  that,  after  the  s^-mpathetic  nervea 
have  been  cut  and  allowed  to  degenerate,  the  receptive  substance 
is  still  capable  of  responding  to  adrenalin.  There  is  evidence  that 
adrenalin  acts  in  conjunction  with  the  internal  secretion  of  the  thjToid ; 
also  with  that  of  the  pancreas,  and  possibly  other  internal  secretions. 


Fig.  246. — Recokd  of  Movement  of  Isolated  Rabbit's  Heart  during  Perfusion 
wiTH  Ringer's  Solution,  showing  Effect  of  introducing  Adrenalin  (1  in 
100,000)  into  Circulating  Fluid  for  a  Period  of  Thirty  Seconds.    (Dixon.). 

The  heart  is  greatly  accelerated  and  the  force  of  beat  increased,  corresponding  to  a 
stimulation  of  the  sympathetic  nerves  to  the  heart. 


The  Pancreas. — The  pancreas  is  an  example  of  a  gland  which 
affords  both  an  external  and  an  internal  secretion.  The  internal 
secretion  of  the  pancreas  is  believed  to  play  a  part  in  the  regu- 
lation of  carbohydrate  metabolism,  to  be  necessar^^  for  the  primary 
stage  in  the  oxidation  of  sugar  within  the  bod\^  (p.  430).  Possibly 
it  also  plays  a  part  in  regulating  the  glycogenic  function  of  the 
liver. 

It  is  believed  b}'  many  that  this  internal  secretion  is  afforded  by 
the  islets  of  Langerhans  (Fig.  248),  which  may  be  looked  upon  as 
a  separate  gland  included  within  the  pancreas.  The  islets  vary  in  size 
in  different  animals.  In  certain  teleostean  fishes  the  islet  material 
is  largeh'  separate  from  the  gland  which  forms  the  external  digestive 
secretion.  Some  have  regarded  the  islets  as  the  exhausted  acini  of 
the    pancreas.       It    has.    however,    been    recently    shown    that    the 


512 


A  TEXTBOOK  OF  PHYSI0LO(;^' 


exhausted  acini  stuiu  quite  differently  from  islet  tissue.  By  other 
authorities  the  islets  are  looked  upon  as  rudimentary  pancreatic  cells, 
but  the  evidence  for  this  cainu)t  be  considered  satisfactory. 

The  Function  of  the  Thyroid  and  Parathyroids.-  The  thyroid  gland 

lies  in  front  of  the  trachea,  and  consists  of  two  lobes,  each  about 
2  inches  long  and   1   inch  wide,  joined   by  an  isthmus.     The  jiara- 


> 

f 

tj    .      ■■ 

0     - 

\ 

- 

r^lA         A  \  A 

1 

'^ 

\ 

*       \ 

o 

t^W' 

A. 

1— H 

.     ,ij 

nnffllffllmniml 

fllll!l 

iiHlmlliml 

^mhmmmmmmMi 

Fro.  247. — Record  of  Artekial  Pressure  and  Intestinal  Movements  in  Cat. 

(Dixon.) 

At  A,  1  c.c.  of  1  in  20,G(>0  adrenalin  was  injected  into  a  vein.  The  arterial  pressure 
rigew,  the  intestinal  movements  are  inhibited,  both  cifocts  corresponding  to 
stimulation  of  the  sympathetic  nerves. 


thyroids  in  mammals  are  small  oval  bodies  6  to  7  millimetres  in  length, 
3  to  4  millimetres  in  breadth,  1-5  to  2  millimetres  in  thickness.  They 
are  usualty  stated  to  be  four  in  number,  and  varying  in  position  in 
different  species  of  animals. 

The  thyroid  develops  as  a  median  endodermal  downgrowth  from 
the  tongue;  to  this  the  lateral  lobes  from  the  fourth  cleft  are  added. 
A  consideiable  portion  of  the  adult  lateral  lobes  are  derived,  however. 


INTERNAL  SECRETIONS 


513 


zym. 


cap. 


-Mi-,. 


_-Jt^ 


C>     fi 


I. 


bid.  c. 


'42^?;. 


i^^:-av 


.■%tjS;|^^A^t::0!^ 


rV.. — ''^ — ; .   ••■ia 


ti-f.ns.  '■. 


-c.a.c. 
-  zym . 


.Fig.  24S.— Islet  of  Lixjerhans  from  Splenic  End  of  Pancreas  of  Dog, 
(Vincent  and  Thompson,  drawn  by  Mrs.  F.  D.  Thompson.) 

V.d.  c.  Red  blood-corpuseles;  c.a.c,  central  acinar  cells  of  pancreas  proper;  cap., 
blood  capillaries;  i.,  islet  of  Langerhans;  I.,  lumen;  trans,  c,  transitional  cells; 
zym.,  zyraogenous  tissue. 


for.  caeo. 
raphe  of  tongue 
hyoid  {2nd  &  3rd  arches) 

susp.  ligament 
thyr  cart.  (4th  &  5th  arches, 
sup.  parathyr. 
from  4th  cleft 
inf.  para  thyr. 
thymic  strand 

thymus  (3rd  cleft) 


Fig.  249.— Diagram  showing  Dkvelopment  of  the  Thyroid  and  Thymtts.  (Keith.) 

The  thi-ee  parts  of  the  thyroid  body  are  indicated  by  a  stippled  liie;  the  position 
nf  flip  i-iarathvroids  on  the  posterior  aspect  of  the  lateral  parts  is  indicated. 


of  the  parathyroids  on  the  po? 


33 


514  A  TEXTBOOK  OF  PHYSIOLOGY 

from  the  median  portion  (Fig.  24f»).  The  cells  fir.st  form  notworks^ 
of  solid  cords.  These  separate  into  solid  masses,  within  which  lumina 
may  appear.  The  mature  gland  consists  of  rounded  closed  spaces  or 
vesicles  filled  with  a  colloid  material,  and  hy  a  single  layer  of  low 


', e.  ves. 


\  '■  •'•,''..'*•.' 

*'<" 

^'•'•''t*.: 

■"T     e.  iiiterves. 

:'•. 

if 

\"\ 

c.  ves. 

Fig.  250.— Thyroid  of  Normal  Dog.     x  120.     (Swale  Vincent.) 

c.  Colloid;  e.  ves.,  epithelium  lining  vesicles;   e.   interves.,  ejtithelial  intervesicular 
tissue;  c.  ves.,  colloid  vesicle. 


Fig.  251. — Pakathykoid  of  Normal  Dog.     x  120.     (Swale  Vincent.) 
S.C.C.,  solid  columns  of  cells;  bl.v.,  bloodvessel. 

columnar  cells  (Fig.  250).  The  vesicles  are  separated  by  connective 
tissue,  which  carries  the  bloodvessels  and  nerves,  Avith  which  the 
gland  is  most  plenteously  supplied.  The  parathyroids  are  built  up  of 
closely  packed  polygonal  cells  divided  up  by  connective-tissue  septa 
into  areas  of  various  shapes  (Fig.  251). 


INTERNAL  SECRETIONS  515 

There  is  a  coti^iderable  divergence  of  opinion  as  to  whether  the 
thp-oids  and  parathyroids  are  one  and  the  same  tissue,  or  whether 
the\-  are  quite  distinct  glands  with  markedly  different  functions. 
According  to  the  tirst  view,  the  two  tissues  are  essentially  the  same, 
and  all  grades  from  normal  th;^Toid  to  normal  parath^Toid  tissue  may 
be  found  when  the  glands  of  a  series  of  different  animals  are  studied. 
The  difference  in  appearance  is  to  be  attributed  to  the  presence  of 
colloid.  After  excision  of  the  thyroid  colloid  a,ppearrj  in  the  par?.- 
thyroid  (Fig.  252). 

Developmentally.  the  parathyroids  arise  from  the  third  and  fourth 
gill  clefts,  the  thyroid  from  a  median  remnant  in  the  ventral  wall  of 
the  embryonic  pharynx.  These  glands  arise  at  different  times,  and 
come  therefore  only  secondarily  into  relation  with  each  other. 

- --vrN::-": •'•'>>"''•*'■'''•' Vi"^-''<  •••    .•     -...•.■j.'...Tr— ^- "^*- 

*••(.      .-•.    :.~}       'C«'-*.-        /'     ••••.■,"•.     ,r.-'t       ••   -'.•. ■  .•■ 

■^-.^        jv-^"; '!"i"''\,V' "••••'• 'v'.'.  "..'■.'■ 

»..;    :.;»S'»-V- •.".•■  .«.>.■..■•.■■■-.■■.■■•-  ■:..^'       •■:   : 


FiQ»r  2^.— Parathyroid  of  \  Dog  Eighty-Three  Days  aftek  Thyroidectomy. 
v-^3HO"y\^^,-G  Vesicles,  Some  of  ^VHICH  contain  Colloid.     (Swale  Vincent  ) 

r.  ve<..  Colloid  vesicle;   e.  ves.,  epithelium  of  colloid  vesicles; 
e.  interve-s.,  intervesicular  epithelial  cells. 

Attention  was  tirst  drawn  to  the  function  of  the  th3Toid  (including 
the  paratluToid)  by  clmical  observations.  In  certain  districts  the 
gland  enlarges  in  adults,  forming  what  is  known  as  a  ''  goitre."  This 
appears  to  be  due  to  an  infection  through  the  drinking-water  of  the 
district  of  the  alimentary  tract  b}'  a  living  organism.  Goitre  has 
been  experimentally  produced  by  drinking  the  residue  filtered  from 
such  Avater,  and  cined  by  the  taking  of  thymol.  Goitre  is  very  localized, 
hence  the  name  "  DerbAshire  neck.'"  The  thjToid  enlargement  Ls 
pathological  in  nature,  and  often  entails  a  deficiency  of  thyroid 
function.  The  children  of  mothers  suffering  from  such  a  deficiency 
of  thjToid  function  suffer  from  a  condition  known  as  "  cretinism." 
Such  endemic  cretinism  is  common  in  Switzerland,  and  in  the 
central  and  Gilgit  valleys  of  India.  It  varies  with  the  prevalence  of 
the  "  endemic  goitre.''  The  "'  cretinism  "  is  due  to  toxic  agencies 
acting  upon  the  th\Toid  and  j)arath3T:oids  of  the  unborn. 


516 


A  TEXTBOOK  OF  PhnSIOLOGY 


There  are  in  general  two  types  of  cretins,  the  )nyxaMlematoiis 
and  the  nervous.  Tne  nervous  type,  met  Avith  chiefly  in  India,  are 
generally  deaf  and  dumb.  The  ui)i)er  Iiml)s  often  assume  a  position 
of  right-angled  flexion,  with  the  thumb  drawn  into  the  palm  and  the 
lingers  closed  over  it.  The  lower  litnbs  exhibit  a  "  knock-kneed  " 
spasticity.  These  cretins  suffer  from  convulsive  movements  of  the 
head,  nystagmus,  internal  squint,  and  idiocy. 

The  myxoedematous  type  shows  marked  interference  with  the 
growth  of  the  skeleton,  leading  to  a  stunted,  pot-bellied  appearance. 
There  is  usually  a  marked  lack  of  mental  efficiency,  a  child  of  twelve 


Fig.  253. — Non-Goitroxjs  Cketixs.     (Pliotograj)hs  kiucily  Jent  by  -Or.  Robert 

Hutchison.) 

to  sixteen  having  the  intelligence  of  a  child  of  two  or  three.  The 
appearance  remains  childish  throughout  life.  Often  fattv  tumours 
make  their  appearance  in  the  region  of  the  collar-bone. 

When  thvToid  deficiency  first  manifests  itself  in  the  adult,  the 
effects  upon  growth  are  naturally  absent.  A  gradual  swelling  of  the 
skin  sets  in,  frequently  accompanied  by  nervous  disorders,  such  as 
headache,  languor,  convulsions,  mental  disturbances,  dulness,  drowsi- 
ness, or  ev^en  hallucinations.  The  skin  becomes  wTinkled,  dry  and 
rough,  swollen  generally,  but  with  a  '*  solid  oedema,"  hence  the  name 
*■  myxoedema  "  (mucous  oedema).  The  swelling  is  at  first  most  notice- 
able on  the  face  (see  Fig.  254).  The  hair  becomes  scanty,  the  scalp 
dry  and  scaly.     The  teeth  often  become  carious. 


INTERNAL  SECRETIONS 


517 


C'retins  and  cases  of  myxoedema  show  marked  iiuprovement  when 
fed  upon  thyroid  gland.  It  was  noticed  that  a  condition — "  cachexia 
tM-reopriva  " — similar  to  myxoedema  was  induced  when  the  goitrous 
thyroid  was  removed  b}'  operation;  hence  it  became  customary  always 
to  leave  a  piece  of  thyroid  tissue. 

In  contrast  to  the  condition  due  to  lack  of  thp'oid  activity  is  that 
known  as  "exophthalmic  goitre,"  or  "Graves'  disease"  (Fig.  255). 
In  this  disease  the  th3'roid  is  generally  enlarged  and  overactive. 
This  "overaction  ''  manifests  itself  in  "nervous  "  symptoms — exoph- 
thalmos and  tachycardia.     On  account  of  the  nervous  symjjtoms, 


Fig.  254. — Typical  Case   of  Myxcedema.     (Photograph-^  kindly   lent    by  Dr. 
Robert  Hutchison.) 

A,  Before  treatment;  B,  after  treatment. 


the  disease  has  been  regarded  by  some  as  primarily  a  lesion  of  the 
sympathetic  nervous  system,  and  not  of  the  thp'oid  gland.  A 
possible  explanation  of  this  may  be  that  man3'  of  the  symptoms 
are  due  to  the  increased  action  of  adrenahn  upon  sympathetic  nerve 
endings,  this  increase  being  due  to  the  excessive  thvroid  secretion 
(cf.  p.  519). 

The  result>  of  extii^pation  experiments,  on  the  whole,  support 
clinical  observation.  There  is,  ho^^'ever,  much  contradiction  in  the 
evidence,  owing  to  the  fact  that  extirpation  of  the  thyroid  and  of  the 
parath3Toids  produces  different  effects  in  different  species  of  animal. 
It  is  difficult  to  produce  all  the  symptoms  of  myxoedema  as  a  result 
of  thyroid  deficiency;  possibly,  therefore,  some  other  factors  come  into 


518 


A  TEXTBOOK  OF  PHVSI()L()(^Y 


this  disease.  By  those  Avho  beheve  that  thyroid  and  parathyroid  aie 
glands  with  different  functions  it  is  claimed  that  extirpation  of  the 
thyroid  produces  symptoms  akin  to  myxoedema.  with  sometimes  a 

slow  death;  while  extirpation  of  the  para- 
Ihyroids  produces  the  licrvOus  symptoms 
of  tetany  convulsions  and  a  quick  death. 
The  evidence  in  favour  of  and  against 
those  views  is  very  conflicting.  Undoubt- 
edly, in  some  cases  the  removal  of  the 
thyroid  produces  the  '"  myxoedematous," 
and  of  the  ])arathyroid8  the  "  nervous  " 
syndrome;  but  in  some  cases  thyroid 
i-emoval  produces  iii  addition  the  nervous 
symptoms,  or  these  alone;  while  extirjia- 
tion  of  the  parathyroid,  instead  of  pro- 
ducing the  nervous  symptoms  of  tetany, 
calls  forth  ''  cachexia.  "  or  deficient  meta- 
bolism of  myxoedema. 

A  substance  rich  in  iodine  has  been 
isolated  from  the  thyroid,  called  iodo- 
thyrin  or  thyreo -iodine.  The  active  part 
of  the  colloidp.l  protein  secretion  of  the 
thyroid  is  often  stated  to  be  this  sub- 
stance. Recent  evidence,  however,  tends 
to  show  that  this  is  not  the  case.  The  true  secretion  passes  into 
f,y,P:  T^io^^  iTrV^ri"  f  Vie' nerves  (the  superior  laryngeal)  to  the  gland  are 


Pig.  25o.^A  Typical  Case  of 
Exophthalmic  Goitre  in  a 
YoTTNG  Woman. 

(From  "Index  of  Differential 
Diagnosis,"  T.  Wright  and 
Sons,  Ltd.) 


Stimulation  of  depressor 
Stimulation  of  nerves, 

depressor. 

Stimulation  of  thyroid  nerves. 

Fig.  256. — To  show  the  Effects  of  Stimulation  of  the  Depressor"  Nerve 
without  and  with  Stimulation  of  the  Nerves  (Superior  Larvng'eal)  to 
the  Thyroid.     (Asher  and  Flack.) 


stimulated,  as  is  demonstrated  by  the  fact  that  certain  actions  are 
augmented  by  this,  just  as  they  are  by  an  intravenous  injection  of 


INTERNAL  SECRETIONS  519 

thjToid  extract.  For  example,  if  the  depressor  nerve  be  stimulated 
before  and  after  excitation  of  the  th\Toid  nerves  (or  injection  of 
thyroid  extract),  the  fall  of  blood-pressure  is  greater  in  the  second 
case  (Fig.  256).  Likewise,  if  adrenalin  be  injected,  the  rise  of  blood- 
pressure  is  greater  in  the  second  case  (Fig.  238). 

The  injection  of  any  of  the  commercial  preparations  of  thp-oid 
extract  produces  these  effects,  but  not  the  separated  product,  "  iodo- 
th^Tin."  As  to  the  exact  chemical  nature  of  the  active  body,  nothing 
definite  is  known.  Its  iodine  content,  no  doubt,  is  of  great  importance, 
but  is  not  the  sole  factor. 

-■""■''"!'"'■'  '.■■■■      '.■■'.-■■■;-:.'.■:■••.  \'?^ 


■*t^-. 


-l/.c. 


Hx. 


n^ii 


Fig.  257. — Poetion  of  Thyjius  Glaxd  of  a  Mo>rKEY.     Low  Power.     (From  Swale 
Vincent,  drawn  l)y  Mrs.  ThomiJson.) 

c,  Cortex;  H.c.,  Hassal's  concentric  corpuscles;  m.,  medulla. 

The  Carotid  Body  is  a  mmute  structure  situated  at  the  bifurcation 
of  the  common  carotid  arter3^  It  is  richh'  supj)lied  Avith  nervous 
■elements,  and  probably  belongs  to  the  group  of  chromophil  tissues, 
with  a  function  akin  to  that  of  the  medulla  of  the  suprarenal  gland. 

The  Thymus  Gland. — In  its  development,  the  thymus  gland  arises 
from  the  gill-clefts,  and  may  be  apparently  entodermal  or  ectodermal 
in  origin,  or  both  (Fig.  257).  In  man  and  the  rabbit  it  is  ento- 
dermal, in  the  mole  it  is  ectodermal,  in  the  guinea-pig  and  pig  it  has 
a  dual  origin.  At  birth  it  Aveighs  about  i  ounce,  and  is  relatively  a 
large  organ.  It  increases  in  size  and  weight  for  some  years  after 
birth,  probably  until  puberty,  and  then  atrophies  slowly. 

It  is  subdivided  by  connective  tissue  into  lobes,  and  each  of  these 
is  made  up  of  several  Ir)bules,  which  are  divided  into  a  darker  cortex" 


520 


A  TEXTBOOK  OF  PHYSIOLOGY 


and  a  pale  medulla.  All  the  lobules  in  eaeh  half  of  the  thymus  are 
attached  to  a  cord  of  medullary  substance,  as  may  be  seen  if  the  organ 
is  pulled  apart.  The  thymus  resembles  in  structure  a  tymphatie 
gland,  but  germinal  centres  are  absent,  and  there  is  nothing  to  cor- 
res])ond  with  a  lymph  sinus.  The  cortex  is  crowded  with  lymphocytes, 
and  is  very  vascular.  The  medulla  is  more  open  in  texture,  and  is 
characterized  by  the  presence  of  the  concentric  corpuscles  of  Hassall. 

c  h    k-  d  e  /  fj 


Fig.  258. — Mesial  Sagittal  Section  through  the  Pituitary  Body  of  an  Adult 
Monkey.     (Herring,  from   Quarterly  Journal  of  Experimental  Physiology.) 

(I.  Optic  chmsma  ;  h.  tongue-like  jiroeess  of  pars  intermedia  :  c,  third  ventricle  ; 
d,  anterior  lobe  :  e,  epithelial  cleft  of  posterior  lobe  :  k,  epithelium  of  pars  inter- 
naedia  extending  over  and  into  adjacent  brain  substance.  The  dark  shading 
indicates  anterior  lolie  proper  ;  the  lighter  shading  shows  the  position  of  the 
epithelium  of  pars  intermedia  :  ij,  nervous  substance  of  posterior  lobe  ;  /,  epithelial 
investment. 


These  are  generallj-  regarded  as  degenerated  products  of  entodermal 
epithelium.  Some  authorities  maintain  that  the  thymic  cells  are  not 
true  lymphocytes,  but  are  of  entodermal  origin. 

The  Function  of  the  Thymus. — By  virtue  of  its  lymphatic  tissue, 
the  thymus  gives  origin  to  the  h'mphocj'tes  of  the  blood,  and  possibly 


INTERNAL  SECRETIONS 


521 


also  plaj's  some  part  in  the  purin  metaboHsm  of  the  body.  In  some 
hibernating  animals  it  also  acts  as  a  storehouse  of  fat.  It  has  long 
been  known  to  butchers  and  others  that  the  thymus  persists  in  castrated 
animals,  and  atrophies  with  the  onset  of  puberty  in  the  intact  animal. 
It  has  been  shown,  also,  that  the  atrophy  is  accelerated  should  the 
bull  be  used  for  breeding  purposes  or  the  imsj)ayed  heifer  become 
pregnant.  It  is  also  suggested  that  the  extirpation  of  the  thymus- 
interferes  with  the  growth  of  the  skeleton.     Rickets  has  been  attri- 


'!S^-, 


i9    55 


-y.n. 


Fig.  259. — Sectiox  through  Portions  of  Pitttitary  Body  of  Dog,  showing 
Glandular  and  Nervous  Portions  and  the  Pars  Intermedia.  (Swale 
Vincent,  drawn  by  Mrs.  Thompson.) 

c.  Cleft  in  glandular  portion  between  glandular  portion  proper  and  pars  intermedia; 
f.g.,  glandular  portion  showing  three  kinds  of  cells;  p.i.,  pars  intermedia;  p.n.., 
nervous  portion. 


buted  to  disease  of  this  organ.  The  evidence  in  favour  of  such  views 
is  not  conclusive.  It  has  recently  been  stated  that  tadpoles  fed  on 
thyi-oid  became  diminutive  frogs,  while  those  fed  on  thymus  became 
giants. 

The  Pituitary  Body.— The  pituitary  body  consists  of  three  portions: 
(1)  The  anterior,  (2)  the  intermediary,  (3)  the  posterior  lobes.  The 
anterior  and  intermediary  lobes  have  a  common  origin  from  a  portion 
of  the  glandular  epithelium  of  the  stomodseum,  known  as  Rathke's 
pouch.     Quite  early  a  differentiation  between  the  U\o  portions  takes 


522  A  TEXTBOOK  OF  PHYSIOLOGY 

place.  The  intermediate  part  is  closely  adherent  to  the  wall  of  the 
posterior  lobe;  its  cells  are  clear,  and  tend  to  form  colloid;  the  anterior 
l)ortion  is  formed  of  columns  of  granular  cells  separated  by  blood- 
channels  (Fig,  258). 

Tne  posterior  lobe,  or  infundibulum,  is  nervous  in  origin.  It  is 
an  invagination  of  the  portion  of  the  develojiing  braiii  known  as 
the  thalamencephalon.  In  some  animals,  such  as  the  cat,  it  retains 
its  central  cavity;  in  others  this  becomes  entirely  obliterated.  Early 
in  development  it  becomes  closely  associated  with  cells  of  the  pars 
intermedia,  so  that  eventually  the  posterior  lobe  becomes  a  com- 
posite structure  of  intermediary  and  nervous  epithelia — a  mass  of 
gland  cells,  neuroolial  cells,  and  nerve  iibres  (Fig.  2511). 


.,... ^^^.^j^iiv«''i^wwwiwV'^/«'''^^''^"''-^'''*v,v...- 

((                      3 

c 

- 

BV      r 

■^j-fT 

•. 

- 

J 

MILK     h 

1  niiiK/lfiliiiM  1  1  1  1  1  IN     1      II        1       1 

:Li 

:  i'iiHiii>H|i'Hi'HlnH<jiiirii!)i  umiiluil  n'l'tn  uuiUl 

-•  ■  -  .-■      -■          _            -  -■.                      ;.      ■ 

Fig.  260. — Record  of  Blood -Pressttee  asd  Milk-Flow  in  Drops  from  0>'e  Nipple 
OF  A  Lactatixg  Cat.     (Dixon.) 

At  A  pituitary  extract  was  injected. 

The  Functions  oJ  the  Pituitary  Body. — The  chief  evidence  of  the 
physiological  action  of  the  pituitary  gland  is  obtained  from  clinical 
experience  and  pathological  findings,  and  from  observations  upon 
the  effects  which  follow  injection  or  feeding  extracts  of  the  gland. 
Owing  to  its  anatomical  position,  it  is  difficult  to  obtain  satisfactory 
evidence  by  means  of  extirpation.  It  has  been  claimed  that  the 
removal  of  the  gland  invariably  causes  death,  often  in  thirty-six  hours. 
Many  such  deaths  are  tmdoubtedly  due  to  post -operative  shock. 
Recently,  skilled  experimenters  have  succeeded  in  keeping  animals 
alive  several  months  after  removal  of  the  pituitary.  The  effects 
claimed  to  result  from  its  removal  are  thus  contradictory. 

The  injection  of  extract  of  the  anterior  lobe  is  Avithout  phj'siological 
action.     Injection  of  extract  of  the  intermediary  and  posterior  lobe 


INTERNAL  SECRETIONS  .     523 

•causes  a  rise  of  blood-pressure,  accompanied  by  marked  diuresis. 
A  second  injection .  generally  does  not  affect  the  arterial  pressure, 
but  the  diuretic  action  is  still  marked — in  fact,  the  active  substance 
may  be  regarded  as  the  most  potent  diuretic  known.  The  smooth 
muscle  of  the  pupil  and  uterus  is  also  affected  by  pituitary  extract, 
and  it  is  used  by  clinicians  to  promote  contractions  of  the  uterus. 

The  contractions  of  the  bladder  are  also  increased  in  the  dog  and 
rabbit  by  the  injection  of  pituitary  extract.  The  excitability  of  the 
pelvic  nerve  supplying  this   viscus  is  increased,   while  that  of  the 


Fig.  261. — A  Case  of  Acromegaly.     (Photograph  kindly  lent  by  Dr.  T.  Heuell 

Atkinson.) 

The  head  measurements  are — Circumference,  2o|  inches;  from  forehead  to  chin, 
11  inches;  from  nape  of  neck  to  chin,  over  nose,  2.5  inches.  The  lower  jaw  pro- 
trudes 1^  inches  in  front  of  the  upper.  The  two  hands  measure  6  inches  across 
the  root  of  the  thumb  and  5  inches  across  the  root  of  the  fingers.  When  closed 
the  hand  measures  15^  inches  round. 

hypogastric  nerves  is  unaltered.  Pituitary  extract  has  no  action 
upon  other  organs  supplied  by  the  autonomic  system,  such  as  the 
heart  and  the  salivary  glands ;  an  action  upon  the  intestine  is  doubtful 
The  extract  of  the  infundibidum  is  also  a  powerful  galactagogue, 
and  the  active  substance  can  be  obtained  from  both  the  intermediary 
and  posterior  lobes  (Fig.  200).  The  active  substance  is  probal)Iy 
derived  from  both  lobes,  but  chiefly  from  the  intermediary  lobes.  Its 
•exact  nature  is  unknown,  liut  its  action  is  closely  allied  to  bodies  of 
the  digitalis  series,  and  it  apparently  acts  directly  upon  muscle  rather 
"than  upon  the  nerve  or  nervous  connections. 


r,24  A  TEXTBOOK  OP  PHYSIOLOGY 

The  function  of  the  anterior  lobe  is  suggested  by  clinical  records 
of  the  results  which  accompany  its  disease;  thus  the  affection  known 
as  "  acromegaly  "  is  associated  with  a  hypertrophy  of  the  anterior 
lobe.  This  affection  begins  about  puberty,  and  is  characterized  by 
progressive  increase  in  the  size  of  the  face  and  limbs  (Kig.  261).  The 
disease  nins  a  s1oa\'  course  to  a  fatal  issue.  Some  attribute  the 
development  of  giants  to  hypertrophy  of  this  organ.  Excessive 
growth  is  also  found  associated  with  h\q)ertrophy  of  the  cortex  of  the 
Buprarenal  gland,  and  there  may  be  some  internal  secretion  common 
to  the  two  glands  which  stimulates  growth. 

It  has  been  suggested  that  the  pituitary  gland  plays  a  part  in 
regulating  the  calcium  metabolism  of  the  body.  The  evidence  of 
this  is  inconclusive.  It  is  also  claimed  that  the  posterior  lobe  helps 
to  regulate  carbohydrate  metabolism,  and  that  after  its  removal  an 
increased  tolerance  to  carbohydrate  is  induced. 

There  is  some  evidence  that  the  pituitary  interacts  with  the 
thyroid  and  sexual  glands,  esi^ecially  the  ovary.  Thus,  after  extirpa- 
tion of  the  thyroid  the  pituitary  is  said  to  show  an  increase  of  colloid 
material,  while  during  pregnancy,  it  is  stated  that  the  pituitary 
increases  in  size — an  effect  also  produced  by  removal  of  the  ovaries 
in  women  and  in  animals. 

The  Pineal  Body  is  a  small  pinkish  body  situated  on  the  dorsal 
aspect  of  the  brain,  underneath  the  posterior  region  of  the  corpus 
eallosum.  It  consists  chiefly  of  neuroglial  and  secretory  cells,  made 
up  into  a  number  of  follicles  often  resembling  adenoid  tissue.  There 
is  little  phj-siological  evidence  of  any  internal  secretion  of  this  body. 
Clinically,  it  is  suggested  that  disease  of  the  gland  is  associated  in  some 
cases  with  obesity,  in  others  with  abnormal  sexual  development  and 
gigantism. 


BOOK    XI 

THE   TISSUE   OF    MOTION 

CHAPTER  LX 
THE  MECHANISM  OF  MOVEMENT 

A  UNICELLULAR  orgaiiism,  such  as  the  amoeba,  moves  by  the  flowmg 
of  its  protoplasm  in  one  or  other  direction,  the  rest  of  the  cell  flowing 
after  the  protrusion  or  pseudopodium.  In  other  unicellular  forms, 
the  development  of  one  or  more  cilia  or  flagella  enables  the  organism 
to  move,  often  with  a  relatively  high  rate  of  speed.  In  the  multi- 
cellular organizations  this  function  of  motion  has  been  assigned  to 
special  cells.  Such  cells  are  termed  the  muscle  cells.  The  full}^ 
specialized  muscle  cell  contracts  with  a  force,  rapidity,  and  frequenc}', 
far  bej'ond  the  poAver  of  less  specialized  protoplasm.  Its  greater  power 
and  efficiency  have  been  acquired  by  the  development  withm  the 
protoplasm  of  long,  and  exceedingly  slender,  contractile  structures — 
the  muscle  fibrils — lying  parallel  to  the  long  axis  of  the  cell  and  in 
the  direction  of  motion.  Fibrils  vary  in  the  degree  of  differentiation. 
Some  exhibit  a  marked  cross-striation,  and  are  termed  striated;  others 
are  unstriated.  The  fibril  affords  the  essential  mechanism  of  rapid 
motion. 

In  the  higher  animals  the  principle  of  locomotion  is  that  the  moving 
part  first  becomes  angular  in  shape,  and  then  straightens  itself  out 
against  some  resisting  substance;  the  principle  being  the  same  whether 
the  organ  of  locomotion  be  fin,  wing,  or  leg.  Force  exerted  against 
resisting  water,  air,  or  earth,  and  reacting  in  proportion  to  the  resist- 
ance, imparts  movement  to  the  body  of  the  animal. 

The  principle  of  the  lever  is  applied  in  the  various  movements  of 
the  body.  There  are  three  kinds  or  orders  of  levers  (see  Fig.  262). 
(1)  The  first  order,  in  which  the  fulcrum  (F)  lies  between  the  force 
applied  (P)  and  the  resistance  overcome  (W),  as  exemplified  in  a  pair 
of  scissors;  (2)  the  second  order,  in  which  resistance  {W)  lies  between 
the  fulcrum  {F)  and  the  force  applied  (P) — e.g.,  in  nutcrackers;  (3)  the 
third  order,  in  Avhich  the  force  (P)  lies  between  the  fulcrum  {F)  and 
the  resistance  ( W).  as,  for  example,  in  a  pair  of  sugar-tongs.  By  means 
of  levers  the  power  applied  max  be  augmented  or  the  rauge  and 
rapidity  of  movement  increased.     In  the  body  the  power  is  usually 

525 


526 


A  TEXTBO(JK  OF  PHYSIOLOGY 


applied  to  the  bonew  in  such  a  way  that  the  latter  is  the  case.  In 
order  that  the  inuscies  may  be  packed  within  the  skin  and  the  body 
made  as  compact  a«  possible,  the  power  is  ap]jlied  at  the  insertion  of 
the  muscles  close  ti>  the  joints  or  fulcra.  All  three  orders  of  levers 
are  exemjilified  in  the  bodj-.  Belonging  to  the  first  order  is  the  move- 
ment by  which  the  head,  jointed  to  the  top  of  the  spine,  is  nodded 
backwards  and  forwards  by  the  neck  muscles  (Fig.  262, 1.).  Another 
example  is  the  straightening  movement  of  the  forearm  bj'  the  action 
of  the  tricejis  muscle.  The  power  is  applied  at  the  insertion  of  the 
muscle  into  the  ulna  just  above  the  elbow-joint,  which  is  the  fulcrum, 
and  the  resistance  (the  weight  of  the  forearm)  lies  bejond.  Range 
and  rajiiditj*  of  movement  of  the  hand  are  here  gained  at  the  expense 
of  power. 

The  second  ordei  of  lever  is  seen  in  the  movement  by  which  the 
calf  muscles  raise  the  body  on  tiptoe  (Fig.  262,  II.).  The  power  is 
applied  at  the  back  of  the  heel,  the  fulcrum  is  at  the  toes,  and  the 
weight  of  the  body  falls  on  the  foot  at  the  ankle-joint.  Here  power  is 
gained  at  the  expeu.ie  of  range  of  movement. 

I.  II.  III. 


[ 


W  r 

Fig.  2G2.- 


W     P       F     P 


W 


DfAGRAM  OF  Three  Kinds  of  Lever  Action. 
/',  Fulcrum ;P,  power;  W,  weight. 
I.  The  head  is  -litcd  back  by  neck  muscles. 

II.  The  toes  rest  on.  the  ground,  and  the  body  is  raised  l)y  the  calf  muscles. 
III.  The  forearm  i-  bent  up  by  the  biceps  muscle. 


Examples  of  the  third  order  of  lever  are  numerous.  In  the  bending 
of  the  forearm  on  the  upper  arm  (Fig.  262,  III.),  the  power  is  applied 
by  the  biceps  muscle  to  the  radius  just  below  the  elbow-joint,  the 
fulcrum  is  at  the  elbow,  and  the  resistance  is  the  weight  of  the  fore- 
arm and  hand.  The  bending  and  the  straightening  of  the  leg  at  the 
knee-joint  are  other  examples.  In  all  these  movements  rapidity  and 
range  of  movement  are  obtained  at  the  expense  of  power. 

We  usually  empL-y  that  combination  of  levers  which  require  the 
least  muscular  effort.  It  is  easier  to  carry  a  weight  with  the  arm 
hanging  fully  extended,  when  it  is  slung  to  the  shoulder  by  the  bones 
and  tendons,  and  the  muscles  have  only  to  maintain  the  grip  of  the 
fingers,  than  it  is  to  carry  it  with  the  arm  bent,  and  much  greater 
muscular  effort.  Man  is  constantly  devising  methods  to  save  the 
expenditure  of  muscular  effort.  Thus  a  drayman  pulls  a  beer -barrel 
up  an  inclined  plane,  which  bears  a  large  part  of  the  weight. 


THE  MECHANISM  OF  M0VE:\[EXT  527 

The  muscular  work  done  by  a  man  is  calculated  by  multiplying  the 
Aveight  lifted  by  the  height  of  the  lift.  Thus  2  kilogrammes  lifted 
through  2  metres  gives  4  kilogramme-metres  of  work.  \Mien  a 
man  runs  upstairs  very  fast  he  may.  in  lifting  his  bod}',  do  seventy 
times  more  work  in  a  minute  than  a  navvy  does  in  the  same  time 
who  is  steadily  shovelling  up  earth.  The  man,  however,  is  spent  at 
the  end  of  such  an  effort;  the  navvy  can  continue  to  shovel  leisurely 
for  hours. 

Excess  either  of  rate  of  work  or  of  load  a\  ill  lessen  efHcienc^^  and 
diminish  output.  vScientific  management  determines  the  suitable  rate 
and  load  for  each  kind  of  labour. 

The  Erect  Posture. — With  the  assumi^tion  of  the  erect  posture  one 
of  the  chief  functions  of  the  system  of  levers  of  the  human  body 
became  that  of  maintaining  the  centre  of  gravity  of  the  body  within 
the  bod}'.  Since  the  centre  of  gravity  of  a  body  always  tends  to  take 
up  the  lowest  possible  position,  it  must  lie  over  the  base  of  support, 
otherwise  the  body  will  topple  over. 

A  dead  man  cannot,  without  support,  be  made  to  stand  in  the 
erect  posture.  If  a  man  standing  erect  faints,  the  head  tends  to  fall 
forward  on  the  chest,  the  trunk  forwards  at  the  hip-joints,  and  the 
whole  body  forwards  over  the  ankle-joints.  Although  the  body  is 
balanced  by  muscular  action,  the  weight  of  the  body  is  borne  by  the 
bones  and  ligaments,  and  thus  fatigue  is  avoided.  In  the  stork  the 
bones  of  the  leg  can  be  so  locked  together  to  balance  the  body  that 
the  bird  can  sleep  restfully  standing  on  one  leg.  In  man  the  main- 
tenance of  the  erect  posture  is  more  of  an  effort,  so  that  for  this,  as 
well  as  other  reasons,  he  seeks  rest  in  the  recumbent  posture. 

The  bod}'  is  maintained  erect  by  the  following  means : 

The  head  is  balanced  by  the  muscles  so  as  to  rest  on  the  top  of 
the  vertebral  column.  As  the  centre  of  gravity  lies  in  front  of  the 
joint,  the  head  tends  to  fall  forwards  in  a  sleejjy  man ;  the  neck  muscles 
must  act  to  keep  it  from  doing  so.  The  vertebral  column  forms  an 
elastic  rod  supporting  the  head  and  trunk ;  below  it  is  fixed  immovablj' 
to  the  broad  pelvic  basin,  into  which  presses  the  weight  of  the  abdo- 
minal organs.  The  centre  of  gravity  of  the  body  is  situated  near 
the  front  of  the  last  lumbar  vertebra.  If  a  plummet-line  could  be 
dropped  from  the  centre  of  gravity,  the  line  would  j)ass  a  little  behind 
the  line  which  joins  the  two  hip-joints.  The  trunk  thus  tends  to 
fall  backwards  at  the  hip-joints;  this  is  prevented  by  the  strong 
ligament  which  passes  from  the  pelvis  to  the  femur  across  the  front  of 
each  joint.  Thus  the  joint  is  locked  and  the  muscles  passing  from 
the  trunk  to  the  thighs  have  simply  to  balance  the  body  upon  the 
heads  of  the  thigh-bones.  To  do  this  but  little  effort  is  required.  At 
the  knee  the  plummet-line  dropped  from  the  centre  of  gravit}^  would 
pass  through  a  line  joining  the  posterior  jiarts  of  both  joints.  The 
weight  of  the  upper  part  of  the  body  th;is  presses  upon  the  flat  articular 
surfaces  of  the  tibiae.  The  great  extensor  muscles  in  front  of  the 
thigh  prevent  the  knees  from  bending,  and  the  body  from  falling 
backwards  whenever  balance  is  disturbed.     Owing  to  the  check  liga- 


528  A  TEXTBOOK  OF  PHYSIOLOGY 

ments  which  lock  together  the  femur  and  the  tibia,  the  knee  can 
neither  be  overextended  nor  bent  to  one  side.  In  a  man  standing  at 
attention  the  pkimmet-line  drawn  from  the  centre  of  gravity  passes 
in  front  of  the  Jine  joining  the  two  ankle-joints;  the  body  is  prevented 
from  falling  forwards  by  the  action  of  the  calf  muscles.  The  weight 
of  the  body  thus  transmitted  is  borne  by  the  spring  of  the  arch  of  the 
foot;  the  balls  of  the  toes  and  the  heel  rest  upon  the  ground. 

The  centre  of  gravity  of  the  body  is  always  kept  over  the  base  of 
support  by  varjdng  the  attitude  of  the  bodj^  Thus  a  man  stoops 
when  carrying  a  child  on  his  back,  but  Avalks  erect  if  it  be  on  his 
shoulders.  If  the  child  be  on  his  arm  he  leans  back,  and  to  the  other 
side.  In  most  of  the  Herculean  feats  of  strength  exhibited  on  the 
stage,  the  strong  man  supports  enormous  weights,  not  by  muscular 
effort,  but  by  so  placing  his  body  that  the  bones  form  pillars  of  support 
on  which  the  weight  rests. 

In  young  children  the  centre  of  gravit}^  is  high,  for  the  head  is 
large  and  the  small  feet  form  but  a  narroAv  base.  A  slight  push  from 
behind  brings  the  centre  of  gravity  outside  the  base,  and  the  child 
must  move  its  feet  quickly  forward  or  fall.  Thus  the  tiny  child  has 
many  tumbles,  for  the  brain  has  to  learn  by  exj)erience  how  to  carry 
out  rapidly  the  appropriate  movements.  The  younger  a  child  the 
more  he  tends  to  stand  with  his  feet  wide  apart.  The  tottering  old 
man  also  widens  his  base  of  support  by  using  a  staff. 

The  body  is  equilibrated  by  means  of  the  proprioceptive  mecha- 
nism of  the  body  (see  p.  6.54)  and  the  co-ordinating  influence  of  the 
cerebellum  and  the  cerebrum. 

Walking. — On  standing  on  one  foot  the  body  is  inclined  to  that 
side,  so  that  the  other  leg  is  left  free  to  move.  In  w^alking,  one  leg, 
say  the  right,  is  slightly  bent  at  the  knee  and  planted  down  in  front 
of  the  other.  The  weight  of  the  body  is  throAvn  on  this  leg,  Avhile  the 
left  leg,  raised  on  the  toes  by  the  action  of  the  calf  muscles,  forms  a 
straight  stiff  rod.  The  left  leg,  by  giving  a  push  to  the  ground,  next 
throAvs  the  body  forAvards.  Thereupon  the  right  leg  straightens  up, 
Avhile  the  left,  slightly  bent  at  the  knee,  swings  forAvard  as  a  pendulum 
and  comes  doAvn  in  front  of  the  right.  It  is  noAV  the  turn  of  the  right 
leg  to  push  off,  and  of  the  left  leg  to  bear  the  Aveight  of  the  bodj\ 
The  length  and  rapidity  of  the  step  in  Avalking  naturally  depend  on 
the  length  of  leg.  A  duck  Avaddles,  a  hen  nnis.  The  longer  a  pen- 
dulum the  slower  it  swings.  Thus  it  is  difficult  for  a  long  and  a  short 
man  to  keep  pace,  and  a  regiment  cannot  maintain  a  regular  march 
Avhen  the  men  are  fatigued,  for  each  soldier  then  falls  into  his  OAAai 
natural  SAving. 

Running. — In  rinming,  both  legs  momentarily  lea\'e  the  ground. 
The  muscles  act  far  more  poAA^erfully  than  in  Avalking.  The  body  is 
raised  and  thrust  forAAard,  not  only  by  the  contraction  of  the  calf 
muscles  of  the  hind-leg,  but  by  the  ixjAverful  action  of  the  extensors 
of  the  thigh,  Avhich  straighten  the  bent  knee  of  the  forward  leg.  The 
body  thus  propelled  forAA'ards  leaves   the  ground,  Avhile  the  hind-leg 


THE  MECHANISM  OF  MOVEMEXT  o29 

••swings  forward  as  a  pendulum  for  the  next  thrust.  The  exact  changes 
which  take  place  during  rapid  movement  have  been  analyzed  by- 
taking  a  succession  of  instantaneoiis  photographs  on  a  tilm.  8uch  a 
film  passed  at  a  correct  speed  through  the  cinematograph  lantern 
faithfully  reproduces  the  movement;  the  different  photographs 
succeed  each  other  so  rapidly  that  they  fuse  together  and  give  the 
sensation  of  a  moving  object.  In  real  life  we  only  get  a  fused  impres- 
sion of  the  position  of  a  moving  animal.  If  an  artist  drew  a  horse 
in  some  of  the  attitudes  revealed  b}-  instantaneous  photography  it 
would  be  deemed  unnatural. 

The  position  of  the  feet  in  walking  and  nmning  can  be  well  seen 
in  the  footprints  made  in  the  firm,  wet  sand  left  by  the  receding  tide. 


o4 


CHAPTER  LXT 
THE  STRUCTURE  AND  PHYSICAL  PROPERTIES  OF  MUSCLE 

The  Structure  of  Muscle. — In  the  vertebrate  animals,  the  muscles 
develop  from  cells  which  line  the  primitive  coelom  or  body  cavity. 
These  cells  become  invaginated  as  buds  from  the  c(jelomic  .surface, 
to  form  a  roM-  of  myomeres  along  each  side  of  the  animal.  These 
flatten,  so  as  to  form  two  plates,  the  inner  of  which  gives  rif.e  to  con- 
nective tissue,  the  outer  to  the  striated  muscle  of  the  body.  The  cells 
which  are  about  to  become  muscle  (the  sarcoblasts)  undergo  a  great 
lengthening,  and  show  signs  of  nuclear  activity.  The  division  of  the 
nucleus  is  amitotic — there  is  no  division  of  the  cell  body — and  many 
nuclei  are  formed  in  one  cell. 

At  this  stage  fibrils,  or,  as  they  are  sometimes  termed,  sarcostyles, 
gradually  appear  in  the  sarcoplasra  of  the  sarcoblast,  faint  at  first, 
l)ut  gradually  becoming  more  distinct.  The}'  first  appear  on  the  inner 
side  of  the  cell,  gradually  pushing  the  nuclei  to  the  outer  side.  The 
formation  of  fibrils  goes  on  until  each  cell  appears  a  mass  of  fibrils, 
with  but  little  interfibrillar  sarcoplasm.  Each  fibril  is  composed 
of  two  kinds  of  substance,  differentiated  by  staining  and  refractive 
liower.  One  substance — the  isotropic — does  not  stain  readily  and 
is  singly  refractile;  the  other — the  anisotropic  substance — stains 
readily  and  is  doubly  refractile.  Each  substance  is  dei)osited  alter- 
nately with  the  other  at  regular  intervals  in  the  fibril.  Thus,  after 
suitable  treatment  the  fibril  may  be  broken  uj)  into  sarcomeres,  or 
sarcous  elements.  The  lines  of  cleavage  take  place  in  the  isotropic 
substance;  each  sarcomere  consists  of  a  portion  of  anisotropic  sub- 
stance, with  half  a  portion  of  isotropic  substance  on  either  side  of 
it.  As  all  the  sarcous  elements  of  the  neighbouring  fibrils  are  in 
jierfect  alignment — isotropic  with  isotropic,  anisotropic  with  aniso- 
tropic— the  general  effect  is  to  give  the  fibres  that  cross-striped 
appearance  from  which  cross-striated  muscle  gets  its  name. 

The  difference  in  the  degree  of  differentiation  of  muscle  is  well 
seen  in  the  human  body.  The  musculature  of  the  trunk  and  limbs 
(the  skeletal  muscles)  djflfers  from  that  of  such  internal  organs  as  the 
bladder,  intestines,  uterus  (smooth  or  non-striated  muscle),  and  also 
from  that  of  the  heart  (cardiac  muscle). 

Voluntary  or  striated  muscle  is  composed  of  a  number  of  separate 
fibres  joined  together  to  form  the  muscle.  Tiie  character  and  number 
of  these  fibres  varies  considerably  with  different  muscles.  In  some 
thev  are  ]iale  and  delicate — so-called  pale  or  white  muscle:   in  others 

530 


.STRUCTURE  AND  PHYSICAL  PROPERTIES  OF  MUSCLE   531 

the\'  are  coarser  and  coloured  red  by  the  presence  of  a  pigment — red 
muscle.  In  general,  it  is  found  that  this  difference  corresponds  to  a 
difference  in  function.  The  white  muscles  are  those  which  are  called 
upon  to  perform  quick  movements  over  short  periods,  whereas  red 
muscles  are  those  which  perform  less  quick  movements,  but  for  longer 
periods  of  time,  and  often  without  any  marked  intervrls  of  rest.  Thus, 
the  leg  muscles  of  the  chicken  are  red,  the  breast  muscles  white;  oa 
the  other  hand,  the  breast  (flying)  muscles  of  the  Avild-goose  are  red. 

The  length  of  the  fibres  also  varies  greath'  with  different  muscles ; 
from  some  muscles  fibres  12  centimetres  long  have  been  obtained. 


7nus.n.~  — 


Fig.  2G3. — Longitudinal  .Section  of  a  Piece  of  Muscle  from  the  Sucker  Cata- 
STONius.  X  1000.  The  Relations  of  the  Dark  and  Light  Elements  during 
Contraction  of  the  Fibril  are  shown  in  A,  B,  C.  (After  Daklgren  and 
Kepner.) 

cap..   Capillaries;   sar.,   sarcoplasm;   mus.   n.,   muscle  nuclei;    «.,   connective  tissue 
nuclei;  Q,  anisotropic  material;  j.,  non-staining  isotropic  material. 


Each  muscle  fibre  shows  under  the  microscope  longitudinal  and 
transverse  striations.  The  fibres  are  composed  of  groups  of  fibrils 
(sarcostyles),  between  which  is  a  varying  amount  of  clear,  finely 
granulated  protoplasm — the  sarcoplasm.  Some  are  rich  in  sarcostjdes 
and  poor  in  sarcoplasm;  others  are  rich  in  sarcoplasm,  and  contain 
relatively  few  sarcostj^les.  In  this  lies  the  difference  between  j)ale 
and  red  muscles.  For  example,  the  red  soleus  muscle  of  the  rabbit 
contains  much  sarcoplasm ;  the  pale  gastrocnemius  is  composed 
mainly  of  sarcostyles.  The  sarcoplasm  evidently  affords  material 
for  sustained  action  to  the  sarcostyles,  which  are  the  contracting 
elements. 


In  ri^or 


In  tetanus 


532  A  TEXTBOOK  OF  J'H^SIOLQGY 

Smooth  Muscle. — A  smooth  muscle  fibre  develops  from  a  single 
tell  with  a  single  nucleus.  Such  cells  specialize  in  the  embryo  out  of 
the  mesenchyme.  Fibrils  are  deposited  Avithin  the  cell,  sometimes 
around  the  nucleus,  sometimes  to  one  side  of  it.  In  the  latter  case, 
the  nucleus  may  appear  on  the  side  of  the  cell.  The  fibrils  are  homo- 
geneous, and  vary  in  number.  There  is  a  considerable  amount  of 
sarcoplasm  in  the  smooth  muscle  fibres,  which  generally  take  the  form 
of  elongated  spindles  with  thin  tapering  ends.  Occasionally,  as  in  the 
aorta  of  3^oung  mammals,  the  ends  may  l)o  branched. 

Cardiac  Muscle. — The  structure  of  cardiac  muscle  has  been  dealt 
with  ill  the  section  on  the  circulatory  s\-steni  (p.  122). 

The  Physical  Properties  of  Muscle. 
— In  speaking  of  muscle,  we  gener- 
ally mean  striated  muscle,  since  this 
is  the  kind  of  muscle  which  forms 
the  flesh  and  has  been  most  investi- 
gated. The  living  muscle  fibre  is 
semi-fluid  and  translucent.  Its  fluid 
nature  has  been  shown  by  the  fact 
that  a  nematode  worm  has  been 
observed  to  traverse  it,  and  after  the 
jiassage  of  the  invader,  the  muscle 
substance  to  return  to  its  previous 
ordered  structure. 

Muscle     is     very     extensile    and 

elastic.      The     former     property    is 

shown  by  the  fact  that  but  a  small 

stretching  force  is  required  to  change 

its  shape,  the  latter  by  the  fact  that 

when  this  stretching  force  is  taken 

off  the  muscle  resumes  its  previous 

form.      Living    muscle   has    a  Avide 

range    of    this    elastic    property;    it 

requires  a  very  considerable  force  to 

overstep  its  limits.     If  a  stretching 

Fig.  264.-EXTEXSIBILITY  of  Muscle  ^0^'^©   ^e   applied   suddenly  and   in- 

iK  Various  States.    (Waller.)         creased  by  equal  increments,  a  living 

Tested  by  50  grammes  applied  muscle   extends   most    at    first    and 

for  short  periods.  then  by  less  amounts  till  the  limit 

of    its    extension    without    rupture 

is    reached.      Conversely,    on    removing    the    extending    force,    the 

muscle  returns  at  first  quickly  and  then  more  slowly  to  its  original 

form.     Rubber  and   most  inorganic   bodies,  such  as  metal  rods,  on 

the  other  hand,   extend  almost  equally  for  each  increment  of    the 

extending  force,  and  return  almost  equally  as  the  stretching  force  is 

removed.     Dead  muscle  is  less  extensible  and  less  elastic  than  living 

muscle  (Fig.  264). 

A  contracted  muscle  is  more  extensible  than  a  resting  one.     This 
gives   us  the  paradox  that,  if  a  muscle  A\ere   loaded   bj'   a   weight 


Fatigued 


.STRUCTURE  AND  PHYSICAL  PR0PERTIK8  OF  MUSCLE    533 

greater  than   it   could    lift,    it    would    actually    lengthen    during    its 
.stimulation. 

The  above  properties  are  of  great  importance  in  the  body.  If  a 
nui.scle  were  not  readily  extensible,  the  sudden  contraction  of  one  set 
of  muscles  would  tend  to  rupture  those  muscles  (the  antagonizers) 
which  perform  the  opposite  action.  Moreover,  the  contraction  of  a 
muscle  acting  through  an  elastic  medium  is  more  efficient  than  through 
a  rigid  medium.  It  is  far  less  jerky  in  its  effects.  The  smooth  working 
of  the  various  body  movements  and  of  the  circulation  depends  greatly 
upon  this  elastic  property.  The  muscles  are  kept  in  a  slight  state 
of  tension,  so  that  no  time  is  lost  in  "  hauling  in  the  slack."  The 
elastic  property  of  the  muscle  insures  its  return  to  the  normal  state 
after  any  contraction  has  been  performed.  Again,  if  the  contracting 
muscle  were  not  more  extensible,  there  would  always  be  the  risk, 
when  trying  to  lift  a  heavy  weight,  that  the  muscle  would  rupture 
either  itself,  or  its  tendon,  or  the  bones  to  which  it  is  attached.  Of 
these  three  structures,  the  muscle  is  least  often  ruptured. 

Muscle  is  also  excitable  or  irritable — that  is  to  say,  it  responds 
with  a  contraction  to  different  forms  of  stimulation.  A  nmscle  may 
be  stimulated  directly  or  indirectly  through  its  nerve.  An  excised 
muscle  maj'  be  directly  stimulated  by  any  sudden  change  in  its  physical 
state — b}'  mechanical,  chemical,  thermal,  or  electrical  stimuli.  Striking 
a  muscle  or  pricking  it  causes  its  contraction;  sudden  heating  or 
cooling  of  a  muscle  may  cause  it  to  contract.  Among  chemical 
excitants,  we  find  that  the  application  of  such  substances  as  ammonia, 
dilute  acids,  strong  saline  solutions,  induce  muscular  contraction. 
Excitation  follows  any  sudden  alteration  in  the  concentration  of 
electrol}i;e8  in  the  fluid  bathing  the  muscle  fibre:. 

In  experimental  work,  the  electrical  method  is  most  generally 
emplo3'ed  for  purposes  of  stimulation,  since  it  is  convenient,  easily 
graduated  and  less  injurious  to  the  tissues.*  The  source  of  the  electro- 
motive force  may  be  a  Daniell  or  a  Leclanche  cell.  To  make  and 
break  the  current,  a  mercury  or  a  spring  key  is  used,  preferably  the 
latter.  To  protect  the  preparation  from  the  current,  a  short- 
circuiting  key  is  used  (the  Du  Bois-Re3'mond  key).  When  shut,  the 
current  is  short-circuited  through  the  metal  blocks,  which  are 
attached  to  a  wooden  or  vulcanite  base;  when  open,  the  current 
flows  to  the  preparation  to  be  excited. 

Sometimes  it  is  desired  to  reverse  the  direction  of  the  current,  or 
to  shunt  it  into  another  preparation.  For  this  purpose,  special 
forms  of  keys  are  used.  For  making  the  actual  stimulation  of 
the  preparation,  electrodes  are  used.  These  may  be  made  of  needles 
insulated  by  a  small  piece  of  cork,  and  soldeced  to  pieces  of  fine  insu- 
lated conductmg  wire.  Such  ordinary  metal  electrodes  tend  to 
polarize,  owing  to  the  electrolysis  which  takes  place  in  the  tissue 
fluids  at  the  pouit  of  application.  For  accurate  work,  therefore,  noii- 
l)olarizable   electrodes   are   required.     A   form   connnonly   employed 

*  Ihc  student  is  advi.ied  to  consult  a  practical  n'.anr.al  fur  details  of  apparatus. 


534 


A  TEXTBOOK  OF  PHYSIOL* )(iY 


consists  of  a  smooth  amalgamated  zinc  rod  dipyjiug  into  a  saturated 
solution  of  zinc  sulphate  contained  in  a  U-tuhe.  Into  the  other  limb 
of  the  tube  is  inserted  a  glass  flange  carrying  a  plug  of  kaolin  paste 
made  up  with  physiological  saline  solution.  The  kaolin  plug  is  pulled 
out  to  a  point  which  serves  as  the  electrode,  or  pieces  of  lamp-wick 
soaked  in  the  paste  may  be  employed  to  make  the  contact. 

p]lectrical  stimulation  may  be  made  either  with  a  constant  current 
or  with  an  induced  current.  With  the  former,  the  current  from  the 
cell  or  battery  is  led  by  a  make-and-break  key  direct  to  the  muscle 
preparation  (Fig.  265).  Stimulation  is  effected  at  the  moment  when 
the  current  is  caused  to  flow  (at  make)  (Fig.  2BQ),  or  stopped  from 


Fig.  265. — Plan  of  the  Use  of  a  Constant  Cukkent  to  Stimulate. 


Fig.  266. 


-ClKCUIT  ARRANGED  WITH  ShORT-CiRCUITING  Ke:-  :  KeY  ShUT.      OPENING 

Key  =  Make  Shock. 


Fig.  267. — Circuit  arranged  with  Short-Circuiting  Ktv:  Key  Open.     Closing. 

Key  =  Break  Shock. 


flowing  through  the  preparation  (at  break)  (Fig.  267).  There  is  no 
sign  of  stimulation  while  the  current  is  actually  passing  through 
the  muscle,  provided  the  current  be  not  too  strong.  If  the  current 
be  strong  or  the  muscle  injured,  a  long-continued  contraction  may 
take  place  both  in  frog  and  human  muscle.  When  muscles  are 
degenerating,  it  is  found  that  the  j)assage  of  even  a  relatively  weak 
current  maj^  cause  this  jorolonged  contraction,  sometimes  termed 
''  galvano-tonus." 

The  contraction  which  occurs  at  the  make  is  stronger  than  the 
contraction  at  the  break  of  the  constant  current.  The  make  con- 
traction starts  from  the  kathode,  the  point  where  the  electric  current 
leaves  the  muscle;  the  break  contiaction  starts  from  the  anode,  the 


STRUCTURE  AND  PHYSICAL  PROPERTIES  OF  :\IU8(:LE   535 

point  Avhere  the  current  enters  the  muscle.  Tne  alteration  of  concen- 
tration of  electrolytes  under  the  kathode  heightens,  while  that  under 
the  anode  dejjresses,  excitability  durmg  the  passage  of  the  current. 
When  the  current  is  broken,  the  effects  are  reversed  (see  p.  5S3). 

To  alter  the  strength  of  a  constant  current,  a  piece  of  apparatus 
known  as  the  rheocord  is  used.  In  its  simplest  form  this  consists 
of  a  Avire  wound  to  and  fro  across  a  board,  with  a  terminal  at  either 


Fi:;.  2GS. — To  illustrate  the  Prixciple  of  the  Rheocord. 

end  and  a  movable  contact  or  slider  between  them  (Fig.  2t3S).  In 
use,  the  cell  is  comiected  to  the  two  terminals  A,  B,  and  the  prepara- 
tion comiected  to  the  end  A,  at  Avhicli  the  current  enters,  and  to  the 
slider  S.  The  current  from  the  cell  can  now  pass  either  through 
the  preparation  or  back  along  the  wire  of  the  rheocord.  Tiie  amount 
which  will  pass  in  either  direction  is  determmed  by  the  position  of  S. 
The  fall  of  potential  in  the  rheocord  is  from  .4  to  B;  therefore,  when 


Fiti.  209. — Diagram  of  an  Induction  Coil  and  its  Connections. 


>S  is  near  to  A,  the  fall  of  potential  from  .4  to  S  is  small,  and  but  little 
of  the  current  will  pass  to  the  preparation.  Tiie  amount  of  current, 
therefore,  going  to  the  preparation  is  directly  proportional  to  the  fall 
of  potential  between  .4  and  S.  It  is  also  inversely  proportiona'  to 
the  resistance  of  the  circuit  through  the  nerve.  Tnis  resistance, 
however,  need  not  be  considered,  since  the  resistance  in  the  nerve 
is  so  many  times  greater  than  that  caused  by  any  change  in  the  position 
oiS. 


r)8C  A  TKXTBOOK  OF  PFfVSrOLOCY 

The  ccn.stant  current  i.s  not  often  employed,  since  it  is  of  low 
electrciuctive  foite  (E.M.F.),  and,  owing  to  its  comparatively  long 
duration,  it  tends  to  cau.^-e  i)olarization  of  the  tissues,  due  to  the 
dissociation  of  electrolytes  from  the  colloid  of  the  muscle  substance.. 
The  induced  current  is  therefore  more  convenient,  since  it  has,  as 
compared  with  the  constant  current,  a  comparatively  high  E.M.F. , 
and,  being  of  very  sh(;rt  duration,  does  not  induce  so  much  polariza- 
tion of  the  tissues  for  ortlinary  exjieriments  it  is  practically  nil. 

The  induction  coil  comjjrises  two  coils — the  primary  and  the^ 
secondary.  The  primary  coil  is  made  up  of  a  few  turns  of  thick  copper 
wire  wound  around  an  iron  core.  The  secondary  coil  consists  of  a 
large  numler  of  turns  of  insulated  fine  copper  wire.  Each  turn  of 
wire  in  the  primary  coil  induces  an  effect  in  every  turn  of  the  Avire 
of  the  secondary  coil.  By  this  means,  therefore,  the  low  E.M.F.  of 
the  current  in  the  primary  circuit  is  transformed  into  a  current 
of  high  E.M.F.  n  the  secondary  circuit,  the  intensity  of  the  current 
fceing  jDroportional  to  the  number  of  turns  of  wire  in  each  coil.  It 
has  been  found  that  the  E.M.F.  of  this  current  var:"ef — 

1.  D'rectly  with  the  intensity  of  the  change  of  current  in  the 
primary  circiit.     The  greater  the  change,  the  greater  the  induction. 

2.  Eirectly  as  the  rate  of  change.  The  more  rapid  the  change,  the 
greater  the  induction. 

3.  With  the  argle  between  the  coils.  When  the  secondary  coiH 
is  at  right  angles,  there  is  no  induction.  It  is  greatest  when  the  wirea 
are  parallel  to  each  other— ?.e.,  in  the  ordinary  position. 

4.  Inversely  as  the  distance  between  the  coils,  being  greatest 
when  the  secondary  is  completely  over  the  primar}'  coil. 

The  induced  current  is  in  the  op^DOsite  direction  to  that  of  the 
jrimar}'  circuit  at  make,  in  the  same  direction  at  break. 

When  the  induced  current  is  employed  for  purposes  of  stimula- 
tion by  means  of  single  shocks,  the  current  from  the  battery  is  led 
into  the  primary  coil  of  the  "  induction  coil  '"  by  means  of  the  two 
top  binding  screws.  There  is  no  direct  connection  of  the  muscle 
with  the  battery,  this  beirg  placed  in  connection  with  the  secondary- 
coil  of  the  ajoparatus,  and  protected  from  stimulation,  except  when 
wanted,  by  a  short-circuiting  key.  A  make-and-break  key  is  placed 
in  the  jrimary  circiit,  and  the  current  in  the  primary  coil  made  to 
induce  an  exciting  current  in  the  f-econdary  coil  of  the  apparatus, 
either  by  closing  tl  e  kej'  (the  make  induced  current)  or  by  opening 
it  (the  break  induced  current).  An  induction  shock  is  produced 
cnly  at  make  or  break  not  while  the  current  is  flowing.  The  strength 
of  the  induced  current  may  be  adjusted  by  varying  the  distance 
between  the  primary  and  secondary  coils.  General^  speaking,  an 
experiment  is  begun  with  the  coils  far  apart,  and  the  .'eccndarj'  coil 
then  advanced  until  the  stimulus  becomes  effective  (Fig.  269). 

The  contraction  obtained  from  a  muscle  at  the  break  of  an  induced 
current  is  stronger  than  that  caused  by  the  make  of  the  current. 
This  is  because  there  is  at  make  a  momentary  self-induced  current 
in  the  primary  coil  which  is  opposite  in  direction  to  that  of  the  battery 


STRUCTURE  AND  PHYSICAL  PROPERTIES  OF  MUSCLE    537 

current.  At  the  break  of  the  current,  an  extra  cuiTent  is  also  pro- 
duced hi  the  ])riiuar\^  coil  in  the  .same  direction  as  the  battery  current ; 
but  the  primary  circuit  being  broken,  it  cainiot  delay  the  rapidity  of  the 
fall  of  the  battery  cm-rent. 

When  rapidly  induced  shocks  (50  to  100  per  second)  are  required 
(the  so-called  faradic  or  tetanizing  curi'ent),  the  primary  circuit  is 
rapidly  made  and  broken  by  means  of  Wagner's  hammer.  The  wires 
from  the  battery  are  connected  to  the  two  l)ottom  screws  of  the  primary 
coil  (Fig.  270).  It  will  be  seen  that  the  current  passes,  via  the  pillar  A 
and  spring  H.  through  the  primary  coil  to  the  electro-magnet  E. 
This  becomes  an  electro-magnet,  and  pulls  down  the  piece  of  steef 
on  the  spring  H,  and  thus  breaks  the  circuit.  E  then,  being  no  longer 
a  magnet,  releases  the  spring  hammer,  which  flies  back,  and  again 
completes  the  circuit;  and  so  the  process  is  repeated.  Every  time  the 
hammer  is  attracted  to  the  magnet  the  current  is  broken,  and  a  break 


r.c 


Fig,  270. — Diagram  to  show  the  Action  of  Wagner's  Hammer. 


shock  induced;  every  time  it  tlies  back  a  make  shock  is  induced 
Here  again  the  make  is  less  in  intensity  than  the  break  shock. 
The  make-and-break  shocks  can  be  equalized  by  placing  a  wire 
from  the  binding  screw  (7)  to  the  top  binding  screw  (1)  of  the  primary 
coil,  and  screwing  up  the  top  screw  S^  out  of  the  way,  and  at  the  same 
time  screwing  up  screw  S^.  The  current  now  passes  into  the  primar}^ 
coil  b^'  this  wire.  E,  as  before,  becomes  a  magnet,  and  pulls  down 
the  armature.  This  short-circuits  the  current  back  to  the  battery. 
There  is  still  left,  however,  a  circuit  for  the  extra  break  current 
(7,  W,  1,PC,  E,  H,  A,  7),  and  this  reduces  the  strength  of  the  break 
current  in  the  secondary  coil,  thereby  equalizing  the  make  and  break 
currents  (Fig-  271). 

Proof  is  required  to  show  that  a  muscle  is  really  stimulated  directly, 
and  not  indirectly,  through  the  nerve-fibres  and  nerve-endings  in 
the  muscle  '.  The  direct  excitability  of  muscle  is  shown  by  the 
following  experiments:  (1)  Parts  of  muscles  which  contain  no  nerve- 
fibres — for  example,  the  end  of  the  frog"s  sartorius — respond  to  direct 


538 


A  TEXTBOOK  OF  PHVSTO].OGY 


stimulation.  (2)  Muscle  Avill  contj-act  in  response  to  certain  chemical 
stimuli — e.g.,  ammonia — which  do  not  excite  nerve.  (3)  The  Sonth 
American  arrow-poison  curare  abolishes  the  action  of  nerve  by 
paralyzing  the  nerve-endings  in  the  muscles;  yet,  under  these  condi- 
tions, the  muscle  is  directly  excitable.  The  experiment  is  generally 
made  as  follows:  Both  the  sciatic  nerves  are  dissected  out  in  the 
thighs  of  a  frog  in  which  the  cerebral  hemispheres  have  been  destroyed. 


Fig.  271. — Diagram  to  show  the  Action  of  the  Helmholtz  Side-AVire. 


Round  one  thigh,  but  not  including  the  nerve,  a  ligature  is  tied. 
Curare  is  injected  into  the  dorsal  lymph  sac,  and  circulates  everywhere 
but  in  the  ligated  thigh.  The  upper  ends  of  both  sciatic  nerves  are 
certainly  exposed  to  the  action  of  the 'drug.  It  is  found  that  stimula- 
tion of  the  nerve -supply  to  the  ligated  side  j^roduces  a  contraction  of 
that  leg,  whereas  stimulation  of  the  nerve  to  the  other  leg  does  not. 
Direct  excitation  of  the  muscles,  however,  causes  a  response  in  both 
legs.     The  block  is  therefore  in  the  nerve-endings. 


CHAPTER  LXII 

THE  CONTRACTION  OF  MUSCLE 

The  great  property  of  muscle  is  its  power  of  craitractility.     When 
a  muscle  contracts — 

1.  It  undergoes  a  change  in  shape,  becoming;  -horter,  tenser,  and 
thicker. 

2.  It  becomes,  as  we  have  seen,  more  elastic  and  m<jre  extensile. 

3.  It  develops  heat. 

4.  It  undergoes  an  alteration  in  its  electrical  condition. 

5.  It  suffers  metabolic  changes,  which  alter  its  chemical  condition. 


Fkj.  272. — The  Ckank  Lever,  Muscle  Board,   and  stand. 


The  Change  in  Form. — The  change  in  form  of  a  muscle,  when  it 
contracts,  is  usually  registered  by  means  of  the  graphic  method.  The 
muscle  most  frequently  employed  for  this  purpose  is  the  gastroc- 
nemius muscle  of  the  frog.  Tne  muscle  is  connected  to  a  magnifying 
lever,  or  myograph.  It  maj'  either  be  pmned  out  on  a  board  in  a 
form  of  apparatus  resembling  Fig.  272,  or  it  may  be  clamped  in  the 
apparatus  shown  in  Fig.  273.  The  writing  lever,  which  should  be  as 
light  as  possible,  is  then  made  to  write  upon  a  smoked  drum,  or  kymo- 
graph.    In  order  to  study  the  time  occupied  l>y  the  contraction,  a 

539 


r>40 


A  TEXTBOOK   OK  1»H VSlOl.O(;Y 


time  tracing  is  simiiltaneously  recorded  on  tlie  drum.  Tills  may  be. 
done  either  with  a  tuning-fork  or.  better,  with  an  electro- magnet 
chronograph. 

When  working  with  single  induction  shoclis,  the  exact  point  at 
which  the  stimuhis  l.s  thrown  into  the  muscle  is  obtained  by  placing 


Fit..  21A. — The  Si.mple  Lever  with  Aftek-Loadixg  Screw. 
F,  Clamp;  L,  lever;  M,  muscle. 

the  kjniiograph  in  the  primary  circuit.  The  drum  carries  a  metal 
striker,  which,  as  the  drum  revolves,  strikes  against  a  piece  of  metal 
mounted  on  the  stand  of  the  drum  but  insulated  from  it.  One 
wire  is  attached  to  the  metal  stand  of  the  drum,  the  other  to  the 
insulated  metal.     The   current   in   the  primary   circuit   is  therefore 


Fig.  274. — Diaor.v.vi  of  the  Apparatcs  for  Recordixg  a  Sixgle  Mu.scular 

Contraction. 


rapidly   made    aad    broken    when    the  striker  hits   and  passes    the 
insulated  metal  (Fig.  274). 

In  recording  a  muscle  curve,  the  muscle  may  have  a  weight  directly 
pulling  on  it.     Th<-  muscle  is  then  said  to  be  '^  loaded."     If,  however. 


THE  CONTRACTION  OF  MUSCLE 


541 


the  weight  be  so  arranged  that  the  muscle  only  raises  it  during  its 
contraction,  it  is  then  said  to  be  '"  after-loaded."  When  the  resistance 
is  slight,  so  that  the  muscle  can  change  its  shape  during  contraction, 


Fig.  275. — A  Single  Muscular  Contractiox  {Frog'.s  Gastrocnemius). 

From  I  to  2  is  the  latent  period;  from  2  to  3,  the  period  of  shortening;  from  15  to  -i, 
the  period  of  relaxation.     Time  in  ,,^7^  seconds. 

the  curve  yielded  is  said  to  be  "  isotonic."  Its  length  alters,  but  the 
tension  remains  eqnal  throughout  the  contraction.  This  is  the  case 
when  the  contraction  is  I'egistered   by  such  forms   of  apparatus  as 


Fig.  27<>. 


Upper  curv 
nemius 

left 


-CoMPAKisux  OF  Contractions  of  Reu  and  White  Muscle  of  Rabbit, 
stimulated  indirectly.      (M.  S.  Pembrey.) 

;t'  is  response  of  the  red  soleus,  and  lower  c\irve  that  of  the  white  gastroc- 
L     Time  marker,  50  per  second.     The  tracing  to   be  read  from  right  to 


are  shown  in  Figs.  272.  273.  When  the  mu.scle  contracts  against  a 
lar^re  resistance,  I0  that  it  can  shorten  but  little,  the  recording  lever 
gives  an  "  isometric  "  curve.  The  muscle  in  these  conditions  remams 
of  approximately  the  same  length,  but  alters  in  tension. 


542  A  7  KXTBOOK  OF  PHYSIOLOGY 

The  length  of  tjuie  taken  by  a  single  contraction  or  twitch  varies 

greatly  with  the  kind  of  muscle  employed.     In  general,  the  response 

of  the   gastrocnemius    of    the    frog   occupies   about   one-tenth  of   a 

second  (Fig.  27'>).     The  following  table  gives  examples  of  the  time  of 

various  muscles 

Seconds. 
Tortoise:  Peetorali- major       ..  *.  ..  ..  1*8 


Semi-nsfmbranosus 

Frog  :  gastruf-neniius  . . 
Hyoglo-*sus  (tongue) 
Rectu«  abdominis 

Wing  muscle  of  w  asp    . . 
Wiug  mu.Mole  ot  honey-bee 
Win2  mu.'«'le  of  bumble-bee 


0-r, 

0-12 
0-2.'i 
0-17 

0-009 
0-005 
n-n04 


The  muscle  curve  may  be  divided  into  three  periods — the  latent 
period,  the  period  of  contraction,  and  the  period  of  relaxation.  In 
the  ordinary  grajjhic  curve  of  the  frog's  gastrocnemius  these  periods 
occupy  approximately  ,  i,^,  ^^^y,  and  j,^;„  of  a  second  respectively. 
In  such  a  curve,  the  length  of  the  latent  period  does  not  represent 
the  true  latent  period  of  the  muscle.  It  is,  in  reality,  much  too  long, 
and  is  due  largeh'  to  the  inertia  of  the  apparatus.  This  may  be  shown 
by  contrasting  the  graphic  curve,  in  which  the  muscle  pulls  upon 
the  writing  lever,  which  is  made  to  record  upon  a  smoked  surface, 
with  the  curve  obtained  when  a  muscle  is  excited,  and  its  change 
of  shape  recorded  photographically.  Under  these  latter  conditions, 
the  latent  period  is  but  (»-001  to  O-OO")  of  a  second.  This  latent  period 
is  probably  due  x>>  the  time  taken  by  the  impulse  to  reach  sufficient 
muscle  fibres  to  bring  about  a  change  in  the  shape  of  the  muscle. 

Although  in  the  graphic  curve  the  length  of  the  latent  period  is 
mainly  due  to  the  inertia  of  the  apjiaratus,  it  is  partly  due  to  another 
factor — namely,  that  the  contracting  muscle  is  more  extensile. 
With  delicate  recording  apparatus  it  can  be  shown  that  the  latent 
period,  represente<l  }>v  a  straight  line  in  the  ordinary-  muscle  curve, 

should  be  rvj -shaped,  owing  to  the  fact 
that,  as  the  muscle  starts  to  contract, 
it  becomes  more  extensile,  and  is 
stretched  somewhat  by  the-  recording 
lever;  thus  the  true  beginning  of  the 
AAAAAAAy^.i^i^A^v*~"v77~  period  of  contraction  is  as  a  rule  not 
'■ recorded. 


Fig.  277.— Cukves.  it  Arrested  When    the   muscle   is    "  indirecth-  " 

CosTRACTioNs    OF    UxLOADED   stimulated— that   is,  when    the  impulse 
MvscLE.     (Kaiser.,  .         ,,  x       j.-         •  i    x      ^i, 

causmg  the  contraction  is  sent    to  the 

muscle  through  the  nerve  supplying  it 
— the  time  taken  for  the  impulse  to  jiass  down  the  nerve  through  the 
nerve-endings  to  stimulate  sufficient  fibres  to  induce  contraction  adds 
considerably  to  the  latent  period  of  contraction.  For  this  reason, 
the  latent  period  of  direct  stimulation  of  a  muscle  is  shorter  than 
that  for  indirect  stimulation  of  the  same  muscle.     In  general,  it  may 


THE  COXTRACTION  OF  MUSCLE  543 

be  stated  that  the  shorter  the  whole  period  of  the  muscle  twitch,  the 
shorter  the  latent  period,  and  vice  versa. 

The  Period  of  Contraction  is  the  period  daring  which  the  mnscle 
shortens  until  the  maximum  shortening  is  reached.     It  is  the  period 


Fig.  278. — Vekatrix  Curve.     (Waller.) 

of  rising  energy.  In  graphic  curves,  this  is  represented  as  too  long, 
sirice  the  recordmg  lever  owing  to  inertia  tends  to  rise  too  high. 
This  can  be  demonstrated  by  arresting  the  lever  at  different  heights 
during  the   process  of   contraction.     At    a  certain  point   before  the 


Fig.  279. — The  Effect  of  Temper.\tube  upon  the  Contraction  of  the 
Gastrocnemius  Muscle.     (Pembrey  and  Phillips.) 

The  time  is  marked  in  ^Jo  second.      The  tracing  should  be  read  from  right  (u  kft. 
Figmres  on  curve  are  the  temperatures  of  the  salt  solution. 

summit  of  the  curve  is  reached  it  will  be  found  that  the  lever  as 
soon  as  it  touches  the  arresting  body,  immediately  starts  to  fall. 
That  point  marks  the  true  height  of  the  contraction  (Fig.  277). 

Tne  difference   in   the  contraction  time  of  different   muscles   is 
mainly  due  to  difference  m  anatomical  structure.     The  quickly  con- 


544  A  TKXTBOOK   OF  PHVSIOIJKJY 

Iracting  nm.scles  are  those  rich  in  sarcostvlcs,  the  slowly  contracting 
muscles  those  containing  abundant  sarcoplasm ;  many  muscles  are 
mixed.     It  has  been  suggested  that,  when  the  number  of  sarcostyles 


I'lG.  280. 

The  npper  curves  show  the  latent  period  and  movements  of  two  levers  on  muscle 
at  15°  C,  the  lower  curves  at  r>°  C.  It  will  be  seen  that  the  latent  period  is 
shorter  at  15°  C.  than  at  5°  C,  also  that  the  rate  of  conduction  given  by  the  dif- 
ference in  the  latent  periods  is  quicker  at  15°  C.  than  at  5°  C.     (V.  J.  Woolley.) 

are  not  greatly  in  excess  of  the  amount  of  sarcoplasm,  the  muscle 
curve  may  show  two  summits — the  first  due  to  contraction  of  the 
sarcostyles,  the  second  due  to  contraction  of  the  sarcoplasm.     This  is 


Fig.  281. — The  Effect  of  Load  upon  the  Contraction  of  the  Gastrocnemius 
Muscle.     (A.  P.  Beddard.) 

the  explanation  sometimes  afforded  of  the  curve  given  by  the  vera- 
ti'inized  muscle  (Fig.  278).  It  is  also  suggested  that  the  slow  response 
of  a  fatigued  muscle  may  be  a  response  of  the  sarcoplasm  after  the 
quickly  responding  sarcostyles  have  ceased  to  respond.     For  example, 


THE  COXTR ACTION  OF  MUSCLE  545 

in  a  fresh  state,  the  triceps  femoris  of  the  rabbit  gives  a  quick  response; 
when  fatigued,  it  yields  a  long-drawn-out  curve. 

The  Period  of  Relaxation  is  from  the  maximum  shortening  of  the 
muscle  to  the  position  of  rest.  The  relaxation  has  been  thought  to 
be  due  to  an  active  process,  but  there  is  little  evidence  of  this  beyond 
•  the  fact  that  there  ar^  special  changes  going  on  diu'ing  it  (see  p.  554). 

The   Conditions   which   affect   Muscular   Contraction. — Beside  the 

■constitution  of  the  muscle  and  the  effect  of  drugs,  such  as  veratrine, 
the  muscle  response  is  affected  by  other  conditions,  such  as  the  strength 
of  stimulus,  the  temperature,  the  amoinit  of  load,  and  previous  activity. 
The  Strength  of  Stimulus. — Striated  muscle  gives  a  graduated 
response  according  to  the  strength  of  stimulus.  With  a  weak  (minimal) 
stimulus,  it  just  contracts.  The  contraction  then  increases  in  amount 
with  the  strength  of  stimulus  until  a  maximal  contraction  is  obtained, 
after  which  no  increased  contraction  is  obtained,  however  much  the 
current   be   strengthened.     The   minimal   contraction   is   due   to   the 


FlJ.  282i^-^OXTI>"UATION    OF   THE    EXPERIMENT   IN    Fli.   231.       SiNGLE   COXTEACTIOXS 
'of  THE  G.\.STROCNEMIFS  WITH  DIFFERENT  LoADS.       (A.  P.  Bcddaid.) 

The  figures  on  the  curves  represent  the  veights  in  grammes  hung  at  the  axis  of  the 
lever;  actual  load  on  muscle  \va,s  in  each  case  one-fifth.  Magnification,  o. 
Tcmg,erature,  12"  C. 

weak  stimulus  only  spreading  to  a  few  fibres.  Probably  any  stimulus 
which  is^ft'ectupl  makes  the  fibres  affected  contract  maximally. 

Temperature. — Cold  (0"  to  3^  C'.)  lengthens  the  whole  curve,  especi- 
ally the  latent  period  and  the  period  of  contraction.  The  rate  of  con- 
fluction  is  also  lessened  by  cold  (Fig.  280).  Frequently  the  relaxation 
is  incomplete.  shoAving  a  "  contraction  i-eniainder."  At  first  the  height 
of  the  contraction  is  increased,  then  dimmished.  Gentle  warmth 
(25^  to  35°  C.)  increases  the  rate  of  all  stages  of  the  curve,  and  greatly 
increases  its  height  ])artly  due  to  an  ineitia  effect  of  the  lever  (Fig.  270). 
Heat  (42°  C.  in  the  frog)  coagulates  the  muscle  proteins,  and  brings 
about  a  condition  of  "  heat  rigor." 

Load. — An  increase  in  load  is  found  generally  to  decrease  the 
amount  of  contraction,  and  lengthen  the  latent  period  (Figs.  281.  282). 
When,  however,  a  muscle  is  fresh  and  in  good  condition,  the  first 
few  increments  of  load  may  give  an  increased  height  to  the  contraction. 
When  the  work  done  bj-  the  muscle  is  calculated — 

Work  done  ^  load  lifted  x  height 


o4G  A  TEXTBOOK  OF  PHYSIOLOGY 

— it  will  te  found  that  the  amount  of  work  done  at  first  increases 
with  the  load,  and  then  diminishes,  giving  a  "  curve  of  load."  The 
actual  height  through  which  the  weight  is  lifted  is  obtained  ])v  dividing 


Fig.  283. — Fatigue:   Fkog's  Gastrocne.mits.     (\\'alkn.) 

Direct  excitation;  125  successive  maximal  contractions  at  intervals  of  li  seconds,, 
showing  at  the  outset  increase  of  height  and  of  duration,  later  (kcrca^:ng  height. 
The  exhaustion  has  not  been  pushed  to  the  end. 

the  height  of  the  curve  by  the  magnification  due  to  the  recording 
lever.  For  purposes  of  "  load  "  experiment,  it  is  better  to  use  the 
form  of  apparatus  shown  in  Fig.  ^73,  since  the  load  can  then  be 
applied  directly  below  the  muscle. 


Fig.  i;S4. — Fatiguk  Cukves  uf  B,  Saktokius  Muscle  in  Kikgek's  .S(iectio>^; 
G,  Sartorius  after  FiFTESN-MiNurE  Immersion  ik  Guanidik  0*1  per  Cent. 
SoLUTUix.     (Camis.) 

Tin.e  in  seconds.     The  staircase  effect  is  seen  and  also  tlie  depressant  effect  of  guanidin 

in  high  concentrations. 

Previous  Activity. — When  curves  are  taken  from  a  j^erfectly  fresh 
muscle  preijaration,  the  first  few  may  show  an  improvement  in  the 
degree  of  contraction.     This  is  known  as  the  ''  staircase  effect,"  and 


THE  CONTRACTION  OF  MUSCLE 


54' 


it  is  suggested  that  it  is  due  to  the  beneficial  action  of  the  meta- 
bolites formed  in  the  previous  contractions.  When  the  contractions 
are  made  to  follow  each  other  without  any  pause  they  finallj'  become 
less  and  less,  and  the  relaxations  become  more  and  more  draAm  out, 
a  well-marked  "'  contraction  remainder  ''  usuall}'  aijpearing,  until 
eventually  the  muscle  gives  no  contraction  at  all;  the  muscle  is 
"  fatigued  "  (Figs.  283.  284). 

■■  Fatigue  "  is  due  mainly  to  the  accumulation  of  the  products  of 
acti\aty  within  the  muscle — in  part,  however,  to  the  usmg  up  of  food 
material.  The  fatigue  products  are  acid  in  nature — chiefly  lactic 
acid.  Fatigued  mu.^cles  j^laced  in  oxygen  recover  more  quickly 
(Fig.  285).  If  the  muscles  be  made  to  conti-act  in  an  atmo.sphere  of 
oxygen,  lactic  acid  does  not  appear,  and  the  onset  of  fatigue  is  much 
dela3"ed  or  postponed  altogether.     Recent  evidence  tends  to  show  that 


B^ 

CO/VT-/fAC 

k 

A        ■ 

-^ 

/PCL  finA'^ 

^rre/f  £Arc/s/o/v 


I? 


15 


»8 


21 


?+ 


Fi(;.  28.5. — Changes  ix  Length  of  a  Pair  of  Excised  Gastkocnemii  aftei;  Fatigue. 

(W.  M.  Fletcher.) 

.1.  Exposed  to  oxygen;  B.  exposed  to  air.  Load  3  grammes,  temperature  Iir  ('.  The 
ordinates  are  measured  directly  from  the  record;  levers  magnified  six  and  a  half 
times. 


27 


lactic  acid  is  not  normaily  a  waste  product,  but  a  stage  in  the  metabolic 
changes  of  the  muscle.  A  muscle  through  which  the  blood  is  cir- 
ctdating  is  fatigued  only  when  either  the  load,  or  the  frequency  of 
contraction  is  made  too  great.  Thus  the  muscles  of  the  skilled  Avork- 
man  perform  thousands  of  contractions  without  fatigue.  So  with  the 
respiratory  muscles  and  the  heart.  To  secm"e  the  maximum  output 
of  athletes  or  workers,  load  and  frequency  must  be  carefully  adjusted 
to  prevent  overstrain. 

Summation. — If  a  muscle  be  given  two  stimuli  m  quick  succession, 
the  effects  of  the  two  are  added  together — "  summated  "' — and  a 
bigger  curve  is  obtained  than  either  of  the  single  curves  would  have 
been  if  recorded  .separately  (Fig.  286).  If,  however,  the  interval 
between  the  stimuli  be  very  short,  so  that  the  second  stimulus  falls 
within  the  latent  period  of  the  first  stimulus,  then,  if  this  be  maximal, 
no   summation   is   obtained,    the   curve  is  unaffected   by  the  second 


54S 


A  TEXTBOOK  OF  PHYSIOLOGY 


stimulus.  Jf,  however,  the  first  stiniuhis  is  not  producing  a  maximal 
contraction,  then  the  second  stimulus  will  add  itself  to  the  first,  and 
again  a  greater  effe3t  is  obtained  than  would  have  obtained  by  either 
-separately. 


Flu.  286. — SuPEKPOsiTiON  OF  Two  Single  Coxtkactioxs. 

ISach  contraction  is  recorded  alone  by  a  break  shock  caused  by  opening  a  fixed  key: 
both  keys  are  then  set,  and  the  recording  plate  striking  them  open  successivelj-. 
causes  two  stimuli  and  a  summation  of  the  two  contiaction.". 


F.m.  287. — CoMFOsiTioj.  of  Tetanus.     (Waller.) 

Stimuli  caused  by  a  spring  interrupting  a  primary  circuit  by  vibrating  in  and  out  of 
a  mercury  cuj);  the  vibration  frequency  is  increased  by  shortening  the  spring. 


THE  CONTRACTION  OF  ilUSCLE 


rAif 


Fig.  288. 

To  be  read  from  right  to  left.  Photographic  curve  of  sartorius  muscle  by  isometric 
method.  At  first  two  submaximal  stimuh,  followed  by  two  pairs  of  maximal 
stimuli,  then  by  a  tetanus,  followed  by  another  pair  of  single  responses.  The 
tension  set  up  in  the  mufcle  during  tettni:s  is  greater  thfn  the  maximal  tension, 
of  a  single  twitch.     [0.  R.  Mines.) 


ikX. 


[-^S:xU 


^.^Lauu^ 


Fig.  289. — Spontaneous  Movements  in  Toad's  Sartokivs  in  7  pee  Cent.  Sodiusi 
Chloride.     (G.  R.  Mines.) 


Temperature  8°  C.     Time  in  seconds. 


A 


•  1  ■  \  •  i 


Fig.  290.— Biceps  Cruris  of  Frog  in  Sodiu.m  Chloride  0*65  peu  Cent.,  Potassium 
Chloride  0*05  per  Cent.     (G.  R.  Mines.) 

A  period  of  one  second  is  marked  below. 


550  A  TPLXTBOOK  OK  PHYSIOLOUV 

Owiiig  to  this  ))roperty  of  summation,  a  iiinnber  of  successive 
stimuli  may  cause  a  number  of  contractions  l>et\\x-en  Avhich  the 
muscle  does  not  properly  relax.  The  greater  the  fre({uency  of  the 
stimuli,  the  less  the  relaxation  between  each  contraction,  until  at  last 
a  long,  fused,  compound  curve  is  obtained,  known  as  the  "  complete 
tetanic  curve."  Tetanus  is  produced  by„  about  30  to  50  stimuli 
per  second  in  the  case  of  frog's  striated  muscle.  The  number  varies 
Avith  the  tem})erature  and  the  state  of  the  muscle.  When  Avarmed. 
more  stimuli  are  required;  when  cooled,  less  are  needed.  If  the 
muscle  be  fatigued,  fewer  stimuli  are  required  to  induce  the  complete 
tetanic  contraction. 


LLiliiUiiJlU 

X    X  V    X    X    ^  X 


nMIMIglilBIHiUlSHli 


J,     -,     -, 

r 

Kci  OS-/, 


Fig.  291. — Sakturius  of  Frog,  sumulated  ALTEKNATiLY  \mth  »jalvaxic  Current 
AND  IndtjctiOjST  Shock  at  Thirty-Second  Intervals.     (G.  R.  Mines.) 

Each  response  to  an  induction  shock  is  marked  with  a  cross.  At  the  beginning  of 
tracing  the  muscle  was  in  NaCl  0*7  per  cent.  ;  at  arrow  fluid  was  changed  to 
NaCl  0-65  per  cent.,  KCl  O'OS  per  cent. 

The  genesis  of  tetanus  is  studied  by  employing  the  vibrating  reed. 
By  varying  the  length  of  the  reed,  the  number  of  stimuli  per  second 
is  easil}'  regulated,  and  all  forms  of  incomplete  to  complete  tetanus 
may  be  obtained  (Fig.  237).  Incomplete  tetanus  is  sometimes  termed 
"  clonus."  Ankle  clonus  may  be  elicited  in  certain  nervous  conditions 
Avhen  the  foot  is  suddenly  bent  up. 

PoAverful  alternating  currents,  A'ibrating  frequently  to  and  fro 
in  opposite  directions — e.g.,  1,000,000  per  second — may  be  passed 
through  muscle  Avithout  producing  excitation,  and  with  suitable 
apparatus,  such  a  current  may  be  sent  through  several  peojole  and 
electric  lamps.     The  foriUer  feel  nothing,  Avhile  the  lamps  gloAv. 


THE  CONTRACTION  OF  MUSCLE 


551 


Muscular  ""  Tone."' — During  life,  the  muscles,  never  fully  relaxed, 
are  kept  in  a  state  of  incipient  conti-action.  or  '"  tonus  '" — a  condition 
dependent  upon  their  connection  with  the  central  nervous  system. 
The  muscles  are  ceaselessly  influenced  by  their  nervous  centres,  whit-la 
ill  turn  are  excited  b}'  messages  reachuig  them  from  all  parts  of  the 
body,  particularly  the  skin,  joints,  and  the  muscles  themselves. 

This  tonus  makes  for  a  general  "  wakefulness  " — a  readiness  to 
contract — on  the  part  of  the  muscle.  It  also  plays  a  considerable 
part  in  the  production  of  heat  within  the  body,  being  reflexly  in- 
creased by  sensations  of  cold,  and  relaxed  bj'  sensations  of  warmth. 
It  is  also  affected  by  mental  states,  such  as  excitement,  anger,  fear. 


X      X     X       X     X      X      X     X      X 


'7Z  \[C'(Uo^y,    t  /^-ar/       t  K-  ^X  -'^y-     t  Na  CI '77. 


Fig;.  292. — Saktokius  of  Frog,  stimulated  at  Intervals  of  Thirty  .:>econu!s 
Alternately  with  Galvanic  Current  and  Induction  Shocks  at  x  .  (G.  R. 
Mines.) 


Spontaneous  Movements. — Amphibian  muscles  in  saline  solutions 
exhibit  sjjontaneous  movements  (Fig.  2S9).  These  movements  will 
continue  in  concentrated  curare  solution,  indicating  that  the  source 
of  the  movements  lies  in  the  contractile  substance  of  the  muscle 
fibres.  This  is  also  proved  by  experiments  on  muscle  containing  no 
nerve  endings,  e.g.,  the  non -neural  regions  of  the  sartorius  muscle. 
Potassium  chloride  at  first  increases  the  movements,  often  causing  a 
very  rapid  rhythm  (Fig.  280),  and  then  stops  them  entirely.  Its  effect 
on  the  excitability  of  the  muscle  tOAvards  galvanic  currents  of  long 
duration,  m  hich  is  increased  m  this  condition  of  the  muscle,  is  a  further 
exaltation  and  then  depression  (Fig.  291).  The  addition  of  calcium 
chloride  leads  to  an  immediate  diminiition  or  cessation  of  the  move- 
ments and  a  fall  in  the  excitabilitv  towards  galvanic  currents  (Fig  292). 


CHAi'TKR  Lxnr 

THE  PRODUCTION   OF  THERMAL  AND  CHEMICAL  CHANGES 

IN  MUSCLE 

That  muscular  exercise i)roduce.s  warmth  is  a  familiar  observation. 
For  this  reason,  hard  muscular  exercise  is  uncongenial  on  a  ver\'  hot 
day,  but  is  resorted  to  when  the  temperature  is  low,  since,  under 
these  conditions,  even  the  habitual  loafer  is  often  constrained  to 
beat  his  arms  across  his  chest  or  stamp  violently  to  keep  his  feet 
warm.  It  is  somewhat  difficult  to  show  by  means  of  the  mercurial 
thermometer  the  development  of  heat  during  the  contraction  of  the 
excised  muscle,  even  when  a  very  sensitive  thermometer  is  inserted 
between  the  mviscles  of  the  thigh,  and  the  sciatic  plexus  stimulated. 
It  has  been  calculated  that  during  a  tetanus  of  two  to  three  minutes^^ 
duration  the  temperature  of  a  frog's  muscle  rises  on  an  average- 
about  0  ir/^  C. 


If  Couples. 


Fig.  2!);?.— SixOLE-PAiR  Thermopile  connected  to  Galvanometep.. 

The  production  of  heat  can  not  only  be  shown  but  measured  hy 
means  of  a  thermopile.  If  a  thermopile  (Fig.  293)  be  placed  between 
the  calf  muscles  of  a  resting  limb  of  a  frog,  and  another  between  the- 
calf  muscles  of  a  limb  which  is  made  to  contract,  and  the  two  thermo- 
piles be  then  connected  with  a  galvanometei .  it  will  be  found  that 
contraction  liberates  sufficient  heat  to  cause  a  deflection  of  the  gal- 
vanometer needle.  When  both  sets  of  muscles  are  at  rest,  no  de- 
flection takes  place.  For  accurate  work,  special  forms  of  apparatus 
are  used  (Fig.  294). 

The  muscle  fibre  has  been  regarded  as  a  heat  engine.  It  has  been 
suggested  that  the  contraction  is  produced  by  the  production  of  heat 
in  the  locality  of  the  fibril,  which  contracts  under  the  influence  of  heat. 
Such  a  conception  is  erroneous.  The  muscle  is  rather  to  be  regarded 
as  a  chemical  machine  Avorking  at  constant  temperature.  It  has  been 
calculated  that  to  behave  as  a  heat  machine  it  would  be  necessary  to 
keep  up  a  temperature  difference  of  10(V  C.  at  two  points  not  more- 


THERMAL  AND  CHEMICAL  CHANGES  IN  I^IUSCLE      553 

than  a  few  t^i  apart.  This  would  mean  an  almost  infinite  loss  of 
heat  by  conduction  between  the  two  points.  It  is  inconceivable  that 
such  differences  of  temperature  exist.  It  has  been  shown,  moreover, 
that  the  heat  is  not  formed  solely  during  the  period  of  contraction  of 
the  muscle.  It  is  formed  both  during  the  contraction  and  during  the 
relaxation  (Fig.  295).  There  is,  moreover,  no  constant  ratio  between 
the  amount  of  work  done  and  the  amount  of  heat  evolved.  High, 
initial  tension  and  strong  excitation  favour  the  production  of  heat. 


Fia.  294. — Double  TutRMoriLE,  Each  of  a  Pair  of  Sartorii  being  in  Contact 
WITH  One  Set  of  Junctions.     (A.  V.  Hill.) 

,-l,  .1.  Junctions  of  iron  and  constantan  in  contact  with  front  sartorius,  M;  B,  B, 
junctions  in  contact  with  rear  sartorius,  M' ;  K  is  bone  of  pelvis  held  by  clamp, 
I)  ;  G,  copper  leads  to  galvanometer:  E.  electrodes — only  two  out  of  four  shown. 
Arrow  shows  direction  of  current.  Only  six  instead  of  twenty-four  to  thirty 
junctions  shown. 

An  isolated  frog's  muscle  at  15-5°  C.  continues  for  about  five  houra 
to  carry  on  the  normal  oxidative  processes  of  life,  but  at  a  declining 
rate.  This  is  due  to  the  gradual  exhaustion  of  the  oxygen  supply, 
and  to  the  gradual  accumulation  of  waste  products  other  than  CO.j. 
Possibly,  also,  the  supply  of  oxidizable  material  becomes  exhausted. 

The  initial  process  of  contraction  consists  largeh*,  if  not  entirely, 
of  the  liberation  of  potential  energy,  which  is  manifested  as  "  tension 
energ}^  "  in  the  excited  muscle.  This  potential  energy'  is  capable  of 
l^eing  used  indifferently  for  the  accomplishment  of  -^Aork  or  the  pro- 
duction of  heat.  The  efficiency  of  the  whole  of  the  processes,  in- 
cluding those  of  recovery,  is  sometimes  as  high  as  50  per  cent. — that 


554 


A  TEXTBOOK  OK   I-HNSIOLOOV 


is  to  say,  50  per  cent,  of  the  energy  of  the  foodstuffs  katabolized  may 
appear  as  Avork,  an  efficiency  much  greater  than  that  of  a  steam 
engine  (10  per  cent.),  and  greater  even  than  the  best  petrol  engine 
(30  per  cent.).*  In  the  muscle  machine,  the  "  free  energy  "  which  is  ti> 
become  mechanical  or  thermal  energy  is  stored  in  certain  unstable 
chemical  compounds,  one  of  which  is  possibly  the  lactic  acid  precursor. 
During  the  preliminary  stage  of  the  contractile  process,  certain 
molecules  are  liberated  in  the  muscle  under  the  iuHiience  of  oxygen 


/00  7 

fo 


Fig.  295. — Galvanometer  Deflection  showing  Fall  of  Temperatuf.e  of  Muscle 
.^TTEE  Excitation  in  Nitrogen,  in  Oxygen,  and  Warmed  when  Dead  as 
Control.     (A.  V.  Hill.) 

The  curve  for  living  muscle  in  nitrogen  nearly  coincides  with  control  curve,  but  the 
curve  for  living  muscle  in  oxygen  after  nitrogen  is  very  considerably  displaced 
to  the  right,  showing  continued  heat  ])roduction  during  relaxation  of  the  muscle. 

and  with  the  production  of  heat — for  example,  lactic  acid  from  its 
unstable  precursor.  Tnese  produce  "  tension  energy,"  occasion 
the  contraction,  and  are  then,  under  the  further  action  of  oxygen 
during  the  relaxation,  removed  or  re^ilaced  in  the  muscle  substance 
complex  with  the  evolution  of  heat.  It  is  conceived,  therefore,  that 
heat  is  developed  in  three  stages:  (1)  During  process  jDreliminary  to 
contraction;  (2)  during  contraction;  (3)  during  relaxation. 

The  Mechanism  of  Muscular  Activity  is  by  no  means  clear.     As  we 
have   seen,  the   application    of   the   laws   of  the  thermodynamics  to 

*  The  efficiency  of  a  labourer  seems  to  be  20-25  per  cent. 


THER:MAL  and  chemical  changes  IX  MUSCLE      555 

muscular  contraction  has  afforded  valuable  information.  The  pheno- 
menon of  contraction  has  also  been  studied  fro]n  the  point  of  vieAv  of 
the  osmotic  properties  of  the  muscle. 

It  has  been  suggested,  after  due  consideration  of  the  time  relations 
of  the  contraction  and  the  distance  in  the  fibril  through  which  osmotic 
force  has  to  act.  that  muscular  contraction  may  be  brought  about 
by  this  force.  Provisionally,  we  may  suppose  that  lactic  acid  is  set 
free,  and  that  combmes  Avith  protein  to  form  a  salt,  with  a  conse- 
quent rise  of  osmotic  pressure  in  the  dim  bands  of  the  muscle  fibrils, 
which  therefore  swell  at  the  expense  of  the  water  in  the  light  bands. 
Granting  that  this  may  be  so,  Ave  do  not  knoAV  hoAv  the  osmotic  equi- 
librium is  upset  by  the  stimulus  or  restored  during  ielrixation. 

The  Changes  in  the  Chemistry  of  Muscle — 1.  The  Chemical  Con- 
stitution of  Muscle. — If  muscle  be  taken  from  an  animal  and  minced, 
and  then  squeezed,  a  plasma  can  be  expressed  horn  it.  This,  like 
blood,  possesses  the  propertA'  of  coagulating  at  body  temperatuTe 
under  suitable  conditions. 

Upon  analysis,  it  contains  from  75  to  78  per  cent,  of  Avater,  20  to 
24  per  cent,  of  organic  and  about  1  to  2  per  cent,  of  inorganic  bodies. 
The  chief  organic  bodies  are  the  proteins,  of  Avhich  there  are  from 
18  to  20  per  cent.  Various  classifications  and  names  have  been  given 
to  these  proteins.  Avhich  apparently  A^ary  in  their  properties  according 
to  their  method  of  jweparation,  the  species  of  animal  used  (mammals, 
birds,  reptilia,  etc.),  the  condition  of  the  muscle  at  the  time  of  death, 
and  the  degree  of  post-mortem  changes.  To  illustrate  the  chaos 
which  perrades  the  nomenclature  of  these  proteins,  it  may  be  men- 
tioned that  the  name  ''  myosin  "  has  been  given  by  different  in- 
A'estigators  to  at  least  three  different  bodies. 

Tne  most  generally  accepted  classification  of  these  proteins  is 
into — (I)  Myosin,  or  paramyosinogen,  Avhich  forms  about  one-fifth; 
and  (2)  myogen,  or  myosinogen,  Avhich  forms  the  other  four-fifths 
Traces  of  albumin  and  globulin  are  also  present,  but  these  probably 
come  from  the  blood  and  lymph,  and  not  from  the  muscle  proper. 

In  the  plasma  of  ""  red  "  muscles  the  colouring  matter  is  also  present. 
This  consists  of  haemoglobin  or  a  closely  allied  conipound  protein — 
myohgematin. 

Myosin,  ov  paramyosinogen,  is  a  globulin  soluble  in  dilute  salt 
solutions  Avhich  coagulates  on  heating  al  about  45°  to  50""  C.  It  is 
pi'ecipitated  by  AAcak  acids,  dialysis,  half-saturation  Avith  ammonium 
sulphate,  etc..  and  gives  the  other  reactions  characteristic  of  globulins 
(see  p.  51 ).  It  is  characterized  by  its  power  of  passing  at  body  tempera- 
ture— probably  under  the  influence  of  an  enzyme  derived  from  the 
muscle — directly  into  an  insoluble  modification  known  as  myosin  fibrin. 

Myosin 
(by  eiizymic  action) 

t 

MVOSI.N    I-ICKIN. 


^^).">f5  A  TEXTBOOK  OF  PHY8IOLO(;V 

Myogen,  or  myosinogen,  on  tlio  other  hand,  is  an  albuniin.  It 
gives  the  characteristic  reactions  for  such,  and  is  therefore  not  [,re- 
ci])itated  by  dialysis,  and  only  by  com])lete  saturation  with  ammonium 
sulphate.  Its  heat  coagulation  tem]:!erature  is  from  55°  to  60°  C. 
Unlike  myosin,  it  is  ap]iarently  not  coagulated  at  body  temperature 
by  an  enzyme,  but  passes  without  such  assistance  somewhat  slowly 
into  a  variety  known  as  sohible  myogen  fibrin,  which  is  coagulated 
by  heating  to  l)ody  temperature  (37  to  40°  C.)  into  insolu])le  mj'ogen 
fibrin. 

Myogex 


•Soluble  .Myogex  J'ibrix 
(I)v  heat  at  37 '-40°  C.) 

Insoicble  Mvooex  J-'ibrix. 

In  the  residue  left  after  the  exjiression  of  muscle  jjlasma  there  is 
a  protein  which  has  been  termerl  myostromin.  This  is  of  the  nature  of 
a  nuclein.  This,  together  with  some  sclero-protein,  the  collagen  of 
the  fibrous  tissue,  probably  forms  the  framework  of  the  fibres.  The 
sclero-protein  collagen  yields  gelatin  on  boiling.  Xucleo-protein  is 
also  present  in  the  nuclei.  A  certain  amount  of  fat  is  present,  either 
in  the  fibre  itself  or  in  the  interstices  of  the  framework. 

Other  bodies  separable  from  the  plasma  comprise — 

Fats  in  small  amounts. 

Glycogen  in  variable  amounts,  varjdng  with  the  "  freshness  "  of 
the  muscle,  its  state  of  "  activity  "'  or  "  rest."  Generally,  it  is  from 
0-5  to  1  per  cent.  It  is  present  also  in  larger  amounts  in  embryonic 
than  in  adult  muscles. 

Dextrose  in  traces  only  if  the  muscle  be  absolutely  fresh. 

Inosit,  CgHg(OH)^  +  H.,0,  a  benzene  compound  having  approxi- 
mately the  same  formula  as  dextrose,  and  sometimes  termed  musclfr 
sugar.  It  does  not  give  the  ordinar}-  tests  for  sugar,  is  not  fermented 
b}'  yeast,  and  is  without  action  upon  polarized  light. 

Sarcolactic  Acid,  CgHgOg,  an  isomer  of  the  lactic  acid  formed  by 
the  fermentation  of  the  lactose  of  milk.  It  is  present  only  in  fatigued 
or  dying  muscle. 

Nitrogenovs  Extractives,  the  chief  of  which  are  creatin  (sec  p.  461); 
hypoxanthin,  and  xanthm  (see  p.  444). 

It  is  claimed  that  there  is  also  present  a  complicated  nitrogenous 
body  known  as  Phosphocarnic  Acid.  It  yields  as  cleavage  products 
succinic  acid,  lactic  acid,  phosphoric  acid,  C0.>,  a  carbohydrate  body, 
and  a  body  known  as  carnic  acid. 

Inorganic  Salts. — The  chief  of  these  is  the  jiotassium  phosjihates. 
Traces  only  of  chlorides  and  sulphates  are  found.  In  addition,  salts 
of  sodium,  magnesium,  calcium,  and  iron,  are  found,  their  relative 
amounts  corresponding  to  the  order  given. 


THERMAL  AND  CHEjMICAL  CHANGES  IX  :\njSCLE     557 

2.  The  Chemical  Changes  induced  by  Activity. — The  methods  used 
for  investigating  tissue  respiration  shoAV  that  an  increased  amount  of 
oxygen  is  used  up,  and  more  CO.,  formed,  when  muscle  is  contracting 
than  when  at  rest.  If  the  hind-limb  of  a  frog  be  tetanized,  it  will  be 
found  the  plasma  expressed  from  the  muscles  gives  the  colour  reactions 
for  lactic  acid.  The  muscles  of  the  resting  limb  give  no  such  reactions. 
If  the  limb  be  made  to  contract  in  an  atmosphere  of  oxygen,  no 
lactic  acid  is  formed,  for  it  is  only  when  the  muscle  is  made  to  con- 
tract with  an  msuflficient  supply  of  oxygen  that  this  acid  is  formed. 
Such  is  the  case  in  man  during  excessive  muscular  exercise.  The 
lactic  acid  then  formed  can  be  shown  in  the  urme  and  in  the  sweat. 
In  the  blood  it  plays  an  important  part  in  the  production  of  the 
<l\spnoea  attendant  upon  such  exercise. 

It  has  been  suggested  that  lactic  acid  might  come  from  muscle 
protein  or  from  the  complicated  body  known  as  ""  jjhosphocarnic  acid." 
However,  researches  into  the  amount  of  nitrogen  and  sulphur  excreted 
in  the  urine  at  rest  and  after  muscular  exercise  tend  to  show  that  the 
protein  metabolism  is  not  greatly  affected  by  nniscular  exercise — 
certainly  not  in  sufficient  amount  to  account  for  the  lactic  acid 
formation. 

Dextrose  is  apparently  the  chief  source  of  the  lactic  acid. 

C,H3.,0,=  2C3HA 

Dextrose      Lactic  acid 

When  ample  oxygen  is  present.  COo  and  Avater  arc  formed  as  the 
A\aste  products  of  contraction  and  any  lactic  acid  that  appears  in 
the  process  is  rebuilt  into  the  muscle  substance. 

CgHj.,(),;  +  6(  ).,=  6C0._-  +  6H0O. 

The  exact  significance  of  the  cre:itin  and  hypoxanthm  present  in 
juuscle  is  not  known.  Tney  do  not  appear  to  be  waste  products.  It 
is  i^ossible  that  the  muscle  may  perform  some  of  its  Avork  at  the  expense 
of  these  bodies,  especially  the  hypoxanthin,  since  muscular  exercise 
after  a  delay  is  followed  by  an  increased  excretion  of  uric  acid  in  the 
urine.  Further,  meat  extiacts  have  a  restorative  effect  upon  muscle 
tone. 

3.  Rigor  Mortis. — When  a  muscle  dies,  either  as  a  result  of  its 
removal  from  the  body  or  by  reason  of  general  bodily  death,  it 
(1)  loses  its  transparency,  and  becomes  opaque:  (2)  shortens:  (3) 
develops  an  acid  reaction,  and  evolve>  carbon  dioxide:  (4)  passes  from 
a  semifluid  to  a  firm,  solid  state,  or  rigor. 

After  death,  this  rigor  supervenes  in  a  more  or  less  definite  order — 
first  the  jaws,  then  neck,  trunk,  upper  and  lower  limbs.  The  rate 
of  onset  varies.  Generally,  several  hours  elapse;  but  if  just  previous 
to  death  the  muscles  have  been  greatly  fatigued,  paiticularly  in  the 
absence  of  oxygen,  the  changes  may  set  in  at  once.  Soldiers  are  said 
to  have  been  found  standing  dead  in  the  trenches,  with  the  rifle  held 
to  the  shoulder,  probably  due  to  .shell-bm'st  and  oxygen  deprivation 
t)y  carbon  monoxide.     After  a  time — generally  two  to  six  days — this 


558  A  TEXTBOOK  OF  PHYSIOLOCV 

rigidity  passes  off.  [u  wasting  diseases,  rigor  may  not  appear  at  all. 
or  appear  early  and  pass  off  quickly. 

Rigor  is  maitily  due  to  the  formation  of  lactic  acid  in  the  absence 
of  oxygen.  The  lactic  acid  thus  formed  alters  the  normal  reaction  of 
the  nmscle,  and  brings  about  coagulation  of  the  muscle  proteins.  If 
the  accumulation  of  lactic  acid  be  prevented,  either  l)y  the  presence 
of  oxygen  or  l)y  perfusion  of  the  muscle  with  saline,  rigor  does  not 
supervene. 

Rigor  may  also  be  induced  in  muscles  by  ])lunging  into  boiling 
water.  In  this  case,  "'  heat  rigor  ""  takes  place.  The  proteins  of  the 
muscles  are  coagulated  without  any  attendant  chemical  changes,  such 
as  acid  formation.  Similarly,  soaking  in  distilled  water  brings  about 
a  "water  rigor."  A  water  pressure  of  400  atmospheres  produces 
rigor  of  the  muscles  of  terrestrial  and  shallow-water  animal;;. 

Smooth  Muscle. — Although  smooth  muscle  is  generally  found  in 
organs  which  [lerform  slow  movements,  in  some  animals  noted  for 
quickness  and  grace,  such  as  the  squid,  there  exists  nothing  but  smooth 
muscle.  In  the  higher  animals  it  gives  motility  to  organs  over 
which  there  is  no  voluntary  control;  hence  the  name  "  involuntary  " 
muscle. 

In  addition  to  a  slow  rate  of  contraction,  with  a  long  latent  period, 
smooth  nmscle  is  characterized  bj^  the  fact  that  it  cannot  be  thrown 
into  complete  tetanus.  Its  contraction  is  of  the  nature  of  a  single 
twitch. 

Smooth  muscle,  like  striated  muscle,  responds  to  a  gradation  of 
stimuli,  and  shows  thermal,  chemical,  and  electrical  changes.  In 
chemical  composition  it  is  probably  much  the  same  as  striated  muscle. 
It  undergoes  bo*:h  chemical  and  heat  rigor. 

Smooth  muscle  possesses  the  property  of  tonus — a  condition 
of  sustained  muscular  contraction,  which  is  influenced  in  the  direc- 
tion of  further  contraction  or  relaxation  by  the  nerve-supply.  Aug- 
mentor  or  accelerator  nerves  increase  tonus,  inhibitory  nerves  relax. 
This  double  nerve-supph'  is  a  characteristic  of  smooth  muscle. 

Smooth  muscle  is  also  characterized  by  the  propertv  of  rhyth- 
micity — periods  of  contraction  alternate  with  periods  of  rest.  This 
seems  to  be  a  function  of  the  nnascle  itself.  Such  is  observed  in  the 
stomach,  intestine,  bladder,  spleen,  and  other  organs. 

Associated  with  smooth  muscle  are  local  nervous  networks  or 
plexuses,  such  as  Auerbach's  and  Meissner's  plexuses  in  the  intestine. 
These  endow  the  muscle  with  the  property  of  peristalsis — co-ordinate 
and  recurring  waves  of  contraction,  j^receded  by  waves  of  relaxation 
which  together  force  the  contents  along  the  muscular  tube 


CHAPTER   LXIV 


•  ANIMAL  ELECTRICITY  " 

Various  tissues  of  the  boch-  displa\-  electrical  currents  when  in 
action  or  when  injured.  Such  currents  are  sometunes  referred  to  as 
"  animal  electricity."  If  a  nerve-muscle  j  reparation  be  placed  upon 
a  glass  plate,  and  by  means  of  a  glass  rod  the 
free  end  of  the  nerve  be  allowed  to  touch  the 
muscle,  a  contraction  occurs  (Fig.  2C6).  This 
is  an  experiment  contrived  bv  Galvani  to  prove 
the  existence  of  animal  electricity.  In  his  first 
experiment,  Galvani  used  metals.  He  found  that 
if  the  hind-limbs  with  the  skin  removed  be  sus- 
pended from  an  iron  stand  by  a  copper  hook 
passed  through  the  lower  part  of  the  vertebral 
column,  contraction  of  a  leg  occurs  every  time  it 
is  made  to  touch  the  iron  stand.  He  supposed 
that  this  contraction  was  due  to  animal  elec- 
tricity. Volta  insisted  that  it  was  due  to  the 
completion  of  tho  circuit  between  the  two  metals 
by  the  wet  tissue  of  the  frog.  From  the  contro- 
vers}'  between  Galvani  and  N'olta  came  about 
the  invention  of  the  galvanic  battery,  and  the 
development  of  electrical  science.  The  discovery 
of  the  electric  fishes  gave  the  crowning  proof  of 
animal  electricity.  The  Malapterurus  was  known 
to   the   ancient  Eg^qstians.    and   figured    in   their 

monuments.  The  electric  eel  of  South  America  gives  a  most  powerful 
shock.  The  natives  used  to  exhaust  wild-horses  by  driving  them 
into  a  marsh  infested  with  these  eels,  and  so  capture  them. 

Animal  currents  now  play  an  important  part  in  the  study  of 
abnormal  conditions  of  the  heart.  It  was  at  first  believed  that  natural 
currents  pre-exist  in  normal  resting  tissues,  but  it  is  now  kno^ni  that 
these  currents  only  occur  when  the  chemico-physiological  condition 
of  the  tissue  is  altered  by  activity  or  injury. 

The  Electromotive  Properties  of  Muscle  and  Nerve. — ^If  a  normal 
muscle  or  nerve  be  connected  by  a  pair  of  non-polarizable  electrodes 
to  a  galvanometer,  no  deflection  of  this  instrument  takes  place,  show- 
ing that  normal  muscle  or  nerve  is  isoelectric.  Perfectly'  ''  normal  " 
mu.scle  is  difficult  to  obtain,  since  it  is  necessarily  injured  m  the  pre- 

559 


Fig.  290.  —  Diagram 
OF  Galvaxi"s  Ex- 
terimext.  cox- 
tkaction  without 
Metals. 


r)()() 


A  TEXTBOOK  OF  PHVSIOLO(;^ 


paration.     A  muscle  which  has  been  soaked  iii  normal  saline  several 
hours  after  its  preparation  is  isoelectric. 

If  a  muscle  which  is  at  rest  in  such  an  isoelectric  condition  be 
damaged — e.g.,  by  heating — it  is  found  that  there  is  now  an  electric 
current  flowing  through  the  galvanometer.     In  such  an  injured  muscle 


Fig.I 


Eoxit 


YartccLLon/. 


Fig.EL 


ElactrotonuH 


Fig.  297.— Diagrams  to  Illustrate  Current  of  Lnjury,  Negative  V'akiatio.v, 
Current  of  Action,  Electrotonus. 

the  injured  part  corresponds  to  the  positive  element  of  a  galvanic 
battery.  The  cuiTent  therefore  flows  in  the  muscle  from  the*injured 
part  to  the  normal  part;  outside  the  muscle  it  Hows  through  the  gal- 
vanometer from  the  normal  t )  the  injured  part.  Tne  '  current  of 
injury  '  is  usually  described  in  terms  of  the  direction  of  the  current 
through  the  galvanometer;  therefore,  the  site  of  injury  is  said  to  be 
negative  (or  zincative,  like  the  zinc  of  the  batterv)  "to  the  normal 


"  ANIMAL  ELECTRICITY 


561 


tissue  (Fig.  297).  The  current  of  injury  can  be  simply  demonstrated 
by  Galvani  s  experiment  already  quoted.  It  may  also  be  shown  in 
nerve  by  placing  the  cut  surface  of  the  nerve  on  one  plug  of  kaolin 
and  the  uninjured  part  on  another.  Then,  if  the  attached  muscles  be 
sufhciently  excitable,  on  bringing  the  kaolin  plugs  into  contact  with 
strong  saline,  which  is  a  good  conductor  of  electricity,  the  muscles 
contract  (Fig.  298). 


Fig.  298.— Diagram  of  the  Experimext  to  show  the  STiMrLAXiON  of  a  Xerve 

BY   ITS    OWX    '-CURREKT    OF   INJURY." 


Fig.  29!». — Diagram  of  the  Experiment  ox  Secondary  Twitch. 


Fig.  ;?(iO. — Diagram  of  the  Experiment  to  show  the  Stimulation  of  a  Muscle 
BY  THE  "  Current  of  Action  ''  of  Another  Muscle. 


A  similar  condition  pertains  when  anv  part  of  a  muscle  or  nerve 
is  more  active  than  the  rest.  The  active  j^art  in  reference  to  the 
current  tlu'ough  the  galvanometer  is  negative  to  the  resting  part. 
Such  a  current  is  termed  the  "  current  of  action."  It  may  be  simply 
ishoM-n  by  laj'ing  tAvo  nerve-muscle  preparations,  A  and  B-,  ujDon  a 
glass  plate,  and  placing  the  nerve  of  one  muscle  (A)  along  the  other 
muscle  (B).  Upon  exciting  the  nerve  of  B,  the  mu.scle  contracts, 
folloAAed  immediately  by  a   contraction    of   A.      Similarly,    if   B  be 

36 


562 


A  TEXTBOOK  OF  PHYSIOLOGY 


tetanized  through  its  nerve  muscle,  A  also  passes  into  the  tetamc 
state  The  muscle  A  is  stimulated  to  contraction  by  the  current  of 
action  in  A,  and  not  by  an3^  spread  of  the  exciting  electric  current. 
This  is  shown  by  using  the  beating  heart  and  a  nerve  muscle  pre- 


f^bt 


o   cd   o  0 

O;    O    (H  +s- 


paration.  If  the  nerve  be  placed  upon  the  beating  heart,  the  muscle 
contracts  with  each  beat  of  the  heart.  Occasionally,  if  the  nerve  be 
ver}'  excitable,  the  muscle  contracts  at  the  end  as  well  as  at  the 
beginning  of  the  heart's  contraction. 

If  two  muscles  be  pressed  together,  excitation  of   either  causes. 


ANIMAL  ELECTRICITY 


563 


contraction  of  both.  In  this  case,  the  current  of  action  in  one  muscfe 
excites  the  other  directly  (Fig.  300). 

Normally,  the  presence  of  such  currents  is  shown  by  the  use  of  the 
galvanometer  and  sj^eciai  apparatus  (Fig.  301). 

If  an  injured  muscle  be  led  off  to  the  galvanometer  and  stimulated, 
it  is  found  that  on  each  single  contraction,  or,  better  still,  on  tetanus, 
the  current  of  injin-y  is  diminished  or  may  be  overbalanced,  since 

7b  Lever 


K 


iOcm. 
Fig.  302. — Keith  Lui  as  Moist  Chamber  and  Electbodes. 

A,  Glass  rod;  B,  B,  tubes  containing  platinum  electrodes;  the  leading  off  electrodt^ 
are  glas.s  tubes  tilled  witb  Ringer's  solution  plugged  by  filter  candles  containing 
zinc  sulphate  and  below  by  cotton-wool  wads  D,  D,  connected  to  muscle  ;  E, 
ebonite  trough  with  glass  sides  enclosed  in  felt  F  ;  G,  Ringer's  solution  immersing 
lower  part  of  muscle;  t1 ,  inlet.  -/,  outlet  for  fluid;  A',  accessory  outlet  for  totallj' 
immersing  muscle  when  •/  i~  closed. 


the  change  from  rest  to  action  is  greater  in  the  uninjured  part  than 
in  the  injured  part.  This  diminution  of  the  injury  current  is  termed 
''negative  variation"  (Pig.  297). 

When  uninjured  tissue  passes  into  action,  there  is  what  is  termed 
a  '•  diphasic  variation."  This  is  because  first  the  part  proximal  to 
the  stimulus  is  active,  theti  the  distal  i^art:  the  action  is  not  simul- 
taneou.'i   throughout   the   whole  of   the   muscle.     When  A  is   active 


564 


A  TEXTBOOK  OF  PHYSIOLOGY 


and  B  at  rest,  there  is  a  current  of  action  through  the  gah'anometer 
from  B  to  A;  when  both  A  and  B  are  active,  there  is  no  deflection. 
When  B  is  active  and  A  at  rest,  there  is  a  current  through  the  gal- 
Aanometer  from  A  to  B. 

If  the  transmission  of  the  active  state  from  A  to  B  is  quick,  the 
isoelectric  interval  is  naturally  short;  if  it  be  long,  the  interval  is 
.correspondingly  increased.  Thus,  the  rate  of  transmission  of  the 
wave  of  activity  may  be  measured.  In  the  nerve  trunk  of  a  frog  it 
is  about  30  metres  per  second;  in  striated  muscle  about  1  metre  per 
second;  in  the  frog's  ventricle  about  ^\  metre  per  second. 


Eio.  303. TvriCAL  Excuesion  of  Sartoeius  Muscle  to  Single  Inductios  Twitch. 

(Keith  Lucas.) 

Read  right  to  left. 


In  the  heart,  the  current  of  action  induces  a  triphasic  variation. 
This  can  probably  be  explained  as  follows :  Sujipose  one  non-polarizable 
electrode  (B)  is  placed  on  the  base  of  the  ventricle,  another  (A)  on  the 
apex.  The  excitator}"  wave  enters  the  base  of  the  ventricle  by  the 
A.-V.  bundle.  B  is  now  negative  to  A.  It  passes  then  to  the  apex. 
A  is  now  negative  to  B.  The  ventricles  contract  in  such  a  mamiei 
•that  the  apex  finishes  contracting  before  the  base.  The  blood  is 
A^Tung  out  from  the  ventricle,  and  the  muscle  round  the  arterial  orifices 
is  the  last  to  contract  ;  B  finally,  therefore,  becomes  negative  to  A. 
The  response  of  the  heart  in  terms  of  negativity  is  therefore  B,  A.  B 
(base,  apex,  base). 

Cutaneous  Currents. — Normally,  the  skin  of  all  vertebrate  animals 
is  traversed  by  an  electric  current  from  without  inwards  (Fig.  305).  This 
current  appears  to  be  caused  mainly  by  the  action  of  the  cutaneous 
glands,  or  of  active  secreting  single  cells  in  the  skin.     When  the  pad 


"ANIMAL  ELECTRICITY 


565 


of  a  cat's  foot  is  made  to  sweat  by  stimulation  of  the  sciatic  nerv-e,  the 
pouring  out  of  the  sweat  is  accompanied  by  an  increase  (a  positive 
variation)  of  the  ingoing  current.  If,  however,  the  effect  of  the  nerve 
be  abolished  by  atropme,  such  a  result  is  no  longer  obtained.  The 
normal  current  of  the  skin  is  found  to  be  increased  by  direct  excita- 
tion, this  increase  or  positive  variation  being  reduced  or  abolished 
by  the  local  application  of  atropine,  chloroform,  or  carbon  dioxide. 


___ 

+  04- 

/ 

\ 

■ 

+  03- 

\ 

- 

+  02 

V 

■ 

+  01- 

/ 

\ 

- 

0 

STIM. 

i 

■J- 

\ 

\ 

-01- 

/ 
i 

-02- 

/ 

■ 

' 

\ 

-03- 

\ 

- 

—04.- 

,  / 

• 

o 

> 

"/ 

- 

V-- 

Vu;.  304. — Analyzed  Uii'hasic  Eesponsk  uf  Saktoeius  at  18°  C.     (Keith  Lucas.) 


Salivary  Glands. — In  the  submaxillarv  gland,  which  has  been 
especially  studied,  the  resting  current  flows  through  the  gland  from 
the  surface  to  the  hilus,  and  therefore  from  the  hilus  through  the 
galvanometer  to  the  surface  (Fig.  306).  When  the  gland  is  made  to 
secrete  by  stimulation  of  the  chorda  tympani  nerve,  the  hilus  becomes 
still  more  galvanometrically  positive — an  effect  abolished  by  atropine. 
vStimulation  of  the  cervical  sympathetic  nerve  has  the  opposite  effect. 

Retinal  Currents. — If  the  ej^eball  and  the  retina  be  connected  to 
a  galvanometer,  a  "  current  of  rest  "  is  observed,  the  direction  of 
M'hich   depends  on  whether  the  outer  or  inner  surface  of  the  retina 


mii 


A  TEXTBOOK  OF  PHYSIOLOGY 


be  used,  (Fig.  307).  When  light  falls  upon  llie  retina,  a  complex 
variation  ensues,  depending  upon  the  strength  and.  duration  of  the 
stimulus,  upon  the  condition  of  the  eye,  whether  adapted  to  light  or 
dark,  fresh  or  fatigued,  and  upon  the  nature  of  the  light,  whether 
Avhite  or  coloured.  In  the  isolated  retina  there  is  first  a  positive  and 
then  a  negative  variation  when  light  falls  on  it.  When  the  light  is  cut 
oflf,  a  positive  variation  is  produced.  As  the  result  of  a  momentary 
flash  there  is  a  short  latent  period — 0-01  second — followed  by  a  short 
negative  A^ariation,   followed   by  a  large  positive  variation,  quickly 

Inner 
surface 


Fig.  305. — ^Skin  Current. 


Fig.  300.— i^LAMD  Current. 


followed  by  another  diminution  of  the  positive  variation,  and  then 
by  a  long-drawn-out  increase  of  the  positive  variation. 

Electric  Tissues. — In  some  fishes  there  is  developed  a  tissue  capable 
of  ])roducing  electricity.  These  fishes  are  either  elasmobranchs,  such 
as  the  rays  (Raia  ocellata,  R.  Isevis,  etc.)  and  the  torpedo  fish  (Tetro- 
narce),  or  teleosts,  such  as  the  electric  eel  (Gymnotus),  the  somewhat 
similar  elongated  fish  (Mormyrus),  the  star-gazer  (Astroscopus),  and 
the  electric   catfish   (Malapterurus).     The   electric  tissue  consists  of 


Current  of 
injury  from 
optic  nerve. 


Retinal  current  di- 
rected in  the  retina 
from  rod  surface  to 
fibre  Surface. 


Fig.  3U7. 


St  Series  of  plate-like  units  know^i  as  electroplaxes  (Fig.  308).  Tiie 
^lectroplax  lies  in  a  compartment  of  connective  tissue  embedded  in  a 
j'elly-like  mass,  through  which  the  nerve  and  blood-supply  pass  to 
it.  In  some  cases  it  is  to  be  considered  as  a  single  cell  with  many 
nuclei,  in  others  a  fusion  of  cells — a  syncytium.  The  discharge  is 
composed  of  about  200  shocks  per  second,  and  the  E.M.F.  may  be 
siiflficient  to  kill  other  fish  in  the  neighbourhood.  In  the  discharge 
of  the  organ  the  current  flows  through  the  organ  from  the  ventral 
t^iithe  dorsal  surface,  and  through  the  gah^anometer  from  the  dorsal 


ANIMAL  ELECTRICITY 


567 


to  the  ventral  surface.  In  Gymnotus  the  shocks  are  from  tail  to  head, 
in  Malapterurus  from  head  to  tail,  the  direction  dependmg  upon  the 
point  of  entrance  of  the  nerves  to  the  organ.  A  giant  ganglion  cell 
and  its  nerve  tibre,  branching  multitudinously,  su]:>plies  the  whole  of 
each  electric  organ  in  this  fish. 

Blaze  Currents.— After  any  living  tissue  has  been  strongly  tetanized 
for  a  short  space  of  time,  a  •■  blaze  "'  current  follows  in  the  same 
direction  as  the  tetanizing  current.  This  is  a  sign  of  life:  dead 
tissue  does  not  give  it.  Seeds  have  been  tested  by  this  means,  and 
their  germinating  power  thus  demonstrated. 

Electrotherapy. — Electricity  is  largely  employed  in  the  treatment 
of  disease.  It  may  act  by  producing  either  chemical  or  thermal 
effects.  In  the  first  case,  the  galvanic  electric  current  is  used,  smce 
it  causes  a  stead}^  migration  of  positive  ions  to  the  negative  pole,  and 
of  negative  ions  to  the  positive  pole.  It  may  be  emplo3'^ed  thera- 
peutically for  three  purposes:  (1)  To  produce  an  alteration  in  the  ionic 


Fig.  308. — Xeevous  Structures  Stippled,  Striated  Structures  indicated  by 
Lines.     (Redrawn  from  Dalilgren  and  Kepner.) 

a.  Diagram  of  muscle  fibre;  h,  of  clectroplax  of  Baja  hat  is  ;  r,  diagi'am  of  electroplax 

of  Raja  Ice  vis. 


content  of  a  region,  as  is  probabh^  the  case  when  used  for  promoting 
the  absorption  of  fluid  effusions.  (2)  To  cause  a  formation  and 
accumulation  of  new  chemical  bodies  at  the  poles.  Such  bodies 
may  have  a  caustic  action,  and  be  used  for  the  destruction  of  hair 
follicles  (superliuous  hairs),  nsevi,  etc.  (3)  By  means  of  the  current 
to  introduce  curative  ions  through  the  skin — the  "  ionic  method  of 
medication."' 

The  faradic  cuiTent  cannot  be  used  for  the  above  purposes,  since  the 
current  is  frequentty  made  and  broken.  The  ions  then  migrate  in 
sudden  movements  or  jerks,  and  act  as  a  stimulus  to  excitable  tissue, 
such  as  muscle.  The  faradic  current  is  of  great  value  in  the  treat- 
ment of  parah'sis. 

If  an  interrupted  cuirent  be  made  to  oscillate  with  extreme 
rapidity  across  the  bod\',  the  ions  do  not  have  sufficient  time  to  act  as  a 
stimulus,  and  remain  more  or  less  stationar3^  fnder  these  conditions, 
ix  po\\eiful  current   (3   ampsres),   six   times   stronger  than  a  current 


-)r>K  A  TEXTBOOK  OF  PHYSIOLOGY 

nc-cessaiy  to  kill  if  j)as.sed  in  ono  direction  only,  may  be  oscillated 
without  any  contraction  being  jiroduced,  provided  it  be  oscillated 
fre(iuently  enougli.  Tl.e  result  of  such  a  current  is  an  agreeable 
sensation  of  heat.  1  his  forms  the  basis  of  "  high-frequency  "  treat- 
ment, or  "  diathermy/'  When  those  high-frequency  currents  are 
passed  through  the  body,  jiart  of  the  electrical  energy  is  transformed 
into  heat,  which  is  prcduced  in  all  jiarts,  both  superficial  and  deep, 
in  which  the  ciUTent  flows.  The  effects  of  diathermy,  so  far  as  can 
be  seen,  are  produced  through  their  thermal  action,  and  the  same 
results  can  bo  obtained  by  the  simple  use  of  hot  baths. 


BOOK   XII 

THE   NERVOUS   SYSTEM 

CHAPTER  LXV 
THE  NEURON 

The  nervous  mechanism  was  evolved  to  correlate  the  multicellular 
organism  with  its  surroundings  and  facilitate  the  pcoi^er  inter- 
action of  the  various  organs.  We  have  seen  in  previous  chapters 
how  the  heart,  the  vaso-motor  mechanism,  the  respiratory  and  diges- 
tive mechanisms,  are  all  correlated  to  the  body  needs  by  the  aid  of 
the  nervous  system.  We  have  now  to  consider  how,  by  the  aid  of  the 
nervous  system,  the  animal  adjusts  itself  to  its  environment. 

The  unit  structure  of  the  nervous  system  is  the  neuron.  It  con- 
sists of  a  nerve  cell,  with  its  processes.  The  neuron  may  have  a 
variety  of  forms,  according  to  the  function  it  subserv^es  (Fig.  309). 
Those  engaged  in  the  perception  of  the  outside  stimulus  are  small, 
with  short  processes — as,  for  example,  the  receptor  cells,  concerned  in 
olfactory  and  \'isual  sensations.  On  the  other  hand,  neurons  which 
conduct  impulses  to  distant  parts  are  supplied  Avith  one  or  more  long 
and  a  number  of  short  processes.  The  cells  of  the  anterior  horn  of 
the  spinal  cord  are  an  example  of  this  type  of  neuron.  They  have 
several  processes,  and  are  termed  multipolar.  In  the  living  cell 
body  there  ma\"  be  seen  a  large,  well-defined  nucleus,  and  numerous 
gi'anules  floating  in  a  homogeneous  fluid.  On  treatment  with  alcohol, 
the  cell  contents  are  precipitated  as  Nissl's  granules — discrete  masses 
which  stain  with  methylene  blue.  These  are  not  found  m  exhausted 
cells,  and  disappear  from  those  cells  whose  axons  are  divided  and 
functional  activity  arrested.  Of  the  processes,  all  but  one  are  short, 
and  branch  like  the  roots  of  a  tree,  till  they  end  in  small,  bud-like 
expansions,  known  as  gemmules.  These  processes  are  known  as 
dendrons.  The  long  process,  known  as  the  axis  cylinder,  or  axon, 
conies  Away  from  a  2>art  of  the  cell  in  which  there  are  no  Nissl's 
granules — a  part  known  as  the  axon  hillock.  The  axon  is  character- 
ized by  its  length  and  by  the  fact  that  it  does  not  divide  until  near 
its  final  terminations. 

The  axon,  or  axis,  cylinder  is  the  essential  conducting  part  of  the 
nerve-fibre.  Mam-  such  fibres  go  to  make  up  the  anatomical "'  nerve." 
Such  fibres  may  be  either  medullated  or  non-medullated. 

56JI 


570 


A    ri:XTB()Ulv  OF  THYSlOLOCiY 


Medullated  nerves  are  so  called  because  in  them  the  axon  is  sur- 
rounded hv  a  cylinder  of  fatty  material,  forming  the  medullary  sheath. 
This  sheath  is  interrupted  at  regular  intervals.  Such  points  are 
known  as  the  nodes  of  Ranvier.  The  neurilemma  is  a  nucleated 
sheath  of  fibrous  tissue,  and  is  continuous  over  the  nodes  of  Ranvier. 

A  non-medullated  nerve,  sometimes  called  a  grey  fibre,  in  con- 
tradistinction to  the  white  medullated  nerve,  consists  merely  of  an 
axon  surrounded  by  the  nucleated  neurilemmal  sheath. 


Fig.  309. — Diagrams  of  Different  Kinds  of  Nerve  Cells.  External  Arrows 
AT  Perceptory  (Receptor)  Surface;  Internal  Arrows  at  Discharging 
(Effector)  Surface  of  Cell.     (RedraA\-n  from  Dahlgren  and  Kepner.) 

a.  Nerve  cell  with  no  process;  h,  nerve  cell  with  one  process  at  effector  end  organ 
attached  to  muscle  tibre;  c,  nerve  cell  with  end  organs  on  two  processes;  d,  nerve 

'  cell  with  impulse  path  independent  of  cell;  e,  nerve  cell  with  multiple  perceptory 
end  organs;  /,  nerve  cell  with  multiple  perceptory  and  discharging  end  organs. 


Medullated  fibres  are  those  of  the  brain  and  spmal  cord,  and  the 
cerebro-spmal  nerves;  the  non-medullated  are  the  post-ganglionic 
fibres  of  the  sympathetic  nervous  system. 

Speculations,  based  on  the  concentration  of  ions  in  the  various  parts 
of  the  nerve  fibre,  have  been  jiut  forward  concerning  the  transmission 
of  the  nervous  impulse.  Histological  means  (staining  with  solutions 
of  silver  nitrate  containing  a  little  nitric  acid)  seem  to  show  that 
chlorides  occur  in  abundance  along  the  course  of  the  axon.  Salts 
of  potassium  appear  mainly  at  the  nodes  of  Ranvier,  and  just  outside 
the  axon  in  the  medullarj'  sheath.     They  are  demonstrated  by  treat- 


THE  NEURON 


571 


ing  the  nerve  with  cobalt  sodium  hexanitrite,  and  after  washing 
differentiating  as  a  black  precipitate  by  adding  ammonium  sulphide. 
Such  methods  destroy  the  integrity  of  the  nerre,  and  set  free  the 
salts  from  their  combination  with  the  colloidal  living  substance. 

It  is  claimed  that  there  is  laid  down  in  the  cytoplasm  of  the  cell 
for  the  purposes  of  conduction  a  .system  of  neuro-fibrils,  which  run 


J^ 


-^ 


\ 


Zj^n 


! 


I 


v;«' 


i'lG,  310. 

1,  Large  Betz  cell  from  human  cerebral  cortex,  .showing  Xissl's  granules  and  cone 
of  origin  of  axon  at  the  base.  2,  Medium-sized  pyramidal  association  cell. 
3,  Anterior.cornual  cell.     4,  Posterior  root  ganglion  cell.     (Mott.) 

from  end  to  end  of  the  cell  processes.  According  to  some  authorities, 
the  neurofibrils  are  not  confined  to  one  nerv^e  unit,  but  freely  leave  one 
neuron  and  pass  into  another,  thus  forming  a  network  throughout  the 
whole  nervous  system.  The  study  of  the  living  nerve  cell  does  not 
reveal  the>e  fibrils;  they  are  artefacts  produced  by  the  method  of 
preparation. 


Fit;.  '311. — PuKTinx  ciF  A  Medullated  Xekve-I-'ibhe  fK'M   >.  Mammal. 

Another  type  of  neuron  is  the  bipolar  nerve  cell  (Fig.  309).  In 
mammals,  these  occur  only  in  the  ganglia  m  connection  with  the 
eighth  nerve;  in  fishes,  they  are  found  in  the  spinal  ganglia  also.  The 
cell  bod\'  is  elliptical  in  shape,  with  two  processes  given  off  from  the 
two  ends  of  the  ellipse.     Such  a  cell  is  the  parent  cell  of  the  unipolar 


572 


A  TlvVTliOOK  OF  PHV,SI()LOGY 


spherical  cell  found  in  the  spmal  ganglia  of  mammals.  The  two  pro- 
cesses of  the  bii)olar  cell  gradually  a])])roach  each  other  during  develop- 
ment until  they  combine  to  form  a  T-sha]ied  junction. 

In  the  cortex  of  the  great  brain  are  other  characteristic  neurons; 
the  cells  are  pyramidal  in  shape;  branching  dendrons  arise  from  each 
angle  of  the  p^Tamid,  and  an  axon  from  the  middle  of  the  base 
(Fig.  310). 

In  the  cerebellum  are  found  neurons  with  large,  pear-shaped  cells, 
with  a  single  axon  at  the  base,  and  a  wonderfully  branched  den- 
dritic process  at  the  stalk  end.  Throughout  the  grey  matter  of  the 
brain  and  spinal  cord  there  are  small  association  cells,  knowai  as  the 
Golgi  cells,  characterized  by  the  fact  that  their  axons,  after  a  short 
course,  divide  into  many  terminal  branches. 


r^-'. 


Fig.  312. — Two  View.s,  taken  at  Twknty-five  Minutes"  Inteeval,  of  the  f-AAJK 
Nerve-Fibee  growing  from  A  Group  of  Embryonic  Spinal  Coed  Cells  into 
THE  LvMPH      (Ross  Harrisoii.) 


Microscopical  preparations  of  the  central  nervous  system  are  iden- 
tified largely  by  the  type  and  arrangement  of  nerve  cells. 

The  neurons  are  held  together  by  a  suj)porting  tissue,  known  as 
neuroglia.  Thej'  are  brought  into  relationship  with  one  another 
through  their  end  terminations — the  dendrons  and  the  axon.  These 
processes  do  not  fuse  together;  the}'  are  in  contiguit}',  not  in  con- 
tinuity. The  intertwining  branches  form  a  synapse;  one  neuron, 
conducting  an  impulse,  induces  an  impulse  in  another  through  the 
synapse.  The  synapses  onh*  allow  conduction  in  a  forward,  not  in 
a  backward,  direction.  For  example,  a  stimulus  can  pass  up  a  motor 
nerve-fibre  as  far  as  the  anterior  horn   cell  but  not  bevond  it  into 


THE  NEURON 


573 


the  spinal  cord.  It  has  been  suggested  that  the  genimules  at  the  end 
of  the  dendrons  are  amoeboid  in  nature,  so  that  this  contiguity  may  be 
rendered  more  complete  at  some  times  than  at  others — for  example, 
that  they  may  be  separated  during  sleep.  There  is  no  evidence  in 
favour  of  this  view. 

The  above  statement  embodies  what  is  known  as  the  neuron  theory. 
Of  recent  years,  the' theory  has  come  in  for  a  considerable  amount  of 
criticism.  Some  lir.ve  affirmed  that  neuro-fibrillce  pass  from  one  neuron 
into  another.  Doubt  has  also  been  expressed  as  to  Avhether  the  neurons 
are  genetically  single  cells,  and  whether  regenerated  nerve-fibres  are  to 
be  regarded  as  parts  of  a  single  cell.  It  is  obvious  that,  should  either 
of  the  above  contentions  be  true,  the  neuron  theory',  as  origmally 
enunciated,  is  no  longer  valid.  On  the  whole,  recent  evidence  tends 
rather  to  conform  the  theory  than  otherwise.  The  development  of  the 
nerve  cell  has  been  watched  in  living  preparations  made  from  the 
embryo,  and  the  outgi"  )wih  of  the  axon  obser\'ed  (Fig.  312). 


-><- 


Fig.  313. -^Portion  of  Rexal  Epithelium  of  Fkog,  showing  Effector  (Motor) 
Nerve  Pnding.s  ix  Cells.     ( Redrawn  after  Smirnow,  from  Dalilgren and  Kepner.) 


Those  nerve-fibres  which  conduct  inwards  towards  the  nervous 
system  are  termed  ingoing,  or  afferent ;  those  which  conduct  outwards, 
the  outgoing,  or  effereiit.  The  nature  of  a  nerve  may  be  ascer- 
tained— (1)  bj'  observing  the  results  of  its  se3tion;  (2)  by  studying 
the  effects  produced  when  the  cut  ends  of  the  nerve  are  stimulated. 
If  an  afferent  nerve  be  divided,  there  results  a  loss  of  sensation  in  the 
area  supplied  bj'  the  nerve.  Stimulation  of  its  peripheral  end  yields 
no  result;  stimulation  of  its  central  end,  on  the  other  hani,  calls 
forth  some.  If  it  be  sensation,  the  nerve  is  termed  sensory;  if 
some  form  of  movement,  excito-motor  ;  if  inhiV)iti<)n.  excito-inhibitory ; 
if  a  secretion,  excito-secretory. 

Section  of  an  efferent  nerve  parah'zes  some  function,  the  movement 
of  muscle,  striped  or  smooth,  secretion  of  a  gland,  etc.  Stimulation 
of  the  central  end  of  such  a  nerve  is  without  result ;  and  stimulation 
of  the  peripheral  end  produces  the  action  which  it  normally  excites. 
This  action  may  either  be  in  a  direction  of  increased  activity — 
augmentor — or  of  decreased  activity — inhibitory.  If  it  excites  a 
muscle,  it  is  termed  motor;  if  the  bloodvessels,  vaso-constrictor ;  if  it 


574 


A  TEXTBOOK  OF  PHYSIOLOGY 


cause  the  .secretion  of  a  gland,  secretory.  Similarly,  it  may  be 
nuisculo-inhibitory,  vaso-inihihiloiy,  secreto-inhibitory,  etc. 

Most  nerves  of  the  body  are  mixed  nerves,  containing  both  afferent 
and  efferent  fibrt^s. 

The  Reflex  Arc. — The  sensory  neuron,  when  stimulated  through  its 
ner\e-ending.  transmits  its  impulse  inwards,  passes  it  on  to  the 
efferent  neuron,  which  transmits  it  outwards,  and  effects  some  action 
or  other.  This  chain — sensory  surface  (receptor),  afferent  conductor 
(the  joining  synapse),  the  efferent  conductor,  the  reacting  organ,  or 
effector — forms  what  is  known  as  the  reflex  arc.  In  any  reflex  arc  at 
least  two  neurons  are  essential.  Genera ll_\',  a  third  neuron  connects 
the  afferent  and  efferent  neurons,  and  in  many  reflex  arcs  several 
connecting  Jieurons  are  interposed  in  the  reflex  path. 

The  receptors   are  classified  according  as 

LA  they  respond   to    stimuli    from — (1)  without 

_^  =r.—z^^j£^ .j^"'l  the  body  (extero-ceptive) ;  (2)  from  the  animal's 
own  tissues — e.g.,  the  muscles,  tendons,  joints, 
or  the  labjTinth  of  the  ear  (proprio-ceptive) ; 
(3)  from  the  viscera  (entero-ceptive). 

The   Conductors   consist  of  the  axons  of 

afferent  and  efferent  neurons,  and  the  synapse 

between    these.      The    code    of    interaction 

between  the  afferent  and  efferent  conductors 

of  the  spinal  cord  has  been  studied  in  what 

is  known  as  the  "  spinal  animal  " — that  is,  an 

animal  in  which  a  division  of  the  cord  has 

been  nuide  in  the  lower  cervical  region.  Such 

an  animal  can  Ik;  kept  in  health  with  careful 

attention,    and    studied    months    after    the 

initial  effects  of    the    lesion    have    subsided 

Fig.  314. — Effector  Nerve  (see  p.  674).     The  conduction  of  the  nervous 

Endings  in  Muscles  of  impulse  in  a  reflex  arc  differs  materially  from 

KUh^e.')   ^^'^^'^^^  ^"""  conduction  in  the  nerve-fibre  only.     This  is 

mainty    owing  to    the    interposition   of    the 

synapses. 

Conduction  across  a  synapse  is  much  slower  than  along  a  nerve - 

fibre,   and  is  easily  fatigued.     Want  of  oxygen  particularly  causes 

failure  of  conduction  at  this  point,  and  drugs  such  as  nicotine  painted 

on  ganglia  paralyze  the  synapses  in  them.     The  s_>niapse  interposes  a 

valve-like  action  in  the  chain  of  conductors,  permitting  conduction  of 

the  impulse  in  one  direction  only — namely,  from  the  receiving  afferent 

to  the  effecting  efferent  neurons. 

The  Effector  Organs  form  the  connection  between  the  efferent 
nerve  and  the  cells  of  the  tissue  affected.  In  some  cases  they  have 
a  definite  structure — for  example,  the  motor  end-plate  in  muscle. 
In  other  cases  there  is  merely  a  '"  receptive  substance,"  dependent 
for  its  nutrition  rather  on  the  cells  of  the  tissue  than  on  the  nerve- 
fibre  with  which  it  is  in  connection.     It  therefore  does  not  degenerate 


THE  NEURON 


i:n') 


when  the  nerve  is  severed.  Such  receptive  substance  may  be  acted 
upon  by  chemical  substances,  and  a  "  chemical  reflex  "  thereby 
evoked.  For  example,  adrenalin  acts  upon  the  effector  organs  in 
connection  Avith  the  sympathetic  system,  and  evokes  actions  identical 
with  those  obtained  b}  stimulation  of  the  various  sympathetic  nerves. 

The  effectors  are  concerned — (1)  in  effecting  the  movements  of 
voluntar}'  muscle;  (2)  in  regulating  the  action  of  smooth  and  cardiac 
nauscle;  (3)  in  evoking  the  secretion  of  glands.  The  functions  of 
these  effectors  have  already  been  dealt  with  in  their  various  sections, 
and  are  also  considered  in  connection  with  the  central  nervous  system 
(c/.  cranial  nerves)  and  the  autonomic  system  (p.  748). 

A  knowledge  of  the  functions  of  the  nervous  S3'stem  is  best  acquired 
by  a  study  of  two  units:  (1)  The  neuron;  (2)  the  reflex  arc. 


Fig.  315. — Diagram  or  Simple  Reflex  Arc. 


The  Function  of  the  Neuron. — The  cell  body  governs  the  nutrition 
of  the  whole  neuron.  Its  power  of  nutrition  probabh'  depends  upon 
the  nucleus  and  the  protoplasm  which,  when  j^recipitated  by  reagents, 
forms  Nissl's  granules.  The  exact  chemical  nature  of  these  granules 
is  not  knoAvn.  The\-  may  be  of  the  nature  of  nucleo-protein,  for  they 
have  a  great  aftinity  for  basic  aniline  dyes,  such  as  methA'lene  and 
toluidin  blue.  When  a  nerve  cell  has  had  a  long  spell  of  continuous 
activity,  these  granules  become  dimmished — '"  chromatolysis,"'  as  it  is 
termed,  occurs  (Fig.  316).  Such,  for  example,  is  the  case  in  the 
nerve  cells  of  the  swalloM'  after  a  day's  flight. 

It  was  found  that  if  one  ej-e  of  a  dog  be  bandaged,  and  the  other 
eye  kept  active  by  leadmg  the  animal  about  for  twenty-four  hours, 
that  in  the  part  of  the  brain  concerned  with  the  vision  of  the 
active  eye  chromatolysis  had  occurred,  but  not  in  the  part  of  the  brain 
connected  with  the  resting  eye. 

Chromatolysis  takes  place  during  asphyxia  and  m  certain  fevers. 
It  also  occurs  in  the  nerve  cell  when  the  axon  is  cut.  In  this  case, 
further  changes  occur,  the  cell  bod}"  becomes  swollen,  the  nucleus 
goes  to  one  side  of  the  cell.     By  observing  in  which  cells  thi.i  -econdarv 


v^ 


576  A  TEXTBOOK  oF  PHYSIOLOGY 

retrograde  degeneration  occur.s,  the  nerve  cells  c(jnnected  Avith  ]y.\r- 
ticiilar  nerve-fibres  can  be  traced.  It  has  been  shown,  moreover, 
that  such  a  degeneration  ma}^  occur  in  other  cells  closely  connected 
■with  the  severed  neuron;  for  example,  cutting  the  j^osterior  roots  of 
a  nerve  causes  chromatolysis  in  the  closely  connected  cells  of  the 
anterior  horn  of  the  sjiinal  cord. 

The  nutritive  function  of  the  nerve  cell  is  most  clearly  seen  in 
the  axon  after  its  section.  When  an  axon  is  cut,  the  part  of  the  axon 
cut  off  from  the  nerre  cell  undergoes  Wallerian  or  primary  degen- 
eration. 

The  Effects  of  Section  of  the  Axon. — In  the  first  place,  the  conduc- 
tion of  impulses  is  interrupted.  A  current  of  injiay  is  set  up  in  the 
nerve  which  soon  subsides,  and  is  followed  by  a  gradual  loss  of 
excitability  and  conductivity;  the  loss  begins  in  the  most  central 
part  of  the  cut  peripheral  end,  and  graduall}'  j)asses  towards  the 
periphery. 

h 


J 


B  C 

Fig.  -MC'. 

A  «ho\\s  pericellular  chromatolysis  of  anterior  horn  cell:  B  shows  perinuclear  chro- 
matolysis; C  shows  degeneration  with  vaciiolation  of  the  cytoi>lasni.     (M.ott.) 

FolloA\ing  u})on  this,  Wallerian  degeneration  occurs.  The  complex 
lipoid  material  of  the  medullated  coat  splits  up,  and  the  lecithin  it 
contains  breaks  down,  yielding  cholin  and  fatty  acid.  The  staining 
properties  of  the  myelin  change,  oAving  to  the  setting  free  of  oleic 
acid,  and  thus  the  degenerate  fibres,  two  or  three  weeks  after  their 
section,  stain  black  with  Marchi's  fluid.  Normal  fibres  do  not  stain 
so.  By  this  staining  reaction  it  is  possible  to  trace  the  course  of 
degenerating  fibres  in,  and  so  unravel  the  structure  of,  the  central 
nervous  system.  Tne  myelin  breaks  up  into  droplets,  and  finally  is 
absorbed.  The  nuclei  multiply  in  the  fibre,  and  finally  the  axon  goes 
and  the  nucleated  sheath  is  alone  left.  Old  degenerated  fibres'  are 
marked  bj-^  their  failure  to  stain  with  the  Weigert-Pal  method. 

Regeneration  of  Nerve. — Even  during  the  degeneration  of  the  axon 
the  first  regenerative  change  begins  to  take  place.     Tnis  consists  of 


THE  XEUROX 


.)/7 


the  proliferation  of  the  neurileminal  cells  of  the  isolated  j^art,  to  form 
a  large  number  of  spindle  cells.     At  the  same  time,  the  products  of 


Fi.i.  317. — Wallekian  Dkuexekatiox  ix  a  Cat.      Marchi  Method  of  Staining. 
X  600.     (Mott,  from  AUbutt's  "  System  of  ilcdicinc") 

degeneration    are    removed    by    invading    leucocj^tei,    possibly    also 
through  the  agency  of  these  spindle  cells  themselves,  so  that,  when 


Fig.  318.^ — A,  .Section  rNDEK  High  Power  sHo^vI^-G  Regeneratiox  aftek  .*^e<:ti<;in 
OF  Sciatic  Xerve  of  Kitten,  One  Month  after  Operation.  Active  Re- 
generation HAS  occurred,  as  SHOWN  BY  OUTGROWTH  OF  XeUKOFIBRII-S  ACROSS 

THE  Seat  of  Lesion,     x  300.     B,  the  same  x  80.     (Mott.) 

all  signs  of  degeneration  are  removed,  the  isolated  part  of  the  ner^e- 
fibre  consists  of  these  proliferated  spindle  cells. 

37 


578  A  TEXTBOOK  OF  PHY8I0L0GY 

Under  suitable  conditions,  the  nerve-fibre  may  become  regenerated, 
wdtli  the  formation  of  a  now  axon,  medullary  sheath,  and  neurilemma- 
(Fig.  318).  There  is  considerable  difference  of  opinion  as  to  what  exactly 
are  the  suitable  conditions,  and  also  as  to  what  is  the  exact  part  played 
b}'  the  spindle  cells  in  this  regeneration.  It  is  held  by  some  authorities 
that  "  peripheral  regeneration  "  or  "  autogenetic  regeneration  "'  may 
take  place — that  is  to  say,  that  full  regeneration  of  the  peripheral 
]iart  may  occur  without  an\^  connection  being  made  with  its  original 
nerve  cell  or  some  other  nerve  cell.  Such  a  view  cannot  be  accejited, 
for  it  has  been  shown  that  in  all  exi^eriments  favouring  this  view 
the  possibility  of  the  central  influence  of  a  nerve  cell  has  by  no  means 
been  excluded.  When  precautions  are  taken — as,  for  example, 
enclosing  the  nerve  in  a  sterilized  rubber  cap,  or  transplanting  to 
regions,  such  as  the  peritoneal  surface  of  the  stomach,  where  no 
invasion  of  nerve-fibres  occurs — then  no  regeneration  takes  place. 
The  central  influence  of  a  nerve  cell  is  necessary'  for  the  true  regenera- 
tion of  nerve.  If  no  central .  connection  is  made,  the  regenerative 
changes  will  not  pass  bej'ond  the  stage  of  the  formation  of  spindle 
cells.  The  question  then  arises  as  to  Avhat  is  the  function  of  these 
sjaindle  cells.  According  to  the  view  of  central  regeneration,  they 
serve  merel}'  as  a  scaffolding  down  which  the  new  axon  grows  from 
the  central  end  of  the  nerve.  According  to  another  view,  the  spindle 
cells,  under  the  influence  of  the  central  nerve  cell,  develop  into  the 
new  peripheial  nerve-fibre,  some  spindle  cells  developing  into  axon, 
some  into  medullary  sheath,  and  some  into  the  new  neurilemma. 
The  former  view  is  generally  accepted. 


CHAPTER  LXVI 
THE  PHYSIOLOGY  OF  THE  NERVE-FIBRE 

Nerve  may  be  stimulated  by  natural  or  artificial  stimuli.  Natural 
stimuli  are  applied  to  the  '"  receptor  "  mechanisms  of  the  body,  such 
as  the  nervous  elements  concerned  in  sight,  smell,  taste,  hearmg, 
touch,  temperature.     These  are  dealt  with  later. 

A  nerve  may  be  artificially  stimulated  in  various  ways :  mechanic- 
ally, by  pinching ;  thermally,  by  a  hot  wire ;  chemically,  bj-  placing  on 
the  nerve  a  few  grammes  of  sodium  chloride,  or  some  glycerme; 
electrically,  the  induced  cuiTent  is  commonly  employed  in  experi- 
mental work  upon  nerve. 

As  judged  by  the  effects  of  its  stimulation  on  a  muscle,  nerve 
responds  to  minimal,  submaximal,  and  maximal  stimulation.  The 
response,  if  any,  is  probably  always  maximal,  but  as  bj*  a  weak  stimulus 
only  a  few  nerve-fibres  are  stimulated,  the  number  of  muscles-fibres 
which  contract  are  corresponding^  few;  hence  the  minimal  con- 
traction evidenced  by  the  lift  of  the  muscle  lever.  In  a  mixed  nerve, 
all  the  fibres  are  not  equally  excitable.  For  example,  on  gradually 
increasing  the  stimulation  of  the  sciatic  nerve  of  a  frog,  first  the  flexor 
muscles,  and  then  the  extensor  muscles,  are  excited  to  contraction. 
Similarly,  in  a  mixed  nerve,  the  vaso-constrictor  fibres  respond  to 
a  stimulation  weaker  than  that  which  affects  the  vaso-dilator  fibres. 
The  nerve  of  a  nerve-muscle  preparation  is  not  equally  excitable  in 
all  parts  of  its  course. 

Immediately  after  making  the  preparation,  the  nerve  is  most 
excitable  at  its  upper  end.  After  a  time  this  passes  off,  and  the  most 
excitable  part  progressively  descends  towards  the  muscle.  A  nerve- 
fibre  is  also  more  excitable  in  the  neighbourhood  of  the  mam  branches 
severed  durmg  its  preparation.  The  increased  excitability  is  probably 
due  to  changes  in  the  nerve  provoked  by  injur}-. 

The  excitabilitv  of  nerve  is  modified  by  various  factors.  It  is 
increased  by  slight  cooling  below  room  temperature,  and  decreased 
by  greater  cold.  It  is  increased  by  gentle  warmth.  Loss  of  water 
at  first  increases  and  then  abolishes  excitabilitN-.  Chemical  sub- 
stances affect  nerve  in  various  ways.  Carbon  dioxide,  chloroform, 
and  ether  depress  the  excitabilitv. 

If  a  constant  (polarizing)  electric  current  be  passed  through  a  nerve, 
it  increases  the  excitability  around  the  negativ'e  pole — the  kathode — 
and  depresses  it  around  the  positive  pole — the  anode. 

The  rate  of  conduction  of  the  nerve-impulse  is  computed  to  be 

579 


580 


A  TEXTBOOK  OF  PHYSIOLOGY 


from  83  to  100  metres  per  second.  It  may  be  estimated  as  follows, 
using  the  sciatic -gastrocnemius  preparation  of  the  frog  :  The  re- 
cording drum  is  arranged  at  a  fast  rate,  with  a  "  striker  "  for  com- 
pleting the  circuit  of  the  primary  current  of  the  induction  coil.  To 
the  secondary  coil  are  attached  two  Du  Bois  keys  in  the  manner  showai 
in  the  diagram  (Fig.  31!)).  From  these  pass  two  pairs  of  electrodes, 
one  of  Avhich  will  be  applied  to  the  upper  portion  of  the  nerve,  the 
other  to  the  lower  portion.  The  latent  period  of  the  muscular  con- 
traction is  determined,  iirst  for  stimulation  by  the  upper  pair  of 
electrodes,  the  lower  ])air  being  short-circuited  by  closure  of  its 
Du  Bois  key;  then  for  stimulation  by  the  lower  pair  of  electrodes,  the 
upper  pair  being  short-circuited.  The  difference  in  time  of  the  latent 
periods  is  determined  by  recording  underneath  the  curves  the  vibra- 
tions of  a  tuning-fork  oscillating  100  times  per  second.  This  difference 
represents  the  time  taken  for  the  nervous  impulse  to  pass  along  the 
length  of  nerve  between  the  two  pairs  of  recording  electrodes  (Fig.  320). 
The  length    is   measured    in    millimetres,   and   the    velocity    of    the 


Pig.  319. Diagram  of  the  Experiment  un  the  Kate  of  Transmission  of  a 

Nervous  Impulse. 


transmission  of  the  nervous  impulse  thus  calculated.  The  rate  of  con- 
duction may  be  measured  more  accm-ately  by  means  of  an  electro- 
meter and  determining  how  long  it  takes  for  the  "  current  of  action  " 
to  pass  between  two  points  of  a  nerve.  The  velocity  may  be  ascer- 
tained in  man  by  estimating  the  time  taken  for  the  impulse  to  pass 
along  the  length  of  nerve  from  the  clavicle  to  elbow,  by  stimulating 
first  at  one  point,  then  at  the  other,  and  recording  the  contraction  of 
the  thumb  muscles  by  means  of  tambours. 

The  impulse  is  conducted  along  a  nerve  in  both  directions.  This 
ean  be  shown  by  the  following  experiments:  The  iliac  end  of  a  dis- 
sected sartoiius  muscle  is  divided  into  two  portions  (Fig.  321).  Stimu- 
lation with  a  weak  induction  shock  at  a  or  a',  whsre  there  are  no 
nerve-fibres,  produces  a  contraction  of  the  one  half  of  the  muscle; 
excitation  at  b  or  b',  where  there  are  nerves,  evokes  contraction  of 
both  halves.  Again,  the  graciHs  muscle  of  the  frog  is  completely 
.separated  into  two  portions  by  a  tendinous  intersection  (Fig.  322), 
Both  halves  of  the  muscle  are  supplied  by  a  single  nerve,  the  individual 
fibres  of  which  divide  and  supply  both  halves  of  the  muscle.  Stimula- 
tion at  a  or  n,    where   there    are    no    nerve-fibres,    causes   only  the 


THE  PHYSIOLOGY  OF  THE  NERVE-FIBRE 


581- 


corresponding  half  of  the  muscle  to  contract;  but  excitation  at  b  or  b\ 
where  the  nerves  lie,  will  cause  both  halves  to  contract.  The  "  action 
current  '"  spreads  along  a  nerve  in  both  directions. 

The  rate  of  conduction  in  nerve  is  modified  by  various  factors. 
Cooling  decreases,  gentle  warmth  raises,  the  rate.  Exact  measure- 
ments of  the  relation  of  temperature  to  conductivity  do  not  affo;rd 
proof  that  the  transmission  of  nervous  energy  is  a  chemical  rather  tlian 


Fig.  320.— Velocity  of  Motor  Ijipulse  ix  Human  Neemi:.     (Waller.) 


a  physical  process.     Its  nature  is  unknown.     Chloroform  and  manj- 
other  poisons  chminish  and  then  abohsh  the  conductivity. 

Unlike  muscle,  the  excised  nerve,  as  the  result  of  activity,  shows 
no  measurable  mechanical,  thermal,  or  chemical  changes.  Like 
muscle,  it  shows  electrical  phenomena^the  current  of  injury,  the 
current  of  aeti<Mi  (negative  variation),  and  electrotonic  currents  (see 
beiow).  »t 


Yiii.  321.  —  Diagram  of  tub 
Sartorius  Experiment  to  show 
the  Transmission  of  a  Nervous 
Impulse  in  Both  Directions. 


Fig.  322.  —  Diagram  of  the 
Gracilis  Experiment  to  show 
the  Transmission  of  a  Nervous 
Impulse  in  Both  Directions. 


The  Effects  oJ  a  Constant  Current.— To  study  these  effects,  a  sciatic- 
gastromemius  preparation  and  non-polarizable  electrodes  are  used. 
Both  make  and  break  of  a  constant  current  excite  the  nerve,  and  cause 
a  contraction  of  the  muscle ;  no  excitation  occurs  while  the  current  is  ■, 
flowing.  The  effect  of  the  make  and  break  stimuli  vary  according  to 
the  strength  of  the  current,  and  according  to  its  direction.     If  it  be 


682  A  TEXTBOOK  (>F   I'HY.SIOLOGY 

flowing  in  the  nerve  from  the  muscle,  it  is  said  to  be  ascending;  if 
towards  the  muscle,  descending  (Fig.  323).  In  other  words,  it  depencls 
upon  the  position  of  the  point  of  entry  of  the  current  (the  anode),  and 
the  point  of  exit  (the  kathode).  When  a  cuiTent  begins  to  flow  at  make, 
excitability  and  conductivity  is  diminished  in  the  region  of  the  anode 
and  increased  in  tlie  neiL'h born-hood  of  the  kathode;  when  the  current 


Fig.  323. — A,  As  "  Asce:st)isg  "  Ctterext.     B,  A  "  DE5CE>-Drs"G  "  CtrRREifT. 

ceases  to  flow,  the  condition  of  de^^ressed  excitability  and  conductivity 
at  the  anode  gives  Avay,  swings  back,  it  may  be  said,  to  a  condition  of 
raised  excitability  and  conductivity,  thus  affording  a  stimulus.  Simi- 
larly, at  the  kathode  the  condition  of  raised  excitability  and  con- 
ductivity swings  back  to  a  condition  of  lowered  excitabilitj'  and 
conductivity.  At  make,  therefore,  the  kathode  is  the  exciting  electrode; 
at  break,  the  anode. 

With  weak  currents,  only  the  more  efficient  stimuli  excite.  The  sudden  increase 
when  the  current  is  made  is  more  effective  than  the  sudden  ''  swing-back"  at  the 
anode  when  the  current  is  broken:  therefore,  with  weak  cuiTents  in  either  direction, 
contractions  occur  only  at  make  : 

Ascending.  Descending. 

Make.         Break.  Make.         Break. 

C.  O.  C.  0. 

With  medium  currents  in  both  directions,  there  occur  contractions  at  make  from 
the  kathode  p.nd  at  break  from  the  swing- back  at  the  anode  : 

Ascending.  Descending. 

Make.         Break.  Make.         Break. 

C.  C.  C.  C. 

With  "  strong"'  currents,  the  effect  is  mcditied  according  to  the  direction  of  the 
current.  AVhen  the  current  is  ascending,  the  anode  lies  between  the  exciting  kathode 
and  the  muscle.  Around  the  anode  the  excitability  and  conductivity  are  so  depressed 
that  no  impulse  gets  through  to  the  muscle,  whicli  is  therefore  only  stimulated  from 
the  anode  at  break.  This  stimulation  sometimes  induces  a  tetanus,  known  as  "  Ritter's 
tetanus."' 

With  a  strong  descending  current,  the  kathode  being  next  the  muscle,  the  impulse 
generated  at  the  kathode  at  make  is  not  blocked  in  any  way,  and  causes  a  contraction. 
At  break,  however,  the  depressed  excitability  and  conductivity  which  supervenes  in 
the  kathodic  region  is  sufficient  to  block  ths  impulse  arising  from  the  anode  at 
break.     We  have,  therefore  : 


THE  PHYSIOLOGY  OF  THE  NERVE-FIBRE 


5.S3 


Ascending. 

Make.         Break. 

0.  C. 


Descending. 

Make.         Break 

C.  0. 


This  regular  order  of  contractions  for  currents  of  different  intensities  is  known    as 
"  Pfliiger's  law  of  contractions." 

The  altei'ed  conditions  at  the  anode  and  at  the  kathode  can  bo 
proved  by  stimulation  in  these  regions  bj'  single  induction  shocks,  using 
ordinary  electrodes.     Fig.  324  shows  the  result  of  such  an  experiment. 


Pig.  324. — Showing  Effect  of  Stimulation  in  Regions  of  Kathode  and  Anode. 

The  above  alterations  of  excitability  are  sometimes  referred  to  as 
■'  electrotonus  "';  they  are  better  described  as  "  electrotonic  alterations 
of  excitability."  The  term  "  electrot3nus  "  is  best  emplo3'ed  for  the 
electrical  currents  which  occur  in  the  nerve  itself  in  the  parts  outside 
that  through  which  the  constant  current  passes.     The  current  which 


^  I '  Anelectrotonic  ^  I ' 
Current 


Fig.  32.J. — Showing  Direction  of  An  electrotonic  and  Katelectrotonic 

Currents. 


is  found  in  the  neighbourhood  of  the  anode  is  termed  the  anelectrotonic 
■current,  that  in  neighbourhood  of  the  kathode  the  katelectrotonic. 
Galvanometric  observations  show  that  the  anelectrotonic  current 
Hows  towards,  and  the  katelectrotonic  current  away  from,  the  polarized 
region  (Fig.  32.1). 


o84  A  TEXTBOOK  OK  PHY810L0(;\ 

\Vlu>n  the  |)olarizing  current  is  broken,  there  occur  '''  after-elcc  tro - 
tonic  currents."  In  the  intrapolar  region  it  is  in  the  opposite  direction 
(unless  the  current  has  Ijeen  strong  and  of  short  duration,  when  it  is 
in  tlie  same  direction);  outside  the  kathode  it  is,  as  before,  away  from 
the  polarized  area;  outside  the  anode  it  is  at  first  towards,  and  after- 
wards awa}^  from,  the  polarized  area. 


Anelectrotonic 

Previously 

Katelectrotonic 

area 

polarized  area 

area 

first  > 

< 

> 

then  < 

If  the  nerve  be  excited  by  a  tetanic  current,  the  electrotonic  currents 
are  weakened  and  the  polarizing  current  strengthened  bj'-  the  "  current 
of  action." 

The  "  paradoxical  contraction  "  of  muscle  takes  place  when  the 
branch  of  a  divided  nerve  is  stimulated  with  a  constant  current,  and 
is  due  to  the  electrotonic  current  spreading  along  the  branch  towards 
the  point  where  the  nerve-branches  ccme  together,  and  thus  exciting 
the  fibres  of  the  nerve  which  supplies  the  muscle. 


CHAPTER  LXVir 
THE  RECEPTOR  MECHANISMS  -CUTANEOUS  SENSATIONS 

The  Receptors  are  classified  as  Extero-ceptive :  Xoii- Distance: 
Touch,  heat,  cold,  j)ain,  taste;  and  Distance:  Smell,  sight,  hearing. 
Proprio-ceptive :  labryinthine  (semicirculai-  canals),  and  kinaesthetic 
(muscles,  tendons,  and  joints).  Entero-ceptive :  those  of  common 
sensibility  (thirst,  hunger,  and  pain). 

In  regard  to  the  extero-ceptive  mechanism,  certain  general  formulae 
or  laws  have  been  formulated  to  describe  the  relations  between  ex- 
ternal stimuli  and  conscious  reactions.  The  most  important  of  these 
is  known  as  the  "law  of  specific  sense  energy,"'  or  '' Miiller's  law." 
It  states  that — (1)  different  stimuli  acting  upon  the  same  sense  mechan- 
ism produce  the  same  kind  of  sensation;  (2)  the  same  stimulus  acting 
ujion  different  sense  mechanisms  calls  forth  different  sensations.  For 
example,  stimulation  of  the  optic  nerve,  whether  b}'  the  normal  means 
of  stimulation  (the  so-called  "  adeciuate  "  stimulus),  the  vibrations 
of  the  ether,  or  by  abnormal  mechanical  means,  such  as  a  blow^  on 
the  eye  (a  so-called  "inadequate"  stimulus),  evokes  the  sensation 
of  light. 

Another  important  law,  known  as  Weber's  law,  states  that  "  the 
just  noticeable  increase  of  a  stinnilus  bears  a  constant  ratio  to  the 
original  stimulus,"  or  "  two  stimuli,  in  order  to  be  discriminated, 
must  be  in  a  constant  ratio,  the  latter  being  independent  of  the  abso- 
lute magnitudes  of  the  stimuli."  The  actual  value  of  ihis  ratio, 
although  constant  for  any  one  sense  mechanism,  varies  from  organ 
to  organ.  For  example,  if  one  candle  added  to  ten  just  perceptibly 
increased  the  illumination,  ten  candles  would  have  to  be  added  to 
a  hundred  to  do  so,  and  one  hundred  to  a  thousand.  The  validity 
of  this  law  has  been  hotly  contested,  since  the  experimental  methods 
employed  to  establish  it  have  yielded  very  inconstant  results.  Un- 
doubtedh',  some  relation  of  the  kind  enunciated  by  Weber's  law  does 
exist,  since  all  judgments  involve  comparison. 

Touch,  Heat,  Cold,  Pain. — ^\'ith  the  exception  of  taste,  the  non- 
distance  receptor  mechanisms  mainl^^  come  luider  the  class  of 
'■  cutaneous  sensations,""  and  are  located  in  the  skin. 

The  Structure  of  the  Receptors  of  Cutaneous  Sensation. — There  is 

a  dearth  of  knoAvledge  as  to  the  structure  of  the  receptor  mechanism 
concerned  in  the  sensations  of  touch,  heat,  cold,  and  pain.  In  the 
skin  various  nerve-endings  have  been  descri])ed : 

585 


58(3 


A  TEXTBOOK  OF  PHYSIOLOGY 


1.  Several  forms  of  end-organs  or  terjninal  cori^uscles,  such  as 
Meissner's  corjjuscles,  Kraiise's  end-bulbs,  Ruffini's  organs,  and  the 
corpuscles  of  Pacini  or  Vater.  Such  terminal  corpuscles  consist  of  a 
coarse  nerve-fibre  or  knot  of  branches  surrounded  by  a  semifluid 
intercellular  substance  enclosed  in  a  capsule. 

Meissner's  Corpuscles  are  oval  bodies  about  -^.^l .  to  jl.  inch  in 
length.  Each  corpuscle  consists  of  flattened  cells  surrounded  by  a 
capsule,  around  which  one  or  two  medullated  nerve-tibres  wind,  to 
enter  at  the  upper  pole.  The  medullated  coat  is  lost  at  the  point 
of  entrance.  These  corjiuscles  occur  particularly  in  the  papillae  of 
the  true  skin,  esiDcciall  v  in  the  jjalms  of  the  hands  and  in  the  soles  of 
the  feet. 

Krause's  End-bulbs  have  the  form  of  aiv  encapsulated  bulb,  the 
axon  of  the  medidlated  nerve  entering  its  lower  extremity  to  ramify 
among  the  ovoid  cells  contained  within  the  capsule. 
They  occur  particularly  in  the  conjunctiva,  the  mucous 
membrane  of  the  mouth,  the  glans  penis  and  clitoris, 
and  the  ligaments  of  joints.  They  also  occur  on  the 
under-surface  of  the  toes  of  guinea-pigs  and  in  the 
wing  of  the  bat. 

RuffinVs  Organs  are  found  in  the  subcutaneous 
tissue  near  the  sweat  glands,  and  in  the  coriura  of 
the  fingers  and  toes;  they  lack  distinct  capsules. 

The  Pacinian   Corpuscle  (Fig.  328)  occurs  in   the 

subcutaneous  tissues  of  the  palm,  fingers,  sole;  in  the 

sexual  organs;  in  the  deep  layers  of  connective  tissue 

near  joints;  and  in  the  mesentery.    Each  corpuscle  is 

of  oval  shape,  and  consists  of  forty  to  fifty  lamellae 

End  concentrically    arranged.      The    lamellae    are    formed 

Bulb  of  the  ^f  connective  tissue,  and  covered  with  endothelium. 

juNCTivA.  A   lymph  space   exists  between  each  lamella  and  its 

(Krause.)         neighbour.     A   medullated   nerve-fibre  enters   at  one 

pole.     Its  axon  passes  through  all  the  lamellae  to  the 

central  core  of    the    corpuscle,  ramifies    therein,  and   ends  in  small 

terminal  buds  near  the  distal  pole  of  the  corpuscle. 

2.  Nerve-endings  in  comiection  with  tactile  hairs.  Fine  medullated 
nerve-fibres  form  a  network  in  the  outer  coat  of  the  hair  follicle,  and, 
losing  their  medullary  sheath,  run  parallel  to  the  hair,  and  finally 
penetrate  and  end  in  the  inner  layer  of  the  hair  sheath  (Fig.  329). 

3.  Single  nerve-fibres  pass  to  the  under-surface  of  the  epidermis, 
lose  their  medullary  sheath,  and  divide  into  fine  filaments,  which  end 
among  the  cells  of  the  epidermis  (Fig.  330) . 

Various  other  special  forms  of  nerve-endings  liave  been  described 
in  different  animals — for  example,  in  the  bill  of  the  duck,  the  skin  of 
the  whale,  etc. 

Methods  of  Investigation. — The  sensation  of  touch  or  pressure 
is  investigated  by  a  series  of  hairs  of  different  thicknesses  attached 
at  right  angles  to  Avooden  rods.  The  hair  is  applied  perpendicularly 
to  the  skin,  and  the  amount  of  j^ressure  required  to  bend  visibly  any 


Fig.  326 


RECEPTOR  MECHANISMS— CUTANEOUS  SENSATIONS      oST 


Fm.  327.^Nerve  Endins  in  a  Special  Connective  Tissue  Organ  in  the  Deeper 
Part  of  the  Cutis,     x  320.     (Ruffini,  from  "  Quain's  Anatomy.") 

«,  Sheath  of  entering  nerve:  h,  sheath  of  terminal  organ;  c,  blood  capillaries;  d,  d,  ter- 
minations of  axons;  e,  spindle-shaped  connective  tissue  core  in  which  these 
terminations  ramify. 


Fig.  32S. — Pacinian  Corpuscle. 


i'lG.  329. — Shoaving  Sensory  Nekve 
Endings  at  the  Base  of  a  Haie. 
(Redrawn  after  van  Gehuchten,  from 
Dahlgren  and  Kejiner.) 


588 


A  TEXTBOOK  OF  PHYSIOLOGY 


hair  being  iinown,  the  threshold  vahie  of  the  sensation  of  pressiue 
can  be  accurately  determined.  For  ordinary'  clinical  purposes,  the 
presence  or  absence  of  sensation  to  the  touch  of  cotton-wool  is  usually 
employed.  To  test  relative  sensitiveness  or  the  power  to  discriminate 
the  part  touched  in  various  parts  of  the  skin,  the  distance  between 
the  points  of  a  jjair  of  comjjasses  is  measured  when  the  points  are  just 
sensed  as  touching  two  jilaces.  Temperature  sensations  may  be 
tested  with  a  hollow  pencil-shaped  rod  in  which  water  of  various 
temperatures  is  circulated.  A  more  common  method  is  to  use  the 
bottom  of  test-tubes  containing  water  at  various  temperatures.  Pain 
may  be  tested  with  the  prick  of  a  needle-point. 

The  Sensations  of  Touch  or  Pressure. — Pressure-pointg  are  closely 
related  to  the  distribution  of  hairs,  each  hair  having  a  pressure-point 


Fig. 


330. — iSensoky  Nekve  End-Organ  in  Exteenal  Epithelium  of  Pig's  Snovt. 
(Redrawn  after  Retzius,  from  Dahlgren  and  Kepner.) 


on  the  surface  corresponding  to  the  situation  of  the  hair  follicle. 
Some  pressure-points  have  no  such  relation  to  the  hair  follicle.  In 
hairless  parts  it  is  suggested  that  pressure  is  associated  with  the 
corpuscles  of  Meissner  and  of  Pacini.  These  jjressure  organs  are  not 
directly  stimulated,  since  the}'  do  not  reach  the  exposed  surface  of 
the  skin.  The  excitation  is  produced  by  the  variation  in  pressure 
in  the  neighbourhood  of  the  end-organ,  as  can  be  shown  by  the  fact 
that  they  are  stimulated  either  by  pushing  against  or  jjulling  on  a  hair. 

The  extent  of  the  surface  to  which  the  stimulus  is  applied  is  an 
important  factor.  For  example,  a  greater  pressure  per  unit  is  required 
for  an  area  of  0-25  square  millimetre  than  one  of  0-5  square  millimetre. 
The  optimum  surface  is  about  0-5  square  millimetre.  Above  or  below 
this  area  the  amount  of  pressure  required  is  increased.  It  has  been 
found  that  the  hair}^  parts  are  more  excitable  and  more  easily  fatigued 
than  the  smooth  areas  of  the  skin. 

In  estimating  weights,  it  is  easier  to  compare  them  applied  succes- 
sively  than  simultaneously.     Further,   the  rapidity  with  which   the 


RECEPTOR  MECHANISMS— CUTANEOUS  SENSATIONS     o8!J 

stimuli  are  successively  applied  influences  the  judgment.  Generally 
speaking,  the  slower  the  rate  of  change,  the  higher  must  be  the  stimulus 
value.  It  is  also  easier  to  judge  of  a  difference  in  weight  than  to 
say  whether  such  a  weight  is  heavier  or  lighter  than  another.  It  is 
easier  to  detect  an  increase  in  weight  than  a  decrease.  The  experi- 
mental results  are  so  variable  that  it  cannot  be  said  that  Weber's 
law  has  been  proved  to  hold  good  for  tactile  impressions. 

The  most  sensitive  parts  are  those  which  ws  use  habitually  as 
organs  of  touch.  Thus,  the  under-surfaces  of  the  tips  of  the  fingers 
and  the  palms  of  the  hand  are  far  more  sensitive  than  the  skin  of 
the  gluteal  region.  Sensitiveness  is  also  marked  in  the  parts  of  the 
body  habitually  moved,  and  increases  from  the  joints  towards  the 
extremities.  It  is  also  greater  along  the  transverse  axis  of  a  limb 
than  in  the  same  distance  along  the  long  axis. 

The  following  table  shows  in  millimetres  the  distance  in  various 
laarts  of  the  body  at  which  the  ]ioints  of  a  compass  are  appreciated 
as  separate: 

Tip  of  tongue  . . 

Under  surface  of  tip  of  finger 

Red  part  of  lip 

Under  surface  of  second  phalanx  of 

finger 
Upper  surface  of  tip  of  finger 
Tij)  of  nose 
Ball  of  thumb 
Centre  of  palm 

Under  surface  of  tip  of  great  toe 
Upper  sufrace  of  second  ])halanx  of 

finger 
Eyelid  

According  to  these  degrees  of  sensitiveness,  it  is  possible  to  locate 
with  precision  the  exact  spot  touched.  Most  people  are  imable  to 
localize  a  touch  on  the  second,  third  or  fourth  toe  to  the  exact  toe 
touched.     By  education  the  local  sign  is  developed. 

The  sensitiveness  of  the  skin  is  increased  after  massage  or  salt 
baths,  blunted  by  cold,  anaemia,  venous  congestion,  or  after  the  appli 
cation  of  solutions  of  certain  drugs,  such  as  atropine,  chloral,  etc. 
In  regard  to  absolute  sensitiveness,  the  most  sensitive  parts  of  the 
body  are  the  forehead,  temples,  back  of  hand,  and  forearm.  These 
.are  said  to  be  able  to  detect  a  pressure  of  0-002  gramme.  Many  ex- 
periments have  been  made  to  determine  the  frequency  with  which 
pressure  stimuli  must  follow  each  other  to  ]:>roduce  a  fused  sensation, 
but  the  results  are  discordant.  The  length  of  time  a  sensation  per- 
sists after  removal  of  the  stimulus  varies  greatly  in  different  parts. 
In  the  finger  it  vanishes  almost  at  once,  on  the  forehead  it  persists 
for  some  little  time,  after  a  moderately  strong  stimulus. 

The    Information    derived    from    Tactile    Sensations. — From    the 

tactile  sensations,  associated  with  the  kinsesthetic  sensations,  which 
occur  when  the  object  presses  heavily  or  is  moved,  we  derive  in- 
formation as  to  form,  size,  and  nature,  of  the  body  touched.  It  may 
be  small  or  big,  smooth  or  rough,  etc.     When  a  large  area  of   the 


1-1 

Under  surface 

of 

lower 

third 

of 

2-3 

forearm  . . 

15-0 

-r-5 

Cheek 
Temples 

15-8 
22-6 

4-.-> 

Forehead    . . 

22-G 

(>-8 

Back  of  head 

27-1 

l)-8 

Back  of  hand 

31-6 

(>•;-)- 7 

Knee 

3(3-1 

S-9 

Buttock      . . 

44-6 

I1-3 

Forearm  and  1 
Neck 

"g 

4.5-1 
54-1 

11-3 

Upper  arm,  thigh, 

•entrc 

of  bac 

k" 

f)7-l 

11-3 

r>90  A  TEXTBOOK  OF  PHYSIOLOGY 

skin  is  uniformly  pressed  upon,  the  sensation  of  pressure  soon 
disappears;  when  a  finger  is  immersed  in  a  bath  of  mercury,  the 
sensation  of  pressure  is  Hmited  to  the  area  dividing  the  regions  of 
different  pressure. 

Judgments  are  formed  from  the  sensations  received  on  the  supposi- 
tion that  there  is  no  displacement  of  the  body  from  the  normal  position. 
Such  a  displacement  ma^^  lead  to  an  erroneous  juflgment .  as  exemplified 
by  the  experiment  of  Aristotle.  A  pea  or  marble  placed  between 
the  first  and  second  fingers,  held  in  the  normal  position,  feels  one  body. 
If  the  fingers  be  crossed,  and  the  pea  be  so  placed  as  to  touch  the 
outer  side  of  both  fingers,  two  peas  are  felt.  So,  too,  the  tip  of  the 
nose,  touched  by  the  fingers  in  this  position,  gives  the  sensation  of 
two  noses,  particularly  if  the  eyes  be  closed  at  the  time. 

The  local  sign  attached  to  the  sensations,  when  received  in  the 
brain,  is  definite  and  precise.  It  is  for  this  reason  that  a  patient's 
nose  shared  in  a  headache  after  a  surgeon  had  transplanted  a  piece 
of  skin  from  his  forehead  to  his  nose  I 

The  Sensations  of  Temperature. — ^Sensations  of  temperature  can 
be  evoked  from  the  Avhole  of  the  skin;  the  fiont  part  of  the  nares; 
from  the  mucous  lining  of  the  beginning  (mouth,  pharynx,  oesophagus) 
and  end  of  the  alimentary  tract  (the  region  of  the  anus);  from  the 
cornea,  conjunctiva,  and  penis.  The  spots  stimulated  by  heat  and 
cold  are  different.  Cold  spots  are  more  numerous  than  hot  spots, 
especially  over  the  extremities.  They  are  generally  arranged  in  curved 
lines.  The  curves  of  the  hot  and  cold  spots  do  not,  however,  coincide. 
It  has  been  suggested,  but  the  evidence  is  very  slight,  that  Krause's 
end-bulbs  and  Ruifinis  organs  are  respectively  the  special  structures 
associated  with  the  appreciation  of  cold  and  warmth. 

Two  views  are  held  as  to  what  constitutes  the  adequate  stimulus 
of  these  sensations.  According  to  one  view,  the  chief  factor  is 
the  alteration  of  the  end-organ  temperature,  whatever  that  may  be, 
a  I'ise  of  temperature  in  the  end-organ  cieating  a  sensation  of  warmth, 
a  fall  in  temperature  producing  the  sensation  of  cold.  Upon  this 
view,  it  is  somewhat  difficult  to  account  for  the  sensation  of  cold 
which  persists  after  removal  of  a  cold  body.  During  this  time  the 
temperature  in  the  end-organ  is  rising.  For  example,  after  a  cold 
penny  (2°  C.)  has  been  applied  to  the  forehead  for  thirty  seconds,  the 
sensation  of  cold  mav  persist  for  twentj-  seconds  after  its  removal. 

According  to  the  second  view,  a  skin  area  gives  no  temperature 
sensation  when  it  is  at  the  so-called  physiological  zero  of 
temperature.  This  point  shifts  with  the  conditions  to  which  the 
part  is  exposed.  Any  alteration  of  temperature  will  give  rise  to  a 
sensation  the  intensity  and  character  of  which  depend  upon  the 
difference  from  this  i^oint  of  reference.  Thus,  if  one  hand  is  put 
into  hot  and  another  into  cold  water,  and  then  both  into  tepid 
water,  the  "hot"  hand  feels  it  cold  and  the  "cold"  hand  warm. 
Probably  it  is  the  difference  between  the  surface  and  deej)  skin 
te^mperatm'e  (surface  and  deep  sense  organs)  which  gives  the  intensity 


RECEPTOR  MECHANISMS— CUTANEOUS  SENSATIONS     591 

of  sensation :  the  surface  and  deep  sense  organs  may  be  compared  to 
a  pair  of  thermo-electric  junctions.  The  adequate  stimulus  depends 
not  only  on  the  intensity  of  the  stimulus,  but  upon  the  actual  size 
of  the  region  stimulated.  It  is  probably  for  this  reason  that  water 
at  37°  C.  feels  warmer  to  the  whole  hand  immersed  in  it  than  does 
water  at  40°  C.  to  one  finger  only.  The  degree  of  sensation  evoked 
also  depends  upon  the  thermal  capacity  and  conductivity  of  the  body 
applied  to  the  skin. 

The  parts  of  the  body  in  which  the  thermal  sense  is  most  acute 
are  the  tip  of  the  tongue,  the  eyelids,  cheeks,  lips,  and  belly.  The 
laundress  tests  the  warmth  of  her  iron  with  her  cheek,  and  not  with 
her  hand,  and  the  bared  elbow  is  used  by  a  good  nurse  to  test  the 
temperature  of  a  hot  bath.  The  temperature  sensations  regulate  to 
a  large  extent  the  tone  of  the  skeletal  muscles,  the  vaso-motor  tone, 
the  activity  and  metabolism  of  the  body.  The  play  of  wind,  sunlight 
and  shadow  stimulate  the  nervous  system  and  prevent  monotony. 

The  Sensation  of  Pain. — It  seems  probable  that  special  "  pain 
spots  "  exist  for  the  appreciation  of  pain.  They  have  a  long  latent 
period  when  subjected  to  weak  stimulation,  and  do  not  react  easily 
to  rapidly  alternating  or  oscillating  stimuli.  They  do  not  coincide 
Avith  pressure-points,  and  are  about  four  times  as  numerous  as  these. 
It  has  been  suggested  that  the  free  nerve-endings  in  the  skin  are  the 
special  organs  excited.  In  support  of  this  view,  it  has  been 
showai — 

1.  That  diminution  of  the  surface  area  stimulated  does  not  diminish 
the  effectiveness  of  the  stimulus. 

2.  That  the  electrical  stimulus  is  more  effective  than  any  other 
form. 

3.  That  the  first  sensation  produced  by  the  application  of  a  corrosive 
is  one  of  pain. 

It  is  stated  also  that  from  the  cornea  only  sensations  of  pain  arise, 
and  that  here  the  only  receptive  elements  are  the  intra-epithelial 
nerve-endings. 

It  is  probable,  however,  that  pain  may  arise  from  excessive  stimu- 
lation of  the  organs  connected  with  the  other  sensations  of  the  skin. 
Excessive  heat  or  cold  produces  the  same  kind  of  sensation  of  pain. 

Protopathic  and  Epicritic  Sensibility.— A  careful  study  of  the  sensory 
changes  associated  with  the  experimental  division  and  regeneration  of 
cutaneous  nerves  in  trained  observers,  has  led  to  a  new  classification 
of  the  sensibilities  of  the  skin.  In  the  area  supplied  by  the  severed 
nerves  the  sensations  of  heat,  pain,  and  cold,  were  lost,  also  sensa- 
tion of  touch  to  cotton-wool,  and  to  the  pulling  of  the  skin  outwards. 
Pressure  inwards  was  appreciated  and  well  localized — that  is.  deep 
pressure — due  to  sensation  in  the  underhung  muscles.  After  seven 
weeks,  sensibility  to  pin-prick  returned,  but  it  required  a  higher 
minimal  stimulus  than  the  normal  parts,  and  produced  a  peculiar 
unpleasant  sensation  which  radiated  and  tended  to  be  localized  in 
remote  parts.     Water  of  38°  to  50°  C.  was  recognized  as  hot,  and 


r)92  A  TEXTBOOK  OK  PHYSIOLOGY 

of  C^  to  24"  C.  as  cold;  but  no  sensations  of  warmth  or  coolness 
were  experienced  from  water  at  intermediate  temperatures.  The 
areas  where  these  sensations  were  experienced  corresponded  to  hot 
and  cold  spots  previously  jnarked  out. 

This  kind  of  sensibility  to  pain  and  tempei'ature  is  termed  proto- 
pathic.  Its  chief  characteristics  are  its  high  threshold  stimulation 
value  and  the  fact  that  it  depends  upon  the  existence  of  specific  end- 
organs.  It  probal^Iy  represents  a  more  primitive  t\'pe  of  nervous 
organization. 

After  a  variable  time  the  skin  again  became  sensitive  to  light 
touch,  compass-points  were  discriminated,  and  varying  degrees  of 
temperature  appreciated.  This  more  delicate  organization  is  termed 
the  epicritic  system.  Epicritic  sensibility  is  characterized  by  low 
threshold  stimulation  value.  Its  re-establishment  may  depend  on 
the  completion  of  a  single  regenerative  process,  rather  than  on  the 
regeneration  of  a  special  system  of  epicritic  nerves. 

The  central  connections  of  the  conductors  associated  with  these 
various  sensations  are  dealt  with  later. 


CHAPTER   LXVIII 
TASTE  AND  SMELL 

Taste — The  Receptor  Mechanism. — The  taste  buds  probably  form 
the  receptor  mechanism  for  tlie  sensation  of  taste,  for  the  sense  of 
taste  is  absent  from  those  parts  of  the  tongue  where  these  organs  do 
not  exist,  and  is  most  acute  in  the  regions  where  they  are  most  abun- 
dant. Further,  section  of  the  glosso-pharyngeal  nerve,  the  nerve  of 
taste,  leads  to  a  degeneration  of  the  sensory  cells  in  these  buds. 

The  taste  buds  are  found  in  many  of  the  fungiform  and  in  all  the 
circumvallate  papilloe  of  the  tongue:  to  a  certain  extent  also  on  the 

A 


l-'iG.   331. — MicKoscopic    View   of    Section    throttgh   Circumvallate    Papu^l.!-: 
A,  epithelial  layor:  B,  taste  buds;  P,  gland;  E,  subepithelial  Ivyei-;  G,  luuscJe. 


soft  palate  and  the  surface  of  the  epiglottis.  They  a.re  best  seen  in 
the  circumvallate  papillae.  These  are  eight  to  fifteen  in  number,  and 
form  at  the  base  of  the  tongue  a  V,  with  the  apex  backwards:  it  is 
calculated  that  there  are  more  than  30,000  taste  buds  in  this  region 
in  the  ox.  They  are  far  more  numerous  in  the  embrj'o  at  the  sixth 
to  the  seventh  month  than  in  the  adult.  Many  of  them  subsequently 
become  infiltrated  with  leucocytes  and  destroyed.  The  fungiform 
(fungus-like)  and  filiform  (rod-like)  papillae  of  the  tongue  are  concerned 
in  the  sensations  of  touch,  temperature,  and  pain. 

The  taste  buds  are  minute  oval  bodies  embedded  in  the  epithelial 
layer,  and  communicating  with  the  surface  by  a  funnel-shaped  opening 

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— the  laste  pore.  Into  this  pore  the  hair-like  processes  of  the  true 
gustatory  cells  project.  These  cells  are  delicate  rod-Hkc  cells,  with 
a  central  nucleus  surrounded  by  granidar  protoj^lasni.  Around  the 
tapered  base  of  the  cell  are  the  fine  ramifications  of  the  nerve  of  taste. 
The  taste  cells  are  supported  externally  on  either  side  by  columnar 
cells — rhe  sustentaciilar  cells.  These  form  no  connection  with  the 
gustatory  nerve  (Fig.  332). 


Fig.  :'>i2. — Taste  Brn  in  Tongue  of  Man.     (Kcdraxui  after  Hein-ani),  from 
Dalilgren  and  Kepner.) 

g.  '..  Gustatory  or  taste  cells;  sup.  c,  supporting  cells;  nv.  f„  nerve  fibrils. 

There  are  four  sensation  qualities  of  taste,  sweet,  salt,  acid,  and 
bitter.  They  may  be  investigated  by  applying  to  the  tongue  test 
soititions  of  various  strengths  at  bod}'  temperature  with  a  fine  camel's- 
hair  brush,  or  by  placing  a  measured  volume  of  the  solution  on  the 
tongue  For  exact  localizing  Avork,  a  form  of  instrument  such  as 
shown  ill  Fig.  333  may  be  used.  It  is  usual  to  employ  ether  and 
chloroform  vapour  with  this  instrument,  since  it  ha,S;  been  found  that 
ether  vapour  blown  on  the  tongue  j^roduces  the  sensation  of  bitterness, 
and  chloroform  vapour  a  sensation  of  sweetness. 


Fig.  333. — Apparatus  for  testing  Taste  Sensations. 
A.  Z.  two-way  tap;  E,  insufflating  bulb;  C,  D,  odoiir  chambers;  1,  2,  clips. 

The  nature  of  the  stimulus  for  taste  is  chemical.     It  is  necessary 
for  a  body  to  be  in  solution  for  the  sensation  to  be  evoked.     A  dry 


TASTE  AXD  8MELL  595 

substance — e.g.,  solid  quinine — applied  to  the  dry  tongue  evokes  no 
sensation  of  taste  Again,  a  ciystal  of  quartz  gives  the  sensation  of 
touch  and  cold,  but  not  of  taste.  A  cr3^stal  of  common  salt  of  the 
same  size  gives  not  only  these  sensations,  but  that  of  saline  taste. 
There  is  no  evidence  to  show  that  the  sensations  of  taste  can  be  elicited 
by  mechanical  stimulation  of  the  tongue.  It  is  probable  that  the 
sensations  evoked  by  electrical  stimulation  are  due  to  the  electrol\-tic 
decomposition  of  the  saliva.  The  various  taste  sensations  are  grouped 
in  different  areas  of  the  tongue. 

The  responsiveness  to  bitter  substances  is  confined  mainly  to  the 
back  and  edges  of  the  tongue.  Acid  is  tasted  all  over  the  dorsum^ 
except  a  small  anterior  part  just  behind  the  tip.  Salt  and  sweet  are 
likewise  apj)ieciated  all  over  the  dorsum,  except  for  an  antero-median 
area  of  the  dorsum,  a  little  posterior  to  the  insensitive  area  for  acid. 
"  Sweet  "is,  however,  in  most  people  liest  appreciated  at  the  tip  of 
the  tongue. 

It  has  been  argued  that  this  distribution  points  to  special  receptors 
for  each  form  of  taste,  and  in  support  of  this  it  is  stated  that  saccharine 
is  sweet  tp  the  tip  and  bitter  to  the  back  of  the  tongue.  In  like 
manner,  stilphate  of  magnesia  is  bitter  at  the  base  and  sweet  or  acid 
in  the  region  of  the  tip.  Further,  the  drug  Gymnenia  sylvestre  affects 
the  sensation  of  sweetness.  After  chewing  the  leaves  of  this  plant, 
sugar  no  longer  tastes  sweet  nor  quinine  bitter.  The  sensations  of 
acid  and  salt  are  unaffected. 

There  is  apparent!}'  no  relation  between  the  chemical  structure 
and  taste  of  substances.  For  example,  sugar,  lead  acetate,  and 
chloroform,  ail  taste  sweet;  magnesium  sulphate  and  various  alka- 
loids, like  quinine  and  strychnine,  evoke  bitter  sensations. 

The  application  of  sugar  and  salt  at  the  same  time  to  opposite  sides 
of  the  tongue  increases  the  effectiveness  of  both  stimuli  (c^.  simul- 
taneous contrast  in  vision,  p.  634),  Again,  after  tasting  Aveak  sulphuric 
acid,  distilled  water  has  a  sweetish  taste  {cf.  successive  contrast,  p.  634), 

It  is  to  be  noted  that  flavours  are  either  smells  or  combinations  of 
taste  and  smell.  Thus,  a  man  with  cold  in  the  head  cannot  aj)preciate 
the  fine  flavour  of  wine.  If  the  nose  be  held,  an  onion,  when  bitten, 
is  indistinguishable  from  an  apple.  The  smell  of  a  strong  cheese 
will  destroy  the  api^reciation  of  the  taste  of  fruit. 

The  nerve  distribution  for  taste  is  associated  in  the  posterior 
thiixl  with  the  glosso-pharyiigeal  nerve,  and  in  the  anterior  two-thirds 
with  the  lingual  branch  of  the  fifth.  The  course  of  the  taste  fibres  is 
complicated  and  still  in  doubt.  The  fibres  from  the  anterior  two- 
thirds  lea\-e  the  lingual  nerve  and  pass  backward  along  the  chorda 
tympani  nerve  to  join  the  seventh  nerve  in  the  Fallopian  aqueduct. 
They  pass  in  the  seventh  nerve  as  far  as  the  geniculate  ganglion, 
A\here  some  join  the  nerve  of  Wrisberg  and  pass  to  the  nucleus  of  the 
ninth  nerve ;  others  are  said  to  pass  along  the  great  superficial  petrosal 
nerve  to  Meckel's  ganglion  and  to  rejoin  the  fifth  nerve.  The  fibres 
from  the  posterior  third  of  the  tongue  pass  to  the  brain  by  wav  of 
the  glosso-pharyngeal  nerve. 


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Smell.^ — The  Receptor  Mechanism  is  formed  by  the  olfactory  cells 
situated  iu  the  mucous  membrane  of  the  upper  meatus  of  the  nose, 
and  covering  the  vipper  part  of  the  superior  turbinate  bone  and  nasal 
septum.  The  middle  and  inferior  meatus  constitute  part  of  the 
respiratory  tract. 

The  nasal  mucous  membrane,  or  Schneiderian  membrane,  is  thick 
and  of  a  yelloAvish  hue,  in  marked  contrast  to  the  reddish  tint  of  the 
respiratory  portion  of  the  nose.  In  section  it  is  seen  to  consist  of 
an  epithelial  layer — the  olfactory  epithelium — which  'rests  upon  a 
basement  membrane,  and  separates  it  from  the  deeper  mucous  layer 
or  corium  (Fig.  334). 


Fig.  334. — Skction  of  Olfactory  Epitheliitm  of  the  Fowl,  showing  sup.  c.  Sup- 
porting Cells;  sen.  c,  Sensory  Cells;  and  ba.  c.  Basal  Cells.  (Eedrawn 
fi'om  Dahlgren  and  Kepner.) 


The  receptor  olfactory  cells  lie  in  the  ej^ithelial  layer.  They 
possess  a  central  nucleus  surrounded  by  a  small  quantity  of  protoplasm, 
from  which  there  passes  towards  the  surface  a  narrow  round  filament 
with  a  cilium  attached.  A  smaller  similar  process,  arising  from  the 
base  of  the  cells,  arborizes  with  the  terminal  ramifications  of  the 
olfactory  nerve.  Supporting  these  cells  are  other  "  sustentacular 
cells."  These  have  a  knife-handle-like  shape,  the  upper  half  being 
cylindrical  in  shape,  and  often  provided  with  stiff  cilia  attached  to 
the  free  border.  The  lower  half  is  narrow,  and  ends  in  a  long  process 
which  joins  with  the  neighbouring  cells.     At  the  boundary  of  the 


TA.STE  AND  SMELL  597 

epithelial  layer  with  the  loose  underlying  connecti\'e  tissue  there  are 
found  supporting  "  basal  cells."'  These  are  irregularl}-  cubical,  being 
broadest  at  the  base  and  tapering  towards  the  surface. 

The  Mode  of  Excitation. — Smells  are  not  destroyed  by  passing 
the  air  containing  them  through  a  long  tube  packed  with  cotton-wool. 
It  is  estimated  that  such  a  tube  removes  particles  r^o^-^jx^  cubic  milli- 
metre in  size.  It  is  known  that  a  gramme  of  musk  will  give  off  its 
odour  for  years,  and  not  weigh  appreciably  less  at  the  end  of  the  time ; 
0-01  milligramme  of  meicaptan  diffused  in  230  centimetres  of  air  is 
perceptible  to  the  sense  of  smell — i.e.,  0-00000004  milligramme  per 
litre,  or  a  dilution  of  1  in  50,000.000.  A  hound  will  follow  every 
zigzag  that  a  fox  takes  across  country. 

It  is  obvious,  therefore,  that  the  mode  of  excitation  is  as  subtle 
as  that  of  the  retina  by  light.  Substances  of  low  molecular 
weight  either  have  no  odour  or  tend  to  irritate  the  nose  rather  than 
evoke  the  true  sense  of  smell.  Increase  in  molecular  weight  often 
increases  the  property  of  smell — for  example,  of  the  paraffins.  In 
the  series  of  alcohols  also  there  is  an  increase  in  the  intensity  of 
odour  as  the  molecular  weight  increases. 

The  Investigation  of  the  Sense  of  Smell. — ^Keenness  of  smell  may  be 
investigated  roughly  by  preparing  a  series  of  solutions  of  camphor 
from  1  in  1,000  to  1  in  1,000,000,  and  placing  them  in  flasks  holding 
10  to  15  c.c,  and  having  an  opening  of  17  millimetres  diameter.     For 


A 

Fig.  335. — The  Olfactometer. 

more  accurate  work,  the  instrument  kno\vn  as  the  olfactometer  is  used 
(Fig.  335).  This  consists  of  two  concentric  cylinders,  the  inner  one 
of  which  ends  in  a  nose-j)iece.  The  outer  cylinder  (-^4)  is  lined  with  an 
odorous  substance.  It  will  be  seen  that,  when  the  inner  cylinder  (B) 
is  pushed  in  level  with  the  oiiter  one,  air  mhaled  through  the  instru- 
ment does  not  pass  over  this  substance:  but  the  more  the  cylinder 
is  drawn  out,  the  greater  the  area  of  the  odorous  substance  exposeti 
to  the  indra\^ai  air.  The  extent  to  which  it  is  necessary  to  draw 
out  the  inner  cjdmder  to  recognize  the  odour  is  the  measure  of  the 
responsiveness  of  the  nose  to  that  particular  stimulus. 

A  classification  of  different  smells  is  verj'  difficult,  almost  impracti- 
cable. Such  classifications  have  been  made,  but  they  cannot  be  re- 
garded as  satisfactorj'.  There  is  an  antagonism  between  certain 
odours — e.g.,  iodoform  is  masked  by  balsam  of  Peru,  musk  by  bitter 
almonds,  ammonia  bj'  acetic  acid. 

The  sense  of  smell  may  be  fatigued.  After  smellmg  tinctiu-e  of 
iodme,  alcohol  and  copaiba  balsam  are  odourless.     Some  people  do 


51)8  A  TEXTBOOK  OK   I ' in'« J ( ) I .i )( ; Y 

not  appreciate  certain  smells — e.g.,  Jiiignonette.  .Such  "  anosmia  '" 
is  probably  congenital,  but  temporary  anosmia  may  occur  in  disease 
of  the  nose  and  in  nerv^ous  conditions.  It  may  be  induced  by  the, 
application  of  drugs,  such  as  cocaine.  Parosmia  (perverted  sense  of 
smell)  and  hyjierosiuia  (increased  sensibility  to  smells)  may  also  occur 
in  neivous  conditions  (hysteria,  etc.). 

Taste  and  smell,  as  we  have  seen,  are  intimately  related.  Jt  is 
possible  for  them  to  be  antagonistic.  This  fact  is  made  use  of  by  the 
physician.  Thus,  "  tinct.  aurantii,"  by  its  odour,  counterac.ts  the 
bitter  taste  of  quinine,  and  effervescing  saline  drinks  (taste)  mask 
the  flavour  (odour)  of  castor  oil. 

The  central  connections  for  smell  are  made  l)y  means  of  the  olfac- 
tory lobes  of  the  brain  (see  p.  71.")). 


CHAPTER  LXIX 
THE  SENSE  OF  VISION 

Section  I 

The  Receptor  Mechanism. — The  perception  of  the  rapid  undula- 
tions of  the  ether  is  usually  confined  to  specialized  nerve  cells,  the 
visual,  cells.  Some  low  forms  of  life  have  a  rudimentary  eye  or  eye- 
spot  (Fig.  336,  e).     The  visual  cells  may  be  scattered  over  the  body 


Fig.  33'J. — Individual  Flagellate  Chla!mvdomo>-as  Reticulata.     (Redrawn  from 

Dahlgreu  and  Kepner.) 

e,  Eyespot  with,  pigment  and  lens:  nu.,  nucleus;  c.  v.,  contractile  vacuole.     X  1,000. 

surface,  but  usually  are  aggregated  together  with  accessory  tissues  to 
form  a  specialized  organ  of  vision,  the  eye.  Various  complicated 
forms  of  eyes  are  described  among  the  invertebrates.  In  the 
higher  animals  the  recejitor  mechanism  for  vision  is  contained 
in.  the  retina,,  the  delicate  nervous   layer  lining  the  posterior  portion 

599 


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of  tlic  eyeball.     The  rest   of  the  eyeball  is   an  accessory  mechatiisnt 
for  focussing  the  vibrations  of  the   ether   upon  the  retina,  in  order 
that  light  may  not  only  be  ap])reciated,  but  vision  rendered  distinct. . 
It  is  convenient,  therefore,  first  to  study  the  structure  of  this  apparatus,, 
and  also  the  ])hysical  laws  which  apjoly  in  connection  with  vision. 

The  Anatomy  of  the  Eye. — The  eye  may  be  compared  to  a  camera, 
with  its  framework,  its  system  of  lenses,  its  diay)hragni,  and  its  sensitive 
plate.  The  framework  of  the  eyeball  consists  of  an  outer  tough, 
opatjue,  fil)rous  coat — the  sclera,  or  sclerotic.  In  front,  this  becomes- 
transparent,  and  forms  one  of  the  systiem  of  lenses — the  cornea.  At 
the  back,  the  sclerotic  is  pierced  by  the  optic  nerve,  which  then  spreads 
out  over  the  posterior  two-thirds  of  the  e^-eball  to  for^n  the  sensitive^ 
plate — the  retina.  Between  the  sclerotic  and  retina  lies  the  black 
pigmented  and  vascular  coat,  the  choroid.  Within  the  eye  is  sus- 
pended the  lens  and  its  supports,  dividing  the  eyeball  into  two 
chambers:  (I)  That  between  the  cornea  and  the  front  of  the  lens — 
the  "  aqueous  chamber  "  — containing  a  watery  fluid  (the  "  aqueous  ") ;' 
(2)  that  between  the  posterior  surface  of  the  lens  and  the  retina — 
the  vitreous  chamber — containing  a  glassy,  jelly-like  mass  (the 
"  vitreous  humour '").  The  aqueous  chamber  is  incompletely  divided 
into  two  by  the  diaphragm,  oi  iris.  To  understand  the  mechanism 
by  which  rays  of  light  are  rendered  distinct  upon  the  sensitive 
retina,  it  is  necessary  for  us  to  study  in  detail  these  accessory  parts. 

Accessory  Parts  and  their  Functions. 

The  Conjunctiva  covers  the  anterior  part  of  the  sclera,  and  is 
reflected  over  the  inner  aspects  of  the  upper  and  lower  eyelids.  It 
consists  of  several  layers  of  stratified  epithelium.  The  anterior 
surface  of  the  cornea  is  covered  by  a  similar  epithelium  continuous 
with  that  of  the  conjunctiva.  The  conjunctiva  is  kept  moistened 
by  the  secretion  of  the  lachrymal  glands — the  tears. 

The  Lachrymal  Glands. — The  lachrymal  glands  closely  resemble 
in  structure  a  serous  gland.  They  are  situated  in  the  upper  outer 
angle  of  the  orbit,  and  jjour  out  their  secretion  by  sev^eral  ducts  situated 
on  the  inner  surface  of  the  ujiper  lid.  Normally,  the  amount  of 
secretion  is  just  sufficient  to  keep  the  conjunctiva  moist,  and  enable 
the  e3relids  to  work  smoothly.  It  is  drained  away  by  a  small  orifice — 
placed  at  the  inner  angle  of  the  eye,  and  thence  into  the  lachrymal 
sac  and  to  the  nasal  duct  which  opens  into  the  inferior  meatus  of  the 
nose.  Excessive  secretion  is  induced  by  foreign  bodies  acting  on  the 
conjunctiva,  irritating  vapours  in  the  nose,  and  by  painful  emotion, 
leading  to  the  formation  of  tears.  The  eyelids,  besides  moistening 
the  conjunctiva  during  the  process  of  winking,  protect  the  eyeball,, 
and,  by  means  of  the  eyelashes,  shade  the  eyes.  They  consist 
of  folds  of  skin  and  areolar  tissue,  kept  in  shape  by  a  plate  of  fibrous 
tissue — the  tarsus.  In  the  skin  are  contained  sweat  glands,  sebaceous 
(Meibomian)  glands,  and  the  eyelashes.  Beneath  the  skin  are  fibres 
of  the  muscle  which   closes   the  lids — the  orbicularis   palpebrarum.. 


THE  SENSE  OF  VISIOX 


COl 


Inserted  into  the  middle  portion  of  the  tarsus  of  the  upper  lid  are 
fibres  of  the  muscle  which  open  the  eye  —  the  levator  palpebrse 
suiserioris. 

The  Cornea  is  the  transparent  layer  in  the  front  of  the  eyeball. 
In  the  adult  human  being  it  is  about  1  millimetre  thick.  It  is  the 
first  of  the  sjstem  of  lenses  of  the  ej'e-camera.  It  is  continuous  at  its 
edges  with  the  sclerotic,  forming  the  corneo -sclerotic  or  sclero -corneal 
junction.  The  angle  at  which  the  cornea  joins  the  iris  within  the 
eyeball  is  known  as  the  corneo-iridic  or  filtration  angle. 


O.N. 
FiC4.  337. — Horizontal  Sectiok  or  Eyeball.     (Parsons  and  Wright.) 

C,  Cornea;  Aq.,  aqueous  humour;  /.,  iris;  S.L.L.,  suspensory  ligament  of  lens; 
C.P.,  canal  of  Petit;  E.B.,  external  rectus:  Scl.,  sclerotic;  Cher.,  choroid;  Bet.y 
retina;  H.M.,  hyaloid  membrane;  31. L.,  macula  lutea;  O.N.,  o"j5tic  nerve;  R.A^, 
retinal  artery;  O.D.,  optic  disc;  I.B.,  internal  rectus;  Vii.,  vitreous  humour; 
C.B.,  cihary  body;  C.Sck.,  canal  of  Schlemm;  L.,  lens. 


Microscopically,  the  cornea  consists  of  a  layer  of  stratified 
epithelium,  in  which  ramify  numerous  delicate  nerves,  resting  upon 
a  homogeneous  layer  (the  anterior  homogeneous  layer  of  Bowman), 
Beneath  this  layer  the  transj)arent  fibres  of  the  cornea  proper  are 
arranged  in  laj'ers,  each  successive  layer  being  at  right  angles  to  the 
next.  Lying  in  minute  tissue-fluid  spaces  between  the  fibres  are 
connective-tissue  cells,  known  as  the  corneal  corpuscles.  In  the 
proper  substance  of  the  cornea  there  run  delicate  plexuses  of  nerve- 
fibres  derived  from  the  ciliary  nerves.  Posterior  to  the  cornea  proper 
comes  a  transparent  elastic  membrane  (Descemet's),  on  the  inner 
surface  of  which  is  the  single  layer  of  flattened  epithelial  ceils  lining 


602 


A  TKXTBUOK  OF  PHYSIOLOGY 


the  aqueous  chamber.  These,  at  the  coiiieo-iridic  angk^  become 
reflected  on  to  the  iris,  the  menibraue  stop])ing  short  at  tb(;  angle. 
The  inner  flbres  of  the  cornea  in  the  neigh V)oiirhoo(l  of  the  corneo  iridic 
angle  continue  on  as  longitudinal  li])res- cribriform  ligameni.  This 
ligament  is  also  composed  of  circular  iibres,  which  are  continued.''  with 
those^sunouudiiig  the  venous  canal  of  iSchlenim  (Fig.  33S). 


Ciliary  Stroma  \ 

YlG.  338. — T«>  SHOW   DtTAILS   OF  THE  CRIBRIFORM  LiGAMEXT,   ClLIARV   ^irSCLE,   AM) 

CoRNEO-iRiDic  Junction.     (Thouiison  Henderson.) 

The  outer  fibres  of  cribriform  ligament  start  at  «  and  end  at  a'.  The  inner  fibres 
start  at  h  and  spread  out  to  act  as  fibrils  of  origin  to  the  longitudinal  fibres  of  the 
ciliary  muscle.  P,  pigment  epithelium  of  iris;  P.L.M..  posterior  limiting  mem- 
brane of  iris  continuous  with  hyahne  layers  (H.L.)  of  ciliary  body;  l>.J^.,Des- 
cemet's  membrane. 


By  its  inner  longitudinal  fibres  it  serves  as  a  j)oint  of  attachment 
for  the  ciliary  muscle  and  the  dilator  pupillee;  by  its  outer  longitudinal 
fibresjt  is  connected  to  the  sclera,  the  fibres  passing  backwards  internal 
to  the  canal  of  Schlemm.  The  circular  fibres  heljo  to  keep  the  ciliary 
mu.scle  in  position. 

The  Sclerotic  Coat  (Sclera)  is  extremely  tough,  being  made  up  of 
white  fibrous  tissue  with  a  small  amount  of  yellow  elastic  tissue.  It 
is  pierced  at  the  back  bj*  the  optic  nerve,  and  at  various  parts  by 
the  veins  bringing  blood  from  the  eyeball  (the  venae  vorticosse).  The 
muscles' moving  the  eyeball  are  inserted  into  the  sclera  just  behind 


THE  SENSE  OF  VISION  003 

the  cornea.  On  its  inner  surface  there  is  a  layer  oi  brown-l)lack 
pigment  cells  (the  lamina  fusca).  The  sclera  is  connected  by  loose 
connective  tissue  to  the  structures  internal  to  it — the  ciliary  borty 
and  the  choroid — the  space  thus  formed  being  knowi:  as  the  supra- 
choroidal  space  (Fig.  345). 

The  Choroid  is  the  vascular  coat  for  the  posterior  part  of  the  eye. 
It  is  connected  with  the  ciliary  body  and  the  iris,  and,  together  with 
them,  constitutes  the  vascular  tract,  or  uvea,  of  the  eye.  Lying  between 
the  sclera  and  the  retina,  the  function  of  the  choroid  is  to  nourish 
these  structures,  ]}articularly  the  retina.  Its  pigment  also  absorbs 
the  light  which  passes  through  the  retina.  The  choroid  consists  mainly 
of  networks  of  bloodvessels  held  together  by  a  stroma  containing 
branched  pigment  cells.  There  is  an  outer  la3'er  of  larger  blood- 
vessels, and  an  inner  close  network  of  wide  capillaries  Next  to  the 
retina  is  a  homogeneous  elastic  membrane,  which  may  be  2  jjc  thick. 
A  similar  elastic  membrane  lies  at  the  back  of  the  cornea,  and  covers 
the  iris  and  ciliary  processes.  The  fluid  within  the  eyeball  is  contained 
b}'  this  membrane,  and  it  is  probably  of  great  importance  in  the 
maintenance  of  the  intra-ocular  pressure. 

The  Ciliary  Body  lies  just  behind  the  corneo-scleral  junction, 
being  continuous  with  the  choroid  behind  and  with  the  iris  in  front, 
and  consists  of  two  portions — -an  outer  muscular  portion,  the  ciliary 
muscle,  and  an  inner  non-muscular  portion.  The  latter  is  dividerl 
into  two  parts — the  pars  plana  and  the  pars  plicata. 

The  Ciliary  Muscle  is  composed  of  smooth  muscle,  anci  also  consists 
of  an  outer  portion  and  an  inner  portion.  The  fibres  of  the  outer 
portion  (Brdcke's  muscle)  run  in  a  meridional  and  radial  direction. 
They  arise  from  the  portion  of  the  cribriform  ligament  derived  from 
the  cornea,  and  pass  backwards  to  be-inserted  in  part  into  the  choroid, 
in  part  into  the  suspensory  ligament  of  the  lens. 

The  inner  portion  consists  of  circular  fibres  (Mijlier'.s  muscle). 
It  arises  indirectly  by  interstitial  tissue  from  the  internal  fibres  of 
the  cribriform  ligament,  and  forms  a  sjihincter  roimd  the  margin 
of  the  lenti. 

The  Pars  Plana  is  the  posterior  smooth  portion  of  the  ciliary  body. 

The  Pars  Plicata  is  the  anterior  inner  portion  of  the  ciliary  body, 
so  called  because  it  is  thrown  into  many  folds^the  ciliary  processes, 
about  seventy  in  number.  Lying  in  the  connective  tissue  of  these 
processes  are  networks  of  wide  capillary  tufts.  Each  process  arises 
from  a  base  of  connective  tissue  continuous  with  the  stroma  of  the 
iris,  and  each  is  covered  by  columnar  epithelium,  within  which  is 
a  set  of  pigment  cells.  Between  the  processes  lie  the  interciliary 
grooves,  lined  by  pigmented  cubical  cells,  and  continuous  with  the 
radial  furrows  on  the  back  of  the  iris.  The  sensory  nerve  supply  of 
the  ciliary  body  comes  from  the  ophthalmic  division  of  the  fifth  nerve. 
The  ciliary  muscle  is  supplied  b}'  the  infeiior  division  of  the  third  nerve. 
The  long  posterior  ciliary  arteries  supply'  the  ciliary  body  with  blood. 


604  A  TEXTBOOK  OF  PHYSIOLOGY 

Functions  of  the  Ciliary  Body. — The  ciliary  inusclc  effects  the  ac- 
commodation of  the  eye  (see  hiter,  p.  (U4);  the  ciliary  processes 
secrete  the  aqueous  humour,  the  pigment  in  the  ciliary  bodies 
assists  the  ins  in  preventing  h'ghl  passing  through  the  periphery  of 
the  lens. 

The  Iris  is  the  pigmented  curtain  or  diaphragm  which  lies  in  the 
aqueous  chamber,  dividing  it  into  an  anterior  chamber  in  front  and 
a  posterior  chamber  behind.  The  ajserture  in  the  centre  forms  the 
pupil  of  the  eye.  At  its  base,  where  it  is  thinnest,  the  iris  is  con- 
tinuous with  the  anterior  part  of  the  ciliary  body,  both  as  regards 
stroma  and  the  pigmented  and  epithelial  cells,  which  lie  on  its  posterior 
surface.  The  epithelial  cells  on  tlie  front  of  the  iris  are  reflected  at 
the  corneo-iridic  angle  on  to  the  back  of  the  cornea.  Both  sets  of 
epithelial  cells,  anterior  and  posterior,  lie  on  basement  membranes, 
in  between  which  there  is  a  delicate  network  of  connective  tissue 
containing  the  pigment  cells  which  give  the  iris  its  characteristic 
colour.  This  connective  tissue  contains  a  network  of  capillaries 
which  run  into  a  large  vein  at  the  base — the  circulus  iridis  major. 
It  also  forms  lymph  spaces,  which  connect  by  minute  crypts  at  the 
base  of  the  iris  w^ith  the  aqueous  fluid  in  the  anterior  chamber.  By 
these  crypts,  therefore,  aqueous  fluid  can  pass  into  the  lymph  spaces 
of  the  iris,  and  thence  into  the  iris  veins. 

In  this  connective  tissue,  also,  lie  the  muscle  fibres  of  the  iris. 
These  are  of  the  smooth  variety,  and  consist  of  two  sets:  (1)  Circular 
fibres,  developed  mostly  near  the  free  pupillary  margin,  and  sphincter 
in  action— -the  sphincter  pupillae;  (2)  meridional  fibres  arranged  about 
the  radial  furrows  of  the  iris.  These  fibres  arise  from  the  innermost 
strands  of  the  cribriform  ligament,  and  terminate  in  the  connective 
tissue  of  the  sphincter  pupillae. 

The  sensory  nerve  of  the  iris  fe  the  nasal  branch  of  the  ophthalmic 
division  of  the  fifth  nerve.  The  motor  nerve  to  the  sphincter  muscle 
is  the  inferior  division  of  the  third  nerve.  This  has  its  cell-station 
in  the  ciliary  ganglion,  and  passes  to  the  iris  as  the  short  ciliary  nerves. 
The  nerve  to  the  dilator  pupillae  is  the  cervical  sympathetic.  Its 
cell-station  is  in  the  superior  cervical  ganglion,  and  the  fibres  reach 
the  eye  through  the  ophthalmic  division  of  the  fifth  and  the  long 
ciliary  nerves. 

The  Function  of  the  Iris. — The  function  of  the  iris  is  to  regulate 
the  amount  of  light  admitted  to  the  eye,  and  to  diminish  spherical 
and  chromatic  aberration  (see  later,  p.  609).  Its  action  is  reflex. 
It  contracts  when  strong  light  falls  on  the  retina  (the  light  reflex). 
When  light  falls  on  one  eye,  the  pupil  of  the  other  eye  also 
contracts  (the  consensual  light  reflex).  The  iris  also  contracts  during 
accommodation  of  the  eye  for  a  near  object,  during  sleep,  and  under 
the  action  of  certain  drugs  known  as  myotics — e.g.,  morphia,  which 
acts  centrally,  and  pilocarpine,  eserine,  etc.,  which  act  locall}' .  Besides 
stimulation  of  the  third  nerve,  section  or  paralysis  of  the  cervical 
sympathetic  nerve  will  cause  contraction  of  the  pupil.     Dilatation  of 


THE  8EN8E  OF  VISION 


605 


the  bloodvessels  of  the  iris  will  help  to  bring  about  its  expansion, 
and  constriction  its  contraction. 

The  iris  dilates  normally  in  weak  light  or  in  the  dark,  and  when 
the  eyes  are  at  rest.  It  also  dilates  under  the  influence  of  strong 
emotion  and  of  pain,  particularly  if  the  pain  is  in  the  region  of  the 
neck.  r!ertain  drugs,  knoAvn  as  mydriatics,  produce  dilatation  of  the 
pupil.  Such  are  atroi)ine,  homatropine,  Avhich  act  locally,  paralyzing 
the  terminations  of  the  third  nerve;  cocaine,  which  acts  locally, 
stimulating  the  endings  of  the  sympathetic  nerve;  curare,  which  acts 
centrally. 


Fia.  339. — Diagram  showing  Nekvb  Supply  of  the  Iris.     (Dixon.) 

///.,  Third  nerve;/,  preganglionic  fibre  to  ciliary  ganglion;  </,  postganglionic  illncir  to 
circular  muscle  (/«).  S.C.G.,  superior  cervical  ganglion  giving  fibres  which  trd 
in  radiating  fibres,  m,  of  the  iris.  Drugs  may  act  upon  the  pupil  at  nerve - 
endings  d  and  e,  or  centrally  at  a. 


In  certain  nerv^ous  diseases,  such  as  locomotor  ataxia,  the  pupil 
does  not  react  to  light,  although  it  still  resj)onds  when  looking  at  a 
near  object  (accommodation).  This  condition  is  known  as  the  Argyll- 
Robertson  pupil,  and  is  probably  due  to  degeneration  of  the  cells  of 
the  ciliary  ganglion. 

The  Lens  consists  of  a  semi-solid  core  —  the  nucleus  —  with 
somewhat  more  fluid  edges.  Its  main  constituent  is  crystallin,  a 
protein  of  the  globulin  type.  It  is  held  in  position  by  a  fine  membrane 
— the  capsule — to  which  is  attached  the  suspensory  ligament,  or 
zonule  of  Zinn.  Structurally,  the  lens  consists  of  a  number  of  "  lens 
fibres  with  serrated  edges."  These  are  formed  by  a  process  (f 
elongation  from  the  layer  of  cubical  cells  from  which  the  lens  is 
originally  derived. 

The  Suspensory  Ligament,  or  zonule  of  Zinn,  is  derived  from  the 
hyaloid  membrane,  which  encloses  the  vitreous  humour  (see  Fig.  337). 
The  canal  of  Petit  is  a  space  enclosed  in  tliis  ligament  in  which  the 


G06 


A  TEXTBOOK  OF  PHYSIOLOGY 


aqueous  humour  passes.     The  fibres  of  the  cih'ary  muscle  are  partly 
attached  to  this  ligament. 

The  Retina  is  a  delicate  nerve-film  covering  the  posterior  two-thirds 
of  the  eye.  It  ends  in  front  in  a  notched  edge — the  ora  serrata.  In 
the  centre  of  the  retina  is  a  round  yellowish  spot,  1  millimetre  in 
diameter,  known  as  the  macula  lutea.  When  viewed  in  the  living 
eye,  however,  it  is  of  a  deep  red  colour.  It  is  depressed  in  the  centre, 
forming  the  fovea  centralis.  Just  to  the  nasal  side  of  the  yellow 
spot  is  the  point  where  the  optic  nerve  leaves  the  eyeball.  It  is  known 
as  the  optic  disc,  or,  since  there  is  no  sensation  of  vision  there,  the 
blind  spot.  Here  the  retinal  artery  enters  the  eyeball,  and  the  retinal 
\-ein  leaves  it-  The  clinician  jiarticularl}^  studies  the  conditioh  of 
the  optic  disc  with  the  ophthalmoscope.  Normally,  it  appears  as  a 
circular  ]-)ink  disc,  from  which  the  artery  and  vein  radiate  out  on  to 
a  rerl  baoksfrouud. 


t  I 

•i  I 
-%■■  I 

#! 


Ksu^. 


^^. 


Fig.  340. — Dca'^ram  of  the  Retina  in  Man.     (Redrawn  after  Lewes-Stohr,  from 

Dahlgren  and  Kepner.) 

vis.  c.  Laying  of  visual  cells  (rods  and  cones),  the  nuclei  and  procei^fces  forming  the 
outer  nuclear  layer;  nv.  c,  layer  of  bijiolar  celly,  the  inner  nuclei  of  which  form 
the  inner  nuclear  layer;  g.c,  ganglion  cells,  forming  the  ganglion  tell  lay«r; 
nv.f.,  nervp  H^re  layer;  swp.  c,  supporting  or  neuroglia  cells. 


Structurally ,  tiie  retina  is  exceedingly  complicated  (Fig.  .340).  It 
contains — (1)  the  receptor  mechanism  (the  rods  and  cones);  (2) 
the  second  (conductor)  neuron;  (3)  the  third  (conductor)  neuron, 
the  elongated  processes  of  which  go  to  form  the  optic  nerve.  The 
cells  of  these  iwurons,  the  interdigitation  of  their  s;yTia]3ses,  and  the 
supporting  cells,  form  the  man^^  layers  of  the  retina.  These  are 
usually  on>mierated  as  follows: 


THE  SENSE  OF  VISION  607 

1  Adjacent  to  the  choroid  is  a  single  layer  of  polygonal  pigment 
cells,  from  which  elongated  processes  containing  fine  pigment  (fuscin) 
granules  pass  into  the  next  layer,  and  end  between  the  rods. 

2  The  receptor  mechanism  of  the  eye,  the  layer  of  rods  and  cones 
A  rod  consists  of  an  outer  elongated  part,  about  30  f-i  long  and  2  ^i 
broad      It  is  transparent,  transverse!}-  striated,  and  in  it  are  to  be 

.found  f)he  minute  pigment  granules  which  form  the  "  visual  puq)le." 
The  uiner  jjart  of  the  rod  spreads  out  somewhat  in  the  shape  of  a 
carrot,  the  upper  part  being  longitudinally  and  the  lower  part  trans- 
versely striated.  From  the  tip  arises  a  rod-fibre,  which  pierces  the 
external  limiting  membrane,  and  swells  out  as  the  rod  granule 
or  nucleus,  finalh'  passing  on  to  form  a  varicose  synapse  '  (see 
Fig.  340 

A  cone  also  consists  of  an  inner  and  outer  portion.  The  outer 
portion  IS  ta]7ering  and  pointing,  about  one-third  the  length  of  the 
corresponding  portion  of  the  rod.  It  is  transversely  striated,  and 
contains  no  pigment.  The  inner  part  of  the  cone  is  broad,  and  ends 
in  a  cone-fibre.  This  is  somewhat  thicker  than  that  of  the  rod,  but, 
like  it,  pierces  the  external  limiting  membrane,  contains  a  nucleus  or 
granule,  and  ends  as  an  arborizing  sjiiapse. 

3.  The  external  limiting  membrane  is  a  well-defined  membrane 
formed  by  the  outer  processes  of  the  sustentacular  fibres.  The  susten- 
tacular  fibres  of  Mil  Her  reach  from  this  layer  to  the  internal  limit- 
ing membrane.  This  membrane  serves  to  support  the  rods  and 
cones 

4  The  external  nuclear  layer  is  made  up  of  the  rod  and  cone  granules 
(the  auclei  of  the  rod  and  cone  fibres),  and  also  of  fine  fibres 
belonguig  to  the  supporting  cells  of  the  internal  limiting  membrane 
(Fig.  340;. 

5  The  outer  molecular  layer  is  really  a  synapse  layer,  consisting  of 
the  ramifying  interdigitations  of  the  rod  and  cone  fibres  and  the 
synapses  of  the  cells  in  the  next  layer — the  bipolar  cells  (Fig.  340). 
It  also  'iiutains  a  few  supporting  cells,  probably  of  a  neuroglial 
nature 

(>  Tht  inner  nuclear  layer  consists  chiefiy  of  the  bipolar  cells  which 
form  the  first  neuron  (Fig.  340).  One  process,  as  we  have  seen,  arborizes 
in  the  preceding  layer;  the  other  passes  into  the  inner  molecular  layer 
of  synapses,  to  end  around  the  terminations  of  the  dendrites  of  the 
ganglion  cells  of  the  optic  nerve.  In  this  layer  are  also  oval  cells, 
termed  spongioblasts,  which  send  a  single  process  into  the  inner 
molecular  layer,  and  other  small  cells,  termed  amacrine  cells,  Avhich 
send  a  short  process  into  the  outer  molecular  layer.  There  are  also 
a  few  bipolar  cells.  The  large  oval  nuclei  of  the  supporting  fibres  of 
Miiller  are  found  in  this  laj^er. 

7  The  inner  molecular  layer  is  a  synaptic  layer  containing  the 
synapses  of  the  bipolar  cells,  and  of  the  ganglion  cells.  It  also 
contains  neuroglial  cells. 

8.  The  layer  of  ganglion  cells  consists  of  the  large  flask-shaped 
ganglion  cells  which  constitute  the  second  set  of  neurons  (Fig.  340). 


<;08  A  TEXTBOOK  OF  PHYSIOLOGY 

Their  deiulrites  pass  outwards   to   arborize  in  the  inner  molecular 
layer;  their  axons  pass  in  towards  the  optic  nerve,  forming 

9.  The  layer  of  non-meduUated  nerve-fibres  (Fig.  ?Ai)). 

10.  The   internal  limiting  membrane  is  formed   by  the  expanded 
bases  of  the  supporting  fibres  of  Midler. 


Section  II 

LAWS  OF  DIOPTRICS 

The  generally  accepted  hypothesis  of  the  phenomena  of  light  is 
that  first  enunciated  by  Thomas  Young — namely,  that  light  is  a  mode 
of  motion  of  the  ether  which  pervades  sjiace.  By  the  molecular 
movements  of  luminous  bodies  the  ether  is  caused  to  vibrate  in  a 
series  of  waves,  forming  a  ray  of  light.  The  component  particles  of  the 
ray  move  at  right  angles  to  the  direction  in  which  the  ra3"  is  travelling, 
just  as  do  the  particles  of  water  in  the  waves  caused  by  disturbing 
the  smooth  surface  of  a  pool. 

Waves  of  big  amplitude  give  rise  to  a  sensation  of  bright  light, 
small  waves  to  one  of  dim  light.  All  the  waves  are  of  very  rapid  rate 
of  vibration— 435,000,000  to  764,000,000  per  second.  Outside  these 
limits  the  eye  is  not  stimulated,  although  there  are  present  both 
infra-red  and  ultra-violet  rajs.  Beyond  the  ultra-violet  rays  come 
the  Rontgen  rays,  and  below  the  infra-red  the  electrical  waves  in 
unbroken  sequence.  The  light  rays,  with  the  low  rate  of  vibration, 
give  rise  to  the  sensation  of  red,  those  with  the  high  rate  to  that  of 
violet.  In  between  Ave  have  the  colours  orange,  green,  blue,  indigo, 
gradually  merging  into  one  another.  Ordinary  sunlight,  as  Isaac 
Newton  showed,  is  composed  of  this  series  of  colours  blended  together. 

Light  travels  through  the  ether  at  about  190,000  miles  per  second. 
A  ray,  falling  upon  a  polished  surface,  is  reflected,  the  angle  with  the 
perpendicular  of  the  reflected  ray  being  equal  to  that  Avhich  the 
incident  ray  makes  with  the  same  perpendicular. 

When  a  ray  passing  through  one  transparent  medium,  such  as  air, 
meets  perpendicularly  another  medium,  such  as  water,  part  of  it 
passes  into  the  new  medium,  and  part  is  reflected  upon  itself.  If, 
however,  the  ray  meets  the  new  medium  obliquety,  the  part  which 
passes  into  the  medium  is  bent  out  of  its  course,  or  refracted.  This 
refracted  ray  is  in  the  same  plane  as  before,  and  in  the  case  of  a  x&.y 
passing  from  a  rarer  to  a  denser  medium  the  deflection  is  toAvard  the 
perpendicular.  The  laAV  for  single  refraction  is  that,  AA^hatever  the 
obliquity  of  the  incident  ray,  the  ratio  of  the  sine  of  the  incident 
angle  to  the  sine  of  the  angle  of  refraction  is  constant  for  the  same 
two  media,  but  \^aries  Avith  different  media.  This  ratio  of  the  angles 
is  known  as  the  index  of  refraction,  and,  knowing  this  index  for  any 
t\A'o  media,  the  direction  which  Avill  be  taken  by  a  ray  of  light  can 


THE  SENSE  OF  VISION  G09 

he  calculated.  Water  refracts  the  ray  more  than  air,  and  glass  more 
than  water. 

When  a  ray  meets  obliquely  a  piece  of  glass  with  j)arallel  surfaces, 
part  of  the  light  is  reflected  and  part  is  refracted — bent  towards  the 
perpendicular  to  the  surface.  On  again  emerging  at  the  other  surface, 
it  is  bent  back  again  to  its  former  direction,  and  therefore  passes  on 
not  in  the  same  line  as  that  in  which  it  struck  the  glass,  but  in  one 
j^arallel  to  it.  So,  when  light  falls  obliquely  on  the  sides  of  a  prism, 
it  is  doubh'  bent,  the  amount  of  deflection  depending  upon  the  shape 
and  material  of  the  prism. 

A  similar  effect  is  caused  bj^  lenses,  both  biconvex  and  biconcave. 
A  biconvex  lens  will  bring  to  a  focus  all  ra^^s  parallel  to  its  principal 
axis — that  is  to  say,  parallel  to  the  line  which  passes  through  the  centres 
of  curvature  of  its  tAvo  surfaces.  Such  a  point  is  termed  the  principal 
focus  of  the  lens.  Couversety,  rays  starting  from  the  principal  focus 
will  emerge  from  the  lens  in  a  parallel  direction. 

Spherical  Aberration. — It  has  been  stated  that  parallel  r-dys  falling 
upon  a  biconvex  lens  meet  at  the  focus.  In  practice,  however, 
this  is  not  the  case,  as  may  be  seen  by  trying  to  focus  the  sun's  rays 
on  a  piece  of  paper  with  a  burning-glass.  The  image  of  the  sun  can 
not  be  reduced  to  an  absolute  j^oint,  because  tli^  rays  which 
meet  the  circumference  of  the  lens  are  more  refracted  than  those 
which  fail  nearer  the  middle  of  the  lens.  This  is  known  as  the  spherical 
aberration  of  the  lens.  If  the  outer  rays  be  cut  off  by  interposing 
a  diaphragm,  it  is  found  that  the  image  is  made  sharper.  The  iris 
acts  as  a  diaphragm  and  sharpens  the  image  in  the  e3'e.  If  the 
central  part  of  the  lens  were  made  more  refrangible  than  the  outer 
jjarts,  then  the  rays  nearer  the  centre  Avould  be  more  refracted  than 
the  outer  rays,  and  a  similar  result  obtained.  Such  is  the  case  with 
the  lens  of  the  eye. 

Chromatic  Aberration. — It  is  found  that,  as  is  the  ease  with  a 
prism,  owing  to  the  dift'erent  degrees  of  refrangibility  of  the  variou.s 
rays  constituting  white  light,  the  latter  is  split  uj)  or  dispersed  into 
its  component  colour.5  in  passing  through  a  lens.  The  violet  ra,ys 
are  bent  most,  the  red  rays  least.  Therefore,  if  a  screen  be  inter- 
posed before  the  focus,  there  will  be  an  image  with  a  violet  centre 
and  a  red  edge;  after  the  focus  there  will  be  an  image  Avitli  a  red 
centre  and  a  violet  margin.  This  is  known  as  chromatic  aben'ation. 
Opticians  remedy  this  by  combining  lenses  of  differejit  powers  of 
dispersion,  forming  therebj'  the  so-called  compound  achromatic 
lens. 

In  a  S3'stem  of  lenses  there  exist  six  cardinal  points.  If  the  position 
of  these  be  known,  then  the  direction  of  all  rays  through  the  S3'stem 
can  easih'  be  traced.  These  six  cardinal  points  are  the  first  and  second 
focal,  the  first  anrl  second  principal,  and  the  first  and  second  nodal 
points. 

The  first  focal  point  is  the  point  so  placed  that  all  raj'S  from  it, 
after  passing  through  the  system,  emerge  parallel  to  the  axis  of  tho- 

39 


()10 


A  TEXTBOOK  OF  PHYSlOLOaY 


system.  The  second  focal  point  is  the  point  to  which  parallel  rays 
arc  gathered  after  |)assing  through  the  system. 

The  principal  point  is  situated  on  the  principal  axis  at  the  point 
where  the  vertex  of  the  spherical  surface  and  the  plane  perpendicular 
to  the  axis  meet.  Rays  which  pass  through  the  fust  principal  ])oint 
after  refraction  pass  through  the  second  principal  point. 

The  nodal  point  corresponds  to  the  centre  of  curvature  of  the  lens. 
It  is  the  ])oint  where  a  ray,  falling  perpendicularly  on  the  surface^ 
and  therefore  passing  through  without  refraction,  cuts  the  axis. 
Rays  which  pass  through  the  first  nodal  point  after  refraction  seem 
to  emerge  froin  the  second  nodal  point  in  a  direction  parallel  to  that 
of  the  incident  rav. 


Fig.  341. — Diagkams  to  illusteate  Refraction. 


In  the  simplest  form  of  optical  system,  where  there  are  only  two 
media  separated  from  each  other  by  a  spherical  surface  {d,  p,  e,  Fig.  341 ), 
n,  the  centre  of  curvature  of  the  surface,  is  known  as  the  nodal 
point.  A  line  drawn  from  a  through  the  vertex  of  the  spherical 
surface  (p)  gives  the  optic  axis  (OA).  Rays  parallel  to  OA  in  the 
less  refractive  medium  {S)  will  be  brought  to  a  point  (F.,)  on  the  optic 
axis  in  the  more  refractive  medium  {R) — the  posterior  principal  focus. 
Rays  parallel  to  OA,  proceeding  from  E,  will  be  brought  to  a  point 
{F^)  on  the  optic  axis — the  anterior  principal  focus.  The  principal 
point  is  at  ^j. 

In  the  eye,  there  are  several  surfaces  between  the  various  media, 
])ut  smce  the  refractive  indices  of  some  are  approximately  the  same — 


THE  SENSE  OF  VISION 


611 


e.(/.,  those  of  the  aqueous  humour  and  the  cornea — the  refracthig 
surfaces  may  be  regarded  as  three  in  number:  anterior  surface  of 
the  cornea,  the  anterior  and  posterior  surfaces  of  the  lens.  There 
are  three  refractive  media— the  aqueous  humour,  the  lens,  and  the 
vitreous  humour.  These  surfaces  and  media  are  arranged  in  such 
a  manner  that  rays  of  light  travelling  from  a  distance — i.e.,  parallel 
rays — are  brought  to  a  focus  upon  the  retina  at  the  point  known  as 
the  yellow  spot,  the  principal  focus  of  the  eyQ.  The  line  drawn 
through  the  centres  of  curv^ature  of  the  cornea  and  lens  to  this  spot 
is  known  as  the  optical  axis  of  the  eyeball  {dr,  Fig.  341). 

Many  careful  measurements  have  been  made  to  determine  the 
cardinal  points  of  the  normal  eye.  The  following  measurements  have 
been  deduced: 


;aiiterior)  jjriiicipal  lcit.us  of  eye 
:l  (posterior)  principal  focus  .  . 
iirineiual  uoiut  .  . 


First  (  ..., 

Second  (pu^sLenui;  pi 

First  principal  point  .  , 
Second  principal  point 
First  nodal  point 
Second  nodal  point    . . 


!2-832()  mm.  in  front  of  cornea. 
22-647    mn:.  behind  cornea. 

1-7532     „ 

2- 1101     „ 

6-9685     „ 

7-3254     „ 


The  princij^al  j^oints  and  nodal  points  are  so  close  together  that 
they  may  be  combined,  giving  what  is  known  as  the  schematic  or 
reduced  ej-'e.  In  such  a  schematic  eye,  the  path  of  the  rays  leading 
to  the  formation  of  the  image  upon  the  retina  can  be  mapped  out. 
The  rays  of  light  travelling  from  A  and  B,  the  extreme  point  of  the 
image,  and  falling  parallel  upon  the  surface,  are  not  refracted,  but 
pass  straight  through  the  nodal  point  [K)  to  the  retina.  The  angle 
formed  by  these  lines  is  known  as  the  visual  angle.  The  rays  jjarallel 
to  the  axis  from  A  and  B  are  refracted  through  the  j^rincipal  focus, 
and  cut.  on  the  retina,  the  first  rays  passing  through  the  nodal  point 
at  a'  and  6'  resi^ectivejy.  Hence  an  inverted  object  [a'  b')  is  produced 
upon  the  retina. 

The  eye,  however,  is  not  a  mathematically  correct  instrument. 
The  various  refractive  surfaces  are  not  usually  so  centred  that  the 
optic  axis  coincides  Avith  the  line  drawn  from  the  point  viewed  to  the 
fovea  centralis  of  the  retina — the  visual  axis.  The  angle  of  one  axis 
to  the  other,  where  they  meet  at  the  nodal  point,  is  usually  about 
5  degrees,  but  may  })e  as  great  as  12  degrees.  Moreover,  since  the 
centre  about  which  the  eye  rotates  is  in  the  optical  and  not  in  the 
visual  axis,  the  line  of  regard  (the  line  joining  the  j)oint-view  to  the 
centre  of  rotation  of  the  eye)  does  not  coincide  with  the  line  of  vision. 

There  is  a  certain  amount  of  spherical  aberration  in  the  normal 
e\Q.  This  is  not  of  much  consequence,  since  it  is  corrected  by  the 
action  of  the  iris.  There  is  also  some  chromatic  aberration,  which 
is  not,  however,  generally  appreciated  psychologically.  It  can  be 
demonstrated  by  looking  at  the  sky  through  the  upper  part  of  a 
window,  and  holding  the  edge  of  a  card  parallel  to  the  upper  side  of 
the  Avindow-frame,  passing  it  from  below  upAvards  and  from  above 
doAvnAvards.     When  the  card  covers  half  the  pupil,  the  window-frame. 


<U2  A  TEXTBOOK  OF  PHYSIOLOGY 

during  the  upAvard  movement,  Avill  be  seen  to  have  a  border  of  blue, 
while  during  the  downward  movement  it  has  a  reddish-yellow  one. 

The  refracting  surfaces  of  the  e3e  are  not  strictly  s])herical,  but 
of  the  forms  known  as  ellipsoids  of  rotation— surfaces  formed  by  the 
rotation  of  an  ellipse  upon  one  of  its  axes.  The  result  of  this  is  that 
their  curvatures  vary  in  different  planes.  Usually,  in  most  eyes, 
the  curve  is  more  convex  in  the  vertical  meridian  than  in  the  hori- 
zontal. Vertical  rays  are  therefore,  after  passing  through  the  eye, 
brought  to  a  focus  nearer  than  horizontal  rays.  For  this  reason, 
stars  are  seen  "  star-shaped."  Were  the  eye  absolutely  correct, 
stars  would  be  luminous  points.  This  defect  is  known  as  astigmatism. 
When,  however,  the  defect  of  vision  is  so  great  that,  owing  to 
differences  in  refraction  in  different  meridians,  tlie  subject  is 
incommoded  seriously,  there  is  present  some  greater  irregularity  of 
the  cornea  or  lens.  It  is  necessary  to  correct  the  defect  by 
reinforcing  the  curvature  of  the  weaker  meridians  by  means  of 
cylindrical  lens. 


Section  III 


THE  ADJUSTMENT  OF  THE  EYE  FOR  DIFFERENT 
DISTANCES 

When  at  rest,  the  eye  is  normally  adjusted  to  focus  parallel 
rsbjs  itpon  the  retina.  For  practical  purposes,  rays  coming  from 
a  distance  greater  than  6  metres  may  be  regarded  as  parallel.  Inside 
this  distance,  the  rays  to  the  normal  eye  become  divergent,  and  for 
a  clear  image  to  be  formed  on  the  retina  it  is  necessary  for  them  to 
be  more  refracted,  otherwise  a  blurred  image  is  formed,  and  the  object 
is  not  distinctly  seen.  Thus,  while  standing  20  feet  from  a  window, 
a  needle  held  2  feet  from  the  eye  is  blurred  when  the  window-sashes 
are  distinct.  Conversely,  when  the  needle  is  seen  clearly,  the  window- 
sashes  are  blurred.  In  looking  at  the  needle  under  these  conditions, 
we  are  conscious  of  the  effort  of  aecommodating  the  eye  for  near 
vision.  Normally,  although  we  are  not  conscious  of  it,  the  effort 
required  helps  us  to  form  our  judgment  of  the  distance  of 
objects.  The  nearer  the  object,  the  greater  the  effort  required  to 
accommodate,  and  the  sooner  fatigue  is  experienced.  Accommodation 
is  brought  about,  not,  as  in  the  camera,  by  altering  the  position  of 
the  sensitive  plate,  but  bj'"  altering  the  refractive  ])ower  of  the  lens. 
When  we  accommodate  for  near  vision,  the  anterior  surface  of  the 
lens  becomes  more  convex.  This  can  be  shown  by  viewing  in  a  dark- 
ened room  the  images  of  a  candle-flame  reflected  from  the  eye  of  a 
subject.  When  the  light  is  properly  adjusted,  three  images  are  seen — 
one  from  the  cornea,  bright  and  erect ;  one  from  the  anterior  surface  of 
the  lens,  apparently  coming  from  near  the  centre  of  the  piipil,  feebler 
than  the  first,  but  erect;  and  a  third,  more  deep-seated,  generally  a 


THE  SENSE  OF  VISIOX 


613 


mere  spot,  and  inverted,  from  the  posterior  surface  of  the  lens.  When 
the  subject  accommodates  for  near  vision,  the  middle  image  alone 
moves.  It  advances  and  grows  smaller,  showing  that  in  the  process 
the  anterior  surface  of  the  lens  moves  forward  and  becomes  more 


Fig.  342. — The  Phakoscope. 


convex.  This  phenomenon  can  also  be  demonstrated  in  daylight  by 
means  of  the  instrument  known  as  the  phakoscope  (Fig.  342).  It 
consists  of  a  dark  box,  roughly  triangular  in  shape,  with  the  angles  of 
the  triangle  bevelled  off,  and  at  S  and  0  fitted  with  windows  (Fig.  343). 


Fia.  34.3.— Di.\GRAM  of  the  Course  of  the  Rays  of  Light  in  the  Phakoscope. 


The  observer's  eye  is  at  0,  the  subject's  at  S.  At  C  two  prisms 
are  arranged  vertically,  and  these  are  illuminated  by  a  lamp,  so  as 
to  allow  two  illuminated  squares  to  fall  upon  the  eye  placed  at  S. 
The  eye  at  S  can  either  be  focussed  for  the  vertical  needle  placed  at 
the  opening  W,  or  for  a  distant  object  beyond  the  opening.     With 


614 


A  TEXTBOOK  OF  PHYSIOLOGY 


the  alteration  of  the  lens  corresponding  to  the  change  of  acconmio- 
dation,  the  images  from  the  anterior  surface  of  the  lens  are  seen  to 
vary,  as  described  above. 

The  Mechanism  of  Accommodation. — According  to  the  received 
hypothesis,   the  meridional  and  radial  fibres  of  the  ciliary  muscle 


Pig.  344. — ^Diagram  to  show  how  Anterior  Surface'of  the  Lens  becomes  jiore 
Convex  during  Accommodation  for  Near  Vision. 

contract  and  pull  forward  the  posterior  part  of  the  ciliary  body 
and  the  anterior  part  of  the  choroid,  witli  the  hyaloid  membrane. 
This  slackens  the  suspensory  ligament  and  diminishes  its  pull  upon 
the  capsule  of  the  lens,  and  the  lens  then,  by  its  own  elasticity,  is  free 
to  assume  a  more  convex  shape.     It  is  further  suggested  that  the 


Fig.  34.5. 


-To  illustrate  the  Movement  of  the  Corneo-Iridic 
Accommodation.     (Thomson  Henderson.) 


Angle  in 


The  ciliary  sphincter  moves  from  c  to  r' ,  the  cribriform  ligament  is  pulled  taut, 
affording  ready  passage  of  aqueous  into  the  supraehoroidal  space.  The  angle 
of  the  anterior  chamber  is  not  deepened  in  an  anatomical  sense. 


circular  fibres  of  the  ciliarj-  muscle,  by  their  contraction,  squeeze  the 
free  edges  of  the  lens  in  a  sphincter-like  manner,  thereby  helping  to 
squeeze  the  anterior  surface  forwards.  The  circular  fibres  are  especi- 
ally well  developed  in  long-sighted  people,  who  accommodate  with 
special  effort.  It  is  said  that  the  lens  becomes  more  movable  in  the 
accommodated  eye,  as  it  can  then  be  made  to  shake  by  sudden 
movements  of  the  head.     The  essential  part  of  the  act  of  accommo- 


THE  SENSE  OF  VISION 


015 


ilation    is    the  translation, of  aqueous  fluid   from    tha  front    to    the 
•circumferential   edge  of   the    lens.     The  excised  lens,    in  itself,  does 
not  possess  elasticity.     It  is   a  jellj'-like  mass.     The   whole  e3^ebaU 
is  distended  with  fluid — aqueous,  vitreous,   and  blood  in  the  blood- 
vessels—  at    a    pressure    of    about    30    mm.    Hg.       The    fluid    is 
secreted    bj^    the    cells    which    line    the  ciliar}'    processes,   and   the 
.intra-ocular  pressure   is    regulated   by   their  secretory   power.      The 
pressure  of  this   fluid    keeps   the   eyeball   distended,    and    maintains 
its    shape    constant    in    accordance    with    the    requirements    of    an 
optical  instrument.      It  keeps    the    suspensory    ligament    taut    and 
the  lens  flattened.     Accepting  the  importance  of  the  fluid,  we  must 
suppose  that  the  circular  fibres  of  the  ciliary  muscle  and  the  radial 
fibres — taking  the  attachment  of  these  to  the  suspensory  ligament 
as   the   fixed  point — by  their  contraction,   pull 
open  the  meshes  of  the  cribriform  ligament,  and 
allow  aqueous  fluid  to  pass  therein.     The  ciliary 
bodj*,  in  its  outer  part,  is  thus  distended  with 
fluid,   and   its   inner  part  approximated  to  the 
circumference  of  the   lens,  and  the  suspensory 
ligament   relaxed.     The   lens   then   takes  on    a 
more  globular  shape,  and  becomes  more  mobile 
in  its  water}'  bed.     By  the  passage  of  more,  or 
less,  fluid  from  the   aqueous  chamber  in  front 
into  the  meshes  of   the  cribriform  ligament  at 
the  circumference,  the  curvature   of  the  lens  is 
controlled  with    the    greatest    nicety.      As    the 
fluid  is  distributed  all  round  the  circumference 
of  the  ej-eball.  the  actual  expansion  of  the  spaces 
in  the  cribriform  ligament  requires  to  be  very 
small  in  order  to   contain    the    fluid    which   is 
translated  and   determine  the  necessarj-  change 
in  the  convexity  of  the  lens.    If  the  meridional 
fibres  of  the  ciliary  muscle  relax  when  the  radial 
and  circular  fibres  contract,  they  will  be  bowed 
inwards.     If  they  contract  Avhen  the  other  fibres 
relax,    they    will    restore    the    accommodated 
eye  to  its  resting  condition.     It  is  conceivable,  and  probable,  that 
these   fibres    act    as    antagonists   to   the   circular  and   radial  fibres, 
and  that  accommodation  is  brought  about  by  the  balanced  action 
of  antagonist  muscles.     During  the  act  of  accommodation,  the  pupil 
contracts   and  the   eyeballs   are   rotated   inwards.     All   the   muscles 
■concerned  in  the  act  of  accommodation  are  supplied  by  the  third  nerve. 
The  Near  Point  oJ  Vision. — The  range  of  accommodation  in  the 
adult  is  such  as  to  all(.w  clear  vision  of  objects  held  up  to,  and  slightly 
within  6  inches  of,  the  eye.     This  can  be  demonstrated  by  making  in 
a  piece  of  cardboard  two  holes  separated  by  less  than  the  diameter 
of  the  pupil.     Holding  these  close  to  the  eye,  a  needle  held  inside 
5  inches  is  seen  as  two,  but  as  it  is  gradually  moved  farther  away 
the  images  fuse,  and  one  needle  only  is  seen  (Fig.  346). 


Aba 


Fig.  346. — Diagram  to 
show  how  the 
Images  of  Near  .a.xd 
Far  Piss  fall  ox 
Retina. 

A,  Near  pin;  B,  far 
pin. 


61G  A  TEXTBOOK  OF  PHYvSIOLOGY 

Children  possess  a  greater  power  of  accommodation  than  adults. 
The  near  point  of  vision  gradually  increases  with  advancing  age,  so 
that  at  about  the  age  of  forty  it  is  outside  the  normal  reading  distance 
of  10  inches,  and  print  has  to  be  held  farther  away  in  order  to  be  read. 
This  is  the  condition  known  as  presbyopia,  and  is  attributed  to  a 
diminished  elasticity  of  the  lens  and  atonicity  of  the  ciliary  mnscle. 
It  is  remedied  by  biconvex  glasses,  which  ho\\)  io  focus  the  rays 
correctly  on  the  retina. 

In  the  condition  known  as  hypermetropia,  or  long  sight,  the 
parallel  rays  are  not  brought  to  a  focus,  because  the  eyeball  is  shorter 
than  normal  in  its  antero-posterior  axis  (Fig.  ?47,  a).     To  see  even 


Fig.  347. — Diagram  showing  A,  Course  of  Parallel  Rays  in  the  Hypeemeteopic 
Eye  ;  B,  Patch-of  Parallel  Rays  in  Hy'permetropk'  Eye  after  Correction 
BY  Means  of  a  Convex  Lens. 

distant  objects  well,  the  subject  has  to  accommodate  slightly,  and 
this  throws  a  strain  upon  the  eye.  The  condition  is  corrected  by  a 
convex  lens  (Fig.  347,  b). 

The  opposite  condition  is  known  as  myopia.  In  this  condition 
a  person  is  short-sighted,  and  cannot  see  distant  objects  at  all.  The 
defect  is  due  to  an  increased  antero-posterior  axis  of  the  eye,  the 
eyeball  being  longer  than  normal  (Fig.  348,  a).  This  being  the  case, 
.  parallel  rays  from  a  distance  are  brought  to  a  focus  in  front  of  the 
retina.  The  defect  is  often  associated  with  some  degree  of  astigma- 
tism, and  is  corrected  bj-  the  use  of  biconcave  lenses  of  suitable 
strengths  (Fig.  348,  b). 

The  standard  lens  for  ophthalmic  j^urposes  is  one  which  has  a 
focal  length  of  1  metre;  its  refractive  power  is  then  said  to  be  1  diopter,, 
or  1  D.     A  2-diopter  (2  D.)   lens   has  therefore   a  focal   length  of  | 


THE  SENSE  OF  VISION 


Gl- 


metre,  a  3-diopter  (3  D.)  lens  one  of  .1  metre,  and  so  on.     Biconvex 
lenses  are  called  +  ,  biconcave  -  ,  lenses. 

Retinoscopy,  or  Skiascopy  affords  an  accurate  method  of  testing 
the  refraction  of  the  eye.  The  direction  is  observed  in  which  the 
"  shadow  "  in  the  eye  moves  Avhen  a  light  is  reflected  into  it  from  a 
mirror.  The  "  shadow  "  is  seen  against  the  illuminated  background 
of  the  eye,  which  appears  a  brilliant  red — choroidal  reflex,  as  it  is 
called.  The  operation  takes  place  in  a  darkened  room,  preferably 
on  an  eye  with  the  pupil  dilated  by  a  drug,  such  as  homatropine. 
From  a  metre  distance  the  eye  is  observed  through  a  small  jilane  or 
concave   mirror   with   a   hole   in  the   centre — the   retinoscope.     The 


Fig.  348. —Diagram  showing  A,  Course  of  Parallel  Rays  in  Myopic  Eye; 
B,  Path  of  Parallel  Rays  in  a  Myopic  Eye  after  Correction  by^  Means 
OF  A  Biconcave  Lens. 


mirror  is  then  slowly  tilted  from  side  to  side.  When  a  plane  mirror 
is  used,  the  shadow  moves  in  the  same  direction  as  the  mirror  is  tilted 
in  the  normal  and  in  the  hypermetropic  eye,  in  the  op^wsite  direction 
in  the  myopic  eye. 

If  the  eye  be  normal,  a  lens  of  1  D.  Avill  bring  about  a  reversal  of 
the  direction.  In  the  case  of  hypermetropic  and  myopic  eyes,  the 
reversal  of  the  image  is  ascertained  b}^  introducing  respectively 
biconvex  and  biconcave  lenses ;  -  1  D.  is  added  to  the  lens,  which 
completelj'  neutralizes  the  shadow:  in  other  words,  is  subtracted 
from  the  strength  of  the  +  lens  used  in  the  case  of  h3-permetropia, 
and  added  to  the  strength  of  the  -  lens  employed  in  mj^opia.  If  a 
concave  mirror  be  used  as  the  retinoscope,  the  shadow  moves  against 
the  direction  in  the  normal  eye  in  hypermetropia,  and  in  the  same 
direction  in  myopia. 


618 


A  TEXTBOOK  OF  PHYSIOLOGY 


Section  IV 

THE  EFFECTS  OF  LIGHT  FALLING  ON  THE  RETINA 

When  those  \'ibi'ations  of  the  ether  which  evoke  the  sensation  of 
light  fall  upon  the  retina,  certain  marked  changes  occur.  In  the  first 
])lace,  there  is  a  variation  of  the  resting  electrical  current.  In  the 
resting  eye,  the  current  is  normally  ingoing;  when  the  eye  is  stimulated 
by  light,  the  current  becomes  outgoing  (Figs.  349,  350). 

Secondly,  there  is  a  movement  of  the  granules  in  the  pigment 
cells  from  the  centre  of  the  cells  into  the  processes  between  the  rods. 
In  a  frog's  e3'e  which  has  been  kept  in  the  dark,  the  pigment  layer 


Fig.  349. — Plotted  Curves  constrltcted  from  Electrometer  Records  of  Eye- 
ball Responses  to  the  Light  from  the  Red,  Green,  and  Violet  Regions 
OF  the  Spectrttm.     (Gotch.) 

The  upper  records  are  fairly  typical,  the  lower  show  the  most  pronounced  resi^onses. 


is  easily  separated  from  the  rods  and  cones.  After  exposure  to  light, 
these  layers  are  difficult  to  separate;  the  pigment  is  much  more  abun- 
dant between  the  outer  limbs  of  the  rods,  and  i:)asses  as  far  as  the 
external  limiting  membrane  between  the  inner  limbs  (Fig.  351). 

Thirdly,  the  visual  jDurple  present  in  the  outer  limbs  of  the  rods  is 
bleached  in  the  parts  upon  which  the  light  falls.  By  this  means, 
therefore,  a  negative  image,  or  optagram,  is  obtained  in  the  retina 
of  an  object,  such  as  a  window  at  which  the  eye  may  have  been  looking 
(c/.  Fig.  352).  When  light  ceases  to  fall,  the  visual  purple  is  again 
regenerated  at  the  expense  of  the  pigment  cells.  For  this  purpose, 
it  is  necessary  for  them  to  be  in  contact  with  the  rods.  If  they  be  in 
any  w^ay  detached,  regeneration  does  not  take  place. 


THE  SENSE  OF  VISIOX 


019 


Fourthl}',  there  is  a  contraction  of  the  inner  hnibs  of  the  cones. 

The  Functions  of  the  Retina. — The  retina  is  able  to  receive  and 
transform  the  ether  vibrations  into  nervous  impulses,  so  that  the 
brain  perceives.  Not  only  is  light  perceived,  but  at  the  same  time 
is  appreciated  the  colour  and  also  the  form  of  external  bodies.  The 
function  of  the  retina  ma}^  therefore  be  said  to  be  to  transform  light 
into  nervous  energy  so  that  luminosity,  form,  and  colour  may  be 
perceived  by  the  brain. 

The  question  arises  as  to  which  part  of  the  retina  is  con- 
cerned in  the  reception  of  the  stimulus  of  the  ether  vibrations.  The 
effects  (described  above)  which  light  produces  on  the  layer  of  rods 
and  cones  and  pigment  la^'er  indicate  that  the  transformation  of 
energy  takes  place  here.  This  is  confirmed  by  the  following  con- 
siderations : 


;^u;ii^:;!i:iiiu 


Fig.  3.")0. — Combined  Action  of  Three  Substances,  A,  B,  C,    in  Dakk  Eye. 
(Einthoven  and  Jolly.) 

Absc,   1  mm. =0*5  second;  ordin.,   1  mm.  =  10  micrcTolts. 


1.  The  bloodvessels  supplying  the  retina  are  distributed  to  the 
anterior  portion  of  the  retina  in  the  nerve-fibre  and  ganglionic  layers, 
the  main  vessel  entering  the  eyeball  at  the  spot  where  the  optic  nerve 
passes  in.  Under  certain  circumstances,  these  vessels  may  be  seen 
as  a  shadow.  This  being  the  case,  they  must  be  perceived  by  the 
parts  of  the  retina  lying  behind  them — namely,  the  layer  of  rods  and 
cones. 

If  a  subject  turn  one  eye  inwards,  and  look  towards  a  dark  wall, 
and  with  a  lens  a  good  light  is  focussed  upon  the  exposed  sclerotic, 
so  as  to  make  a  small  but  strongly'  illuminated  area,  then  on  giving 
the  lens  a  gentle  rocking  or  circular  movement,  the  field  will  appear 
to  the  subject  as  reddish-yellow,  and  dark  figures  will  be  seen  appear- 
ing in  the  field,  which  branch  and  have  the  character  of  the  retinal 
bloodvessels,  of  which  the}'  are  really  the  shadows.  In  the  direct 
line  of  vision  a  small  area  will  be  seen  free  from  these  branching 
shadows.  This  is  the  yellow  spot.  So,  too,  if  a  white  cloud  be 
viewed  through  a  pinhole  in  a  card  held  close  to  the  eye  and  the 
card  be  given  an  up-and-down  movement,  a  number  of  vessels  will 


Ci20 


A  TEXTBOOK  OK  PHYSIOLOGY 


be  seen,  generally  running  horizontally;  if  a  side  to  side,  vertically 
running  vessels  will  be  apparent;  if  a  circular  movement,  the  general 
distribution  of  the  vessels  will  be  visible.  In  the  direct  line  of  vision 
there  is  a  small  area  in  which  no  vessels  are  seen — the  macula  lutea, 
or  yellow  spot. 


A  B 

Fro.  351.— Section^of  Frog's  Retixa.     (After  Englemann.) 
A,  After  exposure  to  light;  B,  when  kept  in  the  dark. 

In  these  experiments  the  movement  of  the  light  or  the  illuminated 
field  is  important.  The  retina  ap2:)reciates  shifting  shadows  better 
than  fixed  ones. 

2.  At  the  point  where  the  o])tic  nerve  loaves  the  eye  there  are 
no  rods  or  cones,Tand  this  spot  is  in,sensitive  to  light.     This  blind 


A.  B. 

Fia.  352. — A.  The  Normal  Appearance  of  the  Retina  in  the  Rabbit's  Eye 
BEFORE  Exposure  to  Light;  a,  the  P]ntrance  of  the  Optic  Nerve;  b,  b,  a 
Colourless  Layer  of  Medullateb  Nerve  Fibres;  c,  a  Layer  of  Deeper 
Colour  separating  the  Lighter  Upper  from  the  More  Heavily  Pigmented 
Lower  Portion.  B,  Optogram  of  a  Window  after  Exposure  of  Eye. 
(Kiihne.) 


spot  is  readil}'  demonstrated  b}'  Fig.  353.  If  the  left  eye  be 
closed,  and  the  right  eye  gazes  at  the  dot  from  the  distance  of  a 
foot,  the  line  will  appear  continuous.  Normally,  we  do  not  notice 
the  blind  spot,  but  fill  in  the  gap  with  sensations  similar  to  those 
falling  on  the  neighbouring  areas  of  the  retina.  The  blind  spot  can 
be  mappetl  out  as  follows:   Let  the  head  rest  in  a  fixed   position. 


THE  SENSE  OF  \'ISTON  621 

as  by  placing  the  chin  in  a  tin  mug,  and  place  a  sheet  of  white  paper 
vertically  in  front  of  it  at  a  distance  of  18  inches.  Draw  a  dot  in  the 
centre  of  the  paper.  Close  one  eye,  and  with  the  other  regard  the  dot. 
Take  a  thin  strip  of  w^hite  cardboard,  and  blacken  about  2  millimetres 
of  the  end.  Move  the  blackened  end  over  the  region  of  the  field  of 
vision  corresponding  to  the  blind  spot,  and  note  the  points  where  the 
black  area  disappears,  marking  them  on  the  white  paper.  A  sufficient 
number  of  these  points  can  be  taken,  and  a  curve  drawn  through  them 
will  indicate  the  margin  of  the  field  of  the  blind  spot. 

3.  At  the  fovea  centralis  there  are  chiefly  cones;  the  other  layers 
of  the  retina  are  thinned  out.     This  is  the  spot  of  acute  vision. 


Fig.  353. — To  demonsteate  the  Blixd  Spot. 

W'hen  held  about  12  inches  away,  with  left  e^e  closed,  the  line  on  the  left  a])p(>ars 

continuous. 

The  Perception  of  Light,  and  the  Relation  of  the  Sensation  to  the 
Stimulus. — We  have  seen  that  the  sensation  of  light  is  due  to  the 
stimulation  of  the  receptor  mechanism  of  the  eye  by  means  of  the 
vibrations  of  the  ether.  According  to  the  amplitude  of  the.se  vibra- 
tions, so  the  sensation  of  light  varies  in  intensity.  According  to  the 
length  of  time  the  waves  fall  upon  the  retina,  so  the  sensation  varies 
in  duration.  The  sensation  evoked  lasts  much  longer  than  the 
stimulus.  The  sensation  of  a  flash  of  lightning  or  of  an  electric  spark, 
for  example,  is  much  longer  than  the  time  during  which  vibrations 
are  actually  falling  on  the  retina.  When  the  stimuli  fall  in  sufficient^ 
quick  succession,  the  sensations  become  fused,  so  that  a  lamp  swung 
quickly  in  a  circle  gives  the  sensation  of  a  ring  of  light.  In  moving 
pictures  such  a  fusion  of  sensation  takes  place.  For  such  a  fusion 
to  take  place,  it  is  necessary  for  the  stimuli  to  be  about  ten  a  second 
for  weak  light,  and  forty  a  second  for  strong  light.  The  length  of 
interval  varies  with  different  colours,  being  longest  with  blue,  shortest 
with  yellow,  and  intermediate  with  red. 

From  the  consideration  of  an  electric  light  and  a  candle  it  is  obvious 
that  the  intensity  of  the  sensation  varies  with  the  luminous  intensity 
of  the  object.  Following  Weber's  law,  it  is  foimd  that  it  is  easier  to 
distinguish  a  slight  difference  in  brightness  between  two  feeble  lights 
than  the  same  difference  in  brightness  between  two  bright  lights. 
The  smallest  difference  which  can  be  appreciated  in  the  case  of  the 
eye  moderately  stimulated  by  light  is  about  -^  ,\^,  of  the  total  luminosity. 
The  total  sensation  is  greater  in  amount  when  light  falls  on  a  large 
area  of  the  retina  than  when  it  falls  on  a  small  area. 

The  eSect  of  a  stimulus  also  varies  according  as  it  falls  upon  an 
eye  accustomed  to  the  daylight  (the  light-adapted  eye)  or  an  eye 
which  has  been  attuned  to  the  dark  (the  dark-adapted  eye).  Upon 
croing  from  the  light  into  the  dark,  it  is  impossible  at  first  to  see  any- 
thing; but  after  a  time  the  eye  becomes  adapted  to  the  darkness, 


(322  A  TKXTBOOK  OF  PHYSIOLOGY 

and  suirouuding  objects  are  localized  and  identified.  The  sensitive- 
ness of  the  retina  has  increased  many  times.  Conversely,  on  emerging 
from  ditrkness  to  light,  one  is  '"  dazzled,"  owing  to  this  extreme 
sensitiveness.  This  soon  passes  off,  and  the  eye  becomes  "  light- 
adapted." 

Experiment  seems  to  indicate  that  the  different  regions  of  the 
retina  have  different  functions.  The  peripheral  regions  are  found 
to  be  relatively  more  sensitive  than  the  fovea  to  feeble  stinnili — that 
is,  to  light  of  moderate  or  short  wave-lengths.  On  the  other  hand, 
the  central  portion  of  the  retina  resj)onds  particularly  to  bright  light 
— light  of  long  wave-lengths.  When  the  eye  becomes  adapted  to 
the  dark — "  dark-adapted  " — the  increased  responsiveness  of  the 
retina  under  these  circumstances  is  in  the  regions  outside  the  fov^ea. 
It  is  much  easier  to  perceive  stars  of  small  magnitude  when  looking 
sideways  than  when  looking  directly  at  them.  It  is  for  this  reason, 
also,  that  a  star  ina.y  be  suddenly  observed  in  the  heavens  during  a 
movement  of  the  head,  and  yet,  when  that  part  of  the  heavens  is 
scanned  directly,  it  cannot  be  seen. 

On  the  other  hand,  as  already  stated,  it  is  known  that  it  is  in  the 
fovea  centralis  that  vision,  especially  form  sensation,  is  most  acute. 
We  alwa3'S  look  directly  at  a  thing  when  we  want  to  appreciate  its 
shape.  At  the  same  time,  the  pupil  is  contracted  to  shut  out  peripheral 
rays.  In  order  to  differentiate  similar  objects  grouped  closely  together, 
it  is  necessary  that  these  shoidd  subtend  an  angle  of  a  certain  magni- 
tude at  the  nodal  point  with  resjject  to  the  eye.  Further,  in  order  that 
objects  ma^^  be  differenliated,  it  is  necessary  that  their  contiguous 
margins  and  the  .space  between  should  form  an  image  on  the  retina, 
which  should  n>>t  be  less  than  a  certain  length.  It  has  been  found 
that  a  subtended  angle  of  63-75  seconds,  equivalent  to  a  retinal 
distance  of  0-00463  millimetre,  is  necessary  for  discrimination.  Double 
stars,  which  sul)tend  an  angle  less  than  this,  appear  to  the  naked  eye 
as  single  stars. 

The  acuteness  of  vision  at  the  fovea  is  ordinarily  tested  b}'  noting 
the  distance  at  which  letters,  which  at  a  given  distance  subtend  an 
angle  of  5  minutes  at  the  eye,  can  be  read.  This  method  may  be 
applied  either  to  ascertain  what  error  of  refraction  may  exist  in  the 
eye,  or,  if  this  be  absent  or  corrected,  what  the  acuteness  of  vision 
in  the  particular  eye  is.  We  shall  see  later  that  it  is  also  in  the  region 
of  the  fovea  that  the  different  colours  are  best  appreciated. 

The  so-called  duplicity  theory  supposes  that  there  are  two  distinct 
visual  mechanisms  in  the  retina — one  that  of  the  rods  and  visual 
purple,  upon  which  depends  achromatic  reactions,  especially  under 
conditions  of  darkness  adaptation;  secondly,  that  of  the  cones,  which 
serves  achromatic  responsiveness  in  bright  light,  and  also  chromatic 
responsiveness.  This  view  is  not  altogether  accepted,  but  it  is  sup- 
ported b}^  the  fact  that  a  great  abundance  of  rods  and  visual  purple 
is  found  in  animals  which  see  badly  in  broad  daylight,  but  which 
have  good  '"  twilight  vision."'  Such  animals  are  the  bat,  owl,  and 
hedgehog.     Cones,  on  the  other  hand,  predominate  in  the  retinae  of 


THE  SENSE  OF  VISION 


623 


animals  which  have  acute  daylight  vision — e.g.,  birds,  such  as  the 
pigeon  and  chicken — but  which  see  imperfectly  in  feeble  or  artificial 
light. 

Further,  in  cases  of  total  colour-blindness  (achromatopsia),  the 
spectrum  is  seen  merely  as  a  band  of  light  of  varying  intensity,  the 
greatest  brightness  being  in  the  regions  outside  the  fovea,  while  in 
man}'"  eases  a  blind  spot  (scotoma)  is  found  in  a  position  corresponding 
to  the  fovea.  In  such  cases  there  is  good  vision  in  twilight,  but  in 
da3'light  a  marked  diminution  in  the  acuity  of  vision,  a  fear  of  strong 
light  (photophobia),  bad  fixation  leading  to  nystagmus  (quick  side- 
to-side  movements  of  the  ej'es). 

In  cases  of  nicotine-poisoning,  with  visual  trouble  (tobacco  ambly- 
opia), there  is  a  loss  of  acuity  of  vision  and  deranged  colour  sensation. 
It  is  the  region  of  the  fovea  which  is  affected. 

In  cases  of  "  night-blindness  "  (hemeralopia  or  nyctalopia)  there 
is,  in  comparison  with  the  normal  colour  sense,  a  shortening  of  the 
violet  end  of  the  spectrum,  and  an  impaired  responsiveness  to  light 
or  short  wave-lengths.  For  this  reason,  a  person  suffering  from  this 
condition  is  vmable  to  see  well  in  twilight  or  artificial  light,  and  is 
said  to  be  night-blind.  This  condition  is  inherited,  transmitted  by 
the  females,  but  present  only  in  the  males  of  a  family. 

The  Perception  of  Colour. — When  white  light  is  passed  through  a 
prism,  it  is  broken  u})  into  a  number  of  colours,  owing  to  the  greater 


Fig.  354. — Wheel  for  mixing  CoLorRs. 


refrangibility  of  some  rays  than  others.  To  most  people,  the  spectrum 
is  made  up  of  six  distinct  colours:  Red,  orange,  yellow,  green,  blue, 
violet.  Normal  individuals  may  therefore  be  said  to  be  "  hexachromic." 
A  few  people,  however,  can,  like  Newton,  see  a  seventh  colour — indigo 
— between  the  blue  and  the  violet.  Thev  are  "  heptachromic." 
White  light  is  therefore  made  up  of  a  fusion  of  these  colours.  This 
can  be  shown  by  passing  the  colours  through  a  second  prism,  when 
they  are  recombined  to  form  "  white  "  light. 

It  is  not  necessary,  however,  that  all  the  colours  be  fused  to  give 


<524  A  TEXTBOOK  OF  PHYSIOLOGY 

a  sensation  of  white.  It  has  been  shown  that  various  pairs  of  colours, 
when  mixed,  will  give  the  sensation  of  "  white."  The  mixing  can 
he  done  by  placmg  the  colours  upon  a  wheel  or  top  which  is  quickly 
rotated  (Fig.  354).  It  is  better,  however,  to  superimpose  on  a  white 
surface  the  different  colours  from  two  spectra.  The  chief  pairs  of 
colours  which  give  white  are  red-green,  blue-yellow.  Such  colours 
are  termed  "  complementary."  If  in  a  good  hght  one  of  these 
colours  in  the  form  of  a  disc  or  letter  be  viewed  steadily  for  a  time 
on  a  white  surface,  and  the  gaze  then  turned  to  another  white 
surface,  the  disc  or  letter  will  appear  after  a  time  in  the  comple- 
mentary' colour.  This  is  Imown  as  the  negative  after-image.  After 
beholding  a  red  letter,  a  green  letter  will  appear  as  the  after-image, 

and  so  on.  ' 

The  different  colours  of  the  spectrum  vary  in  luminosity.  Nor- 
mally, the  yellow  is  the  brightest  part  of  a  spectrum.  But  the  lumin- 
osity of  a  colour  may  vary.  Thus,  any  of  the  colours  of  one  spectrum 
may  be  made  of  equal  luminosity  with  the  yellow  of  another  spectrum 
by  increasing  the  intensity  of  the  white  light  used  to  form  the  spectrum. 
With  feeble  light,  the  maximum  luminosity  shifts  to  the  green,  and 
the  colours  of  the  red  end  of  the  spectrum  become  less  easily  perceived 
than  those  of  the  blue  end.  This  accounts  for  the  order  of  the  changing 
colours  of  a  sunset  or  the  change  of  colours  in  a  flower  garden  as 
tAvilight  passes  into  night. 

Saturation. — Besides  luminosity,  a  colour  possesses  a  degree  of 
saturation.  By  this  is  meant  the  extent  to  which  it  is  mixed  with 
white  lic^ht.  A  fully  saturated  colour  is  entireh"  free  from  white 
light,  svich  as  the  sodium  flame  in  a  dark  room. 

When  colours  are  mixed  which  are  not  complementary,  we  get 
*'  shades."  As  many  as  160  shades  have  been  observed  in  the 
spectrum;  some  shades,  such  as  purple,  are  not  present  in  the 
spectrum.  When  two  colours  are  mixed  which  are  nearer  in  the 
spectrum  than  the  complementary  colours,  a  colour  is  obtained  of 
the  part  of  the  spectrum  between  the  two.  If  the  colours  are 
farther  apart  in  the  spectrum  than  the  complementary  colours,  then 
a  colour  mixed  with  white  light  is  obtained — an  unsaturated  colour. 
By  taking  the  three  colours  red,  green,  violet,  or,  according  to 
other  authorities,  four  colours — red,  yellow,  green,  blue — all  the 
colours  of  the  spectrum  may  be  obtained  by  mixing  in  .  varying 
proportions.     These  are  known  as  the  fundamental  colours. 

In  the  mixing  of  pigments,  the  nature  of  the  pigment  substance 
has  to  be  taken  into  account.  A  blue  and  a  yellow  pigment,  when 
mixed,  give  green,  not  white.  This  is  because  the  blue  pigment 
absorbs  the  red  and  yellow  rays  from  white  light,  and  reflects  the  blue 
and  green  rays.  The  yellow  pigment  reflects  red,  yellow,  and  green, 
and  retains  the  blue.  When  the  pigments  are  mixed,  the  green 
rays  are  the  only  ones  not  absorbed.  By  examination  of  the  light 
reflected  from  any  pigment  with  the  jDocket  spectroscope,  it  can  be 
seen  what  ravs  are  reflected  and  what  are  absorbed. 


THE  SENSE  OF  \'ISIOX 


625 


Colour  Vision. — ^Numerous  theories  have  been  advanced  to  exphiin 
the  phenomena  of  colour  vision.  The  two  classical  views  are  those  of 
Young-Helniholtz  and  of  Hering. 

The  Young-Helmholtz  Theory. — This  theory  assumes  that  there 
-are  three  separate  substances  in  the  retuia  stimulated  by  the 
wave-lengths  of  the  three  fundamental  colours — red,  green,  and 
violet.  Simultaneous  excitation  of  all  three  gives  the  sensation  of 
white,  while  absence  of  stimuli  gives  that  of  black.  The  colour 
sensations  depend  upon  different  degrees  of  stimulation  of  these 
three  substances  (see  Fig.  355).  From  the  diagram,  it  will  be  seen 
that  orange  is  due  to  a  large  stimulation  of  the  red,  and  lesser  stimu- 
lation of  the  green  and  violet  substances.  In  the  sensation  of 
yellow,  the  red  and  green  elements  are  almost  equally  excited,  and  the 
violet  but  little,  and  so  on  according  to  the  manner  indicated  in  the 
diagram. 


Violet. 


Fig.  3.55. — Schema  to  illustrate  the  Young-Helmholtz  Theory  of  Colour 

Visiox.     (Helmholtz.) 

The  curves  represent  the  intensity  of  stimulation  of  the  three  colour  substances: 
1,  The  red-perceiving  substance;  2,  the  green-perceiving;  3.  the  violet-perceiving. 
Vertical  lines  drawn  at  any  point  of  the  spectrum  indicate  the  relative  amount 
of  stimulation  of  the  three  substances  for  that  wave  length  of  the  sj^ectrum. 


The  Hering  Theory. — -According  to  this  view,  the  fundamental 
<;olour  sensations  are  red,  yellow,  green,  and  blue.  These  are  grouped 
together  in  pairs — red-green,  blue-yellow,  and  in  addition  black 
And  white  (black-white).  In  the  retina  are  three  corresponding 
substances — the  green-red,  blue-yellow,  and  black-white.  These 
substances  may  be  stimulated  either  in  an  anabolic  (a  buikling-ui)) 
<lirection  or  in  a  katabolic  (a  breaking-doAvn)  direction.  Thus,  if  one 
or  other  of  the  substances  be  broken  down,  the  receptors  of  the  retina 
are  stimulated  in  such  a  manner  that  red,  yellow,  and  white,  arc 
respective^  appreciated  by  the  brain.  If  the  changes  be  in  an 
anabolic  direction,  then  the  conscious  sensation  is  respectively  green, 
blue,  or  black. 

.4  naholism.  KatahoLism. 

Green.  Red. 

Blue.  Yellow. 

Black.  White. 

40 


020  A  Tli]XTB()OK  OF  PHYSIO  LOU  Y^ 

The  black-white  substance  is  stimulated  also  by  the  sensations- 
of  luminosity.  If,  therefore,  red  and  green  sensations  of  equal  in- 
tensity are  throAvii  on  the  retina,  they  negative  one  another,  and  the 
result  is  a  sensation  of  luminosity. 

Against  this  view  is  the  experimental  fact  that  stinmlation  of  the 
retina  by  the  different  colour  pairs  does  not  produce  electrical  variations 
in  opposite  directions,  as  they  should  do  if  the  substance  were  affected 
in  one  case  in  an  anabolic  and  in  the  other  case  in  a  katabolic  direc- 
tion. As  the  result  of  the  exposure  of  the  retina  to  coloured  lights, 
the  current  of  action  is  in  the  same  direction,  but  with  different  latent 
periods  (Fig.  349). 

Many  experiments  have  been  performed  to  support  one  or  other 
of  these  views.  Considerable  importance  Ras  been  attached  to  the 
evidence  afforded  by  the  condition  of  "  colour-blindness."  It  would 
aj)pear  that  the  varying  conditions  met  with  in  colour-blindness  are 
not  satisfactorily  ex])lained  by  either  hypothesis. 

Colour-Blindness. — Certain  people  are  said  to  be  colour-blind. 
They  are  luiable  to  distinguish  certain  colours  or  shades  which  are 
easily  appreciated  by  the  normal  eye.  The  detect  is  generally  due 
to  one  of  two  conditions,  or  a  combination  of  them:  (1)  The  person 
is  luiable  to  perceive  all  the  six  colours  normally  seen  in  the  spectrum; 
(2)  the  person  is  unable  to  appreciate  the  full  extent  of  the  spectrum, 
especially  of  the  red  end. 

In  the  first  group,  all  degrees  of  colour-blindness  may  be  found. 
Instead  of  perceiving  six  colours,  an  individual  may  only  be  able  to 
see  two  colours;  he  is  therefore  termed  a  dichromic.  If  he  see  three 
colours,  he  is  a  trichromic;  if  four,  a  tetrachromic;  if  five,  a  penta- 
cbromic — as  compared  with  the  normal  person,  who  sees  six  colours, 
and  is  hexachromic.  A  certain  number  of  peox^le  perceive  seven 
colours,  and  are  heptachromic. 

The  commonest  colours  which  are  confused  are  red  and  green, 
two  forms  of  colour-blindness  being  distinguished — the  ''  red-blind  " 
and  the  "  green-blind." 

The  "  red-blmd  "  is  a  dichromic,  with  a  shortening  of  the  red  end 
of  the  spectrum.  He  cannot  see  the  extreme  red  rays.  From  the 
nearer  red  raj^s,  orange,  and  yellow,  the  red  element  is  lacking,  and  it 
appears  as  some  shade  of  green.     Green,  violet,  a,nd  blue,  are  normal. 

The  "  green-blind  "  is  also  a  dichromic.  The  middle  of  the  spec- 
trum appears  to  him  grey,  with  a  patch  of  strong  red  gradually  fading 
into  the  gre}'  on  one  side,  and  the  violet  merging  into  the  grey  on  the 
other.  Such  a  person  can  see  red  w^ell,  and  sees  also  a  variety  of  shades 
of  rose.  Greys  and  greens  are  confused,  both  being  mistaken  for  red. 
"The  case  of  a  small  boy  is  quoted  w^ho  wanted  to  paint  a  picture  with. 
the  dust  from  his  boots,  because  it  was  such  a  pretty  "  rose  "  colour. 

Such  persons  get  greatly  muddled  as  the  result  of  correction. 
Thus,  the  boy  referred  to  above,  having  been  told  that  a  green  was 
green,  judged  a  donke}'  also  to  be  green  in  colour.  So  confusion  arises 
to  the  red-blind.  Having  been  told  that  yellow,  which  appears  to 
him  green,  is  yellow,  he  confuses  it  with  orange  and  red,  which  also 


THE  SENSE  OF  VISION 


627 


appear  green.  Yet  it  is  astonishing  with  what  accuracy  such  a  jjerson 
can  learn  to  name  and  match  colours.  He  does  not  see  the  lips  and 
cheeks  as  red.  but  learns  to  call  them  so.     One  case  of  colour-blindness 


/•-> 


Fm.  ;J5b. — The  Edeidge-Green  Colour  Perception  Lantern. 

The  lantern  consists  of  four  discs:  three  carrying  seven  coloured  glasses — Clear, 
red  A,  red  B,  yellow,  green,  signal  green,  blue,  i)urple — and  one  carrjTng  seven 
modifying  glasses— Clear,  ground  glass,  ribbed  glass,  and  five  neutral  glasses. 
Each  disc  has  a  clear  aperture.  The  diaphragm  is  gi-aduated  in  respect  to  three 
apertures  to  represent  a  o|--inch  railway  signal  bull's-eye  at  60C,  800,  and  1,000 
yards  respectivelj-  when  the  test  is  made  at  20  feet.  The  colours  are  brought 
successively  into  view  by  moving  one  or  more  of  the  handles  to  position,  denoting 
the  colour  or  modifier  in  use,  on  the  scale  at  the  top  of  the  lantern.  The  classi- 
fication of  colour  perception  is  as  follows: 

Heptachromic  appreciatihg  in 

the  spectrum 
Hexachromic  appreciating  in 

the  spectrum 
Pentachromic  appieciariiig  in 

the  spectriim 
Tetrachromic  appreciating  in 

the  spectrum 
Trichromic     appreciatir^g    in 

the  spectrum 
Difhi'oraic  appreciating  in  the 

spectrum 

Totally  colour-blind  appreciating  I^ight  and  Shads  only. 


Red 

Orange 

Yellow 

Green 

Blue 

Indigo 

Violet 

Re(i 

Orango 

Yellow 

Green 

BUk- 

-- 

Violet 

Red 

— 

Yellow 

Green 

Blue 

— 

Violet 

Red 

— 

YeUow 

Green 

"— 

— 

Violet 

Red 

— 

— 

Green 

- 

~ 

Violet 

Red 



— 







Violet 

explained  that  all  colours  appeared  modifications  of  blue  and  j'ellow. 
The  brightest  and  purest  yellow  he  called  yellow;  a  slightly  darker 
and  not  so  pure  a  yellow   was  green  to  him.     A  darker  yellow  still 


€28 


A  TEXTBOOK  OF  PHYSIOLOGY 


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THE  SENSE  OP  VISION  62^ 

Avas  red.  The  brightest  blue  was  violet;  a  less  bright,  blue;  a  dirty 
blue,  purple;  and  a  very  impure  blue,  cerise. 

The  trichromic  sees  red,  green,  and  violet.     Cases  with  a  shortening 

of  the  red  end  of  the  spectrum  are  unable  to  see  red  unless  mixed 

with  some  degree  of  orange.     Such  a  case  sees  shades  minus  the  red 

rays;  therefore,  a  rose  colour,  which  is  a  mixture  of  red  and  violet. 

,  appears  violet  to  him,  and  more  akm  to  blue  than  to  red. 

Since  a  system  of  colour  signals  is  in  vogue  on  sea  and  land,  it  is 
very  necessary  that  persons  employed  in  the  marine  and  railway 
services  should  be  able  to  recognize  the  standard  red.  green,  and 
white  lights  under  all  conditions  in  which  they  are  likely  to  be  placed. 
For  this  reason,  it  is  necessary  to  have  an  efficient  means  of  testing 
colour  vision,  so  that  persons  whose  vision  is  not  satisfactory  may 
be  excluded  from  such  services.  Generally  speaking,  such  persons 
are:  (1)  Those  who  see  three  colours  or  less  in  the  spectrum.  (2)  Those 
who  have  such  a  degree  of  shortening  of  the  red  end  of  the  spectrum 
that  they  are  unable  to  see  distant  red  lights.  This  is  of  the  greatest 
importance  when  it  is  remembered  that  in  foggy  weather  the  extreme 
red  rays  are  the  most  penetrating.  (3)  Those  who,  although  their 
vision  is  normal  when  close,  are  unable  through  msensitiveness  of 
the  central  part  of  the  retinal  apparatus  to  perceive  them  at  a  distance. 

The  test  most  often  emploj^ed  up  till  now  has  been  the  Holmgren 
wool  test.  The  test  colours  u.sed  are  a  light  green  and  a  light  shade 
of  rose,  which  the  candidate  is  asked  to  match  without  naming  the 
colours.     A  red  is  also  used  as  a  confirmatorj''  test. 

It  must  be  acknowledged  that  the  test  is  more  theoretical  than 
practical.  Wool  is  not  a  suitable  material,  and  if  the  dyes  used  be 
different,  the  colours  will  be  different  in  composition.  The  colours 
are  also  liable  to  fade,  some  colours  more  quickly  than  others.  They 
also  become  dirty,  particularly  the  greens,  Avhich  enables  the  colour- 
blind to  pick  them  out.  Again,  the  different  colours  may  have  a 
different  feel.  The  degree  of  luminosity  also  varies— an  excellent 
aid  to  the  proper  identification  for  passmg  the  test. 

Persons  suffering  from  insensitiveness  of  the  retina  wiU  easily 
pass  the  test,  and  others  who  should  not  pass  for  marine  and  railway 
work  will  frequently  do  so  with  a  little  practice  with  the  wools. 

The  best  test  is  one  where  the  spectral  colours  are  used,  where 
the  luminosity  of  the  light  can  be  varied  to  approximate  the  various 
conditions  met  with  on  land  and  sea,  and  the  subject  names  the 
colours  which  he  sees.  Such  are  the  lantern  and  the  spectrum 
apparatus  shown  in  Figs.  35G.  357. 

By  such  means  the  three  groups  of  cases  mentioned  above  are 
detected  with  the  greatest  ease,  while  those  may  be  discrmimated 
who  would  be  rejected  by  the  wool  test,  and  yet  make  useful  servants. 
In  testing  for  colour  vision,  it  must  be  borne  in  mind  that  considerable 
colour  ignorance  exists  among  the  uneducated,  especially  in  regard 
to  shades. 


630  A  TEXTBOOK  OF  PHYSIOLOGY 

Section  V 
BINOCULAR  VISION     VISUAL  JUDGMENT 

The  format  ion  of  visual  judgments  depends  largely  upon  the. 
eyes  acting  together,  the  increased  visual  field  and  the  combinations 
of  eye  movements  greatly  aiding  in  the  formation  of  such  judgments. 

Ocular  Movements. — The  ocular  movements  depend  upon  the 
action  of  six  muscles.  Of  these,  four  arise  from  the  back  of  the 
eyeball,  and  are  termed  the  superior,  inferior,  internal,  and  external 
rectus,  according  to  the  site  of  their  insertion  into  the  side  of 
the  eyeball.  Contraction  of  the  internal  ^muscle  turns  the  eye 
directly  inwards,  of  the  external  muscle  directly  outAvards.  The 
superior  and  inferior  muscles  pass  somewhat  obliquely  to  their 
insertion.  On  this  account,  during  thair  action  they  pull  the  eyeball 
somewhat  inwards  as  well  as  upwards  in  the  case  of  the  superior, 
and  downwards  in  the  case  of  the  inferior  muscle.  This  inwaixl 
deviation  is  corrected  by  the  action  of  two  oblique  muscles.  The 
superior  oblique  passes  along  the  inner  wall  of  the  orbit,  and,  after 
passing  through  a  fibrous  ring,  j^asses  pulley-fashion  backwards  and 
outAvards,  to  be  inserted  into  the  upper  surface  of  the  eyeball.  Acting 
alone,  this  muscle  rotates  the  eyeball  downwards  and  outwards.  The 
inferior  oblique  takes  origin  from  the  front  part  of  the  inner  Avail  of 
the  orbit,  and  passes  beneath  the  eyeball  backAvards  and  outAvards, 
to  be  inserted  into  its  outer  part.  By  its  action,  the  eyeball  is  turned 
upwards  and  outwards.  For  direct  upward  moA'ement,  the. superior 
rectus  and  inferior  oblique  act  together;  for  direct  downward  move 
ment,  the  inferior  rectus  and  superior  oblique.  For  oblique  mov^e- 
ments,  tAvo  recti  and  one  oblique  act  together,  according  to  the  direction 
of  the  movement.  Thus,  in  looking  obliquely  doAAiiAvards  and  out- 
wards, the  external  and  inferior  recti  and  the  superior  oblique  are 
employed.  \Vlien  two  eyes  are  used,  the  same  muscles  are  employed 
in  both  eyes  for  upward  and  dowuAvard  moA^ements;  but  for  looking 
sideways,  the  outer  rectus  of  one  orbit  acts  in  conjunction  Avith  the 
inner  set  of  the  other.  When  converging  the  eyes  upon  a  near 
object,  or  when  intentionally  turning  both  eyes  inwards,  the  inner 
muscles  act  together. 

All  eye  movements  are  normally  so  directed  that  the  image  of  the 
object  looked  at  falls  upon  the  yelloAV  spot  of  both  eyes;  indeed,  it 
is  impossible  voluntarily  to  turn  the  eyes  so  that  this  is  not  the  case. 
It  is  not  possible  to  turn  one  eye  up  and  the  other  doAvn,  or  both  eyes 
outwards.  It  is  stated  that  the  "  seeing  double  "  of  intoxication  is 
due  to  the  fact  that,  under  this  condition,  the  muscles  of  the  eyeballs 
are  relaxed,  the  eyeballs  diA^erge  slightly.  If  we  intentionall}-  diA^erge 
the  eyeballs,  as  by  pressing  on  the  outer  side  of  one,  objects  are  seen 
double.  By  shutting  one  eye,  it  Avill  be  found  that  the  left  image 
belongs  to  the  right  eye,  and  the  right  image  to  the  left  eye.  In  death 
the  eyeballs  diverge  slightly.     Such  a  divergence  may  be  due  to  the 


THE  SENSE  OF  VISION  6;U 

fact  that  in  the  passive  position  the  eyeballs  coincide  with  the  axes 
of  the  eye-sockets,  which  are  somewhat  divergent. 

Normally,  double  vision,  or  diplopia,  is  prevented  by  the  balanced 
action  of  the  ocular  muscles  ;  when  these  muscles  are  relaxed,  excej)! 
for  their  normal  tone,  the  visual  axes  of  the  two  eyes  are  parallel. 
It  sometimes  happens  that  the  balance  is  not  perfect,  and  that 
a  constant  action  of  one  or  more  muscles  is  necessary  to  keep 
the  visual  axes  parallel  for  distant  vision — a  condition  known  as 
heterophoria.     If  in  the  relaxed  condition  of  the  eye  muscles  the  eye 


Fig.  358. — To  illustrate  the  Horopter. 

A  is  the  point  of  regard;  its  retiaal  images  are  formed  on  the  yellow  .spots  at  a,  a', 
b,  b'  are  corresponding  points  of  the  two  retinse,  therefore  the  distance  a  Z(  — the 
distance  a'  b' .  n,  n'  are  the  nodal  points  of  the  two  e3'es.  The  angles  a  n  b, 
n  n'  b',  are  equal  to  each  other  and  to  the  opposite  angles,  A  n  B,  A  n'  B  ;  and  in 
the  triangles  B  G  n,  A  C  n',  the  opposite  angles  at  C  are  equal;  therefore,  in 
these  triangles  the  remaining  angles  at  A  and  B  are  equal.  Therefore  the  point 
B  by  which  the  corresponding  images  b,  b'  are  formed  must  lie  in  the  arc  of  a 
circle  passing  through  the  points  B.  n,  and  n' .  Similarly,  it  may  be  shown  that 
any  other  point  forming  corresponding  images  on  the  two  retina  will  lie  in  the 
circular  arc  n  A  n' . 

iurns  outwards,  the  condition  is  known  as  exophoria;  if  inwards, 
esophoria;  if  upwards  or  downwards,  hyperphoria.  Such  a  condition 
throws  a  strain  upon  the  eye  muscles,  and  entails  considerable  ocular 
distress.  The  trouble  is  corrected  by  the  prescription  of  prisms, 
or  by  operation.  When  the  defect  is  so  marked  that  it  cannot  be 
corrected  by  muscular  action,  we  have  the  condition  of  strabismus, 
«r  squint.  This  results  either  from  the  overact  ion  of  one  or  more 
■of  the  muscles,  or  from  a  deficient  action  or  paralysis  of  one  or  more 
muscles.     In  the  former  case,  it  may  be  cured  by  surgical  operation. 


€32  A  TEXTBOOK  OF  PHYSIOLOGY 

Normally,  when  we  look  at  a  (listant  object,  the  eyes  are  parallel, 
so  that  the  image  falls  upon  the  same  point  in  both  eyeballs — the 
yellow  spot.  When  looking  at  a  close  object,  owing  to  the  position 
of  the  yellow  spot,  the  eyeballs  converge  slightly,  so  that  the  image 
still  falls  on  this  point  of  distinct  vision  in  both  eyeballs.  Thus,  a 
sensation  of  oneness  is  obtahied,  due  to  the  fact  that  the  same  point 
is  regarded  by  the  yelloAv  sjiots  of  both  eyes  at  the  same  time,  and  the 
attention  is  directed  to  the  object  looked  at,  and  not  to  other  objects 
also  in  the  field  of  vision.  That  this  is  the  case  may  be  proved  by 
holding  vertically  at  different  distances  from,  and  in  the  middle  line 
of,  the  body  two  small  rods  or  pencils.  When  we  concentrate 
attention  on  one,  the  other  becomes  blurred  or  double.  This  is  owing 
to  the  fact  that,  Avhen  the  eyes  are  directed  so  that  the  rays  from  one 
fall  on  the  yello-w  s])ots  of  the  retinje,  the  rays  from  the  other  fall  on 
different  parts  of  the  retinae  which  do  not  habitually  work  together 
(c/.  Fig.  346).  Thus,  when  the  near  object  appears  as  one,  the 
rays  from  the  farther  one  fall  on  the  inner  side  of  each  yellow- 
spot  and  the  result  is  two  images  are  seen.  These  appear  the  same 
distance  away  as  the  near  object,  and  when  one  eye  is  closed,  the  image 
on  the  same  side  disappears,  and  is  called  homonomous.  When  the 
distant  object  is  seen  singty,  the  raj's  from  the  nearer  object 
fall  on  the  outer  side  of  each  yelloM^  spot.  The  result  is  that 
two  objects  are  seen,  but  in  this  case,  when  one  eye  is  closed, 
the  image  of  the  opposite  side  disappears,  and  is  knowTi  as  heter- 
onomous. 

It  requires  special  attention  to  see  such  double  images,  and 
as  a  rule  we  are  not  conscious  of  them,  since  attention  is  paid 
only  to  the  object  looked  at,  and  we  do  not  at  the  same  time  try  to 
view  carefully  objects  at  two  markedly  different  distances  from  the 
eyes.  If  such  images  are  formed,  they  are  cerebrally  suppressed, 
and  not  seen.  This  is  particularly  the  case  in  persons  suffering 
from  squint.  Generally  speaking,  right-handed  j^eople  appreciate 
the  right  image  and  suppress  the  left.  The  tendency  to  do  this  is 
illustrated  bj-  asking  a  person  having  both  eyes  oj)en  to  point  carefully 
in  the  middle  line  of  the  body  at  a  distant  object,  either  hand  being 
used.  On  closing  first  one  eye  and  then  the  other,  it  is  found  that, 
viewed  with  one  eye  the  finger  is  still  pointing  correctly,  while  with 
the  other  eye  the  image  of  the  finger  has  moved  to  one  side,  and  the 
finger  is  not  jiointing  at  the  object. 

Each  person  has  a  certain  visual  field.  This  dej^ends  to  a  certain 
extent  upon  the  setting  of  the  eyes,  whether  deep  or  jorotruding, 
and  also  for  each  eye  upon  the  shape  of  the  brow,  bridge  of  nose,  and 
cheek-bones.  A  certain  part  of  the  field  of  vision  is  common  to  both 
eyes.  On  closing  the  eyes  alternately,  it  is  seen  that  part  of  the 
visual  field  is  common  to  both  eyes,  but  that  the  brows  and  nose  cut 
off  part  of  the  field  visible  to  the  other  eye.  There  is  therefore 
marked  advantage  in  a  binocular  visual  field.  From  every  point  in 
this  field  the  rays  of  light  in  a  fixed  position  of  the  eyes  fall  upon 
corresponding  points  of  the  two  retinae.     Each  point  in  the  field  ha» 


THK  SENSE  OF  VISIOX  633 

a  corresponding  point  in  each  retina,  so  that  the  j^eliow  spots  cor- 
respond, and  also  the  mner  and  outer,  upper  and  lower,  parts  of  each 
retina.  For  this  reason,  the  projections  of  the  objects  by  the  cerebral 
apparatus  upon  the  visual  field  correspond  in  position,  and  are  seen 
single.  This  is  facilitated  by  the  fact  that  the  fibres  from  the  retinae 
have  a  special  arrangement,  and  connect  with  definite  brain  areas 
(see  p.  712). 

A  line  jouiing  all  the  jjoints  which  appear  single  in  the  field  of 
vision  isknown  as  the  horopter.  It  assumes  various  forms  for  different 
positions  of  the  eyes.  When  the  visual  lines  are  parallel,  as  in  the 
case  of  very  distant  objects,  the  horopter  is  a  plane  at  infinite  distance 
coinciding  with  the  ground.  When  a  near  object  is  being  looked  at, 
and  the  visual  lines  converge — as,  for  example,  in  looking  at 
points  A  and  B  (Fig.  358) — then  the  horopter  takes  the  form  of 
a  circle. 

Visual  Judgments— The  Perception  of  Distance,  Size,  and  Solidity. — 
'"  Judgments  "  are  performed  in  the  brain,  and  are  in  some  ways 
more  correctly  dealt  with  when  considering  the  cerebral  functions. 
Of  all  judgments,  the  visual  are  perhaps  the  most  easy  of  analysis. 
If  we  were  born  blind,  and  suddenly  acquired  the  power  of  vision, 
we  should  not  immediately  recognize  everything.  In  our  first  applica- 
tion of  the  sense  of  sight,  we  make  great  use  of  touch  to  ascertain 
the  detailed  outlme  of  objects.  By  this  means  we  arrive  at  a  correct 
understanding  of  these  objects,  and  remember  them  later.  This  is 
well  illustrated  by  cases  of  congenital  blindness  in  which  vision  has 
been  restored  by  operation  after  as  long  as  twenty-eight  years.  In 
one  such  case,  aged  eighteen,  when  the  bandage  was  first  removed 
after  the  operation,  the  patient,  in  reply  to  the  question  as  to  whether 
the  surgeon  had  a  beard,  asked  to  be  allowed  to  feel  it,  and  only  on 
touching  it  replied  unhesitatmgly,  "  Yes."  On  bemg  sho\\Ti  a  chair, 
lie  said  he  saw  it,  but  could  not  tell  what  it  was  without  touching  it. 
He  made  many  wild  guesses  as  to  what  an  apple  was,  but  on  touching 
it  said  immediately:  ''  Just  fancy,  an  apple  I" 

Recognition  of  colours  is  soon  learnt.  The  appreciation  of  space, 
size,  and  distance,  comes  but  slowly.  Such  patients  at  first  walk 
warily,  with  hands  extended,  like  a  blmd  man.  One  patient  of  twenty- 
eight  years,  in  taking  his  walks  by  moonlight,  kept  jumping  every 
now  and  again  over  ol:)jects  lying  in  his  path.  These  were  shadows 
which  he  was  doing  his  best  to  avoid,  and  he  would  not  believe  that 
there  were  no  obstacles  in  his  way  until  he  had  satisfied  himself  by 
touch  that  the  ground  was  in  reality  quite  flat. 

A  patient  of  eight  years,  when  taken  on  a  moonhght  night  to 
the  veranda  illuminated  by  three  low-hanging  arc  lamps,  thought 
the  veranda  was  covered  Avith  snow,  and  thought  the  moon  to  be  an 
arc  lamp  quite  near  him. 

Such  cases  also  show  the  interesting  fact  that  objects  are  seen 
at  once  in  their  proper  position,  and  not  upside  down.  The  first  two 
])atients  mentioned  were  each  taught  the  colour  of  two  strips  of  paper 
— red  and  green.     They  were  then  placed  one  above  the  other,  and 


634 


A  TEXTBOOK  OF  PHYSIOLOGY 


a  quick  muI  correct  answer  was  inimediately  given  to  the  question 
as  to  which  colour  Avas  uppermost. 

A  white  object  seen  on  a  dark  background  aj^pears  larger  than  a 
black  object  of  equal  size  on  a  Avhite  background.     This  is  known  as 

irradiation  (Fig.  359).  When  a  white 
striji  is  placed  between  two  black 
strips,  the  edges  of  the  white  strip  near 
the  black  appear  whiter  than  the 
middle  portion ;  the  centre  of  a  white 
cross  placed  on  a  black  background 
appears  shaded.  A  ^hite  dog  may 
appear  clean  indoors,  but  very  dirty 
when  out  on  newly  fallen  snow.  The 
phenomenon  is  known  as  simultaneous 
contrast.  This  contrast  is  also  expe- 
rienced with  colours.  A  neutral  grey 
,  strip  surrounded    by  green    seems  to 

acquire  a  pinkish  hue,  the  tint  of  the  complementary  colour  to  green 
(red).  If  surrounded  by  blue  the  acquired  hue  of  the  neutral  grey 
object  is  yellow.  If  a  grey  strip  surrounded  hy  green  be  viewed 
intently  for  some  time  and  the  gaze  then  transferred  to  a  sheet  of 
white  paper  of  other  white  surface,  the  after-image  of  the  strip  will 
then  appear  greenish  surrounded  by  red.  This  is  laiown  as  successive 
contrast.  Various  speculations  are  put  forward  to  account  for  the 
phenomena.  According  to  the  Helmholtz  view  of  colour-vision  such 
contrast  effects  are  cerebral  in  origin,  and  in  reality  are  errors  of 


Fig.  359. — To  demonstkate 
Irradiation. 

The  white  spaces  appear  larger  than 
the  black.  They  are  the  same 
size. 


\ 

/ 

/ 

\ 

/ 

/ 

\ 

/^ 

\ 

/ 

\ 

B.  L.  R. 

Fig.  360.— Right-  and  Left-Eyed  Images  of  Truncated  Pyramid. 

B,  Truncated  cone;  L,  B,  right-  and  left-handed  images.     By  fixing  the  vision  beyond 
the  book,  L  and  Ji  may  be  made  to  combine  and  give  B. 


judgment.     According  to  the  Hering  view  they  are  retinal  in  origin 
due  to  modified  metabolic  effects  of  the  visual  substances. 

If  a  solid  object  be  viewed  fixedty  by  either  eye  separately,  and 
then  b}^  both  ej-es,  it  is  easily  appreciated  that  separatelj^  the  eyes  view 
the  object  from  a  different  standpoint.  Together  they  view  the 
object  from  the  combined  standpoint,  and  we  have  in  addition  an 
increased  sensation  of  solidity  and  perspective.  This  is  well  seen  by 
looking  vertically  downwards  at  the  truncated  pyramid.  With  both 
eyes  it  has  the  appearance  of  B,  with  the  left  only  it  is  seen  as  L,  and 
with  the  right  eye  only  as  R  'Fig.  360). 


THE  SENSE  OF  VISIOX 


635 


The  effect  of  combining  the  pictures  of  tiie  left  ainl  right  eye  is 
well  seen  in  the  stereoscope.  In  the  more  commonly  used  form,  the 
Brewster  stereoscope,  the  corresponding  picture  for  each  eye  is  viewed 
through  a  curved  prism,  so  placed  with  its  base  outwards  that  the 
rays  from  the  pictures  impinge  on  the  retina 
in  lines  of  convergence  which  meet  at  points 
behind  the  plane  of  the  pictures  (see  Fig.  331). 
A  partition  cuts  off  the  sight  of  the  opposite 
picture,  so  that  each  eye  sees  only  its  own 
picture,  usualh'  slightly  magnified  bj'  the  prism. 
OAying  to  differing  distances  between  the  corre- 
sponding points  in  the  two  indi^'idual  pictures, 
the  effect  of  apparently  differing  distances  is 
obtamed  in  the  combined  picture.  The  nearest 
pomts — that  is,  those  which  require  the  greatest 
convergence  of  the  ojDtic  axes — stand  out  in 
most  marked  relief,  the  most  distant  points, 
which  require  less  convergence,  in  least  relief. 
It  is  not  necessary  to  have  a  stereoscope  to  get 
this  combined  effect.  With  ]3ractice,  it  is 
accomplished  by  merely-  fixing  the  eyes  on  the 
pictures,  and  adjusting  the  eyes  for  distant 
vision.    The  two  pictures  then  gradually  merge 

together,   and   the  whole   effect  of   solidity   is    suddenly   perceived. 
This  is  known  as  haploscopic  vision  (Fig.  362). 

Stereoscopic  pictures  are  obtained  by  drawing  or  photographing 
the  same  scene  from  slightly  different  points  of  view.  The  perception 
of  solidity  is  due  in  the  main   to  a  mental   process  fusing  slightly 


A  c  B 

Fig.  361. — Diagram  of 
A  Stereoscope. 

Two  pbotoffraphs,  A 
and  B,  are  seen  at  C. 
The  rays  of  light  from 
A  and  B  are  refracted 
by  the  prisms  into  the 
eyes  so  that  they 
appear  to  coine 
from  n. 


Fig.  362. — -To  xllttstrate  Haploscdpic  Vision. 

The  distance  between  the  fish  and  tank  is  here  given  as  rather  less  than  the  distance 
between  the  two  pupils,  so  that  the  haploscopic  combination  can  b3  effected 
easily,  with  the  visual  axes  somewhat  convergent.  The  illusion  is  facilitated  by 
holding  a  card  vertically  between  the  eyes,  so  as  to  hide  th-^  fish  from  th?  left 
eye  and  th^  tank  from  the  right  eye. 

different  images  from  the  two  retinse,  the  amount  of  activity  of  the 
eye  muscles  in  converging  the  optic  axes  being  also  an  important 
iactor. 

Judgment   of   size  and   distance   also   depends   largely    upon  the 
degree  of  muscular  effort  put  forth  in  the  convergence  of  the  eyes 


636 


A  TEXTBOOK  OF  PHYSIOLOGY 


and  in  the  mechanism  of  accommodation.  Objects  at  the  near  point 
are  seen  clearly,  and  are  judged  to  bo  near;  those  farther  off  less  and 
less  distinctly,  and  are  judged  to  be  correspondingly  distant. 

Judgment  of  size  is  the  resultant  of  two  factors — ^the  actual  size 
of  the  retinal  image  of  the  object,  and  the  known  or  apparent  distance 
from  the  eye.  Similarly,  we  estimate  distance  by  the  size  of  the 
retmal  image,  and  the  known  or  presumed  size  of  the  object.  An 
object  seen  through  field-glasses  appears  near  at  hand,  but  seen 
tlirough  the  wrong  end  appears  far  away.  The  after-image  of  an 
object  appears  large  or  small,  according  as  the  surface  on  which  it  is 
seen  is  near  or  far  awaj'. 

The  relative  transparency  of  the  air  also  plays  a  part  in  such 
judgments.  A  hazy  atmosphere  turns  a  small  hill  into  a  large 
mountain,  a  very  clear  atmosphere  makes  objects  appear  much 
nearer  than  usual.  In  addition  to  the  size  of  famihar  objects, 
judgment  is  also  aided  by  the  disposition  of  lights  and  shades,  accord- 
ing to  the  position  of  the  objects  in  relation  to  each  other. 


Fig.  303. 


xy^:%%%%%%%^/ 


Fig.  36-1. — Zollner'.s  Lixes. 
The  horizontal  line?  are  parallel. 


Fig.  3(io. 


Mathematical  perspective  also  plays  a  part.  Parallel  lines,  like 
those  of  a  railwaj'-track,  converge  more  and  more  in  jjroportion  ta 
the  distance  away.  We  learn  accurately  to  appreciate  this  per- 
spective, but  many  optical  illusions  are  associated  with  uncommon 
combinations  of  lines.  One  of  the  best  known  is  that  shown  in 
Fig.  363.  The  lines  of  aa,  hb,  are  of  equal  length.  In  Fig.  364,  the 
horizontal  lines  are  parallel. 

To  sum  up,  the  visual  judgment  depend.s  upon  both  monocular 
and  binocular  elements.  The  chief  monocular  elements  are  muscle^ 
sense,  aerial  perspective,  mathematical  perspective,  the  size  of  familiar 
objects,  "and  the  disposition  of  lights  and  shades.  Superimposed  on 
this  is  the' binocular  element,  dite  to  the  fact  that  external  objects, 
particularlj?  those  close  at  hand,  are  not  seen  exactly  the  same 
in  •Both""  eyes.  *  This'  adds  '  greatly  to  'our  judgment  of  •  depth 
and  solidity.'  Visual  judgments  are  made  iiithe  brain.  We  have 
no  exact  knowledge  of  the  seat  of  such  inferences.  The  judg- 
ment may  "  be  influenced  quite  independent  of  any  outside  cause. 
Thus,  in  Fig.  365,  the  vessel  may  be  imagined  to  be  with  its  open 


THE  SENSE  OF  VISION  637 

end  either  towards  or  from  the  observer;  especially  if  one  eye 
be  closed  an  actual  vessel  can  equally  be  "  seen "  in  either  posi- 
tion. 

Apparatus  used  in  Clinical  Investigation  of  the  Eye. 

For  acuity  of  vision,  Snellen's  test-types  are  generally  used  (Fig.  366 ) . 
The  size  of  the  letters  is  so  arranged  that  a  person  with  average  acuity 
is  able  to  read  the  top  letter  at  a  distance  of  60  metres,  the  second 


T  B 

D  L  N 

P  T  E  R 

1 

F  Z  B  D  E 


O  E   L   Z   T   G 


L  p  o  R  r  I]  z 

F'^iG.  366.— Snellen's  Test-Types  keduced  in  Size. 

line  at  36  metres,  the  third  at  24  metres,  the  fourth  at  18  metres, 
the  smallest  at  6  metres.     In  testing  the  acuity,  the  subject  stands 


():}8 


A  TEXTIJOOK  OF  PHYSIOLOGY 


about  6  metres  away,  and  cndoaxours  to  read  the  types.  Defective 
vision  is  usually  recorded  by  stating  the  distance  from  the  tyj^e  as 
numerator,  and  the  distance  at  which  the  last  line  read  by  the  subject 
should  normally   be  read   as  the  denominator.     Normal  vision   (V) 


Fiu.  367. — The  pEKiiiETEH. 


is  4 — ^that  if*,  the  6-metre  type  can  be  read  at  6  metres.  V=/^ 
signifies  that  at  6  metres'  distance  the  subjeot  only  succeeded  in 
reading  type  which  should  normally  be  read  at  36  metres. 

It  is  customary  to  employ  an  instrument  called  a  perimeter  to 
obtain  accurate  details  of  the  extent  of  the  field  of  vision.     The 


THE  SENSE  OF  VISIOX 


639 


periincrcr  (see  Fig.  367)  consists  of  a  quadrant  upon  which  a  white 
spot  can  be  moved,  and  this  quadrant  can  be  revolved  about  a  line 
continuous  with  the  optic  axis.  At  K  is  the  chin-rest,  double,  so  as 
to  enal)le  either  eye  to  be  adjusted  against  0.  The  subject,  having 
taken  his  position,  covers  one  ej^e,  and  fixes  the  eye  that  is  to  be 
examined  on  the  mark  at  /.  The  quadrant  is  then  placed,  say,  in 
the  vertical  meridian,  and  at  the  back  of  the  wheel  which  revolves 
with  the  quadrant  is  inserted  in  the  frame  a  special  chart  adapted  for 
recording  perimetric  observations.  Starting  at  the  extreme  distance, 
the  mark  Ob  is  gradually  moved  along  the  quadrant,  and  at  a  certain 
angle  the  white  spot  will  be  just  visible.  The  angle  indicates  the  limit 
of  vision  in  this  meridian,  and  can  be  recorded  on  the  chart.  Similar 
observations  are  made  in  other  meridia.     In  this  mannei-  tiie  limits 


16C         ^lii.M ^  160 

170    180   i?0    . 

Fig.  308. — Perimetric  Ch-art  of  the  Right  Evf. 

The  thick  Line  surround?  the  area  within  which  ichite  is  visible,  tho  point  C  being 
fixed  by  the  eye  (right);  the  fine  dotted  line  surrounds  the  area  within  which 
green  is  visible.  The  area  of  red  would  be  somewhat  larger,  that  of  blue  larger 
stiU,  though  not  so  large  as  that  of  white.     7?  =  the  situation  of  the  blind  spot. 


of  vision  in  the  different  meridia  of  the  field  of  vision  can  be  recorded. 
It  is  essential  that  the  subject  keep  his  e3''e  fixed  on  /  the  whole  time 
the  .spot  is  being  moved  (Fig.  368). 

The  area  bounded  by  a  line  drawn  through  the  limiting  points  in 
the  different  meridia  is  properly  the  area  of  the  field  of  vision.  If  the 
meridia  be  inverted,  the  figure  traced  corresponds  to  the  sensitive 
portion  of  the  retina.  Perimeters  are  generalh'  so  constructed  that 
the  limiting  marks  in  the  different  meridia  are  inverted  on  the  chart, 
so  that  the  latter  becomes  a  chart  of  the  extent  of  the  sensitiveness 
of  the  retina.     This  is  indicated  in  the  figure  above. 

The  Ophthalmoscope. — The  ophthalmoscope  (Fig.  369)  is  an  ap- 
paratus to  enable  an  observer  to  direct  his  vision  along  the  axis  of 
the  pencil  of  light  illuminating  the  subject's  eye,  thereby  enabling 


{540 


A  TEXTBOOK  OF  PHY810L0GY 


him  to  receive  light  reflected  from  the  retina  of  the  subject,  and  thus 
actually  to  see  the  illuminated  retina.     The  instrument  consists  of 


Fig.  309. — Ophthalwoscopes. 


a  mirror  withja  central  aperture  so  arranged  as  to  reflect  light  from 
some  source  through  the  pupil  into  the  interior  of  the  eye.     The 


Fig.  370. — Examination  of  the  Eye  of  a  Frog  by  Meaxs  of  Oi'HTHALMoscoric 
Mirror  (Direct  Method). 


observer,  looking  through  the  central  aperture,  is  able  to  view  the 
illuminated  posterior  wall  of  the  eye. 


THE  SENSE  OF  VISION 


♦341 


Two  methods  are  usually  adopted  of  using  the  ophthalmoscope, 
one  being  known  as  the  direct,  the  other  as  the  indirect.  In  the  first 
case,  there  is  obtamed  an  erect  view  of  a  small  area  of  the  retma, 
magnified  about  thirteen  times;  in  the  second  case,  a  less  magnified 
iind  inverted  view  is  obtained  of  a  larger  area  of  the  retina. 


Fig.  371.— Examination  of  the  Eye  or  a  Rabbit  after  Atropine  bv  the 

Indikect  Method. 

In  the  direct  method,  the  source  of  light  is  placed  at  the  side  of 
the  head  of  the  subject,  so  that  no  light  falls  directly  on  the  cornea. 
The  mirror,  which  is  somewhat  strongly  concave,  is  held  a  few  mches 
from  the  subject's  eye,  and  is  so  tilted  that  light  is  directed  into  the 
pupil.  The  observer  uses  his  left  eye  to  examine  the  subjecfs  left 
eye,  and  similarh-  his  right  eye  for  the  subject's  right  eye. 


Fig.  372. — To  SH.tw  the  Course  of  the  Rays  of  Light  from  the  Lamp  to  the 
Observer's  Ey'e  by  the  Indirect  Method. 

a,  Lamp;  b,  the  fold  of  lens;  c,  lens;  d,  mirror  of  ophthahrioscope. 


In  the  indirect  method,  a  somewhat  larger  but  less  concave  or 
a  plane  mirror  is  used.  The  mirror  is  held  at  a  distance  of  about 
18  inches,  and  if  the  accommodating  power  of  the  subject  is  intact 

41 


(;42  A  Ti*:x'rHn()K  of  phv.siolouy 

his  eye  will  accommodate  for  the  source  of  light  or  its  imago  formed 
by  the  mirror.  An  inverted  image  of  the  illuminated  area  of  the 
retina  will  be  formed  at  a  certain  distance  behind  the  mirror.  The 
rays  issuing  from  the  eye  are  intercepted  by  a  rather  strong  convex 
lens  held  close  to  the  cornea,  so  that  the  observer,  looking  through 
the  aperture  of  the  mirror,  obtains  a  clear  view  of  a  considerable 
portion  of  the  illuminated  retina. 

Ophthalmosco]ies  are  generally  supplied  with  a  revolving  disc  of 
lenses  of  different  strengths.  These  are  used  to  correct  any  error  of 
refraction  in  the  subject's  or  observer's  eyes. 

It  is  frequently  a  matter  of  difficulty  to  obtain  a  clear  view 
of  the  back  of  the  eye,  or  fundus,  unless  atropine  has  been 
applied  previously'  which  causes  dilation  of  the  pupil.  For  practice  in 
the  use  of  the  ojihthalmoscope,  the  eye  of  an  albino  rabbit  which  has 
been  treated  with  atropine  can  be  advantageously  substituted  for  the 
human  subject. 


CHAPTER  LXX 
HEARING 

The  Receptor  Mechanism. — -The  receptor  mechanism  for  hearing 
in  mammals  consists  of  a  specialized  nerve-epithelium,  contained 
deep  in  the  skull  within  the  cochlea  of  the  internal  ear,  in  what 
is  kno-svn  as  the  organ  of  Corti.  To  this  the  \'ibrations  of  the 
air  are  conducted  by  means  of  the  elaborate  accessory  apparatus  of 
the  external,  middle,  and  internal  ears.  The  fully  developed  spiral 
cochlea  exists  only  in  mammals.  In  birds  its  homologue,  the  lagena, 
is  a  simple,  slightly  curved  tube;  in  reptiles  it  is  rudimentary,  and  in 
amphibians  and  fishes  does  not  exist. 

For  a  long  time  it  was  thought  that  the  whole  of  the  apparatus 
of  tke  ear  was  connected  with  the  sensation  of  hearing.  This  is  now 
known  not  to  be  the  case,  part  of  the  internal  apparatus  being  con- 
nected with  the  sense  of  position  and  equilibration.  The  rudimentary 
forms  of  ears  described  in  lower  forms,  both  vertebrate  and  invertebrate, 
are  connected  with  this  mechanism  rather  than  with  hearing  (see 
p.  654).  It  is  improbable  that  molluscs,  fishes,  etc.,  have  any  sensation 
of  hearing,  although  the  notion  that  they  have  is  one  which  dies  hard. 
Recent  experiments  have  shown  that  snails  are  supremely  indifferent 
to  sounds  of  any  description,  but  are  exceedingly  sensitive  to  touch. 
The  so-called  hearing  of  fishes  is  probably  due  to  tactile  response 
to  the  vibrations  of  the  water  surrounding  them,  rather  than  to 
hearing.  The  fish  in  a  pond  which  came  to  ])e  fed  when  a  bell  was 
rung  did  not  hear  the  bell,  but  felt  the  vibrations  of  the  water  pro- 
duced by  the  approaching  of  the  steps  of  the  bell-ringer.  The  power 
of  hearing  in  amphibians  and  in  reptiles  is  also  very  doubtful,  and 
has  been  assumed  rather  than  proved.  It  is  more  than  probable 
that  siich  apparent  hearing  is  in  reality  due  to  the  vibrations  of 
the  ground  on  which  they  lie,  or,  as  in  the  case  of  fish,  of  the 
surrounding  water. 

The  hearing  poAvers  of  birds  and  mammals  are  undisputed.  From 
the  point  of  view  of  comparative  anatomy,  it  is  interesting  that  the 
bird,  with  its  lovely  range  of  sound  production,  and  therefore  probable 
wide  range  of  hearing,  has  only  the  simple,  slightty  curved  lagena; 
whereas  the  animal  with  the  most  complex  cochlea,  a  shy  rodent  of 
South  America,  .has  a  very  limited  range  of  sound  production  with 
which  to  charm  the  five  whorls  of  the  cochlea  of  his  fellow-kinsmen. 
There  is  therefore  reason  to  suppose  that  the  complexity  of  the 
cochlea  has   to   do  with  sensitivity  rather   than  with   the  range  of 

643 


644 


A  TEXTBOOK  OF  PHY.SK  >LO(  JY 


hearing  powers.      In  cetacea  there  are  1|,  in   man  2-|,   and   in  the 
rodent  Coclogcnys  paca  5  whorls  to  the  cochlea. 

The  External  Ear. — Tn  mammals  this  varies  greatly  in  form,  from 
the  rigid,  almost  immovable  structure  of  man  to  the  easily  movable 
organ  of  most  mammals,  which  in  some  ma^-  be  rigid,  in  others  flapping. 
The  external  ear  consists  essentially  of  two  ])arts — the  auricle,  which 
acts  as  a  sound-catcher  and  reflector;  and  the  external  meatus,  by 
which  the  sound-waves  are  conducted  down  to  the  drum-hccid,  or 
tympanic  membrane.  The  external  ear  is  also  protective  in  function. 
The  bitter  waxy  secretion,  or  cerumen,  and  the  outward  pointing  hairs, 
■deter  insects  from  entering,  while  the  varying  curvature  makes  it 
difficult  for  foreign  bodies  directly  to  im])inge  upon  the  tympanic 
membrane. 

The  tympanic  membrane  separates  the  external  from  the  middle 
ear.     It  is  firmly  fixed  in  a  l)ony  groove,  and  lies  obliquely  to  the 

lumen  of  the  meatus,  the  lower 
margin  being  farther  in  than  the 
upper.  The  membrane  consists 
mainly  of  connective  tissue,  to- 
gether with  a  little  elastic  tissue. 
Some  of  the  fibres  radiate  to  the 
circumference  from  the  umbo,  a 
point  just  below  the  centre  of  the 
membrane,  the  others  being 
arranged  circularly  about  the 
same  point.  Into  the  membrane 
the  first  of  the  three  bones  of  the 
middle  ear  is  inserted  in  such  a 
way  as  to  render  the  membrane 
conical  in  shape,  with  the  con- 
vexity towards  the  meatus.  The 
membrane  thus  curves  slightly 
outwards,  and  is  not  uniformly 
stretched  in  all  dimensions.  The 
value  of  this  arrangement  is  that 
very  slight  changes  of  air-pressure 
produce  relatively  large  move- 
ments of  the  membrane,  and 
It  also  enables  the  membrane 
to  vibrate  to  a  great  range  of  tones. 

The  condition  of  the  membrane  is  examined  by  the  use  of  a  specu- 
lum and  the  reflected  light  from  a  mirror  with  a  central  hole,  attached 
to  the  forehead  of  the  observer  (Fig.  374). 

Across  the  middle  ear  stretches  a  chain  of  three  small  bones,  or 
ossicles — the  malleus,  or  hammer;  the  incus,  or  anvil;  and  the  stapes, 
or  stirrup.  The  stapes  is  inserted  by  ligamentous  tissue  into  the 
fenestra  ovalis. 

The  function  of  the  ossicles  is  to  interpose  a  solid  element  which 


—  Diagram  uf  J^ak,  biiuwixci 
Ossicles. 

A,  Malleus;  B,  incus;  C,  stapes;  D,  ex- 
ternal auditory  meatus;  E,  tympanic 
membrane;  F,  foramen  rotiinchnn;  H, 
Eustachian  tube ;  K,  utricle ;  L,  saccule ; 
M,  semicircular  canals;  N,  cochlea. 
The  shaded  part  of  internal  ear,  the 
bony  labyrinth,  is  full  of  perilymph; 
the  white  part,  the  membranous  laby- 
rinth, is  full  of  endolymph. 

therefore   relatively   great   effects, 


HEARING 


645 


conducts  the  vibrations  of  the  tympanic  membrane  to  the  fluid  of 
the  internal  ear,  which  in  its  turn  excites  the  receptor  mechanism.  In 
the  frog  we  find  onl}^  a  single  cartilaginous  rod — the  columella.  A 
chain  of  bones,  however,  has  considerable  me- 
chanical advantages.  The  handle  of  the  hammer 
is  inserted  into  the  tympanic  membrane,  and 
leads  upwards  to  the  head,  which  is  placed  above 
the  level  of  the  tympanic  membrane,  and  is  fixed 
in  position  by  ligaments  which  pass  to  a  fissure  in 
the  bone,  one  from  a  delicate  forward  pointmg 
process — the  processus  gracilis — another  from  the 
head  of  the  malleus  to  the  roof.  This  is  one  of 
the  fixed  points  about  which  the  bones  rotate. 
The  anvil  is  in  such  a  position  that  its  conical 
process  points  downwards.  This  process  ends  by 
bending  imvards  to  a  flattened  knob  —  the 
lenticular  process.  From  the  base  of  the  anval,  ligaments  pass  to 
the  posterior  wall  of  the  cavity,  while  the  head  of  the  anvil  articulates 
with  the  malleus.  The  stapes  is  fixed  by  the  head  of  the  stirrup  to 
the  lenticular  process  of  the  anvil,  and  passes  horizontally  to  be 
inserted  by  the  foot  of  the  stirrup  into  the  oval  window. 


Fig.  374. — View  of 
Tymvaxic  Mem- 
bra>;k. 


Fig.  375. — Method  of  Examixatiox  of  the  Ear  Drum  bv  Reflected  Light. 


The  malleus  and  incus  rotate  as  one  bone  round  a  horizontal  axis. 
When  the  handle  of  the  malleus  is  pushed  inwards,  the  head  of  the 
bone  moves  outwards,  carrying  with  it  the  body  of  the  incus,  excessive 
movement  being  prevented  by  the  ligaments  of  the  malleus.  The 
descending  process  of  the  incus  is  thereby  moved  inwards,  and  pushes 
the  stapes  against  the  fenestra  ovalis.  The  chain  acts  as  a  bent  lever, 
.so  that,  when  the  malleus  moves  a  certain  distance,  the  stapes  moves 
but  two-thirds  of  that  distance;  the  resulting  impact,  owing  to  the 
order  of  the  lever,  is  increased  b}'"  half,  and  since  the  area  of  the 
tympanic  membrane  is  about  twenty  times  as  great  as  that  of  the 
base  of  the  stapes,  the  force  falling  upon  the  oval  window  at  the  base 
of  the  stapes  is  about  thirty  times  as  great  as  that  falling  on  the  tym- 
panic membrane  at  the  umbo.  For  this  reason,  it  is  easy  to  understand 
that  hearing  is  seriously  interfered  with  when  the  action  of  the  ossicles 
is  deranged  b3'  middle-ear  disease. 


646  A  TEXTBOOK  OF   I'H V.SlOL<i<;Y 

On  the  inner  wall  of  the  niitldlc  (^ar  there  are  two  apertures:  an 
upper  oval  one,  known  as  the  fenestra  ovalis,  or  the  oval  window; 
a  lower,  smaller,  round  one — the  fenestra  rotunda,  or  round  window. 
Each  of  these  is  closed  bj'^  a  menihrano.  Into  that  of  the  oval 
membrane  is  inserted  the  terminal  jjrocess  of  the  cliain  of  ossicles. 

Leading  away  from  the  front  of  the  tympanum  is  a  channel  divided 
into  two  by  a  ledge  of  bone.  The  upper  compartment  contains  a 
muscle — the  tensor  tympani — while  the.  lower  passage  connects  with 
the  pharynx,  and  is  known  as  the  Eustachian  tube. 

The  action  of  two  muscles  of  the  middle  ear  requires  consideration 
— namely,  the  tensor  tympani  and  the  stapedius.  The  tensor  tympani, 
supplied  by  the  fifth  nerve,  arises,  as  we  have  seen,  in  the  upper 
compartment  of  the  channel  leading  from  the  front  of  the  middle 
ear,  and  is  inserted  by  its  tendon,  which  crosses  the  tympanum,  into 
the  inner  part  of  the  handle  of  the  malleus.  Its  action  is  to  maintain 
by  its  tone  a  constant  tension  on  the  tym])anic  membrane.  When  it 
contracts,  it  renders  the  membrane  more  taut — an  action  which  is 
believed  to  limit  the  movement  of  the  membrane,  and  thus  dampen 
the  effect  of  loud  notes. 

The  stapedius  lies  in  a  space  behind  the  tympanum,  and  its  tendon 
passes  througli  a  perforation  in  the  bone  behind  the  oval  window, 
to  be  inserted  into  the  neck  of  the  stapes.  Its  action  is  doubtful. 
It  may  be  that  it  moderates  the  force  of  the  stapes  against  the  fenestra 
ovalis,  or  it  is  possible  that,  by  pulling  on  the  stapes,  it  acts  through 
the  chain  of  ossicles  upon  the  tympanic  membrane,  and  induces 
relaxation  of  it — an  action  antagonistic  to  that  of  the  tensor  tympani. 
It  is  supplied  by  the  facial  nerve,  and  when  this  nerve  is  paralyzed 
loud  sovmds  are  heard  with  painful  intensity.  The  muscles  may  helj) 
to  tune  the  tympanic  membrane  for  the  reception  of  sound. 

The  Eustachian  tube  serves  to  keep  the  pressure  eqvial  on  the 
two  sides  of  the  tympanic  membrane.  It  is  normally  kept  closed 
except  during  the  act  of  swallowing.  This  has  a  double  usefulness. 
If  the  tube  were  always  open,  then,  in  the  first  place,  since  all  parts  of 
the  head  are  affected  by  the  waves  of  sound,  the  tympanic  membrane 
would  tend  to  become  pushed  upon  on  both  sides  at  once,  and  the 
effect  of  the  vibrations  damped.  Secondly,  were  it  open,  there 
would  be  a  great  reverberation  of  our  own  voice  in  our  ears. 

The  equality  of  pressure  on  both  sides  of  the  tympanic  membrane 
is  of  great  importance  for  normal  hearing.  Deafness  from  "  colds 
in  the  head  "  is  due  to  the  occlusion  of  the  passage  by  the  congestion 
of  its  mucous  membrane.  The  Eustachian  tube  allows  the  escape  of 
mucus  from  the  middle  ear.  During  exposure  to  increasing  or  rare- 
fying atmospheric  pressure  hearing  becomes  defective,  unless  the  tube 
be  kept  open  by  swallowing  or  forced  expiratory  movements  with  the 
nose  and  mouth  shut.  It  is  important  for  the  airman  to  keep  the 
pressure  equal  on  both  sides  of  the  tympanic  membrane  in  this  manner 
both  for  the  sake  of  hearing  and  for  the  sake  of  correct  balance. 

The  Internal  Ear  consists  of  a  thick-walled  cavity  in  the  temporal 
bone,  known  as  the  osseous  labyrinth.  It  is  filled  with  a  lymph-like 
fluid,  knowai  as  the  perilymph.     Lj^ing  in  this  perilymph  is  a  smaller 


HEARING 


6t7 


membranous  duplicate  of  the  osseous  labyrinth,  known  as  the  mem- 
branous labyrinth.     This  contains  a  fluid,  known   as  the  endolymph. 


ductus  endolymph. 


sup.  s.c. 


sca'a  media 


from  primitiue  utricle 


cochlear  canal 

Fi.T.  37(>. — Diagram  of  Membraxotjs  I;Abyrixth.     (Keith.) 


Into  the  central  portion  of  the  osseous  labyrinth — the  vestibule — - 
the  fenestra  ovalis  opens.  Anteriorly  from  this  there  arises  a  con- 
voluted tube — the  osseous  cochlea— which  is  wrappel  around  a  central 


Fi  i.  377. 


PS.Q. 


-Diagram  of  Right  Internal  Ear,  seen  from  Above. 
and  Wright,  "Practical  Anatomy.") 


(From  Parsons 


Cock.,  Cochlea;  Prom.,  promontory;  CO.,  carotid  canal;  E.T..  Eustachian  tube; 
I. A.M.,  internal  auditory  meatus;  Ve-ot.,  vestibule;  F.H.E.,  fovea  hemielliptica 
lodging  utricle:  CI'.,  crista  vestibuli;  St..  stapes  fixed  in  f'-nestra  walls;  Aq.F., 
Fallopian  aqueduct  (for  facial  nerve);  Aq.V ..  at^ueductus  vestibuli:  S.S.C, 
P.S.C,  E.S.C.,  superior,  posterior,  and  external  semicircular  canals. 

pillar — the  modiolus.     The  tube  is  divided  into  two  by  a  septum 
parth'  bony — the  spiral  lamina — and  partty  membranous— the  basilar 


048 


A  TEXTBOOK  OF  PHYSIOLOGY 


membrane.  The  up]jer  spiral  .section,  or  staircase,  is  called  the  scala 
vestibuli,  the  lower  one  the  scala  tympani.  The  scala  vestibuli 
begins  at  the  fenestra  ovalis,  and  ascends  to  the  top  of  the 
whorl.  Here  it  connects  bj'  way  of  an  opening  in  the  lamina  spiralis 
—the  helicotrema— with  the  scala  tj'^mpani,  which  descends  to  the 
fenestra  rotunda.  A  membrane — that  of  Rei.ssner — cuts  off  a  part 
of  the  scala  vestibuli,  the  scala  media,  membranous  cochlea,  or  cochlear 
canal.  This  is  bounded  by  the  basilar  membrane  below,  and  ends 
blindl}'"  at  the  top  of  the  cochlea.  Like  all  the  membranous  structures, 
it  is  filled  with  endolymph ;  the  other  two  staircases,  being  bony,  are 
filled  with  perilym]ih.     In  section,  the  scala  media  is  triangular. 


Fig.  378.— Section  (Low  Powkk)  thkough  Takt  oi'  Cochlea,  sH<.)\viNa 
Membranous  Canal  of  the  Cochlea.     (After  Retzius.) 

A,  Basilar  membrane;  B,  rods  of  Corti;  C,  hair  cells;  D,  fibres  of  auditory  nerve; 
E,  tectorial  meml)rane;  F,  membrane  separating  ofE  membranous  canal  of 
cochlea :  G,  wall  of  cochlea. 


Within  this  membranous  cochlea,  or  scala  media,  is  contamed 
the  organ  of  Corti,  the  receptor  mechanism  for  hearing.  The 
organ  of  Corti  is  set  upon  the  upper  aspect,  or  in  respect  to  its 
position  in  the  head,  the  anterior  aspect  of  the  basilar  membrane. 
It  runs  almost  tlie  whole  length  of  the  cochlear  canal,  and  consists 
of  a  set  of  elongated,  cylindrical,  rod-like  cells,  the  outer  and 
inner  rods  fixed  by  an  exjjanded  base  to  the  basement  membrane. 
These  meet  at  their  upper  ends  like  the  beams  of  a  sloping  roof,  the 
outer  cells  fitting  into  a  socket  in  the  inner  cells.  The  inner  rod  may 
be  compared  in  shape  to  the  ulna,  and  the  outer  to  a  swan's  neck, 
head,  and  beak.  From  the  head  of  each  rod  a  flattened  process 
projects,  the  process  of  the  inner  cell  overlapping  that  of  the  outer, 
and  giving,  when  seen  from  above,  an  appearance  like  the  keyboard 
of  a  piano.  The  inner  rods  are  about  half  as  numerous  again  as  the 
outer,  two  outer  rods  thus  fitting  into  three  inner  ones.  It  is  con- 
jectured that  there  are  about  6,000  inner  and  4,000  outer  rods.     Intern- 


HEARING 


64f> 


ally  to  the  inner  rods  is  a  layer  of  columnar  cells  of  the  same  height 
as  the  rods,  with  about  fifteen  to  twenty  short,  stiff  hair-like  processes 
arising  in  crescentic  manner  from  the  surface.  These  are  known  as 
the  inner  hair  cells. 

Externally  to  the  outer  rods  there  are  also  hair  cells — the  outer 
hair  cells.  There  are  generally  three  or  four  rows  of  these,  each  cell 
being  supported  outside  by  a  supporting  cell,  known  as  Deiters'  cell. 
These  c;ells  are  broad  at  their  base  of  attachment  to  the  basilar  mem- 
brane, and  pass  as  narrow  processes  to  be  attached  to  a  fenestrated 
membrane,  or  membrana  reticularis,  which  arises  as  a  sort  of  lattice- 
work from  the  upper  portions  of  the  rods,  and  serves  to  support  the 
free  hairs  of  the  hair  cells.  A  similar  membrane  supports  the  inner 
hair  cells.  Outside  the  hair  cells  are  several  rows  of  columnar  sup- 
porting cells  devoid  of  hairs,  which  become  continuous  with  a  layer 
of  cells  lining  the  whole  of  the  cochlear  canal.  Rising  from  a  con- 
nective-tissue structure  on  the  spiral  lamina  there  arches  over  the 
whole  organ  a  homogeneous  membrane — the  membrane  tectoria. 


aujic 


n)fC 


Fig.  379. — Sectkjx  of  Organ  of  Corti  of  a  Youxg  Guinea-Pig. 
(Redrawn  from  Dahlgren  and  Kepner.) 

dx..  Cells  .0?  Claudius;  li.c.  Hensen's  cells;  d.c,  Deiters'  cells,  or  .supporting  cells; 
aud.c,  auditory  cells,  or  hair  cells  (outer);  p.c.,  oiiter  and  inner  pillar  cells; 
i.aud.c.  inner  auditory  cells,  or  hair  cells;  n.fi.,  nerve-fibres;  vi.t.,  membrana 
tectoria;  ,S.S.C.,  cells  lining  sulcus  spiralis. 


Situated  in  the  spiral  lamina  is  the  spiral  ganglion,  from  which 
the  fibres  of  the  nerve  of  hearing  arise.  Processes  from  these  nerve 
cells  pass  along  to  and  around  the  hair  cells,  the  bases  of  which  do 
not  touch  the  basilar  membrane.  The  central  connections  of  these 
nerv^es  go  to  the  acoustic  nuclei  in  the  pons  (see  p.  699). 

The  part  of  the  membranous  labyrinth  corresponding  to  the 
vestibule  consists  of  two  membranous  sacs — the  saccule  and  the  utricle 
— connected  by  a  small  canal.  From  the  saccule  arises  the  cochlear 
canal.  In  connection  with  the  utricle  are  three  membranous  semi- 
circular oanals,  which  lie  within  three  correspondmg  bony  semicircular 
canals.  These  latter  open  into  the  posterior  and  superior  aspect  of 
the  vesrihule.  This  apparatus  probably  has  no  connection  with 
hearing,  and  is  dealt  with  later  (see  p.  054), 


€50  A  TEXTBOOK  OF  PHYSIOLOGY 

Sound. — Sound  is  the  sensation  ])roduccd  through  the  organ  of 
hearing  by  the  vibrations  emanating  from  vibrating  bodies.  Such 
vibrations  travel  by  the  air  at  the  rate  of  1,100  feet  per 
second. 

Physiologically,  sounds  may  be  divided  into  noises  anii  musical 
tones,  although  one  may  merge  imperceptibly  into  the  other — as, 
for  example,  the  tuning-up  of  an  orchestra.  Many  so-called  noises 
are  in  reality  more  musical  than  otherwise.  Vibrations  of  the  air  at 
regular  intervals  produce  what  is  termed  a  musical  somid;  vibrations 
at  irregidar  intervals  produce  an  unmusical  sound  or  noise.  Sounds 
may  differ  in  pitch,  intensity,  and  quality  or  timbre. 

The  pitch  of  a  note  depends  upon  the  frequency  of  the  vibrations 
in  a  given  time.  The  more  frequent  the  vibrations,  the  higher  the 
note;  the  less  frequent,  the  lower  the  note.  The  range  of  tones 
employed  in  music  varies  between  30  and  4,000  per  second,  although 
it  is  possible  for  the  ear  to  perceive  notes  and  vibration-rates 
as  high  as  40,000  per  second.  The  relation  between  frequency 
of  vibration  and  the  pitch  of  a  note  is  best  shown  by  means  of  the 
siren.  When  the  wheel  is  rotating  slowly,  nothing  is  heard  but  the 
puffs  of  air;  as  the  speed  increases,  the  puffs  begin  to  fuse,  and  then 
produce  a  low  buzz,  rising  with  increasing  speed  to  such  a  height 
that  the  note  finally  becomes  decidedly  unpleasant. 

The  sensibility  to  pitch  varies  in  different  people,  as  does  the  power 
of  distinguishing  notes  of  nearly  the  same  vibration.  This  latter 
defect  may  generall}''  be  improved  by  training,  although  there  are 
certain  people  who  are  "  tone-deaf."  They  can  only  discriminate  a 
few  tones,  and  find  it  impossible  to  recognize  a  time  or  to  sing  in 
tune.  Such  people  only  recognize  the  tune  of  the  National  Anthem 
by  the  fact  that  others  are  standing  up  with  their  hats  off.  The 
extreme  range  of  the  human  voice  is  about  half  the  range  of  the  human 
ear  for  musical  tones. 

The  intensity  or  loudness  of  a  note  depends  upon  the  amplitude 
of  vibration  of  the  sounding  body.  This  is  well  seen  in  the  tuning- 
fork.  When  the  fork  is  vibrating  visibly,  the  note  is  loud,  and  as  the 
visible  vibrations  pass  away,  so  the  note  diminishes  in  loudness  or 
intensity,  the  pitch  remaining  the  same.  If  the  ear  be  held  to  a  vibrat- 
ing tuning-fork,  it  will  be  found  that  the  note  is  loudest  when  the 
limbs  are  vibrating  in  a  plane  at  right  angles  to  the  external  ear, 
since  in  this  position  the  air  is  most  disturbed,  causing  a  greater 
difference  in  pressure  upon  the  tympanum. 

The  quality  or  timbre  of  a  musical  note  enables  us  to  tell  the 
instrument  bj^  which  it  is  j)roduced.  It  is  easy  for  most  people  to 
distinguish  between  the  human  voice,  the  note  of  the  violin,  and  the 
note  of  the  clarionet.  This  is  due  to  the  characteristic  wave-forms 
which  are  being  produced  in  each  case.  Just  as  no  two  great  waves 
of  the  sea  are  exactly  alike,  but  differ  in  the  shape  of  the  crests  and 
wavelets,  so  the  wave-forms  of  different  musical  instruments  vary. 
The  tones  emitted  are  really  compound  tones,  and  contain  numbers 
of  wavelets  or  "  overtones."     The  fundamental  tone  is  due  to  that 


HEARING 


651. 


of  the  large  wave;  the   quality   is   determined  by  that  of    the  large 
wave  and  the  wavelets. 

The  simplest  musical  tone  is  produced  by  a  body  like  a  tuning- 
fork  vibrating  in  simple  harmonic  motion — that  is  to  say.  in  such  a 
manner  that  the  waves  are  all  of  equal  size.  This  can  be  seen  by 
the  tracing  made  by  a  vibrating  tuning-fork  (time-marker)  iqion  a 
revolving  kjinograph.  Such  a  sound  is  uniform,  weak.  a.ud  dull, 
and  quickly  becomes  monotonous.  If  two  tuning-forks  be  .sounded, 
one  of  which  vibrates  twice  as  fast  as  the  other,  there  can  be  heard 
the  tones  of  the  two  forks  and  a  combination  of  the  torjes      The 


Fig.  380. 


-To   ILLUSTRATE   THE   FORMATION    OF   A   COMPOUND   WaVE   rRi'M    TwO 

Pendular  Waves.     (Helmholtz.) 


and  B,  Pendular  vibrations,  B  being  the  octave  of  A.  If  superposed  so  that  e 
coincides  with  d"  and  the  ordinates  are  added  algebraically,  the  non-pendular 
curve  0  is  produced.  If  .superposed  so  that  e  coincides  with  d'  the  non-pcndular 
curve  D  is  produced. 


form  of  vibration  will  vary  according  as  the  forks  produce  at  the  same 
time  rarefaction  or  condensation,  or  one  is  producing  rarefaction  while 
the  other  is  producing  condensation  of  the  air  (curves  C  and  D,  Fig.  380). 
From  an  indefinite  series  of  such  \nbrations,  of  which  the  period  of 
vibration  of  the  fundamental  is  always  a  multiple  of  the  least 
frequent  of  the  series,  an  infinite  variety  of  curves  may  be  obtained, 
yielding  musical  tones  having  the  same  fundamental  pitch,  but 
differing  in  quality  according  to  the  character  of  the  wavelets. 

The  character  of  the  musical  notes  of  different  instruments  may 
be  analyzed  by  means  of  resonators.  A  note  resonates  in  a  cylinder 
having  the  same  wave-length  of  vibrations  that  constitutes  the  original 
note,  or  an  exact  divisor  of  the  wave-length  of  that  note.     If  different 


652  A  TEXTBOOK  OF  PHYSIOLOGY 

notes  be  .sounded  together,  a  cylinder  will  resonate  witli  and  reinforce 
the  note  of  corresponding  wave-length.  So,  too,  will  tense  strings. 
This  can  be  ascertained  on  the  piano.  If  straws  be  attached  to  the 
wires,  it  will  be  seen  that,  when  one  note  is  struck  with  the  loud  pedal 
raised  to  remove  the  action  of  the  damper,  other  strings  than  the  one 
struck  are  vibrating  at  the  same  time.  This  is  because  their  vibration 
numbers  correspond  to  the  overtones.  It  is  the  overtones  which, 
when  not  excessive,  give  a  i:)leasant  fulness  to  the  note.  Uneven 
overtones  give  a  rough,  penetrating  note. 

When  two  different  notes  are  sountled  at  the  same  time,  they 
interfere  with  each  other,  alternately  strengthening  and  weakening 
each  other,  and  giving  a  succession  of  f)hases  known  as  beats.  The 
number  of  beats  per  second  depends  upon,  and  is  equal  to,  the  differ- 
ence of  the  rate  of  vibration  of  the  two  partial  tones.  A  difference 
of  one  vibration  gives  one  beat  per  second,  of  two  vibrations  twa 
beats  per  second.  When  beats  come  very  quickly,  the  alternate 
strengthening  and  weakening  is  lost,  and  a  whirring,  dissonant  sound 
results. 

In  harmony,  or  consonance,  there  is  an  absence  of  beats.  The 
greatest  consonance  is  obtained  from  the  same  note  with  the  same 
overtones.  After  that  come  the  octave  notes,  corresponding  to  the 
note  sounded.  Then  follow  various  chords,  producing  varying  degrees 
of  consonance. 

Theories  of  Hearing. — In  the  present  state  of  knowledge  it  is  not 
possible  to  give  any  full  and  satisfactory  explanation  of  the  function 
of  the  cochlea.  The  problem  to  be  solved  is  whether  sound-waves 
produce  movement  of  the  hair  cells  of  the  organ  of  Corti,  and,  if  so, 
the  nature  of  the  movement  and  the  means  by  which  it  is  produced. 
It  is  generally  held  that  some  form  of  mass  motion,  the  exact  nature 
of  M'hich  is  not  clear,  is  normally  produced  in  the  perilymph  through 
the  to-and-fro  action  of  the  footplate  of  the  stapes  upon  the  mem- 
brane of  the  fenestra  ovalis.  This  mass  movement  of  the  perilymph 
causes  synchronous  movements  of  the  membrane  of  the  fenestra 
rotimda,  and  also  affects  the  endolymph,  producing  therein  waves  of 
compression  and  rarefaction.  As  the  result  of  these  waves,  it  is 
believed  that  either  the  basilar  membrane  or  the  tectorial  membrane 
is  caused  to  vibrate,  and  thus  the  hair  cells  are  affected.  Various 
considerations  arise  as  to  the  nature  of  the  vibration  of  such  mem- 
branes. Is  the  vibration  throughout  the  whole  length,  or  only  in 
part,  or  in  some  particular  part  for  a  particular  sound  ? 

According  to  the  view  of  Helmholtz,  each  portion  of  the  basilar 
membrane  is  set  into  reciprocal  vibration  by  tones  of  a  different 
pitch,  high  tones  being  produced  by  vibration  at  the  basal  extremity, 
where  the  membrane  is  narrowest,  low  tones  in  the  apex  of  the 
cochlea,  where  the  membrane  is  widest  and  most  lax.  Except 
for  the  fact  that  Helmholtz  supposed  that  only  musical  tones  were 
perceived  by  the  cochlea,  and  that  noises  were  appreciated  by  the 
vestibular  apparatus,  his  view  still  meets  with  wide  acceptance.     It 


HEARING  653 

is  now  recognized  that  niuscial  tones  and  noises  are  not  f  undamentall}'- 
different,  and  that  both  are  perceived  by  the  cochlea,  the  vestibular 
apparatus  having  nothing  to  do  with  hearing. 

I  On  embrj^ological  grounds  it  does  not  seem  probable  that  a 
membrane  of  mesoblastic  origin  would  stimulate  hair  cells  of 
epiblastic  origin.  It  has  also  been  pointed  out  that  in  some 
animals — for  example,  the  pig — the  basal  portion  of  the  organ  of 
Corti  rests  ujDon  a  bony  plate  which  takes  the  j^lace  of  the  basilar 
membrane. 

To  meet  these  objections  the  view  that  the  tectorial  membrane 
vibrates  has  been  put  forward  by  several  observers.  As  originally 
put  forward,  it  assumed  that  high-pitched  tones  ca;ised  a  vibration 
of  the  basal  end  of  the  membrane,  and  in  descending  the  scale 
more  and  more  of  the  membrane  was  set  in  vibration,  until 
with  the  lowest  tones  the  whole  membrane  vibrated.  Such  an 
explanation  fails  to  account  for  the  ability  of  the  musician's 
ear  to  perceive  separately  the  different  sounds  from  an  orchestra 
which  reach  it  simultaneously,  and,  furthermore,  does  not  account 
for  partial  defects — "  tone-gaps  " — in  the  range  of  hearing.  The 
view  has  therefore  been  modified  on  the  lines  of  the  Helmholtz  view, 
and  it  is  now  suggested  that  the  tectorial  membrane  vibrates  to 
different  tones  in  different  parts  of  the  cochlea  in  the  same  manner 
as  suggested  for  the  basilar  membrane.  It  is  pointed  out  that  the 
tectorial  membrane  gradually  increases  in  breadth  from  base  to  apex 
after  the  manner  of  the  basilar  membrane,  and  that,  by  virtue  of 
its  elasticit}",  transverse  flexibility,  and  the  fact  that  it  is  attached 
on  one  side  only,  it  makes  a  better  and  more  sensitive  vibrator  than 
does  the  basilar  membrane. 

Auditory  Judgments. — -In  arriving  at  auditory  judgments,  we  are 
aided  bj'  other  senses  and  by  knowledge  previously  acquired.  Nor- 
mally, we  refer  sounds  to  the  exterior  of  the  body,  and  from  the  nature 
of  the  sound  determine  Avhat  it  is,  its  direction,  distance,  and  so  forth. 
According  to  its  quality  and  loudness,  we  pronounce  a  sound  to  be  a 
gunshot  fired  in  a  certain  direction,  close  at  hand,  or  far  away.  The 
direction  of  a  soiuid  is  determined  largely  by  the  force  with  which 
it  strikes  the  two  ears.  Judgment  of  direction  is  aided  by  turning 
the  head  from  side  to  side,  so  that  first  one  ear  and  then  the  other 
receives  the  sound  fulh'.  It  is  easier  to  judge  the  distance  of  noises 
than  of  musical  sounds.  The  power  to  judge  the  distance  of  the  source 
of  sound  depends  on  previous  experience.  Therein  lies  the  effect 
of  distance  imparted  by  the  operatic  chorus,  which,  on  leaving  the 
stage,  by  singing  more  and  more  softly,  gives  the  impres.sion  of  passing 
farther  and  farther  into  the  distance. 


CHAPTER  LXXI 

THE  PROPRIO-CEPTIVE  MECHANISM 

Inasmuch  as  the  force  of  gravity  is  continuously  acting  upon 
the  organism,  it  i.s  necessary  for  it  to  develop  some  mechanism  by  which 
its  position  in  regard  to  gravity  may  be  appreciated,  and  also,  when 
moving,  its  successive  positions  in  space.  In  the  lower  organisms, 
such  a  mechanism  is  developed  from  the  epithelium,  and  is  of  such  a 
nature  that  the  perceiving  tissues  are  stimulated  by  the  positions 
of  small  heavy  bodies  which  press  against  them  b}^  the  force  of  gravity. 
WTien  the  organism  moves  or  changes  its  position,  such  bodies  will  affect 
the  sensitive  surface  by  their  inertia,  or  the  latter  may  be  stimulated 
by  the  flow  of  Hu.:d  over  it.     In  higher  animals,  the  sensitive  receptor 


e 


Fig.  38!.— Tekta'CI-ocyst  (Statocyst)  of  a  Medusa.     (Redrawn  after  Hertwig 
from  Dahlgren  and  Kepner.) 

Stl.  is  the  statolitfi  tuclosed  in  a  pedicle  which  sways  with  the  animal's  motion  and 
affects  the  hairs  which  project  from  the  surface. 


mechanism  has  become  removed  from  the  surface  of  the  bod}^  and 
has  come  to  lie  within  the  head  in  the  vestibular  apparatus,  and 
within  the  body  in  connection  with  the  muscles,  tendons,  and  joints. 
The  proprio-ceptive  mechanism  is  the  mechanism  of  sense  of 
position  and  movement — the  mechanism  by  which  we  are  able  to 
poise  our  bodies  in  space,  by  which,  also,  we  are  able  to  adjust  our 
muscular  movements  to  a  great  degree  of  accuracy,  especially  the 
movements  of  the  limbs.  It  is  this  mechanism  which  enables  a 
man  to  shave  in  the  dark  or  with  his  eyes  shut.  By  the  proprio- 
ceptive mechanism  of  his  head  he  is  aware  of  its  position;    by  the 

654 


THE  PROPRIOCEPTIVE  MECHANISM 


Cm5 


proprio-ccptivc  mechanism  of  the  body  he  is  awixrc  of  the  position  of 
the  razor  in  his  hand,  and  is  able  to  adjust  the  blade  so  as  to  shavo 
without,  at  any  rate,  badly  cutting  himself.  In  this,  of  course,  he  i ; 
aided  by  cutaneous  tactile  sensation,  but  this,  as  wo  shall  see  later. 
is  not  the  factor  controllintr  tlic  main  movements. 

The  Proprio-ceptive  Mechanimi  of  the  Head — The  Labyrinthine 
Sensations  play  an  important  part  in  the  equilibration  of  the 
body.  The  receptor  mechanism  for  these  is,  as  the  name  signifies, 
contained  within  the  bon}''  labyrinth  of  the  middle  ear,  the  utricle, 
and  the  three  membranous  semicircular  canals.  The  utricle  connects 
with  the  saccule,  and  lies  in  the  vestibule  of  the  internal  ear.     From 


i.»*-  •/• 


^-^ 


^jtL- 


L'ti' n' m;k  \i'ii    >  .'  i.i.ii    Crista    of    the    AirpuxLA    of  the 

(jfUiNEA-i'ic.     (H.  I'nngle,  tioin  "  Quain's  Anatomy.") 

In  lowest  part  of  section  nerve-fibres  are  seen  passing  through  the  bone  to  the  loose 
tissue  below  the  crista.  The  epithelial  cells  of  the  crista  are  pear-shaped  sur- 
mounted by  hairlets  projecting  into  a  mucinous  material. 

it  also  arise  the  three  membranous  semicircular  canals  which  lie 
within  the  bony  semicircular  canals,  and  connect  with  the  utricle  by 
five  openings.  The  bony  semicircular  canals  arise  from  the  posterior 
and  superior  aspect  of  the  vestibule,  each  canal  havmg  at  one  end  a 
swelling,  or  ampulla.  They  are  arranged  at  right  angles  to  one 
another,  two  in  a  vertical  and  one  in  the  horizontal  plane.  The 
latter  is  known  as  the  external  canal.  It  lies  horizontally,  with  its 
curves  outwards  and  the  ampulla  in  front. 

Of  the  vertical  canals,  one  is  termed  the  anterior,  or  superior,  the 
other  the  posterior.  The  horizontal  canals  occupy  approximately 
the  same  plane.     The  superior  canal  lies  in  a  plane  inclined  at  an 


€56 


A  TEXTBOOK  OF  PHYSIOLOGY 


angle  of  about  37  degrees  to  the  coronal  plane,  and  the  posterior  canal 
at  an  angle  of  about  37  degrees  to  the  sagittal  plane.  The  superior 
canal  of  one  side  forms,  therefore,  an  angle  of  15  degrees  with  the 
posterior  canal  of  the  opposite  side.  There  is  a  considerable  space 
between  the  bony  and  the  membranous  canals.  The  former  are 
filled  with  jDerilymph,  the  latter  with  endolymph. 

The  special  receptor  mechanisms  lie  within  the  utricle  and  the 
ampullar  of  the  semicircular  canals.  The  specialized  structures  of 
the  ampuUse  are  known  as  the  cristse.  The}^  consist  of  specialized 
nerve-epithelial  hair  cells  and  supporting  cells,  which  lie  upon  a  base- 
ment membrane,  supported  uj)on  a  hillock  of  subendothelial  tissue, 
through  which  pass  the  nerve-endings  of  the  vestibular  part  of  the 
eighth  nerve,  to  arborize  around  the  hair  cells. 

In  the  utricle  and  saccule  there  are  somewhat  similar  structures, 
known  as  the  maculae  (Fig.  383).  These  have,  in  addition,  crystals 
of  calcium  carbonate  (otoliths),  which  lie  among  the  hair  cells. 


Fig.  383. — Portion  of  the  Macula  of  a  Mou.se,  treated  by  Golgi'8  Method  to 
SHOW  Nerve-Endings  in  the  Sensory  Cells  (sen.c).  (Redrawn  after  V. 
Lenhossek  from  Dahlgren  and  Kejjner.) 

h.m..  Basement  membrane;  sup.nu.,  nuclei  of  supporting  cells;  ?(»'./.,  nerve-fibre. 


The  vestibidar  ganglion,  or  ganglion  of  Scarpa,  lies  in  the  internal 
auditory  meatus,  an  upper  nerve-branch  connecting  with  the  utricle 
and  the  ampullae  of  the  superior  and  external  canals,  a  lower  nerve- 
branch  with  the  saccule  and  the  ampullae  of  the  posterior  canals. 
Centrally  the  fibres  enter  the  medulla  oblongata  in  the  region  of  the 
restiform  body,  and  make  connections  as  described  later  (see  j).  699). 

The  first  proof  that  the  semicircular  canals  are  concerned  with 
equilibration  was  adduced  by  Flourens  in  1828.  He  showed  that 
injury  of  one  canal  produced  rotatory  movements  of  the  bodj^  the 
axis  of  rotation  being  at  right  angles  to  the  severed  canal.  He  noticed 
that  the  disturbances,  like  those  produced  by  injury  of  the  cerebellum, 
were  of  a  co-ordinated  nature,  due  to  one  set  of  muscles  contracting 
while  another  set  relaxed.  For  many  years  Flourens"  work  pas.sed 
unnoticed,  but  since  then  it  has  been  many  times  confirmed. 

The  extirpation  of  both  labyrinths  is  attended  with  most  marked 
upset  of  equilibration. 


THE  PROPRIOCEPTIVE  MECHANISM 


657 


The  extirpation  of  one  labyi'iath  in  an  animal  immeiiately  affects 
the  resting  attitude  of  the  animal,  and  also  its  movements  in  spa -e. 
In  the  frog,  the  head  is  incline  1  to  the  side  of  the  lesion.  In  swimming, 
•  the  operated  side  is  lower  in  the  water,  with  an  abluction  and  exten- 
sion of  the  limbs  of  the  opposite  side,  particularly  the  fore-limb. 

In  the  pigeon,  destruction  of  the  msmbranous  labyrinth  produces 
marked  disturbances  of  equilibration.  The  bird  is  unable  to  rest 
quietly,  and  is  continuoush'  performing  inco-ordinate  movemsnts. 
After  a  time  these  pass  off,  and  it  learns  to  a  certain  extent  to  co- 
ordinate its  movements  bv  means  of  sii{ht  and  touch. 


Fig.  384. — Effect  of  Destkuctiox  of  Labyf.ixih  ox  Ox::  I<ide 

IX    A    Pi'JEOX'. 


Extirpation  of  one  labyrinth  produces  a  loss  of  tone  on  the  opposite 
side  of  the  Ijody.  When  onh'  one  canal  is  put  out  of  action,  oscillatory 
movements  of  the  head  are  produced  in  the  plane  corresponding  to 
the  damaged  canal  (Fig.  384).  The  same  results  hold  for  mammals, 
but  the  canals  are  not  so  accessible  as  those  of  the  pigeon. 

The  canals  have  been  stimulated  experimentall} ,  chiefly  the 
external  canal,  owing  to  its  greater  accessibility.  By  plugging  one 
«nd  of  the  canal  behind  an  artificial  opening,  and  introducing  into  it 
a  syringe,  it  has  been  shown  that  pressure  on  the  ampulla  causes  a 
deviation  of  the  ej'es  to  the  op]30site  side,  with  nystagmus  when  the 
e3^es  looked  to  the  same  side  of  the  body.  Rarefaction  produced  an 
opposite  result — a  deviation  of  the  eyes  to  the  same  side  of  the  bod}', 
and  a  nysta,gmus  when  the  eyes  turned  towards  the  opposite  side  of 
the  body 

Like  results  have  been  obtained  upon  the  human  subject  in 
cases  of  middle-ear  disease  svhere  suppuration  has  produced  a  fistulous 
opening  into  the  external  canals. 

42 


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A  TEXTBO(JK  or  PHVSIOLOUY 


Similar  phenomena  may  be  evoked  l)y  changes  of  temperature 
a|)i)lied  'o  the  outer  wall  of  the  labyrinth — as,  for  example,  by  irriga- 
tion of  the  middle  ear  with  tepid  water.  In  irrigation  experiment* 
upon  the  sujierior  canal,  it  has  also  been  shown  that  reflex  forced 
movements  of  the  head,  eyes,  and  trimk,  are  produced  in  the  same 
direction  as  the  wave  of  increased  pressure  in  the  endolymph. 
Stimulation  of  the  labyrinth  bj'  means  of  the  galvanic  current  has 
coufirnii'd  these  resuhs  both  in  animals  and  in  man. 

Passive  rotation  upon  a  turn-table  causes  the  subject  to  turn 
his  head  in  the  opposite  direction,  and  on  stopping  in  the  direc- 
tion of  rotation,  with  a  sensation  of  actual  rotation  in  the  opposite 
direction.  Cases  of  vestibular  trouble  may  be  investigated  by  means 
of  the  turn-table,  and  their  behaviour  compared  with  that  of  normal 
subjects      The   giddiness    and    upset    of    equilibration   produced    by 


i''iG.  '66'k — Ending  uf  ISkkve-Fibees  in  a  Musci.k  Si'ixdle.     (Kuffini,  from 
"  Quain's  Aiiatomy.") 

;),  Nerve  tibies  to  spindle;  a,  annular  endings  of  axon;  ■>,  ';;)iral  endings;  iJ,  dcndi'itic 
endings;  sk,  connective-tissue  sheath  of  spindle. 


shifting  rho  head  from  one  plane  to  another  after  rotation  is  familiar 
in  the  children's  game,  where,  after  turning  round  quickly  with  the 
forehead  resting  on  the  poker,  the  subject  stands  up  and  tries  to 
walk  straight  out  of  the  door  or  to  touch  a  certain  person. 

Comparative  anatomy  also  supports  these  results.  It  has  been 
shown  that  Japanese  waltzing  mice  and  tumbler  pigeons  have  ab- 
normal semicircular  canals. 

The  mode  of  excitation  of  the  receptor  mechanism  is  generally 
believed  to  be  due  to  the  inertia  of  the  fluid  within  the  canals.  Rota- 
tion of  the  head  causes  a  lag  of  fluid  and  pressure  in  the  opposite 
direction,  which  acts  upon  the  hair  cells  of  the  ampulla.  Owing  to 
the  small  size  of  the  canals,  there  is  probably  no  actual  movement  of 
the  fluid,  but  nierety  positive  and  negative  alterations  of  the  fluid - 
pressure  within  the  canals. 


THK  PROPRIOCEPTIVE  MECHANISM  659 

It  is  possible  that  sense  of  movement  is  referable  to  the  semi- 
circular canals,  and  sense  of  position  to  the  end-organ  of  the  utricle. 
Here  the  solid  particles — the  otoliths — play  a  part  by  acting  upon  the 
hair  cells  with  varying  pressures,  according  to  the  position  of  the  head. 

The  Proprio-ceptive  Mechanism  of  the  Body. — The  sensations 
concerned  in  '"  kinsesthetic  sense,"  or  the  "  muscular  sense,"  as  it  is 
sometimes  called,  arise  from  the  muscles  themselves,  the  joints,  and 
tlie  tendons.  As  the  receptor  mechanism  special  sensor^'  nerve  ter- 
minations have  been  described  in  muscle,  the  neuro-muscular  spindles. 
These  are  long,  fusiform  structures  in  connection  with  the  muscle 
tibres.  Into  them  passes  a  medullated  nerve,  which  final]}''  breaks 
up  into  a  non-medullated  plexus  surrounding  the  modified  muscle 
fibre  (Fig.  386). 

In  connection  with  the  tendons  are  found  the  organs  of  Golgi — • 
small  fibrous  capsules  containing  a  plexus  of  non-medullated  nerve- 
fibres  derived  from  a  branch  of  medullated  nerve.  Somewhat  similar 
varicose  nerve  terminations  are  also  found  in  the  synovial  membranes 
and  ligaments  of  joints. 


Fig.    380. — XEUK(;-T-H:KDi>'wrs    Nkkve    I':]xd-()k(;a>-    in    R.^bbit.     (Redrawn    after 
Hiiber  and  De  Witt  from  Dahlgien  and  Kepner.) 

The  nerve-sui)ply  t.>  these  structiu-es  is  large.  It  is  computed  that 
t  wo-thirds  of  the  fibres  of  the  mixed  sciatic  nerve  are  connected  with  the 
proprio-ceptive  system,  and  sensory  in  function.  By  means  of  these 
terminations,  information  is  conveyed  to  the  central  nervous  system 
as  to  the  degree  of  contraction  or  relaxation  of  a  muscle  or  sets  of 
muscle,  and  also  as  to  the  degree  of  extension  or  flexion  of  a  joint. 
The  position  of  a  limb  may  therefore  be  fairly  well  localized,  even  with 
the  Gjes  shut.  Such  information  is  of  great  importance  in  guiding 
and  co-ordinating  the  movements  of  a  limb.  Such  impitlses  do 
not  necessarily  affect  the  consciousness,  but  they  are  of  value  in  aiding 
the  extero-ceptive  mechanism  in  determining  the  size  and  shape  of 
liodies — as,  for  example,  the  amount  and  nature  of  nuiscular  movement 
necessary  to  feel  completely  over  the  surface.  This  sense  is  of 
particular  value  in  determining  the  size  of  a  body  in  the  dark.  The 
weight  of  a  body  is  also  gauged  by  determining  the  amount  of  muscular 
contraction  necessary  to  prevent  it  falling  or  to  raise  it.  The  condi- 
tion of  this  mechanism  may  be  investigated  by  testing  the  judgment 
of  the  indixndual  in  regard  to  moderate  weights,  and  also  in  regard 
to  "  deep  pressure."     Deep  pressure  sensation — e.g.,  the  presstire  of  a 


6G0  A  TEXTBOOK  OF  PHYSI0LO(;V 

pencil-point — is  connected  with  this  mechanism,  and  persists  when 
the  cutaneous  nerves  have  been  cut.  The  nerves  connected  with 
this  sense  pass  into  the  cord  by  the  posterior  roots,  and  have  their 
cell-stations  in  the  posterior  root  ganglion.  The  distribution  of  the 
fibres  is  referred  to  later  (see  p.  673). 

The  sense  of  "balance"  is  due  to  a  co-ordination  of  impulses 
received  from  the  eyes,  the  semicircular  canals,  and  the  organs  of  cuta- 
neous and  kinaesthetic  sensibility.  The  aiinian  is  particulajly  depen- 
dent iipon  his  sense  of  vision.  He  also  derives  much  information  as 
to  the  position  of  his  luachine  by  cutaneous  sensations  fi  cm  his  seat 
and  from  the  ])lay  of  the  wmd  on  his  cheeks.  "J'he  '"  feel "  of  the  joy- 
stick in  which  kinsesthetic  sensations  play  a  part  is  also  important,  as 
well  as  the  impulses  received  from  his  vestibular  apparatus. 

The  Enter o-ceptive  Mechanism. — The  entero-ceptive  mechanism  is 
associated  with  the  sensations  arising  from  the  alimentary  tract  from 
the  beginning  of  the  gullet  down  to  the  rectum.  Various  forms  of 
receptor  mechanisms  have  been  described,  varying  in  nature  from 
free  expansions  of  dendritic  nerve-endmgs  to  the  elaborate  Pacinian 
corpuscle.     The  total  number  of  afferent  hbres  to  the  viscera  is  small 

not  more  than  those  contained  in  a  single  ])osterior  root.     By  means 

of  this  mechanism,  the  orderty  sequence  of  the  movements  of  the 
digestive  tract  is  insured,  usually  without  involving  consciousness  of 
the  process. 

The  different  parts  of  the  tract  vary  to  different  forms  of  stimula- 
tion in  their  power  to  provoke  conscious  sensitivity.  From  the 
beginning  of  the  oesophagus  to  the  junction  of  the  rectum  the 
alimentary  tract  is  insensitive  to  tactile  stimuli.  Heat  and  cold  do 
not  excite  the  mucous  membrane  of  the  stomach ;  the  colon  is  almost 
insensitive;  the  gullet  and  anal  canal,  on  the  other  hand,  are  sensitive, 
to  thermal  stimulation. 

Chemical  stimuli  also  vary  in  effect.  Alcohol  produces  a  feeling 
of  warmth  in  all  parts,  whereas  glycerine  has  a  localized  stinndatory 
effect  i;pon  the  anal  canal.  The  mucous  membrane  of  the  ceso])hagiis 
and  stomach  is  insensitive  to  stimulation  with  weak  hj'droehloric  acid. 

The  sensation  of  thirst  is  due  to  changes  in  the  mouth,  throat, 
and  stomach.  It  is  generally  brought  about  by  a  drying  of  the 
mucous  membrane  of  the  throat  after  the  inhalation  of  dry  or  dusty 
air,  or  the  ingestion  of  salt  or  dry  food.  Wlien  water  is  long  with- 
held, it  is  possible  the  terrible  sensation  of  thirst  also  arises  from  an 
altered  condition  of  the  blood. 

The  sensation  of  hunger  is  evoked  bj-  the  contractions  of  the  con- 
tracted empty  stomach.  It  may  be  satisfied  to  a  certain  extent  by 
swallowing  the  saliva  to  induce  relaxation,  hence  the  efficacj-  of 
chewing  tobacco.  Normally,  food  induces  such  a  relaxation.  It 
maj'-,  however,  be  induced  by  swallowing  an}-  solid  material.  Thus, 
the  natives  on  the  Orinoco  appeased  their  hunger  in  the  time  of 
need  by  eating  baked  earth.  The  distension  of  the  stomach  thus 
induced  satisfies  hunger  by  stopping  its  movements.  The  sensation 
of  fulness  after  a  large  meal  is  due  to  dilatation  of  the  stomach. 


THE  PRUPRIO-CEPTI\  E  MECHANISM 


661 


The  call  to  defaecatioii  is  due  to  distension  of  the  rectum,  and 
may  be  evoked  artiticially.  e.g.,  by  the  introduction  of  fluid,  or  of  a 
balloon  and  its  distension  to  a  pressure  of  about  50  mm.  Hg 
(see  p.  419). 

Pain  is  due  t(j  the  stretching  of  the  ahmentary  tract  by  obstruction 
or  overdistension.  Colic  is  due  to  a  tonic  contraction  of  the  gut, 
which  prevents  peristalsis  from  forcing  on  the  contents  of  the  gut. 
Vague  sensations,  such  as  uneasiness,  tingling,  tickling,  are  due  to 
some  form  of  abnormal  stimulation 
As  a  rule,  pain  in  the  alimentarj'  tract 
is  not  well  localized,  but  is  more 
accurately  localized  in  the  fixed  than 
in  the  movable  viscera.  The  nerves 
subserving  the  pain  sensation  are  the 
sympathetic,  and  the  pain  is  referred 
to  the  superficial  cutaneous  areas 
supplied  by  those  nerves  which  are  in 
connection  with  the  same  segment  of 
the  cord  as  that  from  which  the  sympa- 
thetic supply  of  the  viscus  is  derived. 
The  stimulation  of  the  sympathetic 
nerves  produces  an  irritable  focus  in 
the  cord,  and  this  gives  rise  to  hyi)er- 
sensitivity  and  so  to  pain  felt  in  the 

peripheral  tissues  connected  with  that  Fio.  387. — Diagram  to  explain 
segment  of  the  cord.  In  the  case  of 
the  stomach,  the  hypersensitivity 
affects  the  seventh,  eighth,  and  ninth 
thoracic  nerves;  of  the  intestine,  the 
tenth  and  eleventh  thoracic;  of  the 
rectimi,  the  first,  second,  and  third 
sacral.      An    irritant    applied    to    the 

skin  in  the  area  where  the  pain  is  felt  mav  take  possession  of  the 
sensory  nerve  and  the  attention  of  the  patient  so  that  those  from 
the  viscus  have  no  efifect. 


Referred  Pain  and  Counter- 
Irritation.  (Dixon,  after 
Mackenzie.) 

The  diagram  shows,  also,  how 
irritants  to  tho  slcin  may  cause 
local  dilatation  of  the  vessels 
bv  an  axon  reflex. 


CHAPTER  LXXn 
THE    SPINAL    CORD 

The  nerve-fibres  act  as  conductors  connecting  ihe  receptor  and 
effector  mechanisms.  The  conductors  form  the  nerve  trunks  of  the 
body— the  cranial  and  the  spinal  nerves — and  the  tracts  within  the 
central  nervous  system.  The  conductors  are  the  processes  of  the 
nerve  cells,  or  neurons  ;  these  interlace  and  form  synapses,  through 
which  the  nervous  energy  is  transmitted  from  one  neuron  to  another. 

We  have  to  consider  the  ingoing  neuron,  which  connects  the 
gensory  nerve-ending,  or  receptor,  to  the  central  system,  and  the 
efferent  neuron  —  the  final  common  path  —  which  connects  the 
central  system  to  the  effector  organ.  The  axons,  or  conductors, 
of  these  two  sets  of  neurons  form  the  mixed  nerve  trunks  of  the 
body.  The  arrangement  of  each  spinal  nerve  is  as  follows:  On  the 
postero-lateral  aspect  of  the  spinal  cord  there  enters  the  posterior 
root,  which  has  a  ganglionic  swelling  upon  it — the  posterior  root 
ganglion.  From  the  antero-lateral  aspect  of  the  cord  emerges  the 
anterior  root.  The  two  roots  combine  to  form  the  spinal  nerve.  In 
all  the  thoracic  nerves,  and  some  of  the  sacral,  there  are  not  only  large 
fibres  which  pass  to  the  body-wall  structures,  and  are  known  as 
somatic  fibres,  but  also  small  fibres  which  supply  the  viscera  and 
the  involuntary  muscle  of  the  body,  and  are  known  as  splanchnic 
fibres.  The  course  of  these  latter  fibres  is  dealt  with  when  the 
autonomic  system  is  considered  (see  p.  748). 

The  fibres  of  the  posterior  root  form  the  great  afferent  system, 
the  fibres  of  the  anterior  root  the  great  efferent  system.  Section  of 
a  posterior  root  leads,  therefore,  to  a  cutting-off  of  the  impulses  which 
come  both  from  the  extero-ceptive  and  proprio-ceptive  mechanisms^ 
that  is,  the  sense  organs  which  receive  impulses  from  the  outside 
world,  and  those  which  initiate  the  impulses  which  arise  in  the  inner 
world  of  the  body  itseK.  In  the  case  of  the  spinal  nerve,  the  former 
impulses  include  those  of  touch,  temperature,  pain,  and  the  latter 
those  of  the  kinsesthetic  sense.  Section  of  an  anterior  root  causes 
a  paralysis  of  the  muscles  and  any  other  effector  organ  supplied  bj' 
the  nerve.  Wallerian  degeneration  affects  the  axons,  which  are  cut 
off  from  the  cell  bodies  of  the  neurons. 

The  cells  which  give  origin  to  the  fibres  of  the  posterior  root  are 
situated  in  the  posterior  root  ganglion;  those  of  the  anterior  root 
fibres  in  the  anterior  horn  cells  of  the  spinal  cord.  As  a  consequence 
of  section  of  an  anterior  root,  the  nerve-fibre  deg.enerates  toAvards 

662 


THE  SPIKAL  CORD 


{)0:j 


the  periphery.  The  path  of  degeneration  which  follows  section  of 
the  posterior  root  depends  upon  the  site  of  section.  If  it  be  between 
the  ganglion  and  the  cord.  then,  since  the  nerve  cells  are  in  the  ganglion, 
degeneration  will  take  place  in  the  parts  of  the  fibres  Avhich  enter  the 
spinal  cord;  if.  on  the  other  hand,  it  be  peripheral  to  the  ganglion, 
then  the  nerve-fibres  will  degenerate  towards  the  periphery,  where 
the}^  form  connections  with  the  various  rereptor  mechanisms.     Tho 


Degeneration  of  efferent  and  of  afferent       Degeneration  of  efferent  fibres  below  a 
fibres  below  a  section  of  entire  nerve.  section  of  anterior  root. 


Degeneration  of  afferent  H'oves  bcl3\\-  a 
section  of  posterior  root  beyond  the 
ganglion. 


Degeneration  of  afferent  fibres  above 
a  section  of  posterior  root  above  the 
gangb'on. 


Fig.  388. — Diagr.\m5  to  illvstk.^te  Walleeiax  DEGEyEEATiox  of  Xerve-Roots 

(Waller.) 


ingoing  afferent  fibre  from  the  posterior  root  ganglion  makes  a 
variety  of  connections.  These  are  best  considered  after  the  structure 
of  the  spinal  cord  has  been  described. 

The  Structure  of  the  Spinal  Cord. — The  spinal  cord  is  the  long 
strand  of  nervous  tissue  which  passes  down  the  vertebral  canal  from 
the  base  of  the  brain  to  the  level  of  the  first  lumbar  vertebra — a  length 
of  about  18  inches.  It  develops  in  three  zones  from  the  neural  tube 
(Figs.  389,  360).  From  it  are  given  off  the  anterior  and  posterior 
roots  of  the  spinal  nerves.  In  the  cervical  and  again  in  the  lumbar 
region  there  is  an  enlargement  from  Avhich  arise  respectiA^ely  the  nerves- 


GC-t 


.\  TKXIBOOK   OF   I»HVSJ()|J)(;Y 


of  the  braiihial  and  lumbar  i»luxiiscs.  In  these  enlargenient.s  the  cord 
is  more  or  less  oval  in  section ;  in  other  ]mrts  it  is  nearly  ronncl.  Down 
the  centre  there  runs  a  fine  canal  lined  ))y  ciliated  ei)ithelinm,  while 


post  root  gang. 


spongio-bl. 


germ,  cells 


middle  zone 
t- inner  zone 


ant  root 


Fig.  3S0, — Diagkamjiatic  Section  showixg  the  Three  ZOiS^ES  of  the  Smnal 
NErRAi,  Tube  AT  the  Sixth  Week.     (Keith.) 


post  mes.  (from  post  roots j 

post  /at  (from  post  roots) 
^margin,  (from  post  roots) 

crossed  pyram.  (from 
motor  cortex) 

asc.  cerebellar 


outer  zone 
middle  zone. 

inner  zone 


asc.  cerebellar 


\' cerebellar  (fror.i 
cerebellum) 

ant',  pyram  (from  motor  cortex) 

Fig.  390. — DiAcnAiuiATic  Section  of  Spinal  Cord  to  show  the  Parts  formed  in 
THE  Three  Zones  of  the  Embryonic  Spinal  Cord.     (Keith.) 

two  fissures  in  the  middle  line  dip  into  the  cord  anteriorly  and  pos- 
teriorly. The  anterior  fissure  is  more  or  less  open — a  kind  of  furrow 
— the  posterior  fissure  is  practically'  closed,  being  formed  mainly  (>f 
supporting  neuroglial  tissue. 

On  section,  the  spinal  cord  is  seen  to  l^e  composed  of  white  and 
grey  matter.  The  latter  is  centrally  placed  in  the  shape  of  an  H. 
The  joining  limb  of  the  H  passes  on  either  side  of  the  central  canal 


THE  SPINAL  CORD 


665 


The  grey  matter  consists  luaiiily  of  nerve  cells  and  tiieir  non- 
inedullated  processes ;  the  white  matter  of  the  axons,  or  medullatecl 
nerve  processes.  The  nerve-fibres  in  the  spinal  cord  are  devoid  of 
neurilemmal  sheath.  The  neuroglia,  the  supporting  tissue  of  the 
cord,  is  intimately  woven  into  the  structure  of  the  cord,  particularly 
of  the  grey  matter.  Round  the  central  canal  it  forms  the  substantia 
gelatinosa  centralis,  and  around  the  head  of  each  posterior  horn 
of  grey  matter  is  another  collection  of  neuroglia,  the  substantia 
gelatinosa  Rolandi. 


Fig.      391.  —  Diagrammatic      Section 

THROUGH    SpIXAL    CoRD    IX   ThOKACIC 

Kegiox.     (.Parsons  and  Wright.) 


Fig.  392. — Diagrammatic  Section  of 
SriXAL  Cord  through  Cervical 
Exlakgement.    (Parsons  and  Wright ). 


Fig.  393. — Diagrammatic  Section  of  Spixal  Cord  through  the  Lumbar 
Exl.vrgement.     (Parsons  and  Wright.) 


The  grey  matter  in  each  half  of  the  cord  is  divided  into  a  posterior 
horn,  a  lateral  horn,  and  an  anterior  horn.  In  it  are  various  groups 
of  cells,  the  chief  of  which  may  be  classified  as — ■ 

1.  Posterior  horn  cells.  These  are  small  multipolar  cells,  chiefly 
of  commissural  function. 

2.  Clarke's  column  of  cells — cells,  more  or  less  bipolar  in  form, 
situated  on  the  imier  aspect  of  the  posterior  limb  of  grey  matter, 
near  its  junction  with  the  connecting  limb.  From  it  axons  pass  into 
the  cerebellar  tracts. 

3.  Intermedio-lateral  gi'oup — a  group  of  cells  situated  chiefly 
in  the  lateral  liorn.  From  it  axons  pass  out  into  the  sympathetic 
svstem. 


6B6 


A  TEXTBOOK  OF  PHYSIOLOGY 


4.  Anterior  horn  group — groups  of  large  multipolar  cells  from 
Avhich  the  efferent  fibres  of  the  anterior  root  arise. 

The  white  matter  of  the  spinal  cord  consists  of  tracts  of  fibres 
Avhich  run  mainly  up  and  down.  There  are  fibres— (1)  from  the 
posterior  root  ganglia  of  the  spinal  nerves,  Avhich  ascend  or  desoend 
in  the  spinal  cord;  (2)  from  the  grey  matter  of  the  spinal  cord,  which 
ascend  to  the  brain ;  (3)  from  the  grey  matter  of  the  brain,  which 
<lescend  to  the  spinal  cord;  (4)  commissural  fibres  which  connect 
various  parts  of  the  spinal  cord.     The  corresponding  tracts  are — 


Postcro-latoral  tissuie 
rostero-mediaii  column 


Piistero-mediaii  fissui 
Po.sterior  root  bundle 
rostcro-laterdl  colutiiir 

Subst.  gelat.  of 
dorsal  horn 


ISiindle  of  Flcolisij/ 


Lateral  (cross 
pyramidal  ti 


Commissure 

Anterior  hoi)i  ~ 

Anteroiiieiliaii  fiss 


Fig.  ;?94. — Section  or  Human  Spinal  Cord  from  Upper  Cervical  Pv,kgion. 
Photograph  magnified  about  8  Diameters.  (E.  A.  Schafer,  from  '  Quain's 
Anatomy." ) 


1.  Ascending. — ^The  postero-median  tract  (of  Goll);  the  postero- 
lateral tract  (of  Burdach);  the  marginal  tract  (of  Lissauer). 

Descending. — The  comma  tract. 

2.  Ascending. — The  dorsal  spino-cerebellar  (or  •  the  direct  or 
posterior  cerebellar  tract  of  Flechsig);  the  ventral  spino-cerebellar 
(or  ascending  antero-lateral  or  ventral  cerel^ellar  tract  of  Gowers) ; 
the  spino-thalamic. 

3.  Descending. — The  cortico-spinal  or  pyramidal  tract  (crossed, 
uncrossed,  or  direct) ;  the  rubro-spinal  tract  (prepyramidal  of  Mona- 
kow);  the  vestibulo-spinal  tract  (antero-lateral  descending  of  Loewen- 
thal);  the  olivo-spinal  tract,  the  thalamo-spinal  tract  (of  Helweg). 

4.  Ascending  and  Descending.— The  septo-marginal  tract;  fibres  of 
the  basis  bundles. 


THE  SPINAL  CORD 


()()7 


Eli;.    'M)r>. DiAGK.VM    T(J    SHOW    THE    VaKIOUS   ENDUUENOt'S    AND    EXOGENOLS  TKACi'S 

OF  SriNAi,  Cord.     (Mott.) 

1,  Anterior  horn;  2,  commissural  fibres:  3,  posterior  horn;  4,  crossed  pyramidal  tracts; 
5,  direct  cerebellar  tract;  6,  ant cro- lateral  ascending  tract:  7,  endogenous  (oval 
area  of  Flechsig):  8,  endogenous  tract  (Gombault  and  Philippe's  tract);  9,  endo- 
genous cornu  commissural  tract;  10,  rubro-spinal  and  spino-thalamic  tract; 
II,  direct  pyramidal  tract;  12,  postero-median  column  (of  Oo]l);  13.  postero- 
external column  (of  Burdach);  14,  pjstero-internal  triangle  (endogenous;;  1."), 
comma  tract  (endogenous);  10,  Lissauer's  tract:  17,  teotn-spinal.  spino-tcctal, 
vcstibulo-spinal,  and  cerebro-sjjinal  fibres. 


OGS 


A  TEXTBOOK  OF  PH Y8I0L0GY 


The  Tracts  arising  from  the  Posterior  Root  Ganglia,  and  passing 
into  the  Cord  (Posterior  Columns) — The  Paste  to- Median  Tract  {of 
(•oil). — The  cell-stations  are  in  tlio  posterior  root  ganglia,  especially 
the  sacral  and  linnbar.  I'he  fibres  first  enter  the  postcro-lateral 
cohmui,  and  then  pass  into  the  postero-median,  lying  dorsally  close 
against  the  postero-median  fissure  (12,  Fig.  395).  Thej-  pass  np  to  the 
gracile  nucleus  situated  at  the  junction  of  the  cord  with  the  spinal 
l)ulb.  givino-  off  manv  collaternls  on  the  way. 


DefUtc  nucleus 


'^i^\ 


Direct  cerebellar 


Tactile 

(discrimination) 

Joint  and 

muscle  senses 
(sense  of  position) 

rjon-sensory  recepto' 
(Clarke's  column) 


Deep  sensation 
Superficial  sensation 


Part  of  Gower's  tract 
entering  cerebrum  by 
superior    cerebellar 
peduncle 

Tactile 


Gracilis-  cuneatc  nuclei 
Pain,  heat,  and  cold 


■Tactile  receptor 
-Pain    receptor 
-Heat  receptor 
Cold  receptor 


Fir 


396. — Diagram  to  itLrsTRATE  the  Afferent  Systems  to  Cei!ebrum  Ai>ii> 
Cerebellttm.     (Mott.) 


ThePostero-Lateral  Tract  {of  Burdach). — The  fil)res  arise  like  thepre- 
cerling  and  pass  in  a  more  external  position,  to  end  around  the  cells- 
of  the  cuneate  nucleus  at  the  base  of  the  spinal  bulb  (13,  Fig.  395). 

The  Marginal  Tract  {of  Lissauer)  lies  just  external  to  the  posterior 
horn  of  grey  matter.  The  fibres  arise  from  cells  in  the  posterior  root 
ganglia.     They  are  very  fine  asc;ending  fibres,  Avhich  gradually  form. 


THK  SPINAL  (OHi) 


r;(J!t 


synapses  with  the  posterior  lioru  cells.     Possibly  they  are  connected 
also  with  the  sympathetic  system. 

The  Comma  Tract  {Descending)  intermingles  with  the  tracts  of 
the  postero-median  and  postero-Iaterai  columns.  It  consists  of  the 
descending  processes  of  the  afferent  fibres  of  posterior  root  ganglion 
cells,  Avhich  branch  when  they  reach  the  spinal  cord.  Possibl}'  some 
fibres  of  this  tract  arise  in  the  spinal  cord  itself. 


'th0^^^ 


Direct  ,..  

cerebellar  tract 


Pyramidal  tract 


■Pre-pyramidal 
(rubro-spinal) 


Deiters' 

spinal  tract 
(vestibulo-spinalj 


Anterior  horn  cell 


Fig.   397. — Diagk.vm  to  illustrate  the  Various  Paths  of  Traksmission  from 
Brain  to  Spinal  Motor  Netjkoxs.     (Mott.) 


Tracts  which  pass  from  the  Cord  to  the  Brain  (Lateral  Columns) — 

The  Dorsal  Sjjino-Cerebellar  (the  direct  or  ]:)osterior  cerebellar  tract 
of  Flechsig). — The  large  fibres  of  this  tract  are  derived  from  cells  in 
Clarke's  column  of  the  same  side,  and  pass  in  a  postero-lateral  marginal 
position  (5,  Fig.  395)  into  the  spinal  bulb,  and  thence  by  the 
rest  if  rm  body  to  the  anterior  portion  of  the  superior  vermis  of  the 
cerebellum. 

The  Ventral  Sptno-Cerebellar  Tract  (or  ascending  antero -lateral  or 
ventral  cerebellar  tract  of  Gowers)  arises  on  the  opposite  side  from 


(>70  A  TEXTBOOK  OF  PHYSIOLOGY 

scattered  pcsteiior  horn  cclLs,  aud  ])os.sibIy  from  cells  of  Clarke's- 
column.  It  passes  up  in  the  aiitcro-lateral  marginal  position  of  the 
spinal  cord,  and  passes  through  the  bulb  and  pons,  to  enter  the  superior 
vermis  of  the  cerebellum  by  the  superior  peduncle. 

The  Spino-Thalamic  Trad  consists  of  a  scattered  group  of  fibres 
lying  just  internally  to  the  ventral  spino-cerebellar  tract.  Its  fibres 
pass  upwards,  to  end  mainly  on  the  same  side  in  the  optic  thalannis. 
Some,  however,  end  <»n  botli  sides  in  the  anterior  corpora  quadrigemina 
(10,  Fig.  395). 

Tracts  which  pass  from  the  Brain  to  the  Spinal  Cord — The  Cortico- 
Spinal  or  Pyramidal  Tract. — This  tract,  consisting  of  the  axons  of  the 
large  pyramidal  cells  which  exist  in  the  motor  region  of  the  cerebral 
cortex  (see  p.  723)  passes  down  through  the  Ijrain  stem  in  a  ventral 
]iosition  to  the  base  of  the  bidb.  where  most  of  the  fibres  cross  to 
the  other  side,  forming  the  motor  decussation.  These  crossed  fibres 
come  to  occupy  within  the  spinal  cord  a  postero-lateral  position 
(Fig.  397).  They  gradual^  terminate  during  their  passage  doA^ai  the 
cord  around  the  cells  at  the  base  of  the  posterior  horn  (some  say 
round  the  cells  of  the  anterior  horn).  The  fcAv  uncrossed  or  direct 
fibres  pass  doAvn  on  the  margin  of  the  anterior  fissure  of  the  spinal 
cord ;  some  end  around  the  cells  of  the  same  side,  some  pass  across  the 
anterior  commissure,  and  end  around  the  cells  of  the  opposite  side. 

The  Bulr/O- Spinal  Tract  (or  jjrep;^^-^  midal  tract  of  Monakow). — 
The  fibres  of  this  tract  arise  from  the  cells  of  the  opposite  red  nucleus 
of  the  mesencephalon,  and,  crossing  in  the  mid-brain  (Forel's  decussa- 
tion), pass  through  the  pons  and  bulb  to  the  spinal  cord,  occupyhig 
therein  a  somewhat  triangular  space  just  anterior  to  the  crossed 
pyramidal  tract  (Fig.  397).  The  fibres  terminate  around  or  approximate 
to  the  anterior  horn  cells. 

The  Veslibulo-Spinul  Tract  (antero-lateral  descending  tract  of 
Loewenthal). — -This  consists  of  fibres  Avhich  arise  from  Deiters"  nucleus, 
situated  in  the  upper  part  of  the  medulla  and  lower  parts  of  the 
pons  varolii,  and  pass  down  into  the  spinal  cord  in  an  antero- 
lateral position,  mingling  to  a  certain  extent  with  the  fibres  of  the 
ventral  spino-cerebellar  tract.  It  constitutes  a  pathway  for  impulses 
which  pass  from  the  cerebellum  to  the  spinal  cord ;  its  fibres  end  by 
arborizmg  in  the  proximitj^  of  the  anterior  horn  cells. 

The  Olivo-Spinal  and  Thalamo- Spinal  Tracts  (tract  of  Helweg) 
occupy  an  antero-lateral  position  opposite  the  anterior  horn.  The 
fibres  pass  from  the  thalamus  by  waj^  of  the  inferior  olive  of  the  bulb 
into  the  cervical  region  of  the  spinal  cord,  where  they  gradually  dis- 
appear.    Their  destination  is  not  certainly  knoAvn. 

Fibres  which  pass  from  one  Part  of  the  Spinal  Cord  to  Another 
(Commissural  Fibres). — ^These  fibres,  of  which  there  are  many,  are  not 
grouped  into  very  definite  bundles.  Manj^  pass  up  in  the  lateral 
columns,  others  in  the  so-called  anterior  basis  bundle,  and  form 
connections  with  the  posterior  longitudinal  bundle. of  the  brain  stem; 
others  lie  posteriorly  near  the  postero-median  fissure,  and  form  what 
is  known  as  the  septo-marginal  tract. 


THE  SPINAL  CORD  671 

The  position  of  the  various  groups  of  cells  aud  of  the  above  tracts 
have  been  traced  by  various  means: 

1.  Wallerian  degeneration  (c/.  p.  663) :  If  a  nervous  lesion  be  made, 
.such  as  hemise<;tion  of  the  cord,  and  the  animal  kept  alive  a  sufficient 
time  for  the  nerve-fibre  to  degenerate,  the  path  of  the  degenerated 
hbres  is  then  easily''  traced  by  certain  methods  of  staining.  Thus, 
tv/o  or  three  weeks  after  such  a  lesion,  degenerated  fibres  stain  black 
with  Marchi's  fluid,  owing  to  degradation  of  the  myeline  and  setting 
free  of  oleic  acid.  At  a  much  later  stage  the  degenerated  fibres  do 
not  take  the  Weigert-Pal  stain,  while  normal  fibres  stain  deeply. 
The  pathological  investigation  of  clinical  cases  by  this  method  affords 
valuable  evidence,  especialh^  in  the  case  of  the  sensory  tracts,  where 
the  feelings,  etc.,  of  the  patient  have  been  carefully  investigated. 

2.  Method  of  retrograde  degeneration:  The  position  is  traced  of 
the  cells  which  show  chromatolysis  as  the  resvilt  of  a  nervous  lesion — 
e.g.,  section  of  an  anterior  root  about  three  weeks  before  death. 
The  degeneration  of  different  groups  of  cells  which  follows  amputa- 
tion of  the  leg  at  different  levels  points  to  a  definite  connection  of 
certain  groups  of  anterior  horn  cells  with  definite  muscles. 

3.  Histological  methods — such  as  the  silver  chromate  method  of 
Golgi,*  or  intra vitam  staining  with  methylene  blue.  Certain  neurons, 
wnth  their  processes,  are  picked  out  in  their  entiret}'. 

4.  The  myeUnation  method :  The  Weigert-Pal  method  differentiates 
the  myelinated  fibres  from  those  which  are  not  yet  myelinated.  The 
development  in  the  foetus  of  the  medullary  sheath  of  medullated 
nerves  takes  place  at  different  times  in  the  various  tracts.  It  occurs 
first  in  the  fibres  which  enter  the  cord  from  the  sj)inal  nerves;  next 
in  the  commissural  fibres  between  different  parts  of  the  spinal  cord; 
then  in  fibres  which  pass  from  the  sijinal  cord  to  the  cerebellum; 
and  last  in  the  tracts  which  pass  from  the  great  brain  to  the  spinal 
cord  (the  pyramids).     The  last  become  myelinated  after  birth. 

The  Neural  Arcs, — We  are  now  in  a  position  to  consider  the  chief 
neural  arcs  through  which  sensory  impidses  are  received,  transmitted, 
co-ordinated,  and  made  effective:  the  spinal,  cerebellar,  and  cerebral 
arcs. 

The  ingomg  fibres,  whose  end  processes  make  connection  with  the 
receptors  at  the  periphery,  pass  in  by  the  posterior  root,  in  the 
ganglion  of  which  their  cells  are  situated,  to  form  various  connections 
in  thespinai  cord.  The  chief  of  these  are  illustrated  in  Fig.  397.  and 
may  be  summarized  as — 

1.  With  the  posterior  horn  cells  of  the  same  side. 

2.  With  the  anterior  horn  cells  of  the  same  side. 

3.  With  the  posterior  liorn  of  the  opposite  side. 

4.  With  Clarke's  column  of  the  same  side. 

5.  With  the  lateral  horn  of  the  same  side. 

6.  With  segments  of  the  cord  higher  up,   and  with  the  gracile 

^  This  method  consists  in  hardening  the  uei-vous  tissue  in  potassium  chromate, 
and  soaking  it  in  silver  nitrate,  thereby  causing  a  deposition  of  silver  chromate  in 
the  nerve  coll  anfl  its  processes. 


672  A  TEXTBOOK  OF  [»HYSl()L()(;V 

and  cnmeate  nuclei  of  the  nicdiilla  throiiL'h  llic  postoro-inctliaii  and 
postero-lateral  columns. 

7.  With  other  segments  of  the  cord  lower  doAvn  ])y  the  coinina 
tract. 

The  Spinal  Arc. — This  arc,  in  its  sim])lest  plan,  may  be  regarded 
as  being  made  up  of  the  ingoing  afferent  fibre,  Avhich  ends  around 
the  anterior  horn  cell  of  the  same  side,  and  the  efferent  filjre  from 
this  cell.  It  is  probable  that  the  ingoing  neuron  ends  around  the 
T)osterior  horn  cells  of  the  same  side,  and  a  connecting  neuron  joins 
up  these  cells  to  the  anterior  horn  cells. 

The  Cerebellar  Arc — To  the  Gerebcllum. — Impulses  troju  the 
posteri(jr  root  neurons  reach  the  cerebellum  by  several  ways :  ( 1 ) 
On  the  same  side  by  processes  which  end  in  Clarke's  column,  and 
then  bv  the  neurons  of  this  eolmnn,  the  axons  of  which  form  the 
dorsal  spino-cerebellar  tract,  which  goes  to  the  superior  vermis  by 
way  of  the  inferior  peduncle.  (2)  On  the  opposite  side  by  means 
of  neurons  of  posterior  horn  cells,  axons  of  which  form  the  ventral 
spino-cerebellar  tract.  This  passes  to  the  superior  vermis  by  the 
superior  peduncle.  (3)  By  the  postero-median  and  postero-lateral 
columns  to  the  gracile  and  cuneate  nuclei  in  the  spinal  bulb,  and 
thence  bv  neurons  the  axons  of  which  pass  to  the  cerebelhim  by  the 
inferior  peduncle  (the  arcuate  fibres,  see  pp.  689,  6£0). 

From.  tJie  Cerebellum  axons  pass  to  Deiters'  nucleus,  which  lies  in 
the  upper  part  of  the  bulb,  and  is  connected  with  the  vestibular 
branch  of  the  auditor}'  nerve  (see  p.  698);  thence  by  the  vestibulo- 
spinal tract  to  the  spinal  cord.  Connection  with  the  spinal  cord  is 
also  made  by  way  of  the  posterior  longitudinal  bundle. 

The  Cerebral  Arc — To  the  Cerebrum. — (1)  The  axons  of  the 
posterior  root  neurons  pass  up  to  the  gracile  and  cuneate  nuclei  of  the 
bulb  bj^  the  postero-median  and  jDostero-lateral  columns;  (2)  the 
axons  of  the  neiirons  (the  intermediate  neuron)  of  these  nuclei  pass 
to  the  thalamus  by  a  tract  known  as  the  mesial  fillet;  (3)  the  axons 
of  the  third  relay  of  nem-ons  (the  upper  neuron)  pass  from  the  thalamus 
to  the  cortex. 

From  the  Cerebrum  by  the  cortico-spinal  (pyramidal)  fibres,  crossed 
and  direct,  to  the  anterior  horn  cells. 

Since  the  cerebellum  is  also  connected  with  the  cerebrum,  it  is 
iDOssible  for  impulses  from  the  spinal  cord  to  reach  the  cortex  via 
the  cerebellum,  and  also  to  pass  to  the  S]>inal  cord  from  the  cortex 
through  this  organ. 

The  Functions  oJ  the  Spinal  Cord. — The  chief  functions  of  the  spinal 
cord  are  to  act — (1)  as  a  reflex  centre;  (2)  as  a  conductor  of  impulses 
to  and  from  the  brain. 

The  Spinal  Cord  as  a  Conductor. — This  function  has  been  dealt 
with  in  the  description  already  given  of  the  position  of  the  various 
tracts.  It  remains  only  to  indicate  that  the  impulses  coming  into 
the  spinal  cord  from  the  exteroceptive  and  proprio-ceptive  mechan- 
isms vxndergo  a  redistribution  according  to  their  function  and  destina- 


THE  SPINAL  CORD 


673 


tion.  This  has  been  worked  out  hirgely  from  careful  clinical  observa  ■ 
tions  made  upon  patients  who  are  suffering  from  definite  cord  lesions, 
the  nature  of  the  lesion  in  each  case  being  determined  subsequently 
by  post-mortem  examination.  The  impulses  connected  with  pain 
€ross  at  once  to  the  opposite  side,  and  ascend  in  the  sj)ino-thalamic 
tract.  Thermal  impulses  do  not  cross  quite  so  soon,  but  take  a  very 
similar  course.  Tactile  impulses  pass  up  on  the  same  side  for 
four  or  five  segments  of  the  cord,  and  then  cross,  to  ascend  in  the 
anterior  region  of  the  cord.      Kinsesthetic  impulses,  concerned  with 

Homolateral  impulses  underhing  lu'isciilxi-  sensibility  (passive  positiuQ 
aud  of  movement),  also  jf  touch  and  pressme  for  a  few  segments 


Homo-lateiul 

•unconscious 

impulses 

iunderlying 

co-ordination 

.and  reflex 

muscular 

tone 


Hutero-latcial 
unconscious 
afferent  im- 
pulses under- 
lying muscular 
co-ordinatiuu 
and  reflex  cone 

All  impulses  of 
pain,  of  Iicat 
■  and  cold 
(hetero-Iat-ral) 


Impulses  of  touch  aud  pressure  (hetero-lateral) 

Fig.  398. 

I,  Fibres  in  po-^terior  column;  2,  fibres  in  Clarke's  column;  3,  fibres  to  cells  of  pos- 
terior horn;  4,  fibres  to  cells  of  anterior  horn;  .5,  fibres  to  cells  of  lateral  column: 
6,  dorsal  cerebellar  tract;  7,  ventral  cerebellar  tract;  8,  spino-thalamic  and  tcctal 
tracts;  9,  ascending  fibres  in  anterior  columns.  (W.  Page  ^lay,  bir  jiermission 
of  the  editor  of  Brain.) 


the  sense  of  passive  position  and  movement.  ]iass  up  in  the  postero- 
median and  postero-lateral  columns  of  the  same  side.  Impulses  con- 
cerned in  co-ordination  and  reflex  muscular  tone  which  do  not  enter 
into  consciousness,  pass  up  on  the  same  side  in  the  dorsal  spino- 
cerebellar, and  on  the  opposite  side  in  the  ventral  spino-cerebellar 
tract  (Fig.  398). 

The  Effect  of  Transverse  Secfio7i. — The  effect  of  transverse  section 
depends  according  as  it  is  partial  or  complete.  Section  of  one  half 
(hemi-section)  leads  to  a  loss  of  movement  on  the  same  side  as  the 
lesion  in  the  parts  supplied  by  nerves  arisiag  below  the  site  of  injury. 
It  also  leads  to  a  partial  loss  of  sensation  in  the  same  area.     The  kinges- 

43 


C74 


A  ^1  KXTBOOK  OF  PHV^SI()L()(;^' 


tlietic  and  tactile  sensations  are  niarlvediy  inipa.red,  wliile  tliose  of 
pain  and  teniperatxu-e,  which  cross  soon  after  entering  the  cord,  are 
but  little  aifected  (Fig.  386).  Degeneration  takes  place  on  the  side 
of  the  lesion  in  the  motor  tracts — e.g.,  the  pyramichd,  rubro-spinal. 

In  oom])lete  section — for  example,  in  the  thoracic  area — there  is 
paralysis  below  the  site  of  the  lesion  of  sensation  and  of  all  the 
vohmtar}'  muscles,  and  of  some  of  the  inv^oluntary,  on  both  sides  of 
the  body.  This  leads  to  a  total  loss  of  movement,  a  lowering  of  the 
blood-pressure,  and  loss  of  control  of  the  various  sphincters.  If  the 
section   be  made  high  up    in    tlie   cervical   region,    the   muscles   of 

respiration,  including  the  dia- 
phragm, are  paralyzed,  and 
death  results. 

In  the  spinal  cord  there  takes 
])lacc  an  upward  degeneration  in 
the  ascending  tracts,  and  a  down- 
ward degeneration  in  the  descend- 
ing tracts. 

The  Cord  as  a  Reflex  Centre. — 

In  addition  to  conducting  im- 
pulses to  and  from  the  higher 
parts  of  the  central  nervous 
system,  the  spinal  cord  acts  as  a 
reflex  centre.  Afferent  messages 
entering  the  cord  are  received, 
and  diverted  into  appropriate 
efferent  channels.  Such  reflexes 
are  regulated  by  a  certain  code,- 
Avhich  is  ai)plicable  to  all  the 
reflex  reactions  carried  out  by 
means  of  the  central  nervous 
system.  The  system  has  been 
most  conveniently  worked  out 
in  the  case  of  the  ■'  spinal  animal  " — that  is  to  say,  an  animal  in 
which  the  spinal  cord  is  separated  from  the  higher  parts  of  the  central 
nervous  system,  which  may,  or  may  not,  be  destroyed. 

Such  an  operation  at  first  results  in  '•  spinal  shock."  After  the 
familiar  operation  of  pithing  a  frog  without  destroying  the  spinal 
cord,  the  animal  lies  in  a  state  of  flaccidity,  irresponsive  to  any  form 
of  stimulus.  After  a  time  it  recovers  movement  of  the  hmbs,  and 
assumes  a  nearly  normal  sitting  position.  In  response  to  a  jDinch,  the 
hird-limb  is  drawn  away;  if  a  piece  of  paper  moistened  with  acid  be 
])lcced  on  the  side  of  the  belly,  the  animal  attempts  to  sweep  away  the 
irritant  by  movements  of  the  hind-limb  of  the  same  side  (Fig.  399), 
or,  if  the  stimulation  be  sufficiently  intense,  by  movements  of  the 
limbs  of  both  sides.  Placed  in  water,  the  animal  will  perform  swimming 
movements,  swimming,  however,  somewhat  more  deeply  than  usual, 
owing  to  the  head  being  held  in  a  lower  position  than  normal. 

With  higher  animals— e.gr.,  the  dog— the  effects  of  such  an  operation 


Fig.  :]99.— Showing  Reflex  Action  vy 

COKD      AFTER      REMOVAL      OF      EnTIUE 

Braik. 

The  beaker  contains  weak  siilpluii-ie 
acid. 


THE  SPINAL  COIU) 


675 


a  b 

Fig.  400. — .SaowiNu  Reflex  Action  .^fter  Removal  of  Brain. 
In  a  weak  acid  is  applied :  5  shows  reflex  efforts  at  removal  of  the  stimuluj 


Fig.  401. 

A,  The  recfptivo  tieid  for  the  scratch  reflex  as  revealed  after  low  cervical  transactiou, 

//•  marks  position  of  last  rib. 

B,  Diagram  of  spinal  arcs  involved.      L,  receptive  or  afferent  nervc-j^ath  from  left 

foot;  B,  receptive  nerve-path  from  opposite  foot;  Ra,  Fj3,  receptive  nerve-paths 
from  dorsal  skin  of  left  side;  FC,  the  Anal  common  path,  in  this  case  to  a  flexor 
muscle  of  th:*  hip;  Pa,  Pd,  proprio-s])inal  neurons.  (From  Sherrington's  "'In- 
tegrative Action  of  the  Xervous  System,"  by  permission  of  Yale  University 
Press  and  Messrs.  Constable  and  Co.,  Ltd.) 


076 


A  TEX  1  BOOK   OF   l'H^SlOLOGV 


lire  ccmsidcnibly  more  la.sling  and  nioic  tumplcx.  Below  the  site  f  f 
the  lesion  there  is  total  loss  of  sensation  in  the  skin,  the  skeletal 
muscles  are  inert  and  flabby,  the  8])hincters  are  toneless,  there  is 
increased  loss  of  heat,  and  the  arterial  ])rcssure  of  the  animal  falls 
from  40  to  50  mm.  Hg.  After  a  few  days  many  of  these  symptoms 
}iass  away.  The  arterial  pressure  rises  to  normal;  the  sphincters 
again  act,  so  that  urine  and  faces  are  passed  in  a  normal  manner; 
the  skeletal  muscles  recover  their  tone;  and  sensory  stimuli  applied 
to  the  skin  evoke  reflex  muscular  responses.  It  is  upon  such  an 
animal  that  the  code  of  reflex  actions  has  been  worked  out.  A  second 
section  of  the  cord  at  a  lower  level  does  not  renew  the  shock.     Tlio 


Tig.  402. 

.4.  Scratch  rcfusx  interrupted  by  a  brief  Mexion-rcflex.  The  time  of  applitation  of 
the  stimulus  evoking  scratch  reflex  is  shown  by  the  lowest  signal  line;  that  for 
iiexion-reflex  by  line  immediately  above.  Time  in  fifths.  The  scratc*h  reflex 
returns  with  increased  intensity  after  the  interruption. 

B,  Similar  to  A,  but  the  scratch  reflex  is  interrupted  later  and  returns  more  slovJy 
and  with  marked  irregularity  in  its  beat.  (From  Sherrington's  "  Integrativi- 
Action  of  the  Nervous  System,"  by  permission  of  Yale  University  Pr^ss  and 
Messrs.  Constable  and  Co.,  Ltd.) 


shock  is  caused,  then,  by  cutting  off  the  spinal  from  the  higher 
centres,  not  by  the  lesion  of  the  spinal  cord  itself.  The  chief  reflexes 
studied  have  been — 

1.  The  flexion  reflex.  A  harmful  stimulus  applied  to  the  hind-foot 
causes  the  withdrawal  of  the  foot  from  the  site  of  injury — an  actiwi 
often  accompanied  by  extension  of  the  opposite  hind-limb. 

2.  The  extension  reflex.  The  application  of  gentle  pressure  to 
the  pad  of  the  flexed  limb  induces  the  movements  of  extension  of 
that  limb,  and  of  flexions  of  the  opposite  limb — i.e.,  the  movements 
of  walkins  in  the  normal  animal. 


THE  SPINAL  CORD 


677 


o.  The  scratch  reflex.  Light  stimulation  of  the  "  saddle  "area calls 
forth  movements  corresponding  to  the  familiar  scratching  movements 
indulged  in  by  dogs  removing  a  tiea  or  other  irritant  from  this  area. 

The  first  point  to  be  observed  in  regard  to  such  reflexes  is  that 
a  given  .stimulus  always  evokes  the  same  response.  Thus,  a  pin-prick 
applied  to  the  foot  alway.s  evokes  the  flexor 
and  not  the  extensor  response.  The  reflex 
is  localized. 

Another  important  point  is  that  only  one 
reflex  can  have  charge  of  the  final  effector 
path  at  once.  Just  as  it  would  be  very 
embarrassing  if  the  telephone  exchange 
permitted  several  callers  to  speak  at  once 
down  the  same  final  transmitting  wire,  so 
would  it  be  if  various  afferent  calls  had 
possession  of  the  final  effector  path  at  the 
same  time.  All  kinds  of  inco-ordinate  move- 
ments Avould  be  evoked.  Any  such  inco- 
ordination is  therefore  prevented  by  the  law 
that  only  one  reflex  at  a  time  can  have 
charge  of  the  final  common  path.  This  is 
exemplified  as  follows:  If  the  stimuli"  in- 
ducing the  flexor  and  extensor  reflexes  be 
applied  to  the  foot  at  the  same  time,  one 
or  other  reflex  is  evoked,  and  not  a  com- 
bination of  the  reflexes.  The  same  final 
common  path  is  used  in  both  reflexes,  and 
is  taken  jjossession  of  by  the  stronger 
stimulus.  If  the  stimuli  be  of  equal  inten- 
sity, but  entering  different  levels  of  the  cord, 
then  there  is  a  further  code  of  rules.  For 
instance,  if,  while  the  animal  is  performing 
the  scratch  reflex  as  the  result  of  a  stimulus 
applied  to  the  saddle  area  (/?<i),  J^  stimulus 
of  equal  intensity  be  applied  to  the  scratch- 
ing foot  (L),  the  scratching  ceases,  and  the 
foot  is  Avithdrawn  from  the  harmful  stimulus 
applied  to  the  foot  (Fig.  402).  Or,  again, 
if,  during  the  performance  of  the  scratch 
reflex,  a  stimulus  be  applied  to  the  hind- 
limb  of  the  opposite  side  (B),  the  scratching 
ceases,  and  the  opposite  hind-limb  is  with- 
drawn out  of  harm's  way  (Fig.  4.03).  It  will  be  seen,  therefore,  that 
an  impulse  entering  the  same  segment  of  the  cord,  whether  from 
the  same  or  the  opposite  side,  has  priority-  over  an  impuls3  entering 
the  cord  in  a  more  remote  segment. 

So,  also,  can  it  be  shown  that  for  the  same  level  of  the  cord  an 
impulse  entering  the  same  side  has  priority  over  an  impulse  entering 
at  the  same  level  on  the  opposite  side. 


Ftu.  403.— Scratch  Re- 
flex    CUT     Short     by 

EXCITATIOX  OF  THE  SkIN 

OF  A  Digit  of  Opposite 
Hind  Foot. 

Below  upper  signal  mark 
mark-<  period  of  applica- 
tion uf  stimulus  to 
opi)ositc'  hind  foot;  lower 
signal  marks  application 

■of  stimulus  exciting 
scratch  reflex.  Time  in 
fifths  of  second.  (From 
Sherrington's  "  Integra- 
tive Actionof  the  Nervous 
Sy.stem,"  by  permission 
of  Yale  Univer.sity  Press 
and  Messrs.  Constable 
and  Co.,  Ltd.) 


(.78 


A  TKXTBOOK   OF  PHYSI;)Lo(;Y 


111  regard  to  the  nature  of  tlie  stimuli,  it  lias  been  found  that  the 
.stronger  the  stinndus  the  (|iiiei<er  the  response  (Fig.  4.04).  This  ean 
be  tested  u]ton  the  |)ithed  frog  Iw  vaiions  strengths  of  aeid,  as 
shown  in  Kig.  40;").  The  stronger  inipidse  obtains  possession  of  the 
final  common  path,  and  that  painful  stimuli  (nociceptive)  and  those 
evoking  sexual  feelings  are  more  potent  than  other  forms.  The 
strength  of  the  stimnlns  required  varies  according  to  the  length  of 
time  of  application.  Fatigue  takes  place  in  the  nerve-endings; 
therefore,  after  a  time,  a  stimulus  a])])lied  to  another  reflex  arc  may 
capture  the  final  common  ])ath. 


Fig.  404. — Efi-'ect  of  Intensity  of  Stimulxts  on  8ckat(.h  Kkflex. 

A,  Stimulus  is  very  weak;  one  small  beat  of  characteristic  .slowness  is  evoked  after 
long  latent  period.  B,  increase  in  intensity  of  shocks  with  resulting  shorter 
latent  time  and  a  reflex  movement  of  two  feeble  beats.  C,  further  increase  of 
intensity, of  stimulus;  latent  period  sliortcr  and  a  reflex  of  ten  fairly  quick  and 
ample  beats  ensues.  The  stimulus  lasted  less  than  a  half-second;  the  reflex  is 
'  not  completed  for  more  than  two  seconds  after  cessation  of  stimuhis.  (From 
Sherrington's  "  Integrative  Action  of  the  Nervous  System."  by  ])ermission  of 
Yale  University  Press  and  Messrs.  Constable  and  Co.:  Ltd.) 


There  is  one  exception,  however,  to  the  above  rules.  This  is 
when  the  stimuli  are  of  the  same  character  and  in  adjacent  areas. 
It  may  be  exemplified  as  follows:  If,  as  the  result  f)f  a  stimulus  in 
one  part  of  the  saddle,  the  animal  be  set  scratching,  then  a  similar 
stimulus  applied  in  an  adjacent  area  of  the  saddle  will  cause  an  in- 
creased sweep  in  the  scratching  movements,  so  that  both  irritants 
will  be  dealt  with  and  removed  at  the  same  time.  Similar  stimidi 
in  adjacent  areas  reinforce  one  another,  and  increase  the  general 
reaction. 

Another  important  point  to  be  notic(-d  in  such  reflex  responses  is 
that  there  is  reciprocal  excitation  and  inhibition  of  muscles  (Fig.  407). 
The  response  to  a  stimulus  is  not  simply  the  contra.ction  of  a  muscle  or 


THE  SPINAL  CORD 


()7r» 


group  of  muscles;  at  the  same  time,  the  antagonistic  mviscle  or  grou]> 
of  muscles  is  relaxed.  Thus,  when  the  flexors  contract  and  draw 
up  the  leg,  the  extensors  are  relaxed  (Fig.  407);  and  Avhen  the  ex- 
tensors extend  the  leg.  the  flexors  are  relaxed.  Each  movement 
is  brought  about  by  co-ordinate  contraction  of  one  group  of  muscles 
and  relaxation  of  the  antagonists.  On  this  depends  the  perfect 
balance  of  the  movements  of  a  technician  or  musician. 

In  the  body,  it  is  difficult  to  get  a  reflex  which  does  not  either 
a.ntagonize  or  reinforce  other  reflexes.  This  is  Avell  illustrated  by 
Fig.  409.  Here  the  final  motor  neuron  is  that  to  the  vasto-crureus  of 
the  dog.  It  is  excited  by  stimulation  of  the  ear.  fore-foot,  tail,  and 
])ressure  on  the  pad  of  the  foot  of  the  same  side,  and  by  stimulation 
of  the  shoulder  and  nocuous  stimuli  to  the  hind-foot  of  the  opposite 


""''"i  Li: 


show  that  as  the  strength  of  acid  is  increased  the  reflex  is  more  quickly  performed. 
The  beakers  contain  respectively,  from  left  to  right,  O-l,  0-2,  0'3,  0*4,  Ov"),  and 
1  per  cent,  sulphuric  acid. 


side.  It  is  inhibited  b}"  stimulation  of  the  shoulder  of  the  same  side 
(the  scratch  reflex),  and  by  nocuous  stimuli  of  the  hind-foot  of  the 
same  side. 

Not  only  do  sensory  stimuli  (the  extero-ceptive  mechanism)  react 
upon  the  reflexes  of  the  bod}-,  but  the  impulses  which  arise  from  the 
muscles  themselves  and  from  the  joints  and  tendons  (the  proprio- 
ceptive mechanism),  and  from  the  viscera  (the  entero-cej^tive  mechan- 
ism), also  play  a  part  in  determining  the  effector  nature  of  reflexes. 

The  chief  points  in  connection  with  spinal  reflex  action  may  be 
summarized  as  follows : 

1.  Reflexes  are  lo^al.zed,  definite,  and  purposive. 

2.  Owing  to  the  interposition  of  synapses  in  the  course  of  the 
reflex  arcs,  there  is  marked  delay  in  the  rate  of  conduction  therein, 
A«  compared  with  the  rate  of  conduction  in  nerVe.     The  synapses  also 


<;S0  A  TEXTB()(JK  OF  PHYSIOLOGY 

exert  a  valve-like  action,  so  that  conduction  manifests  itself  in  one  direc- 
tion only .  The  spiapscs  also  offer  a  varying  degree  of  resistance  to  the 
im]uilse,  so  that,  generally,  a  reflex  is  localized ;  but  inider  the  influence 
of  certain  [joisons,  .such  as  strychnine,  a  slight  stimulus  will  evoke  tonic 
nuiseular  spasms  over  the  whole  body. 

3.  In  the  reflex  arc  there  is  a  summation  of  stimuli ;  a  succession 
of  stimuli,  each  of  an  intensitj-'  insufficient  to  evoke  a  response  when 
ajiplied  alone,  will  eventnally  provoke  a  response. 

4.  Excessive  stimulation  leads  to  a  fatigue  in  the  synai)ses,  whicli 
occurs  princi^mlly  in  tlie  connection  between  the  nerve  and  the  effector 
organ. 


Via.  406. — iStitATfH  Reflex  evoked  bv  a  Relatively  Feeble  Stiaujlation  and 
iJiSAPrKAfayG  xinder  that  Stimulation. 

( )i^  increasing  the  intensity  of  the  stimulns  the  reflex  reappear.';.  It  does  not  r. 'appear 
on  reveiting  to  the  original  intensity  of  stimulation.  Time  in  seconds.  {From 
Sherrington's  "Integrative  Action  of  the  Nervous  System,"  by  permission  of 
Yale  University  Press  and  Messrs.  Constable  and  Co., 'Ltd.) 

5.  When  fatigue  is  not  evoked  by  too  frequent  transmission  of 
an  impulse,  it  is  found  that  subsequent  impulses  call  forth  a  reaction 
more  easih'.  This  "  facilitation,"  as  it  is  termed,  is  really  the  basis 
of  habit.  By  facilitation,  good  habits,  if  sufficiently  repeated,  obtain 
preference  over  bad  ones,  if  these  are  not  often  repeated.  Training 
C(Misists  largety  in  the  proper  adjustment  of  the  necessary  reflexes, 
and  in  this  the  law  of  facilitation  takes  a  great  jjart.  The  whole  of 
education  consists  in  the  obtaining  of  facilitation  for  fit  paths,  and  in 
the  inhibition  of  unfit  ones. 

0.  iSucli  inhibition  is  a  law  of  reflex  action.  Only  one  impulse 
can  have  possession  of  the  final  common  path  at  the  same  time,  unless. 


THE  SPINAL  CORD 


08 1 


it  be  of  a,  aimilar  nature.      Stimuli  of  a  harmful  or  sexual  nature  aro 
the  most  potent  in  obtaining  command  of  the  final  common  path. 

The  spinal  cord  has  already  been  referred  to  as  the  reflex  centre 
concerned  in  micturition  and  movements  of  the  large  intestine.     In. 


Fiii.  4:07. — Uial;i:\m  imjicatixo  Conxkctions  axu  .Actiuxs  of  Two  Afferent 
Spinal  Root  Cells  (a  axd  c)  ix  Regaed  to  their  Reflex  Influence  on  the 

EXTENSOPv   AXD   FlEXOK   MuSCLES   OF   THE   TwO   KXEE?. 

a,  Aiferenc  fibre  from  skin  below  knee;  a',  afferent  from  flexor  muscle  of  knee — i.e., 
in  ham.string  nerve;  e  and  e',  efferent  neurons  to  extensor  muscles  of  the  knee, 
loft  and  right;  5  and  5',  efferent  neurons  to  flexor  muscles;  E  and  E',  extensor 
muscles;  F  and  F',  flexor  muscles.  The  sign  +  indicates  that  at  the  synapse 
which  it  marks  the  afferent  fibre  a  (and  a')  excites  the  motor  neuron  to  dis- 
charging activity,  the  sign  —  indicates  that  at  that  synapse  the  afferent  fibre  a 
(and  a')  inhibits  the  discharging  activity  of  the  motor  neurons.  The  effect  of 
strychnine  and  tetanus  toxin  is  to  convert  —  into  +.  (From^  Sherrington's 
•'  Integrative  Action  of  the  Nervous  System,'"  by  permission  of  Yale  University 
Press  and  Messrs.  Constable  and  Co.,  Ltd.) 


di.seases  of  the  si)iiial  cord  affecting  these  centres,  these  processes 
will  be  impaired.  It  also  contains  the  centres  controlling  the  erection 
of  the  penis  and  the  ejaculation  of  the  seminal  fluid.  The  spmal 
cord  is  also  normally  concerned  in  the  process  of  parturition.     It  is- 


(582 


A  TEXTBOOK  OF  imYSlOLOGY 


•possible,  however,  for  this  to  take  place  when  the  influence  of  the 
cord  is  removed. 

The  condition  of  the  s])inal  coi'd  is  investigated  in  man  by  <he 
study  of  certain  su)ierficial  or  true  reflexes,  and  of  certain  tendon  or 


I 


FiLJ.  408. 

A  a.nd^B,  The  llcxion-reflcx  observed  as  a  rcHex  contraction  (A)  of  the  Uexor  luuscL' 
of  the  knco  and  as  a  reflex  relaxation  (B)  of  the  extensor  muscle  of  the  knee. 
The  intensity  of  the  stimulating  shocks  was  feeble,  hence  the  relatively  long 
latent  period.  Time  in  -^^  second  above  and  in  seconds  below.  (From  Sher- 
rington's "  Integrative  Action  of  the  Nervous  System,"  by  j)ermission  of  Yale 
University  Press  and  Messrs.  Constable  and  Co.,litd.) 

deep  reflexes.  An  example  of  the  true  reflex  is  the  plantar  reflex. 
If  the  finger  be  drawn  along  the  sole  of  the  foot  of  a  normal  individual, 
the  foot  is  drawn  away;  if  the  stimulation  be  gentle,  the  big  toe  in 
the  adult  is  tiunied  downwards.  In  certain  cases  of  organic  nervous 
disease  the  l)ig  toe  is  turned  upwards  (the  extensor  response).  This 
IS  known  as  Babinski's  sign. 

Other  superficial  reflexes  are — (1)  The  conjunctival,  closing  the  eye, 


THE  SPINAL  CORD 


()83 


evoked  by  touching  the  conjunctiva;  (2)  the  pupil  reflexes,  by  throwing 
light  on  the  eye,  or  getting  the  subject  to  accomniodate  by  looking 
At  a  near  object. 


b'--  ^ 


Pig.  409. — To  show  Interaction  of  Certain  (iRonps  of  Reflex  Paths  upon  the 
Final  Common  Path  [FG). 

S,  Scratch  recsptor;  c  and  /  are  nxtensor  and  flexor  muscles  of  Itnee  respectively. 
Reflexes  that  act  as  allied  reflexes  on  FC  are  represented  as  having  their  ter- 
minals joined  together.  Reflexes  with  excitatory  effect  ( + )  are  brought  to- 
gether on  the  left,  those  with  inhibitory  (■ — )  on  the  right.  (From  Sherrington's 
"  Integrative  Action  of  the  Nervous  System,"  by  ]ierraission  of  Yale  University 
Press  and  Messrs.  Constable  and  Co..  Ltd.) 


Various  other  reflexes  may  also  be  evoked.  Such  reflexes  show 
that  the  reflex  ar,.^  concerned  is  intact.  If  there  be  no  response, 
then  there  is  damage  to  the  arc  iu  some  part  of  its  course. 


(584 


A  TEXTBOOK   OF   PHVSIOLOOV 


Tendon  reflexes,  of  which  the  knee-jerk  is  an  example,  are  not 
usually  regarded  as  true  reflexes.  They  are  elicited  by  placing  a 
muscle  on  the  stretch,  and  sharply  striking  the  tendon.  As  a  result, 
the  muscle  contracts.  In  the  knee-jerk,  the  quadriceps  extensor  is 
stretched  by  placing  one  knee  over  the  other.  The  patellar  tendon 
of  the  upper  knee  is  then  sharply  struck,  preferably  when  the  subject's 
attention  is  diverted.  As  a  result,  the  foot  is  jerked  up  by  the  sudden 
contraction  of  the  quadriceps  nnisole. 

The  value  of  this  "  reflex  "  is  that  it  shows  the  condition  of  the 
reflex  arc  which  supplies  the  quadriceps  extensor.  If  it  be  not  intact, 
the  muscle  is  toneless,  and  there  is  no  response.  An  excessive  re- 
sponse indicates  that  the  cerebral  control  of  the  reflex  is  missing. 
The  knee-jerk  is,  therefore,  of  great  clinical  value.     It  has  been  taught 


Fir.  410.— Fkog  with  8ti;vchkine  CoNvtrLSiON.s. 


that  it  cannot  be  a  true  reflex,  on  the  grounds  that  the  time  occupied 
between  the  striking  of  the  blow  and  the  muscular  response  is  too 
short  for  an  impulse  to  have  travelled  into  the  cord  and  out  again  to 
the  quadriceps  muscle.  Reflexes  as  short  are,  however,  now  considered 
j)ossible,  and  the  knee-jerk  may  be  regarded  as  an  example  of  a  true 
reflex. 

Another  tendon  reflex  which  is  often  investigated  is  that  known 
as  "  ankle  clonus."  This  is  evoked  by  bending  the  subject's  knee 
slightly  while  supporting  it  with  one  hand.  With  the  other  hand 
the  fore-part  of  the  foot  is  suddenly  "  dorsiflexed,"  and  the  pressure 
maintained.  As  a  result  of  the  sudden  strain,  the  calf  muscles  may 
contract  and  then  relax;  but  as  the  result  of  the  continued  jwessure 
contract  again,  and  so  on,  the  result  being  that  a  series  of  contractions, 
or  "  clonus, 'Vresults.     Ankle  clonus  is  nearly  always  a  sign  of  disease. 


CHAPTER  LXXIII 

THE  BRAIN 

The  central  nervous^system  is  formed  in  the  foetus  by  an  infolding 
of  the  epiblastic  layers.  At  the  anterior  end  of  the  nervous  tube 
thus  formed  the  brain  becomes  developed.  This  is  the  end  of  the 
animal  which  normally  progresses  forwards,  and  it  is  here,  therefore, 
that  develop  the  special  sense  mechanisms  which  serve  to  protect 
the  animal.     This  end  of  the  neural  tube  becomes  thibkened,  and 

rudiment  of  cerebellum 
inf.  med.  uel. 


ceph.  flex. 


ligula 

obex 
nuchal  flex. 


olf  lobs 


restiform  body 


Fia.  411. 


-Lateual'View  of  Cephalic  Part  of  Neural  Tube  in  a  Fifth-Week 
HvMAX  Embryo.     (Keith,  after  His.) 


enlarges  to  form  three  primary  cerebral  vesicles— the  prosencephalon, 
mesencephalon,  and  rhombencephalon.  The  first  and  third  of  these 
again tiivide,  so  that  we  have  eventuall}'  five  primar}''  parts: 


First  primnry  vesicle 


Second  'primary  vesicle  : 
Third  primary  vesicle : 


The  pros-encephalon  (fore-bram). 
The  di-encephalon,  or  thalam- 
encephalon  (between-bra'n) . 
The  mes-encephalon  (mid-bram). 
The  met-encephalon  (hind-brain). 
The  myel-encephalon  (after-bram). 


The  myelencephalon  becomes  developed,  to  form  the  spinal  ))iilb. 
The  bulb  connects  the  spinal  cord  with  the  rest  of  the  brain. 

From  the  metencephalon  develops  the  little  brain,  or  cerebellum, 

685 


686 


A  TEXTBOOK  OF  PHYSIOLOGY 


and  the  pons.     The  cerebellum  lies  dorsally  to  the  pons,  which  bridges? 
its  two  hemi.s]tlicict;,  covering  the  brain-stem  as  it  ascends  from  the 

roof  plate  pineal 


optic,  thalam, 
caudate  nucleus 

cereb.  vesicle 
for.  ^onro 


lam.  terminalis 
olfact  lobe 

nose 


mid  brain 
quad. 


sulcus  of  Monro 
Corp.  mam. 
Injpothalam.  part  3rd  vent 
tuber  ciner. 
-notoch. 
neural  part  of  pituitary 
buccal  pituitary 
'phar. 

Fig.  412.— !^(,'Hematic  Figure  to  .snow  tjie  Parts  derived  from  the  Walls  of 
THE  Fore-Bkain.     (Keith,  after  His.) 

bulb  to  mid-brain.  In  the  region  of  the  bulb  and  pons,  the  central 
canal  of  the  spinal  cord  opens  out,  to  form  the  lozenge-shaped  fourth 
ventricle  of  the  brain. 

The  mesencephalon  consists,  in  the  adult  brain,, 
mainly  of  the  limbs  (crura)  of  the  great  brain,  and 
the  four  bodies  known  as  the  corpora  quadrige- 
mina.  Through  it  runs  the  central  canal,  here 
known  as  the  aqueduct  of  Sylvius.  The  optic 
lobes  of  the  lo\\'er  animals  are  associated  with  this 
part  of  the  brain. 

The  diencephalon,  or  thalamencephalon,  de- 
velops into  the  optic  thalami  and  the  parts  en- 
closing the  third  ventricle  of  the  brain.  From 
the  primary  vesicle,  of  which  this  is  the  hinder 
part,  there  arise  lateral  expansions — ^the  optic 
vesicles,  which  go  to  form  the  retinae  and  optic 
tract  of  the  adult  animal.  These  form  close  con- 
the  oj)tic  thalami  and  with  the 
corpora  quadrigemina  of  the  mid-brain. 

The  prosencephalon  expands  forwards  and 
downwards  at  first,  and  then  from  the  lateral 
aspects  large  hollow  outgrowths  arise — the  cerebral 
hemispheres.  The  dorsal  and  lateral  walls  of 
these  hemispheres  become  greatly  thickened  internally  with  white 
matter,  and  externally  with  a  grey  cortex,  and  thus  the  great  brain 


Fig.  413. — Diaqkaiw 
of  the  Frog's 
Brain. 


1, 


Olfactory     lobo ; 
2,    cerebrum  ;      3, 

tSaLiSphalon';  nections  with 
5,  optic  lobe;  0, 
cerebellum;  7, 
fourth  ventricle 
and  medulla  ob- 
longata. 


THE  BKAL\ 


()87 


is  formed.  This,  in  man,  is  greater  than  all  the  rest  of  the  brain. 
They  enclose  the  expansions  of  the  central  neural  canal,  known  as 
the  lateral  \-eutricles.  The  olfactory  bulbs  are  outgrowths  from  thk 
part  of  the  t)rain. 


Fig.  4!4.— SHon  ings  the  Positiox  assumed  by  Frog  after  Removal  of  Cerebual 

Lobes. 

Voluntary  mov.n'^nt  is   lost.     When  the  mid-brain  is  removc-d   the  fro"  cannot 

control  its  movc-racnts. 


The  cerebral  hcniispheros  are  the  latest  outgrowths  to  be  developed, 
and  arc  especially  marked  in  the  primates  and  man.  In  the  lower 
animals,  on  tht^  othci'  hand,  the  thalamencephalon  and  mesencephalon 
are  more  developed,  parts  which  are  connected  with  primitive  sensa- 
tions and  eiU'-rjons  rather  than  judgments. 


Po  :iH')W  the  Dissection  for  Removal  in  the  Frog  of  the  Foke-Bkain- 
(a)  AND   THE   OrTic   LOBES  (6). 


Fiu. -115 

After  removal  of  those  the  flap  of  skin  iiiay  be  stitched  in  });>sition  again. 


In  the  Lower  vertebrates,  the  brain  is  formed  h\  the  enlargement 
of  the  anterior  end  of  the  spinal  cord,  and  bj-  the  widening  and  division 
of  the  central  canal  to  form  ventricles.  Upon  this  primitive  brain- 
stem are  developed  swellings  in  connection  with  the  senses  of  most 
importance  to  these  lower  forms — namel}',  the  sense  of  smell  and  the 
sense   of   sight.     Usually,   one   or  other  of  these   is   predominantly 


-688  A  TEXTBOOK  OF  PHYSIOLOGY 

developed.  The  brain  of  the  frog  is  seen  in  Fig.  413.  In  reptilia, 
the  brain  is  long  and  narrow,  much  increased  in  size.  It  begins  to 
show  marked  differentiation  with  the  apjoearance  of  the  neopallium — 
the  higher  cortex,  or  brain  proper. 

In  birds,  the  brain  is  broad  and  highly  developed,  the  greatest 
development  being  in  the  sizs  of  the  striate  bodies  (corpora  striata). 
The  thalamus  and  optic  lobes  are  also  highty  organized. 


Fig.  416. — Position  assumed  by  Frog  after  Removal  of  the  Entire  Bkain:  It 
LIES  Limp  and  Flaccid. 

The  fmiction  of  the  brain  may  be  studied  on  the  frog.  If 
the  cerebral  hemispheres  be  destroyed,  preferabty  by  forceps  by 
dissection,  and  the  bleeding  stopped  by  wax  (Kg.  414),  the  frog, 
when  the  shock  has  passed  off,  will  exhibit  spontaneous  movements 
such  as  swimming  when  placed  in  water,  and  turning  over  if  placed  on 
its  back.  If  the  corpora  striata  and  optic  thalami  be  destroyed,  the 
shock  is  greater,  but  the  animal  on  recovery  can  still  jump,  swim, 
climb  an  inclined  board,  and  maintain  its  equilibrium.  If  the  cere- 
bellum and  medulla  oblongata  are  destroyed,  the  power  to  maintain 
equilibrium  vanishes,  and  the  respiratory  movements  of  the  nares  and 
of  the  floor  of  the  mouth  cease.  The  animal  lies  in  a  listless  condition 
(Fig.  416),  but  still  shows  co-ordinated  movements  Avhen  stimulated, 
since  the  spinal  cord  is  still  intact. 

Section  I 

THE  MEDULLA  OBLONGATA  AND  PONS  VAROLII 

The  Medulla  Oblongata. — ^The  medulla  oblongata  may  be  regarded 
as  the  expanded  upper  end  of  the  spinal  cord;  indeed,  it  is  sometimes 
termed  the  spinal  bulb.  In  this  region,  the  central  canal  gradually 
becomes  more  superficial,  and  eventually  opens  out,  to  form  part  of 
the  fourth  ventricle.  On  either  side  of  the  middle  line  posteriorly 
there  are  seen,  at  the  lower  end  of  the  medulla,  prominences  which 
represent  the  terminations  of  the  posterior  cohunns  of  the  cord.  Each 
postero-median  column  ends  in  a  prominence  on  either  side  of  the 
middle  line,  known  as  funiculus  gracilis,  each  postero-lateral  in  a 
more  laterally  placed  funiculus  cuneatus.  Prominent  in  the  mid-line 
anteriorly  are  the  pyramids,  which  are  composed  of  the  pyramidal 
fibres  coming  from  the  cortex,  and  have  not  yet  crossed.  The  decus- 
sation of  these  fibres  takes  place  at  the  lower  end  of  the  medulla. 


THE  BRAIN 


689 


The  lateral  columns  of  the  spinal  cord  pass  outwards  to  the  cere- 
bellum, forming  its  inferior  jjeduncles,  or,  as  they  are  also  calbd, 
the  restiform  bodies.  Between  the  lateral  and  anterior  columns  there 
is,  on  either  side,  an  oval  swelling,  known  as  the  olive. 

Sections  of  various  levels  of  the  medulla  reveal  important  changes, 
as  compared  with  the  cord.  It  is  seen  that,  as  the  result  of  two 
decussations,  the  central  canal  is  set  backwards  and  gradually  opens 
out  into  the  fourth  ventricle,  and  that  the  grey  matter  of  the  cord 
becomes  broken  up  and  scattered.  New  groups  of  grey  matter  also 
make  their  appearance.  The  chief  groups  of  grey  matter  are — 
(1)  The  nuclei  of  the  posterior  columns — the  nucleus  gracilis  and 
cuneatus,  on  either  side,  at  the  lower  level  of  the  medulla  (Fig.  418); 


MCrR 


St.A 


Fig.  417.-  The  Fouuth  Ventkicle.     (Parsons  and  Wright.) 

S.C.Q.,  Superior  corpora  quadrigomina ;  I.C.Q.,  inferior  corpora  quadrigemina ;  F, 
fillet;  S.Cr.P.,  superior  cerebellar  peduncle;  M.Cr.P.,  middle  cerebellar  peduncle; 
CI.,  Clava;  F.C.,  funiculus  cuneatus;  F.G.,  funiculus  gracilis;  E.T.,  Eminenti  i 
teres;  S.F.,  superior  fovea;  St.A.,  striae  acusticpo;  T.A.,  trigonum  acustici; 
I.F.,  inferior  fovea;  T.H.,  trigonum  hypoglossi;  T.V.,  trigonum  vagi. 


(2)  the  inferior  olivary  nucleus.!,  which  makes  its  appearance  in 
the  mid-level  (Fig.  -119);  (3)  the  nuclei  of  the  cranial  nerves,  the 
twelfth  to  the  ninth  appearing  from  below  upwards  at  various 
levels. 

The  Nuclei  of  the  Posterior  Columns. — Around  the  cells  of  the 
gracile  nucleus  end  the  fibres  which  ascend  in  the  postero-median 
column  of  the  cord  (Goll) ;  around  those  of  the  cuneate  nucleus  those 
of  the  postero-lateral  column  (Biuxlach).  From  the  cells  of  these 
miclei  arise  fibres  which — (1)  pass  inwards  and  cross  the  middle  line, 
to  ascend  as  the  mesial  fillet  (Fig.  419);  (2)  pass  inwards  and  upward;! 
on  the  same  side  to  the  cerebellum  by  the  restiform  body — the  internf  i 

44 


Gitd  A  TEXTBOOK  OF  PHYSIOLOGY 

arcuate  fibres  (Fig.  418);  (3)  deeply  inwards  across  the  median  raphe,, 
to  become  external  on  the  ventral  aspect  of  the  medulla,  pass  thence 
superficially  around  the  medulla,  to  enter  the  cerebellum  by  the 
inferior  j)edinicle — the  external  arcuate^fibres  (Fig.  418). 

The  inferior  olive  is  a  characteristically  shaix'd  mass  of  grey  matter. 
From  its  cells  li})res  pass  to  the  cerebellum  by  the  inferor  pedmicle 
of  the  same  side,  but  chiefl}'  by  that  of  the  opposite  side — the  olivo- 
cerebellar fibres. 

Funiculus  gracilis  "  '  "_ 

Postero-mediaii  fissure  '" 

l-'uniculus  cuneatus 
Nucleus  gracilis      ~ 


Desjendiug  root  of  fifth 

Bundle  from  funiculus, 

cuneatus 


.Ji..-- 


Substantia  Rolandi' — , 


liundle  of  Flechsig  _1 

Pyramid  tract  bundles — V — 


I  )ocussation  of  pyramids - 


'^P^-: 


■.,^ 


Caput  of  anterior  horn  — — 


Antero-median  tissun 


\ 


Fkj.  -il8. — Section  across  the  Loweu  Paut  or  the  Metiulla  OBLoNCiATA  in  the 
Middle  of  the  Decussation  of  the  Pyramids.  MACiNiFiED  about  G  Dia- 
meters.    (E.  A.  Scha-fer,  from  "  Quain's  Anatomy.") 

Cranial  Nerves. — The  cranial  nerves  do  not  conform  to  the  spinal 
arrangement  of  an  anterior  and  posterior  root,  the  tAvo  forming  a 
'■  mixed  "  nerve.  Some  of  the  cranial  nerves  consist  almost  wholly 
of  motor  or  effector  fibres.  In  most  of  the  nerves  the  fibres  are  somatic ; 
in  certain  nerves  there  are  splanchnic  fibres  also. 

The  cell-stations  of  afferent  nerves  are  situated  in  ganglia,  cor- 
res2)onding  to  j^osterior  root  ganglia,  on  the  course  of  the  nerve  outside 
the  central  nervous  system.  The  effector  fibres  arise  from  groups  of 
cells  or  "  nuclei ''  corresponding,  in  the  case  of  somatic  fibres,  to  the 
anterior  horn  cells,  and  of  splanchnic  fibres  to  the  lateral  horn  cells 
of  the  spinal  cord. 


THE  BRAIN 


691 


The  Twelfth  Nerve,  or  Hyjjoglossal. — This  is  a  purely  motor  nerve 
siipplj'ing  the  muscles  of  the  tongue.  It  arises  from  a  nucleus  of  grey- 
matter  situated  dorsally  close  to  the  middle  line  (Fig.  419).  The  nerve 
passes  ventrally  outwards.  ii 

The  Eleventh  Nerve. — Anatomically,  this  nerve  consists  of  two 
parts — the  spinal  and  the  accessory  portions.  The  accessory  portion 
arises  from  the  medulla,,  and  is,  in  reality,  a  part  of  the  tenth  nerve. 
It  arises  from  the  same  nucleus  as  part  of  the  tenth  nerve  (Fig.  419), 
and  supjilies  splanchnic  fibres,  which  run  eventually  in  the  tenth 


\estibular  nucleu 

Uenc.  fibres  of  vestib 

Dorsal  nucleus 
tenth 

Fascic.  solitiU- ^ 

Restiform  body 5. 

X-icleus  of  twelfth 


Subst.  gelat. 
I  lesc.  voot  of  fifth 
Subst.  gelat.  - 

Xuel.  ambig.  - 

I--suing  fibres  of 
tenth 


ksuiii^  fibres  of  twelfth  — ^ 
Uiiphe  


Thalamo-olivary  tract 
Hilus  oliva; 

( )livary  nucleus 
Kxt.  arouate  fibres 


Fibi-es  of 
twelfth  and 
-  po.sterior 
longitudinal 
bundle 

Anterior 
-Jongitudinal 
liundle 


Pyramid 
Arcuate  nucleu 


Til..  4] 9. — Sectiox  across  the  Medull.\  Oblongata  at  about  the  Middle  of 
THE  Olivaby  Body.  jMagxified  6  Diameters.  -(E.  A.  Scba^cr,  from  "  Quain's 
Anatomy.") 


nerve.  These  fibres  are  chieflj"  cardio-inhibitory  and  visccro-motor. 
The  spinal  fibres  supply  two  muscles — the  trapezius  and  the  sterno- 
mastoid. 

The  Tenth  Nerve  {the  Vagus,  or  Pnoumogastric). — This  is  composed 
of  afferent  and  efferent  fibres — somatic  and  splanchnic.  The  afferent 
fibres  have  their  cell-stations  in  the  ganglia  of  the  trunk  and  root. 
The  ingoing  fibres  from  these  bifurcate  after  the  manner  of  posterior 
root  fibres.     The  upgoing  branches  are  short,  and  end  around  cells 


<)i)2 


A  lEXTBOOK  OF  PHYSIOLOGY 


known  as  the  jirincipal  nucleus  (Fig-  419).  The  descending  fibres 
(corresponding  to  the  comma  tract  of  the  cord)  are  longer,  and  pass 
into  a  tract  of  fibres  knoAvn  as  the  funiculus  solitarius  (Fig.  419). 
In  this  tract  also  run  corresponding  fibres  from  the  ninth  nerve,  and 
the  intermediate  nerve  of  Wrisberg. 

The  efferent  fibres  arise  chiefly  from  the  so-called  nucleus  ambiguus 
■(Fig.  419),  and  also  from  the  upper  part  of  the  same  nucleus  as  the 
eleventh  nerve.  The  afferent  sensations  brought  u])  bj^  the  tenth 
nerve  are  concerned  with  the  respiratory  and  circulatory  systems. 
Impulses  from  the  superior  laryngeal  nerve  inhibit  inspiration,  and 
bring  about  expiration  and  coughing.     Those  from  the  lung  alveoli 


Optic  ., 

Chiasma 


Optic 
Tract 

Crus . . . 
Cerebri 


{Olfactory  Bull?) 


(Optic  Ner^'e) 


I'iG.  420. — Anteko-Inferior  View  of  the  Crura,  Poks,  and  Bulb  (Diagka.-mmatic), 

TO  ILLUSTRATE  THE  SUPERFICIAL  ORIGIN  OF  THE  CRANIAL  KeRVES. 


regulate  the  depth  and  frequency  of  inspiration,  and  possibly  also  of 
expiration  (see  p.  296).  Those  from  the  heart  (depressor  nerve), 
which  generally  run  in  the  vagus,  go  to  the  vaso-motor  centre,  and 
reflexly  bring  about  a  fall  of  arterial  pressure,  owing  to  vaso-dilata- 
tion  especially  in  the  splanchnic  area.  Other  fibres  of  the  vagus 
have  a  pressor  effect,  and  cause  a  rise  of  arterial  pressure.  Central 
stimulation  of  this  nerve  also  brings  about  reflex  inhibition  of  the 
heart. 

The  effector  functions  of  the  vagus  nerve  may  be  summarized  as 
motor  to  the  levator  palati,  the  constrictors  of  the  pharynx,  the 
muscles  of  the  larynx,  and  to  the  smooth  muscle  of  the  bronchi 
and  bronchioles,  to  the  muscles  of  the  walls  of  the  oesophagus,  stomach, 


THE  BRAIN 


093 


and  small  intestine.     It  is  inhibitory  to  the  heart,  and  secretory'  to  the 
glands  of  the  stomach,  and  possibly  of  the  pancreas. 

The  Ninth  Nerve,  or  Glosso-Pharytigeal  Nerve,  is  essentially  au 
afferent  nerve,  the  cell-stations  of  its  fibres  being  the  jugular  and 
petrosal  ganglia.  The  ingoing  branches  from  the  ganglia  branch, 
on  entering  the  medulla,  passing  slightly  upwards  to  the  cells 
constituting    the    ninth    nucleus,  and  downwards    in    the    fasciculus 


Fig.  421. — Diagram  to  illustrate  the 
Position  or  the  Bulbar  Nuclei  of 
the  Cranial  Nerves. 

Posterior  aspect  of  the  fourth  ventricle 
exposed  by  removal  of  the  pons  and 
cerebellum.  Motor  nuclei  indicated 
bj'  horizontal  lines,  sensory  nuclei  ))j' 
dots.  Median  group  of  motor  nuclei, 
///,  IV,  17,  XII.  Lateral  group  of 
motor  nuclei,  V in,  VII,  X,  XI.  Sen- 
sorv  nuclei.  Is,  VIII,  IX. 


Cora 


I'lu.  422. — Lateral  View  of  the  Kight 
Half  of  the  Bulb  and  Pons  exposed 
BY  A  Vertical  Section,  and  imagined 
AS  Transparent.     (After  Ert).) 

In  tliis  view  the  lateral  group  of  motor 
nuclei.  Vm,  VII,  X,  XI,  lie  farth-r 
from  tho  surface  of  section,  and  ard 
indicated  by  lighter  lines  than  the 
median  group  of  motor  nuclei.  ///, 
IV,   TV,  XII. 


solitarius.  The  afferent  fibres  are  concerned  with  the  sensation  of 
taste  in  the  posterior  third  of  the  tongue,  and  with  common  sensation 
of  this  region  and  of  the  upper  ]iart  of  the  pharynx.  In  the  nerve 
also  run  some  effector  fibres.  These  arise  mainly  from  the  upward 
continuation  of  the  nucleus  ambiguus,  and  supply  the  constrictor 
muscles  of  the  pharynx,  the  stylo-pharyiigeus,  and  levator  palati 
muscles.  The  nerve  also  contains  effector  secretory  fibres  to  the 
parotid  gland,  the  cell-stations  of  which  are  not  exactly  ktiown. 
These  pursue  a  somewhat  devious  course  to  reach  the  gland  (see  p.  374). 


694 


A  TEXTBOOK  OF  l'H^SIOL(K^Y 


The  white  matter  of  the  spinal  bulb  consists  oi  conducting  tracts, 
Loth  ingoing  and  outgoing.     The  chief  ingoing  afferent  paths  are — 

1.  The  mesial  fillet.  The  fibres  of  this  tract  arise  from  the  gracile 
and  cuneate  nuclei,  immediately  cross  the  middle  line  and  pass  up 
in  close  ])roximity  to  and  on  citlier  side  of  it  (Fig.  39H).  This 
crossing  forms  the  sensory  decussation;  the  iibres  of  the  tillet  eventu- 
ally reach  the  optic  thalami  (Fig.  484). 

2.  The  cerebellar  tracts  of  the  cord  pass  up  through  the  medulla 
to  reach  the  cerebellum  (Fig.  431).  They  occupy  part  of  the  area 
known  as  the  reticular  formation  (foiinatio  reticularis). 

3.  The  spino-thalamic  tract  passes  through,  and  joins  Avith,  tlu' 
mesial  fillet  to  reach  the  thalamus. 


Fit:.  423.- 


-Plan  of  the  Oruun  of  thk  Twelfth  and  Texth  Nfuves. 
(A.  E.  Schafer.) 


py>\,  Pyramid;  ri.XIL,  nucleus  of  hypoglossal;  XII.,  hj^poglossal  nerve;  d.n.X.XI., 
dorsal  nucleus  of  vagus  and  accessory;  n.amh.,  nucleus  ambiguus ;/.«.,  fasciculus 
solitarius  (descending  root  of  vagus  and  glosso-pharyngeal; /.6'.?2.,  its  nucleus; 
-Y.,  issuing  fibres  of  vagus;  g,  ganglion  cell  in  vagus  giving  origin  to  a  sensory 
fibre;  d.V .,  descending  root  of  fifth;  c.r.,  corpus  restiforme. 


4.  The  external  and  internal  arcuate  fibres,  which  arise  from  the 
gracile  and  cuneate  nuclei,  and  pass  to  the  cerebellum  either  by  an 
external  course  from  the  opposite  side  or  by  an  internal  com'se  from 
the  same  side. 

The  outgoing  fibres  take  part  in  the  formation  of  the  chief  reflex 
arcs  (Fig.  397) : 

1.  The  vestibulo-spinal,  which  arises  in  the  u])per  part  of  the 
medulla  in  Deiters'  nucleus. 

2.  The  rubro-spinal,  coming  from  the  red  nucleus  of  the  mid- 
brain. 

3.  The  pyramidal  tracts  from  the  cerebral  cortex.  These  lie 
anteriorly  throughout  the  great  part  of  the  medulla,  but  in  its  low  or 


THE  BRAIN 


(J9.5 


Motor 
nucl-ev 


part  most  of  the  fibres  cross  the  middle  line,  to  become  the  crossed 
pyramidal  tracts  of  the  cord,  thus  forming"  the  motor  decussation. 

Tracts  which  may  perhaps  be 
grouped  as  conducting  in  both 
directions  are — 

1.  The    olivocerebellar    fibres, 

which  connect  the  inferior  olive  to 
the  cerebellum. 

2.  The  posterior  dorsal  longi- 
tudinal  bundle  fibres,  in  which  run 
fibres  in  both  directions  b?t\vcen 
the  medulla  and  the  anterior  basis 
bundle  of  the  cord,  and  the  pons  and 
mid -brain.  This  tract  lies  dorsalh^ 
to  the  mesial  fillet,  just  below  the 
central  canal  and  fourth  ventricle. 
The  chief  fibres  of  this  tract  come 
— -(1)  fi'om  the  nuclei  of  the  third 
and  sixth  nerves,  being  concerned 
in  the  regulation  of  eye  move- 
ments, and  by  way  of  the  seventh 
nerve  in  the  movements  of  the 
accessory  apparatus,  such  as  the 
■e3-elids  and  eyebrows  ;  (2)  from 
Deiters'  nucleus  to  the  cord  in  con- 
nection Mith  the  equilibration  of 
the  body  ;  (3)  from  the  twelfth 
nucleus  l^y  waj-  of  the  seventh 
nerve  to  the  orbicularis  muscle  of 
the  mouth. 

In  close  association  ventrally 
with  the  posterior  longitudinal 
bundle  (sometimes  classed  as  part 
■of  it)  is  tbo  anterior  longitudinal 
bundle,  or  tecto-spinal  tract.  In 
it  run  libres  from  the  roof  of  the 
mid-brain  to  the  cord. 


\Ventra,l 
hm-n 


The  Functions  of  the  Medulla 
Oblongata. — The  medulla,  like  the 
spinal  cord,  acts  as  a  conductor 
and  as  a  reflex  centre.  The  centres 
are  those  associated  with  the 
functions  of  the  nerves  arising 
from  it,  of  which  the  vagus  nerve 
is  the  chief.  Here,  therefore,  are 
situated  the  centres  concerned  in 

the  regulation  of  the  heart-beat  (the  cardio-motor  centre),  the  regu 
Jation    of    the    peripheral    resistance    (the    vaso-motor    centre) 


FlU.  424.— DiAGKA.M  OF  A  FiBRE  OF  THE 

PosTEKiOR    Longitudinal     Bundle 

ARISING     FROM    A    CELL    OF    DeITEES' 

^iucLEUs.       (E.     A.     Schafer,     from 
"  Quain's  Anatomy.") 


the 


696 


A  TEXl !',(»( J K  OF  PHYSIOLO(;V 


centre  for  respiration,  and  other  centres  already'  refcried  to,  such 
as  those  for  the  provision  of  saliva  and  gastric  juice  for  mastica- 
tion, swallowing.  ])honation,  and  vomiting. 

The  destruction  of  the  medulla  l)rings  about  dcalh,  owing  to  re- 
spiratory failure.  Tlie  body  of  a  ])ithed  mammal  may  be  kept  alive 
for  some  hours  by  artiticial  res])iration.  The  bl()Otl-y)ressure,  however, 
is  low,  owing  to  the  destruction  of  the  chief  vasomotor  centre. 


Accessory  motor  root  of 
fifth 
Motor  nucleus  of  fifth    ~.' 

Sensory  nucleus  of      / 
fifth  -^ 

Sensory  root  fibres  of 

fifth 

Part  of  superior  olive 

Grey  matter  lateral 

fillet 
White  matter  of 
cerebellar 
hemisphere 


Fifth  nerve 


Piphe  bundle- 
of  fifth 

Posterior  long, 
bundle 

Auterior  long, 
bundle 
Central  tract 


■..,_,      y  >.,_, Central  nucleu.s 

--^2>=^»-»    ¥^^^' Fillet 


Fibres  of  yens 


Fibres  of  pons 


Nuclei  pontis 


Fibres  of  pon."! 

liaphe 


Nuclei  pontis 


Fibres  of  pon* 


Fig.  425. — Section  across  the  Middle  of  the  Pons.    Magisified  about 
4  Diameters.     (E.  A.  S'chafer,  from  "  Quain's  Anatomy.") 


The  Pons  Varolii  is  a  continuation  of  the  medulla  oblongata^ 
surrounded  by  transverse  fibres,  which  form  the  middle  or  transversa 
peduncles  of  the  cerebellum  ;  a  large  part  of  the  anterior  portion  of 
the  pons  is  made  ujd  of  these  transverse  fibres  passing  from  one^sido 
of  the  cerebellum  to  the  other  (Fig.  425).  It  acts  as  a  conductor  to 
ingoing  and  outgoing  fibres,  and  in  it  are  situated  the  nuclei  of  the 
eighth  to  the  fifth  cranial  nerves.  Passing  up  through  the  pons  ?.re 
the  fibres  of  the  ventral  spino-eerebellar  tract  and  of  the  mejial  fillet. 
Passing  downwards  through  the  pons  are  the  fibres  of  the  pyramidal 
tract  from  the  cortex,  which  in  this  region  lie  ventralU^  somewhat- 
scattered  among  the  transverse  fibres.  The  rubro-spinal  fibres  also 
pass  downwards.     In  this  region  the^^  lie  in  the  reticular  formation. 


THE  BRAIN 


697 


FIBRES  TO  NUCL.LEMNISCI 
&CORPORA  QUAORIGEMINA 


PYRAMID 


NERVe-ENOINGo 

in  organ  of  corti 

Fig.  426. — Plak  of  Course  and  Connkctions  of  the  Fibkes  forjung  the 
Cochlear  Root  of  Auditory  Nerve.     (E.  A.  Schafer.) 

r.,  Resliform  body;  v.,  descending  root  of  fifth  nerve;  tub.ac,  tuberculum  acusticum; 
n.acc,  accessory  nucleus;  s.o.,  superior  olive;  n.tr.,  nucleus  of  trapezium;  n.vi., 
nucleus  of  sixth  nerve;  VI.,  issxiing  root-fibre  of  sixth  nerve. 


TO  VERMIS 


FIBRES    O 

VESTIBULAR 
ROOT 


NERVE 
ENDINGS 
IN  MACULAE 
e,  AMPULL/E 


pji 


Fig.  427. — Plan  of  the  Course  axd  Connections  of  the  Fibres  FoiniiNG  the 
Vestibular  Root  of  the  Eighth  Nekve.     (E.  A.  Schafer.) 

r.,  Restiform  body;  V,  descending  root  of  fifth  nerve;  y.,  principal  nucleus  of  vesti- 
bular root;  n.d.,  ceU  of  the  descending  vestibular  nucleus;  D,  nucleus  of  Deiters; 
B,  nucleus  of  Bechterew:  n.t..  nucleus  tecti  (fastigii)  of  the  cerebellum;  p.l.h., 
posterior  longitudinal  bundle. 


(>9S 


A  TEXTBUOK  OF  PHYSIOLOGY 


dorsally  to  tlie  mesial  fillet  (Fig.  425).  More  dorsal  still,  in  a  position 
corresponding  to  that  in  the  medidla  oljJongata,  lies  the  ])osterior 
longitudinal  bundle,  its  fibres  making  eonnections  both  upAvards  and 
doAViiwards. 

The  chief  masses  of  grey  matter  are — I .  Deiters'  nucleus.  2.  The 
nucleus  pontis.  3.  The  superior  olive.  4.  The  nuclei  of  the  eighth 
to  the  fifth  cranial  nerves. 

The  Nucleus  of  Deiters  is  an  important  mass  of  gre}'  matter  lying 
at  the  lower  end  of  the  ])ons,  and  partly  in  the  upper  part  of  the 
spina]  l)ulb.  Around  the  large  cells  constituting^  the  nucleus  end  fibres 
from  the  vestibular  nerve  and  the  dentate  nucleus  of  the  cerebellum. 


/^//i 


Fig.  4-28. — Fla:s  (Tkaxsverse)  of  the  Okigin  of  the  .Sixth  and  of  the  Motor 
Pabt  of  the  ISeventh  Nerve.     (E.  A.  Schaler,  from  "  Quain's  Anatomy.") 

VI.,  Sixth  nerve;  VII.,  seveiitli  nerve;  a.VIl.,  ascending  part  of  root  of  seventh, 
shown  cut  across  near  the  floor  of  the  fourth  ventricle;  g,  genu  of  seventh  nerve- 
root;  n.VI.,  chief  nucleus  of  the  sixth  nerve;  n.'VI.,  accessory  nucleus  of  sixth; 
n.VIl.,  nucleus  of  seventh;  d.V.,  descending  root  of  fifth;  pyr.,  pyramid  bundles; 
VIII.v.,  vestibular  root  of  eighth  nerve. 


From  the  cells  of  the  nucleus  arise  fibres  \vhich  pass  doAvinvards  through 
the  medulla  oblongata,  into  the  antero-lateral  position  of  the  cord— the 
vestibulo -spinal  tract.  Other  fibres  pass  inwards  to  the  middle  line, 
to  ascend  and  descend  in  the  posterior  longitudinal  bundle  (Fig.  427). 
The  ascendmg  fibres  go  chiefly  to  the  sixth  and  third  nuclei,  the 
descendmg  to  the  anterior  horn  cells  of  the  cord.  In  close  proximity 
to  this  nucleus,  formmg  in  reality  its  upper  part  towards  the  cere- 
bellum, is  the  nucleus  of  Bechterew. 

The  Nucleus  Pontis  is  the  name  given  to  the  grey  matter  lying 
between  the  crossing  fibres  of  the  jjons,  aroimd  the  cells  of  ^vhich 
end  fibres  from  the  frontal  and  occipital  cortex- — the  fronto-pontine 


THE  BRAIN  OS)i) 

and  cortico-pontine  fibres.  From  the  cells  arise  the  transverse  fibres, 
which  cross  the  middle  line,  and  pass  by  the  middle  peduncle  to  the 
A^ermis  of  the  cerebellum. 

The  Superior  Olive  is  a  small  mass  of  grey  matter  closely  associated 
with  the  co-ordination  of  the  movements  of  the  eyes  with  the 
mechanism  of  equilibration. 

The  Nuclei  of  the  Cranial  Nerves. — The  eighth  nerve  is  a  wholly 
afferent  nerve.  It  consists  of  two  portions — the  cochlear  and  the 
vestibular.  The  cochlear  portion  is  concerned  with  hearing.  Its 
ceU-station  is  in  the  spiral  ganglion  of  the  cochlea.  Peripherally,  the 
nerve  processes  arborize  around  the  hair  cells  of  the  organ  of  Corti. 
Centrally,  the  axons  pass  into  the  uppermost  part  of  the  medvxlla 
oblongata.  They  branch  on  entering ;  one  set  of  branches  ends  in  a 
nucleus — the  accessory  nucleus— just  anterior  to  the  restiform  body 
(Fig.  426);  the  other  around  cells  in  what  is  laiown  as  the  tuber- 
culum  acusticum,  or  acoustic  tubercle,  a  mass  of  grey  matter  resting 
upon  the  outer  aspect  of  the  restiform  body.  From  the  cells  of  these 
nuclei  arise  fibres  which  go  to  form  the  lateral  fillet  (Fig.  426).  The 
fibres  from  the  accessory  nucleus  pass  transversely  across  in  the  tract 
known  as  the  trapezium,  making  in  their  course  connection  with  the 
superior  olive  and  trapezoid  nucleus  of  i\\Q  same  and  opposite  sides, 
and  then  turning  upwards  in  the  lateral  fillet  to  reach  the  nucleus 
of  the  lateral  fillet  and  the  inferior  corpus  quadrigeminum.  The 
fibres  from  the  tubercidum  acusticum  cross  the  floor  of  the  fourth 
ventricle  superficially  as  the  striae  acusticae,  and,  dipping  inwards 
at  the  middle,  pass  with  those  of  the  trapezium  to  the  superior 
olive  of  the  opposite  side,  and  thence  to  the  lateral  fillet  and  inferior 
corpus  quadrigeminum. 

The  vestibular  portion  of  the  eighth  nerve  is  concerned  with  the 
mechanism  of  equilibration.  It  arises  from  the  cells  of  Scarpa's  ganglion 
in  the  vestibular  portion  of  the  internal  ear.  The  ingoing  fibres 
divide  into  ascending  and  descendmg  branches.  The  ascending 
branches  connect  with  the  principal  vestibular  nucleus  (Fig.  427), 
a  mass  of  grey  matter  situated  just  external  to  the  nucleus  of  Deiters, 
with  which  it  makes  intimate  connection  by  means  of  collaterals. 
The  descending  fibres  end  in  the  descending  vestibular  nucleus,  which 
lies  below  the  prmcipal  nucleus.  Many  fibres  of  the  vestibular  nerve 
pass  directs  by  Avaj'  of  the  restiform  body  to  the  roof  nuclei  of  the 
cerebellum. 

The  seventh  nerve  is  mainly  motor  in  function.  It  arises  from  a 
group  of  cells — the  ssventh  nucleus — which  lie's  in  the  recticular  forma- 
tion just  below  and  somewhat  external  to  the  nucleus  of  the  sixth 
nerve.  The  fibres  pursue  a  somewhat  devious  course  inside  the  pons. 
At  first  they  pass  inwards  towards  the  middle  line;  then  dorsally 
towards  the  floor,  and  iq:)wards  to  a  slightly  higher  level  of  the  pons; 
then,  encircling  the  sixth  nucleus,  they  turn  outwards,  and  emerge 
from  the  lateral  margin   of    the  pons  (Fig.  428).     The  fibres  supply 


700  A  TEXTBOOK  OF  PHYSIOLOGY 

tho  muscles  of  expression  of  t  he  face.  Pai'alvsis  of  the  nerve  leads 
to  a  characteristic  ""  facies  " — an  expressionless,  vacant  look.  In 
addition,  the  stapedius  muscle  of  the  ear  and  certain  muscles  of  the 
scalp  are  also  supplied. 

Certain  afferent  fibres  belonging  to  the  nerve  of  Wrisberg  also 
run  in  the  seventh  nerve.  Their  cell-station  is  in  the  geniculate 
ganglion.  The  fibies  ])assing  inwards  from  the  ganglion  divide  into 
ascending  and  descending  branches,  the  latter  connecting  with  the 
ninth  nucleus.  Periplicrally,  the  fibres  pass  into  the  large  superficial 
petrosal  nerve  and  the  chorda  tympani  nerve,  and  thence  to  the 
fifth  nerve,  furnishing  the  sensation  of  taste  to  the  anterior  two-thirds 
of  the  tongue.  From  the  nerve  of  Wrisberg  also  come  secretory 
fibres  which  go  to  supply  the  submaxillary  and  sublingual  glands 
through  the  chorda  tympani  nerve. 

The  sixth  nerve  arises  from  a  group  of  cells  situated  on  either  side 
of  the  middle  line  just  below  the  floor  of  the  upper  part  of  the  fourth 
ventricle  (Fig.  428).  The  fibres  form  the  motor  nerve  to  the  external 
rectus  muscle  of  the  eyeball.  From  the  sixth  nucleus  other  fibres  ascend 
in  the  posterior  longitudinal  bimdle,  to  emerge  with  the  third  nerve 
and  supply  the  internal  rectus  muscle.  The  oculo-motor  nerves^ 
sixth,  fourth,  and  third,  contain  muscle-sense  fibres,  the  ganglion 
cells  of  which  are  to  be  foimd  in  the  nerve  trunks. 

The  fifth  or  trigeminal  nerve  has  three  nuclei  in  the  medulla: 
one  connected  with  the  central  connections  of  the  sensory  cells  of  the 
Gasserian  ganglion — the  jirincipal  sensory  nucleus  of  the  fifth ;  and  two 
connected  with  the  motor  functions  of  the  nerve — the  chief  and  the 
accessory  motor  nuclei  (Fig.  429).  The  afferent  fibres  of  the  nerve 
enter  the  pons,  and  bifurcate  into  ascending  and  descending  branches, 
The  ascending  pass  to  the  principal  sensory  nucleus,  which  lies  just 
laterally  to  the  principal  motor  nucleus.  The  cells  of  this  nucleus 
give  rise  to  fibres  most  of  which  cross  the  middle  line  and  pass  in 
the  mesial  fillet,  to  end  in  the  optic  thalamus.  Some  fibres  ascend 
in  the  mesial  fillet  of  the  same  side.  The  descending  fibres  form  a  well- 
marked  tract,  which  descend  in  the  reticular  formation  (the  descending 
branch  of  the  fifth)  into  the  cervical  part  of  the  spinal  cord.  In  its 
course  it  forms  connections  with  the  motor  nuclei  of  the  pons  and 
medulla.  It  lies  in  close  association  with  the  substantia  gelatinosa 
Rolandi. 

The  nervo  acts  as  the  nerve  of  common  sensation  to  the  face, 
eyeball,  nose,  and  mouth.  The  fibres  connected  with  the  gustatory 
nerve-endings  in  the  anterior  two-thirds  of  the  tongue  run  in  this 
nerve. 

The  motor  fibres,  which  form  but  a  small  part  of  the  nerve,  arise 
chiefly  from  the  principal  motor  nucleus,  which  is  situated  laterally 
below  the  floor  of  tho  fourth  ventricle  (Fig.  429).  Some  arise  from  the 
accessory  nucleus,  which  is  situated  higher  in  the  pons,  and  in  part  in 
the  mid-brain  (see  Fig.  -129).  The  fibres  are  motor  to  the  muscles  of 
mastication,  the  tensor  palati,  the  tensor  tympani,  and  the  anterior 
belly  of  the  digastric  muscles. 


THE  BRAIN 


701 


Fia.  i2i). — Fi.AN  OF  THE  Okigin  and  PiKLATioxs  OF  THE  FiiTH  Nehve.     (Cajal, 
from  "  Quain's  Anatomy.") 

A,  Gasserian  ganglion;  B,  accessory  motor  nucleus;  C,  main  nucleus;  D,  seventh 
nucleus;  E,  twelfth  nucleus;  F,  sensory  niieleus  of  fifth;  G,  cerebral  trace  of 
fifth;  a,  ascending  branches;  6,  descending  branches  of  sensory  root-fibres; 
c,  d,  e,  ophthalmic,  maxillary,  and  mandibular  branches  of  fifth. 


702 


A  TEXTBOOK  OK   PHVS[()L()(;V 


Section  IT 
THE  CEREBELLUM 

The' Structure  of  the  Cerebellum. —Tlu;  little  brain,  or  cerebellum, 
consists  of  a  middle  lobe,  or  vermis,  and  two  lateral  hemispheres. 
Its  surface  is  thrown  into  manj^  folds,  which  in  section  give  it  a  tree- 
like appearance — the  arbor  vita>.  The  oigan  consists  of  a  grey  cortex, 
and  wliitc  matter  Avithin.     In  the  latter,  near  the  middle  line,  are 


a    i 


--  •  '* 


Vui.  430. — Section  of  Cerebellar  Cortex.     (Sankey,  from 
"  Quain's  Anatomy.") 

a,  Pia  mater;  h,  molecular  layer;  c,  cells  of  Pur^dnjc;  d,  granule  layer;  e,  white  centre. 

ganglia  of  grey  matter — -the  roof  nuclei — and  in  the  middle  of  each 
lateral  lobe  the  dentate  nuclei.  It  is  from  these  nuclei  that  the  axons 
which  leave  the  cerebellum  arise 


THE  BRAIN  703 

In  a  section  of  the  cerebellar  cortex  three  layers  are  to  be  dis- 
tinguished, the  most  characteristic  of  which  is  the  one  in  the 
middle,  in  which  occur  the  flask-shaped  cells  of  Purkinje  (see 
Fig.  430). 

The  apical  dendrites  of  these  cells  ramify  in  the  external  laj^'er, 
Avhile  the  efferent  axon  passes  doAvn  internally  into  the  central  layer 
of  white  matter.     Afferent  tendril  fibres  aborize  round  these  cells. 

External  to  the  Purkinje  cell  laj^er  is  the  outer  molecular  layer, 
which  consists  of  irregular  star-shaped  cells,  neuroglial  cells,  and  the 
dendrites  of  the  Purldnje  cells.  The  axon  of  the  star-shaped  cell 
runs  parallel  to  the  lajmr  for  a  certain  distance,  and  then  turns  down 
to  arborize  around  the  Purkinje  cells. 

Internal  to  the  Purkinje  cell  layer  is  the  nuclear  layer,  or  inner 
molecular  layer,  therein  afferent  fibres — the  so-called  moss  fibres- 
arborize,  forming  curious  mossj^-like  figures.  In  this  layer  are  small 
star-shaped  cells,  irregular  cells  of  Golgi,  and  neuroglial  cells. 

The  underlying  white  matter  is  composed  of  the  afferent  axons 
of  the  tendril  and  moss  fibres,  and  the  efferent  processes  of  the  Purkinje 
cells. 

The  cerebellum  is  connected  to  the  brain-stem  by  three  pairs  of 
peduncles:  The  inferior,  or  restiform  body,  to  the  medulla;  the  middle 
to  the  pons;  the  superior  to  the  mid-brain.  It  is  by  these  three  sets 
of  channels  that  it  receives  messages  from,  and  sends  messages  to,  the 
other  parts  of  the  central  nervous  system.  The  connections  of  the 
cerebellum  may  be  tabulated  as  folloAvs  : 

Afferent  Fibres  to  the  Cerebellum. — From  spinal  cord — (1)  By  the 
dorsal  spino-cerebellar  tract  (direct  cerebellar  tract  of  Flechsig)  to 
the  lower  part  of  the  vermis:  (2)  by  the  ventral  spino-cerebellar 
tract  (antero-lateral  ascending  of  Gowers)  to  the  upper  part  of  the 
vermis  by  the  superior  peduncle. 

From  the  medulla  by  the  inferior  pe<Zi<wc?e— (1)  To  the  vermis  b}^ 
the  internal  arcuate  fibres  of  the  gracile  and  cuneate  nuclei  of  the  same 
side;  (2)  to  the  vermis  by  the  external  arcuate  fibres  from  the  gracile 
and  cuneate  nuclei  of  the  opposite  side;  (3)  to  the  vermis  from  the 
inferior  olive,  chiefl\-  of  the  opposite  side;  (4)  to  the  vermis  by  fibres 
from  Deiters'  nucleus,  and  directly  from  ganglia  of  the  vestibular 
nerve. 

From  the  i^ons  to  the  lateral  hemisphere  b}^  the  terminal  neurons 
in  the  connection  between  cerebrum  and  cerebellum.  These  arise 
from  the  nucleus  pontis  of  the  ojiposite  side,  around  which  the  cortico- 
p(mtme  fibres  terminate,  and  pass  by  way  of  the  middle  peduncle. 

From  the  mid-brain,  optic  thalamus,  and  cerebral  cortex,  on  the 
opposite  side  by  way  of  the  superior  peduncle. 

Efferent  Fibres  from  the  Cerebellum.— Fibres  gather  from  all  parts 
of  the  cerebellum  to  the  roof  and  dentate  nuclei  and  pass  thence — 
(1)  In  the  inferior  peduncle  to  Deiters'  nucleus,  and  thence  to  the 
cord  by  the  vestibulo-spinal  tract;  also  upwards  to  the  sixth  and 
third   nerves,  and  downwards  to   the  cord  in   the  posterior   longi- 


704 


A  TEXTBOOK  OF  PHYSIOLOaY 


Fibres  in 
Superior  Peduncle. 


Mesial  Fillet 


Ventral  Spino 
Cerebellar 
{Go  wens.) 


Postero  MedianiGoll) 
'and  Postero  Lateral 
(Burdach) 


Dorsal  Spino 
Cerebellar 
(Flechsi^.) 


Pig.  431. — Diagram  of  the  Spino-Cerebellar,  Olivo-Tegmental,  Cekebet.io- 
Tegmental,  Ponto-Tegmentai.,  and  Ponto-Cerebellab  Tracts.  (Fvedraun 
after  Van  Geliuchten.) 


THE  BRAIN  705 

tiidinal  bundle;  (2)  in  the  middle  peduncle  to  the  nucleus  pontis  of 
the  opposite  side;  (3)  in  the  superior  peduncle  to  the  red  nucleus, 
superior  corpus  quadrigeminum,  and  third  nucleus  and  optic  thalamus 
of  the  opposite  side  (the  first  neuron  of  the  cerebello -cerebral  path). 

The  Functions  of  the  Cerebellum. — The  cerebellum  was  credited 
by  Gall,  the  founder  of  phrenology,  with  the  control  of  the  organs  of 
generation.  To  this  day  the  bump  of  philoprogenitiveness  is  placed 
in  the  skull  above  the  cerebellum.  We  now  know  that  the  cerebellum 
has  nothing  whatever  to  do  with  this  function. 

Comparative  anatomy  indicates  the  chief  function  of  the  cere- 
bellum. In  a  variety  of  skate  which  lies  at  the  bottom  of  the  sea, 
and  practically  does  not  move,  the  cerebellum  is  almost  absent;  in 
the  common  variety,  which  swims  about  in  search  of  food,  it  is  well 
marked.  All  strong-swimming  fish  and  hard-flj^'ing  birds  have  a  well- 
develoj)ed  cerebellum.  The  cerebellum  is  therefore  indicated  as  the  co- 
ordinating coiitre  for  muscular  movements,  especially  for  those  of 
equilibration.  When  half  the  cerebellum  is  cut  away,  the  animal  is 
at  first  quite  unable  to  stand,  any  attempt  to  do  so  causing  it  to  fall  to 
the  side  of  the  lesion.  There  is  only  slight  loss  of  power  of  the  muscles 
(asthenia),  but  marked  loss  of  tone  (atonia).  After  a  week  or  two 
it  recovers  the  power  to  stand,  although  the  limbs  droop  owing  to 
the  loss  of  power  and  tone ;  but  its  power  of  equilibration  is  so  imper- 
fect that  in  walking  t!  je  limbs  have  to  be  widely  abducted  in  order 
to  correct  the  tendency  ^o  fall  to  the  side  of  the  lesion.  The  con- 
tractions of  the  muscles  during  such  a  purposive  movement  are 
attended  by  tremors  (astasia).  If  such  an  animal  be  excited,  it  will 
fall  toward  the  side  of  the  lesion,  and  turn  completely  over.  This  is 
particular^  well  seen  in  monkej'S.  After  some  weeks  the  symptoms 
disappear.  This  is  due  to  a  cerebral  compensation.  Destruction  of 
the  cerebral  cortex  of  the  opposite  side  leads  to  a  reappearance  of  the 
symptoms.  It  takes  a  much  longer  time  to  recover  from  extirpation 
of  the  whole  cerebellum,  and  even  then  the  mode  of  progression  is 
not  normal.  Owing  to  the  fear  of  falling  daring  diagonal  movements, 
the  animal  performs  galloping  movements  with  the  limbs  wide  apart. 
This  ataxia  presents  marked  difference  from  the  high-stepping  ataxia 
due  to  overaction  of  the  muscles  in  spinal  lesions. 

In  man,  leiions  of  the  cerebellum  may,  or  may  not,  show  symptoms 
according  to  the  rapidity  of  onset.  When  symptoms  are  present, 
there  is  the  staggering  ataxia,  the  marked  tremors,  and,  if  placed  on 
all  fours,  the  tendency  to  turn  over  on  the  side  of  the  lesion.  In 
many  cases,  however,  where  a  cerebellar  tumour  has  been  found 
after  death,  there  have  been  no  marked  symptoms,  owing  probably 
to  the  concomitant  acquirement  of  cerebral  control. 

Stimulation  experiments  have  also  been  conducted  upon  the  cere- 
bellar cortex.  This  is  difficult  to  excite,  but  thus  far  the  experiments 
indicate  that  the  roof  nuclei  are  particularly  concerned  in  the  move- 
ments of  the  eyes  and  head,  the  lateral  nuclei  with  the  movements  of 
the  trunk  and  limbs. 

45 


706  A  TEXTBOOK  OF  PHYSIOLOGY 

The  ceie])cllum  is  therefore  to  be  regarded  as  the  chief  centre  for 
the  muscular  co-ordination  and  adjustment  necessary  for  the  equilibra- 
tion of  the  body.  It  receives  its  chief  impressions  from  the  proprio- 
ceptive mechanisms  of  the  head  and  body,  the  receptor  mechanisms, 
the  semicircular  canals,  and  the  muscles,  joints,  and  tendons,  and  also 
from  the  retinae.  Normally,  these  are  in  accord  with  the  impulses 
from  the  eye.  If,  however,  they  are  not,  then  giddiness  results, 
as  illustrated  by  the  children's  game  already  mentioned,  in  which  the 
subject,  after  w^alking  round  several  times  with  the  forehead  on  a 
poker,  stands  upright  and  attempts  to  walk  straight.  The  resultant 
loss  of  balance  is  due  to  the  conflict  between  the  semicircular  canals, 
which  gi^'c  a  sense  of  rotation  in  the  opposite  direction,  and  the  eyes, 
which  afford  no  evidence  of  any  such  rotation.  The  giddiness  experi- 
enced in  looking  down  from  great  heights  is  also  well  known.  The 
importance  of  the  eyes  is  also  seen  in  the  ataxia  which  results  from 
lesions  of  the  posterior  columns  of  the  cord  affecting  the  kinsesthetic 
mechanisms  of  the  limbs.  A  patient  suffering  from  such  ataxia 
balances  well  so  long  as  his  eyes  are  open.  If  these  be  closed  the 
power  to  equilibrate  ceases.  Should  such  a  person  close  his  eyes 
while  bending  over  a  basin  of  water  to  wash  his  face,  he  will  fall 
forward  into  the  basin.  Such  an  incident  is  in  some  cases  the  first 
sign  of  the  spinal  lesions. 

The  cerebellum  effects  its  control  over  the  muscles  concerned 
m  equilibration  through  the  cerebrum  of  the  opposite  side,  and 
through  the  cranial  nuclei  and  anterior  horn  cells  of  the  cord. 


Section  III 
THE  MESENCEPHALON,  OR  MID-BRAIN 

The  niifl -brain  may  be  looked  upon  as  being  chiefly  made  up  of 
four  peduncles — the  two  cerebral  and  the  two  superior  cerebellar 
peduncles.  Superimposed  upon  the  two  latter  are  the  anterior  and 
posterior  quadrigeminal  bodies,  two  on  either  side.  Through  the 
mid-brain  runs  the  aqueduct  of  Sjdvius,  connecting  the  fourth  ventricle 
to  the  third  ventricle  of  the  great  brain. 

In  section,  a  black  pigmented  zone  on  either  side — the  substantia 
nigra — divides  off  an  anterior  part,  or  crusta,  from  a  posterior  part, 
or  tegmentum.  The  crusta  consists  principally  of  efferent  fibres 
from  the  cerebral  cortex.  In  the  centre  are  situated  the  pyramidal 
fibres,  on  either  side  the  fibres  passing  from  the  cortex  to  the  nuclei 
pontis  and  cerebellum — the  fronto-pontine  and  occipito-pontine 
fibres. 

In  the  tegmentum  ran  the  afferent  tracts,  the  mesial  fillet  to  the 
optic  thalanuis,  the  lateral  fillet  to  the  inferior  corpora  quadrigemina, 
and  the  fibres  which  pass  to  and  from  the  cerebelhun  by  means  of 
the  superior  ])eduncles.  In  it  are  also  situated  masses  of  grey  matt'er 
— (1)  the  red  nuclei;  (2)  the  nuclei  of  the  fourth  and  third  cranial 
nerves. 


THE  BRAIN 


707 


The  red  nuclei  are  so  called  on  account  of  the  colour  they  present 
to  the  naked  eye  on  section  of  the  mid-brain.  They  are  situated 
centrally,  just  on  either  side  of  the  middle  line.  The  nuclei  form 
intimate  connection  with  the  fibres  of  the  superior  cerebellar  peduncles, 
and  with  fibres  from  the  optic  thalamus  and  cerebral  cortex.  Its 
cells  give  origin  to  the  rubro-spinal  tract  (Monakow's  bundle,  or  the 
pre]iyraniifla!   tract).     The   fibres   of   this   tract   almost   immediately 


C-'q.a.'. 


"  ^  q  in.. 


Fig.  432. — Seitii^n  aleo^s  ?»1id-Brain,  through  thk  Anterior  Corpora  Quadri- 

GEAIINA.       PhOTOGKAT'H      MAGNIFIED      ABOUT     3J      DIAMETERS.       (E.      A.      Schafjl', 

from  "  Quain's  Anatomy.") 

sij.,  Aqueluct  of  Sylvius;  c.p..  posterior  commissnre;  gl.-pi.,  pineal  gland;  c.q.a.,  an- 
terior corpus  quadrige.niniim;  c.y.'w?.,  internal  geniculate  body;  c.g.l.,  lateral 
geniculate  hody;  fr.opf.,  optic  tract;  p.p.,  pes;  p.l.b.,  posterior  lonj^itudinal 
bundle;  /?..  ujjper  fiUe;;  /.«.,  re;l  nucleus;  n.III.,  nucleas  of  third  nerve;  III., 
issuing  fibre-  of  third  nerve;  l.p.p.,  locus  pc-rforaiis  posticus. 


cross,  forming  what  is  knowai  as  Forel's  decussation,  and  pass  down 
through  the  jions  and  medulla  to  occup}'  a  position  in  the  cord  just 
anterior  (pre])yramidal)  to  the  crossed  p^Tamidal  tract.  Eventually, 
they  terminate  around  the  cells  of  the  anterior  horn.  From  cells 
in  the  roof  of  the  mid-brain  arise  the  fibres  of  the  tecto-spinal  tract, 
which  cross  the  mid-line  forming  the  fountain  decussation  of  Meynert, 
and  then  pass  into  the  anterior  longitudinal  bundle. 


708  A  TEXTBOOK  OF  PHYSIOLOGY 

The  Cranial  Nuclei. — ^The  nucleus  of  the  fourth  nerve  lies  close  to 
the  middle  line  in  the  lower  part  of  the  mid-brain.  The  fibres  arising 
from  it  pass  dorsally  outwards,  decussating  in  their  course  just  above 
the  aqueduct  of  Sylvius.  The  fourth  nerve  is  effector  in  function, 
supplying  motor  fibres  to  the  superior  oblique  muscle  of  the  eye. 
This  muscle,  acting  in  conjunction  with  the  inferior  rectus,  enables 
the  eye  to  look  directly  downwards.  It  is  to  be  noted  that  the  left 
muscle  is  supplied  by  fibres  from  the  right  side  of  the  mid-brain. 

The  nucleus  of  the  third  nerve  lies  in  the  upper  part  of  the  mid-brain 
in  a  central  position  just  ventrally  on  either  side  to  the  aqueduct  of 
Sylvius.  Its  fibres  pass  ventrally  outwards,  and  go  to  supply  all  the 
muscles  of  the  eyeball  except  the  superior  oblique  and  the  external 
rectus.  An  intimate  communication  is  established  with  the  fourth 
and  sixth  cranial  nuclei  by  means  of  the  posterior  longitudinal  bundle. 
It  is  suggested  that  some  fibres  from  the  sixth  nuclei  run  in  this  bundle 
to  the  third  nuclei,  and  enter  into  the  formation  of  the  third  nerves. 
This  is  particularly  suggested  for  the  fibres  supplying  the  internal 
recti — the  antagonizers  of  the  external  recti  muscles  supplied  by  the 
sixth  nerve. 

The  Inferior  Corpora  Quadrigemina  are  masses  of  white  matter, 
in  the  centre  of  which  are  contained  nerve-cells,  around  which  end 
fibres  of  the  lateral  fillet.  These  fibres  are  connected  with  the  auditory 
nuclei;  the  inferior  cor2Dora  quadrigemina  are  to  be  regarded  as  cell- 
stations  in  connection  with  hearing. 

The  Superior  Corpora  Quadrigemina  are  likewise  made  up  of  white 
matter  and  groujis  of  nerve-celL-.  They  are  to  be  regarded  as  impor- 
tant cell-stations  in  connection  with  vision,  in  particular  in  connection 
with  the  regulation  of  eye  movements.  Around  the  cells  end  fibres 
from  the  optic  tract,  and  also  from  the  lateral  fillet.  From  its  cells 
arise  fibres  which  pass  to  ths  nuclei  of  the  third  nerve,  and  downwards 
in  the  posterior  longitudinal  bundle — probably  to  the  sixth  and 
se\enth  nerve. 

The  Geniculate  Bodies. — In  close  association  with  the  quadri- 
geminal  bodies  are  the  geniculate  bodies,  of  which  there  are  two  pairs 
— the  external  and  internal.  They  are  small,  elevated  masses  of 
nerve-fibres  and  nerve-cells.  Around  the  cells  of  the  external  bodies 
end  fibres  from  the  optic  tract,  while  from  its  cells  arise  fibres  which 
pass  as  the  optic  radiation  to  the  occipital  i^art  of  the  cerebral  cortex 
concerned  in  vision.  The  external  bodies  are  therefore  important 
cell-stations  in  connection  with  sight. 

The  internal  bodies  are  concerned  with  hearing.  Around  the  cells 
terminate  the  fibres  of  the  lateral  fillet  from  the  auditory  nuclei.  The 
cells  give  rise  to  the  auditory  radiations,  which  pass  to  the  tem- 
poral region  of  the  cortex.  The  two  internal  geniculate  bodies  are 
connected  with  each  other  by  v.  Gudden's  commissure,  which  n.ns 
in  the  posterior  part  of  the  optic  tract. 

Passing  upwards,  the  brain-stem  enters  into  association  on  either 
side  with  three  masses  of  grey  matter — the  optic  thalamus  and  the 


THE  BRAIN 


709 


caudate  and  lenticular  nuclei.  The  thalamus  is  the  representative 
of  the  thalaniencephalon  of  the  primitive  brain;  the  caudate  and 
lenticular  nuclei,  of  the  old  brain,  or  archipallium.  Alternating  with 
these  nuclei  of  grey  matter  are  strands  of  white  matter;  hence  the 
name  of  corpus  striatum  given  to  the  whole.  The  relationship  of  these 
structures  is  seen  in  Fig.  433. 

Of  importance  are  the  fibres  which  constitute  the  internal  capsule — - 
the  tract  of  white  fibres  running  anterior^  between  the  caudate  and 


CandaJte  Hujcleas 

■ILeTillcular  NiLclcus 
Chuistrtuw 

Sensory  Fibres 
Sylvian  J'i^siLrB' 


Vi^uaL  Fibres  cf 
Optic  RajdiaJbUiih. 


I'lG.  433. — HoRizoNTAT.  Section  thkotjgh  Right  Cerebral  Hemisphere,  showing 
Position  of  the  Various  Strands  in  the  Internal  Capsule.  (Purves  Stewart, 
after  Beev^or  and  Horsley.) 


lenticular  nuclei,  and  posteriorly  between  the  thalamus  and  the 
lenticular  nucleus.  Through  this  capsule  sweep  the  fibres  to  and 
from  the  various  regions  of  the  cerebral  cortex.  In  the  front 
part  of  the  anterior  limb  run  fibres  connecting  the  frontal  cortex 
with  the  pons  and  cerebellum  (the  fronto-pontine  fibres),  and  fibres 
from  the  thalamus  to  the  frontal  cortex  (the  thalamo-frontal  fibres). 
In  the  neighbourhood  of  the  knee,  or  genu,  of  the  capsule,  run  efferent 
motor  fibres  from  the  cortex.     In  the  posterior  part  of  the  anterior 


710  A  TEXTBOOK  OF  PHYSIOLO(;Y 

limb  niii  libies  connected  Avith  niov^cments  of  the  head  and  eye.s;  in 
the  genu  with  the  movements  of  the  tongue  and  mouth ;  in  thct 
anterior  two-thirds  of  the  posterior  limb  the  fibres  wliich  go  to  form 
the  pyramidal  tract  in  the  following  order  from  before  backwards: 
shoulder,  elbow,  wrist,  fingers,  trunk,  knee,  toes  (Fig.  433). 

In  the  posterior  part  of  the  posterior  limb  of  the  capsule  run 
fibres  from  the  occipital  cortex  to  the  poiis  and  cerebellum  (the 
occipito-pontine  fibres),  and  in  front  of  and  behind  these  other  fibres, 
known  respectively  as  the  auditory  and  optic  radiations,  connected 
with  the  sensory  cortical  areas  for  hearing  and  sight.  The  fibres  of 
the  auditory  radiation  pass  from  the  inferior-corpus  quadrigeminum 
and  internal  geniculate  body  to  the  temporo -sphenoidal  lobe  of  the 
brain;  those  of  the  occipital  radiation  from  the  optic  thalamus  and 
external  geniculate  body  to  the  occipital  cortex. 

The  Optic  Thalamus  consists  of  a  mass  of  white  and  grey  matter 
situated  to  the  inner  side  and  below  the  floor  of  the  third  ventricle 
of  the  brain.  It  receives  fibres  from — (1)  the  cuneate  and  gracile 
nuclei  of  the  opposite  side  by  the  mesial  fillet;  (2)  the  opposite  dentate 
nuclei  of  the  cerebellum  b}'  the  superior  cerebellar  peduncles :  (3)  the 
retina  by  the  optic  tract;  (4)  the  cortex  of  the  same  side.  Its  cells 
give  rise  to  fibres  which  pass — (1)  to  the  cortex  as  the  last  link  of  the 
great  sensory  chain  to  the  motor  area  of  the  cerebral  cortex ;  (2)  to 
the  part  of  the  cortex  concerned  in  vision;  (3)  to  fibres  which  run  in 
the  rubro-spinal  tract  to  the  cord. 

The  Function  of  the  Thalamus. — The  nature  of  the  function  of 
the  thalamus  has  been  adduced  chiefly  as  the  result  of  the  clinical 
evidence  obtained  from  diseases  of  this  part  of  the  brain.  In  a  lesion 
of  the  thalamus  there  is  jiersistent  loss  of  superficial  sensation, 
touch,  pain,  and  temperature  of  half  the  body.  There  is  also 
marked  loss  of  deej)  sensation  and  acute  pains  on  the  affected  side. 
There  may  be  more  or  less  complete  want  of  knowledge  of  structure 
and  form  in  the  sense  of  touch  (astereognosis).  There  is  but  little 
affection  of  the  motor  system.  There  may  be  slight  ataxy  on  the 
affected  side,  or  a  partial  hemiplegia,  which  quickly  passes  off.  There 
may  be  "  choreic  *'  and  "  athetotic  "  (twirling)  movements  of  the 
affected  side.  These,  however,  are  not  due  to  the  thalanms;  only 
sensory  affections  are  caused  by  thalamic  lesions. 

From  the  clinical  evidence  which  has  accumulated,  it  seems  fairly 
certain  that  the  impulses  which  pass  up  the  posterior  columns  of  the 
cord  to  the  gracile  and  cuneate  nuclei  are  so  rearranged  during  their 
passage  up  the  mesial  fillet  to  the  thalamus  that  the  fibres  connected 
with  each  kind  of  cutaneous  sensation  arborize  round  definite  groups 
of  cells  within  the  thalamus,  whence  other  axons  arising  in  these 
groups  convey  the  impulses  to  cortical  areas.  The  thalamus  is  there- 
fore a  great  sensory  centre.  It  responds  to  all  stimuli  capable  of 
evoking  either  pleasure  and  pain  (feeling  tone)  or  consciousness  of  a 
change  in  state.  The  feeling  tone  of  somatic  or  visceral  sensation  is 
the  product  of  thalamic  activity,  and  the  fact  that  a  sensation  is 
devoid  of  feeling  tone  shows  that  the  impulses    which    underlie  its 


THE  BRAIN 


711 


Tluilamus 


Fibr-e-from  bensorij 

nucLeus  qf  C£nibral- 

.ittrve(Vt}i)to  thahuiiui 

Upper  or  mam 


Fibre  of  lower 
or  lateral  filf-et 
Co  corp.  quadt:  post- 


Fibre  of  Tnain 

fillet  to  tlialamus 


Fibre  from  cord 
to  thalaonus 


Oangllon-cell 
of  cerebral  nerve  (fm.) 


\- Sensory  nucleus  of 
I    cerebral  nerve  (Tth.) 


Ganglvon-cell  qf 
cochlear  nerve\ 


QanqlLon-cell 
cf  spinal  nerve 


Jiledian 
plane 


Grey  7natpcr  of 
dorsal  horn 


FIG    434  -Diagram  of  Sensory  Path  from   Peripheral  Nerve  to  Corpora 
QuADRiGEMiNA  AND  THALAMUS.     (E.  A.  Schafer,  from      Quain  s  Anaeomy.   ) 


712 


A  TEXTBOOK  OF  PHYSIOLOOV 


production  make  no  thalamic  appeal.  Most  sensations  in  patients 
with  a  thalamic  lesion  are  of  painful  quality.  One  ])atient,  for  instance, 
could  not  hcj'.r  the  singing  of  hymns.  It  produced  un])leasant  sensa- 
tions on  his  affected  side,  "  and  during  the  singing  he  rul)be(l  his 
affected  hand."  Another  patient,  during  the  scraping  of  his  palm 
on  the  affected  side,  said:  "It  is  a  horrid  sensation.  It  feels  as  if 
my  hand  were  covered  with  spikes,  and  you  were  running  them  in. 
It  is  not  painful,  but  very  unpleasant."  Another  highly  educated 
patient  said :  "  I  crave  to  place  my  right  hand  [the  affected  one]  on 
the  soft  skin  of  a  woman.  It's  my  right  hand  that  wants  the  con- 
solation. I  seem  to  crave  for  sympathy  on  my  right  side.  My  right 
hand  seems  to  be  more  artistic." 

Thalamic  stimulations  have  a  high  threshold  value.  Stimuli  of 
low  intensity  arouse  the  sensory  cortex,  which  is  quick  in  reaction 
and  controls  the  thalamic  centre.  The  aim  of  evolution  is  the  domina- 
tion of  feeling  and  instinct  by  discriminating  mental  activities.     The 

forebram 

optic  vesicle 
epiblast 
neuroblast 
mesob/ast 
mid-brain 

hind-brain 


Fig.  435. — ])iacram  of  the  Elements  which  form  the  Eyeball.     (Keith.) 

sensory  cortex  cerebri  is  an  organ  by  which  attention  can  be  concen- 
trated on  any  part  of  the  body  that  is  stimulated.  The  focus  of 
attention  being  arrested,  the  stimuli  from  this  part  are  sorted  out 
in  the  cortex,  and  brought  into  relation  with  their  sensory  processes, 
past  or  present.  The  thalamus  is  aroused  by  impulses  of  affective 
activity.  It  refuses  to  react  to  those  which  underlie  the  purely  dis- 
criminative aspects  of  sensation.  Long  latency,  persistent  character, 
and  freedom  from  control  mark  the  thalamus  sensations  when  acting 
by  themselves. 

The  Paths  concerned  in  Vision — The  Visual  Tract. — The  optic  nerve  is 
an  outgrowth  of  the  brain  (Fig.  436).  It  consists  in  the  main  of  afferent 
fibres  coming  from  the  retina.  The  study  of  the  degenerations  which 
follow  its  section  shows  that  there  are  also  some  fibres  running  in  the 
nerve  from  the  brain  to  the  eye.  Degenerative  changes  are  found  in 
the  other  optic  nerv^e,  indicating  that  fibres  pass  from  one  retina  to 
the  other  through  the  optic   chiasma,  where  the  two  optic  nervea 


THE  BRAIN 


713 


meet.  From  the  optic  chiasma  the  optic  tracts  pass  backwards  to 
form  connections  on  either  side  with  the  external  geniculate  body, 
the  optic  thalamus,  and  the  superior  corpus  quadrigeminum.  A 
band  of  fibres,  known  as  v.  Gudden's  commissure,  passes  posterior^ 
in  the  chiasma,  connecting  the  two  internal  geniculate  bodies.  These 
fibres  are  not  connected  with  vision,  but  are  probabl}'"  concerned  in 
some  way  with  the  process  of  hearing. 

The  inner  fibres  of  each  optic  nerve  decussate  in  the  chiasma  in 
such  a  way  that  the  fibres  of  the  nasal  half  of  each  retina  pass  to  the 
tract  of  the  opposite  side,  while  the  fibres  of  the  temporal  part  of  each 


'''     "^Sfc^  VISUAi. 
'     ^^^V,\\     CORTEX 

""%. 

:'■                    CELLS  IM  TCCMCNTUM 

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OCULO-        ""^      '    -l"^    ■' 
MOTORIU&  ■    J  ■•           ■■  I       ' 

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T  QUAORIGEMIWUM     T 

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CORPUS      ■ 
GLMICULATUM 
CXTEHVlUM  V 

TRACT    \VS\          J^/Y 

o^. 


Fig.  436. — Diagram  to  show  the  Probable  Course  and  Relations  of  the  Optic 
Fibres.     (From  "  Quain's  Anatomy.") 

To  simplify  the  diagram,  only  single  neurons  are  represented  as  onntiniiing  the  two 
neurons  from  the  re:in?e  in  the  geniculate  and  quadrigeaiinal  bodies  of  each 
side  with  the  visual  cortex.  This  must  not  be  taken  to  imply  that  the  retinal 
impressions  from  the  two  retinae  are  fused  in  these  inlermediate  nuclei. 


retina  pass  to  the  same  side  of  the  brain.  It  is  stated  that  in  man 
the  fibres  coming  from  the  macular  region  of  the  retina  bifurcate, 
and  pass  to  the  external  geniculate  bodies  of  both  sides  of  the  brain. 

From  the  cells  of  the  thalamus  and  external  geniculate  body  arises 
the  oj)tic  radiation,  which  passes  through  the  posterior  portion  of  the 
internal  capsule  to  the  occipital  cortex,  to  end  in  the  neighbourhood 
of  the  calcarine  fissure.     This  is  the  tract  concerned  in  vision. 

From  the  superior  corpus  quadrigeminum  connection  is  made 
with  the  nuclei  of  the  muscles  concerned  in  the  movements  of  the 
eyes.     Fibres  pass  in  the  posterior  longitudinal  bundle  to  the  third. 


714 


A  TEXTBOOK  OF  PHYSIOLOGY 


foiiilh,  and  sixth  nuclei.  The  superior  corpus  quadrigeminum  is  to 
be  regarded  as  the  co-ordinating  centre  for  eye  movements.  It 
is  intimately  related  with  the  chief  centre  of  co-ordination — the 
cerebellum. 

In  mammals,  the  development  of  the  optic  connections  is  measured 
by  the  importance  of  vision  to  the  animal.  The  squirrel  requires 
accurate  vision,  and  has  large  optic  nerves  and  well -developed  anterior 
corpora  quadrigemina.  In  the  rabbit  and  the  hare,  a  wide  panoramic 
vision,  together  with  an  acute  sense  of  hearing,  is  necessary  to  escape 
capture.  The  eyes  are  placed  laterally,  and  the  fibres  of  the  optic 
nerve  cross  almost  completely. 


=£Bi^  suj^ 


sept.  I  acid. 

striae  longitud. 
gyrus  subcallo. 


supra-callosal 

gyrus 


gijruQ  dentatus 


tract  (B) 

mesial  root 
anterior  perforated  space 


uncus 
band  of  Giacomini 
uncus 
temp,  incis. 


','.'■.  -i--^ olfactory  centre 

collateral  fissure 


Fig.   437. — Showing   Connection   of   the   Rhinencephalon    (Oi-faciory   Bulb) 
WITH  the  Hippocampat.  Gyrus  and  the  Uncus.     (Keith.) 


In  birds,  the  optic  chiasma  is  single  and  complete.  The  fibres 
from  each  nerve  interlace  and  alternate,  but  eventually  all  pass  to  the 
opposite  side  around  the  optic  thalami  to  well-developed  geniculate 
bodies.  The  oj^tic  lobes  are  well  marked  in  birds  of  prey.  Vision  is 
as  a  rule  panoramic,  one  eye  for  each  side.  In  owls  and  hawks, 
which  possess  a  considerable  amount  of  binocular  vision,  it  is  probable 
that  all  the  fibres  decussate,  so  that  the  vision,  although  being  binocular, 
is  not  stereoscopic.  In  fishes,  the  optic  nerves  cross  completely,  and 
pass  to  the  opposite  optic  lobe. 

The  effect  of  injury  to  the  visual  tract  in  man  differs  according  to  the 
site  of  the  lesion.  Section  of  the  optic  nerve  causes  total  blindness  in 
the  corresponding  eye.  A  median  section  of  the  optic  chiasma  brings 
about  blindness  in  the  nasal  halves  of  both  retinae,  inducing  a  hemi- 
anopia  in  the  outer  fields  of  vision  of  both  eyes.     Section  of  the  optic 


THE  BRAIN  715 

tract  causes  blindness  in  the  temporal  half  of  the  retina  of  the  same 
side,  and  of  the  nasal  half  of  the  retina  of  the  opposite  side,  resulting 
in  blindness  in  the  field  of  vision  of  the  opposite  side  to  the  lesion. 

A  lesion  of  the  optic  radiation  in  the  internal  capsule  results  in 
a  corresponding  loss  of  vision — a  heniianopia  of  the  opposite  side. 
It  can  be  diagnosed  from  a  lesion  of  the  tract  by  the  fact  that  i*ays 
of  light  thrown  upon  that  |)art  of  the  retina  in  which  vision  is  lost, 
cause  a  reaction  of  the  pupils  to  light,  since  the  reflex  are  is  intact. 
When  the  tract  is  damaged,  this  reflex  is  abolished,  as  the  reflex  arc 
for  light  is  broken.  Moreover,  a  lesion  of  the  optic  radiation  is  also 
associated  with  the  effects  due  to  damage  of  other  tracts  of  the  internal 
capsule,  such  as  loss  of  sensation  and  movement  in  the  opposite  half 
of  the  body. 

A  lesion  of  the  cerebral  cortex  in  the  occipital  region  also  induces 
a  hemianopia  of  the  opposite  side,  in  which  the  light  reflex  is  preserved, 
but  it  is  not  associated  with  hemiansesthesia  or  hemiplegia.  In  this 
case,  the  psychical  processes  in  connection  with  vision  are  interfered 
with. 

The  Caudate  and  Lenticular  Nuclei.— The  functions  of  these  nuclei 
are  not  yet  well  ascertained.  Being  parts  of  the  archipallium,  or  old 
brain,  the}^  are  possibly  associated  with  ''  instinctive  "  mental 
processes. 

The  Paths  in  Connection  with  the  Sense  oS  Smell.— In  many  of  the 
lower  animals  the  sense  of  smell  is  of  great  importance,  and  the  part 
of  the  brain  concerned  in  the  sensation  of  smell  is  highly  developed, 
and  known  as  the  rhinencephalon.  While  the  forebrain  owes  its 
evolution  to  this  sense,  in  higher  animals  it  becomes  of  less  importance. 
The  non-medullated  processes  of  the  receptor  olfactory  cells  pass 
through  the  cribriform  plate  of  the  skull,  to  end  in  the  olfactory 
lobe.  Each  process  forms  an  olfactory  glomerulus  by  interlacing 
with  an  arborizing  dendrite  coming  from  one  of  the  "  mitral  " 
cells  of  the  olfactory  lobe.  The  axons  of  the  mitral  cells  pass 
backwards  in  the  olfactory  tract.  This  divides  the  mesial  root, 
passing  inwards  to  end  around  the  part  of  the  brain  known  as 
the  callosal  gyrus,  and  also  to  make  connection  with  the  uncus 
of  the  opposite  side.  The  exact  connections  of  the  lateral  root 
are  difficult  to  follow,  but  it  makes  connections  eventually  with 
the  uncus  of  the  hippocampal  gyrus  of  the  cortex  (see  Fig.  437)  and 
with  the  thalamus.  Fibres' concerned  in  the  sense  of  smell  pass  in 
the  anterior  commissure  of  the  brain,  connecting  the  region  of  the 
uncus  of  the  two  sides.  The  fornix  is  a  commissure  connecting  the 
hippocampal  gyrus  and  the  thalamus. 


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A  TEXTBOOK  OF  PHYSIOLOGY 


Section  IV 
THE  FUNCTIONS  OF  THE  CEREBRUM 

The  Cerebral  Hemispheres. — The  cerebral  hemispheres  are  the 
latest  outgrowths  of  the  brain  to  be  developed,  and  are  particularly 
well  developed  in  the  higher  apes  and  man.  Particularly  is  this  the 
case  in  man,  where  the  cerebral  hemispheres  reach  a  large  size  and 
become  much  convoluted.  The  convolutions  are  marked  off  by 
fissures  and  sulci. 

The  great  development  of  the  brain  of  man  is  seen  from  the  fol- 
lowing figures  : 


Elephant 

Man    . . 

Horse 

Donkey 

Lion   . . 

Gorilla 

Ourang 

Chimpanzee 

Dog  (St.  Bernard) 

Macaque  monkey 

Rabbit 


in  WeigJtt. 

Body  Weight 

kg 

k^. 

5.443 

3,048,000 

1,431 

66,200 

615 

375,000 

385 

175,000 

210 

119,500 

463 

90,000 

431 

80,000 

406 

80,000 

123 

53,000 

97-7 

7,280 

0-7 

1,420 

Ratio  of  Brain  to 
I   Body  Weight. 


560 

46 
698 
457 
546 
194 
186 
197 
430 

74-5 
146 


Man's  brain  is  only  surpassed  in  weight  by  that  of  the  whale  and 
the  elephant.  It  is  markedly  heavier  than  that  of  the  primates. 
Although  this  indicates  man's  great  intellectual  development,  mere 
weight  of  brain  is  not  in  itself  everything.  One  of  the  heaviest  brains 
on  record  belonged  to  a  bricklayer.  But  many  great  men  have  had 
brains  decidedly  above  the  average  in  weight.  Byron's  brain  weighed 
2,238  grammes,  Cromwell's  2,233  grammes,  (Javier's  1,S30  grammes. 
Many  eminent  men,  however,  have  not  had  such  excejitionally  heavy 
brains.  Helmholtz's  brain  weighed  1,430  grammes.  Gauss's  l^rain 
1,492  grammes.  The  depths  of  the  convolutions  rather  than  the 
absolute  weight  appears  to  be  of  importance. 

The  Functions  of  the  Cerebrum. — The  functions  of  the  cerebrum 
have  been  elucidated  by  studying  the  effect  of  its  removal  or  partial 
removal.  This  varies  with  the  status  of  the  animal  in  the  evolutionary 
scale.  Thus,  in  the  early  experiments  on  this  point  it  was  found 
that  in  a  bony  or  teleostean  fish  the  effect  of  removal  of  the  fore- 
brain  was  scarcely  apparent ;  such  a  fish  immediately  seized  and 
swallowed  a  worm  when  thrown  near  it.  The  fish  either  did  not 
touch  or,  if  seized,  did  not  swallow  a  skein  of  thread  of  about  the 
dimensions  of  the  worm.  When  thrown  one  red  and  four  white 
wafers,  the  red  was  regularly  devoured  first.  The  fish  would  follow 
a  worm  held  in  the  forceps,  but  would  not  attempt  to  swallow  it. 


THE  BRAIN  717 

When  the  worm  was  attached  to  a  thread,  and  the  observer  retired 
from  view,  the  fish  swallowed  both  worm  and  thread.  The  fish  also 
apparently  "'  played  "  in  normal  fashion  with  fish  which  had  not  been 
operated  upon.  These  fish  depend  mainly  npon  vision  for  their 
activities,  and  in  the  operation  the  optic  lobes  are  not  destroyed, 

In  selachean  or  cartilaginous  fishes,  such  as  the  shark,  the  result 
was  different.  These  fish  depend  largety  upon  the  sense  of  smell, 
and  in  them  the  prosencephalon  is  represented  almost  entirely  by 
the  primitive  rhinencephalon,  or  smell-brain.  Thus,  when  sardines 
were  thrown  into  an  aquarium,  the  teleostea  immediately  seized  their 
boot3^  the  selachea  gradually  approached  in  circles.  When,  in  sclachea, 
the  olfactory  lobes,  the  representatives  of  the  cerebrum,  were  taken 
away,  the  fish  was  reduced  from  a  state  of  activity  to  one  of  complete 
quiescence. 

In  the  frog,  after  removal  of  the  cerebral  hemispheres,  the  animal 
appears  at  first  sight  quite  normal.  It  sits  in  normal  fashion,  jumps 
when  pinched,  and  starts  swimming  after  stimulation  just  as  quickly 
as  the  normal  animal.  It  will  catch  its  food  as  normally,  but  shows 
no  power  of  differentiating  between  v/hat  is  food  and  what  is  not. 
It  will  snap  at  anything  moving  like  a  fly. 

In  lizards,  the  loss  of  spontaneity  is  marked ;  the  animals  lie  abottt 
as  if  sleeping.  When  roused,  they  just  move  away.  The  movements 
are  normal,  obstacles  are  avoided,  but  the  animal  does  not  feed  spon- 
taneousl}^  and  exhibits  no  fear,  as  does  the  normal  animal. 

In  birds,  such  as  pigeons,  the  results  are  somewhat  similar  to  those 
on  reptiles.  The  bird  can  balance  itself,  and,  when  thrown  in  the  air, 
can  fly,  avoiding  obstacles.  Wlien  undisturbed,  it  remains  still, 
sleepy  and  motionless.  It  does  not  feed  of  itself,  and  manifests  no 
feelmgs  of  any  sort.  It  was  observed  that  a  brainless  female  pigeon 
responded  in  no  way  to  the  wooing  of  a  male,  nor  showed  any  affection 
or  interest  in  the  young  which  followed  her,  crying  aloud  for  food. 
It  would  push  another  pigeon  out  of  the  waj-,  as  if  it  were  a  stone,  or 
climb  over  it.  It  had  no  fear  of  anything — e.g.,  cat  or  dog;  it  knew 
neither  friend  nor  foe.  The  cerebral  processes  of  birds  are  localized 
chiefly  in  a  great  development  of  the  corpus  striatum;  in  mammals, 
on  the  other  hand,  they  are  more  particularly  dependent  on  the  great 
development  of  the  cerebral  hemispheres. 

In  mammals,  the  operation  of  removal  of  the  cerebrum  is  one  of 
considerable  difficulty,  and  has  only  been  successfully  performed  by 
removing  the  brain  piecemeal  in  successive  operations.  It  has  been 
done  by  several  observers,  chiefly  upon  dogs,  but  also  upon  apes.  In 
the  case  of  a  dog  which  remained  healthy  after  the  final  operation, 
and  was  killed  at  the  end  of  eighteen  months,  it  was  found  post 
mortem  that,  of  the  cerebral  hemispheres,  only  such  traces  had  been 
left  as  were  necessary  to  preserve  the  optic  nerves  from  injurj^  by 
the  operation.  This,  however,  was  successful  only  on  the  right  side; 
on  the  left  side  the  nerve  had  atrophied.  The  optic  thalami  were 
not  injured  by  the  operation,  although  the  grey  matter  of  the  anterior 
part  was  found  to  be  atrophied. 


718  A  TEXTBOOK  OF  PHYSIOLOGY 

After  recovering  from  the  operation,  the  animal  snai)pe(l  at  food 
and  licked  milk  when  it  was  brought  right  against  its  mouth.     It 
took  no  notice  of  another  dog  or  of  a  "  strong-smelhng  "  cat  held  in 
front  of  its  nose.     Taste  was  preserved;  meat  soaked  in  quinine  was 
rejected  with  signs  of  anger.     Tasty  morsels,  however,  were  eagerly 
devoured.     Aftex  a  good  meal  it  curled  up  and  slept  like  an  ordinary 
dog,    but    never    showed    any   signs    of    dreaming.      Sleep  generally 
was  of  shorter  duration  than  normal.       It  could  only  be  awakened 
by  very  loud  noises,  such  as  the  notes  of  a  fog-horn ;  it  then  moved 
its  ears  and  made  pawing  movements  at  them.     The  animal  could 
also  be  awakened  by  blowing  tobacco-smoke  into  its  nose — an  act 
which  sometimes  caused  sneezing.     A  strong  light  on  the  eyes  some- 
times  caused   it    to    turn    the    head   away,    but   men   and    animals 
were     not     recognized.        The    pupils    reacted    to    light    normally. 
Threatening    noises   had   no   effect.     Co-ordination   of   muscles   was 
retained,  and,  when  one  foot  was  injured,  it  could  walk  on  three  legs. 
There  was  always,  however,  some  muscular  weakness,  especially  of  the 
hind-quarters.     The  animal  never  showed  any  signs  of  joy  or  pleasure, 
but  signs  of  rage  when  the  cage  was  touched.     It  showed  no  signs  of 
purposive  movement,  and  was  always  but  "  a  child  of  the  moment." 
Its  tone  feeling  was  due  to  the  preservation  of  the  thalamus.     After 
ligation  of  all  four  cerebral  arteries,  a  dog  may  be  in  a  similar  condition 
for  a  day  or  two,  and  then  recover,  as  a  collateral  circulation  becomes 
established  by  way  of  the  superior  intercostal,  anterior  spinal,  and 
basilar  arteries.     Corresponding  to  the   "  idiot  "  stage,   the  cortical 
cells  are  found  to  have  swollen  nuclei  and  loss  of  Nissl  granules. 

In  marked  contrast  is  the  effect  of  removal  of  one  cerebral  hemi- 
sphere only.     A  dog  from  which  the  left  cerebral  hemisphere  had  been 
removed   fifteen   months   before   appeared   quite   a    "  healthy,    well- 
behaved  animal."     When  greeted,   it  came  wagging  its  tail  to  be 
stroked.     It   would  follow   anyone,   moving  quickly  by  running   or 
even  springing.     He  greeted  a  new-comer  with  a  joyful  bark,   but 
snarled  at  strange  dogs  if  he  did  not  like  the  k)ok  of  them.     He  held 
a  bone  with  his  fore-paws,  but  did  not  use  the  right  foot  so  purpose- 
fully as  the  left.     He  could  turn  round  both  ways,  but  preferred  to  go 
round  to  the  left.     Sensation  was  diminished  over  the  right  side  of 
the  body,  but  was  nowhere  absent.     When  irritated,  he  would  at  first 
move  away,  then  yelp,  and  finally  bite.     Diminished  sensation  was 
well  shown  by  the  dog's  failure  to  respond  to  a  jet  of  air  blown  by  a 
bellows  among  its  hair.      When  this  was  done  on  the  left  side,  the 
dog  turned  round  to  see  what  was  happening,  and  moved  away  from 
the  stinmlus;  when  done  on  the  right  side  in  an  identical  spot,  the 
animal  took  no  notice  at  all.     He  woidd  also  stand  in  cold  water 
with  the  right  paw,  but  immediatel}''  took  the  left  out.     While  running 
and  jumping,  all  obstacles  were  avoided.     Interference  of  vision  was 
shown  by  the  swinging  of  a  club  in  the  fields  of  vision.     In  the  right 
field  this  caused  no  response.     The  left  eyeball  could  be  touched  with- 
out evoking  a  wink.   Touching  an  eyelash  immediately  evoked  a  wink. 
Hearing  was  somewhat  interfered  with,  but  there  was  apparently  no 


THE  BRAIN  719 

disturbance  of  smell  or  taste.  The  animal  was  more  docile  than 
before  the  operation,  and  showed  no  longer  anj'  inclination  to  play 
with  its  companions.  To  a  stranger,  however,  it  appeared  no  less 
intelligent  than  a  normal  dog. 

In  apes  (Macacus  rhesus),  the  effects  of  total  extirpation  of  both 
hemispheres  are  exceedingh'  severe.  In  a  series  of  experiments 
recently  reported,  only  one  animal  out  of  seventeen  lived  any  length 
of  time  (twenty-six  days).  In  this  case,  an  interval  of  forty-four 
days  elapsed  between  the  removal  of  the  first  and  second  hemispheres. 
As  a  result  of  the  operation,  the  movements  of  the  head  and  eyes 
were  in  many  animals  apparently  unaffected;  the  movements  of  the 
extremities,  on  the  other  hand,  were  severeh'  impaired,  in  some 
cases  there  was  marked  tonic  contraction.  Tactile  stimulation, 
such  as  stroking  or  blowing,  produced  raising  of  the  head,  opening 
of  the  eyelids,  widening  of  the  pupils,  and  some  movement  of  the 
limbs.  Stimulation  by  light,  even  intense,  produced  but  a  slight 
reaction  of  the  pupils.  Noises  induced  movement  of  the  ears  and 
eyelids,  and  caused  the  body  to  be  drawn  up  together.  The  animals 
made  noises,  but  showed  no  signs  of  mimicry.  They  exhibited  periods 
of  sleep  and  wakefulness.  When  asleep,  they  had  their  eyelids  firmly 
closed,  made  no  spontaneous  movement  or  sound,  and  did  not  respond  to 
stimulation  such  as  would  arouse  a  normal  animal.  In  one  case  only  were 
swallowing  movements  observed  when  liquid  nourishment  was  given. 

The  removal  of  one  hemisphere,  on  the  other  hand,  had  surprisingly 
little  effect.  A  few  hours  after  the  operation  the  animal  sat  up, 
seized  food,  ate,  and  climbed,  although  there  was  marked  paresis  of  the 
limbs  of  the  opposite  side.  Then  followed  a  period  of  drowsiness,  but 
after  three  or  four  weeks  it  was  difficult  by  superficial  observation  to 
tell  such  an  animal  from  a  sound  one.  Upon  examination,  the  limbs  of 
the  opposite  side  showed  a  certain  degree  of  paresis,  more  marked  in 
the  upper  than  in  the  lower  limb,  hand  and  finger  movements  being 
more  affected  than  elbow  or  shoulder  movements.  Head  movements, 
hardly  disturbed  b}'^  the  operation,  soon  became  j^erfectly  normal. 
In  regard  to  sensation,  there  was  at  first,  at  anj'^  rate  in  some  of  the 
animals,  a  hj^eriesthesia  of  the  opposite  side.  Eventually,  all  animals 
showed  some  degree  of  diminished  sensibility,  but  reacted  to  strong 
stimuli.  All  the  animals  showed  a  marked,  lasting  disturbance  of  vision 
(hemianopia).  The  pupil  light  reflex  remained  normal,  and  the  eye 
movements  undisturbed.  No  disturbance  of  hearing  could  be  demon- 
strated. It  made  no  difference  which  hemisphere  was  extirpated, 
biit  in  two  cases,  after  extirpation  of  the  left  hemisphere,  an  impression 
was  obtained  that  the  left  hand  was  not  so  skilled  as  the  right  had  been. 
In  all  cases  the  completeness  of  the  removal  was  proved  post  mortem. 
The  caudate  and  lenticular  nuclei  and  the  optic  thalamus  were  for  the 
greater  part  destroyed. 

Recently  there  has  been  described  the  case  of  a  child  which  lived 
three  and  three-quarter  years  without  cerebral  hemispheres.  These 
had  been  reduced  to  thin-walled  cysts.  No  trace  of  nerve-fibres 
was  found  in  the  part  of  the  brain  corresponding  to  the  neo-encephalon. 


720  A  TEXTBOOK  OF  PHYSIOLOGY 

The  palsco-encephalon  was  nonnal,  as  well  as  the  rest  of  the  brain, 
except  for  the  lack  of  fibres  arising  from  the  neo-encophalon,  such 
as  the  fibres  to  the  red  nucleus,  to  the  j)ons,  and  to  the  sjDinal  cord. 
Till  the  day  of  its  death  the  child  scarcely  altered  its  behaviour, 
and  presented  a  marked  contrast  to  a  brainless  dog.  It  had  never 
made  any  attempt  to  raise  itself  up,  or  to  take  anything  in  its  hands 
and  hold  it.  The  only  movements  were  those  of  the  face,  which 
sometimes  took  on  an  expression  of  pain.  The  lips  and  tongue  were 
used  in  sucking  and  taking  food  from  a  spoon.  After  two  years  it 
uttered  a  dull  cry,  which  could  be  soothed  by  i^ressing  its  head.  Urine 
and  faeces  were  passed  in  any  position,  and' it  did  not  display  any 
discomfort  at  being  wet.  The  child  appears  not  to  have  shown 
period?  of  wakefulness  and  sleep,  but  to  have  always  slept.  The 
light  reflex  was  present,  the  eyes  being  shut  tightly  when  light  was 
thrown  on  them.  It  was  impossible  to  elicit  any  sign  of  psychic 
reaction,  to  train  or  teach  the  child  in  any  way.  Without  the  mother's 
help,  the  child  would  certainly  have  perished.  New-born  babies 
behave  in  much  the  same  way,  because  in  them  the  connection  between 
the  new  brain  and  the  old  brain  is  not  yet  developed.  The  same  is 
true  for  all  mammals.  These,  unlike  fish,  amphibia,  and  rei^tiles, 
are  almost  wholly  paralyzed  without  the  new  brain.  The  importance 
of  the  new  brain  gradually  increases  as  we  ascend  the  scale,  until  in 
man  it  becomes  paramount. 

There  has  also  been  reported  the  case  of  a  man  from  whom  it  was 
found  post  mortem  that  a  cerebral  hemisphere  had  been  missing. 
Although  hemiplegia  and  hemiansesthesia  were  present,  the  intelligence 
of  this  individual  was  normal.  So  in  many  cases  of  injury  in  man 
large  masses  of  brain  tissue  have  been  lost  which,  while  involving  loss 
of  sensation  or  of  movement,  have  apparently  scarcely  affected  the 
intelligence. 

From  such  evidence,  then,  it  is  clear  that  brainless  animals  are 
incapable  of  jjerceiving  certain  stimuli,  that  they  possess  no  associative 
memory,  are  incapable  of  psychic  processes,  and  are  not  able  to  initiate 
any  of  the  movements  which  normally  result  from  such  processes. 
The  functions  of  the  great  brain  may  therefore  be  grouped  as — (1)  The 
reception  of  impulses  (a  receiving  sensory  mechanism);  (2)  the  storing 
of  the  effects  of  such  imj)ulses,  and  the  association  of  present  with 
stored  impressions  (a  storing  and  associating  mechanism),  resulting 
in  the  highest  processes  of  the  brain — discrimination,  inhibition  of 
emotion,  judgment;  (3)  the  production  of  actions  as  the  result  of 
these  (a  motor  or  discharging  mechanism). 

It  has  been  found  that  the  receptor  and  effector  mechanisms  of 
the  cortex  cerebri  are  more  or  less  localized  in  special  parts.  Such 
localization  has  been  effected  by  five  methods:  (1)  The  effects  of 
removal  of  parts  of  the  cortex;  (2)  the  effects  of  stimulation  of  parts 
of  the  cortex;  (3)  by  clinical  observations  in  cases  of  brain  disease, 
followed  by  an  investigation  of  the  central  nervous  system  after 
•death;  (4)  by  a  histological  examination  of  the  cerebral  cortex;  (5)  by 
a  study  of  the  nerve  tracts  during  their  development. 


THE  BRAIN 


721 


The  localization  of  parts  of  the  brain  which  govern  particular 
movements  was  first  established  by  Hughlings  Jackson's  investigation 
of  those  cases  of  epilepsy  in  which  the  spasm  begins  in  some  parti- 
cular part,  and  spreads  in  a  definite  order  to  the  other  parts  of  the 
body.  The  fits  are  generally  preceded  by  a  sensation  in  the  part 
Avhere  the  spasm  begins — the  aura.  Many  such  cases  have  been 
operated  on,  the  motor  centres  localized  by  electric  excitation  and 
the  offending  centre  removed.  The  results  thus  obtained  in  man 
confirm  the  observations  made  on  the  chimpanzee  and  gorilla.  The 
motor  area  of  the  chimpanzee  is  shown  in  the  accompanying 
figures.       On    the    outer    side    it    occupies    chiefly    the    precentral 


Foot  &  Toes 
Knee 
Hip, 
Shoulder 
Elbow^ 


Great  Toe 


Tactile  &  Muscular  sensation 


Written  Speech^ 
Hand 
Index - 

Thumb-  - 

Upper 

Face 
Lower—  .  , 
Face 

Motor  _  . 
Speech 
Tongue"  ~ 
Lar3'nx- 


Movements 

ii  ye  (probable)  ^^stg^,' 
and 
Smell' 


Hearing, 
Auditory  word 
Memory 


If  Vision  centre 


Fig.  438. 


-Left  Hemisphere,  showing  Situation  of  the  Human  Cortical 
Projection  Centres.     (Mott.) 


convolution  in  front  of  the  fissure  of  Rolando  ;  it  overlaps  slightly 
on  the  inner  side  of  the  hemisphere.  The  localization  corresponds  in 
a  reverse  order  to  the  distribution  of  the  spinal  nerves.  The  order  is 
perineum;  up  the  leg — toes,  ankle,  knee,  hip;  trunk;  down  the  arm — 
shoulder,  elbow,  wrist,  fingers;  neck;  movements  of  mouth,  tongue, 
etc.     Eye  movements  are  situated  farther  forward  in  the  frontal  region. 

The  Efiects  of  Ablation  of  the  Motor  Area, — If  one  of  the  motor 
areas  be  removed,  there  resvdts  a  paralysis  of  voluntary  movements 
in  the  corresponding  part  of  the  body  on  the  opposite  side.  In  the 
dog  this  paralj'sis  ahnost  wholh?'  passes  off;  in  the  ape  to  a  less  degree; 
while  in  man  the  degree  of  recovery  is  very  limited.  So  much  is  this 
the  case  that  the  site  of  a  brain  lesion  can  be  diagnosed  during  life, 
and  verified  after  dealh.  Even  in  man  there  is  a  certain  amount  of 
recovery,  especially  of  limb  movements  made  in  association  with  the 
other  limbs.  Accompanying  the  loss  of  movement  is  a  diminution 
in  the  sensibility,  particularly  in  regard  to  the  position  of  the  part. 
For  example,  a  man  whose  arm  centre  has  been  excised  does  not 
know  the  position  of  the  limb,  or  how  much  it  has  been  passively 

46 


722 


A  TEXTBOOK  OF  PHYSIOLOGY 


moved,  when  his  eyes  are  shut.     Ablation  of  other  regions  of  the  cortex 
have  no  effect  upon  the  motor  mechanism. 

The  Results  of  Stimulation. — Jf  the  brain  be  stimulated  with  an 
adequate  stimulus  in  the  regions  shown  in  Fig.  438,  co-ordinated 
movements  of  the  corresponding  parts  are  evoked  on  the  opposite 


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side  of  the  body.  Too  strong  a  stimulus  leads  to  a  spread  in 
orderly  sequence  to  the  neighbouring  areas.  At  first  the  con- 
tractions are  tonic  in  character,  but  later  these  are  superseded 
by  contractions  of  a  clonic  nature.  This  is  what  takes  place  in 
cortical   epilepsy,   the    convulsive    symptoms    of    which    proceed  in 


THE  BRATN 


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a  definite  order.  Administration  of  tetanus  toxin  or  strychnine 
abolishes  the  co-ordinated  nature  of  the  response.  The  injection  of 
absinthe  into  the  vein  of  an  animal  causes  epileptic  convulsions  of 
a  universal  nature,  which  stop  when  the  carotid  arteries  are  clamped, 
to  begin  again  when  the  blood  carrying  the  poison  flows  through  the 
cortex. 

The  Evidence  from  Structure. — ^The  structure  of  the  cortex  is 
complicated,  and  varies  in  details  in  different  2:)arts.  There  are  five 
layers,  or  laminae  :   (1)  The  outer  fibre 

lamina.      (2)  The    outer    cell    lamina  *  T^ "  ~7*^^^ 

(3)  The  middle  cell  lamina.  (4)  Tlu' 
inner  fibre  lamina.  (5)  The  inner  cell 
lamina. 

The  outer  fibre  lamina  consist  ^ 
principally  of  medullated  fibres  from 
the  underlying  layers.  It  contains  also 
cells  which  give  rise  to  processes  run- 
ning parallel  to  the  brain  surface. 

The  outer  cell  lamina  consists  of 
pyramidal  cells,  the  outermost  being- 
small,  the  middle  ones  medium-sized, 
and  the  most  internal  large  in  size. 
Running  among  the  outer  cells  is  a 
strand  of  fibres  known  as  the  outei' 
line  of  Baillarger. 

The  middle  cell  lamiiia  consists  of  a 
layer  of  small  stellar  cells. 

The  inner  fibre  lamina  consists 
chiefly  of  an  inner  strand  of  fibres 
known  as  the  inner  line  of  Baillarger. 
In  this  lamina  are  also  large  pyramidal 
cells.  These  occur  particularly  in  the 
motor  area  of  the  brain,  and  are  there 
known  as  the  cells  of  Betz. 

The  inner  cell  lamina  consists  of 
various  types  of  cells— Golgi,  stellate, 
pyramidal,  spindle-shaped,  ovoid,  etc. 
Characteristic  are  pjTamidal  cells, 
with  the  axon  passing  towards  the 
surface  of  the  brain — the  cells  of 
Martinotti. 

These  layers  vary  in  structure  and 
in  thickness  in  the  different  parts  of  the  cortex.  They  also  develop 
in  the  embryo  at  different  times.  The  inner  cell  lamina  is  the  first 
layer  to  be  developed,  and  is  well  marked  in  the  lower  mammals. 
This  layer  and  the  inner  fibre  laj^er  is  held  to  be  concerned  in  the 
lower  instinctive  and  voluntary  activities  of  the  animal,  such  as 
feeding,  excretion.  In  man,  these  layers  are  developed  during  the 
fourth  month  of  foetal  life. 


Fig.    440.  — Section    of    Crucial 
Sulcus  of  the  Brain  of  a  Do(; 

STAINED      BY     GOLGl's    METHOD^ 

SHOWING  A  Large  Pyramidal 
Cell  giving  off  a  Large 
Branching  Apical  Dendron. 
Gemmules  can  be  seen  on  the 
Processes,     x  80.   (Mott.) 


724 


A  TEXTBUUK  Ui^'  PHYSIOLOGY 


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THE  BRAIN 


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(Mott.) 


726 


A  TEXTBOOK  OF  PHYSIOLOGY 


The  middle  cell  lamina  is  next  developed,  and  is  believed  to  be 
concerned  in  the  reception  of  sensory  stimuli.  It  is  most  marked  in 
the  sensory  regions  of  the  cortex.  In  man,  it  develops  in  the  sixth 
month  of  foetal  life. 


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Fig.  443.— Fibre  Aerangement  and  Cell  Lamination  of  Visual  Area.    (Mott.) 

Last  to  be  developed  is  the  outer  cell  lamina.  It  is  suggested  that 
this  is  concerned  in  pyschic  processes,  and  is  particularly  marked  in 
regions  concerned  in  these  processes,  especially  in  the  frontal  area 
of  the  brain. 


THE  BRAIN  727 

The  differences  in  thickness  and  structure  are  Avell  seen  in 
Figs.  441-443.  In  the  motor  area  the  second  lamina  is  thick, 
the  third  lamina  is  thin,  and  the  fourth  lamina  contains  the  charac- 
teristic large  pyramidal  cells  of  Bstz. 

In  the  "  visuo-sensory  "  area  the  third  lamina  is  thick,  and  is 
divided  into  two  by  a  strand  of  fibres — the  line  of  Gennari. 

The  "  visuo-psychic  "  area,  except  for  the  absence  of  the  large 
Betz  cells,  resembles  more  the  motor  than  the  sensory  area.  It  is 
obvious  that  from  a  study  of  the  histological  structure  of  areas  of 
which  the  function  is  knowxi  valuable  indications  may  be  obtained  as 
to  the  function  of  the  parts  of  the  cortex  of  which  the  function  has  not 
been  clearh^  ascertained. 

The  Evidence  from  Myelination. — It  has  been  found  that  groups 
of  fibres  going  to  certain  regions  of  the  cortex  in  the  embryo  acquire 
their  medullary  sheaths  earlier  than  other  groups.  These  regions 
of  the  cortex  have  been  shown  to  correspond  closely  with  the  "  sensory 
areas  "  of  the  cortex. 

The    Localization    of    the    Receiving    Sensory  Mechanism.  —  The 

receiving  station  for  cutaneous  and  kinoesthetic  impulses  has  been 
localized  in  the  ascending  parietal  convolution,  which  lies  just  behind 
the  fissure  of  Rolando  (Fig.  444).  Cutaneous  sensations  have  also  a 
receiving  station  in  the  callosal  gyrus  on  the  mesial  aspect  of  the 
brain  (Fig.  444).  It  is  probable  that  the  various  sensations  are  repre- 
sented in  special  parts  of  these  regions.  It  is  known  that  during  their 
passage  from  the  cord  to  the  thalamus  the  various  sensations  become 
grouped,  and  it  is  probable  that  the  final  neurons  from  the  thalamus 
to  the  cortex  establish  communications  with  definite  areas. 

The  motor  and  sensory  areas  around  the  Rolandic  area  are  in 
close  connection.  It  is  for  this  reason  that  epilepsy  is  preceded  by 
the  sensory  "  aura,"  and  stimulation  of  the  sensory  area  leads  to 
movements  which,  with  Aveak  stimluation,  are  localized  in  that  area 
of  the  motor  cortex  which  is  in  most  intimate  communication. 

The  receptive  area  for  vision  is  situated  in  the  occipital  regions  on 
both  the  outer  and  inner  aspect  of  the  brain  (Fig.  444).  The  area  varies 
considerably  in  extent,  being  larger  in  the  dog  than  in  mail.  In  man, 
the  main  centre  is  around  the  calcarine  fissure  on  the  mesial  aspe3t. 
The  occipital  part  of  the  brain  is  connected  with  the  thalamus,  external 
geniculate  body,  and  superior  corpora  quadrigemina,  by  means  of 
the  optic  radiations.  For  instance,  stimulation  of  the  upper  surface 
of  the  right  occipital  lobe  causes  eye  movements  downwards  and  to 
the  left;  of  the  posterior  part,  eye  movements  upwards  and  to  the 
left;  of  the  mesial  surface,  a  turning  of  the  eyes  laterally  to  the  left. 
Extirpation  of  both  occipital  lobes  induces  complete  blindness; 
.ablation  of  one  occipital  lobe  causes  a  crossed  hemianopia.  The 
vision  of  the  fov^ea  is  not  impaired,  since  it  is  represented  on  both 
sides  of  the  brain. 

In  min,  the  visuo-sensory  region  is  confined  to  the  mesial  aspect 
•of  the  brain.     A  lesion  of  the  whole  of  the  left  cuneate  lobe  causes 


728 


A  TEXTBOOK  OF  PHYSIOLOUY 


right  hemianopia — blindness  in  the  right  half  of  each  visual  field. 
A  lesion  of  the  region  above  the  calcarine  fissure  causes  hemianopia 
in  the  right  lower  part  of  the  visual  fields  of  both  eyes;  of  the  region 
below  the  calcarine  fissure,  in  the  right  upper  part  of  both  visual 
fields.  The  external  surface  of  the  occi})ital  lobe  is  probably 
concerned  in  ])sychi(!  ))rocesses  connected  with  the  recognition  of  the 
things  seen. 


sensibilityP^ojecfion- 


,Av^ii5!:2^ 


Parietal  and  temporal 
centres  of  association 


.Olfactory  and 
gustatory  projection 
centre 


'«ntre  of  association 


Fia.  l-4'l. — Diagrams    of    the   "Centrks   of    Projection"     and   "Centres    of 
Association."     (Bolton,  after  Flechsig.) 

The  small  dots  are  placed  in  the  cliief  focus  of  each  centre  of  projection;  around  these 
chief  foci  are  regions  (larger  clots)  to  which  a  smaller  number  of  projection-fibres 
pass. 


The  receptive  area  for  hearing  is  situated  in  the  superior  temporal 
lobes  (Fig.  444).  It  is  connected  with  the  inferior  corpora  quadri- 
gemina  by  the  auditory  radiations,  which  pass  through  the  most 
posterior  part  of  the  internal  capsule.  The  effect  of  stimulation 
points  to  this  region  of  the  brain  as  being  concerned  in  hearing.     In 


THE  BRAIN  729 

the  monkey,  it  induces  a  pricking  of  the  opposite  ear,  with  a  rotation 
of  the  head  to  the  opposite  side.  Ablation  effects  are  not  so  con- 
chisive,  as  it  is  difficult  to  tell  whether  an  animal,  like  a  monkey,  is 
deaf  or  not.  Clinical  evidence  points  to  the  central  part  of  the  lobe  as 
the  true  receiving  station — the  audito-sensory  area — and  to  the  area 
just  behind  this  as  the  part  concerned  in  the  psychic  processes — the 
appreciation  of  the  s'gnificance  of  the  sound  heard. 

The  receiving  stations  for  taste  and  smell  are  probably  present  in 
the  anterior  part  of  the  temporal  lobe,  particularly  in  the  deeper 
aspects.  Electrical  stimidation  of  the  hippocampal  region  causes 
movement  of  the  nostril  and  lip  of  the  same  side.  The  evidence  of 
the  effects  of  ablation  and  of  clinical  observation  are  by  no  means 
conclusive.  It  has  been  suggested  that  sensations  of  hunger  and 
thirst  are  received  in  the  cortex  of  the  anterior  part  of  the  temporal 
lobe  in  its  outer  part. 

The  Association  Areas. — The  cortex  as  a  whole  is  to  be  regarded 
as  one  great  association  centre  concerned  in  the  storing  of  sensations 
as  memories,  and  the  association  of  present  with  past  impressions, 
resulting  in  the  power  of  discrimination,  inhibition  of  emotion,  and 
judgment.  There  is  evidence  that  there  is  some  localization  of  these 
functions.  It  has  already  been  pointed  out  that  the  external  aspect 
of  the  occipital  lobe  in  man  is  concerned  with  the  appreciation  of  the 
significance  of  things  seen.  Further,  in  the  angular  gyrus  of  the  brain, 
on  the  left  side  in  right-handed  people,  there  is  thought  to  be  the 
■"  visual  word  area,"  by  means  of  which  the  meaning  of  written  words 
is  appreciated.  So,  in  regard  to  hearing,  it  has  been  pointed  out  that 
the  posterior  part  of  the  temporal  lobe  is  probably  concerned  in  the 
appreciation  of  the  meaning  of  the  sound  heard,  and  in  this  region  is 
also  situated  the  auditory  word  centre,  which  enables  the  appreciation 
of  the  word  heard. 

These  centres  belong  to  one  of  the  three  great  areas  which  have 
been  designated  as  association  areas.  These  areas  are  the  posterior 
— -in  the  parieto-temporal  region — chiefly  concerned  in  sensorial 
function;  the  middle — in  the  island  of  Reil;  and  the  anterior — in 
the  prefrontal  region.  All  these  regions  are  intimately  connected 
by  association  fibres.  The  exact  function  of  the  island  of  Reil  is 
not  known.  In  regard  to  the  frontal  region,  it  is  suggested  that  this 
is  the  centre  concerned  in  voluntary  attention,  memory,  and  thought. 
Dementia  is  associated  with  the  disorder  of  this  region,  the  degree 
of  permanency  varying  according  to  the  degree  of  dissolution  of  the 
area.  If  this  region  be  not  developed,  then  the  subject  is  generally 
permanent^  imbecile  (amentia),  temporarilj'  insane,  or  liable  to  the 
onset  of  insanitj'.  In  the  frontal  region  the  outer  cell  lamina 
is  particularh-  well  marked.  It  is  the  last  to  develop,  the  first 
to  regress. 

Speech. — The  functions  of  the  cerebral  cortex  are  well  illustrated  in 
the  power  of  speech.  To  give  an  answer  to  a  question  directed  to 
him,  a  man  must — 


730 


A  TEXTBOOK  OF  PHYSIOLOGY 


1.  Hear  the  noise — The  receiving  mechanism. 

2.  Api^reciate  the  meaning  of  the  noise  (the  words) 

3.  Associate  it  with  former  stored  impressions 

4.  By  judgment  formulate  the  answer 

5.  Clothe  the  answer  in  words 

6.  Associate  this  answer  with  the  motor  centres 
concerned  in  the  activation  of  the  muscles  taking  part 
in  the  production  of  speech  movements — lips,  tongue, 
larjmx,  etc. 

7.  Send  impulses  down  the  efferent  tracts  to  the  nerves  to 
these  parts,  and  cause  the  muscles  to  functionate — The  discharging 
mechanism. 


The 
association 
mechanism. 


IiG,  445. — Diagram  of  Left  Cerebral  Hemisphere,  showing  Approximate 
Positions  of  the  Centres  concerned  in  Speech.  (From  Purves  Stewart's 
"Diagnosis  of  Nervous  Diseases.") 


Similarly,  a  great  number  of  processes  are  concerned  in  the  appre- 
ciation of  written  words  and  in  the  power  to  express  the  answer  in 
writing.  It  was  at  one  time  believed  that  a  certain  part  of  the  brain, 
known  as  Broca's  area,  was  especially  concerned,  as  the  special  co- 
ordinating centre,  in  sj)eech.  This  area  is  unilateral,  and  is  situated 
in  a  right-handed  person  in  the  left  inferior  frontal  convolution.  It 
is  undoubtedly  in  intimate  connection  with  the  neighbouring  motor 
areas  concerned  in  the  movements  of  the  tongue,  lips,  and  larynx, 
but  it  has  been  shown  that  it  may  be  diseased  without  any  disorder 
of  speech  (aphasia)  resulting.  The  cases  of  "  motor  "  aphasia,  which 
were  said  to  be  the  result  of  a  lesion  of  Broca's  area,  are  now  said  to 
be  due  to  a  lesion  of  the  lenticular  nucleus,  and  to  a  varying  extent 
of  an  area  known  as  Wernicke's  area.  The  former  lesion  involves 
the  external  capsule,  and  possibly  the  anterior  part  of  the  internal 
capsule,  and  causes  an  inability  to  articulate  (anarthria). 

Wernicke's  area  is  situated  in  the  supramarginal  and  angular 
gyri,  comprising  the  "  visual  word  centre,"  and  in  the  posterior  part 
of  the  superior  temporal  sphenoidal  lobe,  comprising  the  "  auditory 
word  centre."     A  lesion  of  the  area  results  in  "  sensory  aphasia," 


THE  BRAIN 


731 


varying  according  to  the  extent  of  the  lesion.  Sometimes  the  impair- 
ment of  intelligence  is  very  marked ;  in  other  cases,  as  in  the  so-called 
cases  of  ''  motor  "  aphasia,  it  is  but  little  affected.  If  the  auditory 
area  be  destroyed,  there  results  a  loss  of  spoken  word  appreciation 
(sensory  aphasia),  with  great  diminution  of  mental  powers.  If  the 
occipital  lobe  be  affected,  there  will  result  alexia,  or  word  blindness — 
an  inability  to  ajDpreciate  the  meaning  of  written  words. 

It  will  be  seen  that  it  is  improbable  that  tiiere  is  any  localized 
speech  centre,  as  suggested  by  Broca.  Disorders  of  speech  are  due 
to  local  lesions,  bringing  about  a  loss  of  continuity  between  the  cortical 
centres  concerned  in  the  power  of  speech.  "'  Motor  "  aphasia,  there- 
fore, is  probabh'  not  due  to  a  lesion  of  Broca's  area,  but  principally 
to  a  lesion  of  the  lenticular  nucleus,  causing  an  inability  to  articulate, 
often  combined  with  a  lesion  of  the  sensorv  area  of  Wernicke. 


<:^^- 


Fiu.  446. — ^Diagram  of  Speech  Centres.     (After  Bramwell,  from  Purves  Stewart's 
"Diagnosis  oE  Nervous  Diseases.") 

Similarly,  in  the  power  to  read  and  to  clothe  thoughts  in  writing 
there  is  involved  a  number  of  centres  connected  by  association  fibres 
(see  Fig.  446). 

Reaction  Time. — -Various  methods  have  been  devised  for  measuring 
the  "  reflex  time,"  or,  as  it  is  usually  termed,  the  "  reaction  time," 
of  conscious  processes,  such  as  sight,  hearing,  the  response  being  by 
movement  or  speech,  etc.  The  subject  is  usually  told  to  perform 
some  movement,  recorded  on  a  drv;m,  such  as  to  open  an  electric  key 
or  to  depress  a  lever,  directly  he  receives  the  stimulus,  which  is  also 
recorded — e.g.,  the  ringing  of  a  bell,  the  appearance  of  a  coloured  disc. 
The  "  reaction  time  "  is  made  up  of  the  time  taken  in  the  conduction  of 
the  impulse  to  and  from  the  brain,  and  of  the  processes  in  the  brain. 
From  the  knowledge  of  nerve  conduction  and  of  the  reflex  times  of 
simple  arcs  we  can  measure  the  reaction  time  of  more  complicated 
cerebral  processes.  The  more  complicated  the  process,  the  longer 
the  time.     Thus,  if  a  man  has  to  move  his  right  hand  when  a  red  disc 


732  A  TEXTBOOK  OF  PHYSIOLOGY 

is  shown,  and  his  left  liaiid  when  a  green  one  is  shown,  the  time  is  con- 
siderably longer  than  if  he  has  to  make  a  simple  motor  resj^onse  with 
one  hand  to  any  kind  of  disc.  Still  more  complex  is  the  process 
when  the  subject  has  to  speak  different  words  in  response  to  different 
forms  of  stimulation. 

Mind  and  Consciousness. — Extero-,  proprio-,  and  entero-ceptive  im- 
pulses stream  into  the  central  nervous  system  from  the  time  of  its 
embryonic  development  until  death,  ceaselessly  modify  the  pattern 
of  its  structure,  lay  down  the  pathways  of  reflex  actions,  and  establish 
habits.  A  very  large  proportion  of  these  impulses,  and  particularl}'- 
the  proprio-  and  entero-ceptive,  never  enter  nito  consciousness,  and 
yet  occasion  actions  which  are  perfectly  adapted  to  the  end  in  view. 


Fig.  447. — Diagram  of  the  Apparatus  for  the  Determination  of  Reaction 

Time.     (W.  G.  Smith.) 

The  clectro-magnotic  tuning-fork  T,  with  100  vibrations  per  seccud,  is  connected 
with  two  Daniell  cells  and  with  the  chronograph  0.  By  means  of  either  of  the 
two  Du  Bois  keys,  K^  and  K2,  the  chronograph  can  be  short-circuited.  The  key 
A'j  is  closed  and  K.^  is  open;  the  tuning-fork  is  set  vibrating,  but  does  not  affect 
the  chronograph.  The  subject,  whose  reaction  time  is  to  be  determined,  is  told 
to  listen  for  the  sound  of  the  opening  of  the  key  K^,  and  to  close  the  key  A""., 
directly  he  hears  the  sound.  When  the  key  K^  is  ofjened  the  chronograph 
vibrates  in  unison  with  the  tuning-fork  and  the  vibrations  are  recorded  upon  a 
revolving  drum;  the  closure  of  the  key  iVg  by  the  subject  of  the  experiment 
brings  the  chronograph  to  rest.  The  number  of  vibrations  recorded  upon  the 
drum  gives  the  reaction  time  for  sound  in  yw^^''^  ^^  ^  second. 

For  example,  the  character  cf  the  saliva  secreted  is  adapted  according 
as  sand  or  bread  is  put  into  the  mouth.  In  the  one  case  a  watery 
saliva  is  secreted,  in  the  other  a  saliva  containing  the  ferment  ptyalin. 
It  might  be  argued  that  the  salivary  centre  felt,  judged,  and  willed 
an  appropriate  action,  and  yet  none  of  these  processes  enter  into 
consciousness.  We  each  have  from  moment  to  moment  of  our  waking 
life  a  general  consciousness  of  well-being  or  the  reverse,  maintained  by 
proprio-  and  entero-ceptive  impulses  arising  in  the  organs  and  tissues 
of  the  body,  coujjled  with  a  tone  of  feeling  evoked  by  extero-ceptive 
sensations.  These  arouse  in  us  from  time  to  time  emotions  of  in- 
difference, pleasure,  pain,  affection,  hate,  sex,  etc.  The  more  powerful 
extero-ceptive  sensations  not  only  enter  into  consciousness,  but  so 
alter  the  pattern  of  the  brain  structure  as  to  store  memories — in  what 


THE  BRAIN 


733 


manner  we  have  no  knowledge.  The  sensations  of  the  present  moment 
may  arouse  one  or  other  of  these  memories  to  which  it  is  attmied. 
Our  actions  are  controlled  from  moment  to  moment  by  the  sensations 
which  stream  in  at  the  present  time,  and  the  memories  of  j)ast  sensa- 
tions which  are  aroused  b}^  these. 

Our  knowledge,  opinions,  and  beliefs  are,  then,  the  result  of  the 
supply  of  sensations  furnished  by  impulses  acting  on  the  brain  struc- 
ture. Without  such  sensations,  no  mind  or  consciousness  would  be 
manifest.  The  extero-ceptive  mechanism  plays  an  all-important  part. 
This  is  well  seen  in  the  case  of  Helen  Keller,  who,  deaf  and  dumb, 
and  uneducated,  when  her  ej^'es  were  closed,  fell  asleep. 

Memory  forms  the  basis  of  our  experience  and  knowledge,  and  our 
so-called  voluntary  actions,  initiated  by  the  cerebrum,  result  as  in- 
evitably as  a  spinal  reflex  action  from  the  synthesis  of  present  and 


Fig.  448.— Reaction  Times  to  Touch,  Hearixo,   Stciit.     (Waller.) 


memorized  sensations,  some  of  which  inhibit,  and  others  facilitate, 
motor  response.  Education  thus  becomes  of  supreme  power  in 
moulding  the  actions  of  a  man's  life. 

As  the  pattern  of  the  brain  is  ceaselessly  altered  by  instreaming 
sensations  and  metabolic  processes,  the  personality  of  a  man  alters 
from  moment  to  moment.  The  babe  develops  into  the  man  of  genius, 
and  he,  if  he  lives  long  enough,  becomes  a  dotard  in  his  old  age.  By 
the  time  he  is  in  his  second  childhood  the  personality  of  his  prime 
manhood  has  left  him,  for  this  de]:)ends  on  characteristic  responses  to 
sensations,  and  these  can  no  longer  be  aroused  in  a  brain  the  structure 
of  which  has  deteriorated  with  age,  and  from  which  the  store  of 
memories  has  largely  vanished.  We  must  remember  that  the  work 
of  a  genius  is  the  accumulated  result  of  successive  and  innumerable 
moments  of  interaction  of  sensations,  present  and  memorized.  His 
output  results  from  the  inborn  cpialities  of  the  sense  organs  and  brain 
structure  on  the  one  hand,  and  education  on  the  other — the  storage 
of  his  experience — and  that  of  humanity  handed  on  by  oral  or  written 


734  A  TEXTBOOK  OF  PHYSIOLOGY 

tradition.  At  oiie  moment  the  man  of  genius  may  be  conscious  of 
nothing  but  the  desire  to  visit  the  privy,  and  at  another  moment  he 
may  be  conscious  of  the  word  which  makes  perfect  a  line  of  poetry. 

Consciousness  leaves  us  when  the  brain  is  suddenly  rendered 
anaemic  by  closure  of  the  carotid  arteries.  It  leaves  us  in  sleep,  and 
when  a  chemical  agent,  such  as  nitrous  oxide  or  other  anaesthetic, 
interferes  with  the  play  of  chemical  and  physical  forces  in  the  nervous 
tissue.  The  nervous  tissue  acts  as  a  transformer  of  energy,  and  when 
it  becomes  inactive  or  is  destroyed,  that  form  of  energy  which  we  call 
consciousness  ceases. 


CHAPTER  LXXIV 
SLEEP 

Sleep  is  to  be  regarded  as  the  period  of  rest  of  tiie  great  brain, 
and  to  a  certain  extent  of  the  central  nervous  system  and  of  the  body 
generally.  It  is  probable  that  absolute  lack  of  sleep  would  kill  a 
man  even  more  speedily  than  absolute  lack  of  water,  and  certainly 
more  quickly  and  painfully  than  the  withdrawal  of  food.  Yoimg 
puppies  three  to  four  months  old,  deprived  of  sleep  for  four  to  five 
daj's,  died  either  at  once  or,  if  then  allowed  to  sleep,  after  a  few 
days.  The  younger  the  animal,  the  more  speedy  its  death.  The 
body  temperature  began  to  fall  on  the  second  day,  until  just  before 
death  the  temperature  was  about  5°  C.  below  normal.  The  number 
of  blood-corpuscles  became  greatly  diminished,  and  after  death  mam"- 
capillar}'  haemorrhages  were  found  in  the  brain. 

It  is  probable  that  the  greater  the  animal's  need  of  sleep,  the 
quicker  its  death  from  sleeplessness.  Dogs  sleep,  probablj-,  on  an 
average  twice  as  long  as  man,  who  normally  sleeps  about  one-third  of 
his  life.  Some  men  require  considerably  less  sleep  than  others;  wh}-, 
it  is  difficult  to  say.  Children  require,  according  to  age,  from  twelve 
to  ten  hours'  sleep,  women  and  men  from  eight  to  five  hours'.  Birds 
apjjarenth-  require  less  sleep  than  mammals.  Some  mammals  require 
considerably  more  sleep  than  others.  This  is  partly  due  to  the  character 
of  the  sleep,  a  short  profound  sleep  being  as  efficacious  as  a  longer  less 
deep  sleep.  Man  is  a  deep  sleeper;  the  dog  is  a  light  sleeper.  The 
companionship  of  the  dog  has  helped  man  to  attain  to  his  supremacy. 
But  for  the  companionship  and  guardianship  of  the  light  sleeper,  the 
deep  sleeper  would  have  been  destroyed  by  night-prowling,  man- 
eating  enemies. 

Many  observations  have  been  made  upon  man  to  determine  the 
phj'siological  conditions  during  sleep.  Most  marked  is  the  loss  of 
consciousness.  It  is  stated  that  sleep  is  more  profound  in  the  half 
of  the  brain  which  has  been  active  during  the  day,  so  that  right- 
handed  people  when  asleep  flick  away  a  fly  with  the  left  hand,  while 
true  left-handed  people  perform  such  an  act  with  the  right  hand. 
The  depth  of  the  loss  of  consciousness  may  be  gauged  b}'  stimuli, 
such  as  the  ringing  of  a  bell  at  half-hour  intervals  during  the  sleep, 
the  dropping  of  a  lead  ball  from  a  given  height  on  to  a  lead  plate, 
or  the  application  of  electrical  stimuli  of  known  intensit}-.  By  such 
means  it  has  been  determined  that  the  greatest  intensity  of  sleep 
occurs  after  about  an  hour  to  an  hour  and  a  half  from  the  onset  of 

735 


736  A  TEXTBOOK  OF  PHYSIOLOGY 

sleep.  From  the  third  hour  onwards  the  sleep  in  many  cases  is  of  a 
light  type.  In  some  cases  there  is  a  second  rise  in  the  intensity  of 
the  depth  of  sleep  in  the  fourth  to  fifth  hours  after  onset.  This  form 
has  been  said  to  occur  particularly  in  persons  of  a  nervous  tempera- 
ment. Although  the  greatest  refreshment  from  sleep  occurs  during 
the  first  hours,  it  has  been  shown  that  the  subsequent  hours  are  also 
effectual.  It  is  easier  to  do  complicated  mental  work  after  several 
hours'  sleep  than  after  only  a  iew  hours'  sleej),  although  simple  mental 
acts  can  be  performed  equally  well  after  but  a  few  hours'  sleep. 

It  is  in  the  waking  hours  that  dreams  occur,  and  they  are  generally 
of  short  duration.^  The  dreams  of  healthy  sleep  are  frequently  of 
the  past  or  of  a  fantastic  nature.  Only  in  broken  sleep  is  the  day's 
work  continued  or  present-day  affairs  worried  over.  In  healthy  sleep 
the  parts  of  the  brain  most  active  during  the  day  should  rest  most  pro- 
foundly during  the  night.  The  parts  of  the  brain  do  not  fall  asleep 
or  wake  at  the  same  instant.  Response  to  sound  sensations  are  the 
last  to  go  and  the  first  to  return. 

In  addition  to  the  great  brain,  the  other  parts  of  "the  central 
nervous  system  are  also  resting.  The  respiratory  centre  is  affected. 
Respiration  is  slowed  and  deepened,  and  frequently  becomes  some- 
what periodic  (Cheyne-Stokes)  in  type.  The  reflexes  are  depressed, 
the  knee-jerk  is  scarcely  present  or  absent  altogether. 

The  rate  of  heart-beat  is  slowed,  the  heart  beats  less  forcibly,  and 
the  arterial  pressvire  falls,  during  sleep. 

Owing  to  the  relaxation  of  the  muscles  and  of  the  bloodvessels  in 
the  warm,  quiet  state  of  the  body,  the  blood  stagnates  in  the  peripheral 
capillaries  and  veins,  and  the  circulation  is  much  less  rapid.  Less 
oxygen  is  required,  and  the  blood  moving  slowly  through  the  capil- 
laries fulfils  the  metabolic  needs  of  the  resting  tissues.  It  furnishes 
a  reserve  supply  of  "  munitions  "  for  active  service  during  the  waking 
period. 

In  the  brain,  also,  the  venous  side  of  the  circulation  is  more  con- 
gested and  the  blood-flow  sluggish.  When  the  sleeper  is  aroused, 
the  tone  of  the  muscles,  skeletal  and  vascular,  at  once  increases; 
the  blood  is  sent  from  the  periphery  to  the  viscera,  and  the  velocity 
of  the  blood-flow  is  increased  through  the  brain.  The  general  meta- 
bolism is  lessened  during  sleep.  The  carbon  dioxide  output  and  the 
oxygen  intake  show  a  marked  decrease.  The  bodily  temperature  also 
falls  to  its  lowest  point  during  the  night.  In  the  early  morning  hours 
the  bodily  metabolism  is  at  its  lowest  ebb. 

The  bodily  secretions  are  diminished  during  sleeji.  The  "  night  " 
urine  in  healthy  persons  is  less  in  quantity  and  more  concentrated  than 
the  day  urine.  The  amount  of  saliva  is  also  decreased,  and  possibly, 
also,  the  alimentary  juices. 

The  onset  of  sleep  is  flavoured  by  muscular  and  mental  fatigue 
and  by  the  withdrawal  of  all  stimuli  of  the  extero-ceptive  nervous 
mechanism,  especially  light  and  sound. 

Fatigue  produces  a  metabolic  condition  of  the  nervous  tissue 
which  tends  to  put  in  abeyance  the  power  of  response  to  stimulation ; 


SLEEP 


737 


with  the  weakening  or  withdrawtxl  of  the  stimuli  the  ab83^ance  becomes 
complete.  Tlie  over-fatigued  soldier  falls  asleep  in  a  dug-out  in  spite 
of  the  enemy's  shells  bursting  around  him.  We  ordinarily  favour  the 
onset  of  sleejD  by  seeking  the  warm,  quiet,  and  dark  atmosphere  of  our 
beds,  where  the  excitements  of  the  outside  world  are  at  a  minimum. 

Sleep  has  been  attributed  to  a  lessened  circulation  of  blood  through 
the  brain,  caused  hy  the  dilatation  of  the  vessels  of  the  skin  and  of 
the  siDlanchnic  area.  Rest  in  an  armchair  in  a  warm  room  after  a 
heavj^  meal  conduces  to  sleep.     Exposure  to  cold  wind  repels  it. 

The  periodicity  of  sleep  has  been  attributed  to  a  gradual  loss  of 
tone  of  the  vaso-motor  centres.  When  awake  the  vessels  of  the  body 
are  so  regulated  that  the  blood-supply  of  the  brain  is  ample,  but  as 
fatigue  of  the  vaso-motor  mechanism  ensues  the  blood-supply  to  the 
brain  gradually  lessens,  and  the  increasing  ansemia  induces  the  onset 
of  sleep. 


Fig.  4i9. — Cobka  Hypnotized  by  Stroking,  and  made  Stiff  and  Strai  ;kt. 


Another  view  of  sleep  is  that  it  is  due  to  the  accumulation  of  waste 
products  or  fatigue  toxins  within  the  body.  It  has  also  been  suggested 
that  the  synapses  of  the  neurons  are  interrupted  in  slee^)  by  an  amoeboid 
retraction  which  blocks  the  conduction  of  impulses.  There  is  no 
evidence  of  this. 

There  is  no  single  theory  which  satisfactorily  explains  the  phe- 
nomena of  sleep. 

Narcosis. — The  unconsciousness  induced  by  volatile  anaesthetics 
is  due  to  chemical  change  of  the  nerve  cells.  As  the  result  of 
prolonged  ansesthesia,  degenerative  changes  are  induced  in  the  nerve 
cells  and  elsewhere.  The  volatile  ansesthetics  easily  permeate  the 
cell  protoplasm.  Theie  is  no  need  to  evoke  the  lipoid  nature  of  the 
cell  membrane  as  an  explanation.  When  administration  of  the  anses 
thetic  ceases,  the  volatile  anaesthetic  diffuses  again  from  the  cell  into 
the  blood,  and  the  state  of  anaesthesia  gradually  passes  off  as  the 
drug  is  breathed  out. 

Hypnosis. — -The  condition  of  hypnosis  superficially  resembles  that 
of  normal  sleep.  It  may  be  induced  in  many  animals  merely  by 
holding  them  in  a  strange  posture,  as  in  the  well-known  "  experi- 
ment um  mirabile,"  which  consists  in  placing  a  fowl  on  its  back  Avith 
its  beak  to  a  line  chalked  upon  the  ground.     In  man  it  is  produced 

47 


738  A  TEXTBOOK  OF  PHYSIOLOGY 

b}'  suggestion,  generally,  but  not  necessarily,  verbal  in  nature.  It  is 
essential  that  the  subject  have  the  idea  of  sleep  and  be  prepared  to 
surrender  himself  to  the  treatment  of  the  operator. 

Experiment  shows  that  the  condition  differs  in  several  respects 
from  normal  sleep.  The  bloodvessels  of  the  skin  are  constricted, 
the  volume  of  the  limbs  is  diminished,  the  blood-volume  of  the  face, 
and  probably  the  circulation  through  the  brain,  is  increased.  The 
pulse  and  respirations  are  usually  quickened.  The  individual  becomes 
an  automaton.  The  judgment  powers  of  the  higher  centres  are  in 
abeyance,  but  the  receptive  centres  are  alert.  Thus,  the  subject  may 
imhesitatingly  perform  an  order  if  not  too  extravagant  or  believe  a 
fact  suggested  to  him.  If  told  to  perform  a  certain  act  at  a  certain 
hour,  the  act  may  be  done;  if  told  that  he  is  paralyzed,  the  subject 
may  act  as  if  such  were  indeed  the  case. 

Hypnosis  has  been  practised  in  medicine,  but  is  of  doubtfvd  value, 
except,  perhaps,  for  certain  nervous  disorders.  Operations  can  be 
performed  in  the  hypnotic  state,  but  such  operations  are  better  per- 
formed under  ordinary  narcosis.  The  whole  subject  is  surrounded 
by  quackery  and  li3S. 

Hibernation. — Certain  animals  retire  at  times  to  their  shelters  and 
pass  into  a  torpid  state  known  as  "  hibernation."  Such  animals 
include  insects,  amphibians,  reptiles,  and  mammals  such  as  the  dor- 
mouse, squirrel,  hedgehog,  marmot,  bat,  beaver,  and  bear.  As  the 
name  implies,  hibernation  generally  occurs  with  the  approach  of 
cold  weather,  but  this  is  not  necessarily  the  case.  Some  animals 
begin  to  hibernate  in  summer,  or  will  hibernate  Avhen  kept  in  a 
warm  room  away  from  cold.  Cold  is  not  the  cause  of  hibernation; 
in  fact,  intense  cold  stops  it.  It  is  a  device  for  seciu-ing  the  continu- 
ance of  life  during  a  period  when  food  is  lacking.  Before  hibernating 
the  animal  puts  on  fat.  It  has  been  suggested  that  the  state  is  a 
narcosis  induced  by  the  accumulation  of  COg  within  the  body.  The 
body  temperature  falls,  the  excitability  of  the  nervous  system  is 
depressed,  the  frequency  of  respiration  is  slowed,  and  the  heart 
force  and  frequency  are  much  reduced. 

The  awakening  from  hibernation  is  characterized,  in  warm-blooded 
animals,  by  a  sudden  rapid  rise  of  body  temperature,  accompanied 
by  a  greatly  increased  discharge  of  carbon  dioxide  from  the  body. 


CHAPTER  LXXV 
SOUND  PRODUCTION  AND  SPEECH 

The  power  of  speech  is  indicative  of  the  high  cerebral  development 
of  man.  Animals  possess  the  power  of  sound  production,  but  not  of 
speech.  Among  the  insects  sound  is  produced  chiefly  by  a  rapid 
rhythmic  movement  of  one  hard  part  against  another,  such  as  the 
chirping  of  crickets  and  grasshoppers.  The  groan  of  the  death's- 
head  moth  is  possibly  produced  by  the  moth  drawing  air  through  its 
tracheae,  but  more  probably  by  a  rapid  movement  of  the  palps 
against  the  proboscis.  Among  the  animals  higher  in  the  scale  of 
evolution  soimd  is  produced  by  a  blast  of  air  upon  elastic  mem- 
branes. The  voice  of  amphibians  is  due  to  the  driving  of  air  jiast 
the  tightly  stretched  membranes  of  the  larynx ;  the  same  is  true  of 
the  song  of  the  bird  and  of  the  voice  of  mammals  and  man. 

The  speech  organs  are — (1)  The  wind  chest  (the  lungs)  with  the 
wind  tubes  (the  bronchi  and  trachea);  (2)  the  sound-producer  (the 
larynx);  (3)  the  sound  modifier  (the  cavities  of  the  mouth,  nose,  and 
throat). 

The  wind  chest  drives  the  air  through  the  reed  instrument  (the 
larynx);  the  vibration  of  the  reeds  (the  vocal  cords)  produces  the 
I)itch  of  the  sound,  and  the  mouth  and  nose  cavitj%  resonating  like 
the  tube  of  a  trumpet,  amplifies  certain  overtones  and  gives  the  quality 
which  determines  speech. 

The  proper  management  of  the  breath  is  most  important.  We 
have  seen  that  the  breathing  is  regulated  by  the  partial  pressure  of 
CO.,  in  the  alveolar  air,  or,  rather,  by  the  concentration  of  acid 
(H+)  ions  in  the  blood.  We  can  alter  the  breathing  by  means  of 
the  ^will  only  within  narrow  limits.  A  shortage  of  air  and  a  rise 
of  the  partial  pressure  of  CO.2  will  inevitably  cut  short  the  most 
eloquent  periods,  and  give  the  speaker  a  catch  in  his  breath.  We 
must  learn  to  speak  with  a  full  lung,  on  the  complemental  and  not 
on  the  tidal  air-supply.  The  contraction  of  the  belly  muscles  muyt 
balance  the  positive  pressm'e  in  the  thorax  diu*ing  the  singing  of  a 
sustained  note,  so  that  the  circulation  may  continue  unimpaired. 
The  stammerer  fails  to  use  his  diaphragm  properly;  the  bellows 
of  his  wind  chest  is  at  fault,  or,  more  correctly,  the  nerve  centre 
which  plays  upon  the  bellows.  The  vocal  cords  vibrate  in  much 
the  same  way  as  do  the  lips  in  blowing  a  trumpet.  In  a  reed 
pipe  the  air  is  stopped  intermittent^  for  a  moment,  and  then 
let  pass  by  the  vibrating  tongue   or  reed,   so  that  a  set  of  pulses 

739 


740 


A  TEXTBOOK  OF  PHYSIOLOGY 


is  given  to  the  air,  which  is  alternately  rarefied  and  condensed; 
the  number  of  these  pulses  is  determined  by  the  length  of  the  "  tongue  " 
(pendulum).  The  audible  sound  is  produced,  not  by  the  "  tono^ue 
itself,  but  by  the  pulses  of  the  air.  By  placing  the  middle  and  fore 
finger  lightly  on  either  side  of  the  thyroid  cartilage  and  singing  a 
sustained  note,  one  can  feel  the  cords  vibrate.  A  blast  of  air  blown 
through  a  sheep's  trachea  and  larynx  will  give  forth  a  sound  when  the 
cords  of  the  larynx  are  tightened  (Fig.  450).  The  blast  force.3  the  cords 
towards  the  mouth,  and  they  swing  back  owing  to  their  elasticity. 

The  larynx  consists  of  a  stiff-walled  cartilaginous  box  divided  by 
the  membranous  vocal  cords  into  two  chambers  of  unecpial  size,  one 
above  the  other.  The  cords,  placed  one  on  either  side  and  opposite 
each  other,  can  be  tightened  or  slackened,  thickened  or  thinned, 
shortened  or  lengthened,  moved  towards  or  away  from  each  other, 
so  as  to  leave  either  a  wide  or  narrow  slit — the  rima  glottidis — through 
^vhich  the  air  blast  passes. 


Pig.  450. — Expkrimental  Sounds  prodtjced  by  Blowing  through  Sheep's 

Trachea. 


The  vibration  of  the  cords  can  be  discerned  in  man  by  means  of  the 
laryngoscope.  A  small  flat  mirror  (Fig.  451)  is  attached  at  an  angle  to  a 
long  handle,  so  that  the  mirror  can  be  passed  to  the  back  of  the  throat 
and  the  reflection  of  the  rima  glottidis  seen,  when  a  light  is  cast  upon 
it  from  another  mirror.  This  second  mirror,  a  concave  one,  is  fastened 
to  the  forehead,  and  has  a  central  hole  in  it  for  the  eye,  and  is  placed 
so  as  to  reflect  the  light  of  a  lamp  on  to  the  small  mirror  (Fig.  452).  If 
an  intermittent  source  of  illumination  is  used,  and  the  number  of 
intermissions  is  the  same  as  the  number  of  vibrations  of  the  vocal 
cords,  these  appear  as  if  stationary;  but  if  the  intermissions  are  not 
quite  at  the  same  rate,  then  the  cords  ajopear  to  be  slowly  moving. 


SOUND  PRODUCTION  AND  SPEECH 


741 


This  optical  method  employed  for  determining  the  rate  of  vibration  is 
that  of  the  stroboscope.  Lesions  of  the  vocal  cords  or  of  the  neuro- 
muscular mechanism  which  prevent  their  vibration  cause  loss  of  voice. 
The  height  of  a  tone  in  such  a  two-lipped  reed  pipe  as  the  larynx 
depends  on  the  length,  thickness,  and  tension,  of  the  cords,  and  to  a 
certain  degree  on  the  strength  of  the  air-blast. 


Pig.  4.51. — Examination  of  the  I<arynx  by  the  Lakvxgoscope. 

The  shorter  and  more  strongly  stretched  the  membrane,  the  higher 
is  the  tone;  women  and  children  have  a  smaller  larynx  and  shorter 
cords,  and  hence  high-pitched  voices.  At  puberty  there  is  a  rapid 
increase  in  growth,  and  the  breakino-  of  the  voice  is  due  to  the  want 


Fig.  4:52. — To  illustr.\te  the  Manner  in  which  a  View  of  the  Interior  of  thk 

Larynx  is  obtained. 


of  co-ordination  between  the  innervation  and  the  muscular  mechanism 
which  has  so  rapidly  increased  in  strength.  The  new  apparatus  has 
to  be  practised  by  the  growing  lad. 

The  structure  of  the  larynx  has  been  evolved  to  allow  the  read\^ 
alteration  of  the  length  and  tension  of  the  cords.     Four  cartilages — 


742  A  TEXTBOOK  OF  PHYSIOLOGY 

the  cricoid,  the  thyroid,  and  two  arytenoids — are  articulated  and  knit 
together  by  ligaments. 

The  cricoid,  shaped  like  a  signet  ring,  articulates  with  the  inferior 
horns  of  the  thyroid,  and  can  rotate  round  an  axis  which  passes 
through  these  joints.  Each  arytenoid  is  jointed  to  the  ring  plate 
of  the  cricoid  behind  by  a  triangular  surface.  This  joint  allows 
movements  in  three  planes. 

The  cartilages  can  glide  outwards  and  separate  from  each  other. 
They  can  turn  round  a  vertical  axis  {i.e.,  an  axis  in  the  direction  of 
the  trachea),  whereby  their  vocal  processes  which  project  forwards 
are  turned  outwards  or  inwards.  They  can  move  round  an  axis 
which  passes  inwards  and  upwards  from  below  and  outwards,  whereby 
the  vocal  processes  glide  forwards  and  outwards,  or  backwards  and 
inwards.  These  movements  are  limited  by  a  strong  band — the 
crico-arytenoid  ligament. 

The  mucous  membrane  of  the  larynx  is  raised  into  folds  which  run 
from  before  backwards.     The  false  vocal  cords  do  not  reach  so  far 


Fig.  4.53. — View  of  Larynx  obtained  by  the  Laryngoscobe. 

a.    Epiglottis;   b,  thyroid;  c,   vocal  cord;   d,   aryepiglottidean    fold;  e,  cartilage  ut 
Wrisberg;/,  cartilage  of  Santorini;  g,  pharynx. 

middlewards  as  the  true.  The  true  cords  in  section  have  the  shape  of 
a  three-sided  prism.  The  upper  side  of  each  is  vertical  to  the  longi- 
tudinal direction  of  the  windpipe,  the  under  surface  slopes  up  to 
meet  this,  and  the  edges  so  formed  become  sharp  during  vocalization. 
The  cords  run  from  the  vocal  processes  of  the  arytenoids  to  about 
the  middle  of  the  angle  formed  by  the  two  wings  of  the  thyroid  car- 
tilage. The  cords  contain  much  elastic  tissue  and  the  fibres  of  the 
thyro-arytenoideus  muscle.  The  part  of  the  rima  between  the  cords 
is  called  pars  vocalis,  and  the  part  between  the  arytenoid  cartilages 
pars  respiratoria.  The  muscular  mechanism  for  changing  tension, 
length,  and  thickness,  in  addition  to  the  laryngeal  muscles,  includes 
the  sterno-thyroid,  hyo-thyroid,  and  laryngo-pharyngeal  muscles. 
These  act  indirectly,  fixing  the  larynx  and  steadying  it  for  the 
direct  action  of  the  laryngeal  muscles. 

The  Posterior  Crico-Arytenoid  Muscles. — Each  arises  from  the 
posterior  surface  of  the  ring  plate  of  the  cricoid,  and  is  inserted  into 
the  muscular  process  of  an  arytenoid.  They  pull  these  processes  in- 
wards, and  so  turn  the  vocal  process  outwards.     Their  antagonists 


SOUND  PRODUCTION  AND  SPEECH 


743 


are  the  lateral  crico-arytenoid  muscles;  each  arises  from  the 
inner  surface  of  the  ring  of  the  cricoid,  and  is  inserted  on  the 
muscular  processes  of  an  arytenoid.  Thej'  close  the  chink  of  the 
glottis. 

The  arytenoid  muscles,  transverse  and  oblique,  bring  the  two 
ar3i:enoid  cartilages  together.  If  these  muscles  are  slack,  the 
lateral  and  posterior  crico-ar3-tenoids,  acting  together,  widen  the 
ohink. 

The  crico-thyroids  are  the  chief  tighteners  of  the  cords.  The 
fibres  arise  from  the  outer  surface  of  the  ring  on  either  side,  and  run 
upwards  and  backwards  to  the  thjToid.  Thej'  pull  the  front  part  of 
the  ring  up  to  the  thyroid  and  depress  the  ring-plate;  and  this  move- 
ment, carrying  the  arytenoids  with  it,  lengthens  the  distance  between 


A.C 


M.Pr.- 


C.A.L. 


Fig.  45-i. — Scheme  of  Laryngeal  Muscles.     (Parsons  and  Wright.) 

Th.C,  Thyroid  cartilage;  A.C,  arytenoid  cartilage;  Th.A.,  thyro-arytenoideus; 
O.A.L.,  crico-arytenoideus  lateralis;  C.A.P.,  crico-arytenoideus  posticus;  A., 
arytenoideus ;  V.Pr.,  vocal  process  of  arytenoid;  M.Pr..  muscular  process  of 
arytenoid. 


the  vocal  processes  and  the  thyroid.  The  antagonists  are  the  thyro- 
arytenoids, which  run  from  the  anterior  angle  of  the  thyroid  to  the 
vocal  process,  some  of  the  fibres  beginning  and  ending  in  the  elastic 
tissue  of  the  cords.  These  muscles  can  thicken  the  cord  and  press 
its  edge  towards  the  middle  line.  Acting  with  the  crico-thyroid,  they 
increase  the  tension  of  the  cords. 

The  tension  of  the  cords  has  been  measured  by  passing  the  blades 
of  a  scissor-like  sj)ring  gauge  between  them.  The  greatest  tension  is 
produced  by  the  combined  action  of  the  crico-thyroid,  posterior 
crico-arytenoid,  and  thyro-arytenoid — i.e.,  the  pull  is  said  to  be  ecpial 
to  that  of  a  kilogramme.  The  thyro-arytenoids  also  can  vary  the 
tension  of  different  parts  of  the  cords. 

The  whole  length  of  the  cords,  including  the  vocal  processes, 
Anbrates  in  deep  notes,  and  the  tension  is  raised  as  the  pitch  rises. 
For  the  higher  notes,  the  vocal  processes  are  pressed  together  and 
the  shortened  cords  alone  used. 

In  using  the  chest  or  normal  register,  the  chink  is  narrow  and  long. 


744 


A  TEXTBOOK  OF  PHYSIOLOGY 


the  cords  vibrate  in  their  whole  length,  the  pressure  of  the  air  is  re- 
latively large,  the  volume  of  air  used  small,  and  the  strain  of  production 
not  great.  In  using  the  head  register,  the  chink  is  wider  and  shorter, 
the  hind  part  closed,  the  pressure  of  the  air  smaller,  but  more  air  is 
used,  and  so  the  strain  is  greater. 

The  internal  fibres  of  the  thyro-arytenoids  may  contract  alone,  so 
that  the  inner  edges  of  the  cords  are  rendered  tense,  while  the  outer 
thicker  parts  are  slack.  In  whispering  the  air  rustles  past  the-opened 
cords. 

While  the  pitch  of  the  voice  is  given  by  the  number  of  vibrations 
of  the  cords  per  second,  the  changing  quality  depends  on  the  resona- 
tion  of  certain  of  the  overtones  in  the  resonating  cavities  formed  by 
mouth,  nose,  and   throat.     The    mouth    can  be  shut  up  almost  by 


Position  of  rest.  (The  vocal  cords  ar^' 
midway  between  abduction  and  ad- 
duction ) 


Position  during  forced  inspiration.  [(Tl'.e 
vocal  cords  are  in  extreme  abduc- 
tion.) 


Position  during   vocalization. 
^  voice." )     The    vocal    cords 


("Chest 
are    ad- 

ductcd   and   vibrating  in   their  entire 

length. 


Position  during  vocalization.  (FaUetto 
voice.)  The  vocal  cords  are  adducted 
and  vibrating  in  their  anterior  por- 
tions onlv. 


Fig.  455  — Tiagkams  to  illustrate  the  Position  of  the  Vocal  Cords  under 
Various  Circumstances. 


raising  up  the  tongue  and  drawing  in  the  cheeks,  or  it  can  be  opened 
so  as  to  form  a  wide  cavity.  The  pillars  of  the  fauces  are  flexible, 
and  can  be  brought  forwards  against  the  tongue,  or  pulled  widely 
apart.  The  soft  palate,  by  sinking,  can  throw  the  nose  into  the  resonat- 
ing cavity  and  cut  off  the  mouth,  or,  by  rising,  cut  off  the  nose.  By  a 
mean  position  both  cavities  may  come  into  play.  The  tongue  can 
widen  or  narrow  the  mouth  cavit}-,  divide  it  into  sections  and  connect 
these  by  slits,  or  cut  them  off  from  one  another.  In  the  chest  register 
the  passage  for  the  voice  is  wide  and  the  chest  cavity  amplifies  the 
resonance.  In  the  head  register  the  passage  is  narrow  and  the  reson- 
ance is  confined  to  the  cavities  of  the  head.  While  in  singing  and 
vocalization  the  vocal  cords  twang,  in  whispered  speech  the  resonating 
cavities  alone  suffice  for  the  production  of  speech. 


SOUND  PRODUCTION  AND  SPEECH 


745 


Vowels.  —  The  vowels  are  tones  produced  in  the  larynx,  and 
modified  by  the  form  of  the  resonating  cavity.  The  consonants  are 
in  the  main  noises  produced  by  alterations  in  the  resonating  cavity, 
alterations  which  momentarily  check  the  air  blast,  and  so  lead  to  an 
explosive  sound,  or  lead  to  the  vibration  of  lips  or  tongue,  as  the  air 
rushes  through  orifices  which  are  of  changing  form. 

A  {ah) :  The  mouth  is  opened  funnel-shaped  from  behind  forwards, 
the  tongue  lies  flat  on  the  floor. 

0  {go) :  The  mouth  opens  bj^  a  narrow  slit,  the  jaws  and  lips  being 
approximated;  the  tongue  is  drawn  back  so  that  the  mouth  becomes 
a  long  oval  csbvity. 

U  {too) :  The  lips  are  still  more  approximated  and  are  protracted, 
the  tongue  pulled  back  and  arched  still  more.  The  cavity  is  like  a 
round  flask  Avith  two  orifices — a  wider  inlet  and  a  narrow  outlet. 


Fia.  45G. — Shape  of  Mouth  in  Socxding  Diffekent  Vowels. 


A  {pay):  The  point  of  the  tongue  approximates  to  the  hard  palate, 
leaving  a  slit-like  canal:  the  root  of  the  tongue  sinks.  The  mouth 
cavity  takes  the  shape  of  a  small-bellied  flask  with  a  short  and  some- 
what narrow  neck. 

E  (me):  The  point  of  the  tongue  comes  still  nearer  to  the  hard 
palate,  while  the  root  of  the  tongue  is  still  further  pulled  do^^^l.  The 
mouth  is  thus  made  a  larger  cavity,  but  with  a  longer  and  narrower 
neck. 

The  diphthongs  are  produced  b}^  the  passage  from  one  vowel 
sound  to  another,  and  cannot  therefore  be  sustained  on  one  note. 

Sound  is  reflected  when  it  strikes  against  a  smooth  surface,  such 
as  a  wall.  From  the  walls  of  an  enclosure  sound  may  be  reflected  to 
and  fro,  and  the  series  of  echoes  will  produce  a  musical  note,  the  pitch 
of  which  will  not  change  at  the  moment  when  that  of  the  musical 
note  is  changed,  for  it  is  produced  by  the  number  of  echoes  per  minute. 

By  taking  a  number  of  Jugs  and  vases  and  soundmg  a  musical  note 
into  each,  one  can  recognize  each  vase  b}'  the  characteristic  sound 
it  produces.  So  are  the  vowels  recognizable,  produced  as  they  are 
by  the  varjang-shaped  cavity  of  the  mouth. 


746 


A  TEXTBOOK  OF  PHYSIOLOGY 


The  English  Vowel  Sounds. 


Ij  as  in  girl. 

I2      ,,     it. 
Uj     „     fur. 
U2     ,,     hut. 


Aj  as 

in  father 

A. 

,      ball. 

A, 

hat. 

A. 

,      gate. 

El 

,      me. 

E. 

men. 

00 

,      too. 

O1 

,,      not. 

O2 

,      no. 

u. 


book. 


Ai  ,,  hair. 
Ou  ,,  how. 
Oi  ',,     boil. 

Consonants  may  be  classified  as  follows: — -To  note  the  difference 
between  voiced  and  voiceless,  say  "  wonderful,"  and  note  the  break 
in  the  voice  at  /. 

Consonants. 


Voiceless 
Oral. 


Labials 


Voiced  Oral. 


B 
W 


Voiced 
Nasal. 


M 


Labio-dentals        . .          . .          . .          . .                 F 

Lingao-dentals      . .          . .          . .          . .                 Th 

V 

Th 

Z 

Anterior  linguo-palatals             . .          . .                Sh 

T 

Zh 

D 

L 

R  (trilled) 

N 

I'osterior  linguo-palatals             ..          ••                 K                         Gr                         Ns 

HorCh     i            Y 

(R  burred) 

'                             1 

Explosives. — B :  Vocalized,  lips  shut  and  burst  open. 

P:  The  same,  only  not  vocalized. 

D:  Tongue  applied  to  upper  teeth,  vocalization,  and  tongue  with- 
drawn suddenly  so  that  blast  explodes  out. 

T :  The  same,  only  silent. 

G:  Breath  stojiped  by  tongue  against  palate. 

K :  The  same,  silent. 

Qu:  Soft  palate  and  back  of  tongue  act  as  stop. 

Vibratives. — S:  Tip  of  tongue  close  to  front  teeth,  and  air  hisses 
out  between. 

Z:  A  vocalised  hiss. 

Sh:  Tongue  close  to  hard  palate  in  front. 

R  burred:  Tip  of  tongue  drawn  as  far  back  as  possible  and  close 
to  palate. 

R  trilled:  Vibration  of  front  of  tongue  against  front  teeth. 


SOUND  PRODUCTION  AND  SPEECH  747 

F:  Lower  lip  against  edge  of  upper  teeth  and  air  blown  through. 

V:  The  same  plus  vocalization. 

W:  Mouth  not  quite  closed  by  lips  and  a  blast  of  air. 

Th:  Small  passage  between  tongue  and  middle  incisors  and  air 
blown  through. 

M:  Uvula  down,  way  into  nose  open,  equals  a  nasal  B. 

N:  Equals  a  nasal  L. 

Ng:  Equals  a  nasal  G. 

H :  Blast  of  air  through  passage  formed  by  parts  about  the  root  of 
tongue. 

Man's  power  of  speech  depends,  not  on  any  great  alteration  of 
the  somid-producing  mechanism,  but  on  the  perfection  of  the  nervous 
control  over,  and  co-ordination  of,  this  mechanism.  The  stammerer 
lacks  the  power  of  co-ordination,  and  is  made  worse  by  hurry,  ill-health, 
and  nervous  excitement,  better  by  slow  and  deliberate  efforts  at 
speech.     Certain  initial  consonants  are  his  stumbling-block. 

In  lisping  one  consonant  is  used  for  another — t  for  k;  th  for  s; 
/  for  th  ;  10  for  r.  In  the  "  Bread  and  Cheese  Riots  "  of  Richard  II. 's 
time  the  London  mob  put  to  death  all  foreign  workmen  from  Hanse 
towns  who  pronounced  "  biead  and  cheese  "  A\ith  an  accent.  "  Shib- 
boleth "  was  a  test  word  iised  by  Gilead  to  identify  the  Ephraimites 
who  pronounced  it  "  Sibboleth."  A  foreigner,  particularly  a  German, 
can  usualh'  be  detected  by  the  difficulty  he  experiences  in  x^ronouncing 
th  in  the  English  language. 


CHAPTER  LXXVI 

THE  AUTONOMIC  NERVOUS  SYSTEM 

This  system  supplies  the  viscera,  vascular  system,  sweat  glands, 
erector  muscles  of  the  hairs,  and  intrinsic  muscles  of  the  eye — in  fact, 


Post  ganglionic 


Pre- ganglionic  ytbre 
in  sytnpat^he.bi^  cord, 


Po5t;- ganglionic  Ji,bre 
in  spinal  nerve 


Spinal 
cord 


Pre-ganglionic  fibre 
in  sympat/hebic  nerve. 


Distal  ganglion 
in  sympathetic.^ 


Post -ganglionic  fibre, 
tn  sympathetic  nerve    , 


Post-gangllonic  fibre 
in  spinal  nerve      '~ 


Fibre  in  sympabhetic  cord 
passing  thmugh  two  ganglia 

Fio.  457. — Diagram  of  the  Arrangement  of  Fibres  in  the  Sympathetic  Nervous 
System.     (From  "  Quain's  Anatomy.") 

all  secreting  glands  and  muscles  apart  from  the  voluntary  muscles. 
It  consists  of  groups  of  nerve  fibres  of  the  splanchnic  tj^^e  and  the 
ganglia  with  which  they  make  connection.     It  is  so  called  because  it 


THE  AUTONOMIC  NERVOUS  SYSTEM 


749 


is  apparently  self-governing  and  independent  of  cerebral  control. 
The  system  comprises  the  sympathetic  nerves  and  their  associated 
ganglia,  the  sympathetic  nervous  system,  and  certain  cranial  and  sacral 
nerves  and  ganglia,  the  cranial  and  sacral  autonomic  systems.  The 
fibres  are  both  efferent  and  afferent. 

The  Sympathetic  Nervous  System. — The  ganglia  coimected  with 
tliis  system  form  a  well-marked  chain,  the  lateral  chain,  lymg  on  either 
side  of  the  vertebral  column,  and  extending  from  the  neck  to  the 
coccygeal  region.     In  addition  there  are  accessory  ganglia  (collateral 


n 


CO^  MVM/  09/V.S 


Fig.  458. — Diagram  of  ihe  Arrangement  of  Fibres  in  a  Mixed  Spinal  Nekve. 
(From  Purves  Stewart's   "Diagnosis  of  Nervous  Diseases.") 


ganglia),  lying  in  the  abdomen  in  close  connection  with  the  aorta  and 
the  large  branches  arising  from  it — the  semilunar  or  solar,  the 
superior  mesenteric  and  inferior  mesenteric  ganglia. 

These  ganglia  are  connected  with  the  spinal  cord  by  means  of  small 
efferent  medullated  fibres  (the  white  rami)  which  pass  out  by  the 
anterior  roots.  Each  fibre  ends  by  arborizing  round  the  cells  of  a 
ganglion.  These  are  the  preganglionic  fibres.  From  the  cells  of  the 
ganglia  arise  the  terminal  fibres  Avhich  go  to  the  various  effector  organs, 
smooth  muscle,  cardiac  muscle,  or  glands.     These  are  known  as  the 


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A  TEXTBOOK  OF  PHYSIOLOGY 


postganglionic  fibres,  and  are  non-meduUated.  Those  that  pass  back 
to  the  spinal  nerves  form  the  grey  rami  communicantes  (Fig.  459). 
The  cell-stations  of  the  preganglionic  fibres  are  traced  by  the  nicotine 
method.     It  is  found  that  when  a  ganglion  is  painted  with  nicotine 


MD  BIVtIM    /^UTOtlOMIC 


Fig.  459.— The  Autonomic  Nervous  System.     (After  Purves  Stewart.) 
A,  Chromaffinic  tissue  yielding  adrenalin;   .S,  sympathetic  ganglion. 

the  preganglionic  nerve  endings  are  first  stimulated  and  then  paralyzed; 
when  the  effect  of  stimulation  of  the  preganglionic  nerve  is  abolished, 
stimulation  of  the  postganglionic  fibres  arising  from  the  ganglion  still 
has  its  effect.     By  observing  the  effects  of  stimulation  of  the  pie- 


THE  AUTONOMIC  NERVOUS  SYSTEM  751 

ganglionic  fibres  before  and  after  painting  a  ganglion  with  nicotine, 
it  is  possible  to  determine  which  set  of  preganglionic  fibres  makes 
connection  Avith  the  cells  of  the  painted  ganglion. 

By  this  means  it  has  been  found  that  the  preganglionic  fibres  passing 
out  from  the  cord  in  the  white  ramus  maj'  either  end  at  once  in  the 
ganglion  which  they  first  enter,  or  pass  upwards  or  doAvnwards 
to  end  in  neighbouring  lateral  ganglia  in  the  sympathetic  chain, 
or  pass  through  to  connect  with  the  abdominal  group  of  col- 
lateral ganglia.  Each  fibre  has  one  cell-station  in  one  ganglion, 
and  no  more  than  one.  The  white  rami  emerge  from  the  spinal  cord 
by  the  anterior  roots  of  the  second  thoracic  to  the  third  lumbar 
nerves.  On  examining  microscopically  cross-sections  of  these  roots, 
the  sympathetic  fibres  are  distinguished  by  their  small  size.  The 
grey  rami  which  arise  in  the  ganglia  comiected  with  these  fibres  do 
not  necessarily  pass  back  to  the  sj)inal  nerves  coming  from  the  same 
segment  of  the  spinal  cord.  Thus  the  white  rami  for  the  sympathetic 
nerves  to  the  fore-limb  are  the  fourth  to  the  tenth  thoracic;  the  grey 
rami  ascend  to  join  the  nerves  of  the  cervical  nerves  forming  the 
brachial  plexus. 

For  this  reason  it  is  necessary  to  distinguish  between  the  effect 
of  stimulation  on  a  spinal  nerve  when  it  contains  only  the  white  ramus, 
and  the  effect  on  the  same  nerve  when  it  has  received  the  grey  ramus. 

The  origin  of  the  sympathetic  fibres  which  supply  each  part  has 
been  determmed  by  stimulating  the  anterior  roots  of  the  spinal  nerves, 
Thesf"  contain  only  outgoing  preganglionic  fibres. 

The  Function  of  the  Ganglia. — ^The  function  of  the  ganglia  is  that 
of  distributing-stations,  whereby  the  impulses  destined  for  certain 
parts  are  collected  together  into  the  appropriate  efferent  postganglionic 
nerves.  The  execution  of  certain  so-called  reflex  actions  has  been 
ascribed  to  the  ganglia,  but  these  seem  to  be  of  the  nature  of  the 
reflexes  concerned  in  paradoxical  contraction,  and  are  more  correctly 
termed  "'  axon  reflexes."  The  co-ordinate  peristalsis  of  the  intestine 
is,  however,  carried  out  by  the  ganglionic  pfexus  in  its  wall,  and 
this  proves  that  this  plexus  has  the  power  of  executing  functions  of 
the  same  order  as  those  of  the  central  nervous  system.  The  destina- 
tion, origin,  cell-station,  and  effect,  of  the  various  efferent  preganglionic 
fibres  may  be  summarized  as  shoAvn  in  the  first  table  on  p.  752. 

The  Cranial  and  Sacral  Autonomic  Systems. — These  are  character- 
ized by  the  length  of  their  medullated  preganglionic  fibres,  and  by 
the  fact  that  the  ganglia  for  the  most  part  are  situated  either  very 
close  to  or  actually  in  the  organ  supplied.  For  example,  the  ganglia 
for  the  submaxillary  and  sublingual  glands,  are  situated  close  to  the 
glands ;  the  ganglia  for  the  cardiac  fibres  of  the  vagus  are  actually  in 
the  heart  itself. 

The  cell-stations  of  these  fibres  can  be  traced  by  the  nicotine 
method.  For  example,  painting  the  sinii-auricular  groove  of  the 
frog's  heart  with  nicotine  abolishes  the  effect  of  the  vagus  nerve,  but 
not  the  effect  of  direct  stimulation  of  the  groove.     On  the  contrary. 


752 


A  tp:xtbook  of  physiology 


atropine  abolishes  both  effects.  This  is  because  nicotine  paralyzes 
only  the  preganglionic,  atropine  paralyzes  the  postganglionic  nerve 
endings  also. 


Destination. 

Origin. 

'     Cell- Station. 

1 

Effect. 

Head  and  neck 

1-5  Th., 

chiefly 

2  and  3  Th. 

1 

Superior 
cervical 

i        ganglion 

Vaso- constrictor  (?  brain);  dilator 
to  pupil;  secretory  (trophic)  to 
salivary  glands  and  sweat 
glands;  ?  vaso-dilator  to  lower 
lip  and  pharynx. 

{.'pper  limb 

4-10  Th. 

Stellate 

Vaso-constrictor;  .secretory  to 
sweat  glands. 

Thorax 

1-5  Th. 

Inferior 

cervical  and 

stellate 

Accelerator  to  heart;  ?  vaso-con- 
strictor to  heart  and  lungs. 

Abdomen     . .            6-12  Th. 
1-3  L. 

1 

Chiefly  the 

collateral 

ganglia :  solar, 

semilunar, 

superior 

mesenteric 

Vaso-constrictor:  stomach,  small 
intestine,  kidney,  and  spleen. 

Inhibitory:  stomach,  small  in- 
testine. 

Motor:  ileo-colic  sphincter. 

Glycogenic:  liver. 

Pelvis           . .               12  Th. 
1-3  L. 

Inferior 
mesenteric 

Vaso-constrictor  to  pelvic  viscera; 
inhibitory  to  colon;  motor  and 
inhibitory  to  bladder;  motor 
and  inhibitory  to  uterus;  motor 
to  retractor  penis  (dog). 

Lower  limb        , 

11,  12  Th.     1 
1-3  L. 

i 

Lumbar 
ganglia  (B,  7); 

sacral 
ganglion  (1) 

Vaso  -  constrictor;  secretory  to 
sweat  glands. 

The  cranial  autonomic  fibres  may  be  summarized  as  follows: 

Nerve.  Cell-Station.  Function. 


Third  nerve 


Ciliarj'  aanglion 


Motor    to    sphincter    pupillse 
and  ciliary  muscles. 


Seventh  nerve 


Vagus 


(1)  Submaxillary 

(2)  Ganglion  in  hilus 
of  submaxillary 
gland 

Otic  ganglion 


?  Sphenn-palatine 


Terminal  ganglia 
in  organs 


I  (1)  Vaso-dilator  to  tongue;  se- 
cretory and  vaso-dilator  to 
sublingual  gland. 
(2)  Secretory  and  vaso-dilator 

to  submaxillary. 
Secretory  and  vaso-dilator  to 
parotid,  and  ?  vaso-dilator 
to  back  of  tongue. 
?  Secretory  and  vaso-dilator  to 
mucous  membrane  of  nose, 
soft  palate,  and  pharynx. 

Motor  to  oesophagus,  bron- 
chioles, stomach,  small  in- 
testine; inhibitory  to  heart; 
secretory  to  stomach  glands. 


THE  AUTONOMIC  NERVOUS  SYSTEM  753 

The  sacral  autonomic  fibres  run  in  the  pelvic  visceral  nerve.  The 
cell-station  is  in  the  hjrpogastric  plexus  at  the  base  of  the  bladder. 
The  nerve  is — vaso-dilator  to  the  penis;  motor  to  bladder,  colon, 
rectum;  inhibitory  to  sphincter  of  bladder  and  retractor  penis. 

Afferent  Fibres. — Thus  far  we  have  dealt  only  with  the  efferent 
fibres,  which  form  a  great  preponderance  of  the  fibres  of  these  systems. 
The  afferent  fibres  make  no  connections  with  the  cells  of  the  various 
groups  of  ganglia,  their  cells  of  origin  being  situated  in  the  posterior 
root  ganglia.  Their  main  function,  so  far  as  is  known,  consists  in 
carr3'uig  up  impulses  which  help  to  regulate  blood-pressure.  Stimu- 
lation of  the  central  end  of  a  white  ramus  causes  a  rise  in  arterial 
pressure,  due  to  increased  vaso -constriction;  stimulation  of  the  central 
end  of  the  afferent  nerve  from  the  heart  (the  depressor)  causes  a 
great  fall  of  blood-pressure,  due  to  inhibition  of  vaso-constriction, 
especially  in  the  splanchnic  area.  It  is  quite  possible  that  the  efferent 
splanchnic  fibres  to  the  liver  are  reflexly  affected  through  afferent 
fibres  of  this  system;  stimulation  of  the  depressor  nerve  and  states 
of  asphyxia  bring  about  a  conversion  of  glycogen  to  sugar. 

The  reflexes  of  these  afferent  fibres  probably  play  a  great  part  in 
maintaming  the  tone  of  the  abdominal  viscera.  Normally  we  are  not 
conscious  of  our  viscera,  and  they  are  not  sensitive  to  touch  or  a 
cutting  instrument.  Pain  is  produced,  however,  by  the  distension 
of  any  hollow  viscera,  and  under  certain  pathological  conditions  pain 
may  arise;  but  the  pam  is  referred  to  those  parts  of  the  body  wall 
which  are  supplied  b}^  the  same  nerve  roots  as  the  diseased  viscera 
(Fig.  387,  p.  681). 


4B 


BOOK   XIII 
REPRODUCTION 

CHAPTER  LXXVII 
GROWTH  AND  REPRODUCTION 

Living  matter  is  characterized  by  the  fact  that  it  can  grow,  and 
by  the  fact  that  it  can  only  be  produced  by  the  action  of  living  matter; 
that  nothing  but  living  matter  can  organize  the  materials  and  forms 
of  energy  of  the  non-living  into  the  living  world;  that  each  living 
cell  possesses  a  type  of  energy  which  is,  so  to  speak,  attuned  to  the 
retention  of  certain  attributes  of  structure  and  function,  and  to  the 
capacity  of  communicating  these  onward  to  its  offspring — a  capacity 
which  is  termed  heredity;  that  each  living  organism  dies  after  a 
certain  period  of  existence.  A  unicellular  organism  placed  in  a  drop 
of  water  divides  and  divides  into  a  multitude,  but  after  a  time  the 
generations  usually  begin  to  deteriorate,  become  feebler,  and  finally 
die  out.  If,  however,  one  of  the  shoal  be  placed  in  a  vessel  with  one 
of  another  stock  of  the  same  species,  the  two  will  fuse  and  become 
one,  with  vigour  entirely  restored. 

It  has  been  stated  that  a  single-celled  paramoecium  by  successive 
division,  first  of  itself  and  then  of  its  progeny  over  a  period  of  five 
years,  possesses  the  power  to  reproduce  to  the  3,029th  power,  or  a 
volume  of  protoplasm  equal  to  10^^°°  times  the  volume  of  the  earth. 

The  higher  animals  are  vast  colonies  of  cells.  Most  of  these 
eventually  become  feeble,  and  die  in  due  season;  but  the  generative 
cells  fuse,  reinvigorate  each  other,  and  continue  the  race.  Thus 
does  a  man  live  again  in  his  children. 

The  growth  of  the  tissues  depends  upon  the  power  of  their  cells 
to  multiply.  The  tissues  interact  upon  one  another,  so  as  to  restrain 
and  confine  the  growth  of  any  one  tissue  within  its  proper  boundary. 
How  this  restraint  is  brought  about  we  do  not  know.  Loss  of  this 
restraint,  or  the  overpowering  energy  of  growth  of  any  one  tissue 
results  in  the  formation  of  tumours,  benign  or  cancerous. 

It  has  recently  been  shown  that  the  growth  of  human  tissues 
constitutes  a  type  of  its  own,  differing  markedly  from  the  growth  in 
other  mammals,  such  as  the  cow,  horse,  sheep,  pig,  and  other  domestic 
animals.      From    calculations    made    upon    the    animals    during   the 

755 


756 


A  TEXTBOOK  OF  PHYSIOLOG-Y 


period  taken  to  double  their  weight  at  birth,  it  appears  that  in  all 
such  animals,  except  man,  there  is  a  law  of  constant  energy  consump- 
tion, the  total  amount  of  energy  necessary  to  form  1  kilogramme  of 
animal  weight  being  the  same  for  all  animals — 4,808  calories  of  food. 
Man  requires  about  six  times  this  amount. 

Secondly,  in  such  animals  the  same  fractional  part  of  the  food 
energy  taken  in  is  used  for  growth — the  "  growth-quotient  "  being 
34  per  cent.^ — 34  calories  of  each  100  calories  of  food  being  used  for 
growth.  In  man,  the  growth  quotient  is  but  5  per  cent.,  being  greatest 
at  birth,  and  sinking  slowly  to  zero  at  maturity,  when  food  is  used 
only  for  metabolic,  and  not  for  growth  purposes. 

In  regard,  also,  to  the  amount  of  energy  for  each  kilogramme  of 
body  weight  during  the  period  of  life  from  maturity  to  death  (a  period 
of  sixty  years — twenty  to  eighty),  a  calculation  showed  that  each 
human    kilogramme    requires    725,770    calories,    the    other   animals 


'Fi. 


4(30. — Tissues   of  Flat-Worm,  showing  Amitotic  Division   of  Nucleus. 
(Alter  Child,  from  Dahlgren  and  Kepner.) 


mentioned  but  l!)l,fiOO  calories.  What  exactly  determines  this  power 
of  assimilation  it  is  difficult  to  say.  If  it  be,  as  is  suggested,  a  matter 
of  certain  chemical  complexes,  it  is  obvious  that  these  complexes  in 
the  human  cells  can  perform  the  transformations  and  changes  for  a 
greater  number  of  times  than  can  the  cells  of  other  animals  ere  they 
expire. 

Cell  Reproduction. — The  division  of  the  nucleus  precedes  that  of  the 
cell.  Separated  from  its  nucleus,  a  cell  is  unable  to  grow  and  divide. 
The  division  of  the  nucleus  and  of  the  cell  maj^  be  relatively  simple, 
known  as  amitosis,  or  of  complex  nature,  known  as  mitosis,  or 
karyokinesis. 

In  the  first  process,  amitosis,  the  cell  divides  somewhat  in  the 
following  manner :  At  first,  the  nucleolus  elongates  at  right  angles  to  the 
plane  in  which  division  will  subsequently  take  place.  It  then  divides, 
and  the  two  daiighter  nucleoli  pass  apart  to  what  will  be  the  centre 
of  the  new  daughter  cells.     Next,  the  nucleus  divides — rarely  b}'  a 


GROWTH  AND  REPRODUCTION 


757 


gradual  constriction,  in  the  same  niaimer  as  the  nucleolus;  more 
often  in  such  a  manner  that  it  appears  as  if  it  has  been  clean  cut 
through  its  centre  at  the  plane  of  division,  leaving  the  two  halves 
with  flat  parallel  surfaces  where  the  division  took  place.  In  some 
other  cases  it  appears  as  if  the  nuclear  membrane  is  the  important 


Fig.  4(31.- 


-DlAGRAMS    OF    CHROMATIN    CHANGES    DITRING    THE    DIVISION    OF    A    CeLL. 

(Redrawn  from  Dahlgren  a,nd  Kepner.) 


agent  in  the  division.  From  the  old  nuclear  membrane  an  extension 
passes  across  the  middle  of  the  nucleus,  thereby  forming  two  new 
nuclei  with  two  nuclear  membranes.  Finally,  the  cell  body  may 
divide ;  often  it  does  not  do  so.  In  such  cases,  amitosis  is  apparently 
a  terminal  process  in  the  life  activities  of  the  cell,  and  is  a  method 
for  securing  more  nuclear  surface  for  the  cell's  activities,  especially  in 
cases  of  active  metabolism.     In  the  stratified  epithelia  of  vertebrates. 


Fig.  4<)2. — Diagram  to  show  Distribution  of  Chromosomes  to  Daughter  Cells 
IN  Ordinary  or  Somatic  Form  of  Division.     (C.  E.  Walker.) 


for  example,  although  at  first  the  cells  divide  by  the  process  of  mitosis, 
later  on,  towards  the  end  of  the  cell's  activities,  the  process  changes 
to  amitosis,  the  cells  remaining  undivided  (Fig.  460). 

Mitosis  brings  about  an  equal  division  of  this  chromatin  material 
in  the  mother  nucleus,  and  distributes  it  equally  between  the  two 


758  A  TEXTBOOK  OF  PHYiSIOLOGY 

daughter  nuclei.  The  chromatin  is  the  nuclear  material,  which  stains 
deeply  with  basic  dyes,  and  is  probably  nuclein;  to  nucleic  acid  is 
diie  the  affinity  for  basic  dyes. 

The  series  of  changes  in  the  chromatin  are  as  follows  (Fig.  461) :  The 
granules  of  chromatin  of  the  resting  nucleus  (a)  become  assembled 
to  form  a  skein,  or  spireme  {b).  The  nucleus  now  elongates,  its 
membrane  generally  disappears,  and  the  spireme  breaks  down  into 
a  number  of  linear  fragments,  or  chromosomes  (c),  the  number  of 
which  is  constant  for  the  nucleus  of  any  given  species.  Thus,  in 
Ascaris  megalocephala  the  number  is  four;  in  man  the  number  is 
sixteen.  These  chromosomes  now  assemble  in  the  plane  through 
which  the  cell  will  divide,  forming  what  is  sometimes  known  as  the 
equatorial  plate.     The  rods  become  bent  in  the  fashion  of  a  V,  often 


Fig.  463. — Lines  of  Stress  in  a  Magnetic  Field.     (Verworn,  after  Rhumbler.) 

with  the  angles  of  the  V  towards  each  other,  thus  forming  a  radiating 
figure  {d).  These  progressive  changes  are  known  as  the  prophase. 
The  chromosomes  now  divide  longitudinally  to  form  twice  the  number 
of  V's,  or  daughter  chromosomes  (e) — a  change  termed  the  metaphase. 
These  chromosomes  become  assembled  in  two  sets  opposite  each  other 
on  either  side  of  the  plane  of  division,  with  the  angles  of  the  V 
directed  away  from  each  other  (/).  Lastly,  these  two  sets  of 
chromosomes  blend  again  to  form  a  spireme,  acquire  a  nuclear 
membrane  {g,  h),  and  finally  break  down  to  form  once  more 
the  granular  masses  of  chromatin  characteristic  of  the  resting 
nucleus  {{).  These  final  or  regressive  changes  are  known  as  the 
anaphase. 

Frequently,  the  non-staining  portions  of  the  nucleus  form  what 
are  called  the  achromatic  figures  of  mitosis.  This  material  forms  a 
spi  i  ,dle  of  delicate  fibrils  lying  at  right  angles  to  the  plane  along  which 


GROWTH  AND  REPRODUCTION 


759 


the  cell  will  divide.  The  sj)indle  furnishes  the  j)ath  along  which  the 
chromatin  filaments  move,  and  probably  marks  out  the  lines  of  chemico- 
ph3-sical  strain.  These  lines  of  stress  are  verj-  like  those  assumed  by 
iron  particles  within  a  magnetic  field  (Fig.  463).     Mitotic-like  figures 


Fig.  464.  —Lines  of  Stress  in  Living  Dividing  Ovum  of  ToxopREasTES. 
(Verworn,  after  Wilson.) 

The  circumjacent  fluid  is  of  intermediate  density. 

can  be  produced  by  placmg  droplets  of  certain  solutions  coloured  with 
China  mk  on  the  surface  of  other  solutions  of  greater  density.  Such 
figures  may  be  well  seen  in  many  growing  plants  cells — -for  example, 
in  those  of  the  root-tip  of  the  hyacinth. 


Fig.  465. — Hydroid  (Tubularia)  generating  a  Head  at  Each  End  or  a  Frag- 
ment OF  the  Stem  suspended  in  Water.  (Redrawn  after  Loeb,  from  Wilson's 
"The  Cell,"  etc.) 


In  many  animal  cells,  especially  ova  which  divide  as  the  result  of 
fertilization,  the  centrosome  divides  into  two  daughter  centrosomes, 
which  move  to  opposite  sides  of  the  nucleus  and  become  surrounded 
by  rays  to  form  an  achromatic  spindle  connecting  the  two  daughter 
centrosomes,  around  the  equator  of  which  the  chromosomes  arrange 
themselves    (Fig.    467).      In    the    anaphase    stage    the     divergence 


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A  TEXTBOOK  OF  PHYSIOLOGY 


of  the  chromosomes  seems  guided  by  the  spindle,  and  the  new 
nuclei  are  attracted  to,  and  formed  in,  the  neighbourhood  of  the 
daughter  centrosomes.  Some  authorities  hold  this  to  be  as  constant 
and  permanent  a  feature  as  the  division  of  the  chromatin,  but  recent 
evidence  makes  this  unUkely. 

Reproduction. — The  ancients  believed  that  many  forms  of  life,  even 
of  such  a  degree  of  complexity  as  the  insects,  generated  spontaneously 
from  slime  and  similar  dead  matter.  In  recent  times,  the  belief  in 
the  generation  of  the  animate  from  the  inanimate  has  been  confined 
to  the  very  lowest  forms  of  life.  Such  a  belief  is  now  dead.  It  has 
been  conclusively  shown  that  if  a  nutritive  solution,  such  as"  milk,  be 


Fia.  466. — Shjluivjchiu,  and  Enucleated  Fkagjients.     (Eediawa  alter  yerworn.) 

The  lines  show  the  i)lanes  of  section  of  the  entire  animal.  The  middle  piece,  which 
contains  two  nuclei,  regenerates  an  entire  animal.  The  enucleated  fragments 
shown  on  the  right  swim  for  a  time  and  then  perish. 

heated  for  a  sufficient  time  m  sealed  tubes  at  a  high  temperature, 
such  as  200°  C.  it  remains  free  for  all  time  from  all  forms  of  life,  and 
does  not  putrefj^  Life  comes  only  from  the  living.  The  explanation 
of  spontaneous  generation,  which  to  many  has  appeared  apparent, 
is  that  various  forms  of  life,  and  particularly  the  spores  of  bacteria, 
can  withstand  moderate  heating  or  drying  for  a  great  length 
of  time.  Although  apparently  dead,  they  become  revivified  when 
again  put  in  suitable  conditions.  Leuwenhoek,  the  famous  Dutch 
scientist  of  the  seventeenth  centmy,  kept  in  a  piece  of  paper  the  red 
dust  which  he  found  in  the  gutter  of  his  roof,  and  saw  the  little  wheel 
animal,  the  rotifer,  become  active  when  the  dust  was  wet  several 


GROWTH  AND  REPRODUCTION 


761 


months  afterwards.  Radiolaria  gradually  dried  have  become  active 
after  eleven  years,  anguilulge  after  twenty  eight  years.  Corn  foaxnd 
in  Egji^tian  mmnmies  is  stated  to  have  germinated  after  thousands 
of  years. 


Fig.  467. — Diagrams  showing  the  Essential  Facts  of  Reduction  in  the  Male. 
The  Somatic  Number  of  Chromosomes  is  supposed  to  be  Four.  {Redrawn 
from  Wilson's  "The  Cell,"  etc.) 

A,  B,  Division  of  one  of  the  spermatogonia  showing  full  number  of  chromosomes 
(four);C,  primary  spermatocyte  preparing  for  division:  the  chi'omatin  forms  two 
tetrads ;  D,  E,  F,  first  division  to  form  tv/o  secondary  spermatocytes,  each  of 
which  receives  two  dyads;  G,  H,  division  of  the  two  secondary  spermatocytes 
to  form  four  spermatids.  Each  of  the  latter  receives  two  single  chromosomes 
and  a  centrosome  which  passes  into  the  middle  piece  of  the  spermatozoon. 


In  the  development  of  the  multicellular  organism  on  the  lines  of 
a  division  of  labour  and  differentiation  of  function  of  the  cells,  most 
important  was  the  provision  of  special  cells  for  the  reproduction  of  the 
species.  Through  these  cells  the  organism  can,  under  proper  con- 
ditions, give  rise  to  new  individuals,  thus  perpetuating  the  race  and 
winning  immortality,  the  remainder  of  the  individual  perishing  after 
an  allotted  span. 


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A  TEXTBOOK  OF  PHYSIOLOGY 


The  reproductive  cells  may  be  of  two  kinds — asexual  and  sexual. 
The  former  occur  only  in  the  lower  forms  of  life.  The  simplest 
reproduction  is  by  the  dividing  of  the  parent  organism  or  cell  into 
two  daughter  cells.  This  is  accompanied  by  the  changes  in  the 
nucleus,  either  amitotic  or  mitotic.  Sea-stars  may  shed  a  whole 
finger,  which  will  then  develop  into  a  new  individual  like  the  parent. 
A  fragment  of  the  stem  of  a  hydroid  suspended  in  water  will  generate 
a  head  at  each  end  (Fig.  465). 

%  Other  organisms,  such  as  the  polyps,  reproduce  by  a  process  of 
budding.  From  the  parent  organism  a  bud  springs  out,  which  gradu- 
ally develops  into  an  adult  organism  comparable  in  every  way  to  the 
parent.  Such  a  new  organism  may  remain  attached  to  the  parent, 
thereby  forming  a  colony  of  cells,  or  it  may  become  detached,  and 
lead  an  altogether  independent  existence.  The  nucleated  portion 
(Fig.  466)  possesses  the  property  of  regenerating  an  entire  individual, 
but  not  the  non-nucleated  portions. 


Fig.  468. 

A,  Early  stage  in  meiotic  division;  B,  the  pairs  of  chromosomes  separating  in  meiotic 
division.     (C.  E.  Walker.) 


But  the  commonest  form  of  reproduction  is  that  pertaining  to  the 
higher  organisms — namely,  sexual  reproduction.  Li  this  form  of 
reproduction  the  essential  act  consists  in  the  actual  union  of  two 
different  types  of  cell — the  gametes  (the  male  and  the  female  cell) — 
often  from  two  separate  individuals.  The  male  cell  is  termed  the 
spermatozoon.  It  consists  of  little  else  than  nuclear  material.  It 
varies  in  shape,  and  is  small  in  size.  It  is  essentially  active,  its  function 
being  to  seek  out  the  female  cell  and  fertilize  it.  The  female  element, 
on  the  other  hand,  is  essentially  passive.  Often  it  is  large  in  size, 
containmg  a  large  amount  of  reserve  food  material,  at  the  expense  of 
which  the  fertilized  cell  develops. 

These  reproductive  elements  arise  from  undifferentiated  germ 
epithelium.  At  first,  multiplication  of  the  cells  is  by  means  of  the 
karyokinetic  division  already  described,  the  cells  thus  formed  being 
termed  respectively  spermatogonia  and  oogonia.  In  the  final  stages, 
however,  a  new  form  of  cell  division  appears,  known  as  meiotic 
division,  or  heterotype  mitosis.  In  this  form  of  division  but  half 
the  number  of  chromosomes  is  formed,  as  compared  with  the  usual 


GROWTH  AND  REPRODUCTION 


763 


form.  Farther,  when  division  takes  place,  the  chromosomes,  instead 
of  dividing  lengthwise,  di\ade  transversely  into  halves,  one  half  going 
into  each  of  the  new  daughter  cells.  In  this  way  the  daughter  cells 
have  but  half  the  number  of  chromosomes  of  the  parent  cell,  and  it 
is  assumed  that  the  chromatin  material  maj'  be  of  different  quality 
in  the  daughter  cells.  Thus,  supposmg  there  are  four  chromosomes 
(see  Fig.  469),  by  this  form  of  di\asion  various  combinations  may 
occur,  and  it  is  suggested  that  it  is  in  this  way  that  hereditary  characters 
are  handed  on,  and  that  the  offspring  may  differ  among  themselves 
according  to  the  nature  of  the  chromatin  material  derived  from  each 
parent. 

In  the  case  of  the  male  gamete,  the  result  of  ordinary  somatic 
division  yields  cells  known  as  spermatogonia.  These  develop  into 
cells  known  as  primary  spermatocytes.  By  meiotic  division,  the 
primary  spermatocytes  give  rise  first  to  secondary  spermatocytes, 
ani  then  to  the  spermatids,  which  develop  into  the  functional  sperma- 
tozoa. We  have  thus — (1)  a  somatic  division  stage  of  the  primary 
germ  cell;  (2)  a  growth  period  of  the  spermatogonia  to  spermatocytes; 
(3)  a  maturation  period  of  the  spermatocytes  to  spermatids. 


T?iG.  469. — Diagram  to  show  the  Distributiok  of  Chromosomes  to  the  DAtranTEB 
Cells  in  the  Meiotic  or  Reducing  Form  of  Division.     (C.  E.  Walker.) 


In  the  case  of  the  female  gamete,  we  have  the  corresponding 
development  by  the  somatic  type  of  division  of  germ  cell  to  oogonia. 
Then  follows  the  growth  period,  with  the  formation  of  the  primary 
oocjd:es  from  the  oogonia.  Lastly  follows  the  maturation  period, 
with  the  meiotic  division  of  the  cells.  The  essential  difference  between 
the  maturation  of  the  oocyte,  as  compared  v/ith  the  spermatocyte,  is 
that  from  the  oocyte  only  one  mature  ovum,  or  egg,  is  formed,  whereas 
each  primary  spermatocyte  yields  four  mature  spermatids.  In  the 
division  of  the  primary  oocyte,  the  secondary  oocytes  formed  are  the 
large  ovum  and  a  first  "  polar  body."  The  ovum  again  divides  into 
a  mature  egg  and  a  small  second  polar  body,  while  the  first  polar  body 
also  di\ddes.  The  result,  therefore,  of  the  maturation  of  the  oocyte 
is  the  formation  of  one  functional  mature  egg  and  three  functionless 
polar  bodies  (Fig.  470).  The  result  of  the  maturation  of  both  sperma- 
tocyte and  oocyte  is  that  the  amount  of  chromatm  material  is  reduced 
to  "half,  the  full  complement  of  chromatm  being  restored  in  the  fusion 
of  the  male  and  female  gametes  in  the  process  of  fertilization. 


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A  TEXTBOOK  OF  PHYSIOLOGY 


The  Reproductive  Processes  in  the  Male.  —The  sexual  apparatus  in 
the  male  consists  of — (1)  the  testis,   in  which  the  spermatozoa  are 


FiQ.  470. — Diagrams  showing  the  Essential  Facts  in  the  Maturation  of  the. 
OvTJM.  The  Somatic  Number  of  Chromosomes  is  supposed  to  be  Four. 
(Redrawn  from  Wilson's  "The  Cell,"  etc.) 

A,  Initial  phase:  two  tetrads  have  been  formed  in  the  germinal  vesicle;  B,  two 
tetrads  have  been  drawn  up  about  them  to  form  the  eiiuatorial  plate  of  the  first 
mitotic  figure;  C,  the  mitotic  figure  has  rotated  into  position,  leaving  the  remains 
of  the  germinal  vesicle  at  gv;  i>, formation  of  first  polar  body  (pb^) :  each  tetrad 
divides  into  two  dyads;  E,  first  polar  body  formed,  two  dyads  in  it  and  in  the 
egg;  F,  preparation  for  the  second  division;  G,  second  jiolar  body  (pb^)  forming 
and  the  first  dividing :  each  dyad  divides  into  two  single  chromosomes ;  H,-  final 
result:  three  polar  bodies  and  the  egg  nucleus  (  ? ),  each  containing  two  single 


chromosomes   (half  the  somatic   number);   c, 
degenerates  and  is  lost. 


the  egg-centrosome,   which  now 


produced;  (2)  in  higher  animals,  accessory  sexual  glands  (the  prostate, 
vesiculae  seminales,  and  glands  of  Cowper),  which  aid  in  the  formation 


GROWTH  AND  REPRODUCTION 


765 


of  the  seminal  fluid;  (3)  the  intromittent  organ,  or  penis,  by  means  of 
which  the  semen  is  introduced  into  the  female  during  the  act  of  sexual 
intercourse,  or  coitus. 

The  Testes. — The  testes  consist  essential^  of  two  sets  of  cells — 
(1)  the  interstitial  cells,  which  plaj'  a  part  in  the  acquisition  of  second- 
ary sexual  characteristics;  (2)  the  germinal  cells,  from  which  the 
spermatozoa  are  developed,  and  passed  by  a  long  system  of  ducts 
to  the  exterior.  The  testis  is  enclosed  in  a  thick  capsule,  known  as 
the  tunica  albugmea.  From  this  capsule  septa  pass  into  the  testis, 
dividing  it  into  a  number  of  compartments.  In  the  compartments 
are  long  convoluted  semmal  tubules,  lined  by  the  germinal  epithelium. 
In  the  different  layers  of  epithelium  the  various  stages  of  the  "  matura- 
tion of  the  spermatogonia,"  spermatogenesis,  or  may  be  seen.  Most 
external^,  lying  upon  the  basement  membrane,  are  the  spermatogonia, 
supported  by  elongated  "  nurse  cells,"  or  the  ''  cells  of  Sertoli."  Next 
comes  two  laj^ers  of  spermatocytes — large  cells  with  marked  karj^o- 
kinetic  n  iclei — and  then  the  la3'er  of  spermatids — small  cells  with  a 
well-marked  round  nucleus  (Fig.  471). 


spermatozoon 


tail— 


p.iddle  piece- 
head- 


Sertoli  cell- 


A. 


spermatocyte  II 
spermatocyte  I 
spermatogone 

wall  of  tubule 


B. 


EiG.  471. 


.1,  Diagram  of  a  sperinatozoon;  B,  diagram  showing  th?  origin  of  spermatozoa  ivova. 
the  living  cells   (spermatogonia)  of  the  tubules  of  the  testicle.     (Kdth.) 


The  spermatids  also  exhibit  various  stages  of  transformation  to 
spermatozoa.  In  this  process  the  nucleus  becomes  elongated  to  form 
the  head  of  the  cell,  the  main  mass  of  cytoplasm  goes  to  form  the 
middle  piece,  While  a  filament  of  cj^toplasm  grows  out  to  form  the 
whip-like  tail  (see  Fig.  471).  Wiien  fully  mature,  the  spermatozoa 
become  detached,  but  connect  themselves  for  a  time  with  the  free  end 
of  the  Sertoli  cells. 

The  seminal  tubules  are  supported  by  a  number  of  fine  connective- 
tissue  fibres,  in  which  run  the  bloodvessels  and  lymphatics,  and  in 
which  are  also  situated  the  interstitial  cells  which  play  so  important  a 
part  in  the  acquisition  of  the  secondary  male  characteristics  (see  p.  505). 
The  convoluted  seminal  tubules  of  each  compartment  pass  to  join  with 
a  few  straight  tubules  (the  tubuli  recti),  to  form  a  network  known  as 
the  rete  testis.     From  this  emerge  the  vasa  efferentia  (twelve  to  fifteen 


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A  TEXTBOOK  OF  PHYiSIOLOGY 


or  acrosome 


Nucleus 


End  knob 


Middle  piece 


Envelope 
tail 


Axial 
ment 


fila- 


in  number).  These  form  the  epididymis,  the  tubules  gradually  uniting 
to  form  the  vas  deferens.  The  vas  deferens  is  associated  mth  the 
nerves  and  bloodvessels  of  the  testis  in  forming  the  spermatic 
cord. 

The  Accessory  Glands. — The  exact  func- 
Apical  body,  ^j^j^  q£  ^j^^  accessory  glands  is  not  quite 
clear.  The  accessory  secretions,  mixed  with 
the  testicular  secretion,  are  believed  to  aid 
the  movements  of  the  spermatozoa,  prob- 
abl}^  owing  to  their  alkalinity.  It  is  stated 
that  extirpation  of  the  prostate  causes 
sterility,  owing  to  the  withdrawal  of  its 
secretion.  The  prostatic  secretion  is  serous 
and  milky  in  appearance,  amphoteric  in 
°^  reaction.  That  the  accessory  apparatus  is 
of  value  is  shown  b}^  the  fact  that  it 
develops  at  puberty,  and  this  development 
is  prevented  by  earty  castration.  Castration 
after  puberty  leads  to  an  atrophy  of  the 
aparatus. 

The  Seminal  Fluid. — The  seminal  fluid 
consists  of  the  external  secretion  of  the 
testes  combined  with  the  secretion  of  the 
glands  of  the  vas  deferens,  of  the  glands 
of  CoA\^ier,  and  of  the  prostate  and  vesiculae 
seminales.  It  is  a  whitish  viscous  fluid, 
alkaline  in  reaction,  contains  about  90  per 
cent,  of  water,  and  is  of  a  specific  gra^^ty 
of  about  1034.  The  inorganic  substances 
(0-9  per  cent.)  consist  chiefly  of  sodium 
chloride  and  the  phosphates  of  calcium 
and  magnesium.  The  organic  bodies  of 
the  semen  consist  of  nuclein  attached  to 
protamine,  some  albumin  and  proteose, 
fats,  and  the  lipoids  lecithin  and  cho- 
lesterin. 

I  The   spermatozoon  is  the  active  agent 

j  of    reproduction    contained    in    the    male 

•  ejaculation.      It   varies  in  form  A^dth  dif- 

FiG.  472.— Diagra:*!  of  Si'ek-  ferent  tj^pes  of   animal,  but  in  all  higher 

MATozooN.    (Redrawn  from  forms  consists  essentially  of  a  head  piece, 

Wilson's  "The  Cell,"  etc.)      ^  ^-^^^^  ^-^^^^  ^^^  ^  flagellum-like  tail 

piece.  In  man  the  head  is  pear-shaped 
(Fig.  472).  Movements  are  made  by  the  lashings  of  the  flagellum- 
like  tail.  The  movements  are  increased  bj^  weak  alkali,  inhibited 
by  acid  or  distilled  water. 

The  penis  serves  the  purpose  of  introducing  the  seminal  fluid  in 
the  sexual  apparatus  of  the  female.     It  consists  largely  of  erectile 


End  piece 


GROWTH  AND  REPRODUCTION 


767 


tissue,  which,  under  the  influence  of  dilator  nerves,  becomes  engorged 
with  blood,  leading  to  the  erection  of  the  organ.  The  urethra  passes 
through  the  corpus  spongiosum  of  the  penis. 

The  period  of  sexual  life  begins  m  the  male  with  the  onset  of 
puberty,  and  continues  more  or  less  throughout  life.  There  is  un- 
doubtedly a  decline  in  fertility  in  the  later  3'ears  of  life,  but  it  is  not 
uncommon  for  men  of  seventy  or  even  eighty  3^ears  of  age  to  become 
the  fathers  of  children. 

The  Reproductive  Processes  in  the  Female. — The  sexual  apparatus 
of  the  female  consists  of  the  egg-bearing  organ,  or  ovary,  in  which 
the  eggs  are  matured,  and  the  womb,  or  uterus,  in  which  the  foetus 
is  developed  from  the  fertilized  ovum,  or  oosperm.  Accessory  to 
these  are  the  oviducts,  or  Fallopian  tubes,  which  conduct  the    egg 


"=1 


TOXICA  HLBUGlNe* 
^,^^  STBOMA  CAPSULE 


bOuATEO    NEST 


-RIPENING    OV 


OiiCUS    PROliGERUS 


Fig.  473. — Diageammatic    Section    of      Fig.    474. — Ripe    Graafian    Follicle 
Ovary     of     Fifth-Month     Fcetus,  at  Puberty.     (Keith.) 

showing  Nests  of  Germinal  Epi- 
thelium and  Unripe  Graafian 
Follicle.     (Keith.) 


to  the  uterus,  and  the  vulva  and  vagina,  bj'  means  of  which  the  male 
element  is  introduced  into  the  female,  and  through  which  the^fuU- 
time  foetus  is  passed  into  the  world. 

The  ovary  consists  of — (1)  the  germinal  cells,  which  by  maturation 
provide  the  female  gametes,  the  ova;  (2)  the  interstitial  cells,  which 
furnish  an  internal  secretion  concerned  in  the  development  of  the 
secondary  female  characteristics  (see  p.  506).  A  fibrous  stroma 
carries  the  bloodvessels,  lymphatics,  and  nerves,  which  suj)pl3'  the 
organ,  and  its  cellular  elements  form  the  so-called  interstitial  cells 
which  produce  the  internal  secretion.  The  cells  of  the  germinal  epi- 
thelium lie  just  beneath  the  external  capsule — the  tunica  albuginea. 
These  divide  to  produce  the  oogonea,  which,  in  developing  into  ooc3i:es, 
gradually  sink  inwards  into  the  stroma  and  are  surrounded  bj'  a 
laj^er  of  stroma  cells.  Thus  is  formed  an  immature  Graafian  follicle. 
Eventually  the  stroma  cells  divide  to  form  a  layer  round  the  ooc3^te 
and  a  laj'er  of  cells  which  surround  the   follicle.     These   \.\\o  laj^ers 


7G8 


A  TEXTBOOK  OF  I'Fn'SlOLOGY 


multiply,  and  a  fluid  becomes  secreted  between  them,  so  that  a  mature 
follicle  is  formed,  the  outer  layer  of  cells  forming  what  is  known  as 
the  membrana  granulosa,  which  is  enclosed  in  a  fibrous  capsule  derived 
from  the  stroma,  and  an  inner  ovum  surrounded  by  a  mass  of  cells, 
known  as  the  discus  proligerus,  the  remainder  of  the  follicle  being 
filled  with  fluid,  the  liquor  foUiculi.  When  fully  mature,  the  follicle 
is  of  such  a  size  that  it  bulges  the  surface  of  the  ovary,  and  after  a 
time  ruptures,  shedding  the  ovum  into  the  abdominal  cavity  in  the 
neighbourhood  of  the  Fallopian  tube.  This  process  is  known  as 
ovulation.  The  rupture  is  brought  about  by  cellular  activit}-  within 
the  follicle.  The  external  wall  of  the  follicle  towards  the  surface  of 
the  ovary  is  thinned  away  during  the  growth,  so  that  it  ruptures 


CORONA     RftDIATA 


GERMINAL  VESICLE 
(nucleus) 


VOLK    GRANULES 
ZONA     RADlATA 


UMBILICAL    CORD 


I  ,,U>,        T)      ■     AMNION 
V*-'^         LEG    BUD 


Fig.  47.5. — The  Parts  of  a  Mature 
Hitman  Ovum.  Diameter  -jl-^  Inch. 
(Keith,  after  Van  der  Stricht.) 


+   3  TIMES 

Fig.  476. — Human  Embryo  and  Its 
Membranes  at  End  of  First 
Month  :  Embryo  about  \  IxrH, 
THE  Envelope  of  Embryonal  Mem- 
branes ABOUT  AN  Inch.  (Keith, 
after  Kcnmann.) 


finally  under  the  strain  of  the  fluid  secreted  within  the  follicle.  After 
the  rupture,  the  cells  of  the  membrana  granulosa  proliferate  to  form 
a  yellowish  tissue,  known  as  the  corpus  liiteum.  Connective-tissue 
septa  carrying  bloodvessels  become  developed  in  the  corpus  luteum. 
The  corpus  luteum  is  normally  about  |  inch  in  diameter.  At  the  end 
of  three  weeks  it  begins  to  diminish  in  size,  so  that  it  is  a  mere  scar 
at  the  end  of  two  months,  and  is  absent  at  the  end  of  six  months. 
If,  however,  impregnation  takes  place,  the  corpus  luteum  grows  in 
size,  until  at  the  end  of  the  second  month  it  is  '^  inch  in  diameter. 
It  remains  this  size  until  the  sixth  month  of  pregnancy,  when  it 
gradually  decreases  in  size  and  becomes  converted  into  scar  tissue. 
The  functions  of  the  corpus  luteum  have  already  been  mentioned 
(p.  507). 


GROWTH  AND  REPRODUCTION  769 

The  human  uterus  is  a  more  or  less  pear-shaped  muscular  organ 
■about  3  inches  long.  It  consists  of  the  main  upper  part,  or  body,  and 
of  the  neck,  or  cervix.  The  internal  cavity  is  about  2^  inches  long. 
It  is  lined  by  a  mucous  membrane  consisting  of  a  single  layer  of 
epitkelium  and  numerous  mucous  glands  resting  upon  a  fibrous  sub- 
mucous coat.  Normalh',  especially  in  those  who  have  not  had  children, 
the  cavity  is  almost  absent,  being  more  or  less  of  the  nature  of  a 
narrow  chamiel.  The  oviducts  enter  into  the  upper  part  of  the  body; 
the  cervix  connects  with  the  vagina  below. 

The  vaginal  canal  is  noteworth}^  for  its  power  of  extensibility 
during  parturition.  It  is  lined  by  a  mucous  membrane.  This  is 
thrown  into  ruga3,  or  ridges.  The  channel  is  lined  by  a  stratified 
epithelium.  In  the  mucous  membrane  are  glands  which  pour  out  a 
faintly  acid  secretion. 

The  Sexual  Life  oi  the  Female. — In  woman,  the  period  of  sexual 
activit}"  begins  about  the  twelfth  to  seventeenth  year  of  age,  varying 
with  race  and  climate,  being  earlier  in  Southern  and  later  in  Northern 
races.  In  the  temperate  zone  the  e.ge  is  about  thirteen  to  fifteen. 
Besides  the  acquisition  of  the  secondary  female  characteristics,  the 
beginning  of  sexual  life  is  betokened  by  the  onset  of  menstruation,  a 
monthly  loss  of  blood  from  the  uterus — the  menses.  This  lasts  from 
two  to  six  days,  and  usually  from  100  to  200  c.c.  of  fluid,  partly  blood, 
partly  mucous  uterine  secretion,  are  lost.  The  mixture  is  dark  in 
colour,  and  clots  very  slowly  or  not  at  all. 

Just  previous  to  each  period  of  menstruation  the  whole  genital 
tract  becomes  more  richly  supplied  with  blood,  especially  the  uterus. 
The  mucous  membrane  of  this  organ  becomes  swollen,  partly  by 
congestion  of  blood  and  lymph,  and  partly  b}^  a  certain  amount 
of  cell  proliferation.  This,  known  as  the  constructive  stage,  is 
followed  by  the  destructive  stage.  The  bloodvessels  rupture  and 
form  hsematoma  below  the  mucous  membrane,  the  epithelivnn  of  which 
eventually  ruptiires,  and  menstruation  proper  then  ensues.  At  the 
cessation  of  menstruation  there  is  a  period  of  repair  (about  seven  days), 
in  which  the  uterus  returns  to  its  normal  state.  Then  follows  a  period 
of  rest,  or  quiescence,  generally  lasting  about  twelve  or  fourteen 
days. 

The  exact  relationship  of  menstruation  to  ovulation  is  not  known. 
The  shedding  of  the  ovum  is  usually  believed  to  precede  menstruation. 
The  two  processes  are  intimately  related,  and  depend  upon  the  presence 
of  the  ovar^^  When  these  are  removed,  menstruation  ceases.  Men- 
struation also  ceases  during  pregnancy  and  during  the  puerperium — 
the  six  weeks  after  child-birth.  During  lactation,  also,  it  is  usually 
absent.  Women  of  the  poorer  classes  often  suckle  their  children  more 
than  a  year,  in  the  hope  of  deferring  its  return,  and  therefore  the 
chance  of  fertilization.  This  is  not  necessarily  the  case.  Pregnancy 
may  take  place  soon  after  the  birth  of  a  child,  even  before  the  onset  of 
menstruation. 

The  first  stage  of  menstruation  is  attended  Avith  a  certain  auiount 
of  physical  discomfort,    amounting    in    some    cases    to    pain,  which 

49 


770  A  TEXTBOOK  OF  PHYSIOLOGY 

passes  off  during  menstruation.     The   emotional   nature  of  women 
may  change  at  this  time. 

The  period  of  active  sexual  life  in  the  female  ceases  about  forty- 
five  to  Mty  3'ears  of  age — the  climacteric.  The  menopause  is  often 
attended  with  nervous  symptoms,  and  is  the  period  of  life  at  which 
certain  ailments  are  more  prone  to  develop. 

The  Process  of  Insemination. — ^The  process  of  insemination  varies 
in  different  species  of  animals.  In  fishes,  the  sperm  is  shed  into  the 
water  in  the  neighbourhood  of  the  eggs.  With  frogs,  the  male  clasps 
the  female,  and  pours  the  male  secretion  over^the  eggs  as  they  are  shed. 
In  birds,  the  semen  is  introduced  into  the  cloaca  by  the  male  organ, 
and  incorporated  in  the  egg  before  it  is  laid.  In  mammals,  the  egg 
is  not  shed,  and  the  male  secretion  is  deposited  in  the  female  tract 
by  introduction  of  the  penis — the  act  of  coitus.  This  act  is  accom- 
panied iDy  erection  of  the  organ.  This  is  brought  about  by  an  engorge- 
ment with  blood  of  the  vessels  of  the  penis,  so  that  the  organ 
becomes  greatly  increased  in  volume,  its  blood-pressure  raised,  and 
its  temperature  increased.  The  accepted  explanation  is  that,  under 
the  influence  of  the  nervi  erigentes,  the  arterioles  of  the  organ  become 
much  dilated,  while  the  efferent  veins  become  compressed  by  the 
action  of  such  muscles  as  the  ischio-cavernosus,  the  transversus 
perinrei  profundus,  the  bulbo-eaverncsus. 

The  erection  is  controlled  by  the  presence  of  a  centre  in  the  sj)inal 
cord.  If  the  centre  be  destroyed,  erection  is  no  longer  possible. 
The  afferent  stimuli  to  this  centre  may  come  locally  from  the  filling 
of  the  testes  with  semen;  from  the  excitation  of  the  sensory  nerves 
of  the  penis;  from  the  filling  of  the  bladder  (especially  noticeable  in 
3'oung  children);  from  the  rectum,  as  when  haemorrhoids  (piles)  are 
present.  Stimuli  may  also  come  from  the  great  brain — the  sexual 
emotions.  In  animals,  the  sense  of  smell  plays  a  considerable  part 
in  the  process. 

Ejaculation  of  the  semen  is  caused  by  strong  peristaltic  contrac- 
tions of  the  muscles  of  the  vesiculee  seminales  forcing  the  semen  into 
the  urethra.  The  incoming  semen  distends  the  urethra,  bringing 
about  a  rhythmic  contraction  of  the  bulbo-cavernosus  muscle,  which 
ejaculates  the  semen  from  the  urethra.  A  contraction  of  the  ischio- 
cavernosus  and  transversus  perinsei  muscles  also  occurs  at  this  time, 
but  these  probabl}'^  play  but  little  part  in  the  actual  ejaculation  of 
the  semen. 

Ejaculation  is  brought  about  reflexly  through  a  centre  in  the  cord. 
The  impulses  are  brought  to  the  centre  by  mechanical  stimulation 
of  the  sensory  nerves  to  the  penis.  It  may,  however,  be  caused  in 
sleep  as  the  result  of  pressure  of  semen  in  the  vesicles,  or  by 
emotional  impulses  from  the  great  brain  (sexual  dreams).  It  is 
computed  that  there  are  about  60,000  spermatozoa  in  each  c.c.  of 
the  ejaculation,  the  volume  of  Avliich  is  about  5  c.c. 

In  the  female,  a  corresponding  series  of  events  takes  place  during 
sexual  intercourse.  Reflexly  excited,  the  clitoris  becomes  engorged 
and  erected,  the  Fallopian  tubes  and  the  uterus  perform  peristaltic 


GROWTH  AND  REPRODUCTION  771 

contractions,  by  this  means  passing  down  the  mucous  content  of  the 
uterus  to  the  os  uteri.  The  uterus  is  also  said  to  raise  itself,  and 
sink  more  deeply  into  the  vagina,  possibly  to  facilitate  the  entrance 
of  the  semen  into  it.  Finally,  a  copious  secretion  takes  place  from 
the  uterus  and  walls  of  the  vagina  about  the  same  time  as  the  ejacula- 
tions of  the  semen  by  the  male.  The  sexual  act  is  usually  attended 
with  considerable  nervous  excitement,  and  followed  by  a  period  of 
lassitude . 

Fertilization. — Fertilization  consists  in  the  union  of  the  male 
and  female  gametes.  In  the  higher  animals,  the  spermatozoa  of  the 
male  are  deposited  by  the  sexual  act  in  the  neighbourhood  of  the 
uterine  cervix.  Stimulated  probably  b}-  the  vaginal  and  uterine 
secretions  under  chemiotactic  influence,  they  seek  out  the  ovum. 
They  ascend  the  uterus  "  against  the  stream."  The  activity  of  the 
cilia  of  the  uterine  mucous  membrane  is  such  as  to  impede  their 


Fig.  477. — Mature  Ovum  of  a  Bat,  showing  the  Separated  Polar  Bodies,  the 
Female  Proxucleus  and  the  Formation  of  the  Male  Pronucleus  from 
^      the  Head  of  the  Spermatozoon.     (Keith,  after  Van  der  Stricht.) 

In  this  case  the  tail-piece  has  not  been  loft  behind. 

progress.  Only  one  spermatozoon  is  necessarj^  for  fertilization.  The 
race  is  to  the  strong,  and  j)erhai3s  to  the  fleet,  since  it  is  calculated 
that  they  move  from  16  to  20  centimetres  in  an  hour — about  the 
distance  from  the  os  uteri  to  the  Fallopian  tube.  It  may  be,  however, 
that  the  winning  spermatozoon  is  deposited  within  the  uterus  itself 
as  the  result  of  the  relaxation  of  the  cervix  uteri  which  takes  jilace 
during  coitus.  This,  hoM'ever,  is  not  necessarj-,  since  fertilization 
may  take  j)lace  when  the  spermatozoa  are  deposited  only  in  the 
entrance  to  the  vagina. 

The  time  taken  for  fertilization  is  not  known,  but  it  is  known 
that  the  spermatozoa  may  remain  active  in  the  vagina  for  a  period 
of  three  weeks.  The  actual  fertilization  is  said  to  take  place  most 
commonly  in  the  Fallopian  tube,  and  not  within  the  uterine  cavity. 
The  head  and  middle  piece  of  the  fertilizing  spermatozoon  pass  into 


772 


A  TEXTBOOK  OK  PHYSIOLOGY 


the  ovum,  the  tail,  or  flageUum,  being  (generally)  left  behind.  From 
the  head  the  male  pronucleus  is  formed  (Fig.  477) ;  this  combines 
with  the  female  pronucleus  to  form  the  oosj)erm,  thus  completing  the 
process  of  fertilization. 


A-  B.  C. 

Fig.  478. — Showing  the  Prodttction  of  the  Morula  from  the  Ovum.     (Keith.) 
A,  Ovum  after  first  division;  B,  after  second  division;  C,  morula  stage. 

The  stimulus  supplied  by  the  spermatozoon  may  be  imitated  by 
altering  the  relation  of  the  cell  membrane  of  the  ovum  to  its 
environment ;  thus  it  has  been  shown  that  an  unfertilized  frog's 
eggs  may  be  made  to  develop  into  tadpoles  by  the  prick  of  a  pin. 


einbnjogenic  pole 


£::',bryogeiiic  pole 
inner  cell  mass  I      ,enueloping  layer 


uegetatiue  pole 
Fig.  479.— The  Blastula  Stage 


uegetatiue  pole 
enueloping  layer 

Fig.  480. — The  Blastocyst  Stage. 
(Keith,  after  Van  Beneden.) 


The  tadpoles,  however,  do  not  develop  into  frogs.  It  has  been 
ascertained  that  the  chromosomes  in  the  parthenogenetic  larva 
of  frogs  are  of  the  reduced  type.  This  is  a  matter  of  interest,  and 
probably  explains  the   failure   of   the  method  to  produce   complete 


GROWTH  AND  REPRODUCTION 


775 


frogs.  It  also  sheds  light  upon  the  incompleteness  and  the  unlikeness 
of  an  embryonal  rudiment  to  a  human  foetus.  The  organs  existing 
in  ovarian  dermoids  are  rarely  of  the  same  completeness  as  those  of 
parasitic  foetuses.  This  indicates  the  value  of  the  spermatozoon  for 
the  production  of  a  complete  individual.  Similarly,  the  eggs  of  the 
sea-urchin  may  be  made  to  develop  by  placing  them  in  sea-water 
containing  a  small  amount  of  magnesium  chloride.  Nevertheless, 
from  the  point  of  view  of  heredity,  the  male  pronucleus  plays  an 
important  part. 

Segmentation. — ^After  fertilization,  the  oosperm  becomes  fixed  in 
position  in  the  uterus,  and  then  undergoes  a  series  of  divisions,  first 
into  two  cells,  then  into  four,  until  a  mulberry-shaped  mass  of  cells, 
the  morula,  or,  when  large,  blastula,  is  formed  (Fig.  479).  In  this 
morula  a  cavity  then  appears,  forming  a  hollow  sphere — the 
blastocj^st — which  is  single-layered  except  in  one  part.  The  inner 
cells  of  this  part  then  proliferate,  and  convert  the  sphere  into  a 
double-layered  gastrula  with  a  small  pore  (the  blastopore)  connecting 
the  ca\ity  with  the  exterior.  The  outer  of  the  cell  laj-ers  is  known 
as  the  epiblast,  the  inner  as  the  hypoblast.  Between  these  two 
layers  a  third  laj^er  develops,  knoA\ai  as  the  mesoblast  (Fig.  481). 
The  developing  organism  now  differentiates  the  various  systems 
concerned  in  the  division  of  labour  of  the  bodj'.  Different  systems 
become  evolved  from  the  three  layers : 


From  the  Epiblast. 


The  epidermis  and  its  de- 
rivatives— e.gr.,  hair,  nails, 
glands,  and  muscle  of 
sweat  glands,  etc. 

The  epithelium  of  the  nose 
and  mouth,  and  the 
glands  opening  into  them ; 
the  anterior  lobe  of  the 
pituitary  gland. 

The  central  and  peripheral 
nervous  systems. 


From  the  Mesoblast. 


The  supporting  tissues  of 
the  body:  bone, connec- 
tive tissue. 

The  muscles  except  those  of 
the  swe  at  glands  and  iris. 

The  blood  and  lymph 
systems. 

The  excretory  system  ex- 
cept the  epithelia  of 
bladder  and  urethra. 

The  cortex  of  the  supra- 
renal gland. 

The  generative  system. 


From  the  Hypoblast. 


The  epithelia  of  the  ali- 
mentary tract,  including 
the  glands  entering  it. 

The  epithelia  of  the  re- 
spiratory tract. 

The  epithelia  of  the  Eu- 
stachian tube  and  tym- 
panum. 

The  epithelium  of  the  thy- 
roid and  of  the  thymus.  - 

The  epithelia  of  bladder, 
urethra,  and  accessory 
sexual  apparatus. 


Implantation.^The  ovum  is  usually  fertilized  in  the  oviduct,  or 
Fallopian  tube.  It  is  then  passed  by  ciliary  action  into  the  uterine 
cavity,  where  in  the  morula  or  blastula  stage  it  embeds  itself  in  the 
mucous  membrane  of  the  uterus  by  means  of  a  phagocytic  action  of 
its  outer  layer,  which  is  now  known  as  the  tropho blast.  The  corpus 
luteum  is  believed  to  exert  considerable  influence  through  its  internal 
secretion  upon  the  process  of  implantation. 

Immediately  after  fertilization  of  the  ovum,  the  normal  mucous 
membrane  of  the  uterus,  the  endometrium,  undergoes  a  great  increase 


774 


A  TEXTBOOK  OF  PHYSIOLOGY 


in  thickness,  forming  itself  into  two  laj-ers — a  compact  superficial 
and  a  deej)  spongy  layer.  It  is  now  known  as  the  decidua,  and  is 
divided  into  three  portions — the  decidua  basalis,  or  serotina,  upon 
which  the  ovum  rests ;  the  decidua  reflexa,  or  capsularis,  which 
encloses  the  embedded  ovum;  and  the  decidua  vera,  the  remaining 
portion  of  the  mucous  membrane  not  in  contact  with  the  ovum 
(Figs.  482,  483).  At  first  a  space — the  decidual  space — between  the 
two  latter  parts  represents  the  remains  of  the  true  uterine  cavity. 
These  eventually  come  into  contact,  and  fuse  in  the  human  subject 
in  the  fourth  month  of  pregnancy. 


MUCOUS  ' 
MEMBRANE 


ROPHOBLAST 


MUCOUS 

Membrane 

of 
f  UTERUS 


Fig.  481. — Showing  Origin  of  the  Primitive  Ccelom,  the  Mesoblast,  and  Cavity 
OF  the  Amnion  during  Development  of  the  Human  Ovum.  (Keith,  after 
I.  H,  Bryce.) 


From  the  developing  embryo,  two  membranes  are  formed — ^the 
chorion  and  the  amnion  (Fig.  482).  The  chorion  is  the  outer  layer. 
It  early  divides  into  two — an  outer  fused  mass  of  cells,  or  syncytium ; 
an  inner  layer  of  cells,  or  Langhans'  layer.  During  the  first  six  weeks 
the  whole  chorion  becomes  covered  with  vascular  villi.  These,  how- 
ever, soon  disappear  except  in  the  region  of  the  decidua  basalis,  where 
the  ovum  is  attached.  Here  is  formed  the  chorion  frondosum,  its  villi 
and  the  decidua  basalis  fuse  together,  and  form  the  placenta. 

Within  the  chorion  is  the  closed  sac — the  amnion — filled  with 
fl\iid,  in  which  the  embryo  is  bathed. 

The  placenta  is  formed  as  a  separate  organ  about  the  third  month 
of  pregnancy,  gradually  increasing  in  size  according  to  the  foetal  needs 
until  full  term.  It  is  formed  by  a  fusion  of  the  decidua  basalis  and  the 
chorion  frondosum  (Fig.  484).  Blood-sinuses  become  developed  in  both 
the  maternal  and  foetal  portions,  so  that  the  maternal  and  foetal  blood 


GROWTH  AND  REPRODUCTION 


775 


come  into  intimate  juxtaposition,  although,  separated  by  cellular 
membranes,  the}'  do  not  actually  mix.  Through  the  action  of  these 
membranes  oxygen  and  nutrient  material  are  supplied  by  the  mother 
to  the  fcetus,  and  the  waste  products  of  metabolism  of  the  foetus 
transferred  from  the  foetus  to  the  mother. 

Parturition. — After  an  intra-uterine  life  of  varying  duration  accord- 
ing to  the  species,  the  foetus  is  expelled  by  the  process  of  parturition, 
or  labour.  In  woman,  this  occurs  at  about  the  end  of  2S0  daj's. 
"Labour"  is  divided  into  three  stages:  (1)  The  first  stage,  which 
results  in  the  dilatation  of  the  cervix  of  the  uterus  as  the  result  of 
rhjiihmical   contractions    which   become   more   and   more   frequent; 


cavity  of  uterus 

.decidual  cells 
syncytium 
basal  layer  of  chorion 

mesoblast  of  chorion 

decidua  reflexa 


decidua  serotina- 

cavity  of  amnion 

decidual  cells, 
syncytium 
basal  layer  of  chorion 

uterine  vessel 


embryonic  epiblast 
■archenteron 
rimitiue  coelom 

cavity  of  uterus 
esoblast  of  chorion 


Fig.  4S2. — Section   through    Ovum  embedded    ix   the   AYall   of  the  Uterus 
(F.  W,  Jones,  after  Peters  and  Silcnka,  from  Keith's  "Human  Embryology."). 


(2)  the  second  stage,  in  which  the  foetal  membranes  are  ruptured  and 
the  foetus  is  expelled,  usualh'  head  first,  from  the  uterus  b}'  means 
of  prolonged,  sustained  contractions  of  the  uterus  occurring  at  frecp  ent 
intervals;  (3)  the  third  stage,  in  which  the  after-birth  is  expelled. 
The  whole  process  may  take  thirt}'  hours  or  more  in  a  primipara — a 
woman  who  is  having  her  first  child.  In  subsequent  births,  the  process 
is  usually  considerably  shorter.     What  factor  induces  the  onset  of 


776 


A  TEXTBOOK  OF  PHYSIOLOGY 


labour  is  not  known.  The  j^rocess  is  normally  reflexly  controlled 
through  a  centre  in  the  lumbar  cord,  although  the  presence  of  this 
centre  has  been  shown  not  to  be  necessary.     At  term  the  uterus  is 


D£ClOUA     VERA 
'^N^DECIDUA    RETLECTA 

,0ECIDUA     QASALIS 


lA. Blastodermic 

VESICLE. 


DE.C1OUA    VER/^ 


OECIDOA    VERA 


Fig.  483. — Section  of  Uterus  showing  in  Diagrammatic  Manner  the  embedded- 
Ovum  AND  the  UifFERENTIATION  OF  THE  DeCIDFA  INTO  THREE  Parts.      (Keith.) 


uterine  vessel- 


suomuc  layer^ 
of  uterus 


decidua 
syncytium 


syncytium. 

basal  layer. 

mesoblast 
of  chorion 


blood  space 


IiG.  484. — Diagrammatic  Section  of  the  Decidua  Serotina  (formed  from 
THE  Mucous  Membrane  of  the  Uterus)  and  Chorion  to  show  the  Manner 
IN  which  the  Placental  Blood  Spaces  are  formed.     (Keith.) 


of  large  size,  reaching  high  u^  into  the  abdomen.  After  delivery  by 
the  process  of  "  involution,"  it  returns  again  within  the  pelvic  cavity. 
The  involution  is  said  to  be  due  to  the  autolytic  action  of  intracellular 


GROWTH  AND  REPRODUCTION 


777 


enzymes  within  the  uterine  wall, 
within  three  months. 


It  is  a  rapid  process,  and  is  complete 


Serum  Test  for  Pregnancy. — Recently  there  has  been  devised  a 
serum  test  for  pregnancy.  It  is  based  upon  the  view  that  durmg 
pregnancy  the  maternal  serum  acquires  the  power  of  digesting  the 
"  specific  "  albumin  which  passes  into  the  circulation  from  the  placenta. 
In  order  to  test  if  a  subject  be  pregnant,  the  blood-serum  of  the  sub- 


oein 


artery 


artery 

muscular  coat 
blood  spaces 
vein 

chorionic  villus 
decidua  serotina 

-chorion 
amnion. 

decidua  vera 


decidua  reflexa 


ceroiK- 


Fia.  485. — Showino  Arrangement  of  the  Amnion,  Chorion,  and  Decidua  in 
THE  Third  Month,  and  the  Formation  of  the  Placenta.     (Keith.) 


ject  is  added  to  specially  prepared  placental  tissue  placed  in  a  dialyzer. 
If  the  tissue  is  digested  and  amino-acids  pass  through  the  diah^zer, 
it  is  deemed  a  sign  of  pregnancy.  Normal  serum  is  stated  not  to  have 
such  digestive  powers.  It  is  true  that  the  test  is  more  often  positive 
in  the  pregnant  than  in  the  non-pregnant,  but  the  test  is  by  no  means 
certain,  and  it  is  said  that  by  it  even  males  are  occasionally  reported 
to  be  pregnant. 


778  A  TEXTBOOK  OF  PHYSIOLOGY 

Heredity. — It  is  a  familiar  proverb  that  "  like  produces  like." 
"  Men  do  not  gather  grapes  of  thorns,  or  figs  of  thistles."  To 
account  for  this  continuity  of  species,  various  hj-potheses  have  from 
time  to  time  been  propounded.  It  was  at  one  time  believed  that 
a  miniature  animal  existed  preformed  either  in  the  spermatozoon 
or,  more  probably,  in  the  ovum.  Microscopy  showed  that  such  was 
not  the  case.  The  view  of  "  epigenesis  "  states  that  in  the  egg, 
which  is  entirely  different  from  the  structure  of  the  adult,  there  is 
a  successive  formation  of  new  parts  which  do  not  exist  as  such 
within  the  egg.  That  like  should  produce  like  there  must,  however,  be 
some  directing  force  within  the  egg.  Darwin  belie ved  that  the  parents 
contributed  minute  particles  of  all  their  own  tissues  to  the  reproductive 
cells,  and  thus  secured  physical  continuity  of  species — the  theory  of 
pangenesis. 

The  most  commonly  accepted  view  is  that  in  the  simple  repro- 
ductive cells  there  exist,  probably  in  the  chromatin  content  of  the 
nucleus,  complexes  which  determine  the  course  of  development  of 
the  fertilized  ovum.  These  germ  cells  themselves  were  produced 
from  the  pre-existing  germ  cells  of  the  fertilized  ovum  from  which 
each  parent  developed.  The  somatic  cells  of  the  develojDing  embryo, 
and  therefore  of  the  adult,  are  in  reality  the  custodians  of  the  germ 
cells.  They  do  not  form  new  germ  cells;  they  merely  contribute  to 
their  growth  and  development.  The  germ  plasm  is  continuous  from 
one  generation  to  another. 

Since  nuclear  material  is  contributed  by  both  parents,  and  since 
in  the  formation  of  the  germinal  elements  such  material  undergoes 
reduction  in  amount  by  a  special  method  of  cell  division,  it  affords 
an  adequate  exjjlanation  of  why  like  should  produce  like,  and  yet 
at  the  same  time  why  there  should  be  such  a  marked  difference  between 
the  offspring  and  the  parents,  and  also  between  offsjjring  themselves. 
A  litter  of  puppies  resembles  its  parents,  but  there  may  be  marked 
variations  in  colour,  temperament,  and  other  characteristics  of  the 
puppies. 

The  question  arises  as  to  how  these  variations  are  to  be  accounted 
for.  Are  they  to  be  accounted  for  by  heredity  or  by  environment  ? 
It  is  asserted  that  heredity  plays  a  large  part  on  tin  plea  that  in  the 
case  of  the  new-born  puppies  the  ante-natal  environment  has  to  all 
intents  and  purposes  been  the  same.  But  this  is  not  so;  the  condi- 
tions, even  in  the  womb,  will  no  more  be  the  same  for  each  puppy 
than  they  are  for  each  egg  in  a  mass  of  frog's  spawn  developing  in  a 
pond.  The  slight  variations  in  chemico-physica)  conditions  may  have 
the  jjrofoundest  effect  on  development. 

The  further  question  arises  as  to  whether  environment  after  birth 
can  in  any  way  influence  hereditary  characters.  It  is  not  a  question  of 
gathering  figs  of  thistles,  but  whether  a  bad  fig-tree  can  by  environment 
be  made  to  yield  a  strain  of  good  figs.  This  is  a  question  of  great 
importance  to  the  sociologist.  Lamarck  asserted  that  "  all  is  pre- 
served in  reproduction  and  transmitted  to  the  offspring,  that  Nature 
has  made  individuals  to  acquire  or  to  lose  by  the  influence  of  the 


GROWTH  AND  REPRODUCTION  779 

circumstances  to  which  their  race  has  been  for  a  long  time  exposed, 
inckxding  the  results  of  excessive  use  or  disuse  of  an  organ." 

Of  recent  years,  the  action  of  legislators,  sociologists,  and  others, 
has  been  directed  to  the  belief  that,  by  giving  a  good  supply  of  fresh 
air,  exercise,  proper  sanitation,  better  education,  the  individuals  will 
grow  up  stronger  and  healthier,  and  thus  provide  a  better  race.  But 
will  such  methods  convert  bad  stock  into  good  stock  ?  The  test  lies 
in  the  offspring. 

According  to  one  school  of  thought,  such  environmental  conditions, 
although  making  improvement  in  the  individual,  will  not  better  the 
race.  The  hereditary  factor  is  all-important.  Such  is  the  view  of 
Mendelism. 

The  essence  of  the  Mendelian  principle  is  very  easily  expressed. 
It  is,  first,  that  in  a  great  measure  the  characteristics  of  organisms 
are  due  to  the  presence  of  distinct,  detachable  character  separately 
transmitted  in  heredity;  and,  secondly,  that  the  parent  cannot  pass 
on  to  offspring  a  character  which  it  does  not  itself  possess.  Each  germ 
cell,  ovum,  or  sj)erm  may  contain  or  be  devoid  of  any  of  these  characters; 
and  since  all  ordinary  animals  and  plants  arise  by  the  union  of  two 
germ  cells  in  fertilization,  each  resulting  individual  maj-  obviously 
receive  in  fertilization  similar  characters  from  both  parents  or  from 
neither.  In  such  cases  the  offspring  is  "  pure  "  bred  for  the  presence 
of  the  character  in  question,  or  for  its  absence.  On  the  other  hand 
it  may  be  developed  from  the  union  of  dissimilar  germs,  one  con- 
taining a  character,  the  other  devoid  of  it;  the  individual  is  then 
cross-bred,  or  heterozygous.  A  population  thus  consists  of  three 
classes  of  individuals — those  pure-bred  for  the  presence,  having 
received  two  doses,  of  a  character;  those  pure-bred  for  the  absence 
of  the  character,  having  received  none  of  it;  and  the  cross-breds, 
which  have  received  one  dose  only.  A  plant,  though  cross-bred  for 
talhiess,  may  be  as  tall  as  one  pure-bred  for  tallness.  A  dwarf  plant, 
whatever  be  its  parentage,  can  only  produce  dwarf  offspring.  Not 
having  talhiess,  it  cannot  transmit  that  projaerty.  A  cross-bred  tall 
plant  can,  by  self-fertilization,  produce  both  tall  and  dwarf  offspring. 
Fowls  with  silky  feathers  cannot,  if  bred  together,  have  offspring 
with  normal  feathers,  but  two  birds,  normal  to  all  apj)earance, 
can,  if  the}^  be  cross-bred  in  that  respect,  produce  silky  off- 
spring. 

These  results  are  explained  by  assuming  that  a  character  may  be 
either  dominant  or  recessive.  In  breeding,  the  transmission  of  these 
characters  is  said  to  follow  a  definite  law — Mendel's  law.  When  a 
dominant  and  a  recessive  character  are  crossed,  the  first  cross-bred 
generation  possesses  the  dominant  character,  which  may  be  represented 
as  D(R) — e.g.,  the  cross  between  a  tall  and  dwarf  pea  possesses  the 
dominant  character  of  tallness.  The  issue  of  such  cross-breds  (impure 
dominants)  in  the  second  generation  will  be  25  per  cent,  pure 
dommant,  50  per  cent,  mixed  (impure  dominants),  and  25  per  cent, 
recessive.  In  such  a  generation  interbreeding  of  the  dominants  will 
breed  only  dominants,  of  the  recessives  only  recessives,   but  inter- 


7S0  A  TEXTBOOK  OF  PHYSIOLOGY 

breeding  of  the   mixed   impure  dominant  type  again  yields  25  per        " 
cent.   D,   50  per   cent.    D(R),  and   25   per   cent.    R.     'I'his   ma}-   be 
tabulated  as  follows: 

D       K 

\/ 
D(R) 


1L>  2D(R)  IR 


D  1D+2D(R)+1R  R 

Many  experiments  to  prove  this  law  have  been  made  both  upon 
plants  (peas,  beans,  maize,  wheat,  stocks,  etc.)  and  animals  (mice, 
rats,  poultry,  canaries,  moths).  In  peas,  for  example,  it  is  claimed 
that  tall  stems,  yellow  cotyledons,  brown-skinned  seeds,  and  round 
seeds  are  dominant  characters;  while  dwarf  stems,  green  cotyledons, 
white  seeds,  and  wrinkled  seeds  are  recessive  characters.  Among 
animals,  dominant  characters  are  short  hair  in  rabbits,  hornlessness 
in  cattle,  crest  in  poultry,  brown  eyes  in  man,  etc.;  recessive  are  long 
hair  in  rabbits,  horns  in  cattle,  absence  of  crest  in  poultry,  grey  and 
blue  eyes  in  man.  The  explanation  given  of  this  law  is  that  these 
characters,  dominant  and  recessive,  are  segregated  in  two  different 
sets  of  germ  cells. 

Although  the  law  derives  support  from  many  characters,  such  as 
those  mentioned  above,  and  from  various  hereditary  diseases  and  mal- 
formations of  the  human  race,  such  as  brachydactyly,  it  does  not  explain 
all  hereditary  phenomena.  The  cross-breds  of  a  white  and  black,  when 
intermarrying,  do  not  produce  25  per  cent,  pure  white,  50  per  cent, 
mixed.  25  per  cent,  black,  but  oflff?pring  of  varying  degrees  of  duskiness. 

Following  Mendelism,  the  modern  school  of  eugenists,  bent  upon 
the  "improvement"  of  the  race,  maintain  that  race  improvement 
is  solely  a  matter  of  breeding  from  good  stock.  This  may  undoubtedly 
lead  to  physical  fitness,  but  it  is  very  questionable  as  to  whether  it  is 
the  only  way.  It  is  also  a  difficult  question  to  determine  at  what 
fitness  we  are  to  aim.  It  is  well  known  that  "  genius  "  cannot  be 
made  to  breed  true.  A  genius  in  a  family  is  a  "  spontaneous  "  varia- 
tion, as  much  as  a  child  with  six  fingers.  How  do  such  "  spontaneous  " 
variations  arise  ? 

Darwin  stated  that  new  varieties  of  species  arose  by  the  cumulative 
effect  of  natural  selection  upon  small  fluctuating  variations.  It  is  of 
first-rate  importance  to  ascertain  how  new  varieties,  healthy,  intel- 
ligent, honest,  diseased,  feeble-minded,  and  criminal,  arise.  Can  the 
parents'  drunkenness,  for  exami:)le,  affect  the  germ  plasm  ?  At 
present,  "  eugenic  "  principles  seem  of  little  help.  Darwin  confessed: 
'■  Our  ignorance  of  the  laws  of  variation  is  profound."    It  still  is. 

It  has  recently  been  suggested,  as  the  result  of  observations  in 
the  vegetable  kingdom,  that  species  arise  from  one  another  by  dis- 


GROWTH  AND  REPRODUCTION  781 

contiiiuovis  leaps  and  bounds — by  ■"mutations."'  "The  new  species 
appears  all  at  once;  it  originates  from  the  parent  siaecies  without  any 
visible  preparation,  and  without  any  obvious  series  of  transitional 
forms."     This  is  the  mutation  theory  of  De  Vries. 

It  would  seem,  then,  that  the  distinctive  characters  of  a  species 
may  arise  in  two  ways:  (1)  By  the  accumulation  of  fluctuations; 
(2)  suddenly  by  mutation. 

The  extent  to  which  the  acquired  conditions  of  environment  are 
transmitted,  if  at  all,  still  remains  to  be  settled.  That  such  environ- 
mental conditions  are  of  great  importance  is  indicated  by  experiments 
upon  bacteria.  It  is  knawn  that  virulent  organisms  may  be  attenuated 
by  growths  upon  special  media,  and  that  such  diminution  of  virulence 
is  maintamed  so  long  as  the  environmental  conditions  remain  the 
same.  This  would  point  strongly  to  the  conclusion  that  the  effects 
of  the  environment  of  the  race  induced  by  improved  conditions  may 
be  mamtained  in  the  offspring  so  long  as  the  better  environmental 
condition ^  are  maintained.  Herein  lies  the  great  hope  of  the 
humanitarian. 

The  Determination  of  Sex. — The  determmation  of  sex  has  long 
been  a  matter  of  popular  speculation,  but  only  recently  of  scientific 
inquiry.  In  consequence,  many  theories,  although  of  historic  interest, 
are  scarcely  of  scientific  value.  Such,  for  example,  are  the  views  that 
S3X  is  determmed  by  parental  desire;  by  the  element  of  the  more 
healthy  parent;  by  the  relative  age  of  the  parents;  b\"  the  relation  of 
coitus  to  menstruation;  or  whether  the  ovum  comes  from  the  right 
ovary  or  the  left. 

It  is  generally  believed,  and  to  a  certain  extent  it  is  supported 
by  statistical  evidence,  that  more  male  babes  are  born  in  and  after 
times  of  stress,  such  as  war  and  famine.  The  disproportion  between 
the  sexes  (women  are  more  numerous)  is  to  some  extent  accounted 
for  by  the  more  difficult  passage  of  the  male  babe  into  the  world, 
owing  to  his  larger  head,  and  to  the  more  precarious  occupation  of 
males  in  the  community. 

In  recent  lines  of  inquiry,  efforts  have  been  made  to  ascertain 
whether  sex  is  predetermmed  in  the  sexual  elements,  or  whether 
sex  is  determined  by  environmental  conditions  of  the  o\iTm  after 
fertilization.  Evidence  has  been  accumulated  in  favour  of  both 
views.  In  support  of  the  environmental  view,  it  is  claimed  that 
well-matured  frog "s  spawn  develoJ)S  into  an  excess  of  females,  and  that 
ill-matured  eggs  of  certain  caterpillars  yield  an  excess  of  males. 
Differences  of  temperature,  by  affecting  the  nutrition  of  the  mother, 
have  been  shown  to  exert  an  influence  upon  the  sex  of  the 
offspring  of  the  primitive  worm  Dinophilus.  An  experiment  of 
great  interest  is  one  upon  the  annelid  worm  Ophryotrocha 
puerilis.  When  a  female  of  this  species,  with  no  trace  of  hermaph- 
roditism, having  ripe  ova,  was  divided  into  two,  the  head  portion 
of  thirteen  segments  regenerated  seven  segments,  and,  on  being  killed, 
it  was  found  that  the  ova  and  female  apparatus  had  atrophied,  and 
that  the  animal  was  now  male,  with  a  functional  testicular  portion 


782  A  TEXTBOOK  OF  PHYSIOLOGY 

developed.  It  is  suggested  that,  owing  to  the  amputation  and  dimin- 
ished nutritive  conditions,  the  indifferent  germ  cells  had  developed 
into  male  cells.  On  the  other  hand,  experiments  in  the  breeding  of 
mice  have  shown  that  nutritive  changes  and  the  age  of  the  parents 
have  made  but  little  difference  in  the  proportion  of  the  sexes. 

That  feex  in  certain  cases  is  largely  determined  b}^  the  conditions 
of  general  metabolism  is  illustrated  by  the  effects  which  follow  castra- 
tion, by  infection  with  e,  parasite,  of  several  varieties  of  crabs.  In 
all  cases  the  castrated  male  takes  on  female  characteristics,  and 
even  defends  the  parasite  as  if  he  were  protecting  his  eggs.  The 
castrated  female  shows  no  sign  of  altered  structure  or  instinct.  It 
has  been  suggested,  in  the  case  of  the  crab,  that  the  parasite  alters 
the  composition  of  the  male's  blood,  which  tends  to  bring  about  a 
female  condition,  which  may  be  followed  by  the  onset  of  female 
characteristics,  or  even  the  production  of  female  organs  from 
indifferent  germ  cells.  On  the  other  hana  it  may  be  an  internal 
secretion  effect  from  the  traces  of  female  tissues  present  in  male. 

In  support  of  the  view  that  sex  is  predetermined  in  the  ovum  is 
the  fact  that  "'  identical  "  twins — that  is  to  say,  twins  arising  from  the 
same  ovum  and  included  in  a  single  chorion — are  always  of  the  same 
sex.  More  conclusive  is  the  fact  that,  in  certain  mosses,  spores  of 
identical  appearances,  asexually  produced,  are  predetermined  as  male- 
or  female-producing  elements.  In  the  primitive  worm  Dinophilus, 
the  large  fertilized  ova  develop  into  females,  the  small  fertilized  ova 
into  males.  The  same  is  true  for  the  vine  pest  Phylloxera,  and  for 
the  rotifer  Hydatina.  In  certain  parthenogenetic  invertebrates,  such 
as  the  Hymenoptera,  the  unfertilized  eggs  give  rise  to  males,  the 
fertilized  eggs  to  females.  Whether  fertile  queens  or  infertile  worker 
bees  are  developed  from  female  larvae  depends  on  the  nature  of  the 
food  given  them. 

As  to  the  influence  of  the  male  element,  it  has  recently  been  shown 
that  certain  animals,  especially  insects  and  arachnids,  produce  two 
forms  of  spermatozoa.  Half  the  spermatozoa  have  in  their  nucleus 
an  odd  chromosome,  or  x  chromosome;  half  have  not.  In  the  ova 
the  X  chromosome  is  always  present.  Union  of  a  spermatozoon  con- 
taining the  .r  chromosome  with  the  ovum  produces  a  female;  union 
of  a  spermatozoon  without  the  x  chromosome  produces  a  male. 

By  some,  maleness  and  femaleness  are  regarded  as  Mendelian 
characters,  like  shortness  or  tallness:  If  sex  be  due  to  some  factor, 
like  the  x  chromosome,  it  is  possible,  on  the  Mendelian  interpretation, 
that  males  and  females  may  both  be  cross-breeds  (heterozygous),  or 
that  the  male  alone  may  be  heterozygous,  the  female  recessive,  or  the 
female  heterozygous  and  the  male  recessive.  Experiments  tending 
to  support  the  last  view  have  been  made  upon  the  currant  moth. 

It  is  asserted  that  in  vertebrates  castration  suppresses  the 
maleness,  but  does  not  induce  any  expression  of  female  character- 
istics. On  the  other  hand,  the  castrated  female,  while  losing  her  female 
characteristics,  tends  to  develop  markedly  those  of  the  male.  Further 
proof  is  needed  of  such  a  view. 


GROWTH  AND  REPRODUCTIOX  783 

It  will  be  seen  that  we  are  still  far  from  understanding  the  circum- 
stances which  lead  to  the  determination  of  sex.  In  some  cases  it  is 
apparent!}^  due  to  an  initial  difference  m  metabolic  rhji;hm,  in  others 
to  a  predetermined  morphological  difference  m  the  sex  units. 

Death. — Death  is  the  total  cessation  of  the  cell  activities  of  the 
individual.  Cells  are  always  dying  and  bemg  replaced  within  the 
indi\adual.  After  a  time,  however,  either  by  the  process  of  decay 
following  a  natural  adolescence  and  maturity,  or  more  often  as  the 
result  of  disease  or  accident,  one  of  the  vital  functions  fails,  the 
general  metabolism  of  the  body  ceases  to  be  efficient,  and  death 
ensues.  The  custodianship  of  the  genetic  by  the  somatic  cells  is 
finished.  Yet,  if  the  former  have  fulfilled  their  function,  the 
individual  does  not  wholly  die;  life  continues  in  the  offspring.  On 
death,  there  is  a  transformation,  but  no  destruction  of  energy. 
The  disintegrating  cells  pass  into  materials  of  lesser  complexity, 
some  or  all  of  which  are  again  worked  up  into  the  complex  forma- 
tions of  life.  Thus  continues  the  ceaseless  life  and  death  cycle  of 
the  ages. 


INDEX 


Abdomen,  movements  of,  iu  respiration, 

306 
Aberration,  cliromatic,  609 

—  of  lens,  spherical,  609 
Absorption  iu  tlie  stomacli,  388 

—  of  fat,  436 

—  of  food,  421 

—  power  of,  30 
Accessory  glands,  766 
Accommodation,  mechanism  of,  614 
Aceto-acetic  acid,  468 

Acetone,  469 
Achromatic  lens,  609 
Achroodextriu,  67 
Acid,  asimrtic,  41 

—  /3-oxybutyric,  468 

—  fatt}^,  53 

—  glutaniiuic,  41 

—  glycuronie,  63 

—  hiematiu  of  blood,  94 

—  hiematoporphyrin  of  blood,  94 

—  metaprotein,  50 

—  monocarboxylic,  36 
Acromegaly,  case  of,  523 
Adenin,  50 
Adrenalin,  41 

—  action  of,  505,  509 

—  effects  of  injection  of,  504 

—  glycosiu'ia,  434 

--  vaso-constriction  caused  by,  238 
Afferent  fibres,  753 

—  nerves,  245 

Age,  diet  under  various  conditions,  356 
Agglutinin,  109 
Agglutinins,  110 
Air,  aveolar,  281 

—  bubbles   of,  in  heart  after  decompres- 
sion, 309 

—  collection  of,  apparatus  for,  281 

—  composition  of,  281 

—  changes  by  breatliing,  293,  312 

—  complemental,  279 

—  residual,  280 

■ —  supplemental,  280 

—  tidal,  278 

—  volume  of,  278 
Alanin.  40 

Albumiuo-meter,  Esbach's,  465 
Albuminoids,  48 
Albumins,  48 
Albuminuria,  465 

Alcohol,  364 

—  as  source  of  energy,  364 

—  compounds,  34 

—  food  value  of,  352 


^85 


Alcohol,  percentage  of,  in  spirits,  wines, 

and  beer,  365 
Aldehydes,  35 
Alkali  carbonates,  lack  of,  336 

—  metaprotein;  50 

Alkaline  haamatin,  reduced,  of  blood,  94 

—  luematine  of  blood,  94 
Alkaptonuria,  469 
Allantoin,  460 
Allorhythmia,  135,  138 

Altitude,  high,  efiect  of  on  blood,  79 
Alveolar  air,  281 

analysis  of,  291 

collection  of,  apparatus  for,  281 

composition  of,  281 

— ■  —  gases  in,  pressure  of,  269 

Amblyopia,  623 

Amboceptor,  109 

Amino-acids,  44,  422,  423,  424,  425 

Amitosis,  756 

Ammonia,  462 

Ammonium  magnesium  })hosphate,  471 

—  urate,  471 

Amnion,  arrangement  of,  777 
Amceba,  changes  exhibited  by,  2 

—  pro  tens,  1 
Amorphous  urates,  471 
Amphibians,  larval  stage  of,  276 
Ampulla  of  guinea-pig,  crista  of,  655 
Amylolytic  enzymes,  71 
Amylopsin,  starch  digested  by,  399 
-Anabolism,  441 

—  of  fat,  436 
Anacrotic  wave,  215 

Anaesthetized  dog,  respiration  and  blood- 
pressure  of,  290,  291,  293,  294 

Anaphylaxis,  111 

Anelectrotonic  current,  583 

Animal,  decerebrate,  lung  volume  and 
blood-jjressure,  278 

—  electricity,  559 

—  fat,  melting-point  of,  438 

—  life,  cycle  of,  258 

Animals,  exjieriments  on,  dining  period 
of  liunger,  342 

—  hccmoglobin  in,  90 
Ankle  clonus,  684 

Anode,  region  of,  stimulation  in,  583 

Antigen,  109 

Antitoxins,  108 

Aortic  blood -pressure,  178,  197,  198,  199 

excitation  of  depressor  and,  177 

Apncea,  299 

—  forced  breathing  followed  by,  299 
Appetite,  384 

50 


786 


A  TEXTBOOK  OF  PHY8I0L0GY 


Aqueous  huiuour,  255 

Arginin,  42 

Army,  British,  peace  diet  of,  345 

Arteria^  rectse,  474 

Arterial  cannula,  186 

—  pressure,  168,  186 

circumstances  aUccting,  1?2 

curves,  relations  of,  149 

measurement  of,  186 

of  kidney,  247 

record  of,  in  cat,  512 

—  pulse  curve,  215 

—  system,  pulse  wave  in,  217 

—  wall,  deformation  of,  effect  of  surround- 
ing tissues  upon,  190 

Arteries,  contracted,    elongation  of,  with 
rise  of  internal  pressure,  184 

—  coronary,  circulation  in,  238 

—  elasticity  of,  184 

—  relaxed,    elongation   of,    with    rise   of 
internal  pressure,  184 

—  structure  of,  124 

—  velocity  of  flow  in,  208 

Arteriole  muscle,  pressor  atierent  impulses 

affecting,  231 
Avytenoids,  742 
AAscending  "  current,  582 

spar  tic  acid,  41 
Asphyxia,  306 

—  effect  of,  168 

—  of  rabbit,  304 
Association  areas,  729 
Astigmatism,  612 
Atmosj^here,  effects  of,  499 

—  temperature  of,  499 

—  See  also  Air 

Atmospheric  pressure,  diminished,  eflects 
of,  307 

increased,  309 

Auditory  judgments,  653 

—  nerve,  course  and  connection  of  fibres, 
697 

Auricle,  right,  119 

of  calf,  121 

Auriculo-ventricidar  bundle,  121 

—  node,  120 
Autolysis,  69 

Avogadro's  hypothesis,  17 
Axis  cylinder  of  nerve-fibre,  569 
Axon,  569 

—  section  of,  effects,  576 
Axon  reflex,  484 

Bacteria,  life  cycle  of,  258 

Bacterial  action  in  intestinal  digestion,  404 

—  haemolysis,  107 

Barcroft's  blood-gas  apparatus,  262 

Barfold's  test,  61 

Basilar  membrane,  648 

Bathmotropic  fibres,  173 

Baths,  effect  on  metabolism,  499 

Beckmann's  apparatus,  27 

Beef,  composition  and  value  of,  348 

Beer,  alcohol  percentage  of,  365 

Biceps,  cruris  of  frog,  549 

Bile,  391 


Bile,  excretion  of,  447 

—  How  of,  369 

—  formation  of,  447 

—  functions  of,  394 

—  in  urine,  469 

—  mechanism  of  secretion,  394 

—  organic  salts  of,  392 

—  pigments  of,  393 

—  secretion  of,  mechanism,  394 
Binocular  vision,  630 
Biological  force,  15 

Biotic  energy,  15 
Bismuth  meal,  407,  418 
Biuret,  46 
Blastocyst,  772 
Blaze  currents,  567 
Blind  spot,  621 
Blood,  75 

—  absorption  coetticieuts  for,  263 

—  acid  hpematin  of,  94 

—  acid  hrematoporphyrin  of,  94 

—  alkali  of,  diflusiblc,  77 
non-diffusil)le,  77 

—  alkaline  ha?matin  of,  94 
reduced,  94 

—  amount  of,  78 

—  analysis  of,  80 

—  carbon  dioxide  of,  290 

—  clotting  of,  101 

—  coagulation  time  of,  103 

—  corpuscles  of,  86 

—  —  pale,  97 

functions  of,  98 

origin  of.  98 

red,  86 

■ chemistry,  90 

enumeration  of,  87 

• fats  of,  90 

function,  89 

—  ■ origin,  88 

white,  enumeration,  98 

—  -count,  diflerential,  98 

—  effect  of  high  altitude  on,  79 

—  electrical  conductivity  of,  80 

—  fixing  agent  of,  97 

—  flow  of  velocity,  203 

—  gases  of,  259,  263,  275 

extraction  of  by  pump,  259 

pressure  of,  269 

—  heemoglobin  of,  estimation,  96 

—  human,  analj'sis  of,  81 

Haldane's  apparatus  for  determining 

tension  in,  273 
oxygen  cuives  of,  266 

—  in  urine,  466 

—  osmotic  [iressure  of,  80 

—  oxygen  capacity  of,  264 

—  partial,  269 

—  platelets  of,  99 

—  pressure  of,  186 

aortic,  178 

capillary,  221 

carotid,  of  pithed  cat,  230 

fall  of,  177 

in  nipple  of  cat,  522 

in  veins,  225 


INDEX 


787 


Blood -pressure,  inllueneeofpostiueon,  198 

rise  of,  due   to  pressure  on  supra  • 

renal  vein,  509 

—  reaction  of,  76 

—  specific  gravity  of,  76 

—  spectra,  93 

—  supply  of  kidney,  arrangement  of,  474, 
475,  478 

—  tests  for,  112 

biological,  113 

chemical,  112 

guaiacum,  112 

microscopical,  112 

spectroscopical,  112 

—  thrombin  of,  102 

—  velocity  of,  diagram  showing  general 
relations  of,  206 

in  veins,  225 

—  vertebrate,  colour  of,  76 

—  viscosity  of,  80 

—  See  also  Circulation 

Blood -gas,  analysis  of,  by  Topler  pump,  261 

—  apparatus,  Barcroft's,  262 

—  pump,  Hill's,  260 
Bloodvessels,  structure  of,  124 
Body,  chemical  composition  of,  33 

—  fluids,  circulation  of,  115 

—  proprio-eeptive  mechanism,  659 

—  temperature  of,  492 

—  weight  of,  and  sui-face  area,  341 
Bomb  calorimeter,  326 
j8-oxybutyric  acid,  468 

Boyle's  law.  17,  22 
Brain,  685,  716 

—  afferent  systems  to,  668 

—  blood-pressure  in,  222,  240 

—  centres  of,  728 

—  circulation  in,  239 
— •  cortex,  722 

—  fore  part  of,  686 
— ■  functions  of,  716 

—  hemispheres,  709,  716 

—  human  embryo,  685 

—  localization  of  parts  of,  721 

—  of  dog,  crucial  sulcus  of,  723 

—  of  frog,  686 
removal  of,  688 

—  removal  of,  reflex  action  of  cord  after, 
675 

—  results  of  stimulation,  722 

—  section  through   cerebral   hemisphere, 
709 

—  speech  centres,  730 

—  tracts  from  cord  to,  669    670 

—  transmission    from,    of    spinal    motor 
neurons,  669 

—  weight  of,  716 

—  See  also  Cerebellum 
Bread,  355 

Breathing,    abdominal,    influence    of,    on 
the  pulse,  191 

—  anatomical  considerations  of,  284 

—  ert'ects  on  blood-pressure,  237 

—  mechanics  of,  284 

—  regulation  of,  289 

—  types  of,  192 


Bronchial  tubes,  277 

Burdach,  postero-lateral  tract  of,  668 

Cadaverin,  403 
Caisson  disease,  309 
Calcium  carbonate,  472 
from  human  urine,  464 

—  oxalate,  471 

crystals,  461 

Calories  of  foodstuff's,  328 
Calorimeter,  bomb,  326 

—  for  experiments  with  small  animals,  330 
Cane-sugar,  64 

Cannula,    arrangement   of,    for   recording 
blood -pressure,  187 

—  arterial,  186 
Capillaries,  circulation  of,  218 
in,  rate  of  flow,  221 

—  velocity  of  flow  in,  208 
Capillary  blood-pressure,  221 
Carboliydrate,  427 

—  fat  from,  438 

—  foods,  composition  and  value  of,  350 

—  metabolism  of,  428 

—  of  plasma,  85 
Carbohydrates,  59 

—  lack  of,  336 

Carbon,  compounds  of,  34 

—  dioxide,  deficiency  of,  eftects,  302 

—  — ■  excess  of,  effects,  302 
in  blood,  263,  275 

Carbonal  group  of  organic  compounds,  35 

Carbonates,  465 

Carbonic  acid  gas,  19 

Carboxyhffiuioglobin,  91 

Carboxyl  group  of  organic  compounds,  36 

Carchesium,  colony  of  individuals  of,  3 

Cardiac  cycle,  143,  144_^ 

—  impulse,  153 

—  muscle,  532 

—  nerves,  171 

—  —  of  dog,  172 
^  of  frog,  171  ' 

- —  valves,  surface  relations  or,  ]  53 
Cardiometer,  166 

Carotid     artery,     velocity     of     pressure 
curves,  207 

—  blood -pressure  of,  in  pithed  cat,  230 

—  body,  519 

—  pressure,  cft'ect  on,  of  anesthetized  dog 
510 

Castration,  505 

—  effect  of,  on  horn-growth,  506 
Cat,  blood-pressure,  230 

—  ovum  of,  before  maturity,  9 

—  vagus  divided  in,  300 

—  vagus  intact  in,  300 
Catalysts,  68 
Cataphoresis,  31 
Caudate  nuclei,  715 
Cell,  S 

—  anterior  horn,  576 

—  division  of,  chromatin  chanijes  during 
757 

—  lamination  in  motor  area,  725 
of  gyrus  post-central  is.  7'M 


788 


A  TEXTBOOK  OF  PHYSIOLOGY 


Cell,  lamination  of  visual  area,  726 

—  mciotic  division  of,  762,  763 

—  naked,  1 

—  reproduction,  756 

Cells,  camera  lucida  drawing  of,  H 

—  daughter,  distribution  ol'  clironiosonies 
to,  757,  763 

—  gas-secreting  of  Paradise  fisli,  271 

—  survival  of,  13 
Celluloses,  65 
Cephalin,  58 
Cereals,  354 

—  composition  and  value  of,  352 
Cerebellar  arc,  672 

—  cortex,  section  of,  702 
Cerebellum,  702 

—  afferent  fibres  to,  703 

—  afferent  systems  to,  668 

—  efferent  fibres  to.  703 

—  functions  of,  705 

—  structure  of,  702 

—  tracts  of,  704 
Cerebral  arc,  672 

—  circulation,  239 

—  cortex,  development  of,  722 

of  mole  development  of,  722 

— •  —  structure  of,  723 

—  function,  716 

—  hemisphere,  709,  716 

—  —  positions   of    centres   concerned   in 
speech,  730 

—  pressure  gauge,  Hill's,  240 
Cerebro-spinal  fluid,  254 
Cerebrum.     Sec  Brain 

Cervical  ganglion  of  dog,  section  through 
chromophil  cells  in,  508 

—  sympathetic  nerve,  in  rabbit,  dissection 
of,  176 

Chauveau's  hwmodromometer,  204 
Cheese,  composition  and  value  of,  349 

—  food  value  of,  352 

Chemical  composition  of  the  body,  33 

—  influence     affecting     the     glycogenic 
function,  430 

Chemiotaxis,  negative,  12 

—  positive,  12 

Chemistry  of  red  blood-corpuscles,  90 
Chest,  influence  of,  on  the  pulse,  191 

—  register  of  sound,  743 
Cheyne-Stokes  Breathing,  299,  300 
Chicken,    heart   of,   muscular  connection 

between  aiiricles  and  ventricles  in,  140 
Childhood,  diet  of,  363 
Chlorides,  462 

—  distribution  of,  33 

Chloroform,  effect  of.  on  arterial  pressure 
o(  dog,  201 

-on  heart  volume  of  dog,  201 

Chlorophyll,  257 

Cholesterol,  58 

Cholin,  57 

Choroid,  603 

Chorion   arrangement  of,  777 

Chromatic  aberration  of  lens,  609 

Cliromoproteins,  48 

—  of  limbs.  243 


Chromosomes,  757,  758,  761,  762,  763,  764 

Chronotropic  fibres,  173 

Cilial-y  body,  603 

Circulation,  artificial  .schema  of;  183 

to  show  eflect  of  gravity  on,  194, 

196 

—  capillary,  218 

—  cerebral,  239 

—  complete,  time  necessary  for,  209 
— -  coronary,  238 

—  effect  of  change  of  postiu'e  on,  194 

—  examination  of  microscoi)ical,  219 

—  fretal,  248 

—  in  generative  organs,  248 

—  in  head,  242 

—  of  blood,  course  of,  in  mammals,  142 

—  of  limbs,  243 

; —  of  nitrogen  in  Nature,  259 

—  of  salivary  glands,  243 

—  ■ —  physical  factors,  179 

—  oftheb.dy  fluids,  115 
functions  of,  604 

—  muscle,  602,  603 
— •  portal,  246 

—  pulmonary,  236 

—  renal,  247 

—  special,  236 

—  times,  210 

—  Sec  also  Blood 
Circumvallate  papillse,  593 

Climate,  diet  under  varying  conditions  of, 

357 
Clothes,  500 
Clotting  of  blood,  101 
Coagulation  of  blood,  101 
Coagulative  enzymes,  72 
Cobra,  hypnotized  by  stroking,  737 
Cochlea,  membranous,  648 

—  section  of,  648 

Cold,  effect  of,  on  sino-auricular  node  of 
dog,  139 

—  exposure  to,  499 
Cold-blooded  animals,  495 
Collagen,  48 

Colloids,  29 

—  surface  tension  in,  31 
Colostrum,  359 
Colour-blindness,  623,  626 

—  degrees  of,  626 

Colour  of  vertebrate  blood,  76 

—  perception  of,  623 

—  perception  lantern,  Edridge-Green,  627 
— •  reactions  of  i)roteins,  46 

—  saturation,  624 

—  tests  for  proteivis,  52 

—  vision,  625 

—  • —  ajiparatus,  Leonard  Hill,  628 
— •  • —  Hering  theory  of,  625 

—  ■ —  Young-Helmholtz  theory  of,  625 
Colours,  wheel  for  mixing,  623 
Comma  tract,  669 

Complement,  109,  110 
— ■  deviation  of,  110 
Complemental  air,  279 
Compounds,  inorganic,  33 

—  orgiinic,  34 


JNDEX 


789 


Conductors,  neivoiis,  574 
Conjunctiva,  600 

—  human,  end  bulb  of,  586 
Conjunctival  reflex,  682 
Connective  tissue,  5 
Consciousness,  732 
Consonance,  652 
Consonants,  sounds  of,  746 
Cornea,  601 

Corneo-iridic  angle,  movements  of,  614 

—  junction,  602 
Coronary  circulation,  238 
Corpora  quadrigemina,  768 
Corpus  luteum,  507 
Corte's  organ,  648,  649 

of  guinea-pig,  649 

Coughing,  mechanism  of,  295 

Cranial  autonomic  fibres,  summary  of,  752 
system,  751 

—  nerves.  690 
nuclei  of,  699 

superficial  origin  of,  692,  693 

—  nuclei,  708 

Crank  lever  for  muscle  registration,  539 

Creatinin,  461 

Cretinism,  515 

Cretins,  non-goitrous,  516 

Cribriform  ligament,  602 

Crico-arytenoid  muscles,  lateral,  743 

I^osterior,  742 

Crico-thyroids,  743 

Cricoid,  742 

Crural  nerve,  excitation  of,  244 

Crystalloids,  29 

—  dialysis  of,  29 
Cud  chewing,  390 

Current,  constant,  effects  of,  581 

—  of  action,  561 

—  of  injury,  560 
Currents,  blaze,  567 

—  cutaneous,  564 

—  retinal,  565 
Cutaneous  currents,  564 

—  sensation,  585 

receptors  of,  585 

Cybulski's  photohsematochometer,  205 
Cylindrical  tubes,  flow  of  fluid  in.  179 
Cystin,  43 

—  crystals,  470 
Cystinuria,  470 

Cystoplasm,  degeneration  of,  576 
Cytotoxins,  111 

De-aminizing  enzymes,  72 

Death,  783 

Decidua,  formation  of.  774 

Defsecation,  419 

Deglutition,  mechanism  of,  408 

Deiters,  nucleus  of,  698 

Dendrons,  569 

Depressor  fibres,  177 

—  nerves,  excitation   of,    aortic   pressure 
and, 177 

effects  of  stimulation,  518 

—  ■ —  in  rabbit,  dissection  of,  176 
"  Descending"  current,  582 


Dextrius,  66 
Dextrose,  62 

—  katabolisni  of,  426 
Diabetes  mellitus,  435 
Diaphragm,  action  of,  284 
— •  movements  of,  284 

—  spasm  of,  expiration,  297 

inspiration,  297 

Diastole,  144 

—  duration    of,     table     showing     pulse- 
frequencies,  170 

with  different  pulse  frequencies,  168 

Diastolic  filling  of  heart,  160 

Diathermy.  568 

Dicarboxylic  acid,  3ti 

Dicrotic  ware,  215 

Diet,  chemical  composition  of,  328 

—  nitrogen-poor,  sulphates  in.  463 

—  nitrogen-rich,  sulphates  in,  463 

—  peace,  of  British  army,  345 

—  under  varying  conditions,  356 
Dietaries  of  the  world,  346 
Dietetic  methods,  special,  364 
Dietetics,  325,  344 

Diffusion  of  gas,  17 

through  a  liquid  film,' 20 

Digestion  in  the  mouth,  371 

—  in  the  small  intestine,  391 

—  in  the  stomach.  379 

—  mechanical  factors  of,  406 

—  peptic,  385  * 

—  processes  of,  367,  385 

Digestive  action  of  pancreatic  juice,  399 

—  fluids,  secretion  and  activation  of,  367 
Dioptrics,  laws  of,  608 

Dipeptide,  45 

Diplopia,  631 

Disaccharides,  63 

Divers,  311 

Dog,    sinu-auricular    node    of.    effect    of 

clamping,  139 

effect  of  cold  on,  139 

Dog's  heart,  outline  of,  137 

Dorsal  spino-cerebellar  tract,  669 

Dromotropic  fibres,  173 

Ductless  glands,  function.s  of,  503 

Dudgeon       sphygmograph,       suspension 

method  of,  211 
Duodenum,   mucous    membrane   of,   acid 

extract  of,  39S 
Dyspncea,  299 

Ear,  diagram  of,  showing  ossicles,  644 

—  examination  of,  method,  645 

—  external,  644 

—  internal,  646 
right,  647 

—  rabbit's,    lesions   produced    by    ultra- 
violet light  on,  13 

Edridge-Green  colour  perception  lantern, 

627 
Effector  organs,  574 
Eggs,  354 

—  composition  and  value  of,  348 
Eighth  nerve,  course  of,  697 
vestibular  portion  of,  699 


790 


A  TEXTBOOK  OF  PHYSIOLOGY 


Elasticity  of  arteries,  184 
Electric  tissues,  566 
Electrical  change  of  heart,  133 

—  conductivity  of  blood,  80 
Electricity,  animal,  559 

—  constant  current  of,  534 
Electro-cardiogram,  134 

—  and  musical  aortic  murmur  in  man,  156 

—  and  rough  aortic  murmur  in  man,  155 

—  carotid  pulse  of  dog,  155 

—  heart  sounds  of  dog,  155 
— •  normal,  132 

—  of  complete  heart-block,  133 

—  showing    regularly    occurring    ventri- 
cular extra  systoles,  133 

— ■  Avave  of,  214 

Electrodes,   Keith   Lucas   moist  chamber 

and,  563 
Electrometer,  capillary,  562 

—  records  of  eyeball  responses  to  light,  618 
Electro-motive  force,  536 

—  properties  of  muscle  and  nerve,  559 
Electrotherapy,  567 
Electrotonus,  583 

Embryo,  human,  768 

—  rabbit's,  cells  from,  14 
Endolymph,  647 
Endotoxins,  109 

Energy,  direct  method  of  estimating,  331 

—  intake  of,  327 

—  output  of,  328 
English  vowel  sounds,  746 
Entero-ceptive  mechanism,  660 
Enterokinase,  401 
Enzymes,  68,  369 

—  amylolytic,  71 

—  coagulative,  72 

—  de-aminizing,  72 

—  lipolytic,  71 

—  pancreatic,  activation  of,  398 

—  properties  of,  70 

—  proteolytic,  70 

—  sucrolytic,  71 

Epicritic  sensibility,  591,  592 

Epithelium,  5 

Equilibration,  656 

Erythrodextrin,  67 

Esbach's  albumino-meter,  465 

Esophoria,  631 

Ether,  effect  of,  on  heart  of  dog,  201 

Evaporation,  497 

Exophoria,  631 

Eye,  accessory  jmrts  of,  600 

—  adjustment  of,  612 

—  anatomy  of,  600 

—  cardinal  points  of,  611 

—  examination  of,  methods,  641 

—  hypermetropic,  rays  in,  616 

—  images  of  truncated  pyramid,  634 

—  investigation  of,  apparatus  for,  637 

—  movements  of,  630 

—  myopic,  rays  in,  617 

—  of  frog,  examination  of,  640 

—  of  rabbit,  examination  of,  641 

—  right,  perimetric  chart  of,  639 

—  See  also  Vision 


Eyeball,  formation  of,  712 

—  horizontal  section  of,  601 

—  light  responses  to,  electrometer  records 
of,  618 

—  schema  of,  223 

Faeces,  405 
Fat,  53,  428,  437 

—  alisorjition  of,  436 
■ —  acid  value  of,  55 

—  anabolism  of,  436 

—  effect  of,  in  metabolism,  340 

—  forms  of,  55 

• —  from  cajbohydrate,  438 

—  from  protein,  439 

—  iodine  value  of,  55 

—  katabolism  of,  440 

—  lack  of,  336 

—  melting  point  of,  55 

—  metabolism  of,  436 

—  neutral,  53 

—  of  milk,  437 

—  of  pig,  437 

—  of  red  blood-corpuscles,  90 
— •  specific  gravity  of,  55 

—  storage  of,  in  liver,  448 

—  volatile  fatty  acids  in,  55 
Fatigue,  546 

Fatty  acids,  characteristics  of,  55 
Fatty  degeneration,  441 
Feeding,  artificial,  360 

—  metabolism  raised  by,  343 
Fehliug's  solution,  467 

—  test,  61 

for  sugar  in  urine,  467 

Fenestra  ovalis,  646 

—  rotunda,  646 
Fermentation  test,  62 
Ferments,  68 
Fertilization,  771 
Fibrinogen,  formation  ot,  450 

—  of  plasma,  84 

Fish,  composition  and  value  of,  348 

—  cooked,  com])osition  and  value  of,  352 

—  swim-bladder  of,  271 

Fistula,  gastric,  Pawlow's  method  of 
establishing,  381 

Flechsig  tract,  669 

Flour,  354 

Fluid,  How  of,  effect  of  introducing  re- 
sistance, 181 

—  —  in  branching  tubes,  180 
-in  cylindrical  tubes,  179 

—  —  in  rigid  and  elastic  tubes,  182 
in  tube  of  varying  diameter,  180 

■ of  velocity  and  resistance  heads,  180 

—  jiericardial,  254 
• —  pleural,  254 

Fojtus,  circulation  of,  248 

—  nutrition  of,  357 

—  ovary  of  fifth-month,  767 
Food,  absorption  of,  421 

—  calories  table,  328 

—  composition  of,  348 

—  cooking  of,  366 

—  selection  of,  344 


INDEX 


(91 


Food,  value  of,  345,  348 

table  of,  showing  calories,  363 

Foods,    carboliydrate,     composition    and 
value  of,  3c 0 

—  fat,  composition  and  value  of,  349 

—  protein,  cost  of,  348 

—  watery,  composition  and  value  of,  350 
Foodstufis,  352 

Fourth  ventricle,  689 

Freezing-point,  determination  of  lowering 

of,  27 
Frog's  heart,  contraction  of,  128 
diastolic  pressure  of,  129 

—  —  excitability  of,  131 
lever  for  recording,  127 

Fruits,  composition  and  value  of,  351.  352, 

355 
Fundus  of  eye,  642 

Galactose,  62 
Galactosides,  57 
Galvani's  experiment,  559 
Galvanometer,  deflection  of,   temperature 
of  muscle  and,  554 

—  single-pair  thermopile  connected  to,  552 
Galvanotaxis,  positive,  12 
Galvano-tonus,  534 

Ganglia,  function  of.  751 
Gas,  analysis  of,  Haldane's  apparatus  for, 
282 

—  bubbles  of,  in  arteries  of  intestines,  309 
in  veins  of  intestines,  309 

—  diffusion  of,  17 

through  a  liquid  film,  20 

Gas  laws,  17 

Gases,  blood,  259 

extraction  of,  by  pump,  259 

—  pressure  of,  269,  275 

—  solubility  of,  in  salt  solutions,  20 
Gastric  contents,  acidity  of,  deficit,  389 
excess,  389 

examination  of,  388 

—  juice,  380 

action  of,  on  starches,  387 

-on  sugar,  387 

chemical  mechanism  of,  384 

composition  of,  vai'iation,  384 

lipase  of,  387 

mechanism  of  secretion,  383 

nervous  mechanism  of,  383 

secretion  of,  374 

variation  of  composition,  384 

Gastrin,  384 

Gastrocnemii,    excised,    length    of   after 

fatigue,  547 
Gastrocnemius,      contractions     of,     with 

different  loads,  545 

effect  of  temperature  upon,  543 

effect  of  load  upon  contraction  of, 

544 

—  of  frog,  contraction  of,  541 

fatigue  of,  546 

Gay-Lussac's  law,  17,  23 
Gelatin,  48 

Generation,  organs  of,  505 
circulation  in,  248 


Geniculate  bodies,  708 

Gland  current,  563 

Glands,  accessory,  766 

— •  salivary,  565 

Globulins,  48 

Glomerular  secretion,  nature  of,  480 

Glomerulus,  function  of,  478 

Glosso-pharyngeal  nerve,  693 

Glucoproteins,  48 

Glucosamine,  63 

Glutaminic  acid,  41 

Glycin,  40 

Glycogen,  66 

— •  source  of,  427 

Glj'cogenic  function,  427 

—  —  influences  aff"ecting,  428 

of  liver,  447 

Glycosuria,  427,  431,  467 

—  adrenalin,  434 

—  alimentary.  431 

—  pancreatic,  432 

—  phloridzin,  433 

—  pituitary,  434 

—  puncture  (neurogenous),  432 

—  salt,  435 

—  thyroid,  434 
Glycuronic  acid,  63 

Goitre,  exophtlialmic,  case  of,  518 

GoU,  posterior-median  tract  of,  668 

Gonium  pectorale,  4 

Gout,  symptoms  of,  445 

Gowers'  tract,  669 

Graafian  follicle  at  puberty,  767 

Gracilis,  nervous  impulse  in,  581 

Graham,  gas  effusion  of,  18 

Gravity,  centre  of,  528 

Growtli,  755 

— •  effect  of  vitamine  on,  338 

Guaiacum  test  for  blood,  112 

Gymnema  sylvestre,  595 

Gyrus  post-centralis,  cell  lamination  of,  724 

Hfemachromogen,  94 

Hremacytometer,  Thoma-Zeiss,  37 

Hematuria,  466 

Hiemautogram,  216 

Hffimin  crystals,  113 

preparation  of,  112 

Hiumoblast,  89 

Htemodromometer,  Ghauveau's,  204 

Hiemoglobin,  animal,  90 
I    —  of  blood,  estimation  of,  96 
'   — ■  solution,    eff'ect  of,   on  oxygen  curve. 
267 

Haemoglobinuria,  466 

Htemolysis,  105 

—  bacterial,  107 

—  by  foreign  sera,  106 

,    —  by  snake  venoms,  107 

—  chemical,  106 

—  physical,  105 

—  produced  by  vegetable  poisons,  107 
Hsemophilia,  104 

Haemorrhage,  transfusion  in,  228 
Hair  follicles,  486 

—  nerve  endings  at  Ijase  of,  587 


792 


A  TEXTBOOK  OF  PHYSIOLOGY 


Haldane-Penil)iev   resiiiiation   apiiaratiis. 

318 
llaldane's     apparatus     for     deterniiiiing 

tension  in  luimaii  blood,  273 

—  gas  analysis  ap{)anitus,  282 
Hammer  of  Wagner,  action  of,  r>37 
Haploscopic  vision,  63r> 
Haptophors,  108 

Harmony,  652 

Head,  circulation  in,  242 

—  proprio-ceptive  mechanism  of,  655 

—  register  of  sound,  74-1 
Hearing,  643 

—  reaction  time  to,  733 

—  receptive  area  for,  728 

—  receptor  mechanism  foi-,  643 

—  theories  of,  652 

Heart,  anatomy  of,  microscopic,  122 

—  attachment  of,  arterial  and  venous,  151 

—  compensatory  pause  of,  131 

—  contractility  of,  129 

—  diagram  of,  showing  course  of  lilood,  1 42 

—  diastolic  filling  of,  160 

—  electrical  change  of,  133 

—  embryonic,  divisions  of,  117 

—  examination  of,  modes,  152 

—  excitability  of,  128 

—  frog's,  contraction  of,  169 

lever  for  recording,  127 

■ —  hoi'se,  tracings  fiom,  145 

—  human,  sinu-auriculai  junction  in,  120 

—  movements  of,  144 
in  situ,  151 

—  muscle,  127 

—  musculature  of,  152 

—  nerves  of,  171 

—  nutrition  of,  158 

—  perfused,  of  frog,  144 

—  physiology  of,  127 

—  point  of  primary  uegati\ity,  138 

—  preparation  of,  diagram  of,  apparatus 
for,  164 

—  pressure   curves  of,   aortic   and   intra- 
ventricular, 146 

—  rabbits  perfused  with  Locke's  solution, 
159 

perfused  witli  Ringer's  solution,  100 

record  of,  movement  of.  511 

—  right  side  of,  diagram  of,  150 

—  sounds  of,  154 

—  Stanniused,  tetanizing  of,  131 

—  surface  relations  of,  153 

—  systolic  output  and  work  of.  163 

—  tissue    of,     conduction    of    excitatory 
wave,  134 

—  turtle's,  sinu-auricular  junction  in.  120 

—  venous  cistern  of,  147 

—  vertebrate,  nervous  elements  of,  123 
type  of,  118 

■ —  volume  of  output,  tracing  showing,  167 
Heartblock,  complete,   electro- card iagrara 

of,  133  ^ 

Heat  coagulation,  46 

—  formation  of,  by  liver,  451 

—  loss  of.  regulation  of,  496 

—  production  of,  regulation,  496 


Heat  stroke,  494 

Helicotrema,  048 

Helmholtz  side-wire,  action  ot,  538 

Helweg  tract,  670 

Henle  loop,  474 

Henry's  law,  19 

Heredity,  778 

Hering  theory  of  colour  vision,  625 

Heteronomous  vision,  632 

Heterophoria,  631 

Heterotyjie  mitosis,  762 

Hexoses,  59 

Hibernation,  738 

Hill's  blood-gas  jiump,  260 

—  cerebral  pressure  gauge,  240 

—  colour  vision  apparatus,  628 

—  pocket  sphygmometer,  189 
Hippurie  acid,  462 
Histidin,  42 

Histones,  47 

Homonomous  vision,  632 

Hormone  reHex,  368 

Hormones,  394,  397,  503 

Horns,  growth  of,  effect  of  castration  on, 

506 
Horopter,  631 

—  vision,  633 

Horse  blood,  analysis  of,  81 

crystals  of,  oxyhfemoglobin  from,  91 

Hunger,  sensation  of,  660 
Hiirthle's  spring  manometer,  188 
Hydrogen  generated  from  a  Kipp's  appara- 
tus, 18 
Hyperglycfemia,  427 
Hypermetropia,  010 
Hyperphoria,  631 
Hyperpno-a,  299 
Hypersusceptibility,  111 
Hypertonic  solution,  24 
Hypnosis,  737 
Hypoglossal  nerve,  691 
Hypotonic  solution,  24,  26 
Hypoxanthin,  50 

Imbibition,  phenomena  of,  31 

Immune  body,  109 

Immunity,  105,  107 

Impulse,  nerve,  7 

Incus,  644 

Indican,  463 

Induction  coil,  connections  of,  535 

Infant  feeding,  360 

—  newborn,  nutrition  of,  357 
Inorganic  compounds.  33 
Inotropic  fibres,  173 
Insemination,  process  of,  770 
Internal  capsule,  709 

—  secretions,  503 

Intestines,  arteries  of.  gas  bubbles  in,  309 

—  bacteria  of,  403 

—  large,  402 

function  of,  402 

—  —  movements  of,  418 

—  movements  of,  record  of,  in  cat,  512 

—  pendulum  movements  of,  410 

—  peristaltic  contraction  of,  417 


INDEX 


793 


Intestines,  small,  digestion  in,  391 

functions  of,  401 

movements  of,  415 

segmentation  of,  415 

segmenting  its  contents,  411 

—  veins  of,  gas  bubbles  in,  309 
Iodides,  secretion  of,  377 
Iodine  value  of  fat,  55 

Ions,  28 
Iris,  604 

—  function  of.  604 

—  nerve  supply  of,  605 
Iron,  lack  of,  336 
In-adiation,  634 
laocholesterol,  58 
Isotonic  solution,  '24 

Jacquet's    sphygmograpii,    imlse    tracini; 

by,  215 
Jecorin,  58 
Jugular  bulb,  position  of,  213 

—  pulse,  waves  of,  214 
Juices,  activation  of.  369 

—  digestive,  369 

—  pancreatic.  396 

Katabolism,  441 

—  of  dextrose,  426 

—  of  fat,  440 

—  of  plasma,  85 

Kata  thermometer,  500 
Katelectrotonic  current,  5S3 
Kathode,  region  of,  stimulation  in,  583 
Ketones,  35 J 
Kidney,  arterial  pressure  of,  247 

—  blood-sup[>ly  of,  474,  475,  47> 

—  circulation  in,  247 

—  functions  of.  453,  478 

—  of  cat,  decompressed,  310 

—  schema  of,  223 

—  secretory  function  of,  481 

—  tubule  of,  minute  structure  of,  474 
resorption  by.  481 

secretory  function  of,  4^1 

Kipp's     apparatus,    hvdrogen     generated 

from,  18 
Kjeldahl's  method  of  analysis  of  urine,  455 

—  process,  329 
Krause's  end-bulbs,  586 
Krogh's  microtonometer,  270 

Labyi'inth,  membranous,  647 

—  of  pigeon,  effect  of  destruct'on  of,  657 
Labyrinthine  sensations,  655 
Lachrymal  glands,  600 

Lactose,  65,  469 

Langerhans,     isk-t    of,    from    pancreas   of 

dog,  513 
Laryngoscope,  740 
Larynx,  277,  740 

—  examination  of.  741 

—  muscles  of,  743 

—  nerve-supply  of,  295 

—  stimulation  of,  295 

—  view  of,  742 

—  vowels  produced  by,  745 


Lecithins,  56 

—  metabolism  of,  441 
Lens,  605 

—  achromatic,  609 

—  cardinal  points  of,  609 

—  convexity  of,  614 
Lenticular  nuclei,  715 
Leucin,  40 
Leucocytes,  97 

—  migration  of,  99 
Leucocytosi^,  99 

Lever  action,  kinds  of,  526 

—  simple,  with  after-loading  screw,  540 
LcTOlose,  62,  469 

Ligaments,  suspensory,  605 
Light,  effects  of,  on  retina,  618 

—  -  phenomena  of,  608 
Limbs,  circulation  of,  243 
Lipase  of  gastric  juice,  387 
Lipoids,  53,  56 

—  lack  of,  336 

—  of  plasma,  84 
Lipolytic  enzymes,  71 
Liquids,  diffusion  in,  21 
Lissauer,  marginal  tract  of.  668 
Liver,  circulation  in,  246 

—  fat  of,  storage,  448    ' 

—  function  of,  447 
protective,  450 

—  glycogenic  function  of,  447 

—  heat  formation  by,  451 

—  protective  function,  450 

—  venous  reservoir  of,  451 
Load,  effect  of,  in  muscle,  545 
Local  sign  of  touch,  589 

Locke's' solution,  rabbit's  heart   perfused 

with,  159 
Locomotion.  525 
Loewenthal  tract,  670 
Lubrication,  forms  of,  6 
Lucas,  moist  chamber  and  electrodes,  563 
Lungs,  blood-pressure  of,  279 

—  circulation  of,  236 

—  diffusion  of  gases  within,  270 

—  lobe  of,  small,  volume  of,  279 

—  preparation   of,  diagram  of  apparatus 
for,  164 

—  right,  resjiiratory  movement  of  root,  287 

—  surface  relations  of,  153 

—  ventilation  of,  292 

—  volume  of,  279 
Lymph,  250 

—  composition  of,  251 

—  formation  of.  252 

—  movement  of,  254 
Lymphocytes,  97 
Lysin,  42 

Mackenzie's  polygraph,  212 

Macula  of  mouse,  656 

Magnesium,  sulphate  of,  injection,  Tiaube- 

Hering  curves  after,  301 
Malleus,  644 
Maltose,  65 
Mammals,  circulation  in,  course  of,  142 


794 


A  TEXTBOOK  OF  PHYSIOLOGY 


Man,  co)iipros8ioii  oU'ects  on,  308 

—  decompression  t'H'ccts  on,  308 
Manometer,  Hiirthle's  spring,  188 

—  niercmia],  arrangement  of,  for  record- 
ing blood-pressure,  187 

Manubrium  sterni,  28.') 

respiratory  movemeuts  of,  286 

Marclii  method  of  staining,  577 
Marching,  499 

Mastication,  movements  of,  407 
Meat,  354 

—  cooked,  composition  and  value  of,  352 
Meatus,  external  auditoiy,  stimulation  of, 

295 
Medulla  oblongata,  688 

formation  of,  688 

functions  of,  695 

section  of,  690,  691 

Medullated  nerves,  570 
Medusa,  tentaculocyst  of,  654 
Meiotic  division  of  cells,  762  • 

Meissner's  corpuscles,  586 
Membranes,  semi-permeable,  21 

action  of,  25 

Mesencephalon,  706 
Mesonepliros,  475 
Metabolism,  325 

—  during  starvation,  333 

—  methods,  325 

—  of  carbohydrate,  426 

—  of  fat,  436 

—  of  lecithin,  441 

—  of  nuclein,  443 

—  of  protein,  421 

—  protein  excess  -with,  339 

—  special,  421 

—  varying  conditions  of,  341 
Metanephros,  474 
Metaprotein,  43 

Metaproteins,  acid  and  alkali,  50 
Methfemoglobin,  93 

Microscope,  projection,  side  elevation  of, 

562 
Microtonometer,  Krogli's,  270 
Micturition,  act  of,  483 
Mid-brain,  706 

—  red  nuclei  of,  707 

—  section  of,  707 
Milk,  353 

—  composition  and  value  of,  349,  352 

—  fats  of,  353 

—  how  from  nipple  of  cat,  522 

—  human,  colour  of,  359 
composition  of,  359 

—  secretion  of,  358 
Mind,  732 

Mineral  salts,  lack  of,  335 
Mitosis,  757 

—  heterotype,  762 

Molecular  complexity,  law  of,  16 

Molisch's  test,  62 

Monakow  tract,  670 

Monocarboxylic  acid,  36 

Monosaccharides,  59 

Moore's  test,  60 

M  otion,  tissue  of,  525 


Motor  area,  efl'ects  of  ablation  of,  721 
■ lamination  of,  725 

—  decussation,  670 

—  impulse,  velocity  of,  581 
Moutli,  digestion  in,  371 

—  shape  of,  in  sounding  vowels,  745 
Movement,  mechanism  of,  525 
Movements  of  body,  level'  principles,  525 

—  of  heart,  144 

in  situ,  151 

Miiller's  law,  585 

Muscarine,  injection  of,  effect  upon  dog's 

heart,  175 
Muscle,  activity  of,  546 

—  arteriole,     pressor     alferent     impulses 
affecting,  231 

—  board,  539 

—  cardiac,  532 

—  change  in  form  of,  539 

—  chemical  changes  in,  552 
induced  l)y  activity,  557 

—  chemical  constitution  of,  555 

—  chemistry  of,  changes  in,  555 

—  ciliary,  603 

—  contraction  of,  539 

apparatus  for  recording,  540 

conditions  affecting,  545 

Frog's  gastrocnemius,  541 

period,  543 

period  and  movements  of  levers  on 

544 

superposition,  548 

• —  differentiation  of,  530 

—  electromotive  properties  of,  559 

—  excitability  of,  533 

—  extensiljility  of,  532 

—  fatigue  of,  546 

—  inhibition  of,  678 

—  injuries  of,,  by  electricity,  560 

—  irritability  of,  533 

—  laryngeal,  743 

—  lateral  cricoarytenoid,  743 

—  of  rabbit,  contractions  of,  541 

—  physical  properties  of,  530,  532 

—  posterior  crico-arytenoid,  742 

—  reciprocal  excitation,  678 

—  i-elation  of,  545  ' 

—  rhythmicity,  558 

—  section  of  sucker  catastonius,  531 

—  smooth,  532;  558 

—  spontaneous  movements  of,  551 

—  stimulation  of,  561 

—  stimulus  of,  545 

—  structure  of,  530 

—  thermal  changes  in,  552 

—  time  of  contraction,  542» 

—  tonus,  558 

—  unloaded,  contractions  of,  542 
Muscular  activity,  mechanism  of,  554 
— ^  tissue,  5 

—  "  tone,"  551 

Mritton,  composition  and  value  of,  348 

—  fat,  melting-point  of,  438 
Myelination,  evidence  of,  727 
Myogen,  555,  556 

—  fibrin,  insoluble,  556 


INDEX 


795 


Myopia,  616 
Myosin,  555 
ilyosinogei],  555,  556 
JU'ostroniin,  556 
^lyxcedema,  case  of,  517 

Narcosis,  737 

Nature,     nitrogen     in,     circulation     of, 

259 
Nerve  cells.  570 

—  crural,  244 

—  eighth,  697,  699 

—  electromotive  properties  of,  559 

—  endings,  effector,  in  muscles  of  lizard, 
574 

—  fibres  in  muscle  spindle,  658 

medullated,   from  a  mammal,  571, 

572 

physiology  of,  579 

regeneration  of,  578 

—  impulse,  7 

—  regeneration  of,  576,  578 

—  roots,     "Walleriau      degeneration     of 
663 

—  stimulation  of,  176,  561,  573,  579 

—  supply  of  iris,  605 
Nerves,  afferent,  245,  573 

—  cardiac,  171 

of  dog.  172 

of  frog,  171 

—  cranial,  690 
nuclei  of,  699 

—  depressor,  effects  of  stimulation,  518 

—  efferent,  573 

—  iris,  605 

• —  lai-yngeal,  295 

—  medullated,  570 

—  non-meduUated,  570 

—  seventh,  698 

—  sixth,  700 

—  spinal  accessory,  691 
mixed,  749 

—  splauchnic,  429,  510 

—  tenth,  origin  of,  694 

—  trigeminal,  700 

—  twelfth,  origin  of,  694 

—  vagus,  173,  241,  298,  691 

—  vaso-motor.  229,  242,  246 

Nervous  centre,  connections  of,  in  secre- 
tion of  gastric  juice,  374 
of  saliva,  374 

—  conduction,  574 

■ —  elements  of  vertebrate  heart,  123 

—  impulse,  rate  of  transmission,  580 

—  structures,  stippled,  567 

—  system,  569 

autonomic,  748,  750 

stimulus,  7 

sympathetic,  aiTangement  of,  748 

Neural  arcs,  671 
Neurogenous  glycosuria,  432 
Neuroglia,  572 
Neuron,  569 

—  function  of,  575 
Neuro-tendinous     nerve      end -organ      in 

rabbit,  659 


Nicotine,  action  of,  229 
Night-blindness,  623 
Nissl's  granules,  569 
Nitrogen  in  blood,  263 

—  of  urine,  455 
Nitroxyhiemoglobin,  92 
Non-goitrous  cretins,  516 
Nose,  function  of,  277 
Nuclein,  metabolism  of,  443 
Nucleoproteins,  48 
Nucleus  of  Deiters,  698 

—  pontis,  698 

Nutrition,  effect  of  vitaniine  on,  337 

—  of  heart,  158 

Nuts,  composition  and  value  of,  349 

Nylander's  test,  61 

for  sugar  in  urine,  467 

Obesity,  442 

Odour-producing  glands,  6 

Olein,  54 

Olfactometer,  597 

Olfactory  epithelium  of  fowl,  596 

Olivo-spinal  tract,  670 

Ontogeny,  3 

Ophthalmoscopes,  639,  640 

Opsonins,  109,  110 

Optic  fibi'es,  relations  of,  713 

—  thalamus,  710 
Organic  compounds,  34 
Osmosis,  phenomena  of,  22 
Osmotic  pressure,  21,  22 

of  blood,  80 

Osseous  labyrinth,  646 
Ovary,  506,  767 

—  foital,  767 
Ovum,  human,  768 
development  of,  774 

—  embedded  in  uterus,  776 

—  embedded  in  wall  of  uterus,  775 

—  implantation  of,  773 

—  maturation  of,  764 

—  morula  from,  772 

—  of  bat,  771 

—  of  cat  before  maturity,  9 

—  of  toxopreustes,  759 

—  segmentation  of,  773 
Oxalates,  461 
Oxblood,  analysis  of,  81 
Oxidases,  73 

—  action  of,  444 

Oxygen,  atmospheres  of,  lung  exudation 
in,  303 

—  capacity  of  blood,  264 

—  consumption  of,  relationship  of  arterial 
pressure  to,  169 

relationship  of  pulse  to,  169 

— ■  curves  of  human  blood,  266 

—  excess  of,  effects,  303 

—  in  blood,  263,  275 

—  percentage  of,  in  respiration,  293 

—  use  of,  in  man,  342 

—  want  of,  effects,  304 
Oxyhaemoglol^in,  crystals   of,  from   horse 

blood,  91 
Oxyproline,  42 


679 


A  TEXTBOOK  OF  PHYSIOLOGY 


Paciuiau  corpuscle,  586,  587 
Pain,  661 

—  referred,  and  counter-irritation,  661 

—  sensation  of,  591 
Falniitin,  54 
Pancreas,  511 

—  nuclease  of,  443 

—  secretion  of,  395 

Pancreatic  enzj-nics,  activation  of,  398 

—  glycosuria,  432 

—  juice,  396 

digestive  action  of,  399 

flow  of,  368 

mechanism  of  secretion,  397 

Paradise  fish,  gas-secreting  cells  of,  271 
Paramyosinogen,  555 
Parathyroid  glycosuria,  434 

—  of  dog,  after  thyroidectomy,  515 

—  of  normal  dog,  5T4 
Parathyroids,  function  of,  512 
Pars  plana,  603 

—  plioata,  603 
Parturition,  775 

Pawlow's  method  of  establishing  a  gastric 

fistula,  381 
Pentosans,  63 
Pentose,  469 
Pentoses,  59,  63 
Peptic  digestion,  385 
Peptones,  40,  43,  51 
Pericardial  fluid,  254 
Perilymph,  646 
Perimeter,  638 

Perimetric  chart  of  right  eye,  639 
Peristalsis,  true,  417 
"  Peristaltic  rush,"  417 

—  wave  of  small  intestine,  417 
Perspiration,  488 
Phakoscope,  613 

—  rays  of  light  in,  613 
Pharynx,  277 
Phenyl  alanin,  41 
Phenylhydrazine  test,  61 
Phloridzin  glycosuria,  433 
Phosphate  crystals,  471 

—  of  calcium,  471 
Phosphates.  464 

—  distribution  of,  33 

—  lack  of,  336 
Phosphatides,  56 
Phosphoproteins,  48 
Photohaematochonieter,  Cybulski's,  205 
Phototaxis,  12 

Phylogeny,  2 

Physico-chemical  physiology.  17 
Phytocholesterol,  58 
Pigments,  bile,  393 
Pineal  body,  524 
Pituitary  body,  521 

functions  of,  522 

of  adult  monkey,  520 

—  glycosuria,  434 
Placenta,  774 

—  blood  space,  formation  of,  776 

—  formation  of,  777 
Plant  life,  cycle  of,  258 


Plasma,  82 

—  carbohydrate  of,  85 

—  fibrinogen  of,  84 

—  katabolism  of,  85 

—  lipoids  of,  84 

—  proteins  of,  83,  424 

—  salts  of,  85 

—  serum  albumin  of,  84 

—  serum  globulin  of,  83 
Plasmolysis,  24 

—  effect  of,  in  Tradescantia  discolor,  d 
Plethysmograph  and  piston  recorder  230 
Plethysmographic;     method,     velocity 

flow  by,  206 
Pleura,  fluids  of,  254 
Poisons,    vegetable,   hceniolysf     produced 

by,  107 
Polarimetric  tost,  62 
Polygraph,  213 

—  Mackenzie's,  212 
Polypeptides,  40,  43,  45 
Polysaccharides,  65 

—  reactions  of,  66 
Pons  varolii,  688,  696 
section  of,  696 

Pork,  composition  and  value  of,  348 
Portal  circulation,  246 
Post-dicrotic  wave,  215' 
Posterior  longitudinal  bundle,  695 
Postganglionic  fibres,  750 
Postirre,  effect  of,  on  circulation,  194 

—  erect,  527 
Precipitins,  111 
Predicrotic  wave,  215 
Preganglionic  fibres,  749 
Pregnancy,  serum  test  for,  777 
Presbyopia,  616 

Pressure,  arterial,  186 

—  bottle,    arrangement  of,  for  recording 
blood-pressure,  187 

—  osmotic,  21,  22 

—  sensations  of,  588 
Pronephros,  474 

Proprio-ceptivc  mechanism,  654,  659 
Prostate  gland,  506 
Protamines,  47 

Protein  decomposition,  403 

—  digestion  of,  385 

—  -  digestion,  products  of,  424 

—  foods,  cost  of,  348 

—  katabolism,  328 
Proteins,  39,  43,  428 

—  chemical  properties  of,  45 

—  classification  of,  47 

—  compound.  48 

—  constitution  of,  39 

—  derived,  50 

—  excess  of,  in  metabolism,  339 

—  fat  from,  439 

—  in  urine,  465 

—  metabolism  of,  421 

—  of  plasma,  83 

—  physical  properties  of,  45 

—  required  for  weight  atdifterent  ages,362 
Proteolytic  enzymes,  70 

Proteoses,  40,  43,  51 


INDEX 


7i)7 


Protopatliic  sensibility,  591,  592 
Protoplasm,  8 

—  luovenieiits  of,  11 
Ptyaliii,  actiou  of,  378 
Pulmoiiarv  circulation,  236 
Pulse,  211 

—  curve,  arterial,  215 

—  frequency  of,  duration  of  systole  and 
diastole  with,  168 

—  intluenceof  abdominal  breathing  on,  191 
chest  on,  191 

—  investigation  of,  by  spliygmographs,  212 

—  rates,  average  of,  216 

—  tracing  of.  by  Jacquet's  sphygmograph, 
215 

—  venous,  213 

—  wave  in  the  arterial  system,  217 
Pulses,  355 

Purin  bases,  49 

—  bodies,  49,  460 
Purkinje,  cells  of,  703 
Putresein,  403 
Pvrimidin  bases,  49 
Pyrolin,  42 

Rabbit,  siuu- auricular  node  of,  effect  of 
excision,  140 

Rabbit's  heart,  a. v.  bundle  cut,  stimula- 
tion of  right  vagus  nerve,  136 

Reaction  time,  731 

—  —  apparatus  *or  determination  of,  732 
Receptors,  lOS,  574 

—  mechanism  of.  585 

—  of  cutaneous  .sensation,  structure  of,  585 
Rectum,  showing  pelvi-rectal  flexure,  419 
Reflex  arc,  574 

simple,  575 

—  centre,  spinal  cord  as,  674 
Reflexes,  674,  676,  678,  680,  682,  684 

—  tendon,  684 
Refraction,  610 
Regeneration,  peripheral,  578 
Renal  epithelium  of  frog,  573 

—  tubules,  development  of,  473 
resorption  by,  481 

secretory  functions  of,  481 

Rennet,  action  of,  387 
Reproduction,  755,  760 
Reproductive  organs,  female,  767 

male,  764 

Residual  air,  280 
Respiration,  192,  257 

—  air  changes  in,  293,  312 

—  apparatus.  Haldane-Pembrey,  318' 

—  artiHcial,  323 

Schiifer's  method,  322 

Sylvester's  method,  322 

vivator  aj)paratus  for,  324 

—  chamber  for  man,  331 

—  Cheyne- Stokes,  299,  300 

—  effect  of  emotion  on,  202 

—  interna],  320 

—  mechanism  of,  276 

—  record  of,  in  cat.  323 

—  regulation  of,  289 

—  tissue,  320 


Respiration,  tracing  of,  304 
Respiratory  centre,  294 

—  exchange,  determination  of,  317 

increase  of,  by  muscular  work,  319 

internal,  eflect  of  activity  upon,  321 

—  function  of  the  skin,  489 

—  quotient,  319 
Retina,  606 

—  eftects  of  light  on,  618 

—  functions  of,  619 

—  human,  diagram  of,  606 

—  images  on,  615 

—  of  frog,  620 

—  of  rabbit.  620 

—  structures  of,  606 
Retinal  currents,  565 
Retinoscopy,  617 

Retz  cell  from  human  cerebral  cortex,  571 
Rheocord,  principle  of,  535 
Rhinencephalon,  connection  of,  714 
Rhj-thmic  automaticity  of  heart,  127 
Ribs,  first  pair  of,  285 

—  lower-,  movement  of,  287 

—  movement  of,  285 

—  respiratory  movements  of,  286 

—  upper,  movement  of,  286 
Rice,  polished,  336 

Rigor  mortis,  557 
Ringer-solution,  477 

—  rabbit's  heart  perfused  with,  160 
Rubro-spinal  tract,  670 

Ruffini's  organs,  586 
Running,  528 

Saccharose,  64 

Sacral  autonomic  system,  751 

Saliva,  371 

—  composition  of,  372 

—  paralytic  secretion,  375 

—  quantity  of,  373 

—  secretory  pressures  of,  376 
.Salivary  glands,  565 

—  —  circulation  of,  243 

—  —  schema  of,  223 
Salkowski's  test,  58 

"  Salt "  glycosuria,  435 

—  solutions  of,  solubility  of  gases  in,  20 
Salts,  inorganic,  394 

—  of  plasma,  85 

—  organic,  392 

—  proportion  of,  in  blood,  266,  267 
Saponification  of  fat,  53 
Sartorius  muscle,  curve  of,  549 
excursion  to,  564 

fatigue  curves  of,  546 

nervous  impulse  in,  581 

of  frog,  spontaneous  movements  in, 

549 

stimulation  of,  550 

Scala  media,  648 

Schiifer's  method  of  artificial  respiration. 

322 
Sciatic  nerve  of  kitten,    regeneration   of, 

577 
Sclera,  602 
Scleroproteins,  48 


793 


A  TEXTBOOK  OF  PHY810L0GY 


Scratch  reflex,  676,  677,  678,  680 

receptive  field  for,  67 f' 

Sebaceous  glands,  487 
Secretion,  368 

—  meclianism  of,  358 
Segmentation  of  ovum,  773 

—  rli_ytliniic,  414 
Semicircular  canals,  655 
Seminal  fluid,  766 
Sensations,  cutaneous,  585 

Sensory  mechanism,  localization  of,  727 

—  path  from  peripheral  nerve.  711 
Sera,  foreign,  liwniolysis  by,  106 
Serin,  40 

Serum  allmmin  of  plasma,  84 

—  globulin  of  plasma,  83 

—  test  for  pregnancy,  777 
Seventh  nerve,  function  of,  699 
origin  of,  698  ' 

Sex,  determination  of,  781 

—  diet  under  various  conditions,  356 
Sexual  characteristics,  504,  505 
Sexual  life,  female,  769 

Shellfish,  composition  and  value  of,  348 

Sigliing,  296 

Sinu-auricular  node,  119 

Sixth  nerve,  origin  of,  698,  700 

Skiascopy,  617 

Skin,  absorption  by,  489 

—  current,  566 

—  effect  of  atmosphere  ujwn,  499 

—  electric  currents  of,  564 

—  function  of,  485 
of  pigment,  490 

—  parts  of,  485 

—  respiratory  function  of,  489 

—  section  of,  486 

—  sensations,  585 
Sleep,  735 
Smell,  593 

—  excitation  of,  597 

—  receiving  stations  for,  729 

—  receptor  mechanism  of,  596 

—  sense  of,  investigation  of,  597 

■  paths  in  connection  with,  715 

Snake  venoms,  hfemolysis  by,  107 
Snellen's  test-types,  637 

Soaps,  55 

Sodium  urate,  459,  471 
Solubility  of  gases,  2  3 
Solutions,  hypertonic,  24 

—  phj'siological,  26 
Sound,  650 

—  experimental  production  of,  in  sheep's 
trachea,  740 

—  intensity  of,  650 

—  pitch  of,  650 

—  production  of,  739 

—  quality  of,  650 

—  Mave,  formation  of,  651 
Sounds  of  the  heart,  154 
Spectra,  blood,  93 
Speech,  729 

—  centre  of,  731 

—  production  of,  739 
Spermatozoon,  765,  766 


Spherical  aberration  of  lens,  609 
Sphingomyelin,  58 

Sphygniograph,      Dudgeon,       suspension 
method  of  using  the,  211 

—  investigation  of,  pulse  by,  212 

—  Jacquet's,  pulse  tracing  by,  21 5 
Sphygmometer,  armlet,  188  " 

—  Leonard  Hill  pocket,  189 
Sphygmoscope,  188 
Spinal  accessory  nerve,  691 

—  arc,  672 

—  bulb,  white  matter  of,  694 

—  cord,  662 

• — ■  — -as  reflex  centre,  674 

commissural,  fibres  of,  670 

conductor,  impulses  of,  672 

effect  of,  transverse  section  through, 

673 

embryonic,  664 

exogenous  tracts  of,  667 

functions  of,  672 

posterior  columns  of,  necrotic  areas 

in,  311 

reflex  action  of,  674 

sections  of,  665,  666 

structure  of,  663 

tracts.  666 

tracts  from  brain  to,  669,  670 

tracts  of  from  posterior  root  ganglia, 

668 

—  nerve,  mixed,  arrangement  of,  749 
Spino-tlialamic  tract,  670 

Spirits,  alcohol  percentage  of,  365 
Spirometer,  280 
Splanchnic  area,  198 

—  nerves,  effect  of  stimulation  of,  429,  510 

—  organs,  246 
Spleen,  247 

—  function  of,  447,  451 
Stapedius,  646 
Stapes,  644 

Starch,  action  of  gastric  juice  on,  387 

Starches,  65 

Starvation,  metabolism  during,  333 

Stearin,  54 

Stereoscope,  635 

Stimulus  of  muscle,  strength  of,  545 

—  of  nervous  system,  7 
Stomach,  absorption  in,  388 

—  contents,  examination  of,  388 

—  digestion  iii,  379 

—  digestive  processes  in,  385 

—  movements  of,  411 

—  of  cat,  changes  in  shape  during  diges- 
tion, 407 

digestion  in,  406 

shadows   of  contents  after  feeding, 

411 

—  outline  of,  379 

—  position  of,  380 

—  why  not  itself  digested,  388 
Stress,  lines  of,  758,  759 
Stromuhr,  203,  204 
Strychnine  convulsions  in  frog,  684 
Stylonychia,  enucleated,  fragments  of,  700 
Sulilingual  gland,  374 


INDEX 


799 


Submaxillary  glaud,  o74 
Succus  entericus,  400 

mechanism  of  secretion,  400 

use  of,  401 

Sucker  catastonius,  muscle  of,  531 

Sucrolytic  enzymes,  71 

Sugar,  action  of  gastric  juice  on,  387 

—  concentration  of  in  arterial  blood,  429 
in  urine,  429 

—  content,  in  glycosuria,  431 

—  in  urine,  267 

—  splitting  of,  430 
Suggestion,  effect  of,  234 
Sulphates,  462 

—  inorganic,  462 

—  organic,  463 
Sulphur,  neutral,  462,  463 
Summation  of  muscle,  547 
Superior  olive,  699 
Suprarenal  body,  508 

of  dog,  section  of,  507 

Surface  tension  in  colloids,  31 
Susjwnsory  ligament,  605 
Swallowing,  mechanism  of,  408 

—  nervous  mechanism  of,  410 

—  shadow  in  cesophagus  after,  410 
Sweat  glands,  487 

Sylvester's  method  of  artificial  respiration. 

322 
Synapse,  572 
Systole,  144  . 

—  duration     of,     table     showing    pulse- 
frequencies,  170 

with    ditferent    pulse    frequencies, 

168 
Systolic  output  and  work  of  heart,  163 

Tactile  sensations,  589 
Taste,  593 

—  bud  in  tongue  of  man,  594 

—  effect  of,  233 

—  nerve  distribution  for,  595 
• —  receiving  stations  for,  729 

—  receptor  mechanism  of,  593 

—  sensations,  apparatus  for  testing,  594 
Temperament,  diet  under  various  condi- 
tions, 356 

Temperature,  body,  492 

—  effect  of,  on  muscle,  545 

upon  gastrocnemius  muscle,  543 

—  external,  effect  of  raising,  497 
metabolism  increased  by,  343 

—  normal,  492 

—  regulation  of,  495 

—  sensations  of,  590 

—  variations  of,  493 
Tendon  reflexes,  684 
Tensor  tympani,  646 
Testes,  505,  765 
Toet-types,  Snellen's,  637 
Tetanus,  550 

—  composition  of,  548 
Thalamo-spinal  tract,  670 
Thalamus,  function  of,  710 
Thermometer,  Kata,  500 
Thermopile,  double,  553 


Thermopile,     single-pair,     connected     to 

galvanometer,  552 
Thermotaxis,  negative.  12 
Thirst,  sensation  of,  660 
Thoma-Zeiss  hemacytometer,  87 
Thorax,  compression  of,  163 

—  movements  of,  in  respiration.  306 
Thrombin  of  blood,  102 

Thymus  gland,  519 

—  development  of,  513 

—  function  of,  520 

—  gland  of  monkey,  519 
Thyroid,  742 

— ■  development  of,  513 

—  function  of,  512 

—  glycosuria,  434 

—  of  normal  dog,  514 
Tidal  air,  278 

Tissues,  combination  of,  5 

—  formation  of,  3 

—  gases  in,  pressure  of,  269 

Toad,  auricle  and  ventricle  of  record  of 

contraction,  128 
Tone,  muscular,  551 
Tonometers,  264 

Topler  pump  for  blood-gas  analysis,  261 
Torpedo  Ocellata,  auricle-ventricle  of,  130 
Touch,  reaction  time  to,  733 

—  sensation  of,  586.  588 
Toxins,  108 
Toxophor,  108 
Trachea,  277 

Tracts,  spinal  cord,  666 
Transfusion  in  hemorrhage,  228 
Transport,  mechanism  of,  115 
Traube-Hering  curves,  301 
Trigeminal  nerve,  700,  701 
Trioses,  59 
Tripeptide,  45 
Trommer's  test,  61 

—  —  for  sugar  in  urine,  467 
Trophoblast,  773 
Trypsin.  399 
Tryptophan,  42 
Tympanic  membrane,  644 

view  of,  645 

Tyrosin,  41 

Ultra-violet  light,    lesions    produced   oit 
rabbit's  ear  by,  13 

yeast  cells  photographed  by,  10 

Umbilical  vessels,  248 
Urea,  456 

—  formation  of,  448 

—  nitrate,  457 

—  oxalate,  457 
Ureometer,  458 

Ureters,  passage  of  urine  along,  482 
Uric  acid,  444,  458,  471 

—  —  crystals,  460 
formation  of,  448 

source  of,  endogenous,  444 

' —  exogenous,  444 

Urinary  deposits,  470 
Urine,  453 

—  abnormal  constituents  of,  465 


800 


A  TEXTBOOK  OF  PHVSJOLOCY 


Urine,  analyses  of,  155 

—  bile  in,  469 

—  Wood  in,  46ti 

—  -  colour  of,  454 

— -  composition  of,  -155 

—  formation  of,  rate,  429 

—  nitrogen  total  of,  455 

—  nitrogenous  constituents  of,  455 

—  passage  of,  through  ureters,  482 

—  proteins  in,  465 

—  secretion  of,  473 

—  sugar  in,  431,  467 

—  transparency  of,  454 
Uriniferous  tubules,  course  of,  475 
Urobilin,  454 

Urochrome,  454 

Uroerythrin,  455 

Uterus,  ovum  embedded  in,  776 

Vagi,  intluence  of,  296 
Vago-synipathetic,  excitation  of,  170 

—  stimulation  of,  contraction  of  frog's 
heart  showing,  169 

Vagus,  in  cat,  300 

—  influence  of,  upon  respiratory  move- 
ments, 296 

Vagus  nerve,  691 

electrical  changes  in,  298 

in  rabbit,  dissection  of,  176 

inter-auricular  septum  of,  124 

periphereal  end  of,  effect  of  stimu- 
lating, 241 

excitation,  173 

stimulation  of,  in  cat's  heart   175 

Valin,  40 

Vascular  system,  changes  of  i)ressure  in, 
227 

Vaso-constrictor  nerves,  233,  238,  242 

Vaso-dilator  nerves,  242 

Vaso-motor  centie,  reflex  action,  233 

—  mechanisms,  246 

—  nerves,  229 

distribution  of,  231 

Vegetables,  composition  and  value  of,  350 

—  green,  355 
Vegetarianism,  364 

Veins,  blood-flow  in,  rate  of,  226 

—  blood-pressure  in,  225 

—  blood-velocity  in,  225 

—  structure  of,  125 

—  velocity  of  flow  in,  208 

—  venous  pressure  of,  226 
Velocity  ot  blood,  in  veins,  225 

—  of  biood-flow,  203 
Venous  pulse,  213 

Venous  reservoir  of  liver,  451 
Venous  system,  pressure  in,  226 
Ventilation,  principles  of,  312 
Ventral  spino-cercbellar  tract,  669 


Ventricle,  right,  of  calf,  121,  122 
Veiatrin  curve,  543 
Vertebrate  heart,  type  of,  118 
Vestibule,  647 
V'estibulo-spinal  tract,  670 
Viscosity  of  blood,  80 
Vision,  binocular,  630 

—  near  point  of,  615 

■ —  paths  concerned  in,  712 

—  reaction  time  to,  733 

—  receptor  mechanism  of,  599 

—  sense  of,  599 
Visual  angle,  611 

—  area,  cell  lamination  of,  726 

—  judgments,  633 

—  tract,  712 
Vital  force,  15 

Vitamines,  effect  of,  on  growth,  338 
on  nutrition,  337    " 

—  lack  of,  336 

Vivator  apparatus   for    artificial    respira- 
tion, 324 
Vocal  cords,  positions  of,  744 
Volatile  fatty  acids  in  fat,  55 
Vol  vox  globator,  colony  of  cells,  4 
Vomiting,  415 
Vowels,  produced  by  larynx,  745 

—  shape  of  mouth  in  sounding,  745 

Wagner's  hammer,  action  of,  537 

Walking,  528 

Wallerian  degeneration,  576 

• in  cat,   Marchi  juethod  of  staining. 

577 
Warm-blooded  animals,  495 
AVater,  33 

—  diffusion  of  gas  through,  20 

—  lack  of,  334 

—  vapour,  498 
Weber's  law,  585 
Weaning,  362 

Weight,  at  different  ages,  protein  for,  362 

Wernicke's  area,  730 

Wheel  for  mixing  colours,  623 

Wines,  alcohol  percentage  of,  365 

Work,  diet  under  various  conditions  of,  356 

—  inetabolism  increased  during,  343 
Woultfc's  bottle,  18 

Xanthin,  50 

Yawning,  296 

Yeast  cells,  jihotographed  by  nltravi(jlet 

light,  10 
Young-Helmholtz  theory  of  colour  vision, 

625 

Zollner's  lines,  636 
Zymogen,  369 


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Testbook  of  physiology. 


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