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H,  C.  NEWLAND,  Ph.  D.. 

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H.  C.  NEWLAND,  Ph.  D.. 

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Digitized  by  the  Internet  Archive 
in  2017  with  funding  from 
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Philip  D.  Gendreau 

Biology  is  the  study  of  living  things,  including  human  beings.  The  out  of  doors  is  the  best 
classroom  and,  although  the  school  laboratory  has  to  be  used  for  class  work,  one  should  go 
to  nature  to  confirm  the  truths  that  are  learned  from  books  and  experiments. 


PROBLEMS  IN  BIOLOGY 


BY 

GEORGE  W.  HUNTER,  Ph.D. 


Lecturer  in  Methods  of  Education  in  Science 
Claremont  Colleges,  Claremont,  California 
Formerly  Head  of  the  Department  of  Biology 
Dewitt  Clinton  High  School,  New  York 


AMERICAN  BOOK  COMPANY 

NEW  YORK  CINCINNATI  CHICAGO 

BOSTON  ATLANTA 


IN  CANADA  FROM 

W.  J.  GAGE  & COMPANY  LIMITED 

TORONTO  - ONTARIO 


Copyright,  1936 


AND  1931,  BY 

AMERICAN  BOOK  COMPANY 
CoPYEiGHT,  Philippine  Islands,  1934 
All  rights  reserved 

H.  BIO. 

W.  P.  IS 


MADE  IN  U.S.A. 


PREFACE 


The  modern  textbook  in  biology  to  be  successful  must  do  a 
number  of  things  well.  First  of  all,  it  must  contain  enough  factual 
subject  matter  not  only  to  give  the  student  a basis  for  thinking 
out  his  problems  but  also  to  give  the  teacher  a wide  enough  choice 
of  material  to  fit  into  the  various  environments  where  the  text 
is  to  be  used.  It  might  be  advantageous  to  have  a text  written 
for  environmental  conditions  under  which  it  was  to  be  used,  but 
such  a plan  would  be  impractical  because  of  varying  conditions 
in  different  parts  of  the  country.  Since  it  is  impractical  to  make 
texts  to  interpret  given  small  areas  the  next  best  thing  is  to  give 
wide  choice  of  material.  This  text  does  this. 

Second,  the  modern  text  must  give  to  the  teacher  a variety  of 
problems^  demonstrations,  projects,  and  interesting  leisure  time 
activities  in  order  that  the  need  of  the  individual  student  may  be 
adequately  met.  Nothing  is  more  difficult  for  the  overloaded 
teacher  than  to  attempt  to  adjust  the  work  to  the  individual  needs 
of  a large  number  of  pupils.  This  book,  with  its  many  exercises 
and  questions,  graded  to  the  needs  of  a heterogeneous  group, 
squarely  meets  the  problem  of  individual  differences.  Projects, 
demonstrations,  surveys,  and  reports  are  suggested  also  in  sufficient 
numbers  to  fill  the  time  of  a widely  diverging  group. 

Another  thing  the  modern  text  should  do  is  to  give  the  student 
adequate  help  in  testing  his  own  factual  knowledge  and  his  own 
ability  to  organize  his  materials.  Self-testing  exercises  are  useful 
for  this  purpose.  All  of  the  units  included  in  the  text  have  such 
devices.  Formal  summaries  are  purposely  omitted.  Instead,  out- 
line summaries  are  used.  In  this  way  the  pupil  builds  up  a series 
of  generalizations  and  uses  them  intelligently  for  the  summary 
which  he  makes  as  an  index  of  his  mastery  of  the  thought  content 
of  the  unit. 

This  book  follows  the  approved  unit  structure,  and  each  unit  is 


V 


1203"/’8 


VI 


PREFACE 


built  on  a general  plan  which  has  been  tested  and  found  to  give 
satisfactory  results.  The  unit  is  introduced  by  a number  of  survey 
questions  intended  to  motivate  the  group  in  the  work  which  follows 
and  to  give  the  teacher  an  opportunity  to  find  out  what  “apper- 
ceptive mass”  exists  in  the  minds  of  the  pupils.  This  device  may 
be  used  to  organize  the  work  of  superior  students  who  have  a basic 
knowledge  of  the  material  of  the  unit  and  who  may  therefore  be 
allowed  to  organize  some  project  as  their  share  of  the  class  work. 
The  preview  follows,  giving  a brief  introduction  to  the  problems  of 
the  unit,  and  is  both  an  organizing  and  a motivating  device.  Next 
come  the  problems,  many  of  which  are  introduced  by  laboratory 
exercises  or  demonstrations,  with  opportunity  for  individual  work 
where  it  is  practical.  Numerous  exercises  and  problem  questions 
give  opportunity  for  individual  pupil  assignments  and  reports. 
The  organization  of  the  unit  by  the  pupil  is  provided  for  in  the 
outline  summaries,  in  the  attainment  tests,  in  individual  check-up 
on  the  answers  to  the  survey  questions,  and  in  the  self-testing 
exercises.  In  these  ways  the  teacher  has  an  opportunity  for 
individual  work  with  students.  The  recitation  period  may  consist 
of  individual  reports  on  rather  large  blocks  of  the  unit,  interspersed 
with  rapid-fire  questions  where  it  is  obvious  that  the  student 
organization  of  the  topic  has  left  unexplained  some  vital  point. 

The  author  wishes  to  thank  the  following  for  their  critical 
reading  of  the  manuscript  in  its  entirety  or  in  part  and  their 
valuable  suggestions : Charles  W.  Finley,  State  Teachers  College, 
Upper  Montclair,  New  Jersey ; Frank  M.  Wheat,  Head  of  Depart- 
ment of  Biology,  George  Washington  High  School,  New  York ; 
Paul  B.  Mann,  Evander  Childs  High  School,  New  York ; Ada  L. 
Weckel,  Head  of  Department  of  Science,  High  School,  Oak  Park, 
Illinois ; George  W.  Hunter  HI,  Assistant  Professor  of  Biology, 
Wesleyan  University,  Middletown,  Connecticut ; and  Lena  Newton, 
Department  of  Biology,  Hartford  Public  High  School,  Hartford, 
Connecticut.  Thanks  are  also  due  Loran  W.  Kitch,  Herbert 
Hoover  High  School,  Glendale,  California ; Roy  Knapp,  Principal 
of  Antelope  Valley  Joint  Union  High  School,  Lancaster,  California ; 
and  Mrs.  Karyn  B.  Sanders,  Downey  Union  High  School,  Downey, 
California,  for  constructive  criticisms  on  teaching  devices. 


TABLE  OF  CONTENTS 


PAGE 

WHY  AND  HOW  WE  STUDY  BIOLOGY 1 

PART  I 

LIVING  THINGS  IN  RELATION  TO  EACH  OTHER 
AND  THEIR  SURROUNDINGS 

UNIT  I.  THE  WORLD  WE  LIVE  IN  AND  WHAT  WE 
TAKE  FROM  IT 

PROBLEM 

I.  How  Is  A Tree  Fitted  TO  Live  IN  Its  Natural  Surroundings?  21 

II.  What  Are  the  Building  Materials  of  the  World  and 
♦ How  Are  They  Used? 23 

III.  What  Are  Foods  and  How  Are  They  Used?  ...  30 

IV.  How  Does  Man  Control  His  Environment?  ...  32 

UNIT  11.  WHAT  IS  BEING  ALIVE?  THE  FUNCTIONS 
OF  LIVING  THINGS 

I.  What  Do  We  Mean  by  Reactions  to  Stimuli?  ...  39 

II.  How  Are  Living  Things  Alike  and  How  Do  They  Differ?  43 

III.  What  Are  Cells  and  How  Do  They  Produce  Others?  . 46 

IV.  What  Do  We  Mean  by  Adaptation? 49 

UNIT  III.  HOW  ARE  PLANTS  AND  ANIMALS 
MUTUALLY  DEPENDENT? 

I.  What  Are  the  Inter-relationships  OF  Plants  AND  Animals?  57 

II.  To  Know  Something  of  the  Structure  and  Life  History 

OF  THE  Grasshopper 62 

III.  To  Know  Something  about  the  Structure  and  Life 

History  of  the  Butterfly 65 

IV.  Wh.\t  Do  We  Mean  by  Communal  Life  and  Division 

OF  Labor?  ..........  69 

V.  What  Are  the  Characteristics  OF  Other  Groups  OF  Insects?  75 

VI.  Why  Are  Insects  So  Numerous? 80 

VII.  Of  What  Use  Are  Flowers  to  Plants?  ....  83 

VIII.  How  Are  Fruits  Formed? 86 

IX.  What  Are  Some  Adaptations  in  Insects  for  Carrying 

Pollen? 88 

X.  What  Are  Some  Specific  Examples  of  Cross  Pollination?  91 

vii 


TABLE  OF  CONTENTS 


viii 


UNIT  IV.  HOW  AND  WHY  DO  SEED  PLANTS 


SUCCEED  IN  LIFE? 

PROBLEM  page 

I.  What  Are  Weeds  and  What  Do  They  Do?  , . . 101 

11.  Why  and  How  Should  Weeds  Be  Eradicated?  , . . 105 
HI.  How  Are  Fruits  and  Seeds  Scattered?  ....  108 


PART  II 

GREEN  PLANTS  MAKE  THE  FOOD  OF  THE  WORLD 

UNIT  V.  WHY  DO  SEEDS  GERMINATE? 

' I.  Where  Are  Baby  Plants  Found? 116 

11.  What  Are  the  Tests  for  the  Organic  Nutrients?  . . 118 

III.  What  Factors  Are  Necessary  to  Awaken  the  Embryo 

WITHIN  THE  Seed? 120 

IV.  What  Becomes  of  the  Parts  of  the  Embryo  during  Its 

Growth  into  a Young  Plant? 122 

V.  What  Makes  a Young  Plant  Grow? 123 

VI.  Where  Is  the  Food  Supply  of  Different  Seeds?  . . 125 

VII.  How  Does  the  Corn  Grain  Make  Use  of  Stored  Food?  . 128 

UNIT  VI.  GREEN  PLANTS  AS  FOOD  MAKERS  AND 
FOOD  USERS 

I.  What  Do  Plants  Take  from  the  Soil?  ....  137 

II.  What  Factors  Influence  the  Growth  of  Roots?  . . 140 

III.  How  Does  the  Structure  of  a Root  Fit  It  for  Its  Work?  143 

IV.  How  Do  Root  Hairs  Take  in  Water  and  Soil  Salts?  . 147 

V.  What  Purposes  Do  Roots  Serve?  .....  150 

VI.  Where  Does  the  Green  Plant  Manufacture  Food?  . 151 

VII.  What  Raw  Materials  and  Conditions  Are  Needed  to 

Make  Food? 154 

VIII.  What  Are  the  Products  and  Results  in  Food  Manu- 
facture? ..........  160 

IX.  How  Is  Food  Circulated  in  the  Plant?  ....  166 

X.  Why  Are  Plants  Modified? 172 

PART  III 

RELATIONSHIPS  AND  INTER-RELATIONSHIPS 
OF  LIVING  THINGS 

UNIT  VII.  THE  PLANT  WORLD  AND  HOW  IT 
AFFECTS  MANKIND 

I.  How  Do  We  Classify  Plants?  .......  179 

II.  What  Are  Bacteria  and  Where  Are  They  Found?  . . 181 


TABLE  OE  CONTENTS  ix 

PROnLKM  PAGE 

HI.  What  Aue  Some  Useful  Things  That  Bacteria  Do?  . 186 

IV.  What  Are  Yeasts  and  Wh.vt  Do  They  Do?  . , . 190 

V.  To  Learn  arout  Some  De.structive  Fungi  ....  193 

VI.  Wh.vt  .\re  Molds?  What  Do  They  Do?  ....  198 

VH.  Wh.vt  Are  Some  Ex.vmples  of  Common  Algae?  . . . 200 

V'lII.  Wh.vt  Is  the  Life  History  of  a Moss  Plant?  . . . 202 

IX.  Wh.vt  Is  the  Life  History  of  a Fern  Plant?  . . . 204 

X.  Wh.vt  Are  Some  Examples  of  Spermatophytes?  . . 205 


UNIT  VIII.  HOW  DO  WE  CLASSIFY  THE  ANIMALS? 

I.  What  Are  the  Characteristics  of  One-celled  Animals?  217 
II.  Wh.vt  .Yre  the  Ch.vracteristics  of  Some  Simpler  Inverte- 


BR.VTES? 223 

III.  What  Are  the  Characteristics  of  the  Arthropods?  . 232 

IV.  What  Are  the  Ch.vracteristics  of  the  Mollusks?  . . 240 

V.  What  Are  the  Characteristics  of  the  Fishes?  . . . 242 

VI.  What  Are  the  Characteristics  of  Amphibians?  . . 250 

VII.  What  Are  Characteristics  of  the  Reptiles?  . . . 256 

VIII.  What  Are  the  Characteristics  of  Birds? 260 

IX.  What  Are  the  Characteristics  of  Mammals?  . . . 268 

X.  What  Story  Is  Told  by  the  Fossils? 271 

XL  What  Is  Man’s  Place  in  Nature? 274 


UNIT  IX.  WHAT  EFFECTS  HAVE  THE  SURROUND- 
INGS ON  THE  LIVES  OF  PLANTS  AND  ANIMALS? 

I.  What  General  Biological  Relations  Exist  between 

Plants  and  Animals? 282 

H.  Wh.vt  Do  We  Mean  by  the  Nitrogen,  Oxygen,  and 

C.vRBON  Cycles  in  Nature?  ......  285 

III.  Wh.vt  Is  Symbiosis  and  How  Does  It  Differ  from 

Parasitism  ? 287 

IV.  How  Does  Man  Disturb  the  Balance  of  Nature?  . . 289 

V.  How  Do  the  Factors  of  the  Environment  Affect 

Ecological  Relationships?  ......  290 

VI.  Why  Do  Plants  and  Animals  Form  Communities?  . . 298 

VII.  What  Is  an  Ecological  Succession? 300 

VIII.  What  Do  We  Mean  by  Geographic  Distribution  of 

Living  Things? 305 


X 


TABLE  OF  CONTENTS 


PART  IV 

THE  BIOLOGY  OF  MAN 

UNIT  X.  HOW  DOES  THE  HUMAN  MACHINE  DO  ITS 
WORK? 

I*EOBLEM  PAGE 

I.  What  Is  the  General  Structure  of  the  Human  Body?  314 

H.  What  Is  the  Structure  of  the  Skin? 316 

HI.  What  Is  the  Relation  of  Muscles  to  Bones?  . . . 318 

UNIT  XI.  HOW  DOES  MAN  DETERMINE  THE 
VALUES  OF  FOODS? 

I.  What  Do  Foods  Do  for  Us? 327 

II.  What  Do  Vitamins  Do  for  Us? 333 

III.  What  Is  the  Relation  of  Work,  Environment,  Age, 

Sex,  and  Digestibility  of  Foods  to  Diet?  . . . 335 

IV.  What  Is  the  Best  Proportion  of  Nutrients  for  Our 

Daily  Diet? 340 

V.  What  Is  the  Daily  Calorie  Requirement?  . . .341 

VI.  How  Can  the  Relative  Cheapness  of  Foods  Be  Deter- 
mined ? . 345 

VII.  What  Is  Adulteration?  . . . . . . . . 348 

VHI.  What  Is  the  Truth  about  Stimulants  and  Narcotics?  . 350 
IX.  How  Does  the  Pure  Food  and  Drugs  Act  Work?  . . 355 

UNIT  XII.  HOW  IS  FOOD  PREPARED  FOR  BODY  USES? 

I.  What  Is  a Gland  and  How  Does  It  Do  Its  Work?  . . 361 

H.  What  Is  the  Structure  and  Work  of  the  Mouth  Cavity?  363 
HI.  What  Are  the  Parts  of  the  Digestive  Tract?  . . . 367 

IV.  What  Digestive  Changes  Take  Place  in  the  Stomach?  . 369 

V.  What  Work  Is  Done  by  the  Pancreas?  ....  373 

VI.  What  Are  the  Functions  of  the  Liver?  ....  375 

VII.  How  Are  Foods  Absorbed  and  How  Do  They  Get  into 

THE  Blood? 376 

UNIT  XHI.  HOW  ARE  FOODS  CIRCULATED  AND 
USED  IN  THE  BODY? 

I.  What  Is  the  Composition  and  What  Are  the  Uses  of 


Different  Parts  of  the  Blood?  .....  386 

II.  What  Are  the  Functions  of  Some  of  the  Endocrine 

Glands  ? 392 

HI.  How  Does  the  Blood  Circulate  through  the  Body?  . 395 

IV.  What  Is  Respiration? 403 

V.  What  Are  the  Mechanics  of  Breathing?  ....  406 


TABLE  OF  CONTENTS 


XI 


rnOULEM  PAGE 

VI.  Wii.vT  Aue  the  Reasons  for,  and  the  Best  Methods  of 

\entie.vtion  ? 409 

VII.  Wmat  Are  the  Organs  of  Excretion  and  How  Do  They 

Function? .411 


UNIT  XIV.  now  HAS  MAN  BECOME  THE  CON- 
QUEROR OF  THE  WORLD? 

I.  ^^'H.■vT  Are  the  Chief  Responses  of  Plants  and  Animals?  422 
II.  How  Do  Simple  Plants  and  Animals  Respond  to  Stimuli?  424 
III.  What  Are  Sense  Organs  and  What  Do  They  Do?  . . 427 


IV.  How  Is  Man’s  Body  Controlled?  .....  429 

V.  What  Part  Do  tpie  Sense  Organs  Play  in  the  Control 

OF  THE  Body? 435 

VI.  Wh.\t  Behaviors  Are  Instinctive? 441 

VH.  How  Are  Habits  Formed? 443 

VIII.  What  Are  Some  Good  Health  Habits?  ....  447 

IX.  What  Are  Some  Effects  of  the  Drink  Habit?  . . . 449 


PART  V 

MAN’S  INTER-RELATIONSHIP  WITH  OTHER 
LIVING  THINGS 

UNIT  XV.  HOW  DOES  MAN  CONTROL  HIS  ENVIRON- 
MENT FOR  HEALTH? 

I.  How  May  We  Control  the  Growth  of  Bacteria?  . 

II.  How  Do  Bacteria  Cause  Disease? 

HI.  How  Do  We  Get  Bacterial  Diseases?  . . . . 

IV.  Why  Is  Quarantine  Necessary? 

V.  What  Is  Immunity? 

VI.  What  Are  the  Differences  between  Active  and  Passive 

Immunity  ? 

VII.  How  Is  Malaria  Caused  and  Transmitted? 

VIII.  How  Was  the  Control  of  Yellow  Fever  Brought 

About?  

IX.  What  Are  Other  Disease  Carriers  and  What  Diseases 

Do  They  Carry?  

X.  What  Diseases  Are  Caused  by  Worms  and  How  May 

We  Fight  Them? 

XI.  How  May  We  Improve  Conditions  at  Home? 

XII.  How  May  We  Improve  Conditions  at  School?  . 

XIII.  How  May  We  Help  Improve  Conditions  in  Our  Com- 

munity?   

XIV.  What  Protective  Health  Agencies  Should  Exist  in  a 

Community  ? 


457 

461 

463 

471 

474 

476 

482 

487 

489 

492 

497 

501 

503 

507 


Xll 


TABLE  OP  CONTENTS 


UNIT  XVI.  HOW  DOES  MAN  CONTROL  HIS  EN- 
VIRONMENT FOR  WEALTH? 

PROBLEM  PAGE 

I.  How  Are  Plants  Used  as  Food? 520 

II.  What  Are  Other  Economic  Values  of  Plants?  . . . 528 

III.  What  Is  the  Value  of  Animals  as  Food  for  Man?  . . 530 

IV.  What  Are  Other  Economic  Values  of  Animals?  . . 537 

V.  What  Harm  Is  Done  by  Animals? 544 

VI.  What  Is  the  Economic  Importance  of  Birds?  . . . 547 

VII.  How  Can  We  Recognize  Some  Common  Birds?  . . . 551 

VIII.  What  Is  the  Economic  Importance  of  Insects?  . . 560 

UNIT  XVII.  HOW  DOES  MAN  CONSERVE  HIS 
NATURAL  RESOURCES? 

I.  What  Are  the  Values  of  Trees? 574 

II.  Why  Is  the  Conservation  of  Forests  Necessary?  . . 579 

III.  What  Is  Being  Done  for  the  Conservation  of  Fish  and 

Other  Aquatic  Animals? 587 

IV.  What  Is  Being  Done  for  the  Conservation  of  Birds?  . 594 

V.  What  Is  Being  Done  for  the  Conservation  of  Mammals?  598 

VI.  How  Is  Conservation  Applied  to  Man?  ....  599 

UNIT  XVIII.  HOW  DOES  MAN  CONTROL  THE  IM- 
PROVEMENT OF  LIVING  THINGS? 

I.  How  May  Environment  Affect  Plants  and  Animals?  . 608 

II.  How  Do  Living  Things  Reproduce  and  Develop?  . .611 

III.  What  Are  the  Laws  of  Heredity? 620 

IV.  What  Determines  Heredity? 626 

V.  How  Are  New  Varieties  of  Plants  and  Animals  Pro- 
duced?   631 

VI.  How  Do  the  Laws  op  Heredity  Apply  to  Man?  . . 636 

UNIT  XIX.  HOW  MAY  BIOLOGY  AID  IN  MY  OWN 
IMPROVEMENT? 

I.  How  Can  I Choose  a Vocation? 646 

II.  Fop.  What  Vocations  May  Biology  Help  Prepare  Me?  649 

UNIT  XX.  WHO  ARE  SOME  OF  THE  MAKERS  OF  BIOLOGY? 


I.  Who  Were  Some  Early  Workers  in  Biology?  . . . 657 

11.  Who  Were  Some  of  the  Conquerors  of  Disease?  . . 659 

III.  What  Are  Some  Great  Names  in  the  Study  op  Progres- 

sive Development?  ........  665 

IV.  What  Are  Some  Great  Names  in  Natural  History?  . 668 

V.  What  Are  Some  Great  Names  Connected  with  Plant  and 

Animal  Breeding? 670 


WHY  AND  HOW  WE  STUDY  BIOLOGY 


The  study  of  biology.  The  word  biology  comes  from  two  Greek 
words,  bios  (life)  and  logos  (word  or  study).  Biology,  then,  is  the 
study  of  things  that  are  alive,  both  plants  and  animals.  Man  lives 
in  a world  filled  with  living  things.  Some  are  his  friends  and  some 
are  his  enemies.  It  is  essential,  if  he  is  to  be  master  of  this  world, 
that  he  should  understand  the  living  things  that  are  around  him. 
His  master}^  is  due  to  his  understanding  of  the  processes  of  life  in 
nature.  There  are  many  ways  in  which  this  conquest  is  achieved. 

Biology  in  relation  to  health.  It  is  most  important  that  we 
control  the  living  things  that  harm  our  health.  We  live  in  a 
world  that  is  filled  with  tiny  enemies  — some  in  the  water,  some 
in  the  ground,  some  eni-iclT_ 

living  on  plants,  some  soil 

t 

BACTERIA 

i 


living  on  animals.  We 
call  them  parasites 
because  they  take 
nourishment  from  a 
living  organism  and 
give  nothing  in  return. 


cause.. 


Ceruse 

Ct:i5ease 


flccVor- 
cheese 


Some  of  the  work  done  by  bacteria.  Can  you  add  any 
others  not  given  in  the  diagram  ? 


The  smallest  and  yet  most  widespread  of  these  parasites  are  the 
tiny  bacteria  or  germs  existing  almost  everywhere  about  us,  in 
water,  soil,  food,  and  air.  They  play  a tremendous  part  in  shaping 
the  destiny  of  man.  They  help  him  in  that  they  act  as  scavengers, 
causing  things  to  decay;  they  give  flavor  to  cheese  and  butter; 
they  assist  the  tanner ; and  they  are  invaluable  aids  to  the  farmer. 
But,  on  the  other  hand,  they  cause  the  decay  of  meat,  fish,  vege- 
tables, and  fruits;  they  sour  milk  and  sometimes  spoil  canned 
goods;  more  than  this,  they  cause  diseases  such  as  diphtheria, 
tuberculosis,  and  typhoid  fever. 

Hundreds  of  scientists  are  devoting  their  lives  to  the  study  of 
germs  and  their  control,  which  makes  up  that  subdivision  of  biol- 
ogy known  as  bacteriology.  A great  bacteriologist,  Louis  Pasteur, 

1 


2 


WHY  AND  HOW  WE  STUDY  BIOLOGY 


once  said,  “It  is  within  the  power  of  man  to  cause  all  parasitic 
diseases  to  disappear  from  the  world.”  This  prophecy  is  gradually 
being  fulfilled.  It  is  estimated  that  from  75  to  90  per  cent  of  all 
sickness  is  preventable  and  that  the  economic  loss  in  the  United 
States  each  year  from  disease  and  death  is  about  13,000,000,000. 
This  loss  could  be  largely  prevented  if  we  were  willing  to  use  the 
knowledge  we  now  have  in  the  methods  of  controlling  and  ex- 
terminating disease.  It  may  be  the  lot  of  some  boys  and  girls 
who  read  this  book  to  do  their  share  to  bring  about  this  condition 
of  affairs. 

The  economic  values  of  biology.  There  are  other  reasons  why 
we  should  know  something  about  biology.  Plants  and  animals 
can  live  together  on  the  earth  only  because  food  is  supplied  by 
green  plants.  Probably  many  of  us  do  not  realize  that  if  all 
the  green  plants  were  gone  from  the  earth  there  would  be  no 
animals.  We  shall  see  later  why  this  is  true.  We  all  know  that 
man’s  food  supply  is  determined  very  largely  by  his  ability  to 
grow  and  develop  plants  that  produce  food  for  him  and  for  the 
animals  which  he  eats. 

Plants  and  animals  are  useful  to  man  in  other  ways  than  for  food. 
He  uses,  for  clothing  and  ornaments,  animal  products  such  as  wool, 
fur,  leather,  hides,  ivory,  coral,  and  mother-of-pearl.  Plants  also 
provide  him  with  many  kinds  of  building  materials.  Much  of  his 
clothing,  and  the  thread  with  which  he  sews  it,  come  from  plant 
fibers.  In  hundreds  of  ways  plants  are  made  use  of  in  the  arts  and 
trades.  It  is  the  duty  of  every  boy  and  girl  to  know  something  of 
these  uses. 

The  conservation  of  our  natural  resources.  Still  another  reason 
why  we  should  study  biology  is  that  we  may  work  intelligently  for 
the  conservation  of  our  natural  resources,  especially  our  forests. 
The  forest,  aside  from  its  beauty  and  its  health-giving  properties, 
holds  water  in  the  earth.  It  keeps  the  water  from  evaporating 
from  the  soil  on  hot  days  and  from  running  off  the  surface  on  rainy 
days.  Regions  that  have  been  deforested,  such  as  parts  of  China, 
Italy,  and  France,  are  now  subject  to  floods,  and  are  in  many 
places  barren.  Our  supply  of  timber  and  to  a large  extent  our 
future  water  power  depend  on  the  forests. 


VALUE  OF  BIOLOGY 


3 


Vocational  knowledge.  Sooner  or  later  the  boys  and  girls  who 
read  this  hook  must  (liink  of  the  kind  of  work  tliey  are  going  to  do. 
Selecting  a vocation  is  one  of  the  most  important  decisions  that 
one  will  ever  have  to  make.  Through  a study  of  biology  you  will 
learn  something  about  such  professions  as  medicine,  nursing, 
forestry,  agriculture,  or  the  teaching  of  science  which  might 
appeal  to  you  as  worth-while  vocations.  Your  teacher  may  give 
you  the  inspiration  which  will  determine  your  future  career. 
.Many  years  ago,  a professor  in  college  inspired  me  to  become  a 
teacher  of  biology  and  1 have  never  regretted  my  choice.  Perhaps 
you  will  be  as  fortunate. 

Use  of  leisure  time.  It  is  a wonderful  world  we  live  in,  but  not 
many  of  us  know  how  to  enjoy  it  fully.  Many  boys  and  girls  of 
today  think  that  they  are  getting  all  there  is  out  of  life  if  they  go 
regularly  to  the  “ movies  ” or  meet  with  their  crowd  at  games  or 
parties.  But  no  one  has  really  got  very  much  out  of  this  world 
until  he  or  she  has  learned,  among  the  other  things,  the  fun  of 
hiking,  of  collecting,  of  observing  nature,  of  taking  trips  to  the 
shore,  to  the  canyon,  and  up  a mountain  with  an  end  in  view. 
The  interest  that  comes  in  observing  and  collecting  insects  or 
flowers  makes  life  much  more  worth  while.  A study  of  biology 
will  give  one  the  information  and  incentive  for  such  excursions. 

Reading  values  of  biology.  The  papers  and  magazines  of  today 
contain  many  discussions  and  stories  which  deal  with  biological 
subject  matter.  The  daily  paper  has  its  column  of  health  hints,  its 
stories  of  animial  doings,  and  its  statistics  about  animal  and  plant 
products.  The  average  person  with  no  biological  training  reads 
without  being  able  to  judge  of  the  truth  contained  in  these  state- 
ments. The  study  of  biology  ought  to  give  us  some  knowledge 
and  should  certainly  show  us  where  to  go  for  accurate  information 
so  that  we  can  tell  whether  our  newspaper  “ science  ” is  true  or 
false.  It  will  also  open  to  us  a wealth  of  books  which  are  accurate 
and  fascinating  to  read.  The  names  of  such  books  are  given  from 
time  to  time  in  the  pages  which  follow. 

Open-mindedness  a by-product.  There  is  no  doubt  that  in 
spite  of  living  in  an  age  which  is  noted  for  its  products  of  scientific 
thinking,  many  people  are  satisfied  to  have  others  do  their 


4 


WHY  AND  HOW  WE  STUDY  BIOLOGY 


thinking  for  them.  They  believe  almost  anything  they  are  told 
without  taking  the  trouble  to  investigate  the  truth  of  it.  Politi- 
cians are  able  to  lead  the  public  around  by  the  nose,  because 
people  are  too  indolent  to  find  out  the  truth  for  themselves.  The 
study  of  science  ought  to  make  young  people  disgusted  with  such 
lack  of  thinking.  After  one  has  experimented,  observed,  and  read 
about  scientific  findings  and  facts  he  is  not  so  easily  fooled  and 
he  wants  to  be  shown,  not  told.  This  open-mindedness  should 
come  through  the  study  of  science.  A boy  or  girl  who  has  learned 
to  think  straight  will  be  more  likely  to  live  straight  and  be  just 
that  much  more  worthy  a citizen  of  tomorrow. 

Biology  in  its  relation  to  society.  The  study  of  biology  should 
be  part  of  the  education  of  every  boy  and  girl,  because  society  itself 
is  founded  upon  the  principles  which  biology  teaches.  Plants  and 
animals  are  living  things,  each  taking  what  it  can  from  its  sur- 
roundings ; they  enter  into  competition  with  one  another,  and 
those  which  are  the  best  fitted  for  life  outstrip  the  others.  Health 
and  strength  of  body  and  of  mind  are  factors  in  man  which  tell  in 
winning.  The  strong  may  hand  down  to  their  offspring  the 
characteristics  which  make  them  the  winners.  An  understanding 
of  the  laws  of  heredity  ought  to  make  each  one  of  us  better  able  to 
assume  the  duties  of  parenthood,  duties  which  all  too  often  are  not 
understood  by  the  boy  and  girl  of  today. 

Biology  should  develop  character.  Finally,  if  one  studies 
biology  with  earnest  purpose  he  cannot  help  but  gain  in  moral  and 
ethical  character  through  the  unfolding  of  truth  and  the  knowledge 
gained  of  the  working  of  the  laws  of  nature  in  the  everyday  world 
around  us.  As  Shakespeare  once  said,  a seeker  in  the  great  out-of- 
doors  : 

“ Finds  tongues  in  trees,  books  in  the  running  brooks, 

Sermons  in  stones,  and  good  in  everything.” 

Where  we  should  study  biology.  In  a modern  high  school  a 
good  deal  of  time  is  spent  by  boys  and  girls  in  outside  activities  — 
athletics,  dramatics,  debating,  and  the  like ; but  too  little  emphasis 
has  been  placed  on  some  outside  interest  that  might  come  directly 
from  the  study  of  biology.  Although  we  must  be  in  the  schoolroom 
much  of  the  time,  the  ideal  place  to  study  biology  is  out-of-doors, 


WllKIiK  \VF.  SHOULD  STUDY  BIOLOGY 


5 

for  as  one  biologist  oiico  said,  “ d'hc  place  where  a plant  or  animal 
lives  is  just  as  important  as  the  plant  or  the  animal  itself. ’’  One  of 
the  most  interesting  lessons  1 ever  saw  taught  was  given  in  a vacant 
lot  near  a high  school  in  the  city  of  Chicago  — a place  that  seemed  to 
have  little  in  it  except  weeds  and  piles  of  refuse.  But  the  teacher 
knew  the  possibilities  of  that  lot,  and  the  pupils  were  having  a 
wonderful  time  studying  the  living  things  which  they  found  there. 


Photo  hy  Shipp  — U.  S.  Forest  Service 

These  surroundings  make  an  ideal  outdoor  laboratory.  Why? 


Some  were  watching  the  activities  of  an  ant  colony,  while  others 
were  watching  to  see  how  a spider  built  a geometrical  web.  Every 
boy  and  girl  in  the  group  had  a problem  that  was  most  interesting 
to  him  or  her.  But  how  much  more  interesting  might  be  a trip 
to  a canyon  or  a meadow  brook  or  a sea  beach ! For  some  of  us 
this  might  be  possible  at  almost  any  time. 

But  if  we  cannot  go  to  the  field  for  study,  then  we  can  bring  the 
field  to  the  laboratory  or  schoolroom.  If  each  member  of  the  class 
would  bring  in  some  small  living  things  and  would  arrange  to  care 

H.  BIO  — 2 


6 


WHY  AND  HOW  WE  STUDY  BIOLOGY 


for  them,  the  schoolroom  would  soon  be  a place  much  like  the 
out  of  doors.  A balanced  aquarium  may  be  started  and  observa- 
tions can  be  made  on  the  life  developing  there.  One  can  grow 
plants  and  learn  how  to  take  care  of  them.  One  might  bring  in  all 
sorts  of  living  things  and  keep  them  in  a vivarium.  The  labora- 
tory becomes  a place  for  studying  nature  at  first  hand,  and  that  is 
what  makes  biology  interesting. 


Students  at  work  in  an  indoor  laboratory.  What  are  some  of  the  good  features  in  this 
laboratory  ? 


In  some  communities  it  is  possible  to  have  a plot  of  ground  near 
the  school  which  can  be  kept  as  an  experimental  garden.  Here 
much  can  be  learned  about  plants,  their  care,  and  their  insect 
friends  and  enemies. 

Some  interesting  activities.  Another  way  to  maintain  interest 
in  biology  is  to  form  a hiking  and  collecting  club.  There  are  so 
many  interesting  things  to  do  in  the  field.  One  can  make  collec- 
tions of  local  plants,  flowers,  or  insects.  A school  museum  can 
be  started,  and  one  can  always  have  a good  deal  of  fun  trying  to 


INTERESTING  ACTIVITIES 


7 


identify  new  forms.  Trips  to  various  localities  will  help  us  under- 
stand why  some  animals  and  plants  thrive  there  while  others  are 
found  in  different  places,  and  to  know  what  kinds  of  living  things 
to  expect  in  different  places  — under  stones,  under  the  barks  of 
trees,  in  the  water,  and  in  galls  on  leaves.  All  these  places  and 
many  more  harbor  animals,  usually  insects. 

Another  interesting  experience  that  some  can  have  is  that  of 
collecting  fossils,  which  are  the  evidence  of  life  in  times  past. 
Many  parts  of  the  country  have  fossil  remains,  and  it  is  very  easy 
to  get  some  local  expert  in  geology  to  help  you  label  your  findings. 
Start  a collecting  club  and  exchange  specimens  with  boys  and  girls 
in  other  localities.  Thus  you  can  do  a good  piece  of  constructive 
work  for  your  school  by  adding  to  the  school  museum.  You  will 
be  surprised  to  find  many  people  who  are  willing  to  help  you  in  this 
work. 

Have  you  a biology  club  in  your  school  ? If  not,  then  organize 
one  at  once,  using  10  to  20  of  the  most  interested  members  of  your 
classes  as  a nucleus.  This  organization  will  help  keep  interest  in 
the  work  and  will  later  in  the  year  be  of  much  help  in  presenting 
demonstrations  and  projects,  in  planning  exhibits  and  in  helping 
in  the  care  of  the  living  things  in  the  laboratory.  Such  a club  can 
take  charge  of  the  school  collections,  help  classify  them,  and  add  to 
them  when  possible. 

How  to  prepare  for  a field  trip.  The  boy  or  girl  who  will  go 
afield  must  do  several  things  to  prepare  for  the  trip.  Chief 
among  these  is  to  get  or  prepare  collecting  nets,  insect  killing 
bottles,  collecting  boxes,  and  spreading  boards.  Field  trips  will 
be  of  most  value  if  materials  are  found  and  brought  back  for  later 
study  in  the  school  laboratory. 

How  to  make  an  insect  net.  An  insect  net  can  easily  be  made 
in  the  following  way:  Cut  a 36-inch  piece  of  stout  wire  (#12 
spring  brass  wire  is  good),  bend  it  into  a loop  nine  to  twelve  inches 
in  diameter,  and  then  twist  the  ends  and  bend  them  so  that  they 
will  lie  in  two  shallow  grooves  which  have  been  made  in  an  old 
broom  handle.  Fasten  the  wire  in  place  with  fine  wire  twisted 
tightly  around  the  end  of  the  broom  handle  at  the  place  where  the 
two  heavy  wires  lie  along  the  grooves.  Make  a net  of  cheesecloth 


8 


WHY  AND  HOW  WE  STUDY  BIOLOGY 


or  bobbinet,  which  should  be  18  inches  deep  and  large  enough  to  go 
over  the  loop.  Such  a net  can  be  used  for  catching  flying  insects, 
for  dredging  or  scraping  insects  out  of  long  grass,  and  for  dipping 

insects  or  other  small 
animals  out  of  shallow 
ponds  or  brooks. 

The  cyanide  bottle. 
Cyanide  of  potassium 
fumes  are  best  for  kill- 
ing an  insect  quickly. 
Since  these  fumes  are 
deadly  to  man  as  well 
as  other  animals,  such 
a bottle  must  be 
handled  very  carefully. 
To  make  a cyanide 
bottle,  take  a wide- 
mouthed bottle  of 
about  6 to  8 ounces 
capacity,  and  place  in 
it  two  or  three  pieces 
of  cyanide  of  potas- 
sium the  size  of  a chest- 
nut. Do  not  breathe 
the  fumes  ! Cover  at 
once  with  sawdust  and 
pour  in  liquid  plaster 
of  Paris  to  a depth  of 
about  one  inch.  The  plaster  will  harden  quickly.  Cork  the 
bottle  tightly  and  keep  it  closed  except  when  placing  insects  in- 
side. Label  the  bottle  like  that  in  the  diagram  so  that  you  will 
know  it  contains  a poison. 

Collecting  water  forms.  Some  of  the  members  of  the  party  should 
have  quart  jars  so  that  living  water  animals  may  be  captured  and 
brought  back  alive.  Be  sure  to  collect  with  the  fish,  frogs,  or  water  in- 
sects a small  amount  of  some  of  the  green  plants  growing  under  water 
so  that  you  may  have  living  plants  to  start  a balanced  aquarium. 


♦ 12 

Ijrass 

•vire 


Read  your  text  and  then  explain  the  figure.  Can  you  sug 
gest  any  other  ways  to  make  an  insect  net  ? 


HOW  TO  PREPARE  FOR  A FIELD  TRIP 


9 


lumps  of 
cyccTxiaCe 


Why  do  we  cover  the  cyanide  with 
plaster  of  Paris  ? 


Collecting  boxes.  After  killing  in  the  cyanide  bottle,  the 
insects,  if  butterflies  or  moths,  may  be  wrapped  in  little  pieces  of 
stiff  paper  which  are  folded  in  triangu- 
lar form  so  as  to  fit  the  shape  of  the 
wings.  But  a collecting  box  should  be 
made  to  hold  some  of  the  specimens. 

A cigar  box,  with  a sheet  of  quarter- 
inch  cork  glued  in  the  bottom,  and  a 
supply  of  insect  pins  are  all  that  is 
necessary. 

Spreading  insects.  To  prepare  winged 
insects  for  mounting  it  is  necessary  to 
spread  their  wings  out.  While  the 
specimen  is  still  flexible,  pin  it  down  on 
a thin  board  of  soft  pine  or  cigar  box 
wood  by  placing  insect  pins  close  to  the 
sides  of  the  body,  not  through  it,  then 
pull  the  wings  out  flat  and  hold  them 
down  to  the  board  with  pieces  of  glass  until  they  are  dry.  Place  a 
small  piece  of  pith  between  the  legs  so  as  to  keep  them  in  a natural 
position.  When  the  insect  is  dry,  you  can  mount  it  on  a pin,  and 
place  it  on  cork  in  a case  not  over  an  inch  or  so  in  depth.  Boxes 
, , - having  glass  tops,  in  which  certain 

brands  of  chewing  gum  come,  may 
be  obtained  for  this  purpose  or  boxes 
may  be  made  in  the  manual  train- 
ing department  of  the  school. 

The  art  of  preparing  caterpillars 
by  blowing  is  described  in  Hodge’s 
Nature  Study  and  Life  or  in  any  good 
book  on  entomology.  Why  not  try 
this  as  a future  project? 

Mounting  your  insects.  After  the 
trip  is  over,  the  insects  may  be  dried 
carefully  and  then  placed  in  Riker 
. mounts  if  such  are  available,  but 

A spreading  board.  Explain,  after  read- 

ing  your  text,  the  use  of  this  board.  homemade  mounts  are  not  difficult 


10 


WHY  AND  HOW  WE  STUDY  BIOLOGY 


to  make.  Get  two  plates  of  glass  of  the  same  size,  4X5  inch 
negatives  will  do.  Cut  thin  strips  of  wood,  not  thicker  than  the 
largest  specimen  you  wish  to  mount,  glue  to  one  piece  of  glass,  then 
fasten  your  insect  in  place  on  the  glass  with  a tiny  drop  of  glue, 
using,  if  possible,  a bit  of  the  dried  plant  upon  which  it  was 
feeding  as  a part  of  your  mount.  The  other  glass  may  then  be 
placed  on  the  wooden  sides  and  the  whole  thing  permanently 
sealed  by  binding  around  the  edges  with  bicycle  tape  or  passe 
partout  paper.  Life  histories  of  insects  can  be  worked  out  in  such 
cases  and  can  be  handled  readily,  which  makes  them  very  useful  in 
class  work. 

An  ants’  nest.  An  ant  colony  makes  a fascinating  study  for  the 
schoolroom.  To  make  a suitable  nest  take  a piece  of  roofing  slate 
or  a flat  tile,  glue  to  it  pieces  of  wood  about  a quarter  inch  high  so 
as  to  make  an  oblong  area  six  by  eight  inches  or  larger,  with  two 
little  openings  between  the  wood  strips;  get  a piece  of  window 
glass  to  fit  over  it  and  then  place  the  slate  in  a shallow  tray  which 
will  hold  water  and  will  make  a moat  around  your  colony  of  ants, 
which  may  easily  be  found  under  flat  stones.  Take  a small 
trowel  and,  when  the  colony  is  found,  scrape  up  as  many  of  the 
eggs,  larvae,  and  ants  as  possible.  Be  sure  to  get  one  or  more  of 
the  winged  queens  by  digging  down  into  the  nest.  Take  your 
colony  home  in  a well-corked  bottle,  dump  the  contents  into  your 
prepared  nest,  smooth  down  the  earth,  and  place  the  glass  over  the 
top.  Cover  it  with  a black  cloth  or  some  opaque  object  so  as  to 
exclude  the  light.  Within  a day  or  two  the  life  of  the  colony  will 
be  quite  normal  and  you  can  study  the  ants  at  leisure.  Feed  them 
from  time  to  time  by  placing  sugar  or  crumbs  of  bread  just  outside 
the  wood  strips. 

An  insect  cage.  Frequently  we  wish  to  bring  living  insects  into 
the  laboratory  in  order  to  study  their  feeding  or  other  habits.  For 
this  purpose  an  insect  cage  may  be  made  by  taking  a shallow  flower 
pot  in  which  earth  and  some  green  plant  has  been  placed.  Cover 
this  with  a lamp  chimney  having  a bit  of  cheesecloth  placed  over 
the  top.  If  the  plant  within  the  pot  is  a food  plant  and  is  kept 
watered,  it  will  be  possible  to  keep  the  captured  insects  alive  for 
a considerable  period  of  time. 


A BALANCED  AQUARIUM  11 

Practical  Exercise.  What  insects  found  in  j’our  locality  might  be  kept  in 
the  lamp  chimney  cage? 

A balanced  aquarium.  Frequently, 
trips  may  be  made  to  a stream  or  pond. 

In  such  an  event,  collect  snails  and 
other  small  mollusks  by  scraping  the 
muddy  bottom  of  the  stream  with  your 
dip  net.  Catch  any  fish  that  you  can 
with  insect  larvae,  small  water  beetles, 
water  striders,  or  other  forms  of  insect 
life.  Be  sure  to  collect  several  kinds 
of  water  plants,  especially  those  with 
green  leaves  under  water. 

Use  as  your  aquarium  a large  clear 
glass  jar  of  any  shape,  and  cover  the 
bottom  with  smooth  pebbles.  Fasten 
the  water  plants  down  by  tying  small 
weights  to  the  base  of  their  stems. 

Use  pond  water  for  the  aquarium, 
transferring  the  fish  and  other  living 
things  directly  into  it  from  the  jars 
you  brought  them  home  in.  Place  the 
aquarium  in  a well-lighted  part  of  the 
room,  moving  it  away  from  the  direct 
sunlight  if  the  growth  of  the  green 
plants  becomes  too  rapid.  Add  more 
snails  if  the  sides  of  the  aquarium  become  covered  with  a green 
growth.  In  this  way,  your  aquarium  will  be  kept  in  balance,  which 
means  that  the  plant  life  supplies  the  animals  with  food  in  sufficient 
quantity  while  the  animals  give  the  plants  enough  wastes  to  allow 
them  to  make  food  in  the  sunlight.  The  interesting  story  of  how 
plants  do  this  will  be  told  later. 

Other  interesting  problems.  Out  of  the  field  trips  and  the 
collecting  of  insects  and  other  animals  will  come  many  other 
instructive  problems.  Some  pupils  may  become  interested  in  the 
classification  of  animals,  others  in  making  a survey  of  the  locality 
to  see  where  different  animals  are  most  plentiful,  and  others  in  the 


sicCcs 
■wire  screen, 

A homemade  insect  cage.  Make 
the  uprights  about  24  inches  and  the 
sides  of  the  cage  18  inches  wide. 
Place  a shallow  pan  in  the  bottom, 
fill  it  with  earth,  and  put  in  plants  on 
which  the  insects  may  feed. 


12 


WHY  AND  HOW  WE  STUDY  BIOLOGY 


various  ways  in  which  animals  protect  themselves  or  are  protected 
by  their  surroundings.  In  fact,  there  are  so  many  problems  that 
it  will  be  almost  impossible  for  us  to  note  them  all  here.  Let  us 
now  turn  to  some  plant  problems  or  projects  that  will  come  out  of 
a fall  field  trip. 

Plant  studies  in  the  field.  The  fall  of  the  year  usually  finds  a 
good  many  plants  in  blossom,  although  most  of  these  have  com- 
posite blossoms.  One  interesting  project  might  be  the  collection 
and  naming  of  all  the  fall  wild  flowers  you  can  find  in  your  neigh- 
borhood. You  might  also  make  a collection  of  the  fruits  and  seeds 

of  the  same  plants.  But 
flowers  are  not  the  only 
things  to  collect.  A leaf 
collection  can  easily  be 
made  in  the  fall  and 
mounted  in  the  way  sug- 
gested for  insects,  except 
that  no  wood  need  be  used 
between  the  plates  of  glass. 
Interesting  mounts  of  skel- 
eton leaves  may  be  pre- 
pared by  placing  collected 
leaves  in  trays  of  water 
until  the  leaf  tissue  has 
rotted  away,  leaving  the 
skeleton  of  veins  and  ribs  as  a delicate  tracing.  These  make 
valuable  aids  in  the  laboratory  study  of  leaves.  Another  interest- 
ing and  easy  method  of  obtaining  good  leaf  illustrations  for  your 
notebook  is  to  make  blue  prints  of  them.  Weed  and  flower 
collections  may  be  mounted  in  a similar  manner. 

Some  members  of  the  class  may  become  interested  in  making 
a collection  of  weeds,  and  some  may  wish  to  make  a survey  of 
weeds  found  in  their  locality.  Weed  eradication  may  be  studied 
as  well,  thanks  to  the  various  government  pamphlets  which  are 
easily  obtainable.  Many  of  us  do  not  even  know  the  trees  com- 
mon to  our  neighborhood.  A survey  of  trees  might  be  conducted 
to  determine  where  different  types  may  be  found  and  then  sug- 


OTHER  OUTDOOR  ACTIVITIES  13 

gestions  might  bo  made  as  to  where  trees  could  advantageously  be 
planted  in  a town.  Such  a survey  might  result  in  real  civic  better- 


A collection  of  fern  leaves  made  by  high  school  pupils. 

ment.  A survey  of  forest  trees  would  be  another  interesting 
project.  Planting  and  raising  seedling  trees  is  certainly  another 
worth-while  activity. 

Other  outdoor  activities.  Birds  are  most  plentiful  in  the  spring 
and  should  then  be  studied  out  of  doors.  But  birds  can  always  be 
attracted  to  your  own  home  by  means  of  nesting  boxes,  drinking 
fountains,  and  by  feeding  stations.  Photographing  wild  birds  is  a 
pleasure  worth  working  for.  A census  of  the  number  and  kinds  of 
birds  that  frequent  your  neighborhood  and  the  kind  of  nests  they 
build  are  interesting  projects.  Through  bird  trapping  and  band- 
ing much  can  be  learned  about  the  migrating  and  nesting  of  birds. 

Gardening.  Gardening  and  the  study  of  the  life  of  some  com- 
mon garden  plants  will  interest  some  of  us.  Others  may  want  to 
make  a study  of  certain  garden  or  other  plant  pests  and  how  to 
eradicate  them.  Still  another  study  might  be  that  of  the  plants 
which  do  damage  to  crops  or  trees  of  our  neighborhood.  In  short. 


14 


WHY  AND  HOW  WE  STUDY  BIOLOGY 


these  pages  have  only  begun  to  suggest  some  of  the  activities  that 
will  grow  out  of  our  study  of  biology.  Most  of  these  are  things  we 
can  do  out  of  school  hours  and  they  certainly  are  worth  while  from 
every  viewpoint. 

The  value  of  city  surveys.  Not  all  of  the  outdoor  work  is 
collecting,  nor  is  the  country  the  only  place  to  make  a field  trip. 
We  have  spoken  of  studies  in  vacant  lots  and  tree  surveys  in  a city. 
Of  still  more  practical  importance  are  sanitary  surveys  which  tell 
us  of  the  sanitary  conditions  of  our  neighborhood.  What  are  the 
conditions  in  the  meat  stores  ? Are  the  goods  there  kept  under 
sanitary  conditions?  Are  the  streets  of  your  city  well  watered 
and  cleaned?  Are  the  garbage  and  ash  collections  regular  and 
sufficient?  Are  the  schools  well  lighted,  properly  heated,  and 
effectively  swept?  Are  there  efficient  and  well-kept  playgrounds, 
baths,  and  parks?  All  these  and  more  can  be  worked  out  in  the 
field  by  a group  of  pupils  of  biology,  thus  proving  that  biology  has 
a part  in  citizenship.  A group  of  young  people  have  more  than 
once  rid  a town  of  mosquitoes  or  flies,  just  by  making  a survey, 
discovering  the  sources  of  these  pests,  and  then  proceeding  to 
eradicate  them  by  the  methods  which  they  learned  in  biology  class. 

Practical  Exercise.  How  many  of  the  above-mentioned  things  can  be  done 
by  the  members  of  your  biology  class  ? Give  reasons  why  they  can  or  cannot 
be  done. 

The  use  of  the  laboratory.  It  is  said  that  on  one  occasion,  John 
Hunter,  a well-known  Scottish  physician,  who  was  a teacher  of 
Jenner,  and  lived  from  1728  to  1793,  was  present  at  a discussion 
concerning  the  digestive  system  of  birds.  The  meeting  broke  up 
without  any  decision  and  at  the  next  meeting  several  persons 
brought  quotations  from  the  works  of  such  old  philosophers  as 
Aristotle,  Hippocrates,  and  Galen  to  prove  their  previous  state- 
ments. But  John  Hunter  brought  in  a dissected  bird  and  showed 
the  organs  in  their  natural  position.  This  naturally  settled  all 
arguments. 

Unfortunately  we  cannot  do  all  of  our  work  out  of  doors.  We 
must  use  the  laboratory,  and  of  course  we  must  take  the  authority 
of  books.  It  goes  without  saying  that  if  we  were  to  spend  our 


THE  USE  OF  THE  LABORATORY 


15 


time  in  rediscovering  the  hundreds  of  thousands  of  facts  already 
known  about  plants  and  animals,  we  would  not  get  very  far  with 
any  new  discoveries.  So  we 
rely  on  texts  and  reference 
books  because  they  have  been 
written  by  specialists,  and  in 
this  way  we  may  make  an 
earlier  start  toward  discoveries 
of  our  owm. 

Biology,  more  than  any  sub- 
ject you  are  now  studying, 
ought  to  prepare  you  to  think 
logically.  The  method  of  the 
experiment  is  much  like  the 
steps  of  an  act  of  real  thinking. 

In  our  attempt  to  solve  a prob- 
lem through  an  experiment  we 
use  four  steps : first,  we  state 
our  problem ; second,  we  do 
certain  things  to  try  to  find  out 
something  about  it ; third,  we  observe  and  analyze  what  we  have 
done ; and  fourth,  we  draw  a conclusion  as  the  result  of  what  we 
have  seen.  These  are  the  steps  taken  by  any  one  who  really 
accomplishes  anything  in  the  way  of  constructive  work.  But  in 
an  experiment,  if  we  really  want  to  prove  our  point,  it  is  necessary 
to  establish  a control.  For  example,  suppose  we  want  to  know 
what  effect  exercise  has  on  the  rate  of  our  heart  beat.  We  can 
first  take  the  pulse  rate  when  quietly  sitting  at  our  desk  or  when 
lying  down,  and  then  we  can  take  a definite  amount  of  exercise 
and  again  take  the  pulse  rate.  In  this  way  we  establish  a contrast 
between  the  heart  beat  when  we  are  at  rest  and  when  we  have  had 
exercise.  The  rate  of  the  pulse  when  we  are  at  rest  is  known  as 
the  control.  Which  of  the  two  rates  of  the  pulse  just  obtained 
would  be  of  real  value  in  giving  us  correct  information  about  our 
normal  heart  beat?  Experiments  and  projects  with  the  proper 
controls  will  give  us  the  techniques  we  need  to  be  thinkers  and 
doers  in  this  world. 


John  Hunter,  a physiologist  and  surgeon,  car- 
ried on  much  biological  research.  He  always 
sought  the  truth  through  observations  and  ex- 
periments on  lower  animals. 


16 


WHY  AND  HOW  WE  STUDY  BIOLOGY 


Clear  thinking  should  come  from  science  study.  Psychologists, 
the  people  who  study  the  science  of  the  mind,  tell  us  that  those  of 
us  who  like  and  understand  our  work  and  make  its  ideals  our  own 
ideals  get  much  more  general  value  from  its  study  than  those  who 
do  not.  If,  for  example,  in  science  we  consciously  try  to  see  why 
each  step  of  an  experiment  is  performed  and  actually  practice  the 
method  of  the  experiment  in  other  similar  cases,  we  may  carry  over 
this  method  of  thought  to  other  subjects  and  even  apply  it  in  our 
daily  life.  The  scientific  method  of  thinking  has  resulted  in  new 
inventions,  in  discoveries,  and  in  straight  thinking  the  world  over. 
Why  not  try  consciously  to  apply  our  method  of  doing  and  think- 
ing in  science  to  other  kinds  of  doing  and  thinking  in  daily  life  ? 
This  would  give  us*  the  greatest  values  from  biology  that  we  could 
hope  to  get. 

Method  of  use  of  this  book.  In  the  pages  that  follow,  a regular 
procedure  will  be  used  which  has  been  shown  by  actual  experiment 
in  schools  to  be  one  of  the  best  ways  to  study  introductory  science. 
In  the  first  place,  our  work  is  divided  into  units,  each  of  which  has 
some  practical  or  definite  relation  to  our  own  lives.  Nothing  has 
been  included  in  the  text  that  does  not  directly  or  indirectly  in- 
fluence the  lives  of  each  one  of  Us. 

Each  unit  is  introduced  by  a series  of  survey  questions  which  are 
intended  to  find  out  what  you  already  know  about  the  subject 
matter  of  the  unit.  This  is  followed  by  a brief  preview,  or  intro- 
duction to  the  work  of  the  unit,  which  will  give  you  a bird’s-eye 
view  of  the  subject  matter  of  the  unit.  It  might  be  said  to  be  a 
“ selling  ” device  by  which  each  of  you  may  become  interested  in 
the  work  of  the  particular  section  or  unit.  The  preview  is  followed 
by  a series  of  problems  which  explain  the  unit.  Each  problem 
usually  includes  demonstration  or  laboratory  work,  and  enough 
text  is  given  so  that  this  laboratory  work  is  explained.  The 
references  given  at  the  ends  of  the  units  should  be  used  when 
available.  The  problems  will  be  largely  your  work,  and  your 
understanding  of  biology  will  depend  largely  upon  your  thorough- 
ness in  the  laboratory  or  field  or  library.  At  the  end  of  each 
problem  and  at  the  end  of  the  unit  are  certain  self-testing  devices 
which  will  help  you  to  know  whether  you  have  mastered  the 


iMKTIlOD  OF  I'SF  OF  THIS  HOOK 


17 


contents  of  the  unit.  When  you  have  tested  yourself,  check  back 
on  the  survey  (luestions  to  see  if  you  have  any  corrections  to 
make  there.  After  tliis  is  done  you  are  ready  to  make  your  report 
to  the  class  on  the  unit  or  such  part  of  it  as  your  teacher  may 
assign  to  you.  To  prepare  for  this  recitation  make  an  outline 
summary  for  your  workbook.  This  will  help  you  to  organize 
the  material  in  the  unit  in  the  best  possible  way,  and  thus  come 
to  a complete  understanding  of  the  material,  contained  therein. 
If  you  understand  this  plan  of  the  book,  you  will  be  able  to  get 
better  results  in  its  use. 

The  last  unit  in  the  book  gives  short  and  interesting  stories  about 
a few  scientists  who,  by  much  work  and  perseverance,  made 
remarkable  discoveries  that  have  so  largely  contributed  to  our 
knowledge  of  biology.  The  lives  of  these  men  may  be  studied  in 
relation  to  the  unit  in  which  their  work  is  discussed  or  they  may  be 
studied  at  the  completion  of  the  other  units. 


Useful  References 

Anthony,  Field  Book  of  North  American  Mammals.  Putnam,  1928. 
Burgess,  Birds  You  Shoidd  Know.  Little,  Brown,  1933. 

Cheyney,  What  Tree  Is  That?  Appleton,  1927. 

Downing,  Our  Living  World.  Longmans,  Green,  1924. 

Elton,  Animal  Ecology.  Macmillan,  1927. 

Fuller,  The  Doorway  to  Nature.  Day,  1931. 

Georgia,  Manual  of  Weeds.  Macmillan,  1914. 

Hodge,  Nature  Study  and  Life.  Ginn,  1902. 
limes.  The  Modern  Aquarium.  Innes,  1931. 

Lutz,  Field  Book  of  Insects.  Putnam,  1921. 

IMann  and  Hastings,  Out  of  Doors.  Holt,  1932. 

Mathews,  Field  Book  of  American  Wild  Flowers.  Putnam,  1929. 
Morgan,  Field  Book  of  Ponds  and  Streams.  Putnam,  1930. 

Needham  and  Lloyd,  Life  of  Inland  Waters.  Thomas,  1930. 

Thomson,  New  Natural  History.  Putnam,  1926. 

Wyman  and  Burnell,  Field  Book  of  Birds  of  the  Southwestern  United  States 
Houghton  Mifflin,  1925. 


Survey  Questions 

Can  you  give  the  meaning  of  the  term  “ environment  ” ? Is  it  correct 
for  us  to  speak  of  our  chemical  environment?  Explain.  What  is  the  dif- 
ference between  a chemical  and  a physical  change?  Do  you  know  the 
chemical  elements  which  are  most  common  in  your  environment?  What 
is  a food  ? How  would  you  define  it  scientifically  ? 


18 


PART  I.  LIVING  THINGS  IN  RELATION  TO 
THEIR  ENVIRONMENT  AND  TO  EACH 
OTHER 

UNIT  I 

THE  WORLD  WE  LIVE  IN  AND  WHAT  WE 
TAKE  FROM  IT 

Preview.  In  our  previous  experience  with  science  in  the 
elementary  and  junior  high  schools  we  have  learned  something 
about  our  environment  and  what  we  get  out  of  it.  We  know  a 
little  about  the  air  and  how  we  use  it,  about  water  and  how  it 
serves  us,  of  fire,  of  the  weather,  and  many  other  useful  facts  that 
help  us  in  our  daily  living.  But  now  we  are  ready  to  learn  some- 
thing more  about  this  environment  from  a different  angle. 

Biologists  realize  more  than  ever  before  that  living  things  are 
dependent  upon  their  environment  and  that  they  are  composed 
of  many  of  the  chemical  substances  that  are  found  in  that  environ- 
ment, Thus,  our  knowledge  of  biology  depends  upon  an  under- 
standing of  the  chemists’  and  physicists’  conception  of  the  world 
about  us.  This  unit  will  help  us  to  understand  some  of  these 
important  facts  about  our  surroundings.  The  physicist  calls 
anything  that  occupies  space  matter.  The  chemist  in  his  turn 
reduces  all  matter  into  over  ninety  simple  substances  called 
chemical  elements,  substances  that  cannot  be  broken  into  more 
simple  substances.  These  elements  are  given  symbols  by  the 
chemist,  such  as  0 for  oxygen,  H for  hydrogen,  N for  nitrogen, 
and  C for  carbon.  The  soil  and  other  things  in  nature  are  com- 
posed largely  of  combinations  of  elements  known  as  chemical 
compounds.  A few  of  these  compounds,  such  as  water,  iron  rust, 

19 


20 


THE  WORLD  WE  LIVE  IN 


socCiutn. 


50.59 


59. 


and  table  salt,  are  simple,  inasmuch  as  they  contain  only  two  or 
three  elements;  but  the  greater  number  of  compounds  found  in 
nature  are  very  complex.  The  chemist  uses  several  symbols  to 
designate  the  binding  together  of  elements  into  compounds. 
Several  symbols  together  are  known  as  a formula.  For  example, 
H2O  is  the  formula  for  water  and  indicates  that  two  parts  of  hy- 
drogen combine  with  oxygen  in  a definite  proportion  by  volume. 

. ^ . . 1 1 r A chemical  com- 

insaocvaw  i«  blood  Serum  pound  is  a combina- 

tion  of  two  or  more 
elements  in  which 
each  of  the  elements 
loses  the  character- 
istics which  distin- 
guished it.  For  ex- 
ample, if  fine  iron 
filings  and  flowers 
of  sulphur  are 
mixed,  each  element 
will  retain  its  own 
peculiar  properties, 
can  still  be  recog- 
nized, and  can  be 
easily  separated  by 
means  of  a magnet 
which  will  attract 
the  iron.  But,  if  the 


vnadnesmm.  3.7^  [ 

CaSdumJ? 


potassium 


chlorine. 


55.27 


SO4. 

CO3 

brominei' 

According  to  analysis,  scientists  have  found  that  the  per- 
centages of  chemical  substances  in  sea  water  are  quite  similar  to 
those  found  in  the  blood  serum  (after  Osborne). 


45. 


SocCiirm 


magnesium 

(..Calcium 

-potassiixm 


.chlorine^ 


mixture  is  heated  in  a test  tube,  several  important  changes  in  the 
mixture  will  take  place.  A solid  black  substance  is  obtained 
which  is  not  attracted  by  a magnet.  The  elements  can  no  longer 
be  separated  by  mechanical  means.  This  black  substance  is  a 
compound  called  iron  sulphide.  It  has  several  properties  quite 
different  from  those  of  either  the  iron  or  the  sulphur.  Rocks, 
humus,  organic  food  substances,  and  the  bodies  of  plants  and 
animals  are  all  composed  of  chemical  compounds. 

Professor  H.  F.  Osborne  of  Columbia  University  has  pointed 
out  that  the  chemical  substances  found  in  sea  water  correspond 


SURROUNDINGS  OF  A TREE 


21 


very  nearly  with  those  in  the  human  blood.  There  are  other 
facts  also  which  prove  that  some  of  the  same  chemical  elements 
found  in  the  environment  somehow  or  other  become  organized 
into  the  tremendously  complex  material  of  which  we  find  living 
plants  and  animals  composed. 

PROBLEM  1.  HOW  IS  A TREE  FITTED  TO  LIVE  IN  ITS 
NATURAL  SURROUNDINGS? 

Field  Exercise.  Observe  a tree  in  its  natural  environment.  Bring  in 
all  the  information  you  can  to  class  concerning  where  a given  tree  grows, 
its  form,  size,  characteristics,  etc.  The  findings  of  the  class  can  be 
tabulated  on  the  board,  and  from  this  a general  statement  can  be  made 
concerning  the  characteristics  of  all  trees. 

As  Joyce  Kilmer  well  said,  there  is  no  poem  as  lovely  as  a tree. 
Trees  are  so  commonplace  that  we  are  not  likely  to  consider  what 
life  would  be  without  them.  They  grow  straight  and  tall,  even  in 
cities  where  life  for  them  must  be  very  difficult.  The  problem 
before  us  is,  “ How  do  they  do  it?  ’’  How  can  a tree  (or  any  other 
green  plant  for  that  matter)  develop  into  the  great  bulk  that  they 
have?  They  cannot  make  something  out  of  nothing.  It  takes 
several  acorns  to  weigh  an  ounce,  but  an  oak  tree  weighs  several 
tons.  Where  does  this  increase  come  from  ? Evidently  the  young 
tree  must  take  something  from  its  surroundings  in  order  to  grow. 
What  are  the  substances  it  uses  ? And  how  does  it  do  this  ? 

The  skeleton.  Let  us  take  a typical  tree,  such  as  the  maple 
or  ehn.  We  notice  in  winter  it  is  a skeleton,  a straight  trunk  or 
main  stem  and  many  branching  limbs  which  spread  out  into  ever 
smaller  and  smaller  branches.  These  are  covered  with  buds  which 
in  spring  will  produce  leaves  or  flowers  or  both.  Under  the 
ground  we  know  there  are  roots,  which,  in  the  same  manner  as  the 
branches,  spread  out  widely  and  continually  branch  so  that  in 
many  trees  there  is  almost  as  much  of  the  tree  below  ground  as 
above  it.  Evidently  the  roots  anchor  the  tree  in  the  ground, 
while  the  branches  place  the  buds  and  leaves  in  the  most  favorable 
position  possible. 

Leaves.  In  the  summer  the  tree  is  covered  with  green  leaves. 
These,  we  notice,  are  set  as  far  out  as  possible  on  the  branches. 
Evidently  sunlight  influences  them,  for  a bird’s-eye  view  of  the 

H.  BIO  — 3 


22 


THE  WORLD  WE  LIVE  IN 


An  American  elm  in  summer. 


tree  shows  that  the  leaves  are  placed  so  that  they  shade  each  other 
but  little,  and  present  their  flat  surfaces  at  right  angles  to  the 
sun’s  rays.  The  leaves,  as  we  shall  later  see,  are  food  factories 

and  do  their  work  by 
energy  received  from 
the  sun’s  rays. 

Roots.  If  we  were 
to  examine  the  roots, 
we  would  find  here 
evidences  that  they 
take  in  water,  besides 
anchoring  the  tree  and 
giving  it  firm  support. 
Trees  growing  near 
irrigating  ditches  or 
sewers  often  fill  them 
with  masses  of  fine 
roots  which  have 
sought  out  the  water. 
The  smaller  rootlets 
are  covered  with  tiny 
absorbing  organs  called 
root  hairs. 

However,  the  tree 
must  take  other  ma- 
terials than  water  from 
its  surroundings  in 
order  to  grow,  for  no 
thing  can  live  and 
grow  on  water  alone. 
Our  problem  now  be- 
comes more  difficult,  and  we  cannot  answer  it  completely.  But 
we  do  know  that  the  green  plant,  taking  substances  from  the  air 
and  soil  surrounding  it,  manufactures  the  material  we  call  organic 
food,  and  uses  this  food  to  make  its  living  material. 

To  discover  just  what  a tree  takes  from  its  surroundings  involves 
the  knowledge  of  some  chemistry.  Most  of  us  have  had  some 


L.  \V.  Brownell 

The  same  tree,  as  above,  during  the  winter. 


IU'IL1)1N(J  MATEKIALS 


23 


of  this  knowledge  from  a course  in  general  science,  but  we  must 
now  review  some  of  the  elementary  facts  in  order  to  answer  the 
problems  which  follow. 

S elf-T esting  Exe acisE 

A tree  has  (1),  (2),  (3),  and  green 

(4).  The (5)  serve  to  anchor  the  tree  in  the  ground 

and  take  in  ((>).  The  stein  holds  to  the  light  the 

(7),  which  arc  the  (8)  (9).  The  tree 

takes  (10)  materials  from  its  environment  and  makes  them 

into (11)  and (12)  matter. 

PROBLEM  II.  WHAT  ARE  THE  BUILDING  MATERIALS  OF 
THE  WORLD  AND  HOW  ARE  THEY  USED? 

Matter.  Matter  and  energy  are  the  fundamental  things  in  the 
world.  Matter  is  anything  which  has  weight  or  occupies  space. 
The  tree  is  made  of  matter,  as  is  the  surrounding  soil,  the  water, 
and  even  the  air  which  it  uses.  Matter  is  usually  present  in  one 
of  three  forms,  a gas,  a solid,  or  a liquid  ; and,  as  we  know,  is  capable 
of  being  changed  from  one  form  to  another.  For  example,  a 
liquid,  water,  may  be  changed  into  a vapor,  steam,  by  heating,  or 
into  a solid,  ice,  by  freezing.  In  biology,  matter  is  usually  thought 
of  as  being  of  two  sorts,  organic,  or  that  which  comes  from  living 
things,  and  inorganic,  or  the  material  that  never  has  been  alive. 

Energy.  When  a tree  grows,  or  the  roots  push  their  way 
through  the  soil,  or  take  in  water,  energy  is  being  exerted. 
Energy  means  the  power  or  ability  to  do  work.  There  are  five 
kinds  of  energy : mechanical,  electrical,  chemical,  heat,  and  light 
energy.  To  perform  its  work  the  tree  uses  light  energy,  chemi- 
cal energy,  and  heat  energy,  which  it  may  change  into  mechanical 
energy.  Any  one  form  of  energy  may  be  changed  into  another 
form.  We  may  observe  such  a change  when  we  strike  a nail  with 
a hammer  and  discover  that  the  nail  becomes  hot.  Our  mechani- 
cal energy  has  turned  into  heat  energy. 

Demonstration  1.  Show  some  elements,  as  carbon,  iron,  phosphorus, 
and  sulphur. 


24 


THE  WORLD  WE  LIVE  IN 


Forms  of  matter.  Both  living  and  non-living  things  are  made 
up  of  chemical  elements.  There  are  over  ninety  elements.  The 

common  ones  that  are  found  in 
a tree  are  oxygen,  carbon,  nitro- 
gen, and  hydrogen;  while  a 
number  of  others,  less  com- 
mon, such  as  sulphur,  potas- 
sium, iron,  and  phosphorus, 
are  also  found  in  the  composi- 
tion of  most  plants  and  ani- 
mals. Many  of  these  same 
elements  are  found  in  soil,  in 
air,  and  in  water.  Some  ele- 
ments are  gases,  such  as  oxygen 
and  nitrogen.  Some  are  solids, 
such  as  carbon  and  sulphur, 
and  two  which  are  not  found 
in  the  composition  of  the  tree 
are  liquids,  mercury  and  bromine.  Elements  are  simple  substances. 
For  example,  iron,  so  far  as  we  know,  has  nothing  but  iron  in  it ; 
and  oxygen  nothing  but  oxygen  in  it.  It  is  easy  to  separate  some 
elements  from  their  compounds  and  not  so  easy  to  get  others. 
Carbon,  for  example,  in  its  pure  state  is  obtained  when  we  collect 
on  a sheet  of  white  paper  the  black  substance  from  the  smoke 
of  a candle.  Soot  is  almost  pure  carbon.  The  yellow  sulphur  that 
we  buy  at  the  drug  store  is  an  element.  It  is  not  so  easy  to 
obtain  oxygen  in  a pure  state.  This  element  is  often  combined 
in  nature  with  other  elements  to  form  substances  called  com- 
pounds. A simple  compound  containing  oxygen  is  water. 

Demonstration  2.  The  separation  of  water  into  its  elements.  If 

by  means  of  the  apparatus  shown  in  the  diagram  an  electric  current 
is  passed  through  water  to  which  a little  sulphuric  acid  has  been  added, 
we  find  that  the  water  separates  into  two  gases.  In  one  tube  the  gas 
present  occupies  just  half  as  much  space  as  in  the  other  tube.  The 
gas  present  in  the  smaller  quantitj^’  proves  upon  test  to  be  oxygen 
as  it  causes  a glowing  splinter  to  burst  into  flame.  The  other  gas,  color- 
less, tasteless,  and  odorless  like  the  oxygen,  differs  from  it  by  igniting 
with  a slight  explosion  when  a burning  match  or  splinter  is  introduced 


The  percentage  of  different  chemical  elements 
that  are  found  in  the  human  body.  How  do  you 
account  for  such  a large  proportion  of  the  gas 
oxygen? 


OXYGEN 


25 


into  tlie  tube.  As  the  gas  bums,  drops  of  water  are  formed,  showing 
tliat  it  is  passing  back  to  its  original  condition,  that  is,  it  is  uniting 
with  o.xygen  to  form  water.  This  gas  is  hydrogen.  Elements  always 
unite  in  definite  proportions  to 
form  compounds,  as  in  water  the 
proi)ortion  by  volume  is  always 
two  parts  of  hydrogen  to  one 
part  of  oxygen. 

Oxygen,  when  carefully  pre- 
pared, is  found  to  be  colorless, 
odorless,  and  tasteless.  Com- 
bined with  other  substances,  it 
forms  a very  large  part  of  the 
composition  of  water,  rocks, 
minerals,  and  the  bodies  of 
plants  and  animals. 

Oxygen  has  the  very  important  property  of  uniting  with  many 
other  substances.  The  chemical  union  of  oxygen  with  another 
substance  is  called  oxidation.  When  a candle  burns,  the  oxygen 
in  the  air  unites  with  the  carbon  in  the  candle  and  forms  a gas, 
called  carbon  dioxide,  which  puts  out  a flame.  This  gas  may  be 
tested  for  as  follows  : 

Demonstration  3.  Burn  a candle  in  a closed  jar.  After  the  candle 
goes  out,  remove  it  carefully  (the  gas  in  the  jar  is  heavier  than  air). 
Add  a spoonful  of  lime  water  — screw  down  the  top  of  the  jar  and  shake 

so  as  to  mix  the  gas  in  the  jar 

carbort  dioxicCe, 

Cai^boYi  and. 

,^vat©t^  vapoi^ 
in  the  smoks 


kt-  and 
:t  energy 


ccr-boTi 


of 

Why  is  the  burning  of  a match  an  example  of 
oxidation  ? 


with  the  lime  water.  What  hap- 
pens to  the  limewater  ? This  test 
with  limewater  shows  that  carbon 
has  been  oxidized,  forming  carbon 
dioxide. 

Practical  Exercise  1.  Burn  a 
number  of  different  substances  in 
closed  jars  and  test  in  each  case  for 
carbon  dioxide.  How  many  of  the 
substances  produce  carbon  dioxide 
when  burned? 

Oxidation.  Oxidation  may 
take  place  slowly,  as  in  the 
rusting  of  an  iron  nail,  which 
is  caused  by  oxygen  uniting 


26 


THE  WORLD  WE  LIVE  IN 


with  the  element  iron.  Slow  oxidation  of  chemical  compounds  is 
constantly  taking  place  in  nature  and  is  a part  of  the  process  of  de- 
cay and  of  breaking  down  of  complex  materials  into  simpler  forms. 

One  of  the  most  important  effects  of  oxidation  lies  in  the  fact 
that,  when  anything  is  oxidized,  heat  is  produced.  This  heat 
may  be  of  the  greatest  use.  Coal,  in  being  oxidized,  gives  off 

heat;  this  heat  boils 
the  water  in  the  tubes 
of  a boiler;  steam  is 
generated,  wheels  of 
an  engine  are  turned, 
and  work  is  performed. 
The  energy  released  by 
the  burning  of  coal 
has  been  transformed 
into  work  or  power. 
We  shall  find  later 
that  the  oxidation  of 
certain  materials  in 
the  bodies  of  plants 
or  animals  releases 
energy  which  is  used 
to  perform  work. 
The  heat  of  the  hu- 
man body  is  main- 
tained by  the  constant 
slow  oxidation  of  food 
materials  within  the 
body. 

Forms  of  energy.  Energy  has  been  shown  to  be  the  power  to 
do  work.  The  energy  locked  in  the  coal  before  it  is  released  by 
the  process  of  burning  is  known  as  'potential  or  stored  energy. 
The  energy  released  by  the  burning  process  is  kinetic  or  active 
energy.  The  potential  energy  held  in  the  water  of  the  San 
Francisquito  dam  became  kinetic  energy  when  the  dam  gave  way 
and  let  the  great  volume  of  water  rush  down  the  fertile  Santa 
Clara  valley,  bringing  death  and  destruction  to  its  inhabitants. 


The  energy  held  in  the  water  in  this  dam  was  sufficient  to 
uproot  trees,  sweep  buildings  from  their  foundations,  and 
dislodge  rocks,  when  a wall  of  the  dam  broke. 


COMPOSITION  OF  J.IVINO  'nilNOS 


27 


Conservation  of  energy.  Pliysicnl  science  teaches  us  that 
energy,  such  as  that  released  so  disastrously  in  that  California 
yalley,  may  neyer  be  lost,  created,  or  destroyed.  It  always  is, 
and  ahvaj'S  has  been.  The  great  force,  released  when  the  flood 
rushed  down  the  yalley,  dug  deep  channels  in  the  soil,  moyed  huge 
rocks,  smashed  houses,  and  left  countless  other  ruins  in  its  ruthless 
path.  If  the  water  could  haye  been  harnessed  to  a turbine,  it 
might  haye  turned  a dynamo,  produced  electricity,  lighted  a city, 
or  turned  tho  wheels  of  factories.  Energy  may  be  changed  from 
one  form  to  another,  but  it  can  neyer  be  created  or  destroyed ; it 
is  eyerlasting ! 

Practical  Exercise  2.  Give  three  examples  of  transformation  of  energy  that 
help  to  make  life  more  comfortable  for  you. 

Water  in  living  things.  Water  forms  an  important  part  of  the 
substance  of  plants  and  animals.  This  is  seen  when  a number  of 
green  leaves  are  weighed,  placed  in  a hot  oven  for  a few  moments, 
and  then  reweighed.  The  same  experiment  made  with  a soft- 
bodied  animal,  as  the  oyster,  would  show  the  presence  of  a greater 
percentage  of  water  than  was  found  in  leaves.  Some  jellyfish 
are  over  90  per  cent  water.  Over  65  per  cent  of  the  human  body 
is  water. 

Mineral  matter  in  living  things.  If  a piece  of  wood  is  burned 
in  a very  hot  fire,  the  carbon  in  it  will  all  be  consumed,  and  even- 
tually nothing  will  be  left  except  a grayish  ash.  This  ash  consists 
of  mineral  matter  which  the  plant  has  taken  up  from  the  soil  dis- 
solved in  water,  and  which  has  been  stored  in  the  wood  or  leaves. 
All  living  things  contain  small  quantities  of  mineral  substances. 

Practical  Exercise  3.  Weigh  several  different  substances  such  as  soil,  apple, 
meat,  dried  beans,  celery,  etc.  Dry  out  each  substance  in  an  oven  under  slow 
heat  (do  not  char) . After  several  hours  reweigh  and  determine  percentages  of 
water  lost  by  each  substance.  Then  try  to  burn  out  all  organic  material. 
The  gray  residue  is  the  ash  or  mineral  content.  What  per  cent  of  the  orig- 
inal weight  is  the  ash  ? 

Gases  present  in  living  things.  Some  gases  are  found  in  a free 
state  in  the  bodies  of  plants  or  animals.  Oxygen  is  of  course 
present  wherever  oxidation  of  organic  matter  is  taking  place,  as  is 
carbon  dioxide.  Other  gases  may  be  present  in  minute  quantities. 


28 


THE  WORLD  WE  LIVE  IN 


Materials  found  in  tree.  Our  experiments  have  shown  us  that 
elements  may  be  separated  from  compounds,  and  elements  may  be 
built  up  into  compounds.  In  a living  tree  similar  processes  are  con- 
tinually going  on.  Water,  with  mineral  salts  such  as  iron,  potas- 
sium, and  sulphur  dissolved  in  it,  comes  from  the  earth.  Nitrogen, 
which  is  an  absolute  necessity  for  building  living  material,  is  taken 
from  the  earth  in  the  form  of  very  complicated  compounds  which 
usually  come  from  the  decaying  bodies  of  plants  and  animals  and 
are  found  in  the  black  soil  we  call  humus.  Oxygen  and  carbon 
dioxide  come  from  the  air  and  are  taken  into  the  plant  through 
holes  in  the  leaves.  All  together,  the  tree  is  a wonderful  laboratory, 
for  out  of  these  raw  materials  it  builds  foods  and  from  these  foods 
it  builds  its  own  wonderful  structure.  The  leaves  not  only  make 
food  in  the  sunlight,  but  they  digest  and  circulate  it  to  all  parts 
of  the  plant.  This  may  be  done  in  darkness  as  well  as  in  light. 

The  table  on  the  opposite  page  gives  us  the  characteristics  of 
the  most  common  elements  that  are  found  in  the  tree  and  its  en- 
vironment. It  will  also  tell  us  how  to  identify  each  of  these  ele- 
ments by  testing  for  those  properties  by  which  they  are  known, 
where  they  are  found,  and  what  use  they  have  in  nature. 

Self-Testing  Exercise 

Matter  is  anything  that  has (1)  or  occupies (2). 

It  may  be  in  the  form  of  a (3),  a (4),  or  a (5). 

Energy  is (6)  to  do (7).  One  form  of  energy  may  be 

(8)  into  another,  as  is  seen  in  making (9)  by  means  of 

water  power.  Energy  may  be  stored  in  a substance  as (10) 

energy,  but  when  released  to  do  work,  it  is  (11)  energy. 

Both (12)  and (13)  things  are  made  up  of 

(14)  elements.  There  are  over (15)  in  all.  The  commonest 

ones  found  in  living  things  are (16),  (17),  

(18),  and (19).  Elements  combine  in (20)  propor- 
tions to  form (21),  as  two  parts  of  (22)  and  one 

part  of (23)  form  water.  When  anything (24)  with 

oxygen,  we  say (25)  is  taking  place.  If  an  organic  substance 

is  (26)  or  oxidized,  it  gives  off (27)  (28). 

If (29)  turns (30),  when  used  as  a test  for  this  gas  we 

know  that (31)  ........  (32)  is  present. 


MATERIALS  FOUXI)  IN  LIVING  THINGS 


29 


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30 


THE  WORLD  WE  LIVE  IN 


PROBLEM  III.  WHAT  ARE  FOODS  AND  HOW  ARE  THEY 
USED? 

Foods.  What  is  a food?  We  know  that  if  we  eat  a suitable 
amount  of  proper  foods  at  regular  times,  we  shall  be  able  to  go  on 
doing  a certain  amount  of  work,  both  physical  and  mental.  We 
know,  too,  that  day  by  day,  if  our  general  health  is  good,  we  may 
be  adding  weight  to  our  bodies,  and  that  added  weight  comes  as 
the  result  of  eating  food.  A similar  statement  may  be  made  with 
reference  to  plants  and  foods.  If  food  is  supplied  in  proper  quan- 
tity and  proportion,  plants  will  live  and  grow ; if  their  food  sup- 
ply is  cut  off,  or  even  greatly  reduced,  they  will  suffer  and  may  die. 


Compare  this  turkey  leg  with  other  materials  used  as  food,  by  making  similar  analysis  of  them. 


However,  only  a small  part  of  a food,  as  potatoes,  can  be  used 
by  the  body.  For  a food  is  made  up  of  a combination  of  wastes  — 
as  water  in  vegetables,  skins  of  fruits,  and  tendons  in  meat  — 
and  nutrients  which  repair  or  build  up  the  body  or,  when  oxidized  in 
the  body,  furnish  it  with  energy.  The  organic  nutrients  found  in 
foods  are  carbohydrates,  fats  or  oils,  and  proteins. 

Carbohydrates.  Starch  and  sugar  are  common  examples  of 
this  group  of  substances.  The  former  we  find  in  our  cereals  and 
most  of  our  vegetables.  Several  kinds  of  sugar,  such  as  cane 
sugar,  beet  sugar,  and  glucose  or  grape  sugar,  are  commonly  used 
as  food.  Glucose,  the  natural  sugar  of  grapes,  honey,  and  fruits, 
is  manufactured  commercially  from  starch  by  the  action  of  dilute 
acids.  It  is  used  as  an  adulterant  in  sirups,  honey,  and  candy. 


FOODS 


31 


Fats  and  oils.  Fats  and  oils  form  a part  of  tlio  composition 
of  plants  and  animals.  Fxamidcs  of  food  containing];  fal.  arc : 
butter  and  cream,  oils  from  nuts  and  olives,  and  fat  from  animals. 

Proteins.  Proteins  contain  the  element  nitroj2;en  in  addition 
to  carbon,  hydrogen,  and  ox^'^f^en  of  the  carbohydrates  and  fats 
and  oils.  They  include  some  of  the  most  complex  substances 
known  to  the  chemist,  and,  as  we  shall  see,  have  a chemical  com- 
position very  similar  to  that  of  living  matter.  Proteins  occur  in 
different  substances.  ^Miite  of  egg,  lean  meat,  beans,  and  peas 
are  examples  of  substances  composed  largely  of  proteins. 

Vitamins,  ^'itanlins,  substances  the  composition  of  which  is 
practically  unknown  as  yet,  are  also  necessary  parts  of  a diet. 
We  shall  learn  more  about  them  in  Unit  XL 

Inorganic  nutrients.  Water  and  various  salts,  some  of  which, 
as  calcium  found  in  drinking  water,  form  important  parts  of  the 
diet  of  plants  and  animals.  Later  we  shall  see  that  green  plants, 
although  they  use  precisely  the  same  nutrients  (carbohydrates, 
oils,  and  proteins)  as  we  do,  take  into  their  bodies  the  chemical  ele- 
ments from  which  these  are  formed.  From  these  raw  food  ma- 
terials organic  foods  are  manufactured  in  the  body  of  the  plant. 

The  tree.  Foods  in  a fluid  form  are  circulated  to  all  parts  of 
a tree.  It  grows  by  elongating  its  roots  and  its  branches,  and 
by  putting  on  a thin  layer  of  living  matter  on  all  parts  of  its  body. 
This  layer  grows  more  in  summer  than  in  winter.  If  we 
should  cut  down  a tree,  we  can  see  the  concentric  rings  in  its 
trunk  which  mark  its  yearly  growth.  How  did  the  tree  do  this? 
Here  again  the  chemical  laboratory  is  at  work.  The  organic 
foods  which  were  made  consist  of  the  same  elements  that  are 
found  in  the  living  stuff  of  the  tree.  These  foods  were  used,  not 
only  to  supply  energy  so  that  the  tree  may  do  work,  but  they 
give  it  the  materials  out  of  which  to  build  its  living  material. 

Self-Testing  Exercise 

A nutrient  is  anything  that  supplies (1),  and (2)  or 

(3)  up  the (4)  of  living  things.  Foods  are  made  up  of 

(5)  and (6).  The  organic  nutrients  are (7), 

(8)  or (9),  and (10). 


32 


THE  WORLD  WE  LIVE  IN 


PROBLEM  IV.  HOW  DOES  MAN  CONTROL  HIS 
ENVIRONMENT? 

Natural  environment.  Besides  the  chemical  elements  in  our 
surroundings,  temperature,  absence  or  presence  of  water,  the  kind 
of  earth  surface,  the  presence  of  different  salts  in  the  soil  or  water, 
all  may  play  a part  in  determining  what  kind  of  life  will  be 
present  in  a given  locality.  Mountain,  plain,  desert,  lake,  woods, 
tropical  jungle,  each  has  its  own  inhabitants  and  these  inhabitants 
are  limited  to  life  in  that  particular  part  of  the  world. 


Photo  by  Douglas-Nesmith  & Associates 

A city  apartment  house.  Why  do  we  consider  this  a favorable  artificial  environment  ? 

Man,  while  he  is  like  other  animals  in  requiring  heat,  light, 
water,  and  food,  differs  from  them  in  that  he  has  come  to  live  in  a 
more  or  less  artificial  environment.  Men  who  lived  on  the  earth 
thousands  of  years  ago  did  not  wear  clothes  or  have  elaborate 
homes  of  wood,  brick,  or  stone.  They  did  not  use  fire,  nor  did  they 
eat  cooked  foods.  But,  by  slow  degrees,  man  has  come  to  live  in 
an  environment  changed  from  that  of  other  animals.  He  has 
learned  to  build  houses  and  to  use  fire.  The  living  together  of 
men  in  communities  has  caused  certain  needs  to  develop.  Many 
things  can  be  supplied  in  common,  as  water,  milk,  and  fuel.  Wastes 


NATURAL  ENVIRONMENT 


33 


of  all  kinds  in  a town  or  city  liavo  to  bo  disposed  of.  Homes  are 
now  placed  close  together,  or  built  one  on  top  of  another,  as  in 
modern  apartment  buildings.  Fields  and  trees,  in  fact  most 
aspects  of  country  outdoor  life,  have  virtually  disappeared  in  a 
large  city.  City-dwelling  man  has  come  to  live  in  an  artificial 
environment. 

Care  and  improvement  of  the  environment.  Man  can  modify 
or  change  his  surroundings  by  making  this  artificial  environment 
favorable  to  live  in.  He  can  heat  his  dwellings  in  winter  and  cool 


Why  do  we  call  this  an  unfavorable  natural  environment  ? 


them  in  summer  so  as  to  maintain  a moderate  and  nearly  con- 
stant temperature.  He  can  have  windows  in  his  dwellings  to 
let  light  and  air  pass  in  and  out.  He  can  have  light  at  night  and 
shade  from  intense  light  by  day.  He  can  have  pure  water  in  his 
home,  and  drains  or  sewers  to  carry  away  his  wastes.  He  can 
plan  parks  and  playgrounds  so  that  the  city  people  may  have 
breathing  spaces,  as  do  people  in  the  smaller  towns.  He  can  see 
to  it  that  people  ill  with  communicable  diseases  are  isolated  or 
quarantined  from  others.  Best  of  all,  he  is  slowly  learning  to  con- 
trol the  tiny  parasites,  plant  and  animal,  that  cause  and  spread 


34 


THE  WORLD  WE  LIVE  IN 


diseases.  This  care  of  the  artificial  environment  is  known  as 
sanitation,  while  the  care  of  the  individual  for  himself  is  known 
as  hygiene. 

Self-Testing  Exercise 

The  environment  is  our (1).  With  man  much  of  this  en- 
vironment is  (2).  He  can (3)  his  environment  while 

other  living  things  (4)  do  this.  The  (5)  of  the 

artificial  environment  is  called  (6),  the  care  of  the  individual 

for  himself  without  considering  his (7)  is (8). 

Organization  of  work.  In  each  unit  there  are  certain  funda- 
mental things  that  we  must  learn  and  do.  Everything  in  a unit 
is  not  of  equal  importance.  It,  therefore,  is  necessary  for  you  to 
decide  on  the  most  important  material  from  which  you  will  make 
your  recitation.  To  make  this  organization,  a summary  outline 
which  you  can  use  as  a guide  is  helpful,  as : 

The  tree  a living  thing  Energy  — forms  of 

What  does  it  use  in  its  environment?  Conservation  of 
How  does  it  get  it  ? Foods  and  nutrients 

Matter  — what  is  it  ? Kinds  of  each 

Elements  and  compounds  Control  of  environment  by  man 

Oxygen  and  oxidation 
Elements  found  in  living  things 

In  all  except  the  first  two  or  three  units,  there  will  be  no  sum- 
mary outline  and  you  will  be  expected  to  make  one  for  your  note- 
book. You  should  also  test  your  knowledge  of  the  unit  in  the 
following  ways  : (1)  answer  and  check  all  of  the  survey  questions ; 
(2)  perform  all  assigned  exercises  or  laboratory  work  ; and  (3)  check 
with  your  teacher  the  various  self-testing  exercises,  including  the 
final  test  on  fundamental  concepts  and  the  attainment  test. 

Test  on  Fundamental  Concepts 

Make  in  your  notebook  two  vertical  columns,  one  headed  CORRECT  and  the  other 
INCQRRECT.  In  the  first  column  place  the  number  of  the  statements  you  think  are  right,  in 
the  second  the  ones  you  think  are  wrong.  Your  grade  = number  right  X 4. 

I.  The  environment  (1)  contains  the  same  chemical  elements  as  do 
the  living  things  in  it ; (2)  has  the  same  chemical  composition  as  living 
things ; (3)  is  everything  that  surrounds  us ; (4)  can  be  controlled  by 
man ; (5)  determines  the  kind  of  plants  or  animals  living  in  it. 


TESTS 


35 


II.  Matter  ((>)  is  anything  that  has  weight;  (7)  is  easily  destroyed; 
(S)  is  material  in  the  form  of  »as,  liciuid,  oi’  solid;  (D)  can  be  €hanj2;ed 
from  one  foi-m  to  another;  (It))  is  or»;anie  oi'  inor<>;anic. 

III.  Energy  (II)  ean  be  either  gaseous  or  licjuid;  (12)  is  power  to  do 
work;  (Id)  may  be  released  by  oxidation;  (14)  is  potential  or  kinetic; 
(lo)  is  storeil  in  the  foods  we  eat. 

1\’.  Foods  (lb)  contain  waste  material;  (17)  are  all  obtained  in 
their  final  state  from  the  soil;  (18)  contain  nutrients;  (19)  ai’e  used 
by  plants  and  animals  to  n'lease  energy  and  to  build  and  roi)air  tis- 
sue; (20)  are  made  by  green  plants. 

V.  Man  (21)  can  control  his  environment;  (22)  needs  green  plants 
to  make  food ; (23)  is  not  able  to  oxidize  food  to  release  energy ; 

(24)  is  composed  of  the  same  chemical  elements  as  his  environment; 

(25)  is  the  only  living  thing  that  can  permanentlj^  change  his  environment. 

Achievement  Test 

1.  How  can  you  make  ox}^gen? 

2.  How  do  you  test  for  carbon  dioxide? 

3.  What  chemical  and  physical  happenings  take  place  when  you 
burn  a match  ? 

4.  What  are  the  chemist’s  symbols  for  oxygen,  nitrogen,  carbon,  hydro- 
gen, and  carbon  dioxide? 

5.  What  is  meant  by  the  term  “conservation  of  energy”?  How 
could  3mu  perform  a demonstration  to  prove  it? 

G.  How  can  you  distinguish  between  the  natural  and  artificial  factors 
of  3’our  environment? 

Practical  Problems 

1.  List  the  ways  in  which  a tree  and  man  use  their  environments. 
List  the  natural  and  artificial  factors  of  your  environment. 

2.  Take  some  factor  of  the  environment  in  your  community  that 
you  think  is  poor  and  make  definite  suggestions  for  its  improvement. 

3.  Show  some  example  of  conservation  of  energy  taken  from  your  own 
home  environment ; from  the  country  in  which  you  live. 

Useful  References 

Downing,  Our  Living  World,  pp.  309-350.  Longmans,  Green,  1924. 
Hunter  and  Whitman,  Problems  in  General  Science.  “Control  of  Environ- 
ment,” pp.  15-34.  American  Book,  1934. 

Somerville,  How  a Tree  Grows.  Oxford  University  Press,  1927. 


SURVEY  QUESTIONS 


What  do  we  mean  by  “ being  alive  ” ? Why  do  plants  and  animals 
turn  toward  or  away  from  the  source  of  light  ? Are  they  affected  by  other 
factors  of  their  environment  ? Could  you  name  some  things  that  aU  hving 
things  can  do  ? What  is  meant  by  the  term  “ adaptation  ” ? 


UNIT  II 

WHAT  IS  BEING  ALIVE?  THE  FUNCTIONS  OF  LIVING 
THINGS 

Preview.  We  have  seen  in  our  study  of  elementary  science, 
several  differences  between  living  and  non-living  matter.  Water, 
for  example,  when  cooled  sufficiently,  becomes  ice,  or,  if  heated 
to  the  boiling  point,  becomes  vapor.  In  order  to  be  changed  it 
has  to  be  acted  upon  by  outside  forces.  But  when  a plant  or  an 
animal  grows,  or  moves,  or  in  some  other  way  manifests  energy, 
that  energy  is  released  by  the  living  thing  itself. 

We  think  of  things  as  being  alive  when  they  do  something.  Yet 
water  may  turn  a wheel  and  generate  electricity  which  has  a force 
capable  of  “ doing  something.”  Such  a force  may  set  off  a blast 

36 


PREVIEW 


37 


of  dynamite.  Or  electricity,  in  the  form  of  a flash  of  lightning, 
may  destroy  a tree. 

It  is  not  easy  to  tell  exactly  what  it  is  to  be  alive,  any  more  than 
it  is  easy  to  tell  what  electricity  is  or  what  radioactivity  is.  Elec- 
tricity is  a servant  of  man,  but  the  greatest  expert  cannot  tell 
what  the  force  actually  is.  Life  is  a manifestation  of  forces,  like 
a flame  or  electricity.  Every  living  thing,  as  we  shall  see  later, 
is  like  a steam  engine  or  any  other  machine,  in  that  it  is  a medium 
used  for  the  transformation  of  energy.  So  to  understand  the 
meaning  of  life  we  had  better  start  by  trying  to  see  how  living 
things  act  in  their  normal  environment  when  outside  forces  influ- 
ence them. 

One  of  the  world’s  great  biologists,  Jacques  Loeb  (zhak  lob), 
some  years  before  his  death  attempted  to  prove  that  all  living 
things  are  more  or  less  automatically  controlled  by  the  factors 
of  their  environment.  He  assumed  that  all  living  matter  is  sensi- 
tive and  that  it  responds  or  reads  to  the  forces  of  its  environment, 
in  very  definite  ways.  These  forces  we  call  stimuli  (sing,  stimulus) ; 
the  response  which  is  made  to  such  a stimulus  we  call  a tropism. 
Loeb  and  his  followers  have  shown  quite  conclusively  that  living 
matter  responds  very  definitely  to  temperature,  touch,  chemical 
substances,  electricity,  and  various  other  factors  of  the  environ- 
ment. The  behavior  of  plants  and  animals  in  response  to  these 
various  stimuli  is  one  indication  of  being  alive. 

Response  to  stimuli  is  evidenced  by  activity  or  movement. 
Movement  in  living  things  is  brought  about  by  changes  within 
the  living  material  of  which  the  organism  is  composed,  while  the 
movement  of  non-living  things,  as  an  engine,  is  brought  about  by 
the  force  of  burning  coal  or  exploding  gasoline.  This  activity 
is  due  to  the  fact  that  living  things  are  like  engines  in  another 
* respect : while  the  engine  oxidizes  fuel  to  release  energy,  they 
oxidize  the  food  taken  into  their  bodies  and  release  energy  in  the 
form  of  motion  or  other  kinds  of  work. 

Any  living  thing,  plant  or  animal,  must  get  food  and  digest  it, 
must  circulate  this  digested  food  to  various  parts  of  its  body,  must 
assimilate  or  make  the  prepared  food  into  a part  of  itself,  must 
excrete  or  get  rid  of  wastes,  and  must  reproduce  or  form  new 

H.  BIO  — 4 


38 


WHAT  IS  BEING  ALIVE? 


plants  or  animals.  Adaptability  is  also  a characteristic  of  living 
things.  We  say  that  a plant  or  animal  adapts  itself  to  its  sur- 
roundings, meaning  that  some  structure  of  the  animal  or  plant 
has  made  it  possible  for  the  organism  to  live  under  the  conditions 
in  which  it  is  placed. 

A little  over  two  hundred  years  ago,  a Dutchman,  Anton  van 
Leeuwenhoek  (la'ven-hdbk),  became  interested  in  lenses.  He 


Anton  van  Leeuwenhoek  was  at  first 
only  interested  in  grinding  lenses  and  mak- 
ing crude  microscopes  so  that  he  could 
see  things  bigger  than  the  naked  eye 
could  see  them.  But  later  he  became  in- 
terested in  observing  minute  animals  that 
could  not  be  seen  with  the  naked  eye. 
Through  his  discoveries  and  observation, 
incentive  was  given  to  the  study  of  bac- 
Culver  Service  teria. 


looked 


ground  hundreds  of  them,  and  used  them  in  various  combinations 
to  magnify  tiny  plants  and  animals.  With  these  improved  lenses 
he  was  able  to  see  tiny  organisms  swimming  in  drops  of  pond  water, 
and  it  is  even  thought  that  he  probably  saw  living  bacteria.  An 
English  doctor,  Robert  Hooke  (1635-1703),  examined  a small  section 
of  cork,  which  is  the  bark  of  an  oak  tree,  and  found  it  was  made  up 
of  tiny  compartments,  like  rooms,  which  he  called  cells,  a term  which 
is  now  universally  used  for  the  unit  of  structure  in  living  things. 


STIMULI 


39 


The  name  cell  is  not  very  descriptive.  Hooke  saw  the  dead  walls 
around  tlie  spaces  tliat  during  the  life  of  the  plant  contained  living 
matter.  But  it  was  not  until  more  recent  times  that  biologists 
found  that  the  contents  of  the  cell  is  the  important  living  sub- 
stance. This  living  material  has  been  named  protoplasm  (Gr. 
protos,  first;  plasma,  formative  material).  While  we  rarely  see 
it  or  feel  it,  nevertheless  observation  has  shown  it  to  be  always 
present  where  there  is  life.  It  is  a sticky,  semi-fluid  substance, 
somewhat  like  the  white  of  an  egg  in  consistency.  Its  chemical 
composition  is  very  difficult  to  discover  and  it  is  probable  that 
there  are  a number  of  different  kinds  of  protoplasms  in  the  bodies 
of  plants  and  animals.  Under  the  microscope  it  seems  to  be  either 
granular,  or  made  of  tiny  bubbles  floating  in  a more  fluid  medium, 
or  it  sometimes  appears  to  be  made  up  of  delicate  fibers  or  threads, 
forming  a network  of  infinite  complexity.  The  cell  is  always  found 
in  the  structure  of  living  things,  just  as  bricks  make  up  the  structure 
of  a wall  or  a house. 

PROBLEM  I.  WHAT  DO  WE  MEAN  BY  REACTION  TO 
STIMULI? 

Demonstrations.  1.  Reaction  to  water.  Plant  some  bean  seeds 
in  sawdust  in  a box  with  glass  front.  Water  the  seeds  in  one  end  of 
the  box  only.  How  do  the  roots  grow? 

2.  Reaction  to  light.  Put  oxalis  or  other  plant  in  a place  where  it 
will  receive  light  on  one  side  only.  Put  some  earthworms  in  a pan 
covered  at  one  end.  What  happens  in  each  case? 

3.  Reaction  to  gravity.  Place  a pocket  garden  (see  page  142),  in 
which  radish  seeds  are  germinating,  on  end  and  then  turn  it  two  or 
three  times  at  intervals  of  24  hours.  What  happens? 

4.  Reaction  to  chemical  stimuli.  Make  observations  on  young 
seedlings  growing  in  an  excess  of  water.  What  do  you  observe?  Can 
you  offer  any  explanation? 

5.  Reaction  to  temperature.  Put  some  beans  in  moist  sawdust  in 
vessels.  Put  one  vessel  in  the  ice-box,  another  in  a moderately  warm 
room,  and  the  third  in  an  oven  where  the  temperature  is  over  160°  F. 
Observe  what  happens. 

Water.  It  is  a well-known  fact  that  living  things  need  water, 
in  order  to  sustain  life.  The  roots  of  green  plants  grow  toward  a 
source  of  water.  Some  animals  appear  to  be  stimulated  to  move 
toward  water,  whereas  others  move  away  from  moisture.  Water 
is  of  so  much  importance  to  man  that  from  the  time  of  the  Caesars 


40 


WHAT  IS  BEING  ALIVE? 


until  now  he  has  spent  enormous  sums  of  money  to  bring  pure 
water  to  his  cities. 


U.  S.  Forest  Service 


An  irrigated  ranch.  Why  is  the  vegetation  unusually  thick  along  the  water  edge  ? 

Light.  Light  is  another  important  factor  of  the  environment. 
A study  of  the  leaves  on  any  green  plant  growing  near  a window 
will  convince  one  that  the  stems  of  such  plants  grow  toward  the 
light,  and  that  the  leaves  grow  in  positions  to  get  a maximum 
amount  of  sunlight.  All  green  plants  are  thus  influenced  by  the 
sun.  We  say  an  organism  is  positively  influenced  by  a stimulus 
when  it  turns  or  moves  toward  that  stimulus,  and  that  it  is  nega- 
tively responsive  when  it  turns  or  moves  away  from  the  stimulus. 
Other  plants  which  are  not  green  seem  either  indifferent  or  nega- 
tively influenced  by  the  stimulus  of  light.  The  direction,  as  well 
as  the  intensity  of  light,  is  an  important  factor.  Animals  may  or 
may  not  be  attracted  by  light.  A moth,  for  example,  will  fly 
toward  a flame  ; an  earthworm  will  move  away  from  light.  Some 
animals  prefer  a moderate  or  weak  intensity  of  light  and  live  in 
shady  forests  or  jungles,  prowling  about  at  night.  Others  seem 
to  need  strong  light.  Man  himself  is  most  comfortable  and  works 
most  efficiently  in  a moderate  intensity  of  light. 


TKOPISIMS 


41 


Gravity.  Another  factor  influencing  both  plants  and  animals 
is  gravity.  The  main  or  top  roots  of  plants,  for  example,  tend  to 
grow  downward.  Lateral  roots,  on  the  other  hand,  grow  in  an 
approximately  horizontal  direction.  Careful  experiments  in 
which  other  forces  are  substituted  for  the  pull  of  gravity  have 
proven  that  gravity  is  the  attractive  force.  The  stem,  on  the 
other  hand,  grows  upward.  This  seems  to  be  a negative  response 
to  gravity.  Many  animals  show  this  response  to  gravity  in  very 
definite  ways.  The  maintenance  of  one’s  equilibrium  is  un- 
doubtedly a response  to  gravity,  as  has  been  proved  in  some  of 
the  lower  animals,  such  as  shrimps  and  fishes. 

Food  or  chemical  substances.  Plants  are  greatly  influenced  by 
the  presence  or  absence  of  chemical  substances  in  the  soil.  You 
have  probably  noticed  the  differences  between  plants  that  grow  near 
the  sea,  where  salt  is  found  in  the  soil,  and  those  growing  inland. 
No  one  who  has  traveled  in  a country  where  the  soil  is  impregnated 
with  alkali  can  fail  to  see  the  differences  between  vegetation  there 


and  in  other  regions  where  no  alkali  exists  but  where  similar  condi- 
tions of  temperature  and  moisture  are  found.  Since  the  mineral 
salts  of  the  soil  are  absorbed  by  the  plant  and  later  built  into  it,  we 
can  easily  see  that  responses  of  this  sort  are  of  the  utmost  importance. 

Temperature.  Living  things  are  affected  by  heat  or  cold. 
Animals  and  small  plants  that  are  able  to  move  in  the  water  fre- 


42 


WHAT  IS  BEING  ALIVE? 


quently  go  away  from  a temperature  that  becomes  unfavorable 
to  their  existence.  In  cold  weather,  green  plants  either  die  or 
temporarily  suspend  their  life  activities.  They  become  dormant. 
Likewise,  small  animals,  such  as  insects,  which  might  be  killed 
by  cold,  usually  hibernate  under  stones  or  boards.  Their  life 
activities  are  slowed  down  until  the  coming  of  warm  weather. 
Bears  and  some  other  large  animals  go  to  sleep  during  the  winter 
and  awake,  thin  and  hungry,  on  the  approach  of  warm  weather. 
Animals  and  plants  used  to  certain  temperatures  frequently  die  if 
they  are  put  in  a colder  or  hotter  climate.  Even  man,  one  of  the 
most  adaptable  of  all  animals,  cannot  stand  great  changes  without 
discomfort  and  sometimes  death.  He  heats  his  houses  in  winter 
and  sometimes  cools  them  in  summer,  so  as  to  have  the  amount 
of  heat  most  favorable  to  his  health ; namely,  about  68°  Fahrenheit. 

The  value  of  tropisms.  A study  of  hundreds  of  experiments 
with  plants  and  animals  shows  us  that  their  instinctive  responses  or 
tropisms  are  of  the  greatest  use  to  them.  Response  to  a favorable 
stimulus  results  in  placing  the  living  plant  or  animal  where  it  can  get 
food,  light,  or  more  moisture  and  thus  better  succeed  in  the  world. 
In  general,  tropisms  bring  the  plants  or  animals  into  adjustment 
with  their  environment  so  that  they  may  obtain  what  they  need  in 
order  to  succeed  in  the  surroundings  in  which  they  must  live. 

Practical  Exercise.  Make  a list  of  as  many  responses  to  stimuli  in  the  plant 
world  as  you  can  find  and  classify  them  under  the  headings  given  above.  Do 
the  same  thing  for  animals.  Then  make  a list  of  your  own  responses  and 
classify  them  in  the  same  manner.  Do  you  differ  markedly  in  your  responses 
from  plants?  From  lower  animals?  If  so,  how? 

Self-Testing  Exercise 

Tropisms  are  the  (1) (2)  of  plants  and  animals  to 

certain  (3)  in  their  (4).  Roots  of  plants  react 

(5)  to  gravity  while  the  stems  react  (6) . Roots  grow 

toward  (7),  and  leaves  usually  turn  toward  the  (8). 

Earthworms  will  move (9)  the  light.  Tropisms  help  bring  plants 

and  animals  into  (10)  with  their  (11),  so  that  they 

can  (12)  there.  Plants  are  affected  by  the  (13) 

(14)  found  in  the  soil.  Living  things  are  affected  by 

(15)  and (16). 


SKNSATION  AND  MOTION 


43 


PROBLEM  II.  HOW  ARE  LIVING  THINGS  ALIKE  AND  HOW 


DO  THEY  DIFFER? 


Laboratory  Exercise.  Compare  a living  plant  and  a living  animal, 
witli  ret'crcnce  to  life  functions.  Use  living  grasshoppers  under  glass  tum- 
blers placed  over  a bean  seedling,  a small  living  weed  or  a grass  plant. 
Use  the  text  of  the  i)roblem  which  follows  as  a laboratory  guide. 

If  we  attempt  to  compare  an  insect  with  the  plant  on  which 
it  feeds,  we  see  several  points  of  likeness  and  difference  at  once. 
Both  plant  and  insect  are  made  up  of  parts,  each  of  which,  as  the 
stem  of  the  plant  or  the  leg  of  the  insect,  appears  to  be  distinct,  but 
which  is  a part  of  the  whole  living  plant  or  animal.  Each  part  of 
the  living  plant  or  animal  which  has  a separate  work  to  do  is  called 
an  organ.  Plants  and  animals,  therefore,  are  spoken  of  as  organisms. 


abdComen. 


Read  your  text  carefully  and  compare  the  uses  of  the  parts  of  the  plant 
and  the  insect  given  in  the  diagram. 


In  spite  of  the  apparent  differences  between  a green  plant,  such 
as  a tree,  and  an  animal,  like  the  grasshopper,  the  life  functions 
or  processes  are  very  similar,  as  we  shall  see  in  the  paragraphs  that 
follow. 

Irritability  and  motion.  We  have  already  shown  that  all  living 
things  respond  to  various  stimuli.  The  stem  of  a green  plant 
turns  toward  the  light,  an  earthworm  shuns  the  sun’s  rays.  Plants, 
as  well  as  animals,  move,  as  is  observed  in  the  movements  of  roots 
toward  a source  of  water,  or  the  movements  of  fish  in  a stream 
so  that  they  head  up  against  the  current. 


44 


WHAT  IS  BEING  ALIVE? 


In  what  ways  are  the  circulations  of  a plant  and  an  animal  alike  ? 
In  what  ways  do  they  differ  ? 


Food  taking.  It  is  not  so  easy  to  prove  at  this  time  that  all  living 
things  take  food.  We  know  animals  will  die  without  a food 

supply.  We  also 
know  that  some 
plants,  like  molds 
or  mildews,  grow 
on  food  substances. 
But  green  plants 
live  in  soil  appar- 
ently without  food 
if  they  have  a mod- 
erate water  supply. 
This  is  possible  be- 
cause green  plants 
make  organic  food 
substances  out  of 
the  materials  ob- 
tained from  the 
soil,  of  water,  and 
a part  of  the  air.  Both  plants  and  animals  use  organic  food  sub- 
stances in  exactly  the  same  way,  that  is,  they  get  energy  out  of 
them  to  do  work,  and  they  build  up  their  bodily  material  out  of 
the  food  they  use. 

Respiration.  Respiration  is  the  process  by  which  oxygen  is 
supplied  to  the  body  cells  and  carbon  dioxide  is  removed.  As  a 
result  food  is  oxidized  and  energy  is  released.  The  processes  are 
the  same  in  both  plants  and  animals  as  will  be  shown  in  detail 
later.  Plants  release  enough  energy  to  force  their  way  through 
the  compact  earth;  animals  release  their  energy  in  the  activity 
we  associate  with  running,  swimming,  flying,  etc. 

Nutrition.  The  foods  of  plants  and  animals  must  be  made 
liquid  so  that  they  may  pass  freely  to  various  parts  of  the  organism 
to  be  used  there.  In  order  to  do  this  they  must  be  digested,  or 
changed  to  a form  that  will  enable  it  to  be  taken  in  by  the  smallest 
units  of  body  structure,  the  cells.  The  way  this  is  done  will  form 
the  basis  of  an  important  problem  later  on  in  our  course.  Then 
these  foods  must  be  absorbed  or  taken  into  the  organs  of  circulation, 


FUXCTIOXS  OF  LIVIXG  THINGS 


45 


which  are  woody  tubes  in  plants  and  blood  vessels  in  animals. 
Then  this  digested  food  must  finally  become  part  of  the  living 
organism  by  as^^itniladon. 

Excretion.  Wastes,  such  as  water,  carbon  dioxide,  and  urea,  arc 
formed  in  the  body  by  oxidation  and  other  changes.  If  these  wastes 
are  not  eliminated  at  once,  they  interfere  with  the  normal  working 
of  the  bod}".  Therefore  excretion  is  a necessary  body  function. 

Reproduction.  Reiiroduction,  or  the  formation  of  new  organisms, 
is  the  outcome  of  all  the  nutritive  processes.  Plants  and  animals 
have  various  methods  of  giving  rise  to  new  plants  and  animals. 
Put  the  result  is  the  same  in  both  cases ; that  mysterious  something 
we  call  life  is  started  again  as  a seed,  an  egg,  or  a baby  animal  to 
become  in  time  a parent  of  another  generation  of  life.  Some  of 
the  material  in  the  following  units  deal  with  this  life  function. 

Practical  Exercise.  List  for  comparison  the  evidences  of  life  processes  (men- 
tioned in  preceding  paragraphs)  in  a common  plant  and  in  an  animal. 


H.  Armstrong  Roberts 

Animals  and  plants  give  rise  to  new  organisms.  These  offspring  resemble  their  parents  and 
each  other.  Yet,  very  seldom  do  we  find  two  individuals  exactly  alike. 


Self-Testing  Exercise 

Living  things,  because  they  are (1)  of (2)  are  called 

organisms.  Both  plants  and  animals  have  similar  (3), 


46 


WHAT  IS  BEING  ALIVE? 


They  both  respond  to (4),  use (5)  to  grow  or  release 

....,...(6),  and  respire.  Nutrition  is  the  process  by  which  living 
things (8), (9),  (10),  and (11)  food. 


PROBLEM  III.  WHAT  ARE  CELLS  AND  HOW  DO  THEY 
PRODUCE  OTHERS? 


Laboratory  Exercise.  Put  a drop  of  muddy  water  on  a slide.  Cover 
with  a cover  slide  and  observe  it  under  a compound  microscope.  Adjust 
the  lenses  until  the  particles  in  the  water  can  be  plainly  seen. 

Scrape,  with  a sterilized  toothpick,  the  membrane  on  the  inside  of  the 
cheek.  Place  a small  bit  of  the  material  in  a drop  of  pure  water  on  a glass 

slide  and  stain  it  with  a small 
drop  of  diluted  fountain  pen 
ink  or  methylene  blue.  Notice 
the  irregular  blue  structures  or 
cells.  Find  a deeper  blue  body 
inside  the  cell.  This  is  the 
nucleus.  The  outer  faint  blue 
line  marking  the  edge  of  the 
cell  is  the  cell  membrane. 

Peel  the  skin  from  one  of 
the  fleshy  leaves  forming  an 
onion  bulb,  mount  a small  bit 
of  it  in  water  to  which  is 
added  a drop  of  dilute  tinc- 
ture of  iodine.  Examine  it 
under  a microscope.  Note 
Chlonoplast  the  cells.  Plant  cells  differ 
from  animal  cells  in  that  they 
have  a delicate  wood  wall  out- 
side the  membrane.  Draw 
two  or  three  animal  and  plant 
cells  in  your  notebook.  Make 
each  cell  at  least  one  inch  in 
diameter.  Label  all  parts. 


. jiiDileus 


.Cell  wall 


-vacuole 


:ytoplasm 


What  are  the  characteristics  of  a plant  cell! 
does  Elodea  differ  from  animal  cells? 


An  examination  of  the  delicate  leaves  of  the  Elodea,  a water 
plant  used  in  aquariums,  shows  cells  with  many  large  spaces  or 
vacuoles,  which  are  filled  with  a non-living  fluid  instead  of  proto- 
plasm. Forming  a part  of  the  protoplasm  are  many  small  ovoid 
bodies,  most  of  which  are  green  in  color.  These  are  the  chloroplasts 
(klo'rd-plasts)  or  chlorophyll  (klo'ro-fil)  bodies  (Gr.  chloros,  green ; 
phyllon,  leaf).  We  shall  see  later  that  they  are  of  the  utmost  im- 
portance to  each  one  of  us,  as  it  is  by  means  of  the  action  of  the  sun 
upon  them  that  food  is  manufactured  in  the  green  parts  of  plants. 


TlSSl'KS  AND  OIKJANS 


47 


III  living  I’ilodoa,  an  interesting  phenomenon  may  be  observed. 
Tlie  protoplasm  in  tlie  cell  body  is  seen  to  be  constantly  in  motion, 
flowing  slowly  in  the  direc- 
tion of  the  arrows  shown 
in  the  diagram.  This 
streaming  of  protoplasm  is 
one  of  the  manifestations 
of  life  within  the  cell.  In 
many  cells  this  movement 
may  be  observed,  and  we 
have  reason  to  believe  that 
the  protoplasm  in  most 
living  cells  is  in  motion, 
thus  affording  a circulation 
of  the  cell  contents. 

Tissues  and  organs.  The 
cells  which  form  certain 
parts  of  the  veins,  the  flat 
blade,  or  other  portions  of  a leaf,  are  found  in  groups  or  aggrega- 
tions, and  are  more  or  less  alike  in  size  and  shape.  Such  a 
collection  of  cells  is  called  a tissue.  Examples  of  tissues  in  ani- 
mals are  the  cells 
covering  the  outside 
of  the  body,  forming 
the  skin  or  epidermal 
tissue ; muscle  tis- 
sue, which  produces 
movement;  and 
bony  tissue,  which 
forms  the  framework 
to  which  the  muscles 
are  attached.  Tissue 
cells  often  differ 
greatly  in  size  and 
shape.  A large  plant  or  animal  is  ordinarily  made  up  of  more, 
not  larger,  cells  than  a smaller  organism. 

Collections  of  tissues  which  act  together  in  the  performance  of 


Cells,  tissues,  and  organs  in  plants  and  animals.  Explain 
this  illustration. 


Onion  cells  and  epithelial  cells.  In  what  ways  are 
these  plant  and  animal  cells  alike  ? In  what  ways  are 
they  different? 


48 


WHAT  IS  BEING  ALIVE? 


work  form  organs.  Such  an  organ  is  a leaf,  made  of  supporting 
cells,  green  cells,  spongy  cells,  etc. ; or  the  human  arm,  with  its 
bony  supporting  tissue,  its  nerves  and  muscles,  its  blood  vessels 
and  connective  tissue. 

How  cells  form  others.  Cells  can  grow  only  to  a certain  size. 
When  this  limit  is  reached,  the  cell  splits,  forming  two  cells.  In 
this  process,  which  is  of  very  great  importance  in  the  growth  of 
both  plants  and  animals,  the  nucleus  elongates  and  divides ; the 
halves  separate  and  go  to  opposite  ends  of  the  cell.  Then  the  rest 
of  the  protoplasm  divides  equally  and  two  cells  are  formed,  each 


Plant  and  animal  cells  multiply  by  division. 


containing  a nucleus.  Each  cell  will  have  exactly  the  same  char- 
acteristics possessed  by  the  original  cell.  This  process  is  known  as 
direct  cell  division.  Usually  a more  complicated  process  of  division 
known  as  mitosis  occurs  in  most  cells.  See  diagram  on  page  49. 

The  chromosomes  and  their  functions.  If  we  now  examine  a 
specially  prepared  and  stained  cell,  for  example,  the  egg  cell  of  a 
worm  or  a frog,  we  shall  find  that  the  nucleus,  when  stained  with 
certain  dyes,  shows  numerous  small  deeply  stained  bodies  within 
it.  These  structures  are  called  chromosomes  (kro'md-somz ; 
Gr.  chro7na,  color;  soma,  body),  or  color-bearing  bodies.  The 
number  of  these  chromosomes  in  each  body  cell  of  a given  kind  of 
plant  or  animal  is  always  the  same.  For  example,  forty-eight  are 
found  in  man,  four  in  a certain  worm,  and  eight  in  one  kind  of  lily. 
In  plants  and  animals  there  are  two  distinct  kinds  of  cells,  one 
group  called  the  sornatic  or  body  cells,  which  form  the  bulk  of  the 
body,  and  the  sex  cells  which  pass  on  the  heredity  qualities  to  the 
next  generation.  The  sex  cells  are  able  to  do  this  by  means  of 


CELL  DIVISION 


49 


the  chromosomes,  wiiicli  are  believed  to  be  the  bearers  of  the 
hereditary  qualities  which  can  be  handed  down  from  parent  to 


An  animal  cell  showing  mitotic  division.  During  this  division  the  chromatin  granules  form 
a coiled  thread  which  finally  breaks  up  into  chromosomes.  Each  chromosome  splits  into  two 
similar  parts  which  go  to  the  opposite  ends  of  the  cell,  where  they  become  a part  of  two 
new  nuclei.  At  the  same  time  a small  structure,  the  centrosome,  separates  into  two  parts.  A 
wall  forms  midway  between  the  two  nuclei,  and  the  cell  divides,  forming  two  cells. 


Self-Testing  Exercise 

Cells  are  the  units  of (1)  of  plants  and  animals.  A plant 

cell  differs  from  an  animal  cell  by  having  a (2) (3)  and 

containing (4).  All  cells  contain  a (5).  Cells  grow 

by (6).  Hereditary  qualities  are  handed  down  from  one 

generation  to  another  by  means  of  the (7)  in  the (8) 

(9).  A collection  of  like  cells  is  called  a (10). 

An  organ  is  made  up  of  a (11)  of (12)  acting  to- 
gether to  do (13). 


PROBLEM  IV.  WHAT  DO  WE  MEAN  BY  ADAPTATION? 

Demonstration  6.  Show  by  means  of  charts,  pictures,  and  actual 
examples,  a number  of  adaptations  such  as  bills  and  legs  of  birds  ; wings 
of  insects ; teeth  of  carnivorous  animals.  Protective  coloring  in  in- 
sects, and  adaptations  in  plants,  especially  in  cactus,  pitcher  plant, 


50 


WHAT  IS  BEING  ALIVE? 


Mention  several  ways  in  which  this  cactus  is  fitted  to  live  in 
the  desert. 


and  thistle,  are  strik- 
ing examples.  Op- 
portunity should  be 
given  for  all  members 
of  the  group  to  go,  if 
possible,  to  a good 
museum  where  such 
material  is  on  dis- 
play. 

Practical  Exercise. 

List  as  many  different 
examples  of  plant  and 
animal  adaptations  as 
you  can.  Be  prepared 
to  explain  them  before 
the  class.  If  possible, 
bring  to  class  examples 
or  diagrams  of  the 
animals  or  the  plants 
which  show  these  adap- 
tations. 


Adaptability,  a function  of  living  things.  Not  only  are  plants 
and  animals  fitted  to  live  under  certain  conditions,  but  each  part 


of  their  bodies  may  be  fitted  to  do  certain  work.  I notice  that  as 
I write  the  fingers  of  my  right  hand  grasp  the  pen  firmly  and  the 
hand  and  arm  execute  some  very  complicated  movements.  This 

they  are  able  to  do 
because  of  the  move- 
ment made  possible 
by  the  arrangement 
of  the  delicate  bones 
of  the  arm,  a complex 
system  of  muscles 
which  move  the 
bones,  and  a direct- 
ing nervous  system 
which  plans  the  work. 
Because  of  the  pe- 
culiar fitness  in  the 
structure  of  the  hand 
for  this  work  we  say 
it  adapted  to  its 


Wright  Pierce 


How  does  the  beak  of  the  eagle  fit  it  for  catching  and  using  it§ 
food? 


ADAPTATIONS 


51 


How  is  this  low  plant  with  large  succulent  leaves  fitted  to  live 
in  a desert  ? 


function  of  ^nispin.c; 
objects.  A stnictiiri' 
which  is  useful  to  an 
orj!:anisni  in  some 
special  wa}'  is  called 
an  adaptation. 

I’lach  part  of  a 
plant  or  animal  is 
usually  suited  for 
some  particular 
work.  The  root  of 
a green  plant,  for 
example,  is  able  to 
take  in  water  by 
having  tiii}^  absorb- 
ing root  hairs  grow- 
ing from  it.  The  stems  have  tubes  to  convey  liquids  up  and 
down  from  roots  to  leaves,  and  are  strong  enough  to  support  the 
leafy  part  of  the  plant.  The  thin,  flat  leaves  are  arranged  to  re- 
ceive a very  large  amount  of  sunlight  and  to  act  as  solar  engines, 
that  is,  using  energy  from  the  sun.  Each  part  of  a plant  does 
work,  and  is  fitted, 
by  means  of  certain 
structures,  to  do  that 
work.  The  lungs  of 
a land  animal  are  able 
to  take  oxygen  from 
the  air,  while  the  gills 
of  a fish  can  take  their 
supply  of  oxygen 
only  from  the  water; 
that  is,  from  the  air 
that  is  dissolved  in 
water.  It  is  because 
of  such  adaptations 
that  organisms  are 
able  to  live  within 


Wright  Pierce 

What  might  be  the  advantages  of  a large  flat  leaf  to  a plant  ? 


LIBRARY  OF  THE  UNIVERSITY 

OF  ALBERTA 


52 


WHAT  IS  BEING  ALIVE? 


their  particular  environments.  Some  adaptations  are  protective, 
as  the  bark  of  trees,  the  spines  or  thorns  on  some  plants,  the  shells 
of  turtles,  the  feathers  of  birds,  the  heavy  hairy  coats  of  a dog  or 
a cat,  the  strong  teeth  of  a tiger.  The  trunk  of  the  elephant,  the 
long  neck  of  the  giraffe,  the  pouch  of  the  kangaroo,  the  flipper  of 
the  whale,  or  the  web  on  the  wing  of  the  bat  are  all  adaptations 
for  various  purposes. 

Practical  Exercise.  Classify  the  above  adaptations  according  to  their 
specific  uses.  Make  a table  giving  at  least  five  kinds  of  adaptations  found 
in  plants,  and  five  kinds  found  in  animals. 

Self-Testing  Exercise 

An  adaptation  is  a (1)  that  is (2)  to  an  organism 

in  some  (3).  By  means  of  (4),  (5)  and 

(6)  are  enabled  to  (7)  in  various  environments. 

Without  adaptations (8)  would  be  impossible. 

Review  Summary 

Test  your  knowledge  of  the  unit  by : (1)  Answering  and  rechecking  the 
survey  questions;  (2)  performing  the  assigned  exercises;  (3)  checking  with 
the  teacher  your  scores  on  the  various  tests,  and  if  you  do  not  have  a perfect 
score,  try  again  the  parts  you  missed  ; (4)  doing  as  much  of  the  optional  work 
as  has  been  assigned  to  you ; and  finally  filling  in  the  following  outline  as  fully 
as  possible  for  your  notebook. 

Functions  of  living  things 
Reaction  to  stimuli 
water 
light 
gravity 

chemical  substances 
temperatures 
value  of 
Food  taking 
Respiration 

Test  on  Fundamental  Concepts 

Make  two  columns  on  your  notebook.  Head  one  CORRECT,  the  other  INCORRECT. 
Place  in  these  columns  the  numbers  of  the  sentences  you  think  are  right  and  those  you  think 
are  wrong.  Your  grade  will  be  the  number  correct  X 4. 

I.  Tropisms  (1)  are  reactions  to  the  various  stimuli  in  the  environ- 
ment ; (2)  are  structures  which  cause  reactions  to  stimuli ; (3)  make 
it  possible  for  green  plants  to  live  without  the  sun ; (4)  are  brought 
about  by  food,  water,  light,  heat,  chemical  substances,  and  other  factors 
of  the  environment ; (5)  bring  the  organism  into  adjustment  with  its 
environment. 


Nutrition 
Excretion 
Reproduction 
Cell  unit  of  structure 
parts 

functions  of 
formation  of 
Adaptations 
of  living  things 


TESTS 


53 


II.  Both  plants  and  animals  (6)  arc  made  up  of  cells  : (7)  react  to 
stimuli;  (S)  have  tlie  same  life  i)roccsses ; sensation,  motion,  respira- 
tion, nutrition,  excretion,  and  rcj)roduction  ; (9)  make  food  ; (10)  re- 
lease cncv^y  from  their  food  in  order  to  do  work. 

III.  Cells  (11)  are  made  of  living  material ; (12)  arc  always  green  in 
color;  (13)  all  contain  nuclei;  (14)  in  both  plants  and  animals  are 
exactly  alike ; (15)  are  units  of  building  material  in  living  things. 

IV.  Growth  in  organisms  takes  place  (16)  by  increase  in  the  size  of 
the  cells  ; (17)  by  increase  in  the  number  of  the  cells  ; (18)  by  increase 
in  the  number  of  chromosomes  in  the  cells  ; (19)  when  cells  composing 
them  divide ; (20)  when  the  living  matter  takes  in  more  food. 

V.  A living  thing  (21)  is  adapted  to  live  in  a given  environment  when 
it  has  structures  which  fit  it  for  that  life ; (22)  is  adapted  to  do  a given 
piece  of  work  when  it  has  structures  that  fit  it  for  that  work ; (23)  may 
adapt  itself  to  any  environment ; (24)  reacts  to  stimuli ; (25)  will  die 
if  taken  from  its  original  environment. 

Achievement  Test 

1.  How  do  plants  or  animals  react  to  stimuli? 

2.  How  would  you  perform  at  least  one  experiment  to  show  tropism  ? 

3.  How  can  you  distinguish  between  living  and  non-living  things? 

4.  Have  you  seen  a cell?  Name  the  parts  and  uses  of  each  part. 

5.  How  can  you  make  a classification  of  adaptations  and  show 
clearly  just  what  you  mean  by  this  classification? 

Practical  Problems 

1.  Show  specifically  how  man  has  made  use  of  the  fact  that  certain 
plants  or  animals  react  to  the  stimulus  of  light. 

2.  Prove  how  some  tropism  is  of  value  to  a plant ; to  an  animal. 

3.  Explain  fully  how  your  leg  is  adapted  to  its  uses. 

Useful  References 

Burlingame  and  others.  General  Biology.  Holt,  1928. 

Caldwell,  Skinner,  and  Tietz,  Biological  Foundations  of  Education.  Ginn. 
1931. 

Plunkett,  Outlines  of  Modern  Biology.  Holt,  1934. 

Shipley,  Hunting  under  the  Microscope.  Macmillan,  1928. 

Wells,  Huxley,  and  Wells,  The  Science  of  Life.  Doubleday,  Doran,  1934. 


H.  BIO  — 5 


SURVEY  QUESTIONS 

Do  you  think  it  is  true  that  plants  and  animals  depend  on  each  other  ? 
Can  you  give  any  examples  to  prove  this  ? Can  you  distinguish  between 
full-grown  and  baby  insects  ? Do  you  know  why  insects  are  numerous  ? 
Why  do  insects  visit  flowers  ? Do  you  know  why  seeds  are  formed  ? 


UNIT  III 

HOW  ARE  ANIMALS  AND  PLANTS  MUTUALLY 
DEPENDENT? 

Preview.  Anyone  who  has  been  in  the  field  cannot  help  thinking 
that  insects  have  something  to  do  with  flowers  and  green  plants. 
Grasshoppers  eat  the  green  leaves,  beetles  crawl  over  the  golden- 
rods,  butterflies  light  on  flowers  or  deposit  their  eggs  on  some 
plant  that  their  young  will  use  as  food.  Almost  everywhere  honey- 
bees can  be  seen  busily  at  work  among  the  flowers.  What  are  they 
all  doing?'  Is  it  something  that  we  can  discover  for  ourselves? 

If  we  were  to  take  a single  tree  for  observation,  we  might  find 
birds  nesting  in  the  branches ; perhaps  a squirrel  or  two  has  a home 
there  ; insects  of  many  kinds  may  be  found  on  its  leaves,  or  under 

54 


PRRVIKW 


55 


its  bark  ; while  an  examination  of  ilie  soil  around  its  roots  would 
show  us  many  other  living;  forms  such  as  the  pupae  and  nymphs  of 
insects.  Perhaps  our  tree  might  have  queer  looking  growths  called 
galls  on  the  leaves  or  stems.  Those,  if  examined,  would  be  found 
to  b('  the  homes  of  tiny  insects  and  bacteria.  If  the  tree  had 
flow('rs  we  should  be  sure  to  see  numerous  insects  on  them. 

I'^ach  insect  has  its  own  favorite  food  plant  or  plants,  and  in 
many  cases  the  eggs  are  laid  on  the  plant  so  that  the  young  may 
have  food  close  at  hand.  Some  insects  like  the  rotted  wood  of 
trees.  An  American  zoologist,  Packard,  has  listed  462  species 
of  insects  that  live  upon  oak  trees  alone.  Everywhere  insects  are 
engaged  in  taking  their  nourishment  from  plants,  and  millions  of 
dollars  of  damage  is  done  every  year  to  gardens,  fruits,  and  cereal 
crops  by  these  animals.  Insects  in  turn  are  the  food  of  birds ; 
cats  and  dogs  may  kill  birds  ; lions  and  tigers  live  on  large  defense- 
less animals  such  as  deer  or  cattle ; and  finally,  man  eats  the 
bodies  of  both  plants  and  animals.  But  if  we  reduce  this  search 
for  food  to  its  final  limit,  we  see  that  green  plants  provide  all  the 
food  for  animals.  For  the  lion  or  tiger  eats  the  deer  which  feeds 
upon  grass  or  green  shoots  of  young  trees,  and  the  cat  eats  the  bird 
that  lives  on  weed  seeds  or  on  insects  that  eat  plants.  Green 
plants  supply  the  food  of  the  world. 

On  a field  trip  no  one  can  fail  to  observe  that  plants  often  give 
animals  a home.  The  grass  shelters  grasshoppers  and  smaller 
insects.  Some  insects,  such  as  the  tent  caterpillar,  build  their 
homes  in  the  trees  or  bushes  on  which  they  feed,  while  others 
tunnel  through  the  wood,  making  homes  there.  Spiders  build 
webs  on  plants,  often  using  the  leaves  for  shelter.  Birds  nest  in 
trees,  and  many  wild  animals  use  the  forest  as  their  home.  Man 
has  learned  to  use  many  kinds  of  plant  products  to  aid  him  in 
making  his  home,  wood  and  various  fibers  being  the  most  important 
of  these  products. 

So  far  it  has  seemed  as  if  green  plants  benefited  animals  and 
received  nothing  in  return.  We  shall  see  later  that  plants  and 
animals  together  form  a balance  of  life  on  the  earth  and  that  each 
is  necessary  for  the  other.  Certain  substances  found  in  the 
body  wastes  of  animals  are  necessary  to  the  life  of  a green  plant. 


56  HOW  ARE  ANIMALS  AND  PLANTS  DEPENDENT? 

One  of  the  most  interesting  relationships  for  study  are  those 
that  exist  between  insects  and  flowers.  Flowering  plants,  as  we 
know,  produce  seeds  and  fruits,  and  from  these  come  new  genera- 
tions of  plants.  Not  all  of  us  realize,  however,  the  very  close 
dependence  of  these  plants  on  the  insects  that  visit  them.  If  it 
were  not  for  these  insect  visits,  many  plants  would  not  produce 
seeds. 

In  the  latter  part  of  the  eighteenth  century  a German  named 
Christian  Konrad  Sprengel  worked  out  the  facts  that  the  structure 
of  certain  flowers  seemed  to  be  adapted  to  the  visits  of  insects. 
Certain  facilities  were  offered  to  an  insect  in  the  way  of  easy  foot- 
hold, sweet  odor,  and  food  in  the  shape  of  pollen  and  nectar,  the 
latter  a sweet-tasting  substance  manufactured  by  certain  parts  of 
the  flower  known  as  the  nectar  glands.  Sprengel  further  dis- 
covered the  fact  that  pollen  could  be  and  was  carried  by  insect 
visitors  from  the  anthers  or  pollen-bearing  organ  of  the  flower  to 
the  top  of  the  part  that  produced  the  seeds.  It  was  not  until  the 
middle  of  the  nineteenth  century,  however,  that  an  Englishman, 
Charles  Darwin,  worked  out  further  the  relation  of  insects  to 
flowers  by  his  investigations  on  the  cross-pollination  of  flowers. 
By  this  we  mean  the  transfer  of  pollen  from  the  pollen-producing 
organ  of  one  flower  to  the  seed-producing  organ  of  another  flower 
of  the  same  kind. 

Many  species  of  flowers  are  self-pollinated,  but  Charles  Darwin 
found  that  some  flowers  which  were  self-pollinated  did  not  produce 
as  many  seeds,  and  that  the  plants  which  grew  from  their  seeds 
were  smaller  and  weaker  than  plants  from  seeds  produced  by 
cross-pollinated  flowers  of  the  same  kind.  He  also  found  that 
plants  grown  from  cross-pollinated  seeds  tended  to  vary  more 
than  those  grown  from  self-pollinated  seeds.  This  has  an  important 
bearing,  as  we  shall  see  later,  in  the  production  of  new  varieties 
of  plants.  Darwin  studied  for  many  years  the  pollination  of 
flowers,  and  discovered  in  almost  every  case  that  showy,  sweet- 
scented,  or  otherwise  attractive  flowers  were  most  likely  to  be 
cross-pollinated  by  insects.  He  also  found  that,  in  the  case  of 
flowers  that  were  inconspicuous  in  appearance,  often  a compensa- 
tion appeared  in  the  odor  which  apparently  rendered  them  attrac- 


INSECTS  AND  FLOWERING  PLANTS 


57 


tive  to  certain  insects.  The  so-called  carrion  flowers,  pollinated 
by  flies,  are  good  examples,  their  odor  being  like  that  of  decayed 
flesh.  Other  flowers,  which  open  at  night,  are  white  and  provided 
with  a powerful  scent  so  as  to  attract  night-flying  moths  and  other 
insects.  All  these  and  many  other  interesting  facts  about  insects 
and  flowers  and  their  interrelationships  will  be  found  in  the  pages 
that  follow. 

PROBLEM  I.  WHAT  ARE  SOME  OF  THE  INTERRELATIONS 
BETWEEN  PLANTS  AND  ANIMALS? 

Field  Exercise.  To  determine  whether  conditions  of  mutual  aid  exist 

between  insects  and  flowering  plants. 

Materials.  An  insect  net,  cigar  boxes  containing  sheets  of  cork, 
insect  pins,  and  a cyanide  bottle  are  useful.  (Caution:  Do  not  smell 
the  cyanide  : the  fumes  are  deadly  poison.) 

Object  of  trip.  The  object  of  this  trip  is  threefold ; 

1.  To  find  out  some  of  the  relations  of  mutual  help  existing  between 
plants  and  animals. 

2.  To  learn  to  know  a fev/  common  insects,  and  to  collect  them  for 
later  study. 

3.  To  have  such  an  enjoyable  time  that  you  will  wish  to  go  again 
by  yourself. 

Method.  Your  trip  should  include  fields  and  waste  lots  covered  with 
weeds  and  trees.  Look  for  six-legged  animals  (insects)  on  plants. 
Do  they  receive  any  protection  from  such  plants?  Shelter?  Food? 
Give  examples  under  each  of  these  headings.  Do  you  find  any  insects 
laying  their  eggs  upon  plants?  Why  do  you  think  they  do  this? 

Follow  a bee  until  it  alights  on  a flower.  Try  to  find  out  exactly 
what  it  gets  from  the  flower  and  how  it  does  it.  Now  observe  where 
it  goes  next.  Do  bees  visit  flowers  of  the  same  kind  in  succession? 

Look  for  other  flying  insects  that  are  on  flowers.  (Extra  credit 
may  be  given  for  the  working  out  of  the  relation  between  a butterfly 
and  a flower.) 

Carefully  observe  the  goldenrod  blossoms  for  yellow  and  black 
beetles  (locust  borer)  about  an  inch  long.  What  are  they  doing? 
Observe  grasshoppers  or  other  insects  on  stalks  of  grass.  What  are 
they  doing  there? 

Strip  the  bark  from  fallen  trees.  Look  carefully  for  any  signs  of 
living  things.  Collect  any  living  animals  you  may  see.  If  a small 
stream  or  pond  is  available,  scrape  or  dredge  through  the  aquatic 
plants  near  the  shore  and  see  what  animals  you  can  find.  What  are 
they  doing  there? 

pig  into  rich  soil  near  the  roots  of  grain  or  other  plants  and  note  what 
living  animals  may  be  there.  Ask  help  from  your  instructor  in  their 
identification. 


58  HOW  ARE  ANIMALS  AND  PLANTS  DEPENDENT? 


Laboratory  Exercise.  How  to  identify  an  insect.  If  possible,  use 
a living  bee  from  an  observation  hive,  although  some  observation  may 
be  made  in  the  field  and  reported  to  the  class. 

Examine  its  body  carefully.  Notice  that  it  has  three  regions  : a front 
part  or  head;  a middle  part,  the  thorax,  divided  into  three  portions  or 
segments;  and  a hind  portion,  segmented  ^ and  hairy,  the  abdomen. 

How  many  pairs  of  legs  does  it  have  ? The  legs,  jointed  and  provided 
with  tiny  hooks  at  the  end,  are  attached  to  the  thorax.  Two  pairs 
of  delicate  wings  are  attached  to  the  upper  or  dorsal  side  of  the  thorax. 
To  which  segments  of  the  thorax  are  they  attached?  The  entire  body 
has  a tough  covering  or  exoskeleton  composed  of  chitin  (kitin),  a sub- 
stance chemically  much  like  a cow’s  horn.  This  exoskeleton  in  the 
bee  is  partly  covered  with  tiny  hairs  which  form  a vesture  ^ over  the 
body.  The  muscles,  which  provide  for  movement,  are  fastened  to 
the  interior  of  the  exoskeleton,  for  there  is  no  internal  skeleton. 

Is  there  any  movement  of  the  abdomen  of  a living  bee  ? The  animal 
breathes  through  tiny  openings  called  spiracles  (spir'd-k’l),  which  are 
found  on  each  segment  of  the  abdomen  and  lead  into  branching  air 
tubes.  Bees  have  compound  eyes  composed  of  numerous  units  called 
ommitidia.  Simple  eyes  or  ocelli  are  usually  also  present.  Bees  are 
provided  with  a pair  of  jointed  feelers  called  antennae.  Wings  are 
not  found  on  all  insects,  nor  is  a vesture ; but  the  other  structures  just 
given  are  characteristics  of  the  great  group  of  animals  we  call  insects. 


The  honeybee.  How  many  of  the  parts  labtled  here  can  you  find  on  your  specimen? 


Common  forms  of  insects.  Inasmuch  as  there  are  more  than 
450,000  different  kinds  of  insects,  it  is  evident  that  it  would  be  a 
hopeless  task  for  us  even  to  attempt  to  recognize  all  of  them. 

1 Segmented  (seg'ment-ed)  : separated  into  sections  or  parts. 

2 Vesture  (ves'tur)  : a covering. 


COMMON  FOUMS  OF  INSFCTS 


59 


Hut  \vc  can  luarn  to  distinguish  a few  examples  of  the  common 
forms  that  might  be  seen  on  a field  trip.  In  the  fields,  on  grass,  or 
(Ml  flowering  plants  we  may  find  members  from  at  least  six  of 
the  twenty  orders  of  insects.  These  may  be  known  by  the  follow- 
ing characters : 

The  order  II ijmenoptera  (hi-men-op'ter-d,  membrane  wings), 
to  which  the  bees,  wasps,  and  ants  belong,  is  the  only  insect  order 
of  which  some  of  the  members  are  provided  with  true  stings. 
This  sting  is  placed  in  a sheath  at  the  extreme  hind  end  of  the  abdo- 
men. All  structures  which  the  honey  bee  has  are  possessed  by 
this  group  of  insects. 

Butterflies  and  moths  will  be  found  hovering  over  flowers. 
They  belong  to  the  order  Lepidoptera  (lep-i-dop'ter-d,  scaled 
wings)  (see  p.  68).  This  name  is  given  to  them  because  their 
wings  are  covered  with  tiny  scales,  which  fit  into  little  sockets 
much  as  shingles  are  placed  on  a roof.  The  wings  are  always 
large  and  usually  brightly  colored;  the  legs  are  small,  and 
one  pair  of  them  is  often  inconspicuous.  These  insects  take 
liquid  food  through  a long  tubelike  organ,  called  the  proboscis 
(pr6-b6s'is). 

Grasshoppers,  found  almost  everywhere,  katydids,  and  crickets, 
black  grasshopper-like  insects  often  found  under  stones,  belong  to 
the  order  Orthoptera  (6r-th6p'ter-d,  straight  wings).  Members  of 
this  group  may  usually  be  distinguished  by  their  strong,  jumping 
hind  legs,  by  their  chewing  or  biting  mouth  parts,  and  by  the  fact 
that  the  hind  wings  are  folded  up  under  the  somewhat  stiffer 
front  wings. 

Another  group  of  insects  sometimes  found  on  flowers  in  the  fall 
are  flies.  They  belong  to  the  order  Diptera  (dip'ter-d,  two  wings). 
These  insects  are  usually  rather  small  and  have  a single  pair  of  gauzy 
wings.  Some  of  man’s  worst  enemies  are  found  in  this  group  of  in- 
sects, which  includes  the  house  fly,  mosquitoes,  stable  fly,  and  botfly. 

Bugs,  members  of  the  order  Hemiptera  (he-mip'ter-d,  half 
wing),  have  mouth  parts  that  are  fitted  for  piercing  and  sucking. 
They  are  usually  small  and  many  of  them  have  a pair  of  delicate 
membranous  wings  covered  with  outer  wings  which  are  somewhat 
thickened. 


60  HOW  ARE  ANIMALS  AND  PLANTS  DEPENDENT? 


The  cicadas,  aphids, 
and  scale  insects  belong 
to  the  order  Homoptera 
(ho-mop'ter-d,  similar 
wings).  Their  mouth- 
parts  are  formed  for 
sucking. 

The  beetles  belong 
to  the  order  Coleop- 
tera  (kol-e-op'ter-d, 
sheath  wings),  and  are 

A wasp  stinging  a caterpillar.  Why  is  the  wasp  a member  often  Called  ^ ‘ buSS  ’ ’ 
of  Hymenoptera  ? ® 

by  the  uninformed. 
Any  beetle  will  show  the  following  characteristics : The  body  is 
usually  heavy  and  broad.  Its  exoskeleton  is  hard  and  tough. 
This  chitinous  body  covering  is  better  developed  in  the  beetles 
than  in  any  other  of  the  insects.  The  three  pairs  of  legs  are 


C.  Clarke 


Notice  the  differences  in  the  two  grasshoppers  shown  here.  The  male  grasshopper  has  a 
rounded  abdomen  while  the  abdomen  of  the  female  is  more  taper'ng  and  ends  in  an  ovipositor 
Or  egg  depositor,  formed  from  blunt  spines.  Which  of  the  above  insects  is  the  female  ? 


COMMON  FORMS  OF  INSECTS 


61 


stout  and  ratlicr  short. 
Tlic  outer  wiiij^s  are 
hard  anti  tit  like  a 
sliield  over  the  under 
wings,  which  are  efti- 
eient  organs  of  flight. 
The  mouth  parts,  pro- 
vided witli  an  upper 
and  lower  lip,  arc  fitted 
for  biting.  They  con- 
sist of  heav}'-  curved 
pincher-shapcd  mandi- 
bles (man-di-b'l),  which 
are  provided  with  palpi 


A water  scorpion.  Why  is  it  classified  as  a member  of 
Hemiptera  ? 

(pal'pi),  organs  of  taste  and  smell. 


Practical  Exercise  1.  Look  up  in  a reference  book  the  names  of  other  orders 
of  insects  than  those  that  have  already  been  given.  Give  examples  of  insects 
in  each  of  these  orders. 


This  June  beetle  has  just  lighted  on  a grape  leaf  and  is  folding  his  wings  under  his  brown 
outer  covers.  The  sheathlike  beetle  wings  are  characteristic  of  the  order.  What  other  charac- 
teristics do  they  have  ? How  would  you  tell  a beetle  from  a bug ? How  do  beetles  breed? 


62  HOW  ARE  ANIMALS  AND  PLANTS  DEPENDENT? 


Self-Testing  Exercise 

Everywhere  in  nature  we  find (1) (2)  on  plants  or 

using  them  for (3) . Insects  also  are  seen  to  visit (4) . 

(5)  are  the  most  numerous  of  all (6).  An  insect  has 

(7)  body  parts ; (8)  pairs  of  legs ; an  exoskeleton 

composed  of  (9)  and  breathes  through (10).  The 

eyes  are (H)-  The  parts  of  the  insect’s  body  are  called  the 

(12),  (13),  and  (14),  Bugs  have  mouth 

parts  fitted  for (15)  and (16).  Beetles  have 

(17)  pairs  of  wings,  the  outer  acting  as  a (18)  for  the  delicate 

inner  pair.  Grasshoppers (19)  their  food.  Some  of  man’s 

worst  enemies  are  members  of  the  order (20) . Bees  and  wasps 

are  able  to (21). 

PROBLEM  II.  TO  KNOW  SOMETHING  OF  THE  STRUCTURE 
AND  LIFE  HISTORY  OF  THE  GRASSHOPPER 

Laboratory  Exercise.  Use  living  red-legged  grasshoppers  if  possible. 
Find  the  three  parts : head,  thorax,  and  abdomen.  Is  there  an  exo- 
skeleton? 

Find  the  three  segments  in  the  thorax?  They  are  called  from 
anterior  to  posterior,  prothorax,  mesothorax,  and  metathorax.  Which 
bear  legs?  Which  bear  wings?  The  membrane-like  wings,  out- 
growths of  the  body,  lie  straight  along  the  back  when  at  rest. 

Study  the  hind  leg  carefully.  Compare  it  with  the  diagram.  Can 
you  find  all  these  parts?  Move  the  leg.  How  is  it  used?  Can 


\ayer* 


Identify  these  parts  in  your  specimen. 


you  find  any  adaptations?  How  are  the  wings  placed  when  not  in 
use?  When  flying?  Are  there  any  differences  in  the  two  pairs  of 
wings?  Into  how  many  segments  is  the  abdomen  divided?  Are  all 


MrSC^ULAJl  ACTIVITY 


(33 


of  tluMii  coinpleto?  The  eiul  of  the  abdomen  is  modified  in  the  female 
iido  an  ovipositor  or  egg  layer  (see  diagram). 

On  each  side  of  the  abdomen  in  eight  of  the  segments  (in  the  red- 
legged  grasshopper)  arc  found  tiny  openings  called  spiracles.  There 
are  also  two  i)airs  of  spiracles  on  the  thorax.  These  spiracles  o])en  into 
little  tubes  called  tracheae  (traT(5-c).  The  tracheae  divide  and  subdi- 
vide like  the  branches  of  a tree,  so  that  all  jiarts  of  the  body  cavity  are 
reacheil  by  their  fine  endings.  Is  there  any  movement  of  the  abdomen 
of  the  living  grasshopper?  Describe  this  movement.  Air  is  drawn  in 
by  the  exjiansion  of  the  abdomen  and  forced  out  when  it  contracts, 
l^y  means  of  the  tracheae,  air  is  brought  in  contact  with  the  blood. 

Muscular  activity.  Insects  have  the  most  powerful  muscles  of 
any  animals  of  their  size.  Relatively,  an  enormous  amount  of 
energy  is  released  during  jumping  or  flying.  The  tracheae  pass 
directly  into  the  muscles  and  other  tissues  so  that  a supply  of 
oxygen  is  directly  at  the  place  where  energy  is  being  released. 


•crvstattine 

l«Jn3 


single  unit  of 
compounci 

eye  o^'Wot^er- 


boffcment 
'Tnamtoro-ne. 
nerve  fiber 


What  two  insect  heads  are  shown  here  ? 
Read  your  text  carefully. 


Food  taking.  The  grasshopper  is  provided  with  two  pairs  of 
jaws,  a fork-like  pair,  the  maxillae  (mak-sil'e),  and  a pair  of  hard 
toothed  jaws,  the  mandibles.  These  parts  when  not  in  use  are 


64  HOW  ARE  ANIMALS  AND  PLANTS  DEPENDENT? 


covered  by  two  flaps,  the  upper  and  lower  lips.  The  leaf  upon 
which  the  grasshopper  feeds  is  held  in  place  in  the  mouth  by  means 
of  the  maxillae,  while  it  is  cut  into  small  pieces  by  the  mandibles. 

Eyes.  An  examination  of  the  compound  eye  of  a grasshopper 
with  a lens  shows  the  whole  surface  to  be  composed  of  tiny  six- 
sided  lenses  called  facets  (fas'ets).  Each  facet  marks  the  surface 

of  a unit  (ommati- 
dium)  of  the  com- 
pound eye.  Each 
unit  probably  gives  a 
separate  impression 
of  light  and  color. 
Since  each  unit  is 
separated  from  its 
neighbor  by  a layer 
of  pigment,  a com- 
pound eye  is  most 
favorable  for  per- 
ceiving the  move- 
ment of  objects.  The 
grasshopper  also  has 
three  simple  eyes,  or 
ocelli,  on  the  front  of 
the  head.  The  simple  eyes  probably  are  able  only  to  perceive 
light  and  darkness. 

Practical  Exercise  2.  Explain  why  an  insect  easily  perceives  a moving  object. 

Other  sense  organs.  The  segmented  feelers,  or  antennae,  have 
to  do  with  the  sense  of  touch  and  smell.  The  auditory  organ  or 
ea,r  of  the  grasshopper  is  found  under  the  wing  on  the  first  segment 
of  the  abdomen.  Covering  the  body  and  on  the  appendages  are 
found  sensory  hairs  which  make  the  insect  sensitive  to  touch. 
Thus  the  armor-covered  animal  is  put  in  touch  with  its 
surroundings. 

Life  history.  In  the  fall  of  the  year  the  female  grasshopper 
digs  a hole  in  the  ground.  She  thrusts  her  abdomen  into  the  hole 
and  lays  from  twenty  to  thirty  eggs  in  small  oval  or  bean  shaped 


Life  history  of  a grasshopper.  Explain  what  is  meant  by  a 
life  cycle;  a metamorphosis. 


ORASSHOPPERS 


65 


pockets.  These  hatch  out  in  the  spring  as  tiny  wingless  grass- 
hoppers called  nymphs.  The  young  insects  molt  or  cast  off  their 
hard  e.xoskeleton  several  times.  At  each  shedding  of  the  ‘‘skin” 
tlie  grasshopper  gets  larger.  Since  this  molting  results  in  a series 
of  changes  in  form  from  the  young  nymph  to  an  adult  with  wings, 
the  whole  process  is  called  a metamorphosis  or  change  of  form. 
The  grasshopper  is  said  to  have  an  incomplete  metamorphosis 
because  the  changes  in  form  are  not  great.  The  nymphs  can  be 
recognized  in  the  earliest  stages  as  grasshoppers. 

In  the  fall  most  of  the  adults  die,  only  a few  surviving  the  winter. 
In  the  South  and  West,  some  grasshoppers  have  more  than  one 
brood  in  a summer,  which  makes  them  more  numerous  and  there- 
fore more  of  a pest  to  the  farmers. 

Relatives  of  the  grasshoppers.  Among  the  near  relatives  of 
the  grasshopper  are  the  brown  and  black  crickets,  cockroaches, 
“ waterbugs,”  katydids,  praying  mantis,  and  many  others. 

Self-Testing  Exercise 

Grasshoppers  belong  to  the  order (1)  because  they  have 

wings  placed (2)  along  the  back.  The  mouth  parts  are  fitted 

for  (3) . The  organs  of  touch  and  smell  in  insects  are  called 

(4),  the  organ  of  hearing,  the (5),  is  usually  found  under 

the  (6).  Insects  which  pass  through  a series  of (7) 

before  they  (8)  adults  are  said  to  undergo  a (9) . 

Insects  have  to (10)  in  order  to  grow  larger. 

PROBLEM  m.  HOW  TO  KNOW  SOMETHING  ABOUT  THE 
STRUCTURE  AND  LIFE  HISTORY  OF  A BUTTERFLY 

Laboratory  Exercise.  Examine  a butterfly  carefully  with  a mag- 
nifying glass.  What  do  you  find  covering  the  body  and  wings?  Note 
that  the  legs  are  smaller  and  weaker  than  those  of  the  grasshopper. 
How  many  pairs  do  they  have?  Are  they  all  the  same  size?  Ex- 
amine a small  portion  of  a wing  under  a compound  microscope.  Draw 
a scale  showing  how  it  fits  into  the  membranous  wing.  What  name 
is  given  to  this  order  of  insects?  Why?  The  mouth  parts  of  the 
butterfly  are  modified  into  a long  proboscis,  a sucking  tube  through 
which  the  insect  sucks  nectar  from  the  flowers. 

F^ractical  Exercise  3.  Prepare  the  life  histories  of  several  different  butter- 
flies. If  possible,  use  material  that  you  have  collected  and  mounted. 


66  HOW  ARE  ANIMALS  AND  PLANTS  DEPENDENT? 


C.  Clarke 


The  life  history  of  the 
monarch  butterfly.  If  it  is 

possible  to  find  some  milk- 
weed on  our  trip,  we  are 
quite  likely  to  find  hovering 
near  it  a golden  brown  and 
black  butterfly,  the  monarch 
or  milkweed  butterfly.  The 
female  frequents  the  milk- 
weed in  order  to  lay  eggs ; 
she  may  be  found  doing  this 
at  almost  any  time  from 
June  until  September. 

Egg  and  larva.  The  eggs, 
tiny  mound-shaped  dots,  a 
twentieth  of  an  inch  in 
length,  are  fastened  singly 
to  the  under  side  of  milk- 
weed leaves.  Some  instinct 
leads  this  butterfly  to  de- 
posit her  eggs  on  the  milk- 
weed, for  the  young  feed 
upon  this  plant.  The  eggs 
hatch  out  in  four  or  five 
days  into  caterpillars.  Each 
caterpillar  will  shed  its  skin 
several  times  before  it  is  full 
grown.  These  caterpillars 
possess,  in  addition  to  the 
three  pairs  of  true  legs,  four 
pairs  of  prolegs  which  are 
fleshy  structures  found  on 


The  female  monarch  butterfly  lays 
her  eggs  on  the  edge  of  the  milkweed 
leaf.  The  egg  hatches  and  the  green, 
black,  and  white  caterpillar  feeds  on 
the  milkweed.  Later  the  caterpillar 
fastens  itself  to  the  midrib  of  a leaf. 


HUTTKKFLIKS 


67 


the  abdominal  sogmonts. 
d'he  animal  at  this  stage  is 
known  as  a larva. 

Formation  of  pupa.  After 
a life  of  a few  weeks  at  most, 
the  caterpillar  stops  eating 
and  begins  to  spin  a tiny  mat 
of  silk  upon  a leaf  or  stem. 
It  attaches  itself  to  this  web, 
head  downward,  and  sheds 
its  skin  again.  After  this 
molt,  it  is  without  legs  or 
mouth  parts.  It  hangs  to  the 
stem  in  a dormant  stage  and 
is  known  as  the  chrysalis 
(kris-d-lis)  or  pupa.  During 
this  stage  many  changes  take 
place  and  the  caterpillar 
gradually  changes  into  a 
butterfly. 

The  adult.  After  some 
weeks  of  inactivity  in  the 
pupa  state,  the  pupa  case 
splits  along  the  back,  and 
the  adult  butterfly  emerges. 
At  first  the  wings  are  soft  and 
much  smaller  than  in  the 
adult.  Within  fifteen  min- 
utes to  half  an  hour  after  the 
butterfly  emerges,  however, 
the  wings  expand  and  dry, 
and  the  insect  is  ready  to  fly 

The  skin  splits  and  a light  green  chrys- 
alis emerges,  which  gradually  changes 
its  shape.  After  a time  the  butterfly 
comes  out  of  its  chrysalid  shell.  It  clings 
to  the  shell,  spreading  and  stretching  his 
wings  until  they  are  dried  and  strength- 
ened. 


C.  Clarke 


68  HOW  ARE  ANIMALS  AND  PLANTS  DEPENDENT? 


How  do  the  structures  you  found  in  your  specimen  compare  with  these  in  the  diagram? 


away.  The  female  insect,  after  her  marriage  flight,  deposits  her 
eggs  on  a milkweed  plant. 

Since  this  butterfly  in  most  parts  of  the  United  States  has  at 
least  two  broods  a year  and  since  the  young  feed  on  the  milkweed 
and  dogbane,  both  common  weeds,  we  see  some  cause  for  its 
wide  distribution  and  great  numbers.  The  metamorphosis  of  the 
butterfly  is  said  to  be  complete  because  it 
passes  through  several  distinct  changes  of 
form. 

Moths.  Moths  are  familiar  to  most  of  us, 
but  they  can  usually  be  seen  only  at  night  be- 
cause of  their  night-flying  habits.  Certain 
differences  between  them  and  butterflies  are 
noted  in  the  following  table : 


Butterfly 

Antennae  threadlike,  usually  knobbed  at  tip. 
Fly  in  daytime. 

Wings  held  vertically  when  at  rest. 

Pupa  naked. 

Moth 


Antennae  feathery  or  threadlike, 
knobbed. 

Usually  fly  at  night. 


anal  ^ 
proleg 

ai-mil  horn. 


Caterpillar  of  moth.  Find 
the  parts  of  the  adult  Insect 
here.  Does  this  agree  with 
your  definition  of  an  insect  ? 


WASPS 


60 


Winf>;s  hold  horizontally  or  folded  over  the  body  when  at  rest. 
Pupa  usually  covered  by  a cocoon  or  case. 

The  Proniethea  nioth,  the  Polyphemus  or  American  silkworm 
moth,  aiul  the  Cecropia  moth  are  among  the  largest  and  most 
commonly  collected. 


Self-Testing  Exercise 

Butterflios  are  called (1)  because  of  the (2)  on  the 

wings.  The  adults  lay  their (3)  on  plants  which  the 

(4)  will  feed  upon.  This  stage  is  followed  by  the (5)  stage. 

In  this  stage  the  chiysalis  is  usually  attached  by  a (6) 

(f)  to  the (8)  plant. 

PROBLEM  IV.  WHAT  DO  WE  MEAN  BY  COMMUNAL  LIFE 
AND  DIVISION  OF  LABOR? 

Individual  Projects.  Give  a report  on  the  life  habits  of  a solitary  wasp. 

Work  out  with  diagrams  the  life  history  of  some  communal  insect. 

Keep  a hive  of  bees  and  report  to  the  class  on  their  habits. 

Make  an  ants’  nest  and  keep  a colony  of  ants  in  it. 

Solitary  wasps.  Some  bees  and  wasps  lead  a solitary  existence, 
the  digger  wasps  being  an  example.  Each  female  wasp  burrows 
in  the  ground  or  in 
wood  and  constructs 
a nest  in  which  she 
lays  her  eggs.  The 
nest  is  provisioned 
with  spiders  and  in- 
sects which  are  not 
killed  but  are  stung 
into  insensibility. 

The  nest  is  closed  up 
after  food  is  sup- 
plied. When  the 
young  hatches  it 
finds  plenty  of  food 
near  at  hand  to 
nourish  it  during  its 
growth. 


H.  BIO  — 6 


70  HOW  ARE  ANIMALS  AND  PLANTS  DEPENDENT? 

Bumblebees.  In  the  life  history  of  the  bumblebee  we  see  the 
beginning  of  the  instinct  to  live  together.  Some  of  the  female 
bees  (known  as  queens)  burrow  into  the  ground  in  the  fall  and  sleep 
all  winter.  They  lay  their  eggs  the  following  spring  in  masses  of 

pollen,  which  they 
gather  and  place  in 
holes  in  the  ground, 
often  in  a deserted 
mouse  hole.  The 
young  hatch  as  larvae, 
then  pupate,  and 
finally  become  workers 
(imperfect  females)  in 
which  the  egg-laying 
apparatus,  or  ovi- 
positor, is  modified  to 
be  used  as  a sting. 
The  workers  bring  in 
pollen  to  the  queen, 
in  which  she  lays  her 
eggs.  Several  broods 
of  workers  are  raised 
during  a summer.  In 
the  early  fall  a brood  of  males  and  egg-laying  females  or  queens 
are  produced  instead  of  workers.  The  males  leave  the  hive  as 
soon  as  they  are  able  to  fly,  and  never  return.  They  mate  with 
the  queens  and  then  die.  They  live  in  all  about  three  or  four 
weeks.  The  young  queens  also  leave  the  hive,  although  they 
occasionally  return.  By  means  of  these  queens  the  brood  is 
started  the  following  year. 

Practical  Exercise  4,  Report  on  the  life  story  of  some  South  American 
wasps.  Read  Howe’s  Insect  Behavior,  Chapters  ii  and  iv-xii  inclusive. 

The  Honeybee.  The  most  wonderful  communal  life  has  been 
developed  among  the  honeybees.^ 

1 Their  daily  life  may  be  easily  watched  in  the  schoolroom,  by  means  of  one  of  the 
many  good  and  cheap  observation  hives  now  made  to  be  placed  in  a window  frame. 
Directions  for  making  a small  observation  hive  for  school  work  can  be  found  in 


larva 

t 


Compare  the  life  history  of  the  bumblebee  with  that  of  the 
solitary  wasp.  How  does  it  differ  ? 


THE  llOXEVliEE 


71 


A prosperous  colony  may  have  fifty  thousand  bees  during  the 
summer  season,  but  under  the  unfavorai)le  conditions  of  winter 
the  colony  may  be  reduced  to  as  few  as  ten  thousand  bees. 
Division  of  labor  is  well  seen  in  a well-established  hive.  Here  the 
(lueen,  attended  by  workers,  does  nothing  but  lay  eggs.  Most  of 
the  eggs  are  fertilized  by  the  sperm  cells  of  a male  and  develop 
into  workers;  the  unfertilized  eggs  develop  into  males  or  drones. 
After  a short  existence  in  the  hive  the  drones  are  usually  driven 
out  by  the  workers. 

The  cells  of  the  comb  are  built  by  the  workers  out  of  wax  secreted 
from  the  under  surface  of  their  bodies.  The  cells  of  the  comb  are 
made  in  two  layers,  back  to  back,  opening  on  opposite  sides.  They 


A small  apiary  such  as  anyone  living  in  the  country  could  have.  What  are  the  men  doing? 


are  hexagonal  in  cross  section  and  are  of  different  sizes,  the  smaller 
cells  being  used  for  honey  storage  and  for  the  development  of  the 
workers,  the  larger  cells  for  housing  the  drones.  The  queen  lays 
one  egg  in  each  cell,  and  the  young  are  hatched  after  three  days,  to 
begin  life  as  white  footless  grubs.  For  a few  days  they  are  fed  on 
partly  digested  food  called  bee  jelly,  regurgitated^  from  the  stomach 
of  the  youngest  workers  or  nurses.  Later  they  receive  pollen  and 

Hodge,  Nature  Study  and  Life,  Chapter  xiv.  Bulletin  No.  1,  U.  S.  Department  of 
Agriculture,  entitled  The  Honey  Bee,  by  Frank  Benton,  and  Farmers’  Bulletin  447 
on  Bees,  by  E.  F.  Phillips,  give  useful  information  to  the  bee  keeper. 

1 Regurgitate  (re-gur'jl-tat)  ; to  cast  out  again  from  the  stomach. 


72  HOW  ARE  ANIMALS  AND  PLANTS  DEPENDENT? 


honey  to  eat.  A little  of  this 
mixture,  known  as  bee  bread, 
is  put  into  the  cells,  and  the 
lids  covered  with  wax  by  the 
working  bees,  and  the  young 
larvae  allowed  to  pupate. 
After  about  two  weeks  of 
quiescence  in  the  pupal  state, 
it  changes  into  a fully  de- 
veloped adult  and  chews  its 
way  out  of  the  cell.  It  takes 
its  place  in  the  hive,  first 
caring  for  the  young  as  a 
nurse,  later  making  excur- 
sions to  the  open  air  after 
food  as  an  adult  worker. 

When  the  colony  becomes 
large,  it  is  time  to  have  a 
new  queen.  The  workers 
provide  for  this  by  building 
one  or  more  larger  cells  in 
each  of  which  a single  egg  is  placed.  When  these  eggs  hatch,  they 
are  fed  on  special  food  which  causes  rapid  development.  The 
first  new  queen  that  hatches  kills  the  other  young  queen  and  then 
there  may  be  a fight  to  the  death  between  the  old  and  the  new 
queen.  More  often  the  old  queen  with  several  thousand  of  the 
older  workers  leave  the  hive  and  start  a new  colony  elsewhere. 
This  is  called  swarming.  They  usually  settle  around  the  queen, 
often  hanging  to  the  limb  of  a tree.  While  the  bees  are  swarming, 
certain  of  the  workers,  acting  as  scouts,  determine  on  a site  for 
their  new  home ; and,  if  undisturbed,  the  bees  soon  go  there  and 
construct  their  new  hive.  This  instinct  is  of  vital  importance  to 
the  bees,  as  it  provides  them  with  a means  of  forming  a new  col- 
ony. A swarm  of  domesticated  bees  may  be  easily  hived  in  new 
quarters. 

Division  of  labor  in  the  hive.  The  work  of  the  hive  is  divided 
among  the  various  kinds  of  bees  in  a most  interesting  manner. 


THK  1 1 ONE V REE 


73 


Wo  hfivo  soon  tliat  tho  qiioon  lays  all  tlio  o^S^,  acting  as  a sort  of 
tribal  inothor.  Tho  oggs  are  all  forlilizod  by  one  drone,  who 
places  the  sperm  colls  within  tho  body  of  the  queen  on  her  nuptial 
flight.  The  young  workers  feed  the  larvae  and  act  as  nurses. 
The  older  bees  take  turns  in  a number  of  duties;  some  attend  to 
the  queen  and  drones,  some  act  as  sanitary  police,  keeping  the 
hive  clean  of  tlirt  and  bodies  of  dead  bees,  others  ventilate  the 
hive  b}'  buzzing  with  their  wings,  while  many  others  work  in  the  field 
gathering  pollen  and  nectar  from  flowers. 

The  nectar  is  swallowed  and  kept  in  the  crop,  or  honey  stomach, 
until  after  the  bee  returns  to  the  hive,  where  it  is  regurgitated 
into  the  cells  of  the  comb.  It  is  now  thinner  than  what  we  call 
honey.  To  thicken  it,  the  bees  swarm  over  the  open  cells,  moving 
their  wings  very  rapidly,  thus  evaporating  some  of  the  water  in 
the  honey.  A hive  of  bees  has  been  known  to  make  over  thirty- 
one  pounds  of  honey  in  a single  day,  although  the  average  is  very 
much  less  than  this. 


C.  Clarke 

A tiny  ant  drags  home  a cabbage  butterfly,  to  add  to  its  store  of  food,  which  is  needed  for  the 

young. 


74  HOW  ARE  ANIMALS  AND  PLANTS  DEPENDENT? 


Ants.  Ants  are  the  most  truly  communal  of  all  the  insects. 
Their  life  history  and  habits  are  not  so  well  known  as  those  of  the 
bee,  but  what  is  known  shows  even  more  wonderful  specialization. 

The  nest  of  a colony  consists  of  underground  galleries  with 
enlarged  storerooms,  nurseries,  etc.  The  inhabitants  of  a nest 
may  consist  of  winged  males  and  females,  and  wingless  workers, 
which  act  as  gatherers  of  food,  nurses,  and  protectors.  We  may  find 
ant  nests  almost  anywhere  in  our  yards  or  gardens.  Many  nests 
are  found  under  large  flat  stones,  chiefly  because  stones  hold  the 
heat  of  the  sun  and  keep  the  nest  from  cooling  too  rapidly  at  night. 

The  entire  communal  life  of  the  ants  might  be  said  to  be 
based  upon  the  perception  of  odor.  If  an  ant,  although  one  of  the 
same  species,  is  put  into  a colony  to  which  it  does  not  belong,  it 
will  be  set  upon  and  either  driven  out  or  killed.  Ants  never 
really  lose  their  community  odor ; those  absent  for  a long  time,  on 
returning,  apparently  will  be  easily  distinguished  by  their  odor,  and 
eagerly  welcomed  by  the  other  members  of  the  nest.  The  commu- 
nication of  ants,  as  seen  when  they  stop  each  other,  away  from  the 
nest,  is  evidently  a process  of  smelling,  for  they  caress  each  other 
with  the  antennae,  the  organs  with  which  odors  are  perceived. 


fauL  G.  Howes 


Some  ants  live  on  a sweet  fluid  which  is  given  off  by  aphids  or  plant  lice.  They  induce  the 
aphids  to  exude  this  fluid  by  stroking  them  with  their  antennae.  Such  aphids  are  carefully 
watched  and  cared  for  by  the  ants. 

Ant  larvae  are  called  grubs.  They  are  absolutely  helpless  and 
are  taken  care  of  by  nurses.  The  pupae  may  often  be  seen  as 
they  are  being  carried  in  the  mouths  of  the  nurse  ants,  who  bring 
them  to  the  surface  for  sun  and  air.  They  are  wrongly  called 
ants’  eggs  in  this  stage. 


CHARArTERISTICS  OF  INSECTS 


75 


Some  species  of  ants  are  among  the  most  warlike  of  any  insects.  In 
the  case  of  the  robber  ants,  which  live  entirely  by  war  and  pillage,  the 
workers  have  become  modified  in  structure,  and  can  no  longer  work, 
but  only  fight.  Some  species  go  further  and  make  slaves  of  the  ants 
preyed  upon.  These  slaves  do  all  the  work  for  their  captors,  even 
to  making  additions  to  the  nest  and  acting  as  nurses  to  their  young. 

Practical  Exercise  6.  Report  on  the  life  in  an  ant  colony  in  South  America  as 
described  in  Beebe’s  Jungle  Days,  or  the  life  of  the  army  ants,  Chapter  xiv,  in 
Howe’s  Insect  Behanior. 


Self-Testing  Exercise 

Some  wasps  lead (1)  lives  but  most (2), (3), 

and  wasps  show (4)  life.  In  the  case  of  the  honeybees  we 

have  a (5)  with  a single  fully-developed  (6)  or 

(7),  several  hundred (8)  or (9)  and  many 

thousands  of  (10).  The  latter  have  many  duties  such  as 

gathering (11)  and (12)  from  flowers, (13) 

the  young, (14)  and (15)  the  hive.  They  also  make 

(16),  which  they  store  in  cells  made  of (17).  Ants 

also  have  a complicated  communal  life,  some  acting  as (18), 

others  as (19),  and  still  others  as (20).  The  com- 
munal life  of  ants  is  dependent  upon (21).  Each  colony  seems 

to  have  its  own  peculiar . (22).  Bees,  ants,  and  wasps  belong  to 

the  order (23). 

PROBLEM  V.  WHAT  ARE  THE  CHARACTERISTICS  OF  OTHER 
GROUPS  OF  INSECTS? 

The  Flies.  There  is  an  order  of  insects  called  Diptera,  which 
is  characterized  by  having  only  two  gauzy  wings.  The  members  of 
this  group  of  insects  frequently  found  on  a field  trip  are  mosquitoes, 
gnats,  botflies,  and  the  house  fly. 

The  head  of  the  common  fly  is  freely  movable  and  is  provided 
with  mouth  parts  for  sucking  and  lapping.  The  foot  shows  wonder- 
ful adaptation  for  clinging  to  smooth  surfaces,  as  it  is  provided  with 
sticky  pads  bearing  tubelike  hairs. 

The  second  pair  of  wings  is  changed  into  a pair  of  small  knobs, 
called  balancers.  This  name  suggests  their  use,  for  if  they  are  re- 
moved, the  fly  is  unable  to  balance  itself. 

The  development  of  the  fly  is  extremely  rapid.  A female  may 


76  HOW  ARE  ANIMALS  AND  PLANTS  DEPENDENT? 


Why  does  the  house  fly  belong  to  the  order  of  insects  known 
as  Diptera  ? 


lay  from  one  hun- 
dred to  two  hundred 
eggs.  These  are 
usually  deposited  in 
garbage  or  manure. 
In  warm  weather, 
within  a day  after 
the  eggs  are  laid, 
the  young  maggots, 
as  the  larvae  are 
called,  hatch.  After 
about  one  week  of 
active  feeding,  these 
wormlike  maggots 
become  quiet  and 
go  into  the  pupal  stage,  whence  under  favorable  conditions  they 
emerge  within  less  than  another  week  as  adult  flies.  The  adults 
breed  at  once,  and  in  a short  summer  there  may  be  over  ten 
generations  of  flies.  This  accounts  for  the  great  number  of  flies 
in  late  summer.  Fortunately  few  flies  survive  the  winter. 

Practical  Exercise  6.  Discuss  the  fly  problem  as  it  exists  in  your  commu- 
nity. What  steps  might  you  take  to  abate  the  fly  nuisance  ? 

The  life  history  of  a beetle.  The  May  beetle  or  June  bug  and 
potato  beetle  are  examples  of  beetles.  Many  beetles  lay  their 
eggs  in  the  ground, 
where  they  hatch 
into  cream-colored 
grubs.  A grub  differs 
from  the  maggot  or 
larva  of  the  fly  in 
possessing  three  pairs 
of  legs.  These  grubs 
live  in  burrows  in  the 
ground,  where  they 
feed  on  the  roots  of 
grass  and  garden 

plants,  The  larval  compare  the  life  history  of  the  fly  with  that  of  the  bumblebee. 


THE  CICADA 


77 


form  remains  iindergroiiiKl  from  two  to  three  years,  the  latter 
part  of  this  time  as  an  inactive  pupa.  During  the  latter  stage 
it  lies  dormant  in  an  ovoid  area  excavated  by  it.  Eventually 
the  wings  (which  are  biidhke  in  the  pupa)  grow  larger,  and  the 
adult  beetle  emerges  fitted 
for  its  life  in  the  open  air. 

This  group  of  insects  in- 
clude some  of  man’s  best 
friends,  as  the  ladybird 
beetle,  and  some  of  his 
worst  enemies,  as  the  po- 
tato beetle. 

Life  history  of  the  ci- 
cada. The  seventeen-year 
cicada  lays  her  eggs  in  slits 
which  she  makes  in  the 
twigs  of  trees.  Immedi- 
ately after  hatching,  the 
young  drop  to  the  ground 
and  bury  themselves  in  the 
earth.  They  stay  there  for 
seventeen  years.  In  the 
South  these  insects  live  only  thirteen  years  underground.  They 
obtain  their  food  by  sucking  the  juices  from  the  roots  of  plants. 
During  this  stage  they  somewhat  resemble  the  grub  of  the  beetle 
(June  bug)  in  habits  and  appearance.  When  they  are  about  to 
molt  into  an  adult,  they  climb  above  the  ground,  and  fasten 
themselves  to  some  firm  object,  as  a wooden  fence  or  a tree 
trunk.  The  skin  then  splits  along  the  back  and  the  adult  cicada 
emerges. 

Aphids.  The  aphids  are  among  the  most  interesting  of  the 
Homoptera.  They  are  familiar  to  all  as  tiny  green  lice  seen  swarm- 
ing on  the  stems  and  leaves  of  the  rose  and  other  cultivated  plants. 
They  suck  the  juices  from  stem  and  leaf.  Plant  lice  have  a 
remarkable  life  history.  Early  in  the  year  the  eggs  develop  into 
wingless  females  which  produce  living  young,  all  females.  These 
in  turn  reproduce  in  a similar  manner,  until  the  plant  on  which 


The  full  grown  larva  of  the  Colorado  potato  beetle 
drops  to  the  ground  and  burrows  in  the  soil,  forming 
there  a pupa  which  later  develops  into  the  adult. 


78  HOW  ARE  ANIMALS  AND  PLANTS  DEPENDENT? 


they  live  becomes  overcrowded  and  the  food  supply  runs  short. 
Then  a generation  of  winged  aphids  is  produced.  These  fly  away 


Life  history  of  the  seventeen-year  cicada.  What  are  the  chief  differences 
between  this  life  history  and  the  others  shown? 


to  other  plants,  and  reproduction  goes  on  as  before  until  the 
approach  of  cold  weather,  when  males  and  females  appear.  Ferti- 
lized eggs  are  then  produced  which  give  rise  to  young  the  following 
season. 

Dragon  flies  and  their  relatives.  The  dragon  fly  receives  its 
name  from  the  fact  that  it  preys  on  insects.  The  adult  eats 
mosquitoes  and  other  insects  which  it  captures  while  flying.  Its 
four  large,  lacelike  wings  give  it  power  of  very  rapid  flight,  while 
its  long,  narrow  body  is  admirably  adapted  for  the  same  purpose. 
The  large  compound  eyes  placed  at  the  sides  of  the  head  give 
keen  sight.  It  possesses  powerful  jaws  (almost  covered  by  the 
upper  and  lower  lips). 

These  insects  deposit  their  eggs  in  the  water,  and  the  fact  that 
they  may  be  often  seen  with  the  end  of  the  abdomen  curved  down 


DRAGON  FLIES 


79 


under  the  surface  of  the  water  in  the  act  of  depositing  the  eggs 
has  given  rise  to  the  belief  that  they  were  then  engaged  in  sting- 
ing something.  The  egg  hatches  into  a form  called  a nymph, 
which  in  the  dragon  fly  is  characterized  by  a greatly  developed 
lower  lip.  When  the  animal  is  at  rest,  the  lower  lip  covers  the 
large  biting  jaws,  which  can  be  extended  to  grasp  and  hold  its 
prey.  It  may  live  as  a nymph  from  one  summer  to  as  long  as 
two  years  in  the  water.  It  then  crawls  out  on  a stick,  molts 
by  splitting  the  skin  down  the  back,  and  comes  out  as  an 
adult. 

A closely  related  form  is  the  damsel  fly.  This  may  be  distin- 
guished from  the  dragon  fly  by  the  fact  that  when  at  rest  the  wings 
are  carried  close  to  the  abdomen,  while  in  the  dragon  fly  they  are 
held  in  a horizontal  position. 

Another  near  relative  of  the  dragon  fly  is  the  May  fly.  These 
insects  in  the  adult  stage  have  lost  the  power  to  take  food.  Most 
of  their  life  is  passed  in  the  larval  stage  in  the  water.  The  adults 
sometimes  live  only  a few  hours,  just  long  enough  to  mate  and 
deposit  their  eggs.  These  insects  belong  to  the  order  Odonata. 


C.  ClarU 


The  adult  dragon  fly  has  just  emerged  from  the  nymph  stage.  Where  does  the 
nymph  pass  its  life?  On  what  kind  of  food  does  it  live?  Why  do  dragon  flies 
often  light  on  the  water  film  ? Are  adult  dragon  flies  of  any  use  to  man  ? 


80  HOW  ARE  ANIMALS  AND  PLANTS  DEPENDENT? 


Self-Testing  Exercise 

The  hind  wings  of  the  flies  are  for (1).  The (2) 

of  a fly  is  a maggot.  The  beetle  has  a larval  stage  called  a (3), 

which  has (4)  pairs  of (5).  A dragon  fly  in  the  larval 

stage  is  called  a (6).  Aphids (7)  their  food  and  do 

much  harm  in  the (8)  stage. 

PROBLEM  VI.  WHY  ARE  INSECTS  SO  NUMEROUS? 

There  are  over  450,000  different  known  species  of  insects,  or 
almost  three  times  as  many  as  all  other  animals  put  together. 
From  the  standpoint  of  numbers  they  are  a successful  group. 
Why  is  this  so?  Several  reasons  can  be  given.  Scores,  often 
hundreds,  of  eggs  are  laid  by  a single  mother,  and  sometimes  before 
a month  has  passed  each  little  female  insect  that  has  hatched  is 
ready  to  lay  eggs  in  its  turn.  This  life  cycle  may  be  repeated  sev- 
eral times  during  a season.  They  grow  rapidly,  they  are  often 
adapted  to  use  food  that  other  animals  will  not  use,  as  witness  the 


The  moth  clinging  to  the  trunk  of  an  elm  tree  The  yellow  crab  spider  on  the  yellow  center  of 
is  so  similar  in  coloring  to  the  bark  that  it  is  the  flower  and  the  white  crab  spider  against  the 
not  noticeable  at  a distance.  background  of  white  petals  are  inconspicuous 

as  they  lie  in  wait  for  some  visiting  insects. 


HOW  AKE  INSECTS  PKOTECTED? 


81 


liundrocls  of  forms  (hat 
live  on  weeds  and  decayed 
food,  and  they  have  nu- 
merous ways  of  escaping 
their  enemies.  Such  is  the 
house  fly.  On  the  other 
hand,  such  insects  liave 
many  enemies  so  that  few 
forms  become  over  abun- 
dant. Many  can  fly  and 
thus  have  an  easy  way  of 
escaping  their  enemies. 

Then  many  species  are 
very  tiny,  thus  escaping 
detection.  The  fact  that 
many  species  pass  through 
a metamorphosis  is  an  un- 
doubted advantage,  for 
often  there  is  a long  qui- 
escent stage  either  passed 
out  of  sight  in  the  ground 
or  under  bark  of  trees  or 
stones.  The  pupae  of 
many  insects  are  covered, 
so  that  birds  or  their  ene- 
mies would  not  notice  them.  Many  adults  have  either  a hard  body 
covering  or  are  covered  with  hairs.  In  addition  many  have  odor 
or  taste  disagreeable  to  birds,  which  are  their  chief  enemies. 

If  we  examine  insects  in  their  native  haunts,  we  find  that  many 
of  them  have  interesting  means  of  protection.  The  grasshopper 
is  colored  like  the  grass  on  which  it  lives.  The  katydid,  with 
its  green  body  and  wings,  can  scarcely  be  distinguished  from  the 
leaves  on  which  it  rests.  The  walking  stick,  which  resembles  the 
twigs  on  which  it  is  found,  and  the  walking-leaf  insect  of  the  tropics 
are  other  examples.  This  is  called  'protective  resemblance. 

Some  insects  are  provided  with  means  of  defense,  such  as  poison 
hairs  or  stings.  Those  animals  which  are  harmful  are  sometimes 


82  HOW  ARE  ANIMALS  AND  PLANTS  DEPENDENT? 


Paul  Griswold  Howes 

A leaf  hopper  mimics  the  central  part  of  the  flowers  upon  which  it  was  found. 
Find  the  insect. 


brightly  colored  or  marked  as  if  to  warn  animals  to  keep  off  or  to 
take  the  consequences.  They  are  said  to  show  warning  coloration. 
Examples  of  such  insects  may  be  seen  in  many  varieties  of  beetles, 
especially  the  spotted  ladybirds  and  potato  beetles.  Wasps  show 
yellow  bands,  while  many  forms  of  caterpillars  are  conspicuously 
marked  or  colored. 

Larvae  of  insects,  such  as  caterpillars,  which  are  harmless,  are 
brightly  colored  and  protrude  horns,  or  pretend  to  sting  when 
threatened  with  attack.  These  animals  appear  to  mimic  animals 
similar  in  appearance,  which  really  are  protected  by  a sting  or  by 
poison.  Some  butterflies  which  birds  eat  look  like  those  that  are 
avoided  by  them  and,  therefore,  must  be  distasteful.  Such  imita- 
tion is  particularly  well  shown  by  the  monarch  and  the  viceroy 
butterflies.  Some  harmless  flies  imitate  bees,  and  thus  seem  to 
receive  a certain  protection.  When  a harmless  insect  resembles 
a harmful  one,  we  call  it  mimicry. 

Practical  Exercise  7.  Write  a paragraph  giving  reasons  why  insects  are 
more  numerous  than  other  forms  of  animals. 

Field  Exercise.  Find,  mount,  and  exhibit  to  the  class  different 
examples  of  insects  showing  protective  resemblance,  warning  color- 
ation, and  mimicry. 


A SIMPLE  FLOWER 


83 


Self-Testing  Exercise 

Protective  coloriiiji;  or  reseinl)lance  is  seen  in  the  (1) 


(2)  and  (d).  Protective  mimicry  is  seen  in  the 

(4)  and  (5)  hntterflies.  Insects  are  a (()) 

group.  Many  insects  (7),  and  thus  escape  their  enemies. 


The  (8)  stage  is  a help,  because  it  provides  a long  quiescent 

(9)  during  whicli  the  insects  are  hidden  from  sight.  Many 

insects  are (10)  colored. 


PROBLEM  VII.  OF  WHAT  USE  ARE  FLOWERS  TO  PLANTS? 

Laboratory  Exercise.  The  structure  of  a simple  flower. 

The  floral  envelope.  Examine  a simple  flower,  such  as  a lily.  The 
expanded  portion  of  the  flower  stalk,  which  holds  the  parts  of  the 
flower,  is  called  the  receptacle.  The  green  leaflike  parts  covering  the 
unopened  flower,  when  taken  together,  are  called  the  calyx.  Each  of 
these  parts  is  a sepal.  How  many  petals  does  your  specimen  have? 
What  use  do  they  seem  to  have?  The  more  brightly  colored  structures 
are  the  petals.  How  many  do 
you  find?  When  joined  to- 
gether, the  petals  form  a corolla. 

The  corolla  is  of  importance  in 
making  the  flower  conspicuous. 

Of  what  value  would  this  be? 

Frequently  the  petals  or  corolla 
have  bright  marks  or  dots  which 
lead  down  to  the  base  of  the 
cup  of  the  flower,  where  a sweet 
fluid  called  nectar  is  secreted  by 
nectar  glands.  It  is  principally  this  food  substance,  later  made  into  honey 
by  bees,  that  makes  flowers  attractive  to  insects. 

The  essential  organs  of  the  flower  consist  of  the  stamens  and 
pistil  (or  pistils),  the  latter  being  in  the  center  of  the  flower.  How 
many  stamens  do  you  find  in  your  specimen?  Cut  crosswise  through 
the  swollen  part  of  the  pistil.  How  many  divisions  do  you  find? 
Are  the  parts  of  the  flower  in  multiples  of  each  other?  In  a single 
stamen  the  boxlike  part  at  the  end  is  the  anther;  the  stalk  which 
holds  the  anther  is  called  the  filament.  The  anther  is  in  reality  a 
hollow  box  which  produces  a large  number  of  little  grains  called 
pollen.  Each  pistil  is  composed  of  a rather  stout  base  called  the  ovary, 
which  contains  the  ovule  or  future  seeds,  and  a more  or  less  lengthened 
portion  rising  from  the  ovary  called  the  style.  The  upper  end  of  the  style 
is  called  the  stigma. 

Practical  Exercise  8.  Draw  a longitudinal  section  of  the  flower  and  label 
all  parts.  Show  the  essential  organs  in  color. 


84  HOW  ARE  ANIMALS  AND  PLANTS  DEPENDENT? 


Pollen  grains  may  take 
various  forms.  What  might 
be  the  value  of  the  spine- 
like structures  on  the  pollen 
grains  ? 


Pollen.  Pollen  grains  of  various  flowers,  as  seen  under  the  micro- 
scope, differ  greatly  in  form  and  appearance.  Some  are  relatively 
large,  some  small,  some  rough,  others 
smooth,  some  spherical,  and  others  angular. 
They  all  are  alike,  however,  in  having  a 
thick  wall,  with  a thin  membrane  under  it, 
the  whole  inclosing  a mass  of  protoplasm. 
At  its  earliest  stage  the  pollen  grain  is  a 
single  cell,  but  at  the  time  of  pollination  it 
contains  two  or  three  cells. 

Germination  of  pollen  grains.  When 
pollen  falls  on  the  stigma  of  a flower,  it 
sticks  there  because  there  is  a sticky  fluid 
formed  by  the  stigma.  This  substance 
seems  to  stimulate  the  growth  of  a pollen 
tube.  The  walls  of  the  pollen  grain  break 
and  a threadlike  tube  is  formed.  Ripe 
pollen  grains  usually  contain  two  nuclei.  One,  called  the  genera- 
tive nucleus,  forms  two 
sperms,  or  male  nuclei. 

The  other  or  tube  nucleus 
is  not  concerned  in  fertili- 
zation. 

Fertilization  of  the  egg 

cell.  If  we  cut  the  pistil 
of  a large  flower  (as  a lily) 
lengthwise,  we  find  that 
the  style  is  composed  of 
a spongy  material.  This 
material  is  easily  pene- 
trated by  the  growing 
pollen  tube  which  dis- 
solves a pathway  for  itself 

by  means  of  enzymes  Explain,  v^ith  reference  to  your  text,  the  stages  in  the 
which  it  pours  out.  The  of  a polleo  srain. 

ovary  of  the  flower  is  seen  to  be  hollow,  containing  one  or  more 
structures  which  appear  to  grow  out  of  its  walls.  These  are  the 


FERTILIZATFON 


85 


ovules  wliich,  as  we  will  see,  uiuler  certain  conditions  become  seeds. 
When  the  pollen  f>;rain  ^('nninates,  the  pollen  tube  s^ws  down- 
ward throuj>;h  the  spongy  center  of  the  style  until  it  enters  the 
space  within  the  ovary.  Here  the  tube  seems  to  be  attracted  to 
an  ovule  and  usually  enters  it  through  a tiny  opening  in  the  ovary 
wall  called  the  micropyle.  You  can  easily  find  this  area  in  a 
bean  seed. 

Under  the  ovule  is  a clear  area  of  living  matter,  called  the  embryo 
sac.  Here  are  formed  several  nuclei,  one  of  which,  with  the  living 
matter  around  it,  is  the  egg  nucleus. 


pollen,  ^min. 
^..anther 


Explain  this  diagram  after  reading  your  text. 


The  length  of  time  taken  by  a pollen  tube  to  grow  down  to  the 
ovary  varies  greatly  in  different  plants.  In  some  cases  the  pollen 
tube  will  reach  the  ovary  in  three  days  ; in  other  cases,  for  example 
the  oak,  it  takes  nearly  a year  for  the  tube  to  grow  a tenth  of  an 
inch.  Ultimately  the  sperm  nucleus  reaches  the  egg  cell  and  unites 
with  it.  The  union  of  the  sperm  nucleus  with  the  nucleus  of  the 
egg  cell  in  the  ovule  is  known  as  fertilization.  The  union  of  the 
sperm  nucleus  and  the  egg  cell  results  in  a fertilized  egg.  This  egg, 
by  constant  divisions  of  the  cells,  forms  an  embryo  or  baby  plant. 
This  is  contained  in  the  seed  and,  as  we  know,  will  develop  into  an 
adult  plant  if  given  proper  environmental  conditions. 

Practical  Exercise  9.  Make  a series  of  diagrams  for  your  workbook  to 
show  just  how  the  sperm  nucleus  reaches  the  egg  cell  in  order  to  bring  about 
fertilization. 

H.  BIO  — 7 


86  HOW  ARE  ANIMALS  AND  PLANTS  DEPENDENT? 

Self-Testing  Exercise 

The  parts  of  a flower  are  (1),  (2),  (3), 

(4),  and  (5).  Essential  organs  are  the  (6) 

and  the  (7).  Pollen  is  produced  in  the  (8).  Egg 

cells  are  found  in  the  (9).  Fertilization  of  the  (10) 

by  a (11)  nucleus  from  the  pollen  (12)  causes 

an (13)  or (14)  plant  to  be  formed. 


PROBLEM  VIII.  HOW  ARE  FRUITS  FORMED? 

Laboratory  Exercise.  Examine  an  unopened  pea  or  bean  pod. 
Compare  it  with  a pea  or  bean  flower  or  with  drawing.  Find  the  parts 
of  the  flower  in  the  fruit.  What  becomes  of  the  petals  and  sepals?  What 
happens  to  the  pistil  ? Where  do  the  seeds  grow  ? 

The  pod  of  a bean,  pea,  or  locust  illustrates  well  the  growth 
from  the  flower.  The  flower  stalk,  the  ovary,  and  the  remains 
of  the  style,  the  stigma,  and  the  calyx,  can  be  found  on  most 


Can  you  explain  where  and  how  seeds  are  formed  after  studying  this  diagram  carefully  ? 


FOKMATTOX  OF  FRFITS 


87 


Can  you  find  all  parts  of  the  flower  in  the  ripened  fruit? 


unopened  pods.  If  the  pod  is  opened,  the  seeds  will  be  found 
fastened  to  the  ovary  wall  each  by  a little  stalk  called  the  fimiculiis 
(fu-nik'u-lws).  That  part  of  the  ovary  wall  which  bears  the  seeds  is 
the  placenta  (pld-sen'td).  The  walls  of  the  pod  are  called  valves. 

The  pod,  which  is  in  reality  a ripened  ovary  with  other  parts 
of  the  flower  attached  to  it,  is  considered  a fruit.  By  definition, 
a fruit  is  a ripened  ovary  together  with  any  parts  of  the  flower  that 


U.  S.  Department  of  Agriculture 

Why  have  so  few  grains  appeared  in  this  ear  of  corn?  Remember  the  corn  cob  bears 
pistillate  flowers ; the  “ silks  ” are  the  long  styles  with  stigmas  at  the  tips. 


88  HOW  ARE  ANIMALS  AND  PLANTS  DEPENDENT? 


may  he  attached  to  it.  The  chief  use  of  the  fruit  is  to  hold  and  to 
protect  the  seeds ; it  may  ultimately  distribute  them  where  they 
can  reproduce  young  plants. 

Each  seed  has  been  formed  as  a direct  result  of  the  fertilization 
of  the  egg  cell  (contained  in  the  embryo  sac  of  the  ovule)  by  a 
sperm  nucleus  of  the  pollen  tube. 

Practical  Exercise  10.  Describe  with  the  aid  of  diagrams  the  growth  into 
a fruit  of  some  flower,  not  given  in  the  text. 

Self-Testing  Exercise 

In  a pod,  the  seed  is  fastened  to  the  ovary  wall  by  the (1). 

The  (2)  is  the  part  of  the  wall  of  pod  that  bears  the 

(3).  The  pod  is  a (4)  (5)  and  is  called  a 

(6).  The  chief  use  of  the (7)  is  to  protect  the 

(8).  Seeds  are  formed  as  a direct  result  of  the • • (9) 

of  the  (10)  cell  in  the  embryo  sac  by  the (11)  nu- 
cleus in  the (12)  tube. 

PROBLEM  IX.  WHAT  ARE  SOME  ADAPTATIONS  IN  INSECTS 
FOR  CARRYING  POLLEN? 

Insects  as  pollinating  agents.  Insects  often  visit  flowers  to 
obtain  pollen  as  well  as  nectar.  In  so  doing  they  may  transfer 
some  of  the  pollen  from  one  flower  to  another  of  the  same  kind. 
This  transfer  of  pollen,  called  cross-pollination,  is  of  the  greatest 
use  to  the  plant,  as  we  shall  see  later.  Sir  John  Lubbock  observed 
bees  and  wasps  to  learn  how  many  trips  they  made  daily  from  their 
homes  to  the  flowers,  and  found  that  a wasp  went  out  on  116  visits 
during  a working  day  of  16  hours,  while  a bee  made  almost  as 
many  visits  and  worked  almost  as  long  as  the  wasp.  It  is  evident 
that  in  the  course  of  so  many  trips  to  the  fields  a bee  must  light 
on  hundreds  of  flowers. 

Nectar  and  nectar  glands.  The  bee  is  attracted  to  a flower  for 
food.  This  food  may  consist  of  pollen  or  nectar.  Nectar  is  a 
sugary  solution  that  is  formed  in  the  flower  by  little  collections 
of  cells  called  the  nectar  glands.  The  nectar  glands  are  usually 
so  placed  that  to  reach  them  the  insect  must  first  brush  the  stamens 
and  pistil  of  the  flower.  Frequently  the  location  of  the  nectaries 
(nectar  glands)  is  made  conspicuous  by  brightly  colored  markings 


ADAPTATIONS  IN  A BEE  89 


on  the  corolla  of  the  flower.  The  row  of  dots  in  the  tiger  lily  is 
an  example. 

Practical  Exercise  11.  Study  a dead  bee,  to  discover  al,daptations  for 
carrying  pollen.  ITsc  diagram  in  text  to  help.  Hand  lenses  are  essential 
and  a compound  microscope  will  be  found  useful. 


Adaptations  in  a bee.  If  we  look  closely  at  a bee,  we  find  the 
body  and  legs  more  or  less  covered  with  tiny  hairs,  many  of  them 
branched.  The  joints  in  the  legs  of  the  bee  adapt  it  for  com- 
plicated movements ; the  arrangement  of  stiff  hairs  along  the 
edge  of  a concavity  in  one  of  the  joints  of  the  hindmost  pair  forms 
a structure  called  the 
pollen  basket,  adapted 
to  hold  pollen.  Bees 
collect  pollen  and  force 
it  into  this  concavity 
by  means  of  a pollen 
press  (wrongly  called 
the  wax  shears),  located 
between  the  two  large 
joints  of  the  hind  pair 
of  legs.  Pollen  ob- 
tained by  the  bee  in 
this  way  is  taken  to 
the  hive  to  be  used  as  food.  But  while  the  insect  is  gathering 
pollen  for  itself,  some  is  caught  on  the  hairs  and  other  projections 
on  the  body  or  legs  and  is  carried  from  flower  to  flower  (see  page  72) . 


collection  cf 
)3ollen  stores 

What  part  of  the  leg  holds  pollen  ? 


attlic  reticm. 
to  the  hive 


Why; 


Field  Exercise.  In  any  locality  where  flowers  are  abundant,  try 
to  answer  the  following  questions : How  many  bees  visit  the  locality 
in  ten  minutes?  How  many  other  insects  alight  on  the  flowers? 
Do  bees  visit  flowers  of  the  same  kind  in  succession,  or  fly  from  one 
flower  on  a given  plant  to  another  on  a plant  of  a different  kind?  If 
the  bee  alights  on  a flower  cluster,  does  it  visit  more  than  one  flower  in 
the  same  cluster?  How  does  a bee  alight?  Exactly  what  does  the 
bee  do  when  it  alights?  Try  to  decide  whether  color  or  odor  has  the 
most  effect  in  attracting  bees  to  flowers. 

The  cross-pollination  of  flowers  is  not  planned  by  the  bee ; it  is 
simply  an  incident  in  the  course  of  the  food  gathering.  The  bee 
visits  a large  number  of  flowers  of  the  same  species  during  the 


90  HOW  ARE  ANIMALS  AND  PLANTS  DEPENDENT? 


course  of  a single  trip  from  the  hive,  and  it  is  then  that  cross- 
pollination takes  place. 

Other  flower  visitors.  Other  insects  besides  the  bee  are  pollen- 
izing  agents  for  flowers.  Among  the  most  useful  are  moths  and 
butterflies.  Both  of  these  insects  feed  only  on  nectar,  which  they 
suck  through  a long  tubelike  proboscis.  The  heads  and  bodies 
of  these  insects  are  more  or  less  thickly  covered  with  hairs,  and 
the  wings  are  thatched  with  tiny  hairlike  scales.  All  these 
structures  are  of  some  use  to  the  flower  because  they  collect  and 
carry  pollen ; but  the  palp,  a fluffy  structure  projecting  from 
each  side  of  the  head  of  a butterfly,  collects  a large  amount  of 
pollen,  which  is  deposited  upon  the  stigmas  of  other  flowers  when 
the  butterfly  pushes  its  head  down  into  the  flower  tube  after  nectar. 

Flies  and  a few  other  insects  are  agents  in  cross-pollination. 
Humming  birds  are  also  active  in  pollinating  some  flowers. 
Snails  are  said  in  rare  instances  to  carry  pollen.  Man  and  animals 
may  pollinate  a few  flowers  in  brushing  past  them  through  the  fields. 

Practical  Exercise  12.  Devise  an  experiment  to  determine  if  a given  in- 
sect is  attracted  to  a given  flower  by  color  or  by  odor. 

List  in  a table  the  plants  in  your  neighborhood  that  are  pollinated  by  butter- 
flies, bees,  beetles,  flies,  bugs,  or  other  insects. 


Butterflies 

Bees 

Beetles 

Flies 

Bugs 

Other  Insects 

Self-Testing  Exercise 

(1)  is  accomplished  by  the  insect  visitors  to  flowers.  The 

chief  adaptations  in  the  bee  for  carrying  pollen  are  the (2)  on 

the  legs  and  body.  The  bee  uses  pollen  for (3)  and  carries  it 

to  the  hive  in (4) (5),  concavities  on  the (6) 

pair  of  legs (7),  (8),  (9),  (10), 

(11),  and  other  animals  may  aid  in  cross-pollinating  flowers. 

These  animals  visit  flowers  for (12)  and  not  to (13)  them 


CKOSS  I’OLLINATION 


91 


PROBLEM  X.  WHAT  ARE  SOME  SPECIFIC  EXAMPLES  OF 
CROSS-POLLINATION  ? 

Demonstration.  Sonic  of  the  material  in  the  following  paragraphs 
will  he  available  for  study.  If  possible,  supplement  the  text  with  charts 
which  can  be  used  as  a basis  for  discussion.  SnaiKlragon  may  be  sub- 
stituted for  butter-and-eggs. 


sti^ract 

anther 

pollen. 


.nectar- 


Butter-and-eggs.  From  July  to  October  in  the  East,  the  very 
abundant  weed  called  “ butter-and-eggs  ” may  be  found,  especially 
along  roadsides  and  in  sunny  fields.  It  bears  a tall  and  con- 
spicuous cluster  of  yel- 
low and  orange  flowers 
known  to  botanists  as 
a spike,  the  flowers 
being  arranged  so  that 
they  come  out  directly 
on  main  stalk. 

The  corolla  projects 
into  a spur  on  the 
lower  side ; an  upper 
two-parted  lip  shuts 
down  upon  a lower 
three-parted  lip.  The 
four  stamens  are  in 
pairs,  two  long  and 
two  short. 

Certain  parts  of  the 
corolla  are  more  brightly  colored  than  the  rest  of  the  flower. 
Butter-and-eggs  is  visited  by  bumblebees,  which  apparently 
are  guided  by  the  orange  lip  to  alight  just  where  they  can 
push  their  way  into  the  flower.  The  bee,  seeking  the  nectar 
secreted  in  the  spur,  brushes  its  head  and  thorax  against  the 
stamens.  It  may  then,  as  it  pushes, down  after  nectar,  leave 
some  pollen  upon  the  pistil,  thus  effecting  self-pollination.  Later 
in  visiting  another  flower  of  the  same  kind,  the  bee  may  leave 
some  of  the  pollen  of  the  first  flower  on  the  pistil  of  the  second 
flower,  thus  causing  cross-pollination. 


By  means  of  the  text  and  diagram  explain  how  the  bee 
transfers  pollen  from  one  flower  to  another  of  “ butter-and- 
eggs.” 


92  HOW  ARE  ANIMALS  AND  PLANTS  DEPENDENT? 

Cross-pollination  of  clover.  In  a clover  head,  which  is  a closely 
massed  cluster  of  little  flowers,  cross-pollination  is  usually  effected 

by  bumblebees  which  work 
rapidly  from  one  flower  to 
another  in  the  same  group, 
inserting  their  tongues  deep 
into  the  flower  cups. 

Cross-pollination  of  a 
composite  head.  The 
daisy,  aster,  and  sunflower 
are  examples  of  a com- 
posite head.  The  flower 
cluster  has  an  outer  circle 
of  green  parts  which  look 
like  sepals,  but  in  reality 
are  a circle  of  leaflike 
parts.  Taken  together 
these  form  an  involucre  (in'v6-lu-ker).  Inside  the  involucre  is 
a whorl  of  brightly  colored,  irregular  flowers  called  the  ray  flowers. 
They  appear  to  act,  in  some  instances  at  least,  as  an  attraction  to 
insects  by  showing  a 
definite  color  (see  the 
common  yellow 
daisy).  The  flowers 
occupying  the  center 
of  the  cluster  are  the 
disk  flowers.  Pollen 
is  carried  easily  from 
one  flower  to  another 
even  by  an  insect 
which  crawls. 

Devices  to  secure 
cross-pollination. 

There  are  many  other 
examples  of  adapta- 
tions to  secure  cross- 

...  . . The  length  of  the  filaments  and  height  of  the  stigma  may  make 

pollination  by  means  the  seif -pollination  of  loose-strife  impossible.  Why  ? 


How  does  pollination  take  place  in  a daisy? 


SE  LF-PO  LLTNATION 


93 


of  tho  visits  of  insects, 
'riie  mountain  laurel 
shows  a remarkable 
adaptation  in  haviiiii;  the 
anthers  of  the  stamens 
caught  in  little  pockets  of 
the  corolla.  The  weight 
of  the  visiting  insect  on 
the  corolla  releases  the 
anther  from  the  pocket  in 
which  it  rests  so  that  it 
springs  up,  dusting  the 
bod}'  of  the  visitor  with 
pollen. 

In  some  plants,  self- 
pollination  is  prevented 
by  certain  devices,  as  in 
the  primroses,  in  which 
the  stamens  and  pistils 
are  of  different  lengths  in 
different  flowers.  Short 
styles  and  long  filaments 
with  high-placed  anthers 
are  found  in  some  flowers, 
and  long  styles  and  short 
filaments  with  low-placed 
anthers  in  others.  Polli- 
nation is  most  likely  to  be 
effected  by  some  of  the 
pollen  from  a low-placed 
anther  reaching  the  stigma 
of  a short-styled  flower,  or 
by  the  pollen  from  a high 
anther  being  placed  upon 
a long-styled  pistil.  There 
are,  as  in  the  case  of  the 
spiked  loose-strife,  flowers 


Wright  Pierce 


A species  of  yucca  found  in  the  Southwest.  It  is 
almost  stemless,  and  has  a stout  flower  stalk  12  to  15 
feet  high  carrying  a cluster  of  fragrant,  creamy  white, 
bell-shaped  flowers. 


94  HOW  ARE  ANIMALS  AND  PLANTS  DEPENDENT? 

having  pistils  and  stamens  of  three  lengths.  Pollen  grows  best 
on  pistils  of  the  same  length  as  the  stamens  from  which  it  came. 

The  stamens  and  pistil  ripen  at  dif- 
ferent times  in  some  flowers.  The 
“ Lady  Washington  ” geranium,  a 
common  house  plant,  shows  this 
condition. 

Pollination  of  the  yucca.  A very 
remarkable  instance  of  insect  help  is 
found  in  the  pollination  of  yucca,  a 
semitropical  lily  which  lives  in  the 
washes  and  semi-desert  regions  in 
our  Southwest.  The  anthers  of  this 
flower  reach  nowhere  near  the  stigma, 
and  the  plant  has  to  depend  upon 
insects  for  fertilization.  The  insect 
which  accomplishes  this  is  the  pro- 
nuba  (pro'nu-bd)  moth.  The  female 
moth  gathers  pollen  from  the  anthers 
of  these  blossoms  and  shapes  it  into 

The  pollination  of  yucca.  What  is  the  ,,  , ^ 

moth  doing  in  the  lower  figure?  a pellet.  She  flies  to  another  flower, 

and  inserts  her  ovipositor  into  the 
ovary  of  the  flowers  and  lays  her  eggs  among  the  ovules.  She 
then  thrusts  the  pollen  ball  into  the  opening  which  extends  the 
length  of  the  style.  When  the  egg  hatches,  the  caterpillar  feeds 
on  some  of  the  young  seeds  which  have  developed  along  with  the 
larva.  Later  it  bores  its  way  out  of  the  seed  pod  and  escapes  to 
the  ground,  leaving  the  plant  to  develop  the  remaining  seeds 
without  further  molestation. 

How  the  fig  is  pollinated.  The  pollination  of  the  fig  is  another 
wonderful  example  of  adaptation.  The  fig  is  not  a fruit  but  a 
cluster  of  fruits,  growing  inside  the  inturned  ends  of  a fleshy 
flower  stalk.  There  may  be  three  kinds  of  flowers  in  the  clusters, 
some  bearing  only  stamens,  some  with  only  pistils  with  long 
styles,  and  others,  pistils  with  short  styles.  Some  fig  flower 
clusters  have  long-styled  pistillate  flowers  only,  others  contain 
both  short-styled  and  staminate  flowers,  the  latter  above  the 


POLI.IXATION  UV  THE  WIND 


95 


pistillate  flowers.  All  of  these  flowers  are  visited  by  a little  wasp 
{Blastophaga  g rosso  rum).  When  it  visits  the  short-styled  and 
staininate  fi”;,  it  lays  itsej»:ji;s  in  the  ovary,  which  it  can  easily  reach 
with  its  ejyg-deposilini’;  or{>:an  (the  ovipositor).  The  females  which 
hatch  work  tlu'ir  way  out  and  in  doinj';  so  brush  aj>;ainst  the  staini- 
nate  flowers,  thus  collecting  pollen  on  their  bodies.  They  then 
seek  other  figs  in  order  to  lay  their  eggs.  If  a wasp  reaches  another 
short-styled  flower  cluster,  the  eggs  are  laid  and  development  takes 
place  as  before.  But  if  it  flies  to  a long-styled  cluster,  it  cannot 
reach  the  ovary  to  deposit  its  eggs.  In  both  cases,  however,  the 
wasp  has  carried  pollen  to  the  stigma  and  pollination  takes  place 
with  the  subsequent  development  of  seeds.  The  figs  we  eat  are 
developed  from  the  long-styled  pistillate  flowers.  By  importing 
the  wasps  to  California  it  is  possible  to  grow  figs  where  for  years 
it  was  believed  that  the  climate  prevented  them  from  ripening. 

Pollination  by  the  wind.  Not  all  flowers  are  dependent  upon 
insects  for  cross-pollination.  Many  of  the  earliest  spring  flowers 
appear  almost  before  the  in- 
sects do.  In  many  trees, 
such  as  the  oak,  poplar,  and 
maple,  the  flowers  open  be- 
fore the  leaves  come  out. 

Such  flowers  are  usually  de- 
pendent upon  the  wind  to 
carry  the  pollen  from  the 
stamens  of  one  flower  to  the 
pistil  of  another. 

Among  the  adaptations 
that  a wind-pollinated  flower 
shows  are  : (1)  The  develop- 
ment of  many  pollen  grains  to 
each  ovule.  In  flowers  which 
are  pollinated  by  the  wind,  a 
large  number  of  the  pollen 
grains  never  reach  their  des- 
tination and  are  wasted.  Therefore  thousands  of  pollen  grains 
must  be  formed  to  every  ovule  produced . 


A wind-pollinated  flower.  What  devices  are  shown 
that  aid  in  cross-pollination? 


96  HOW  ARE  ANIMALS  AND  PLANTS  DEPENDENT? 


(2)  The  anthers  are  usually  held  high  and  exposed  to  the  wind 
when  ripe.  The  common  plantain  and  timothy  grass  are  excellent 
examples. 

(3)  The  pistil  of  the  flower  is  peculiarly  fitted  to  retain  the  pollen 
by  having  feathery  projections  along  the  sides  which  increase  the 

surface  of  the  stigma. 
All  our  grains,  wheat, 
rye,  oats,  and  others, 
have  the  typical 
feathery  pistil  of  the 
wild  grasses  from  which 
they  have  been  de- 
veloped. 

(4)  The  corolla  is 
often  entirely  lacking. 
It  would  only  be  in  the 
way  in  flowers  that  are 
dependent  upon  the 
wind  to  carry  pollen. 


Practical  Exercise  13. 

Name  five  plants  that  have 
a large  proportion  of  pol- 
Explainhow  [en  grains  to  each  flower. 

Study  a diagram  of  a grass 
flower.  Why  is  pollination 
easily  accomplished  by  the  wind?  What  is  the  “silk”  of  Indian  corn? 
Name  a flower  that  has  no  corolla.  (Look  up  in  a good  botany.) 


Why  are  the  flowers  of  the  willow  imperfect  ? 

cross-pollination  might  take  place. 


Imperfect  flowers.  Some  flowers,  the  wind-pollinated  ones  in 
particular,  are  imperfect ; that  is,  they  lack  either  stamens  or 
pistils.  In  such  flowers,  cross-pollination  must  of  necessity  be 
depended  upon.  In  some  trees,  as  the  willow,  staminate  flowers 
(those  which  contain  only  stamens)  are  developed  on  one  plant, 
and  pistillate  flowers  (those  which  bear  only  pistils)  on  another. 
Other  species  have  staminate  and  pistillate  flowers  on  the  same 
plant.  The  oak,  hickory,  beech,  birch,  walnut,  and  chestnut  are 
familiar  examples. 

Practical  Exercise  14.  Show  by  means  of  diagram  how  pollination  might 
take  place  in  the  willow. 


TESTS 


97 


Self-Tes^ping  Exercise 

Certain  flowers,  as  butter-an(l-ef>;gs,  arc  esi)ecially  fitted  to  receive 
(1),  which  cause  both (2)  and (3)  pollina- 
tion. A composite  head  is  composed  of (4)  and (5) 

flowers.  Some  flowers,  as  the  yucca,  are  only  pollinated  when  certain 

insects  (0)  their  (7)  in  them  and  the  seeds  are 

(S)  by  the  younp;  i)arasites  which  hatch  out.  Self-pollination 

is  usually  impossible  in  flowers  which  have  the  (9)  and 

(10)  maturingat (11)  times  or  placed  on (12) 

flowers.  Some  plants  have  only (13)  or (14)  flowers 

and  are  pollinated  by  the (15). 

Review  Summary 

Check  your  knowledge  of  the  unit  by  (1)  answering  all  survey  questions; 
(2)  performing  all  assigned  exercises ; (3)  checking  with  your  teacher  on  all  the 
tests  and  making  up  all  incorrect  work;  and  finally  (4)  making  an  outline  of 
the  unit  for  your  notebook. 

Test  on  Fundamental  Concepts 

Make  two  vertical  columns  in  your  notebook,  one  headed  CORRECT  and  the  other  IN- 
CORRECT. In  one  column  write  the  numbers  of  the  statements  you  believe  to  be  true.  In 
the  other  the  statements  you  think  are  false.  Your  grade  = correct  answers  times  2. 

I.  All  insects  (1)  have  two  pairs  of  wings;  (2)  have  three  body 
parts  ; (3)  have  mouth  parts  adapted  to  chewing ; (4)  have  three  pairs 
of  legs ; (5)  have  an  external  skeleton  of  chitin. 

II.  All  insects  breathe  (6)  through  their  wings;  (7)  by  taking  air 
out  of  the  water  they  drink ; (8)  through  holes  in  the  head ; (9)  by 
pumping  air  into  their  trachea;  (10)  by  swallowing  air. 

III.  Insects  may  feed  by  (11)  sucking  through  a proboscis,  as  the 
butterfly;  (12)  chewing  by  means  of  the  mandibles,  as  the  grass- 
hopper; (13)  sucking  through  a beak,  as  the  cicada;  (14)  lapping 
liquid  food,  as  the  beetle;  (15)  piercing  and  sucking,  as  the  bugs. 

IV.  The  life  history  of  an  insect  may  (16)  have  four  different 
stages ; (17)  be  passed  entirely  underground  as  in  the  beetle  ; (18)  show 
an  incomplete  metamorphosis  as  in  the  grasshopper;  (19)  show  a 
complete  metamorphosis  as  in  the  house  fly ; (20)  last  for  thirty  or 
more  years. 

V.  Insects  are  very  numerous  because  (21)  they  produce  many 
young  in  a season ; (22)  they  may  be  colored  like  their  surroundings 


98  HOW  ARE  ANIMALS  AND  PLANTS  DEPENDENT? 


and  thus  avoid  capture  ; (23)  they  all  taste  badly  to  birds ; (24)  many 
have  a long  quiescent  period  during  metamorphosis ; (25)  they  have 
few  enemies. 

VI.  Insects  when  they  visit  flowers  may  (26)  go  there  to  lay  their 

eggs;  (27)  carry  pollen  from  one  flower  to  another  of  a different 
kind ; (28)  pierce  holes  in  the  flowers  in  order  to  steal  nectar ; 

(29)  transfer  pollen  from  the  anthers  of  one  flower  to  the  pistil  of 
another  flower  of  a different  species,  thus  causing  self-pollination; 

(30)  carry  pollen  away  without  intending  it,  and  thus  cross-pollinate 
flowers. 

VII.  Fertilization  of  a flower  takes  place  when  (31)  a pollen  tube 
is  formed  ; (32)  an  insect  visits  a flower ; (33)  the  sperm  nucleus  unites 
with  the  egg  cell ; (34)  pollen  germinates  on  the  stigma  and  grows  a 
pollen  tube ; (35)  any  two  cells  meet. 

VIII.  Flowers  have  (36)  essential  organs  called  calyx  and  corolla; 
(37)  stamens,  pistil,  petals,  and  sepals ; (38)  structures  called  anthers, 
which  produce  pollen ; (39)  organs  called  ovaries,  which  hold  the  egg 
cells  ; (40)  the  possibility  of  producing  seeds  if  they  are  pollinated. 

IX.  Effective  adaptations  in  insects  for  bringing  about  cross-pol- 
lination are:  (41)  hairs  on  the  legs  and  body;  (42)  a long  piercing 
beak ; (43)  fluffy  palps,  as  in  the  butterfly ; (44)  smooth  bodies,  as  in 
the  ant ; (45)  pollen  baskets,  as  in  the  bee. 

X.  The  flowers  most  effectively  adapted  for  bringing  about  cross- 
pollination are  : (46)  flowers  with  only  stamens  or  pistils ; (47)  flowers 
with  essential  organs  of  different  lengths ; (48)  flowers  having  the 
stamens  and  pistils  ripen  at  different  times ; (49)  showy  flowers  with- 
out essential  organs ; (50)  flowers  which  prevent  insect  visitors  from 
reaching  the  pollen. 


Achievement  Test 

1.  How  can  you  tell  an  insect  from  other  animals? 

2.  Where  would  you  look  for  the  different  orders  of  insects?  From 
how  many  of  the  orders  of  insects  have  you  been  able  to  find  and 
collect  representatives  ? 

3.  How  many  kinds  of  larvae  and  pupae  in  each  of  the  above  orders 
of  insects  can  you  name  ? 

4.  Have  you  ever  studied  an  observation  hive  of  bees  ? Describe  it. 

5.  How  could  you  make  an  artificial  ant’s  nest  and  study  the  life 
of  the  colony? 


TESTS  99 

fi.  What  arc  sonio  ('xarni)les  of  protective  eoloration  or  resemblance 
and  warniiifi;  coloration? 

7.  What  are  the  parts  of  a flower  and  the  uses  of  each  part? 

S.  How  would  you  f;('rininate  pollen  "rains  in  order  to  see  a,  pollen 
tube? 

t).  How  would  you  make  a diagram  for  your  notebook  that  would 
describe  fertilization  in  a flower? 

10.  How  can  you  show  that  a flower  like  the  pea  or  apple  blossom 
will  form  a fruit?  (Diagram  for  notebook.) 

11.  What  are  all  the  adaptations  in  a bee  for  carrying  pollen?  In 
a butterfly? 

12.  How  can  j'ou  distinguish  between  self-pollination  and  cross- 
l)ollination? 

13.  How  can  you  show  by  diagram  the  way  in  which  a bee  pollinates 
butter-and-eggs,  clover,  a daisy?  (Draw  diagrams  in  notebook.) 

14.  How  does  cross-pollination  in  the  yucca  or  the  fig  take  place? 

15.  How  can  jmu  show  that  pollination  takes  place  in  (a)  a chestnut 
or  oak,  (6)  pine  cone,  (c)  timothy  grass? 

Practical  Problems 

1.  ]\Iake  a collection  of  insects  and  classify  them  according  to  the 
information  given  on  pages  59-61. 

2.  What  insects  are  most  abundant  in  your  locality?  How  can 
you  account  for  this? 

3.  Select  some  flower  and  And  out  exactly  how  it  is  pollinated. 
Make  diagrams  to  illustrate  and  explain  your  answer. 


Useful  References 

Coulter,  Barnes,  and  Cowles,  Botany.  Volume  Three,  pp.  825-878. 
American  Book  Company,  1931. 

Downing,  Our  Living  World.  Chapters  ii,  iii,  and  vi.  Longmans,  Green, 

1924. 

Holman  and  Robbins,  Textbook  of  General  Botany.  Wiley,  1927. 

Lutz,  Field  Book  of  Insects.  Putnam,  1921. 

Palmer,  Field  Book  of  Nature  Study.  Comstock,  1927. 

Snodgrass,  Anatomy  and  Physiology  of  the  Honey  Bee.  McGraw-Hill, 

1925. 

Transeau,  General  Botany.  World  Book,  1923. 


Why  are  weeds  so  plentiful  ? Why  do  weeds  grow  in  places  where 
other  plants  cannot  exist?  Do  you  know  the  common  weeds  in  your 
locality  and  the  ways  to  eradicate  them  ? Can  you  give  a scientific  defini- 
tion of  a fruit  ? Of  what  values  are  fruits  to  plants  that  produce  them  ? 


Photo  by  Wright  Pierce 


UNIT  IV 

HOW  AND  WHY  DO  SEED  PLANTS  SUCCEED  IN  LIFE? 

Preview.  Our  study  will  now  be  directed  to  two  main  problems ; 
first,  what  plants  are  most  successful  in  their  battle  of  life  and, 
second,  what  fits  them  for  this  success. 

If  you  will  go  out  any  fall  afternoon  into  the  fields,  a city  park, 
or  even  a vacant  lot,  you  can  hardly  escape  seeing  how  seeds  are 
scattered  by  the  parent  plants  and  trees.  Several  hundred  little 
seedling  trees  may  be  counted  under  the  shade  of  a single  maple 
or  oak  tree.  But  nearly  all  these  young  trees  are  doomed  to  die, 
because  of  crowding  and  lack  of  sun.  Plants,  like  animals,  are 
dependent  upon  their  surroundings  for  food  and  air.  They  need 
light  even  more  than  animals  need  it,  because  the  soil  directly 

100 


CJKOWTIl  OF  WEEDS 


101 


under  the  shade  of  a tree  gives  raw  food  material  to  the  plants, 
and  they  must  have  sunlight  in  order  to  make  it  into  food.  Over- 
crowding is  often  seen  in  tiie  garden  where  young  beet  or  lettuce 
plants  are  growing,  'fhe  gartlener  assists  nature  by  thinning  out 
the  young  plants  so  that  they  may  not  be  handicapped  in  their 
battle  for  life  by  an  insufficient  supply  of  air,  light,  and  food. 

It  is  evidently  of  considerable  advantage  to  a plant  to  be  able 
to  place  its  progeny  ^ at  a considerable  distance  from  itself,  in  order 
that  the  young  plants  may  be  provided  with  sufficient  space  to 
get  nourishment  and  foothold.  Some  plants  accomplish  this, 
particularly  weeds,  more  completely  than  others,  and  thus  they 
are  the  more  successful  ones  in  the  battle  of  life.  Besides  depriv- 
ing other  plants  of  soil  salts  and  water,  weeds  do  much  harm. 
Some  are  poisonous  to  cattle  and  sheep,  as  the  loco-weed,  hemlock, 
and  laurel.  Other  weeds,  as  the  wild  onion  or  garlic,  may  be  eaten 
by  cows,  and  the  milk  produced  will  be  ruined  in  flavor.  Some 
weeds  are  hosts  to  injurious  parasitic  insects  or  fungi ; witness  the 
Hessian  fly,  which  lives  in  some  wild  grasses,  and  the  wheat  rust, 
which  lives  in  the  barberry.  The  pollen  of  the  ragweed  and  of 
other  weeds  undoubtedly  cause  some  people  to  have  “hay  fever.” 

Weeds  are  introduced  often  into  lawns  and  fields  because  their 
seeds  are  mixed  with  the  good  seeds  which  are  sown  there.  We 
should  use  every  method  possible  to  prevent  weeds  from  producing 
seeds.  Poisons  are  used  in  some  cases  ; sheep,  which  seem  to  prefer 
some  weeds  to  grass,  are  also  a great  aid  in  keeping  down  these 
pests ; and  birds  that  eat  weed  seeds  are  the  most  valuable  of  all. 

PROBLEM  I.  WHAT  ARE  WEEDS  AND  WHAT  DO  THEY  DO? 

Weeds  are  plants  that  grow  in  places  where  they  are  not  wanted. 
They  are  generally  stronger  and  faster  growing  than  other  plants 
and  therefore  they  rob  crops  of  food,  moisture,  and  sunlight. 
Any  vacant  lot  near  the  school  will  make  a good  laboratory  for  the 
study  of  weeds.  In  such  an  area  we  shall  find  numerous  plants, 
many  alike,  and  all  growing  closely  together  in  soil  that  not  infre- 
quently appears  so  dry  and  stony  that  it  hardly  seems  possible 

1 Progeny  (proj'e-nl)  ; offspring. 


H.  BIO  — 8 


102  HOW  DO  SEED  PLANTS  SUCCEED  IN  LIFE? 


that  plants  could  grow  there.  But  weeds  do  grow  and  flourish 
under  what  seem  impossible  conditions  for  other  plants.  Let  us 
see  some  reasons  why. 

Laboratory  Exercise.  Visit  a roadside,  vacant  lot,  or  meadow  and 
observe  the  weeds  growing  there.  Collect  and,  with  the  aid  of  one  of 
the  references  given  at  the  end  of  the  unit,  try  to  classify  the  various 
weeds  growing  in  this  area.  Take  one  weed  and  study  it  carefully  to 
determine  why  it  is  successful  in  surviving.  Estimate  the  number  of 
seeds  produced,  ways  of  scattering  seeds,  protection  of  seeds,  and  other 
adaptations  of  the  plant  to  its  environment,  etc. 

Weeds  produce  many  seeds.  One  fact  readily  observed  is  that 
many  seeds  are  produced  by  weeds,  be  they  daisies,  dandelions, 
tumbleweeds,  or  ragweed.  The  table  that  follows  shows  approx- 
imately the  number  of  seeds  produced  by  an  average  sized  plant. 
In  your  project  on  weeds,  determine  as  accurately  as  possible  the 
number  of  seeds  produced  by  a plant  and  check  the  result  against 
this  table.  The  number  of  seeds  will  vary  in  different  locations. 


Estimate  of 

Seeds  Produced  by  a Single  Large  Weed 

Dandelion 

1,700 

Crabgrass 

89,600 

Cocklebur 

9,700 

Russian  thistle  . . . 

150,000 

Oxeyed  daisy  . . . 

9,750 

Pigweed 

305,000 

Prickly  lettuce  . . . 

10,000 

Purslane  (large)  . . . 

1,250,000 

Beggar  ticks  .... 

10,500 

Tumble  mustard  . . 

1,500,000 

Ragweed 

23,000 

Lambs  quarters  . . . 

1,600,000 

Burdock 

24,500 

Worm  seed  .... 

26,000,000 

Individual  Project.  Make  a collection  of  weed  seeds,  showing  kinds 
and  means  of  dispersal. 


Weeds  have  good  methods  of  seed  dispersal.  We  have  all 
seen  a dandelion  or  a thistle  and  know  the  feathery  parachutes 
by  which  their  seeds  travel.  Many  of  us  have  spent  much  time 
and  energy  in  picking  beggar-ticks  or  burdock  burs  from  our 
clothes  after  a scramble  through  a weed-infested  lot.  Weed 
seeds  or  fruits  may  have  hooks,  prickles,  fluffy  outgrowths,  or  other 
appendages,  which  are  used  for  carriage ; they  may  roll  along  the 
ground  as  the  Russian  thistle,  or  tumbleweed  ; or  they  may  have 
fruit  that  bursts  when  ripe,  scattering  their  seeds.  Some  seeds  have 


SEHl)  DISPERSAL  OF  WEEDS 


103 


cork-like  coveriiif^s  and  float  long  distances  in  streams.  Birds 
eat  some  seeds  and  scatter  them  undigested,  far  from  the  parent 
plants.  A study  by  some  school  children  showed  that  common 
weeds  given  a start  in  one  place  might  within  three  years,  under 
av('rage  conditions,  spread  from  an  area  four  acres  to  over  three 
hundretl  ticres  in  extent  around  the  point  where  they  first  came  up. 
Why  not  make  a study  in  your  home  locality  to  determine  the 
rate  of  spread  of  some  weed? 


Wright  Pierce 

The  Russian  thistle,  a tumbleweed,  breaks  loose  when  dry  and  is  blown  about  by  the  wind, 
scattering  its  seeds  as  it  rolls  along. 


Laboratory  Exercise.  Select  a common  weed  in  your  community, 
and  bring  it  into  the  laboratory.  Thrash  out  the  seeds.  Collect  and 
count  the  seeds  and  estimate  a possible  total  number  of  seeds  which 
may  be  scattered  over  a given  area  by  several  hundred  weeds. 

Weeds  have  great  vitality.  Those  of  us  who  have  tried  to  get 
rid  of  weeds  from  a garden  or  from  the  lawn  know  some  of  the 
devices  these  pests  have  to  maintain  themselves : long  and  tough 
roots  and  stems ; roots  which  develop  wherever  the  stem  touches 
the  ground;  leaves  protected  by  thorns  or  hairs;  roots  which 


104  HOW  DO  SEED  PLANTS  SUCCEED  IN  LIFE? 


store  food  which  help  the  plant  to  get  a better  start  in  the  spring ; 
the  ability  to  stand  excessive  heat  and  cold ; and  the  ability  to 
maintain  themselves  in  wet  or  dry  conditions.  They  often  grow 
luxuriously  under  conditions  that  would  kill  an  ordinary  plant 
and  grow  so  rapidly  that  they  choke  out  their  less  favored  com- 
petitors. Particularly,  their  seeds  have  great  vitality,  and  may 

stay  alive  in  the  soil 
as  long  as  twenty- 
five  years  after  dis- 
persal from  the 
parent  plant. 

Practical  Exercise  1. 

Find  a number  of  dif- 
ferent ways  in  which 
weeds  in  your  locality 
show  vitality. 

Weeds  have  good 
methods  of  self- 
protection. Some 
structures  by  which 
weeds  protect  them- 
selves have  already 
been  noted,  such  as 
the  hairs  of  the 
mullein  or  the  prickly 
stem  and  the  leaf  of 
the  thistle.  Many 
grow  low  to  the 
ground,  as  the  dan- 

The  field  daisies  are  able  to  grow  in  poor  soil  and  they  are  delion.  Some  are 
thus  able  to  smother  the  useful  plants.  distasteful  tO  ani- 

mals and  others  have  a disagreeable  odor,  as  the  wild  onion,  tansy, 
or  yarrow.  Most  weeds  have  the  ability  to  resist  disease  and 
some,  such  as  the  dodder,  are  parasites  and  get  their  living  from 
host  plants,  giving  nothing  in  return. 

Individual  Project.  Collect  and  bring  to  class  twenty-five  common 
weeds.  Mount  them  in  passe-partout  frames  under  glass.  The  col- 
lection will  be  of  much  value  in  weed  identification. 


IIAltMFUL  WEEDS 


105 


Weeds  grow  where  other  plants  cannot  live.  Many  weeds, 
because  of  long  roots  and  siiiall  leaf  surface,  are  fitted  to  live  where 
there  is  little  water  supply,  or  even  in  drouglit  or  desert  condi- 
tions. Such  are  the  Russian  thistle,  some  of  the  true  thistles, 
the  poisonous  loco  weed,  and  our  common  ragweed.  Many,  at 
least  when  young,  can  get  along  in  the  shade  of  competing  plants, 
their  rapid  growth  enabling  them  to  get  into  the  sunlight  later  on. 
Such  arc  the  mustards  which  often  color  entire  fields  yellow  with 
their  tiny  four-petalcd  flowers.  Still  other  weeds  seem  to  thrive 
under  conditions  of  soil  not  suitable  for  other  plants.  Such  are 
some  of  our  desert  and  alkali-loving  plants. 

Self-Testing  Exercise 

Weeds  are  plants  that (1)  where  they  are  not (2). 

They  are  usually (3)  and (4)  faster  than  agricultural 

plants.  They  rob  crops  of (5), (6),  and (7). 

Weeds  produce  many  (8).  tVeeds  are  plentiful  because 

they  have  good  methods  of  (9)  (10),  have  great 

(11)  and (12)  where  other  plants  cannot. 

PROBLEM  n.  WHY  AND  HOW  SHOULD  WEEDS  BE 
ERADICATED  ? 

Harmful  weeds.  Weeds  do  harm  in  a number  of  ways.  They 
reduce  the  farmer’s  crops  tremendously.  We  have  already  seen 
that  they  force  slower  growing  plants  out.  Think  of  the  amount 
of  productive  labor  lost  through  keeping  weeds  out  of  gardens  and 
fields.  Weeds  are  often  introduced  into  fields  through  the  mixing 
of  their  seeds  with  those  of  grains,  or  other  crops  bought  for  plant- 
ing. We  can  learn  to  identify  such  seeds  under  the  microscope, 
and  some  farmers  have  such  a test  made  to  see  if  the  seed  they 
buy  is  pure.  Weeds  take  the  minerals  and  water  from  the  soil 
much  faster  than  the  competing  crops  because  they  grow  so 
quickly.  Poisonous  weeds,  such  as  the  loco  weed,  may  kill  or 
injure  cattle.  Some  parasitic  weeds  like  dodder,  in  the  far  West, 
kill  great  numbers  of  other  plants.  Another  weed,  the  tall  bar- 
berry, harbors  another  much  more  dangerous  parasite,  the  wheat 
rust.  Some  wild  grasses  are  inhabited  by  the  pupae  of  the  Hes- 


106  HOW  DO  SEED  PLANTS  SUCCEED  IN  LIFE? 


sian  fly,  an  enemy  of  the  wheat  plant.  Ragweed  and  many  others 
scatter  pollen  which  causes  hay  fever  to  some  people. 


Individual  Project.  Make  a survey  of  your  community  or  town 
for  the  tall  barberry  that  harbors  wheat  rust.  Destroy  the  barberry 
by  using  either  kerosene  or  rock  salt  on  the  ground  over  the  roots. 


Poisonous  weeds.  Poison  ivy,  poison  oak,  and  poison  sumach 
cause  very  painful  blisters  to  most  people  who  touch  them.  Iron 
chloride  is  an  excellent  preventative,  and  in  potassium  permanga- 
nate dissolved  in  water  is 
a standard  relief  agent. 

Poison  ivy  is  an  ex- 
ample of  a weed  that  is 
extremely  poisonous  to 
touch.  It  is  a climbing 
plant  which  attaches  it- 
self to  trees  or  walls  by 
means  of  tiny  air  roots 
which  grow  out  from 
the  stem.  It  has  leaves 
divided  in  three  parts, 
which  aid  in  distinguish- 
ing it  from  its  harmless 
climbing  neighbor,  the 
Virginia  creeper,  which 
has  leaves  divided  in  jive 
parts.  Every  boy  and 
girl  should  know  how 
poison  ivy  looks  in  order 
to  avoid  it. 

Numerous  other  poi- 
sonous common  plants 
are  found,  one  of  which 
deserves  special  notice 
because  of  its  presence 
L.  TF.  Browneu  yacant  city  lots.  The 

Above,  poison  ivy  leaves.  Below,  leaves  of  Virginia  J KhoItit- 

creepL.  How  do  they  differ?  JuHSOn  Weed  IS  a bUShy 


POISONOUS  WEIRDS 


107 


plant,  from  two  to  five  feet  higli,  bearing  large  leaves.  It  has 
white  or  i)urplish  flowers,  and  later  bears  a four-valved  seed  pod 
containing  many  hundred  seeds.  These  plants  contain  a powerful 
poison,  and  children,  through  ignorance,  are  sometimes  made 
seriously  ill  by  eating  the  seeds  or  other  parts. 


Wright  Pierce 

A field  of  lupines.  These  are  useful  plants,  as  they  give  nitrogen  to  the  soil. 


Useful  weeds.  Some  weeds  are  not  harmful,  but  are  beautiful 
or  useful  in  some  ways.  The  daisy  in  New  York,  and  the  filaree  in 
California,  are  dear  to  those  who  love  flowers.  Water  cress,  dande- 
lion, and  some  other  weeds  are  used  as  food,  and  certain  weeds  are 
used  for  medicinal  purposes.  Plowed  under  they  may  act  as 
fertilizer,  and  in  some  places  they  form  a protective  covering  over 
the  soil,  thus  preventing  it  from  being  washed  away. 

Practical  Exercise  2.  Discuss  the  different  methods  of  weed  control  used 
in  your  community. 


108  HOW  DO  SEED  PLANTS  SUCCEED  IN  LIFE? 


How  may  we  eradicate  weeds?  We  have  seen  the  harm  that 
weeds  do.  How  can  we  get  rid  of  them?  The  best  way  would 
be  by  not  letting  them  get  started.  In  the  fall,  burn  over  all  lots 
that  contain  weeds.  Prevent  as  many  weeds  as  possible  from 
producing  seeds,  especially  those  near  gardens  or  fields  of  grain. 
This  can  be  done  by  cutting  the  weeds  before  the  seeds  mature. 
Keep  weeds  out  of  roadside  areas  by  early  cutting.  Since  sheep 
like  some  kinds  of  weeds  better  than  grass,  they  can  be  used  in 
some  localities  to  keep  down  the  weeds.  But  in  the  main,  de- 
stroying the  weeds  before  they  get  a start  seems  to  be  the  most 
effective  means  of  ridding  a place  of  them. 


Self-Testing  Exercise 

Weeds  are  injurious  to  man  because  they  (1)  his  crops. 

Some  weeds  may  (2)  cattle.  Weeds  harbor  dangerous 

(3).  Hay  fever  is  caused  by  the  pollen  of  (4). 

Wheat  rust  is  a (5).  Farmers  often  (6)  weed 

seeds  with  (7).  Weeds  may  be  eradicated  by (8), 

and (9)  them  before  their  seeds (10).  Some  weeds 

are  (11)  to (12),  and  some  for  (13).  Poi- 

son ivy  differs  from  Virginia  creeper  by  having  a leaf  divided  into 

(14) (15).  Some  poisonous  weeds  are (16) 

(17)  and (18) (19). 

PROBLEM  III.  HOW  ARE  FRUITS  AND  SEEDS  SCATTERED? 

Individual  Project.  Examine  the  fresh  or  preserved  fruits  of  huckle- 
berry, blackberry,  wild  strawberry,  wild  cherry,  black  haw,  wild  grape, 
tomato,  and  currant.  Report  how  many  of  the  above  have  seeds  with 
hard  coatings.  Notice  that  in  most,  if  not  in  all,  edible  fruits  the  fruit 
remains  green,  sour,  and  inedible  until  the  seeds  are  ripe.  In  the 
state  of  nature,  how  might  this  be  of  use  to  a plant? 

Adaptations  for  seed  dispersal : fleshy  fruits  with  hard  seeds. 

Plants  are  fitted  to  scatter  their  seeds  by  special  appendages  or 
adaptations  either  in  the  fruit  or  in  the  seed.  Various  agents, 
as  the  wind,  water,  birds,  and  other  animals,  make  it  possible  for 
the  seeds  to  be  taken  away  from  the  parent  plant. 


DlSPKliSAL  OF  SEEDS 


109 


Flosliy  fruits,  Hint  is,  such  fruits  as  contain  considerable  water 
when  ripe,  are  eaten  by  animals  and  the  seeds  are  passed  off 
undigested.  Most  wild  fleshy  fruits  have  small,  hard,  indigestible 
seeds.  Birds  are  responsible  for  scattering  the  seeds  of  many 
berries  and  other  small  fruit.  Bears  and  other  berry-eating  ani- 
mals aitl  in  this  as  well.  Some  seeds  have  especial  adaptations 
in  the  way  of  spines  or  projections.  Insects  use  these  projections 
in  order  to  carry  them  away.  Ants  plant  seeds  which  they  have 
carried  to  their  nests  for  food  supply.  Nuts  are  sometimes  planted 
by  scpiirrels  and  blue  jays. 

Hooks  and  spines.  Some  fruits  which  are  dry  and  have  a hard 
external  covering  when  ripe  possess  hooks  or  spines  which  enable 
the  whole  fruit  to  catch  in  the  coats  of  animals  and  are  thus  carried 
away  from  the  parent  plant.  Thus  the  whole  fruit  cluster  may  be 
carried  about  and  the  seeds  scattered.  In  many  of  the  compos- 
ites, as  in  the  cockleburs  and  beggar-ticks,  the  fruits  are  provided 
with  strong  curved  projections  which  bear  many  smaller  hooklike 
barbs. 

Pappus.  The  dandelion  is  an  example  of  a plant  in  which  the 
whole  fruit  is  carried  by  the  wind.  The  parachute,  or  pappus,  is 
an  outgrowth  of  the  ovary 
wall.  IMany  other  fruits,  no- 
tably that  of  the  Canadian 
thistle,  are  provided  with  the 
pappus  as  a means  of  getting 
away  from  the  parent  plant. 

In  the  milkweed  the  seeds 
have  developed  a silky  out- 
growth which  carries  them  long 
distances  from  the  parent  plant. 

Dehiscent  ^ fruits  and  how 
they  scatter  seeds.  One  of  the 
many  methods  of  scattering  How  are  the  seeds^oMhe  Canadian 

seeds  is  seen  in  dry  fruits. 

These  simply  split  to  allow  the  escape  of  the  seeds.  Examples  of 
common  fruits  that  split  open,  called  dehiscent  fruits,  are  seen  in  the 

1 Dehiscent  (de-Ms'ent)  ; opening  along  a definite  line  to  discharge  contents. 


no  HOW  DO  SEED  PLANTS  SUCCEED  IN  LIFE? 


follicle  (fol'i-k’!)  of  the  milkweed,  a fruit  which  splits  along  the 
edge  of  one  valve,  the  pod  or  legume  of  the  pea  and  the  bean,  and 
the  capsule  of  Jimson  weed  and  the  evening  primrose.  The  wild 
geranium,  a capsule  with  five  chambers,  splits  along  the  edge  of 
each  chamber,  snaps  back,  and  throws  out  the  seed  for  some  dis- 
tance. Jewel  weed  and  witchhazel  fruits  burst  open  in  a somewhat 
similar  manner. 

Winged  seeds.  The  seeds  of  the  pine,  held  underneath  the 
scales  of  the  cone,  are  prolonged  into  wings  which  aid  in  their 

dispersal.  The  seeds 
of  many  of  our  trees 
are  thus  scattered. 

Other  methods. 
Sometimes  whole 
plants  as  the  tumble- 
weeds are  carried  by 
the  high  winds  of  the 
fall.  Some  seeds  or 
fruits  (for  example, 
the  coconut)  may  fall 

How  are  these  particular  fruits  fitted  for  scattering  their  seeds?  . , ,1  , .. 

into  the  water  and  m 

a few  days  will  be  carried  to  a new  place,  the  fibrous  husk  providing 
a boat  in  which  the  seed  is  carried.  The  seeds  of  swamp  plants 
collect  in  the  mud  along  the  banks  of  ponds  and  streams,  and  birds 
which  come  there  to  feed  carry  them  away  on  their  feet.  The 
great  English  naturalist,  Charles  Darwin,  raised  eighty-two  plants 
from  seeds  thus  carried  by  birds.  It  is  probable  that  most  of 
the  vegetation  on  the  newly  formed  coral  islands  of  the  Pacific 
Ocean  may  have  come  from  seeds  brought  to  them  by  birds  and 
by  water. 

Practical  Exercise  3.  Name  five  fruits,  other  than  those  mentioned  above, 
that  scatter  their  seeds  through  the  opening  of  pods.  Name  five  trees  that 
produce  winged  seeds.  Why  has  the  Russian  thistle  become  a pest  over  such 
a large  area  in  a relatively  short  time  ? 

Indehiscent  fruits.  Dry  fruits  which  do  not  split  open  to 
allow  of  the  escape  of  their  seeds  are  known  as  indehiscent  fruits. 
Such  are  nuts,  one-seeded  fruits  usually  with  hard  outer  covering, 


STRUGGLE  FOR  EXISTENCE 


111 


the  so-called  key  fruits  of  the  maple  or  ash,  and  many  others. 
Corn,  wheat,  oats,  etc.,  are  indehiscent  fruits.  A grain  is  simply 
a one-seetled  fruit  in  which  the  wall  of  the  ovary  has  grown  so 
close  to  that  of  the  seed  that  they  cannot  be  separated.  Some 
indehiscent  fruits  are  light  and  carried  by  the  wind,  others  may 
be  scattered  by  animals. 

Individual  Project.  Make  a survey  of  your  neighborhood  to  show 
at  least  some  examples  in  every  method  of  dispersal  discussed  in  this 
unit.  Make  another  classification  of  ways  of  dispersal,  if  you  prefer. 

The  struggle  for  existence.  Those  plants  which  provide  best 
for  their  young  are  usually  the  most  successful  in  life’s  race. 
Plants  which  combine  with  the  ability  to  scatter  many  seeds  over 
a wide  territory,  the  additional  characteristics  of  rapid  growth, 
resistance  to  dangers  of  extreme  cold  or  heat  and  to  attacks  of 
parasitic  enemies,  inedibility,  and  peculiar  adaptations  to  cross- 
pollination or  self-pollination,  are  usually  called  weeds.  They 
flourish  in  the  sterile  soil  of  the  roadside  and  in  the  fertile  soil 
of  the  garden.  By  means  of  rapid  growth  they  kill  other  plants 
of  slower  growth  by  usurping  their  territory.  Slow-growing  plants 
are  thus  actually  exterminated.  Many  of  our  common  weeds 
have  been  introduced  from  other  countries  and  have,  through  their 
numerous  adaptations,  driven  out  other  plants  which  stood  in 
their  way.  Such  is  the  Russian  thistle.  First  introduced  from 
Russia  in  1873  in  flaxseed,  it  spread  so  rapidly  that  it  is  now  one 
of  the  greatest  pests  in  our  Northwest.  Water  cress,  introduced 
in  Australia  by  those  who  were  fond  of  eating  it  in  England,  has 
become  such  a pest  that  it  chokes  navigable  rivers  and  has  to  be 
dredged  out  frequently. 

Practical  Exercise  4.  Sum  up  all  the  ways  in  which  weeds  are  successful 
in  the  struggle  for  existence. 

Self-Testing  Exercise 

Seeds  of  fleshy  fruits  are  scattered  by  (1).  Animals 

scatter  seeds  that  possess  (2),  or  (3).  The  wind 

carries  the  seeds  of  (4),  (5)  (6),  and 

(7)  great  distances.  Another  common  agent  for  dispersing 


112  HOW  DO  SEED  PLANTS  SUCCEED  IN  LIFE? 


seeds  is  (8).  The  plants  that  (9)  are  those  that 

scatter  their (10)  over  a wide (11),  grow (12), 

resist  dangers  of  (13)  and  (14),  and  attacks  of 

(15). 


Summary  Outline 

Make  an  outline,  similar  to  the  ones  you  have  used  in  the  previous  units. 
Fill  it  in  for  your  notebook.  Use  it  to  make  a summary  recitation  of  the 
unit.  Test  your  knowledge  of  the  unit  by  (1)  answering  and  rechecking  the 
survey  questions ; (2)  performing  correctly  all  assigned  exercises ; (3)  checking 
the  answers  to  the  various  tests  with  your  teacher  and  correcting  all  errors. 


Test  on  Fundamental  Concepts 

Make  two  columns  in  your  notebook,  one  headed  CORRECT  and  the  other  INCORRECT. 
Place  the  numbers  of  the  statements  you  think  correct  and  incorrect  under  their  respective 
columns.  Your  grade  equals  correct  statements  X 4. 

I.  Weeds  are  abundant  because  (1)  animals  do  not  eat  them; 
(2)  they  produce  many  and  hardy  seeds ; (3)  they  have  many  devices 
to  scatter  seeds ; (4)  birds  never  eat  their  seeds ; (5)  they  can  live  in 
localities  where  other  plants  cannot  exist. 

II.  Weeds  do  harm  because  (6)  they  occupy  the  places  that  other 
plants  might  have  in  our  gardens ; (7)  they  harbor  dangerous  para- 
sites; (8)  some  are  poisonous;  (9)  sheep  may  eat  them;  (10)  some 
cause  disease,  as  hay  fever. 

III.  Weeds  may  be  fought  by  (11)  planting  large  areas  to  garden 
crops;  (12)  burning  over  the  infested  areas;  (13)  plowing  them  under 
in  the  fall;  (14)  having  sheep  feed  on  the  infested  area;  (15)  cutting 
them  in  the  spring  and  early  summer. 

IV.  Seeds  and  fruits  are  scattered  by  (16)  having  fluffy  outgrowths 
which  carry  them  through  the  air;  (17)  having  hooks  or  barbs; 
(18)  splitting  and  letting  the  seeds  out;  (19)  man;  (20)  rabbits  and 
chickens. 

V.  The  most  successful  plants  in  the  struggle  for  existence  are  those 
which  (21)  are  able  to  scatter  their  seeds  at  a distance;  (22)  have 
been  introduced  where  they  have  no  natural  enemies,  as  water  cress 
in  Australia ; (23)  grow  faster  than  others  which  occupy  the  same 
area ; (24)  are  best  fitted  to  endure  unfavorable  conditions ; (25)  pro- 
duce few  seeds. 


TESTS 


113 


Achievement  Test 

1.  TTnw  can  you  idcuitify  10  coninion  woods? 

2.  How  can  you  r('co,u:nizo  poison  ivy,  poison  oak,  poison  suiiiac? 

d.  W’liat  ar('  tho  antidotos  Tor  tlioso  poisons? 

•1.  What  aro  at  l('a-<t  t('n  w('od  soods? 

5.  What  aro  fivo  ways  in  which  a wood  scatters  seeds?  Scatters 
fruit  ? 

0.  Wliat  are  some  fruits  tliat  are  scattered  in  different  ways? 

7.  What  are  the  best  wa.ys  of  controlling  weeds  in  your  locality? 

S.  Wdiat,  if  any,  weeds  in  your  locality  harbor  dangerous  parasites? 
If  so,  what  have  you  done  toward  exterminating  these  enemies? 

Practical  Problems 

1.  Make  a weed  garden,  using  a pocket  germinator,  and  test  which 
seeds  germinate  most  quickly. 

2.  Compare  the  number  of  seeds  produced  by  some  weed  with  that 
of  some  food-producing  plant,  as  wheat.  How  do  they  compare? 

3.  IMake  a list  of  all  weeds  eaten  as  food ; used  as  medicine. 


Useful  References 

.Vtwood,  Civic  and  Economic  Biology.  Blakiston,  1922. 

Downing,  Our  Living  World.  Longmans,  Green,  1924. 

Georgia,  Manual  of  Weeds.  Macmillan,  1914. 

Hodge  and  Dawson,  Civic  Biology.  Ginn,  1918. 

The  following  pamphlets  will  be  found  very  useful  in  helping  to 
identify  common  weeds : 

Farmers  Bulletin  86,  531,  660. 

U.  S.  Dept,  of  Agric.  Bui.  28,  Weeds  and  Bow  to  Kill  Them. 

Bui.  161,  Conn.  Agric.  Station  (New  Haven). 

Bui.  31,  70,  Iowa  Agric.  Exp.  Station  (Ames). 

Bui.  50,  66,  Kansas  Agric.  Station  (Manhattan). 

Bui.  183,  Kentucky  Agric.  Station  (Lexington). 

Bui.  267,  Michigan  Agric.  College  Exp.  Station. 

Bui.  62,  North  Dakota  Agric.  Station  (Fargo). 

Bui.  59,  Ohio  Agric.  Station  (Wooster). 

Bui.  150,  South  Dakota  Agric.  Station  (Brookings). 

Bui.  48,  Univ.  of  Wise.  Agric.  Exp.  Station  (Madison). 


SURVEY  QUESTIONS 

Do  plants  need  food?  Can  you  tell  what  conditions  are  necessary  for 
a seed  to  grow  or  germinate  ? What  causes  an  engine  to  move  ? Could 
we  say  living  things  have  to  have  fuel  in  order  to  work  and  live  ? Do  you 
know  what  has  to  happen  to  this  fuel  before  it  can  be  used  ? Are  there 
any  differences  between  the  way  you  and  the  seed  make  use  of  food? 


114 


Photo  by  L.  W.  Brovmell 


PART  II.  GREEN  PLANTS  MAKE  THE 
FOOD  OF  THE  WORLD 


UNIT  V 

WHY  DO  SEEDS  GERMINATE? 

Preview.  We  have  seen  in  a previous  unit  that  the  pollination 
of  flowers  usually  results  in  the  growth  of  a fruit  containing 
seeds  from  which  new  plants  grow.  The  purpose  of  the  next 
few  pages  is  to  sho\Y  how  this  baby  plant,  or  embryo,  grows  into 
an  adult.  Every  boy  and  girl  knows  that  a dry  seed,  after  lying 
dormant  and  apparently  dead  sometimes  for  months,  will  wake 
up  and  show  signs  of  life  when  certain  outside  conditions  are 
favorable.  Evidently  some  conditions  outside  the  seed  start 
the  growth  of  the  little  baby  plant  within  the  seed  coats.  There 
are  several  things  which  are  absolutely  necessary  for  germination, 
as  this  beginning  of  growth  is  called.  The  seed  must  first  be  pro- 
vided with  a protective  coat  which  keeps  the  delicate  baby  plant 
within  from  being  harmed.  Then  it  must  be  able  to  live  for  long 
periods  under  adverse  conditions  such  as  extreme  dryness  or  lack 
of  soil.  Many  seeds,  especially  those  of  weeds  and  some  garden 
seeds,  such  as  the  radish,  cabbage,  carrot,  cauliflower,  cucumber, 
and  turnip,  may  live  for  as  long  as  ten  years  before  being  germi- 
nated, but  the  average  age  that  a seed  lives  is  much  less  than  this. 
The  stories  of  germinating  of  wheat  found  in  the  Tombs  of  the 
Pharaohs  may  be  disbelieved,  although  recently  some  lotus  seeds, 
believed  to  be  at  least  four  hundred  years  old,  were  taken  from  a 
dried  lake  bed  in  the  Gobi  Desert,  and  were  successfully  germi- 
nated. But  the  reason  that  these  seeds  retained  their  vitality  was 
because  they  were  protected  from  decay  by  the  peat  bog  in  which 
they  were  embedded. 


115 


116 


WHY  DO  SEEDS  GERMINATE? 


Two  sets  of  factors  are  necessary  for  the  growth  of  seeds: 
first,  the  presence  of  food  substances  inside  the  seed  in  order  to 
give  the  baby  plant  a start  in  life  ; and,  secondly,  certain  stimulat- 
ing factors  outside  the  seed,  such  as  air,  moisture,  and  warmth. 
Experiments  which  you  can  do  yourself  and  observations  you  can 
make  in  almost  any  garden  show  the  necessity  of  these  factors 
very  clearly.  One  value  you  will  get  from  this  unit  will  be  the 
opportunity  you  have  for  determining,  by  means  of  certain  simple 
experiments,  the  factors  which  control  the  beginnings  of  growth 
in  a seed. 

It  is  a trite  but  true  saying  that  we  grow  because  we  use  food. 
The  same  is  true  of  plants.  Certain  food  substances,  the  organic 
nutrients  (such  as  carbohydrates,  fats,  and  proteins),  are  found 
in  seeds.  We  eat  peas  and  beans.  If  we  test  these  seeds,  we  can 
show  the  presence  of  foodstuffs  within  them.  The  pea  or  bean 
seedling  uses  the  locked-up  energy  within  the  foods  in  order  to 
break  out  of  the  seed  coat  and  force  their  growing  roots  and  stems 
through  the  soil.  The  little  plants  also  grow  in  size.  This  indi- 
cates quite  clearly  that  some  of  the  nutrients  within  the  seed  are 
transformed  in  some  mysterious  manner  into  the  living  material 
out  of  which  the  plant  is  built.  Later  we  shall  be  able  to  make  a 
comparison  of  the  manner  in  which  these  nutrients  are  used  by  the 
plant  with  the  way  in  which  we  use  these  same  food  substances. 
It  will  be  sufficient  to  say  here  that  the  foods  which  are  really 
outside  of  the  baby  plant  must  be  changed  from  a solid  food  sub- 
stance into  a liquid  form  so  that  the  cells  out  of  which  it  is  formed 
may  absorb  the  food  substances  into  their  own  bodies.  This 
process  of  changing  insoluble  foods  into  soluble  food  substances 
is  called  digestion. 

PROBLEM  I.  WHERE  ARE  BABY  PLANTS  FOUND? 

Laboratory  Exercise.  Make  a drawing  of  a bean  pod.  Mark  all 
the  parts  of  the  flower  that  you  can  find  in  it.  What  is  a pod?  Now 
open  the  pod  and  examine  the  seeds.  How  are  they  attached? 
Remove  a bean,  open  it,  and  find  the  tiny  future  stem  and  leaves  of 
the  baby  plant  between  the  two  “ halves  ” of  the  bean  called  the 
cotyledons.  Referring  to  the  next  paragraph,  draw  and  label  all  the 
parts  of  the  bean  seed. 


THE  BEAN 


117 


The  bean.  If  we  open  ca  bean  pod,  we  find  the  seeds  lying 
along  one  edge  of  the  pod,  each  one  attached  to  the  inner  wall  at 
the  placenta  by  a little  stalk  through  which  it  gets  its  nourishment. 
The  stalk  leaves  a scar  on 
the  coat  of  tlie  l)ean,  called 
the  hihini  (In'l-am).  The 
tiny  hole  near  the  hi  him 
is  the  micropijle  (ml'kr6- 
pil).  Turn  to  the  diagram 
on  page  So,  showing  the 
fertilization  of  an  ovule. 

Find  there  the  little  hole 
through  which  the  pollen 
tube  reached  the  embryo 
sac.  This  small  structure, 
the  micropyle,  remains 
and  is  found  in  the  seed. 

The  thick  seed  coat,  the 
testa,  is  readily  removed 
from  a soaked  bean.  The 
seed  then  separates  into 
two  parts : the  cotyledons 
or  seed  leaves.  The  rodlike  part  between  the  cotyledons  is  called 
the  hypocotyl  (hi'p6-k6t'il).  This  will  later  form  the  root  and 
part  of  the  stem  of  the  young  bean  plant.  The  first  true  leaves, 
very  tiny  structures,  are  folded  together  between  the  cotyledons, 
and,  with  the  future  stem,  are  known  as  the  plumule  (ploo'mul). 
All  the  parts  of  the  seed  within  the  seed  coats  form  the  embryo 
or  young  plant.  A bean  seed  contains,  then,  a tiny  plant  pro- 
tected by  a tough  coat. 

Practical  Exercise  1.  Using  a number  of  seeds,  show  to  the  class  the  pres- 
ence of  an  embryo  in  each.  Does  it  occupy  the  same  position  in  each  case? 

Write  in  your  notebook  a good  definition  of  a seed. 

Food  in  the  cotyledons.  The  laboratory  work  shows  us  that 
a seed  really  contains  a baby  plant  or  embryo,  with  a sufficient 
supply  of  food  to  give  it  a start  in  life.  The  problem  now  before 
us  is  to  find  out  how  the  embryo  of  the  bean  is  adapted  to  grow 

H.  BIO  — 9 


.....remains  of  stigmcc 
ancC 


A pod  opened  to  show  aUachment  of  seeds.  Find 
the  parts  of  the  flowers. 


118 


WHY  DO  SEEDS  GERMINATE? 


into  an  adult  plant.  Up  to  this  stage  of  its  existence  it  has  had 
the  advantage  of  food  and  protection  from  the  parent  plant.  Now 
it  must  begin  the  battle  of  life  alone.  We  shall  find  in  all  our  work 
with  plants  and  animals  that  the  problem  of  food  supply  is  one 
of  the  most  important  problems  to  be  solved  by  the  growing 
organism.  Let  us  see  if  the  embryo  is  able  to  get  a start  in  life 
(which  many  animals  get  in  the  egg)  from  food  provided  for  it 
within  its  own  body. 


Self-Testing  Exercise 

The  bean  pod  contains (1)  which  under  favorable  condi- 
tions will (2).  The (3)  is  the  baby  plant  within  the 

(4).  Its  parts  are  the  (5),  the  (6),  and 

the (7),  The (8)  contain  the  food  supply  for  the 

(9). 


diluted: 

stanch 

paste.. 


PROBLEM  II.  WHAT  ARE  THE  TESTS  FOR  THE  ORGANIC 
NUTRIENTS  FOUND  IN  SEEDS? 

Demonstration  1.  Test  for  starch.  Boil  water  with  some  laundry 
starch  in  a test  tube,  then  cool  it,  and  add  to  the  mixture  two  or  three 

drops  of  iodine  ^ solu- 
tion. The  mixture  in 
the  test  tube  turns 
purple  or  deep  blue. 
It  has  been  learned 
after  many  experi- 
ments that  starch  is 
turned  purple  or 
dark  blue  by  iodine. 
Therefore,  iodine  so- 
lution is  used  as  a 
test  for  the  'presence  of 
starch. 

Demonstration  2. 
Test  for  oils.  If  a 

substance  is  rubbed 
on  brown  paper  or  is 
placed  on  paper  and 
then  warmed  in  an 
oven,  the  presence  of 

1 Iodine  solution  is  made  by  simply  adding  a few  crystals  of  iodine  to  95  per  cent 
alcohol ; or,  better,  take  by  weight  1 gram  of  iodine  crystals,  f gram  of  iodide  of 
potassium,  and  dilute  to  a dark  brown  color  in  weak  alcohol  (35  per  cent)  or  dis- 
tilled water. 


NUTRIENTS  IN  THE  BEAN 


119 


vhite 

of 

in 

solution. 


nitric 
-l-acid. 
and 
heat  = 


Cool, 

4- add  in 
excess, 
ammonia = 


oil  will  be  shown  by  a translucent  spot  on  the  paper.  Since  the  propor- 
tion of  oil  in  beans  is  small,  it  is  better  to  try  this  test  with  a walnut. 

Demonstration  3.  Test  for  protein.  Another  nutrient  present 
in  the  bean  cotyledon 
is  protein.  Several 
tests  are  used  to  de- 
tect the  presence  of 
tliis  nutrient.  The 
following  is  one  of  the 
best  known : 

Place  in  a test  tube 
a bit  of  hard-boiled 
white  of  egg.  Pour 
over  it  an  SO  .per  cent 
nitric  acid,  and  heat 
the  tube  gently.  Note 
the  color  — a lemon 
yellow.  Wash  thor- 
oughly and  add  a 
little  ammonium  hy- 
droxide ; the  color 
turns  a deep  orange. 


Practical  Exercise  2.  Test  a number  of  substances  for  the  presence  of 
starch,  fat,  and  protein.  Give  your  findings  in  tabular  form.  What  is  the 
value  of  knowing  these  tests  ? 


Nutrients  in  the  bean.  If  we  mash  up  a small  piece  of  a bean 
cotyledon  which  has  been  previously  soaked  in  water,  and  test  it 
with  iodine  solution,  the  characteristic  blue-black  color  appears, 
showing  the  presence  of  starch.  If  a little  of  the  stained  material 

is  mounted  in  water  on  a glass  slide 
under  the  compound  microscope,  we 
shall  find  that  the  starch  is  in  the 
form  of  little  ovoid  bodies  called 
starch  grains.  The  starch  grains  and 
other  food  products  are  made  use  of 
by  the  embryo. 

A test  of  the  cotyledon  of  a bean 
with  nitric  acid  and  ammonium 
hydrate  shows  us  the  presence  of 
protein.  Beans  are  found  by  many 
tests  to  contain  about  23  per  cent  of  protein,  59  per  cent  of 
carbohydrates,  and  2 per  cent  of  oils.  The  young  plant  within 


Cells  from  a potato,  imder  microscope. 
Which  part  of  the  cell  turns  blue  with 
iodine  ? 


120 


WHY  DO  SEEDS  GERMINATE? 


a bean  is  thus  shown  to  be  well  supplied  with  nourishment  until 
it  is  able  to  take  care  of  itself.  In  this  respect  it  is  somewhat  like 
a young  animal  within  the  egg,  such  as  a bird  or  fish.  All  of  our 
cereal  foods  are  made  from  seeds  or  grains  that  contain  proteins, 
carbohydrates,  and  oils.  Seeds  also  contain  water  and  mineral 
matter,  as  can  be  shown  by  simple  experiments. 

Self-Testing  Exercise 

(1)  solution  is  used  to  (2)  for  the  presence  of 

starch.  If  the (3)  tested  turns  dark (4)  or (5)  > 

we  know  that  starch  is  present.  Oil  is  known  by  the  presence  of  a 

(6)  spot  when  the (7)  is  heated  on (8).  To 

test  for  protein  we  add (9) (10)  to  the  substance  : if 

it  turns (11) (12),  it  is  an  indication  that (13) 

is  present.  If (14)  (15)  is  then  added  to  the  sub- 
stance and  it  turns  a deep  (16)  color,  we  may  be  sure  that 

it  is  a protein. 


PROBLEM  III.  WHAT  FACTORS  ARE  NECESSARY  TO 
AWAKEN  THE  EMBRYO  WITHIN  THE  SEED? 

Demonstration  4.  To  show  how  much  water  is  needed  for  the 
germinating  of  peas. 

Materials.  Soaked  and  dry  peas,  sawdust,  cups. 

Method.  Place  an  equal  amount  of  moist  sawdust  in  the  bottom  of 
each  of  two  cups.^  Put  ten  soaked  peas  in  each.  In  a third  cup  con- 
taining dry  sawdust  put  ten  dry  peas.  Keep  the  seeds  in  one  cup 
partially  covered  with  water,  those  in  the  second  slightly  moistened,  and 
those  in  the  third  dry.  Keep  the  cups  covered  in  a moderately  warm 
place.  Examine  them  daily  for  four  days.  Tabulate  your  results. 

Conclusion.  Which  amount  of  water  seems  best  for  germination? 
Give  your  reasons. 

How  much  water  does  a seed  need  in  order  to  germinate? 

The  exact  amount  of  water  which  is  most  favorable  for  the  ger- 
mination of  a seed  can  be  determined  only  by  careful  experiment. 

1 Pupils  performing  this  or  any  other  experiments  must  remember  that  the  suc- 
cess of  an  experiment  depends  upon  the  accuracy  with  which  it  is  performed  and 
the  exclusion  of  all  factors  from  the  experiment  except  the  one  which  they  are  try- 
ing to  prove.  For  example,  in  the  experiment  on  the  effect  of  different  amounts  of 
moisture,  all  the  other  factors  — temperature,  light,  food,  etc.  — must  be  the  same 
in  each  of  the  three  cups ,'  the  only  variable  factor  being  moisture. 


TEMPKKATURE  FOR  GROWING  SEEDS 


121 


An  ovorsupply  of  water  may  prevent  {growth  of  seeds  almost  as 
effectually  as  no  water  at  all.  In  general  the  amount  most  favor- 
able for  germination  is  a moderate  supply.  Seeds  rapidly  lose 
their  vitality  if  kept  in  a very  moist  atmosphere,  especially  if  the 
moist  air  is  hot.  If  seeds  are  given  too  much  water  they  drown. 

Demonstration  6.  To  show  the  best  temperature  for  germinating 
peas. 

Matcnnls.  Soaked  peas,  sawdust,  boxes. 

Method.  Plant  twenty  soaked  peas  in  each  of  three  boxes  containing 
moist  sawdust.  Put  one  box  in  a place  where  the  temperature  is 
about  150°  F.,  another  where  the  temperature  is  about  70°  F.,  and  the 
third  where  the  temperature  is  about  40°  F.  Give  to  all  the  same  con- 
ditions of  air,  light,  and  moisture.  Observe  them  for  four  days. 
Tabulate  the  daily  observations. 

Conclusion.  State  what  temperature  seems  best  for  germinating 
peas.  Give  reasons. 

What  is  the  best  temperature  for  germinating  seeds?  Here 
again  our  experiment  answers  the  question  only  for  the  seed  with 
which  we  are  working.  Peas  germinate  best  at  one  temperature, 
corn  another,  wheat  still  another  — or  more  properly,  each  variety 
of  a seed  has  a certain  temperature  (called  its  optimum)  at  which 
it  germinates  best.  It  is  this  fact  that  makes  possible  the  earlier 
germination  of  some  garden  seeds. 

Demonstration  6.  To  show  that  air  is  necessary  for  germinating 
peas. 

Materials.  Soaked  peas,  bottles,  sawdust. 

Method.  Place  an  equal  amount  of  moist  sawdust  in  the  bottom  of 
two  bottles.  Fill  one  bottle  full  of  peas  and  close  it  securely  with  a 
stopper.  Put  about  twenty  peas  in  the  bottom  of  the  other  bottle. 
Examine  the  bottles  daily  for  four  days. 

Conclusion.  In  which  bottle  did  germination  take  place?  Why? 

Why  is  air  necessary  for  germination  ? All  living  things  respire 
or  use  oxygen  in  order  to  release  energy  and  a seed  is  no  exception 
to  the  general  rule.  Without  an  ample  supply  of  oxygen  it 
cannot  release  from  its  food  supply  the  energy  necessary  for  its 
growth.  Hence  a constant  supply  of  fresh  air  is  an  important 
factor  in  the  germination  of  seeds.  If  the  seeds  are  planted  in  the 
ground  it  is  necessary  for  the  soil  to  be  sufficiently  loose  so  that 
air  can  penetrate  it. 


122 


WHY  DO  SEEDS  GERMINATE? 


Self-Testing  Exercise 

In  order  for  seeds  to  germinate  they  need  a (1)  supply  of 

(2),  a certain  degree  of  (3),  and  (4).  The 

amount  of  (5)  required  for  germination  varies  with  the  kind 

of  (6).  If  too  much  ........  (7)  is  used,  some  seeds  will 

(8)  or  decay. 

PROBLEM  IV.  WHAT  BECOMES  OF  THE  PARTS  OF  THE 
EMBRYO  DURING  ITS  GROWTH  INTO  A YOUNG  PLANT? 

Germination.  If  you  plant  a number  of  soaked  kidney  beans 
in  damp  soil  or  sawdust  and  at  the  end  of  each  day  remove  one, 
you  will  be  able  to  obtain  a complete  record  of  the  growth  of  the 
kidney  bean.  The  first  signs  of  germination  are  the  breaking  of 


Stages  in  the  growth  of  a bean.  Note  the  direction  of  growth  in  the  root.  How  does  the  cotyle- 
don get  out  of  the  ground  ? What  has  happened  to  the  hypocotyl  in  the  right-hand  figure  ? 

the  testa  and  the  pushing  outward  of  the  hypocotyl  to  form  the 
first  root  which  grows  downward.  A later  stage  shows  the 
hypocotyl  forming  an  arch  and  dragging  the  bulky  cotyledons 
after  it.  The  stem,  as  soon  as  it  is  released  from  the  ground, 
straightens  up.  The  cotyledons  open,  and  between  them  the 


GERMINATION 


123 


biidliko  plumule  grows  upward,  forming  the  first  true  leaves  and 
all  of  the  stem  above  the  cotyledons.  As  growth  continues,  we 
notice  that  the  cotyledons  become  smaller  and  smaller,  until  their 
footl  contents  are  completely  absorbed  by  the  young  plant.  The 
young  plant  now  has  roots  and  leaves  and  is  able  to  care  for  itself 
and  may  be  said  to  have  passed  through  the  stages  of  germination. 

Laboratory  Exercise.  Examine  several  stages  in  the  growth  of  the 
{)ea  or  bean.  iMake  drawings  for  your  workbook  to  illustrate  at  least 
three  of  the  stages  described  below. 

Practical  Exercise  3.  Look  up  in  seed  catalogs  or  gardening  books  how 
deep  you  should  plant  several  different  kinds  of  seeds.  Is  there  any  relation 
between  the  depth  of  planting  and  the  size  of  the  seed?  If  so,  explain  this. 


Self-Testing  Exercise 

When  a bean  seed  germinates,  the (1)  first  grows (2). 

Then  it  develops  an (3)  which  draws  up  the (4)  as  it 

grows  upward.  Later  the (5)  develops.  During  this  growth  the 

(6)  are  used  up  as (7)  by  the (8) (9). 


PROBLEM  V.  WHAT  MAKES  A YOUNG  PLANT  GROW? 

Demonstration  7.  To  prove  that  growing  seeds  oxidize  food. 

Materials.  Bottle,  rubber  stopper,  thistle  tube,  delivery  tube,  soaked 
peas,  blotting  paper,  and  limewater. 

Method.  Put  some  soaked  peas  in  the  bottom  of  a bottle  containing 
some  soaked  blotting  paper.  Fit  the  bottle  with  a rubber  stopper  con- 
taining a thistle  tube  and  a delivery  tube. 

Watch  for  evidences  of  growth  in  the  bottle.  At  the  end  of  forty- 
eight  hours,  insert  the  delivery  tube  in  a tube  of  limewater.  Pour 
water  through  the  thistle  tube  into  the  bottle.  What  happens  to  the 
limewater  ? Why  was  water  poured  through  the  thistle  tube  ? 

Conclusions.  Remembering  what  you  have  learned  in  your  previous 
experiments,  account  for  what  happened.  Why  did  the  seeds  start 
to  grow?  From  what  source  did  the  seeds  get  their  energy  to  grow? 

Write  a brief  statement,  using  proof  to  show  that  energy  is  stored 
in  food  and  that  it  can  be  released  and  used  only  by  oxidation. 

What  makes  an  engine  go.  If  we  examine  the  sawdust  or  soil 
in  which  the  seeds  are  growing,  we  find  it  forced  up  by  the  growing 
seeds.  Evidently  work  was  done ; in  other  words,  energy  was 


124 


WHY  DO  SEEDS  GERMINATE? 


example  of  release  of  en- 
placed  in  the  fire  box  and 
furnace  is  opened  so  as  to 
make  a draft  of  air  which 
will  reach  the  coal.  The 
coal  burns,  heat  is  released, 
causing  the  water  in  the 
boiler  to  make  steam,  the 
engine  wheels  to  turn, 
and  work  is  accomplished. 
Let  us  see  what  happens 
from  the  chemical  stand- 
point. 

Coal  is  formed  largely 
from  dead  plants,  which 
were  long  ago  pressed  into 
the  present  hard  form  of 
coal.  It  contains  a large  amount  of  the  chemical  element  carbon. 
We  have  already  observed  one  of  the  effects  of  the  oxidation  of 
carbon  as  proved  by  the  limewater  test.  Let  us  now  apply  this 
test  to  the  oxidation  of  food  substances  in  our  own  bodies. 

Demonstration  8.  To  prove  that  food  materials  are  oxidized  by  the 
human  body.  Expel  air  from  the  lungs  through  a tube  into  a bottle 
of  limewater.  Note  what  happens.  As  a control  pass  air  from  the 
room  through  limewater.  Explain  your  results. 

Oxidation  in  our  bodies.  In  life  the  temperature  of  the  body 
(98.6°  Fahrenheit)  is  due  to  oxidation  within  the  cells.  Food  is 
also  oxidized  within  the  human  body  to  release  energy  for  our 
daily  work.  In  fact,  all  living  things,  both  plant  and  animal, 
release  energy  as  the  result  of  oxidation  of  food  within  their  cells. 

Self-Testing  Exercise 

The  presence  of (1) (2)  in  large  amounts  in  the  air 

surrounding  seeds  growing  in  a closed  jar  indicates  that  they  have 

(3)  food  within  their  bodies.  The (4)  of (5) 

in  the  body  releases (6)  to  do  work.  When  seeds  grow  they  take 

in (7)  and  give  off (8) (9). 


released  by  the  seeds.  A familiar 
ergy  is  seen  in  an  engine.  Coal  is 
lighted,  and  the  lower  door  of  the 


Why  is  the  growth  of  seeds  in  flask  B greater  than 
that  in  flask  A ? 


ENDOSPERM  IN  SEEDS 


125 


PROBLEM  VI.  WHERE  IS  THE  FOOD  SUPPLY  OF  DIFFERENT 
SEEDS? 

Laboratory  Exercise.  To  study  the  structure  and  composition  of 
a grain  of  corn. 

Materials.  Soak  corn  grains,  some  whole  and  some  cut  lengthwise 
at  right  angles  to  the  fiat  surface. 

Method  and  Observations.  In  whole  corn  grain  find  a light-colored 
area  on  one  side.  This  marks  the  position  of  the  embryo. 

In  a grain  cut  lengthwise  at  right  angles  to  the  flat  side  find  the 
embryo.  Describe  its  shape,  position,  and  relative  size  compared 
with  'the  rest  of  the  corn  grain.  The  area  outside  of  the  embryo  is 
known  as  the  endosperm.  Place  iodine  on  the  surface  of  the  cut 
corn  grain.  Describe  what  happens.  Test  a grain  of  corn  for  protein. 

Conclusion.  What  nutrients  are  present  in  the  corn?  Where  are 
they  found  ? 

Endosperm  the  food  supply  of  com.  We  find  that  the  one 
cotyledon  of  the  corn  grain  does  not  serve  the  same  purpose  to  the 
young  plant  as  do  the  two  cotyle- 
dons of  the  bean.  We  find  both 
starch  and  protein  in  the  corn 
cotyledon,  and  it  is  evident  from 
our  tests  that  the  endosperm  is  the 
chief  source  of  food  supply.  The 
study  of  a thin  section  of  the  corn 
grain  under  the  compound  micro- 
scope shows  us  that  the  starch 
grains  in  the  endosperm  are  large 
and  regular  in  size.  When  the 
embryo  has  grown  a little,  an  ex- 
amination shows  that  the  starch 
grains  near  the  edge  of  the  cotyle- 
don are  much  smaller  and  quite 
irregular,  having  large  holes  in 
them.  This  means  that  the  starch 
is  being  used  by  the  young  plant. 

Seeds  with  endosperm.  In  the 
seeds  of  the  pea  and  bean  we  have  found  that  the  embryo  takes 
up  all  the  space  within  the  seed  coats.  There  are  some  plants 
that  have  food  stored  outside  of  the  embryo  Such  a plant  is  the 


Longitudinal  section  of  a grain  of  corn. 
Find  the  embryo.  Is  the  corn  a seed  or 
a fruit  ? Why  ? 


126 


WHY  DO  SEEDS  GERMINATE? 


aspara^s 


y>inc^ 


castor  heaxL 


T^oCo'^' 

•peanut 


Seeds  always  contain  a food  supply  which  may  be  either  in  the  coty- 
ledons of  the  embryo  or  in  an  endosperm  outside  of  the  embryo. 


castor  bean.  A section  cut  vertically  through  the  castor  bean 
discloses  a white  oily  mass  directly  under  the  seed  coats.  This 
mass  is  called  the  endosperm.  If  it  is  tested  with  iodine,  it  will  be 

found  to  contain 
starch;  oil  is  also 
present  in  consid- 
erable quantity. 
Within  the  endo- 
sperm lies  the  em- 
bryo, a thin,  whitish 
structure. 

Monocotyledons, 
dicotyledons,  and 
polycotyledons.  Plants  that  bear  seeds  having  but  a single  cotyle- 
don in  the  embryo  are  called  monocotyledons.  Although  we  find 
many  monocotyledonous  plants  in  this  part  of  the  world,  the  group 
may  be  said  to  be  characteristic  of  the  tropics.  Sugar  cane  and 
many  of  the  large  trees,  such  as  the  date  palm,  palmetto,  and 
banana,  are  examples.  Among  the  common  monocotyledons  of 
the  north  temperate  zone  are  corn,  lilies,  grasses,  grains,  and 
asparagus. 

Dicotyledons,  or  plants  having  two  cotyledons  in  the  seed,  are 
those  with  which  we  come  in  contact  most  frequently  in  daily 
life.  Many  of  our  garden  vegetables,  peas,  beans,  squashes, 
melons,  etc.,  all  of  our  great  hardwood  forest  trees,  beech,  oak, 
birch,  chestnut,  and  hickory,  the  shade  trees  of  our  city  streets, 
elm,  maple  and  poplar,  all  of  our  fruit  trees,  pears,  apples,  peaches, 
and  plums,  and,  in  fact,  a very  large  proportion  of  all  plants 
living  in  the  north  temperate  zone,  are  dicotyledons. 

A third  type  of  plant,  with  more  than  two  cotyledons,  is  the 
group  called  the  poly  cotyledons,  represented  by  the  pines  and  their 
kin.  Such  plants  furnish  most  of  the  lumber  and  shingles  used 
in  the  construction  of  frame  houses.  The  soft  woods,  as  the  pines, 
hemlocks,  spruces,  and  other  “ evergreens,”  are  also  of  much 
value  in  the  manufacture  of  paper.  The  wood-pulp  industry  has 
grown  to  such  proportions  as  to  be  a menace  to  our  softwood 
forests. 


KH  LF-TKST I NO  EXERCISE 


127 


Brooklyn  Botanical  Garden,  Brooklyn,  N.  Y 

The  upper  picture  shows  date  palms  growing  in  Algeria ; the  lower  left  shows  a white  oak 
tree  ; and  the  lower  right  shows  a white  pine  tree.  Why  are  these  trees  classified  as  mono- 
cotyledons, dicotyledons,  and  polycotyledons  respectively. 

Self-Testing  Exercise 

Seed  plants  are  divided  into  three  groups  : (1), (2), 

and (3).  In  the  first,  the  food  is  stored  in  the (4), 

while  in  the  second  group  it  is  in  the (5).  Corn  is  a (6), 

while  the  bean  is  a (7).  The  pine  is  an  example  of  a 

(8). 


128 


WHY  DO  SEEDS  GERMINATE? 


PROBLEM  VII.  HOW  DOES  THE  CORN  GRAIN  MAKE  USE 
OF  STORED  FOOD? 

Demonstration  9.  How  is  the  endosperm  used? 

Remove  the  endosperm  from  some  corn  grains  that  have  just  started 
to  sprout.  Place  them  in  moist  sawdust  side  by  side  with  some  normal 
sprouted  grains.  Give  each  lot  of  seedlings  the  same  conditions  of 
water,  light,  and  air. 

Watch  them  carefully  for  at  least  two  weeks.  What  differences  do 
you  observe  in  the  rates  of  growth  in  the  two  lots  of  seedlings? 

Conclusion.  What  is  the  relation  of  the  endosperm  to  growth? 

Changes  in  the  food  supply  of  a seed  during  germination.  We 

have  learned  that  the  chief  source  of  the  food  supply  of  the  corn 
grain  is  the  endosperm  which  contains  starch  and  also  some  pro- 
tein in  its  outer  parts.  These  foods  are  in  an  insoluble  form.  In 
order  that  the  growing  embryo  may  make  use  of  the  stored  nutri- 
ents they  must  be  changed  into  a soluble  form  so  that  they  may 
be  carried  out  of  the  endosperm  through  the  cotyledon  to  the 
growing  parts  of  the  embryo.  Starch  can  easily  be  changed  by 
the  process  of  digestion  into  grape  sugar  or  glucose  ^ which  is 
soluble.  We  know  that  the  germinating  corn  grain  has  a sweeter 
taste  than  that  which  is  not  growing.  This  is  noticed  also  in 
sprouting  barley  or  malt.  The  germinating  grain  contains  grape 
sugar  which  has  been  formed  from  the  starch.  This,  with  protein 
which  has  also  been  digested  in  the  endosperm,  passes  from  cell 
to  cell  and  thus  reaches  the  growing  part  of  the  embryo. 

This  process  of  chemical  change  or  digestion  cannot  take  place 
in  dry  seeds.  Water  must  be  absorbed  by  the  seed,  first,  in  order 
to  allow  digestion  to  take  place  and,  second,  to  allow  the  soluble 
material  to  dissolve  and  pass  through  the  cells.  This  digestion 
cannot  take  place  without  a moderate  degree  of  warmth.  For 
this  reason  moisture  and  warmth  are  necessary  for  germination. 

Test  for  grape  sugar.  Just  after  the  test  for  starch  was  worked 
out,  a chemist  by  the  name  of  Fehling  prepared  a solution  which 
is  named  in  honor  of  him  and  which  is  used  as  a test  for  glucose. 
An  American  chemist.  Dr.  Benedict,  modified  this  solution  and  we 
can  now  use  either  the  Fehling  or  the  Benedict  solution  as  a test 
for  glucose. 

1 Grape  sugar,  or  glucose,  is  a simple  kind  of  sugar'  found  in  many  plants  and  is 
the  form  in  which  digested  starch  is  passed  on  to  the  plant  cells. 


DIGESTIONS 


129 


Demonstration  10.  To  show  the  test  for  grape  sugar. 

Materials.  Glucose,  Fciiliiig’s  or  Benedict’s  solution,^  test  tubes, 
Bunsen  burner. 

Method.  Place  in  a test  tube  a little  glucose  and  water.  Add  to  it 
'-an  equal  volume  of  Eehling’s  solution.  Heat  the  mixture  to  the  boiling 
point. 

If  the  color  of  the  mixture  becomes  brick  red  after  heating  a short 
time  with  Fehling’s  solution,  then  grape  sugar  is  present,  a precipitate 
will  be  formed  having  a red,  yellow,  or  green  color,  depending  upon  the 
amount  of  sugar  present. 

Conclusion.  Is  Fehling’s  solution  a test  for  cane  sugar?  Explain. 

Laboratory  Exercise.  Wash  some  dry,  imsprouted  corn  grains  and 
test  them  for  grape  sugar.  Then  cut  some  corn  grains  that  have  just 
begun  to  germinate,  lengthwise,  through  the  embryo,  and  test  for 
grape  sugar.  Look  for  changes  in  color  between  the  embryo  and 
endosperm. 

Using  a diagram,  fill  in  with  correct  colors  the  changes  that  took 
place  when  germinating  corn  was  tested. 

Digestion.  The  change  of  starch  to  grape  sugar  in  the  corn 
is  due  to  a process  called  digestion.  If  you  chew  for  a little  time 
a bit  of  unsweetened  cracker  — which  we  know  contains  starch  — 
it  will  begin  to  taste  sweet,  and  if  the  chewed  cracker  is  tested  with 
Fehling’s  solution,  some  of  the  starch  will  be  found  to  have  changed 
to  grape  sugar.  Here,  again,  the  process  of  digestion  has  taken 
place.  Both  in  the  corn  and  in  the  mouth,  this  change  is  brought 
about  by  the  action  of  chemical  substances  known  as  digestive 
ferments,  or  enzymes  (en'zimz).  Such  substances  have  the  power 

1 Fehling’s  solution  may  be  made  as  follows : Add  35  g.  of  copper  sulphate  to 
500  cc.  of  water.  Solution  No.  1. 

To  160  g.  caustic  soda  (sodium  hydroxide)  and  173  g.  Rochelle  salt,  add  500  cc. 
of  water.  Solution  No.  2. 

For  use  mix  equal  parts  of  solutions  1 and  2.  This  may  also  be  obtained  from 
druggists,  in  tablets. 

Benedict’s  second  solution.  — Copper  sulphate 17.3  g. 

Sodium  citrate 173.0  g. 

Sodium  carbonate  (anhydrous)  . . . 100.0  g. 

Make  up  to  1 liter  with  distilled  water. 

With  the  aid  of  heat  dissolve  the  sodium  salts  in  about  600  cc.  of  water.  Pour 
through  filter  paper  into  a glass  graduate  and  make  up  to  850  cc.  with  distilled 
water. 

Dissolve  the  copper  sulphate  in  about  100  cc.  of  water,  and  make  up  to  150  cc. 
with  distilled  water.  Pour  the  carbonate  citrate  solution  into  a large  beaker  and 
add  the  copper  sulphate  solution  slowly  with  constant  stirring. 

— After  Hawke’s  Biochemistry. 


130 


WHY  DO  SEEDS  GERMINATE? 


under  certain  conditions  to  change  insoluble  foods  — solids  — 
into  soluble  substances.  The  result ' is  that  foods  which  before 

digestion  would  not  dissolve  in 
water  will  dissolve  after  being 
digested.  Enzymes  do  their 
work  without  being  changed  or 
used  up  in  the  process  so  that 
a very  small  amount  of  an 
enzyme  may  cause  a very  large 
amount  of  food  to  be  digested. 
Enzymes  are  formed  in  cells, 
both  in  plants  and  in  animals, 
and  are  responsible  for  many 
important  changes  in  these 
living  things. 

The  action  of  diastase  on 

Explain  what  has  happened  here.  What  does  starch.  The  enzvme  found  in 
it  show?  1 1 1 11 

the  cotyledon  of  the  corn,  which 
changes  starch  to  grape  sugar,  is  called  diastase  (di'd-stas).  It 
may  be  separated  from  the  cotyledon  and  is  prepared  by  chemists 
for  use  in  the  form  of  a powder. 

Demonstration  11.  To  show  how  starch  is  changed  to  sugar.  To  a 

little  starch  in  half  a cup  of  water  add  a very  little  diastase  (1  gram)  and 
put  the  vessel  containing  the  mixture  where  the  temperature  will  remain 
nearly  constant  at  about  98°  Fahrenheit.  Test  part  of  the  contents  at  the 
end  of  half  an  hour,  for  starch  and  for  grape  sugar.  If  the  rest  of  the 
mixture  is  tested  the  next  morning,  it  will  be  found  that  the  starch  has  been 
completely  changed  to  grape  sugar.  Starch  and  warm  water  alone  under 
similar  conditions  will  not  react  to  the  test  for  grape  sugar. 

Digestion  has  the  same  purpose  in  plants  and  animals.  In 

our  own  bodies  we  know  that  solid  foods  taken  into  the  mouth  are 
broken  up  by  the  teeth  and  moistened  by  saliva.  If  we  could 
follow  that  food,  we  should  find  that  eventually  it  became  part  of 
the  blood.  It  was  made  soluble  by  digestion,  and  in  a liquid  form 
was  absorbed  into  the  blood.  Once  a part  of  the  body,  the  food  is 
used  either  to  release  energy  for  body  activities  or  to  build  up  the 
body  tissues. 


equal 

volumes 

of  ^rape 

sugar' 

ancC 

T^hlingis 

solutwn.. 


4-  heat 


REVIEW  SUMMARY 


131 


A SUMMARY  OF  FOOD  SURSTANCES  AND  THEIR  TESTS 


Name 

Chemical  Composition 

Test 

i St  arch 

Contains  Carbon  (C) 

llvdrogen  (H) 
Oxygen  (0) 

Solution  of  iodine  turns  it  dark 
blue. 

Grape  sugar 

Contains  Carbon  (C) 

Ilytlrogen  (H) 
Oxygen  (0) 

Forms  brick-red  precipitate 
when  heated  to  boiling  with 
Fehling’s  solution. 

P’orms  greenish,  yellow,  or  red 
precipitate  when  boiled  with 
Benedict’s  solution. 

Fats  and  oils 

Contain  Carbon  (C) 

Hydrogen  (H) 
Oxygen  (0) 

Leave  a grease  spot  on  paper 
after  heating. 

May  be  extracted  by  mashing 
up  substance  with  ether. 

Proteins 

Contain  Carbon  (C) 

Hydrogen  (H) 
Oxygen  (0) 
Nitrogen  (N) 
and  usually  Sulphur  (S) 
and  other  elements 

Turn  yellow  when  heated  with 
strong  nitric  acid,  and  then 
turn  orange  after  addition 
of  ammonium  hydroxide 

Burning  test  (odor) 

Coagulation  test  (white  of  egg) 

Mineral  matter 

Such  elements  as  Sodium 
(Na),  Calcium  (Ca), 
Iron  (Fe),  and  Potas- 
sium (K) 

Remains  as  grayish  ash  after 
burning  food  in  hot  flame  for 
long  period. 

Water 

Hydrogen  (H) 

Oxygen  (0) 

Passes  off  from  food  when 
heated,  as  water  vapor,  and 
can  be  collected  on  cold 
metal  or  glass,  as  drops  of 
water. 

Self-Testing  Exercise 

Check  correct  answers  for  your  workbook. 

Digestion  is  brought  about  by:  (1)  heating  the  food  in  the  body, 
(2)  chewing  the  food  well;  (3)  enzymes;  (4)  adding  grape  sugar  to  a 
substance. 

Digestion  is  necessary  for  plants  and  animals  because : (1)  it  gives 
them  the  nutritious  part  of  their  food ; (2)  it  breaks  food  into  small  par- 
ticles ; (3)  it  releases  energy  in  foods ; (4)  it  makes  substances 

soluble. 


132 


WHY  DO  SEEDS  GERMINATE? 


Review  Summary 

Test  your  knowledge  of  the  unit  by : (1)  Answering  and  rechecking  the 
survey  questions;  (2)  performing  the  assigned  exercises ; (3)  checking  with 
the  teacher,  your  scores  on  the  various  tests,  and  if  you  do  not  have  a perfect 
score  trying  again  the  parts  you  missed;  and  finally,  (4)  making  an  outline 
and  filling  it  in  as  fully  as  possible  for  your  notebook. 

Test  on  Fundamental  Concepts 

In  a vertical  column  under  the  heading  CORRECT  write  numbers  of  all  statements  you 
believe  are  true.  In  another  column  under  INCORRECT  write  numbers  of  untrue  statements. 
Your  grade  = right  answers  X 4. 

I.  An  embryo  (1)  is  found  in  all  seeds;  (2)  is  a young  plant;  (3)  will 
not  be  formed  unless  the  flower  has  been  pollinated ; (4)  in  the  bean 
consists  of  the  testa  and  plumule ; (5)  is  the  part  of  the  seed  that  grows 
into  a young  plant. 

II.  Among  the  factors  necessary  for  germinating  seeds  are: 

(6)  food  but  no  water;  (7)  light;  (8)  air,  water,  heat,  and  food; 
(9)  a temperature  of  100°  or  over;  (10)  rich  soil  and  an  abundance  of 
water. 

III.  Organic  foods  (11)  are  found  in  the  cotyledons  of  the  bean; 
(12)  are  found  chiefly  in  the  cotyledon  of  the  corn ; (13)  contain  carbohy- 
drates, fats,  and  proteins ; (14)  are  necessary  for  the  germination  of  seeds ; 
(15)  can  be  determined  by  simple  tests. 

IV.  The  food  supply  of  (16)  seeds  is  found  within  the  embryo  of 
seeds  having  an  endosperm;  (17)  the  corn  seed  is  found  in  the  cotyle- 
don; (18)  the  castor  bean  is  stored  in  the  endosperm;  (19)  dicoty- 
ledonous seeds  is  always  stored  in  the  endosperm ; (20)  seeds  is  stored 
in  the  form  of  organic  nutrients. 

V.  Seeds,  in  order  to  use  the  food  contained  in  them  must  (21) ' 
have  it  in  a soluble  condition ; (22)  use  it  as  a solid ; (23)  digest  it  first ; 
(24)  change  it  to  such  condition  as  will  get  into  the  cells;  (25)  be 
exposed  to  a high  temperature. 

Achievement  Test 

1.  How  do  you  make  the  tests  for  the  different  nutrients  found  in 
food? 

2.  What  are  all  the  experiments  on  germination?  What  factors  are 
necessary  to  insure  germination  of  seeds  ? 

3.  How  can  you  prove  that  living  things  burn  or  oxidize  food  in  order 
to  release  energy? 

4.  How  can  you  make  tests  to  prove  that  all  living  things  have  to 
digest  food  before  they  can  use  it? 


REFERENCES 


133 


Practical  Problems 

1.  Provo  wliat  orfianio  nutrionts  aro  i)rcscnt  in  a poa,  a grain  of  corn, 
a lima  bean,  and  a snnflowor  seed.  Tahnlato  ^yonr  rosidts. 

2.  I’rovo  that  some  seed  other  than  corn  digests  its  food  supi)ly  before 
using  it  for  growtli. 

d.  What  conditions  outside  a seed  are  necessary  to  make  it  grow? 
W'liat  conditions  inside  the  seed? 

4.  Compare  an  engine  with  a i)lant  or  an  animal.  In  what  ways  are 
they  alike? 

5.  Why  is  air  necessary  for  growth  of  seeds? 

().  How  could  you  determine  whether  light  is  necessary  for  the  germi- 
nation of  seeds? 


Useful  References 

Burlingame  and  others,  General  Biology.  Chapter  IV.  Holt,  1922. 
Coulter,  Barnes,  and  Cowles,  Textbook  of  Botany,  Vol.  Two.  American 
Book,  1930. 

F.ikenberry  and  Waldron,  Educational  Biology.  Ginn,  1930. 

Ganong,  The  Teaching  Botanist.  Macmillan,  1910. 

Holman  and  Robbins,  Textbook  of  General  Botany,  pp.  285-308.  Wiley, 
1928. 

Hunter,  Laboratory  Problems  in  Biology.  Unit  V.  American  Book, 
1932. 

Transeau,  General  Botany.  Chapter  VI.  World  Book,  1923. 


H.  BIO  — 10 


SURVEY  QUESTIONS 

How  can  roots  take  substances  from  the  soil?  Why  do  farmers  use 
fertilizers  ? Is  it  true  that  green  plants  are  the  largest  food  manufactories 
in  the  world.  What  do  we  mean  by  “ corn  on  hoof  ” ? Why  do  we  plant 
trees  in  city  parks?  What  value  might  green  plants  be  in  your  home? 


Photo  by  Wright  Pierce 


UNIT  VI 

GREEN  PLANTS  AS  FOOD  MAKERS  AND  FOOD 
USERS'^ 

Preview.  All  of  you  will  agree  with  the  statement  that  food  is 
probably  the  most  important  material  in  the  world.  There  would 
be  little  chance  for  life  on  the  earth  if  our  food  supply  was  taken 
away  and  we  had  no  way  of  getting  a new  one.  This  is  exactly 
what  would  happen  if  green  plants  would  disappear  from  the 
earth.  If  you  think  it  out,  you  can  easily  prove  that  all  animals 
are  dependent  on  green  plants  for  food.  For  example,  cows  eat 
grass,  and  in  turn,  give  man  milk  and  meat.  Plants  may  furnish 
man  with  food  directly  as  vegetables,  cereals,  and  fruits.  Even 
the  walrus  and  seal  in  the  arctic  regions,  which  at  first  sight  would 

134 


PREVIEW 


135 


seemingly  be  deprived  of  all  plant  food,  yet  live  on  fish  which  in 
turn  exist  almost  entirely  on  sea  weeds  and  small  microscopic  plants. 
Invariably  we  start  with  green  plants  which  furnish  food  for  animals. 

The  green  leaves  of  plants  are  really  solar  engines  which  get 
power  from  the  sun  and  which  manufacture  foods  only  when  the 
sun  gives  them  this  power.  In  order  to  make  food  the  plant  must 
have  certain  raw  material  on  which  to  work  : carbon  dioxide  from 
the  air,  and  water  and  mineral  salts  from  the  soil.  Another  sub- 
stance must  be  present  in  the  leaves,  a green  coloring  matter 
called  chlorophyll.  This  substance  seems  to  be  able  to  use  the 
radiant  energy  of  the  sun  better  than  any  other  living  material. 

But  since  the  raw  material,  out  of  which  foods  are  made,  is  in 
the  soil,  the  air,  and  the  water  which  the  plant  receives,  it  is 
evident  that  we  must  account  for  some  way  of  getting  these  various 
substances  into  the  leaf.  If  one  of  the  seedlings  of  a bean  is 
placed  in  sawdust  and  is  given  light,  air,  and  distilled  water,  it 
will  die  after  the  food  in  the  cotyledons  is  used  up.  Soil  is  part 
of  its  natural  environment  and  the  roots  which  come  in  contact 
with  the  soil  are  very  important  structures.  Not  only  does  soil 
hold  water,  but  this  water  contains  certain  dissolved  mineral 
salts  which  are  absolutely  necessary  for  the  life  of  the  plant. 
Distilled  water  does  not  contain  these  mineral  salts  which  come 
from  the  soil,  consequently  the  plant  will  die.  You  have  all  read 
of  how  plants  can  be  kept  alive  by  feeding  them  “ plant  pills.’’ 
These  ‘‘  plant  pills  ” contain  the  necessary  mineral  salts  which, 
when  dissolved  in  water,  are  absorbed  through  the  roots  into  the 
plant.  These  salts  form  a very  important  part  of  the  living  matter 
of  which  both  plants  and  animals  are  composed.  Hence  the 
plant  cannot  grow  without  a small  quantity  of  these  materials. 

One  of  our  big  problems  is  to  discover  just  how  these  dissolved 
mineral  substances  are  taken  in  by  the  roots.  We  say  roots 
absorb  them,  but  how?  A good  scientist  is  not  content  with  a 
statement ; he  wants  proof.  To  obtain  this  proof  he  must  use  a 
microscope  and  then  he  will  see  that  the  lower  part  of  the  small 
roots  are  covered  with  tiny  outgrowths  from  the  living  cells  of 
the  root  which  immensely  increase  the  absorbing  surface  of  the 
roots.  These  little  projections,  called  root  hairs,  are  the  organs  by 


136 


GREEN  PLANTS  AS  FOOD  MAKERS 


means  of  which  soil  water,  with  the  dissolved  mineral  materials, 
are  taken  into  the  root.  But  again  we  are  met  with  a problem. 
Food  is  manufactured  in  the  leaves  of  the  plant,  but  all  parts  of 
the  plant  need  that  food.  It  is  common  knowledge  that  food  is 
stored  in  seeds,  in  fruit,  in  stems  such  as  the  asparagus  and  in  the 
roots  such  as  turnips,  radishes,  and  carrots.  How  then  does  the 
food  get  from  the  leaves  to  the  various  parts  of  the  plant,  and  how 
does  the  water  get  from  the  roots  to  the  leaves  themselves  where 


In  the  growth  of  the  bean  plant,  notice  the  gradual  decrease  in  size  and  final  disappear- 
ance of  the  cotyledons.  How  does  the  plant  obtain  food  for  grov/th  after  the  cotyledons 
have  been  used? 

it  is  used  in  the  manufacture  of  foods?  Here  again  we  must  call 
the  microscope  into  play.  You  are  all  familiar  with  the  fact 
that  a celery  stem  is  made  up  of  a watery  material  with  long, 
threadlike  fibers  in  it.  If  we  were  to  examine  one  of  these  thread- 
like structures  under  the  microscope,  we  should  find  that  it  was 
made  up  of  a large  number  of  little  tubes  of  various  diameters, 
some  large  and  some  small.  The  larger  tubes  carry  water,  some 
of  the  smaller  ones,  food  substances.  We  shall  later  find  that  these 
bundles  of  tubes,  called  fihrovascular  bundles,  are  arranged  in  a 


rOM POSITION  OF  SOIL 


137 


(h'finito  way  in  tlio  stoin  ; tluil.  tliroii{2;h  tliose,  in  tho  innoi-  hark  of  a 
woody  stoni,  food  passes  down  from  the  leaves,  while  in  the  wootly 
stem  inside,  soil  water  passes  up  to  the  leaves. 

Again  you  might  ask  the  question,  how  do  solid  foods  pass 
through  such  tiny  tubes?  Not  in  a solid  state,  but  in  the  form 
of  dissolved  food  substances.  We  shall  find  that  these  foods  are 
actually  digested  or  made  soluble  by  means  of  certain  peculiar 
substances  called  enzymes  which  arc  found  in  the  cells  in  different 
parts  of  the  plant.  Some  of  these  enzymes  seem  to  have  the 
ability  to  change  solid  foods  into  soluble  form,  while  others  change 
the  soluble  foods  back  into  insoluble  substances.  In  this  way  we 
have  starches,  proteins,  and  oils  stored  in  different  parts  of  the 
plant.  It  will  be  the  purpose  of  this  unit  to  explain  to  us  these 
various  processes  so  that  we  may  really  understand  how  the  plant 
makes  food,  how  it  transports  it,  and  how  it  stores  its  surplus 
which  is  used  for  the  benefit  of  the  animal  world,  including  man 
himself. 

PROBLEM  I.  WHAT  DO  PLANTS  TAKE  FROM  THE  SOIL? 

Composition  of  soil.  As  any  one  knows,  the  soil  is  composed 
of  different  substances  in  different  localities.  Contrast  the  black 
soil  of  ^Minnesota  or  Illinois  with  the  sandy  soil  of  Maine  or  Cali- 
fornia, or  the  red  clay  of  Virginia.  If  we  examine  a small  mass 
of  garden  soil  carefully,  we  find  that  it  is  composed  of  numerous 
particles  of  varying  size  and  weight.  Between  these  particles, 
if  the  soil  is  not  caked  and  hard  packed,  we  can  find  tiny  spaces, 
which  are  formed  and  enlarged  when  the  soil  is  tilled.  They 
allow  the  air  and  water  to  penetrate  into  the  ground.  If  we  exam- 
ine some  soil  under  the  microscope,  we  find  considerable  water 
clinging  to  the  particles,  thus  forming  a delicate  film  around  each 
one. 

Under  the  microscope,  also,  most  soils  are  seen  to  contain  par- 
ticles of  different  kinds.  Some  are  tiny  pieces  of  rock,  like  those 
still  being  formed  where  solid  rock  is  exposed  to  the  weather. 
Rain,  cold,  and  ice,  working  alternately  with  heat,  chip  off  pieces 
of  rock.  These  pieces  in  time  may  be  worn  smaller  by  the  action 
of  winds,  running  water,  and  in  some  places  by  glaciers.  These 


138  GREEN  PLANTS  AS  FOOD  MAKERS 

processes  of  soil  making  are  aided  by  oxidation.  A glance  at  some 
crumbling  stones  will  give  you  an  example  of  this  yellow  oxide  of 
iron  (rust)  with  which  they  are  covered.  So  by  slow  degrees  the 
earth  became  covered  with  a coating  of  what  we  call  inorganic  soil. 
Later,  generation  after  generation  of  tiny  plants  and  animals  which 
lived  in  the  soil  died,  and  their  remains  formed  the  first  organic 
materials  of  the  soil. 

We  shall  later  learn  more  about  the  bacteria  or  germs  that  live 
in  the  soil  (see  Unit  VII,  Problem  III).  It  is  sufficient  at  this 


Note  the  slopes  that  are  gradually  being  worn  down  and  are  forming  soil  in  this  canyon.  Much 
desert  soil  is  formed  in  this  way. 

time  for  us  to  know  that  due  to  certain  bacteria,  dead  plants  and 
animals  are  changed  through  decay  into  matter  which  can  be  used 
by  living  plants.  Living  things  must  have  nitrogen  in  order  to 
make  living  matter.  This  nitrogen  comes  partly  from  the  de- 
cayed material  already  in  the  soil,  partly  from  fertilizers  added  by 
man,  and  partly  from  fresh  nitrogen  supplies  taken  from  the  air 
and  “ fixed  ” in  a usable  form  by  certain  bacteria  which  live  in  the 
roots  of  leguminous  plants  like  the  bean  or  clover. 


WATER  IN  SOIL  139 

Practical  Exercise  1.  Road  some  good  reference  book  and  report,  on  Iiow 
soil  is  formed. 

You  are  all  familiar  with  the  dilTerence  between  so-called  rich 
soil  and  poor  soil,  ddie  dark  soil  contains  more  dead  plant  and 
animal  matter,  which  forms  the  portion  called  humus. 

Humus  contains  organic  matter.  It  is  easy  to  prove  that 
black  soil  contains  organic  matter,  for  if  equal  weights  of  carefully 
drietl  humus  and  of  soil  from  a sandy  road  are  heated  red-hot  for 
some  time  and  then  reweighed,  the  humus  will  be  found  to  have 
lost  considerably  in  weight,  and  the  sandy  soil  to  have  lost  very 
little.  The  material  left  after  heating  is  inorganic  material, 
the  organic  matter  having  been  burned  out. 

Demonstration  1.  To  find  out  if  all  kinds  of  soil  hold  the  same 

amounts  of  water. 

Fill  funnels  of  equal  size  with  equal  volumes  of  gravel,  sand,  barren 
soil,  rich  loam,  leaf  mold,  and  finely  pulverized  leaves  — all  dry  — then 
l)our  equal  amounts  of  water  on  them  and  measure  all  that  runs  through. 
Which  funnel  holds  the  most  water? 


Soil  water  a solution  of  mineral  salts.  Water,  as  it  passes 
through  the  soil,  gradually  dissolves  very  minute  portions  of  the 
chemical  compounds  of  which  the  soil  is  composed,  so  that  soil 
water  is  really  a dilute  solution  of  mineral  salts. 

A plant  needs  mineral  matter  to  make  living  matter.  Living 
matter  (protoplasm),  besides  containing  the  chemical  elements 
carbon,  hydrogen,  oxygen,  and  nitrogen,  contains  very  minute 
proportions  of  other  elements  which  make  up  the  basis  of  certain 


140 


GREEN  PLANTS  AS  FOOD  MAKERS 


minerals.  These  are  calcium,  sulphur,  iron,  potassium,  magne- 
sium, phosphorus,  sodium,  and  chlorine. 

That  plants  will  not  grow  well  without  certain  of  these  mineral 
substances  can  be  proved  by  the  growth  of  seedlings  in  a so-called 
nutrient  solution.  If  certain  ingredients  are  left  out  of  this  solu- 
tion, the  plants  placed  in  it  will  not  develop  into  adult  plants. 

Practical  Exercise  2.  Make  a table  in  which  you  indicate  the  relative 
amount  of  water  that  can  be  held  by  different  kinds  of  soils. 

What  kind  of  soil  would  you  expect  to  find  in  a desert  ? Covering  the  forest 
floor?  In  a river  valley? 


Self-Testing  Exercise 

Humus  or  (1)  containing  (2)  (3)  will 

hold  (4)  much  better  than  inorganic  soil.  When  water 

passes  through  the  (5),  it  takes  out  certain  mineral  salts 

which  it  holds  in  (6).  Such  water  is  called  (7) 

water. 


PROBLEM  II.  WHAT  FACTORS  INFLUENCE  THE  GROWTH 
OF  ROOTS? 

Root  system.  Examine  the  root  of  a bean  seedling  grown  in 
sawdust.  The  long  main  root  is  called  the  ^primary  root.  Other 
smaller  roots  which  grow  from  the  primary  root  are  called  secondary, 
and  the  roots  growing  from  the  latter  are  called  tertiary  roots  or 
rootlets.  What  functions  do  these  roots  appear  to  have?  Most 
of  the  roots  examined  take  a more  or  less  downward  direction. 
Does  gravity  act  on  the  growing  root?  This  question  may  be 
answered  by  a simple  experiment. 

Demonstration  2.  To  show  the  effect  of  gravity  on  a growing  root. 

Plant  mustard  or  radish  seeds  in  a pocket  garden.  A very  convenient 
form  of  pocket  germinator  may  be  made  in  a few  minutes  in  the  following 
manner : Obtain  two  cleaned  four  by  five  negatives  (window  glass  will 
do) ; place  one  flat  on  the  table  and  on  it  place  half  a dozen  pieces  of 
colored  blotting  paper  cut  slightly  smaller  than  the  glass.  Now  cut  four 
thin  strips  of  wood  so  as  to  fit  on  the  glass  just  outside  of  the  paper. 
Next  moisten  the  blotter,  place  on  it  some  well-soaked  radish  or  mustard 
seeds  or  grains  of  barley,  and  cover  it  with  the  other  glass.  The  whole 
box  thus  made  should  be  bound  together  with  bicycle  tape.  Seeds  will 
germinate  in  this  box,  and  with  care  may  live  for  two  weeks  or  more. 


ROOTS 


141 


Place  the  pocket  garden  on  one  edge,  and  allow  the  seeds  to  germinate 
until  the  root  has  grown  to  a length  of  about  half  an  inch.  Then  turn  it 
at  right  angle.s  to  the  first  position  and  allow  it  to  remain  for  one  day 
undisturbed.  Turn  it  again.  In  a daj'  or  so  examine  it.  Describe  your 
results. 


The  part  of  the  root  near  the  growing  point  is  the  one  most 
sensitive  to  the  change.  This  experiment  indicates  that  the  roots 


are  influenced  to 
grow  downward  by 
the  force  of  gravity 
and  that  the  grow- 
ing point  is  most 
responsive  to  this 
stimulus. 

Demonstration  3. 
Does  water  affect 
the  course  taken  by 
roots? 

Divide  the  in- 
terior of  a shallow 
wooden  box  with 
glass  side  into  two 
parts  by  a ])artition 
with  an  opening  in 
it.  Fill  the  box  with 
sawdust.  Plant  peas 
and  beans  in  the 
sawdust  on  one  side 
of  the  partition,  and 
water  them  very 
slightly,  but  keep  the 
other  side  of  the  box 
well  soaked.  After 
two  weeks,  take  up 
some  of  the  seed- 
lings and  note  the 
position  of  the  roots. 


What  is  the  length  of  the  root  system  as  compared  with  the  height 
of  the  adult  plant  in  each  case  ? 


Water  a factor  which  determines  the  course  taken  by  roots. 

Water,  as  well  as  the  force  of  gravity,  has  much  to  do  with  the 
direction  taken  by  roots.  If  radish  seeds  germinate  on  the  under 
side  of  a moist  sponge  suspended  in  the  air,  their  roots  will  turn 
against  gravity  and  cling  to  the  wet  surface  of  the  sponge.  Water 
is  always  found  below  the  surface  of  the  ground,  but  sometimes 


Wright  Pierce 

A pocket  garden.  The  illustration  shows  what  will  happen  to  growing  roots  when  they  are 
influenced  by  gravity.  In  the  upper  picture  the  pocket  garden  was  placed  vertically  for  three 
days.  Revolve  your  book  ninety  degrees  to  the  right  and  explain  the  second  picture.  What 
happened  to  the  pocket  garden  in  the  third  picture  ? 


142 


STRUCTURE  OP  A ROOT 


143 


at  a groat  depth.  Most  trees  and  all  grasses  have  a greater  area 
of  surface  exposed  by  the  roots  than  by  the  branches.  The  roots 
of  alfalfa  and  sugar  beets,  in  our  Western  States,  often  penetrate 
the  soil  for  a distance  of  ten  to  twenty  feet  below  the  surface,  until 
they  reach  tliat  part  of  the  soil  which  is  always  moist  with  under- 
ground water. 

Self-Testing  Exercise 

A root  system  consists  of (1), (2),  and (3) 

roots.  The  end  of  the  root  is (4)  to (5)  and  turns 

toward  the  center  of  the  (6).  Roots  also  respond  to 

(7)  in  their  environment  and  will  penetrate  many (8) 

into  the  (9)  in  order  to  get  it.  The  effect  of  (10) 

on  roots  is  seen  by  planting  seeds  in  a (11)  garden. 

PROBLEM  III.  HOW  DOES  THE  STRUCTURE  OF  A ROOT 
FIT  IT  FOR  ITS  WORK? 

Demonstration  4.  The  finer  structure  of  a root.  Use  a prepared 
slide  or  hand  sections  of  bean  roots  stained  with  eosin  or  iodine  and 
place  it  under  a microscope. 

How  a root  is  built.  If  we  study  the  diagram  on  page  144  and 
compare  it  with  what  we  see  under  the  microscope,  we  find  the  root^ 
is  made  up  of  cells,  the  walls  of  which  are  rather  thin.  Over  the 
lower  end  of  the  root  is  a collection  of  cells,  most  of  which  are  dead, 
arranged  loosely  so  as  to  form  a cap  over  the  growing  tip.  This  is 
evidently  an  adaptation  which  protects  the  young  and  actively  grow- 
ing cells  just  under  the  root  cap.  In  the  body  of  the  root  a central 
cylinder  of  wood  can  easily  be  distinguished  from  the  surrounding 
cortex.  It  is  in  the  cortex  of  fleshy  roots  that  foods  are  stored,  as 
in  the  carrot  or  turnip.  In  a longitudinal  section  a series  of  tube- 
like structures  may  be  found  within  the  central  cylinder.  These 
structures  are  made  up  of  cells  which  have  grown  together  end  to 
end,  the  long  axis  of  the  cells  running  the  length  of  the  main  root. 
In  their  development  these  cells  have  grown  together  in  such  a 
manner  as  to  lose  their  small  connecting  ends,  and  now  form  con- 
tinuous hollow  tubes  with  rather  strong  walls.  Other  cells  have 

1 Sections  of  tradescantia  roots  are  excellent  for  demonstration  of  these 
structures. 


144 


GREEN  PLANTS  AS  POOD  MAKERS 


developed  greatly  thickened  walls,  which  give  mechanical  support 
to  the  tubelike  cells.  Collections  of  such  tubes  and  supporting 
woody  cells  together  make  up  the  fibrovascular  bundles  in  the 

,centel  cylbder  ®y 

bundle  system  of  tubes  water 

is  sent  quickly  from  the  roots 
to  all  parts  of  the  plant  body, 
preventing  withering  of  leaves, 
and  enabling  the  leaf  to  use 
water  in  food  manufacture. 


Laboratory  Exercise.  What 
are  root  hairs  and  where  are 
they  found  ? 

Grow  radish  or  mustard  seeds 
on  blue  blotting  paper  in  Syra- 
cuse watch  glasses,  covering 
each  watch  glass  with  a thin 
A root,  highly  magnified.  Find  and  give  the  glass  plate.  Describe  the  struc- 
functions  of  the  root  cap,  the  woody  bundles,  and  t>lirGS  VOU  SGG  growing  from  tllG 
the  root  hairs.  roots.  These  are  called  root 

hairs.  Where  are  they  the  longest?  Where  the  most  abundant? 

Place  root  hairs  of  radish  or  mustard  on  a glass  slide.  Mount  in  a 
drop  of  water  and  cover  with  a cover  slip.  Examine  with  the  low 
power  of  a microscope.  What  can  you  say  of  the  thickness  of  their 
walls?  Of  how  many  cells  does  a root  hair  consist?  If  the  root  were 
covered  with  these  thin-walled,  delicate  structures,  what  effect  would 
they  have  upon  the  amount  of  absorbing  surface  of  the  root? 


Practical  Exercise  3.  What  would 
you  say  was  the  use  to  the  plant  of 
a carrot  root?  Of  the  aerial  roots 
of  an  ivy  plant  ? 

How  would  you  go  to  work  to 
find  out  what  food  substances  are 
stored  in  a turnip  or  radish  root? 
Of  what  value  would  these  sub- 
stances be  to  the  plant  ? 


Root  hairs.  Root  hairs  vary  in  length  according  to  their  position 
on  the  root,  the  longest  root  hairs  being  found  some  distance  back 
from  the  tip.  They  are  outgrowths  of  the  outer  layer  of  the  root, 
the  epidermis,  and  are  of  very  great  importance  to  the  living  plant. 

A single  root  hair  examined  under  a compound  microscope 
will  be  found  to  be  a long,  threadlike  structure,  almost  color- 
less in  appearance.  The  cell  wall,  which  is  very  flexible  and  thin, 


ROOT  HAIRS 


145 


is  made  up  of  cellulose.  Clinging  close  to  the  cell  wall  is  the  pro- 
toplasm of  the  cell,  the  outer  border  forming  a very  delicate 
membrane.  The  interior  of  the 
root  hair  contains  many  vacuoles, 
or  spaces,  tilled  with  a tluid  called 
cell  sap.  Forming  a part  of  the 
living  protoplasm  of  the  root  hair, 
sometimes  in  the  hairlike  prolonga- 
tion and  sometimes  in  that  part 
of  the  cell  which  forms  the  epi- 
dermis, is  found  a nucleus.  The 
nucleus,  the  membrane,  and  the  rest 
of  the  protoplasm  are  alive ; the  cell 
wall,  formed  by  the  living  matter  in 
the  cell,  is  dead.  The  root  hair  is 
part  of  a living  plant  cell  with  a 
membrane  and  wall  so  delicate  that 
water  and  dissolved  mineral  substan- 
ces from  the  soil  can  pass  through  them  into  the  interior  of  the  root. 

Functions  of  the  root  hairs.  If  a root  containing  a fringe  of 
root  hairs  is  washed  carefully,  it  will  be  found  to  have  tiny 
particles  of  soil  still  clinging  to  it.  Examined  under  the  micro- 
scope, these  particles  of  soil  seem  to  be  cemented  to  the  sticky 


The  growth  of  a root  hair.  What  are 
root  hairs,  according  to  this  diagram? 


c.yCbpT.as!n_ 
nucleus 


In  the  right-hand  picture  we  see  a germinating  grain  of  corn,  showing  the  position  and  actual 
size  of  the  root  hairs.  In  the  left-hand  picture  a small  portion  of  the  root  is  seen,  with  the  soil 
surrounding  it,  both  highly  magnified.  Where  is  water  held  in  the  root  ? What  root  structures 
come  in  contact  with  the  water  ? How  and  why  do  these  structures  take  up  water  ? Explain 
how  water  gets  from  them  to  other  parts  of  the  plant. 


146 


GREEN  PLANTS  AS  FOOD  MAKERS 


surface  of  the  root  hair.  The  soil  contains,  besides  chemical  com- 
pounds of  various  mineral  substances,  — lime,  potash,  iron,  silica, 
and  many  others,  — much  organic  material.  Acids  of  various  kinds 
are  present  in  the  soil.  They  dissolve  certain  mineral  substances 
in  the  water  which  is  absorbed  by  the  root  hairs.  Root  hairs  also 
give  off  small  amounts  of  acid,  which  assist  in  dissolving  minerals. 


A solution  of  phenolphthalein  will  lose  its  color  if  an  acid  is  added  to  it.  Explain  why  the 
solution  of  phenolphthalein  (on  the  right)  is  losing  its  color. 


We  say  that  the  delicate  root  hairs  absorb  water,  and  since 
absorption  is  a process  common  to  both  plants  and  animal  cells 
we  shall  study  this  phenomenon  carefully  in  the  next  problem. 


Self-Testing  Exercise 

A root  is  made  up  of  (1).  The  outer  layer,  called  the 

(2),  is  prolonged  into  many  (3)  walled  structures 

called  (4)  (5).  These  take  (6)  and 

(7) (8)  out  of  the  soil.  Root  hairs  give  off  a small 

amount  of (9),  which  aids  in (10)  mineral  salts. 


IMBIBITION 


147 


PROBLEM  IV.  HOW  DO  ROOT  HAIRS  TAKE  IN  WATER 
AND  SOIL  SALTS? 

Demonstration  6.  To  show  diffusion  in  gases  and  liquids. 

(a)  Open  a bottle  of  carbon  bisulphide  at  one  point  in  the  school 
room.  Show,  by  raising  of  hands,  the  time  it  takes  for  the  odor  of 
the  gas  to  become  noticeable  in  different  parts  of  the  room,  (b)  Place 
a little  i)owdered  eosin  in  a glass  of  water.  Leave  undisturbed  for  some 
hours.  How  long  will  it  be  before  the  entire  glass  of  liquid  is  colored? 

Diffusion.  We  all  know  that  certain  substances,  such  as  the 
odor  of  tobacco  smoke  or  the  perfumes  of  flowers,  pass  rapidly 
from  the  point  where  they  are  given  off  and  tend  to  spread  in  all 
directions  through  the  air.  The  odor  of  the  orange  blossoms  in 
California  is  a memory  to  those  who  have  driven  near  the  orange 
groves.  Substances  which  will  dissolve  in  liquids  will  also  diffuse 
through  the  liquids.  In  the  diffusion  of  both  gases  and  liquids 
particles  of  the  substance  pass  from  the  place  where  they  are  most 
concentrated  to  where  they  are  less  concentrated,  or  lacking,  the 
rate  of  travel  being  much  slower  in  liquids  than  in  gases. 

Imbibition.  The  passage  of  water  from  point  to  point  by 
capillarity  ^ does  not  account  for  soil  water  getting  inside  the  cell. 
It  has  to  go  through  the  cellulose  wall  and  the  delicate  membrane 
of  protoplasm  within.  The  walls  of  cells,  like  wood,  absorb  soil 
water  readily  by  a process  known  as  imbibition  (im-be-bish'un) 
or  absorption.  This  brings  the  soil  water  in  contact  with  the  cell 
membrane.  Inside  the  cell  membrane  is  a liquid  which  would 
diffuse  freely  with  the  soil  water  if  the  membrane  were  removed. 
But  a membrane  acts  peculiarly  toward  diffusing  substances. 

Osmosis.  The  process  by  which  water  with  dissolved  substances 
passes  through  the  cell  membrane  is  called  osmosis. 

Demonstration  6.  To  show  the  process  of  osmosis. 

Carefully  break  away  part  of  the  shell  of  an  egg  so  as  to  expose  the 
delicate  skin  or  membrane  underneath.  Thus  we  have  a picture  of 
the  relation  of  the  cell  membrane  (like  the  egg  skin)  to  the  cell  wall 
(like  the  egg  shell).  Suspend  this  egg  in  a glass  of  cold  water  half  an 
hour.  What  happens? 

If  we  test  the  water  in  the  glass  for  protein,  the  organic  sub- 
stance of  which  white  of  egg  is  composed,  we  shall  find  none. 

1 Capillarity  (kap-i-lar'i-ti)  : rise  of  liquids  in  a tube. 


148 


GREEN  PLANTS  AS  POOD  MAKERS 


Evidently  the  egg  membrane  will  permit  the  passage  of  water 
but  not  of  protein.  Such  a membrane  is  said  to  be  semi-'perme^le 
(pur'me-d-b’l).  It  is  this  kind  of  membrane  that  surrounds  plant 
and  animal  cells.  It  will  permit  certain  substances  such  as  water 
to  pass  through  it  readily  in  either  direction,  and  it  will  permit 
certain  substances  in  solution  to  pass  less  readily,  while  still  other 
substances  will  not  be  permitted  to  pass  through  at  all. 

Demonstration  7.  Fill  the  lower  end  of  a thistle  tube  with  a solution 
of  grape  sugar  and  water.  Tie  tightly  over  it  an  animal  membrane 
(as  a sausage  bladder  or  fish  intestine),  and  place  the  tube  in  water,  as 
shown  in  the  diagram  on  page  149.  After  a short  time  observe  your 
apparatus.  What  has;  happened?  Why?  At  the  end  of  an  hour,  test 
the  water  in  the  beaker  with  Fehling’s  solution.  Explain  your  result. 


If  we  could  see  the  separate  particles,  or  molecules,  of  the  water 
and  of  the  solution  of  water  and  sugar,  they  would  be  found  to 
arrange  themselves  on  each  side  of  the  membrane  so  as  to  cover 
it  completely.  More  water  molecules  are 
hitting  oh  the  outside  of  the  membrane  than  on 
the  inside  because  some  of  the  inside  molecules 
are  sugar ; that  is,  the  concentration  of  water 
molecules  is  greater  outside  the  membrane 
than  inside.  Since  the  water  passes  through 
the  membrane  more  readily  than  the  sugar  the 
flow  of  water  into  the  tube  is  more  rapid  than 
the  flow  out  of  the  tube,  and  the  water  gradu- 
ally rises  in  the  thistle  tube.  This  passage 
of  water  through  a semipermeable  membrane 
is  known  as  osmosis  (5s-mo'sis).  It  will  be 
seen  that  the  greater  flow  of  water  mole- 
cules is  always  from  the  point  of  greater 
concentration  of  water  to  the  point  of  lesser 
concentration  of  water.  If  the  solution  is 
completely  inclosed  in  a vessel  with  rigid 
walls,  the  entrance  of  more  water  will  cause 
Osmosis  in  an  egg.  Ex-  ^ pressure  by  the  solution  within  these 

plain,  with  reference  to  the  dosed  walls  and  will  prevent  the  entrance 
text,  why  water  will  rise  in  ^ 

the  tube.  of  any  more  water.  This  is  known  as 


ABSORPTION  and  osmosis 


140 


After  reading  the  text,  explain  what  has  happened 
in  the  right-hand  tube  and  beaker. 


osmotic  pressure.  But  if  the  walls  of  the  vessel  are  less  rigid,  as 
in  the  egg  iiieiiibrane,  the  osmotic  pressure  will  cause  the  mem- 
brane to  swell  and  tlistend  until  it  eventually  may  burst. 

Why  root  hairs  absorb  water  and  soil  salts.  The  wall  of  the 
root  hair  readily  takes  in  water  and  dissolved  soil  salts  by  imbi- 
bition. The  membrane  sur- 
rounding the  protoplasm  of 
every  living  cell  is  a semi- 
permeable  membrane,  which, 
while  allowing  water  and 
mineral  salts  in  solution  to 
pass  or  diffuse  toward  the  in- 
side, will  also  allow  some  dif- 
fusion outward  of  the  water 
and  soluble  materials  within 
the  cell.  But  the  inward  flow 
is  much  greater  than  the  out- 
ward flow.  As  soon  as  the 
outer  cells  have  increased  their 

holdings  of  soil  water,  an  osmosis  inward  from  cell  to  cell  is  started 
because  the  water  tends  to  flow  from  the  place  of  its  greater  con- 
centration to  the  place  of  lesser  concentration.  Mineral  salts  in 
solution  are  carried  along  with  the  water  so  that  the  needed  soil 
substances  are  carried  along  from  cell  to  cell,  until  they  reach  the 
small  tubes  of  the  central  cylinder.  The  osmotic  pressure  in  the 
root  hairs  is  sufficient  to  cause  enough  force  in  these  tubes  to  raise 
a column  of  water  to  a considerable  height  in  the  stem.  This  is 
known  as  root  pressure. 

Physiological  importance  of  diffusion  and  osmosis.  The 

processes  of  diffusion  and  osmosis  are  of  great  importance  not 
only  to  a plant,  but  also  to  an  animal.  Foods  are  digested  in  the 
food  tube  of  an  animal ; that  is,  they  are  changed  into  a soluble 
form  so  that  they  may  pass  through  the  walls  of  the  food  tube  and 
become  part  of  the  blood.  The  inner  lining  of  part  of  the  food 
tube  (small  intestines)  is  composed  of  millions  of  small  fingerlike 
projections  called  villi,  which  look  somewhat,  in  size  at  least,  like 
root  hairs.  These  villi  are  (unlike  a root  hair)  made  up  of  many 

H.  BIO  — 11 


150 


GREEN  PLANTS  AS  FOOD  MAKERS 


cells,  through  which  liquid  food  passes  into  the  blood.  The 
process  of  absorption  in  animals  is  not  entirely  understood,  but 
it  takes  place  largely  by  diffusion  and  osmosis.  Without  these 
processes  we  would  be  unable  to  use  most  of  the  food  we  eat. 


Self-Testing  Exercise 

In  liquids  and  gases (1)  of  substances  tend  to  pass  from  a 

place  where  they  are  more (2)  to  a place  of  less  ........  (3) 

by  means  of (4).  If  this  takes  place  through  a (5) 

(6),  osmosis  is  said  to  take  place.  Mineral  salts  in  the 

(7)  pass  with  the  water  through  the (8) (9) 

into  the  (10) (11). 

PROBLEM  V.  WHAT  OTHER  PURPOSES  DO  ROOTS  SERVE? 

Besides  the  purposes  of  anchorage  and  water  absorption  roots 
have  other  functions.  They  absorb  oxygen  as  well  as  water  from 
the  soil  into  which  they  reach.  The  rows  of  dead  trees  around  a 
pond  that  has  been  raised  by  damming  indicates  that  one  cause 
of  the  death  of  these  trees  was  lack  of  oxygen.  They  were  actually 
drowned.  The  so-called  “ cypress  knees,”  projections  of  the  roots 
from  cypress  trees,  which  grow  in  water,  are  adaptations  to  obtain 
oxygen,  as  they  are  not  found  on  cypress  trees  living  in  dry 
localities.  Food  is  stored  in  fleshy  roots,  like  the  carrot,  turnip, 
or  parsnip.  Such  stores  of  food  enable  the  plants  that  produce 
seeds  every  other  year  (biennials)  to  get  an  early  start  the  second 
year  from  this  stored  food.  Some  plants  like  the  ivy  produce  roots 
on  the  stem,  which  help  it  in  climbing.  Such  roots  are  called  ad- 
ventitious. Another  type  of  air  roots  is  found  in  tropical  plants, 
such  as  orchids.  These  have  thickened  roots  with  the  special 
function  of  absorbing  and  holding  water.  Some  plants,  such  as 
the  strawberry,  or  couch  grass,  develop  new  plants  by  taking  root 
wherever  the  reclining  stem  happens  to  touch  the  ground.  Still 
another  type  of  root  is  seen  in  the  dodder,  a parasitic  plant.  The 
root  of  this  plant  pushes  its  way  into  the  stems  of  certain  plants 
from  which  it  absorbs  its  food. 


THE  STRUCTURE  OF  A LEAP 


151 


Practical  Exercise  4.  Fill  out  tlio  following; 


Types  of  Roots 

Functions 

Adaptations 

Examples 

Self-Testing  Exercise 

Roots  act  as (1)  and  absorb (2)  as  well  as  . 

(3).  Some  roots  store  (4).  Plants  may  (5)  by 

means  of  (6).  Many  plants  produce (7)  wherever 

the (8)  happens  to (9)  the  ground (10) 

plants  absorb  food  from  the (11)  on  which  they (12), 

PROBLEM  VI.  WHERE  DOES  THE  GREEN  PLANT 
MANUFACTURE  FOOD? 

The  primary  function  of  the  green  leaf  is  the  manufacture  of 
food  from  the  raw  materials  which  are  absorbed  through  the  cell 
w'alls. 

Laboratory  Exercise.  Examine  a leaf  of  maple  or  oak.  Notice 
that  it  consists  of  two  parts  : a stem,  the  petiole,  and  a broad  expanded 
part,  the  blade.  Note,  also,  that  the  petiole  leads  into  a number  of 
branching  veins  which  support  the  blade.  Notice  the  arrangement 
of  leaves.  Can  they  all  receive  full  sunlight?  Estimate  the  amount 
of  green  leaf  surface  in  a plant  in  the  room  by  multiplying  the  surface 
area  of  one  leaf  by  the  number  of  leaves  on  the  plant.  Place  in  red  ink 
the  cut  end  of  a growing  shoot  from  a young  tree  or  shrub.  Leave  for 
24  hours.  What  happens? 

State  uses  of  the  veins.  Explain  how  the  leaf  is  fitted  to  receive  light. 

The  structure  of  a leaf.  In  the  experiment  with  the  red  ink 
and  young  shoots  we  shall  find  that  the  fluid  has  gone  into  the 
skeleton  or  framework  of  the  leaf.  Let  us  examine  a simple  leaf 
more  carefully.  It  shows  usually  (1)  a flat,  broad  blade,  which 
may  take  almost  any  conceivable  shape;  (2)  a stalk,  or  petiole, 
which  spreads  out  into  veins  in  the  blade ; (3)  stipules,  a pair  of 


152 


GREEN  PLANTS  AS  FOOD  MAKERS 


outgrowths  from  the  petiole  at  its  base.  In  many  leaves  the 
stipules  fall  off  early.  Some  leaves  are  compound,  that  is,  each  of 


How  do  these  leaves  differ?  The  two  leaves  on  the  left  show  netted  veining. 


the  little  leaflike  parts  or  leaflets  is  in  reality  a section  of  the  leaf 
blade  which  is  so  deeply  indented  that  it  is  cut  away  to  the  midrib 
or  central  vein,  as  in  the  rose  leaf  shown  in  the  figure  below. 

The  cell  structure  of  a leaf.  The 
outer  covering  of  a leaf,  on  both  the 
upper  and  the  lower  surfaces,  is 
called  the  epidermis,  and  is  com- 
posed of  large,  irregular  cells.  The 
under  surface  of  a leaf  seen  through 
a microscope  usually  shows  many 
tiny  oval  openings,  called  stomata 
(sto'md-td,  sing,  sto'ma).  Two  kid- 
ney-shaped cells,  the  guard  cells,  are 
found  on  each  side  of  the  stoma.  These 
cells,  by  changes  in  their  size  and 
shape,  depending  on  the  amount  of 
water  they  contain  and  their  osmotic 
„ . . .u  pressure,  control  the  size  of  the  stoma. 

pound  leaves?  Study  of  the  leaf  in  cross  section 


THE  CELL  STRUCTURE  OF  A LEAF 


153 


sliows  that  the  stomata  open  directly  into  air  chambers  which  pene- 
trate between  and  around  the  loosely  arranged  cells  of  spongy  tis- 
sue composing  the  under  part 
of  the  leaf.  The  position  of  the 
stomata  varies  in  different  kinds 
of  leaves.  i\Iost  have  stomata 
only  in  the  under  epidermis, 
but  some,  as  the  water  lily, 
have  them  in  the  upper  epi- 
dermis only.  Still  others  have 
them  in  both  surfaces.  The 
under  surface  of  an  oak  leaf  of 
ordinar}^  size  contains  about 
2,000,000  stomata.  Under  the 
upper  epidermis  is  a layer  of 
green  cells  closely  packed  to- 
gether (called  collectively  the 
palisade  layer).  These  cells  are 
more  or  less  columnar  in  shape 
and  have  tiny  green  bodies  in 
them.  Air  can  easily  pass 
through  the  stomata  and  be- 
tween the  cells  of  the  spongy 
tissue  until  it  reaches  the  pali- 
sade layer.  In  a section  of  a leaf  cut  through  a vein,  we  find 
the  veins  to  be  composed  of  a number  of  tubes  made  up  of,  and 

strengthened  by,  thick- 
walled  cells.  The  veins 
are  a continuation  of 
the  tubes  of  the  stem 
which  form  the  frame- 
work of  the  blade  of  the 
leaf. 

Practical  Exercise  6. 

Study  the  opposite  diagram 
A cross  section  through  a leaf,  seen  through  the  com-  Carefully  and  draw  one  for 
pound  microscope.  State  the  use  of  the  vein,  the  stoma,  your  workbook  that  Will  show 
the  air  spaces,  the  palisade  layer,  the  epidermis.  all  the  structures  mentioned 


Upper  epidtermis  of  leaf 


stoma 


guard,  cell 
nuclcccs 
■chloroplast 

- -Vacuole 


lower  epicCermis  of  leaf 

Compare  the  upper  and  lower  surfaces  of  the  leaf. 


154 


GREEN  PLANTS  AS  FOOD  MAKERS 


in  the  text.  In  this  diagram  make  arrows  to  show  (a)  how  air  gets  to  the 
cells,  (b)  how  water  gets  to  the  cells,  and  (c)  how  food  materials  made  in  the 
palisade  layer  might  get  out  of  the  leaf. 

Self-Testing  Exercise 

A green  plant (1)  food  in  its (2).  The 

(3)  is  fitted  for  its  work  by  being (4)  and  exposing  a 

(5)  surface  to  the  (6).  It  contains  many  small  openings 

called (7),  through  which (8)  passes.  The  size  of 

the (9)  is  controlled  by (10) (11).  A leaf 

is  made  up  of  a (12), (13),  and (14). 

PROBLEM  VII.  WHAT  RAW  MATERIALS  AND  CONDITIONS 
ARE  NEEDED  TO  MAKE  FOOD? 

Demonstration  8.  How  does  water  get  into  leaves? 

Where  is  the  passageway  of  water  from  the  roots  to  the  leaves? 
Place  a young  growing  pea  or  bean  seedling  in  red  ink  (eosin)  and 
leave  in  the  sun  for  a few  hours.  What  happens?  What  happens 
after  a wilted  plant  is  given  water?  Why?  Place  celery  stalks  in  red 
ink  and  leave  for  a few  hours  in  the  sunlight.  Cut  thin  sections  of  the 
stem.  Where  does  the  colored  water  rise?  It  is  obvious  from  these 
experiments  that  water  rises  through  the  minute  tubes  or  ducts  in  the 
stems.  We  will  find  later  in  most  woody  stems  that  these  bundles  of 
tubes  are  arranged  in  a very  regular  way. 

What  raw  materials  are  needed  ? If  we  think  back  to  our  work 
on  foods  in  the  last  unit,  we  may  remember  that  organic  foods 
consist  of  the  elements  carbon,  oxygen,  hydrogen,  nitrogen,  and 
small  amounts  of  certain  elements  found  in  the  soil,  such  as 
calcium,  iron,  potassium,  and  sodium.  If  the  leaf  is  to  manu- 
facture organic  food  substances,  then  we  must  see  where  these 
elements  might  come  from.  Water  is  made  up  of  oxygen  and 
hydrogen ; carbon  dioxide,  a gas  given  off  in  the  breath,  is  in  the 
air  in  small  quantities,  while  nitrogen  in  a usable  form  is  in  soil 
that  contains  humus.  Here  then  are  the  raw  materials.  How 
do  they  get  into  the  leaf  ? 

We  have  just  seen  that  water  can  get  from  the  roots  up  through 
the  stem  and  into  the  leaves.  This  water,  if  it  comes  from  the  soil, 
has  dissolved  in  it  mineral  matter,  including  nitrates  from  which 
the  plant  may  obtain  nitrogen.  Carbon  dioxide,  which  is  taken 


EFFECT  OF  LIGHT  ON  PI^VNTS 


155 


out  of  tho  air,  is  anothor  of  the  raw  materials.  This  gas  enters  the 
leaf  through  the  stomata  aiul  thus  comes  in  contact  with  the  living 
cells  of  the  leaf  which  arc  the  manufacturers. 

Demonstration  9.  To  show  the  effect  of  light  on  green  leaves. 

Place  oxalis  or  nasturtium  ])lants  near  a window.  After  several  days, 
notice  the  position  of  the  blades  of  the  leaves.  Notice  also  the  leaf 
stalks.  Account  for  the  i)osition  of  the  leaves  and  stems. 


Effect  of  light  on  plants.  Evidently  sunlight  has  something  to 
do  with  the  life  of  a green  plant;  for  in  young  plants  which  have 
been  grown  in  total  darkness,  no  green  color  is  found  in  either  stems 


or  leaves,  the  latter  often 
being  reduced  to  mere  scales. 

The  stems  are  long  and  more 
or  less  reclining,  as  those  of 
a sprouting  potato  kept  in 
darkness.  We  can  explain 
the  changed  condition  of  the 
seedling  grown  in  the  dark 
only  by  assuming  that  lack 
of  light  has  some  effect  on  the 
protoplasm  of  the  seedling 
and  induces  the  growth  of 
the  stem.  If  seedlings  have 
been  growing  on  a window 
sill,  or  where  the  light  comes 
in  from  one  side,  you  have 
doubtless  noticed  that  the 
stem  grows  towards  the 
source  of  light  and  the  leaves 
tend  to  arrange  themselves 
so  as  to  receive  as  much 
light  as  possible  on  their  up- 
per surfaces.  The  illustra- 
tion here  shows  very  plainly 
the  effect  of  light  on  a grow- 
ing plant.  A hole  was  cut  in  one  end  of  a box  and  barriers  were 
erected  in  the  interior  of  the  box  so  that  the  seeds  planted  in  the 


Wright  PiiTce 

Explain  why  this  plant  has  grown  toward  the  right 
of  the  box  instead  of  the  left. 


156 


GREEN  PLANTS  AS  FOOD  MAKERS 


sawdust  received  their  light  by  an  indirect  course.  The  young 
seedling  in  this  case  responded  to  the  influence  of  the  stimulus 
of  light  so  that  it  grew  out  Anally  through  the  hole  in  the  box  into 
the  open  air.  This  growth  of  the  stem  to  the  light  is  of  very 
great  importance  to  a growing  plant,  because  food  making  depends 
largely  on  the  amount  of  sunlight  the  leaves  receive. 

Practical  Exercise  7.  Why  do  the  leaves  of  lettuce  or  cabbage  when 
“headed”  turn  white? 


Effect  of  light  on  leaf  arrangement.  It  is  a matter  of  common 
knowledge  that  green  leaves  turn  toward  the  light.  Place  growing 


Brooklyn  Botanical  Garden,  N.  Y. 

Why  are  the  leaves  of  these  plants  well  arranged  for  obtaining  sunlight  ? Why  do  they  need  a 
great  deal  of  sunlight  ? 


pea  seedlings,  oxalis,  or  any  other  plants  of  rapid  growth  near 
a window  which  receives  full  sunlight.  Within  a short  time  the 
leaves  will  be  found  in  positions  to  receive  the  most  sunlight 
possible.  Careful  observation  of  any  plants  growing  outdoors 
shows  us  that  in  almost  every  case  the  leaves  are  so  arranged  as 
to  get  much  sunlight.  The  ivy  climbing  up  a wall,  the  morning- 
glory,  the  dandelion,  and  the  burdock,  all  show  different  arrange- 
ment of  leaves,  each  presenting  a large  surface  to  the  light.  Leaves 
are  often  definitely  arranged,  each  fitting  in  between  others  so  as 
to  present  their  upper  surface  to  the  sun.  Such  an  arrangement 
is  known  as  a leaf  mosaic.  Examples  of  such  mosaics  are  seen  on 
trees  having  leaves  that  come  out  from  the  branch  alternately,  first 


CA  K BO  1 1 Y D RAT  E M A KING 


157 


on  one  side  and  then  on  the  other.  In  the  horse-chestnut,  where 
the  leaves  come  out  opposite  each  other,  the  older  leaves  of  an  up- 
right branch  have  longer  petioles  than  the  younger  ones.  In  the 
case  of  the  dandelion,  a rosette  or  whorled  cluster  of  loaves  is  found. 
Here  the  leaves  are  arranged  spirally  on  a very  short  stem.  Leaves 
with  long  petioles  are  nearest  the  ground  while  those  with  shorter 
petioles  alternate  with  them,  filling  the  space.  In  the  mullein  the 
entire  plant  forms  a coyic.  The  old  leaves  near  the  bottom  are 
very  large,  and  the  younger  ones  near  the  apex  are  much  smaller  and 
come  out  close  to  the  main  stalk.  In  every  case  each  leaf  receives 
a large  amount  of  light. 

Practical  Exercise  7.  Bring  into  class  as  many  examples  of  various  leaf 
arrangement  as  possible. 

The  sun  a source  of  energy.  We  have  already  learned  that  green 
plants  are  the  great  food  makers  for  themselves  and  for  animals. 
We  are  now  ready  to  learn  hoiu  green  plants  make  food.  We  know 
the  sun  is  the  source  of  most  of  the  energy  that  is  received  on  this 
earth  in  the  form  of  heat  and  light.  Every  one  knows  what 
“ burning  glass  ” will  do  when  it  focuses  the  sun’s  rays  on  a piece 
of  paper.  Solar  engines  have  not  come  into  any  great  use  as  yet, 
because  fuel  is  cheaper,  but  some  day  we  undoubtedly  shall  harness 
the  energy  of  the  sun  to  do  our  everyday  work.  Experiments  have 
shown  that  as  much  as  80  per  cent  of  the  radiant  energy  falling  on 
certain  green  leaves  is  absorbed.  A small  part  of  this  energy  is  used 
by  the  leaf ; but  part  is  changed  to  heat,  raises  the  temperature  of 
the  leaf,  and  is  later  lost  to  the  air  if  the  air  is  cooler  than  the  leaf. 
Regulation  of  this  temperature  is  obtained  in  much  the  same  way 
as  in  our  own  bodies,  by  evaporation  of  water.  We  perspire ; the 
leaf  passes  off  water  vapor,  largely  through  the  stomata. 

Relation  of  light  and  air  to  starch  in  leaf.  We  can  readily  test 
how  light  affects  the  amount  of  starch  found  in  a leaf.  We  do  this 
by  pinning  strips  of  black  cloth,  such  as  alpaca,  over  portions  of 
several  leaves  of  a growing  hydrangea  which  has  previously  been 
placed  in  a dark  room  for  a few  hours,  and  then  putting  the  plant 
in  direct  sunlight  for  an  hour  or  two.  We  remove  the  partly  cov- 
ered leaves,  boil  them  to  soften  the  tissues,  and  extract  the  chloro- 
phyll with  wood  alcohol  (because  the  green  color  of  the  chlorophyll 


158 


GREEN  PLANTS  AS  FOOD  MAKERS 


starch  made 


worm  alcohol 
©Ktracts, 
green  ccdoiT' 


What  effect  does 
sunlight  have  on  green 
leaves  ? Describe  the 
experiment  which  will 
prove  this. 


interferes  with  the  blue  color  of  the  starch  test). 
A test  with  iodine  shows  that  starch  is  present 
only  in  the  portions  of  the  leaves  exposed  to  sun- 
light. From  this  we  infer  that  the  sun  has  some- 
thing to  do  with  the  amount  of  starch  found  in  a leaf. 

The  necessity  of  air  for  making  carbohydrates 
may  easily  be  proved.  If  parts  of  several  leaves 
on  a plant  are  covered  with  vaseline  and  exposed 
to  the  sun  for  several  hours,  they  will  be  found  to 
contain  no  starch,  while  those  parts  of  the  leaf 
without  vaseline,  but  exposed  to  the  sun  and  air, 
will  contain  starch.  The  part  of  the  air  used  in 
carbohydrate-making  is  carbon  dioxide,  which  is 
present  in  the  atmosphere  in  very  small  amounts. 

Air  is  necessary  for  the  process  of  making  sugar 
and  starch  in  a leaf,  not  only  because  carbon 
dioxide  gas  is  absorbed  but  also  because  the  leaf 
is  alive  and  must  have  oxygen  in  order  to  do 
its  work.  It  takes  this  oxygen  from  the  air. 

Practical  Exercise  8.  Explain  why  some  plants  do  so 
poorly  in  the  house.  Why  are  trees  in  cities  often  so 
sickly  ? 

Demonstration  10.  To  show  the  need  of  chloro- 
phyll for  making  carbohydrates. 

Place  a plant  with  variegated  leaves,  as  Coleus,  in 
sunlight  for  an  hour  or  two.  Test  several  leaves  with 
iodine  after  removing  the  chlorophyll  with  methyl 
alcohol.  Do  all  the  leaves  show  presence  of  starch? 
Do  all  parts  of  the  variegated  leaves  show  starch  ? 
Why  is  chlorophyll  necessary  ? 

Demonstration  11.  To  show  the  need  of  carbon 
dioxide  for  making  carbohydrates. 

Place  a green  plant  in  a wide-mouth  jar  which 
contains  carbon  dioxide  gas.  Place  the  jar  in  bright 
sunlight.  Place  another  plant  in  a jar  in  which 
carbon  dioxide  is  removed  by  means  of  soda  lime 
(see  diagram).  After  24  hours  test  leaves  from  both 
plants  for  starch.  Results? 

Chlorophyll  necessary  for  making  carbohy- 
drates. In  the  palisade  layer  of  the  leaf,  we  find 
cells  which  are  almost  cylindrical  in  form,  In 


USE  OF  ClILOliOPIIYLL 


159 


the  protoplasm  of  these  cells  arc  found  a number  of  tiny  green 
bodies,  tlie  chloroplasts  or  chlorophyll  bodies.  If  the  leaf  is 
placed  in  wood  alcohol,  we  find  that  the  bodies  still  remain,  but 
that  the  color  is  extracted,  going  into  the  alcohol  and  giving  to 
it  a beautiful  green  color.  The  chloroplasts  are,  indeed,  simply 
part  of  the  protoplasm  of  the  cell  colored  green.  These  bodies 
are  of  the  greatest  importance  directly  to  plants  and  indirectly  to 
animals.  The  chloroplasts,  by  means  of  the  energy  received  from 
the  sun,  manufacture 
sugars  and  then  starch 
out  of  certain  raw  ma- 
terials obtained  from  the 
soil  and  the  air.  These 
raw  materials  are  soil 
water,  which  is  passed 
up  from  the  roots  through 
the  bundles  of  tubes  into 
the  veins  of  the  leaf,  and 
carbon  dioxide  from  the 
air,  which  is  taken  in 
through  the  stomata  or 
pores.  A plant  with  va- 
riegated leaves,  as  the 
tradescantia  or  “wander- 
ing Jew,”  makes  starch 
only  in  the  green  part  of  the  leaf,  though  these  raw  materials 
reach  all  parts  of  the  leaf. 

Changes  in  color  in  leaves.  Green  leaves  are  really  solar  engines 
and  like  all  machinery  wear  out  after  long  usage.  It  has  been 
estimated  that  the  total  working  life  of  a green  leaf  is  about  1500 
hours.  In  the  fall  we  find  leaves  changing  color,  and  we  used  to 
think  this  was  due  to  the  action  of  frost.  Now  we  think  it  is  due 
to  the  breaking  down  of  the  green  coloring  matter  in  the  leaf. 
This  disintegration  seems  to  be  an  oxidation  process.  As  the 
chlorophyll  disappears  from  the  leaves,  the  yellow  color,  which  is 
present  in  the  leaf  cells,  can  now  be  seen.  But  other  autumn 
colorations  are  not  yet  fully  understood. 


aiv 


air> 


Si 

d'r-J 

(op . ) 

-Soda  lime 

pebbles 

COi 

pj'e;5erat  ccir 

for  use — 


.Soda  lime 
pebbles. 


Explain  the  difference  in  growth  of  the  two  plants. 


160 


GREEN  PLANTS  AS  FOOD  MAKERS 


Practical  Exercise  9.  Make  a collection  of  leaves  showing  as  many  color 
changes  as  possible. 

Self-Testing  Exercise 

Water  rises  in  the  stem  of  plants  through (1) (2). 

The  green  leaf  needs  (3),  (4),  and  (5) 

(6)  in  order  to  manufacture  organic  food.  These  materials 

enter  the  plants  through  the (7)  in  the  leaves  and  through 

the  (8)  in  the  soil.  Plants  growing  in  total  darkness  are 

without  (9)  (10)  (11).  This  material  is 

known  as (12). 

PROBLEM  VIII.  WHAT  ARE  THE  PRODUCTS  AND  RESULTS 
OF  FOOD  MANUFACTURE? 

Comparison  of  carbohydrate-making  and  milling.  The  manu- 
facture of  carbohydrate  by  the  green  leaf  is  not  easily  understood. 
The  process  has  been  compared  to  the  work  of  a mill.  In  this 
case  the  mill  is  the  green  part  of  the  leaf.  The  sun  furnishes  the 
motive  power,  the  chloroplasts  constitute  the  machinery,  and  soil 
water  and  carbon  dioxide  are  the  raw  products  taken  into  the 
mill.  The  manufactured  product  is  sugar  which  is  later  changed 
into  starch.  A certain  by-product  (corresponding  to  the  waste 
in  a mill)  is  also  given  out.  This  by-product  is  oxygen.  To  un- 
derstand the  process  better,  we  must  refer  to  the  diagram  of  the 
leaf  (page  161).  Here  we  find  that  the  cells  of  the  green  layer 
of  the  leaf,  under  the  upper  epidermis,  perform  most  of  the  work. 
The  carbon  dioxide  is  taken  in  through  the  stomata  and  reaches 
the  green  cells  by  way  of  the  intercellular  spaces  and  by  diffusion 
from  cell  to  cell.  Water  reaches  the  green  cells  through  the  veins. 
It  then  passes  into  the  cells  and  there  becomes  part  of  the  cell  sap. 
The  light  of  the  sun  easily  penetrates  the  cells  of  the  palisade  layer, 
giving  the  energy  needed  to  make  the  starch.  This  whole  process 
is  a very  delicate  one,  and  will  take  place  only  when  external 
conditions  are  favorable.  If  the  light  from  a spectrum  is  allowed 
to  fall  on  a leaf  of  a plant  that  has  been  kept  in  the  dark,  starch 
will  be  formed  only  in  the  blue  and  red  parts  of  the  spectrum, 
since  chlorophyll  absorbs  light  of  these  wave  lengths  most  readily. 
For  example,  400  much  heat  or  too  little  heat  stops  carbohydrate- 


PROTEIN-MAKING 


161 


niakint^  in  the  leaf.  The  leaf  eni>:ine  works  rapidly  under  favorable 
conditions  and  makes  sugar  in  such  (luantities  that  it  clogs  up  the 
conducting  tubes  and  slows  uj)  the  process  of  food  making.  Some 
form  of  sugar  is  probably  the  first  protluct  formed  but  almost  im- 
mediately some  of  the  sugars  are  changed  to  starch.  One  theory 


light  ener^x  Wg^itenergjy" 


food. 

is 

carried 
by  , 

special 

tubes 


7. 

') 

0 1 4, 

0 LfoocC 

1 o_ 

9 

9 

0 

A' 

‘9  a Oo®^ 

vateris 
Carried 
to  leaf 
hy  ' 
tubes 
connected 
vith  roots 


iso’iyetx 
ofr N/hen 
foocC  is 
macCe 


The  leaf  food  factory.  Where  is  the  light  energy  used? 
How  do  the  raw  materials  get  to  the  factory?  Where  do  waste 
products  go  ? Where  do  the  manufactured  products  go  ? 


assumes  that  carbon  dioxide  (CO2)  and  water  (H2O)  first  form 
formaldehyde  (CH2O),  and  from  this  simple  compound  glucose 
(C6H12O6)  is  formed.  A study  of  the  diagram  will  show  you  how 
this  might  happen.  But  at  night  the  foods  are  changed  into  a 
soluble  form,  transported  to  other  parts  of  the  plant,  and  the  leaf 
is  ready  to  begin  its  work  again  with  the  shining  of  the  sun.  This 
building  up  of  carbohydrates,  with  the  release  of  oxygen  by  the 
chloroplasts  in  the  presence  of  sunlight,  is  called  'photosynthesis. 

Manufacture  of  fats.  Inasmuch  as  tiny  droplets  of  oil  (or  fats) 
are  found  inside  the  chlorophyll  bodies  in  the  leaf,  we  believe  that 
fats,  too,  are  made  there,  probably  by  a transformation  of  the 
starch  already  manufactured. 

Protein  making  and  its  relation  to  the  making  of  living  matter. 

Protein  is  a part  of  the  food  which  is  necessary  to  form  protoplasm. 
It  is  present  in  the  leaf  and  is  found  also  in  the  stem  and  root. 


162 


GREEN  PLANTS  AS  FOOD  MAKERS 


Proteins  can  be  manufactured  in  any  of  the  cells  of  green  plants 
where  starches  or  sugars  and  certain  salts  are  found.  The  presence 
of  light  does  not  seem  to  be  a necessary  factor  for  the  process. 
How  they  are  manufactured  is  a matter  of  conjecture.  The 
minerals,  nitrates,  sulphates,  and  phosphates  in  the  soil  water 
give  nitrogen,  sulphur,  and  phosphorus,  and  the  sugar  or  starch 
gives  carbon,  hydrogen,  and  oxygen,  all  of  which  elements  are 
found  in  proteins.  Proteins  are  probably  not  made  directly  into 
protoplasm  in  the  leaf,  but  are  transported  to  other  parts  of  the 
plant,  stored  there  and  used  when  needed,  either  to  form  new 
cells  or  to  repair  waste. 

Enzymes  and  their  work.  It  is  a matter  of  common  knowledge 
that  starch  food  is  stored  in  fruits,  seeds,  roots,  and  stems.  We 
also  know  that  starches  cannot  pass  from  one  part  of  the  plant  to 
another  because  they  are  insoluble  substances.  The  particles  of 
which  they  are  formed  cannot  go  through  the  membranes  which 
surround  each  cell  in  the  plant.  To  make  possible  the  circulation 
of  food  from  one  part  of  the  plant  to  another  insoluble  foods  must 
be  made  soluble.  This  is  done  by  means  of  substances  called 
enzymes.  We  have  little  knowledge  of  their  actual  composition, 
but  we  do  know  that  they  have  the  power  to  speed  up  chemical 
action  in  the  cells  so  as  to  cause  certain  insoluble  substances  to 
become  soluble.  Each  nutrient  requires  a specific  enzyme  to 
change  it  from  an  insoluble  to  a soluble  form.  This  process  which 
seems  to  go  on  in  almost  all  plant  cells  as  well  in  the  darkness  as 
in  the  daylight,  is  called  digestion. 

Functions  of  food.  While  plants  and  animals  obtain  their 
food  in  different  ways,  they  probably  make  it  into  living  sub- 
stance {assimilate  it)  in  the  same  manner.  Foods  serve  exactly 
the  same  purposes  in  plants  and  in  animals ; they  either  are  used 
to  build  living  matter  or  they  are  burned  (oxidized)  to  furnish 
energy  (power  to  do  work).  If  you  doubt  that  a plant  exerts 
energy,  note  how  the  roots  of  a tree  bore  their  way  through  the 
hardest  soil,  and  how  stems  or  roots  of  trees  often  split  hard  rocks. 

Relation  of  carbohydrate-making  to  human  welfare.  Leaves 
which  have  been  in  darkness  show  starch  to  be  present  soon  after 
exposure  to  light.  A corn  plant  may  send  almost  half  an  ounce 


EVx\P()HAT10N  OF  WATER 


1G3 


of  reserve  food  into  the  ears  in  a single  day.  The  formation  of 
fruit  and  the  growth  of  grain,  potatoes,  and  other  food  crops 
show  tlie  economic  importance  of  the  work  of  green  leaves.  Not 
onh'  do  plants  make  their  own  food  and  store  it  away,  but  they 
make  food  for  animals  as  well;  and  the  food  is  stored  in  such  a 
stable  form  that  it  can  be  kept  and  sent  to  all  parts  of  the  world. 
Animals,  herbivorous  and  tlesh-eatiug,  man  himself,  all  are  depend- 
ent upon  the  starch-making  processes  of  the  green  plant  for  the 
ultimate  source  of  their  food.  When  we  consider  that  in  1928  in 
the  United  States  the  total  value  of  all  farm  crops  was  about 
812,000,000,000,  and  when  we  realize  that  these  products  came 
from  the  air  and  soil  through  the  energy  of  the  sun,  we  may  under- 
stand why  the  study  of  plant  biology  is  of  great  importance. 

Practical  Exercise  10.  Make  a table  in  which  you  list  all  the  food  products 
obtained  in  your  community  from  green  plants. 

Water  is  given  off  from  the  leaf.  Much  more  water  is  taken  in 
by  the  plant  than  is  used  by  the  plant.  This  water  is  given  off 
through  the  leaves. 

Demonstration  12.  Take  some  well-watered  potted  green  plant,  as  a 
geranium  or  hydrangea,  cover  the  pot  with  sheet  rubber,  fastening  the 


rubber  close  to  the  stem  of  the  plant.  Next  weigh  the  plant  with  the 
pot.  Then  cover  it  with  a tall  bell  jar  and  place  the  apparatus  in  the 
sun.  In  a short  time  drops  of  moisture  are  seen  to  gather  on  the  inside 
of  the  jar.  If  after  a few  hours  we  weigh  the  potted  plant  again,  we 
find  it  weighs  less  than  before.  Obviously  the  loss  comes  from  the 
water  vapor  which  has  escaped  from  stem,  or  leaves,  or  both, 


164 


GREEN  PLANTS  AS  FOOD  MAKERS 


Evaporation  of  water.  During  the  day  an  enormous  amount 
of  water  is  taken  up  by  the  roots  and  passed  out  through  the 
leaves  in  the  form  of  vapor.  So  rapid  is  this  evaporation,  or 
transpiration,  in  a small  grass  plant,  that  the  water  evaporated 
in  a day  may  weigh  more  than  the  plant.  It  is  estimated  that 
nearly  half  a ton  of  water  may  be  given  off  into  the  air  during 
twenty-four  hours  by  a grass  plot  25  by  100  feet,  the  size  of 
the  average  city  lot.  It  is  estimated  that  a corn  plant  in  the 
Central  West  gives  off  more  than  forty  gallons  of  water  during 
its  lifetime.  Nearly  20,000  lbs.  of  water  is  given  off  between 
June  and  November  by  a good-sized  birch  tree.  Fields  of 
wheat  are  said  to  give  off  an  amount  of  water  equal  to  nearly 
20  per  cent  of  the  total  rainfall  on  their  area.  The  amount 
of  water  lost  by  plants  through  evaporation  is  many  times 
more  than  the  amount  that  goes  into  making  food  and  living 
matter. 

Factors  in  transpiration.  The  amount  of  water  lost  from  a 
plant  varies  greatly  under  different  conditions.  The  humidity 
of  the  air,  its  temperature,  and  the  temperature  of  the  plant  all 
affect  the  rate  of  transpiration.  The  stomata  also  tend  to  close 
under  some  conditions,  thus  helping  to  prevent  evaporation. 
Certain  experiments  indicate  that  the  plant  probably  has  some 
control  over  the  stomata.  The  stomata  are  usually  closed  at 
night  but  remain  open  from  shortly  after  sunrise  until  late  in  the 
afternoon.  They  begin  to  close  in  the  middle  of  the  afternoon,  and 
thus  decrease  the  amount  of  water  lost  in  the  latter  part  of  the 
day.  Plants  droop  or  wilt  on  hot,  dry  days  because  they  cannot 
obtain  water  rapidly  enough  from  the  soil  to  make  up  for  the  loss 
through  the  leaves.  Hairs  on  the  leaf  surface,  waterproofing  of 
outer  cells,  a decrease  in  leaf  area,  close  grouping  of  leaves,  the 
absence  of  leaves,  as  in  the  cactus,  and  the  turning  of  leaves 
edgewise  to  light  are  all  modifications  which  help  to  hold  water 
in  the  body  of  the  plant. 

Green  plants  give  off  oxygen  in  sunlight.  In  still  another  way 
green  plants  are  of  direct  use  to  animal  life.  During  the  process 
of  sugar-making,  oxygen  is  given  off  as  a by-product.  This  may 
easily  be  proved  by  the  following  experiment. 


KESl’lliATION  BV  LEAVES 


165 


plant. 


Demonstration  13.  Place  any  {>;reen  water  i)lant  in  a battery  jar 
partly  lilhal  with  wat('rP  cover  the  i)lants  with  a ^lass  funnel,  and 
invert  a test  tube  full  of  water  over  the  mouth  of  the  funnel.  Place 
tlu'  a.i)paratus  in  a warm  sunny  window.  Bubbles  of  f>:as  are  seen  to 
rise  from  tlu'  plant.  .Vfter  several  hours  in  the  direct  sunlight,  enough 
of  the  gas  may  be  obtained  by  dis- 
placement of  the  water  to  i)rove, 
by  the  rapid  oxidation  of  a glow- 
ing splinter  of  wood  in  the  gas, 
that  oxygen  is  present. 

That  oxygon  is  given  off  as  a 
by-product  by  green  plants  is  a 
fact  of  far-reaching  importance. 

Tlie  green  covering  of  the  earth 
gives  to  animals  an  element 
that  they  must  have,  while  the 
animals  in  their  turn  supply 
to  the  plants  carbon  dioxide, 
a compound  used  in  food  mak- 
ing. Thus  a widespread  relation 
of  mutual  helpfulness  exists  be- 
tween plants  and  animals. 

Respiration  by  leaves.  All  living  things  require  oxygen.  It 
is  by  means  of  the  oxidation  of  food  materials  within  the  plant’s 
body  that  the  energy  used  in  growth  and  movement  is  released. 
A plant  takes  in  air  with  its  oxygen  largely  through  the  stomata 
of  the  leaves,  to  a less  extent  through  the  lenticels  ^ in  the  stem,  and 
through  the  roots.  Thus  rapidly  growing  tissues  receive  the 
oxygen  necessary  for  them  to  perform  their  work.  One  of  the 
products  of  oxidation  in  the  form  of  carbon  dioxide  is  also  passed 
off  through  these  same  organs.  It  can  be  shown  by  experiment 
that  a plant  uses  up  oxygen  in  the  darkness  and  gives  off  carbon 
dioxide ; in  the  light  the  amount  of  oxygen  given  off  as  a by- 
product in  the  process  of  carbohydrate-making  is  much  greater 
than  the  amount  used  by  the  plant  in  respiration. 

1 Water  contains  air  in  solution,  including  some  carbon  dioxide,  but  the  amount 
may  be  too  small.  Immediate  success  with  this  experiment  will  be  obtained  only 
if  the  w'ater  has  been  previously  charged  with  carbon  dioxide. 

2 Lenticels  (Ign'ti-sgls)  : lens-shaped  spots  or  warts  on  the  surface  of  young 
stems  and  shoots  of  peach,  apple,  and  other  trees. 

H.  BIO — 12 


Explain  just  what  is  happening  here  and  the 
conditions  necessary  to  bring  it  about. 


166 


GREEN  PLANTS  AS  FOOD  MAKERS 


Practical  Exercise  11.  Fill  out  the  following  table  on  the  work  of  the  leaf. 


Part 

Function 

What  Happens 

What  Causes  It  to  Happen 

Self-Testing  Exercise 

Green  plants  manufacture (1), (2),  and 

(3).  The  manufacture  of (4)  by  green  plants  in  the  presence 

of  sunlight  is  called  (5) (6)  is  not  a necessary 

factor  for  protein-making.  In  order  for  food  to  circulate  from  one 

part  of  the  plant  to  another,  the  (7)  food  must  be  made 

(8).  This  change  is  caused  by (9),  and  is  known  as 

(10).  Food  is  needed  for  (11)  and  (12). 

Green  plants  give  off (13) (14), (15),  and 

(16). 

PROBLEM  IX.  HOW  IS  FOOD  CIRCULATED  IN  A PLANT? 

The  circulation  and  final  uses  of  food  in  green  plants.  We 

have  seen  that  cells  of  green  plants  make  food  — ■ especially  the 
cells  that  are  in  the  leaves.  But  all  parts  of  the  bodies  of  plants 
grow.  Roots,  stems,  leaves,  flowers,  and  fruits  grow.  Seeds 
are  storehouses  of  food.  We  must  now  examine  the  stem  of  some 
plant  in  order  to  see  how  food  is  distributed,  stored,  and  finally 
used  in  the  various  parts  of  the  plant. 

The  structure  and  growth  of  a dicotyledonous  or  woody  stem. 
If  we  cut  a cross  section  through  a young  willow  or  apple  stem,  we 
find  it  shows  three  distinct  regions.  The  center  is  occupied  by 
the  spongy,  soft  pith;  surrounding  this  is  found  the  rather  tough 
wood,  while  the  outermost  area  is  bark.  More  careful  study  of  the 
bark  reveals  the  presence  of  three  layers — an  outer  layer,  epidermis, 
a middle  green  layer,  cortex,  and  an  inner  fibrous  layer.  The  inner 
layer  is  made  up  largely  of  tough  fiberlike  cells  known  as  bast  fibers. 


DICOTYLEDONOUS  STEM 


1G7 


Tlio  most  important  parts  of  this  inner  bark,  so  far  as  the  plant 
is  concernetl,  are  manj^  tubelike  structures  known  as  sieve  tubes. 


,,barW 


Explain  growth  in  this  stem. 


These  are  long  rows  of  living  cells,  having  perforated  sievelike 
ends.  Through  these  cells  food  materials  pass  downward  from 
the  upper  part  of  the  plant,  where  they  are  manufactured. 

In  the  wood  will  be  noticed  a number  of  lines  called  medullary 
rays,  or  pith  rays,  radiating  outward  from  the  pith  toward  the 
bark.  These  are  thin  plates  of  pith  which  separate  the  wood  into 
a number  of  wedge-shaped  masses.  The  masses  of  wood  contain 
many  elongated  cells,  which,  placed  end  to  end,  form  thousands  of 
little  tubes  connecting  the  leaves  with  the  roots.  In  addition  to 
these  are  many  thick-walled  cells, 
which  give  strength  to  the  mass  of 
wood.  The  bundles  of  tubes  with 
their  surrounding  hard-walled  cells 
are  the  continuation  of  the  bundles 
of  tubes  which  are  found  in  the 
root.  In  sections  of  wood  which 
have  taken  several  years  to  grow, 
we  find  so-called  annual  rings.  The 
distance  between  one  ring  and  the 
next  (see  diagram)  usually  repre- 
sents the  amount  of  growth  in  one 

~ J.1  i 1 1 ledonous  stem,  showing  arrangement  and 

year.  Crrowth  takes  place  from  a parts  of  the  bundles  and  the  other  tissues. 


168 


GREEN  PLANTS  AS  FOOD  MAKERS 


layer  of  actively  dividing  cells,  known  as  the  cambium  layer.  This 
layer  forms  wood  cells  from  its  inner  surface  and  bark  from  its 
outer  surface.  Thus  new  wood  is  formed  as  a distinct  ring  around 
the  old  outer  wood  and  new  bark  inside  the  old  bark. 

In  a very  young  dicotyledonous  stem  before  the  wood  of  the 
bundles  has  formed  an  annual  ring,  these  individual  fibro-vascular 
bundles  are  quite  separate,  arranged  in  a circle  around  the  cen- 
tral pith.  Each  bundle  consists  of  three  parts : the  outer  part, 
phloem,  made  up  of  the  bast  fibers  and  sieve  tubes,  through 
which  liquids  pass  downwards;  the  middle  part,  cambium,  or 

growth  portion  which  soon 
develops  also  between  the 
bundles  and  thus  forms  the 
cambium  layer;  and  an 
inner  part,  xylem,  made  up 
of  woody  fibers  and  ducts 
with  woody  walls  through 
which  liquids  pass  upward 
through  the  stem. 

Use  of  the  outer  bark. 
The  outer  bark  of  a tree  is 
protective.  The  cells  are 
dead,  but  the  heavy  woody 
skeletons  prevent  the 
evaporation  of  fluids  from 
within.  The  bark  also 
protects  the  tree  from 
attacks  of  plants  or  animals 
which  might  harm  it.  Most 
trees  are  provided  with  a 
layer  of  corklike  cells.  This 
layer  in  the  cork  oak  is 
thick  enough  to  be  of  com- 
mercial importance.  There 
are  many  lenticels  scattered 
through  the  surface  of  the  bark.  These  can  be  seen  easily  in  a 
young  stem  of  apple,  beech,  or  horse-chestnut. 


In  this  experiment  the  willow  twig  was  girdled  by 
taking  off  the  bark.  Can  food  now  reach  the  part  be- 
low the  ring?  Why  have  roots  come  out  above  the 
ring  ? Why  has  a sprout  appeared  below  the  ring  ? 


MOXOCOTVLEDONOUS  STEM 


1G9 


Demonstration  14.  To  show  that  food  passes  downward  in  the 
bark.  It'  a freshly  cut  willow  (wii^  is  placed  in  water,  I'ools  develop 
from  that  part  of  the  stem  which  is  under  water.  If  the  stem  then 
is  girdletl  by  removinjr  the  bark 
in  a rin<>:  just  above  where  the 
roots  are  growing,  the  latter  will 
eventually  die,  and  new  roots 
will  appear  al)ove  the  girdled 
area.  The  passage  of  food  ma- 
terials takes  place  in  a downward 
direction  outside  the  wootl  in  the 
layer  of  bark  which  contains  the 
bast  libers  and  sieve  tubes. 

This  experiment  with  the  twig 
explains  why  trees  die  when 
girdled  so  as  to  cut  the  sieve 
tubes  of  the  inner  bark.  Many 
of  the  birches  of  our  forests 
have  been  killed,  as  a result  of 
being  girdled  by  thoughtless 
visitors.  In  the  same  way  gnaw- 
ing animals  frequently  kill  fruit 
trees.  To  a small  extent  food 
substances  are  conducted  in  the 
wood  itself,  and  food  passes 

from  the  inner  bark  to  the  cen-  7 cor„s‘taik.  whadrTth.  differences  m .he 
ter  of  the  tree  byway  of  the  pith  arrangement  of  the  fibrovascular  bundles  here 
. and  in  a dicotyledonous  or  vascular  stem  ? 

rays  m winch  starch  is  stored. 

Structure  and  growth  of  a monocotyledonous  stem.  A piece  of 
cornstalk  is  made  up  of  pith,  through  which  are  scattered  numer- 
ous stringy,  tough  structures  called  fibrovascular  huiidles.  The 
latter  are  the  woody  bundles  of  tubes  and  fibers  which  pass 
through  the  pith  and  run  into  the  leaves,  where  (in  young  speci- 
mens) they  may  be  followed  as  veins.  The  outside  of  the  corn 
stem  is  formed  of  large  numbers  of  fibrovascular  bundles,  which, 
closely  packed  together,  form  a hard,  tough  outer  rind.  Thus  the 
woody  material  on  the  outside  gives  mechanical  support  to  an 
otherwise  spongy  stem.  In  a very  young  stem  epidermis  is  present. 

In  the  monocotyledonous  stem  the  bundles  are  scattered  and 
the  cambium  layer  is  absent.  The  bundles  increase  in  number  as 


170 


GREEN  PLANTS  AS  FOOD  MAKERS 


the  stem  grows  older.  As  in  dicotyledonous  bundles,  the  sieve 
tubes  are  toward  the  epidermis  and  the  xylem  tubes  toward  the 
center  of  the  stem.  (See  page  171.) 

What  causes  water  to  rise  in  a stem.  We  have  already  seen  that 
osmosis  is  responsible  for  getting  water  inside  the  root,  and  that 
the  pressure  exerted  by  this  water  (root  pressure)  is  frequently 
capable  of  forcing  fluids  a considerable  distance  up  a living  stem 
sometimes  20  or  30  feet  in  height.  But  during  most  of  the  year 
root  pressure  plays  a ver}^  unimportant  part  in  this  phenomenon. 
It  has  been  found  that  in  the  very  tiny  tubes,  such  as  we  find  in 
wood,  the  rising  column  of  water  is  held  together  by  the  force  of 
cohesion.  A core  of  water  in  tubes  2^  of  an  inch  in  diameter 
will  withstand  a pull  of  over  4600  pounds  to  the  square  inch,  so  it 
is  certain  that  this  force  is  an  important  factor  in  raising  water 
in  the  tubes  of  tall  trees.  Also  a very  large  amount  of  water  is 
evaporated  every  day,  a tree  of  average  size  using  from  75  to 
100  gallons  of  water  daily,  most  of  which  passes  out  through  the 
stomata.  This  evaporation  causes  a pull  on  the  volume  of  water 
in  the  fibrovascular  bundles  and  ordinarily  is  the  most  important 
factor  in  the  rise  of  fluids  in  stems. 

Digestion  and  storage  of  food.  Much  of  the  food  made  in  the 
leaves  is  stored  in  the  form  of  starch.  But  starch,  being  insoluble, 
cannot  be  passed  from  cell  to  cell  in  a plant.  In  our  study  of  the 
root  hair  we  found  that  substances  in  solution  (solutes)  will  pass 
from  cell  to  cell  by  osmosis.  In  our  study  of  a growing  seedling 
we  found  that  a solid  food  substance,  starch,  was  digested  in  the 
corn  grain  by  an  enzyme,  thus  becoming  a diffusible  substance 
v/hich  could  pass  from  cell  to  cell.  This  process  of  digestion 
seemingly  may  take  place  in  all  living  cells  of  the  plant,  although 
most  of  it  is  done  in  the  leaves.  In  the  bodies  of  all  animals, 
including  man,  starchy  foods  are  changed  in  a similar  manner,  but 
by  other  enzymes,  into  soluble  grape  sugar. 

The  food  material  may  be  passed  along  in  a soluble  form 
until  it  comes  to  a place  where  food  storage  is  to  take  place, 
and  then  it  can  be  transformed  again  by  the  action  of  a re- 
versible enzyme  into  an  insoluble  form  (starch,  for  example) ; 
later,  when  needed  by  the  plant  in  growth,  it  may  again  be  trans- 


DIGESTION  AND  STORAGE  OF  FOOD 


171 


:-->-FooH.  travels 
cLo'wn- 

goes 

- vp 


formed  and  sent  in  a 
soluble  form  tliroii<!:h 
the  stem  to  the  ])lace 
where  it  will  b('  used. 

In  a similar  man- 
ner, protein  seems  to 
be  chan<2;ed  and  trans- 
ferred to  various 
parts  of  the  plant. 

Some  forms  of  pro- 
tein are  soluble  and 
others  insoluble  in 
water.  White  of  egg, 
for  e X ample,  is 
slightly  soluble,  but 
can  be  rendered  in- 
soluble by  heating  it 
so  that  it  coagulates. 

Insoluble  proteins 
are  digested  within 
the  plant ; how  and 
where  is  but  slightly 
understood.  Soluble 
proteins  pass  down 
the  sieve  tubes  in  the 
bast  and  then  may  be 
stored  in  the  bast  or 

medullary  rays  of  the  wood  in  an  insoluble  form,  or  they  may  be 
stored  in  the  root,  fruit,  or  seeds  of  a plant.  This  stored  food  forms 
not  only  our  cereal,  potato,  and  other  crops,  but  also  our  fruits. 


Fluids  pass  up  and  down  the  tubes.  Raw  materials  travel 
upward  and  manufactured  foods  downward. 


Self-Testing  Exercise 

The  center  of  a dicotyledonous  stem  is  the  (1).  The  outer 

area  of  bark  of  a tree  gives (2)  to  the  wood.  The  inner  layer 

is  made  up  of  (3)  (4) . It  contains  the  (5) 

(6)  through  which  food  materials  pass  downward  to  the  roots. 

Growth  takes  place  in  the  . (7)  forming  new (8)  and 


172 


GREEN  PLANTS  AS  FOOD  MAKERS 


a new  inner  layer  of (9).  The  breathing  holes  on  the  sur- 
face of  bark  are  called (10).  The  main  bulk  of  a monocoty- 

ledonous  stem  is  made  up  of (11),  through  which (12) 

(13)  are  scattered.  The  rise  of  water  in  a stem  is  brought 

about  by  the  (14)  of  water  from  the  tree  and  by  the 

(15)  of  (16).  Foods  are  (17)  and  are 

transported  to  all  parts  of  the (18). 

PROBLEM  X.  WHY  ARE  PLANTS  MODIFIED? 

Modified  stems.  We  have  already  seen  that  the  factors  of  the 
environment,  light,  heat,  gravity,  moisture,  air  currents,  and  other 

factors  act  upon  the  living 
substance  of  plants,  caus- 
ing them  to  react  in  vari- 
ous ways.  The  changes 
which  take  place  usually 
fit  the  plant  to  succeed 
better  in  its  battle  for  life. 
Thus  various  modifications 
of  stems  have  been  brought 
about.  The  potato  tuber 
is  simply  a much  thickened 
storage  stem.  The  tiny 
projection  growing  within 
the  eye  is  a bud,  which 
may  give  rise  to  a branch 
later.  Some  stems  have 
come  to  exist  underground 
because  of  the  protection 
thus  afforded.  The  pest 
called  couch  grass  or  quick 
grass  has  such  a stem. 
Bulbs,  like  the  onion  or 
lily,  are  examples  of  stems  which  have  become  shortened  and 
covered  with  thickened  leaves,  filled  with  food.  Still  other  stems, 
like  that  of  the  dandelion,  have  become  reduced  in  length,  which 
prevents  them  from  being  broken  off  by  grazing  animals. 


Cross  sections  of  a potato  and  of  an  onion.  How 
can  you  show  that  these  are  modified  stems  ? 


TESTS 


173 


Clinihinj;  stems,  as  a result  of  the  stimulation  of  the  sun,  twist 
around  a support  in  a f>:iven  direction,  sometimes  revolving  with 
and  sometimes  against  the  course  of  the  sun. 

W’e  also  find  stems  and  leaves  modified  to  become  holdfasts  as 
the  tendrils  found  in  clind)ing  plants.  Thorns,  a protection  from 
animals,  may  be  modified  parts  of  leayes  or  of  stems. 

Practical  Exercise  12.  Make  a list  of  the  niodified  stems  found  in  your 
locality.  Show  how  each  inoditication  ina}'^  be  of  use  to  the  plant. 


Self-Testing  Exercise 

A modified  stem  is  one  that  has  probably  been  changed  by  the 

(1)  in  the  (2).  IModified  stems  nia}’'  be  in  the  form 

of (3)  as  in  the (4).  Some  stems  may  be (5), 

while  others  may  be (6),  forming (7). 


Review  Summary 

Test  your  knowledge  of  the  unit  by  (1)  rechecking  the  survey  questions; 
(2)  performing  all  assigned  exercises;  (3)  checking  with  your  teacher  all  tests 
and  making  up  all  missed  parts ; (4)  making  an  outline  of  the  unit  for  your 
notebook. 


Test  on  Fundamental  Concepts 

In  a vertical  column  under  the  heading  correct  write  numbers  of  all  statements  you  believe 
are  true.  In  another  column  under  incorrect  write  numbers  of  untrue  statements.  Your 
grade  = number  of  right  answers  X 2. 

I.  Roots  (1)  grow  toward  water;  (2)  are  affected  by  gravity; 
(3)  may  take  carbon  dioxide  from  the  soil ; (4)  always  store  food ; 
(5)  hold  a plant  firmly  in  the  ground. 

II.  A root  is  able  to  take  in  water  (6)  because  it  is  made  of  woody 
tissue  ; (7)  by  means  of  osmosis  ; (8)  because  it  has  a root  cap  covering 
each  tiny  root;  (9)  through  minute  root  hairs;  (10)  because  it  gives 
off  an  acid. 

III.  Roots  are  useful  to  plants  because  they  (11)  may  store  food; 
(12)  grow  against  gravity;  (13)  absorb  mineral  matter  from  the  soil; 
(14)  act  as  anchors  ; (15)  take  in  oxygen  through  their  stomata. 

IV.  The  process  by  which  food  is  made  by  green  leaves  is  known  as 
(16)  transpiration;  (17)  protein-making;  (18)  nutrition;  (19)  photo- 
synthesis ; (20)  osmosis. 


174 


GREEN  PLANTS  AS  FOOD  MAKERS 


V.  Green  plants  breathe  through  (21)  lenticels;  (22)  root  hairs; 
(23)  stomata;  (24)  guard  cells ; (25)  epidermal  cells. 

VI.  Food  in  plants  is  made  soluble  by  (26)  water ; (27)  enzymes ; 
(28)  the  palisade  layer  of  cells ; (29)  oxygen ; (30)  digestion. 

VII.  A green  plant  (31)  makes  sugar;  (32)  gives  off  nitrogen; 
(33)  is  a solar  engine;  (34)  manufactures  proteins  and  fats  by  a 
process  known  as  photosynthesis ; (35)  gives  off  oxygen  in  sunlight. 

VIII.  Dicotyledonous  stems  (36)  grow  from  a thin  layer  called 
cambium;  (37)  show  annual  rings  of  growth;  (38)  have  a large  area 
of  pith  and  a rind ; (39)  pass  foods  downward  through  the  sieve  tubes 
just  outside  the  cambium;  (40)  contain  pith  rays. 

IX.  Monocotyledonous  stems  (41)  have  scattered  fibrovascular 

bundles;  (42)  grow  by  having  these  bundles  arranged  in  a ring, 
growth  taking  place  from  the  cambium ; (43)  have  a strong  rind 
formed  of  bundles  and  epidermis ; (44)  contain  meduUary  rays ; 

(45)  have  annual  rings. 

X.  Stems  (46)  are  pathways  for  food  and  water;  (47)  owe  their 
strength  to  the  tough  walls  of  the  cells  of  which  they  are  composed ; 
(48)  might  be  called  organs  of  circulation  and  support;  (49)  may  be 
modified  into  leaves ; (50)  may  be  modified  into  tendrils  to  help  in 
climbing. 

Achievement  Test 

1.  How  can  you  devise  an  experiment  that  would  show  the  amounts 
of  water  which  various  soils  can  hold  ? 

2.  What  are  root  hairs,  where  are  they  found,  and  what  do  they  do  ? 

3.  How  can  you  prove  that  root  hairs  give  off  an  acid  ? 

4.  How  can  you  devise  an  experiment  to  illustrate  the  principle  of 
osmosis  ? 

5.  How  can  you  show  that  the  sun  affects  the  direction  of  growth 
of  a green  plant? 

6.  How  can  you  make  a diagram  to  show  the  cell  structure  of  a leaf  ? 

7.  How  can  you  prove  by  experiment  what  factors  are  necessary  for 
sugar-making  in  a green  plant  ? 

8.  What  are  the  chief  differences  in  the  structure  of  monocoty- 
ledonous and  dicotyledonous  stems? 

9.  How  can  you  prove  that  water  or  food  passes  up  and  down  in  a 
stem? 


REFERENCES 


175 


10.  IIow  can  you  devise  experiments  to  prove  that  food  in  a root 
has  to  become  soluble  before  it  can  pass  to  another  part  of  the  plant? 

11.  What  are  the  functions  of  the  various  parts  of  a living  plant? 

Practical  Problems 

1.  Show  why  a region  well  supplied  with  trees  is  more  likely  to  have 
frequent  rains  than  a desert  region. 

2.  Ex])lain  fully  how  you  are  dependent  for  your  food  upon  grass. 

3.  iNIake  a table  in  3mur  notebook  to  show  how  raw  food  materials 
get  into  a green  plant,  just  where  each  goes,  and  what  becomes  of  it,  what 
results,  and  what  by-products  are  passed  off.  Use  colors. 

4.  Sum  up  the  differences  between  dicotyledonous  and  monocoty- 
ledonous  plants. 


Useful  References 

Dana,  Plaiits  a7id  Their  Children.  Pp.  99-129.  American  Book. 

Duggar,  Plant  Physiology.  Macmillan,  1921. 

Coulter,  Barnes,  and  Cowles,  A Textbook  of  Botany,  Vol.  I.  American 
Book,  1930. 

Gager,  General  Botany.  P.  Blakiston,  1926. 

Hodge,  Nature  Study  and  Life,  Chapters  IX,  X,  XI.  Ginn. 

Holman  and  Robbins,  Textbook  of  General  Botany.  Wiley,  1927. 
McDougal,  The  Green  Leaf.  Appleton,  1930. 

Transeau,  General  Botany.  World  Book,  1923. 


SURVEY  QUESTIONS 

How  many  different  plants  can  you  identify?  Do  you  know  how  to 
use  a key  in  order  to  identify  new  ones  ? Do  you  know  in  what  groups  of 
plants  the  common  trees  belong?  Can  you  tell  how  a fern  reproduces? 
How  does  a tree  ? Do  you  know  any  plants  that  are  distinctive  to  your 
locality  ? 


176 


Photo  by  Wright  Pierce 


PART  III.  RELATIONSHIPS  AND  INTER- 
RELATIONSHIPS OF  LIVING  THINGS 


UNIT  VII 

THE  PLANT  WORLD.  HOW  DOES  IT  AFFECT 
MANKIND? 

Preview.  Every  boy  or  girl  who  takes  hikes  in  the  open  fields, 
along  streams,  or  on  a mountain  cannot  help  noticing  tremendous 
numbers  of  different  plants  and  animals  of  which  he  does  not 
know  the  names.  Every  walk  I take  up  a canyon  or  along  a stream 
brings  me  in  contact  with  some  plants  or  animals  I do  not  know 
by  name.  But  I have  considerable  satisfaction  in  knowing  that 
if  I do  see  a form  new  to  me  I can,  in  all  probability,  identify  it. 
If  I take  the  specimen  home  to  my  library  and  compare  it  with 
certain  pictures  and  descriptions  that  are  found  in  reference  books 
of  classification,  I may  be  able  to  name  my  specimen.  This 
identification  is  made  possible  by  biologists  who  decided  that  it 
was  necessary  to  give  names  to  things  in  order  to  place  them 
correctly  in  the  plant  or  animal  world  and,  over  a period  of  years, 
have  worked  out  appropriate  names.  At  first  such  names  were 
short  descriptions  in  Latin,  which  was  the  universal  language 
of  scholars.  Then  a young  Swede  named  Linnaeus,  who  lived 
during  the  eighteenth  century,  made  up  a system  of  shorter 
names,  which  enabled  the  naturalist  more  easily  to  identify  and 
name  the  specimen.  Just  as  you  or  I have  a family  name  and  a 
given  name,  so  Linnaeus  gave  plants  and  animals  two  names,  the 
specific  and  the  generic.  This  means  very  little  until  we  know 
that  all  animals  and  plants  may  be  placed  in  groups,  of  which  the 
members  have  common  characters  which  distinguish  them  from  all 
other  plants  or  animals.  Such  groups  we  call  species  (spe'shez). 

177 


178 


THE  PLANT  WORLD 


A group  of  different  species  all  of  which  showed  general  relation- 
ships to  one  another  might  be  called  a genus  (je'nws).  The  specific 
name  corresponds  to  the  given  name  and  the  generic  to  the  family 
name,  but  the  generic  name  is  always  placed  first  as  my  name  is 
printed,  Hunter,  George  W.,  in  the  telephone  book. 

But  what  is  the  use  of  all  this,  you  ask.  One  very  large  division  of 
the  study  of  biology,  that  of  taxonomy  or  classification,  depends  upon 
an  understanding  of  the  use  of  scientific  terms  used  by  Linnaeus  and 
his  followers.  We  want  to  be  able  to  place  all  plants  and  animals 
in  the  places  they  belong  in  the  tree  of  life.  To  the  average  boy 
or  girl,  who  enjoys  field  trips  and  who  likes  to  collect  specimens,  a 
superficial  knowledge  of  the  great  groups  of  plant  and  animal  life 
is  enough.  But  days  and  years  of  hard  work  may  be  necessary  be- 
fore the  scientist  masters  enough  knowledge  to  enable  him  to  know 
how  to  classify  all  living  things  correctly.  Fortunately  for  the 
layman,  our  museums,  botanical  gardens,  and  zoological  parks  have 
specimens  of  various  kinds,  but  in  order  to  get  much  pleasure  out 
of  such  a visit  he  should  be  able  to  recognize  at  least  the  principal 
plant  and  animal  groups.  The  pages  that  follow  are  written  be- 
cause every  citizen  should  have  some  knowledge  along  these  lines. 

In  addition  to  the  pleasure  of  knowing  the  names  of  plants  there 
is  satisfaction  in  learning  something  about  their  life  histories,  the 
place  they  occupy  in  nature’s  scale  of  life,  and  best  of  all,  we  can 
learn  something  about  the  good  or  harm  some  of  these  forms  do  to 
mankind. 

Look  at  the  enormous  damage  done  to  crops  each  year  by 
parasitic  fungi  such  as  molds,  mildews,  rusts,  and  other  plant 
diseases.  Black  stem  rust  alone  costs  some  of  the  wheat- 
raising states  in  a single  year  almost  as  much  as  they  put  into 
their  state  system  of  public  instruction  for  that  year.  And  yet, 
paradoxical  as  it  seems  to  say  it,  some  of  these  plants  add  much 
to  man’s  comfort  and  control  the  future  of  man’s  expansion  on  the 
earth.  What  would  we  do  without  yeast  to  make  our  bread  rise 
or  give  us  commercial  alcohol?  And  how  much  we  enjoy  the 
flavor  imparted  to  certain  foods  by  molds. 

Man  is  dependent  primarily  on  the  world’s  crops  and  the  world’s 
crops  are  dependent  upon  the  amount  of  raw  materials  in  the 


PL.\NTS  ARE  PI^VCED  IN  GROUPS 


179 


ground  used  by  plants  in  food  manufacture.  Nature’s  law  tells 
us  that  food  cannot  be  made  without  certain  raw  materials.  One 
of  the  basic  elements  needed  in  protein  food  manufacture  is 
nitrogen,  which  is  present  in  the  air  but  is  not  available  for  use. 
One  kind  of  bacteria  is  able  to  take  it  from  the  air,  nature’s  store- 
house, and  to  fix  it  in  a form  usable  by  green  plants.  These  nitrogen- 
fixing bacteria  are  among  man’s  best  friends. 

PROBLEM  I.  HOW  DO  WE  CLASSIFY  PLANTS? 

Laboratory  Exercise.  Collect  a number  of  common  plants  in  flower 
at  the  time  you  take  this  work,  and  see  if,  by  using  the  information  you 
find  later  on  in  this  unit,  you  can  identify  them.  Use  all  the  help  you 
can  get,  such  as  simi)le  kej^s  which  are  found  in  any  good  botany  or  in 
popular  books  on  identification  of  flowers. 

Plants  are  placed  in  groups.  If  we  plant  a number  of  pea  seeds 
so  that  they  will  all  germinate  under  the  same  conditions  of  soil, 
temperature,  and  moisture,  the  seedlings  will  differ  one  from 
another  in  a slight  degree.  But  in  a general  way  they  will  have 
many  characters  in  common,  such  as  the  shape  of  the  leaves,  the 
length  of  tendrils,  and  the  form  of  the  flower  and  of  the  fruit.  More- 
over, if  the  seeds  from  these  peas  are  planted,  they  in  turn  will 
give  rise  to  plants  which  will  closely  resemble  the  parent  plants 
from  which  the  seeds  came.  Such  plants  are  said  to  belong  to  the 
same  species.  A species  is  a small  group  of  plants  or  animals  hav- 
ing certain  characteristics  in  common  that  make  them  different 
from  all  other  plants  or  animals.  Similar  species  are  placed 
together  in  a larger  group  called  a genus  (plu.  genera).  For 
example,  many  species  of  peas  — the  wild  peas,  beach  peas,  sweet 
peas,  and  many  others  — are  all  grouped  in  one  genus  called 
Lathyrus  (lath’i-rws)  because  they  have  certain  structural  char- 
acteristics in  common. 

Practical  Exercise  1.  Give  a good  definition  of  a species ; of  a genus. 

Genera  of  plants  or  of  animals  are  brought  together  in  still 
larger  or  more  inclusive  groups,  the  classification  being  based  on 
general  likenesses  in  structure.  Such  plant  and  animal  groups 
are  called,  as  they  become  successively  larger,  family,  order,  class, 
and  phylum.  This  is  called  a system  of  classification. 


180 


THE  PLANT  WORLD 


Classification  of  plants.  Four  great  divisions  or  phyla  of  the 
plant  kingdom  are : the  Thallophyta  (tha-16f'i-td),  known  as  thallus 
plants,  which  do  not  have  roots,  stem,  or  leaves ; the  Bryophyta 


sperkatophyta 

proctuce 
seecCs 


PTERIDOPHYTA 

ferns 


AkTHROPODA  CHORDATA 

erastacectns  | man, 
insects  I niammals 


khinoderkata 

starfish— 


ItEMATHELMlNTHES 
rounct'fcoms 


COELENTERATA 

^ hyctra 


BRyOPHYTA 

mosses 


thallophyta 

simple  plants 

Scientists  believe  that  all  plants  and  animals  may  have  developed 
from  a common  ancestor  which  may  have  lived  in  the  ocean. 


(brl-6f'i-td),  which  include  the  mosses;  the  Pteridophyta  (ter'i- 
dof'i-td),  which  include  the  ferns;  and  the  Spermatophyta  (spur'- 
md-tof'i-td),  which  embrace  the  seed-producing  plants. 


Practical  Exercise  2.  Of  what  use  is  a system  of  classification?  Write  a 
brief  paragraph  on  this  subject. 


Self-Testing  Exeecise 

Living  things  are  placed  in  groups  based  on (1)  of  structure. 

A group  containing  individuals  which  are  (2)  in  (3) 

and  which  will (4)  others  of  the  same  kind  is  called  a 

(5).  Species  are  placed  in  a (6)  and  more (7)  group, 

which  is  called  a (8) . These  groups  in  turn  are  placed  in 

still  larger  groups,  called,  as  they  grow  more  inclusive,  (9) 

(10), (11),  and (12). 


now  WE  GET  BACTERIA  FOR  STUDY 


181 


PROBLEM  II.  WHAT  ARE  BACTERIA  AND  WHERE  ARE 
THEY  FOUND? 

The  simplest  plants,  called  thallophytes  (Lat.  thallus,  young 
branch;  Gr.  phyton,  plant),  have  many  forms.  They  may  be 
single-celled  or  many-celled.  They  may  or  may  not  have  chloro- 
phyll, but  they  never  possess  the  organs  of  root,  stem,  and  leaves 
found  in  the  higher  plants. 

The  bacteria  are  probably  the  smallest  and  simplest  in  structure 
of  all  the  organisms.  They  are  usually  classified  as  thallophytes. 
They  have  cell  walls  but  do  not  have  any  chlorophyll,  and  are 
therefore  not  able  to  manufacture  their  own  carbohydrate  food. 

How  bacteria  were  discovered.  As  early  as  1683  Leeuwen- 
hoek is  believed  to  have  seen  bacteria  with  his  newly  invented 
microscope.  But  it  was  not  until  1865  that  Louis  Pasteur,  the 
famous  Frenchman,  discovered  the  relation  between  bacteria  and 
disease  in  silkworms.  Pasteur  had  shortly  before  this  proved 
that  bacteria  caused  fermentation  and  that  when  floating  germs 
got  into  nutrient  fluids  such  fluids  would  “ go  bad  ’’  and  would 
decay.  Pasteur  and  Robert  Koch,  one  in  France,  the  other  in 
Germany,  were  the  first  people  to  actually  apply  the  idea  of  pro- 
tecting animals  against  disease  by  inoculating  them  with  injec- 
tions of  a culture  of  weakened  organisms  that  caused  the  disease. 
Pasteur  made  this  application  to  man  in  his  treatment  for  the 
prevention  of  rabies  or  hydrophobia. 

Demonstration  1.  To  prepare  and  sterilize  culture  media.  To  a 
100  c.c.  of  hot  filtered  beef  broth  add  1^  grams  of  the  seaweed  agar- 
agar.  If  agar  cannot  be  obtained,  use  gelatin.  Add  a little  baking 
soda,  if  necessary,  so  that  the  liquid  is  faintly  alkaline.  Boil  the  mix- 
ture and  filter  through  several  layers  of  absorbent  cotton  into  a sterilized 
Erlenmeyer  flask.  Close  the  mouth  of  flask  securely  with  a plug  of 
cotton  and  boil  flask  half  an  hour  in  a sterilizer.  If  the  agar  mixture  is 
not  clear,  it  should  be  filtered  again. 

Pour  the  hot  nutrient  agar  into  Petri  dishes  which  have  been 
sterilized  with  dry  heat  for  several  hours.  Keep  Petri  dishes  in  a dry 
place,  free  from  dust  until  ready  to  use  them. 

How  we  get  bacteria  for  study.  To  obtain  cultures  of  bacteria 
for  study,  it  is  first  necessary  to  find  some  material  in  which  they 
will  grow,  then  to  kill  all  living  matter  in  this  food  material  by 


182 


THE  PLANT  WORLD 


heating  it  to  the  boiling  point  (212°  Fahrenheit)  for  half  an  hour 
or  more  (this  is  one  method  of  sterilization),  and  finally  to  protect 
the  culture  medium,  as  this  food  is  called,  from  other  living  things 
that  might  feed  upon  it. 

Many  bacteria  thrive  in  a mixture  of  beef  extract  and  gelatin 
or  agar-agar,  a substance  derived  from  seaweed.  This  mixture, 
after  sterilization,  is  poured  into  flat  sterilized  dishes  with  loose- 
fitting  covers.  These  Petri  dishes,  so  called  after  their  inventor, 
are  the  traps  in  which  we  collect  and  study  bacteria. 

Demonstration  2.  Making  a pure  culture  of  bacteria.  Transfer  from 
an  infected  and  incubated  culture  medium  some  bacteria  on  point  of  a 
sterile  needle  to  the  sterile  surface  of  a Petri  dish  which  contains  sterile 
agar.  Watch  the  growth  of  the  colonies  for  several  days.  Are  these  col- 
onies all  alike  in  appearance? 

How  we  may  isolate  bacteria  of  one  kind  from  the  other.  In 

order  to  get  bacteria  of  a given  kind  to  study,  it  becomes  necessary 
to  grow  them  in  what  is  known  as  a pure  culture.  This  is  done 

after  first  growing  the  bacteria  in 
some  medium  such  as  beef  broth 
or  gelatin,  or  on  potato.  When 
the  colonies  of  bacteria  appear  or 
the  beef  broth  becomes  cloudy, 
one  form  may  be  isolated  from 
the  others  by  the  following  proc- 
ess. A platinum  needle  is  first 
passed  through  a flame  to  steri- 
lize it.  After  the  needle  is  cooled 
it  is  dipped  in  a colony  contain- 
ing the  kind  of  bacteria  we  wish 
to  study.  The  needle  is  then 
quickly  drawn  across  the  surface 
of  a dish  of  sterile  culture  medium, 
and  the  dish  is  immediately 
covered  to  prevent  any  other 
forms  of  bacteria  from  entering.  When  we  have  succeeded  in 
growing  only  one  kind  of  bacteria  in  a given  dish,  we  have  a pure 
culture. 


Each  spot  on  this  culture  medium  indi- 
cates a colony  of  bacteria.  The  different 
sizes  and  shapes  of  the  spots  show  that 
there  might  be  more  than  one  type  of  bac- 
teria present.  How  could  you  make  a 
pure  culture,  that  is,  one  containing  only 
one  kind  of  bacteria,  if  you  have  a steri- 
lized culture  medium  and  this  Petri  dish 
containing  colonies  of  bacteria  ? 


SIZE  AND  FORM 


183 


Laboratory  Exercise.  Observe  under  a coinpouiid  microscope  the 
various  forms  of  bacteria  seen  in  Petri  dish  of  ap;ar  which  lias  been  ex- 
posed to  tlie  air.  Make  drawings  of  these  bacteria. 


bacilli 


Size  and  form.  In  size,  bacteria  arc  the  most  minute  plants 
known.  A bacterium  of  average  size  is  about 
length,  anti  perhaps  of  iin  inch  in  diameter.  Some  species 

are  much  larger,  others  smaller.  They 
are  so  small  that  several  million  are 
often  found  in  a large  drop  of  impure 
water  or  sour  milk.  Three  well-defined 
forms  of  bacteria  are  recognized : a 
spherical  form  called  a coccus;  a rod- 
shaped bacterium,  the  bacillus;  and  a 
spiral  form,  the  spirillum.  Some  bac- 
teria are  capable  of  movement  when 
living  in  a fluid.  Tiny  lashlike  threads 
of  protoplasm  called  flagella  project 
from  the  body,  and  by  a rapid  move- 
ment cause  locomotion.  Bacteria  re- 
produce with  almost  incredible  rapidity. 

It  is  estimated  that  a single  bacterium, 
by  a process  of  division  called  fission, 
might,  if  unchecked,  give  rise  to  nearly 
17,000,000  others  in  twelve  hours. 

Under  unfavorable  conditions  bacteria 
stop  dividing  and  form  rounded  bodies  called  spores.  The  spore 
is  usually  protected  by  a wall  and  can  withstand  very  unfavor- 
able conditions  of  dryness  or  heat ; even  boiling  for  several  minutes 
will  not  kill  some  forms. 


How  would  you  describe  the  dif- 
ferent kinds  of  bacteria?  How  do 
they  move  about  ? 


Laboratory  Exercise.  To  determine  some  places  where  bacteria 
may  be  found.  Expose  a number  of  Petri  dishes  containing  nutrient 
agar  for  3 minutes  each  in  as  many  of  the  following  conditions,  and 
as  many  others,  as  possible ; 

(а)  to  the  air  of  the  schoolroom. 

(б)  in  the  halls  of  the  school  while  pupils  are  passing. 

(c)  in  the  halls  of  the  school  when  pupils  are  not  moving. 

(d)  at  the  level  of  a dirty  and  much-used  city  street. 

(e)  at  the  level  of  a well-swept  and  little-used  city  street. 


184 


THE  PLANT  WORLD 


(/)  in  a city  park, 

(g)  in  a factory  building. 

(h)  to  dirt  from  hands. 

(i)  to  contact  with  scrapings  from  the  interior  of  the  mouth. 

(j)  to  contact  with  decayed  vegetable  or  meat. 

(k)  to  contact  with  dirty  coin  or  bill. 

(l)  to  contact  with  two  or  three  hairs  from  a pupil’s  head. 

Cover  the  dishes  securely  and  place  them  in  a warm  dark  place. 

After  three  to  five  days,  note  the  conditions  of  the  various  plate 

cultures.  Each  day  count  the  number  of  spots  {colonies)  of  bacteria 
and  molds  growing  on  the  culture  medium.  Make  a table  to  show 
your  results. 


Petri  Dish  Exposed 

Number  of  Colonies  op  Bacteria 

1st 

Day 

2nd 

Day 

3rd 

Day 

4 th' 
Day 

5th 

Day 

6 th 
Day 

7th 

Day 

8th 

Day 

ia)  Air  of  schoolroom 

ih)  Busy  halls  of  school 

(c)  Quiet  hall  of  school 

id)  Busy  city  street 

(e)  Etc. 

Where  are  bacteria  found  in  abundance?  What  are  the  factors  in 
your  environment  by  means  of  which  bacteria  may  get  to  your  body? 
Is  it  true  that  “ bacteria  are  found  anywhere  but  not  everywhere  ”? 

Where  bacteria  are  most  numerous.  As  the  result  of  our 
studies,  we  may  draw  some  inferences  concerning  the  presence  of 
bacteria  in  our  own  environment.  They  are  evidently  present 
in  all  air,  and  in  greater  quantity  in  air  that  is  moving  than  in 
quiet  air.  Why  ? That  they  stick  to  particles  of  dust  was  proved 
by  exposing  a sterile  culture  dish  in  a schoolroom.  Bacteria  are 
present  in  great  numbers  where  crowds  of  people  live  and  move. 
The  air  from  dusty  streets  of  a populous  city  contains  more  bac- 
teria than  does  the  cleaner  air  of  a village  street.  The  air  of  a 
city  park  contains  relatively  few  bacteria  when  compared  with  the 


WllKKIO  lUCTEKlA  AKE  FOUND 


185 


air  of  a near-by  street  ; tlie  air  of  the  woods  or  high  mountains 
contains  fewer  still.  Why? 

Fluids  the  favorite  home  of  bacteria.  Tap  water,  standing 
water,  milk,  vinegar,  wine,  cider,  all  can  be  proved  to  contain 
bacteria  by  e.xperiments  similar 
to  those  already  suggestetl. 

Spring  or  artesian  well  water 
would  have  very  few,  if  any, 
bacteria,  while  the  same  quan- 
tity of  river  water,  if  it  held 
any  sewage,  might  contain  un- 
told millions  of  these  little 
organisms. 

Individual  Project.  Deter- 
mine by  experiment  whether  bac- 
teria will  grow  without  fluids  being 
present . Try  dry  and  moist  beans. 

Demonstration  3.  To  deter-  Growth  of  bacteria  in  an  impure  drop  of  water 
mine  the  foods  most  f3.v0r3.Dl6  placed  on  a sterilized  culture  medium, 
for  the  growth  of  bacteria. 

Materials.  Raw  meat,  cooked  meat,  white  of  egg,  beans,  Indian 
meal  flour,  cake,  sugar,  butter,  test  tubes,  and  absorbent  cotton. 

Method.  Moisten  all  of  the  above  food  substances.  Place  small 
particles  of  them  in  test  tubes  with  a little  distilled  water.  Expose  all  to 
the  air  for  half  an  hour.  (This  can  be  done  during  a class  period.)  Plug 
the  tubes  with  absorbent  cotton  and  allow  to  stand  for  several  days. 

Note  the  appearance  and  odor  of  the  various  substances  after  five 
days. 

In  which  substances  w^as  there  rapid  growth  of  bacteria? 

Food  of  bacteria.  Bacteria,  since  they  contain  no  chlorophyll, 
are  unable  to  make  carbohydrate  food,  but  must  absorb  their 
foods,  ready  formed,  from  decaying  organic  matter.  Some  bacteria, 
how'ever,  seem  able  to  build  up  the  protein,  which  they  need  for 
growth,  out  of  absorbed  carbohydrates  and  simple  inorganic  nitrog- 
enous substances. 

What  bacteria  do  to  foods.  When  bacteria  feed,  they  digest 
the  food  substances  by  means  of  enzymes  which  they  secrete. 
The  food  is  decomposed  and  eventually  rots.  The  material  left 
behind  after  the  bacteria  have  finished  their  meal  is  quite  different 
from  its  original  form.  It  is  broken  down  by  the  action  of  the 


186 


THE  PLANT  WORLD 


bacterial  enz5niies  into  gases,  fluids,  and  some  solids.  It  has  an 
offensive  odor,  and  contains  poisons  which  come  as  a result  of  the 
work  of  the  bacteria. 

Demonstration  4.  To  show  how  light  affects  the  growth  of  bacteria. 

Cover  with  black  paper  one  of  two  Petri  dishes  in  which  bacteria 
are  growing.  Place  the  dishes  in  a light  warm  place  for  a few  days. 
Compare  the  growth  of  bacteria  in  the  exposed  dish  with  the  growth 
in  the  covered  dish. 

Bacteria  and  air.  We  have  seen  that  plants  need  oxygen  in 
order  to  perform  the  work  that  they  do.  This  is  equally  true  of 
all  animals.  But  not  all  bacteria  need  air  to  live ; in  fact,  some 
are  killed  by  the  presence  of  air.  Bacteria  which  live  without  free 
oxygen  are  called  anaerobic  bacteria.  They  need  oxygen,  as  do  all 
other  living  things,  but  they  obtain  it  by  breaking  down  the  foods 
on  which  they  live,  and  utilizing  the  oxygen  freed  in  this  process. 
Those  that  grow  or  thrive  in  the  presence  of  oxygen  are  called 
aerobic  bacteria. 

Self-Testing  Exercise 

Bacteria  are  found  almost (1).  Bacteria  can  be  obtained 

for  study  by  exposing  a (2)  medium  containing (3) 

to  the (4)  for  a few  minutes.  Under  proper  conditions  of 

(5)  they  grow  rapidly.  There  are  three  common (6) 

of  bacteria : the (7)  form,  called  coccus,  the (8)  ba- 
cillus, and  a (9)  form,  the  spirillum.  They  prefer (10) 

to  all  other  food.  Many  forms  are  (11)  by  (12) 

to  light.  Some  forms  obtain  their (13)  by  breaking  down 

the  food  substances  on  which  they  live. 

PROBLEM  III.  WHAT  ARE  SOME  USEFUL  THINGS  THAT 
BACTERIA  DO? 

Bacteria  cause  decay.  Imagine  a world  cluttered  up  with  dead 
plants,  dead  animals  of  all  kinds,  dead  bodies  of  fish  in  the  waters, 
insects  in  the  grass,  cattle  in  the  fields.  Did  you  ever  think 
what  this  world  would  be  like  if  nothing  could  decay?  Bacteria 
are  responsible  for  decay.  These  bacteria  are  most  numerous  in 
rich,  damp  soils  containing  large  amounts  of  organic  material. 


USEFUL  BAUTERIA 


J87 


They  are  useful  because  they  feed  upon  dead  bodies  of  plants  and 
animals  which  otherwise  would  soon  cover  the  surface  of  the  earth 
to  the  exclusion  of  everything;  else.  Bacteria  may  be  considered 
scavengers.  They  oxidize  organic  materials,  changing  them  to 
compounds  that  can  be  absorbed  by  plants  and  used  in  building 
protoplasm,  ^^'ithout  bacteria  it  would  be  impossible  for  life  to 
exist  on  the  earth,  for  green  plants  would  be  unable  to  get  the  raw 
food  materials  in  forms  that  they  could  use  in  making  food  and 
living  matter. 

Relation  of  bacteria  to  fermentation.  Bacteria  continue  the 
process  of  fermentation  begun  by  the  yeasts.  In  making  vinegar 
the  yeasts  first  make  alcohol  which  the  bacteria  change  to  acetic 
acid.  The  lactic-acid  bacteria,  which  sour  milk  by  changing  the 
milk  sugar  to  an  acid,  are  useful  when  they  sour  the  milk  for  the 
cheese  maker. 

Other  useful  bacteria.  Certain  bacteria  give  flavor  to  cheese 
and  butter,  others  give  flavor  to  sauerkraut,  while  still  other 
bacteria  aid  in  the 
“ curing  ” of  to- 
bacco, in  the  prep- 
aration  of  the 
dye  indigo,  in  the 
“ retting  ” or  fer- 
mentation of  cer- 
tain fibers  of  plants 
for  the  market,  as 
hemp,  flax,  and 
ramie,  in  the  rot- 
ting of  animal  mat- 
ter from  the  skel- 
etons of  sponges, 
and  in  the  process 
of  tanning  hides 
to  make  leather. 

Relation  of  bac- 
teria to  free  nitrogen.  It  has  been  known  since  the  time  of  the 
Romans  that  the  growth  of  clover,  peas,  beans,  and  other  legumes 


Explain  from  the  text  and  diagram  what  is  meant  by  the  nitrogen 
cle.  What  is  the  value  of  nitrogen-fixing  bacteria  ? 


188 


THE  PLANT  WORLD 


causes  soil  to  become  more  favorable  for  the  growth  of  other 
plants,  but  the  reason  for  this  has  been  discovered  in  late  years. 

found  little  nodules 
or  tubercles ; in  each 
nodule  exist  millions 
of  bacteria,  which 
take  nitrogen  from 
the  air  in  the  soil  and 
build  it  into  nitrites 
which  are  converted 
by  other  bacteria 
into  nitrates.  In  this 
form  it  can  be  used 
by  the  plants.  Only 
these  bacteria,  of  all 
living  plants,  have 
the  power  to  take 
free  nitrogen  from 
the  air  and  make  it 
over  into  a form  that 
can  be  absorbed  by 
the  roots.  They  live  in  a symbiotic  ^ relationship  with  the  plants 
on  which  they  form  tubercles,  for  the  legumes  provide  them  with 
organic  food.  Ammonia  from  plant  and  animal  wastes  is  also 
acted  on  by  bacteria  to  produce  nitrates.  All  the  compounds  of 
nitrogen  are  used  over  and  over  again,  first  by  plants,  then  as  food 
by  animals,  eventually  returning  to  the  soil  again,  or  in  part  being 
released  as  free  nitrogen. 

Rotation  of  crops.  The  facts  mentioned  above  are  made  use 
of  by  progressive  farmers  who  wish  to  produce  as  large  crops  as 
possible  from  a given  area  of  ground.  Plants  that  are  hosts 
for  the  nitrogen- fixing  bacteria  are  raised  early  in  the  season. 
Later  these  plants  are  plowed  in  and  a second  crop  of  a different 
kind  is  planted.  The  latter  grows  quickly  and  luxuriantly  because 
of  the  nitrates  left  in  the  soil  by  the  bacteria  which  lived  with  the 

1 symbiotic  (sim'biot'ik)  : The  living  together  in  intimate  association  of  two  dis- 
similar organisms. 


On  the  roots  of  the  plants  mentioned  are 


Explain  by  use  of  this  diagram  where  the  nitrogen-fixing 
bacteria  live. 


ROTATION  OF  CROPS 


189 


first  crop.  For  this  reason,  clover  is  often  grown  on  land  in  which 
it  is  proposed  to  plant  corn  later,  the  nitrates  left  in  the  soil  giving 
noiirishinent  to  the  young  corn  plants.  In  well-managed  farms, 
different  crops  are  planted  in  succession  in  a given  field  in  different 
years  so  that  one  crop  may  replace  some  of  the  elements  taken  from 
the  soil  by  the  previous  crop.  This  is  known  as  rotation  of  crops. ^ 

Five  of  the  elements  necessarj^  to  the  life  of  the  plant  which 
may  be  taken  out  of  the  soil  by  constant  use  are  calcium,  nitrogen, 
phosphorus,  potassium,  and  sulphur.  Several  methods  are  used 
by  the  farmer  to  prevent  the  exhaustion  of  these  and  other  raw 
food  materials  from  the  soil.  One  method,  known  as  fallowing, 
is  to  allow  the  soil  to  remain  idle  until  bacteria  and  oxidation  have 
renewed  the  chemical  materials  used  by  the  plants.  This  is  an 
expensive  method  if  land  is  high  priced.  The  more  common 
method  of  enriching 
soil  is  by  means  of  fer- 
tilizers and  materials 
rich  in  plant  food. 

Manure  is  most  fre- 
quently used,  but 
many  artificial  ferti- 
lizers, most  of  which 
contain  nitrogen  in  the 
form  of  some  nitrate, 
are  used  because  they 
can  be  more  easily 
transported  and  sold. 

Such  are  ground  bone, 
guano  (bird  manure), 
nitrate  of  soda,  and 
many  others.  Most 
fertilizers  contain  other  important  raw  food  materials  for  plants, 
especially  potash  and  phosphoric  acid.  Both  of  these  substances 
are  made  soluble  by  the  action  of  the  carbon  dioxide  in  the  soil, 
and  in  this  form  they  can  be  taken  into  the  roots. 

^ Crop  rotation  is  not  only  a process  to  conserve  the  fertility  of  the  soil,  but 
also  a sanitary  measure  to  prevent  infection  of  the  soil. 


Is  this  a good  plan  for  rotating  crops  ? Why  ? 


190 


THE  PLANT  WORLD 


Practical  Exercise  3.  What  are  the  direct  values  of  bacteria  to  (1)  market 
gardening;  (2)  fruit  raising;  (3)  manufacturing? 

Self-Testing  Exercise 

Bacteria  which  cause  (1)  are  useful.  More  and  better 

crops  are  made  possible  through  the (2) (3)  bacteria. 

Bacteria  are  used  in  the  processes  of  (4)  fibers  of  plants, 

(5)  of  hides,  (6)  tobacco,  and  giving  (7) 

to  some  animal  products. 


PROBLEM  IV.  WHAT  ARE  YEASTS  AND  WHAT  DO  THEY  DO? 

Fermentation.  It  is  of  common  knowledge  that  the  juice  of 
fresh  apples,  grapes,  and  some  other  fruits,  if  allowed  to  stand 
exposed  to  the  air  for  a short  time,  will  ferment.  That  is,  the 
sweet  juice  will  begin  to  taste  sour  and  to  have  a peculiar  odor, 
which  we  recognize  as  that  of  alcohol.  The  fermenting  juice 
appears  to  be  full  of  bubbles  which  rise  to  the  surface.  If  we 
collect  enough  of  the  gas  in  these  bubbles  to  make  a test,  we  find 
it  is  carbon  dioxide. 

Evidently  something  changed  some  part  of  the  apple  or  grape, 
namely,  the  sugar  (C6H12O6),  into  alcohol  (C2H5OH)  and  carbon 
dioxide  (CO2).  This  chemical  process  is  known  fermentation. 

Home  Experiment.  To  determine  the  conditions  favorable  for  the 
growth  of  yeast.  Label  three  pint  fruit  jars  A,  B,  and  C.  Add  one 
fourth  of  a compressed  yeast  cake  to  two  cups  of  water  containing  two 
tablespoonfuls  of  molasses  or  sugar.  Stir  the  mixture  well  and  di- 
vide it  into  three  equal  parts  and  pour  into  the  jars.  Place  covers 
on  the  jars.  Put  jar  A in  the  ice  box  on  the  ice  and  jar  B over  the 
kitchen  stove  or  near  a radiator.  Heat  jar  C by  immersing  in  a pan 
of  boiling  water,  and  then  place  it  next  to  B.  After  forty-eight  hours, 
see  if  bubbles  have  made  their  appearance  in  any  of  the  jars. 

Which  jars,  if  any,  show  bubbles  on  the  surface?  Describe  the 
conditions  which  favor  the  growth  of  yeast.  Explain  how  you  know 
that  yeast  has  grown. 

Yeast.  If  a small  piece  of  compressed  yeast  cake  is  shaken 
up  with  some  molasses  and  water  and  the  mixture  allowed  to 
stand  overnight  in  a warm  place,  fermentation  will  take  place. 
Examination  of  a drop  of  the  settlings  from  the  mixture  shows  that 
the  common  compressed  yeast  cake  contains  millions  of  tiny  yeast 


(COMMERCIAL  YEAST 


191 


plants.  In  its  simplest  form  a yeast  i)lant  is  a single  cell,  ovoid 
in  shape  and  usually  containing  one  or  more  vacuoles.  The  cells 
reproduce  by  a process  called  budding.  Under  certain  conditions 
spores  are  found. 

An  enzyme  causes  fermentation.  It  has  been  proved  that  if 
yeast  cells  are  ground  up  until  they  are  destroyed,  the  juice 


filtered  from  them  is  able 
to  cause  fermentation. 

Similar  experiments  have 
b(‘eii  made  with  bacteria, 
sliowing  that  enzymes 
formed  within  the  cells 
cause  fermentation. 

These  enzymes  are  called 
zymases. 

Commercial  yeast. 

Cultivated  yeast  is  now 
supplied  in  compressed 
or  dried  yeast  cakes.  In 
both  cases  the  yeast 
plants  are  mixed  with 
starch  and  other  sub- 
stances and  pressed  into  a cake.  The  compressed  yeast  cake  must 
be  used  fresh,  as  the  yeast  plants  begin  to  die  rapidly  after  two  or 
three  days.  The  dried  yeast  cake  contains  a much  smaller  number 
of  yeast  plants,  but  is  probably  more  reliable  if  the  yeast  cannot 
be  obtained  fresh. 


Life  history  of  yeast.  Follow  the  arrows  and  work  out 
what  happens  after  the  germination  of  the  spores.  How 
many  spores  are  produced  in  the  sac  or  ascus  shown  at  the 
bottom  of  the  diagram? 


Home  Experiment.  To  determine  the  conditions  favorable  for  the 
growth  of  yeast  in  bread.  Make  a small  amount  of  dough  by  mix- 
ing flour,  sugar,  salt,  and  water  in  proportions  to  make  a thick  paste. 
Knead  with  a little  yeast  which  has  previously  been  mixed  with 
water.  Now  place  one  lot  of  dough  in  the  ice  box,  one  at  the  tem- 
perature of  the  room,  and  one  in  a warm  place  (over  95°  F.).  Later 
bake  each  lot  and  use  in  the  laboratory. 

Which  of  the  three  lots  has  risen  the  most?  Which,  after  baking, 
has  the  best  appearance?  The  best  taste?  What  makes  the  holes 
in  the  bread? 

What  caused  the  dough  to  rise?  What  are  the  best  conditions  for 
this  to  take  place  ? Will  the  mixture  rise  if  no  yeast  is  added  ? Why  ? 


192 


THE  PLANT  WORLD 


Bread  making.  Most  of  us  are  familiar  with  the  process  of 
bread  making.  The  materials  used  are  flour,  milk  or  water,  or 
both,  salt,  a little  sugar  to  hasten  the  process  of  fermentation,  or 
“ rising,’’  as  it  is  called,  some  butter  or  lard,  and  yeast. 

After  the  materials  are  mixed  thoroughly  the  bread  is  put  aside 
in  a warm  place  (between  70°-75°  Fahrenheit)  to  ‘‘  rise.”  If  we 

examine  the  dough 
after  a few  hours,  we 
find  many  holes  in  it, 
which  give  the  mass 
a spongy  appear- 
ance. The  yeast 
plants,  owing  to 
favorable  condi- 
tions, have  grown 
rapidly  and  made 
bubbles  of  carbon 
dioxide.  Alcohol  is 
present,  too,  but 
this  is  evaporated 
when  the  dough  is 
baked.  The  baking 
cooks  the  starch  of 
the  bread,  drives  off 
the  carbon  dioxide  and  alcohol,  and  kills  the  yeast  plants,  besides 
forming  a protective  crust  on  the  loaf. 

Sour  bread.  In  the  “ rising  ” of  bread,  bacteria  always  do 
part  of  the  work  of  fermentation.  Certain  of  these  plants  form 
acids  after  fermentation  takes  place.  The  sour  taste  of  the  bread 
is  usually  due  to  this  cause,  and  may  be  prevented  by  baking  the 
bread  before  the  acids  form,  by  having  fresh  yeast,  good  fresh 
flour,  and  clean  vessels  with  which  to  work. 

Importance  of  yeasts.  Since  yeast  cells  do  not  contain  chloro- 
phyll they  cannot  make  their  own  food  but  must  get  it  already 
made.  Their  food  consists  mostly  of  fruit  juices  and  other  sugar 
solutions.  If  a fruit  syrup  is  left  exposed  to  the  air  wild  yeast 
plants  will  settle  on  it,  and  multiply  rapidly,  causing  fermentation. 


Explain  the  process  by  which  bread  becomes  light  ? 


TO  LEAHX  AROl’T  SOME  DESTRUCTIVE  FUNGI  193 

They  may  f>:et  into  caimed  substances  put  up  in  sugar  and  cause 
tiieni  to  “ work,”  giving  them  a peculiar  flavor.  But  they  can  be 
easily  killed  Iw  heating  to  the  temperature  of  boiling.  On  the  other 
hand,  yeast  gives  us  leavenetl  bread. 

Many  interesting  experiments  with  j^east  may  be  tried  as  home 
projects.  For  exc('llent  suggestions,  see  Conn’s  Bacteria,  Yeasts, 
and  Molds  in  the  Home,  pp.  274-278. 

Practical  Exercise  4.  I low  may  yeasts  he  useful  to  man  ? Where  are  yeasts 
found?  Give  proofs.  What  produefs  are  formed  when  bread  rises?  What 
becomes  of  tliese  products?  It  is  said  that  yeast  i)lants  are  at  once  the 
friemls  of  man  and  yet  make  him  their  slave.  Exj)lain  what  this  means. 

Self-Testing  Exercise 

Yeasts  cause (1)  by  changing (2)  into (3) 

(4)  and  (o).  An  enzyme  called (6)  causes 

fermentation (7)  also  cause  bread  to  rise,  because  of  the 

bubbles  of (8) (9)  formed  during  their (10) 

growth  when  the (11)  is  put  in  a (12)  place. 

PROBLEM  V.  TO  LEARN  ABOUT  SOME  DESTRUCTIVE  FUNGI 

j\Iost  of  US  are  familiar  with  some  fungi,  as  the  edible  mushrooms 
and  the  so-called  “ toadstools  ” found  in  parks  or  lawns.  We 


L.  W.  Brownell 

These  poisonous  fungi  (amanita  muscaria)  are  found  during  the  summer  and  early  autumn 
along  roadsides  near  trees,  in  groves,  and  in  woods.  How  can  you  tell  them? 


194 


THE  PLANT  WORLD 


have  already  seen  some- 
thing of  their  characteris- 
tics. They  are  as  much 
dependent  upon  the  green 
plants  for  food  as  are  ani- 
mals. But  some  of  the 
fungi  require  dead  organic 
matter  for  their  food. 
This  may  be  obtained  from 
decayed  vegetable  or  ani- 
mal material  in  soil,  from 
the  bodies  of  dead  plants 
and  animals,  or  even  from 
foods  prepared  for  man. 
Fungi  which  feed  upon 
non-living  organic  material 
are  known  as  saprophytes. 
Examples  are  the  mush- 
rooms, yeasts,  and  molds. 

Some  parasitic  fungi.  Some  fungi  prefer  living  plants  or  animals 
for  i^heir  food  and  are  therefore  classed  as  parasites.  An  example 
is  the  chestnut  blight  or  canker,  which  has  killed  chestnut  trees 
by  the  thousands  in  the  eastern  part  of  the  United  States.  It  pro- 
duces millions  of  tiny  spores,  which,  blown  about  by  the  wind, 
light  on  the  trees,  sprout,  and  send  under  the  bark  thread-like 
mycetia  which  absorb  the  food  circulating  in  the  living  cells,  even- 
tually causing  the  death  of  the  tree.  The  chestnut  canker,  in- 
troduced from  abroad  on  chestnuts  planted  near  the  city  of  New 
York  in  1904,  within  ten  years  had  destroyed  practically  every 
chestnut  tree  in  the  eastern  part  of  the  United  States. 

Another  fungus  which  does  much  harm  to  trees  is  the  shelf  or 
bracket  f unpus.  The  shelflike  body  is  in  reality  the  reproductive 
part  of  the  plant;  in  its  lower  surface  are  formed  millions  of 
asexual  spores,  which,  when  they  fall  on  a dead  or  a dying  tree 
trunk,  may  start  a new  fungus  growth.  The  true  body  of  the 
plant,  a network  of  threads,  is  found  under  the  bark.  Once 
established,  it  spreads  rapidly.  There  is  no  remedy  except  to 


BhA("K  STKM  CKAIN  liUST 


195 


kill  the  tree  aiul  burn  it,  so  as  to  destroy  the  spores.  Each  year 
many  fine  trees,  sound  exce{)t  for  a slight  bruise  or  other  injury. 


! 


are  infected  and 
eventually  killed 
by  this  fungus. 


Field  Exercise. 

On  a field  trip  we 
may  see  a number  of 
trees  which  arc  in- 
fected with  fungi. 

C'ount  the  number 
of  perfect  trees  in  a 
given  area.  Com- 
pare it  with  the 
number  of  trees  at- 
tacked by  fungus. 

Does  the  fungus  aj)- 
pear  to  be  trans- 
mitted from  one  tree 
to  another  near 
at  hand?  In  how 
many  instances  can  jmu  discover  the  point  where  the  fungus  first  at- 
tacked the  tree?  How  do  the  spores  leave  the  spore  case?  How  do 
they  germinate  on  the  tree  which  they  attacked? 


L.  ir.  Brownell 

Shelf  fungi  (Femes  applanatus)  as  often  seen  growing  on  the 
trunks  of  trees.  They  cause  enormous  losses  by  causing  the 
timber  to  decay. 


Black  stem  grain  rust.  Wheat  rust  is  probably  the  most  destruc- 
tive parasitic  fungus.  For  hundreds  of  years  this  rust  has  been 
the  most  dreaded  of  plant  diseases,  because  it  destroys  the  one 
harvest  upon  which  the  civilized  world  is  most  dependent.  For 
a long  time  past  the  appearance  of  rust  has  been  associated  with 
the  presence  of  barberry  bushes  in  the  neighborhood  of  the  wheat 
fields.  Although  laws  were  enacted  in  1760  in  New  England  to 
provide  for  the  destruction  of  barberry  bushes  near  infected  wheat 
fields,  nothing  was  actually  known  of  the  relation  existing  be- 
tween the  rust  and  the  barberry  until  comparatively  recent  years. 
It  has  now  been  proved  beyond  doubt  that  the  wheat  rust 
passes  part  of  its  life  as  a parasite  on  the  common  barberry  and 
from  there  gets  to  the  wheat  plant,  where  it  undergoes  a compli- 
cated life  history.  The  wheat  leaf,  its  nourishment  and  living 
matter  used  as  food  by  the  parasite,  soon  dies,  and  no  grain  is 
produced. 


196 


THE  PLANT  WORLD 


It  is  estimated  that  in  the  grain-raising  states  of  the  Middle  West 
668,338,000  bushels  of  grain  have  been  destroyed  by  black  stem 
rust  in  the  13  years  from  1915  to  1927  inclusive.  This  has  meant  a 
yearly  average  loss  of  almost  $55,000,000.  The  only  way  to  prevent 
this  pest  is  to  break  the  chain  of  the  life  cycle  by  destroying  the 
barberry  bushes  on  which  the  spores  grow  in  the  spring  of  the  year. 


The  life  history  of  wheat  rust.  How  would  you  go  to  work  to  exterminate 
this  pest  ? Explain. 


Blister  rust.  The  pine  tree  blister  rust  is  a recent  importation 
from  Europe  that  threatens  our  white  pine  forests.  This  rust 
passes  one  stage  on  the  currant  and  gooseberry,  so  that  the  only  way 
to  control  it  is  to  remove  all  currant  and  gooseberry  bushes  from 
the  neighborhood  of  such  trees. 

Mildews.  Another  group  of  fungi  that  are  of  considerable 
economic  importance  is  made  up  of  the  sac  fungi.  Such  fungi 
are  commonly  called  mildews.  Some  of  the  most  easily  obtained 


MILDEWS 


197 


spociiiieiis  come  from  the  lilac,  rose,  or  willow.  These  fungi  do 
not  penetrate  the  host  plant  to  any  depth,  but  cover  the  leaves  of 
the  host  with  the  whitish  threads  of  the  mycelium.  Hence  they 
may  be  killed  by  means  of  applications  of  some  fungus-killing 
fluid,  as  Bordeau.x  mi.xture.  They  obtain  their  food  from  the 
outer  layer  of  cells  in  the  leaf  of  the  host.  Among  the  useful 
plants  preyed  upon  by  this  group  of  fungi  are  the  plum,  cherry, 
and  peach  trees.  The  diseases  known  as  black  knot  and  peach 
curl  are  caused  by  these  fungi. 

Potato  wart  is  another  fungus  disease  which  was  introduced 
into  this  country  in  1911  and  has  now  spread  over  the  eastern 
part  of  the  United  States.  It  attacks  the  potato  tuber,  so  that 
the  disease  may  not  be  noticed  until  time  to  harvest  the  crop. 

1 Since  its  spores  may  be  dormant  in  soil  for  several  years,  the  only 
way  to  combat  the  pest  is  to  rotate  other  crops  on  the  field  as 
well  as  to  destroy  all  infected  tubers. 


GR.VIN  DESTROYED  BY  STEM  RUST  IN  THIRTEEN  YEARS 
1915  to  1927,  Inclusive 


State 

Wheat 

(Bushels) 

O.YTS 

(Bushels) 

Barley 

AND 

Rye 

(Bushels) 

Total 

All 

Grains 

(Bushels) 

Average 
Annual 
Stem  Rust 
Losses 
All 
Grains 
(Dollars) 

Total 
Loss  1927 
All 
Grains 
(Dollars) 

Colorado  .... 

2,469,000 

176,000 

541,000 

3,186,000 

$ 218,000 

Trace 

Illinois  .... 

4,992,000 

50,156,000 

353,000 

55,501,000 

2,275,000 

$ 8,707,000 

Indiana  .... 

2,974,000 

1,479,000 

Trace 

4,453,000 

481,000 

Trace 

Iowa 

4,246,000 

33,761,000 

2,143,000 

40,150,000 

1,580,000 

729,000 

Michigan  . . . 

6,487,000 

15,831,000 

453,000 

22,771,000 

1,409,000 

765,000 

Minnesota  . 

86,002,000 

50,345,000 

3,498,000 

139,845,000 

11,742,000 

18,592,000 

Montana  .... 

14,863,000 

221,000 

Trace 

15,084,000 

1,154,000 

Trace 

Nebraska  . . . 

18,505,000 

3,922,000 

276,000 

22,703,000 

2,437,000 

Trace 

No.  Dakota  . . . 

202,316,000 

14,788,000 

4,606,000 

221,800,000 

22,191,000 

19,075,000 

Ohio 

4,806,000 

2,694,000 

80,000 

7,580,000 

562,000 

247,000 

So.  Dakota  . . . 

76,209,000 

37,574,000 

4,170,000 

117,953,000 

9,385,000 

9,297,000 

Wisconsin  . . . 

4,456,000 

10,349,000 

2,417,000 

17,312,000 

1,109,000 

375,000 

Total 

428,325,000 

221,386,000 

18,627,000 

668,338,000 

54,543,000 

57,787,000 

These  are  official  estimates  of  the  Plant  Disease  Survey,  Bureau  of  Plant  Industry,  United 
States  Department  of  Agriculture.  The  money  value  of  the  grain  destroyed  in  the  thirteen- 
year  period  was  $709,081,000,  basing  calculations  on  the  farm  prices  for  December  1 of  each  year 
and  disregarding  any  effect  the  reduced  production,  caused  by  rust,  may  have  had  on  the 
market  price.  Losses  for  1927  are  preliminary. 


198 


THE  PLANT  WORLD 


Self-Testing  Exercise 

The (1)  are  plants  which  are  either  parasites  or  saprophytes, 

the  latter  living  on (2) (3)  matter  and  the  former  on 

(4)  plants  and  animals.  The (5)  fungi  do  enormous 

damage  to (6)  every  year.  The  black  stem  wheat  rust,  which 

lives  on  two (7), (8)  and (9),  does  a yearly 

damage  of  almost  $55,000,000.  The  pine  tree (10) 

(11)  is  another  recent  importation  from (12).  It  lives  on  two 

hosts:  the (13)  or (14),  and  the (15).  To 

curb  the  damage  from  such  parasites  one  of  the (16)  plants 

must  be  destroyed. 

PROBLEM  VI.  WHAT  ARE  MOLDS?  WHAT  DO  THEY  DO? 

Demonstration  5.  To  determine  the  conditions  favorable  for  the 
growth  of  mold.  Place  pieces  of  bread  in  each  of  four  wide-mouthed 
bottles  or  jars.  Add  a little  water,  and  expose  all  four  bottles  to 
the  air  of  the  living  room  or  kitchen  for  half  an  hour.  Then  cover  the 
bottles  and  plunge  one  into  boiling  water  for  a few  moments.  Place 
this  and  a second  jar  side  by  side  in  a moderately  warm  room.  Place 
the  third  jar  in  the  ice  box  and  the  fourth  in  a hot  dry  place. 

Notice  day  by  day  any  changes  that  occur  in  the  contents  of  the 
jars.  In  which  jar  does  growth  appear  first?  Do  all  jars  have  a like 
growth  of  mold  at  the  end  of  a given  period  of  time? 

How  does  the  mold  get  on  the  bread?  Where  does  it  come  from? 
Why  did  you  add  water  to  the  jars?  What  conditions  must  you  have 
for  the  growth  of  mold?  Conversely,  how  would  you  keep  molds 
from  getting  a foothold  on  foods? 

Physiology  of  the  growth  of  mold.  Molds,  in  order  to  grow 
rapidly,  need  food,  darkness,  oxygen,  moisture,  and  moderate  heat. 
They  obtain  their  food  from  the  materials  on  which  they  live. 
This  they  are  able  to  do  because  they  have  rhizoids  ^ which  give 
out  digestive  enzymes  which  change  the  starch  of  the  bread  to 
sugar  and  the  protein  to  a soluble  form  which  can  be  absorbed  by 
the  cells.  These  absorbed  foods  are  then  used  to  supply  energy 
and  make  protoplasm.  Thus  molds  act  like  animals,  except  that 
digestion  takes  place  outside  of  the  body. 

What  can  molds  live  on  ? Molds  feed  upon  all  cakes  and  breads, 
upon  meat,  cheese,  and  many  raw  vegetables.  They  are  almost 
sure  to  grow  upon  flour  if  it  is  allowed  to  get  damp.  Jelly  and 
other  foods  containing  moisture  are  particularly  favorable  to  the 

1 Rhizoids  (ri'zoids)  : rootlike  filaments  or  threads. 


now  TO  PRF.VKNT  MOLDS 


199 


j^rowth  of  niokls.  Loathor,  clotli,  paper,  or  oven  moist  wood  will 
give  food  onoup:h  to  support  their  growth.  At  least  one  trouble- 
some disease,  n'ngivorni,  is  due  to  the  growth  of  molds  in  the  skin. 

What  mold  does  to 
foods.  Mold  usually 
changes  the  taste  of  the 
material  it  grows  upon, 
rendering  it  “ musty  ” 
and  sojiietimes  unfit  to 
eat.  Eventually  food 
will  be  spoiled  com- 
pletely because  bacterial 
decay  sets  in.  Some 
molds  are  useful.  They 
give  the  flavor  to  Gor- 
gonzola, Roquefort, 

Camembert,  and  Brie 
cheeses.  But,  on  the 
whole,  molds  are  pests 
which  the  housekeeper 
wishes  to  get  rid  of. 

How  to  prevent  molds.  As  we  have  seen,  moisture  is  favorable 
for  the  growth  of  mold ; conversely,  dryness  is  unfavorable. 
Inasmuch  as  the  spores  of  mold  abound  in  the  air,  materials  which 
cannot  be  kept  dry  should  be  covered.  Jelly,  after  it  is  made, 
should  at  once  be  tightly  covered  with  a thin  layer  of  paraffin  or 
waxed  paper,  which  excludes  the  air  and  possible  mold  spores. 
To  prevent  molds  from  attacking  fresh  fruit,  the  surface  of  the 
fruit  should  be  kept  dry  and,  if  possible,  each  piece  of  fruit  should 
be  WTapped  in  paper.  Why?  Mold  spores  may  be  killed  in  a 
few  minutes  with  dry  heat  at  212°  F.  Dry  dusting  or  sweeping 
will  raise  dust,  which  usually  contains  spores  of  mold  and  bacteria. 
Use  a dampened  broom  or  dust  cloth  frequently  in  the  kitchen,  if 
you  wish  to  preserve  foods  from  molds. 


Life  history  of  bread  mold.  There  may  he  a sexual 
stage  in  the  life  history  (shown  in  center  of  diagram)  in 
which  the  formation  of  a zygospore  results.  What  value 
might  this  be  to  the  mold  ? 


Practical  Exercise  6.  Where  may  mold  spores  be  found  ? What  must  they 
have  in  order  to  grow?  On  what  part  of  foods  do  molds  grow?  How  would 
you  prevent  mold  spores  from  getting  into  food  ? 


200 


THE  PLANT  WORLD 


Self-Testing  Exercise 

Molds  grow  under  favorable  conditions  of (1), (2), 

(3),  and (4)  heat.  They  spoil  many (5)  and 

cause (6).  Some  molds  give (7)  to  cheese.  Molds 

may  be  kept  out  of  food  by  keeping  the  food (8)  and  well 

(9).  Molds  send  out  rootlike  threads, (10),  which  give 

off (11) (12)  and  absorb (13). 

PROBLEM  VII.  WHAT  ARE  SOME  EXAMPLES  OF  COMMON 
ALGAE? 

The  Fungi  which  include  all  the  plants  which  we  have  so  far 
studied  in  this  unit  constitute  one  large  division  of  thallophytes. 
We  now  come  to  the  other  main  group,  the  algae.  In  the  classifi- 
cation given  below  we  find  three  classes  of  algae. 

The  Algae.  The  algae  are  nearly  all  water  plants,  although  some 
few  species  may  be  found  on  tree  trunks  and  rocks  which  are  exposed 
to  moisture.  They  are  a large  group  of  chlorophyll-bearing  plants, 
although  in  some  forms  the  characteristic  green  color  of  chlorophyll 
is  masked  by  some  other  coloring  matter,  usually  red  and  brown. 
They  have  many  forms,  ranging  from  single  cells  to  filamentous 
colonies  or  even  long  ribbon  or  rope-like  masses  many  feet  in  length, 
as  in  some  seaweeds.  Our  attention  is  called  to  them  in  an  un- 


I.  The  Green  algae  are  of  countless  forms,  unicellular,  filamentous,  plate-like,  and  in  irregular 
masses  of  cells.  There  are  both  fresh-water  and  salt-water  forms,  and  others  live  on  land.  The 
so-called  “ Red-Snow  ” is  a form  living  in  snow  patches.  Pleurococcus  and  vaucheria  are  also 
examples.  Some  5000  species  have  been  described. 

II.  The  Brown  algae  are  nearly  all  marine  plants.  We  know  them  as  seaweeds.  About 
1000  species  are  known. 

III.  The  Red  algae,  mostly  marine,  are  our  most  delicate  and  beautiful  seaweeds.  There  are 
about  3000  named  species. 

IV.  The  Fungi  are  without  chlorophyll.  There  are  about  75,000  species  in  all.  Many  of 
them  are  harmful.  There  are  two  classes:  Phycomycetes,  the  molds;  and  Eumycetes,  yeasts, 
mushrooms,  and  puffballs.  Bacteria  are  usually  classed  as  Fungi. 


SOME  EXAMPLES  OF  AL(JAE 


201 


pleasant  way  at  times,  when,  after  multiplying  very  rapidly  during 
the  hot  summer,  they  die  sucklenly  in  the  early  fall  and  leave  their 


ccH  voU 

.—nucleus 
-cbloroplost 
a single  cell 


a colony 
of  Wo 
Cell^ 


ancC 
oc  color^ 
of  four 
cells 


Pleurococcus.  Explain  how  a colony 
of  Pleurococcus  might  come  into  ex- 
istence. 


remains  in  our  water  supply.  Much 
of  the  unpleasant  taste  and  odor  of 
drinking  water  comes  from  this  cause. 

Some  examples  of  algae.  One  of 
the  simplest  algae  is  Pleurococcus 
(pldo-ro-kokhfs).  This  little  plant 
consists  of  a single  tiny  cell,  which 
by  division  may  give  rise  to  two  or 
more  cells  which  cling  together  in  a 
mass.  The  green  color  on  tree  trunks, 
stone  houses,  etc.,  is  often  due  to 
millions  of  these  little  plants. 

Spirogyra,  a pond  scum,  is  known 
to  every  boy  or  girl  who  has  observed 
a small  pond  or  sluggish  stream.  It 
grows  as  a slimy  mass  of  green  threads 
or  filaments.  Under  the  low  power 

of  the  microscope,  the  body  is  seen  to 
be  a filament  made  up  of  elongated 
cylindrical  cells,  each  of  which  con- 
tains a spirally  wound  band  of  chlo- 
rophyll. Spirogyra  may  reproduce 
asexually  by  division  of  the  cells.  It 
may  also  reproduce  sexually.  When 
this  happens,  the  cells  of  two  adjoin- 
ing filaments  push  out  portions  of  their 
cell  walls  which  meet,  forming  a bridge. 
The  cell  walls  in  the  middle  of  the 
bridge  dissolve.  The  protoplasm  of 
the  cells  thus  joined  condenses  into 
two  tiny  spheres,  and  ultimately  the 
contents  of  one  cell  passes  through 
the  connecting  tube  and  mingles  with 
, ^ , the  cell  of  the  neighboring  filament. 

A single  cell  of  Spirogyra.  Is  the  cell  i - i , ,,  /• 

flat  or  round  in  cross  section?  ihlS  prOCeSS  by  whlCh  tWO  Cells  01 


202 


THE  PLANT  WORLD 


nearly  equal  size  fuse  to  form  a single  cell  is  called  conjugation. 
The  result  of  this  process  of  fusion  is  a thick-walled  resting  cell 
which  is  called  a zygospore  (zi'go-spor)  or  zygote.  The  cell  thus 
formed  can  withstand  considerable  extremes  of  heat,  cold,  and 
dryness.  After  the  zygospore  is  formed,  the  cell  walls  break  and 
the  zygospore  falls  to  the  bottom  of  the  pond.  Under  favorable 
conditions,  it  will  germinate  and  form  a new  filament. 

Self-Testing  Exercise 

The  simplest  green  plants  are  the ( 1 ) . The (2)  of 


two  cells  of  nearly  equal  size  to  form  one  cell  is  called (3) . This 

method  of  reproduction  is  characteristic  of (4).  A 

(5)  is  a thick-walled  resting  cell. 


PROBLEM  VIII.  WHAT  IS  THE  LIFE  HISTORY  OF  A MOSS 
PLANT? 

The  Bryophyta  consist  of  two  groups  of  plants,  the  liverworts 
and  the  mosses.  Both  are  small  plants  and  nearly  all  forms  live 

on  land.  They  show 
a much  greater  de- 
velopment of  tissues 
than  the  algae  and 
may  be  either  ihallus- 
like  (liverworts)  or 
have  stems  with 
rootlike  projections 
(rhizoids)  and  very 
simple  leaves,  as 
the  mosses. 

The  Moss  Plant. 
One  of  the  mosses 
frequently  seen  and 
easily  recognized  is 
the  “ pigeon- wheat  ” 
moss.  A leafy  moss 
plant  has  rhizoids, 
an  upright  stem,  and 


The  life  history  of  a moss.  Refer  to  the  numbers  in  your 
text  and  work  out  the  stages  in  the  life  history. 


r.AMETOPTTYTR 


203 


Kroon  loavos.  In  tlio  plants  wliich  havo  a stalk  and  capsule  (1), 
the  stalk  ki'ows  out  of  the  leafy  plant. 

Sporophyte.  The  capsule  is  the  sporauKiuiu  or  spore  case  (2). 
The  stalk  and  capsule  toKother  form  the  sporophyte  (spoTo-fIt)  or 
spore-produciuK  Kf'neration  of  the  moss. 

Gametophyte.  The  spore  (3)  nates  into  a threadlike  pro- 
tonema  (4).  The  protonema  soon  develops  rhizoids,  and  tiny 
buds  appear  which  form  the  adult  plants.  These  may  ki'ow  only 
leaves,  or  they  ma}’-  develop  into  plants  (5)  that  bear  the  rosettes 
of  leaves  which  hold  either  sperm  or  egg  cells,  for  these  are  pro- 
duced on  separate  plants.  These  two  kinds  of  plants  form  the 
sexual  generation  (called  the  gametophyte)  of  the  moss  (6,  7,  8, 
9).  After  a sperm  has  been  transferred  to  the  egg  cell,  fertiliza- 
tion or  fusion  of  these  two  cells  takes  place  (10).  This  process 
results  in  the  growth  of  the  sporophyte  which  bears  the  asexual 
spores.  These  spores  produce  a leafy  moss  plant  which  bears 
organs  producing  eggs  and  sperms.  This  life  history  is  known  as 
alternation  of  generations. 

Practical  Exercise  6.  Why  do  we  call  the  life  history  of  moss  alternation  of 
generations  ? 


BR-YOPHYTA 


These  plants  are  small  and  live  mostly  on  land.  There  are  about  16,000  known  species. 


Self-Testing  Exercise 

Bryophytes  include  (1)  and  (2).  The  mosses 

show  (3)  of  generations  in  which  an  (4)  stage  is 

followed  by  a (.5)  stage.  A spore  gives  rise  to  a (6) 


204 


THE  PLANT  WORLD 


which  grows  into  moss  plants,  produces  (7)  and  (8). 

After  fertilization  the  fertilized  egg  grows  into  a (9),  which  gives 

rise  to (10)  spores. 

PROBLEM  IX.  WHAT  IS  THE  LIFE  HISTORY  OF  A FERN 
PLANT? 

The  pteridophytes  are  a group  which,  when  the  world  was 
younger,  played  a very  important  part  in  the  vegetation  on  the 
earth.  Some  coal  is  made  very  largely  from  their  bodies.  They 
have  true  roots,  stems,  and  leaves,  but  reproduce  like  the  mosses, 
by  forming  spores.— 

Life  history  of  a fern.  The  common  fern  begins  life  as  a spore. 
This  germinates  into  a tiny  heart-shaped  body  called  a pro- 


The  life  history  of  a fern,  (i)  Adult  plant,  (2)  a leaflet  showing  sori  or  groups 
of  spore  cases,  (3)  a section  through  a sorus,  (4)  a spore  case  opening,  (5)  a 
spore  which  germinates  into  (6)  a prothallium  which  in  turn  produces  organs 
containing  (7)  sperms  and  (8)  eggs.  When  an  egg  is  fertilized  it  gives  rise  to 
(9)  a new  fern  plant. 

thallium  which  contains  sex  organs  holding  sperm  and  egg  cells. 

This  is  called  the  gametophyte  generation  of  the  plant  because 


LIFE  HISTORY  OF  A FERN 


205 


it  holds  tho  male  and  female  gametes  or  sex  cells.  Tliesc  cells 
after  fertilization  produce  structures  (fronds)  which  bear  the 
asexual  spores.  These  spores  when  ripe  germinate  and  the  life 
cycle  begins  over  again,  a sexual  generation  alternating  with  an 
asexual  generation. 

Practical  Exercise  7.  Compare,  by  means  of  labeled  diagrams,  the  life  his- 
tories of  the  moss  and  fern. 


These  pteridophytes  include  three  classes;  the  true  ferns,  the  horsetails,  and  the  club  mosses. 

There  are  about  8000  known  species. 

Self-Testing  Exercise 

The (1)  or  ferns  have (2)  of  generations  in  their  life 

history.  In  the  gametophyte  generation,  a small (3)  structure, 

called  a (4),  holds  the (5)  and  the (6)  cells. 

The  fertilized  egg  produces  leafy  structures  which  bear  (7) 

spores.  The  pteridophytes  include  the (8),  the  (9), 

and  the (10). 

PROBLEM  X.  WHAT  ARE  SOME  EXAMPLES  OF 
SPERMATOPHYTES  ? 

The  spermatophytes  (Gr.  sperma,  seed),  or  seed-bearing  plants, 
include  two  groups : 

The  gymnosperms  (Gr.  gymnos,  naked),  or  naked-seed  plants, 
are  a small  group  related  to  the  ferns  on  one  side  and  the  flowering 
plants  on  the  other.  Two  classes  are  found  : the  cycads,  of  which 
group  the  so-called  tree  ferns  are  examples,  and  the  conifers  or 
evergreens,  as  pines,  spruces,  firs,  hemlocks,  cypress,  and  others. 
There  are  only  about  450  species  of  gymnosperms.  The  cycads 
are  practically  confined  to  the  tropical  regions.  They  have  leaves 
much  like  the  ferns  and  their  stems  are  covered  with  scales.  In 


206 


THE  PLANT  WORLD 


their  life  history  as  well  as  their  appearance  they  show  relationship 
to  the  ferns.  They  bear  two  kinds  of  reproductive  bodies  in 
conelike  structures  on  separate  plants. 

The  conifers  are  the  trees  we  call  evergreens  and  most  of  them 
have  needle-like  leaves.  The  evergreens  include  the  sequoias,  the 
largest  and  oldest  trees.  The  eggs  and  sperms  are  borne  in  pistil- 
late or  staminate  cones.  Seeds  are  produced  in  the  scales  of  the 


pistillate  cones,  and  when  the  cone  dies,  the  seeds  are  released  by 
the  curling  backwards  of  the  dry  scales  or  sporophylls. 

The  angiosperms  (Gr.  angeion,  case  or  vessel),  or  true  flowering 
plants,  of  which  we  already  know  something,  are  a very  large 
group,  including  all  of  our  common  grasses  and  grains,  and  all 
trees,  shrubs,  and  plants  that  bear  flowers.  There  are  more  than 
240,000  known  species.  They  are  grouped  in  two  great  classes, 
the  monocotyledons  and  the  dicotyledons. 


Brooklyn  Botanic  Gardens,  Brooklyn,  N.  Y. 

What  are  the  characteristics  of  a cycad  ? 


WHAT  ARK  SOMK  KXAMPLKS  OF  S1>FKMAT()FH YTFS?  207 


If  we  suninuirize  the  facts  we  already  know  about  flowering 
plants,  they  are  brielly  these;  Seeds,  which  are  formed  in  the 
fruits  as  the  result  of  pollination  and  later  fertilization,  give  rise 
under  favorable  conditions  to  young  seedlings.  The  conditions 
which  waken  the  embryo  within  the  seed  to  activity  and  growth 
are  favorable  conditions  of  moisture,  temperature,  air,  and  food 
materials.  We  have  learned  tluit  under  favorable  conditions  the 
young  plant  grows  into  an  adult  and  in  course  of  time  produces 
flowers,  ddie  flower  is  really  a modified  branch  which  contains 
the  male  and  female  ganietophytes  of  the  flowering  plant.  The 
female  gametophyte  is  contained  within  the  ovary  of  the  flower 
and  is  called  the  ovule.  The  male  ganietophytes  are  the  pollen 
grains  which  contain  the  sperm  cells. 

Botanists  have  shov/n  that  in  the  flowering  plants  or  spermato- 
phytes  there  e.xists  an  alternation  of  generations,  as  in  the  mosses 
and  ferns.  The  pollen  grain  is  believed  to  be  a spore,  which 
develops  into  the  male  gametophyte  (the  pollen  tube),  while  the 
embryo  sac  in  the  ovary  of  the  flower  is  another  spore,  within 
which  is  found  the  female  gametophyte.  Most  of  the  life  of  the 
flowering  plant  is  passed  evidently  in  the  asexual  or  sporophyte 
stage. 


5PfRMAT0PHYTA 


The  flowering  plants  are  further  divided  into  monocotyledons 
and  dicotyledons.  A brief  description  of  a few  of  the  most  im- 
portant families  of  these  plants  is  given.  These  particular  ones 
were  selected  because  they  are  likely  to  be  seen  by  the  average 
boy  or  girl  who  takes  field  excursions  or  hikes.  The  total  number 
of  known  species  of  plants  of  these  groups  is  more  than  240,000. 


208 


THE  PLANT  WORLD 


L.  W.  Brownell 

Yellow  Lady’s  Slipper  (orchid  family). 


Monocotyledons.  The  Grass 
Family.  We  are  all  familiar 
with  the  narrow  parallel- veined 
leaf  of  the  grasses.  The  stems 
are  usually  round  and  the 
flowers  are  borne  in  structures 
called  spikelets.  The  flowers 
have  three  stamens  and  a 
single  pistil,  which  produces 
one  seed.  The  one-seeded  fruit 
is  called  a grain.  Examples  of 
grasses  are  wheat,  rye,  timothy, 
wild  grasses,  sugar  cane,  and 
bamboo.  The  sedges,  near 
relatives  of  the  grasses,  have  un- 
jointed,  triangular  stems,  while 
grass  stems  are  always  jointed. 

The  Palm  Family.  The  palm 
is  known  from  other  mono- 
cotyledons because  it  usually 
has  a woody  stem.  There  are 
about  1200  species  of  palms  in 
the  world.  Though  mostly 
inhabitants  of  the  tropics, 
there  are  a few  species  found 
in  the  southern  part  of  this 
country. 

The  Lily  Family.  The  mem- 
bers of  this  family  are  known 
to  most  of  us.  Hyacinths, 
tulips,  lily-of-the- valley,  as  well 
as  the  tiger  lily  and  other 
lilies,  are  members  of  this 
family.  Several  food  plants, 
as  asparagus  and  onions,  be- 
long in  this  group.  They  have 
the  typical  liliaceous  flower. 


DICOTYLEDONS 


209 


with  tlio  parts  in  throes  and 
with  a brightly  colored  and 
often  conspicuous  corolla. 
They  have  bulbs,  rootstalks, 
etc.,  which  enable  them  to 
grow  rapidly  at  the  coming 
of  a favorable  season.  The 
yucca,  well  known  in  our  South- 
west, is  one  of  this  family. 

The  Arum  Family.  The 
members  of  this  family  may  be 
tohl  by  their  peculiar  flower 
cluster,  a spikelike  structure 
known  as  a spadix.  In  the 
Jack-in-the-pulpit  this  is  sur- 
rounded by  a large  leaflike 
structure  called  the  spathe. 
The  calla  lily  and  skunk  cab- 
bage are  our  best-known  ex- 
amples. 

The  Orchid  Family.  These 
plants  are  noted  for  their 
beautiful  flowers.  In  the 
tropics  one  member  of  this 
group  is  conspicuous  because 
of  its  habit  of  living  in  trees 
as  an  air  plant  or  epiphyte.  A 
few  orchids  live  in  secluded 
places  in  our  north  temperate 
zone,  but  most  have  disap- 
peared because  of  overpicking. 
Never  pick  an  orchid,  if  you 
are  lucky  enough  to  find  one ; 
photograph  it  instead. 

Dicotyledons.  Legume  Fam- 
ily. This  is  one  of  the  best- 
known  and  most  easily  recog- 


L.  W.  Brownell 

Perennial  peas  (legume  family). 


L.  W.  Brownell 

Wild  strawberry  blossoms  (rose  family). 


210 


THE  PLANT  WORLD 


h.  W.  Brownell 

Watercress  (mustard  family). 

The  Buttercup  Family  is  a very ' 
and  conspicuous  flowers  in  which 
the  same  color.  They  have  a 


nized  families  of  the  dicoty- 
ledons. The  legumes  always 
have  irregular  flowers,  as  the 
sweet  pea,  and  produce  fruit 
which  is  a pod.  Most  of  the 
legumes  have  compound  leaves. 
Examples  are : peas,  beans, 
clover,  lupines,  and  peanuts, 
while  locusts  and  acacias  are 
examples  of  trees. 

The  Rose  Family  can  be  told 
by  the  flower  in  which  the  parts 
come  out  in  fives,  the  sepals 
and  petals  making  a cup  from 
which  the  stamens  spring. 
Roses,  and  the  blossoms  of 
strawberries,  blackberries,  rasp- 
berries, cherries,  pears,  and 
apples  are  examples, 
large  family,  which  bears  solitary 
the  calyx  and  corolla  are  usually 
large  and  indefinite  number  of 


I 


L.  ir.  Brownell 


The  Globe  flower  is  a member  of  the  buttercup  family. 


DK’OTN  LKDONS 


211 


stanu'iis  and  j)istils.  Ex- 
amples aro:  buttercaips,  aiu'in- 
ones,  peony,  tulip  ti'ees,  maj>;- 
iiolias,  and  man}’  others. 

Thf  Mustard  Fuuuhj  lias  a 
peculiar  llower  of  four  petals 
and  sepals  distinct  from  each 
other  and  six  stamens.  Many 
of  our  most  troublesome  weeds 
belong  to  this  family,  as  well 
as  many  gartlen  vegetables, 
cabbage,  turnips,  radishes,  and 
watercress. 

The  Mint  Family  also  has 
a characteristic  flower.  The 
corolla  is  like  a tube  and  has 
two  lips.  The  pistil  has  two 
carpels,  but  there  are  five  sta- 
mens. The  plants  usually  have 
a characteristic  odor  and  square  stems.  Spearmint,  lavender,  and 
thyme  are  members  of  this  family. 

The  Willow  Family  is  best  known  by  the  poplars  and  willows. 
These  trees  have  the  naked  flowers  in  catkins  with  separate  male 


L.  W . Brownell 

Blossoms  of  the  crack  willow  (willow  family). 


212 


THE  PLANT  WORLD 


and  female  flowers  on  different 
individuals. 

The  Carrot  Family  can  easily 
be  recognized  by  the  umbrella- 
shaped flower  cluster.  These 
plants  are  usually  perennial 
herbs.  The  leaves  are  usually 
deeply  indented.  Examples  are 
the  carrot,  fennel,  and  celery. 

The  Heath  Family  can  be 
recognized  by  the  fact  that  its 
flowers  have  a five-parted 
corolla  which  is  more  or  less 
united  in  a bell  and  most  of 
the  group  have  simple  ever- 
green leaves.  Laurel,  blue- 
berries, wintergreen,  heather, 

L.  IV.  Brownell.  i i i i i 

Mountain  laureKheath  family).  ^ud  rhododendrous  are  mem- 

bers of  this  group. 

The  Composite  Family  is  the  largest  group  of  the  flowering  plants, 
having  over  13,000  species.  The  flowers  are  very  small  and  grouped 


Many  fields  are  infested  with  wild  carrot  (carrot  family). 


L.  W.  Brotmell 


TEST  ON  FUNDAMENTAL  CONCEITS 


213 


in  cliistors  known  ns  compound 
heads.  They  i^rodiice  numer- 
ous s('eds.  The  "[roup  includes 
many  of  our  weeds,  such  as 
raj2;weed,  thistles,  dandelions, 
daisies,  and  cocklehurs,  and 
many  of  our  most  beautiful 
^[aixlen  flowers,  as  asters,  sun- 
flowers, aiul  chrysanthemums. 

S E L F-  T K S T I X G 1 % X E U C I S E 

The  seed  plants  or (1) 

are  divided  into  two  great 

groups;  the  (2),  those 

producing  naked  seeds,  and  the 

.(3),  or  (4) 

plants,  in  which  the  seed  is 
usually  inclosed  in  a (5). 


L.  TF.  Brownell 
Daisies  (composite  family). 


Review  Summary 

Test  your  knowledge  of  this  unit  by;  (1)  answering  and  rechecking  the 
survey  questions ; (2)  performing  all  assigned  exercises  and  in  this  case  identi- 
fj’ing  a few  common  examples  of  plants ; (3)  checking  up  with  your  teacher 
on  the  tests  and  doing  over  the  parts  you  missed;  and  (4)  making  an  outline 
of  the  unit  for  your  w’orkbook. 

Test  on  Fundamental  Concepts 

In  a vertical  column  under  the  heading  CORRECT  write  numbers  of  all  statements  you 
believe  are  true.  In  another  column  under  INCORRECT  write  numbers  of  untrue  statements. 
Your  grade  = right  answers  X 2. 

I.  Living  things  are  classified  (1)  into  groups,  the  members  of  which 
are  like  one  another ; (2)  into  species,  genus,  order,  class,  and  phylum ; 
(3)  because  they  are  then  more  convenient  to  study , (4)  by  placing 
them  in  groups  which  have  certain  characters  in  common  ; (5)  as  species 
when  they  produce  others  like  themselves  and  their  offspring  also  pro- 
duce others  like  their  ancestors. 

II.  Bacteria  (6)  are  small  colorless  animals ; (7)  are  found  in  all 
decaying  things  ; (8)  reproduce  rapidly  by  fission  ; (9)  may  form  spores 
and  thus  live  under  unfavorable  conditions;  (10)  are  often  parasites. 


214 


THE  PLANT  WORLD 


III.  Useful  bacteria  (11)  cause  decay  of  dead  organic  matter; 
(12)  give  flavors  to  foods;  (13)  cause  diseases;  (14)  take  nitrogen  from 
the  air ; (15)  make  fertilizers. 

IV.  Bacteria  (16)  are  killed  by  sterilization;  (17)  in  milk  cause  it 
to  sour  ; (18)  fix  the  nitrogen  in  the  air  ; (19)  will  grow  readily  in  hot, 
dry  places,  provided  they  have  food ; (20)  may  be  killed  by  exposure 
to  sunlight. 

V.  Fungi  (21),  such  as  wheat  rust,  are  responsible  for  great  losses  to 
crops  each  year  ; (22)  are  able  to  make  their  own  food  ; (23)  like  molds, 
give  flavor  to  cheese ; (24)  are  more  useful  than  harmful ; (25)  may  be 
used  as  foods. 

VI.  Yeast  plants  (26)  are  a kind  of  fungi ; (27)  cause  fermentation  by 
means  of  their  growth  in  fluids ; (28)  cause  bread  to  rise  because  they 
give  off  carbon  dioxide  gas  in  their  growth ; (29)  produce  carbon 
dioxide  and  alcohol  in  food  substances ; (30)  reproduce  by  a process 
called  budding. 

VII.  Algae  (31)  are  chlorophyll-bearing  plants ; (32)  cannot  make  car- 
bohydrate food;  (33)  have  thread-like  roots;  (34)  may  reproduce  by 
division  of  cells;  (35)  are  one  source  of  contamination  of  our  drinking 
water. 

VIII.  The  main  groups  of  the  plant  kingdom  are  (36)  the  angio- 
sperms,  dicotyledons,  and  algae ; (37)  algae  and  fungi ; (38)  the 
mosses,  lilies,  palms,  and  trees ; (39)  the  thallophytes,  bryophytes, 
pteridophytes,  and  spermatophytes ; (40)  phyla. 

IX.  Alternation  of  generations  (41)  occurs  when  a plant  gives  rise  to 
other  plants  just  like  itself ; (42)  is  best  seen  in  the  algae;  (43)  in  a 
plant  takes  place  in  two  stages,  one  producing  sexual  cells,  the  other 
asexual  spores ; (44)  occur  in  the  moss  and  fern,  when  the  life  history 
shows  an  alternating  of  the  part  of  the  plant  bearing  asexual  spores 
with  that  part  which  bears  sexual  cells ; (45)  occur  in  flowering 
plants,  when  the  pollen  grain  and  ovules  represent  the  sexual  genera- 
tion, while  the  seed  and  the  plant  that  grows  from  it  is  the  asexual 
generation. 

X.  Spermatophytes  (46)  are  seed-producing  plants ; (47)  are  flower- 
ing plants  only ; (48)  include  both  gymnosperms  and  angiosperms ; 
(49)  grow  by  means  of  asexual  spores ; (50)  include  all  of  our  common 
flowers,  shrubs,  and  trees. 


TIOS'FS 


215 


ArillKVKMlOXT  'Fest 

1.  Flow  would  you  fi:row  hactxu-ia  ? 

2.  What  is  tho  favorite  food  of  haetoria? 

3.  What  are  the  faetors  iieeessary  for  haeteria  to  grow? 

4.  Ill  what  ways  are  bacteria  useful  to  the  farmer? 

5.  \\'hat  are  at  least  five  parasitic  fungi  that  do  harm? 

().  Flow  woulil  3'’ou  prevent  mold  growth? 

7.  How  can  ,vou  explain  the  process  of  making  bread? 

8.  What  examples  of  all  the  four  large  groups  of  plants  have  you 
found  in  3'our  environment? 

9.  ^^’here  would  .vou  find  the  following  plants : red  algae,  pleuro- 
coccus,  yeast,  puffballs,  pigeon- wheat  moss,  Christmas  fern? 

10.  How  many  flowers  of  the  families  of  flowering  plants  mentioned 
in  this  unit  have  you  been  able  to  identify? 


Practical  Problems 

1.  Make  a table  showing  all  the  ways  in  which  bacteria  affect  your 
daily  life  for  good  or  ill. 

2.  Make  similar  tables  for  both  molds  and  yeasts. 

3.  iMake  a collection  of  your  local  flowering  plants  and  classify 
them  according  to  some  simple  key. 

4.  Identify  all  the  harmful  plants  in  your  locality.  To  do  this  get 
the  use  of  a good  manual  on  weeds  or  one  of  the  state  publications  on 
weeds.  The  manual  published  by  the  University  of  Iowa  is  one  of  the 
best. 


Useful  References 

Broadhurst,  Home  and  Community  Hygiene.  Lippincott,  1925. 
Conn,  Bacteria,  Yeasts  and  Molds  of  the  Hom,e.  Ginn,  1917. 
Downing,  Our  Living  World.  Longmans,  Green,  1924. 

Marshall,  N.  L.,  The  Mushroom  Book.  Doubleday,  Page,  1904. 
Mathews,  Field  Book  of  American  Wild  Flowers.  Putnam,  1929. 


SURVEY  QUESTIONS 


Can  you  distinguish  between  invertebrate  and  vertebrate  animals? 
How  many  kinds  of  insects  can  you  recognize?  How  many  mollusks 
live  in  your  locality  ? How  many  kinds  of  fishes,  reptiles,  and  birds  can 
you  identify  ? How  many  mammals  can  you  identify  ? What  is  a fossil  ? 


UNIT  VIII 

HOW  DO  WE  CLASSIFY  ANIMALS? 

Preview.  In  the  classification  of  animals,  as  well  as  of  plants, 
there  is  one  underlying  principle  which  is  used  to  show  relationships. 
Living  things  which  have  similar  structures  or  organs  in  similar 
parts  of  their  bodies  are  almost  certainly  related  to  each  other. 
Where  structures  are  similar  and  are  found  in  corresponding 
positions,  they  are  said  to  be  homologous.  For  example,  the  wing 
of  a bat,  the  wing  of  a bird,  the  foreflipper  of  a dolphin,  the  fore- 
leg of  a dog,  and  the  arm  of  a man  are  homologous  structures  and 
show  that  these  animals  are,  in  a way,  related  to  one  another.  On 

216 


ONE-CELLKD  ANIMALS 


217 


the  other  hand,  we  often  find  that  organs  whicli  do  not  have  the 
same  structure  or  origin  are  used  for  similar  purposes.  Such  are 
the  wings  of  a bird  and  the  wings  of  a butterfly.  Such  structures 
are  analogous.  Analog}'  is  likeness  \n  function,  regardless  of  origin. 

In  our  study  of  biology  so  far  we  have  attempted  to  get  some 
notion  of  the  various  factors  which  act  upon  and  interact  with 
living  things.  We  have  examined  a number  of  forms  of  plants 
and  have  found  all  grades  of  complexity  from  the  one-cclled  plant, 
Pleurococcus,  to  the  complicated  flowering  plants  of  considerable 
size  and  with  many  organs.  So  in  animal  life  the  forms  we  study 
will  show  a constant  change,  and  the  change  is  toward  greater 
complexity  of  structure  and  of  function.  A worm  is  simpler  in 
structure  than  an  insect,  and  shows  by  its  sluggish  actions  that 
it  is  not  so  high  in  the  scale  of  life  as  its  more  lively  neighbor. 

We  are  probably  aware  of  the  fact  that  we  are  better  equipped 
for  the  battle  for  life  than  lower  animals,  for  we  are  thinking 
creatures  and  can  change  our  surroundings  if  they  are  unfavorable, 
while  the  lower  forms  of  animals  are  largely  controlled  by  stimuli 
which  come  from  without,  such  as  temperature,  moisture,  light, 
and  the  presence  or  absence  of  food. 

There  are  a great  many  ways  of  arranging  animals  in  groups. 
One  way  is  to  put  all  animals  that  have  no  backbones  into  a large 
group  called  the  invertebrates  as  opposed  to  those  which  have  a ver- 
tebral column,  the  vertebrates. 


PROBLEM  I.  WHAT  ARE  THE  CHARACTERISTICS  OF  ONE- 
CELLED  ANIMALS? 

Habitat  of  Protozoa.  Protozoa,  or  one-celled  animals,  are  found 
in  water,  seemingly  never  at  any  great  depth.  They  appear  to 
be  attracted  to  the  surface  by  light  and  by  the  supply  of  oxygen. 
Every  fresh-water  lake  swarms  with  them ; the  ocean  contains 
countless  myriads  of  many  different  forms. 

Demonstration  1.  To  show  a living  amoeba.  To  obtain  amoebas, 
crush  sortie  water  plants  and  let  the  mass  remain  undisturbed  for  a week 
or  so.  Living  animals  will  usually  be  found  in  the  scum  that  forms. 
Mount  a bit  of  the  scum  and  observe  it  under  a compound  microscope. 
Describe  the  amoeba  as  to  shape  and  size. 


218 


HOW  DO  WE  CLASSIFY  ANIMALS? 


Amoeba.  The  simplest  of  all  animals  is  the  amoeba,  a tiny  cell, 
which  changes  its  shape  as  it  moves  about  in  the  water.  It  has 
no  organs  of  locomotion,  nor  of  sensation,  yet  it  is  aware  of  the 
nearness  of  food.  It  has  no  mouth,  but  takes  in  food  at  any  point 
in  its  body.  It  is  able  to  change  this  food  into  living  matter, 

for  it  grows,  and 
when  it  reaches  a 
certain  size,  divides 
to  form  two  amoebas. 

Several  theories 
have  been  advanced 
to  account  for  its 
locomotion ; such  as 
the  flowing  of  the 
protoplasm,  a rolling 
motion  of  the  cell, 
and  most  recently 
the  belief  that  the 
amoeba  moves  by  a 
series  of  body  con- 
tractions. 

Although  but  a 
single  cell,  the 
amoeba  appears  to 
be  aware  of  the  ex- 
istence of  food  when 
it  is  near  at  hand. 
Food  may  be  taken 
into  the  body  at  any  point,  the  semifluid  protoplasm  surrounds 
and  takes  in  the  bit  of  food,  with  a little  water.  Thus  a food 
vacuole  is  formed.  Digestion  takes  place  in  the  vacuole  by  means 
of  enzymes.  As  the  food  vacuole  is  circulated  by  the  constant 
streaming  of  the  protoplasm  within  the  cell,  the  digested  nutrients 
pass,  by  osmosis,  from  the  vacuole  into  the  protoplasm.  Parts  of 
the  food  material  that  cannot  be  used,  such  as  the  shells  or  outer 
coverings  of  tiny  plants,  are  passed  out  of  the  food  vacuole.  Waste 
products,  other  than  carbon  dioxide,  resulting  from  oxidation  col- 


state  the  use  of  each  part  that  is  labeled. 


T1I1<]  PARAMKClUM 


219 


loct  in  the  contractile  vacuole,  which  will  burst  and  expel  them. 
The  cell  absorbs  oxyj>:en  from  the  air  in  the  water  by  diffusion, 
and  passes  out  carbon  dioxide.  Thus  respiration  takes  place 
throu»:h  eveiy  part  of  the  outer  covering  of  the  cell. 

The  amoeba  reproduces  by  splitting  into  two  cells,  each  of  which 
resembles  the  parent  cell,  except  that  it  is  of  smaller  size.  When 
these  new  cells  become  the  size  of  the  parent  amoeba,  they  each 
divide,  ddiis  is  a kind  of  asexual  reproduction.  When  conditions 
unfavorable  for  life  come,  the  amoeba,  like  some  one-celled  plants, 
encysts  itself  within  a membranous  wall,  forming  a sporelike 
structure.  Upon  return  of  favorable  conditions,  the  cover  dis- 
appears and  life  begins  again,  as  before. 

Laboratory  Exercise.  To  learn  something  of  the  activities  of  a one- 
celled  animal,  Paramecium.  Use  material  taken  from  the  surface  of 
a hay  infusion  made  by  placing  a little  hay  in  a beaker  of  water  and 
letting  the  material  stand  for  several  weeks.  Place  a drop  of  the  infu- 
sion on  a slide,  cover  with  a cover  glass,  and  mount  it  under  a com- 
pound microscoiie. 

Do  the  moving  structures  appear  to  have  any  definite  shapes?  Do 
they  move  with  any  definite  end  forward?  Do  they  collect  in  any 
localit}'?  If  so,  what  influences  them  to  do  this? 

Heat  a needle  and  introduce  it  at  one  side  of  the  cover  glass.  Is 
there  any  movement  on  the  part  of  a Paramecium? 

Notice  some  of  the  animals  grouped  around  small  masses.  Why  do 
you  suppose  they  are  there?  Notice  other  animals  with  reference  to 
the  position  of  air  bubbles  or  to  threads  of  Spirogyra  to  which  they  are 
attached.  How  do  they  lie  with  reference  to  the  air  bubble?  What 
might  the  animal  get  from  the  air  bubble,  if  it  is  to  do  work?  How 
would  a cell  covered  with  a membrane  take  anything  from  an  air 
bubble?  What  might  it  give  in  exchange? 

Drop  a little  fountain-pen  ink  on  a slide  containing  Paramecia. 
Note  the  long  structures  (trichocysts)  thrown  out  by  the  animal. 

Write  a paragraph  explaining  how  a Paramecium  reacts  to  the  stim- 
uli in  its  environment.  Make  drawings  to  illustrate  your  conclusion. 

The  Paramecium.  This  one-celled  animal  is  elliptical  in  outline, 
but  somewhat  flattened.  The  rounded  (anterior)  end  of  the 
body  usually  goes  first.  As  the  Paramecium  pushes  its  way 
between  dense  substances  in  the  water,  the  cell  body  is  seen  to 
change  its  shape  as  it  squeezes  through. 

The  cell  body  is  almost  transparent,  and  consists  of  semi- 
fluid protoplasm  bounded  by  a very  delicate  membrane,  the  pellicle, 


220 


HOW  DO  WE  CLASSIFY  ANIMALS? 


.cilia 


.■raicronucleus 
rnacrorjux^leus 
-orctl  ^n>£7ve 


through  which  project  numerous  delicate  threads  of  protoplasm 
called  cilia  (sil'i-d).  These  threads  by  striking  the  water  more 
strongly  in  one  direction  cause  movement  of  the  cell.  The  cilia  can 
reverse  their  beat  so  that  the  animal  can  back  up  if  it  strikes  an 

obstacle.  Because  the  cilia  strike 
the  water  in  a diagonal  direction  and 
because  of  the  shape  of  the  body,  the 
Paramecium  takes  a spiral  course 
through  the  water. 

Imbedded  in  a dense  but  clear  area 
just  under  the  pellicle  are  numerous 
defensive  structures  called  trichocysts 
(trik'o-sists).  These  may  be  thrown 
out  under  certain  conditions  and  are 
believed  in  some  forms  to  contain 
poison  which  paralyzes  their  prey  or 
protects  them  from  enemies. 

The  locomotion  of  the  Paramecium 
is  caused  by  the  movement  of  the 
cilia.  The  current  of  water  caused 
by  the  cilia  carries  tiny  particles  of 
food  into  the  oral  groove  on  one  side 
of  the  cell  and  into  a funnel-like 
opening,  the  gullet.  Inside  the  gul- 
let the  cilia  are  grown  together  so 
that  they  form  a platelike  structure 
called  the  undulating  membrane.  By 
means  of  this  structure  the  particles  of  food  are  forced  to  enter  the 
cell  body.  Once  within  the  cell  body,  the  particles  of  food  mate- 
rials are  gathered  within  a small  area  called  a food  vacuole.  A 
food  vacuole  is  a tiny  space  filled  with  fluid  containing  food  par- 
ticles. These  vacuoles  circulate  on  a regular  course  around  the 
cell,  the  food  being  gradually  digested  and  the  contents  of  the 
vacuole  thus  distributed  to  all  parts  of  the  cell.  One  or  two  larger 
contractile  vacuoles  may  be  found ; their  purpose  seems  to  be  to 
pass  off  liquid  waste  material  from  the  cell  body.  This  is  done  by 
the  pulsation  of  the  vacuole,  which  ultimately  bursts,  passing  the 


-gullcJb 

-|ooct  vacuole^ 


Contrctcit/ile/ 

vacuole^ 


The  Paramecium.  Which  end  goes 
first  ? Where  is  the  mouth  ? How  does 
food  get  inside  the  cell?  How  is  it 
circulated  ? 


TIIK  PARAMECIUM 


221 


fluid  waste  to  the  outside.  The  cell  inenibrane  breaks  at  regular 


intervals  to  discliar<>:e  solid  food  waste, 
breaks  at  nearly  the  same  place  each 
time,  the  opening  is  called  the  anal 
spot.  Just  as  in  all  other  living  things 
food  must  become  part  of  the  living 
matter  before  it  is  of  use  to  the  cell 
and  before  energy  can  be  released, 
oxygen  must  unite  with  the  food. 
Oxygen  passes  into  the  cell  through 
the  cell  membrane;  thus  respiration 
takes  place.  In  a cell  that  has  been 
stained,  the  nucleus  is  seen  to  be  a 
double  structure,  consisting  of  one 
large  and  one  small  portion,  called 
respectively  the  macronuclens  and  the 
micronucleus. 

Sometimes  a Paramecium  may  be 
found  in  the  act  of  dividing  by  the 
process  known  as  fission.  In  this 
process  both  the  micronucleus  and 
the  macronucleus 


Since  the  cell  membrane 


nxxcleus 


■where 
T?recxlc 
occunff 


Cell  division  in  Paramecium.  What 
is  the  process  called?  Describe  ex- 
actly what  happens. 


Conjugation  in  Parame- 
cium. Explain  how  this 
takes  place. 


elongate  and  sep- 
arate into  two 
parts  formingtwo 
micronuclei  and  two  macronuclei.  The  cell  elon- 
gates, a second  gullet  appears,  and  the  cell  breaks 
into  two  parts,  each  half  provided  with  nuclei 
and  a gullet.  This  is  asexual  reproduction. 

Frequently  another  type  of  reproduction 
may  be  observed.  This  is  called  conjugation, 
and  resembles  conjugation  in  the  simple  plants. 
Two  cells  of  equal  size  attach  themselves 
together  as  shown  in  the  diagram.  The  cell 
membranes  dissolve  at  the  point  of  con- 
tact. Complicated  changes  take  place  in  the 
nuclei  of  the  two  cells.  Finally  fragments  of  the 


222 


HOW  DO  WE  CLASSIFY  ANIMALS? 


material  forming  the  micronuclei  of  each  cell  pass  over  and  unite 
with  material  forming  the  nuclei  of  the  opposite  cell.  After  this 
mutual  exchange  of  nuclear  material  the  cells  separate.  It  is  be- 
lieved that  this  stage  of  reproduction,  as  in  the  plants,  is  a sexual 
stage. 

Practical  Exercise  1.  Compare  an  amoeba  and  Paramecium  as  to  size, 
shape,  method  of  locomotion,  method  of  taking  in  food,  digesting  food,  excret- 
ing waste,  and  reproducing. 

The  cell  as  a unit.  In  the  daily  life  of  a one-celled  animal  we 
find  the  single  cell  performing  all  the  vital  activities  which  we 
shall  later  find  that  the  many-celled  animal  is  able  to  perform. 
In  the  amoeba  no  definite  parts  of  the  cell  appear  to  be  set  off  to 
perform  certain  functions ; but  any  part  of  the  cell  can  take  in 
food,  can  absorb  oxygen,  can  change  the  food  into  protoplasm,  and 
excrete  the  waste  material.  The  single  cell  is,  in  fact,  an  organism 
able  to  carry  on  the  business  of  living  as  effectually  as  a very 
complex  animal. 

Practical  Exercise  2.  Draw  a cell  and  label  all  its  parts.  Give  the  use  of 
each  part.  How  do  cells  move  about?  What  do  we  mean  by  conjugation? 
Why  is  the  cell  called  a “unit  of  structure”?  Why  is  a cell  called  an 
organism  ? 


The  principal  classes  of  Protozoa,  examples  of  which  we  may  have  seen  or  read  about,  are  — 

Class  I.  Rhizopoda  (root-footed).  Having  no  fixed  form,  with  pseudopodia.  Either  naked 
as  Amoeba  or  building  limy  {Foraminifera)  or  glasslike  skeletons  (Rndiolaria) . 

Class  II.  Mastigoph'ora.  They  move  by  means  of  long  whiplash  threads  of  protoplasm,  called 
flagella.  Examples  are  Euglena  and  Monosiga. 

Class  III.  Infuso'ria  (in  infusions).  Usually  active  ciliated  Protozoa.  Examples,  Parame- 
cium, Vorticella. 

Class  IV.  Sporozo'a  (spore  animals).  Parasitic  and  usually  non-active.  Example,  Plas- 
modium malariae. 


FOR  I FE  HA 


223 


Self-Testing  Exercise 

Frotozoa  arc (I)  composed  of  one (2).  Examples 

are  the  amoeba,  which  (d)  by  chaiif;'inj2;  its  body  form  and 

the  Faramecinm,  which  mo\'es  by  means  of (4),  tiny  threads 

of (')).  These  oncvcelled  animals  carry  on  all  the (G) 

of  higher  animals,  including (7). 


PROBLEM  II.  WHAT  ARE  THE  CHARACTERISTICS  OF  SOME 
SIMPLER  INVERTEBRATES? 


Porifera  (Lat.  porus,  pore;  ferre,  bear)  or  sponges.  The  body 
of  a sponge  contains  many  pores  through  which  water  bearing  food 
particles  enters.  They  are  classified  according  to  the  skeletons 
they  possess  into  limy,  glasslike,  and  horny  fiber  sponges.  The 
last  named  are  the  sponges  of  commerce.  Most  sponges  live  in 
salt  water ; they  are  never  free  swimming.  There  are  about  2500 
known  species. 


Calcai'^ecc 


batli  Sponge 


POT^IFEI^A 


The  following  is  the  classification  of  Porifera : — 

Class  I.  CaZcoVea,  having  limy  spicules  in  the  body.  The  GranZia  seen  along  our  northeastern 
coast  is  an  example. 

Class  II.  Hexactinel'lida.  Sponges  having  glasslike  spicules,  arranged  on  three  axes.  Exam- 
ple, Venus’s  flower  basket. 

Class  III.  Demospon'giae.  Sponges  with  glasslike  spicules,  not  arranged  on  three  axes,  or 
with  skeleton  of  horny  fiber,  the  latter  type  represented  by  the  bath  sponge. 


The  structure  of  a sponge.  The  simplest  kind  of  sponge  is  in 
the  shape  of  an  urn,  attached  at  the  lower  end.  Cut  lengthwise, 
such  an  animal  is  seen  to  be  hollow,  its  body  wall  pierced  with 
many  tiny  pores  or  holes.  These  pores  open  into  a central  cavity, 
which  in  turn  opens  by  a large  hole,  called  the  osculum  (os'ku-lwm) 
or  mouth,  into  the  surrounding  water. 


224 


HOW  DO  WE  CLASSIFY  ANIMALS? 


A microscopic  examination  shows  the  pores  of  the  sponge  to  be 
lined  on  the  inside  with  cells  having  collars  of  living  matter  sur- 
rounding a single  long  cilium  called 
flagellum  (fla-jel'um).  The  flagella, 
lashing  in  one  direction,  set  up  a cur- 
rent of  water,  bearing  food  particles, 
toward  the  large  inner  cavity  where 
they  are  digested.  The  digested  food 
then  passes  by  osmosis  to  the  other 
cells  of  the  body.  From  some  of  the 
cells  in  the  jelly-like  middle  layer  of 
the  body  lime  is  secreted  to  form  the 
spicules,  and  the  reproductive  cells, 
eggs,  and  sperms  occur.  The  spicules 
form  the  skeleton  of  the  sponge. 

Practical  Exercise  3.  Make  a diagram  of  a simple  sponge  showing  how  food 
is  taken  in  and  waste  given  out  from  the  body.  How  does  a sponge  breathe? 

Coelenterates.  The  Coe- 
lenterates  are  a large  group 
of  animals,  practically  all  of 
which  are  found  in  salt 
water.  They  include  the 
beautiful  sea  anemones, 
jellyfish,  and  corals. 

The  Hydra.  This  little 
creature  is  shaped  like  a 
hollow  cylinder  with  a circle 
of  arms  or  tentacles  at  the 
free  end.  It  is  found  at- 
tached to  dead  leaves,  sticks, 
stones,  or  water  weeds  in 
fresh-water  ponds.  When 
disturbed,  it  contracts  into 
a tiny  whitish  ball,  a little 
larger  than  the  head  of  a 
pin.  The  outer  layer  of  the 


Longitudinal  section  of  Hydra.  How  does  food 
get  into  the  body  ? How  many  layers  of  cells  are 
found  here  ? 


Longitudinal  section  of  a simple 
sponge.  How  does  this  animal  get 
its  food  ? 


COELENTERATA 


225 


animal  serv'cs  for  protection  as  well  as  movement  and  sensation, 
certain  cells  being  fitted  for  each  of  those  different  purposes. 

'Fhe  tentacles  are  provided  with  thousands  of  minute  darts  or 
stinging  cells,  by  means  of  which  prey  is  killed.  The  tentacles 
then  reach  out  like  arms,  grasp  the  food,  bend  over  with  it,  and 
pull  it  toward  the  mouth.  Certain  cells  lining  the  hollow  digestive 
cavity  pour  out  a fluid 
which  digests  the  food. 

Other  cells  with  long 
cilia  circulate  the  food, 
while  still  other  cells 
lining  the  cavity  put 
out  pseudopodia,  which 
surround  and  take  in 
the  food  particles. 

The  outer  layer  of  the 
animal  does  not  digest 
the  food,  but  receives 
some  of  it  already  di- 
gested from  the  inner 
layer.  Oxygen  is 
passed  through  the 
body  wall,  for  there  are 
no  special  organs  for 
respiration. 

Reproduction.  The 
Hydra  reproduces  asex- 
ually  by  budding,  as  is  seen  in  the  diagram.  The  bud  appears  on 
the  body  as  a little  knob,  the  body  cavity  extending  into  it.  After 
a short  time  (usually  a few  days)  the  young  hydra  separates  from 
the  old  one  and  begins  life  alone.  This  is  asexual  reproduction. 

The  Hydra  also  reproduces  by  sex  cells.  The  sperms  develop  in 
little  groups  near  the  free  end  of  the  animal,  and  the  egg  cells  de- 
velop near  the  base.  The  sperms,  when  ripe,  are  set  free  in  the 
water ; one  of  them  unites  with  an  egg,  which  is  usually  still  at- 
tached to  the  body  of  the  Hydra,  and  development  begins  which 
results  in  the  growth  of  a new  hydra. 


Colony  of  Obelia. 
■ A jellyfish. 


Amer.  Mus.  of  Nat.  Hist. 


Why  are  the  Obelia  and  jellyfish  classified  as  coelenter- 
ates  ? In  what  way  are  they  similar  ? In  what  ways  are 
they  unlike  each  other  ? 


226 


HOW  DO  WE  CLASSIFY  ANIMALS? 


Practical  Exercise  4.  Study  the  diagram  on  page  224  and  construct  a cross 
section  of  the  animal.  Label  all  parts  shown. 


Ai'ztho^oa: 

SQCx.  ai^rnone 


Obeli  a 


jel^fish 


Class  I.  Hydrozo'a.  Simple  animals  as  hydra,  or  colonial  in  habit  as  the  hydroids.  They 
produce  new  individuals  by  budding,  and  the  eggs  and  sperms  are  usually  produced  in  a free- 
swimming  jellyfish,  which  buds  off  from  the  original  colony.  This  is  an  example  of  alterna- 
tion of  generations.  Examples  : Hydra  and  Obe'lia. 

Class  II.  Scyphozo'a.  Marine  jellyfish,  mostly  of  large  size.  Example, 

Class  III.  Anthozo'a.  Hydralike  animals,  usually  attached,  with  many  tentacles,  disposed 
in  circlets  in  multiples  of  five.  They  may  be  single  or  colonial.  The  sea  anemones  and 
corals  are  the  best-known  examples. 

Class  IV.  Ctenophora,  or  sea  walnuts,  well  known  along  our  eastern  coast,  are  sometimes 
given  as  a separate  phylum  and  sometimes  as  a class  of  the  coelenterates. 


Jellyfish.  At  first  sight  you  would  not  say  a jellyfish  was  re- 
lated to  the  Hydra,  but  we  find  that  a part  of  the  life  of  the 
jellyfish  is  passed  as  a colony  of  hydralike  animals  which  give 
rise  to  free-swimming  jellyfish  as  the  sexual  stage  of  their  life 
history.  This  alternation  of  an  asexual  generation  with  that 
of  a sexual  generation,  which  produces  the  eggs  and  sperm 
cells,  is  seen  in  many  plants  and  is  best  shown  in  this  group  of 
animals. 

Echinoderms.i  These  are  spiny-skinned  animals  which  live  in 
salt  water.  They  show  radial  symmetry.  There  are  about  4500 
named  species. 

The  starfish.  By  far  the  most  important  enemy  of  the  oyster 
and  other  salt-water  mollusks  ^ is  the  starfish.  The  common 
starfish,  as  the  name  indicates,  is  shaped  like  a five-pointed  star. 
A skeleton  of  lime  which  is  made  up  of  thousands  of  tiny  plates 

1 Echinoderm : (e-ki'no-dffrm). 

2 Mollusk : popularly  called  shellfish.  Has  soft  body  protected  by  shell. 


EClIlNODEKMS 


227 


gives  shape  to  the  body  and  arms.  Slow  movement  is  effected 
by  means  of  tiny  suckers,  called  tube  feet.  The  mouth  is  on  the 
undersurface  of  the  animal,  and,  when  feeding,  the  stomach  is 
protruded  and  wrapped  around  its  prey.  The  body  covering  of 
the  starfish,  as  well  as  that  of  the  sea  urchin  and  others  of  this 
group,  is  spiny;  hence  the  name  echinoderm,  which  means  spiny- 
skinned,  is  given  to  the  group. 

Starfish  are  enormously  destructive  of  young  clams  and  oysters, 
as  is  shown  by  the  evidence,  collected  by  Professor  A.  D.  Mead 
of  Brown  University.  A single  starfish  was  confined  in  an 
aquarium  with  fifty-six  young  clams.  The  largest  clam  was 
about  the  length  of  one  arm  of  the  starfish,  the  smallest  about 
ten  millimeters  in  length.  In  six  days  every  clam  in  the  aquarium 
was  devoured. 

In  order  to  capture  and  kill  mollusks,  the  starfish  wraps  itself 
around  the  valves  of  the  shell  and  actually  pulls  them  apart  by 
means  of  its  tube  feet,  some  of  which  are  attached  to  one  valve 
and  some  to  the  other  of  its  victim.  The  mollusk  can  withstand 


A3t€roid:ea_ 


OphiuroicCea 


Eihinoidea--'  'Holot'huroidea  ^Crinoidea 


sea  urcht 


Sea  Sea.  featlier 


Class  I.  Asteroi'dea,  or  starfishes. 

Class  II.  Ophiuroi'dea,  the  brittle  stars  or  snake  stars. 

Class  III.  Echinoi'dea,  or  sea  urchins. 

Cl.\ss  IV.  Holothuroi'dea.  including  the  sea  cucumbers. 

Class  V.  Crinoi'dea,  or  stonelike,  deep-sea  forms,  now  almost  extinct ; sea  lilies  and  sea 
feathers. 


a strong  pull,  but  not  a long  one,  and  so  it  eventually  gives 
way.  Once  the  soft  part  of  the  mollusk  is  exposed,  the  stomach 


228 


HOW  DO  WE  CLASSIFY  ANIMALS? 


of  the  starfish  envelops  it  and  covers  it  with  the  secretions  of  di- 
gestive glands,  and  it  is  rapidly  digested  and  changed  to  a fluid. 

Hundreds  of  thousands  of  dollars’  damage  is  done  annually  to 
the  oysters  in  Connecticut  alone  by  the  ravages  of  starfish. 


Practical  Exercise  6.  What  echinoderms,  if  any,  exist  in  your  community  ? 
What  would  you  consider  the  chief  characteristics  of  the  echinoderms  ? 


Platyhelminthes  (Gr.  platys,  flat;  hehninthos,  worm),  or  flat- 
worms.  These  are  usually  small,  ribbon-  or  leaf-like,  and  flat. 
They  live  in  water.  Most  flatworms  are  parasitic.  The  most 
commonly  known  ones  are  the  tapeworm  and  the  liver  fluke. 
There  are  about  5000  known  species. 


PLATYHELMINTHK 


Turbellaria-/  IrematocCa  N— Cestocta 


•non  .parasitic  , 


taps 


Nemathelminthes  (Gr.  nematos,  a thread),  or  roundworms. 
These  three-layered,  elongated  threadlike  animals  are  often  par- 
asitic. Vinegar  eels,  the  horsehair  worm,  the  pork  worm  or  trichina, 
and  the  dread  hookworm  are  examples.  About  15,000  species  are 
known.  Examples  of  these  worms  will  be  discussed  later  in  the  unit 
“How  Does  Man  Control  His  Environment  for  Health? ” 


awrow*  tiornv 


THE  EAKTHWORM 


229 


Annulata  (Lat.  annulus,  a riiis)-  segmented  worms  are 

long,  jointed  creatures  composed  of  body  rings  or  segments.  The 
digestive  tract  is  a tube  within  a tubelike  body.  They  have  no 
jointed  appeiulages.  There  are  about  4000  known  species. 


[ ANNULATA  || 

Chaetopoctg _ ^ HiriicCinea 


Class  I.  Chaetop'oda.  Many  bristles  along  the  sides  of  the  body.  Examples  are  the  earth- 
worm or  sandworni. 

Class  II.  Hirudin'ea.  Without  bristles  and  having  suckers  at  both  ends  of  the  body.  Ex- 
amples are  the  leeches  or  bloodsuckers. 


Laboratory  Exercise.  Study  of  a living  earthworm.  Put  several 
earthworms  in  shallow  tin  trays  with  moist  blotting  paper  in  bot- 
tom. Have  paper  wet  at  one  end  of  tray  and  dry  at  the  other.  At 
which  end  of  the  tra}^  do  the  worms  gather?  Wet  the  paper  uni- 
forml}^  and  then  cover  one  half  of  the  tray  with  an  opaque  object. 
What  happens  to  the  worms?  How  do  earthworms  react  to  light 
and  presence  of  moisture? 

Count  the  number  of  rings  (segments)  in  your  worm  and  compare 
with  the  estimates  of  others  in  the  class.  What  conclusions  do  you 
draw  ? 

Watch  a worm  move.  Describe  exactly  what  happens. 

Notice  the  little  swelling  located  about  the  thirty-first  segment 
from  the  anterior  tip.  This  is  the  ditellum  and  forms  a bag  in 
which  the  eggs  are  placed  when  laid.  Rub  the  upper  and  lower  sur- 
face of  the  worms  with  your  fingers.  Any  differences?  Account  for 
this. 

Find  the  mouth  and  posterior  opening  of  the  food  tube.  Can  you 
find  any  other  structures  or  openings? 

Make  a diagram  of  the  first  forty  and  the  last  five  segments  of  the 
earthworm. 

The  earthworm.  The  common  earthworm  is  familiar  to  most 
of  us.  It  has  an  elongated  body  made  up  of  segments  or  rings.  It 
is  sensitive  to  food,  to  odors,  to  heat,  to  light,  and  to  other 
stimuli.  Four  rows  of  tiny,  movable  bristles  called  setae  are 
found  on  all  the  segments  except  the  first  three  and  the  last. 
Locomotion  is  accomplished  by  the  thrusting  forward  of  the 

H.  BIO — 16 


230 


HOW  DO  WE  CLASSIFY  ANIMALS? 


-upper  lip 

^brain 

^pharyi7x 

--nerve  const 


.laectrt/ 

-testis- 


anterior  end  ; the  setae  there  are  anchored,  then  a wave  of  muscular 
contraction  passes  down  the  body,  shortening  the  body  by  drawing 
up  the  posterior  end. 

How  the  earthworm  digs  holes.  The  earthworm  is  not  provided 
with  hard  jaws  or  teeth.  Behind  the  mouth  opening  is  a part  of 
the  food  tube  called  the  pharynx.  It  acts  as  a suction  pump  and 

draws  particles  of  the  soil  into 
the  food  tube.  Organic  matter 
in  the  soil  is  used  as  food  and 
the  unused  soil  is  passed  out 
of  the  body  and  deposited  on 
the  surface  of  the  ground,  in 
the  form  of  little  piles  called 
worm  casts.  Charles  Darwin 
calculated  that  fifty-three 
thousand  worms  may  be  found 
in  an  acre  of  ground  and  that 
ten  to  fourteen  tons  of  soil 
might  pass  through  their  bodies 
in  a single  year. 

Life  processes  of  the  earth- 
worm. The  digestive  tract  of 
the  earthworm  is  an  almost 
straight  tube  inside  of  another 
tube.  The  latter  is  divided 
by  partitions  which  mark  the 
boundary  of  each  segment. 
The  outer  cavity  is  known  as 
the  body  cavity,  and  the  inner 
cavity  as  the  digestive  tube. 
Food  is  digested  within  the 
food  tube,  passed  through  the  walls  of  this  tube  by  means  of 
osmosis,  and  is  absorbed  by  the  blood  which  carries  it  to  various 
parts  of  the  body.  The  earthworm  has  no  gills  or  lungs.  The 
moist  skin  acts  as  an  organ  of  respiration,  taking  in  oxygen  and 
giving  off  carbon  dioxide.  The  nervous  system  is  on  the  ventral 
side  of  the  body  but  forms  a ring  around  the  food  tube  in  the 


.ovctr^ 


crop 


dorsal  avXeiy 


J — intestine. 


A longitudinal  section  through  an  earthworm. 
In  what  segments  are  the  hearts,  the  crop,  the 
gizzard,  the  brain,  the  reproductive  organs  ? 


HKI’KODUCTION 


281 


anterior  end  of  tlie  body  with  a tiny  brain  just  above  the  pharynx 
in  the  third  anterior  body  segment. 

Reproduction.  The  earthworm  has  both  male  and  female  sex 
cells  present  in  its  body  and  hence  is  said  to  be  hermaphroditic 
(her-maf'rb-dit'ik).  In  order  to  have  the  eggs  fertilized  when 
they  are  laid  a mutual  exchange  of  sperm  cells  takes  place  between 
two  worms,  the  sperms  being  placed  in  four  little  sacs  on  the  under 


4 

become 

inatxrre. 


side  of  each  worm. 

Later  a swollen 
area  called  the  cli- 
tellum  (about  one 
third  the  distance 
from  the  anterior 
end)  forms  a girdle 
which,  as  it  passes 
toward  the  anterior 
end  of  the  earth- 
worm, receives 
from  body  open- 
ings the  eggs,  the 
sperms  received 
from  the  other 
earthworm,  and  a 
nutritive  fluid  in 
which  the  eggs  live. 

• 1 A secretion,  given  off  by  the  clitellum  of  the  earthworm,  hardens, 

The  fertilized  eggs  forming  a cocoon  or  girdle  which  surrounds  the  body.  What  is 
xu  1 rx  X the  use  of  this  girdle  ? 

are  then  left  to 

hatch.  The  bags  or  cocoons,  formed  from  the  cast-off  girdle,  may 
be  found  in  manure  heaps  or  under  stones,  in  May  or  June. 


.sperms’ 

food,  ^ 

/"Smhryos 
:^Tn. 

Sn  the 

Capsule 


Practical  Exercise  6.  What  worms  are  found  in  your  locality?  Are  there 
any  useful  ones?  Any  harmful  ones?  What  is  the  difference  between  a 
worm  and  a caterpillar? 


Self-Testing  Exercise 

Check  the  true  statements  in  your  workbook. 

T.  F.  1,  Invertebrates  have  a backbone  and  an  internal  skeleton. 
T.  F.  2.  Protozoa  are  single-celled  animals. 

T,  F.  3.  Sponges  live  only  in  the  ocean. 


232 


HOW  DO  WE  CLASSIFY  ANIMALS? 


T.  F.  4.  Examples  of  coelenterates  are  sea  anemones  and  starfish. 

T.  F.  5.  The  Platyhelminthes  are  the  roundworms. 

T.  F.  6.  An  example  of  an  annulata  is  an  earthworm. 

T.  F.  7.  The  earthworm  has  a digestive  tract  inside  the  body  cavity. 
T.  F.  8.  Starfish  are  echinoderms. 

T.  F.  9.  The  Nemathelminthes  are  the  roundworms. 


PROBLEM  III.  WHAT  ARE  THE  CHARACTERISTICS  OF  THE 
ARTHROPODS? 

Arthropoda  (Gr.  arthros,  joint;  pous,  foot).  All  animals  which 
are  jointed,  have  limy  or  chitinous  ' exoskeletons,  and  jointed 
appendages  belong  to  this  phylum,  Arthropoda.  They  live  in 
water,  or  on  land,  or  in  the  air.  Most  of  them  undergo  a meta- 
morphosis. There  are  about  500,000  known  species,  more  than  all 
the  rest  of  the  animal  kingdom  put  together.  These  animals  are 
similar  to  the  annelids  or  worms  in  that  their  bodies  are  composed 
of  a number  of  segments. 


Onyekophora 

peripctt'urs 


Class  I.  Onychophora.  These  are  simple  wormlike  animals.  They  live  on  land. 

Class  II.  _ Myriapoda  (thousand  legs) . They  have  long  bodies  with  many  segments  and  many 
paired  jointed  appendages.  Centipedes  and  millepedes  are  examples. 

Class  III.  Crustacea.  They  live  mostly  in  the  water  and  breathe  by  means  of  gills.  The 
head  and  thorax  are  fused  into  a hard  covering.  They  have  a “ crusty  ” exoskeleton,  strength- 
ened with  lime.  Examples : crabs  and  lobsters.  . . j 

Class  IV.  Insecta.  The  largest  of  all  classes  of  animals  (over  450,000  species).  Body 
segmented ; three  regions ; head,  thorax,  and  abdomen.  Three  pairs  of  jointed  legs. 
Usually  compound  eyes.  Breathe  through  tracheae  or  air  tubes. 

Class  V.  Arachnida  (a-rak'ni-da).  This  group  has  no  antennae,  four  pairs  of  legs,  and  a pair 
of  claw-like  appendages  on  each  side  of  the  mouth.  Head  and  thorax  cornbined  as  in 
Crustacea.  The  spiders,  “daddy-long-legs,”  scorpions,  mites,  and  ticks  are  in  this  class. 


THE  CRAYFlSIf 


233 


The  crayfish.  Those  animals  liaviiifi;  a limy  exoskeleton,  living 
in  the  water,  anil  breathing  by  means  of  gills  are  called  crustaceans. 
riie  crayfish  is  one  of  the  best  known  representatives  of  the 
crustaceans.  The  bodj'  is  covered  with  a hard  skeleton,  called 
e.voskelcton,  composed  largely  of  lime.  This  forms  an  unjointed, 
shieldlike  structure,  the  carapace,  over 
the  anterior  part  of  the  body,  the  ab- 
domen being  segmented  and  movable. 

The  coloring  of  the  shell  usually  re- 
sembles that  of  its  natural  surroundings 
and  therefore  serves  as  a protection  to 
the  animal. 

Crayfishes  dart  backwards  through  the 
water  with  great  rapidity,  or  they  move 
forward  by  crawling  on  the  bottom. 

They  have  five  pairs  of  walking  legs  at- 
tached to  the  under  side  of  the  head-thorax 
region.  These  legs  are  jointed,  and  the 
first  three  pairs  bear  pincers.  The  large 
pincher  claws  or  chelipeds  (keli-ped)  are 
used  for  food-catching  and  for  defense  as 
well  as  for  locomotion. 

Under  the  abdomen,  one  pair  on  each 
segment  except  the  last,  are  found  jointed 
appendages,  made  up  of  three  parts 
called  swimmerets.  The  last  pair,  together 
with  the  last  segment  of  the  abdomen, 
form  a powerful  tail  used  in  swimming. 

How  the  crayfish  gets  in  touch  with  its 
surroundings.  Two  pairs  of  “ feelers,’’  the  longer  pair  called  the 
antennae,  the  shorter  forked. pair,  the  antennules  (little  antennae), 
are  on  the  front  of  the  head.  The  longer  feelers  appear  to  be 
used  as  organs  of  touch  and  smell.  The  smaller  antennules  hold 
at  their  bases  little  sacs  called  balancing  organs. 

Just  above  the  antennules,  projecting  on  short,  movable  stalks, 
are  the  compound  eyes.  These  eyes  are  made  up  of  many  small 
structures  each  of  which  is  a very  simple  eye.  Such  an  eye 


State  how  the  appendages  are 
used  by  the  crayfish.  1—5  are 
appendages  found  in  the  head 
region;  6-13,  on  the  thorax; 
and  14-19  on  the  abdomen. 


234 


HOW  DO  WE  CLASSIFY  ANIMALS? 


probably  does  not  have  very  distinct  vision.  A crayfish,  however, 
easily  distinguishes  moving  objects  and  prefers  darkness  to  light, 
as  has  been  proved  by  experiment. 

Food-getting.  The  food  of  the  crayfish  is  obtained  with  the  aid 
of  the  pincer  claws  and  shoved  toward  the  mouth.  It  is  pushed 
on  by  three  pairs  of  small  appendages  called  foot  jaws  or  maxil- 
Upeds,  and  to  some  degree  by  two  smaller  paired  maxillae  just 
under  the  maxillipeds.  Ultimately  the  food  reaches  the  true 
jaws,  or  mandibles,  and,  after  being  ground  between  them,  is 
passed  down  the  gullet  into  the  stomach. 

Digestion.  Food  which  has  not  been  ground  up  previously  into 
pieces  small  enough  for  the  purpose  of  digestion  is  still  further 
masticated  by  means  of  three  strong  projections  or  teeth  called 
the  gastric  mill,  one  placed  on  the  mid-line  and  two  on  the  side 
walls  of  the  stomach. 


The  stomach  is  divided  into  two  parts.  The  entrance  to  the 
posterior  part  is  lined  with  tiny  projections  which  make  it  act 
as  a strainer  for  the  food  passing  through.  Thus  the  larger 
particles  of  food  are  kept  in  the  anterior  end  of  the  stomach. 
Opening  into  the  posterior  end  of  the  stomach  are  two  large 
digestive  glands,  whose  juices  further  prepare  the  food  for  absorp- 
tion by  the  walls  of  the  stomach  and  intestine.  Once  in  the  blood, 


THE  CRAYFISH  235 

the  fluid  food  is  circulated  through  the  body  directly  to  the  tissues 
which  need  it. 

The  gills.  The  pluiiie-like  gills  are  outside  of  the  body,  but  are 
kept  moist  by  being  well  protected  by  the  overhanging  carapace. 
The  blood  of  the  crayfish  passes  by  a series  of  veins  into  the  long 
axis  of  the  gill,  where  the  blood  vessels  divide  into  very  minute 
tubes,  the  walls  of  which  are  extremely  delicate.  Oxygen,  dis- 
solved in  the  water,  passes  into  the  blood  by  osmosis,  during  which 
process  the  blood  loses  some  carbon  dioxide. 

Circulation.  The  circulation  of  blood  takes  place  in  a system 
of  thin- walled  open  vessels  which  allow  the  blood  to  come  in  direct 
contact  with  the  tissues.  The  heart  lies  on  the  dorsal  side  of  the 
body,  inclosed  in  a delicate  bag  (see  diagram). 

Excretion  of  wastes.  On  the  basal  joint  of  the  antennae  are 
found  two  projections,  in  the  center  of  which  are  tiny  holes.  These 
are  the  openings  of  the  green  glands,  organs  which  eliminate  the 
nitrogenous  waste  from  the  blood,  corresponding  to  the  human 
kidneys. 

Practical  Exercise  7.  Study  the  diagram  on  page  234  and  make  a diagram 
of  a cross  section  through  a crayfish  in  the  region  of  the  walking  legs.  Ex- 
plain how  a crayfish  might  become  aware  of  the  presence  of  food.  How  might 
it  catch  living  prey? 

Nervous  system.  The  internal  nervous  system  of  a crayfish 
consists  of  a series  of  collections  of  nerve  cells  called  gariglia 
(gan'  gli  a),  connected  by  means  of  a nerve  cord.  Posterior  to 
the  gullet,  this  chain  of  ganglia  is  found  on  the  ventral  side  of 
the  body.  At  the  anterior  end  it  encircles  the  gullet  and  forms  a 
brain  in  the  head  region.  From  each  of  the  ganglia,  nerves  pass 
off  to  the  sense  organs  and  into  the  muscles  of  the  body.  These 
nerve  fibers  are  of  two  sorts,  those  bearing  messages  from  the 
outside  of  the  body  to  the  central  nervous  system  (these  messages 
result  in  sensations),  and  those  which  take  outgoing  messages 
from  the  central  nervous  system,  which  result  in  muscular 
movements. 

Life  history.  The  sexes  in  the  crayfish  are  distinct.  The  eggs 
as  they  pass  to  the  outside  of  the  body  of  the  female  are  fertilized 
by  the  sperm  cells.  The  eggs,  which  are  provided  with  yolk 


236 


HOW  DO  WE  CLASSIFY  ANIMALS? 


or  food  material,  are  glued  fast  to  the  swimmerets  of  the  female, 
where  they  develop.  The  young  cling  to  the  swimmerets  for 
several  weeks  after  hatching. 

North  American  lobster.  In  structure  the  lobster  is  almost 
the  counterpart  of  its  smaller  cousin,  the  crayfish.  It  is  highly 
sensitive  to  changes  in  temperature,  and  migrates  from  deep  to 
shallow  water,  or  vice  versa,  according  to  changes  in  the  tempera- 
ture of  the  water.  The  food  supply,  which  is  more  abundant 


L.  W.  Brownell 


A rock  crab.  Crabs  differ  mainly  from  crayfish  in  having  the  abdomen  much  reduced. 
Crabs  molt,  or  change  their  shells,  with  great  frequency  when  they  are  young,  but 
rarely  after  they  are  fully  grown. 

near  the  shore,  also  aids  in  determining  the  habitat  of  the  lobster. 
As  it  is  the  color  of  the  bottom  and  as  it  passes  much  of  its  time 
among  the  weed-covered  rocks,  it  is  able  to  catch  living  food, 
even  active  fishes  falling  prey  to  his  formidable  pincers.  It 
moves  around  freely  at  night,  usually  remaining  quiet  during  the 
day,  especially  when  in  shallow  water.  It  eats  some  dead  food 
and  thus  is  a scavenger,  as  is  the  crayfish. 

Several  other  relatives  of  the  crayfish  are  the  crabs  of  various 
species,  used  for  food,  on  our  eastern  and  western  coasts ; the 
shrimps  and  prawns,  thin  shelled  and  small ; the  fiddler  crab,  well 
known  to  boys  and  girls  of  the  eastern  coast,  and  the  sea-spiders. 


INSECT  AND  CRUSTACEANS 


237 


These  last-named  ones  are  deep  sea  crabs  and,  in  some  parts  of  the 
world,  grow  to  an  enormous  size. 

Insects  and  Crustaceans.  We  have  already  discussed  the 
characteristics  of  all  insects  and  the  distinguishing  features  of 
certain  orders  of 
insects  in  Unit  III. 

The  bodies  of  all 
insects  are  divided 
into  three  distinct 
regions:  head, 
thorax,  and  ab- 
domen. Insects 
have  three  pairs 
of  legs,  breathe 
through  tracheae, 
usually  have  two 
pairs  of  wings,  and 
undergo  a com- 
plete or  incom- 
plete metamor- 
phosis. They  are 
found  every^vhere 
that  life  can  exist. 

Insects  differ 

structurally  from  crustaceans  in  having  three  regions  in  the  body 
instead  of  two.  The  number  of  legs  is  always  definite  in  the  in- 
sects ; in  the  crustaceans  the  number  sometimes  varies,  but  is 
always  more  than  three  pairs.  The  exoskeleton  is  composed 
wholly  of  chitin  ^ in  the  insects,  but  it  is  sometimes  strengthened 
with  lime  in  the  crustaceans.  Both  groups  have  compound  eyes, 
but  those  of  the  Crustacea  are  stalked  and  movable.  The  other 
sense  organs  do  not  differ  greatly.  The  most  marked  differences 
are  physiological.  The  crustaceans  take  oxygen  from  the  water 
by  means  of  gills,  while  the  insects  are  air-breathers,  using  for  this 
purpose  air  tubes  called  tracheae.  Both  insects  and  crustaceans, 
because  of  their  exoskeleton,  must  molt  in  order  to  grow. 

1 Chitin  (kl'tin)  •.  a horny  substance  forming  the  outer  covering  of  insects. 


Life  history  of  a moth.  Why  is  the  moth  classified  as  an  insect  ? 
How  does  it  differ  from  a crustacean? 


238 


HOW  DO  WE  CLASSIFY  ANIMALS? 


There  are  a number  of  orders  of  insects,  but  examples  of  the 
following  orders  are  the  ones  most  commonly  found. 

Order  1.  Coleop'tera  (sheath  wings).  Hard  outer  wings,  forming 
cover  for  under  wings.  Biting  mouth  parts.  Complete  meta- 
morphosis. Examples  : all  beetles  and  fireflies,  etc. 

Order  2.  Dip'tera  (two  wings).  Insects  with  two  wings,  a few 
with  none.  Mouth  parts  fitted  for  sucking  or  piercing.  Com- 
plete metamorphosis.  Examples  : all  flies,  mosquitoes,  gnats,  etc. 
There  are  40,000  described  species  and  it  is  estimated  that  there 
are  more  than  300,000  as  yet  undescribed. 

Order  3.  Ephemer'ida.  Insects  having  complete  metamorphosis 
and  biting  mouth  parts.  They  have  long  setae  which  project 
from  the  end  of  the  abdomen.  The  adult  lives  only  a day  or  two, 
lays  eggs,  and  dies.  Examples  : the  mayflie's. 

Order  4.  Hemip' ter  a (hall  wings).  Sucking  mouth  parts.  Incomplete 
metamorphosis.  Two  pairs  of  wings  or  none.  Examples : 
chinch  bugs  and  squash  bugs. 

Order  5.  Homop'tera  (similar  wings).  Two  pairs  of  wings  alike, 
sucking  mouth  parts,  incomplete  metamorphosis.  Examples ; 
cicadas,  plant  lice,  scale  insects. 

Order  6.  Hymenop'tera  (membrane  wings).  Four  membranous 
wings.  Mouth  parts  fitted  for  biting  and  sucking.  Often  long 
ovipositor  modified  into  sting.  Complete  metamorphosis.  Ex- 
amples : bees,  ants,  and  wasps,  gall  and  ichneumon  flies. 

Order  7.  Lepidop'tera  (scale  wings).  Four  wings,  covered  with 
scales.  Mouth  parts  long  sucking  tube.  Complete  metamor- 
phosis. Examples  : Moths  and  butterflies. 

Order  8.  Neurop'tera  (veined  wings).  Four  membranous  wings 
with  many  veins.  Biting  mouth  parts.  Complete  metamor- 
phosis. Examples  : ant  lions,  dobson  flies,  etc. 

Order  9.  Odon'ata.  Complete  and  incomplete  metamorphosis. 
Biting  mouth  parts.  Adults  are  expert  flyers,  have  large  eyes, 
live  mostly  in  water.  Examples : dragon  flies  and  damsel  flies. 

Order  10.  Orthop'tera  (straight  wings).  Four  wings,  front  pair 
straight  and  leathery.  Biting  mouth  parts.  Incomplete  meta- 
morphosis. Examples : grasshoppers,  crickets,  and  cockroaches. 

Order  11.  Siphonap't,era  (tube;  wingless).  Largely  parasitic. 
Sucking  mouth  parts.  Wingless.  Complete  metamorphosis. 
Examples : fleas. 

Order  12.  Trichop'tera  (hairy  wings)  have  four  hairy  wings,  rudi- 
mentary mouth  parts,  complete  metamorphosis.  Examples  : caddis 
flies. 

Arachnids  (spiders)  and  myriapods.  The  body  of  a spider,  like 
that  of  the  crustaceans,  has  only  two  divisions,  cephalothorax 
(head  thorax)  and  abdomen.  Spiders  have  four  pairs  of  walking 
legs,  usually  four  pairs  of  simple  eyes,  and  breathe  by  means  of 


SPIDKKS  AND  MYRIAPODS 


239 


lunglike  sacs  in  the  abdomen. 

They  have  no  wings  or  com- 
pound eyes.  The  silk  with 
which  tliey  spin  their  webs  is 
secreted  by  means  of  glands  in 
a liquid  form.  On  e.xposure  to 
air  this  fluid  hardens  and  forms 
a very  tough  thread  which  is 
light  and  strong. 

We  are  all  familiar  with  the 
harmless  “ thousand  loggers  ” 
found  under  stones  and  logs.  It 
is  a representative  of  the  group 
of  animals  known  as  the  mille- 
pedes. These  animals  have  a 

rounded  body  divided  into  two  regions, 
head  and  trunk,  and  have  two  pairs  of 
legs  on  each  body  segment.  They  live 
in  damp  places  and  feed  on  decaying 
vegetable  matter.  They  are  entirely 
harmless.  The  centipedes  are  long 
flattened  animals  -with  one  pair  of  legs 
on  each  segment.  Both  the  millepedes 
and  centipedes  are  representatives  of 
the  class  Myriapoda. 

Practical  Exercise  8.  Make  four  diagrams 
to  show  the  likenesses  and  differences  between  a 
crustacean,  an  insect,  a myriapod,  and  a spider. 
Use  books  of  reference  for  information.  Use 
colors  for  different  structures,  as  yellow  for  exo- 
skeletons, blue  for  nervous  system,  red  for  blood 
vessel  or  heart,  etc. 

Practical  Exercise  9.  Name  all  the  arthro- 
pods you  have  found  living  in  your  environ- 
ment. Which  live  in  water?  On  land?  In 
both  habitats? 

Practical  Exercise  10.  Study  the  diagrams 
of  the  Arthropods.  How  many  legs  has  the  crab, 
the  centipede,  the  insect,  the  spider?  Study  a 
real  crab  and  centipede  to  see  how  they  differ 
u.  s.  Bureau  of  Entomology  from  the  insects.  From  the  above  study  can  you 
Why  is  a centipede  an  Arthropod  ? make  a working  definition  of  an  Arthropod  ? 


Is  a spider  an  insect ? Why? 


240 


HOW  DO  WE  CLASSIFY  ANIMALS? 


Self-Testing  Exercise 

Arthropods  are  animals  which  have (1) (2)  and  legs 

and  have  a hard (3) (4)  made  of  either (5), 

(6),  or  both.  There  are  four  common  (7) ; crus- 
taceans, which  live  mostly  in (8)  and  breathe  by  means  of 

(9) ; insects,  a (10)  group,  which  has  the (11) 

divided  into (12)  parts,  and  has  three (13)  of  jointed 

(14);  the  myriapods  which  have  (15)  bodies  with 

(16)  pairs  of (17) ; and  the  arachnida,  spiders,  with 

(18)  pairs  of  legs  and  no (19),  and  (20) 

pairs  of  simple  eyes.  The  spiders  spin (21)  from  silk  which  they 

(22)  by  means  of  glands. 

PROBLEM  IV.  WHAT  ARE  THE  CHARACTERISTICS  OF  THE 
MOLLUSKS? 

Most  mollusks  have  shells  composed  mostly  of  lime,  either 
bivalve  (two-valved),  as  the  oyster,  clam,  mussel,  and  scallop, 
or  univalve  (with  one  valve),  as  the  snail.  Usually  the  univalve 
shell  is  spiral  in  form.  Inside  the  shell,  which  is  formed  by  a 

delicate  structure  called 
the  mantle,  is  found  the 
soft,  unsegmented  body, 
from  whence  it  gets  the 
name  mollusk  (Latin  7nol- 
lis,  soft).  Other  mollusks, 
for  example  the  garden 
slug,  have  no  shell  what- 
ever, and  one  highly 
specialized  form,  the  squid, 
has  an  internal  shell. 

Pelecypods.  Between 
the  mantle  and  the  body 
of  the  mollusk  is  a space, 
the  mantle  cavity,  in  which 
hang  the  platelike  gills. 
By  means  of  cilia  on  the 
mantle  and  gills,  a con- 
stant current  of  water  is 


A fresh-water  mussel  (clam)  half  buried  in  the  mud. 
Explain  how  it  moves  and  how  it  gets  its  food. 


MOLLUSKS 


241 


■foot  ■moutii 
A gastropod  (snail).  Why  is  this  a mollusk? 


iTiaintained  through  the  mantle  cavity,  bearing  oxygen  to  the  gills 
and  carbon  dioxide  away  from  them.  In  most  mollusks,  this 
current  of  water  passes  into 
and  out  from  the  mantle 
cavity  through  muscular 
tubes  called  siphons. 

The  food  of  clams  or 
oysters  consists  of  tiny 
organisms  which  are  carried 
in  the  current  of  water  to 
the  mouth  of  the  animal,  this  water  current  being  maintained  in 
part  by  the  action  of  cilia  on  the  palps  or  liplike  flaps  surround- 
ing the  mouth.  A single  muscular  foot  enables  the  clam  to  move 
about  slowly. 

Gastropods.  Snails,  whelks,  slugs,  and  the  like  are  called 
gastropods  (stomach-footed)  because  the  foot  occupies  so  much 
space  that  most  of  the  organs  of  the  body,  including  the  stomach, 
are  covered  by  it. 

Cephalopods.  Another  class  of  mollusks  are  those  known  as 
cephalopods  (sef'a-l6-p6dz).  The  name  means  head-footed.  As 


Amphineura 


l^le<^podCoc 


clam. 

Cephalopo^ 


Class  I.  Pelecyp'oda  (hatchet-footed).  Shells  of  two  valves  or  parts.  Clams,  oysters,  scallops, 
mussels,  etc. 

Class  II.  Cephalop'oda  (head-footed).  Foot  partly  surrounds  head-^cf'bears  tentacles  or 
grasping  organs.  Squid,  octopus,  cuttlefish,  etc. 

Class  III.  Gastrop'oda  (belly-footed).  With  or  without  shells,  which  are  usually  of  one  piece 
and  coiled.  Snail,  whelk,  slug. 

Class  IV.  Scaphoda.  With  a tapering  tubular  shell,  with  a spadelike  foot  for  burrowing. 
Tooth  shells. 

Class  V.  Amphineura.  Simple  marine  mollusks.  Protected  by  a shell  of  eight  arched 
segments.  Chiton. 


242 


HOW  DO  WE  CLASSIFY  ANIMALS? 


the  figure  of  the  squid  shows,  the  mouth  is  surrounded  with  a 
circle  of  tentacles.  The  shell  is  internal  or  lacking. 

To  this  group  of  animals  belong  also  the  octopus,  or  devilfish ; 
the  paper  nautilus ; and  the  pearly  nautilus. 

Practical  Exercise  11.  From  a study  of  the  diagrams  and  of  the  text,  make 
up  a good  definition  of  a mollusk.  What  mollusks  are  common  in  your 
environment  ? 

Mollusca.  These  animals  are  soft-bodied  animals,  often  pro- 
vided with  a shell,  which  is  secreted  by  a part  of  the  body  called 
the  mantle.  They  usually  have  a single  muscular  foot  on  the 
ventral  side.  Over  60,000  species  are  known.  There  are  five 
classes  of  mollusks,  but  only  three  classes  are  widely  known. 

Self-Testing  Exercise 

A mollusk  is  a (1)  animal.  It  usually  has  a (2) 

which  is  (3)  by  the  mantle.  This  (4)  is  either 

(5)  as  in  the  oyster,  or  (6)  as  the  snail.  Most 

mollusks,  living  in  the  water,  take  in  water  through (7)  tubes 

called (8).  Common  examples  of  mollusks  are (9), 

(10),  and (11). 

PROBLEM  V.  WHAT  ARE  THE  CHARACTERISTICS  OF  FISHES? 

Vertebrates.  The  animals  we  have  studied  thus  far  have  had 
any  skeleton  they  may  possess  on  the  outside  of  the  body.  They 
are  called  invertebrates.  In  higher  animals,  for  example  the  fish, 
the  skeleton  is  inside  the  body.  They  are  called  vertebrates.  WTile 
the  exoskeleton  of  invertebrates  is  dead  material  secreted  by  the 
body  cells  the  endoskeleton  of  vertebrates  is  made  up  of  cartilage 
and  bone,  living  material,  capable  of  growth  and  repair.  The 
skeleton  of  all  vertebrates  has  two  main  divisions,  the  axial  skeleton, 
consisting  of  the  skull  and  vertebral  column  and  the  appendicular 
skeleton,  consisting  of  two  pairs  of  limbs  together  with  the  girdles, 
the  bones,  by  which  the  limbs  are  attached  to  the  vertebral  column. 
The  vertebral  column  and  skull  protect  the  delicate  spinal  cord 
and  brain.  The  limbs  support  the  body  and  aid  locomotion. 
Vertebrates  are  segmented  but  these  segments  have  been  highly 
modified  to  form  the  various  organs.  Vertebrate  animals  deserve 
(^ore  of  our  attention  than  other  forms  of  life  because  man  himself  is 


THE  BODY  OF  A FISH 


243 


;i  vertebnite.  'riierc  are  37,000  known  species  of  vertebrates, 
'riiese  species  are  divided  into  five  groups  or  classes:  Pisces,  or 
fishes;  Amphibia,  or  amphibians;  lieptilia,  or  reptiles;  Aves, 
or  birds  ; Mammalia,  or  mammals. 


hearL.... 

skeleton... 

intestine--! 


nerve. - 
cord 


invertebrate/ 


ver-tebirccte 


Cross  section  of  an  invertebrate  and  of  a vertebrate.  In  what  ways  are  they  similar? 

In  what  ways  do  they  differ? 

Laboratory  Exercise.  Adaptations  in  a fish.  How  is  the  body  of 
the  fish  fitted  for  life  in  the  water?  IMention  three  different  adapta- 
tions for  swimming.  Watch  the  fish  carefully  and  locate  its  organs 
of  locomotion.  How  many  single  fins  are  there?  How  many  paired 
fins  ? 

Try  to  discover  what  fins  are  used  in  forward  motion,  in  turning,  in 
moving  backward.  Is  the  body  used  in  locomotion.  How  is  each 
particular  fin  adapted  or  fitted  to  do  its  work? 

What  structures  do  you  find  on  the  surface  of  the  body?  How  are 
these  structures  placed  with  reference  to  each  other?  Feel  the  body 
of  the  fish.  What  adaptation  for  protection  exists  here?  Note  the 
color  both  above  and  below.  Remembering  that  many  of  the  enemies 
of  the  fish  are  below  him  and  some  above,  explain  how  the  animal 
receives  protection  from  its  color.  What  are  the  principal  adaptations 
for  protection  in  the  fish? 

Look  at  the  living  fish  carefully  and  observe  the  movements  of  the 
mouth.  What  is  the  relation  of  the  movement  of  the  mouth  to  that  of 
the  operculum,  the  flap  which  covers  the  gills?  Note  position  and 
color  of  the  gills.  What  gives  them  this  color?  Put  a few  grains  of 
carmine  in  the  water  in  front  of  the  mouth  of  the  fish.  Trace  the 
course  of  the  carmine.  Where  does  it  come  out?  What  gas  is  in  the 
water  ? How  does  the  fish  use  this  gas  ? How  might  this  gas  come  in 
contact  with  the  gills?  Write  a paragraph  and  illustrate  with  a 
diagram,  showing  how  a fish  breathes. 

The  body.  The  long,  spindle-shaped  body,  pointed  at  the 
anterior  end,  with  its  smooth  surface,  admirably  adapts  a fish 
for  swimming.  Mucus^  secreting  cells  in  the  skin,  and  the  position 

1 Mucus : a sticky  slippery  secretion  found  on  the  membranes  lining  various 
body  cavities,  as  the  nose  or  mouth. 


244 


HOW  DO  WE  CLASSIFY  ANIMALS? 


of  the  scales,  overlapping  in  a backward  direction,  are  other 
adaptations  for  life  in  water. 

The  paired  fins  are  called  pectoral  and  pelvic  fins  because  they 
are  attached  to  the  bones  forming  the  pectoral  and  pelvic  girdles. 
These  fins  are  homologous  to  the  forelimbs  and  hindlimbs  of 
higher  animals.  The  dorsal,  anal,  and  caudal  fins  are  not  paired. 

A fin  is  composed  of  a thin  membrane  or  skin  stiffened  by  long 
slender  spines  of  bones  or  cartilage  called  rays.  The  caudal  fin 
is  light  and  strong,  and,  as  powerful  muscles  are  attached  to  it, 
can  push  against  the  water  with  sufficient  force  to  move  the  body 
forward.  The  flattened,  muscular  body  of  the  fish,  tapering 


dons-al  fin 


Name  all  the  adaptations  you  can  find  in  the  body  of  this  fish  and  show  how  each 
is  an  adaptation. 


toward  the  caudal  fin,  is  moved  from  side  to  side  with  an  undulating 
motion  which  results  in  the  rapid  forward  movement  of  the  fish. 
The  caudal  fin  is  the  principal  fin  of  locomotion.  The  paired  fins 
are  used  for  turning  and  balancing. 

The  sense  organs.  The  eyes,  globular  in  shape,  are  on  each 
side  of  the  head.  They  are  unprotected  by  eyelids,  but  their 
tough  transparent  outer  covering  and  their  position  in  the  sides 
of  the  head  afford  some  protection.  A fish  becomes  aware  of  the 
presence  of  food  by  smelling  it  rather  than  by  seeing  it.  The 
nostrils,  small  pits  unconnected  with  the  mouth  cavity,  contain 
organs  for  smelling.  In  the  catfish,  the  barbels,  or  horns,  receive 
stimuli  of  feeling,  smell,  and  taste. 


UlLLS  OP  A PISH 


245 


Along  each  side  of  most  fishes  is  a line  of  tiny  pits,  provided  with 
sense  organs  and  connected  with  the  central  nervous  system.  This 
area,  calletl  the  lateral  line,  is  believed  to  be  sensitive  to  mechanical 
stimuli  of  certain  sorts.  Tlie  car  of  the  fish  is  under  the  skin  and 
serves  partly  as  a balancing  organ. 

Breathing.  A fish,  when  swimming  quietly  and  when  at  rest, 
seems  to  be  biting  even  if  no  food  is  present.  Investigation  shows 
us  that  under  the  broad,  flat  plate,  or  operculum  (6-pur'ku-lffm), 
on  each  side  of  the  head,  lie  two  pairs  of  long,  feathery  structures, 
gills.  The  skeleton  of  the  gill,  or  the  gill  arch,  is  composed  of 


Explain  why  a fish  in  an  aquarium  is  continually  opening  and  closing  its  mouth. 


several  pieces  of  bone  which  are  hinged  in  such  a way  as  to  give 
great  flexibility.  Covering  the  bony  framework,  and  extending 
from  it,  are  numerous  delicate  gill  filaments.  These  structures  are 
guarded  by  a series  of  tooth-like  projections,  the  gill  rakers,  which 
aid  in  straining  small  particles  of  food  from  the  water.  Each 
filament  contains  two  blood  vessels  ; one  taking  blood  to  the  gills, 
where  it  gives  up  its  supply  of  carbon  dioxide,  the  other  vessel 
taking  the  blood  with  its  load  of  oxygen  back  over  the  body.  A 
thin  membrane  separates  the  blood  in  the  filament  from  the  water 
bathing  the  gills.  An  exchange  of  gases  through  the  walls  of  the 
gill  filaments  results  in  a loss  of  carbon  dioxide  and  a gain  of  oxygen 
by  the  blood. 

H.  BIO  — 17 


246 


HOW  DO  WE  CLASSIFY  ANIMALS? 


gill 
filament, 
gill  ard]a. 


Digestive  system.  The  gullet  leads  directly  into  a baglike 
sto?nach.  There  are  no  salivary  glands  in  the  fishes.  There  is, 
however,  a large  liver,  which  appears  to  be  used  as  a digestive 

gland.  The  liver  contains 
a good  deal  of  oil  and  there- 
fore is  in  some  fishes,  as  the 
cod,  of  considerable  eco- 
nomic importance.  Many 
fishes  have  outgrowths  like 
a series  of  pockets  from  the 
intestine.  These  structures, 
called  the  pyloric  caeca  (pi- 
lor'ik  se'ka),  are  believed 
to  secrete  a digestive  fluid. 
The  intestine  ends  at  the 
vent,  or  anus,  which  is  usu- 
ally located  on  the  ventral 
side  of  the  fish,  immediately 
in  front  of  the  anal  fin. 

Swim  bladder.  An  organ 
of  unusual  significance, 
called  the  swim  bladder, 
occupies  the  region  just 
dorsal  to  the  food  tube. 
The  size  of  the  swim  bladder 
can  be  changed  by  contrac- 
tion or  expansion  of  its 
walls.  The  fish  uses  this 
organ  to  make  changes  in 
position  so  that  the  water 
displaced  will  equal  its  own 
weight.  In  some  fishes  it  is 
used  as  a lung. 

Circulation  of  the  blood.  In  fishes  the  heart  is  a muscular 
organ,  with  two  connecting  chambers : a thin- walled  auricle,  or 
receiving  chamber,  and  a thick-walled,  muscular  ventricle  from 
which  the  blood  is  forced  out.  The  blood  is  pumped  from  the 


..L.-filamenL 
|.-.arte^ 
L-giU  ardh 


Explain,  by  careful  study  of  the  diagram,  how 
the  blood  receives  oxygen  and  how  it  gets  rid  of 
carbon  dioxide  in  the  gill. 


EGCi-l^WING  HABITS  OF  BONY  FISHES 


247 


heart  to  the  wliere  it  loses  carbon  dioxide  and  receives  oxygen  ; 
it  then  passes  on  to  otiier  parts  of  the  body,  until  it  reaches  very 
tiny  tubes  called  capillaries.  From  the  capillaries  the  blood 
returns,  in  veins  of  gradually  increasing  diameter,  to  the  heart 
again.  During  its  course  around  the  body  some  of  the  blood 
passes  through  the  kidneys  and  is  there  relieved  of  its  nitrogenous 
waste.  Circulation  of  blood  in  the  fish  is  rather  slow.  Since  the 
temperature  of  the  blood  is  nearly  that  of  the  water  in  which  the 
fish  lives,  fishes  are  called  cold-blooded  animals. 

Nervous  system.  As  in  all  other  vertebrate  animals,  the 
nervous  system  of  the  fish  consists  of  the  brain  and  spifial  cord. 


Diagram  of  a fish  cut  lengthwise  to  show  the  relative  position  of  the  internal  organs.  The 
veins,  arteries,  and  all  smaller  organs  are  omitted.  Where  would  the  gills  be  with  reference 
to  the  heart?  Why?  The  swim  bladder  is  attached  to  the  food  tube.  What  is  the  value 
of  this  ? 

Nerve  cells  located  near  the  outside  of  the  body  send  messages 
to  the  brain,  where  they  are  received  as  sensations.  Cells  of  the 
central  nervous  system,  in  turn,  send  out  messages  which  result 
in  the  movement  of  muscles. 

The  egg-laying  habits  of  the  bony  fishes  (teleosteans).  The  eggs 
of  most  bony  fishes  are  laid  in  great  numbers.  The  number  varies 
from  a few  thousand  in  the  trout  to  many  hundreds  of  thousands 
in  the  shad  and  several  millions  in  the  cod.  The  time  of  spawning 
is  usually  spring  or  early  summer.  After  the  eggs  are  laid  the 
male  usually  deposits  milt,  consisting  of  millions  of  sperm  cells, 
in  the  water  just  over  the  eggs.  The  sperm  cells  move  rapidly 
through  the  water  to  the  egg  cells,  and  unite  with  them,  thus 
bringing  about  fertilization.  Some  fishes,  as  sticklebacks,  sunfish. 


248 


HOW  DO  WE  CLASSIFY  ANIMALS? 


toadfish,  etc.,  make  nests,  but  usually  the  eggs  are  left  to  develop 
by  themselves,  somietimes  attached  to  some  submerged  object,  but 
more  frequently  free  in  the  water.  Some  eggs  which  have  a tiny 
oil  drop  are  buoyed  up  to  the  surface,  where  the  heat  of  the  sun 


V.  S.  Bureau  of  Fisheries 

The  pigfish  or  hogfish  is  a bony  fish.  It  is  found  from  New  York  to  Mexico.  The  eggs  are 
laid  in  the  early  spring,  and  may  hatch  within  2 or  3 days.  A recently  hatched  larva  is  about 
1.5  millimeters  long.  A young  fish  of  several  months  is  26  or  more  millimeters  long. 

aids  development.  Both  eggs  and  developing  fish  are  exposed  to 
many  dangers,  and  are  eaten,  not  only  by  birds,  fish  of  other 
species,  and  other  water  inhabitants,  but  also  by  their  own 
relatives  and  even  parents.  Consequently  very  few  of  the  eggs 
ever  reach  maturity. 


FISIIIvS 


249 


Practical  Exercise  12.  Give  a brief  ilennition  of  a fisli  that  will  fit  all  fishes. 
rsinj>:  the  tliagrain  on  pa<>:e  217,  reeonstruet  a cross  section  passing  through 
the  heart.  Use  colors  for  the  dilTerent  organs. 

.\fter  watching  a lish  swim  make  a diagram  to  illustrate  how  a fish  moves 
forward  in  the  water. 

Fishes.  All  fishes  five  in  the  water.  They  usually  secure 
oxygen  by  means  of  gills.  They  move  by  means  of  appendages 
called  fins.  Four  of  these  fins  are  paired  and  are  homologous  to 
the  legs  and  arms  of  man.  They  all  possess  a vertebral  column. 


FISHeS 


■butterfly 

Dipnocm 


Order  1.  Elasyrtobranrh.  Fishes  which  have  a soft  skeleton  made  of  cartilage,  and  exposed 
gill  slits.  Examples : sharks,  skates,  and  rays. 

Order  2.  Ganoid.  Fishes  which  once  were  very  numerous  on  the  earth,  but  which  are  now 
almost  extinct.  They  are  protected  by  platelike  scales.  E.xamples : gars,  sturgeon,  and 
bowfin. 

Order  3.  Teleostanx,  or  Bomj  Fishes.  They  compose  95  per  cent  of  all  living  fishes.  In  this 
group  the  skeleton  is  bony,  thegiUs  are  protected  by  an  operculum,  and  the  eggs  are  numer- 
ous. Most  of  our  common  food  fishes  belong  to  this  class. 

Order  4.  Dipnoan,  or  Lung  Fishes.  This  is  a very  small  group.  In  many  respects  they  are 
more  like  amphibians  than  fishes,  the  swim  bladder  being  used  as  a lung.  They  live  in 
tropical  Africa,  South  America,  and  Australia,  inhabiting  the  rivers  and  lakes  there. 


Self-Testing  Exercise 

Fishes  have  an (1) . The  central  part,  formed  of  irregular-shaped 

bones,  is  called  the  (2)  (3).  In  addition  there  is  an 

exoskeleton  which  may  take  the  form  of  (4),  The  fish  is 

adapted  for  life  in  the  water  by  the (5)  of  its  body,  ........ 

(6)  glands  in  skin,  and  (7)  for  breathing.  The  fish  has  a 

(8)  (9),  a (10)  chambered  heart  and  a well- 

defined  nervous  system  consisting  of  a (11),  (12) 

(13),  nerves,  and (14)  organs.  Many (15)  are 

laid  but  only  a (16)  reach  maturity  as  the (17)  are 

exposed  to  many  . (18)  and  are  eaten  by  other  ........  (19) 

as  well  as  other  enemies. 


250 


HOW  DO  WE  CLASSIFY  ANIMALS? 


PROBLEM  VI.  WHAT  ARE  THE  CHARACTERISTICS  OF 
AMPHIBIANS? 

Laboratory  Exercise.  Adaptations  in  a living  frog.  Examine  the 
skin,  note  body  shape,  shape  of  head,  etc.,  of  a frog.  What  adapta- 
tions for  its  life  in  the  water  can  you  find? 

Examine  the  appendages.  How  are  they  adapted  for  locomotion? 
Note  their  position  in  relation  to  the  long  axis  of  the  body.  What  are 
the  positions  of  the  webbed  toes,  and  of  the  legs,  when  at  rest  and  when 
swimming  or  jumping. 

Compare  the  position  of  the  eyes  of  the  frog  with  those  of  a fish ; 
with  your  own  eyes.  In  which  directions  can  a frog  see?  Note  the 
eardrum  just  back  of  the  eye.  What  evidence  have  you  that  a frog 
can  hear? 

Watch  a frog  catch  a fly  or  other  prey  and  explain  how  it  is  done. 
Examine  the  mouth  of  a dead  frog.  Where  is  the  tongue?  How  is  it 
attached?  How  might  it  be  used?  Does  a frog  have  teeth?  How 
do  you  think  it  eats  its  food  after  catching  it? 

Look  for  movements  of  the  throat,  nose,  and  abdomen  of  a quiet 
frog.  Does  the  frog  open  its  mouth  while  breathing?  Can  it  breathe 
under  water?  Can  you  describe  the  process  of  breathing  in  a frog? 

Sense  organs.  The  frog  is  well  provided  with  sense  organs. 
The  eyes  are  large,  globular,  and  placed  on  each  side  of  the  head. 
When  the  frog  goes  under  water,  a delicate  fold,  called  the  nictitating 
membrane  (or  third  eyelid),  is  drawn  over  each  eye.  The  vision 
of  a frog  is  much  keener  than  that  of  the  fish.  The  external  ear, 
tympanum  (tim'pd-nwm),  is  located  just  behind  the  eye  on  the 
side  of  the  head.  Frogs  hear  sounds  and  distinguish  various 
calls  of  their  own  kind,  as  is  proved  by  the  fact  that  they  recognize 
the  warning  notes  of  their  mates  when  any  one  is  approaching. 
The  inner  ear  has  to  do  with  balancing  the  body  as  it  does  in  fishes 
and  other  vertebrates.  Touch  is  a well-developed  sense.  Frogs 
respond  to  changes  in  temperature  under  water,  and  go  into  a 
dormant  state  for  the  winter  when  the  temperature  of  the  air 
becomes  colder  than  that  of  the  water.  Taste  and  smell  are 
probably  not  strong  sensations  in  a frog. 

Food-getting  and  digestion.  The  frog’s  mouth  is  large  and  can 
be  opened  very  wide.  Its  sticky  tongue  is  long  and  flexible.  It 
is  attached  to  the  front  of  the  floor  of  the  mouth  and  can  be 
thrown  out  with  great  rapidity  to  secure  living  prey.  The  mouth 
leads  into  a short  tube,  the  gullet,  which  widens  into  a long  stomach. 


FROG 


251 


The  stomach  in  turn  leads  into  a narrow,  nuich-coiled  small  in- 
testine, which  widens  to  form  the  large  intestine,  the  last  part  of 
which  is  the  cloaca  (Latin,  sewer).  The  kidneys,  urinary  bladder, 
and  reiu-odiictive  organs  {ovaries  or  testes)  open  into  the  large  intes- 
tine. Several  glands,  the  gastric  glands,  the  liver,  and  the  pancreas, 
produce  digestive  fluids.  These  digestive  fluids  by  means  of 
enzymes  change  in- 
soluble food  mate- 
rials into  a soluble 
form  which  may  be 
absorbed  and  become 
part  of  the  blood. 

All  these  different 
structures  are  built 
up  from  cells,  which 
differ  greatly,  depend- 
ing upon  their  func- 
tion or  use.  Study 
the  diagram  and  see 
how  many  of  the  cells  shown  you  can  locate  in  the  correct 
structures. 

Breathing.  The  frog  takes  air  into  its  mouth  by  lowering  the  floor 
of  the  mouth  and  drawing  air  in  through  the  two  nostril  holes.  Then 
the  little  valvelike  flaps  over  the  holes  are  closed,  the  floor  of  the 
mouth  is  raised,  and  the  frog  forces  the  air  down  into  the  baglike 
lungs.  ^Mien  the  nostril  flaps  are  liftecl  the  air  is  forced  back  to 
the  mouth  by  the  pressure  of  the  body  wall  and  the  contraction  of 
the  lungs.  Then  the  mouth  floor  is  raised  and  the  air  is  forced  to 
the  exterior.  The  lungs  contain  air  spaces  surrounded  by  walls 
filled  with  small  blood  vessels,  by  means  of  which  oxygen  is  taken 
up  and  carbon  dioxide  is  given  off.  The  skin  also  is  provided  with 
many  tiny  blood  vessels  which  absorb  oxygen  and  give  off  carbon 
dioxide. 

Practical  Exercise  13.  How  does  a frog  breathe  diiring  his  winter  sleep  at 
the  bottom  of  a pond? 

Circulation.  The  frog  has  a well-developed  heart,  composed 
of  a thick-walled  muscular  ventricle  and  two  thin-walled  auricles. 


This  shows  some  of  the  cells  in  the  body  of  the  frog.  What 
difference  do  you  find  in  muscle  cells  in  the  wall  of  the  stomach 
and  in  the  leg? 


252 


HOW  DO  WE  CLASSIFY  ANIMALS? 


The  heart  pumps  the  blood  through  a system  of  closed  tubes  to 
all  parts  of  the  body.  Oxidation  must  take  place  in  the  cells  of  the 
body  wherever  work  is  done.  Food  in  the  blood  is  taken  to  the 

muscle  cells  or  other 
cells  of  the  body  and 
there  oxidized.  The 
products  of  oxidation, 
chiefly  carbon  dioxide, 
and  any  other  organic 
wastes  given  off  from 
the  tissues  must  be 
eliminated  from  the 
body.  As  we  know,  the 
carbon  dioxide  passes 
off  through  the  lungs 
and  to  some  extent 
through  the  skin  of  the 
frog,  while  the  nitrog- 
enous wastes  are  elimi- 
nated by  the  kidneys. 

Nervous  system. 
The  frog  has  a brain 
and  spinal  cord  and  in  general  its  central  nervous  system  resembles 
that  of  man. 

Reproduction  and  life  history.  The  eggs  of  the  common  frog 
are  laid  in  shallow  water  in  the  early  spring.  Masses  of  several 
hundred,  which  may  be  found  attached  to  twigs  or  other  supports 
under  water,  are  deposited  at  a single  laying.  Immediately 
before  leaving  the  body  of  the  female  they  receive  a protective 
coating  of  jellylike  material,  which  swells  up  after  the  eggs  reach 
the  water.  The  upper  side  of  the  egg  is  dark,  the  light-colored  side 
being  weighted  down  with  a supply  of  yolk  (food).  The  eggs  are 
fertilized  in  the  water  by  sperms  which  are  discharged  about  the 
same  time  as  the  eggs.  The  fertilized  egg  soon  divides  into  many 
cells  and  in  a week  or  ten  days,  if  the  weather  is  warm,  it  devel- 
ops into  a tiny  oblong  body  with  a wide  tail  and  indistinct  head, 
which  wriggles  itself  free  of  the  inclosing  jelly.  This  form  is  known 


A dissected  frog.  Seen  from  the  under  side.  What 
systems  are  represented  in  this  figure  ? What  parts  are 
left  out  of  the  drawing  or  are  not  labeled? 


REPRODUCTION  AND  LIFE  HISTORY 


253 


as  a “tadpole”  or  “ polliwog;.”  At  first  it  is  attached  to  some 
water  weetl  by  means  of  a suckerlike  jirojectioii ; but  in  one  or 
two  weeks’  time,  dependiiiH;  upon  temperature,  it  frees  itself 
and  becomes  a free-swimming  tadpole.  A mouth  is  formed  at 
the  suckerlike  projection,  and  the  tadpole  begins  to  feed  upon 
algae  and  other  tiny  water  plants.  At  this  time,  gills  are  present 
on  the  outside  of  the  body.  Later,  these  gills  are  replaced  by 
others  which  grow  out  under  the  fold  of  the  skin.  Water  reaches 
the  gills  through  the  mouth  and  passes  out  through  a hole  on  the 
left  side  of  the  body.  As  the  tadpole  grows  larger,  legs  appear. 
The  hind  legs  grow  out  first.  At  the  same  time  the  tail  becomes 
shorter  and  shorter.  Shortly  after  the  legs  appear,  the  gills  are 
absorbed,  and  lungs  take  their  place.  At  this  time  the  young 
animal  may  be  seen  coming  to  the  surface  of  the  water  for  aii 


Trace  the  life  history  of  the  frog.  How  long  does  it  take  for  the  frog  to  pass  through 
this  metamorphosis  ? (Use  the  frog  common  to  your  locality  to  answer  this  question.) 

Changes  in  the  diet  of  the  animal  also  occur ; the  long,  coiled 
intestine  is  transformed  into  a much  shorter  one.  The  animal, 


254 


HOW  DO  WE  CLASSIFY  ANIMALS? 


now  insectivorous  in  its  diet,  becomes  provided  with  tiny  teeth  and 
a mobile  tongue,  instead  of  the  horny  jaws  used  in  scraping  off 
algae.  After  the  tail  has  been  completely  absorbed  and  the  legs 
have  become  full  grown,  there  is  no  further  structural  change, 

and  the  metamorphosis  is 
complete. 

Practical  Exercise  14.  Make  a 
series  of  diagrams  to  show  changes 
in  methods  of  breathing  in  the  frog, 
from  hatching  to  adult. 

Compare  the  metamorphosis  of 
a frog  with  an  insect.  Can  you 
find  four  stages  in  each : egg,  larva, 
pupa,  adult? 

Toad.  One  of  the  nearest 
relatives  of  the  frog  is  the  com- 
mon toad.  Its  ugly  appear- 
ance has  given  it  a bad  name. 
Toads  do  not  cause  warts,  and  do  much  good  in  our  gardens  by 
eating  harmful  insects.  Their  eggs  are  laid  in  strings,  and  like  those 
of  the  frog,  are  deposited  in  fresh-water  ponds.  As  many  as  eleven 
thousand  eggs  have  been  laid  by  a single  toad.  The  egg-laying 
season  of  the  toad  is  later  than  that  of  the  frog.  Toad  tadpoles 
differ  from  those  of  the  frogs,  by  being  darker  in  color,  and 
having  a more  slender  tail  and  a relatively  larger  body. 

Other  amphibians.  The  tree  frogs  or  tree  toads  are  familiarly 
known  to  us  in  the  early  spring  as  the  “ peepers  ” of  the  swamps. 
They  are  among  the  earliest  of  the  frogs  to  lay  their  eggs.  During 


L.  W.  Brownell 

Why  is  the  red  salamander  an  amphibian? 


AMPHIBIA 


255 


adult  life  they  spend  most  of  their  time  on  the  trunks  of  trees. 
Another  common  ampiiibian  is  the  newt,  a salamander.  This 
smooth-skinned,  four-limbed  animal,  often  incorrectly  called  a 
lizard,  pas.ses  its  larval  life  in  the  water,  where  it  breathes  by  means 
of  external  jziills.  Later  it  loses  its  gills,  becomes  provided  with 
lungs,  and  comes  out  on  land,  but  after  two  years  it  goes  back  to 
the  water  again  to  lay  its  eggs. 

Some  salamanders  never  have  lungs,  but  breathe  through  the 
moist  skin.  Still  other  amphibians  are  the  mud  puppies,  sirens 
or  mud  eels,  and  the  axolotl. 

Practical  Exercise  16.  Xanie  all  the  amphibians  in  your  locality.  Why  is 
the  frog  an  amphibian?  What  other  animals  outside  the  amphibians  could 
you  consider  as  amphibious  animals? 

Practical  Exercise  16.  Compare  the  life  history  of  a toad  with  that  of  a 
frog. 

Amphibia.  As  the  name  indicates  {amphi,  both,  and  bios,  life), 
members  of  this  group  live  during  their  life  history  both  in  water 
and  on  land.  In  the  earlier  stages  of  their  development  they  take 
oxygen  into  the  blood  by  means  of  gills.  When  adult,  however, 
they  breathe  by  means  of  lungs.  At  all  times,  but  especially 
during  the  winter,  the  skin  serves  as  a breathing  organ.  The  skin 
is  soft  and  unprotected  by  bony  plates  or  scales.  The  heart  has 
three  chambers : two  auricles  and  one  ventricle.  Most  amphib- 
ians undergo  a metamorphosis,  or  change  of  form,  the  young 
being  unlike  the  adults.  About  1500  species  are  known. 


Order  1.  Urode'la.  Amphibia  having  poorly  developed  appendages.  Tail  persistent 
through  life.  Examples : mud  puppy,  newt,  salamander. 

Order  2.  Anu'ra.  Tail-less  Amphibia,  which  undergo  a marked  metamorphosis,  breathing  by 
gills  in  larval  state,  by  lungs  in  aduit  state.  Examples : toad  and  frog. 


256 


HOW  DO  WE  CLASSIFY  ANIMALS? 


Self-Testing  Exercise 

Frogs  are  adapted  to  their  environment  by  having  (1) 

feet  and  a thin  skin  filled  with (2)  (3)  by  means 

of  which  they (4)  oxygen.  The  frog  breathes  air  by  means  of 

(5).  The  short (6)  leads  into  a bag-like (7) 

which  in  turn  opens  into  a much-coiled  small  (8).  The 

heart  is (9)  chambered (10)  are  laid  in  water  and 

develop  into (11)  which  breathe  by  (12).  These 

are  replaced  by  (13).  The  tadpole  feeds  on  (14) 

(15),  but  the  adult  frog  eats (16).  A relative  of  the 

frog  is  the  (17).  It  lays  its  eggs  in (18)  in  the 

water  while  those  of  the  frog  are  found  in (19).  Toads  are  of 

much (20)  in  gardens  where  they • • (21) (22) 

insects.  Other  examples  of (23)  are  newts  and  salamanders. 


PROBLEM  VII.  WHAT  ARE  CHARACTERISTICS  OF  THE 
REPTILES? 


Turtles’  adaptations  for  life.  The  turtles  form  a group,  including 
both  sea  and  land  animals,  the  latter  called  tortoises.  The  body 

is  short  and  broad. 


How  does  the  three-toed  box  turtle  seem  fitted  to  its 
environment  ? 


and  is  covered  on 
the  upper  and  lower 
sides  by  a bony 
framework  of  plates 
cemented  to  the  true 
bone  underneath. 
This  shell  is  an  adap- 
tation for  protection. 

The  long  neck  and 
powerful,  horny  jaws 
are  factors  in  pro- 
curing food.  Turtles 
have  no  teeth.  Prey 
is  seized  and  held 
by  the  jaws  which 


LIZARDS  257 

have  sharp,  chisel-like  edges  while  the  claws  of  the  front  legs  are 
used  to  tear  the  food. 

Turtles  are  very  strong  for  their  size.  The  stout  legs  carry 
the  animal  slowly  on  land.  In  some  water  turtles  the  front  limbs 
are  modified  into  flippers  for  swimming.  The  strong  claws  are 
used  for  tligging,  especially  at  the  egg-laying  season,  for  some 
turtles  tlig  holes  in  sandy  beaches  in  which  the  eggs  are  de- 
posited. 

Turtles  are  mostly  aquatic  in  habit.  Among  the  exceptions 
are  the  box  tortoise  and  the  giant  tortoise  of  the  Galapagos  Islands. 
Many  of  the  salt-water  turtles  are  of  large  size,  the  leatherback 
and  the  green  turtle  often  weighing  six  hundred  to  seven  hundred 
pounds  each. 

Lizards.  Lizards  may  be  recognized  by  their  long  body  with 
four  legs  of  nearly  equal  size.  The  body  is  covered  with  scales. 
The  animal  never  lives  in  water,  is  active  in  habit,  and  does 
not  undergo  a metamorphosis.  Lizards  are  generally  harmless 
creatures,  the  poisonous  Gila  monster  of  New  Mexico  and  Arizona 
being  one  exception.  Lizards  are  of  economic  importance  to  man 
because  they  eat  injurious  insects.  The  iguana  of  Central  America 
and  South  America,  growing  to  a length  of  three  feet  or  more,  has 
the  distinction  of  being  one  of  the  few  edible  lizards. 


Wright  Pierce 

The  Gila  monster  is  the  only  poisonous  lizard  in  the  United  States.  It  is  brilliantly  colored  in 
red  and  black.  What  may  be  the  value  of  this  coloring? 


258 


HOW  DO  WE  CLASSIFY  ANIMALS? 


Snakes.  Probably  the  most  disliked  and  feared  of  all  common 
animals  are  snakes.  This  feeling,  however,  is  rarely  deserved, 
for,  on  the  whole,  our  common  snakes  are  beneficial  to  man, 
for  they  live  largely  on  injurious  animals,  such  as  rodents,  insects, 
and  slugs. 

Locomotion.  Snakes  are  almost  the  only  vertebrates  without 
appendages.  Although  the  limbs  are  absent,  the  pelvic  and 
pectoral  girdles  are  developed.  The  very  long  backbone  is  made 
up  of  a large  number  of  vertebrae.  As  many  as  four  hundred  are 


Wright  Pierce 

The  rattlesnake  is  one  of  the  few  poisonous  snakes.  The  snake  is  coiled,  with 
rattlers  buzzing,  ready  to  strike. 


found  in  the  boa  constrictor.  Ribs  are  attached  to  all  the  vertebrae 
in  the  region  of  the  body  cavity.  They  progress  with  a gliding 
motion  caused  by  pulling  and  pushing  the  body  along  the  ground, 
a leverage  being  obtained  by  means  of  the  broad,  flat  scales,  or 
scutes,  on  the  under  side  of  the  body. 

Feeding  habits.  The  mouth  is  a wide,  slitlike  opening  extending 
nearly  around  the  anterior  end  of  the  head,  and  is  therefore  capable 
of  wide  distention.  A snake  holds  its  prey  by  means  of  incurved 
teeth.  In  the  poisonous  snakes  two  of  these  teeth  are  hollow  or 
grooved,  and  serve  as  a duct  for  the  passage  of  poison.  The 
poison  glands  are  at  the  base  of  the  curved  fangs  in  the  upper  jaw. 


KEPTILES 


259 


The  tongue,  an  organ  of  touch  aiul  taste,  is  very  long  and  forked 
at  tlie  end.  The  food  is  swallowed  whole,  and  jiushed  down  by 
rhythmic  contractions  of  the  muscles  surrounding  the  gullet. 
Snakes  usually  refuse  other  than  living  prey. 

Alligators  and  crocodiles.  Crocodiles  arc  mostly  confined  to 
Asia  and  Africa,  while  alligators  are  natives  of  North  and  South 
America.  The  chief  structural  tlifference  between  them  is  that 
the  teeth  in  alligators  are  set  in  long  sockets,  while  those  of  the 
crocodiles  are  not.  Both  of  these  lizardlike  animals  have  broad, 
vertically  flat  tenet!  tails  adapted  to  swimming.  Their  skins  ai-e 
very  tough  and  are  covered  with  bony  scales. 


Amer.  Mus.  of  Nat.  Hist. 

Why  is  the  alligator  classified  as  a reptile? 


Practical  Exercise  17.  Give  a good  definition  of  a reptile.  What  reptiles 
are  common  in  your  locality? 

Practical  Exercise  18.  What  is  one  character  by  which  you  can  distinguish 
a reptile  from  an  amphibian?  In  what  part  of  this  country  are  reptiles  most 
numerous  ? Why  ? 

Reptiles.  These  animals  are  characterized  by  having  scales 
developed  from  the  skin.  In  the  turtle  they  have  become  bony 
and  are  connected  with  the  internal  skeleton.  Reptiles  always 
breathe  by  means  of  lungs,  differing  in  this  respect  from  the 
amphibians  and  fishes.  They  have  the  same  temperature  as  their 
surroundings  and  usually  hibernate  as  soon  as  winter  comes. 
They  show  their  relationship  to  birds  by  laying  large  eggs, 
incased  in  a leathery,  limy  shell.  There  are  about  1500  known 
species. 


260 


HOW  DO  WE  CLASSIFY  ANIMALS? 


Chelonia 

turtle 


Lacertilia 


Ophidia 


Order  1.  Chelo'nia  (turtles  and  tortoises).  Flattened  reptiles  with  body  inclosed  in  bony 
case.  No  teeth  or  sternum  (breastbone).  Examples:  snapping  turtle,  box  tortoise. 
Order  2.  Lacertil'ia  (lizards).  Body  covered  with  scales,  usually  having  two-paired  ap- 
pendages. Examples  : fence  lizard,  horned  toad. 

Order  3.  Ophid'ia  (snakes).  Body  elongated,  covered  with  scales.  No  limbs  present. 
Examples  : garter  snake,  rattlesnake. 

Order  4.  Crocodil'ia.  Fresh-water  reptiles  with  elongated  body  and  bony  scales  on  skin. 
Two-paired  limbs.  Examples : alligator,  crocodile. 


Self-Testing  Exercise 

Reptiles  are  animals  which  have (1)  or (2)  plates 

developed  from  the (3).  They  always  breathe  by  means  of 

(4) (5),  (6),  (7),  (8), 

and  (9)  are  examples  of  reptiles. 

PROBLEM  VIII.  WHAT  ARE  THE  CHARACTERISTICS  OF 
BIRDS? 

Adaptations  of  birds.  Birds  are  distinguished  from  all  other 
animals  by  their  covering  of  feathers  and  by  the  modification  of 
the  fore  limb  into  a wing  for  flight.  Hollow  bones,  feathers,  and 
air  sacs  inside  of  the  body  cavity  give  buoyancy  to  the  body  and 
aid  it  in  staying  up  in  the  air.  The  body  is  conically-shaped. 
The  tail  acts  as  a rudder.  The  bill  is  horny  and  adapted  for 
securing  food.  The  legs  show  variations  for  running,  perching, 
scratching,  or  swimming. 

The  wing  is  a modified  arm,  with  the  fingers  very  much  reduced. 
To  the  posterior  edge  of  the  wing  are  fastened  long  quill  feathers 
which  overlap  and  make  a broad,  stiff  surface  for  pressing  against 
the  air.  The  wing  is  jointed  and  moves  in  flight  like  a horizontal 
figure  eight.  Powerful  breast  muscles  are  attached  to  the  wing 


ADAPTATIONS  OF  lORDS 


2G1 


bones  and  give  great  strength  in  nioveinent.  The  rate  of  inove- 
inent  of  the  wing  tliffers  greatly  in  different  birds.  The  wing  of  a 
bird  is  slightly  concave  on  the  lower  surface  when  outstretched. 
Thus  on  the  downward  stroke  of  the  wing  more  resistance  is 
offered  to  the  air.  The  soaring  of  birds  is  probably  accomplished 
by  very  slight  movements  of  the  wings  which  result  in  making 
use  of  wind  currents. 

The  tail  is  sometimes  used  in  balancing;  its  chief  function, 
however,  appears  to  bo  that  of  a rudder  during  flight.  Most  birds 
have  under  the  skin  of  the  tail  a large  oil  gland,  whence  comes  the 
suppl}’’  of  oil  that  is  used  in  waterproofing  the  feathers  when  they 
preen  themselves. 


Crown, 


Find  and  list  all  the  adaptations  in  this  bird.  Explain  the  value  of  each  adaptation  named. 


Thinly  feathered  and  featherless  areas  can  be  found  on  the  body 
of  any  bird,  although  these  areas  are  so  well  covered  by  the  over- 
lapping feathers  that  no  bare  places  are  to  be  seen.  There  are 
several  kinds  of  feathers  on  the  body  of  a bird.  Soft  down  feathers 
make  a warm  body  covering ; larger  feathers,  known  as  contour 

H.  BIO — 18 


262  HOW  DO  WE  CLASSIFY  ANIMALS? 

feathers,  give  the  rounded  contour  to  the  body.  In  the  wings  we 
find  quill  feathers  ; these  are  adapted  for  service  in  flight  by  having 

long  hollow  shafts, 
the  whole  making  a 
light  structure  and 
offering  considerable 
resistance  to  the  air. 
Feathers  are  devel- 
oped from  the  outer 
layer  of  the  skin,  and 
are  formed  in  almost 
exactly  the  same 
manner  as  are  the 
scales  of  a fish  or  a 
lizard.  Feathers  are 
shed  or  moulted  one 
or  more  times  dur- 
ing the  year,  and  lost 
or  broken  feathers 
are  replaced.  Some 
birds  moult  twice  a 
year,  having  differ- 
ent colored  feathers 
in  the  summer  and 
winter  seasons. 

Many  bones  are  hollow  or  have  large  spongy  cavities.  Some 
bones,  notably  the  breastbone,  are  greatly  developed  in  flying 
birds  for  the  attachment  of  the  muscles  used  in  flight. 

The  ankle  of  a bird  is  long  and  reptile-like  and,  like  the  foot,  is 
covered  with  scales.  The  most  extraordinary  adaptations  are 
found  in  the  feet  of  various  birds : some  for  perching,  others  for 
swimming,  others  for  scratching,  etc.  By  looking  at  the  feet  of  a 
bird  we  are  able  to  decide  almost  certainly  its  habitat,  method  of 
life,  and  perhaps  its  food. 

In  the  perching  birds  we  And  three  toes  in  front  and  one  behind, 
the  hind  toe  playing  an  important  part  in  clinging  to  the  perch. 
The  three  toes  in  front  curve  around  the  perch,  often  meeting  the 


Compare  this  bird  with  an  airplane.  In  what  ways  are  they 
similar,  and  in  what  ways  different  ? 


RlliDS 


263 


posterior  too,  which  is  curved  also.  The  tendons  of  the  leg  and 
foot  are  self-locking.  In  the  llainingocs  and  other  birds,  which 
do  not  perch,  balancing  appears  to  be  autoniatic,  for  these 
birds  are  able  to  iiiaintain  an  upright  position  even  when  asleep. 
In  swallows,  rapid  and  untiring  flyers,  the  feet  arc  small.  In 
the  case  of  the  parrots,  where  the  foot  is  used  for  holding  food, 
climbing,  and  clinging,  we  find  the  four-clawed  toes  arranged 
two  in  front  and  two  behind. 

The  form  of  the  bill  shows  adaptation  to  a wonderful  degree, 
varying  great I3'  according  to  the  habits  of  the  bird.  A duck  has  a 
flat  bill  for  pushing  through  the  mud  and  straining  out  the  food; 
a bird  of  prey  has  a curved  or  hooked  beak  for  tearing ; the  wood- 
pecker has  a sharp,  straight  bill  for  piercing  the  bark  of  trees  in 
search  of  the  insect  larvae  underneath.  Birds  do  not  have  teeth. 
The  edge  of  the  bill  may 
1 appear  to  be  toothed,  as  in 
''  some  fish-eating  birds ; how- 
ever, the  projections  are  not 
true  teeth.  Frequently  the 
tongue  has  sharp,  toothlike 
edges  which  serve  the  same 
purpose  as  the  curved  teeth 
of  the  frog  or  snake. 

Respiration.  The  rate  of 
respiration,  of  heartbeat,  and 
the  body  temperature  are  all 
higher  in  the  bird  than  in 
man.  i\Ian  breathes  sixteen 
or  eighteen  times  a minute. 

Birds  breathe  from  twenty  to 
sixty  times  a minute.  The 
lungs  of  birds  are  connected 
to  large  air  sacs,  found  in  the 
abdominal  cavity  of  the  body, 
which  hold  reserve  air  and 
help  make  the  bird  lighter.  A bird  may  be  compared  to  a high- 
pressure  steam  engine.  In  order  to  release  the  energy  which  it 


Wright  Pierce 

What  are  the  adaptations  of  the  Golden  eagle  ? 


264 


HOW  DO  WE  CLASSIFY  ANIMALS? 


uses  in  flight,  a large  quantity  of  fuel  which  will  oxidize  quickly 
must  be  used.  Birds  are  large  eaters,  and  the  digestive  tract  is 
fitted  to  digest  the  food  quickly.  As  soon  as  the  food  is  absorbed 
by  the  blood,  it  may  be  sent  rapidly  to  the  places  where  it  is 
needed,  by  means  of  the  strong  four-chambered  heart  and  large 
blood  vessels. 

The  high  temperature  of  the  bird  is  a direct  result  of  this  rapid 
oxidation ; furthermore,  the  feathers  and  the  oily  skin  form  an 

insulation  which 
does  not  readily 
permit  the  escape 
of  heat.  This  in- 
sulating cover  is 
of  much  use  to  the 
bird  in  its  flights 
at  high  altitudes, 
where  the  temper- 
ature is  often  very 
low. 

The  nervous 
system  and  the 
senses.  The  cen- 
tral nervous  sys- 
tem of  a bird  is 

The  sharp-edged,  chisel-like  bill  of  the  woodpecker  made  these  WOll  developed, 
holes  in  the  tree.  Red-headed  woodpeckers  also  have  the  un-  Attached  tO  the 
usual  habit  of  storing  nuts  of  various  kinds  in  the  crevices  and 

holes  they  make  in  the  bark  of  certain  trees.  fairly  large  brain 

is  the  spinal  cord 

which  extends  the  length  of  the  body.  From  this  cord  nerves  are 
given  off.  Sight  is  probably  the  best  developed  of  the  senses. 
The  keen  sight  of  a hawk  is  proverbial.  Hearing  is  also  well 
developed  in  most  birds.  The  sense  of  smell  does  not  appear  to 
be  well  developed,  and  is  especially  deficient  in  seed-eating  birds. 

Nesting  habits.  Among  the  most  interesting  of  all  instincts 
shown  by  birds  are  those  of  nest  building.  Birds  incubate  their 
eggs,  that  is,  hatch  them,  by  the  heat  of  their  bodies.  Hence 
a nest  is  needed.  The  ostrich  is  an  exception;  it  makes  no 


Wright  Pierce 

What  can  you  tell  about  the  habits  and  characteristics  of  the  birds  which  made  these  nests? 

265 


266 


HOW  DO  WE  CLASSIFY  ANIMALS? 


nest,  but  lays  its  eggs  on  the  ground.  Birds  immune  from  the 
attacks  of  enemies  because  of  their  isolation  or  their  protective 
coloration  (as  the  gulls  and  terns)  build  a rough  nest  among  the 
rocks  or  on  the  beach.  The  eggs,  especially  those  of  the  tern,  are 
marked  and  colored  so  as  to  be  almost  indistinguishable  from  the 
rocks  or  sand  on  which  they  rest.  Other  birds  have  made  their  nest 
a place  of  refuge  as  well  as  a place  to  hatch  the  eggs. 

Care  of  the  young.  After  the  eggs  have  been  hatched,  the  young 
birds  in  most  cases  are  quite  dependent  upon  the  parents  for 
food.  Most  young  birds  are  prodigious  eaters.  As  a result  they 
grow  very  rapidly.  It  has  been  estimated  that  a young  robin 
eats  two  or  three  times  its  own  weight  of  food  every  day.  In  the 
case  of  the  pigeons  and  some  other  birds,  food  is  swallowed  by 
the  mother,  partially  digested  in  the  crop,  and  then  regurgitated 

into  the  mouths  of 
the  young  nestlings. 

Relationship  of 
birds  and  reptiles. 
The  birds  afford  an 
interesting  example 
of  how  the  history 
of  past  ages  of  the 
earth  has  given  a 
clue  to  the  struc- 
tural relation  which 
birds  bear  to  other 
animals.  Several 
years  ago,  two  fossil 
skeletons  were  found 
in  Europe  of  a bird- 
like creature  which 
had  not  only  wings 
and  feathers,  but 
also  teeth  and  a lizardlike  tail.  From  these  fossil  remains  and 
certain  structures  (as  scales)  and  habits  (as  the  egg-la5dng  habits), 
naturalists  have  concluded  that  birds  and  reptiles  in  distant 
times  were  closely  related  and  that  our  existing  birds  probably 


Museum  of  Natural  History 

The  eggs  of  a dinosaur,  a large  land  reptile  which  lived  mil- 
lions of  years  ago.  This  nest  of  eighteen  eggs  was  found  in 
Mongolia. 


CLASSIFU^ATION  OF  lUKDS  AND  REPTILES  267 


(lovelopocl  from  a roptilc-liko  ancestor  many  ages  ago.  The 
recently  discovered  eggs  of  the  extinct  dinosaurs  are  another  link 
in  the  chain  of  relationship. 


Practical  Exercise  19.  Make  a coniprohensivc  definition  of  a bird.  What, 
evidences  of  relationship  ilo  you  timl  between  reptiles  and  birds?  What 
adaptations  woidd  you  expect  in  a bird  of  prey,  swinunor,  wader? 


Laboratory  Exercise.  Tsing  the  text  as  a guide,  study  a living 
bird  to  find:  (1)  adaptations  for  flight;  (2)  for  food  getting;  (3)  for 
protection. 


Ratitxxe  APasseres  Gallinae  T^ptores  Limicoloce^ 


wrefens  T** 

An^eres 

swimmers 


Order  1.  Rali'tae.  Running  birds  with  no  keeled  breastbone.  Examples : ostrich,  casso- 
wary. 

Order  2.  Pas'seres.  Perching  birds ; having  three  toes  in  front,  one  behind.  Over  one  half 
of  all  species  of  birds  are  included  in  this  order.  Examples:  a sparrow,  thrush,  swallow. 

j Order  3.  Galli'nae.  Strong  legs,  feet  adapted  to  scratching.  Beak  stout.  Examples : 
jungle  fowl,  grouse,  quail,  domestic  fowl. 

P Order  4.  Rapto'res.  Birds  of  prey.  Hooked  beak.  Strong  claws.  Examples:  eagle,  hawk. 

' Order  5.  Limicolae.  An  order  of  the  shore  birds,  wings  long,  thin,  flat,  and  pointed.  Legs 

j usually  very  long.  Bills  are  sometimes  long.  Examples : plover,  snipe,  sandpiper. 

' Order  6.  Longipennes.  Drivers  and  swimmers.  Legs  short,  toes  webbed.  Examples : 
gull,  tern. 

: Order  7.  Colum'bae.  Like  Gallinae,  but  with  weaker  legs.  Examples : dove,  pigeon. 

Order  8.  Pici.  Woodpeckers.  Two  toes  point  forward,  two  backward,  and  adaptation 
for  climbing.  Long,  strong  bill. 

Order  9.  Psitiaci.  Parrots.  Hooked  beak  and  fleshy  tongue. 

Order  10.  Coccyges.  Birds,  with  powerful  beaks,  using  their  feet  as  a means  of  progression. 
E.xamples : kingfisher,  toucan,  and  cuckoo. 

I Order  11.  Macrochires.  Birds  having  long,  pointed  wings,  without  scales  on  metatarsus. 
Examples  : swift,  humming  bird,  and  goatsucker. 

1 Order  12.  Anseres.  _ Birds  with  four  toes,  front  ones  fully  webbed,  tail  not  always  well 
developed,  bill  with  toothlike  projections  along  its  sides.  Examples  : ducks,  geese,  swans. 


Self-Testing  Exercise. 

Birds  are  characterized  by  having  an  (1)  covering  of 

(2) ; (3) ; (4)  modified  for  (5) ; 


268 


HOW  DO  WE  CLASSIFY  ANIMALS? 


(6)  sacs ; (7)  bones ; (8)  on  the  legs  (which 

show  their (9)  to  the  reptiles) ; a bill  but  no  true (10)  ; 

(11)  temperature;  a rapid  (12)  beat.  They  lay 

(13)  covered  with  a (14)  (15).  The 

(16)  in  leg  and  bill  show  clearly  what  kind  of (17)  the 

bird  leads  and  the (18)  of  (19)  it  uses. 

PROBLEM  IX.  WHAT  ARE  THE  CHARACTERISTICS  OF 
MAMMALS? 

Practical  Exercise  20.  Make  brief  descriptions  in  your  workbook  of  two 
mammals  such  as  a cat  and  a horse.  How  do  they  differ?  How  are  they  • 
similar  ? 

Mammals.  Mammals  are  characterized  by  being  warm  blooded, 
by  having  a four-chambered  heart,  a diaphragm,  and  well-developed 
lungs.  The  most  characteristic  features,  however,  are  that  they 

have  a hairy  cover- 
ing at  some  period 
of  their  existence 
and  bring  forth  their 
young  alive.  The 
young  are  nourished 
on  milk  secreted  by 
glands  known  as  the 
mammary  glands ; 
hence  the  term 
“mammals.”  Mam- 
mals are  considered 
the  highest  of  verte- 
brate animals,  not 
only  because  of  their  complicated  structure,  but  because  of 
their  mental  development. 

Individual  project.  Visit  a museum  and  study  the  skeletons  and 
mounted  bodies  of  a seal  and  of  a whale.  Why  do  we  consider  these 
animals  mammals  rather  than  fishes  or  amphibians? 

Carnivores.  Carnivorous  mammals  are  to  a large  extent  flesh 
eaters.  In  a wild  state  they  hunt  their  prey,  which  is  caught  and 
torn  with  the  aid  of  well-developed  claws  and  long,  sharp  canine 
teeth. 


MAMMALS 


All  flosh-eatin<i: 
iiiainnuils  are  wan- 
(Icrinj^  hiiiitert^; 
many,  as  the  bear 
aiul  lion,  have 
homes  or  dens  to 
which  they  retreat. 

Some,  as  bears  and 
raccoons,  live  part 
of  the  time  upon 
berries  and  fruit. 

Rodents.  Mam- 
mals known  as 
rodents  have  the 
teeth  so  modified 
that  on  both  up- 
per and  lower  jaws 
two  prominent 
teeth,  incisors,  are 
used  for  gnawing. 

These  teeth  keep 
their  chisel-like 
edges  because  the  back  part  of  the  teeth  is  softer  and  wears 
away  more  rapidly  than  the  front  part.  The  canine  or  dog  teeth 
are  lacking.  We  are  all  familiar  with  the  destructive  gnawing 
qualities  of  one  of  the  commonest  of  all  rodents,  the  rat. 

Ungulates : hoofed  mammals.  This  group  includes  most  of 
the  domesticated  animals,  as  the  horse,  cow,  sheep,  and  pig. 
Many  of  these  animals  came  under  the  subjugating  influence  of 
man  and  now  they  form  an  important  part  of  the  world’s  wealth. 

The  order  of  ungulates  is  a very  large  one.  It  is  characterized 
by  the  fact  that  the  nails  have  grown  down  and  become  thickened 
as  hoofs.  In  some  cases  only  two  (the  third  and  fourth)  toes  are 
largely  developed.  Such  animals  have  a cleft  hoof,  as  the  ox, 
deer,  sheep,  and  pigs.  They  are  the  even-toed  ungulates.  The 
deer  family  contains  the  largest  number  of  species  and  individuals 
among  our  native  forms,  and  in  fact  the  world  over.  Among  them 


2b<) 


U.  S.  Bureau  of  Biological  Survey 


The  beaver  is  a rodent. 
How  does  he  differ  from 
other  mammals  ? What 
kinds  of  food  does  he  eat  ? 


U.  S.  Bureau  of  Biological  Survey 


270 


HOW  DO  WE  CLASSIFY  ANIMALS? 


are  the  common  Virginia  deer  of  the  Eastern  states,  and  the 
moose  and  antelope.  The  bison,  or  buffalo,  is  closely  related 
to  the  deer.  Formerly  bisons  existed  in  enormous  numbers  on 
our  Western  plains.  They  are  now  almost  extinct. 

Primates.  Man  is  placed  in  the  highest  order  of  mammals,  the 
primates,  because  he  walks  upright  and  the  fore  appendages 
(arm)  are  each  provided  with  hands  for  grasping.  Nails  instead 
of  claws  are  present.  The  primates  have  the  same  characteristics 
as  other  mammals,  but  may  be  said  to  be  superior  to  them  in 
having  a more  highly  developed  brain  and  nervous  system. 


Order  1.  Edentata.  Toothless  or  with  very  simple  teeth.  E.x:amples : anteater,  sloth, 
armadillo. 

Order  2.  Cetacea.  Adapted  to  marine  life.  Examples:  whale,  porpoise. 

Order  3.  Sirenia.  Fishlike  in  form ; pectoral  limbs  paddle-like.  Examples ; manatee, 
dugong. 

Order  4.  Rodentia.  Incisor  teeth  chisel-shaped,  usually  two  above  and  two  below.  Ex- 
amples : beaver,  rat,  porcupine,  rabbit,  squirrel. 

Order  5.  Ungulata.  Hoofs;  teeth  adapted  for  grinding.  Examples:  (a)  odd-toed;  horse, 
rhinoceros,  tapir  ; (6)  even-toed ; ox,  pig,  sheep,  deer. 

Order  6.  Insectivora.  Small,  insect-eating,  furry  or  spiny  covered  ; long  snout.  Example : 
mole. 

Order  7.  Carnivora.  Long  canine  teeth,  sharp  and  long  claws.  Examples : dog,  cat,  lion, 
bear,  seal,  and  sea  lion. 

Order  8.  Chiroptera.  Fore  limbs  adapted  to  flight,  teeth  pointed.  Example  ; bat. 

Order  9.  Primates.  Erect  or  nearly  so,  fore  appendage  provided  with  hand  having  nails. 
Examples : monkey,  ape.  Anatomically,  man  is  placed  with  this  group  of  mammals. 

Practical  Exercise  21.  Name  a common  example  of  each  order  of  mammals 
found  in  your  locality.  What  are  the  chief  characteristics  of  the  carnivora? 


STORY  TOr.D  BY  FOSSILS  271 

The  rodents?  Tlie  iiiiKuhiles?  W’liicli  Kroup  is  most  useful  in  your  locality? 
Most  luirniful?  Which  ineinhers  should  he  destroyed?  Protected? 

S K L r KSTI N (}  1*]  X 10  UCISE 

Mammals  arc  characterized  l)y  having (1)  blood, 

(2)  heart, (d),  and  a muscular  wall  just  below  these  organs 

called  a (4).  Mammals  have (5)  on  the  body  and 

(h)  their  young.  The  important  orders  are  tlie (7) 

or  gnawers,  the  (8)  or  hoofed  animals,  tlie  (9), 

with  sliarp  teeth,  and  the (10),  which  includes  man. 

PROBLEM  X.  WHAT  STORY  IS  TOLD  BY  THE  FOSSILS? 

We  have  learned  that  animals  may  be  arranged  in  groups, 
beginning  with  very  simple  one-celled  forms  and  culminating  with 
man  himself.  These  groups  are  believed  by  some  scientists  to  rep- 
resent, in  a way,  different  stages  in  the  evolution  or  development  of 
life  on  the  earth. 

We  know  that  in  the  millions  of  years  that  life  has  existed  on 
the  earth  that  there  have  been  many  changes.  According  to  present- 
day  evidences,  living  things  at  first  were  very  simple  in  structure, 
but  as  time  went  on  more  and  more  complex  types  appeared. 

Many  of  you  have  probably  had  the  interesting  experience  of 
finding  in  rocks,  not  far  from  the  shore,  shells  or  other  evidences 
of  life.  Sometimes  these  were  simply 
casts  in  rock  which  once  held  the 
remains  of  animals  and  plants.  In- 
frequently, we  find  actual  preserved 
specimens,  as  insects  in  amber.  All 
these  things  are  called  fossils.  If  we 
study  the  geology  of  the  rocks  in 
which  fossils  are  found,  we  learn  that 
these  rocks  were  once  laid  down  under 
water  in  layers,  and  that  the  animal 
or  plant  remains  were  caught  there, 
then  covered  up,  and  preserved.  We 
also  find  that  the  rocks  nearer  the  teeth.* 


The  Archaeopteryx  is  the  earliest 
known  bird.  According  to  fossil  skele- 


272  HOW  DO  WE  CLASSIFY  ANIMALS? 

surface  contain  remains  of  living  things  that  inhabited  the  earth  in 
fairly  recent  time,  while  those  deeper  in  the  earth  contain  fossils 
of  animals  and  plants  that  are  unlike  any  that  are  now  living, 
and  are,  therefore,  thought  to  have  lived  millions  of  years  ago. 
In  this  way  scientists  have  learned  that  the  earliest  forms  of  life 
upon  the  earth  were  very  simple,  and  that  gradually  more  and 
more  complex  forms  appeared,  as  the  rocks  formed  latest  in 
time  show  the  most  highly  developed  forms  of  plant  and  animal 
life. 

Some  evidences  of  ancient  forms  of  life.  From  a study  of 
fossils  from  various  rock  formations  all  over  the  world  the  following 
very  interesting  facts  have  been  discovered  : that  the  oldest  rocks 

contain  very  simple 
plants  and  animals,  al- 
most all  marine ; that 
there  came  a period  in 
which  many  kinds  of 
invertebrates  lived,  at 
this  time  land  plants 
appeared ; then  came 
the  age  of  fishes,  many 
of  which  were  great 
armored  beasts,  long 
since  gone.  Still  later 
we  have  an  age  of  am- 
phibians. During  this 
last  period  great  forests 
flourished  from  which 
our  anthracite  coal  beds 
were  formed.  Then 
came  a time  when  mon- 
strous reptiles  roamed 

Unearthing  the  bones  of  huge  animals  which  at  one  OVer  the  earth,  SOme 
time  lived  in  Wyoming.  These  bones  are  reliM  of  a e xi  { 

mighty  race  that  perished  in  forgotten  ages.  Ot  them  oO  tO  7U  feet 

in  length.  Later  these 
great  animals,  dinosaurs,  vanished  and  huge  batlike  animals  and 
birds  appeared.  During  this  time  the  beginnings  of  our  modern 


GEOLOCJIC  HISTOEY  OF  THE  HOUSE 


273 


mammalian  life  camo  into  existence.  All  of  these  clianp:es  have 
taken  tens,  or  more  likely  lumdreds  of  millions  of  years,  as  we  can  t ell 
from  the  thickness  of  the  rock  deposits  in  which  the  fossils  arc  found. 


Amer.  Mus.  of  Nat.  Hist. 

This  giant  dinosaur,  over  sixty  feet  long,  lived  in  Wyoming  millions  of  years  ago. 


Other  evidences  of  organic  evolution.  Evidences  of  changes 
in  form  through  past  ages  have  been  found  in  the  study  of  the 
elephants,  which  have  changed  from  a trunkless  and  relatively 
small  animal  to  the  huge  elephant  of  today.  The  great  saber- 
toothed  tiger,  which  once  roamed  the  fields  of  California,  has 
given  way  to  the  modern  type. 

In  certain  of  the  higher  animals  we  find  traces  of  organs  that 
are  no  longer  used,  although  they  may  have  been  of  value  to 
the  animals  in  the  past.  The  appendix  in  man  is  small  and  use- 
less, but  in  some  animals,  it  is  large  and  performs  an  important 
digestive  function.  The  muscles  of  the  ears  of  human  beings  are 
useless,  but  in  lower  animals  they  are  of  great  value  in  aiding  the 
hearing. 

Geologic  history  of  the  horse.  That  developmental  changes 
have  taken  place  in  certain  types  of  animals  is  shown  by  a study 
of  a series  of  fossil  horse  skeletons,  which  have  been  reconstructed 
so  that  we  can  pretty  certainly  tell  what  ancient  horses  . look  like. 

The  fossils  of  leg  bones  show  that,  ages  ago,  the  remote  ancestors 
of  the  horse  were  probably  small  animals  the  size  of  a domestic 
cat,  with  five-toed  feet.  The  earliest  horse  we  have  knowledge 


274 


HOW  DO  WE  CLASSIFY  ANIMALS? 


of  had  four  toes  on  the  fore  and  three  toes  on  the  hind  feet.  Thou- 
sands of  years  later  there  existed  a larger  horse,  the  size  of  a sheep, 
with  three  toes  on  each  foot.  Through 
a series  of  changes  there  was  eventually 
produced  our  present  horse,  an  animal 
with  legs  adapted  for  rapid  locomotion, 
with  feet  particularly  fitted  for  life  in 
open  fields,  and  with  teeth  which  serve 
Equus  scotti  well  to  seize  and  grind  herbage. 


Hippidium. 


yresohippus 


€ehippus  Protorohippus 

Redrawn  from  Photo  of  Amer. 
Mus.  of  Nat.  Hist. 

In  what  ways  has  the  horse 
changed  through  the  ages  ? 


Practical  Exercise  22.  From  outside  sources 
construct  a diagram  to  show  the  different  geologic 
ages  in  this  country.  In  what  kind  of  rocks 
would  you  look  for  fossils?  Visit  a museum 
and  describe  some  evidences  of  development  seen 
therein.  What  examples  of  change  have  you 
seen  in  the  world  today?  List  them. 


Self-Testing  Exercise 

The (1)  forms  of (2) 

on  the  earth  are  believed  to  have  been 
very  (3),  while  those  that  devel- 
oped   (4)  are  more  (5). 

(6)  or  remains  of  animals  and 

plants (7)  in (8)  tell  us  the 

story  of  (9)  of  life  on  the  earth. 

Once,  ages  ago,  there  existed (10) 

horses  having (11)  toes  on  the  fore 

feet.  Later,  as  life  on  the  earth  changed, 
there  was  a gradual  development  in  these 
(12)  so  that  today  we  have  horses 


with (13)  toe,  and  longer  legs  fitted 

for  more (14)  locomotion. 


PROBLEM  XL  WHAT  IS  MAN’S  PLACE  IN  NATURE? 

There  is  no  doubt  that  man  is  young  compared  to  some  animals, 
but  he  is  vastly  older  than  was  once  believed.  Very  good  evi- 
dences in  the  form  of  skulls  found  in  the  caves  of  France  and  the 
gravel  pits  of  England  show  that  man  has  lived  on  the  earth  tens  of 


WHAT  IS  MAX’S  PLACT]  IN  NATURE? 


275 


thoiisaiuls,  probably  hundreds  of  thousands  of  years,  500,000  to 
1,000,000  years  b('inf>:  the  latest  estimate. 

I’arts  of  skeletons  found  in  Java  and  hairope  show  a type  of 
man  mueh  lowc'r  than  any  savaj>;e  liviii”;  today.  Arrowheads,  of 
a kind  older  than  any  made  within  the  memory  of  man,  have 
been  found  amoiifi:  the  bones  of  e.xtinct  bisons  under  the  soil  of 
our  Western  plains.  Races  of  men  must  have  once  existed  there 
who  have  now  vanished. 

lA’idences  in  the  forms  of  fossil  bones  and  parts  of  skulls  show 
also  that  man  has  been  changing  during  these  many  centuries. 
11  is  arms  used  to  bo  longer,  his  frame  more  massive,  his  jaw  and 
face  more  ape-like.  This  does  not  mean  that  man  has  ascended 
from  an  ape  ; it  simply  shows  a gradual  development  or  evolution 
through  many  thousands  of  years  from  some  stock  which  gave 
rise  to  the  apes  and  to  man  separately.  Just  as  we  now  have  been 
able  artificially  to  im])rove  plants  and  animals  through  scientific 
breeding,  so  ^Mother  Nature  has,  by  a hit-and-miss  method,  im- 
proved the  breed  of  man  on  the  earth.  How  these  changes  have 
been  brought  about  is  only  conjecture,  but  we  do  know  that  there 
are  great  differences  between  the  men  on  the  earth  today  and  those 


Amer.  M us.  of  Nat.  Hist. 


From  fossils  that  have  been  discovered  in  many  parts  of  the  world,  Dr.  J.  H.  McGregor  has  given 
us  his  idea  of  the  probable  appearance  of  prehistoric  man  in  different  stages  of  development. 

of  yesterday.  But  there  are  also  as  great  structural  differences 
between  the  Bushmen  of  Africa  and  the  white  men  of  England  or 


276 


HOW  DO  WE  CLASSIFY  ANIMALS? 


America  as  there  are  between  those  same  Bushmen  and  some  of 
the  early  races  of  man.  Undoubtedly  there  once  lived  upon  the 
earth  races  of  men  who  were  much  lower  in  their  mental  organi- 
zation than  are  the  present  inhabitants.  If  we  follow  the  early 
history  of  man  upon  the  earth,  we  find  that  at  first  he  must  have 
been  little  better  than  one  of  the  higher  vertebrates.  He  was  a 
nomad,  wandering  from  place  to  place,  living  upon  whatever  ani- 
mals he  could  kill  with  his  hands  and  whatever  edible  plants  he 
found.  Gradually,  he  learned  to  use  weapons  to  kill  his  prey, 
first  using  rough  stone  implements  for  this  purpose.  As  man  be- 
came more  civilized,  implements  of  bronze  and  of  iron  were  used. 
About  this  time  the  subjugation  and  domestication  of  animals 
began  to  take  place.  Man  then  began  to  cultivate  the  fields, 
and  to  have  a fixed  place  of  abode  other  than  a cave.  The  be- 
ginnings of  civilization  were  long  ago,  but  even  today  the  world 
is  not  entirely  civilized. 

Demonstration.  The  skeleton  of  man  compared  with  other  mam- 
mals. Use  skeletons  of  a fish,  frog,  bird,  dog  or  cat,  and  man.  If 
this  material  is  not  available  in  school,  visit  a museum.  Observe  the 
kinds  and  places  of  the  different  bones  in  body  of  each  skeleton.  In 
what  ways  do  the  various  skeletons  agree?  How  do  they  differ? 

Why  is  man  a mammal  ? Although  we  know  that  man  is  sepa- 
rated by  a gap  from  all  other  animals  by  the  power  of  speech,  we 
must  ask  where  we  are  to  place  him  structurally.  If  we  attempt 
to  classify  man,  we  see  at  once  he  must  be  grouped  with  the 
vertebrate  animals  because  of  his  possession  of  a vertebral  column. 
Evidently,  too,  he  is  a mammal,  because  the  young  are  nourished 
by  milk  secreted  by  the  mother  and  because  his  body  has  at  least 
a partial  covering  of  hair.  Among  the  different  orders  of  mammals 
man  most  closely  resembles  anatomically  the  primates  to  which 
the  monkeys  and  apes  belong. 

If  we  compare  several  skeletons  of  different  mammals,  we 
find  certain  definite  likenesses  in  body  plan.  In  the  first  place, 
all  vertebrates  have  the  same  general  parts  of  the  skeleton : the 
skull,  vertebral  column,  the  front  and  rear  appendages,  and  the 
bony  girdles,  pectoral  (shoulder)  and  pelvic  (hip),  which  connect 
the  appendages  with  the  main  or  axial  skeleton.  Then,  too,  they 


TESTS 


277 


all  have  the  same  general  plan  of  digestive  system,  the  same  kinds 
of  circulatory,  respiratory,  and  excreting  systems,  although  here 
more  variations  are  evident  among  the  fishes,  amphibians,  and 
mammals,  hiven  the  nervous  system,  which  seemingly  ought  to 
show  very  great  changes  in  structure,  is  not  as  different  as  one 
might  expect.  Moreover,  if  you  compare  the  skeleton  of  an  ape 
with  that  of  man,  you  notice  some  striking  likenesses  which  set 
their  two  skeletons  off  from  those  of  the  other  vertebrates.  Both 
show  a more  or  less  upright  posture ; they  both  have  well-marked 
fingers  and  toes;  the  general  shape  of  the  head  is  similar,  the 
pectoral  and  pelvic  girdles  are  markedly  alike,  and  a detailed 
study  would  show  many  other  similarities.  If  we  follow  the  same 
principles  for  the  study  of  relationships  here  as  we  have  in  other 
animals,  we  are  forced  to  the  conclusion  of  a close  structural  re- 
lationship between  the  apes  and  man. 

Self-Testing  Exercise 

Man  is  a (1)  because  he  has  a backbone.  Man  is  a 

(2)  because  he  has  hair,  and  the (3)  are  nourished 

by  (4)  secreted  by  the (5)  (6).  He  is  a 

(7)  and  must  be  placed  anatomically  with  the (8). 

This  does  not  mean  he  is (9)  from  the (10),  for 

man  has  existed  with  his  present (11)  for (12),  perhaps 

(13)  of  thousands  of  years. 

Review  Summary 

Test  your  knowledge  of  the  unit  by:  (1)  rechecking  the  survey  questions; 
(2)  performing  all  the  assigned  exercises ; (3)  checking  with  the  teacher  your 
answers  on  the  various  tests  and  trying  again  the  ones  you  missed;  and, 
finally,  (4)  making  an  outline  and  filling  it  in  as  fully  as  possible  for  your  note- 
book. 

Test  on  Fundamental  Concepts 

In  a vertical  column  under  the  heading  CORRECT  write  the  numbers  of  all  statements  you 
believe  are  true.  In  another  column  under  INCORRECT  write  numbers  of  untrue  state- 
ments. Your  grade  = number  of  right  answers  X 2. 

I.  Classification  of  living  things  is  based:  (1)  upon  likeness  and 
differences  in  structure;  (2)  upon  relationships  shown  by  analogies 
in  use  of  parts ; (3)  upon  relationships  shown  by  homologies  in  struc- 
ture ; (4)  upon  the  place  where  they  live ; (5)  on  the  way  in  which 
they  grow. 

H.  BIO  — 19 


278 


HOW  DO  WE  CLASSIFY  ANIMALS? 


II.  The  protozoans  (6)  always  have  cilia ; (7)  are  single-celled 
animals ; (8)  never  live  in  the  water ; (9)  reproduce  by  dividing ; 
(10)  reproduce  by  budding. 

III.  The  coelenterates  (11)  live  in  the  ocean;  (12)  have  baglike 
bodies  with  a mouth  at  one  end ; (13)  are  usually  hxed  and  do  not 
move  from  place  to  place ; (14)  may  show  an  alternation  of  generations ; 
(15)  include  corals,  sea  anemones,  and  hydra. 

IV.  The  arthropods  (16)  have  no  definite  number  of  legs;  (17)  al- 
ways have  a limy  shell;  (18)  have  an  exoskeleton ; (19)  have  jointed 
legs  and  jointed  body;  (20)  have  compound  eyes. 

V.  Mollusks  (21)  are  soft-bodied  animals;  (22)  always  have  a 
shell ; (23)  usually  have  a shell ; (24)  live  only  on  land ; (25)  include 
snails,  oysters,  clams,  and  squids. 

VI.  Fishes  (26)  are  the  only  animals  that  live  in  the  water; 
(27)  have  their  limbs  modified  into  fins;  (28)  breathe  by  taking 
oxygen  out  of  water  by  means  of  gills ; (29)  use  the  ear  as  a balancing 
organ ; (30)  lay  many  eggs  which  are  fertilized  outside  the  body. 

VII.  Amphibians  (31)  include  turtles,  snakes,  and  tortoises  ; 
(32)  always  have  moist  skin  with  no  scales  in  it ; (33)  often  undergo 
a metamorphosis,  part  of  the  life  being  in  the  water  and  part  on  land  ; 
(34)  always  have  both  lungs  and  gills  at  the  same  time  in  their  life 
history ; (35)  include  the  toads,  frogs,  and  salamanders. 

VIII.  Reptiles  (36)  have  no  teeth ; (37)  are  never  poisonous ; 
(38)  always  have  scales  on  the  skin ; (39)  always  breathe  by  lungs ; 
(40)  show  their  relationship  to  birds  by  laying  eggs  with  shells. 

IX.  Birds  (41)  show,  by  scales  on  their  legs,  relationship  to  reptiles  ; 
(42)  have  modified  arms  or  forelegs  which  are  used  in  flying;  (43)  al- 
ways build  a nest  in  which  are  laid  many  eggs;  (44)  have  a four- 
chambered  heart ; (45)  have  a skeleton  composed  of  light  and  hollow 
bones,  with  large  breastbone  to  which  wing  muscles  are  attached. 

X.  Mammals  (46)  are  at  the  top  of  the  evolutionary  scale ; (47)  have 
a four-chambered  heart,  a more  or  less  heavy  covering  of  hair,  and 
suckle  their  young ; (48)  always  stand  erect ; (49)  are  found  as  the 
most  recent  fossils;'  (50)  include  man. 

Achievement  Test 

• 1.  What  is  the  name  of  at  least  one  animal  from  each  of  the  phyla 
of  the  invertebrates  and  the  vertebrates? 


TESTS 


279 


2.  What  are  the  (lifTerencos  between  spiders  and  insects? 

3.  \\'Iierc  wouUl  you  look  for  liydra,  crayfish,  clams,  and  toads? 

4.  How  can  you  distin.a'uish  between  an  aini)hibian  and  a rci)tilc? 

5.  What  is  the  life  history  of  a fro”-  common  in  your  locality? 

6.  Where  and  what  fossils  may  be  found  in  your  locality? 

Practical  Problems 

1.  Make  a collection  of  all  invertebrates  that  you  can  find  in  your 
community.  Classify  them  and  arrange  them  in  evolutionary  order. 

2.  Fill  out  the  following  table. 


Structures 

Fish 

Amphibian 

Reptile 

Bird 

Mammal 

Organs  of 
digestion 

Protective 

structures 

Locomotion 

Organs  of 
breathing 

Organs  of 
excretion 

Parts  of  nervous 
system 

Sense  organs 

Useful  Reference  Books 

Chapman.  Handbook  of  Birds  of  Eastern  North  America.  Appleton, 
1932. 

Ditmars,  Snakes  of  the  World.  Macmillan,  1931. 

Dickerson,  Frog  Book.  Doubleday,  Doran,  1906. 

Hornaday,  American  Natural  History.  Charles  Scribner’s  Sons,  1914. 
Jordan  and  Evermann,  American  Food  and  Game  Fishes.  Doubleday, 
Doran,  1923. 

Lucas,  Animals  of  the  Past.  Amer.  Mus.  of  Nat.  Hist.,  1922. 

Palmer,  Field  Book  of  Nature  Study.  Comstock,  1927. 


SURVEY  QUESTIONS 

Do  you  know  how  plants  are  helpful  or  harmful  to  one  another  ? What 
is  a balanced  aquarium?  What  is  an  oxygen  cycle?  A carbon  cycle? 
What  do  you  understand  by  symbiosis?  What  are  parasites?  What 
factors  caused  the  type  of  vegetation  shown  in  this  desert  in  Arizona  ? 


PUoto  by  Frank  M,  Wheat 


UNIT  IX 

WHAT  EFFECTS  HAVE  THE  SURROUNDINGS  ON  THE 
LIVES  OF  PLANTS  AND  ANIMALS? 

Preview.  If  bees,  in  their  search  for  nectar,  visited  the  flowers 
of  an  apple  tree,  they  would  make  possible  the  development  of 
apples  on  this  tree.  This  development  might  be  hindered  by 
other  insects  which  prey  upon  ripening  fruit,  in  which  case  man 
may  step  in,  and  with  a poisonous  spray  kill  the  insects  and  thus 
save  the  fruit. 

But  how  did  the  bees  benefit  by  this  visit?  They  obtained 
nectar  to  make  into  honey,  and  pollen  to  make  into  bee  bread 
for  feeding  the  young.  These  will  in  turn  replenish  the  hive  the 

280 


PREVIEW 


281 


following  year  with  more  workers,  that  will  make  honey  for 
man,  unless  some  prowling  animal  robber  gets  it  first.  Charles 
Darwin  saw  this  interrelationship  of  plant  and  animal  as  a chain 
of  haiipenings  when  ho  pointed  out  that  the  size  of  the  clover 
crop  in  England  depended  upon  the  number  of  cats  in  a given 
region.  His  friend  Huxley  immediately  went  him  one  better  and 
said  the  clover  crop  depended  upon  the  number  of  old  maids. 
^^’hen  asked  to  explain,  he  gave  the  following  chain  of  events. 
Old  maids  keep  cats,  cats  prey  upon  mice,  mice  eat  bumblebees 
and  also  provide  them  with  places  to  build  their  nests,  bumble- 
bees pollinate  clover,  and  on  this  pollination  depends  the  size  of 
the  next  year’s  crop.  A perfectly  logical  chain  of  events! 

This  unit  will  explain  to  us  some  of  these  interrelationships 
between  plants  and  animals  and  may  also  show  us  how  man  some- 
times interrupts  or  displaces  a link  in  the  chain  of  interrelation- 
ships, which  results  in  changing  completely  the  fauna  ^ or  flora  ^ of 
a region.  The  best  example  of  this  perhaps  is  the  case  of  the  man 
in  Australia  who  wanted  a bit  of  watercress  to  remind  him  of  the 
old  daj^s  in  bonny  England.  Today,  the  rivers  of  Australia  are 
choked  with  this  same  cress,  which,  having  no  enemies  and  finding 
conditions  favorable,  has  literally  overrun  the  brooks  and  rivers. 

We  cannot  fail  to  see  that  some  animals  and  plants  are  fitted  to 
live  under  conditions  totally  unsuitable  for  others.  A fish  could 
not  live  under  the  same  conditions  as  a lizard,  nor  would  we  expect 
to  find  seaweeds  growing  in  desert  places  where  cactuses  are 
found.  Such  things  are  quite  evident,  and  if  we  travel  in  this 
vast  country  of  ours  we  shall  also  find  that  plants  and  animals 
live  in  more  or  less  different  communities,  and  that  there  are  dif- 
ferent climatic  zones,  in  which,  because  of  common  needs,  certain 
types  of  animal  or  plant  life  are  always  found.  Such  zones  can 
be  seen  particularly  well  on  a mountainside.  Any  one  who  has 
climbed  the  Katahdin  mountain  in  Maine,  or  Mt.  Washington  in 
New  Hampshire,  or  any  10,000-foot  peak  of  the  Rockies  or  Sierra 
Nevada,  has  had  the  experience  of  working  his  way  through  forests 
out  into  an  area  of  stunted  trees  and  finally  out  on  the  bare  rocks 

1 Fauna  (fo'nd)  : the  animals  of  a given  region. 

2 Flora  (flo'rd)  : the  native  plants  of  a given  region. 


282 


LIVES  OF  PLANTS  AND  ANIMALS 


above  the  timber  line.  We  might  think  that  these  different  regions 
(life  zones)  were  due  entirely  to  temperature.  On  the  mountain- 
side this  is  largely  true,  but  we  find  that  all  the  factors  we  have 
already  discussed  are  at  work  determining  the  places  where  living 
things  shall  be  found.  The  amount  of  water  present  in  the  soil, 
the  kinds  of  soils  there,  the  ranges  in  the  temperature,  the  wind, 
and  many  other  factors  play  their  parts.  One  big  problem  in  the 
geographical  distribution  of  organisms  is  to  find,  first,  adaptations 
of  organisms  for  life  in  various  localities,  and  then  the  place 
where  a certain  kind  of  living  thing  has  made  its  start  in  an  area, 
and  finally  how  life  spreads  from  this  area  to  other  areas. 

On  the  whole,  nature  establishes  a balance  in  life  and  there 
is  give  and  take  between  all  living  things.  That  part  of  biology 
which  deals  with  the  relationships  of  organisms  to  each  other  and 
to  their  environments  is  called  ecology. 

PROBLEM  I.  WHAT  GENERAL  BIOLOGICAL  RELATIONS 
EXIST  BETWEEN  PLANTS  AND  ANIMALS? 

Each  place  where  plants  and  animals  are  found  living  together 
supports  a characteristic  community  of  plants  and  animals.  This 
living  together  seems  to  be  determined  largely  by  the  conditions 
of  the  environment  in  which  they  are  placed.  Groups  living 
together  in  a pond  or  slow-flowing  stream  will  be  quite  different 
from  groups  living  in  a rapid  mountain  stream  or  in  the  ocean.  The 
communities  of  animals  and  plants  living  in  dry  or  desert  localities 
would  differ  to  a still  greater  extent  from  any  of  those  first  men- 
tioned. Only  certain  animals  and  plants  will  live  and  flourish  in  an 
indoor  aquarium,  but  in  all  such  groups  the  animals  and  plants 
living  together  have  certain  fundamental  relationships  to  each  other 
and  to  their  surroundings. 

Study  of  a balanced  aquarium.  Perhaps  the  best  way  for  us 
to  understand  this  relation  between  plants  and  animals  is  to 
study  an  aquarium  in  which  plants  and  animals  live  and  in 
which  a balance  has  been  established  between  the  plant  life  on 
one  side  and  animal  life  on  the  other.  Here  we  see  many  evidences 
of  the  relationship  between  the  environment  and  the  living  things 
in  the  water.  The  plants  are  buoyed  up  by  the  water,  they  do  not 


A BALANCED  AQUAIUUM 


283 


have  Stroup;  stems,  and  the  loaves  are  usually  divided  and  present 
little  resistance  to  the  water.  The  roots  are  small  and  are  not  of 
much  use  as  an  anchor.  The  fish  are  obviously  adapted  for  life 
in  the  water,  as  we  have  already  seen.  Even  the  snails  have 
adaptations  for  their  life  in  the  water. 

We  have  learned  that  green  plants,  in  favorable  conditions  of 
sunlight,  heat,  moisture,  and  with  a supply  of  raw  food  materials, 
give  off  oxygen  as  a by-product  while  manufacturing  food  in  their 
green  cells.  We  know 
the  necessary  raw  ma- 
terials for  carbohydrate 
manufacture  are  carbon 
dioxide  and  water,  while 
nitrogenous  material  is 
necessary  for  the  making 
of  proteins  within  the 
plant.  In  previous  ex- 
periments we  have 
proved  that  carbon  di- 
oxide is  given  off  by 
living  things  when  oxida- 
tion occurs  in  the  body.  The  crawling  snails  and  the  swimming 
fish  give  off  carbon  dioxide  which  is  dissolved  in  the  water ; the 
plants  themselves,  at  all  times,  oxidize  food  within  their  bodies, 
and  so  must  pass  off  some  carbon  dioxide.  The  green  plants  in 
the  daytime  use  up  the  carbon  dioxide  obtained  from  the  various 
sources  and,  with  the  water  which  they  take  in,  manufacture 
carbohydrates.  While  this  process  is  going  on,  oxygen  is  given  off 
to  the  water  of  the  aquarium,  and  is  used  by  the  animals  there. 

The  plants  are  continually  growing,  but  the  snails  and  fish 
eat  parts  of  the  plants.  Thus  the  plant  life  gives  food  to  the 
animals  within  the  aquarium.  The  animals  give  off  certain 
nitrogenous  wastes.  These  materials,  with  other  nitrogenous 
matter  from  dead  animals  and  parts  of  the  plants,  form  part  of 
the  raw  material  used  for  protein  manufacture  in  the  plant.  This 
nitrogenous  matter  is  prepared  for  use  by  several  different  kinds 
of  bacteria  which  break  down  the  dead  bodies  and  change  the 


Why  will  it  not  be  necessary  to  change  the  water  in  this 
aquarium  ? 


284 


LIVES  OF  PLANTS  AND  ANIMALS 


material  into  soluble  nitrates  which  can  be  absorbed  by  the  plants. 
The  green  plants  manufacture  food,  the  animals  eat  the  plants 
and  give  off  carbon  dioxide  and  nitrogenous  waste,  from  which  the 
plants  in  turn  make  more  food  and  living  matter.  The  plants 
give  oxygen  to  the  animals,  and  the  animals  give  carbon  dioxide 
to  the  plants.  Thus  a balance  exists  between  the  plants  and 
animals  in  the  aquarium. 

Practical  Exercise  1.  Make  a debit  and  credit  balance  sheet  illustrating  the 
relations  existing  in  a balanced  aquarium. 

What  would  be  the  condition  of  the  balance  sheet  if  the  aquarium  were 
put  in  a dark  room  ? If  several  extra  snails  and  fish  were  introduced  ? 

Relations  between  green  plants  and  animals.  What  goes  on 
in  the  aquarium  is  an  example  of  the  relation  existing  between  all 
green  plants  and  animals.  Everywhere  in  the  world  green  plants 
are  making  food  which  becomes,  sooner  or  later,  the  food  of 
animals.  Man  does  not  feed  to  a great  extent  upon  leaves,  but 
he  eats  many  roots,  stems,  fruits,  and  seeds.  When  he  does  not 
feed  directly  upon  plants,  he  eats  the  flesh  of  plant-eating  animals, 
which  in  turn  feed  directly  upon  plants.  And  so  it  is  the  world 
over;  the  plants  are  the  food  makers  and  supply  the  animals. 


carbon  dioxidfe 
(CO*) 


plants 

v/ifh  chlorophyll 
“build  |bod:  which 
coritains  stored 
<zn<zT^^  obtained 
•fr-om.  tJae. 

^UY2 

enei'-gy  |romthesUT2 


siraple 

/ 


yr 


/ 1 

eney^y  released 


Plants  and  animals  on  the  earth  show  the  same  relation  to  each  other  as  do  the  plants  and 
animals  in  a balanced  aquarium.  Can  you  explain,  with  the  aid  of  the  diagram,  why  this  is  true  ? 


This  is  well  seen  in  the  distribution  of  grazing  animals  in  relation 
to  forage  crops.  Green  plants  also  give  to  the  atmosphere  every 
day  a very  considerable  amount  of  oxygen,  which  the  animals  use. 


CARBON  AND  OXYGEN  CYCLES 


285 


Self-Testing  Exercise 

(1)  and (2)  live  together  in  communities.  The  place 

where  they  live  together  is  called  a (3).  A balanced  aquarium 

shows  the  (4)  between  animals  and  plants,  the  former  give 

(5) (6),  and (7)  wastes  to  the  plants  which  in 

turn  (8)  organic  food  and  oxygen  which  the  (9) 

(10).  This  illustrates  the  give  and  take  between  plants  and 

animals  in  the (11). 

PROBLEM  II.  WHAT  DO  WE  MEAN  BY  THE  NITROGEN, 
OXYGEN,  AND  CARBON  CYCLES  IN  NATURE? 

Nitrogen  cycle.  The  animals  supply  much  of  the  carbon  dioxide 
that  the  plant  uses  in  carbohydrate  making.  They  supply  some  of 
the  nitrogenous  matter  used  by  the  plants,  another  part  being 
given  the  plants  from  the  dead  bodies  of  other  plants,  and  still 
another  part  being  prepared  from  the  nitrogen  of  the  air  through 
the  agency  of  bacteria  which  live  upon  the  roots  of  certain  plants. 
These  bacteria  are  the  only  organisms  that  can  take  nitrogen  from 
the  air.  Thus,  in  spite  of  all  the  nitrogen  in  the  atmosphere, 
plants  and  animals  are  limited  in  the  amount  available.  Eaten 
in  protein  food  by  an  animal,  nitrogen  may  be  given  off  as  nitroge- 
nous waste,  get  into  the  soil,  and  be  taken  up  by  a plant  through 
the  roots.  Eventually  the  nitrogen  forms  part  of  the  food  supply 
in  the  body  of  the  plant,  and  then  may  become  part  of  its  living 
matter.  When  the  plant  dies,  the  nitrogen  is  returned  to  the  soil. 
Thus  the  usable  nitrogen  is  kept  in  circulation.^ 

Practical  Exercise  2.  Illustrate  what  is  meant  by  the  nitrogen  cycle  with 
reference  to  your  own  environment. 

Make  a diagram  to  show  the  way  the  nitrogen  cycle  works  out  in  life  on 
the  earth. 

Carbon  and  oxygen  cycles.  There  are  also  two  other  cycles 
in  nature  that  are  easily  seen.  Oxygen  dissolved  in  the  water  is 
taken  up  by  the  fish  in  the  aquarium,  and  is  released  in  the  form  of 
an  oxide  of  carbon  or  carbon  dioxide.  In  this  form  it  is  taken 

1 A small  amount  of  nitrogen  gas  is  returned  to  the  atmosphere  by  the  action  of 
the  decomposing  bacteria  on  the  ammonia  compounds  in  the  soil.  (See  figure  of 
nitrogen  cycle.) 


286 


LIVES  OF  PLANTS  AND  ANIMALS 


How  does  the  diagram  of  an  amoeba,  or  head  of  a fish,  or  a cross  section  through  the 


by  green  plants  in  the  aquarium  and  during  the  starch-making 
process  in  the  sunlight  it  is  released  as  a by-product  in  the  form 
of  pure  oxygen  gas.  It  is  now  in  the  water  ready  for  the  fish  to 
use  again.  This  same  process  is  repeated  on  a large  scale  wherever 
we  find  green  plants,  sunlight,  and  animals. 

The  carbon  cycle  can  also  easily  be  shown.  The  fish  in  the 
aquarium  eats  some  of  the  green  plant,  thus  getting  carbohydrate 
food  which  contains  the  element,  carbon.  As  they  swim  about 
releasing  energy  they  oxidize  the  carbohydrate  food  in  their 
bodies  and  thus  liberate  the  carbon  in  the  form  of  carbon  dioxide. 
This  gas  is  used  by  the  green  plant  in  the  sunlight  to  build  carbo- 
hydrates and  the  cycle  is  completed  again.  Of  course,  the  aqua- 
rium shows  what  goes  on  in  a larger  way  in  the  world  of  living  things. 

Practical  Exercise  3.  After  carefully  studying  the  text  make  a diagram  in 
the  form  of  a circle  to  illustrate  the  way  the  carbon  cycle  exists  in  nature.  Use 
arrows.  Make  a second  diagram  to  show  the  oxygen  cycle  in  nature. 


Self  Test  Exercise 

The (1)  available  for  plant  and  animals  is (2)  over 

and  over  again  by  plants  by  making (3)  (4),  Cer- 
tain   (5)  break  down  substances  containing (6)  and 

put  it  into  the (7)  as (8)  organic  material.  Then 

green  plants  take  it  up  and  (9)  it  into  (10)  food 

and (11)  matter.  There  are (12)  and (13) 

cycles  in  nature.  Oxygen  is  given  off  by (14)  plants,  is  used 

by  (15),  and  breathed  out  as  an  (16)  of  carbon. 

Carbon  is  given  off  into  the  atmosphere  by  animals  as (17) 

(18)  and  is  used  by  (19)  plants  to  manufacture 

(20).  In  such  form  it  is (21)  by  animals  and  after 


SYMBIOSIS 


287 


body  of  an  insect,  with  the  lower  epidermis  of  a leaf  show  that  living  things  breathe? 


being (22)  in  the  body  is  passed  into  the  air  again  as 

(23)  (24),  thus  completing  the  cycle. 


PROBLEM  III.  WHAT  IS  SYMBIOSIS  AND  HOW  DOES  IT  DIFFER 
FROM  PARASITISM? 


Symbiosis.  Plants  and  animals  are  seen  in  a general  way  to 
be  of  mutual  advantage  to  each  other.  Some  plants,  called 
lichens,  show  this  mutual  partnership  in  the  following  interesting 
way.  A lichen  is  composed  of  two  kinds  of  plants,  one  of  which 
at  least  may  live  alone,  but  the  two  plants  have  formed  a partner- 
ship for  life,  and  have  divided  the  duties  of  such  life  between  them. 
In  most  lichens  the  alga,  a green  plant,  forms  starch  and  nourishes 
the  fungus.  The  fungus,  in  turn,  produces  spores,  by  means  of 
which  new  lichens  are  started  in  life ; moreover,  the  alga  is 
usually  protected  by  the  fungus,  which  is  stronger  in  structure 
than  the  green  part  of  the  combination.  This  process  of  living 
together  for  mutual  advantage  is  called  symbiosis  (sim-bi-o'sis). 
Some  animals  also  combine  with  plants ; for  example,  the  hydra 
with  certain  of  the  one-celled  algae. 

Animals  also  frequently  live  in 
this  relation  to  each  other,  the 
tiny  protozoans  living  in  the  diges- 
tive tracts  of  the  termites  or  white 
ants.  These  little  animals  act  as 
digestive  cells  for  the  termites, 
making  it  possible  for  them  to 
digest  the  wood  fibers  on  which  they  live.  In  return  these  proto- 
zoans are  protected  by  their  hosts.  A somewhat  similar  situa- 


Aigae  and  fungi  in  a lichen.  Explain  this 
relationship. 


288 


LIVES  OF  PLANTS  AND  ANIMALS 


Lichen  on  a rock. 


How  do  lichens  differ  from  other 
plants  ? 


tion  prevails  in  our  own 
large  intestine,  where 
certain  types  of  useful 
bacteria  live.  They  help 
keep  down  the  putrefy- 
ing bacteria  while  receiv- 
ing a home  and  food  in 
return.  Other  examples 
are  the  bacteria  which 
live  symbiotically  in  the 
roots  of  certain  plants; 
and  the  sea  anemones 
which  are  carried  around 
on  the  shells  of  some 
hermit  crabs  to  places 
where  food  is  plentiful,  and  they  aid  the  crab  in  protecting  it  from 
its  enemies.  In  a general  way  the  food  relations  between  green 
plants  and  animals  may  be  said  to  show  a symbiotic  relationship, 

because  the  plants 
could  not  make  food 
without  the  wastes 
from  the  animals, 
and  the  animals 
could  not  exist  with- 
out foods  made  by 
green  plants. 

Parasitism.  Not 
all  life  is  give  and 
take.  Some  plants 
and  animals  live  at 
the  expense  of  others, 
giving  nothing  and 
taking  all.  Such 
plants  and  animals 
are  known  as  para- 

Mistletoe  on  the  branches  of  a sycamore  tree.  Notice  that  sitCS.  Examples  are 
the  branches  to  the  left  bear  no  leaves.  They  have  been  ’ . i i i 

killed  by  the  parasite.  Seen  in  the  dodder 


MAN  AND  THE  BALANCE  OF  LIFE 


289 


and  mistletoe  among  plants,  and  many  insects  and  worms,  among 
animals.  In  every  case,  the  parasite  lives  on  another  plant  or 
animal  known  as  its  host.  In  some  cases,  the  host  is  a temporary 
one,  and  in  others,  it  is  a permanent  one,  the  parasite  remaining 
with  it  until  death.  Many  plant  and  animal  diseases  are  caused  by 
parasites,  and  man  has  come  into  the  picture  to  such  an  extent  that 
ho  is  now  engaged  in  wiping  parasitic  disease  off  the  face  of  the 
earth. 

Practical  Exercise  4.  Give  as  many  examples  of  symbiosis  as  you  can,  using 
references  and  museum  material.  Explain  how  symbiosis  in  a large  sense 
exists  in  the  world  about  you. 

Self-Testing  Exercise 

Symbiosis  is  a living (1)  for (2) (3).  It 

is  a (4),  sometimes  between (5)  and (6)  as 

in  the  hydra  and  algae  and  sometimes  between  two  plants  as  the 

(7)  and  the (8)  in  a lichen ; or  between  two  animals 

as  in  the  (9)  (10)  and  (11)  anemone.  A 

(12)  lives  on  another  (13)  organism  known  as  a 

(14),  taking  food  from  it  but  giving (15)  in (16). 

Many  parasites  do (17),  causing (18)  or (19)  of 

their  hosts (20)  is  continually  combating (21). 

PROBLEM  IV.  HOW  DOES  MAN  DISTURB  THE  BALANCE  OF 
NATURE? 

Man  and  the  balance  of  life.  Man  has  come  to  disturb  the 
balance  of  life  in  many  ways.  He  has  introduced  water  to  regions 
and  made  them  support  plant  and  animal  life  some  of  which 
are  parasites ; he  has  placed  new  plants  in  new  localities  and  had 
them  exterminate  the  native  plants ; and  unwittingly  he  has  dis- 
turbed the  balance  which  nature  had  established.  He  has  brought 
into  this  country,  insects  which  are  doing  millions  of  dollars  of 
damage  every  year,  witness  the  browntail  moth  and  the  gypsy 
moth  in  New  England,  and  he  is  now  going  to  the  ends  of  the 
earth  to  find  the  natural  enemies  of  these  imported  pests ; as  is  seen 
in  the  importation  of  the  ladybird  beetle  from  Australia  to  feed 
upon  the  imported  citrus  scale  insects  brought  to  California  from 
Australia  in  1868.  He  is  killing  off  wolves  and  coyotes  which 


290 


LIVES  OF  PLANTS  AND  ANIMALS 


Wright  Pierce 

Compare  these  environmental  conditions  with  those  on  the  next  page.  What  differences  in 
animal  life  would  you  expect  to  find? 


prey  upon  our  deer  and  he  is  protecting  useful  birds  which  prey 
upon  harmful  insects.  Man  is  probably  making  more  changes 
in  life  on  the  earth  than  any  other  living  factor.  But,  on  the 
whole,  his  influence  is  beneficial,  as  we  will  see  in  the  units  which 
follow. 

Practical  Exercise  6.  What  is  a parasite?  Give  three  examples  other  than 
those  stated  in  the  text. 

Practical  Exercise  6.  How  could  a student  become  a parasite  in  the  school  ? 
Explain.  How  might  you  become  a parasite  at  home  ? How  can  you  avoid 
this? 

Practical  Exercise  7.  Look  up  the  term  m-prophyte.  How  does  it  differ 
from  a parasite  ? Give  examples  of  each  in  your  environment,  if  possible. 

Self-Testing  Exercise 

A (1)  exists  in  (2)  between  organisms  living  in  a 

region.  Many (3)  prey  upon  others,  using  them  as (4) 

and  thus  holding  them  in  check.  Man  has  often (5)  this  balance 

by (6)  new (7)  or (8). 

PROBLEM  V.  HOW  DO  THE  FACTORS  OF  THE  ENVIRONMENT 
AFFECT  ECOLOGICAL  RELATIONSHIPS? 

Ecology  is  the  study  of  plants  and  animals  in  relation  to  their 
natural  surroundings.  Living  things  can  be  shown  to  be  affected 


TK.MPEKATUKE 


291 


.4.-  , 


Wright  Pierce 


In  a desert,  we  find  that  plants  are  succulent  and  have  spines,  bristles,  and  rigid  walls.  Why? 

by  two  general  sets  of  factors  in  their  environment,  forces  and 
things.  These  forces  are  temperature,  light,  gravity,  and,  to  a 
lesser  extent,  such  factors  as  the  presence  or  absence  of  winds,  the 
presence  or  absence  of  electrical  storms,  and  the  pressure  of  the 
atmosphere. 

The  things  that  affect  living  plants  and  animals  are  natural  or 
man-made  objects  with  which  they  come  in  contact,  such  as 
foods  of  all  kinds  and  the  presence  of  other  living  or  dead  plants 
and  animals  in  the  vicinity. 

Temperature.  We  have  already  observed  the  effect  of  tempera- 
ture on  the  growth  of  seedlings.  We  know  that  certain  tropical 
forms  of  life  flourish  only  in  heated  areas,  and  that  there  are  plants, 
such  as  the  lichens  of  the  frozen  tundras  of  the  north,  that  will 
grow  only  in  extreme  cold.  Animal  life  can  equally  well  be  shown 
to  be  dependent  upon  temperature  conditions.  One  of  the  most 
striking  examples  of  this  was  seen  in  1882  when  fish,  abundant  in 
the  Gulf  Stream,  were  found  dead  and  dying  by  the  millions  in  a 
large  area  off  the  eastern  coast  of  the  United  States.  This 
catastrophe  was  believed  to  have  been  caused  by  the  cold  arctic 
current  being  shifted  by  long-continued  easterly  and  northerly 
winds,  the  cold  water  displacing  that  of  the  Gulf  Stream,  thus 


292 


LIVES  OF  PLANTS  AND  ANIMALS 


In  the  tropics,  where  heat  and  rainfall  are  plentiful,  vegetation  is  abundant.  Why  is  this  true  ? 

causing  the  death  of  the  fish.  Fish  breeders  know  how  sensitive 
young  fish  are  to  changes  of  temperature,  and  any  fisherman  knows 
that  the  trout  will  go  into  deep  water  or  will  lie  in  the  cool  spring 
holes  during  hot  weather. 

We  know  plants  either  die  or  become  dormant  in  winter,  while 
many  animals  hibernate  (become  inactive)  during  the  cold 
weather.  But  we  are  not  so  apt  to  think  of  the  effect  of  con- 
tinuous cold  or  equally  continuous  warmth  as  seen  in  the  arctic 
regions  or  in  the  tropics.  The  wealth  of  tropical  vegetation  and 
animal  life  is  due  in  part  to  the  higher  temperature.  Animals 
develop  faster  and  go  more  quickly  through  their  life  cycle.  In 
southern  California  the  heat  often  transforms  garden  biennials 
into  annuals  and  the  converse  is  seen  in  cold  countries  where 
annuals  may  be  changed  for  a time  to  biennials.  High  temperature 
seems  to  increase  the  amount  of  certain  pigment  in  birds  and  other 
animals  so  that  they  are  more  highly  colored  in  hot  climates. 

On  the  other  hand,  some  fish,  as  the  trout  and  salmon,  are 
found  only  in  cold  water.  Dr.  H.  B.  Ward  of  the  University  of 
Illinois  says  that  when  salmon  ascend  a stream  to  lay  their  eggs 
they  will  invariably  take  the  cooler  branch  of  the  river.  In 
ascending  the  side  of  a mountain  we  find  different  types  of  animals 


Lid  1 IT 


293 


Am.  Mus.  Natural  Hist. 

Mosses,  lichens,  and  dwarf  shrubs  are  the  only  vegetation  found  in  the  arctic  region, 
(tundra  zone). 


and  plants  at  different  elevations,  the  determining  factor  being 
largely  differences  in  temperature.  Animals  normally  living  in 
the  tropics,  if  brought  to  this  country,  may  live,  but  rarely  repro- 
duce. In  such  cases  all  the  environmental  factors  except  that  of 
temperature  are  the  same. 

Light.  It  is  easy  to  pick  examples  of  the  effect  of  light  on  green 
plants.  For  example,  we  have  the  turning  movements  of  leaves 
and  stems,  the  shape  and  color  of  plant  leaves,  and  the  presence  or 
absence  of  plants  in  a given  region.  But  only  recently  has  it  been 
discovered  that  the  flowering  of  certain  plants  depends  on  a lack, 
rather  than  an  abundance,  of  sunlight.  Such  is  the  chrysan- 
themum, which  flowers  when  the  days  become  shorter. 

Plants  and  animals  are  sometimes  grouped  according  to  the  in- 
tensity of  light  in  the  environment.  Their  activity  depends  upon 
light,  as  is  seen  in  the  comparative  activity  of  bees  on  a sunny  and 
on  a dark  day,  or  the  activity  at  night  of  some  nocturnal  animals, 
as  the  owl  or  coyote.  Green  plants  are  tremendously  changed  if 
kept  in  an  environment  lacking  in  light.  Compare  the  sprouts 
of  a potato  kept  in  darkness  with  one  grown  in  the  light. 

Examples  of  light  affecting  animals  are  many.  We  know  that 
many  animals  respond  negatively  to  strong  light,  as  owls,  bats, 

H.  BIO  — 20 


294 


LIVES  OF  PLANTS  AND  ANIMALS 


and  worms.  Many  animals  that  prey  on  other  animals  are  noc- 
turnal in  their  habits.  On  the  other  hand,  most  animals  can 
be  shown  by  experiment  to  respond  to  light  by  definite  turning 
movements.  The  well-known  flight  of  the  moth  to  death  in  the 
flame  of  a candle  is  an  example.  Experiments  on  the  tropisms  of 
insects  show  that  a mechanical  turning  to  the  source  of  light  is  a 
very  general  reaction  made  by  all  insects. 

Gravity.  The  roots  of  plants  respond  positively  to  gravity  by 
growing  toward  the  center  of  the  earth,  while  the  stems  respond 
negatively  by  growing  away  from  the  center  of  the  earth.  If  a 
plant  stem  which  usually  grows  erect  is  placed  in  a horizontal 
position,  it  will  soon  erect  itself.  This  response  is  readily  seen  in 
trees  and  grasses  which  have  been  beaten  down  by  wind  and  rain. 

If  boxes  containing  germinating  seeds  are  fixed  on  the  rim  of  a 
horizontally  placed  wheel  which  is  rotated  rapidly,  a force  stronger 
than  gravity  is  introduced  and  the  growing  stems  will  tend  to  grow 
toward  the  center  of  the  wheel  and  the  roots  will  grow  toward  the 
circumference. 

Water.  We  need  only  to  look  at  the  luxuriant  growth  of  plants 
along  a stream  or  irrigation  ditch  to  realize  the  part  water  plays 
in  plant  life.  To  anyone  who  has  visited  the  Imperial  Valley  of 
California,  where  water  has  made  the  desert  “ blossom  as  the  rose,” 
the  role  of  water  is  evident.  But  an  oversupply  of  water  kills  plants, 
as  we  can  see  along  the  shores  of  any  artificial  lake  where  the  trees 
standing  in  the  water  are  killed.  The  drying  up  of  lakes  has  been 
responsible  for  the  extermination  of  many  fish,  just  as  the  bringing 
of  water  to  new  localities  may  mean  new  animal  life  in  that  locality. 

We  have  seen  in  the  balanced  aquarium  some  of  the  adaptations 
necessary  for  life  there.  Plants  which  live  entirely  in  the  water 
often  have  slender  parts  with  finely  divided  leaves.  Their  roots 
are  apt  to  be  short  and  stout.  The  interior  of  such  a plant  is  made 
up  of  spongy  tissues  which  allow  the  air  dissolved  in  the  water  to 
reach  all  parts  of  the  plant.  If  the  plant  has  floating  leaves,  as  in 
the  pond  lily,  the  stomata  are  all  in  the  upper  side  of  the  leaf. 

Animal  life  is  also  restricted  to  those  forms  which  can  easily 
move,  feed,  and  breathe  in  water.  In  the  case  of  insect  larvae, 
as  the  mosquito,  we  often  find  adaptations  which  enable  them  to 


WATER 


295 


get  oxygen  from  the  air  or,  as  in  other  larvae,  by  gills  from  the  water. 
Animals  living  in  water  are  often  shaped  for  living  under  stones. 
They  are  frequently  jjrotected  from  their  enemies  by  having  the 
same  color  or  appearance  as  the  bottom  of  the  sea.  They  always 
have  devices  for  catching  their  food,  as  evident  in  the  mouth  parts 
of  the  crayfish,  or  cilia  in  unicellular  animals  which  sweep  food  in 
a water  current.  The  tiny  microscopic  animals  and  plants,  called 
collectively  the  plankton,  which  serve  as  food  for  other  animals,  are 


Wright  Pierce 


On  the  left  side  of  the  illustration,  we  see  only  the  type  of  vegetation  that  is  charac- 
teristic of  the  desert,  while  on  the  right,  where  the  land  has  been  well  irrigated,  a grove  of 
orange  trees  produces  an  abundant  yield  of  fruit. 


found  only  in  the  upper  levels  of  the  water,  because  light  penetrates 
only  a few  feet  and  the  oxygen  supply  is  deficient  at  greater  depths. 

Sunlight  heats  the  water  rather  uniformly  to  a depth  of  30  to 
50  feet  in  small  bodies  of  water  and  to  a greater  depth  in  the  ocean, 
due  to  the  stirring  up  of  the  surface  water  by  wind.  Great  depths 
have  very  low  temperatures.  Life  there  is  naturally  much  re- 
stricted and  few  living  things  are  found.  There  are  some  fishes 
living  at  great  ocean  depths  which  are  adapted  to  withstand  the 
great  pressure  of  the  tons  of  water  pressing  in  upon  them.  How- 
ever, we  know  very  little  about  their  internal  structure  because  they 


296  LIVES  OF  PLANTS  AND  ANIMALS 

burst  when  brought  to  the  surface  where  the  pressure  is  so  much 
less.  Few  forms  of  life  have  adaptations  which  enable  them  to 
get  along  with  the  shortage  of  oxygen  at  greater  depths. 


R.  I.  Nesmith 

The  beavers  are  social  animals  and  live  in  lodges,  the  entrances  to  which  are  under  water. 
In  order  to  raise  the  stream  level  high  enough  to  protect  these  lodges,  they  build  dams  of  logs, 
sticks,  sod,  mud,  and  other  debris.  Do  you  know  how  they  get  the  logs  to  the  dam? 

Plants  growing  in  dry  or  desert  conditions,  as  cactus,  sagebrush, 
and  aloe,  show  a leaf  surface  invariably  reduced,  sometimes  in  the 
form  of  spines,  as  in  the  cactus.  The  stem  may  be  thickened  to 
store  water  and  a covering  of  hairs  or  some  other  material  may 
be  present  to  lessen  the  loss  of  moisture  by  evaporation.  If  the 
water  or  saturated  soil,  in  which  the  plant  lives,  contains  salts, 
such  as  sea  salt  or  the  alkali  salts  of  some  of  our  western  lakes, 
plants  living  there  show  many  characteristics  which  those  in  desert 
conditions  show. 

Animals  living  under  such  conditions  are  usually  few  and 
restricted  to  those  that  can  burrow  to  depths  so  that  they  may 
escape  the  heat,  or  lizards  and  snakes  which  are  able  to  escape  the 
heat  by  taking  shelter  under  rocks.  All  forms  of  animal  life  found 
there  are  able  to  live  on  small  quantities  of  water.  The  desert 


VARYING  FACTORS 


297 


kangaroo  rat  comes  out  at  night  and  burrows  deep  in  the  sand 
during  the  day.  One  of  the  ground  squirrels  avoids  the  hot  sun 
by  running  from  one  bush  to  another  to  get  shade.  Both  of  these 
animals  die  if  exposed  to  the  sun  for  any  length  of  time. 

Practical  Exercise  8.  Make  a list  of  all  the  plants  in  your  locality  that  are 
dependent  upon  a large  supply  of  water;  those  which  can  exist  with  a very 
small  amount  of  water. 

Soil  conditions.  Plants  grow  only  in  soils  to  which  they  are 
adapted.  Some  plants,  as  the  blueberry,  require  acid  soils,  while 
others  are  killed  by  acid  in  the  soil.  The  liming  of  soils  is  one 
e.xample  of  how  the  farmer  keeps  the  soil  in  condition  for  the  crops 
he  is  growing.  The  type  of  soil  also  affects  the  animals  living  in 
them.  Alud,  sand,  or  clay  will  each  contain  different  species  and 
numbers  of  plants  or  animals.  Earthworms,  for  example,  are  not 
found  living  in  acid  soils. 

Food  conditions.  For  both  plants  and  animals  food  is  a factor 
which  determines  the  presence  or  absence  of  life.  Mineral  matter 
is  so  necessary  for  the  growth  of  plants  that  manure  or  artificial 
fertilizer  is  employed  to  fill  the  need  where  the  element  nitrogen 
is  lacking.  The  presence  of  animal  life  in  water  is  often  dependent 
upon  the  presence  of  plankton  or  minute  forms  of  plant  and 
animal  life  which  live  near  the  surface  of  larger  bodies  of  water. 
Chemical  substances  necessary  for  plants  and  animals  often  de^ 
termine  where  they  will  live. 

Varying  factors.  Other  factors,  such  as  strong  winds,  electricity 
in  the  atmosphere,  the  pressure  of  the  air  at  different  altitudes,  and 
the  presence  of  dust  or  chemical  fumes  in  the  atmosphere,  may  all 
play  decided  parts  in  determining  what  living  things  may  exist  in 
given  localities. 

Practical  Exercise  9.  List  all  the  factors  of  the  environment  that  affect 
your  daily  life  and  give  an  example  of  how  each  one  affects  you.  How  does 
water  affect  the  life  in  your  community?  What  effect  has  temperature  on 
plants  in  your  locality?  Do  you  know  any  places  near  your  home  where  un- 
favorable factors  in  the  environment  prevent  life?  Are  such  factors  forces 
or  things  ? Explain. 

Practical  Exercise  10.  Make  a table  naming  all  the  factors  of  the  environ- 
ment which  affect  plants  and  animals  and  show  how  each  factor  affects  both 
plants  and  animals. 

Practical  Exercise  11.  From  reference  books,  obtain  a list  of  plants  and 
animals  adapted  to  live  under  conditions  lacking  water ; on  alkali  plains ; in 


298 


LIVES  OP  PLANTS  AND  ANIMALS 


salt  water;  in  a fresh-water  lake.  What  adaptations  would  the  plants  and 
animals  in  the  above  list  show?  (Read  Jordan  and  Kellogg,  Animal  Life,  or 
Kinsey’s  Introduction  to  Biology.) 


Self-Testing  Exercise 

(I) (2)  are  affected  by  the  factors  of  the 

(3),  such  as (4), (5), (6),  and (7)- 

Plants  living  in  water  have (8)  tissues  which  hold (9) 

and  are  apt  to  have  (10)  leaves  and  (11)  roots. 

Animals  living  in  water  show (12)  for  such  life.  The 

(13)  of  the  water  is  of  much  importance  to  the (14)  or 

(15)  living  in  it.  At  great  depths  it  is  very (16).  Lack  of 

water  results  in  adaptations  in  plants  for (17)  (18) 

such  as  (19)  or  (20)  or  (21)  stems. 

Desert  animals  can  get  along  without  much  water,  but  they 

(22)  in  the  ground  or  keep  in  the  (23)  much  of  the  time. 

Temperature  is  a very  important  (24)  in  determining  not 

only  the (25)  and (26)  found  in  a given (27) 

but  also  how  they  will (28).  Animals  and  plants 

(29)  (30)  in  hot  areas,  as  witness  the  changing  of  garden 

(31)  into  (32)  in  southern  California.  Many  fish, 

as  trout  or  salmon,  are  only  found  in  (33)  water.  Some 

animals  can  only  live  in  water  containing  certain  (34). 

Plants  and  animals  may  be  influenced  not  only  by  the (35) 

but  also  by  the (36)  of  light. 


PROBLEM  VI.  WHY  DO  PLANTS  AND  ANIMALS  FORM 
COMMUNITIES? 

Societies.  All  of  the  factors  referred  to  act  upon  the  plants  we 
find  living  together  in  a forest,  a sunny  meadow,  along  a roadside, 
or  at  the  edge  of  a pond.  Any  one  familiar  with  the  country 
knows  that  we  find  certain  plants,  and  only  those  plants,  living 
together  under  certain  conditions,  and,  in  a similar  way,  only 
certain  animals  will  be  found  to  be  associated  together. 

Plants  and  animals  associated  under  similar  conditions,  as  those 
of  a forest,  meadow,  or  swamp,  are  said  to  make  up  an  association 
or  community.  If  we  investigate  such  an  association,  we  find  it 
to  be  made  up  of  certain  dominant  species  of  plants ; that  here  and 


SOCIETIES 


2U9 


there  definite  communities  exist,  made  up  of  groups  of  the  same 
kind  of  plants,  while  certain  animals  will  be  found  living  on  the 
plants  or  among  them.  Evidently  conditions  of  food  and  shelter 
are  responsible  for  this  close  association.  We  can  see  that  each 
one  of  these  plant  groups  in  the  community  evidently  came 
originall}"  from  a single  individual  which  flourished  under  the 
peculiar  conditions  of  soil,  water,  light,  etc.,  that  were  found  in 
this  spot.  These  single  plants  have  evidently  given  rise  to  like 
plants  which  made  up  a family  group,  and  thus  have  popu- 
lated the  locality.  This  is  often  seen  in  a pine  grove,  or  in  an 


Wright  Pierce 


A plant  society.  Can  you  name  the  various  plants  that  are  living  together  in  this  group? 

What  conditions  and  adaptations  make  it  possible  for  them  to  live  together  in  one  society  ? 

area  covered  almost  exclusively  with  ferns.  Later,  seeds  of  other 
plants  may  be  carried  there  by  the  wind,  birds,  or  other  animals, 
and  we  find  widely  different  plants  living  under  similar  conditions. 
They  all  need  the  same  substances  from  the  air,  the  water,  and  the 
soil.  They  all  need  sunlight ; they  use  the  same  food.  Therefore 
there  must  be  competition  among  them,  especially  between  those 
near  to  each  other.  The  plants  which  are  strongest  and  best 
fitted  to  get  what  they  need  from  their  surroundings,  live ; the 
weaker  ones  are  crowded  out  and  die. 

But  their  lives  are  not  all  competition.  The  dead  plants  and 
animals  give  nitrogenous  material  to  the  living  ones,  from  which 
the  latter  make  living  matter ; some  bacteria  provide  certain  of 
the  green  plants  with  nitrogen;  many  of  the  green  plants  make 


300 


LIVES  OF  PLANTS  AND  ANIMALS 


food  for  other  plants  lacking  chlorophyll,  while  some  algae  and 
fungi  actually  live  together  in  such  a way  as  to  be  of  mutual  benefit 
to  each  other.  The  larger  plants  may  shelter  the  smaller  ones, 
protecting  them  from  wind  and  storm,  while  the  trees  provide 
humus  which  holds  the  moisture  in  the  ground,  giving  it  off  slowly 
to  other  plants.  Animals  scatter  seeds  far  and  wide,  and  man  may 
even  start  entire  colonies  in  new  localities. 

Practical  Exercise  12.  Describe  some  plant  or  animal  community  you 
have  seen.  What  forms  of  life  are  associated  together  ? 

Could  you  have  a plant  community  in  the  laboratory  or  school  yard  ? What 
conditions  would  you  expect  to  find?  What  plants  living  together? 

Self-Testing  Exercise 

Conditions  of (1)  (2)  (3)  and  

(4)  are  the  chief  factors  which (5)  what  plants  and  animals 

will  live  together  in  (6).  Life  in  such  (7)  is  not 

all  (8)  but  a mutual  give  and  take.  The  animals  and  plants 

best  (9)  to  live  under  such  (10)  crowd  out  the 

(11). 

PROBLEM  VII.  WHAT  IS  AN  ECOLOGICAL  SUCCESSION? 

Changes  in  environment  cause  changes  in  life.  Changes  are 
always  taking  place  in  plant  and  animal  communities.  Some- 
times these  changes  are  brought  about  artificially,  as  when  a forest 
fire  sweeps  a country  or  man  introduces  water  by  irrigation  into  a 
desert  region.  But  always  there  are  changes  going  on,  which 
cause  plant  and  animal  associations  to  change  in  a given  locality 
and  often  to  move  to  new  localities.  Most  of  these  changes  are 
very  slow,  so  that  we  rarely  notice  them.  Here  is  an  example 
quoted  by  Elton : A hole  in  a beech  tree  was  first  used  by  an  owl 
as  a nest ; then  with  the  growth  of  the  tree  the  hole  became 
smaller  and  was  used  by  starlings.  Later  it  became  too  small  for 
them  to  enter,  and  the  hollow  was  filled  by  a wasps’  nest. 

How  plants  invade  new  areas.  New  areas  are  tenanted  by 
plants  in  a similar  manner.  After  the  burning  over  of  a forest, 
we  find  a new  generation  of  plants  springing  up,  often  quite  unlike 
the  former  occupants  of  the  soil.  First  come  the  fireweed  and 


now  ANLMALS  GET  IN  NEW  AREAS 


301 


territory,  and  new  lands  are 
captured,  held,  and  lost  again 
by  the  plant  communities. 

How  animals  get  a foothold 
in  new  areas.  There  are 
many  ways  in  which  animals  spread  over  new  areas.  Transporta- 
tion to  quite  distant  parts  may  take  place,  as  when  polar  bears  or 
seals  are  carried  on  ice  floes  long  distances  or  when  insects  and 
other  small  forms  like  crustaceans  and  snails  may  be  carried 
hundreds  of  miles  by  ocean  currents.  Birds  may  carry  encysted 
microscopic  forms  or  even  the  eggs  of  mollusks  or  crustaceans  in 
little  balls  of  mud  which  stick  between  their  toes.  Man  himself 
may  play  a very  important  part  in  the  distribution  of  animals  in 


Frank  M.  Wheat 

In  the  giant  cactus,  woodpeckers  drill  their 
nesting  holes.  In  following  years,  these  holes 
are  often  used  as  nests  in  turn  by  small  owls  (elf 
owls ),  sparrow  hawks,  screech  owls,  fly  catchers, 
and  wrens. 


other  light-loving  weeds,  brought  by  means  of  their  wind-blown 
seeds.  With  these  are  found  patches  of  berries,  the  seeds  of  which 
were  brought  by  birds  or  other  animals.  A little  later,  quick- 
growing trees  having  seeds  easily  carried  for  some  distance  by  the 
wind,  like  the  aspen,  or  seeds  often  distributed  by  birds,  as  the  wild 
cherry,  invade  the  territory. 
h]ventually  we  may  have  the 
area  retenanted  by  the  same 
kind  of  inhabitants  as  formerly, 
especially  if  the  destruction  of 
the  original  forest  was  not 
complete. 

In  like  manner,  on  the 
upper  mountain  meadows  or 
by  the  sand  dunes  of  the  sea- 
shore, wherever  plants  place 
their  outposts,  the  advance  is 
made  from  some  thickly  in- 
habited area,  and  this  advance 
is  always  aided  or  hindered 
by  agencies  outside  of  the 
plant  — the  wind,  the  soil, 
water,  or  animals.  Thus  the 
seeds  obtain  a foothold  in  new 


302  LIVES  OF  PLANTS  AND  ANIMALS 

new  countries.  One  of  the  best  instances  of  animals  having 
spread  when  introduced  by  man  is  the  case  of  rabbits  in  Aus- 


Wright  Pierce 

If  this  desert  region  of  southern  California  should  be  thoroughly  irrigated,  what  kind  of 
plant  society  might  succeed  these  Joshua  trees  ? 

tralia.  They  have  now  become  so  numerous  that  they  are  a 
serious  pest.  The  English  sparrow  in  America  and  the  English 
starling  in  New  Zealand  are  other  examples  of  introductions  of 
animals  which  have  become  pests  because  of  lack  of  enemies  to 
hold  them  in  check. 

Practical  Exercise  13.  Make  a list  of  all  the  new  forms  of  life  introduced 
by  man  into  your  own  environment. 

Food  relations.  Animals  are  confined  to  certain  localities 
because  a food  supply  is  there,  and  may  migrate  to  new  localities 
when  the  food  supply  gives  out.  Overpopulation  with  subsequent 
lack  of  food  brought  about  great  migrations  of  the  house  rat 
across  Russia  in  1727,  which  was  the  beginning  of  the  occupation 
of  all  Europe  by  this  species  of  rat. 

Food  cycles  exist,  one  animal  being  dependent  upon  another 


FOOD  REL^VTIONS 


303 


or  on  plants  and  inovins;  away  when  the  food  gives  out.  Such  a 
footl  chain  or  cycle  would  be  seen  in  the  warblers  which  eat  insects 
living  in  trees,  as  plant  lice  and  boring  beetles.  The  warblers 
are  in  turn  preyed  upon  by  hawks.  In  the  same  forest  there  may 
be  mice,  whose  chief  food  is  acorns,  and  the  mice  are  eaten  by 
owls.  This  is  another  example  of  a food  cycle. 

Sometimes  we  have  a sudden  invasion  of  an  animal  after  food, 
such  as  the  locust.  The  famous  plague  of  grasshoppers  in  Utah 
in  earl}'  pioneer  days 
was  stopped  by  a 
similar  migration  of 
gulls  from  the  Great 
Salt  Lake  which  came 
to  feed  on  the  grass- 
hoppers. Thus  a 
balance  of  life  is  main- 
tained. 

Ecological  succes- 
sions have  already 
been  spoken  of. 

When,  for  example,  a 
lake  area  gradually 
fills  in  and  dries  up, 
different  animals  come 
to  occupy  the  marsh 
and  forest  land,  taking 
the  place  of  the  forms 
of  life  that  lived  in  the  water.  Meantime  a new  group  of  plants 
has  come  to  occupy  the  area  because  the  factors  of  the  environment 
have  been  changed.  Study  the  diagram  above  and  see  what 
changes  have  taken  place.  Man  has  played  a very  large  part  in 
attracting  new  animal  forms  into  regions  that  he  has  irrigated  or 
reclaimed  for  agriculture.  Here  are  an  entirely  new  set  of  animals 
which  feed  upon  the  introduced  plants. 

Life  succession  in  a hay  infusion.  Still  another  example  of  an 
ecological  succession  may  be  seen  in  a hay  infusion.  If  we  place  a 
wisp  of  hay  or  straw  in  a glass  jar  nearly  full  of  water,  and  leave 


Redrawn  from  an  article  by  Dachnowski  from 
Bulletin  16,  Geological  Survey  of  Ohio 

Plant  successions  in  an  area  where  a lake  has  slowly 
filled  in. 


304  LIVES  OF  PLANTS  AND  ANIMALS 

it  for  a few  days  in  a warm  room,  certain  changes  are  seen  to 
take  place  in  the  contents  of  the  jar;  the  water  after  a little 
while  gets  cloudy  and  darker  in  color,  and  a scum  appears  on  the 
surface.  If  some  of  this  scum  is  examined  under  the  compound 
microscope,  it  will  be  found  to  consist  almost  entirely  of  bacteria. 
These  bacteria  evidently  aid  in  the  decay  which  (as  the  un- 
pleasant odor  from  the  jar  testifies)  is  taking  place.  As  we  have 
learned,  bacteria  flourish  wherever  the  food  supply  is  abundant. 

The  bacteria  them- 
selves release  this 
food  from  the  hay  by 
causing  it  to  decay. 
After  a few  days 
small  one-celled  ani- 
mals appear  which 
multiply  with  won- 
derful rapidity.  Hay 
is  dried  grass,  upon 
which  the  wind  may 
have  scattered  some 
of  these  little  organ- 
isms in  the  dust  from 
dried-up  pools.  Ex- 
isting in  a dormant 
state  on  the  hay, 
they  are  awakened 
by  the  water  to  active 
life.  In  the  water, 
too,  there  may  have  been  some  other  living  cells,  plant  and 
animal. 

At  first  the  multiplication  of  the  tiny  animals  within  the  hay 
infusion  is  extremely  rapid ; there  is  food  in  abundance  and  near 
at  hand.  After  a few  days  more,  however,  several  kinds  of  one- 
celled  animals  may  appear,  some  of  which  prey  upon  others. 
Consequently  a struggle  for  life  begins,  which  becomes  more  and 
more  intense  as  the  food  from  the  hay  is  used  up.  Eventually 
the  end  comes  for  all  animals  unless  some  green  plants  obtain  a 


bacteria  of 


The  development  of  life  in  a hay  infusion.  How  can  you 
account  for  the  bacteria  that  attacked  the  hay? 


EFFECT  OF  BARRIERS  ON  PLANT  LIFE 


305 


foothold  within  the  jar.  If  such  a thing  happens,  food  will  be 
manufactured  within  their  bodies,  a new  food  supply  arises  for  the 
animals  within  the  jar,  and  a balance  of  life  results. 

Practical  Exercise  14.  Look  for  examples  of  ecological  succession  in  your 
laboratory.  Any  evidences  of  this?  Where? 

t'isit  a burned-over  area  and  note  the  new  jdants  which  come  up.  How 
do  they  differ  from  the  old  ones? 

Might  a garden  show  examples  of  ecological  succession?  Give  examples. 

Self-Testing  Exercise 

(1)  are  always  taking  piace  in  animal  and  plant (2). 

New  (3)  invade  areas  which  have  been  (4) 

(5),  or  animals  (6)  or  shift  their  (7) 

because  of  lack  of  (8)  or  other  causes.  Such  a change  is 

called  an (9) (10). 

PROBLEM  VIII.  WHAT  DO  WE  MEAN  BY  GEOGRAPHIC 
DISTRIBUTION  OF  LIVING  THINGS? 

Range  of  plants  and  animals.  Plants  and  animals  inhabiting  a 
given  territory  or  area  are  called  the  flora  or  fauna  of  that  range  or 
area.  We  find  out  the  range  of  a given  form  by  collecting  it  in 
as  many  places  as  possible.  This  kind  of  work  is  interesting  to 
boys  and  girls  because  they  can  determine  the  range  of  certain 
plants  and  animals  in  their  own  locality. 

The  areas  in  which  given  species  of  plants  or  animals  are  found 
may  be  very  limited  or  very  wide.  Some  trees,  for  example,  the 
western  redwood,  have  a rather  limited  range  in  the  extreme  north- 
west while  the  western  yellow  pine  or  the  eastern  hemlock  has  a 
much  wider  range.  Some  of  these  areas  were  much  larger  in 
ancient  geological  times  than  they  are  now.  That  certain  areas 
have  become  discontinuous  is  seen  in  the  distribution  of  elephants, 
which  once  were  found  over  a large  part  of  the  earth’s  surface. 
Man  may  reduce  or  increase  the  range  of  an  animal,  as  when  he 
nearly  exterminated  the  buffalo,  or  introduced  a pest  such  as  the 
orange  scale  in  California  or  the  gypsy  moth  in  Massachusetts 
or  the  chestnut  canker  on  Long  Island. 

Barriers  and  their  effect  on  plant  and  animal  life.  Any  one  who 
has  seen  the  Sierra  Nevada  mountains  and  knows  the  difference 


306 


Compiled  by  Forrest  Shreve 


LIFE  ZONES 


307 


in  life  on  the  western  and  eastern  slopes  can  tell  what  effect  a 
mountain  may  have  in  the  distribution  of  a given  kind  of  plant 
or  animal.  Living  things  on  one  side  of  that  range  are  quite 
different  from  those  on  the  other.  Natural  barriers  may  be 
mountains,  deserts,  large  bodies  of  water,  and  even  rivers.  Climatic 
conditions,  especially,  limit  the  range  of  plants,  which  cannot 
endure  great  differences  in  rainfall,  in  temperature,  humidity, 
wind,  or  sudden  atmospheric  changes.  Some  plants  and  animals 
have  special  adaptations  which  enable  them  to  cover  large  areas, 
such  as  parachutes  on  seeds 
and  the  wings  of  birds.  For 
such  plants  and  animals  the 
geographic  range  will  be 
greater  than  for  less  favored 
forms. 

Life  zones.  Reference  has 
already  been  made  to  the 
fact  that  a zonal  distribu- 
tion of  plants  and  animals  is 
easily  seen  in  climbing  any 
high  mountain.  Any  area 
in  which  most  of  the  plants 
or  animals  belong  to  single 
or  relatively  few  groups  of 
plants  and  animals  is  called  a 
life  zone.  Life  zones  are  often  rather  sharply  marked,  but  usually 
show  transitional  areas  between  them.  A region  which  has  been 
carefully  studied  and  which  shows  this  zonal  distribution  in  a 
marked  way  is  the  San  Francisco  mountain  region  in  north 
Arizona.  Here  a mountain  nearly  13,000  feet  in  height  rises 
out  of  a desert  plain.  This  mountain  shows  successively  two  types 
of  desert  zone,  a lower  and  upper,  each  with  its  own  desert  fauna 
and  flora,  cactuses,  sagebrush,  a few  birds,  mice,  lizards,  and  snakes. 
Then  a region  at  between  6000  and  7000  feet  of  pinon  pines  and  red 
cedars,  inhabited  by  more  birds  and  a few  mammals.  Between 
7000  and  8200  feet  we  find  forests  of  Douglas  and  balsam  fir,  with 
such  mammals  as  meadow  mice,  chipmunks,  deer,  lynx,  and  puma. 


Zonal  distribution  of  plants  on  a mountain 
rising  from  a desert  in  Arizona.  Give  cause  for 
different  zones. 


308 


LIVES  OF  PLANTS  AND  ANIMALS 


Distribution  of  animals  on  the  continents.  How  do  you  account  for  the  facv 

Where  and  why  do  you 


Higher  still,  between  8200  and  9500  feet,  we  find  a typical  Canadian 
vegetation,  timber  pine,  Douglas  and  balsam  fir  and  aspens,  while 
the  woodchuck,  porcupine,  rabbit,  marten,  fox,  wolf,  and  other 
northern  forms  are  found.  From  9500  to  11,500  feet  we  find  a 
fauna  and  flora  almost  like  that  of  northern  Canada  and  called 
Hudsonia.  Stunted  spruce  and  pine  exist  up  to  the  timber  line  with 
a few  typical  mountain  mammals  such  as  the  marmot  and  pika  or 
mountain  hare.  Above  this  area  lies  the  rocky  Alpine  zone,  snow- 
clad  for  one  half  of  the  year  even  in  this  warm,  sunny  climate. 
Lichens  on  the  rocks  and  a few  low  herbs  are  the  only  plant  life 
visible,  while  a few  insects  and  an  occasional  mammal  of  the 
Hudsonian  zone  are  the  only  signs  of  animal  life. 

Ecological  realms.  The  facts  that  the  ecologist  has  found  out 
concerning  life  zones  have  been  put  to  practical  use  by  the  Biological 
Survey  of  the  United  States  Department  of  Agriculture.  A life 
zone  map  has  been  prepared  so  that  the  settler  going  into  a new 
region  will  know  at  once  the  kind  of  plants  and  animals  best 
adapted  to  live  there.  In  addition,  the  character  of  the  soil,  the 


ECOLOGICAL  REALMS 


309 


that  some  of  the  same  animals  are  found  in  both  North  America  and  Eurasia? 
find  other  similarities  ? 


rainfall,  temperature  range,  and  the  particular  cereals,  fruits,  and 
vegetables  that  can  grow  in  the  region  are  available. 

Different  parts  of  the  world,  each  with  its  several  life  zones,  are 
known  as  realms  or  regions.  Australia  has  long  been  set  aside  as 
a distinct  realm  because  its  peculiar  fauna  and  flora  differ  from 
those  in  other  parts  of  the  earth.  North  America,  South  America, 
the  Arctic,  the  Antarctic,  Oriental  Africa,  Eurasia,  and  Australia 
constitute  the  world  realms.  Each  of  these  regions  has  animals 
and  plants  peculiar  to  itself,  although  resemblances  are  often  found 
in  their  inhabitants.  The  Eurasian  fauna  and  flora  resemble 
closely  those  of  North  America.  This  is  thought  by  geologists  to 
mean  that  in  former  times  these  regions  were  connected  by  land. 


Self-Testing  Exercise 

Animals  and  plants (1)  a given  area  are  called  the (2) 

and  (3)  of  that  (4).  Barriers  that  affect  the  range 

of  plants  and  animals  may  be (5), (6),  and  bodies  of 

(7). 

H.  BIO  — 21 


310 


LIVES  OF  PLANTS  AND  ANIMALS 


A mountain  near  a desert  may  show (8) (9).  Each 

of  these  (10)  has  (11)  and  (12)  peculiar 

to  itself. 

Review  Summary 

Test  your  knowledge  of  the  unit  by : (1)  rechecking  on  all  the  survey  ques- 
tions; (2)  performing  all  assigned  exercises ; (3)  checking  with  your  teacher  all 
tests  and  doing  over  the  parts  you  missed ; (4)  making  an  outline  of  the  unit 
for  your  notebook. 

Test  on  Fundamental  Concepts 

In  a vertical  column  under  the  heading  CORRECT  write  numbers  of  all  statements  you 
believe  are  true.  In  another  column  under  INCORRECT  write  numbers  of  untrue  statements. 
Your  grade  = number  of  right  answers  X 3J. 

I.  The  balance  of  life  (1)  means  that  living  plants  and  animals  are 
mutually  dependent  upon  each  other ; (2)  is  shown  by  a poor  garden 
crop  in  a dry  year ; (3)  in  a certain  region  is  often  disturbed  by  man 
when  he  cultivates  wild  areas ; (4)  is  shown  in  a balanced  aquarium ; 
(5)  was  disturbed  in  Australia  by  the  introduction  of  water  cress. 

II.  The  grouping  of  plants  and  animals  in  associations  (6)  is  due 
to  the  kind  of  food  available;  (7)  is  called  a habitat;  (8)  differs 
according  to  the  environment;  (9)  is  seen  in  a balanced  aquarium; 
(10)  is  brought  about  by  the  ability  of  certain  living  things  to  live 
together  under  certain  conditions. 

III.  Plants  and  animals  may  be  prevented  from  living  in  certain 
localities  by  (11)  too  much  light ; (12)  lack  of  certain  salts  in  the  soil; 
(13)  lack  of  water;  (14)  too  much  water;  (15)  lack  of  oxygen. 

IV.  Symbiosis  (16)  is  the  process  of  living  together  for  mutual 
advantage  ; (17)  is  a partnership  between  two  living  things  ; (18)  occur 
when  green  plants  give  food  to  animals  and  depend  upon  certain  wastes 
from  them  in  order  to  make  this  food ; (19)  is  a bad  thing,  because  it 
is  a one-sided  relationship  ; (20)  is  the  same  as  parasitism. 

V.  Ecological  succession  (21)  occurs  when  changes  in  environment 
cause  changes  in  forms  of  plants  and  animals  living  in  a given  place; 
(22)  is  never  brought  about  by  man ; (23)  is  often  caused  by  man ; 

(24)  is  often  caused  by  immigrations  of  animals  due  to  lack  of  food ; 

(25)  results  in  new  forms  being  found  in  a given  locality. 

VI.  Life  zones  (26)  are  found  on  the  sides  of  a high  mountain 
where  life  forms  characteristic  of  the  tropics  to  the  arctic  may  be  found 
from  the  base  to  the  summit ; (27)  are  illustrated  by  the  temperate 
zone,  the  torrid  zone,  etc. ; (28)  are  usually  well  marked  but  show 


TESTS 


311 


transitional  areas  l)etwpen  them ; (29)  are  areas  in  which  most  of  the 
])lants  or  animals  found  belong  to  single  or  relatively  few  animal  or 
plant  groui)s;  (30)  are  not  usually  sharply  marked. 

Achievement  Test 

1.  How  many  animal  or  plant  societies  have  you  found  in  your 
locality? 

2.  How  would  you  stock  an  aquarium  and  keep  it  balanced? 

3.  How  can  jmu  illustrate  the  nitrogen,  carbon,  and  oxygen  cycles? 

4.  What  are  all  the  factors  of  the  environment  which  affect  living 
things  in  your  own  environment? 

5.  What  is  the  meaning  of  symbiosis,  and  can  you  give  exam- 
ples? 

6.  Have  you  any  local  parasites  and  how  are  they  controlled? 

7.  What  is  the  effect  of  water  upon  the  life  in  your  region? 

8.  How  has  man  controlled  or  changed  life  by  use  of  water? 

9.  What  geographic  region  do  you  live  in  and  what  are  the  chief 
characteristics  of  its  flora  and  fauna? 

Practical  Problems 

1.  Select  some  locality  near  you  and  try  to  work  out  the  animal 
and  plant  communities  there. 

2.  Alake  a map  for  your  notebook,  showing  zonal  distribution  of 
plants  and  animals  for  your  locality. 

3.  Take  an  area  in  your  own  yard  one  foot  square  and  list  all  the 
living  things  you  can  find  there. 

Useful  References 

Coulter,  Barnes,  and  Cowles,  Textbook  of  Botany,  Vol.  Three.  American 
Book,  1931. 

Downing,  Our  Living  World.  Longmans,  Green,  1924. 

Elton,  Animal  Ecology.  Macmillan,  1927. 

Flattely  and  Walton,  The  Biology  of  the  Sea  Shore.  Macmillan,  1922. 
Howts,  Insect  Behavior.  R.  C.  Badger. 

Needham,  General  Biology.  Comstock,  1917. 

Pearse,  Animal  Ecology.  McGraw-Hill,  1926. 

Schimper,  Plant  Geography.  Oxford  University  Press. 

Wells,  Huxley,  and  Wells,  The  Science  of  Life.  Book  six.  Doubleday, 
Doran,  1934. 


SURVEY  QUESTIONS 


Have  you  ever  seen  an  interscholastic  track  meet  and  noticed  the 
different  ways  in  which  the  athletes  use  their  muscles  ? Why  must  the 
members  of  a football  team  train  ? Do  you  know  why  we  have  a skeleton  ? 
Can  you  give  the  uses  of  the  skin  ? Do  you  know  what  constitutes  good 
posture  ? Do  you  know  what  are  the  most  sensible  kinds  of  shoes  ? 


312 


Wide  World  Photo 


PART  IV.  THE  BIOLOGY  OF  MAN 

UNIT  X 

HOW  DOES  THE  HUMAN  MACHINE  DO  ITS  WORK? 

Preview.  I suppose  every  boy  and  girl  who  reads  these  pages 
has  seen  an  interscholastic  track  meet  and  perhaps  envied  the 
perfect  coordination  of  every  part  of  the  bodies  of  the  men  who 
run  hurdles,  high  jump,  or  pole  vault.  Perhaps  you  have  tried 
some  of  these  feats  yourself  and  have  discovered  how  difficult  it 
is  to  make  the  different  muscles  coordinate  at  exactly  the  right 
time.  It  is  a very  wonderful  machine,  this  body  of  ours,  and  we 
cannot  help  but  feel  a real  reverence  for  it  when  we  think  of  the 
delicate  mechanism  which,  with  its  numerous  adjustments  and 
adaptations,  can  do  work  so  efficiently.  Unlike  a man-made 
machine,  the  body  is  self-directed,  and  with  care  will  far  outlast 
most  machines  made  of  iron  and  steel. 

In  all  animals,  and  the  human  organism  is  no  exception,  the  body 
has  been  likened  to  a machine  in  that  it  turns  over  the  latent  or 
potential  energy  stored  up  in  food  into  kinetic  energy  (mechanical 
work  and  heat),  which  is  manifested  when  we  perform  work.  One 
great  difference  exists  between  an  engine  and  the  human  body. 
The  engine  uses  fuel  unlike  the  substance  out  of  which  it  is  made. 
The  human  body,  on  the  other  hand,  uses  for  fuel  the  same  sub- 
stances as  those  out  of  which  it  is  formed ; it  may,  indeed,  use 
part  of  its  own  substance  for  fuel.  The  human  organism  does 
more  than  purely  mechanical  work.  It  is  so  delicately  adjusted 
to  its  surroundings  that  it  will  react  promptly  and  efficiently  to 
stimuli  from  without ; it  is  able  to  utilize  its  fuel  (food)  in  the  most 
economical  manner ; it  is  fitted  with  machinery  for  transforming 
the  energy  received  from  food  into  various  kinds  of  work ; it 

313 


314  HOW  DOES  THE  HUMAN  MACHINE  DO  ITS  WORK? 


provides  the  machine  properly  with  oxygen  so  that  the  fuel  will 
be  oxidized ; and  the  products  of  oxidation  are  carried  away,  as 
well  as  other  waste  materials  which  might  harm  the  effectiveness 
of  the  machine.  Most  important  of  all,  the  human  machine  is 
able  to  repair  itself. 

No  boy  or  girl  can  go  into  the  big  game  of  life  and  expect  to  be 
a helpful  member  of  society  with  an  insufficient  knowledge  of  the 
human  machine.  Neglect  or  lack  of  proper  care  of  our  bodies  may 
defeat  some  of  our  life’s  fondest  ambitions.  The  efficient  citizen 
should  be  the  healthy  citizen. 

PROBLEM  I.  WHAT  IS  THE  GENERAL  STRUCTURE  OF  THE 
HUMAN  BODY? 

Laboratory  Exercise.  The  structure  of  the  human  body.  Use 

manikin  or  good  chart. 

Note  the  covering  of  skin.  Can  you  think  of  any  uses  for  this 
structure?  What  general  uses  would  the  muscles  have?  Note  their 
position  with  reference  to  the  skeleton  and  the  organs  of  the  body 
cavity.  Take  off  the  covering  and  examine  the  organs  within  the 
body  cavity.  The  thin  layer  of  muscles  that  separates  the  heart  and 
lungs  from  the  abdominal  cavity  is  the  diaphragm.  Use  a good  text 
figure  to  locate  the  parts  of  the  digestive  tract : stomach,  small  and 
large  intestines,  liver,  and  pancreas.  Locate  the  kidneys,  and  the 
tubes  (ureters)  leading  to  the  bladder  and  thence,  outside  of  the  body. 

Skin  and  muscles.  If  we  are  thinking  of  the  body  as  a machine 
which  does  work,  then  it  is  obvious  that,  while  the  skin  is  partly  a 
protective  organ,  the  muscles  are  structures  by  which  work  is  largely 
accomplished.  The  diagram  (p.  320)  shows  that  they  are  attached 
to  bones  which  serve  as  levers  and  thus  accomplish  movement. 

Other  body  structures.  In  spaces  between  the  muscles  are 
found  various  other  structures  — blood  vessels,  which  carry  blood 
to  and  from  the  great  pumping  station,  the  heart;  connective 
tissue,  which  holds  groups  of  muscle  or  other  cells  together;  fat 
cells,  scattered  in  various  parts  of  the  body ; various  gland  cells, 
which  manufacture  the  enzymes  which  digest  our  foods ; and  the 
cells  of  the  nervous  system,  which  aid  in  directing  the  various 
parts  of  the  body. 

Body  cavity.  Within  the  cover  of  skin,  bone,  and  muscle  is  a 
cavity  filled  with  various  organs.  A thin  wall  of  muscle  called 


THE  NEKVOl’S  SYSTEM 


315 


the  diaphragm  (di'«-fniin)  divides  the  body  cavity  into  two  unequal 
cavities.  In  the  upper  one,  thoracic  cavity,  are  found  the  heart, 
lungs,  and  esophagus;  in  the  lower,  the  abdominal  cavity,  are  the 
stomach,  intestines,  the  liver,  the  kidneys,  and  other  structures. 

Digestion  and  excretion.  The  mouth  cavity  leads  into  a food 
tube  into  which  food  passes  and  from  which  digested  or  liquid 
food  is  absorbed  into  the  blood  to  be  carried  to  the  cells  of  the 
various  organs  which  do  the  work.  Emptying  into  this  food  tube 
are  various  groups  of  gland  cells,  which  pour  digestive  fluids  over 
the  solid  foods,  thus  aiding  in  changing  them  to  a soluble  form. 
Solid  waste  materials  are  passed  out  through  the  posterior  end  of 
the  food  tube,  while  liquid  wastes  are  eventually  excreted  by  means 
of  the  skin  and  of  organs  called  kidneys. 

The  nervous  system.  This  complex  machine  is  much  more 
than  a mechanical  engine.  It  is  self-directed.  All  its  functions 
are  either  directly  or  indirectly  under  its  control.  Not  only  are 
animals  able  to  receive  outside  stimuli  through  certain  parts  called 
sense  organs,  but  they  react  to  them,  and  there  is  internal  co- 
ordination and  control  as  well.  The  complicated  machine  does 
its  work  automatically;  the  heart  beats,  the  glands  secrete,  the 
chest  rises  and  falls  without  any  conscious  direction  on  our  part. 
The  nervous  system  gives  sensation,  it  gives  internal  control  and 
coordination.  In  man  it  does  more.  It  also  gives  him  control 
over  his  conscious  activities.  He  is  able  to  make  a selection  or 
choice  of  his  daily  acts.  As  such  he  is  a “ thinking  ” animal  and 
has  become  master  of  the  earth. 

Practical  Exercise  1.  Make  in  tabular  form  for  your  workbook  a summary 
of  work  done  by  the  different  parts  of  the  body. 

Self-Testing  Exercise 

Check  in  your  workbook  the  statements  that  are  true. 

T.  F.  1.  The  human  body  is  like  a machine  because  it  can  repair 
itself. 

T.  F.  2.  Food  is  oxidized  in  the  human  body  as  is  fuel  in  an  engine. 

T.  F.  3.  The  skin  is  an  organ  of  protection  but  not  of  excretion. 

T.  F.  4.  The  nervous  system  gives  sensation  as  well  as  body  control. 

T.  F.  5.  Movement  is  accomplished  in  the  body  because  muscles 
are  attached  to  bones  which  act  as  levers. 


316  HOW  DOES  THE  HUMAN  MACHINE  DO  ITS  WORK? 


PROBLEM  II.  WHAT  IS  THE  STRUCTURE  OF  THE  SKIN? 

Laboratory  Exercise.  To  find  out  some  functions  of  the  skin. 

Hand  lens.  Ether  or  alcohol.  Large  glass  jar.  Two  thermometers. 
Model  or  illustration  showing  section  of  skin. 

Find  out  whether  all  parts  of  the  skin  of  the  arm  are  equally  sensi- 
tive, by  touching  various  parts  of  it  with  the  sharp  point  of  a pencil. 
Cool  a large  glass  jar,  and  hold  the  hand  and  wrist  in  the  jar  for  a few 
moments,  closing  the  opening  of  the  jar  with  a cloth  or  a towel.  What 
collects  on  the  inner  surface  of  the  jar? 

What  happens  when  you  take  violent  exercise?  Weigh  yourself 
before  and  after  a period  of  hard  work  in  the  gymnasium.  Is  there 
any  loss  in  weight?  How  do  you  account  for  it? 

Place  a few  drops  of  ether  or  alcohol  on  the  back  of  your  hand  and 
note  the  evaporation  of  the  liquid.  What  sensation  do  you  feel  while 
the  evaporation  takes  place? 

Study  the  model  or  diagram  of  skin  on  page  317.  Locate  the  two 
layers.  Find  and  describe  the  sweat  glands,  oil  glands,  and  sense 
organs.  Draw  a diagrammatic  sketch  of  the  model  and  label  all 
parts.  Write  a statement  giving  the  functions  of  each  part. 

Conclusions.  Is  the  skin  an  organ  of  sensation?  What  passes  off 
through  the  skin?  What  effect  on  your  bodily  comfort  does  this  last 
function  have? 

The  skin.  Covering  the  body  is  the  protective  structure 
called  the  skin.  Under  the  epidermis,  a layer  of  dead  cells,  there 
are  delicate  sense  organs,  lying  in  the  dermis  or  true  skin,  which 
give  us  sensations  of  touch,  pressure,  and  temperature.  The  skin 
aids  also  in  passing  wastes  out  of  the  body  by  means  of  sweat 
glands,  and  it  plays  an  important  part  in  equalizing  the  tempera- 
ture of  the  body. 

Nails  and  hair.  Nails  are  outgrowths  of  the  horny  layer  of  the 
epidermis.  A hair  is  also  a growth  of  the  epidermal  layer,  although 
it  is  formed  in  a deep  pit  or  depression  in  the  dermis ; this  pit  is 
called  the  hair  follicle. 

The  glands  of  the  skin.  Scattered  through  the  dermis,  and 
usually  connected  with  the  hair  follicles,  are  tiny  oil-secreting 
glands,  the  sebaceous  (se-ba'shus)  glands.  The  secretion  of  these 
glands  keeps  the  hair  and  surface  of  the  skin  soft  and  pliable. 
The  other  glands  in  the  dermis,  known  as  sweat  glands,  are  to  be 
found  in  profusion,  over  2,500,000  being  present  in  the  skin  of  a 
normal  man.  These  glands  excrete  certain  wastes  from  the  blood 
in  the  water  they  pass  off. 


SKIN  INFECTIONS  AND  THEIR  CARE 


317 


Tlie  skin  is  first  of  all  an  organ  of  protection  against  man’s 
microscopic  foes,  the  bacteria.  But  a dirty  skin  harbors  bacteria. 
Moreover,  the  skin 


pores,  through  which 
the  perspiration  and 
oil  pass,  are  easily 
clogged  with  dirt. 
Frequent  washing  is 
necessary  if  we  wish 
to  keep  the  skin 
clean.  Pride  in  one’s 
own  appearance  for- 
bids a dirty  skin. 
Powder  or  rouge  does 
not  clean  the  skin; 
it  may  cover  up  dirt. 


hair. 


oil  planet 


•nsoTy  . I 
nervo  . o 

^nsrvetb  1-^ 
Woo^VfeSSelT'3 
^ nerve  ’■  "g® 
to  sveot  -j  u 
(glcrncC 


''fexL  cells 


sucTocwtcxTieow^ 
cci^ecc 

For  those  who  can  a section  through  the  skin.  What  are  the  uses  of  the  various 

stand  it,  a cold 

shower  or  sponge  bath  should  be  taken  every  day  with  a brisk  rub- 
down  afterward,  since  this  exercises  the  blood  vessels  of  the  skin. 
Soap  should  be  used  daily  on  surfaces  exposed  to  dirt,  because  it 
combines  with  the  oil  of  the  skin,  thus  aiding  in  the  removal  of 
the  dirt  held  there.  Exercise  in  the  open  air  is  important  to  all 
who  desire  a good  complexion.  To  have  the  “ glow  of  health  ” 
one  must  exercise  the  skin,  as  well  as  keep  it  clean. 

Skin  infections  and  their  care.  We  are  all  aware  of  the  fact 
that  sometimes  a scratch  or  cut  becomes  infected;  bacteria  multiply 
there  and  cause  pus.  Pimples  are  often  caused  by  the  infection 
in  the  skin  pores  of  rod-shaped  bacteria,  while  boils  are  usually 
caused  by  the  infection  of  the  hair  follicle  with  pus-forming 
bacteria  — the  streptococci  (strep-tb-k5k'sl). 

Whenever  the  skin  is  broken,  it  is  necessary  to  prevent  the 
entrance  and  growth  of  bacteria.  This  may  be  done  by  washing 
the  wound  with  weak  antiseptic  solutions  such  as  a three  per  cent 
carbolic  acid  solution,  a three  per  cent  lysol  solution,  or  by  painting 
the  wounded  part  with  solution  of  iodine  or  mercurochrome.  These 
solutions  should  be  applied  immediately.  A burn  or  scald  should 


318  HOW  DOES  THE  HUMAN  MACHINE  DO  ITS  WORK? 


be  covered  at  once  with  a paste  of  baking  soda,  with  olive  oil,  or 
with  a mixture  of  limewater  and  linseed  oil.  These  tend  to  lessen 
the  pain  by  keeping  out  the  air  and  reducing  the  inflammation. 

The  relation  of  clothing  to  the  skin.  Clothes  are  primarily  for 
protection.  They  may  be  classed  as  either  good  or  bad  conductors 
of  heat.  Good  heat  conductors,  such  as  linen  or  cotton,  allow  the 
temperature  outside  of  them  to  replace  that  of  the  layer  of  air 
directly  around  the  body,  while  silk  and  wool  are  poor  conductors 
and  protect  the  body  from  a lower  temperature  outside.  Warmth 
of  clothing  is  largely  dependent  on  the  amount  of  air  held  between 
its  fibers.  Cool  clothes  have  little  air  space  in  the  meshes  of  the 
cloth,  while  loosely  woven  underclothes  are  warmer  because  they 
absorb  perspiration  rapidly  and  dry  out  quickly.  Hence  they 
do  not  feel  cold  or  clammy  to  the  perspiring  skin  as  linen  and 
cotton  do.  Young  people  can  wear  linen  or  cotton  underclothes 
safely  all  the  year  round  if  they  make  proper  changes  in  the  weight 
of  their  outside  garments.  Older  persons,  on  the  other  hand,  need 
to  wear  woolen  underclothes  in  the  winter  because  these  keep  out 
cold  and  absorb  perspiration  without  chilling  the  skin. 

Self-Testing  Exercise 

The  skin  is  composed  of  (1)  layers,  the  (2)  and 

(3),  the  latter  is  the (4)  layer  and  is  largely (5). 

The  skin  excretes  certain  wastes  through  the (6)  glands.  An 

open  wound  may  become  infected  by  (7)  which  cause 

(8).  Boils  are  an  example  of  an (9)  by (10). 

The  skin  is  a (11)  covering  consisting  of  the  epidermis,  a layer 

of (12) (13),  and  the  living (14)  which  con- 
tains the  (15)  and  (16)  glands,  (17) 

(18), (19),  and (20) (21). 

PROBLEM  III.  WHAT  IS  THE  RELATION  OF  MUSCLES  TO 
BONES? 

Laboratory  Exercise.  To  study  the  use  of  the  muscles  and  bones. 

Frogs  preserved  in  formalin,  mounted  skeletons  of  frog,  manikin, 
human  skeleton,  or  good  diagram. 

Note  the  “ flesh  ” forming  the  muscle  of  the  leg.  (A  muscle  is 
attached  to  the  bone  by  a tough  tendon.) 

Holding  your  leg  still,  raise  the  foot  up  and  down.  Where  do  you 
feel  the  contraction  of  the  muscle?  Referring  to  the  manikin,  deter- 


BONES  AND  MUSCLES 


319 


mine  how  these  nuisclos  are  attached  to  the  bones?  At  how  many 
points  are  tliey  attachetl? 

I'lxplain  how  nioveniont  of  the  les  results  from  contraction  (shorten- 
ing) of  certain  of  the  muscles.  What  must  occur  when  some  of  the 
muscles  contract?  (Look  at  the  position  of  the  muscle  on  the  opposite 
side  of  the  leg.) 

Note  the  shaj)e  of  3'our  upper  arm.  To  what  is  the  rounded  surface 
due?  ^love  it  and  watch  what  happens  to  the  muscles.  Now 
e.xamine  the  skeleton  or  a diagram  to  see  if  you  can  make  out  just 
where  the  muscles  are  attached.  Why  do  muscles  cause  movement? 
Explain  fulhu  What  use,  other  than  movement,  have  muscles? 

Practical  Exercise  2.  From  a study  of  diagrams  and  skeletons  of  a man 
and  of  some  other  mammal,  as  a cat  or  a dog,  make  labeled  diagrams  for  your 
workbook  to  show  the  position  of  the  main  parts  of  the  skeleton,  vertebral 
column,  skull,  shoulder  and  pelvic  girdles,  and  the  appendages. 

Bones  and  muscles.  The  body  is  built  around  a framework  of 
bones.  These  bones,  which  are  bound  together  by  tough  ligaments, 
fall  naturally  into  two  great  groups  : 
the  bones  of  the  trunk  and  head, 
namely,  the  vertebral  column,  ribs, 
breast  bone,  and  skull,  which  form 
the  axial  (ak'si-dl)  skeleton ; and 
the  bones  of  the  appendages  (the 
framework  of  the  arms  and  legs), 
which,  together  with  the  bones  at- 
taching them  to  the  axial  skeleton, 
form  the  appendicular  (ap-en-dik'u- 
Idr)  skeleton. 

To  the  bones  are  attached  the 
muscles  of  the  body.  Movement 
is  accomplished  by  the  contraction 
of  muscles,  which  are  attached  so 
as  to  cause  the  bones  to  act  as 
levers.  Muscles  usually  act  in 
pairs  : one  muscle  extends  while  the 
other  flexes  or  bends.  Bones  also 
protect  the  nervous  system  and 
other  delicate  organs.  The  bony  cranium  (kra'm-um),  inclosing 
the  brain,  is  an  example  of  such  protection.  The  internal  skeleton 
also  gives  form  and  rigidity  to  the  body. 


320  HOW  DOES  THE  HUMAN  MACHINE  DO  ITS  WORK? 


Hygiene  of  muscles  and  bones.  Young  people  especially  need 
to  know  how  to  prevent  certain  defects  which  are  largely  the  result 

of  bad  habits  of  'posture. 
Good  posture  is  a con- 
dition of  equilibrium  of 
the  body  which  can  be 
maintained  for  some  time, 
such  as  standing  or  sitting 
erect.  Standing  erect  is 
a good  habit ; round 
shoulders  are  an  indica- 
tion of  a bad  habit.  The 
habit  of  keeping  a wrong 
position  of  bones  and  mus- 
cles, once  formed,  is  very 
hard  to  correct. 

Round  shoulders  are 
most  common  among  peo- 
ple whose  occupation 
causes  them  to  stoop.  A 
wrong  position  at  one’s 
desk  is  among  the  causes. 
Exercises  which  strengthen 
the  muscles  of  the  back 
are  helpful  in  forming  the 
habit  of  erect  carriage. 

Slight  curvature  of  the  spine  either  backward  or  forward  is 
helped  most  by  exercises  which  tend  to  straighten  the  body, 
such  as  stretching  up  with  the  hands  above  the  head.  Lateral 
curvature  of  the  spine,  too  often  caused  by  a “ hunched-up  ” 
position  at  the  school  desk,  may  also  be  corrected  by  exer- 
cises which  tend  to  lengthen  the  spinal  column.  If  your  pos- 
ture is  not  good,  study  your  own  defects  and  find  out  from  an 
orthopedic  specialist  just  what  you  should  do  to  correct  it. 
Then  go  to  work  to  correct  it.  Remember  it  takes  a long 
time  to  overcome  results  of  wrong  posture  that  may  have  taken 
years  to  form.  ^ 


Muscles  work  in  pairs  — Explain  what  is  happening  to 
the  foot  in  (6). 


CARE  OF  THE  FEET 


321 


Importance  of  good  posture.  It  is  the  duty  of  every  girl  and 
boy  to  have  good  posture  and  erect  carriage,  not  only  because  of 
the  better  state  of  health  which  comes 
with  it,  but  also  because  self-respect  de- 
mands that  we  make  the  best  of  the  gifts 
that  nature  has  given  us.  An  erect  head, 
straight  shoulders,  and  elastic  carriage  go 
far  toward  making  their  owner  both  liked 
and  respected.  The  person  who  stands 
erect  and  has  good  posture  is  usually  the 
one  who  has  good  mental  poise  as  well. 

Practical  Exercise  3.  Make  an  outline  of 
what  you  would  do  to  correct  (a)  flat  feet,  (6)  a 
lateral  spine  curvature,  (c)  round  shoulders, 

(d)  protruding  abdomen. 

Care  of  the  feet.  Our  health  depends 
to  a large  degree  upon  exercise.  Little 
exercise  is  possible  without  the  use  of  the  feet.  Most  of  us  have 
known  foot  discomfort  of  one  sort  or  another.  Let  us  see  how 
to  avoid  such  difficulties. 

IMany  foot  troubles  come  from  either  too  tight  or  too  loose 
shoes  chafing  the  foot,  thus  causing  the  skin  to  respond  to  the 
irritation  by  forming  callous  spots  which  grow  thicker  and  thicker, 
developing  into  corns.  But  a much  more  serious  effect  comes 
from  the  use  of  badly  shaped  shoes  with  high  heels.  If  you  look 
at  the  human  skeleton,  you  will  see  that  the  bones  of  the  foot  form 
an  arch  from  the  toes  to  the  heel,  so  that  the  foot,  between  the  ball 
and  the  heel,  should  touch  the  ground  only  slightly.  High-heeled 
shoes  throw  the  weight  forward  to  the  ball  of  the  foot,  pressing  the 
bones  of  the  arch  into  unnatural  positions  and  straining  the  ten- 
dons which  fasten  the  muscles  to  the  bones.  The  foot  in  a natural 
position  on  the  ground  is  also  seen  to  touch  along  the  edges  outside, 
but  not  in  the  middle  of  the  foot.  This  arch  is  weakened  by  the 
use  of  too  narrow  and  too  pointed-toed  shoes. 

Practical  Exercise  4.  Make  an  outline  drawing  of  the  sole  of  your  shoe  as 
you  stand.  Then  make  an  outline  of  your  bare  foot  as  you  stand  on  the  first 
outline.  How  do  the  tWQ  outlines  compare?  Are  you  wearing  proper  shoes? 


-ear 

..shoulder 


-ankle./ 


In  good  posture,  the  head  is 
directly  over  the  feet.  A line 
dropped  from  the  ear  passes 
through  the  middle  of  the 
shoulder,  the  hip,  knee,  and  ankle. 


322  HOW  DOES  THE  HUMAN  MACHINE  DO  ITS  WORK? 


Tight  shoes,  high  heels,  and  “ toeing  out  ” all  tend  to  cause 
strain  on  the  arch  and  consequently  cause  flat  feet.  A severe 
case  produces  strain  known  as  a “ broken  arch,”  and  this  con- 
dition may  produce  severe  pain  or  even  nervous  disorders.  An 
orthopedic  specialist  should  be  consulted  in  such  cases. 

Self-Testing  Exercise 

The  body  is  built  around  a framework  of (1).  These  form  a 

central (2)  skeleton  and  attached  portions  called  collectively  the 

....  (3)  skeleton.  Muscles  are  attached  to (4)  which  act  as 

(5).  Muscles  usually  act  in (6),  one (7)  while 

its  opposite  is (8) . Good  posture  is  necessary  for  good 

(9)  and  can  only  be  obtained  by  constant (10).  Posture  is  a 

position  of (11)  of  the  body.  Tight  shoes  cause (12) 

on  the (13)  while  high  heels  may  cause (14)  arches. 

Review  Summary 

Test  your  knowledge  of  the  unit  by ; (1)  rechecking  on  all  the  survey  ques- 
tions ; (2)  performing  all  the  assigned  exercises ; (3)  checking  with  your  teacher 
the  scores  of  the  various  tests  and  doing  over  those  that  you  missed ; (4)  making 
an  outline  of  the  unit  for  your  notebook. 

Test  on  Fundamental  Concepts 

In  a vertical  column  under  the  heading  CORRECT  write  numbers  of  all  statements  you 
believe  are  true.  In  another  column  under  INCORRECT  write  numbers  of  untrue  statements. 
Your  grade  = right  answers  X 4. 

I.  The  body  may  be  compared  with  a machine  because  (1)  it  does 
work ; (2)  it  is  made  of  organs ; (3)  it  has  a self-directing  mechanism ; 
(4)  it  oxidizes  substances  to  release  energy;  (5)  it  provides  for  the 
disposition  of  its  waste  products. 

II.  The  skin  (6)  is  of  no  value  as  a protection ; (7)  is  a heat-regulat- 
ing mechanism ; (8)  protects  the  body  against  invasion  from  germs ; 

(9)  can  best  be  kept  clean  by  covering  with  rouge  or  powder ; 

(10)  contains  many  pores  leading  from  sweat  glands  which  must  be  kept 
open  if  the  skin  is  to  function  properly. 

III.  The  skeleton  (11)  is  a framework  to  which  muscles  are  at- 
tached ; (12)  acts  as  a protection  for  the  soft  parts  of  the  body ; (13)  is 
made  largely  of  lime;  (14)  gives  shape  to  the  body;  (15)  is  entirely 
external  in  man. 


USEFUL  KEFEKENCES 


323 


IV.  Muscles  (16)  usually  work  iii  ])airs;  (17)  are  usually  attached 
to  bones,  which  act  as  levers;  (18)  never  give  form  to  the  body;  (10)  are 
cai)able  of  contraction  and  relaxation;  (20)  are  only  fully  develoi)od  in 
people  who  exercise. 

Good  posture  (21)  comes  as  a result  of  a jn-oper  Ijalance  or  ecpii- 
librium  of  body  parts;  (22)  is  the  result  of  round  shoulders;  (28)  is  an 
iiulication  of  good  mental  as  well  as  physical  health ; (24)  is  not  necessary 
for  health ; (25)  may  be  obtained  through  proper  exercise  and  care  of  the 
body. 


Achievement  Test 

1.  What  is  the  general  plan  of  man’s  body  make-up? 

2.  What  would  jmu  do  in  case  of  a skin  infection? 

3.  What  are  the  functions  of  each  part  of  the  skin? 

4.  How  could  you  show  the  ways  in  which  the  leg  muscles  work  in 
walking?  In  running?  In  jumping? 

5.  How  would  jmu  protect  yourself  from  foot  troubles? 

Practical  Problems 

1.  Visit  a museum  and  make  a series  of  diagrams  for  your  workbook 
to  show  the  relationship  of  man  to  the  other  mammals. 

2.  Study  diagrams  and  the  foot  of  the  human  skeleton  in  order  to 
locate  the  arches  in  your  foot.  Make  an  impression  of  the  foot  on 
smoked  paper  and  decide  if  your  arches  are  in  good  condition.  What 
exercises  should  you  take  if  they  are  not?  (See  the  Metropolitan  Life 
Insurance  pamphlet,  “Foot  Health.”) 

3.  Prove  that  a given  bone  acts  as  a lever  for  certain  muscles  in  your 
body. 

4.  What  fii’st  aid  would  you  administer  for  a broken  bone  in  your 
leg?  For  a bad  scratch  made  by  a rusty  nail? 

Useful  References 

Elwyn,  Yourself,  Inc.  Coward-McCann,  1930. 

Lewin,  Posture  and  Hygiene  of  the  Feet.  Funk  and  Wagnalls,  1929. 
Hance,  The  Machines  We  Are.  Crowell,  1932. 

Metropolitan  Life  Insurance  Company,  Foot  Health. 

Walter,  Human  Skeleton.  Macmillan,  1918. 

Williams,  Personal  Hygiene  Applied.  Chapter  VI.  Saunders,  1931. 


SURVEY  QUESTIONS 

What  are  vitamins  and  what  do  they  do  ? Do  you  know  why  milk  is  a good 
food?  Why  do  we  eat  so  many  different  kinds  of  foods?  What  makes 
foods  cheap  or  expensive?  Is  it  true  that  all  cheap  foods  are  poor  foods? 
Do  you  know  what  adulteration  means  ? Give  an  example. 


Photo  by  H.  Armstrong  Roberts 


UNIT  XI 

HOW  DOES  MAN  DETERMINE  THE  VALUES  OF  FOODS? 

Preview.  Anyone  reading  advertisements  in  a magazine  today 
cannot  help  noticing  the  number  of  food  slogans  that  the  pro- 
ducers of  food  place  before  the  public.  “ An  apple  a day  keeps 
the  doctor  away,”  “ Take  your  daily  orange  juice,”  “ Eat  yeast 
and  get  your  vitamins,”  “ Drink  a quart  of  milk  a day,”  etc.  We 
naturally  want  to  know  just  how  many  of  these  statements  are 
true.  The  facts  concerning  what  we  should  eat  and  why  we  should 
eat  certain  foods  are  certainly  worth  knowing. 

Every  one  knows  that  the  human  machine  needs  fuel.  A 
locomotive  uses  coal,  water,  and  oxygen.  A living  animal  gets 

324 


PllEVIEW 


325 


food,  water,  and  oxygen  from  its  environments  Both  the  non- 
living and  the  living  machine  do  the  same  thing  with  fuel  or  food, 
ddiey  oxidize  it  and  make  use  of  the  energy  thus  released.  They 
both  receive  heat  as  a direct  result  of  this  oxidization  or  burning. 
In  addition,  however,  the  living  organism  may  use  food  to  repair 
parts  that  have  broken  down  or  even  build  new  parts.  Thus 
food  'may  be  defined  as  something  that  can  be  used  by  the 
body  of  a plant  or  animal  to  release  energy,  or  to  form  material 
for  the  growth  or  repair  of  that  body.  However,  we  must  not 
think  of  our  body  as  taking  the  foods  and  burning  them  directly, 
thus  providing  us  with  heat  and  energy  to  do  work.  It  is  a much 
more  complicated  process  than  this  might  sound.  Our  digestive 
organs  first  have  to  break  down  the  food  materials  into  such  forms 
that  they  can  be  taken  into  the  blood  and  carried  to  all  part!l  of 
the  body.  The  millions  of  cells  of  which  the  body  is  composed 
must  be  given  more  material  which  will  form  new  living  matter. 
These  cells  must  also  be  provided  with  food  material  which  is 
oxidized  to  release  energy  when  muscle  cells  move,  or  gland  cells 
secrete,  or  brain  cells  work. 

Experiments  have  proved  that  an  animal  may  be  provided  with 
what  seems  to  be  the  foods  necessary  to  burn  and  make  tissue, 
and  yet  it  will  die.  Professor  Mendel  of  Yale  and  his  students 
have  shown  that  unless  animals  receive  proteins  that  contain 
certain  so-called  amino  acids  they  will  die,  although  their  diet 
is  apparently  sufficient  in  quantity  and  quality.  It  has  been 
found  that  in  certain  proteins  there  are  these  amino  acids  which 
are  used  by  the  animal  to  build  up  its  tissues.  So  important  are 
these  substances  that  the  Germans  have  called  them  “ building 
stones,’’  for  without  them  no  growth  can  take  place.  Animal 
proteins  appear  to  have  more  of  these  amino  acids  than  do  plants. 
Hence  we  see  the  value  of  a mixed  diet  which  includes  both  plant 
and  animal  foods.  Milk  appears  to  have  both  the  necessary 
amino  acids  and  certain  other  substances  called  vitamins  of  which 
we  shall  hear  more  later.  Certain  mineral  salts,  as  calcium,  iron, 
sodium,  and  potassium,  are  also  needed  by  the  body. 

^ Animals  and  some  plants  get  organic  food  from  their  environment ; but  green 
plants  make  organic  food  from  materials  which  they  get  from  their  environment. 

H.  BIO  — 22 


326  HOW  DOES  MAN  DETERMINE  THE  VALUE  OF  FOOD? 


We  live  in  an  age  where  practical  applications  of  science  are 
found  at  every  turn.  It  is  right  that  this  should  be  so,  for  we  are 
more  and  more  surrounded  by  the  things  made  by  science  and  the 
things  done  by  science.  Foods,  which  not  so  many  years  ago  were 
used  directly  from  the  stream  or  field,  are  now  put  through  a manu- 
factured process  which  changes  them  very  greatly.  Sometimes 
the  raw  plant  or  animal  substances  are  put  into  cans  and  pre- 
served for  our  use.  It  is  little  wonder  that  as  food  in  these  new 
forms  began  to  be  marketed  that  the  unprincipled  food  handlers 
began  to  adulterate  or  misbrand  their  foods,  thus  cheating  the 
purchaser.  State  government,  and  later  the  United  States  govern- 
ment, began  to  inspect  such  foods,  and  found  that  nearly  half  the 
total  number  of  samples  examined  were  adulterated.  The  Pure 
Food  and  Drugs  Act  of  1906,  with  its  subsequent  requirements, 
was  the  result  of  these  investigations.  At  the  present  time,  due 
to  official  examinations  and  inspection,  only  a very  small  amount 
of  adulterated  or  misbranded  food  is  shipped  from  one  state  to 
another.  But  materials  manufactured  and  sold  in  the  same  state 
may  still  be  adulterated,  since  the  Pure  Food  and  Drugs  Act  does 
not  control  this  situation. 

One  feature  of  adulteration  that  the  Pure  Food  and  Drugs  Act 
does  not  cover  in  a very  satisfactory  way  is  the  labeling  of  patent 
medicines.  While  the  presence  of  certain  habit-forming  drugs 
and  poisons  must  be  shown  on  the  label,  there  are  scores  of  other 
deadly  poisons  that  may  get  into  medicines  without  appearing  on 
the  label  at  all.  The  labeling  of  patent  medicines  is  controlled 
by  the  Pure  Food  and  Drugs  Act ; but  the  purchase  of  such  medi- 
cines is  in  the  hands  of  the  American  public.  Uneducated  people 
will  not  read  labels  very  carefully,  with  the  result  that  the  patent 
medicine  industry  thrives  and  people  throw  away  several  hundred 
million  dollars  each  year  and  do  what  is  far  worse,  damage  them- 
selves while  they  spend  their  good  money. 

A bad  situation  still  exists  with  reference  to  the  liquor  question. 
Many  people  hoped  that  when  the  Prohibition  Amendment  was 
repealed  that  there  would  be  less  drinking.  But  records  show 
that  there  is  a steadily  increasing  toll  of  deaths  from  the  use  of 
cheap  or  “ bootleg”  liquor,  and  what  is  worse,  a rapidly  rising  acci- 


THE  NUTRIENTS 


327 


dent  and  death  rate  from  drunken  driving.  One  of  the  more  serious 
problems  that  confront  us  as  a nation  is  that  of  controlling  the  per- 
son who  has  taken  just  enough  to  drink  so  that  he  is  uncertain  in 
his  reactions  anti  so  is  liable  to  drive  carelessly.  Every  young  per- 
son who  reads  these  lines  should  try  to  educate  others  as  to  the 
dangers  of  tlrinking,  especially  when  driving  a car,  for  we  will  solve 
our  liquor  problem  only  through  adequate  education. 


PROBLEM  L WHAT  DO  FOODS  DO  FOR  US? 

Practical  Exercise  1.  Make  a list  of  foods  that  you  have  eaten  in  the  last 
24  hours.  By  referring  to  tables  in  government  bulletins  or  any  good  lab- 
oratory manual,  classify  the  foods  under  the  following  headings. 


1 

X UTRIEXTS 

Much 

Little 

None 

Carbohydrates  . . 

Proteins  

Fats 

What  are  the  uses  of  foods  ? If  we  use  the  simile  of  the  human 
body  and  the  engine,  then  it  is  obvious  that  body  heat  and  the 
energy  we  release  in  our  daily  work  comes  from  the  foods  we  eat. 
But  unlike  an  engine,  which  cannot  repair  itself  if  damaged,  we  not 
only  repair  injuries  to  our  bodies  but  can  actually  increase  in  weight. 
Food  then  furnishes  material  for  body  growth,  for  repair  of  waste, 
for  heat,  and  for  work  when  oxidized  in  the  cells  of  the  body. 

The  nutrients.  Foods  contain  substances  called  organic  nutri- 
ents. These  we  have  already  learned  are  proteins,  carbohy- 
drates, and  fats  or  oils.  Foods  also  contain  waste.  A leg  of 
lamb  contains  bone  and  tendons ; oysters  and  clams  have  shells ; 
potatoes  and  turnips  have  skins ; and  bananas  and  oranges  have 
outer  coverings  which  cannot  be  used.  All  foods  have  some  waste. 
In  addition,  they  contain  various  amounts  of  mineral  salts  and 
frequently  a large  amount  of  water. 

Proteins  are  nutrients  which  contain  nitrogen  in  addition  to 
carbon,  oxygen,  and  hydrogen.  Foods  containing  a high  propor- 
tion of  proteins  are  lean  meats,  eggs,  some  nuts,  peas,  and  beans. 

Carbohydrates  contain  carbon,  hydrogen,  and  oxygen,  having 


328  HOW  DOES  MAN  DETERMINE  THE  VALUE  OF  FOOD? 

the  two  latter  elements  in  the  proportion  found  in  water.  Foods 
rich  in  carbohydrates  are  cereals,  breads,  cakes,  fruits,  and  jellies. 
Sugars  are  pure  carbohydrates.  Fats  and  oils  contain  carbon, 
hydrogen,  and  oxygen,  but  their  chemical  formula  shows  a rela- 
tively small  proportion  of  oxygen.  Examples  of  foods  containing 
fats  are  butter,  lard,  suet,  olive  oil,  and  mayonnaise  dressing. 

The  fuel  value  of  food.  In  various 
experiments  it  has  been  agreed  that 
the  energy  stored  in  foods  as  a source 
of  heat  should  be  stated  in  heat  units 
called  Calories.  A Calorie  is  the 
amount  of  heat  required  to  raise  the 
temperature  of  one  kilogram  of  water 
one  degree  Centigrade.  This  is  about 
equivalent  to  raising  the  temperature 
of  one  pound  of  water  four  degrees 
Fahrenheit.  The  fuel  value  of  differ- 
ent foods  may  be  computed  by  burn- 
ing a given  portion  of  each  food  in  a 
calorimeter.  It  has  thus  been  found 
that  a gram  of  fat  will  liberate  9.3 
Calories  of  heat,  while  a gram  of  carbo- 
hydrate or  protein  will  each  liberate 
only  about  4 Calories.  The  burning 
value  of  fat  is,  therefore,  over  twice 
that  of  carbohydrates  or  proteins. 

Fats  and  oils  have  the  highest 
energy  value  of  all  foods.  But  be- 
cause of  their  rather  indigestible  qualities  and  because  one  soon 
tires  of  an  excessive  amount  of  fat,  carbohydrates  are  more  used  to 
release  energy.  Cereals,  bread,  potatoes,  and  other  starchy  vege- 
tables should,  for  this  reason,  be  a part  of  our  daily  diet. 

Tissue  building  and  repair  of  waste.  But  it  is  not  sufficient 
for  man  to  “count  his  Calories.”  We  are  made  of  living  matter, 
protoplasm.  Living  cells  may  waste  away,  and  need  to  be  repaired 
.or  replaced.  New  cells  must  be  formed.  According  to  Rose 
it  is  estimated  that  the  body  of  a baby  at  birth  contains  about 


thermometer 
shov/ing  clwnge. 


L-^>/ater  arounoC  bomb 
wccrmect  by  burnings 
of  food. 

A bomb  calorimeter.  Explain  how  it 
works. 


VAIA^K  OF  IMiOTFlN 


329 


-UHH)  C'alorios  of  burnable  inalerial,  wliile  that  of  a full-|’TO\vn  man 
avera^ies  about  7t),t)l)()  (^alories.  Where  did  this  ojrowth  come 
from?  I'ivideiith',  the  tissues  use  food  for  building  purposes. 

Wq  luue  already  seen  that  carbohydrates,  fats,  and  proteins 
all  contain  the  elements  carbon,  oxygen,  and  hydrogen,  and  that 
proteins  alone  contain  the  element  nitrogen.  We  have  learned 
also  that  the  protoplasm,  which  forms  a large  part  of  the  body, 
is  thought  to  be  a very  complex  compound  composed  of  car- 


Professor  Hopkins  showed  the  value  of  milk  as  a good  food.  Explain  his  experiment  and 
results  as  given  in  the  above  diagram. 


bon,  hydrogen,  oxygen,  nitrogen,  and  ten  or  more  other  chemical 
elements.  If  living  matter  is  to  grow,  it  must  have  the  proper 
elements  for  building.  And  these  it  can  obtain  from  food.  Pro- 
teins, although  they  may  be  oxidized  to  release  energy,  are  usually 
utilized  to  give  the  body  its  nitrogen,  from  which,  in  part,  hving 
protoplasm  is  manufactured. 

Demonstration  1.  Feed  two  white  rats  of  equal  weights  for  a period  on 
different  dietaries,  using  in  one  case  an  incomplete  protein  (such  as  gliadin 
of  wheat)  and  the  other  with  a complete  protein  (such  as  in  milk)  con- 
taining the  essential  amino  acids.  A striking  contrast  may  be  obtained 
by  feeding  both  with  exactly  the  same  foods  except  that  one  has  a given 
amount  of  milk  substituted  for  the  same  amount  of  water.  Let  the  class 
watch  the  growth  of  the  two  animals  and  report  on  the  final  results. 
Weigh  the  rats  once  a week.  Keep  all  conditions  except  that  of  food 
exactly  the  same  for  both  rats. 

Not  all  proteins  are  good  tissue  builders.  Recent  feeding  experi- 
ments have  shown  that  not  all  proteins  are  capable  of  building 


330  HOW  DOES  MAN  DETERMINE  THE  VALUE  OF  FOOD? 


tissues.  It  has  been  found  that  the  complex  chemical  substance 
called  protein  may  be  broken  by  the  chemist  into  simpler  proteins 
called  amino  acids.  Some  of  these  amino  acids  are  useful  in  tissue 
building,  and  others  are  not.  If  a protein  contains  the  amino-acids 


that  will  form  the 
living  material  of  the 
body,  it  is  called  com- 
plete ; if  it  cannot  be 
used  alone  for  tissue 
building,  it  is  called 
an  incomplete  pro- 


There  are  twenty  different  amino  acids.  Where  any  number  tein.  If  tWO  ratS  are 

of  these  are  bound  up  chemically  they  form  a protein.  j • j.  j.  • 


fed  on  diets  contain- 


ing different  amino  acids,  one  may  thrive,  while  the  other  wastes 
away  and  dies.  For  example,  gelatin  is  a very  poor  type  of 
protein,  because  it  does  not  contain  all  the  amino  acids  necessary 
for  tissue  building  or  tissue  repair.  Wheat,  which  contains  a 
protein  called  gliadin,  does  not  contain  all  the  amino  acids,  al- 
though corn  does  contain  one  amino  acid  that  is  complete.  For 
this  reason  corn  makes  an  excellent  food  for  cattle  as  well  as  for 
man.  On  the  other  hand,  the  proteins  (casein  and  lactalbumin) 
in  milk  contain  the  amino  acids  necessary  for  growth.  It  is  esti- 
mated that  there  are  twenty  of  these  amino  acids  commonly 
found  in  proteins,  and  that  all  of  those  essential  for  growth  are 
found  in  lean  meat,  cheese,  milk,  eggs,  and  a few  grains  and  nuts. 
So  it  happens  that  probably  most  of  us,  without  realizing,  have 
used  for  food  the  proteins  containing  all  the  essential  amino  acids. 

The  value  of  water.  It  has  long  been  known  that  water  and 
the  various  mineral  salts  it  contains  are  essential  to  life.  The 
human  body,  by  weight,  is  about  two  thirds  water.  The  cells  of 
the  body  are  made  up  of  a jelly-like  watery  protoplasm,  and  these 
same  cells  can  be  provided  with  food  only  by  means  of  the  blood, 
which  is  over  eighty  per  cent  water.  All  moist  inner  surfaces  of 
the  body,  as  in  the  mouth,  throat,  digestive  tract,  or  lungs,  must 
have  water  in  order  to  remain  constantly  moist.  Water  is  abso- 
lutely essential  in  passing  off  the  wastes  of  the  body.  Water 
makes  up  a very  large  proportion  of  fresh  fruits  and  vegetables ; 


TIllO  MIXIORAL  HRQUlKKiMENT 


331 


it  is  also  present  in  lai’se  proportion  in  milk  and  ep;gs,  is  less 
abundant  in  meats,  and  is  lowest  in  dried  foods  and  nuts.  The 
amount  of  water  in  a given  food  is  often  a decided  factor  in  its  cost. 

Vitamins.  These  health-regulating  substances  must  be  a part 
of  every  diet.  We  know  that  they  occur  in  milk  and  in  certain 
vegetables.  l\'e  shall  learn 
more  about  them  in  the  second 
problem. 

The  mineral  requirement 
' of  the  body.  Minerals  are  also 
necessary  for  bodily  health  and 
j growth.  It  is  comparatively 
' recent  1}^  that  scientists  have 
' learned  that  very  small  quan- 
tities of  mineral  substances 
play  a very  important  part  in 
the  efficiency  of  the  human 
machinery.  Take  for  example 
the  mineral  calcium  or  lime. 

For  a long  time  it  was  known 
that  lime  formed  an  important 

part  of  the  skeleton.  A glance  ^hls  diagram  gives  the  probable  amount  of 
I at  the  diagram  shows  what  a minerals  found  in  the  body  of  a person  weigh- 
large  part  of  the  weight  of  the  pounds. 

• body  is  made  up  of  the  two  minerals,  calcium  and  phosphorus, 
most  of  which  is  found  in  our  bones.  But  calcium  has  other  uses 
in  the  body  which  are  as  important  as  bone  building.  The  clotting 
^ of  our  blood,  without  which  we  would  bleed  to  death  from  the 
smallest  cut,  appears  to  depend  largely  on  the  presence  of  minute 
amounts  of  calcium  in  the  blood.  Calcium  also  helps  to  control 
the  contraction  of  muscles,  the  regular  beating  of  the  heart,  and  the 
I response  of  nerves  to  stimulation.  Lack  of  calcium  and  phos- 
' phorus  causes  stunted  growth,  soft  bones,  and  defective  teeth. 
Milk  is  one  of  the  most  important  sources  of  calcium  for  the  body 
and  for  this  reason  should  be  included  in  the  daily  dietary. 

Phosphorus  is  also  an  important  bone  builder  and  seems  to  be  a 
i necessary  factor  along  with  sodium  in  keeping  our  blood  neutral. 


ounces  in  a 125  lb.  person. 

calcium 

29.6 

phosphorus 

19.8 

potassium 

6.9 

sulphur 

^.9 

socCium 

6. 

chlorine 

6. 

magnesiixm 

1. 

iron 

.00 

iocCine 

trorce 

fluorine 

If 

silicon. 

.. 

manganese 

•• 

332  HOW  DOES  MAN  DETERMINE  THE  VALUE  OF  FOOD? 


Compounds  of  magnesium,  potassium,  and  phosphorus  aid  the 
body  in  the  performance  of  many  of  its  important  functions. 
Iron  is  an  essential  part  of  the  red  coloring  matter  of  the  blood, 
without  which  oxygen  could  not  be  carried  to  the  cells.  From 
sodium  chloride,  our  table  salt,  comes  the  hydrochloric  acid  in  our 
gastric  juice.  Iodine  is  necessary  in  the  body  in  order  to  prevent 
goiter,  while  sulphur  and  a number  of  elements  all  seem  to  be 
necessary  for  the  building  material  of  the  body.  In  general,  the 
various  salts  may  be  considered  as  regulators  of  bodily  activity. 

Our  minerals  come  largely  from  vegetables  and  fruits,  eggs,  and 
especially  from  milk.  Meats  are  a source  of  iron,  while  fish  and 
other  sea  foods  are  rich  in  iodine.  Water  is  often  a source  of 
minerals,  and  table  salt  gives  us  most  of  our  sodium. 

If  one  will  compute  the  minerals  in  the  diet  served  in  many 
homes,  which  consists  so  largely  of  meat,  potatoes,  and  white  bread, 
he  will  easily  see  how  lacking  such  foods  are  in  the  mineral 
essentials. 

Practical  Exercises  2.  From  the  charts  given  in  any  laboratory  workbook, 
determine  the  actual  percentage  of  nutrients  in  beef,  potatoes,  oysters,  and 
corn  meal.  Do  all  foods  have  equal  nutritive  value  ? 

From  these  charts  make  a table  containing : 

(a)  Five  foods  rich  in  protein  (15  per  cent  or  more). 

(b)  Five  foods  rich  in  carbohydrates  (50  per  cent). 

(c)  Five  foods  rich  in  fat  (50  per  cent  or  more). 

(d)  Five  foods  having  a high  fuel  value  (1500  Calories  or  more  per  pound). 

(e)  Five  food  substances  that  are  over  50  per  cent  water.  How  would 
water  affect  the  cost  of  food,  providing  you  had  to  pay  for  the  water? 

(/)  Two  foods  rich  in  mineral  salts. 

In  your  opinion,  which  of  the  foods  given  are  the  best  tissue-building 
foods?  Remember  that  living  matter  is  made  up  of  carbon,  oxygen,  hydro- 
gen, nitrogen,  sulphur,  and  a minute  amount  of  mineral  salts.  Which  do  you 
consider  the  best  energy-producing  foods?  Explain. 

Roughage.  Certain  parts  of  foods  rich  in  carbohydrates,  usually 
the  cellulose  walls  of  plant  cells,  contain  indigestible  material 
which  is  useful  in  stimulating  the  muscles  in  the  large  intestine 
and  thus  causing  the  waste  matter  to  be  thrown  off  regularly. 
This  prevents  constipation.  Bran,  whole  wheat,  fresh  fruits,  and 
vegetables  provide  the  best  sources  of  these  materials. 

Flavors  and  condiments.  Most  of  us  are  aware  that  flavoring 
materials  such  as  pepper,  mustard,  and  other  condiments  are  not 
true  foods.  While  flavoring  extracts,  meat,  and  vegetable  flavors 


VITAMINS  AND  THEIR  USES 


333 


do  not  liave  food  value,  they  are  of  "reat  value  in  making  the 
food  more  appetizing  and  increasing  the  secretion  of  gastric  juice. 

What  are  the  essentials  of  an  adequate  food  supply?  One 
writer  has  said  that  “an  adequate  food  supply  should  include 
(1)  sufficient  organic  nutrients  in  digestible  form  to  yield  the 
needed  energy,  (2)  protein  sufficient  in  amount  and  appropriate  in 
kind,  (3)  adequate  amounts  and  proportion  of  various  ash  con- 
stituents or  inorganic  foodstuffs,  and  (4)  sufficient  of  each  of  essen- 
tial vitamins.”  The  problems  which  follow  will  help  us  to  find 
out  just  what  this  statement  means. 

Self-Testing  Exercise 

A food  is  anything  that  furnishes  (1)  and  (2)  or 

(3)  up  the  body.  Foods  as  purchased  may  contain  waste, 

(4)  (5),  (6),  and  (7).  The  or- 
ganic nutrients  are  (8),  (9)  or  (10),  and 

(11).  Proteins  contain (12) (13),  the  “build- 
ing stones”  of  the  body.  If  a protein  contains  the (14) 

(15)  essential  for (16),  it  is  said  to  be  a (17) 

protein (18)  are  essential  to  a diet  because  they  act  as 

(19)  of  various  bodily (20). 

PROBLEM  II.  HOW  DO  VITAMINS  HELP  US? 

Vitamins  and  their  uses.  Most  wonderful  of  all  food  substances 
are  the  regulating  substances  called  vitamins.  While  chemists 
are  only  beginning  to  learn  about  their  chemical  composition  a 
great  deal  is  known  about  what  they  do  for  us  and  what  troubles 
their  absence  will  bring  about.  There  are  six  of  these  health-regu- 
lating substances  known : they  are  called  vitamins  A,  B,  C,  D,  E, 
and  G. 

Vitamin  A is  necessary  for  normal  growth  and  protects  us  against 
infections.  Rats  fed  on  a diet  lacking  in  vitamin  A are  stunted 
in  growth  and  soon  develop  an  eye  disease  in  which  the  glands 
which  lubricate  the  eye  fail  to  give  off  fluid  and  in  consequence 
the  eye  becomes  much  inflamed.  A similar  condition  is  found  in 
people  who  lack  this  vitamin  in  their  food.  Vitamin  A is  found  in 
vegetables  that  have  a yellow  color,  such  as  carrots  and  turnips. 


334  HOW  DOES  MAN  DETERMINE  THE  VALUE  OF  FOOD? 


Yellow  corn,  for  example,  contains  much  more  than  white  corn.  It 
is  also  found  abundantly  in  green  leafy  vegetables,  as  spinach. 
Here  again  it  is  found  more  plentifully  in  the  outer  green  leaves 
of  lettuce  than  in  the  bleached  portion.  Egg  yolk  and  butter  both 
contain  vitamin  A,  but  cod-liver  oil  has  it  in  greatest  concentration. 


Milk  is  a good  source 
of  vitamin  A,  as  are 
some  animal  glands, 
especially  liver. 


Lack  of  vitamin  B 
causes  a disease  of  the 
nervous  system  called 
beriberi.  This  disease 
was  once  very  preva- 
lent in  the  Orient,  but 
since  the  sources  of 
vitamin  B have  been 
found,  the  disease  has 
been  almost  stamped 
out.  This  control  was 
simple  for  this  vitamin 
is  found  in  many  green 
leaves,  stems,  roots. 


What  vitamins  are  essential  to  the  diet? 


and  fruits  being  good  sources.  The  bean  or  hulls  of  rice,  toma- 
toes, and  fruit  juices,  as  well  as  milk,  are  good  sources.  Yeast 
contains  large  amounts  of  it,  as  does  egg  yolk,  and  it  is  found  in 
various  animal  tissues. 

Vitamin  C prevents  scurvy  and  helps  the  growth  of  the  teeth. 
It  is  found  abundantly  in  citrus  fruits  and  in  many  green  vegetables, 
as  well  as  tomatoes  and  potatoes.  Raw  milk  also  contains  this 
vitamin. 

Vitamin  D prevents  the  bone  disease  called  rickets  and  helps 
build  the  bones  and  teeth.  It  is  found  most  abundantly  in  cod- 
liver  oil,  in  fish  liver,  salmon,  and  yeast,  while  egg  yolk,  butter, 
and  milk  also  contain  good  quantities  of  it.  It  has  been  found 
that  the  ultra-violet  rays  of  the  sun  build  this  vitamin  in  various 
food  substances,  and  even  in  our  own  bodies.  This  is  done  by  the 


TllK  RELATION  OF  DIOESTI BI LITV  TO  DIET  335 


action  of  the  ult ra-\  iolot  rays  on  a kind  of  fat  in  tlio  body  called 
erqosterol. 

\’itainin  hi  is  found  most  abundantly  in  the  <’;crni  of  wheat,  but 
also  in  many  seeds  and  oreen  leaves  as  well  as  in  milk.  Its  lack, 
according  to  a group  of  workers  at  the  University  of  California, 
will  cause  rats  to  become  sterile.  We  do  not  know  much  about 
its  effects  on  other  mammals. 

N'itamin  G,  or  as  it  is  sometimes  called,  is  found  principally 
in  yeast,  milk,  and  lean  meats.  Its  lack  has  been  considered  the 
' cause  of  the  dread  disease  pellagra,  of  which  there  were  more  than 
two  hundred  thousand  cases  in  the  southern  part  of  this  country 
i as  late  as  1918.  Recent  investigations  have  cast  doubt  on  the 
fact  that  vitamin  G is  connected  with  the  prevention  of  pellagra. 

Self-Testing  Exercise 

Among  the  be.st  sources  of  vitamin  A are (1),  (2), 

(3),  and (4)  (5).  Among  the  best  sources  of 

vitamin  B are (6), (7),  and (8).  Among  the 

best  sources  of  vitamin  C are  ........  (0) (10),  and (11) 

(12).  The  best  source  of  vitamin  D is (13)  

(14).  Rickets  maj^  be  cured  by  including (15) (16)  in 

the  diet.  Scurvy  is  caused  by  lack  of (17) (18).  Beri- 
beri is  caused  by  lack  of (19)  (20).  Lack  of  vitamin 

* A causes  an (21)  (22).  Its  presence  jirotects  us  from 

1 (23)  diseases. 

PROBLEM  III.  WHAT  IS  THE  RELATION  OF  WORK,  ENVIRON- 
MENT, AGE,  SEX,  AND  DIGESTIBILITY  OF  FOODS  TO  DIET? 

I The  relation  of  work  to  diet.  It  has  been  shown  experimentally 
that  a man  doing  hard,  muscular  work  needs  more  food  than  a 
person  doing  light  work.  The  exercise  gives  the  individual  a 
hearty  appetite ; he  eats  more  and  needs  more  of  all  kinds  of 
food  than  a man  or  boy  doing  light  work,  for  he  needs  more  food 
i for  the  extra  energy  release. 

The  relation  of  environment  to  diet.  The  temperature  of  the 
i body  is  maintained  at  98.6°  in  winter  as  in  summer,  but  much 
more  heat  is  lost  from  the  body  in  cold  weather.  Hence  we  need 
I more  heat-producing  food  in  winter  than  in  summer.  We  may 


336  HOW  DOES  MAN  DETERMINE  THE  VALUE  OP  FOOD? 


MINERALS 

VITAMINS 

WT. 

GRAMS 

CALOR- 

IES 

WT. 

FAT 

GRAMS 

WT. 

CARBO. 

GRAMS 

WT. 

PROT. 

GRAMS 

CAL- 

CIUM 

PROS 

PHOR 

US 

IRON 

A 

B 

c 

D 

E 

BEVERAGES 

Cocoa 

1 cup 

255 

240 

12 

24 

9.5 

XXX 

XXX 

X 

XXX 

XX 

X 

Grape  Juice 

1 cup 

199 

200 

50 

X 

X 

XX 

XX 

XX 

XX 

Orange  Juice 

1 cup 

232 

100 

25 

X 

XXX 

XX 

XXX 

BREADS 

Coffee  cake 

3x3x4" 

117 

333 

12.08 

48 

8 

X 

X 

X 

Muffins,  graham 

1 large 

78 

200 

3.5 

35 

6.5 

X 

XX 

X 

X 

X 

Waffles,  plain 

1 6"diam. 

26.7 

100 

4 

12.5 

3.5 

X 

X 

X 

X 

Rolls,  French 

1 roll  , 

36.8 

100 

1 

20 

3 

X 

X 

X 

Ham  sandwich 

1 slice  2x4x| 

39 

200 

14 

13.7 

5 

X 

X 

X 

Lettuce  and  tomato 

ft  ft 

1 slice  2x4  x| 

sandwich 

59 

108 

6 

11 

2 

X 

X 

X 

XX 

X 

CAKE 

Gingerbread 

31 

100 

2 

18 

2 

X 

X 

X 

X 

White 

V42'i]" 

42 

135 

5 

16 

3 

X 

X 

X 

CEREALS 

Farina  * 

^ cup 

170 

100 

.5 

21 

3 

X 

X 

XX 

Oats,  rolled  -•!= 

1 cup 

280.5 

100 

1.83 

16.67 

4.2 

X 

XX 

X 

X 

XX 

X ■ 

Wheat,  shredded 

1 bis. 

27.4 

100 

.49 

20.59 

3.51 

X 

XX 

X 

X 

XX 

X 

CRACKERS 

Saltines 

6 

23 

98 

3 

15 

2.4 

Uneedas 

4 

28.4 

105 

2.3 

19 

2.5 

FATS 

Butter 

1 Tbsp. 

13 

100 

11 

.13 

XXX 

X 

X 

X 

Olive  Oil 

1 Tbsp. 

11.11 

100 

11.11 

FRUITS 

Apple  § 

1 

212 

100 

.64 

23 

.64 

X 

X 

X 

XX 

Canteloupe  § 

1 4Jl"diam. 

510 

100 

24 

1.5 

XX 

XX 

XX 

X 

Figs,  dried 

l^i  large 

31 

100 

24 

1.4 

X 

XX 

X 

X 

Oranges  § 

1 large 

268 

100 

.3 

23 

1.61 

X 

XX 

X 

XX 

XXX 

Peaches,  fresh  § 

3 med. 

290 

100 

.3 

23 

1.5 

X 

X 

X 

XX 

Prunes,  stewed 

2&2T.  juice 

60 

100 

24 

.5 

X 

X 

XX 

NUTS 

Brazil  nuts 

2 nuts 

15.5 

100 

9.5 

1 

2.5 

XX 

Peanuts,  sh’I'd 

single  nuts 

20-24 

18.2 

100 

7 

4.5 

4.69 

X 

X 

X 

XX 

XX 

PIES 

Apple 

4^^  arc 

136 

300 

13.8 

42 

2.25 

X 

X 

X 

Custard 

4"arc 

118 

200 

7.2 

29.5 

4.5 

X 

X 

XX 

XX 

Lemon  meringue 

3' arc 

85 

450 

13.5 

76 

5.8 

X 

X 

Raisin 

4^''arc 

85 

256 

9 

52 

2.25 

X 

X 

X 

X 

X 

EGGS 

Plain 

1^3 

67.5 

100 

7.09 

9.05 

X 

X 

X 

XXX 

XXX 

X 

X 

X 

FISH 

Creamed  codfish 

Vz  cup 

60 

100 

5 

5.5 

8 

X 

X 

X 

XXX 

XX 

XXX 

Mackerel,  broiled 

4'i2'ilJ^' 

62 

100 

5 

14 

X 

X 

X 

Salmon,  canned 

^ cup 

52 

100 

6 

11 

X 

X 

X 

XX 

X 

^ CooJted 


§ As  purchased 


VITA^riXS  AND  THEIR  USES 


337 


MINERALS 

VITAMINS 

WT. 

GRAMS 

CALOR- 

IES 

WT. 

FAT 

GRAMS 

WT. 

GARBO. 

GRAMS 

WT. 

PROT. 

GRAMS 

CAL- 

CIUM 

PHOS 

PHOR 

US 

IRON 

A 

B 

C 

D 

E 

CHEESE 

American,  pale 

cube 

22.8 

100 

0 

.07 

6.5 

XX 

XX 

XX 

XX 

MEATS 

Chicken  meat 

1 med.  slice 

55 

100 

5.57 

12.5 

X 

X 

Beef,  round  pot  roast 

1 slice 

43 

88 

5 

13 

X 

X 

Steak,  broiled  club 

3x2'4'''z  ^ 

51 

100 

6.5 

10 

X 

X 

Lamb,  chops,  broiled 

11arge2x2xlJ£ 

46 

100 

6.5 

10 

X 

X 

Pork,  bacon 

4-5  small  pcs. 

14 

100 

9.5 

3 

X 

X 

Ham,  boiled 

4^i'4x^" 

37 

100 

8 

7 

X 

X 

XX 

HamOurger 

2Ji''diam.xl'' 

56 

100 

5 

14 

X 

X 

X 

XX 

Frankfort 

^oflink,3?4''l. 

40 

100 

7.4 

.44 

7.8 

X 

MILK 

Whole 

% cup 

144.5 

100 

5.8 

7 

4.7 

XXX 

XX 

XXX 

XX 

X 

X 

X 

Malted 

2 Tbsp. 

25.7 

100 

.77 

19.71 

3.57 

XX 

XX 

X 

XX 

X 

X 

X 

PUDDINGS 

Bread  pudding 

% cup 

66.8 

259 

12 

8 

29 

X 

X 

X 

X 

Cup  custard 

% cup 

210 

225 

9 

25 

10 

X 

X 

X 

XX 

X 

X 

SALADS 

Combination 

cup 

90 

34 

.2 

6 

2 

XX 

XXX 

XX 

XX 

XX 

XX 

Fruit 

^ cup 

87 

198 

16 

11 

2 

X 

X 

XX 

XXX 

XXX 

X 

Lettuce,  French 

dressing 

1 serv. 

78 

237 

25 

2 

.8 

XX 

XXX 

XXX 

X 

XX 

XXX 

XX 

Tomato  and  lettuce 

1 serv. 

149 

194 

19 

5 

2 

X 

XX 

X 

XXX 

XX 

XXX 

X 

Salad  Dressings 

French 

2 Tbsp. 

24 

133 

15 

Mayonnaise 

1 Tbsp 

14 

100 

10 

.6 

2 

X 

X 

XX 

SOUPS 

Consomme 

1 cup 

214 

5 

.2 

1 

Cream  of  cleartomato 

1 cup 

240 

269 

19 

18 

7.5 

XX 

XX 

X 

XX 

XX 

XX 

X 

X 

Split  pea 

1 cup 

260 

93 

.04 

12 

10 

X 

XX 

XX 

XX 

XX 

X 

SWEETS 

Chocolate  fudge 

iVax^xl"' 

25.5 

97.8 

2.2 

19 

.5 

X 

X 

X 

XX 

X 

Jelly  beans 

B^l  large 

28 

100 

24 

1 

Nut  bar 

2!!3'il" 

62 

330 

14 

47 

4 

X 

X 

X 

X 

X 

Suckers 

1^3 

26 

TOO 

25 

VEGETABLES 

Asparagus 

5 stalks 

112 

25 

.13 

13.82 

2.07 

X 

XX 

XX 

XXX 

String  beans 

1 cup 

108 

45 

.32 

7 

2.44 

XX 

XX 

XX 

XX 

XX 

X 

Cabbage,  shred'd 

1 cup 

63.3 

20 

.19 

3.55 

1.01 

XX 

X 

XXX 

X 

XX 

XXX 

Corn  on  cob 

1 ear  6" 

130 

100 

I 

19.5 

3 

X 

X 

X 

X 

XX 

Onions 

3 or  4 med. 

205 

100 

.62 

20.33 

3.3 

X 

X 

X 

X 

XX 

Peas,  canned 

^cup 

180.5 

100 

.36 

17.73 

6.52 

X 

XX 

XX 

XX 

XX 

Potatoes,  plain 

1 

120 

10O 

.12 

22.09 

2.64 

X 

X 

X 

X 

XX 

X 

Tomatoes,  canned 

442 

100 

.88 

17.70 

5.31 

X 

XX 

X 

XX 

XX 

XXX 

Sauerkraut 

3 Tbsp.  heap. 

100 

16 

3 

1 

X 

XX 

X 

X 

XX 

X 

After  Tables  of  Food  Values,  A.V.Bradley,  Santa  Barbara  State  Teachers  College,  Santa  Barbara,  Calif. 


338  HOW  DOES  MAN  DETERMINE  THE  VALUE  OF  FOOD? 


use  carbohydrates  for  this  purpose,  as  they  are  economical  and 
easily  digested.  The  inhabitants  of  cold  countries  get  their 
heat-producing  foods  largely  from  fats.  In  tropical  countries 
and  in  hot  weather  a considerable  amount  of  fresh  fruit  should 
be  used  in  the  diet. 

The  relation  of  size  and  age  to  diet.  Age  is  a factor  in  determin- 
ing not  only  the  kind  but  also  the  amount  of  food  to  be  used. 
Young  children  require  a large  proportion  of  protein  in  their  diet 
in  order  to  grow.  They  are  also  more  active  than  older  persons 
and  so  use  a large  amount  of  food  as  fuel  in  proportion  to  their 
weight.  The  body  constantly  increases  in  size  and  weight  until 
young  manhood  or  womanhood,  and  then  its  size  and  weight 
remain  nearly  stationary,  varying  with  health  or  illness.  It  is 
evident  that  adults  require  food  only  to  repair  the  waste  of  cells 
and  to  release  energy.  Elderly  people  need  much  less  protein 
than  do  younger  persons. 

The  relation  of  sex  to  diet.  As  a rule,  boys  need  more  food 
than  girls,  and  men  than  women.  This  seems  to  be  due,  first,  to 
the  more  active  muscular  life  of  the  man,  and,  second,  to  a layer 
of  fatty  tissue  directly  under  the  skin  of  the  woman,  which  acts  as 
an  insulating  layer  against  loss  of  heat  from  the  body.  Larger 
bodies,  because  of  greater  surface,  give  off  more  heat  than  smaller 
ones.  Men  are  usually  larger  than  are  women,  — another  reason 
why  they  require  more  food. 

The  relation  of  digestibility  to  diet.  Food  must  be  digested 
in  order  to  be  used  in  the  body.  Animal  foods  in  general  can  be 
more  completely  digested  within  the  body  than  plant  foods.  This 
is  largely  due  to  the  fact  that  plant  cells  have  woody  walls  that 
the  digestive  juices  cannot  dissolve.  Heat  causes  the  starch 
grains  to  swell  and  thus  break  these  woody  walls.  This  is  one 
reason  for  the  thorough  cooking  of  vegetable  foods.  Cereals 
and  legumes  are  less  digestible  foods  than  milk  and  eggs.  The 
agreement  or  disagreement  of  food  with  an  individual  is  largely  a 
personal  matter.  Jack  Spratt,  for  example,  cannot  eat  raw  toma- 
toes without  suffering  from  indigestion,  while  Mrs.  Spratt  can 
digest  tomatoes  but  not  strawberries.  Each  individual  should 
learn  early  in  life  the  foods  that  disagree  with  him  and  leave  such 


APPKTITE  AND  DIKT 


339 


burst 

-}-h0cct 

/ 

CT” 

pop  corn 
^th  its 
starch,  grains 


potato  starch 
grains^ 

boUin^ 


foods  out  of  liis  diet,  for  “ wliat  is  one  man’s  meat  may  be 
another  man’s  poison.” 

The  relation  of  appetite  to  diet.  Every  one  likes  some  things 
better  than  others.  Through  experimentation  it  has  been  found 
that  foods  whicli  are 
enjoyed  cause  a flow 
of  digestive  juices, 
not  only  in  the 
mouth  but  also  in 
the  stomach.  The 
sight,  odor,  and  taste 
of  food  we  like  actu- 
ally aid  in  diges- 
tion. “Digestion 
waits  on  appetite.” 

If  we  use  common 
sense  in  the  selec- 
tion of  foods,  and 

take  care  to  avoid  sugccr- 

foods  that  we  cannot 
easily  digest,  we  shall 
find  that  the  appetite  is  often  a guide  in  the  selection  of  foods. 

Acidosis  and  how  to  prevent  it.  The  body  is  a very  delicate 
machine.  Its  parts  must  be  adjusted  to  a nicety  or  trouble  results. 
The  blood  is  normally  alkaline.  If  fat  is  not  completely  oxidized 
in  the  body,  the  partly  oxidized  fat  remains  in  the  tissues  as  a 
fatty  acid.  This  changes  the  alkalinity  of  the  blood  to  acidity 
and  trouble  immediately  follows.  This  condition,  called  acidosis 
or  “ kotosis,”  is  often  benefited  by  eating  fruits  and  vegetables 
and  avoiding  use  of  meats  and  fats. 


V''.- 


Stccrcte 
chandcs  to 


^arains  enlarge 
■ SncC  breccdc 
did^tive 


Explain  what  happens  to  starch  when  it  is  heated? 

it  is  digested? 


Self-Testing  Exercise 

A man  needs (1) (2)  when  he  does  hard  physical 

work  than  when  he (3)  a (4)  life.  A (5) 

person  needs  more  food  than  a (6)  one,  for  he  has  more 

(7)  to  feed (8)  plays  a part  in  the  kind  as  well  as 

the (9)  of  food  needed  by  the  body.  What  is  one  man’s 


340  HOW  DOES  MAN  DETERMINE  THE  VALUE  OF  FOOD? 


meat  is  another  man’s  (10),  so  we  should  learn  what  we  can 

(11).  Acidosis  may  be  combated  by  a diet  in  which  an  excess 

of (12)  and (13)  is  present. 

PROBLEM  IV,  WHAT  IS  THE  BEST  PROPORTION  OF 
NUTRIENTS  IN  OUR  DAILY  DIET? 

The  nutritive  ratio.  Inasmuch  as  all  living  substance  contains 
nitrogen,  it  is  evident  that  protein  food  must  form  a part  of  the 
diet ; but  protein  alone  is  not  a safe  choice.  If  more  protein  is 
eaten  than  the  body  requires,  the  liver  and  kidneys  have  to 
work  overtime  to  get  rid  of  the  excess  of  protein,  which  forms 
a poisonous  waste  harmful  to  the  body.  We  must  take  foods 
that  will  give  us,  as  nearly  as  possible,  the  proportion  of  the 
different  chemical  elements  as  they  are  contained  in  protoplasm, 
as  well  as  an  amount  necessary  to  supply  energy  to  the  body.  It 
has  been  found,  as  a result  of  studies  by  Atwater  and  others, 
that  a man  who  does  moderate  muscular  work  requires  nearly 
one  quarter  of  a pound  of  protein,  the  same  amount  of  fat,  and 
a little  less  than  one  pound  of  carbohydrate  to  provide  for  the 
growth,  waste,  and  repair  of  the  body  and  the  energy  used  up 
in  one  day.  The  proportion  of  protein  in  the  diet  is  called  the 
nutritive  ratio. 

The  protein  requirement  varies  with  the  age  and  size  of  a person, 
but  not  with  the  activity.  For  the  child,  from  12  to  15  per  cent 
of  the  total  Calories  should  be  protein.  Protein  is  necessary  for 
the  building  and  the  repair  of  the  body.  Therefore  larger  amounts 
are  needed  during  growth.  The  child  requiring  2000  Calories 
needs  from  240  to  300  Calories  of  protein.  Whereas  the  adult, 
who  has  ceased  growing,  needs  but  10  per  cent  of  his  total  in 
protein.  Therefore  with  an  energy  requirement  of  2500  he  would 
need  about  250  protein  Calories.  Activity  has  never  been  shown 
to  break  down  the  body  cells  any  more  than  the  use  of  the  brain 
destroys  brain  cells.  Therefore  protein  does  not  need  to  be  in- 
creased because  one  is  doing  muscular  work.  Milk,  meat,  and 
eggs  are  just  as  essential  for  the  school  teacher  as  for  the  man  who 
is  doing  severe  muscular  work. 


BASAL  METABOLISM 


341 


Atwater,  Chittenden,  and  \'oit  have  worked  out  tables  in 
which  they  have  given  the  proportion  of  the  various  nutrients 


C.M.OIUKS  I’ROM 
I’UOTKINS 

C.VLORIKS  FROM  F.\T 

Calories  fro.m 
Carhohydrate.s 

Atwater  .... 

14 

32 

54 

('hittciulcn  . . . 

10 

30 

60 

Voit 

25 

20 

55 

that  should  be  present  in  every  100  Calories  of  food.  Any  of  the 
three  standards  might  be  used. 

Knowing  the  proportion  of  the  different  nutrients  required 
as  well  as  the  foods  containing  vitamins  and  minerals,  it  will  be 
easy  for  you  to  determine  from  tables  (such  as  on  pages  336-337) 
the  best  combinations  of  foods  for  a well-balanced  diet. 

Self-Testing  Exercise 

The  protein  requirement (1)  with  the  age  and  (2) 

and  not  with  the  (3).  A man  who  does  moderate  muscular 

work  requires  nearly (4) (5)  from  protein, (6) 

(7)  from  fat,  and (8)  (9)  from  carbohydrate. 

PROBLEM  V.  WHAT  IS  THE  DAILY  CALORIE  REQUIREMENT? 

Workbook  Exercises.  Foods  taken  into  the  body  having  the  pro- 
portions of  the  nutrients  given  above  constitute  a balanced  ration  or 
diet  because  they  provide  the  body  with  the  right  proportion  for  tissue 
building  as  well  as  for  fuel  food. 

Compare  the  life  you  lead  with  that  of  a day  laborer.  Would  your 
needs  be  the  same  ? 

Compare  your  life  with  the  life  of  an  Eskimo  in  the  Arctic  regions. 
Would  the  proportion  of  the  nutrients  needed  by  him  be  the  same  as 
you  need?  Explain. 

Would  the  same  proportion  of  nutrients  be,  needed  for  all  occupa- 
tions and  in  all  localities? 

Are  there  any  other  factors  that  might  cause  different  proportions 
of  the  nutrients  needed  by  individuals? 

Would  a vegetarian  diet  contain  the  protein  necessary  for  the  body? 
How  would  it  compare  with  a diet  containing  only  meat?  Are  there 
any  reasons  why  a wholly  vegetable  diet  is  unwise  ? 

Malnutrition.  When  the  body  cells  do  not  receive  a proper 
amount  of  food  or  the  right  kinds  of  food,  then  a loss  in  body  weight 


342  HOW  DOES  MAN  DETERMINE  THE  VALUE  OF  FOOD? 


may  occur,  and  we  say  that  person  is  undernourished,  or  is  suffer- 
ing from  malnutrition.  An  undernourished  person  is  likely  to  be 
susceptible  to  disease,  to  tire  easily,  and  to  be  sensitive  to  cold  and 
exposure.  Frequently,  girls  having  large  bones  in  their  skeleton 
attempt  to  get  thinner,  and  find  all  too  soon  that  they  have  only 
made  themselves  ill  without  much  reducing  their  body  weight, 
which  is  largely  due  to  these  heavy  bones.  Never  take  up  a “fad” 
diet  without  first  consulting  your  own  or  the  school  physician. 

Basal  metabolism^  The  activities  of  a living  plant  or  animal, 
which  include  all  the  processes  that  are  involved  in  the  building 
up  and  breaking  down  of  protoplasm  in  the  body,  are  known  col- 
lectively as  the  metabolic  processes  (Gr.  metaholos,  changeable). 
These  changes  release  heat  as  a by-product  and  this  heat  can  be 
measured  in  calories.  The  heat-producing  activity  of  the  body 
during  sleep  or  rest  represents  the  energy  which  is  essential  for 
carrying  on  the  vital  processes  and  is  known  as  basal  metabolism. 
It  is  represented  in  a man  of  average  weight  (about  150  pounds) 
by  about  65  Calories  an  hour. 

Method  of  computing  energy  requirement.  The  energy  re- 
quirement of  a person  depends  primarily  upon  his  age,  size,  and 
activity.  This  requirement  is  most  easily  understood  if  expressed 
in  Calories  per  pound  per  day.  The  following  table  shows  the 
variation  in  the  energy  requirement  of  the  average  healthy  indi- 
vidual due  to  age. 


Ages  .... 

1 

6 

10 

14 

16-18 

20 

Average  Wt.  . 

22  lbs. 

44  lbs. 

66  lbs. 

99  lbs. 

100-150  lbs. 

120-160  lbs. 

Calories  per  lb. 
Total  Calories 

45 

35 

35 

33 

20-33 

20 

per  day  . . 

1000 

1550 

2300 

3300 

2600-4400 

2400-3200 

The  above  table  shows  that  the  small  child  needs  a much  larger 
amount  of  food  in  proportion  to  his  weight  than  the  older  child 
or  adult.  The  larger  individual  needs  a larger  amount  of  food 
than  the  smaller  person,  but  if  the  weight  is  multiplied  by  the 
Calories  per  pound,  this  factor  is  taken  into  account.  For  example. 


Metabolism ; me-tab'6-Iiz’m. 


CALOKIE  REQUIREMENT 


343 


one  f()urteen-yoar-()l(l  boy  may  wei^b  100  pounds  and  another 
140  pounds  and  both  bo  healthy  boys,  but  the  larger  boy  will 
need  a much  larger  amount  of  food.  The  above  recpiirement 
will  vary  also  with  the  activity  of  the  child,  the  less  active  one 
will  need  less  food.  The  difference  in  the  energy  requirement 
of  an  adult  due  to  the  type  of  activity  is  shown  in  the  follow- 
ing figures ; 


Type  ok  Activity 

Average  Calories  per 
Pound  per  Hour 

Sleeping  or  lying  awake  . . 

Sitting 

Typewriting 

Standing 

Walking  at  moderate  rate  . . 

Active  exercise 

one  half 

two  thirds 

nine  tenths 

three  fourths 

one  and  one  half 

one  and  three  fourths 

Suppose  that  a man  weighing  150  pounds  spent  his  24-hour 
day  by  sleeping  8 hours,  sitting  8 hours,  typing  2 hours,  standing 
4 hours,  walking  2 hours,  he  would  require  2570  Calories  a day. 

150  X -3-  X 8 = 600  sleeping  150  X f X 4 = 450  standing 

150  X -f  X 8 = 800  sitting  150  X 1|-  X 2 = 450  walking 

150  X X 2 270  typing 

From  these  two  tables  one  can  easily  compute  his  own  energy 
requirement. 


Workbook  Exercise.  Check  up  your  day’s  total  Calories  by  com- 
paring it  with  your  requirement  by  body  weight  and  by  the  tables  given 
on  pages  342  and  343. 

Head  your  paper  : Name , age , weight lbs. 

Daily  Calorie  needs 

Amount  used 

Discrepancy 

How  does  your  day’s  total  Calories  compare  with  that  given  in  the 
table  of  daily  needs  of  a person  of  your  age,  doing  the  kind  of  work  you 
did  for  the  day  ? How  can  you  account  for  any  discrepancy  ? 

_ Can  you  suggest  any  improvement  in  your . diet  ? Check  on  the 
vitamin  content  of  your  diet. 


344  HOW  DOES  MAN  DETERMINE  THE  VALUE  OF  FOOD? 


Workbook  Exercise.  What  proportion  of  my  daily  diet  goes  into 
(a)  basal  metabolism,  (b)  growth,  (c)  activity,  (d)  excretion?  Using 
the  diagrams  furnished  and  your  own  daily  diet,  check  on  your  age 
and  sex  to  see  the  proportion  of  your  daily  food  that  should  go 


The  upper  chart  is  for  boys,  the  lower  one  for  girls.  The  relative  amount  of  Calories  needed 
for  different  ages  are  for  (B),  space  between  base  line  and  first  graph,  basal  metabolism, 
(G)  growth,  (A)  activity,  and  (E)  excretion,  spaces  between  graphs  {after  Holt). 


(a)  into  your  basal  metabolic  needs,  (h)  into  growth  of  your  body, 
(c)  into  your  daily  activity  (This,  of  course,  will  vary,  depending  on 
the  kind  of  work  you  do  out  of  school),  (d)  the  amount  that  goes 
into  excretion  or  body  wastes.  Remember  that  your  growth  calories 
must  come  from  protein  food  and  that  activity  should  come  largely 
from  carbohydrates  and  fats.  Compare  carefully  to  see  how  near 
your  proportions  are  to  the  ideal  condition. 

Do  you  eat  the  correct  proportions  of  nutrients  to  give  your  dietetic 
needs  as  shown  by  the  charts  given  above  ? 


CIIEAl’XESS  OF  FOODS 


345 


Self-Testing  Exercise 

Write  tlie  numbers  of  the  correct  answers  in  ,your  workbook. 

A i)erson  asleep  uses,  per  pound  of  body  weight  i)er  hour,  (1)  one 
Calorie  ; (2)  j C'alorie  ; (3)  10  Calories ; (4)  i-  Calorie. 

.Vcidosis  may  be  avoided  by  using  (5)  orange  juice;  (G)  soda  mint 
tablets ; (7)  hot  water  before  meals  ; (8)  red  meats  in  the  dietary. 

Roughage  (9)  helps  give  the  body  proteins  ; (10)  adds  Calories  to  the 
dietary;  (11)  aids  in  regulating  bowel  movement. 

The  protein  requirement  of  the  total  Calorie  requirement  of  the  body 
I is  (12)  10  per  cent;  (13)  25  per  cent;  (14)  100  per  cent;  (15)  50  per 
cent. 

I PROBLEM  VI.  HOW  CAN  THE  RELATIVE  CHEAPNESS  OF 
FOODS  BE  DETERMINED? 

Practical  Exercise  3.  To  find  the  relation  of  the  value  of  food  to  its  cost  in 
the  family  dietary.  Make  a careful  record  of  all  purchases  of  food  in  your 
home  for  one  week.  Find  out  what  the  average  weekly  cost  is  by  dividing 
the  total  cost  by  the  number  in  your  family. 

Using  the  tables  on  pages  336-337  and  your  daily  calorie  requirement, 
make  out  a cheap,  appetizing  but  well-balanced  menu  for  one  person  for  a 
period  of  one  week.  Multiply  the  result  by  the  total  number  in  your  family. 
Compare  the  total  cost  thus  obtained  with  that  worked  out  from  your  home 
dietary. 

Are  you  living  as  economically  as  you  might  ? What  inexpensive  substitutes 
might  you  introduce  in  place  of  meat? 

The  relation  of  cost  of  food  to  diet.  It  is  a mistaken  notion  that 
the  best  foods  are  always  the  most  expensive.  A study  of  the 
tables  on  pages  336  and  337  will  show  us  that  fuel  and  tissue- 
building materials  as  well  as  vitamins  are  present  in  foods  from 
! vegetable  sources,  as  well  as  in  those  from  animal  sources ; and 
i the  vegetable  foods  are  usually  cheaper.  The  American  people 
' are  far  less  economical  in  their  purchase  of  food  than  most  other 
nations.  A comparison  of  the  daily  diets  of  persons  in  various 
occupations  in  this  and  other  countries  shows  that  as  a rule 
we  eat  more  than  is  necessary  to  supply  materials  for  fuel  and 
i repair.  Another  waste  of  money  by  Americans  is  due  to  the  false 
; notion  that  a large  proportion  of  the  daily  diet  should  be  meat. 

Many  people  think  that  the  most  expensive  cuts  of  meat  are  the 
1 most  nutritious.  The  falsity  of  this  idea  may  be  seen  by  a careful 
, study  of  the  table  on  page  346. 


346  HOW  DOES  MAN  DETERMINE  THE  VALUE  OF  POOD? 


FATS  CAR^^^^^TES  RJE^AU^ 


FOOD 

MATERIALS 

1 PRICE  PERI 

1 POUND  1 

25  CENTS 

WILL  BUY 

POUNDS  OF  NUTRIENTS  AND  CALORIES  OF  FUEL 
VALUE  IN  25  CENTS  WORTH 

1 LB.  2 LBS.  3 LBS. 

CENTS 

POUNDS 

2,000  CAL.  4,000  CAL.  6,000  CAL. 

Beef,  round 

35 

^ POUNDS  1 

■1^  CALORIE! 

s 

Beef,  sirloin 

50 

.50 

m 

Beef,  shoulder 

30 

.83 

m 

Mutton,  leg 

40 

.03 

m 

Pork,  loin 

30 

.83 

Pork,  salt,  fat 

30 

.83 

Ham,  smoked 

45 

.56 

m 

Codfish,  fresh, 
dressed 

25 

1.00 

Oysters,  90  cents 
per  quart 

45 

.56 

■ 

Milk,  15  cents 
per  quart 

m 

3.33 

Butter 

62 

.40 

Cheese 

40 

.03 

Eggs,  60  cents 
per  dozen 

40 

.63 

1 

Wheat  bread 

m 

2.00 

Corn  Meal 

6 

4.17 

''W%\ 

Oat  Meal 

10 

2.50 

1 

m 

n 

Beans,  white,  dried 

12M 

2.00 

mmm. 

Rice 

10 

2 50 

\ 

Potatoes  $1.50 
per  bushel 

2^ 

10.00 

Sugar 

6 

4.17 

■ ■ 

Table  showing  cost  of  various  foods.  Check  these  prices  with  present  prices  in  your 
community. 


Preparation  of  foods.  Much  loss  occurs  in  the  improper 
cooking  of  foods.  Meats  especially,  when  overdone,  lose  much 
of  their  flavor  and  are  far  less  digestible  than  when  they  are 
cooked  properly.  The  chief  reasons  for  cooking  meats  are  that 


FOOD  HABITS 


347 


tlio  muscle  fibers  may  be  loosened  and  softened,  in  which  condition 
they  are  dij^ested  more  easily,  and  that  the  bacteria  and  other 
parasites  in  the  meat  may  be  killed  by  the  heat.  The  common 
method  of  fiyin^  makes  foods  difficult  to  digest.  A good  way  to 
prepare  meat,  either  for  stew  or  soup,  is  to  place  the  meat,  cut  in 
small  pieces,  in  cold  water,  and  allow  it  to  simmer  for  several 
hours.  Rapid  boiling  toughens  the  muscle  fibers  just  as  the  white 
of  egg  becomes  solid  when  heated.  Boiling  and  roasting  are 
excellent  methods  of  cooking  meat.  In  order  to  prevent  the  loss 
of  the  nutrients  in  roasting,  it  is  well  to  baste  the  meat  frequently ; 
thus  a crust  is  formed  on  the  outer  surface  of  the  meat,  which 
prevents  the  escape  of  the  juices  from  the  inside. 

\Tgetables  are  cooked  in  order  that  the  cells  containing  starch 
grains  may  be  broken  down.  This  allows  the  starch  to  be  reached 
more  easily  by  the  digestive  fluids.  Inasmuch  as  water  may 
dissolve  out  nutrients  from  vegetable  tissues,  it  is  best  to  boil 
such  foods  rapidly  in  a small  amount  of  water.  This  gives  less 
time  for  the  solvent  action  to  take  place.  Vegetables  should  be 
cooked  with  the  outer  skin  left  on  whenever  it  is  possible. 

Practical  Exercises  4.  1 . Why  should  foods  be  cooked  ? Give  three  reasons. 

2.  Why  is  a mixed  diet  necessary? 

3.  Name  five  common  errors  in  selecting  foods. 

4.  Of  what  use  are  inorganic  nutrients  ? 

5.  Of  what  use  are  condiments  and  flavoring  substances? 

6.  Of  what  use  are  soups  as  food  ? 

7.  Why  do  we  use  fruit  in  a daily  dietary? 

8.  Is  the  use  of  tea  or  coffee  justifiable  in  a daily  diet?  Why  do  people 
drink  them  ? 

9.  Why  are  cheap  cuts  of  meat  cheap  ? 

10.  Defend  the  statement,  “ The  average  American  family  wastes  enough 
in  the  kitchen  to  support  a French  family.” 

Food  habits.  Habits  play  a very  important  part  in  our  life 
activities.  We  do  not  think  much  about  our  daily  activities,  for 
once  having  learned  the  reasons  for  performing  certain  acts,  those 
acts  become  habits.  The  habit  of  brushing  teeth  properly,  of  the 
choice  of  the  right  kinds  and  proportions  of  food,  of  the  avoidance 
of  tea  and  coffee,  — these  and  other  useful  acts  should  become  auto- 
matic. Some  health  habits  that  are  worth  acquiring  are : 

(1)  Have  your  meals  at  regular  hours. 

(2)  Take  time  to  eat  and  enjoy  your  meals. 


348  HOW  DOES  MAN  DETERMINE  THE  VALUE  OF  FOOD? 


(3)  Chew  your  food  thoroughly  before  swallowing  it. 

(4)  Do  not  take  an  excessive  amount  of  any  one  food  to  the 
exclusion  of  others.  Learn  to  eat  a balanced  diet. 

(5)  Eat  plenty  of  foods  containing  vitamins. 

(6)  Avoid  too  great  a proportion  of  highly  flavored  or  spiced 
foods. 

(7)  Avoid  greasy  or  fried  food. 

(8)  Avoid  foods  that  you  know  do  not  agree  with  you. 

(9)  Avoid  foods  that  you  cannot  digest  easily  and  properly. 

(10)  Do  not  eat  when  tired.  Rest  a few  minutes  before  begin- 
ning your  meal. 

(11)  Drink  plenty  of  water,  at  least  six  glasses  a day,  preferably 
between  meals. 

Self-Testing  Exercise 

Foods  are  cheap  if  they  supply (1)  and (2)  materials 

in  good  quantity  for  the  price  paid (3)  foods  can  be  spoiled 

by (4)  cooking.  Eating  the  right  kinds  of  foods  in  the  right 

way  should  become  a (5). 

PROBLEM  VII.  WHAT  IS  ADULTERATION? 

Pure  Food  Law.  In  1906  Congress  passed  a Pure  Food  and 
Drugs  Act  that  defined  adulteration  and  remedied  to  some  extent 
conditions  in  the  preparation  of  foods  that  enter  into  interstate 
commerce.  Before  the  passage  of  this  act,  about  half  of  nearly 
2000  samples  of  food  examined  in  several  different  states  were 
shown  to  be  adulterated.  In  Massachusetts,  the  State  Board  of 
Health  made  examinations  of  food  for  adulteration  as  early  as 
1883.  At  that  time  over  60  per  cent  of  all  foods  examined  were 
found  to  be  adulterated.  Today  both  adulteration  and  misbrand- 
ing of  food  are  forbidden  under  severe  penalties. 

Demonstration  2.  To  study  some  forms  of  food  adulteration  and 
some  means  of  detecting  adulterants. 

Put  some  butter  in  a spoon  and  heat  it  over  a lamp.  If  it  is  good 
butter,  it  will  boil  quietly,  with  much  foam.  Oleomargarine  or  poor 
butter  will  splutter  and  crackle,  with  little  foam. 

Place  half  a teaspoonful  of  coffee  to  be  tested  on  the  surface  of  the 
cold  water  in  the  glass.  Leave  it  for  not  more  than  five  minutes. 


ADULTERANTS 


349 


If  the  material  sinks,  leaviii";  a hrownisli  trace  in  the  water  as  it  sinks, 
it  probably  contains  a larj^e  amount  of  chicory.  If  it  floats  for  five 
minutes,  it  is  coifec.  U'hat  happens  to  the  specimen  you  tested? 

Plaw  half  a teasimonful  of  mashed  canned  peas  or  beans  in  a beaker 
containing  one  teaspoonful  of  water  and  10  drops  of  hydrochloric 
acid.  Set  the  beaker  in  a dish  of  boiling  water.  Drop  a new  iron 
nail  into  the  mixture.  Roil  for  ten  minutes.  Stir  constantly.  If  the 
nail  turns  green,  copj^er  has  been  used  to  color  the  peas. 

Put  a teaspoonful  of  milk  in  a beaker.  Add  twice  the  amount  of 
hydrochloric  acid  to  which  a drop  of  ferric  chloride  has  been  added. 
Mix  by  rotating  the  beaker  gently.  Place  the  beaker  in  a pan  of 
boiling  water  and  leave  for  five  minutes.  If  there  is  a purple  or 
lavender  color,  formaldehyde  was  present  in  the  milk. 

Adulteration.  The  substitution  of  some  cheaper  substance, 
i the  subtraction  of  some  valuable  substance  from  a food,  or 
: the  addition  of  poisonous  or  decomposed  substances,  with  a 
view  to  cheating  the  purchaser,  is  known  as  adulteration.  Ex- 
^ amples  of  common  substitutions  in  foods  are  cottonseed  oil 
for  olive  oil ; apple  parings  or  core  for  other  fruits  in  jellies ; sac- 
charine, which  is  several  hundred  times  sweeter  than  sugar, 
in  candy,  ginger  ale,  and  other  drinks ; glucose  or  brown  sugar 
for  maple  sugar;  and  cereals,  which  cost  less,  for  meats  in 
sausage.  But  such  adulterations  are  not  actually  harmful.  Other 
examples  of  added  ingredients  which  may  be  harmful  to  health 
are  arsenic,  salicylic  acid,  borax,  and  boracic  acid. 

; Still  another  type  of  adulteration  is  seen  in  the  mixing  or  adding 
to  the  substance  of  colors  of  dyes.  Such  artificial  coloring  is  seen 
in  the  addition  of  copper  sulphate  to  give  a green  color  to  canned 
' vegetables,  annatto  to  give  color  to  butter,  coal-tar  dyes  of  many 
( colors  to  give  coloring  to  candy,  jellies,  flavoring  extracts,  soft 
I drinks,  and  even  meats  or  sausage. 

Examples  of  the  taking  away  of  a valuable  part  of  the  food  are 
seen  in  the  abstraction  of  cocoa  butter  from  chocolate,  butter  fats 
from  milk,  or  the  essential  oils  from  spices. 

Probably  the  food  which  has  suffered  most  from  adulteration 
I is  milk,  as  water  can  be  added  without  the  average  person  being 
j the  wiser.  By  means  of  an  inexpensive  instrument  known  as  a 
I lactometer,  this  cheat  can  easily  be  detected.  Before  the  Pure 
Food  Law  was  passed  in  1906,  milk  was  frequently  treated  with 


350  HOW  DOES  MAN  DETERMINE  THE  VALUE  OF  FOOD? 


substances  like  formalin,  a harmful  preservative,  to  keep  it  sweet 
for  a longer  time. 


FEDERAL  FOOD  & DRUGS  ACT 

HERE  ARE  ITS  POWERS 
THE  SALE  OF  ‘ 

AND  LIMITATIONS  REGARDING 
PATENT  MEDICINES” 

IT  APPLIES  ONLY  TO  PRODUCTS  THAT 
ARE  MADE  IN  ONE  STATE  AND  SOLD  IN 
ANOTHER  (INTERSTATE  COMMERCE). 

IT  DOES  NOT  APPLY  TO  PRODUCTS 

THAT  ARE  SOLD  IN  THE  SAME  STATE  AS 
THAT  IN  WHICH  THEY  ARE  MADE  (INTRA- 

IT PROHIBITS  "FALSE  OR  MISLEADING- 

STATEMENTS  (IN  OR  ON  THE  TRADE 

STATE  COMMERCE). 

IT  DOES  NOT  PROHIBIT  false  or 

MISLEADING  STATEMENTS  IN  NEWSPAPER 

PACKAGE  ONLY)  REGARDING  COMPOSITION 

AND  SOURCE  OF  ORIGIN. 

IT  PROHIBITS-  false  and  fraudulent-- 

STATEMENTS  (IN  OR  ON  THE  TRADE 

ADVERTISEMENTS.  CIRCULARS.  WINDOW 
DISPLAYS,  ETC. 

IT  DOES  NOT  PROHIBIT  any  kind 

of  a lie  REGARDING  CURATIVE  EFFECTS 

PACKAGE  ONLY)  REGARDING  CURATIVE 
EFFECTS. 

IT  REQUIRES  the  manufacturers 

OF  NOSTRUMS  TO  DECLARE  (IN  OR  ON  THE 

IF  THAT  LIE  IS  TOLD  ELSEWHERE  THAN  IN 

OR  ON  THE  TRADE  PACKAGE! 

IT  DOES  NOT  REQUIRE  -patent 

MEDICINE”  MAKERS  TO  DECLARE  EVEN 

TRADE  PACKAGE  ONLY) THE  PRESENCE  AND 
AMOUNT  OF  ALCOHOL,  MORPHINE.  OPIUM. 
COCAINE.  HEROIN.  EUCAINE.  CHLOROFORM. 
CANNABIS  INDICA.  CHLORAL  HYDRATE  AND 

ACETANILID  AND  THEIR  DERIVATIVES. 

THE  PRESENCE  OF  SUCH  DEADLY  POISONS 

AS  PRUSSIC  ACID,  CARBOLIC  ACID,  ARSENIC, 
STRYCHNINE  - NOR  ANY  OF  SCORES  OF 
OTHER  DANGEROUS  DRUGS! 

American  Medical  Association 


Read  this  carefully.  In  what  respects  is  this  a good  law  ? What  changes  would  you  suggest 

in  it  ? 


Self-Testing  Exercise 

Adulteration  is  the (1)  of  some (2)  substance  in 

a food,  the  subtraction  of  some (3)  substance  from  a food  or 

the  addition  of  some (4)  substance  to  a food.  Saccharine  is  a 

substitute  for (5),  chickory  for (6),  and  cottonseed 

oil  for (7) (8). 

PROBLEM  VIII.  WHAT  IS  THE  TRUTH  ABOUT  STIMULANTS 
AND  NARCOTICS? 

Stimulants.  We  have  learned  that  food  is  anything  that 
supplies  building  material  or  releases  energy  in  the  body;  but 
some  materials  used  by  man,  presumably  as  food,  do  not  come 
under  this  head.  Such  are  tea  and  coffee.  When  taken  in  moder- 


DANtJERS  FROM  ALCOHOL 


351 


ate  quantities,  tliey  produce  a temporary  increase  in  the  vital 
activities  of  tlie  person  takin<2;  them.  This  stimulation  is  due  to  the 
presence  of  a drug  calletl  caffcin.  which  acts  upon  the  nervous  sys- 
tem as  a whip  acts  on  a tired  horse.  In  moderation,  tea  and  coffee 
appear  to  be  harmless  to  most  adults.  Some  people,  however,  can- 
not use  either,  even  in  small  quantities,  without  ill  effects.  It  is 
the  habit  of  relying  upon  the  stimulation  given  by  tea  or  coffee 
that  makes  them  a danger  to  man.  Cocoa  and  chocolate,  although 
both  contain  a stimulant,  are  in  addition  good  foods,  having  from  12 
per  cent  to  21  per  cent  of  protein,  from  29  per  cent  to  48  per  cent 
of  fat,  and  over  30  per  cent  of  carbohydrate  in  their  composition. 

Demonstration  3.  To  show  the  effect  of  alcohol  on  white  of  egg. 

To  some  fresh  white  of  egg  in  a test  tube  add,  drop  by  drop,  50 
per  cent  alcohol  (about  the  i)roportion  in  whiskey).  What  happens? 
Remember  white  of  egg  is  like  protoplasm  in  its  chemical  makeup. 
Tlie  teacher  should  explain  that  this  does  not  happen  to  the  body  cells. 

Demonstration  4.  To  show  the  effect  of  alcohol  on  Paramecia.  To 
a grooved  slide  containing  culture  of  Paramecia  add  drop  by  drop  some 
50  per  cent  alcohol.  What  happens  at  first?  What  happens  later? 
How  do  you  account  for  this? 

Is  alcohol  a food?  The  question  of  the  use  of  alcohol  is  still 
of  much  interest  among  physiologists  and  doctors.  Experiments 
by  Professor  Atwater  in  this  country  and  by  Durig  and  Millanby 
in  England  confirm  the  fact  that  small  quantities  of  alcohol  are 
oxidized  in  the  body  and  therefore  may  be  used  in  place  of 
either  fat  or  carbohydrate  foods.  Raymond  Pearl  has  pointed 
out  that  mortality  from  alcohol  is  usually  amongst  the  hard 
drinkers  and  that  there  is  very  little  difference  in  the  death  rate 
between  the  abstainers  and  the  moderate  drinkers.  But,  un- 
fortunately, there  are  plenty  of  people  who  do  not  know  how  to 
control  their  appetites. 

Alcohol  a poison.  On  the  other  hand,  we  know  that  although 
alcohol  may  technically  be  considered  as  a food,  it  has  a harmful 
effect  on  the  body  tissues  which  foods  do  not  have.  According 
to  Professor  Chittenden,  one  of  the  great  dietary  experts  of  this 
country,  alcohol,^  although  it  is  oxidized  in  the  body,  has  a harmful 

1 Alcohol  is  made  up  of  carbon,  oxygen,  and  hydrogen.  It  is  very  easily  oxidized, 
but  it  cannot,  as  is  shown  by  the  chemical  formula,  be  of  use  to  the  body  in  tissue 
building,  because  of  its  lack  of  nitrogen. 


352  HOW  DOES  MAN  DETERMINE  THE  VALUE  OF  FOOD? 


effect  upon  the  liver  and  circulation,  because  it  burns  too  fast 
and  hence  throws  into  the  circulation  substances  which  are  harmful 
to  health.  A commonly  accepted  definition  of  a poison  is : any 
substance  which,  when  taken  into  the  body,  tends  to  cause  the 
death  of  the  organism  or  serious  detriment  to  its  health.  This 
indicates  that  alcohol  is  a poison.  Furthermore,  statistics  appear 
to  indicate  that  certain  diseases,  notably  cirrhosis  of  the  liver, 
are  greatly  increased  by  the  excessive  use  of  alcohol. 


There  seems  to  be  a close  relation  between  the  death  rate  per  100,000  from  alcoholism 
(lower  graph)  and  from  cirrhosis  of  the  liver,  a disease  caused  by  alcohol  (upper  graph).  When 
the  prohibition  amendment  went  into  effect  in  1919,  there  was  a decrease  in  this  disease,  but  it 
is  again  becoming  a more  frequent  cause  of  death. 

Dangers  from  alcohol.  Now  that  the  repeal  of  the  prohibition 
amendment  has  allowed  freer  drinking,  it  is  time  for  us  to  take  stock 
of  the  results.  Some  are  very  definite  and  easy  to  find.  First 
there  is  no  doubt  that  the  curve  of  deaths  from  diseases  caused  by 
alcohol  are  definitely  on  the  increase.  The  deaths  from  alcoholism 
in  nineteen  large  cities  in  the  United  States,  which  dropped  in  1920 
to  less  than  a sixth  of  what  they  were  in  1916,  have  mounted  today 
almost  as  high  as  they  were  before  prohibition.  While  the 
deaths  from  bootleg  liquor  are  not  as  many,  we  still  have  plenty 
of  newspaper  references  to  them.  But  worst  of  all  is  the  mounting 


EFFECTS  OF  ALCOHOL 


353 


toll  of  the  (Iriiiiken  driver.  In  1934  a lar^o  insurance  company 
estimated  that  there  were  thirty’-six  thousand  persons  killed  in 
automobile  accidents,  one  every  fifteen  minutes  in  the  year.  The 
death  rate  was  10  per  cent  higher  than  in  1933.  In  1927  there 
were  23,200,000  motor  vehicles  in  use  and  25,533  deaths.  In 
1934  there  were  about  24,000,000  motor  vehicles  and  over  36,000 
deaths,  an  increase  all  out  of  proportion  to  the  increase  in  the 
number  of  motor  vehicles.  It  looks  as  if  we  would  have  to  find 
another  reason  for  reckless  slaughter  and  that  reason  maybe  alcohol, 
i Experiments  made  in  this  country  in  1924  with  as  small  an 
! amount  of  alcohol  as  is  found  in  a glass  or  two  of  beer  showed  that 
j the  effect  of  this  much  alcohol  was  to  narrow  the  eye  span  of  the 
j dri\'er,  to  reduce  the  distance  the  eye  can  see  clearly  by  one  third, 
( and  to  confuse  the  perceptions  of  colors  so  that  red  and  green 
j lights  could  not  always  be  distinguished. 

I The  effect  of  alcohol  on  the  mortality  of  offspring.  Experi- 
j menters  have  worked  with  guinea  pigs  and  white  rats  to  learn  if 
alcohol  has  any  effect  upon  the  birth  rate  and  death  rate  of  the 
offspring.  They  found  that  the  death  rate  is  much  higher  in  the 
animals  born  from  alcoholic  parents  than  in  those  from  non- 
1 alcoholic  parents.  The  rate  of  development  of  the  young  is  faster 
in  the  non-alcoholic  animals. 

; A somewhat  similar  study  was  made  in  England,  comparing  the 
children  of  twenty-one  mothers  who  drank  with  those  of  twenty- 
I eight  mothers  who  were  sober  and  whose  husbands  did  not  drink. 

! The  drinking  mothers  lost  55  per  cent  of  their  babies  before 
! they  were  two  years  old,  while  the  non-drinking  mothers  lost  less 
I than  24  per  cent  of  their  children  during  the  same  period, 
i Susceptibility  to  disease  increased  by  alcohol.  A good  many 
experiments  have  been  made  which  prove  that  alcohol  causes 
increased  susceptibility  to  disease.  Some  experiments  made  by 
Dr.  E.  G.  Stillman  of  the  Rockefeller  Institute  show  that  mice 
intoxicated  with  alcohol  have  much  less  resistance  to  pneumonia 
germs  than  normal  mice. 

Death  rates  in  different  occupations.  Reports  from  England, 

, where  certain  occupations  give  a special  temptation  to  drink, 

, show  that  if  100  be  accepted  as  an  average  death  rate,  the  rate 


354  HOW  DOES  MAN  DETERMINE  THE  VALUE  OF  FOOD  ? 


among  brewers  is  129,  among  hotel  keepers  160,  and  among 
barkeepers  218.  On  the  other  hand,  the  death  rate  among  clergy- 
men is  only  56,  for  agricultural  workers  60,  and  in  the  medical 
profession  88. 

Project.  Try  to  obtain  from  your  health  department  statistics  which 
will  enable  you  to  get  the  percentage  of  people  who  die  from  diseases  brought 
about  or  affected  by  alcohol.  Estimate  the  number  of  deaths  for  the  current 
year.  Compare  with  the  number  of  deaths  from  the  same  causes  before  pro- 
hibition. Make  your  comparison  on  a proportionate  basis. 

The  use  of  tobacco.  A well-known  authority  defines  a narcotic 
as  a substance  “ which  directly  induces  sleep,  blunts  the  senses,  and, 
in  large  amounts,  produces  complete  insensibility.”  Opium,  chloral, 
and  cocaine  are  examples  of  narcotics.  Tobacco  owes  its  narcotic 
influence  to  a strong  poison  known  as  nicotine.  Its  use  in  killing 
insect  parasites  on  plants  is  well  known.  In  experiments  with 
jellyfish  and  other  simply  organized  animals,  the  author  has  found 
as  little  as  one  part  of  nicotine  to  one  hundred  thousand  parts  of 
sea  water  to  be  sufficient  to  affect  profoundly  an  animal  placed 
within  it.  Nicotine  in  a pure  form  is  so  powerful  a poison  that 
two  or  three  drops  would  be  sufficient  to  cause  the  death  of  a 
man  by  its  action  upon  the  nervous  system,  especially  upon  the 
nerves  controlling  the  beating  of  the  heart.  It  has  been  demon- 
strated that  tobacco  has,  too,  an  important  effect  on  muscular 
development. 

Practical  Exercise  6.  Why  should  boys  in  training  stop  smoking  ? Make 
a list  of  the  harmful  results  which  come  from  smoking. 


Self-Testing  Exekcise 

Check  the  correct  statements  for  your  workbook : 

T.  F.  1.  Tea,  coffee,  and  alcohol  are  stimulants. 

T.  F.  2.  Cocoa  and  chocolate  contain  no  stimulating  material. 

T.  F.  3.  Alcohol  may  be  a food  as  well  as  a poison. 

T.  F.  4.  A narcotic  poison  induces  sleep  by  quickening  the  heart 
action,  thus  producing  insensibility. 

T.  F.  5.  Opium,  chloral,  nicotine,  and  cocaine  are  examples  of  nar- 
cotics. They  are  all  habit-forming  drugs. 


THE  IH’KE  FOOD  AND  DIU'GS  ACT 


355 


PROBLEM  IX.  HOW  DOES  THE  PURE  FOOD  AND  DRUGS 
ACT  WORK? 

Project.  Make  a collection  of  the  labels  of  patent*  inedicines  and 
classify  each  under  one  of  the  heads  in  the  following  paragraphs. 
Report  in  class. 

Project.  Make  a collection  of  free  samples  of  patent  medicines 
and  classify  under  the  heads  found  in  the  following  paragraphs. 

Drugs.  A certain  proportion  of  people  are  addicted  to  the  use 
of  drugs  found  in  patent  medicines.  A glance  at  the  street-car 
advertisements  shows  this.  As  is  pointed  out  by  Dr.  Arthur  J. 
Cramp  of  the  American  Medical  Association,  the  United  States 
, patent  office  requires  that  in  order  to  patent  an  article  it  must  be 
I both  new  and  useful.  This  requirement  would  automatically  pre- 
i vent  the  patenting  of  practically  all  so-called  “ patent  medicines  ” 
because  they  are  usually  combinations  of  drugs  that  have  long 
, been  used  by  the  medical  profession  and  frequently  given  up 
^ by  reputable  physicians  in  favor  of  more  effective  or  safer  drugs. 
Patent  medicines  depend  upon  secrecy  and  mystery  for  their  very 
existence.  Hence  they  are  not  patented  at  all,  for  if  they  were 
their  formulae  would  be  open.  The  Pure  Food  and  Drugs  Act  has 
^ at  least  caused  some  of  the  harmful  products  used  in  the  formula 
to  be  placed  on  the  label  so  that  people  who  buy  may  know  what 
they  are  getting. 

Bracers.  Most  of  the  medicines  advertised  contain  alcohol  in 
greater  quantity  than  beer  or  wine,  and  many  of  them  have  habit- 
1 forming  drugs  in  their  composition.  Not  only  are  many  “ sarsapa- 
rillas  ” and  “ bitters  ” put  on  the  market,  but  they  are  often  sold 
! to  persons  who  are  opposed  to  alcohol.  A dose  of  one  of  these 
' medicines  usually  contains  about  as  much  alcohol  as  the  same 
amount  of  whisky.  Such  “ bracers,”  as  the  American  Medical 
Association  have  called  this  type  of  medicine,  are  of  course  habit- 
formers.  Any  one  who  begins  to  take  them  will  soon  become 
dependent  upon  them. 

Heart  depressants.  Another  kind  of  medicine  commonly  sold 
is  the  poison  acetanilid  (as-et-an'i-lid),  a powerful  heart  depres- 
sant contained,  even  at  the  present  time,  in  a good  many  of  the 
so-called  headache  powders.  Although  the  Pure  Food  and  Drugs 


356  HOW  DOES  MAN  DETERMINE  THE  VALUE  OF  FOOD? 


Act  now  requires  that  the  label  show  a statement  of  the  alcohol, 
acetanilid,  cocaine,  opium,  and  certain  other  harmful  drugs  con- 
tained in  a patent  medicine,  many  people  do  not  read  the  label, 
so  the  danger  continues.  What  is  far  worse,  the  use  of  such  drugs 
often  leads  to  the  drug  habit.  There  is  danger  also  from  prussic 
acid,  arsenic,  and  other  deadly  drugs  not  covered  by  the  law. 

Cure-alls.  Perhaps  the  worst  thing  about  patent  medicines  is 
that  they  rarely  cure  any  one,  and  they  take  an  immense  amount 
of  money  from  people  who  can  ill  afford  to  spend  it.  Nearly 
$300,000,000  a year  is  estimated  to  be  spent  for  patent  medicines 
alone  in  this  country.  Many  people,  incurably  ill  with  tuberculosis 
or  cancer,  make  their  condition  worse  through  the  purchase  of  cough 
or  cancer  cures,  which  probably  contain  a habit-forming  drug  or 
alcohol.  Think  how  much  more  good  the  money  thus  spent 
would  have  done  had  it  been  invested  in  proper  foods  and  good 
nursing,  or  in  gaining  the  advice  of  a reliable  physician. 

Due  to  the  fact  that  the  present  law  does  not  require  the  publish- 
ing of  the  composition  of  the  medicine  on  the  label,  the  public 
is  being  continually  fooled  into  paying  big  prices  for  worthless 
or  even  dangerous  combinations  of  drugs.  Think  of  paying  $3.00 
for  a few  cents’  worth  of  washing  soda  and  salt.  Or  $.50  for  $.01 
worth  of  Epsom  salt.  Yet  this  is  being  done  every  day.  To 
paraphrase  a great  showman : “ There  are  some  people  who 
always  want  to  be  fooled.”  Are  any  friends  of  yours  in  this 
class  ? 

One  of  the  reasons  why  people  buy  patent  medicines  is  because 
they  read  the  glowing  testimonials  written  by  people  who  say 
they  have  been  cured  by  patent  medicines.  Investigation  of 
such  letters  often  shows  that  they  have  been  written  by  people 
who  were  paid  for  writing  them.  There  is  a regular  business  in 
the  buying  and  selling  of  patent  medicine  testimonials.  Such 
testimony  is  worthless,  and  in  cases  where  the  testimonial  is  written 
in  good  faith  how  do  we  know  that  the  person  who  wrote  it  really 
did  receive  the  benefits  testified  to  from  that  particular  medicine. 
Frequently  we  know  he  did  not  because  death  notices  of  people 
who  wrote,  saying  that  they  have  been  cured  of  tuberculosis  or 
kidney  trouble  by  this  or  that  nostrum,  have  been  found  in  the 


TESTS 


357 


same  issue  of  the  paper  containing  the  testimonial  which  says  “ I 
have  been  cured.”  The  moral  is;  do  not  believe  the  testimonial. 

Self-Testing  Exercise 

Check  the  correct  statements  for  your  workbook: 

T.  F.  1.  The  Pure  Food  and  Drugs  Act  requires  that  the  trade 
package  declare  the  presence  of  all  poisonous  drugs  in  a patent  medi- 
cine. 

T.  F.  2.  The  Pure  Food  and  Drugs  Act  prohibits  fake  or  mislead- 
ing statements  in  newspapers  and  circulars  concerning  the  curative 
powers  of  a drug. 

T.  F.  3.  Testimonials  are  valuable  because  they  prove  that  persons 
are  cured  of  disease  by  patent  medicines. 

T.  F.  4.  “ Bracers  ” are  valuable  because  they  help  people  to  forget 
their  troubles. 

T.  F.  5.  Some  people  may  be  cured  by  patent  medicines. 

Review  Summary 

Check  your  knowledge  of  this  unit  by : (1)  rechecking  the  survey  questions ; 
(2)  performing  all  assigned  exercises ; (3)  checking  with  j'-our  teacher  the  scores 
of  the  various  tests  and  doing  over  the  parts  you  missed ; and  finally  (4)  making 
an  outline  for  your  notebook. 

Test  on  Fundamental  Concepts 

In  vertical  column  under  the  lieading  CORRECT  write  numbers  of  all  statements  you  be- 
lieve are  true.  In  another  column  under  INCORRECT  write  numbers  of  untrue  statements. 
Your  grade  = right  answers  X 2-J-. 

I.  Foods  (1)  may  contain  organic  nutrients,  salts,  vitamins,  and 
water ; (2)  are  never  oxidized  in  the  body ; (3)  always  build  tissues ; 
(4)  should  never  be  used  unless  they  contain  vitamins ; (5)  are  neces- 
sary for  growth,  work,  and  well  being. 

II.  Proteins  (6)  are  necessary  for  growth;  (7)  must  contain  the 
amino  acids  necessary  for  tissue  building  if  they  are  to  be  called  com- 
plete ; (8)  may  contain  several  or  all  eighteen  amino  acids ; (9)  in 
gelatin  furnish  tissue-building  material;  (10)  in  milk  contain  all  the 
amino  acids  necessary  for  growth. 

III.  Foods  (11)  containing  vitamin  A promote  growth  and  prevent 
the  eye  disease  called  xerophthalmia;  (12)  when  taken  in  the  right  pro- 
portions, form  a balanced  ration;  (13)  containing  vitamin  B prevent 
loss  of  sleep;  (14)  containing  vitamin  C prevent  scurvy;  (15)  will 
never  contain  vitamin  D unless  they  are  placed  in  the  sunlight. 


358  HOW  DOES  MAN  DETERMINE  THE  VALUE  OF  FOOD? 


IV.  The  factors  which  determine  the  amount  of  food  one  should 

eat  are  (16)  the  kind  of  work  he  does;  (17)  the  size  of  his  skeleton; 
(18)  his  age;  (19)  where  he  lives  and  the  time  of  year;  (20)  his 
appetite. 

V.  A diet  is  well  balanced  (21)  when  it  contains  all  the  vitamins; 
(22)  when  10  to  20  per  cent  of  its  Calories  are  protein;  (23)  when  it 
has  the  right  proportion  of  nutrients  to  make  living  matter  and  supply 
the  body  with  energy  for  the  kind  of  work  we  have  to  do ; (24)  when 
the  food  is  properly  cooked  ; (25)  when  it  contains  all  the  nutrients. 

VI.  The  Pure  Food  and  Drugs  Act  (26)  prevents  the  use  of  patent 
medicines ; (27)  prevents  the  use  of  stimulants ; (28)  prohibits  false 
or  fraudulent  statements  (on  trade  packages  only)  regarding  the 
curative  effects  of  patent  medicines;  (29)  has  prevented  the  use  of 
certain  harmful  drugs  ; (30)  applies  only  to  the  products  which  are  made 
in  one  state  and  sold  in  another. 

VII.  Alcohol  (31)  is  a narcotic  poison;  (32)  is  a food,  because  it 
can  be  oxidized  in  the  body ; (33)  is  found  in  many  patent  medicines  ; 
(34)  causes  greater  susceptibility  to  disease ; (35)  never  hurt  anybody. 

VIII.  Patent  medicines  (36)  are  safe  to  take  if  you  know  what  they 
contain ; (37)  rarely  cure  and  may  do  much  harm ; (38)  must  state 
on  the  label  the  presence  of  such  deadly  drugs  as  arsenic,  strychnine, 
and  prussic  acid ; (39)  must  state  on  the  label  the  presence  of  alcohol, 
morphine,  opium,  and  cocaine ; (40)  often  have  false  claims  made  for 
them  in  the  newspapers  and  such  statements  are  lawful. 

Achievement  Test 

1.  What  is  the  difference  between  a nutrient  and  a food? 

2.  Why  are  some  proteins  better  tissue-building  foods  than  others  ? 

3.  How  can  you  make  a dietary  containing  the  necessary  vita- 
mins? 

4.  What  are  “ the  essentials  of  an  adequate  food  supply  ”? 

5.  What  foods  are  harmful  to  you? 

6.  How  do  you  judge  a cheap  and  an  expensive  food? 

7.  What  are  your  own  calorie  needs? 

8.  How  would  you  make  up  an  individual  100-Calorie  dietary  giv- 
ing the  correct  proportions  of  carbohydrates,  fat,  and  proteins? 

9.  What  are  the  strong  and  weak  points  of  the  present  Pure  Food 
and  Drugs  Act? 

10.  What  is  an  adulterant  under  the  law? 


TKSTS 


359 


1 ].  TTow  would  you  make  fivo  tests  for  the  detection  of  adulterants? 

12.  \\'hat  are  both  sides  of  the  alcohol  (luestion? 

13.  W hat  proof  have  we  that  alcohol  is  a poison? 

14.  What  are  the  chief  tyj^es  of  fakes  in  the  patent  medicine  game? 


Practical  Problems 

1.  Give  examples  of  ten  cheap  foods  that  are  good  foods.  Justify 
your  statement. 

2.  It  is  said  that  an  American  eats  twice  as  much  meat  as  a French- 
man. Are  there  any  reasons  why  he  should  do  this? 

3.  A boy  weighing  12")  lbs.  uses  about  150  Calories  in  slowly  walking 
3 miles.  How  many  Calories  will  he  use  in  taking  a 10-niile  hike? 
Suppose  he  should  speed  up  his  rate  of  walking.  Would  he  use  more 
Calories  for  the  same  distance? 

4.  Estimate  your  own  Calorie  needs  for  a hike  of  12  miles,  walking 
moderately  all  the  way. 

5.  If  food  costs  5 cents  per  100  Calories,  would  it  be  cheaper  to  pay 
8 cents  for  carfare  or  walk  a mile  and  a half  to  school? 

6.  Suppose  you  were  ill  and  had  to  use  milk  as  a food.  How  much 
milk  per  day  would  you  have  to  take  to  supply  your  basal  metabolism 
for  24  hours? 

7.  iMake  a collection  of  patent  medicine  labels  to  show  the  various 
kinds  and  amounts  of  alcohol  and  poisons  contained  therein.  Classify 
them  according  to  the  harm  they  do;  according  to  the  drugs  they 
contain. 


Useful  References 

Adventures  in  Biology.  N.  Y.  Association  of  Biology  Teachers  (for 
projects). 

Carpenter  and  Carpenter,  The  Foods  We  Eat.  American  Book,  1925. 
Cramp,  N'ostrums  and  Quackery,  Vols.  I and  H.  American  Medical 
Association,  1921. 

Emerson,  Haven,  Alcohol:  Its  Effects  on  Man.  Appleton-Century,  1934. 
Farmers’  Bulletins : 23,  34,  42,  85,  93,  121,  128,  132,  142,  182,  249,  256, 
295,  298,  717,  817,  824,  975,  1313,  1383. 

Rose,  The  Foundations  of  Nutrition.  Macmillan,  1927. 

Sherman,  Chemistry  of  Food  and  Nutrition.  Macmillan,  1932. 

Sherman  and  Smith,  The  Vitamins.  Chemical  Catalogue,  1931. 

Wdreat  and  Fitzpatrick,  Everyday  Problems  in  Health.  American  Book, 
1935. 

W^illiams,  Personal  Hygiene  Applied.  Saunders,  1931. 


SURVEY  QUESTIONS 

Why  do  you  chew  food  ? What  do  we  mean  by  the  term  “ digestion  ” ? 
Do  you  know  what  does  the  digesting  of  food?  Do  plants  digest  their 
foods  ? Where  do  we  digest  foods  ? How  and  why  do  we  digest  foods  ? 
Do  you  know  how  to  avoid  having  indigestion  ? 


Photo  by  H.  Armstrong  Roberts 


UNIT  XII 

HOW  FOOD  IS  PREPARED  FOR  BODY  USE 

Preview.  It  seems  a far  cry  from  the  chemistry  laboratory, 
with  its  bottles  and  test  tubes,  its  acids  and  its  bases  and  all  of 
the  complicated  formulae  that  we  see  in  chemistry  books,  to  our 
own  digestive  tract.  But  to  the  physiologist  the  human  body 
is  a marvelous  chemical  laboratory  which  in  the  complexity 
of  its  working  makes  our  science  laboratory  in  school  seem  very 
insignificant.  We  have  learned  that  organic  food  substances  are 
found  in  the  leaves  of  plants.  This  food  has  to  be  taken  to  other 
parts  of  the  plant  in  order  to  be  used.  Before  it  can  be  trans- 
ported from  one  part  of  the  plant  to  another,  it  has  to  be  made 
soluble  so  that  it  can  pass  from  one  cell  to  another  by  the  process 
of  diffusion  through  a cell  membrane.  This  change  of  food  from 

360 


WHAT  IS  A GLAND? 


3{)1 

an  insoluble  to  a soluble  form,  you  remember,  was  brought  about 
by  agents  called  enzymes.  Several  dilferent  kinds  of  enzymes  were 
found  in  the  plant  cells,  and  in  those  cells  digestion  took  place. 

Somewhat  the  same  condition  exists  in  animals.  If  food  is  to 
be  of  use  to  man,  it  must  be  changed  into  a soluble  form  that 
can  pass  through  the  walls  of  the  alimentary  canal,  or  food  tube. 
This  process  is  carried  out  by  the  various  enzymes  which  bring 
about  digestion. 

In  nearly  all  vertebrate  animals,  food  is  taken  into  the  mouth  and 
passed  through  a food  tube,  in  which  it  is  digested.  This  tube  is 
composed  of  different  portions,  named,  respectively,  as  we  pass 
from  the  mouth  downward,  pharynx  (far'inks),  gullet,  stomach, 
small  intestine,  and  large  intestine.  Attached  to  this  food  tube 
or  lying  in  its  walls  are  structures  called  glands.  It  is  within  the 
cells  of  these  glands  that  the  enzymes  are  manufactured  which 
cause  digestion  to  take  place. 

PROBLEM  1.  WHAT  IS  A GLAND  AND  HOW  DOES  IT  DO 
ITS  WORK? 

In  addition  to  the  alimentary  canal  proper,  and  connected  with 
it,  we  find  a number  of  digestive  glands.  These  are  the  salivary 
glands  of  the  mouth,  the  gastric  glands  of  the  stomach,  the  pan- 
creas (pan'kre-as)  and  the  liver,  both  connected  with  the  small 
intestine  by  ducts,  and  the  intestinal  glands  in  the  walls  of  the 
small  intestine.  Besides  these  glands  which  aid  directly  in  diges- 
tion, there  are  several  others  known  as  the  endocrine  (en'd6-krin) 
or  ductless  glands,  because  they  have  no  ducts  or  tubes  to  carry  off 
their  contents.  These  glands  give  their  secretions,  which  contain 
substances  known  as  hormones,  directly  into  the  blood.  We  shall 
study  their  functions  later.  * 

Demonstration  1.  A simple  gland.  (Microscopic  preparation.) 
Under  the  microscope,  notice  the  structure  of  a gland  in  both  cross 
and  longitudinal  sections.  With  what  is  the  wall  lined?  What  is 
the  shape  of  the  gland  ? If  work  is  done  by  a gland,  then  it  must  have 
food  to  do  this  work.  Might  the  material  poured  out  of  a gland  be 
manufactured  from  the  food  it  gets? 

What  structures  would  of  necessity  go  to  a gland  to  take  food  there? 
Write  a paragraph  telling  the  uses  and  structure  of  a gland. 


362  HOW  FOOD  IS  PREPARED  FOR  BODY  USE 

Structure  of  glands.  In  its  simplest  form  a gland  may  be  a 
collection  of  cells  which,  by  means  of  their  own  activity,  manu- 
facture and  pour  out  a substance  known  as  a secretion.  The 
nectar  gland  of  a flower  is  such  a collection  of  ceils.  In  animals, 
glands  are  usually  tubular,  such  as  the  gastric  gland  shown  on 
page  371,  or  like  little  sacs,  as  in  the  diagram.  In  all  animal 
glands  there  is  a rich  blood  supply  to  and  from  the  secreting  cells 

that  line  the  tubes  or  sacs,  and 
tiny  nerves  which  control  the 
gland  cells  and  blood  supply. 

Enzymes  and  their  work. 
Certain  gland  cells  form  secre- 
tions containing  the  chemical 
activators  called  enzymes,  which 
we  have  already  learned  cause 
digestion  in  plants.  In  animals 
the  enzymes  secreted  by  the 
cells  of  the  glands  and  poured 
out  into  the  food  tube  act  upon 
insoluble  foods  so  as  to  change 
them  to  a soluble  form.  They 
are  the  product  of  the  activity 
of  the  cell,  although  they  are 
not  themselves  alive.  Some 
enzymes  render  certain  foods 
soluble,  others  work  in  the  blood,  and  still  others  probably  act 
within  the  cells  of  the  body  as  an  aid  to  oxidation,  when  work  is 
done.  Enzymes  are  very  sensitive  to  changes  in  temperature  and 
to  the  degree  of  acidity  or  alkalinity  of  the  material  in  which  they 
act.  We  shall  find  that  the  enzymes* from  glands  in  the  walls  of 
the  mouth  will  not  be  active  very  long  in  the  stomach  after  the 
change  from  the  alkaline  medium  in  the  mouth  to  the.  acid  medium 
in  the  stomach.  Enzymes  seem  to  be  able  to  work  indefinitely, 
provided  the  surroundings  are  favorable.  A small  amount  of  diges- 
tive enzyme,  if  it  had  long  enough  to  work,  could  digest  a large 
amount  of  food.  They  act  as  catalyzers  or  activating  agents, 
causing  chemical  actions  to  take  place  rapidly  instead  of  slowly. 


A gland  cut  lengthwise.  Explain  how  a gland 
might  obtain  its  secretions. 


SALIVARY  GI^VNDS 


3G3 


Demonstration  2.  To  show  the  use  of  digestion. 

In  one  tliistle  tube  place  some  saliva  mixed  with  starch  paste.  In 
a second  tube  place  some  paste  and  water.  Fasten  membrane  covers 
over  the  thistle  tubes,  and  wash  carefully  all  starch  or  other  material 
on  outside  of  lube.  Then  place  the  two  thistle  tubes,  large  end  down, 
in  a beaker  containing  just  enough  warm  water  to  cover  the  membrane 
on  the  tubes. 

Next  test  some  saliva  with  Fehling’s  solution.  Is  there  any  grape 
sugar  })rcsent? 

At  the  end  of  the  laboratory  jieriod  test  the  contents  of  the  beaker 
with  iodine  and  with  Fehling’s  solution.  Was  there  any  starch  in  the 
water  ? ^^'as  there  anj^  grape  sugar  ? How  did  it  get  into  the  beaker  ? 

Salivary  glands.  ^Ye  arc  all  familiar  with  the  substance  called 
saliva  which  acts  as  a lubricant  in  the  mouth.  Saliva  is  manu- 
factured in  the  cells  of  three  pairs  of  glands  which  empty  into  the 
mouth,  and  which  are  called,  according  to  their  position,  the 
parotid  (beside  the  ear),  the  siibmaxillary  (under  the  jawbone), 
and  the  sublingual  (under  the  tongue). 


Self-Testing  Exercise 

The  glands  necessary  for  digestion  are  the (1) (2), 

(3), (4),  and (5).  They  secrete (6) 

that  cause  digestion  of  the  (7).  Starches  are  changed  to 

(8)  by  enzymes  in  the (9).  Glands  may  be  in  the 

form  of  (10)  or  (11).  Small (12)  control 

the (13)  cells  and  the  blood (14)  to  them. 


PROBLEM  II.  WHAT  IS  THE  STRUCTURE  AND  WORK  OF 
THE  MOUTH  CAVITY? 

Laboratory  Exercise.  Comparison  of  mouth  of  a frog  and  of  a 

man.  Compare  the  open  mouth  of  the  frog  with  the  diagram.  Do 
the  same  studying  of  your  own  mouth.  Can  you  find  all  structures 
shown  in  the  diagrams? 

In  man  the  mouth  cavity  and  the  internal  surface  of  the  food 
tube  are  lined  with  mucous  membrane.  The  mucus  secreted  from 
gland  cells  in  this  lining  makes  a smooth  surface  so  that  the  food 
can  slip  down  easily.  The  roof  of  the  mouth  is  formed  by  a plate 
of  bone  called  the  hard  palate,  in  front,  and  a softer  continuation 


364  HOW  FOOD  IS  PREPARED  FOR  BODY  USE 


to  the  back,  called  the  soft  'palate.  These  separate  the  nose 
cavity  from  that  of  the  mouth.  The  space  back  of  the  soft 
palate  is  called  the  phar'yn.x,  or  throat  cavity.  The  gullet  and 


Comparison  between  the  mouth  of  frog  and  of  man. 


trachea  or  windpipe  lead  off  from  the  pharynx.  There  are  also  open- 
ings here  to  the  Eustachian  tubes  and  to  the  nose.  The  lower 
part  of  the  mouth  cavity  is  occupied  by  a muscular  tongue.  The 
tongue  is  used  in  moving  food  about  in  the  mouth,  and  in  starting 

it  on  its  way  to  the 
gullet. 


eplglottisr 


A longitudinal  section  through  the  head,  showing  the 
throat  and  its  connections.  How  is  the  throat  connected 
with  the  nose  ? with  the  stomach  ? with  the  lungs  ? 


Laboratory  Exercise. 
What  conditions  are 
favorable  or  unfavor- 
able for  the  digestion 
of  starch?  Place  in 
test  tubes  an  equal 
amount  of  starch  paste. 
In  the  first  tube  add 
water ; to  a second, 
saliva ; to  a third, 
saliva  and  a few  drops 
of  weak  acid ; to  a 
fourth  tube  saliva  and 
a base  such  as  weak 
sodium  hydroxide. 
Place  all  these  tubes 
in  water  of  about 
99°  F.  for  20  minutes. 
Test  the  contents  of 


THE  TEETH  365 

each  tul)P  witli  Fehling’s  solution.  In  which  tube  or  tubes  has 
clijicstion  tak('n  place? 

'bake  twt)  test  tnl^es,  place  in  each  tube  an  equal  amount  of  starch 
paste  and  saliva.  Place  one  tube  in  warm  water,  the  other  in  the  ice- 
box. Test  each  for  <irape  sugar  after  one  hour.  In  which  tube  do  yon 
find  sugar?  'bhe  al)ove  experiments  show  that  the  enz^mies  in  the 
saliva  under  certain  coiulitions  change  starches  to  sugars.  You  will 
remember  that  starch  in  the  growing  corn  grain  was  changed  to  grape 
sugar  liy  an  enzyme  called 
diastdsc.  In  saliva  a similar 
action  is  caused  b}^  an 
enzyme  called  pti/alin  (tl'd- 
lin),  or  salivary  amylase;  but 
this  enzyme  acts  only  in  an 
alkaline  metlium  at  about 
the  temperature  of  the  bod^^ 

The  teeth.  The  teeth  of 
man,  unlike  those  of  the 
frog,  are  used  in  the  me- 
chanical preparation  of  the 
food  for  digestion.  Instead 
of  holding  prey,  they  crush, 
grind,  or  tear  food  so  that 
more  of  its  surface  may  be 
exposed  to  the  action  of 
the  digestive  fluids.  The 
first  or  “ milk  ” teeth  of 
man  are  only  twenty  in  kinds  of  teeth  in  their  place  in  the 

number,  while  the  second 

or  “ permanent  ” set  contain  thirty-two  teeth.  These  teeth  are 
divided,  according  to  their  structure,  into  four  groups ; these  are 
the  incisors,  or  cutting  teeth ; the  canines ; the  premolars;  and 
the  flat-top  molars,  or  grinding  teeth. 

Each  tooth,  as  the  figure  shows,  is  composed  chiefly  of  hard 
bone  or  dentine.  The  crown  of  the  tooth  is  covered  with  enamel, 
the  hardest  substance  in  the  body.  In  the  interior  is  a pulp 
cavity,  which  during  the  life  of  the  tooth  contains  nerves  and  blood 
vessels  which  give  the  tooth  its  nourishment.  The  tooth  is  held 
in  its  bony  socket  in  the  jaw  by  cement. 

When  a tooth  dies,  bacteria  often  set  up  an  irritation  at  its  base 


366  HOW  FOOD  IS  PREPARED  FOR  BODY  USE 


and  form  a center  or  focus  of  infection  from  which  poison  gets 
into  the  blood.  As  a result  of  this,  very  serious  diseases  may 

occur,  of  which  the  most  com- 
mon are  rheumatism  of  the 
joints  and  neuritis  or  inflam- 
mation of  the  nerves.  Infected 
teeth  should  be  extracted,  as 
this  usually  removes  the  cause 
of  the  trouble. 

Practical  Exercise  1.  Using  a 
small  mirror,  count  your  teeth, 
giving  the  number  under  each  of 
the  following  heads : 

(a)  Incisors,  broad  cutting  teeth 
in  front. 

{h)  Canines,  pointed  sharp  teeth 
next  to  the  incisors. 

(c)  Premolars,  grinders  with  two 
points  on  the  biting  surface. 

(d)  Molars,  teeth  with  more  than 
two  points,  in  the  back  of  the 
mouth. 

Practical  Exercise  2.  Examine 
carefully  with  a flash  light  each  of 
your  teeth  and  answer  the  following 
questions.  Mark  the  points  asked 
for  on  the  chart  copied  from  the 
diagram. 

With  a bracket,  label  each  group  of  teeth.  With  a cross,  mark  all  the 
teeth  you  have  lost  or  that  have  not  grown.  Mark  all  cavities  not  filled  in 
your  teeth  by  a spot  where  the  cavity  exists.  If  teeth  have  been  filled, 
mark  with  appropriate  title. 


A section  through  a tooth.  Why  is  a cavity 
painful  ? Why  is  a tooth  sometimes  so  hard 
to  pull  ? 


Care  of  the  teeth.  Too  much  emphasis  cannot  be  placed  on 
the  proper  care  of  the  teeth.  They  should  be  carefully  brushed 
each  morning  and  evening.  Use  a medium  stiff  brush  and  work 
the  bristles  in  a vertical  direction  away  from  the  gum  so  as  to  get 
between  the  teeth.  After  that,  a rotating  movement  over  the  sur- 
face and  between  the  teeth  will  dislodge  any  remaining  particles 
of  food.  Above  all,  massage  the  gums  with  your  brush  and  polish 
the  surface  of  the  teeth  both  in  back  and  in  front,  for  this  helps 
remove  the  bacterial  film.  Dental  silk  should  be  used  after  meals. 

It  has  been  found  that  fruit  acids  are  very  beneficial  to  the  teeth. 
Vinegar  diluted  to  about  half  strength  with  water  makes  an 


PARTS  OF  THE  DTOESTIVE  TRACT 


3{)7 


excellent  deiitnl  wash.  If  one  has  an  acid  mouth,  a good  tooth 
paste  mixed  with  castile  soap  may  be  used  to  clean  the  teeth. 

The  teeth  sliould  be  cleaned  by  a reliable  dentist  at  least  every 
six  months.  In  this  way  deposits  which  cover  the  teeth  may  be 
removed  and  decay  prevented.  If  decay  once  starts,  sooner  or 
later  the  tooth  will  be  lost. 

Practical  Exercises  3.  What  are  the  uses  of  (a)  the  incisors,  (b)  the  canines, 
(c)  the  preniolars,  ami  {<!)  the  molars? 

How  many  teeth  are  there  in  the  first  set  of  teeth?  When  do  they  begin  to 
come,  ami  when  do  they  go? 

What  makes  teeth  decay?  Why  should  we  clean  the  teeth  night  and  morn- 
ing? How  should  we  brush  them? 

What  is  a focal  infect  ion?  What  harm  may  it  do?  What  harm  might 
come  from  swallowing  fluids  which  pass  through  a mouth  containing  decayed 
teeth? 

How  often  should  one  visit  the  dentist?  Why? 


Self-Testing  Exercise 

Food  passes  from  the (1)  into  the (2)  and (3) 

on  its  way  to  the  stomach.  The  enzymes  in  (4)  change 

(5)  to  sugars.  A tooth  is  composed  chiefly  of (6). 

The  crown  of  the  tooth  is  covered  with (7).  The  interior  of 

the  tooth  is  called  the  (8)  (9).  A decayed  tooth 

may  be  the  source  of  a (10)  (11).  The  saliva 

contains  the  enzjmie, (12). 

PROBLEM  III.  WHAT  ARE  THE  PARTS  OF  THE  DIGESTIVE 
TRACT? 

If  we  are  to  understand  the  work  of  the  parts  of  the  food  tube, 
it  is  necessary  that  we  know  something  about  their  structure. 
One  can  learn  about  the  digestive  tract  through  the  study  of  charts 
or  models,  but  it  is  much  easier  to  understand  if  we  can  see  its 
parts  as  they  would  really  appear  in  a living  person.  This  we 
cannot  do,  but  we  have  a good  substitute  in  the  frog.  Let  us 
examine  the  digestive  tract  of  a frog  in  order  to  compare  it  with 
man. 

Laboratory  Exercise.  To  compare  the  digestive  system  of  a frog 
with  that  of  man. 

Opened  frogs  preserved  in  4 per  cent  formalin.  Manikin  showing 
digestive  tract. 


368  HOW  FOOD  IS  PREPARED  FOR  BODY  USE 


Note  in  the  frog  the  glistening  membrane  {'peritoneum)  lining  the 
body  cavity.  A similar  membrane  is  found  in  man. 

In  man,  the  body  cavity  or  space  in  which  the  internal  organs  rest 
is  divided  into  two  parts  by  a wall  of  muscle,  the  diaphragm,  which 
separates  the  heart  and  lungs  from  the  other  internal  organs.  In  the 
frog  no  muscular  diaphragm  exists.  Numerous  blood  vessels  can  be 
found  in  the  frog,  especially  in  the  walls  of  the  food  tube,  which  carry 
the  digested  nutrients  to  other  parts  of  the  body. 

Notice  the  large,  reddish  brown  organ  covering  most  of  the  other 
organs.  This  is  the  liver.  Count  the  lobes  or  divisions  of  the  liver 
and  compare  the  position  and  general  structure  with  the  liver  of  man 
(use  manikin).  Lift  up  the  middle  lobe  of  the  liver  and  find  the  gall 
bladder,  a greenish  sac.  This  contains  bile,  a secretion  from  the  liver. 
Now  compare  with  the  manikin  to  see  if  you  can  locate  where  the  bile 
gets  into  the  food  tube. 

The  food  tube  begins  at  the  mouth,  continues  as  a short,  wide  gidlet 
into  the  stomach,  (just  under  the  liver).  Compare  these  structures  in 
the  frog  with  similar  structures  in  man.  The  stomach  of  the  frog 
leads  into  a long  coiled  small  intestine  and  thence  into  a very  short 
large  intestine.  The  large  intestine  opens  into  the  cloaca  (page  252)  into 
which  the  ureters  and  urinary  bladder  also  drain.  The  cloaca  opens  to 
the  exterior  by  means  of  the  anus. 


Compare  part  by  part,  the  digestive  tract  of  the  frog  with  that  of  man.  Are  there  any  structures 
found  in  one  and  not  in  the  other  ? 


THE  DIGESTIVE  TRACT  OF  MAN 


369 


Note  that  all  tho  orfijaiis  arc  held  in  i)lacc  by  a fold  of  tlie  body 
cavity  linin'?  called  the  incsentcri/.  What  is  its  use?  A cream-colored 
body,  the  pancreas,  can  be  located  between  the  stomach  and  the  first 
bend  in  the  small  intestine. 

The  digestive  tract  of  man.  Comparing  the  food  tube  of  man 
and  its  glands  part  by  part  with  that  of  the  frog,  we  find  a striking 
similarity  as  to  parts.  The  lower  part  of  the  digestive  tube  in  the 
frog  is  relatively  much  shorter  than  that  of  man,  whose  small  in- 
testine is  about  20  feet  in  length.  The  large  intestine  is  also  rel- 
atively shorter.  We  find  that  in  general  the  uses  of  the  parts  are 
quite  similar  in  spite  of  their  difference  in  size  and  the  method  of  life. 

Self-Testing  Exercise 

The  digestive  tract  of  man  consists  oT  a (1),  beginning 

at  the (2)  and  ending  at  the (3).  Ducts  from  several 

(4)  which  aid  in  digestion  empty  into  it.  The  parts  of  the 

food  tube  are  (5),  (6),  (7),  (8), 

(9)  and  (10)  (11).  The  largest  glands 

are  the (12)  and (13). 

PROBLEM  IV.  WHAT  DIGESTIVE  CHANGES  TAKE  PLACE  IN 
THE  STOMACH? 

Demonstration  3.  To  determine  the  conditions  most  favorable  for 
gastric  digestion. 

Use  five  test  tubes  or  beakers  and  some  boiled  white  of  egg.  In  the 
first  tube  put  minced  white  of  egg  and  water ; in  the  second  minced 
white  of  egg  and  0.2  per  cent  hydrochloric  acid ; in  the  third,  fourth, 
and  fifth  minced  white  of  egg,  0.2  per  cent  hydrochloric  acid,  and 
pepsin. 

Keep  the  first  three  in  a warm  place  at  about  a temperature  of 
blood  heat  for  several  hours.  Keep  the  fourth  in  an  ice  box  or  sur- 
rounded by  cracked  ice.  Keep  the  fifth  in  boiling  water  for  15  or  20 
minutes,  then  place  it  in  the  warm  place  with  the  first,  second,  and 
third. 

Test  the  first  with  biuret  test  ^ for  the  presence  of  a soluble  protein 
(a  peptone).  Test  the  second,  third,  fourth,  and  fifth  with  biuret 
test  and  note  results. 

1 Biuret  solution ; To  the  material  to  be  tested  add  its  own  bulk  of  concentrated 
caustic  soda.  Then  add  a drop  or  two  of  weak  copper  sulphate  solution.  A 
violet  or  blue  color  shows  the  presence  of  unchanged  protein,  a rose  pink  the 
presence  of  peptone. 


370  HOW  FOOD  IS  PREPARED  FOR  BODY  USE 


What  conditions  are  necessary  for  the  digestion  of  protein?  What 
is  the  effect  of  an  extreme  heat  and  cold  on  the  action  of  hydrochloric 
acid  and  pepsin  with  a protein?  Make  a table  giving  all  results  of 
the  above  tests  of  conditions  necessary  for  the  digestion  of  protein. 


Chewing  and  swallowing.  After  food  has  been  chewed  and 
mixed  with  saliva,  it  is  rolled  into  little  balls  and  pushed  by  the 
tongue  into  such  position  that  the  muscles  of  the  throat  cavity 
may  seize  it  and  force  it  downward.  Food,  in  order  to  reach  the 
gullet  from  the  mouth  cavity,  must  pass  over  the  glottis  which  is 
the  opening  into  the  trachea.  When  food  is  in  the  process  of 
being  swallowed,  the  upper  part  of  the  gullet  forms  a trapdoor 
over  this  opening.  When  this  trapdoor,  called  the  epiglottis,  is  not 
closed,  and  food  ‘‘goes  down  the  wrong  way,”  we  choke,  and  the 
food  is  expelled  by  coughing. 

The  esophagus.  After  food  leaves  the  mouth  cavity,  it  gets 
beyond  our  direct  control,  and  the  muscles  of  the  gullet,  stimulated 
to  activity  by  the  presence  of  food  in  the  tube,  push  the  food  down 

by  a series  of  slow-moving 
muscular  contractions  until  it 
reaches  the  stomach.  These 
wayelike  movements,  peri- 
stalsis, occur  also  in  the  stomach 
and  the  small  intestine.  Peri- 
staltic movement  is  caused  by 
muscles  which  are  not  under 
voluntary  nervous  control,  al- 
though anger,  fear,  disgust, 
or  other  unpleasant  emotions 
may  slow  them  or  even  stop 
them  entirely. 

Stomach  of  man.  The 

Food  passes  through  the  digestive  tract  by  stoiuach  is  a pear-shaped  Organ 
means  of  a series  of  successive  wavelike  move-  , , j.  , , , , 

ments,  which  are  under  the  control  of  the  Capable  Ot  holding  abOUt  three 
nervous  system.  The  constricted  portion  is  Onnnqifp  tn  thp  cmllpt 

always  preceded  by  an  area  of  relaxation.  pmbS.  UppOSlie  bO  Xne  gUlieX, 

the  end  which  empties  into 
the  small  intestine  is  provided  with  a ring  of  muscle  called  the 
pylorus  (pi-lo'rz^s).  When  this  muscle  relaxes,  it  permits  the 


3 


GASTRIC  GLANDS 


871 


passage  of  food  from  the  stomach.  There  is  also  another  ring 

of  muscle  guarding  the  entrance  to  the  stomach. 

Gastric  glands.  'The  folded  wall  of  the  stomach  is  dotted  with 

thousands  of  tiny  pits,  the  mouths  of  the  gastric  glands.  The 

gastricglandsare  little  . , 

mouth  of  dlancC  opsns 

• 4.  _ .-4- 


into  the  stcmoidh. 


neck  oftheglancC 

JdCl- secreting 
cell  on  irjnei' 
imorrgirt  of  gland 


raw' 
■materials 
are 
flcrnisl 

Ulls 

by  the 
btoooC.; 
streai 


..cell  secreting' 

‘ fluid:  Containing 
ipeps-iix,  ^ 


tubes,  the  lining  of 
which  secretes  the 
gastric  juice.  AVhen 
we  see  or  even  think  of 
appetizing  food,  this 
secretion  is  given  out 
in  considerable  quan- 
tity. Just  as  the 
mouth  “ waters  ” at 
the  sight  or  thought 
of  certain  well-liked 
foods,  the  gastric 
glands  of  the  stomach 
also  pour  out  their 
secretions  under  simi- 
lar stimuli.  Gastric 
juice  is  slightly  acid 
in  its  chemical  reac- 
tion, containing  about 
0.2  per  cent  free 
hydrochloric  acid.  It 
also  contains  two 
enzymes : one  very 
important,  called 
pepsin,  and  the  other,  less  important,  called  rennin.  Rennin 
curdles  or  coagulates  a protein  found  in  milk ; after  the  milk  is 
curdled,  the  pepsin  is  able  to  act  upon  it.  “ Junket  ” tablets, 
which  contain  rennin,  are  used  sometimes  in  the  preparation  of  a 
dessert  from  milk. 

Action  of  gastric  juice.  If  proteins  are  treated  with  artificial 
gastric  juice  at  the  temperature  of  the  body,  they  will  become 
swollen  and  then  gradually  change  to  substances  {peptones)  which 


ly  of  t]-2e  gland 
•vipers  most  of  the 
S0oretii?gis  done 

Gastric  glands  secrete  a substance  which  is  changed  into 
pepsin  in  the  presence  of  acid.  The  secretion  of  these  glands 
forms  the  gastric  fluid. 


372  HOW  FOOD  IS  PREPARED  FOR  BODY  USE 


are  soluble  in  water.  This  is  due  to  the  action  of  the  enzyme 
pepsin. 

The  hydrochloric  acid  found  in  the  gastric  juice  acts  upon  lime 
and  some  other  salts  taken  into  the  stomach  with  food,  changing 
them  so  that  they  may  pass  into  the  blood  and  eventually  form 
the  mineral  part  of  bone  or  other  tissue.  This  acid  also  has  a 
decided  antiseptic  influence  in  preventing  growth  of  bacteria,  some 
of  which  cause  decay,  others  of  which  cause  disease. 

Experiments  on  digestion  in  the  stomach.  Some  very  interest- 
ing experiments  have  been  made  by  Professor  Cannon  of  Harvard 
with  reference  to  the  movements  of  the  stomach  contents.  Cats 
were  fed  with  a material  having  in  it  subnitrate  of  bismuth,  a 
harmless  chemical  that  is  visible  under  the  fluoroscope.  It  was 
found  that  shortly  after  food  reached  the  stomach,  a series  of 
waves  began  which  sent  the  food  toward  the  pyloric  end  of  the 
stomach.  If  the  cat  was  feeling  happy  and  well,  these  contrac- 
tions continued  regularly,  but  if  the  cat  was  cross  or  bad  tempered, 
the  movements  would  stop.  These  experiments  were  repeated  on 
men,  with  like  results,  and  show  the  importance  of  cheerfulness 
at  meals.  Pleasant  conversation  and  a cheerful  mind  at  the  table 
will  go  far  toward  making  the  food  taste  better  and  also  toward 
causing  it  to  digest  properly. 

Other  experiments  showed  that  food  which  was  churned  into 
a soft  mass  was  permitted  td  leave  the  stomach  only  when  it 
became  thoroughly  permeated  by  the  gastric  juice.  It  is  the 
acid  in  the  partly  digested  food  that  causes  the  pyloric  ring  of 
muscle  to  open  and  allow  the  food  to  escape  little  by  little  into  the 
small  intestine. 


Self-Testing  Exekcise 

The  food  passes  through  the (1)  and (2)  by  a series 

of  (3)  (4).  The  stomach  is  a (5)  organ. 

The  (6)  (7)  secrete  a (8)  which  empties 

into  the (9).  This (10)  is  slightly (11)  in 

chemical  reaction,  and  contains  two  enzymes,  (12)  and 

(13).  The  enzyme  (14)  digests  the (15) 

in  the  stomach.  Our  digestion  is  affected  by  our 


(16). 


THE  PANCREAS 


373 


PROBLEM  V.  WHAT  WORK  IS  DONE  BY  THE  PANCREAS? 

Demonstration  4.  What  is  the  action  of  pancreatic  juice  on  starch? 

Add  some  artificial  pancreatic  juice  (made  by  mixing  5 grains  of 
pancreatin  and  10  grains  of  baking  soda  in  100  c.c.  of  water)  to  some 
dilute  starch  paste.  Keep  it  at  about  body  temi)erature  for  a few 
hours,  then  test  with  Fehling’s  solution.  What  occurred  when  Feh- 
ling’s  solution  was  atlded?  What  was  the  action  of  pancreatic  juice 
on  starch? 

Demonstration  5.  What  is  the  effect  of  pancreatic  juice  on  protein  ? 

losing  artificial  inincreatic  juice  instead  of  a mixture  of  hydrochloric 
acid  and  jiepsin,  carry  out  an  experiment  as  described  for  the  test  for 
the  third  tube  in  the  Demonstration  on  page  369.  Was  any  of  the 
white  of  egg  digested? 

Demonstration  6.  What  is  the  effect  of  pancreatic  juice  on  oils  and 
fats  ? 

Shake  up  oil  and  water.  What  happens?  Then  add  a little  alka- 
line substance,  e.g.,  baking  soda.  What  happens?  Now  shake  up 
water  with  artificial  pancreatic  juice.  What  happens?  What  is  the 
effect  of  pancreatic  fluid  on  oils? 

Make  a table  to  show  the  effect  of  pancreatic  juice  on  nutrients. 

Position  and  structure  of  the  pancreas.  The  partly  digested 
food  in  the  small  intestine  comes  in  contact  almost  simultaneously 
with  secretions  from  the  liver,  the  pancreas,  and  the  intestinal 
glands.  We  shall  first  consider  the  function  of  the  pancreas. 
The  pancreas  is  one  of  the  most  important  digestive  glands  in  the 
human  body.  It  is  a rather  diffuse  structure,  resembling  the 
salivary  glands.  Its  duct  (joined  with  the  bile  duct  from  the 
liver)  empties  into  the  small  intestine  a short  distance  below 
the  pylorus. 

i Work  done  by  the  pancreas.  Starch  paste  added  to  artificial 
pancreatic  fluid  and  kept  at  blood  heat  is  soon  changed  to  sugar. 

! Proteins,  under  the  same  conditions,  are  broken  down  into  the 
amino  acids.  Fats,  which  so  far  have  been  unchanged  except  to 
be  melted  by  the  heat  of  the  body,  are  changed  by  the  action  of 
the  pancreatic  fluid  and  the  bile  into  substances  which  can  pass 
through  the  walls  of  the  food  tube.  If  we  test  pancreatic  fluid, 
I we  find  it  strongly  alkaline  in  its  reaction.  If  two  test  tubes,  one 
containing  olive  oil  and  water,  the  other  olive  oil  and  a weak 
solution  of  caustic  soda  (which  has  an  alkaline  reaction),  are 
i shaken  violently  and  then  allowed  to  stand,  the  oil  and  water  will 
I quickly  separate,  while  the  oil  and  solution  of  caustic  soda  will 


374  HOW  FOOD  IS  PREPARED  FOR  BODY  USE 


remain  for  some  time  in  a milky  emulsion.  If  this  emulsion  is 
examined  under  the  microscope,  it  will  be  found  to  be  made  of 

millions  of  little  droplets  of 
fat,  floating  in  the  liquid. 
The  presence  of  the  caustic 
soda  helped  the  forming  of 
the  emulsion.  Pancreatic  fluid 
emulsifies  fats  and  changes 
them  into  fatty  acids  and 
soft  soaps.  Fat  in  these  forms 
can  be  absorbed.  The  above 
changes  are  brought  about 
by  three  enzymes : amylase 
(am'i-las),  which  breaks  down 
starches  to  simpler  sugars ; 
trypsin  (trip'sin),  which, 
working  with  other  enzymes 
of  the  small  intestine,  breaks 
protein  into  amino  acids  ; 
and  lipase  (lip'as),  which 
breaks  the  fats  into  fatty  acids  and  glycerin.  These  fatty 
acids  become  soap  when  mixed  with  the  alkaline  material  in 
the  intestinal  juice. 

Conditions  in  which  the  pancreas  does  its  work.  The  secre- 
tion of  the  pancreatic  juice  is  brought  about  by  the  action  of  a 
hormone  called  secretin.  This  substance,  which  is  formed  in  some 
of  the  cells  lining  the  small  intestine  just  below  the  pylorus,  is 
released  into  the  blood  at  the  time  food  passes  from  the  stomach 
through  the  pylorus.  This  food  is  acid,  and  the  acid,  on  touching 
the  lining  of  the  small  intestine,  causes  the  formation  of  secretin 
in  its  walls.  This  secretin  passes  into  the  blood  and  stimulates 
the  pancreas  and  liver  to  release  their  fluids.  This  is  an  example 
of  hormone  control. 

Self-Testing  Exercise 

The  pancreatic  fluid  changes  (1)  to  simple  (2) ; 

(3)  to (4)  (5),  and  proteins  into (6) 


Milk,  a form  of  emulsion,  as  seen  under  the 
microscope.  The  fat  globules  appear  in  groups. 
The  circle  shows  one  group  of  globules  highly 
magnified. 


FUNCTIONS  OF  THE  LIVEH 


375 


(7),  Tliosc  chanfiies  arc  caused  by  the  enzymes,  (8), 

(9),  and  (10).  The  hormone  (11)  causes 

tlie  pancreas  to  secrete  (12)  (13),  which  is 

(14)  in  its  reaction. 


PROBLEM  VI.  WHAT  ARE  THE  FUNCTIONS  OF  THE  LIVER? 

Liver.  The  liver  is  the  larg;est  gland  in  the  body.  In  man,  it 
is  found  just  below  the  diaphragm,  a little  to  the  right  side  of  the 
body.  The  liver  is  not  primarily  a digestive  gland,  although  it 
secretes  daily  about  a quart  of  bile.  Bile  contains  no  enzymes, 
although  it  may  have  the  power  of  rendering  more  active  the 
enzyme  in  the  pancreatic  fluid  that  acts  upon  fats.  Certain  sub- 
stances in  the  bile  aid  especially  in  the  absorption  of  fats.  Bile 
seems  to  be  mostly  a waste  product  from  the  blood.  The  color 
of  bile  is  due  to  certain  waste  substances  which  come  from  the 
destruction  of  worn-out  red  corpuscles  of  the  blood.  This  destruc- 
tion takes  place  in  the  liver  (and  also  in  the  spleen,  a large  ductless 
glandlike  organ  near  the  stomach.)  The  bile  stimulates  the 
peristaltic  movements  of  the  intestine,  thus  preventing  extreme 
constipation.  It  also  has  a slight  antiseptic  effect  in  the  intestine 

The  liver  a storehouse. 

Perhaps  the  most  important 

function  of  the  liver  is  the 

formation  and  storing  of  a 

material  called  glycogen,  or 

animal  starch.  The  liver  is 

supplied  with  blood  from  two 

sources.  Some  comes  from 

the  heart,  but  a greater 

amount  comes  directly  from 

the  walls  of  the  stomach  and 

intestine  (see  diagram  on 

page  378).  The  liver  normally  glandular  secretions  aid  in  the  digestion  of 

^ ° ^ the  food  m the  small  intestine? 

contains  about  one  fifth  of  all 

the  blood  in  the  body.  This  blood  is  very  rich  in  food  ma- 
terials, and  from  it  the  cells  of  the  liver  take  out  sugars  to  form 


376  HOW  FOOD  IS  PREPARED  FOR  BODY  USE 


glycogen.!  Glycogen  is  stored  in  the  liver  until  such  a time  as  a 
food  is  needed  that  can  be  quickly  oxidized ; then  it  is  changed 
to  sugar  and  carried  off  by  the  blood  to  the  tissue  which  requires 
it,  and  there  used  for  this  purpose.  Glycogen  is  also  stored  in 
the  muscles,  where  it  is  oxidized  to  release  energy  when  the 
muscles  are  exercised. 


Self-Testing  Exercise 

The  liver  stores (1),  which  is  later  changed  into (2) 

when  the  tissues  need  it.  The  bile  is  secreted  by  the (3). 

It  is  a (4)  (5)  from  the  blood  and  it  probably 

(6)  in  the  absorption  of  (7).  The  liver  contains 

about  (8)  (9)  of  all  the  blood  in  the  body.  The 

bile  (10)  the (11)  movements  of  the  intestine. 

PROBLEM  VII.  HOW  ARE  FOODS  ABSORBED  AND  HOW  DO 
THEY  GET  INTO  THE  BLOOD? 

Laboratory  Exercise.  How  is  the  surface  of  the  digestive  tube 
increased? 

Study  the  structure  of  tripe  (stomach  wall  of  a ruminant)  and  the 
microscopic  slide  of  a cross  section  of  the  small  intestine.  Remember 
that  the  chief  function  of  the  small  intestine  is  to  get  food  into  the 
blood. 

Make  a tube  of  paper  having  a diameter  of  one  inch.  Then  try  to 
make  a tube  having  the  same  diameter  but  having  a fluted  wall. 
Which  takes  more  paper?  Which  would  present  more  surface? 
Study  the  diagram  of  a villus.  How  is  it  fitted  to  be  an  absorbing 
organ? 

Structure  of  the  small  intestine.  The  small  intestine  in  man 
is  a slender  tube  nearly  twenty  feet  in  length  and  about  one  inch 
in  diameter.  As  one  of  the  chief  functions  of  the  small  intestine 
is  that  of  absorption,  we  must  look  for  adaptations  which  increase 
the  absorbing  surface  of  the  tube.  This  end  is  gained  in  part 
by  the  inner  surface  of  the  tube  being  thrown  into  transverse 
folds  which  not  only  retard  the  rapidity  with  which  food  passes 
down  the  intestine,  but  also  give  more  absorbing  surface. 

1 It  is  known  that  glycogen  may  also  be  formed  in  the  body  from  protein,  and 
possibly  from  fatty  foods. 


THE  VILLI 


377 


The  villi.  But  far  more  important  for  absorption  are  millions 
of  little  projections  which  cover  the  inner  surface  of  the  small 
intestine.  So  numerous  are  these  projec- 
tions that  the  whole  surface  presents  a 
velvety  appearance.  Collectively,  these 
structures  are  called  the  villi  (sing,  villus). 

They  form  the  chief  organs  of  absorption  in 
the  intestine,  several  thousand  being  dis- 
tributed over  every  square  inch  of  surface. 

By  means  of  the  folds  and  the  villi  the 
small  intestine  is  estimated  to  have  an 
absorbing  surface  equal  to  twice  that  of  projections,  ofwhat 
the  surface  of  the  body.  Between  the  villi 
are  found  the  openings  of  the  intestinal  glands  which  secrete  the 
intestinal  juice,  which  contains  at  least  one  hormone  and  several 
enzymes  with  which  it  assists  the  pancreatic  fluid  to  do  its  work. 


A section  through  the  small 
intestine.  What  are  the  tiny 
use  are 


Explain  this  section  through  the  small  intestine,  giving  the  uses  of  each  part. 


The  internal  structure  of  a villus  is  best  seen  in  a longitudinal 
section.  We  find  the  outer  wall  made  up  of  a thin  layer  of  cells, 
the  epithelial  layer.  These  cells  absorb  the  fluid  food  from  within 


378 


HOW  FOOD  IS  PREPARED  FOR  BODY  USE 


the  intestine.  Underneath  these  cells  lies  a network  of  very  fine 
blood  vessels  and  in  the  center  of  the  villi  are  spaces  which,  because 

of  their  white  ap- 
pearance after  the 
absorption  of  fats, 
have  been  called 
lacteals. 

Absorption  of 
foods.  While  diffu- 
sion and  osmosis  are 
important  factors  in 
the  passage  of  food 
and  water  through 
the  walls  of  the  in- 
testine, most  physi- 
ologists agree  that 
the  living  matter  in 
the  cells  lining  the 
intestine  exerts 
energy  that  affects 
the  absorption  of  the 
substances  that  pass 
into  the  blood  and 
lacteals.  This  is 
proven  by  the  fact 
that  if  these  cells  are 
injured  or  poisoned, 
then  absorption  fol- 
lows the  laws  of 


Explain  from  the  diagram  and  text  how  the  various  nutrients 
reach  the  blood. 


osmosis  and  diffusion.  Ordinarily  the  cells  lining  the  intestine  are 
like  tiny  chemical  laboratories.  Since  the  object  of  digestion  is  to 
furnish  the  cells  with  building  material  as  well  as  energy  foods,  it 
is  evident  that  amino  acids,  after  having  been  absorbed  into  the 
blood,  can  get  into  the  cells  by  a similar  process.  Fats,  for  example, 
in  the  form  of  fatty  acids  and  glycerol,  enter  the  epithelial  cells  of 
the  villus  and  during  the  process  of  passing  through  them  are 
changed  back  into  fat  particles. 


AHSOliPTlON  OF  FOOD 


379 


This  Huid  or  lymph  tlien  passes  into  the  lacteals  and  other  lym- 
phatics and  eventually  reaches  the  blood.  On  the  other  hand, 
simple  sugars  and  amino  acids  pass  directly  into  the  blood  and 
reach  the  blood  vessels  which  carry  them  to  the  liver,  where, 
as  we  have  seen,  sugar  is  taken  from  the  blood  and  stored  as 
glycogen.  From  the  liver,  the  food  within  the  blood  is  carried  to 
the  heart,  pumped  to  the  lungs,  returned  to  the  heart,  and  is 
pumped  to  the  tissues  of  the  body.  A large  amount  of  water  and 
some  salts  are  also  absorbed  through  the  walls  of  the  stomach  and 
intestine. 

Large  intestine.  The  large  intestine  has  somewhat  the  same 
structure  as  the  small  intestine,  except  that  it  lacks  the  villi  and 
has  a greater  diameter.  Considerable  absorption,  however,  takes 
place  through  its  walls  as  the  mass  of  food  and  refuse  material  is 
slowly  pushed  along  by  the  peristaltic  movements  of  the  muscles 
within  its  walls.  At  the  point  where  the  small  intestine  widens 
to  form  the  large  intestine,  a baglike  pouch  is  formed.  From 
one  side  of  this  pouch  is  given  off  a small  tube,  usually  from 
one  to  eight  inches  long,  closed  at  the  lower  end.  This  tube,  the 
rudiment  of  what  is  an  important  part  of  the  food  tube  in  the 
lower  vertebrates,  is  called  the  vermiform  appendix. 


Practical  Exercise  4.  Summarize  the  different  pathways  by  which  food 
reaches  the  heart  and  general  circulation  by  filling  in  the  following  table : 


Foods 

Where  Absorbed 

Form 

Adaptations  for 

Paths  to  Heart 

Constipation.  In  the  large  intestine  live  billions  of  several 
species  of  bacteria  which,  on  the  whole,  may  be  said  to  be  useful 
because  they  break  down  and  decay  the  indigestible  parts  of 
the  food  we  have  eaten.  But  these  same  bacteria  in  their  life 
processes  make  and  give  off  toxins.  These  substances  are  easily 


380 


HOW  FOOD  IS  PREPARED  FOR  BODY  USE 


absorbed  through  the  walls  of  the  large  intestine,  and,  when  they 
pass  into  the  blood,  cause  headaches  and  sometimes  serious 
trouble.  Hence  it  follows  that  the  intestine  should  be  emptied  of 
this  matter  as  frequently  as  possible,  at  least  once  a day.  Con- 
stipation is  one  of  the  most  serious  ills  the  American  people  have 
to  deal  with,  and  it  is  largely  brought  about  by  the  life  we  lead, 
with  its  wrong  kinds  of  food  and  its  lack  of  exercise,  fresh  air, 
and  sleep.  Fruit  with  meals,  especially  at  breakfast,  plenty  of 
water  between  meals  and  before  breakfast,  and  plenty  of  fresh 
vegetables  and  cereals  to  supply  the  bulk  sufficient  to  stimulate  the 
muscles  of  the  intestine,  all  will  aid  in  preventing  constipation. 
Exercise,  particularly  of  the  abdominal  muscles,  and  regular  times 
for  the  elimination  of  wastes  will  help  to  correct  this  evil. 

Hygienic  habits  of  eating.  Any  habits  we  may  form  of  chewing 
our  food  thoroughly  will  aid  digestion.  The  smaller  the  pieces 
of  food  the  more  surface  will  be  presented  to  the  digestive  fluids 
containing  the  enzymes  and  the  more  complete  will  be  the  digestion. 
Undoubtedly  much  indigestion  and  other  discomfort  is  due  to 
hurriedly  eaten  meals  with  consequent  lack  of  proper  chewing 
of  food.  It  is  a good  rule  to  go  away  from  the  table  feeling  a little 
hungry.  Eating  too  much  overtaxes  the  digestive  organs  and 
prevents  their  working  to  the  best  advantage.  Still  another 
cause  of  indigestion  is  eating  when  in  a fatigued  condition.  It  is 
always  a good  plan  to  rest  a short  time  before  eating,  especially 
after  any  hard  manual  work.  Eating  between  meals  is  condemned 
by  physicians  because  the  blood  is  brought  to  the  digestive  organs 
at  a time  when  it  should  be  more  active  in  other  parts  of  the  body. 
The  excessive  use  of  ice  cream  sodas  and  cold  drinks  between 
meals  is  bad  for  this  reason  and  because  it  dulls  appetite  for 
regular  meals. 

Practical  Exercise  5.  1 . Tell  where  each  part  of  a meal  of  bread  and  butter, 

meat,  rice  pudding,  and  nuts  is  digested. 

2.  Why  should  we  chew  starchy  foods  well  before  swallowing? 

3.  Why  is  soup  eaten  at  the  beginning  of  a meal?  (Remember  it  is  ab- 
sorbed rapidly.) 

4.  Why  are  partly  cooked  foods  harder  to  digest  than  well  cooked  foods? 

5.  Name  three  easily  digested  foods  and  tell  why  they  are  easy  to  digest. 

6.  Name  three  foods  difficult  to  digest  and  tell  the  reasons  why. 

7.  Give,  in  detail,  the  digestion  of  a meal  of  milk,  bread,  and  apple  sauce. 


SELF-TESTING  EXERCISE 


381 


TABLE  OF  CHEMICAL  DIGESTION 


I’lack  ok  Di- 
li kstion 

Skcuktion 
Foil  MED 

Enzyme 

Contained 

Medium 

Heouiued 

Substance 

Digested 

End  Product 
Formed 

Moutli 

Saliva 

Ptyalin 

Alkaline 

Starch 

Grape 

sugar 

Stomach 

Cast  ric 
juice 

Pepsin 

Rennin 

Acid 

Acid 

Protein 

Casein  of 
milk 

Proteoses 

and 

peptones 

Curd 

Small 

Intestine 

<1 

Pancreatic 

juice 

Intestinal 

juice 

Amj’lase 

Trypsin 

Lipase 

Erepsin 

Maltase 

Sucrase 

Lactase 

Alkaline 

Alkaline 

Alkaline 

Alkaline 

Alkaline 

Alkaline 

Alkaline 

Starch 

Proteins 

Fats 

Proteoses 
and  pep- 
tones from 
stomach 
Maltose 
(grape 
sugar) 
Cane  sugar 
Milk  sugar 

Grape 

sugar 

Amino 

acids 

Fatty  acid 
and 

glycerol 

Amino 

acids 

Glucose 

Glucose 

Glucose 

Self-Testing  Exeecise 

Check  the  correct  statements  in  your  notebook : 

T.  F.  1.  The  villi  are  hollow  hairs  which  suck  up  digested  food. 

T.  F.  2.  A villus  absorbs  food  through  the  cells  covering  its  surface. 
T.  F.  3.  The  large  intestine  contains  many  bacteria  which  cause  the 
decay  of  the  wastes  held  therein. 

T.  F.  4.  The  digestive  fluids  in  the  small  intestine  ultimately  change 
proteins  to  amino  acids  in  which  form  they  pass  into  the  blood. 

T.  F.  5.  The  gastric  juice  changes  sugar  to  starches. 

T.  F.  6.  The  surface  of  the  small  intestine  is  increased  by  the  villi. 


382  HOW  FOOD  IS  PREPARED  FOR  BODY  USE 


Review  Summary 

Check  your  knowledge  of  the  unit  by ; ( 1 ) Answering  and  rechecking  the 
survey  questions;  (2)  performing  the  assigned  exercises;  (3)  checking  with 
the  teacher  your  scores  on  the  various  tests  and  doing  over  those  that  you 
missed ; and  finally  (4)  making  an  outline  of  the  unit  for  your  notebook. 

Tests  on  Fundamental  Concepts 

In  a vertical  column  under  the  heading  CORRECT  write  numbers  of  all  statements  you 
believe  are  true.  In  another  column  under  INCORRECT  write  numbers  of  untrue  statements. 
Your  grade  = number  of  right  answers  X 4. 

I.  The  digestive  tract  of  man  (1)  is  a straight  tube  extending  from 
the  mouth  to  the  anus ; (2)  is  the  structure  including  the  glands 
through  which  food  passes ; (3)  consists  of  the  diaphragm,  blood,  and 
muscles ; (4)  may  be  compared,  part  by  part,  with  that  of  the  frog ; 
(5)  consists  of  the  mouth  (including  teeth),  pharynx,  gullet,  stomach, 
and  small  and  large  intestines. 

II.  A gland  (6)  is  a collection  of  cells  which  secrete  substances 
which  are  of  use  to  the  body;  (7)  found  in  the  stomach  secretes 
saliva ; (8)  found  emptying  into  the  small  intestine  is  called  the 
pancreas ; (9)  does  its  work  by  means  of  enzymes  contained  in  its 
secretion ; (10)  of  digestion  is  controlled  by  the  nerves. 

III.  Digestion  (11)  is  necessary  in  order  to  change  solid  food  into  a 
soluble  form;  (12)  is  brought  about  by  enzymes;  (13)  is  principally 
brought  about  in  the  large  intestine;  (14)  of  fats  takes  place  in  the 
small  intestines;  (15)  of  starches  takes  place  chiefly  in  the  stomach. 

IV.  The  teeth  (16)  are  composed  chiefly  of  dentine;  (17)  are  of  no 
value  in  preparing  food  for  digestion;  (18)  are  divided  into  four 
groups  on  a basis  of  structure;  (19)  should  be  brushed  frequently 
with  a gritty  powder;  (20)  if  allowed  to  decay,  can  make  serious 
trouble  through  focal  infection  at  the  base  of  the  root. 

V.  Absorption  of  food  (21)  is  necessary  if  the  cells  are  to  get  nourish- 
ment ; (22)  takes  place  largely  in  the  stomach ; (23)  is  brought  about 
by  the  villi ; (24)  takes  place  largely  by  osmosis  through  the  cells  of 
the  villi ; (25)  is  not  necessary  unless  we  are  growing,  for  our  cells  do 
not  need  food  for  other  purposes. 

Achievement  Test 

1.  How  would  you  make  a comparison  of  the  digestive  tract  of  the 
frog  and  of  man  and  what  are  the  parts  with  the  functions  of  each? 


USEFUL  REFERENCES  383 

2.  How  would  3^011  perforin  an  experiment  to  show  how  digestion 
takes  j)lace,  and  what  changes  it  brings  about? 

3.  What  are  the  functions  of  each  group  of  teetli?  Are  your  teetli 
in  good  condition?  Have  you  liad  tliein  looked  over  within  six 
months?  Do  ,vou  brush  them  twice  daily  in  the  approved  manner? 

4.  How  do  jmu  keeji  from  having  indigestion? 

Practical  Problems 


Fill  out  the  following  Table: 


ClA.\1)8 

Location 

Juice 

Enzymes  oh 
Fekments 

Action  of 

Result  of 
Its  Action 

How  Te.st  I 
for  Action  j 

Useful  References 

Adventures  in  Biology.  New  York  Association  of  Biology  Teachers.  (For 
individual  projects.) 

ERyn,  Yourself,  Inc.,  Coward-McCann,  1930. 

Fisher  and  Fisk,  How  to  Live.  Funk  & Wagnalls,  1932. 

Harrow,  Glands  in  Health  and  Disease.  Dutton,  1922. 

Hawk,  What  We  Eat  and  What  Happens  to  It.  Harpers,  1919. 

Kellogg,  The  Itinerary  of  a Breakfast.  Funk  & Wagnalls,  1926. 

Wheat  and  Fitzpatrick,  Everyday  Problems  in  Health.  American  Book, 
1933. 

Winslow  and  Hahn,  The  New  Healthy  Living.  Bobbs-Merrill,  1929. 


UNIT  XIII 

HOW  ARE  FOODS  CIRCULATED  AND  USED  IN  THE 

BODY? 

Preview.  As  we  have  thought  of  the  digestive  system  as  a 
chemical  laboratory,  so  we  might  think  of  the  blood  as  a moving 
chemical  workshop.  Not  only  is  the  blood  the  carrier  of  food  from 
the  food  tube  to  the  cells  of  the  body,  but  it  also  takes  away  the 
waste  products  from  these  same  cells  to  those  parts  of  the  body 
that  can  expel  them.  It  transports  oxygen  to  the  cells  where 
oxidation  takes  place,  and  carries  away  the  waste  products  of 
this  oxidation.  It  conducts  heat  to  all  parts  of  the  body,  thus 
keeping  the  temperature  even.  The  white  corpuscles  in  the  blood 
act  as  sanitary  police,  standing  guard  at  all  times  to  protect  the 

384 


SURVEY  QUESTIONS 

How  does  food  and  oxygen  get  to  the  body  cells  ? Why  is  blood  from 
arteries  redder  than  blood  from  veins?  How  is  the  human  heart  built 
and  how  does  it  work  ? Why  do  we  breathe  more  deeply  after  exercise  ? 
How  do  we  get  air  into  the  lungs  ? Why  do  we  ventilate  a room  ? 


PREVIEW 


385 


body  in  case  of  infection.  The  blood  also  contains  substances, 
antibodies,  which  help  combat  any  disease  germs  entering  the  body. 

The  blootl  circulates  through  the  body  by  means  of  a network 
of  tubes  and  is  controlled  by  the  heart.  Imagine  a pump  so 
built  that  it  is  self-regulating,  so  strong  that  it  works  day  and 
night  without  rest,  so  powerful  that  it  lifts  several  tons  of  weight 
the  height  of  the  body  every  day,  year  in  and  year  out.  Such  is 
the  human  heart.  Although  the  two  sides  of  the  heart  are  sepa- 
rate and  distinct  from  each  other,  yet  every  drop  of  blood  that 
passes  through  the  right  side  of  the  heart  also  passes  through  the 
left  side.  It  requires  from  twenty  to  thirty  seconds  for  the  blood 
to  make  a complete  circuit  from  the  ventricle  back  again  to  the 
starting  point.  This  means  that  the  entire  volume  of  blood  in 
the  human  body  passes  through  the  various  organs  of  the  body 
three  or  four  thousand  times  a day. 

One  of  the  uses  of  the  blood  in  its  capacity  as  a carrier  is  to 
transport  certain  chemical  activating  substances  known  as  hor- 
mones. There  are  a good  many  such  substances,  the  chief  of  which 
are  manufactured  by  certain  glands  known  collectively  as  the 
endocrines.  These  structures,  of  which  the  thyroid  gland  is  a 
well-known  example,  have  no  ducts  or  connections  with  the  food 
tube  or  other  organs.  Consequently  their  secretions  can  get  out 
only  through  the  medium  of  the  blood  stream.  The  blood  dis- 
tributes the  hormones  to  the  body  cells,  where  they  cause  very 
great  changes  to  take  place  through  their  chemical  actions. 

Most  of  us  have  had  the  experience  of  chopping  down  a tree,  of 
digging  a deep  hole,  or  of  lifting  a heavy  rock.  In  a very  short 
time  we  notice  that  we  breathe  more  quickly  and  deeply,  that  we 
get  hot  and  perspire,  and  that  after  a time  we  become  fatigued. 
What  does  this  sequence  of  events  mean?  Evidently  we  can  go 
back  to  our  old  analogy  of  the  engine.  To  do  more  work  we  make 
a hotter  fire,  to  get  a hotter  fire  we  increase  the  amount  of  oxygen 
that  gets  to  the  fire  by  regulating  the  draft.  And  we  know,  too, 
that  if  we  are  to  keep  up  the  fire,  we  must  remove  the  ashes  and 
other  wastes  frequently.  A very  similar  condition  exists  in  the 
human  body.  We  have  learned  that  plants  and  animals  need 
oxygen  in  order  to  release  energy,  just  as  coal  is  burned  to  give 


386  FOODS  CIRCULATED  AND  USED  IN  THE  BODY 


heat  to  run  an  engine.  As  a draft  of  air  is  required  to  make  a fire 
under  the  boiler,  so,  in  the  human  body,  plenty  of  oxygen  must  be 
given  to  the  tissues  so  that  food  may  be  oxidized  there,  releasing 
energy  for  work  and  forming  the  wastes,  carbon  dioxide,  water, 
and  urea  (nitrogen  product).  This  oxidation  takes  place  in  all 
the  cells  of  the  body,  be  they  portions  of  a muscle,  a gland,  or  the 
brain.  Here  again  the  blood  plays  its  part",  for  it  carries  the 
oxygen  to  the  cells  and  takes  av/ay  the  waste  products  to  be 
excreted  either  through  the  skin  or  the  kidneys.  The  smooth 
running  of  this  body  machine  of  ours  is  only  continued  because 
of  the  exchanges  of  food  and  wastes  made  possible  by  means  of 
this  wonderful  system  of  tubes  and  pumps  which  makes  up  the 
circulatory  system. 

PROBLEM  I.  WHAT  IS  THE  COMPOSITION  AND  WHAT  ARE 
THE  USES  OF  THE  PARTS  OF  THE  BLOOD? 

Composition  of  the  blood.  We  learned  in  a former  unit  that 
the  chief  function  of  the  digestive  organs  is  to  change  foods  so  that 
they  can  pass  into  the  blood.  The  chemical  composition  of  the 
blood  is  very  complex  and  varies  in  different  parts  of  the  body. 
The  fluid  part  is  the  plasma,  which  consists  of  about  90  per  cent 
water  and  the  various  organic  food  substances,  digested  sugars, 
fats,  amino  acids,  mineral  salts,  and  numerous  other  substances, 
among  which  are  enzymes  and  hormones.  The  blood  also  holds 
three  kinds  of  bodies : the  red  corpuscles,  the  white  corpuscles, 
and  the  blood  platelets. 

Laboratory  Exercise.  To  study  the  corpuscles  of  the  blood.  Place 

a drop  of  frog’s  blood  on  a glass  slide.  Cover  and  examine  under  a 
compound  microscope.  What  are  the  color  and  shape  of  the  corpus- 
cles that  are  most  numerous  and  most  easily  seen?  What  are  the 
other  irregular-shaped  corpuscles,  more  transparent  and  not  so  easily 
seen?  Are  corpuscles  cells?  Can  you  prove  your  statement? 

Using  a slide  containing  a drop  of  your  own  blood,  note  that  red 
corpuscles  have  no  nucleus.  Are  they  cells?  Do  you  find  colorless 
corpuscles  as  well?  How  do  they  compare  with  the  red  in  number? 
Compare  the  structure  of  blood  corpuscles  in  man  with  those  of  a frog. 

So  small  and  so  numerous  are  the  red  corpuscles  that  about  five 
million  of  them  are  found  in  a cubic  millimeter  of  normal  blood. 


COMPOSITION  OF  THE  BLOOD 


387 


, -kS/hite  Corpuscle 

L.recC  corpuscle. 

Are  the  red  corpuscles  cells?  Explain. 


Their  red  color  is  tine  to  an  iron-protein  combination  called  haemo- 
globiti.  Haemoglobin  will  combine  chemically  with  oxj^gen, 
forming  a bright  red 
compound  called 
oxyhaonoglobin.  In 
the  parts  of  the 
botly  where  oxida- 
tion is  going  on,  the 
haemoglobin  gives 
up  its  oxygen  sup- 
pi}',  At  the  same 
time  the  plasma 

takes  up  the  carbon  dioxide  which  is  given  off  by  the  cells.  The 
result  of  this  interchange  of  gases  causes  a change  in  the  color 
of  the  blood  from  a dull  to  a bright  red. 

The  colorless  corpuscles,  of  which  several  kinds  are  found  in  the 
blood,  are  irregular  in  outline,  as  they  constantly  change  their 

form.  The  color- 
less corpuscles  are 
less  numerous  than 
the  red,  the  ratio 
being  about  1 to 
700  in  a normal 
person.  They  in- 
crease in  number 
during  certain  dis- 
eases. They  have 
the  power  of  move- 
ment, for  they  are 
found  not  only 
inside  but  also 
outside  the  blood 
vessels,  showing 
that  they  have 

When  germs  or  any  foreign  organisms  enter  the  body,  the  WOrked  their  Way 
colorless  corpuscles,  phagocytes,  accumulate  and  either  ingest  between  the  Cells 
the  germs  directly  or  with  the  aid  of  certain  substances,  opsonins, 

destroy  them.  that  form  the  walls 


^erms 


CcAsj-lcfirs  cor-picffcle— 


388  FOODS  CIRCULATED  AND  USED  IN  THE  BODY 


of  the  blood  tubes.  Like  the  amoeba,  the  colorless  corpuscles 
feed  by  engulfing  their  prey.  This  fact  has  a very  important 
bearing  on  the  relation  of  the  corpuscles  to  certain  diseases  caused 
by  bacteria  within  the  body.  If,  for  example,  bacteria  get  into  a 
wound,  colorless  corpuscles,  called  phagocytes  (fag'6-sit),  at  once 
surround  the  spot  and  attack  the  bacteria  which  cause  the 
inflammation.  The  blood  contains  certain  antibodies  called 
opsonins  (6p's6-mn),  which,  when  present,  enable  the  corpuscles 
to  engulf  and  digest  the  bacteria.  If  the  bacteria  are  few  in 
number,  they  are  quickly  destroyed.  If  bacteria  are  present  in 
great  quantities,  they  may  prevail  and  kill  the  phagocytes.  The 
dead  bodies  of  the  phagocytes  thus  killed  and  the  destroyed 
tissue  help  form  pus  which  also  contains  many  dead  and  living 
bacteria.  When  such  an  infection  occurs,  we  must  come  to  the 
aid  of  the  colorless  corpuscles  by  washing  the  wound  with  an 
antiseptic. 

Laboratory  Exercise.  What  causes  blood  to  clot  ? Wash  your  finger 
thoroughly  with  soap  and  water.  Holding  the  finger  down,  prick  it 
with  a sterilized  needle.  Draw  off  three  drops  of  blood,  placing  each 
drop  on  a clean  microscopic  slide.  Place  the  first  slide  at  once  on  ice. 
To  the  second  add  a drop  of  5 per  cent  sodium  oxalate  solution. 
Leave  the  third  drop  exposed  to  the  air  of  the  room.  At  intervals  of 
one  minute  draw  a clean  hair  through  each  drop. 

Note  how  long  it  takes  the  third  drop  of  blood  to  clot.  Compare 
this  drop  with  the  drop  on  ice  and  the  drop  to  which  the  sodium  oxalate 
was  added. 

Laboratory  Demonstration.  ’Let  fresh  beef  blood  stand  over  night. 
What  happens?  Whip  fresh  beef  blood  briskly  with  an  egg  beater.  A 
stringy  almost  colorless  substance  will  stick  to  the  beater.  This,  if  washed 
carefully  and  tested  with  nitric  acid  and  ammonia,  is  found  to  contain  a 
protein  substance.  It  is  called  fibrin  (fi'brin) . 

In  blood  within  the  circulatory  system  of  the  body,  the  fibrin 
is  held  in  a fluid  state  called  fibrinogen  (fi-brin'6-j6n).  Blood 
plasma,  then,  is  made  up  of  a thin  liquid,  serum,  and  of  fibrinogen 
which  coagulates  under  certain  conditions,  entangling  the  blood 
corpuscles  in  a network  of  fine  threads,  thus  forming  the  clot. 

The  clotting  of  blood  prevents  bleeding  to  death.  It  is 
nothing  more  than  another  example  of  the  work  of  enzymes.  A 
substance  called  thrombin  is  the  active  agent  in  changing  fibrin- 


liEUVnON  OP  LYMPH  TO  THE  BLOOD 


389 


cube 


T'ecC 

corpuscle. 


ogcn  to  the  insoluble  fibrin  of  a clot.  This  change  seems  to  be  due 
largely  to  the  action  of  minute  bodies  in  the  blood  known  as  blood 
platelets.  Under  abnormal  conditions  these  blood  platelets  break 
down,  releasing  some  substances  which  (if  the  blood  has  the 
necessary  content  of  calcium)  cause  the  thrombin  to  do  its  work. 

Relation  of  lymph  to  the  blood.  The  tissues  and  organs  of  the 
botly  are  interlaced  by  a network  of  tubes  which  carry  the  blood. 
Outside  the  blood 
tubes,  in  spaces  be- 
tween  the  tissue  cells, 
is  another  fluid,  much 
like  plasma  of  the 
blood.  This  is  the 
lymph.  It  is  a color- 
less or  yellowish 
liquid  in  which  some 
colorless  corpuscles, 
or  leucocytes,  are 
found.  The  Ijunph 
bathes  all  portions  of 
the  bodj^  not  reached 
by  the  blood.  It 
acts  as  the  medium 
of  exchange  between 
the  blood  proper  and 
the  cells  in  the 
tissues  of  the  body. 

By  means  of  the 
food  supply  thus 

brought,  the  cells  of  the  body  are  able  to  grow,  the  fluid  food 
being  changed  to  the  protoplasm  of  the  cells.  By  means  of  the 
oxygen  brought  by  the  red  blood  corpuscles  and  passed  over 
through  the  lymph,  oxidation  may  take  place  within  the  cells. 
Lymph  not  only  gives  food  to  the  cells  of  the  body,  but  also 
takes  away  carbon  dioxide  and  other  waste  materials,  which  are 
ultimately  passed  out  of  the  body  by  means  of  the  lungs,  skin, 
and  kidneys. 

H.  BIO  — 26 


oorpujcle- 


The  relation  of  cells  to  the  blood.  Explain  exactly  what 
happens  in  the  muscle  (shown  in  the  center  of  the  diagram) 
when  it  does  work. 


390  FOODS  CIRCULATED  AND  USED  IN  THE  BODY 


Disease-resisting  functions  of  the  plasma.  It  is  common 
knowledge  that  some  of  us  “ take  ’’  catching  or  communicable 
diseases  more  easily  than  others.  Some  fortunate  persons  are 
immune  to  certain  diseases,  that  is,  they  do  not  take  them,  because 
certain  antibodies  are  present  in  their  blood.  These  antibodies 
act  in  different  ways,  but  their  work  is  directed  against  bacteria 
which  get  into  the  body  and  cause  disease.  Some  antibodies, 
called  lysins,  have  the  power  to  dissolve  bacteria.  Others,  called 
agglutinins,  cause  the  bacteria  in  the  blood  to  clump  together  in 


The  diagram  on  the  left  shows  free  swimming  typhoid  bacteria.  The  diagram  on  the  right 
shows  the  bacteria  clumped  together  by  agglutinins  which  are  produced  by  the  body  cells  as 
a protective  measure.  The  bacteria  are  stationary  and  can  be  more  easily  destroyed  by  the 
white  corpuscles. 


little  inactive  masses,  so  that  they  are  an  easy  prey  for  the  phago- 
cytes and  lysins.  We  have  already  heard  of  the  work  of  the 
opsonins,  another  kind  of  antibody.  Agglutinins  and  certain 
other  antibodies  called  precipitins,  which  precipitate  the  bacteria 
from  solution,  have  become  a great  help  to  physicians  in  deter- 
mining whether  a person  has  a given  disease.  For  example,  a test 
known  as  the  Widal  (ve-dal')  test  is  now  used  in  all  hospitals  to 
determine  if  a person  has  typhoid  fever.  A few  drops  of  blood 
from  the  patient  is  allowed  to  stand  until  the  serum  has  separated. 
This  is  then  diluted  with  a weak  salt  solution  and  to  this  are  added 
some  living  typhoid  bacteria.  If  the  person  has  typhoid,  the 
bacteria  added  to  his  serum  will  immediately  become  clumped 
together  or  agglutinated,  thus  showing  that  his  antibodies  are 


lU.OOD  TRANSFUSION 


391 


already  formed  and  at  work.  This  is  only  one  of  a number  of 
tests  that  have  been  developed  in  recent  years.  Just  as  each 
disease  is  caused  by  a specific  kind  of  organism,  producing  a 
specific  kind  of  toxin  or  poison,  so  the  blood  forms  specific  anti- 
bodies to  fight  each  kind  of  organism  or  its  to.xins. 

Blood  transfusion.  It  has  been  found  that  there  are  four  types 
of  human  blood.  About  50  per  cent  of  all  people  have  one  type. 
.After  heav}"  losses  of  blood  as  in  an  accident  or  in  an  operation, 
and  in  some  illnesses,  blood  is  sometimes  injected  into  a vein  of 
the  patient  by  transfusion  from  an  artery  of  a donor.  Before  this 
operation  is  performed,  it  is  necessary  to  make  a test  to  see  if  the 
two  persons  have  blood  of  the  same  type.  This  is  done  by  means 
of  the  agglutinin  test.  Red  corpuscles  of  the  person  who  is  to 
give  the  blood  are  added  to  the  blood  of  the  patient.  If  the  red 
corpuscles  are  agglutinated,  then  the  bloods  are  of  two  different 
types  and  transfusion  cannot  be  made.  Certain  lysins  called 
haemohjsins  may  also  be  present  in  blood  that  will  dissolve  foreign 
red  corpuscles  of  the  volunteer  in  the  blood  of  the  patient.  Tests 
may  be  made  for  these  haemolysins  by  adding  washed  red  cor- 
puscles of  the  volunteer’s  blood  to  the  serum  of  the  patient’s  blood. 
If  the  corpuscles  are  dissolved,  this  blood  cannot  be  used  for  trans- 
fusion. 


Self-Testing  Exercise 

Blood  consists  of  a fluid  part  called (1)  and  three  kinds  of 

cells  : (2)  corpuscles, (3)  corpuscles  and (4) 

(5).  Red  corpuscles  take  up (6)  by  means  of  the 

(7)  they  contain.  There  are  several  kinds  of  (8) 

corpuscles,  all  of  which  are  (9)  in  outline  and  have  the 

power  of  (10).  Those  called (11)  feed  on  bacteria 

in  the  blood.  Blood  clots  because  of  the  coagulation  of  the 

(12)  it  contains.  This  is  brought  about  through  the  action  of 

the  substance (13).  Plasma  besides  containing (14) 

contains  antibodies.  Among  these  are (15), (16),  and 

(17).  Lymph  acts  as  a medium  of  exchange  between  the 

(18)  and  the (19)  cells.  Blood  transfusions  can  be 

performed  only  if  persons  have  blood  of  the  same (20).  This 

can  be  found  out  by  means  of (21). 


392  FOODS  CIRCULATED  AND  USED  IN  THE  BODY 


PROBLEM  II.  WHAT  ARE  THE  FUNCTIONS  OF  SOME  OF 
THE  ENDOCRINE  GLANDS? 


-pineal  planet 


parccthyroioCs. 

xyiyroicL J 

Xhymxjcs  I 


liv-er* 

-pccncreocS 

-.spl©e«. 

-occCrcnal^ 

"kidney®! 


The  endocrine  or  ductless  glands  and  their  secretions.  In 

addition  to  all  the  functions  already  mentioned,  the  blood  has 

another  very  wonder- 
ful work.  We  have 
already  mentioned 
the  hormones  (from 
the  Greek  word  hor- 
mon,  meaning  “ to 
excite”).  These 
chemical  activators, 
produced  by  the  en- 
docrine or  ductless 
glands  in  various 
parts  of  the  body,  go 
into  the  blood  stream, 
and  stimulate  another 
organ  or  organs  in  the 
body.  The  blood  is 
the  only  means  of 
communication  be- 
tween these  glands 
and  the  tissues  on 
which  their  hormones 
act.  Scientists  are 
just  beginning  to  ap- 
preciate the  tre- 
mendous influence  on 
life  of  some  of  these  glands,  among  which  are  the  thyroid  and 
parathyroid,  small  glands  located  in  the  neck ; the  adrenals 
(ad-re'nal),  tiny  glands,  closely  attached  to  the  kidneys;  the 
pituitary  body,  at  the  base  of  the  brain ; parts  of  the  pancreas; 
and  parts  of  the  egg-producing  and  sperm-producing  organs,  the 
ovaries  and  testes.  The  thymus  and  spleen,  although  not  true 
glands,  are  often  included  with  those  mentioned  above. 


The  approximate  positions  of  the  endocrine  glands  are 
indicated  in  the  diagram. 


ENDOCRINE  GLANDS 


393 


The  thyroid.  The  thyroid  gland  secretes  a substance  which  is 
made  up  of  over  sixty  per  cent  iodine.  This  substance  largely 
controls  the  rate  of  oxidation  in  the  body  and  hence  a person’s 
basal  metabolism.  Underactivity  of  the  gland  causes  a condition 
known  as  cretinisfn,^  which  can  usually  be  cured  by  giving  the 
patient  more  thyroid  extract.  Overactivity  of  the  gland  causes 
the  disease  known  as  exophthalmic  ^ goiter^  a condition  of  extreme 
nervousness,  with  loss  of  weight  and  other  symptoms,  such  as  pro- 
truding eyeballs  and  irregular  heart  action. 

In  some  parts  of  the  country  where  the  water  supply  comes 
from  mountain  sources  many  people  are  troubled  with  a slight 
enlargement  of  the  thyroid  gland.  This  trouble  comes  from  a lack 
of  iodine  in  the  water  supply.  This  iodine  deficiency  in  the  water 
can  usually  be  corrected  by  eating  foods  rich  in  iodine,  such  as 
sea  foods  and  certain  vegetables,  or  by  putting  a minute  drop  of 
iodine  in  the  drinking  water. 

The  adrenal  glands.  The  adrenal  glands  produce  a secretion, 
adrenin,  which  acts  upon  the  muscles  and  the  nervous  system. 
It  causes  a faster  beating  of  the  heart,  a heightened  blood  pressure, 
and  other  indications  of  increased  muscular  activity.  It  is  indeed 
the  emergency  hormone  of  the  body.  It  is  this  hormone  that 
enables  the  sprinter  to  make  his  final  burst  of  speed  at  the  tape, 
or  the  football  player  to  make  a desperate  stand  when  almost 
exhausted.  It  explains  the  “strength  of  desperation.”  Adrenin 
has  been  prepared  in  the  laboratory  and  is  known  commercially 
as  adrenalin  (ad-re'nal-m) . It  is  used  in  medicine  to  contract 
the  blood  vessels,  hasten  the  clotting  of  blood,  and  to  strengthen 
the  heart  beat. 

The  pituitary  and  thymus  glands.  The  pituitary  gland  has  much 
to  do  with  body  size.  Dwarfs  appear  to  lack  or  have  very  small 
pituitary  glands,  while  giants  always  have  abnormally  large  ones. 
Dr.  Harvey  Cushing  of  the  Harvard  Medical  School,  who  is  an 
authority  on  the  work  of  the  pituitary  body,  says:  “The  Lewis 
Carroll  of  today  would  have  Alice  nibble  from  a pituitary  mush- 
room in  her  left  hhnd  and  a lutein  (a  pigment  obtained  from  a 

' 1 Cretinism  (kre'tm-izm)  : idiocy  accompanied  by  physical  deformity. 

2 Exophthalmic  (ek'sof-thal'mik)  : pertaining  to  a disease  causing  protrusion  of 
i eyeballs. 


394  FOODS  CIRCULATED  AND  USED  IN  THE  BODY 


portion  of  the  ovary)  in  her  right  hand  and  presto ! she  is  any 
height  desired.” 

The  thymus,  a little  understood  structure  found  near  the 
thyroid  gland,  gradually  disappears  as  we  grow  past  adolescence. 

It  seems  to  have  some 


influence  on  the  sex 
glands  and  on  the  lime 
content  of  bone. 

The  reproductive 
glands.  Some  part  of 
the  ovaries  and  testes 
have  long  been  known  to 
control  the  development 
of  the  so-called  secondary 
sex  characteristics  which 
give  us  the  difference 
in  appearance  between 
females  and  males.  It  is 
not  too  much  to  say  that 
hormones  are  responsible 
for  many  sex  characteris- 
tics, as  experiments  with 
fowls  and  other  animals 
have  proved.  But  popu- 
lar statements  on  the  effect 
of  grafting  these  glands 
from  other  animals  in 
human  beings  are  greatly 
exaggerated  and  can  be  for  the  most  part  disbelieved. 

The  pancreas  and  liver.  It  has  been  known  for  many  years 
that  the  pancreas  produces  another  secretion  besides  that  which 
passes  into  the  digestive  tract.  But  investigators  have  now  dis- 
covered that  this  internal  secretion,  with  its  hormone,  is  produced 
in  groups  of  cells  known  as  the  Islands  of  Langerhans  (lang'er-hans) 
in  the  pancreas.  If  this  hormone  is  not  present,  then  sugar,  which 
normally  is  stored  in  the  liver  as  glycogen,  is  allowed  to  go  directly 
into  the  blood,  where  it  soon  appears  in  excessive  quantities. 


A giant  8 feet  9 ‘ inches  tall  and  a normal  man  5 feet 
6 inches  tall.  What  do  scientists  consider  the  cause 
of  unusually  large  or  small  people  ? 


ClKCn’LATION  OF  TllF  BLOOD 


395 


causinp;  a disease  called  diabetes  (di-d-be'tez).  Work  by  Dr. 
Baiitiiip:  and  his  co-workers  of  Toronto  University  has  resulted 
in  the  production  of  the  substance  insulin,  which  contains  the 
hormone.  Now  a person  whose  pancreas  has  lost  the  power  to 
ref>;ulate  the  storap:c  of  glycogen  in  the  liver  may  find  relief  through 
a proper  diet  and  insulin  in  prescribed  doses. 

Practical  Exercise  1.  Make  a report  on  some  one  of  the  endocrine  glands. 
Use  Harrow’s  (rlands  in  Ilenlth  arid  Disease  or  articles  from  Hygeia. 

Practical  Exercise  2.  Statistics  show  that  diabetes  is  increasing  rapidly  in 
this  country  in  spite  of  insulin.  The  reason  given  is  the  rich  and  heavy  diet. 
What  recommendations  would  you  make  for  betterment  of  this  condition? 


Self-Testing  Exercise 

Hormones  are  chemical (1)  and  are  produced  by 

(2)  glands.  Underdevelopment  of  the  thyroid  causes  cretinism, 

overactivity  causes  (3)  (4).  The  (5) 

produce  the  emergency  hormone.  The (6)  gland  seems  to 

regulate  body  size.  The  pancreas  produces  a hormone  which  regu- 
lates the  storage  of (7)  in  the  liver.  If  sugar  goes  directly 

into  the  blood,  we  have (8)  and  must  use (9). 

PROBLEM  III.  HOW  DOES  THE  BLOOD  CIRCULATE 
THROUGH  THE  BODY? 

Circulation  of  the  blood.  The  blood  is  the  carrying  agent  of 
the  body.  Like  a railroad  system,  it  takes  materials  from  one 
part  of  the  human  organism  to  another.  This  it  does  by  means 
of  the  organs  of  circulation,  — the  heart  and  blood  vessels.  These 
blood  vessels  are  of  three  kinds : the  arteries,  elastic  muscular 
tubes,  which  carry  blood  away  from  the  heart ; the  veins,  thin- 
walled  vessels  containing  valves  which  bring  the  blood  back  to  the 
heart ; and  the  capillaries,  which  connect  the  smallest  arteries 
with  the  smallest  veins.  The  organs  of  circulation  thus  form  a 
system  of  connected  tubes  through  which  the  blood  flows. 

Demonstration!.  What  is  the  structure  of  the  heart  ? Refer  to  the 
diagram  of  the  heart,  with  the  arteries  and  veins  connected  with  it. 
Where  do  the  chief  arteries  lead  to  and  from  where  do  the  large  veins 
come?  Obtain  the  heart  of  a recently  killed  steer  and  examine  it,  not- 
i ing  the  four  chambers,  the  valves,  and  the  blood  tubes  leading  to  and 


396  FOODS  CIRCULATED  AND  USED  IN  THE  BODY 

from  it.  The  upper  chambers  are  called  the  right  and  left  auricles 
respectively ; the  lower  chambers,  the  right  and  left  ventricles.  Which 
have  the  thicker  walls  ? What  is  probably  the  use  of  these  walls  ? 

Notice  the  position  of  the  valves  and  the  direction  of  their  move- 
ment. In  what  direction  do  arteries  lead?  Veins? 

Do  the  chambers  all  connect  with  one  another?  Write  a paragraph 
describing  the  structure  of  the  heart. 

The  structure  of  the  heart.  The  heart  is  a cone-shaped  mus- 
cular organ  about  the  size  of  the  fist.  It  is  surrounded  by  a loose 


How  does  the  blood  get  from  the  left  ventricle  to  the  right  ventricle  ? 


membranous  bag  called  the  'pericardium,  the  inner  lining  of  which 
secretes  a fluid  in  which  the  heart  lies.  If  we  should  cut  open  the 
heart  of  a mammal  down  the  midline,  we  could  divide  it  into  a 
right  and  a left  side,  each  of  'which  has  'within  the  heart  no  connec- 
tion 'with  the  other  side. 

Practical  Exercise  3.  To  make  an  apparatus  that  will  demonstrate  the  fact 
that  the  heart  is  a double  force  pump. 

The  heart  in  action.  The  heart  is  constructed  on  the  same 
plan  as  a force  pump,  the  valves  preventing  the  reflux  of  blood 
into  the  auricles  when  it  is  forced  out  of  the  ventricles.  Blood 
enters  the  auricles  from  the  veins  because  the  muscles  of  that  part 
of  the  heart  relax;  this  allows  the  space  within  the  auricles  to 


THE  COURSE  OF  THE  BLOOD  IN  THE  BODY  397 

fill.  Almost  immediately  the  muscles  of  the  ventricles  relax,  thus 
allowing  blood  to  pass  into  the  chambers  within  the  ventricles. 
Then,  after  a short  pause,  during  which  time  the  muscles  of  the 
heart  are  resting,  a wave  of  muscular  contraction  begins  in  the 
auricles  and  ends  in  the  ventricles,  with  a sudden  strong  contrac- 
tion which  forces  the 
blood  out  into  the  ar- 
teries. Blood  is  kept 
from  flowing  backward 
by  the  valves,  which 
act  in  the  same  manner 
as  do  the  valves  in  a 
pump.  The  blood  is 
thus  made  to  pass  into 
the  arteries  upon  the 
contraction  of  the  ven- 
tricle walls. 

Practical  Exercise  4. 

Why  is  the  heart  a force 
pump?  Why  is  the  heart 
said  to  be  double? 

The  course  of  the 
blood  in  the  body. 

There  are  two  distinct 
systems  of  circulation 
in  the  body.  The 
pulmonary  • circulation 
takes  the  blood  through  the  right  auricle  and  ventricle,  to  the 
lungs,  and  passes  it  back  to  the  left  auricle.  This  is  a relatively 
short  circulation,  in  which  the  blood  receives  oxygen  in  the  lungs 
and  gives  up  carbon  dioxide.  The  longer  circulation  is  known  as 
the  systemic  circulation;  in  this  system,  the  blood  leaves  the  left 
ventricle  through  the  great  dorsal  artery  called  the  aorta.  Through 
ever-branching  arteries  blood  passes  to  the  muscles,  the  nervous 
system,  kidneys,  skin,  and  other  organs  of  the  body.  It  gives 
up  food  and  oxygen  in  these  tissues,  receives  the  waste  products 
of  oxidation  while  passing  through  the  microscopic  tubes,  capil- 
laries, and  returns  to  the  right  auricle  through  veins  which  join 


Explain  how  the  heart  is  a force  pump. 


398  FOODS  CIRCULATED  AND  USED  IN  THE  BODY 


and  increase  in  size  until  they  form  two  large  vessels  known  as 
the  venae  cavae. 

Portal  circulation.  Some  of  the  blood,  on  its  way  to  the  heart, 
passes  to  the  walls  of  the  food  tube  and  to  its  glands.  From  these 
parts  it  is  sent  with  its  load  of  absorbed  food  to  the  liver.  Here 
the  vein  which  carries  the  blood  (called  the  ^portal  vein)  breaks  up 
into  capillaries  around  the  cells  of  the  liver,  which  takes  out  the 
excess  sugar  and  stores  it  as  glycogen.  From  the  liver,  the  blood 
passes  directly  to  the  right  auricle.  The  portal  circulation  con- 
nects the  stomach  and  the  small  intestine  with  the  liver.  It  is 
the  only  part  of  the  circulatory  system  where  the  blood  passes 
through  two  sets  of  capillaries  on  its  way  from  auricle  to  auricle. 

Demonstration  2.  To  show  circulation  in  the  web  of  a frog’s  foot. 

Examine  under  a compound  microscope  the  web  of  the  foot  of  a living 
frog.  Note  the  network  of  tiny  blood  vessels,  capillaries.  Those 
vessels  in  which  the  blood  moves  in  spurts  are  tiny  arterioles ; the 
larger  vessels  in  which  the  blood  moves  slowly  or  steadily  are  veins. 

Structure  of  the  arteries,  veins,  and  capillaries.  A distinct 
difference  in  structure  exists  between  the  arteries  and  the  veins  in 
the  human  body.  The  arteries,  because  of  the  greater  strain 
received  from  the  blood  which  is  pumped  from  the  heart,  have 
thicker  muscular  walls,  and  in  addition  are  very  elastic.  Veins 
are  much  thinner-walled  than  arteries  and  have  small  valves  which 


Explain  the  difference  between  an  artery,  a vein,  and  a capillary. 


BLOOD  PJiESSUJiE 


399 


ojxm  in  the  diivction  of  the  blood  (low.  Capillaries  arc  a net- 
work of  very  thin- walled  vessels  throiij2;h  which  food,  oxygen,  and 
colorless  corpuscles  pass  out  to  the  tissues. 

The  pulse  and  blood  pressure.  The  pulse  is  caused  by  the 
contraction  of  the  ventricle  which  causes  a wave  of  distention  to 
travel  along  the  blood  vessel.  This  pulse  can  easily  be  felt  in  the 
larger  arteries  that  arc  near  the  surface  of  the  body.  As  the  blood 
is  forced  from  the  heart  into  the  arteries  it  comes  under  pressure 
caused  by  the  resistance  given  to  the  flow  of  blood  by  the  small 
capillaries.  Thus  a definite  blood  pressure  is  caused,  which  is 
seen  when  the  blood  spurts  from  a cut  artery.  Blood  pressure  can 
easily  be  measured  by  an  instrument  called  the  sphygmomanometer. 

Practical  Exercise  6,  Visit  a physician  and  have  him  explain  what  happens 
when  he  takes  your  blood  pressure,  and  the  significance  of  what  he  finds. 

Lymph  vessels.  The  lymph  is  collected  from  the  various  tissues 
of  the  body  by  ducts  provided,  like  the  veins,  with  valves.  The 
pressure  of  the  blood  within  the  blood  vessels  continually  forces 
more  plasma  into  the  lymph ; thus,  a slow  current  is  maintained 
from  the  lymph  spaces  into  lijm'ph  tubes.  On  its  course  the  lymph 
passes  through  many  lijm'ph  glands,  where  impurities  appear  to 
be  removed.  The  lymph  ultimately  passes  into  a large  tube,  the 
thoracic  (th6-ras'ik)  duct,  and  empties  into  the  blood  stream  in  the 
neck  region. 


Explain,  with  reference  to  your  text,  why  it  is  that  blood  flows  in  one  direction  in  the  veins. 


400  FOODS  CIRCULATED  AND  USED  IN  THE  BODY 


The  lacteals.  We  have  already  learned  that  part  of  the  digested 
food  (chiefly  sugars,  amino  acids,  salts,  and  water)  is  absorbed 


Diagram  of  the  circulatory  system.  The 
vessels  containing  arterial  blood  are  red, 
those  containing  venous  blood  are  blue, 
and  the  lymphatics  are  yellow. 


directly  into  the  blood  through  the 
walls  of  the  vilh  and  carried  to  the 
liver.  Fat,  however,  is  passed  into 
the  spaces  in  the  central  part  of 
the  villus  known  as  the  lacteals. 
This  fluid  or  lymph  then  passes 
from  the  lacteals  into  other  lym- 
phatics, and  eventually  drains  into 
the  blood  system  by  way  of  the 
thoracic  duct.  Shortly  after  a 
meal  the  lacteals  are  filled  with  a 
white  fatty  substance,  but  at  other 
times  they  are  filled  with  a fluid 
very  similar  to  the  lymph  in  the 
other  lymphatics. 

Laboratory  Exercise.  What  is  the 
effect  of  exercise  on  the  heartbeat  ? 

Place  the  middle  finger  of  the  right 
hand  two  inches  from  the  ball  of  the 
thumb,  to  locate  the  pulse.  Count  the 
number  of  beats  per  minute.  The 
normal  rate  in  men  is  seventy-two 
beats  per  minute ; in  women,  seventy- 
six.  It  is  higher  in  children. 

Then  under  the  direction  of  a 
leader,  take  a hard  setting-up  drill 
for  three  minutes  with  the  windows 
open.  Count  the  pulse  beats  as  be- 
fore and  tabulate  the  result.  Note 
any  difference  in  respiration. 

What  effect  did  the  exercise  have 
on  the  rate  of  the  heartbeat?  Can 
you  explain  the  reason?  Can  you 
explain  the  difference  in  the  rate  of 
respiration?  Show  in  your  table  the 
difference  between  the  normal  pulse 
and  the  one  taken  after  exercising. 


The  effect  of  exercise  on  the  circulation.  Exercise  in  modera- 
tion is  of  undoubted  value,  because  it  sends  more  blood  to  parts 


TJiEATMEXT  OF  CUTS  AND  lUUJISES 


401 


of  the  body  where  increased  oxidation  is  taking  place  as  the 
result  of  the  exercise.  The  best  forms  of  exercise  are  those  which 
give  work  to  as  many  muscles  as  possible  — w'alking,  out-of-door 
sports,  any  exercise  that  is  not  violent.  Exercise  should  not  be 
attempted  immediately  after  eating,  as  this  causes  a withdrawal  of 
blood  from  the  digestive  tract  to  the  muscles  of  the  body.  Neither 
should  e.xercise  bo  continued  after  becoming  tired,  as  poisons  are 
then  formed  in  the  muscles,  which  cause  the  feeling  we  qqW  fatigue. 
Overdoing  in  any  sport  or  game  is  dangerous.  Fatigue  is  a signal 
to  rest.  Remember  that  extra  w'ork  given  to  the  heart  by  extreme 
e.xercise  may  injure  it,  causing  possible  trouble  with  the  valves. 
Older  people  and  those  who  through  excessive  use  of  stimulants 
or  tobacco  or  other  causes  have  developed  arteriosclerosis f 
hardening  of  the  arteries,  need  to  be  especially  careful.  “ A man 
is  as  young  as  his  arteries,”  because  the  hardening  of  the  wall 
raises  the-  blood  pressure,  and  if 
the  inelastic  artery  wall  breaks, 
due  to  overexercise,  death  may 
result  through  apoplexy. 

Treatment  of  cuts  and  bruises. 

Blood  which  oozes  slowly  from  a 
cut  will  usually  stop  flowing  by 
the  natural  means  of  the  forma- 
tion of  a clot.  A cut  or  bruise 
should,  however,  be  washed  in  a 
weak  solution  of  lysol  or  some 
other  antiseptic  in  order  to  pre- 
vent bacteria  from  obtaining  a 
foothold  on  the  exposed  flesh. 

If  blood  gushes  from  a wound,  in 
distinct  pulsations,  an  artery  has 
been  severed.  A tight  bandage 
known  as  a tourniquet  (toor'm-ket) 
must  be  tied  between  the  cut  and  the  heart.  If  a vein  is  cut,  the 
blood  flows  smoothly.  In  this  case,  a tourniquet  is  applied  on  the 
side  of  the  cut  away  from  the  heart. 

1 Arteriosclerosis : ar-te'ri-o-skle-ro'sis. 


What  kind  of  blood  vessel  has  been  cut? 


402  FOODS  CIRCULATED  AND  USED  IN  THE  BODY 


Laboratory  Exercise.  What  methods  should  be  used  to  stop  the 
flow  of  blood  in  case  of  an  accident  ? Decide  first  whether  the  blood  is 
issuing  from  an  artery  or  from  a vein.  How  would  you  know?  Then 
apply  a tourniquet  made  from  a stick  or  ruler  and  a handkerchief  or 
towel,  using  a stone  or  knife  to  press  down  on  the  blood  vessel. 

Imagine  an  artery  severed  in  the  arm  below  the  elbow  and  practice 
applying  a tourniquet  there.  Apply  a tourniquet,  if  the  artery  cut  is 
above  elbow.  Does  the  pulse  in  the  wrist  stop  when  the  tourniquet  is 
applied  ? Explain  reason. 

Conclusion.  How  would  you  make  a tourniquet?  Describe  fully. 
Where  must  a tourniquet  be  placed  when  an  artery  is  cut?  Where 
when  a vein  is  severed  ? What  is  the  use  of  the  tourniquet  ? 

The  effect  of  alcohol  upon  the  blood.  Alcohol,  when  taken 
habitually,  causes  several  very  serious  effects  upon  the  blood  and 
blood  vessels.  The  bodily  resistance  against  disease  which  is 
brought  about  by  the  presence  of  specific  antibodies  is  greatly 
weakened  in  those  who  use  alcohol  to  excess.  Drinking  also  has 
an  injurious  effect  upon  the  colorless  corpuscles,  as  it  lowers  their 
ability  to  fight  disease  germs.  Place  a drop  of  alcohol  on  a slide 
containing  active  amoebas,  if  you  wish  to  see  the  effect  on  a similar 
type  of  cell.  Alcohol  acts  on  the  nerve  centers  controlling  the 
heart  and  blood  vessels.  Alcohol  may  even,  in  cases  of  long  and 
severe  drinking,  cause  changes  to  take  place  in  the  walls  of  the 
blood  vessels  which  may  result  in  the  breaking  of  the  vessel  or  the 
formation  of  a blood  clot  in  the  vessel.  Such  an  injury  in  blood 
vessels  in  the  brain  causes  apoplexy  and  often  results  in  sudden 
death. 

Self-Testing  Exercise 

The  circulation  of  the  blood  is  brought  about  by  a heart  which  acts 

as  a (1)  (2).  Blood  passes  out  from  the  heart 

through (3),  then  into  the  tissues  by  means  of  the (4), 

returning  to  the  heart  again  by  way  of  the (5).  There  are 

two  important  systems  of  circulation  in  the  body : the (6)  to 

and  from  the  lungs,  and  the (7)  which  leaves  the  heart  from 

the  (8)  ventricle  and  passes  out  to  all  the  body  organs. 

Arteries  are  (9)  and  (10),  capillaries  are  very 

(11),  and  veins  have (12)  walls  and  have 

(13)  to  keep  the  blood  from  running  backward.  The  pulse  is  caused 
by  the  gushing  of  blood  from  the (14),  when  the  walls  of  the 


THE  ()H(JANS  OF  RESPIRATION  IN  MAN 


4():-5 

(15)  contract.  Blood  jirossuro  is  caused  l)y  the (Hi) 

of  the  tiny (17)  against  the  blood  forced  from  the 

(IS). 


PROBLEM  IV.  WHAT  IS  RESPIRATION? 

Laboratory  Exercise.  A comparison  of  the  respiratory  tract  of  a 
frog  and  a mammal.  Oi)en  a frog’s  mouth  and  find  the  slitliko  open- 
ing (glottis)  just  back  of  the  tongue.  Insert  a Idowpipe  or  a glass  tube 
aud  blow  down  the  short  windpijje  (trachea)  which  branches  into  two 
divisions  leading  to  the  lungs  (bronchial  tubes).  What  happens  to  the 
lungs? 

Examine  a section  cut  through  a frog’s  lung.  Is  it  hollow?  Now 
comi)are  the  baglike  lungs  of  the  frog  with  the  more  com}dicated  lungs 
of  man  (see  diagram).  Do  you  find  the  same  structures  leading  to 
the  lungs  of  man?  (Read  your  text.)  Which  part  of  the  lungs  of 
man  would  be  elastic?  Which  part  of  the  frog’s?  Why? 

If  blood  vessels  were  found  in  the  walls  of  these  sacs,  what  gas  might 
be  brought  in  the 
blood  to  this  point? 

What  gas  might  be 
in  the  air?  How 
might  the  exchange 
of  these  gases  take 
place  ? Where  might 
it  take  place? 

The  organs  of 
respiration  in  man. 

We  have  noted  the 
fact  that  the  lungs 
are  the  organs  which 
give  oxygen  to  the 
blood  and  take  from 
it  carbon  dioxide. 

Air  passes  through 
the  nostrils  into  the 
windpipe.  This 
cartilaginous  tube, 
the  top  of  which 

..  , r 14-  tissue  is  cut  away  from  one  of  the  lungs  to  show  the  air 

may  easily  be  lelt  tubes.  Trace  the  course  of  air  from  the  nose  to  the  air  sacs. 

as  the  Adam’s  apple 

of  the  throat,  divides  into  two  bronchi  (bron'kl).  The  bronchi 
within  the  lungs  break  up  into  a great  number  of  smaller 


larvrxiC 

vojcte.  box 


404  FOODS  CIRCULATED  AND  USED  IN  THE  BODY 


bronchial  tubes,  which  divide  somewhat  like  the  small  branches 
of  a tree.  The  bronchial  tubes  are  lined  with  ciliated  cells,  the 
cilia  of  which  are  constantly  in  motion.  They  lash  with  a 
quick  stroke  toward  the  outer  end  of  the  tube,  that  is,  toward 
the  mouth.  Hence  any  foreign  material  in  the  tubes  will  be 
raised  first  by  the  action  of  the  cilia  and  then  by  coughing  or 
“ clearing  the  throat.’’  The  bronchial  tubes  end  in  very  minute 
air  sacs,  little  pouches  having  elastic  walls,  into  which  air  is 
taken  when  we  inspire,  or  take  a deep  breath.  In  the  walls 
of  these  pouches  are  numerous  capillaries.  Through  the  very 
thin  walls  of  the  air  sacs  a diffusion  of  gases  takes  place,  which 
results  in  the  blood  giving  up  carbon  dioxide  and  taking  up  oxygen. 
As  a result  of  this  process  the  color  of  the  blood  becomes  a brighter 
red,  due  to  the  combination  of  the  oxygen  with  the  haemoglobin 
in  the  red  corpuscle. 

Demonstration  3.  To  determine  changes  that  take  place  in  the  au 
in  the  lungs. 

Breathe  on  the  bulb  of  a thermometer  and  record  any  changes. 
Breathe  gently  on  any  glass  or  polished  metal  surface.  Note  what 
happens.  Take  a moderate  breath,  and  force  air  (tidal  air)  by  means 
of  a glass  tube  through  lime  water.  Notice  what  occurs.  Force  the 
last  part  of  a deep  expiration  (reserve  air)  through  limewater.  Note 
result. 

Thrust  a lighted  splinter  into  a bottle  of  air.  How  long  does  it 
burn?  Now  fill  a glass  jar  with  expired  air  by  the  downward  displace- 
ment of  water.  Invert  the  jar,  keeping  it  covered.  Remove  the 
cover,  and  introduce  into  the  jar  a lighted  wood  splinter.  How  long 
does  it  continue  to  burn?  What  does  this  indicate?  Why?  (Air 
loses  about  one  fourth  of  its  oxygen  while  in  the  lungs.) 

What  are  the  changes  that  take  place  in  blood  in  the  lungs  ? What 
does  air  gain  in  the  lungs?  What  does  it  lose?  What  is  one  reason 
for  deep  breathing? 


Composition  of  Fresh  Air  and  of  Air  Expired  from  the  Lungs 


Constituents 

In  Outdoor  Air 

In  Air  Expired 

FROM  THE  Lungs 

Oxygen 

20.96 

16.4 

Carbon  dioxide 

.04 

4.1 

Nitrogen  and  other  gases  . . 

79. 

79. 

Water  vapor 

variable 

.5 

CELL  KESPIRATrON 


405 


I As  the  table  shows,  there  is  a loss  of  nearly  5 per  cent  of  oxyp;en, 
and  a corresponding:  f2;ain  in  carbon  dioxide  and  water  vapor,  in 
expired  air.  'riiere  are  also  some  organic  waste  substances  in 
ex{)ired  air  which  are  not  shown  in  the  table. 

Cell  respiration.  It  has  been  shown,  in  the  case  of  very  simple 
animals,  such  as  the  Paramecium,  that  when  oxidation  of  food 
takes  place  in  the  cell,  energy  will  result.  In  man  the  oxygen 
taken  into  the  lungs 
is  not  used  there, 
but  is  carried  by 
the  blood  to  all 
parts  of  the  body 
where  work  is  done. 

Cell  activity  de- 
mands food  and 
oxygen. 

When  oxidation 
of  food  takes  place  Explain  this  diagram, 

in  the  cell,  energy  is 

released  for  cell  work  and  certain  wastes  are  formed.  The  waste, 
carbon  dioxide,  is  given  off  to  the  blood  when  any  food  containing 
carbon  is  burned.  When  proteins  are  burned,  other  wastes  con- 
taining nitrogen  are  formed.  These  must  be  passed  off  from  the 
cells,  as  they  are  poisons.  This  is  done  by  the  lymph  and  the 
blood,  which  take  the  waste  materials  to  points  where  they  may  be 
excreted  or  passed  out  of  the  body.  Water,  another  waste  product, 
is  excreted  by  the  skin  and  kidneys. 


Self-Testing  Exercise 

An (1)  of  oxygen  and (2) (3)  takes  place 

in  the  blood  as  it  passes  through  the  walls  of (4) (5)  of 

the  lungs.  Air  entering  the  lungs  has  about  (6)  per  cent 

more (7)  than  expired  air.  Respiration  takes  place  in  the 

(8)  of  the  body.  As  a result  of  cell  activity  after (9) 

and  (10)  are  taken  into  the  cell (11)  (12), 

(13)  and (14)  wastes  are  given  off. 

H.  BIO  — 27 


406  FOODS  CIRCULATED  AND  USED  IN  THE  BODY 
PROBLEM  V.  WHAT  ARE  THE  MECHANICS  OF  BREATHING? 

Demonstration  4.  To  show  the  mechanics  of  breathing. 

Pass  a glass  Y tube  through  a rubber  stopper.  Fasten  two  small  toy- 
balloons  to  the  branches  of  the  tube.  Put  the  stopper  in  the  small 
end  of  a bell  jar.  Adjust  the  tube  so  that  the  balloons  hang  free 


in  the  jar.  Attach  a 
string  to  the  middle  of  a 
piece  of  sheet  rubber. 
Tie  the  rubber  over  the 
large  end  of  the  jar. 


To  what  structures  in 
our  bodies  may  the  bal- 
loons and  rubber  sheet  be 
compared?  Pull  down 
the  string  gently.  What 
effect  does  the  lowering 
of  the  sheet  rubber  have 
on  the  balloon?  Why? 
Push  the  rubber  into  the 
bell  jar  to  form  an  arch. 
What  happens  to  the 
balloons?  Why?  Ex- 
plain how  this  experi- 
ment may  be  compared 
to  breathing? 


The  pleura.  The 

lungs  are  inclosed  in  a 
thin,  elastic,  membra- 
nous sac,  the  pleura. 
This  membrane  is  com- 
posed of  moist  tissue. 
In  breathing,  when  the 


lungs  become  larger,  the  smooth,  moist  surface  of  the  pleura 
prevents  the  friction  that  otherwise  would  occur  between  the 
lung  and  the  walls  of  the  chest. 

The  mechanics  of  breathing.  In  every  breath  there  are  two 
movements,  inspiration  (taking  air  in)  and  expiration  (forcing  air 
out).  An  inspiration  is  produced  by  the  contraction  of  muscles 
between  the  ribs,  together  with  the  contraction  of  the  diaphragm, 
the  muscular  wall  forming  the  floor  of  the  chest  cavity ; this 
results  in  pulling  the  diaphragm  down  and  pulling  the  ribs  up- 
ward and  outward,  thus  increasing  the  space  within  the  chest 


COMMON  DISEASES  OF  THE  NOSE  AND  THROAT  407 


cavity  for  the  air  to  rush  in.  Then  the  diaphragm  relaxes  and 
rises  and  the  muscles  between  the  ribs  relax.  This  pressure  forces 
the  air  out  of  the  lungs,  thus  producing  expiration.  During  these 
processes  an  exchange  of  oxygen  in  the  air  and  of  carbon  dioxide 
in  the  blood  takes  place. 

Practical  Exercise  6.  Explain  the  difference  between  breathing  and  respi- 
ration. 

Hygienic  habits  of  breathing.  Every  one  ought  to  accustom 
himself  to  inspire  slowly  and  deeply  in  the  open  air.  A slow 
expiration  should  follow.  Take  care  to  force  all  the  air  out. 
Breathe  through  the 
nose  to  warm  the  in- 
spired air  before  it 
enters  the  lungs.  Re- 
peat this  exercise 
several  times  every 
day.  This  will  prevent 
certain  of  the  air  sacs, 
otherwise  used  only  in- 
frequently, from  be- 
coming hardened  and 
permanently  closed. 

Deep  breathing  should 
become  a habit  with 
growing  girls  and 
boys.  It  can  best  be 
practiced  with  win- 
dows open,  after  rising 
in  the  morning  and 
just  before  retiring  at 
night. 

Common  diseases  of  the  nose  and  throat.  Catarrh  is  a dis- 
ease to  which  many  people  with  sensitive  mucous  membrane  of 
the  nose  and  throat  are  subject.  It  is  indicated  by  the  constant 
secretion  of  mucus  from  this  membrane.  Chronic  catarrh  should 
be  attended  to  by  a physician.  Often  we  find  children  breathing 
entirely  through  the  mouth  because  the  air  passages  in  the  nose 


Diagram  showing  the  capacity  of  the  lungs.  The  tidal  air 
is  that  taken  in  an  ordinary  breath.  Complemental  air  is 
that  taken  in  a very  long  breath.  In  a forced  expiration  we 
can  expel  from  75  to  100  cubic  inches  of  reserve  air.  What 
is  left  in  the  lungs  is  residual  air. 


408  FOODS  CIRCULATED  AND  USED  IN  THE  BODY 


are  closed.  If  this  condition  continues  for  any  length  of  time,  the 
nose  and  throat  should  be  examined  by  a physician  for  adenoids, 
growths  of  soft  masses  of  tissue  which  fill  up  the  nose  cavity  and 
prevent  normal  breathing.  Many  a child,  backward  at  school, 
thin  and  irritable,  has  been  changed  to  a healthy,  normal  child, 
by  the  removal  of  adenoids.  Sometimes  the  tonsils,  at  the  back 
of  the  mouth  cavity,  become  diseased  and  enlarged,  causing 
serious  throat  troubles  and  sometimes  acute  rheumatism  and 
heart  disease. 

Relation  to  health.  We  all  know  that  exercise  in  moderation 
has  a beneficial  effect  upon  the  human  organism.  Exercise, 
besides  training  the  muscles,  increases  the  activity  of  the  heart 
and  lungs,  causing  deeper  breathing  and  giving  the  heart  muscles 
increased  work ; it  liberates  heat  and  carbon  dioxide  from  the 
tissues  where  the  work  is  taking  place,  thus  increasing  the  respi- 
ration of  the  tissues  themselves,  and  aids  mechanically  in  the 
removal  of  wastes  from  tissues.  Exercise  is  of  immense  impor- 
tance to  the  nervous  system  as  a means  of  rest. 

Demonstration  5.  To  show  the  prone-pressure  method  of  artificial 
respiration. 

Place  the  person  face  downward  with  his  head  turned  to  the  side 
and  supported  on  his  arm.  Kneel  astride  him  at  the  bend  of  his 
knees  and  slowly  but  strongly  press  down  and  forward  with  the 
hands,  keeping  the  arms  straight,  immediately  over  the  lower  part  of 
the  chest  cavity.  Hold  this  pressure  for  about  three  seconds  and 
then  swing  the  weight  of  the  body  off  suddenly,  thus  allowing  the 
lungs  of  the  subject  to  fill  'with  air.  After  two  seconds  repeat  the 
pressure  as  before.  Count  the  seconds  as  you  perform  this  operation 
so  as  to  make  the  total  number  of  respiratory  movements  twelve 
to  the  minute. 

Why  time  these  movements  twelve  to  the  minute?  Why  press 
down  on  the  ribs  ? What  structures  play  a part  when  this  is  done  ? 

Suffocation  and  artificial  respiration.  Suffocation  results  when 
the  supply  of  oxygen  is  shut  off  from  the  lungs.  It  may  be  brought 
about  by  an  obstruction  in  the  windpipe,  by  a lack  of  oxygen  in 
the  air,  due  to  inhaling  some  other  gas  in  quantity,  by  drowning, 
or  from  a severe  electric  shock.  In  any  one  of  the  above  cases,  the 
person’s  life  may  be  saved  by  prompt  recourse  to  artificial  respira- 
tion. The  prone-pressure  method  is  considered  one  of  the  best. 


REST  METirODS  OF  VENTILATION 


409 


Do  not  give  up  work  if  the  patient  does  not  at  once  show  signs 
of  recovery.  Persons  who  have  been  under  water  for  some  time 
liave  been  resuscitated  after  four  to  five  hours’  work.  Prompt, 
regular,  and  continued  effort  is  the  thing  that  counts. 


Self-Testing  Exercise 

In  breathing  there  are  two  movements, (1)  and (2). 

In  the  first  movement  the (3)  are  pulled  up  and  outwards, 

and  the (4)  is  lowered,  thus  making  a larger  space  within  the 

chest  cavity  into  which (5)  may  pass (6)  is  a pas- 
sive movement,  the  air  being  forced  out  by  the  return  of  the (7) 

and (8)  to  their  former  positions.  We  inspire  about 

(9)  times  a minute.  About (10) (11)  inches  of  air  are 

taken  into  the  lungs  during  a “ long  ” breath.  To  perform  artificial 
respiration  by  the  prone-pressure  method  we  place  the  patient  face 

(12),  kneel  astride  him,  and  slowly  but  strongly  press 

(13)  and (14)  just  over  lower  part  of  the (15) 

(16)  at  a rate  of (17)  times  a minute.  Keep  this 

pressure  up  for (18)  seconds,  release  suddenly,  rest (19) 

seconds,  and  repeat. 


PROBLEM  VI.  WHAT  ARE  THE  REASONS  FOR,  AND  THE 
BEST  METHODS  OF  VENTILATION? 

Demonstration  6.  To  show  methods  of  ventilating  rooms. 

jMake  a grooved  box  8 X 10  inches  at  base,  8 inches  high,  with 
sliding  glass  door.  Place  on  side  and  have  4 half-inch  holes,  two  at 
top  and  two  at  bottom,  bored  in  each  end  and  fitted  with  corks. 
Place  three  candles  in  the  box.  Light  the  candles. 

With  all  the  corks  in  place,  how  long  (take  exact  time)  do  the  candles 
burn  ? 

Remove  the  upper  corks  from  both  ends.  How  long  do  the  candles 
burn? 

Remove  the  lower  corks.  How  long  do  the  candles  burn? 

Remove  the  upper  and  lower  cork  from  one  end.  How  long  do 
the  candles  burn?  Remove  the  upper  corks  from  one  end  and  the 
lower  ones  from  the  opposite  end.  How  long  do  the  candles  burn? 

Make  cross-section  sketches  and  explain  the  different  trials.  Use 
dotted  lines  and  arrows  to  represent  the  course  of  the  air. 

What  is  the  best  method  of  ventilating  a room?  Why  should  people 
sleep  with  windows  open?  Make  a diagram  to  show  how  to  ventilate 
a room.  How  would  you  ventilate  through  a window  without  making 
a draft?  Can  you  explain  the  school  system  of  ventilation? 


410  FOODS  CIRCULATED  AND  USED  IN  THE  BODY 

Need  of  ventilation.  We  have  all  experienced  a certain  dis- 
comfort in  a crowded  auditorium  or  schoolroom  after  a short  time. 
Some  people  think  that  this  discomfort  is  caused  by  lack  of  oxygen 
in  the  air  or  by  the  presence  of  too  much  carbon  dioxide.  But 
experiments  conducted  by  the  New  York  State  Ventilation  Com- 
mission and  in  many  laboratories  have  shown  that  this  discomfort 
comes  largely  from  two  sources,  the  rise  in  temperature  and  the 
increase  in  humidity  in  the  air.  The  source  of  this  heat  and 
moisture  is  largely  the  bodies  of  the  people  who  are  in  the  room. 

In  order  to  get  rid  of  excess  moisture,  reduce  the  heat,  and  remove 
the  other  products  of  respiration  from  the  air,  ventilation  is  necessary. 
Ventilation  is  defined  as  adequate  replacement  of  used  air  with 
fresh  air.  In  addition,  air  in  buildings  contains  dust,  with  its  load 
of  bacteria,  odors  of  various  kinds,  and  sometimes  poisonous  gases. 

Methods  of  ventilation.  In  many  of  our  schools  and  public 
buildings  we  still  go  on  the  assumption  that  from  1800  to  3000 
cubic  feet  of  air  are  needed  for  each  person  in  a room  and  that  there- 
fore air  should  be  changed  frequently  enough  to  give  this  quota. 
But  recent  research  shows  that  of  far  more  importance  is  air  con- 
ditioning. Modern  buildings  are  now  supplied  with  air  by  means 
of  air-conditioning  units.  This  air  is  washed  so  as  to  remove  dust 
and  bacteria ; then  it  is  supplied  with  the  proper  amount  of  mois- 
ture, more  than  we  get  in  a heated  room  in  winter  and  less  than  we 
get  in  humid  weather  in  summer.  A relative  humidity  of  about 
50  has  been  found  best  for  winter.  A temperature  of  about  68°  F. 
is  found  best  suited  to  mental  work,  so  the  temperature  is  kept  at 
this  level  by  means  of  thermostats. 

Unfortunately  in  many  school  systems  of  ventilation  it  is 
necessary  to  close  all  windows  in  order  to  have  the  fans  do  their 
work  properly.  In  such  systems  the  air  is  often  too  dry  and  warm. 
Consequently,  when  we  go  from  a warm,  dry  room  into  the  cool, 
outdoor  air,  the  skin  becomes  chilled  and  we  may  take  cold. 

A far  better  method  of  ventilation  is  the  open  window  with  a 
window  board  inserted  so  as  to  prevent  direct  air  currents. 

Practical  Exercise  7.  Make  a survey  of  the  temperature  conditions  in  your 
own  school.  Take  hourly  temperature  records  in  several  different  rooms. 
Make  the  report  cover  at  least  one  week. 


VENTILATION  OF  SLEEPING  KOOMS 


411 


Ventilation  of  sleeping  rooms.  Sleeping  in  badl}^  ventilated 
rooms  is  freciuently  the  cause  of  much  cliscomfort  and  often  of 
illness.  W'iiulows  should  be  open  top  and  bottom,  but  no  direct 
draft  should  l)e  allowed. 

This  ventilation  may 
often  be  managed  with 
the  use  of  screens. 

In  cities  especially, 
the  night  air  is  purer 
than  day  air,  because  the 
factories  have  stopped 
work,  the  dust  has 
settled,  and  fewer  people 
are  on  the  streets.  The 

old  myth  of  night  air  ^ is  this  a good  method  of  window  ventilation?  Why? 

being  injurious  has  long 

since  been  exploded,  and  thousands  of  people  of  delicate  health, 
especially  those  who  have  weak  throats  or  lungs,  are  regaining 
health  by  sleeping  out  of  doors  or  with  the  windows  wide  open. 
The  only  essential  in  sleeping  out  of  doors  is  that  the  body  be 
kept  warm  and  the  head  be  protected  from  strong  drafts. 

Self-Testing  Exercise 

Ventilation  is  the (1)  of (2)  air  with (3) 

air.  From (4)  to (5)  cubic  feet  of  air  are  needed  in 

a room  by  every  person  per  hour.  Sleeping  rooms  are  best  venti- 
lated by  opening  the  window  (6)  and  (7),  but  a 

(8)  should  be  avoided.  Ventilate  the  lungs  by (9) 

(10). 

PROBLEM  VII.  WHAT  ARE  THE  ORGANS  OF  EXCRETION 
AND  HOW  DO  THEY  FUNCTION? 

Laboratory  Exercise.  The  structure  of  the  kidney.  Some  idea  of 
the  internal  structure  of  the  kidney  of  man  may  be  gained  by  examina- 
tion of  a sheep’s  kidney.  Get  the  butcher  to  leave  the  mass  of  fat 
around  the  kidney.  What  is  the  use  of  this  fat?  Notice,  after  re- 
moving the  fat,  that  the  kidney  appears  to  be  closely  wrapped  in  a 
thin  coat  of  connective  tissue ; this  is  called  the  cafsule. 


412  FOODS  CIRCULATED  AND  USED  IN  THE  BODY 


Remove  the  kidney  from  this  capsule.  Notice  its  color  and  shape. 
The  depression  called  the  hilum  is  deeper  than  the  corresponding  region 
in  a kidney  bean.  The  hollow  tube  passing  out  from  this  region  is 
called  the  ureter.  Blood  vessels  also  enter  and  leave  the  kidney  at 
the  hilum. 

Cut  the  kidney  lengthwise  into  halves.  Try  to  find  the  following 
regions  : (1)  the  outer  or  cortical  region  (note  its  color) ; (2)  the  inner 
or  medullary  layer  (this  layer  is  provided  with  little  projections,  which 
are  the  pyramids  of  Malpighi,  so  called  after  their  discoverer,  Marcello 
Malpighi,  a celebrated  Italian  physiologist) ; (3)  the  cavity  or  pelvis 
of  the  kidney.  At  the  summit  of  each  pyramid  is  a small  opening 
through  which  escapes  into  the  pelvis  the  secretion  formed  in  the  little 


tubules,  which  make  up  the  pyra- 
mids, and  in  which  the  real  work 
of  excretion  is  performed. 

Where  is  the  waste  taken  from 
the  blood  in  the  kidney?  Where 
does  this  waste  pass  out  of  the 
body? 

Organs  of  excretion.  All  the 

life  processes  which  take  place 
in  a living  thing  result  ulti- 
mately, not  only  in  the  giving 
off  of  carbon  dioxide,  but  also 
in  the  formation  of  organic 
wastes  within  the  body.  The 
retention  of  the  wastes  which 
contain  nitrogen  is  harmful  to 
animals.  In  man,  the  skin  and 
kidneys  remove  these  wastes 
from  the  body,  hence  they  are 
called  the  organs  of  excretion. 

The  human  kidneys,  like 
those  of  the  sheep,  are  com- 
posed of  masses  of  excretory 
tubules.  The  outer  end  of 


The  organs  of  excretion.  Note  the  blood  supply  of  these  tubuleS  ultimately 

to  the  kidneys.  Of  what  use  is  the  bladder  ? 

opens  into  the  pelvis,  the  space 
within  the  kidney;  the  inner  end  forms  a tiny  closed  sac.  In 
each  sac,  the  outer  wall  of  the  tube  has  grown  inward  and  carried 
with  it  a very  tiny  artery.  This  artery  breaks  up  into  a mass  of 


WASTES  GIVEN  OFF  BY  THE  liLOOD 


413 


artery  veitx. 


capillaries,  which,  in  turn,  unite  to  form  a small  vein  as  they 
leave  the  little  sac.  Each  of  these  sacs  contains  a number  of 
blood  vessels,  the  glomcndus 
(gib  nier  'do  lus). 

Wastes  given  off  by  the 
blood  in  the  kidney.  In  the 
glomeruli  the  blood  loses  by 
osmosis,  through  the  very  thin 
walls  of  the  capillaries,  first,  a 
considerable  amount  of  water 
(amounting  to  nearly  three 
pints  daily) ; second,  a nitrog- 
enous waste  material  known 
as  urea;  third,  salts  and  other 
waste  organic  substances. 

These  waste  products  pass 

. , , . r J.U  1 ’J  Each  kidney  is  composed  of  a large  number 

into  the  pelvis  Ot  the  kidney  of  long  tubules.  The  blood  flows  through  the 
nnd  thmno-h  rlnpt<?  nrpfprcj  glomeruli  (mass  of  blood  capillaries)  and  then 
ana  tmougn  aucis,  ureiers,  through  the  capillaries  surrounding  the  tubules. 

into  the  bladder.  wastes  from  the  blood  pass  through  the  walls 

’ of  the  blood-vessels  (glomeruli)  into  the  tubules, 

The  waste  products  from  which  lead  to  the  bladder, 
the  kidney,  together  with  the 

water  containing  them,  are  known  as  urine.  Urine  normally  con- 
sists of  about  96  per  cent  water  and  4 per  cent  dissolved  solids. 
The  total  amount  of  nitrogenous  waste  leaving  the  body  each  day, 
by  means  of  the  kidneys,  is  about  twenty  grams.  After  the  blood 
has  gone  through  the  glomeruli  of  the  kidneys  it  is  purer  than  in 
any  other  place  in  the  body,  because  it  has  lost  much  of  its  nitrog- 
enous waste  in  them  and  before  going  to  them  it  gave  up  a large 
part  of  its  carbon  dioxide  in  the  lungs.  So  dependent  is  the  body 
upon  the  excretion  of  its  poisonous  material  that  in  cases  where 
the  kidneys  do  not  do  their  work  properly,  death  may  ensue 
within  a few  hours.  Since  the  blood  which  passes  through  the 
kidneys  is  being  continually  depleted  of  water,  one  should  drink 
plenty  of  water  to  make  good  this  loss. 

Diet  plays  a very  important  part  in  the  care  of  the  kidneys.  If 
we  overbalance  our  diet  with  too  much  protein  food,  we  throw 
increased  work  on  these  organs.  The  nitrogen  in  proteins  cannot 


414  FOODS  CIRCULATED  AND  USED  IN  THE  BODY 


be  oxidized,  so,  combined  with  other  elements  into  urea  and 
other  wastes,  it  is  eliminated  through  the  kidneys. 


Laboratory  Exercise.  To  study  the  skin  as  an  organ  of  excretion 
and  of  heat  control.  Examine  the  diagram  of  a cross  section  of  skin. 
Locate  the  epidermis,  dermis,  sweat  glands,  oil  glands,  nerves,  and 
blood  vessels. 

Examine  the  surface  of  your  skin  with  a hand  lens.  Where  is  the 
epidermis  and  what  structures  does  it  contain?  What  structures 
are  found  in  the  dermis? 

Insert  your  hand  in  a clean,  dry  fruit  jar.  Wrap  a towel  over  the 
opening  of  the  jar  so  as  to  allow  no  air  to  get  in  between  your  hand 
and  the  sides  of  the  jar.  What  happens  in  the  jar?  What  is  given 
off  from  the  hand  ? 

Weigh  yourself.  Note  the  weight.  Exercise  violently  for  half  an 
hour.  Weigh  yourself  again.  Note  the  weight.  Was  there  any 
change  in  weight?  How  must  the  change  of  weight  have  been 
brought  about  ? Remember  that  when  oxidation  of  food  or  tissue  takes 

place  in  the  body,  three  prod- 
— .TTZouth,  c|  gland  nets,  at  least,  are  formed: 

heat,  nitrogenous  wastes,  and 
water. 

(Food  + oxygen  = carhon 
dioxide  + water  + organic 
wastes  + heat  + muscular 
energy.) 

Take  the  temperature  of 
the  body  before  and  after 
exercise  by  placing  a clinical 
thermometer  in  the  mouth. 
Account  for  any  change  in 
temperature. 

What  three  substances  are 
given  off  from  human  bodies 
that  might  affect  the  air  of 
a closed  room  ? Are  you 
more  comfortable  on  a hot 
humid  day  or  on  a hot  dry 
day?  Explain. 


The  skin  as  an  organ  of 
excretion.  We  have  already 


A sweat  gland.  Explain,  with  reference  to  the  text, 
where  the  water  that  is  given  off  comes  from.  The 
waste  materials. 


learned  that  the  skin  is  an 
organ  of  protection.  Let 
us  now  see  how  it  aids  in 


excretion.  The  glands  already  studied  form  the  excretion  known 
as  perspiration,  a watery  solution  containing  little  carbon  dioxide, 


COLDS  AND  FEVEKS 


415 


urea,  and  some  salts  (common  salt  among  others).  The  com- 
bined secretions  from  these  glands  amount  normally  to  a little 
over  a pint  during  twenty-four  hours.  At  all  times  a small  amount 
of  i)erspiration  is  given  off,  but  this  is  evaporated  or  is  absorbed 
1)3'  tlic  underwear.  Since  this  passes  off  unnoticed,  it  is  called 
insensible  perspiration. 

Regulation  of  the  heat  of  the  body.  The  body  temperature  of 
a person  engaged  in  manual  labor  will  be  found  to  be  but  little 
higher  than  the  temperature  of  the  same  person  at  rest.  The 
muscles,  equal  to  nearly  one  half  the  weight  of  the  body,  release 
about  five  sixths  of  their  energy  as  heat.  At  all  times  they  are 
giving  up  some  heat.  The  temperature  of  the  body  is  largely 
regulated  b}'  the  activity  of  the  sweat  glands.  The  blood  carries 
much  of  the  heat,  liberated  in  the  various  parts  of  the  body  by  the 
oxidation  of  food,  to  the  surface  of  the  body,  where  it  is  lost  in 
the  evaporation  of  sweat.  In  hot  weather  the  blood  vessels  of 
the  skin  are  dilated  ; in  cold  weather  they  are  made  smaller  by  the 
action  of  the  nervous  system.  The  blood  thus  loses  water  in 
the  skin,  and  as  the  water  evaporates,  we  are  cooled  off.  The 
object  of  increased  perspiration,  then,  is  to  remove  heat  from  the 
bod}'.  With  a large  amount  of  blood  present  in  the  skin,  per- 
spiration is  increased ; with  a small  amount,  it  is  diminished. 
Hence,  we  have  in  the  skin  an  automatic  regulator  of  body  tem- 
perature. 

Practical  Exercise  8.  Why  is  the  amount  of  perspiration  noticeably  in- 
creased m hot  weather  and  after  doing  hard  work? 

j Colds  and  fevers.  The  regulation  of  blood  passing  through 
i the  blood  vessels  is  under  control  of  the  nervous  system.  If  this 
mechanism  is  interfered  with  in  any  way,  as  for  example  through 
bacterial  toxins  released  in  the  body,  the  sweat  glands  may  not 
do  their  work,  perspiration  may  be  stopped,  and  the  heat  from 
[oxidation  held  within  the  body.  The  body  temperature  goes  up, 
and  a fever  results. 

If  the  blood  vessels  in  the  skin  are  suddenly  cooled  when  full  of 
blood,  they  contract  and  send  the  blood  elsewhere.  As  a result  an 
' increase  of  blood  in  the  internal  organs  or  a congestion  may  follow. 


416  FOODS  CIRCULATED  AND  USED  IN  THE  BODY 


Colds  are,  in  reality,  a congestion  of  membranes  lining  certain 
parts  of  the  body,  as  the  nose,  throat,  windpipe,  or  lungs,  together 


Explain  this  diagram.  What  has  happened  in 
the  lower  figure  ? 


portant  also  are  rest  in  bed,  fresh 
and  free  bowel  movements. 


with  a growth  of  bacteria 
which  were  present  in  the 
mouth  or  throat.  Some  colds 
are  communicable  and  gain 
entrance  to  the  body  when 
the  resistance  is  low. 

When  suffering  from  a cold, 
it  is  therefore  important  not 
to  chill  the  skin,  as  a full 
blood  supply  should  be  kept 
in  it  and  thus  kept  from  the 
seat  of  the  congestion.  For 
this  reason  hot  baths  (which 
bring  the  blood  to  the  skin), 
the  avoiding  of  drafts  (which 
chill  the  skin),  and  warm 
clothing  are  useful  factors  in 
the  care  of  colds.  Very  im- 
air,  plenty  of  water  to  drink. 


Practical  Exercise  9.  What  is  a congestion  and  how  is  it  caused  ? How  do 
we  “ take  cold  ” ? Is  there  more  than  one  kind  of  cold? 


Self-Testing  Exercise 

Body  temperature  is  regulated  by  action  of  nerves  in  the (1). 

They  either  cause  the  small  blood  vessels  to (2)  or (3), 

thus  placing  more  or  less (4)  at  the (5)  of  the  body 

where  the (6)  heat  may  be  (7)  by  perspiration.  The 

kidneys  are  organs  of (8) (9)  waste  is  passed  out 

as (10).  An  oversupply  of (11)  food  may  make  too 

much  work  for  the  kidneys. 

Review  Summary 

Test  your  knowledge  of  the  unit  by:  (1)  rechecking  the  summary  ques- 
tions; (2)  performing  all  the  assigned  exercises;  (3)  checking  with  the  teacher 
on  all  tests  and  trying  over  the  parts  you  missed ; (4)  and  finally  making  an 
outline  of  the  unit  for  your  notebook. 


TESTS 


417 


Test  of  Fundamental  Concepts 

In  a vertical  column  under  the  heading  CORRECT  write  numbers  of  all  statements  you  believe 
are  true.  In  another  column  under  INCORRECT  write  numbers  of  untrue  statements.  Your 
grade  = right  answers  X -. 

I.  The  blood  contains  (1)  fluid  food  in  its  plasma;  (2)  red  and 
colorless  corpuscles ; (3)  haemoglobin  in  its  white  corpuscles ; (4)  en- 
zymes and  hormones;  (5)  a substance  called  fibrinogen,  which  acts  in 
causing  the  blood  to  clot. 

II.  Blood  is  necessary  for  the  body  because  (6)  it  acts  as  a medium 
of  exchange  between  the  body  cells  and  the  source  of  their  food  supply ; 
(7)  it  contains  regulative  substances  called  vitamins;  (8)  it  acts  as  a 
carrier  for  the  chemical  activators  called  hormones;  (9)  only  through 
the  blood  is  oxygen  carried  to  the  cells  and  carbon  dioxide  carried 
away;  (10)  it  carries  waste  materials  away  from  the  cells. 

III.  Antibodies  (11)  help  to  make  us  immune  to  diseases  caused 
by  bacteria;  (12)  called  lysins  can  dissolve  bacteria;  (13)  called 
agglutinins  cause  bacteria  to  stick  together;  (14)  are  specific  and 
fight  specific  toxins ; (15)  are  made  use  of  in  the  Widal  Test. 

IV.  The  endocrine  glands  (16)  are  the  salivary,  gastric,  and 
intestinal;  (17)  are  those  glands  which  have  no  ducts;  (18)  include 
the  thyroid,  parathyroid,  thymus,  adrenal,  the  pituitary,  and  parts  of 
the  pancreas,  the  ovaries,  and  testes;  (19)  such  as  the  adrenals  may 
increase  body  activity ; (20)  such  as  the  pituitary  probably  control 
growth  in  the  body. 

V.  The  blood  circulates  (21)  because  it  is  alive;  (22)  because  the 
heart  acts  as  a force  pump ; (23)  because  arteries  and  veins  are  con- 
nected by  capillaries  ; (24)  through  the  body  cells ; (25)  to  all  the  cells 
in  the  body. 

VI.  The  lungs  (26)  are  the  chief  organs  of  excretion  in  the  human 

body ; (27)  are  organs  for  the  exchange  of  oxygen  and  carbon  dioxide ; 
(28)  are  masses  of  tiny  air  sacs,  which  are  thin  walled  and  covered  with 
capillaries ; (29)  are  made  larger  or  smaller  during  the  process  of 

breathing ; (30)  take  in  oxygen  and  give  off  water,  carbon  dioxide, 
some  organic  wastes,  and  heat. 

VII.  Respiration  (31)  is  a process  by  which  oxygen  reaches  the 
^ body  cells  and  carbon  dioxide  is  removed  from  them ; (32)  is  the 
I same  as  expiration  and  inspiration ; (33)  takes  place  in  body  cells ; 

! (34)  and  breathing  mean  the  same  thing;  (35)  is  raising  and  lower- 
, ing  the  ribs  and  diaphragm. 


418  FOODS  CIRCULATED  AND  USED  IN  THE  BODY 


VIII.  Ventilation  (36)  is  necessary  in  order  to  raise  the  temperature 
of  a room;  (37)  removes  carbon  dioxide  and  renews  oxygen;  (38)  is 
necessary  because  moving  air  helps  to  keep  a room  more  comfortable ; 
(39)  removes  moisture,  heat,  carbon  dioxide,  and  other  products  of 
respiration  and  renews  the  supply  of  oxygen;  (40)  is  best  brought 
about  in  sleeping  rooms  by  having  the  windows  open  top  and  bottom, 

IX.  Body  wastes  are  removed  (41)  from  the  cells  by  the  blood 
which  carries  the  nitrogenous  wastes  to  the  kidneys ; (42)  from  the  kid- 
neys in  the  form  of  urea;  (43)  in  a gaseous  state;  (44)  from  the  body 
by  the  kidneys ; (45)  best  by  taking  cathartics. 

X.  The  skin  (46)  regulates  body  heat ; (47)  furnishes  protection 
against  germs ; (48)  is  an  organ  of  excretion ; (49)  contains  millions 
of  sweat  glands  under  nervous  control ; (50)  should  be  kept  warm  if 
one  has  a cold,  for  this  keeps  blood  from  the  internal  organs  and  thus 
prevents  congestion. 


Achievement  Test 

1.  What  do  blood  corpuscles  look  like  under  the  compound  micro- 
scope? 

2.  How  would  you  demonstrate  the  capillary  circulation  in  the  web 
of  the  frog’s  foot? 

3.  How  would  you  make  a tourniquet  and  what  would  you  do 
in  case  of  an  accident  where  loss  of  blood  occurs  ? 

4.  Why  is  blood  transfusion  not  possible  between  some  people  and 
possible  between  others  ? 

5.  What  are  the  endocrine  glands  and  what  is  the  function  of 
each? 

6.  How  could  you  make  a diagram  of  circulation  of  blood  in  your 
own  body? 

7.  How  can  you  prove  that  you  oxidize  materials  (food  or  tissues) 
in  your  own  body? 

8.  How  can  you  demonstrate  the  prone-pressure  method  of  arti- 
ficial respiration? 

9.  How  can  you  demonstrate  the  best  method  of  ventilating  a 
room  and  show  why  it  is  the  best  method?  Do  you  practice  this  in 
your  sleeping  room? 

10.  How  could  you  demonstrate  the  changes  that  take  place  in 
air  in  your  lungs  ? 


USEFUL  REFER EX(T.S 


419 


Practical  Problems 
1.  Fill  out  the  followin'’;  table: 

WASTES  OF  THE  HUMAN  BODY 


W.\.STE 

WUEKE  FoK.MKD 

llow  E.xcheted 

Organs  Used  in 
Process 

2.  Fill  out  the  table  below  as  completely  as  you  can : 


Part  ok  Blood 

Substance  oh  Structure 

Functions 

Useful  References 

I^roaxlhurst,  How  ]Ve  Resist  Disease.  Chaj^ters  V-VII,  inc.  Lippincott, 
1923. 

Fisher  and  Fisk,  How  to  Live.  Chapter  IV.  Funk  & Wagnalls,  1925. 
Harrow,  Glands  in  Health  and  Disease.  Dutton,  1928. 

Hunter  and  Whitman,  Science  in  Our  Social  Life.  American  Book,  1935. 
Kimber  and  Gray,  Textbook  of  Anatomy  and  Physiology.  Pp.  184-298, 
Macmillan,  1926. 

iNew'  York  Commission  on  Ventilation.  School  Ventilation.  Bureau  of 
Publications,  Teachers  College,  Columbia  University,  1931. 

Winslow,  C.  E.,  Fresh  Air  and  Ventilation.  Dutton,  1926. 


SURVEY  QUESTIONS 
What  do  we  mean  by  the  term  behavior  ? By  what  things  or  forces  may 
plants  and  animals  be  affected  ? What  are  your  sense  organs  ? What  are 
the  parts  of  your  nervous  system  ? What  is  an  instinctive  act  ? What  is 
a habit?  How  and  why  can  man  control  things  in  his  environment? 

^ - 1 

Wide  World  Photo  j 


UNIT  XIV  j 

HOW  HAS  MAN  BECOME  THE  CONQUEROR  OF  THE  | 
WORLD?  i 

r 

Preview.  We  have  seen  many  instances  in  which  plants  and  ' 
animals  respond  to  stimuli.  In  our  study  of  plants  we  found 
examples  of  responses  to  light,  gravity,  and  moisture.  These 
simple  responses  are  called  tropisms.  But  if  we  are  asked  to 
explain  why  these  responses  took  place,  we  can  only  say  that 
protoplasm  exhibits  the  power  of  irritability  by  means  of  which 
the  organism  is  preserved  from  injuries  and  can  obtain  from  its 
environment  the  materials  needed  to  carry  on  its  life  processes. 

The  reactions  of  a dog  to  the  sound  of  his  master’s  voice  or  to  , 
the  odor  of  a piece  of  meat  seem  to  be  quite  a different  matter  ' 

420  f 

1 


PREVIEW 


421 


from  these  simple  responses.  However,  biologists  and  psychol- 
ogists agree  that  it  is  only  carrying  a little  further  this  matter  of 
response  to  a stimuli.  It  is  held  by  some  people  that  most  of 
our  everyday  actions,  of  which  we  do  not  think,  are  due  to  reac- 
tions to  certain  stimuli.  Most  of  the  acts  which  we  perform 
during  a day’s  work  are  the  results  of  the  automatic  working  of 
various  parts  of  our  body.  The  heart  pumps  the  blood  which 
circulates  its  loatl  of  food,  oxygen,  and  wastes ; the  movements 
of  breathing  are  performed ; the  kidneys  and  skin  discharge  the 
wastes  from  the  body;  and  the  nerves  carry  messages  to  and 
from  the  brain.  These  many  complicated  acts  go  on  every  day 
within  the  body  and  are  seemingly  undirected,  but  they  are  in 
reality  under  the  control  of  the  autonomic  nervous  system. 

On  the  other  hand,  the  body  may  also  be  influenced  by  what 
goes  on  around  it.  Our  entire  day  at  school  may  be  colored  by 
what  happened  at  the  breakfast  table.  Or  suppose  we  oversleep, 
eat  our  breakfast  hastily,  run  to  school,  reaching  there  a few 
minutes  late,  and  therefore  are  marked  tardy.  This  sequence 
of  events  will  influence  our  entire  day.  The  digestive  glands 
in  the  stomach  have  not  been  properly  stimulated,  due  to  our 
hastily  eaten  breakfast.  Certain  internal  secretions  of  the  glands, 
poured  into  the  blood  when  we  ran  to  school  and  when  we  were 
declared  late,  might  arouse  our  emotions,  and  cause  us  to  do  and 
sa}^  many  things  for  which  we  would  probably  be  sorry  later. 
All  of  the  actions  were  really  initiated  through  changes  in  our 
environment.  The  fact  that  we  overslept  made  breakfast  later, 
our  hurry  made  school  seem  further  away,  the  closed  door  gave 
us  a decided  jolt  and  changed  the  smooth  running  of  our  nervous 
machine.  So  conditions  do  modify  our  life  activities. 

Most  of  our  activities  are  habits ; that  is,  we  have  learned  to 
do  them  so  well  that  we  can  now  do  them  without  thinking. 
Habits  may  be  broken,  but  to  do  this  we  must  become  conscious 
of  them,  and  earnestly  try  to  break  them.  Either  we  shall  become 
slaves  to  habits  or  habits  will  serve  us.  That  is  the  thing  that 
every  person  should  realize  while  still  in  high  school.  Later,  good 
habits  cannot  be  acquired  or  bad  habits  cannot  be  broken  so  easily 
and  one  will  eventually  become  conquered  by  his  habits- 

H.  BIO  — 28 


422  MAN  BECOMES  THE  CONQUEROR  OF  THE  WORLD 


PROBLEM  I.  WHAT  ARE  THE  CHIEF  RESPONSES  OF 
PLANTS  AND  ANIMALS? 

Demonstration  1.  To  show  some  tropisms  in  plants  and  animals. 

Grow  some  bean  seedlings  in  a glass  dish  which  is  kept  watered  at 
one  side  only.  Grow  some  bean  seedlings  in  unequal  illumination. 
Examine  oxalis  or  clover  at  night  and  in  the  morning,  in  order  to  ob- 
serve “ sleep  ” movements  of  leaves.  Touch  a leaf  of  a sensitive  plant 
with  a pencil. 

Place  Euglena  in  a vessel  with  unequal  light  illumination. 

In  the  first  two  cases,  note  the  arrangement  of  roots  against  the 
glass  side  of  the  dish.  What  leaf  movements  of  oxalis  and  sensitive 
plant  are  noticeable?  Where  in  the  vessel  do  you  find  Euglena  most 
abundant? 

What  forces  act  upon  plants  and  animals?  How  do  they  affect 


them? 


How  plants  and  animals  receive  stimuli.  In  the  simplest 
plant  and  animal  cells  which  live  by  themselves  there  are  no 


specialized  parts  which  are  es- 
pecially fitted  to  receive  out- 
side stimuli.  The  amoeba,  for 
example,  is  influenced  by 
temperature,  food,  and  other 
stimuli,  but  it  has  no  sense 
organs.  Some  tiny  plant-like 
animals  (or  animal-like  plants) 
such  as  Euglena  (u-gle'nd)  have 
a tiny  structure  called  an  eye- 
spot,  which  seems  to  be  more 
sensitive  to  light  than  other 
parts  of  the  cell. 


The  more  complex  single- 
celled  animals,  as  Paramecia, 
have  parts  of  the  cell  (cilia) 
more  sensitive  to  touch  than 
other  parts.  Animals  and,  to 
a lesser  degree,  plants,  as  they 
become  more  complex  in  struc- 


Euglena.  Would  you  call  it  a plant  or  an  ani- 
mal ? Give  your  reasons. 


ture,  tend  to  have  special  parts  set  aside  to  receive  stimuli.  These 
special  parts  of  complex  animals  are  called  sense  organs. 


KESPOKSES  OF  THE  PLANT 


423 


Responses  of  plants  and  animals.  The  responses  which  plants 
and  animals  make  to  cerlain  definite  stimuli  are  called  tropisms. 
Such  responses  may  be  either  positive  or  negative,  and  appear 
to  be  mechanical  behaviors.  They  may  be  listed  as  follows : 
Phototropism  or  response  to  light 
Geotropism  or  response  to  gravity 
Hydrotropism  or  response  to  water 
Thigmotropism  or  response  to  contact 
Cliemotropism  or  response  to  chemical  substances 
Thermotropism  or  response  to  temperature  changes 
Galvanotropism  or  response  to  electricity 
Animals  I I^^^^^^^opism  or  response  to  water  currents 
I Anemotropism  or  response  to  air  currents 
The  response  of  roots  to  gravity,  the  growth  of  stems  toward  the 
source  of  light,  the  opening  of  some  flowers  in  the  daytime  and 
others  only  at  night,  the  climbing  of  plants  by  means  of  tendrils  or 
other  organs  stimulated  by  touch,  are  a few  of  the  many  examples 
which  might  be  mentioned. 

Practical  Exercise  1.  Make  a list  of  all  tropisms  that  you  have  ever  seen 
plants  or  animals  exhibit. 

Some  parts  of  the  plant  are  more  sensitive.  White  a plant 
as  a whole  is  sensitive  to  stimuli  of  different  kinds,  it  is  certain  that 
some  parts  are  more  sensitive  than  others.  For  example,  experi- 
ments show  that  in  the  root  an  area  of  not  more  than  one  milli- 
meter in  length  is  most  sensitive  to  gravity,  as  the  turning  response 
takes  place  there.  Some  tips  of  stems  show  a similar  sensitive- 
ness, and  so  do  certain  parts  of  growing  leaves. 


Plants 
and  ^ 
Animals  | 


Self-Testing  Exercise 


Check  in  your  workbook  the  correct  statements : 


T.  F. 
T.  F. 
T.  F. 
T.  F. 
stances. 
T.  F. 


1.  The  tip  of  the  root  responds  most  readily  to  gravity. 

2.  Euglena  has  an  eyespot  which  is  sensitive  to  light. 

3.  Geotropism  is  response  to  the  stimulus  of  gravity. 

4.  Phototropism  is  response  to  the  stimulus  of  chemical  sub- 

5.  Rheotropism  is  response  to  water  current. 


424  MAN  BECOMES  THE  CONQUEROR  OF  THE  WORLD 


T.  F.  6.  The  amoeba  has  no  special  organs  of  sense. 

T.  F.  7.  If  touched,  the  leaves  of  sensitive  plants  show  thermo- 
tropism. 

T.  F.  8.  The  responses  of  simple  animals  to  stimuli  are  always 
positive. 


PROBLEM  n.  HOW  DO  SIMPLE  PLANTS  AND  ANIMALS 
RESPOND  TO  STIMULI? 

Demonstration  2.  To  show  the  use  of  the  pulvinus  to  a plant. 

Study  a stained  longitudinal  section  of  a bean  stem  to  show  the 
pulvinus.^  What  might  be  the  use  of  it?  How  is  it  able  to  do  that? 

The  mechanism  of  responses  in  plants.  Some  of  the  results 
of  responses  are  easily  seen  in  plants,  but  the  method  by  which 
the  responses  are  brought  about  is  not  so  easy  to  see.  For  example, 
we  say  leaves  place  themselves  so  as  to  get  as  much  light  as  possible. 

But  this  movement  is  different 
from  that  found  in  animals 
which  have  an  internal  skele- 
ton with  muscles  attached. 
The  changes  in  position  in 
parts  of  plants  are  often  pro- 
duced by  a more  rapid  growth 
of  the  cells  on  one  side  of  a 
structure  than  on  the  other, 
this  growth  having  been  ex- 
cited by  an  external  stimulus, 
such  as  gravity,  water,  light, 
(2)  In  the  or  heat.  Such  are  the  curving 
movements  of  roots  or  stems. 
The  turning  of  the  leaves  in  a horizontal  position  is  brought  about 
by  the  more  rapid  growth  of  tissues  on  one  side  of  the  leaf  stalk 
than  the  other. 

Changes  in  the  position  of  leaves  are  often  brought  about  by 
special  structures  at  the  base  of  the  petiole,  as  may  be  seen  in  the 
bean  plant.  These  structures,  called  pulvini  ^ (sing,  pulvinus), 

1 Pulvinus  (pul-vi'niis) : cushionlike  enlargement  of  petiole  at  its  point  of  inser- 
tion on  the  stem. 


Clover  leaf.  (1)  In  the  morning. 

evening.  Explain  the  difference. 


HESPOXSES  OF  THE  SIMPLEST  ANIMALS 


425 


contain  thin-walled  cells  filled  with  water,  and  the  position  of  the 
leaf  probably  depends  on  the  relative  ainount  of  water  in  these 
cells.  The  more  rapid  movements  of  the  opening  and  closing  of 
flower  petals  ; the  changes  in  position  of  leaflets  of  the  pea,  clover, 
alfalfa,  oxalis,  and 
other  plants  at  night 
and  in  the  morning ; 
and  the  relatively 
rapid  response  of  the 
leaves  of  the  sensitive 
plant  to  outside  stimuli 
are  all  explained  by 
changes  in  the  water 
content  of  the  cells  in 
the  pulvini,  or  by  rapid 
and  temporary  fluc- 
tuations in  growth  on 

opposite  sides  of  the  What  is  the  pulvinus?  What  use  is  it  to  a leaf? 

leaves,  or  by  a combination  of  both.  But  other  than  external 
stimuli  may  influence  and  modify  the  growth  and  actions  of  plants. 
We  know  that  enzymes  play  an  important  part  in  the  storage  of 
food  in  fruits  and  seeds,  and  there  seem  to  be  evidences  of  vitamin 
and  hormone  action  as  well.  It  is  probable  that  the  protoplasm 
of  a plant  is  under  much  the  same  control  as  is  the  protoplasm  of 
an  animal. 

Demonstration  3.  To  show  responses  of  Paramecium. 

Place  a drop  of  Paramecia  culture  in  a grooved  slide.  At  intervals, 
heat  the  water  at  one  end  of  the  slide  by  introducing  a hot  needle  into 
it.  Note  the  actions  of  the  Paramecium  as  the  water  becomes  warmer. 
Single  out  one  Paramecium  and  make  a diagram  showing  exactly  how 
it  gets  away  from  the  heated  area.  This  reaction  is  known  as  the 
“ avoiding  reaction.”  How  does  a Paramecium  escape  from  an 
unfavorable  environment? 

Responses  of  the  simplest  animals.  We  have  already  seen 
that  amoebas  and  Paramecia  seem  to  respond  to  the  presence  of 
food.  Examination  of  a drop  of  hay  infusion  containing  Para- 
mecia will  show  many  collected  around  masses  of  food,  indicating 


426  MAN  BECOMES  THE  CONQUEROR  OF  THE  WORLD 

that  they  are  attracted  by  it.  In  another  part  of  the  slide  we  may 
find  a number  of  the  Paramecia  lying  close  to  the  edge  of  an  air 
bubble,  with  the  greatest  possible  amount  of  their  surface  exposed 
to  its  surface.  These  animals  are  evidently  taking  in  oxygen  by 
diffusion.  They  are  breathing.  A careful  inspection  of  the  jar 
containing  Paramecia  shows  thousands  of  tiny  whitish  bodies 
collected  near  the  surface  of  the  jar.  Some  force  or  forces  keep 
them  close  to  the  surface.  Professor  Jennings  and  others  have 
made  careful  studies  of  the  reactions  of 
Paramecia  and  other  one-celled  animals 
to  various  stimuli,  and  have  found  that 
in  general  they  react  positively  toward 
favorable  and  negatively  toward  un- 
favorable conditions  in  their  environ- 
ment. For  example,  if  a slide  contain- 
ing Paramecia  is  heated  at  one  side, 
the  animals  will  back  off  from  the  un- 
favorable stimulus,  then  shoot  forward 
until  they  encounter  the  heat,  then 
again  back  off  and  repeat  the  opera- 
tion until  they  escape  from  the  heated 
area. 

This  method  of  escape  from  the  un- 
favorable environment  is  called  the 
method  of  trial  and  error.  It  is  an  ex- 
ample of  the  way  in  which  some  of  the 
lower  organisms  react  to  the  unfavor- 
able conditions  of  their  environment. 
If  by  such  methods  they  do  not  es- 

Trial  and  error  method  of  a Para-  , n , -i.,.  ,i 

mecium.  Explain  what  has  hap-  capo  from  harmful  couditious,  they 
pened,  using  the  figures  as  guides.  p0nsh 

Different  intensities  of  light,  different  kinds  of  light,  the  passage 
of  a current  of  electricity  through  the  water,  different  chemical 
substances  placed  in  the  water,  as  well  as  many  other  factors,  cause 
very  definite  responses  on  the  part  of  these  one-celled  organisms. 
The  responses  in  general  save  the  organism  from  harm,  or  help 
it,  and  thus  may  be  said  to  be  adaptive  responses. 


SENSE  ORGANS  AND  WIIAT  THEY  DO 


427 


Self-Testing  Exercise 

Changes  in  the  (1)  of  leaves  are  brought  about  by  a 

structure  called  the (2).  Faramecia  react (3)  to 

a favorable  environment  and  (4)  to  an  unfavorable  one. 

Faramecia  can  be  observed  to (5)  to  the  presence  of 

(6),  (7)  and  (8).  If  Faramecia  cannot  escape 

from (9)  conditions,  they  die.  Flants  change  their  positions 

in (10)  to  such  stimuli  as (11), (12), 

(13),  and (14). 


PROBLEM  III.  WHAT  ARE  SENSE  ORGANS  AND  WHAT  DO 
THEY  DO? 

Demonstration  4.  To  show  types  of  sensory  structure  in  certain 
animals. 

Materials.  Insects  with  different  types  of  antennae.  Crustaceans 
with  antennae  and  antennules.  Grasshoppers,  with  wings  removed  to 
show  tympanic  membrane.  Model  of  vertebrate  eye  and  ear.  Living 
crickets,  earthworms,  crayfish,  and  living  goldfish.  Food,  such  as 
apple  or  meat.  Weak  acetic  acid. 

Method.  Arrange  preserved  specimens  and  models  so  that  they 
may  be  passed  around  in  class  or  observed  on  the  demonstration  table. 
Living  material  should  be  placed  in  pans  or  aquariums  where  they 
can  be  fed,  and  stimulated  with  weak  acid. 

Note  the  hairs  projecting  from  the  antennae  and  antennules  of  the 
insects  and  crustaceans.  They  are  sensory  in  nature.  Note  in  the 
grasshopper  the  sensory  organ,  which  receives  sound.  Study  the 
model  of  the  human  ear.  Does  our  ear  do  more  than  receive  sound? 
Study  the  model  of  the  human  eye.  Compare  it  with  a camera. 

Observe  carefully  what  happens  when  food,  such  as  a bit  of  apple, 
is  placed  in  a dish  containing  live  crickets  or  earthworms.  Note  also 
what  happens  when  crayfish  or  goldfish  are  fed  meat.  How  do  they 
become  aware  of  the  presence  of  food? 

Flace  some  cotton  soaked  in  weak  acid  close  to  anterior  end  , of  an 
insect,  a worm,  and  a crayfish.  What  happens? 

How  do  animals  become  aware  of  food  or  harmful  substances? 

Sense  organs  and  what  they  do.  Most  plants  do  not  react 
quickly  to  stimuli,  because  they  have  no  special  sense  organs. 
Nor  have  the  one-celled  animals  any  special  part  of  the  cell  fitted 
to  receive  stimuli.  But  in  animals  composed  of  numerous  cells, 
division  of  labor  soon  appears,  and  we  have  organs  fitted  to  receive 
light  stimuli  (eyes),  touch  stimuli  (tactile  hairs,  etc.),  and  sound 


428  MAN  BECOMES  THE  CONQUEROR  OF  THE  WORLD 


stimuli  (sensory  hairs,  tympana  of  insects,  and  the  ears  of  higher 
animals).  These  end  organs  or  structures  at  the  outside  of  the 
animal,  when  connected  by  nerves  to  organs  of  movement,  like 
muscles,  bring  about  reactions  to  stimuli  which  result  in  obtaining 

food,  in  escaping  from  ene- 
mies, and  in  many  other  im- 
portant functions. 

Some  examples  of  sense 
organs.  One  of  the  simplest 
sense  organs  is  a sensory  hair 
which  contains  nerve  cells. 
These  cells  have  become 
modified,  so  that  when  they 
are  stimulated  they  send  a 
message  inward  to  another 
kind  of  nerve  cell  in  the  cen- 
tral part  of  the  body.  This 
cell  in  turn  sends  a message 
which  stimulates  a muscle  to 
work,  and  the  animal’s  body  is  involuntarily  moved  either  away 
from  or  toward  the  source  of  the  stimulus.  This  type  of  response 
is  known  as  a simple  reflex. 

There  are  many  kinds  of  sensory  structures  in  the  lower  animals. 
The  antennae  of  insects  are  for  feeling  and  for  receiving  odors  and, 
in  some  insects,  sound  waves.  A few  insects  like  the  locust  have 
tympanums,  or  ears.  In  some  animals  the  “ ear  ” assists  in  bal- 
ancing while  in  other  animals  the  ear  is  an  organ  of  hearing  as 
well  as  for  balancing.  In  the  shrimp,  the  “ ear  ” is  a tiny  pit, 
the  wall  of  which  is  lined  with  sensory  hairs.  In  this  pit  are  small 
grains  of  sand  or  other  substances,  which  move  about  as  the  animal 
changes  its  position,  and  thus  assist  in  making  the  animal  aware 
of  its  position  in  space.  A German  named  Kreidl  (kri'd’l)  showed 
in  an  experiment  that  shrimps,  after  molting,  place  small  grains 
of  sand  in  their  statocysts  (stat'6-sists)  or  balancing  pits.  He  kept 
the  shrimps  in  an  aquarium  containing  small  particles  of  iron  which 
the  shrimps  took  in  place  of  sand.  Using  a magnet,  Kreidl  then 
found  that  its  pull  against  gravity  affected  the  shrimps  as  did  the 


The  fine  hairs  of  the  appendages  of  the  lobster 
are  organs  of  touch  and  they  make  the  animal 
sensitive  to  its  surroundings. 


now  IS  MAN’S  BODY  CONTROLLED? 


429 


force  of  gravity  wlien  sand  grains  were  in  the  statocysts.  This 
showed  that  the  statocysts  are  balancing  organs. 

Light-receiving  devices  arc  of  various  kinds,  from  the  simple 
eyespot  in  hhiglena  or  small  groups  of  sensory  cells  to  the  com- 
plicated compound  eye  of  insects  and  the  camera-like  structure 
of  man’s  eye. 


Practical  Exercise  2.  Fill  in  the  following  table,  listing  the  various  kinds 
of  sensory  structures  found  in  each  animal  you  have  studied. 


1 

Anim.\l 

Structure 

Where  Found 

How  Used 

Self-Testing  Exercise 

In  higher  animals, (1)  from  special  structures  carry 

(2)  to  organs  of  movement  which  bring  about (3).  When  an 

animal  (4)  moves  away  or  toward  the (5),  the  re- 
sponse is  a (6).  Light-receiving  devices  vary  from  the 

(7)  in (8)  to  the (9) (10)  in  man. 

PROBLEM  IV.  HOW  IS  MAN’S  BODY  CONTROLLED? 

Laboratory  Exercise.  The  anatomy  of  the  nervous  system.  In  a 

frog  from  which  the  organs  of  the  body  cavity  have  been  removed, 
note  the  white  glistening  cords  {nerves)  which  seem  to  come  from 
under  the  backbone.  Follow  the  course  of  some  of  the  larger  nerves. 
To  where  do  they  lead?  Now  turn  the  frog  over  and  with  sharp 
scissors  and  a scalpel  remove  very  carefully  the  bony  covering  (the 
skull)  from  the  whitish  body  (the  brain). 

How  many  parts  appear  to  be  in  the  brain?  Notice  the  white 
elongated  hemisphere  of  the  forebrain  or  cerebrum.''-  The  two  anterior 
projections  of  the  cerebrum  are  called  olfactory  lobes.  Where  do  these 
lobes  seem  to  lead?  What  do  you  think,  from  the  name,  their  use  is? 

Just  back  of  the  cerebrum,  find  two  large  lobes,  known  as  optic 
lobes,  which  have  to  do  with  sight.  Look  at  the  chart.  Are  the  eyes 
connected  wdth  the  optic  lobes?  Back  of  the  optic  lobe  we  find  the 
cerebellum  ^ and  medulla,^  the  latter  running  directly  into  the  spinal 
cord,  from  which  rise  the  spinal  nerves  you  have  noted. 

' Cerebrum  : ser'e-britm,  2 Cerebellum  ; ser'e-bel'wm.  ^ Medulla  : me-dul'a. 


430  MAN  BECOMES  THE  CONQUEROR  OF  THE  WORLD 

Compare,  part  by  part,  the  brain  of  the  frog  with  a model  of  the  brain 
of  man.  In  what  respect  is  a frog’s  nervous  system  like  that  of  man? 
How  does  it  differ  ? Write  a description,  comparing  the  nervous  sys- 
tem of  the  frog  with  your  own,  using  charts  and  models  as  a guide. 

The  sense  organs  of  man.  We  have  seen  that  simpler  forms 
of  life  perform  certain  acts  because  outside  forces  acting  upon 
them  cause  them  to  react.  All  many-celled  animals,  including 
man,  are  put  in  touch  with  their  surroundings  by  what  we  call 
special  sense  organs.  The  senses  of 
man,  besides  those  we  commonly 
know  as  sight,  hearing,  taste,  smell, 
and  touch,  are  those  of  temperature, 
pressure,  and  pain.  It  is  obvious  that 
such  organs,  to  be  of  use,  must  be  at 
the  outside  of  the  body.  Thus  we 
find  eyes  and  ears  in  the  head,  and 
taste  cells  in  the  mouth,  cells  in  the 
nose  for  smelling,  and  others  in  the 
skin  which  are  sensitive  to  heat  or 
cold,  pressure  or  pain. 

The  nervous  system.  In  the  ver- 
tebrate animals,  including  man,  the 
nervous  system  consists  of  two  divisions.  One,  including  the 
brain,  spinal  cord,  and  nerves,  makes  up  the  central  nervous 
system.  The  other  division,  called  the  autonomic  nervous  system, 
consists  of  small  collections  of  nerve  cells  called  ganglia.  These 
ganglia  are  mostly  included  in  two  chains  parallel  to  the  spinal 
cord.  This  system  transmits  stimuli  from  the  central  nervous 
system  to  the  heart,  glands,  and  muscles  of  the  internal  organs. 

Strangely  enough,  we  do  not  see  with  our  eyes  or  taste  with 
our  taste  cells.  These  organs  receive  the  stimulations  which  are 
sent  inward  by  means  of  a complicated  system  of  greatly  elongated 
cell  structures,  until  the  sensory  message  reaches  an  inner  station, 
in  the  central  nervous  system.  We  see  and  hear  and  smell  in  our 
brains. 

Neurons.  The  unit  of  structure  of  the  nervous  tissue  is  a cell, 
called  a neuron.  It  is  a mass  of  protoplasm  containing  a nucleus. 


Some  parts  of  the  body  are  more 
sensitive  to  certain  stimuli  than  are 
others.  The  diagram  on  the  left 
shows  an  organ  that  is  concerned  in 
the  sensation  of  touch;  the  one  on 
the  right,  concerned  in  the  sensation 
of  pressure. 


NEURONS 


431 


_.yiuclexjrs 
cell  hoc^ 


...axon_ 


^protective 

sVieoet-Vi- 


The  body  of  the  nerve  cell  is  usually  irreg:ular  in  shape,  and  differs 
from  other  cells  by  possessing:  several  delicate,  branched,  proto- 
plasmic projections  ctdled  dcndriies.  One  of  these  processes,  the 
axon,  is  much  longer  than  the  others  and  ends  in  a muscle  or  in  a 
network  of  endings  around  anot  her  nerve  cell.  It  is  not  certain  that 
these  two  nerve  cells  are  actually  in 
contact,  but  a stimulus  is  transmitted 
from  one  cell  to  the  other  by  means 
of  this  network.  Such  an  interlock- 
ing of  fibers  is  called  a synapse.  The 
axon  forms  the  pathway  over  which 
nervous  impulses  travel  to  and  from 
the  ner\'e  centers. 

A nerve  consists  of  a bundle  of 
tiny  axons,  bound  together  by  con- 
nective tissue.  As  a nerve  ganglion 
is  a center  of  activity  in  the  nervous 
system,  so  a cell  body  is  a center 
of  activity  of  the  neuron  and  may 
send  an  impulse  over  the  thin  strand 
of  protoplasm  (the  axon)  prolonged 
many  hundreds  of  thousands  of  times 
the  length  of  the  cell  body.  Some 
neurons  in  the  human  body,  although 
visible  only  under  the  compound 
microscope,  give  rise  to  axons  several 
feet  in  length. 

Because  some  axons  originate  in 
organs  that  receive  stimuli  and  send 
them  to  the  central  nervous  system, 
they  are  called  sensory  axons.  Other  axons  originate  in  the  central 
nervous  system  and  pass  outward,  producing  movement  of  muscles. 
These  are  called  motor  axons.  The  neurons  possessing  these  axons 
are  either  sensory  or  motor  neurons.  When  neurons  connect  sen- 
sory with  motor  neurons  they  are  called  associative  neurons. 

Reflexes  and  their  place  in  our  lives.  We  have  seen  that 
reflexes  play  a very  important  part  in  the  responsive  life  of  simple 


terminal  Joranches 


A neuron.  Where  might  such  a cell 
be  found?  Where  might  the  termi- 
nal branches  be  ? 


432  MAN  BECOMES  THE  CONQUEROR  OF  THE  WORLD 

animals.  They  are  equally  important  in  our  own  lives.  The 
involuntary  brushing  of  a fly  from  the  face,  or  the  attempt  to 

move  away  from 
the  source  of  an- 
noyance when 
tickled  with  a 
feather,  are  exam- 
ples of  reflexes. 
In  a reflex  act,  a 
person  does  not 
think  before  act- 
ing. The  nervous 
impulse  comes 
from  the  outside 
sensory  cells  to  motor  cells  in  the  spinal  cord,  or  in  the  cerebellum, 
the  lower  part  of  the  brain.  The  message  is  short-circuited  back 
to  the  surface  by  motor  nerves,  without  ever  having  reached  the 
thinking  centers. 

Practical  Exercise  3.  Make  a list  of  all  the  reflex  acts  that  you  have  made 
during  the  past  twenty-four  hours.  Approximately  what  proportion  of  your 
actions  are  reflexes  ? 

The  brain  of  man.  In  man,  the  central  nervous  system  con- 
sists of  a brain  and  spinal  cord  inclosed  in  a bony  case  and  the 
nerves  which  leave  them.  From  the  brain,  twelve  pairs  of  nerves 
are  given  off ; thirty-one  pairs  more  leave  the  spinal  cord.  The 
brain  has  three  divisions.  The  cerebrum  makes  up  the  largest 
part.  In  this  respect  it  differs  from  the  cerebrum  of  the  frog  and 
lower  vertebrates.  It  is  divided  into  two  lobes,  the  hemispheres, 
which  are  connected  with  each  other  by  a broad  band  of  nerve 
fibers.  The  outer  surface  of  the  cerebrum  is  gray.  It  shows  many 
convolutions  or  folds  which  give  a large  surface.  The  cell  bodies 
and  synapses  of  the  neurons  are  found  in  this  part  of  the  cerebrum. 
Holding  the  cell  bodies  and  fibers  in  place  is  a kind  of  connective 
tissue.  The  inner  part  (white  in  color)  is  composed  largely  of  nerve 
fibers  which  pass  to  other  parts  of  the  brain  and  down  into  the 
spinal  cord.  Below  the  cerebrum  lies  a smaller  portion  of  the 
brain,  the  cerebellum.  The  two  sides  of  the  cerebellum  are  con- 


PARTS  OF  THE  NERVOUS  SYSTEM 


433 


nected  by  a band  of  nerve  fibers,  the  pons,  which  run  around  into 
the  lower  part  of  the  brain  or  medulla  oblongata.  The  medulla  is 
the  enlarged  beginning  of  the  spinal  cord,  and  is  made  up  largely 
of  fibers  running  longitudinally. 

Functions  of  parts  of  the  central  nervous  system  of  the  frog. 
From  studies  of  lower  animals  scientists  have  learned  about  the 
functions  of  various  parts  of  the  central  nervous  system  in  man. 

It  has  been  found  that  if  the  entire  brain  of  a frog  is  destroyed 
or  separated  from  the  spinal  cord,  the  frog  will  continue  to  live. 
It  will  not  move  or  croak,  but  if  acid  is  placed  upon  the  skin  the 
legs  will  make  movements  to  push  away  and  to  clean  off  the  irritat- 
ing substance.  The  spinal  cord  is  thus  shown  to  be  a center  of 
defensive  movements.  If  the  cerebrum  is  separated  from  the 
rest  of  the  nervous  system,  the  frog  seems  to  act  a little  differently 
from  the  normal  animal.  It  jumps  when  touched,  and  swims  when 
placed  in  water.  It  will  croak  when  stroked,  or  swallow  if  food 
is  placed  in  its  mouth.  But  it  manifests  neither  hunger  nor  fear, 
and  is  in  every  sense  a machine  which  will  perform  certain  actions 
after  certain  stimulations.  Its  movements  are  automatic.  The 
cerebellum  and  medulla  then  must  be  the  centers  of  muscular 
coordination  and  automatic  or  involuntary  movements.  If  we 


....olfactory  lobes.-.- 
cerebral  lobes 


olfactory.  iM] 

-lobes  Vf 

.cerebral 
lobes 
optic 
lobes' 

'.cerebeHu' 

' medulla 

b spinal 
corcC 

of  a perch,  frog,  alligator,  pigeon,  and  cat.  Can  you  tell,  from  diagrams,  why  a cat  has 
more  intelligence  than  a pigeon  or  a fish  ? 


'‘spinal 

Cord 


vcereWfluw 
■medwlla 

5piml  Cardi}-  ™ spinal  cord- 


watch  the  movements  of  a frog  which  has  the  brain  uninjured  in  any 
way,  we  find  that  it  acts  spontaneously.  It  tries  to  escape  when 
caught.  It  feels  hungry  and  seeks  food.  It  acts  like  a normal  frog. 
This  shows  that  the  cerebrum  is  the  center  of  all  voluntary  activities. 


434  MAN  BECOMES  THE  CONQUEROR  OF  THE  WORLD 


Localization  of  functions.  In  a general  way,  our  central 
nervous  system  is  like  that  of  the  frog.  The  autonomic  activi- 
ties are  largely  con- 
trolled outside  the 
brain.  The  cerebel- 
lum and  spinal  cord 
take  care  of  the  ha- 
bitual reflexes  which 
we  learned  when 
growing  into  child- 
hood. The  cerebrum 
has  to  do  with  a large 
number  of  conscious 
activities. 

A large  part  of  the 
area  of  the  outer 
layer  of  the  cerebrum 
seems  to  be  given  over  to  some  one  of  the  different  functions  of 
hearing,  sight,  touch,  and  movements  of  body  parts.  The  move- 
ment of  the  smallest  part  of  the  body  appears  to  have  its  definite 
localized  center  in  the  cerebrum.  In  addition,  certain  areas  have 
to  do  with  association  and  memory;  that  is,  the  cells  store 
memories  of  past  acts  or  things.  Those  areas  have  to  do  with 
our  voluntary  actions,  for  the  stored  memories  are  really  stored 
sensory  impressions.  Voluntary  acts,  then,  are  the  completion  of 
reflexes.  Even  reasoning  may  be  explained  as  the  association  of 
concepts,  the  relation  of  which  is  not  close.  Reasoning  is  per- 
ceiving relationships  in  seemingly  unrelated  facts. 

Functions  of  the  nervous  system  of  man.  There  are  several 
types  of  activities  over  which  the  nervous  system  has  control. 
The  first  are  the  so-called  autonomic  activities  of  the  body.  The 
heart  beats  and  we  breathe  when  we  are  asleep  as  well  as  when 
we  are  awake.  Our  glands  emit  secretions  and  our  kidney  cells 
excrete  wastes,  all  without  any  consciousness  on  our  part. 

A second  kind  of  function  is  the  kind  of  activity  which  once 
was  learned  but  now  has  become  “ second  nature  ” or  habitual. 
If  we  have  well-regulated  body  machines,  we  get  up  in  the  morning, 


motor  areoc 


sensoi^crrect 


thinking' 
laaming-  omdi 
V-ndierstcmdiing' 

Cerebrixm 

visual  area 

Cerebellum 


z.i msCCulla 


•coorctinoction 


According  to  the  observations  of  physicians  and  the  experi- 
mentations of  scientists  certain  functions  are  thought  to  be 
controlled  by  different  portions  of  the  brain. 


FUNCTIONS  OF  NERVOUS  SYSTEM 


435 


aiitoinatically  wash,  clean  our  teeth,  dress,  go  to  the  toilet,  eat 
our  breakfast,  walk  to  school,  and  even  perform  such  complicated 
lU’ocesses  as  that  of  writing,  without  thinking  about  or  directing 
the  machine.  Certain  acts  which  once  we  learned  consciously 
have  become  automatic. 

Early  in  our  lives  we  begin  to  gain  a higher  control  of  our  body 
activities.  We  then  make  conscious  choice;  we  weigh  one  course 
of  action  against  another  and  decide  which  is  the  best  course  for 
us  to  follow  — in  short,  we  think.  This  is  the  highest  type  of 
conscious  activit3\ 

Through  the  sense  organs  the  nervous  system  keeps  us  in  touch 
with  the  outside  world. 

Self-Testing  Exercise 

Check  the  correct  statements  in  your  workbook : 

T.  F.  1.  Man’s  body  is  controlled  by  his  brain. 

T.  F.  2.  A neuron  is  a nerve  cell. 

T.  F.  3.  The  autonomic  nervous  system  regulates  functions  which 
are  bejmnd  our  control. 

T.  F.  4.  We  see  and  hear  in  our  brain. 

T.  F.  5.  Sensory  nerves  send  outgoing  messages. 

T.  F.  6.  ]\Iotor  nerves  send  messages  toward  the  central  nervous 
sj^stem. 

T.  F.  7.  The  human  brain  consists  of  convolutions,  hemispheres, 
and  thirty-one  pairs  of  nerves. 

T.  F.  8.  There  are  three  types  of  functions  over  which  the  human 
brain  has  control : the  autonomic,  activities  such  as  the  beating  of  the 
heart,  or  secreting  of  glands ; the  habitual ; and  those  having  to  do 
with  conscious  thought  processes. 

T.  F.  9.  The  cerebellum  controls  our  conscious  activities. 

T.  F.  10.  More  of  our  daily  actions  are  voluntary  than  habitual. 

PROBLEM  V.  WHAT  PART  DO  THE  SENSE  ORGANS  PLAY 
IN  THE  CONTROL  OF  THE  BODY? 

Laboratory  Exercise.  Blindfold  a pupil.  Then  lightly  touch  the 
back  of  his  hand  with  the  two  points  of  the  dividers.  Begin  with 
them  close  together  and  gradually  move  them  apart.  Have  the 
blindfolded  person  tell  as  soon  as  he  feels  the  two  points  separately. 


436  MAN  BECOMES  THE  CONQUEROR  OF  THE  WORLD 


Experiment  further  on  various  parts  of  the  body,  and  record  the  re- 
sults in  the  form  of  a table. 


Place  Touched 

Distance  between  Points 

Back  of  Hand  . . 

Palm  of  Hand  . . 

Finger  Tips . . . 

Wrist 

Upper  Arm . . . 

Back  of  Neck  . . 

Back 

Which  part  of  the  body  seemed  most  sensitive  to  touch  ? 

Laboratory  Exercise.  With  a ruler  and  a pen,  draw  a square  inch 
on  the  underside  of  your  wrist.  Heat  a wire  nail  until  it  feels 
very  hot.  Now  lightly  touch  all  parts  of  the  skin  within  the  square 
area.  Do  all  parts  feel  the  heat,  or  only  the  sense  of  slight  pressure 
of  the  nail?  Mark  with  a little  cross  all  spots  that  are  sensitive  to 
heat. 

Now  cool  off  the  nail  by  placing  it  on  ice.  Wipe  it  dry  and  apply 
while  still  cold  in  the  same  way  to  the  area  marked  off  on  the  wrist. 
Do  you  feel  the  sensation  of  cold  in  all  spots?  Mark  as  before,  this 
time  using  a dot. 

Do  all  parts  of  the  skin  feel  heat  and  cold?  What  does  this  mean? 

Laboratory  Exercise.  What  is  the  relation  between  taste  and  smell  ? 

Cover  your  eyes  and  hold  your  nose  tightly  with  the  fingers. 
Have  another  pupil  place  on  your  tongue  very  small  pieces  of  peeled 
apple,  peeled  raw  potato,  peeled  raw  turnip,  and  onion.  Have  the 
pieces  exactly  the  same  taste?  Have  some  one  record  the  results. 
Are  you  aware  of  the  different  flavors?  Are  you  aware  of  them  with 
the  nostrils  open?  Try  the  experiment  with  a number  of  other  sub- 
stances, as  sugar,  vinegar,  vanilla,  mustard,  salt,  and  spices. 

Rub  the  tongue  dry.  Place  a little  sugar  on  it.  In  what  condition 
must  materials  be  in  order  to  be  tasted  ? 

In  tabular  form  note  those  substances  which  are  recognized  by 
taste  only  and  those  which  are  recognized  by  taste  and  smell. 


TASTE 


437 


KkCOONIZED  HY  T.\8TE 

UEl’OtiNIZKD  BY  TaSTE  .YND  SmELL 

Apple  .... 

Onion  .... 

Potato  .... 

Turnip  .... 

Salt 

Sugar  .... 

Mustard  . . . 

Vanilla  .... 

Vinegar  .... 

What  is  the  relation  of  taste  and  smell  in  distinguishing  flavors? 


Taste.  The  surface  of  the  tongue  is  folded  into  a number  of 
little  projections  known  as  papillae  (pd-pil'e).  In  the  folds 
between  these  projections, 
near  the  root  of  the  tongue, 

I are  located  the  organs  of 
I taste.  These  organs  are 
(Called  taste  huds. 

I Each  taste  bud  consists 
;Of  a collection  of  spindle- 
shaped  neurons,  each  cell 
tipped  at  its  outer  end 
rwith  a hairlike  projection. 

These  cells  send  fibers  in- 
ward to  other  cells,  the  fibers  from  which  ultimately  reach  the 
brain.  The  sensory  cells  are  surrounded  by  a number  of  pro- 
tecting cells  which  are  arranged  in  layers  about  them.  Thus 
i H,  BIO  — 29 


A taste  bud.  Where  is  the  sensation  of  taste  found  ? 


438  MAN  BECOMES  THE  CONQUEROR  OF  THE  WORLD 


the  organ  in  longitudinal  section  looks  somewhat  like  an  onion 
cut  lengthwise. 

Four  kinds  of  substances  may  be  distinguished  by  the  sense  of 
taste.  These  are  sweet,  sour,  bitter,  and  salt.  Certain  taste 
cells  located  near  the  back  of  the  tongue  are  stimulated  only  by  a 
bitter  taste.  Sweet  substances  are  perceived  by  cells  near  the 
tip  of  the  tongue,  sour  substances  along  the  sides,  and  salt  about 
equally  all  over  the  surface.  Taste  and  smell  are  often  confused 
and  many  things  which  we  believe  we  taste  are  in  reality  perceived 
by  the  sense  of  smell. 

Smell.  The  sense  of  smell  is  located  in  the  membrane  lining 
the  upper  part  of  the  nose.  Here  are  found  a large  number  of  rod- 


shaped cells  which  are  con- 
nected with  the  fore  brain 
by  means  of  the  olfactory 
nerve.  In  order  to  perceive 
odors,  it  is  necessary  to  have 
them,  either  as  minute  par- 
ticles of  solid  matter  or  as 
gases,  diffused  in  the  air. 


Olfactory  cells.  Where  is  the  sense  of  smell 
located? 


If  we  wish  to  smell  particularly  well,  we  sniff  so  as  to  draw  the  air 
higher  in  the  nasal  chambers  and  nearer  the  olfactory  cells. 

Hearing.  The  organ  of  hearing  is  the  ear.  The  outer  ear 
consists  of  a funnel-like  organ  composed  largely  of  cartilage  which 
is  of  use  in  collecting  sound  waves,  and  the  auditory  canal,  which 
is  closed  at  the  inner  end  by  a tightly  stretched  membrane,  the 
tympanic  membrane.  The  function  of  the  tympanic  membrane 
is  to  receive  sound  waves  or  vibrations  in  the  air,  which  are  trans- 
mitted, by  means  of  a complicated  apparatus  found  in  the  middle 
ear,  to  the  inner  ear. 

Middle  ear.  The  middle  ear  is  a cavity  inclosed  by  the  temporal 
bone,  and  separated  from  the  outer  ear  by  the  tympanic  membrane. 
A little  tube  called  the  Eustachian  tube  connects  the  inner  ear 
with  the  mouth  cavity.  By  allowing  air  to  enter  from  the  mouth 
the  air  pressure  is  equalized  on  the  tympanic  membrane.  For 
this  reason  we  open  the  mouth  at  the  time  of  a heavy  explosion 
and  thus  prevent  the  rupture  of  the  delicate  tympanic  membrane. 


HEARING 


439 


Placed  directly  against  the  tympanic  membrane,  and  connecting 
it  with  another  membrane  which  separates  the  middle  from  the 
inner  ear,  is  a chain  of  three  tiny  bones,  the  smallest  of  the  body. 
The}^  are  held  in 

extfi-mal  middle 


auditory 

■nerve.., 


-Cochlecc 


iastadbion  tube 


Explain  from  the  diagram,  how  we  hear? 


place  by  very  small 
muscles  which  are 
delicately  adjusted 
so  as  to  tighten  or 
relax  the  mem- 
branes guarding  the 
middle  and  inner 
ear. 

The  inner  ear. 

The  inner  ear  is  one 
of  the  most  com- 
plicated, as  well  as 
one  of  the  most 
delicate,  organs  of  the  body.  Deep  within  the  temporal  bone 
there  are  found  two  parts,  one  of  which  is  called,  collectively,  the 
semicircular  canals,  the  other  the  cochlea  (kokde-d). 

It  has  been  discovered  by  experimenting  with  fish,  in  which 
the  semicircular  canal  region  forms  the  chief  part  of  the  ear, 
that  this  region  has  to  do  with  the  equilibrium  or  balancing  of  the 
body. 

That  part  of  the  ear  which  receives  sound  waves  is  known  as  the 
cochlea  (Lat.,  snail  shell)  because  of  its  shape.  This  complicated 
organ  is  lined  with  sensory  cells  provided  with  cilia,  and  its  cavity 
is  filled  with  a fluid.  It  is  believed  that  somewhat  as  a stone 
thrown  into  water  causes  ripples  to  emanate  from  the  spot  where 
it  strikes,  so  sound  waves  are  transmitted  by  means  of  the  fluid 
filling  the  cavity  to  the  sensory  cells  of  the  cochlea  and  thence 
to  the  brain  by  means  of  the  auditory  nerve. 

The  character  of  sound.  When  vibrations  which  are  received 
by  the  ear  follow  one  another  at  regular  intervals,  the  sound  is  said 
Ito  be  musical.  If  the  vibrations  come  irregularly,  we  call  the 
sound  a noise.  If  the  vibrations  come  slowly,  the  pitch  of  the 
sound  is  low ; if  they  come  rapidly,  the  pitch  is  high.  The  ear 


440  MAN  BECOMES  THE  CONQUEROR  OF  THE  WORLD 


is  able  to  perceive  as  low  as  thirty  vibrations  per  second  and  as 
high  as  almost  thirty  thousand. 

Seeing.  The  organ  of  vision,  the  eye,  is  almost  spherical,  and 
fits  into  a socket  of  bone,  the  orbit.  A stalklike  structure,  the  optic 
nerve,  connects  the  eye  with  the  brain.  Free  movement  is  made 
possible  by  means  of  six  little  muscles  which  are  attached  to 

the  outer  coat  of  the 
eyeball,  and  to  the 
bony  wall  around 
the  eye. 

The  wall  of  the 
eyeball  is  made  up 
of  three  coats.  An 
outer  tough  white 
coat  of  connective 
tissue  is  called  the 
sclerotic  (skle-rot'ik) 
coat.  In  front,  where 
the  eye  bulges  out 
a little,  this  outer 
coat  is  replaced  by  a transparent  tough  layer  called  the  cornea. 
A second  coat,  the  choroid  (ko'roid),  is  supplied  with  blood  vessels 
and  cells  which  contain  pigments.  The  iris  is  part  of  this  coat 
which  we  see  through  the  cornea  as  the  colored  part  of  the  eye. 
In  the  center  of  the  iris  is  a small  circular  hole,  the  pupil.  The 
iris  is  under  the  control  of  muscles,  and  may  be  adjusted  to  varying 
amounts  of  light,  the  hole  becoming  larger  in  dim  light,  and 
smaller  in  bright  light.  The  inmost  layer  of  the  eye  is  called  the 
retina  (ret'i-nd).  This  is,  perhaps,  the  most  delicate  layer  in  the 
entire  body.  Despite  the  fact  that  the  retina  is  less  than  of 
an  inch  in  thickness,  there  are  several  layers  of  cells  in  its  com- 
position. The  optic  nerve  enters  the  eye  from  behind  and  spreads 
out  over  the  surface  of  the  retina.  Its  finest  fibers  are  ultimately 
connected  with  numerous  elongated  cells,  which  are  stimulated 
by  light.  The  retina  is  dark  purple  in  color,  this  color  being  due 
to  a layer  of  cells  next  to  the  choroid  coat.  This  accounts  for  the 
black  appearance  of  the  pupil  of  the  eye,  when  we  look  through 


What  happens  to  the  eye  when  we  pass  from  a brightly 
lighted  room  into  a dark  room  ? 


SEEING 


441 


it  into  the  darkened  space  within  the  eyeball.  The  retina  acts 
as  the  sensitized  plate  in  the  camera,  for  on  it  are  received  the 
impressions  which  arc  transformed  and  sent  to  the  brain  and  result 
in  sensations  of  sight.  The  eye,  like  the  camera,  has  a lens.  This 
lens  is  formed  of  transparent,  elastic  material.  It  is  directly  behind 
the  iris  and  is  attached  to  the  choroid  coat  by  means  of  delicate 
ligaments.  In  front  of  the  lens  is  a small  cavity  filled  with  a 
watery  fluid,  the  aqueous  humor,  while  behind  it  is  the  main  cavity 
of  the  eye,  filled  with  a transparent,  almost  jelly-like,  vitreous 
humor.  The  lens  itself  is  elastic.  This  circumstance  permits  a 
change  of  form  and,  in  consequence,  a change  of  focus  upon  the 
retina  of  the  lens.  By  means  of  this  change  in  form,  or  accommoda- 
tion, we  are  able  to  see  both  near  and  distant  objects. 

Practical  Exercise  4.  Make  a diagram  to  show  exactly  what  changes  take 
place  in  the  eye  when  you  look  from  your  book  out  of  the  window  to  focus  on 
something  coming  down  the  far  end  of  the  street. 

Self-Testing  Exercise 

There  are  areas  on  the  skin  that  are  sensitive  to  (1), 

(2),  and (3).  The  organs  of  taste  are  the (4) 

(5).  The  kinds  of  substances  distinguished  by  taste  are 

(6),  (7),  (8),  and  (9).  The 

sense  of  smell  is  located  in  the (10)  lining  the (11) 

part  of  the  nose.  The  organ  of  hearing  is  the (12).  It  is 

composed  of  the  (13),  (14),  and  (15) 

(16)-  The  (17)  receives  the  sound  waves  which 

are  transmitted  to  the (18)  by  the (19) (20) . 

The  eye  is  covered  by  three  coats  (21), (22),  and 

, (23).  Impressions  of  seeing  are  made  on  the (24), 

which  are  carried  to  the  (25)  by  the  (26) 

(27).  The  (28)  in  form  of  the  lens  of  eye  is 

called (29). 

PROBLEM  VI.  WHAT  BEHAVIORS  ARE  INSTINCTIVE? 

Demonstration  5.  What  actions  of  a newly  hatched  chick  are  in- 
stinctive ? 

Place  a newly  hatched  chick  on  a small  tray,  with  food  and  water. 
Place  on  the  tray  small,  bright-colored,  distasteful  substances.  Watch 
[the  chick  and  make  careful  record  of  all  its  actions.  List  as  many  as 
you  can  as  instinctive.  Are  instinctive  acts  always  useful? 


442  MAN  BECOMES  THE  CONQUEROR  OF  THE  WORLD 


Instinctive  behavior.  In  many  animals  certain  important 
behaviors  in  life  are  instinctive,  that  is,  they  are  performed  for 
the  first  time  without  being  learned.  A wasp  lays  its  eggs  in  the 
body  of  a caterpillar,  which  it  first  paralyzes  by  stinging;  the 
oriole  weaves  its  nest;  the  swallow  builds  its  nest  of  mud; 
the  trapdoor  spider  makes  its  tunnel  in  the  ground  and  furnishes 
it  with  a door  — all  these  and  thousands  of  other  examples  might 
be  given.  The  complicated  activities  of  the  pronuba  moth  (see 
page  94)  can  be  explained  only  by  instinct,  for  the  moth  dies 

without  ever  seeing  her 
offspring. 

Instincts  can  best  be  ex- 
plained, as  workers  with 
insects  have  shown,  as  a 
chain  of  inborn  automatic 
responses  or  simple  re-  i 
flexes.  For  example,  an  | 
insect’s  making  a nest,  j 
stinging  the  prey,  and  lay-  ! 
ing  eggs  are  a series  of  be-  : 
haviors,  each  one  depend- 
ing upon  the  one  before. 
If  we  interrupt  the  se- 
quence, as  by  removing 
most  of  the  food  supply 
from  the  nest,  or  by  giving 
a fly  paper  soaked  in  meat  1 
juices,  instead  of  decayed 
flesh,  in  which  to  lay  its  ' 
eggs,  the  life  cycle  is  ended  , 
because  the  insect  cannot  ■ 
modify  its  actions.  As  Professor  Hodge  says,  a housefly  is  about 
as  intelligent  as  a shot  rolling  down  a board.  Once  the  chain  of 
behaviors  is  set  in  motion  by  some  outside  stimulus,  it  continues 
until  the  life  cycle  is  completed  by  egg  laying. 

Modification  of  instinctive  behavior.  Although  the  French 
naturalist,  Fabre  (fa'br’),  found  that  a certain  wasp  which  drags  ' 


The  squash  bug  fastens  her  brown  shiny  eggs  with 
care  beside  the  midrib  of  the  underside  of  a large 
squash  leaf  which  the  larvae  will  feed  upon  as  soon 
as  they  hatch. 


MODIFICATION  OF  INSTINCTIVE  BEHAVIOR  443 


its  si'^sshopper  prey  by  one  antcmia  would  not  touch  its  prey  if 
both  aiiteiiiiae  were  cut  off,  yet  tliere  are  examples  of  instinctive 
behaviors  beinj>;  modified  for  the  benefit  of  the  animal.  Some 
insect  larvae,  if  they  have  consumed  all  of  the  plant  on  which  they 
usually  feed,  will  eat  other  kinds  of  leaves  and  thus  save  their 
lives.  Fish  and  frogs  can  be  taught  to  form  new  associations,  for 
after  many  errors  they  will  learn  to  avoid  obstacles  placed  between 
them  and  their  food.  A dog  can  be  taught  to  refrain  from  eating 
a lump  of  sugar  placed  on  his  nose  until  a word  is  spoken,  because 
he  has  formed  new  connections  which  considerably  change  his 
natural  behavior.  Such  modified  responses,  which  are  caused 
by  new  stimuli,  are  said  to  be  conditioned.  The  new  response 
made  by  the  dog  is  conditioned  by  an  association  formed  by  the 
dog’s  master. 

Practical  Exercise  6.  Think  of  some  of  your  pets,  as  a dog  or  a bird,  and 
make  a list  of  the  instinctive  acts  performed  by  this  animal.  Have  you  ever 
tried  to  condition  one  of  these  instinctive  responses?  Why  are  instincts 
important  in  the  lives  of  animals  ? Give  some  examples  of  household  pets  that 
show  how  instincts  may  be  modified. 


Self-Testing  Exercise 

Instincts  are  usually  explained  as (1) (2) (3). 

Instinctive  acts  may  be  (4)  in  some  lower  animals.  When 

simple  (5)  become  modified,  they  are  said  to  be (6). 

Such  a reaction  is  usually  caused  by  a (7)  or  different (8) . 

If  some  animals  are  not  able  to (9)  their (10),  they  die. 

PROBLEM  VII.  HOW  ARE  HABITS  FORMED? 

Some  of  our  earliest  acts  or  behaviors  are  instinctive.  Babies 
do  not  have  to  be  taught  to  suck ; but  as  they  grow  older  they 
modify  this  instinct.  They  learn  to  take  food  from  a spoon  and 
to  wait  for  it.  Later  on  they  learn,  by  a series  of  trials,  to  stand 
erect  and  then  to  walk.  There  is  a difference  between  the  instinct 
of  sucking  and  the  habits  which  are  learned  through  repetition 
when  the  child  is  compelled  to  take  other  food  than  its  mother’s 
milk.  A habit  might  be  called  an  acquired  automatic  activity. 


444  MAN  BECOMES  THE  CONQUEROR  OF  THE  WORLD 


Practical  Exercise  6.  For  every  good  habit  formed  there  is  an  opposite 
bad  habit.  From  the  list  of  good  habits  named  below  name  the  opposite  bad 
habits. 


perseverance  reliability 

obedience  correct  speech 

orderliness  conscientiousness 

industriousness  optimism 

habits  of  good  posture  cooperation 

regular  toilet  habits  confidence 

honesty  independence 

truthfulness  diligence 

promptness  accuracy 


neatness 

punctuality 

courtesy 

observation 

inventiveness 

classification 

openmindedness 

reasonableness 

alertness 


unselfishness 

sociability 

modesty 

poise 

attentiveness 

enthusiasm 

self-reliance 

frankness 

patience 


Which  of  the  above-named  habits  do  you  have?  What  habits  should  you 
form? 


Habit  formation.  One  object  of  education  is  the  training  of 
the  different  areas  in  the  cerebrum  to  do  their  work.  When  we 
first  tried  to  write,  we  had  to  exert  conscious  effort  in  order  to 
make  the  letters.  Now  the  act  of  forming  the  letters  is  done 
without  our  thought.  By  training,  the  act  has  become  a habit. 
The  actual  performance  of  the  action  is  then  taken  up  by  the 
cerebellum,  medulla,  and  spinal  ganglia.  Thus  the  thinking 
portion  of  the  brain  is  relieved  of  this  work. 

It  is  surprising  how  little  real  thinking  we  do  during  a day,  for 
most  of  our  acts  are  habitual.  Habit  takes  care  of  our  dressing, 
our  bathing,  our  care  of  the  body  organs,  our  methods  of  eating. 
Even  our  movements  in  walking  and  our  style  of  handwriting 
are  matters  of  habit  formation.  We  are  bundles  of  habits,  be  they 
good  ones  or  bad  ones. 

Different  kinds  of  habits.  Habits  are  of  many  kinds.  They 
may  concern  health  and  well-being,  as  proper  tooth  brushing,  eat- 
ing at  regular  times,  maintaining  a correct  posture,  and  hundreds 
of  simple  things  we  do  automatically.  Some  concern  our  dress  and 
our  actions  in  society.  We  walk,  ride,  dance,  skate,  or  drive  a car 
without  consciously  thinking  about  what  we  are  doing.  Our  habits 
of  disposition  have  become  a very  important  part  of  our  lives.  We 
may  frequently  be  sad  or  be  happy,  sing  or  cry,  or  be  kind,  or  be 
cross.  We  may  form  our  habits  of  thought,  too : concentration 
or  scatter-brain  methods,  ability  to  think  through  our  problems, 
or  inability  to  do  any  real  thinking  — it  all  depends  upon  ourselves. 
Man  has  conquered  many  factors  in  his  environment  through 


FOKiMINCJ  KIUIIT  HABITS 


445 


training  his  body  to  do  certain  things  effectively.  The  most 
important  thing  is  the  control  of  his  nervous  system,  because  it  is 
through  the  effective  use  of  it  that  he  gets  things  done.  If  you 
will  be  conqueror  in  your  sphere  of  life,  learn  how  to  control  your 
own  thoughts  and  (.leeds.  In  this  way  you  will  be  prepared  to 
conquer  in  the  bigger  field  of  activity  which  you  will  enter  later. 

Habits  must  be  formed  early.  We  have  often  heard  the  saying, 
“ You  can’t  teach  an  old  dog  new  tricks.”  This  is  all  too  true 
of  habit  forming.  We  exercise  our  muscles  and  they  grow  larger. 
Not  so  with  our  brain  cells.  We  probably  ail  have  the  same 
number  of  neurons,  but  there  is  an  unlimited  number  of  possible 
connections  between  them,  which  may  result  in  a great  many 
habitual  activities.  Every  time  a new  act  is  performed  a new 
connection,  synapse,  is  made  between  two  neurons.  While  the 
nervous  system  is  3mung  the  cells  are  plastic,  and  pathways  are 
easily  established  between  cells.  These  pathways,  like  a rut  in 
soft  mud,  become  deeper  and  deeper  with  use.  Habits  are,  there- 
fore, readily  formed  at  this  time.  Practice  makes  perfect  ” is  a 
truism,  but  it  illustrates  how  a habit  is  formed.  Fortunate  are 
the  bo3’’S  and  girls  of  the  age  who  read  this  book,  for  they  are  able 
to  form  good  habits  easily.  But  a man  or  woman  of  middle  age 
has  formed  habits,  and  to  change  them  and  make  new  ones  is  very 
difficult.  The  nervous  system  is  no  longer  plastic. 

Practical  Exercise  7.  What  are  the  best  ways  of  forming  good  habits? 
Write  a short  composition  on  this  for  your  workbook. 

What  is  the  advantage  of  forming  good  habits  in  life?  Does  habit-forming 
relieve  part  of  the  nervous  system  from  work?  Explain  fully.  Explain  the 
increased  effectiveness  and  power  acquired  through  good  habits. 

Importance  of  forming  right  habits.  Among  the  habits  which 
should  be  acquired  early  in  life  are  those  of  studying  properly,  of 
concentrating  the  mind,  of  learning  self-control,  and,  above  all,  of 
being  content.  Get  the  most  out  of  the  world  about  you.  Re- 
member that  the  immediate  effect  of  the  study  of  some  subjects 
in  school  may  not  be  great,  but  the  cultivation  of  correct  methods 
of  thinking  may  be  of  the  greatest  importance  later  in  life.  The 
men  and  women  who  have  learned  how  to  concentrate  on  a prob- 
lem, how  to  weigh  all  evidences  with  unbiased  minds,  and  then  to 


446  MAN  BECOMES  THE  CONQUEROR  OF  THE  WORLD 


decide  on  what  they  believe  to  be  right,  are  the  efficient  and  happy 
ones  of  their  generation. 

“ The  hell  to  be  endured  hereafter,  of  which  theology  tells,  is  no 
worse  than  the  hell  we  make  for  ourselves  in  this  world  by  habitually 
fashioning  our  characters  in  the  wrong  way.  Could  the  young  but 
realize  how  soon  they  will  become  mere  walking  bundles  of  habits, 
they  would  give  more  heed  to  their  conduct  while  in  the  plastic  state. 
We  are  spinning  our  own  fates,  good  or  evil,  and  never  to  be  undone. 
Every  smallest  stroke  of  virtue  or  of  vice  leaves  its  never-so-little  scar. 
The  drunken  Rip  Van  Winkle,  in  Jefferson’s  play,  excuses  himself 
for  every  fresh  dereliction  by  saying,  ‘I  won’t  count  this  time!’ 
Well!  he  may  not  count  it,  and  a kind  Heaven  may  not  count  it; 
but  it  is  being  counted  none  the  less.  Down  among  his  nerve  cells 
and  fibers  the  molecules  are  counting  it,  registering  and  storing  it  up 
to  be  used  against  him  when  the  next  temptation  comes.  Nothing  we 
ever  do  is,  in  strict  scientific  literalness,  wiped  out.  Of  course  this 
has  its  good  side  as  well  as  its  bad  one.  As  we  become  permanent 
drunkards  by  so  many  separate  drinks,  so  we  become  saints  in  the 
moral,  and  authorities  in  the  practical  and  scientific  spheres,  by  so 
many  separate  acts  and  hours  of  work.  Let  no  youth  have  any 
anxiety  about  the  upshot  of  his  education,  whatever  the  line  of  it  may 
be.  If  he  keep  faithfully  busy  each  hour  of  the  working  day,  he  may 
safely  leave  the  final  result  to  itself.  He  can  with  perfect  certainty 
count  on  waking  up  some  fine  morning,  to  find  himself  one  of  the  com- 
petent ones  of  his  generation,  in  whatever  pursuit  he  may  have  singled 
out.”  — William  James,  Psychology.  (Permission  of  Henry  Holt  & Co.) 

Some  rules  for  forming  good  habits..  Professor  Horne  gives 
several  rules  for  making  good  or  breaking  bad  habits.  They  are : 
First,  act  on  every  opportunity.  Think  of  the  good  habits  you  would 
hke  to  form  and  then  form  them.  Second,  make  a strong  start. 
No  half-hearted  effort  ever  was  successful  in  forming  a habit. 
Third,  allow  no  exception.  You  cannot  establish  the  new  pathway 
in  the  nervous  system,  if  you,  like  Rip  Van  Winkle,  “ don’t  count 
this  one.”  Fourth,  for  the  had  habit  establish  a good  one.  Most  of 
us  know  our  own  faults.  Some  of  us  have  far  too  many.  Per- 
haps it  is  only  a little  thing  such  as  forgetting  some  of  the  numerous 
conventionalities  that  make  up  table  manners ; it  may  be  some- 
thing far  more  important,  an  uncontrolled  emotion  or  feeling. 


GOOD  HABITS 


447 


Anyway,  there  is  some  opposite  helpful  habit  you  can  substitute 
in  its  place.  For  example,  instead  of  saying  sometimes,  “ That 
noise  drives  me  wild,”  say  nothing,  but  think  to  yourself,  “ there’s 
no  noise  that  1 can’t  stand  when  necessary.”  Fifth,  use  effort  of 
will.  Habits  which  are  rooted  when  young  in  moral  and  religious 
training  are  those  which  in  later  life  will  do  more  than  any  others 
to  steer  us  straight  on  the  course  we  would  take  through  life. 

Practical  Exercise  8.  Explain  how  you  would  break  some  specific  bad 
habit  by  using  the  rules  quoted  above. 

Make  a list  of  habits  of  mind  that  you  would  like  to  acquire.  How  would 
you  go  to  work  to  do  this? 

Self-Testing  Exercise 

A habit  is  an  acquired (1)  act.  Learning  to (2)  is 

such  an  act.  Habits  are  most  easily  formed  when  we  are (3). 

“ Practice  makes  perfect  ” is  a good  rule  in (4) (5). 

In  forming  a habit : Act  on  every  (6) ; make  a strong 

(7) ; allow  no (8) ; replace (9)  habits  with 

(10)  habits;  use  your (11)  of (12). 

PROBLEM  VIII.  WHAT  ARE  SOME  GOOD  HEALTH  HABITS? 

Health  habits  for  the  nervous  system.  The  nerve  cells,  like 
all  other  cells  in  the  body,  are  continually  wasting  away  and  being 
rebuilt.  Oxidation  of  food  material  increases  when  we  do  mental 
work.  The  cells  of  the  brain,  like  muscle  cells,  are  not  only 
capable  of  fatigue,  but  they  show  this  in  changes  of  form  and  of 
contents.  Food  brought  to  them  in  the  blood,  plenty  of  fresh  air, 
and  rest  at  proper  times,  are  essential  in  keeping  the  nervous  system 
in  condition.  One  of  the  best  methods  of  resting  the  brain  cells 
is  a change  of  occupation.  Tennis,  golf,  baseball,  and  other 
outdoor  sports  combine  muscular  exercise  with  brain  activity  of  a 
different  sort  from  that  of  business  or  school  work. 

Necessity  of  sleep.  But  change  of  occupation  will  not  rest 
exhausted  neurons.  For  this,  sleep  is  necessary.  Especially  is 
sleep  an  important  factor  in  the  health  of  the  nervous  system  of 
growing  children.  A child  needs  ten  hours  of  sleep,  an  adult, 
eight  hours.  When  a person  is  sleeping,  his  brain  cells  have  oppor- 
tunity to  rest  and  to  store  food  and  energy  for  their  working  period. 


448  MAN  BECOMES  THE  CONQUEROR  OF  THE  WORLD 


Sleep  is  one  way  in  which  all  the  cells  in  the  body,  and  par- 
ticularly those  of  the  nervous  system,  get  their  rest.  The  nervous 

system,  by  far  the  most  delicate 
and  hardest-worked  set  of  tissues 
in  the  body,  needs  rest  more  than 
do  other  tissues,  for  much  of  its 
work  of  directing  the  body  ends 
only  with  sleep  or  unconscious- 
ness. The  afternoon  nap,  snatched 
by  the  brain  worker,  gives  him  re- 
newed energy  for  his  evening’s 
work.  It  is  not  hard  application 
to  a task  that  wearies  the  brain ; it 
is  continuous  work  without  rest. 

Health  habits  for  the  sense  or- 
gans. Overstimulation  of  any  of 
the  sense  organs  is  a bad  thing. 
The  ear  may  be  overstimulated 

What  has  happened  to  the  dark  granules  noiseS  ; the  eye  by  tOO 

bright  light;  the  olfactory  cells 
by  too  heavy  odors,  the  taste  cells  by  too  highly  seasoned  food. 

The  most  frequent  habits  of  abuse  of  the  eyes  are  using  them  for 
reading  in  a dull  or  flickering  light  or  in  too  bright  a light  which 
makes  a glare  on  the  page.  We  should  avoid  looking  directly  into 
the  source  of  any  light. 

The  eyes  are  also  subject  to  infection  and  injury  from  dust,  cin- 
ders, flying  bits  of  metal,  etc.  Certain  trades  in  the  past  have 
taken  a high  toll  of  eye  injuries,  although  now  workers  are  pro- 
tected by  proper  goggles.  In  case  of  soreness  or  irritation  place  a 
drop  of  newly  prepared  weak  solution  of  argyrol  in  each  eye.  This 
may  prevent  serious  eye  trouble. 

Many  eyes  are  imperfect  because  the  curvature  of  the  lens  is  not 
normal.  Such  defects  are  a cause  of  headaches,  and  should  be 
remedied  by  having  an  oculist  prescribe  corrective  glasses. 

Practical  Exercise  9.  Make  two  lists  — one  of  habits  practiced  by  you 
that  are  detrimental  to  health  and  the  other  one  of  habits  that  promote  good 
health.  What  can  you  do  to  improve  your  health  ? Show  what  habits  would 
result  in  the  protection  of  your  eyes. 


THE  RELATION  OF  ALCOHOL  TO  EFFICIENCY  449 


Self-Testing  Exercise 

(1), (2),  and  (3)  (4)  are  necessary 

to  keep  brain  cells  health}'.  Change  of  occupation  is  good  for  exhausted 

neurons  but (5)  is  better.  The  most  frequent  abuses  to  the  eyes 

are  reading  in  a (6)  or (7) (8)  or  in  a (9). 

PROBLEM  IX.  WHAT  ARE  SOME  EFFECTS  OF  THE  DRINK 
HABIT? 

The  drink  habit.  Although  prohibition  has  made  it  harder  for 
all  people  to  obtain  liquors,  many  still  drink  and  some  seemingly 
cannot  help  it.  Let  us  see  why. 

The  first  effect  of  drinking  alcoholic  liquors  is  that  of  exhilaration. 
After  the  feeling  of  exhilaration  is  gone,  for  this  is  a temporary 
state,  the  drinker  feels  depressed  and  less  able  to  work  than  before 
he  took  the  drink.  To  overcome  this  feeling,  he  takes  another 
drink.  The  result  is  that  before  long  he  finds  a habit  formed  from 
which  he  cannot  easily  change. 

The  economic  effect  of  alcoholic  poisoning.  In  the  struggle 
for  existence,  it  is  evident  that  the  man  whose  intellect  is  the  quick- 
est and  keenest,  whose  judgment  is  most  sound,  is  the  man  who 
is  most  likely  to  succeed.  The  deadening  effect  of  alcohol  upon  the 
nerve  centers  must  place  the  drinker  at  a disadvantage. 

Dr.  Parkes  experimented  with  two  gangs  of  men,  selected  to  be 
as  nearly  similar  as  possible,  in  mowing.  He  found  that  with  one 
gang  abstaining  from  alcoholic  drinks  and  the  other  not,  the 
abstaining  gang  could  accomplish  more.  On  taking  away  the 
alcohol  from  the  one  gang  and  giving  it  to  the  other,  the  same 
results  were  obtained.  Similar  results  were  obtained  by  Professor 
Aschaffenburg  of  Heidelberg  University,  who  found,  experimentally, 
that  men  “ were  able  to  do  15  per  cent  less  work  after  taking 
alcohol.”  Many  other  experiments  along  the  same  lines  have 
been  made.  In  typewriting,  in  typesetting,  in  bricklaying,  and 
in  the  highest  type  of  mental  work,  the  result  is  the  same.  The 
quality  and  quantity  of  work  done  by  men  on  days  when  they 
take  alcohol  is  less  than  on  days  when  they  take  no  alcohol. 

The  relation  of  alcohol  to  efficiency.  We  have  already  seen 
that  neither  is  work  done  as  well  nor  is  as  much  accomplished  by 


450  MAN  BECOMES  THE  CONQUEROR  OP  THE  WORLD 


drinkers  as  by  non-drinkers.  Some  relation  of  alcohol  to  efficiency 
is  shown  by  the  chart  below,  which  was  made  prior  to  prohibition. 
In  a series  of  experiments  reported  by  the  Medical  Research 
Committee  in  1919  and  1920  it  was  shown  that  alcohol  invariably 


This  chart  was  made  prior  to  prohibition.  Can  you  explain  why  the  above  facts  were  true? 


had  a disturbing  effect  on  skilled  movements  even  when  the  dose  of 
alcohol  administered  was  only  forty  cubic  centimeters  a day. 
Small  accidents  also  happened  on  the  days  when  the  alcohol  was 
given.  In  another  experiment  a “dotting  machine”  was  used  in 
which  the  subject  tried  to  make  dots  in  a series  of  small  red  circles 
as  these  circles  passed  by  a small  window  in  the  machine.  In- 
variably more  mistakes  were  made  when  alcohol  was  taken,  and 
there  was  much  uncertainty  even  when  doses  as  small  as  ten  cubic 
centimeters  were  given. 

The  relation  of  alcohol  to  crime.  A study,  made  just  before 
the  eighteenth  amendment  was  passed,  of  more  than  2500  habitual 
users  of  alcohol,  showed  that  over  66  per  cent  had  committed  crime. 
Of  23,581  criminals  questioned,  20,070  said  that  alcohol  had  led 
them  to  commit  crime. 

The  relation  of  alcohol  to  pauperism.  Studies  of  certain  families 
which  have  long  been  a heavy  burden  on  the  state  show  that 
alcohol  is  at  least  partly  responsible  for  their  condition.  Alcohol 
weakens  efficiency  and  moral  courage,  and  thus  leads  to  begging, 
pauperism,  petty  stealing  or  worse,  and  ultimately  to  life  in  some 


TEST  ON  FUNDAMENTAL  CONCEPTS  451 

public  institution.  In  Massachusetts,  of  3230  inmates  of  such 
institutions,  GO  per  cent  were  alcoholics. 

Practical  Exercise  10.  Sum  up  the  reasons  why  alcohol  harms  a person 
through  its  elTecls  on  the  nervous  system. 


Self-Testing  Exercise 

Alcohol  is  a (1).  There  seems  to  be  a direct  correlation 

between  drinking  and  (2),  and  between  drinking  and 

(3).  Some  experiments  show  that  drinkers  are (4) 

(5)  than  non-drinkers.  The (6)  of (7)  is 

liard  to  overcome.  Alcohol  has  harmful  effects  upon  the (8) 

system. 

Review  Summary 

Check  your  knowledge  of  the  unit  by:  (1)  rechecking  on  the  survey  ques- 
tions; (2)  performing  the  assigned  exercises;  (3)  checking  with  your  teacher 
the  scores  of  the  various  tests  and  doing  over  all  missed  parts;  (4)  making  an 
outline  of  the  unit  for  your  workbook. 


Test  on  Fundamental  Concepts 

In  a vertical  column  under  the  heading  CORRECT  write  numbers  of  all  statements  you  be- 
lieve are  true.  In  another  column  under  INCORRECT  write  numbers  of  untrue  statements. 
Your  grade  = right  answers  X 2L 

I.  Sense  organs  (1)  are  never  located  at  the  surface  of  the  body ; 

(2)  usually  consist  of  cells  which  are  capable  of  receiving  stimuli; 

(3)  in  lower  animals  are  usually  located  in  hairs  or  other  structures 
at  the  outside  of  the  body;  (4)  put  animals  in  touch  with  their  sur- 
roundings ; (5)  are  usually  more  numerous  at  the  anterior  end  of  an 
animal. 

II.  A reflex  (6)  is  a structure  formed  on  the  outside  of  animals ; 

(7)  is  seen  in  plants  when  the  leaves  close  up  in  response  to  heat  or  light ; 

(8)  is  the  result  of  a stimulus  and  results  in  movement ; (9)  is  seen 
wdien  we  involuntarily  withdraw  our  finger  from  a hot  object;  (10)  is 
the  result  of  a nerve  impulse  traveling  to  a nerve  center,  where  it  is 
translated  into  movement  by  means  of  an  outgoing  nerve  impulse. 

III.  Stimuli  (11)  travel  by  means  of  nerves;  (12)  are  received 
through  sense  organs;  (13)  often  are  felt  as  pain,  pressure,  heat; 
(14)  are  of  no  value  to  man;  (15)  are  the  means  by  which  we  are 
aware  of  our  surroundings. 


452  MAN  BECOMES  THE  CONQUEROR  OF  THE  WORLD 


IV.  We  see  (16)  by  means  of  the  retina  which  receives  the  light 
images ; (17)  in  the  brain  and  not  in  the  eye ; (18)  because  the  retina 
transforms  the  stimulus  caused  by  the  light  waves  and  transmits  them 
by  the  optic  nerve  to  the  brain ; (19)  because  our  eye  is  like  a camera 
— the  eye  becoming  deeper  or  more  shallow  as  we  focus ; (20)  when 
through  a change  of  shape  the  lens  is  focused  on  an  object. 

V.  The  sense  organs  of  man  (21)  are  the  nose,  tongue,  eyes,  and 
skin ; (22)  are  all  external ; (23)  are  connected  by  nerves  with  the  central 
nervous  system ; (24)  are  made  up  of  sensory  cells ; (25)  are  not  deli- 
cate enough  to  need  protection,  and  so  do  not  have  any. 

VI.  Instincts  (26)  are  actions  that  are  performed  without  having 

first  been  learned ; (27)  are  behaviors  which  are  useful  because  they 
help  preserve  the  race ; (28)  are  acts  that  are  carefully  thought  out 
before  they  are  performed ; (29)  may  be  modified  or  conditioned 

through  teaching ; (30)  serve  to  avoid  dangers. 

VII.  Habits  (31)  may  be  either  harmful  or  useful;  (32)  are  learned 
activities  ; (33)  may  be  mental  or  physical ; (34)  make  up  a large  part 
of  our  life  activities ; (35)  cannot  easily  be  learned  by  young  people. 

VIII.  The  following  are  good  rules  for  forming  desirable  habits : 
(36)  never  use  will  power ; (37)  allow  no  exceptions  to  occur ; 
(38)  never  make  a strong  start ; (39)  have  a real  desire  to  build  the 
habit ; (40)  act  on  every  opportunity  to  make  the  desired  reaction. 


Achievement  Test 

1.  How  can  you  demonstrate  what  a tropism  is  and  how  it  causes 
a living  thing  to  react  ? 

2.  What  are  the  different  stimuli  that  affect  the  lives  of  plants  and 
animals  ? 

3.  What  is  meant  by  the  method  of  trial  and  error  ? 

4.  How  can  you  demonstrate  a reflex  act  ? 

5.  Locate  the  parts  of  your  nervous  system,  and  tell  the  uses  of 
each  part. 

6.  How  do  we  taste,  touch,  and  feel  hot  or  cold  objects? 

7.  How  do  we  hear? 

8.  How  do  we  see?  How  can  we  compare  the  human  eye  to  a 
camera  ? 

9.  How  would  you  define  instinct? 

10.  What  is  meant  by  a “ conditioned  ” reflex? 


ITSEFUL  REFEKENCES  453 

11.  How  can  you  take  the  i)roi)er  steps  in  forming  a good  habit  or 
breaking  a bad  one? 

12.  W’liy  cannot  one  “ teach  an  old  dog  new  tricks  ”? 


PiL\CTic.\L  Problems 

1.  Fill  out  the  following  table  with  reference  to  the  sense  organs  in  the 
human  body. 


Organs 

Location 

What  They  Do 

How  They  Do  It 

, 2.  Show  exactly  what  happens  in  j’-our  nervous  system  when  you  touch 

a hot  object  in  the  dark. 

3.  How  would  you  go  to  work  to  eradicate  a bad  habit? 

4.  Show  that  some  act  of  your  daily  life  is  a “conditioned  reflex.” 

Useful  References 

Dorsey,  Why  We  Behave  Like  Human  Beings.  Chap.  vi.  Harper,  1925. 
Emmerson,  Alcohol:  Its  Effect  on  Man.  Appleton-Century,  1934. 
iFabre,  The  Wonders  of  Instinct.  Century,  1918. 

Hunter,  Laboratory  Problems  in  Civic  Biology.  Pp.  161-168,  inc.  Ameri- 
' can  Book  Company. 

Imms,  Social  Behavior  of  Insects.  Dial  Press,  1931. 

James,  Talk  to  Teachers  on  Psychology.  Holt,  1914. 

Jew'ett,  Control  of  Body  and  Mind.  Ginn. 

'Loeb,  Forced  Movements,  Tropisms  and  Animal  Conduct.  Chap,  xviii. 
Lippincott,  1918. 

Watson,  Psychology  from  the  Standpoint  of  a Behaviorist.  Lippincott, 
1924. 

Wells,  Huxley,  and  Wells,  The  Science  of  Life.  Doubleday,  Doran,  1934. 


H.  BIO  — 30 


SURVEY  QUESTIONS 


Why  do  people  have  a longer  expectancy  of  life  today  than  30  years  ago? 
Why  do  some  people  take  a catching  disease  and  others  who  are  exposed 
do  not?  Why  are  people  vaccinated  against  smallpox?  How  are  children 
made  immune  against  diphtheria?  What  are  the  purposes  of  a Medical 
Center,  as  the  Cornell  Medical  Center,  New  York,  shown  here? 


454 


Ewing  Galloway 


PART  V.  MAN’S  INTERRELATIONSHIP  WITH 
OTHER  LIVING  THINGS 

UNIT  XV 

HOW  DOES  MAN  CONTROL  HIS  ENVIRONMENT 
FOR  HEALTH? 

Preview.  The  body  has  been  likened  to  an  engine,  in  that  each 
requires  fuel  and  oxygen  to  work,  produces  wastes,  and  must  have 
irequent  rest  in  order  to  do  efficient  work.  Both  the  machine  and 
body  may  eventually  wear  out.  But  we  do  not  speak  of  a sick 
machine,  although  we  do  speak  of  a sick  person.  What,  then,  is 
health?  It  is  evidently  a state  in  which  the  human  machine 
iruns  efficiently.  It  is  a state  of  well-being,  or  being  well.  A 
person  may  so  abuse  his  body  through  lack  of  sleep,  or  exercise, 
jor  proper  food  that  soon  his  body  will  not  function  properly.  He 
may  poison  his  body  with  alcohol  or  nicotine,  and  injure  some  of 
his  internal  organs  so  that  he  never  recovers  his  former  efficiency. 
He  may  meet  with  an  accident  and  be  crippled,  or  he  may  be 
attacked  by  some  microscopic  foes,  bacteria,  and  suffer  from 
infectious  diseases.  Diseases  caused  by  these  microorganisms 
cause  more  than  half  the  common  ailments  of  young  people. 

We  have  already  learned  something  concerning  the  relation 
of  bacteria  and  other  colorless  plants  to  disease.  It  is  the  purpose 
3f  this  unit  to  show  how  some  animals  play  a part  in  the  cause  and 
bpread  of  disease.  It  is  obvious  that  the  relation  is  twofold. 
Animals  may  be  parasites  in  man,  causing  certain  diseases,  or 
they  may,  acting  as  hosts,  carry  a parasite  for  part  of  their  life 
t histories.  The  malarial  parasite  and  the  hookworm  are  examples 
1 of  the  first  type ; the  mosquito,  which  carries  the  malarial  parasite, 
, I 455 


456  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 

and  the  flea,  which  transmits  bubonic  plague  bacilli,  are  examples 
of  the  second  type. 

It  is  comparatively  recently  that  we  have  discovered  some  of  the 
very  definite  ways  in  which  these  parasites  do  us  harm.  I am  not 
an  old  man,  but  I can  well  remember  how  my  father  used  to  keep 
me  in  at  dusk  as  he  pointed  to  the  mist  rising  from  the  lowlands 
next  the  river  and  said,  “ See  the  malaria  rising  there.’’  We  did 
not  know,  little  more  than  30  years  ago,  that  a certain  kind  of 
mosquito  carried  the  organism  that  causes  malaria  and  that  the 
only  connection  between  the  mist  and  malaria  was  that  those 
low-lying  marshlands  were  alive  with  the  mosquitoes  which  carry 
the  disease  organisms  within  their  bodies. 

In  the  control  of  diseases,  prevention  is  far  more  important  than 
attempts  to  cure.  Experimentation  and  experience  have  taught 
us  that  health  is  closely  associated  with  conditions  in  man’s 
environment.  We  have  learned  to  isolate  the  sick  from  the  well, 
so  that  diseases  may  not  be  communicated.  Many  diseases  have 
been  partially  or  entirely  controlled  through  scientific  investiga- 
tion and  health  education.  Immunity  or  protection  against  dis- 
ease may  be  both  natural  and  acquired.  The  former  is  the  immu- 
nity that  one  has  at  birth  and  stays  with  one  throughout  his  life. 
The  latter  is  acquired  through  the  use  of  antitoxins,  weakened 
living  germs,  dead  germs,  or  extracts  containing  poisons  made  by 
germs,  introduced  into  the  body. 

Doubtless  it  seemed  irksome  and  needless  to  some  of  you  that 
during  an  attack  of  measles  the  doctor  insisted  not  only  that  you 
should  be  isolated  from  the  rest  of  the  young  people  in  the  family 
but  also  that  you  be  kept  in  a darkened  room  for  several  days.  But, 
measles  is  not  an  eye  disease  and  you  may  have  wondered  why 
he  did  this.  If  you  had  been  older  and  wiser,  you  would  have 
realized  that  certain  parasitic  diseases  are  more  feared  for  the 
harm  they  may  do  the  individual  in  later  life  than  what  they 
do  at  the  time.  Doctors  could  tell  you  of  many  cases  where 
measles  or  scarlet  fever  have  left  a trail  of  weakened  body 
organs  which  have  made  people  semi-invalids  and  sent  some 
to  early  graves.  It  pays  to  care  for  oneself  at  the  time  of  an 
illness. 


THE  (JKOWTH  OF  BACTERIA 


457 


Wo  also  hoar  a fiood  doal  nowadays  about  tho  increase  in  the 
lon^tii  of  tho  life  span.  In  ovory  country  except  India  in  which 
vital  statistics  are  available  the  expectation  of  life  is  steadily 
len^theninji;.  In  Mn«:land,  for  example,  in  the  decade  between  1870- 
1880  the  average  expectancy  of  life  for  a child  at  birth  was  42.98 
years.  In  1922  it  was  56.95  years.  In  Massachusetts,  where 
vital  statistics  have  been  kept  for  a longer  period  than  some  other 
states,  in  1855  the  expectancy  of  life  was  39.77  years,  in  1920  it 
was  55.25.  In  the  United  States  (registration  area),  in  1901,  the 
expectancy  of  life  was  49.24  years,  in  1926  it  was  57.74  years, 
and  at  the  present  time  it  is  over  59  years.  Why  is  this  so? 
Principally  because  we  are  gaining  mastery  over  the  diseases 
caused  by  bacteria  and  especially  diseases  of  young  children. 
Dr.  \dncent  of  the  Rockefeller  Foundation  said  recently  that  80 
per  cent  of  the  illnesses  of  man  could  be  avoided  if  people  were 
willing  to  obey  health  laws  and  live  as  well  as  they  know  how. 
Then,  too,  we  are  learning  that  health  is  closely  associated  with 
conditions  in  man’s  environment  and  that  it  pays  from  every  view- 
point to  have  good  sanitation  and  housing.  We  are  learning  to 
quarantine  the  sick,  so  that  diseases  may  not  be  so  easily  com- 
municated as  in  the  past.  And  we  have  built  many  and  vast 
“temples  of  healing”  — hospitals  and  sanitariums,  where  the  sick 
are  brought  back  to  health. 


PROBLEM  I.  HOW  MAY  WE  CONTROL  THE  GROWTH  OF 
BACTERIA? 

I Demonstration  1.  To  show  the  effect  of  temperature  on  the  growth 
of  bacteria. 

Inoculate  with  bacteria  four  tubes  containing  bouillon.  Put  number 
one  in  the  ice  box,  number  two  in  a dark  box  at  a moderate  temperature, 
number  three  in  a box  at  a hot  temperature  (120°  F.  or  over),  and  boil 
inumber  four  for  15  minutes  and  then  place  with  number  two. 

Note  in  which  tube  the  greatest  and  least  amount  of  growth  takes  place. 
Note  the  odor  as  well  as  the  color  of  bouillon. 

Describe  the  effect  of  intense  heat  on  bacteria?  Would  the  sand  of 
a desert  contain  many  bacteria?  The  ice  of  the  polar  regions?  From 
'this  experiment  we  derive  the  very  important  method  of  fighting  bacteria 
jby  means  of  sterilization.  Give  a definition  of  sterilization. 


458  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 


Sterilization.  Bacteria  grow  very  slowly,  if  at  all,  in  the  tem- 
perature of  an  ice  box,  very  rapidly  from  70°  to  98°,  and  much  less 
rapidly  (or  are  killed)  at  a higher  temperature.  Those  bacteria 
which  form  spores  resist  a great  deal  of  heat  and  may  even  be 

boiled  for  some  time  without  injury. 
The  practical  lessons  drawn  from 
these  facts  are  many.  We  boil  our 
drinking  water  if  we  are  uncertain 
of  its  purity ; we  cook  foods  that 
we  believe  might  harbor  bacteria, 
and  thus  keep  them  from  spoiling. 
The  industry  of  canning  is  built 
upon  this  method  of  sterilization. 

Canning.  Canning  is  simply  a 
method  by  which  first  the  bacteria 
in  a substance  are  killed  by  heating 
and  then  the  substance  is  put  into 
vessels  and  covered  so  that  no  more 
Why  and  when  is  a pressure  cooker  used ? bacteria  Can  gain  entrance.  The 

use  of  canned  goods  has  completely 
changed  the  life  of  the  sailor  and  the  soldier,  who  in  former  times 
used  to  suffer  from  various  diseases  caused  by  lack  of  a proper 
balance  of  food. 

Practical  Exercise  1.  What  is  the  “ cold  pack  ” method  of  canning  ? What 
scientific  principles  are  used  in  canning? 

Cold  storage.  Man  has  learned  to  use  cold  to  keep  bacteria 
from  growing  in  foods.  The  refrigerator  at  home  and  cold  storage 
on  a larger  scale  enable  us  to  keep  foods  for  a more  or  less  long 
period.  If  food  is  frozen,  as  in  cold  storage,  it  might  keep  without 
growth  of  bacteria  for  years.  But  frozen  foods  after  thawing  are 
particularly  susceptible  to  the  bacteria  of  decay.  For  that  reason 
products  taken  from  cold  storage  must  be  used  as  soon  as  possible. 

Demonstration  2.  To  determine  the  effect  of  pasteurization  on  the 
keeping  quality  of  milk. 

Place  half  of  the  milk  in  a sterilized  jar,  cover,  and  leave  in  a warm 
place  for  24  to  48  hours. 

Place  the  remainder  of  the  milk  in  another  jar,  cover,  and  put  it 
in  the  double  boiler  or  pasteurizing  apparatus.  Keep  the  hot  water 


PASTE  UK  I Z AT  ION 


459 


surrounding:  the  jar  from  160°  to  180°  F.  for  al)out  30  minutes.  This 
is  known  as  pasteurization.  Afterwards  treat  exactly  as  you  did  the 
first  jar  of  milk. 

Wliat  is  the  odor  of  milk  in  each  jar  after  24  and  48  hours?  What 
is  the  taste  of  the  milk  in  each  jar  after  24  and  48  hours? 

Wliat  are  found  in  milk  that  cause  it  to  sour?  How  do  you  know? 
Wliat  is  the  use  of  pasteurization? 

Pasteurization.  Milk  is  one  of  the  most  important  food  sup- 
plies of  mankind.  It  is  also  one  of  the  most  difficult  things  to  get 
in  good  condition.  This  is  due  in  part  to  the  fact  that  milk  is 
often  produced  at  long  distances  from  the  place  where  it  is  used 
and  must  be  brought  first  from  farms  to  the  railroads,  then  shipped 
by  train,  taken  to  the  milk  supply  depot,  bottled,  and  again  taken 
by  delivery  wagons  to  the  consumers.  During  each  successive 
handling  and  exposure  to  the  air  the  milk  receives  more  bacteria. 
When  we  remember  that  much  of  the  milk  used  in  San  Francisco, 
St.  Louis,  Chicago,  New  York,  and  other  large  cities  is  from  twelve 
to  thirty-six  hours  old  before  it  reaches  the  consumer,  and  when 
we  realize  that  bacteria  grow  very  rapidly  in  milk,  we  see  the  need  of 
finding  some  way  to  protect  the  supply  so  as  to  make  it  safe,  par- 
ticularly for  babies  and  young  children.  This  is  done  by  pasteuri- 
zation, a method  named  after  the  French  bacteriologist,  Louis 
Pasteur. 

Preservatives.  A few  substances  check  the  development  of 
bacteria  and  in  this  way  preserve  the  food.  Preservatives  are  of 
two  kinds,  those  harmless  to  man  and  those  that  are  poisonous. 
Of  the  former,  salt  and  sugar  are  examples ; of  the  latter,  formalde- 
hyde and  possibly  benzoic  acid. 

Sugar.  We  have  noted  the  use  of  sugar  in  canning.  Small 
amounts  of  sugar  are  readily  attacked  by  yeasts,  molds,  and 
bacteria,  but  a 40  or  50  per  cent  solution  will  effectually  prevent 
such  growths.  Preserves  are  fruits  boiled  in  about  their  own 
weight  of  sugar.  Condensed  milk  is  preserved  partly  by  the  sugar 
■added  to  it ; so  are  candied  fruits. 

Salt.  Salt  has  been  used  for  centuries  to  keep  foods.  Meats 
|are  smoked,  dried,  and  salted ; some  are  put  down  in  strong  salt 
iSolutions.  Fish,  especially  cod  and  herring,  are  dried  and  salted. 
I'The  keeping  of  butter  is  due  to  the  salt  mixed  with  it.  Vinegar 


460  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 


is  another  preservative.  It,  like  salt,  changes  the  flavor  of  mate- 
rials kept  in  it  and  so  cannot  come  into  wide  use.  Spices  are  also 
all  used  as  preservatives. 

Harmful  preservatives.  Certain  chemicals  and  drugs,  used  as 
preservatives,  seem  to  be  on  the  border  line  of  harmfulness.  Such 
are  benzoic  acid,  borax,  and  boracic  acid.  These  chemicals  may 
be  harmless  in  small  quantities,  but  unfortunately  in  canned 
goods  we  do  not  always  know  the  amount  used ; also,  as  a rule, 
food  that  needs  such  a preservative  is  of  bad  quality  in  the  first 
place.  The  Pure  Food  Law  makes  it  illegal  to  use  any  of  these 
preservatives  in  food  (excepting  very  small  amounts  of  benzoic 
acid).  Food  which  contains  this  preservative  must  be  so  labeled 
and  should  not  be  given  to  children  or  people  with  weak  digestion. 
Unfortunately,  people  do  not  always  read  the  labels,  and  thus  the 
Pure  Food  Law  is  ineffective  in  its  working. 

Demonstration  3.  To  determine  the  most  effective  disinfectants. 

Inoculate  test  tubes  containing  bouillon  with  germs  from  a Petri  dish 
culture.  Number  and  label  the  tubes.  Expose  all  tubes,  unplugged, 
to  air. 


To  tube  one  add 
two  add 
three  add 
four  add 
five  add 
six  add 
seven  add 
eight  add 
nine  add 
ten  add 
eleven  add 
twelve  add 


1 drop  formalin. 

5 drops  formalin. 

1 drop  lysol. 

3 drops  lysol. 

1 drop  iodine. 

5 drops  iodine. 

4 drops  carbolic  acid. 

10  drops  carbolic  acid. 

1 drop  bichloride  mercury  solution. 

5 drops  bichloride  mercury  solution. 
5 drops  mercurochrome. 

15  drops  mercurochrome. 


Tabulate  daily,  for  a week  or  more,  the  results  for  the  contents  of  each 
tube  on  a table. 

Which  of  the  above  is  the  best  disinfectant?  Why  do  you  answer 
as  you  do?  (Remember  that  according  to  definition  an  antiseptic  may 
retard  the  growth  of  bacteria  but  will  not  of  necessity  kill  them;  a 
germicide  destroys  all  bacteria  if  used  properly;  while  a disinfectant 
is  a solution  used  to  kill  disease  germs,  usually  in  the  excreta  of  sick 
people.) 

Practical  Exercise  2.  Using  the  data  from  the  preceding  demonstration, 
classify  the  materials  used,  as  antiseptics,  germicides,  or  disinfectants.  Give 
a reason  for  each. 


BACTEIUAL  DISEASES 


461 


Disinfection.  Frequently  it  becomes  necessary  to  destroy 
bacteria  witli  chemicals.  This  process  is  called  disinfection. 
Although  sunlight,  dry  heat,  steam,  and  electricity  kill  germs,  we 
commonly  apply  the  term  “disinfectant”  to  such  substances  as 
iodine,  mercurochrome,  potassium  permanganate,  chloride  of  lime, 
carbolic  acid,  formaldehyde,  lysol,  and  bichloride  of  mercury.  Of 
these,  the  last  named  is  one  of  the  most  powerful  as  well  as  the 
most  dangerous  disinfectant  to  use.  As  it  attacks  metal,  it  should 
not  be  used  in  a metal  pail  or  dish.  It  is  commonly  put  up  in 
tablets  which  are  mixed  to  form  a 1 to  1000  solution.  Care 
must  be  taken  of  both  the  tablets  and  the  solution  to  avoid  a 
possible  accidental  poisoning. 

Formaldehyde  in  solution,  called  formalin,  is  used  as  a disin- 
fectant. When  vaporized,  it  sets  free  an  intensely  pungent  gas. 
Carbolic  acid  is  an  excellent  disinfectant  although  it  will  not 
kill  spores  of  bacteria.  If  used  in  a solution  of  about  1 part  to  25 
of  water,  it  will  not  burn  the  skin.  It  is  of  particular  value  in 
disinfecting  skin  wounds.  Lysol  is  another  excellent  disinfectant, 
because  it  can  be  used  with  soap.  Iodine  is  often  used  as  a skin 
disinfectant  and  in  open  wounds.  One  of  the  newest  germicides 
is  mercurochrome.  It  is  particularly  valuable  for  wounds  and 
skin  bruises  in  which  bacteria  might  thrive. 

Self-Testing  Exercise 

(1)  kills  bacteria.  Canning  makes  use  of  the  principle 

of (2).  Pasteurization  of  milk  is  performed  best  by  heating 

for  (3)  minutes  to  a temperature  of  from  (4)  to 

(o)  F.  Harmless  preservatives  are (6), (7), 

(8),  and (9).  Antiseptics  are  used  to (10) 

the (11)  of (12).  Disinfectants  are  used  to 

(13) (14).  A germicide (15)  all (16). 

PROBLEM  II.  HOW  DO  BACTERIA  CAUSE  DISEASE? 

Bacterial  diseases.  Bacteria  cause  many  diseases  in  man.  They 
accomplish  this  by  becoming  parasites  in  the  human  body.  Mil- 
lions upon  millions  of  bacteria  exist  in  the  human  body  at  all  times 
— in  the  mouth,  on  the  teeth,  and  especially  in  the  lower  part  of 


462  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 


the  food  tube.  Some  in  the  food  tube  are  believed  to  be  useful, 
some  harmless,  and  some  harmful;  others  in  the  mouth  cause 
decay  of  the  teeth,  while  a few  species  may  cause  disease.  Such 

disease-causing  bacteria  are 
called  pathogenic. 

It  is  known  that  bac- 
teria, like  other  living 
things,  take  in  food,  form 
organic  wastes  within  their 
own  bodies,  and  give  off 
some  of  them.  These 
wastes,  called  toxins,  are 
poisonous  to  the  host  on 
which  the  bacteria  live, 
and  cause  the  symptoms 
of  certain  diseases.  Each 
species  of  bacteria  forms 
its  own  specific  toxin,  and 
this  has  a specific  action 
on  the  body,  causing  the 
symptoms  of  a specific  disease.  As  bacteria  can  multiply  rapidly 
in  the  body,  they  may  become  very  numerous  before  the  body 
defenses  gain  control  of  the  situation.  When  the  bacteria  die,  as 
they  may  in  great  numbers  during  the  progress  of  the  disease, 
their  bodies  break  down,  and  the  released  protoplasmic  constit- 
uents, particularly  the  proteins,  separate  from  each  other  and 
split  into  smaller  and  smaller  molecular  groups,  as  do  the  proteins 
when  changed  to  amino  acids  during  digestion.  These  split  pro- 
teins, as  they  are  called,  are  extremely  poisonous  to  the  body 
tissues  and  act  as  toxins  in  the  body. 

Some  bacteria  break  down  the  body  tissues,  besides  producing 
toxins.  They  may  destroy  the  intestinal  lining,  or  destroy  the 
blood  corpuscles,  break  down  tissues  in  wounds,  or,  as  in  tubercu- 
losis, destroy  areas  of  living  tissue.  In  such  ways  they  may  cause 
specific  symptoms  of  disease. 

It  was  estimated  not  many  years  ago  that  bacterial  diseases 
caused  annually  almost  50  per  cent  of  the  deaths  of  the  human 


A microphotograph  of  a Petri  dish  containing  a pure 
culture  of  bacteria  that  cause  cholera. 


now  WE  GET  DISEASES 


463 


race.  A vory  large  proportion  of  these  diseases  might  have  been 
prevented  if  pt'ople  were  educated  sufficiently  to  take  the  proper 
precautions  to  prevent  the  spreading  of  bacteria.  Such  precau- 
tions might  have  savctl  the  lives  of  some  3,000,000  people  yearly 
in  I'lurope  and  America,  'ruberculosis,  typhoid  fever,  bubonic 
plague,  diphtheria,  pneumonia,  blood  poisoning,  and  a score  of 
other  diseases  ought  not  to  exist.  But  within  the  last  decade, 
tlue  to  the  sacrifices  and  discoveries  of  men  in  medical  science,  the 
control  of  a number  of  bacterial  diseases  has  been  made  possible. 
It  is  estimated,  for  example,  that  with  the  cooperation  of  the  people, 

: diphtheria  might  have  been  stamped  out  in  New  York  state  by  the 
; end  of  the  3Tar  1930.  That  this  has  not  happened  is  due  certainly 
i to  the  number  of  uninformed  people  who  will  not  or  do  not  know 
I how  to  cooperate  with  the  medical  authorities.  A large  amount 
; of  the  present  misery  of  this  world  might  be  prevented,  and  this 
earth  made  cleaner,  better,  and  safer,  by  the  cooperation  of  young 
people  in  carrying  out  and  enforcing  health  regulations. 

Practical  Exercise  3.  Make  a table  to  show  all  the  ways  in  which  bacteria 
may  cause  disease  and  give  an  example  under  each  heading. 

Self-Testing  Exercise 

Bacteria  cause  almost (1) (2) (3)  of  the 

(4)  of  the  human  race.  Many  of  these  might  have  been 

(5)  if  people  would  (6)  with  the  medical  authori- 

; ties.  Bacteria  cause  disease  either  by  forming (7)  and  releasing 

(8),  or  by (9)  on  the (10),  thus  breaking 

■ them  down. 

PROBLEM  III.  HOW  DO  WE  GET  BACTERIAL  DISEASES? 

, How  we  get  diseases.  Bacteria  causing  infectious  diseases  enter 

I the  body  either  by  the  mouth,  nose,  or  other  body  openings,  or 
through  a break  in  the  skin.  They  may  be  carried  by  means  of 
air,  food,  or  water,  but  are  more  often  transmitted  directly  from 
the  person  who  has  the  disease  to  a well  person.  They  may  be 
acquired  through  personal  contact,  as  kissing;  in  a spray  of 
tiny  droplets  which  are  expelled  into  the  air  as  a person  talks; 


464  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 


by  handling  or  using  articles,  such  as  towels,  handkerchiefs,  cups, 
or  dishes  used  by  sick  persons;  or  by  drinking  or  eating  foods 
which  have  received  some  of  the  germs. 

Practical  Exercise  4.  Make  a table  to  show  all  the  ways  in  which  bacteria 
gain  entrance  to  the  body  and  name  a disease  which  gets  into  the  body  under 
each  heading. 

Project.  To  make  a curve  showing  decrease  of  tuberculosis  in  your 
own  state.  (Use  State  Board  of  Health  or  Public  Health  Service 
Reports  for  this  and  following  projects.) 

Tuberculosis.  One  of  the  diseases  responsible  for  the  greatest 
number  of  deaths,  perhaps  one  tenth  of  the  total  on  the  earth,  is 
tuberculosis.  Fisher  estimates  that  tuberculosis  has  cost  this 
country  between  $500,000,000  and  $1,000,000,000  a year,  by  its 
toll  of  death,  loss  of  work,  maintenance  of  hospitals,  sanitariums, 
etc.  But  this  disease  is  slowly  but  surely  being  overcome.  It  is 
believed  that  within  perhaps  fifty  years,  with  the  aid  of  good  laws 


The  number  of  deaths  per  100,000  from  tuberculosis  has  been  steadily  decreasing  each  year. 
If  this  rate  continues  there  will  be  very  few  deaths  in  1940  from  this  disease. 


and  sanitary  living,  it  might  become  almost  extinct.  In  1900,  the 
death  rate  in  the  United  States  was  195.2  for  each  100,000  inhab- 
itants, in  1934  the  death  rate  in  the  same  area  was  less  than  60  per 
100,000.  In  other  words,  according  to  Dr.  Louis  J.  Dublin,  there 


TIBKKCULOSIS 


4G5 


are  about  130,000  fewer  persons  dyin^  from  tuberculosis  each  year 
ill  the  United  States  than  would  have  died  if  the  tuberculosis 
death  rate  for  1900  still  held  for  this  area. 

Tuberculosis  is  caused  by  the  growth  of  bacteria,  called  the 
tubercle  bacilli,  within  the  lungs  or  other  tissues  of  the  human  body. 
In  tlie  lungs  they  form  little  tubercles  full  of  germs,  which  close  up 
the  delicate  air  passages,  while  in  other  tissues  they  may  cause 
hip-joint  disease,  scrofula,  lupus,  and  other  diseases,  depending 
on  the  part  of  the  body  they  attack.  Tuberculosis  may  be  con- 
tracted by  taking  bacteria  from  people  who  have  the  disease,  or 
by  drinking  milk  from  tubercular  cows,  for  the  germ  that  affects 
cattle  causes  some  of  the  tuberculosis  in  children.  Dr.  William 
H.  Park,  a noted  authority  on  bovine  (cow)  tuberculosis,  states 
that  in  a large  number  of  cases  investigated  by  him  57  per  cent  of 
abdominal  tuberculosis  in  very  young  children  and  47  per  cent  of 
such  tuberculosis  in  children  under  five  years  of  age  were  of  the 
bovine  type.  Fortunately,  the  germs  of  bovine  tuberculosis  can 
be  killed  by  pasteurization  of  milk  of  doubtful  purity. 

Practical  Exercise  6.  Name  some  ways  in  which  tuberculosis  might  be 
passed  from  one  person  to  another. 

Most  of  us  probably  take  into  our  lungs  at  one  time  or  another 
bacteria  causing  tuberculosis.  Yet  the  bacteria  seem  able  to  gain 
a foothold  only  under  certain  conditions.  It  is  only  when  the 
tissues  are  in  a wornout  condition,  when  we  are  “ run  down,’’  as 
we  say,  that  the  parasite  may  obtain  a foothold  in  the  lungs  or 
other  organs.  The  disease  may  be  arrested,  and  a permanent 
cure  can  be  made  by  a life  in  which  the  patient  takes  complete  rest 
for  several  weeks  or  months,  together  with  as  much  fresh  air  and 
sunlight  as  possible  and  a diet  of  plenty  of  nourishing  foods. 
The  object  of  this  kind  of  life  is  to  build  up  the  body  resistance, 
so  that  the  germs  are  made  harmless. 

Tuberculosis  is  a serious  disease  to  combat,  because  of  the  con- 
ditions which  help  to  cause  it.  Contrary  to  common  belief,  it  is 
not  inherited  ; but  unfortunately  in  families  where  there  are  tuber- 
cular persons,  it  is  difficult  to  prevent  giving  the  germs  to  people 
living  with  them,  especially  if  they  live  in  small  crowded  homes 


466  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 


with  little  ventilation.  Children  of  tubercular  parents  are  often 
handicapped  by  a weak  constitution  and  are  therefore  very  sus- 
ceptible to  the  disease. 

Practical  Exercise  6.  Tuberculosis  is  said  to  be  a social  disease.  Explain 
this  statement. 

Project.  To  determine  the  seasonal  variation  in  the  number  of  cases 
of  diphtheria  in  your  state. 

Diphtheria.  This  disease  is  caused  by  bacteria  which  grow 
rapidly  in  the  throat  and  form  a false  membrane  there.  But 
the  most  serious  results  come  from  the  toxin,  thrown  off  by  the 
bacteria,  which  get  into  the  blood  and  not  only  cause  suffering  1 
and  fever  but  also  may  have  very  serious  after-effects  on  various  I 
body  organs.  As  diphtheria  is  a throat  disease,  it  may  easily  be  I 
conveyed  from  one  person  to  another  by  the  droplet  method  of 
infection. 

Other  diseases  spread  through  mouth  spray.  Influenza,  pneu- 
monia, whooping  cough,  and  certain  kinds  of  colds,  and  many 
of  the  so-called  children’s  diseases,  are  caused  by  bacteria  or  other 
microscopic  organisms.  Nearly  all  are  spread  by  the  “ droplet  ’ 
method  ” of  infection.  In  our  army  during  the  World  War,  ! 
influenza,  coupled  with  pneumonia,  was  responsible  for  fourteen  * 
times  as  many  deaths  as  were  caused  by  shells  and  poison  gases. 
This  disease  is  periodically  epidemic,  the  last  bad  outbreak  pre- 
vious to  this  being  in  1889.  Influenza  is  apparently  spread  largely 
by  human  carriers,  or  people  who  have  a slight  attack  but  are 
capable  of  passing  the  disease  on  in  its  most  serious  form. 

Project.  Use  the  report  on  infectious  diseases,  United  States  Public 
Health  Reports,  or  your  State  Department  of  Health  bulletin  to  deter- 
mine the  decrease  in  typhoid  in  your  state  for  the  past  ten  years. 

Typhoid  fever.  Typhoid  fever,  not  many  years  ago,  was  one 
of  the  most  common  germ  diseases  in  this  country  and  Europe. 
Today  it  is  one  of  the  less  important  of  the  communicable  diseases. 
Typhoid  bacilli  multiply  very  rapidly  in  the  intestine  and  are 
passed  off  from  the  body  with  the  excreta  from  the  food  tube. 

If  these  bacilli  get  into  the  water  supply  of  a town,  an  epidemic  of 
typhoid  will  result.  In  one  early  epidemic  in  this  country  there 
were  5000  cases  of  typhoid  in  a city  of  only  30,000  inhabitants. 


WATEK  SUPPLIES 


467 


Chicago  and  otlun-  cities  which  once  obtained  tlieir  drinking  water 
from  lakes  jjolhited  with  sewage  alwa3'-s  liad  a high  death  rate  from 
typhoitl.  In  the  \Tar  1891,  the  death  rate  from  typhoid  was  over 
170  i)er  100,000  inhabitants,  dkxlay  it  is  less  than  3 per  100,000. 

Water  supplies.  pure  water  we  mean  water  free  from  all 
organic  impurities,  including  disease  germs.  Water  from  springs 
and  deep  driven  wells  is  the 
safest  water ; that  from  large 
reservoirs  next  best ; while 
water  that  has  drainage  in  it, 
river  water  for  example,  is  very 
.unsafe  unless  properly  treated 
jwith  chemicals, 
i The  water  from  deep  wells 
or  springs,  if  properlj’-  pro- 
tected, will  contain  few  bac- 
teria. Water  taken  from 
shallow,  unprotected  wells  may 
have  from  100  to  20,000  bac- 
teria per  cubic  centimeter. 

Water  taken  from  protected 
streams  into  which  no  sewage  flows  usually  has  few  bacteria  (from 
50  to  300  bacteria  per  cubic  centimeter),  and  these  are  destroyed 
if  exposed  to  the  action  of  the  sun  and  the  constant  aeration 
(mixing  with  oxj^gen)  which  the  surface  water  receives  in  a large 
lake  or  reservoir.  But  water  taken  from  a river  into  which  the 
sewage  of  towns  and  cities  flows  may  contain  many  hundreds  of 
thousands  of  bacteria  to  the  cubic  centimeter,  and  must  be  filtered 
and  chlorinated  before  it  is  fit  for  use.  The  water  is  passed 
[through  settling  basins  and  sand  filters  which  remove  about  98 
per  cent  of  the  germs.  Final  treatment  with  liquid  chlorine  in 
7ery  small  amounts  kills  the  remaining  bacteria.  A few  fortunate 
fities,  such  as  Los  Angeles  and  New  York,  bring  their  water 
supplies  from  protected  areas  far  up  in  the  mountains,  but  even  here 
the  water  is  usually  chlorinated. 

I We  have  already  seen  the  danger  of  typhoid  fever  from  unpro- 
tected water  supplies.  Fortunately  most  large  cities  now  protect 


Notice  the  difference  between  the  case  rate 
per  100,000  in  1910  and  1930.  Give  at  least 
three  reasons  for  this  decrease. 


468  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 


their  supplies,  either  by  filtration  plus  chlorination  or,  as  in  the 
case  of  Chicago,  by  means  of  a drainage  canal  which  carries  off 
the  sewage  from  lake  water  before  it  is  chlorinated. 


Practical  Exercise  7.  What  methods  of  protection  of  water  supplies  are 
employed  by  your  community?  Visit  the  city  water  supply  and  report  on  its 
conditions.  Ask  your  teacher  to  give  you  references  for  Glenn’s  reports  on 
the  water  systems  of  certain  cities  in  this  country.  Report  on  some  one 
system  and  compare  it  with  your  own  city  supply. 


®"'@  © © © @ @ 


Milk  and  disease.  Another  source  of  infection  is  milk.  Fre- 
quently epidemics  used  to  occur  which  were  confined  to  users  of 

®milk  from  a certain 

dairy.  Upon  inves- 
tigation it  would  be 
found  that  a case  of 
typhoid  had  oc- 
curred on  the  farm 
where  the  milk  came 
from,  that  the  germs 
had  washed  into  the 
well,  and  that  this 
water  was  used  to 
wash  the  milk  cans. 


\ , 

\ 

\ 

/ 

/ 

^ / 

\ .f. 

'1 

, / 
? / 

X 

HjyctePark  Dorchester  "Kilton, 

The  small  dots  in  the  diagram  show  the  number  of  cases  of 
diphtheria  which  occurred  in  three  towns,  among  people  who 
received  milk  from  dairy  X.  What  may  have  been  the  reason 
for  the  cases  of  diphtheria  which  occurred  in  H of  Milton  ? 


Once  in  the  milk,  the  bacteria  multiplied  rapidly,  so  that  the 
milkman  gave  out  cultures  of  typhoid  in  his  milk  bottles. 

Most  large  cities  now  send  inspectors  to  the  farms  from  which 
milk  is  supplied.  These  men  examine  and  score  the  health  of  the 
cows,  the  cleanliness  of  their  surroundings,  the  health  of  the 
workers,  the  care  and  construction  of  the  utensils,  and  the  methods 
of  handling  the  milk.  Farms  that  do  not  attain  certain  standards 
of  cleanliness  are  not  allowed  to  have  their  milk  become  part  of  the 
city  supply. 

Care  of  a city  milk  supply.  Besides  caring  for  milk  in  its  pro- 
duction on  the  farm,  proper  transportation  facilities  must  be 
provided.  Some  of  the  milk  used  in  Boston,  Chicago,  and  New 
York  is  forty-eight  hours  old  before  it  reaches  the  consumer.  Milk 
used  in  the  last-named  city  is  said  to  come  from  eight  states  and 
from  Canada.  During  shipment  it  is  kept  in  refrigerating  cars, 
and  during  transit  to  customers  it  is  iced. 


CAKUIKRS  AND  TYPHOID 


469 


Practical  Exercise  8.  W’lint  regulations  are  there  in  your  community  con- 
ceruiiig  tlu'  farms  from  whicli  milk  is  supi)liecl?  Coiicerniiig  the  sale  of  milk? 

All  luit  the  highest  grade  milk  should  be  pasteurized.  Why? 

Milk  .slu)ul(l  bo  bottled  by  inachincry,  if  possible,  to  insure  no 
personal  contact  ; it  should  be  kej)t  in  clean,  cool  places;  and  no 
milk  should  be  sold  by  dipping  it  directly  from  cans.  Why  is  this 
method  of  dispensing  milk  likely  to  contaminate  it? 


Project.  Write  or  give  a report  in  class  on  a visit  to  a dairy. 

Project.  Investigate  the  sale  of  milk  in  your  school  and  vicinity  and 
report  your  findings  to  the  class. 

Carriers  and  typhoid.  A third  and  more  serious  method  of 
spreading  typhoid  fever  comes  through  “carriers.”  These  are 
people  who  have 
had  typhoid  fever 
ind  who  till  harbor 
the  living  germs  in 
their  bodies.  Sev- 
eral epidemics  of 
typhoid  have  been 
traced  to  carriers 
w h o w o r k e d in 
dairies  or  on  farms 
which  produced 
milk.  The  well- 
known  “Typhoid 
Alary”  through  her 
careless  habits  gave 
typhoid  to  people  for 
whom  she  cooked. 

Still  another 
method  of  spreading 
typhoid  is  through  carelessness  in  preparation  of  uncooked  vege- 
tables. Several  epidemics  of  typhoid  fever  have  been  traced  to  raw 
oysters  which  were  “fattened”  for  the  market  in  water  that  was 
contaminated  with  sewage.  This  practice  has  been  discontinued. 

Laboratory  Exercise.  Plot  curves  from  board  of  health  tables  to  show 
the  mortality  from  a certain  disease  during  various  seasons  of  the  year. 

H.  BIO  — 31 


The  consumer  is  in  danger  of  having  his  food  and  dishes 
contaminated  by  the  unclean  hands  of  a ivorker.  A line  drav?n 
from  the  center  circle  to  any  of  the  persons,  material,  or 
utensils  will  mean  eventual  danger  to  the  consumer. 


470  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 


Practical  Exercise  9.  Show  how  typhoid  fever  might  be  eradicated  in  this 
country.  Think  back  to  your  general  science  work  and  show  the  different 
methods  by  which  people  can  be  protected  from  this  disease. 

Septic  sore  throat.  This  disease  is  characterized  by  severe  sore 
throat  and  fever,  and  is  often  followed  by  heart  or  kidney  trouble. 
This  is  another  disease  carried  by  milk,  and  is  caused  by  a strep- 
tococcus. The  disease  is  probably  given  to  cows  by  human 
beings  who  may  be  carriers.  The  cow  may  harbor  the  germ  for 
several  weeks  and  persons  drinking  unpasteurized  milk  from  such  a 
cow  may  take  the  disease.  Several  severe  epidemics  have  been 
recorded,  in  Baltimore,  Chicago,  Lee,  Massachusetts,  in  1928,  and 
other  cities,  but  the  worst  was  an  outbreak  of  2000  cases  in 
Boston,  in  1911. 

Tetanus.  The  bacillus  causing  tetanus  is  another  toxin-forming 
germ.  It  lives  in  dust  and  dirt  and  is  often  found  on  the  skin. 
It  enters  the  body  through  cuts  or  bruises.  It  seems  to  thrive 
best  in  less  oxygen  than  is  found  in  the  air.  It  is  therefore  im- 
portant not  to  use  adhesive  tape  over  wounds  until  they  have 
been  treated  with  antiseptics.  The  low  death  rate  from  tetanus  in 
the  World  War  was  due  largely  to  the  fact  that  wounds  were  washed 
with  powerful  antiseptics  and  anti-tetanus  serum  was  administered 
as  soon  as  possible  after  the  wounded  were  reached. 

Other  diseases  caused  by  bacteria.  A group  of  bacteria  which 
cause  pneumonia,  erysipelas,  and  other  common  infections  besides 
septic  sore  throat  are  the  so-called  streptococci.  Other  coccus 
forms,  the  staphylococci  (stM-i-l6-k6k'si),  are  responsible  for  boils 
and  abscesses.  A micrococcus  causes  one  of  the  pernicious  vene- 
real diseases,  which  produces  terrible  results.  Other  forms  of 
micrococci  probably  cause  cerebro-spinal  meningitis  (men-in-jl'tis), 
formerly  a fatal  disease  of  the  spinal  cord  but  now  often  treated 
successfully  with  serums.  Anthrax  or  splenic  fever,  Malta  fever, 
whooping  cough,  bubonic  plague,  gas  gangrene,  one  form  of 
dysentery,  cholera,  and  many  other  diseases  are  definitely  associ- 
ated with  specific  forms  of  bacteria.  In  all  of  these  diseases, 
contact  with  the  person  ill  with  the  disease  or,  in  some  cases, 
with  a carrier  of  the  disease,  is  usually  sufficient  to  cause  its 
spread. 


REASONS  FOR  QUARANTINE  471 

Practical  Exercise  9.  Make  a table  with  the  following  headings  and  fill  out 
for  each  disease  mentioned  in  this  unit. 


Disease 

Caused  by 

Method  of  Transfer 

Prevention 

Self-Testing  Exercise 

Raw  milk  is  safe  if  it  comes  from  (1)  (2)  cows 

and  has  careful  (3).  Infectious  diseases  are  usually  trans- 
mitted through (4) (5).  Bacteria  usually  enter  the 

body  through (6)  (7)  or  breaks  in  the (8). 

(9)  is  gradually  being  conquered  by  proper  treatment. 

Typhoid  may  be  prevented  through  protection  of (10)  and 

(11)  supplies,  and  detection  and  isolation  of (12). 

PROBLEM  IV.  WHY  IS  QUARANTINE  NECESSARY? 

Reasons  for  quarantine.  We  all  know  that  when  a person  has 
a communicable  disease,  the  doctor,  acting  under  orders  of  the 
local  board  of  health,  puts  the  patient  and  sometimes  the  entire 
family  under  quarantine.  Since  this  often  seems  needless,  espe- 
icially  if  one  has  a mild  attack  of  the  disease,  we  ought  to  know  the 
reason  underlying  such  action.  Communicable  diseases  become 
epidemic  if  they  are  not  controlled.  Measles,  for  example,  is  a dis- 
ease easily  passed  from  one  person  to  another.  It  is  especially 
communicable  among  children,  one  of  whom  may  have  a very  light 
I case  but  may  pass  the  germs  to  some  one  else  who  will  have  a 
• severe  attack  of  it.  Scarlet  fever,  colds,  and  influenza  are  other 
i|  diseases  which  are  readily  spread  and  may  become  epidemic, 
i Since  this  is  true,  the  reason  for  the  isolation  of  the  patient 
I becomes  evident.  And  every  one  should  be  unselfish  enough  to 
I see  this  and  to  cooperate  with  the  health  authorities  for  the  com- 
> mon  good  of  the  community. 

[ I The  following  table  shows  important  facts  about  some  common 
i diseases. 


472  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 


Disease 

Means  op  Communication 

Incubation  Period  (Approximate)  and 
Early  Symptoms 

Chicken  pox  . . 

Discharges  from  nose 
or  throat  of  a pa- 
tient 

21  days.  Rash. 

Diphtheria  . . . 

Nose  or  throat  dis- 
charges ; sometimes 
infected  milk 

2 to  5 days.  Begins  like  a cold. 

Measles  .... 

Nose  or  throat  dis- 
charges 

9 to  11  days.  Begins  like  a cold. 
Reddish  spots  appear  on  the 
third  day. 

German  measles  . 

Nose  or  throat  dis- 
charges 

Unknown,  though  longer  than 
measles. 

Mumps  .... 

Nose  or  throat  dis- 
charges 

Unknown,  probably  about  2 
weeks.  Pain  in  salivary  glands. 

Infantile  paralysis 

Nose,  throat,  or  bowel 
discharges  of  pa- 
tient or  carrier 

Not  known.  Fever,  headache, 
vomiting,  weakness  of  one  or 
more  muscle  groups. 

Scarlet  fever  . . 

Discharges  from  nose, 
mouth,  ears.  In- 
fected milk 

2 to  7 days.  Begins  like  a cold ; 
in  24  hours  evenly  diffused 
bright  red  spots  under  skin. 

Smallpox  . . . 

All  discharges  of  a 
patient ; particles 
of  skin  and  scabs 

About  12  days.  Fever  and  back- 
ache. Red  shotlike  pimples  on 
face  and  hands,  become  blisters. 

Septic  sore  throat 

Discharges  from  nose 
or  mouth 

Varies  with  resistance.  Short. 

Whooping  cough  . 

Discharges  from  nose 
or  mouth 

14  days.  Cough  worse  at  night. 
“Whooping  ” develops  in  about 
two  weeks. 

Incubation  period  of  disease.  Quarantine  regulations  often 
affect  not  only  the  person  having  the  disease,  but  also  all  those  of 
the  family  who  were  exposed  ” ; that  is,  who  came  in  personal 
contact  with  the  person  who  has  the  disease.  If,  for  example,  you 
have  measles,  the  doctor  will  keep  at  home  the  other  children  in 
the  family  who  have  not  had  the  disease.  The  period  of  quaran- 
tine for  measles  lasts  in  most  states  fifteen  days.  Why  this  pre- 
caution? 

Consider  what  we  already  know  of  germs.  We  found  it  took  a 
certain  length  of  time  for  colonies  of  germs  to  appear  in  a culture 
medium  after  exposure.  In  the  same  way  it  takes  a certain 
amount  of  time  in  the  case  of  a disease  for  the  germs  to  become 
so  abundant  in  the  body  that  they  give  off  sufl&cient  toxins  to 


IXCrBATION  PEIUOl)  OF  DISEASE 


473 


cause  tlie  symptoms  of  the  disease.  This  period,  between  the 
time  when  tlie  ^erms  enter  the  body  and  the  time  the  symptoms  of 
disease  appear,  is  called  the  incubation  period.  Since  this  period 


Two  days  after  her  party  Janet  developed  measles.  Since  she  was  not  ill  with  the  disease 
at  the  time  of  the  party,  how  do  you  account  for  the  other  cases  which  developed  ? 


varies  for  different  diseases,  the  period  of  quarantine  also  varies, 
as  seven  days  for  scarlet  fever,  fourteen  days  for  whooping  cough, 
twenty-one  days  for  chicken  pox.  If,  after  one  has  been  exposed 
to  an  infectious  disease,  no  symptoms  develop  within  the  time  of 
the  recognized  incubation  period,  it  is  safe  to  assume  that  he  will 
not  get  the  disease. 

Practical  Exercise  10.  Study  the  diagram.  How  have  similar  cases  worked 
out  in  your  own  school?  Diagram  them. 

Why  is  it  necessary  for  protection  of  others  to  know  the  incubation  period  of 
a disease? 

Practical  Exercise  11.  Why  should  persons  ill  with  an  infectious  disease 
be  isolated  until  they  are  well?  What  methods  has  the  Board  of  Health  for 
warning  strangers  of  the  presence  of  the  disease  in  a home  ? 

What  is  the  reason  for  quarantine  and  by  what  should  it  be  followed  to  be 
effective?  Why  is  there  a quarantine  station  at  the  entrance  of  San  Francisco, 
Boston,  or  New  York  harbor?  Why  is  it  of  particular  value  there? 

Practical  Exercise  12.  What  do  we  mean  by  disinfection?  What  are  the 
rules  of  your  local  Board  of  Health  in  regard  to  disinfection. 

What  should  be  done  to  the  body,  clothing,  and  hair  of  a person  who  has 
been  ill  with  an  infectious  disease  before  he  is  allowed  to  go  among  well  persons 
again?  Why  is  this  necessary? 

Can  a person  have  the  germs  of  a disease  in  the  body  and  still  not  show 
symptom.s  of  the  disease?  How  might  such  a person  be  a danger  to  others? 


474  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 

Self-Testing  Exercise 

Check  the  correct  statements  for  your  workbook ; 

T.  F.  1.  The  incubation  period  of  a disease  is  the  period  between 
the  time  the  germs  causing  the  disease  enter  the  body  and  the  symp- 
toms of  the  disease  appear. 

T.  F.  2.  All  communicable  diseases  have  the  same  length  incuba- 
tion period. 

T.  F.  3.  Children  who  have  been  exposed  to  a catching  disease 
should  remain  at  home  during  the  incubation  period. 

T.  F.  4.  Communicable  diseases  do  not  become  epidemic. 

T.  F.  5.  Quarantine  means  the  isolation  of  a person  who  has  a 
communicable  disease. 

T.  F.  6.  The  length  of  quarantine  differs  with  different  diseases. 

T.  F.  7.  Epidemics  cannot  be  prevented. 

T.  F.  8.  We  only  catch  a disease  from  people  suffering  from  that 
disease. 

PROBLEM  V.  WHAT  IS  IMMUNITY? 

The  meaning  of  immunity.  It  is  a matter  of  common  knowl- 
edge that  some  persons  in  a family  will  have  a very  light  attack  of 
a communicable  disease,  while  others  may  have  it  severely.  Some 
one  else  may  be  exposed  again  and  again  to  this  same  disease  and 
not  take  it,  because  he  is  immune  to,  or  able  to  resist,  that  particu- 
lar disease,  while  those  who  take  it  are  susceptible  to  its  attack. 
Immunity  against  disease  may  be  individual,  or  it  may  be  racial. 
Negroes,  for  example,  are  very  susceptible  to  measles  and  tuber- 
culosis, but  are  less  susceptible  than  white  people  to  malaria,  yel- 
low fever,  and  smallpox.  There  are  also  great  differences  as  to 
the  degree  of  immunity  from  the  same  disease  in  different  species 
of  animals.  Tuberculosis  of  the  bovine  type  may  occur  in  chil- 
dren as  well  as  in  cattle,  hogs,  and  horses.  The  human  tubercu- 
losis germ  attacks  only  guinea  pigs,  monkeys,  and  man.  Smallpox 
and  cowpox  are  probably  caused  by  different  types  of  the  same 
organism.  Plague  attacks  rats,  ground  squirrels,  mice,  and  guinea 
pigs,  as  well  as  man.  A long  series  of  laboratory  tests  show  that 
most  germs  that  cause  illness  in  man  develop  ordinarily  in  man 


ACQUIRED  IMMUNITY 


475 


[• 


I 


only,  while  a few  diseases,  like  anthrax  and  glanders,  are  primarily 
diseases  of  certain  animals  but  may  attack  man. 

Immunity  may  be  modified  by  external  conditions.  A certain 
amount  of  immunity  is  evidently  natural  to  individuals,  races,  or 
species,  but  there  is  much  variation,  as  we  have  seen,  even  among 
individuals  of  the  same  family.  Resistance  to  disease  also  is 
modified  by  the  condition  of  the  individual  exposed.  Overworked, 
tired,  and  “ run-down  ” persons  are  much  more  likely  to  take 
diseases  than  those  who  are  in  good  physical  trim.  Resistance  to 
disease  may  also  be  weakened  by  the  use  of  drugs  and  alcohol 
as  shown  by  the  susceptibility  of  heavy  drinkers  to  pneumonia. 

Acquired  immunity.  It  has  been  a matter  of  common  knowledge 
for  centuries  that  persons  who  once  have  infectious  diseases  do  not 
usually  have  them 
a second  time.  A 
Greek  historian,  de- 
scribing a visitation 
of  plague  in  Athens, 
more  than  twenty 
centuries  ago,  noted 
that  those  who  had 
plague  and  recovered 
were  safe  from  it 
thereafter.  The 
Chinese,  in  order  to 
make  their  children 
immune  to  smallpox, 
gave  them  the  dis- 
ease in  a mild  form 
by  placing  in  the 
nose  a little  of  the 
pus  from  one  of  the 
eruptions.  It  was  the  chance  statement  of  a dairymaid  in  Eng- 
land when  she  said,  “ I’ve  had  cowpox  and  can’t  take  smallpox,” 
that  led  Edward  Jenner  to  make  his  first  experiments  that  have 
resulted  in  almost  stamping  out  smallpox  through  vaccination. 
And  so  today  when  we  think  of  acquired  immunity  obtained  by 


The  first  vaccination  against  smallpox  by  Dr.  Jenner. 


476  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 


this  or  that  antitoxin  or  anti-serum  or  vaccine,  we  must  remember 
those  pioneers,  Jenner  and  Pasteur,  who  took  the  first  steps  in 
controlling  germs,  and  began  the  work  which  may  result  finally 
in  preventing  many  diseases. 

How  the  body  protects  itself.  We  have  already  learned  that 
the  blood  contains  small  amounts  of  various  protective  sub- 
stances, known  collectively  as  antibodies.  These  help  the  cells  of 
the  body  combat  harmful  bacteria,  the  poisons  or  toxins  which  the 
bacteria  give  out,-  and  the  poisonous  “ split  proteins  ” which  are 
thrown  into  the  blood  when  these  bacteria  die.  When  any  protein 
substance  decays,  or  is  only  partly  digested,  it  breaks  down  into 
simpler  substances.  Some  of  these  simpler  proteins  are  poisonous 
and  are  called  ptomaines  (to'ma-inz ; Gr.  ptoma,  dead  body). 
Ptomaine  poisoning,  while  not  so  common  as  was  once  thought, 
sometimes  causes  discomfort  and  even  death. 

Practical  Exercise  13.  With  the  help  of  a physician,  list  all  the  diseases 
for  which  immunity  has  been  developed. 

Practical  Exercise  14.  What  is  immunity?  Why  are  some  persons  more 
likely  to  take  a disease  than  others?  Why  do  some  people  have  a disease  more 
severely  than  others  ? Why  does  travel  bring  increased  likelihood  of  disease  ? 

Self-Testing  Exercise 

Check  the  correct  statements  for  your  workbook : 

T.  F.  1.  A person  is  immune  to  a catching  disease  if,  when  ex- 
posed to  it,  he  does  not  take  it. 

T.  F.  2.  Negroes  are  much  more  susceptible  to  measles  and 
tuberculosis  than  white  people. 

T.  F.  3.  The  resistance  to  a disease  is  largely  determined  by  a 
person’s  physical  condition. 

T.  F.  4.  Protective  substances,  antibodies,  in  the  blood  help  the  body 
to  combat  bacteria  and  their  poisons. 

T.  F.  5.  Toxins  are  useful  substances  in  the  blood  which  help  keep 
us  well. 

PROBLEM  VI.  WHAT  ARE  THE  DIFFERENCES  BETWEEN 
ACTIVE  AND  PASSIVE  IMMUNITY? 

Active  and  passive  immunity.  All  toxins,  when  they  enter  the 
human  body,  cause  the  body  cells  to  react  to  the  poison.  If  the 


ANTITOXINS 


477 


colls  arc  able  to  manufacture  the  protective  substances,  antibodies, 
rapidly  enough  to  counteract  the  work  of  the  bacteria  or  their 
poisons,  we  recover  from  the  disease.  In  such  a case  as  this,  the 


^crisis 


onset 


cdnv«a:lesceT2ce 


periocC  of 
incubatioi? 


2jectioii 


^ f 

periocl^ 
ofin2mu:r2i^ 

Read  your  text,  study  the  diagram  carefully,  and  then  explain  how  the  body  produces  an 
immunity  against  a specific  disease. 

body  cells  do  the  work  in  fighting  the  disease,  and  the  immunity 
thus  acquired  is  said  to  be  active.  In  case  the  body  cells  themselves 
do  not  work,  and,  instead,  an  antitoxin  is  used,  which  is  manufac- 
tured outside  the  body,  we  have  an  example  of  passive  i7nmunity. 
Let  us  consider  the  latter  case  first,  as  it  is  easier  to  understand. 

What  are  antitoxins  and  how  are  they  used  ? An  example  of 
passive  immunity  is  that  obtained  by  the  antitoxin  treatment  for 
diphtheria.  This  treatment,  as 
the  name  denotes,  is  a method 
of  neutralizing  the  toxin  given 
off  by  the  bacteria  into  the  body. 

It  was  discovered  by  a German, 

Von  Behring,  that  the  serum  of 
the  blood  of  an  animal  immune 
to  diphtheria  is  capable  of  neu- 
tralizing the  poison  produced 
by  the  diphtheria-causing  bac- 
teria. Horses  develop  large 
quantities  of  antitoxin  when 
given  the  diphtheria  toxin  in 
gradually  increasing  doses. 


The  early  use  of  antitoxin  in  cases  of  diph- 
theria greatly  decreases  the  death  rates  from 
this  disease. 


478  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 

The  serum  of  the  blood  of  these  horses  is  then  carefully  tested 
and  is  used  to  inoculate  the  patient  suffering  from  or  exposed  to 
diphtheria,  and  thus  the  disease  is  checked  or  prevented  alto- 
gether. The  laboratories  of  boards  of  health  prepare  this  antitoxin 
and  supply  it  fresh  so  that  it  can  be  safely  used  at  some  distant 
point  without  danger  to  those  who  are  inoculated  with  it. 

It  has  been  found  from  experience  in  hospitals  that  deaths  from 
diphtheria  are  largely  preventable  by  the  early  use  of  antitoxin. 
It  is  therefore  advisable,  in  a suspected  case  of  diphtheria,  to  have 
antitoxin  used  at  once. 

Schick  test  and  its  value.  By  the  Schick  test  it  is  possible  to 
determine  if  a person  is  immune  to  diphtheria.  A very  minute  dose 

of  diphtheria  toxin 
is  injected  under  the 
skin  of  the  forearm. 
If  the  person  is  im- 
mune, no  reaction 
takes  place,  because 
the  blood  is  provided 
with  antitoxins.  But 
if  the  person  is  sus- 
ceptible, some  hours 
later  a slight  red  spot 
appears  where  the 
toxin  was  injected. 
This  is  a danger  signal  and  shows  that  the  person  would  take 
diphtheria  if  exposed  to  it.  To  such  a person  a treatment,  known 
as  the  toxin-antitoxin  treatment,  is  given.  Small  amounts  of  a 
mixture  of  diphtheria  toxin  and  antitoxin  are  injected  into  the 
susceptible  person,  with  the  result  that  he  becomes  immune  by 
a combination  of  active  and  passive  immunity.  A recent  modi- 
fication of  this  treatment  is  the  following.  A toxoid,  which  is  the 
toxin  treated  with  chemicals  to  make  it  harmless,  is  used.  This 
toxoid  is  inoculated  instead  of  the  antitoxin,  thus  giving  the  child 
immunity. 

The  following  clipping  from  a New  York  paper  indicates  the 
progress  made  in  wiping  out  this  dread  disease. 


How  does  this  diagram  show  the  value  of  giving  children  toxin- 
antitoxin  to  prevent  diphtheria  ? 


ANTITOXINS 


479 


“Quoted  as  an  evidence  of  the  efficacy  of  inoculation  against  diph- 
theria, the  statement  is  made  that  there  were  222G  fewer  cases  of  diph- 
theria  in  New  York  in  1929  than  there  were  in  the  i)receding  year.  The 
numher  of  those  dying  from  the  disease  here  last  year  was  180  less  than 
the  number  who  died  of  it  in  1928. 

“The  jn-ogress  made  in  recent  years  has  warranted  the  prediction  that 
in  five  years  the  disease  will  be  exterminated.” 

The  Dick  test  and  treatment  promise  to  do  as  much  in  combating 
scarlet  fever  as  the  Schick  test  has  done  in  reducing  the  death  rate 
; from  diphtheria.  In  the  Dick  test  a diluted  toxin  produced  by 
the  bacteria  which  cause  scarlet  fever  is  injected  into  the  arm.  A 
j redness  indicates  that  the  person  is  susceptible  to  scarlet  fever, 
i Treatment  is  then  given  in  the  form  of  subsequent  doses  of  toxin 
I which  helps  the  body  to  produce  its  own  antitoxin  and  thus  build 
up  an  active  resistance  against  the  disease.  A similar  test,  known 
as  the  tuberculin  test,  is  now  used  to  determine  the  presence  of 
tuberculosis  germs.  A drop  of  tuberculin,  which  contains  the 
, tuberculosis  toxin,  is  placed  under  the  skin.  If  a red  spot  develops 
there  it  shows  the  presence  of  tuberculosis  germs  in  the  body. 

Other  antitoxins.  Tetanus,  commonly  called  lockjaw,  once 
a much-dreaded  infection,  has  now  been  almost  stamped  out 
through  the  use  of  a tetanus  antitoxin.  During  the  World  War 
, soil-infected  wounds  were  treated  with  this  antitoxin  and  as  a 
' result  the  death  rate  from  tetanus  was  much  lower  than  in  previ- 
; ous  wars.  An  antitoxin  was  also  used  successfully  against  gas 
; gangrene.  Antitoxins  are  also  used  for  certain  types  of  dysentery 
and  against  snake  venoms. 

Active  immunity.  Vaccination  against  smallpox.  In  1796  Jen- 

ner  first  proved  that  inoculation  with  virus  taken  from  a cow  was 
1 capable  of  preventing  smallpox.  Years  later  Louis  Pasteur  proved 
that  inoculation  of  chickens  with  an  old  weakened  culture  of  chicken 
cholera  bacteria  caused  the  chickens  to  be  slightly  ill  for  a short 
time,  but  made  them  immune  to  chicken  cholera.  Their  body  cells 
were  stimulated  by  the  weakened  germs  to  manufacture  antibodies 
; which  soon  got  the  better  of  the  germs  and  provided  immunity. 

1 So  it  is  with  vaccination  against  smallpox.  Smallpox  is  caused 
, by  a filterable  virus  which  means  the  organisms  are  too  small  to 


480  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 


be  seen  with  the  most  powerful  microscope.  The  virus  used  for 
inoculation  probably  contains  the  organisms  which  cause  cowpox, 
which  is  a weakened  smallpox  organism.  Therefore  when  vacci- 
nation “ takes/ ^ the  body  has  been  stimulated  by  the  virus  to 
produce  its  own  antibodies.  These  antibodies  make  the  body 
actively  immune  to  the  disease. 

Smallpox  has  been  in  the  past  a great  scourge ; 90  out  of  every 
100  persons  in  Europe  used  to  have  it.  As  late  as  1898,  in  Russia 


1921 192219Z31924192519261927 192019291930  I mi  19221923  i9‘24 1925  19;?S  1927 1929  19<?c)  1930 
deaths  00020OOOI  o ctoLhs  20  1 56  58  236  5 2 10  7 


1921192219231924192519261927192319291930  1921  1922  1923  192419251926  192719291929  1930 


Massachusetts  has  a law  requiring  all  persons  to  be  vaccinated  against  smallpox  infection. 
California,  at  one  time,  had  such  a law,  but  repealed  it.  Notice  the  number  of  cases  and  deaths 
from  smallpox  in  California  as  compared  with  Massachusetts  from  1922  to  1930. 

over  50,000  persons  lost  their  lives  from  this  disease  in  a year. 
In  some  places  smallpox  has  been  brought  under  absolute  control 
by  vaccination,  though  in  other  places,  unfortunately,  there  are 
outbreaks,  due  to  the  fact  that  some  people  do  not  believe  in 
vaccination. 

Rabies,  or  hydrophobia.  Rabies  (ra'bi-ez),  which  is  caused  by 
a filterable  virus,  is  communicated  in  the  saliva  from  one  dog  to 
another  by  biting.  It  is  also  transmitted  to  man  by  the  bite  of  an 
infected  animal.  The  great  French  bacteriologist,  Louis  Pasteur, 
discovered  a method  of  treating  this  disease  which  is  a success  if 
begun  soon  after  the  person  has  been  bitten  by  the  infected 
animal.  Here  again  the  treatment  is  based  upon  the  inocu- 
lation of  the  patient  with  a weakened  organism  which  causes 


THE  MEC'IIANISM  OF  ACTIVE  IMMUNITY 


481 


the  body  cells  to  set  up  a resistance  and  produce  an  active 
ininiunity. 

Vaccination  against  typhoid.  The  principle  underlying  vacci- 
nation against  typhoid  is  that  of  working  up  an  active  immunity 
by  introducing  into  the  body  large  numbers  of  dead  typhoid  germs. 
The  presence  of  the  dead  bacilli  stimulates  the  blood  to  make 
antibodies  and  thus  an  active  immunity  is  acquired.  This  ini- 
munit}'  protects  the  person  against  the  invasion  of  living  germs. 

During  the  Spanish- American  ^Yar  in  the  army  of  107,000  men 
more  than  20,000  were  disabled  with  typhoid.  Since  1914,  after 
vaccination  against  typhoid  was  introduced,  the  disease  has  been 
almost  stamped  out  in  the  army,  and  the  death  rate  for  the  entire 
country  has  been  so  much  reduced  that  it  is  now  a disease  of 
relatively  little  importance. 

The  Widal  test,  by  means  of  which  it  is  possible  to  determine  at 
once  whether  a person  has  typhoid,  has  been  described  on  page  390. 

The  mechanism  of  active  immunity.  Active  immunity  is 
thus  brought  about  in  a number  of  different  ways : by  the  intro- 
duction of  living  organisms,  by  the  introduction  of  attenuated  or 
weakened  organisms,  by  the  introduction  of  dead  organisms,  and 
by  the  introduction  of  extracts  containing  the  products  of  bacteria. 
All  of  these  substances  may  be  called  vaccines. 

The  underlying  principle  is  the  same  in  all  cases  ; certain  cells  of 
the  body  are  roused  or  activated  to  form  antibodies,  and  the  invad- 
ing organisms  are  destroyed  and  their  toxins  neutralized.  These 
conditions  are  brought  about  through  the  work  of  the  lysins, 
precipitins,  agglutinins,  opsonins,  and  phagocytes  already  men- 
tioned in  Unit  XIII.  You  should  read  that  unit  carefully  again 
in  connection  with  the  present  unit. 

Other  vaccines  are  made  and  used  successfully  against  boils, 
another  against  paratyphoid,  and  still  others  for  plague  and  for 
cholera.  When  tests  show  sensitiveness  to  certain  pollens,  serums 
are  made  from  them  and  a certain  amount  of  immunity  from 
hay  fever  is  thus  received.  But  we  are  just  at  the  beginning  of 
discoveries  along  this  line  and  it  will  no  doubt  be  the  work  of  the 
physicians  and  scientists  of  the  future  to  perfect  many  more  ways 
of  producing  immunity  against  protein  poisons  and  germ  disease. 


482  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 


Practical  Exercise  16.  Study  the  diagram  on  page  480.  Show  exactly  why 
the  changes  noted  there  occurred. 

Practical  Exercise  16.  What  is  the  principle  underlying  the  antitoxin 
treatment  for  diphtheria?  The  Schick  test?  The  Dick  test?  What  is  the 
principle  underlying  vaccination  against  smallpox  ? Against  typhoid  ? Against 
boils  ? Explain. 

Practical  Exercise  17.  Make  a list  of  all  germ  diseases  that  are  now  treated 
by  the  passive  method  of  immunity ; the  active  method  of  immunity. 

Positive  health  the  goal.  In  the  preceding  pages  we  have  seen 
what  science  has  done  in  combating  disease.  But  many  of  these 
diseases  can  be  avoided  simply  by  keeping  in  good  condition. 
If  we  keep  our  bodies  in  good  physical  condition  through  the  use 
of  proper  food,  exercise,  and  sleep ; if  we  maintain  a calm  poise 
and  untroubled  mind ; if  we  avoid  worry  and  are  cheerful  in  spite 
of  difficulties ; then  we  have  gone  far  toward  keeping  well.  We 
now  have  the  knowledge  about  communicable  diseases  and  how  to 
fight  them ; let  us  use  this  knowledge  if  it  is  necessary.  But  for 
most  of  us  health  is  something  that  can  be  earned,  if  we  are  willing 
to  pay  the  price.  All  that  we  have  to  do  is  to  treat  our  bodies  in 
such  a way  that  they  will  give  us  the  most  efficiency,  for  very  few  of 
us  have  really  poor  bodily  machines  to  start  with. 

Self-Testing  Exercise 

When  poisons  enter  the  body,  the  cells  react  by  forming 

(1).  The  two  kinds  of  acquired  immunities  are (2) 

and  (3).  In  the  first,  immunity  is  acquired  through  the 

use  of (4) ; and  in  the  second  through  the  use  of (5). 

The  Schick  test  is  used  to  determine  whether  a person  is (6) 

to  (7).  This  disease  may  be  eradicated  by  the  use  of 

(8).  Diseases  that  may  be  stamped  out  by  the  use  of 

vaccination  are:  (9),  (10),  (11),  and 

(12). 

PROBLEM  VII.  HOW  IS  MALARIA  CAUSED  AND 
TRANSMITTED? 

The  cause  of  malaria.  The  study  of  the  life  history  and  the 
habits  of  the  Protozoa  has  resulted  in  finding  many  parasitic 
forms,  and  the  consequent  explanation  of  some  diseases.  An 
amoeba-like  parasite,  of  which  at  least  three  species  exist,  causes 


CAUSE  OF  MAL.VRIA 


483 


different  types  of  malaria.  This  disease,  not  many  years  ago,  was 
thought  to  be  caused  by  bad  air.  (Hence  the  name,  from  Italian 
mala,  bad ; aria,  air.)  But  the  work  of  a number  of  scientists 
has  shown  that  the  disease  is  carried  by  a mosquito  and  is  caused 
by  an  amoeba-like  organism,  called  Plasmodium  malariae.  When 
a female  mosquito  of  the 
species  Anopheles  (a-nof'e- 
lez)  sucks  blood  from  a 
person  having  malaria, 
this  parasite  passes  with 
the  blood  into  the  stomach 
of  the  mosquito.  After 
about  twelve  days  in  the 
mosquito’s  body,  the 
parasites,  having  passed 
through  the  sexual  stages, 
establish  themselves 
within  the  salivary  glands 
of  the  mosquito.  If  the 
infected  mosquito  then 
bites  a person,  it  passes 
the  parasites  into  the 
human  blood  with  its 
saliva.  These  parasites 
enter  the  corpuscles  of 
the  blood,  increase  in  size, 
and  then  form  spores. 

The  rapid  process  of  spore 
formation  results  in  the 
breaking  down  of  the  blood  corpuscles.  The  spores  then  escape 
into  the  blood  stream.  The  sudden  release  of  the  spores  and  the 
poisons  are  thought  to  cause  the  chills  and  the  fever  so  character- 
istic of  malaria.  The  escaped  parasites  may  enter  other  blood 
corpuscles  and  in  forty-eight  or  more  hours,  depending  on  the  kind 
of  malaria,  repeat  the  cycle.  The  spores  feed  upon  the  red 
corpuscles,  and  destroy  half  or  even  four  fifths  of  the  normal 
number.  This  accounts  for  the  pale,  anaemic  condition  of  a person 


The  malarial  parasite  passes  its  life  cycle  from  a 
mosquito,  to  man,  and  back  again  to  a mosquito. 
Trace  the  life  history  of  the  parasite  in  the  above 
diagram. 


484  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 


who  has  malaria.  The  only  cure  for  the  disease  is  frequent  doses 
of  quinine.  This  kills  the  parasites  in  the  blood. 


Workbook  Exercise.  Using  the  text  and  diagram,  work  out  a life 
cycle  of  the  malarial  parasite. 

Demonstration  4.  To  show  life  history  of  a mosquito. 

Use  charts  or  material  in  Riker  mounts,  to  show  history  of  any  mosquito. 


The  malarial  mosquito.  Fortunately  for  mankind,  not  all 
mosquitoes  harbor  the  parasite  which  causes  malaria.  The  harm- 
less mosquito  (Culex)  maybe  usually  distinguished  from  the  mos- 
quito which  carries  malaria  (Anopheles)  by  the  position  of  the  body 
and  legs  when  at  rest.  Culex  lays  eggs  in  tiny  rafts  of  one  hundred 


acCuIt 


pupa 


cccCult. 


How  does  the  common  mosquito,  Culex  (on  left),  differ  in  the  various  stages  of  growth  from  the 
malarial  mosquito,  Anopheles  (on  right)  ? 


or  more  in  standing  water ; thus  the  eggs  are  distinguished  from 
those  of  Anopheles,  which  are  not  in  rafts.  Rain  barrels,  gutters, 
and  old  cans  may  breed  in  a short  time  enough  mosquitoes  to 
annoy  a whole  neighborhood.  The  larvae  are  known  as  wigglers. 
They  appear  to  hang  on  the  surface  of  the  water,  head  down,  in 
order  to  breathe  through  a tube  at  the  posterior  end  of  the  body. 
In  this  stage  they  may  be  recognized  by  their  peculiar  movement 
when  on  their  way  to  the  surface  to  breathe.  The  pupa,  dis- 
tinguished by  a large  head  and  thoracic  region,  breathes  through 
a pair  of  tubes  on  the  thorax. 


EXTEUMlXATlOxN  OF  MOSQUITOES 


485 


Practical  Exercise  18.  I 'so  tlie  iliap:nun  ami  coinj)are  tlie  life  histories  of 
the  Anopheles  ami  Culex  so  that  you  ean  (let ermine  tlie  harmful  form  at  any 
sta^e  in  its  life  history. 

How  may  mosquitoes  be  exterminated?  The  fact  that  both 
larvae  and  pupae  lake  air  from  the  surface  of  the  water  makes  it 
possible  to  kill  the  mosquito  during  these  stages  by  pouring  oil 
on  the  surface  of  the  water  where  they  breed.  The  introduction  of 


U.  S.  Department  of  Agriculture 

Dusting  with  Paris  green  from  an  airplane  to  destroy  the  malarial  mosquito  larvae  on  the 
surface  of  water  in  the  swamp  and  lake. 


minnows,  goldfish,  or  other  small  fish  where  the  mosquitoes  breed 
will  do  much  in  freeing  a neighborhood  from  this  pest.  Draining 
swamps  or  low  land  which  holds  water  after  a rain  is  another 
method  of  extermination.  Since  the  beginning  of  historical  times, 
malaria  has  been  prevalent  in  regions  infested  by  mosquitoes. 
iThe  ancient  city  of  Rome  was  so  greatly  troubled  by  periodic 
ioutbreaks  of  malarial  fever  that  a goddess  of  fever  came  to  be 
Iworshiped  in  order  to  lessen  the  severity  of  what  the  inhabitants 
Ibelieved  to  be  a divine  visitation.  At  the  present  time  malaria 

J H.  BIO  — 32 


486  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 

is  being  successfully  fought  and  conquered  in  Italy  by  the  draining 
of  the  mosquito-breeding  marshes. 

The  problem  of  malaria  has  affected  nearly  13,000,000  of  the 
inhabitants  of  the  United  States,  principally  those  of  the  southern 
states.  Mississippi,  with  over  90  per  cent  of  its  population  living 
in  districts  where  the  malarial  mosquito  is  found,  Florida  with  80 
per  cent  of  her  population  exposed  to  malaria,  and  Arkansas, 
with  75  per  cent  living  in  malarial  districts,  present  the  most 
serious  problems  from  a health  standpoint.  In  Arkansas,  Mis- 
sissippi, and  other  southern  states  successful  fighting  of  malaria 
by  draining  marshes,  oiling  standing  water,  and  screening  houses 
has  greatly  reduced  the  number  of  cases  of  malaria. 

Project.  To  make  a survey  of  your  neighborhood  to  determine  if 
there  are  any  breeding  places  for  mosquitoes.  How  can  these  places 
be  reduced? 

Other  protozoan  diseases.  Many  other  diseases  of  man  are 
probably  caused  by  parasitic  protozoans.  Dysentery  of  one  kind 
is  caused  by  the  presence  of  an  amoeba-like  animal,  Endamoeba, 
in  the  digestive  tract.  These  parasites  are  far  more  widely  spread 
than  was  ever  thought  and  many  people  suffer  from  the  effects  of 
this  parasite  without  knowing  what  actually  causes  them  to  be  ill. 

Another  group  of  protozoan  parasites  are  called  trypanosomes. 
These  are  parasitic  in  insects,  fish,  reptiles,  birds,  and  mammals 
in  various  parts  of  the  world.  They  cause  several  diseases  of 
cattle  and  other  domestic  animals,  being  carried  to  the  animal  in 
most  cases  by  flies.  One  of  this  family  is  believed  to  live  in  the 
blood  of  native  African  zebras  and  antelopes.  Seemingly  it  does 
them  no  harm,  but  if  one  of  these  parasites  is  transferred  by  the 
dreaded  tsetse  (tse'tse)  fly  to  one  of  the  domesticated  horses  or 
cattle  of  that  region,  the  animal  dies. 

The  tsetse  fly  also  carries  to  the  natives  of  Central  Africa  a 
trypanosome  which  causes  the  dreaded  and  incurable  sleeping 
sickness.  This  disease  has  killed  more  than  fifty  thousand 
natives  yearly,  and  many  Europeans  have  succumbed  to  it.  Its 
ravages  are  largely  confined  to  an  area  near  the  large  Central  Afri- 
can lakes  and  the  upper  Nile,  for  the  fly  which  carries  the  disease 


YELLOW  FEVER 


487 


lives  near  water,  seldom  goins;  more  than  150  feet  from  the  banks 
of  streams  or  lakes.  The  Ilritish  government  has  attempted  to 
control  the  disease  in  Uganda  by  moving  all  the  villages  at  least 
two  miles  from  the  lakes  and  rivers.  Among  other  diseases  that 
may  be  due  to  protozoans  is  kala  azar,  a fever  in  hot  Asiatic 
countries  which  is  probably  carried  by  the  bedbug,  and  African 
tick  fever,  carried  by  a spiderlike  creature  called  the  tick.  In  this 
country  many  fatal  diseases  of  cattle,  as  “tick  fever,”  or  Texas 
cattle  fever,  are  caused  by  protozoa. 

Self-Testing  Exercise 

Malaria  is  caused  by  a (1)  which  is  carried  by  the 

(2) (3).  It  lives  part  of  its  life  in  the  body  of  the (4) 

and  part  in (5).  Vlien  the (6)  bites  a person,  it  passes 

■the  (7)  into  the  (8)  with  its  saliva.  Malaria  can  be 

leradicated  by  (9)  the  (10)  (11)  of 

(12).  Other  diseases  probably  caused  by  protozoans  are (13), 

(14) .(15) (16),  and (17) (18). 

PROBLEM  VIII.  HOW  WAS  THE  CONTROL  OF  YELLOW 
I FEVER  BROUGHT  ABOUT? 

Yellow  fever  and  mosquitoes.  Another  disease  carried  by 
[mosquitoes  is  yellow  fever.  In  the  year  1878  there  were  125,000 
cases  and  12,000  deaths  in  the  United  States,  mostly  in  Alabama, 
Louisiana,  and  Mississippi.  During  the  French  attempt  to  con- 
istruct  the  Panama  Canal,  the  work  was  at  a standstill  part  of  the 
time  because  of  the  ravages  of  yellow  fever.  Before  the  war  with 
Spain,  thousands  of  people  were  ill  in  Cuba.  But  today  yellow 
fever  has  almost  disappeared,  both  there  and  in  the  Canal  Zone, 
through  proper  control  of  the  fever-carrying  mosquito  Aedes. 

BThe  knowledge  that  Aedes  carries  the  disease-producing  agent 
that  causes  yellow  fever  is  due  to  the  experiments  in  1900  of  a 
^commission  of  United  States  army  officers,  headed  by  Dr.  Walter 
Reed.  One  of  these  men.  Dr.  Jesse  Lazear,  lost  his  life  in  an  ex- 
periment to  prove  that  yellow  fever  is  transmitted  by  mosquitoes. 


488  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 

He  allowed  himself  to  be  bitten  by  a mosquito  that  was  known 
to  have  bitten  a yellow  fever  patient,  contracted  the  disease,  and 
died  a martyr  to  science  Others,  soldiers,  volunteered  to  test 
further  by  experiment  how  the  disease  was  spread,  so  that  in  the 
end  the  commission  was  able  to  prove  that  AMes  transmitted  yel- 
low fever.  The  accompanying  illustration  shows  the  result  of  this 


jyear  1901 

■^0(1 

--1  ■ 1 1 M 1 

200 

/ 

/ 

\ 

/ 

. antiiuosquito 
' campaign  b^an 

too 

1 

\ 

y 

/ 

0 

\ 

/ 

dug.SeptCkt.XovDec.Jan  .Teb.  Mac 

In  1900,  experiments  were  carried  on  to  find  the  cause  of  yellow  fever.  In  1901,  it  was  dis- 
covered that  the  Aedes  mosquito  transmitted  yellow  fever  and  a campaign  against  mosquitoes 
was  immediately  started.  The  above  chart  shows  the  effect  of  such  a campaign  in  Havana. 


discovery  for  the  city  of  Havana.  For  years  the  cause  of  yellow 
fever  has  evaded  the  best  efforts  of  the  scientist.  At  first  investi- 
gators thought  it  was  caused  by  a protozoan  parasite  like  malaria, 
but  the  latest  researches  conducted  in  all  areas  where  yellow  fever 
still  exists  seem  to  indicate  the  cause  to  be  a filterable  virus,  an 
organism  so  small  that  it  will  pass  through  a very  fine-pored 
filter. 

Practical  Exercise  20.  Read  the  Health  Heroes  Series  by  Hallock  and  Tur- 
ner, and  make  a report  to  the  class  on  yellow  fever. 


Self-Testing  Exercise 

A commission  headed  by  Dr (1)  proved  that  the  Aedes  mos- 
quito carries  (2)  (3) . This  disease  was  eliminated 

in  Havana  by (4)  the (5)  (6)  of  mosquitoes, 

(7)  the  buildings,  and  introducing  (8)  (9). 


THE  HOUSE  FLY 


489 


PROBLEM  IX.  WHAT  ARE  OTHER  DISEASE  CARRIERS  AND 
WHAT  DISEASES  DO  THEY  CARRY? 

Demonstration  5.  Observe  the  foot  of  a house  fly  under  a com- 
pound microscope.  Why  it  is  able  to  cany  bacteria. 

Allow  a fly  to  walk  across  a sterile  agar  plate.  Cover  the  plate  and 
set  it  aside  in  a warm  place  for  several  days.  Describe  the  plate. 

Demonstration  6.  The  life  history  of  the  typhoid  fly. 

E.\])ose  i)ioces  of  raw  beef  where  flies  will  light  on  them.  After  a 
few  hours,  cover  this  meat  in  glass  dishes  or  small  battery  jars  with 
screen  covers. 

Watch  the  meat.  In  jneces  on  which  eggs  were  laid  by  the  flies 
tlcscribe  the  stages  of  development  as  they  appear.  Do  the  larvae 
grow?  They  are  called  maggots.  State  how  the  pupae  differ  from 
the  larvae.  Watch  to  see  the  adults  emerge  from  the  pupal  case. 

flow  long  does  a complete  life  history  take  ? How  many  generations 
of  flies  might  develop  during  a hot  summer? 


The  house  fly.  We  have  already  learned  that  mosquitoes  of 
different  species  carry  malaria  and  yellow  fever.  Another  addition 
to  the  black  list  of  disease-carriers  is  the  house  or  typhoid  fly.  The 
development  of  the 
house  fly  is  extremely 
rapid.  A female  may 
lay  from  one  hundred 
to  two  hundred  eggs 
at  one  time.  These 
are  usually  deposited 
in  filth  or  manure. 

Dung  heaps  about 
stables,  outdoor  toilets, 
neglected  garbage 
cans,  and  fermenting 
vegetable  refuse  form 
the  best  breeding 
places  for  flies.  In 
warm  weather,  the  eggs 
hatch  a day  or  so  after  they  are  laid  and  the  larvae  or  maggots 
jcrawl  out.  After  about  one  week  of  active  feeding  these  wormlike 
maggots  become  quiet  and  go  into  the  pupal  stage,  whence  under 
, favorable  conditions  they  emerge  within  less  than  another  week  as 
adult  flies.  The  adults  breed  at  once,  and  in  a short  summer 


Paul  Griswold  Howes 

A blue-bottle  fly  depositing  eggs  in  the  bill  of  a dead  starling, 
which  will  furnish  food  for  the  young  larvae. 


490  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 


there  may  be  over  ten  generations  of  flies.  This  accounts  for  the 
great  number  of  flies  in  July  and  August.  Fortunately,  rela- 
tively few  flies  survive  the  winter. 

The  foot  of  the  fly  shows  a wonderful  adaptation  for  clinging  to 
smooth  surfaces.  Two  or  three  pads,  each  of  which  bears  tubelike 

hairs  that  secrete  a 
sticky  fluid,  are  found 
on  its  under  surface. 
It  is  by  this  means  that 
the  fly  is  able  to  walk 
upside  down,  and  carry 
filth  and  bacteria  on  its 
feet. 


Project.  To  determine 
the  breeding  places  of 
flies  in  your  neighbor- 
hood. 


The  house  fly  a dis- 
ease carrier.  The  com- 
mon fly  is  recognized 

Foot  of  a house  fly.  Why  is  the  fly  a carrier  of  diseases  ? everywhere  aS  a pest. 

Flies  have  long  been  known  to  spoil  food  through  their  filthy 
habits,  and  they  are  blamed  for  spreading  several  diseases  caused 
by  bacteria.  It  has  been  found  that  a single  fly  might  carry  on 
its  feet  anywhere  from  500  to  6,600,000  bacteria,  the  average 
number  being  over  1,200,000.  Not  all  of  these  germs  are  harm- 
ful, but  they  might  easily  include  those  of  typhoid  fever,  tuber- 
culosis, “ summer  complaint,’’  and  possibly  other  diseases.  A 
pamphlet  published  by  the  Merchants’  Association  in  the  city  of 
New  York  shows  that  the  rapid  increase  of  flies  during  the  summer 
months  has  a definite  correlation  with  the  increase  in  the  number 
of  cases  of  “ summer  complaint.”  Observations  in  other  cities  seem 
to  show  that  the  increase  in  the  number  of  typhoid  cases  in  the 
early  fall  is  due,  in  part  at  least,  to  the  same  cause. 


Project.  If  vital  statistics  of  your  community  are  available,  work 
out  a correlation  between  the  increase  of  flies  and  the  increase  of 
certain  diseases. 


DISEASE  CAHKIERS 


491 


Cleanliness  which  tleslroys  tiie  breeding  places  of  flies,  the 
frequent  removal  anti  destruction  of  garbage,  rubbish,  and  manure, 
the  covering  of  all  food  when  not  in  use,  and  especially  the  careful 
screening  of  windows  and  doors  during  the  breeding  season  are 
wise  precautions  taken  to  prevent  the  spread  of  diseases  by  flies. 
Far  more  important  than  to  “ swat  the  fly  ” is  to  remove  their 
breeding  places ! 

Practical  Exercise  20.  What  is  the  best  method  for  destroying  flies  in  your 
home?  Knowing  when  and  where  flies  breed,  when  would  be  the  best  time 
to  ‘‘  swat  the  fly  ”?  How  would  this  method  compare  with  other  ways  of 
extermination? 

Other  insect  disease  carriers.  Fleas  and  bedbugs  have  been 
added  to  those  insects  proved  to  carry  disease  to  man.  Bubonic 
plague,  which  is  primarily  a disease  of  rats,  is  transmitted  from 
infected  rats  and  ground  squirrels  to  man  by  fleas.  Fleas  are  also 
believed  to  transmit  from  rats  to  rats  a form  of  leprosy  found  only 
in  these  animals.  It 
is  thought  probable 
that  bedbugs  trans- 
mit relapsing  fevers. 

Typhus  fever  is 
transmitted  by  body 
lice. 

Animals  other  than 
insects  that  may 
spread  disease.  The 
common  brown  rat 
is  an  example  of  a 
mammal,  harmful  to 
civilized  man,  which 
has  followed  in  his 
footsteps  all  over  the 
world.  Starting  from  China,  it  spread  to  eastern  Europe,  thence  to 
western  Europe,  and  in  1775  it  had  arrived  in  this  country.  In 
seventy-five  years  it  reached  the  Pacific  coast  and  it  is  now  fairly 
common  all  over  the  United  States,  being  one  of  the  most  prolific 
of  all  mammals.  Rats  spread  bubonic  plague,  the  “ Black  Death  ” 


Boccillics 

rnan 


ground 

Sc^irrel 


Explain  from  the  diagram,  how  the  bubonic  plague  is  carried? 


492  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 


of  the  Middle  Ages,  a disease  estimated  to  have  killed  25,000,000 
people  during  the  fourteenth  century.  Fleas  bite  the  infected 
rat  and  then  transmit  the  disease  to  man.  In  1900  the  plague 
gained  entrance  on  our  western  coast.  It  killed  more  than  100 
persons  during  the  next  four  years,  and  small  outbreaks  have 
occasionally  occurred  ever  since.  The  ground  squirrels  of  Cali- 
fornia became  infected  with  the  plague,  doubtless  from  the  rats 
which  lived  in  their  burrows,  so  that  now  the  danger  of  other  out- 
breaks of  the  plague  will  be  present  until  all  the  ground  squirrels 
are  exterminated.  Over  a million  rats  were  killed  in  fighting  the 
last  outbreak  of  bubonic  plague  in  California  and  efforts  are  being 
made  in  all  large  cities  to  eradicate  this  pest. 

Practical  Exercise  21.  Look  up  Farmers  Bulletin  896  and  report  on  the 
best  way  to  exterminate  rats. 

Project.  Make  a survey  of  your  neighborhood  to  determine  where 
rats  breed. 

Self-Testing  Exercise 

The  house  fly  may  carry  (1)  and  (2)  bacteria 

on  its  feet.  It  breeds (3)  in (4)  or (5)  during 

the  warm  season.  Fleas  are  carriers  of  (6)  (7), 

which  they  get  from  (8)  (9)  and  (10) 

(11).  This  disease  can  be  eradicated  by  exterminating  all 

(12)  and  (13).  Body  lice  transmit  (14) 

(15). 

PROBLEM  X.  WHAT  DISEASES  ARE  CAUSED  BY  WORMS 
AND  HOW  MAY  WE  FIGHT  THEM? 

Other  parasitic  animals  cause  disease.  Other  animals  besides 
those  mentioned  have  been  found  to  cause  illness.  Chief  among 
these  are  certain  roundworms  and  flat  worms,  which  live  as  parasites 
not  only  in  man  but  in  many  animals  and  plants.  The  parasite 
frequently  becomes  fastened  to  its  host  during  adult  life  and  is 
reduced  to  a mere  bag  through  which  the  fluid  food  prepared  by  its 
host  is  absorbed.  Sometimes  a complicated  life  history  results 
from  parasitic  habits.  Such  is  the  life  history  of  the  tapeworm 
and  of  the  liver  fluke,  a fiatworm  which  kills  sheep. 


TAPEWORMS 


493 


Cestodes  or  tapeworms,  'riicse  parasites  infest  man  and  many 
other  vertebrate  animals.  One  tapeworm  {Taenia  solium)  passes 
through  two  stages  in  its  life  history,  the  first  within  a pig,  the 
second  within  the  intestine  of  man.  The  developing  eggs  are 
passed  off  with  wastes  from 
the  intestine  of  man.  The 
pig,  an  animal  with  dirty 
habits,  may  take  in  the 
tapeworm  embryos  with  its 
food.  These  develop  within 
the  intestine  of  the  pig,  but 
soon  make  their  way  into 
the  muscles  or  other  tissues, 
where  they  are  known  as 
bladder  worms.  If  man 
eats  undercooked  pork  con- 
taining them,  he  is  likely  to 
become  a second  host  for 
tapeworms. 

Another  common  tape- 
worm ( Taenia  saginata) 
parasitic  on  man  lives  part 
of  its  life  as  an  embryo 
within  the  muscles  of  cattle. 

The  adult  tapeworm  con- 
sists of  a round  headlike 
part  provided  with  hooks, 
by  means  of  which  it  fastens  itself  to  the  wall  of  the  intestine. 
This  head  now  buds  off  a series  of  segment-like  structures,  which 
are  practically  bags  full  of  sperms  and  eggs.  These  structures, 
called  proglottids,  break  off  from  time  to  time,  thus  allowing  the 
developing  eggs  to  escape.  The  proglottids  have  no  separate 
digestive  systems,  but  the  whole  body  surface,  bathed  in  digested 
food,  absorbs  it  and  thus  they  are  enabled  to  grow  rapidly. 

Roundworms.  Still  other  wormlike  creatures  called  round- 
worms  are  of  importance  to  man.  Some,  as  the  vinegar  eel  found 
in  vinegar,  or  the  pinworms  parasitic  in  the  lower  intestine,  partic- 


The  bass  tapeworms  infest  the  small-mouthed  black 
bass.  The  mature  posterior  segments  of  the  worm, 
filled  with  eggs,  break  off  and  pass  from  the  host. 
The  eggs  are  liberated  and  settle  to  the  bottom  of 
the  lake,  where  they  are  eaten  by  small  crustaceans, 
called  Cyclops,  which  in  turn  are  eaten  by  small  fish 
which  form  the  food  of  the  bass. 


494  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 


ularly  of  children,  do  little  or  no  harm.  The  Ascaris,  a larger 
roundworm,  sometimes  infests  children  but  is  rarely  dangerous  to 
its  host. 

The  pork  worm  or  trichina  (tri-ki'na),  however,  is  a parasite 
which  may  cause  serious  injury.  It  passes  through  the  first 

part  of  its  existence 
as  a parasite  in  a 
pig  or  other  verte- 
brate (cat,  rat,  or 
rabbit)  ; it  is  en- 
closed in  a tiny  sac  or 
cyst,  in  the  muscles 
of  its  host.  If  un- 
dercooked pork  con- 
taining these  cysts  is 
eaten  by  man,  the 
covering  is  dissolved 
off  by  the  action  of 
the  digestive  fluids, 
and  the  living  tri- 
china becomes  free 
in  the  intestine  of 
man.  Here  it  repro- 
duces, and  the  young  pass  through  the  intestinal  wall  into  muscles, 
causing  inflammation  there  and  resulting  in  a painful  and  often 
fatal  disease  known  as  trichinosis.  The  government  at  one  time 
inspected  pork  for  trichina,  but  since  a microscopic  examination  of 
meat  was  necessary  and  it  was  impossible  to  examine  all  killed  hogs 
in  this  way,  the  practice  has  been  discontinued  with  the  result  that 
trichinosis  is  on  the  increase.  All  pork  should  be  well  cooked. 

Filaria  are  small  roundworms  that  cause  various  tropical  dis- 
eases — the  most  serious  of  which  is  elephantiasis.  The  parasites 
possibly  enter  the  body  in  drinking  water  and  some  are  probably 
introduced  by  the  bite  of  a mosquito. 

Practical  Exercise  22.  Find  out  from  local  physicians  if  there  has  ever  been 
a case  of  trichinosis  in  your  community.  If  so,  try  to  find  out  why  it  occurred. 

What  kind  of  inspection  of  meats  do  you  have  in  your  community  ? 


lodg&  in 

human. 

ynusales 

Causing 

trichinosis 


"Worm.  15 
a 

in  tnixscle 
of  pig 


undei"^ 
Cooked: 
poi~k  is 
£ateia_. 

_ the  \v6nn 
is  fneecC  by 
diofestive 
^juices 


young  breo-k  / 
ourt  cy  the'^ir 
intestine 
of  maix  and 
migrate. 


In  what  way  may  poorly  cooked  pork  be  harmful  to 


THE  IIOOKWOIIM 


495 


Demonstration  7.  Use  a microscopic  slide  to  show  hookworm.  Why 
is  it  culled  “ hookworm  ”? 

The  hookworm.  Tlie  account  of  the  discovery  by  Dr.  C.  W. 
Stiles  of  the  Bureau  of  Animal  Industry,  that  the  laziness  and  shift- 
lessness of  the  “ poor  whites  ” of  the  South  is  partly  due  to  a para- 
site called  the  hookworm,  reads  like  a fairy  tale. 

The  pt'ople,  largely  farmers,  become  infected  with  a larval  stage 
of  the  hookworm,  which  develops  in  moist  earth.  It  enters  the 
body  usuall}^  through  a break  in  the  skin  of  the  feet,  for  adults 
and  children  alike,  in  certain  localities  where  the  disease  is  com- 
mon, go  barefoot  to  a considerable  extent. 

A complicated  journey  from  the  skin  to  the  intestine  now  follows. 
The  larvae  pass  through  the  veins  to  the  heart,  from  there  to  the 
lungs,  where  they  bore  into  the  air  passages,  and  eventually  reach 
the  intestine  by  way 
of  the  throat.  One 
result  of  the  injury  to 
the  lungs  is  that  many 
persons  thus  infected 
are  subject  to  tuber- 
culosis. The  adult 
hookworms,  once  in 
the  food  tube,  fasten 
themselves  to  the 
walls  which  they 
puncture;  and  then 
they  feed  upon  the 
blood  of  their  host. 

The  loss  of  blood 
from  this  cause  is 
not  sufficient  to  ac- 
count for  the  blood- 
lessness of  the  person  infected,  but  it  has  been  discovered  that  the 
hookworm  pours  out  into  the  wound  a poison  which  prevents  the 
blood  from  clotting  rapidly ; hence  a considerable  loss  of  blood 
occurs  from  the  wound  after  the  hookworm  has  finished  its  meal 
and  gone  to  another  part  of  the  intestine. 


the  human 
. excr-etcr 
.infects  soil 

f 

fr&TO  stomach 
to  intestines 
hooKs  oix-fe 
the  “NvcalL 


svexilowect 


vorm  entens 
skin  from. 
cCirt  between 
the  toes 


CarriecC 
Ik  to  heart 

\ 

-v  pumped 
' to  Vessels 
;;  in  lun^s 


. breaks 
into  the 
air  sa<zs 


up  through 
VinoCplpe 
to  the 
mouth. 


Explain,  from  the  diagram,  how  one  may  become  infected 
with  hookworm. 


496  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 


The  prevention  of  hookworm  lies  in  sanitary  toilets  and  in 
proper  covering  for  the  feet.  The  remedy  for  the  disease  is  very 
simple : thymol,  which  weakens  the  hold  of  the  hookworm,  fol- 
lowed by  Epsom  salts,  which  helps  pass  it  from  the  body. 

For  years  an  area  in  the  South  undoubtedly  was  retarded  in  its 
development  by  this  parasite  ; hundreds  of  millions  of  dollars  were 
wasted  and  thousands  of  lives  sacrificed.  But  today,  thanks  to 
modern  science,  the  conditions  are  much  improved.  The  Rocke- 
feller Foundation  has  made  a study  of  conditions  all  over  the  world 
and  finds  that  in  almost  all  semitropical  countries  the  hookworm 
is  present  and  that  in  some  parts  of  the  world  about  90  per  cent  of 
the  people  are  infected. 

The  following  editorial  appeared  in  the  Atlanta  Constitution  a 
few  years  ago.  Would  it  be  written  today? 

‘‘The  hookworm  is  not  a bit  spectacular  : it  doesn’t  get  itself  discussed 
in  legislative  halls  or  furiously  debated  in  political  campaigns.  Modest 
and  unassuming,  it  does  not  aspire  to  such  dignity.  It  is  satisfied  simply 
with  (1)  lowering  the  working  efficiency  and  the  pleasure  of  living  in  some- 
thing like  two  hundred  thousand  persons  in  Georgia  and  all  other  Southern 
states  in  proportion ; with  (2)  amassing  a death  rate  higher  than  tubercu- 
losis, pneumonia,  or  typhoid  fever ; with  (3)  stubbornly  and  quite  effectu- 
ally retarding  the  agricultural  and  industrial  development  of  the  section ; 
with  (4)  nullifying  the  benefit  of  thousands  of  dollars  spent  upon  educa- 
tion ; with  (5)  costing  the  South,  in  the  course  of  a few  decades,  several 
hundred  millions  of  dollars.  More  serious  and  closer  at  hand  than  the 
tariff ; . . . making  the  menace  of  the  boll  weevil  laughable  in  compari- 
son— it  is  preeminently  the  problem  of  the  South.” 

Practical  Exercise  24.  Debate  the  statement  from  the  Atlanta  Constitution, 
using  tuberculosis  as  the  opposing  disease. 

Self-Testing  Exercise 

Check  the  true  statements  for  your  workbook : 

T.  F.  1.  One  form  of  tapeworm,  parasitic  in  man,  lives  as  an  embryo  in 
the  muscles  of  cattle. 

T.  F.  2.  The  tropical  disease,  elephantiasis,  is  caused  by  small  round- 
worms. 

T.  F.  3.  People  who  live  in  hookworm-infested  districts  should 
never  go  barefoot. 


HOME  CONDlTlONvS  497 

T.  F.  4.  The  sovcniincnt  oxainiiics  all  jiork  to  see  if  it  has  trichina. 

F.  ■).  Sonic  tapeworms  arc  <2:ivcn  to  jiigs  by  man. 

4\  F.  ().  'rrichina  is  a romuhvorm  that  causes  the  disease  called 
trichinosis. 

T.  F.  7.  Hookworms  are  taken  into  the  body  by  drinking  impure 
water  containing  their  eggs. 


PROBLEM  XI.  HOW  MAY  WE  IMPROVE  CONDITIONS  AT 
HOME? 

The  bedroom.  Our  work  in  general  science  has  shown  us  the 
need  of  ventilation,  especially  in  our  bedrooms.  The  sleeping 
porch,  so  often  found  in  country  homes,  is  one  of  the  most  healthful 


Underwood  and  Underwood 

A street  market.  Why  is  this  not  a sanitary  way  to  sell  food  ? 


of  modern  conveniences.  Such  a condition  as  this  is  manifestly 
impossible  for  most  people  in  a crowded  city.  Until  comparatively 
recent  times,  many  tenement  houses  were  built  so  that  the  bed- 
rooms had  very  little  light  or  air ; but  now,  due  to  housing  laws, 
wide  airshafts  and  larger  windows  are  required.  Laws  in  some 


498  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 


cities  require  that  every  room  in  a modern  apartment,  except  the 
bathroom,  must  have  at  least  ninety  square  feet  of  floor  area,  that 
every  room  must  have  one  outside  window,  and  that  at  least 
twenty  per  cent  of  a lot  (except  a corner  lot)  should  not  be  built 
upon. 

In  certain  city  tenements  tuberculosis  is  believed  to  have  been 
spread  by  people  occupying  rooms  in  which  a previous  tenant  had 
tuberculosis.  A new  tenant  should  insist  on  a thorough  cleaning 
of  all  the  rooms  and  removal  of  old  wall  paper  before  occupancy. 

Practical  Exercise  24.  Why  should  we  have  rugs  in  our  bedroom  instead  of 
carpets?  How  would  you  clean  your  bedroom?  If  you  use  the  room  for 
study  as  well  as  sleeping,  draw  a plan  for  the  arrangement  of  furniture  and 
give  reasons  for  its  disposal.  Show  how  you  would  get  the  best  ventilation 
for  sleeping. 

Sunlight  is  of  great  importance  to  health.  Every  home  should 
have  sunlight  for  a part  of  the  day  at  least  in  its  living  and  sleeping 
rooms.  Sunlight  is  still  the  greatest  germicide  we  know. 

A student  lamp,  or  shaded  incandescent  light,  should  be  used 
for  reading,  so  that  the  eyes  are  protected  from  direct  light.  Gas 
is  a dangerous  servant,  because  it  contains  carbon  monoxide. 
It  has  been  estimated  that  fourteen  per  cent  of  the  total  product 
of  the  gas  plant  leaks  into  the  streets  and  houses  of  the  cities  sup- 
plied. This  forms  an  unseen  menace  to  health  in  cities. 

Practical  Exercise  26.  Contrast  indirect-  and  direct-lighting  systems  in 
your  home  from  the  standpoint  of  efficiency  and  protection  of  your  eyes. 

Care  of  food  in  the  home.  Although  we  can  buy  many  foods 
in  sealed  packages,  much  of  our  food  is  exposed  to  the  handling  of 
people  who  may  be  careless.  Vegetables  and  meats  are  too  often 
exposed  to  dust,  dirt,  and  handling.  Raw  fruits  and  vegetables 
should  be  carefully  washed  before  being  eaten. 

In  the  summer,  our  houses  should  be  provided  with  screens.  All 
food  should  be  carefully  protected  from  flies.  Dirty  dishes,  scraps 
of  food,  and  garbage  should  be  quickly  cleaned  up  and  disposed  of 
after  a meal. 

Carelessness  in  dishwashing  may  mean  the  spreading  of  disease. 
Dr.  Broadhurst  of  Teachers  College,  New  York,  learned,  through  a 
series  of  tests  with  several  hundred  glasses  and  cups  smeared  with 


CAKE  OF  FOOD  IN  THE  HOME 


499 


I saliva,  that  when  ilishes  are  hand  washed  and  not  rinsed  all  the 
bacteria  are  not  removed.  Some  of  the  bacteria  are  not  destroyed 
unless  boiling  hot  water  is  used.  At  the  time  of  the  influenza 
epidemic  during  the  World  War  an  investigation  was  made  of 
: 66,000  men,  half  of  whom  ate 
from  plates  which  were  washed 
in  boiling  water,  the  other  half 
; from  mess  plates  which  were 
washed  carelessly  by  the  men. 

I The  influenza  rate  was  51  per 
1000  among  the  men  who  ate 
I from  properly  washed  dishes, 

^and  252  per  1000  among  the 
; men  who  ate  from  mess  plates.  These  facts  show  plainly  the 
need  of  proper  washing  of  dishes. 

' Milk  at  home  should  receive  the  best  of  care.  It  should  be  kept 
on  ice  and  in  covered  bottles,  because  it  readily  takes  up  the 
i odors  of  other  foods.  If  we  are  not  certain  of  its  purity  or  keeping 
1 qualities,  it  should  be  pasteurized  at  home.  Why?  Experiments 
' made  with  good  fresh  milk,  which  at  the  first  observation  contained 
: about  30,000  bacteria  per  cubic  centimeter,  showed  that  twenty- 
four  hours  later,  if  kept  at  the  temperature  of  the  average  ice  box 
(below  50°  Fahrenheit),  there  were  about  the  same  number  of 
’ Ibacteria  present ; while  some  of  the  same  milk  exposed  to  a 
temperature  of  68°  Fahrenheit  showed  500,000,000  bacteria  to  the 
cubic  centimeter. 

Demonstration  8.  To  determine  the  bacterial  content  of  milk  of 
: ivarious  grades  and  from  different  sources. 

j Put  a couple  of  drops  of  certified,  pasteurized,  raw,  etc.,  milk,  in 
separate  Petri  dishes  containing  sterile  agar.  Cover  the  dishes  and 
!put  them  in  a warm  dark  place  (about  90°  F.)  for  24  hours.  Which 
dish  shows  the  greatest  number  of  colonies?  The  greatest  number  of 
different  colonies?  Which  is  the  best  kind  of  milk  to  use?  Why? 

,,  Demonstration  9.  To  determine  the  bacterial  content  of  distilled 
! water,  rain  water,  tap  water,  dilute  sewage. 

Put  several  drops  of  the  various  kinds  of  water  on  dishes  containing 
jSterile  agar.  Cover  the  dishes  and  put  them  in  a warm  dark  place  for 
. [24  hours.  Which  dish  contains  the  greatest  number  of  colonies?  The 
igreatest  number  of  different  colonies?  Which  is  the  best  water  to  use  for 
::  drinking  purposes?  For  cooking?  For  laundry?  Why? 


cases  of  influ:er25a 
and  dishwashing 

>51  per  1000 

when  dishes 
are  washed 
in  boiling 
hot  watei' 

252  per  1000 

Mc/hen  dishes 
awe-  noE 

conre-oClX 

washed 

Explain,  from  text,  what  this  diagram  means. 


500  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 


Practical  Exercise  27.  What  general  facts  have  you  learned  about  refriger- 
ation ? What  types  of  refrigerators  are  most  efficient  ? The  most  costly  to  pur- 
chase? The  most  costly  to  run?  What  recommendation  would  you  make  for 
the  average  small  family  living  in  the  country?  In  the  city? 

Practical  Exercise  28.  What  insects  are  household  pests  ? Which  of  these 
damage  foods?  What  would  you  do  to  rid  a house  of  ants?  Roaches? 

Practical  Exercise  29.  Is  cold-storage  food  as  good  as  fresh  food?  Give 
reasons  for  your  answer.  Recent  tests  have  shown  that  the  majority  of  cheap 
ice  boxes  do  not  keep  the  temperature  below  50°  F.  Such  boxes  usually  have 
the  ice  wrapped  in  newspapers  when  it  is  put  in  the  box.  What  effect  does 
the  paper  have  on  the  efficiency  of  the  ice  box? 


Home  water  supplies.  We  have  already  learned  why  water 
which  comes  from  a shallow  well  or  unprotected  spring  should  be 
carefully  tested  and  protected  against  pollution.  Ice  for  use 
in  drinking  water  should  be  carefully  washed,  for  experiments 
show  that  although  nearly  all  bacteria  in  ice  are  killed  after  storage 
of  a few  weeks,  yet  disease  germs  are  often  found  on  the  outside  of 
pieces  of  ice  because  it  is  handled  by  disease  carriers  or  persons  of 
careless  personal  habits.  Water  coolers  and  filters  are  usually 
traps  for  bacteria  and  are  often  dangers  rather  than  aids  in  sani- 
tary living.  Moreover,  a water  cooler  in  a house  is  frequently  ac- 
companied by  a common  drinking  cup. 

Practical  Exercise  30.  Show  what  you  would  do  to  protect  a home  water 
supply  of  uncertain  purity.  Make  a report  to  the  class. 

Disposal  of  wastes.  In  country  homes  where  cesspools  receive 
human  wastes,  great  care  should  be  used  in  locating  them,  espe- 
cially if  the  water  supply  is  from  a shallow  well.  A septic  tank 
costs  little  more  to  install  and  is  much  safer  than  the  ordinary 
cesspool.  In  city  houses  the  disposal  of  human  wastes  is  pro- 
vided for  by  a system  of  sewers.  Garbage  should  be  disposed 
of  each  day.  The  garbage  pail  should  be  frequently  sterilized  by 
rinsing  it  with  boiling  water  and  plenty  of  lye  or  soap.  Remember 
that  flies  frequent  the  uncovered  garbage  pail,  and  that  they  fly 
from  it  to  your  food. 

Practical  Exercise  31.  Make  a diagram  for  your  workbook  to  show  the 
method  of  sewage  disposal  in  your  community ; in  your  home. 

Find  out  the  method  of  garbage  collection  and  disposal  in  your  town. 
Make  suggestions  for  improvement  of  this  service,  if  needed. 


SCHOOL  SURROUNDINGS 


501 


Self-Testing  Exercise 

The  best  known  germicide  is  (1).  Some  cities  require 

the  rooms  of  all  aj)artments  to  have (2)  (3).  Gas 

leaks  are  harmful  because  of  the  danger  of (4) (5). 

Bacteria  on  dishes  can  only  be  destroyed  by (6) (7). 

Foods  should  be  protected  from (8).  iMilk  in  home  should 

be  kept  on  (9)  to  prevent  (10)  of  (11). 

Water  supplies  should  be  (12)  and  (13)  against 

pollution.  A septic  tank  is (14)  than  a (15). 

PROBLEM  Xn.  HOW  MAY  WE  IMPROVE  CONDITIONS  AT 
SCHOOL? 

School  surroundings.  For  forty  weeks  in  the  year  from  five  to 
six  hours  a day  are  spent  by  the  average  boy  or  girl  in  the  schoolroom. 
It  is  part  of  our  environment  and  should  therefore  be  considered 
as  worthy  of  our  care.  A schoolroom  should  be  not  only  attractive, 
but  also  clean  and  sanitary.  City  schools,  because  of  their  loca- 
tion, poor  janitor  service,  or  the  selfishness  and  carelessness  of  chil- 
dren who  use  them,  may  be  very  dirty  and  unsanitary.  Bacteria 
thrive  in  warm  moist  places  where  food  is  present,  and  float  in  the 
air  with  particles  of  dust.  Experiments  show  that  there  are  many 
more  bacteria  in  the  air  when  pupils  are  moving  about,  for  then 
dust,  bearing  bacteria,  is  stirred  up  and  circulated  through  the 
air.  Sweeping  and  dusting  with  dry  brooms  or  dusters  stirs  up 
the  dust,  which  settles  in  some  other  place  with  its  load  of  bacteria. 
Professor  Hodge  tells  of  an  experience  in  a school  in  Worcester, 
Massachusetts.  A health  brigade  was  formed  among  the  children, 
whose  duty  was  to  clean  the  rooms  every  morning  by  wiping  all 
exposed  surfaces  with  damp  cloths.  In  a school  of  425  pupils  not 
a single  case  of  communicable  disease  appeared  during  the  entire 
year.  Hundreds  of  schools  have  tried  experiments  similar  to  this 
and  always  with  the  same  result,  a pleasanter  and  cleaner  building 
and  better  health  of  pupils. 

Pupils  should  be  unselfish  in  the  care  of  a school  building. 
Papers  and  scraps  dropped  by  some  careless  boy  or  girl  make  the 
surroundings  unpleasant  for  hundreds  of  others.  Chalk  thrown 

H.  BIO  — 33 


502  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 


by  some  mischievous  boy  and  then  tramped  under  foot  causes 
dust  particles  in  the  air,  which  may  irritate  the  lungs  of  a hundred 
schoolmates.  Colds  may  be  spread  by  spitting  in  the  halls  or  on  the 
stairways.  Do  not  be  the  one  to  do  such  an  unsportsmanlike  act. 


Keystone  View  Co. 

Why  might  this  be  considered  an  ideal  high  school  building  ? 


Project.  To  form  a service  squad  in  your  school.  Make  a report 
on  such  school  conditions  as  may  be  remedied  by  concerted  or  indi- 
vidual student  action  and  present  it  to  the  class.  If  conditions 
warrant  it,  ask  your  principal  to  hold  a clean-up  week,  have  a health 
assembly,  or  in  some  other  way  start  public  sentiment  in  the  school 
for  better  cooperation  and  a more  sanitary  school  plant. 

Demonstration  10.  To  show  the  effect  of  the  use  of  a duster  and 
of  a damp  cloth  upon  bacteria  in  the  schoolroom. 

Expose  a dish  of  sterile  agar  for  a few  minutes  in  a room  which  is 
being  dusted  with  a dry  cloth  or  feather  duster.  Expose  another  dish 
of  sterile  agar  in  a room  which  is  being  dusted  with  a damp  cloth.  Cover 
the  two  dishes  and  keep  them  in  a warm  place  for  24  hours.  What  is 
the  result? 

Lunch  time  and  lunches.  Lunches  should  be  clean,  tasty,  and 
well  balanced.  In  most  large  schools,  lunch  rooms  are  part  of  the 
equipment  and  balanced  lunches  can  be  obtained  at  low  cost. 
Do  not  make  a lunch  entirely  from  cold  food,  when  hot  can  be 


INSPP]CT1()N  OF  FACTORIES 


503 


obtained.  Do  not  cat  sweets  only.  Ice  cream  is  a good  food,  if 
taken  with  something  else,  but  be  sure  of  the  quality  of  your  ice 
cream.  More  than  250  samples  of  ice  cream  collected  and  exam- 
ined in  Washington,  I).  C.,  contained  from  37,500  to  365,000,000 
bacteria  per  cubic  centimeter.  The  condition  of  ice  cream  de- 
pends largely  on  the  sanitary  conditions  of  the  place  where  it  was 
manufactured.  Above  all,  be  sure  that  all  the  food  you  eat  is  clean. 
Stands  on  the  street,  exposed  to  dust  and  germs,  often  have  for 
sale  food  that  is  far  from  fit  for  human  consumption.  If  you 
eat  your  lunch  on  the  street  near  your  school,  remember  not  to 
scatter  refuse.  Paper,  bits  of  lunch,  and  the  like,  scattered  on 
I the  streets  around  your  school,  show  lack  of  school  spirit  and 
i lack  of  civic  pride. 

Project.  Get  help  from  your  teacher  or  the  local  board  of  health 
' in  testing  the  purity  of  ice  cream  and  other  foods  sold  from  stands 
outside  the  school.  Test  foods  in  your  own  school  cafeteria  at  the 
same  time  as  a control  to  see  which  conditions  are  better. 

; Self-Testing  Exercise 

Check  the  correct  statements  for  your  workbook : 

T.  F.  1.  Schools  are  often  dusty  because  of  the  movement  of  chil- 
dren through  the  halls. 

T.  F.  2.  Feather  dusters  are  better  than  wet  cloths  because  the 
cloths  stain  the  woodwork. 

I T.  F.  3.  Luncheons  should  be  tasty  as  well  as  clean  and  well-balanced. 

T.  F.  4.  Ice  cream  is  always  a safe  food  because  freezing  kills 
; bacteria. 

T.  F.  5.  If  foods  are  exposed,  the  sunlight  will  kill  the  bacteria. 

I PROBLEM  Xni.  HOW  MAY  WE  HELP  IMPROVE  CONDITIONS 
IN  OUR  COMMUNITY? 

Inspection  of  factories  and  public  buildings.  It  is  the  duty  of  a 
city  to  inspect  the  condition  of  all  public  buildings,  especially  of 
factories.  Certain  trades  where  dirt  or  poisonous  fumes  are  given 
off  are  dangerous  to  health,  hence  care  for  the  workers  becomes 
a necessity.  In  such  places  the  machinery  must  be  protected 
by  hoods  or  ventilators  to  carry  off  the  fumes,  and  the  workmen 
I must  be  provided  with  dust  and  fume  masks.  Often  goggles  are 
[provided  to  protect  the  eyes  from  dust  or  bright  light.  There 


504  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 

are  other  occupations  where  noise,  monotony  of  work,  or  too  rapid 
movement  causes  fatigue  and  frequently  accidents.  Workmen  in 
such  trades  must  be  protected,  and  many  state  laws  now  provide  for 
proper  gas  masks,  wheel  and  belt  protectors,  efficient  lighting  and 

other  devices  that 
protect  workmen 
from  the  particu- 
lar hazard  to  which 
they  are  exposed. 
Factories  are  in- 
spected as  to  clean- 
liness, the  amount 
of  air  space  per 
person  employed, 
ventilation,  toilet 
facilities,  and 
proper  fire  protec- 
tion. Tenement 
inspection  should 
also  be  thorough 
and  should  aim  to 
provide  safe  and 
sanitary  homes  for 
workers  and  their 
families. 

Inspection  of  food  supplies.  In  all  cities  certain  regulations  for 
the  care  of  public  food  supplies  are  necessary.  Inspectors  are 
appointed  to  see  that  the  laws  are  enforced  and  that  foods  are  pro- 
tected for  the  thousands  of  people  who  are  to  use  them.  All  raw 
foods  on"  stands  should  be  covered  with  glass  so  as  to  prevent  in- 
sects or  dust  laden  with  bacteria  from  coming  in  contact  with  them. 
Meats  must  be  inspected  for  diseases.  Inspection  of  cold-storage 
plants,  of  factories  where  foods  are  canned,  and  of  bakeries  must 
be  and  is  part  of  the  work  of  a city  in  caring  for  its  citizens. 

Practical  Exercise  31.  Visit  a factory  in  your  neighborhood  and  report  to 
the  class  on  all  the  protection  devices  you  found.  Have  you  any  suggestions 
for  improvement? 


SEWAGE  DISPOSAL 


505 


Project.  lnsi)ect  the  ooiulitions  in  your  own  home  block  or  in  the 
town  in  which  you  live.  Make  a map  showing  tiie  buildings.  Locate 
all  houses,  stores,  factories,  etc.  Indicate  any  cases  of  communicable 
ilisease  on  the  map.  Mark  all  heaps  of  refuse  in  the  street,  all  un- 
coveretl  garbage  pails,  any  street  stands  or  push  carts  which  sell 
uncovered  fruit,  and  any 
stores  which  have  an  ex- 
cessive number  of  flies. 

Note  any  other  unsanitary 
coiulitions  and  mark  them 
with  appropriate  symbols. 


Sewage  disposal.  Sew- 
age disposal  is  an  impor- 
tant sanitary  problem  for 
every  city.  Some  cities, 
like  New  York,  pour  their 
sewage  directly  into  rivers 
which  flow  into  the  ocean. 


Consequently,  much  of 
the  liquid  which  bathes 
the  shores  of  Alanhattan 


Island  is  dilute  sewage. 

Other  cities,  like  Buffalo 
or  Cleveland,  send  their 
sewage  into  the  lakes  from 
which  they  obtain  their 
supply  of  drinking  water. 

The  city  of  Chicago  has 

built  a huge  drainage  canal  which  diverts  water  from  Lake  Michi- 
gan. Through  this  canal  the  sewage  is  diluted  and  is  carried 
eventually  into  the  Mississippi  River  by  way  of  the  Illinois  River. 


Inspectors  are  employed  by  the  government  to  inspect 
and  stamp  all  meat  sent  to  other  states. 


While  there  is  not  a noticeable  increase  in  the  bacterial  content  of 


the  Illinois  River  at  the  point  where  it  flows  into  the  Mississippi, 
this  drainage  canal  has  done  harm  in  another  way.  The  fish  in  the 
upper  Illinois  River  have  been  driven  out  or  killed  by  the  factory 
refuse  and  other  wastes  which  come  down  the  canal.  This  is  only 
one  example  of  the  pollution  of  rivers  by  sewage  and  especially  by 
factory  wastes.  All  over  the  eastern  part  of  our  country  rivers 
have  been  made  open  sewers,  and  now  the  conservation  of  our  fish. 


506  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 


as  well  as  the  water  supply  of  many  of  our  cities,  is  becoming  a 
serious  problem. 

The  best  way  to  avoid  the  pollution  of  rivers  is  by  proper  sewage 
disposal,  even  if  this  method  is  expensive.  Sewers  for  large  cities 
are  planned  so  that  the  dilute  sewage  is  carried  to  a sewage  dis- 
posal plant,  usually  situated  a short  distance  outside  of  the  com- 
munity. Here  the  solid  wastes  are  screened  out,  and  then  the 
smaller  particles  are  precipitated  out.  The  disposal  of  the  solid 
material,  called  sludge,  is  still  a serious  problem.  In  some  cities 
this  sludge  is  dried,  treated,  and  used  as  fertilizer.  The  fluid 
sewage,  after  the  solid  matter  is  taken  out,  is  usually  run  over 
filter  beds  composed  of  coarse  sand.  In  these  filters  bacteria 
oxidize  the  remaining  organic  matter  of  the  sewage,  so  that  the 
liquid  which  flows  off  is  harmless  and  odorless.  But  such  water 
is  never  used  until  it  is  first  treated  with  chemicals,  such  as 
chlorine,  in  order  to  kill  any  harmful  germs  that  may  be  left. 

Practical  Exercise  33.  Report  on  an  up-to-date  method  of  sewage  disposal 
in  some  city  or  community.  Compare  the  conditions  of  this  city  with  those 
existing  in  your  community. 


The  work  of  the  department  of  street  cleaning.  Another  city 
problem  is  the  disposal  of  refuse  and  garbage.  The  city  streets. 


A B 


Culture  A was  exposed  to  the  air  in  a well-cleaned  and  watered  street  in  a residential 
section  of  a city.  Culture  B was  exposed  to  the  air  in  a crowded  street  in  a business  section 
of  the  same  city.  How  do  you  account  for  the  differences  and  results? 

when  dirty,  contain  countless  millions  of  germs  which  have  come 
from  decaying  material  or  from  people  and  animals  more  or  less 


DEPARTMENT  OF  STIiEET  CLEANING 


507 


diseased.  In  most  large  cities  a department  of  street  cleaning  not 
only  cares  for  the  removal  of  dust  from  the  streets,  but  also  has  the 
removal  of  garbage,  ashes,  and  other  waste  as  a part  of  its  work. 
'Phe  disposal  of  solid  wastes  is  a tremendous  task.  In  Manhattan, 
New  York,  the  dry  wastes  are  estimated  to  be  1,000,000  tons  a year 
in  addition  to  about  175,000  tons  of  garbage.  In  some  cities,  such 
as  Minneapolis,  garbage  must  be  wrapped  in  paper.  This  aids 
burning  it  in  the  city  incinerator.  In  many  cities  the  garbage  is 
removed  in  carts,  and  part  of  it  is  burned  in  huge  furnaces.  The 
( animal  and  plant  refuse  are  sometimes  cooked  in  great  tanks,  the 
fats  extracted  from  this  material,  and  the  solid  matter  sold  for 
fertilizer.  Ashes  are  used  in  some  places  for  filling  marsh  land. 
iThus  the  removal  of  waste  matter  may  pay  for  itself  in  a large 
1 city. 

Practical  Exercise  33.  Report  to  the  class  on  the  conditions  existing  in  you) 
community  with  reference  to  disposal  of  garbage,  ashes,  and  other  wastes. 
What  rules  exist?  Is  the  collection  of  garbage  and  ashes  a city  or  private 
I function?  What  is  done  with  reference  to  street  cleaning? 

Self-Testing  Exercise 

Check  the  correct  statements  for  your  workbook: 

T.  F.  1.  Some  occupations,  such  as  trades  which  have  dust  or 
poisonous  fumes,  are  dangerous. 

T.  F.  2.  Food  supplies  which  are  not  packed  in  containers  do  not 
need  to  be  inspected. 

T.  F.  3.  The  government  inspects  all  food  so  there  is  no  danger 
ito  the  consumer. 

! T.  F.  4.  People  could  safely  drink  dilute  sewage  if  it  were  first 
.filtered  and  chlorinated. 

T.  F.  5.  Pollution  of  our  streams  with  sewage  not  only  drives  out 
ior  kills  the  fish  but  makes  the  polluted  stream  a menace  to  health. 

T.  F.  6.  The  best  method  of  sewage  disposal  for  large  cities  is 
Itreating  it  with  chemicals. 

i PROBLEM  XIV.  WHAT  PROTECTIVE  HEALTH  AGENCIES 
SHOULD  EXIST  IN  A COMMUNITY? 

Practical  Exercise  34.  Compare  the  functions  of  your  local  board  of  health 
with  those  listed  in  the  diagram  on  page  508.  How  many  departments,  if 
hny,  has  it?  How  large  a community  does  it  serve?  How  many  board  mem- 
bers are  there?  Are  they  paid  or  volunteer  workers?  What  work  do  they  do? 


508  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 


Are  there  any  laboratories  ? If  so,  describe  them.  Do  the  local  health  officers 
concur  with  all  the  activities  shown  on  the  diagram  ? To  what  extent  ? 

Has  your  locality  an  efficient  board  of  health?  If  not,  what  suggestion 
can  you  make  for  improvement? 


Public  hygiene.  Although  it  is  absolutely  necessary  for  each 
individual  to  obey  the  laws  of  health  in  order  to  keep  well,  it  has 
become  necessary  also,  especially  in  large  cities,  to  have  a depart- 
ment or  board  of  health  to  exercise  general  supervision  over  the 
health  of  the  people  living  in  the  community.  In  addition  to  such  a 
body  in  cities,  supervision  over  the  health  of  citizens  is  also  exercised 
by  state  boards  of  health.  Since  1912  the  United  States  Public 
Health  Service  has  had  general  supervision  over  interstate  quaran- 
tine and  public  health.  Its  valuable  reports  and  reprints  are  avail- 
able for  schools  and  should  be  used  in  your  project  and  classwork. 

The  functions  of  a city  board  of  health.  The  administration 
of  the  board  of  health  of  a city  includes  a number  of  divisions, 

each  one  of  which 
has  a different  work 
to  do.  Each  is  in  it- 
self important,  and, 
working  together, 
the  entire  machine 
provides  ways  and 
means  for  making  a 
great  city  a safe  and 
sanitary  place  in 

The  health  departments  of  various  cities,  counties,  or  states  which  tO  live.  A 
have  a number  of  divisions.  How  many  are  there  in  your  city  local  health  board, 
and  state  departments  of  health  ? t , 

according  to  an  au- 
thority, Dr.  C.  E.  A.  Winslow,  should  supervise  the  food  supplies  and 
sanitation  of  a city.  It  should  from  its  laboratories  take  care  of  the 
communicable  diseases  by  means  of  vaccines  and  antitoxins.  It 
should  have  a department  of  child  hygiene  and  should  carry  on 
health  campaigns  through  its  department  of  publicity  and  educa- 
tion. Finally,  it  should  publish  the  vital  statistics  of  the  community. 

The  division  of  communicable  diseases.  Communicable  dis- 
eases are  chiefly  spread  through  personal  contact.  It  is  the  duty 
of  a government  to  prevent  a person  having  such  a disease  from 


Till']  DIVISION  OF  COMiMUNICARLE  DISEASES  509 

sproadiiifi;  it  ainon^  his  noi^hbors.  This  is  dono  by  the  board  of 
health  recniirin^  tlio  (luarantine  or  the  isolation  of  the  person 


Nai.  T.  B.  Assn. 

Some  health  agencies,  schools,  and  sanitariums  provide  camps  for  children  who  are  under- 
nourished or  who  have  been  in  direct  contact  with  persons  suffering  from  tuberculosis. 

i having  the  disease.  No  one  save  the  doctor  and  the  nurse  should 
! enter  the  room  of  the  person  quarantined.  After  the  disease  has 
I run  its  course,  the  clothing,  bedding,  etc.,  in  the  sick  room  are  dis- 
infected.  This  is  known  as  terminal  disinfection. 

Tuberculosis,  which  not  many  years  ago  killed  fully  one  seventh 
of  the  people  who  died  from  disease  in  this  country,  now  kills  less 
i than  one  tenth.  This  decrease  has  been  brought  about  largely 
.through  the  treatment  of  the  disease.  Since  it  has  been  proved 
^ that  tuberculosis,  if  treated  early  enough,  is  cured  by  quiet  living, 
good  food,  and  plenty  of  fresh  air  and  light,  we  find  that  numerous 
sanitariums  have  come  into  existence  which  are  supported  by 
private  or  public  means.  At  these  sanitariums  the  patients  live 
! out  of  doors,  and  sleep  in  the  open  air^  and  have  plenty  of  nourish- 


510  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 


ing  food  and  little  exercise.  Hundreds  of  sanitariums  are  now 
established  in  various  parts  of  the  country  and  are  maintained  by 
taxation  as  a part  of  the  expenditure  of  the  city,  county,  and  state 
boards  of  health.  There  are  many  private  sanitariums  as  well, 
maintained  by  various  benevolent  orders.  In  this  way  and  by 
laws  which  require  proper  air  shafts  and  window  ventilation  in 
tenement  houses,  by  laws  against  spitting  in  public  places,  and  in 
other  ways,  the  boards  of  health  in  our  towns  and  cities  are  waging 
war  on  tuberculosis. 

Work  of  the  division  of  school  and  infant  hygiene.  Besides 
the  division  of  communicable  diseases,  the  division  of  sanitation, 
which  regulates  the  general  sanitary  conditions  of  houses  and  their 
surroundings,  and  the  division  of  inspection,  which  looks  after  the 
purity  and  conditions  of  sale  and  delivery  of  milk  and  foods,  there 
is  another  division  which  most  vitally  concerns  school  children. 
This  is  the  division  of  school  and  infant  hygiene,  which  supervises 
the  care  of  the  children  of  the  city. 

Adenoids.  Many  children  suffer  needlessly  from  enlarged 
tonsils  and  adenoids  — growths  in  the  back  of  the  nose  and  mouth 
which  cut  off  part  of  the  normal  supply  of  air  to  the  lungs.  A child 
suffering  from  these  growths  is  usually  a “ mouth  breather.”  The 
result  to  the  child  may  be  deafness,  chronic  running  of  the  nose, 
nervousness,  and  lack  of  power  to  think.  His  body  cells  are 
starving  for  oxygen.  A very  simple  operation  removes  these 
growths.  Cooperation  of  the  children  and  parents  with  the  doc- 
tors or  nurses  of  the  board  of  health  will  do  much  in  removing  this 
handicap  from  many  young  lives. 

Eyestrain.  Another  handicap  to  a boy  or  a girl  is  eyestrain. 
In  a survey,  sometime  ago,  twenty-two  per  cent  of  the  school  chil- 
dren of  Massachusetts  were  found  to  have  defects  in  vision.  Tests 
for  defective  eyesight  may  be  made  easily  at  school  by  competent 
doctors,  and  if  the  weakness  is  corrected  by  procuring  proper 
glasses,  a handicap  on  future  success  will  be  removed. 

Physical  examinations.  Decayed  teeth  are  another  handicap 
cared  for  by  this  division.  Free  dental  clinics  have  been  established 
in  many  cities,  and  if  children  will  do  their  share  in  caring  for  their 
teeth,  the  chances  of  their  success  in  later  life  will  be  greatly  aided, 


PHYSICAL  EXAMINATIONS 


511 


In  the  schools  of  Elizabeth,  N.  in  1925  there  were  nearly  13,000 
children  examined  for  physical  defects.  These  were  placed  in 
four  groups,  depending  on  the  condition  of  physical  well-being. 
Here  the  group  that  was  in  best  health  showed  the  best  school 
grades,  while  those  in  poorest  health  had  the  poorest  grades.  Boys 
and  girls,  if  handicapped  with  poor  eyes  or  teeth,  do  not  have  a 
fair  chance  in  life’s  competition.  In  a certain  school  in  New  York 
there  were  236  pupils  marked  “ C ” in  their  school  work.  These 
children  were  examined,  and  126  were  found  to  have  bad  teeth, 
54  to  have  defective  vision,  and  56  to  have  other  defects,  as  poor 
hearing,  adenoids,  enlarged  tonsils,  etc.  Of  these  children,  185 
were  treated  for  these  various  difficulties,  and  51  did  not  take 
treatment.  During  the  following  year’s  work  176  of  these  pupils 
improved  from  “ C ” to  “ B ” or  ‘‘A,”  while  60  did  not  improve. 
If  defects  are  such  a handicap  in  school,  what  will  be  their  effect 
on  the  chances  of  success  in  life  outside? 

The  department  of  school  hygiene  deserves  the  earnest  coopera- 
tion of  every  young  citizen,  girl  or  boy.  If  each  of  us  would 
honestly  help  by  maintaining  quarantine  in  the  case  of  communi- 
cable disease,  by  observing  the  rules  of  the  health  department,  by 
acting  upon  reliable  advice  in  case  of  eyestrain,  bad  teeth,  or 
adenoids,  and  most  of  all  by  observing  the  rules  of  personal  hygiene, 
the  community  in  which  we  live,  a generation  hence,  would  be  com- 
posed of  stronger,  more  prosperous,  and  more  efficient  citizens. 

Practical  Exercise  36.  Make  an  outline  of  all  the  health-protective  agencies 
in  your  community. 

Practical  Exercise  36.  Tell  what  is  being  done  in  your  own  school  to  check 
on  the  health  of  the  students.  Is  there  any  “ follow  up  ” of  those  who  are 
not  well? 

Self-Testing  Exercise 

Check  the  correct  statements  for  your  workbook: 

T.  F.  1.  The  function  of  the  U.  S.  Public  Health  Service  is  to 
control  my  city  health  department. 

T.  F.  2.  Quarantine  is  a protective  measure  and  should  be  obeyed. 

T.  F.  3.  Tuberculosis  can  be  controlled  entirely  through  sani- 
tariums. 

T.  F.  4.  Children  whose  health  is  poor  usually  have  poor  school 
grades. 


512  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 


Review  Summary 

Test  your  knowledge  of  the  unit  by : (1)  rechecking  on  the  survey  ques- 
tions ; (2)  performing  the  assigned  exercises ; (3)  checking  with  your  teacher 
your  scores  on  the  various  tests  and  doing  over  those  that  you  missed ; (4)  mak- 
ing an  outline  of  the  unit  for  your  work  book. 


Test  on  Fundamental  Concepts 

In  a vertical  column  under  the  heading  CORRECT  write  numbers  of  all  statements  you  be- 
lieve are  true.  In  another  column  under  INCORRECT  write  numbers  of  untrue  statements. 
Your  grade  = right  answers  X 2. 

I.  Quarantine  (1)  is  necessary  because  it  gives  the  patient  a rest; 
(2)  is  necessary  because  by  isolating  a person  sick  with  a disease  we  may 
keep  others  from  having  it ; (3)  is  useless  except  in  early  stages  of 
disease ; (4)  is  an  unselfish  action  because  it  protects  others ; (5)  should 
be  enforced  on  all  persons  who  have  had  contact  with  a person  ill 
with  communicable  disease  until  the  incubation  period  of  that  disease 
has  been  passed, 

II.  Immunity  (6)  means  that  a person  can  never  take  a certain 
disease,  no  matter  if  he  is  exposed  to  it ; (7)  is  always  specific,  that  is, 
against  one  disease  (A  person  may  be  immune  to  smallpox  and  be 
susceptible  to  measles) ; (8)  is  never  restricted  to  certain  races,  whites 
and  Negroes  being  equally  susceptible  to  tuberculosis;  (9)  is  natural 
to  some  people  but  not  to  others;  (10)  is  not  modified  by  a person’s 
condition. 

III.  Active  immunity  (11)  is  gained  by  means  of  antitoxins; 
(12)  takes  place  when  the  body  helps  to  fight  the  disease  by  making 
antibodies  in  the  blood  ; (13)  is  brought  about  against  smallpox  through 
vaccination ; (14)  is  gained  in  typhoid  through  the  introduction  of  dead 
germs  with  their  toxins;  (15)  is  not  possible  unless  the  blood  makes 
antibodies. 

IV.  Passive  immunity  (16)  occurs  when  the  body  fights  the  disease 
by  making  its  own  antitoxins;  (17)  is  seen  in  the  antitoxin  treatment 
against  diphtheria ; (18)  is  brought  about  when  an  antitoxin  is  formed 
outside  the  body  and  is  injected  into  the  body  to  help  fight  the  disease ; 
(19)  is  brought  about  by  Schick  or  Dick  test;  (20)  is  not  useful,  for  sta- 
tistics show  it  has  not  reduced  the  death  rate  in  diphtheria. 

V.  The  way  to  keep  well  (21)  is  to  have  immunity  against  all  the 
diseases  given  at  once  and  get  it  over  with;  (22)  is  to  keep  the  body 


ACHIEVEMENT  TEST 


513 


resistance  high  through  sensible  living ; (23)  is  to  avoid  people  whom 
you  think  have  communicable  diseases;  (24)  is  to  have  plenty  of 
nourishing  food  at  regular  times,  identy  of  sleep,  and  work  and  play 
in  moderation;  (25)  is  never  to  worry,  and  to  take  proper  precautions 
in  case  of  illness  of  others. 

VI.  Animals  (26)  may  cause  disease,  as  the  malarial  parasite; 
(27)  may  cause  disease,  as  the  Culex  mosquito ; (28)  may  spread 
disease,  as  the  house  fly ; (29)  may  be  parasites  in  two  different  hosts, 
neeiling  both  to  complete  their  life  cycle;  (30)  are  only  harmful  if 
they  are  parasites. 

VII.  Malaria  (31)  may  be  controlled  by  killing  off  the  Anopheles 
mosquito ; (32)  is  only  known  in  the  tropics ; (33)  is  caused  by 
'mosquitoes  ; (34)  may  be  cured  by  taking  quinine  ; (35)  is  caused  by  a 
protozoan. 

VIII.  The  following  animals  may  act  as  carriers  of  human  disease : 

(36)  rats ; (37)  birds  ; (38)  pigs ; (39)  flies  ; (40)  fleas. 

IX.  We  may  improve  conditions  in  our  community  (41)  by 
always  voting  for  all  public  measures  without  investigating  their 
value  because  those  who  make  the  laws  know  best ; (42)  by  making 
sure  that  our  public  water  supply  is  protected  by  chlorination  and 
filtration  if  the  source  is  not  pure;  (43)  by  insisting  upon  pure  milk 
and  regulations  that  provide  for  it ; (44)  by  patronizing  all  stores 
equally,  clean  and  dirty  ones ; (45)  by  cooperation  with  the  health 
idepartment. 

X.  The  protective  health  agencies  of  much  value  in  a community 

are  (46)  the  city  council ; (47)  the  board  of  aldermen ; (48)  the 
board  of  health ; (49)  hospitals  and  sanitariums ; (50)  the  division 
of  school  health  and  hygiene. 

Achievement  Test 

1.  How  have  you  cooperated  with  the  health  authorities  in  the 
matter  of  quarantine  after  exposure  to  a communicable  disease? 

2.  What  is  the  value  of  acquired  immunity? 

3.  What  is  the  story  of  malaria  in  Microbe  Hunters? 

4.  What  is  the  story  of  yellow  fever  in  either  Microbe  Hunters  or 
i Health  Heroes? 

5.  How  may  malaria  and  yellow  fever  be  controlled  ? 

6.  How  may  we  get  rid  of  flies? 


514  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 


7.  What  are  all  the  insects  that  spread  diseases  ? Suggest  a way 
to  control  them. 

8.  Have  you  made  a fly  and  mosquito  survey  of  your  neighbor- 
hood? What  did  you  find? 

9.  Have  you  made  a survey  of  your  home  and  surroundings  and 
estimated  the  yearly  damage  done  to  them  by  rats?  What  is  it? 

10.  What  do  the  reports  of  the  Rockefeller  Foundation  say  about 
the  extent  hookworm  has  been  controlled  ? 

11.  How  do  the  various  unfavorable  factors  of  your  environment 
affect  your  home  and  how  may  you  prevent  such  factors  from  doing 
harm? 

12.  Have  you  a service  squad  in  your  school?  What  do  you  do 
to  make  its  work  effective  ? 

13.  What  facts  do  you  know  about  sewage  and  garbage  disposal 
in  your  community? 

14.  How  is  the  health  department  of  your  community  organized 
and  how  does  it  do  its  work? 


Practical  Problems 

1.  Describe  the  process  of  making  vaccines.  Ask  your  teacher 
for  references. 

2.  Suppose  your  city  was  threatened  with  a typhoid  epidemic. 
Outline  the  probable  procedure  of  the  Board  of  Health  and  list  your 
part  in  fighting  the  epidemic. 

3.  Suppose  your  home  was  made  uncomfortable  from  mosquitoes 
coming  from  an  unknown  source.  The  rest  of  the  community  is 
not  bothered  by  them.  Outline  your  procedure  in  ridding  your  home 
of  these  pests. 

4.  What  do  you  know  of  the  sanitary  conditions  of  your  own 
home?  Can  you  locate  sewers,  cesspool,  or  septic  tanks,  etc.?  Do 
you  know  if  your  water  supply  is  tested  regularly  and  is  adequately 
protected?  Do  you  have  regular  garbage  collection?  Do  you  know 
how  garbage  is  disposed  of?  How  is  the  food  in  your  home  protected? 
Are  you  properly  screened  against  insects?  How  high  a score  would 
you  and  your  home  make  on  the  following  score  card? 


a.  Environment 

Pure  air 10 

Pure  water 10 

Well-drained  soil 10 

Plenty  of  sunlight 10 

Not  too  great  extreme  of  heat  or  cold 5 

Foods  supplied  from  home  garden 5 

Foods  cheap  and  good 5 


PRACTICAL  PROBLExMS  515 

b.  Water  in  my  home 

Safe  supply 10 

Ample  supj^)ly 10 

All  parts  ot  home  supplied 10 

Plumbing  in  gootl  eomlition 10 

Soft  water  provided 10 

c.  Care  of  foods  in  my  home 

Clean  kitchen  and  utensils 10 

Gootl  refrigeration 10 

Sterilization  and  pasteurization 10 

Proper  use  of  preservatives 10 

Protection  from  insects,  etc 10 

d.  Household  pests 

No  flies 10 

No  mosquitoes 10 

No  body  pests  (fleas,  bedbugs,  head  lice) 10 

No  food  or  cloth  pests  (roaches,  ants,  weevils,  clothes  moths,  etc.)  10 
No  rats  or  mice 10 

e.  Removal  of  wastes 

E.xposed  plumbing 10 

All  porcelain  fixtures 10 

Have  a working  knowledge  of  system 10 

Sewer  connections  or  septic  tank 10 

Garbage  pail  properly  kept 10 

/.  Personal  health  habits 

Setting-up  drill  and  deep  breathing 5 

Cool  rub  or  shower  every  day 5 

Teeth  brushed  morning  and  night 5 

Slow  eating  at  meals 5 

Food  chewed  well 5 

No  overeating 5 

Cheerfulness  at  meals  . . . 5 

Regular  toilet  habits 5 

Wash  hands  often  5 

Clean  shoes  and  clean  linen 5 

Loose,  comfortable  clothing 5 

Feet  warm  and  dry 5 

Regular  play  hours 5 

Exercise  in  open  air  two  hours  a day 5 

Regular  work  and  study  hours  (at  least  two  hours) 5 

Proper  lighting  for  study 5 

Bed  before  10  p.m 5 

Sleep  in  open  air  or  with  windows  open  top  and  bottom 5 

No  coffee,  tea,  or  cigarettes 5 

g.  Protection  against  disease 

Vaccinated  for  smallpox 5 

Teeth  examined  twice  a year 5 

, All  teeth  cavities  filled 5 

! Eyes  examined  once  a year 5 

Glasses  used  when  necessary  5 


516  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  HEALTH 


Keep  more  than  five  feet  distant  from  those  who  cough  or  sneeze  . 5 

Take  care  to  use  handkerchief  if  you  cough  or  sneeze 5 

Stay  in  the  house  if  you  have  a cold 5 

All  clothing  clean  and  sterile  at  all  times 5 

Wounds  properly  disinfected 5 

h.  Clothing,  bathing,  and  ventilation 

Proper  outer  clothing 10 

Proper  and  clean  underclothing 10 

Bathing  twice  a week  at  least 10 

Proper  bedroom  hygiene 10 

Proper  home  ventilation 10 

i.  Lighting  my  home 

Sunlight  plentiful 10 

Windows  ample,  wall  papers  good  reflectors 10 

Artificial  light  economical 10 

Proper  lighting  for  all  kinds  of  work 10 

Good  systems  of  lighting  used 10 

Total  Possible  Score 500 


5.  What  do  you  know  about  the  sanitation  of  your  own  com- 
munity? Its  water  supplies,  milk  and  food  inspection,  garbage  and 
ash  disposal,  sewage  disposal?  What  agencies  care  for  each  of  the 
above?  What  would  you  do  in  case  of  a typhoid  outbreak  in  your 
city?  Septic  sore  throat?  Tuberculosis  of  children? 

6.  Is  your  school  adequately  ventilated?  Is  its  heating  plant, 
the  sanitary  condition  of  its  toilets,  gymnasium,  and  the  methods  of 
cleaning  the  best  possible? 

7.  What  is  the  Board  of  Education  doing  to  protect  your  health? 

8.  Do  you  have  a sanitary  code  in  your  community?  If  so.,  who 
administers  it?  What  do  you  know  about  it?  Is  there  adequate 
inspection  of  food  supplies?  Care  of  milk?  Do  you  know  where 
the  milk  you  drink  comes  from  and  how  it  is  cared  for? 

9.  To  what  extent  in  the  past  have  you,  as  a young  citizen, 
cooperated  with  the  authorities  to  make  your  town  a more  sanitary 
and  safer  place  to  live  in? 

Useful  References 

Andress,  Aldinger,  Goldberger,  Health  Essentials.  Ginn,  1928. 
Broadhurst,  Home  and  Community  Hygiene.  Lippincott,  1929. 
Broadhurst,  How  We  Resist  Diseases.  Lippincott,  1923. 

Bulletins  and  Publications  of  Committee  of  One  Hundred  on  National 
Health. 

Conn,  Bacteria  Yeasts  and  Molds.  Revised.  Ginn,  1932. 

De  Kruif,  Microbe  Hunters.  Harcourt,  Brace,  1926. 

Downing,  Science  in  the  Service  of  Health.  Longmans,  1930. 

Farmers’  Bulletins:  70,  658,  851. 

Haggard,  H.  W.,  What  You  Should  Know  about  Health  and  Disease. 
Harper,  1928. 


USEFUL  REFERENCES 


517 


Hunter,  Laboratory  Problems  in  Cine  Biology.  American  Book  Company. 
Hunter  and  Wliitman,  Science  in  Our  Social  Life.  American  Book,  1935. 
liygeia.  American  Metlical  Association. 

Bark  and  Williams,  Who's  Who  among  the  Microbes.  Century,  1929. 
Public  Health  Reprints;  54,  78,  lOb,  192,  234,  302,  341,  441,  448,  499, 
530,  080,  723,  821,  827,  850. 

Reports  of  Boards  of  Health  of  California,  Illinois,  New  York,  Virginia, 
etc. ; and  of  the  (dty  of  New  York  and  other  cities. 

Ritchie,  Primer  of  Sanitation.  World  Book,  1925. 

School  Hygiene.  American  School  Hygiene  Association. 

Tobey,  Rulers  of  the  Plagues.  Scribner’s,  1930. 

Tolman,  Hygiene  for  the  Worker.  American  Book  Company. 

Winslow  and  Hahn,  The  A‘ew  Healthy  Living.  Bobbs-Meri'ill,  1929. 
Zinsser,  Textbook  of  Bacteriology.  Appleton,  1927. 


H.  BIO  — 34 


SURVEY  QUESTIONS 

What  do  we  mean  by  economic  value  ? What  plants  have  the  greatest 
economic  value  in  your  locality  ? Why  are  birds  called  the  farmer’s  best  ! 
friends  ? How  can  you  conserve  bird  life  in  your  community  ? What  crops  ! 
are  damaged  by  insects?  How  are  insect  pests  controlled ? i 


Ewing  Galloway 

UNIT  XVI 

HOW  DOES  MAN  CONTROL  HIS  ENVIRONMENT  FOR 
WEALTH? 

Preview.  To  the  boy  or  the  girl  living  in  the  city  green  plants 
seem  to  have  little  direct  value.  Although  we  see  vegetables  for 
sale  in  stores,  and  we  know  that  fruits  have  a money  value,  we  are 
not  likely  to  realize  that  the  wealth  of  our  nations  depends  upon 
growing  crops  more  than  it  does  on  manufactories  and  business 
houses.  The  economic  or  “ dollars  and  cents  ” value  of  plants  is 
enormous,  and  our  lives  depend  on  the  food  which  they  supply. 

Another  great  source  of  wealth  is  the  animals  man  uses  for  food, 
as  a source  of  raw  material  for  clothing,  furs,  dyes,  oils,  perfumes, 

518 


PREVIEW 


519 


and  many  other  commodities.  But  both  plants  and  animals  have, 
in  another  sense  from  the  above,  an  economic  value.  If  plants, 
such  as  weeds,  destroy  our  crops  by  taking  their  place,  or  if  animals, 
such  as  coyotes,  destroy  sheep  by  killing  them,  then  they  are  harm- 
ful in  a “ dollars  and  cents”  way. 

^^'e  have  already  learned  that  man  plays  a very  important  part 
in  disturbing  the  balance  of  life  as  it  exists  on  the  earth.  This  has 
been  brought  about  by  the  increased  population  and  the  conse- 
quent necessary  increase  in  food  and  other  supplies.  Through 
planting  crops  which  have  nitrogen-fixing  bacteria  associated  with 
I them,  it  has  become  possible  for  the  earth  to  supply  more  crops. 

^ By  irrigating  large  areas  of  practically  desert  land  man  has  been 
able  to  raise  large  crops  of  grains,  vegetables,  and  fruits. 

1 iNIan  is  also  constantly  finding  new  uses  for  animal  products. 
Fishes,  such  as  the  dogfish,  which  were  formerly  unmarketable, 
because  they  were  not  thought  good  to  eat,  are  now  an  article  of 
I food  under  the  name  of  the  grayfish.  This  is  only  one  instance  of 
how  man,  as  the  thinking  animal,  exploits  other  forms  for  his  own 
benefit.  iNIore  people  on  the  earth  means  a need  for  more  food. 
Vlan  has  come  to  realize  the  way  in  which  he  has  been  wasting  the 
living  things  which  he  needs  and  he  is  emphasizing  methods  of 
conservation  as  well  as  the  use  for  food  of  plants  and  animals  that 
formerly  were  not  considered  as  fit  for  food. 

Those  of  us  who  live  in  farming  communities  are  aware  of  the 
harm  done  by  many  insects  and  know,  too,  that  our  bird  friends  do 
i a good  deal  to  help  make  it  possible  for  the  farmer  to  raise  his  crops. 
But  those  of  us  who  do  not  know  the  birds  as  friendly  fighters  in 
I our  behalf  should  have  some  evidence  along  this  line.  Moreover, 

I all  of  us  ought  to  know  a few  common  birds  so  we  may  be  able  to 
recognize  them. 

Birds  not  only  eat  insects  but  some  of  them  eat  weed  seeds,  thus 
keeping  these  pests  somewhat  more  under  control.  Even  the 
birds  which  do  eat  crops  make  up  for  this  by  feeding  in  part  upon 
insects  or  harmful  rodents. 

To  understand  the  value  of  birds  better  a few  examples  of  in- 
sect damage  will  be  given  and,  when  possible,  it  will  be  shown 
how  insects  are  controlled  by  the  birds  which  feed  upon  them. 


520  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  WEALTH 


PROBLEM  I.  HOW  ARE  PLANTS  USED  AS  FOOD? 

Leaves  as  food.  Grazing  animals  feed  almost  entirely  on  tender 
shoots,  leaves,  or  blades  of  grass.  We  can  realize  the  economic 
value  of  grass  when  we  consider  the  fact  that  for  the  last  ten  years 
the  hay  crop  in  this  country  was  worth  well  over  $1,000,000,000  a 
year.  And  this  does  not  take  into  account  the  wild  grasses  used 
as  forage  by  numerous  grazing  animals. 

Certain  leaves  and  buds  are  used  as  food  by  man.  Lettuce, 
kale,  spinach,  and  broccoli  are  examples.  A cabbage  head  is  a 


What  vegetables  are  leaves  ? Do  you  know  any  others  ? 


large  leaf  bud.  An  onion  is  a compact  budlike  mass  of  thickened 
leaves  which  contain  stored  food. 

Practical  Exercise  1.  Make  a table  of  foods  to  be  filled  out  from  material 
found  in  this  unit  and  in  books  of  reference.  Fill  out  the  first  column  of  this 
table  by  placing  in  it  ten  leaves  used  as  food  by  man. 

FOOD  OF  MAN 


Leaves 

Stems 

Roots 

Seeds 

Flowehs 

Fhuits 

Stems  as  food.  If  one  were  asked  to  name  a stem  used  as  food, 
he  would  probably  mention  either  asparagus  or  celery.  Sugar 


STEMS  AS  FOOD 


521 


Wright  Pierce 


Can  you  name  stems,  other  than  those  given  above,  that  are  used  for  food  ? 

cane  certainly  ought  to  be  named  also,  since  over  half  of  the 
> world’s  supply  of  sugar  comes  from  this  source.  Maple  sugar  is  a 
much  used  commodity  obtained  from  the  sap  drawn  from  the 
’ trunks  (enlarged  stems)  of  sugar  maples.  Over  16,000  tons  of  this 
I sugar  is  produced  every  spring.  The  pithy  stem  or  trunk  of  the 
sago  palm,  grown  by  the  native  of  the  East  Indies,  is  made  into  a 
meal  or  flour.  This  flour  is  shipped  to  all  parts  of  the  world  and 
is  used  for  making  starch,  puddings,  and  for  thickening  soups. 
I Another  stem,  the  potato,  growing  underground,  forms  one  of 
man’s  staple  articles  of  diet  in  this  country. 

Practical  Exercise  2.  Fill  out  a second  column  in  your  table  with  ten  dif- 
ierent  stems  used  as  food. 

1 Roots  as  food.  Roots  which  store  food  for  plants  form  an  impor- 
jtant  part  of  man’s  vegetable  diet.  Beets,  radishes,  carrots,  pars- 
nips, sweet  potatoes,  and  many  others  might  be  mentioned. 


522  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  WEALTH 


Read  the  table  below  and  tell  which  of  these  roots  contains  the  most  nutrients. 

The  following  table  shows  the  proportion  of  nutrients  in  some 
of  the  more  common  roots  : 


i 


Water 

Proteins 

Carbo- 

hydrates 

Fat 

Mineral 

Matter 

Carrot  . . . 

89 

0.5 

5 

0.2 

1.0 

Parsnip  . . . 

81 

1.2 

8.7 

1.5 

1.0 

Turnip  . . . 

92.8 

0.5 

4. 

0.1 

0.8 

Sweet  potato 

74  - 

1.5 

20.2 

0.1 

1.5 

Beet  .... 

82.2 

0.4 

13.4 

0.1 

0.9 

Practical  Exercise  3.  Add  ten  roots  to  your  list  of  foods.  Using  the  above  ■ 
table,  figure  out  the  roots  which  give  you  the  most  food  for  your  money  at  ! 
current  prices. 


Seeds  as  foods.  Our  cereal  crops,  corn,  wheat,  oats,  etc.,  have  j 
played  a very  important  part  in  the  civilization  of  man  and  are  i 
now  of  much  importance  to  him  as  food  products.  Bread  made  | 

i 

i 


SEEDS  AS  FOODS 


523 


% 


What  seeds,  other  than  those  given  here,  do  you  use  for  food? 

from  wheat  flour  is  frequently  called  the  “ staff  of  life.”  Our 
grains  are  the  cultivated  progeny  of  wild  grasses.  Domestication 
of  plants  and  animals  marks  epochs  in  the  advance  of  civilization. 

The  man  of  the  stone  age  hunted  wild  beasts  for  food,  and  lived 
like  one  of  them  in  a cave  or  wherever  he  happened  to  be ; he  was 
a nomad,  a wanderer,  with  no  fixed  home.  He  may  have  dis- 
covered that  wild  roots  or  grains  were  good  to  eat;  perhaps  he 
stored  some  away  for  future  use.  Then  came  the  idea  of  growing 
things  at  home  instead  of  digging  or  gathering  the  wild  fruits  from 
the  forest  and  plain.  The  tribes  which  flrst  cultivated  the  soil 
nade  a great  step  in  advance,  for  they  had  as  a result  a flxed  place 
;or  habitation.  The  cultivation  of  grains  and  cereals  gave  them  a 
r Store  of  food  which  could  be  used  at  times  when  other  food  was 
f!  Scarce.  The  word  “ cereal  ” was  derived  from  Ceres,  the  Roman 
i goddess  of  agriculture.  From  earliest  times  the  growing  of  grain 
f S,nd  the  progress  of  civilization  have  gone  hand  in  hand.  As 


524  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  WEALTH 


nations  have  advanced  in  power,  their  dependence  upon  the  cereal 
crops  has  become  greater  and  greater. 

“ Maize,  Indian  corn,  has  played  a most  important  part  in  the 
history  of  the  New  World,  as  regards  both  the  red  men  and  the  white 
men.  It  could  be  planted  without  clearing  or  ploughing  the  soil. 
There  was  no  need  of  threshing  or  winnowing.  Sown  in  tilled  land, 

it  yields  more  than  twice  as 
much  food  per  acre  as  any 
other  kind  of  grain.  This 
was  of  incalculable  advan- 
tage to  the  English  settlers 
in  New  England,  who  would 
have  found  it  much  harder 
to  gain  a secure  foothold 
upon  the  soil  if  they  had 
had  to  begin  by  preparing 
it  for  wheat  or  rye,”  says 
John  Fiske.  {The  Discovery 
of  America.  Houghton 
Mifflin  Co.) 

Today,  in  spite  of  the 
great  wealth  which  comes 
from  our  mineral  resources, 
live  stock,  and  manufac- 
tured products,  a very 
good  index  of  our  country’s 
prosperity  is  the  size  of  the  corn  and  wheat  crop.  According  to  a 
recent  report,  the  value  of  farm  property  in  the  United  States  is 
more  than  157,245,000,000,  a sum  greater  than  that  invested  in  all 
manufactures  in  the  United  States. 

Com.  Over  2,330,000,000  bushels  of  corn  were  raised  in  the 
United  States  during  the  year  1933.  This  figure  is  so  enormous 
that  it  has  but  little  meaning  to  us.  Iowa  and  Illinois  are  the  great- 
est corn-producing  states  in  this  country,  each  having  a yearly 
record  of  over  300,000,000  bushels.  The  figure  on  page  525  shows 
the  principal  corn-producing  areas  in  the  United  States. 

Indian  corn  has  many  uses.  It  is  a valuable  food.  It  has  a 
large  proportion  of  starch,  from  which  corn  syrup,  starch,  and 


WrWit  Pierce 

What  part  of  the  cauliflower  is  used  for  food  ? 


GRAINS 


525 


alcohol  are  made.  Alachine  oil  and  soap  are  made  from  corn  grain. 
The  leaves  anti  stalks  make  excellent  fodder  or  they  can  be  made 
into  paper  and  artificial  silks.  The  husks  are  used  in  mattresses ; 
the  cobs  are  used  for  fuel  or  ground  up  for  meal  for  live  stock ; and 
the  pith  in  the  stalk  is  used  as  a protective  belt  placed  below  the 
water  line  of  our  huge  battleships. 


More  corn  is  raised  in  certain  areas  of  the  United  States  than  in  other  areas.  How  can  you 
account  for  this  ? 


Wheat.  Wheat  is  the  crop  of  next  greatest  importance  in  this 
country.  Over  527,000,000  bushels  were  raised  in  this  country  in 
1933,  representing  a total  money  value  of  about  $357,000,000, 
although  during  the  World  War  our  farmers  received  over 
$2,000,000,000  yearly  for  a crop  of  less  than  1,000,000,000  bushels. 
Seventy-two  per  cent  of  all  the  wheat  raised  comes  from  the  North 
Central  States  and  the  far  West.  Much  of  the  wheat  crop  is 
exported,  thus  indirectly  giving  employment  to  thousands  of  people 
on  railways  and  steamships.  Wheat  is  used  chiefly  for  manufac- 
ture into  flour.  The  germ,  or  young  wheat  plant,  is  sifted  out  dur- 
ing this  process  and  made  into  certain  breakfast  foods.  Flour 
making  forms  the  chief  industry  of  Minneapolis,  Minnesota,  and 
of  several  other  large  and  wealthy  cities  in  this  country. 

Other  grains.  Of  the  other  cereal  grains  raised  in  this  country, 
oats  is  the  most  important  crop,  more  than  722,000,000  bushels 


526  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  WEALTH 


having  been  produced  in  1933.  Barley  and  rye,  grains  much  like 
wheat,  are  produced  in  smaller  quantity.  One  of  the  most  impor- 
tant grain  crops  for  the  world  is  rice.  The  fruit  of  this  grasslike 
plant,  after  threshing,  screening,  and  milling,  forms  the  principal 
food  of  probably  one  third  of  the  human  race. 


How  can  you  account  for  the  location  of  these  wheat-producing  areas  in  the  United  States  ? 
Why  is  wheat  such  an  important  crop  in  this  country  ? 


Practical  Exercise  4.  Obtain  from  government  publications  or  the  World 
Almanac  the  following  facts:  (1)  amount  invested  in  manufactures  for  the 
current  year;  (2)  amount  invested  in  agriculture  for  the  current  year; 
(3)  the  size  and  value  of  the  corn  crop;  and  (4)  the  size  and  value  of  the 
wheat  crop. 

Practical  Exercise  6.  What  agricultural  products  are  raised  in  your  com- 
munity? About  what  proportion  of  wealth  is  invested  in  agriculture  as 
against  manufactories?  Do  they  raise  any  "corn  on  the  hoof”  in  your 
community  ? 

Practical  Exercise  6.  List  in  your  table  ten  important  grains  used  as  foods. 
Give  ten  different  uses  of  grains. 

Practical  Exercise  7.  If  there  is  a flour  mill  in  your  locality,  visit  it  and 
report  to  the  class  on  your  trip. 

Garden  fruits  and  vegetables.  Vegetables  have  come  to  play 
an  important  part  in  the  diet  of  man.  People  are  using  more 
vegetables  and  less  meat,  and  are  more  healthful  and  feel  better 
for  it.  Market-gardening  forms  the  lucrative  business  of  many 
thousands  of  people  near  our  great  cities  and  in  many  of  our  south- 
ern states.  Some  of  the  important  garden  fruits  are  squash, 
cucumbers,  pumpkins,  melons,  tomatoes,  peppers,  strawberries. 


OKCMlAlil)  AND  OTHER  FRUITS 


527 


Wright  Pierce 

Which  of  the  above  fruits  are  raised  in  your  locality?  What  others  are  raised  there? 


raspberries,  and  blackberries.  As  many  as  1000  carloads  of  melons 
were  shipped  from  the  Imperial  Valley,  California,  during  a single 
day  in  1930.  Alore  than  $165,000,000  worth  of  fruits  are  canned 
or  dried  each  year  in  addition  to  what  is  sold  fresh.  Beans  and 
peas  are  important  as  foods  because  of  their  relatively  large  amount 
of  protein.  Canning  green  corn,  peas,  beans,  asparagus,  toma- 
toes, etc.,  has  become  an  important  industry. 

Orchard  and  other  fruits.  In  the  United  States  nearly 
144,000,000  bushels  of  apples  were  grown  in  the  year  1933. 
Peaches,  pears,  plums, 
avocados,  apricots,  and 
cherries  also  are  raised 
in  large  orchards,  espe- 
cially in  California  and 
in  Georgia. 

The  grape  crop  of  the 
world  is  commercially 
valuable,  because  of  the 
beverage  made  from  the 
juice  and  raisins  pro- 
duced from  the  grapes. 

The  culture  of  the  citrus 
fruits,  lemons,  oranges, 
and  grapefruit  has  in- 
creased in  recent  years  wrmt  pierce 

because  of  the  discovery  why  are  citrus  fruits  valuable  foods? 


528  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  WEALTH 


of  their  values  as  producers  of  vitamins.  Figs,  olives,  and  dates 
also  are  grown  now  in  the  Southwest ; they  are  staple  foods  in 
the  Mediterranean  countries  and  are  sources  of  wealth  to  the 
people  there,  as  are  coconuts,  bananas,  and  many  other  fruits  in 
tropical  countries.  Nuts  form  one  of  our  important  articles  of 
food,  largely  because  of  the  great  amount  of  protein  contained 
in  them.  Walnut  ranches  are  now  very  profitable,  especially  in 
California. 

Beverages  and  condiments.  The  coffee  and  cacao  beans  and 
the  leaves  of  the  tea  plant,  products  of  tropical  regions,  form  the 
basis  of  very  important  beverages  of  civilized  man.  Black  and 
red  pepper,  mustard,  allspice,  nutmegs,  cloves,  and  vanilla  are  all 
products  from  various  fruits  and  seeds  of  tropical  plants. 

Practical  Exercise  8.  Report  to  the  class  on  the  current  value  of  crops  men- 
tioned in  this  problem.  Which  crop  is  most  valuable  in  California,  Washing- 
ton, Florida,  Arizona,  New  York,  Michigan?  Consult  government  bulletin 
and  World  Almanac  for  information. 


Self-Testing  Exercise 

(1), (2),  and (3)  are  examples  of  leaves 

used  as  food;  (4), (5),  and (6)  are  stems 

used  as  food (7)  are  the  largest  crops  raised  in  our  country. 

Fruits,  as  (8),  (9),  (10),  (11),  and 

(12),  are  of  great  importance (13)  is  the  largest 

cereal  crop  in  the  United  States,  with (14)  a close  second. 


PROBLEM  II.  WHAT  ARE  OTHER  ECONOMIC  VALUES  OF 
PLANTS? 

Many  of  our  industries  would  not  be  in  existence  were  it  not 
for  certain  plant  products  which  furnish  the  raw  materials.  Many 
cities  of  the  East  and  South,  for  example,  depend  upon  cotton 
to  give  employment  to  thousands  of  factory  hands. 

Cotton.  Of  all  our  native  plant  products  cotton  is  probably  of 
the  most  importance.  More  than  thirteen  million  bales  of  five 
hundred  pounds  each  are  raised  annually. 

The  cotton  plant  thrives  in  warm  regions.  The  seeds  of  the 
fruit  have  long  filaments  attached  to  them.  Bunches  of  these 


vfxji-:tabli<:  fibers 


529 


filaments,  after  treatment  or  ginning,  are  easily  twisted  into  threads 
from  which  are  manufactured  cotton  cloth,  such  as  muslin,  calico, 
cretonne,  and  gingham.  In  addition  to  the  fiber,  cottonseed  oil, 
a substitute  for  olive  oil,  is 
made  from  the  seeds,  the  hulls 
are  used  for  making  artificial 
silk,  rayon,  and  the  refuse 
makes  fodder  for  cattle. 

Other  vegetable  fibers. 

Among  the  other  important 
vegetable  fibers  are  Alanila 
hemp,  which  comes  from  the 
I leaf-stalks  of  a plant  of  the 
banana  family,  and  true  hemp, 
which  is  the  bast  or  woody 
fiber  of  a plant  cultivated  in 
most  warm  parts  of  the  earth. 

These  fibers  are  used  for  twine 
or  rope.  Flax  is  another  im- 
portant fiber  plant,  grown  largely  in  Russia,  Ireland,  Belgium,  and 
other  parts  of  Europe.  Flax  is  becoming  a more  important  crop 
in  this  country  although  it  is  raised  here  chiefly  for  its  seeds.  Linen 
cloth  is  made  from  the  bast  fibers  of  the  stem  of  this  herb.  Burlap 
!and  coarse  bags  are  made  from  the  fiber  of  the  jute  plant,  raised 
in  India. 

Vegetable  oils.  Some  of  the  same  plants  which  give  fiber  also 
produce  oil.  Cottonseed  oil  pressed  from  cotton  seeds,  linseed 
,oil  from  the  seeds  of  the  flax  plant,  and  coconut  oil  (the  covering 
of  the  nut  produces  a fiber)  are  examples.  One  of  the  important 
industries  of  California  is  olive  culture,  the  fruit  being  used  as  a 
table  delicacy,  while  oil  pressed  from  the  fruit  is  used  largely  in 
salad  dressings. 

Drug-producing  plants.  Quinine,  the  specific  remedy  for 
malaria,  was  known  by  the  Indians  in  South  America  before  the 
white  men  came.  It  is  made  from  the  bark  of  the  cinchona  tree. 
South  America  also  furnishes  us  with  cocaine,  a habit-forming 
drug  made  from  the  leaves  of  the  coca  tree  of  Peru.  Morphine 


Blossom  and  bolls  of  a cotton  plant. 


530  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  WEALTH 


and  opium  come  from  the  poppy.  Many  of  our  pleasant  oils  and 
flavors,  as  eucalyptus,  wintergreen,  and  peppermint,  come  from 
plants. 

Tobacco,  although  a poisonous  plant  because  of  the  nicotine  it 
contains,  is,  nevertheless,  one  of  this  country’s  important  crops. 
Nearly  1,400,000,000  pounds  were  raised  in  1933,  having  a total 
value  of  about  $181,000,000.  Atropine  and  belladonna,  both  poi- 
sons used  as  drugs,  are  from  plants  related  to  the  tobacco. 

Practical  Exercises  9.  Make  a table  to  show  the  value  of  the  chief  fiber 
crops  in  your  section  of  the  country  during  the  past  year.  Get  information 
from  your  local  Chamber  of  Commerce. 

What  other  crops  are  of  value  in  your  locality  and  why  ? 

The  use  of  tobacco  has  greatly  increased  since  the  World  War.  Give  three 
possible  reasons  why  this  is  so. 

Self-Testing  Exeecise 

Our  clothes  lines  are  made  from  (1).  Burlap  bags  are 

made  from  (2).  Linen  comes  from  (3).  The 

coca  tree  gives  us (4) (5),  although  a poisonous 

plant,  is  one  of  the  largest  crops  we  raise (6)  is  the  most 

important  fiber  plant  in  this  country. 

PROBLEM  m.  WHAT  IS  THE  VALUE  OF  ANIMALS  AS  FOOD 
FOR  MAN? 

Indirect  use  of  animals  as  food.  Just  as  plants  form  the  food 
of  animals,  so  some  animals  are  food  for  others.  Protozoa  and 
many  forms  of  tiny  plants,  known  as  plankton,  which  are  swarm- 
ing near  the  surface  of  bodies  of  fresh  and  salt  water,  form  the  food 
supply  of  many  forms  of  life.  Many  fish  live  on  plankton  or  on 
smaller  fish  which  feed  on  plankton.  Some  fishes,  as  the  menhaden, 
the  shad,  and  others,  are  provided  with  gill  rakers  by  means  of 
which  they  strain  these  minute  organisms  from  the  water.  Other 
fishes  are  bottom  feeders,  as  the  blackfish  and  the  sea  bass,  living 
almost  entirely  upon  mollusks  and  crustaceans.  Still  others  are 
hunters,  feeding  upon  smaller  species  of  fish,  or  even  upon  their 
weaker  brothers.  Such  are  the  bluefish,  the  weakfish,  the  barra- 
cuda, and  others.  The  right  whale,  the  largest  of  all  mammals, 
strains  protozoa  and  other  small  animals  and  plants  out  of  the 


MOLLUSKS  AS  FOOD 


531 


wator  by  moans  of  hanfiin'!;  platos  of  whaleboiio  or  balocn,  the  slon- 
der  filaments  of  wiiicli  form  a sieve  from  the  top  to  tlie  bottom  of 
the  mouth. 

In  a balanced  aquarium  the  plants  furnish  food  for  the  tiny 
animals  and  some  of  the  larf>:er  ones,  for  example,  the  snails.  The 
smaller  animals  are  eaten  by  the  larger  ones.  The  waste  matter 
given  off  by  the  animals  and  their  death  and  decay  furnish  the 
plants  with  the  required  nitrogen  and  other  material.  Thus  we  see 
the  acpiatic  world  is  a great  balanced  aquarium.  Man  disturbs 
this  ecological  balance  when,  as  in  the  Illinois  River,  he  dumps  his 
untreated  sewage  and  factory  wastes  into  the  stream  near  its  source. 
The  immediate  result  has  been  the  destruction  of  fish  life  for  a dis- 
tance of  about  100  miles.  It  has  been  estimated  by  Professor  Forbes 
that  the  Illinois  River,  before  it  was  polluted  by  the  Chicago  drain- 
age canal,  produced  annually  over  150,000,000  pounds  of  fish  food. 
On  the  other  hand,  diluted  sewage  in  a river  may  be  utilized  by  the 
bacteria  which  in  turn  are  used  by  microscopic  animals  and  these  in 
turn  by  crustaceans  and  snails  which  form  the  food  of  fishes. 

Practical  Exercise  10.  Explain  how  living  things  in  any  body  of  water  in 
your  locality  indirectly  produce  food  for  man. 

Direct  use  of  animals  as  food ; lower  forms.  The  forms  of  life 
lower  than  the  mollusks  are  of  little  use  directly  as  food,  although 
the  Chinese  are  very  fond  of  sea  cucumbers  (page  227),  which  are 
preserved  by  drjdng  and  are  called  trepang.  Sea  urchins  are  eaten 
in  the  West  Indies,  under  the  name  of  sea  eggs.’’ 

Mollusks  as  food.  The  oyster.  The  oyster  industry  is  very 
profitable.  Hundreds  of  boats  and  thousands  of  men  are  engaged 
in  dredging  for  oysters.  Three  of  the  most  important  of  our  oyster 
grounds  are  Long  Island  Sound,  Narragansett  Bay,  and  Chesa- 
peake Bay.  The  western  coast  also  produces  oysters,  but  they  are 
inferior  to  those  of  the  eastern  coast. 

Oysters  are  never  found  in  muddy  water,  for  they  would  be 
quickly  smothered  by  the  sediment.  They  cling  to  stones  or 
shells  or  other  objects  which  project  a little  above  the  bottom. 
Here  food  is  abundant  and  oxygen  is  obtained  from  the  air  in  the 
water  surrounding  them.  Oyster  raisers  usually  throw  oyster 


532  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  WEALTH 

shells  into  the  water  to  provide  places  of  attachment  for  the  young 
oysters. 

In  some  parts  of  Europe  and  of  this  country  where  oysters  are 
raised  artificially,  stakes  or  brush  are  sunk  in  shallow  water  so 
that  the  young  oysters,  after  the  free-swimming  stage,  may  find 
some  object  to  which  they  can  fasten  and  escape  the  danger  of 
smothering  in  the  mud  on  the  bottom.  After  the  oysters  are  a 
year  or  two  old,  they  are  taken  up  and  transplanted  in  deeper  water 


Dredging  for  oysters.  In  some  places,  oysters  are  gathered  by  means  of  long-handled  tongs. 

In  other  places,  dredges  are  used. 

suitable  for  growth.  At  the  age  of  three  or  four  years  they  are 
ready  for  the  market. 

Clams  and  scallops.  Other  mollusks  used  for  food  are  clams 
and  scallops.  Two  species  of  the  former  are  known : one  as  the 
“round,”  another  as  the  “long”  or  “soft-shelled”  clam.  The 
former  {Venus  mercenaria)  was  called  by  the  Indians  “quahog,” 
and  is  still  so  called  in  the  Eastern  States.  The  blue  area  of  its 
shell  was  used  by  the  Indians  to  make  wampum,  or  money.  The 
quahog  is  now  extensively  used  as  food.  The  “long”  clam  (Mya 
arenaria)  is  considered  better  than  the  round  clam  for  food  by  the 
inhabitants  of  Massachusetts  and  Rhode  Island.  This  clam  was 
highly  prized  as  food  by  the  Indians.  It  has  been  introduced  on 


CRUSTACEANS  AS  FOOD 


533 


the  Pacific  coast  and  is  rapidly  coining  into  favor  there.  Dredg- 
ing for  scallops,  another  delicacy  of  the  inollusk  family,  is  an 
important  industr}^  along  certain  parts  of  our  coasts. 

Practical  Exercise  11.  What  mollusks  are  used  for  food  in  your  locality? 
Find  out  by  inquiry  in  local  markets  just  where  each  comes  from. 

If  you  live  where  shellfish  are  produced,  make  a report  to  the  class  on  this 
industry. 

Why  may  raw  oysters  or  clams  be  a source  of  disease? 

Crustaceans  as  food.  Crustaceans  are  of  considerable  value 
as  food.  The  lobster  is  highly  esteemed  as  food,  but  has  become 
scarce  as  the  result  of  overfishing.  Laws  have  been  enacted  in 
most  lobster-producing  states  against  overfishing.  Egg-carrying 


A lobster  pot.  The  lobster  crawls  forward  and  swims  backward.  He  crawls 
through  the  openings  in  the  nets  into  the  chamber  containing  the  bait,  but 
when  he  tries  to  leave  by  swimming  backward  he  gets  caught. 


lobsters  must  be  returned  to  the  water ; all  smaller  than  six  to  ten 
and  one  half  inches  in  length  (the  law  varies  in  different  states) 
must  be  put  back ; and  other  restrictions  are  placed  upon  the  tak- 
ing of  these  animals,  in  the  hope  of  saving  the  race  from  extinction. 
The  United  States  Bureau  of  Fisheries  and  several  eastern  states 
are  now  hatching  out  millions  of  little  lobsters  each  year,  keeping 
them  until  they  are  large  enough  to  care  for  themselves  and  then 
liberating  them.  The  spiny  lobster  of  the  western  coast  is  also 
In  danger  of  extinction  through  overfishing.  In  consequence  a 
ong  closed  season  has  been  declared,  from  the  first  of  March  to 
]he  fifteenth  of  October  of  each  year.  This  protects  the  females 
luring  the  egg-laying  season. 

H.  BIO  — 35 


534  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  WEALTH 


Several  other  common  crustaceans  used  as  food  by  man  are  near 
relatives  of  the  crayfish.  Among  them  are  the  shrimp  and  the 
prawn,  thin-shelled,  active  crustaceans  common  along  our  coasts. 
In  spite  of  the  fact  that  they  form  a large  part  of  the  food  supply 
of  many  marine  animals,  especially  fish,  they  do  not  appear  to  be 
decreasing  in  numbers. 

Another  edible  crustacean  of  considerable  economic  impor- 
tance is  the  blue  crab.  Crabs  are  found  inhabiting  muddy  bot- 
toms of  salt  water  inlets ; in  such  localities  they  are  caught  in  great 
numbers  in  nets  or  traps  baited  with  decaying  meat.  They  are, 
indeed,  among  our  most  valuable  sea  scavengers,  although  they  are 
hunters  of  living  prey  also.  The  young  crabs  differ  considerably 
in  form  from  the  adult.  They  undergo  a complete  metamorphosis. 
Immediately  after  molting  or  shedding  of  the  outer  shell,  in  order 
to  grow  larger,  crabs  are  known  as  “ shedders,’’  or  soft-shelled 
crabs,  and  are  considered  a great  delicacy.  On  the  western  coast 
a large  deep-sea  crab  is  caught  which  is  an  excellent  article  of  food. 

Practical  Exercise  12.  List  all  the  crustaceans  you  know  that  are  found 
in  your  locality.  Which  ones  are  directly  or  indirectly  used  for  food? 

Practical  Exercise  13.  Make  a report  on  the  lobster  industry  of  the  United 
States.  (See  Readers  Guide  or  Herrick’s  The  American  Lobster,  Bui.  U.  S. 
Fish  Com.  1895.) 

Practical  Exercise  14.  If  you  have  ever  caught  any  kind  of  crustaceans, 
describe  your  methods  to  the  class. 

Fish  as  food.  Fish  are  used  as  food  the  world  over.  The  pres- 
ent value  of  the  yearly  catch  of  the  world  is  estimated  at  over 
$777,000,000.  From  very  early  times  herring  were  caught  by 
the  Norsemen.  Fresh- water  fish,  such  as  whitefish,  perch,  pick- 
erel, pike,  and  the  various  members  of  the  trout  family,  are 
esteemed  food  and,  especially  in  the  Great  Lake  region,  form  impor- 
tant fisheries.  But  by  far  the  most  important  food  fishes  are  those 
which  are  taken  in  salt  water.  Here  we  have  two  types  of  fish- 
eries : those  where  the  fishes  come  up  a river  to  spawn,  such  as  the 
salmon,  sturgeon,  or  shad,  and  those  where  the  fishes  are  taken  on 
their  feeding  grounds  in  the  open  ocean.  The  eggs  of  the  sturgeon 
are  used  in  the  manufacture  of  the  delicacy  known  as  caviare. 
Herring  are  the  world’s  most  important  catch,  though  not  in  this 
country.  The  salmon  of  our  western  coast  are  taken  to  the  value 


AMPHIBIA  AND  REPTILES  AS  FOOD 


535 


of  over  S45, ()()(), 000  a year.  Ood  fishing  also  forms  an  important 
industry,  over  7000  men  being  employed  and  over  $30,000,000  of 
codfish  being  taken  each  year  in  this  country. 

Practical  Exercise  16.  Make  a list  of  the  different  fishes  found  in  a local 
market.  Clet  and  record  i)rice  per  pound  in  a column  opposite  name  of  fish. 
In  a third  column  give  apiu'oximate  distance  of  local  market  from  source  of 
production.  In  fourth  column  give  your  reasons  for  price  per  pound  of  given 
fish. 

How  do  fish  compare  in  economic  importance  with  other  animals  used  as 
food  in  your  locality? 

Amphibia  and  reptiles  as  food.  Frogs  live  in  streams  and 
ponds  in  all  sections  of  the  eastern  part  of  the  United  States  and 
along  the  INIississippi 
valley.  They  are  used 
to  a great  extent  for 
food  as  their  large  hind 
legs  are  esteemed  a 
great  delicacy.  Certain 
reptiles,  as  the  iguana, 
a lizard-like  animal,  are 
used  as  food  by  people 
of  other  nations.  Many 
of  the  edible  salt-water 
turtles  are  of  large  size, 
the  leatherback  and  the 
green  turtle  often 
weighing  six  hundred 
to  seven  hundred 
pounds  each.  The  flesh 
of  the  green  turtle  and 
of  the  diamond-back 
terrapin,  an  animal  found  in  the  salt  marshes  along  our  south- 
eastern coast,  is  highly  esteemed  as  food.  Unfortunately  for  the 
preservation  of  the  species,  these  animals  are  usually  taken  dur- 
ing the  breeding  season  when  they  go  to  sandy  beaches  to  lay 
their  eggs. 

Practical  Exercise  16.  What  amphibia  or  reptiles  in  your  part  of  the 
country  are  used  as  food? 


536  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  WEALTH 


Honey  and  wax.  The  honeybee  gathers  nectar,  which  she 
swallows,  keeping  the  fluid  in  her  crop  until  her  return  to  the  hive. 
Here  it  is  forced  out  into  the  cells  of  the  comb.  It  is  now  thinner 
than  honey.  To  thicken  it,  the  bees  swarm  over  the  open  cells, 
moving  their  wings  very  rapidly,  thus  evaporating  some  of  the 
water.  A hive  of  bees  may  make  between  30  and  80  pounds  of 
honey  during  a season.  Over  60,000,000  pounds  of  honey  is 
produced  in  this  country  every  year. 

Practical  Exercise  17.  Report  on  a trip  to  an  apiary,  or  on  a study  of  an 
observation  beehive. 

Birds  as  food.  Birds,  both  wild  and  domesticated,  form  part 
of  our  food  supply.  But  our  wild  game  birds  are  disappearing  so 
rapidly  that  we  cannot  consider  them  as  a source  of  food.  Our 
domestic  fowls,  chicken,  turkeys,  ducks,  etc.,  form  an  important 
food  supply.  Eggs  of  domesticated  fowls  are  of  great  importance 
as  food,  and  egg  albumin  is  used  for  other  purposes,  such  as 
clarifying  sugars  and  coating  photographic  papers. 

Practical  Exercise  18.  Give  a report  on  the  different  birds  in  your  locality 
that  may  be  used  as  food. 

Mammals  as  food.  When  we  consider  the  amount  of  wealth 
invested  in  cattle  and  other  domesticated  mammals  bred  and  used 
for  food  in  this  country,  we  see  the  great  economic  importance  of 
these  animals.  In  1928  nearly  $3,000,000,000  worth  of  meat-pro- 


For  what  two  valuable  purposes  are  sheep  raised  ? 


ECONOMIC  VALUES  OF  ANIMALS 


537 


diicing  animals  were  owned  in  the  United  States.  The  United 
States,  Argentina,  and  Australia  are  the  greatest  producers  of 
cattle.  Other  products,  such  as  milk,  butter,  and  cheese,  are  ob- 
tained from  cows  and  goats.  In  this  country  many  hogs  are  raised 
for  food.  Their  meat  is  used  fresh,  salted,  smoked  as  ham  and 
bacon,  and  pickled.  Sheep,  which  are  raised  in  great  quantities 
in  Australia,  Argentina,  Russia,  Uruguay,  and  this  country,  are 
one  of  the  world’s  greatest  meat  supplies.  Deer,  many  game 
animals,  seals,  walruses,  etc.,  are  available  as  food  for  people  in 
certain  parts  of  the  earth. 

Practical  Exercise  19.  From  the  information  obtained  from  your  local 
Chamber  of  Commerce  or  other  sources,  make  a report  to  the  class  on  the 
value  of  food  mammals  in  your  community. 

Self-Testing  Exercise 

(1)  and (2)  are  important  shellfish  used  as  food. 

Crustaceans  used  as  food  are (3), (4),  and 

(5) (6)  made  from  the  nectar  of  flowers  by  the (7) 

is  an  important  foodstuff.  The  (8)  catch  of  food  fishes  is 

estimated  to  be  over  (9).  While  birds  are  important  as 

food,  (10)  are  by  far  the  most  important  food  producers. 

Most  large  animals (11)  upon (12)  ones.  Factory 

(13)  may  not  safely  be  dumped  into  (14)  as  they 

(15)  the  fish  there.  The  right  whale  lives  upon (16) 


animals  which  it (17)  out  of  the  water  by  means  of  hanging 

plates  of (18). 

PROBLEM  IV.  WHAT  ARE  OTHER  ECONOMIC  VALUES  OF 
ANIMALS? 


i Domesticated  animals.  The  domestication  of  the  dog,  the  cow, 
the  sheep,  and  especially  of  the  horse,  marks  epochs  in  the  advance 
' of  civilization.  Beasts  of  burden  are  used  the  world  over : horses 
almost  everywhere  ; certain  cattle,  as  the  water  buffalo,  in  tropical 
: Malaysia ; and  camels,  goats,  and  the  llamas  in  some  other  coun- 
tries. 

Practical  Exercise  20.  Obtain  from  local  sources  the  approximate  value  of 
I domesticated  animals  in  your  locality,  and  tell  why  you  think  your  figures 
1 are  accurate. 


538  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  WEALTH 


C.  Clarie 

Two  female  silkworm  moths  and  some  of  the  eggs  they  have  laid. 


A tray  of  well-developed  silkworm  larvae  feeding  on  mulberry  leaves.  They  rarely  leave  their 
box  containing  food  until  they  are  ready  to  search  for  a place  to  spin  their  cocoons. 


TIIK  SFLKWOKM 


539 


A mass  of  silkworm  cocoons  among  the  branches  of  a mulberry  tree. 


C.  Clarke 

A raw  cocoon  and  a silken  skein  that  has  been  made  from  the  raw  material.  Can  you 
describe  the  process  by  which  silk  thread  is  made  from  the  silk  in  the  cocoon? 


540  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  WEALTH 


Uses  of  animal  fibers.  Pure  silk  goods  are  manufactured  from 
raw  silk,  which  is  a fiber  produced  by  the  silkworm,  the  caterpillar 
of  a moth.  It  lives  on  mulberry  leaves  and  makes  a cocoon  from 
which  the  silk  is  obtained.  China,  Japan,  Italy,  and  France,  be- 
cause of  cheap  labor,  are  successful  silk-raising  countries.  But 
the  manufacture  of  silk  goods,  from  imported  raw  silk,  is  still  one 
of  our  great  industries  in  spite  of  the  production  of  rayon,  one 
kind  of  artificial  silk  produced  from  wood  pulp. 

There  are  in  this  country  more  than  1000  woolen  mills,  with 
nearly  200,000  wage  earners.  They  produce,  yearly,  woolen  and 
worsted  goods  valued  at  about  $900,000,000.  These  mills  use  both 

domestic  and  im- 
ported wool.  Nearly 
45,000,000  sheep  are 
raised  in  this  country 
for  their  wool. 

Goat’s  hair,  espe- 
cially that  of  the 
Angora  and  of  the 
Cashmere  goats, 
camel’s  hair,  and 
alpaca  are  much 
used  in  the  clothing  ; 
industries.  j 

Practical  Exercise  21.  \ 

Give  a brief  report  on  • 
any  of  your  local  indus-  < 
tries  which  use  animal 
fibers.  I' 

Furs.  The.  furs  of  ; 
many  domesticated 
and  wild  animals, 
especially  the  carni-  ■ 
vores,  are  of  much  ‘ 
economic  impor-  j 

The  skunk  is  now  raised  for  its  valuable  fur. 

tance.  The  Alaskan 

fur  seal  fisheries,  which  once  amounted  to  millions  of  dollars  annu-  , 
ally,  have  greatly  decreased  because  of  over-killing  of  the  seals.  i 


PERFUMES 


541 


Only  about  54,000  seals  were  killed  in  1933.  Otters,  skunks,  sables, 
weasels,  fo.xes,  and  minks  are  of  considerable  importance  as  fur 
producers.  Even  cats  are  now  used,  the  fur  usually  masquerad- 
ing under  some  other  name.  The  fur  of  the  beaver,  one  of 
the  largest  of  the  rodents  or  gnawing  mammals,  is  now  difficult  to 
procure,  but  fur  of  considerable  value  is  obtained  from  the  muskrat, 
squirrel,  rabbits,  and  other  rodents.  The  furs  of  the  rabbit  and 
nutria  are  used  in  the  manufacture  of  felt  hats.  The  quills  of  the 
porcupine  (greatly  developed  and  stiffened  hairs)  have  a slight 
commercial  value  for  decorative  purposes. 

Animal  oils.  Whale  oil,  obtained  from  the  “ blubber  ” of 
whales,  and  formerly  used  for  illumination,  is  now  much  used  as  a 
lubricating  oil.  Neat’s-foot  oil  comes  from  the  feet  of  cattle  and 
is  used  for  lubrication.  Tallow  from  cattle  and  sheep,  and  lard 
from  hogs,  have  so  many  well-known  uses  that  comment  is 
unnecessary.  Cod-liver  oil  from  the  codfish  is  used  medically. 
Much  oil  is  obtained  also  from  the  menhaden  of  the  Atlantic 
coast,  which  is  used  in  dressing  leather  and  making  paints.  Men- 
hadens are  also  used  in  great  quantities  for  fertilizers. 

Hides,  horns,  hoofs,  etc.  Leather  made  from  the  skins  of 
cattle,  horses,  sheep,  goats,  alligators,  and  snakes  is  used  for  shoes, 
pocketbooks,  coats,  gloves,  and  for  many  purposes.  Leather 
manufacture  is  one  of  the  great  industries  of  the  Eastern  states, 
hundreds  of  millions  of  dollars  being  invested  in  manufacturing 
plants.  Horns  and  bones  are  utilized  for  making  combs,  buttons, 
handles  for  brushes,  etc.  Glue  is  made  from  the  animal  matter 
in  bones,  horns,  and  hoofs.  Ivory,  obtained  from  the  tusks  of  the 
elephant,  walrus,  and  other  animals,  forms  a valuable  commercial 
product.  It  is  largely  used  for  knife  handles,  piano  keys,  and 
combs. 

Perfumes.  The  musk  deer,  musk  ox,  and  muskrat  furnish  a 
valuable  perfume  called  musk.  Civet  cats  also  give  us  a somewhat 
similar  perfume.  Ambergris,  a basis  for  delicate  perfumes,  is 
formed  in  the  intestines  of  the  sperm  whale. 

Practical  Exercise  22.  Tabulate  the  various  products,  other  than  meat,  that 
are  obtained  from  animals.  In  the  next  column  indicate  the  ones  used  in  your 
local  industries.  In  the  last  column  show  uses  of  raw  products  to  man. 


542  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  WEALTH 


Direct  use  of  protozoans.  The  protozoans  have  played  an  impor- 
tant part  in  rock  building.  Chalk  beds  and  limestone  rocks  are 
made  up  to  a large  extent  of  the  tiny  skeletons  of  protozoans 
called  foraminifers.  The  skeletons  of  some  species  are  used  to 
make  a polishing  powder. 

Sponges  and  coral.  The  sponges  of  commerce  are  the  skeletons 
of  animals  that  live  attached  to  the  bottom  of  the  sea,  and  are 
composed  of  tough  fibers  of  a material  somewhat  like  that  of  a 
cow’s  horn.  This  fiber  is  elastic  and  has  the  power  to  absorb 

water.  The  warm  waters 
of  the  Mediterranean  Sea 
and  the  West  Indies  fur- 
nish most  of  our  sponges. 
The  sponges  are  pulled  up 
from  their  resting  places 
on  the  bottom  by  means 
of  long-handled  rakes 
operated  by  men  in  boats, 
or  they  are  secured  by 
divers.  They  are  then 
spread  out  on  the  shore  in 
the  sun,  and  the  living 
tissues  allowed  to  decay. 
Then  after  treatment  con- 
sisting of  beating,  bleach- 
ing, and  trimming,  the 
bath  sponge  is  ready  for 
the  market. 

Some  forms  of  coral,  the 
skeleton  of  marine  organ- 
isms, are  of  commercial 
value.  The  red  or  pre- 
cious coral  of  the  Mediter- 
ranean Sea  is  highly  prized 
for  ornamental  purposes. 

Pearls  and  mother-of-pearl.  Pearls  are  prized  the  world  over. 
Most  of  the  finest  come  from  the  oysters  and  clams  in  the  waters 


The  pearl-like  shells  of  fresh-water  mussels  are  used 
in  button-making.  These  mussels  are  extensively 
cultivated  in  the  United  States  for  this  purpose. 


VALUE  OF  SNAKES 


543 


iirouiul  Ceylon.  It  seems  likely  that  the  most  perfect  pearls  are 
due  to  the  growth  within  the  mantle  of  the  clam  or  oyster  of  cer- 
tain parasites  which  are  stages  in  the  development  of  a tlukeworm. 
The  irritation  thus  set  up 
in  the  tissue  causes  mother- 
of-pearl,  the  substance 
that  lines  the  interior  of 
the  shell,  to  be  deposited 
around  the  source  of  irrita- 
tion, with  the  subsequent 
formation  of  a pearl. 

The  pearl-button  in- 
dustry in  this  country  is 
largely  dependent  upon 
the  fresh-water  mussel, 
the  shells  of  which  are 
used.  This  mussel  was 
being  so  rapidly  depleted 
that  the  national  govern- 
ment has  worked  out  a 
means  for  its  artificial 
propagation. 

Usefulness  of  the  toad. 

The  toad  is  of  great  eco- 
nomic importance  to  man 
because  of  its  diet.  No 
less  than  eighty-three 
species  of  insects,  mostly  injurious,  have  been  proved  to  enter  into 
the  toad’s  diet.  A toad  has  been  observed  to  snap  up  128  flies 
in  half  an  hour.  Thus  it  could  easily  destroy  very  many  insects 
during  a day  and  do  an  immense  service  to  the  garden  during  the 
summer.  Toads  also  feed  upon  slugs  and  other  garden  pests. 

Value  of  snakes.  Probably  the  most  disliked  and  feared  of  all 
animals  are  the  snakes.  This  feeling,  however,  is  rarely  deserved, 
for,  on  the  whole,  our  common  snakes  are  beneficial  to  man.  The 
black  snake,  gopher  snake,  and  milk  snake  feed  largely  on 
injurious  rodents  (rats,  mice,  etc.),  the  green  garden  snake  eats 


Wright  Pierce 

Chuckwalla  — a stout-bodied  lizard  of  the  deserts 
of  southwestern  United  States.  It  feeds  on  the  buds 
and  flowers  of  plants.  Its  flesh  is  used  by  some 
people  for  food. 


544  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  WEALTH 


injurious  insects,  and  the  little  DeKay  snake  feeds  partly  on  slugs. 
If  it  were  not  that  the  rattlesnake  and  copperhead  are  venomous, 
they  also  could  be  said  to  be  useful,  for  they  devour  English 
sparrows,  rats,  mice,  moles,  and  rabbits. 

Practical  Exercises  23.  Classify  the  animals  mentioned  in  the  preceding 
sections  as  to  direct  or  indirect  economic  importance.  Add  as  much  as  you  can 
to  the  list. 

Make  a list  of  all  the  ways  in  which  animals  living  in  your  environment 
help  indirectly  to  make  you  comfortable. 

Food  of  herbivorous  animals.  We  must  not  forget  that  other 
animals  besides  insects  and  birds  help  to  keep  down  the  rapidly 
growing  weeds.  Herbivorous  animals  the  world  over  devour, 
besides  the  grass  which  they  eat,  untold  multitudes  of  weeds, 
which,  if  unchecked,  would  drive  out  the  useful  plants  of  the 
pastures,  the  grasses  and  grains. 

Self-Testing  Exercise 

Animals  furnish  us  with  (1),  (2),  (3), 

and (4)  for  clothing.  Animal  oils  are  obtained  from  the 

(5),  (6),  (7),  and  (8).  Ivory  is 

made  from  the (9)  of (10) ; glue  from (11) 

and (12);  leather  from  the  skins  of (13), (14), 

and  ..(15);  perfumes  from  (16)  (17);  and 

pearls  from (18).  Coral  is  used  for (19) (20). 

Sponges  are  (21)  (22).  The  toad  (23) 

(24).  Most  snakes  are (25)  to  man. 

PROBLEM  V.  WHAT  HARM  IS  DONE  BY  ANIMALS? 

Animals  destructive  to  other  animals  used  as  food.  Directly  or 
indirectly,  animals,  in  their  struggle  for  life,  destroy  quantities  of 
plants  and  other  animals,  that  man  uses  as  food.  Starfish  are 
enormously  destructive  to  young  clams  and  oysters,  as  the  follow- 
ing evidence,  collected  by  Professor  A.  D.  Mead,  of  Brown  Uni- 
versity, shows : A single  starfish  was  confined  in  an  aquarium 
with  fifty-six  young  clams.  The  largest  clam  was  about  the 
length  of  an  arm  of  the  starfish,  the  smallest  about  ten  millimeters 
in  length.  In  six  days  every  clam  in  the  aquarium  had  been 


DESTRUCTIVE  ANIMALS 


545 


devoured.  Hundred  of  thousands  of  dollars’  damage  is  done 
annually  to  oysters  in  Connecticut  alone  by  the  ravages  of  star- 
fish. During  the  breeding  season  of  clams  and  oysters,  the  boats 
dredge  up  tons  of  starfish  which  are  thrown  on  shore  to  die  or  to 
be  used  as  fertilizer. 

The  liver  fluke  kills  thousands  of  sheep  every  year.  Tapeworms 
in  cattle  anti  trichina  in  hogs  spoil  much  valuable  food.  Round- 
worms  enter  the  bodies  of  food  fish  as  parasites  and  kill  large 
numbers  annually.  Boring  mollusks,  such  as  the  whelk,  destroy 
multitudes  of  other  mollusks  as  food.  Parasitic  insects  abound 
which  kill  useful  insects,  some  of  which,  like  the  honeybee,  pro- 
duce food.  We  can  hardly  estimate  the  harm  done  by  one-celled 
parasites  and  their  carriers,  the  ticks,  mites,  etc.,  for  they  are 
enormously  destructive  to  cattle. 

Fish  feed  upon  crustaceans  and  mollusks.  The  dogfish,  shark, 
and  other  elasmobranchs  destroy  many  lobsters,  crabs,  and 
other  crustaceans,  while  many  bottom-feeding  fish  eat  mollusks. 
Fish  are  cannibals  also,  eating  the  eggs  and  young  of  their  own 
kind.  Salmon  eggs  are  a favorite  food  of  the  western  trout. 
Birds  eat  many  fish  and  much  other  food.  Large  numbers  of  fish 
are  killed  by  minks,  otters,  seals,  and  other  fishing  mammals. 
At  one  time  it  was  estimated  that  an  annual  loss  of  fish  equal  to 
$20,000,000  was  caused  by  carnivorous  animals,  such  as  those  men- 
tioned above  and  others.  This  amount  is  rapidly  decreasing. 

Practical  Exercise  24.  Make  a table  to  show  the  kinds  of  damage  done  by 
the  animals  common  to  your  locality.  Can  you  estimate  the  loss  in  dollars 
and  cents?  Get  information  from  local  farmers,  cattle  and  sheep  raisers, 
and  your  Chamber  of  Commerce. 

Rats  as  pests.  David  E.  Lantz  of  the  Bureau  of  Biological 
Survey  is  authority  for  the  statement  that  the  rat  is  the  most 
destructive  mammal  in  the  world.  He  estimated  the  actual 
money  loss  from  destruction  of  property  by  rats  each  year  in  this 
country  to  be  over  $200,000,000.  Rats  destroy  the  timber  in 
houses,  they  cause  fires  by  gnawing  matches,  they  destroy  great 
quantities  of  standing  grain  and  stored  food,  they  kill  myriads  of 
young  chickens  and  other  poultry  and  untold  numbers  of  young 
birds.  Worst  of  all,  they  spread  diseases,  especially  bubonic 


546  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  WEALTH 

plague.  The  fighting  of  rats  alone,  in  the  epidemics  of  plague  in 
this  country,  has  cost  millions  of  dollars. 

Practical  Exercise  25.  Make  a report  on  methods  of  control  of  rats  and 
mice  in  your  community.  Consult  Lantz,  House  Rats  and  Mice,  and  Farmers’ 
Bulletin  896,  United  States  Department  of  Agriculture. 

Cats.  Many  cats  are  kept  as  pets,  and  many  run  wild.  Cats 
of  both  kinds  do  much  injury  by  killing  birds.  Forbush,  former 
state  Director  of  Ornithology  of  the  State  of  Massachusetts,  esti- 


Bureau  of  Biological  Survey 


The  rat  is  an  enemy  of  the  farmer. 
Notice  the  damage  that  he  has  done  in 
this  corn  crib. 


Wright  Pierce 


Cats  destroy  many  birds.  A bell 
placed  on  the  neck  of  your  pet  will  warn 
your  feathered  friends. 


mated  that  they  killed  in  New  England  as  many  as  1,500,000  birds 
annually.  While  this  number  seems  almost  impossible  to  believe, 
226  cats  under  observation  in  Massachusetts  have  been  known  to 
kill  624  birds  in  one  day.  Cats  also  spread  disease  germs. 

Animals  that  prey  upon  man.  The  toll  of  death  from  animals 
which  prey  upon  or  harm  man  directly  is  relatively  small.  Snakes 
in  tropical  countries  kill  many  cattle  and  not  a few  people.  The 
loss  of  life  from  snake  bites  should  soon  be  much  reduced,  thanks 
to  the  manufacture  of  antivenin  serums. 

Alligators  and  crocodiles  feed  not  only  on  fishes,  but  often 
attack  large  animals,  as  horses  and  cows,  and  even  man. 


BIKDS  BAT  INSKrTS 


547 


C'arnivorous  animals  which  arc  not  domesticated,  such  as  lions 
and  tiiiers,  still  iidlict  damaiie  in  certain  parts  of  the  world,  but  as 
the  tide  of  cixilization  advances,  their  numbers  are  slowly  but 
surely  decreasing;,  so  that  as  important  factors  in  man’s  welfare 
they  may  be  considennl  almost  neiili'^ible. 

Practical  Exercises  26.  What  harm  is  done  in  your  locality  by  any  of  the 
above-mentioned  animals?  How  can  cats  be  kept  from  killing  birds?  Give 
all  the  reasons  you  can  for  and  against  keeping  cats.  What  agencies  control 
the  harmful  animals  in  your  state? 


Self-Testing  Exercise 

Many  oysters  are  destroyed  annually  by (1).  Rats  destroy 

1 thousands  of  (2)  worth  of  (3)  every  year.  Many 

'fishes  are  killed  by  (4)  (5),  (6),  and  other 

i fish  (7)  (8).  Animals  that  are  known  to  attack  men 

are  the  (9),  (10),  (11),  and  (12). 


PROBLEM  VI.  WHAT  IS  THE  ECONOMIC  IMPORTANCE  OF 
BIRDS? 


Birds  eat  insects.  The  food  of  birds  makes  them  of  great 
importance  to  agriculture  in  our  country.  A large  part  of  the  diet 


If  birds  cannot  get  insects  they  eat  grains. 
;ere  is  the  remains  of  an  ear  of  corn  after  a 
« :ow  has  eaten. 


L.  W.  Brownell 

Some  birds  seem  to  prefer  insects  to  seeds. 
Here  is  a young  thrasher  being  fed  an  insect 
by  its  parent. 


548  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  WEALTH 


of  many  of  our  native  birds  includes  insects  harmful  to  vegetation. 
Investigations  undertaken  by  the  United  States  Department  of 

Agriculture  (Division  of 
Biological  Survey)  show 
that  a surprisingly  large 
number  of  birds,  once 
believed  to  harm  crops, 
really  perform  a service 
to  farmers  by  killing  in- 
jurious insects.  Even 
the  much  maligned  crow 
eats  mice  and  harmful 
insects  as  well  as  grain 
and  fruit.  Swallows  in 
the  southern  states  kill 
the  cotton  boll  weevil, 
one  of  our  worst  insect 
pests.  Our  earliest 
visitor,  the  bluebird,  in- 
cludes grasshoppers,  ants, 
spiders,  weevils,  tent 
caterpillars,  army  worms, 
cutworms,  and  the  cod- 
ling moth  in  its  diet. 
The  robin,  whose  pres- 
ence in  the  cherry  tree 
we  resent  during  the  spring  and  early  part  of  the  summer, 
includes  all  of  the  above  and  several  other  pests  in  its  diet.  It 
has  a 95  per  cent  insect  diet  until  June,  and  after  that  time  about 
40  per  cent  of  its  food  is  insects.  Many  birds  vary  their  diet, 
using  the  food  substances  which  are  most  abundant  around 
them.  The  swifts  or  swallows  eat  flies,  the  cuckoos  and  blue 
jays  eat  hairy  caterpillars,  which  are  eaten  by  few  other  birds ; 
and  much  of  the  winter  food  of  the  chickadees  consists  of  eggs 
of  aphids  or  plant  lice.  Ants  are  eaten  by  many  species  of 
birds;  beetle  larvae  are  preferred  by  crows,  blackbirds,  and 
robins.  A pair  of  nesting  robins  were  observed  to  dig  out  and  eat 


The  food  of  some  of  our  most  familiar  birds.  Which  of 
these  birds  should  be  protected? 


BIRDS  KAT  WEED  SEEDS 


549 


from  50  to  70  cutworms  and  earthworms  in  one  day.  Many 
observations  of  the  feedino;  of  yoiino;  birds  by  their  parents  indicate 
tliat  birds  eat  a larg-e  amount  of  food  in  proportion  to  their  size 
and  conseciuently  tlestroy  vast  numbers  of  injurious  insects. 
Some  idea  of  tlie  amount  of  food  eaten  may  be  had  from  the  data 
given  by  Professor  llodge.  He  says  a pair  of  house  wrens,  very 
tiny  birds,  were  observed  to  feed  their  five  nestlings  230  insects, 
mostly  large  cabbage  caterpillars,  in  one  day.  A young  robin 
three  weeks  old  ate  70  cutworms  in  one  day ; a young  tanager,  150 
cutworms  in  a day  besides  other  food ; and  a young  phoebe  just 
out  of  the  nest,  as  manj"  as  200  good-sized  grasshoppers  in  a day. 

Without  the  birds  the  farmer  would  have  a hopeless  fight 
[against  insect  pests.  The  effect  of  killing  native  birds  in  great 
numbers  is  now  well  seen  in  Italy  and  Japan,  where  insects  have 
increased  and  do  great  damage  to  crops  and  trees. 

Practical  Exercise  27.  List  the  names  of  all  birds  that  you  know.  Make  a 
table  for  your  workbook,  giving  the  harm  and  value  to  man  of  each  bird. 

Birds  eat  weed  seeds.  Not  only  do  birds  aid  man  in  his  battles 
with  destructive  insects,  but  nearly  300  species  of  birds  eat  the 
seeds  of  weeds 
also.  Our  native 
sparrows  (not  the 
English  sparrow), 
the  mourning 
dove,  bobwhite, 
rose-breasted 
grosbeak,  horned 
lark,  crow  black- 
bird, and  other 
: birds  feed  largely 
upon  the  seeds  of 
many  of  our  com- 
mon weeds.  An 
t examination  of 
: the  stomachs  of  a 

t number  of  these  What  is  the  economic  importance  of  the  owl  ? 

H.  BIO  — 36 


550  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  WEALTH 

birds  showed  that  they  had  consumed  over  one  hundred  kinds 
of  weed  seeds.  The  Biological  Survey  estimated  that  the 
various  seed-eating  native  sparrows  saved  the  farmer  the  sum  of 
$89,260,000  in  1910.  The  tree  sparrows  alone  in  the  state  of 

Iowa  are  estimated  to  eat 
875  tons  of  weed  seeds 
every  winter.  Not  all 
birds  are  seed  or  insect 
eaters. 

Other  foods  of  birds. 

Some,  as  the  cormorants, 
ospreys,  gulls,  and  terns, 
are  active  fishers.  Near 
large  cities  especially,  gulls 
act  as  scavengers,  destroy- 
ing much  floating  garbage 
that  otherwise  might  be 
washed  ashore  to  become 
a menace  to  health.  The 
buzzards  of  the  West  and 
South,  and  the  vultures  of 
India  and  semi-tropical 
countries,  are  of  immense 
value  as  scavengers.  Birds 

The  golden  plover  spends  the  summer  in  the  north-  nrpv  HiawLcs  nnrl  nwk 

ern  part  of  North  America  and  the  winter  in  the  south.  (.naWKS  anU  OWlS, 

Explain  why  it  takes  a different  route  north  in  the  living  mammals,  in- 
spring from  the  one  it  takes  south  in  the  fall.  it  i i 

eluding  many  harmful 
rodents,  as  gophers,  field  mice,  and  rats.  The  Biological  Survey 
has  estimated  that  owls  and  hawks  are  worth  about  $20  apiece  a 
year  to  the  farmer  because  of  the  field  mice  they  eat. 

Geographical  distribution  and  migrations.  Most  of  us  are  aware 
that  some  birds  remain  in  a given  region  during  the  whole  year, 
while  other  birds  appear  with  the  approach  of  spring,  and  depart 
southward  with  the  warm  weather  in  the  fall  of  the  year.  Such 
birds  we  call  migrants,  while  those  that  remain  in  one  place  the 
year  round  are  called  permanents.  For  any  one  locality  the  migrants 
fall  into  three  groups : those  that  arrive  in  the  spring  from  the 


SOME  COMMON  BIRDS 


551 


south  and  remain  until  fall  are  called  siunmer  residents;  those  that 
come  south  during  the  winter  for  food  and  to  escape  the  severe 
cold  are  called  winter  residents;  and  those  that  remain  only  a few 
days  or  a week  in  a locality  when  passing  to  the  north  or  south 
are  called  transients. 

In  Europe,  where  the  problem  of  bird  migration  has  been  studied 
carefully,  migrations  appear  to  take  place  along  well-defined  paths. 
These  paths  usually  follow  the  coast  very  exactly,  although  in 
places  they  may  take  the  line  of  the  coast  that  existed  in  former 
geological  times.  In  this  country  the  Mississippi  valley  forms  one 
line  of  migration,  while  the  north  Atlantic  seacoast  forms  another 
: route.  Just  why  birds  migrate  is  not  fully  known.  Evidently  food 
I shortage  in  the  fall  starts  them  on  the  path  southward,  but  why 
they  return  is  not  so  clear.  They  seem  to  have  some  instinct 
which  brings  them  back  year  after  year  to  the  same  nesting  places. 

Self-Testixg  Exercises 

Mark  in  your  workbook  the  correct  statements  : 

T.  F.  1.  Few  birds  are  entirely  useful. 

T.  F.  2.  No  insect  pest  can  be  entirely  controlled  by  birds. 

T.  F.  3.  Birds  feed  on  the  food  that  is  most  abundant  at  the  time. 

T.  F.  4.  Robins  do  more  harm  than  good,  for  they  eat  our  cherries. 

I T.  F.  5.  Birds  of  prey  are  scavengers. 

T.  F.  6.  Most  of  our  migrants,  as  the  finches,  warblers,  and 
swallows,  feed  upon  harmful  insects. 

T.  F.  7.  Most  owls  are  harmful  because  they  feed  upon  rodents. 

1 PROBLEM  Vn.  HOW  CAN  WE  RECOGNIZE  SOME  COMMON 

BIRDS? 

1 It  has  been  estimated  that  during  the  year  there  are  between 
100  and  500  species  of  birds  to  be  found  in  localities  in  various 
parts  of  the  United  States.  The  desert  regions  of  the  Southwest 
’naturally  have  the  fewest,  the  eastern  seaboard  states  may  have 
1200  to  300,  while  there  have  been  about  500  species  identified  in 
the  northern  and  central  parts  of  California. 

Field  Exercise.  Make  a survey  of  your  neighborhood  to  find  out 
jthe  number  of  different  birds  that  are  residents  or  migrants  there. 


552  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  WEALTH 


The  following  descrip- 
tions will  help  one  to 
recognize  a few  of  our 
common  birds  which  are 
of  decided  economic  value 
or  harm.  The  size,  color 
markings,  food,  and  fa- 
miliar habits  of  some  of 
our  common  birds  will  be 
given,  with  a brief  state- 
ment of  the  reason  why 
they  are  man’s  friends  or 
enemies. 

Robin.  A bird  known 
to  all  of  us  makes  an 
excellent  type  for  com- 
parison with  other  less- 
known  birds.  The  robin 
is  nine  to  ten  inches  long.  The  male  is  brownish  gray  above, 
tinged  with  olive,  with  brown  wings,  and  black  on  the  head  and  the 
tail.  The  throat  is  light  gray  with  black  spots,  and  the  breast 
is  brownish  red.  The  female  is  duller  in  color  with  paler  breast. 
The  robins  live  near  houses  and  in  orchards  and  make  their  nests 
of  grass  and  mud,  in  trees  or  on  buildings.  The  robin  is  a true 
thrush,  whose  pleasing  song  delights  us  in  early  spring.  Its  eco- 
nomic value  is  often  discussed  as  it  eats  much  fruit  early  in  the 
season.  Its  diet  usually  consists  of  about  40  per  cent  insects, 
most  of  which,  as  ground  beetles,  caterpillars,  plant  lice,  and  cut- 
worms, are  harmful.  From  February  to  May,  in  the  east,  its  food 
is  almost  entirely  insects.  The  western  robin  has  done  damage 
to  olive  and  other  fruit  orchards  when  insect  food  was  scarce, 
but  like  its  eastern  relative,  it  consumes  a large  percentage  of 
insects  most  of  the  time. 

Bluebird.  This  is  one  of  our  earliest  migrants.  Its  cheery 
note  and  blue  coat  are  easily  recognized.  It  is  six  and  one  half 
to  seven  inches  in  length.  The  male  is  bright  blue  above,  and 
chestnut  underneath.  The  female  is  duller  in  color.  It  nests  in 


CIlinCADEE 


553 


holes  in  trees  or  posts  and 
in  bird  lioiises.  Its  food 
consists  from  about  70  to 
90  per  cent  of  insects, 
la rgcl y grasshoppers, 
beetles,  spiders,  and  cater- 
pillars. 

Chickadee.  This  is  a 
^ small  bird,  about  five  and 
, a quarter  inches  long.  It 
I is  often  an  all-3Tar-round 
resident.  The  crown  of 
hhe  head  and  throat  are 
i black,  the  cheeks  white, 

;the  back  gra}^  and  the 
abdomen  usually  a dirty 
white.  Its  food  is  about 

70  per  cent  insect  and  30  ^ hlnehird  and  her  young. 

per  cent  seeds  in  the  summer.  In  the  winter  it  devours  large 
jlquantities  of  eggs  laid  by  insect  pests.  One  bird  was  found  to 
ihave  eaten  more  than  430  eggs  of  the  plant  louse  in  a single  day. 
I Professor  Sanderson  of  Cornell  University  has  estimated  that  they 


Chickadee  serving  lunch. 


554  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  WEALTH 


A house  wren  bringing  a caterpillar  to  her  young. 


eat  over  8,000,000,000  insects  in  Michigan  every  year.  On  that 
basis  what  good  must  they  do  in  the  United  States?  The  chicka- 
dee is  certainly  one  of  man’s  best  bird  friends. 

House  wren.  This  little  migrant  nests  around  our  homes. 
It  is  a great  songster,  and  is  a decided  asset  to  us  because  of  its 
varied  diet  of  cutworms,  spiders,  weevils,  and  May  flies.  It  has 
a 98  per  cent  insect  diet.  One  wren  was  observed  to  catch  600 
insects  in  one  day.  Its  worst  enemies  are  cats  and  larger  birds. 
A proper  nesting  box  with  a small  entrance  is  one  of  its  best  means 
of  protection.  The  house  wren  is  not  quite  five  inches  long.  The 
upper  part  is  brown,  the  lower  grayish  brown  and  white.  The  wings, 
flanks,  and  tail  are  slightly  barred.  It  can  be  recognized  easily  by 
its  small  size,  coloring,  incessant  singing  or  chattering,  and  by  the 
fact  that  its  tail  is  frequently  held  erect  when  the  bird  is  at  rest. 

Song  sparrow.  Another  of  our  earliest  visitors  is  the  song 
sparrow.  The  male  is  about  six  and  one  half  inches  long.  It  is 
brown  above  with  the  head  reddish-brown  with  blackish  streaks. 
A streak  of  gray  runs  through  the  center  of  the  crown,  and  there 
is  a characteristic  brown  stripe  on  the  sides  of  the  throat.  The 
breast  is  streaked  with  brown  on  a white  ground.  Its  nest  is 
usually  on  the  ground  or  in  a low  bush.  It  is  a friendly  bird 
and  is  often  seen  near  houses,  though  it  prefers  moist  areas  farther 


PHOEBE  555 

away  from  man.  It  oats  some  insects,  but  like  most  of  the  native 
sparrows  it  feeds  mainly  upon  weed  seeds. 

American  goldfinch.  This  bright  yellow  songster  is  one  of  our 
most  attractive  birds.  It  is  often  called  the  wild  canary.  It  is 
about  five  inches  long.  The  male  has  a bright  yellow  body  with  a 
black  cap,  and  black  and  white  tail  and  wings.  The  female  is 
t brownish  olive  above  and  yellowish  white  beneath.  The  gold- 
i finch  eats  seeds  of  weeds,  preferring  those  of  the  dandelion  and 
f thistle,  two  of  our  greatest  weed  pests. 

! Yellow  warbler.  A bird  often  confused  with  the  goldfinch  is  the 

I yellow  warbler.  Like  all  warblers,  this  is  a small  bird  about  five 
inches  in  length.  Its  color  is  jtIIow,  with  breast  flecked  with  red- 
blish  brown  (it  has  no  black  on  the  head  as  does  the  goldfinch). 

' It  nests  near  houses  in  low  trees  or  bushes.  It  is  of  much  economic 
importance  because  of  its  preference  for  the  browntail  and  gypsy 

I moth  caterpillars,  and  other  enemies  of  the  forest  trees.  It  also 
eats  cankerworms  and  insects  injurious  to  crops.  We  are  spend- 
ing millions  of  dollars  every  year  to  fight  these  pests,  and  the 
warblers,  besides  being  beautiful  birds,  are  helping  us  in  this  fight. 

Phoebe.  Another  tireless  hunter  of  insect  pests  is  the  phoebe. 
This  bird  is  a flycatcher,  seizing  insects  on  the  wing.  It  builds  a 


Insects  are  the  preferred  food  of  phoebes. 


L.  W.  Brownell 


556  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  WEALTH 

nest  of  mud  — often  under  old  bridges,  around  barns,  or  some- 
times under  a barn  floor.  Its  food  consists  of  browntail  and 
gypsy  moths,  grasshoppers,  cankerworms,  beetles,  flies,  and  in 
the  South  cotton-boll  weevils.  The  phoebe  is  about  seven  inches 
long,  dusky  olive-brown  above,  yellowish  white  underneath,  with 
wings  and  tail  dusky.  The  head  is  slightly  crested,  and  the  bill 
and  feet  are  black.  It  is  one  of  our  early  visitors. 

Barn  swallow.  Another  bird  with  nesting  habits  similar  to 
those  of  the  phoebe  is  the  barn  swallow,  which  makes  a nest  plas- 
tered to  the  rafters  of  a barn  or  outbuilding.  While  most  birds 
decrease  in  number  with  the  cutting  of  forests  and  the  building  of 
cities,  the  barn  swallow  has  increased  because  it  feeds  on  insects 
which  live  on  crops  in  cleared  fields.  It  eats  moths  of  cutworms, 
codling  moths,  leaf  cutters,  and  many  flies,  bugs,  and  beetles.  In 
the  South  it  is  an  enemy  of  the  cotton-boll  weevil.  This  swallow 
is  between  six  and  seven  inches  in  length.  It  is  dark  steel  blue 
above,  with  throat  and  upper  breast  chestnut;  the  lower  breast 

and  abdomen  buff.  The  tail 
is  deeply  forked,  showing 
white  markings  when  spread. 

Catbird.  Another  bird 
which  nests  near  houses  and 
prefers  the  company  of  man  is 
the  catbird.  From  early  May 
to  late  October  its  various 
calls  and  songs  are  the  de- 
light of  all  bird  lovers,  for  it 
is  a great  mimic  and  somewhat 
of  a tease.  The  catbird,  al- 
though it  eats  much  fruit,  is 
an  insect  feeder  and  gives  its 
young  insect  food.  Like  other 
birds,  it  eats  the  food  most 
abundant  at  the  time.  Birds 
taken  from  a canker-infested 
orchard  made  insects  95  per  cent  of  their  diet,  although  normally 
they  eat  over  60  per  cent  fruit.  A catbird  is  about  nine  inches 


L.  W.  Brownell 

Catbird  entering  nest. 


DOWNY  WOODPECKER 


557 


in  length,  and  of  a dark  grayish  color,  with  the  top  of  head  and 
the  tail  blackish,  with  a distinct  chestnut  patch  under  the  tail. 

Downy  woodpecker.  The  woodpeckers  are  familiar  to  most 
boys  and  girls  because  of  their  conspicuous  color  and  their  peculiar 
habits.  The  male  downy 
woodpecker  is  six  and  a half 
inches  long,  black  and  white 
barred,  with  a patch  of  scarlet 
on  the  upper  side  of  the  neck. 

It  runs  quickly  up  and  down 
the  trunks  of  trees,  tapping 
the  wood  to  locate  insect 
holes.  The  bill  is  strong, 
sharp  at  the  end,  and  is  used 
as  a chisel  in  boring  into  wood. 

The  tongue  is  spearlike,  one 
to  one  and  a half  inches 
long,  and  is  used  to  pull  out 
the  larvae  which  lurk  beneath 
the  bark.  On  the  average 
about  65  per  cent  of  the  food  of 
woodpeckers  is  insect,  largely 
maple,  birch,  apple,  and  other  borers.  Woolly  aphids,  caterpillars, 
and  chrysalids  are  also  its  prey.  The  woodpeckers,  called  sap- 
suckers,  live  up  to  their  name  and  are  said  to  cause  a yearly  damage 
of  over  $1,250,000  to  the  lumber  industry.  On  the  other  hand, 
they  destroy  large  numbers  of  insects  injurious  to  the  same  trees. 

Flicker.  This  bird,  a woodpecker,  is  twelve  inches  long.  The 
male  is  brown  above  and  golden  yellow  under  the  wings  and  tail, 
brown  spots  on  breast,  a scarlet  crescent  on  back  of  the  neck,  and 
a black  crescent  on  the  breast.  It  has  a white  rump  which  is 
conspicuous  in  flight  and  makes  an  easily  recognized  mark.  The 
flicker  is  generally  useful,  feeding  upon  plant  lice,  ants  (which 
make  up  about  45  per  cent  of  its  food),  grasshoppers,  caterpillars, 
and  weed  seeds.  Like  other  woodpeckers,  it  nests  in  hollow  trees. 

Baltimore  oriole.  This  bright-colored  and  attractive  bird  is 
about  seven  and  one  half  inches  long.  The  male  has  the  upper 


558  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  WEALTH 


back,  wings,  and  throat  black,  with  the  outer  tail  feathers,  breast, 
and  under  parts  orange.  The  female  is  not  so  brilliantly  colored, 

being  yellow  instead  of 
orange.  The  hanging 
nests  of  the  oriole,  often 
woven  with  bits  of  string, 
cloth,  and  other  materials, 
are  a common  sight  in 
elm  trees  near  our  homes. 
These  birds  prefer  inhab- 
ited areas  and,  because 
of  their  protected  nests, 
are  increasing  in  spite  of 
cats  and  the  English  spar- 
rows. They  feed  largely 
upon  insects.  As  high  as 
92  per  cent  insect  diet 
has  been  recorded  in  the 
summer  season.  The 
cankerworm,  tussock, 
browntail,  and  forest  tent 
A flicker  caterpillars  were  found  in 

the  stomachs  of  northern 
birds,  while  those  examined  in  the  south  contained  many  cotton- 
boll  weevils. 

Screech  owl.  This  is  a small  owl  and  one  of  the  most  useful, 
as  it  feeds  upon  field  mice  and  other  small  destructive  rodents  as 
well  as  upon  some  moths,  caterpillars,  and  beetles.  It  is  about  as  ) 
large  as  a quail,  about  nine  and  one  half  inches  in  length.  Its 
general  coloring  is  gray  on  the  under  parts  and  reddish  brown  above.  ; 
The  eye  is  yellow.  It  usually  nests  in  hollow  trees.  | 

Crow.  Our  common  crow,  a glossy  black  bird  from  sixteen  to 
nineteen  inches  long,  is  one  of  the  few  birds  that  may  do  more  ; 
harm  than  good.  In  the  early  spring  the  crow  is  useful,  80  per 
cent  of  its  diet  being  insect  larvae,  such  as  wireworms  and 
May  beetle  larvae.  It  also  eats  field  mice,  but  later  does  much  ■ 
harm  in  the  newly  planted  corn  fields.  In  parts  of  the  country 


L.  W.  Brownell 


BIRDS  HARMFUL  TO  MAN 


559 


where  they  are  most  abundant 
they  cause  liarm  by  killing 
useful  birds. 

English  sparrow.  The  Eng- 
lish sparrow  is  an  example  of 
a bird  introduced  for  the  pur- 
pose of  insect  destruction, 
that  has  done  great  harm 
because  of  its  relation  to  our 
native  birds.  Introduced  at 
Brooklyn  in  1850  for  the 
purpose  of  exterminating  the 
cankerworm,  it  soon  aban- 
doned a diet  largely  of  insects 
in  favor  of  one  of  grain  and 
has  driven  out  many  of  our 
native  insect  feeders.  In- 
vestigations by  the  Depart- 
ment of  Agriculture  show  that 
in  the  country  these  birds  and 
their  young  feed  to  a large 
extent  upon  grain,  thus  show- 
ing them  to  be  injurious  to 
agriculture.  Dirty  and  very 
prolific,  they  have  long  since 
worked  their  way  from  the 
East  to  the  Pacific  coast. 
The  English  sparrow  has  be- 
come a national  pest,  and 
should  be  exterminated  in 
order  to  save  our  native  birds. 

Birds  harmful  to  man. 
While  there  are  a few  birds 
that  do  both  harm  and  good, 
like  the  crow,  catbird,  blue 
jay,  cedar  waxwing,  and  robin, 
there  are  others  that  are  bad, 


L.  W.  Brownell 

Is  the  screech  owl  a beneficial  or  harmful  bird? 
Why? 


L.  W.  Brownell 

A warbler  feeding  a young  cowbird  which  is 
nearly  as  large  as  its  foster  mother. 


560  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  WEALTH 


and  we  can  find  little  or  no  good  to  say  about  them.  The  English 
sparrow  is  the  greatest  bird  pest,  for  reasons  given  above.  The 
cowbird  never  builds  a nest  nor  cares  for  her  young.  She  lays 
her  eggs  in  the  nests  of  smaller  birds,  usually  warblers,  where  later 
the  young  cowbirds  cause  the  death  of  the  rightful  inhabitants  of 
the  nest.  Cooper’s  hawk,  the  sharp-shinned  hawk,  and  the  great 
horned  owl  kill  smaller,  beneficial  birds. 

Practical  Exercise  28.  Try  to  find  a nest  containing  eggs  and  watch  the  de- 
velopment of  the  young  over  a given  period.  Report  your  findings  to  the  class. 

Practical  Exercise  29.  Make  a table  for  your  workbook  in  which  you  name 
as  many  local  birds  as  you  can.  List  them  as  useful,  harmful,  or  harmless,  and 
in  a fifth  column  give  evidence  for  your  statements. 

Practical  Exercise  30.  Make  a study  of  the  feeding  habits  of  some  one  bird 
and  report  on  it. 

Practical  Exercise  31.  What  methods  of  protection  of  birds  do  you  find  in 
your  community  ? What  means  have  you  taken  to  protect  birds  that  live  near 
your  home  ? 

Self-Testing  Exercises 

The  robin  is  about  (1)  (2)  long,  (3) 

(4)  on  breast, (5)  on  wings,  and (6)  on  head. 

The  chickadee  may  be  recognized  by  its  (7).  It  is  about 

(8)  inches  in  length,  head  and  throat (9),  abdomen 

dirty  (10)-  The  American  goldfinch  is  (11);  the 

bluebird (12)  in  general  color.  The  yellow  warbler  is  about 

(13)  inches  long  and  has  no (14)  on  its (15). 

The  barn  swallow  is  between (16)  and (17)  inches 

long,  dark  (18)  (19)  above,  breast  and  abdomen 

(20),  tail  deeply (21).  The  Baltimore  oriole  is  about 

(22)  inches  long.  The  male  oriole  is  brightly  colored  with 

(23),  with  throat,  and  upper  back (24).  Owls  may 

usually  be  told  by  the (25)  beak  and  prominent  ........  (26) 

eyes. 

PROBLEM  VIII.  WHAT  IS  THE  ECONOMIC  IMPORTANCE  OF 
INSECTS? 

Useful  insects.  We  have  learned  that  many  insects  pollinate 
flowers ; that  in  many  cases  insects  are  preyed  upon,  and  supply 
an  enormous  multitude  of  birds,  fishes,  and  other  animals  with 
food.  Dr.  Forbes  of  the  University  of  Illinois  estimates  that 
many  of  the  smaller  fresh- water  fishes  consumed  over  fifty  per  cent 
insect  food,  mostly  larvae. 


USEFUL  INSECTS 


561 


The  carrion  beetles  and  many  water  beetles  act  as  scaveng-ers. 
The  sexton  beetles  bury  dead  carcasses  of  animals.  Ants  in 
tropical  countries 
are  particularly 
useful  as  scaven- 
gers. Insects 
often  do  a service 
by  eating  harmful 
weeds ; thus  many 
harmful  plants 
are  kept  in  check. 

The  “ ladybug,” 
or  ladybird  beetle, 
is  the  natural 
enemy  of  the  cot- 
tony-cushion scale. 

It  may  often  be 
found  also  feeding 
on  the  plant  lice, 
or  aphids. 

The  ichneumon  fly,  indirectly,  does  man  considerable  good 
because  of  its  habit  of  laying  its  eggs  and  leaving  its  young  to 
develop  in  the  bodies  of  caterpillars  which  are  harmful  to  vegeta- 
tion. Some  of  the  ichneumons  even  bore  into  trees  in  order  to 
deposit  their  eggs  in  the  larvae  of  wood-boring  insects. 

Cochineal  and  lac.  Among  the  many  products  of  insect  origin 
is  cochineal,  a red  coloring  matter  which  consists  of  the  dried 
bodies  of  a tiny  insect,  one  of  the  plant  lice  which  live  on  the  cactus 

plants  in  Mexico  and  Central 
America.  The  lac  insect,  an- 
other one  of  the  plant  lice, 
feeds  on  the  juices  of  certain 
trees  in  India  and  pours  out  a 
substance  from  its  body  which 
after  treatment  forms  shellac. 

Gall  insects.  Oak  galls, 
growths  caused  by  wasp-like 


L.  W.  Brownell 

The  larvae  of  the  ichneumon  fly  attach  themselves  to  the  body 
of  a caterpillar.  They  grow  by  sucking  the  blood  from  their 
host  and  finally  they  spin  cocoons.  In  this  illustration  cocoons  of 
an  ichneumon  fly  are  fastened  to  a Spingidae  larva  which  feeds 
upon  the  leaves  and  stems  of  various  plants. 


Lrc.® 
insect 

anovtth. 

Why  is  the  lac  insect  useful  to  man  ? 


adult' 

female' 


562  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  WEALTH 


insects,  give  us  products  used  in  tanning,  and  in  making  pyrogallic 
acid  which  is  much  used  in  developing  photographs. 

Economic  loss  from  insects.  While  birds  do  hold  insects  in 
check,  the  money  value  of  crops,  forest  trees,  stored  foods,  and 
other  materials  destroyed  annually  by  insects  is  beyond  belief.  It  is 
estimated  that  they  destroy  yearly  one  tenth  of  the  country’s  crops, 
which  is  estimated  to  be  a yearly  loss  of  at  least  $2,000,000,000. 

Insects  which  damage  garden  and  other  crops.  Grasshoppers 
and  the  larvae  of  various  moths  do  considerable  harm  here, 


The  corn  worm  does  much  damage  to  corn.  How  does  it  do  this  ? 


especially  the  “ cabbage  worm,”  the  cutworm,  which  eats  all  kinds 
of  garden  truck,  and  the  European  corn  borer  which  destroys  our 
corn. 

Among  the  beetles  which  are  found  in  gardens  is  the  potato 
beetle  which  eats  the  leaves  of  the  potato  plant.  This  beetle 
formerly  lived  upon  a wild  plant  of  the  same  family  as  the  potato, 
and  began  to  infest  potato  fields  when  that  crop  was  introduced 
in  Colorado,  evidently  preferring  cultivated  forms  to  wild  forms 
of  this  family. 

The  one  beetle  doing  by  far  the  greatest  harm  in  this  country 
is  the  cotton-boll  weevil.  Imported  from  Mexico,  since  1892  it 
has  spread  over  nearly  the  entire  cotton-growing  area  of  the 


INSECTS  WHICH  DAiMACE  CROPS 


5(38 


South.  Many  Southern  fanners  have  been  forced  to  produce 
other  crops  in  the  place  of 
cotton.  An  example  is  seen  in 
the  tlecrease  of  production  of 
the  once  famous  sea  island 
cotton.  As  late  as  1916,  117- 
559  bales  were  produced ; in 
1924  the  record  gave  only  5 
bales  ginned. 

The  beetle  lays  its  eggs  in 
the  young  flower  buds  and  the 
larvae  feed  upon  the  substance 
within  the  bud,  thus  causing 
it  to  drop  off  and,  conse- 
quently, produce  no  cotton 
fiber.  Later  in  the  season 
the  beetle  lays  its  eggs  in  the  young  fruit  or  bolls  of  cotton.  These 
do  not  drop  off,  but  the  bolls  become  discolored  and  the  cotton 
is  ruined.  It  is  estimated  that  this  pest  destroys  yearly  over  one 


Life  history  of  cotton-boll  weevil.  At  what 
time  during  its  life  does  the  weevil  do  the  most 
harm? 


564  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  WEALTH 

half  of  the  cotton  crop,  thus  indirectly  affecting  each  one  of  us 
through  the  increased  price  of  cotton.  The  boll  weevil,  because 
of  the  protection  offered  by  the  cotton  boll,  is  very  difficult  to 
exterminate.  Some  weevils  are  destroyed  by  birds,  millions  are 
killed  each  winter  by  cold,  insects  are  introduced  to  prey  on 
them,  and  the  infected  bolls  and  stalks  are  burned,  but  at  the 
present  time  they  are  one  of  the  greatest  pests  the  South  knows. 

The  bugs  are  among  our  most  destructive  insects.  The  most 
familiar  examples  of  our  garden  pests  are  the  squash  bug;  the 
chinch  bug,  which,  by  sucking  the  juice  from  the  leaves  of  grain, 
does  yearly  damage  estimated  at  $20,000,000 ; and  the  plant  lice, 
or  aphids.  The  dreaded  phylloxera,  living  on  the  grape,  destroys 
immense  numbers  of  vines  in  the  vineyards  of  France,  Germany, 
and  California. 

The  Japanese  beetle,  in  larval  form,  was  introduced  into  this 
country  from  Japan  in  the  soil  surrounding  the  roots  of  a plant. 
It  was  first  observed  in  1916  in  New  Jersey  and  by  1923  it  had 
infested  about  2500  square  miles  in  New  Jersey  and  Pennsyl- 


Life  history  of  the  Japanese  beetle.  What  is  one  of  the  best  ways  of  eradicating  this  insect  ? 


vania.  Since  that  time  it  has  spread  to  other  states.  The 
adult  beetle  is  about  three  fourths  of  an  inch  in  length.  It  is 
a bright  metallic  green  with  coppery  brown  wings.  It  feeds  upon 
the  foliage  of  fruit  trees,  shade  trees,  vines,  and  also  attacks  the 


INSECTS  OF  THE  HOUSE  AND  STOREHOUSE  5G5 


oarh'  fruits.  The  hirva  lives  below  ground  and  feeds  upon  the 
roots  of  plants. 

The  spread  of  the  Japanese  beetle  is  being  fought  by  the  use  of 
sprays,  treatment  of  the  soil,  and  by  the  importation  of  insects 
that  lay  their  eggs  in  the  larvae  of  adult  beetles. 

The  Medfly  or  ^lediterranean  fruit  fly,  which,  since  its  appear- 
ance in  Spain  in  1842,  has  spread  to  all  parts  of  the  world,  was 
discovered  in  Florida  in  April,  1929.  It  was  found  to  breed  in 
all  fruits,  and  also  to  attack  peppers,  tomatoes,  lima  beans,  and 
eggplants.  The  state  of  Florida  as  well  as  the  National  Govern- 
ment immediately  took  steps  to  eradicate  it.  No  fruit  was  per- 
mitted to  go  out  of  the  infested  areas.  All  the  trees,  vines,  and 
other  vegetables  on  wdiich  the  flies  fed  were  destroyed,  and  all 
trees  in  near-by  areas  w^ere  sprayed  at  frequent  intervals.  These 
methods  proved  so  effective  that  after  November  16,  1930,  no 
flies  or  infested  fruits  or  vegetables  were  found.  The  Federal 
quarantine  on  Florida  products  was  then  lifted. 

Insects  which  harm  fruit  and  forest  trees.  Great  damage  is 
done  to  trees  by  the  larvae  of  moths.  Massachusetts  has  already 


The  larva  of  the  gypsy  moth  strips  the  foliage  from  trees  and  shrubs.  The  range  and  spread  of 
this  insect  has  been  carefully  mapped.  Is  it  present  where  you  live? 

H.  BIO  — 37 


566  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  WEALTH 


spent  more  than  $5,000,000  in  trying  to  exterminate  the  acci- 
dentally imported  gypsy  moth.  The  codling  moth,  which  bores 
into  apples  and  pears,  is  estimated  to  ruin  yearly  $3,000,000  worth 
of  fruit  in  New  York  alone,  which  is  only  one  of  the  important 
apple  regions  of  the  United  States.  Probably  one  of  the  worst 
insect  pests  to  the  dweller  in  a large  city  is  the  tussock  moth,  which 
destroys  our  shade  trees.  The  caterpillar  may  easily  be  recognized 
by  its  hairy,  tufted  body  and  red  head.  The  eggs  are  laid  in  what 
look  like  masses  of  foam  on  the  outside  of  the  cocoon  attached 
to  the  bark  of  a shade  tree.  By  collecting  and  burning  the  egg 
masses  in  the  autumn,  we  may  save  many  shade  trees. 

The  larvae  of  some  moths  damage  trees  by  boring  into  the  wood 
of  the  tree  on  which  they  live.  Such  are  the  peach,  apple,  and 
other  fruit-tree  borers  common  in  our  orchards.  Some  kinds  of 
beetles  produce  boring  larvae  which  eat  their  way  into  trees  and 
kill  thousands  of  forest  and  shade  trees  annually.  The  hickory 
borer  threatens  to  kill  all  the  hickory  trees  in  the  eastern  states. 

Among  the  bugs  most  destructive  to  trees  are  the  scale  insect 
and  the  plant  lice.  A number  of  years  ago  the  citrus  growers  of 
California  had  their  trees  threatened  with  destruction  by  the 
cottony-cushion  scale.  But  a ladybird  beetle  which  feeds  on  the 
scale  was  introduced  from  Australia  and  today  the  danger  from 
the  scale  is  under  control. 

Insects  of  the  house  and  storehouse.  Weevils  are  the  greatest 
pests  of  stored  grains,  frequently  ruining  tons  of  corn,  wheat,  and 
other  cereals.  Cockroaches  will  eat  almost  any  kind  of  foodstuffs. 
The  carpet  beetle  is  a recognized  foe  of  the  housekeeper;  the 
larvae  feed  upon  all  sorts  of  woolen  material.  The  larvae  of  the 
clothes  moth  do  an  immense  amount  of  damage,  especially  to  stored 
clothing.  Fleas,  lice,  and  bedbugs  are  among  man’s  personal  foes. 
Besides  being  unpleasant,  some  of  them  are  disease  carriers. 

Man’s  place  in  the  chain  of  insect  life.  We  have  seen  that  man 
is  frequently  directly  responsible  for  the  introduction  of  insect 
pests.  He  may  be  indirectly  responsible  for  them  by  planting 
crops  on  which  they  can  feed,  for  an  increase  in  easily  obtainable 
food  means  more  insects.  Birds  and  other  natural  enemies  will 
do  much  in  keeping  down  the  number  of  insects,  but  man  himself 


METHODS  OF  CONTROL  OF  INSECT  PESTS 


567 


lias  to  do  some  of  the  If  the  fanners  do  not  plant  certain 

crops,  the  insects  cannot  j2:et  footl  and  they  perish.  Naturally 
fanners  do  not  want  to  lose  their  crops,  so  they  have  gone  to  the 
Bureau  of  Entomology  of  the  United  States  Department  of  Agri- 
culture, the  various  state  experiment  stations,  and  others  for 
help. 

Methods  of  control  of  insect  pests.  In  general  we  have  three 
different  methods  for  controlling  insect  enemies.  The  first  is  to 
learn  what  their  natural  enemies  are  and  then  introduce  these 
enemies  so  that  the  balance  may  be  kept  in  a natural  way.  An 
historic  case  has  been  mentioned  on  page  566.  But  man  has  made 
a step  further.  He  has  found  that  fumigating  with  hydrocyanic  gas 
will  kill  the  scale  insects  left  on  the  trees.  Insects  may  be  destroyed 
by  (a)  picking  (as  in  the  case  of  the  potato  beetle)  or  by  (6)  contact 
poisons,  which  kill  by  covering  up  the  spiracles  of  the  insect  so  that 
it  cannot  breathe,  or  by  (c)  stomach  poisons,  which  are  sprayed 
on  the  leaves  to  be  eaten  by  the  insects.  Man  has  learned  to 
develop  plants  that  mature  faster  than  the  insects  do  or  plant  his 
crops  early  or  late,  thus  escaping  damage. 

The  control  of  the  cotton-boll  weevil  seems  to  depend  upon 
early  planting  so  that  the  crop  has  an  opportunity  to  ripen  before 
the  insects  in  the  boll  grow  large  enough  to  do  harm.  Various 
state  and  government  agencies  are  at  work  upon  the  problem,  and 
ultimately  the  boll  weevil  may  do  more  good  than  harm  by  bringing 
about  the  culture  of  a type  of  cotton  plant  that  ripens  very  early 
and  by  forcing  the  farmers  of  the  South  to  produce  diversified 
crops,  which  can  be  marketed  to  an  advantage  if  the  cotton  crop 
is  a failure.  Another  method  is  by  crop  rotation,  for  in  this  way 
insects  may  be  deprived  of  food  plants  on  which  to  lay  their  eggs. 

Work  of  Bureau  of  Agriculture.  Most  of  these  methods  of 
destroying  insects  have  been  worked  out  for  the  farmer  by  differ- 
ent bureaus  of  the  Department  of  Agriculture.  The  Bureau  of 
Entomology  works  in  harmony  with  the  other  divisions  of  the 
Department  of  Agriculture,  giving  the  time  of  its  experts  to  the 
problems  of  controlling  insects  which,  for  good  or  ill,  influence 
man’s  welfare  in  this  country.  The  destruction  of  the  malarial 
mosquito ; the  destruction  of  harmful  insects  by  the  introduction 


568  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  WEALTH 


of  their  natural  enemies,  plant  or  animal;  the  improvement  of 
the  honeybee ; and  the  introduction  of  new  species  of  insects  to 
pollinate  flowers  not  native  to  this  country,  are  some  of  the  prob- 
lems to  which  these  men  have  devoted  their  time. 

All  the  states  and  territories  have,  since  1888,  established  state 
experiment  stations,  which  work  in  cooperation  with  the  govern- 
ment in  the  war  upon  injurious  insects.  These  stations  are  often 
connected  with  colleges,  so  that  young  men  who  are  interested 
in  this  science  may  have  opportunity  to  learn  and  to  help. 

Bulletins  on  insects  and  their  control  are  published  by  the 
various  state  stations  and  by  the  Department  of  Agriculture. 
Probably  the  most  useful  of  these  are  the  Farmers’  Bulletins, 
issued  by  the  Department  of  Agriculture. 

The  outline  has  been  made  up  largely  from  these  sources. 

ECONOMIC  IMPORTANCE  OF  INSECTS 
Beneficial  Insects 

Silk  moth.  — Larva  spins  a cocoon  from  which  silk  is  made. 

Honeybee.  — Adult  produces  honey  and  pollinates  flowers. 

Bumblebee.  — Adult  pollinates  red  clover  and  fruit  trees. 

Ichneumon  fly.  — Female  lays  eggs  in  the  bodies  of  harmful  larvae  (as  the  grape- 
vine caterpillar  and  the  tree  borers) . The  developing  parasites  feed  on  the  hosts 
and  kill  them. 

Dragon  fly.  — Adult  feeds  on  mosquitoes. 

Ladybird  beetle.  — Adult  feeds  on  scale  insects  and  aphids. 

Gall  insect.  — The  developing  larvae  cause  galls  from  which  ink  is  made. 

Household  Pests 

House  fly.  — Adult  carries  typhoid,  tuberculosis,  summer  complaint,  and  other 
intestinal  diseases.  To  exterminate,  it  is  necessary  to  prevent  breeding  and  kill 
overwintering  flies. 

Mosquito.  — Adult  carries  malaria  and  yellow  fever.  May  be  exterminated  by 
destroying  the  breeding  places. 

Body  louse.  — Adult  carries  typhus.  Insects  may  be  killed  by  sterilizing  infected 
clothing  and  by  bathing  patients  in  an  antiseptic  solution. 

Flea  on  rats.  — Adult  carries  bubonic  plague.  Kill  the  rats. 

Clothes  moth.  — Larvae  eat  clothing:  wool,  fur,  etc.  They  may  be  controlled  by 
shaking  or  brushing  the  clothing,  and  exposing  it  to  the  sun.  The  use  of 
camphor  or  naphthaline  on  clothing  which  is  packed  away  deters  the  moth 
from  laying  its  eggs  there. 

Buffalo  carpet-beetle.  — Larva  eats  carpets.  Spray  benzine  in  the  cracks  in  the  floor 
and  on  the  carpet. 

Cockroach.  — Adults  are  scavengers  and  are  numerous  around  sinks  and  where  food 
is  kept.  They  may  be  exterminated  with  poison  bait.  Cleanliness  is  necessary. 


Garden  and  Fruit  Tree  Pests 

Potato  beetle.  — Larva  eats  leaves  of  the  potato  plant.  Spray  infected  plants  with 
arsenate  of  lead  or  Paris  green. 


ECONOMIC  IMPOKTANCE  OF  INSECTS  569 

Cabbage  butterfly.  — Larva  oats  loaves  of  cabbages  and  may  bo  destroyed  by  a spray 
of  arsenate  of  lead  or  Paris  green. 

Hawk  moths.  — Larva  feoils  on  loaves  of  grape  and  tomato  vines.  Spray. 

Rose  beetles.  — Adults  food  on  loaves  and  blossoms  of  the  rose.  Spray  with  a soap 
solution. 

Codling  moth. — Larva  injures  api)les  and  pears.  Spray  with  arsenate  of  lead  at 
the  time  petals  fall. 

San  Jose  scale.  — .\dults  suck  juices  from  the  leaves  and  young  twigs  of  fruit  trees. 
Killed  by  ladybird  beetles  and  by  fumigation. 

Aphids.  — Adult  females  suck  juice  from  leaves  and  young  twigs.  Spray  with 
nicotine  sulphate. 

Boll  u'orm  or  corn  worm.  — Larva  lives  in  the  ears  of  corn. 

European  corn  borer.  — Feeds  on  stalks,  roots,  and  ears  of  corn  plant.  Controlled 
by  burning  cornstalks  in  the  fall. 


Fouest  .VXD  Sh.vde  Tree  Pests 

Tussock  moth.  — Larva  eats  leaves  of  shade  and  fruit  trees.  Destroy  egg  masses 
and  spray  in  early  spring. 

Gypsy  moth.  — Damage  and  extermination  the  same  as  for  tussock  moth. 

Forest  tent  caterpillar.  — Larva  eats  leaves  of  shade  and  fruit  trees.  Destroy  nests 
and  spray. 


Self-Testing  Exercise 

!Mark  in  your  workbook  the  correct  statements : 

T.  F.  1 . The  cotton-boll  weevil  has  done  so  much  harm  in  the  South 
that  that  region  will  never  recover  economically. 

T.  F.  2.  The  tussock  moth  destroys  annually  many  corn  fields. 

T.  F.  3.  Nature  usually  has  a natural  check  on  destructive  insects, 
as  in  the  case  of  the  ladybird  beetle  and  San  Jose  scale. 

T.  F.  4.  Larvae  which  feed  upon  crops  may  be  killed  by  fumigation. 


Review  Summary 

Test  your  knowledge  of  the  unit  by:  (1)  rechecking  on  the  survey  ques- 
tions; (2)  performing  all  assigned  exercises;  (3)  checking  with  your  teacher 
the  scores  of  the  various  tests  and  trying  again  those  that  you  missed ; (4)  mak- 
ing an  outline  of  the  unit  for  your  notebook. 


Tests  on  Fundamental  Concepts 

In  a vertical  column  under  the  heading  CORRECT  write  numbers  of  all  statements  you 
believe  are  true.  In  another  column  under  INCORRECT  write  numbers  of  untrue  statements. 
Your  score  equals  right  answers  X 2h 

I.  Plant  foods  (1)  come  from  grain,  vegetables,  sugar  cane,  and 
orchards ; (2)  are  valued  roughly  in  the  following  order : grains, 

vegetables,  orchard  fruits,  and  citrus  fruits ; (3)  are  valued  at  more 
than  animal  foods ; (4)  may  come  from  all  parts  of  a plant. 


570  MAN  CONTROLS  HIS  ENVIRONMENT  FOR  WEALTH 


II.  Animal  foods  (5)  come  mostly  from  bivalves ; (6)  are  obtained 
from  animals  in  every  phyla  of  the  animal  kingdom;  (7)  come  only 
from  mammals ; (8)  depend  in  the  long  run  upon  the  sun. 

III.  Animal  products  are:  (9)  rayon,  flax,  cocaine,  cottonseed  oil, 
and  lumber  ; (10)  pearls,  sponges,  piano  keys,  and  tallow;  (11)  knife 
handles,  pen  holders,  buttons,  and  glue ; (12)  silk,  felt,  and  shoes. 

IV.  Examples  of  animals  that  are  indirectly  useful  are : (13)  snakes ; 
(14)  sheep;  (15)  toads;  (16)  chickens;  (17)  house  wren. 

V.  Examples  of  harmful  animals  are:  (18)  starfish;  (19)  trout; 
(20)  the  cobra  of  India;  (21)  parasitic  worms;  (22)  screech  owl. 

VI.  Birds  should  be  protected  because  (23)  they  feed  on  fruit  and 
grain;  (24)  they  eat  weed  seeds;  (25)  they  eat  injurious  insects; 
(26)  they  furnish  us  with  much  meat. 

VII.  Birds  (27)  that  eat  weed  seeds  are  useful ; (28)  eat  fruit  only 
when  seeds  are  scarce  ; (29)  usually  go  southward  as  soon  as  their  young 
are  old  enough  to  fly;  (30)  always  migrate;  (31)  usually  destroy 
more  fruit  than  insects. 

VIII.  Insects  (32)  can  only  be  destroyed  by  other  insects  ; (33)  such 
as  the  ladybird  beetle  and  honeybee  are  destructive  to  home  gardens ; 
(34)  such  as  the  aphids  and  gypsy  moths  destroy  the  early-ripening 
fruits  ; (35)  destroy  stored  grains. 

IX.  Insects  are  controlled  (36)  by  birds;  (37)  by  contact  and 
stomach  poisons  ; (38)  by  rats  and  mice ; (39)  by  picking  and  burning ; 
(40)  by  destroying  their  breeding  places,  their  eggs,  and  their  young. 

Achievement  Test 

1.  What  are  the  cheapest  and  most  nutritious  roots,  stems,  and 
leaves  as  food? 

2.  What  cereal  crops  are  of  the  most  importance  in  your  locality? 

3.  What  is  your  most  -valuable  local  fruit  crop? 

4.  Which  of  your  local  industries  are  dependent,  directly  or  in- 
directly, upon  plants? 

5.  What  fish  are  the  cheapest  in  local  markets  and  why? 

6.  What  “ shell  fish  ” are  locally  obtained  and  what  are  they 
used  for? 

7.  Have  you  ever  kept  bees?  How  much  honey  do  they  produce 
to  a hive  ? 


TESTS 


571 


8.  What  ara  ton  useful  birds  in  your  community?  Tell  specifi- 
cally why  each  is  useful. 

9.  flow  would  you  protect  five  useful  birds? 

10.  What  are  ten  insects  that  do  harm?  How  does  each  do  harm? 
How  could  you  set  rid  of  each? 

11.  What  are  five  useful  insects  that  affect  you  directly  or 
indirectly? 

12.  What  agencies  can  you  call  upon  to  help  in  the  extermination 
of  harmful  insects? 


Practical  Problems 

1.  Make  a survey  of  the  plants  and  animals  used  in  your  locality 
for  (a)  food,  (6)  clothing,  (c)  other  uses.  List  all  in  order  of  economic 
importance. 

2.  IMake  a bird  house  for  your  yard  and  report  on  the  birds  that 
inhabit  it. 

3.  JMake  a bird  bath  for  your  yard  and  keep  a list  of  different  bird 
visitors. 

4.  Make  a list  of  all  insects  that  trouble  your  garden  and  try  to 
find  out  the  birds  which  prey  upon  them. 

Useful  References 

De  Kruif,  Hunger  Fighters.  Harcourt,  Brace,  1928. 

DePuy,  Our  Insect  Friends  and  Foes. . Winston,  1925. 

Dooming,  Our  Living  World.  Longmans,  Green,  1924. 

Farmers’  Bulletins,  513,  630,  740,  801,  896,  1294,  1326,  1346,  1353,  1371. 
U.  S.  Dept,  of  Agriculture. 

Henderson,  The  Practical  Value  of  Birds.  Macmillan,  1927. 

Herrick,  Insects  Injurious  to  the  Household  and  Annoying  to  Man. 
Macmillan,  1926. 

Hornaday,  The  American  Natural  History.  Scribner’s,  1926. 

Jordan  and  Evermann,  American  Food  and  Game  Fishes.  Doubleday, 
Doran,  1923. 

Sanderson,  Insect  Pests  of  Farm,  Garden  and  Orchard.  Wiley,  1921. 
Toothaker,  Commercial  Raw  Materials.  ' Pp.  58-78.  Ginn,  1927. 

Wells,  Huxley  and  Wells,  The  Science  of  Life.  Doubleday,  Doran,  1934. 


SURVEY  QUESTIONS 

What  are  the  chief  economic  values  of  forests  ? How  are  trees  able  to 
affect  the  climate  ? What  do  we  mean  by  conservation  ? Do  we  speak  of 
the  conservation  of  human  life  ? What  agencies  in  your  community  and 
in  the  nation  are  working  for  the  conservation  of  our  natural  resources  ? 


UNIT  XVII 

HOW  DOES  MAN  CONSERVE  HIS  NATURAL 
RESOURCES? 

Preview.  No  one  who  has  ever  read  Joyce  Kilmer’s  poem  en- 
titled “ Trees  ” can  ever  forget  what  a tree  meant  to  him.  And 
no  one  who  has  ever  hiked  through  a forest  of  yellow  pine  or  red- 
wood can  forget  the  majesty  of  those  tree  companions.  Those 
of  us  who  have  been  brought  up  in  New  England  can  never  forget 
our  days  in  the  woods  or  the  wonderful  elms  lining  the  roadways 
along  which  we  went  to  school. 

Trees  are  not  only  beautiful,  but  they  mean  a great  deal  to 
man’s  welfare  because  they  influence  the  climate,  give  homes  to 

572 


PREVIEW 


573 


many  animals,  provide  millions  of  feet  of  lumber,  and  help  to 
protect  and  regulate  the  water  supply  of  the  country.  No  one 
who  has  traveled  over  the  great  Southwest  can  fail  to  realize  the 
value  of  forest  trees.  Great  areas  of  land  lie  devastated,  sub- 
ject to  flootls  in  winter  and  droughts  in  summer.  Yet  these 
areas,  if  given  water  supply,  would  be  capable  of  producing  crops 
in  abundance.  Irrigation  has  proved  this  in  regard  to  similar 
areas.  Irrigation  projects,  which  now  provide  homes  and  em- 
ployment for  thousands  of  people,  besides  producing  annually 
great  quantities  of  food  supplies,  would  be  impossible  were  it  not 
for  protected  forest  areas  somewhere.  Moreover,  nearly  800 
western  communities,  with  a total  population  of  nearly  3,000,000, 
depend  for  their  water  supplies  upon  streams  coming  from  areas 
protected  by  national  forests.  When  the  earth’s  surface  is  covered 
by  trees,  the  roots  prevent  soil  from  being  washed  away  and  they 
hold  moisture  in  the  ground.  Devastation  of  immense  areas  in 
China  and  considerable  damage  by  floods  in  parts  of  Switzerland, 
France,  and  the  United  States  have  resulted  where  the  forest 
covering  has  been  removed.  The  annual  spring  “ freshets  ” in 
the  East ; the  floods  in  the  Ohio  and  Mississippi  valleys ; and 
the  damage  done  by  sudden  storms  along  stream  beds  in  the 
Southwest,  are  all  examples  of  the  great  destruction  that  can  be 
wrought  by  water  which  is  not  controlled  by  forests  at  the  river 
sources.  It  has  been  estimated  that  the  carrying  power  of  water  is 
increased  sixty-four  times  if  its  rate  of  flow  is  doubled ; that  is,  the 
transporting  power  of  water  varies  as  the  sixth  power  of  its  velocity. 
This  accounts  for  the  tremendous  destruction  produced  by  a 
mountain  stream  in  a flood. 

Besides  holding  water  in  the  ground  in  some  localities  forests 
are  used  as  windbreaks  and  to  protect  mountain  towns  against 
avalanches.  In  winter  they  moderate  the  cold,  and  in  summer 
reduce  the  heat  and  lessen  the  danger  from  storms.  The  nesting 
of  birds  in  woods  protects  many  valuable  plants,  which  otherwise 
might  be  destroyed  by  insects. 

The  increasing  population  has  meant  the  necessity  of  more 
food,  more  and  better  water  supplies,  more  power  to  light  cities 
and  run  machines,  and  more  fuel.  The  balance  of  nature  has 


574  HOW  DOES  MAN  CONSERVE  HIS  RESOURCES? 

necessarily  been  disturbed  by  man  in  his  ever  increasing  demand 
for  food  and  other  supplies.  In  consequence,  he  must  learn  how 
to  conserve  the  supplies  which  he  now  has  and  which  are  so  nec- 
essary to  him. 

Although  in  biology  we  are  not  directly  concerned  with  methods 
of  conservation  which  deal  with  our  mines  or  our  fuels,  we  are 
indirectly  studying  the  conservation  of  water  supplies  when  we 
deal  with  the  problem  of  the  protection  of  our  forests.  This 
unit  is  also  concerned  with  the  conservation  of  useful  plants  and 
animals.  There  are  two  general  methods  to  consider : first,  how 
to  protect  our  useful  plants  and  animals ; second,  how  to  eliminate 
harmful  ones. 

Our  personal  health  is  the  largest  problem  of  conservation  with 
which  we  have  to  deal.  The  study  of  present-day  statistics  shows 
us  the  imperative  need  of  the  conservation  of  human  health  and 
human  life.  Communities  are  doing  much  more  for  the  health  of 
the  people  than  they  did  twenty  or  thirty  years  ago,  but  there  are 
still  too  many  careless  individuals  who  do  not  do  all  they  can  to 
care  for  themselves  properly  and  who  forget  the  rights  of  others 
in  a democracy.  Conservation  means  protection  or  care  of  the 
natural  gifts  that  nature  has  given  us. 

PROBLEM  I.  WHAT  ARE  THE  VALUES  OF  TREES? 

Prevention  of  erosion  by  covering  of  organic  soil.  Streams 
unprotected  by  forests  may  dig  out  soil  and  carry  it  far  from  its 
original  source.  Results  of  the  carrying-power  of  streams  may 
be  seen  in  the  deltas  formed  at  the  mouths  of  great  rivers.  The 
forest  prevents  the  erosion  of  soil  by  holding  back  the  water  and 
letting  it  out  gradually.  This  it  does  by  covering  the  inorganic 
soil  with  humus  or  decayed  organic  material  which,  like  a big 
sponge  over  the  forest  floor,  holds  water  through  long  periods  of 
drought.  It  is  estimated  that  the  forest  floor  can  absorb  and  hold 
for  some  time  a rainfall  of  four  or  five  inches.  The  roots  of  the 
trees,  too,  help  hold  the  soil  in  place  and  prevent  erosion. 

Regulation  of  rainfall  and  water  supply.  The  gradual  evapora- 
tion of  water  through  the  stomata  of  the  leaves  cools  the  atmos- 


PKKVKNTIOX  OF  EHO.SION  in'  (X)VEU1N(;  SOIL  575 


pliore  and  this  tc'iuls  to  j)r(Hai)itato  tlie  inoisturo  in  thn  air,  caiisin«; 
rains.  'Flu'  rainfall  is  ,a:r('al('r  and  more  re<2;ular  in  forested  area. 

Regulation  of  the  water  supidy  is  most  important  if  the  rivers 
are  to  he  used  for  water  j)ower  or  navi, i>:at ion.  Several  cities  on  the 
.\tlantic  coast,  such  as  Savannah,  W ilnun<>:ton,  and  Philadelphia, 
owe  their  importance  to  their  position  on  navif2;able  rivers  supplied 
with  water  lar«;cly  by  the  Appalachian  forests.  Should  these 
forests  be  destroyed,  it  is  possible  that  the  frequent  freshets  which 


Wright  Pierce 

Erosion  caused  by  overcutting  in  a small  area.  Why  has  this  gully  appeared  since  the  trees 
were  cut  down? 


would  follow  would  so  fill  the  rivers  with  silt  and  debris  that  the 
ship  channels  in  them,  already  costing  the  government  millions  of 
dollars  a year  to  keep  dredged,  would  become  too  shallow  for  ships. 
If  this  should  occur,  these  cities  would  soon  lose  their  importance. 

The  story  of  how  this  very  thing  happened  to  the  old  Greek  city 
of  Poseidonia  is  graphically  told  in  the  following  lines  : 

“It  was  such  a strange,  tremendous  story,  that  of  the  Greek  Poseidonia, 
later  the  Roman  Paestum.  Long  ago  those  adventuring  mariners  from 
Greece  had  seized  the  fertile  plain  which  at  that  time  was  covered  with 
forests  of  great  oak  and  watered  by  two  clear  and  shining  rivers.  They 
drove  the  Italian  natives  back  into  the  distant  hills,  for  the  white  man’s 


576  HOW  DOES  MAN  CONSERVE  HIS  RESOURCES? 


burden  even  then  included  the  taking  of  all  the  desirable  things  that  were 
being  wasted  by  incompetent  natives,  and  they  brought  over  colonists  — ■ 
whom  the  philosophers  and  moralists  at  home  maligned,  no  doubt,  in  the 
same  pleasant  fashion  of  our  own  day.  And  the  colonists  cut  down  the 

oaks,  and  plowed  the 
land,  and  built  cities, 
and  made  harbors,  and 
finally  dusted  their 
busy  hands  and  busy 
souls  of  the  grime  of 
labor  and  wrought 
splendid  temples  in 
honor  of  the  benign 
gods  who  had  given 
them  the  possessions 
of  the  Italians  and 
filled  them  with  power 
and  fatness. 

“Every  once  in  so 
often  the  natives 

Matlon — U.  S.  Forest  Service  ,1,1  « n 

Gully  farm  land  badly  in  need  of  forestation.  ooked  USt  U y down 

from  the  hills  upon 

this  fatness,  made  an  armed  snatch  at  it,  were  driven  back  with  bloody 
contumely,  and  the  heaping  of  riches  upon  riches  went  on.  And  more 
and  more  the  oaks  were  cut  down  — mark  that ! — for  the  stories  of 
nations  are  so  inextricably  bound  up  with  the  stories  of  trees  — until  all 
the  plain  was  cleared  and  tilled ; and  then  the  foothills  were  denuded,  and 
the  wave  of  destruction  crept  up  the  mountain  sides,  and  they,  too,  were 
left  naked  to  the  sun  and  the  rains. 

“At  first  these  rains,  sweeping  down  torrentially,  unhindered  by  the 
lost  forests,  only  enriched  the  plain  with  the  long-hoarded  sweetness  of  the 
trees ; but  by  and  by  the  living  rivers  grew  heavy  and  thick,  vomiting  mud 
into  the  ever  shallowing  harbors,  and  the  land  soured  with  the  undrained 
stagnant  water.  Commerce  turned  more  and  more  to  deeper  ports,  and 
mosquitoes  began  to  breed  in  the  brackish  soil  that  was  making  fast  be- 
tween the  city  and  the  sea. 

“Who  of  all  those  powerful  landowners  and  rich  merchants  could  ever 
have  dreamed  that  little  buzzing  insects  could  sting  a great  city  to  death  ? 
But  they  did.  Fevers  grew  more  and  more  prevalent.  The  malaria- 
haunted  population  went  more  and  more  languidly  about  their  business. 


USES  OF  WOOD 


577 


The  natives,  hardy  and  vigorous  in  the  hills,  were  but  feebly  repulsed. 
Carthage  demanded  tribute,  and  Rome  took  it,  and  changed  the  city’s  name 
from  Poseidonia  'to  Paestum.  After  Rome  grew  weak,  Saracen  corsairs 
came  in  by  sea  and  grasped  the  slackly  defended  riches,  and  the  little 
N\-inged  poisoners  of  the  night  struck  again  and  again,  until  grass  grew  in 
the  streets,  and  the  wharves  crumbled  where  they  stood.  Finally,  the 
wretched  remnant  of  a great  people  wandered  away  into  the  more  whole- 
some hills,  the  marshes  rotted  in  the  heat  and  grew  up  in  coarse  reeds  where 
corn  and  vine  had  flourished,  and  the  city  melted  back  into  the  wasted 
earth.”  — Elizabeth  Bisland  and  Anne  Hoyt,  Seekers  in  Sicily.  John 
Lane  Company. 

Uses  of  wood.  Even  though  we  have  many  materials  for  build- 
ing and  fuel,  wood  is  still  the  one  most  used.  Practically  all  build- 
ings use  wood  some  place  in  their  construction.  Wood  outlasts 
iron  under  water,  and  also  is  lighter.  It  is  cheap  and,  with  proper 
care  of  the  forests,  the  supply  is  practically  inexhaustible.  When 
wood  is  burned  without  air,  wood  alcohol  is  given  off.  Partly 
burned  wood  is  charcoal,  the  best  of  which,  used  in  medicine,  comes 
from  the  willow  trees.  Much  of  the  soft  wood  (the  coniferous  trees, 
spruce,  balsam,  hemlock,  and  pine)  and  poplars,  aspens,  with  some 
other  species,  of  our  forests  are  used  for  making  paper  pulp.  The 
daily  newspapers  and  cheap  books  are  responsible  for  inroads  on  our 
forests.  Since  it  is  not  necessary  to  take  the  largest  trees  to  make 
pulp,  many  young  trees  of  not  more  than  six  inches  in  diam- 


Figure  A shows  the  method  used  when  sawing  a log  for  trim.  Figure  B shows  the  common 
method  of  sawing  a log.  A is  known  as  quarter  saw  and  B as  plain  saw. 

eter  are  being  sacrificed.  Of  the  hundreds  of  species  of  trees  in 
our  forests,  the  conifers  are  probably  most  sought  after  for  lumber. 


578  HOW  DOES  MAN  CONSERVE  HIS  RESOURCES? 


Pine,  especially,  is  probably  used  more  extensively  than  any  other 
wood.  It  is  used  for  all  heavy  construction  work,  frames  of 
houses,  bridges,  masts,  spars,  and  timber  of  ships,  floors,  rail- 
way ties,  and  many  other  purposes.  Cedar  is  used  for  shingles, 
cabinet  work,  lead  pencils,  etc. ; hemlock  and  spruce  for  heavy 
timbers.  Another  use  for  our  lumber,  especially  odds  and  ends  of 
all  kinds,  is  in  the  packing-box  industry.  Hemlock  bark  is  still 


Asahel  Curtis 

Modern  methods  of  lumbering  result  in  a more  rapid  destruction  of  the  forests.  Why? 


used  for  tanning.  Some  of  the  soft  woods,  as  the  poplars,  are  used 
for  making  excelsior  used  in  packing.  Wood  pulp  from  the  fiber  of 
aspen,  basswood,  cottonwood,  and  other  trees  is  chemically  treated 
and  used  for  making  artificial  silk,  rayon.  The  hard  woods,  ash, 
red  gum,  beech,  birch,  cherry,  chestnut,  elm,  maple,  oak,  and 
walnut,  are  used  largely  for  the  “trim’’  of  our  houses,  for  manu- 
facture of  furniture,  for  spokes  of  wagon  or  car  wheels  and  for 
many  other  purposes.  Our  hard  wood  supply  is  rapidly  becoming 
exhausted,  particularly  ash  and  hickory,  and  our  only  remedy  is 
to  plant  more  trees  of  this  kind. 


GOOD  FOliESTJiY  579 

Practical  Exercise  1.  List  all  the  various  forest  products  found  in  your 
coniinunity  and  give  the  uses  of  each. 

If  there  is  in  your  community  an  industry  which  uses  forest  products, 
visit  it  and  give  a report  of  your  visit  to  the  class. 

Other  values  of  the  forest.  We  have  learned  that  forests 
regulate  the  water  supply.  Much  organic  soil  is  formed  from  de- 
cayed trees  and  other  vegetation.  The  forest  gives  a refuge  for 
wild  animals,  particularly  game  such  as  deer,  elk,  and  antelope. 
There  are  now  nearly  12,000,000  acres  set  aside  as  refuges  for  wild 
birds  and  game,  that  they  may  not  become  extinct  as  have  some 
native  wild  animals.  The  clear  streams  of  the  forest  are  the 
homes  of  many  of  our  best  game  fishes.  And  perhaps,  best  of  all, 
the  forest  has  become  the  playground  for  lovers  of  the  out  of  doors 
in  our  nation. 


Self-Testing  Exercise 

Trees  protect  the  soil  by  preventing  (1).  Land  covered 

with  trees  can (2) (3)  water  better  than  land  barren 

of  trees.  Paper  pulp  is  obtained  largely  from  (4)  wood. 

Evaporation  of  water  through  the  stomata  of  the  leaves  makes  the 

surrounding  air (5).  Wood  pulp  is  used  for  making 

(6)  and  (7)  (8) (9)  (10)  are 

used  for  the  “ trim  ” of  our  houses. 

PROBLEM  II.  WHY  IS  THE  CONSERVATION  OF  FORESTS 
NECESSARY? 

Field  Exercise.  To  study  the  forest  resources  of  my  community. 

Divide  the  area  to  be  covered  into  districts  and  let  each  member  of  the 
class  work  over  a small  area.  Count  the  number  and  kind  of  market- 
able trees,  estimate  their  size  or  approximate  age,  etc.  Make  maps 
showing  these  areas,  to  scale,  so  that  the  maps  made  by  the  entire 
class  may  be  put  together  and  an  estimate  of  the  entire  region  may 
be  formed.  Since  this  is  an  economic  project,  it  will  be  necessary  to 
get  the  help  of  practical  lumbermen  or  field  workers. 

What  are  the  forest  resources  of  your  community?  What  special  tree 
products  give  factories  employment  in  your  home  city. 

Good  Forestry.  The  total  forest  area  of  the  United  States 
today  is  less  than  494,000,000  acres.  More  than  80,000,000 
acres  have  been  burned  or  cut,  so  that  today  they  are  waste  land. 
We  have  more  waste  forest  land  than  the  combined  forest  areas  of 


580  HOW  DOES  MAN  CONSERVE  HIS  RESOURCES? 

western  Europe.  Our  present  forests  are  rapidly  decreasing,  due 
to  the  demands  of  an  increasing  population,  a woeful  neglect  on 
the  part  of  the  owners  of  the  land,  and  wastefulness  on  the  part  of 
cutters  and  users  alike. 

In  some  parts  of  Central  Europe,  the  value  of  the  forests  to  the 
country  was  recognized  as  early  as  1300  a.d.,  and  many  towns 
consequently  bought  up  the  surrounding  forests.  The  city  of 
Zurich  has  owned  forests  in  its  vicinity  for  600  years  and  has  found 
them  a profitable  investment.  Europe  has  long  led  the  way  in 
showing  other  countries  how  to  care  for  forests  and  how  to  make 
them  pay.  In  our  country  we  have  a Forest  Service  in  the  De- 
partment of  Agriculture  which,  with  numerous  state  and  university 

Schools  of  Forestry,  is 
teaching  the  people  of 
this  country  the  best 
methods  for  the  pres- 
ervation of  our  forests. 
TheFederal  Government 
has  set  aside  a number 
of  tracts  of  mountain 
forest,  principally  in  the 
western  states  and 
Alaska,  which  are  under 
the  control  of  the  Na- 
tional Forest  Service. 
These  National  Forest 
preserves  have  at  the 
present  time  an  area  of 
about  162,000,000  acres, 
an  area  greater  than  the 
total  area  of  the  New 
England  States,  New 
York,  New  Jersey,  Delaware,  Pennsylvania,  Maryland,  Virginia, 
and  West  Virginia.  In  addition  to  this  there  are  almost  25,000,000 
acres  privately  owned  that  are  within  the  National  Forest  areas. 
New  York  has  established  for  the  same  purposes  the  Adirondacks, 
the  Catskill  Mountain,  and  other  Forest  Preserves,  with  2,345,000 


Haasia  — U.  S.  Forest  Service 


White  pine  forest.  Is  this  good  forestation  ? Why  ? 


FOREST  WASTES 


581 


acres  of  timber  land  ; Pennsylvania  has  preserves  of  more  than 
1 /ioO. (){)()  acres,  and  many  other  states  have  followed  their  example. 
t\'isconsin,  Minnesota,  and  Michigan  have  larp:e  areas  set  aside. 
The  total  area  of  state  parks  in  1933  was  more  than  8,500,000 
acres. 

Forest  Wastes.  Our  forests  are  being  cut  down  at  the  rate  of 
about  10,000,000  acres  a year.  But  man  loses  much  of  this  wood 
by  wasteful  methods  of  lumbering.  Hundreds  of  thousands  of 
dollars’  worth  of  lumber  is  left  to  rot  annually  because  the  lumber- 
men do  not  cut  the  trees  close  enough  to  the  ground,  or  because 
through  careless  felling  of  trees  many  smaller  trees  are  injured. 
This  is  particularly  true  among  the  large  trees  in  our  western 


A cigarette  may  have  caused  this  destruction. 

forests.  There  has  been  great  waste  also  in  the  lumber  mills. 
In  fact,  man  wastes  lumber  in  every  step  from  the  forest  to  the 
finished  product,  and  is  just  beginning  to  devise  methods  of  pre- 
venting these  wastes. 

H.  BIO — 38 


582  HOW  DOES  MAN  CONSERVE  HIS  RESOURCES? 


Wright  Pierce 

Our  water  supply  depends  upon  our  forests.  It  takes  one  day  to  destroy  a forest  but  a hundred 
years  to  grow  it. 

Indirectly,  man  is  responsible  for  fire,  one  of  the  greatest  enemies 
of  the  forest.  Most  of  the  great  forest  fires  of  recent  years,  the 
losses  from  which  total  in  the  hundreds  of  millions  of  dollars,  have 
been  due  to  smokers,  to  railroads,  or  to  carelessness  in  making 
camp  fires  in  the  woods.  It  is  estimated  that  fires  have  destroyed 
over  12,000,000  acres  of  forest  and  caused  a money  damage  of  over 
$17,000,000  in  a single  year.  In  the  past,  great  forest  fires  have 
devastated  Minnesota,  Wisconsin,  and  Michigan  with  a loss  of 
thousands  of  lives  and  hundreds  of  millions  of  dollars.  In  addition 
to  the  loss  in  timber,  the  fires  often  burn  out  the  organic  matter 
in  the  soil  (the  “ duff  ”)  forming  the  forest  floor,  thus  preventing 
the  growth  of  new  forests  for  many  years  to  come. 

The  United  States  Forest  Service  and  the  state  forestry  depart- 
ments are  constantly  on  guard  against  forest  fires.  Fire  lookouts 
are  established  at  places  most  favorable  for  observation  of  large 
areas.  When  a fire  starts,  notice  is  sent  at  once  to  the  forest 
rangers  in  that  locality  so  that  the  fire  may  be  put  out  before  it 
spreads.  State  and  Federal  governments  alike  do  their  best  to 
protect  our  forests.  We  must  do  our  share  in  this  work  by 


FOHKST  WASTES 


583 


Photo  by  C.  H.  Park  — U.  S.  Forest  Service 

The  travels  of  the  forest  ranger  often  carry  him  through  rough  and  dangerous  country  and  over 
mountain  ranges  ten  to  fourteen  thousand  feet  in  altitude. 

exting;uishing  camp  fires  or  bonfires  which  we  may  start  in  the 
woods. 

Other  enemies  of  the  forest  are  numerous  fungus  plants,  insect 
parasites  which  bore  into  the  wood  or  destroy  the  leaves,  and 
grazing  animals.  The  chestnut  blight  has  killed  most  of  the  chest- 
nut trees  in  the  eastern  states  and  has  gone  as  far  south  as  the 
Carolinas.  Our  only  hope  for  the  chestnut  appears  to  be  in  finding 
some  trees  that  are  immune  to  the  disease.  The  Englemann  spruce 
beetle  has  destroyed  millions  of  feet  of  lumber  in  the  Rocky 
Mountains,  and  the  Black  Hills  beetle  has  done  great  damage  in 
South  Dakota:  Hundreds  of  other  insects,  such  as  the  gypsy  and 
browntail  moths,  are  doing  very  great  damage  to  the  trees,  especially 
in  the  eastern  states.  Live  stock,  especially  sheep,  may  do  much 
harm  in  a forest  by  eating  young  shoots  and  trampling  on  young 
trees.  Storm,  wind,  and  lightning  do  damage  also,  as  uprooted 
trees  soon  die  and  make  excellent  places  for  fire  to  start. 

Practical  Exercise  2.  What  are  the  enemies  of  trees  in  your  community? 
Can  you  name  them? 

How  are  forest  areas  protected  against  fire  in  your  state?  Enumerate  all 
the  methods  of  protection. 


584  HOW  DOES  MAN  CONSERVE  HIS  RESOURCES? 


Methods  of  forest  conservation.  Back  of  all  life  on  the  earth 
are  the  food  supplies  made  by  the  green  plants.  Back  of  our 
water  supplies  and  our  rich  soil  lie  our  forests.  Our  forest 
areas  are  lessening  each  year.  We  already  lack  hardwoods  for 
trim  and  furniture  and  our  pulp-wood  reserves  are  dwindling 
rapidly. 

It  is  evident  that  we  must  replant  our  forests  as  they  are  used, 
plant  new  areas,  make  use  of  waste  products  from  the  forests,  or 
we  must  obtain  substitutes  for  some  of  the  forest  products. 
Formerly,  lumber  companies  burned  the  sawdust  and  other  waste 
from  the  mills ; now  fuel  alcohol  and  other  valuable  products 
are  obtained  from  them.  It  is  estimated  that  more  than  300,000,- 
000  gallons  of  fuel  alcohol  could  be  made  annually  from  the  wood 
thus  wasted.  It  is  estimated  that  20  per  cent  of  the  timber  now 
wasted  might  be  used  in  building.  Railroads  use  15  per  cent  of  our 
timber  for  ties ; treatment  of  these  ties  with  creosote  or  other 
chemicals  resulted  in  the  annual  saving  of  1,500,000,000  board  feet. 
Substitutes  are  being  found  for  wooden  boxes,  which  take  a very 
large  amount  of  cut  lumber.  And  since  it  is  estimated  that  25  per 
cent  of  a tree  in  the  forest  is  lost  in  the  cutting  and  40  per  cent  is 
wasted  in  the  mill,  it  is  evident  that  less  wasteful  methods  will 
conserve  a large  amount  of  the  lumber  now  lost. 

Better  management  is  needed  in  our  forests,  especially  those 
under  private  control.  Forests  should  be  kept  thinned.  Too 
many  trees  are  almost  as  bad  as  too  few.  They  struggle  with 
one  another  for  foothold  and  light,  which  only  a few  can  obtain. 
The  cutting  of  a forest  should  be  considered  as  a harvest.  The 
oldest  trees  are  the  “ ripe  grain,”  and  the  younger  trees  are  to  be 
left  to  grow  to  maturity.  Several  methods  of  renewing  the  forest 
are  in  use  in  this  country.  (1)  Trees  may  be  cut  down  and  young 
ones  allowed  to  sprout  from  cut  stumps.  Beech,  chestnut,  and  the 
redwood  of  California  are  among  the  trees  that  grow  in  this  way. 
This  is  called  coppice  growth.  (2)  Areas  or  strips  may  be  cut  out 
so  that  seeds  from  neighboring  trees  are  carried  there  by  the  wind 
to  start  new  growth.  (3)  Forests  may  be  artificially  planted. 
Two  seedlings  planted  for  every  tree  cut  is  a rule  followed  in 
Europe.  (4)  The  most  economical  method  is  to  thin  a large  area 


METHODS  OP"  FOREST  CONSERVATION 


585 


by  cut  tin«:  t he  largest  trees  so  as  to  make  room  for  the  younger  ones 
to  grow  up. 

In  1925  it  was  estimated  that  we  were  using  up  our  forest  about 
four  times  as  fast  as  it  was  growing,  so  that  we  need  much  more 
planting  if  we  are  to  keep  our  forests  at  approximately  their  present 
area.  State  forestry  stations  and  the  national  government  are 
now  reforesting  cut  areas,  and  many  lumber  companies  have 
begun  to  follow  their  e.xample.  Railroads  annually  are  planting 
thousaiuls  of  young  trees.  Farmers  have  begun  to  realize  that  the 


V.  S.  Forest  Service 

A planting  crew  setting  out  seedlings  in  burned  over  forest  land. 

high  price  of  lumber  makes  a wood  lot  often  more  productive  than 
other  areas  of  similar  size  on  the  farm.  Forestry  is  becoming  more 
and  more  a practical  business ; hundreds  of  young  men  are  going 
out  from  schools  of  forestry  each  year,  prepared  to  help  in  this 
work. 

Practical  Exercise  3.  What  methods  of  eliminating  waste  are  found  in  a 
modern  sawmill?  (Look  up  in  Readers’  Guide  to  Periodical  Literature.) 

Are  there  any  individual  examples  of  the  conservation  of  forest  or  forest 
supplies  in  your  community?  Be  specific. 

Project.  To  make  a tree  survey.  Select  a convenient  area  of 
your  community  and  map  it  to  scale.  Houses,  stores,  churches. 


586  HOW  DOES  MAN  CONSERVE  HIS  RESOURCES? 


schools,  and  other  buildings  should  be  shown.  Conventional  signs 
for  different  kinds  of  trees  may  be  used  and  a key  attached  to  the  map. 
Where  the  tree  is  not  recognized,  a reference  book  should  be  taken  into 
the  field  and  the  tree  identified.  The  list  of  reference  books  at  the 
end  of  the  unit  will  give  you  some  of  the  best  books  likely  to  be  found 
in  a school  or  public  library.  It  would  be  well  to  prepare  with  your 
report  specimens  of  leaves,  buds,  twigs,  fruits,  and  flowers,  if  obtain- 
able. If  the  survey  is  made  in  winter,  then  winter  twigs  might  be 
shown. 

Practical  Exercise  4.  Write  a paragraph  for  your  workbook  on  the  best 
methods  of  reforestation  in  your  locality.  If  you  live  in  the  city,  discuss  tree 
protection  in  streets  and  parks. 

Practical  Exercise  5.  Get  information  from  any  sources  you  can  on  the 
extent  and  location  of  national  forest  preserves  within  the  boundaries  of  your 
state.  Also  the  state  parks  or  forest  preserves.  Make  a map  of  the  state  and 
locate  all  the  above.  If  you  have  been  to  a national  park  or  forest  preserve, 
tell  about  the  work  of  the  forest  rangers  there. 

A city’s  need  of  trees.  The  city  of  Paris,  well  known  as  one 
of  the  most  beautiful  of  European  capitals,  spends  over  $100,000 
annually  in  caring  for  and  replacing  some  of  its  90,000  trees.  All 
over  the  United  States  municipal  governments  are  beginning  to 
realize  what  European  cities  have  long  known,  that  trees  are  of 
great  value  to  a city.  For,  besides  being  beautiful,  trees  protect 
the  streets  and  buildings  from  the  direct  rays  of  the  sun.  The 
growth  of  trees  along  the  street  and  in  front  of  houses  increases 
the  value  of  the  property.  For  these  reasons,  cities  are  planting 
trees  and  protecting  them.  Many  cities  have  appointed  city 
foresters  who  care  for  the  trees  in  the  parks  and  along  the  streets. 
Many  municipalities  plant  trees  and  tax  the  property  owners  who 
receive  benefit  thereby,  for  trees  and  shrubs  have  an  ornamental 
value  that  can  be  expressed  in  dollars  and  cents.  Perhaps  the 
most  hopeful  sign  is  that  people  everywhere  are  beginning  to 
realize  the  value  of  our  trees  and  the  need  for  their  protection  and 
conservation. 

Tree  surgery.  Another  sign  of  the  appreciation  of  our  trees, 
especially  in  cities,  is  found  in  the  work  of  the  tree  surgeon.  Just 
as  a dentist  takes  out  decayed  material  from  a tooth  and  protects 
the  tooth  by  placing  within  it  an  antiseptic  filling,  so  tree  surgeons 
take  out  rotted  parts  of  a living  tree,  clean  it  with  antiseptic  solu- 
tions, and  fill  the  cavity  with  cement  or  other  durable  substances. 
When  a large  limb  is  cut  off,  the  cut  portion  is  treated  with  an 


TREE  SUJiC.ERY 


587 


antiseptic  and  coated  with  a waterproof  covering.  Not  infre- 
(pientl}^  large  limbs  are  wired  or  in  other  ways  supported  so  as 
to  relieve  stress  during  storms.  Such  care  often  lengthens  the  life 
of  a tree  many  years. 

Practical  Exercise  6.  In  what  southern  states  are  there  coniferous  forests? 
In  what  northern  states  are  such  forests  found?  The  supply  of  hardwoods 
comes  from  the  deciduous  and  mixed  forests.  Where  are  most  of  our  decid- 
uous forests? 


In  repairing  a tree  which  is  decayed,  the  affected  portions  are  first  cut  out.  Then  the  cavity 
is  treated  with  an  antiseptic  to  prevent  any  further  decc  y,  and  is  filled  with  cement. 


Self-Testing  Exercise 

Man  is  responsible  for  a (1)  per  cent  of  the  forest  fires 

each  year.  The  chestnut (2)  has  killed  most  of  the  chestnut 

trees  in  the  (3).  We  (4)  trees  four  times  as  fast 

as  we (5)  them.  Trees  in  a city  have  an (6)  value, 

(7)  (8)  is  used  to  protect  trees.  Our  forests  are 

conserved  by (9)  old  areas, (10)  new  areas,  and 

(11)  unnecessary  wastes (12)  of  cut  areas  is  under  the  super- 
vision of (13)  and (14)  forestry  stations. 

PROBLEM  III.  WHAT  IS  BEING  DONE  FOR  THE  CONSERVA- 
TION OF  FISH  AND  OTHER  AQUATIC  ANIMALS? 

The  conservation  of  fresh-water  fishes.  W^e  have  learned  that 
the  food  supply  of  many  of  our  fishes  depends  upon  plankton, 
tiny  plants  and  animals  living  in  the  water.  In  many  parts  of  the 
United  States  these  little  organisms  have  been  exterminated,  and 
the  food  fish  with  them,  by  the  pollution  of  our  streams  and  lakes. 


588  HOW  DOES  MAN  CONSERVE  HIS  RESOURCES? 


If  crude  sewage  is  discharged  into  a river  untreated,  the  organic 
matter  absorbs  much  or  all  of  the  dissolved  oxygen  in  the  water, 
which  is  absolutely  essential  for  plant  and  animal  life.  Oil  wastes 
poured  out  by  oil-burning  steamers  are  becoming  a nuisance  along 
our  shores  and  are  responsible  for  the  death  of  many  food  fish. 
If  our  fish  and  other  water  animals  are  to  be  preserved,  we  must 
stop  the  pollution  of  our  national  waterways.  Dr.  Henry  B.  Ward 
is  authority  for  the  estimate  that  if  rivers  now  polluted  with 
sewage  and  factory  wastes  were  clean,  they  would  put  $100,000,000 
a year  into  the  pockets  of  taxpayers  from  the  sale  of  marketable 
fish.  In  addition  to  this  thousands  of  persons  could  enjoy  rivers 
for  fishing,  boating,  and  bathing. 


The  continental  shelf  off  New  England.  What  effect  does  this  have 
on  Gloucester,  Massachusetts? 

Migration  of  fishes.  Some  fishes  change  their  habitat  at  dif- 
ferept  times  during  the  year,  moving  in  vast  schools  northward  in 
the  summer  and  southward  in  the  winter.  In  a general  way  such 
migrations  follow  the  coast  lines.  Examples  of  such  migratory 
fish  are  the  cod,  menhaden,  herring,  and  bluefish.  The  migrations 
are  due  to  temperature  changes,  to  the  quest  of  food,  and  to  the 
spawning  instinct.  Salmon  and  some  other  fish  pass  up  rivers  to 
spawn ; the  eel,  on  the  contrary,  leaves  the  rivers  and  spawns  in 
the  ocean.  Some  fish  migrate  to  more  shallow  water  in  the  sum- 
mer, and  to  deeper  water  in  the  winter ; here  the  reason  for  the 
migration  is  doubtless  the  change  in  temperature.  All  of  these 
habits  are  studied  by  the  fishermen,  who  are  thus  able  to  catch  fish 
where  and  when  they  are  most  plentiful.  The  cod  and  herring 
fisheries  are  notable  examples. 


COXSEliVATION  DIMUNG  SPAWNING  SEASON  589 


The  spawning  habits  of  fish.  'I'he  s{):iwning  habits  of  fish  are  of 
great  importance  to  us  because  the  fish  are  caught  in  vast  numbers 
at  the  time  of  migration.  Many  of  our  most  desirable  food  fishes, 
notably  the  salmon,  shad,  sturgeon,  and  smelt,  pass  up  rivers  from 
the  ocean  to  deposit  their  eggs,  swimming  against  strong  currents 
much  of  the  way,  some  species  leaping  rapids  and  falls,  in  order  to 
deposit  their  eggs  in  localities  where  the  conditions  of  water  and 
footl  are  suitable  and  the  water  is  shallow  enough  to  allow  the  sun’s 
rays  to  warm  it  suffi- 
ciently to  cause  the 
eggs  to  develop.  The 
Chinook  salmon  of  the 
Pacific  Coast,  which  is 
used  in  the  western  can- 
ning industry',  travels 
over  a thousand  miles 
up  the  Columbia  and 
other  rivers,  to  the  head- 
waters where  it  spawns. 

The  salmon  begin  to 
pass  up  the  rivers  in 
early  spring,  and  reach  the  spawning  beds,  shallow  deposits  of  gravel 
in  cool  mountain  streams,  before  late  summer.  Here  the  fish,  both 
males  and  females,  remain  until  the  temperature  of  the  water  falls 
to  about  54°  Fahrenheit.  The  eggs  and  milt  are  then  deposited, 
and  the  old  fish  die,  leaving  the  eggs  to  be  hatched  out  the  follow- 
ing spring  in  the  water  warmed  by  the  sun. 

Need  of  conservation  during  spawning  season.  The  shad 
within  recent  times  have  abandoned  their  breeding  places  in 
the  Connecticut  River  and  have  almost  disappeared  from  other 
rivers  where  they  breed,  partly  because  they  are  caught  at  the 
breeding  season  and  partly  because  of  the  pollution  of  the  rivers 
in  which  they  breed.  The  salmon  have  been  exterminated  along 
our  eastern  coast  within  the  past  few  decades.  Only  a few  years 
hence,  our  western  salmon  will  be  extinct  if  fishing  is  continued 
at  the  present  rate.  More  fish  must  be  allowed  to  reach  their 
breeding  places. 


590  HOW  DOES  MAN  CONSERVE  HIS  RESOURCES? 


V.  S.  Bureau  of  Fisheries 


Taking  spawn  from  fish.  The  fertilized  eggs  are  placed  in  tanks  supplied  with  running  water. 

The  sturgeon,  the  eggs  of  which  are  used  in  the  manufacture  of 
the  delicacy  known  as  caviar,  is  an  example  of  a fish  that  is  almost 
extinct  in  most  parts  of  the  world  because  it  was  taken  at  the 
breeding  season.  Other  food  fish  taken  at  such  a time  are  also 
in  danger.  Fortunately,  the  government,  through  the  Bureau 
of  Fisheries,  and  various  states,  by  wise  protective  laws 
and  by  artificial  propagation  of  fishes,  are  beginning  to  turn 
the  tide.  Certain  days  of  the  week  the  salmon  are  allowed  to 
pass  up  the  Columbia  River  unmolested.  Obstructions  must 
be  removed  which  might  prevent  fish  from  passing  up  or  down 
rivers.  Closed  breeding  seasons  protect  our  trout,  bass,  and 
other  game  fish ; also  the  catching  of  fish  under  a certain  size  is 
prohibited. 

Each  fisherman  should  pledge  himself,  first,  to  fight  against  the 
pollution  of  streams  with  factory  wastes  and  sewage  ; second,  to  be 
a real  sportsman  and  obey  all  laws  with  reference  to  limit  and  size 
of  the  catch ; third,  never  catch  fish  during  their  breeding  season ; 
and  fourth,  to  moisten  the  hands  before  handling  undersized  fish 


AKTIFKMAL  PROPAGATION  OF  FISHES 


591 


U.  S.  Bureau  of  Fisheries 

Stocking  a stream  with  young  fish  which  have  been  grown  in  a hatchery. 

that  are  to  be  returned  to  the  water.  The  use  of  barbless  hooks 
in  fishing  in  streams  containing  undersized  fish  is  a sportsmanlike 
way  of  allowing  the  small  ones  to  get  off  unharmed. 

Artificial  propagation  of  fishes.  Many  fish  hatcheries,  both 
government  and  state,  are  artificially  fertilizing  millions  of  fish 
eggs  of  various  species,  and  protecting  the  young  fry  until  they  can 
take  care  of  themselves.  In  1933  there  were  over  7,000,000,000 
eggs  and  fish  placed  in  ponds  and  streams  in  this  country.  In 
this  process  the  ripe  eggs  from  a female  are  first  squeezed  out  into 
a pan  of  water ; in  a similar  manner  the  milt  or  sperm  cells  are  ob- 
tained, and  poured  over  the  eggs.  After  the  eggs  are  thus  fertilized, 
they  are  placed  in  receptacles  supplied  with  running  water  and  left 
to  develop  under  favorable  conditions.  Shortly  after  the  egg  has 
segmented  (divided  into  many  cells)  the  embryo  may  be  seen 
developing  on  one  side  of  the  egg.  The  rest  of  the  egg  is  made 
up  of  food  or  yolk,  and  when  the  baby  fish  hatches  it  has  the  yolk 
attached  to  its  ventral  surface  for  some  time.  Eventually  the  food 
is  absorbed  into  the  body  of  the  fish.  The  young  fry  are  kept  under 


592  HOW  DOES  MAN  CONSERVE  HIS  RESOURCES? 


ideal  conditions  until  they  are  shipped,  sometimes  thousands  of 
miles,  to  their  new  homes. 

It  has  been  found  that  if  trout  are  kept  in  breeding  ponds  until 
they  are  3 or  4 inches  long  that  their  chance  of  survival  is  very 
much  better  than  if  very  young  fish  are  planted. 

Practical  Exercise  7.  What  laws  does  your  state  have  for  the  protection  of 
fish?  Is  there  a chapter  of  the  Isaak  Walton  League  in  your  community?  If 
so,  what  is  this  organization  doing  for  the  conservation  of  wild  life?  Is  there 
any  work  in  conservation  being  done  by  other  organizations  ? 

Practical  Exercise  8.  Why  is  stream  pollution  an  important  factor  in  con- 
servation ? Why  do  fish  migrations  play  an  important  part  in  their  conserva- 
tion or  destruction  ? 

The  conservation  of  shellfish.  The  problem  of  conserving 
shellfish  is  concerned  in  part  with  the  extermination  of  their 
natural  enemies.  If  we  could  kill  off  all  starfish  and  boring 
mollusks,  the  oysters  and  clams  would  be  much  more  plentiful. 
But  over-fishing  is  the  most  important  danger.  The  oysters  of 
Chesapeake  Bay  were  thought  inexhaustible  until  they  were 
almost  fished  out.  Then  the  state  of  Maryland  discovered  that 
oyster  culture  was  necessary  if  this  great  asset  was  to  be 
preserved. 

Oysters  pass  the  first  few  days  of  their  existence  as  free-swimming 
larvae.  Then  they  settle  on  the  bottom,  and  if  they  do  not  find 
some  solid  object  which  raises  them  above  the  mud  of  the  bottom, 
they  will  die.  Oysters  are  now  protected  by  cultivation.  On  the 
bottom,  in  certain  areas  of  water,  are  placed  bunches  of  twigs, 
broken  rocks,  or  old  oyster  shells  to  which  the  young  oysters 
attach  themselves.  The  depth  of  the  water  in  which  oysters  grow 
varies,  but  the  usual  depth  of  the  beds  is  10  to  15  feet  at  low  tide. 
After  they  have  grown  to  approximately  the  size  of  a quarter  or 
half  dollar  these  “seed”  oysters  are  spread  over  the  bottom  of 
the  oyster  beds.  They  are  usually  ready  for  the  market  in  three 
or  four  years. 

Clams  and  scallops  have  been  nearly  depleted  in  some  areas,  and 
it  has  become  necessary  to  conserve  the  supply  by  having  closed 
seasons  and  by  transplanting  the  “soft  clam”  of  the  east  to  the 
Pacific  Coast,  where  it  thrives. 

About  1894  it  was  discovered  that  the  shell  of  the  fresh-water 


CONSERVATION  OF  SHELLFISH 


593 


“ clam  ” or  mussel  was  valuable  in  making  pearl  buttons.  The 
imlustry  became  so  important  that  the  number  of  adult  clams  was 
rai)idly  depleted.  Today,  were  it  not  for  the  work  of  Professor 
Lefevre,  Curtis,  and 
others,  the  fresh- 
water mussel  would 
be  practically  ex- 
terminated. But  in 
studying  the  life  his- 
tory of  the  mussel  it 
was  found  that  one 
stage  is  passed 
attached  to  the  gills 
of  certain  fish.  Now 
the  United  States 
Government  raises 
young  mussels  to  the 
free-swimming  stage, 
allows  the  larvae  to 
attach  themselves  to 
the  gills  of  the  fish,  and  then  releases  the  fish  which  later  will 
deposit  the  young  mussels  in  localities  favorable  for  their  de- 
velopment. 

Lobsters  are  being  conserved  by  taking  the  fertilized  eggs  and 
raising  the  young  in  hatcheries  until  they  are  large  enough  to  care 
for  themselves. 

Practical  Exercise  9.  What  methods  are  used  to  conserve  shellfish  in  your 
locality  ? 


hrood 

poucii 

r-eleorses 

IcLi^va 


Indies 

sperms  into 
Neater:  Some 
Teacl2  <sg^s  . i 
m dnpodf^uoh 

drops  to 
bottom , 
becomes 

adCu.lt. 


larvct  develops 
ofd’l’ish  ' 


Life  history  of  a fresh-water  mussel. 


Self-Testing  Exercise 

Fish  should  not  be  caught  during  the (1)  season.  Shell- 
fish are  killed  by  (2).  The  freshwater  mussel  passes  its 

larvae  stage  attached  to  the  (3)  of  a (4).  Many 

fishes  spawn  in (5) (6) (7)  of  our  streams 

costs  us  millions  of  dollars  a year  in  marketable  fish.  The  supply  of 

fish  would  soon  be  exhausted  were  it  not  for (8) (9). 

Caviar  is  prepared  from  the  eggs  of  the (10). 


594  HOW  DOES  MAN  CONSERVE  HIS  RESOURCES? 

PROBLEM  IV.  WHAT  IS  BEING  DONE  FOR  THE 
CONSERVATION  OF  BIRDS? 

We  have  already  learned  that  birds,  with  few  exceptions,  are 
of  very  great  value  to  man,  through  their  destruction  of  weed  seeds 
and  of  insects  harmful  to  crops.  But  in  spite  of  this  fact,  many 
species  of  birds  have  been  almost  exterminated  in  this  and  other 
countries,  and  the  total  number  of  birds  has  decreased  to  an 
alarming  extent.  This  has  been  due  largely  to  killing  for  food  and 

“ sport,”  and  for  plumage. 
A few  decades  ago  the  spray- 
ing of  trees  was  unknown; 
today  $10,000,000  or  more 
a year  is  spent  for  labor 
and  sprays.  It  is  estimated 
by  Dr.  Hornaday,  of  the 
New  York  Zoological  Park, 
that  a yearly  toll  of  $520,- 
000,000  now  collected  by 
insects  might  be  saved  if 
we  had  as  many  birds  as 
formerly. 

The  American  passenger 
pigeon,  once  very  abundant 
in  the  Middle  West,  is  now 
extinct.  Audubon,  the 
greatest  of  all  American  bird 
lovers,  gave  a graphic  ac- 
count of  the  migration  of  a flock  of  these  birds.  So  numerous 
were  they  that  when  the  flock  rose  in  the  air,  the  sun  was 
darkened,  and  at  night  the  weight  of  the  roosting  birds  broke 
down  large  branches  of  the  trees  in  which  they  rested.  Today 
not  a single  specimen  of  this  pigeon  can  be  found,  because 
they  were  slaughtered  by  the  hundreds  of  thousands  during  the 
breeding  season.  As  late  as  1869  one  Michigan  town  marketed 
11,888,000  pigeons  in  forty  days.  The  wholesale  killing  of  the 
snowy  egret  to  furnish  ornaments  for  ladies’  headwear  is  another  ^ 


Dr.  Alfred  O.  Gross 


In  early  colonial  times  the  heath  hen  was  very 
abundant  from  Maine  to  the  Carolinas.  But 
hunters,  disease,  and  fire  have  exterminated  the 
entire  race.  A lone  survivor  lived  for  some  years 
on  Martha’s  Vineyard  Island  across  the  sound  from 
the  Marine  Biological  Laboratory  in  Massachusetts, 
and  was  under  the  protection  of  conservation  or- 
ganizations of  the  state  of  Massachusetts. 


CONSERVATION  OF  BIJtDS 


595 


example  of  the  improvidence  of  our  fellow-countrymen.  It  was 
killetl  durin«;  its  breeding  season;  and  for  every  egret  killed,  an 
entire  bird  family  was  blotted  out  of  existence.  Prairie  chickens  are 
nowunknown  in  many  states  wiiere  they  were  abundant  before  1900, 
ddie  same  thing  will  happen  to  the  quail  where  it  is  unprotected. 

Hawks,  owls,  shrikes,  crows,  and  jays  all  play  a small  part  in  the 
destruction  of  our  native  birds.  The  English  sparrow  has  done 
great  harm  in  driving  away  useful  birds.  Squirrels  and  particu- 
larly rats  are  veiy  destructive  of  eggs  and  young  birds.  Small 
boys  with  air  guns,  and  persons  who  kill  for  food,  are  responsible 
for  the  death  of  many  birds.  But  according  to  Forbush,  the  house 
cat  is  the  worst  enemy  of  our  feathered  friends.  He  estimated 
from  many  observations  that  the  average  pet  cat  kills  at  least 
50  birds  a year. 

Home  conservation  methods.  Nesting  boxes  can  be  easily 
made  and  are  a great  asset  for  a home.  Birds  are  cheerful  and 
colorful  as  well  as  useful  neighbors.  Wrens  are  often  attracted  to 
boxes  having  small  holes  not  larger  than  one  and  one  eighth  inches 
in  diameter.  The  boxes  should  be  placed  so  that  cats  cannot 
get  access  to  them.  During  the  winter  birds  may  be  kept  around 
the  home  by  feeding.  Suet  baskets  and  nuts  put  on  shelves  in 
trees  and  inaccessible  to  cats  are  the  best  means  of  providing  food. 
Bird  baths  also  are  means  of  attracting  birds. 

Bird  migrations  in  relation  to  conservation.  It  has  long  been 
known  that  certain  birds  breed  in  the  far  north  and  spend  the 
winter  in  the  tropics.  The  golden  plover  is  a notable  example, 
for  it  nests  in  the  Arctic  and  winters  in  southern  South  America, 
making  a yearly  round  trip  of  more  than  16,000  miles,  while  the 
arctic  tern  may  make  a round  trip  of  22,000  miles  in  one  year. 
Wild  ducks  and  geese  are  examples  of  game  birds  that  make  these 
pilgrimages  each  year.  The  bobolink  migrates  from  the  northern 
part  of  our  country  to  a tropical  part  of  South  America.  It  is 
largely  due  to  this  migratory  instinct  that  many  of  our  birds  have 
been  subject  to  slaughter  by  hunters.  Many  states  have  laws 
which  allow  the  killing  of  small  “bags”  of  ducks  and  other  game 
birds,  but  do  not  sufficiently  protect  migrating  birds.  It  has  been 
estimated  that  5,000,000  hunters  go  out  every  season  for  birds  or 


596  HOW  DOES  MAN  CONSERVE  HIS  RESOURCES? 


other  animals.  Thanks  to  the  treaty  of  1916  with  Great  Britain, 
more  than  500  kinds  of  migrating  birds  are  protected  in  this 
country  and  Canada  from  capture,  killing,  or  sale.  All  over  this 
country,  owing  to  the  work  of  the  Audubon  Society,  of  Dr.  Horna- 
day,  and  of  other  leaders,  we  have  awakened  to  the  fact  that  our 
birds  are  valuable  assets  and  we  have  enacted  laws  prohibiting 
the  killing  of  game  birds  during  the  breeding  season,  and  of  most 
wild  birds  at  any  time. 

State  and  government  methods  of  protection.  In  1909  the 

Federal  Government  framed  a law  known  as  the  Lacey  amendment. 


U . S.  Bureau  of  Biol.  Survey 

What  is  your  state  doing  for  the  protection  of  birds  ? 


which  prohibits  shipping  of  birds  from  a state  where  it  is  illegal 
to  kill  them.  In  the  tariff  act  of  1913  a law  went  into  effect,  which 
protects  migratory  game  birds  as  well  as  insect-eating  birds,  such 
as  robins,  orioles,  and  swallows.  Later,  the  law  was  amended  to 
forbid  the  importation  for  commercial  purposes  of  egret  plumes 
(taken  from  breeding  egrets),  or  any  wild  bird  skins. 

Many  states  now  have  protective  laws  for  the  birds.  New 
York  State  has  a law  which  forbids  the  sale  of  all  game  birds,  no 
matter  where  they  were  taken. 


OTHER  MEANS  OF  CONSERVATION 


•597 


Other  means  of  conservation.  Several  private  organizations 
are  at  work  for  the  protection  of  our  birds.  Most  prominent  are 
the  Audubon  Societies  of  the  various  states,  all  federated  under 
a national  organization.  Among  other  things  they  distribute 
much  interesting  literature  which  can  be  used  in  school.  The 
Isaak  \\'alton  Leagues  are  particularly  interested  in  protection  of 
game  fish  and  birds,  and  the  American  Ornithologists  Union  helps 
through  the  interest  taken  by  many  students  and  scientific  men 
interested  in  bird  life.  Fortunately  for  the  average  citizen,  some 
public-spirited  people  who  have  money  are  willing  to  spend  it  for 
the  common  good.  Not  only  are  there  many  private  game  pre- 
ser\'es  in  various  parts  of  the  country,  but  also  several  bird  sanctu- 
aries have  been  established,  notably  the  Rainey  Sanctuary  of  over 
26,000  acres  in  Louisiana.  Private  game  and  bird  refuges  and 
preserves  are  estimated  to  include  nearly  800,000  acres  in  this 
country  and  over  150,000  acres  in  Canada.  In  addition  to  this, 
the  United  States  Government  has  created  a total  of  102  wild 
life  refuges,  most  of  them  affording  protection  to  birds. 

Practical  Exercise  10.  What  are  some  important  factors  in  the  destruction 
of  bird  life?  Discuss  the  good  and  bad  points  in  owning  a cat. 

Practical  Exercise  11.  How  may  we  attract  birds  about  our  homes? 

Practical  Exercise  12.  What  laws  in  your  state  protect  birds  ? What  socie- 
ties have  organizations  in  your  community  for  the  protection  of  birds? 

Practical  Exercise  13.  Why  are  bird  migrations  important  from  the  stand- 
point of  conservation  ? Using  outside  sources,  work  out  the  migration  routes 
of  at  least  5 birds.  (Read  Wetmore,  Migrations  of  Birds,  Harvard  University 
Press.) 


Self-Testing  Exeecise 

Check  the  correct  statements  for  your  workbook : 

T.  F.  1.  Every  cat  kills,  on  an  average,  over  50  birds  in  a year. 

T.  F.  2.  Passenger  pigeons,  once  very  abundant,  were  shot  in  such 
numbers  that  they  have  been  completely  exterminated. 

T.  F.  3.  Some  migratory  birds  make  a round  trip  of  over  22,000 
miles  each  year. 

T.  F.  4.  The  Federal  government  has  no  laws  protecting  migra- 
tory birds. 

T.  F.  5.  Individuals  cannot  do  anything  to  save  bird  life. 

T.  F.  6.  The  egret  is  still  being  killed  for  its  feathers. 

T.  F.  7.  The  quail  has  been  exterminated  by  hunters. 

H.  BIO  — 39 


598  HOW  DOES  MAN  CONSERVE  HIS  RESOURCES? 


Bureau  of  Biol.  Survey 

National  bison  range  in  Montana. 


PROBLEM  V.  WHAT  IS  BEING  DONE  FOR  THE 
CONSERVATION  OF  MAMMALS? 

Conservation  of  mammals.  It  was  not  so  many  years  ago  that 
the  people  of  this  country  thought  the  vast  herds  of  buffalo  that 
covered  the  western  plains  were  inexhaustible ; but  ten  years 
of  extensive  killing  nearly  exterminated  them.  Today  a few  thou- 
sand exist,  protected  by  law.  Without  doubt,  the  species  would 
have  died  out  had  it  not  been  for  the  fact  that  they  breed  in  cap- 
tivity. The  same  story  may  be  told  of  the  Alaskan  fur  seal,  almost 
exterminated  a few  years  ago  by  overhunting  during  their  migration 
after  breeding.  One  of  the  two  great  herds  of  Alaskan  seals, 
the  Pribilof  (so  called  because  they  went  to  the  Pribilof  Islands 
to  breed),  was  reduced  from  several  million  to  less  than  215,000 
animals  in  1910.  Today,  through  governmental  control  of  fishing 
and  protection  during  the  breeding  season,  the  herd  consists  of 
nearly  600,000  seals.  As  time  goes  on  and  the  furs  of  wild  animals 
become  scarcer  through  overkilling,  we  find  more  imperative  the 
need  for  protection  and  conservation  of  many  of  these  wild  forms. 

Already,  breeding  of  some  fur-bearing  animals  in  captivity  has 
been  tried  with  success,  and  substitutes  for  wild  animal  skins  are 
coming  more  and  more  into  the  markets.  Black-  and  silver-fox 
raising  has  been  tried  successfully  in  many  parts  of  this  country 


CONSERVATION  OF  MAMMALS 


599 


National  Park  Service 

Buffalo  on  protected  ranges  are  increasing  rapidly. 

and  Canada.  Sometimes  $2500  to  $3000  is  given  for  a single  ani- 
mal and  $25,000  has  been  reported  to  have  been  paid  for  a pair  of 
breeding  foxes.  Skunks,  martens,  minks,  and  other  animals  are 
also  being  bred  for  the  market.  At  last,  partly  awake  to  our  duty 
toward  the  wild  animals  of  this  country,  the  government  has  made 
some  wise  laws  and  established  a few  reservations  in  our  National 
Parks,  so  that  the  future  for  wild  life  in  this  country  is  safer. 


Self-Testing  Exercise 

Check  the  correct  statements  for  your  workbook: 

T.  F.  1.  Overhunting  has  exterminated  the  buffalo. 

T.  F.  2.  The  fur  seals  are  now  increasing  in  numbers  because  they 
are  protected  during  the  breeding  season. 

T.  F.  3.  Raising  of  fur-bearing  animals  is  a profitable  business. 

T.  F.  4.  The  need  for  protecting  the  seal  is  becoming  more  im- 
perative each  year. 


PROBLEM  VI.  HOW  IS  CONSERVATION  APPLIED  TO  MAN? 

We  have  mentioned  in  several  of  the  preceding  units  examples 
of  conservation  as  applied  to  human  life.  The  work  of  communities 
in  giving  their  inhabitants  pure  water  and  milk  supplies  has  resulted 


600  HOW  DOES  MAN  CONSERVE  HIS  RESOURCES? 


in  the  lowering  of  the  death  rate  in  those  places ; the  discoveries 
of  men  of  science  have  been  applied  toward  the  cure  and  prevention 
of  disease,  as  we  can  see  in  the  reduction  of  malaria,  yellow  fever, 
and  hookworm.  The  splendid  work  of  Dr.  Banting  of  Toronto  in 

his  discovery  of 
insulin  and  its  ap- 
plication in  the 
treatment  and  re- 
lief of  diabetes  is 
another  example 
of  work  for  the 
conservation  of 
human  life. 

Health  exami- 
nations, both  indi- 
vidual and  those 
given  in  schools  and  colleges,  should  aid  individuals  in  keeping  in 
good  physical  condition.  There  are  a number  of  agencies  which 
work  directly  for  health  conservation. 

The  health  work  of  the  National  Government.  The  United 
States  Public  Health  Service  covers  practically  all  phases  of  the 
nation’s  health.  It  establishes  quarantines  against  diseases  com- 
ing from  other  countries;  it  assists  local  communities  in  main- 
taining fights  against  epidemics  ; it  has  established  sanitariums  and 
hospitals  for  care  of  government  employees,  soldiers,  and  sailors. 
It  maintains  laboratories  for  investigation,  research,  and  statistics 
concerning  diseases.  It  has  a department  of  industrial  hygiene 
which  looks  after  the  health  of  those  in  the  various  industries, 
and  in  many  other  ways  has  general  supervision  of  the  nation’s 
health. 

State  and  city  supervision  of  health.  Most  states  now  have 
well-established  departments  of  health  which  do  in  general  the 
same  work  as  the  United  States  Public  Health  Service.  For 
example.  New  York  State,  which  has  an  unusually  efficient  organ- 
ization, has  the  following  divisions : Child  Hygiene,  Public  Health 
Education,  Tuberculosis  and  Communicable  Diseases,  Vital 
Statistics,  Sanitation,  Laboratories  and  Research,  Public  Health 


■timey 

ccverccgis  .span  of  life 

uncCer  Caesar.s 

iSyear^l 

Franca  be|bre  1800, 

1800 

32  ^eocr-s  1 Service 

1850 

57r««>'-i  1 

1880 

40_yectr^  | 1 ©80 

>914- 

4K5jy‘ectr.s  | 

19  29 

STy^cxr-s  1 

Isas' 

1 

\930 

? y<2.ar~s 

Can  you  give  several  reasons  for  the  increasing  average  span  of 
life  as  indicated  in  the  diagram  ? 


SPECIAL  HEALTH  AGENCIES 


601 


Nursing,  and  Venereal  Diseases.  It  also  publishes  a weekly 
bulletin  called  Health  News.  Large  cities,  such  as  New  York, 
Chicago,  and  Los  Angeles,  have  health  departments  organized 
along  the  same  general  lines,  for  health  conservation. 

Special  health  agencies.  One  of  the  most  important  private 
agencies  for  health  conservation  is  the  Rockefeller  Foundation, 
chartered  in  1913  to  promote  the  well-being  of  mankind  throughout 
the  world.  It  has  done  notable  work  since  its  foundation  in 
eradicating  hookworm,  yellow  fever,  and  malaria  in  different  parts 
of  the  world.  It  cooperates  with  other  agencies,  such  as  hospitals, 
schools  of  hygiene,  and  universities,  and  has  devoted  millions  of 
dollars  and,  what  is  far  more,  the  minds  and  lives  of  its  scientists 
to  the  end  that  the  span  of  human  life  could  be  lengthened  and 
man’s  life  on  the  earth  be  made  safer.  It  is  cooperating  with 
the  Health  Section  of  the  League  of  Nations,  and  in  this  way 
is  aiding  in  the  eradication  of  diseases  in  all  countries.  It, 
together  with  such  agencies  as  the  Millbank  Memorial  Founda- 
tion, the  National  and  State  Tuberculosis  Associations,  the 
National  Cardiac  Association,  the  American  Society  for  the  Pre- 
vention of  Cancer,  the  Eye-Sight  Conservation  Council,  the 
Nutritional  Laboratory  of  the  Carnegie  Institute  at  Boston,  the 
National  Health  Council,  American  Red  Cross,  and  the  McCormick 
Institute  for  Infectious  Diseases  in  Chicago  are  supported  by 
private  or  public  philanthropy,  and  are  doing  much  to  aid  in  the 
splendid  work  of  health  conservation. 


Self-Testing  Exercise 

Check  the  correct  statements  for  your  workbook : 

T.  F.  1.  The  periodic  health  examination  is  one  of  the  best  means 
of  keeping  well. 

T.  F.  2.  Every  state  maintains  a health  department. 

T.  F.  3.  The  law  requires  every  person  to  have  a health  examina- 
tion every  year. 

T.  F.  4.  The  Rockefeller  Institute  is  interested  only  in  finding  the 
causes  of  diseases  in  all  parts  of  the  world. 

T.  F.  5.  Sanitation  is  a form  of  conservation. 


602  HOW  DOES  MAN  CONSERVE  HIS  RESOURCES? 


Review  Summary 

Test  your  knowledge  of  the  unit  by ; (1 ) rechecking  on  the  survey  ques- 
tions ; (2)  performing  all  the  assigned  exercises ; (3)  checking  with  the  teacher 
your  answers  on  the  tests  and  trying  again  the  parts  you  missed ; (4)  making 
an  outline  of  the  unit  for  your  workbook. 

Test  on  Fundamental  Concepts 

In  a vertical  column  under  the  heading  CORRECT  write  numbers  of  all  statements  you 
believe  are  true.  In  another  column  under  INCORRECT  write  numbers  of  untrue  statements. 
Your  score  equals  right  answers  X 3|. 

I.  Trees  protect  the  soil  (1)  by  having  a mat  of  roots  which  holds 
water  ; (2)  by  shedding  leaves  which  form  humus  : (3)  by  shading  the 
ground,  thus  preventing  evaporation  of  water;  (4)  by  preventing 
erosion. 

II.  Wood  is  used  (5)  for  making  this  book;  (6)  for  fuel;  (7)  for 
making  rayon ; (8)  for  making  silk. 

III.  Some  of  the  enemies  of  the  forest  are  (9)  man;  (10)  fire; 
(11)  weeds;  (12)  insects. 

IV.  Some  methods  of  conservation  of  forests  are:  (13)  thinning 
the  present  forest  area;  (14)  replanting  depleted  area;  (15)  building 
of  National  Parks;  (16)  use  of  tree  surgery. 

V.  Conservation  of  animals  which  form  part  of  our  food  is  seen 
(17)  in  the  artificial  propagation  of  the  fresh- water  mussel ; (18)  in 
transplanting  clams  and  oysters  from  the  eastern  to  the  western 
coast;  (19)  in  the  artificial  propagation  of  salmon;  (20)  in  removing 
restrictions  against  catching  fishes  during  their  breeding  season. 

VI.  Conservation  of  birds  is  seen  (21)  in  the  extermination  of 
the  passenger  pigeon ; (22)  in  keeping  of  cats ; (23)  in  the  establish- 
ment of  bird  sanctuaries ; (24)  in  the  passing  of  laws  to  protect 
migratory  birds. 

VII.  Wild  mammals  are  being  conserved : (25)  by  the  establishment 

of  national  parks  and  game  preserves ; (26)  by  the  establishment  of 

breeding  farms ; (27)  by  game  laws  which  limit  shooting  of  many 
animals  to  certain  seasons  of  the  year ; (28)  by  hunting  of  mountain 
lions  and  other  predatory  animals. 

VIII.  Conservation  is  being  applied  to  man  (29)  through  health 
examinations  and  follow-up  work ; (30)  partly  by  means  of  the  U.  S. 
Public  Health  Service  and  its  supervision;  (31)  in  the  reduction  of 
hours  of  labor  with  more  time  for  play;  (32)  through  the  establish- 


TKSTS 


603 


nicnt  of  lioaltli  asoncies  such  as  the  Rockefeller  Fouiidation,  the  Na- 
tional Tuberculosis  Association,  and  the  National  Cardiac  Association. 

Achievement  Test 

1.  What  arc  the  chief  methods  of  forest  protection  in  your  locality? 

2.  ^^’hat  agencies  are  at  work  in  your  state  : 

(a)  for  the  conservation  of  trees? 

(b)  for  the  conservation  of  shellfish  and  crustaceans? 

(c)  for  the  conservation  of  fish? 

(d)  for  the  conservation  of  bird  life? 

(e)  for  the  conservation  of  mammals? 

(/)  for  the  conservation  of  human  beings? 

3.  What  is  each  agency  doing  in  your  community? 


Practical  Problems 

1.  Make  a table  in  which  you  note  all  the  agencies  at  work  to  con- 
serve health  in  your  locality  and  show  (1)  what  each  aims  to  do; 
(2)  the  machinery  used  to  accomplish  this  aim;  and  (3)  the  results 
accomplished. 

2,  i\Iake  a similar  table  for  wealth. 

Useful  References 

Farmers^  Bulletins:  265,  493,  513,  609,  621,  630,  963,  1208,  1209,  1239, 
1241,  1417. 

Henderson,  The  Practical  Value  of  Birds.  Macmillan,  1927. 

Hornaday,  Wild  Life  Conservation  in  Theory  and  Practice.  Yale  Uni- 
versity Press,  1914. 

kletcalf,  A Text-hook  of  Economic  Zoology.  Lea  and  Febiger,  1931. 

Pack,  The  School  Book  of  Forestry.  American  Tree  Association,  1922. 
Pack,  Trees  as  Good  Citizens.  American  Tree  Association,  1922. 

Rohan,  Our  Forests.  Nelson,  1928. 

Wetmore,  Migrations  of  Birds.  Harvard  University  Press,  1926. 

Yard,  Book  of  National  Parks.  Scribner’s,  1928. 


SURVEY  QUESTIONS 

Have  you  ever  thought  which  factor  was  more  important  in  your  life, 
heredity  or  environment?  What  does  the  farmer  in  your  locality  do  to 
increase  the  yield  of  his  crops  ? Do  you  know  what  is  meant  by  artificial 
selection  ? \^at  are  Mendel’s  laws  ? What  is  meant  by  social  inheritance  ? 


Photo  by  Ewing  Galloway 


UNIT  XVIII 

THE  IMPROVEMENT  OF  LIVING  THINGS  BY  MAN 

Preview.  As  you  look  at  the  boys  in  your  class,  you  notice  that 
each  boy  seems  to  be  more  or  less  like  every  other  boy ; he  has  a 
head,  body,  arms,'"  and  legs,  and  even  in  minor  ways  he  resembles 
each  of  the  other  boys  in  the  room.  Moreover,  if  you  should  ask 
any  particular  boy,  no  doubt  he  would  tell  you  that  he  resembled 
in  certain  respects  his  mother  or  his  father.  If  you  should  ask  his 
parents  whom  he  resembled,  they  would  say,  “We  can  see  traits 
of  his  grandfather  (or  his  grandmother)  in  him.” 

The  law  of  nature  which  causes  a child  to  possess  characters 
like  either  or  both  of  his  parents,  and  like  their  parents  as  well, 

604 


PREVIEW 


G05 


is  called  heredity.  If  we  consider  our  own  individual  cases,  we  shall 
probably  find  that  we  resemble  our  ancestors  not  only  in  physical 
characters  but  also  in  mental  qualities.  The  ability  to  play  the 
piano  well  or  to  paint  well  may  be  as  much  a case  of  inheritance  as 
the  color  of  one’s  eyes  or  the  shape  of  one’s  nose.  We  are  a complex 
of  phj'sical  and  mental  characters,  received  from  all  our  ancestors. 

But  no  boy  in  the  class  is  exactly  like  any  other  boy;  even 
brothers  are  different  in  appearance  and  in  action.  Each  one  of  us 
tends  to  be  slightly  different  from  his  or  her  parents.  Each  plant, 
each  animal,  varies  in  a small  degree  from  its  immediate  ancestors, 
and  it  may  vary  to  a great  degree.  This  tendency  among  plants 
and  animals  to  be  different  from  their  ancestors  and  from  each  other 
is  called  variation.  Heredity  and  variation  are  the  corner  stones 
on  which  all  the  work  in  the  improvement  of  plants  and  animals, 
including  man  himself,  is  built. 

Charles  Darwin  was  one  of  the  first  scientists  to  suggest  how  the 
laws  of  heredity  apply  to  the  development  of  plants  and  animals. 
He  knew  that  although  animals  and  plants  are  like  their  ancestors, 
they  also  tend  to  vary.  In  nature,  he  believed,  the  variations 
which  best  fit  a plant  or  animal  for  life  in  its  own  environment  are 
the  ones  which  are  handed  down,  because  those  individuals  having 
variations  not  fitted  for  life  in  that  particular  environment  will  die. 
Thus,  said  Darwin,  since  favorable  variations  survive  and  repro- 
duce, and,  as  the  descendants  of  each  of  these  individuals  also 
tend  to  vary  slightly,  a new  type  of  plant  or  animal,  fitted  for  that 
special  place,  is  gradually  formed.  Darwin  reasoned  that  if  favor- 
able variants  are  developed  in  nature,  then  man,  by  selecting  the 
variations  he  wanted,  could  form  new  varieties  of  plants  and 
animals  much  more  quickly  than  nature.  When  we  compare  the 
improved  breeds  of  dogs  with  the  original  wild  dog,  or  cultivated 
fruits  like  the  apple  and  peach  with  their  wild  ancestors,  no  one 
can  doubt  that  man  has  done  much  in  the  way  of  improving  do- 
mesticated plants  and  animals. 

Every  farmer  knows  that  to  produce  good  results  he  must  first 
have  good  seed  or  good  stock.  The  plants  or  animals  must  come 
from  sturdy  parents.  Then  they  must  have  favorable  conditions 
in  which  to  grow,  or  they  will  not  produce.  They  must  have  care. 


606  IMPROVEMENT  OF  LIVING  THINGS  BY  MAN 


On  abandoned  farms  the  plants  soon  tend  to  revert  or  go  back  to 
wild  conditions.  And  if  we  are  to  produce  better  plants  and 
animals,  we  must  continually  select  the  best  products  for  breeding 
as  well  as  give  them  the  best  possible  environment. 

Heredity  is  a much  more  complicated  process  than  we  once 
thought.  Laws  of  heredity  discovered  by  Gregor  Mendel  and 
worked  out  more  recently  by  a number  of  scientists  have  shown 
that  the  breeder  may  be  able  to  get  much  more  exact  results  than 
was  thought  possible  a few  years  ago. 

There  has  been  a good  deal  of  discussion  among  people  lately 
as  to  the  comparative  importance  of  environment  and  heredity 

in  the  lives  of  people. 
The  philanthropist  says, 
“Give  me  an  opportunity 
to  improve  the  conditions 
of  the  slum  dwellers  and 
I will  make  happy  and 
healthy  individuals  out  of 
them.”  And  the  breeder 
of  plants  or  animals  says, 
“I  cannot  improve  my 
plants  or  animals  unless  I 
give  them  proper  condi- 
tions of  food  and  water 
and  air  in  their  surround- 
ings. But  even  if  I give 
them  the  best  of  these 
conditions,  I cannot  make 
a poor  animal  or  plant  of 
poor  stock  into  one  having 
good  qualities.” 

We  have  learned  from 
observation  that  environ- 
ment does  play  a very  big 
part  in  the  lives  of  plants 
and  animals.  Not  only  will  a plant  or  animal  die  if  it  is  deprived 
of  any  one  environmental  factor,  but  frequently  it  will  be  con- 


Trees  growing  on  a rock  sent  long  roots  over  the 
sides  of  the  rock  to  the  soil  lying  beside  it.  How 
has  the  environment  changed  the  tree? 


PREVIEW 


G07 


siderably  changed  or  modified  if  a single  factor  is  modified.  Take 
the  case  of  tlie  potato  plant  sprouting  in  the  cellar:  it  is  quite  a 
ditferent  organism  from  the  one  growing  in  its  natural  environ- 
ment. Look  at  the  (.lifferences  between  trees  grown  near  the  top  of 
a mountain  where  they  are  exposed  to  the  wind  and  those  of  the 
same  kind  growing  on  the  protected  slopes  of  the  same  mountain, 
or  notice  the  differences  in  the  trees  growing  on  the  north  and  on 
the  south  sides  of  a valley.  Hundreds  of  examples  might  be  given 
to  show  not  only  that  the  environment  determines  the  kind  of 
organisms  living  there,  but  also  that  the  plant  or  animal  may  be 
considerably  modified  or  changed  through  the  action  of  the 
environment  on  it. 

But  it  is  still  somewhat  a discussed  question  as  to  whether  the 
changes  thus  brought  about  will  be  handed  down  to  the  offspring 
of  the  plant  or  animal.  We  know  that  seeds  from  a wind-blown 
tree  if  they  take  root  in  a protected  side  of  the  mountain  will  grow 
tall  and  straight  like  the  others  around  it.  Mice  whose  tails  had 
been  cut  off  were  bred  for  numerous  generations  without  producing 
any  tailless  offspring.  Lamarck,  the  French  naturalist,  who  first 
noted  that  the  influence  of  the  use  or  disuse  of  organs  on  the  organ- 
ism is  very  great,  followed  this  statement  with  another,  that  the 
effects  of  such  influences  were  handed  down  by  heredity  to  the 
offspring.  Most  modern  experiments  do  not  uphold  Lamarck’s 
views,  although  there  are  a few  that  are  believed  to  show  the  effect 
of  environment  upon  the  offspring. 

We  have  seen  that  instinct  plays  an  important  part  in  the  lives 
of  animals  lower  than  man.  A baby  chick  just  hatched  pecks  at 
a bad-tasting  caterpillar  and  receives  a sense  impression,  so  that 
after  a few  more  mistakes  of  the  same  kind,  it  learns  that  such 
caterpillars  are  not  good  and  must  be  left  alone.  Man  not  only 
learns  to  profit  by  experience,  as  does  the  chick,  but  in  addition 
he  passes  on  this  knowledge  to  others.  While  he  cannot  hand  on 
this  knowledge  by  heredity,  he  can  teach  others,  and  they  in  turn 
can  teach  their  generation.  In  a similar  way  the  human  race  has 
made  wonderful  progress,  the  benefits  of  which  we  are  now  en- 
joying. This  great  mass  of  experience,  which  results  in  better 
health,  better  training,  and  material  things  as  radios,  automobiles. 


608  IMPROVEMENT  OP  LIVING  THINGS  BY  MAN 


and  airplanes,  is  called  our  social  inheritance.  Our  lives  may  then 
be  said  to  be  influenced  by  three  factors : training  or  social  inher- 
itance, environment  or  what  we  come  in  contact  with,  and  heredity 
or  what  we  are.  It  is  self-evident  that  a handicap  such  as  poor 
health  or  lack  of  education  would  play  an  important  part  in  one’s 
success  or  failure  in  life.  Some  men  have  become  great  in  spite  of 
handicaps,  but  it  was  because  their  heredity  was  such  that  they 
could  not  be  denied  success.  Great  men  and  great  minds  have 
stood  out  in  spite  of  the  most  unfavorable  environments,  witness 
Abraham  Lincoln  and  William  Shakespeare.  The  list  could  be 

multiplied  indefinitely.  There 
are  other  factors  at  work  be- 
sides those  of  environment 
which  produce  great  men. 
Sometimes  the  heredity  of 
such  men  is  easily  followed,  for 
certain  distinguished  families 
have  held  a place  in  the  world 
for  a number  of  generations. 
The  reasons  for  the  sudden 
emergence  from  obscurity  to 
greatness,  as  in  the  case  of 
Napoleon  or  Lincoln,  is  not 
so  easy  to  understand,  but  we  may  be  sure  that  heredity  played 
a very  large  part. 

People  today  have  a chance  to  live  longer  than  their  ancestors 
because  their  environment  is  better.  The  sanitary  conditions  are 
much  improved  and  disease  germs  are  being  controlled  by  provid- 
ing the  race  with  the  best  environment  possible. 

PROBLEM  I— HOW  MAY  ENVIRONMENT  AFFECT  PLANTS  AND 
ANIMALS? 

Demonstration  1.  How  may  gravity  affect  growing  seedlings? 

Grow  radish  or  mustard  seeds  in  a pocket  garden  placed  on  edge, 
until  the  roots  are  a half  inch  long ; then  turn  it  on  another  edge  and 
examine  again  after  24  hours.  Repeat  after  another  24  hours. 

Which  part  of  the  root  grows  down  each  time  the  garden  is  turned  ? 


C 


ABC  is  a triangle  representing  the  three  factors 
which  affect  a person’s  life.  If  one’s  training  and 
environment  are  changed  and  heredity  remains 
the  same,  a different  surface  is  made  possible. 


PLANTS  AND  THEIR  ENVIRONMENT 


609 


What  causes  roots  to  turn  downward?  Compare  tliese  plants  with 
plants  f?rowinf>:  in  soil.  What  other  changes  have  taken  place? 
Alight  these  changes  be  due  to  changes  in  the  environment? 

Demonstration  2.  What  substances  are  necessary  for  plant 
growth  ? 

Partly  fill  five  jars,  the  first  with  distilled  water,  the  second  with 
nutrient  solution  ^ without  potassium  nitrate ; the  third  with  nutrient 
solution  without  calcium  phosphate;  the  fourth  with  nutrient  solution 
without  ferric  chloride ; and  the  fifth  with  nutrient  solution.  Place 
in  the  jars  corn  seedlings  with  their  roots  in  the  liquids.  Keep  them 
under  observation  for  two  or  more  weeks.  In  which  jar  does  the 
most  vigorous  growth  take  place?  What  has  soil  environment  to  do 
with  plants? 

Demonstration  3.  How  may  different  foods  affect  an  animal? 

Feed  two  white  rats  for  several  weeks  upon  the  same  amounts  by 
weight  of  gluten  feed  plus  water  and  gluten  feed  plus  milk. 

What  differences  do  you  notice  in  the  appearance  and  weight  of  the 
rats  at  the  end  of  this  period?  Do  differences  in  composition  of  foods 
have  an  effect  upon  rats? 


Plants  and  their  environment.  Numberless  examples  of  the 
effect  of  the  environment  upon  plants  and  animals  are  known  to 
all.  Besides  those  just  given,  the  familiar  bleaching  of  celery 
or  lettuce  when  the  sun  is  kept  from  them,  the  changes  in  the  size 
and  color  of  plants  having  little  or  much  exposure  to  the  sun,  the 
effect  of  lack  of  water  on  plants,  especially  in  a country  where 
irrigation  is  practiced,  all  these  and  more  are  everyday  examples. 

But  the  scientist  goes  even  further  with  his  experiments.  Bon- 
nier, a French  botanist,  divided  a dandelion  plant  and  planted 
part  of  it  at  a high  altitude  in  the  mountains,  while  the  other  part 
was  planted  in  the  valley.  Two  quite  different  plants  resulted. 
Two  lots  of  corn  produced  from  seeds  from  the  same  cob,  one 
lot  planted  in  wide  rows  and  the  other  crowded,  will  be  astonish- 
ingly different.  Under  certain  conditions  environment  seemingly 


1 A nutrient  solution  known  as  Sack’s  solution  may  be  made  as  follows : 


Potassium  nitrate  . 
Sodium  chloride 
Calcium  sulphate  . 
Magnesium  sulphate 
Calcium  phosphate 
Ferric  chloride  . . 

Distilled  water  . . 


1.00  gram 
0.50  gram 
0.50  gram 
0.50  gram 
0.50  gram 
0.005  gram 
1000.00  grams 


Add  the  ferric  chloride  at  the  time  the  solution  is  to  be  used,  by  adding  a drop 
or  so  to  the  solution  in  the  bottle  used  for  the  seedlings. 


610  IMPROVEMENT  OF  LIVING  THINGS  BY  MAN 


affects  heredity,  at  least  for  a few  generations.  Professor 
MacDougal  of  the  Desert  Laboratory  of  the  Carnegie  Institute 

has  injected  various 
solutions  of  salts  into 
the  ovaries  of  several 
species  of  plants  and 
has  found  that  the 
seeds  which  grew  pro- 
duced plants  which 
differed  in  the  plant 
leaf  and  body  of  the 
parent  plant  and  these 
variations  persisted 
through  several  gener- 
ations. 

Practical  Exercise  1. 

Using  one  of  the  books  of 
reference,  make  as  long  a 
list  as  you  can  of  modifica- 
tions in  plants  brought 
about  by  changes  in  the 
environment. 

Animals  and  their 

Wright  Pierce  . 

A tree  beside  a hillside.  Notice  how  the  sweeping  winds  environment.  Pro- 
have  caused  the  limbs  to  grow  to  one  side  of  the  tree.  fesSOr  ToWCr  Carried 

on  a series  of  experiments  with  the  potato  beetle  and  found  that 
in  some  cases  color  changes  brought  about  by  the  beetles  living 
in  a changed  environment  were  apparently  handed  down  to  the 
future  generations.  Dr.  Guyer  induced  eye  defects  in  rabbits, 
which  were  handed  down  to  later  generations  of  rabbits.  Professor 
Stockard’s  experiments  in  which  he  subjected  guinea  pigs  to  the 
fumes  of  alcohol  indicate  that  the  young  are  profoundly  affected, 
many  dying,  and  those  which  survived  were  undersized  and  nervous. 
These  effects  were  transmitted  to  the  grandchildren.  Dr.  Hyde 
reports  that  eyeless  forms  of  fruit  flies  appear  if  the  temperature 
gets  above  a certain  degree,  while  Dr.  Morgan  tells  of  certain 
color  changes  in  fruit  flies  that  appear  as  soon  as  high  humidity 
becomes  a factor  in  the  environment.  The  developing  eggs  of 


now  DO  LIVING  THINGS  RLPRODUCK? 


Gil 


fish,  pliicod  in  water  coiilaiiiin^'  large  amounts  of  niagnesiuin  salts, 
may  produce  one-eyed  fisli.  Ih-essure  or  other  mechanical  stimuli 
may  cause  the  developing  eggs  of  some  marine  animals  to  develop 
into  many  ditlerent  sorts  of  abnormal  forms  which  do  not  become 
adults.  William  Beebe  has  induced  great  changes  in  the  colors 
of  birds  by  keeping  them  in  unusual  conditions  of  humidity. 
However,  the  greatest  evidence  seems  to  support  the  fact  that 
plants  and  animals  do  not  in  general  hand  down  the  changes 
brought  about  by  the  environment. 

Practical  Exercise  2.  Can  you  give  any  examples  of  how  environment  has 
caused  changes  in  animals?  Do  you  see  any  relation  between  environment 
and  adaptations?  Explain  to  the  class. 

Practical  Exercise  3.  Write  a 300-word  paragraph  on  environment  as  a 
factor  in  molding  one’s  life. 

Self-Testing  Exercise 

Roots  grow (1)  because  they  are  affected  by (2). 

The  kinds  and  amounts  of  food  of  an  animal  or  a plant  will  affect 

its (3)  and (4).  Two  rows  of  corn  plants  from  the 

same  ear  in  different  environments  will  be (5).  It  has  been 

shown  by  a few  experiments  that (6)  caused  by  environment 

may  sometimes  be (7). 

PROBLEM  II.  HOW  DO  LIVING  THINGS  REPRODUCE 
AND  DEVELOP? 

Let  us  now  try  to  discover  why  it  is  that  plants  and  animals  tend 
to  hand  down  unchanged  the  characteristics  that  we  think  of 
as  inheritable.  The 
simplest  one-celled 
plants  and  animals 
grow.  But  since 
they  take  in  food 
and  oxygen  and  give 
off  body  wastes 
through  their  cell 
membranes  and 
walls,  the  size  of  the 
cell  body  is  limited. 

This  limitation  is 


A. 


A2 


Which  has  the  greater  surface  area,  A or  i and  2 ? Why  do 
cells  divide  ? 


612  IMPROVEMENT  OF  LIVING  THINGS  BY  MAN 


due  to  the  fact  that  though  the  volume  grows  in  proportion  to  the 
cube  of  its  diameter,  the  surface  grows  according  to  the  square  of 
its  diameter.  Two  bricks  cemented  together  have  less  surface 
than  two  separate  bricks.  Therefore  in  order  to  live,  the  cell  must 

get  more  surface.  It  does  this 
by  cell  division.  In  our  study 
of  the  amoeba  we  saw  that  a 
single  cell  formed  two  cells  by 
division. 

Animals  and  plants  grow 
larger  by  a multiplication  of  the 
cells.  The  growth  of  roots, 
buds,  leaves,  and  seeds,  the 
development  of  a kitten,  and 
the  shooting  up  of  a boy  or  a 
girl  at  adolescence  are  examples 
of  rapid  cell  division. 

New  plants  may  be  formed 
by  vegetative  propagation. 
Most  of  you  know  that  if  a 
chestnut,  poplar,  or  willow  tree 
is  cut  down  young  shoots  soon 
come  up  around  the  main  stem. 
The  big  redwoods  of  California 
grow  in  a similar  manner,  as  one 
can  see  who  has  traveled  through  the  cut  forests  of  northwestern 
California. 

Some  readers  may  have  “slipped”  geraniums  or  other  plants  or 
have  tried  the  experiment  with  the  willow  twig  shown  on  page  168. 
Many  plants  are  growing  from  cuttings  made  from  an  older  plant ; 
bananas  and  sugar  cane  are  grown  entirely  in  this  way.  Each 
cutting  or  “slip”  will  produce  all  the  parts  of  the  plant  because  “a 
bud  is  a promise  of  a branch.” 

There  are  many  natural  methods  of  vegetative  propagation 
which  the  nurseryman  has  taken  advantage  of  in  growing  plants 
for  sale.  We  all  know  what  a pest  “quack”  or  “quick”  grass  is 
in  a lawn.  Here  the  stem  of  the  plant  forms  runners  or  branches 


Regeneration  of  a flatworm.  The  shaded  area 
shows  the  newly  regenerated  parts. 


GRAFTING 


G13 


tiecC  up 

•vith. 

rafficc 


Explain  how  grafting  of  fruit  tree  is  done. 


which  firow  al()nt>:  the  strike  root  every  little  way, 

thus  forming  new  jilants.  Strawberries  and  many  other  plants 
are  propapited  in  this  way. 

d'he  stems  of  some  plants, 
like  raspberries,  blackberries, 
or  firapes,  take  root  if  they 
bend  over  and  touch  the 
‘iround.  This  process  is  often 
artificially  produced  and  is 
called  layering. 

Ferns  and  other  plants  have 
underground  rootstocks  w'hich 
form  new  shoots  that  become 
new  plants.  Tubers,  as  the 
potato,  and  bulbs,  as  the  onion 
or  lily,  are  other  examples  of 
growth  known  as  vegetative 
propagation.  Such  methods  of 
growth  give  fixed  types  of  plants  and  are  much  used  by  plant  breeders 
to  propagate  certain  plants  which  usually  cannot  reproduce  them- 
selves. 

A familiar  method  of  reproducing  desirable  varieties 

of  fruit  trees  is 
by  grafting.  This 
consists  in  apply- 
ing a portion  of  a 
tree  of  the  desired 
variety  (called 
the  scion)  to  an- 
other tree  of  a 
nearly  related 
kind  (called  the 
stock).  The  two 
parts  must  be  so 
placed  that  the 
cambium  surface  of  the  scion  comes  in  contact  with  the  cambium 
of  the  tree  to  which  it  is  applied,  thus  putting  it  in  direct  com- 


Grafting. 


"budslick  Tshap€c£ 

cut  in  “bark 


iviserte<l 

Explain  how  budding  is  accomplished. 


bud  tied 
in  place/, 
with  itifpa 


614  IMPROVEMENT  OF  LIVING  THINGS  BY  MAN 


munication  with  a supply  of  food  from  the  tree  which  is  already 
established.  Peach,  apricot,  apple,  and  pear  trees  are  often  grafted. 
Another  similar  method  is  called  budding,  which  is  used  largely  in 
the  citrus  industry.  A bud  of  the  desired  tree  is  inserted  under 
the  bark  of  the  stock.  The  branches  growing  from  the  bud  or  scion 
will  bear  the  same  variety  of  fruit  as  the  original  tree. 

Grafting  is  also  practiced  in  animals.  Hydra,  worms,  insects, 

and  frogs  all  have 
been  used  experi- 
mentally. Sur- 
geons graft  skin 
after  a severe  burn, 
or  new  bones  after 
a severe  operation 
or  accident.  A 
similar  process 
takes  place  when 
we  cut  ourselves  and  the  wound  heals : new  tissues  are  formed  by 
the  growth  of  cells. 

Regeneration.  In  certain  animals,  lost  parts  grow  again  by  cell 
division.  A flatworm  may  be  cut  into  as  many  as  twenty  pieces, 
each  one  of  which  will  grow  into  or  regenerate  a new  worm.  Earth- 
worms regenerate  lost  segments  and  starfish  lost  rays.  Crusta- 
ceans regenerate  lost  antennae  or  other  appendages  ; it  is  common 
for  the  fiddler  crab,  when  caught  by  a claw,  to  detach  the  claw,  in 
his  struggle  to  escape  from  his  enemies.  A new  claw  will  grow 
out  later  on  the  stump  of  the  old  one. 

Home  Project.  Make  a successful  bud  or  graft  and  demonstrate  it 
to  the  class. 

Practical  Exercise  4.  Make  a table  in  which  you  have  as  headings  all  the 
different  ways  in  which  plants  or  animals  are  Under  each 

heading  place  examples  that  you  have  personally  seen. 

Practical  Exercise  5.  Find  out  from  such  a magazine  as  Hygeia  all  the 
reliable  information  you  can  about  gland  grafting.  Compare  this  with  adver- 
tisements on  gland  grafting  taken  from  newspapers.  Do  you  believe  the 
advertisements  ? 

Practical  Exercise  6.  List  ten  fruit  trees  that  can  be  grafted  or  budded. 

Vegetative  propagation  and  reproduction  in  lower  and  higher 
plants.  Vegetative  propagation  is  a form  of  asexual  repro- 


Professor  Morgan  grafted  parts  of  earthworms  and  produced 
(1)  a very  long  worm,  (2)  a two-tailed  worm,  (3)  a very  short 
worm. 


vecjetativp:  pj{opac;ati()n  and  repj{Oduction  615 


duct  ion,  since  (he  new  organism  is  formed  by  a cell  or  cells  separat- 
ing from  a single  parent.  Other  examines  of  this  type  of  repro- 
duction is  seen  in  the  reproduction  of  yeast  or  mold,  which  form 
asexual  spores.  Such  spores  under  favor- 
able conditions  produce  new  plants. 

New  living  organisms,  however,  are  usu- 
ally formed  by  other  methods.  If  two  cells, 
from  two  plants  or  animals  of  different 
sexes,  come  together  to  form  a new  indi- 
vidual, we  call  this  a case  of  sexual  repro- 
duction. In  some  plants,  like  Spirogyra, 
already  studied,  a kind  of  sexual  spore  is 
formed  by  a process  we  call  conjugation. 

Two  filaments,  lying  side  by  side,  send 
out  little  projections  from  adjoining  cells, 
which  meet,  and  the  contents  of  the  cells 
in  one  filament  pass  over  and  mix  with  the 
cell  contents  of  the  other  filament.  The 
cells  thus  formed  become  resting  spores 
(zygospores)  which  will  develop  into  new 
plants.  The  cells  which  formed  these 
spores  are  called  gametes. 

In  the  algae  we  have  a step  higher  in 
the  development  of  gametes.  In  the  vau- 
cheria  (v6-ke'ri-d),  a branched  alga,  two 
structures  may  be  produced  from  the  fila- 
ment. One  contains  a large  gamete  which 
is  called  an  egg.  The  other  contains  small 
gametes,  called  sperms,  each  with  two  cilia. 

The  sperms  when  set  free  appear  to  be 
chemically  attracted  to  the  egg  cells.  If  a sperm  (male  gamete) 
fuses  with  an  egg  (female  gamete),  it  is  said  to  fertilize  the  egg  cell. 
From  the  fertilized  egg  a new  plant  will  eventually  grow.  This 
method  of  development,  which  is  found  in  all  higher  plants  and 
animals,  is  known  as  sexual  reproduction. 

We  have  already  learned  how  sexual  reproduction  takes  place 
in  the  flowering  plants.  The  flower  holds  pollen  grains  and  ovules 


Conjugation  in  Spirogyra. 
Explain  the  diagram. 


616  IMPROVEMENT  OF  LIVING  THINGS  BY  MAN 


or  undeveloped  seeds.  At  an  early  stage  the  pollen  grain  contains 
but  a single  cell.  A little  later,  however,  three  nuclei  may  be  found 


A part  of  a filament  of  Vaucheria.  Explain 
how  a new  plant  is  formed. 


in  the  protoplasm.  Hence  we 
know  that  at  least  three  cells 
exist  there,  two  of  which  are 
sperm  cells  or  male  gametes. 
We  have  learned  that  within 
the  ovary  of  the  flower  is  an  egg 
cell.  It  is  to  this  cell  that  one 
of  the  sperm  nuclei  of  the  pollen 
tube  grows,  ultimately  uniting 
with  it.  The  union  of  the 


sperm  nucleus  with  the  nucleus  of  the  egg  to  form  a single  cell  is 
known  as  fertilization.  This  single  cell  formed  by  the  union  of  the 
pollen-tube  sperm  cell  and  the  egg  cell  is  now  called  a fertilized  egg 
or  zygote  and  is  the  beginning  of  a baby  plant,  or  embryo.  The 


second  sperm  nucleus 
unites  with  another  nu- 
cleus in  the  embryo  sac 
and  grows  into  food  sub- 
stances called  the  en- 
dosperm, which  in  some 
plants  is  a very  impor- 
tant part  of  the  seed 
since  it  supplies  the  grow- 
ing embryo  with  nourish- 
ment. 

Practical  Exercise  7. 

Make  a series  of  labeled  dia- 
grams to  illustrate  different 
stages  in  the  development  of 
sexual  reproduction  in 
plants.  Make  a distinction 
between  asexual  and  sexual 
reproduction  without  using 
the  words  “sex”  or  “sex 
cells.” 

Field  Exercise.  During 
the  first  warm  days  in 
March  or  April,  look  for 


pollerz  tahJ  ’ 


em 


tq  (j. 


^ggnucleu$ 


Q I fertile  e^  ^perm-L-ih  \ \ 
fm  u "Will  form  fuses  ( 'r\$\ 
i*:  j ^ I embryo  vithe^^-''  U/' 

'fertilUecC 
i:  nucleus^ 

^l^roctuceA-^  / ’ 

-fbocC  ^ ' 

\i  fuses  with 
nucleuc^^ 


Explain  bow  fertilization  takes  place  in  plants. 


DKVKLOPMIOXT  OF  ANIMALS 


G17 


gelatinous  masses  of  frogs’  eggs  attached  to  sticks  or  water  weeds  in 
sliallow  ponds,  ('ollect  some  and  kee[)  them  in  a shallow  dish  in  a win- 
dow at  liome  until  tiu'y  hatch.  Make  experiments  to  learn  whether 
temp('ra( urc'  alTi'cts  tin-  development  of  the  eggs  in  any  way.  Place 
eggs  in  dishes  of  wat('r  in  a warm  room,  in  a cold  room,  and  in  the 
refrigerator.  Make  observations  for  several  weeks  as  to  the  rate  of 
development  of  each  lot  of  eggs.  Also  try  placing  a large  number  of 
eggs  in  one  dish,  thus  cutting  (lown  the  supply  of  available  oxygen,  and 
in  another  dish  near  by,  under  the  same  conditions  of  light  and  lieat, 
place  a few  eggs  with  plenty  of  water.  Do  both  batches  of  eggs  develoj) 
with  the  same  rapidity?  In  all  these  experiments  be  sure  to  use  eggs 
from  the  same  egg  mass,  so  as  to  make  sure  that  all  are  of  the  same  age. 


V / circuUitory  s/stem 
'•eiK.reW^ 

fd-ide-stiw  avetem 
trafpirato^  syetitm 


Development  of  animals.  Many-celled  animals  are  formed 
in  much  the  same  way  as  are  many-celled  seed  plants.  A com- 
mon bath  sponge,  an  earthworm,  a fish,  or  a dog,  — each  of 
them  begins  life  as 
a fertilized  egg  cell. 

As  in  the  flowering 
plant,  this  cell  was 
formed  by  the  union 
of  two  other  cells, 
a tiny  (usually  mo- 
tile) cell,  the  sperm, 
and  a larger  one, 
the  egg.  After  the 
egg  is  fertilized  by 
a sperm  cell,  it 
splits  into  two,  then 
into  four,  then  into 
eight,  then  into  six- 
teen cells,  and  so 
on.  As  the  number 
of  cells  increases,  a 
hollow  ball  of  cells 
called  the  hlastula  is  formed  ; later  this  ball  sinks  in  on  one  side,  and 
a double-walled  cup  of  cells,  called  a gastrula,  results.  Practically 
all  animals  pass  through  the  above  stages  in  their  development 
from  the  egg,  although  these  stages  are  often  not  plainly  seen  be- 
cause of  the  presence  of  food  material  (yolk)  in  the  egg. 


blastula 


All  animals  pass  through  the  above  stages  in  the  process  of 
their  development  from  an  egg. 


618  IMPROVEMENT  OF  LIVING  THINGS  BY  MAN 

In  an  older  stage  three  layers  of  cells  are  noticeable.  Those 
of  the  outside,  developed  from  the  outer  layer  of  the  gastrula, 
are  called  the  ectoderm;  this  later  gives  rise  to  the  skin,  nervous 
system,  etc.  An  inner  layer,  developed  from  the  inner  layer  of 
the  gastrula,  is  called  the  endoderm;  this  forms  the  digestive  and 
circulatory  systems.  A middle  layer,  called  the  mesoderm,  lying 
between  the  ectoderm  and  the  endoderm,  gives  rise  in  higher 
animals,  to  the  muscles,  the  skeleton,  and  other  internal  organs. 
At  a very  early  stage  in  development,  in  some  animals  the  two-  or 
four-cell  stage,  the  so-called  sex  cells  may  be  found,  so  that  we  may 
say  that  almost  from  the  beginning  the  sex  cells  are  set  apart  from 

the  other  cells  of  the  de- 
veloping organism. 

We  have  already  discussed 
the  development  of  insects, 
of  fishes,  and  of  frogs, 
and  have  learned  that  in 
every  case  the  fertilization  of 
the  egg  has  resulted  in  the 
development  of  the  animal, 
sometimes  through  a compli- 
cated life  history  called  a 
metamorphosis.  We  have 
found  in  all  of  these  that  the 
egg  developed  without  any 
care  on  the  part  of  the 
parent.  In  higher  forms  we 
find  fewer  eggs  fertilized  and 
much  more  care  taken  of  the 
egg  and  young.  In  birds  the 
egg  is  incubated  or  hatched 
outside  the  body  of  the 
mother.  But  in  the  mam- 
mals the  young  develop  within  the  mother’s  body  and  consequently 
are  protected  for  a much  longer  time  than  those  of  the  lower  forms. 

Development  of  birds.  The  white  of  the  hen’s  egg  is  accumu- 
lated during  the  passage  of  the  real  egg  (which  is  on  the  yolk  or 


— embryo 

sHell 

^ oclbvcmen. 
— -yollc 

airspace 


„<am'br7'o 
.... -.srhell 
albujnen 
— ^IxxicC 

...ycXkscxA 


Above,  a section  through  a bird’s  egg  showing 
tiny  embryo  connected  to  the  yolk,  which  is  sur- 
rounded by  albumen. 

Below,  the  egg  has  been  incubated  for  some 
days.  Various  organs  have  already  developed,  and 
can  be  recognized. 


DEVELOPMENT  OE  A MAMMAL 


G19 


yellow  portion)  to  the  outside  of  the  body.  Before  the  egg  is  laid 
a shell  is  secreted  over  its  surface.  If  the  fertilized  egg  of  a hen 
is  broken  and  carefully  examined,  on  the  surface  of  the  yolk  will  be 
found  a little  circular  disk.  This  is  the  beginning  of  the  growth 
of  an  embryo  chick.  If  the  development  is  followed  in  a series  of 
eggs  taken  from  an  incubator  at  intervals  of  six  hours  or  less,  this 
spot  will  be  found  to  increase  in  size ; and  later  the  little  embryo 
will  lie  on  the  surface  of  the  yolk.  Still  later  small  blood  vessels 
can  be  seen  reaching  into  the  yolk  for  food,  and  the  tiny  heart  can 
be  seen  beating  as  early  as  the  second  day  of  incubation.  After 
about  three  weeks  of  incubation  the  little  chick  hatches  and 
emerges  in  almost  the  same  form  as  the  adult. 

Development  of  a mammal.  In  most  mammals  after  fertiliza- 
tion the  egg  undergoes  development  within  the  body  of  the  mother. 
The  blood  vessels,  in- 


pla<ient<T.„^ 


.....umVilicoJ  cond 

.Hood  vessel- 
of  parent- 


stead  of  connecting 
the  embryo  with  the 
yolk  as  in  the  chick, 
are  attached  to  an  ab- 
sorbing organ,  known 
as  the  'placenta.  This 
structure  sends 
branchlike  processes 
into  the  wall  of  the 
uterus  (the  organ 
which  holds  the  em- 
bryo) and  absorbs 
nourishment  and  oxy- 
gen by  diffusion  from  the  blood  of  the  mother.  After  a length 
of  time,  which  varies  in  different  species  of  mammals  (from  about 
three  weeks  in  a guinea  pig  to  twenty-two  months  in  an  elephant), 
the  young  animal  leaves  the  protecting  body  of  the  mother,  or  is 
born.  The  young  are  born,  usually,  in  a helpless  condition  and 
are  nourished  by  milk  furnished  by  the  mother  until  they  are  able 
to  take  other  food.  Higher  in  the  scale  of  life,  fewer  eggs  are 
formed,  but  those  few  eggs  are  more  carefully  protected  and  cared 
for  by  the  parents.  The  chances  of  becoming  adults  are  much 


fluid, 


In  a mammal,  the  embryo  is  attached  by  the  umbilical  cord 
to  the  placenta  of  the  parent.  Fluids  surrounding  the  embryo 
in  the  uterus  serve  to  protect  it  against  shock. 


620  IMPROVEMENT  OF  LIVING  THINGS  BY  MAN 


greater  than  are  the  young  of  lower  animals  which  produce  many 
eggs  but  take  no  care  of  them. 

Practical  Exercise  8.  Make  a series  of  colored  diagrams  for  your  workbook 
to  show  stages  in  development  in  (1)  fish,  (2)  frog,  (3)  bird,  (4)  mammal.  Use 
the  same  colors  in  each  series  to  show  the  same  parts.  Get  help  from  as  many 
sources  as  you  can. 

What  would  you  say  were  the  outstanding  differences  in  development  in  the 
groups  just  mentioned  ? 


Self-Testing  Exercises 


Check  the  correct  statements  for  your  workbook. 


T.  F.  1.  Cells  grow  in  size  in  order  to  have  more  food-absorbing 

surface. 

T.  F.  2. 

T.  F.  3. 

from  parts  of 


T.F. 

4. 

duction. 

T.  F. 

5. 

one. 

T.  F. 

6. 

sperms. 

T.  F. 

7. 

T.  F. 

8. 

T.  F. 

9. 

T.  F. 

10. 

T.  F. 

11. 

T.  F. 

12. 

Starfish  and  earthworms  regenerate  lost  parts. 
Vegetative  propagation  means  producing  new  plants 
others. 

Grafting  and  budding  are  examples  of  sexual  repro- 


If  we  have  an  arm  amputated,  we  will  regenerate  another 
Sexual  reproduction  involves  the  fusion  of  eggs  and 
An  ovule  is  an  egg  cell. 

Birds  reproduce  asexually  as  well  as  sexually. 

All  animals  are  produced  from  eggs  and  sperms. 

The  endoderm  is  the  outer  layer  of  a developing  animal. 
The  lower  the  animal  the  more  eggs  are  produced. 
Mammals’  eggs  develop  within  the  body  of  the  mother. 


PROBLEM  III.  WHAT  ARE  THE  LAWS  OF  HEREDITY? 


Heredity  and  the  work  of  Gregor  Mendel.  By  far  the  most 
important  discovery  for  the  plant  and  animal  breeder  was  made  by 
Gregor  Mendel,  the  abbot  of  a monastery  at  Brunn,  in  what 
is  now  Czechoslovakia.  About  1865,  Mendel  bred  peas  in  his 
monastery  garden  and  found  that  certain  characters,  such  as  color 
of  seeds,  color  of  flowers,  smooth  and  wrinkled  coats,  and  other 
characters,  are  inheritable.  Then  he  began  a long  series  of  experi- 
ments in  which  he  crossed  or  hybridized  peas  having  some  of  these 


LAWS  OF  HEKFDITV 


G21 


difforont  charact ors.  For  oxaiiiple,  ho  crossed  tall  plants  with 
short  ones,  and  sinoolh  peas  with  wrinkled  ones.  The  results  of 
these  crossings  showed 
that  tliese  characters 
are  always  transmitted 
to  the  next  generation 
as  not  as  blend- 

ings of  the  two  oppos- 
ing characters.  This 
was  his  first  great  dis- 
covery, the  inheritance 
of  uuif  characters. 

The  law  of  domi- 
nance. But  Alendel 
found,  in  crossing  peas, 
that  the  first  generation 
of  hybrids^  always 
showed  a curious  result. 

One  character  would 
appear,  while  its  oppo- 
site would  seemingly  be 
lost.  If,  for  example, 
smooth  and  wrinkled 
peas  were  crossed,  the 
hybrids  were  all  smooth.  If  tall  and  short  pea  plants  were  bred) 
the  hybrids  were  all  tall,  and  similar  results  were  obtained  with 
other  pairs  of  characters  with  which  he  experimented.  This  gave 
rise  to  the  statement  that  certain  unit  characters  are  dominant 
over  others  which  are  called  recessive  characters. 

The  law  of  segregation.  But  these  recessive  characters  were 
not  really  lost.  If  some  of  the  hybrid  smooth-coated  peas  are 
fertilized  by  others  of  the  same  kind  and  their  seeds  planted,  the 
next  generation  (known  to  breeders  as  the  F2  generation)  will 
include  some  pea  plants  bearing  smooth  peas  and  some  bearing 
wrinkled  peas,  in  the  ratio  of  75 : 25.  One  quarter  of  all  the  peas 

1 Hybrid  : a plant  or  animal  that  contains  a pair  of  widely  different  unit  char- 
acters — as  smooth  and  wrinkled  skins  in  peas. 


tollCl^rid)  talUb/brid)  short 


If  a tall  plant  is  crossed  with  a short  plant  their  off- 
spring I the  Fi  generation)  will  all  be  tall.  If  these  tall 
hybrids  are  then  crossed,  their  offspring  (the  F2  genera- 
tion) will  be  in  the  proportion  of  one  tall,  two  tall  hybrid 
and  one  short. 


622  IMPROVEMENT  OF  LIVING  THINGS  BY  MAN 


show  the  recessive  character.  If  these  peas  having  the  recessive 
character  are  crossed  with  each  other  in  another  generation,  they 
will  produce  all  wrinkled  peas,  the  recessive  character ; and  such 
peas,  when  bred  again  and  again  with  peas  of  the  same  kind, 
will  continue  to  produce  wrinkled  peas.  The  recessive  character 
has  been  segregated  out  and  is  now  known  as  an  extracted  recessive. 


If  peas  with  yellow  seed  coats  are  crossed 
with  peas  with  green  seed  coats,  their  off- 
spring will  be  yellow  hybrids.  Yellow  is 
dominant  to  green  in  color.  If  these  hybrids 
are  cross-poilinated,  the  F2  generation  will  be 
25  per  cent  yellow,  50  per  cent  yellow  hybrids, 
and  25  per  cent  green. 


P 


irmdOa  (^12, 


■e 


g)  r 


RJ2  Ri*  rer-  -i'r 
3tnootr2  smootii  "wHoklecC 
l^bi'idCs 


If  peas  with  smooth  seed  coats  are 
crossed  with  peas  wtih  wrinkled  seed  coats, 
their  offspring  will  all  be  smooth-coated 
hybrids.  Smooth  is  dominant  to  wrinkled. 
If  these  hybrids  are  then  crossed,  the  F2 
generation  will  be  25  per  cent  smooth,  60 
per  cent  hybrid,  and  25  per  cent  wrinkled. 


This  shows  MendeFs  Law  of  Segregation.  Its  importance  in  plant 
and  animal  breeding  can  readily  be  seen. 

The  75  per  cent  of  F2  peas  which  are  seemingly  all  smooth-coated 
are  in  reality  25  per  cent  smooth  and  50  per  cent  mixed,  that  is, 
having  both  characters,  the  recessive  hidden  by  the  dominant. 
If  we  can  separate  the  pure  dominants,  they  will  produce  only 
dominants,  while  the  mixed  hybrids  will  continue  to  breed  domi- 
nants and  recessives  in  the  ratio  of  25  per  cent  dominant,  50  per 
cent  mixed,  and  25  per  cent  recessives. 

In  crossing  white  rats  with  black  ones  black  is  dominant  over 
white,  as  is  seen  in  the  figure  on  page  624.  But  in  the  F2  generation, 
as  in  the  peas  of  Mendel’s  experiments,  the  recessive  color  is  segre- 
gated out.  This  law  of  segregation  works  so  that  when  pure 
dominants  are  mated  with  hybrids  there  is  a segregation  of  50% 
dominants  and  50%  hybrids  and  when  recessives  are  mated  with 


LAW  OF  SEOHFOATION 


623 


n 


grsen  vrt'inklecC 


f2R 


Rr 


rR 


liybrids  we  have  50%  recessives  and  50%  dominants  in  the  next 
generation.  The  production  of  plants  or  animals  having  dominant 
and  recessive  character  is  based  on  the  laws  of  chance.  In  hybrid 
[X'as  (Fi,  page  022),  for  example,  half  the  pollen  grains  would 
bear  germ  cells  con- 
taining the  deter- 
miner of  “ smooth  ” 

{R)  and  half  the 
determiner  of  “ wrin- 
kled ” (/’),  while  in 
the  ovule,  half  would 
contain  the  deter- 
miner “ smooth  ” 
and  half  “ wrinkled.” 

Crossing  them,  we 
have  in  the  F2  gen- 
eration, the  result 
shown  in  the  dia- 
gram. 

Dihybrids  and 
others.  Though 
breeding  for  one  pair 
of  characters  is  com- 
paratively easy  to 
understand,  we  often 
find  breeders  cross- 
ing for  two  or  more 
pairs  of  characters. 

This  is  purely  a 
matter  of  mathematics  (on  paper)  as  the  diagram  on  this  page 
shows,  but  it  is  too  difficult  to  study  in  an  elementary  course  in 
biology.  At  the  present  time  most  of  the  really  worth  while 
work  in  plant  and  animal  breeding  is  being  done  by  this  method 
of  Mendel.  Not  only  does  this  enable  breeders  to  fix  the  unstable 
hybrid  characters,  but  also  it  enables  them  to  combine  worth- 
while characters  such  as  immunity  to  diseases  of  various  kinds, 
early  ripening,  color  or  size  of  fruit,  and  resistance  to  drought. 


Yy 

0 

>fellow  round 

yY 

round 

round 

YY 

-Q 

yellov/ round 

Yy 

■p 

yellow/j^nd 

0 

yalb/ round 

yy 

YV 

-Q 

yellov  round 

Yy 

yellov^wnd 

0 

yello^round 

groen  round 

VY 

yellosv^Wnnklal 

Yy 

yeilowYrtnklal 

yY 

yello\V''Wh'n)itel 

gnaen-^frinkled 

Dihybrids  carry  two  characters.  Here  one  parent  is  carry- 
ing two  dominant  characters  — yellow  color  and  smooth  seed 
coat.  The  other  parent  is  carrying  two  recessive  characters  — 
green  color  and  wrinkled  seed  coat.  In  Fi  generation  all  four 
characters  are  present  but  only  the  dominant  ones  show.  If 
these  hybrids  are  crossed,  the  proportion  of  the  F2  generation 
can  be  predicted  if  the  characters  are  arranged  as  single  pairs 
above  and  on  the  side  of  a series  of  squares.  The  possible 
combinations  of  characters  are  given  in  the  squares. 


624  IMPROVEMENT  OF  LIVING  THINGS  BY  MAN 


Practical  Exercise  9.  Make  a colored  diagram  for  your  workbook  to  show 
the  following  examples  of  Mendel’s  laws  of  dominance  and  segregation. 
Work  out  your  diagram  to  the  Fs  generation : Colored  flowers  of  peas  are 
dominant  over  white.  Green  color  in  pod  is  dominant  over  yellow.  Gray 
coat  color  in  mice  is  dominant  over  white. 

The  practical  results.  Already  some  progress  has  been  made 
in  the  application  of  Mendel’s  laws  to  hybridization.  The  United 


States  Depart- 
ment of  Agricul- 
ture  is  now 
producing  cold- 
resistant  fruits 
and  grains  in  the 
Alaska  experi- 
ment station.  A 
hybrid  which  is  a 
cross  between  the 
watermelon  and 


] the  citron  has 


produced  a fruit 
that  will  resist 


In  rats,  the  black  color  has  been  found  to  be  a dominant  char-  “ wiR  ” a serioUS 
acter,  and  the  white  color  is  a recessive  character.  If  two  rats  ’ 

of  the  second  generation  (Fi ) are  mated,  why  would  they  probably  f UUgUS  diseaSe  of 
have  one  white  and  three  black  offspring?  . „ 


melons.  Rust- 


resisting  wheats  also  have  been  produced  in  this  country;  while 
in  England  experiments  on  wheat  have  resulted  in  the  production 
of  resistance  to  disease,  “ hardness  ” of  grain,  and  increase  in  the 
size  of  the  grain  and  of  the  head  — all  characters  which  mean 
greater  productiveness.  But  most  of  the  hybridizing  is  still  done 
on  a hit-or-miss  principle,  with  few  permanent  results.  Luther 
Burbank,  the  great  hybridizer  of  California,  destroyed  tens  of 
thousands  of  plants  in  order  to  get  one  or  two  with  the  charac- 
ters which  he  wished  to  preserve. 

Animal  breeding.  It  has  been  pointed  out  that  the  domesti- 
cation of  wild  animals  — horses,  cattle,  sheep,  goats,  and  dogs  — 
marked  great  advances  in  civilization  in  the  history  of  mankind. 
As  the  young  of  these  animals  were  bred  in  captivity,  the  people 
owning  them  would  undoubtedly  pick  out  the  strongest  and  best 


IMiOHLEMS  IN  xVNlMAL  lUiEEDING 


625 


of  the  ()fTsprin»:,  killing  tho  others  for  food.  Thus  man  uncon- 
sciously aided  nature  in  producing  a stronger  and  a better  stock. 
Later,  he  Ix'gan  to  recognize  certain  characters  tliat  he  wished 
to  have  in  horses,  dogs,  or  cattle,  and  by  slow  processes  of  breeding 
and  of  “ crossing  ” or  hybridizing  one  nearly  allied  form  with 
another,  the  numerous  groups  of  domesticated  animals  began  to 
be  developed. 

Some  domesticated  animals.  Our  domesticated  dogs  are  de- 
scended from  a number  of  wolf-like  forms  in  various  parts  of  the 
world.  All  the  present  races  of  cats,  on  the  other  hand,  seem  to 
be  traced  back  to  Egypt.  Modern  horses  are  first  noted  in  Europe 
and  Asia,  but  far  older  forms  flourished  on  the  earth  in  earlier 
geologic  periods.  It  is  interesting  to  note  that  America  was  the 
original  home  of  the  horse,  although  at  the  time  of  the  earliest  ex- 
plorers the  horse  was  unknown  here.  The  wild  horse  of  the  West- 
ern plains  has  descended  from  horses  introduced  by  the  Spaniards. 
The  horse,  which  for  some  reason  disappeared-  in  this  country, 
continued  to  exist  in  Europe,  and  man,  emerging  from  his  early 
savage  condition,  began  to  make  use  of  the  animal.  We  know  the 
horse  was  domesticated  in  early  Biblical  times,  and  that  it  was  one 
of  man’s  most  valued  servants.  In  more  recent  times,  man  has  be- 
gun to  change  the  horse  by  breeding  for  certain  desired  characters. 
In  this  manner  the  various  types  of  horses  familiar  to  us  as  draft 
horses,  coach  horses,  hackneys,  saddle  horses,  and  trotters  have 
been  established  and  improved. 

It  is  needless  to  say  that  all  the  various  domesticated  animals 
have  been  tremendously  changed  by  breeding  since  they  were 
brought  under  the  control  of  civilized  man.  When  we  realize 
there  were  in  1934  nearly  12,000,000  horses,  over  67,000,000  cattle, 
over  51,000,000  sheep,  and  about  56,000,000  swine  on  farms  in  this 
country,  representing  a money  value  of  over  $3,562,000,000,  we 
see  how  very  important  a part  the  domestic  animals  play  in  our 
lives. 

Present  problems  in  animal  breeding.  In  spite  of  the  fact 
that  this  vast  amount  of  money  is  represented  by  our  domesticated 
animals,  it  could  and  should  be  much  more.  Crosses  in  fowls 
have  been  obtained  that  produce  as  many  as  300  eggs  from  one 


626  IMPROVEMENT  OF  LIVING  THINGS  BY  MAN 


hen  in  a year ; yet  the  average  hen  lays  less  than  100  eggs  per  year. 
A few  cows  of  superior  breeding  in  some  of  the  state  experiment 
stations  produce  as  much  as  1000  pounds  of  butter  fat  each  in  a 
year,  but  the  average  cow  produces  little  more  than  200  pounds 
a year,  A bulletin  of  the  Department  of  Agriculture  says,  “ Good 
judges  believe  that  in  the  entire  country  one  fourth  of  the  cows 
kept  for  their  milk  do  not  pay  for  their  cost  of  keeping,  and  nearly 
a fourth  more  fail  to  yield  annual  profit.”  This  means  that  many 
farmers  do  not  know  what  their  cows  are  producing.  It  means  that 
many  farmers  are  poor,  through  either  carelessness  or  ignorance. 
The  scientific  breeding  of  milk  cows  would  mean  millions  of  dollars 
in  the  pockets  of  the  farmer,  and  an  increase  in  that  much-needed 
commodity,  milk.  This  is  only  one  of  the  many  problems  of  con- 
servation that  will  eventually  be  solved  by  our  animal  breeders. 

Practical  Exercise  10.  Make  a list  of  all  the  kinds  of  domesticated  animals 
and  plants  in  your  locality  that  are  useful  to  man.  Indicate  on  the  list  all 
those  that  you  know  have  been  improved  by  such  factors  as  : selection,  budding, 
grafting,  crossing  or  hybridizing,  use  of  Mendel’s  laws,  etc.  After  discussion 
in  class  make  a revised  table  for  your  workbook. 

Self-Testing  Exercise 

Mendel  discovered  through  experimentation  the  inheritance  of 

(1) (2).  Through  breeding,  some  of  these (3) 

(4)  can  be (5).  Most  new (6)  produced 

by  Luther  Burbank  were  (7).  Certain  unit  characters  are 

(8)  over  other  characters  which  are  (9).  If  two 

hybrids  are  mated,  their  offspring  will  be (10)  per  cent  re- 
cessive and  (11)  per  cent  dominant  in  respect  to  any  unit 

character. 

PROBLEM  IV.  WHAT  DETERMINES  HEREDITY 

Chromosomes  the  bearers  of  heredity.  We  have  learned  that 
a cell  contains  a nucleus,  in  which  are  certain  very  minute  struc- 
tures known  as  chromosomes  (because  they  take  up  color  when 
stained).  When  cells  divide,  each  chromosome  divides  by  splitting 
lengthwise,  so  that  equal  amounts  of  each  chromosome  are  thus 
carried  into  the  new  cells  formed  from  the  original  cell.  These 
chromosomes  are  believed  to  be  the  structures  which  contain  the 


CIIKOMOSOMKS  THE  BEAREIiS  OF  HEREDITY  627 


genes  ovdeterniinersoi  the  qualities  which  may  be  passed  from  parent 
to  offspring;  in  other  words,  the  qualities  that  are  inheritable. 

The  germ  cells.  It  has  been  found  that  certain  cells  of  the  body, 
the  egg  and  the  sperm  cells,  before  uniting  usually  contain  only 
half  as  many  chromosomes  as  do  the  body  cells. ^ In  preparing 
for  the  process  of  fertilization,  half  of  these  elements  have  been 
eliminated  by  reduction  division  (diagram,  p.  G30),  so  that  when  the 
egg  cell  and  the  sperm  cell  are  united  they  will  have  the  same 
number  of  chromosomes  as  the  other  cells  of  the  body. 

We  have  already  learned  that  in  the  process  of  fertilization  the 
nuclei  of  the  sperm  and  of  the  egg  cell  unite,  or  fuse,  to  form  a new 
nucleus  in  the  fertilized  egg.  This  fertilized  egg  will  contain  an 
equal  number  of  chromosomes  from  each  parent.  Since  the 
inheritable  characters  are  contained  in  the  chromosomes,  both 
parents  will  hand  down  an  equal  number  of  .characters  to  their 
offspring.  In  this  way  characters  from  each  parent  are  handed 
down  to  the  new  individual. 

Investigations  of  heredity  have  centered,  in  recent  years,  on 
the  composition  and  action  of  the  chromosomes.  It  has  been 
found  that  they  differ  in  number  according  to  the  species  of  the 
animal.  In  the  fruit  fly  there  are  eight  chromosomes  in  each  body 
cell ; in  the  mosquito  Culex  there  are  six,  in  the  rat  sixteen,  in  the 
frog  twenty-six,  in  certain  crustaceans  more  than  one  hundred  and 
fift}^  in  one  spider  a hundred  and  sixty-eight.  In  some  animals,  as 
has  been  shown,  the  number  differs  with  sex.  Man  is  believed  to 
have  forty-eight. 

Professor  Morgan,  of  the  Institute  of  Technology,  Pasadena, 
California,  has  found,  as  a result  of  investigations  on  the  fruit  fly 
(drosophila),  that  each  chromosome  is  actually  composed  of  genes 
or  the  inheritable  material  that  represents  unit  characters,  and 

1 This  is  not  quite  exact,  for  it  has  been  found  that  in  some  animals  at  the  time 
when  the  chromosomes  are  reduced  in  number,  there  is  an  even  number  in  the 
female  sex  cells  but  an  odd  number  in  the  male  sex  cells.  When  the  male  cells 
divide  to  reduce  the  number  of  chromosomes,  some  sperm  cells  receive  an  odd 
and  some  an  even  number  of  chromosomes.  Therefore,  after  fertilization,  some 
eggs  have  an  even  and  some  an  odd  number  of  chromosomes.  The  fertilized  egg 
cells  with  the  odd  number  of  chromosomes  develop  into  male  animals ; the  cells 
with  the  even  number  of  chromosomes  become  females.  The  sex-determining 
chromosome  is  known  as  the  X-chromosome  and  is  found  in  some  wortns,  many 
insects,  myriapods,  spiders,  and  some  mammals,  including  man. 


628  IMPROVEMENT  OF  LIVING  THINGS  BY  MAN 


that  some  of  these  characters  are  linked  together  in  the  same  sex. 
This  would  explain  some  of  the  characters  common  only  to  male 
or  to  female  animals. 

It  is  plain  that  with  forty-eight  chromosomes,  each  of  which  is 

probably  made  up  of  a 


^hite  <2.ye. 


normal  vring’-t 


"vennilion  <^e 
tniniature'wihif/r 


rudimentary  •w\t 


complete^ 


_.J..re^  e 


-.nor mol  v/ind' 


. .miniotujrc- 


j-forVea:  in'^ks 
..bair 


large  number  of  genes 
or  determiners,  hered- 
ity in  man  is  a very 
complicated  matter  at 
best.  For  a number 
of  unit  characters  have 
been  found  which  are 
inheritable  according 
to  Mendel’s  laws,  and 
undoubtedly  others 
will  be  added  as  we 
learn  more  about  the 
working  of  these  laws. 

But  this  mechanism 
of  heredity  is  not  as 
simple  as  it  seems.  In 
the  first  place  the 
genes  are  ultra-microscopic.  One  scientist  has  said : “ If  we 
magnified  a hen’s  egg  to  the  size  of  the  world  (which  would  make 
atoms  rather  larger  than  eggs  and  electrons  barely  visible),  we 
could  still  get  a gene  into  a room  and  probably  on  a small  table.” 
Moreover,  each  chromosome  probably  contains  hundreds  if  not 
thousands  of  genes.  It  is  clear  then  that  experiments  which  will 
attempt  to  separate  the  genes  and  make  new  characters  appear  in 
the  offspring  will  be  extremely  difficult,  to  say  the  least. 


Diagram  of  chromosomes  of  the  fruit  fly,  showing  that 
genes  for  certain  characteristics  are  found  in  different 
parts  of  the  chromosomes. 


Practical  Exercise  11.  Make  a diagram  of  a chromosome  and  place  in  it 
genes  or  determiners  for  some  of  the  unit  characters  given  on  pages  630-631. 


At  the  time  of  fertilization  of  the  egg  cell  the  genes  or  determiners 
in  the  sperm  cell  are  added  to  those  in  the  egg  cell  and  are  then 
handed  down  as  unit  characters.  Thus  a child  inherits  characters 
from  both  parents. 


CHROMOSOMES  629 

Here  is  what  Professor  II.  S.  Jennings,  geneticist,  of  Johns 
Hopkins  University  says  concerning  the  genes: 

“ ]']vcry  pair  of  human  parents  contains  thousands  of  i)airs  of  the 
l)aekets  (genes)  of  elunnieals  on  which  devclopiiieiit  depends.  From 
these  a set  is  drawn  almost  at  random  (subject  to  the  condition  that 
one  i)acket  is  taken  from  each  i)air  possessed  by  each  parent) ; this 
constitutes  the  heritage  of  the  child.  Any  pair  of  parents  may  thus 
produce  not  merely  thousands  but  millions  of  different  combinations, 
each  yielding  a child  of  different  characteristics.  There  is  no  way  of 
controlling  the  combinations  that  shall  enter  into  a child  of  given 
parents  ; there  is  no  i)rospect  that  there  ever  will  be.  It  is,  therefore, 
impossible  to  predict  what  kind  of  offspring  will  be  produced  by  a given 
pair  of  parents  — save  in  a few  respects,  in  cases  where  the  constitution 
of  both  packets  of  a particular  pair  are  known  for  each  parent.  If  both 
parents  have  the  corresponding  pairs  defective  in  the  same  manner  — 
lacking,  for  example,  something  required  for  producing  a normal 
mind  — then  their  children  will  be  all  defective  like  the  parents ; 
feeble-minded  parents  will  produce  feeble-minded  children.  But  if, 
as  may  well  be  the  case,  the  feeble  mind  is  due  to  defects  in  different 
packets  in  the  two  parents,  then  all  experimental  breeding  shows  that 
the  two  parental  stocks  may  supplement  one  another,  so  that  the 
defect  will  not  appear  in  the  offspring.  These  characteristics  that 
are  predictable  are  extremely  few.”  — From  Prometheus  by  Jennings, 
published  by  E.  P.  Dutton  & Co. 

More  recently  we  have  found  that  heredity  is  complicated  by 
another  factor.  We  have  already  learned  that  the  hormones  play 
a very  important  part  in  regulating  life  activities  and  that  the  over- 
activity or  underactivity  of  certain  glands  may  produce  profound 
changes  in  an  organism.  The  under-  or  overdevelopment  of  the 
pituitary  gland,  for  example,  causes  a dwarf  or  a giant  to  result, 
and  other  of  our  ductless  (endocrine)  glands  have  almost  as 
startling  results.  The  use  of  the  X-ray  in  experimental  biology 
has  brought  about  strange  results.  Professor  Muller  of  the 
University  of  Texas  has  recently  produced  about  100  new 
varieties  of  fruit  fly,  which  breed  true,  simply  by  keeping  the  flies 
under  the  X-ray  for  certain  periods  of  time.  We  are  finding  out 
that  our  problems  of  breeding  are  not  as  easy  to  solve  as  we  first 
hoped. 


Practical  Exercise  12.  Make  a report  on  the  action  of  some  one  endocrine 
gland.  Get  material  from  Harrow’s  “ Glands  in  Health  and  Disease,”  or 
use  the  Readers  Guide  to  find  titles  of  articles  on  the  endocrines. 

H.  BIO  — 41 


630  IMPROVEMENT  OF  LIVING  THINGS  BY  MAN 


Tnofher  ■' 
reprocCuctive 


Offspring  are  part  of  their  ancestors.  If  you  receive  characters 
from  your  parents  and  they  received  characters  from  their  parents, 

then  you  must  have 
some  of  the  char- 
acters of  the  grand- 
parents.  As  a 
matter  of  fact  each 
of  us  does  have 
some  traits  or  line- 
aments which  can 
be  traced  back  to 
a grandfather  or 
grandmother.  In- 
deed, as  far  back 
as  we  are  able  to 
go,  ancestors  have 
contributed  some- 
thing. 


periocC  of 
gr-oN^th. 


The  “ mother  ” reproductive  cells  divide  and  one  of  the  resulting 
cells  grows  larger.  During  this  period  of  growth  each  cell  divides 
in  such  a way  that  one  half  of  the  chromosomes  goes  to  each  of  the 
daughter  (or  resulting)  cells.  Each  female  cell  gives  rise  to  one 
egg  and  three  small  cells.  The  egg  has  most  of  the  yolk  and  is 
generally  the  only  one  that  will  be  fertilized.  The  large  male  cell 
divides,  and  gives  rise  to  four  sperms,  all  the  same  size,  and  all 
of  which  can  function.  Each  sperm  will  contain  one  half  the 
number  of  chromosomes  found  in  the  large  cell.  One  sperm 
unites  with  the  mature  egg  in  the  process  of  fertilization. 


Practical  Exercise 
13.  Study  the  dia- 
gram carefully.  How 
can  you  account  for 
the  different  combina- 
tions in  the  four  ferti- 
lized eggs  shown  at 
the  bottom  of  the  di- 
agram? What  seems  to  be  the  reason  for  the  “ reduction  ” division? 

Turn  over  to  the  diagram  on  page  628.  Make  a similar  diagram  for  your 
workbook  that  will  show  how  a chromosome  in  an  egg  and  a sperm  cell  might 
contain  genes. 


Characters  known  to  be  inheritable.  The  following  table 
indicates  some  of  the  characters  in  man  that  have  been  proved  to 
be  inheritable  according  to  the  laws  of  Mendel. 


Dominant  Character 
Black  or  brown  eye 
Pigmented  iris 
Dark  skin 
Curly  hair 
Dark  hair 

Congenital  white  lock 
Beaded  hair 
Nervous  temperament 


Recessive  Character 
Blue  or  gray  eye 
No  pigment  in  iris 
Light  skin 
Straight  hair 
Light  hair 
Normal  hair 
Straight  hair 
Phlegmatic  temperament 


CIlARAC’TKliS  KNOWN  TO  BE  INHERITABLE  631 


Miicli  study  li;is  boon  given 
susceptibility  to  diseases.  The 
inately  correct. 

Dominant  Character 
'rwo-jointetl  fingers 
Extra  digit 

Congenital  cataract  of  eye 
.\hnorinally  short  limbs 
Hairless  or  toothless  condition 
Spotted  hair  coat 


to  the  inheritance  of  defects  and 
following  list  probably  is  approxi- 

Recessive  Character 
Normal  fingers 
Normal  number  of  digits 
Normal  condition  of  eye 
Normal  limbs 
Normality 
Normality 


Cases  where  the  defect  is  recessive  to  the  normal  condition  are 
much  more  difhcult  to  find,  but  the  following  examples  appear  to 
be  well  established,  according  to  Guyer : 


Dominant  Character 
Normal  pigment 
Normal  intellect 
Normal  intellect 


Normality 

Normality 

Normality 

Normality 


Recessive  Character 
Albino  skin 
Feeble-mindedness 

Alcoholism  (when  based  on  feeble- 
mindedness) 

Susceptibility  to  cancer 
Tendency  to  asthma  or  hay  fever 
Probable  susceptibility  to  tuberculosis 
Lack  of  muscular  control 


Self-Testing  Exercise 

Chromosomes  are  the (1)  of (2)  characters.  The 

fertilized  egg  contains (3)  or (4)  from  both  parents. 

(5)  are  definite  in  number  for  each  species  of  animal  or 

plant.  The  triangle  of  life  consists  of  •••(6),  (7), 

and  (8).  Certain  characteristics,  such  as  (9), 

(10),  and (11),  appear  to  be  inherited  according  to 

IMendel’s  Laws.  Dark  skin  is  a (12)  character,  light  skin  a 

(13)  character.  One’s  heredity  may  be  affected  by  the 

(14)  from, the  endocrine  glands.  The  size  of  giants  and 

dwarfs  appears  to  be  determined  by  the  size  of  the (15)  gland. 


PROBLEM  V.  HOW  ARE  NEW  VARIETIES  OF  PLANTS  AND 
ANIMALS  PRODUCED 

Laboratory  Exercise.  To  determine  whether  there  is  individual 
variation  in  any  one  measurement  of  the  members  of  a given  class. 

With  a string  carefully  measure  the  length  of  your  arm  from  the 
finger  tips  to  the  elbow.  Take  measurements  on  back  of  hand. 


632  IMPROVEMENT  OF  LIVING  THINGS  BY  MAN 


Verify  your  figures  by  having  your  neighbor  take  the  measurement 
for  you.  Do  the  same  thing  for  him.  The  instructor  will  give  you  an 
individual  number.  Hand  in  your  results  with  your  number  to  one 
pupil  in  the  class,  who  will  tabulate  the  figures  on  the  board. 

Make  a graph  showing  individual  variation  in  circumference  of  the 
wrist  in  the  members  of  your  class.  What  are  your  conclusions? 


Two  types  of  variations  occur.  Variations  in  nature  appear  to 
be  of  two  types.  If  we  measure  the  size  of  a large  number  of  peas 
or  beans,  we  find  that  though  most  of  them  are  of  a certain  size, 


01  2^^3<d7Q9‘ioa\\ 


Cases  3 5 do  20  34  47  54-  44  40  Z\  20  5 


The  number  of  markings  on  a random  313  sunflower  seeds  was  counted.  The  result  of  this 
experiment  is  recorded  in  the  diagram. 


others  will  be  a little  larger  or  a little  smaller,  and  a very  few  will 
be  very  large  or  very  small.  A graph  can  be  made  from  the  results, 
which  shows  an  even  curve,  known  as  Quetelet’s  (ketdaz)  Curve. 
Such  variations  are,  to  a large  degree,  changes  brought  about  as 
the  result  of  differences  in  environment  upon  the  plants  produc- 
ing the  seed  and  are  called  fluctuating  variations.  Such  fluctuating 
variations  would  not,  therefore,  influence  the  heredity  of  the  next 
generation,  as  they  have  no  influence  upon  the  sex  cells.  On  the 
other  hand,  some  variations  are  due  to  certain  combinations  of 
chromosomes  and  as  such  are  inheritable.  This  makes  the  problem 
very  difficult  for  the  scientific  plant  or  animal  breeder. 

Occasionally,  however,  sudden  changes  or  discontinuous  varia- 
tions occur.  Such  was  the  famous  ancon  ram  which  suddenl.y 


VAJUATIONS 


633 


appeared  in  1701  in  Massachusetts.  This  ram  had  such  short  legs 
that  it  could  not  jump  fences.  Hornless  cattle,  albinos,  and  the 
famous  beardless  wheat  found  by  Mr.  Fultz  are  examples  of  such 
variations.  These  are  called  mutants  or  sports.  The  term  “mu- 
tant ” has  of  later  years  been  associated  with  the  Dutch  naturalist, 
Hugo  de  \'rics.  \Try  rarcl}^,  as  he  found, 
chance  mutations  appear  which  breed  true. 

In  the  evening  primrose,  for  example,  he  found 
eight  different  mutations.  This  means  that 
new  species  in  nature  may  arise  suddenly,  in- 
stead of  by  very  slow  degrees,  as  Darwin  be- 
lieved. The  reason  that  such  variations  as 
these  always  breed  true  is  because  the  germ  or 
sex  cells  of  the  animal  or  plant  are  affected  and 
thus  the  variations  can  be  handed  down  to  the 
next  generation.  It  is  easily  seen  that  such 
variations  would  be  of  immense  value  to  breed- 
ers, as  plants  and  animals  much  unlike  their 
parents  might  be  formed  and  perpetuated. 

About  1910,  a bean  mutant  appeared  in  the 
South  which  was  adapted  to  life  in  the  cotton 
belt.  As  a result,  more  than  6,000,000  acres  of 
these  beans  were  grown  by  1917.  Mutants  bearded 

have  appeared  in  tobacco,  barley,  wheat,  oats, 
tomatoes,  and  potatoes.  One  of  the  important  parts  of  the  work 
of  the  plant  breeder  is  to  discover,  isolate,  and  breed  useful 
mutations. 

Practical  Exercise  14.  Read  and  report  to  class  something  about  the  life 
and  work  of  De  Vries. 

Practical  Exercise  16.  Make  a list,  using  any  source  material,  of  at  least 
ten  plants  and  five  animal  mutants. 

Practical  Exercise  16.  What  type  of  variation  is  probably  seen  in  the 
curve  you  constructed  as  the  result  of  your  Laboratory  study  on  page  631? 

Selective  planting.  By  selective  planting  we  mean  choosing 
the  best  plants  and  planting  their  seeds  with  a view  of  improving 
the  weld  in  some  definite  ways.  In  doing  this  we  must  not  neces- 
sarily select  the  most  perfect  fruits  or  grains,  but  must  select  seeds 
from  the  best  plants.  Experiments  in  corn  selection  at  the  Uni- 


The  beardless  wheat  is 


634  IMPROVEMENT  OF  LIVING  THINGS  BY  MAN 


versity  of  Illinois  have  shown  that  the  oil  content  of  the  grain,  the 
starch  content,  the  position  of  the  ear  on  the  plant,  and  other 
factors  could  be  improved,  but  no  new  factor  has  been  produced. 

In  a government  test  of  corn  to  increase  the  yield,  ears  were 
chosen  from  plants  that  gave  a high  yield ; seed  from  these  ears 
was  planted  in  rows  alternating  with  seed  from  equally  good- 
looking  ears  from  the  same  kind  of  corn  not  selected  for  its  high 
yield.  Note  the  results  with  eight  pairs  of  ears. 


Pounds  of  Corn  Yielded  by  the  Seed  op  One  Ear 

Field  Ears 

Ears  from  High-Yielding  Parents 

170  lbs. 

177.5  lbs. 

139.5 

180 

139 

199 

173 

197 

154 

172 

133 

176 

156.5 

194 

153 

200.5 

What  per  cent  of  increase  was  there  from  the  selected  corn? 
If  the  seed  from  the  field-grown  corn  yielded  42  bushels  per  acre, 
what  would  have  been  the  gain  per  acre  by  planting  seed  from  the 
selected  corn  ? State  results  both  in  bushels  and  in  dollars,  assum- 
ing corn  to  be  worth  50  cents  per  bushel. 

In  selecting  wheat  we  might  breed  for  a number  of  different  char- 
acters, such  as  more  starch,  or  more  protein  in  the  grain,  a larger 
yield  per  acre,  ability  to  stand  cold  or  drought,  or  to  resist  plant 
disease.  But  although  selection  is  the  one  most  important  method 
for  bettering  production  of  crops,  it  is  after  all  a hit-or-miss  method, 
as  we  do  not  know  whether  we  are  selecting  variations  that  are 
inheritable.  Therefore  in  order  to  produce  new  varieties  of  plants, 
another  method  is  used,  known  as  hybridization. 

Practical  Exercise  17.  Suppose  you  were  selecting  seed  corn  from  an  acre 
for  a large  yield.  How  would  you  go  about  making  the  selection?  Would 
you  select  from  large  plants  with  large  ears  or  plants  bearing  large  kernels  of 
corn?  Give  reasons. 

Hybridization.  We  have  already  learned  that  pollen  from  one 
flower  may  be  carried  to  another  of  the  same  species  and  produce 


llYBIilDIZATION 


()35 

seeds.  If  pollen  from  one  plant  is  placed  on  the  pistil  of  another 
of  an  allied  species  or  variety,  fertilization  may  take  place  and  new 
plants  will  be  eventually  produced  from  the  seeds.  This  process 
is  known  as  hybridizine;,  and  the  plants  produced  by  this  process 
known  as  hybrids.  This  process  is  a most  painstaking  one,  if 
worth-while  results 
are  to  be  obtained. 

The  two  plants  to 
be  crossed  must  be 
selected  with  great 
care,  they  must  be 
carefully  protected 
from  possible  self- 
pollination,  and  the 
transfer  of  pollen 
must  be  so  re- 
stricted that  no 
pollen  except  the  desired  kind  shall  reach  the  pistil.  After  the 
transfer  of  pollen,  the  flower  must  be  covered,  to  prevent  any  other 
alien  pollen  from  reaching  the  pistil. 

Hybrids  are  extremely  variable  and  often  are  apparently  unlike 
either  parent  plant.  Most  hybrids  have  to  be  perpetuated  by 
means  of  some  of  the  methods  of  vegetative  propagation,  as  they 
rarely  breed  true  and  often  do  not  produce  seeds. 

Practical  Exercise  18.  What  kind  of  plants  would  you  select  for  a hybridiz- 
ing experiment  ? Why  are  all  parts  of  the  flower  except  the  pistil  cut  away  in 
the  diagram  above?  What  will  happen  to  the  pollen  placed  on  the  stigma? 
Why  is  the  flower  covered  after  artificial  pollination? 

Self-Testing  Exercise 

All  plants  and  animals  in  nature  tend  to (1) (2) 

tends  to  make  living  things  like  their  ancestors (3)  varia- 
tions do  not  influence  heredity (4)  variations  or 

(5)  produce  new  kinds  of  plants  that  breed  true.  In  selective  planting 

the  farmer  picks  out  the (6)  from  the (7) (8) 

rather  than  most  perfect  (9) (10)  (11) 

produces  no  new (12)  in  plants. 


636  IMPROVEMENT  OF  LIVING  THINGS  BY  MAN 


PROBLEM  VI.  HOW  DO  THE  LAWS  OF  HEREDITY  APPLY 
TO  MAN? 

Since  our  knowledge  of  heredity  has  been  increased,  the  demand 
has  become  more  urgent  that  we  do  something  to  prevent  the  race 
from  handing  down  diseases  and  other  defects,  by  applying  to 
man  some  of  the  methods  we  employ  in  breeding  plants  and 
animals.  This  is  not  a new  idea.  The  Greeks  in  Sparta  had  it  ; 
Sir  Thomas  More  wrote  of  it  in  his  Utopia;  and  today  it  is  brought 
to  us  as  the  science  of  eugenics  (u-jen'iks).  This  word  comes  from 
the  Greek  word  eugenes,  which  means  well  born.  Eugenics  is  the 
science  of  being  well  born,  or  born  well,  healthy  and  fit  in  every 
way.  A tendency  to  cancer,  tuberculosis,  epileptic  fits,  or  feeble- 
mindedness is  a handicap  which  it  is  not  merely  unfair,  but 
criminal,  to  hand  down  to  posterity. 

Two  notorious  families.  Studies  have  been  made  on  a number 
of  different  families  in  this  country,  in  which  mental  and  moral 
defects  were  present  in  one  or  both  of  the  parents  as  far  back  as  it 

was  possible  to  trace  the 
family.  The  “Jukes” 
family  is  a notorious  ex- 
ample. “Margaret,  the 
mother  of  criminals,  is  the 
first  mother  in  the  family 
of  whom  we  have  record.” 
Up  to  1915  2094  members 
of  this  family  had  been 
traced ; 1600  were  feeble- 
minded or  epileptic,  310 
were  paupers,  more  than 
300  were  immoral  women, 
and  140  were  criminals. 
The  family  has  cost  the 
state  of  New  York  more 
than  $2,500,000,  besides  immensely  lowering  the  moral  tone  of  the 
communities  in  which  members  of  the  family  live. 

Another  careful  investigation  concerned  the  so-called  “Kallikak” 
family.  This  notorious  family  was  traced  to  Martin  Kallikak,  a 


o- 


i 666b  6 6 „ _ j 

'5ooctescend0nts,all  normal  Martin, Jr: 


ib44'66' 

446ii655ii4i4iii 

□t- 

^leborab  ffl  J 

#4455"  iTi  464 

O means  normal  woman;  □,  normal  man;  the 
solid  black  indicates  feeble-mindedness,  and  the  small 
black  circle  means  died  in  infancy.  A study  of  the 
Kallikak  family  was  made  by  Goddard,  who  traced 
back  the  history  from  Deborah. 


SOCIAL  PARASITES 


637 


yoiin*’;  yoldior  of  tlie  War  of  tlie  Rovohition,  and  a feeble-minded 
girl,  who  have  had  480  known  descendants.  Of  these  33  were 
sexually  immoral,  24  confirmed  drunkards,  3 epileptics,  and 
143  feebk'-minded.  'riie  man  who  started  this  terrible  line  of 
immoralit}'  and  feeble-mindedness  later  married  a normal  Quaker 
g'irl.  From  this  couple  a line  of  496  descendants  was  traced,  and 
in  no  instance  were  there  any  cases  of  feeble-mindedness.  The 
evidence  and  the  moral  speak  for  themselves. 

Parasitism  and  its  cost  to  society.  Hundreds  of  families,  such 
as  those  described,  exist  today,  spreading  disease,  immorality,  and 
crime  in  all  parts  of  this  country.  The  cost  to  society  of  such 
families  is  very  great.  Just  as  certain  animals  or  plants  become 
l^irasitic  on  other  plants  or  animals,  these  families  have  become 
parasitic  on  society.  They  not  only  do  harm  to  others  by  corrupt- 
ing, by  stealing,  and  by  spreading  disease,  but  they  have  to  be 
protected  and  cared  for  by  the  state  out  of  public  money.  It  is 
estimated  that  between  25  per  cent  and  50  per  cent  of  all  prisoners 
in  penal  institutions  are  feeble-minded.  Largely  for  them  the 
poorhouse  and  the  asylum  exist.  They  take  from  society,  but 
they  give  nothing  in  return.  They  are  social  parasites. 

The  remedy.  One  unfortunate  fact  is  that  feeble-minded 
people  have  little  sense  of  morality,  for  they  do  not  have  a normal 
mental  de^nlopment.  Feeble-mindedness  is  a very  serious  prob- 
lem, for  it  is  estimated  that  at  the  lowest  figure  there  are  probably 
300,000  feeble-minded  persons  in  this  country,  most  of  whom  are 
free  to  breed  their  kind.  The  only  real  remedy  seems  to  be  to 
segregate  the  feeble-minded  according  to  sexes  in  asylums  and  to 
prevent  their  marriage  and  the  possibilities  of  perpetuating  a low 
and  degenerate  race.  Remedies  of  this  sort  have  been  tried  suc- 
cessfully in  Europe  and  are  now  meeting  with  success  in  various 
parts  of  this  country. 

Traits  that  are  inherited.  Eugenics  shows  us,  on  the  other  hand, 
in  a study  of  families  in  which  brilliant  men  and  women  are  found, 
that  the  descendants  have  received  good  inheritance  from  their 
ancestors. 

The  famous  Edwards  family  is  often  used  to  show  the  results 
of  good  heredity.  In  1667  two  brilliant  people  married  in  Hart- 


638  IMPROVEMENT  OF  LIVING  THINGS  BY  MAN 


ford,  Connecticut.  They  were  Elizabeth  Tuttle  and  Richard 
Edwards.  From  this  couple  came  a long  line  of  descendants  most 
of  whom  were  more  than  ordinary  minds.  Numerous  college 
presidents,  professors,  writers,  lawyers,  and  leaders  were  in  the 
list,  while  from  the  daughters  of  Elizabeth  Tuttle  descended  two 
presidents  of  the  United  States  and  many  others  of  note.  The 
chart  below  shows  the  inheritance  in  another  notable  family. 

Many  other  similar  cases  might  be  cited.  Although  we  do  not 
tnow  the  precise  method  of  inheritance,  we  do  know  that  musical 


3os\(^nyexif5(3'^oaJ.  Erasmus  Darvin 

Mil  I C3 


G<5«ltOT2. 


H-fO  LtjO 
lirO  ' [5p~7)raoS 

i5o^J5S55SJa 


SlrFmncjs  ^ivVoualas 
Oalt^n  Caaltoft. 


jSir  Georgel  Sir  Franci?  Wajor-  Horae® 

M)ar'win.  hjarvin.  Leonard 

TJarvin  hIb 


The  family  tree  of  Charles  Darwin.  B,  means  marked  scientific  ability;  H,  very  marked 
scientific  ability. 


and  literary  ability,  calculating  ability,  remarkable  memory, 
mechanical  skill,  and  many  other  mental  and  physical  characters 
are  inheritable  and  “run  in  families.”  The  Wedgewood  family, 
from  which  three  generations  of  Darwins  have  descended,  and  the 
Galton  family  are  examples  of  a scientific  inheritance  ; the  Arnolds, 
Hallams,  and  Lowells  were  prominent  in  literature ; the  Balfours 
were  political  leaders ; the  Bach  and  Mendelssohn  families  were 
examples  showing  inheritance  of  musical  genius.  A comparison 
of  fathers’  and  sons’  college  records  at  Oxford  University  shows 
it  is  usually  “like  father,  like  son”  as  regards  grades.  The  fathers 
who  did  well  had  sons  who  did  well  also.  It  is  said  that  26  out 
of  46  men  chosen  to  the  Hall  of  Fame  of  New  York  University  had 
distinguished  relatives.  Blood  does  tell.  Or  rather  the  genes 
in  the  chromosomes  tell  the  story. 


639 


study  this  chart  carefully.  What  evidence  have  v/e  that  heredity  plays  a part  in  shaping  the  careers  of  individuals  in  certain  families? 
(Redrawn  from  chart  by  Dr.  H.  H.  Laughlin,  Department  of  Genetics,  Carnegie  Institution  of  Washington) 


640  IMPROVEMENT  OF  LIVING  THINGS  BY  MAN 


How  to  use  our  knowledge  of  heredity.  Two  applications  of 
this  knowledge  of  heredity  stand  out  for  us  as  high  school  students. 
One  is  in  the  choice  of  a mate,  the  other  in  the  choice  of  a vocation. 
As  to  the  first,  no  better  advice  can  be  given  than  the  old  adage, 
“ Look  before  you  leap.’’  If  this  advice  were  followed,  there 
would  be  fewer  unhappy  marriages  and  divorces.  Remember  that 
marriage  should  mean  love,  respect,  and  companionship  for  life. 
The  heredity  of  a husband  or  a wife  counts  for  much  in  making 
this  possible.  And,  even  though  you  are  in  high  school,  it  is 
only  fair  to  yourselves  that  you  should  remember  the  responsibility 
that  marriage  brings.  You  should  be  parents.  'Will  you  choose 
to  have  children  well  born  ? Or  will  you  send  them  into  the  world 
with  an  inheritance  that  will  handicap  them  for  life  ? 

Practical  Exercise  19.  Work  out  the  inheritance  of  certain  traits  or  peculi- 
arities in  your  own  family. 

Practical  Exercise  20.  Look  up  the  history  of  one  of  the  families  mentioned 
on  page  639  and  see  what  you  can  find  out  about  their  mental  inheritance. 
Use  all  sources  of  help,  such  as  Davenport’s  Heredity  in  Relation  to  Eugenics, 
Walter’s  Genetics,  or  Guyer’s  Bemg  Well  Born. 


Self-Testing  Exercise 

Feeble-mindedness  could  be  stamped  out  if  (1)  of  such 

persons  could  be  (2).  Blood  or  (3)  count,  as  is 

proven  by  the  (4),  (5),  and  (6)  families. 

Parasitism  in  (7)  is  largely  caused  by  the  (8)  or 

socially  unfit  people.  The  science  of  being  well  born  and (9) 

is  called (10). 


Review  Summary 

Test  your  knowledge  of  the  unit  by:  (1)  rechecking  on  the  survey  ques- 
tions ; (2)  performing  all  assigned  exercises ; (3)  checking  with  your  teacher 
on  all  tests  and  trying  again  the  ones  you  missed ; (4)  making  an  outline  of  the 
unit  for  your  workbook. 


Test  on  Fundamental  Concepts 

In  vertical  column  under  the  heading  CORRECT  write  numbers  of  all  statements  you  be- 
lieve are  true.  In  another  column  under  INCORRECT  write  numbers  of  untrue  statements. 
Your  grade  = right  answers  X 2b 

I.  The  environment  (1)  may  change  the  form  and  traits  of  a plant 
or  an  animal ; (2)  affects  the  offspring  of  plants  and  animals ; 


TEST  ON  FUNDAMENTAL  CONCEPTS  ‘ 641 

(3)  causes  changes  in  organisms  that  ma}’-  be  inheritable;  (4)  causes 
changes  in  organisms  that  arc  not  inheritable. 

II.  Examples  of  asexual  reproduction  are  (5)  conjugation  of  spir- 

ogyra ; (b)  budding  of  yeast ; (7)  egg  laying  of  fish ; (8)  grafting 

of  trees. 

III.  Hereditary  qualities  are  believed  to  be  handed  down  from 
one  generation  to  another  (9)  through  the  protoplasm  of  the  body 
cells  ; (10)  by  means  of  genes  found  in  the  chromosomes;  (11)  unless 
the  environment  changes;  (12)  through  the  sex  cells  only. 

IV.  Variations  (13)  are  changes  in  structure  which  may  occur  in  all 
succeeding  generations  ; (14)  are  continuous  or  discontinuous ; (15)  if 
continuous,  are  valuable  to  plant  or  animal  breeders,  as  they  form  new 
varieties  that  breed  true;  (16)  cause  various  types  of  animals  to  be 
developed. 

V.  Hybridizing  (17)  consists  in  crossing  two  related  species; 

(18)  always  results  in  the  formation  of  offspring  that  breed  true; 

(19)  results  in  the  formation  of  plants  which  differ  from  their  parents; 

(20)  is  a method  of  breeding. 

VI.  Genes  are  (21)  believed  to  contain  the  determiners  of  unit 
characters ; (22)  found  in  all  body  cells ; (23)  found  in  the  chromo- 
somes ; (24)  found  in  both  sperm  and  egg  cells. 

VII.  Mendel’s  laws  of  heredity  (25)  show  that  certain  character- 
istics are  inheritable;  (26)  are  not  used  by  breeders  as  they  are  not 
reliable ; (27)  show  that  certain  characters  are  dominant  over  others ; 
(28)  show  that  unit  characters  may  be  segregated  out  in  the  ratio  of 
3 : 1 in  the  second  filial  generation. 

VIII.  Studies  of  various  families  show  that  (29)  feeble-mindedness 
is  inherited;  (30)  artistic  ability  is  inherited;  (31)  tuberculosis  is 
inherited ; (32)  persons  possessing  good  characteristics  will  usually 
have  children  with  good  characteristics. 

IX.  Observation  of  the  laws  of  heredity  make  possible  (33)  the 
development  of  plants  that  have  desirable  characters;  (34)  the 
improvement  of  the  human  race;  (35)  the  gradual  elimination  of 
plants  or  animals  that  possess  undesirable  characters ; (36)  the  pro- 
duction of  animals  that  are  entirely  different  from  their  parents. 

X.  Mutants  (37)  breed  true;  (38)  do  not  breed  true;  (39)  vary 
largely  from  their  ancestors ; (40)  are  used  as  starting  point  for  a new 
species  of  plants  or  animals. 


642  IMPROVEMENT  OF  LIVING  THINGS  BY  MAN 


Achievement  Test 

1.  What  scientific  proof  can  you  give  that  environment  influences 
organisms  ? 

2.  What  are  some  hereditary  qualities?  How  are  hereditary  qual- 
ities handed  down? 

3.  What  is  the  purpose  of  reproduction  in  plants  and  animals? 

4.  What  are  five  plant  or  animal  hybrids? 

5.  How  can  you  work  out  Mendel’s  laws  with  a hybrid?  With  a 
di-hybrid  ? 

6.  What  are  the  chief  problems  in  plant  or  animal  breeding  in 
your  community? 

7.  What  is  the  mechanism  by  which  inheritable  characters  from 
a father  or  mother  are  handed  down,  “ even  unto  the  third  and  fourth 
generation  ”? 

8.  How  would  you  make  a diagram  of  heredity  in  your  own  family, 
going  back  as  far  as  your  parents  can  remember?  Are  there  any 
definite  examples  of  heredity  which  come  out  in  your  generation  (eye 
color,  hair  texture,  musical  or  other  ability,  etc.)  ? 

9.  Explain  the  meaning  and  the  application  of  the  word  “ eu- 
genics.” 

Practical  Problems 

1.  Could  living  things  improve  physically  or  mentally  if  it  were 
not  for  heredity? 

2.  Go  to  a nearby  nursery  and  find  out  how  many  of  the  newer 
and  better  plants  are  raised  through  hybridization. 

3.  To  what  extent  do  farmers  in  your  locality  use  selection  to 
improve  their  crops?  Get  as  many  examples  as  you  can. 

4.  If  there  is  an  institution  for  feeble-minded  or  criminally  insane  in 
your  neighborhood,  find  out  how  many  there  are  in  the  institution  and 
how  much  it  costs  the  state  per  year  to  run  the  institution.  What 
does  it  cost  your  father  a year  in  taxes? 

5.  What  institutions  in  your  state  are  maintained  because  of  poor 
heredity  ? 

Useful  References 

Caldwell,  Skinner,  and  Tietz,  Biological  Foundations  of  Education.  Ginn, 

1931. 

Conklin,  Heredity  and  Environment.  Princeton  University  Press,  1923. 
Downing,  Elementary  Eugenics.  University  of  Chicago  Press,  1928. 
Farmers’  Bulletins:  195,  461,  576,  619,  887,  952,  1040,  1167,  1192,  1209, 

1263,  1332,  1369. 


USEFUL  KEFEHENCES 


G43 


Cloddanl,  The  Kallikak  Family.  Macmillan,  1919. 

(Iu3'('r,  Heing  Well- Horn.  Eohh.s-Merrill. 

Jenninfrs,  The  Hiologicol  Basis  of  Human  Nature.  Norton,  1930. 

Journal  of  Heredity,  Numerous  Articles.  American  (lenetic  Associa- 
tion, W’ashinfjiton. 

Morgan,  Theory  of  the  Gene.  Yale  University  Press,  1928  (Teachers). 
^^'alter,  Genetics.  Macmillan,  1922. 


SURVEY  QUESTIONS 

What  vocation  are  you  interested  in?  What  abilities  and  physical  con- 
ditions are  necessary  to  a successful  professional  man  or  woman  ? What 
advantage  would  a hobby  or  some  definite  interest  be  to  you  in  choosing 
a life  work  ? For  what  kinds  of  work  might  biology  partially  prepare  one  ? 


UNIT  XIX 

HOW  MAY  BIOLOGY  AID  IN  MY  OWN  IMPROVEMENT? 

Preview.  High  school  is  the  time  of  life  when  we  dream  dreams 
as  well  as  work  and  play.  And  one  of  the  dreams  that  most  of  us 
indulge  in  sometimes  during  a study  period,  sometimes  on  the 
way  to  school,  sometimes  in  the  quiet  of  our  own  room,  is  the 
dream  of  our  future  and  our  life  work.  Most  of  us  sooner  or  later 
will  come  under  the  influence  of  some  strong  personality,  and  the 
leadership  of  that  teacher  or  friend  or  parent  may  have  much  to 
do  with  the  forming  of  our  plans  for  future  work.  In  my  own 
case,  it  was  a professor  in  college  who  gave  me  the  inspiration  to 
devote  my  life  to  teaching.  I have  always  been  happy  in  my 

644 


PREVIEW 


645 


choice.  Rut  uro  all  people  satisfietl  with  their  choice?  I well 
remember  sittiiijj;  at  dinner  with  a very  wealtliy  stockbroker  once 
and  liearinj’:  him  say  to  a distinguished  naturalist  who  was  one  of 
tiie  party,  “ I’d  gladly  give  up  all  of  this  wealth  to  be  able  to  take 
one  trip  with  you  to  South  America.” 

Success  is  one  of  the  greatest  assets  of  life  and  he  who  wins  it 
through  an  interesting  life  work  is  most  fortunate.  It  is  not  easy 
to  determine  what  we  ought  to  do  with  our  lives;  for  what  we 
would  like  to  do  may  not  be  the  thing  we  ought  to  do.  There  are 
many  people  who  find  their  work  most  uncongenial  because  they 
are  not  physically  and  mentally  fitted  for  their  positions.  One  of 
the  things  for  you  to  do  now  is  to  begin  to  think  about  your  future. 
Make  an  analysis  of  your  strong  and  weak  points,  your  likes 
and  dislikes,  your  abilities  and  your  handicaps.  Then  you  will 
be  able  better  to  determine  whether  you  are  fitted  for  the  vocation 
which  you  think  you  would  like  to  make  for  your  life  work.  Per- 
haps some  of  the  possibilities  that  come  from  your  study  of  biology 
may  interest  you.  Think  it  through  carefully  and  then  investigate 
further  if  you  believe  you  are  fitted  for  the  work  you  have  in  mind. 

The  one  thing  which  we  should  have  learned  from  the  preceding 
units  is  how  to  take  care  of  ourselves  physically.  Not  only  have 
we  learned  certain  facts  about  posture  in  relation  to  health,  but  we 
have  found  out  certain  facts  about  diet,  the  values  of  vitamins, 
the  way  to  have  good  digestion  and  to  keep  it,  as  well  as  many 
other  facts  which  aid  in  hygienic  living.  We  have  also  learned 
some  of  the  reasons  for  environmental  improvement  and  care. 
These  are,  after  all,  facts  related  to  health  conservation  and 
should  be  so  used  by  us. 

Probably  the  biggest  asset  we  can  have  is  real  knowledge  of  our 
own  mind  and  how  it  works.  We  can  either  be  slaves  or  masters  of 
self.  It  lies  with  each  one  of  us.  For  the  ability  to  face  life  with 
a smile,  to  be  always  cheerful,  no  matter  what  the  cost,  to  think 
straight  and  clean,  to  make  the  most  of  every  opportunity,  is 
something  that  each  of  us  can  acquire.  If  we  do  learn  this  lesson, 
it  will  be  worth  more  than  all  the  facts  that  many  books  contain. 

Another  thing  we  should  aim  to  do  is  to  cultivate  a hobby. 
Learn  to  like  to  do  some  one  thing  better  than  others  and  make 

H.  BIO  — 42 


646  HOW  MAY  BIOLOGY  AID  IN  MY  IMPROVEMENT? 

that  one  thing  a way  of  using  your  leisure  time.  Some  of  us  like 
to  hike,  to  collect  flowers  or  rocks  or  insects.  Others  of  us  may 
enjoy  bird  study  and  may  make  a collection  of  photographs  of 
birds  and  their  nests.  Such  a collection  is  far  more  interesting, 
both  in  the  getting  and  in  the  keeping,  than  are  the  birds  or  the 
nests  themselves.  Others  of  us  enjoy  fishing;  while  others  get 
enjoyment  out  of  gardening,  either  out-of-doors  or  in  the  house. 
A flower  or  vegetable  garden  is  a practical  kind  of  hobby  and 
often  means  extra  money  for  the  one  who  tends  to  it.  In  all 
events,  have  something  to  do  in  your  leisure  moments. 

Another  result  of  this  study  ought  to  be  a certain  amount  of 
interest  in  the  future.  We  have  seen  so  many  instances  of  fine 
men  devoting  their  lives  to  science  and  the  betterment  of  humanity, 
that  some  of  us  cannot  help  being  stirred  by  their  records.  The 
lives  of  Pasteur,  Reed,  Noguchi,  Bruce,  all  have  made  thrilling 
stories.  It  is  natural  to  wonder  if  there  are  not  some  fields  that 
this  study  of  biology  has  opened  our  eyes  to.  That  there  are 
fields  of  work  open  are  obvious ; medicine,  nursing,  teaching, 
agriculture,  forestry,  laboratory  technology,  collecting,  natural 
science,  research  work,  all  of  these  and  other  vocational  possibilities 
present  themselves  to  us. 

PROBLEM  I.  HOW  CAN  I CHOOSE  A VOCATION? 

The  most  important  problem  for  most  of  us  is,  “ What  am  I 
going  to  do  after  I leave  high  school?  Will  it  be  college  and  a 
profession?  Or  am  I better  fitted  for  a trade  or  business?  I 
cannot  afford  to  be  a ‘ square  peg  in  a round  hole.’  ” Some  things 
are  obvious.  If  one  has  inherited  color  blindness,  he  cannot  be- 
come a locomotive  engineer.  The  musical  profession  would  be 
distasteful  to  one  who  had  no  musical  sense.  Since  different  voca- 
tions demand  certain  physical  and  mental  traits  or  characteristics, 
we  must  possess  those  characteristics  if  we  want  to  succeed  along 
certain  lines  of  work. 

Self-analysis  necessary.  To  choose  our  life  work  wisely,  we 
must  first  analyze  our  abilities  and  habits,  both  of  which  are  very 
important.  Do  we  have  good  posture?  Are  we  neat  in  person 
and  dress?  Do  we  dress  quietly  and  in  good  taste?  Are  we 


AIULITIKS  KEEDKI)  IN  JJFE 


047 


coiirleous?  Do  we  know  how  to  use  our  speaking  voice?  Do 
we  cultivate  smiles  instead  of  ill  temper?  Ji)o  we  have  good 
table  manners?  Impressions  made  on  employers  are  largely  based 
on  an  estimate  of  such  habits.  Much  of  our  life  we  control,  and 
the  formation  of  habits  of  industry,  alertness,  promptness,  thor- 
oughness, orderliness,  tolerance,  honesty,  reliability,  and  open- 
mindedness  will  go  far  in  making  for  success  in  life. 

Abilities.  Certain  natural  abilities,  tendencies,  and  instincts 
dependent  on  physical  and  mental  heredity  must  be  considered 
also  in  choosing  a vocation.  Good  health  is  first  of  all.  Certain 
kinds  of  work  — mining,  farming,  forestry,  stock  raising,  and 
many  trades  — demand  a good  constitution,  if  one  is  to  “ make 
good.”  Persons  who  become  leaders  in  commercial  life  must  have 
executive  power,  system,  energy,  resourcefulness,  and  capacity  to 
form  sound  judgments.  Professional  life  makes  demands  upon 
muscles  and  brain  in  still  another  way.  Let  us  examine  a few 
cases  to  see  just  what  this  means. 

Abilities  needed  for  the  professions.  For  the  ministry  high 
ideals,  faith,  sympathy,  power  in  thought  and  in  word,  capacity  for 
sacrifice,  combined  with  knowledge  acquired  from  books  and 
people,  are  essentials.  For  the  medical  profession,  certain  skill  of 
hand  and  eye  which  aids  in  making  a delicate  dissection,  nerve, 
good  eyesight,  ability  to  search  for  causes  and  to  draw  conclu- 
sions, together  with  sympathy,  tact,  and  love  for  the  work,  are 
essential  to  success.  For  engineering,  mathematical  and  con- 
structive abilities  are  outstanding,  while  a lawyer  needs  high 
reasoning  powers  and  ability  to  deal  with  men.  The  teacher 
should  be  well  educated  and,  in  addition,  must  love  boys  and  girls. 
Health,  tact,  good  nature,  imagination,  inventiveness,  and  enthu- 
siasm are  some  of  the  qualities  which  make  the  successful  teacher. 

Abilities  needed  in  commercial  life.  For  all  commercial  life 
reliability,  promptness,  energy,  cheerfulness,  and  high  moral 
character  are  the  basis.  Stenographers  and  clerks  need,  in  addi- 
tion, special  skills  which  will  be  increased  in  practice.  If  one  is 
to  become  a manager  or  a promoter  of  a business,  organizing  and 
executive  ability,  good  judgment,  caution,  and  a knowledge  of 
business  affairs  are  necessary.  The  business  man  or  woman  should 


648  HOW  MAY  BIOLOGY  AID  IN  MY  IMPROVEMENT? 

know  people  and  have  what  we  call  “business  sense’’  for  leader- 
ship. 

Abilities  necessary  for  trades.  For  the  mechanical  lines, 
knowledge  of  the  trade  is  an  essential,  with  skill  of  eye  and  of  hand. 


A research  worker  in  his  laboratory.  What  qualities  does  such  a man  have  to  possess  in  order 
to  be  successful? 


Accuracy  and  loyalty  are  essentials,  if  one  is  to  succeed.  For 
industries  of  a semi-professional  nature,  such  as  illustrating,  cartoon 
drawing,  or  engraving,  the  artistic  abilities  should  be  cultivated, 
and  imagination,  inventiveness,  and  appreciation  of  what  the 
public  wants  should  be  joined  with  the  purely  mechanical  abilities 
which  have  to  do  with  drawing  or  color  work.^ 

Practical  Exercise  1.  Make  a list  of  vocations  and  under  each  vocation 
place  the  qualities  you  think  most  essential  for  success  in  that  field. 

Practical  Exercise  2.  Choose  a vocation  in  which  you  are  interested  and 
list  the  qualifications  necessary  to  be  successful.  In  the  class  discussion  that 
follows  note  the  overlapping  of  qualifications.  In  what  fields  might  one 
safely  switch  his  lifework? 

1 For  further  information  as  to  the  conditions  necessary  to  become  efficient  in 
any  line  of  work,  read  Parsons,  Choosing  a Vocation,  Houghton  Mifflin  Company, 


MEDICINE 


m 


Self-Testing  Exercise 

Before  choosing  ii  vocation  one  slionkl  make  an (1)  of  his 

(2)  and (3).  Probably  the  most  important  quality 

that  one  should  i)osscss  is (4) (5).  Some  of  the  gen- 
eral abilities  needed  in  all  vocations  are (6),  (7), 

(S), (9),  and (10).  A business  man  should 

show (11) (12) ; a teacher  should  have (13) 

and (14). 

PROBLEM  II.  FOR  WHAT  VOCATIONS  MAY  BIOLOGY 
HELP  PREPARE  ME? 

Medicine.  A great  physician  once  wrote  the  following  to  a 
friend  in  answer  to  the  question  : “ Shall  my  son  prepare  for  medi- 
cine?” — “ There  is  nothing  on  earth  greater  or  more  beautiful 
than  man,  and  the 
study  of  mankind 
is  the  most  diffi- 
cult and  exalted 
subject  of  thought 
and  of  action. 

Human  develop- 
ment and  ambi- 
tion, human  life 
and  ills  are  all  in 
the  highest  degree 
remarkable  and 
touching.  But 
you  must  bring 
keen  eyes  and 
acute  ears;  a great 
gift  for  observa- 
tion ; patience  and  yet  more  patience ; an  iron  will  strengthened 
by  opposition,  but  yet  a warm  and  tender  heart,  comprehending 
and  feeling  every  sorrow ; a reverent  spirit  and  austerity  that  is 
superior  to  sensuality,  money,  or  eminence ; adroit  fingers  and 
health  of  body  and  soul ; furthermore  a decent  appearance,  and 


Keystone  View  Co.  Inc. 

Physicians  must  be  prepared  to  work  at  any  place.  Here  are 
several  doctors,  on  board  a ship,  performing  an  operation. 


650  HOW  MAY  BIOLOGY  AID  IN  MY  IMPROVEMENT? 


polished  demeanor.  All  of  these  you  must  possess  if  you  would 
not  be  an  incompetent  or  unhappy  physician.” 

While  the  life  of  the  physician  has  its  compensations,  one  must 
be  first  of  all  strong  in  body  and  mind  if  he  wishes  to  follow  this 
path.  Eight  to  ten  years  of  preparation  with  no  financial  returns 
makes  the  profession  impossible  for  some.  And  yet  if  you  have 
the  divine  fire  and  know  that  to  be  the  one  profession  for  your  life, 
do  not  give  it  up.  There  are  always  ways  of  borrowing  the  money, 
and  opportunities  are  open  for  him  who  wants  to  do  the  work. 
It  takes  many  years  before  one  is  established,  but  they  are  years  of 
unforgettable  experiences.  And  one  has  the  great  satisfaction  of 
knowing  he  is  really  doing  some  good  in  the  world.  The  physician 
has  social  position  in  the  world  and  is  often  a valued  member  of 
his  community. 

Practical  Exercise  3.  Note  the  qualifications  you  think  necessary  to  become 
a successful  physician,  placing  them  in  order  of  importance.  Have  you  added 
or  subtracted  from  the  list  given  in  the  text  ? 

Other  health  work.  Other  opportunities  in  relation  to  health 
are  research  in  medicine,  the  work  of  the  medical  missionary, 
public  health  work,  which  is  growing  rapidly  in  scope,  hospital 
research,  the  army  and  navy  and  foreign  service,  nursing,  medical 
inspection  of  schools,  and  medical  service  in  corporations. 

Dentistry,  pharmacy,  and  nursing  are  all  occupations  requiring 
special  training  and  characteristics.  One  of  the  most  splendid 
life  occupations  for  girls  who  are  strong  and  who  have  the  spirit  of 
service  is  that  of  the  nurse.  Training  is  obtained  in  a regular 
school  where,  in  addition  to  physiology,  anatomy,  hygiene,  and 
home  economics,  the  prospective  nurse  is  trained  in  actual  care  of 
the  sick.  There  are  many  branches  of  this  profession,  the  most 
fascinating  of  which  is  that  of  the  school  nurse  or  visiting  nurse. 
Social  welfare  is  most  important  to  all  and  this  opportunity  is  a 
large  one.  The  nurse  must  have,  in  addition  to  good  health, 
sympathy,  tact,  understanding  of  people,  and  a desire  for  social 
service. 

Practical  Exercise  4.  List  your  qualifications  for  nursing.  How  do  they 
compare  with  those  for  the  physician?  Would  you  change  the  list  for  the 
crofession  of  dentistry?  Of  pharmacy? 


AC.KICULTURE 


651 


Teaching.  Ai\y  ono  familiar  with  tlie  growth  of  education  in 
this  country  during  the  last  few  decades  cannot  help  feeling  that 
here  iiuleed  is  a vocation  that  is  worth  while.  Not  only  is  there 
opportunity  to  teach  a subject  in  which  one  is  interested,  but  what 
is  far  more,  b}'  e.xample  and  leadership  one  is  able  to  influence  for 
good  many  young  people.  Teaching,  however,  makes  big  de- 
mands. A college  education  with  specialization  in  the  subject 
matter  of  biology,  an  e.xtra  your  of  training  in  methods  and  practice 
teaching  and  a lot  of  time  devoted  to  reading  and  field  work  should 
be  the  training  of  the  teacher  of  biology.  Salaries  are  not  large 
but  they  are  sufficient,  and  one  enjoys  a certain  social  place  in  the 
community.  To  be  a successful  teacher  a love  for  the  subject  and 
a love  for  children  are  essentials.  The  teacher  must  be  forever 
young  and  see  with  the  eyes  of  youth.  Tact,  health,  and,  above 
all,  a sense  of  humor,  must  be  part  of  the  native  equipment  of  the 
teachers  of  biology.  Then  an  analytical  mind,  perseverance,  a 
desire  to  hold  to  the  truth  at  all  costs,  are  all  essential  to  good 
teaching  in  science.  Of  course,  all  these  are  in  addition  to  training 
and  knowledge  of  subject  matter. 

Practical  Exercise  6.  What  are  the  necessary  qualifications  for  the  teaching 
profession?  Do  all  teachers  have  these  qualities?  What  would  you  list  as 
the  most  important  outside  of  good  health? 

Agriculture.  A large  percentage  of  the  farmers  of  this  country 
have  no  real  love  for  their  work  and  have  simply  taken  it  up 
because  the  farm  was  theirs  by  inheritance  or  they  had  other  easy 
reasons  for  going  into  the  work.  But  for  the  young  man  with  a 
strong  body  and  love  for  the  out-of-doors,  what  could  be  a better 
calling?  To  become  a scientific  agriculturist  requires  a great  deal 
of  study,  including  four  years  in  an  agricultural  college  in  the  study 
of  the  practical  applications  of  the  chemistry  of  soils,  of  the  laws  of 
Mendel  in  plant  or  animal  breeding,  and  much  else  that  the  modern 
farmer  needs  to  know  to  make  his  business  pay.  The  life  of  the 
modern  farmer,  thanks  to  automobiles,  good  roads,  and  radios,  has 
become  much  more  pleasant  and  interesting  than  it  was  a few 
years  ago.  Specialized  agriculture,  particularly  in  the  fruit  farms 
of  the  far  west,  offers  most  attractive  inducements.  Experimental 
animal  and  plant  breeding,  although  it  may  be  carried  on  at  the 


652  HOW  MAY  BIOLOGY  AID  IN  MY  IMPROVEMENT? 


Today  farmers  depend  largely  upon  machinery  to  do  their  work  for  them.  This  farmer  is  using 
a tractor  for  plowing. 

farm,  is  usually  done  at  some  of  the  state  institutions  for  the 
promotion  of  agriculture. 

Practical  Exercise  6.  What  qualifications  should  a farmer  possess?  Do 
you  think  the  average  farmer  is  well  fitted  for  his  job?  Why? 

Forestry.  A new  and  attractive  profession  has  opened  up  in 
late  years  through  the  need  of  protection  and  development  of  our 
forests.  Schools  of  forestry  in  different  states  train  young  men 
to  become  foresters,  either  for  the  government  or  for  private 
industry.  Forest  rangers  live  a life  in  the  open.  It  is  their  duty 
to  patrol  the  forests,  to  watch  for  and  to  fight  forest  fires,  to  prevent 
illegal  cutting,  to  control  regular  cattle  grazing  in  forest  reserves, 
to  replant  burnt  over  areas,  and  to  protect  in  every  way  our  great 
national  asset,  the  forests.  The  lover  of  the  out-of-doors  will  do 
well  to  think  seriously  of  this  as  a life  vocation. 

Practical  Exercise  7.  List  the  qualifications  most  essential  for  the  life  of 
a forest  ranger. 

If  possible,  visit  or  tell  of  a visit  to  a ranger  station.  What  would  be  the 
routine  life  of  a ranger? 


TIIP]  XATUKALIST  Oil  KESEAUCII  WORKER  653 


The  naturalist  or  research  worker.  Tlicrc  arc  many  oppor- 
tunities for  tiie  really  able  student  in  research  work  carried  on 
by  some  of  the  government  agencies  engaged  in  the  conservation 
of  our  natural  resources.  The  United  States  Biological  Survey, 
a division  of  the  Department  of  Agriculture,  has  done  much  to 
protect  and  conserve  our  bird  population,  and  has  general  super- 
vision over  the  wild  animal  life  of  this  country.  It  is  one  of  the 
bureaus  that  employ  many  field  workers.  The  United  States 
Bureau  of  Fisheries  is  interested  in  the  conservation  of  our  national 
fish,  shellfish,  and  sealing  resources.  Alany  fish  hatcheries  in 
various  parts  of  the  country  and  various  state  agencies,  such  as  the 
New  York  State  Conservation  Department,  state  departments  of 
agriculture,  fisheries,  and  conservation,  offer  attractive  possibilities 
for  research  work  of  a utilitarian  sort. 

Practical  Exercise  8.  What  do  you  consider  the  most  outstanding  qualifi- 
cations of  a research  worker? 


William  Beebe  has  explored  the  sea  and  studied  the  animals  and  plants  there,  by  means  of  a 
large  steel  sphere  (Bathysphere)  four  and  a half  feet  in  diameter.  It  is  equipped  with  a tele- 
phone and  electric  wires  and  connected  to  the  surface  with  a heavy  steel  cable. 


654  HOW  MAY  BIOLOGY  AID  IN  MY  IMPROVEMENT? 


Since  this  unit  of  work  is  largely  for  each  one’s  own  personal 
use,  a series  of  test  questions  is  unnecessary.  If  the  unit  has 
started  you  thinking  about  your  life  work  and  the  ways  in 
which  you  may  be  able  to  fit  into  the  niche  where  you  belong, 
then  these  pages  have  served  their  purpose.  It  is  well,  however, 
to  see  what  standards  of  attainment  we  have  reached. 

Test  on  Fundamental  Concepts 

In  a vertical  column  under  the  heading  CORRECT  write  numbers  of  all  statements  you  be- 
lieve are  true.  In  another  column  under  INCORRECT  write  numbers  of  untrue  statements. 
Your  grade  = right  answers  X 4. 

I.  Self-analysis  is  necessary  in  choosing  a vocation  (1)  because 
certain  abilities  and  habits  are  necessary  for  success  in  certain  pro- 
fessions ; (2)  unless  a job  is  already  made  for  us,  then  we  should  take 
it  no  matter  whether  we  want  to  do  it  or  not ; (3)  otherwise  we  may 
be  a “ square  peg  in  a round  hole  ” ; (4)  so  that  we  may  determine 
whether  we  are  fitted  for  the  work  we  wish  to  take  up ; (5)  as  well  as 
good  health. 

II.  To  be  a successful  physician  (6)  one  should  have  a good  social 
position  so  as  to  get  in  with  the  best  people ; (7)  one  must  be  willing 
to  work  hard  without  adequate  pay  for  at  least  ten  years ; (8)  it  is  not 
necessary  to  like  dissection  nor  to  have  good  eyesight,  as  most  of  the 
work  is  done  in  an  office  and  consists  in  making  prescriptions  ; (9)  one 
must  have  good  eyes,  a steady  hand,  a scientific  mind,  and,  above 
all,  a pleasant  personality;  (10)  one  must  have  good  health  or  other 
qualifications  will  not  matter. 

III.  Dentistry,  public  health  work,  and  nursing  (11)  all  require 
special  qualifications,  namely,  leadership  and  social  position;  (12)  re- 
quire training  in  hygiene,  anatomy,  and  chemistry;  (13)  require 
health  as  a basis  for  all  other  qualifications;  (14)  require  such  attri- 
butes as  tact,  sympathy,  understanding  of  people,  and  desire  to  be  of 
use  to  others  ; (15)  are  neither  lucrative  nor  interesting  and  should  not 
be  considered  as  professions. 

IV.  Teaching  (16)  is  not  a worth-while  profession  as  it  pays  such 
small  salaries;  (17)  requires  health,  tact,  sense  of  humor,  love  of  the 
work,  and  a love  of  children;  (18)  has  a high  death  rate  and  is  there- 
fore classified  as  a dangerous  profession;  (19)  of  biology  requires  an 
analytical  mind,  an  ability  to  seek  for  the  truth,  and  a love  of  nature ; 
(20)  should  not  be  taken  up  as  a temporary  profession  because  long 
and  careful  training  is  necessary  to  become  a good  teacher. 


USEFUL  KEFEKENCES 


G55 


To  be  successful  in  agriculture  or  forestry  (21)  one  must  have 
good  liealtli,  for  much  of  the  work  is  out-of-doors;  (22)  one  must  have 
training  along  specialized  lines  such  as  plant  and  animal  breeding, 
tree  culture,  etc. ; (23)  it  is  not  necessary  to  have  any  special  training 
e.xcept  a love  for  the  out-of-doors ; (24)  at  least  four  years  in  a school 
of  agricnltnre  or  forestry  is  desirable;  (25)  all  one  needs  is  tact, 
optimism,  and  executive  ability. 


Achievement  Test 

1.  What  are  the  chief  characteristics  necessary  to  become  a suc- 
cessful plyysician?  A dentist?  A nurse? 

2.  AVhat  type  of  mind  makes  the  best  teacher?  The  best  research 
worker  ? 

3.  What  characteristics  would  best  fit  one  for  agriculture?  For 
forestry? 

4.  What  training  would  be  necessary  for  each  of  the  above  voca- 
tions? 


Useful  References 

Dorsey,  Why  We  Behave  Like  Human  Beings.  (Harper  & Bros. 
1925.) 

James,  Psychology.  Briefer  Course.  (Henry  Holt  & Co.  1923.) 
Parsons,  Choosing  a Vocation.  (Houghton  Mifflin  Co.  1909.) 
Spillman,  Personality.  (Gregg  Publishing  Co.  1919.) 


This  photograph  is  taken  from  an  old  print  of  William  Harvey,  explaining 
to  King  Charles  how  blood  circulates  in  the  body.  Why  was  Harvey’s  dis- 
covery so  important  ? Do  you  know  the  names  of  any  scientists,  natural- 
ists, and  physicians  who  made  discoveries  that  have  made  possible  much 
of  our  knowledge  in  science  today  ? 


Culver  Service 


UNIT  XX 

WHO  ARE  SOME  OF  THE  MAKERS  OF  BIOLOGY? 

Preview.  This  unit  is  intended  primarily  for  reference  and 
should  be  used  in  connection  with  the  other  units  of  work.  When, 
for  example,  you  are  studying  about  bacteria,  read  here  and  else- 
where on  the  life  of  Louis  Pasteur.  Every  bird-lover  should  know 
something  about  the  life  of  Audubon.  Modern  applications  of 
biology  to  plants  and  animals  are  intimately  connected  with  the 
names  of  Mendel  and  Burbank. 

If  we  were  to  attempt  to  group  the  men  associated  with  the 
study  of  biology,  we  should  find  that  in  a general  way  they  are 
connected  either  with  discoveries  of  a purely  scientific  nature  or 

656 


LIFE  COMES  FROM  LIFE 


657 


with  tlie  iinprovoinent  of  man’s  condition  by  the  application  of 
certain  scientific  discoveries.  The  first  p^roup  is  necessary  in 
order  that  the  second  p:roiip  may  work  further  on  the  results. 
It  was  necessary  for  men  like  Charles  13arwin  and  Gregor  Mendel 
to  formulate  their  theories  before  Luther  Burbank  or  any  of  the 
men  now  working  in  the  Department  of  Agriculture  could  benefit 
mankind  by  producing  new  varieties  of  plants.  The  discovery  of 
scientific  truths  must  be  made  before  the  men  of  modern  medicine 
can  apply  them  to  the  cure  or  prevention  of  disease.  Since  we 
are  most  interested  in  discoveries  winch  touch  directly  upon 
human  life,  the  men  of  whom  this  chapter  treats  will  be  those 
who,  directly  or  indirectly,  have  benefited  mankind. 

PROBLEM  L WHO  WERE  SOME  EARLY  WORKERS  IN  BIOLOGY? 

The  discoverers  of  living  matter.  The  names  of  a number  of 
men  living  at  different  periods  are  associated  with  our  first  knowl- 
edge of  cells.  About  the  middle  of  the  seventeenth  century  micro- 
scopes came  into  use.  In  1667,  an  Englishman  named  Robert 
Hooke  sliced  a piece  of  cork  with  a razor  and  looked  at  it  through 
a lens.  He  saw  that  the  cork  was  made  up  of  many  tiny  boxes 
or  cells.  But  he  saw  only  the  dead  cell  walls  and  not  the  more 
important  living  matter.  It  was  not  until  1838  that  two  German 
friends,  Schleiden  (shll'den)  and  Schwann  (shvan),  working  on 
plants  and  animals,  discovered  that  both  of  these  forms  of  life 
are  built  up  of  units  called  cells  and  that  these  cells  were  composed 
of  living  material.  Other  biologists  gave  the  name  protoplasm  to 
all  living  matter,  and  a little  later  Professor  Huxley,  a famous 
Englishman,  friend  and  champion  of  Charles  Darwin,  called 
attention  to  the  physical  and  chemical  qualities  of  protoplasm  so 
that  it  came  to  be  known  as  the  chemical  and  physical  basis  of  life. 

Life  comes  from  life.  Another  group  of  men,  after  years  of 
patient  experimentation,  proved  the  fact  that  life  comes  from  life. 
In  ancient  times  it  was  thought  that  life  arose  Spontaneously; 
for  example,  that  fish  or  frogs  grew  out  of  the  mud  of  the  river 
bottoms,  and  that  insects  came  from  dew  or  the  rotting  of  meat. 
Redi  (ra'de),  an  Italian  physician,  1629-1694,  was  the  first  to  show 


658  WHO  ARE  SOME  OF  THE  MAKERS  OF  BIOLOGY? 

by  simple  experiments  that  flies  laid  their  eggs  in  decaying  meat, 
which  accounted  for  the  maggots  found  there.  But  the  con- 
troversy frequently  raged  between  those  who  believed  that  life 
arose  spontaneously  and  those  who  believed  that  all  life  came  from 

previous  life.  It 
was  believed  that 
bacteria  arose  spon- 
taneously in  water, 
even  as  late  as  1876, 
when  Professor 
Tyndall  proved  by 
experiment  the  con- 
trary to  be  true. 

Physiology.  In 
1651  William 
Harvey,  physician 
of  Charles  I of 
England,  showed 
that  living  things 
came  from  egg  cells. 
It  was  much  later, 
however,  that  the 
part  played  by  the 
sperm  in  fertilizing  the  egg  cell  was  carefully  worked  out.  It  is  to 
Harvey,  too,  that  we  owe  the  discovery  of  the  circulation  of  the 
blood.  He  showed  that  blood  moves  in  a complete  circuit  in  the 
body  and  that  the  heart  pumps  it.  Up  to  his  time  the  arteries 
had  been  thought  to  be  air  tubes,  because  after  death  they  were 
empty  of  blood.  Harvey  might  be  called  the  father  of  modern 
physiology  as  well  as  of  embryology.  The  heading  of  this  unit 
shows  an  old  print  of  Harvey  demonstrating  the  circulation  of 
blood  to  the  king. 

Van  Leeuwenhoek,  who  lived  from  1632  to  1725,  is  known  as  the 
maker  of  the  improved  microscope,  although  his  simple  lenses 
were  far  from  equaling  our  modern  instruments.  We  also  connect 
his  name  with  the  confirmation  of  Harvey’s  work  on  the  circulation 
of  the  blood,  for  it  was  he  who  first  saw  the  circulation  of  blood  in 


Tyndall  used  this  apparatus  to  help  disprove  the  theory  that 
bacteria  arose  spontaneously.  He  put  nutritive  fluids  in  the  cul- 
ture tubes  which  were  enclosed  in  a box  containing  air.  The 
sides  of  the  box  were  sticky  so  that  all  dust  particles  in  air  weie 
held.  A beam  of  light  was  used  to  see  if  any  free  particles  were 
floating  in  the  air.  The  tubes  were  heated.  No  organisms  ap- 
peared in  the  tubes,  as  long  as  they  were  kept  in  the  dust-free  air. 


EDWARD  JEXNER  AND  VACCINATION 


G59 


the  c;ii)illaries.  He  says  in  speakiiifi;  of  circulation  in  a tadpole’s 
tail,  that  “ d’hus  it  ai)i)ears  that  an  artery  and  a vein  ai’e  one  and 
the  same  vessel,  prolonj;ed  and  extended.” 

A lon»;  list  of  other  names  mi<2;ht  be  added  to  show  how  gradually 
our  knowledge  of  the  working  of  the  human  body  has  been  in- 
creased. At  the  present  time  we  are  far  from  knowing  all  the 
functions  of  the  various  parts  of  the  human  engine,  as  is  shown  by 
the  number  of  investigators  in  physiology  at  the  present  time. 
Present-day  problems  have  much  to  do  with  the  care  of  the  human 
mechanism  and  with  its  surroundings.  The  solution  of  these 
problems  will  come  from  the  application  of  hygiene,  preventive 
medicine,  and  sanitation. 

Self-Testing  Exercise 

In  1G67  Robert  Hooke  discovered  (1) (2)  and 

(3)  independently  found  that  all (4)  and 

(5)  are  made  of  cells (G)  discovered  the  circulation  of  the 

blood (7)  first  proved  that  flies  developed  from  eggs. 

PROBLEM  II.  WHO  WERE  SOME  OF  THE  CONQUERORS 
OF  DISEASE? 

In  the  preceding  units  of  this  book  we  have  learned  something 
about  our  bodies  and  their  care.  We  have  found  that  man  is 
able  within  limitations  to  control  his  environment  and  make  it 
better.  All  of  the  scientific  facts  that  have  been  of  use  to  man 
in  the  control  of  diseases  have  been  found  out  by  men  who  have 
devoted  their  lives  to  this  work  in  the  hope  that  their  experiments 
and  their  sacrifices  of  time,  energy,  and  sometimes  of  life  itself 
might  make  for  the  betterment  of  the  human  race.  Such  men  were 
Jenner,  Lister,  Koch,  and  Pasteur. 

Edward  Jenner  and  vaccination.  The  civilized  world  owes  much 
to  Edward  Jenner,  the  discoverer  of  the  modern  method  of  vaccina- 
tion. He  was  born  in  Berkeley,  a little  town  of  Gloucestershire, 
England,  in  1749.  As  a boy  he  showed  a strong  liking  for  natural 
history.  He  studied  medicine  and  also  gave  much  time  to  the 
working  out  of  biological  problems.  As  early  as  1775  he  began 


660  WHO  ARE  SOME  OF  THE  MAKERS  OF  BIOLOGY? 

to  associate  the  disease  called  cowpox  with  that  of  smallpox,  and 
gradually  the  idea  of  inoculation  to  prevent  this  terrible  scourge, 
which  killed  or  disfigured  hundreds  of  thousands  every  year  in 
England  alone,  was  worked  out  and  applied.  He  believed  that 
if  the  two  diseases  were  similar,  a person  inoculated  with  the  mild 
disease  (cowpox)  would  after  a slight  attack  of  this  disease  be 
immune  to  the  more  deadly  and  loathsome  smallpox.  It  was  not 
until  1796  that  his  theory  was  generally  accepted,  as  at  first  few 
people  would  submit  to  vaccination.  War  at  this  time  was  being 
waged  between  France  and  England,  so  that  the  former  country, 
usually  quick  to  appreciate  the  value  of  scientific  discoveries,  was 
slow  to  give  this  method  a trial.  In  spite  of  much  opposition,  how- 
ever, by  the  year  1802  vaccination  was  practiced  in  most  of  the  civ- 
ilized countries  of  the  world.  At  the  present  time  the  death  rate 
from  smallpox  in  Great  Britain,  the  home  of  vaccination,  is  less 
than  .3  to  every  1,000,000  living  persons.  This  shows  that  the 
disease  is  practically  wiped  out  in  England.  An  interesting  com- 
parison might  be  made  between  these  figures  and  those  of  France 
in  1754  before  vaccination  was  practiced.  A French  physician 
then  stated  that  “ every  tenth  death  was  due  to  smallpox,  and  one 
fourth  of  manhood  was  either  killed  by  it  or  crippled  and  dis- 
figured for  life.” 

Another  interesting  comparison  may  be  made  between  Mas- 
sachusetts and  California,  two  states  having  nearly  equal  popula- 
tions. In  Massachusetts  vaccination  is  required  by  law  of  all 
children  who  attend  school ; in  California  no  such  law  exists  and 
in  addition  there  are  a good  many  people  who  do  not  believe  in 
vaccination.  During  the  period  between  1921  and  1926  there 
were  64  cases  of  smallpox  in  Massachusetts,  a case  rate  of  .3  per 

100.000.  During  the  same  period  there  were  26,985  reported 
cases  in  California,  a case  rate  of  104.1  per  100,000.  In  1931  the 
case  rate  for  Massachusetts  and  New  Jersey  was  less  than  .5  per 

100.000,  while  in  Kansas  and  South  Dakota  the  rates  were  133 
and  107  per  100,000.  Such  comparisons  speak  for  themselves. 
Since  some  stubborn  opposition  to  vaccination  is  found  even 
nowadays,  Jenner  must  have  had  an  extremely  hard  time  in  his 
day  to  have  his  idea  accepted.  He  had  many  failures,  due  to  the 


LOUIS  PASTKUJi, 


mi 


imperfect  methods  of  his  time,  but  he  lived  loiif>;  eiiouf;h  to  receive 
many  iioiiors  and  to  see  vaccination  used  throughout  the  civilized 
world. 

Louis  Pasteur.  The  man  who,  from  a biological  point  of  view,  has 
done  more  than  any  one  other  person  to  benefit  mankind  directly 
was  Louis  Pasteur. 

Born  in  1822,  in  the 
mountains  near  the 
border  of  southeast- 
ern France,  he  spent 
the  early  part  of 
his  life  as  a normal 
country  boy,  fond  of 
fishing  and  not  very 
partial  to  study.  He 
inherited  from  his 
father,  however,  a 
fine  character  and  a 
grim  determination, 
so  that  when  he  be- 
came interested  in 
scientific  pursuits,  he 
settled  down  to  work 
with  enthusiasm  and 
energy. 

At  the  age  of 
twenty-five  he  be- 
came well  known 

throughout  France  What  are  some  of  the  discoveries  for  which  Louis  Pasteur  is 
° noted  ? 

as  a chemist.  Shortly 

after  this  he  became  interested  in  bacteria,  and  it  was  in  the  field 
of  bacteriology  that  he  became  most  famous.  First  as  professor  at 
Strasbourg,  then  at  Lille,  and  later  as  director  of  scientific  studies 
in  the  ficole  Normale  at  Paris,  he  showed  his  interest  in  the  ap- 
plication of  his  discoveries  to  human  welfare. 

In  1857  Pasteur  showed  that  bacteria  are  connected  with  the 
process  of  fermentation,  and  that  it  is  not  a purely  chemical 
H.  BIO  — 43 


662  WHO  ARE  SOME  OF  THE  MAKERS  OF  BIOLOGY? 

process  as  had  been  thought  up  to  that  time.  This  discovery 
led  to  very  practical  ends,  for  France  was  a great  wine-producing 
country,  and  with  a knowledge  of  the  cause  of  fermentation  it  was 
possible  to  check  the  diseases  which  had  spoiled  wine. 

In  1865-1868  Pasteur  turned  his  attention  to  a silkworm  dis- 
ease which  threatened  to  wipe  out  the  silk  industry  of  France  and 

Italy.  He  found  that  this 
disease  was  caused  by  two 
tiny  organisms,  one  a pro- 
tozoan, the  other  a bacte- 
rium. After  careful  study 
he  made  certain  recom- 
mendations which,  when 
carried  out,  resulted  in  the 
complete  conquest  of  the 
disease  and  the  saving  of 
millions  of  dollars  to  the 
people  of  France  and  Italy. 

His  greatest  service  to 
mankind  came  later  in  his 
life  when  he  applied  certain 
of  his  discoveries  to  the 
treatment  of  disease  in 
people.  First  experiment- 
ing upon  chickens,  he 
proved  that  a vaccine  made 
from  the  germs  which 
caused  chicken  cholera  could  be  reduced  to  any  desired  strength. 
He  then  inoculated  chickens  with  the  vaccine  of  reduced  strength, 
giving  them  a mild  form  of  the  disease,  and  found  that  this  made 
them  immune.  This  discovery,  first  applied  to  chicken  cholera, 
laid  the  foundation  for  all  future  work  in  the  uses  of  serums, 
vaccines,  and  antitoxins. 

Pasteur  is  perhaps  best  known  through  his  study  of  rabies.  The 
great  Pasteur  Institute,  founded  by  popular  subscriptions  from 
all  over  the  world,  has  successfully  treated  many  thousands  of 
cases  of  rabies  with  a death  rate  of  less  than  one  per  cent.  But 


Culver  Service 

Robert  Koch. 


ROBP]RT  KOCH 


663 


more  than  that,  it  was  the  place  where  Roux  (roo),  a fellow  worker 
with  Pasteur,  discovered  the  antitoxin  for  diphtheria,  which  has 
saved  thousands  of  human  lives.  There  also  were  established  the 
principles  of  inoculation  against  bubonic  plague,  lockjaw,  and 
other  germ  diseases. 

Pasteur  died  in  1895  at  the  age  of  seventy-three,  beloved  by 
his  countrymen  and  honored  by  the  entire  world. 

Robert  Koch.  Another  name  associated  with  the  battle  against 
disease  germs  is  that  of  Robert  Koch  (kok).  Born  in  Germany, 
in  1843,  he  later  became  a 
practicing  physician,  and 
about  1880  was  called  to 
Berlin  to  become  a member 
of  the  sanitary  commission 
and  professor  in  the  school 
of  medicine.  In  1881  he 
discovered  the  germ  that 
causes  tuberculosis  and 
two  years  later  the  germ 
that  causes  Asiatic  cholera. 

His  later  work  was  directed 
toward  the  discovery  of  a 
cure  for  tuberculosis  and 
for  other  germ  diseases. 

He  died  in  1910. 

Lister  and  antiseptic 
treatment  of  wounds.  A 
fourth  great  benefactor  of 
mankind  was  Sir  Joseph 
Lister,  an  Englishman  who 
lived  from  1827  to  1912, 

As  a professor  of  surgery  he  first  used  antiseptics  in  the  operating 
room.  By  the  use  of  carbolic  acid  and  other  antiseptics  on  the 
surface  of  wounds,  on  instruments,  and  on  the  hands  and  clothing 
of  the  operating  surgeons,  germs  were  prevented  from  infecting  the 
wounds.  This  single  discovery  has  done  more  to  prevent  death 
after  operations  than  any  other  of  recent  time. 


Culver  Service 

Lord  Lister.  What  has  resulted  from  Lister’s  dis- 
covery of  the  use  of  antiseptics? 


664  WHO  ARE  SOME  OF  THE  MAKERS  OF  BIOLOGY? 

Morton  and  anaesthesia.  One  can  well  imagine  what  a horrible 
thing  an  operation  was  in  the  early  days  of  surgery  when  no 
anaesthetics  were  used.  The  first  use  of  ether  in  surgery  was 
made  by  Dr.  T.  G.  Morton  in  the  Massachusetts  General  Hospital 

on  October  16,  1846.  Later 
chloroform  was  used,  and  up 
to  the  present  time  no  better 
agents  have  been  found. 
The  use  of  anaesthetics  was 
one  of  the  great  discoveries 
in  medicine,  as  they  relieve 
suffering  and  make  operations 
so  much  easier  and  safer. 

Modern  workers  on  the 
blood.  At  the  present  time 
several  names  stand  out 
among  investigators  of  the 
blood.  Paul  Ehrlich  (ar'liK), 
a German  born  in  1854,  is 
justly  famous  for  his  work  on 
the  blood  and  its  relation  to 
immunity  from  certain  dis- 
eases. His  able  research 
work  has  given  the  world  a 
much  better  understanding 
of  acquired  immunity  and  has  enabled  physicians  to  fight  the 
dread  venereal  disease,  syphilis,  with  good  results. 

Another  name  associated  with  the  blood  is  that  of  Elias  Metch- 
nikoff,  a Russian  born  in  1845.  He  first  advanced  the  belief  that 
colorless  blood  corpuscles,  or  phagocytes,  do  service  as  the  sanitary 
police  of  the  body.  He  has  found  that  there  are  several  different 
kinds  of  colorless  corpuscles,  each  having  different  work  to  do. 
Much  of  the  more  modern  work  done  on  the  blood  is  founded 
directly  on  the  discoveries  of  Metchnikoff. 

Other  workers.  Many  other  names  could  be  added.  Walter 
Reed,  the  leader  of  the  fight  against  yellow  fever;  Major  Ross, 
who  discovered  the  malarial  parasite ; Carrel,  who  was  responsible 


MODERN  WORKERS  ON  THE  BLOOD 


065 


for  the  Carrol-Dakiii  treatinoiit  of  wounds  diiriiifi;  the  war; 


Noguchi,  the  Japanese  who  prepared  antitoxins  against  snake 


venom  and  who  gave  his  life  in  j\Li 
yellow  fever  ; Pdexner,  for  his 
discoveries  in  connection 
with  infantile  paralysis;  and 
the  Dicks,  husband  and  wife, 
who  have  worked  out  a 
method  of  treatment  for 
scarlet  fever ; and  many 
others. 


T,  1928,  in  an  attempt  to  conquer 


Self-Testing  Exercise 

Jenner  first  used  the  modern 

method  of (1)  against 

(2) . This  disease  has 

been  practically  wiped  out 

in  states  where  (3)  is 

(4)  by  law,  Louis 

Pasteur  was  the  first 

(5) .  He  laid  the  foundation 

. . Dr.  Hideyo  Noguchi, 

for  all  modern  work  m 

(6)  (7),  a fellow  worker  with  Pasteur,  prepared  the 

(8)  against  (9).  Lister  first  used  (10)  in 

surgery.  Koch  discovered  the (11)  which  causes  tuberculosis. 


PROBLEM  III.  WHAT  ARE  SOME  GREAT  NAMES  IN  THE 
STUDY  OF  PROGRESSIVE  DEVELOPMENT? 

Charles  Darwin.  Another  important  line  of  biological  investi- 
gation is  the  study  of  the  progressive  development  of  life  on  the 
earth.  The  idea  of  evolution  was  known  to  the  Greek  philosophers 
and  we  now  call  Aristotle  the  father  of  the  idea  of  evolution.  In 
the  early  part  of  the  nineteenth  century  the  name  of  a French 
naturalist  stands  out  as  he  advanced  a theory  of  descent  in  which 
the  environment  played  a considerable  part.  But  the  name  of 
Darwin  is  most  indelibly  associated  with  modern  thought  on  pro- 
gressive development. 


666  WHO  ARE  SOME  OP  THE  MAKERS  OP  BIOLOGY? 


Charles  Darwin  was  born  on  February  12,  1809,  a son  of  well- 
to-do  parents,  in  the  pretty  English  village  of  Shrewsbury.  As  a 
boy  he  was  very  fond  of  out-of-door  life,  was  a collector  of  birds’ 
eggs,  stamps,  coins,  shells,  and  minerals.  He  was  sent  to  Edin- 
burgh University  to  study  medicine,  but  the  dull  lectures,  coupled 

with  his  intense  dislike 
for  operations,  made 
him  determine  never 
to  become  a physician. 
Instead,  he  was  greatly 
interested  in  natural 
history,  and  in  the  pro- 
ceedings of  a student 
zoological  society. 

In  1828  his  father 
sent  him  to  Cambridge 
to  study  for  the  min- 
istry. His  three  years 
at  this  university  were 
wasted  so  far  as  prepa- 
ration for  the  ministry 
was  concerned,  but  they 
were  invaluable  in  shap- 
ing  his  future.  He 
made  the  acquaintance 
of  one  or  two  professors 
who  were  naturalists 
like  himself,  and  in  their 


Cl 


J LL 


company  he  spent  many  happy  hours  roaming  over  the  country- 
side collecting  beetles  and  other  insects.  In  1831  an  event  occurred 
which  changed  his  career  and  helped  him  to  become  one  of  the 
world’s  greatest  naturalists.  He  received  word  through  one  of  his 
friends  that  the  position  of  naturalist  on  the  ship  Beagle  was  open 
for  a trip  around  the  world.  Darwin  applied  for  the  position,  was 
accepted,  and  shortly  after  started  on  an  eventful  five  years’  trip 
around  the  world.  He  returned  to  England  a famous  naturalist 
and  spent  the  remainder  of  his  long  and  busy  life  writing  books 


PIUKJRESSIVK  DEVP:L()PMENT 


667 


in  whicli  ho  nttoinptod  to  account  for  the  chanp:os  of  form  and 
habits  of  plants  and  animals  on  the  earth.  Ills  theories  established 
also  a foundation  upon  which  plant  and  animal  breeders  were  able 
to  work.  Two  of  his  best  known  books  are  Origin  of  Species  and 
Plants  and  Animals  under  Domestication.  We  have  studied  about 
some  of  his  work  on  pollination  (page  56)  and  his  theory  of 
“natural  selection”  (page  605). 

His  interpretation  of  the  ways  in  which  all  life  changes  and 
develops  was  due  not  only  to  his  information  and  experimental 
evidence,  but  also  to  an  iron  determination  and  undaunted  energy. 
In  spite  of  almost  constant  illness  brought  about  by  eyestrain,  he 
accomplished  more  than  most  well  men  have  done.  He  died  on 
the  19th  of  April,  1882,  at  seventy-four  years  of  age. 

Other  workers.  Associated  with  Darwin’s  name  we  must  place 
also  the  names  of  two  other  co-workers  on  heredity.  Alfred 
Russel  Wallace,  an  Englishman,  who,  working  independently  and 
at  about  the  same  time,  reached  many  conclusions  similar  to 
those  of  Darwin.  Thomas  Henry  Huxley  did  much  to  make 
people  understand  Darwin’s  work,  as  he  was  a wonderful  teacher 
and  lecturer. 

In  recent  years  there  have  been  many  new  facts  discovered 
which  make  us  doubt  that  Darwin’s  explanation  for  some  of  the 
phenomena  he  described  may  be  the  best  that  can  be  given.  But 
the  evidences  for  the  development  of  plant  and  animal  life  are 
stronger  than  ever  and  no  thinking  scientist  can  deny  this  remark- 
able story  which  is  written  in  the  rocks,  and  in  the  relationships  of 
living  things  as  shown  in  structural  and  vestigial  evidences,  in 
embryological  development,  and  in  geographical  distribution,  all 
facts  that  Darwin  pointed  out  after  years  of  study, 

Self-Testing  Exercise 

(1)  is  called  the  father  of  evolution (2) 

(3)  was  the  founder  of  the  modern  theory  of  progressive  develop- 
ment. The  foundation  for  Darwin’s  life  work  were  laid  in  a 

(4)  around  the (5)  in  the  ship (6).  Alfred  Russel 

(7)  worked  (8)  of  Darwin,  but  came  to  the  same 

(9). 


668  WHO  ARE  SOME  OF  THE  MAKERS  OF  BIOLOGY? 

PROBLEM  IV.  WHAT  ARE  SOME  GREAT  NAMES  IN 
NATURAL  HISTORY? 

Linnaeus.^  The  one  name  that  stands  out  in  the  early  science  of 
classification  of  plants  is  that  of  Carl  von  Linne,  known  to  us  as 
Linnaeus.  Modern  classification  of  plants  (and  subsequently  of 
animals)  dates  from  the  time  of  the  publication  of  his  great  work, 

in  which  all  the  forms  of 
plants  known  at  that  time  were 
described  and  arranged  accord- 
ing to  a definite  system. 

Louis  Agassiz. 2 In  this 
country  the  names  of  pioneers 
in  natural  history  stand  out 
above  a host  of  others.  They 
are  Audubon  and  Agassiz. 
Louis  Agassiz  was  born  in 
Switzerland  in  1807.  Coming 
to  this  country  in  1846,  he 
soon  became  one  of  the  best- 
known  and  best-liked  profes- 
sors at  Harvard.  He  founded 
the  great  Harvard  Museum  of 
Comparative  Zoology.  He 
was  most  interested  in  marine 
life  and  he  established  the  first 
summer  school  for  the  study 
of  natural  history  on  the  island 
Culver  service  of  Penikese  off  Cape  Cod, 
Massachusetts,  in  1873.  This  was  the  beginning  from  which 
sprung  the  world-famous  marine  laboratory  at  Woods  Hole, 
Massachusetts,  where  many  of  the  biologists  of  this  country  have 
had  at  least  a part  of  their  training. 

John  James  Audubon  (1785-1851)  was  French  by  birth  and 
education.  He  was  educated  as  a gentleman  in  a wealthy  family, 
and  studied  drawing  among  other  subjects.  But  he  always  was  a 


1 Linnaeus : li-ne'?!ts. 

2 Agassiz  : ag'd-se. 


JOHN  JAMES  AUDUBON 


669 


collector  and  often  returned  from  rambles  in  the  country  loaded 
down  with  specimens.  Later  in  life  this  must  have  given  him  the 
background  his  genius  needed,  lie  lost  his  money  while  still  a 
young  man,  sold  his  property  near  Philadelphia,  and  moved  west 
with  his  young  wife  to  Louisville,  Kentucky.  Here  he  began  a life 
of  wandering  and  careful  study  of  birds  which  has  given  to  us  some 
of  our  most  valuable  information  on  the  bird  life  of  that  region 
west  of  the  Alleghenies. 

His  descriptions  of  the 
killing  of  immense  num- 
bers of  passenger  pigeons 
and  of  an  Indian  swan 
hunt  give  us  the  reasons 
for  the  disappearance  of 
these  two  birds  from  our 
country.  Audubon  is 
best  known  for  his  won- 
derful work  on  North 
American  birds,  which  he 
illustrated  with  colored 
plates  drawn  by  himself. 

He  traveled  in  all  acces- 
sible parts  of  United 
States  and  Canada  for 
material.  As  a result 
of  this  work  he  became 
famous.  He  died  in 

comparative  comfort  at  chanes  l.  mizmann 

his  home  on  the  banks  of  the  Hudson  in  upper  Manhattan  on 
January  27,  1851. 


Self-Testing  Exercise 


Linnaeus  made  the (1)  system  of (2) 

(3) (4)  trained  many (5)  in  this  country  at  the  first 

seashore  (6)  on  the  island  of  Penikese.  This  laboratory 

later  gave  rise  to  the  now  famous  one  at  (7)  (8), 

(9).  Audubon  was  a great (10)  and  a painter  of 

(11). 


670  WHO  ARE  SOME  OF  THE  MAKERS  OF  BIOLOGY? 


PROBLEM  V.  WHAT  ARE  SOME  GREAT  NAMES  CONNECTED 
WITH  PLANT  AND  ANIMAL  BREEDING? 

Weissman.  August  Weissman,  a German,  showed  that  the 
protoplasm  of  the  germ  cells  (eggs  and  sperms)  is  handed  down 
directly  from  generation  to  generation,  these  cells  being  different 

from  the  others  in  the  body  al- 
most from  the  beginning  of  the 
development  of  the  embryo. 

Workers  with  Chromosomes. 
In  1883  a German  named 
Boveri  discovered  that  the 
chromosomes  of  the  egg  cell 
and  of  the  sperm  cell  are  at 
the  time  of  fertilization  just 
half  the  number  of  those  of  the 
other  cells  (see  page  627),  so 
that  a fertilized  egg  is  really  a 
whole  cell  made  up  of  two  half 
cells,  one  from  each  parent. 
The  chromosomes,  we  remem- 
ber, are  known  to  be  the 
bearers  of  the  hereditary  quali- 
ties handed  down  from  parent  to  child.  Some  of  the  most  impor- 
tant work  on  the  chromosomes  has  been  done  by  Thomas  Hunt 
Morgan,  who  is  now  a professor  at  the  California  Institute  of 
Technology.  He  and  his  students  have  worked  with  a little  fruit 
fly,  in  the  chromosomes  of  which  have  been  isolated  the  tiny  genes 
which  have  been  found  to  be  the  structures  which  pass  on  the 
heredity  qualities  from  parent  to  offspring. 

Mendel.  Turning  to  the  practical  applications  of  the  scientific 
work  on  the  method  of  heredity,  the  name  of  Gregor  Mendel,  an 
Austrian  monk,  stands  out  most  prominently.  Mendel  was  born 
in  1822.  He  early  entered  the  monastery  at  Brunn,  where  he  lived 
until  his  death  in  1884.  In  1865,  after  several  years  of  experimen- 
tation, he  published  the  results  of  his  work  on  inheritance  in  peas. 
But  his  work  created  no  interest  at  the  time  and  remained  un- 
known until  the  year  1900,  when  it  became  world-famous.  The 


DE  VKIES 


07 1 


application  of  his  inotliods  to  plant  and  animal  raising  are  of  the 
utmost  importance  in  assisting  the  breeder  to  develop  the  qualities 
he  desires  and  breed  for  those  (qualities  only. 

De  Vries.  Another  name  often  mentioned  with  reference  to 
plant  breeding  is  that  of  Hugo  de  Vries,  the  J)ulchman  who 


has  showed  that  in  some 
cases  new  kinds  of  plants 
arise  by  sudden  and  great 
variations  known  as  niu- 
tation.s.  Professor  Morgan 
has  actually  produced  iKn\ 
species  of  fruit  Hies  as  a 
result  of  his  careful  study 
of  mutants.  De  \'ries’s 
work,  with  that  of  scores 
of  other  workers  in  hered- 
ity, is  paving  the  way  for 
the  practical  plant  and 
animal  breeders. 

Burbank.  We  must  not 
close  without  a mention  of 
Luther  Burbank,  whose 
work  with  plant  hybrids 
has  won  him  everlasting 
recognition  as  a benefactor 
of  man.  He 'was  born  in 
Lancaster,  Massachusetts, 
on  March  7,  1849,  and  he 
died  at  his  home  in  Santa  Rosa,  California,  on  April  11,  1926.  As 
a boy  he  was  interested  in  the  out-of-doors  and  particularly  in 
plant  life.  He  was  known  as  the  Wizard  of  Santa  Rosa  because 
there  his  experimental  farm  was  located  and  there  he  developed 
most  of  his  new  and  improved  plant  forms.  The  Burbank  potato, 
with  its  large  yield,  would  alone  be  a monument,  but  he  followed 
this  with  literally  hundreds  of  improved  and  new  forms.  He  pro- 
duced a cross  between  a plum  and  an  apricot,  which  he  called  a 
plumcot.  He  crossed  a small  cream-colored  berry  with  a large 


Brown  Brothers 

Luther  Burbank.  Name  four  improved  forms  of 
plants  for  which  he  was  responsible. 


672  WHO  ARE  SOME  OF  THE  MAKERS  OF  BIOLOGY? 


blackberry.  Then  he  selected  for  breeding  the  best  hybrid  berries 
for  several  generations,  and  finally  succeeded  in  obtaining  a large 
white  blackberry  with  a pleasing  flavor.  By  crossing  plums  which 
were  resistant  to  cold  and  frost  with  plums  which  had  many  other 
desirable  qualities,  he  obtained  a large  juicy  plum  with  a small 
stone,  and  which  will  grow  in  practically  any  conditions  of  climate 
and  soil.  He  produced  rapid-growing  walnuts,  and  many  other 
new  forms  of  fruits  and  vegetables.  His  work  was  almost  entirely 
hybridizing  and  he  destroyed  thousands  of  plants  in  order  to  obtain 
the  ones  with  exactly  the  qualities  he  wished  to  perpetuate.  He 
estimated  that  he  raised  over  1,000,000  plants  every  year  for 
breeding  purposes.  At  his  death  there  were  over  5000  different 
forms  of  plants  growing  on  his  experimental  farm. 

Self-Testing  Exercise 

Boveri  discovered  that  the  ( 1 ) and  (2)  before 

fertilization  had  just  (3)  the  number  of  chromosomes  found 

in  the  (4)  (5) . Gregor  Mendel  worked  out  certain 

(6)  of  (7)  in  (8).  These  have  been 

(9)  today  by  many  plant  and  animal  (10).  Luther 

Burbank  improved  plants  largely  through  (11)  and  

(12). 

Achievement  Test 

1.  What  are  some  names  of  persons,  not  mentioned  in  this  unit, 
who  are  well  known  in  modern  biological  sciences?  In  medicine?  In 
public  health? 

2.  How  would  you  classify  the  names  in  this  unit  under  the  headings 
given  and  tell  two  things  for  which  each  person  is  famous? 

3.  Why  is  Mendel’s  work  on  heredity  considered  so  important? 

Interesting  Things  to  Do 

1.  Make  a bibliography  of  the  books  about  different  phases  of  biology 
that  you  have  read. 

2.  Read  for  pleasure  the  biographies  of  some  of  the  great  men  of  biology. 

Useful  References 

Darwin,  Life  and  Letters  of  Charles  Darwin.  Appleton,  1911. 

De  Kruif,  Microbe  Hunters.  Harcourt,  Brace,  1926. 


USEFUL  KEFE FENCES 


673 


l)e  Kruif,  Hunger  Fighters,  llairourt,  l^racc,  1928. 

I)()\vninf>:,  Science  in  Service  of  Health.  Longmans,  Green,  1930. 
Gruenherg,  Modern  Science  and  People’s  Health.  Norton,  1926. 
llalloek  and  Turner,  Health  Heroes.  Series.  Metropolitan  Life  Insur- 
ance, 1928. 

Hartzog,  Triumphs  of  Medicine.  Doubleday,  Doran,  1927. 

Harwood,  New  Creations  in  Plant  Life.  Macmillan,  1922. 

Hunter  and  Whitford,  Readings  in  Science.  Pp.  17-41.  Macmillan, 
1931. 

Locy,  Biology  and  Its  Makers.  Holt,  1908. 

Tracy,  American  Nat  wrists.  Dutton,  1930. 

\’allery-Radot,  The  Life  of  Pasteur.  Doubleday,  Doran,  1923. 
^^■illiams-Lllis,  Men  IL/m  Found  Out.  Coward-McCann. 


1 

I 

i 


GLOSSARY  OF  IMPORTANT  TERMS 


The  diacritical  marks  arc  those  used  in  the  Webster  scliool  dictionaries. 


Abdomen  (tlb  do'mPii) ; the  posterior 
region  of  the  l)ody,  behind  the 
thorax,  of  an  insect  ; the  region  of 
the  body  below  the  chest  in  man. 

Absorption  (ilb  sorp'shan) : the  proc- 
ess of  taking  up  liquid  food  or 
other  substances  through  the  walls 
of  cells. 

Adaptation  (ild'itp  ta'shttn) : fitness 
for  surroundings ; fitness  to  do  a 
certain  kind  of  work ; changes 
which  a plant  or  an  animal  has 
undergone  that  fit  it  for  the  con- 
ditions in  which  it  lives. 

Adenoids  (Sd'e  noids) : fleshy  growths 
in  the  back  of  the  nose  cavity  which 
clog  the  air  passages. 

Adrenaline  (5d  re'ndl  m) : commer- 
cially prepared  adrenin,  a secretion 
of  the  adrenal  glands. 

Adrenals  (id  re'nnls) ; two  small 
ductless  glands  situated  just  above 
the  kidneys. 

Adulterant  («  dfd'ter  ont) : a sub- 
stance put  in  another  to  cheapen 
it  ; usually  reducing  its  strength  or 
otherwise  injuring  it. 

Aerobie  (a  er  o'bik)  organisms:  bac- 
teria or  other  organisms  which 
require  free  oxygen,  as  opposed  to 
anaerobic  organisms  (bacteria  and 
some  parasitic  worms)  which  do  not 
require  free  oxygen. 

Agglutinin  (a  gldb'ti  nm) : antibodv 
found  in  blood,  which  causes  bacteria 
to  be  clumped  together,  preparatory 
to  their  destruction  by  the  colorless 
corpuscles. 

Albumin  (al  bu'min) : a protein  form- 
ing an  important  part  of  the  blood, 
and  found  also  in  many  animal  and 
vegetable  substances. 

Alimentary  (ftl'i  men'td  ri)  canal:  the 
food  tube. 

Alternation  of  generations  : the  alter- 
nating of  a sexual  with  an  asexual 


generation  in  the  life-history  of  a 
l)lant  or  an  animal. 

Amino  acid  (ilm'i' no  Ss'id) : a part 
of  a complex  protein  ; one  of  the 
simpler  substances  into  which  a pro- 
tein may  be  broken  down  in  the 
body. 

Analogy  (d  niH'b  ji) : likeness  in  func- 
tion. 

Antenna  (an  iSn'd)  (]j1.  Antennae) : a 
jointed  feeler  on  the  head  of  an 
insect  or  of  a crustacean. 

Anterior  : nearer  t he  head  end  (Zool.)  ; 
facing  outward  from  the  axis  (Bot.). 

Anther  (jin'ther) : the  part  of  the 
stamen  which  develops  and  con- 
tains pollen. 

Antibodies  (an'ti  bod'iz) : substances 
found  in  the  blood,  which  fight 
against  bacteria  or  toxin  which  may 
enter  the  body. 

Antiseptic  (an'tt  sgp'tik) ; a substance 
which  prevents  the  growth  of  harm- 
ful microorganisms. 

Antitoxin  (an'ti  tok'sm) : a substance 
that  neutralizes  a toxin  or  poison 
produced  by  invading  disease  germs. 

Anus  (a'nds) : the  posterior  opening  of 
the  food  tube. 

Aorta  (a  or'td) : the  large  artery  leav- 
ing the  left  ventricle  of  the  heart. 

Appendage  (dpen'daj):  a jointed 
organ  attached  to  the  side  of  the 
body. 

Arachnid  (d  rak'nid) : any  of  the 
class  of  animals  including  the  spiders 
and  scorpions. 

Artery  (iir'ter  i) : a tube  which  con- 
veys blood  from  the  heart. 

Aseptic  (d  sgp'tik) : free  from  pus- 
forming bacteria  or  other  harmful 
organisms. 

Asexual  (d  sgk'shu  dl) : having  no  sex. 

Assimilation  (d  sim'i  la'shdn) : the 
converting  of  digested  food  into 
living  matter. 


676 


GLOSSARY  OF  IMPORTANT  TERMS 


Auricle  (6'rl  k’l) : a chamber  in  the 
heart  which  receives  blood. 

Autonomic  nervous  system : a part  of 
the  nervous  system  not  under  con- 
trol of  the  will ; it  is  sometimes 
called  the  sympathetic  nervous 
system. 

Axon  (ak'son) : the  main  elongation  of 
a neuron. 

Bacillus  (bd  sil'ws) : a rod-shaped 
bacterium. 

Bacteria  (bak  te'ri  d) ; microscopic 
one-celled  plants,  some  of  which 
cause  specific  diseases. 

Bacteriology  (bak  te'ri  ol'o  ji) : a study 
of  bacteria. 

Bast : tough,  fiberlike  cells  composing 
the  inner  layer  of  bark. 

Biennial  (bl  en'i  dl) : a plant  which 
completes  its  life  cycle  in  two  years 
— producing  leaves  the  first  year 
and  fruit  and  seed  the  second. 

Bile  : a fluid  secreted  by  the  liver. 

Biology  (Gr.  bios,  life ; logos,  word  or 
discourse) : the  study  of  matter  in 
a living  state ; the  study  of  plants 
and  animals. 

Bivalve : mollusk  having  shell  con- 
sisting of  two  distinct  parts  or 
valves  connected  by  a hinge. 

Blade  : the  flat  portion  of  a leaf. 

Blastula  (blas'tu  Id) ; a stage  in  the 
segmentation  of  an  egg  in  which  the 
cells  form  a hollow  ball  with  a wall 
one  layer  thick. 

Bryophyta  (bri  of'i  td) : the  phylum  of 
plants  to  which  the  mosses  belong. 

Bud : an  undeveloped  branch. 

Calorie  (kal'o  ri) : a heat  unit,  namely, 
the  amount  of  heat  required  to  raise 
the  temperature  of  one  kilogram  of 
water  one  degree  Centigrade. 

Calorimeter  (kal'o  rim'e  ter) : a ma- 
chine for  measuring  amount  of  heat 
in  foods. 

Cambium  (kam'bi  um) : the  layer 
between  the  wood  and  the  inner 
bark  where  growth  takes  place. 

Capillaries  (kap'i  la  riz) ; minute  tubes 
which  connect  arteries  with  veins. 

Capillarity  (kap'i  lar"!  tl) ; a phenome- 
non shown  by  liquids  rising  in  fine 
tubes. 


Carapace  (kar'd  pas) : a bony  or  chi- 
tinous  case  covering  an  animal’s 
back,  as  the  crayfish. 

Carbohydrate  (kar'bo  hi'drat) : a class 
of  nutrients  composed  of  carbon, 
oxygen,  and  hydrogen,  having  the 
oxygen  and  hydrogen  in  the  same 
proportion  as  water. 

Carbon : an  element  found  in  all  or- 
ganic compounds. 

Carbon  dioxide  : a gas,  a product  of 
the  oxidation  of  carbon. 

Carnivores  (kar'ni  vors) : an  order  of 
flesh-eating  mammals,  including  the 
cats,  dogs,  bears,  etc. 

Cell : the  structural  and  physiological 
unit  in  plant  and  animal  bodies.  A 
small  mass  of  protoplasm  in  most 
cases  inclosed  in  a cell  mem- 
brane and  usually  containing  a nu- 
cleus. 

Cell  membrane : the  delicate  living 
covering  of  a cell. 

Cell  sap : water,  with  materials  in 
solution,  found  in  the  vacuoles  of 
plant  cells. 

Cellulose  (sel'u  los) : a dead  substance 
found  in  the  walls  of  plant  cells. 

Cephalothorax  (sef'd  16  tho'raks) : an- 
terior division  of  body  of  some 
animals,  consisting  of  the  united 
head  and  thorax. 

Cerebellum  (ser  e beTum) : part  of 
the  brain  between  the  cerebrum  and 
the  medulla  oblongata. 

Cerebrum  (ser'e  hrum) ; the  anterior 
part  of  the  brain. 

Chemical  compound : a substance 
formed  by  the  combination  of  chem- 
ical elements. 

Chemical  element : a simple  sub- 
stance ; one  which  cannot  be  broken 
into  simpler  substances. 

Chitin  (kl'tin)  : a hard,  nitrogenous 
substance  present  in  the  exo-skele- 
ton of  insects. 

Chlorophyll  (klo'ro  fil) : the  green 
coloring  matter  of  plants. 

Chloroplasts  (klo'ro  plasts) : small 
bodies  of  protoplasm  which  contain 
chlorophyll. 

Choroid  (ko'roid) : the  middle  coat  of 
the  eye. 

Chromosome  (krd'mo  som) ; a deeply 
staining  body  in  the  nucleus  of  a 


r.LOSSAliV  OF  IMPORTANT  TERMS  ()77 


cell,  supposed  to  carry  the  deter- 
niiners  of  hereditary  (pialities. 

Chrysalis  t krls'h  lls) : the  uncovered 
pupal  sta>ie  of  butterflies. 

Cilium  (sll'l  lan) : a tiny  hairlike 
thread  of  prt)toplasm  extendinfj; 
from  a cell. 

Cloaca  (klb  fi'ka) : the  common  cavity 
into  which  the  digestive,  urinary, 
and  rei)roducf ive  systems  open  in 
some  kinds  of  vertebrates. 

Coccus  (kbk'i/s) : a spherical-shai^ed 
bacterium.  _ 

Cocoon  (kb  kdbn') : a silky  covering 
around  a pupa;  the  egg-case  of 
spiders. 

Coelenterata  (sb  Ibn'ter  a'td) : phy- 
lum of  animals  including  the  corals 
and  jellyfishes. 

Coleoptera  (kbl'e  bj/ter  d) : the  order 
of  insects  to  which  beetles  belong. 

Communicable  disease : a disease 
that  can  be  passed  direct  1}^  from 
one  person  to  another. 

Compound  eye  : an  eye  made  up  of 
many  simple  eyes  or  ommatidia. 
Insects  have  compound  eyes. 

Conjugation  (kon'jdo  ga'shun) : the 
temporary  union  of  two  sex  cells  of 
equal  size,  with  a fusion  of  nuclei 
and  interchange  of  nuclear  ma- 
terial. 

Connective  tissue  : collections  of  cells 
which  support  and  connect  other 
tissues. 

Conservation  : preserving  or  protect- 
ing. 

Contractile  vacuole  : a small  cavity, 
found  in  the  cytoplasm  of  many 
protozoans,  which  appears  and  dis- 
appears with  regularity.  It  is  be- 
lieved to  be  an  organ  of  excretion. 

Corolla  (kb  rbrd) : the  petals  of  a 
flower  taken  together. 

Corpuscles  (kbr'pus’ls) : the  red  and 
the  colorless  cells  in  the  blood. 

Cortex  (kor'tbks) : a fleshy  portion  of 
the  root,  outside  the  central  cylin- 
der ; the  inner  layer  of  bark. 

Cotyledon  (kot'l  le'ddn) : leaf  of  an 
embryo,  in  a seed. 

Cross-pollination  : taking  pollen  from 
the  anther  of  one  flower  and  placing 
it  on  the  stigma  of  another  flower. 

Crustacea  (krtis  ta'she  d) : class  of 


animals  including  tlie  lobsters,  cray- 
fish, and  crabs. 

Culture;  a growth  of  baederia  or 
other  microorganisms  in  a prci)ared 
nutrient  medium. 

Cycad  (sl'kitd) : family  of  tro])ical 
gymnosperms. 

Cyst  (slst) : a hard  sac  or  capsule  in- 
cluding a one-celled  animal  in  its 
resting  stage. 

Cytoplasm  (sl'tb  phiz’m) : the  living 
substance  of  the  cell  outside  of  the 
nucleus  and  inside  the  cell  mem- 
brane. 

Deciduous  (de  sld^i  us) : falling  off  at 
maturity.  ^ 

Dehiscent  (de  his'mt) : oi)ening  along 
a definite  line  to  discharge  contents. 

Dendrites  (dbn'drlts) : delicate  proto- 
plasmic branched  endings  of  a 
neuron. 

Dentine  (dSn'tin) : material  compos- 
ing the  main  part  of  a tooth. 

Dermis  (dtir'mis) ; the  layer  of  skin 
below  the  epidermis. 

Diaphragm  (di'd  frain) : the  muscular 
partition  between  the  thorax  and 
the  abdomen. 

Diastase  (di'd  stas) : an  enzyme 
formed  in  plants  which  changes 
starch  to  grape  sugar. 

Dicotyledon  (di  koth  le'dun) ; a plant 
that  bears  seeds  having  two  cotyle- 
dons. 

Diffusion : the  passage  of  particles  of 
a substance,  either  gas  or  liquid, 
from  a point  of  greater  to  a point  of 
lesser  concentration. 

Digestion : the  process  of  preparing 
food  for  absorption. 

Dihybrid.  Mendelian  term  for  a 
cross  between  organisms  which 
differ  in  two  pairs  of  alternative 
characters. 

Diptera  (dip'ter  d) : an  order  of  insect 
having  two  wings,  as  the  flies. 

Disease  : a state  in  which  part  of  the 
body  does  not  function  properly. 

Disinfectant  (dis'm  fek'tdnt) ; some- 
thing which  kills  bacteria. 

Dominant : a Mendelian  term  applied 
to  that  unit  character  which  stands 
out  to  the  exclusion  of  the  other  or 
recessive  character. 


678 


GLOSSARY  OF  IMPORTANT  TERMS 


Dorsal  (dor'sdl) : of  or  pertaining  to 
the  back  or  top  side. 

Ductless  glands : glands  which  have 
no  communication  with  an  outer 
surface,  and  which  manufacture 
hormones. 

Ecology  (e  kol'o  jt) : study  of  plants 
and  animals  in  relation  to  their 
natural  surroundings. 

Ectoderm  (ek'to  durm) : the  outer 
layer  of  cells  in  an  embryo. 

Egg  : the  female  gamete,  the  ovum. 

Embryo  (em'bri  5) : the  early  stage  of 
a developing  plant  or  animal. 

Embryo  sac  : the  structure  within  the 
ovule  which  holds  the  egg  cell. 

Emulsion  (e  mul'shun) : a mixture  of 
liquids  which  do  not  dissolve,  the 
particles  of  one  floating  as  small 
globules  in  the  other. 

Enamel : hardest  part  of  a tooth. 

Encyst  (6n  sist') : to  become  inclosed 
in  an  impermeable  envelope  or  cyst. 

Endocrine  glands  (gn'do  krin) : duct- 
less glands. 

Endoderm  (en'do  durm) : the  inner 
layer  of  cells  in  an  embryo,  giving 
rise  to  the  digestive  tract,  etc. 

Endoskeleton  (en'do  skel'e  tun) : a 
skeleton  inside  the  body  as  opposed 
to  the  outer  or  exoskeleton. 

Endosperm  (gn'do  spurm) : food 

stored  in  the  seed  outside  the  em- 
bryo. 

Energy  : work  power  ; ability  to  per- 
form work.  It  may  be  latent  or 
kinetic. 

Environment  (gn  vi'rwn  ment) : the 
surroundings  of  an  organism. 

Enzyme  (gn'zim) ; a substance  which 
brings  about  a chemical  action, 
assisting  in  digestion. 

Epidermis  (gp'f  dhr'mis) : an  outer 
layer  of  cells  ; the  outside  skin. 

Epiglottis  (ep'i  glot'is) : a covering 
over  the  opening  into  the  trachea. 

Erosion  (e  ro'zhi/n) : the  wearing 
away  of  rocks  by  water,  wind,  gla- 
ciers, and  other  agents. 

Esophagus  (e  sof'd  gus) : muscular 
tube  leading  from  the  pharynx  to 
the  stomach ; gullet. 

Essential  organs : the  stamens  and 
pistils,  parts  of  a flower  which  have 


to  do  with  the  production  of 
seeds. 

Eugenics  (u  jen'iks) : the  science 
which  deals  with  race  improvement 
through  heredity. 

Eustachian  tube  (u  sta'ki  dn) : the 
canal  connecting  the  tympanic  cav- 
ity with  the  pharynx,  named  for  its 
discoverer,  Eustachio,  an  Italian 
physician. 

Euthenics  (u  then'iks) ; the  science 
which  deals  with  race  improvement 
through  betterment  of  the  environ- 
ment. 

Excretion  (eks  kre'shwn) ; elimination 
of  waste  products  from  an  organ- 
ism. 

Exoskeleton  (ek'so  skgl'e  tdn) : an 
outside  skeleton. 

Expiration  : process  of  forcing  air  out 
of  lungs. 

Fi,  F2,  etc.:  abbreviations  indicating 
the  successive  generations  follow- 
ing crossing  or  hybridizing. 

Fatigue  (fd  teg') ; the  effect  produced 
by  prolonged  stimulation  on  the 
cells  of  an  organism. 

Fats  : a class  of  nutrients  composed  of 
much  carbon  and  hydrogen  with  a 
little  oxygen. 

Fermentation  (fur'men  ta'slum) : the 
chemical  transformation  of  organic 
substances  through  the  agency  of 
enzymes  or  ferments,  or  through 
the  agency  of  bacteria. 

Fertilization  (fur'ti  If  za'shdn) : the 
union  of  an  egg  cell  and  a sperm  cell. 

Fibrinogen  (fl  brin'o  jen) : a soluble 
protein  substance  in  the  blood 
plasma. 

Fibrovascular  bundles  : collections  of 
tubular  cells,  supported  by  woody 
cells,  which  conduct  fluids  in  plants. 

Fin : a fold  of  skin,  with  skeletal 
supports,  used  for  swimming. 

Fission  (fish'dn) : division  of  a cell 
into  two  cells  of  equal  size. 

Flagellum  (fid  jgl'dm) : a threadlike 
projection  of  certain  cells,  which  is 
used  for  locomotion. 

Focus  of  infection : a center  of  bac- 
terial infection,  often  at  the  base  of 
a tooth,  from  which  toxins  reach 
the  blood. 


GLOSSARY  OF  IMPORTANT  TERMS  679 


Fossils:  j)otrifio(l  n'lnuins  or  iinprps- 
sioris  of  liviniz:  of  past  ages. 

Frond  : leaf  of  a fern. 

Fruit:  a ripened  ovary  together  with 
any  parts  of  the  flower  adhering  to 
it. 

Function  (funk'slu/n) : the  normal 
action  of  an  organ  or  organs. 

Fungi  (fun'ji) ; i)lants  without  true 
roots  or  stems,  containing  no  chlo- 
roi)liyll  ami  ileiiending  upon  organic 
fooil  for  their  nourishment. 

Gamete  (gUm'et) : a sex  cell. 

Gametophyte  (gd  me'td  fit) : a stage 
in  the  life  history  of  a moss  or  fern 
in  which  sex  cells  are  produced. 

Ganglion  (giin'gll  on)  (pi.  Ganglia);  a 
group  of  nerve  cells  situated  out- 
side of  the  brain  or  spinal  column. 

Gastric  (gilsYrik)  glands;  digestive 
glands  found  in  the  walls  of  the 
stomach. 

Gastropod  (giis'trd  pod) ; a mollusk 
with  univalve  or  no  shell. 

Gastrula  (gas'trdo  la) : a cuplike 
structure  formed  by  the  invagina- 
tion or  turning  in  of  the  blastula. 

Genes  : elements  in  the  chromosomes 
of  the  germ  cells  which  carry  the 
hereditary  traits. 

Genetics  (je  net'iks) : the  study  of 
heredity. 

Geotropism  (je  ot'ro  pfz’m) : response 
to  gravity. 

Germ  cells  ; eggs  or  sperm  cells. 

Germination  (jfir'mi  na'shiin) : the 
beginning  of  growth  in  a seed  or  a 
liollen  grain. 

Gill  rakers  : small  spinelike  structures 
attached  to  gill  arches  of  fish  which 
prevent  escape  of  food. 

Gills : breathing  organs  for  use  in 
water. 

Gland  : an  organ  which  secretes  mate- 
rial to  be  used  in  or  excreted  from 
the  body. 

Glomeruli  (glo  mer'do  li ) : bunches  of 
looped-  capillaries  in  the  kidneys  in 
which  the  blood  loses  its  urea. 

Glycogen  (gli'ko  jen) : animal  starch, 
found  in  the  liver. 

Guard  cells  : epidermal  cells,  found  on 
each  side  of  a stoma. 

Gullet  (gul'gt) : a muscular  canal 


extending  from  the  jiharynx  to  the 
stomach;  the  esophagus. 

Gymnosperm  (jim'no  si)urm) : plants 
having  seeds  not  enclosed  in  an 
ovary. 

Habit : an  acquired  reflex  act  involv- 
ing no  thought. 

Haemoglobin  (he'mb  glo'bin) : red  col- 
oring matter  of  t he  blood. 

Haemolysin  (he'mo  iT'sIn) : sub- 

stance in  blood  which  destroys 
foreign  red  corpuscles. 

Heliotropism  (he'll  ot'ro  plz’m) : re- 
sponse to  sunlight. 

Hemiptera  (he  imp'ter  d) ; the  order  of 
insects  to  which  the  bugs  (half 
wing)  belong. 

Heredity  (he  red'l  ti) : transmission  of 
qualities  from  parent  to  child. 

Hermaphroditic  (her  maf'ro  dtt'ik) : 
having  both  male  and  female  sex 
organs. 

Hilum  (hi'lwm) : a scar  on  the  testa 
left  where  the  seed  was  attached  to 
the  pod. 

Homology  : likeness  in  structure  and 
position. 

Homoptera  (ho  mop'ter  d) ; the  order 
of  insects  to  which  plant  lice  and 
scale  insects  (similar  wings)  belong. 

Hookworm : parasitic  worm  which 
“ hooks  ” itself  to  the  wall  of  the 
intestine. 

Hormones  (hor'mbnz) : substances 
produced  by  some  of  the  glands  of 
the  body,  which  stimulate  certain 
physiological  activities. 

Host : an  animal  or  plant  furnishing 
food  to  a parasite. 

Humus  (hu'mus) : vegetable  mold,  a 
black  or  dark  colored  substance 
formed  by  the  decay  of  organic 
substances  in  the  soil. 

Hybrid  (hi'brid) : the  offspring  of 
parents  which  have  specific  differ- 
ences. 

Hydrogen  (hi'dro  jen) : a gaseous 
element  found  in  water  and  many 
other  compounds. 

Hygiene  (hi'ji  en) : a study  of  the 
preservation  of  health. 

Hymenoptera  (hi'men  op'ter  d) ; order 
of  insects  to  which  bees  and  wasps 
(membrane  wings)  belong. 


680 


GLOSSARY  OF  IMPORTANT  TERMS 


Hypocotyl  (hi'po  kot'il) : the  part  of 
the  developing  embryo  which  forms 
the  root  and  the  lower  part  of  the 
stem. 

Imbibition  (im'bi  bish'itn) : a form  of 
diffusion  that  results  in  the  swelling 
of  material  taking  in  a fluid. 

Immunity  (i  mu'ni  ti) : the  successful 
resistance  of  an  organism  to  infec- 
tions from  microorganisms. 

Imperfect  flowers : flowers  having 
only  one  kind  of  essential  organs, 
either  stamens  or  pistils. 

Incubation  (in'ku  ba'shwn)  period : the 
time  the  germs  of  a disease  enter 
the  body  until  the  symptoms  of  the 
disease  appear. 

Indehiscent  (fn'de  his'cnt) : not  open- 
ing at  maturity  along  a definite  line 
to  discharge  contents. 

Infectious  (in  fgk'shus) : caused  by 
disease-producing  organisms,  or 
germs. 

Inheritance  : that  which  is  passed  on 
by  heredity. 

Insecta  : class  of  insects. 

Inspiration : the  act  of  taking  air  into 
the  lungs. 

Instinct  (in'stinkt) ; a tendency  to 
perform  an  act  which  is  performed 
for  the  first  time  without  being 
learned. 

Insulin  (in'su  lin) : a hormone  pro- 
duced in  “ Islands  of  Langerhans  ” 
in  the  pancreas ; remedy  for  dia- 
betes. 

Intestine  (in  tes'tin) : the  food  tube  in 
vertebrates  from  the  pyloric  end  of 
the  stomach  to  the  anus.  It  is 
divided  into  the  small  and  the  large 
intestine. 

Invertebrate  : an  animal  not  having  a 
backbone. 

Iris : the  colored  portion  of  the  eye, 
having  the  pupil  in  the  center. 

Kidneys  : glands  which  secrete  urine. 

Eanetic  (ki  net'ik) : energy  employed 
in  producing  motion. 

Lacteal  (lak'te  dl) : lymph  vessel  in 
the  villi. 

Larva  (lar'vd) : a young  stage  in  the 
development  of  some  forms  of  ani- 


mals, which  becomes  self-sustaining 
but  which  does  not  have  the  char- 
acteristics of  the  adult. 

Latent  (la'tent) ; lying  dormant  but 
capable  of  development. 

Legume  (leg'um) : plant  which  bears 
seeds  in  pods  — pea,  bean,  and  the 
like ; also  the  fruit  or  seed  of  such 
plants. 

Lenticel  (Ign'tl  s6l) ; a breathing  hole 
in  the  bark  of  a tree. 

Lepidoptera  (lepfl  dop'ter  d) : order  of 
insects  to  which  moths  and  butter- 
flies (scale  wings)  belong. 

Leucocyte  (lu'ko  sit) : a white  blood 
corpuscle  which  destroys  foreign 
organisms,  as  bacteria. 

Lichen : a composite  organism  con- 
sisting of  a fungus  and  an  alga. 

Ligament  (lig'd  mmt) : a band  of  con- 
nective tissue  binding  one  bone  to 
another. 

Lipase  (lip'as) ; the  digestive  enzyme 
that  splits  fats  into  fatty  acids  and 
glycerol. 

Liver  (liv'er) ; a digestive  gland  which 
secretes  bile. 

Lymph  (limf) : plasma  and  colorless 
corpuscles  outside  of  the  blood 
vessels. 

Lysins  (li'slnz) ; antibodies  which  have 
power  to  dissolve  bacteria  in  the 
blood. 

Macronucleus  (mak'ro  nu'kle  us) : the 
large  nucleus  of  a Paramecium,  as 
opposed  to  the  micronucleus,  or 
small  nucleus. 

Maggot : the  larva  of  an  insect. 

Mammary  (mam'd  ri)  glands : milk- 
secreting  glands  found  in  mammals. 

Mandible  (man'di  b’l) : in  insects,  a 
hard  cutting  jaw. 

Mantle  : the  soft  outer  fold  of  skin  in 
mollusks  which  secretes  the  outer 
shell. 

Maxilla  (mak  sll'd) : an  appendage 
near  the  mouth  of  arthropods,  modi- 
fied in  insects  to  form  an  organ  for 
getting  food. 

Maxilliped  (mSk  sil'I  pSd) : an  appen- 
dage next  to  the  maxilla  in  arthro- 
pods. Foot  jaw. 

Medulla  oblongata  (me  dhl'd  6bl6n- 
ga'td) : the  portion  of  the  brain 


GLOSSARY  OF  IMPORTANT  TERMS  G81 


between  the  eerehelluni  jind  the 
spinal  cord. 

Medullary  rays:  thin  i)lates  of  i)ith 
which  separate  tlie  wood  of  dicoty- 
ledonous stems  into  wedf^e-shaped 
masses. 

Mesoderm  (mCs'A  dilrm) : the  middle 
layer  of  cells  in  a young  animal 
embryo. 

Metabolism  (m(5  tJlb'd  llz’m) : changes 
taking  place  continually  in  living 
cells  which  may  result  in  either 
building  up  or  breaking  down  the 
cells. 

Metamorphosis  (mSt'd  mor'fd  sis) : 
change  of  form  undergone  from  egg 
to  adult,  as  in  insects. 

Micronucleus  (mi'krd  nu'kle  iis) : the 
small  nucleus  in  a Paramecium. 

Micropyle  (mi'krd  pll) : the  hole 
where  the  pollen  tube  enters  the 
embryo  sac. 

Midrib  : central  vein  of  a leaf. 

Migrant  (mi'grdnt) : an  animal  which 
moves  from  one  place  to  another 
and  back  regularly  at  stated  sea- 
sons of  the  year.  Many  birds  mi- 
grate to  warmer  regions  for  the 
winter. 

Mimicry  (mim'ik  ri) : the  imitation  in 
form  or  color  of  a harmful  insect  by 
a harmless  one  which  is  protected 
thereby. 

Mitosis  : a complex  type  of  cell  divi- 
sion, characterized  by  an  equal  dis- 
tribution of  chromatic  material. 

Molecule  (mdl'e  kul) : unit  of  a 

’ chemical  substance. 

Mollusca : the  phylum  of  animals  to 
which  the  clam  belongs. 

Monocotyledon  (mon'd  kdt'l  le'diin) : 
a plant  that  bears  seeds  having  but 
one  cotyledon. 

Monoecious  (md  ne'sh-ws) : having 
staminate  and  pistillate  flowers  on 
the  same  plants. 

Motor  neuron : a neuron,  or  nerve 
cell,  the  branches  of  which  end  in 
an  effector  (muscle  or  gland)  which 
brings  about  activity. 

Mucous  (mu'kws)  membrane  : a deli- 
cate, moist  membrance  lining  all 
body  passages  which  have  an  exter- 
nal opening. 

Muscle  (mtls'd) ; a contractile  tissue 


cai)able  of  bringing  about  move- 
menf . 

Mutation  (mu  ta'shdu) : a heritable 
modification  arising  from  internal 
causes  in  an  organism. 

Mycelium  (mi  se'li  um) : the  thread- 
like body  of  a mold,  or  other  fungus. 
The  individual  threads  are  called 
hyplue. 

Myriapoda  (nur'T  il])'d  da) : class  of 
animals  to  which  centipedes  and 
millipedes  belong. 

Narcotic  (nilr  kot'ik) : a substance 
which  blunts  the  senses  and  in  large 
quantities  causes  insensibility. 

Nectar  (iiek'tdr) : a sweet  fluid  se- 
creted by  certain  groups  of  cells 
knovm  as  nectar  glands  in  a flower. 
From  this  substance  bees  make 
honey. 

Nemathelminthes  (nem'a  thel  mln'- 
thez) : a phylum  of  animals  to 
which  the  unsegmented  round- 
worms  belong. 

Neuron  (nti'ron) : a nerve  cell  and  its 
branches. 

Nitrate  (ni'trat) : a soluble  salt  of 
nitric  acid. 

Nitrogen  (nl'tro  jen) : a gaseous  ele- 
ment, found  in  many  organic  com- 
pounds and  forming  almost  four 
fifths  of  the  atmosphere. 

Nitrogen-fixing  bacteria : bacteria 
which  take  free  nitrogen  from  the  air 
in  the  soil  and  build  into  nitrites 
which  are  later  converted  into  ni- 
trates. These  nitrates  can  be  used 
by  the  plants. 

Nucleus  (nu'kle  iis) : the  center  of 
activity  in  the  living  cell. 

Nutrient  (nu'tri  mt) : nourishing  sub- 
stance contained  in  foods. 

Nutritive  (nu'trt  tiv)  ratio : the  pro- 
portion of  protein  in  the  diet. 

Oils  : a class  of  nutrients  composed  of 
much  carbon  and  hydrogen,  with  a 
little  oxygen. 

Ommatidium  (om'd  tid'f  dm) : one 
of  the  elements  of  a compound 
eye. 

Operculum  (6  pur'ku  lum) : a lid  or 
flap  covering  the  gills  of  fishes. 

Opsonin  (op'so  nin) : a substance  in 


682 


GLOSSARY  OF  IMPORTANT  TERMS 


the  blood  which  helps  colorless 
corpuscles  destroy  bacteria. 

Organ : each  part  in  an  animal  or 
plant  which  performs  some  special 
work. 

Organic  : pertaining  to  living  things. 

Organism : a body  which  is  made  up 
of  organs  or  parts,  each  of  which 
has  a special  function  ; any  animal 
or  plant. 

Osculum  (os'ku  \um) : the  large  open- 
ing at  the  end  of  a sponge. 

Osmosis  (6s  mo'sis) : diffusion  of 
water  through  a semi-permeable 
membrane,  the  greater  flow  being 
toward  the  lesser  concentration  of 
water. 

Ovary  (6'vd  ri) ; in  a plant,  the  base 
of  a pistil,  containing  the  ovules ; 
in  an  animal,  the  egg-forming  gland. 

Ovipositor  (6'vi  poz'i  ter) : a special- 
ized structure  for  depositing  eggs, 
found  in  insects. 

Ovule  (6'vul) : a rounded  structure 
in  the  ovary,  which  may  become  a 
seed. 

Oxidation  (ok'si  da'shdn) : the  chemi- 
cal union  of  oxygen  with  some  other 
substance. 

Oxygen  (ok'si  jen) ; a gaseous  element 
found  in  the  air  and  in  many  com- 
pounds. 

Oxyhaemoglobin  (ok'si  he'mo  glo'bin) : 
a combination  of  oxygen  with 
haemoglobin. 

Palate  (pal'at) : the  roof  of  the  mouth. 
The  hard  palate  is  supported  by 
bone ; the  soft  palate  is  a fold  of 
mucous  membrane  lying  posterior 
to  the  hard  palate. 

Palisade  layer : a layer  of  green  cells 
under  the  upper  epidermis  of  a leaf. 

Palpus  (pal'pws)  or  palp  : in  arthro- 
pods, an  appendage  attached  to  a 
mouth  part ; usually  an  organ  of 
touch  or  taste. 

Pancreas  (pan'kre  ds) ; a digestive 
gland.  It  secretes  pancreatic  juice. 

Pappus  (p&p'ms)  ; a downy  or  fluffy 
outgrowth  from  the  ovary  wall. 

Parasite  (par'd  sit) ; an  organism 
which  secures  its  living  directly 
from  another  living  organism  with- 
out giving  anything  in  return. 


Parathyroids : the  four  small  endo- 
crine glands  attached  to  the  thyroid 
glands. 

Pasteurize  (pas'ter  Iz)  (from  Pasteur 
the  scientist) : to  heat  milk  to  about 
140°  Fahrenheit  for  about  30  min- 
utes for  the  purpose  of  killing  bac- 
teria in  it. 

Pathogenic  (path'o  jen'Ik)  organisms  : 
bacteria  or  protozoa  which  cause 
disease. 

Pectoral  girdle  : bones  which  support 
the  anterior  pair  of  appendages  in 
vertebrates. 

Pelvic  girdle  : the  bony  arch  to  which 
the  posterior  pair  of  appendages  are 

, attached  in  vertebrates. 

Pepsin : the  enzyme,  in  the  gastric 
juice,  which  begins  the  digestion  of 
proteins. 

Peptones  (pep'tonz) ; substance  pro- 
duced by  the  action  of  pepsin  on 
proteins. 

Perennial  (per  en'I  dl) ; lasting  or  con- 
tinuing more  than  two  years. 

Perfect  flowers : flowers  with  both 
stamens  and  pistils. 

Peristaltic  (per'!  stal'tik) : wavelike 
movements  of  the  muscles  of  the 
food  tube. 

Petal : one  of  the  leaflike  parts  of  the 
corolla. 

Petiole  (p6t'I  ol) : the  stalk  of  a leaf. 

Phagocyte  (fag'o  sit ) : a colorless  cor- 
puscle which  destroys  bacteria. 

Pharynx  (far'Inks) : the  part  of  the 
alimentary  canal  between  the  mouth 
and  the  esophagus. 

Phloem  (flo'em) : that  part  of  the 
fibrovascular  bundle  which  contains 
the  sieve  tubes. 

Photosynthesis  (fo'to  sin'the  sis) : the 
process  of  making  starch  out  of 
carbon  dioxide  and  water  by  the 
aid  of  sunlight,  as  is  done  by  a green 
cell. 

Phototropism  (fo'tot'ro  plz’m) : reac- 
tion to  light. 

Phylum  (fi'ldin) ; a large  division  of 
the  plant  or  the  animal  kingdom. 
It  is  composed  of  classes. 

Physiological  (fiz'l  oloj'I  kdl)  division 
of  labor ; performance  of  different 
kinds  of  work  by  different  parts  of 
an  organism. 


CLOSSAK’V  OF  LM 

Physiology  (flz'l  (^I'o  jl) : study  of  the 
functions  of  plants  and  animals. 

Pistil:  a structure  in  the  llower  con- 
taining the  ovary,  in  which  the 
seeds  are  foriiK'd. 

Pistillate:  having  pistils  but  no 

stamens. 

Pith:  the  soft,  sjiongy  tissue  in  the 
center  of  a dicotyledonous  stem  and 
between  the  vascular  bundles  of  a 
juonoeotyledonous  stem. 

Pituitary  (pi  tu'I  ta  ri)  body:  small 
endocrine  gland  located  in  the  base 
of  the  brain. 

Placenta  (phi  sen'tri) : absorbing  organ 
which  nourishes  the  embryo. 

Plankton  (id;'\nk't(5n) : small  plants 
and  animals  which  live  near  the 
surface  of  bodies  of  water. 

Plasma  (pliiz'mri) : the  colorless  fluid 
part  of  blood. 

Platyhelminthes  (plat 'I  hgl  mm'thez) : 
the  phylum  of  animals  to  which  the 
flat  worms  belong. 

Pleura  (pldb'rd) : the  membrane 
which  covers  the  lungs  and  lines 
the  cavity  containing  them. 

Plumule  (plob'mtil) : the  part  of  the 
embryo  above  the  cotyledons  which 
develops  into  the  stem  and  leaves. 

Pollen  grain : a small  cell  in  the 
stamens  of  a flower  which  con- 
tains the  sperm  nucleus  or  male 
gamete. 

Pollination  (pol'i  na'shwn) : the  trans- 
fer of  pollen  from  the  anther  to  the 
stigma.  Self-pollination  is  transfer 
between  parts  in  the  same  flower ; 
cross-pollination  is  transfer  between 
different  flowers,  or  between  flowers 
on  different  plants. 

Polyp  (pol'ip) : a simple  coelenterate, 
as  a sea  anemone  or  a single  coral 
individual. 

Posterior  (p6s  te'ri  er) ; nearer  the 
last  or  tail  end  of  an  animal. 

Precipitins  (pre  sip'i  tinz) : antibodies 
or  precipitating  substances  formed 
in  the  blood  as  a reaction  to  the 
introduction  of  certain  foreign  pro- 
teins. 

Primary  root : the  main  root  of  a 
plant . 

Proboscis  (pro  bos'Is) : a slender  suck- 
ing tube  found  in  insects. 


FOKTANT  TERMS  ()83 

Proglottids : rejiroductive  body  seg- 
ments of  a tapeworm. 

Proleg:  an  unjointed  abdominal 

appendage  of  insect  larvie. 

Protective  resemblance  : the  likeness 
of  living  organisms  in  color  or  form 
to  their  immediate  surroundings, 
thus  securing  protection  fi-om  attack 
of  enemies. 

Proteins  (i)r6'telnz) : nitrogenous  com- 
pounds found  in  the  bodies  of  plants 
and  animals;  a class  of  nutrients 
composed  of  nitrogen,  carbon, 
hydrogen,  and  oxygen,  together 
with  other  elements  in  some  cases. 

Prothallium  (pro  thal'i  um) : the  re- 
duced gametophyte  of  ferns. 

Protoplasm  (pro'to  plaz’m) : the  liv- 
ing substance  of  plants  and  animals. 

Protozoa  (proffb  zo'ci) : a phylum  con- 
taining one-celled  animals. 

Pseudopodium  (su'do  po'di  um) : a 
projection  of  protoplasm  used  for 
locomotion  in  protozoans. 

Pteridophyta  (ter'i  dof'i  td) : a phy- 
lum of  plants  to  which  the  ferns 
belong. 

Ptomaine  (to'ma  m) : poisonous  mate- 
rial probably  the  result  of  decompo- 
sition of  proteins. 

Ptyalin  (tl'd  lin) : an  enzyme  in  the 
saliva,  which  changes  starchy  foods. 

Pulmonary  (pul'mo  na  ri) : pertaining 
to  the  lungs. 

Pulvinus  (pul  vl'nus) : a special  motor 
organ  at  the  base  of  the  petiole  of  a 
leaf. 

Pupa  (pu'pd) : the  quiescent  stage  in 
insect  development  preceding  the 
adult. 

Pylorus  (pi  lo'rws) ; the  opening  from 
the  stomach  into  the  intestine. 

Quarantine  (kwor'dn  ten) : isolation 
of  the  sick  to  prevent  the  spread  of 
communicable  disease. 

Recessive  : a Mendelian  term  applied 
to  that  unit  character  which  is 
subordinate  to  another. 

Reflex : simplest  type  of  nervous 
response. 

Regeneration  (re  jen'er  a'shwn) : the 
growing  again  of  a part  of  an  animal 
which  has  been  lost. 


684 


GLOSSARY  OF  IMPORTANT  TERMS 


Reproduction  (re'pro  duk'shun) : the 
process  by  which  organisms  produce 
offspring.  In  asexual  reproduction 
a new  organism  is  formed  by  the 
separation  of  a cell  or  cells  from  a 
single  parent ; in  sexual  reproduc- 
tion two  cells  from  two  plants  or 
two  animals  of  different  sexes  come 
together  to  form  a new  individual. 

Respiration  (res'pf  ra'shwn) ; taking 
in  oxygen  and  giving  out  of  prod- 
ucts formed  by  oxidation  by  living 
cells. 

Resuscitation  (re  siis'I  ta'shwn) : re- 
vival from  unconsciousness. 

Retina  (ret'i  nd) : the  coat  of  the  eye 
in  which  the  optic  nerve  fibers 
terminate. 

Rhizoid  (ri'zoid) ; one  of  the  root- 
like bodies  in  fungi  and  some  other 
plants. 

Rodents : gnawing  mammals. 

Root  hairs  : epidermal  cells  elongated 
from  the  root. 

Ruminant  (rdo'mi  ndnt) : an  animal 
that  chews  a cud. 

Saliva  (sd  li'vd) ; the  secretion  of  the 
salivary  glands. 

Saprophyte  (sap'ro  fit) : an  organism 
which  derives  its  nourishment  from 
dead  organic  matter,  as  a mold  or  a 
mushroom. 

Sclerotic  coat  (skle  rot'il^;) : the  outer 
coat  of  the  eye. 

Scurvy : disease  caused  by  lack  of  a 
vitamin. 

Secretin  (se  kre'tin) : a hormone 
which  causes  the  pancreas  to  give 
out  its  digestive  fluid. 

Secretion  (se  kre'shdn) : material 
formed  by  the  activity  of  glands. 

Seed : a structure  formed  in  a fruit 
as  a result  of  the  fertilization  of  the 
egg  cell. 

Segment ; one  of  a number  of  serial 
divisions  of  an  animal’s  body  or  of 
an  organ. 

Self-pollination : shedding  pollen 

directly  on  the  stigma  of  the  same 
flower. 

Sensory  (sen'so  ri) : having  direct  con- 
nection with  any  part  of  the  seat  of 
sensation. 

Sepal  (se'pdl) ; a leaflike  part  of  the 


calyx  or  outer  circle  of  parts  in  a 
flower. 

Serum  (se'rdm) : the  liquid  part  of 
the  blood  plasma. 

Setae  (se'te) : bristles  used  for  locomo- 
tion in  earthworms  and  other  ani- 
mals. 

Sexual  (sek'shu  dl) : pertaining  to  or 
having  sex. 

Siphon  (si'fon) : a tube  through 
which  water  may  pass  into  and  out 
from  the  mantle  cavity  of  a mollusk. 

Species  (spe'shez) : the  smallest  group 
of  organisms  having  characteristics 
in  common  that  make  them  differ- 
ent from  all  other  organisms. 

Sperm  cell : the  male  sex  cell  or 
gamete. 

Spermatophyta  (spffr'md  tofff  td) : 
phylum  which  contains  the  seed- 
producing  plants. 

Spinal  cord  : a cord  of  nervous  tissue 
lying  in  the  vertebral  column. 

Spiracles  (spir'd  k’ls) : breathing  holes 
in  the  abdomen  in  insects. 

Spirillum  (spi  riLdm) : a spiral  form  of 
bacteria. 

Spleen  (splen) : ductless,  glandlike 
organ  near  the  stomach. 

Spongy  tissue : a layer  of  loosely 
placed  cells  in  the  leaf. 

Sporangium  (spo  ran'ji  um)  ; a sac 
containing  spores. 

Spore  (spor) : a reproductive  cell 
capable  of  growing  into  a mature 
organism.  It  may  be  produced 
sexually  or  asexually. 

Sporophyte  (spo'ro  fit) : spore-bearing 
part  of  a plant. 

Stamen  (sta'mSn) : an  organ  of  the 
flower  in  which  pollen  is  formed. 

Staminate : having  stamens  but  no 
pistils. 

Statocyst  (sta,t'6  slst) ; semi-organs  or 
balancing  pits,  formed  in  crusta- 
ceans and  some  other  animals. 

Sterilize  (st6r'i  liz) : to  destroy  bac- 
teria and  other  organisms,  usually 
by  heating. 

Stigma  (stig'md) : the  part  of  a pistil 
which  receives  the  pollen  grains. 

Stimulant  (stlm'u  Idnt) : a substance 
which  causes  temporary  activity  of 
nerve  or  muscle. 

Stimulus  (stlm'u  Ids) : an  agent  which 


GLOSSARY  OF  IMPORTANT  TERMS  685 


causes  an  organism  or  some  part  to 
react  when  affect eii  by  it. 

Stipule  (stlp'iil) : a lea  (like  outgrowth 
at  the  base  of  the  ])etiole. 

Stoma  (sto'nui)  (.j)!.  Stomata):  a 
breathing  hole  in  a leaf. 

Stomach  (stuni'T/k):  a sac-like  part 
of  the  food  tube  between  gullet  and 
intestine. 

Streptococci  (strfji'td  kdk'si) : spheri- 
cal bacteria  in  the  form  of  chains. 

Sweat  glands  : excretory  glands  in  the 
skin. 

Swimmeret  (swim'er&t):  one  of  the 
paired  appendages  on  the  abdomen 
of  crustaceans. 

Symbiosis  (sim'bl  o'sts) : a condition 
in  which  two  organisms  of  different 
kinds  live  together  in  a mutually 
beneficial  partnership. 

Synapse  (sl'nilps) : point  of  junction 
between  two  neurons. 

Tactile  corpuscle : sense  organ  of 
touch. 

Tarsus  (tar'sus) : the  ankle  bones  ; 
also  the  last  region  of  the  leg  of  an 
insect . 

Taste  bud  : end  organ  of  taste  found 
on  the  tongue. 

Teeth : limy  structures  in  the  mouth 
of  man  and  other  animals,  consist- 
ing of  incisors  or  cutting  teeth ; 
canines,  tearing  teeth  ; and  molars 
and  premolars,  crushing  and  grind- 
ing teeth. 

Tendon  (tfin'dan) : a band  of  con- 
nective tissue  attaching  muscle  to 
muscle  or  muscle  to  bone. 

Tentacle  (tgn'td  k’l) : a flexible  or- 
gan at  the  anterior  end  of  an 
animal  used  for  feeling,  grasping, 
etc. 

Testa  (tgs'td) : the  thick  outer  coat  of 
a seed. 

Testes  (tSs'tSz) : sperm-producing 
glands. 

Thallophyta  (thd  lof'l  td) : phylum  of 
plants  which  do  not  have  roots, 
stems,  or  leaves. 

Thoracic  (tho  ras'ik) : pertaining  to 
the  chest  region. 

Thorax  (tho'raks) : the  part  of  the 
body  between  the  head  and  the 
abdomen. 


Thyroid  (thi'roid):  large  endocrine 
gland  below  the  i)harynx. 

Tissue:  a collection  of  cells  all  more 
or  less  alike  and  having  the  same 
function. 

Tourniquet  (tcmr'nl  k6t) : a device  for 
arresting  bleeding. 

Toxins  (tbk'sinz) : poisons  produced 
by  bacteria. 

Trachea  (tra'ke  d) : the  windpipe  ; 
also  a respiratory  tube  of  insects. 

Transpiration  (tr^n'spl  ra'shwn) : the 
giving  off  of  water  vapor  from 
plants. 

Trichina  (tri  ki'nd) : pork  worm,  a 
parasitic  roundworm  causing  the 
condition  called  trichinosis. 

Tropism  (tro'piz’m) : a definite  re- 
sponse of  an  organism  to  one  of  the 
forces  in  its  environment. 

Trypanosome  (trip'd  no  som') : pro- 
tozoan which  causes  a disease  such 
as  sleeping  sickness. 

Tympanum  (tim'pd  ndm) : the  ear- 
drum. 

Urea  (u're  d) : a nitrogenous  waste 
excreted  in  the  urine. 

Vaccination  (vak'si  na'shdn) : inocu- 
lation with  a vaccine,  containing 
living  or  dead  microorganisms  or 
their  toxins,  in  order  to  protect  the 
body  from  disease. 

Vaccine  (vak'sin) : a substance  made 
from  living  or  dead  organisms, 
which,  when  inoculated  into  the 
body,  protects  it  against  a specific 
disease. 

Vacuole  (vak'u  6l) : a space  in  proto- 
plasm containing  air,  water,  sap,  or 
food  material. 

Variation  (va'ri  a'shdn) : in  biology, 
the  occurrence  of  differences  be- 
tween individuals  of  the  same 
species. 

Vein : a tube  which  conveys  blood  to 
the  heart. 

Venae  cavae  (ve'ne  ka've) : vessels 
through  which  the  blood  returns  to 
the  right  auricle  of  the  heart. 

Ventilation  (v6n'tf  la'shwn) : changing 
of  air  in  a room  or  building. 

Ventral  (vgn'trdl) : the  opposite  of 
dorsal. 


686 


GLOSSARY  OF  IMPORTANT  TERMS 


Ventricle  (ven'tri  k’l) : a muscular 
chamber  of  the  heart,  which  forces 
the  blood  out. 

Vermiform  appendix  (vhr'mi  form) : 
a narrow  tube  about  four  inches 
long,  closed  at  the  outer  end,  near 
the  beginning  of  the  large  intestine 
of  man. 

Vertebrae  (vur'te  bre) : bones  of  the 
vertebral  column. 

Vertebrate  : an  animal  having  a back- 
bone. 

Villus  (vfl'fts) : a minute  projection, 
an  absorbing  organ  of  the  small 
intestine. 

Vitamins  (vi'td  mmz) ; any  of  the 


group  of  constituents  in  food  which 
are  considered  necessary  to  prevent 
various  diseases  and  to  stimulate 
growth. 

Voluntary  (vor-ifn  ta  ri) : subject  to 
the  will  (used  with  reference  to 
muscles),  as  opposed  to  involun- 
tary. 

Xylem  (zi'lgm) : the  inner  woody  part 
of  a fibrovascular  bundle  which  con- 
ducts water  up  the  stem. 

Zygospores  (zi'go  spors)  or  Zygotes : 
spores  formed  by  union  of  sex 
cells. 


WEIGHTS,  MEASURES,  AND  TEMPERATURES 


As  the  metric  system  of  weights  and  measures  and  the  Centigrade  measure- 
ment of  temj)eratures  ai'e  em])loyed  in  scientific  work,  the  following  tables 
showing  the  English  equivalents  of  those  in  most  frequent  use  are  given  for  the 
convenience  of  those  not  already  familiar  with  these  standards.  The  values 
given  are  approximate  only,  but  will  answer  for  all  practical  purposes. 

W'EUiHT  Measures  of  Length 


Kilogram 

kg. 

2\  pounds 

Metric 

English 

Equivalents 

Gram  •.  . 

gm. 

1 1-  gr;iin<5  flY- 

oirdupois. 

, . Kilometer  . . 

ot  an  ounce 

km. 

1 of  a mile. 

avoirdupois. 

m. 

39  inches 

Meter  . . . 

Capacity 

Liter  . . 

1. 

01  cubic  inches,  Decimeter  . . 

or  a little 

dm. 

4 inches. 

more  than 

1 quart,  U.  S.  Centimeter  . . 

measure. 

cm. 

1 of  an  inch. 

Cubic  cen- 
timeter 

cc. 

A of  a cubic  Millimeter  . . 

inch. 

mm. 

of  an  inch. 

The  next  table  gives  the  Fahrenheit  equivalent  for  every  tenth  degree  Centi- 
grade from  absolute  zero  to  the  boiling  point  of  water.  To  find  the  correspond- 
ing F.  for  any  degree  C.,  multiply  the  given  C.  temperature  by  nine,  divide  by 
five,  and  add  thirty-two.  Conversely,  to  change  F.  to  C.  equivalent,  subtract 
thirty-two,  multiply  by  five,  and  divide  by  nine. 


Cent. 

Fahr. 

Cent. 

Fahr. 

Cent. 

Fahr. 

Cent. 

Fahr. 

100  . . 

. 212 

50  . 

. . 122 

0 . . 

. 32 

- 50  . . 

. - 58 

90  . . 

. 194 

40  . 

. . 104 

- 10  . . 

14 

- 100  . . 

. - 148 

80  . . 

. 176 

30  . 

. . 86 

- 20  . . 

. - 4 

70  . . 

. 158 

20  . 

. . 68 

- 30  . . 

. - 22 

AVjsolute  zero 

60  . . 

. 140 

10  . 

. . 50 

- 40  . . 

..  - 40 

- 273  . . 

. - 459 

687 


688 


APPENDIX 


Laboratory  Equipment 

The  following  articles  comprise  a simple  equipment  for  a laboratory  class  of 
ten.  The  equipment  for  larger  classes  is  proportionately  less  in  price.  The 
following  articles  may  be  obtained  from  any  reliable  dealer  in  laboratory  sup- 
pUes : such  as 


1 platform  balance,  with  rider,  weighing  to  100  gms.,  with  weights  on  car- 
rier. 

1 bell  jar,  about  365  mm.  high  by  165  mm.  in  diameter. 

10  wide  mouth  bottles,  with  corks  to  fit. 

10  25  cc.  dropping  bottles  for  iodine,  etc. 

25  250  cc.  glass-stoppered  bottles  for  stock  solutions. 

100  test  tubes,  assorted  sizes,  principally  6"  X 
50  test  tubes  on  base  (excellent  for  demonstrations). 

2 graduated  cylinders,  one  to  100  cc.,  one  to  500  cc. 

1 package  filter  paper  300  mm.  in  diameter. 

10  flasks,  Erlenmeyer  form,  500  cc.  capacity. 

2 glass  funnels,  one  50,  one  150  mm.  in  diameter. 

30  Petri  dishes,  100  mm.  in  diameter,  10  mm.  in  depth. 

10  feet  glass  tubing,  soft,  sizes  2,  3,  4,  5,  6,  assorted. 

1 aquarium  jar,  10  liters  capacity. 

2 specimen  jars,  glass  tops,  of  about  1 liter  capacity. 

10  hand  magnifiers,  vulcanite  or  tripod  form. 

2 compound  demonstration  microscopes  or  1 more  expensive  compound 
microscope. 

300  insect  pins,  Klaeger,  3 sizes  assorted. 

10  feet  rubber  tubing  to  fit  glass  tubing,  size  | inch. 

1 chemical  thermometer  graduated  to  100°  C. 

15  agate  ware  or  tin  trays  about  350  mm.  long  by  100  wide. 

1 gal.  95  per  cent  alcohol.  (Do  not  use  denatured  alcohol.) 

1 set  gram  weights,  1 mg.  to  100  g.  2 books  test  paper,  red  and  blue. 


1 razor,  for  cutting  sections. 

1 box  rubber  bands,  assorted  sizes. 
1 support  stand  with  rings. 

1 test  tube  rack. 

5 test  tube  brushes. 

10  pairs  scissors. 

10  pairs  forceps. 

20  needles  in  handles. 

10  scapels. 

12  mason  jars,  pints. 

12  mason  jars,  quarts. 

1 alcohol  lamp. 

1 gross  slides. 


10  Syracuse  watch  glasses. 

1 steam  sterilizer  (tin  will  do). 

1 spool  fine  copper  wire. 

2 bulb  pipettes, 
limewater. 

1 oz.  iodine  cryst. 

1 oz.  potassium  iodide. 

6 oz.  nitric  acid. 

6 oz.  ammonium  hydroxide. 

6 oz.  benzol. 

6 oz.  chloroform. 

^ lb.  copper  sulphate, 
i lb.  sodium  hydroxide. 


APPENDIX 


689 


ICK)  cover  slips  No.  2. 

1 mortar  and  pestle. 


I 11).  rochelle  salts. 
()  oz.  glycerine. 


Fehling  or  Benedict  solution. 


The  following  items  may  be  made  or  obtained  locally : 

Pocket  garden. 

\'entilation  box. 

Foods  containing  proteins  and  oils. 

Soil : saiul,  clay,  gravel,  loam,  humus. 

Seeds:  peas,  beans,  radish,  corn. 

Starch,  sugar. 

The  agar  or  gelatine  cultures  in  Petri  dishes  may  be  obtained  from  the  local 
board  of  health  or  from  any  good  druggist.  These  cultures  are  not  difficult 
to  make,  but  take  a number  of  hours  of  consecutive  work  to  prepare. 


Prepar.\tion  of  Culture  of  Protozoa 


If  it  is  impossible  to  buy  cultures  of  Paramecia  for  study,  they  can  be  pre- 
pared in  the  school  laboratory.  Fill  a sterilized  battery  jar  about  half  full  of 
water  and  add  a small  handful  of  hay  stems  cut  in  short  lengths.  Keep  the 
jar  in  a fairly  light  place.  In  a few  days  a scum  will  form  on  the  surface  of  the 
water,  in  which  bacteria  will  be  found.  Later  protozoans,  including  Paramecia, 
will  appear. 


ir:« 


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Uimm<  ^ ' 


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!'il!i!t!'J  V'  .■• 


Si 


-Ht 


i -.f . 'If .:,/Mlii'l 

? " ,/oJ  ilrHJj  : '■' 

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'.hi.i:  : 


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iV(  Kfu  ■■'  I'w:  ,y.  ■ 

, •;  ;^ ..  J-  . . P'A  ; 


I-:;;!  :*;LrAi|' 

jl,'  pP 

••n  /,t 


').;'  ■ 1 ! ('.'■' 

■1,^!  v-,>„^.rf’'  V 

" •'■‘•..A'  k.'  -.P-.  . h - 


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2 t'uUi  ■ 


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iip 


INDEX 


Abilities,  families  of  inferior,  (l.'Ki ; fam- 
ilies of  superior,  (i.'vS-dHl) ; neecled  for 
commercial  life,  ()47-()  lS  ; needed  for 
professions,  (147 ; needcil  for  trades, 
(>4,s 

Absorption,  147 ; from  larsre  intestine, 
377-379;  from  small  intestine,  379, 
3SU 

Accommodation,  of  eye,  441 
Acidosis,  prevention  of,  339 
Acquired  reactions,  443 
Active  immunity,  aetpiired,  475-476; 
mechanism  of,  4S1  ; vaccination 
against  smallpox,  479-4S() 

Activities,  acciuired  automatic,  443 ; 

inborn  automatic,  442  ; reflex,  428 
Adam’s  apple,  403 
Adaptability,  of  living  things,  50-52 
Adaptation,  40-52  ; a function  of  living 
things,  50-52 

Adaptations,  for  seed  dispersal,  108-111  ; 
of  birds,  260-263  ; of  fishes,  243  ; of 
frogs,  250  ; of  turtles,  256-257 
Adaptive  responses,  meaning  of,  426 
Adenoids,  408,  510 

Adrenal  glands,  effect  of  secretion,  393  ; 

location  of,  392 
Adrenaline,  393  ; use  of,  393 
Adrenin,  effect  on  body,  393 
Adulteration,  of  foods,  348-350 
Aedes,  yellow  fever  mosquito,  487-488 
Agassiz,  Louis,  pioneer  in  natural  history, 
668 

Age  and  size,  relation  of  diet  to,  338 
Agencies,  of  health,  507-511 
Agglutination  test,  390-391 
Agglutinins,  antibodies,  390 
Agriculture,  bacteria  in,  187-189  ; pro- 
fession, 651-652 

Air,  composition  of  expired,  404  ; com- 
position of  inspired,  404 ; in  lungs, 
407 ; needed  by  plants  for  making 
carbohydrates,  157-158 ; needed  for 
germination,  121 
Air  sacs,  in  lungs,  403 
Air  tubes,  403-404 

Alcohol,  and  susceptibility  to  disease, 
353  ; dangers  from,  352-353  ; death 
rates  from,  353-354  ; economic  effect 
of  drinking,  449  ; effect  on  blood,  402  ; 
effect  on  mortality  of  offspring,  353  ; 
relation  to  crime,  450 ; relation  to 
efficiencv,  449-450 ; relation  to  pau- 
perism, 450-451 

Algae,  200-202  ; characteristics  of,  200- 
201  ; examples  of,  201-202 


Alimentary  canal.  See  Digestive  tract. 
Alligators,  259 

Alternation  of  generation,  of  ferns,  204- 
205  ; of  mosses,  202-203 
Amino  acids,  329-330 
Amoeba,  217-219;  demonstration  to 
show,  217;  life  processes  of,  218-219 
Amphibians,  , 250-255  ; characteristics 
of,  255  ; classification  of,  255  ; used  as 
food,  535 

Amylase,  an  enzyme,  374 
Anaesthesia,  Dr.  Morton  and,  664 
Angiosperms,  207-213;  dicotyledons, 
209-213;  monocotyledons,  208-209 
Animal  breeding,  624-625 ; present 
problems  in,  625-626 
Animals,  and  plants  mutually  dependent, 
54-96 ; classification  of,  216-277 ; 
compared  with  plants,  43-45  ; develop- 
ment of,  617-620 ; economic  value 
other  than  food,  537-544 ; effect  of 
surroundings  on,  280-309,  610-611; 
harmful,  544-547  ; mechanism  of  re- 
sponse in,  425-426 ; one-celled,  217- 
222  ; relation  between  plants  and,  282- 
284  ; response  of,  422,  423  ; valuable 
for  food,  530-537 
Annual  rings,  167 

Annulata,  characteristics  of,  229 ; clas- 
sification of,  229 ; examples  of,  229- 
231 

Anopheles,  malarial  mosquito,  48,3-4S6 
Antennae,  sensory  organs  in  insects,  58, 
64,  428 

Anther,  of  flower,  83,  84 
Antibodies,  385  ; agglutinins,  390  ; anti- 
toxin, 477 ; lysins,  390 ; opsonins, 
388  ; precipitins,  390  ; production  of, 
476-477  ; work  of,  385,  390,  476 
Antiseptic  solutions,  317 
Antiseptics,  and  Lord  Lister,  663 
Antitoxin,  discovery  of  diphtheria,  663 ; 
how  used,  477-478  ; kinds,  478-479  ; 
meaning  of,  477 

Ants,  73,  74-75 ; how  to  make  nest  for, 
10 

Aorta,  397 

Aphids,  77-78  ; and  ants,  74 
Appendicular  skeleton,  319 
Appendix,  vermiform,  379 
Appetite,  relation  to  diet,  339 
Aquarium,  balanced,  11,  282-284,  286 
Arachnida,  232,  238 
I Arachnids,  2.38-239 
Archaeopteryx,  earliest  known  bird, 

I 271 


691 


692 


INDEX 


Aristotle,  on  progressive  development, 
665 

Arteries,  395  ; structure  of,  398 
Arteriosclerosis,  cause  of,  401 
Arthropoda,  232-242  ; characteristics  of, 
232-233  ; classification  of,  232 
Artidcial  propagation,  of  fishes,  591-592 
Artificial  respiration,  408-409 
Artificial  selection,  605-606,  633-634 
Arum  family,  of  flowers,  208,  209 
Asexual  reproduction,  of  Paramecium, 
221.  See  Vegetative  propagation 
Associative  axon,  431 
Audubon,  work  on  birds,  668-669 
Auricles,  396,  397  , 

Autonomic,  nervous  system,  430 ; func- 
tions of,  434 
Axial  skeleton,  319 

Axon,  associative,  431  ; motor,  431  ; of 
neuron,  431 ; sensory,  431 

Bacillum,  form  of  bacteria,  183 
Bacillus  pestis,  cause  of  bubonic  plague, 
491 

Bacteria,  aerobic,  186 ; anaerobic,  186 ; 
and  air,  186 ; cause  of  pus,  317 ; 
control  growth  of,  457-461  ; diseases 
caused  by,  463-470  ; demonstration  to 
show  effect  of  temperature  on,  457 ; 
destruction  of  white  corpuscles,  388 ; 
effect  on  food,  185-186  ; forms  of,  183  ; 
how  cause  diseases,  461-463 ; how 
discovered,  181 ; how  gePffor  study, 
181-182  ; pure  culture  of,  182 ; rela- 
tion to  fermentation,  187  ; relation  to 
free  nitrogen,  187-188 ; size  of,  183  ; 
things  done  by,  186-189 ; what  are, 
181  ; where  found,  183-184 ; where 
numerous,  184-185 ; work  done  by, 
1-2,  185-189 

Bacterial  diseases,  461-463 ; and  milk, 
468  ; and  water  supplies,  467  ; diph- 
theria, 466  ; how  get,  463-470  ; im- 
munity to,  474-481  ; necessity  of 
quarantine  in,  471-473 ; septic  sore 
throat,  470 ; spread  through  mouth 
spray,  466 ; tetanus,  470 ; tubercu- 
losis, 464-465 ; typhoid  fever,  466- 
467 

Bacteriology,  definition  of,  1 
Balance  of  life,  55-56 
Balance  of  nature,  and  man,  288-290 
Banting,  Dr.,  work  with  insulin,  395, 
600 

Bark,  of  tree,  structure  of,  166-167  ; use 
of,  167-168 

Barriers,  and  effect  on  living  things, 
305-308 

Basal  metabolism,  meaning  of,  342 
Bast  fibers,  166,  168 
Bathysphere,  of  William  Beebe,  653 
Bean,  growth  of  plant,  136;  laboratory 
exercise  on  seed,  117;  nutrients  in 


seed,  119-120;  stages  in  growth,  122- 
123;  structure  of  seed,  117 
Beebe,  William,  653 
Beetle,  carrion,  561  ; Japanese,  564-565, 
life  history  of,  76-77,  563 ; lady- 
bird, 561  ; potato,  77 
Beetles,  classification  of,  60-61,  238 
Biology,  activities  connected  with  study 
of,  7-16 ; and  conservation,  2 ; and 
self-improvement,  644-654 ; early 
workers  in,  657-659  ; economic  values 
of,  2-7 ; how  to  study,  6-16 ; in 
relation  to  society,  4 ; makers  of,  656- 
672 ; meaning,  1 ; prepares  for  voca- 
tion, 649-654  ; reading  values  of,  3 ; 
where  to  study,  4-6  ; why  study,  1-4 
Birds,  adaptations  of,  260-263  ; care  of 
young,  266 ; classification  of  birds, 
267 ; common,  551-560 : bluebird, 

552- 553  ; catbird,  556-557  ; chickadee, 

553- 554 ; crow,  558 ; downy  wood- 
pecker, 557  ; English  sparrow,  559  ; 
flicker,  557,  558 ; goldfinch,  555 ; 
oriole,  557-558 ; phoebe,  555-556 ; 
robin,  552 ; screech  owl,  558,  559 ; 
song  sparrow,  554-555 ; swallow, 
556  ; warbler,  555,  559  ; wren,  554 ; 
economic  importance  of,  547-551 ; 
food  of,  547-549  ; harmful,  559-560 ; 
methods  of  conservation  of,  594-597 ; 
migration  of,  595-596  ; nervous  system 
of,  264 ; nesting  habits  of,  264,  265, 
266 ; relation  to  reptiles,  266-267 ; 
reproduction  of,  618-619  ; respiration 
of,  263-264 ; sense  organs  of,  264 ; 
state  and  federal  government  methods 
of  conservation,  596 ; used  for  food, 
536  ; work  of  Audubon  on,  668-669 

Blackberry,  production  of  white,  672 
Black  stem  rust,  195-196,  197 
Bladder,  swim,  of  fish,  246 
Blastula,  617 
Blister  rust,  196 

Blood,  cause  of  clotting,  388-389 ; cir- 
culation of,  395-401  ; circulation  in 
fish,  246-247  ; circulation  in  frog,  251- 
252  ; composition  of,  386  ; corpuscles 
of,  386-389  ; effect  of  alcohol  on,  402  ; 
how  food  gets  into,  377-397  ; platelets, 
389 ; pressure  of,  399 ; relation  of 
lymph  to,  389  ; transfusion  of,  391 
Blood  plasma,  composition  of,  386 ; 

disease-resisting  function  of,  390-391 
Blood  platelets,  function  of,  389 
Blood  serum,  388,  chemical  composition 
of,  20-21 ; compared  with  sea  water, 
20-21 

Blood  vessels,  395 ; structure  of,  398- 
399.  See  Arteries,  Capillaries,  and 
Veins. 

Bluebird,  552-553 ; food  of,  548 
Body:  how  body  protects  itself,  475-476 ; 
regulation  of  heat  of,  415 


INDEX 


Bones,  relation  to  rnusolos,  310-322 
Bony-fish,  e^;<^-la\■in^  lial)its  of.  217-248 
Boveri,  work  on  chromosomos,  ()7() 
Bracers,  in  im'dicines.  3.5o 
Bracket  fungus,  104-10.j 
Brain,  420;  localization  of  functions  in, 
434;  i)art.s  of,  4.32  ; structure  of,  432- 
4.3.3 

Brains,  of  wirious  vt'rlt'hrates,  433 
Bread  making,  atui  \ea.st,  102-103 
Breathing,  hygienic  habits  of,  407 ; 
mechanics  of,  40G-407  ; of  fish,  245  ; 
of  frotr,  251 

Breeding,  animal,  G24-625 ; i)lant  and 
animal,  G7U-G72  ; practical  results  in, 
G24  ; present  i)rohlems  in,  G25-G2G 
Breeding  experiments,  Mendel’s,  G20- 
G23 

Bronchial  tubes,  403-404 

Bruises,  treatment  for,  401 

Bryophyta,  180  ; classification  of,  203  ; 

mosses,  202-203 
Bubonic  plague,  cause  of,  401 
Budding,  method  of,  G13,  G14;  of  yeast, 
101 

Bumblebees,  70  ; life  history  of,  70 
Bundles,  fibrovascular,  13G-137,  144, 
168,  170,  171 

Burbank,  Luther,  work  on  plant  breed- 
ing, 624 ; fruits  and  vegetables  im- 
proved by  him,  671-672 
Bureau  of  Agriculture,  work  on  insect 
control,  567-568 

Butter-and-eggs,  how  pollinated,  91 
Buttercup  family,  210-211 
Butterfly,  compared  vnth  moths,  OS- 
GO  ; laboratory  exercise  on,  G5.  ^See 
Monarch  butterfly. 

Cactus,  301,  302 

Calorie,  defined,  32S  ; need,  34.3-344 
Calorie  requirement,  workbook  exercises 
on  daily,  343 

Calories,  needed,  of  various  nutrients, 
341 

Calorimeter,  use  of,  328 
Calyx,  of  flower,  83 
Cambium  layer,  167-168 
Canning,  and  bacteria,  458 
Capillaries,  395,  396 ; structure  of,  398, 
399 

Carapace,  of  crayfish,  233 
Carbohydrate-making,  compared  to 
milling,  160-161 

Carbohydrates,  30-31  : air  needed  bv 
plants  to  make,  157 ; chlorophyll 
needed  bv  plants  to  make,  157-158; 
light  needed  by  plants  to  make,  157- 
158 

Carbon  cycle,  286 

Carbon  dioxide,  demonstration  on  need 
of  plants  for,  158-159;  test  for,  25 
Carnivores,  268-269 


693 


Carrell,  preparation  of  Dakin  solution 
by,  G64-()G5 

Carriers,  and  typhoid,  469 
Carrot  family,  212 
Catbird,  556-557 
Cats,  liarm  done  by,  546 
Cell,  as  a unit  of  structure  and  function, 
222;  body,  ()27-G28 ; described  by 
Hooke,  38-39;  division  of,  48,  612- 
613;  germ,  627;  guard,  152,  1.53; 
laljoratory  exercise  on  plant  and 
animal,  46 ; mitotic  division  of,  49 ; 
multiplication  of,  48-49  ; of  Elodea,  46  ; 
respiration  of,  405;  sap,  145;  sex,  48- 
49,  627 ; structure  of,  46 ; structure 
of  leaf,  152-153 
Centipede,  239 

Central  nervous  system,  430  ; functions 
of,  434-435 
Cephalopods,  241-242 
Cerebellum,  429 ; function,  432,  433, 
434  ; position  of,  432 
Cerebrum,  429 ; function  of,  433,  434  ; 
size  in  various  lower  animals,  433 ; 
structure  of,  432 

Character-determiners,  in  chromosomes, 
626-627 

Characters,  dominant,  621,  630-631  ; 
inheritable,  630-631  ; law  of  unit,  621  ; 
recessive,  621,  630-631 
Chemical  elements,  in  human  body,  24 
Chestnut  blight,  194 
Chewing  food,  need  for,  370 
Chickadee,  553-554  ; food  of,  548 
Chlorophyll,  135;  demonstration  to  show 
use  to  plant,  158 ; needed  by  plants, 
157-159 

Chloroplasts,  159  ; function  of,  46  ; com- 
pared to  mill,  160 

Chromosomes,  bearers  of  heredity,  626- 
627 ; behavior  in  reduction  division, 
627,  630;  functions  of,  48-49;  loca- 
tion of  genes  in  fruit  fly,  627-628 ; 
number  in  body  cells,  627  ; number  in 
sex  cells,  627-628 ; workers  on,  670- 
671 

Cicada,  life  history  of,  77,  78 
Cilia,  of  Paramecium,  220 
Circulation,  demonstration  to  show  in 
plant,  168-169  ; effect  of  exercise  on, 
400-401  ; in  a plant,  166-177  ; of  blood 
in  body,  395-401  ; portal,  398 ; 
pulmonary,  397-398  ; systemic,  397 
Circulatory  system,  diagram  on,  400 ; 

of  fish,  246-247 ; of  frog,  251-252 
City  supervision,  and  health,  600-601 
Clams,  used  for  food,  532-533 
Classification,  devised  by  Linnaeus,  668  ; 
of  living  things,  177-178;  of  plants, 
180 

Cloaca,  of  frog,  368 
Clothing,  relation  to  skin,  318 
Clover,  how  pollinated,  92 


694 


INDEX 


Coccus,  kind  of  bacteria,  183 
Cochineal,  insect  origin,  561 
Cochlea,  function  of,  439 
Codling  moth,  566 

Coelenterata,  characteristics,  224 ; clas- 
sification, 226  ; examples  of,  224-225 
Colds,  cause  of,  415-416 
Cold  storage,  and  bacteria,  458 
Coleoptera,  60-61,  238 
Color  in  leaves,  cause  of  change  in,  159 
Commercial  life,  abilities  needed  for, 
647-648 

Communal  life,  of  insects,  69-75 
Communicable  diseases,  508-510 
Communities,  plant  and  animal,  298-300 
Community,  improvement  of  conditions 
in,  503-507  ; inspection  of  food  sup- 
plies, 504,  505 
Composite  family,  212-213 
Composite  flower,  pollination  of,  92 
Compounds,  meaning  of  chemical,  19-21 
Conditions,  improve  community,  503- 
507  ; improve  home,  597-600  ; improve 
school,  501-503 
Conifers,  206 

Conjugation,  in  Spirogyra,  201-202,  615 ; 

of  Paramecium,  221-222 
Conqueror,  how  man  has  become  world, 
420-451  ; of  disease,  659-665 
Conservation,  applied  to  man,  599- 
601  ; of  birds,  594-597 ; of  fish  and 
other  aquatic  animals,  587—593 ; of 
forests,  581-587 ; of  mammals,  598- 
599  ; of  natural  resources,  2,  572-601  ; 
of  trees,  574-581 
Constipation,  379-380 
Contractile  vacuole,  of  amoeba,  219 ; 

of  Paramecium,  220 
Coral,  economic  value  of,  542 
Corn,  cross  section  of  grain  of,  125 ; 
cross  section  of  stalk  of,  169;  en- 
dosperm of,  125 ; use  of  food  supply 
during  germination,  128 ; uses  of, 
524-525 

Corn  worm,  harm  done  by,  562 
Corolla,  of  flower,  83 
Corpuscles,  red,  387  ; white,  387-388 
Cortex,  of  stem,  166 
Cotton,  uses  of,  528-529 
Cotton-boll  weevil,  562-564  ; control  of, 
567  ; life  history,  563  ; spread  of,  563 
Cotyledons,  bean,  117  ; food  in,  117-118 
Cowbird,  559,  560 

Crab,  fiddler,  236 ; rock,  236 ; used  for 
food,  534 

Crayfish,  antennae,  233 ; appendages, 
233 ; circulatory  system  of,  235 ; 
description  of,  233 ; digestion  of,  234- 
235 ; eyes,  233-234 ; excretion  of, 
235  ; food-getting,  234  ; gills,  235  ; 
life  history  of,  235-236 ; locomotion 
of,  233 ; nervous  system  of,  235 ; 
skeleton  of,  233 


Cretinism,  cause  of,  393 
Crocodiles,  259 

Crops,  damaged  by  insects,  562-565 ; 
rotation  of,  188-189 

Cross-pollination,  88 ; artificial,  684-635  ; 
devices  to  secure,  92-94 ; specific  ex- 
amples of,  91—96 
Crow,  548,  558-559 

Crustaceans,  as  food,  533-534  ; compared 
with  insects,  237 ; crab,  534 ; lobster, 
533 ; shrimp,  534 

Culture  medium,  for  bacteria,  181-182 
Cure-alls,  medicine,  356-357 
Cuts,  treatment  of,  401 
Cycads,  205-206 

Cycle,  carbon,  286 ; nitrogen,  285 ; 
oxygen,  285-286 

Cypress  knees,  150 

Dakin  solution,  664-665 
Damsel  fly,  79  ; order  of,  238 
Darwin,  Charles,  family  tree  of,  638; 
on  natural  selection,  605 ; on  polli- 
nation of  flowers,  56 ; on  progressi\'e 
development,  665-667 ; on  variation, 
605 

Decay,  caused  by  bacteria,  186-187 
Dehiscent  fruits,  scattering  seeds  by, 
109-110 

Dendrites,  of  neuron,  431 
Development,  of  birds,  618-619 ; of 
mammals,  619-620  ; progressive,  665- 
667 

de  Vries,  Hugo,  mutants,  633 ; on  plant 
breeding,  671 
Diabetes,  cause  of,  395 
Diastase,  action  on  starch,  130 
Dick  test,  479  ; for  scarlet  fever,  665 
Dicotyledonous  stem,  circulation  of  food 
in,  170-171  ; cross  section  of,  167 ; 
growth  of,  167-168  ; structure  of,  166- 
167 

Dicotyledons,  126,  127 ; buttercup 

family,  210-211;  carrot  family,  212; 
composite  family,  212-213 ; heath 
family,  212  ; legume  family,  209-210  ; 
mint  family,  211  ; mustard  family, 
211  ; rose  family,  210  ; willow  family, 
211-212 

Diet,  best  proposition  of  nutrients  in, 
340-343  ; relation  of  appetite  to,  339  ; 
relation  of  cost  of  food  to,  345-346  ; 
relation  of  digestibility  to,  338-339 ; 
relation  of  environment  to,  335, 
338  ; relation  of  sex  to,  338 ; relation 
of  size  and  age  to,  338 ; relation  of 
work  to,  335 

Diffusion,  147  ; demonstration  showing, 
147  ; physiological  importance  of,  149- 
150 

Digestibility,  of  food,  relation  to  diet, 

338-339 

Digestion,  129-130 ; demonstration  to 


INDEX 


695 


show  of,  ; experiments  to 

show  stomacii,  :i7  J : liVKiene  of,  .isO  ; 
in  rra.\  fisli,  ; in  frof^,  2.')()— 

2.')1  ; in  mouth,  ;h)4-;3(>5 ; in  plants, 
171:  in  small  intestine,  37;3-;374 ; 
in  stomach,  .'3()9-372 ; meaninp:  of, 
129;  purpose  of,  130 ; salivary,  .364- 
365  : table  of  chemical,  3S1 
Digestive  organs,  of  fish,  246;  of  frog, 
3l)S  : of  man,  36S,  369-3S0 
Digestive  system,  of  fish,  246  ; laboratory 
study  of  frog’s,  367-368;  laboratory 
stud.\'  of  man’s,  367-368 
Digestive  tract,  description  of  man’s, 
369 : laboratory  study  of  frog’s,  367- 
368 ; laboratory  stud.v  of  man’s, 
367-368  : parts  of,  368-369 
Dihybrid,  623  : breeding  of,  623 
Dinosaur,  273  ; eggs  of,  266-267 
Diphtheria,  antitoxin  treatment  for, 

477- 478  , cause  of,  466  ; prevention  of, 
478 ; Schick  test  of  susceptibility  to, 

478- 479 : toxoid,  478 ; transmission 
of.  472 

Diptera,  59 , classified,  238 ; discussed, 
75-76 

Disease,  some  conquerors  of,  659-665 
Disease  carriers,  Aedes  mosquito,  487- 
488  • Anopheles  mosquito,  483-484  ; 
bedbuar,  491  body  louse,  491  ; flea, 
491 , house  fl.v,  489-491  ; people,  469 
Diseases,  carried  by  insects,  483-484, 
487-488,  489-491  ; caused  by  proto- 
zoans, 482-486 ; caused  by  worms, 
492-496 ; how  caused  by  bacteria, 
461-463,  how  get,  463-470;  of  nose 
and  throat,  407-408  ; spread  by  rats, 
491-492.  See  also  Bacterial  diseases. 
Disinfectant,  laboratory  problem  to  show 
most  effective,  460 

Disinfection,  need  of,  461  terminal,  509 
Division,  cell,  cause  of,  611-613  ; process 
of,  48  49 
Dodder,  105 

Domesticated  animals,  economic  value 
of,  537 

Dominance,  Mendel’s  law  of,  621 
Dominant  characters,  621.  630-631 
Dragon  flies,  78-79  ; classification,  238 
Drug-producing  plants,  529-530 
Drugs,  in  medicine,  355 
Duct,  thoracic,  399 

Ductless  glands,  361,  392-395  ; adrenal, 
393  ; location  of,  392  ; pancreas,  392  ; 
parathyroid,  392  ; pituitary,  393-394  ; 
reproductive,  392,  394-395 ; secretions 
of,  392  ; thymus,  394 ; thvroid,  393 
Dwarfs,  probable  cause  of,  393 

Ear,  diagram  of,  439 ; in  fish,  245 ; in 
frog,  250 ; inner,  439 . middle,  438- 
439 ; organ  of  hearing,  438 ; outer, 
438 


Earthworm,  grafting,  614 ; laboratory 
exercise  on,  229;  life  process  of,  230- 
231;  locomotion  of,  229-2.30;  repro- 
duction of,  231;  segments  of,  229; 
setae  of,  229 

Echinodermata,  characteristics,  226-228 ; 
classification,  227 

Echinoderms,  characteristics,  226:  clas- 
sification, 227 : examples,  226-228 
Ecological  realms,  308-309 
Ecological  succession,  300-305 
Ecology,  282 

Economic  importance,  of  birds,  547-551 ; 
of  insects,  560-569 

Economic  values,  of  animals,  530-544 ; 
of  plants,  520-530 

Ectoderm,  development  of,  618  ; systems 
formed  from,  617,  618 
Edwards,  Jonathan,  family  of,  637-638 
Egg,  development  of  fertilized,  617- 
618  ; in  Vaucheria,  615 
Egg  ceU,  617 

Elements,  found  in  living  things,  29; 
found  in  the  environment,  29 ; mean- 
ing of,  19 

Elodea,  cells  of,  46;  protoplasm  of,  47 
Embryo,  86;  development  of  bird,  618; 
factor  necessary  to  awaken,  120,  121  ; 
in  plant,  616 ; protection  in  birds, 
618-619  ; piotection  in  mammals,  619- 
620;  of  bean,  117;  what  becomes  of 
parts  during  growth,  122-123 
Embryo  sac,  in  flower,  85 
Emulsion,  374 

Endocrine  glands,  361 ; adrenal,  393 ; 
location  of,  392  ; pancreas,  392,  394 ; 
pituitary,  393-394  ; reproductive,  392, 
394-395  ; secretions  of,  392  ; thymus, 
394;  thyroid,  392,  393 
Endoderm,  development  of,  618 ; sys- 
tems formed  from,  617,  618 
Endosperm,  how  formed,  610;  of  corn, 
125 ; of  other  seeds,  125-126 
Energy,  conservation  of,  27 ; forms  of, 
26;  kinetic,  313;  potential,  313; 
sun,  source  of,  157 

Energy  requirement,  how  to  compute, 
342-343 

Environment,  affecting  animals,  610- 
611;  affecting  plants,  608-610;  cause 
of  changes,  300-305  ; factors  affecting 
ecological  relationship,  290—297  ; how 
man  controls  natural,  32-34  ; improve- 
ment of  natural,  33-34  ; man  control 
for  health,  455-511;  man  control  for 
wealth,  518-569  ; relation  to  diet,  335, 
338  ; versus  heredity,  606-607 
Enzymes,  129,  137 ; diastase,  130 ; in 
plants,  162,  171 ; work  of,  361,  362 
Ephemerida,  order  of  insects,  238 
Epidermis,  human  body,  316;  of  leaf, 
152,  153;  of  root  hairs,  144;  of  stem, 
166 


696 


INDEX 


Epiglottis,  370 

Erhlich,  Paul,  on  immunity,  664 
Erosion,  prevented  by  trees,  574,  575 
Esophagus,  368,  370 
Essential  organs,  of  flower,  83 
Eugenics,  meaning  of,  636 
Euglena,  how  receive  stimuli,  422 
Evaporation,  from  plants,  factors  in, 
164 

Evolution,  evidences  of,  271-273;  of 
horse,  273-274  ; workers,  665-667 
Examination,  physical,  510-511 
Excretion,  kidneys,  412-414 ; need  of, 
45  ; of  crayfish,  235  ; organs  of,  412- 
415 : skin,  414-415 
Excretory  organs,  412-415 
Exercise,  effect  on  circulation,  400-401 
Existence,  struggle  for,  111 
Exophthalmic  goiter,  393 
Expiration,  meaning  of,  406 ; process  in 
man,  407 

Eye,  description  of,  440-441 

Eyes,  of  crayfish,  233-234;  of  fish,  244; 

of  insects,  58,  64 
Eyespot,  of  Euglena,  422 
Eyestrain,  510 

F,  meaning  of,  621 

Factors,  affecting  life,  608  ; necessary  for 
germination,  120—121 
Families,  of  inferior  ability,  636-637 ; 

of  superior  ability,  638-639 
Fatigue,  effect  on  nerve  cell,  448 
Fats,  31  ; digestion  of,  373-374;  manu- 
factured in  leaf,  161  ; required  in  diet, 
328 

Feet,  care  of,  321-322 
Fermentation,  and  yeast,  190 ; relation 
of  bacteria  to,  187 
Fern,  life  history  of,  204-205 
Fertilization,  adaptations  of  plants  for, 
91-94,  95-96;  in  flowers,  84-86,  615- 
616  ; in  frog,  252  ; in  Vaucheria,  615 
Fever,  cause  of,  415 
Fibers,  useful  vegetable,  529 
Fibrinogen,  in  blood,  388 
Fibrovascular  bundles,  136-137,  144, 
167-168,  169 
Fig,  pollination  of,  94-95 
Filament,  of  flower,  83  ; of  gill  of  fish, 

246  ; of  Spirogyra,  201-202,  615 
Filterable  virus,  479-480 

Fins,  of  fish,  244,  246 

First  aid,  for  burns  and  scalds,  317-318 ; 

for  skin  wounds,  318 
Fish,  as  food,  534-535;  body  of,  243- 
244  ; breathing  of,  245  ; characteristics 
of,  242-249  ; circulatory  system,  246- 

247  ; classification  of,  249  ; digestive 
system  of,  246 ; egg-laying  habits, 
247-248  ; fins,  244  ; gills  of,  245-246  ; 
laboratory  exercise  on,  243 ; lateral 
line  of,  245 ; nervous  system,  247 ; 


reproduction  of,  247-248 ; sense  or- 
gans, 244-245  ; swim  bladder,  246 
Fishes,  242-249 ; artificial  propagation 
of,  591-592 ; conservation  of  fresh- 
water, 587-588 ; conservation  of 
ocean,  588  ; migration  of,  588  ; spawn- 
_ ing  habits  of,  588-589 
Fission,  of  Paramecium,  221 ; process  of 
cell  division,  183 

Fixation,  of  nitrogen,  by  bacteria,  188 
Flatworm,  regeneration  in,  612 
Flatworms,  Platyhelminthes,  228  ; harm- 
ful, 492-493 

Flexner,  on  infantile  paralysis,  665 
Flicker,  557,  558 

Flies,  characteristics  of,  75-76 ; classifi- 
cation of  various,  59,  238 ; develop- 
ment of  house,  75-76 ; dragon,  78-79 ; 
life  history  of  house,  76 
Flowers,  artificial  pollination  of,  634- 
635  ; cross-pollination  by  insects,  91  ; 
cross-pollination  of  composite  head, 
92  ; devices  of,  to  secure  pollination, 
92-95 ; essential  organs  of,  83 ; hy- 
bridization of,  634-635 ; imperfect, 
96 ; laboratory  exercise  on  structure, 
83  ; pollinated  by  wind,  95-96 ; use 
to  plants,  83-86 

Food,  and  ecological  succession,  302-303  ; 
animals  valuable  as,  530-537  ; care  in 
home,  498-499 ; definition  of,  30 
digestion  in  plants,  171-172;  digestion 
in  stomach,  369-372  ; fuel  value  of, 
328;  functions  of,  162;  how  ab- 
sorbed, 378-379 ; how  man  deter- 
mines value,  324-357 ; how  prepared 
for  body  use,  360-381 ; in  cotyledons, 
117-118;  made  by  plants,  134-173: 
need  of,  328-329  ; nutrients  in,  30-31 , 
plants  used  as,  520-528  ; preservation 
of,  458-460  ; raw  material  needed  by 
plants  to  make,  154-155 ; relation  of 
cost  to  diet,  345-346 ; response  of 
plants  and  animals  to,  41 ; storage  in 
plants,  171—172 

Food  conditions,  how  living  things  are 
affected  by,  297 
Food  habits,  good,  347-348 
Food  making,  in  green  cells,  and  human 
welfare,  162-163 ; products  of,  160- 
162  ; results,  162-165 
Food  nutrients,  30-31,  327-328;  tests 
for,  118-119,  131 

Foods,  determination  of  relative  cheap- 
ness of,  345-348 ; how  circulated  and 
used  in  body,  384-416 ; inorganic, 
31  ; mineral  requirement  in,  331-332; 
nutrients  in,  30-31,  118-119,  327-328  ; 
preparation  of,  346-347 ; uses  of,  327- 
332 

Food  substances,  tests  of,  131 
Food  supplies,  care  in  home,  498-499; 
inspection  of,  504,  505 


INDEX 


()97 


Food  supply,  essontinls  of  an  adequate,  I Giants,  probable  cause  of,  .393 

.332  Gills,  of  crayfish,  233 ; of  fish,  245, 

24G 


Food-taking,  of  plants  and  animals,  44 
Food  vacuole,  of  amoeba,  2 IS;  of  Para- 
mecium, 221) 

Forestry,  gooil,  57i)-5Sl  ; iirofession  of, 
()52 

Forests,  methods  of  conservation  of, 
5S4-r)S.5 : need  of  eonser\  ation,  579- 
5S7  : wastes  in,  5S1-5S3 
Forest  trees,  injured  by  insects,  565 
Fossils,  story  told  by,  271-274 
Frog,  breathing  of,  251  ; circulatory  sys- 
tem, 251-252;  digestion  of,  250-251; 
digestive  system,  367-36S ; digestive 
tract  compared  with  man,  3()S ; food- 
getting, 250,  251  ; laboratorv  study  of, 
250;  life  history  of,  252-254;  mouth 
compared  with  man’s,  363,  364  ; re- 
production of,  252-254 ; resiiiratory 
tract  compared  with  that  of  man,  403  ; 
sense  organs,  250 
Fruit,  definition  of,  87-88 
Fruit  fly,  jNIediterranean,  566 
Fruits,  how  formed,  86-88  ; used  as  food, 
526-528 

Fruit  trees,  injured  by  insects,  565-566 
Fuel  value,  of  foods,  328 
Functions,  of  living  things,  36-52 
Fungi,  characteristics  of,  181  ; destruc- 
tive, 193-197  ; kinds  of,  181-199 
Fungus,  shelf,  194-195 
Furs,  value  of,  540-541 

Gall  insects,  value  of,  561-562 
Gamete,  female,  205,  615  ; male,  205,  615 
Gametophyte,  of  fern,  204-205  ; of  moss, 
203 

Ganglion,  430 

Garden  fruits,  and  vegetables,  used  as 
food,  526-527 
Gardening,  13-14 
Gases,  in  living  things,  27-28 
Gastric  digestion,  conditions  most  fa- 
vorable for,  369-370 
Gastric  glands,  371 

Gastric  juice,  action  of,  371-372,  com- 
position of,  371 
Gastropods,  241 
Gastrula,  617 

Generation.  See  Alternation  of  genera- 
tion 

Genes,  definition  of,  626,  627  ; function 
of,  627 ; location  in  chromosomes  of 
fruit  fly,  627-628 
Genus,  178,  179 

Geographic  distribution,  of  living  things, 
305-309 

Germ  cells,  627  ; development  of,  630 ; 

Weissman’s  study,  670 
Germination,  factors  necessary  for,  120- 
121;  of  seeds,  115-130;  use  of  food 
supply  of  corn  during,  128 


Gland,  moaning  of,  361 ; structure  of, 
362 

Glands,  ductless,  361,  392-395;  en- 
docrine, 361,  392-395;  gastric,  361, 
371;  intestinal,  377  ; liver,  361  ; loca- 
tion in  man,  392;  lympli,  399;  of 
skin,  316-317;  oil,  .316,  317;  pan- 
creas, 3t)l  ; salivary,  363;  sebaceous, 
316,  317;  sweat,  3i6-317,  414,  415 
Glomerulus,  of  kidneys,  413 
Glottis,  370 

Glycogen,  394-395  ; in  liver,  375,  376 
Goiter,  cause  of,  393 
Goldfinch,  American,  555 
Grafting,  in  animals,  614;  in  trees,  613, 
614 

Grass  family,  208 

Grasshopper,  62-65 ; characteristics  of, 
59  ; diagram  of,  62  ; eyes  of,  63,  64  ; 
food-taking  of,  64-65 ; laboratory 
exercise  on,  62-63 ; life  history  of, 
64-65  ; muscular  acti^■ity  of,  63  ; near 
relatives  of,  65  ; order  of  insects,  59, 
238  ; sense  organs  of,  64 
Gravity,  294 ; demonstration  on  effect 
on  roots,  140-141  ; effect  on  plants 
and  animals,  41 

Green  plants,  make  food  of  world,  115- 
173 

Growth,  of  plant,  cause  of,  123-124 
Guard  cells,  of  stomata,  152,  153 
Gullet,  364,  368 
Gulls,  at  Salt  Lake  City,  303 
Gymnosperms,  205-206 

Habit,  effect  of  drink,  449-451 
Habits,  different  kinds  of,  444-445 ; 
food,  347-348 ; formation  of,  444- 
445 ; hygienic  breathing,  407 ; im- 
portance of  forming  right,  445-446 ; 
meaning  of,  443  ; of  eating,  380  ; rules 
for  forming,  446-447 
Haemoglobin,  387,  404 
Hairs,  roots,  135-136 
Harvey,  William,  656  ; on  circulation  of 
blood,  658  ; on  germ  cells,  658 
Hawks,  560 
Hay  fever,  106 
Hay  infusion,  life  in,  303-305 
Health,  agencies,  507-511,  601;  and 
biology,  1—2  ; man  control  of  environ- 
ment for,  455-511;  positive,  482; 
work  of  department  of,  508-511 
Health  habits,  of  nervous  system,  447- 
448  ; of  sense  organs,  448 
Health  work,  of  national  government, 
600  ; profession,  650  ; special  agencies 
in,  601 ; state  and  city  supervision  of, 
600-601 

Hearing,  organ  of,  in  man,  438 


698 


INDEX 


Heart,  auricles  of,  395,  396;  compared 
to  force  pump,  397 ; in  action,  396- 
397  ; of  fish,  246-247 ; of  frog,  251- 
252  ; structure  of,  395-396 ; ventricles 
of,  395,  396 

Heart  beat,  laboratory  study  on  effect 
of  exercise  on,  400 

Heart  depressants,  medicine,  355-356 
Heat,  necessary  for  ' germination,  121  ; 

regulation  of  body,  415 
Heath  family,  of  flowers,  212 
Heath  hen,  594 

Hemiptera,  order  of  insects,  59,  61,  238 
Heredity,  604-605 ; applied  to  man. 
636-640;  bearers  of,  626,  627-629; 
in  black  and  white  rats,  622-623 ; 
laws  of,  620-624 ; mechanism,  627- 
628  ; use  of  knowledge  of,  640  ; versus 
environment,  606-607 ; what  deter- 
mines, 626-631 

Heredity  in  Relation  to  Eugenics,  Daven- 
port, 638 

Hessian  fly,  101,  105-106 
Hilum,  of  bean,  117 
Hogfish,  life  history  of,  248 
Home,  care  of  food,  498-499 ; care  of 
water  supplies  in,  500 ; disposal  of 
wastes,  500 ; improvement  of  condi- 
tions in,  497-500 ; ventilation  of, 
497-498 

Homoptera,  order  of  insects,  60,  238 
Honey,  used  for  food,  536 
Honeybee,  classification  of,  59,  238 ; 
laboratory  study  of,  58  ; life  of,  70-73  ; 
structure  of,  58 
Hoofed  mammals,  269-270 
Hooke,  Robert,  observed  cells,  38-39, 
657 

Hooks,  in  seed  dispersals,  109 
Hookworm,  life  history  of,  495 ; pre- 
vention of,  496 

Hopkins’  experiment,  on  white  rats,  329 
Hormones,  361,  392 
Horse,  geologic  history  of,  273-274 
House  fly,  carrier  of  diseases,  489-491 ; 
foot  of,  490 

Human  body,  structure  of,  314-315 
Human  machine,  how  it  works,  313-322 
Human  welfare,  and  food  making,  162- 
163 

Humus,  composition  of,  139 
Hunter,  physician,  14-15 
Huxley,  657 ; on  Darwin’s  work,  667 
Hybridization,  method  of  breeding,  634- 
635  ; practical  results  of,  624 
Hybrids,  meaning  of,  621  ; proportion 
in  different  generations,  621-623 
Hydra,  reproduction,  of,  225 ; structure 
of,  224-225 ; tentacles  of,  224,  225 
Hydrophobia,  treatment  for,  480-481 
Hygiene,  definition  of,  34 ; of  muscles 
and  bones,  320;  public,  508;  school, 
510 


Hymenoptera,  order  of  insects,  59,  60, 
238 

Hypocotyl,  of  bean,  117 

Ichneumon  fly,  561 
Imbibition,  147 

Immunity,  acquired,  475-476 ; active, 

476- 477 ; antibodies  in,  481  ; Erh- 
lich’s  work  on,  664 ; establishing 
active,  479-481  ; establishing  passive, 

477- 479  ; natural,  475  ; meaning  of, 
474-475  ; mechanism  of  active,  481  ; 
modified  by  certain  conditions,  475 ; 
passive,  476-477 

Imperfect  flowers,  96 
Improved  plum,  developed  by  Burbank, 
671-672 

Improvement,  of  living  things  by  man, 
604-640 

Incubation  period,  of  a disease,  472-473 
Indehiscent  fruits,  seed  scattered  by, 
110-111 

Infections,  skin,  317-318 
Inheritance,  social,  607-608 
Inorganic  nutrients,  23,  31 
Insect,  laboratory  exercise  on,  58 ; parts 
of  an,  58 

Insect  control,  methods  of,  566-569 
Insect  net,  how  to  make,  7-8 
Insects,  adaptations  for  carrying  pollen, 
72,  88-90 ; beneficial,  568 ; cage  for, 
10-11;  characteristics  of,  237;  col- 
lecting, 8-9 ; common  forms  of, 
58-61 ; compared  with  crustaceans, 
237 ; eaten  by  birds,  547-549 ; eco- 
nomic importance  of,  560-569  ; forest 
and  shade  tree  pests,  569  ; garden  and 
fruit  tree  pests,  568-569 ; harm  done 
by,  562-566  ; harm  done  to  trees,  565  ; 
household  pests,  568 ; killing  of,  8 ; 
method  of  controlling,  566-569 ; 
mounting,  9-10;  orders  of,  59-61, 
238 ; protective  resemblances,  79, 
80-82  ; spreading,  9 ; useful,  560-562  ; 
why  so  numerous,  80-82 
Inspection,  of  food  supplies,  504,  505 ; 

of  public  buildings,  503-504 
Inspiration,  meaning  of,  406-407 
Instinctive  behaviors,  441-443 ; modi- 
fication of,  442-443 

Instincts,  442 ; modification  of,  442- 
443 

Insulin,  in  treating  diabetes,  395 
Interrelations,  of  plants  and  animals, 
57 

Interrelationship,  of  man  and  other  liv- 
ing things,  455-672 
Intestinal  glands,  377 
Intestine,  absorption  from  large,  379 ; 
absorption  from  small,  378-379  ; rela- 
tion of  constipation  to  large,  379-380  ; 
structure  of  large,  379 ; structure  of 
small,  376;  villi  in  small,  377-378 


INDEX 


()99 


Invertebrates,  217,  242;  nnnulatos,  229- 
2.40:  coeliMilorati'.s,  224  220;  ooliiiio- 
(kM  ins.  220  22s : XiMiiallK'lmiutlu's, 
22.S  : IMatv  lu'lininf  lu's,  22,s  ; I’orilVra, 
22.4-224;  simpk'r,  22.4-241 
Irritability,  420  ; in  plants,  424,  424-42.') ; 

in  simplest  animals,  424-42.") 

Islands  of  Langerhans,  value  of,  494-395 

Japanese  beetle,  control  of,  505;  harm 
done  by,  504-505 ; life  history  of,  504 
Jellyfish,  225,  220 

Jenner,  Edward,  and  vaccination,  475- 
470,  059  -001 

Jennings,  H.  S.,  on  frcnes,  029 
Jimson  weed,  100-107 
Joshua  trees,  402 
Juke  family,  history  of,  0.40 

KaUikak  family,  040,  037 
Kidneys,  elimination  of  wastes  through, 
413-414  : laboratory"  exercise  on  struc- 
ture of,  411-412;  structure  of,  412- 
41.4 

Kinetic  energy,  313 

Koch,  Robert,  work  on  germ  diseases, 
002,  003 

Laboratory,  use  of,  14-10 
Lac  insect,  value  of,  501 
Lacteals,  378,  400 
Ladybird  beetle,  501 
Langerhans,  Islands  of,  394-395 
Large  intestine,  absorption  from,  379 ; 
bacteria  in,  379 ; relation  to  consti- 
pation, 379-380 
Larva,  of  butterfly,  00-07 
Laws,  of  heredity,  020-024 
Leaf,  blade  of,  151  ; cell  structure  of, 
152-153  ; demonstration  on  transpira- 
tion of,  103 ; manufacture  of  carbo- 
hydrates in  green,  100—101 ; manufac- 
ture of  fats  in  green,  101  ; manufac- 
ture of  protein  in  green,  101-102; 
petiole  of,  151;  stipules  of,  152; 
structure  of,  151-152 ; water  given 
off  by,  103 

Leaf  arrangement,  cone,  157 ; effect  of 
light  on,  150-157 ; mosaic,  150 ; 
rosette,  157 

Lamarck,  on  effect  of  en-^dronment,  007 
Leaves,  changes  in  color,  159;  com- 
pound, 152;  position  of,  21-22,  150- 
157  ; used  as  food,  520 
Leeuwenhoek,  improved  microscope,  38, 
058-059 

Legume  family,  209-210 
Lenticels,  105,  108 
Lepidoptera,  59,  08,  238 
Lichen,  287  ; on  rock,  288 
Life  span,  000 
Life  zones,  307-308 

Light,  effect  on  animals,  40,  293-294 ; 


I effect  on  leaf  arrangement,  150-157; 
effect  on  plants,  40,  155-150,  29.4-294  ; 
needed  by  green  plants  for  making 
carbohydrates,  157-1.58 
I Light  stimuli,  retaiv.  d by  eyes,  427,  429 
' Lily  family,  208-209 
Linnaeus,  system  of  classification  by, 
008 

Lipase,  an  enzyme,  474 
Lister,  Sir  Joseph,  work  on  antiseptics, 
003 

Liver,  308 ; a gland,  301  ; functions  of, 
375-370;  storage  of  glycogen,  370 
Living  things,  development  of,  017-020; 
effect  of  chemical  substances  on,  41, 
297 ; effect  of  food  on,  41,  297;  effect 
of  gra-^dty  on,  41,  294;  effect  of  light 
on,  40,  293-294  ; effect  of  temperature 
on,  41-42,  291-293  ; effect  of  water  on, 
40-41,  294-297;  functions  of,  30-52; 
improvement  of,  004-040  ; in  relation 
to  their  enx’ironment,  19-111;  inter- 
relationship with  man,  455-072;  rela- 
tionships and  interrelationsliii^s  of, 
177-309;  reproduction  of,  011-017 
Lizards,  257,  543 

Lobster,  catching,  533  ; conservation  of, 
592-593;  North  American,  230;  sense 
organs  of,  428  ; used  for  food,  533 
Locomotion,  of  amoeba,  218 ; of  Para- 
mecium, 220 

Loeb,  work  on  tropisms,  37 
Lungs,  403  ; air  in,  407  ; changes  in  air 
in,  404 ; organs  of  respiration  in  man, 
40.4-405 ; pleura,  400 
Lymph,  379  ; relation  to  blood,  389 
Lymphatics,  system,  378,  400 
Lymph  glands,  399 
Lymph  vessels,  399 
Lysins,  antibodies,  390 

Machine,  human,  313-322 
Malaria,  cause  of,  482-484 ; how  trans- 
mitted, 484-480 

Malarial  mosquito,  484 ; extermination 
of.  485-480 

Malnutrition,  cause  of,  341-342 
Mammals,  carnivores,  208 ; character- 
istics of,  208-209 ; classification  of 
higher,  270  ; conservation  of,  598-599  ; 
development  of,  019-020 ; primates, 
270 ; rodents,  209 ; ungulates,  209- 
270  ; used  for  food,  5.40-537 
Man,  a mammal,  270-277  ; and  balance 
of  nature,  289-290 ; conservation 
applied  to,  599-001  ; control  of  en- 
\dronmeiit  for  health,  455-511;  con- 
trol of  en\dronment  for  wealth,  518- 
509  ; fossils  of  ancient,  275-270  ; how 
become  conqueror  of  world,  420-451  ; 
improvement  of  living  things  by, 
004-040 ; interrelationship  with  liv- 
ing things,  455-072 ; laws  of  heredity 


700 


INDEX 


Man  — Continued 

applied  to,  636-640 ; place  in  nature 
of,  274-277  ; sense  organs  in,  430 
Mandibles,  of  beetles,  61 
Material,  needed  by  plant  for  food- 
making, 154-155 

Matter,  forms  of,  24-25 ; meaning  of, 
19,  23 : 

Medfly,  566 

Medicine,  profession  of,  649-650 
Mediterranean  fruit  fly,  566 
Medulla  oblongata,  429 ; functions  of, 
433,  434  ; location  of,  433 
Medullary  rays,  167 

Mendel,  Gregor,  670-671  ; work  on 
heredity,  620-624 

Mendel,  Professor  at  Yale,  work  on 
proteins,  325 

Mesoderm,  development  of,  618 ; sys- 
tems formed  from,  617,  618 
Metabolism,  basal,  meaning  of,  342 
Metamorphosis,  65 ; of  frog,  253 ; of 
monarch  butterfly,  66,  67 ; of  silk- 
worm moth,  538-539 
Metchnikoff,  theory  concerning  phago- 
cytes, 664 

Micropyle,  of  bean,  117  ; of  ovule,  85 
Migrants,  550-551  ; summer  residents, 
551 ; transients,  551  ; winter  resi- 
dents, 551 

Migration,  of  birds,  550-551,  595-596; 

of  Ashes,  588 
Mildews,  fungi,  196-197 
Milk,  and  disease,  468 ; care  of,  468- 
469 

Millepede,  239 

Milling,  compared  with  making  of  car- 
bohydrates, 160-161 
Mimicry,  in  insects,  81,  82 
Mineral  matter,  in  living  things,  27 
Mineral  requirement,  of  body,  331-332 
Mineral  salts,  in  soil,  139 ; needed  by 
plants,  140 ; taken  in  by  root  hairs, 
149 

Mint  family,  211 
Mistletoe,  288 

Mitosis,  a form  of  cell  division,  48,  49 
Modification,  of  stems,  172-173 
Molds,  198-199;  effect  on  food,  199; 
food  of,  198-199;  growth  of,  198; 
life  history  of,  199  ; prevention  of,  199 
Mollusca,  characteristics  of,  242  ; classi- 
fication of,  241 

Mollusks,  226  ; as  food,  531-533  ; char- 
acteristics of,  240,  242 ; classification 
of,  241 ; examples  of,  240-241,  242 
Monarch  butterfly,  life  history  of,  66-68 
Monocotyledons,  126,  127  ; arum  family, 
209 ; grass  family,  208 ; lily  family, 
208-209 ; orchid  family,  209 ; palm 
family,  208 

Morgan,  Thomas  Hunt,  work  on  fruit 
fly,  627-628,  670 


Morton,  and  anaesthesia,  664 
Mosquito,  malarial,  484-486;  yellow 
fever,  487-488 

Moss,  life  history  of,  202-203 
Moth,  codling,  566  ; life  history  of,  237  ; 
tussock,  566 

Mother-of-pearl,  value  of,  542,  543 
Moths,  classifications  of,  59,  238;  com- 
pared with  butterflies,  68-69 
Motion,  characteristic  of  living  things,  43 
Motor  axon,  431 

Mouth  cavity,  363-367 ; structure  of, 
363-364 ; teeth,  365-366 
Mucous  membrane,  in  food  tube,  363 
Muscles,  314 ; relation  to  bones,  318- 
322 

Mussel,  life  history  of  fresh-water,  593 
Mustard  family,  210,  211 
Mutants,  examples  of  occurrence,  632- 
633  ; importance  in  breeding,  633 
Mutations,  671 
Myceiia,  of  fungi,  194 

Nails,  outgrowths  of  epidermis,  316 
National  government,  and  health,  600 
Natural  immunity,  475 
Naturalist,  profession,  653 
Naturalists,  068-669 
Natural  resources,  conservation  of,  2, 
572-601 

Natural  selection,  theory  of  Darwin,  605 
Nature,  man’s  place  in,  274-277 
Nemathelminthes,  characteristics  of, 
228 ; classification  of,  228 ; harmful, 
493-496 

Nerve,  description  of,  431 
Nervous  system,  autonomic,  430;  cen- 
tral, 430  ; functions  of,  434-435  ; good 
health  habits  of,  447-448  ; laboratory 
exercise  on,  429-430  ; of  birds,  264 ; 
of  crayfish,  235  ; of  fish,  247  ; of  frog, 
252  ; parts  of,  429 

Neuron,  associative,  431  ; description 
of,  430-431  ; diagram  of,  431 ; motor, 
431  ; sensory,  431 
Neuroptera,  order  of  insects,  238 
Nictitating  membrane,  in  frog,  250 
Nitrogen,  cycle,  187-188,  285 ; fixation, 
188  ; relation  of  bacteria  to  free,  187- 
188 

Nitrogen-fixing  bacteria,  187-188 
Noguchi,  665 

Nose,  common  diseases  of,  407-408 
Nucleus,  in  cells,  46,  48 ; in  root  hair, 
145 

Nutrients,  327-328 ; best  proportion  in 
diet,  340-343 ; calories  needed  of 
various,  340 ; how  and  where  digested, 
381 ; meaning  of,  30  ; organic,  30-31 ; 
test  for  in  beans,  119-120;  test  for 
oil,  118-119;  test  for  protein,  119; 
test  for  starch,  118 
Nutrition,  processes  of,  44-45 


INDEX 


701 


Nutritive  ratio,  340 

Nuts,  iiow  st'ods  are  scattered,  109 

Odonata,  order  of  insects,  79,  23S 
Oil  gland,  3 Hi.  317 

Oils,  from  animals,  541  ; in  foods,  31  ; 
test  for,  lli»-119;  useful  vegetable, 
.529 

Olfactory  cells,  4.3S 
Olfactory  lobes,  in  brain.  429.  433 
One-celled  animals,  217-222;  amoeba, 
217-219;  Paramecium,  220-222 
Operculum,  of  fisli,  243,  245 
Opsonins,  in  blood,  338 
Optic  lobes,  in  brain,  429,  433 
Orchard,  and  other  fruits,  527-528 
Orchid  family,  of  flowers,  208,  209 
Organ,  meaning  of,  43,  47-48 
Organic  nutrients,  30-31  : in  bean,  119- 
120;  in  seeds,  118-120;  tests  for,  131 
Organism,  meaning  of,  43,  222 
Organs,  and  tissues,  47-48;  end,  428; 
of  digestion,  368-369;  of  excretion, 
412—413.  See  Sense  organs. 

Oriole,  Baltimore,  557-558 
Orthoptera,  order  of  insects,  59,  60,  238 
Osculum,  of  sponge,  223 
Osmosis,  147-148 ; demonstrations 
showing,  147,  148,  149 ; ph3"siological 
importance  of,  149-150 
Osmotic  pressure,  148-149 
Ovary,  of  flower,  83,  85 
Ovules,  in  flowers,  83,  85 
Oxidation,  25-26 ; of  food,  328,  405, 
415;  in  our  bodies,  124 
Oxygen,  24,  25 ; cj-cle,  285-286 ; given 
off  by  green  plants,  164-165;  need-'d 
bv  plant,  121,  158;  needed  in  body, 
403-405  ; properties  of,  25  ; test  for, 
25 

Oxyhaemoglobin,  387 
Owl,  549  ; screech,  558,  559 
Oysters,  as  food,  531-532 ; mollusk, 
240-242 

Palate,  of  man,  hard  and  soft,  363-364 
Palisade  layer,  of  leaf,  153 
Palm  family,  208 
Palpi,  of  beetles,  61 

Pancreas,  a gland,  361  ; hormone  of, 
394-395  ; position  and  structure,  373, 
375  ; secretion  of,  374  ; work  done  by, 
373-374 

Pancreatic  juice,  digestion  done  by,  373, 
374  ; enzymes  in,  374 
Pappus,  in  seed  dispersal,  109 
Paramecium,  219-222;  cilia,  220;  con- 
jugation of,  221-222  ; fusion  of,  221  ; 
response  to  stimuli,  425-426 
Parasites,  fungi,  194;  mistletoe,  228; 

worms,  228,  492-496 
Parasitism,  288-289 ; social,  cause  of, 
637  ; remedy  for,  637-638 


I Parathyroid,  gland,  392 
Passenger  pigeon,  594-595,  669 
Passive  immunity,  476-479 
Pasteur,  Louis,  1-2;  life  of,  661-663;  on 
bacteria,  181,  479;  work  on  rabies, 
480 

Pasteur  Institute,  662-663 
Pasteurization,  and  bacteria,  459 
Patent  medicines,  bracers,  355 ; cure- 
alls,  356-357  ; drugs,  355  ; heart  de- 
pressants, 355-356 
Pathogenic  bacteria,  462 
Pearls,  how  olflained,  542-543 
Peas,  factors  necessary  for  s<'rniination, 
120-121  ; Mendel’s  experiment  on  he- 
redity in,  621-622 
Pelecypods,  240-241 
Pellagra,  deficiency  disease,  334,  335 
Pellicle,  in  Paramecium,  219-220 
Pepsin,  in  gastric  juice,  371 
Peptone,  form  of  protein,  371-372 
Pericardium,  of  heart,  396 
Peristalsis,  370 

Pests,  insect,  562-566,  568-569 ; rats, 
545-546 

Petals,  of  flower,  83 

Petri  dish,  use  of,  182 

Phagocytes,  function  of,  387,  388,  481  ; 

Metchnikoff’s  theory  concerning,  664 
Pharynx,  of  man,  364 
Phloem,  168 
Phoebe,  555-556 
Photosynthesis,  160-161 
Phototropism,  155-158 
Phylum,  in  classification,  177,  178 
Physical  examination,  510-511 
Pigfish,  life  history  of,  248 
Pith,  166;  rays,  167 
Pituitary  gland,  392,  393-394 
Placenta,  function  of,  117;  of  bean,  87 
Plankton,  295,  530,  587 
Plant,  cause  of  growth,  12.3-124 ; cell, 
46-47 ; comparison  of  animal  with,  43  ; 
growth  of  bean,  136;  need  of  mineral 
matter,  139-140  ; world,  how  it  affects 
mankind,  177-213 

Plant  and  animal  breeding,  670-672 ; 
Burbank,  671-672;  de  Vries,  671; 
Mendel,  670-671 
Planting,  selective,  63.3-634 
Plants  and  animals  mutually  dependent, 
54-96;  classification  of,  179-213; 
compared  with  animals,  43-45 ; dem- 
onstration to  show  effect  of  light  on, 
155,  158;  drug-producing,  529-530; 
economic  values  other  than  food, 
528-530  ; effect  of  light  on,  155-157  ; 
effects  of  surroundings  on,  280-309 ; 
factors  affecting  plants,  39-42 ; how 
affected  by  en^^ronment,  290-297 ; 
mechanism  of  response  in,  424-425 ; 
poisonous,  105-107  ; production  of  new 
varieties,  632-635 ; raw  material 


702 


INDEX 


Plants  — Continued 

needed  by,  154-155;  relations  be- 
tween animals  and,  282-284  ; reproduc- 
tion of,  83-85,  201-202,  202-203, 
204,  611-616;  responses  of,  422- 
423  ; society  of,  298-300  ; success  in 
life  of  seed,  100-111  ; take  food  from 
soil,  137-140  ; used  as  food,  520-528  ; 
why  modified,  172-173 
Plasma,  blood,  386 

Platyhelminthes,  228 ; classification  of, 
228 

Pleura,  406 
Pleurococcus,  201 
Plumcot,  how  produced,  671 
Plumule,  of  bean,  117 
Pocket  garden,  140-141,  142 
Poison  ivy,  106 

Pollen,  84 ; carried  by  insects,  88- 
90 

Pollen  grain,  development  of,  616  ; ger- 
mination of,  84 

Pollination,  agents  causing,  88-90  ; arti- 
ficial, 634-635  ; cross,  56,  88 
Polycotyledons,  126,  127 
Pons,  position  of,  432-433 
Porifera,  characteristics,  223  ; classifica- 
tion, 223 

Portal  circulation,  378,  398 
Posture,  320  ; importance  of,  321 
Potato  beetle,  77,  562 
Potential  energy,  313 
Precipitins,  antibodies,  390 
Preservatives,  and  bacteria,  459-460 ; 
harmful,  460 ; salt,  459-460 ; sugar, 
459 

Pressure,  blood,  399;  osmotic,  148; 
root,  149  ; sense  of,  430 

Primary  root,  140 
Primates,  270 
Proboscis,  59 

Products,  stored,  damaged  by  insects, 
566 

Professions,  abilities  needed  for,  647 ; 
agriculture,  651-652 ; forestry,  652 ; 
health  work,  650 ; medicine,  649- 
650 ; research  worker,  653 ; teach- 
ing, 651 

Progressive  development,  665-667 
Pronuba  moth,  pollination  of  yucca  by, 
94 

Propagation,  artificial,  of  fishes,  591- 
592 : vegetative,  612-616 
Protection,  of  birds,  594-597 
Protective  resemblance,  of  insects,  80, 
81 

Protein  requirement,  by  body,  340 
Proteins,  31  ; amount  needed  daily, 
340;  digestion  in  man,  369,  371- 
372,  374  ; food  rich  in,  327  ; made  by 
green  plants,  161-162;  not  all  good 
tissue  builders,  329-330 ; test  for, 
119;  use  of,  329-330 


Protoplasm,  characteristics  of,  39 ; dis- 
covery of,  657-659 

Protozoa,  classification,  222  ; habitat  of, 
217 

Protozoan  disease,  malaria,  483-486 ; 
other,  486-487 

Protozoans,  direct  uses  of,  542 
Pteridophyta,  180  ; classification  of,  205  ; 

ferns,  204-205 
Ptomaines,  476 
Ptyalin,  an  enzyme,  365 
Public  hygiene,  508 
Pulmonary  circulation,  397-398 
Pulse,  399 

Pulvinus,  use  to  leaf,  424-425 
Pupa,  of  butterfly,  67 
Pure  culture,  of  bacteria,  182 
Pure  Food  and  Drugs  Act,  326,  348- 
349 ; how  does  it  work,  355-357 ; re- 
quirements of,  350 
Pus,  cause  of,  317 
Pylorus  valve,  of  stomach,  370-371 

Quarantine,  by  board  of  health,  508- 
509  ; why  necessary,  471-473 
Quetelet’s  Curve,  632 

Rabies,  treatment  for,  480-481 
Rainfall,  affected  by  trees,  574-577 
Ratio,  nutritive,  340 
Rats,  harm  done  by,  545-546 ; spread 
diseases,  491-492 

Reactions,  to  stimuli,  39-42,  422-426 
Realms,  ecological,  308-310 
Receptacle,  of  flower,  83 
Recessive  characters,  621,  630-631 ; 

extracted,  622 
Red  blood  corpuscles,  387 
Redi,  work  to  show  how  life  begins,  657- 
658 

Reduction  division,  of  germ  cells,  627, 
630 

Reed,  Walter,  investigator  of  yellow 
fever,  487,  664 

Reflex,  arc,  432 ; conditioned,  443 ; 
importance  of,  431-432;  meaning  of, 
428  ; nature  of,  432 

Regeneration,  earthworms,  614  ; of  flat- 
worm,  612 

Rennin,  enzyme  in  gastric  juice,  371 
Reproduction,  45 ; by  budding,  191, 
614;  by  grafting,  613-614;  cell  di- 
vision, 48,  612-613 ; in  Paramecium, 
221-222;  of  birds,  618-619;  of  cray- 
fish, 235-236;  of  earthworm,  231; 
of  fern,  204-205;  of  fish,  247-248; 
of  frog,  252-254 ; of  living  things, 
611-617;  of  mammals,  619-620;  of 
molds,  199 ; of  mosses,  202-203 ; of 
plants,  83-88,  615-616;  of  Spirogyra, 
201-202,  615 ; regeneration,  612,  613, 
614;  sexual,  615-616;  vegetative 
propagation,  613-614 


INDEX 


Reproductive  glands,  394 
Reptiles,  Joti  Jtil) ; t-haractcristics  of, 
239;  classiticatioii  of,  200;  relation 
to  birds,  2t>()-  2()7 
Research  worker,  profession,  (>53 
Residents,  I)ird,  551 

Resources,  e.onservat  ion  of  natural, 
572-001 

Respiration,  artifieial,  408-409;  cell, 
405;  comparison  of  frog  with  man, 
403 : of  birds,  203-204 ; by  leaves, 
105;  need  of,  44;  organs  of,  403- 
404 

Responses,  adaptive,  420;  conditioned, 
443  ; of  living  things,  37 ; of  plants 
and  aidmals,  422-420 
Rickets,  deliciency  disease,  334-335 
Rind,  of  corn  stem,  109 
Ringworm,  199 
Robin,  552  ; food  of,  548-549 
Rodents,  209 

Roosevelt  family  tree,  039 
Root,  structure  of,  143-144 
Root  cap,  143,  144 

Root  hairs,  22,  135-136 ; function  of, 
145-140  ; how  take  in  water,  147-150  ; 
laboratory  exercise  on,  144  ; structure 
of,  144-145  ; why  absorb  water,  149 
Rootlets,  140 
Root  pressure,  149 

Roots,  factors  influencing  growth,  140- 
143 : influence  of  gravity,  140-141  ; 
influence  of  water  on,  141,  143;  pur- 
poses of,  150  ; use  ot,  21,  22-23  ; used 
as  food,  521-522 
Root  systems,  140-141 
Rose  family,  209,  210 
Ross,  Major,  investigator  of  malarial 
fever,  664 

Rotation,  of  crops,  188-189 
Roughage,  needed  by  body,  332 
Round  worms,  228 ; harmful,  493-496 
Russian  thistle,  dispersal  of  seeds  of, 
102,  103 

Rust,  black  stem  grain,  195-196,  197 ; 
pine  tree  blister,  196 

Sac  fungi,  196-197 
Salamander,  an  amphibian,  254-255 
Saliva,  function  of,  363 
Salivary  glands,  363  ; parotid,  363  ; sub- 
lingual, 363 ; submaxillary,  363 
Salmon,  as  food,  534-535 ; spawning 
habits,  588-589 

Salt,  as  a preservative,  459-460 
Sanitation,  definition  of,  34 
Saprophytes,  194 

Scallops,  mollusk,  240-241  ; used  for 
food,  533 

Scarlet  fever,  and  Dick  test,  479 
Schick  test,  478-479 
Schleiden,  on  cells,  657 
School,  improvement  of  conditions. 


703 


I 501-503;  luncli  and  lunch  time,  502- 
503;  surroundings,  501-502 
School  hygiene,  510 
Schwann,  on  cells,  657 
Scurvy,  deficiency  disease,  334 
Sebaceous  glands,  316,  317 
Secondary  roots,  140 
Secretin,  374 
Secretion,  of  glands,  362 
Seed  dispersal,  dehiscent  fruits,  109- 
110;  iiidehiscent  fruits,  110-111;  of 
fleshv  fruits,  108-109;  of  hard  seeds, 
109;'  of  weeds,  102-103 
Seed  plants,  why  succeed  in  life,  100- 
111 

Seeds,  85  ; dispersal  of  weed,  102-103 ; 
factors  necessary  for  germination, 
120-121;  germination  of,  115-130; 
location  of  food  supply  on  different, 
125-126;  of  weed,  eaten  by  birds, 
549-550;  produced  by  weeds,  102; 
used  as  food,  522-526 
Seeing,  organ  of,  440-441 
Segmented  worms,  229-231 
Segregation,  Mendel’s  law  of,  621-622 
Selective  planting,  633-634 
Self-analysis,  in  selecting  a vocation, 
646-647 

Self-improvement,  biology  and,  644-654 
1 Sensation,  43 

Sense  orgais,  422;  demonstration  to 
show  types  of,  427 ; function  of,  427- 
429,  435;  health  habits  of,  448;  of 
birds,  264  ; of  man,  430  ; part  played 
in  control  of  body,  435-441 
Sensory  neuron,  431 
Sepals,  of  flowers,  83 
Septic  sore  throat,  470 
Serum,  blood,  388 

Sewage  disposal,  in  community,  505- 
506 

Sex,  relation  to  diet,  338 
Sexual  reproduction,  in  flowering  plants, 
615-616  ; in  Spirogyra,  201-202,  615 
Shellfish,  conservation  of,  592-593 ; life 
history  of,  593 
Sieve  tubes,  167,  168 
Silkworm  moth,  fibers  made  by,  540 ; 

life  history  of,  538-539 
Siphonaptera,  an  order  of  insects,  238 
Skeleton,  human,  axial,  319  ; appendicu- 
lar, 319;  of  crayfish,  233 
Skin,  314;  clothing  and  the,  318;  in- 
fections, 317-318;  laboratory  study 
of,  414;  organ  of  excretion,  414-415; 
structure  of,  316-317 
Sleep,  necessity  of,  447-448 
Small  intestine,  absorption  from,  378- 
379 ; digestion  in,  374 ; glands  in, 
377 ; movement  of,  370 ; structure 
of,  376,  377  ; villi  in,  377-378 
Smallpox,  active  immunity,  479-480 ; 
and  vaccination,  475-476 


704 


INDEX 


Smell,  location  of,  438 ; olfactory  cells, 
438 

Snakes,  feeding  habits  of,  258-259  ; 

locomotion  of,  258  ; value  of,  543-544 
Social  inheritance,  607-608 
Social  parasitism,  cause  of,  637 ; remedy 
for,  637-638 

Societies,  plants  and  animals,  298-300 
Society,  cost  of  parasitism  to,  637 
Soil,  composition  of,  137-139 ; condi- 
tions of,  affect  life,  297  ; mineral  salts 
in,  139 ; relation  to  plants,  137-140 ; 
water  held  in,  139 
Sound,  character  of,  439-440 
Sound  stimuli,  how  received,  427-428, 
430 

Span  of  life,  600 

Sparrow,  English,  559,  560,  595 ; song, 
554-555 

Spawning,  habits  of  fishes,  588-589  ; 
need  of  conservation  during,  589- 
591 

Species,  177,  179 
Sperm,  617  ; in  Vaucheria,  615 
Spermatophyta,  180;  angiosperms,  206- 
213  : classification  of,  207  ; examples 
of,  205-213  ; gymnosperms,  205-20G 
Spiders,  238-239 

Spinal  cord,  429  ; function  of,  433,  434 
Spines,  in  seed  dispersal,  109 
Spiracles,  of  insects,  58,  63 
Spirillum,  kind  of  bacteria,  183 
Spirogyra,  201  ; conjugation  of,  201- 
202,  615 

Split  proteins,  462,  476 
Sponges,  economic  value  of,  542 ; struc- 
ture of,  223-224 
Spongy  tissue,  of  leaf,  153 
Spore,  of  bacteria,  183 
Sporophyte,  of  moss,  203 
Sprengel,  on  adaptation  of  flowers,  56 
Stamen,  of  flower,  83 
Starch,  effect  of  heat  and  digestion  on, 
339;  test  for,  118 

Starch-making.  See  Carbohydrates. 
Starfish,  discussed,  226-228  ; harm  done 
by,  544-545 

Statocysts,  in  shrimps,  428-429 
Stem,  dicotyledonous,  166-169 ; growth 
in,  167 ; modified,  172-173 ; mono- 
cotyledon ous,  169-170;  rise  of  water 
in,  170-171 ; used  as  food,  520-521 
Sterilization,  and  bacteria,  458 
Stigma,  of  flower,  83 
Stimulants,  effect  on  body,  350-351 
Stimuli,  how  simple  animals  receive,  422, 
425-426 ; how  simple  plants  receive, 
422,  424-425  ; light,  427,  429  ; mean- 
ing of,  37 ; Paramecium  respoiids  to, 
425-426 ; pressure,  430 ; reaction  of 
living  things  to,  39-42 ; sound,  427- 
428,430;  touch,  427,  428 
Stomach,  digestion  of  food  in,  369-372 


Stomata,  152-153 

Storage,  cold,  458;  of  food,  in  plants, 
171-172 

Stored  products,  insects  harmful  to, 

565-566 

Struggle,  for  existence.  111 
Sturgeon,  534,  590 
Style,  of  flower,  83 
Succession,  ecological,  300-305 
Sugar,  as  a preservative,  459 ; storage 
in  liver,  375-376;  test  for  grape,  128- 
129 

Sun,  source  of  energy,  157 
Sunlight,  necessary  for  carbohydrate 
making,  157-158,  160-161 
Survey,  value  of  city,  14 
Swallow,  barn,  556 ; food  of,  548 
Sweat  glands,  316,  317  ; function  of,  415 
Swim  bladder,  of  fish,  246 
Swimmerets,  of  crayfish,  233 
Symbiosis,  287-288 
Synapse,  431 

System,  circulatory,  395-401 ; digestive, 
367-369 ; excretory,  412-415 ; nerv- 
ous, 429-435 

Systemic  circulation,  397 

Tadpole,  252-253,  2.54 
Tapeworm,  228,  493;  harm  done  by, 
545  ; in  bass,  493 

Taste,  buds,  437 ; location  of,  437-438 
Taioaomy,  178 
Tea,  a stimulant,  350-351 
Teaching,  profession  of,  651 
Teeth,  care  of,  366-367  ; effect  of  decay, 
365-366  ; kinds,  365  ; number  of,  365  ; 
structure  of,  365,  366 
Teleosteans,  bony  fish,  247-248 
Temperature,  291-293;  effect  on  plants 
and  animals,  41—42 
Tentacles,  of  hydra,  224,  225 
Tertiary  roots,  140 
Testa,  seed  coat,  117 
Tetanus,  cause  of,  470 
Thallophyta,  180 ; bacteria,  181 ; classi- 
fication of,  200;  fungi,  193-197; 
molds,  198-199  ; yeasts,  190-193 
Thoracic  duct,  399 
Thorax,  of  insects,  58,  62,  237 
Throat,  common  diseases  of,  407-408; 

septic  sore,  470 
Thrombin,  in  blood,  388-389 
Thymus  gland,  394 
Thyroid  gland,  392,  393 
Tissue  building,  328-329 
Tissues,  47-48 

Toad,  an  amphibian,  254 ; usefulness 
of,  543 

Toadstools,  193-194 
Tobacco,  use  of,  354 
Tonsils,  enlarged,  408 
Touch,  how  stimuli  received,  427,  428 ; 
I organ  of,  lobster,  428 


INDEX 


705 


Tourniquet,  how  to  uso,  41)1-402 
Toxin,  fornu'd  by  hacttMia,  402 
Toxin-antitoxin  treatment,  47s 
Toxoid,  47.S 

Trachea,  of  man,  iiti  l ; of  insects,  Od 
Trades,  abilities  needed  for,  04S 
Traits,  iidierited,  Od.s-OdO 
Transfusion,  of  blood,  301 
Transients,  bird,  551 
Transpiration,  factors  in,  104 
Trees,  cause  of  growth,  31  ; city’s  need 
of,  5b0 : injured  by  insects,  5f)5-500  , 
materials  found  in,  2S,  20  ; position  of 
leaves,  21-22;  pre\ent  erosion,  574; 
repair  of,  .5tS()-5t>7  ; skeleton,  21,  22; 
uses  of  wood,  577-578 ; values  of, 
574-570 

Tree  surgery,  580-587 
Trial  and  error,  method  of  response,  425- 
426 

Triangle,  factors  in  life,  608 
Trichina,  404  ; harm  done  by,  545  ; life 
history  of,  494 

Trichocysts,  of  Paramecium,  220 
Trichoptera,  order  of  insects.  238 
Tropisms,  420  423 ; meaning  of,  37 ; 
value  of,  42 

Trypanosomes,  diseases  caused  bj',  486- 
487 

Trypsin,  an  enzyme,  374 
Tsetse  fly,  diseases  carried  by,  486-487 
Tuberculosis,  and  Koch,  662,  663  ; care 
of  persons  having,  509-510  ; cause  of, 
465-466  ; effect  of,  464-465 
Tumbleweed,  dispersal  of  seeds  of,  102, 
103 

Turtle,  adaptations  of,  256-257 
Tussock  moth,  566 
Tympanum,  in  frog,  250 
Tyndall,  John,  apparatus  and  experiment 
to  disprove  spontaneous  generation, 
658 

Typhoid  fever,  carriers  of,  469  ; cause  of, 
467  ; Widal  test  for,  390-391 

Ungulates,  269-270 
Unit  characters,  621 
Urea,  413 

Urine,  excreted  by  kidneys,  413 
Useful  bacteria,  183-189 

Vaccination,  against  smallpox,  475-476, 
479-480 ; against  typhoid  fever,  481  ; 
and  Jenner,  659-661  ; to  acquire  im- 
munity, 475-476 

Vacuole,  of  amoeba,  218-219  ; of  Para- 
mecium, 220 

Van  Leeuwenhoek,  38,  658-659 
Variation,  continuous,  632  ; Darwin  on, 
605  ; discontinuous,  632-633  ; mean- 
irig  of,  605  ; types  of,  632-633 
Varieties,  production  of,  new  animal, 
632-635  ; new  plant,  632-635 


! Vaucheria,  reproduction  of,  ()15,  616 
j Vegetables,  used  as  food,  526-527  ; uses 
I of  fibers  of,  529  ; uses  of  oils  of,  529 
j Vegetation  areas,  in  United  States,  30() 
I Vegetative  propagation,  612-616;  l)ud- 
(ling,  614;  grafting,  613-614;  regen- 
eration, 612,  614 

j Veins,  395  ; structure  of,  398  ; valves  of, 
i 399 

Venae  cavae,  398 

Ventilation,  methods  of,  410;  need  of, 
410;  of  bedroom,  411,  497-498 
Ventricles.  Sec  Heart. 

Vertebrates,  242  ; groups  of,  243 
Vessels,  blood,  395,  398;  lymph,  399 
Villi,  377-378  ; where  found,  149-150 
Virginia  creeper,  106 
Virus,  filterable,  479-480 
Vitality,  of  weeds,  103-104 
Vitamins,  31,  331  ; diseases  caused  by 
deficiency  of,  334  ; list  of  foods  con- 
taining, 336-337  ; names  of,  333 ; 
sources  of,  333-335,  336-337  ; use  to 
body,  33.3-335 

Vocation,  biology  prepared  for,  649-654 ; 
choosing  a,  646-648 

Wallace,  A.  R.,  on  progressive  develop- 
ment, 667 

Warbler,  559  ; yellow,  555 
Wasp,  60  ; life  history  of  solitary,  69 
Waste  disposal,  in  community,  505-507  ; 
in  home,  500 

Water,  294-297 ; absorbed  by  root 
hairs,  149  ; cause  of  rise  in  stem,  170- 
171  ; composition  of  sea,  20-21  ; dem- 
onstration on  electrolysis  of,  24-25 ; 
effect  on  plants,  39-40 ; evaporation 
from  plant,  164  ; given  off  by  leaf,  163  ; 
held  by  soil,  139  ; in  living  things,  27  ; 
necessary  for  germination,  120-121  ; 
value  to  body,  330-331 
Water  supplies,  and  diseases,  467 ; in 
home,  500 ; regulated  by  trees,  574- 
577 

Wealth,  man  controls  environment  for, 
518-569 

Weeds,  eradication  of,  108 ; harmful, 
105 ; methods  of  protection,  104 ; 
place  of  growth,  105  ; poisonous,  106- 
107 ; seed  dispersal  of,  102-103 ; 
seeds  of,  eaten  by  birds,  549-550  ; use- 
ful, 107  ; vitality  of,  103-104  ; w^hat 
are,  101-102 

Weissman,  August,  work  on  germ  cells, 
670 

Wheat,  rust,  101,  105,  195-196,  197; 

mutant,  633  ; uses,  525-526 
White  corpuscles,  387-388 
Widal  test,  for  typhoid  fever,  390- 
.391 

Willow,  girdled  twig  of,  168 ; family, 
211-212 


706 


INDEX 


Windpipe,  of  man,  364 
Winged  seeds,  110 

Wood,  of  dicotyledonous  stem,  166,  167  ; 

uses  of,  577-578 
Woodpecker,  downy,  557 
Work,  relation  to  diet,  335 
World,  how  man  has  become  conqueror, 
420-451 

Worms,  228-231 
Wren,  house,  554 


Yeast,  190-193  ; and  bread  making,  191- 
192 ; commercial,  191  ; conditions 
favorable  for  growth  of,  190 ; impor- 
tance of,  192-193  ; life  history  of,  191 
Yellow  fever,  discovery  of  cause,  487- 
488  ; how  spread,  487 
Yucca,  93  ; pollination  of,  94 

Zones,  life,  307-308 
Zygospore,  615  ; of  Spirogyra,  202 
Zygote,  how  formed,  616 
Zymase,  an  enzyme,  191 


Xylem,  167 


lDnC.?^.T^ON  LIBR-^jy 


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