TII i:

< II KM 1C A L J! A SIS

ANIMAL I!()I)Y.

Tf!

TV

•|- 1 1 1 :

CHE M I C A L BASIS

OF THE

ANIMAL BODY.

3ppcnlrir to JFostcr's <Tr.rt^l3ooh of iJljystology.

in KDITION.)

BY

A. SHERIDAN LEA, M.A., D.Sc., II

tmivEKsrrv LECTURER IN PRTMOLOOT ix THE UXITCESITT OP CAMBUDO:, nxiow or

C.UUS COLLUiE, CAMBR1DOI

Dorft:

MACMI LI A .\ A \ 1) CO.

i. i. <>\ i"

1898,

[All

FPS & STATIONERS,

VANMEVAR * CO .

fONQt 8T T&RONTO.

Copyright, 1892,
BY MACMILLAN AND Co.

SSnttorrsttg lirrss:
JOHN WILSON AND SON, CAMBRIDGE, U.S.A.

PREFACE.

rniIK following Appendix has been written upon tin- same
•*• lines us in t'onner editions, save that it has been enla
ami in reality now eon>titutes a treatise on the chemical sub-
stances occurring in the animal body. As in former editions

• •ntirely the work of Dr. A. Sheridan I.
The references given, though extensive, are not intended to
.liaiistive. An effort has been mad"- to make tin- ivfcr-

:it work as complete as possible : other i

are to pajiers which themselves give full i-efereiices and will
therefore serve as a guide t<> the literature of the subject ;
and some have been inserted in order to inform the student
of the dates at which important results \\ere iirst descrii

\Ve desire to express our thanks to .Messrs. Wintei
Heidelberg for the six figures which have been taken from
Krukenbei-'/s Gfrundriu der ///• •//••////>•. y,-,-/,, ////>•••//- n
an<l t") rrofosor Kiihne for the large number which ha\e
taken from his Li-ln-inn-li ,/,/• phyiiologitchen ('I' 1^68).

A few have liei-u drawn in wood from the plates in Fii:

. I////* ./,•/• physiologitchen Chemie (1858).

\Ve are also indebted to Dr. S. K'uhcmann for reailing the
proots from pa-jv !»1 to page ^lo', in which tin- t"'\t contains
many formula1, and involves special chemical knowle.:

The volume is paged separately from the rest of the T
Uook. and has an index of its own. Indeed it ma\ he regarded
as an independent work. The reference! to the body oi the
Te\t-l!ook are -iven in paragraphs.

M. l-o-l I i;.

A BHEBIDAK i.i \

July, is: i-.'.

PART V.- APPENDIX.

THE CHEMICAL BASIS OF THE
ANIMAL BODY

BY

A. SHERIDAN LEA, M.A., S.-.D., F.R.S.,

IN IMM MIII.IM.I is ini isi\ii:Miv OK CAMBRIDGE;

I I.I.I <>\\ i>l < Ul - . i.l.l.l.'.K, 0 \MUHIlM.I

APPENDIX.

THE CHEMICAL BASIS OF THE ANIMAL P.nhY.

Tin ;mim;il liody, from a chemical point of view, may be
•led as ;i mixture of various representatives of three lai-e
( la— es of chemical substances, viz. proteids, carbohydrates ami
in association with smaller quantities of variou- saline and
other crystalline bodies. By proteids are meant bodies contain-
ing carbon, oxygen, hydrogen, and nitrogen in a certain proportion,
varying within narrow limits, and bavin:: certain general feature-;
they are frequently spoken of as albuminoids. I'.y carbohydrate.-,
are meant. Marches and sugars and their allies. \\V have al<o
seen that the animal body may be considered as made np on the
one hand of actual 'living substance.' sometimes spoken 0
protoplasm -ee § 5), in its various modifications, and on the other
band of numerous lifeless products of metabolic a<ti\it\. \Ve do
• pre-ent know anything definite about the molecular coin-
portion of the active living substance; but when we submit
living substance to chemical analysis, in which act it i- killed,
we always obtain from it a considerable quantity of the material
spoken of as protejd. And many anth' far as to speak of

living substance or protoplasm as being purely pioteid in nature;
they regard the living protoplasm as proteid material, which in
Mom death to life has aSSUIll ill character- and

>re-umahly has been changed in con-t ruction, but still is p:
matter; they sometimes speak of protoplasm as ' living pp-tcid
or 'living albumin.' It is worthy of notice. 1,
simple forms of living matter, like that constituting tin- b«-dy • •(
a white corpuscle, forms which we may fairly - "ii-id<T II tin-
nearest approach to native protopla-m. when they can be obtained
in ^utlicient quantity for chemical ana! found to contain

4 CHEMICAL BASIS OF THE ANIMAL BODY

some representatives of carbohydrates and fats as well as of pro-
teids. We might perhaps even go as far as to say that, in all
forms of living substance, the proteid basis is found upon analysis
to have some carbohydrate and some kind of fat associated with
it. Further, not only does the normal food which is eventually
built up into living substance consist of all three classes, but, as
we have seen in the sections on nutrition, gives rise by meta-
bolism to members of the same three classes ; and as far as we
know at present, carbohydrates and fats, when formed in the
body out of proteid food, are so formed by the agency of living
substance, by the action of some living tissue. Hence there is at
least some reason for thinking it probable that the molecule of
living substance, if we may use such a phrase, is far more com-
plex than a molecule of proteid matter, that it contains in itself
residues so to speak not only of proteid,, but also of carbohydrate
and fatty material.

The plasmodium of ^tlialiurn septicurn, a myxomyeaetous fungus,
presents a convenient source of extremely primitive protoplasm which
maj* be obtained in large quantities. It occurs as an extended, yel-
low, gelatinous mass, frequently of considerable thickness, on the
surface of heaps of spent tan or other similar decaying vegetable
matter, and exhibits very active movements both internally and more
particularly at its edges, of an essentially amoeboid nature. It has
been .carefully analysed by Reinke, Studien uber das Protoplasma,
Berlin, 1881. See also Krukenberg, Unters. a. d. physiol. Inst.
Heidelb., Bd. n. 1882, S. 273.

Whether this be so or not, for at present no dogmatic state-
ment can be made, there is no doubt that when we examine the
various tissues and fluids of the animal body from a chemical
point of view we find present in different places, or at different
times in the same tissue or fluid, several varieties and derivatives
of the three chief classes ; we find many forms of proteids, and
bodies closely allied to proteids, in the forms of mucin, gelatine,
&c. ; many varieties of fats ; and several kinds of carbohydrates.

We find, moreover, many other substances which we may re-
gard as stages in the constructive or destructive metabolism of
the various forms and phases of living matter, and which are im-
portant not so much from the quantity in which they occur in the
animal body at any one time as from their throwing light on the
nature of animal metabolism ; these are such substances as urea,
uric acid, other organic crystalline bodies, and the extractives in
general.

In the following pages the chemical features of the more
important of these various substances which are known to occur
in the animal body will be briefly considered, such characters
only being described as possess or promise to possess physio-

CHKMK'AL I'.ASIS OF TIIK ANIMAL j;nl>Y.

:1 intrivst. The iihy>iul. i^i.-al function <,f any .-nk-tam ••
must depend ultimately on its molecular including it- chemical
natiuv ; and though at ).re-ent our chemical knowledge of the
c..n-tituents of an animal hody ^ives u- luit little insight into
their physiological properties. it cannot \»- d«uil.t»-d that such
chemical int'orniation as is attainable is a n<-r,-^,,iv preliminary
to all physiological study.

These form the principal solids of the mu-cular. nervous. ami
ulandular tissue-. of the scrum of Mood, of si-rous lluids, and of
lyinjih. In a healthy c-ondition, sweat, tears. Idle, and urine con-
tain mere traces, if any, of ]>roteids. Tlieir general j.eiventa-e
eom]iosition may lie taken as lyini; within the following limits: —

C 50-0 to 55-0 ........... 50-0 to :,:,-( i

H 6-9 „ 7* ........... 6-8 „ 7-3

N 15-0 „ 18-0 ............ 15-4 „ is-ii

(» L'li-u .. L':5-r» ........... ^2-8 „ 24-1

S (I-:1. .. 2-0 ........... 0-4 „ 5-0

1 1 "1 '1 ie-Seyler.2) (Drechsel.)

The ei.m],n>itj.iii of the true ]iroteids lies go • onstaiitlv within
the ahove limits that conclusions as to the jnoteid nature nf any
Milistance whose juirity is assui-ed may lie drawn with -at'ety from
the re-nit-- of it^ ultimate analysis. This is important in
where a suli-tance i> with ditlieulty. if at all, oUaincd in a < «\\-
dition such that it yields mme of the reactions characteristic <if
jiMteid-. Kidine and < 'hittenden's analy-e-:: .,f j.eptones
from alluimoses. which they quote with considerali].
alone -how a jiei-eenta-e comj,n>iti.in lyin^ aj.precialily out -ide
the aliove limit-.

In addition t.» tin- al«ive c.in-t it in-nt-, jimli-ids nnliniirily l«-a\.-.ni
lUiiitinn a variable ([iiantity "I" a-h. In tin- rase nf r^-allmniiii flu-
|irinci|ial .-mi-t it iient- »\ tin- a-li an- fldnrido ••!' -i'<liinii and
sjiiin. tlie latt.T c\cei'dinur tlie f<>nmr in aiimunt. Tin- r- iiiain<l<-r
ci.ii-i-t- ..f -ndiiini and |>nla--iiiin, in «-«.inliiiiat imi with phosphoric,
siil|ilinric, and carlmnic aciil-, and \.T\ -mall ipiant it ii- ••(' . alfiuin,
iiia^iii--iiini. and imn, in iininii \\itli tin- -aine acid-. 'I'licn- may !"•
alx. a trare ..|' -ilica.4 Tin- a-li "f M finii-allniiiiiii cnntain- an •

1 Tin- i-licini-try .>f [.r..t«-ii|s and :illi.-.l -ii'.-iaii. . •«. t..^.-i ! •
lit. r;iiiirc .if tin- vulijr. i, i~ \i-r\ full\ II-. iii-. I .iii'l rrrorili'i! in I'

ill j,:uli •hlniri:'- II, a, •In;, ', •>,,,! \\,\ ill II-

illiil ill Hrilsti-in1-; llunill'url, • H'l III (IHK^ -'••

- l/,IMl. ,1. /./-v.v ;,.,//,

< (Jnirlin. //./'•••/. ./. • ' Bdrni 8 205.

0 . PEOTEIDS.

of sodium chloride, but the ash <>t' tin- proteids of muscle contains an
exceixs of potash salts and phosphates. The nature of the connection
of the ash with the proteid is still a matter of obscurity, and it is not
known whether they constitute an integral part of its molecule or are
merely adherent impurities. There is a certain amount of probability
that the latter is the case, inasmuch as an increasing number of pro-
teids have in recent times been obtained practically free from any
ash-residue on ignition. It is, however, possible that in their natural
condition as constituents of the animal tissues and fluids the proteids
are combined with salts, the separation of which we are now speaking
being an artificial result of the processes employed to effect that
separation. The sulphur in proteids is present partly in a stably
combined condition, partly loosely combined. The latter is removed
by boiling with alkalis, the former is not. The proportions of the
two differ in the several proteids.1

Proteids met with in the animal body are all amorphous, the
only apparent exception being haemoglobin : this substance is
however not a pure proteid but a compound of a proteid globin
with the less complex haematin. It is to the latter that the
power of crystallising is due.

Some are soluble, some insoluble in water, some are character-
istically soluble in moderately concentrated solutions of neutral
salts, and all are for the most part insoluble in alcohol and ether ;
they are all soluble in strong acids and alkalis, but in becoming
dissolved mostly undergo decomposition. Their solutions exert
a left-handed rotatory action on the plane of polarisation, the
amount depending on various circumstances, and differing for the
several proteids.

Crystals into whose composition certain proteid (globulin) elements
largely entered were long since observed in the aleurone-grains of
many seeds.2 Similar crystalloid compounds are also described as
occurring occasionally in the egg-yolk of some animals (Amphibia and
Fishes). By appropriate methods they may be separated and re-
crystallized from their solution in distilled water, most readily by
Drechsel's method of alcohol dialysis.8 The crystals consist in no
case of pure proteids, but are always compounds of the latter with
some inorganic residue such as lime or magnesia. These recrystal-
lized, and hence presumably pure, compounds have been frequently
analysed with a view to establishing a formula for proteids which
should give some clue to their molecular magnitude. An excellent
summary of the endeavours to arrive at a definite formula for proteids.
based on the above analyses and on those of haemoglobin and certain
compounds of egg-albumin with salts of copper and silver is given by

1 A. Kriiger, Pfliiger's Arch. Bd. XLIII. (1888), S. 244.

2 For literature down to the year 1877, see Weyl, Zt. f. physiol. Ch. Bd. r., S. 84.
See also Hoppe-Seyler's Handbuch, Ed. v. p. 259." Vines, Jl. of Physiol. Vol. in.
(1880), p. 102. Chittenden and Hartwell, .//. of Ph i/siol. Vol. xi. (1890), p. 435.

3 .//. f. i>rakt. Cliem. N. F. Bd. xix. (1879), S. 331.

CHKMK \i. BASIS "i nil: ANIMAL J;OI>Y. :

iSim^i-.1 A- tin- rr.-ult nl' tlh->e. \arion-. formulae havi- IMVII proposed
liy the several oli-.erver-. Very little real importance can ho \\ever he
attached t« these formulae. \»r. M l>iveli>el oh-er\e>. in >,> large a
molecule an analytical emu- of -01 p.c. \\ould h:i\e tin- same ini|»ir-
tance a- would one of -1 j,.(-. in ordinary aiialv.--. Tli--\ ;_M\e u- a'
.in idt-a of the ntinlinul lua^nit mli- of lh«- pmti-iil nioli-culf. I'lii
apart from this tln-y tlimu n ...... uv lij^ht on tin- >nlijt-.-t than alr.-a«l\

•••(1 in Lii-lirrktihn'- oldi-r formula.

General reactions of the proteid*.*

\. Heated with strong nitric acid, they or thrir s.iluti«ui> turn
\fllo\v. and this colour is, on the addition of ammonia. <>r caustic
soda or potash, changed to a deep orange hue. (Xantlmjuntci.
reaction. )

If much protoid. except albumoses and peptones, )>«• present a
yellow precipitate is obtained at tin- same time. \Vitli less pn,-
teid their solutions merely turn yellow on Imiling and nrange on
the addition of the alkali: if only a trun- of proteid is present n<"
yellow colour is observed until after the addition of the alkali.

•_' With Millon's reagent3 they give, when present in >uth-
cient quantity, a precipitate, which turns red on heating It they
are only present in traces, no precipitate is obtained. l>ut men-lv
a red colouration of the solution when heated.,

If mixed with an excess of concentrated solution of sodium
ite, and one or two drops of a dilute solution of cupi;
pliate. a violet colour is obtained, which deepens in tint on ln.il-
iii'_r ( 1'iotrowski's reaction.4)

The above serve to detect the smallest traces of all pi

4. Render the tluid >tn>ngly acid with acetic acid, and add a
feu drops of a solution of ferrocyanide of potassium: a \-\

-hews the presence of proteids, except true peptone- and
>ome forms of allum;

1,'ender the tluid. a- l.efore. strongly acid wit i:

add .in equal volume of a coin-, nt rated -olution of sodium >ul-
phate. ami boil. A precipitate i- formed if pi I l"-p-

present

M, <l. ,'l"/^. "• fall' Mrm. 1KH7. Sn. 5J-
:lul,ii. fn.ni .!.••:'.- !•!••
\i\ S.M9 Cliiti.-ii.l.-n an.l Wliit.-li..uw. ^ !>hy»x>1. <'!>• ) V« n

* Consult in all ca.— 1 1..,,,.,. RerlerVi //.//"•/, ,/. ;»/,y«"/. path. r/,/-m. Annl^c

• • also Kniki-nl.«Tu'. >>'-'• U / \ -- \r

I xxriii. (1849), |. ««'

/ II I • / IM. vx,.

8 PROTEIDS.

This reaction is particularly useful, not merely because it effects
a very complete precipitation of the proteids which are present (except
peptones), but also because the reagents employed do not produce any
decomposition of other substances which may be present, and do not
interfere with certain other tests whicli it may be necessary to apply
after the removal of the proteids by filtration. It is of use more par-
ticularly in the determination of sugar in blood.1

The following reactions are specially used for freeing solutions
from all proteids by precipitation.

6. Acidulate faintly with acetic acid and add tannic acid.

7. Acidulate with hydrochloric acid and add the double iodide
of mercury and potassium. (Briicke's reagent.2)

8. Add hydrochloric acid until the reaction is strongly acid ;
then add phosphotungstic acid.

The following methods are often additionally useful for freeing
solutions from all proteids.

i. Precipitate by excess of absolute alcohol, having previously
made the solution neutral or faintly acid.

ii. Prepare a solution of ferric acetate by saturating acetic acid
with freshly precipitated ferric oxide, avoiding all excess of free acid.
Add this to the solution and boil ; the whole of the proteids are pre-
cipitated together with the iron; the latter as a basic salt.8 In some
cases a mixture of ferric chloride and an excess of sodium acetate is
employed.4

iii. Boil the solution for a few minutes with a little hydrated
oxide of lead in presence of a little lead acetate.6

In recent years various neutral salts, more particularly neutral
ammonium sulphate,6 have been largely employed for effecting
the precipitation and separation of the several proteids.

All proteids yield a characteristic violet colouration with simul-
taneous slight fluorescence upon treatment with glacial acetic.
acid and strong sulphuric acid (Adamkiewicz' reaction). The
reaction is best obtained by adding to the suspected solution or
substance a mixture of one volume of strong sulphuric acid and
two volumes of glacial acetic acid and boiling.7 The violet-col-

1 See Gamgee's Phi/siol. Chem. Vol. i. p. 195.

2 Sitzb. d. Wien. Akad. LXIH. 2 (1871), Feb. Hft.

3 Hoppe-Seyler, Hdbch. S. 264.

4 Seegen, Pfliiger's Arch. Bd. xxxiv. (1884), S. 391-

5 Hofmeister, Zt.f. physwl. Chem. Bd. 11. (1878), S. 288.

6 Wenz, Zt.f. Biol. Bd. xxu. (1886), S. 10. Kuhne, Verhand. d. Naturhist.-Med.
Ver. Heidelb. N. F. Bd. in. 1885, S. 286. See also Halliburton, Jl. of Physwl. Vol. v.
(1883), p. 172.

1 Hammarsten, Pfliiger's Arch. Bd. xxxvi. (1885), S. 389.

( INIMICAL P.ASIS <>F TH1-: ANIMAL i:«»l>Y. «.

mired siilutii.ii obs.-r\ed it' proteiiU are prc-cnl givefl ;ui ah-orption
liainl between tin- line-, I, and /'in tin- solar -pe.-t nun.

•jeiieral method .-an be ^i\cn t'-.r the quantitative estimation

nf the various prot.-id- For this -..me -p.-. 'ial manuals should be
con-iilted and use made of tin- reaction- which aiv -p.-. itically
characteristic <>i cadi 'mtfiil as

- «.f ililt'fi-ciit |>n. trill-; ri-i- t.i <liMi-ri-nt heights in capillary
tulics. It is jM.ssil.lc tliat tlii> t'art may IH- nf u^.- in i|i-tci-tiii^ and
• •st imatini; thi-ir Approximate relative amount-.1

CLASSIFICATION OF THK PKOTKII
The following classification is both convenient and c.m.

CLASS I. Naticc "Hnunins.

Soluble in distilled water. Solutions coagulated on heating,
especially in presence of a dilute (acetic) acid. Not precipitated
.rbonates of the alkalis or by sodium chloride, m- generally
by solutions of neutral salts.

1. K^g-allminin. Serum-albumins.

II. Dt-rirnl nil, H minx ( .I///////-

In-olul.le in distilled water ami in dilute neutral >alinc solu-
tions ; soluble in a<-id< and alkali^. Solutions not coagulated l,v
lioil:

1 Acid-alliumin. '1. Syntonin. .".. Alkali-alliumin 4. Ca>ein
or Native alkali-alliumin.:

CLASS III. (Hal i nl'

In-olulde in distilled water, solul.lc in dilute saline solui
Soluble in /•• /•//«//////. acids and alkalis- if the acid- and alkalis
•ronir they ate rapidly changed into member^ of ('la II
:ly precipitated by -atuiatiii- their dilute -aline -,,lu
tions with neutral -alt- inch U -odium chloride or magnesium
sulphate.

ii. Traiil.-. /.

vl.T. lldlrh K.I •'• I-i'l'-M1''

i.wh ,1. CAtfM. 15.1 iii S. MO. Dultowil i i>ky* ft nut (:»| T. 7 (I88J).

Nr ».

3 Ca«oin iliff.-rs in inanv r<->]»-> is fr-mi tli<- ..tlirr m.-int...^ ..f tl.

.illi.-.l t,, tli. 'in Ilian I- tin- in. i • otluT

.1 ly pp. ipitability by neutral *nlt* it nhcwii nornn affinity t.. the
globulin*

10 PROTEIDS.

1. Crystallin, the globulin of the crystalline lens. 2. Vitellin.
3. Paraglobulin or Serum-globulin. 4. Fibrinogen. 5. Myosin.
6. Globin.

CLASS IV. Fibrins.

Insoluble in water. Soluble with difficulty in strong acids and
alkalis, and undergoing a simultaneous change into members of
Class II. Soluble by the prolonged action of moderately strong
(10 p.c.) solutions of neutral salts, with simultaneous change into
members of Class III.

CLASS V. Coagulated proteids.

Products of the action of heat on members of Classes I., III.,
and IV., or of Class II. when precipitated by neutralisation and
heated in suspension in water. They are also obtained by the
prolonged action of alcohol in excess upon members of Classes I.,
III., and IV. Their solubilities, except in solutions of neutral
salts, are in general similar to, but less than those of Class IV.

CLASS VI. Albumoses and peptones*

The true peptones are extremely soluble in water. They are
not precipitated by acids, alkalis, neutral salts, or many of the
reagents which precipitate other proteids. They are precipitated
but not coagulated by even the prolonged action of alcohol. Pep-
tones are readily diffusible, albumoses less so. Some of the albu-
moses are readily soluble in water, some are less soluble. They
are distinguished from peptones by being precipitated when their
solutions are saturated with neutral ammonium sulphate. They
yield precipitates with many of the reagents which precipitate
other proteids, and it is specially characteristic that the precipi-
tates they yield with nitric acid and with ferrocyanide of po-
tassium in presence of acetic acid disappear when warmed and
reappear on cooling.

CLASS VII. Lardacein or amyloid substance.

Insoluble in water, dilute acids and alkalis, and saline solu-
tions. Converted into members of Class II by strong acids
and alkalis.

1 The albumoses are classed with the peptones partly from their close relationship
to these substances and partly for convenience.

CHEMICAL I'.ASIS OF TI1K AMMAI. |HH>Y. 11

'I'm: CIIKMISTKY I»K nn: SIYIKAL l'i:»i King.1

LM I .V-////V
Egg-albumin

A- obtained in tin- solid form by evaporating its solutio:
dryue-s at 40 J, preferably in vacuo.it forms a semi-transparent,

brittle mass, of a pale yellow culourL tasteless aiisl inodorous. l)i^-
snlviMl in wa_ter it yields a clear neutral colourk'ss solution. This
solut: Mali's on heating, but the temperature at which tin-

coagulation takes place varies considerably with the coiiccntrati' >i i ,
and is largely dependent upon the presence ,,\ absence <>i' salts.
The moiv commonly observed inn) »erat lire is 7<l-7.", , but C.antfer
--that coa-jula may also be obtained at .14 and »i.". . The
more dilute the solution is, the higher is the temperature at which
it coagulates, thus linallv resembliii"; a solution of allmiuni from
\vhieh the salts ha\e been removed by dialysis. ;; \\'lien luv-
ei])itaj.ed from solution by excess of alcohol it is ivadilv eoaiMi-
lated by tin- procipitajjt, so that it is now usually insoluble in
water. In this resjieet it di tiers somewhat rharaeteristieally from
senim-albumin, which is not so immediately, though it is ulti-
mately, coagulated by the action of alcohol.

tn (',, \-\\\ and Berard,4 bv applying tin- iiii'tlmil ..t
heat-OOagolation to filtered \\hitr c.f <"^'^, cua^ula inav In- <•!•-
tain.-.l at .".:•.•.. i',7 . 7'J . 7«1 . and SL' . tli.; lirM tu,, 1.,-in- du.- t..
^1'ilniliiis. thi- «itlifi-< t» albumin-.

Strong aci(ls especially nitric acid, cause a coagulation similar
to tTiat produced bv lu-at or by tlie i>roloiit:ed action of alcohol:
Fh"e idlrujjlill becjj|ues JtrofoUlldly cjiaiiL[e_d bv the action of the
;u^id, and doi-s n.,i di--olvc UJMUI romoval of the acid M-'i
• •uric chloride, nitrate ..)' sihcr. ami lead acetate, precipitate the
albumin, forming with it insoluble .•oiupuiinds of variable com-
:on.

:•• acid in excess oivev no pi.-, ipn.it. •. luit when the
solution i- concentrated the albumin is transformed into a ti.m-
parent jelly. A similar jelly is produced when strong caii-tn-
:i i- added to a eom-i-iit rated solution of r^'-albumiu. In

1 In :iil<litiini tc. tin- «(.rk< aln-:i«ly .|ii..trd ...n-iilt 11. il.-trin. //./'. 7. ./
IM. in .-•-!:» I (I. fc-r all il:it:i ronr.Tiiin^ I In- |.r

- < '/i i mil ni>/>liii>ti--i it Ai / '• I Miicean.

:,.|i| S-.. .\i.,t HI Mmly'ii Ja*TM-
l*rirl,t. \i. (I--I I. S T.

- Upta him / IM ' ^^M 1871 .luli-IIH

' ' ' / I M8), p. 170

12 PROTEIDS.

both these cases the substance is profoundly altered, becoming in
the one case acid- in the other alkali-albumin.

The specific rotatory power, which is stated to be independent
of the concentration, is variously given as (a)D= — 35'5° (Hoppe-
Seyler), or — 3779° (Starke). The latter agrees closely with Haas'
determination1 (a)D= — 381° and is probably the most correct of
the three values.

Preparations. The fibrous network in white of egg is broken
up with scissors and violently agitated in a flask till a thick froth
is formed. The flask is then inverted, whereupon the foam rises
to the top, carrying the larger part of the fibrous debris with it.
The clear subnatant fluid is now carefully drawn off and filtered
through fine muslin ; .to this an equal volume of water is added,
and the whole is finally filtered through coarse paper. From this
point onwards two methods may be employed.

1. For ordinary purposes the fluid may be very carefully and
faintly acidulated with acetic acid, filtered and the filtrate purified
by dialysis.

2. To obtain the purest albumin proceed as follows : 2 Saturate
the fluid with magnesium sulphate at 20°, filter and saturate the
filtrate with sodium sulphate. Dissolve the precipitate of albu-
min thus obtained in water and precipitate again with the sodium
salt, and after repeating this process several times remove the
last traces of salt by dialysis and concentrate to dryness at 40°.

According to recent researches egg-albumin may be obtained in
a crystalline^orm by slow evaporation of its solutions in presence
of neutral ammonium sulphate. The separation takes place at
first in the form of minute spheroidal globules of various sizes, and
finally minute needles, either aggregated or separate, make their
appearance. It has not as yet been found possible to obtain
these so-called crystals from solutions which have been freed
by dialysis from the ammonium salt. Further investigation is
needed to establish their real nature.3

The primary digestive products obtained during the peptic diges-
tion of egg-albumin have been studied by Chittendeii and Bolton.4

2. Serum-albumin.

This is the sole proteid. apart from the globulins, which occurs
in_s£r_um.5 Pure solutions of this proteid closely resemble those

1 Pfluger's Arch. Bd. xn. (1876), S. 378.

2 Starke, loc. cit.

a Hofmeister, Zt.f. physiol Chem. Bd. xiv. (1889) S. 165. Gabriel, ibid. Bd. xv.
Hf. 5 (1891) S. 456.

4 Stud. Lab. Physiol. Chem. Yale Univ. Vol. u. (1887), p. 126.

5 'Serum casein ':of Kiihne and Eichwald was shewn by Hammarsten to consist

CHEMICAL BASIS <>r mi; ANIMAL J'.oDV. l::

^-albumin in their oviicral reactions, l.ut tin- difference of
the two is clearly shewn by tin- following statement.- ; —

1. When t'n-.- from -alts and in 1 — 1%"> p.c. s.ilutiun it ci.a^u-

'ii heating to 50°. The addition of sodium chloride raises

the coa^ulatm- l'"int to 75° — 800.1 Under thr conditions in

which it occurs in serum it is not found to shew aiiv opalesccnce

on heating at any temperature below 60°, and it nia\ rded

oagulating completely at 75.°

I'.y fractional heat-coagulation <.f serum freed I'mm ..rlc.bulin Halli-
burton- lias obtained e\ id.-nee of th«- e\i-tenee in the scnun of maiiv
animals of three albumins coagulating at 70-73°, 77-7* . and S'j
in .-OKI serum only two (,f these albiiinins nccur.

'_'. It is iij^t reudilv (Mia^ulateil by alrnhol._i.r precijiitated by
ether: e^-alluiiniii is, and must readily by alcohol.

.".. It is ditlieult tn makt' any one definite statement as i<> the
specific rotatory pn\v(-r of serum-albumin since it appear< t«> ditler
fur the substance as obtained from dilVerent animals. Starke
oive- it as (o)D = — 62'6° for human scrum-albumin, and — »i
iiat of the horse.

4. It is not very readily precipitated by strong hydrochloric
, and the precipitate is readily soluble on the further addition
<>f acid: the reverse is the case for c^u-a

.". Precipitated or coagulated serum-albumin is more rcadijv
soluble in nitric acid than is c^rr-^

('.. When precipitated by alcohol it is, a- aln-ad\
immediately though it is ultimately c..aoiilated by the action of
the precipitant, than is eo

7. According to (Jauthiei-'1 the follouiim reagent
c^'o albumin but not serum-albumin : L'"

;!|-hat.- of copper 1 p.c. : 700 <-.<-. glacial a- •

To be added ill the ratio of ]() c.c. to '_' . . uf the fluid t" be
••I.

S. Ivj'-i-alliiiiiiin if injected subi'iitaneously or into a VC.H.
ain'eai-s unaltered in the urine; scrum-albumin similarly inJL'c^ed
does not thus normally pass out by Mu» kidney,

Si-nuii-albjiniin is found not only in blood-serum, but also jp^
IviniVltT both that contaiiiedln tip- proper lymphatic channel

. . r<.ntirin--il t.\ I l:illil'iirt..ii. .//. /V,v«i.».'. Vol.

1 Stark-, la •,' 8 I-

- .//. /'//»/>/,./. v..l. \. i-x-i. |. i :.•_'. Mm -• .»'- • v-'l \i 1 1 -'.mi. |
i Ifalr'i /. i: : \ . , :ii.

14 PROTEIDS.

that diffused in the tissues ; in chyle, milk, transudations, and
many pathological fluids.

It is this form in which albumin generally appears in the urine.

Scherer described' two proteids which he obtained from the contents
of ovarial cysts, and to which he gave the names of metalbuinin and
paralbumin.1 Hammarsten concludes from his researches 2 that they
are really identical. Metalbumin seems to be associated with some
carbohydrate substance resembling glycogen (?), since it yields, on
heating with sulphuric acid, a body which reduces Fehling's fluid as
does dextrose.8

Neither egg- nor serum-albumin can be obtained in a condition such
that They leave no ash residue on ignition. Al. Schmidt asserted *
that they could be by means of dialysis, and that in this condition
they were no longer coagulable by heat. On this point a keen con-
troversy was carried on for some time, for the details of which see
Rollett's article on Blood in Hermann's Hdbch. d. Physiol. Bd. iv.
Th. 1, S. 93. The whole difficulty seems to have turned on the ex-
treme sensitiveness of dialysed solutions of albumin to the presence
or absence of traces of acid or alkali, and on the fact that such dialysed
albumin is largely changed into an albuminate.6

Preparations of pure serum-albumin. Centrifugalised serum is
saturated at 30° with magnesium sulphate, and the precipitated
globulin 6 is washed on the filter with a saturated solution of the
salt. The filtrates are then saturated at 40° with sodium sul-
phate; by this means the serum-albumin is precipitated. The
precipitate is dissolved in water, reprecipitated by sodium sul-
phate, and the process repeated several times. The final product
is then freed from salts by dialysis, precipitated by excess of
alcohol, washed with this, and finally with ether, and dried by
exposure to the air."

The facts on which this method is based were clearly stated by
Denis.8 Schafer rediscovered9 the precipitability of serum-albumin
by sodium sulphate in presence of the magnesium salt. Halliburton
has shewn 10 that this is due to the action of the double sulphate of
magnesium and sodium MgNa2(S04)2 6 H20.

1 Ann. d. Chetn. u. Pharm. Bd. 82 (1852), S. 135.

2 Maly's Bur. Bd. xi. (1881), S. 11. Zt. physio/. Ch. Bd. vi. (1882), S. 194.

3 Landwehr, Pfliiger's Arch. Bd. xxxix. (1886), S. 203. Zt. physiol Chem. Bd.
vui. (1883), S. 114. Hilger, Annal. d. Chem. Bd. 160 (1871), S. 338. Plo'sz, Hoppe-
Seyler's Med.-Chem. Unters, (1871), S. 517. Obolensky, Pfliiger's Arch. Bd. iv.
(1871), S. 346.

* Pfliiger's Arch. xi. (1875), S. 1.

5 Werigo, Pfliiger's Arch. Bd. XLVIII. (1890), S. 127.

6 Hammarsten, Zt. f. physiol. Ch. Bd. vui. (1884), S. 467.

7 Starke, loc. cit. (sub. egg-albumin), S. 18.

8 Etudes sur le sang, Paris, 1859, p. 39.

9 Jl. of Physiol. Vol. in. (1880), p. 184.
10 Ibid. Vol. v. 1883, p. 181.

CHEMICAL i:.\sl> <»F THK ANIMAL BODY. 1.',

CLA» II. />> :ri'-'d AUmmimt (Albtiminates).
\ . Acid-albumin.

When a native iilluiniiii in solution. such as egg- or serum-
albumin, is treated for some little time with a dilute acid, such
us hydrochloric. its properties become entirely changed" The
:n;irU.-il changes are (1) that tin- solution is no longer eoa^-
ulaj_ed by lii-;it : ( _ ) that when the solution is can-fully neutral-
ised the whole of the proteid is thrown down as a ]>rt'ci])itatG ; in
other words, the serum-albumin, which was soluble in war
at least in a neutral fluid containing only a small «|iiantity <>f
neutral salts, li^s become converted into a substance insoluble in
\vatyr "i" in similar m-ntral thuds. The Imily into which scrnni-
albiimin thus becomes converted by the action of an acid i<
spoken of a< "i-iil-ullniiiiiii. Its characteristic t'eatnn-s are that it
is insolultlc in distilled water, and in neutral saline solutions,
such asj.hose of godic chlddde. that it is readily solulde iii"dUnte
njMds or dilute alkalis, and that its solutions in acids or alkalis
ar" pot- po:nrnla^d by builing. (When suspended, in the undis-
solved state, in water, and heated to 75° C., it becomes coagulated^*
and is then undistinguishable from coagulated serum-albumin, or
indeed from any other form of coagulated proteid. It is evident
that the substance when in solution in a dilute acid is in a dif-
t'.'ivnt condition from that in which it is wln-n precipitated liy
neutralisation. It' a quantity of serum- or e^-albumiii be ti
with dilute hydrochloric acid.it will lie found that the eon version
of tin- natrve albumin into acid-albumin is gradual ; a specimen
heat'-d to 75° C. immediately after the addition of the dilute acid,
will coagulate almost Bfl usual: and another specimen taken at
the -;ime time, will give hardly any precipitate on neutralisation.
S.ime time l;iter the interval depending "ii the proportion of the
acid to the albumin, on temperature, and on other circumstances,
the coagulation will be |e88, and the neutralisation precipitate
will be , on^iderable. Still later tin- coagulation will be ab-ent.
and the whole of the proteid will be thrown down on neutrali-
"ii.

i-i.iivi-r>i<'ii "f tin- native albiiinins in s,,lnti..i, int.. a.-i<l-:dl.uinin
l.y dilute arid- i> facilitated I»y heatiiij,-; f t'-ni|>erat un-s l.i-l.>\\
at wliicli tin- albumins respe.-t ivelv n.a^idate. ' Tlie ••••n\ i-rsmn
treiiidv rapiil it :i str«>n^ acid is adiled tT. a <-..n. •rut rated s..luti..n <-f
tin- ].n.tei.|; thus when a little ^la.-ial iOStlC Mid : "it., muli-

lllted \\Ilite of ,-^ the wh-.l.- -. .| i. I i lie. lilt., a \ell-.\N t Fa II- | .11 Tell t jelly

. .. .\k«d H.I. i.xxxiv. (1-

Arch. I:.! I

16 PROTEIDS.

consisting of acid-albumin. A similar jelly is formed, only gradually,
if the albumin is placed in a ring-dialyser and floated on dilute acids
(1-2 p. c.)1

Globulins are more readily converted into acid-albumin than
are the native albumins. Coagulated proteids or fibrin require
for their conversion the application of the acids, preferably hydro-
chloric, in a concentrated form, the products thus obtained being
practically indistinguishable from the products of the action of
dilute acids on the more readily convertible proteids. As ob-
tained -by the action of acids on the various proteids the products
exhibit certain not very marked differences, which however in-
dicate that each proteid yields its own special acid-albumin. The
researches of Morner2 have shewn that, contrary to earlier views,3
acid-albumins differ distinctly from the alkali-albumins. These
differences may be more appropriately considered after the prep-
aration and properties of the latter have been described.

Preparation 1. Serum or diluted white of egg is digested at
40 — 50° for several hours with 1 — 2 p.c. hydrochloric acid. The
solution is now filtered, carefully neutralised, the precipitate col-
lected on a filter and washed with distilled water.

2. Acid-albumin may be rapidly prepared by adding glacial
acetic acid to white of egg which has been chopped with scissors
and strained through muslin. A jelly is thus formed which can
be dissolved in warm water, and from this solution the acid-albu-
min can be precipitated by neutralisation and washed as before.

2. Syntonin.

Although this substance is merely the acid-albumin which re-
sults from the action of acids on the globulin (myosin) contained
in muscles, and in its more obvious properties^is at first sight
identical with other acid-albumins, it merits a short and separate
description, not only on account of its historical interest in the
chemistry of muscles, but also because recent work has shewn it
to be distinctly different from the similar products of the action of
acids on other proteids, and its properties and reactions have been
more fully studied than those of any other form of acid-albumin.

Liebig, unacquainted with the existence of myosin in the dead
muscle, was the first to prepare it by the action of dilute (•! p.c.) hy-
drochloric acid on the nmscle substance,4 and he regarded it as the

1 Johuson, Jl. Chem. Soc. 1874, p. 734. Ber. d. deutsch. chem. Gesell. 1874, S. 826.
Rollett, loc. cit.

2 The original is in Swedish, but is fully abstracted in Maly's Jahresbericht, Bd.
vn. (1877), S. 9, and is also published in extenso in Pfliiger's Arch. Bd. xvn. (1878),
S. 468. A convenient resume is given on p. 541.

8 Soyka, Pfluger's Arch. Bd. xii. (1876), S. 347.
4 Annalen d. Chem. n. Pharm. Bd. 73 (1850), S. 125.

CHEMICAL BASIS OF THE AMIMAL BODY. 17

chief and rhuracteri>t ic proteid of muscles (mu>ch>-tibrin). Kiihue,
li..\vcvi-r. .-hewed in his famous researches on muscle-plasma1 that its
formation i> dm; to tin- convt-r>ive action of tlie acid on niyo>in.

,"H-ii(ii>n. r>y_t,he action of O'l ]).c. hydrochloric nejd, on
yuj^jimisin (see belowY or ^treatment of 'finely chopped and
thoroutfhlif washed muscle substanper preferably from the frog,
with the same acid. It may he ) ir^'ciyitated from its solution by^
, and freed froni^ salts by washing, but in this case

^

can- must be exercised as toThe extent of the washing, sine-
tonin is distinctly altered by the prolonged action of water, espe-
cially as regards its solubility in dilute acid and linie-\s.

The reactions specially characteristic of this substance and its
distinction from other forms of acid-albumin and from alkali-
albumin are indicated in the following statements.8

1. It is soluble in, Tune-water and this solution is coagulated.
though incompletely, by boiling (Kiihne).

I*. K is insoluble in acid phosphate_Qf_SDda (NaH,PO4) ; other
aeid-alhumius are soHilde (Morner). In presence of this salt it
does not pass into solution on the addition of alkali until the
whole of the aeid phosphate has been converted into the neutral
I !'<>,). In this respect it differs from alkali-albumin, whieh
is soluble under tlie same conditions lon«rTefore the emiveixioii nf
tlu' acid into the neutral phosphate is complete.

3. It is soluble in dilute sodium carbonate.

4. When precipitated from its acid solution by neutralisation
the_preeipitate is more gelatinous than that of the other aqd-
albumins, and less readily soluble in alkalis (Morner).

5. It- >]"-eific rotatory power when dissolved in dilute hydro-
chloric acid or sodium carbonate is independent of the concent ra-
tion. and is given as (a)u = — 72° (Hoppe-Seyler).

Syiitonin lia> I ..... n stated to l>c ca|.:il.l<- of r.-<'.ni\ i-r.-i-'ii into m\
or some ^'lolniliii clo>cly reM-iiililing it. by .-ohition in lim.
<lition of ;imnionium chloride (" an amount just >h..rt of >at nrat ion.
and m-utrali>atimi \vitli acetic acid. Tin- nnitral fluid thus linally
obtaiiii'd is allowed to full drop by dn-p into di.-till
which a tine concilium gradually

Hoppr-S.-ylcr .states tliat by similar tn-atnn-nt all form- of acid-albu-
min may be converted into ^lobulins resembling myosin.'

/'i-otodatma, I - 15.

- Ki.l ..... , /,..-. dL .\nh.f. Phynot. J»hrg. 1881, a 196.

8 Seo M'TIKT, /<«?. fit.

» A I):»nil.-w>ky. '/.I. /: i'hVsi.J. ri,,m. IM. N ! - - I ) N. 158.

'- n,ib,-h. ,i tl iss.-j), s. aai.

18 PROTEIDS.

3. Alkali-albumin.

- or_egg-albumin or washed muscle be tteafed with
dilute alkali instead of with dilute acid, thejroteid undergoes"^
change in many ways similar tci-tbat which was brought about by
the acicT The alkaline solution, when the change has become
complete, is no longer p.nn|rn1nt,p.d by heat, the proteid is wholly
precipitated on neutralisation, and the_ precipitate^ insoluble in
water and in_jieutral solutions of sodiimicHiToride, is readily solu-
ble in dilute acids or alkalis.

Alkali-albumin may be prepared by the action not only of
dilute alkalis but also of strong caustic alkalis on native albumins
as well as on coagulated albumin and other proteids. The jelly
produced by the action of caustic potash on white of egg (p. 11)
is alkali-albumin ; the similar jelly produced by strong acetic acid
is acid-albumin.

In short, the general statement may be made that under other-
wise similar conditions, if an alkali is employed instead of an
acid to act on proteids. alkali-albumin is formed instgadjof acid-
ajbumin! In the opinion of many authors 1 th£ precipitates ob-
tained by neutralising the acid or alkaline solutions which arise
djiring the preparation of acid- and alkali-albumin respp-f-tivp.1v
are to be regarded as identically the same. According to this
view the neutralisation precipitate is itself neither acid- nor alkali-
albumin, but becomes either the one or the other by solution in
either an acid or alkali, entering at the same time into union with
the acid or alkali.

Danilewsky 2 has utilised the tropaeolins for the purpose of deter-
mining the fixation of acids or alkalis by proteids, and on this he has
based a classification of these substances. The tropaeolins are soluble
in water, the one (tropaeolin 00) yielding a yellow, the other (tro-
paeolin OOO No. 1) an orange solution. The first is changed to a
lilac colour by acids, but not by salts which have an acid reaction to
litmus. The second is turned to bright carmine by free alkalis, but
not by salts which have an alkaline reaction to litmus.

It is however on the whole more prnbnhlp 3 that acid- and
alkali-albumin are distinct, though very closely allied substances,
and we might go even so far as to say that probably every proteid
yields its own kind of either the one or the othp.r prntp.i'H on t.rp.at-

B"^^HMMBIMaMV^MM«^^HHHMMMMMHM^V>MMMi^MMBHHBMM^HH^MM^l^M_M^^^^MWKV"l*^

ment with acids and alkalis. But as yet we do not possess any
means of distinguishing between the several forms of each sub-
stance by any ordinary reactions.

1 Soyka, Pfluger's Arch. xii. (1876), S. 347.

2 Centralb.f. d. med. Wiss. 1880, No. 51.

3 Morner, Pfluger's Arch. Bd. xvn. (1878), S. 468. But see also Kieserit/.ky.
Inaug.-Diss., Dorpat, 1882. Abstr. in Maly's Jahreslter. Bd. xn: (1882), S. 6, and
Rosenberg, Inaug.-Diss., Dorpat, 1883. Abstr. in Maly, Bd. xm. (1883), S. 19.

(HLMICAL BASIS <>F Till. ANIMAL UnhV. I'.t

The chief though somewhat unsatisfactory evidence which is
advanced as to the difference of the two products is the following:

1. Al]tali-albuniin_is_in general more soluble than acid-albumin.

2. Wh.-ii pi-eclated h^ neutralisation tin- former (ajjj^li) i*
t. the latter (acid) iXn]£Ie viscid, transparent. an

atino us.

3. \Vhen dissolved in a lainiinum of alkali and heated to
00° in scaled tubes, alkali-albumin coagulates. .-u-jd-allmimp

4. When alkali-albumin is dissolved in NaaHP04 it js iu,f pp.-
cjpitated on the addition of an acid until aTTTTie salt has IK-CM
converted into XaH-iHV (Of. above, p. 17.)

Acid-albumin can IK- coiivertc^l into alkali-albirmjn }j\- tht;
actjiui of strong alkalis, but the rcycr.-c conversion of tin- imuhjpt
thus obtained or of an ordinarily prepared alkali-nlhiiinin into
acid-albumin is stated to b

'I'hc rotatory ]io\vcr of alkali-albumin varies accnrdinu' t<- n-
source; thus when prepared by strong caustic potash tVom scruni-
allmmin, the rotation rises from -56° (that of scrnni-albuinin)
to -86°, for yellow light. Similarly prepared from c^-albumin,

om - 38-5° to -47°, and if from coagulated whit-- of
it rises to-58'8°. Hence the existence of various forms of alkali-
alliumin is probable.

The <ulistance 'protein,' described by Mulder.- appeal-, it" it
at all, to be closely connected with this body. All sul>-
sei|iient observers have however failed to confirm his views.
and it is only meiit ioned here from its historical iir Since

Mulder's time the name has been applied to various forms of
proteid

"'ii-iitwn. The best method is that originally introduced by
Lielierkuhn.:: Purified white of e«^ (see p. 1 I i i- made int.. a.

bj^ the ad3itioji__ \vith rapid stirring of strong nqustip- ^»\-.\
Avoiding as far as possible all excess of ihc_jaj(' i The jelly i*-
ut into small Tumps and \va-hed in distilled watei.

,/ rim n,,,,!. until the lumps are quid- white throughout.
The lumps of purified albumin are tli.-n di<snlved in water .JiSL
gentlv heating on a water-bath, the solution jjlteml and the
alkali-albiinijii precipitated by rarefuladdition of m-i-tic add.
The precipitate is then thoroughly WftsTieTl with distilled \

.k:i. /-»-. ,;t. S.'C al-. S,. \lilot.. /•.. fi I'"*! .('firm N 1 U fl I-"- > 1
,/. Ch. ,>. I'h.tnn. IM XVMII (1838), 8 "I

.' 1',, --,.,,, !,,rf - .\nnitl H.I i\\\\i < II-

L'O PROTEIDS.

The product thus obtained is very pure, but there is a consider-
able loss of material during the washing of the gelatinous lumps,
owing to the solubility of the substance in the alkali which is
being removed. The pure substance itself is also slightly solu-
ble in water.

4. Casein.1

This is the well-known proteid existing charactejiatically_in
milk and in no other fluid or secretion of the body.'2

It has recently been proposed to call this proteid 'caseinogen ' and
to use the name casein for the product of its decomposition»_the clot
or curd, which is formed by the action of renntn^ugon_Jt. This
nomenclature would have the advantage of indicating a relationship
between the two proteids similar to that between fibrin and fibri-
nogen, rayosin and myosinogen (Halliburton).

Preparation? Fresh milk is diluted with 4 volumes of jlis-
tilled water and acidulated with acetic acid until the diluted
imTk contains from -075 to O'l p.c. of the acid. If the milk has
been diluted with ordinary tap-water rather more acid must be
added. I The precipitated casein is now washed two or three times
by decantation with water, as rapidly as possible* dissolved in the
least quantity of dilute caustic soda which suffices for its solution,
and filtered through a series of filters until the filtrate is quite
clear and only faintly opalescent. This filtrate is then somewhat
diluted, the casein again precipitated by the careful addition of
acetic acid, and the whole process of washing, solution, and repre-
cipitation carried out a second time. The final product is now
freed as far as possible from water, worked up into an emulsion
with 97 p.c. alcohol, collected on a filter, washed with alcohol,
finally with ether, dried by exposure to the air, and finally in vacuo
over sulphuric acid.

Casein may also be separated from inilk by precipitation with an
excess of sodium chloride * or magnesium" sulphate.5 I'he latter pro-
cedure is chiefly of use for the preparation of casein from human milk,
from which it can scarcely be precipitated by means of acids.

Pure casein as obtained by the above method i& a fine, snow-
white powder, which on ignition of even large quantities of the

1 Our knowledge of the chemistry and properties of casein are based chiefly upon
the researches of Hammarsten. His papers were mostly published originally in
Swedish or Latin, but are fully abstracted by himself in Maly's Jahresbericht d. Thier-
chem., to which reference will in each case be made.

2 For methods of conducting a complete analysis of milk see Pfeiffer, Die Anali/se
der Milch, Wiesbaden, 1887.

3 Hammarsten, Maly's Bericht. Bd. vn. (1877), S. 159.

4 Hammarsten, Maly's Ber. Bd. iv. (1874), S. 135.

5 Hoppe-Seyler, Hd'dch. d. phys.-path. chem. Anal. Aufl. iv. (1875), S. 241.

CHEMICAL I!A>IS <»F Till: ANIMAL HoDV. L'l

substam •«• (4 —6 tfrin.) leaves scarcely a tract- of ash. h i- prac-
ticiillv insoluble in water, but is soluble in alkalis, carbonates and
phosphates (if the alkalis, lime- and baryta-water. From the-.-
solutions it inav In- precipitated by excess of neutral salts such as
sodium chloride. anoMjy dilute acids, in which it is a^ai'n soluble
ifatiy^x^ss °^ ac*^ ls prcs^rct- Its reactions thus correspond
closely to those of acid- and alkali-albumin, but as will be
ently shewn it is in many ways perfectly distinct from these
substances. Solutions of pure c.ist'in an- in )t cna^ulatrd liy l.oil-
inuf, but if heated to 130 — loQ" in sealed tubes a coagulation is
obtained.

\Vln-n ;u-iil> arc aildfd t« diluted milk l<> effect the jtrecijiitat i«.n of
.•;i-.-iii IK. precipitate is obtained until the >nluti(in ha- a di-tinetly
acid react inn; this has usually l>cen att riluited to the pre>eiic.- in milk
<«f potassium phosphate. ' Hanniiarsten has houi-vn- shewn - that the
.-ame hidils ^ ..... 1 for solution- of ca-ein free fr..m thi> -alt.

When jin-jiiired from milk by magnesium snljihate (see below),
freed by ether from fats, and dissolved in water, casein possesses
a specific rotatory power (0)0= —80°; in dilute alkaline solu-
tions. of -76°; in strong alkaline solutions, of -91°; in
dilute solutions, of - 87°.3

Although purified casein leaves no ash-residue on ignition. Ham-
in, trsten found that it contained a m/ixtnnt and fairly laiye amount
of phosphorus, as a mean -S47 ]>.c. From this fact and its be-
haviour towards sodium chloride in dilute solution-, he r«-_;ards
ca-ein as bein^ a nucleo-albumin 4 (see below). This viev.
iv-ponds with the ie-ult- previously obtained by I.ubavin/' who
found that a pho.-phorised ( nuclein ) constituent of . a-.-m is sep-
1 out a- an insoluble residue during the digestion of i-a-ein
with gastric juice.

\_i_t the vii-ws of inaiiv authors0 milk <'oiituin.s HQ-
oidv. lnit at least two forms of |U-otei(l u hirh pass under the ojie
I lainiiiar.-teii 7 has criticised these views and conclude- that
ii is a unitary substance, and not a mixture i.r compound

A, tm, i »j ,-,,111111 nn eatrin. This ha- b,-, n fully studied by
Hainmar-teii. \\bo-. iv-ults may be summaiised a- folio,

' Kiilnu-. /../ir'.. tl.,.h,,»»l. &**. I-'

kUlr'i /;, ,. MI B

Hoppe-Serler, //-//«•/,. (K-i. r.) p 286.

Hoppe-Seylcr'H .»/.'/../!.».. ('ntmnch. Ilf M »«»3.

Mill.,,, „' ( . .nun ail!.-. /

Maly
IM v

22 PEOTBIDS.

trary to the older views that the formation of the clot is rather
of the nature of a precipitation than a true ferment action, we
now know that by the action of rennin the clotting of casein is
due_to a specific action of the enzyme which results in the form-
ation of a substance (tyrein) differing essentially from casein." It
had been considered that the separation of the clot was due to
the formation of lactic acid from milk-sugar,1 but this is not so ; 2
pure casein free from every trace of lactic acid clots with rennin.
The specific action of the enzyme is further shewn by the fact
that simultaneously with the formation of the clot, a by-product
is formed having the properties of a soluble albumin.^ Further,
the clot is entirely different from casein : jt is mucli less soluble
^i acids and alkalis than the latter,* always leaves as ordinarily
prepared a large and constant residue of. ash (calcium phosphate)
on ignition, and even it it ~5e~Treed from the calcium salt by
special methods 5 and dissolved in dilute alkalis, is not capable of
being made to yield a clot by the renewed action of rennin.

It may be remarked here that no efforts to obtain a ' curd ' from
milk by purely chemical means, such as the addition of acids or neu-
tral salts, have resulted in tbe production of a substance which by
further treatment can be made to yield a typical ripening 'cheese.'
The latter can only be made by the use of rennin.

The calcium salt plays an all-important part in the clotting of
casern! Casein freed from this salt and dissolved in dilute alkali
wlfl not yield a clot ; dialysed milk similarly yields no clot, but
if the dialysate be concentrated and added to the milk it now
clots on the addition of fenrTtTT vviien pure casein is dissolved in
iTme^water and neutralisecTwith phosphoric acid it ndw clots with
rennin. The action of the salt in the whole process appears to be
that it Determines not so much the action of the ferment on the

casein, but^ rather the subsequent separation from solution oQlie
altered product.6 JN either Is the calcium salt alone essentiaTTfor
be replaced, but with less efficient results, Jjv the similar

salts of magnesium, barium, and strontium.7

The question as to the identity or the reverse of casein and
alkali-albumin as obtained by the action of alkalis on other pro-
teids has given rise to much controversy. Some authors have

1 Soxhlet, Jn.j. pr. Chem. Bd. vi. (1872), S. 1.

2 Hammarsten, Maly's Ber 11. (1872), S. 118, iv. (1874), S. 135. Heintz, Jn. f
prakt. Chem. N. F. Bd. vi. (1872), S. 374.

3 Hamraarsteu. See also Koster (Swedish) in Maly's Ber. Bd. xi. (1881), S. 14.
* Al. Schmidt, Beitr. z. Kennt. d. Milch, Dorpat, 1874.

5 Koster; foe. cit. S. 14.

6 For further observations on the influence of salts on the clotting of milk and
casein see Ringer, Jl. of Physiol. Vol. xi. (1891), p. 464, xii. (1891), p. 164.

' Lundberg (Swedish). See Maly's Ber. Bd. vi. (1876). S. 11

CHEMICAL BASIS OF THK ANIMAL BUl>Y.

con.-ideivd tin-in to be identical,1 but that they are m-t M U -ntti-
ciently -hewn by th.- following facts. Solutions of alkali-albumin
In- made to clot by the action of pure rennjn. If milk

In- added to tin- solution and impure rennet,] e. extract of
tin- niuc.ui> membrane containing rennin, be allowed to act upon
it, in -onie cases a separation of the alkali-albumin may take
place, owin^' to the formation of lactic acid which then preeipi-

the allnimin. In the absence of the milk -n-_rar n«> change
i- produced which can in any way be regarded as analogous t»
the dotting i if casein. When milk is clotted the se]>aratiun uf the
casein is so complete that none is found in the ' whey.' and Ham
marsten has shewn that if alkali-albumin be added to milk and
the mixture be then clotted, alkali-albumin may be obtained fnmi
the whev on breaking up the curd, It has further been shewn -
that although casein i- \ei\ resistant to the action of acids, it
may by treatment with them be converted into acid-albumin w i 1 1 1
complete loss of all clotting powers, ami still more readily into
alkali-albumin by the action of alkalis.

A farther difference of tin- t\\.> sul»tances was urged l.\ /aim <>n

tin- ba>is i.i hi> e.\]H-riineiit> MH tin- till rat i ...... l' milk tln-Mii^h |IMI-MUS

eartheiiNvare (liattery-cells).8 He I'mmd that scilutions of ulkali-allm
min ]>a» thi'Dii^h the \\alU «\ the relU as rapidly a> <1" -.>luti«-ii> «•!"
M-riim-albiimin . \\Iim milk Imwever is filtered hy tlii- nietlnnl. .
il-ie- nut |>a^-. and the liltrati- fi.n>i>t> "i' \\ater. .-alt^. and the i-na^nla-
l>le pi-Mteid uf the milk. Whether thi> mdi«-ate> any difference be-

t\\ecll the t\\M >||li>talice> i> Il<>\\eVer d< Mlht t'll 1. 1"1' it !•» .-till all n|.fll

<|iiestiMii whether ea-ein is truly in .sMlntimi in milk. Furtlier it i>
>tated that tin- ra>ein al>M pa— «•.-. int.. the filtrate it" the liltrati. >n is
).r..l..n^ed.4 and S, .xhlet >tat.- that if lim-ly di\ nleil (i-mulsified) fat
-peiided in a >..lnti..n <.f alkali-albumin the filtrati..n of tin- -nl>-
>tanee is rendered as inip..--il'l>' a- that <>\ ca-i-in in milk.

The crucial distinction between the two substances is the fact
t hat casein can be clotted by reiinin with simultaneous format ioi i
of a soluble ]iroteid by-|jrodiict. whereas^io true clot can ever k'
i >l ttained from ordinary alkiili-i'lbiiiuin

•r Uu- removal of"casc'in from milk by j.iv. ipitati<m. th

[i It rate contains a small amount of coagulablu ])rui>-iil.

sj)oken of as 'laetalbninin,' closely resembliiiLj serum-albumin in

eneral properties, but dilleriim slightly as t.. n
.]•>• power and th«- tempeiat UP- .n which it ...adulates when
heated.6

tit.

tiil!.«TU, lor. nt.
/., -.-.. I": -.-r* Arch. H.I. u -.98.

•',. /. ,/ mea I ?*•

ft Sell-li.-!. . Mil- OM>1. S

1885), S. IW. Hallil.urt.m. .// tfPkg**, Vol XI.

24 PROTEIDS.

In addition to these, according to the older views, milk, even
when quite fresh, frequently contained traces of a proteid which,
since it yielded the biuret reaction, was usually spoken of as a
peptone, and was by some observers called ' lactoprotein.1 It
was stated to increase in amount in the milk on standing for some
time, and more especially if warmed to 40°, and to be consider-
ably increased during the clotting induced by rennin.2 Eecent
researches have however shewn that perfectly fresh milk contains
no substance whicn yields a biuret reaction, its presence being due
to its formation during the processes employed in its separation.3
If the milk undergoes an acid (lactic) fermentation a substance
may now be obtained from it which yields a biuret reaction, but
is not a true peptone, but a primary albumose.

When milk is kept for some time at a temperature above 50°
and below its boiling point, a firm skin is formed over its surface
composed largely of casein.4 Its formation is not to be regarded
as being specially characteristic of milk, for pure casein dissolved
in dilute alkalis exhibits the same phenomenon, as also do alkali-
albumin, chondrin, gelatin, and the filtrate from 1 p.c. starch when
it is concentrated on a water-bath. Its formation is probably due
to the rate of evaporation from the surface of the milk being
more rapid than the fluid diffusion into the upper layer ; 5 and in
accordance with this it is found that its appearance is considerably
facilitated by blowing a rapid stream of air or any indifferent gas,
such as carbonic oxide, over the surface of the warmed milk.

Our knowledge of the chemical properties of casein as already
described is based entirely upon researches carried out upon the
milk of cows. There is no reason to suppose that all that has
been said does not apply equally well to the milk of other ani-
mals. Nevertheless human milk shews, apart from the difference
of composition (see § 513), certain differences from cow's milk,
which are due to a distinct but characteristic difference in the
reactions of the casein contained in each.6 This is shewn by the
following facts. (1) Human milk clots less firmly than cow's
milk, and sometimes not at all with rennin. (2) The casein in
hurrian~milk, 011 the addition of acetic acid, yields a very imper-
fect jprecipitate whicn is finely floccuientTaTmost granular as com-
pared with the compact and coarsely flocculent precipitate yielded

1 Hamrnarsten, Maly's Bericht. Bd. vi. (1876). S. 13. Palm (Russian), Ibid. Bd.
xvi. (1886), S. 143. For other references see Halliburton, loc. cit. p. 459.

2 Hoppe-Seyler, Handbuch d. phi/s.-path. chem. Anal. 1883, S. 480.

3 Neumister, Zt. f. Biol. Bd. xx'iv. (1888), S. 280.

4 Sembritzky, Pfliiger's Arch. Bd. xxxvu. (1885), S. 460. See also Maly's Ber.
Bd. xvu. (1887), S. 157.

5 Hoppe-Seyler, Virchow's Arch. Bd. xvn. (1859), S. 420.

6 Simon, Animal Chemistry (Sydeuham Soc.), Vol. n. 1846, p. 53. Also in "Die
Frauenmilch u. s. w." Berlin, 1838. Biedert, Virchow's Arch. Bd. i>x. (1874), S.
352. Biel, see Abst. in Maly's Ber. Bd. iv. (1874), S. 166. Langgaard, Virchow's
Arch. Bd. i.xv. (1875), S. 352.

CHEMICAL BASIS OF THK ANIMAL linDY. 25

by cow's milk. (3) Th_e <"isein in human milk is, as already
stated, very incompletely precipitated by the addition of acids.
and can only be completely precipitated by saturation with imiLf-
nesium sulphate.1 (4) Casein irom hitman milk is less solu hie
in water than is that of the cow.

The primary di«;r>tivr prodm" • l>tain«-d hy the action

of pepsin on casein have hern dr-eril>rd and studiril l.y Chittrndrii
and Pain'

CLASS III. GM'tilhiii.

Besides the derived alhimiins there are a nuinher of native
j^nbjjds which (litter from tin.1 alhuinins in not heinij soluije in
distilled waiter ; they need for their solution tjje presence <>f ;in
uh it ma

appj-ecjahle. t liou^h it may be a small, quantity of a neutral saline

suhstaiier such as sodium chloride. ThusTTiev reseinhle the alhu-
iniiiates in not hein^ soluhle _m distilletl \vajj-r. hut djjler from
thc'in in heiiiLj soluhle in dilute'^'dium chloride or other neutral
saline solution.-/' Their~ur''iieral characters may he stated as follows.
They are insoluhle in water, soluhle in dilute ( 1 j».r.) solutions
lium chloride; they are also sojiibje in dilute neids and
alkalis, Itein^ changed on solution into acid- and alkali-alhumin
respectively unless the acids and alkalis are exceedingly dilute
and their action is not prolonged. The saturation with solid
sodium chloride or other neutral salts of their Miline solutions
1'ivcij.itates most members of this class.

1. Crystallin. (Globulin of tk« eryttoUii

This form of ^lohulin is usually regarded as identical^ with
vitt-TTiii. Tt is howev.'r convenient to treat it separately, inasmuch

;|s ij_eall I'" pivpaivd jj, a | Hi 1 e forill. whel'eas \Jtellill lias IlOt as
ohtailied t'lvi ^tVolll lecithin (see I.eloW).

/• . /»t,->it<»ii* Crystalline leii^-s. in which it occurs to the
i of L1 1 -t'.'J p.p.. are rnhheil up in a mortar with a little fine
sand and a few civ-tal- ••!' IM, k -alt : the n. 'iien e\tr

with water and tiltered. The liJtrate .•ontains the crvsfallin and
some -eruin-alhiiiiiiii. Thelornier is separated from the laf
copious dilution with distilled water and a current ot

carlionie anhv.lride thmu-jh the diluted mixtir upon the

:allin is precipitated.
A diluto dine solution of this j.n.t. -id OOftgulattt at 75°.

Makria. ln«> I'-' rt. (II

,ijol. <V..) -'156.

\ik..ljnkin (l;u-M:u.). Al.st in M
4 Uptwliinskv, I'll..-, r - I 15,1. MM (I-

!'«• PKOTEIDS.

Bdchamp has recorded l some determinations of its specific rota-
tory power which must however be accepted with caution.

2. Vitellin.2

This constitutes the characteristic proteid constituent of egg-
volk and is also largely present in caviar Some at least of the
globulins present in vegetable protoplasm, and more particularly
in the crystals of the aleurone grains, appear to be identic-ill in
their genera J properties and reactions with vitellin. As obtained
in conjunction with some lecithin by exhaustion of egg-yolk witli
ether, it consists of a white, pasty, granular mass, insoluble^ in
water, readily soluble jiLsolutions of sodium chlojride which may
be easily filterecT Unlike other true globulins it cannot be pre-
cipitated from this solution by saturation with sodium_chloride.
Its saline solutions (lu p.c. NaCl^ are coagulated by heating to
2$°. It is readily soluble in 1 p.c. sodium carbonate, is incom-
pletely precipitated from this solution by dilution with water,
but fairly completely by the additional passing of a stream of
carbonic acid gas through the diluted solution.

As has been already stated, vitej.lin_Js associated in egg-yolk
with lecjthin and (?) njiclein. It has not as yet been obtained
free from admixture with the former, and a theory has been ad-
vanced that it is really a complex substance resembling in this
respect haemoglobin, which on treatment with alcohol splits up
into coagulated proteid and lecithin. It is possible that pure
vitellin free from lecithin might be obtained by prolonged ex-
traction with ether in a tjoxhlet or other form of apparatus.

Fre"my and Valenciennes have described3 a series of proteids, viz.
ichthin, ichthidin &c. derived from the eggs of fishes and amphibia.
They appear to be closely related to vitellin but have not been suffi-
ciently investigated.

The primary products obtained from vitellin by the digestive
action of pepsin have been examined and described by Neu-
meister.4

Preparation. Egg-yolk is extracted with successive portions
of ether as long as the residue yields any colour to the solvent.
The pasty residue thus obtained is dissolved in a minimal amount

1 Compt. Rend. T. xc. (1880), p. 1255.

2 Dumas et Cahours, Ann. Chem. e.t Phi/s. (3) T. vi. p. 422. Hoppe-Seyler, Med.-
chem. Unters. (Tubingen), Hft. 2 (1867), S! 215. Weyl, Arch. f. Physiol. Jahrg. 1876,
S. 546. Pfliiger's Arch. Bd. xn. (1876), S. 635. Zt. f. phys'fot. Chem. Bd. i. (1877),
S. 72.

8 Compt. Rend. T. xxxvin. pp. 469, 525, 570.

4 Zt. f. Biol. Bd. xxin. (1887), S. 402. Cf. Chitteuden and Hartwell, .//. of
Physiol. Vol. xi. (1890), p. 441.

CHEMICAL I'.ASiS OF TIM: \M.\1AL UuDV. 1.'7
of 8 — 10 p.c. sodium chloride solution, {nnecipiteted from th.

the additii ..... f ;H: ol \\ater, and purified by resolution m

tin- salt and reprecipitation by tin- addition of water. Tin- opera -
tionsmust In* conducted as rapidly as possible since the pj-o-
loii,ued"licti(m of water renders tin- vitellin insoluble in saline
solutions. rTanyattempt is made t» separate tin- vitellin from
lecithin residues by means of alcohol it is at OIK c converted into
ordinary coagulated p

:;. Paraglobulin.

This proteid «IOMHN iiHjstdiaracteristically in blood-serum (al-o
in lymph), in amounts nowknowri to be much larger than \\a-
at one time Mipin^-d, and thus constituting about one-half of tlu-
total proteids of the .serum. -

partition* The older methods con>i.-i.-d in flj diluting
serum ten-fold with water and j'assin^ a jirolon^ed current of
carbonic acid -as; (lj) saturatin- serum with sodium chloride.
The amount of precipitate thus obtained rej»re>ent- only a small
part of the total paxaglobulin present in the scrum.4 and the only
satisfactoi-y method of preparing it pure and in considerable i|iian-
tity is as follow- : '.'> serum is saturated at ."»() with magnesium
sulphitj.e, liv nuuins o£ w'liicl| paraulobulin is tiuantitativelv |ue-
ripitjited The precipitate collected bv filtratign i.s_jj_istril.»uU'd
dirou^h a small volume of a saturated solution of the magnesium
salt, cijllectedjon a filter and \vashed with. satiuai»'<l solution of
M^S()4. JJy this means it is separated from the larger part of
tLe serum-albumin.

T» cir.-cl \[< tiliul alld I'olllliletr se^qilltioll fl'om t hi- lat tcl pro-
teid. two methods may be_udi4Jed. (a) Ti:-1 ]•!• ipitatl ifl dis-
solved in water, then largely diluted and the para^lobulin further
separated out by jiassing a stlX'ajlMjiLd^- (^) '""' J'''''''!''!^!1'
is dissolved as l)efore in water, the jiara^lohulin again salted out
bv M-S<),. this pn,ccs< ivpeat'-d s.-\,-ral tini''-. and the final pro-
diii • •eijjroin the nmunesiuni salt by di.^

1 This i- tin- Mil.-tanrr t.. «hi.li Al. Srhmiilt j;:iv.- the iiaim- <>f til.riii" |
|. In -/,. C. A,»it. „. /'in/sml. .lat.ru "-''I 1'tl"

i ./,. r..i M (187f) s.4i.-!. //-.< l« i';«'i pn-\i..ii-h

'IMM-II ili-sri-ilM-i| iin.l.T tli«- naiiH- ' .-..•nun ra<i-in' l.y I'aniiin. (Vircli.
S. 17.) Tin- iiaim- j.aniulol.uliii is .In.- to Knlin«- (/

NOW in-iK-rally ami ino-t a|i|ir<>|>riati-l\ known l.\ I In- latt.T i

of nranMdobolio, as >iiL:^cstrii t>\ I|O|>|K--S"

- llanunar-t.-ii. I'lln. l'..| \MI i I Wfrfrf,

1--I . -

l'ln/»iol. ('hem. Vol. 1 ;

4 Hammar-t. n. I,*-. r,t. II.'MiMii-. I'tln-:. :

• ll.i.iun. r~l, n. ... Mil \\m 'A. I
I'hi/siol. t'/i<m. H<l. vni. (ISH.-{), >•

|»liat.- for tli.' <|iiantiiativ.' s.'jiaration loliuliiin ('

Init Ilainniar-I.'n r. tin- ir«-inT.il nirtli-«l -

28 PROTEIDS.

Pure paraglobulin is insoluble in water. If dissolved in a
m.i/tii'm.al anwunt of alkali it is precipitated by "03 to '5 p.c. of
JiaQl. On the addition of more than *5 p.c. of the salt it oes

again into_solution and does not begin to be reprecipitated on the
addition of more salt until at, least 20 p.c. NaCJ. has been added.
It is not completely precipitated by saturation of its solutions
with NaCl (Hammarsten). Its dilute saline solutions .coagulate
on heating to 75 °.1 Dissolved in dilute solutions of NaCl or
MgS04 its specific rotatory power is stated to be (a)D = — 47 '8°.2

Paraglobulin occjrrs in smaller amounts (£ — |) in chyle, lymph,
and serous fluids. Hammarsten by means of saturation with
MgS04 was the first to shew that hydrocele fluids frequently
contain paraglobulin, thus largely shaking the importance of Al.
Schmidt's views as to the part it plays in the process of blood-
clotting.

Globulins which are not regarded as differing essentially from
paraglobulin are also stated to occur in urine.3

Cell-ylobulins. Halliburton has described under this name 4 some
forms of globulin which Qccnr in lymph-corpuscles and may be ex-
tracted from them by solutions of sodium-chloride. Of these one, ce1Ir
glbbulin-q, occurs in minute quantities only and is characterised by
coagulating at 48 — 50°. The other, cell-globulin-/?, is more copiously
present in the corpuscles and coagulates in dilute saline solutions at
75°. The latter resembles paraglobulin very closely in properties
other than the identity of their temperatures of heat coagulation in
dilute saline solution, e. g. precipitability, &c. He considers thaj
cell-globulin-/? differs from true paraglobulin, or_ plasma-globulin as
he terms it, by possessing the power of hastening the clotting^of di-
luted salt- plasma, and he regards^ the so-called 'fibrin-ferment T as^
identical with ^ell-globulin-^ and "arising from the disintegration of
leucocytes.

The proteid constituent of the stroma of red blood-corpuscles con-
sists chiefly of a globulin usually regarded as identical with paraglo-
bulin, since its saline solutions coagulate at 75° and it is precipitated
from the same by saturation with sodium chloride and a current of
carbonic anhydride.5 Halliburton considers it to be identical with

plied it somewhat differently to Denis. On the use of ammonium sulphate for
separating globulins and serum-albumin see Michailow (Russian), Abst. in Malv's
Bericht. Bd. xiv., xv. (1884-5), Sn. 7, 157. Pohl, Arch. f. exp. Path. u. Pharm. Ed.
xx. (1886), S. 426.

1 Halliburton, .//. ofPhi/siol. Vol. v. (1883), p. 157.

2 Fre'de'ricq, Arch, de BioL T. I. (1880), S. 17. Bull. Acad. roi/. de Belgique (2),
T. iv. (1880), No. 7. (See Maly's Bericht. 1880, S. 171.)

3 Lehmaun, Virchow's Arch. Bd. xxxvi. (1866), S. 125. Edlefsen, Arch. f. kiln.
Med. Bd. vn. (1870), S. 67. Also Central b. f. med. Wiss. 1870, S. 367. Senator,
Virchow's Arch. Bd. LX. (1874), S. 476. Heynsius, Pfliiger's Arch. Bd. ix. (1874), S.
526 (foot-note). Fuhry-Snethlage, Arch. Mi'n. Med. Bd. xvn. (1876), S. 418.

4 Proc. Hoi/. Soc. Vol. XLIV. (1888), p. 255. Jl. of Pfn/swl. Vol. ix. (1888).
p. 235.

5 Hoppe-Seyler, Physiol. Chem. S. 391. Kiihne, Lehrbuch, S. 193. Wooldridge,
Arch. f. Phi/siol. Jahrg. 1881, S. 387. Hoppe-Seyler, Zt.f.physiol. Chem. Bd. xm.
(1889), S. 477.

CHEMICAL BASIS OF THE ANIMAL BOI>\.

cell-globulin-/?, and arc-mints thus for tin- curlier statements a.s t<. tin-
tibrinoplastic properties of tin- stroma-glubulins.1

/

4. Fibrinogen.-

f 7

This globnliq oec-irs in blood-plasma together with para^lolMi-
lin Uidaeram^aJiQUpiri. During blood-clotting it is converted
~ "

Iy7~ir noTentirely, into tibriu (but see below). It is ;dso
found in clivle. serous thuds and transudations. more particularly
in hydrocele tluids.::

In its iji-neral reactions it resembles para^lohulin bnt is
markedly distinguished from the latter by tin- following charac-
teristics. (1) A* it occurs in plasma 4 or in dilute solutions of
sodium chloride (1 — 5 p.c.), it maculates at ~>~> — .")Q^ (2} It is
very readily' precipitated by^ the addition of sodium chloii de to
its salijir snlutiuj^s until the wlndr contains 10 p.c. NaC'l. whriv-
as paraultiliiilin is not appivcial.dv precipitated until at least

-. «'t the sodium salt lias lieen added.

ii:' Salted jilasma, obtained by Cjintrifu^alisinu blood
\vhose _eoa^nlat_ion is ]irevented l»v the addition of a certain pn.-
])ortion of mauiiesium sulphate, is nn^ed with aii__e<iual volunif
of_a satunited (35\S7 p.c. at 14° C.)° solution of sodium chloride;
the fibriiiogeu is thus preci])itated while the pin-aul"bulin ivniauis
jn sohition. The adhering plasma may !»• ivTnoved by washing
with a solution of snjiuin p.liloridp, and the fibrino^en finally
purified by bein^ several times dissolved in and repiveii'itatrd l,v
sodiyju

Haiiiniar>tfii's statfim-nts as to tin- nature and propt-rt ii-> i.f tiliri-
iio<rcn liavi- IM-CII tin- sulijfi-t of inii'-li «-ontro\ci>y lu't\\n-n lniiisi-lf. Al.
Schmidt, and

When a fluid containing purified
tibnn bv the action of fibrin-ferment, thejmiount ofjj]aiii iojiu^l

i .//. «/'/Vi,/siW. V..]. \. (1*89), p. 532.

- llamin: 1 psahl. Vol. \ 1. \^.'< BfTtcAl.

B. 15. I'tluu'-r's Arrh. 15.1. \l\. (1-771. S. I'll . M

:|; \\\ (1883), S. 437. Maly's />••''' MI ( I »--'), S. 1 1. Al Nlmii.lt.
I'llii-.-r's Arch. H.I. M (1"7-J), S. 4KI;' xj. (1-::.). > Ml! MM (1876), ^ 14«
" I.i-lm- \ mi .Ifii frrmciit QerinoiuigMneb*ioiuiff0o a ^

/ Vol. l\ (I—:!), i

S, :;i:i ; |~- \'..l. i \n ' l.n-lwiu -

/•. L887, S. -J-JI. Zt. /I i: "I. H.I XMV. I-
S 174. './/. I'l.if,,..':. \ • 1 x

lla.niniirsten, Maly viu. (I87H). S

4 Fr.'.l.Tic.]. .\,m. &

Hull, dr l'Ar,,,l. r..y. </•• A'.///"/'/,. I i KH (1H77), No. 7. " Kocherchca nur la coo-

stitiitinn <lu |il:i.mn:i s.in^nin " I '.in-. 1878.

•'• li.iinini' -mi. QMWM, PA jpwi Cktm \'.>1 i p. 41.

.l;i>i. C/nm. /'/!//.•.. i

30 PROTEIDS.

is always less than that of the fibrinogen which disappears at the
"same time.1 The Deficit thus observed is at least partly accounted
for by the simultaneous appearance of a globulin which coagu-
lates, when heated in saline solution, at 64°. Although at first
sight it seems very tempting to regard the process of fibrin-for-
mation from fibrinogen as partaking of the nature of a hydrolytic
(?) cleavage of which this globulin is one product, this view is
not as yet established. Hammarsten considers it is more prob-
able that the globulin really represents a portion of the fibrin
\yliich has gone into solution during its formation, basing liis
views on the earlier work of Denis,2 who showed that j ncj,er
speciaT~circumstances a form of fibrin may be obtained winch is
soluble in solutions of sodium chloride, the solution coagulating
at 60 — 65° (see below, p. 33). AT Schmidt holds that Hain-
mars ten's fibrinogen as coagulating at 55° is in reality a sort of
modified or " nascent " fibrin and not truly a globulin.

The viscid secretion of the vesicula seminalis of the guinea-pig is
very rich in proteids and possesses the power of clotting. The pro-
teid which it contains is not in all respects a typical globulin, but in
many ways it resembles fibrinogen. When dissolved in a little lime-
water it coagulates when heated to 55°. The secretion itself clots
readily and firmly on the addition of a small quantity of the aqueous
extract of a blood clot.8

The fibrinogen of invertebrate blood yields fibrin by the action of
fibrin ferment, but differs from vertebrate fibrinogen by coagulating
at 65° when heated.4

5. Myosin

When an irritable contractile muscle passes into rigor, the sub-
stance of which the muscle-fibres are chiefly composed undergoes
a change, analogous to the clnf-.fr'npr nf hlnnrl-plnsTna, which results
in the formation of a clot, of myosin.5 By appropriate methods
(see § 59) the muscle-fibres may be broken up and their contents
obiajned as a viscid, slightly opalescent fluid (muscle-plasma),
which .filters with Tiifficulty and clots ^at "temperatures above G£.
This muscle-plasma may be diluted with solutions of varying
strengths of several neutral salts, whereby its clotting may be
delayed, and the nature and phenomena of the processes involved
in the clotting investigated along the lines previously employed
in the elucidation of the phenomena of the clotting of blood-

1 Hammarsten, Pfliiger's Arch. Ed. xxx. (1883), Sn. 459, 465, 475.

2 " Nouvelles e'tndes chimiques, etc." Paris, 1856, p. 106. " Memoire sur le sang,"
1859.

3 Landwehr, Pfliiger's Arch. Bd. xxm. (1880), S. 538.
< Halliburton, ,11. of Phi/siol. Vol. vi. (1884), p. 321.

5 Kiihne, " Das Protoplasma," 1864. Lehrbuch,- S. 272.

BASIS OP i IN: \MMAI. BODY. 31

pla-ma.1 The more important hctfl winch have thus l»e,-n made
out may IM- lirietly summarised a- i'.>lln\\>. Mu>d« --plasma con-
t_ai_ns a uloliuliii-foreruuiier <>f myosin (• niyosino^.-n ") wTuVTi
resi-mltles lilirino^en in coagulating at ^'t . This pmteid i- r,,n-
\vrted into mvo>m on tin- occurrence oi' dotting liy tin- action of
a .-pecitic ferment. which is regarded a> l>einu do>dy related t...
if not identical with, an alluimose (see below). Tin- serum. which
is left in small (|uantitie.s only aftt-r the formation of tin- dot.
contains m-otdds winch coitLrulat<- at 47°"

o."» . (niyoLjlobuliu) 73°, an albumin <:Iosdy n-<i-nil»lin^ scrum-
all.uniin.

ii'n->iti<iti.:> (\) Finely dioj.jwd mnsde-substeiice is wa-lit-d
rapidly with cold water, to remove serum-alimmin and colouring
matters (baemOglODin , the residue is sijueexed out in linen, and
extiaeti-d for at l-a-t '2 4 hours with H' )>.<•. solution of N'ij^'l in
\yhidi mvosin ia readily soluhle. Tin- extract is now liltejvTl lirst
through muslin and then thnniLfh jiajier: the filtrate is a more or

vjadd and Quiescent solution of mvosin. From this the
III\OMII may lie prepared in a run- condition l>y allowing it-
solution in the ammonium salt to drop into a lar^e exei-^s oi ili-^
The myt ts.ii! gradually settles out in a tloccule^nt

^

ina_-<. which may lie further ]>urilied h_v resolution in a minimal
amount of neutral salt and reinvci]iitation by jiourin^ into an
excess of distilled \v;iter. '1'his jiiiritication must lie conducb-d
and at htw tem)>e.ratures. for myo<in is somewhat readily
liy the )>rolonue(l action of water and liecomes in^oluhlc
in saline -olutioiis.4 (2) The tiuely dioj.j.i-d and \\ashed mu-d«-
is divided into tw ..... jual portions: to one of the •iifud-

(deci-normal) hydrochloric acid is m /r /'////// added until a distim-t
acid reaction is nl.tained as shewn \<\ tropaeolin ( M ) ( see aliove.
p. IS). The two portions an- then intimately mixed to-.-ther.
allowed to -land some time, strained through muslin, tillered ami
the myosjn precipitated from the liltrate l'\ c'aieful nentrali-atiou
with veiy dilute alkali or lime-water.

Apart from the general reactions which diaraeten-e ifijo>m a>
a ^lol.ulin. it is distinu'iiishcd hy the low tenii>erat ure i
aL yvhieh its siTline solutions constantly coagulate. !•
larinj ash residing on incineration, consisting ehielly of >alts of
lime. As already stated, it is coiiyerted into an in-oljd'le j
Ity the prolonged action of water, ami into syntoiiin l_>v the action

oj_iicids. Thesi- StlltstaiK-' led to lie capable of reeon\er

sion into ni\ p. 17). It is also stated r> that it

1 II:illHiiirt..n,.//. »/ / • IM

lirinani. /j. f -, H ; iv. (1880), & 384.

:,!!••« .-.ky, /j't'. : •:>• IM. v. (1

« \Vr>l. '/J '/. l>ltl,snJ. r/,.m I'.. I
'" llallil«nrt«.li. lir nl }> I 1-

32 PROTEIDS.

myosin is dissolved in NaCl or MgS04 (10 and 5 p.c. respectively)
it yields a renewed clot on mere dilution with water.

According to .N'usse l inyosin constitutes the anisotropous substance
(see above § 56) of the unaltered muscle-fibre, and the activity of con-
traction is inversely proportional to the amount of this substance
which is present in the fibres of different animals.

Globulins to which the name of myosin is applied are described
as occurring in vegetable protoplasm2 and in the cells ofThi'

Myosin is readily digested by pepsin, more slowly by trypsin.
The primary products arising from the digestive action oF the
former enzyme have been studied by Kiihne and Chittenden.4

6. Globin.

When haemoglobin is allowed to undergo decomposition spon-
taneously by exposure to the air an. insoluble proteid is bbtanied
of which very little is known, but to which the name of globin
was given by Preyer.5 It appears to be perhaps an outlying
member of the globulin class of proteids, but unlike a true glob-
ulin is scarcely soluble in dilute acids and imperfectly soluble
in alkalis and solutions of sodium chloride. It is converted into
acid and alKaii-albumm by the action of strong acids and alkalis
respectively, and is stated to yield no trace of ash on incineration

CLASS IV. Fibrin.

This proteid is ordinarily obtained by ' whipping ' blood with
a bundle of twigs until clotting is complete ; the fibrin which
adheres to the twigs is then washed in a current of water until
all the haemoglobin of the entangled corpuscles is removed and it
is now quite white. The washing is greatly facilitated if the
fibrin is very finely chopped before it is washed, and if it is fre-
quently kneaded and squeezed with the hand during the washing.
In this way it may be obtained quite white in a few hours. The
washing is also much facilitated if the blood is mixed with an
equal bulk of water before it is whipped. It is obvious that fibrin
prepared by the above method must be in an extremely impure
condition, for it contains a not inconsiderable admixture of the

1 "Anat. u. Physiol. d. Muskelsubst." Leipzig, 1882. BioJ. Centra/It. Bd. n.
(1882-3), S. 313. Zt. f. phi/siol. Chem. Bd. vn. (1882), S. 124.

2 Weyl, Zt. phi/Sid^ Chem. Bd. i. (1877), S. 96.

3 Pldsz, Pfliiger's Arch. Bd. vu. (1873), S. 377.

4 Zt.f. Biol. Bd. xxv. (1889), S. 358. See also Chittenden and Goodwin, Jl. of
PKifsiol. Vol. xii. (1891), p. 34.

'5 "Die Blutkrystalle," Jena, 1871, S. 166.

CHEMICAL BASIS OF THK ANIMAL lioDV.

remain- of tin- white corpuscles an«l the .-tmmata of tin- red l It
can only he prepared pure during the chtttiiii; of i-itljej filtered or
ceiitrifu^alised iced-plasma oii_aaJjLi|>lasiiia, or by theaction of
purilied li Iain-ferment on pure tihrinoi/en. In accordance with

fibrin as ordinarily obtained lea. :riable amount of

granular residue which contains phosphorus durini: it- digestion
by pepsin. NII -uch residue i- observed \vhni lilnin I'rmu til'
jtlasma is di-i'-t'-d \vitli JM-JISJII (set- l»clu\v. j. 4'2 ), luit in im otlit-r

iitial ivxj,,.(-t d»«-- tin- inn- liln'in diltcr frum tin- ntlin
liilirin. a- ordinarily olitaiiu-«l. rxhjbits a tilaiut-ntous struc'tinv.
tin- riiinjM.nciit threads lu'-s.^sin^ an t'lasticjtv much ^ivatcr
that itt' any utln-r kumvn solid )in»tcid

It' allowed to f«irn7 gradually in laryi- ma»f>, tin-
structure is n-'t >n imticralilc. and it ivsriuMrs in this i'urni
india-rulilir]- Sucli lunijis of lilirin aiv cajialdc of licin^ split in
any direction, and no definite arrangement of paiallel luindle^ oi

'•an lie made nut

Filirin is insolnhle in \vater jind ,/j'/,it, s^jim. ^..Imioi^ :
also ordj^jirily insolnlde in dilute acids (HC1) & their action

|>lac,- at ordinary tein|)e]'atures and is not prolonged, nit-rely
liecoinin^ swollen and transparent in the acid and returning t"

spinal >tate if the acid i> removed by an ezoeafl "1 Wt1
careful addition of an alkali JSyjjro loured action at ordinary
tej^})eratuivs. or a shorter action at 40°, the jihjiu is profoundly
cjian^ed and certain forerunners of the peptones which mayije
tinully formed (at 40 J) n,re ]n-odnced It is similarly insoluble in
<|ilute alkalis_and ammonia, hut }':_i^s;j> more readily into solution
inj.lu-se rea;ientsr if their action is prolonged or the temperature
is raised, than i> the case with dilute acids The heha\ i«>ur of
tihrin towards solutions (,f neutral salt- is peculiar and important
I ready Maic'd, tihrin pre)>aivd hy simply whipping hlood i-
insolulile in dilute saline solutions I'.nt it- -i.luhility is de|H-nd-
ent upiin the conditions under which it is separated out from the
blood. In accordance \\ith tin-. I Jenis - descrihed three form- of
tilirin to which he gave the name- of 1 l-'ihrine . oncivte ll|(,di

'_' Fil.iine -lolnilme. :; I-'ii.rme .-oncn-te j.uie. Th-
is what \\e now know as ordinary tihrin olitained hy \\hippini; ar-
terial hlood (human in Peiii-' \\oiki Tlie -e. ond he ohtained hy
the -jii.ntaneoiis clotting of human \eiion- I'lood. and thi- ieadil\
-well- up to a slimy ma-- in 10 ]>.<-. NaCl. The third h-

i liy 'whijipinu' human venous hloo<l under certain precau-
tion-, and found it to he -oluhle in ilil olution h\ 01
iwo hour-' treatment with th< W , <t)ur
Hammar.-ten'- pai t ial conlirmat imi of I »eni^' -tatement - tli>
hut little reason for doubt mi,' the accuracy of so careful

' Ilaiiiiiiarstc-ii. I'tlu. • I ! : NMI (1880), S. 481 ; XXX. (1883), S. 440.

I ••:•••

34 PKOTEIDS.

The possible solubility of fibrin under certain conditions in saline
solutions of moderate strength obtained considerable importance
in the controversy between Schmidt and Hammarsten as to the
nature of the processes involved in the clotting of blood. When
on the other hand fibrin is subjected to the prolonged action
of more concentrated (10 p.c.) solutions of neutral salts, and
the salt solution is frequently renewed, the fibrin may be finally
completely dissolved, being converted into members of the glob-
ulin class.1 Most observers agree that the globulin thus chiefly
formed coagulates at 55 — 56°. Green obtained in addition one
coagulating at 59 — 60°, the two differing further in their solubili-
ties in 1 and 10 p.c. solutions of NaCl. These changes are
brought about by the salts in the entire absence of any putre-
factive phenomena, and the resulting globulins cannot be made
to yield fibrin again by any treatment with fibrin-ferment.

When fresh unboiled fibrin is simply washed till it is white
and digested with pure active trypsin, it is largely converted
into coagulable proteids during the initial stages of the ferment
action.2 These proteids are characteristically globulins and one
is closely related to paraglobulin, as judged of by its coagulating
in saline solutions at 75° and possessing a specific rotatory power
(in 10 p.c. NaCl) of (o),>=-4810.3 The second globulin pro-
duct of the ferment action coagulates at 55 — 56°, and in this
respect more closely resembles fibrinogen.4 Whether the whole
of the globulin thus obtained is a product of the conversion of
the fibrin, or whether a portion of it is due to globulin existing as
such in the raw fibrin, is not yet stated. Similar globulins are
produced by the action of pepsin in its earlier stages on raw
fibrin. If the fibrin is boiled or treated for some time with al-
cohol before digestion with either of the above enzymes, mere
traces, if any, of these globulins are obtained.

The purest fibrin always leaves a small but fairly constant ash-
residue on incineration. Of the inorganic constituents of winch
this residue is composed it is probable that sulphur is the only
element which enters essentially into the composition of the
fibrin.

When boiled in water or treated for some, time with alcohol it
loses its elasticity, becomes much more opaque, is much less
soluble in the various reagents which dissolve the original fibrin
with comparative ease, is attacked with much greater difficulty

1 Green, .//. ofPki/siol. Vol. vin. (1887), p. 373. Limbourg, Zt. / phi/siol. Chem
Bd xin. (1889), S. 450. The latter contains a complete list of references to the
literature of the subject excepting Pldsz, Pfliiger's Arch. Bd. vn. (1873), S. 382.

2 Briicke, Wien. Sitzber. Bd. xxxvii. (1859), S. 131. Kiihne, Virchow's Arch. Bd.
xxxix. (1867), S. 130. Lehrbuch, S. 118. Kistiakowsky, Pfluger's Arch. Bd. ix.
(1874), S. 446.

3 Otto, Zt. f. physiol. Chem. Bd. vm. (1883), S. 130.

4 Hasebroek, Zt. f. physio/. Chem. Bd. xi. (1887), S. 348. Herrmann, Ibid. S.
508. But see Neumeistef, Zt. f. Biol. Bd, xxm. (1887), S. 398. Salkowski, Ibtd.
Bd xxv. (1889), S. 97.

CHEMICAL BASIS OF THE ANIMAL 1;<>1>Y.

liy pepsin ami try].siii. and is in fad indi-tin^ui-hable from all
other coagulated pn.teids.

A peculiar property «>f this body remain- yet to l.e in.-uti<
vix. itsjiower of decomposing hydrogen dinxid"- !':•• 68 of fibrin
placed in this lluid, though themselves underiMiinj,' m> change.

-..on become covered with bubble- i.f oxy-.-ll ; alld ^Uaiacllll

turned 1'lue by tibriu in pie-ence .,f h\dr«--eu dioxid-
turpentine.

When globulin, niyosin. and tilirin are compared each with the
other, it will l.e -ecu that they form a series in which nn|os_mi-
ijjU-rmcdiate between ^lobnjm and tihriu. (Ilobulin is e\e. -s-ivelv
s^lubleiii even tlie most dilute acids and jdkajjs ; tibrin is aln
insoluble in these ; while myosin, though m ( »re soluble thai i
fibrin, is less soluble than globulin. (ilobulin a«>aimILi^oJ\ex
wjth__the^ greatest ease in a very clihija^solution of sodium chlo-
^'•T^MvosiiL on the other hand, dissolve's with dijliculty ; it is
much more soluble in a 10 per cent, than in a one per cent. -<.lu-
tinii iif sodium chloride ; and even in a 10 per cent solution the
myo>in can hardly be said to be di>snlved. -<. viscid is the ie>ult-
inu lluid and with such difficulty does it filter. Fibrin a«j;ain
dissolves with ^rcat ditliculty ami very slowly in even a 10 per
cent. >oluti'"''n of sodium chloi-ide. and ni a one ]M-I- cent, solution
it is practically insoluble "VYTien it is remembered that tibrin
and myosin are. both of them, the results of clotting, their simi-
larity is intelligible. Myosin is in fact a somewhat more soluble
form of tibrin, deposited not in thread- or filament- but in clumps
and ma-

<'i.\-s \". ( ',,<i>inlnted Proteids.

Tr J

These are insoluble in watei\ dilute ac^tls and alkalis, and

SfllJllV SobiH'r>m of nil <ttr»'iiirtbs In fact they ale really

luble o^nly in strong acids and strong alkalis, though j.n.loi:
action of even dilute acids and alkalis will died >..me solution.
especially at hi-h tcmpciat UL-. ljurinu solution in stnniu acjds
destructive decomposition takes place, but some
ajiionnt ui acid- or alkali-allmmin is always produced, together
with some jteptonu and allied snb

Very little i- known of the chemi< ten-tic- ..f this

class. TJ.ey are produced by huatinir to 100° (-'. solut

siTiiiii-iilbmiiin H^MJli* «iis|»«iniftl in \\ntfr nr dissolved in

lino qf>1iiti..i.s b\ h..ilin» tori -h"rt time tibrin -iisjM-nded in
water, or preci].itate<l acid- and alkali-albumin -u-jH-uiled in

ter. They are readily converted at the t«-nn>erature of the
body into ]*-].toncs. bv the action of uastru mice in an acjd. or of

iHTe:i|jc j^ce j|f :m alkaline medium.

All proteids in solutinn are precipitated bv an eyes. ,,f v.
. If the precipitant be rapidly removed th-

36 PROTEIDS.

soluble in water, but if the precipitated proteid& are subjected for
some, time to tbe a^|,jnp of VliM n1i-n|ii»1 they are,"\\-itli the excep-
tion of peptones, coagulated and lose, their solubility. It appears,
however, that the proteids contained in the aleurone-grams of
plants are exceedingly resistant to this coagulating action of
alcohol.1

CLASS VI. Albumoses and Peptones.

When any of the proteids already described are submitted to
the digestive action of pepsin or trypsjn, certain subtances are
formed,~in~tlie earlier stages of the action. . wiiicTTare intermediate
b'eTween the proteid undergoing digestion, and the proteidproduct
(peptone} which finally results from the action of the enzymes.
When the digestive fluid employed is pepsin in presence of dilute
(•^"p.c.) hydiQchloric acid, a small portion of the, proteid may be
at first Converted into a form of ordinary acid-albumin.2 It_ is
obtained by neutralising a peptic digestive mixture at an early
stage of the digestion, and has been frequently and almost, usu-
ally confounded with the ' parapeptone ' of Meissner. As will be
explained later on. the two substances are quite distinct forms of
proteid. At a later stage of the digestion the first-formed "acid-
albumin disappears, a considerable amount of parapeptone is
formed, and other products make their appearance, which are
known collectively under the name of albumoses.3 By a more
prolonged action of the pepsin a considerable portion of these
albumoses is further changed into the final product peptones ; 4
beyond this stage no further change can be brought about by the
action of pepsin. If trypsin be employed in an alkaline solution
(•25 p.c. Na.2C03) the decomposition of the proteid is much more
complifiaJied and profound. Instead of acid-albumin a small amount
of alkali-albumin makes its ap]3£aian.ce, together witn more or less
(see above, p. 34) of the cog.gulabl.e globulins in the earliest stages
of the digestion. Albumoses speedily make their appearance, to
be somewhat rapidly and it may be largely converted into pep-
tones, of which some are in their turn partially, though never
completely, converted into leucin, tyrosiu, and other less well-
defined crystalline products. Simjlaj prodnp|.s of the decompo-
sition of proteids may be obtained by the action of acids alone, in

* Vines, Jl. of Physiol. Vol. in. (1880), p. 108.

2 To this substance the name ' syntonin ' was formerly applied ; this term is how-
ever most appropriately used to denote that form of acid-albumin which results from
the action of acids on myosin. (See above, p. 16.)

3 Kiihne, Verhand. d. naturhist.-med. Ver. Heidelb. N. F. Bd. i. (1876), S. 236.
Schmidt-Miilheim (Arch. f. Physiol. 1880, S. 36) named these antecedents of the
true peptones ' propeptone.' See also Virchow's Arch. Bd. i. (1880), S. 575.
Jahresber. d. Thierarzneischule, Hannover, 1879-1880. Biol Central!/. Bd. i.
(1881-2), Sn. 312, 341, 558.

* Name due to Lehman n 1850, Pfujsiol. C/iem. (Ed. Cav. Soc.) Vol. n. p. 53.
Peptones were first definitely described bv Mialhe, Jn, de P/utnn. et de Cftim.
(3 Ser.) T. x. 1846, p, 161."

CHEMICAL BA8I8 OF Tin: ANIMAL

the absence of :ill en/ynie, tin- preponderance of any one or more
of the products being dependent upon tin- cuncentralion of the
acids, tin- temperature at which they arc employed, and tin- dura-
lion i'i' their action. 1'roteids may al-o In- peptoni-ed by means
of water acting at high temperature- under considerable pi.
I'.y employing tin- above means for ellecting tin- decomposition of
proteids, the products (pTOteid) which may In- obtained, and which
been very exhau-tively dealt with and described
;hne ami his pupils, are numerous It will hence conduce to
clearness in the subsequent description of each separate pmduct
if this is preceded l>y a short statement <»f the views which have
from time to time been held as to the general digestive changes
which proteids may undergo.

tir>t distinct experimental demonstration of the aohfont action

of gastric juice was due tn Keaumur (17.~iL'). \\liicli wa> foil,, \\i-d at
intervals by those of Stevens (1777). Spallan/ani (17s.'o. and !
niont ils.'Jl). The chemical nature of the product* ari-in^ fr..m the

suliitinii \\a> ii«'t. h»ue\cr. docriiuMl until tin- year l.SKi l.y Miallic
under tin- name ->f ' all»uininu>»-; ' IM thex- tlie name »i jK-ptun.- uas
>iil»-e«|iu-ntly ^iven l.y Lelmiann in 1S.">(>. and their nmst important,
properties fairly fully docrilied liy Mulder in IS^S. In this >aiiic
year < 'nrvisart first published his views as to the .-pecilic proteolytlO
powers of pancreatic juice, and tlie>e were tinally >he\\n to l,r c,,rre.-t
l.y Kiilme in 1SH7. I)in-inur this latter period (1859—1862) M. i-m-r
ami lii> j.upil>Miad ].ul.lished the results of roearclies ,.n the products
which are formed during

researches. When an alkali was added t»> the tiltered
fluid resnltini; from the acid peptic digestion of any proteid, to an
amount just short of that required for exact neutralisation, a pre-
eipitate was dhtained which he named /»•,•<'/» i<t«i«. In its gen-
eral reactions it resembled a< id-albumin or syntonin, but was
distinctively characterised by its incapability of ninlergning con-
ver>ion into a peptone by the further action of pep-in. !!•• ] -inted
out at the same time that it might be digested by an infu-imi «>f
the pancreas Alter the n-mnval of the parapeptone h ..... < a-ion-
ally obtained a further precipitate by the addition of acid, to nut
more than -ii.". to -1 p. c.. (n tin- filtrate ; this -nb-tance I,,, named
nn fn/H i>tn,i,: lie further d.---rili«-il a iv-idne insoluble in dilute
acids, but soluble in dilute alkalis, which made if
during the dk"-ti"n "f casein, and to which he gave the na:

dyspepton* moral of the above |.roducts theie -till

remained in snlntimi tbiee BabstanOM -ailed IVSJMM t i\ d\
and '--peptone, and charactei i-rd as follows: —

; precipitated by -troirj nitric acid and bv
in Jin-sen, e ..f , id.

1 /.t. /: ml. M,<1. !?.!.•. MI S. I . MI v s I MI ^ "i

:.-,,,,,.- la I.i'lilliaiin :

38 PKOTE1DS.

2>-peptone , not precipitated by strong nitric acid nor by potas-
sium ferrocyanide unless in presence of an excess of strong acetic
acid.

e-peptone ; not precipitated by nitric acid nor by the potas-
sium salt, whatever be the amount of acetic acid simultaneously
added.

These statements of Meissuer led to considerable subsequent
controversy, and the occurrence of the several products he de-
scribed was, with the exception of parapeptone and c-peptone,
denied by those who repeated his experiments. There is now
but slight reason for doubting that the divergent views are due
to the fact that Meissner's digestive extracts frequently contained
only small amounts of pepsin, while those of subsequent observers
were much more actively peptic, so that in their case several of
the intermediate products described by Meissuer were rapidly
peptonised and thus missed. Further it was urged that Meissner's
parapeptone was not a specific product of peptic action, for it was
said to be identical in all its chemical properties with ordinary
acid-albumin or syntonin Hence it was that Brucke,1 opposing
Meissner, put forward the view, which has since been most gen-
erally accepted, that the sole products of a peptic digestion are
parapeptone and peptone, — the former being due to the action of
the acid necessary for the activity of the pepsin, the latter making
its appearance as the sole final specific product of the ferment's
action on the first formed parapeptone, Schiff alone appears to
have supported Meissner.2

The researches of Kilhne. From what has been already said it
is at once evident that Meissner's view implied a decomposition
or splitting-up of the primary proteid molecule, inasmuch as he
held that his parapeptone was incapable of conversion into pep-
tone by the further action of pepsin Brucke on the other hand
regarded the process of peptonisation by gastric juice as not
necessarily involving any decomposition of the proteid molecule.
Kiihne, impressed with the profound and obvious decomposition
which trypsin brings about when it acts on proteids, reverted
once more to the possibilities implied in Meissner's views. In so
doing he found further confirmation of the idea that even in gas-
tric peptonisation the proteid is not merely changed but split up,
in the fact that only a portion of the gastric peptones can be
made to yield leucin and tyrosin by the action of trypsin ; from
which it follows that during a complete gastric peptonisation at
least two distinct peptones are formed. In accordance with this
he assumed that the original proteid molecule must itself consist
of two parts, of which each yielded its corresponding peptone

1 Sitzb d. Wien. Akad. Bd. xxxvii. (1859), S. 131 ; XLIII. (1861), S. 601.

2 Lecons sur la digestion, J867, T. i. p. 407 , u. p. 12.

CHEMICAL BASIS "K Tin: ANIMAL I;<>DY.

during th'- hydration which loads to the formation of JH-J.I.
He found al-o further continuation ut' this probability in tin- work
of Schut/enb< This, observer, decomposing proteids with

.icids at 100' ('., came to the conclusion that halt' the proteid
molecule is readily decomposable l»y the acids, whik- the other
hall' is jieculiarly resistent and is obtained in the final products
as an extraordinarily indigestible but true proteid, t<> which he
gave tlie characteristic name of ' hemiprotein.' Convinced thus
of the doulde nature of the proteid molecule. and seeing hut little
hope of separating i'roin each other in a mixture the two pep-
tones which must presumably ie-uh from the gastric peptoni-a-
tion of a proteid, Kuhne endeavoured to establish their exi-tence
by trying to discover the primary products intermediate hetween
the proteid and the jx-ptones, — antipeptone on the one hand and
hemipeptone on the other.3 Iii this his endeavours were at once
•d liy his being in posses-ion of a large amount of a proteid
identical with that first described and carefully examined by
r>ence-.lones, and hence called by his name.4 A renewed exami-
nation of this substance revealed that it was capable of <-on-
\ei-ion by pepsin into a peptone which was readily further

•nposfd by irypsin.-'' It was jM fact the product intermediate
between the original proteid and the hemij>eptone. and to it
Kuhne gave the name of hemialbunio.se It now was only i.
sary to obtain the corresponding a Ibumose precursor of the anti-
peptone, to peptonise this, and shew that the peptone thus obtained
would yield no leucin or ty rosin by even prolonged treatment with
trypsiu. Tliis Kuhne succeeded in doing by a fractionate.l peptic

:ion'; and thu- established his own views, and in don

shewed how acelllate a.S il whole MeisHlcl'- statement-

This will be evident from the detailed description of ti
products ,,f the decomposition of proteids by prpsin, tr\ p-in, and
arid-, which i> given below. The fundamental notion, then, of
Kulmc's view i- that an ordinary native albumin or fibrin con-
tain- within it-.-lf t \\ •• residues, \\hi«-h h. lively an

anti-r.-i.liie and a hemi-residuc The iv-ult of eitlier p,-p-
tryptic di-e-tion i- U) split up the albumin or fibrin, and to pio-
diu-e on the part of the anti-rc<idue ant i]x-ptone. and mi th-
of the hemi-roi.lue lnMiii]M-pt<inr. t lie latter being distinguished
from the former by its bring su-ceptible ,,f further change by

, ,•,„„.• d. not*M*rm*l. iw. ii,-i,irii, • • \ i :

?OC clnm. I'ari-. T XML [1875 , pp. U

T \\tv. ].i.. j i f. BM Bbd M.I!-. Jot • •'•• IM r. (H

» Tli«- naiii.- ' li.-iiiiiM-i.t. ..... ' w:i.s -;i».-ii in ..nli-r L. r..m.-\ the idc* th«l •

IHM.I..II.- for.n-.l fr..iu ..... I li:ilf "f tli- .,ripn:il J.r..|,-i,| innlmilf ' :uHi|"

..tli.-r lian.l tl.at it is llial ("Tin »( |H-|I|<IIH- «!ii.'h «i';

anv fiirtli.-r .l.TMi,,,H.siiiL' :i''li"ii "f tli" ngtMlU whirli 1-1 I- 11

, / ; i- • : . ,/. t'hrm.U.ri< HI. (I

1 Kiiliii-. y.t /: I!''"!. 1M. MX. (1S83), S. 209
K-.iliuc it. Cliitt.'ii'l-n. /'•"/. S. 1T1

40 PKOTEIDS.

tryptic digestion into leucin, tyrosin, &c., each peptone being pre-
ceded by a corresponding anti- or hemi-albumose. Antipeptone
remains as antipeptone even when placed under the action of the
most powerful trypsin, provided putrefactive changes do not
intervene. Kiihne's views may be conveniently exhibited in the
accompanying tabular forms.

DECOMPOSITION OF PROTEIDS BY ACIDS.

1.
By -25 p. c. HC1 at 40° C.

Albumin.

Antialbumate. Hemialbumose.

I i

Antialbumid. Hemipeptone. Hemipeptone.

By 3—5 p. c. H2S04 at 100° C.
Albumin.

Antialbumid. Hemialbumose.

I I

Hemipeptone. Kemipeptone.

Leucin, Tyrosin, etc. Leucin, Tyrosin, etc.

DECOMPOSITION OF PROTEIDS BY DIGESTIVE FERMENTS (ENZYMES).

Albumin.

p

• ( Antialbumose. Hemialbumose.

|] § \ \ |

I ( Antipeptone. Antipeptone. Hemipeptone. Hemipeptone. \ •-

ts i \

i • \ \

Leucin, Tyrosin, Leucin, Tyrosin,
etc. etc.

The several products (antipeptone, &c.) are given in duplicate,
on the hypothesis (of which there is now but little doubt) that
the changes of digestion are essentially hydrolytic changes, accom-
panied by a deduplication ; that just as a molecule of starch splits
up into at least two molecules of dextrose, or as a molecule of

CIIKMICAI. 15ASIS <>F T11K A.MI.MAI. I'.

cane--ui!ar .-plits up into ;i molecule ut' de\tio>,- ami a molecule
of levulovc, v() ;( molecule of antialhunio-r, fur in-tance. >j.lits tij.
into at Ira-t two molecules <»f antipeptone, and so on.

Having thus brielly stated tin- -i.-j^ by which mn ],].
knowledge has been reached of tin- possible product- i.f a diges-
tive conversion of prof.-ids. it now remain* to dt-al with the-,-
products -eriatim. In so doin^ it will be l..->t tn de-cjil,- tii-t
such product- aa arise nio-t largely and characteristically during
tin- ai-tion of acids, anil to tn-at of tin- allminosf> and jti-]'toni-s
subsequently.

Ai(tnill>inni't> This sul'stanct- i<. arrordinn to Kiihnc, identical
with .Mi-issuer's j.arapcptoiH' It is nio>t ivadilv t'onm.-d l.y the
fairly prolonged action of dilute acids at 40°, luit it may also
inakj' its a])pearauce. but to much smaller extent, during a
pel 'tic digestion in which but little ])ei>sin is present. It i- oB-
tained, mixed in some cases with variable qua'ntities of an ordi-
nary acid alltuniin, Ky neutralising the di^estiiiL; mixture, from
which it is thus precipitated. As already stated, it is cliarai t< r-
ised Ity the i>n>i>erty that it canliTtt 1>e converted int<i a pei'Tone
liy the most lU'oloii'^ed action of even the iim>t active ] < IMII.
w'liile on the other hand it is readily ]ie]itonised l»v trvi'sin ami
yields then^ antipeptone, but im leuein or tyrosi,!!. Apart fn in
its lit-haviour with pepsin and trypsin, it resi-ml-les oidina]\
alliumin and syntonin in it-< general i hemieal reactions Hut the
latter are chemically quite, distinct from antiall.umate nr jara-
peptone, for either of them may be peptoni j -in. and the

jH-jtiones thus formed may he j.artly made to yield leuein and
-in hy the suh<«Mjuent action of trj'psin.

1 Vy_the furtl i er prolonged or active treatment of
antialbuniate with acids it is converted into the substance '" "birli
Kithne ^ave the name of antialbumid It is in all \ iden-

tical with the • hemijirotein ' of Sdiiit/enber^er, and al-o probably
with the dysprptone of Mejssner. so far as the lattei \\as not pi
hap- largely compos,-,! of nucleins. It also makes its apix-araiier.
but in very small amount, during a peptic digestion, ami in mm-
siderable ([iiantity duriiiLT u jiancreatii". It is characterised la its
n-latively mvat insolubility in tlilut<' »'-'\\\* --""I nlkidis s,, that it
separates out as a granular residue during a pancreatic dJL."
This iv-idue is readily soluble in 1 p. ••. rai;
tated by neutralisation, it is now soluble in 1 p c sodium

houate. From either of tlie-e s,,lllt|o||s it I

precipitated by the addition of a little sudium chloride Injlilut*?
alkaline solution (1 p - N.i.cn.) it may b<- 1'artlv c<m\er[e(i
into a peptone by the action of trvpsin. durinir wlii<'li i>roce-s the
larger )>art sejtarates out into a gelatin" lum or dot. which

is quite unacted upon by pepsin and can only be ] •! by

42 PROTEIDS.

the prolonged action of very active trypsin in presence of a con-
siderable amount (5 p. c.) of sodium carbonate. The_peptone
thus produced is antipeptone. for it yields no ImjcJn or tyrosin
by the action of trypsin.

It has been suggested above that Meissner's dyspeptone might have
consisted largely of nuclein, and this possibility becomes very great
in the light of the statements previously made as to the nature «.t'
casein (sefc p. 20) and the fact that it was during the digestion of this
proteid that he obtained the so-called dyspeptone. Even as regards
the similar residue left during a peptic digestion of fibrin, it has been
stated that here also the dyspeptone is merely a residue (nucleins)
from the cellular elements which are ordinarily entangled in the
fibrin; in support of this it is stated that no dyspeptone is obtained
during the digestion of fibrin prepared from filtered plasma.1 There
is_however now no doubt from Kuhne's researches that anti-albumjd
is a true proteid, not a mere undigested residue of nucleins. and that
its properties are generally such as Meissner described for his dys-

The albumoses. Tb^e are the true primary products^ of the
action oj the proteolvtic enzymes on proteids; and give_rise~by the
further action of the ferments to the corresponding_peptones. In
accordance with Kiihne's views already stated there must of ne-
cessity be at least two albumoses, antialburnose the forerunner of
antipeptone, and hemialbumose of hemipeptone.

Antialbumose.2 This substance is ohtaiiifid as a neutralisation
precipitate at a_certaiu earlv sta^p of a fra pinnated peptic diges-
tion of proteids. limits ordinary chemical reactions it is indis-
tinguishable from acid-albumin or svntonin. It may be converted

O __^ — — _ __ — __^ _ *' *J

into a peptone by the furtlier action of pepsin, and still more
readily by the action of trypsin, so that it does not make its ap-
gearance in the final products of either a prolonged peptic or a
short trvptic digestion. The peptone, into which it may be con-
verted by either pepsin or trypsin, is antipeptone, for it^cannot
be made to yield any trace of leucin or tyrosin by even the most
prolonged and energetic treatment with trypsin, and in this fact,
lies the distinction between antialbumose and either acid-albumin
or syntonin. During its peptonisation by trypsin some antialbu-
mid is simultaneously formed. Antialbumose differs from para-
peptone by the fact that the latter can only 1 3 peptonised by
trypsin, the former by either pepsin or trvpsjn.

Hemialbumose? This is the best known, most characteristic

1 Hammarsten, Pfliiger's Arch. Bd. xxx. (1883), S. 440.

2 Kuhne n. Chittenden, Zt.f. Biol. xix. (1883), Sn. 170, 194.

3 Schmidt-Miilheim. antea loc. cit. Salkowski, Yirchow's Arch. Bd. 81. (1880),
S. 552. Kuhne and Chittenden, loc. cit. and Zt.f. Biol. Bd. xx. (1884), S. 11.
Herth, Monatsheftef. Chem. Bd. v. (1884), S. 266. Straub (Dutch). See Maly's

CHKMK AI. P,AM> <>1 THK ANIMAL l;«»l>\. J.;

and most frequently olitaiiit'd by-product of proteid xvumi'

It was first noticed amPisoIatetl by Meissner under tin- name of

</-peptone. i- identical with Ilence-Jone-' pn.t.-id in tin- mine of

:ualacia. and lias also been known under tin- name of • pro-
peptone.' Of late years il ha> hei-n j. , ;l- i^-iirrin^ n..t

infretiuently in grim-.- ami it is more than probable tTTat many' of
tin- older statements as to tin- occurrence of peptones in urine
and other fluids referred n-ally to the orcunvne,. of hemialbu-
nio-«-. It i- al>o >tat«-il t_o_ori_2ir nonuallv i^ tin- inanuw of
Ijoiif-.- aiuj_iii reivhr()s])inalthnil.4 Sis. n-ailily pe^oniseS

by tryi'-iir\vitK the simultaniMms formation from tin- peptone of
much leucin ami tyrosin, hemialhunios,. x^rj-flv makes it^ ap-
j^earance in anv a]>precial)le <|uantitY in the final products of a
ijancreatie digestion. It is hest inviiare*! W the action of a small
iiinoiint of verv active i»ei>sin on a _eonsuleraMi- niass of lilirjn.
previously >\\rllftl up into a gelatinous mass liy the aetion~of
••J p.c. H< 1 at 40° 5. Under the action of the ]»epsin the lilirjn
lii|ii^: JOOD afl tin- i- '•iini]iK>te. dilute sodium carbonate is

added until the reaction is just faintly nlU-:ilit-,,- l.y which ni'-ans
a bulky precipitate is obtained. This is removed by filtration ami
the tiltrat.- now contains a UxgB amount of heinialhuniosc and but
little [K-jitone, and may be utilised directly for the feestfl charac-

' LC of the albuillOSe.

paration of pun //»•////////" -dkowski).6 Acidulate the

filtrate de-.-ribed above strongly with acetic acid, add an •
('.'<~-~> ^riiis. to eai-h 100 •• .dium chloride, ami agitate the

mixture until it i> saturated with salt. The hcmialbiini'
thus preeijiitated : it N now collected on a filter, washed with
saturated solution of sodium chloride. di--1.l\c,l a^ain in v,
and reprecipitated by acetic acid and >«»liuin chloride. This
ie repeated, and the final prodad i- then di^-olved in a
minimal amount of water and fr ..... 1 from salt hydialy-is" h
may thi-n be concentrated, jm-cijutated by alcohol ;md drie.i

sulphuric acid and then at 1 "

^i'lllimiHui-. Th/- pure dry substance, is not
readih -olnhle in distilled water, but readily sohible in </•</"> »\

Bd. X1T. (1884), 8.M II.nnl.iiru" r (Dm. li) - Id \M

1 This i-\|iri'»imi inay !.«• coOTeotentll ' ,-''ii<-r.ill\ the ch»ii/;i'«

tnliirril liv tin- uiii.ruMiii-*-'! f'-rin-

-.ilkc.u.ski ii I., i hr<- v"ii llarn ' <'tO.

Fleii ei Vii

' Hallil.nrt..,,

i.-tail.i IH-O '/J. f. /•'<•• I '-I M\ (1
- Anli-itiui- /ur D.-ir-l.-ll pin. •.!••! .-h.-in. I'r.ipar.it.- \'

: Dnriti" tli.- .li.ilx-i- S..IIIP low of albumuao* •.. ei arc ulicht

fnsihl,-. l-ir ia tin- |N-pt..m-!«. 'A I'. /{>•>' . IM i ' 'Not* on |.

44 PROTEIDS.

acids, alkalis, and neutral salts (sodium chloride). These solu-
tions give the following characteristic reactions : —

/ 1. Acidulate fairly strongly with acetic acid and add a few
drops of saturated solution of sodium chloride ; a precipitate is
formed which disappears on warming and comes down again on
cooling. If excess of the salt is added the precipitate does not
dissolve on warming.

f 2. Add carefully a few drops of pure nitric acid ; a precipitate
is formed if the acid is not in excess, which disappears on warm-
ing and comes again on cooling.

/• 3. Add acetic acid, avoiding all excess, and then a trace of
potassium ferrocyanide ; a precipitate is formed which disappears
on warming and reappears on cooling.

/ 4. On the addition of caustic soda in excess and a trace of
sulphate of copper the ordinary biuret reaction is obtained, TJijg
reaction distinguishes hemialbumose from other soluble proteids.
with the exception of peptones.

Hemialbumose has so far been spoken of as being one uniform
substance only. Kiihne and Chittenden in their earlier work 1 at
first distinguished merely between a soluble and insoluble form ;
more recently they have described four closely allied, but distinct
forms of the albumose.2 (1) Protalbumose. Soluble in hot and
cold water and precipitable by NaCl in excess. (2) Deuteroal-
bumose. Soluble in water, not precipitated by NaCl in excess,
unless an acid be added at the same time. (3) Hcteroalbumose.
Insoluble in hot or cold water ; soluble in dilute or more concen-
trated solutions of sodium chloride, and precipitable from these
by excess of the salt. (4) Dysalbumose. Same as heteroalbumose,
except that it is insoluble in salt solutions.3 Hemialbumose as
ordinarily prepared may hence be regarded as a mixture of these
several albumoses in varying proportions according to the condi-
tions of its preparation.

The preceding statements as to the existence of four forms of
hemialbumose are however contested by Herth, Straub, and Ham-
burger (loc. cit. on p. 42).

The peptones. Kecent work has shewn that in all probabil-
ity the various substances which have been described as peptones
have consisted to some extent, if not largely, of a mixture of true
peptones with variable quantities of albumoses. Our knowledge
of the nature and properties of tme peptones is at present in a

1 Zt. f. Bid. Bd. xix. (1883), T. 174.

2 Ibid. Bd xx (1884), S. 11.

3 For further details the original papers of Kiihne and Chittenden must be con-
sulted, more especially Zt. f. Biol. Bd. xx. (1884), S. 11. See also Neumeister, Zt f.
Bid. Bde. xxm. ( 1887), S. 381 ; xxiv. (1888), S. 267; xxvi. S 324. The preparation
and separation of the albnmoses is conveniently given in Kohmann's " Anleitung /urn
chemischen Arbeiteu." Berlin, 1890, S. 48.

( HK.MK Al. BASIS OF THK ANIMAL

>t;tt'- of transition, MI that it i> on tin- whole advisable to ;_;i\e
some acciiuut of th'- oldei work U well a- of tin- ln»ic ivet-nl.

i,,irnti<iii "J ji' />' I »r this tin- \\ • \l.il\ ' lleith.-

Hennino.-i. ' K"-s,d.4 Hofmeister,* and I.<'\\ •• >hould be consulted.
The oeneral properties and reactions ..t th.- peptones obtained by
tin- aln.v.- authors may In- stated as follow.-. A- piv, -ipitate.l l.y
alcohol th.-y c.,u-ist of a whit ..... ' \.-llo\vi>h j.o\vdt-r. which is

.sr,.pie and extraordinarily soluhh- in water. and in some

11 be deliquescent 1'nle-- thorooghly dehydrated

the ]>o\vdcr ma\ melt on tomtit- \\anniiiL: Kroni tln-ir neutral

aqueous solutions they ;nv j.reeijiitated \\ith ditlieulty by a large

» of alcohol, bein^r unchaiiued in the ].ro.-»->s and not becom-

• 'adulated or insoluble by prolonged e\)H.sun- to the action of
the jireeijiitant. The ])recipitation occur.- with ditlieulty if at all
in ]>re-cncr ..f hydrochloric acid Peptones are not jTeeijiitated
by many of the reagents \\hich precipitate other ]>roteids, but are
]ireeij.itat'Ml by taiinie acid, mercuric chloride, nitrates of mercury,
and by phoephotungStic and ]>hos]ihomolyhdic acids in jin-scncc of
hydrochloric or other mineral acids: al-o by the doul>le i«nlide> of
].ota>sium and mercury or potas^inni and bismuth, in ]-r.

:on^ mineral acids. A very characteristic reaction is the

' biuret ' or jiiitk coloration which is obtained on the addition of

of caustic soda and a inert trm-f of sulphate of copper.

The sli^hte-t eZCeSfi of the copper salt ^ive> a violi-t coh

is the case with all other pioteid.v whirh deepen- in tint on b(»il-

iii'_r This biuret reaction is however now known to be yielded

al-o by the albillll<>-es (see above). IVptolies are all

and diflusible.

The <littiisil.ility «'f peptones is relatirel;/ ^reat in comparison \\ith
that ot' otlier forms of pr..tenl- : it l- ho\\,.\ .-r iif/so/uf- />/ small \\li.-n
compared with that of cr\ .-tal 1 im- Mihstam-.- -uch as Miiliiini chlori<lf.
and licMicr thi-v mav be separated from admix. -.1 salts l.\ dial\si-. \1
statements as to their :d»s-lute <littiisil.il it \ . a- ba-e,| on .-arli.-r state-
ments. mn-t however b. I \\ith caution, in view of tin- t:

ti, ,],:,' ,iir information a- t.. the properties ,,f the true

lias 1 ..... 11 obs.-rved that the complete separation
.,f p.-ptune'< from .ill";: :''!•• by taking ;idvantaoe .,! the

fa. -I that the litt.'i an all com].le(elv piecipitable b\
with neutral ammonium sulphate. VtteiBU th not.7

I'.y means of this .liileivnce iii the behaviour of the two classes of

1 1 'Humor's .\<-rh IM. ix

- /.i. /; ,,l,,,si,,i. Ckem. H.I

« " I).- l;i iiiitnn- i-t .In n'.l- j.hx -.i..l.iu'i'| ..... I'1-- PapttW*
« /.i. I. ,,!,,,•..., I. <•/„,„. IM III. (If
/ 1881), S

. ; - I , i;.| vxx. :i-

- \\ 15,1 \MI u--.,! S.I I '.indl.d. Mlurkut.-mrd

Ver. llri.|.-ll..-r._'. IM ni 1888 - '-'86

4G PBOTEIDS.

substances to the ammonium salt, Kiilme and Chittenden have
prepared what they regard as the true pure peptones as follows.1
The products of a digestion are neutralised, filtered, very faintly
acidulated with acetic acid and saturated with the ammonium
salt. The filtrate from the precipitate thus obtained is largely
freed from the excess of salt by careful concentration on a water-
bath. The ammonium salt is then got rid of by the addition of
baryta water and barium carbonate in slight excess, and after
filtration these reagents are finally removed by the careful addi-
tion of dilute sulphuric acid. The peptone thus obtained may be
still further purified by precipitation with phosphotungstic acid.2
The pure peptones thus prepared are strikingly non-precipitable
by many of the reagents by which other proteids may be precipi-
tated, more especially by ferrocyauide of potassium in presence
of acetic acid, a reagent by which practically all other proteids
in solution are precipitated. No quantitative statements have as
yet been made as to their rotatory power or diffusibility. They
are stated to have such an affinity for water that a small portion
of the dry substance when moistened with water exhibits the
same phenomena as does phosphoric anhydride under similar con-
ditions. They also yield an intense ' biuret ' reaction with caustic
soda and sulphate of copper.

Antipeptone may be obtained by the action of either pepsin or
trypsin on antialbumose, or by the action of trypsin 011 antialbumate
or antialbumid. When purified no leucin or tyrosin can be obtained
by the most prolonged action of trypsin oil this peptone.

Hemipeptone is best obtained by the action of pepsin on hemi-
albumose. When purified and digested with trypsin it yields much
leucin and tyrosin, and in this respect alone does it differ from
antipeptone.

Amphopeptone. This is the mixture of anti- and hemi-peptone re-
sulting from the action of pepsin on proteids.

Notwithstanding the probable formation of peptones in large
quantities in the stomach and intestine, to judge from the results
of artificial digestion, a very small quantity only can be found in
the contents of these organs.3 They are probably absorbed as
soon as formed. Another point of interest is their reconversion into
other forms of proteids, since this must occur to a great extent in
the body. We are however as yet ignorant of the manner in which
this reverse change is effected.

It is now generally considered that the peptones are products
of the hydrolytic decomposition of the proteids from which they
are formed. This view is based partly upon general considera-
tions as to the probable nature of the change, from observations

1 Zt. f. Biol. Bd. xxii. (1886), S 423.

2 Hirschler, Zt. f. physiol. Chem. Bd. xi. (1887), S. 28. Otto, Ibid. Bd. vin.
(1883), S. 136.

3 Schmidt-Mulheim, Arch. f. Phi/siol. 1879, S. 39.

< HKMICAL HAMS UK THF. ANIMAL r,i»DV.

of the conditions under which th. .1. and which an-

kiinwn I" in- hydrolytie in other ; he conversion of

starch iutn -ugar l.y the action <,f en/ynic- ami add-. Th.
further a certain amount of direct evidence that their formation
ompanied by the a.--nmption ..t' water.1 Finally then- i- an
im-rca-in-.: amount of evidence. l.a-.-d ..n analyst-- i.f pioteid- ami
the peptone- whidi may be formed from them, that the .
contain !••-- carlion, i, e. more hydrogen < and "\\genthan the
former.- lint this latter evi.t merel) -nuiie-iive.

: home out hy analx -latin-peptones^ The

one inijiortant fact in connection with the n-lationsliij. of the
]M-]itone- to the mother prott-ids is tluit the\
stated, jiroducts i.f the deci.mjmsition of the latter and of
smaller molecular weight, an assumption which is warranted
not only l.y the whole tendency of iv-ent in\ e^ti^at ion. hut

• •ially by the fact that whereas ordinary proteid-
non-dill'usil.le, peptones, and to a !•• the all.umoses,

are ilillu>il.le.

A 'inliiiL; to the views of some observers it is said to be. pos-
sible to eli'eet a partial reconversion of peptones into the more
primary proteids from which they were obtained, hy nn-.i:
prolonged heating to 140 — 170°, and possibly by mean- of a
dehydrating a-jeiit such as acetic anhydride.* I'.ut little i>- how-
BVei delinitely known as to the real nature of the product- ob-
tained by these mean

It was at one time stated that when peptone- an- injected into

the hl..od-Ves.-els, the blood speedily loses its j.oWel of I'lottillg

i.-moval from the body.'1 This action is now known to be
due to the albumo-e- with which tlie i>ei>tones wen- nijxed.''' TM
cli.tting may similarly be j.revented l.y the injection of a 1 p.c.
XaCl extract of the pharynx and millet "f the leech : the
ot this has not as yet been fully worked out."

During the pancreatic- dige-nun (.f pn-ti-id- >"in.- l.\ -pr.Mlurt n
it- ajipearanci- \\hicli gi\i'- a i-liaract. ri-t ii- \ i.-let i-r pink c.'l-Tat i«n mi
tlie addition i-f I. n. mine, or «\ clilnrine in the pri-i-in-i- •-! ft

l»:inil.-w.ki. <',n,r,,lh. f.,1,,,,,1. IFiM.18M Nr U IM1 Efl II

--:i). j.. i:»o

fit. Kulili" II. niitti'mlni. /-'• I I. \IX 80S vv::

Tatarin..ff. rHIH,.t. /;.„,/. I' '•;. us--|). p 7l:«. H"l"

.

. . . .

15,1 ,, ,,. K],lir< |'tl,1L.. : I IM M.MM UV.M.

Bat we abo Chittflodaa and Solli rfl VoL xn p.«,o«U*

' ll.-nni., • II ..... '

I'.-ki-lharinir. riluifr's Arch. 15.1. XXII "'"*'

m,r/ r,, . Heidelberg, IM m. : '». N"'" •* XXI"

imidt-Mlilheim, Arc* f. PkgtUL 1880

• 1'i.llii/

T n , ; u. /'harm. Bd

XVJH DifkiniM.ii. M. -/ MiH'ol. \

48 PKOTEID6,

Tlie colour is not due to the peptones or albuinoses (Kuhne). The
colouring matter obtained by the addition of these reagents has been
examined by Krukenberg : and nn>re recently by Stadelniann.-

CLASS VII. Lardacein, or the so-called amyloid substance.*

The substance, to which the above name is applied, is found as
a pathological deposit in the spleen and liver, also in nuinerous
other organs, such as the blood-vessels, kidneys, lungs, &c.

It is insoluble in water, dilute acids and alkalis, and neutral
saline solutions.

In percentage composition it is almost identical with other
proteids,* viz. : —

O. and S. H. N. C.

24-4 7-0 15-0 53-6

The sulphur in this body exists in the oxidised state, for boil-
ing with caustic potash gives no sulphide of the alkali. The
above results of analysis would lead at once to the ranking of
lardacein as a proteid, and this is strongly supported by other
facts. Strong hydrochloric acid converts it into acid-albumin,
and caustic alkalis into alkali-albumin. When boiled with dilute
sulphuric acid it yields leucin and tyrosin ; 5 by prolonged putre-
faction indol, phenol, &c. 6 On the other hand, it exhibits the
following marked differences from other proteids : — It wholly
resists the action of ordinary digestive fluids ; it is coloured red,
not yellow, by iodine, and violet or pure blue by the joint action
of iodine and sulphuric acid. From these last reactions it has
derived one of its names, ' amyloid,' though this is evidently badly
chosen ; for not only does it differ from the starch group in com-
position, but by no means can it be made to yield sugar : ' this
latter is one of the crucial tests for a true member of the carbo-
hydrate group. According to Heschl 8 and Cornil 9 anilin-violet
(methyl-auiliu) colours lardaceous tissue rosy red, but sound
tissue blue.

The colours mentioned above, as being produced by iodine and
sulphuric acid, are much clearer and brighter when the reagents are
applied to the purified lardaceiu. When the reagents are applied to
the crude substance in its normal position in the tissues, the colours
obtained are always dark and dirty-looking.

1 Verhand. d. jihys.-med. GeseU. Wiirzburg, Bd. xvm. (1884), NT. 9, S. 7.

- Zt. f. Biol. Bd. xxvi. (1890), S. 491.

3 Virchow, Compt. Rend. T. xxxvu. p. 492, 860.

* C. Schmidt, Ann. d. Chem. u. Pharm. Bd. ex. (1859), S. 250, and Friedreich
u. Kekule, Virchow's Archiv, Bd. xvi. (1859), S. 50.

8 Modrzejewski, Arch. f. exp. Path. u. Phann. Bd. i. (1873), S. 426.

6 Weyl, Zt. f. physiol'Chem. Bd. i. (1877), S. 339.

7 C. Schmidt, lor. cit.

8 Wien. med. IVochensckr. No. 32, S. 714.

9 Compt. Rend. T. LXXX. (1875), p. 1288.

CHEMICAL HAS IS OF THK AM MAI. BODY,

Purified lardaeein i.> readily soluble in moderately dilute
ammonia, and can, by evaporation, be obtained from this .solution
in the form of tough, gelatinous flakes ami lumps ; in this form it
gives feeble reactions only with iodine. If the excess of ammo-
nia i> expelled, the x'lution becomes neutral, and is precipitated
by dilute acids.

iHii-'itinn. The gland or other tissue containing tin- body
is cut up into small pieces, and as much as possible of the sur-
rounding tissue removed. The pieces are then extracted several
times with water and dilute alcohol, and if not thus rendered
colourless are repeatedly boiled with alcohol containing hydro-
chloric acid. The residue after this operation is digested at 40°
( '., with active artificial gastric juice in excess. Everything except
lardaivin, and small quantities of niuciu, nucleiu, keratin, together
with some portion of the elastic tissue, will thus be di»»l\ed and
removed.1 From the latter impurities it may be separated by
fractional decantatiou of the finely-powdered substance from
water, alcohol, and ether.

In opposition to the older statements it has recently been
stated that lardacein may be digested by pepsin in presence of
hydrochloric acid.2 The writer's own experiments lead him to
believe in the results obtained by the earlier authorities

The known products of decomposition of proteids are very

numerous, varying in nature and relative amount with the con-
ditions and reagents by means of which they are produced, and
it may be similarly, though tit a much less extent, with the kind
of proteid employed. These products belong for the most part to
well-known classes of chemical substances, and in many cases
representatives of several consecutive members of any -i\en
homologous series are obtained during the decomposition-

A -tudy of these products has not, however, up to the present
time thrown any extended light upon the more minute molecular
structure of the proteids. and the reason is not fai It

consists simply in the fact that we possess no guaran;
tenon ,,!' the purity of those proteid- which can be obtained m
suHicient amounts for the purposes of experiment. The\ may
I.e. and pmhahly are. mixture- ••!'. it may be, several closely .'Hied
rabetances, BO that the numerous products which arise duiin- the
d'-ci.mposition <>f what is regarded in the cxj>erinient a

uniform Mih-tance. represent really the deoompodtfao-piodaoti

/ proteid molecules, and thus throw no light "ii the
structure of any onf. Ami the matter is still furtln-i complicated

1 Kiilincnn.l Kii.ln.-lt. '. ~.\,.f>. IM vvxoi il*65),8.66.

a Kwtjiirin. H'/.w. nud. Jahrb. 1886, 8. 181.

4

50 PKOTEIDS.

by the fact that the final products of any given decomposition do
not at all necessarily represent the primary mode of breaking
down of the proteid molecule ; many of them may be the out-
come of some secondary decomposition of the first-formed pro-
ducts. It may hence suffice to give a short account of the more
generally important researches on the decompositions of proteids
and to refer the reader for details to some larger work.1

The products of the decomposition of proteids by acids (HC1)
have been elaborately studied by Hlasiwetz and Habermann.2
These observers subjected proteids (casein) to the action of boil-
ing concentrated hydrochloric acid in presence of stannous chlo-
ride for three days. From the fluid thus obtained they were able
~to separate out by repeated crystallisations leucin, tyrosin, glu-
tamic and aspartic acids and ammonia; the mother liquor from
the above yielded no further well-defined substances. Schutzen-
berger,3 treating proteids in presence of a little water with an
excess of baryta in sealed tubes at 200 — 250°, observed a more
profound breaking down of these substances as judged by the
products of their decomposition. In addition to the products
described by Hlasiwetz and Habermann he obtained small quan-
tities of carbonic, oxalic, and acetic acids, together with other
amido-acids homologous with leucin, amido-acids of other series,
leuceins,4 gly co-protein, tyroleucin,5 &c. The chief difference in
the results obtained by the two sets of observers turns upon the
non-occurrence of carbonic, oxalic, and acetic acids among the
products of the action of hydrochloric acid. Drechsel 6 has how-
ever shown that if the noii-crystallisable residue from Hlasiwetz
and Habermann's experiments be appropriately treated with
baryta in sealed tubes it readily yields carbonic acid, so that the
difference may turn out after all to be more apparent than real.
Interesting as are the above researches they do not as yet enable
us to form any clear idea of the probable molecular composition
of proteids. According to Schiitzenberger the relative amounts of
carbonic acid and ammonia which make their appearance are the
same as would have arisen from a similar treatment of urea with
caustic baryta, and from this and the fact of the preponderating
appearance of amido-acids by the action of the alkaline oxide,

1 Ladenburg's Handirorterbuch d. Chem. Bd. in. S. 541. Beilstein's Hdbch. d.
Chem. Bd. HI. S. 1258.

2 Anzeig. d. Wie.n. Akad. 1872, S. 114; 1873, Nr. 15. Ann. d. Chem. u. Pharm.
Bd. 159 (1871), S. 304, Bd. 169 (1873), S. 150. Jn. f. prakt. Chem. (2) Bd. VH.
S. 397. See also E. Schulze, Zt.f. phi/swl. Chem. Bd.'ix. (1885), Sn. 63, 253.

3 Ann. de Chim. et. de Ph>/s. (5 Scr.) T. xvi. (1879), p. 289. Bull, de la Soc. Chim.
xxin. 161, 193, 216, 242, 385, 433; xxiv. 2, 145 ; xxv. 147. Also in Chem. Centralb.
1875, Sn. 614, 631, 648, 681, 696; 1876, S. 280; 1877, S. 181. Compt. Rend. T. 101,
(1886), p. 1267. See also Nasse, Pfliiger's Arch. Bde. vi. (1872), 589; vn. 139;
viii. 381.

4 Compt. Rend. T. 84 (1877), p. 124.

5 Ibid. T. 106 (1888), S. 1407.

6 Jn.f prakt. Chem. (N. F.) Bd. xxxix. (1889), S. 425.

BASIS OF TIM: \MMAI. r,m>Y. ,M

he regards tin- pr.-teids as complex meides : that i- to >.
coinl'ination- .if inva with amido-acid- helonoinu t" -e\eral >*fiefl
such a- tin- leiicir ami aspartic.1 In >u|.j...rt ..f this view the
\viirk nf (Irimaux- may In- mentioned. I'.v fn-i:
tic anhydride aiul urea he ol.tained a MiL-tance iv-riiiM.
pr.'t.-id in -evi-ral of its reactions, ami yielding a-pnrtic a«-i.l.
carbonic acid ami ammonia l.y treatment with haryta. It has
not howe , : IH-.-II -hown that thi- >ul>-tanr,- ran !-«• math-

and furth.-i, n.. nnr ha- ever -ii--<-r.-d.-d in <.l,tain-
ini,' uiva as a direct j.ruduct of tin- decomposition "f a prnti-id.
Kurtln-i'. aa a^ninst the view nf the ui'cidc nature uf j.r.'tei.ls,

AS to the pruliahle nnn-e\i-teii.-f ..f aiiiid.>-.i< id

itU-s in tile I'l'oteid llinlecule must Hut he In-t xj^ht of.8

Tin- i»ldiT >tati-iuriit> ..t r.e.-liaiii|. 4 and IJittt-r5 a- t«. tin- furiiiatinii
of ur.-a from j.roteids l.y the arti"ii «\ ]><>ta»ium juTinaii^ana1
«MT<>iiei.u>.''' The iii.ot reeriit refutation of their \ie\vs i- due t«.

:i." \\lio tinds that trarr- ..f ^naiiidin may make their a|.|.ear-
aiiee luit no urea. Tlii- >ul»tauce mij^lit ln>\ve\i-r lie ea>ily mistaken
for urea >inee it> compoondfl \\ith oxalic and nitric aci.U closely

.l.h- tlioxi- .,f urea with the >ame aeid>. Although ^uaiiidin
when Loilc.l with >nl].hiirie arid ..r l.ar\ ta water readily yield- urea
(and -imiiltaneou-ly amnnmia) thi> can in m> \\ay lie taken a- imply-

i |i..>.-iLle ftiriiiatimi of urea from proteiil- directly. <,»uite
-tallirn- La-e railed 'ly.-atin,' which readily \iidil- un-a
when Loileil with Laryta water," has Leeii isolated from aimm^ the
products of the decompo>ition <.f ea-ein Ly liydn.cliloric acid and
.-hloridr of /inc. Tin- formula "f tlii- La.-e i> u'i\en - < II \ • ».
thu- placing it in .-lo>e eompn.-it ional relation-hip with K
( ,11 \ i >. and Kreatinin C.I^N.O.

-•I :is yet be said that we p,,>-,-s> anv ival km-ul

nf the <-MM-titUti"M «'f pmtei.!-. alld the i|Urstinll will jmilialily

:M unsnlv.-d iiniil some ••utin-ly m-w dej.aitnre i- ma.le in
\in-_,' the ju-nlih-in, "i uniil some ne\\ |.n.p.-it\ "f pioteid-i-

d l.v which theii al.M.lnte purity niav l.e det,-rmii
th,. , preliminary In the whu'le in\ i-t i-at inn. The 8O-

crystallised ]n-..teid- (see :d..,ve, p. r.) have nol

, s-l.ut/,, attcmpu u. »yndMllM ptoteid*. Me C'o»/rf.

..i
i;.i XXM

I I XX ,. -

I I XMM '

1219.

urakt. <•!„ I '

IM. in. <\

,«,.s.*,,,

;l«

r.i' PROTEIDS.

been prepared in sufficient quantity l to admit of the easy and
decisive application of the modern methods of organic chemistry
to the elucidation of their molecular structure. Work in this
direction on a really large scale could scarcely fail to yield im-
portant results. Schrotter 2 has recently described the preparation
of benzoylated ethers of the albumoses, and intends to apply the
method to other proteids and to study the products of decom-
position and oxidation of these substances. Whether any real
advance will be made in this direction cannot be foretold, but
this new departure is of considerable prospective importance.

No account of the constitution of proteids would be complete
without a reference to the views and theories of Pfliiger, and of
Low and Bokorny. Pfliiger 3 starting from the characteristic dif-
ferences between the products obtained by decomposing dead pro-
teids by chemical means out of the body, and the products which
arise by the natural decomposition (metabolism) of living proteids
(protoplasm) in the body, has put forward a view as to the dif-
ference of living and dead proteid. He considers that in dead
proteid the nitrogen exists in the amide foun. while in living
proteid it is present in the less stable cyanic form. The build-
ing-up of living proteid from dead he regards as being carried on
by the ether-like union of the isomeric living and dead proteid
molecules, accompanied by the 'elimination of water. During this
process the nitrogen of the dead proteid passes into the cyanic
condition, and if this is repeated and accompanied by polymerisa-
tion the formation of a large and unstable living proteid molecule
may be readily accounted for. He further draws attention to the
readiness with which polymerisation occurs in the cyanic series
and the extraordinarily high molecular energy of cyanogen. Low
and Bokorny 4 deal also with the probable mode by which, in the
case at least of plant cells, the complex proteid molecule may be
built up out of the simpler substances from which these obtain
their nitrogen. They consider there is evidence of the existence
in living plant cells of some substance of an aldehyde nature.
Starting with formic aldehyde, by its union with ammonia the
aldehyde of aspartic acid might be obtained, and by polymerisa-
tion of the latter in presence of sulphur and with the exit of
water a substance with the same composition as an ordinary proteid
would arise. Their speculations are ingenious, but it cannot by
any means be said that their views are established. Asparagin,
from which aspartic acid is readily obtained, undoubtedly plays
an all-important part in the constructive nitrogenous metabol-

1 But see Chittenden and Hartwell JL of Physiol. Vol. xi. (1890), p. 435.

2 Ber. d. deutsch. chem. Gesell. Jahrg. xxn. (1889), S. 1950.

3 Pfliiger's Arch. Bd. x. (1875), S. 332.

4 Low and Bokorny's work may be most conveniently quoted by reference to the
following volumes of Maly's Jahresbe.richt d. Tkierchem'. Bde. x. (1880), S. 3 ; xi. 391 ,
394; xn. 380; xm. 1; xiv. 349, 474; xvi. 8; xvn. (1887), 395. See also Bid.
Centralb. Bd. I. (1881), S. 193; vin. (1888), S. 1.

CHEMICAL I'.ASIS OF THE ANIMAL I'.nDV.

ism of jilants; l)iit as yet tin- aldeh\ dc of aspartic acid has not
been prepared by any chemical means, and P>aum:iim l has cast
great doubt <>n the reliability of the methods by which tin- above
authors have endeavoured to prove the existence of aldehydes in
the protoplasm of the living plant cells. And it is probably sig-
nificant that the reactions by which the presence of the aldehydes
i^ supposed to be shown are only well marked in the case of the
cells nf the lowest plants; in the case of animal cells they are
more usually wanting.

THK KN/YMI.S OK SOLUBLK I'N«>I:I; AM/KM KKUMKNTS.*

Chemists have for a long time been familiar with an extensive,
and still increasing class of reactions which occur solely, or in
^ome cases most readily, in presence of minute quantities of some
< ubstance which does not itself appear to enter directly into the

Mii : in other words the causative agent is found to have
it-elf undergone no obvious change during the reactions which it
has set up between the other sul tstances. Striking instances of
Mich reactions are observed in the preparation of ether from
alcohol by means of sulphuric acid and in the manufacture of
sulphuric acid itself. In the former case a small quantity of
sulphuric acid is theoretically able to convert an indefinitely

quantity of alcohol into ether, and in practice the limit is

mined simply by the occurrence of secondary decompoftitioiu
between the reagents. Similarly during the manufacture of sul-
phuric acid a minute quantity of nitric oxide suttices in the pres-

of water to convert an indefinitely large amount of -ulphurons
anhydride into sulphuric acid. Of late years a large numl
reactions have been found to depend for their OOOUTTBl ..... upon the

nee of the minutest traces of water; thus ,//•// chlorine has
no action on dry sodium, and dry hydrochloric acid gas and

'•u do not react even when exposed to bright sunlight.
neither do ,//•_// oxygen ami carbonic oxide explode on the passage
of an electric spark. The fact of immediate interest in each of
the aliove instances i- that a minute trace of the substance which
determines the occurrence "f the reaction is abl -luce

change in an indefinitely large ma-< of the other reagent- without
• ing any final alteration. Turning to t he cheini-t r\

1 rtln-.T's Af,-h. H.I. \\iv (I8*-M. S. 4«H(

Cktm. IM. \ (18C

: It :i|,|,r:irs :ul\ i-:il.l.- I'. n->- tin- t.-mi 'ni/Mi..-' iKnlin.. ' •/. /.Ay*»o/.

];,| | i - .liiMi- mi..: t in. 'lit* fin-

. -rallv, n-.TMii- tl ..... M.T naiin- "f ' f. rin.-nt ' f..r tin- «>i i-'li M J«Mt

iiirli it u;i> lir-t aj.|ilM-i|. If tlii« IM^ .1 ...... it uill !«• . ..n\ i-nii-nt t» n-

/.\ni.i|\-i- ' t-> ili'ii.iti- tli.- i-lian^f.* |ir>Mliin>i| l.y tin- <-iu.\ iiu-« in tli.
-iiLsta'tircs, and t.. a|.|.ly tin- ti-rin ' f.Tiiinitati..ii ' f.tlM- a. ti«n „( the orgmnilH
nt- In tl, •'* I" tin- <;.-rinaii ' F- rm. •iitwirlaiMi:'

>i..n

..th.T -ii

f.Tinrnt-

an. I ' fiTtii<-iitati»ii ' to M .ii

54 ENZYMES OR SOLUBLE FERMENTS.

of animal and vegetable cells it is found that in many cases sub-
stances may be extracted from them which possess to an even
more striking degree the property of inducing change in an indef-
initely large mass of certain other substances without themselves
undergoing any observable alteration. These agents are known
as the enzymes or soluble ferments, and the essential conception
of an enzyme is summed up in the above statement of the most
remarkable characteristic of their activity. Further investigation
of these enzymes shows that their activity is dependent upon
many subsidiary factors which are more or less common to them
all. Thus their activity is largely dependent upon temperature,
being absent at sufficiently low temperatures, increasing as the
temperature is raised to a certain optimal point which varies
slightly for different enzymes, then again diminishing as the tem-
perature is further raised, and finally disappearing. By^the action
of jL-£ufficiently high temperature they permanently lose their
characteristic powers and are now spoken of as being killed.'
Again the enzymes' are extremely sensitive to the reaction,
whether acid, alkaline, or neutral, of the solutions in which they
are working, also to_the presence or absence of various salts, some
of which merely inhibit their action while others permanently
destroy it ; and their activity is in all cases lessened and finally
stopped by the presence .of an excess of the___rjroducts to whose
formation they have given rise. ItTias been already said that an
enzyme may be killed by exposure to a high temperature, but this
only holds good when they are in solution, or if in the solid form
they are heated in a moist condition. When perfectly dry they
may be heated to 100° — 160° without any permanent loss of
their powers.1 It will be seen that so far the enzymes have been
characterised solely with reference to the peculiarity of their
mode of action and to the influence of surrounding conditions
upon that activity, and the question of their probable chemical
composition has been left untouched. Notwithstanding the fre-
quent endeavours which have been made to prepare the enzymes
in a pure condition, it is unwise to lay any great stress upon the
results of the analysis of these so-called ' pure ferments,' bearing
in mind that, as in the case of the proteids, no criterion of their
purity exists. This much however may be said. In the major-
ity of cases, analysis shows that their composition approximates
.more nearly to that of a proteid than of any other class of syb-
^stances, and this is apparently true even when they do not yield
to any marked degree the reactions (xanthoproteic, &c.) which
are characteristic of a true proteid. Ordinarily it is almost im-
possible to obtain an enzyme solution of any considerable activity
which is free from proteid reactions, and hence many authors are

1 Hiifner, Jn.f. pralct. C/iem. Bd. v. (1872), S. 372. Al. Schmidt, Centralb. f. d.
med. ir?s,«. 1876, 'S. 510. Salkowski, Virchow's Arch. Bd. i.xx. (1876). S. 158; i.xxxi.
(1880), S. 552. Hiippe, Mittheil. d. Kaiserl. Gesundheitsamtes, i. 1881.

CHEMICAL BASIS <>F THK ANIMAL r."l>Y.

inclined to regard these bodies as being really of proteid nature.
I Jut this is ;i point which is ;is yet l>y n<> means settled, as the 1'<>1
lowing consideration^ show. The Mile means at mir disposal of
determining tlie presence of an en/vine is that of ascertaining the
change which it is able to bring about in other >ul>stau<-es, and
since the activity of the en/vines is extraordinarily great, a minute
trace suffices to produce a most marked effect From this it f«»l-
|o\\stliat the j)iiritied en/vines whicli give distinct proteid iva. -
lions might merely consist of very small quantities .,f a true
non-proteid en/vine adherent to or mixed with a residue of in. -it
proteid material Again on the other hand it is similarly possible
that the purified en/vines which have been described as devoid of
juot -id reaction really consist of some inert non-proteid material
with which a trace of what is ivally a true jnoteid en/yme ;
mixed, the amount of enzyme being too small to yield any of tin-
reactions characteristic of proteids. The occurrence or absence of
proteid reactions in a solution of an en/yme cannot therefore set-
tle the nature of the enzyme, and for similar reasons a mere anal-
ysis of the separated enzyme is also inconclusive ; the balance of
appears to be in favour of the view that the

are_proteid in nature. Imt this is still an OJM-II question.

Many nf the puritied enzymes have been analy/ed and tli«- r«->ults
slinw in many cases a percentage of carbmi c..ii>ideralily !•• \\<T than
that (»f a true proteid. Kulim-'s pure>t trypsin li:id tin- f«>llo\\ ing
pn-, ,-ntage coinp«.sitinn : C = 47'22 — 48-09 ; H — 7'1">— 7. 1 1 :
N = 11' •;•»'.)— 1::-tl : S = 1-7:5— 1-Sf, F..I- ntli.-r anal

Aug. Schmidt.1 1 1 iii'ncr.- I'>artli.a I!ut >c.- al>.> \N'urt/. * and Lo\\ . •

The en/ymes are possessed of certain properties, nmiv o
common to them all. by means of which they may be sep;i
from the tissues in \\hich they primarily occur, and i-olated fioin
tlic -olution- \\\\\< obtained Soluble in wat.-l. they may b.
• •ijiitated unchanged from this solution by the addition -

• absolute .-ill-oil. •!. They may also in man\
precipitated from their a(|iieons or other solution by satu:
with neutral ammonium ^ilphate1- They arc convenient 1\ -olu

ble in glycerine1 from which thc\ may a- bcfoie ]„• pie.'i]
bv an exceSfl of ale,. hoi. None of the en/\ ditl'usihle and

,a\ readily be ! :iv admixed ditlu-ible

1 /tiini'i Iii.-ii. Tiil)iiii;.-ii, 1-71

\ i Bd ^ i-:.' -

/ .lal.rs. M

' < • /, /. r K( (1880), ]• 1879 I XOLp

I 1!,| \\vii (1R82). S

Ktthn< I \and.d.maturk.-med \- Ili-id.-ll,. m IHH6, S. 46.1 AI-« ''.ntralb.
,.,/ , . ;i i»k<>w(KiiH.-iun). **> Bt

•i.-h. niiiK. i '»••».

56 ENZYMES OR SOLUBLE FERMENTS.

substances by means of dialysis.1 They possess further the re-
markable property of adhering with great tenacity to any finely
divided precipitate which is formed in the solutions in which
they are present, more particularly if the precipitate is of a viscid
or gelatinous nature.2 It is not however possible to base upon
the above properties any general method of preparing the en-
zymes which is equally applicable to each of them; some are
most readily prepared in a fairly pure state by one method, some
by another, and very many by the conjoined application of two
methods. A further consideration must not be lost sight of in
connection with the separation of the enzymes from the parent
tissues ; thjs is the fact that in some cases the enzymes do not
exist in thlTfree and active conditions in tbp. p.plls of the reapec-
tive tissues, but in the form of an inactive antecedent, to which
the name of ' zymogen ' is usually applied.3 Hence to obtain an
active extract it is frequently necessary to treat the tissue with
some such reagent as shall ensure the conversion of the zyrnogen
into the active enzyme.

During prolonged digestions it is essential to insure the absence
of any changes due to the development of bacteria or other organ-
isms. The most suitable antiseptics for this purpose are salicylic
acid (*1 p.c.) and thymol ('5 p. c.). These reagents are dissolved
in a small quantity of alcohol and added in the above proportions
to the digestive mixture.

It is frequently a matter of the utmost importance to determine
whether the hydrolytic power of any given preparation is due to
the action of a soluble enzyme or of a ferment (organised). The
discrimination is most readily effected by carrying on the diges-
tion in presence of chloroform, which is inert towards the enzymes
but inhibits the activity of ferment organisms.4

SPECIAL DESCRIPTION OF THE MORE IMPORTANT ENZYMES.5
Ptyalin.

While occurring chiefly and character! stir».g,,1]y i" gallon ^ a similar
enzyme may be obtained in minute amount, but fairly constantly,
from almost any tissue or fluid of the body, more particularly in
the case of the pig. It was first separated out from saliva, but
in an impure condition, by Mialhe, who precipitated the saliva
with an excess of absolute alcohol.6 It has been prepared in the

1 Maly, Pfluger's Arch. Bd. ix. (1874), S. 592.

2 Briicke, Sitzb. d. Wien. Akad. Bd. xnn. (1861), S. 601. Danilewsky, Vir-
chow's Arch. Bd. xxv. (1862), S. 279. Cohnheim, Virchow's Arch. Bd. xxvm.
(1863), S. 241.

3 Heidenhain, Pfliiger's Arch. Bd. x. (1875), S. 583.

4 Miintz, Compt. Rend. T. LXXX. (1875), p. 1255.

5 Consult the article ' Fermente' by Emmerling in Ladenburg's HandwOrterbuch
d. Chem. Bd. iv. 1887, S. 95.

6 Compt. Rend. T. xx. (1845), pp. 954, 1485.

CHEMICAL BASIS <>F TIM: ANIMAL r.«»Dv.

purest (') ftirni by Cohnheim.1 His iinjtlntil i-mi<i<t-. in the addi-
tion of phosphoric acid to the saliva until it is strongly arid ; the
mixture is then neutralised by tin- careful addition of lime-v
whereupon a copious precipitate of phosphate of lime is formed.
This carries down with it a large proportion ..f tin- proteids which
an- present, together with all the ptyalin. On extraction of the
precipitate with a volume of water equal to that of the saliva
originally employed, the en/vme passes chiefly into solution, since
less thinly adherent to the precipitate than are the pro-
teids ; it may now be purified still further by rej>eating the above
process .nid finally precipitating with absolute alcohol. Prepared
in this way. the enzyme is obtained as a fine white amorphous
powder. Dissolved in water it is extremely active in hyilmlysin..
starch, and the solution yields none of the reactions mo>t t ypieallv
rTiaracteristic of proteids. On these ^rounds it is asserted that
ptyalin is not a proteid, but the evidence is not conclude.
More recently this enzyme has been prepared as follows.8 Saliva
is diluted with an eijual volume of water, and saturated with
neutral ammonium sulphate. The precipitate thus formed is
treated on the filter for five minuU's with strong ali-ohol. removed
from the filter, and further treated with absolute alcohol for one
or two days. It is now dried at 30°, and yields, on extraction
with a volume of water equal to that of the original >al
solution which is actively zymolytic, and is stated to be five from
all proteid reactions. The hydrolytic activity of ptyalin is most
marked in neutral or nearly neutral solution
An amylolytic enzyme is found in urine.4

experiments have as yet established tin- existence of anv
of ptyalin (ptyalinogen).6

The amylolytic enzyme of the pancreas.

The_. secret ion of the pancreas is even inure active than saliva
in_ejjerTingthe hydrolysis ot starch.'' This property is dej»endent,
upon the ''presence In this secretion of an en/yme \\hich in many
closely resembles ptyalin, but d tilers from it markedly in
its greater power of effecting a more complete deconipnsition of
the_sUirch than can ptyalin. Under ordinary conditions the only
sugaF~Tornie«l by the action of ptyalin on -tardi is mall..-- . n.

ver, the aetion is prolonged, small amounts of d> -\tros.
it is stated, also make their appeal -he re-ult of the fur-

.rcl.owV.4rrA. B.I. \\MII (|M;:H. S. .Ml

ivvkow, l«r. rit.

* I^anplcv and Kvos, .//. ofPkytiol, \ ><\ i\ 18.

ill. «••<• n-f I . -u!i !'••!. -;M. :

' I.Hfll^lcV , .//. (•/'/'/!//>/"/. Vl'l. I.

Ki ... /. - I IT Mal» in HormannV lldbrk. d.

/'hi/.*,..' Id! \ .' S i

58 ENZYMES OR SOLUBLE FERMENTS.

ther action of the enzyme on tlie first-formed maltose.1 But this
is by no means quite certainly the case, and without doubt no
dextrose is obtained during a digestion of moderate duration.
The pancreatic enzyme, on the other hand, not only rapidly con-
verts starch into maltose, but further converts this maltose into
dextrose in considerable quantity during a digestion of relatively
short duration in comparison with that required for its production
by the action of ptyalin.2 The secretion of the pancreas is of ex-
tremely complicated composition, and contains in addition to the
amylolytic at least two other well characterised enzymes ; from
these the former has as yet been only very imperfectly separated,
so that scarcely anything is known of its chemical nature as dis-
tinct from its converting powers. According to von Wittich the
amylolytic enzyme is separable from the others by treating the
gland with ether and alcohol before its extraction with glycerine,
to which reagent it then yields only the amylolytic enzyme ; 8
Hiifner, however, obtained a mixture of enzymes by von Wittich's
method.4 Experiments on the separation of the enzymes have
also been made by Danilewsky 5 and Paschutin ; 6 but the most
successful outcome of any method which may be employed simply
results in the production of an extract which is preponderatingly
amylolytic, but is by no means free from the other enzymes. An
active amylolytic .extract is best prepared by Roberts' method,7 in
which the finely minced pancreas is extracted for five or six days
with four times its weight of 25 p.c. alcohol, the mixture being
frequently stirred. The pancreas of the pig yields the most cer-
tainly active extracts, and more particularly if the gland is kept
for 24 hours after removal from the body, and is then treated for
a few hours with dilute (-5 p.c.) acetic acid before its final ex-
traction with alcohol.

Benger's ' liquor pancreaticus ' is, when freshly prepared, possessed
of extraordinarily active araylolytic powers. From it an extremely
pure and active solution of the enzyme may be obtained by adding to
it four times its volume of strong alcohol and filtering off the precipi-
tate thus formed; the precipitate is then rapidly washed with alcohol,
dried in the air, and dissolved in water.

The secretion and extracts of the small intestine possess to a

1 Musculus mid Gruber, Zt.f. pht/siol. Chem. Bd. n. (1878), S. 177. Musculus
uud T. Mering, Ibid. S. 403. v. Mering, Ibid. Bd. v. (1881), S. 185.

2 Brown and Heron, Liebig's Ann. Bd. cxcix. (1879), S. 165. Ibid. Bd. cciv,
(1880), S. 228. Proe. Roy. Soc. No. 204 (1880), p. 393. Confirmed also by the
author's own experiments.

3 Pfliiger's Arch. Bd. 11. (1869), S 198.

* Hiifner, Jn.f.prakt. Chem. N. F. Bd. r. (1872), S. 372.

5 Virchow's Arch. Bd. xxv. (1862), S. 279. But see Lossuitzer, Dtss. Leipzig,
1864.

B Arch. f. Anat. u. Physiol. Jahrg. 1873, S. 382.

• Proc.'Roy. Soc. Vol. xxxn. (1881), p. 145. See also Digestion and Diet, 1891,
pp. 16, 69.

( HKMICAL BASIS OF T1IK ANIMAL I'.ODV.

slight extent tin- power of slowly liydn.lysinx starch into maho-e .
tlii- conversion being more rapid if portion- ot tin- nun -i.il> mem-
brane of tin- intestine he tim-ly divided and immersed in the
.-tarch solution.1 The tissue and its extracts, on tin- other hand.
possess to a very marked extent the power of rapidly ellerting *
conversion • if maltose into dextrose ; tlr icat phy.-iol.

significance, inasmuch as it points to the probability that the car-
bohydrate- an- absorbed from the intestine as dextro-e and not as
maltose, — a view which is supported by the fact that maltose dot--
not appear to be capable of direct assimilation, but is excreted
laivly unchanged if injected into the blood.2 If this \te so, then
- dextrose that the liver receives its supply of carbohydrate
material for the formation of glyco^en. a fact which is of no
small inteiv.-t when we know that the liver discharges the carbo-
hydrate which results from the reconversion of -Jyco^en into
sugar a- dextro-e.3 (See also suit glycogen.)

( 'aiu---ULcar ha> been shown by I»ernard t» he similarly incapable <>f
a.— imilatioii: if injected into the blood it is excreted in tin- urine
iinrhan^iMl. \\'lit-n taken through tin- alimentary canal it i- probably
inverted nr converted into a mixture <>f dextrose and la-\ul»>e, \sliirh
are then a>-imilal>le.

Tin- <-Mii\.-r-i.'ii nf hepatic glycop-n int«» .-u^ar a- a preliminary t«« it-
di-i'liar:4'- from the liver has more usually been regarded a- dependent
iipmi tlie aeth ity «-f .-cnue ,-pei-ial hepat ie en/yine. Tin- \ie\\ i- n»\\
no longer tenable in face «•!' the ne^atne e\ idence a- \« it- t-xi-ten,-.-
olitained by moi-i- recent <.b-ei-\ .-r-.4 (S.-.- al-« >nb ^lye..^eii.)

Pepsin.

This is the characteri-tiy proteolytic ,^/.viiie of ^a.-tri<' juic.-
It was first separated out" in an approximately pure form by

"

Hi- method \\a- a- toll«i\v>. Tin- miie-.n- membrane »{ the -t..m.i.-h
i- -.eparat.-il t'r..m the mu-eiilar c.iat-. tinely chopped and dip--te.I \\itli
:i laru'e volume of ."> p. c. phosphoric acid. Tin- fluid thu- ..bta; ..... 1 i-
-fraim-d off through linen, and filtered, and lii ..... wafer is added until
the reaction i> ju.-t not .[iiite neutral : by thi- uie.i ipitati- »\

' Dniwii ami H.-n-i. .MM (1880), p. 3!W. I I. IM.

\',.||a. M-.l- -rrMtrl, ;„ \ IM. Mil.

H..iir.|in-l..i. <;„„,,!. /;,„,/. T. \, vii. (1883), |- I«XN'
. ..iiii.-riii:iiiii. I'llu-.-r', .I,./, H.I 01. Philip- (Dutrh I'

, (I88I , - Bouranelot, Compt. RrmH.

Eonn ii-^»).|-. !''•"» i'...nr.|iiri..i. ./» ./• ' i-'' -' ribwFlfW

Eonn ii-^»).|-. !''•"» ...nr.|iir..i. .» .• -' -

,-r. riluirrr-- .In-/,. IM. xiv. (1877). - nU X-N M -79). 8.

M in.. I Knit^-liin.-r. / / "I ^Xl%

uliis in.. I \ M. rinu'. /^ /". l'hit*i«i. ('firm. IM. ll .IT.

,/. v..l ^ (I--11. p m l"l I-

./ '

'.

I ./ ' / • ' (») T. .

II r . / i: ! x.o. 1 1 •»••,!). S. 601. Se« «ko In. l-.r.v«. St*r

60 ENZYMES OR SOLUBLE FERMENTS.

calcium phosphate is obtained to which all the pepsin is adherent.
The precipitate is now filtered off, dissolved in a minimal amount of
dilute hydrochloric acid and again precipitated by the addition of lime-
water; this second precipitation frees the pepsin largely from the
proteids which were at first carried down with it. This second pre-
cipitate is now as before dissolved in dilute hydrochloric acid. From
this the pepsin is separated as follows. Cholesterin is dissolved in a
mixture of four parts of alcohol and one of ether, and this solution is
introduced below the solution of pepsin by means of a long thistle-
tube. As soon as the cholesterin comes in contact with the water it
separates out and the separation is completed, as a finely granular
mass, by violently shaking the vessel in which the mixture is con-
tained. The pepsin adheres now to the cholesterin, which is filtered
off, washed first with water faintly acidulated with acetic acid and
finally with pure water. On treating the mass with pure ether in a
separating-funnel the cholesterin goes into solution in the ether which
forms an upper layer, below which is an aqueous solution of pepsin,
which must be shaken up several times with renewed portions of ether
until all the cholesterin has been extracted. The aqueous solution of
the enz3rme thus obtained is exposed to the air until it is free from
ether, and is then filtered. It may be further purified by dialysis,
and is now found to give none of the reactions characteristic of pro-
teids, and to be precipitable only by the acetates of lead. It yielded
no trace of opalescence on the addition of tannic acid, though this is
capable of detecting one part of proteid in 100,000 of solvent.1

From the reactions of the pepsin solution obtained by Briicke's
method, it seems justifiable to consider that the enzyme is not
really a proteid. The same conclusion may be deduced from the
more recent investigation of Sundberg.2 No analyses of purified
pepsin appear to have been made as yet, so that the views as to
its non-pro teid nature are based solely upon the reactions of its
solutions as described by Briicke and Sundberg, reactions which,
as already pointed out, are not really conclusive.

Preparation of peptic digestive fluids. If a few drops of a
glycerine extract of gastric mucous membrane be added to dilute
(•2 p. c.) hydrochloric acid, or if the tissue be simply extracted for
a short time with the dilute acid and the extract be filtered, a
solution is obtained which suffices for demonstration and ordi-
nary purposes.3 When however a peptic extract is required for
research purposes it is essential to adopt some more elaborate
method which yields a product as free as possible from admixed
substances ; one of the best is that of Maly.4 The mucous mem-
brane is digested, as in Briicke's method, with phosphoric acid
and the fluid precipitated with lime-water. The precipitate of

1 Hofmeister, Zt. f. physiol. Chem. Bd. 11. (1878), S. 292.

2 Zt. f. physiol. Chem. Bd. ix. (1885), S. 319. But see Low, Pfliiger's Arch. Bd.
xxxvi. (1885), S. 170.

3 See also Kiihne and Chittenden, Zt. f. Biol Bd. xix. (1883), S. 184.

4 Pfliiger's Arch. Bd. ix. (1874), S. 592.

CHEMICAL BASIS OF THE ANIMAL I'.oDV. r,i

< -a!, him phosphate is then tillered off, washed, and di— .d\ed in
dilute hydrochloric acid, and this solution is then dialysed until
it is five from chlorine and phosphate-, and «>n acidulating with
hydrochloric acid is ready fur use.

< hvinu' to tin- relatively slow diffiisil.ility of allmmn.se.s and peptoii.^.
men- dialysis "1 a solution of pepsin in which these suhstanc.

:t does not. within any reasonalde time, siitlice to yield an e\eii
Comparatively pure solution of tin- en/yme.

Many form- of commercially prepared pepsin arc ohtained l>y d.
iiii,' tin- irastric mucous nifinlirain- \\ith dilute hydrochloric acid; tin-
BOltttioD thus ohtaiiifd is thru >at uratt-d with soinc >alt siicli as Na<'l.

», or CaCl... wlu-n-ujMin a .-cum rises to the surface, consisting
chiftly of j.rotcid niattt-i- to which the pepsin is adherent. This scum
is then removed, frequently mixed witli milk-sugar and dried at a low
temperature.1

IVpsin does not exist preformed in the cells <»f tin- gastric
t^litijd s , hut as a /yinogen to which tin- name of iH.'j)sino^en i s
«jiv«Mi ; this is ivadily cunvciifd into pepsin by tin- action <»f
hydrochloric acid.2

I'nlikc ptyalin the hydrolytic activity of pepsin igjmanifggted
ojily '" presence of an acii,l. The most ctlicu-nt acid in this
i for artificial digestions is hydrochloric of a strength of
•'2 p. c.:j The average percentage of this acid may be statt-d a^
•'2 p. c. in normal gastric juice, but it varies slightly in the case
of different animals.1 Other acids may lie substituted for tin-
hydrochloric, the optimal percentage varying for the se
acid

A remarkalde peptonisin^ en/yme (papain). exits in tin- milky juice
of an Ma>t and \\'e>t Indian plant, Carica 1'apaya. Any di-criptimi
of thi> en/yme and its properties lies outside the scope ••«' this \\ork:
all necessary information may lie uhtaim-d 1-y referring to the pap.-i-

(ploteil !ielo\\/'

of jiejisin and other en/\ |iiently found in

urine ; the literature of the subject up to the present date is fully
Diluted iii the papers to which a n-feiem ••• is hnv "

:, Mah •>./ '. H'l. ill. (187.-H -

-h), lt.nl. H

• KlM.-in iind Crut/.iM-r, I'Hu-.T1- Arr.h. 1M. \in. (IS74). S. \~>2

\ , in. (1881), |. -\ an. I K.lkin.v /'•••/ V»l. vil. (\»M), p. :I7I.

.. 1'tlu^.TH .\,.l,. IM. \\\1

KVII i I--

• Bidder and s. -imii.it. I>" \'.,.i.«i I »•• amimUm

I'tlntr.T's .\ ,<•!,. IM. \i\ (1879), v

, i.Uon iind Iii.-t.Tirl,. .!..,•/,. f. .\,,,,i. ». /'/,./>-./. Jali r«. 1860, S. 6M. I
in Mah's Btrlckt. Mil. \. I

• Wnrte et Boachnt, r,,,,,,^ /,•.„./. T. i\\\.\ \Vurt/. /
KO.B 1879; I KOI !• 787 I'"l;ik (l)ntdi). 8«e Ab»t. in Mmly'f Jahntbtr.

. M.,r-':../ //'/,./.<.../. V.,1. v 1 1-- M p. 336.

..l.-lm:um. , 15. 1 IXli

•lIu-MMii) A!.-i in \: : I maim. l'Hui:«'r'-

I'.'l. M.I. (1887), S. 14!j. llclwea, Ibid. B«I xi.m

62 ENZYMES OR SOLUBLE FERMENTS.

Trypsin.

The proteolytic enzyme of pancreatic juice. This appears to
have been first separated from the other enzymes which exist
iTT pancreatic ]uice by DamlewskyT* More recently .Kulim7""!!; i s
prepared it in quantity and in what must be presumed to be a
pure (?) form, by an elaborate and lengthy process, for the details
of which his original work must be consulted.2 The composition
of the enzyme as prepared by Kiihne was found to be remarkably
complex, as shown by the fact that when dissolved in water and
boiled it is split up with the formation of 20 p. c. coagulated
proteid and 80 p. c. albumose. It might at first sight appear
probable from this that the purified enzyme was in reality a
mixture of the true enzyme with other substances (proteid) to
whose decomposition on boiling the coagulated proteid and albu-
mose were due, and some authors have taken this view.3 This
seems however to be negatived by the fact that Kiihne digested
his trypsin for several weeks in dilute alkaline solution and did
not observe the formation of the least trace of peptone, leucin,
or tyrosin. The percentage composition of the enzyme has been
quoted on p. 55, from which it appears to contain distinctly less
carbon than a true proteid.

Preparation of solutions of trypsin for digestion experiments..
The following method due to Kiihne yields an extraordinarily
pure and active tryptic solution ; unfortunately it is a somewhat
lengthy process.4

One part by weight of pancreas which has been extracted with
alcohol and ether is digested at 40° for 4 hours with 5 parts of •! p. c.
salicylic acid. The residue after being squeezed out is further
digested for 12 hours with 5 parts of -25 p. c. Na2C03, and the residue
is again squeezed out. The acid and alkaline extracts are now mixed
together, the whole made up to -25 — '5 p. c. Na2C03, and digested
for at least a week in presence of -5 p. c. thymol. By this means all
the first formed albiimoses are fully converted into peptones; this is
essential. At the end of the week the fluid is allowed to stand in
the cold for 24 hours, filtered, faintly acidulated with acetic acid, and
saturated with neutral ammonium sulphate. By this means all the
trypsin is separated out and may be collected on a filter, where it is
washed with the ammonium salt (sat. sol.) till free from peptones.
It is now finally dissolved off the filter in a little '25 p. c. solution
of Xa2C03, to which thymol is added and thus an extremely active
and very pure digestive solution is obtained. Ten grams of the
original pancreas yield 80 — 100 c. c. of extract.

1 Virchow's Arch. Bd. xxv. (1862), S. 279.

2 VerhandL d. naturhist.-med. Ver. Heidelbg. (N.F.), Bd. I. (1876), S. 194.

3 Low, Pfluger's Arch. Bd. xxvn. (1882), S. 209.

* Verhand. d. naturhist.-med. Ver. Hcidelby (N.F.), Bd in. (1886), S. 463. Also
Ceniralb.f. d. med. Wiss. 1886, Nr. 45.

CI1KMICAL BASIS OF T1IK AM MAI. 1;<>1>Y.

I'.eitij.-r's 'liiiiK.r paitcn-at icti> ' contains in addition t«>

tin- cn/\ nifs I.., tli Iriicin an<l kyraein together with pr»tt-i.i

actively protfolyt it- that th«- >niall amount re<|unvd to \ idd an acti\«-
dii;..-tive solution introduce^ an amount «\ impurities which inav \«-
in-^lected in many ca-i->. The al>»\(- impurities may !>•• lar^. i

rid of by precipitating oul the .-n/vines \\ith aid. h.. 1 u desorib

Although trvpsin exhibits its liydrolytic jxiwers to tin-
advantage in presence "f an alkali, its activity is scared y~so

• ly related to_th_e alkali as is that of in-psiit to dilute hy<]i» »-
c-hloric acid. Thus it will digest pruti-ids, although much luTiic
slowly in a m-utral solutimi and i-vt-n in jin-scncc of dilute ('01-

' hydrochloric acid, Imt tin- slight. •-! exoen < 1 p. c. ) of the
arid d.--n'.y- it.1 In connection \vith these >tat«-nn-ni> it nm-t
h«i\vi-vi-r In- Imriif in mind that pr<>t«-ids ]iavc tin- JM.W.T *>f readily
(•uiiiliiniii^ with acids, hence the addition of say -1 j». «:. of hydm-
<'lil"ric acid to a digestive mixture dues n»t imply that th.
then '1 p. c. of free acid in the solution.-

This comparative independence of tryptic activity in its rela-
ti"iis t<> the reaction of the digestive mixture i< dmilitless »»f r«m-
siderable physiological .significance. The reacticm of the contents
of the small intestine is very variable. The chyme as diseh
from the stomach is of course acid, and this aridity is lar-.'ly
diminished by the advent of the stronulv alkaline bile and pan-
crejitic jniei-. so that the reaction may become alkaline within a
short distance of the pylorus. On the other band the alkaline
;.>n mavjtot be at all appreciable until the lower end of tin*

• ine is reaclied, and fn-nuently, at least in dogs, the reacti.m
ntly aci<TTriroii^T7(iut, whether they are fed on prot.-ids or on

a mixture of carliohyTTrates and fat.:; The acidity in the latter

[fl not -urj. rising bearing in mind the ivadim-ss with which

the earbohy.lrat.-- undergo a lactic tci mentation, e-pe.-ially inside

the intestin.-. and it mi^ht therefore have been abnormal in tin-

do-j whose food does not normally contain carbohydrates. On

the other hand in man. living on a mixed diet, the possibility of

a laetie fermentation is always present.4 It is impossible to makf

jj'U«-ral statement as t" the reaction of ihe contents ^>f_^'

small intestine ; it varies at different times, ami drjNMuls upon the

!,!..•. Virrliow's Arek. IM. X^MN (ItST), > n" Ili-i-li-iiliain. 1'ti
Arrfi. 15.1 \ '( " «/- /• ''"I "I

v l.il|illnTl,'iT (Sw.'.,|i.|| • I XIII.

•.«'•, '/A f. i>hi/niiJ. Chnn. Hi I. i. I!-"

;»../. H' ... 1880 N... :»l. v. .1. Vi-l.l.-n. />•••'•>• •'• i H.I. \\»n

. . S. |«C,. Cf. I.an-l.'v :in,| ' .»•/ V.,1 n

iimi.lt-Miilli.-im. Arek. I. /Vi./«W. .Inhrg. 1879. S. .19. Ciwh. /'.'/ IH80.8.
••123. F,«-:i. .//. /'/,

mil. n- .

niiivi-f Miilk-Miu'.irl int.. H'l " I I'-

ll' t

64 ENZYMES Oil SOLUBLE FERMENTS.

kiiid_and relative amount of the several food-stuffs, the_changes
these undergo and the amount of alkaline secretions with which
they are mixed. Ail the evidence we do possess Igjids^ to the
belief that intestinal digestion to be of use must be capable ^f
being carried on in a mixture which may be alkaline, or_neutral,
or even frequently acid. Although the acidity of the intestinal
contents may be due to hydrochloric acid in the upper end of the
duodenum, the acidity is elsewhere much more probably due to
lactic or butyric acids, and it is interesting in this connection to
notice that according to Liudberger,1 the former of these two
acids exerts a distinctly favouring influence on tryptic digestion,
especially in presence of bile and sodium chloride. Thus in
presence of '02 p. c. lactic acid and 1 — 2 p. c. bile and sodium
chloride fibrin may be digested more rapidly than in a neutral
solution and fully as quickly as in a solution of moderate alka-
linity. But the presence of -05 p. c. of lactic acid stops the
digestion.

Traces of trypsin have been stated to be found in urine ; this
is somewhat doubtful.2

Trypsinogen.

The zymogen of trypsin. Heidenhain first showed that the
pancreas contains, in its absolutely fresh and normal condition,
no ready-made enzyme, but an antecedent of the same.3 This
body is readily converted into the active enzyme by the action of
dilute acids (1 c.c. of 1 p.c. acetic acid to each 1 grin, of gland-
substance) and a conversion also takes place if the gland is kept
for some time, especially in the warm, this resulting most prob-
ably from the spontaneous acidification which it thus undergoes.
The zymogen is soluble in strong glycerine without conversion into
the enzyme ; it is also soluble in water, in which it is gradually
changed into the enzyme, most rapidly when warmed, probably
under the influence of the acid reaction which the solution
acquires.4

Pialyn.5

In addition to the two pancreatic enzymes which have already
been described, both the secretion and the gland-substance contain
a third substance which has not as yet been isolated, of which,
therefore, but little is known from a chemical point of view, but
which must be regarded as an enzyme in virtue of the typical
conditions under which it is able to effect a hydrolytic decompo-

1 loc. cit. ref. 1 , on p. 63.

2 For litt. see ref. 1, sub Pepsin, on p. 61.

3 Heidenhaiu, Pfliiger's Arch. Bd. x. (1875), S. 581. See also Podolinski, Ibid.
Bd. xni. (1876), S. 422. Weiss. Virchow's Arch. Bd. LXVIII. (1876), S. 413.

* Kiihne, Lehrb. d. phi/siol. Chem. 1868, S. 120.

6 From ir'ia.p = fat, and \vtiv = to split up or decompose.

CHEMICAL BASIS OF THE A M.MAI. i;oDY. 65

of neutral fats into ^l\«,-iuit- and free fatty arid. !'>• i
in-w attention t<> tin- exi-teii'--- of this en/yme.1 It is most
it in tin- Mil. -i. in. ••• of tin- freth gland or in its secre-
utl may l.e extracted fr«»ia tin- former by means of j

i y case it is essential to ensure that the gland
"t iicquired an acid reaction I'.-fore extraction, and that all
<n in the exl .tl»eiit. sine.- tin- en/yme is pecu-

liarly .sensitive to acids other than .1 i- readily desti

\>\ thfin- Hence a dilute alkaline solution should l»e empl
ami according to Paschutin sodium Uiearbonate mixed \\ ith the
normal carbonate is the most efficient solvent*

presence of tin- ••n/yme is tested f"i- \<\ adding tin- exti;,
minion .-f nil "f hitter aliiiniid>. -T ..th.-r neutral oil or fat. with
£iiiii arahic: the mixture i> then nn».st can-fully m-utrallM-d and di-

1 at 40°, togfthtT with a minimal amount of lu-utrul .-• i
litmu> sidutioii. In prrst-ncc uf the »-n/yine tin- mass turn-
less rabidly red, nwin^j to the liberation of the free fatty acid.

\ niic nature of the active agent is shown by the fact
that its activity is greatest at about 40°, is destroyed by boiling,
ami is dej.eiident upon the reaction of the digestive mixture.
greatest in \n> : a dilute alkali, although it will >ln>\v itself

in a neutral solution. It will also be observed that the decom-
position which jiialyn effects is typically hydmlytic.

Rennin.

tl of the mucous memhrane «»f tin- stomach of young
il>, and more especially of the calf, have been known
time immemorial to |M(^,^- a m.,>t remarkahle jH.wer of
HL; milk to clot, and rennet was commonlx employed l.\ tin-
:ie manufa't ure i. f cheese. The active agent in \<\»
is in more recent times supposed to be eitln-r the
acidity of the extract itself or tin- j.n>duction of la.
inilk-suirar (lactose) by means of some active j,nn< ipl.- in the
it/ and ffemmaraton, howev.-i. >h..u.d that this

•mtenahle ; and we now know that the sulmtance to
whii'h the dotting is due is MM- (o whi'h the na;

at may be conveniently ^iven.4 The en/ynnc nature of the
•• a^ent in rennet is tl -.\\n l-\ th-- t;. pi-al i.-l.it ..... ship

shits in its activity to the rea !n- solution in

it ii present,* to the t- n it \vhi<-h its activity is

1 Comfit. Am</. T. XXTUI. (1»49), p. 949. Sea *bo hit Ltfmt d*
(IftM). p |

:«), 8.30t.
• Arck.f. Anal. » /'A»«o/. J*hr; IN*.

4 ThU wune tttmt man conveaient than UM mora oommoolj wed expr««kMU
' the rranet ferment ' or ' the nilk-cardlioc ferroeat'

5 H»mm«r*«n (Hweduh). S« Abrt/la Malr's Brid*. lt.1 a B 111.

/. prakt. Ck*m. (N.F.) Bd. n. (1871), & 374. See ako Al Schmidt
6

66 ENZYMES OR SOLUBLE FERMENTS.

greatest, to the fact that the briefest exposure to 100° or the more
prolonged exposure to lower temperatures (70° or above) * suffices
to destroy its active properties, and to the fact that a minute
trace suffices to clot a relatively enormous amount of casein.2

Nothing is known as to the chemical nature of rennin. Extracts of
the gastric mucous membrane contain both rennin and pepsin. Harn-
marsten 8 has obtained it free from the latter enzyme by fractional pre-
cipitation with either magnesium carbonate or normal lead acetate, by
which pepsin is more readily precipitated than is rennin. He further
endeavoured to separate out the enzyme, after freeing it from pepsin,
by precipitation with the acetates of lead in presence of a trace of
ammonia; this precipitate was then carefully decomposed with very
dilute sulphuric acid, and the enzyme finally separated by means of
cholesterin. (Vide preparation of pepsin, p. 59.) The reactions of
the purified enzyme described by Heidenhain seem to indicate that it
is not a proteid.

Aqueous and glycerin extracts of the gastric mucous membrane
are usually found to be active in clotting milk,4 but the activity
of a faintly acid extract is in all cases greater. This is due to the
existence of a rennin zymogen (renninogen) which is readily con-
verted into the enzyme by the action of acids.5 The preparation
of highly active and permanent solutions of rennin is of consider-
able commercial importance in connection with the cheese-making
industry. . The most efficient extractive is sodium chloride, 5 — 15
p.c. ; and permanency is attained by the addition of alcohol, or in
some cases thymol.6

Although rennin is most copiously present in the gastric mucous
membrane of the calf, it may be obtained from the tissue of almost
any stomach, if not as ready-made enzyme, at least in the form of
a zymogen (Hammarsten). It occurs also in the stomach of chil-
dren 7 and of man ; 8 and Roberts has described a similar enzyme
in the pancreas of the pig, ox, and sheep.9 Rennin is stated to
occur in traces in urine.10

Maly's Bericht. Bd. iv. (1874), S. 159. Langley, Jl. of Physiol. Vol. in. (1881),
p. 259.

1 Mayer, Die Lehre von dem chem. Fermenten, 1882. See also Maly's Ber. Bd. x.
(1880), S. 208.

2 400,000—800,000 times its own weight. Hammarsten. See Maly's Bericht. Bd.
vii. (1877), S. 166.

3 Maly's Bericht. Bd. n. S. 121. See also Friedberg, JL Amer. Ch. Soc. May,
1888, p. 15.

* Hammarsten, loc. cit. See also Erlenmeyer, Sitzb. d. k. b. Akad. d. Wiss.
Miinchen, 1875, Hft. 1.

5 Hammarsten, loc. cit. Langley, Jl. ofPhi/siol. Vol. in. (1881), p. 287.

6 Soxhlet, Milchzeitung, 1877, Nos. 37, 38. Chem. Centralb. 1877, S. 745. Nessler,
Landwirth. Wochenblatt. f. Baden, 1882, S. 57. Friedberg, Jl. Amer. Ch. Soc. May,
1888, p. 15. Kinger, J/. of Physiol. Vol. xn. (1891). Note 2, p. 164.

7 Zweifel, Centralb. f. d. med. Wiss. 1874, No. 59. Hammarsten, Ludwig's
Festgabe, Leipzig, 1875.

8 Schumberg, Virchow's Arch. Bd. xcvu. (1884), S. 260. Boas, Centralb. f. d
med. Wiss. 1887, No. 23.

9 Proc. Roy. Soc. No. 29, 1879, p. 157.

10 See Helwes, Pfliiger's Arch. Bd. XLIII. (1888), S. 384.

CHKMICM. I'.ASIS OF THK ANIMAL U«.M»V.

Fibrin-ferment.

I'.uchanan'- wi.rk (1831) on tin- dotting of blood, more par-
ticularly his exj.,-riments with 'washed rl..t.' when examined ii:
the ; 'tir present knowledge, -li..u< dearly that i

din;,' with that fa. tor in tin- whole process which

independently red l.\ Alexander s. hmidt and more spe-

.iK-d l>y him in 1*7'J under the name of ' til>ri:
nient.' ' It- • !iad Keen ton-shadowed in some experiments

mad-- ke. in which he showed that the Hliriintplastic aetion

of precipitated paraglobulin was parti] dejM-ndent upon

the admixture of some other >ul. stance, which he regarded as the
truly tilirinoplastic fat-tor. Thus, he showed among other things
nore a serum is diluted before the paraglohulin is precipi-

from it liv means of CO,., the less marked are its tiluino-

-.2 Further. Mantegazza had in 1871 put forward

the view, also held }.y Uuchaiian, that the white coi),u>cles play

imjx>rtant part in the formation i.f tilirin, without in any
:isin^' the substance which he suggested was prob-
ably dis' I Mum them as the determinant of the whole
process.8 The time was thus rijN- for Schmidt's discovery.4 He
prepared the ferment l>y juvcipitatint: serum with !."• — ijO vol-

•iur alcohol ; the precipitate was treated for ///
14 da\> with the alcohol to insure complete (?) coagulation and
insolubility of the proteids; after which time it was removed W

ion. dried in vacuo over sulphuric acid, pulverised, and

with distilled water in volume equal to twice that of

the xeiuin originally employed. The ferment solution thus ob-

i i- by no means pure, and n< 'ti\e. M • : ••ntly

aarsten has obtained the ferment in solution free from pnra-
glol.uliu.5 11^- saturates serum with magnesium Milphate at 30°,
and "'Iters otl the precipitated para^Iobu^iu at the same temj_M-ra-
t_ure. Th>' filtrate he dilutes with nine volumes ot water, and t«»
tln^ adds gradually, and with continuous stirring, dilute caustic
so<la until a IM-I inaiient. llocculent. ami fairly c<»pious i>re<-ipitat<'
j§ fanned. Tliis precipitate carries the ferment down mechani-
cally, and i- finally washed, pressed. -u-|«-ndcd in water, dissolved
by a< i to a neutral -olutiou.and dialysed till free from

ordinary puriMtses an extremely active ferment solution

l»e must readily ofiuined by Hamgee's method »f extra* tii i ;_'

< >-called ' wasjied IdcxKl dot ' with 8 p.c. solution of sodium

chloride.* The solution in this case contains ti large amount of

1 An account of Buchanan '• experimeot* ha* beea jfvM br Gamgee. Pkytiol.
Ckm,< . i 8«e abo Jl. of l^ v»o/. Vol. n. (1879). p 145.

Al.th.), 1867, 8. 891.

\ !«t. in Ma

rrt.n:..r'« .)-.', I!

Ibid. R! KTl x \ x I -

QHBgM

68 ENZYMES OR SOLUBLE FERMENTS.

globulins m solution, as also does^the similar extract which may
be equally efficiently prepared from ordinary washed fibrin.1

In no case as yet has the fibrin-ferment been obtained in a con-
dition of such purity as to justify any dogmatic statement as to Its
chemical composition. All the solutions whose preparation has been
described above ^leld strong proteid reactions, and Halliburton 2
has argued from his own experiments and a criticism of preceding
work that the ferment is really a proteid identical (?) with what
he had previously called ' cell-globulin ' (antea, p. 28). On the
other hand it is possible by appropriate methods to free the .^alt-
extracts of fibrin very completely from proteids without anv great
loss of ferment activity, certainly without any such loss as would
necessarily be the case if the active substance were a globulin.3
It may be said that the apparent ferment-powers in such cases
are in reality due to the presence of calcium sulphate, which is
now known to promote the clotting of a dilute salt-plasma to an
extraordinary degree ; 4 but as against this the fact may be quoted
that solutions free from proteid reaction, and which had been
freed from salts by careful dialysis, lost their activity on heating
to 60 — 70°, which they would not have done had the activity
been due merely to calcium sulphate.

When Schmidt's method is applied to blood received directly
from an artery into an excess of alcohol no ferment can be ob-
tained from the precipitate thus obtained. LtL is. hence evident
that the living, circulating blood contains no preformed ferment.
and the question thus arises from what does it take its origin
during the clotting of blood and presumably as an immediate
antecedent to that clotting ? Buchanan held distinctly the view
that the active agent in the whole process was in some way con-
nected with, if not derived from, the white corpuscles, a view also
held later on by Mantegazza. Schmidt also took this view, bas-
ing it on an elaborate series of investigations for which his orig-
inal works must be consulted.5 Lowit, experimenting with
lymph as well as blood, while denying that the white corpuscles
break down at clotting in the way Schmidt described, still connects
them with the production of the initiative factor in the whole
process.6 Still further evidence in the same direction may be
derived from the experiments of Rauschenbach 7 and Halliburton,8
and of Fano, who observed that wTien "peptone-plasma is freed' as

1 Lea and Green, Jl. of Physiol. Vol. iv. (1883), p. 386.

2 Jl. of Physiol. Vol. ix. (1888), p. 265.
8 Lea and Green, loc. cit.

* Green, Ibid. Vol. vm. (1887), p. 354.

5 Pfluger's Arch. Bd. ix. (1874), S. 353; xi. (1875), Sn. 291, 515.

6 Sitzb. d. Wien. Akad. (2 Abth.), Bd. LXXXIX. (1884), S. 270; xc. S. 80.

7 Inaug.-Diss. Dorpat, 1883. See also the Dissertations (Dorpat) of F. Hoffmann,
1881. Samson-Himmelstjerna, 1882; Heyl, 1882.

8 loc. cit. See also Kriiger, Zt.f. Biol. xxiv. (1888), S. 189.

CHEMICAL BASIS OF THE ANIMAL BODY. 69

completely as possible from \vhit«- <nrjm-.lt-> it canuot be made to

dot in tin. u-ual way by the addition of water.1

In addition t<- the red ami white ci.r|-u>cles blood also contains, as
already -l.--i.Tit'. -d :hir«l >tructural element, tin- 'j.lat.

• vend "I'M-rvere have end. -avoured tii connect t lie first cause of
the clotting of blood with some breaking down and di>aj>]>< ara;
these structures.* Th; as yet insufficiently supported, and is

c« -in hated by several observers; 3 bearing in uiind however how little
i> known about the origin and nature <>f th«--t- platelet* tin- <jii.-ti..n
of tlu-ir relationship to blood-clotting must still be regarded as await-
ing a decisive answer.

In addition to the undoubted relationship of leucocytes to
fibrin-formation it aj-jd-ars that the protoplasm of many other
iioth animal and vegetable, may exert an influence similar
:iat of the white corpuscles of blood.4

:• u'.nil.d the leucocyte-, as entirely secondary and \ery
ictnrs in the process of clotting, as also the fil>rin-fer-
iiiij,' to hi* view Mood-plasma contains in itself all the
element > requisite for the formation of fibrin, which he cons id' .

; no sense tin- outcome of any fermentative process. He described

coagulable proteids A- £- and (7-fibrinogen. The la>t of tlie-e

- in minimal ijiiantities in plasma, is identical with the -ul>-

•• ordinarily known as tihrino^en. and clots on the addition of

fibrin-ferment. According to his \ lew clotting U due tn a tn

• f lecithin from it> conildnat i«n with A-UOnaOf/SD t«> /y-!il»rino-
iiich means both the tibrinogens disappear and fibrin takes
their place.*

information which we possess as to tin- nature of th«-

tU'rin-f.-nii'-nt is mm !i less complete and satisfactory than in tin*

case of otlii-r .•n/ym.-- Hut that il is proix-rlv plai-i-d in tin- class

of tlu _ |_- _ -hown hy the typical facts that its activity

_ ^y ili-]M'iideiit ni'on t<-iii|M-ra(iiie. hring ili-stroyi'ir '•_ lu-at-

i"njj_to JtiJ ; that Li d«M/s_jiot alTtM t tin- aniouiit but only tin- "fati*

of r|ianov of filirino^'-n^Tnto t'j"''ii ; that it is can if<I* down l>y

nous j.ivipii. it«--; funii'-d in Hs solutions Hamni'-r<t«-n). JTO-

dm-fs a ' haiioy whi«-h is out of all proportion to tin- mass of

Pkifuol. Jahrj?. 1881, 8. 2fs II i->.-. ^aiO.

i (1878), p.
./« Pkyiial. 1878. p. 692. BilXox.T... Vir. IL.W'K Arrh. IM \

I'..! I XXXM

low ' hKmatuli!.vt-> ' are identical with Binoirr tru.-

hvmatoblaiu are the cell* described br Neumann. IHadfldach. and other* ai>

«F.i ..f.d.mf.l u t,loe.cit. Rchimroelboach,

4 K.H i .Mlimnnn. rjMtf I -* I

/ -nrf. 1886. l.adwi^'" Ft***rift, 1887. See al«o
Halh

70 ENZYMES OK SOLUBLE FERMENTS.

enzyme employed, and is not, so far as we know, used up in the
change which it induces, since it is present in serum

Muscle enzyme.

The phenomena of the clotting of muscle-plasma compared with
those of blood-plasma and the relationship of the process to the
presence of neutral salts and to temperature suggest at once that
the change is probably one in which some enzyme plays a part.
Immediately after Schmidt's discovery of the fibrin-ferment the
question of the existence of a rnyosin-ferment was investigated
under his guidance,1 and resulted in the discovery of the exist-
ence in muscles of an enzyme which appeared to be identical
with fibrin-ferment rather than specifically myosinic. The later
work of the Dorpat School further confirmed the above, but failed
to establish the existence of an enzyme, differing from fibrin-fer-
ment and specifically active in promoting the clotting of muscle-
plasma.2 More recently it has been shown that by applying
Schmidt's method to muscles which have been treated for some
time with alcohol, a solution may be obtained which hastens the
clotting of diluted muscle-plasma, does not facilitate the forma-
tion of fibrin in blood-plasma, and, unlike fibrin-ferment, requires
to be heated to 100° before it loses its activity.3 The active
agent in the solution is therefore not identical with fibrin-ferment
and may be spoken of as a myosin-ferment.

Urea-ferment.

When urine is exposed to the air its acidity at first increases,
but in most cases this speedily gives way to a marked alkalinity,
which is accompanied by the evolution of ammonia. This is due
to a hydrolytic fermentative change resulting from the appear-
ance and development in the urine of certain micro-organisms of
which the best known is the Torula ureae.4 Normally urine is
free from these organisms and may be kept in the excised blad-
der for an indefinite period without exhibiting any tendency to
become alkaline ; 5 in certain abnormal conditions it may undergo
an active alkaline fermentation while still in the bladder. The
part played by the organisms was for a long time regarded as
similar to that of yeast-cells in promoting alcoholic fermentation.
Soon however evidence was adduced which showed that the

1 Michelson, Dlss. Dorpat, 1872.

2 Grubert, Diss. Dorpat, 1883. Klemptner, Ibid. Kugler, Ibid.
8 Halliburton, Jl. of Physiol. Vol. vin. (1887), p. 159.

* Midler, Jn. f. prakt. Chem. Bd. LXXXI. (1860), S. 467. Pasteur, Compt. Rend.
T. L. 1860, p. 869. van Tieghem, Ibid. T. LVIII. 1864, p. 210. But see also Jaksch,
Zt. f. physiol. Chem. Bd. v. (1881), S. 395. Leube, Virchow's Arch. Bd. c. (1885),
S. 540. Miquel, Bull, de la Soc. Chim. T. xxix. (1878), p. 387 ; xxxi. p. 391 ;
xxxii. (1879), p. 126.

• '" Cazeneuve et Livon, Compt. Rend. T. i.xxxv. (1877), p. 571. Bull, de la Soc.
Chim. T. xxvni. (1877), p. 484.

CHKMICAL BASIS OF THK ANIMAL r,«>DY. 71

c hange was not necessarily due solely to tin* lid- and growth <>f

•rganisms in tin- solution, for it was found that the fern,
tion might be •upletc in presence of an amount of carbolic

acid wliidi is t'atal to th-- de\.-lopment of micro-organisms.1 The
probable of an en/yme as a possible fa.-t >r in tin- whole

•ss which was thu- demon-nated wa- reduced to a certainty
by the exjH-riments of Mu-cnlu-.- Kmplovm- the thick mucous

•rh he precipitated the iniicin with al-
cohol, dried tin- jirei-ij.itate at a low teiujK-ratnre, extracted it
with water and found the extract to possess active hydndytic
; a solution of urea. The proof of the existence of the
In a pathological mucous urine in which there i
OjUently no reason to suspect i. ;ice of any micro-organisms

still Ifft (»|XMI tin- (|Uc>ti«.ii ()f the isolation of the ir«'in

the mi. lo-oiuiani^m it-elf. When urine which \>\ exj.<,si;
the air has .-nt.-ivd into active alkaline f.-i iii'-ntat ion an. I. M
shown l»y microscopic examination, is full of Torulae, is flliciently
vni'- <-a] table of bydrolisin.u' urea can l»o precipitated
by alcohol from the dear filtrate. If on the other band the until-
tered urine he precipitated with an excess of alcohol and'th*
••d with alcohol and dried in the air, a po\\,i
:ie«l which i- itself extraordinarily active, and yields to an

• soluble eiixyme which raj. idly <-on\erts
inunoiiia and carbonic acid. The rapidity of the c.mv.
udes the intervention of any developing or^ani-m. and that
lian^e is truly due to an en/ynie i- shown by the fact that it
ith e,|ual readiness in presence of chloroform.8

-oiiu' iiitt-rot tc. notice ln-r«- that frmn \\hat lia> IM-.-M said
\\h.'>»- activity tin- feriiu-Mtatinii is dm- <\« n-.t
tr^e tlit-ir i-n/yiiif int.. tin- Mirmmidiiin inediuin; \\ln-ii killt-.l
ic.ili.J. tln-y yii-ld it n-ailil- italile

Thi> li..l<ls p».<l aU«> in tin- case of invcrtin. \\hidi :
found in tin- liltrat.- !>..;• \\liili- it ina\ n-adily IM- .-\t ra.-t. ••:

tin- .-.-II- when killed l-y ether .T al.-..||,d.4 Similarly it appear- that

\ield an en/ynie «ho>e acti-m i>
•ryp-in.0

The nio-t j.rolit: of the urea enzyme is in all case- the

mucous urine passed in inflammatory conditions of the bladder.

II:- i U

I i \\MII 1 1 -:«.). i •-• I.\\M

<mpt. Rtnd 1 i \\MII j.
1 Le«.

4 Mopp^Seyler. !:•< <l. A
'

i Kjo|,|»hl(I>.. Al-t in

Indu*!. IH^I.N.K. |«. .'. •'»*«"•

* I!
l>1ni*inl. Cktm. Bd. XI. (IWT K . Salkuwnki. /J ' H>-J Bd xx\ (IBM).

72 ENZYMES OR SOLUBLE FERMENTS^

In this c«ise the enzyme appears to be closely associated with the
mucin and is presumably a secretory product of the mucous mem-
brane, for it is frequently obtained when there has been no opera-
tive use of surgical instruments which could account for the intro-
duction of micro-organisms from the exterior.

In concluding this account of the more important enzymes of
the animal body it may not be out of place to say a few words on
the probable mode of action of the ferments and enzymes.

The term fermentation was applied originally to the changes,
accompanied by characteristic frothing, foaming, and evolution of
gases, which saccharine solutions such as the expressed juice of
fruits or infusions of grain undergo on exposure to the air. The
chemical changes and products of the fermentation were studied
from the earliest times, and in 1680 Leuwenhcek described, with
the aid of the newly-invented microscope, the small, spherical par-
ticles which are now known as yeast-cells, to be the exciting cause
of the whole process. He did not however ascribe any organisa-
tion to these particles, and it was not until 1835 and 1837 that
Cagniard de Latour and Schwann respectively but independently
took up the investigation where Leuwenhoek had left it, and estab-
lished firmly and finally the organised and plant-like nature of the
yeast-cell and the absolute dependence of fermentation upon its
presence in the fermenting fluid.1 The yeast-cell having thus been
definitely recognized as the cause of the fermentation, the interest-
ing question at once arose as to how the known cause produces
the observed effect, and to this question many answers have been
given, of which the following are the more important.

Liebig regarded the ferments as substances in a state of pro-
gressing decomposition during which the equilibrium of their
constituents is upset and a rapid motion of their minuter parts
established. When brought into contact with other decomposable
substances the motion of the ferment's particles is communicated
to the former, whereupon it also undergoes a decomposition result-
ing in the formation of the simpler products which make their
appearance and are characteristic of the fermentation. According
to this view the organised nature of the yeast-cells is left out of
account and the phenomena attributed entirely to the purely
chemical decomposition of their constituent substance, set going
at the outset by oxygen.2 Pasteur regarded alcoholic fermenta-

1 Erxleben in 1818 had described and spoken of yeast as a vegetative organism,
as also in 1825 had Desmazieres, who ascribed to it an animal rather than vegetable
nature.

2 Ann. d. Chem. u. Pharm. Bd. xxx. (1839), Sn. 250, 363. Stahl in 1734 had ex-
pressed practically identical views.

CHEMICAL BASIS "1 I Hi: ANIMAL

tit'ii as indissolnhly connected with the vegetative LM'owth, multi-
plication, and metabolism of the yeast-cell. According to this view
sii^ar is tin- food-stuff out of whii-h the organism obtains the ma-
terial requisite for its metabolism and growth, the products of tin-
fermentation beinu' thus, as it wen-, the e\cn-tiunary residues of
tin- metabolised food.1 A third vi»-\v attributes tin- fermentative
uposition to the production l>y the organic -d t« -nm-ntsof solu-
ble unorganised ••! ix vines to whose activity tin- decomposition is
diii-. Th >-ceived its chief sui»i>urt DUD tin- discovery that

a part at l«-ast i>f the change which siujar undergoes in presence of
may be obtained by means of the soluble enzyme ' invi-rtin '
which can readily be extracted from tin- dead cells.2 But as yet
all efforts to obtain an i-nxyuie capable of carrying tin- decomposi-
tion beyond the initial stage of inversion have been fruit less. \
• cnling to von Nageli tin- living substance of the organised ct-11 is
to be regarded as being in continuous and rapid molecular vibra-
tion, ami the decomposition of the fermentable substance as tin-
result of the direct transference of these vibrations to this sub-
is by means of which its equilibrium is upset and it is split
up into simpler and therefore more stable products.1 To discuss
the merits of these various theories and the experiments upon
which they are based is quite impossible within any reasonable
limits of brevity. We shall perhaps be not far wrong in consider-
ing that as regards the organised ferments the changes they effect
;>e, iii their earlier stages, partly the outcome of the action of
some soluble en/vine, and partly the result of that cycle of meta-
bolic (chemical) processes which occur continuously in their proto-
plasm, in virtue of which «they are sjMiken of as -living.' Simi-
larly in the higher animals we find a large number of Simpler
>n by means of isolal.le en/.ymes. by which un-
doubtedly the labours of the protoplasm in i»erformiii'_: its own

•implicated activities an1 materially lightened. l'>ut v.
still fare to face with nunilttrless decompositions which cam.

reproduced outside tin- limits of living matter and which

t be explained with reference to anything other than the

activity of living matter

The .jeiier.il ( oiiditious and factors which characterise the action
of tin- soluble ferments or enzymes have already been mentioned

.; without making any suggestion as to the prohahl.
in which tln-v produce and .airy mi tin- decompositions to which

tln-y -jive rise. Liebij - of the mode of action ot yeast,

lince n left !; ind life of the cell entirely out •••'

w WM keenly attarked »" n. ./. Cl>n* u I'h.irm. Bd. < MM

: 8«« lW«nr in wply, A**. Ckim. l'ky> « v. r I \\* .

• rtinir |«-wfr »f yemrt wo flmt dt.i nnif;iiit in I "47. I^rthHot

-MI. a ml II - prepand it in t!i«- I.. rin ••( ;»

<• reference* on |<

I

74 ENZYMES OR SOLUBLE FERMENTS.

account, and was based simply upon the supposed properties of
the changing cell-substance, might obviously therefore be applied
to any ordinary soluble enzyme. There is however no evidence to
show that the enzymes are in the state of change or decomposi-
tion which Liebig supposed ; on the contrary they are observed to
be on the whole remarkably stable substances, from the point of
view that a minute trace can produce a profound decomposition in
a relatively enormous mass of material, during an almost indefi-
nitely long time, without itself undergoing any proportionate altera-
tion or destruction.1 The theory of v. Nageli previously quoted
was applied by its author to explain the fermentative power of
the living cell, and is thus not directly applicable to the non-living
enzymes. Mayer, it is true, has put forward a view which is essen-
tially a development of v. Nageli's and is applicable to the en-
zymes. These substances are in all cases produced solely and
entirely by the activity of living cells or organisms, and Mayer
regards them as retaining in themselves a portion of that molecu-
lar motion which is supposedly so characteristic of the living
parent cell from which they have been separated.2 It cannot how-
ever be said that these theories afford any real insight into the
probable mode of action of an enzyme, and we must look for it in
some other direction.

Attention has been already drawn (p. 53) to the existence of a
large and increasing class of chemical reactions whose occurrence
is determined by mere traces of some substance which does not
itself at the same time undergo any change during the decomposi-
tions which it initiates, and the enzymes have been compared to
these substances. Now in the case of the reactions of which we
are now speaking it is known in some and probable in all that the
process which takes place is in general terms the following. The
determinant substance interacts with one of the reagents to form
a compound which can now enter into combination with the other ,
the result is the formation of a more complex compound which at
once decomposes, giving rise to products of which one is the origi-
nal determinant substance in an unaltered form, the others the
product characteristic of the reaction.3 This suggests at once that
the enzymes may play their part in a manner similar to that of
the determinant in the above reactions, a view which has been put
forward but scarcely receives the attention that it deserves.4

1 Berzelius explained fermentation as the outcome of a mysterious 'catalytic ac-
tion,' or 'action by presence ' or ' contact.' He thus compared ferments to platinum-
black, which is able, in minute quantity, to cause a liberation of oxygen from peroxide
of hydrogen without itself undergoing any recognisable change. This is however no
explanation, for it does not amount to more than saying that given the contact of
two substances capable of reacting on each other, a certain reaction takes place.

2 Die Lehre von den chem. Fermenten, Heidelb 1882.

3 Vide the reactions in the continuous etherification process and the manufacture
of sulphuric acid. See also Traube (Ber. d. deutsch. chem. Gesell. 1885, S. 1890), on
the part played by water in determining the explosion of O and CO.

4 Kiihne, Lehrb. d. physiol. Chem. 1868, S. 39. Hoppe-Seyler, Med.-chem. Unters.

CHEMICAL BASIS (>F II IK ANIMAL 1;«»DV.

In most ca>es it is known, ami it i- probable in all. tint the
soluble ferment- act by lirin^int; about a union of water with the

m-es uj.on which they act. This process mi^ht be supposed

to take place in tin- following way. Tin- en/vim- uniting with the

Mib-tam •»• to he decomposed, the compound thus formal i-, now

able to unite with water. and this final moiv complex and 1;

loSB stal)lr comjKMind undergoes a dr. •ompoMtion ,,f which the

original en/vine i- one product, tin- oth.-i- heiiiL' the hydrated and

substance whos.- lormatioii is characteristic of the

whole process It is impossible within convenient limits to hrin-

ill the diiv.t evidence in favour of the above view

as to the mode of action of en/ vim. ; it must suffice to say that as

is jH-psm there is some reason for thinking that it can enter
•mhination with hydrochloric acid. Finally it maybe stated
that the chai. i phenomena of xyinolysis in « onnection with

the iiitluen,,- .,t heat, the ellect of various saltsand dilution, the
cessation of the change in presence of an excess of the produ*
that cha: ire such as careful consideration shows ini^ht

wvera] j-oint- of view be e\j>ected on the supposition th.it
the above theory of en/vine action is true.

mical action i> in all ca-<-> arr-nnpatiied \>\ an evolution or ab-
S'Tpti'in uf h.-at. ami it will add t«> the cc.iupleti'iie>s ..f tlii> account of
tin- f'Tin. •'..• >n>id«T hrietly tin- heat-plieiioineiiauliii-li :ic,-..iii|iaiiy

tile cllelllH-al action due to tile ell/VllM- Lielij^r regarded tile ferillellta-

• 1011 of sugar as necessitating a con-i-lnrd.!.- couxiiiiptioii
.\\liich he supposed to be derived from the deOOmpOtlBg ftlblh

lain "f th«- feriii.Mit >uli-tanci-. Hoppe-Seyler on the other hand put

id the general vir\\ that heat i- .-\-ol\-ed in i-very i-a-e i.f t.Tinent

i, basing it UJHUI iixperiinent> in \\lucli lie ol»>er\ed a distinct

iiip.-ratur.- during the action of pancreatic upon

I, luit more particularly up PII tin- opinion that the heat of com-

tlie product- -I /yniol\-i> i- in all CM6B less than tl
tin- .in^inal >ub-tanci- from which the jirodi. uied.1

And this is undoubtedly tl ..... orivet \u-\v. In addition t.. Ib.ppe-

••bservers ha\ 1 .1 n-- of temperature during

. r. ;/. in the ca>e of the formation of fibrin.- the dotting

of milk. a and the inv« : .im---u^ar.4 Mftl J OO the Othei hand

observed a CMii-derahh- ubsnrpt ion of heat during th«- a< 1 1 ...... t |»cp«in

on pn.t.-id-i and ptyalin on starch.* Tin-- -in-lit- it ma\

di-conlant. ami in reality they m-it IHT H|N>ak ht :
-t the evolution of heat diiriM-4 the action of tin- (-11 /vines; M

Wittich. I'riiiRpr'ii .IrrA. »d v. (I87S). S. 4-1.V \V

!«•»(»). p :
V lift 4. 1-:

'

M i. 6. See Ate. in M«ly'« Hrrickt. ISM), ft

309 Out MI« aim MUM», //»'/ 1879, 8. 16.

• Kunk-!. niuj-r- 1 ' Ui \\ 1-79.8 509 But M« Nijpli. /**«/. Bd XXII.

| !|0

• I'llutr-r'.. Art* Bd. XXII (1880). SIM

76 MUCIN.

a matter of fact they could scarcely be expected to do so, since it is ex-
tremely difficult to make allowance for the heat which may be simply
absorbed or set free as the result of the varying solubilities of the orig-
inal substance and the products of its decomposition. The real proof
of the correctness of Hoppe-Seyler's view is the fact, already stated,
that the heat of combustion of the products of zymolysis is less than
that of the substance from which they are derived.1

NITROGENOUS NON-CRYSTALLINE BODIES ALLIED TO PROTEIDS.

These resemble the proteids in many general points, but exhibit
among themselves much greater differences than do the proteids.
As regards their molecular structure nothing satisfactory is known.
Their percentage composition approaches that of the proteids, and
like these they yield, under hydrolytic treatment, large quantities
of leucin and in some cases tyrosin. They are all amorphous.

Mucin.

This is the substance which gives to many animal secretions,
such as saliva, bile, synovial fluid, &c., their characteristic ropy
consistency. It may also be obtained by the use of appropriate
solvents from the tissues themselves, such, as submaxillary gland,
tendons, and umbilical cord. It is peculiarly copious in the secre-
tion which may be collected on stimulating the mantle of Helix
pomatia, or in an extract of the tissues of this animal. The gen-
eral phenomena of the formation of mucin by mucous cells, and
more particularly the characteristic behaviour of the mucous
granules in relation to the secretory activity of the sub-maxillary
gland,2 leave but little doubt that mucin is to be regarded as de-
rived from the true proteids; in conformity with this it yields
many of the reactions characteristic of the proteids (Millon's and
xanthoproteic), and by the action with mineral acids some form
of acid-albumin is usually obtained. During this treatment (or
with alkalis) moreover a second product generally makes its ap-
pearance, which belongs to the group of carbohydrates and by
heating with acids may be made to yield a reducing sugar. Not-
withstanding the views which. have frequently been advanced
that mucin is in reality a mixture of proteid and carbohydrate
material, it is now known with considerable certainty that it is
a unitary substance which, from what has been already said,
might be almost regarded as an animal glucoside. It further

1 For heat of combustion of physiologically important substances see Rechenberg.
Inaug. Diss. Leipzig, 1880, and Jn. f. prakt. Chem. (N. F.) Bd. xxii. (1880), Sn. 1,
223. See also Stohmann, Ibid. Bd. xxxi. (1885), and Landwirth Jahrb. Bd. xm. S.
513. Rubner, Zt. f. Biol. Bde. xix. (1883), S. 313 ; xxi. Sn. 250, 337. Berthelot et
Andre, Compt. Rend., T. ex. (1890), p. 884.

2 Langley, Jl. of Physiol. Vol. x. (1889), p. 433.

( IIKMICAL BASIS OF THK ANIMAL 1!«H»V.

,ip|H-ars that th«- substance at tir>t secreted by tin- mu<ou>
(nf Helix) may not be typical niiicin, luit a sort of mucinogen
whii-h readily gives rise to mucin on treatment with dilute
(til i ».c.) caustic potash.1 If it be assumed for tin- moment that

is only «»nt- kind of mucin, then the following general state-
ments as to this substance may be additionally made. It is pre-
cipitated from its solution.-, by a<rti<- or hydrochloric acids, the
precipitate being soluble in excess of the latter hut not of the
former acid. In its precipitated form it swells up strongly in
water hut does not go into true solution ; the addition of dilute
alkalis (/I — •'_' p.c. ) »r of lime-water lead> to its ready solution.
from which it can again he pie. ipitated by the addition •
acid. It may be extracted from any mucigenous tissue hy the

! dilute alkalis or lime-water, and in solution is somewhat
chnra lly precipitated hy hasic lead acetate. Our knosvl-

"f mucin i.s ho\\e\«-r in an extremely transitional condition.

and recent investigations have shown that probably the mu<-in>

d from ditleivnt >our<-es are really distinct substances, ju-t

lamiliar with ditl'erent forms of proteids. From this it

follows that no general statement of the properties of the nun-ins

made which would he other than misleading, nn«l it

will conduce to clearne>s to ^ive a hrief account of this suhstam e

::om each of the chief sources from which it has

Mucin is not a constituent of normal hile

when freshly secreted, hut is found in it as the result of the

tory activity of the internal epithelium of the ^all-Madder.

bait prep.i). .'. il'aijkull). liile is mixed with

• t al.-olutc alcohol and centrifiiLiiiliM'd ; the pivcjpi-

nuicin which is thus ohtaim-d i- then dis-ol\ed in \\.itcr

and the ahove j-nx5ess repeated two or three tiuic^. An aqueous

solution of thi< mucin is precipitated hy acetic and hydr«H-hlorie

soluhle in excess of either acjd. and \ield- -tlon-ly

:d reactions. This mucin dilleis from that ohtanied

from otli. in not yielding any ledu.-in^ siil.-tam ,- when

hoiled witii acids, and in the soluhil-ity of its precipitate obtained

hy n. acetic acid in an excess of this acid. It also con-

phosphoms, and is by some regarded aa more closely alli.-d

to the niicleo-all.iimins (see p. 89) than to the true nui-

'he 8vb-maxill>i r;i <//.'/j//3 Tin- -l.md ii finely
minc.-d. washed, and extracted with \\.itrr: the ext ItOM

,. 1'll.u-. rV 190.

.i. f. P.VM../. Cktm, IM. % |I«*I).S 171. Mil I I HH.I). S III

ktlll. Ibid. MI

llm.M /: i*Ay«W. Ckfm. xii. (18«a). 8. 1«». Com..

otln-r lit.-r:itiir.- «ilH,|..|i.k%. Il..(,|,.. S.-\|. r - mrti.-chrm. Unteri. lift. 4 { 1 87 1 ), 8. 590.

>>. ii,r n. n»:i

78 MUCIN.

and hydrochloric acid is added up to 1 — 15 p.c. The mucin is
thus precipitated at first, but at once passes into solution, from
which it is precipitated by the addition of a volume of water equal
to three to live times that of the original solution. This precipi-
tate is then again dissolved in dilute hydrochloric acid and repre-
cipitated by water, the process being repeated several times. As
thus prepared and thoroughly washed it possesses a distinctly
acid reaction ; it may be dissolved to a neutral solution by the
cautious addition of very dilute alkalis, and now exhibits the fol-
lowing properties. It is readily precipitated by acetic acid, much
less readily in presence of sodium chloride ; this salt on the other
hand greatly facilitates the precipitation of mucin by alcohol, which
again does not take place in presence of a trace of free alkali.
Any excess of alkali, especially on warming, at once changes the
substance so that its characteristic ropiness is permanently lost,
and boiling with dilute mineral acids yields a reducing substance.
It gives the usual reactions for proteids and is strongly precipi-
tated by the acetates of lead and by CuS04 and by excess of NaCl
and MgS04.

The mucin of Helix pomatia.1 Hammarsten distinguishes be-
tween the mucin contained in the secretion of the mantle and
that which may be derived from the foot of this animal. Mantle-
mucin. The secretion of the mantle contains a mucigenous sub-
stance precipitable by acetic acid which is exceedingly insoluble
in water, but is readily converted into true mucin by the action-
of dilute ('01 p.c.) caustic potash. From its solution in alkali it
may be purified by precipitation with acetic acid, washing, re-
solution in alkali and reprecipitation with acid. When dissolved
in a trace of alkali the solution yields the reactions typical of
other mucins, but it differs from these in the fact that the precipi-
tate formed on the addition of hydrochloric acid (or acetic) is not
soluble in excess of the acid. Foot-mucin. It may be obtained
by extracting the foot with .01 p.c. KHo; from this solution it is
now precipitated by the addition of hydrochloric acid (not acetic)
up to •! — '2 p.c., redissolved in alkali and reprecipitated with acid,
the process being repeated several times. Solutions of this mucin
resemble those of mantle-mucin in all essential respects, the only
difference which is stated to be characteristic of the two being that
in presence of sodium chloride, mantle-mucin, like that of the
submaxillary gland, is not precipitated by faint acidulation with
acetic acid, whereas under similar conditions solutions of foot-
mucin cannot even be neutralised without yielding an opalescence
or precipitate.

The mucin of tendons? The tendo Achillis of the ox is cut into

1 Hammarsten, Pfliiger's Arch, Bd. xxxvi. (1885), S. 373. Gives previous
literature.

2 Lobisch, Zt. f. physiol. Chem. Bd. x. (1886), S. 40. Gives previous literature.

( IIKMICAL BASIS OF THK AM.MM. BODY.

thin slices, washed with distilled water and extra, ted with half-
saturat'-d liuu--w.it.-r , the mucin is thus di-sol\vd. and is purified
by prei ipitation with cither acetic or hydrochloric acids, re-solu-
tion in dilut-- alkali, and repie.-ipitation with ;K'U\<. In ii

• .us it resembles tin- nuicins previously described, hut appears
GTer from them in its distinctly ;.'!•••. HPT to the .;

,ind alkalis.

••in of the umbilical cord.1 May be extia< t.-d by means of

i and is readily precipitated from tin- solution 1 acid.

ra to differ from thi- other nnu-ins in containing more

tnd a considerable amount of sulphur: it lie- i:
•.vhat midway between the proteids and true niucin-.

•d boilini: \\ith -ulphurie acid nuicins yield leucin
and t\i'-.in, but the pr.Hlucts of their decomposition have not been
t fully stud:

ial mucins exhibit differences in percentage

composition which lie within somewhat similar limits t" those al-
ready assigned (p. 5) to the proteids. A comparison of these seems to
v the statement that on the whole the mucins contain slightly
M and distinctly less nitrogen than do the prot«

i "'searches <»n nmciii L:nul\vi-)ir * .il>t;iiin-d a xil.-tance to

\\hich li.- ^ave the name of "auiiiial-^uin " I'n-m its general >imil:ir-

tlit- \t-^ftal'le products of tli<- >ann- name. II.- was at tir>t in-

1 t«i n-^ard the iimciii> as iiii\tiin-s <>f tliis carlmliydrati' with

pp.t«-i«l >ul'-tancrs. l>ut this view he .siil.sc.|iifiitly iiK.ditit-d.4

Kiirtlit-r invf-ti^atinii lias led him to regard aiiiinal-^iii. :rrin^

in many ti--iu-s of the \n»\\. and tc. >|n-cnlate <>n its pliy>i"l"^ical and

•al significance. '' IN i>"lati"ii ficiiii tin- >.\.i;il ti--

.ind c.iinplicated. ami t"..r this I.amlucln

:s must be consulted. It ili«M>l\i-^ in \ .idily

n^j Milutioii. fr«'in wliich it iua\ i.itatid l»y alc->li<'l. Ii,

alkaline sulution it n-adily di--"l\'-^ cupric o\id«- \vhicli luccd

<>ii I..,ilinj4: \\li.-n l.oiled \\ith dilute mineral arid* it yi«-Id> a p-ducin^

if iM.t altered l.y di^e-tinn \\ith -aliva «-r
JIM.-.- (see also bel<>w under carl">liydratcs).

It ha- I.een alp-ady -tat«-il that puritied niucin (e\r.-pt ..f l.il.-)
yield- a .•ai!...li\«lrate \\li.-n li. at.-d with acid- or >t

-ideraMe i-iui- ii d --ii .1- t" \\li' th. T .uiiliial-

in the tissues M ft i

•li.- iimcins ..r whether it i- in all ra-e- • their

decomposition. The .-\idence at hand mi tin- jH.int iiclu-

:,t it may \»- -aid that, while iimcin i-

-.1 (Swedish). See Abst. in Maly'n Btrirkl. 1880.

8 :i

. rmanti. H>ol. Cmlr,, 1887-88), >

tiot. Ckem -HI), 8. 75; Till. (1883), S. 128.

• Ibi>l. IM IX. S

• ( it ,,. (1885), S. 3«9. IflUger'c Arrk Bde. xxxti. (1686).

80 GELATIN.

accompanied by animal-gum, the latter has by no means been proved
to take its origin from the former. The whole subject requires
further investigation.

Gelatin or G-lutin.1

The ultimate fibrils of connective tissue and the organic matter
of which bones are largely composed consist of a substance named
in the first case ' collagen,' in the second ' ossein.' They are ob-
tained either by digesting carefully cleansed tendons with trypsin,
which dissolves up all the tissue-elements except the true collage-
nous (gelatiniferous) fibrils,2 or by extracting bones with dilute
acids in the cold, by means of which the inorganic salts are dis-
solved and the ossein remains as a swollen elastic mass which re-
tains the shape of the original bone. As thus prepared they are
insoluble in water, saline solutions, and either cold dilute acids or
alkalis ; in the former, however, (acids) they swell up to a trans-
parent gelatinous mass. When subjected to prolonged boiling
with water, more especially under pressure as in a Papin's diges-
ter, they are gradually dissolved, and the solution now contains
true gelatin into which they have been converted by hydrolysis,
and has acquired the characteristic property of solidifying into a
jelly on cooling. The conversion of collagen into gelatin may be
still more easily effected by a shorter boiling in presence of dilute
acids, but in this case, unless the process be carefully regulated,
the first-formed gelatin is further hydrolysed into what are often
spoken of as gelatin-peptones. Although insoluble in dilute acids
collagen is readily dissolved by digestion with pepsin in presence
of an acid passing rapidly through the condition of gelatin into
that of gelatin-peptone, and although collagen is not acted upon
by trypsin in alkaline solution, it is readily hydrolysed by this
enzyme after a short preliminary treatment with dilute acid or
boiling water, the products as before being known as gelatin-pep-
tones. When gelatin is exposed for some time in the dry condi-
tion to a temperature of 130° it is reconverted into a substance
closely resembling collagen, which may be again converted into
gelatin by treatment with water under pressure at 1200.3

Gelatin obtained by the above means from connective tissue or
bones is, when dry, a transparent, more or less coloured and brittle
substance.4 It is insoluble in cold water, but swells up into an
elastic flexible mass which now dissolves readily in water when
warmed. When the solution is again cooled it solidifies charac-

1 Glutin must not be confounded with the vegetable proteid ' gluten.'

2 Kuhne u. Ewald, Verhnnd. d. naturhist.-med. Ver. Heidelb. Bd. i. N.F. (1877),
S. 3. See also Etzinger, Zt.f. Biol. Bd. x. (1874), S. 84. Ewald, Ibid. Bd. xxvi.
(1889), S. 1.

3 Hofmeister, Zt.f. physiol. Chem. Bd. ir. (1878), S. 313. Weiske, Ibid. vn.
(1883), S. 460.

4 Pure gelatin is colourless, e. g. fine isinglass prepared from the bladder of the
sturgeon. Glue is impure gelatin made from hides, &c.

CHEKIOAL BASIS <>i' Tin: ANIMAL BODY.

teristically into a jelly even when it contains as little as ] j.. c. of

also readily soluble in tin- cold in dilute acids and

alkalis. The proteid reactions of gelatin are so feeble that they

must IM- regarded .is din- entirely to unavoidably admix. -d traces of

;d impurities; more particularly i- it to !..- noticed that the

usual ivai tion of pmteids with Millmi's reagent i> entirely want-

: which indicates tin- probable absence of aromatic (hen-

111 its molecule and ••orn->j..inds t" tin- ah>.-!:
ti amon^ the products of its decomposition. Notwithstand-
ing that it i- in no sense a pr»teid, its percentage composition ap-
mates to that of tin- latter • lass of substances and maybe
D as C = 50"76, H=7'la, () = L'.",i'l, N = 1S-.TJ, from which
it apju-ars t-i contain distinctly less carlion than do the pi..-

i Uo Stated to contain no sulphur when pure, hut ordinarily it
:ns a .-mall amount ( •."• p. <-.).' C. -latin i- pie. i]pitat--i hy luit
few salts, vi/.. : mcicuri- chloride and the douhle i<Klide of mer-
cury and potassium in acid solution. Several acids on the othei
hand ]>iecipitate it readily, such as j»hos].hotungstic and meta-
phoephorie, also taurocholic and tannic. Of the two last-named
\i. -Ms an njialescciice in presence of 1 part of
11 in 300,000 of .solution, and the latter in still morv dilute
- The ).re< -ipitaliility with tannic acid seems to depend
on the j^resence of neutral salts.8 The specific rotator}' power of
:i in aijueous solution or in presence of a trace of alkali i>
to be i ")„=- 130° at 30° C. and to be reduced to -111'
or -114 on the addition of more alkali or acetic acid.4 This

• Mnlirminx-

When decomposed in seal tul>es \\ith caustic-1. . • latin

\a on the whole the same products as do the proteid-. •'• with

\.-ejition of ty rosin ; neither tin- m.r any ..tlu-r substance of

illy ai-i'inatic >.ri.- is ,\,r «.htained during any decom-

posit: latin, whether l»y chemical or jmtn-faetive |n.K-fS8ea.*

volon^ed lioilin.u with hydrochloric a. id it lycin

ucin. ^lutamii- a. id. and ammonia.7 and with sul-

id aspartic acid as well.8

I prolonged boiling with water (1 } i.e. so-
lution hoiled for 30 hours), or sh -.it -nt in a I'.q.in's diges-

1 IIamm«nrt«n 'A. f. pkyilol. Chm. Bd. in. (18S5), 8. 905.

Mavitthyl - 95

» \N>i»k.-. CM
1 .1 I. I'.ir /'.-- TuLingeo, 1864. Abo in Hoppc Scylcr'» mtd.<ktm. Unttrt.

• SchfitaenberKer ct Bourgeois, Comfit. Km,! I i \ \ \ 1 1 , i «?«). p. MS.

See Abut, in M«ljr'« Brrirkt. 1876. > u JeunerK, J* /
Cktm VI. Wojl Xt.f. ftytiol. Cktm M

m

UW Bd i xxx (1879), i- A'.ih .limi lift

<*.

,4ii<inl. Ct.,m M. u. (1878). S. 299. Hire* liionUore down
to that date. TaUriooff, Compt. Remd. T. xcrtt. (1889), p :

6

82 GELATIN.

ter, also by heating with hydrochloric acid (4 p.c. at 40°), or still
more readily by pepsin in presence of acid or by trypsin,1 gelatin
loses its power of solidifying on cooling, and is converted into
more highly soluble and now diffusible substances, to which the
name of gelatin-peptones has been given. A similar change
occurs when gelatin is taken into the stomach.2 From the con-
ditions under which the change is effected and from certain evi-
dence deducible from analysis there can be but little doubt that
the conversion takes place as the result of hydrolysis, as in the
case of the formation of true peptones from proteids.

Eecent researches have shown that the hydrolytic decomposi-
tion of gelatin by digestive enzymes gives rise to products analo-
gous to those obtainable by the same method from the proteids.
Thus during both its peptic and tryptic digestion certain primary
products are formed to which the name gelatoses or glutoses may
be applied, and which have so far been distinguished as proto- and
deutero-gelatose. Accompanying these, in variable amount, are
other products known as gelatin-peptones. The latter are to be
regarded as a product of the further action of the enzymes on the
first formed gelatoses and, like the true peptones in their relation-
ship to the albumoses, may be separated from them by their non-
precipitability on saturation with ammonium sulphate, a reagent
which completely precipitates the gelatoses. Protogelatose is
partially precipitated by saturation of its solution with common
salt, and completely so on the simultaneous addition of acetic
acid. Deuterogelatose is not precipitated by either of the above
reagents.3 The so-called true gelatin-peptones have not yet been
obtained in sufficient quantity to admit of their complete exami-
nation. The products of the digestion of gelatin appear to give
a distinct biuret reaction with caustic soda and sulphate of cop-
per, and like the peptones (and albumoses) are not precipitated
by taurocholic acid, which precipitates gelatin from its solutions.4

When the spores of Penicillium are sown on a surface of gelatin, as
soon as the mycelium is well developed the subjacent gelatin liquefies
sometimes to a considerable depth, so that the Penicillium finally
floats on a layer of fluid separated, by some distance from the re-
maining still solid gelatin. The fluid in this layer now yields an
intense biuret reaction. A similar liquefaction is observed during
the growth of certain bacteria and other micro-organisms on gelatin.

The fact has already been referred to (§ 524) that gelatin taken as
food, while it materially lessens both the nitrogenous, and to some

1 Schweder, Inauq.-Diss. Berlin, 1867.

2 Uffelmann, Arch. f. kUn. Med. Bd. xx. (1877), S. 535.

3 Chittenden and Solley, .//. of Physiol. Vol. xii. (1891), p. 23. See also Klug,
Pfliiger's Arch. Bd. XLVIII. (1890), S. 100. The latter author describes further a
product to which he gives the name apoglutin. It makes its appearance as an
insoluble substance, hence resembling antialbumid or dyspeptone, during the diges-
tion of gelatin.

4 Emich, Monatshefte f. Chem. Bd. vi. (1885), S. 95.

CIIK.MIC.M. I'.AMS ol Till: AM.MAL P,nl»Y.

slight extent the non-nitro^enou- in.-t;il...li-in ..f tin- l....ly. ami thus

re aide t.» undergo a destructive metabolism .-.imilar to ti
tin- pn-teid-, cannot, "ii tin- other hand, play any part in th,
structhe nitni^eiioii> metaboli.-in which lead- to tin- format imi ..f pr<(-
In other word- tin- nitr-'^'-n contained in gelatin cannot In-
built up into the nitn . i.i-oteid.1 \\ V .|.. not
any information which enable- u- to formulate an\ n-a-on for this
il behaviour of gelatin. It ha- l>«-rn .1 that tin- al

-:diie- in gelatin (-•••• al««\i-) nii^lit a.-.-oiint for tin- pln-
iioni.-non.- luit experiment- in \\hich animaU ha\.- l..-.-!i f.-.l \\ith
:n have not continued thi> vi«-\v.8 It aj.pear- that a
coii-idt-raldr ainou1 'in i- ili'4«--ti-d and al>-oi-hrd in i»ian.

.ippi-ars in tic .ind nn-at (iiiu>i-h-) may contain a> niurli

.itin: furthi-i. \|..-riiii.-nt- >ho\v that a do^' may

; tin- ^'l.itin adniini-ti-rcd in tin- form of

11^' tln-«- fart> in mind and kiio\\in^ that p-latin u\>-

pear» to !><• ni"i«- nadil\ im-taii<di>cil than proti-id.-. \\f may regard

t a \alualdi- f l->tuff. hut not a- a f 1 \\hirh can supply

tin- nitro^eiiini> m 'In- ti--m-- tliem-eh e-. The fai-t- thus

: max >iipply an e\].lanat imi <•!" the heiielicial effi-.-t- \\hi<-h art-
>upp.-ed t.. re-ult from tlie UM- of jellie> in training diets.6

Chondrin.

Tli«- matrix «>f liyalim- cartilage is composed of an »-la-ti'-. -emi-
xnvnt sul. -tancr which i< insululili- in cold <»r hot water and
11 up aj.pivcial.lv liy t ivat iin-nt with i-itln-r water or
tlilut' at id. I'.y jirulmiL'f'l treatment with water umlt-r

:re in a l(a].iir< .li-j«-ster it 18 gradually dissolved and yields
iition wlii« li gelatinises mi runliuo and now contains th«-
nice usually -jMikfii of as chondrin. The hyaline mat;
.age appear^ tints to hear tin- same relationshij' to chondrin
that the groand-sabatanoe of connective-tissue (collagen) d

id 1- therefore frei|Ueilily Spoken of as 'cliolldl

The -ul.-tanre known as chondrin. which is obtained in solution
by the action of -ii]«-rheated water on hyaline cai t ilao«'. exhibits

• icteri<tic n-actioii-.' It is precipitate,!
which does not. even if iii .-, Mi-id, -rabh- exec--. ivdi--,dve the

te; minute quantities of minei similarly cause a

•<• to apjM-ar which is in this case i .duble in the

slightest excess of tin- acids. These reaction to distinguish

••••n chondrin and -j'-latin. and a further di-tinction maybe

on the basi-. of the fact tli.it -«,]ut j, .n- ,,f chondrin are pre-

i ted by several reagents such as alum, normal lead acetate,

H.I. xin run), ft •-••.•: ^. SOB.

•' II. rrti.inn II K«- \\> • ',r»rh. ti. H" k, 1876, & 86.

'•/ / ,..»/. Miin. hen. 1885.

il».. Kt/in

* K' uiritioiial. m««UlMi1ir anil )

gelatin w« IlermaonV //<//Wi .//•/,,,. ..^. 1 5.1 M H .195.

lewbott u. Ful.ini. MolewhoCt's t'nt,n*cA Bd. xi 104.

84 CHONDRIN.

and other metallic salts (of Ag and Cu), which yield no precipitate
with gelatin, while on the other hand mercuric chloride and tan-
nin do not precipitate chondrin but are characteristic precipitants
of gelatin (see above). Choudrin is powerfully laevorotatory ; in
faintly alkaline solution (a)D = - 213'5° ; in presence of excess of
alkali this becomes (a)D = - 55'20°.:

By prolonged treatment with boiling water, or shorter heating
with dilute (1 p.c.) sulphuric acid or stronger hydrochloric acid,
chondrin is decomposed with the formation of a nitrogenous crys-
tallisable product which characteristically reduces alkaline solu-
tions of cupric oxide.2 Opinions however differ considerably as to
the real nature of this reducing substance. It was at one time
regarded as a true carbohydrate, and more recently Landwehr has
identified it with his animal-gum.3 (See above sub mucin.) There
is now but little doubt that it contains nitrogen, is possessed of
distinct acid properties, and exhibits marked carbohydrate affini-
ties apart from its reducing powers.4 According to the older and
some recent observers its solutions are laevorotatory,5 but v. Mer-
ing states that it is dextrorotatory.6 Its real nature cannot be
regarded as yet as definitely established. When the action of the
boiling acids is prolonged, or if caustic alkalis or barium hydrate
is employed, chondrin undergoes a further profound decomposition
resulting in the formation of a large number of crystalline pro-
ducts ; with regard to these the fact of chief importance and
interest is the general presence among them of leucin, and the
entire absence of tyrosin and glycin (glycocoll), and the occurrence
of aspartic and glutamic acids in very minute traces only, if at all.7

We have so far spoken of chondrin as a distinct and individual sub-
stance; the view has however been put forward that it is in reality
merely a mixture of mucin and gelatin,8 and the outcome of more re-
cent work seems to be tending towards the strengthening of this view.9
When hyaline cartilage is extracted with baryta water or dilute alkalis
a solution is obtained which yields reactions typical of the so-called
chondrin and closely resembling those characteristic of mucin; the
undissolved residue when boiled with water is dissolved into a solution
which gives the reactions in general typical of gelatin. Morner,
treating sections of hyaline cartilage in succession with dilute hydro-
chloric acid (•! — -2 p.c.) and caustic potash (*1 p.c.), finds that
rounded masses of the matrix are dissolved out and leave thin a resid-

1 de Bary, loc. cit. (sub gelatin).

2 v. Mering, Inaug.-Diss. Strassburg, 1873.

3 Pfliiger's Arch. Bd. xxxix (1886), S. 198.

4 Krukenberg, Zt. f. Bid. Bd. xx. (1884), S. 307. Morner (Swedish). See abst.
in Maly's Bericht. 1887, S. 308, 1888, S. 217.

5 Petri, Ber. d. deutsch. chem. Gesell. Jahrg xn. (1879), S. 267.

6 See Hoppe-Seyler's Hdbch. d. physiol.-path chem. Anal. (5 Auf. 1883), S. 301.

7 Schiitzenberger et Bourgeois, cit. (sub gelatin).

8 Morochowetz, Verhand. d. naturhist.-med. Ver. Heidelbg. Bd. i. (1876), Hft. 5.

9 Krukenberg, Morner, loc. cit.

rilF.MK AI. l',A>IS OF TIIK ANIMAL BODY,

mil network. The «li>.-"hed |>urt~ lar^'-h «i a Mihstaiu-i- (cluui-

dlOiniieoid) With marked atHuiti*-* t<> inuciii. wherea> tin- tindi»"lvrd

rk. 1'V treatment with acids or sup«-rh.-.r
largely into typical ^.-latin. For further detail- the original paper-

ly quoted >h.>uld be o.n-ult.-.l.

Elastin

This is the characteristic component of tlie elastic fibres which

the removal of gelatin, mm-in, fats, etc., from tissues

such as •• liiMniiMituin iiurhae." Some of the more important

in which it di tiers from the substances which have been )>n-\ i«ni<ly

art- sutliri.Milly statrd l.y ili-xTil.in^ th,. m.-tli..*! »\ it-

preparatitin in a i>uiv form.1 Li^'»«'"tuin mn-hai- «i an ««\ is cut

intit tin'- -li--.--. tn-atrd t'c.r thn-c or fmir days with l.uiling water,

tln-n tor -..in.- hours with 1 j i.e. caustic potash at 100°C and >uU--

(ju«-ntlv with wat«-r Tlii- ]>r<»ci->-* i- then n-jM-at.-d with 10 p.c.

I Finally it is ti.-;,- _: \ hours in thf cold with 5

wasln-d with water, boiled with '.».". }>.r..alco-

nd extracted for at least two w.M-ks with rther to remove

• • of adln-ivnt fat. I'.y the al»ovc nn-thod it may l>e ob-
d as a pale ytdlowish |>owd»-i in which th»- shajx- of fragments

of tin- original clastic fibres may be still distinguished under tin-
When uioi-t it i> yellow ami elastic, but on drying

- Brittle and may with ditliculty lie j.ulveri-ed \\\ a raor-
Suljihur jiroliahly din-s m.t enter int.. it- composition ('). It

. ed by >tl<>nur alkalis at 100°(.', and it also goes into
Dilution when treated with mineral acids at the same tem{«nuure ;
1'iit in the latter case the solution involves decomposition with tin-

much leucin (30 — 40 p.c.) and traces ••_'.". |

tvrosin when the acid employed j> sulphuric.- I: -n-.n- li\«ln>-
ehh.rii- acid be enijiloyed with chloride of xinc the same crystalline
•1'tained together with ammonia. gljOOOOll, and an
ami. I id. l>ut ii" ^lutamic or aspartii- acids.-'1 In this

respert it diH'er- fr»m botli ordinary j.roteids and gelatin, -inc.- the
r when ximilarh tiv.n.-.l \ i.-ld the ojulamic and a-;
•lyco. oil. and the latter never yield- tin- lea-t

huflllU' the ptltlefactlVe dec.i||||Mi-.i(|on of .-l.l-till J'lo-

-imilar t«> the above are obtained to^.-thej with *»\w |H-p

like -llh-taiice « Wild! tle.ited with -1lp-lhe.lt. -.1
with dilute hvdio, hlori. a. id at 1<HI (' «.l with \p-lli

1 ami alkaline medium re-.)

and uiiiler^'oe- a tin VG . haiiu'.-. during

'in--.! many »\ \\ho- ' reactioim are

'II f. pkvnol. <'>>«H IM M (JHH^).S no ( !Mtt.-ii.l.-n an.l

li M

« Wui. i.: I ; :i

86 ELASTIN. KERATIN.

analogous to those of the digestive products of proteids.1 It is
however as yet uncertain whether a true elastinpeptone can be
obtained ; it is more probable that during the digestion only some
of the primary substances (elastoses) make their appearance, since
they are completely precipitated by saturation with neutral am-
monium sulphate.2 Elastin is also rapidly corroded and dissolved
by the action of papai'n. (Gamgee.)

Hilger 3 has obtained a somewhat similar substance from the
shell and yolk of certain snakes' eggs.

Keratin.

Hair, nails, feathers, horn, and the epidermal structures in gen-
eral are composed chiefly of keratin, admixed however with small
quantities of proteids and other substances, from which it may be
freed by thorough extraction with water, alcohol, ether, and dilute
acids in succession, followed by digestion with pepsin and trypsin
(Kiihne) and a renewed washing with the above reagents. A con-
venient source which readily yields a pure product, owing to the
comparatively simple composition of the mother substance, is
found in the shell-membrane of ordinary eggs.4 The percentage
composition of keratin is in general allied to that of the true pro-
teids, but varies within somewhat wide limits according to the
source from which it has been prepared and particularly with re-
gard to the sulphur which it contains This latter element varies
in amount from -5 to 5'0 p.c. and leads to the formation of sul-
phides of the metal when keratin is dissolved in alkalis, Unlike
the proteids, gelatin and elastin, keratin is quite unaffected by the
most prolonged and active digestion with either pepsin or trypsin.
On the other hand, when decomposed at high temperatures by
either caustic baryta or strong hydrochloric acid, it yields large
quantities of leucin (15 p.c.), tyrosin (3 — 4 p.c.) and other pro-
ducts which are in general identical with those obtained by the
similar treatment of proteids.5 It is soluble in strong alkalis when
heated, and is further stated to be dissolved by prolonged treat-
ment with superheated water ; in the latter case a product is ob-
tained to which, since it somewhat resembles an albumose, the
name keratinose has been given, and which may now be digested
by means of pepsin.6 Further investigation in this direction is
however needed before any positive statements can be made re-
specting any truly digestive products derivable from keratin, or
indeed as to the characteristic differences of the keratins from
different sources.

1 Horbaczewski, loc. cit.

2 Chittenden and Hart, loc. cit.

3 Ber. d. deutscli. chem. Gesell. 1873, S. 166. See also Krukenberg, Vergl.-physiol.
Stud. ii R. 1. Abth. S. 68.

* Lindwall (Swedish). See abst. in Maly's Jahresber. 1881, S. 38.

* Horbaczewski, Sitzb. d. k. Akad. d. Win. Wien. Bd. LXXX. (1879), 2 Abth.
Juni-Hft. Bleunard, Compt. Rend. T. LXXXIX. (1879), p 953, T xc. (1880), p. 612.

'; Krukenberg, Sitzb. d. Jena, Gesell. f. Med. u. Xat.-wtss. 1886, S. 22.

(•INIMICAL I'.ASIS n|- Till: ANIMAL

Lin<l\vall ('r>f. <-,t.) d>-*i-ril»eil tin- format i-m "f an all.iimiiiatr an<l :i

.' album".-!-) .-ub-taiire during tin- t n-atnu-iit ••! k>
with <lilnt«- (1 — - p.*'.) run-tic -»da at digestion temperatures.

Neurokeratin.1

Whi-ii tli-- -ubstunce of the I'rain or any ma-s of inedullated

a is thoroughly extracted with water, alcohol. and ether. ami

then di^e-ted with jK-jisin and tryp-in in succession, a residue is

obtained which cloaelj leflemblea tin- ordinary keratins, and con-

stitutes al»out I"- — ll" l'.' . of the wholi- 1-; i it ha-

Q it> medullary constituents l>y alcohol and rthrr- This

nt-urokfi-atin, so nann-d from th, irom which it

is obtained. It i- characterised l.y its somewhat greater resistance

to those decomposing ;io,.nt< who-,.- action on keratin ha- been

iv described. The determination --t it- udotenoe in tissues

which are not oliviou>ly epidermal in the adult is of .•.•n-nlerahl»>

vological and morphological interest, since it throws some

light upon the developmental origin of the structures in which it

•M-nt or absent.-

Although it i- not found a- a constituent of any mammalian

tissue, this substance eom)N.<ex the ( hief part <>f the exoskelet-.n

rtebrates. It is hy man\ d as the animal

"^ue of cellulose of plants, and from this point of view it

possesses considerable morphological interest The m<>*\ < »\\-

••ni which it may l.e j-iepaied i> the . l.-an-ed

>.s or lolisterv Thi> i- tir>t thoroughly e\ti

with dilute hydr.M-hloiic a. id and caustic p .-r which it is

dcohol and ether, and may l.e tinalh
: l.y the action of j.ei inanimate of j.otasli.5 It
.liite aiiiiirphoii- -ul.stance. which oft.-n retain- the -!i.i]« of
iimeiit from which it ha- l.een pn- pa ret I. It i- m-olul.le
•her than concentrated min- i >n- h as

Milpi hydi'K hlc.ii. The immediate adiliti'

..l.al.ly reprecipitate- the chitin in an uualUJred

\Vhell heated \S 1th c,.||C.-ntlate,l hvdl'N hl"ll'- acid it is

:ito -ly. •o-amin and .1 I which the i

.il.l. Vtihattd. n,tt*rhitt..t*«l I ||. ... P. i I I-
Kulr ll"J- M ^X»l (I1*'"'). -s ttL

KM
* t ^teinbrfigK^ II-

XM

,.Av«.o/ rkfm.JU ii (l«> Hot Me abo 8ai.

lb<d i

H. /'A¥.,W J»hr. ir,2

ll,U*k ,i. /av.iW-/., i -. Aafl. I8SS, 8. 188.
Knik

88 CHITIN. NUCLEIN.

is the characteristic product. l A similar decomposition is observed
when sulphuric acidpis employed.

Glycosamin (C6H13N06). Crystallises from alcohol in fine needles,
is dextrorotatory, and reduces Fehling's fluid to the same extent as does
dextrose, but is not fermentable. By treatment with nitrous acid a
carbohydrate (C6H12O6) (?) is obtained which also reduces cupric
oxide, but is similarly unfermentable. This is doubtless the sub-
stance'which led to certain erroneous statements as to the production
of a true dextrose from chitiu.2

Nuclein. C29H49N9P3022 (?).

The nuclei of cells, both animal and vegetable, differ distinctly
in chemical composition from the remaining substance of the cells.
As a result of this difference it is possible to separate the nuclei
approximately by various means from the adjacent cell-substance.
The name nuclein is given to the material of which the nuclei or
parts of nuclei thus isolated chiefly consist. When, however, the
statements of the various authors who have dealt with nuclein
are compared with regard to the reactions, decompositions, and
more especially the percentage composition of their preparations,
it appears probable that 110 definite substance exists to which the
one name nuclein may be fitly applied. It may be that_the dis-
crepancies are due to the existence of several kinds_QJLjmclein ; 3
but this, is_as yet scarcely proved^and it is on the whole" more
probable that the different results of the various Authors must be
attributed to the impurity of the substance on which~they^op-
erated.4 In accordance with this viewTt is to be observed that
the percentage of phosphorus obtained in even the most reliable
analyses is stated to vary from 2'3 to 9'6 p.c.

After the above precautionary remarks we may now give an
account of the preparation and properties of the so-called nuclein.
When a mass of cells such as pus,5 yeast,6 nucleated red blood-
corpuscles,7 salmon-milt,8 or egg-yolk 9 is extracted with water and
dilute (-5 p.c.) hydrochloric acid, the cells are largely broken up

1 Ledderhose, loc. cit. and Ibid. Bd. iv. (1880), S. 139.

2 Berthelot, Compt. Rend. T. XLVII. (1858), p. 227. Journ. de la Phi/siol. T. n.
p. 577.

3 Hoppe-Seyler, Hdbch. d. physiol.-path. chem. Anal. (5 Auf.), 1883, S. 303.
Phi/siol. Chem. S. 85.

* Worm-Miiller, Pfluger's Arch. Bd. vm. (1874), S. 190. Bunge, Physiol.-pathol.
Chem. (Transl. by Wooldridge, 1890), p. 89

5 Miescher, Hoppe-Seyler s Med.-cliem. Untersuch. Hft. iv. (1871), S. 452. Hoppe-
Seyler, Ibid. S. 486.

"6 Hoppe-Seyler, Ibid. S. 500. Kossel, Zt. phi/siol. Chem. Bd. in. (1879), S. 284 ;
iv. (1880), S. 290; vn. (1883), S. 7. Unters. ub. d. Nudeme u. ihre Spaitunc/sprod .
Strassb. 1881. Loew, Pfluger's Arch. Bd. xxn. (1880), S. 62.

7 Bruntou, Jl. Anat. and Phi/stol. 2 Ser. Vol. in. 1869, p. 91. Pldsz, Hoppe-
Seyler's Med.-chem. Unters. Hft. iv. (1871), S 461.

"8 Miescher, Verhand. d. Natforsch. Geseil. Basel, Bd. vi. (1874), S. 138.

9 Miescher, Hoppe-Seyler's Med.-chem. Unters. Hft. iv. (1871), S. 502. Worm-
Miiller, loc. cit. »

BASIS OF Tin: ANIMAL r,«>i>\. 89

ami dissolved, ami the urn-lei separated from them. A further

purification i- obtained l.y treatment \\ith alcohol and ether ami

final digestion with jx-jisiii in a«-id solution, which does not

the substance of the nuclei.1 Tin- final residue thus obtained i-

••d with dilute acid, di--ol\ed in ak caustic soda,

j'itated liy hydriH-hlouc acid. ami wa-hed with water and

ali-iih"l. i by the above methods, nuclein jg ftp amorphous

sulistanee,jjeh in phosphorus. which is set fire a- pho-j.i

wJlen it js iKMtebTwitlTalkalis. At the same time some form of

TiTusually makes Its appearance, aa also do the crystalline

ances of the xanthin series, ^iinnin (?) and hyjM.xanthin.

when the nuclein is ln-at«-d with dilute mineral acids instead of

alkalis.1 It-appears, however, that the absolute and relative

aim iimt of the above possible products of its deconnmsition varies

with the source from which the nuclein is nhtflinml

I'mlt-r tli»- iiaim- 'adi-nin' K<>>,>cl lia- in««ri- n-ccntly ilf..-ril»cd a m-\v
base which lie ..l.tained \>\ tli«- di-c..inj...>it imi ••! miclrin fn«iii \ra-t-r.-lU
with dilute >.ul]iluiric arid and heat.1 It i> <Tv>talliin-, n-adily ->lulilr
in warm \vat«-r and can-tic alkali-, and \\ln-n treated with nitrous acid

IM.XHIitllin. (See lieloW.)

il N,-r-H20=C4H4X40-r-NlI1.

When egg- «>r -eniin-alliuniin is precipitated with iiii'tuph<>.sphi>ric
i phoaphorised substance is obtained which exhibit- many ..f the
:-tic nf nuclein.4 It di>e- imt, li"\ve\er. yield any
• •f tin- xanthin ha-e- when treated with acid-.''

Nucleo-albumins.

While th.- nuclei may be regarded as coinixised j.rim -ij.all\ ..i

the somewhat unsatisfactorily • li.n nucli-ins. tin-re is evi-

the existence6 of closely allied <ul'-tam •••- t., which, -in.-.-

'o be a compound of nuclein ami a pn-leid. the name

nucleo-all.uniin has been Driven. < Mir kn- "f these -ul'-

••8 is as yet rudimentary and imjH-rl'ei t. and sUl.se<|Uent

invest iu'ati'Mi mu-t d.-cid-- tln-ir real nature and their relat n-n-hip

to tin- nucleins.

The more characti-ri-tic reaetioux of the nucleo-alhumins m.iv
be- stated as foil lul.l.- in very dilute alkalis, the

> It *bo fwbto the action of iry|*in Bokar, Xi.f f*i»»J. Ckm. IU i .

,,«W. Cktm. Bd. r. (I- MII

WM -

./. rfrm C,wl\ 1885, So. 79. 1928. Xt ,.h*,i,J. <'/.,
8. 8&0 S<hiiull MM (1889), H. 432. Brahtw, /&•</. Bd. xiv. (1990),

naim, tirr. d d rhrm. f,fttH (|W»M|. S S9» fflilKvr'i Arrk. 11.1 M MI

/,y«o/. Ckrm. Bd xm. (1889). S. «9S.

• \\ xm .I-T4.. S 194.

90 NUCLEO-ALBUMINS.

readily reprecipitated by acetic acid ; and the constancy in prop-
erties of the product obtained by repeated solution and jprecipita-
tion seems to show that" they are not mere mixtures^ of nuclein
and proteicL Their beliaviour towards alkalis and acetic acid is
such as to lead to an easy confusion with the mucins. When
digested with pepsin they yield peptones and albumoses, and a
phosphorised residue which is in most respects identical with
nuclein, but does not appear to yield products of the xanthin
series. when decomposed bv acids. They are, like~the globulins,
precipitated i'rom solution by neutral salts, — the precipitate be-
coming swollen and slimy when the precipitant is sodium chloride
or magnesium sulphate, but not so when sodium sulphate is
employed.

It is impossible as yet to give any general method of separating
the nucleo-albumins from Jhe parent protoplasm. Eefefence to
the works quoted below is essential whendealing with any inves-
tigation as to their presence in particular cases.

When casein is digested with pepsin a residue of nuclein is
left; and it appears probable that casein may be in reality a com-
pound of this substance with a proteid, or that it is_a nuclep-
albunain.1 Egg-yolk is also considered by some authors to contain
nuclein as a nucleo-albumin, which is further stated to be ferru-
ginous,2 but by others the yolk is spoken of as yielding only
nuclein. Whichever view be correct, the nuclein of yolk does
not^yield members^ of the xanthin series by decomposition with
aciots,^^- resembling in this respect the nuclein from milk. .Syn-
ovia! fluid 4 and bile C?) 5 are also stated to contain substances
which, though resembling muciu in physical properties, are prob-
ably nucleo-albumins.

It may be pointed out that in some of the above cases the
micleo-albumin is obtained from non-nuclear_sources. When, on
the other hand, aqueous extracts are made of certain nucleated
structures, there is evidence that apart from the nuclein of the
nuclei, some nucleo-albumin is obtained whose presence is referred
rather to the cell-protoplasm than to the nuclei : this is the case
with liver-cells,6 the cells of the submaxillary gland,7 and lymph-
corpuscles.8 Non -nucleated red blood-corpuscles do not yield any
nucleo-albumin?""

1 Lubavin, Hoppe-Seyler's Med.-chem. Unters. Hf. iv. (1871), S. 463. See also
Ber. d. deutsch. chem. Gesell. 1877, S. 2238. Hammarsten, Zt. f. phi/siol. chem. Bd.
vii. (1883), S. 273.

2 Bunge, Zt. f. phi/siol. Chem. Bd. ix. (1885), S. 49. Sec also his Text-book,
p. 100.

3 Kossel, Arch. f. Pki/siol. Jabrg. 1885, S. 346.

4 Hammarsten (Swedish). See Abst. in Maly's Ber. Bd. xn. (1882), S. 480.

5 Paijkull, Zt. f. phi/siol. Chem. Bd. xu. (1888"), S. 196.

6 Pldsz, Pliige'r's Arch. Bd. vn. (1873), S. 371. Hammarsten, Ibid. Bd. xxxvi.
(1885), S. 351.

7 Hammarsten, Zt. f. phi/siot. Chem. Bd. xu. (1888), S. 174.

8 Halliburton, .//. of Phi/siol. Vol. TX. (1888), p. 235.

9 Halliburton and Friend, Ibid. Vol. x. (1889), p. 543.

< m:\iit AL BASIS OF mi: AMMAI. r.«>i>Y

CAEBOHYDRAT1

Certain member- only of tli. !as. h;i\,- b.-.-n f,,und

in tin- human body ; of these. the m-.-i important and wide

ill-Mr..-.- <;_diic,.se). with which

- in. ih.-.-. and milk--

it, which has the .saint- ]»-K .-nta^c ci.mpo-u n>n as a
C Hi.M and possesses a distinctly in

l.i-s.-d with tin- Carbohydrates. Tin- i- i] -in>-e

now known to l..-l"ic_' t«. th«- ben/.,'. below, p.

_'h the above-mentioned carbohydrates may 1»- d.-t.

ind srcn-tions .if the animal body. their j.j.

in the several cases is not so mu< h due to their introduction into

•••nil in which they tl. ;r as to their pio-

duction fn.m other meml.ers ..f the carbohydrate ui'.up <-\i-tnc_'

in fo- these i- -t,u. h, and it \\ill jx-rhaj.s conduce

: \i-ry l»rielly with thi- JMH-II'
stauce and some of the products of its de. ..

Till. SIAK. H <;i:..u-.
1. Starch «'.. II,, Og)..

Starch occurs characteristically in plants and is formed iii their
i parts under tin- determinant influence of the chloroj.hyll-

rorj-U-cles. The e\;|.'t Illode of its formation is hoWe\

:n plant-tissues in tin- form of Drains which

:id s||M]M- ac. •oidlliL: to the plant, hut which possess

:ion ch.ua. t.-ristic ..f e\hihitinx a stratitied strii'-tuiv.

which is much more marked in -..me cases < potato-stnrch ) than

in oth.-is. and the phenomena of double-refraction when examined

in iH.lari-.-d 1 « idered as a \\lmle the Drains app.

Mipos.-d , 1 'stances of which the chief both in i|uan-

iid importance is call.-d ^ranulose and the other

Ids the blue colour cb.M. '.IP b

on the addition of iodine, may be dissolved out by the

:n-4 a c.-llulosic skeleton ..f tb-

Tllis so-called celllllos,. is II": ll \Mtll old

cellulose, &8 shown by its ready solubility in several n-;i
which do not di<-.,lve the latt-i \\li-n tr.-ated \\ith boiling

tin- Drains ^\\,-}\ up and finally burst, yielding a un
\19 maSS of starch-paste of which tin- < bl'-t lit is the

1 I li«- r.irl«.»i\<lrml«i nw v.-ry fully tn«atr<| in Tollcnn' /A//^A. >l KMrmkydratr.
BmiUa. I**- Cfciiarf, Pi 5«7 H •*).

|H-rl.;i|.. -.in.- oliRht doaht m* to thin iitetitilv, l-w-i IM* •

i|.|.;ip-nt liff. ronce in the » lextroM MM t«M

lii-.l from .linlM-tir urin.' ( S«T Mill- r
« Bn.wn .-xn-l II MC V.-l \\\\ (1-T'.»). |» «N. Lfcbi/c'» A mm. Bd.

CXC1X >

92 STARCH.

granulose. The mass thus obtained cannot be regarded as a true
solution of starch, and it filters with extraordinary difficulty,
leaving a gelatinous residue on the filter, however dilute the
starch-paste may be which is used for the filtration. When sub-
jected to hydrolytic agencies such as superheated water, dilute
acids and enzymes the starch passes rapidly into true solution,
yielding at the same time a series of successive products to be
described below.

Many attempts have been made to assign a definite formula to
this substance. The outcome of these is that the molecule of
starch is certainly not C6HioO5 but n (C6Hio05), where n is not
less than 5 or 6 and is probably much larger.

When starch is converted into dextrose by treatment with dilute
boiling sulphuric acid, it is found that 99 parts of starch yield 108 of
dextrose.1 Thus

[(C6H1005)6 -f H20] (mol. = 990) + 5H20 = 6C6H12O6 (mol. = 1080).

Most recently, and in continuation of previous researches, it has
been shown, by an application of Raoult's method, that the molecule
of soluble starch must probably be represented by the formula 5 (C12
H200io)2o-2 Formulae based on analyses of the supposed compound of
starch with iodine are probably valueless, since there is but little rea-
son to suppose that any such definite compound exists.

2. Soluble Starch (Amylodextrin) (C6H1005)n.

When starch-paste, heated to 40° C. on a water-bath, is digested
with a small amount of saliva and the whole stirred so as to
effect a thorough mixture of the two, the paste rapidly loses its
opalescent appearance, becoming limpid and clear like water:
the moment this change has taken place the digesting mixture
should be boiled to cut short the further action of the ptyalin.
The fluid thus obtained contains the first product of the hydrolysis
of starch to which the name of ' soluble starch ' has been given.
Its solution filters readily, and the filtrate yields with iodine the
pure blue characteristic of the original unaltered starch. On the
addition of an excess of alcohol the soluble-starch is precipitated,
the precipitate after drying being but little soluble in cold water
although it readily dissolves in water at 60 — 70° C. It also
yields a characteristic precipitate with tannic acid, and differs in
this respect from the dextrins.3 It is dextrorotatory

(a)D=:-f- 194-8° [(«),= 216°],
and does not reduce Fehling's fluid. The same substance may be

1 Sachsse, Sitzb. d. Natforsch. Gesell. Leipzig, 1877. Chem. Centralb. 1877,
No. 46.

2 Brown and Morris, Jl. Chem. Soc. Vol. LV. July, 1889, p. 462.

3 Griessmayer, Anna/, d. Chem. Bd. CLX. (1871),'S. 40.

CHK.MICA!. BASIS "1 i Hi: ANIMAL 1:«>DV.
>imilarly obtain* ,1 l.y tin- limited action of malt-extract or pau-

The dextrins i< II < >,)„.«

When the hydn-lytie action of saliva, malt >i jum i

•an-h-pa-te is prolonged, tin- lir-t-fornied soluble-tan li

idly changed into a nmnbei • to which

il name of dextrin is LJIVII. These pn»lii' t- an- inter

'•n soluble-starch ami th> A'hieh result

'inplete hydrolysis of starch, and are probably v.-iv num«-r-
•he similarity in tin- pn>|>erties of tin- siicrr-MVely f<

rini,' their >eparation and char nn-ly

:lt. They .in; all precipitable by alcohol, and differ fr-.m
.Ide-.-turch in yielding no precipitate with tanni-- acid.

If during the earlier stages of the h\dio-
i-paste, si; jiortimis of the solution he t

I iy the addition of iodine, it may he observed that the pure Mm-
whi-'h it yields at first passes gradually through violet ami
di-h-violet to ivddish-hrown, the latter colour being supposedly
due to tl. the solution of erythrodextrin, whence the

I '.ut little is definitely known i.f tins dextrin as a chemical
individual, its chief characteristic Kein^ the colour it yields with
violet observed during the earlier ^ta^e* of ii\dro-
is due to an admixture of the Idue due t" so]uMr--tan -h
with the iv d of the erythrodextrin.

i. -\trin, whii-li i> MTV impure, omtainini; de\t r..-
•iitly unaltrrt-il .-.tar.-li. iiMiall y \ i.-l.; ng red colour*-

he atlilition of

When, during the ]>,;,!,,.

• lysis of starch under ordinary conditions, the addition ,,f

i'Mline ceases to give any colouration, the fluid now contains much

r together with a con-id. -rahle hut variable proj.ortion of this

ii has received its name from it- U'haviour t"\\anl-

.••IdiiiL' no colour with this rea : • I* , t'

ned during ' "/•'/ artificial di^«--ti ...... f

ii \\ith sjiliva ( -be 8epa'

its .solution by c-oncentration airl the addition of an excess
of alcohol. A- thus prepared it \\ith much adl

<ise (see below), from which it cannot 1» | freed by

wash: h alcohol or by successive solution in water and

Mtion with alcohol A partial separation ma\ IK; ob-

ible raloe of * in certain CM6§, ••• Brown and Morrin. eil. »*f>

ftwot. Cktm. Bd. ir. (I MO), S

.

94 DEXTRIN.

tained by fermenting off the sugar with yeast (O'Sullivan) or by
dialysis, since dextrin is non-diffusible. If however the mixture
be warmed with a slight excess of mercuric cyanide and caustic
soda, the whole of the sugar is destroyed in reducing the mercuric
salt, leaving in solution a non-reducing dextrin.1 As thus pre-
pared it appears to possess a constant dextrorotatory power (a)D =
194-8° [(a)j= 216°], and as precipitated by alcohol is a white
amorphous powder very soluble in water.

Maltodextrin.' This substance is described as appearing during
the earlier stages of a limited hydrolysis of starch-paste with diastase,
and it may perhaps similarly occur when saliva or pancreatic juice
is employed. It differs from the dextriiis previously described as
follows. It is more soluble in alcohol and distinctly diffusible; it
reduces Fehling's fluid, has a lower specific rotatory power

and is completely convertible into maltose by the further action of
diastase. It will therefore not be found among the products of a pro-
longed hydrolytic degradation of starch.

When starch-paste is hydrolysed outside the body with diastase
or with animal enzymes some dextrin is always obtained together
with the sugars which make their characteristic appearance dur-
ing the process. Considerable difference of opinion has been
expressed as to the possibility of a complete conversion of these
dextrins into sugar by the renewed action of the enzyme upon
them after their isolation, but the balance of opinion appears to
be that the conversion is in many cases either impossible or takes
place with slowness and difficulty. If this is so then the course
of an artificial and normal digestion of starch is, as regards the
final products, very different in the two cases, for there is no evi-
dence that in the body any carbohydrate is absorbed as dextrin
from the alimentary canal. The conditions however under which
the two digestions are carried on are markedly different, and
more particularly with respect to the very complete and continu-
ous removal of digestive products in the natural process as com-
pared with their accumulation in an ordinary artificial digestion.
Now there is no doubt that the products of an enzymic hydrolysis
are inhibitory to the further action of the enzyme,3 and this is
probably the cause of the observed difference. In accordance
with this, if a starch digestion be carried on in an efficient dia-
lyser, the starch may be practically entirely converted into sugar,
the small residue of dextrin being due rather to inefficiency of the

1 It should be carefully borne in mind that probably many forms of dextrin exist,
especially among the earlier products of hydrolysis, none of Avhich give any colour-
ation with iodine.

2 Brown and Morris, loc. cit. p. 561.

3 See also Lindet, Compt. Rend. T. cvui. (1889), p. 453, with special reference to
maltose.

P.ASIS < >F Till: AM.MAI. i:«»hV. 95

apparatus tli.ui t.. th«- chemical resistance of tin- dextrins to com-
;oii into su^'ur.1 Although this statement is leased
upon e\jHTim--i;i- in. i.l'' \\ith saliva. there is no reason to suppose
that tin; same will n<»t hold «MMM! in tin- <-a.se of tin- pan< ;
jui'-e l.y whose action tic arl.ohydrat. u of thr

Ion. We shall then-fop- n..; AP-M^ j,,

eluding that in tin- animal \» h is completely •

into -uijar pn-vious ; lion, and if this I..- thr cast- the

i' thf i»hysiolo^ist in thr primary PPM! arts of si
is becomes very smaK far as a study of

icts is essential to tin- rln.-idation of thr prol.abl.- mol,
.d -tru« -turr of thr parent-substance.

\Vh tr.l with dilutr lioilinjF acids, the \w»\

which 'n. nurd in rapid succession,

liolr Iwin^ finally convrrtril into dextroae.*

I Animal-gum < '.jH^O.o^HjO) <

s is, accord i i iu' to I.andwrhr, a form of carliohydrat.- which
l.y thr proliin.jrd ai-tion MI >n]H-rhratr.l water
tnd mucoiis glands, and is found also in mil!,
urinr. It has already IM-I-II l«riefly dewrihcd al.o\.- < ]» 7'.' ) v.

:ct«M-istii-s havr U-en jjiven. To these- may ln-re be
! that it yi.dds no colouration with iodine, is very frrl.ly
.ttory and appears to form a compound with < upric
: the latter is obtained whrn can-tic -..da and sulph.
copj- l.-d to its solution, and may 1..- n-,-d for the separa-

tion of anim.tl -L'uin from urine.8

Qlycogen t« ,H:,« >.)..

This su 'lom a pun-ly chemical point of •

•ly lik-' M.ii h. lip -inularity lirim; mo>t mark, d \\li.-n the

nlllctS of til'

Mil fair in thr animal I..N| l.ut little

doul.t that it may be regarded from thr ph\>i..l..-i. al side as truly

ninial anali^'iir ..f the vegetal'' -u'-h it is fre-

• inrntly spokrn of as • animal -tar. li ' It N 1 as a

iturnt of th«- liver l.y In-rnard ' and. simultaneously though
inde|H-ndrntly. !.\ EenMO.1 In more r««<-eiit i iiaa been

found to 'ies in iijiiny tissues of the

M V,,l M IH90). p. SM.

• «-o W.-hl. ll'r ,1 .1. rktm. f^N.//.. J»hrk' XXMI (I*-K)|. S 9101.
• I.., «., IS85. S. .169. See •!*> Wedeaaki.

ytool. Chrm. H.I xn: \*3.

MM (1W7), |. 57». Gat.
HtMom. 1-

\rtk.f.palk. .Imif. M. Pkytiol. Bd. xi (l»57), 8. 39».

96 GLYCOGEN.

adult body, as for instance the muscles,1 also in white blood- and
pus-corpuscles 2 and other contractile protoplasm (Aethalium sep-
ticum),3 in which its presence is significantly connected with their
specialised activity, not as an essential, as some have supposed,
but as a convenient accessory. It is also conspicuously found in
the tissues of the embryo before the liver is functionally active,4
and is present in large quantities in many rnollusks, as for in-
stance the common oyster5 (9'5 p.c.).

It is at present uncertain whether the glycogen obtainable from
muscles is identical with that of the liver. It is stated that muscle-
glycogen yields a distinctly more purple colour with iodine than does
liver glycogen,6 but their identity is still an. open question.7

Preparation of glycogen. The liver of an animal (rabbit or
dog), previously fed with copious meals of carbohydrate, is excised
as rapidly as possible, cut into small pieces, and thrown into an
excess of boiling water, at least 400 c.c. to each 100 gr. of liver.
After being boiled for a short time, the pieces are removed, ground
up as finely as possible in a mortar with sand or powdered glass,
returned to the original water, and boiled again for some time. On
faintly acidulating the boiling mass with acetic acid a large amount
of the proteid matter in solution is coagulated and may be removed
by filtration. The filtrate is now rapidly cooled, and the proteids
finally and completely precipitated by the alternating addition of
hydrochloric acid and of a solution of the double iodide of mer-
cury and potassium (Briicke's reagent),8 as long as any precipi-
tate is formed. The precipitated proteids are again removed by
filtration, the glycogen precipitated by the addition of two vol-
umes of 95 p.c. alcohol,9 collected on a filter, washed thoroughly
with 60 p.c. spirit, and finally with absolute alcohol and ether
(Briicke).10

The above method suffices in cases where there is much glycogen
present and no quantitative result is desired ; as a matter of fact
there is a not inconsiderable loss during its application. The ac-
curate determination of glycogen in tissues is a matter of some
difficulty, primarily because it is not easy to ensure the complete
separation into solution of the glycogen from the tissue, and sec-

1 Nasse, Pfluger's Arch. Bd. ii. (1869), S. 97.

2 Hoppe-Seyler, Med.-chem. Unters. Hft. 4 (1871), S. 486.

8 See refs. on p. 4. Also Kiihne, Physiol. Chem. 1868, S. 334.
4 See Preyer's Speeialle Physiol. d. Embryo, Leipzig, 1885, S. 271.
* Bizio, Compt. Rend. T. LX'TI. (1866), p. 675.

6 Naunyn, Arch. f. exp. Path. u. Pharm. Bd. in. (1875), S. 97. Boehm n.
Hoffmann, Ibid. Bd. x. (1878), S. 12. Nasse, Pfluger's Arch. Bd. xiv. (1877), S. 479.

7 See also Musculus u. v. Mering, Zt.f. physiol. Chem. Bd. n. (1878), S. 417.

8 Prepared by saturating a boiling 10 p.c. soluti of potassium iodide with
freshly precipitated iodide of mercury ; on cooling, th. is filtered and the filtrate
employed as directed.

" So that the mixture contains 60 p.c. of alcohol.
1° Sitzb. d. Wien. Akad. Bd. LXIII. (1871), 2 Abth. Feb.-Hft., S. 214.

CHKMICAL I'.A Till; AM.MAJ, JinDV. •..;

ondarily owin^ l<t a possible loss during the pn-cip italic. n and i.-
1 i.f tin- proteids with wliifli it i.-ah\.i\s l.tr^.-l\ contaminated.

The lirst ditliculty may be L • TOUM.- \>\ the addition of caustic

h which di-solve-. tli.' ti-*ui- fragment... and thus liheratex the

al-« by .-\tra.-ti. .11 in a 1'apin's digester,1 in which ra-e the

.solution i> a^'ain \ery compl

is, when pure, an auiorphus whit.- jMiwd.-r, readily
sulut»l'- in ss.it<-i with which it yields a solution which i> u-u-
ally, luit in>t alway>. njulcsccnt. This solution contains n»
which are visible under the inicr..>, ,.)»• and tilt«T>
!y without diminution of the ..j... ; the latter m.iv

!y removed by the addition of free alkalis or arctic acid.
I'nder ordinary conditions it is readily precipitated I'.v alcohol
when the mixture contains 60 }>.«•. of the precipitant, hut if
i in 0'5 — 1*0 p.c. solution, even an excess of absolute
alcohol is stated not to cause its precipitation. The precipita-
tion tikes place at once on the addition of a trace of sodium
ohlori

.1 characteristic port-wine colouration with iodine, which

does not howe\er distinguish it from eiythrodextrin since in both

cases the colour, contrary to the older and current statements, dis-

apjH-ars mi wanning and returns on cooling. On the other hand,

ire not precipitated by 60 p.c. alcohol, even the m-.^t

.i'lc of these substances requiring at least 8f> p.c. of alco-

hol for their precipitation, ami Usually more. It appears that

the reaction with iodine is most delicate in presence of sodium

chloride.4

Aqueous solutions of ^l\ro._ren are strongly dextrorotatory, but
•atements as to its sjH-citic rotatoi must be received

with caution. [Boehm .///./ //..//«//«// 6"(a)n = -h226-7°. h
in •«» ]...-. solution (a)D = +203-5° to + 225-6°. Landwehr" (a)D =
-r-213-30].

Tht' iiioK-i'iilar ina^iiitiide <»f ^lyi-i.^.-n. like that "1 >taivh, is un-

M^ pri'cipitati-s with taiinic acid. al><> \\itli

calcium alid luiriniii hydrati-.0 and \\itli basic lead

h. .\\.-\i-r !"• pl.i.-.-il <»n the determination "t tlie
:n an analysis of thettv

' H.-hm. I-flup-r1- ^^^l (IMO), x

n fully treated by KuU in Zt.f. Bid. 1

S. 161. whoro al»o th« lit«»rnt |.r«h«i»iirelr qootad. S ••• n.l.liti..n»lly N

«TII (1886] > MJ, and \M^

Jaknttt. 1887, 8. SO4. ( 'nuner. #./. Biot.
67.

» K -m. GtMil. Jahrfc- I8«2. S. 1300.

. ! XXXM. (1M6V V 485.

» A,. > 4W.

• PflU^er - 8ft.

vui. (|HH;

.I«M>. rttiu:- '•"*

7

98 GLYCOGEN.

The hydrolytic products obtained by the action of enzymes and
dilute boiling acids on glycogen have not been as fully studied as
they have in the case of starch, but the general course of the de-
composition is the same in both cases. Thus when treated with
dilute mineral acids at 100°C., the opalescence disappears, some,
dextrin is formed en passant, and finally the solution contains
only dextrose.1 On the addition of saliva or pancreatic juice to
a solution of glycogen at 40°, the first change observed is an •im-
mediate disappearance of the opalescence, followed by a rapid con-
version into some form of dextrin and a considerable proportion
of a sugar which is apparently identical with maltose.2 Some
trace of dextrose may perhaps at the same time be formed.

The change which glycogen in the liver undergoes post-mortem
and presumably also during life is strikingly different from that
which has been described above. Whereas by ordinary enzyinic
hydrolysis, maltose is the chief final product obtained, there is
now no doubt that in the liver little if any maltose is formed, the
so-called liver-sugar being apparently identical with true dex-
trose. This fact throws considerable light on the mode of con-
version of glycogen into sugar by the liver. It has been most
usually taught that this conversion is due to some fermentative
action ; if this were so then the enzyme which is the active agent
must be possessed of powers differing from those of most other
enzymes since it forms dextrose and not maltose. But as a mat-
ter of fact it does not appear possible to extract any appreciable
quantity of enzyme from the liver, and if a trace is obtained it is
of one whose action on starch and glycogen yields chiefly maltose
and not dextrose. It is hence a legitimate conclusion that the
conversion of glycogen into sugar by the liver is the outcome of
the specific metabolic activity of the hepatic cells, and not of any
enzymic action.3 It is also significantly probable, from what has
been already said (see above, p. 59), that the liver receives its
carbohydrates supplied in the form of dextrose, and there is no
doubt that diabetic sugar is closely related to, if not identical
with, true dextrose.

The dextrin which some observers have obtained from muscles is
not to be regarded as a specific constituent, but as formed from their
glycogen by some post-mortem change. Horse-flesh is peculiarly rich
in glycogen, and it was chiefly from this source that dextrin was ob-
tained in large amount.4

1 Maydl, Zt. f. physiol. Chem. Bd. HI. (1879), S. 194. Kiilz u. Borntrager,
Pfluger's Arch. Bd. xxiv. (1881), S. 28. Seegen, Ibid. Bd. xix. (1879), S. 106.

2 Musculus u. v. Mering, Zt. f. physiol. Chem. Bd. u. (1878), S. 403. Seegen,
loc. cit. Kiilz, Pfluger's Arch. Bd. xxiv. (1881), S. 81.

3 Eves. JL of Physiol. Vol. v. (1884), p. 342 (contains lit. to date). See more
recently Langendorff, Arch. f. Physiol. 1886. Suppl.-Bd. S. 277. Panormow, Klin.
Wochenb. 1887, No. 27. Dastre, Arch, de Physiol (4) T. i. (1888), p. 69.

* Limpricht, Liebig's Ann. Bd. cxxxm. (1865), S. 293.

< m:\ncAi. BASIS OF itu: ANIMAL r.nu^.

... CeUulose (( ll •

Although tiu«- cellulose is never fciiii<l as a constituent of the
animal ti.-Mi.--.it possesses no inconsiderable interest fur tin- ph\--

-t in \i.-\\ .-I ill-- t'.i.-t tliat in the hcrhivora a lar^e amount

: .iinl ,i: Q that It does nut iva;

Mally in the excreta. In man also there i- n« doul.t that

•-tii'ii and absorption of cellulose may occur, tin- pi
In-iii^ facilitated by tin- tact that in those more succulent \.
and fruits in which it is taken by man, the cell-wall
comparatively non-liu'nitied and hence more easily acted ii]mn bv
the dL'e-ti\e agents.

Tin- li^niticati-.n ..f tin- ei-11-wull \\liirli has taken place in th.-.-e

which tin- name '\\cn.dy' i> ordinarilv applied i- due

, -uli-taiier called li^nin. \"»-ry littl.- i> kii"\\n "f

i cli.-inical indiviilual: it appears t.. c.nitain nmre rarlH.n than

.-(•llulii>e. [ts discrimination from oelluloM dapeadi <HI th<

that it i- e..l"iin-il yi-ll..\\ l.y t In- act i..n ..f Seluil/.-'s n-:i^t-ut i -•-.- \ >,-},, \\ )
and d.-t-p l»rn\n l.\ that <•! iodine and sulphuric nciil. \Vln-n t:
with pldi.p.^'liu-in an<l .-tmii;,' liydr"chl.>ric acid it turn- n-d : it is
4-nlniired hri^ht \t-ll.iu l.y the ;icti«n «.f aniline -ulphati- ..r i-)il<>rid<>
anil th. -id.-.-. |iirnt additii.n «f hyilr'.clil»ric acid.

l-'uith'-r. although ;,t present but little is known as to how the
.-llulosu is brought about in the aliment.

.dellCe of the pos.-ible e\i-ten<'c of a -]

me t» whose solvent action the change i- din-. I'.ut as yet
ta almost entirely upon exju-riineiits with and

ilde organism-.1

•--.1 to -tai.-h and iii -ome cases (Date, I'hyt.-le-
phas) pl.r. it of a Store < ••• material, beiii'_' di--

.Miably b\ -..in.- en/yni'-. and utilised during ,uermin
i .-ll-wall of \.-ir,. table cell- is coni|K)sed of cellulose, which in
!1- i- pun- and muel. -i-tant t- jent-

the ulder c.-H- \\1|. i .Hid

-ted with oth.-r -ub-tan-e-. When pure it is soluble in OIL-
reagent only which is a solution of hy.i

ii ammonia- Wh-n ti..it.-d \\ith -tmn^ sulphuric
-•Ihilose is changed and yi.-ld- a -ub>tan«'e which 18 col-

observed on the addition

\.l r MI (1890), p. 497. CooUiw
•lire.

pond a« T l|.h»t«of copper in flotation. t<> whk-h MIIM am mot

fhl.iri.l.« has U-rn a.l.l.-l. i-« j.r--. ipiUUed with rstutir »ud« : the hjdrmtfd rnpn
I'taincd U wwihed, ami diMolved to Mtnntkn in SO p.c. mmrooi
- prepare! l.y (.

• »n of the copper being effected hr drawing • current of air through the floid
in which the taming* are immerMd. (CroM and Bermn. Cr//«/ow, ISM. p. 6 )

100 CELLULOSE.

of iodine after the action of chloride of zinc (Schulze's reagent).1
These reactions afford a means of detecting cellulose.

By treatment with strong sulphuric acid cellulose may be dis-
solved with the formation of a dextrin-like product: on diluting
with water and boiling it is finally converted into a sugar which
is apparently identical with dextrose.2

As already stated cellulose is undoubtedly digested in the ali-
mentary canal more especially of herbivora, but also to a less ex-
tent of man.3 We know however but little of the real nature of
the digestive processes which are involved in this. Two views
are open to us. It has long been known that under the influence
of putrefactive organisms, as from sewer-slime, cellulose is disin-
tegrated and dissolved with an evolution of marsh-gas and car-
bonic anhydride.4 This is usually known as the marsh-gas fer-
mentation of cellulose. In accordance with this it is possible that
a similar factor is at work in the alimentary canal, more especially
of the herbivora with their large caecum in which the food stays
for some time. This accords with the marked occurrence of marsh-
gas in the gases of their intestine and its increased presence in the
intestine of man when largely fed with a vegetable diet.5 On the
other hand it is possible that the digestion may turn out to be due
to some definite enzyme,6 but as yet no such enzyme has been
obtained with certainty from the secretions or tissues of the
alimentary canal. Possibly the organisms which as stated above
can cause the decomposition of cellulose do so by means of some
specific enzyme. It remains for further research to throw a
decisive light on the possibilities to which attention has been
drawn.

Some difference of opinion exists as to the physiological sig-
nificance of cellulose digestion. There is at present no evidence
that the cellulose of food as such is a food-stuff in the same sense
that starch is. As far as the existing evidence goes we shall not
perhaps be far wrong in supposing that cellulose digestion is
primarily important as liberating from the cells the true food-
stuffs which they contain. At the same time the products formed

1 The reagent used is prepared as follows. Iodine is dissolved to saturation in a
solution of chloride of zinc, sp.gr. 148, to which 6 parts of potassium iodide have been
added. See also Bower, Pract. Bot., 1891, p. 506. Cross and Bevan (loc. cit. p. 7)
recommend the following. Zinc is dissolved to saturation in hydrochloric acid, and
the solution evaporated to sp.gr. 2-0 ; to 90 parts of this solution are added 6 parts
of potassium iodide dissolved in 10 parts of water, and in this solution iodine is finally
dissolved to saturation.

2 Flechsig, Zt. f. Physiol. Chem. Bd. vu. (1883), S. 523.

3 Bunge, Phi/siol. and Path. Chem. 1890, pp. 81, 191.

4 Popoff, Pfl'iiger's Arch. Bd. x. (1875), S. 113. Van Tieghem, Compt. Rend. T.
LXXXVIII. (1879), p. 205. Hoppe-Seyler, Ber. d. d. ckem. Gesell. Jahrg. xvi. (1883),
S. 122. Zt.f. physiol. Ch. Bd. x. (1886), Sn. 201, 401.

6 Tappeiner, Ber. d. d. chem. Gesell. Jahrg. xv. (1882), S. 999 ; xvi. Sn. 1734, 1740.
Zt.f. Bid. Bd. xx. (1884), S. 52. (Gives literature to date.) Ibid. S. 215; xxiv.
(1888), S. 105.

6 Hofmeister, Arch.f. Thierheilk. Bd. vn. (1881), S. 169; xi. (1885), Hfte. 1, 2.

( HKMICAL j;AMS OF TIIK ANIMAL BODY. 1"!

during the solution of the cellulose may, if they are oxidised in
the body, contribute to its energy and thus be of u>

Tunicin i < ',; H J0« >,)„.

This substance constitutes the chief part of the mantle of Tuni-
cate (Ascidians) and appears to have been first described 1
Schmidt.- who drew attention to its similarity t«> vegetable cellu-
lose. This view was confirmed by Berthelot, \vli< . h< >\\
that it is much more resistant to the action of at ids than :
cellulose/1 In other respects the two may be regarded as i<leir

• >nlam-e with this it is found that tunirin is soluble in
Bohweuer's reagent (see above), from which it may be reprecip-
'. by hydrochloric acid and thus purified. It is further
coloun-d blue by the addition of iodine after preliminary b
nn-nt \vitli sulphuric acid. It is soluble in concentrated sulphuric
aci.l. ami if uat.-r l»c added to this solution ami it be boiled for
>ome time, a su^ar which is apparently identical with ordinary
dextrose is obtained.4

1 in the pure form by treating the mantles for some
days with water in a Papin's digester, then in succession with
boiling dilute hydrochloric acid, strong caustic potash and water.
A-, thus obtained it retains the form of the parent tissue.

THK SiuARS.

The researches i,f Kmil Fischer have thrown a Hood of li^-ht on

•I t he sugars.'"' In jthenyl-hydraxin <',H,.NHNII

i reagent which forms with the sugars compounds

known as hyd: md osazones. These provided for tin- first

time by their various solubilities, melting-pointt, and rotatory

l\iate means of detecting, sepa n.l char.-

:he several members of this class of carbohydrates. Hence
possible to investigate the occurrence of sugars among

•••1 ]'l"i!ucts of the reactions employed III the.

•H! -\llthetir ppnllict io||. It W..ul,l

b- -re to enter into the details !

.iv that he h.is ni>t m.-i .tlieti-*ed both

i < >., ti,.. ahore Me Webke, Cktm. Ctrtra, - b*rjc

•1.1. W«i»k .olM a. FtecMf.

I.M (1S46), > -IIH.
I 149.

•/. d. ektm. OttA I8T», S. 1938. Compt. fa»d. T I\\M\
755. Seh&fer, UeWg'* A* •> .S .312.

• Fiwh-r HM given » cood«BMd accon • wurhM. »

- ,l..-h*m '-..-//. J»hrfc xxili. (IWK)), ^ .'IU •>( tin* an
/ Ckt i«90, p. ISSS. KM abo SchaUt. ll.oi. Ctntralb.

102 DEXTROSE.

dextrose and Itevulose, and definitely established the fact that they
an- respectively an aldehyde and ketone of the hexacid alcohol
C6H8(OH)C, but has in addition succeeded in producing artificial
sugars containing seven, eight, and nine carbon atoms.1 In connec-
tion with the latter an interesting question . arises as to the prob-
able effects on animal metabolism of their introduction into the
body instead of the natural sugars.

The osazones. The compounds of the sugars to which this
generic name is applied are formed when solutions of the sugars
are warmed for some time on a water-bath with phenyl-hydrazin
and dilute acetic acid, and separate out either in an amorphous or
crystalline state. Their formation takes place in two stages. In
the first the sugar combines, as do the aldehydes and ketones, with
one molecule of the base to form a compound which is in most cases
readily soluble and is known as a hydrazone. In the second stage
the first-formed hydrazone is oxidised by the excess of pheuyl-
hydrazin present, and the substance thus produced unites with
another molecule of the base to form the osazone. As already
stated the osazones of the various sugars differ characteristically
in their solubilities, melting-points, and rotatory powers. They
hence afford an invaluable means not only for detecting and iso-
lating the sugars, but also for discriminating between sugars whose
optical and reducing powers may afford an insufficient distinction.
Further, in some cases the osazones have provided a means of
ascertaining the molecular formula of certain sugars and of deter-
mining the constitution of others. The characteristic properties
of the several osazones are given below under the respective sugars.

THE DEXTROSE GROUP.
1. Dextrose (Glucose, Grape-sugar).

C6H1206. [COH-(CH.OH)4-CH2.OH].

Is found in minute but fairly constant quantities as a normal
constituent of blood, lymph, and chyle. Its occurrence in the
liver has been already referred to (§ 465) in connection with
diabetes, a disease which is characterised by the large amount of
dextrose which is present in the blood and the still larger amount
in the urine. The question whether dextrose is a normal constit-
uent of urine has led to much dispute, but it now appears
probable that it is present in minute amounts.2 The experimental
difficulties of detecting traces of sugar in this excretion are con-
siderable. There is no dextrose normally in bile.

1 Fischer u. Passmore. Ber. d. d. chem. Gesell. Jahrg. xxm. (1890), S. 2226.

2 For literature and results see Neubauer u. Vogel, Analyse des Hams (Ed. ix.
1890), S. 41.

CHKMICAL BASIS < U • THK ANIMAL ln»l>Y.

The probability that it is as dextrose that tin- carl >« 'hydrates are
finally ahs.'H'cd from the alimentary canal ha> all-

i to p. .".'.». This c.inv>p,,mU \\ith tin- t'ai-t that
is tin- most ivadily assimilable i-.m compara-

tive injections of tin- various sugars int<> the hhtod-vessels ami
rvations on their subsequent appearance in the urii

When pa iv. dextrose is colourless and crystallises from it-
aqueous s.>luti"ii in six-sided tables or prisms, often agglcum
int-) warty lumps. The crystals will dissolve in tln-ir own weight
of cold watvr. requiring however some time for tin- process; they
ivadily soluble in hot water. I».-\trose is somewhat
sparingly soluble in cold ethyl-alcohol, more soluble in warm;
slowly soluble, hut in considerable quantity, in in«-thyl-al«-ohol,
and insoluble in ether.

It may l.e prepared by eom-rntratin.i: dial.eti«- urine until it
Yields crystals of <l«-xtro>r: these are then purified li\ i..i\-t,il-
lisaticn fr.im methyl-alcohol. It may al-o In- eonvcniently \<\-<--
par.'d l>y thi- action of hydrochloric acid on canr-M. 'l\vd

in alcohol.1 A freshly prepared cold aqueous solution of de\
possesses a specific rotatory powvr for monochromatic y.-llcw
Qght "f (a):, =-f~100°- This rapidly falls, especially on \varm-
in.i:. until it may \>e taken as (a),, =-f-52'50 for solutions which
do not contain more than 10 p.c. of the sugar. The rotation is
however dependent on the concentration of the solution being
with very dilute solutions.

Tin- s|..cilic r.'!:it..rv |>»u«-r «\ a >ul»taiic.- i- tin- unmuiit.
in ili'-jri-i--. l-v wliii-li tin- plain- «>f pnlari»-il lij^lit is rntatdi by a solu-
\\lii.-h i-.uitaiii> 1 ^rain "f tin- >nli>tanr«- in each 1 c.c. \\li-
in a la\i-r 1 ilcin. in tlii- >inrc tin- atinniiit «.f r^1

in any 'jivi-ii case 18 ilin-i-tly pr<'p.-rl imial t-- tin- >:

. al-' t.i tin- ««-ij:lit .if Mil-tan.-.- in .siiluti.ui ami tin-
.f tin- tiiii.l lay.-r in uliidi it i* examined we have

(a) = -' . \\ln-n- (.1) i- tin- .-p.-.-il

power. /- i- tli.- u.'i^ht in -nun- ••! tli.- -ill-tan.-.- in 1 .-..-. ..f t)n> solu-
ti-.M. / is tin- thickneM in <l.-.-i: tin- tlni.l lay.-rai

.,|,-,r\'d rotation. Tlii- .•.|ii:iti"ii pm\ i.l<- a m.-ans of <

- <|uantitati\''ly \>\ im-asiirinjr tin- rotation | i solu*

.f unknown .-.-n.-.-nt ral i»n in a l.i\.-r of known t liirkin--s. tin-
\ pou.-r IM-JIIL; kno\\ n.-

I for nn'asiirinj: tin- amount «>f r.-r

pro.iii.-.-.l l-\ an ojiti.-allx a.-ti\r -ill. -t. inc.- .ir.- kiio«i .llyas

li^'lit
rhtly luminous so.liiiin-tlain.'. tin- .l.-t.-rn

iN I !(.| XM [IMfl

rmtruroi>ntji anil tncthixU urc l.nn«l.ilt. /fat opliickr

:••* organ. > JI"p|» v- •'. fxilk. rftrm. .l».i/. 1883, 8.

...trunKai. -n IMO. p. SWH Mq.

104 DEXTROSE.

made for the monochromatic light corresponding to the D line of the
solar spectrum. In this case the specific rotatory power is represented
by (a)D. In another class the mean yellow light of an argand or
paraffin lamp is employed. In this form of polarimeter the field of
the instrument when adjusted for use is of a pale pinkish-violet
colour, called from the extreme sensitiveness with which it changes
from pink to violet or the reverse the 'transition tint' (teinte de
passage). This colour is complementary to yellow (jaune), and specific
rotatory powers determined for this particular colour are represented
by (a)j. For any given substance (a)D is always less than (a)j, and

for ordinary purposes (a)D = -i.?/Co> or (a)o : («)j : : 21-65 : 24. Hence

it is important in all cases to state clearly whether a given determi-
nation has been made for monochromatic yellow light or for the 'tran-
sition tint ' of mean yellow light.

Dextrose, like all alcohols, readily forms compounds with acids
and many salts ; of these the latter are the more important and are in
many cases characteristic, as for instance those with caustic alkalis
and sodium chloride. When heated many of these compounds,
more particularly those of bismuth, copper, and mercury, are de-
composed, the decomposition being accompanied by the precipita-
tion either of the metal (Hg) or of an oxide (Cu20). This fact
provides the basis for the more important methods of detecting
the presence of dextrose and other sugars with similar reducing
powers, and of estimating them quantitatively in solution, since
it is found that the amount of reduction effected by any given
sugar is, under given conditions, a constant quantity.1

Phenyl-glucosazone. C18H22N4O4. [C6H10O4 (C6H5. N2H)S].

This compound of dextrose with phenyl-hydrazin crystallises in
yellow needles. It is almost insoluble in water, very slightly
soluble in hot alcohol, melts at about 205°, and is laevo-rotatory
when dissolved in glacial acetic acid. The phenyl-hydrazin test
for dextrose is applied as follows. To 50 c.c. of the suspected
fluid (e.g. diabetic urine) add 1 — 2 grm. hydrochloride of phenyl-
hydrazin, 2 grm. sodium acetate, and heat on a water-bath for
half an hour ; or else add 10 — 20 drops of pure phenyl-hydrazin
and an equal number of drops of 50 p.c. acetic acid and warm as
before.2 On cooling, if not before, the glucosazone separates out
as a crystalline or it may be amorphous precipitate. If amorphous
it is dissolved in hot alcohol, the solution is then diluted with
water and boiled to expel the alcohol, whereupon the compound
is obtained in the characteristic form of yellow needles. By the

1 The description of the various methods employed for the detection and estima-
tion of dextrose and other sugars lies outside the scope of this work. Full details
are given in Neubauer u. Vogel, Analyse des Hams, and Tollens' Handbuch der
Koklenki/drate.

2 Fischer, Ber. d. d. chem. Geseil. Bd. XXH. (1889), S. 90 (foot-note).

CHEMICAL BASIS OF THK ANIMAL T.oDV. 105

above method it is possible to obtain the crystals from fluids
which contain only 0-5 gnu. per litre.

An important property of dextrose is its power of undergoing
fermentations Of these the principal are : (1) Alcolwlic. This is
produced in aqueous solutions of dextrose, under the influence of
yeast. The decomposition is the following : C«H12OC = 2C»H6O -f-
2CO2, yielding (ethyl) alcohol and carbonic anhydride. Higher
alcohols of the fatty series are found in traces, as also are gly-
cerin, sui -cinic acid, and probably many other bodies. The fer-
mentation is most active at about 25°C. Below 5°C. or above
45°C. it almost entirely ceases. If the saccharine solution con-
tains more than 15 per cent, of sugar it will not all be decom-
posed, as excess of alcohol stops the reaction. (2) Lactic. This
is best known as occurring in milk when it turns sour owing to
the conversion of lactose into lactic acid. But dextrose and
other sugars may also be converted into lactic acid (C6H12O« =
2CSH«O8), the conversion being ordinarily due to the presence
of some specific micro-organism l which is specially active in
presence of decomposing nitrogenous material, such as decaying
cheese.3 A similar change is rapidly produced when dextrose is
mixed with iinely divided gastric mucous membrane.3 There is
also some evidence of the existence of an unorganised ferment
(enzyme) in the mucous membrane of the stomach which can
convert lactose and dextrose (?) into lactic ficid.4 On prolonged
standing the lactic fermentation is apt to pass into (3) Butyric.
This results from the appearance and action of another specific
organised ferment on the first formed lactic acid, the change
IM -in g accompanied by the evolution of hydrogen and carbonic
anhydride —

2C3H60, = C,H7. COOH. + 2COS + 2H2.

Lactic and butyric fermentations are most active at 35° and 40 J
•lively; they probably occur constantly in the alimentary
eanal with a carbohydrate diet and may in some cases lie remark-
ably predominant The hydrogen evolved during butyric fermen-
tation probably plays some important part in the production of
the fii-cal and urinary pigments from those of bile (see below).

I>e\tr..-e i- tin- sujjur which is characteri>t irally formed by the
action i if boiling dilute mineral acids <m SIIUMI- i-f the c.nie-^ugar
group, iinil (in March and dextrin. When it is dissolved in concen-
trated sulphuric acid it i> >aid to be partly n-com erted into a. true

1 F.isti-r. /'<nli. -SV. Trnns. 1^-7 :. ji fJ.Y <j,i.irt. Jl. Micros. Sri. Vol. xvni. (1878),

&177. Miirpm.-uui. (.'rntr<ill> .nillinisfitl Brffftnsonglhft. II. (1886), 8. 117.

;,.t. |8M A I. st. iii M:ily'> r,.r,.-ht. Iss], S. 468.

- Ili-liscli, I'rr/xinilliin i>f' tin-fir iicul. Lictii^'s A»ti. IM I \I. (l-»7), S. 174.

. i.i.-i.i-1^ .JH,, i;,i ouaaa (1874), 8. M7.
4 BbUBBMnton is\\.-.li»|i). See Almt. in Maly's lirr IM n. (1872), S. 118.

106 L^VULOSE. GALACTOSE.

dextrin which may be precipitated by the addition of alcohol, and is
capable of reconversion into dextrose by mineral acids.1

2. LaDvulose

C6H1206. [CH2. OH — CO — (CH. OH)8 — CH2. OH].

This is the ketone corresponding to the aldehyde dextrose. It
is best known as occurring mixed with dextrose in many fruits,
also in honey, and is stated to occur occasionally in urine. It is
a characteristic product of the action of dilute mineral acids on
cane-sugar, which is hereby decomposed into equal parts of dex-
trose and laevulose, and since when the change is complete the
original dextro-rotatory power of the solution has become leevo-
rotatory, the cane-sugar is said to have been ' inverted.' A simi-
lar inversion takes place in the stomach and small intestine (see
under cane-sugar). In its general reactions lasvulose behaves like
dextrose, but may be at once distinguished from the latter by its
powerful Isevo-rotatory action on polarised light : this varies con-
siderably with the temperature and concentration of the solution.
It yields with phenyl-hydrazin an osazone identical with that
derived from dextrose. It forms a compound with calcium hydrate
which unlike that yielded by dextrose is extremely insoluble and
may thus be employed for the separation of the two sugars.

2. Galactose (Cerebrose) C6H1206.

When milk sugar (lactose), see p, 113, is boiled with dilute
mineral acids it is decomposed into a molecule of dextrose and
one of galactose

Ci2H22On -{- H20 ^ C6Hi2Oe -f- C6H12O6.

The two sugars may be separated by crystallisation and by taking
advantage of the greater solubility of galactose in absolute alcohol.2
In its general reactions and behaviour galactose resembles dextrose
but is possessed of a considerably greater specific rotatory power
[(a)D=-f~ 83°] which increases with the concentration and rise
of temperature.3 It yields with phenyl-hydrazin an osazone
(phenyl-galactosazone) which has the same composition as phenyl-
glucosazone and very similar solubilities. It differs however from
the latter in melting at 190 — 193° and in being optically inactive
when dissolved in glacial acetic acid. It has recently been
shown that the sugar which was described by Thudichum4 as
resulting from the action of boiling dilute sulphuric acid on cer-

1 Musculus u. Meyer, Zt. f.physiol. Chem. Bd. v (1881), S. 122.

2 Fudakowski, E'er. d. d. chem. Gesell. Jahrg. 1875, S. 599. Soxhlet, Jn. f. pr.
Chem. (2) Bd. xxi. (1880), S. 269.

3 Meisjsl, Jn. f. pr. Chem. Bd. xxn. (1880), S. 97.

4 Jn.f.pr. Chem. Bd. xxv. (1882), S. 19.

C1IKMICAL BASIS (•] TIIK ANIMAL 1J»>I)Y. 107

tain ( -onstitnents of the brain substance, and was named by

him ceivhrosc, is really identical with galactose.1

(ialaetose is fermentiblr with yeast, ItuL less readily so than is
dextrose.

•I. Glycuronic acid. C,H10O7. [COH -,< II .< Mi ,,<<>< >H].

This acid was first obtained as a compound, campho-gljCUIOnic
acid, in the urine of do^s after the administration of camphor,-
and sul)sequently as urochloralic acid after tin- administration
hloral.:; Sine.- then it has been found in urine a> ethereal or
iducose-like compounds, with an extensive series of members of
the fatty or aromatic series after the introduction of the ap-
propriate substances into the animal body.4 It is probable
that traces of compounds of this acid occur normally in urine,
sine,- tin- excretion is usually slightly la-vo-rotatory, and it is
known that indol and skatol which are formed in the alimentary
canal readily reappear in the urine as compounds of glycu-
ronic acid; viz. indoxyl- and Bkatoxyl-glycuronic acid, when intro-
duced into the body. The compounds of glycuronic acid are
all la-vo-rotatory, and some of them reduce metallic salts on
boiling, and may hence lead to errors in the determination of

i in urine.

Glycuronic acid does not occur in the free state in the animal
body. Chemically it is closely related to dextrose; when oxi-
di>ed with bromine it yields saccharic acid,6 C6H10O8, [COOH -
(i I£. OH)4 -COOH], — an acid which is also readily obtained by
the oxidation of dextrose with nitric acid. Saccharic acid can he
converted into glycuronic acid by reduction with sodium amal-
^am.'; Like dextrose, glycuronic acid is dextro-rotatory, but to a
extent, (a)0 = -f- 194°, reduces Fehling's Huid to the same
••tit as does dextrose, and forms with phenyl-hydra/.in a yellow
-talline compound which melts at 114 — 115°. The acid jv
known only as a syrup soluble in alcohol and water. When
boiled in the latter solvent it loses a molecule of water and yields
an anhydride (lactone), C«H80«, which is crystalline, insoluble in
alcohol, soluble in water, dextro-rotatory, ami reduces Fchling's
fluid powerfully.

I Thierfcldcr, '/A. f. />// //W. f '/,/•//, 15,1 \i\. ( 1-vn. s. ^t'.i Hrown and Murri-.
Jl. CA .1. i MI. (is'.to), p. 57.

n M.-x.-r, 7.1. /: phi/ai'ol. Cli> w IM. in. (IH7H), S. 422.
rinK. H.,,1. IM.'vi. (|HSL.), S. l-o

4 For vory full li.«t ..f tin- \;iri..ii(« Htilwtances which when introduced into tlu> body
n-:i|ip«-;ir in the urine as paired compounds «itli ^Ixcuronic acid, and for references
to date (l-'.iit) to the literature "f the .-iitij-M-t, see Neiiliauer u. Vo^el, //iiriniini'
Kd. i\ l-'iu. p. nr,

'•> Thierfelder. /.' / ,>l,,/xiol. Cliem. Bd. xi (1887), S. 388. Sec also Bd. MII '
(I88'.r, -

1 i- u Pilot v, If,;-. ,1. ,1 chem Gciell. Jahrg. xxiv. (1891). S. :,ji.

108 INOSIT.

The formation of the compounds of glycuronic acid, to which
attention has been drawn, is of great and increasing interest.
There can be little doubt that the acid has its origin in the carbo-
hydrate (dextrose) of the body, but it is not yet possible to ex-
plain exactly how each particular compound arises after the
introduction of the corresponding substance into . the animal
organism.1

Inosit. CCH1206 + 2H20. [CH.OH]6.

This substance has the same percentage composition as a sugar,
and possesses a distinctly sweet taste; in virtue of which prop-
erties it appears to have been usually classed with the carbo-
hydrates. It does not, however, yield any of the reactions most
typical of this class of substances; for instance, it exerts no
rotatory power on polarised light, does not reduce metallic salts,
does not undergo alcoholic fermentation, and does not react with
phenyl-hydrazin. On account of these peculiarities, the view was
long ago expressed that it is not a carbohydrate at all; and
this has recently been shown to be the case by Maquenne, who
has proved that it belongs really to the benzol series.2 Struc-
turally it may be represented by a closed ring of six CH . OH
groups.

Tnosit occurs but sparingly in the human body ; it was found
originally by Scherer 3 in the muscles. Cloetta showed its pres-
ence in the lungs, kidneys, spleen, and liver,4 and Miiller in the
brain.5 It occurs also in diabetic urine, and in that of 'Bright's
disease,' and is found in abundance in the vegetable kingdom, —
more especially in unripe beans, from which it may be conven-
iently prepared.6 It is also found in the urine after the ingestion
of an excess of water into the body.7

It is prepared from aqueous extracts of the mother tissues by
acidulating with acetic acid and boiling to remove any coagulable
proteids. The filtrate from these is then precipitated with normal
lead acetate and filtered, and the inosit is finally precipitated from
this filtrate by means of basic lead acetate in presence of ammonia.
The lead compound is decomposed with sulphuretted hydrogen,
and after the addition of alcohol and ether to the solution,
inosit separates out by crystallisation.8

Pure inosit forms large efflorescent crystals (rhombic tables) ;

1 In the case of camphor and chloral see Fischer u. Piloty, loc. cit. S 524.
- Compt. Rend. T. civ. (1887), pp. 225, 297, 1719.

3 Ann. d. Chem. u. Pharm. Bd. LXXIII. (1850), S. 322.

4 Ibid. Bd. xcix. S 289.

5 Ibid. Bd. cm. S. 140.

6 Vohl, Ibid. Bd. xcix. (1856), S. 125 ; ci. S. 50.
? Kiilz, Centralb.f. d. med. Wiss. 1875, S. 933.

8 Marine', Ann. d. Ch. u. Pharm. Bd. cxxix. S. 222. See also Boedeker, Ibid. Bd.
cxvii. S. 118.

CHEMICAL P.ASIS OF THE ANIMAL IJODY. 109

in microscopic preparations it is usually obtained in tufted lumps
<>f fine crystals.

FIG. 1. INOSIT CRYSTALS. (After Kiihue.)

Readily soluble in water, it is only slightly so in dilute alcohol,
and is insoluble in absolute alcohol and ether.

Although inosit admits of no direct alcoholic fermentation.it
has been stated to be capable of undergoing a lactic fermentation
in presence of decomposing proteid (cheese) and chalk, yield-
ing ordinary (ethylidene-) lactic acid and some butyric acid.1
It had been previously stated that the acid thus obtained is
sarcolactic (ethylene- or para-) lactic acid.2 These assertions are
ly reconcilable with our present knowledge of the chemical
constitution of inosit.

Reactions of inosit.

(i) Sclierer's test.9 The suspected substance is treated- with
,' nitric acid and evaporated nearly to dryness on porcelain.
< »n tin- addition of a little ammonia and a few drops of freshly
prepared and not too dilute solution ot calcium chloride, a bright
jiink or rose-coloured residue is obtained on renewed evaporation
it' inosit is present.

(ii) Gallois' text. When inosit in concentrated solution is
treated with a few drops of 2 p.c. mercuric nitrate solution, or
Liebig's solution for the estimation of urea, and the mixture i>
evaporated to dryneSB, it yields a y«-llo\v residue which on bem-
more strongly heated turns rosy red; this disappears on cooling,
and returns again on renewed heating.4

1 V.,1,1. ll.r. </. d. chem. Gftell. Jahrg. 187

IMA Ann. -/. r/,,m. n. I In,,;,,. H.l • I \ I 1-71). S 333.
» Ann. d. Chem. u. /'harm. H.I. i.xxxi. (Is:..
4 Zt.f. anal. Chem. Bd. iv. (1865), S. 264.

110 CANE-SUGAR.

(iii) Seidel's reaction.1 A small amount (say -03 gr.) of the
suspected substance is evaporated to dry ness in a platinum cruci-
ble with a little nitric acid (sp. gr. 1-1 — 1-2), and the residue is
treated with ammonia and a few drops of a solution of strontium
acetate. If inosit is present, a greenish colouration is observed,
together with a violet precipitate.

THE CANE-SUGAR GROUP.

I. Saccharose. (Cane-sugar.) C12H22Oa.

Although it is not found as a constituent of any animal tissue,
this sugar possesses no inconsiderable interest in view of the fact
that it is a food-stuff which is largely consumed by man, and
may constitute in many cases no small part of the total carbo-
hydrates with which the body is supplied.

Cane-sugar is chiefly distinguished from the others by the fact
that it does not reduce metallic salts, and does not form a com-
pound with phenyl-hydrazin ; but the property which is of great-
est interest to the physiologist is the ease with which it may
be 'inverted' or converted into equal parts of dextrose and
laevulose : —

C12H22OU -f H20 = C6H12O6 (dextrose) -f C6H12O6 (kevulose).

This inversion is readily brought about by treatment with dilute
mineral acids at 100°, or even at 40° or below if the action is
more prolonged ; 2 it is also the result of the action of enzymes,
more especially of invertin from yeast, and is characterised ex-
perimentally by the change in the rotatory power of the solution,
which from being originally dextro-rotatory becomes Isevo-rotatory;
hence the name ' inversion.' For cane-sugar (a)D = -{-66° 5 f°r
Iffivulose (a)D = —100°. The rotatory power of the latter is
largely dependent upon temperature and concentration.

When cane-sugar is injected into the blood-vessels or tissues of
an animal it is eliminated in an unaltered condition, and is thus
shown to be non-assimilable.3 On the other hand, it may be
introduced in large amounts into the alimentary canal without
reappearing externally in the urine. From this it may be con-
cluded that it undergoes some change before or during absorption,
and this change is most probably that of inversion. This change
may take place in the stomach, partly under the influence of the
acid of the gastric juice, but also as the result of the action of a
soluble enzyme ; 4 it is even more marked in the small intestine,

1 Dissertation, Dorpat, 1884. Quoted by Fick. (Pharm. Zi. f. Russl.) See
Abst. in Ber. d. d. chem. Gesell. Jahrg. xx. (1887). Ref. Bd. S. 320.

2 Cf. Wohl, Ibid. Jahrg. xxm. (1890), S. 2087.

3 Bernard, Lecons de Phi/siol. exp. T. i. 1855, p. 219.

4 Leube, Virchow's Arch. Bd. LXXXVIII. (1882), S. 222. Cf. Hoppe-Seyler,

CHEMICAL BASIS OF THE ANIMAL BODY. Jll

where the aeti\t- ai;ent is without doubt an en/yme.1 From
this it appears that cane-sugar conforms to tin- apparently
ral rule that the carbohydrates leave the alimentary canal
as dextrose.

( 'ane-sugar readily undergoes a lactic-acid fermentation in pres-
"f sour milk to which /inc. oxide is added for the fixation of
the acid as u is formed.

1*. Maltose. <Y.Il,,<>u + H,« >.

This is the sugar which is characteristically formed, together
with de.xtrins, by the action of malt-extract (diastase) on star< -h-
paste. It was first described by Dubrunfaut2 as arising in this
I >ut its existence was for some time doubted until firmly
established hy O'Sullivan.3 Later researches showed that it is
similarly the chief sugar which is formed by the action of saliva
ami pancreatic juice upon starch-paste or upon glycogen, being
accompanied in the case of pancreatic juice by a variable but dis-
tinct amount of dextrose if the action of this secretion be pro-
li-n -'-.I.* Maltose is also formed by the action of dilute acids
ujM.n stan-h-j »aste, but in this case it is difficult to prevent the
simultaneous formation of dextrose into which it is readily con-
verted by acids, yielding 98 — 99 p. c. of the latter sugar.6 It is
therefore usually prepared from the products of the action of malt-
extract on starch -paste.6

.Maltose is very soluble in water, also in alcohol, but less so in
the latter solvent than is dextrose. It crystallises in fine needles
which are however not very easily obtained. Solutions of maltose
are dextro-rotatory ;,,,,! reduce metallic salts; it is therefore not
easily distinguished from dextrose by merely qualitative tests.
A< tii«- nerv-^ity of discriminating between the two sugars is one
•I iient ocrurrence, the following characteristic differences be-
tween their optical and reducing powers are of great importance.
For maltose in 10 p. c. solution at 20°C. (a)D = + 1400,7 tor dex-
trose (a)D = -j-52'5°. When maltose is boiled with Fehling's

Yin-how's Arch. Bd. x. (18.r.f,|. S. in Koebner, Diss. Breslau, (1859). Al.st. in
Ili-iili- 11 Metaner's Jahre* _' .•»'..

;il><-. <;,,tr,,n,. i. ,1 ,„.</. H'/v. isf.s, S. 289. Pjisrliutin. Air/,. /; .{nut. H.
AVi//.«.W. .Jahri,'. (1*71). S. :C4. Bernard, '.'«:. /««'./. </. J'<n-i*. l.*7.'!, p. -.'(Ml. Br«.\vi,
iin.l M.-n.n, I,i«-l.ii;'s .\nn. IM < . i\ ( I - ..MM. 1880,

p. 393 Vi-ll:i. M.-li-sclmtt's r,,t.r*,t,-l,. \M. Mil (\^\). S. 40.

('/,,,„. ,t /'/M/.S-. (:t) T \\i (1841 , p 178

' .//. ('!„• J. \..l \. (lx7i>l, p. :.7'.i. Cf. Musmlii> u (Jriilx-r. '/A

;/.sW. t •/„•„,. B<l u. (1-7- 7'M. S. 177.
1 Mus< iilu-i ii \<Hi M.-riiiL,'. '/J. /'. II/II/SKI/. <'li- in. IM i. (1877-78 ).S. :»'.i:i: ii (1878),
Kill/.. iMlii^'-r's .!/••/!. IM \\i\ (1--<I ). S. SI. I'.n.wn :ui.| Hrn.n, I.n-l.i-'>
Ann. IM. • v

:i<M. von MoriiiR, Zt. f. vhi/tiol. Chem. IM. v. (l*sl), S. 185.
. r.Cktm. CJi, IM. \\\ - iu.

8 Soxhli-t. Jn.f.pr. L'hrm. (2), IM. XXI. (18SM). IliT/.fi-ld. I.ii-l.i-V Ann. Bd. CCXX
(1884), S. I'll.

7 Metal, loc. cit. Brown and Heron make it lew = +135*4.

112 MALTOSE.

fluid 1 the amount of cuprous oxide which separates out is only
about two-thirds of that which would be reduced by an equal
weight of dextrose, or in other words 66 parts of dextrose reduce
as much as 100 parts of maltose. Bearing in mind that maltose
may be readily converted into dextrose by boiling with dilute
acids with a corresponding change of its optical and reducing
powers, while dextrose is of course unaltered by this operation, it
is easy to base upon the above facts a method of identifying the
two sugars. As a further difference between the two it may
be stated that Barfoed's reagent2 is not reduced by maltose,
whereas it is by dextrose.3 In this respect maltose resembles
lactose (milk-sugar) which also does not reduce this reagent.

Phenyl maltosazone. C2JJ.S2N4O9.

This compound of maltose is obtained by the action of phenyl-
hydrazin upon it in presence of acetic acid in the way already
described (p. 104) for the preparation of the analogous compound
with dextrose. It crystallises readily in minute yellow needles
and is characterised by being (unlike phenyl-glucosazone) soluble
in about 75 parts of boiling water, and still more soluble in hot
alcohol. Its melting point 206° is practically the same as that of
phenyl-glucosazone.

The researches of Brown and Heron (see above, p. 59) showed
that whereas pancreatic juice rapidly converts starch-paste into
maltose and a little dextrose, an extract of the mucous membrane
of the small intestine or the tissue itself, while acting but feebly
on starch-paste rapidly converts maltose into dextrose. They
hence surmised that maltose would be found to be a non-assimil-
able sugar, requiring like cane-sugar to be converted into the
vsimpler dextrose before absorption. More recent experiments have
confirmed this view,4 for it has been found that if maltose be in-
jected into the blood-vessels it is largely excreted in an unaltered
form in the urine.5 The converting action of extracts of the in-
testinal mucous membrane is strikingly less than that of the
tissue itself ; from this it may perhaps be inferred that the change
into dextrose takes place rather during than previous to absorp-
tion. This fact corresponds closely to the well-known views as to
the changes which peptones similarly undergo during their passage

1 Solution of hydrated cupric oxide in caustic soda, in presence of the double
tartrate of sodium and potassium (Rochelle salt). See Soxhlet, loc. cit.

2 Dissolve I part of cupric acetate in 15 parts of water : to 200 c. c. of this solution
add 5 c.c. of acetic acid containing 38 p.c. of glacial acid. Jn.f.pr. Chem. (2), Bd. vi.
(1872). S. 334.

8 Musculus n. von Mering, loc. cit.

4 But cf. previously Bimmerinann, Pfliiger's Arch. Bd. xx. (1879), S. 201.

5 Philips, Diss. Amsterdam, 1881. See Abst. in Maly's Bericht. 1881, p. 60. See
also Bourquelot, Compt. Rend. T. XCYII. (1883), pp. 1000, 1322; T. xcvin. p. 1604.
Journ. de t'Anat. et de la Physiol. T. xxn. (1886), p. 161.

CHK.MICAL U.VSIS OF THE ANIMAL BODY. 113

through the walls of the intestine into the neighbouring blood-
vet- fj :)U!»).

3. Lactose (Milk-sugar). CuH^On + H,O.

It is fouiul characteristically and solely in milk, in (juautities
varying with the class of animal and at different times with the
same animal.1 The percentage is relatively high in human milk.
It is also said to occur in the urine of lying-in women and
sucklings. -

I' i-' / 1" ration. The casein is precipitated from diluted milk by
the addition of acetic acid. The filtrate fmm this is boiled to
coagulate, the remaining proteids, which are then removed by fil-
tration. This final filtrate is then concentrated, and on prolonged
standing yields crusts of milk sugar which are purified by recrys-
tallisation fmm hot water.

It yields, when ]>ure, hard colourless crystals, belonging to the
rh«>mbic system (four-sided prisms). It is less soluble in water
than dextrose, requiring for solution six times its weight of cold,
but only two parts of boiling, water; it is entirely insoluble in
alcohol Mid in ether. It is fully precipitated from its solutions by
the addition of basic lead acetate and ammonia.

Solutions of many metallic salts are readily reduced by boiling
with lactose, but the reducing power is less than that of dextrose.
Thus 1 c. c. of Fehling's thud which is reduced by 5 mgr. of dex-
trose requires 6'7 m.^r of lactose provided that certain conditions
as to the dilution of the solution, duration of boiling, \-e.. are
attended to.3 These are important for the accurate volumetric
estimation of lactose. The specific rotatory power of lactose is
(a)D=-r-52'3°, and is independent of the concentration in solu-
tions which contain up to 35 p. c. at ordinary temperatures. Its
rotatory power is thus identical with that of dextrose. It is, how-
readily 'distinguishable from dextrose by its smaller solubility
in water, insolubility in alcohol, and incapability of undergoing
direct alcoholic fermentation with yeast It also does not reduce
I'.aifoed's reagent, and in this resembles maltose. When boiled
with dilute mineral acids it yields eipial molecules of dextrose and
ua lactose (see p. 106), and since the specific rotatory power of the
latter of these is high [(a)D = -j-83°], this increase of rotatory
(and reducing) power on treatment with acids affords a further
convenient means of discrimination between lactose and dextm>e.

1 Sec <;.>rnp Hcs.-iiK'/., f.flir/,.,1 /./,- ,W .<"/,, • I'hnn d. mensch.

Xillinni./*- u. <;,nnsxmittrl,:\ Allll (I-VI). I'ul. I. S. L'.'.O./ s»/.

: Ilufmfintcr, /J /". f,lti/M»l. ('In m Mil. i. (1877), S. loi. Sco Ncubauor u. Vogel,
Analyse </. //nrns, li'Td.-il. I- n>. s I-

..l.-w.-iM u. T..I1.-!,.. /•'< . '/ •/ chem. Getell. 1878, S. 2076. S.xhk-t, /A. f.
prakt. Chtm. (-2), IM \\i I -MI. s

8

114 • I.ACTOSK.

Fhenyl-lactosazonc. C'.J41 f 82N40,.

This compound of lactose with pheiiyl-hydrazin is formed under
conditions similar to those already described for the preparation
of the analogous compound of dextrose. It is soluble in 80 — 90
parts of boiling water and melts at about 200°. It crystallises
readily in the form of yellow needles which, unlike the crystals
of phenyl-maltosazone, are usually aggregated into clusters.

Lactose is readily capable of undergoing a direct lactic fermen-
tation and this occurs characteristically in souring milk. The
exciting cause is doubtless ordinarily an organised ferment, but
there is also some evidence of the existence in the alimentary
canal of an enzyme which can effect the same conversion. The
circumstances and products of the conversion are the same as for
dextrose and saccharose.

Although isolated lactose is unaffected by yeast, milk itself is cap-
able of undergoing, under the influence of certain ferments, an
alcoholic fermentation, and this has been employed from very early
times by the inhabitants of certain districts of Russia in the prepara-
tion of Kumys and Kephir. from niare's-rnilk. Of late years these
fluids have attracted much attention in virtue of their supposed thera-
peutic action in certain wasting diseases. Very little is as yet known
as to the real nature of the changes which occur during the fermenta-
tion, but they are probably extremely complex and due to the presence
of several organised ferments.1 Kephir ferment is a commercial
article in Russia, obtainable at the apothecaries.

The non-assimilability of saccharose and maltose has already
been referred to, and experiment has shown that lactose is simi-
larly incapable of assimilation, for when injected into the blood-
vessels it appears unaltered in the urine.2 It is therefore
presumably changed in the alimentary canal into some form of
sugar which is assimilable, it may be into dextrose and galactose.
It does not appear that any such conversion can be markedly
observed, if at all, under the action of any of the secretions of the
alimentary canal ; hence the change may more probably take place,
as in the case of maltose, rather during than before the passage of
the sugar through the intestinal walls.

This non-assimilability of lactose is certainly remarkable when
it is remembered that it is in this form that young animals receive

1 There is an extensive literature on this subject, of which the following are of
most comprehensive interest. Biel, Unters. uber den Kunu/s, Wien, 1874, and St.
Petersburg, 1881. Abst. in Maly's Benefit. 1874, p. 166, 1886, p. 159. Struve, Ber.
d. d. chem. Gesell. Jahrg. 1884, Sn. 314, 1364. Krannhals, Deutsch. Arch. f. klin. Med.
Bd. xxxv. (1884), S. 18. Hammarsten (Swedish). See Abst. in Maly's Benefit.
1886, p. 163.

2 Dastre, Compt. Rend. T. xcvi. (1883), p. 932. Compl. Rend. Soc. Biol. (9), T. I.
(1889), p. 145. De Jong (Dutch Diss.). See Maly's Bericht, 1886, p. 445

CHEMICAL BASIS OF THE ANIMAL BODY. 11.-,

their supply of carbohydrate food. It might more probably have
IMM-H expected that they should be shielded as far as possible from
any avoidable excessive digestive labour by the presentation of a
diivrtly assimilable sugar. We cannot as yet offer any other ex-
planation of the observed facts than the one that since lactose is
incapable of diivet (alcoholic) fermentation, not only is the milk
while it is accumulated in the breast less liable to fermentative
decomposition, but also the tendency to fermentative disturban< •»•
in the alimentary canal of the young animal is largely diminished.
Both saccharose (cane-sugar) and maltose1 are similarly not
dirfctly fermentable, and both again in the adult are apparently
converted into fermentable dextrose during, or at least, immedi-
ately before, absorption. The subject is one which requires further
investigation.

FATTY ACIDS AND FATS, THEIR DERIVATIVES
AND ALLIES.

I. ACIDS OF THE ACETIC SERIES.

General formula C,,H2B+i.COOH (monobasic).

This, which is one of the most complete homologous series of
organic chemistry, runs parallel to the series of monatoniic alco-
hols. Thus formic acid corresponds to methyl alcohol, acetic acid
to ethyl (ordinary) alcohol, and so on. The several acfds may
yarded as being derived from their respective alcohols by
simple oxidation taking place in two stages, the first yielding an
aldehyde, the second an acid by direct union of oxygen with the
aldehyde.2 Thus with ethyl alcohol

(i) CH, . CH3 . OH + O = CH, . COH + H,O,
(ii) CH,.COH + 0 = CH,.COOH

The successive members differ in composition by CH2, and the
boiling points rise successively by about 19°C. Similar rela-
tioii> hold good with regard to their melting-points and specific
gravities. The acid properties are strongest in those where n
he least value. The lowest members of the series are volatile
li« | u ids, acting as powerful acids; these successively become less

1 Horace Hrown Private communication to author. Cf. V. MeriiiR, '/A. f.

:: I r, (1881), s

-' The views as to the possiMe importance of the aldehydes have already been
referred to when treating of pn.teids (see p. 52). It is further interesting to notice
that a simple polymerisation, to which it is very prom-, of the lowest Imeth ) aldehyde
II i i "II. Mould yield a sulistamv h.-miiir the composition of a carholn drate. ThlB is
indeed a view which is held hy many as to the mode of formation of starch in plants.
Cf. Miller I' .in in 1880, Sec. 1, p. 726.

116 ACIDS OF THE ACETIC SERIES.

and less fluid ; and the highest members are colourless solids,
closely resembling the neutral fats in outward appearance. Con-
secutive acids of the series present but very small differences of
chemical and physical properties, hence the difficulty of separat-
ing them : this is further increased in the animal body by the
fact that exactly those acids which present the greatest similar-
ities usually occur together.1

The free acids are found only in small and very variable quan-
tities in various parts of the body ; their derivatives on the other
hand form most important constituents of the human frame, and
will be considered further on.

Some of the lower acids of the series have been obtained by
treating proteids with molten caustic potash. They also occur
among the products of the putrefaction of proteids, as for instance
in old cheese.

Of the primary alcohols from which this series of acids is de-
rived only two have as yet been obtained from animal tissues or
secretions, viz. ethyl2- and cetyl-alcohol,3 C2H5 . OH and C16H33 .
OH, — the former from muscle, brain, and liver, the latter in union
with palmitic acid in spermaceti and the secretion of the caudal
glands of birds.

Formic acid. H . COOH.

When pure is a strongly corrosive, fuming fluid, with power-
ful irritating odour, solidifying at 0° C., boiling at 100° C., and
capable of being mixed in all proportions with either water
or alcohol. It has been obtained from various parts of the
body, such as .the spleen, thymus, pancreas, muscles, brain, and
blood ; in the latter its presence may be due to the action of acids
on the haemoglobin. It also occurs in minute traces in urine. It
is excreted by some ants (Formica rufa) in a fairly concentrated
form and may be present to the surprisingly large extent of 40 p.c.
in the secretion of certain caterpillars.4 The separation of so acid
a fluid from the alkaline cell-substance is remarkable and of con-
siderable interest. When heated with strong sulphuric acid it is
decomposed into carbonic oxide and water. It is further charac-
terised by readily effecting the reduction of metallic salts, as of
mercury or silver, when heated with their solutions.

Acetic Acid. CH3 . COOH.

It is distinguished by its characteristic odour ; its boiling-point
is 100° C. ; the anhydrous acid solidifies at about 17°. It is solu-
ble in all proportions in alcohol and in water.

1 For details on this series see Hoppe-Seyler's Hdbch. d, phys. path. chem. Anal.
1883, S. 85 et seq.

2 Rajewski, Pfliiger's Arch. Bd. xi. (1875), S. 122.

3 De Jonge, Zt.f. physiol. Chem. Bd. in. (1879), S. 225.

4 PoultOD, The colours of animals, Internat. Sci. Ser. 1890, p. 274.

CHEMICAL BASIS OF THE ANIMAL BODY. 117

It may In- formed in the stomach as the result of fermentative
changes iu the food, and is frequently present in diabetic mine, as
also in traces in normal uriiie. In other organs and fluids it exists
only in minute tra

With I'crru- chlnride it yields a blood-red solution, decolourised by
hydrocloric acid. (It differs in this last ivacti'in fmni siilphocyanide
Of iron.) Heated vrith alcohol and sulphuric acid, the characteristic
<>f acetic ether (ethyl-acetate) is obtained.

Acetone. CH, . CO . CH,.

This substance is the typical member of the general class known
as ketones, and may be prepared by the dry distillation of calrinm
or barium acetate.

Ketoues are characterised by containing the group CO (carbonyl) in
the same way that the aldehyde- an- characterised by the group ('< »1 1.
and the acids by the group COOH. The ketones are closely related
to the aldehydes and may be regarded as derived from them 1>\- dis-
placing the H of the COH group by some monad (alcohol) radicle.
They are most usually prepared by the dry distillation of the calcium
.-alts of the appropriate acids. Ketones, like the aldehydes, unite
readily and directly with phenyl-hydrazin, yielding a class of com-
pound-. known as hydrazones. (Cf. p. lOii.)

Acetone is a volatile liquid, soluble in water, boiling at 56°, and
possessed of an agreeable ethereal odour. It may be obtained in
considerable quantity by distillation from the urine and blood of
diabetic patients and accounts for the peculiar ethereal odour which
these frequently evolve.1 This symptom is of serious prognostic
importance, and it has been supposed by many authors that tin-
fatal diabetic coma which rapidly supervenes is caused by the pres-
ence of acetone.2 The urine of diabetic patients frequently ex-
hibits a reddish-violet colouration with ferric chloride, supposedly
due to the presence of aceto-acetic acid (CH8 . CO. CH2 .('<>< >H >
which readily yields acetone by its decomposition.

Acetone is also not infrequently 'found in the urine and
breath (?) of children in apparently normal health.3

Acetone gives a characteristic reaction with iodine in presence
of an alkali (formation of iodoform) and colour-reactions with
sodium nitro-prusside and fuchsin.4

Propionic acid. C2H8 . COOH.

This acid closely resembles the preceding one. It p..--.
a very sour taste and pungent odour; H soluble in water, boils

1 Vim JukM-li. • •mirif n. fhnrrtiinr, Horlin, IS1- history ami

liti-ratim- of the «ubii>< t Cf '/.t . / /./,•/.«;»/. CV,, ,„ IM. vi. (1882), S. 541.
- cf. (Janice's />A ./W .r/,,,,, V,,! i 1880. p l'.-

/ /'//(/.<"•/. -Tali'
4 Consult IfeubMMr nd N'«>t;'-l. // •< «><

118 ACIDS OF THE ACETIC SERIES.

at 141° C., and may be separated from formic and acetic acid
by taking advantage of the superior solubility of its lead salt
in cold water.

It occurs in small quantities in sweat, in the contents of the
stomach, and in diabetic urine when undergoing fermentation.
It is similarly produced, mixed however with other products,
during alcoholic fermentation.

It is stated to have been found occasionally in normal urine.

Butyric acid. C8H7 . COOH.

There are two possible isomeric acids of the general formula
€8H7 . COOH, the normal or primary, CH8 . CH2 . CH2 . COOH and
iso- or secondary, CH(CH3)2 . COOH.

Normal butyric acid. An oily colourless liquid, with an odour
of rancid butter, soluble in water, alcohol, and ether, boiling at
162° C.

Found in sweat, the contents of the large intestine, faeces, and
in urine. It occurs in traces in many other fluids, and is plenti-
fully obtained when diabetic urine is mixed with powdered chalk
and kept at a temperature of 35° C. It exists, in union with gly-
cerin as a neutral fat, in small quantities in milk, and gives the
characteristic odour to butter which has become rancid.

It is the principal product of the second stage of lactic fermen-
tation (see p. 105), and is ordinarily prepared from this source.

Isobutyric acid. Occurs in fasces and among the putrefactive
products from proteids, also in certain fruits such as the banana.

Valeric or Valerianic acid. C4H9 . COOH.

Four isomeric forms of this acid exist. Of these the one here
described is the isoprimary CH(CH8)2CH2 . COOH. (Isopropyl-
acetic acid.)

An oily liquid, of burning taste and penetrating odour as of de-
caying cheese ; soluble in 30 parts of water at 12°C., readily soluble
in alcohol and in ether. Boils at 175° C.

It is found in the solid excrements, and is formed readily by
the decomposition, through putrefaction, of impure leucin, am-
monia being at the same time evolved ; hence its occurrence in
urine when that fhiid contains leucin, as in cases of acute atrophy
of the liver.

Caproic acid. C5HU . COOH.

Caprylic acid. C7H15 . COOH.
Capric (Eutic) acid. C9H19 . COOH.

These three occur together (as fats) in butter, and are con-
tained in varying proportions in the faeces from a meat diet and

CHEMICAL BASIS OF THE .AM .MA L BODY. ll'.t

the first two in sweat. The first is an oily fluid, slightly soluble
in water, the other- an- -"lids ami scarcely soluble in water; they
are soluble in all proportions in alcohol and in ether. They may
be prepared from butter, and separated by the varying solubilities
of their barium salts.

Laurie or Laurostearic acid. CnH2s . COOH.
Myristic acid. CWH,7 . COOH.

These occur as neutral fats in spermaceti, in butter and other
fats. They present no points of interest.

Palmitic acid, c, ,11 ,
Stearic acid. C17H,5 . ('< x »H.

These are solid, colourless when pure, tasteless, odourless, crys-
talline bodies, the former melting at 62° C., the latter at 69*2° C.
In water they are quite insoluble; palmitic acid is more readily
soluble in cold alcohol than stearic : both are readily dissolved
by hot alcohol, ether, or chloroform. Glacial acetic acid dissolves
tin-in in large quantity, the solution being assisted by warming.
They readily form soaps with the alkalis, also with many other
metals. The varying solubilities of their barium salts afford the
means of separating them when mixed : ' this method may also
be applied to many others of the higher members of this series.

These acids in combination with glycerin (see below), together
with the analogous compound of oleic acid, form the principal
constituents of human fat. As suits of calcium they occur in the
and in 'adiporiiv,' and probably in chyle, blood, and serous
fluids, as salts of sodium. They are found in the free state in
decomposing pus. and in the caseous deposits of tuberculosis.

Tin- '-\jsteiice of mar£aric acid. a> obtained from natural fats, in-
termediate to the above two. is not now admitted. >inci- Heintz has
shown2 that it is really a mixture of palmitic and stearic acids.
Mar^aric acid possesses the anomalous melting-point of .V.)-9° C. A
mixture of «iO part.- >tearic arid and l<> of pal mi I ic acid, melt- at d"'-;; .
A true mari:aric arid mav lio\\e\er In- prepared h\- replacing the group
<>H in eetyl-alcohol (C16HM . Oil) by the Kroup ( '< )( >H.

Wln-n animal (proteid) tissues are buried for some
tiim- in damp ground or othcr\vi.-e e\p(i<ed t<> nn>i-nire jM the
absence of any free supply "t they aiv frequently found

to have undergone a peculiar change 1-y which they are converted
into a waxy or fatty substance. This is known as adipocire. It
consists, not of true neutral fats, but of the ammonium, and in
some cases calcium, salts of the highest fatty acids palmitic and

1 HHnt/., Poggemlorff'a Anital. d. Phys. «. < '/,• •, I!. I \. n. S. 588.
at

120 OLEIC ACID. NEUTRAL FATS.

stearic, or of the free acids themselves.1 Practically nothing is
definitely known as to the agencies and mode of this conversion.
It may be the result of a purely chemical change, or perhaps it is
more probably due to the action of some micro-organism.2 On
either view of its formation the occurrence of adipocire is of
extreme interest as showing a possible direct formation of the
higher fatty acids and hence of fats from proteids. It is however
supposed by some authors that the adipocire is formed entirely
by change and aggregation from the fats present in the tissues at
death.3 This view is probably incorrect.

II. ACIDS OF THE OLEIC (ACRYLIC) SERIES. C^^.COOH
(monobasic).

The acids of this series bear the same relationship to the ole-
fines (C2H4) that those of the acetic do to the paraffins (CH4).
Some of the higher members of the series are found as glycerin
compounds in various fats.

They bear an interesting relation to the acids of the acetic series,
breaking up when heated with caustic potash into acetic acid and
some other member of the same series : — thus,

Oleic acid. Potassium acetate. Potassium palmitate.

Ci7H33.COOH-h2KHO= KC2H302 + KC16H3102+IL.

Oleic acid. C17H33 . COOH.

This is the only acid of the series which is physiologically im-
portant. It is found united with glycerin in all the fats of the
human body.

When pure it is, at ordinary temperatures, a colourless, odour-
less, tasteless, oily liquid, solidifying at 4° C. to a crystalline
mass. Insoluble in water, it is soluble in alcohol and in ether.
It cannot be distilled without decomposition. It readily forms
with potassium and sodium hydroxide soaps which are soluble in
water : its compounds with most other bases are insoluble. It
may be distinguished from the acids of the acetic series by its
reaction with nitrous acid which converts it into a solid (elaidic
acid) and by the changes it undergoes when exposed to the air.
It may be converted into stearic acid

C17H33 . COOH + H2 = C17H35 . COOH.

THE NEUTRAL FATS.

These may be considered as ethereal salts formed by replacing
the exchangeable atoms of hydrogen in the triatomic alcohol

1 Ebert, Ber. d. d. chem. Gesell. Bd. vnr. (1875), S. 775.

2 Kratter, Zt. f. Biol. Bd. xvi. (1880), S. 455. Lehmann, Sitzb. d. nhus.-med.
Gesell. Wiirzburg, 1888, S. 19.

3 Zillner, Viertelj.f. ger. Med. u. off. Sanhatsw. (N.F.) Bd. XLIV. (1885), S. 1.

CHEMICAL BASIS OF THE ANIMAL BODY'. li'l

glycerin (see below), by the acid radicles of the acetic and oleic
series. Since there are three such exchangeable atoms of hydro-
gen in glycerin, it is possible to form three classes of these eth<--
real salts; only those, however, which belong to the third da--
occur as natural constituent.- of the human body: those of the
tirst and second are of theoretical importance only.

The following reaction which repivsrnt* the formation of tri-
palmitin from glycerin and palmitic acid is typical for all the
others.

(ilvo-riii. Palmitic acid. Tri-palmitin.

C.H. (OH), + 3 (CUHM . CO . OH) =C,H6 (C15H81 . CO . 0),+ 3 H2O.

They possess certain general characteristics. Insoluble in water
and but slightly in alcohol, they are readily soluble in ether,
chloroform, benzol, &c. ; they also dissolve one another. They
are neutral bodies, colourless and tasteless when pure ; they are
not capable of being distilled without undergoing decomposition,
and yield as a result of this decomposition solid and liquid hydro-
carbons, water, fatty acids, and a peculiar substance, acrolein,
resulting from the decomposition of the glycerin. (See below.)

They POS-I-.-S no action on polarised light.

They may readily In- decomposed into glycerin and their respec-
tive fatty acids by the action of caustic alkalis, or of superheated
steam.

Palmitin (Ti -i-palmitin). C8H5 (C,6H81 . CO . 0)8.

1'almitin is but slightly soluble in alcohol either cold or hot,
readily so in ether, from which, when pure, it crystallises in fine
needles; if mixed with stearin it generally forms shapeless lumps,
although the mixture may at times assume a crystalline form,
and wa- then regarded as a distinct body, namely margarin.
\Yhfii pun- it melts at 62° and solidifies again at 45°.

It is most conveniently obtained from palm-oil by removing tin-
free palmitic and oleic acids by alcohol and repeatedly crystallising
tin- residue from ether.

Stearin (TH->t.-urin). C,HS (C17H86 . CO . 0),.

This is the hardest and least fusible of the ordinary fats of the
liody ; is also the least soluble, and hence is the first to crystallise
out from solutions of the mixed tats. Ueadily soluble in ether
and in Iniliny alcohol. It crystallises usually in square talilr-
or glittering plates. It present- pi-culiaritii-s in its fusing-points,
mdting tirst at ">° , then solidifying as the temperature is further
1. and melting finally and permanently at 71°.

Preparation. From mutton suet, its separation from palmitin
and olfin In-ing effected by repeated crystallisation from ether,
stearin l>rin- th«- loa-t soluble. It is, however, very difficult to
obtain it pure l»y tin- process.

IL'1' NEUTRAL FATS.

Olein (Tri-olein). C8H6(C17H33 . C0.0)8.

Is obtained with difficulty in the pure state, and is then fluid
at ordinary temperatures. It is somewhat soluble in alcohol, very
soluble in ether. It readily undergoes oxidation when exposed to
the air, and is converted by mere traces of nitrous acid into a
solid isomeric fat, tri-elaidin. Olein is saponified with much
greater difficulty than are palmitin and stearin.

Preparation. From olive oil, either by cooling to O° C. and
pressing out the olein that remains fluid, or by dissolving in hot
alcohol and cooling, when the olein remains in solution while the
other fats crystallise out.

The fats which occur in the animal body are mixtures of the
above three substances in varying proportions. The normal fat of
each animal or class of animals is however characterised by the
constant preponderance of one of the three ; thus in the fat of
man and carnivora palmitin is in excess over the other two. In
the fat of herbivora stearin predominates, and in that of fishes
olein. Butter contains, in addition to the above, several fats
formed by the union of glycerin with the radicles of the lower
acids of the acetic series.

There is no doubt that a large part of the fat laid on in the
animal body during fattening cannot be accounted for by the fat
given in the food, and must hence arise from a conversion of proteids
or carbohydrates into fat. (See §§ 506, 507.) The question as to
how the storage arises from these food-stuffs is one which has
given rise to a prolonged controversy. On the one hand Voit
and his followers urged that although carbohydrates do lead to a
rapid storing of fat in the body, they do so not directly by being
themselves converted into fat, but indirectly ,by protecting the
proteids from the metabolism they would otherwise have under-
gone. According to this view fat is formed from proteids only.
Lawes and Gilbert on the other hand took the view that carbo-
hydrates are directly converted into fat. While there is no doubt
that proteids can give rise directly to fat as shown by the storage
of fat during "nitrogenous equilibrium" (see § 522), there is
also now equally no doubt that carbohydrates can lead to a direct
storage of fat by being themselves converted into fat. This is
the incontrovertible outcome of the most recent experiments,
which have proved that with a diet rich in carbohydrates, so that
the. storage of fat is sufficiently rapid, more fat is laid on than
could possibly have been formed from the proteids in the food
given.1

1 Meissl u. Strohmer, Sitzb. d. Wien. Akad. Bd. LXXXVIII. 1883, IIL Abth. July.
Tscherwinskv, Landwirth. Versuchsstat. Bd. xxix. (1883J, S 317. Chaniewski, /K.
f. Bid. Bd.'xx. (1884), S. 179. Rubner, Ibid. Bd. xxii. (1886), S. 272. Munk,
Vircnow's Arch. Bd. ci. (1885), S. 91. Biol. Centralb. Bd. v. (1885-86), S. 316. See
also Voit, Ibid. Bd. vi. (1886-87), S. 243.

dlKMICAL BASIS OF T1IK ANIMAL BODY. IL':;

Glycerin (< i hverol). C3H6(OH),.

tlready stated, glycerin i-; ;i triutomic alcohol, the neutral fats
being ethereal salts rarmed from it with the radicles of the higher
fatty acids and oleic arid.

When pure, glycerin is a viscid, colourless liquid, of a well-,
known sweet taste. It is soluble in water and in alcohol in all
proportions, insoluble in ether. Exposed to very low temperatures
it becomes almost solid; it boils at 290° and may be distilled
without decomposition in the absence of air.

It dissolves the alkalis and alkaline earths, also many oxide-.,
such as those of lead and copper; many of the fatty acids are
also soluble in glycerin.

It possesses no rotatory power on polarised light.

It is easily recognised by its ready solubility in both water and
alrohol, its insolubility in ether, its sweet taste, and its reaction
with liases. When sufficiently heated, especially in presence of a
dehydrating agent, glycerin is decomposed, loses two molecules of
water and yields acrolein. C|H6(OH), = ('.,II4< )+L'H20. This
substance possesses an intensely penetrating, irritating and pungent
odour so that its formation enables glycerin to be readily idm ti-
tled. It is the cause of the peculiar smell arising from overheated
tats. Chemically it is the aldehyde of allyl alcohol (derived from
tin- oil-tines) and is intermediate between this substance and acry-
lir acid, which is a homologue of oleic acid. (.See above.)

(Jlycerin is formed in traces during the alcoholic fermentation
of sugar \ It is prepared in bulk by distilling in a current of
superheated steam the fluid residue left after the saponification of
tat- with lime.

Soaps.

When iifittral fats are heated with lime or caustic alkalis under
ne they are decomposed, the metal combining with the free
fatty or oleic acid to form a salt, leaving the glycerin in solution.
These >;ilts are called soaps, being soluble in water if the metal is
an alkali, insoluble if it is calcium, lead, or other similar metal.
The reaction which takes place during the above saponitication is

Tri -t.-riu. l'"t;isxium sterftte. (il\ci-rin

C«H,(Ci,Hu . CO.O), -f 3KHO = 3(C17H88.COOK) -f C3H6(OH),.

A similar decomposition into glycerin and free fully acid ran be
i-tle.-ted by pancreatic juice (see p. 64), the acid uniting with the
alkali of tin- juice or of the bile to form a son].. This drcomji.iv.j-

tion is however quantitatively inconsiderable but qualitatively of
great importance for the absorption of fats, owing to the extra<>r-

1 r.iM.-ur, Ann. <L <'lf m. >t. /'harm. IM. < \ i ( 1*58), S. 338.

124

LACTIC ACIDS.

dinarily great emulsifying power of a mixture of bile, free fatty
acids and soluble soaps. The same decomposition takes place
when fats, more especially butter, turn rancid.

III. ACIDS OF THE GLYCOLIC AND OXALIC SERIES.

When one atom of hydrogen in ,a paraffin is replaced by
hydroxyl a primary monatomic alcohol is obtained ; if a second
atom is replaced a parallel series of diatomic alcohols may be pre-
pared, which are known as glycols. The replacement of a third
atom of hydrogen by hydroxyl yields the triatomic alcohols (e. g.
glycerin). Further, just as the monatomic alcohols yield acids
by oxidation, so also do the glycols ; but from the latter two series
of acids can be obtained, known respectively as the glycolic and
oxalic (succinic) series. Thus at first :

Ethvl-glycol. Glvcolic acid.

C2H4(OH)2 -f- 02 = CH2(OH) . COOH.+ H2O.

By further oxidation a member of the glycolic series can be
converted into a member of the oxalic series, thus :

Glycolic acid. Oxalic acid.

CH2(OH) . COOH + 02 = (COOH)2 + H2O.

The acids of the glycolic series are monobasic, those of the
oxalic dibasic.

The following table exhibits the above relationships in a con-
venient form.

Paraffin

Alcohol

Acid

Glycol

Acid I

Acid II

Methane

Methyl

Formic

Carbonic I

CH4

CH3(OH)

H . COOH

„

CO(OH).(OH)

Ethane

Ethyl

Acetic

Ethyl-Glycol

Glvcolic

Oxalic

C2H6

C2H5(OH)

CHg.COOH

C2H4(OH)2

CH2(OH) . COOH

(COOH)2

Propane

Propyl

Propionic

Propyl-glycol

Lactic

Malonic

C8H8

C8H7(OH).

C2H5 . COOH

C3H6(OH)2

C2H4(OH) . COOH

CH2(COOH)2

Butane

Butvl

Butvric

Butyl-glycol

Oxvbutvric

Succinic

C4Hio

C4H9(OH)

C3H-.COOH

C4H8(OH).2

C3H6(OH) . COOH

C2H4(COOH)2

GLYCOLIC ACID SERIES.
Lactic (hydroxy-propionic) acid. C3H608.

This, after carbonic acid, is to the physiologist the most important
acid of the series.

If lactic acid is regarded as derived from propionic acid
CH8 . CH2 . COOH, it may be noticed at once that two isomeric

1 This acid is frequently classed in the preceding group of acids as the first of
the glycolic series.

CHEMICAL BASIS OF Till: ANIMAL P,<>I>Y. 125

lactic acids must be capable of being formed from it. These acids
will have the following formula; respectively: CH8.CH(OH).
COOH an.l riL (nil,. rila. COOH, Of these the first is known

ethylidene-lactic acid, the second as hydraerylic acid.

In adilitiiiu to the above a third acid, isoineric with ethylidene-
lactic acid is known, namely sarcolactic or para lactic acid. Of
these three acids only two occur in the body, hydracrylic being
absent. A fourth acid, to which the name of ethylene-lactic acid
ha- been given, has also been described as isomeric with hydra-
i iv lie acid. It is however probable that this acid is really acetyl-
lactic acid, hydracrylic acid being the true ethylene-lactic acid,
below.)

The several forms of lactic acid are all syrupy colourless fluids,
soluble in all proportions in water and in alcuhol, and to a slight
extent iii ether. They possess an intensely sour taste, and a
stmng acid reaction. When heated in solution they may partially
distil over in the escaping vapour, but are usually decomposed
during the process. They form salts with metals, of which those
with the alkalis .are very soluble and crystallise with difficulty.
The calcium and zinc salts are of the greatest importance, as will
be seen later on, inasmuch as by their varying solubilities they
at lord a means of separating the several acids each from the other.

1. Ethylidene-lactic acid. CH, . CH(OH) . COOH.

This is the ordinary form of the acid, obtained characteristically
as the chief product of the lactic fermentation of sugars (see p. 105).

From this source it may be readily prepared by adding a little old
chei-M.' and sour milk to a solution of cane sugar t<> \\hirli some car-
lionatcof /inc is added. The whole is kept warmed to 40° or 45° for
ten day> or a fortnight, hcing vigorously stirred at frequent intrnals.
Tin- lactic aci»l i- fixed as a lactate by the /inc salt as fast as it is
formed. thi> removal of free acid heing essential to the progress of the
fermentation which does not take place in an acid solution. The
crusts of /inc-lactate formed during the above process are purified by
-tallisini:, the acid is then liberated from the compound 1>\ the
action ,,)" >iilphurettcd hydrogen, and extracted hy shaking up with
ether, in which it is soluble. By a similar process lactic acid may In-
read ily o I it aiued from lactose.

Lactic acid occurs in the contents of the stomach and intestine,
more particularly during " (li('t rich in carbohydrates, and maybe
readily funned by the digestion of gastric mucous membrane with
solutions of dextrose or saccharose.1 According to Heint/2it is
found also in muscles, and according to Gscheidleu3 in the
ganglionic cells of the grey substance of the brain.

1 Maly, Ann. d. Chrm. n. Phnrm. H.I. ci.xxm. (1S74), S. i'27.

2 Ann. <1. <•/„,„. „. /'>,<,,-,„. IM . i vi! f|v7l i. S. 314.
• Pfliiger'a Archiv, Bd. vin. (1873-74), S. 171.

126 LACTIC ACIDS.

The most important salts of this acid are those of zinc and
calcium.

Zinc lactate. Zn (C3H5Os)2 + 3H2O. Soluble in 53 parts of
water at 15° ; in 6 parts at 100°. Almost insoluble in alcohol.

Calcium lactate. CA (CsHjOs)" + 5H2O. Soluble in 9'5 parts
of cold water ; soluble in all proportions in boiling water. In-
soluble in cold alcohol.

2. Sarcolactic acid.

This form of the acid is isomeric with the preceding one. In
its general chemical behaviour as tested by the various decom-
positions it can undergo it is found to be identical with ethylidene-
lactic acid, the sole observable difference being in the different
solubility of its calcium and zinc salts. But both sarcolactic acid
and its salts differ strikingly from the preceding acid and its salts
as regards their physical properties, for the former exert a distinct
rotatory action on polarised light while the latter do not. This
peculiar kind of isomerism, chemical identity with physical
difference, has been called ' physical isomerism ' to distinguish it
from the ordinary form of chemical isomerism. It is now more
usually and correctly called ' stereochemical isomerism ' in accord-
ance with the theory which is held as to the nature, and cause of
the phenomenon. (See below.)

This acid has not yet been prepared synthetically and is only
known as occurring characteristically in muscles1 to which it
gives their acid reaction,2 and in blood.3 In the latter it is found
more particularly, as might be expected, after the muscles have
been in a state of contracting activity.4 It is also found in urine,
very markedly in cases of phosphorus poisoning, and in the same
excretion after violent muscular exertion,5 or artificial stimulation
of groups of muscles,6 and very strikingly after extirpation of the
liver in birds,7 and frogs.8 It is also stated to be formed in vari-
able and slight amount during the lactic fermentation of dextrose.9
Lactic acid has also been frequently described as a constituent of
various pathological fluids ; in these cases it is probable that the
acid is often the sarcolactic acid.10

As occurring characteristically in muscles it is hence found in

1 Wislicenus, Ann. d. Chem. u. Pharm. Bd. CLXVII. (1873), S. 302.

2 Liebig, Ann. d. Chem. u. Pharm. Bd. LXII. (1847), S. 326.
8 Gaglio, Arch.f. Physiol. Jahrg. 1886, S. 400.

4 Spiro, Zt. f. physiol. Chem. Bd. i. (1877), S. 111. Cf. Von Frey, Arch. J
Physiol. Jahrg. 1885, S. 557. Also Marcuse, loc. cit. below.

» Colasanti and Moscatelli. See ref. in Maly's Bericht. 1887, S. 212.

6 Marcuse, Pfluger's Arch. Bd. xxxix. (1886), S. 425.

7 Minkowski, Centralb. f. d. med. Wiss. 1885, No. 2. Arch.f. exp. Path. u. Phar-
makol. Bd. xxi. (1886), S.40.

8 Marcuse, loc. cit. But see Nebelthau, Zt.f. Biol. Bd. xxv. (1889), S. 123.

9 Maly, Her. d. d. chem. Gesell. Jahrg. 1874, S. 1567.

10 Cf. Maly. Abst. in Maly's Jahresb. 1871, S. 333. Fluid from ovarial cyst.

CHEMICAL BASIS OF THE ANIMAL BODY. 1L'7

large quantities in Liebig's 'extract of meat* which is the most
convenient source for its preparation l

Liebig's extract is dissolved in four parts of warm water. To this
solution two volumes of 90 p. c. alcohol are added and the precipitate
is removed by tiltration. The filtrate, after concentration, is again
precipitated with four volumes of alcohol. The filtrate from this
second precipitate is finally concent rated, acidulated with sulphuric acid.
and extracted with r\ce» of .-ther which dissolves out the sarcolactic
acid. On evaporating off the t-ther and dissolving the residue in
\\ater, the pure acid may he ohtained hy forming its zinc salt, which
i> puritied by ery>talli.-at ion and decomposed by sulphuretted hydrogen.

F«>r the method of detecting and separating this acid from urine see
Salkowski and Leube.2

Tin- /inc and r;il< iuni salts of sarcolactic acid are much more
soluble both in water and alcohol than are those <>f ethylidene-
lactic acid.

xn,;-i>lii,'titte. Zn (C8H6O3)2 + 2H2O. Soluble in \~~~>
of water at 15° or 964 parts of boiling 98 p. c. alcohol.

t '"Icium sarcolactate. Ca (C,H6O3)2 + 4H2O [ ? 4^ H2OJ. Solu-
ble in r_' 4 jiarts of cold water, soluble in all proportions in boiling
water or alcohol.

The free acid is dextro-rotatory, but the true value of (a)D is
unknown owing to uncertainty as to the purity of the acid. The
salts on the other hand are all bjevo-rotatory. For the zinc salt,
when one part is dissolved in 18 of water (a)D = -7'6°.

FI-. :.' Xivc SM.-. 01. \CTATE.
(After Kulme.)

FII. .'t CM i M M Svi:. -in \CTATE.

(. \ftiT Klllllll' )

Both this acid and the juvcedinu one yield an intense yellow
rnlniuation when added to ail c.xtreniely dilute (almost colourless)
solution of ferric chloride. This reaction is sour-times useful.3

1 See Oamgee, Physiol. Chemist, ,,. V..1 i 1880. p. 361.

// • ,11
* Uffelmann, Arch.f. kl(n M-><l. Ud. x.\vi. (l^so). S 431.

128 LACTIC ACIDS.

When the formula of ethylidene-lactic acid is examined it is found
to contain what is known as an asymmetric carbon atom : that is to
say, an atom of carbon whose affinities are saturated by four dissimilar
H

I
radicles. Thus H2C— C— COOH.

OH

According to the hypothesis of Van't Hoff and Le Bel such a sub-
stance must be possessed of optically active properties, since all sub-
stances which do rotate the plane of polarised light contain an
asymmetric carbon atom. It is known however in certain cases, as for
instance raceinic acid, that although the substance contains one (or
more) asymmetric carbon atoms it may still be optically inactive since
it is composed of a mixture of isomeric bodies possessing equal and
opposite rotatory powers. From this point of view it is probable that
ethylidene-lactic acid may be such a mixture, and that at present only
one of the optically active isomers of which it is composed has been
obtained, viz. sarcolactic acid.

In support of this view it is interesting to notice that a dextro-
rotatory lactic acid can be obtained from the optically inactive
ethylidene-lactic acid, by applying to its ammonium salt Pasteur's
method for the separation of a mixture of isomeric substances whose
rotatory powers are equal and opposite. This consists in growing the
organism Penicillium glaucum in a dilute solution of the mixture;
one of the isomers is found to be more readily destroyed by the plant
than is the other, so that at a certain stage only one is left in solution.1
When treated in this way ethylidene-lactic acid yields a dextro-
rotatory solution.2 When a current of dry air is passed through sar-
colactic (or ethylidene-lactic) acid heated to 150°, two molecules of the
acid lose two molecules of water and yield a solid crystalline substance
known as lactide (C3H402)2. When boiled with water this is recon
verted into optically inactive lactic acid, thus effecting the reconver
sion of the optically active into the inactive form of the acid.

The Van't Hoff-Le Bel hypothesis of what was originally called
' physical ' isomerism is based upon considerations of the spaciaC
relationships of the constituents of an organic substance ; hence the
more recent use of the expression ' stereochemical ' instead of
' physical.'3

The acid reaction of dead muscle is undoubtedly due to the
presence of sarcolactic acid, as was first clearly shown by Liebig
in 1847.4 In certain cases the reaction of muscle which is still
irritable may become acid, and this has usually been regarded as
due to the development of this acid during its activity. In recent

1 Compt. Rend. T. LI. (1860), p. 153.

2 Lewkowitsch, Ber. d. d. chem. Gesell. Jahrg. 1883, S. 2720.

3 See Miller's Elements of Chem. (Armstrong and Groves), Part III. Sec l
(1880), p. 983, for details of the Van't Hoff-Le Bel hypothesis.

4 That living (irritable) muscle in a state of rest is reallv alkaline was first
demonstrated by Du Bois Reymond in 1859. Monatsber. d. Berl. Akad. 1859, S.
288. See his Gesammel. Abhdl. Bd. 11. 1877, S. 3.

CHEMICAL BASIS OF THE ANIMAL BODY. 129

times, notwithstanding the evidence of the production of large
amounts of sarcolactic acid during muscular contraction (see
above), the view has been put forward that the acid reaction of
contraction is due rather to other substances, as for instance acid
phosphates, than to the acid.1 This view is by no means proved
ami is incompatible with the preponderating evidence of the re-
searches already quoted on the relationships of this acid to mus-
cular activity, and of more recent observations.2 It is possible
that the acid reaction of active muscle is of complex origin, being
partly due to lactic acid, which by acting on an alkaline phos-
phate may convert it into an acid salt, while finally there is an
excess of the lactic acid, most marked in rigor.

There is but little doubt that the glycogen normally present in
muscles is diminished in amount during their contracting activity.
and it has been frequently urged that the acid reaction of muscle
is due to the formation of sarcolactic acid from this glycogen.
This view seems to rest entirely on the fact that during activity
glycogen disappears and lactic acid is formed, but is devoid of
convincing experimental evidence. It is known that a muscle
free from all glycogen can become acid during activity, and bear-
ing in mind that the acidity of active muscle is proportional to its
power of doing work, and to the work it is called upon to do,3 it is
most probable that the lactic acid is a product of the breaking
down of the complex (nitrogenous) molecule whose decomposition
is the source of the energy which the muscle can set free.4
Glycogen is according to this view to be regarded rather as a con-
venient accessory to the activity than as either the basis of this
activity or of the lactic acid which arises during the activity.

3. Ethylene-lactic acid CHa(OH) . CH, . COOH.

This acid has been usually described as accompanying sarcolac-
tic acid in extracts of muscles, and as being isolable from this by
taking advantage of the varying solubilities of the zinc salts of
tin- two acids.6

More recent researches have however made it probable that
what has usually been described as ethylene-lactic acid, obtain-
able from muscle-extract, is really acetyl-lactic acid, CH, . CH
(C,H8Oa) COOH, the true ethylene-lactic acid being hydracrylic
acid, which does not occur in the animal body.6

« Aatawhewsky. 7*. f. phytlol. Chem. Bd. iv. (1880), S. 397. Weyl u. Zi-itl-r,
/'•i'l. IM vi. (is-

» WfTtt.or. IMhiirrr's .In/,. IM. xi.vi. (1890), S. 63. Cf. Warren, Pflugers Arch.
Bd. xxiv. (isxi). S .391. it L i

'• H-i.l.-nli:iin. M.. Imninrhr f^ixtunij Wiinnmit.nrk. „. ,SV..//»m.svi/.- bei der Muikcl-
th;n;,,l.;ii. I^ij,/;.;. HC,4. K:mk«-. 1\ MUMS. Leipzig. 1865. Hermann, Untert. rf.rf.

tfir, ,/,>.-',/. M,,J;,!n. Berlin. 1 -'',:

« Cf UVrflirr /"-. Of I .llihurt. .„..//. PhyM, Vol. VIM. (1887), p. 154.

« Wislicfuus. Ann <t. f'h.m. «. /V»ii-»i. IM. 01 NX n M»7:»). s- ;

• Siegfried, Ber. d. d. chem. Gesell. Jahrg. 1889, S. 2711.

9

130 OXALIC ACID.

Hydroxy-butyric acid.1 CH8 . CH (OH) . CH2 . COOH.

This acid is the next homologue to the lactic acids in the
glycolic series. It is frequently found in the urine of acute dia-
betes, usually accompanied by aceto-acetic acid [CH8 . CO . CH2 .
COOH]. The pure acid is sirupy and laevo-rotatory. (a)D = -23'4.
For its separation from urine and estimation see Kiilz2 and
Stadelmann.3

OXALIC ACID SERIES.
Oxalic acid. (CO . OH),.

This acid does not occur in the free state in the human body.
Calcium oxalate, however, is a not unfrequent constituent of urine,
and enters into the composition of many urinary calculi, the. so-
called mulberry calculus consisting almost entirely of it, and it is
very commonly found in urinary deposits. As ordinarily precipi-
tated from solutions of calcium salts by the addition of a salt
of oxalic acid, the calcium oxalate is usually amorphous. To
obtain it in the crystalline form dilute solutions of the two
reagents must be allowed to mix very slowly, as by diffusion. In
urine the case is different ; the oxalate is at first in dilute solution,
probably dissolved by the sodium dihydric phosphate (NaH2P04)
to which the acidity is normally due. On standing the urine
cools and the oxalate separates out in a crystalline form, viz.
rectangular octohedra, which is characteristic and striking, and
usually unlike that of any other constituent of urinary deposits.

FIG. 4. CALCIUM OXALATE. (After Funke.)

In some cases it presents the anomalous forms of rounded
lumps, dumb-beils, or square columns with pyramidal ends, but
these forms are uncommon.

The crystals are insoluble in ammonia and acetic acid, but
readily soluble in hydrochloric or other mineral acid, also
slightly so in solutions of acid phosphates and urates of

1 See Neubauer u. Vogel, Analyse d. Earns, 1890, S. 110.
a Zt.f. Biot. Bd. xxni. (1887), S. 329.
» Ibid. S. 456.

( HKMICAL BASIS OF THE ANIMAL BODY. 131

sodium. The above characteristics serve to identify this salt,
but in practice the microscopical appearance is usually of most
use.

Succinic acid. COOH . CH, . CH2 . COOH.

This is the- third acid of the oxalic series, being separated from
oxalic acid by the intermediate malonic acid, CH.(COOH)2. It
may occur in the spleen, the thymus, and thyroid bodies, hydro-
cephalic and hydrocele fluids. It has also been stated to occur
normally in urine, but this is very doubtful,1 as also is the state-
ment that it is found in this excretion after taking food rich in
asparagin, e. g. asparagus.2 It is obtained as a product of the
putrefaction of proteids.3

Succinic acid crystallises most usually in the form of large
four-sided prisms, occasionally as rhombic tables. It is soluble
in about 20 parts of cold water, much more so in hot ; it is also
soluble iii alcohol, more especially if hot, and is but very slightly
so in ether.

The crystals melt at 180° C., and boil at 235° C., being at the
same time decomposed into the anhydride and water. The
alkali salts of this acid are soluble in water, insoluble in alco-
hol and in ether.

Preparation. Apart from the synthetic methods, it may
n-adily be obtained by the fermentation of malic* or tartaric6
acids, which are closely related to succinic, the former being
hv.lroxy-succinic, COOH. CH2.CH(OH). COOH, and the latter
dihydroxy-succinic acid, COOH. CH(OH) .CH(OH) . COOH.

Some of the amido-derivatives of succinic acid, viz. asparagin
and asjiartic acid, are of considerable interest; they will be
described later on.

Cholesterin. C26H440 or C,6H420.e

This substance is described here rather for the sake of conveni
ence than from its possessing any relationship to those which have
preceded it.

Cholesterin is the only alcohol which occurs in the human
body in the free state. (The triatomic alcohol glycerin is al-
ways found combined as in the fats ; and cetyl-alcohol is ob-

Salkowski, PflOger'B Arch. Bd. iv. (1871), S. 94.

v I u,), /j. r. ;iA.y»»of. Chen. Bd. I. (1877), S. 213.

Salkf.w;«ki. K.'u. H'., Ber. d. d. them. Getell. 1880, 8. 189.
I.iobig, Ann. d. Chem. u. Pharm. Bd. LXX. (1849), Sn. 104, 363.
Konip, Ber. d. d. ehem. Griell. 1882, S. 172.

Howe. Ann. d. Chrm. u. Pharm. Bd. cxcn. (1878), S. 175. Schulze u. Barbieri,
Jn. f. pnd-t. Chem. Bd XXV. (1882), Sn. 159, 458.

132 CHOLESTERIN.

tained only from spermaceti.) It is a glittering white crystalline
substance, soapy to the touch, crystallising in fine needles from
its solution in ether, chloroform, or benzol ; from its hot alcoholic
solutions it is deposited on cooling in rhombic tables ; this is the
characteristic form and of great importance for the identification
of cholesterin.

Fig. 5. CHOLESTEKIN CKYSTALS. (After Funke.)

When dried it melts at 145°, and distils in closed vessels at
360°. It is quite insoluble in water and in cold alcohol, but
soluble in solutions of bile salts.

Solutions of cholesterin possess a left-handed rotatory action
on polarised light, (a)D = -3'5 in ethereal solution, =- 37° in
chloroforrnic.

Cholesterin occurs in small quantities in the blood and many
tissues, and is present in abundance in the white matter of the
cerebro-spinal axis and in nerves. It is a constant constituent of
bile, and forms frequently nearly the whole mass of some gall-
stones. It is found in many pathological fluids, hydrocele, the
fluid of ovarial cysts, &c., also in faces and milk.1 It also oc-
curs in the substance of the crystalline lens, more especially in
' cataract.'

Preparation. Gall-stones supply the most convenient source
of cholesterin. These are pounded, extracted with boiling water
and dissolved i-n boiling alcohol. The solution is filtered through
a heated filter, and the cholesterin separates out in a fairly pure
condition as the filtrate cools. It is purified by resolution in boil-
ing alcohol to which some caustic soda has been added ; from this
it again separates on cooling, and is finally washed with cold al-
cohol and water.

1 Tolmatscheff, Hoppe-Seyler's Med. Chem. Untersuch. Hf. 2 (1867), S. 272.
Schmidt-Mulheim, Pfliiger's Arch. Bd. xxx. (1883), S. 384.

CHEMICAL BASIS OF THE ANIMAL BODY. 133

Cholesteriu is characterised, apart from its crystalline form, l>y
some striking reactions which may be obtained even with micro-
scopic quantities.

(i) When the crystals are treated with concentrated sulphuric
add they usually turn violet or red. On the addition of a little
iodine the play of colours is very marked, the crystals being vari-
ously coloured, — blue, red, green, violet.1

(ii) When dissolved in chloroform, the solution turns blood-
red on the addition of an equal volume of concentrated sulphuric
acid : this turns to blue, green, and finally yellow, the. change of
colour being very rapid if the solution is freely exposed to the air
in an open dish. The sulphuric acid under the chloroform exhibits
a green fluorescence.2

(iii) When evaporated to dryness on porcelain with a few drops
of concentrated nitric acid, a yellow residue is obtained, which
turns red if treated, while still hot, with ammonia.

COMPLEX NITROGENOUS FATS AND THEIR DERIVATIVES.*
Lecithin. C^

Occurs widely spread throughout the body. Blood (red-cor-
puscles),4 bile, and serous fluids contain it in small quantities,
while it is a conspicuous component of the brain, nerves, yolk
of egg, semen, pus, white blood-corpuscles, and the electrical
organs of the ray. It occurs also in yeast6 and other vegetable
cells, and in small amount in milk.6

Tin- presence of lecithin in the red blood-corpuscles may prove to
be of no inconsiderable importance in connection with the possible
fixation liy them of carbonic anhydride.7 Setschenow has shown that
lecithin :u-t- like a base towards carbonic anhydride, each molecule of
the suli-taiH ••• being able to combine loosely with approximately one
molecule of the anhydride (-092 gr. lecithin fixes 2'7 cc. of CO,)
at a partial pressure of 56mm.8 Further, it is stated that red M ..... 1-

I figures in Fi-.nkc. Atlas d. />/i//.W. Cl,,m. Leipzig, 1858, Taf vi Fig. 2, .T
This work should !><> consulted for the crystalline forms of all physiologically im
jiortant substances. See also Ultzmonu u Hoffmann, ./if/a* d. £Tam*M%M>fe \Virn.

- <-f. Hnn-hanl. Innng. Dlts. Rostock, 1889. Al^t in /.'•». </. <f. chem. Gesell.

- 752.

•r a fuller account of the several substance* comprised in this group see
( Jan. •/. Chemistry, Vol. i. (1880), p. 425 et seq.

« Cf. HopptSeyfar, Phygiol. Chem. 1877, S

• BopptJMiTbr, '/.i. / /./,./.<;../. <'i,»n. IM. u. (is:s). s. 42: ; R<i in. s. .374.

9 Tolmatflcneff, al-o S. hmi<lt .Mulhcim, li>r. fit. (su!> Choleotprin).
7 Al S-hini.lt, It.,-, d •! U IM. MX. (1867 5 •!<>. Xunt7.,

./. mnl. ll'-s<. i MOW, Il.td. 1877. S. 625; IHT'.t. S.

I r.-,|rric.|. Cornet. Rend. T. LXXXIV. 1877,
p. 661. Mathiou ot I'rliain. //•/'/. ]. I

•<di..now. M,m. d, l'.\m,L /HI/- St. IVtor«l. T \ xv i (1879), No. 13. p. 19.

134 LECITHIN.

corpuscles contain about -75 p.c. of lecithin,1 hence 100 grm. red cor-
puscles might therefore hold in loose combination rather more than
22 cc. of carbonic anhydride. It is of course possible that the lecithin
does not exist in a free state in the unaltered corpuscles, and is there-
fore in living blood incapable of playing the part above ascribed to it.
Still the possibility that it may do so is distinctly worth some con-
sideration, bearing in mind how scanty is our knowledge of the real
conditions which determine the fixation of carbonic anhydride by the
blood.

When pure, it is a colourless, slightly crystalline substance,
which can be kneaded, but often crumbles during the process.
It is readily soluble in cold, exceedingly so in hot alcohol ; ether
dissolves it freely though in less quantities, as also do chloroform,
fats, benzol, carbon, disulphide, &c. It is often obtained from its
alcoholic solution, by evaporation, in the form of oily drops. It
swells up in water and during the action, as observed under the
microscope, extremely curious curling filamentous processes can
be seen to protrude from the edge of the solid. These are the so-
called ' myelin forms.' 2

Preparation. Usually from the yolk of egg, where it' occurs in
union with vitellin. Its isolation is complicated, and the reader
is referred to Hoppe-Seyler.3

Lecithin is easily decomposed ; not only does this decomposi-
tion set in at 70° C., but the solutions, if merely allowed to stand
at the ordinary temperature, acquire an acid reaction, the sub-
stance being decomposed. Acids and alkalis, of course, effect this
much more rapidly. If heated with baryta water it is completely
decomposed, the products being cholin, glycerinphosphoric acid,
and barium stearate. This may be thus represented : —

Glycerinphosphoric
Lecithin. Stearic acid. acid. Cholin.

C44H90NP09 + 3H20 = 2C18H3602 + C3H9P06 + C5H15NO.,

When treated in an ethereal solution with dilute sulphuric acid,
it is merely split up into cholin and distearyl-glycerinphosphoric
acid. Hence it has frequently been regarded as a sort of salt of
cholin with distearyl-glycerinphosphoric acid. It appears how-
ever more probable from the most recent researches that it is
really an ethereal compound of this acid with the cholin.4 It
appears also that there probably exist other analogous compounds
in which the radicles of oleic and palmitic acids take part.

1 Hohlbeck, Ref. in Hoppe-Sevler, Physiol. Chem. 1877, S. 402.

2 See M'Kendrick, General Physiology, 1888, p. 19.

3 Hdbch. d. phys.-path. chem. AnaL, 1883, S. 166.

4 Hundeshagen, Jn. f. prakt. Chem. Bd. xxvin. (1883), S. 219. Gilson, Zt. f.
physiol. Chem. Bd. xn. (1888), S. 585.

CHEMICAL BASIS OF THE ANIMAL IinPY. l:;r,

In accordance with these views the constitution of lecithin may
be most adequately represented by the following formula : —

/j.(CllHta_1O.)j

\0.PO(OH

NO.CSH4. (CH,),N.OH,

where CaH^Oj represents the radicle of a fatty acid which in
ordinary lecithin appears to be that of stearic, viz. Ci8H86O .

Glycerinphosphoric acid. C,H9P06. [C8H6. (OH)2. 0. PO (OH ) ,].

Occurs as a product of the decomposition of lecithin, and hence
is frequently found in those tissues and fluids in which the latter
is present. It may occur occasionally in urine.1

The acid is dibasic and forms salts which are usually, so far as
they are known, soluble in cold water, but the lead salt is an ex-
ception to this rule and may hence be used as a precipitant. The
salts are insoluble in alcohol.

It may be prepared by the decomposition of lecithin \\l\f\\
boiled with caustic alkalis or baryta. It may also be synthetised
by the direct action of phosphoric anhydride or glacial phosphoric
acid on glycerin. The formation by this method may be regarded
as resulting from the union of one molecule of glycerin with one
of phosphoric acid and elimination of one molecule of water.

Cholin. C5H16N02. |(CH,)8 = N^c CHS(OH ) 1 • tn
ethyl-ammonium hydroxide.

Discovered by Strecker a among the products of the decomposi-
tion of pigs'-bile and subsequently of ox-bile, whence tin- nuim-
cholin. It does not occur in the free state except as a product of
the decomposition of lecithin, but has been mvntly obtained in
extracts of the suprarenals.3 It is a colourless fluid, of oily con-
sistence, possesses a strong alkaline react inn. and t'nriii^ \\ith acids
very deliquescent salts. The salts with hydrochloric acid and
with the chlorides of platinum and of gold are tin- most important.

Cholin is a most unstable body, mere heating of its aqueous
solution sufficing to split it up into glycol. trimethvlamin and
ethylene oxide.

Since it is a product of the decomposition of lecithin it is best

1 Sutnitsdiowsky, '/.(. f. phi/iiol. Chem. Bd. iv. (1880), S. 214. But see also
Robii; Pkarm, T. n \> :>TJ. ami Chrw. C.nt,,,!!.. is«8, S. 186.

a .Inri. d. Chfm. n. I'luirm. 15,1. .\\iil. (l»6a). S. 3.VJ ; H.I. cxi.vin. (1868), S. 76.
• Marino-Zuco, Rend. d. /?. accad. d. Lincei, 1888, p. 835.

136 CHOLIN. NEUKIN.

prepared from the yolk of egg.1 The process is elaborate but
consists roughly in decomposing the residue of the yolk, left after
complete extraction with alcohol and ether, by boiling it for at
least an hour with caustic baryta. At the end of this period the
barium is precipitated by a stream of carbonic acid, the filtrate is
concentrated, extracted with absolute alcohol, and from this solu-
tion the cholin is precipitated as a salt by the addition of
platinum chloride. It is finally separated from this salt by means
of sulphuretted hydrogen.

Wurtz a has obtained it synthetically, first by the action of gl ycol
CH2 . OH

chlorhydrin on trimethylamine, and then by that of ethylene
CH2.C1
oxide on a concentrated aqueous solution of trimethylamine.

Cholin when pure is an oily liquid with a strong alkaline re-
action soluble in alcohol or ether. It yields crystalline com-
pounds with acids and some salts of which the double salts formed
with hydrochloric acid and the chlorides of either gold or platinum
crystallise readily and are employed for the detection and separa-
tion of the base. The platinum salt is readily soluble in water,
insoluble in alcohol. The gold salt is but slightly soluble in cold
water, but soluble in hot alcohol.

When boiled in concentrated solution cholin is decomposed into
glycol and trimethylamine.

(CH3)3 = N = C2H4(OH)2 + N (CH.),.

XCH2 . CH2(OH)

By oxidation with concentrated nitric acid it yields the ex-
tremely poisonous alkaloid muscarin C5Hi5NO3.3 Cholin is itself
possessed of poisonous properties, and arising as it does from the
decomposition of lecithin and protagon is now recognised as one
of the alkaloidal products or ptomaines (see below) which occur
in putrefying animal tissues.4

r /OH i

Neurin. C5H13XO. (CH3)3 = N\CH _ CH , trimethylvinyl-

ammonium hydroxide.

This substance is closely related to cholin both in composition
and origin, but is much more powerfully toxic than that body.

1 Diakonow, for ref. and details see Hoppe-Seyler's Hdbch. d. phi/s.-path. chem.
Anal. 1883, S. 163.

2 Ann. d. Chem. u. Pharm. Supl.-Bd. vi. Sn. 116, 201. Cf. Baever, Ibid. Bd.
CXL. (1866), S. 306.

3 Schmiedeberg u. Harnack, Arch. f. exp. Path. u. Pharm. Bd. vi. (1876), S. 101.
Cf. Berlinerblau, Ber. d. d. chem. Gesell. Jahrg. xvn. (1884), S. 1139. But see
also Bohm, Arch.f. exp. Path. u. Pharm. Bd. xix. (1885), S. 87.

4 Brieger, Zt. ' f. klin. Jfed. Bd. x. (1885), S. 268. See also Brieger's works
referred to below, sub Ptomaines.

CHEMICAL BASIS OF TU K ANIMAL BODY. 1,;7

It was first described as a product of the decomposition of pro-
tagon by caustic baryta,1 and until recently the names cholin and
neurin were applied interchangeably to the basic product of the
action of baryta on lecithin or protagoii first described under the
name choliu.2 The researches of Brieger have however shown
that neurin differs distinctly both in composition and properties
from tlu- older cholin, and have further identified it as one of the
most commonly occurring and actively toxic of tin- alkaloidal basic
products of the putrefactive decomposition of animal tissues known
under the name of the ptomaines8 (see below). Like cholin it
is in the pure state a sirupy fluid, with strongly alkaline reaction
and is extremely soluble in water. It forms with hydrochloric
acid and platinum chloride characteristic double salts which crys-
tallise readily. The double salt which neurin forms with gold
chloride crystallises in yellow needles ; it is but slightly soluble
in cold water, though soluble in hot water

Frotagon. C16oH808N6PO85(?).

A crystalline substance, containing nitrogen and phosphorus,
obtained by Liebreich* from the brain and regarded by him as its
principal constituent. The researches of Hoppe-Seyler and I)iak-
onow tended to show that protagon was merely a mixture of leci-
thin and cerebriu. A repetition of Liebreich's experiments has
however led Gamgee and Blankenhorn 6 to confirm the truth of
his results, and further confirmation has been afforded still mon-
recently.6 Protagon appears to separate out from warm alcohol
on gradual cooling in the form of very small needles, often arranged
in groups : it is slightly soluble in cold, more soluble in hot alcohol,
and in ether. It is insoluble in water, but swells up and forms a
gelatinous mass. It melts at 200° and forms a brown sirupy fluid.

Preparation. Finely divided brain substance, freed from blood-
vessels and connective tissue, is digested at 45° C. with alcohol
(85 p. c.) as long as the alcohol extracts anything from it. The
united extracts are filtered while hot, and the protagon separates
out from the filtrate on cooling to 0°. It is next thoroughly ex-
tracted with ether to get rid of all cholesterin and other bodies
sol ul tie in ether, and finally purified by repeated crystallisation
from warm ale,, hoi.

By treatment with boiling solution of caustic baryta protagon is

J Lichrei.-h, II. r. ,L ,1. ch.m. (fftrll. .Tahrtf. II. (lSf,'.n. S. 1-J

•liMinrti.m i" made between rholin and neurin in the latest edition (1883)

of H»|p[x--Sr\ It-r's I/itnilliiK/, il. /i/ii/*.-/Hlt/i. rh. ill. Allill.

8 Brieffe^ li>r. </. <l. chem. Getell. Jahrg. xvi. (1883), Sn. 1190, 1406; xvn. Sn.
516, 11.-17.

4 .\nn. //. r/,,m. „. />/«//•;«. M. . \\xiv. (If

6 Jl. of Phi/si,,!. Vol. n. (IHT'.i). j, ll.! AN., in /.i. f. f>hi/tiol. Chem. B<1. in.
(1879), S'. 260.' (iivf-s hi>t<.rv :in<l literatim- "f Tin- Miliji-rt to date.

6 Baumstark. ZLf.pkytUL Chan. I5d. i\. (1885), S i

138 CEREBRIK CHARCOT'S CRYSTALS.

decomposed, yielding the several products which result from the
decomposition of lecithin under the same conditions, together with
an additional product known as cerebrin.

Cerebrin.1 CnH88N08 (?).

Is found in nerves, in pus corpuscles, and largely in the brain.
In former times many names were given to the substance when in
an impure state, ex.gr. cerebric acid, cerebrote, &c. It was first
prepared by W. Miiller 2 who constructed the above formula from
his analysis; the mean of these is C, 6845. H, 11-2. N, 4-5.
O, 15 '85. Great doubts are however thrown upon the purity of
Miiller's preparations by the researches of later observers. From
a later investigation it appears to contain less nitrogen than is
stated above, the carbon and hydrogen beirig the same (C, 68 '74.
H, 10-91. N, 1-44. O, 18-91).3

It is prepared from brain substance by extraction with alcohol
and purified by recrystallisation from this solvent ; its complete
separation however from lecithin &c. is difficult, but is attained
by treating the mixture with boiling barium hydrate : this, while
it has no effect on the cerebrin, decomposes the lecithin.

It is a light, colourless, exceedingly hygroscopic powder, which
swells up strongly in water, slowly in the cold, rapidly on heating.
When heated to 80° it turns brown, and at a somewhat higher
temperature melts, bubbles up, and finally burns away. It is in-
soluble in cold alcohol, or ether ; warm alcohol dissolves it readily.
Heated with dilute mineral acids, cerebrin yields a sugar which
has recently been shown to be identical with galactose. (See
above p. 106.)

Charcot's Crystals.

These remarkable crystals, whose chemical nature and signifi-
cance have been the subject of much surmise, were first described
by Charcot4 in the spleen and blood of leukhaemic patients.
Later researches have confirmed their characteristic appearance in
this disease, and have further shown that they occur in health,
more particularly in semen, but also in various tissues ; 6 they are
also found in asthmatic expectorations. They may be readily
obtained from semen by extracting with warm water, to which a
little ammonia had been added, the residue which remains after

1 See Gamgee, Physwl. Chem. Vol. i. p. 439.

2 Ann. d. Chem. u. Phai-m. Bd. cv. (1858), S. 361.

8 Geoghegan, Zi. f. physiol. Chem. Bd. in. (1879), S. 332. See also Parcus, Jn.
f. prakt. Chem. (N.F.) Bd. xxiv. (1881), S. 310.

* Compt. Rend. Soc. Biol., 1853. Gaz. Hebd. I860, p. 755.

5 Zenker, Arch. f. klin. Med. Bd. xvnr. (1876), S. 125. Schreiner, Ann. d.
Chem. u. Pharm. Bd. 194 (1878), S. 68. Cf. Maly's Jahresb. iiber Thierchemie,
1878, S. 86.

CHEMICAL BASIS OF THE ANIMAL BODY. 139

semen has been treated with boiling alcohol. The crystals sepa-
rate out from this solution on concentration, and may be purified
by reerystallisation.

FIG. 6. CHARCOT'S CRYSTALS. (Krukenberg.)

The crystals are insoluble in alcohol, ether, and chloroform,
slightly soluble in cold and readily so in hot water. Dilute acids
iiiid alkalis also dissolve them readily.

It has been stated that the crystals are in reality a compound
of phosphoric acid with a nitrogenous base to which the name
spermin1 has been given, and the formula C2H6N(?) has been
assigned. This base is obtained by the addition to the crystals
of baryta water which forms a phosphate of barium and liberates
tin- base. It is soluble in water and alcohol, yielding strongly
alkaline solutions; it may be reconverted into Charcot's crystals
l>y the action of phosphoric acid.1 This base was at one time,
'led as closely related to, if not identical with ethylinimine
< II;. NH.2 It has however been recently shown that the two
substances are not identical, and it has further been stated that
the composition of spermin is most probably represented by the
formula C0H26N4.8

AMIDES AND AMIDO-ACIDS. THEIR DERIVATIVES
AND ALLIES.

\\IIDO-ACIDS OF THE ACETIC SERIES.

1. Amido formic acid. NHt.COOH.

This substance is identical with carbamic acid, one of the amiil<>-
il'-rivatives of carbonic acid, the first acid of the oxalic acid series.
It will be described under the oxalic group.

1 Sdirr-inor, Inc. cit.

Abel, Ber. d. d. chem. Getell. Jalirt; \\i (1888), S. 758. Ktliy-
liiiiniiiic appears (see next ref.) to be nothing but pipcrazinc, Hof man's dicth\ Irnc-
dianiiinv

Majort a. Schmidt, Ibid. Jahrg. xxir. (1891), 8. 241. 1'ochl.
S. 359.

140

GLYCIN. SARKOSIN.

2. Glycin. C2H6N02. [CH2 (NH2) . COOHJ. (Amido-acetic acid.)
^Also called Glycocoll and Glycocine.)

Does not occur in the free state in the animal body, but enters
into the composition of several important substances, more espe-
cially hippuric and glycocholic acids. It is also a product of the
action of hydriodic acid on uric acid, and of boiling acids and
caustic alkalis on gelatin : hence the name glycocoll or gelatiii;

FIG. 7. GLYCIN CRYSTALS. (After Funke).

sugar, since it possesses a sweet taste. It crystallises in large,
colourless, hard rhombohedra, or four-sided prisms, which are
easily soluble in water (1 in 4-3), insoluble in cold, slightly solu-
ble in hot alcohol, insoluble in ether.

Its solutions possess an acid reaction, but a sweet taste. Glycin
has also the characteristic property of uniting with both acids and
bases, to form crystallisable compounds, as also with salts. In
this it exhibits its amidic nature, which is further clearly evi-
denced by the method of its synthetic production by the action
of monochloracetic acid on ammonia: —

CH2 (Cl) . COOH -f 2NH3 = CH2 (NH2) . COOH + NH4 Cl.1

Preparation. Either synthetically as above or more usually by
the decomposition of hippuric acid by prolonged boiling with
hydrochloric acid, whereby it is split up into glycin and benzoic
acid, the latter being separated by crystallisation and shaking up
with ether in which glycin is insoluble.

3. Sarkosin. C3H7N02. [CH2 . KH (CH3) . COOH]. (Methyl-
glycin.)

Like glycin in its general chemical properties it further resem-
bles it in that it is never found in the free state as a constituent

1 Mauthner u. Suida, Monatshefte f. Chem. Bd. xi. (1890), S. 373.

CHEMICAL BASIS OF THE ANIMAL J!«U)V. Ill

of the animal body. It is however a substance of considerable
interest and importance, not merely on account of its chemieal
relationship to kreatin (see below) but as having been employed
in a well-known series of experiments intended to elucidate tin-
probable mode of formation of urea in the body. It was stated
that when sarkosin is administered to an animal in quantities
siu-h that tin- nitrogen given as sarkosin is equal to the daily
output of nitrogen as urea by the animal, the urea disappears
from the urine and is replaced by a new substance.1 The latter
appeared to be a compound of sarkosin and carbamic acid, known
generally by the name of methyl-hydantoic acid, — NH, . CO . N
(CH,) . CH» . COOH. This substance may be regarded as arising
from the union of one molecule of sarkosin with one of carbamic
acid and elimination of one molecule of water, or as being urea in
whieh two atoms of hydrogen are replaced by methyl and a resi-
due of acetic acid respectively : — NHS . CO . N (CH8) (CH2. COOH).
The conclusions drawn from these observations were that just as
methyl-hydantoic acid is supposedly formed by the union of
sarkosin with carbamic acid and subsequent dehydration, so also
would urea be formed if, instead of sarkosin, ammonia were pres-
ent, tn unite with the carbamic acid, form ammonium carbainate
(NH4. NH2. CO2) and by loss of water yield urea. Subsequent
repetition of these ingenious experiments has shown that they
are in no way conclusive, for in most cases the sarkosin is largely
excreted in an unaltered condition, methyl-hydantoic acid being
formed in very minute quantities if at all.2 It is further interest-
in;: to note that the purely chemical reactions which most readily
yield methyl-hydantoic acid out of the body, involve the inter-
action of sarkosin with cyanic compounds such as ammonium or
j'ota— ium cyanate.3 Moreover it has been shown that at the
temperature of the body sarkosin and urea in solution do not
yi<-ld methyl-hydantoic acid, although they do in ]>resen
baryta, especially when boiled.4 These facts show that Schultzen's
experiments do not strongly favour the carbamic-acid origin of
1 1 re; i ; they further show that the methyl-hydantoic acid is prob-
ably not Conned by a direct union of >arko>in and urea, ami are,
from a purely chemical point of view, rather in favour of a cyanic
in of urea.

4. Taurin. C,H7NSO,. [CH, (NH,) . CH, (SO, . OH) ]. Amido-
ethylsulphonic acid.

Isethionic acid, CH, (OH) . CH, . SO, (< >II ). like glycolic acid,

1 Srlnilt/.on, Ber. d. d. rh, ,„. /;. „ Y | *:•_•. S. 578.

« Baumaim u. von Mi-rin^. //-«/. lsT.\ S. :>*4 K. Salkowski, Ibid. S. 6.38.
A1-... /.'. I. /-Ai/MV. di.m. IM. iv (issn), sn. .V,, Inl. Hut nee also Sdiiff.-r, //./»/.
.•:,: ; 15.1. MI. (1883), S

8 Baumaim u. HopiKvSeyler, Ber. d. d. cheat. Getell. 1874, S. 34. Salkowski,
Ibid. S. Mr,.

4 Hauiiiuiiii u. Hoppe-Seyler, l»c. fit. Itaumaou, Ibid. S. -'

142

TAUKIN.

CH2 (OH). COOH. contains two hydroxyls replaceable by amidogen
NH2, so that two isomeric amido-derivatives can be formed from
it. Of these one is amido-iseth ionic acid CH2 (OH) . CH2 . S02
(NH2), the other amido-ethylsulphonic acid or taurin.1

Taurin is stated to occur in traces in the juices of muscles and
of the lungs, but it is known chiefly as a constituent of tauro-
cholic acid, which is one of the characteristic acids of bile, more
especially of the carnivora, and above all, of the dog.

It crystallises in colourless, regular, four- or more, usually six-
sided prisms ; these are readily soluble in water, less so in
alcohol. The solutions are neutral. It is a very stable com-
pound, resisting temperatures of less than 240° C ; it is not acted
on by dilute alkalis and acids, even when boiled with them. It
is not precipitated by metallic salts.

Preparation. Ox-bile is boiled for several hours with dilute
hydrochloric acid. The fluid residue is separated from the resin-
ous scum, and freed from any remaining traces of bile acids by
means of lead acetate, the excess of precipitant being removed by
sulphuretted hydrogen. The final filtrate is then concentrated to
crystallisation, and the taurin finally purified by recrystallisation

FIG. 8. TAURIN CRYSTALS. (After Kiihne.)

from

water. The use of the lead salt may be omitted in many
cases and the taurin purified by several crystallisations from
water.

The behaviour of taurin when introduced into the alimentary canal is
remarkable. In the case of man the larger part reappears in the urine
in combination with carbamic acid as tauro-carbamic acid. In dogs
a large part is excreted unaltered, together with some tauro-carbamic
acid. In herbivora (rabbit) on the other hand a portion of it is ex-

1 Taurin has usually been regarded as identical with amidoisethionic acid.
This is not the case. Seyberth, Her. d. d. chem. Gesell. 1874, S. 391. Erlenmeyer,
Neu. Rep.f. Pharm. Bd. xxm. (1874), S. 228.

CHEMICAL BASIS OF THE ANIMAL BODY. 143

creted in the urine, but the larger part is oxydised, leading to a large
iiH-rrase of sulphates in the urine together with some hyposulphite.
Injffti-il suhcutaiifously it is largely excreted in an unaltered form.1

' ro-carbamic acid. NHaCO . NH(CHa) . CH2 . (SO,OH). The
remarks which have been already nuule respecting the nature and for-
mation of sarkosin-carbaraic acid apply generally to this acid. It is
most easily obtained as a potassium salt by the action of potassium
cyanute mi taurin.2

5, Kreatin. C<H,N8Oa. [NH : C(^HS) ' CH..COOH].

(M'-ihyl-mianidinacetic acid.)

By the union of ammonia with cyanamide a strongly alkaline
base guanidin is obtained : CN . NHa -f NH8 = NH . C(NH2)2 (see
below). When sarkosin is employed instead of ammonia a similar
reaction takes place, resulting in the formation of kreatin :
• N NHa+CHa.NH(CH8).COOH=NH : C(NH.,).N(CH8).CHa.COOH.3
Since sarkosin is methyl-amidoacetic acid it is at once obvious
that kn-atin may be regarded as being methyl-guanidinacetic
acid.4 When cyanamide is treated with boiling baryta water it
taki-s u\> a molecule of water and yields urea, CN. (NH2) +HaO
'(NH2)a, hence as might be expected, kreatin yields by simi-
lar treatment sarkosin and urea. This is to the physiologist the
most important chemical property of kreatin, bearing as it does so
closely upon one possible source and mode of formation of urea in
tin- body. (See sub urea.)

Kivatin occurs as a constant and characteristic constituent of
muscles and their extracts to an amount which is variable, but
may be taken as from 0'2 - 0-3 p. c. on the weight of the muscle.6
It is also found in nervous tissue, and is said to occur in traces
in several fluids of the body. It must however be carefully borne
in mind that kivatin very readily loses a molecule of water and
thus becomes kivatinin, and that the latter with equal readiness
takes up a molecule of water to form kreatiu. Hence the kreatin
nhiaiiu'd during any analysis need not at all necessarily imply its
presence as such in the original tissue or tin id unless due allow-
ance has been made for the possible effect of the methods em-
ployed upon the reciprocal conversions of kreatin and kivatinin.
This is the cause of the conflicting statements as to the occurrence
of kreatin in urine ; as a matter of fact this excretion always con-
tains kreatin in. It is on the whole most probable that any

1 xilkownki, Der. d. d. chem. GeteU. 1872, S. 637. Virchow's Arch. Bd. LVIII
(1873) ; S. 4fiO.

kowski, Virchow's Arch. Bil. i.vm. (IK73), S. 460. Ber. d. d. chem. Gesell.
187.3, Sn. 744, II'.M, 1 :»!•.'. Huj.|«Tt. //./,/. 1278.

» Volhard, Sitsb. d. bayer. Akad. 1868, Hit. 3, S. 472. Also Zt.f. Chem. 1869,
S. 318.

4 Cf Horbaczewski, Wien. mrd. Jahrb. 1885, S. 459.

• Voit, Zt.f. Bid. Bd. iv. (1868), S. 77

144

KREATIN.

kreatin which may be found in urine is due to the conversion of
kreatinin into kreatin during its extraction, since it has been
shewn l that the more rapidly the separation is effected, the less

FIG. 9. KREATIN CRYSTALS. ( Krukenberg after Kiihne.)

is the quantity of kreatin obtained, and the greater, the amount
of kreatinin.

In the anhydrous form kreatin is white and opaque, but crys-
tallises with one molecule of water in colourless transparent
rhombic prisms.

The crystals are soluble in 75 parts of cold water, extremely
soluble in hot ; slightly soluble in absolute alcohol, they are more
soluble in dilute spirit and are insoluble in ether. The aqueous
solutions are neutral in reaction.

Kreatin is a very weak base, scarcely neutralising the weakest
acids, with which it forms soluble crystalline compounds.

Preparation. Most conveniently from ' Liebig's Extract.' This
is dissolved in 20 parts of water and precipitated by a slight ex-
cess of basic acetate of lead. The filtrate is then freed from the
lead salt by means of sulphuretted hydrogen and concentrated at
moderate temperature (avoid boiling) to a thin syrup. On stand-
ing in a cool place for two or three days the kreatin crystallises
out. The crystals are removed by filtration, washed with 88 p. c.
alcohol, and purified by recrystallisation from water.2

Kreatin yields no very striking reactions by means of which it
can readily be identified. It reduces Fehling's fluid by prolonged
boiling without any separation of cuprous oxide. On boiling in
presence of alkaline mercuric oxide, a transient red colour is ob-
tained and finally a separation of metallic mercury. The reac-

1 Dessaignes, Jn. de Pharm. et Chim. (3) T. xxxii. (1857), p. 41.

2 The mother-liquor from the kreatin may be used for the preparation of
hypoxanthin and sarcolactic acid. Drechsel, Darstell. physiol.-chem. Prdparate,
1889, S. 29.

CHEMICAL BASIS OF THK ANIMAL BODY. 145

tions of kreatinin on the other hand are striking (see below), and
hence kivutiu may be identified with most certainty by conversion
into kreatinin, and the determination of the presence of the latter
substance. The conversion is readily effected by boiling with di-
lute mineral acids, during which process kreatin loses one molecule
of water : C4H9N,O8 = C«H7N8O + H20.

M- -1111011 has already been made of the possible and very
probable genetic relationship of urea to muscle-kreatin (see
§ 484). This is a question to which brief reference will again
be made under urea,

r /NH - CO -i

G. Kreatinin. C4H7N,0. NH : C

L \N(CH,).CH2J

Kreatinin as already stated is simply a 'dehydrated form of
kivatin. It occurs normally as a constant constituent of urine,
varying however in amount from 0'5 to 4*9 grm. per diem accord-
ing to the amount of proteid food (meat) eaten.1 It is not a nor-
mal constituent of mammalian muscle but is found in the muscles
of some fishes,2 and has been obtained from sweat.8 It crystal-
lises in colourless prisms or tables according to the conditions
under which the separation takes place and the mode of pre-
paration, and frequently, owing to imperfect development, the
< nstals assume a very characteristic 'whetstone' form.

Fio. 10. KREATINIS CRYSTALS. (Krukenberg after Kiihne.)

Ki'-atinin is readily soluble in cold water (1 in 11*5), also in
alcohol, but is scarcely soluble in ether. The aqueous solutions
an- usually alkaline, but some observers regard the alkalinity as
<luc to impurities.4 It acts as a powerful base, forming compounds

1 Volt, /««-. ,-it. (sub kreatin).

J Kriik.-nlMTj.'. f'nt.ra. iihi/sioi. fn*t. Hcidclb. Bd. iv. Hf. 1. 0881), 8. 33.
* Onpranii-a, /Ml. It. Arr-nl. m.<L /.'..ma, Ann. VIM. (1882), No. 6.
« Salkowski, Zt.f.phytiol. Chem. Bde. iv. (1880), S. 133; XH. (1888), S. 211.

10

146 KREATININ.

with acids and salts which crystallise well. Of these the most
important is the salt with chloride of zinc (C^TNsO^ZnCla, both
on account of its characteristic crystalline form and of its general
insolubility in comparison with the other compounds of this sub-

FIG. 11. KREAirxiN-ziNC-CHLORiDE CRYSTALS. (Krukenberg after Kiihne.)

stance. Hence its formation is employed not merely for the de-
termination of kreatinin but for its separation from solutions. It
crystallises in warty lumps composed of aggregated masses of
prisms, or fine needles.

This compound is formed when a concentrated neutral solution
of the zinc salt is added to a not too dilute solution of krea£inin,
and since it is almost insoluble in alcohol it is frequently con-
venient to employ alcoholic rather than aqueous solutions of the
two substances.

Preparation.1 This does not admit of any useful brief descrip-
tion, but the principles involved are the following : —

(i) By the action of dilute boiling mineral acids on kreatin.

(ii) By concentrating large volumes of urine to a small bulk.
From this the kreatinin is obtained as a compound either by the
addition of chloride of zinc or by precipitation with mercuric
chloride. From these compounds it is then separated by boil-
ing with hydrated oxide of lead, and is finally purified by
crystallisation.

It may also be precipitated by phospho-tungstic and phospho-
molybdic acids.2

Apart from the characteristic formation of the compound with
zinc chloride, kreatinin yields several well-marked reactions, of
which the following are the more striking.

1 For details see Hoppe-Seyler, Phys.-path. chem. Anal. 1883, S. 182, and
Neubauer u. Vogel, Horn-analyse, 1890, S. 228.

2 For recent synthesis see Horbaczewski, loc. cit. (sub kreatin).

(INIMICAL BASIS OF THK ANIMAL BODY. 147

1. jr»///'.s i-i'iiction.1 To the suspected solution a few
drops of very dilute sodium i; ] are
added, and then, drop by drop, sum.- dilute caustic soda If
kreatinin is prex-nt a fine but transient niliy-ivd colour is ob-
tained which speedily passes into yellow. If the solution is now
acidulated with acetic acid and \\aiined it turns at first greenish
and finally blue.2 This last colour is due to the formation of
Prussian-blue.8 Weyl's reaction is extremely delicate and suf-

10 detect '0287 p. c. of kreatinin in pure solution, or '066 p. c.
in urine. According to Krukenberg the reaction is best obtained
by adding the caustic soda first and then a few drops of nm. ni-
trated solution of the nitro-prusside. (Juareschi recommends the
use of 10 p. c. solutions of the respective reagents.4

When applied to urine the absence of acetone should be ascer-
tained, since it also gives a similar ruby-red colour, but no sub-
sequent blue can be obtained from it, and the solution when
yellow turns red again on the addition of strong acetic aeid.
Hydantoin or methyl-hydantoin also yields the red colouration.

2. Jaffe's reaction.6 On the addition of an aqueous solution
of picric acid and a few drops of dilute caustic soda an intense
red colouration is produced. This suffices to detect '1 part of

•iuin in 5000 of water. Acetone alone gives a similar
colouration, but to a comparatively very feeble extent

I'.v prolonged boiling of kreatinin with r'ehlinu's fluid, reduc-
tion takes place, but there is no simultaneous separation of cuprous
oxide, and it appears that kreatinin may prevent the separation «'f
the oxide when the reduction is due not to itself but to such a
substance as dextrose.6

7 Leucin. C,H,,NOS. [CH8 . (CH,),CH(NH,)COOH].
(a-Amido-caproic acid.)

Is a characteristic product of the decomposition of proteids and

gelatin whether by the action of boiling acids, caustic alkalis, or

putrefactive influences. It occurs normally in variable amounts

in the pancreas, spleen, t hymns, thyroid, salivary glands, liver,

&c., and also in plants, more especially in those parts in which

reserve materials are accumulated, such as bulbs, tub.-]>, and

. It is also typically formed during the tryptic (pancreatie)

lion of proteids to an extent which amounts on the average

» Ber. d. d. chem. Getell. 187

- s.-iiuwski. /.t. /: /./M/.I/W. < '!„,„. n,i,.. iv. (iHso). s. m : \\. (1885), 8. 127.

9 Krnkcnbere, \'< i/,.?,,,!. </. />//</«••-»"•/. '•'•>. VVnr/.lnirs:. IM. xvm. (1884), S. 5.
roiitiriii.'.l by SalkowBki. Cf ( '..lasanti, M.-l.-s.-h-.tt's Untert. Bd. xni. (1888),
Hf. 6.

* Ann. di chim. t. difnrm - (1887), p. 195.

i'. phy»iol. Chem. Hcl. x. (ISHfi), S. 399.

8 Worm Mull.-r. I'lliiger's Arc/,. IM. \\\ n. (1882), S. 59.

348 LEUCIK

to some 8 — 10 p. c. on the proteid digested, and is in this case
always accompanied by tyrosin. It may occur in the urine, more
particularly in cases of acute yellow atrophy of the liver ; but its
presence in this excretion in other and more general diseased con-
ditions of the liver is by no means so constant or certain as it pre-
sumably would be on the common assumption that a large part of
the urea leaving the body is due to its formation from leucin under
the converting action of the liver.1

As usually obtained in a more or less impure form it crystal-
lises in rounded fatty-looking lumps which are often collected
together and sometimes exhibit radiating striation. When pure,
it forms very thin, white, glittering flat crystals. It is extremely
soluble in hot water, less so but still very soluble in cold water,
soluble in alcohol, insoluble in ether. The crystals feel oily to the
touch, and are without smell and taste. Leucin is particularly
soluble in presence of acids and alkalis. The aqueous solutions
are laevorotatory, acid and alkaline solutions on the other hand
dextrorotatory.

Preparation, (i) From horn shavings by prolonged boiling
with sulphuric acid, 5 of acid to 13 of water. The resulting

FIG. 12. LEUCIN CRYSTALS. (Krukenberg.)

fluid is neutralised by baryta and filtered, the excess of baryta
removed by the cautious addition of dilute sulphuric acid, and
the final filtrate concentrated to crystallisation. It is separated
from tyrosin by repeated crystallisation, taking advantage of the
great solubility of leucin and the slight solubility of tyrosin.
(ii) From the products of the tryptic (pancreatic) digestion of
proteids. After prolonged digestion, using thymol and salicylic
acid to prevent putrefaction, the fluid is filtered, moderately con-
centrated, and set aside to crystallise ; by this means a large part

1 Cf. Salkowski, Die Lehre vom Ham, 1882, S. 427. Lea. Jl. of Phusiol. Vol.
xi. (1890), p. 258.

CHEMICAL BASIS OF THE. ANIMAL BODY. 1 !'.»

of the accompanying tyrosin is removed. The filtrate is now
further concentrated, treated with excess of hot alcohol, which
precipitates the peptones, and filtered while hot. If much leucin
is present ;i lari;e part of it crystallises out on cooling the aleo-
holir filtrate, ami tin- rest on concentrating by slow evaporation.
There is a large loss of leucin by both the above methods, and
the resulting product is far from pure. To obtain pure leucin
it should be synthetised by the action of ammonia on a-brom-
caproic acid.1

M an approximately quantitative separation of leucin from solu-
tions when- it is mixed with "ther substance.-, e. g. an extract of tis-
siie-, or a digestive mixture, is a matter of great difficult v. Advantage
may in smut- ease> In- taken of its behaviour toward > hydrated oxide of
copper, with which it forms a compound. -

For ordinary practical purposes the microscopic appearance of
the crystals affords tin- must convenient means for recognising
leucin, and in this way very minute traces may be determined
with certainty. The confirmation of the clue thus afforded by
tin- application of chemical tests is however not easy unless a
tail amount of material is at hand, and that in a pure condition.
In the latter case the following tests may be applied, (i) When
'i illy heated to 170° leucin sublimes and yields a charac-
teristic odour of amylamin The only other substance of physio-
logical importance ordinarily met with which yields a sublimate
on heating is hippuric acid, due to its decomposition and the sub-
limation of the benzole acid thus set free, (ii) »sv// </•»/•'.-<• /•.>/.
< >nly applicable to very pure leucin. The suspected substance is
evaporated carefully to dryneu with nitric acid on the lid of a
platinum crucible; the residue, if it is leucin, will be almost
transparent ami turn yellow or brown on the addition of caustic
soda. If this be again very carefully concentrated with the al-
kali an oily drop is obtained, which runs over the platinum in a
-pheroidal state.

The optical properties of leucin have not as yet been fully
worked out. Experiment shows that its solutions are sometimes
optically active, at other times inactive, dependently upon the
source and mode of formation of the leuein. This corresponds
to the expectations as to its optical behaviour based, in ac-
• •ordance with the Van't HoH-I.e I'.el hypothesis, upon its con
Mitutional formula.'

The possible relationship of leucin to the formation of urea in

1 IIufli.T. .In f.i>r,,kt. ('htm. (2) Bd. I. (1-

'\-t.\\ H:il,iTiii:inii. .\nn. il. ('!„,„ ii I'li'irm. IM. • i \i\ . i I -:•:>.-

• For details see Mautlim-r. '/.'. / i>h>i*iol. Cf,,m. IM. vn. (1
Srhiil/..-, //•/./. IM. ix. ..uit-.i,. /

S. U.V.t. I.ij.piiiaiui, I - i.'i S< luilre u. BoMhard, Zt. f. phenol, '

Bd. x. (188C,), S i:u

150

CYSTIN.

the body has been already pointed out (§ 488). It will be further
considered under urea.

AMIDO-ACIDS OF THE LACTIC SERIES.

Cystin. (C8H6NS02)2 . [S . C(CH8)(NH2) . COOH]2.
pholactic acid.1

Amido-sul-

Is the chief constituent of a rarely occurring urinary calculus
in men and dogs. It may also occur in renal concretions, and in
gravel, and is occasionally found in urine, from which it separates
out as a greyish sediment on standing. It is prepared from this
sediment, or better still from cystic calculi, by solution in am-
monia. This solution is then allowed to evaporate spontaneously
and yields the cystin in regular, colourless, six-sided tables of very
characteristic appearance. Cystin may be separated from urine
by taking advantage of the formatioa of a sodium salt of ben-
zoyl-cystin when it is shaken up with a few drops of benzoyl-
chloride.2

FIG. 13. CYSTIN CRYSTALS. (After Funke.)

Cystin is insoluble in either water, alcohol, or ether, readily
soluble in ammonia, differing in this respect from uric acid, also
in many alkaline carbonates and in mineral acids. Its solutions

1 The constitution of cystin has been variously stated by different authors, and
will only be known with" certainty when its synthesis has been accomplished.
Slightly different formulae have been assigned to it, containing respectively 5, 6, and
7 atoms of hydrogen. The literature is fully quoted by Kiilz, Zt. f. Biol. Bd. xx.
(1884), S. 1. Cf. Baumann, Zt. f. physiol. Ch'em. Bd. vni. (1884), S. 299.

2 Goldmann u. Baumann, Zt. f. phi/siol. Chem. Bd. xn. (1888), S. 254. Udranskv
u. Bamnann, Ibid. Bd. xv. (1891), S. 87.

CHEMICAL BASIS OF THE ANIMAL IIODV. 151

are strongly la •vnmtatury, (a)D =-205<9° in hydrochloric acid
112 j>. c.1 or if the acid is dilute (a)D = -214°.2

Apart from the characteristic crystalline form and its solubility
in ammonia, the fact that cystin is one of the few crystalline sub-
stances, occurring physiologically, which contain sulphur, ren-
ders its detection \vi Thus when boiled with caustic
alkalis a sulphide of the alkali is obtained which gives a dark
stain on silver foil; also a brown or black colouration appear-
when cystin is boiled in a test-tube with a solution of oxide of
lead in caustic soda.3

AMIDO-ACIDS OF THE OXALIC SERIES.

1. Carbamic acid. NH,(COOH).

Carbonic acid is more usually classed at the head of the acids
of the glycolic (lactic) series. It exhibits however a remarkable
difference from the remaining acids of this group, since they are
all monobasic, whereas carbonic acid is dibasic. It may therefore
be more appropriately classed with the dibasic acids of the oxalic
series. In virtue of the two replaceable hydroxyls which it con-
tains, it yields two amido-derivatives, of which the first is car-
bamic acid, the second urea (NH2)2CO or carbamide. Carbamic
acid is a substance of peculiar interest to the physiologist on
account of the important part it is frequently supposed to play
in the formation of urea in the animal body. It is formed by the
direct union of equal molecules of dry ammonia and carbonic
anhydride, a second molecule of ammonia uniting witli it at the
same time to yield the ammonium salt or ammonium carl »a mate.
Thus 2NH8 + CO8 = NH4 NH,CO, : simple dehydration of this
salt yields urea (NH2)3CO. This point will be returned to further
on when discussing the probable mode of formation of urea in the
body.

Carbamic acid is unknown in the free state; its best known
salt i- that with ammonium, but many others have been prepared.
It further apjM-ars that some of its salts occur in serum, and it is
^tate.l to I..- formed during the oxidation of glycin, leucin.
ami tyrosin by means of potassium permanganate in alkaline
solution.4 Ammonium carbamate i- extremely soluble in water.

i Mautlm..,-. 7.i / pkgM. '(.'hem. Bd. vn. (1883), S. 225. Cf. Drechael, .1

i:

- Bamnanii, iif. <-,!. S. :tn:t

8 The following literatim' may ho a<Miti«mally con.siiltoil on the occurrence of
cystin in iiriii.-. /.< t. ;./.•/.</../. ft,', m. 15.1.- l\. I •_>'.•. -_'M>: \ll --'.VI; \n
Vin-how's .liW/. I 3 Lit M,; - Ja 1884 S. 465. Berl. klin.

tck. I**'.*. No. If,. '/.< /. /.//». .\f"l. ll.'l. \^ - .325.

1 Dn-. hsrl, II, r. il.l:. s. (,'. |'/itr M-illi. nntum-iss. CI. .Tllli. I -7 "•

./»/. /'. prnk-t. Chrm. (•>) H.I. XII. ( 1«75). - I. (1877), 8. 180 ; XXII. (1M

\>-rh. f. ri»i*i»l. Jahrjf. 1880, S. 550. But see »Uo ll.,fin. i-t.-r. 1:
.1 1M \n (1871 8

152 ASPARTIC. GLUTAMIC.

in which solution it is gradually converted into the carbonate.
At ordinary pressures when heated to 60° it is decomposed into am-
monia and carbonic anhydride, but under pressure at 130° -140°
it yields urea. When electrolysed in told aqueous solution by a
rapidly and continuously commutated current the salt similarly
loses water and yields urea (Drechsel). The dehydration may be
represented as taking place in the following way : —

+ H20.
ii.

or by the action first of H2 and then of O.1

2. Aspartic (or asparaginic] acid. C4H7N04. [COOH . CH2 . CH
. COOH]. Amido-succinic acid.

This acid is chiefly obtained from plant extracts, and occurs
notably in beet-sugar molasses. It may be synthetised, but is
most conveniently prepared by boiling asparagin with caustic
alkalis or mineral acids. It is also a typical product of the action
of boiling mineral acids and caustic baryta on both vegetable and
animal proteids (antea p. 49) and of acids on gelatin,2 being
usually accompanied by its homologue, glutamic acid. It is also
now recognised as a product in minute quantities of the pancrea-
tic digestion of fibrin3 and vegetable glutin,4 although it does
not occur as a constituent of any animal tissue or secretion. It
crystallises in rhombic prisms which are but sparingly soluble in
cold water or alcohol, but readily soluble in boiling water. Its
solutions, if strongly acid, are dextrorotatory, but if alkaline, Isevo-
rotatory. It forms a characteristic readily cry stalli sable compound
with oxide of copper, which is practically insoluble in cold, but
soluble in boiling water, and may be used for the separation of
aspartic acid from solutions in which it is mixed with other
substances.5

3. Glutamic (or glutaminic) acid. C5H0N04. (Amido-pyro-
tartaric acid).

This acid is homologous with aspartic acid. The circumstances
and conditions under which it occurs are in general the same as
for aspartic acid, but it has not as yet been obtained by the action
of pancreatic enzymes on proteids and is never found in any
animal tissues or secretions. But as a product, often to a large
amount, of the artificial decomposition of proteids it acquires some

1 Cf. Ludwig's Festschrift, 1887, S. 1.

2 Horbaczewski, Sitzb. d. k. Akad. d. Wiss. Wien. Bd. LXXX. (2 Abth.) Juni-
Hft. 1880.

3 Radziejewski u. Salkowski, Ber. d. deutsch. chem. Gesell. Jahrg. vu. (1874),
S. 1050.

* v. Knieriem, Zeitsch. f. Bid. Bd. xi. (1875), S. 198.

5 Hofmeister, Sitzb. d. k. Akad. d. Wiss. Wien, Bd. LXXV. (1877), 2 Abth.
Marz-Hft.

CHEMICAL BASIS OF THE ANIMAL BODY. 153

considerable importance. It is always prepared by treating pro-

t.-ids with boiling mineral acids.1

It crystallises in rhombic tetrahedra or octahedra ; is not very
soluble in cold, but readily soluble in hut water; insoluble in
alcohol and in ether. Its aqueous and acid solutions possess a
dextrorotatory power.

I Asparagin. C4H8X20,+ H2O. [COOH . CHa. CH (NH2).

<|>M LJ. Amido-succinaraic acid.

Although asparagin is not found as a constituent of the animal
body it is a substance of considerable interest to the physiologist.
Not only is it closely related to aspartic acid, into which it may
be converted by the action of boiling acids and alkalis, yielding at
the same time ammonia, but it undoubtedly plays a most impor-
tant part in the constructive proteid metabolism of plants. Further
it exists iii not inconsiderable amount in many plant-tissues used
as food by man, and is known, like so many of the members of
the numerous class of amido-acids to which it belongs (leucin,
•jlycin, &c.) to give rise to urea when taken into the body of <-ar-
nivora,2 and to uric acid in that of birds.3

In plant.- asparagin, like leucin, is found chiefly in those parts
which afford a store of reserve material, such as bulbs, tubers, &c., and
the cotyledons of seeds. The amount is however largely im-n-a-ed
during germination, and it is therefore present in frequently very
large quantities in seedlings, as for instance those of yellow lupins
(30 p. c.). The increase in the young growing plant is ni»-t probably
due chiefly to a formation of asparagin out of tin- decomposition of
• -proteid-, although some may be formed synthetically. The
amount i.- greatest when the seeds are germinated in the dark and the
seedling sub.-ei|iient ly grown for -Mine time in .-emi-obsciirity and
shielded from the access of carbonic anhydride. 1'nder the> ..... mdi-
tions the formation of non-nitrogenous (? carbohydrate) material is
simultaneously prevented; and putting the two i\\<-\< together it ap-
pears probable that the disappearance of a-paragin in seedlings grown
under ordinary conditions is tine to its consumption f,,r the synthetic
production of proteids.4 It is conceivable that the amido-acids and
amides may similarly play some part in the synthetic nietaboli-m ..('
animal tissues, though to a presumably much -lighter extent, bearing
in mind how in plants constructive im taholi-m preponderates so
largely over the destructive.*

Asparagin crystallises readily in large rhombic pii<m- which
tan not very s.'.lnbli- in e«>ld. hut n-adily soluble in hut water.
and are insoluble in absolute ale. .1ml ami in ether. Its solutions

H. Kn-ii.l.-r. .f». f prnlt . ('he,,,. (2) IM. III. (1871), 8. 314.
v. KiiH-ri-in. Xi f. /.'»•/ I
3 v. Kiii.Tirin. /',i,/. MIL (1-7"
« Cf Vii,,^. /V,v>"./-;v »f I'l'ini*. |-|.. r-'». 150, 174.
• Lea, Jl. ofPhysiol.'Vol. xi. (1890), p. 258.

154 ASPAKAGIN.

are dextrorotatory. It may be prepared synthetically,1 but is
usually obtained by crystallisation from the expressed juice or
extracts of the seedlings of peas, beans, or lupins.2 Mercuric
nitrate yields a precipitate with aspardgin which may be used for
its separation from vegetable extracts.3 Urea-ferment converts it
into succinic acid.4

One point of interest with respect to asparagin remains to be
briefly mentioned. Seeing that in plants the nitrogen requisite
for the construction of proteids appears to be obtained largely
from asparagin, is there any evidence that in animals also the
nitrogen of this substance can take the place of that of proteids ?
The answer to this question may be stated as follows: When
asparagin is administered to carnivora or birds practically the
whole of it is converted into urea or uric acid respectively.5 Thus
in carnivora at least there is no diminution of proteid metabolism,
such as is observed under a gelatin diet, when asparagin is added
to the food. In herbivora on the other hand there appears to be
somewhat distinct evidence that a part of the nitrogen in proteids
may be replaced by that of asparagin.6

The question as to the importance of the nitrogen of asparagin as a
possible replacer of that of proteids arose first in connection with the
dispute already referred to (p. 122) on the mode of formation of fats in
the animal body. In the experiments of Weiske and Wildt 7 on which
Voit chiefly based his original views, a diet of potatoes was largely
used. The amount of proteid in these was calculated from the total
nitrogen they contained, on the assumption that there was no nitrogen
present in them in any form other than that of proteids. As a matter
of fact potatoes contain a not inconsiderable quantity of asparagin,8 so
that making allowance for this the total amount of proteid given in
their experiments was much less than they supposed, and might not
have sufficed to account for the fat stored up. This difficulty would
obviously be got over if it could be shown that the nitrogen of asparagin
can play the part of the nitrogen of proteids.

1 See recently Piutti, Chem. Centralb. Bd. xtx. (1888), S. 1459.

2 Piria, Ann. de Chim. et de Phys. (3) T. xxn. (1847), p. 160. Schulze u.
Bosshard, Zt.f. phi/siol. Chem. Bd. ix. (1885), S. 420.

3 Schulze, E., Ber. d. d. chem. Gesell. 1882, S. 2855.

4 Bufalini, Ann. di chim. e di farmac. (4) T. x. (1889), p. 207.

& Von Knieriem, loc. cit. But cf. von Longo, Zt. f. phusiol. Chem. Bd. i. (1877),
S. 213.

6 Weiske, Zt.^f. Biol. Bd. xx. (1884), S. 277. Weyl, Biol. Centralb. Bd. n.
( 1882-83), S. 277. These give copious references to literature up to date. In
addition see Voit, Sitz. d. Bai/r. Akad. 1883, S. 401. Rohmann, Pfluger's Arch. Bd.
xxxix. (1886), S. 21. (On storage of glvcogen.)

' Zt.f. Biol. Bd. x. (1874), S. 1

8 Schulze u. Barbieri, Landwirth. Versuchs-Stat. Bd. xxi. (1877), S. 63.

CHEMICAL BASIS OF THE ANIMAL BODY. 155

THE UREA AND URIC ACID GROUP.1
1. Urea. (NH3),CO. (Carbamide).

This is tin- chief nitrogenous constituent of normal urine in
mammalia and some other animals. The urine of birds also con-
tains a small amount, more particularly on a meat diet Average
normal human urine contains from 2'5 — 3-2 p.c., the average total
daily r.\rivti<>n varying from 22 — 35 grams or as a mean 30 grams.
It is also found in minute quantities in normal blood 2 (-OHf* p.r. )
serous fluids, lymph, and aqueous humour: it is not usually met
with in the tissues except that of tin- liver.3 It is never present
in normal mammalian muscles, but may make its appearance there
under certain pathological conditions. Under ordinary conditions
the amount of urea in sweat is almost inappreciable, but the older
statements of its occurrence in this excretion have recently received
continuation, and it appears that this source of nitrogenous loss to
tin- body may have to be taken into account4

FIG. 14. UREA CRYSTALS SEPARATED BY SLOW EVAPORATION FROM
AQUEora SOLUTION. (After Funkc.)

When pure it crystallises from a concentrated solution in t In-
form of IOIIL:, thin glittering needles. If deposited slowly from
dilute solutions, the form is that of four-sided prisms with pyrami-
dal ends; these are always anhydrous. When tin- separation
rapidly, as for instance from a strong alcoholic solution on
•--slide, the typical crystalline form is not readily obwned.
but rather that of irregular dendritic crystals.

Urea is very soluble in mid water, distinctly less soluble in cold
alcohol, readily so in hot ; it is insoluble in anhydrous ether and

1 For full details of tin- NMtfaM, pMOOtiM, Md methods of detcriniiiini: and

dealing practically with tin- in<'inl>«Ts of this £r»ii]i, consult in all caw»H NmhaiuT 11.

.[ti>ili/xf il>ti Ifnrna. Salkow.ski U. Letlbe, Die I.thr- mm Hum. Hoppc

r. /'/ii/xio/. -;«;///. rfiiin. Antllt/Kt.

' • d II ' tw!g, 1 -"l

» Hut ne ii..|,|,,- s,.yi,T, /.i. t: ,,/i •/.„•/.»/. r< nssi), S.348.

« ArpUinsky, 1'tlutrVr's Ar.-l,. H,| XLVI. (18i»0). S. 594.

156

UKEA.

in petroleum-ether.1 It possesses a somewhat bitter, cooling taste,
resembling saltpetre.

Preparation, (i) From urine by concentration to a sirupy
state, extraction of the residue with absolute alcohol, and concen-
tration of the alcoholic extract, by slow spontaneous evaporation
in a warm place, until the urea crystallises out. This is then
purified by recrystallising from alcohol, decolourising with char-
coal if required. Or the urea may be precipitated as nitrate by
the addition of pure colourless nitric acid to strongly concentrated
urine cooled to 0°. The nitrate is then decomposed in water by
the addition of barium carbonate, and the urea extracted as before
with alcohol, (ii) Synthetically in many ways, of which the
most usual and convenient is by mixing equivalent proportions of
ammonium sulphate and potassium cyanate; the ammonium
cyanate thus formed is evaporated to dryness, whereupon it
undergoes a molecular transformation to urea, which is then ex-
tracted with alcohol : thus NH4 . CON = NH2 . CO . NH2 .

It is interesting to note that the above synthesis of urea, obtained
in 1828 by Wohler, was the first instance in which a substance
ordinarily elaborated by the specific activity of the animal body
was artifically prepared.

Urea readily forms compounds with acids and bases ; of these the
following are important as a means of detection and identification.

Nitrate of urea. (NH2)2 CO . HN03.

Obtained by the addition of a slight excess of pure colourless
nitric acid to a moderately concentrated solution of urea. The
nitrate should separate out rapidly in the form of six-sided or
rhombic tables, frequently aggregated in piles, but the successful
obtaining of typical crystals requires some attention to the con-
centration of the solution.

FIG. 15. CRYSTALS OF NITRATE OF UREA. (Krukenberg after Kiihne.)

1 Petroleum-ether consists of the products, with low boiling-points (up to 120°),
of the distillation of ordinary petroleum. It is also known commercially under the
name of ligroin.

CHEMICAL BASIS OF THE ANIMAL BODY. ir.7

The crystals are but slightly soluble in nitric acid, or alcohol,
more soluble in cold water, and much more so in hot water. They
are insuluhle in ether.

Oxalate of urea. [(NHt)aCO],.H2C804 + H2O.

Obtained by the addition of concentrated aqueous solution of
oxalic acid to a concentrated aqueous solution of urea. This salt

Fio. 16. CRYSTALS OF OXALATE OF UREA. (Krukenberg after Kiihue.)

crystallises out in rhombic tables closely resembling those of the
nitrate, but they are frequently aggregated into a characteristic
prismatic form. As in the case of the nitrate some care is required
with respect to the concentration of the respective solutions during
its preparation.

The crystals are less soluble in oxalic acid than in water, but
may in other respects be taken as resembling those of the nitrate
in respect of their solubilities.

Of the many salts which urea forms with other bases and salts
those which it yields with mercuric oxide and nitric acid are of
most importance. When a solution of mercuric nitrate is added
to one of urea a precipitate is formed which, dependently upon tin-
concentration and relative amounts of the two solutions, may con-
tain some one of three possible salts, consisting of [(NHa)sCO]j.
\'O3)2 united with 1,2, or 3 molecules of mercuric oxide (HgO).
When tin- solutions are fairly neutral and itifntr, the salt with
:) molecules of HgO is formed [(NH,), C0]2 . Hg(NO.), . 3 HgO.
This is the salt formed in the reactions on which Liebig's vol-
umetric method for the determination of urea is based.

The other more important reactions of Urea.

1. Urea may be heated dry in a tube to 120° without brin-_:
decomposed ; on further raising the temperature it melts at 132-601

1 Reissert, Ber. d. d. chem. Getell. Ed. xxm. (1890), S. 2244.

158 UKEA.

and afterwards gives off ammonia, and if heated to 150° for some
time is converted largely into biuret : 2(NH2)3CO=NH2.CO.NH.CO
(NH2)+NH3. On further heating to a higher temperature (200° )
it is largely converted into cyanuric acid. When biuret is dis-
solved in water and treated with caustic soda and dilute sulphate
of copper it yields the well-known pink colour employed for the
detection of peptones, and hence called the ' biuret reaction.' In
the application of the test to urea some caution is requisite while
heating the suspected substance to avoid carrying the decomposi-
tion beyond the biuret stage. When boiled in aqueous solution
with strong sulphuric acid or alkalis it is gradually decomposed,
under assumption of two molecules of water, into carbonic acid and
ammonia ; the same decomposition ensues by simple heating of the
aqueous solution in sealed tubes, to 180°. This forms the basis
for the older 'Bunsen method' of estimating urea. A similar
change (hydration) is produced under the influence of several
micro-organisms which are found in urine undergoing alkaline
fermentation. Of these the best known is the Micrococcus ureae 1
from which a soluble hydrolytic enzyme may be extracted.2 (See
above, p. 70.)

2. When treated with nitrous acid, e.g. impure yellow nitric
acid, it is decomposed finally into carbonic anhydride, nitrogen, and
water: (NH2)2CO -f 2HNO.2 = C02-|-2N2 + 3H20. A similar de-
composition is obtained by the action of sodium hypochlorite or
hypobromite : (NH2)?CO -f 3NaBrO = SNaBr + C02+N2-f-2H20.
Since the volume of nitrogen evolved is constant for a given weight
of urea, this latter reaction forms the basis of a method for the
quantitative determination of urea. (Knop-Hiifner. )

3. When a crystal of urea is treated with a drop of concentrated
freshly prepared aqueous solution of furf urol — - C5H402 (aldehyde
of pyromucic acid) and then immediately with a drop of hydro-
chloric acid (sp. gr.= riO) a play of colours is observed which
passes rapidly from yellow through green, blue, and violet to a final
brilliant purple. The test may be also applied by the addition of
three drops of the acid to a mixture of one drop of 1 p.c. aqueous
urea solution and '5 cc. of aqueous furf urol solution.3

Detection in Solutions. In addition to the microscopic appear-
ance of the crystals obtained on evaporation, the nitrate and oxa-
late should be formed and examined. Another part should give a
precipitate with mercuric nitrate, in the absence of sodium chloride
but not in the presence of this last salt if in excess ; in presence
of sodium chloride the mercuric nitrate reacts first with the sodium
salt in preference to the urea. A third portion is treated with

1 Pasteur, Compt. Rend. T. L. (1860), p. 869. Van Tieghem, Ibid. T. LVIII. (1864),
p. 210. Jaksch, Zt. f. ph^siol. Cttem. Bd. v. (1881), S. 395.

2 Musculus, Pfluger's Arch. Bd. xn. (1876), S. 214. Lea, Jl. of Phusiol. Vol. vi.
(1885), S. 136.

3 Schiff, Ber. d. d. ckem. Gesell 1877, S. 773.

CHKMICAL IIASIS OF THK ANIMAL BODY. 159

nitric acid containing nitrous fumes; if urea is present, nit:
and carbonic acid will be obtained. To a fourth part pun- nitric
acid in excess and a little mercury an- adiled, and the mixture is
warmed. In presence of urea a mlmi /•/!•** mixture of gases (X and
COS) is given off. A tifth jiortioii is treated, after evaporation to
dryness, in the way above described for the application of the
biuret reaction, and a sixth part is tested with furfurol.

Quantitative determination. The methods are based on some
of the reactions above described. They consist of (i) Precipita-
tion by a standardised solution of mercuric nitrate (Liebig).
(ii) Decomposition into carbonic acid and nitrogen by means of
sodium hypohromite, and measurement of the volume of nitrogen
(Knop-Hiifner). (iii) Conversion into carbonic acid and ammonia
by heating in a sealed tube with an ammoniacal solution of barium
chloride, and determination of the weight of barium carbonate
obtained. ( Hunsen.)

Although simple in principle, the above methods, and especially
the first, require the careful observance of certain precautions to
ensure accuracy. The needful precautions have recently been
most assiduously investigated, more particularly by Pttiiger and
his pupils, and of these and of the application of the methods a
full account is given in Neubauer and Vogel's exhaustive work /'/•
'//>•'• des ffarn*.

The determination of the total nitrogen in urine is also of great
importance, and is now usually carried out by Kjeldahl's method.1
This consists in converting all the nitrogen of a measured portion
of urine int.. ammonia by boiling with fuming sulphuric acid and
the sul)se.|uent addition of potassium permanganate. The am-
monia is then expelled from the acid solution by distillation with
an excess of caustic soda or potash, the ammonia l.eing received
into a measured volume of standardised acid, whose diminution of
acidity due to the absorption of ammonia is finally determined by
titration with standard alkali.

The synthesis of urea by molecular transformation of ammonium
cyanate indicates an undoubtedlyclo-,. ivliitimishipof un-a to cyanic
acid, and then- an- other reactions which enforce the same idea.
Thus by the union of water with cyanamide, which is readily
affected by treatment with 50 p.c. sulphuric acid, urea is obtained:
— ON. N 1 1 . -f H,O = (NH,), CO. It is further stated that when
potassium cyanate and acid potassium tartrate an dissolved in
water and the mixture is kept for some time, a not inconsiderable
amount of urea is formed along with some carbonic acid,2 thus
affording experimental support of Salk«\\»ki's view3 that urea

1 /.I. f. nnnl. <'h,m. It.l xxtl. (188.1). S. 366.
3 Hoppe-S.-vl.-r. Pkytie < - *09.

• Zt. f. phyiiol. L'hem. Bd. I. (1877), 8. 41.

1GO UKEA.

might arise in the body from the union of two molecules of cyanic
acid and one of water : CO.NH+CO.NH+H20 = (NH2)2CO+CO2.
The final formation of cyanuric acid (CO.NH)8 by the action of
heat on dry urea is further evidence in the same direction. On
the other hand there are a number of reactions resulting in the
production of urea, which leave but little doubt that urea, while
closely related to cyanic acid, is truly the amide of carbonic or
carbamic acid. Thus by the action of ammonia on phosgene
gas: — COCl2-r-2NH3 = CO(NH2)2 + 2HCl: of ammonia on
diethyl-carbonate : — CO.(C2H50)2 + 2NH3 = CO(NH2)2 + 2C2H5.
OH : — reactions which are strictly analogous to the formation of
acetamide CH3 . CO(NH2) by the action of ammonia on acetyl
chloride CH3 . COC1, and on ethyl-acetate CH3 . COO (C2H5).

It is interesting to observe here that acetamide yields methylcyanide
by treatment with phosphorous pentoxide : — CH3 . CO (NH,) = CH3.
CN+H.O.

Acetamide is also formed by the dry distillation of ammonium
acetate, the change being one of simple dehydration ; and this re-
action is one of general applicability, amides being formed by the
removal of one molecule of water from the ammonium salt of a
monobasic acid or of two molecules of water from that pf a dibasic
acid, e.g. ammonium oxalate yields oxamide. Now although urea
has not been formed by the dehydration of ammonium carbonate,
it is readily rehydrated into the carbonate by the action of acids,
alkalis, superheated water, or the urea ferment. Further, if instead
of operating on ammonium carbonate the ammonium salt of car-
bamic acid (see p. 151) be heated in sealed tubes to 140°, or if it
be electrolysed with a rapidly commutated current, it loses a mole-
cule of water and is converted into urea.

When the purely chemical facts above stated are applied to the
formation of urea in the animal body it is at once obvious that
urea might originate from some cyanic source, or from a simple
dehydration of ammonium carbonate or carbamate. A full dis-
cussion of the possibilities thus indicated lies outside the scope of
this work, but it may not be out of place to indicate, as briefly as
may be, the various views which have been put forward concern-
ing the probable way in which urea originates in the body.1

There is little reason for doubting that the larger part of the
nitrogen which leaves the body as urea was at one time a constit-
uent of the nitrogenous muscle-substance (see § 484.) There is
equally no doubt, both from general considerations and from the
fact that no urea can ever be detected in muscles normally, that
the nitrogen does not make its exit from the muscles as ready-
made urea. Neither until recently had urea been obtained by

1 The literature of the subject is very fully quoted in Bunge's Physiol. and
pathol. Chemistry, 1890. Lecture xvi. pp. 310-348.

CHK.MICAL I'.ASIS OF THK ANIMAL BODY. 161

any purely chemical means from the products of the

ti< in of proteids.

older statements of I'>.:« hanip and Hitter that urea may be ob-
tained from pi-oteid.s by the action of j»>t:i»imu permanganate have
Keen shown to In- erroneous.1 It is at nio>t pOMiblfl that a trace of
^uaiiiilin may he funned, ami ^uanadin can hy the act inn of water be
ci.nverteil into urea ami ammonia: NH.C(NH2).,-J-H^Oss:(lJ(^)tOO
-f-NHj.a Divch>el has however obtained from among the product> of
tin- decom|M»ition of casein with concentrated boiling hydrochloric
aciil ami chloride of zinc a base to which lie has given the name of
• l\-atiii.' When boiled with haryta water in excess it yields urea.3

What knowledge have we of the possible or probable form un-
der which the nitrogen may make its primary exit from the
muscles > The connection of muscle-kreatiu with urea-formation
has IMM-II already discussed (§ 484, 485) and the evidence of the
connection may be briefly summed up as follows. A considerable
amount of kivatin exists (?) in the muscles at any one time, hence
probably a considerable amount is continuously being formed;
tlp-iv is no evidence that any of this kivatin leaves the body as
Mich, hence. it is presumably converted into some other substance
befoiv being discharged, and this other substance is probably urea,

ing that kreatin may be readily decomposed into urea and
sarkosiu. Tln-iv are further reasons for supposing that the nitro-

: leaves tin- muscles as a compound containing comparatively
little carbon, and kivatin answers to this requirement, since it
contains only four atoms of carbon to three of nitrogen.4 If thi>
latter view be correct it implies that the nitrogen is not split off
in the form of amido-acids, since there is not sufficient carbon in
proteids to convert their nitrogen into the amido-acids with which
\\e have t<. deal iii the body. On the other hand when these
amido-acids (olycjii. leiiein, aspartic acid and asparnoin ) are in-
troduced into the body they are partly converted into urea, so that
if formed they would account for a portion at least of the urea
ted

When pioteid- are decomposed by caustic alkalis, more espe-
cially baryta, or during putrefaction, they yield much ammonium
carbonate, which by simple dehydration would give nn-a. Xow
although ammonium carbonate, like many other salts of this base,
is readily converted into urea when administered to man or other
animals, there is no evidence, although it is a possibility, that the
nitrogen leaves the tissues as ammonium carbonate.

1 Lww. .In. f. jmdt. r/,rm. (2) IM. ii. (1870). S. 289. Tappcincr, A'tfn. t&cht.
GettU. d. \\'i»*. 1871. See Abut, in Malv -71, S. II.

* LdWeil, Ann. <l. Cli-in. u. I'lmrm. l\-l. c< I. (1S^'

./ ,1. rhem. Getell. 1890, S. 3096. Cf. Arch. f. I'hi/iiol. Jahrg. 1891, S.
254 et ueq.

4 Munge, loc. cit. pp. 320, 328.

11

162 UREA.

The above statements seem to embrace all that can be suggested
as to the tissue-antecedents of urea, and it remains now to con-
sider the probable mode and seat of their conversion into urea.
As regards kreatin it may be that it is split up into urea and sar-
kosin, the latter being, like other amido-acids, also converted into
urea. When the ainido-acids are compared with urea it is not
conceivable, with our present chemical knowledge, how they can
give rise to urea in any way other than by being broken down
into an ammonia stage and a subsequent synthesis of urea from
this product. The synthesis may however involve any one of the
three following processes. The ammonia may unite with carbonic
acid to form ammonium carbonate, which is then dehydrated into
urea (Schmiedeberg). Again, it may unite with carbamic acid to
form the carbamate, which again by loss of one molecule of water
yields urea (Drechsel).1 But in the third place the ammonia
residues may unite with some cyanic compound to form urea in
accordance with the possibilities indicated above (pp. 156, 160)
(Salkowski and Hoppe-Seyler). The view that some cyanic resi-
dues may be involved in the formation of urea, while at present
devoid of any striking positive evidence in its support, is at first
sight most attractive, especially when it is borne in mind how
great the molecular energy of the cyanogen compounds is, so that
during their degradation in the tissues much energy would be set
free. Pfliiger,2 following Liebig, has called attention to this great
molecular energy of the cyanogen compounds, and has suggested
that the functional metabolism of protoplasm, by which energy is
set free, may be compared to the conversion of the energetic un-
stable cyanogen compounds into the less energetic and more stable
amides. In other words, ammonium cyanate is a type of living,
and urea of dead nitrogen, and the conversion of the former into
the latter is an image of the essential change which takes place
when a living proteid dies.

If we accept this view it is perhaps difficult to understand how
the cyanic compounds, poisonous as they are known to be, could
play a part in the body. But it is apparently the (ON) group
which confers on the compounds their poisonous properties ; and
if cyanic acid be truly carbamide CO . NH this group is non-
existent in it, and it has been recently stated that cyanuric acid
(CO . NH)3 when introduced into the body leads to an increased
excretion of urea.3

One difficulty in connection with this view is that as yet cyanic
acid has never been obtained by the artificial decomposition of pro-
teids. But on the other hand the proteids are the chief and only
source of the cyanogen compounds, for which the starting-point is

1 Cf. above sub sarkosin, p. 140, and carbamic acid, p. 151.

2 Pfluger's Arch. Bd. x. (1875), S. 337.

3 Coppola, Rendic. d. R. Ace. d. Lined, 1889, pp. 378, 668. Ann. di Chim. e
difarmac. (4) T. x. (1889), p. 3.

CHEMICAL BASIS OF THK ANIMAL BODY. 163

found in fern 'cyanide of potassium, prepared l>y fu.-in^ nitron-nous
animal refu.-e \\itli potassium carhonate and iron. Then- i> further
evidence of tin- existence in the body i.f cyanic re-idiies, as shown by the
exit fn'in it of SulphocyUMtee (HCNS), \vliich an- found in both saliva
and mure part icularly in urine.1 Tin- existence ..f sulphur in the>e
salts -U^I-M.-. at once that it ari-e> fn-m the decomposition Off proteid.-,
into wh<.x- compo>ition sulphur enters as a constant and charaeteri-t ic
constituent. The formation of ralphocjUUC acid in the body has
recently Keen investigated, and it i* worthy of note that it i> stated
•ur in the uriiu- only nf those animals \\hich excrete their nitro-
gen chiefly in the form of urea.2

The various ways by wliich it has l>een suggested that urea may
arise in the body all imply that whatever be the form in which
the nitrogen initially leaves the tissues, the substance or sub-
stances in which it makes its exit undergo their final (synthetic?)
eon version in some other organ of the body. In the case of leucin
then- i> distinct evidence that the conversion is effected in the
liver, and there is increasing evidence that this organ is largely
concerned in the presumably synthetic changes which lead to the
formation of urea in mammals and of uric acid in birds. Thus
Schroder has shown that the conversion of ammonium carbonate
into urea occurs in the liver,3 and a similar relationship to the
formation of uric acid in liinls has additionally been proved*
Further there are many observations which show, when the liver
is diseased, a marked diminution in the excretion of urea, with a
frequently increased output of ammonia.6 After extirpation of
the liver in birds tin- urine contains not only more ammonia but
a larjre amount of sarcolactic acid.0 It would lie however prema-
ture tn regard this fact as showing that in birds uric acid is partly
formed l.y the converting activity of the liver brought to bear
Upon ammonia and lactic acid. When urea is given to birds it
reappears externally as uric acid,7 but this change is not effected
after extirpation of the liver.

Xit/i.tfifitfri/ t'l-i-ua. The hydrogen atoms of urea can he replaced
hy alcohol- and acid-radicle-. The results an- >ul.st it uted un-a* in the
.ise. or iin-ides as they are called in the. second, when the h\dro-
U'en i> replaced l.y the radicle of an acid. Many of them are called
acids, -ince the hydrogen from the amido ^n>up. if not all replaced as
al.ove, can be replaced by a metal. Tims the snl.-t itution of oxalyl

1 Munk. Yin-how's Arrh. Bd. LXIX. (IsTT), S 354. Gscheidlen, Pfliiger'a Arch.
!',.! or. (1-:: . s. 401.

8 Hruylants, Bull. iif I'acad. dr mf<\. ,lc lifl^/nf, (4) T. u. (1888), p. 18 et tea.

/'.ill,, n. ri.mm. 11.1. \v. (I • I ; 1J.I. \IX. (1885), b. 373.

S.il.-iiK.n, Yin-liuw's A, •'•/,. 15,1. \. vn 141

* MinkowMki. Arch. f. er,,. /'•,//<. H. /'luirm. IM. XXI. (!'

6 Koster, IM SptrmtHtaU^T. xi.iv. (iWT'.i), j.. i.vr llall.-rv..nl.'ii. .-lt,-/i. •
r<ith. i/. I'harm. Ikl. xn. (1880), S. 'J.-J7. Stadelmann, Deuttch. Arch. f. Uin. M»l.
I?.!. \\MII I!--.-!). S. 526.

Minkowski, loc. cit. See also Marctue, PflUger'n Arrh. R<1. xxxix. (1886), 8.
425.

7 Meyer u. Jafft', Ber. d. d. ekem. Gttell. Bd. X. (1877), 8. I

164

UKEA.

/NH.CO

(oxalic acid) gives parabanic acid, COV I ; of tartronyl (tar-

XNH.CO

tronic acid), dialuric acid, CO v /CHOH; of mesoxalyl

NH.CO
XNH. CO x
(mesoxalic acid), alloxan CO x / CO. These substances are

XH . CO

interesting as being also obtained by the artificial oxidation of uric
acid. The close chemical relationship of urea to uric acid will be
explained below.

Uric acid. C6H4X403.

The chief constituent of the urine in birds and reptiles; it
occurs only sparingly in this excretion in man (-2-1 grm. in 24
hours) and most mammalia. It is normally present in the spleen,

Rapidly separated.
FIG. 17. CRYSTALS OF URIC ACID.

Slowly separated.
(Krukenberg after Kiihne.)

and traces of it have been found in the lungs, muscles of the heart,
pancreas, brain, and liver. Urinary and renal calculi often consist
largely of this substance, or its salts. In gout, accumulations of
uric acid salts may occur in various parts of the body, more espe-
cially at the joints, forming the so-called gouty concretions.

It is when pure a colourless, crystalline powder, tasteless, and
without odour. The crystalline form is very variable, differing
according to the concentration of the solution from which the
crystals are obtained, the rate at which they are formed, and
whether they are separated out spontaneously or by the addition
of acids to either solutions of the acid or to urine. Hence it is
extremely difficult to illustrate them within reasonable limits,
and for figures of the various possible forms some special work
must be consulted.1 The impure acid crystallises much more

i See Ultzmann and K. B. Hofmaim, Atlas der Harnsedimente, "Wien, 1872.
Also Funke, Atlas d. physiol. Chem. Leipzig, 1858.

CHEMICAL BASIS OF THE ANIMAL BODY. It,-,

readily than does the purified. The following figure shows addi-
tionally some very characteristic forms in which uric acid sepa-
rates out from urine either spontaneously or after tin- condition of
hydrochloric acid.

FlG. 18. CRYSTM- «r I'm. ATM.. (After Funke.)

C acid is remarkably insoluble in water (1 in 14,000 or
15,000 of cold water, 1600 of boiling). Ether and alcohol do not
Ive it appreciably, (hi the other hand, sulphuric acid takes
it u]' in tin- i-old without decomposition, ami it is also readily
soluble in many salts of the alkalis, as in the caustic alkalis
tbem>elves : ammonia however scarcely dissolves it, and in this
re-pert it ilitleix conveniently from cystin. It is fairly soluble
in ulyreiin. and soluble to some extent in solutions of lithium
carbonate.

FlO. 19. (Krtik r Kuhno.)

Urinary sediment, sli i'-tly the most usual form of crystals

of aciil sodium unite. ('..II N iN'4Og.

166 URIC ACID.

Salts of Uric acid. Of these the most important are the acid
urates of sodium, potassium, and ammonium ; these salts are fre-
quently still called ' lithates,' the term ' lithic ' acid being used
for uric acid. The sodium salt which is the most common con-
stituent of many urinary sediments crystallises in many different
forms, these not being characteristic, since they are almost the
same for the corresponding compounds of the other two bases. It
is very sparingly soluble in cold water (1 in 1100 or 1200), more
soluble in hot (1 in 125). It is the principal constituent of several
forms of urinary sediment, and composes a large part of many
calculi ; the excrement of snakes contains it largely. The potas-
sium resembles the sodium salt very closely, as also does the
compound with ammonium; the latter occurs generally in the
sediment from alkaline urine.

FIG. 20. (Krukenberg after Kiihne.)

Urinary sediment from alkaline urine. The large crystals consist
of ammonio-magnesium phosphate (triple phosphate, XH4MgP04-f-
6H20). A few crystals (octahedra) of calcium oxalate are also shown.
The remaining crystals represent the form of acid ammonium urate,
C5H3(NH4)N4O3. The rounded objects are urinary fungi.

Preparation. The amount of uric acid in mammalian urine is
too small to make it a source of the acid. Crystals may however
be readily obtained from human urine by adding to it 2 — 3 p. c.
of strong hydrochloric acid and letting it stand for one or two
days in a cool place. The crystals form on the sides, of the con-
taining vessel.

On the large scale it is usually prepared from guano, or from
snake's excrement. From the latter it is obtained by boiling with
caustic potash (1 part alkali to 20 of water) as long as ammonia
is evolved ; in the filtrate a precipitate of acid urate of potassium
is formed by passing a current of carbonic acid ; this salt is then
washed, dissolved in caustic potash, and decomposed by carefully
filtering its solution into an excess of dilute hydrochloric acid.

CHEMICAL BASIS OF THE ANIMAL BODY. 1C7

By similar treatment uric acid is ivadily obtained from fowl's
excrement, a convenient source of the acid.

ititication of uric acid. The crystalline forms afford some
clue, luit are so numerous that some forms which may at any
tiiin' present themselves are scarcely characteristic. The rhombic,
tables, • dumb-bell,' and 'whetstone' crystals are on the whole
most characteristic.

i. Murcxid test. The suspected substance is treated in a por-
celain dish with a few drops of strong nitric acid ami evaporated
on ••/til/I/ to dry ness, by preference on a water-bath. The residue
thus obtained will, if uric acid is present, be of a yellow or more
frequently red colour, which turns to a brilliant reddish purple on
exposure to the vapours of ammonia. On the subsequent addition
of a drop of caustic soda the colour is changed to a reddish blue.
This di>ap pears on warming, whereas the similar colour obtained
by the above process from guanin does not. This is an important
means of distinguishing between the two substances.

Tin- te.-t depends on tin- formation of murexid, which is the arid

UDinonilUn >alt »f purpuric acid, the ai-id it-elf l>ein<f unknown in the

-tate. Uric acid is decomposed when heated with nitric arid,

yielding alloxan and then alloxantin ; by the action of ammonia the

latter is converted into imin-xid (NH4) C8H4N6O6 -f- H20.

The murexid test is so striking and characteristic that it suf-
fices completely for the identification of uric acid. The following
tests may be applied in confirmation if required, but not for the
purposes of initial detection.

ii. ^'•Jiiff's reaction.1 The substance is dissolved in sodium
carbonate, and a drop is then placed on filter paper previously
moistened with nitrate of silver. A yellow or almost black
colouration, due to the formation of metallic silver by reduction
of its nitrate, is at once obtained.

iii. When a solution of urie aeid in eau-tic soda is boiled with
a small amount of Fehlinu's fluid, reduction occurs with produc-
tion of a greyish precipitate of urate of cuprous oxide. If the cop-
per salt is in excess red cuprous acid is obtained.

ni'itinn <>f iirir iif'nl iii xuliitioii* (i/fiif). The accurate
quantitative determination of uric acid is a matter of some dif-
ficulty: for details some standard work- (quoted sub urea)
should be consulted. It will suffice to indicate here the princi-
ple- of the more usually employed methods.

i. ,sW/.-<;//W. /-/,/' '//<»/.- When an ammoniacal solution

' An,,. ,/. ('/„,„. ii. rhnrm. \\>\ < i\

H ••/. Jahrb. 1884, S. 597. Cf < 'aiii-r.-r. /. 1 Diol. Bd. XXVII.

(1890 -

168 UKIC ACID.

of nitrate of silver is added to a solution of uric acid, to which an
ammoniacal mixture of magnesium chloride and ammonium chlo-
ride has been previously added, the uric acid is precipitated as a
magnesio-silver salt. This is collected, washed, and decomposed
by sodium or potassium hydrosulphide, whereupon the uric acid
passes again into solution as a urate of the alkali. On the addi-
tion of an excess of hydrochloric acid to this solution the urate is
decomposed, uric acid separates out and is collected and weighed.

ii. Hay craft's method.1 When uric acid is precipitated by am-
moniacal solution of nitrate of silver in presence of the ammonio-
magnesic mixture as above described the precipitate is stated to
contain one atom of silver to each molecule of uric acid. The
uric acid is hence determined by dissolving the precipitate in nitric
acid, in which solution the silver is then estimated volumetrically
with a standard solution of potassium sulphocyanate.2

Chemical constitution of uric acid. Notwithstanding the fre-
quent and careful investigation of uric acid and of the extremely
numerous products of its decomposition, its constitution has until
recently been a matter chiefly of surmise and conjecture, and
many constitutional formula? have been assigned to it. When
uric acid is treated with concentrated hydriodic acid at 160-170°
it is decomposed into glycin, ammonia, and carbonic anhydride

C5H4N4O3 + 5H20 = CH2(NH2) . COOH . -f 3C02 + 3NH8.

By reversing this decomposition as it were, namely by fusing to-
gether at 200 - 230° glycin and urea, uric acid was for the first
time obtained artificially ; 3 when sarkosin is used instead of urea
methyl-uric acid is obtained. Uric acid has also been prepared
by fusing together trichlor-lactamide or trichlor-acetic acid and
urea.4 The high temperatures at which the above reactions were
conducted and the uncertainty as to the nature of the products
intermediate between the reagents and the finally formed uric
acid precluded them from being regarded as syntheses in the strict
sense of the word. A true synthesis of uric acid has been recently
discovered by Behrend and Koosen,5 from which it appears that the
constitutional formula first assigned to the acid by Medicus,6 is a
true representation of its constitution. This view had been pre-
viously stated by E. Fischer as a result of his analytical investiga-
tions of uric acid.7

1 Brit. Med. Jl. 1885, p. 1100. .//. of Anat. and Phijsiol. Vol. xx. p 695. Zt. f.
anal. Chem. Bd. xxv. (1885), S. 165. Zt.f. physwl. Cltem. Bd. xv. (1891), S. 436. '

2 Volhard, Jn. f.pr. Chem. (2) Bd. ix. (1374), S. 217.

3 Horbaczewski. Monatsh.f. Chem. Bd. in. (1882), S. 796. Ber. d. deutsch. chem.
Gesell. Jahrg. (1882), S. 2678.

* Horbaczewski, Monatsh. f. Chem. Bd. vi. (1885), S. 356; Bd. vm. (1887), Sn.
201, 584.

5 Ann. d. Chem. u. Phurm. Bd. CCLI. (1889), S. 235.

6 Ibid. Bd. CLXXV. (1875), S. 230.

7 Ber. d. deutsch. chem. Gesell. 1884, Sn. 328, 1785.

CHEMICAL BASIS OF THE ANIMAL BODY. 169

NH — CO
Uric acid. CO C — NH

I II >co.

NH — C— Nil

An inspection of the above formula shows at once that uric
acid contains the residues of two molecules of urea. This cor-
responds to the fact that nearly all the possible decompositions of
uric arid yield either a molecule of urea along with the more spe-
citie product of the decomposition, frequently itself a derivative of
nrra, or else some substance which can by further change be de-
composed into urea and some other product which is as before
l'rei[Uemly a derivative of urea. The close chemical relationship
of urea and uric acid is thus clearly shown, and may be further
t-niphasi/ed by the following reactions, which illustrate and
amplify at .the same time the general statement which has
just been made.

The decomposition of uric acid takes place in two stages, yield-
ing two series of products, of which one is headed by allox; n
and the other by allantoin ; from these two substances respec-
tively tin: other members of each series are derived by subsequent
decomposition.

1. Alloxan series.

By careful oxidation with nitric acid uric acid is decomposed
into a molecule of alloxan and one of urea.

NH — CO NH — CM

II II

CO C — NH CO CO NH,N

| || ) CO || /CO.

NH -C-NH +H,0+0 = NH— CO + NH/

Alloxan is itself a substituted urea or ureide (antea, p. 164),
\\y.. mrsoxalyl-nrea, and by oxidation ran In- further converted
into parabauic acid (oxalyl-urea) and carbonic anhydride.

NH — CO NH — CO

CO CO CO

NH — CO + 0=NH — CO + CO,.

By heating with alkalis parabanic acid is hydrated and yields
oxaluric acid.

MI —CO MI — CO

CO

CM

Ml _CO + H,0 = NH, CO. OH.

170

URIC ACID.

The latter by prolonged boiling with water is converted into
urea and oxalic acid.

NH — CO

CO

NH2

NH

8v
)CO

CO. OH
+ CO. OH

2. Allantoin series.

By oxidation with potassium permanganate uric acid is decom-
posed into allantoin and carbonic anhydride.

NH — CO NH — CO NH,

CO C — NH

I I! )co

NH — C — NHX

CO

CO

-f H20 -f 0 = NH — CH — NH + C02.

When allantoin is boiled with nitric acid it is hydrated and
decomposes into a molecule of urea and one of allanturic acid.

NH — CO NH2 NH — CO

CO CO CO

k/NH9

H — CH — NH-f-H20 = CO

Allanturic acid is itself a substituted urea, viz. glyoxyl-urea, and
may be converted into parabanic and hydantoic acids.

NH — CO NH — CO NH2 CO. OH

I I I

2 CO CO CO

I I I

NH — CH(OH) = NH — CO + NH

Of these two acids the parabanic may as before be converted
into oxalic acid and urea, and hydantoic acid is a derivative, by
simple hydration, of hydantoin, which is itself a substituted urea,
viz. glycolyl-urea, containing a residue of glycolic acid, [CH2(OH).
COOH].

NH — CO NH2 CO. OH

CO CO

NH — CH2 (Hydantoin) + H20 = NH CH2. (Hydantoic acid. )

The above reactions and decompositions show clearly how close
is the chemical relationship of urea and uric acid, and the connec-
tion is still more evident when it can be shown that many of the
products described above as obtained during the decomposition of
uric acid, viz. the ureides, can be prepared from urea directly.

CHEMICAL BASIS OF THK ANIMAL BODY 171

Thus parabanic acid (oxalyl-urea) is readily formed by the action
of phosphorus oxychloride on a mixture of urea and oxalic acid :

NH— CO

MI, CO. OH CO

C0\ 1 = J

NHa + CO.OH NH — CO-f2H,0.

When the close chemical relationship of urea to uric acid is
taken into account, the statement that those substances which
when introduced into the body of a mammal lead to an increased
excretion of urea, when introduced into the organism of birds are
converted into uric acid,1 needs excite no surprise. There is fur-
ther distinct evidence, already referred to under urea, that tin-
conversion is affected in the liver.2 "VYr k\\<>\\- nothing as y.-t a-
to the cause of the slight divergence of metabolism which leads
to the preponderating formation of urea in mammals and of uric
acid in birds and reptiles. It is certainly not due, as some have.
supposed, to insufficient oxidation in the latter, since the excretion
of uric acid is not increased in mammals by artificial disturbance
of the respiratory interchange,3 and it is exactly in birds that the
most active oxidational changes, as shown by their higher tem-
perature, is observed. Bearing in mind how readily uric acid
yields urea as one product of its oxidational decomposition, it has
been supposed that a good deal more uric acid is formed in tin-
mammalian body than is excreted in the urine. In support of
this view it may be pointed out that uric acid when introduced
into mammals is largely excreted as urea, and that some of the
known products of the artificial ox i da t inn of uric acid are occa-
sionally found in their urine, e.g. oxalic acid, oxaluric acid
(hydrated parabanic acid), and allantoin.4 The latter substance
is apparently increased (?) by the administration of uric acid.6

3. Oxaluric acid. C,H4Nj04. (Hydrated parabanic acid.)

Occurs in minute traces in normal urine, from which it is ex-
tracted by filtering a large quantity of urine very slowly through
a relatively small amount of animal charcoal. The charcoal after
being washed with distilled water is extracted with boiling alcohol,
to which it yields the oxaluric acid as an ammonium salt. The
free acid is a white crystalline powder, not very soluble in water :
it- alkaline salts are readily soluble.6

1 For liti-ritiire nee Bunge, Phi/iiol. path. Chrmistrv, i>. .141. Horl>:uv
Mnnatsf.fl / Cl.rm. Bd. X. (1889), S. 624. Sit:l>. d. HW. Akad, Bd. xcviu. (1889),
3 A I.-

.-.I-.. •-..!: Srhnuler, Arch. f. Phyiiol. 1880. Suppl.-Bd. S. 113. Ludwig'a
Feitsrhritf, ISH;. S. 98.

» Senator. Vir. -how's Arrh. B<1. xi.n. (1*68), S. 35

« Salkowski u. Ixsnbe. Die fshre vom I/arn (1882), S. 100.

• 8alkow*ki. lirr. ,1. d. rhrm. tlrvtt. I-;., > 71'J. 1878. 8. 500.

• For .!. 'tails nee Hoppe-Seyler, Phyt.-path. Anal. 1832, S. 159. Neubaner u.
Vogel, Jftinxinalyte, 189O, S. 239.

172

ALLANTOIN.

4. Allantoin. C4H6N408. (Diureide of glyoxylic acid.)

The characteristic constituent of the allantoic fluid, more espe-
cially of the calf, as also in foetal urine and amniotic fluid ; it occurs
also in the urine of many animals for a short period after their
birth. Traces of it are sometimes detected in this excretion at a
later date. It is obtained in urine after the internal administra-
tion of uric acid.1 It has also been found in vegetable tissues.2
It crystallises in small, shining, colourless, hexagonal prisms.
They are soluble in 160 parts of cold water, more soluble in hot,
insoluble in cold alcohol and ether, soluble in hot alcohol. Car-
bonates of the alkalis dissolve them, and compounds may be
formed of allantoin with metals but not with acids. The salts
with silver and mercury are important as providing a means of
separating allantoin from its solutions.

FIG. 21. CRYSTALS FROM CONCENTRATED URINE OF CALF. (After Kiihne.)

The large central crystal composed of an aggregation of small prisms
is allantoin: those below it are crystals of kreatiri, kreatinin and oxa-
late of lime. The large prisms in the upper part of the figure consist
of magnesium phosphate.

Allantoin gives no reactions which are sufficiently striking to
admit of its detection in urine or other fluids ; it must therefore
in all cases first be separated out and then examined. The separa-
tion may be effected in several ways, of which those more usually
employed consist in its precipitation with nitrate of mercury or
silver.3 From the urine of calves or from their allantoic fluid,
allantoin may usually be obtained in crystals by mere concentra-
tion and subsequent standing till crystallisation occurs.

1 Salkowski, loc. cit.

2 Schulze u. Barbieri, Jn. f. pr. Chem. Bd. xxv. (1882), S. 145. Schulze u.
Bosshard, Zt.f. pkysiol. Chem.'Bd. ix. (1885), S. 420.

3 For details see Hoppe-Sevler, loc. cit. S. 162. Neubauer u. Vogel, loc. cit.
S. 222.

CHEMICAL 11ASIS OF TIIK ANIMAL BODY. 173

Preparation. Allantoiu may !»«• ea-ily obtain. -d l.y tin.- careful
oxidation of uric acid with pota-sium permanganate.1 It may
also In- syntht-ti.M'd by prolonged heating to 100° of a mixture of
idyoxylic aciil and urea,2 or of the latter substam-e with mooxalic
acid.8

As prepared artificially it crystalli>e> readily in large, pri-maiic
hexagonal crystals.

FIG. 22. CRYSTALS OF ALLANTOIN I-I:I.I-M:I u BY THE OXIDATION
OF UKIC Ann. (After Kiihne.)

In addition to the crystalline form and precipitability with
nitrates of mercury and silver, allantojn is further chnrart
by yielding Schiff s reaction with furf urol (see above, p. 1 58, sub
urea), but less readily and with less intense colouration than does
urea. It also reduces Fehling's fluid on prolonged lioiliim.

THE XANTHIN GROIT.'

This -jronp comprises a number of substances closely related t<>
uri'e a<-id ami to each other. Some of them occur in small annumis
in the tissues (muscles) and excretions (urine) of the body and are
to he regarded as being, like urea and urie acid, typical products
of the downward destructive metabolism <>f pmteids. Some of
t luMii are closi-ly n-laied to certain alkaloids which occur in plants
(thi-obromin and call'ein ), and which jirobably play some not unim-
p-irtant part in the nutritional changes of the animal body, sine.-
they an- constantly consumed, in sonic form or other, by the !
part of the human race. This relationship ,,f tin- xanthin-bodies
Stable alkaloids is further interesting when it is

| ( -liui-, /;,,-. >i. ,i. ,-ifm. <;. •<••/;. IM MI i-

mnaiix, Cnmjit. /innl. T. s.'t (ISTf,), ji. 62.

Ch,m. JI. Vol. I

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thoir so|tarnti<>ii ami .ii-. riiainatiou, »ee Neubaucr U. Vogei, Anaiyte drt Hants,
1890. Sec. 20O— 219.

174

XANTHIN.

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CHEMICAL BASIS OF THK ANIMAL BOPV. 175

remembered that the latter are regarded by plant-pliysiologists as
products of the vegetable organism, and are thus found
chiftly in those parts of the plant which are on their way to re-
moval, viz. the bark, leaves, and seeds.

Many nu-iubers of this ^nmp are both derivable from and con-
vertible into other members of the group by simple chemical
jiror.-sses, but this relationship of the one to the other will be
more fully appreciated by consideration of the properties and
reactions of the separate substances. Tlu-ir relationships to uric
u«i.l and cai h other are in many cases indicated by comparison
of their formulae.

1. Xanthin. C5H4N NH — CH

CO C— NH

\

N'H — c = N

|^ ^CO (Fischer)1.

— C = N

First discovered in a urinary calculus, and called xanthic oxide.
M"iv ivivntly it has been found as a normal, though very scanty,
constitiifiit of urine, muscles, and several other tissues, such as
the. liver, spleen, thymus, brain-substance, &c. It occurs in larger
quantities, together with hypoxanthin, in 'extract of meat,' and
is also found in traces in vegetable tissues, — lupins, malt-seed-

Fi... U:i. XVMIIIN IMI.KM. III..HIDE, I'l" •->». X AM HIM NITRATE,

C,I1,N,", HC1. (Kul.u.-.) c, II.N.o. -.IIXns. (Kiihne.)

lings, and tea. In nearly all cases it is accompanied by hypo-
xantliin. Tli<' amount which is present in any of the above
turaefl and fluids is so small that none of them, except perhaps
theextrart "f meat, affords a convenient source for its prepara-
tion.2 To obtain it in quantity guanin is treated with nitrous
acid,8 and the nitro-product thus obtained is reduced in amnionia-
cal -olution with ferrous sulphate. It may also be prepared
.ntiticiallv from hydrocyanic acid and water in presence of acetic
a.id.» Wli.-n pun- it is a mlmirless powder, requiring about
14,000 parts of water for its solution at ordinary

1 (i) far. d. d. chem. GweU. 1882, S. 453. (ii) Ann. d. Chem. u. Pharm. Bd
• i \ \ 18821 v

2 For it»'f«epamti.iii fn.m urine see Nenbauor, Zt.f.anal. Chem. IM vn. (1868),

irt, «ee St&deler, .!/. ' ». 1'hnrm. !?.i axn

(1860). \oubauer, Zt.f. anal. C1/,. m. IMf. u. (1863), S. 26, vi. (1867), S. :n.

8 Fischer, loe. cil. (ii).
« Gantier, Compt. Rend. T. 98 (1884), 1523.

176 XANTHIN.

and 1400 at 100°. Insoluble in alcohol and in ether, it dissolves
readily in dilute acids and alkalis (characteristically in ammonia)
forming crystallisable compounds.

Reactions. The discrimination of members of the xanthin
group is not easy, since from their close relationship they yield
many reactions in common. The following are characteristic of
xanthin.

i. WeideVs reaction.1 The substance is warmed with freshly
prepared chlorine-water and a trace of nitric acid as long as any
gas is evolved : it is then carefully evaporated to dryness and, if
xanthin is present, the residue turns pink or purplish-red on the
access of ammonia fumes. Carnin gives a similar colouration if
but little chlorine-water is used, while guanin and adenin do
not.

ii. Hoppe-Seyler's reaction. When xanthin is introduced into
some caustic soda with which some chloride of lime has been
mixed, each particle of the substance surrounds itself with a dark
green ring which speedily turns brown and then disappears.

FIG. 25. CRYSTALS OF XANTHIK SILVER-NITRATE, C5H4N4O2 . AgNO3.
(Krukenberg after Kiihne.)

iii. Strecker's test? When evaporated to dryness on porcelain
with nitric acid a yellow residue is obtained which turns reddish-
yellow on the addition of caustic soda or potash (not of ammonia),
and reddish-violet on subsequent warming. Distinctive from
uric acid.

iv. Xanthin is more readily soluble in ammonia than is uric
acid.

v. Xanthin yields in solution in dilute nitric acid a character-
istic crystalline compound with nitrate of silver, which differs
from the similar compound of hypoxanthin both in the forms
which it presents and in its greater solubility in nitric acid of sp.
gr. 1-1 at 100°. It is therefore used as a means of separating
xanthin and hypoxanthin.

1 Ann. d. Chem. u. Pharm. Bd. CLVIII. (1871), S. 365. This reaction was given
by its author for hvpoxanthin, but apparently in error. Cf. Kossel, Zt. f. phi/siol.
Chem. Bd. vi. (1882), S. 426. Salomon, Ber. d. d. chem. Gesetl. 1883, S. 198.

- Ann. d. Chem. u. Pharm. Bd. cvm. (1858), S. 146.

CHEMICAL BASIS OF THK ANIMAL BODY. 177

vi. The compound of xanthin with hydrochloric acid is far
less soluble in water than are tin- similar compounds of hyjtuxan-
thin and guanin, and hence affords a further means of separating
tin -so bases.

Hy treatment with hydro< -hloric acid and potassium chlorate
xanthin is converted into alloxan and urea (Fischer).

Tin- older and frequently ivjieated >tatement> that xuntliin ami
hypo xanthin can In- obtained from uric arid \>\ tin- art ion of sodiuni-
ainali^alu, as also that hTpOXUltluO can he converted into xanthin by
treat inent with nitric acid, have recently Keen shown to he erroneous.
Notwithstanding the similarity of their composition these three sub-
stanco are incapable of interconversion.1

L'. Heteroxanthin. r II, N4< >, (M.-thyl-xanthin?).

This substance occurs in minute quantities in the normal urine
of man- and the dog,3 along with xanthin and hypoxanthin and
another closely allied xanthin-base, paraxanthin. It occurs in
larger amount in the urine of leukhaemic patients. It is crystal-
line, hut not very characteristically so, is soluble with difficulty
in (old water, much more soluble in hot water, is insoluble in
alcohol ami in ether. It may, as also may paraxanthin, be separated
from other xanthin-bases by taking advantage of the relatively
slight solubility of it< sodium salt in caustic soda. It also yields
with hydrochloric acid a relatively insoluble salt which crystal-
lises readily, whereas the corresponding salt of paraxanthin is
readily soluble. They may by this means be separated the one
from tin- other.

Il-'teroxanthin does not give the ordinary reaction for xanthin
with nitric acid and caustic soda, but yields a brilliant colouration
on the application of Weidel's test (see sub xanthin). Like the
otln-i xanthin-bases it gives an insoluble salt with an ammoniacal
solution of nitrate of silver.

Paraxanthin. C7H8N402 (I)imethylxanthin ?) Isonieride of

Theoliromin.

Like heteroxanthin it oc.-ur- in very small amounts in urine.1
It i- Miluble with difliculty in cold water, but is more soluble
than xanthin ; is much more soluble in hot water, insoluble in
alcohol and in ether. It crystallises readily in characteristic tlat.
somewhat irregular, six-sided tables when its solutions are slowly
evaporated, or in needles if rapidly. It forms, as do the preceding

1 Iv ,,1,,/g,;,!. Ch.m. H.I. vi. (IHS2), S. 4-.'s Fis.h.T. 11. r d. d. chen.

Gf»>

i---.. s :u«>:

in..,,, '/j , ' .,„. H.|. M (!««.:), S. 412.

4 Tlm.li.-lmm. '.!fi»n/.« nf rh. M»l. V..1 i ID..II, /trr. ,1. d

s. i-.i:,. issr,, .-HIM;. '/.>. /: k-im. M*-<i. H.I. MI. (Suppl.-IIft.) (1884),

{>hy$iol. Cl il-'-'l). S. 319.

12

178 CAKNIK

substances, a crystalline salt with nitrate of silver ; this like the
corresponding compound of xanthin is soluble in strong nitric acid
(sp. gr. I'l) at 100°, and may thus be separated from hypoxanthin.
It may be separated from xanthin by means of its greater solubility
in cold water, and from heteroxanthin by the difference in the solu-
bility of its salts with sodium and hydrochloric acid.

Paraxanthin gives Weidel's reaction but not the ordinary
xanthin test with nitric acid and caustic soda.

An inspection of Fischer's formula for xanthin shows the pos-
sibility of the existence of at least two isomeric di-methyl deriva-
tives of this base according to the replacement by methyl CH3 of
the hydrogen atoms in the three NH groups which it contains.
Of these one has for some time been known as theobromin ; para-
xanthin is probably another isoiner, and more recently Kossel has
described a third, theophyllin. By substitution of (CH8) for
hydrogen in the third (NH) group trimethyl-xanthin or caffein
is obtained. In connection with the isomeric relationship of
paraxanthin and theobromin it is of great interest to observe that
the physiological action of the two bases is the same.1

4. Carnin. C7H8N403.

Closely allied in composition to the preceding base, but as yet
of unknown constitution, carnin occurs only as a constituent of
' extract of meat,' of which it forms about one per cent.,2 although
it has been stated to occur also in urine (?).3

It is prepared by precipitating extract of meat with baryta-
water, avoiding all excess of the precipitant. The filtrate from
this is now precipitated with basic acetate of lead, which carries
down all the carnin. This precipitate is repeatedly boiled with
water which dissolves out the lead salt of carnin, which is then
decomposed by sulphuretted hydrogen, and the carnin obtained
by concentration of the aqueous nitrate from the sulphide of
lead*

It crystallises in white masses composed of very small irregular
crystals ; it is soluble with great difficulty in cold, readily soluble
in hot water, insoluble in alcohol and in ether. It unites with
acids and salts to form crystallisable compounds. Of these the
more important are the salts with basic lead acetate, soluble in
boiling water, and with nitrate of silver, insoluble in strong nitric
acid and ammonia. Carnin gives Weidel's reaction when only a
small amount of chlorine-water is employed, but the test fails if
any excess is used.

Carnin bears an interesting relationship to hypoxanthin, into

1 Salomon, Verh. d. physiol. Gesell. Berlin. Arch.f. Physio!. 1887, S. 582.

2 Weidel, Ann. d. Che'm. u. Pharm. Bd. CLVIII. (1871), S. 353.
8 Pouchet, Journ. de Thtrap. T. vn. (1880), p 503.

4 Krukenberg u. Wagner, Sitzb. d. phys.-med. Gesell. Wiirzburg, 1883, No. 4.

CHKMir.u. r.AMS OF THE ANIMAL BODY. 179

which it may he converted by treatment with chlorine or nitric-
acid, or still more readily by bromine.

C7H8N4O8 + Br2 = C6H«N4O . HBr -f CH,Br + CO,.

I' In- latter may be isolated from its hydrobromic acid salt by
means of caustic soda.

5. Hypoxanthin or Sarkin. ( ll^N/t.

NH — CH

I II

00 ' — N\

NH — C = N

(?).

Closely related to xanthiu and usually occurring witli it in tin-
tissues and fluids of the body. It- constitutional formula has not
yc-t l>eeii definitely ascertained, but it will probably be found to
contain the group N = CH — N in the place of one urea residue
in xanthiu.1 On this supposition three formulae are obviously
1'o-sil.le, and the correct one has still to be determined. Hypo-
xanthin may be obtained from normal muscles, and hence is found
in larger amounts in 'extract of meat.' It occurs also in the
spleen, liver, and medulla of bones, and in considerable quantity
in. the blond - and urine3 of leukhiemic patients; also in normal
urine4 and in vegetable tissues — lupins,6 malt-seedlings, and

FlO. 26. Ih I-M\ \\TIIIN--II \ l i: Ml l: \ i l . ' ' .HjN^O • AgNOt.
(KrukcnU-rg after Kuliiie.)

It i^ obtained from fluids or tissue extracts by means of tin-
processes already mentioned I'm the extraction of xanthin. and
is separated from the latter by taking advantage of the slighter

1 I- -/. ,/. ,-!„,„. Getell. 18-

•*s.-l. '/.l. f. ph,,itol. Cliriii. IW. v. (1881), S. 267.

n hc.w'.M Arrl,. \kl cix. (1877), 8. 390.

4 (,. S:il,.i,,,,ii. Zt. f phi/tiol. Chem. Salkow»ki, Virchow'f Arch. Bd. L. (1870),
S. 195.

6 Salomon, Verhnnd. d f,fiVtiol. Gettll. Nor. 12, 1880. Arch. f. Phyiiol. 1881, S.
166.

6 Baginskr, Zt. f. j^siol. Chen Bd. vm. (1883—4), S. 395.

180

HYPOXANTHIN.

solubility of its salt with nitrate of silver in boiling nitric .acid
(sp. gr. I'l). The crystalline form of this salt is characteristic.

It also yields crystalline salts with nitric and hydrochloric
acids.

Hypoxanthin is soluble in 300 parts of cold and 78 of boiling
water, insoluble in cold alcohol and in ether, soluble in 900 parts
of boiling alcohol. It does not yield either Weidel's reaction or
the reaction with nitric acid and caustic soda so characteristic of
the other xanthin bases. It gives no green colouration with

FIG. 27. HYPOXANTHIN-NITRATE, C5H4N40 . HN03. (Kiihne.)

FIG. 28. HYPOXANTHIN-HYDROCHLORIDE, C5H4N40 . HC1. (Kiihue.)

caustic soda and chloride of lime such as xanthin does (Hoppe-
Seyler's reaction), but after treatment with hydrochloric acid
and zinc, it yields a ruby-red colouration on the addition of an
excess of caustic soda (Kossel). In this reaction it resembles
adenin.

During the putrefactive decomposition of proteids (fibrin) or
by the action of boiling water, dilute acids, or gastric and
pancreatic enzymes, hypoxanthin can be obtained in minute
amounts.1 This was at first regarded as evidencing a direct
formation of xanthin bases from proteids. The researches of
Kossel have however shown that the source of the hypoxanthin
in the above cases is probably the nuclein of the corpuscles en-
tangled in the fibrin, since he finds that, by similar treatment,

1 Salomon, Ber. d. d. chem. Gesell. 1878, S. 574. Krause, Inauq.-Diss. Berlin,
1878. Chittenden, .//. of Physwl. Vol. n. (1879), p. 28.

(•INIMICAL BASIS OF THE ANIMAL BODY. 181

isolated nucleiu yields no inconsiderable amount of hypoxanthin.1
'I'll'- nuclein huwever from egg-yolk does not yield hypoxanthin.
and thus resembles the nuclein derivable from ca-ein.- Although
the xanthin-bases undoubtedly result in the body from tin- meta-
bolism .if iiitr.^.-nous (proteid) tissues there is as yet no evidence as
to the manner in which they can be formed from true proteids.8
Tin- urn. -tic relationship of hypoxanthin to nuclein probably ac-
counts for the marked occurrence of the former in leukhaemic
blood.

Bearing in mind the close chemical relationship of uric acid,
xanthin, and hypoxanthin, and regarding the xanthin ba.->
distinctly and typically products of the downward metabolism
of nitrogenous ti>sues, the i|iiestion at once suggests it.-elf
whether in the body there is any anteeedental relationship be-
tween these substances and uric acid or urea . As with kreatin
(above, p. 162), so with the xanthin bodies, the disproportion
between the amount presumably arising in the tissues and that
which is actually excreted makes it probable that they are con-
•mething else, uric acid (or urea), before leaving the
body. And in support of this belief there is a certain amount
of experimental evidence which was wanting in the case of
kreatin. It is found that hypoxanthin administered to a dug
does not reappear as such externally in the urine,4 and that when
given to fowls it leads to an increased excretion of uric acid
amounting to some 60 p. c. of the hypoxanthin employed.'1 Since
the latter iv-ult is obtained in fowls with extirpated livers, it ap-
that the coii\cr>ion is not effected in this oigan, although it
is known that normally no inconsiderable portion of the uric acid
i> formed in their liver.

<;. Adenin. C,H,N

This base was obtained by Kossel * during the treatment of

pancreatic ti>-ue for the preparation of hypoxanthin. It bears
the >ame relationship to the latter that guanin <lo,.> to xanthin.
ami can similarly be convert,-.! into hypoxanthin by the action of
nitrous acid. It is stated to have been found in urine."

1 'A f. ;./•-/>•/«/. Ch,,n. H.I.-. 111. (1>7'.M. S. _'-i. \\ J'.Hi. \ i:,i'. ••(•-. v i. »-j:;. vn 7
'•'.LIST'S Arch. H.I. xxn

ndi <l. i.hytiol. Geiell.. I / . I8C

./. d. chem. Gesell. 188(i. -- MO Hut tux also Salomon, //.«/.
8. IK

4 I'.a^il.sky, Zf. f. },h,,nol. Chrm. H.I Mil (]v-t). S. 397.

. M.i.-li. -In/., f. fij>. l',itl>. ii. /'/Kin,,. I!.!.- \\iii (1SS7), S. U.«.

ilso RtadtliM ' l,.-i.,w.

•I. d. ••/„„!. G'..s- /. is-:,. M, ; t\ )>hiliiol. Chem. Bde. X. |i

MI. (1888), S. '.'41. \M (18M > I S-liimllrr .//"./ . MM

•.»•)» ilir«-< tii. us fur .-••|.:ir:it i"ii <>f xanthin, hvfioxanthin. cnanin. an<i
a.li-nin. Thuiss, //-/</. H.I. MIL > 898 I'.rnh.
ir.T. I' id. H.I. x\i 160

St;i.lth;if:i-n. Vin-h-... - 390.

182 GUANIK

When pure it crystallises in needles from aqueous solutions.
Is soluble in 1086 parts of cold water, readily in hot water, in-
soluble in ether, slightly soluble in hot alcohol. Yields crystal-
line compounds with acids, also with some salts. The compound
with nitrate of silver is soluble in hot nitric acid (sp. gr. 1*1), and
is thus separable, together with hypoxauthin, from xanthin. It
also yields a readily crystalline compound with picric acid, which
is very insoluble in cold water (1 in 3500) and may be used
for its quantitative separation from solutions (Bruhns, loc. cit.).
It does not give the ordinary reactions characteristic of the
xanthin bodies, but like hypoxanthin shows a red colouration on
the addition of an alkali after treatment with hydrochloric acid
and zinc.

7. Guanin. C5H5X50. NH — CH

If H == C C — NH

J JL:

| \CO (Fischer).1

NH — C = tf

It was first obtained from Peruvian guano, which still provides
the most convenient source for its preparation.

The guano is finely powdered and boiled with milk of lime as long
as it yields a coloured filtrate. The residue is then repeatedly ex-
tracted with boiling solution of sodium carbonate; the filtrate on the
addition of acetic acid yields a precipitate of guanin and some uric acid,
from which it is separated by boiling with somewhat dilute hydro-
chloric acid. A hydrochloride of guanin is formed which is crystal-
line, and from this compound the guanin is separated by the addition
of concentrated ammonia.2

Guanin is also found in small quantities in the pancreas, liver,
and muscle extract, and among the products of the action of acids
on some nucleins.3 It may also occur in urine, more especially of
pigs, in which case it is also found in many of their tissues ; * ad-
ditionally in the retinal tapetum of fishes and in their scales,5 as
also in the integument of amphibia and reptiles,6 and in vegetable
tissues.7

It is a white amorphous powder, insoluble in water, alcohol,
ether, and ammonia. Its insolubility in the latter distinguishes

1 loc. cit. (sub xanthin).

2 Strecker, Ann. d. Chem. u. Pharm. Bd. cxvin. (1861), S. 152.

3 Kossel, Zt. f. physiol. Chem. Bd. vin. (1884), S. 404.

4 Pecile, Ann. d. Chem. u. Pharm. Bd. CLXXXIII. (1876), S. 141. Cf. Salomon,
Arch. f. Physiol. 1884, S. 175. Arch. f. Path. Anat. Bd. xcv. (1884), S. 527.
Virchow, Arch. f. path. Anat. Bde. xxxv. (1866), S. 358, xxxvi. S. 147.

5 Kiihne u. Sewall, Unters. a. d. physiol. Inst. Heidelb. Bd. in. (1880), S. 221.

6 Ewald u. Krukenberg, Ibid. Bd. iv. Hft. 3. (1882), S. 253, Zt. f. Biol. Bd. xix.
(1883), S. 154.

7 Schulze u. Bosshard, Zt.f. physiol. Chem. Bd. ix. (1885), S. 420.

CHK.MK \L 11ASIS (>F TIIK ANIMAL 1;<>1>Y. 183

it from xanthiii and hypoxanthin. It unites with acids, alkalis,
and salt- t«> form crystallisalde compounds. Of its compounds
with acids the most characteristic aiv tho-e with hydrochloiie and
nitric acids.

The compound with nitrate of silver is extremely insoluble in
1 Milling nitric acid.

' <;i VMN IM DKOCIII.ORinK

Fio. 30. GUANIX SITI: MI.

ii«.. _;». » i < \ > i > M i i MI' 'v it i.» »n i i»r. , *• tu. uv. \jt .\ -> i > .> i i K \ i r. ,

( I! N,<). HC1 - I LI i. ( After Kiihne.) C6II6N6<> • HNO,+ 4HjO. (After Kulnu- )

• Reactions. By treatment with nitric acid and caustic soda
(Strecker's test) it yields a colouration closely resembling that
given l.y xaiitliin, l>ut does not respond to WeideFs test (see
above, p. 177).

reactions.1 (i) A yellow crystalline precipitate «n
the addition <»f a saturated aqueous solution of picric acid t» a
solution of guanin-hydrochloride , insoluble in cold water.

(ii) An orange-coloured crystalline precijiitate, very insoluble
in water, on the addition of a concentrated solution of pota>sium
chroinate. (iii) rrismatic yellowish-brown cry-tals on the ad-
dition of a concentrated solution of feni<yanide of potassium.
Xanthin and hypoxanthin when similarly treated do not yield
the last two precipitate-.

l'.\ treatment with nitrous acid guanin may be readily con-
verted into xanthin. (Cf. adenin into hypo\:int!iin b\ similar
l'.\ oxidation it yields guanidin Ml < (Ml p . paia-
banic acid (see aliove, p. 171 ) and carbonic anliydride. a decompo-
sition which obviously corresponds to the formula given abo\
•_;u; niin.

C,H5N60-|-3.0-|-H2<) = MI (Ml -hC.H.N.O.

1 Zt.f.iJtytiol. ('/.• m IM. i S. 233.

184 GUANIDIN.

8. Guanidin. CN8H6. NH2

NH = C .

NH2.

Although this substance does not occur in the free state in any
tissue or fluid of the animal body, it is of considerable interest,
for it has been obtained by the direct oxidation of proteids (p.!61j
and may be made to yield urea by treatment with boiling dilute
sulphuric acid or baryta water. NH : C (NH2)2 + H20 = (NH2)2 CO
-+- NH3. Further, it affords a connecting link between the xanthin
series and kreatin (p. 143), the latter substance being, as already
stated, methylguanidin-acetic acid, while guanidin is itself the chief
product of the oxidation of guanin.

It may be readily synthetised in several ways; of these its
formation by the action of alcoholic ammonia on chlorpicrin (tri-
chlornitromethan) CC13 (NO2) or on cyanogen iodide shows clearly
its constitution. In the first case

CC18 (N02) + 3NH3 = NH : C (NH2)2 + 3HC1 + HN02.

In the second CNI + 3NH3 = NH : C (NH2)2 + NHJ, or in
other words guanidin may be regarded as a compound of cyana-
mide and ammonia CN . NH2 + NH3 = NH : C (NH2)2. The
relationship to kreatin may now be at once made evident by
comparing the reaction just given with that for the synthesis of
kreatin from cyanamide and sarkosin : —

NH,

CN . NHa -4- CH2 . NH(CH3). COOH = NH : C /

XN(CH3).CH2.COOH.

Xanthin derivatives.

The monomethyl (?) derivative of xanthin (heteroxanthin) has
already been described, as also one of the possible dimethyl derivatives,
viz. paraxanthin.

When the (silver or) lead salt of xanthin (PbC5H2N402) is dried
and heated in sealed tubes at 100° with methyl iodide, iodide of lead
is formed together with dimethyl-xanthin.1 The substance thus
obtained is identical with theobromin, long known as the character-
istic alkaloidal constituent of cocoa-beans, the fruit of Theobroma
cacao. A third presumably dimethyl derivative of xanthin has re-
cently been described as occurring in tea, viz. theophyllin.2 When
the silver salt of theohroinin is further treated as above with methyl
iodide it is converted into methyl-theobromin or trimethylxanthin,
which is identical with the vegetable alkaloid, long known under the
synonymous names of theine or caffeine, as occurring in the leaves or
seeds of many plants such as tea and coffee, also in the Brazilian
* guarana ' prepared from the fruit of Paulinia sorbiiis, in ' mate ' of

1 E. Fischer, loc. cit. (sub xanthin).

2 Kossel, Zt.f. physiol. Chem. Bd. xin. (1889), S. 298.

CIIKMK'AL I'.ASIS OF Till: ANIMAL 1;<>I>V. 185

South America, an infu>i«m »i the h-a\e- ,,i" / /' x,',x-. n,

kola-nuts u.-ed a- food MI ( '«-nt nil Africa (tin- I'ruit of .S/r«//</
(ti-innliKitn), in Smith African • hush-tea.' ami in many other plants
from \\hich st iinnlat ini; beverage- an- "kained liy infusion.1 Apart
from tin- clOM chemical relationshipof tin- alkaloida] principles of the
abo\ c plant> t.» tin- nitro<4eiiou- cr\-talline • c\t ract i\ e- ' of muscle-,
it is inteiv-t iiiu t.i notice further that they s.-.-m to bear tin- .-aim-
j^eiieral relationship to the or^anism> in which they respect ively occur.
There can I't- luit little ilmilit that the xanthin h«.<lie> (and uric aci<l)
an- typically prmluct> «i tin- i|n\\nuanl e\cret i.inary nit m^en-nis
inetaKc'lisin of animals. The alkaloidal principles of plants, in this
case theohroinin ami caffeine, may lie >imilarly re^irde.! a^ BXCn-
tionary pmilm-ts ami are hence I'miml collected in t ho^,. part- of the
plant uliich are more immediately or ultimately cast off, \\7.. the
leaves, -.-, d-. and hark. The facts already stated render the consump-
tion of theolu-omin and caffeine in -..me form or other by practically
the \\hole human race !.->> surprising than it mi^ht at first si^ht
appear. Their universal use also indicate- that they >upply -ome
distinct \\ant of the economy which cannot a- yet he explained purely
with reference to their relationship to the nitrogenous extract!
animal ti--iie.-. hut rather to the physiological effect their invest ion
produces. In moderate do-e- they exert an a^iveahh- >timulatin^
action wherehy the >ensati<uis of fatigue and drou-ine-- are removed,
the body bein^ thus enabled to exert it.-elf with le-s sense of effort

and less initial stimulus, and the mind is more acti\e. clearsighted

and insistent to the depre--ing effects of unpleasant influences. There
i- no evidence, as was at one time assumed, that they act in any uay

by reducing the activity of nitrogenous metabolism.1 In the case of

and cho,-,, late we have to deal not merely with the stimulating
• - of the theohroinin they contain, but al-o with the fact that
they are of extreme nutrient value, owin^ to the lar-je amount of fats
("i<> p.c. ). proteid- (1» p.c.). and carbohydrate- \\hich enter into their
comjiosition. The comparative physiological action of xanthin. theo-
broinin. caffeine, and some of their derivatives have recently been

studied by Pilehne.*

TIIK AROMATIC SERIES.

1 . Benzole acid C,H6 . COOH.

This is not found a- a normal ron-i it uent of the body. When
urs in (chielly herbivorous) urine its presence i* usually dun
•••rinentative decoiiip..-iti..n of hipj.uric acid whereby beii/oie
acid and u'lyi'in ( ijlycocollj are 1'i.rined.

C II .00, Nil OH « "<>H +11 "

= C.H,.COOH. + CH,(MI .» C I

.lliil Chlirrli, ('/„•„,. nfroinmnH lit'-, 1HHO. p. UT

I HH-hon. I1--

.1 --A. /: l'h>i»u>l. ./ '/i. II.

rixirm. H.I. xv. (188LM. S. .'J, ami <-f. |{.,^!,ar!i. 1'llu- ;

186 HIPPURIC ACID.

The acid is usually prepared by the above decomposition of
hippuric acid, which is readily effected by a short boiling with
mineral acids or, less readily, with caustic alkalis. It is also
obtained by the dry distillation of gum-benzoin from which the
acid separates by sublimation. The sublimed acid generally
crystallises in fine needles which are light and glistening. It is
soluble in about 200 parts of cold or 25 of boiling water and very
soluble in alcohol, ether, and petroleum-ether,1 in which latter
hippuric acid is insoluble. When precipitated from solutions, either
by cooling or the addition of acids to its salts in the cold, the
crystalline form is usually much less distinct.

Apart from the crystalline form benzoic acid is characterised by
its property of readily subliming, even at 100°, thus resembling
leucin and differing markedly from hippuric acid. As a result of
this it passes off freely in the vapours arising from its boiling
aqueous solutions, so that in concentrating fluids, such as urine, in
which its presence is conjectured, they should be first rendered
alkaline with sodium carbonate, thus forming a non-volatile salt.
Benzoic acid may be additionally recognised by the following test :
when treated with a little boiling nitric acid and evaporated to
dryness, the residue thus obtained yields, on further heating, an
unmistakable odour of nitrobenzol.

When introduced into the body benzoic acid is readily and
largely converted into hippuric acid, while at the same time small
quantities of succinic acid may at the same time make their
appearance. The chief interest in the acid centres in the above
relationship to hippuric acid, a fact discovered by Wbhler in 1824
and specially interesting as being the first known instance of a
well defined synthesis effected by the animal body, and the start-
ing-point for the disproval of Liebig's views as to the funda-
mental difference in the metabolic processes of animal and plant
tissues.

2. Hippuric acid. C7H602. [C6H5 . CO . NH . CH2 . COOH.]
(Benzoyl-gly cin. )

This acid is found in considerable quantities (1'5 — 2*5 p.c.) in
the urine of herbivora, and also, though to a much smaller amount
(0*1 — 1*0 grm. per diem) in the urine of man. It is undoubtedly
formed in the body by the union, with dehydration, of benzoic
acid and glycin (see § 419.) This mode of its formation may be
readily observed out of the body by heating together dry benzoic
acid and glycin in sealed tubes to 160°.

C6H5.COOHH-CH2(NH2).COOH=C6HS.CO . NH.CH2.COOH4-H20.

1 Petroleum-ether consists ordinarily of a mixture of the more volatile hydro-
carbons obtained by distillation during the fractionating of crude petroleum, and
boils up to about 120°. The most volatile petroleum-ether boils up to about 80°.

CHEMICAL BASIS OF THK ANIMAL P.nPY. 187

Its constitution is further characteristically shown \>y it- pro-
duct i. .a hy the action of ben/amide on monochlor-ftoetio acid : —

C6H6.CO . NH2+CHSC1 . COOH=C.H, . o > N 1 1 < ' 1 1 _.. a x )H.+ 1 1 « ;

ami al.-o by that of benzoyl-chloride on glycin : 1
C.H6.CO.C1+CH, (NH,) . COOH=C,H5 . < « »M I .CH8.CO( > II +11 < 1
It may be readily obtained from tin- urine of horses or co\\ -.
more particularly when they are out to ^rass, — t\\e perfect It/ /
urine hoileil with milk of lime in slight excess, by which means
the arid U tixe.l as a hippurate of calcium. It i> then tilteivd. the
filtrate concentrated to a email bulk ami treated when cold with
hydrochloric acid in slight excess; this decompo>es the calcium
salt, litteratinu hippuric- acid, whii.'h separates out at once, owiiiL;
to its comparatively slight soluliility. It is then puritied liy >•
recrystallisations from boiling water, but it is extremely dithVult
to obtain it colourless.

II. Hn-i'i i:i« \. ii. CRTSTALS. (After Kunke.)

When rapidly separated out from its aqueous solutions, a

the above met hod of its j. reparation, it assumes the form of tine
needle-. I ',y >lo\vi-r cry-t a 1 lisat ion it yield- hmx foursided pri-m-
or cnlumns with ]i\ ramidal ends; the-e are frequently arranged

• >ups and present a semitran-pnrent. milky appearance.
When ] Hi re they are odourles- and of a somewhat hitter taste.
They rei|iiire <i(M> parts of water for their -olution at 0°, arc'
readily >oluble in hot wat--r, al-o in alcohol anil to a nt in

ether. They are conveniently insoluble in petroleum-ether, in
virtue of which hippuric acid can be readily separated from hcn/oic
acid which is soluble in this reagent. Its solutions redden litmu--
paper.

1 Baum. Zt.f. /%- !'• I ix. (!."«.')). S. 4f,:,

8 To avoid fermentative .lci..in|>.)!»itiun int.. Iwn/ui.- a. j,| ntnl gl\-\ -in.

188 HIPPURIC ACID.

Hippuric acid is monobasic, and forms salts which (except the
iron salts) are readily soluble in water ; from these solutions, if
sufficiently concentrated, excess of hydrochloric acid precipitates
the acid in fine needles. When heated with concentrated mineral
acids it is • resolved into benzoic acid and glycin. The same de-
composition occurs readily in presence of putrefactive organisms.

Apart from the characteristics already stated the acid may be
recognised by the following reactions. When gently heated in a
small tube the acid does not at once sublime as does benzoic acid,
but melts and solidifies again on cooling. If more strongly heated
it melts as before, but is now decomposed, yielding a sublimate of
benzoic acid accompanied by an odour like that of new hay, while
oily red drops are observed in the tube. When treated with boil-
ing nitric acid (see above sub benzoic acid) and evaporated to
dryness the residue on being heated yields the marked and
characteristic odour of nitrobenzol (Llicke's reaction J). As al-
ready stated hippuric acid owes its formation in the body to a
union of benzoic acid with glycin, so that its source must be
sought for in the modes by which benzoic acid (aromatic sub-
stance) is introduced into or arises in the body. The source is
probably of more than one kind. Hay and grass were long since
stated2 to contain some substance which yields hippuric acid in
the body : this may be extracted by means of dilute sulphuric
acid, less readily by caustic potash.3 More recent researches have
shown the presence in grass, hay, and many fruits and berries not
only of some benzoic acid but also of substances such as quinic
acid (OH)4 C6H7 . COOH, which readily yield benzoic acid and are
hence a source of hippuric acid.4 A further source is found in
the aromatic (benzoic) products of the putrefaction of proteids,
such as in especial phenyl-propionic acid (C6H5 . CH2 . CH2 . COOH)5
which in its amidated form is more particularly a product of the
decomposition of vegetable proteids,6 and yields benzoic acid by
oxidation. This substance has been found in the rumen of cows
fed with hay.7 These facts coupled with the marked occurrence
of putrefactive changes in the alimentary canal of herbivora
probably account for the preponderance of hippuric acid in their
urine. In carnivora it appears that some traces of hippuric acid
may be observed during starvation, originating here from the
aromatic residues of the tissue proteids; also during an exclu-
sively meat-diet.8 When fed on a mixed diet some of the

1 Arch.f. path. Anat. Bd. xix. (1860), S. 196.
- ,Nleissner u. Shepard, Die Hippursditre. 1866.

3 Weiske, Zt.f. Biol. Bd. xn. (1876), S. 241.

4 For refs. see Salkowski u. Leube. Die Lehre vom Harn, 1882, S. 131.

5 E. u. H. Salkowski, Zt. f. phi/siol. Chem. Bd. vn. (1885), S. 161.

9 Schulze u. Barbieri, Ber. d'. d. chem. Ges. 1883, S. 1711. Jn. f. prakt. Chem.
(N.F.) Bd. xxvu. (1883), S. 337.

7 Tappeiner, Zt. f. Biol. Bd. XXH. (1886), S. 236.

8 Salkowski, E., Ber. d. d. chem. Gesell. 1878, S. 500. Arch. f. path. Anat. Bd.
73 (1878), S 421.

CHEMICAL BASIS OF T1IK ANIMAL BODY.

hippuric acid arises from the ben/oie and allied constituents of
tin- vegetable part of the food, and probably not an inconsiderable
amount from the putrefactive products of tin- proteids in the ali-
mentary canal; in accordance with tin- it i- found that disinfec-
tion of tin- alimentary canal in do^s with calomel diminishes the
outjnit of the acid.1 Ty rosin, notwithstanding its aromatic con-
stitution, does iiot give rise to hippuric acid when administered to
nan.1

The classical researches of Bunge and Sc hmiedeberg3 li;i\
shown that the >yiithetic. production of hippuric acid by the
union of beuzoic acid and ulycin takes place chietly in the kid-
ney of carnivora (dogs). In herbivora (rabbits) it appears that
a considerable formation of hippuric acid may be observed on the
-:ion of benzoic acid even after exclusion nf the kidneys.4 and
the same is the case with frogs. Pathological observation.- on
man seem to indicate that in them the kidneys play at least some
part in the synthetic production of hippurir acid from benzoic.6
When benzoic acid is administered to birds it reappears in the ex-
creta as ornithuric acid: the latter when boiled with hydrochloric
acid splits up into benzoic acid and ornithin. the latter having the
composition of diamido-valerianic acid.6

a Tyrosin. c,HnN():; . [( HI . C6H4 . CH2 . CH . (NH,) . CooH].
>xyphenyl-a-amidopropionic acid.

The earlier work on the synthesis of ty rosin indicated the prob-
able presence in its molecule of some aromatic (phenyl) radicle.
The more recent successful synthesis by the action of nitrous acid
mi para-amidophenyl alanin " has confirmed this view and defi-
nitely established its constitution.8 It always accnnij'anies leiicin.
though less in amount, as a product of the pancreatic di^otiun of
proteids, l>ut not of gelatin, also as a 'product of their putrefactive
decomposition as well as of the action of boiling mineral acid* and
alkalis. It is also perhaps found normally in small quantities in
the pancreas and its secretion and in the splr.-n. and tracet have

I n described as obtained from various tis>ue- ,,t the body'1 l-

is normally absent in urine, but. makes its appearance together with
leucin in this excretion in several diseased conditions of the liver,
notably acute yellow atrophy, also in pbo«.p horns poisoning ; there

>. ,,/,,/giol. Cl,.m. H,|. \. (1886), S

../. IM \i (i--
» /t, r,nh. „. /'/,.!,•//• . H.I. vi. (in:r,). s

H.I. M- ». See «l»o II. 'fTiii.'iiin. A //.../. 15,1 M -339.

« \V S:il..iii,.n. '/.< i- /./../"••/. <'!>•• i». H-l. in. (!><:'.»). S 365.

• .lanrMrl.l ii. s,t..kvi«. .1 ••>. i ••.• Pod 1871 8 268.

• Jnfl ,/. ,•!,.,„. GtM& i

M.ii.in i- a :uiii.l..jiP.pi..iii.- :i.'i-l : CII, . CH i v 'H

•:.-niin-\iT M. Lii'p.. /'• '/. '/ -lirm. Gttflt. 1882, S. 1544. I. i. •!,;_••< Anna!.
1M -.'M 1889 8. 161

9 v. Gortip-Itaancz, fahrb. d. phytiol. Ckem. Bd. i\ I-:-, j,;, U

190

TYROSIK

is however some conflict of opinion as to its constancy in such cases.
It is also present in not inconsiderable quantities, along with leucin,
in many plant tissues.

Tyrosin crystallises in exceedingly fine needles which are usu-
ally collected into feathery masses. The crystals are snow-
white, tasteless, and odourless. If crystallised from an alkaline
solution tyrosin often assumes the form of rosettes composed of
fine needles arranged radiately.

The crystals are very sparingly soluble in cold water (1 in
2000 at 20°), much more soluble in boiling water (1 in 150) ;

FIG. 32. TTROSIN CRYSTALS. (Krukenberg.)

they are almost insoluble in strong alcohol (1 in 13500) and
quite insoluble in ether. They are readily soluble in acids and
particularly so in ammonia and other alkalis and in solutions of
alkaline salts.

Preparation, (i) The products of a prolonged pancreatic diges-
tion of proteids are neutralised and filtered ; the filtrate when
concentrated usually yields crusts of tyrosin crystals, which may
be readily purified by solution in a little boiling water from
which they separate out on cooling after concentration if neces-
sary, (ii) Horn shavings are boiled for 24 hours with sulphuric
acid (5 of acid to 13 of water). The sulphuric acid is then sepa-
rated by the addition of lime, and the filtrate from the calcium
sulphate yields as before crusts of tyrosin crystals on concentra-
tion and cooling. These are then purified by recrystallisation
from boiling water.1 Any leucin at first present in the crystal-

1 These methods suffice for the preparation of small amounts of tyrosin for
purposes of study. For full details of its preparation and most productive
separation from leucin see Hlasiwetz and Habermann, quoted sub leucin. See
also E. Schulze, Zt. f. physiol. Chem. Bd. ix. 1885, Sn. 63, 253, on the separation
of amido-acids.

UIK.MK'AL IIASIS OF TIIK ANIMAL BODY. 191
line crusts remains in the mother-liquors from which the tyrosiu

lias lirrll M-parat.'d.

Apart fn-iii its crystalline form and characteristic solubilities
tyrosiu may he ivadily recognised l»y several well-marked
n-actions.

Hi'ri'in HHH'* i-i'irtio/i. When heated with Millon's reagent so-
lutions of tyrosiu yi.-ld a hrilliant crimson or pink colouration
which, if much tymsin is present, is accompanied tinally l>y a
similarly coloured precipitate. Tin- test in its original form was
applied liy heating with a M>luti«m of mercuric nitrate in presence
of nitrous acid.1

1'iriti'x /•ox/inn? If tyrosin is moistened on a wateh-ojass with
etinci-ntrated sulphuric acid and warmed for rive or ten minutes
on a water kith, it turns pink, owini: to the formation of tyrosin-
sulphonic acid — C9H10 (SO,OH) NO, + 2H80. Tliis is then diluted
with water, warmed, neutralised with kirinm < a rlion ate, and filtered
while, hot. The filtrate yields a violet colour on the careful addi-
tion i if very dilute peirhloride of iron. The colour is readil
stmyed hy any 6X0688 of the iron sah.:;

Tiie remarks made mi p. 149 on the optical properties of leucin,
apply also to tyrosin.4

\Yhen tyr«»in i- Mihject.-d to putrefactive decomposition it yields
paraoxyphenylacetic acid OH . C6H4-CiL .<(»( )[|.. pwaozyphenrl-
in-i-jiiniiif (hydropaiacomarie) acid <»II . < ,.II4 ('H.-( II .' <n>n..
/^-jilieiiN •l]ir'>]ii<iiiii>-(hvdriicinu;iiiiir) acid (',-,11 . < II . < II . < »><>M..
phenol, !',H, . OIL, and paral<n->,d CH, . C,H4 . <ML5 These >ul.-
>Jam-fs occur normally in Miiall and varialdi- amounts in uriiu- and
an- mcriMM-d in (ju;intity in tins excretion !>y tin- administra«tion of
:\T"-in. Their presence is \\itliout dmibt cliit-tly due to j.ntrt i

.'(•c.urrin^ in the alimentary canal in corre>[>ondencc with tin-
facts that the bodies in question are found most markedly in the urine
of herl.ivora, in increased quantity in that of men under ft regetablfl
.nid largely disa|i]iear under the intlueiice of drills Midi ;t-> calo-
mel. which likens or prevents the occurrencr «'f putrefactive changes
in the intestine.6 In the absence of thoe putrefactive pi.
ro> in when administered m not excessive amounts i> apparent!;.
pletely o\idi-ed and does not. as frequently stated. ^: to any

increa~ed output of urea.7 In large (lose.s tyro>in reappears externally

1 I. ifhip's Ann.il. l',.i. I.XXXMI. (1S.VJ). S.

- I.i.-t.i-'s At,,,,,!. IM i.xxxi: - L'.'H

* For other !••.•..•< imp.. riant n-:u-tii.ns see \Vnrntrr. ' f. Pkytiol. Bd. I.
(1887). S. l'J4. l'.lran>/.ky. Zt f. i>h,/si,J ( t,,m. 1M. xn. (is.sS). S. 355.

-«•<: Maiitliurr, I/ --'), alao Si:

. li.l LZZXT. (1883), April-Hft. Srliul/.r. /
(1885). Sn l.i|i)>in:iiiii. /.'" ./. •/. dum, Cettll. 1884. S. i83«.

\V-vl, Zt. f. «|MM£ ( •!,.,„. ll.l. Ill I liatiinaiiii. I'-nl. lit! i\

S. 304. Sehottan, //•„/. n.i. MI. (18« - H /' d.

li.iiiinaiiii, />'i'l. s

« Bauniai.n. /4. f },h<niol. Chem. IM x - 129.

Mllt/.-M 11 Nrn.kl. /J / /.V- IM MM.

/>;.« ! 1-71 Mrii-'ger. 'A. f. /'AVW. Cl,.i». H.l u (1*7*). G

H.'.hinann. fieri, kiln. U'orhentch. 1888. " Nrn. 43, 44. I'ol.: . -/«io/. Chem

H.I \i\ (1-

192

TYROSIN.

NH.CO
in the form of tyrosin-hydantoin * OH . C6H4 - C2H8 '

XCO. NH
This substance is the anhydride of tyrosin hydantoic acid 2

OH . C6H4 - C2H3 (NH . CO . NH2) COOH.

and analogous to the similar compounds excreted after the ingestion
of sarkosin and taurin. (See pp. 141, 143.) It yields tyrosin, am-
monia, and carbonic dioxide when heated with baryta in sealed
tubes.

4. Kynurenic acid. C10H7N08. [C9H5N . OH . COOH.] Oxy-
chinolin-carboxylic acid.

This acid occurs characteristically but in variable amounts in
the urine of dogs, but does not appear to have been found normally
in that of man. It was first described by Liebig.3 It is most
readily separated horn fresh urine by precipitation with phospho-
tungstic acid after the addition of hydrochloric acid ; it is then

FIG. 33. CRYSTALS OF KYNURENIC ACID. (After Kiihne.)

liberated from the precipitate by the action of baryta.4 It may
also be obtained by concentrating the urine to one-third of its
bulk, acidulating with hydrochloric acid and allowing it to stand
in a cool place for several days until the separation of the acid is
complete.5 It may be separated from admixed uric acid by solu-
tion in dilute ammonia. It is practically insoluble in cold water,
slightly so in boiling water, and readily soluble in hot alcohol and

1 Blendennann. Ibid. Bd. vi. (1882), S. 234.

2 Jaffe', Ibid. Bd. vn. (1883), S. 306.

3 Liebig's Annalen, Bd. 86 (1853), S. 125, Bd. 108 (1858), S. 354.

4 Hofmeister, Zt. f. phi/siol. Chem. Bd. v. (1881), S. 67. Cf. Brieger, Ibid.
Bd. iv. S. 89.

6 Schmiedeberg u. Schultzen, Liebig's Annalen, Bd. CLXIV. (1872), S. 155.

CHEMICAL BASIS <»!• T1IK ANIMAL iionv. 193

in dilute ammonia. It crystallises in long brilliant white needles
which when kept under acidulated water an- often changed into
Ion;; glittering foursided prisms.

Tins arid forms >alts of which that with barium crystalline-
readily and in a very characteristic triangular form.

Apart from its crystalline form and tliat of its barium salt this
acid may he readily recognised by the following reaction. "When
heated on a water bath with hydrochloric acid and chlorate of
potash and evaporated to dryuess a reddi>h residue is obtained,
which turns at first to a brownish green on the addition of am-
monia, and finally to an emerald green.1

:J4. CRYSTALS OF BARIUM KTXI-RKNATE. (After Kulmc.)

I'.v prolonged heating to 250 — 260° kynuivnic acid
carbonic anhydride and is converted into kynurin (o.\y« •hinolin )
C9H«N (OH), and when heated with /inc dust in a current of
hydro-en it is converted into chinolin C,H6N (OH) -f- H, =
C II N + ll-jO. These reactions throw considerable liu-ht on the
constitution of the acid.2

The amount of kynurenic acid in the urine is increased on the
:ion of isatin. a product of the oxidation of indigo.3 Under
ordinary conditions its amount in this excretion is dependent upon
the nature of the food supplied to the animal, being greatest under
a pioteid diet, and is not related to the occurrence or absence of
putrefactive processes in the alimentary canal 4

PhenoL C,H6.OH. Oxybenxol. (Gufcolio or pheny Ho acid.)

This substance is formed, together with indol and skatol. dur-
ing the putrefactive decompo>ition ,,f protvids, more es|>criully in
prolonged putrefactive pancreatic digestions.6 From these it may

1 Jaffa', 7.1. f. ph,i»i<J. ('/„•„,. 1M. vn. (1SS2-."

2 Kr - 1 5. 1 MI |l»: ". s. 1673. 3/ono/<A. /. Ckem
15.1 ii ^57.

s Ni ! I':iih. u. PHarm. R.I. in

iinanii. '/.t f. iJu/tint. c/lfm H,I. x. (issr,). s i:ti Hut . f . Haagen, Inaog -

Iv.ni-sl. • - Crntr.ill: I <l M- •/ H -.8.214.)

• Banmann. '/.< f }>h n.<i»i. <'/,.•„, IJ,j. - 50, MI •.»:.() Uri.-^-r. Ibid.

Bd. in. (1879). S. 1.-J4. Odernmtt. Jn.f. prai-t. Chtm. Bd. xvm. (1878), S. S49.

13

194 PHENOL.

be obtained by simple distillation. In accordance with this it is
formed in not inconsiderable quantity in the alimentary canal,
more especially when putrefactive processes in its contents are
increased either pathologically or as the result of experimental
interference.1 On the phenol thus formed a small proportion is
passed out in the faeces,2 the larger part however is excreted in
the urine as an ethereal salt of sulphuric acid, viz. phenylsul-
phate of potassium. The latter is typical of an extensive series
of similar ethereal sulphates which make their appearance in
urine after the ingestion of aromatic substances.

Their nature and constitution was first definitely ascertained by
Bauinann,3 although it had previously been shown that phenol,
.even after it has been administered as such, does not exist in the
free state in urine but may be set free by distillation with a
mineral acid.4

Phenyl-sulphuric acid.5 C6H6 . O . S02OH. Apart from its
abundant presence in urine as an alkaline salt after the admin-
istration of phenol this compound occurs normally in small
quantities in most urines, more particularly in those of herbivora,
since in these animals the conditions for its formation are espe-
cially provided by the preponderance of aromatic compounds in
their food and the more marked activity of putrefactive changes
in their alimentary canal. The total sulphates in urine consist
therefore partly of this ethereal sulphate (together with the
similar compounds of kresol, indol, and skatol, see below) and of
ordinary sulphates. The relative amounts of the sulphuric acid
contained in these two forms is ascertained by acidulating with
acetic acid and adding barium chloride, by which the sulphuric
acid present as ordinary sulphates is precipitated as barium sul-
phate. The filtrate from this is now boiled with hydrochloric
acid, by whose action the ethereal sulphates are decomposed,
yielding phenol and sulphuric acid, which again forms barium
sulphate ; from this the amount of the ethereal salts of sulphuric
acid may be at once determined.6 While the probable mode of

1 E. Salkowski, Ber. d. d. chem. Gesell. 1876, S. 1595. Ibid. 1877, S. 842. Cen-
tralb. f. d. Med. Wiss. 1876, S. 818. Arch. f. Pht/siol. Jahrg. 1877, S. 476. Brieger,
Zt.f.'phi/siol. Chem. Bd. n, (1878), S- 241. G. Hoppe-Seyler, Ibid. Bd. xn. (1888), S. 1.

2 Brieger, Ber. d. d. chem. Gesell. 1877, S. 1027. Jn, f. prakt. Chem. Bd. xvn.
(1878), S. 134.

3 Pfliiger's Arch. Bd, xin. (1876), S. 285. Ber. d. d. chem. Gesell. 1876, S. 55.
Baumann uud Herter, Zt. f. phi/siol. Chem. Bd. i. (1877), S 244. See also
Baumann, Ibid. Bd. n. (1878), S. 335, Bd. x. (1886), S. 123. For a list of
substances which when administered leave the body as ethereal sulphates, see
Hermann's Hdbch. d. Physiol. Bd. v. Th. 1, S. 508.

4 Buliginsky, Hoppe-Seyler's Med. chem. Unters. Hft. 2, 1866, S. 234. Hoppe-
Seyler, Pfluger's Arch. Bd. v. (1872), S. 470.

5 Not to be confounded with phenolsulphonic acid, C6H4 (OH). SO2 OH.

6 For the accurate separation of the ethereal sulphates which usually occur
mixed in urine, some special works should be consulted, such as Neubauer u. Vogel,
Analyse des Harns, or Salkowski n. Leube, Die Lehre vom ffarn. Cf. Baumann, Zt
f.physiol. Chem. Bd. i. (1876), S. 70, Ibid. Bd. vi. (1882), S. 183.

CHEMICAL BASIS OF Till: ANIMAL BODY. l-j:,

formation of this acid is undoubtedly due to tin- primary produc-
tion of phenol l.y putrefactive processes from proteids, and the
subsequent colligation of this phenol with sulphuric acid, very
little is known of the seat or mode of this union. It has not
definitely connected, if at all, with any distinctly synthetic
activity of tin- kidney.1

Since, as lias been said, phenol does not exist in the free state
in urine, its detection necessitates the decomposition of its com-
pound, vix. the phenylsulphate of potassium. This is best l-nui-lit
about by distilling the urine (200 c.c.) with strong hydrochloric
acid (40 c.c.) or 5 p.c. of sulphuric acid until about 150 c.c. of
distillate has passed over. The distillate contains free phenol,
which is tested for qualitatively by the reactions described below,
and estimated quantitatively by the formation of a compound
with bromine, tribromphenol, C6H2Br8.OH.2

J'/n /in/ reactions (i). A violet-blue colouration on the addition
of neutral solutions of perchloride of iron. This colour is similar
to that yielded by salicylic acid, but the absorption spectra of the
two are stated to be different.3 It is destroyed by excess of the
reagent and is also not obtained in presence of acids and alkalis
alcohol.4 (ii) When a solution of phenol is mixed with
one quarter of its bulk of ammonia and a few drops of chloride
of lime solution (1 to 20 of water) and gently warmed it yields a
blue colouration.5 (iii) When boiled with Milloifs reagent a
marked and persistent pink or red colour similar to that yielded
by tyrosin is obtained.6 (iv) Mere traces of phenol give a yel-
h crystalline precipitate on the addition of bromine water.
This reaction is used as stated above for the quantitative estima-
tion of phenol. Of these reactions (iii) and (iv) are the most
delicate, (v) On the addition of furfurol (Cjl^Oj, aldehyde of
pyromucic acid) solution ('5 p.c.) and strong suliihuric acid, phenol
yields a brilliant red colour which finally turns to blue.7

6, Kresol. r,,H4. OH. CH3. M.-thylphenol.

This lioniologue of phenol exists in three isomeric forms, ortho-,
. and metakresol. It i^ now known that the phenols which
may be obtained by the distillation of urine with acids consist
preponderatingly of parakre«»l, accompanied in some cases by
orthokresol and possibly (?) by metakresol in minute amounts.
Like phenol it is not found free in urine, but as kresylsulphuric

i Christian! n. B.iinnami. '/J. t. /.*//.«.»/. Chfm. Bd. II. (1878), S. 350. See aliw
i Bd. J

itri.a

uk.-nh.-ri,'. Vrrh.o.dl. d /.A,,.*,/.-./..,/. <;f*,ll. :„ \Viir-Jntn,, B.I. xvitl (1884),

« II. •*,,,.. I.i.-l.iKV Annul. B.I. l»a (l*7f, > I'-l

irokl, I'll... I'-l v rl-7-.'l. S. 353.

• 1'lu / 173 See also Alnufo, Ibid., Bd

xvii. (i-:- . s Ki7

.rmi!./.ky. /,t / i>fiii»iol. Chem. Bd. xil. (1888), Sn 355.

196 PYROCATECHIK

acid,1 C7H7O . S02OH. The general conditions of its presence in
urine are practically identical with those for the occurrence of
phenylsulphuric acid.2 When introduced into the animal body
the three isomeric kresols undergo distinctly different oxidational
changes.3

Reactions. On the addition of an excess of bromine water to
its solutions parakresol yields a brominated derivative, but the
compound is only obtained in a separate and crystalline form
after prolonged standing, differing characteristically from the
analogous compound of phenol, which under similar circumstances
is formed rapidly. It yields a reddish yellow colouration with
potassium nitroprusside and caustic potash, which turns bright
pink on the addition of an excess of acetic acid.4 Aceton gives
a similar reaction. With furfurol and sulphuric acid the reaction
is closely similar to that which phenol gives.5

7. Pyrocatechin. C6H4 (OH)2, Orthodioxybenzol.

This substance occurs, in small amounts in human urine united
with sulphuric acid as a mono-ethereal compound OH . C6H4 . O .
S02OH. It is more plentifully present in the urine of herbivora,
especially of the horse, and is largely increased in amount by the
administration of benzol or phenol.6 It is also stated to occur in
cerebrospinal fluid." When present in urine it (together with
hydrochinon) confers on this excretion, especially if alkaline, the
property of turning successively greenish, brown, and finally dark-
brown or almost black on exposure to the air, and of readily re-
ducing solutions of metallic salts, a fact to be taken into account
when dealing with the presence or absence of sugar in the urine.
Solutions of pyrocatechin turn emerald green on the addition of
a few drops of very dilute solution of ferric chloride, avoiding all
excess of the reagent. If the green solution is now acidulated
with tartaric acid, it turns violet on the subsequent addition of a
little ammonia and purplish-red on the addition of excess. The
green colour may be restored by excess of acetic acid.8 It may

1 Baumann, Ber. d. d. chem. Gesell. Bd. ix. (1876), S. 1389. Zt. f. ph>/siol.
Chem. Bd. 11. (1878), S. 335. Preusse; Ibid. S. 355. Brieger, Ibid. Bd. iv.
(1880), S. 204.

2 Baumann u. Brieger; Ibid. Bd. in. (1879), S. 149. Baumann, Ibid. IT. S.
304. For the detection and separation of the kresols and phenol see Baumaun
u. Brieger, Ber. d. d. chem. Gesell. Bd. XH. (1879), S. 804. Baumann, Zt. f.
physiol. Chem. Bd. vi. (1882), S 183. Brieger, Ibid. Tin. (1883), S. 311.

'3 Preusse, Ibid. Bd. T. (1881), S. 57.
* v. Jacksch, Zt.f. klin. Med. Bd. vm. (1884), S. 130.

5 Udranszky, cit. (sub phenol).

6 See Baumann, Pfl tiger's Arch. Bd. xn. (1876), S. 63, Baumann u. Herter, Zt.
f. physiol. Chem. Bd. I. (1877), S. 248, Baumann u. Preusse, Ibid. Bd. ill. (1879), S.
156. Brieger, Arch. f. phi/siol. Jahrg. 1879, Suppl.-Bd. S. 61. Nencki u. Giacosa,
Zt. f. physiol. Chem. Bd. 'IT. (1880), S. 325. Schmiedeberg, Arch. f. exp. Path. u.
Pharm. Bd. xiv. (1881), S. 288.

7 Halliburton, Jl. of Physiol. Vol. x. (1889), p. 247.

8 Ebstein u. Miiller, Yin-how's Arch. Bd. LXT. (1875), S. 394. See also Jacquemin,
Rev. Med. de PEst. T. TIII. (1877), p. 90.

(INIMICAL UASIS <>r THK ANIMAL K<>I>Y. I'.i?

be distinguished from hydrochinon by yielding a precipitate \vitli
normal acetate ill lead which is Soluble in acetic acid, whereas the
latt' T substance does not No simple directions can be given for
the separation and estimation of pyrocatechin in presence of
phenol, kivsnl, and hydrochinon.1

Hut little is known as to the source of this substance in urine
apart t'r«>m its probable formation from the phenol produced by
putrefactive changes in tin- alimentary canal. In herbivora there
is some evidence that it is derived from certain aromatic consti-
tuents of their food.-

8. Hydrochinon. C«H4 (OH)2. Pared i o. xy he nxol.

II kfl not yet been described as occurring normally in urine, but
only as the result of the invest ion of phenol. It exists in urine
as an ethereal compound with sulphuric acid, and is largely tin-
cause of the dark colour which this excretion assumes after tin-
absorption of phenol on exposure to the air. It resembles pvr<>-
cati-chin in effecting the reduction of metallic salts, but differs
from it in being nearly insoluble in cold benzol and in not yield-
ing any precipitate with normal lead acetate. This latter property
sutlices for its separation from pyroeatechin. It is readily con-
verted by oxidation into chinon C,,Hi( }-- whose characteristic odour
affords a further means of identification, ami when heated in an
open test-tube it yields a blue sublimate.3

The third known isomeric dioxyben/ol. vix. meta-dioxybeii/ol
••sore-in, has not yet been found in the animal body or in
urine.

Tin: IM>K;O SKIMKS.
'

1. Indol. (Ml N

Indol oeniix <-haracteri<tically in the f;eces. to which with

skatol it impait> their ]»eculiai Iv unplea-ant odour.1 It- pi-

In-ie is due to its formation during tin- putrefactive decomposition

of proteid^ which u-ually «iccur> t' extent in the

alimentary canal, part of the ind<>l leaving the body in the urine

:im -alt of indoxyl-iilpliurie •''"/'•'), the

mder bi-ing excreted with the f.i-ce<. It may readily be

obtained, contaminated b\ varying' '|iiantities of phenol and

/: /,/,v.<,V r/,,,,,. H,| M <i --:.' i, 8. 188. Schmiedeberg, Joe.

. • -

,,/n/.W. 'V(.»i. Mil n (1*7*1. Si.

t,. the 1;' .ni:lv i|""'' nlarly

I'.Miiinann 11 I'rm--.- .I"/. /I fifn/^ol. ./<//.• ^iippv-

•M.UIII II. 1 '

l!:niii,:n.n. /' '/. I',. I \ i

1 l;.|.!/irj.-\\ski. .\rrl, / .|;j,i.' H, /'/,.,«,./ I-

198 INDOL.

skatol (see below), by acidulating and distilling the products of a
not too prolonged alkaline putrefactive pancreatic digestion of
proteids, preferably of liver or fibrin. Indol passes over into the
distillate, from which it is extracted by shaking up with ether,
and is left behind as an impure oily liquid when the ether is
driven off by heat.1 It may also be prepared by heating moist
proteids slowly to a red-heat with excess of caustic potash, the
indol as before passing over into the distillate.2 Indol is a crys-
talline body which when pure melts at 53°. It is soluble in
boiling water, alcohol, and ether.

Reactions. A strip of pine-wood moistened with hydrochloric
acid is coloured bright crimson when dipped into an alcoholic
solution of indol.3 Its alcoholic solution turns red when treated
with nitrous (fuming nitric) acid, and its aqueous solution gives a
copious red precipitate with the same reagent.4 This reaction is
more delicate if carried on by the addition of strong nitric acid
first, and of a 2 p.c. solution of potassium nitrite subsequently.5
When indol in dilute solution is mixed with a little sodium nitro-
prusside and then with a few drops of caustic soda it turns at
once violet-blue, and pure blue on subsequent acidulation with
acetic acid.6 Skatol yields neither of the above reactions. Iridol
also forms a well-marked crystalline compound with picric acid
(trinitro-phenol) when added in benzolic solution to a solution of
the acid in benzol, so also does skatol.

It has been already stated that a part of the indol formed in the
alimentary canal leaves the body in the urine as a potassium salt of
indoxylsulphuric acid; by oxidation this may be readily decomposed
into indigo-blue and acid potassium sulphate: — 2C8H6NKS04 -\- 02
= C16H10N2O2-h2KHSO4.7 By the action of powerful reducing
agents indigo-blue may be made to yield indol, which by oxidation
may be again converted into indigo-blue. This shows that indol is
the mother substance of the indigo series. The constitution of indol
is elucidated by its formation from orthonitrophenylchlorethylene
C6H4 (NO,) - CH = CHC1. When this is reduced with tin and hydro-
chloric acid it yields C6H4 (NH2) — CH=:CHC1, and this when
heated to 160° — 170° with sodium-ethylate (NaO . C2H5) yields
sodium chloride, ethyl-alcohol and indol.8

1 Neiicki, Ber. d. d. chem. Gesell. Bde. vn. (1874), S. 1593, vni. S. 336, 722.
Brieger, Zt. f. physio!. Chem. Bd. in. (1879). S. 134. Cf. Koukol-Yasnopolsky,
Pfluger's Arch. Bd. xii. (1876), S. 78. Baumann, Zt. f. phi/siol. Chem. Bd. i.
(1877), S. 63. Weyl, Ibid. S. 339. See specially E. Salkowski, Ibid. Bd. vm.
(1884), S. 417.

2 Kiihne, Ber. d. d. chem. Gesell. Bd vm. (1875), S. 206. Nencki, Jn. f. prakt
Chem. (N. F.), Bd. xvn. (1878), S. 97.

3 This reaction depends on the presence of coniferin in the pine-wood. Phenol
under similar conditions yields a blue colouration. But see Udrauszky, Zt. f.
physiol Chem. Bd. xu. (1888), S. 367.

* Cf. Nencki, Ber. d. d. chem. Gesell. Bd. vm. (1875), S. 722.

5 E. Salkowski, loc. cit.

6 Legal, Bresl. artzl. Zeitsch. Nrn. 3 u. 4, 1883.

7 Baumann u. Brieger, Zt. f. physiol. Chem. Bd. in (1879), S 254.

8 Lipp, Ber. d. d. chem. Gesell. Bd. xvn. (1884), S. 1067.

CHEMICAL I'.ASIS OF THK ANIMAL BODY. U»'J

-. Indoxylsulphuric acid. CSH6N . 0 . SO,OH. The indican

of urine

A substance was long ago described as frequently occurring in
tin- urine and <miietimes in the sweat of man and other animals
whirh yielded by the action of acids tin- blue colouring matter
as one of the products of its decomposition. It w;i- re-
at tliat time as identical with the indican kn«>\vn t» occur
in several plants (Indigofera tinctoria, l>atis tim-tuna ) Ilnjij.e-
Seyl.-r <m the other hand, having regard to the iiivat'-r ease with
which the indican of plants undergoes decomposition, regarded
tlii'iii as most probably different substances.1 This view was con-
tinued by the researches of Baumann. who first proved that urinary
indie an is not a glucoside, as is that of plants, but is in reality
an ethereal eninjinund of sulphuric acid with indoxyl (C8H6N . < 'II
analogous to those already described above as derived from phenol.
,A< - Indol. as previously stated, is a characteristic product
of the putrefaction of ]>r»teids. Further, when administered to
animals, it leads to a correspondingly increased output of urinary
indii -an,:{ an increase which is similarly observed as the result of
either a normally, pathologically, or experimentally in<-i
activity of putrefactive processes in the alimentary canal.4 Hence
indican is under normal conditions more plentiful in the urine of
herbivoia than of carnivora. It is al.-o increased in carnivorous
urine under a meat diet, is not increased by the administration of
gelatin and is l.-ast during starvation, although in the latin
it may not entirely disappear.6 These facts correspond again to
tin- experimental observations that gelatin does not yield indol
during its putrefactive decomposition,0 whereas inucin does,7 and
the latter substance constitutes a part at least of the content < "I
the alimentary canal during starvation. These statements show
cl.-arlv the origin and mode of formation of urinary indican. the
•rmed indol undergoing oxidation into indoxyl, which is
siil.si..|uently united t«i the elements of sulphuric acid and exm-tcd
as an ethereal compound

Indoxyl-sulphuric acid is nut known in the free state; it< m<.st
important salt is that with ]><,ta — mm, the form in which it occurs

1 For f>:irlior literature *••<• II /*iW -/x///i rlrm. An<il, Anfl. 4.
1875. s I'M. .-in. 1 /'/,,,,„, Ckem 1881,8 ^41.

- .-I ,-.-/,. M.I. MM. (1876). S :<u| 29 ' ;/-./s,V CI,,,,, M.|. i ||877),

MI. (1879), 8. 254 Cf. <• ll..|,]»-*>.-U.T . / MM

» Jnff. t'.nir.ilh f. d. mrd. Wiu. 1872, Sn. 2. 481, 497.
UCXM877). 8 72.

nrtwi-iU-r. M<ttl,.-il. <l. M -/. Kln.H. M.I 11. (1886).

<;i\i-« lit.T.-itnre to data.
Muii.T. //.»./ s. 341. /;• '"/•. WtdmtA, !u of

• •XJHTilll.'llti '"I ( ''-t'i )

« Nen.-ki. /.'• - '/ ./ Ml MI (1874), - ^>« »lw> Abrt. in

dbwA is:-. ^ ;i \v..\i. /.• i pkg$bt • •«- M.I i. n-r:i, s 339.

; WaU-lili, .In f'. rr,,k-t. L'htm iNM'.). M-l. \MI. (1878), S. 71.

200 INDIGO-BLUE.

in urine.1 When warmed in aqueous solution with hydrochloric
acid it decomposes into indoxyl and potassium sulphate : —

C8H6N . O . S02 . OK + H2O = C8H6N (OH) + KHS04.
Indoxyl by oxidation is converted into indigo-blue : —
2C8H6N (OH) + 02 = C16H10N202 + 2H20.

The blue colouration which results from the above reaction affords
the one test for the presence of indican in urine. The test is
applied as follows (Jaffe'). A small volume of urine (10 c.c.) is
mixed with an equal volume of strong hydrochloric acid and
2 — 3 c.c. of chloroform. A strong solution of chloride of lime
is then added drop by drop, shaking after the addition of each
drop. If indican is present the layer of chloroform which settles
on standing will be coloured more or less brilliantly blue accord-
ing to the amount of indican in the urine.2 The formation of
indigo-blue is also the basis for the quantitative estimation of
indican. The latter is converted into indigo-blue by oxidation
and the indigo-blue is estimated either by weighing or colori-
metrically or spectrophotometrically.3

3. Indigo-blue. C16H10N2O2.

It is formed, as stated above, from indican, and gives rise to the
bluish colour sometimes observed in sweat and urine.

It may, by slow formation from indican, be obtained in fine
crystals ; these are insoluble in water, slightly soluble, with a
faint violet colour, in alcohol and in ether. Chloroform dissolves
them to a slight extent, as also does benzol. Indigo is soluble in
strong sulphuric acid, forming at the same1 time two compounds
with the acid, indigo mono- and di-sulphonic acids. The sodium
salts of these acids are soluble in water and, when mixed with
sodium sulphate, constitute the crude ' indigocarmine ' of com-
merce, and in a purer form the sulphindigotate of soda used in
certain experiments on the nature of the excretory activity of the
kidney and other glands (see § 416). These soluble sulphonates
give an absorption band in the spectrum which lies to the red side
of and close to the D line. This may be used to detect indigo.

Indigo as ordinarily seen possesses a pure blue colour ; it leaves
a reddish copper-coloured mark when pressed with a hard body,
and the crystals exhibit the same colour if seen in reflected light.

Treated with reducing agents in strongly alkaline solution in-

1 For its isolation and preparation from urine see Baumann u. Brieger, Zl.
f. physiol. Chem. Bd. in. (1879), S. 254. See also Baumann u. Tiemanu, Ber.
'd. deutsch. Chem. Gesell. xn. (1879), Sn. 1098, 1192 ; and xm. (1880), S. 408.

2 Jafft', Pfluger's Arch. Bd. HI. (1870), S. 448. Cf. Senator, Centralb. f. d. med,
Wiss. 1877, S. 357.

3 For details and literature see Xeubauer u. Vogel, Die Harnanalyse, 1890,
S. 492.

CHEMICAL BASIS OF T1IK ANIMAL BODY. _ul

digo is decolourised, being reduced to indigo-white. The latter
contains two atoms of hydrogen nn>re than indigo, is ivcon\
into indigo-blue by exposure to the air, ami thus piovi
convenient reaction for the detection of either indigo or of re-
ducing substances such as dexin

r /NH\ i

1. Skatol. C.H.N. CJV ;CH. .Methyl-indol.
L ^ C^

CH,

Skatol was first noticed and detinitely described by Brit ••_•

ring in human fares together with indol. the latter u-ually
being less in amount than the former.1 Later researches have
shown that the conditions of it- production are in general the
-aim- as tln»e for the formation of indol, so that the two sub-
-lance- iiccur mixed in variable proportions among the products
of the putrefactive decomposition of proteids2 or brain-sub-tam-e '•*
ami of the action of caustic potash at high temperatures on pio-
teid-.4 In tin- former case it apjniars to be produced at a later
than i- imlol. -o that on tlie whole it is most preponderant
the longer the putrefactive change is allowed to proceed. Its
nee in the fares is thus due to causes similar to tho-e which
ace. milt for the presence of indol, and the resemblance is further
shown by the fact that a portion of the fir-t -formed skatol is
al. -orbed, oxidi-ed. and appears externally in the urine as ska:
sulphuric acid (see below).

•••I is tWined in -mall ipiant itics during the preparation «•! ind.,1
hv reduction f n. in indigo/' It may In- partly mm erted into indol by
j,a--i: !».iir- through a red-hot porcelain tube.* Tlie c'.n.-ti-

tntin: I ua- f.ire>lia«l"\ved I -v its prepa rat !• ni fnnn the barium

-alt- ,,i ..rtho-nitrociiniini,- a. -id. (< 'I I :),< '1 1 . < . CiM»ir and

clearlv proved bv it- -\nthetic pi-.idiictinii fn.ni pn>p\ lidcne-pheny lliv-
drax.i \II . N ' CII . Ml.. <'H3, the ],r.,durt ..f the ai-ti.ui ..f

aldehyde (CH, . CH.. «'< Ml ) on phenylhydra/in ((',11 .Ml.

» ttrr. tl. ,1. cl.rm. Crs,!!. TM. X. (IS7T). S. 10a;. .In f. /.»•„
IM xvii. .1-"- > l.'l A dOMlj >iinil;ir. if not i.li-iitirul. stil^tui.

n.itirfil. I. lit nut rli-:irh rli:ir:u trri"«'<l. l.v Nni.-ki. :i- ainniiir the

]ir<M|in-t« ••( flu- |.utr« t i MijHi-iii ..... .f ir«'l:itiu. ami !• .iiimni; tli-»i-

'nilar iliTniiii<>.iiiiiii <>( pr-'

'nilar iliTniii|i<

/. </. i/,../. if-- i-:-. s -»•• i: ii 11 s:iik,.«.-ki

IM.'xii. (is: • H'l MII (1884),

S. 417— 4t",r,. Ci.iitaiii-* V.TV full n-l". previous lid-nittire.

n.-ki. /'.../. IM. IV. (1880), 8. 371. St.,rklv. .In I j.r.dt. C/.tm. (1
15.1. \\iv (I--I). S. 17.

IM. xvii. (IH7SI. E
s IV, xui. (issfi). S. 2339.

' ', , 1. xiu. (18&3). j.. :i7x. S«« »b»tr. in Ber. rf. «/. chtm.
Gr*'<l I" -

t K. p. 356. Ab»Lloc.e,t

202 SKATOXYL-SULPHUKIC ACID.

When this substance is heated with zinc chloride it loses NH3
and yields skatol 1

:NTH
C6H/ CH.

Since the condition of the occurrence and formation of skatol
are on the whole the same as those for indol, and since these sub-
stances further resemble each other in being both volatile and
hence passing over in the vapours arising from their heated solu-
tions, the method previously described for the preparation of indol
from putrefactive products may be applied for the preparation of
skatol. The separation of the two depends chiefly on the fact
that skatol is much less soluble in water than is indol, so that if
the mixed substances are dissolved in a minimal amount of ab-
solute alcohol, then on the addition of 8 — 10 volumes of water,
indol remains in solution while skatol is precipitated.2 Skatol is
unaffected by being boiled with moderately strong caustic soda,
whereas indol is decomposed. This difference in behaviour to
caustic alkalis provides a further means by which the former
may be obtained free from the latter.

Skatol is a crystalline substance which melts when heated to
93°, and has a powerfully unpleasant odour, somewhat like that
of indol.

Reactions. Many of the reactions of skatol resemble so closely
those of indol that they provide no means for distinguishing be-
tween the two substances. Skatol is however characterised by
yielding only a milky opacity instead of a red colouration on the
addition of fuming nitric acid to its aqueous solutions (see sub in-
dol), in not giving the reaction with a strip of pine-wood dipped
in hydrochloric acid which indol does,3 by its lesser solubility in
water and greater resistance to the action of caustic soda.

5. Skatoxyl-sulphuric acid. C9H8N . 0 . S02OH.

The close relationship between indol and skatol is further
shown by the fact that the latter, like the former, after absorp-
tion from the alimentary canal is oxidised, the product being
skatoxyl C9H8N , OH, which unites, as does indoxyl, with the
elements of sulphuric acid and leaves the body in the urine as a
potassium salt of the above acid.4 This salt may be isolated from

1 E. Fischer, Ber. d. d. chem. Gesell. Bd. xix. (1886), S. 1563. Liebig's Ann.
Bd. ccxxxvi. (1886), S. 116.

2 Brieger, Ber. d. d. chem. Gesell. Bd. xn. (1879), S. 1985. Zt. f. pkysiol. Chem
Bd.iv. (1880), S. 414.

3 When, however, a strip of pine-wood is dipped into an alcoholic solution of
skatol and subsequently into strong hydrochloric acid, it is coloured first crimson,
which turns to bluish violet. Fischer, Liebig's Ann. Bd. ccxxxvi. (1886), S. 140.

* Brieger, Zt. f. physiol. Chem. Bd. iv. (1880). S. 414. Baumann u. Brieger,
Ibid. Bd. in. (1879), S. 255. G. Hoppe-Seyler, Ibid. Bd. vii. (1883), S. 423.

CHEMICAL BASIS OF THE ANIMAL BODY. 203

urine by methods similar to those used for the preparation of
indoxyl-enlphuric acid.

( )ur knowledge of tin- quantitative formation of skatol'in the
alimentary canal and of its relationship t«i tin- simultaneous pro-
duction of indol is far less complete than is that respecting the
latter substance. Notwithstanding the close chemical relation-
ship of the two it appears that their physiological behaviour is
markedly ditleivnt. In the tirst place it seems that the absorp-
tion of skatol is less complete than that of indol. since it pre-
ponderates in the normal fares:1 in accordance with this but
little of its ethereal sulphate is found normally in urine.- Fur-
ther, whereas by the ingestion of indol nearly the whole of the
sulphates of the urine may be converted into the ethereal com-
pound with indoxyl, when skatol (synthetically prepared) is
similarly employed a large part reappears in the t';eces ; and
although at tirst the ethereal sulphates are increased, they sub-
sequently diminish even with continued injection of skatol, and
are stated to finally disappear, [ndoxyl-snlphuric acid may be
regarded as a urinary chromogen, since it yields a pigment, indigo,
.idational decomposition; so also may skatoxyl-sulphuric
acid, but it is found that the amount of pigment-forming mate-
rial specifically present in the urine of a dog fed with skatol is
not so directly proportional t" the amount of skatoxyl-sulphuric
acid as it is to the similar compound of indoxyl when indol is
administered. It has been suggested that a large part of the
skatolic chromogen exists as a compound of skatoxyl and glycu-
runic acid." When Jaffa's test (see p. 200) for urinary indican is
applied to urine which contains skatoxyl compounds the results
obtained are as follows. The urine turns dark red or violet on
the addition of hydrochloric acid, bright crimson on the addition
of nitric acid, and a similar colour is obtained if it is warmed
with hydrochloric acid and ferric chloride. The colouring mat-
ter thus obtained is probably formed from the skatoxyl (not
known in the free state), and by reduction may be made to
yield skatol.

•"1 li;i- recently IM-I-H ile-erilieil :is •iirrinu' in a vegetal"!

sue, namely tin- wood <>f an Ka>t Indian tree. Celt is ret imlosa.*

— nt fr»m the faecen of the dog.
- Hi.' rhii-f n-i-iinl •>( its ..<•< nrn iu-e is in a ca»e of diabetes mellitus with

clisiiirUnri-. Otin. PlluiirrV A»-l, IM \XMII !--»).>

M. • '..//I. 15,1. xii dssH). - I 10 \ .-iinilar c.iin|Miun.J ..f

iml'i\\ 1 \\iili ^hiiir"iiic :niil ha* been tlcscrilx-.l. S<-liinio(lcberK. .1 /'nth.

n. rtinrw. lid . "xiv. (issi). g j,l,'i.- tin- lilt-ratlin- «>f this >ub*ttnce

>.ilk-.w^ki. Zr. /: i>h>t»i»l. Chftn. IM MM S 117. i\. (I --4'. Mi I
« Dniistrui. rimrm. .11. V,,l \i\ (1889), \> IDlo />,, ,1 ,1 . ,•>„,„ CeteU.
(Referate), IM \\n (isv.i,.s. ui Proc. Roy. Soc. Vol M.M (1889), p. all.

204 PTOMAINES.

THE PTOMAINES.

The now extensive literature of these substances may be most con-
veniently and inclusively indicated by reference to the following
publications. Selmi (to whom the name ptomaine is due), Sidle
ptomaine od alcaloidi cadaverici. Bologna, 1878. Gautier, Compt.
Rend. T. xciv. (1882), p. 1119. Guareschi e Mosso, Arch. ital. de
Biol. T. ii. (1883), p. 367; HI. (1883), p. 241. Abstr. in Jn. f.
prakt. Chem. (N.F.), Bd. xxvii. S. 425; xxvm. S. 504. Brieger,
Zt. f. physiol. Chem. Bd. vn. (1883), S. 274. Ber. d. d. chem. Qexell.
Bd. xvi. (1883), Sn. 1186, 1405. E. u. H. Salkowski, Ibid. S. 1191.
Brieger, Ibid. Bd. xvn. (1884), Sn. 515, 1137, 2741; xix. (1886), S.
3119. Ueber Ptomaine, i., u. Berlin, 1885; HI. 1886: gives litera-
ture to date. See resume with references by O. Schultz, Biol. Centralb.
Bd. vi. (1886-87), Sn. 685, 726, 739. Gautier, Bull. deVacad. de
med. Jan. 12, 19, 1886 (largely on the leukomaines). Udranszky u.
Baumann, Zt. f. physiol. Chem. Bd. xm. (1889), S. 562. Brieger,
Virchow's Arch. Bd. cxv. (1889), S. 483. The last contains a most
useful list of known ptomaines, with empirical and constitutional
formulae, name of discoverer with date of discovery, sources, action,
and characteristic reactions.

Although the substance to which the above name has been
given (from Tn-oi/Aa, a corpse) are now known to belong chiefly to
the class of compounds called amines,1 so that they provide no
chemical sequence to the bodies previously described, their charac-
teristic production during the putrefactive decomposition of animal
tissues seems to make this a suitable place for treating of them.

The ptomaines as a group may be said to closely resemble the
class of substances long known under the name of alkaloids and
obtained from plant tissues. The resemblance is shown not
merely in their chemical constitution, but more obviously in their
similar solubilities in various fluids, in their general behaviour
towards reagents, and in some cases even in their specific reactions,
and more especially in their frequently powerful (poisonous) action
on the animal organism, the actions of certain ptomaines being
almost identical with those of certain vegetable alkaloids. The
ptomaines may therefore be regarded as alkaloids of animal origin.
The close similarity of- the two classes of substances has hence
endowed the ptomaines with very considerable interest from a
medico-legal point of view, in virtue of the not infrequent use of
the vegetable-alkaloids for criminal purposes and the now obvious
possibility that the detection of alkaloids in the corpse may afford
no reliable information as to the administration of the same dur-

1 An amine is, strictly speaking, a compound ammonia in which one or more
atoms of hydrogen have been replaced by some oxygen-free radical. Several of the
ptomaines, however, contain oxygen in their molecule, as do also many of the vegetable
alkaloids. The constitution of those ptomaines which contain oxygen has not in
most cases as yet been as definitely determined as has that of those which contain
uone.

CHEMICAL BASIS OF TIIH ANIMAL BOD\

iii'4 lif'1.1 They are further of considerable and increasing patho-
tl interest, and that from tw.i point* of view. In tin- tir-t
place, as products of tin- u'-n.-ml putrefactive change- which
animal tissues undeigo, they may account tor tip- severe symptom*
and not infrequent death which iv-ult- t'r«»ni tin- consuinption a*
food of fish, sausages, ami tinned-meats. In the second there
appears to he increasing evidence of the formation of s)
ptomaines liy tin- organism- rhararii-ri>tir of sp.-cific disea-.
that the pathological conditions may be dm- rather to the products
formed hy the organisms than to tin- organism* tln-m-elves diivcth .
a possibility of no small importance in the liidit of recent prophy-

laetie le-eaivh.

While the general reactions of the ptomaines place them, as

already stated, side hy side with the vegetable alkaloid-, their
specific reactions and properties exhibit considerable diflei.
both in comparison with ea,ch other and with those of the alka-
loids- Some are liquid and highly volatile so that they pass off
readily during distillation of their aqueous solutions, othei
liquid and noil-volatile, others aijain solid and crystalline. They
exhibit equally marked diHeivnces in their solubilities. Thu-
neither ben/ol nor petroleum-ether will extract them from their
iqiieniis solution. Kther on the other hand dissolves out a
fe\v of the ptomaines from an acid solution and a lar^e majority
from an alkaline solution. Some are more particularly soluble in
chloroform, a few are insoluhle in any of il rents. Amyl-

alcohol is the one reagent in which as a class they appear to be
almost Ljenerally soluble ( Ihie^er). Their behaviour with the
u-i'ial alkalojdal precipitant- (mercuric and platinic chlorides,
tannie acid, the double iodides of potassium with nn-rcury and
other metal-. \-c.) i- equally varied. Tin y are all j-recipitated by
phospho-molybdk a-'id. ami most of tin-in yield crystalline com-
pounds with a >olution of iodine in hydriodic acid. 1'o-si-s-ed of
an alkaline reaction they further act as powerful reducing ayeiit-,
many of them <-onvertin.^ ferri- into fern.cv ani«le-. the reduction
bein-4 evidence. 1 by the formation of Prussian blue on the simulta-
neoii- addition of ferric chloride. This projN-rty is ho\',

t-y many vegetable alkaloids and not by every ptomaine .

i not therefore be regarded aa a specific • bh6M

-iib-i ...utii-r). Some of the ptomaines <

are extraordinarily poisonou-. producing eH-.-ts which ar<
qiiently sjM-cific, Imt in many cases similar to those of certain

table alkaloids. Others a^ain are quite in.

The separation of the ptomaines, a- of the vegetable alkali

involves the application of methods Sta--< Uto's, Hrieger's)8 which

1 For owe* in point nee HUIOHIMIIH. .1"A ./ /'/,,/ ,„ (Itciho.T) ».!••
Xix " 481.

^
* L'ntert. Ob. Ptomaine, n. 1885. B

206 PTOMAINES.

admit of no suitably brief description. The principle involved in
each consists in preparing a concentrated alcoholic, ethereal, or
chloroformic extract of the mother-substance, and from this
crystalline compounds of the alkaloids are prepared by the addi-
tion of suitable reagents.1 A further means for their final separa-
tion consists in the formation of benzoylated compounds which are
insoluble in water.2

Alkaloidal substances, some poisonous, others inert, may also be
obtained both from normal but more particularly from pathological
urines.3

The first distinct evidence that the poisonous properties of cer-
tain (septic) fluids might be due to a specific chemical substance
rather than necessarily to the action of organisms in those fluids
is apparently due to Panum, who seems to have dealt with a
septic alkaloid in a very pure form, although he did not definitely
characterise it as a chemical substance.4 This was followed by a
series of observations all tending in the same direction, but none
of the observers obtained the supposed specifically toxic substances
in forms which enabled them to be spoken of as chemical in-
dividuals until Nencki in 1876 5 isolated from the products of
the pancreatic putrefaction of gelatin a well-crystallised base
C8HUN, to which he assigned the constitutional formula

/CH3
C6H5 — CH and hence the name isophenyl-ethylainm.

XNH

Since then the ptomaines have been in most cases fairly definitely
and in some cases absolutely characterised as regards their chemi-
cal composition and constitution. They belong typically to the
class of substances known as amines and are in many cases dia-
mines. Two of the most clearly defined ptomaines are cadaverin
and putrescin. These are found in corpses which have undergone
putrefactive decomposition, cadaverin appearing in the earlier
stages of putrefaction, and putrescin preponderating in the later.
The latter is largely present in putrid herrings.6 The former is
identical with pentamethylen-diamine NH2 (CH2)5NH2.7 The
latter has been shown to have the constitution of tetramethylen-
diamine NH2 (CH2)4NH2. They have both recently been obtained
as conspicuous constituents of urine from a case of cystinuria, and

1 For description of these methods see Halliburton, Chem. Physio', and Pathol.
1891, p. 175. Otto, toe. at. S. 103.

- Udranszky u. Baumann, Zt. f. phi/siol. Chem. Bd. xm. (1889), S. 562.

3 For details and literature see Neubauer u. Vogel, Anal. d. Hams. 1890, S 241
et seq.

* Published originally in Danish in Bibliothek. f. Ldqer, April, 1856, S. 253
Fully abstracted in Schmidt's Jahrbiicher d. yes. Med. Bd. ci. (1859), S. 213, and
republished in Virchow's Arch. Bd. LX. (1874), S. 301, with literature up to date.

6 Ueb. d. Zersetz. d. Gelatine u. s. w. Bern, 1876. See later Jn. f. prakt. Chem.
Bd. xxvi. (1882), S. 47.

6 Bocklisch, Ber. d. d. chem. Gesell. Bd. xvm. (1885), Sn. 86, 1922; xx. (1887),
S. 1441.

7 Ladenburg, Ibid. Bd. xix. (1886), S. 2585.

CHEMICAL BASIS OF THE ANIMAL BODY. 207

uj'1't-ar t<> owe their origin to putrefactive processes occurriiiL1 in

the intestine.1 They are both somewhat viscid fluids uhirh

illise at low temperatures, and yield readily crystallisable

compounds with acids and salts of gold, platinum, and mercury.

Their henzoyl compounds are insoluble in water and hemv atlord

a convenient means for their separation. Cholin and the highly

toxic neurin, whn-h really belong to this class, have already been

: il>ed. (See above pp. 135, 136.)

This name has been applied by Gautier2 to those
basic (alkali tidal) sul>stances which occur in linn;/ tissues and are
to be regarded as products of their normal metabolism and thus
distinct from ptomaines. They are obtained by extracting finely
minced ox-flesh with an extremely dilute aqueous solution of
oxalic acid. According to Gautier this extract may contain the
following six liases: Xanthokreatiniii, r5Hi0N40; Chrysokreatinin,
CSH8N4O, Amphikivatinin, C8H19N7O4, Pseudoxanthin, C4H5N»O
and two, as yet unnamed, with the composition CnH24N,,,<>. and
ClaH,5NnO8 respectively. They probably stand in close relation-
ship to ]>araxanthin, C7H8X4O2, heteroxanthin, C«H6N4O2, and
adenin C;H-NT6 (see above, p. 181), and it is interesting to note
that comparing the formulie of the leukomaines with each other
and with those of kreatinin C4H7N80 and kreatin C4H9N8Oj they

•"ii ml to differ in several cases by the group CNH.
The leukiiniaines are regarded by Gautier as feebly toxic alka-
loidal products of metabolism from which the organism is
normally freed either by their excretion, since they are found in
urine (see above), or by destructive oxidation, and it has further
-uggested that their abnormal retention in the economy may
the i a use of certain obscure pathological conditions.3

THE BILE-ACIDS.

1. Cholalic (or cholic) acid. C^H^O,.

To avoid confn>i..n the t.-nu •••ln.lic' should be in all cases used as
synonym..^ \\ith • rliolalir. ' I >«-mar<-a\ . who first described choUlk
a.-'nl a- a pr-nlnet i-f tin- .!••.•.. iii|i..-.it i..n ..f bile-acids, gave it tin- naim-
of chnlic arid.4 Tin- iiaiin- 'i-lu'lalir' is |..-rlia|» tin- ln-tt.T. >ino- it
in. IK -at i- tin- in. -tli.. «1 1'V \\lii<-li tin- l.ilr-a«-i«l* IM d000mpOWd
it- j.p-parati vi/. l.y t r.-atnnMit with alkalis. The name

1 ri!niti-/kv ii Haamann, lot. tit. Sea also Stadthagen u Rrieger, Virchow'g
Artl, 190.

r In alca< --lion tmrtSrifniK

t\»»n» aniinmir. Paris, 1886. Bull, de I'ura d. dt ' The name

is .Ifriv.-.l fpun A*v«»ua. ix-ranionally used to denote whit* of egg, and hence to
iinlir:itf their i>rii;iii fnun iin>t.-.

H..u.-har.l. r,.,n,.t. I;. (1886), pp. 669, 727. I

4 Li. Kite's .Un ltd xxvii (1838), 8 270.

208 CHOLALIC ACID.

was first applied by Ginelin 1 and subsequently by Strecker 2 to the
acid which is now always known as glycoeholic. The acid now known
as taurocholic was originally called 'choleic' by Dernarcay, and the
same name has been quite recently used to denote an acid (C25H4204)
closely related to cholalic acid (see below).

This acid occurs in traces as a product of the decomposition of
the bile-acids in the small intestine, in larger quantities in the
contents of the large intestine, and in the faeces of man and many
animals. In icterus the urine is also stated to frequently contain
traces of this acid. Its principal interest lies in its being the
starting-point, by its union with glycin or taurin, for the acids
which, as sodium salts, exist characteristically in bile (see
below).

Owing to the readiness with which ox-bile can be obtained in
large quantities, this has been most frequently used for the prep-
aration of cholalic acid, whose properties as usually given hence
refer to the acid as obtained from this source. More recent re-
searches have however demonstrated comparatively unimportant
but still distinct differences in the composition and properties of
the acid as it occurs in the bile-acids of different animals. The
description of the acid which here follows refers to that form
which is obtained from ox-bile.

Preparation. This depends upon the decomposition of the
bile-acids (glycocholic and taurocholic) by means of alkalis at
boiling temperature. It is not however necessary to employ the
purified acids for this purpose since the raw bile suffices. The bile
is boiled for twenty-four hours with as much caustic baryta as it
will hold in solution, concentration during this operation being
avoided by means of a condenser attached to the mouth of the
flask. When the decomposition is complete the fluid is filtered
while still hot, and the filtrate concentrated until crystals, con-
sisting of the barium salt of the acid, are copiously formed. These
are then purified by recrystallisation from boiling water and de-
composed by the addition of hydrochloric acid. The free cholalic
acid is finally obtained in a pure form by solution in a small
volume of boiling alcohol from which it separates out in the
crystalline form on cooling.

As thus prepared the acid possesses the following properties.
The crystals obtained from hot alcoholic solutions are usually in
the form of large rhombic tetrahedra or octahedra, containing 2£
molecules of water of crystallisation which may be driven off by
heating to 100° C. The crystals are but slightly soluble (1 in
750) either in water, even when boiling, or in ether, but readily
soluble in alcohol. This acid may also be obtained in an amor-
phous form by concentrating its solutions to dryness, and is now

1 Die Verdauung nach Versuchen, 1826.

2 Liebig's Ann. Bd. LXV. (1848), S. 1.

CHKMK'AL BASIS OF THE ANIMAL BODY. 209

iisoluble than when crystallised. If the amorphous acid is
di><ol\vd in ether it may IK- sc[ Mrat e. 1 out by evaporation in four
• >r M\-sided prisms which are anhydrous. When the sodium salt
of cholalic acid is decomposed under ether by the addition of
hydrochloric acid, the acid may be obtained in rhombic plat---
containing one molecule of water. The alkali and barium salt- oi'
eh'ilalie aeid are soluble in water and in alcohol, especially when
warm, and yield, like the free acid, dextro-rotatory solution-.
rW solutions of the anhydrous acid («)D = -}- 50°. When
tallised with 2£ H2O, (a)D = -f-35°. In alcoholic solutions of the
sodium salt (a)D = -}- 310g4 (Hoppe-Seyler).

The constitution of cholalic acid is scarcely as yet definitely

rCOOB

known, but may be represented by CWH31 J (CHjOH),.1 It yields

I GHOH

with iodine a compound which, like that resulting from the inter-
action of iodine and starch, possesses a brilliantly blue colour and
is specifically distinctive, since it cannot be obtained either from
the bile-acids or choleic acid (see below) or the products of the
decomposition of cholalic acid.2

When cholalic acid is prepared from human bile it exhibits

ii differences, more especially as regards the lesser solubili-

t its alkali and barium salts, which led to its being regarded

as di-tinct from that obtained from ox-bile, and hence it was called

anthropoeholalic acid. It appears however that the bulk of the

acid is identical with that from ox-bile, the slight difference being

due to an admixture with another acid either choleic, as was first

supposed, or fell:

add, C86H42O4. Is ol.tained in small ani<>unt> mixed with
rholalir arid during tin- preparation .if tin- latter from "\-l>ilr. It

from cholalic acid in the solubility of iti >alt>and the products

of its oxidational decomposition.4

1 ;: '';. Obtained in small aniouuN from human
I'ile during the preparation i.f i.rdinary rlmhilii- arid. It i- rhararter-
i-ed \>\ the extn-nie i iis< •! ii hi 1 i t y ••!' its barium and maijne-iuiii -alt-.
It :il-- \ ielcl^ ;i less brilliant lVttcnk"tVr r.'a.-ti..n (-•>• l..-l,,\\ ) than

••holalir arid.

The l.il.-arid> of the pig and goose when di ..... mp"-rd \iehl f.-n
rholalie arid called re>j.ert ivrl y hy<>-cholalic acid ('_ II, « ',. and cheno-
cholalir

/ ,/ ,/,-,„ Stag. IM. xx. (IR87). S. 1968.

* M% S. 683 an.l Zt f. pkytiol. Ckem. Bd. xi. (1887), S. 306. See al«O
H.I \;

* S«-h..tt.-n. /.i. i. phifiitJ. Chem. Bd. x. (1886), S. - 268.

ff. ll. r. d. d. ckem. Guett. Bd. xviu. (1885), S. 3039.
6 Schotteu, /or

14

210 DYSLYSIK GLYCOCHOLIC ACID.

2. Dyslysin. C^H^O,.

When cholalic acid is heated to 200° C. or boiled for some time
in solution with hydrochloric or sulphuric acid it loses two mole-
cules of water and yields a resinous anhydride called dyslysin,
from its insolubility in water, alcohol, and alkalis. As resulting
from the dehydration of cholalic acid it is found sometimes in
small amount in the faeces. It is a non-crystalline substance
which is soluble in an excess of ether, also in solutions of cholalic
acid or of its salts. By treatment with boiling alkalis it may be
reconverted by hydration into cholalic acid.

The various forms of cholalic acid which may be prepared from
the bile of different animals each yield a corresponding form of
dyslysin.

3. Glycocholic acid. C^H^NO,,.

This substance was first described by Gmelin (1826), by whom
it was then named ' cholic acid.' It is found not in the free state
but as a sodium salt, chiefly in ox-bile but also in that of man,
mixed in both cases with a much smaller and variable amount of
taurocholic acid, also present as a sodium salt. In carnivora it
occurs, if at all, in such minute traces only, that it may be said
to be absent from the bile of these animals ; hence their bile-acid
consists entirely of taurocholic acid.1 In icterus the urine may
contain small quantities of glycocholic acid.

Preparation. This may be affected in several ways, using ox-
bile as the source ; of these the following is as convenient as any
(Drechsel).2 The bile is mixed with washed sand and evaporated
on a water-bath until it presents a pulverisable mass. This is
then extracted in a flask with strong boiling alcohol and yields a
green solution, which is filtered, decolourised with animal char-
coal, and concentrated to a sirup. The latter is then dissolved
in a minimal quantity of absolute alcohol and precipitated by an
excess of ether. The precipitate which consists of glycocholate
of soda together with the corresponding salt of any taurocholic
acid which is present in the bile, is collected, dissolved in a little
water, and acidulated with sulphuric acid in presence of some
ether as long as any precipitate is formed. By this means the
acids are separated from their sodium salts, and on standing a
crystalline mass of glycocholic acid is obtained, practically free
from taurocholic acid, which, since it is, unlike the glycocholic,
extremely soluble in cold water, remains in solution in the mother
liquor. The crystals may be purified by recrystallisation from

1 For earlier references to the bile-acids of various animals see Bayer, Zt. f.
physiol. Chem. Bd. in. (1879), S. 293.

2 Anleit. z. Darstell. physiol. -chem. Praparate, 1889, S. 33.

CHEMICAL BASIS OF Till; ANIMAL BODY. 211

}u.'t water in which they are soluble, separating out again as their
solution cools.1

The acid crystallises in fine glistening needles. which require
about 300 parts of c..ld hut only li!0 ..f hot water for their solu-
tion. They are also very soluble in alcohol, hut practically in-
snluhlc in ether. The salts ut' tliis acid, more especially those
with tin- alkalis, an- extremely soluble e-ven in c..ld water. also
in alcohol, but very slightly BO if at all in ether. I'.oth tip
acid and its salts are dextro-rotatory: for the former, in alcoholic
solutions, (a)D = +29-0°, for the latter (a)D=+L).V7 < ll»ppe-
Sevl.-r). (llycocholic acid is a compound of cholalic a.-id and
gly< -in ( glycocoll) or amido-acetic a. id. When boiled with hy-
orolysing agenta such as dilute acids or alkalis it takes up one
molecule of water and is resolved into its components: —

Cholalic acid.

, 4- H80 = <JH2 (NH,) COOH + C^H^O,.

It is thus analogous in constitution to hippuric acid, in which
glycin is similarly united to henzoic acid.

If di-s,,l\,..l in concentrated sulphuric acid and then \vanm-d.
cholic acid l>v tin- n-niiival «\ one m»lrcule "t" \vati-r yii-ld> iilyi-'u-li
acid. C.j.-.HuNn.. Tin- l-ariiiin >alt nf this la->t acid is iii>«>ltil>li- in
. which fact is nf importance. >ince cholmiic acid j -.early

tin- .-aim- -1'i-rilic rotatory power a^ <;1\ coeliolic acid.

I Taurocholic acid. « II \

This acid is foun<l to some extent in ox-hile, and is more ]>len-
tifully present in that of man. The bile of the dog Contains
tanroeholic acid alom-, unmixed with

»n rntinii. The. method de-crihcd ahove suflices to obtain
olvcocholic acid free from tanroeholic. On the other hand it is
not l.v any means easy to ol.tain the hitter free from the former,

iirocholic acid is extremely soluhlr in water (its crystals are
deliqiieNi-ent) and this solution can readily dissolve the much l«-s
readilv solnlde olycocholjc acid. Hence the mother liquor from

lycocholic acid crv-taN contains not merely the tauroch<ilic
acid but some of the former acid also. This difficulty is avoided
by employing as a source for its preparation dog*bil6 in which
there is no glycocholic acid. Tin- bile is treated a.s ah
scribed down to the stage at which the taurocholate ,,f soda is
precipitated from its alcoholic .solution by an excess of ether.
The precipitate is now dissolved in water and the acid precip,
as a lead salt by tin- addition of ammonia and /»'.-•/• "tate.

f i.tlic-r nictliixU -Mini- -JM <-ial work nhouM i.-li M

Hopp*' - in ll« rm:im>'- •/ I'/iytioi.

Hd. v .1 i : MUius. /*. f.fkftU. Chrm. Hit. xi. (1887). S. 331

212 TAUKOCHOLIC ACID.

This is next washed, suspended in alcohol, and decomposed by
sulphuretted hydrogen. After removal of the sulphide of lead
by filtration the alcoholic filtrate is concentrated and the tauro-
cholic acid precipitated by an excess of ether. This yields a sirupy
mass which may become partly crystalline on standing : the
crystals at once deliquesce on exposure to the air.1 As dog-bile
is not readily obtainable in large quantity at any one time, it may
be desirable sometimes to obtain taurocholic acid from the mother
liquor left in the preparation of glycocholic acid. The separation
is effected by the addition of a little ammonia and normal lead
acetate. This precipitates both glycocholic and cholalic acid, but
not taurocholic. After the removal of this precipitate the tauro-
cholic acid is prepared as already described by the addition of
basic lead acetate to the filtrate.

This acid, as already stated, is extremely soluble in water and
in alcohol, but not in ether ; so also are its salts with the excep-
tion of the one formed on the addition of basic lead acetate in
presence of ammonia, which is insoluble in water and in alcohol.
The acid and its salts are dextro-rotatory ; for the sodium salt
in alcoholic solution (a)D = -f 24'5°. If dissolved in water the
rotatory power is less, and in this respect it resembles glycocholic
acid.

When hydrolised it readily takes up a molecule of water and is
decomposed into taurin and cholalic acid : —

Taurin Cholalic acid.

C26H45NS07 + H20 = NH2 . CH2 . CH2 . S02OH + C24H4005.

This decomposition may, as in the case of glycocholic acid, be
brought about by the action of dilute acids or alkalis, but even
mere boiling of an aqueous solution of the acid also suffices,
a fact which demonstrates how unstable a substance it is,
both absolutely and as compared with glycocholic acid. Tau-
rocholic acid has not as yet been observed in the urine in
icterus, but since cholalic acid does occur together with glyco-
cholic acid, it is probable that the non-appearance of taurocholic
acid is due to its decomposition before excretion as a result of its
instability.

Taurocholic acid possesses a remarkable power of effecting the
complete precipitation of ordinary proteids from their solutions,
whereas peptones if present at the same time remain unprecipi-
tated. This is possibly of some not inconsiderable importance in
connection with the changes which proteids undergo in the small
intestine, since it leads to the retention of the peptones in a state
of solution and hence facilitates their absorption, while the less
completely altered proteids are precipitated and thus further ex-

1 Parke, Hoppe-Seyler's Med.-chem. Unters. Hft. 1. (1866), S. 160.

CHEMICAL I'.ASIS OF Tin: AMMAL i;ui>v. in:;

posed to tin- action of the digestive enzymes.1 It is al>o poeai
nl powerful antiseptic properties.2

The ariils (.litaiiird ip.in tin- l.ile <.f dit'tWi-nt auiinaU differ slightly
in pn.pert ii-s ami c(.in|...>it imi. dependent ly. a> already -tati-d. up-m the

dii't'ereiir.-> I iet \\een t In- >e\ i Tal forms of cholalic acid with which either

the u'lyrin i.rtaurin U iv.-pei-' ively united.

'/x.a

The following is the mure usual method of obtaining the i
tion. Bile, which may l.e very considerably diluted, or a dilute solu-
tion of bile-salts or acids is mixed in ;i porcelain dish with a i'.-w
drops of a 10 p. 0. solution of cane-sugar. Concentrated sulphuric
acid is now added to the mixture with constant stirring to an ex-
tent not e \cefdini: rt of its volume, the addition of the acid l.ein^
_ulated that the temj.erature of the mixture is not allowed
t<. ri-M- a!)Ove70°C. Hereupon a brilliant cherry-red colour makes
its appearance and rapidly assumes a magnificent purple tint. < 'n
standing for >oine time the colour becomes darker J'.nd of a more
distinctly blue tint. The reaction may al-o be obtained by tin-
addition of first the acid and then the Mi-ar solution. The suc-
cess of the test depends on the careful avoidance of any excessive
• \ temperature during the addition of the sulphuric acid and
more especially of an\ »f siinar which by beinj,' charred by

the acid MJves a brown colouration and masks the typical pinjlc.4
The purple solution if diluted with alcohol (not \\ith water, which
lie colour) shows with a spectroscope a characteristic ab-
sorption spectrum consisting , ,f t\\,, ab-<n -].t imi bands, (me bel
hand K abutting on M. and a second adjoining the Kline. In the
earli' i -t' the reaction a third naimu band near I) mal.

appearance but disappears later on.6

I'ettenl, M-ti.in depends upon the pn-eme in all bile-

of their cholalic acid constituent. < »n the first addition of
sulphuric acid, if the solution be at all concentrated, a whit
cipitate may often he ob-erved coii-i>tin^ of cholalic acid ; this js
ill— ..Ived «.n the further addition of acid, after which the d
tlC colour makes its appearance. h has ;,].,, iv,eiit]\
shown that the reaction depends upon the formation of fur-

|',,| n (|sv»). S. M» •
Hammanrtcn. I'tl m. (1870

...li. :i.iil t.. ^olatiu and its |M-|ituin-» *«••• Kinirli.

Vfalru Emich, i di See ml»o Undberger (Swedlnh) See AbKr. in M

./<iln. t:»4.

:.-r. .\»»nl. ,f. r/ir,,,. „. /'/,.„•„,. 15.1 MI 1-1 i s
4 '\'« avniil tin- iim-n.U tin- i-ni|il<i\ir.

Ula. i:il :ii-ii| to I i.f Wfl i I ••( »ul|.h:

,1 I,, thil • Ml ': • -..;nii..ii iim«t IM- IM-:III-.| l.y
ininiiT<iiiii in iMiilini:

(•/„,„. f$,i i u Mann • i:»

214 PETTENKOFER'S REACTION.

f urol 1 by the action of the sulphuric acid upon the sugar,
the colour arising from the interaction of furfurol with cholalic
acid.2

It is important to remember that an extended series of sub-
stances other than cholalic acid and the bile-acids (pigments and
other substances which are charred by sulphuric acid) either
interfere with the brilliancy of the reaction or else themselves
yield a purple colour which closely resembles that due to the
bile-acids. Among the latter those of chief importance are pro-
teids, amyl-alcohol, oleic acid, the higher fatty acids, and cho-
lesterin.3 A further element of uncertainty is introduced by the
fact that if the suspected solution be extremely dilute no charac-
teristic colour is obtained although bile-acids may be present.
All the above militate against the detection of bile-acids in fluids
such as urine, in which their determination is a matter of not in-
frequent importance. The application of Pettenkofer's reaction
in its original form has hence been modified in details by many
observers with a view to rendering it more decisive and delicate.
The decisiveness of the reaction is ensured by careful spectro-
scopic examination of the absorption spectrum of the coloured
solution, since the colours produced by the majority of those
substances which yield a reaction resembling that produced by
cholalic acid, show no absorption bands in their spectra. Some
few however do exhibit absorption bands which fortunately oc-
cupy a different position in the spectrum from those shown by
cholalic acid (Udranszky). If the suspected solution is ex-
tremely dilute it may frequently be made to yield Pettenkofer's
reaction directly by a previous concentration on the water-bath.
A further modification which is applicable to dilute solutions is
the following. A little cane-sugar is dissolved in the solution
and a strip of filter-paper dipped into it and then air- dried.
When dry one drop of concentrated sulphuric acid is applied to
the paper with a glass rod. If bile-salts are present (even to the
extent of -03 p. c.) a distinct violet stain may be observed on the
paper after standing for a quarter of a minute : the stain is most
easily seen by transmitted light.4 Instead of sugar an aqueous
(O'l p. c.) solution of furfurol may be used to great advantage as
follows. One drop of this solution is added to 1 c. c. of the sus-
pected solution, either aqueous or alcoholic, in a test tube. To
the above is then added 1 c. c. of concentrated sulphuric acid and
the mixture is cooled under water so that its temperature does
not exceed 50° — 60° C. To detect bile-acids in urine with ab-
solute certainty it is essential to separate them from this excre-

1 Also known as furfuraldehyde C4H3O . COH, the aldehvde of pyromucic acid
C4H3O . COOH.

2 Mylius, Zt.f. physiol. Chem. Bd. xr. (1887), S. 492.

3 For a complete list of these see Udranszkv, loc. rit. S. 358.

4 Strassburg, Pfliiger's Arch. Bd. iv. (1871)', S. 461.

CHEMICAL BASIS OF THK ANIMAL ISnpy.

tion before applying IVttenkofer's test. This is effected either by
precipitation with basic It-ad acetate or extraction with alcohol or
chloroform.1

THE COLoriMNC MATTKKS AND I'KIMENTS
()K THK ANIMAL BODY

ILEMOGLOBIN AXI> ITS DKl:l\ATI\

1. Haemoglobin.2 This is the well-known constituent of the
red corpuscles to which tin- dark colour ot' tin- lilooil from an
a>phyxiated animal is due. It is also present to a less and
.somewhat variable amount in ordinary venous Mood, in proem -.•
«»f correspondingly variable amounts of the coniDounoT which it
forms ;en, namely oxy-ha-moglobin. In iiornTal arterial

blood it is probably present in mere traces, if at all, since here its
athnities for oxygen arc completely satisfied to form oxy-ha-iuo-
globin. Hai'inoglobin is chiefly ot interest as an oxygen-carrier or
respiratory pigment, in virtue of the ease with whieh it ah-orbs
and unites in loose combination with oxygen when meivh
posed to this gas. and again gives it up when brought into rela-
tionship with the oxygen-free tissues of the body. The conditions
and phenomena of this fixation and liberation of oxygen by luemo-
glol.in have been very fully investigated ; the fundamentally im-
portant facts in connection with it have already been stated in
some detail in an earlier part of tlii- work ;j ."43 et seq.), so that
it is now only necessary to add ><«me farther detail* of ha-moglobin
more purely chemical characi

Owing to the ea-e and avidity with which lui-moglobin unites
with oxygen to form the distinct and stable comiiound known as
oxy_-ha-nio^li>biii. it< investigation i- atTended with considi-rable
experimental ditlii'iilties . hence our knowledge of it as a chemi-

ibatanoe is on the whole le-< complete than is that ol'
h.eino^lobin. Ha'inoglobin iriay be obtained in a crystalline
but with some considerable difficulty owing to its extreme
solubility in water. The crystaK may be prepared by sealing up

a concentrated aqueous solution of oxy-htemoglobin in gla-^ tubes

from which, it iv. all remaining air is displaced by hydro-

gen : on prolonged standing all tip disappear- during the

putrefactive reduction which en-u.-. and finally, more readily on

exposure to a low temperature, crystals of ha-mogiohjn make their

r il.-t.-iiN —I! - i i>hif».-initli. ' I !«<H3, 8. 399,

ami NiMiliatn-r 11. \'M^>-|, .!».///,>• ./. // ui. .

-' Tin- Mii^le name hmncwlobin i" n«'«l li- : «liat i- i

ami usually ralli-il • r«'.iir •.•,! ' liii-inncloliiu, us distinrt fnun •
a<loption nf tin- name as li.-n- o«ed iff both simpler ami tii«>n- I

•First .lcs.Til»-.| l.y Kulm,-. Vio'li..*'.* An-h. M. X\\M. (!•'.). S. 4*3.

216 HAEMOGLOBIN.

appearance in the fluid.1 A similar production and formation of
crystals is frequently observed when crystals of oxy-haemoglobin
are sealed up with Canada balsam under a cover-slip and kept for
some time.2 The form of the crystals obtained from the blood of
different animals has not yet been fully investigated. They ex-
hibit to a marked degree the phenomena of pleochroism, being ap-
parently trichromatic.3

Pleochroism is that property possessed by many crystals of appear-
ing to differ more or less in colour, in accordance with the direction
from which they are viewed by transmitted light. The phenomena
are usually investigated by means of a single Nicol prism. For
further details consult some special work on mineralogy or the article on
this subject in the " Encyclopaedia Britannica," Vol. xvi. p. 375.

As ordinarily seen the crystals of haemoglobin have a dark red
appearance, unlike the bright scarlet of oxy-haemoglobin, with a
strong purple or bluish tint They are extremely soluble in water,
much moie_aQ than the crystals of oxy-haemoglobin. The optical
properties of solutions of haemoglobin have already been suffi-
ciently described (§ 346, and see below Fig. 36, No. 5). One of
the most remarkable properties of haemoglobin is its power of
uniting directly with any one of several gases, such as oxygen,
carbon monoxide, nitric oxide and, as recent research has shown,
possibly carbon dioxide ; the compounds which are thus formed
have in the case of the first three gases a definite and constant
composition, crystallising more or less readily in characteristic
forms and snowing in aqueous solutions absorption spectra which
are constant and characteristic for each. (See below.)

The chemical composition of haemoglobin does nqt as vet admit
of being represented by any definite formula, and indeed its per-
centage composition has not been determined by direct analysis.
It must be inferred from a knowledge of the probable composi-
tion of the more stable and easily crystallisable oxy-haemoglobin
and of the quantitative relationships whicR hold good between
haemoglobin and oxygen during its conversion into oxy-haemo-
globin. As will be seen later on, analysis of purified crystals of
oxy-haemoglobin shows that these probably differ in composition
as prepared from the blood of different animals, and the same
statement therefore probably holds good for haemoglobin. When
decomposed in the absence of oxygen (air), as for instance by~The
action_of organic acids,'niore dilute mineral acids, orjasat of all by
caustic alkalis, it ;yields ajjroteid, of which but little is known
(see p. 32), and a coloured substance called by Hoppe-Seyler
haemochromogen. The latter on exposure to air absorbs oxygen

1 Hiifner, Zt. f. physiol. Chem. Bd. iv. (1880), S. 382. Cf. Nencki u. Sieber,
Ber. d. d. cfiem. Gesell. Bd. xix. (1886), Sn. 129,410.

2 A. Ewald, Zt.f. Biol. Bd. xxn. (1886), S. 459.

3 A. Ewald, loc. cit.

CIIK.MICAL BASIS OF THK ANIMAL IH»I»V. LM7

and becomes ordinary ha-matin : it is in fact the substance usually
spoken of as reduced ha-matin. (See I..-1..-..

L'. Oxy-haemoglobin. When luemo^lobiu is exposed ti> tin-
air it rapidly unites. molecule^ tor molecule, \vitli oxygen, thus
becoming oxy-lui-iiKixl' >bin, the characteristic constituent of the
red-corpuscles to which the scarlet colour of arterial b|u<>d is du«-.'
readily set free from the corpuscles b\ i h- addition to
defibrinated Mood of such rluids as alcohol, ether, chloroform.
wa_ter, and solutions of bile-salts. or^jbj_jx'jji^edl^fivexiii" "and
thawing the blood : when, thus set free it passes7 into soIutiou"iM
the jidjaeent serum. Froiu this solution it may !»• obtained a-
Aith more or less readiness. dependency upon the kind
of animal whose lilood is n-.-d f..r its preparation see vj ."-U,1, the
ditl'crciicc l.riim due. j-arily at least, to tlu- varying soluliility of
tin- several haemoglobins.

.iitain rapidly a microscopic preparation of o\y-ha-nio^lol.in
Is it >utli< -es t<» take a drop of the blood of some animal
WOOee ha-nioulol.in ery>talli-e- r.-adily (rat, guinea-]ii^, or d-
mix a drop of it on a slide with a minute drop of water, and allow
the mixture to evaporate until a rin^ of dried substance is formed
at the periphery. It' it lie now cnveivd with a rover-slip, ery-taN
usually form in a short time, especially if it he kept cooled. I :
the preparation of axy-hflemoglobin crystals IIM ;i ]aii,re scale many

methods, the >ame in general principles hut diilerin^ >om(-what
in detail, have lieen proposed, the ditlieulty of the ju-eparatiou
varyin.u' cousideialily acconlinu to the kind of him id u>ed.-
laJ»«ratory ]>urpo<es lar^e ((iiantities of crystallised o\y-ha-nn>-
^'lohin may he \. i\ readily ohtained from do^'s hloi.d ;>> follows
Kiihue). 'JJn^ blood is detihrinated and strained tlirouyh tine
muslin : it is then placed Fn a llask and etlier is julded with
frequent shaking until the 1-lood i- ju>t • lak\ .n-] ai.-nt.

The tlask is imw -iiiiMiuided 1. in^ mixture of ice ;ind -alt

and in a short time it- content- u-ually liec.,me almo-t ;
from the m;i- rVStalfl which form in it. Ti. then

centrifu^'ali-ed oil', dk-"l\ed in a minim"! amount of 0

...1,-d !•• It . and after the additio: •! its

hulk d alcohol a^ain imnier-.-d in ;i flee/in^' mixture.

The -•-•Miid crop . |fl thu> ohtained may he a^ain \<

talli-ed U aln-.nly d- I '-hed

with water at »>' r-ontainin-j -•'• p '' "t alcnhol. and may he diie.l
-ulphurie acid at O'.and an- now fairly stable.

.•>\>\\\ is uniti-.l • ^ in tin- lil.»»l .•( all I, wiili i«.»

In in\«Tti-l>r:iii- i,l,. ; illy fmui'l in f».>luti.m in the pliwma,

I. ut tli.-r<- :in- :i few (riirht • i«N :i"'l litermture Me

I!;illilnirt..n. ''I,. ! <in<l I'.it

r fnll-r -i

l>ln/.<,ol. '

- 18 I! !. /'AyWo/. / 'ctttchr. f. C I

,«1. T. 109 (1890), }.

218

OXY-H.EMOGLOBIN.

The crystals obtained from the hgemofflobin of various animals
differ in their crystalline torn! The following figure shows some
of the most typical forms.1

FIG. 35. CRYSTALS OF OXY-H«MOGLOBIN. (After Funke.)
a. Squirrel, b. Guinea-pig, c. Cat, or Dog, d. Man, e. Hamster.

Apart from these differences in crystalline form the oxy-hsemo-
globin of different animals varies in its solubility, in the amount
of water of crystallisation with which its crystals are united, and
also apparently in its percentage composition. The crystals are
pleochroic but to a less extent than are those of haemoglobin.2
As against these differences it is important to notice that the
close relationship of the various forms of oxy-hsemoglobin, from
whatever blood they may be obtained, is shown by the fact that
the spectroscopic properties are in all cases identical, as also are
the products of decomposition and the compoundL forme_d_yyith
' ases! Numerous analyses^of oxy-haemoglobin have been made,3
ut these while they tell us at most that it consists of oxygen,
hydrogen, nitrogen, and carbon together with iron as a character-
istic constituent and some* sulphur, and seem "to indicate that it
differs in composition as obtained from different animals, do^ not
as yet enable us to assign with any certainty a definite formula
to its composition, "it is nowever certain that its molecular
weight is enormously great (13,000 — 14,000).4

1 For a discussion of the various crystalline forms of oxy-haemoglobin see
Halliburton, Chem. Physiol. and Pathol. 1891, p. 270.

2 A. Ewald, loc. cit. (sub haemoglobin).

3 See Hammarsten's Lehrb. d. physiol. Chem. 1891, S. 57; or Halliburton's
Text-book of Chem. Physiol. Pathol. 1891, p. 286.

* Marshall, Zt. f. physiol. Chem. Bd. vn. (1882), S. 81. Kiilz, Ibid. S. 384.
Cf. Zinoffsky, Ibid. Bd. x. (1886), S. 16, and see Hiifner, loc. cit.

< 'INIMICAL BASIS «)F TIIK AM MA I. I5«.!»V

FlO. 36. (Afl.-r I'n-yi-r ami < iaint:.-. < I"' ^i''1 1 1: \ <n »\\ n i v- •.. i "ins is

1. 11 am 01 ooKOximuTHnr, <N (BBDOCSD) I! » M....I ..mv. \M. <>t

<'\KII.)N .M.>\.i\||» II I MM.. I ..IIIN

1 to i liniiiR (I ) low than '01 p.r., (2) -09 p.c.,

(:«) •'
5. -lining about -2 •

'. ' inojil.diin

In oarh »f tlio .»ix raw-t t tro«cop« mw 1 i •

thickness. Th- ! , Ac.) uidicate Fraoenl -. ami t no figures ware-

lengths expressed in UW.OtHitli uf a millimeter.

220 OXY-H.EMOGLOBIN.

The spectroscopic appearances of solutions of oxy-haemoglobin
have been already sufficiently described and figured (§ 345). (For
convenience of reference Fig. 75 is reproduced here.) When its
solutions are heated or it is treated either in solution or as a solid
with_ acids or alkalis, it may be readily decomposed, yielding a
proteid as in the case of haemoglobin and a coloured residue, viz.
naematin. (See below.) The oxygen which is loosely combined
with haemoglobin in the formation of oxy-haemoglobin may be
readily removed by several means of which the following are
those most usually employed.

(i) The solution is warmed to 40° and the gas driven off by
exposure to the vacuum of a mercurial pump, (ii) A current of
some neutral gas such as hydrogen or nitrogen is passed through
the solution, (iii) The solution is treated with a few drops of
some reducing agent such as Stokes' fluid.1 This is prepared by
adding tartaric or citric acid to a solution of ferrous sulphate, and
then ammonia until it is strongly alkaline. This reagent does not
keep and must be freshly prepared each time it is required. In-
stead of Stokes' fluid, ammonium sulphide may be used, but in
this case some slight manipulation is frequently required to ensure
reduction. A few drops of the sulphide are added to the solution,
which is then gently warmed : if on examination with the spectro-
scope it is found that the reduction has not taken place, as shown
by the persistence of the two bands of oxy-haemoglobin, a little
more of the sulphide may be added and the mixture again care-
fully warmed.

The amount of oxygen, removable by the means just described,
with which one gram of haemoglobin (from dog's blood) can unite
is usually stated as being T59 c.c. at 0° and 760 mm. Hg. this
constant being taken as independent of the concentration of the
solutions employed.2 Quite recently some doubt has been cast on
the quantity being thus constant ; and it has been stated that
several modifications of haemoglobin exist which, while they can-
not be discriminated by their purely chemical characteristics,
exhibit a marked difference as to the amount of oxygen with
which the same quantity of each can unite under similar external
conditions ; the results thus obtained are stated to hold good for
the compound of oxygen with haemoglobin as it exists in the red
blood-corpuscles of the dog,3 and further for the haemoglobin of
guinea-pigs and geese.4 Further investigation must decide the
interesting questions raised by the above statements.

There appears to be a consensus of opinion that haemoglobin,
and more particularly oxy-haemoglobint possesses to a slight

1 Proc. Roy. Soc. June, 1864. Phil. May. November, 1864.

2 Hiifner, Zt. f. physiol. Chem. Bd. i.' (1878), Sn. 317, 386. See also Jn. f.
prakt. Chem. Bd. xxn. (1880), S. 362.

3 Bohr u. Tornp, Skandinav. Arch. f. PJnjsiol. Bd. HI. Hft. 1, 2 (1891), S. 69.
Bohr, Ibid. Sn. 76, 101.

4 Jolin, Arch.f. Physiol. Jahrg. 1889, S. 265.

CHEMICAL BASIS OF TIIK ANIMAL I'.oDV. 1'LM

degree the properties of an acid. This view appears to he
on the following fads. ( Jxy-ha-moglnhin i- extraordinarily >oluhli>
in alkalis and in this solution appear- to he more stable than
ordinarily. It i< further slated that it has a feeble j.o\\
facilitating tin- evolution of carbon-dioxide from dilute solutions

liuni carbonate.1 It is hence often supposed that in the r.-.l
blood-corpuscles the haemoglobin is united to the alkalis of which
their stronia partially consists. If the above views are . •
they may a«i>t in explaining to sonic slight extent the diMicultio
in undeistanding the causes of the exit of carlioii-dioxide from
venous blood during its passage through the lung-. (See £ 357.)
But the possibility here indicated must be received with the
greatest caution; for it has been shown that although a dilute
alkaline solution of Oxy-hffimoglobiD when exposed to a low
partial pressure of carbon-dioxide ah.-orhs le.-< of this gas than
sutn'ces to convert the alkali into bicarbonate, thus acting like
an acid, at higher partial pressures it absorbs more than can
be accounted for by the change of the alkali into bicarbonate.
In the latter case the ha^moglobin seems to act like a feeble
base.2 It is interesting here to notice that if the immediately
preceding statements hold good. the ha-nioglobin must \»
increasingly acid properties in proportion as the carbon-dioxide
begins to be evolved from the blood, and might thus further
that exit. The power apparently possessed by ha-moglobin of
it-df uniting directly with carbon-dioxide will lie referred to

later on.

.". Carbon-monoxide haemoglobin. When a ooxnnt oi

boil-monoxide is pa^-ed through a solution of OXy-h&moglobin the

n is driven oil' and its place taken by the tirst-nanied «,'as.
The compound thn> formed iv>ult<. like OXJ-hflemoglobin, from the
union of one molecule of the gas with one of ha-nioglobin. It
further resembles oxy-ha-mogloliin in beinur readily crystallisable :!
in forms isoiiiorphous with those of the former, but the crystals
are on the whole less soluble, brighter coloured and more stable
than are tho-e of oxy-hiemoglobin.4 They are distinctly dichro-
matic (see p. L'lfi). The compoinul of carbon-mono\ide with
h.cmoglol)in is much more stable than is oxy-ha-moglobin, so that
the -as i- not pclled by the action of o\ \ --en. a fact which

fully explains the fatal result of breathing carbon-monoxide.
Finally the spectrum of carbon-nioiio\i.|e ha-ninglohin while
similar at first sight to that of oxy-lia-mog|obin. dilli-rs distinctly

Illutkryttallr. 1H71, S . 7n

•M-IH-IIMW. .!/ I I \\\l l»7'.l. «>lllirlllfil lit

Xunt/. Mfriiiaini's ll.llx-h. ,1. 1 B i\ Hi -' (ISM >

r |trc|i:iratiiin in ijiiantitv .^T Kill/.. '/J. f. jih', • IM \n

4 (':irlii)ii.|iioiin\iilr hiFinoglohin i-* uiiaffiTti-il liy <-itli<T )• > liang«* or

the action ()f |i;iin-n'.itii juii'r Bopp^StjrW, IMi ••'). s in

222 CAKBOX-DIOXIDE HEMOGLOBIN.

from it in the position of its two absorption bands (see Fig. 36,
No. 6). The spectrum of this compound undergoes no change by
the action of any of the reducing agents described on p. 220 :
this affords a further characteristic means of discriminating be-
tween the compounds of carbon-monoxide and oxygen with
haemoglobin. Since the determination of this compound in blood
is frequently of considerable importance in medical jurisprudence,
many tests for its presence have been devised additionally to the
evidence afforded by the spectroscope. One of the oldest and
best is due to Hoppe-Seyler.1 It consists in adding to the sus-
pected blood twice its volume of caustic soda of sp. gr. 1-3. If
carbon-monoxide haemoglobin is present it yields a brilliant red
precipitate, differing entirely in appearance from the brownish-
green mass observed if oxy-haemoglobin is present. For further
tests consult the literature quoted below.2

4. Nitric oxide haemoglobin. If a current of nitric oxide
be passed through a solution of carbon-monoxide haemoglobin, the
carbon-monoxide is displaced by the former gas.3 The compound
thus obtained is still more stable than is carbon-monoxide haemo-
globin. It may be crystallised and in solution exhibits two
absorption bands very similar to those of oxy-haemoglobin but
slightly nearer the red end of the spectrum ; these bands are not
affected by reducing agents. If prepared by passing the gas
through ordinary blood, the latter should first be freed from
oxygen by a current of hydrogen and care must be taken to
neutralise the nitrous acid formed during the process.

5. Carbon-dioxide haemoglobin. The possible union of
carbon-dioxide with haemoglobin has already been referred to
(p. 221), and more recent researches have thrown further, though
still far from complete light upon this possibility. There appears
to be no doubt that a solution of haemoglobin takes up a much
larger volume of carbon-dioxide than can be accounted for as the
result of a merely physical absorption. Thus in one set of experi-
ments it was found * that 1 gr. of haemoglobin could unite witli
2-366 c.c. of the gas at a temperature of 18 4° and partial pressure
of 31-98 mm. of Hg, the latter being a mean average partial
pressure of carbon-dioxide in venous blood according to the older

1 Virchow's Arch. Bd. xm. (1858), S. 104. .For a recent modification of this
test see E. Salkowski, Zt. f. physiol. Chem. Bd. xn. (1888), S. 227.

'2 Jaderholm (Swedish),' Abst. in Maly's Jahresb. 1874, S. 102. Weyl u. von
Anrep, Arch. f. Physiol. Jahrg. 1880, S. 227. Zaleski, Zt. f. physiol. Chem. Bd. ix.
(1885), S. 225. Knnkel, Sitzb. d. Wiirzb. physik.-med'. Gesell. 1888, Sitz. 9.
Katayama, Virchow's Arch. Bd. cxrv. (1889), S. 53. Welzel, Verhandl. d. physik.-
med.~ Gesell. Wurzb. (N. F. ) Bd. xxm. (1889), S. 3.

3 L. Hermann, Arch.f. Anat. u. Physiol. Jahrg. 1865, S. 409.

* Bohr, see Beitrdge z. Physiol. Ludwig, gewidmet, 1887, S. 164. Centralb. f.
Physiol. Bd. iv. (1890), S. 253. Skandinav. Arch. f. Physiol. Bd. m. Hf. 1/2
(1891), S. 47. See also Jolin, Arch.f. Physiol. Jahrg. 1889, Sn. 277, 285.

CHEMICAL BASIS OF Till-: ANIMAL BOD\
established data,1 while that in arterial blood is L'I-US mm.- It

is furlher stated that lli.- stron-, T solutions nl' li.riuou'lobiii absorb
relatively LeSfl Carbon-dioxide than tin- weaker, aiul thai, as in the
case of oxy-hemqglohui (see p. L!L!l ) various modification-, »i
ha-miiLjlubin i-xisi possessing dillerenl powers «,t' uniting with this

< >n comparing the amounts of carbon-dioxide ami of 01
..!• ( '( > or N'( ) which may unite with a ^ivm weight of haemoglobin
it is at once evident that tin; mode of union »t' the form-
must In- ditlerent from that of the latter three, with which, as
already stated, ha-moidobin unites molecule for molecule. This
difference in behaviour is very probably due to the decomposition
which lia-moolobin undergoes when a current of carbon-dioxide is
•I through it,3 and indeed it is hence probable that the so-
called carbon-dioxide h.emo^lobin i- rather a compound of the gas
with a coloured product of the decomposition of ha-mo^lobin, viz.
tuemochromogen, which has been shown by Hoppe-Seyler to unite
with carbon-monoxide (see below). The compound, whatever be
it- true nature, is stated to exhibit a one-banded absorption
trum closely similar to that of ha-mo^lobin, but the centre of the
band lies slightly more towards the violet end of the spectrum.4
Piohr state- that tin- absorption of carbon-dioxide is independent
of the simultaneous presence of oxygen.5

Tin- ai-eiiratt- ipiantitat ivi- determination of the amount <>f h;em<>-

k'l.'liin in any jjiven snlut KMI i- a matter <•!' extn-iue imp..rt:iin-i-. n.it

mi-rely in connection with several of the statemente oonteinad in the

•iini; il.--<-ript i..n <>(' (UBmoglohin and it- cniiipMiinds with gases,
l>nt al>.' in many in\ e>t i^at i.ms \\lii.-li turn «.n tin- \aryin^ aiii«mit*
«.t" tin- >iil>-tanei- umler < 1 1 He re n t i-xpi-riim-ntal r< unlit i<m-. and lurtln-r
t'..r rlinii-al purposes. It may tln-n-t'..re n<>t l>e <>ut «•! plan- t«. il.-.<Tiln-
hrii-tly tin- prim-iples »n \\lii.-li the ili-teriiiinat i»ns are l>a-.-.l. r.-l'.-rniiL:
tin- n-adi-r t>. sp.-cial \\.irk- fi.r the detail- "t tin- n->pi-i-t ive |

The ini-thiiils eiiipl.-yi-d fall under tw.. <-ateg.'ries : chemical ami

pll\ -i. :il.

1. Chemical. ". Tin- ainmint ..f iron pre-ent in KM) par
ha-mogloKin has Keen frequently determined for thfl ''1 ..... 1 ..f \arimis
animals. It may !>>• -tat.-. I t- !».• al>"iit • p.e. II. •ne.- it" a

siiliitmn of thi> lahttanoe be evaporated t.. drym--- and tin- ri->i<ln.'

iiii-ini-rati-il, the ainmiiit >'t" lia'iiK.^l.'liin may In- inf.-rrrd I'r-.m the

• • WulffLfru'. I'!! IM vi (is;.'i. S J.I. Straiwliurp, Ibid. \
Nnwhnnin. //•»/. I

- Hut <-f M.il.r, I'.nlr.ill. t /'/,,/>"•/. H-l. i. (ISS7). S. -JM. n. (1888), S. 4.-I7. uh.i
makett it inii.-li l'->s. An ..nlint: t.. th • tin- j.:irti;il pri-xxuro i>f '
M<M»1 in ICM than that of expiri'.l air. ami tl : -r.-at.T. If tlii> >li.-til.l
|in>\.- to !»• tin- <-:i»r> on further nn< ••ti^ati.ni. it u.nil.l apjK-ar that tho ffutoont
iiii.T. lianyo whirh taken plai-c in tin- IIIIIL'* < annut !»• tin- pviilt «if a jmn-ly .iiffunivo

\v In-Ill to IM- ($ .

-li|. See Abut. In M IIS

* T.-nij.. /•». "t. and see aLv. :<.• KoalaMtaMbiBdamg dm Blutea,"
KopcnhaL''-!!. 1887.

• tndmav. Arch.f. Phyriol. Bd. III. (1891), S. 62.

L'l'4. SPECTROPHOTO^IETRY.

amount of iron, existing as oxide of iron, in this residue.1 b. Since
tlu' volume of oxygen which unites with a given quantit}- of ha-ino-
globin is known with considerable accuracy (but see above, p. 2l'l),
the amount of this substance may be determined by saturating its
solution with oxygen and then estimating the volume of the gas
which is united to the hiemoglobin. The determination is made
either by extracting the oxygen with a mercurial pump or displacing
it by carbon-monoxide, or estimating it in the solution by a volu-
metric process with sodium sulphite and indigo.2 These methods are
inferior to the following.

2. Physical. These may be again divided into two : colorimetric
and spectrophotometric.

(i) Colorimetric method. The principle of this method may be
briefly stated as follows. A standard solution of haemoglobin is pre-
pared from pure crystals of the substance. The tint of the solution
in which the haemoglobin is to be determined is then compared with
that of the standard solution: if it is not the same when examined
under the same conditions, it must be equalised by either of the
methods to be next described; and from the operations necessary to
produce equality of tint the relative concentrations of the two solu-
tions may be inferred, and hence the absolute concentration of the
unknown solution. The methods more usually employed consist
either in diluting one or the other of the solutions until their tint
is the same when examined in layers of equal thickness (Hoppe-
Seyler),3 or else in determining the different thicknesses of the fluid
layer of each which exhibits the same tint (Duboscq). Since in the
latter case the concentrations of the two solutions are inversely pro-
portional to the thicknesses of their layers when their tint is the
same, the amount of haemoglobin in the solution of unknown strength
can be at once inferred.4 For clinical purposes Gower's haemo-
globinometer is perhaps most frequently employed. In this instru-
ment a measured volume of blood is diluted till it has the same tint
as that of a standard mass of gelatin coloured with carmine and
picrocarmine.5 There are, however, many other forms of colorimeter
designed for clinical use.

(ii) Spectrophotometric method. All coloured substances in solu-
tion possess the power of absorbing light. With a given thickness
of a given substance the amount of light transmitted by the solution
bears to the incident light a ratio which, while it varies for different
parts of the spectrum, is constant for any one portion, and is there-
fore characteristic of each substance. Hence if the absolute absorb-

1 Pelouze, Compt. Rend. T. i. (1865), p. 880.

* Grehant, Compt. Rend. T. LXXV. (1872), p. 495. Quiuquaud, Ibid. T. LXXVI.
p. 1489. Schiitzenberger et Risler, Ibid. p. 440.

3 Hdbch. d. physiol. patkol.-chem. Anal. Aufl. 5 (1883), S. 435

4 For a description of Duboscq's and other apparatus see G. u. H. Kniss,
Kolorimetrie u. quant. Spektralanal. 1891, S. 7 et seq. This work gives a most
excellent account of the best physical methods employed for the determination of
colouring substances in solution" A useful review of methods up to date (1882) is
given by Lambling, " Des proce'des de dosage de I'lie'raoglobine," Nancy, 1882. Of.
later, E. von Fleischl, Med.Jahrb. 1885, S. 425. Malassez, Arch. d. Physiol. 1886,
p. 257.

5 For details see Gatngee, Physiol. Chem. Vol. i. p. 184.

CHEMICAL HASIS OF THE ANIMAL BODY.

ing power of a given thickness of tin- >uh>tanc.- is determined once
for all for a given region of tin- >pectrtnn under ^iven conditions, it
becomes possible to determine tlit- amount «.f that >uh-tance in any

solution <>f unknown concentration bj examining the solution under

the ,-ame conditions in the same part of tin- spectrum and ascertaining
liu\v iinich li.u'ht it ha> absorbed. Li-t / In- t In- inten.-it \ <>f the inci-
dent light, and 1' its reduced inteii>ity al't.-r pa»in;_' through in 1
.•I a coloured solution, each of which reduces the initial intercity by

!. tli.-n it follows that /' = —.

nm

This is triii- whatever be the intensity of tin- incident ray; hence tin-
intensity may be taken = 1, and we have. /' = —

Again, let E denote the reciprocal of the number which represents

in centimeters that thickne>s of layer of the ab>orbiiig solution which
reduces tin- inten>itv of the incident ray t" ,'0 of its initial intensity
during it- pa->ai,'e through this layer.1 Then if the solution be exam-
ined in a layer which is always 1 cm. thick, this layer may be regarded

a> made up of E layers, each of thickne-> cm. Hence if in tin-
formula previously given we put n = 10 and m = E, we find that
the roidual intensity 1' of light after passing through a layer 1 cm.

thi.-k .- I> = W* = 10~*»

\\hence E=— log. /'.

It can also be proved that E, the ( ffirient of extinction. i>

directly proportional to the amount of colmirin^ matter present in

the eolation, or in other wordfl, t«. it- 'concentration;'1 whence if the

• •ntration be represented by C,

n

K = some constant 3 A, or C = AE.

This constant A having been determined om-e for all for a given
substance in ;i solution i,f Known concentration and for
„/' //'. ni, the concentration of any solution of the same sub

stance of unknown strength i- olitaim-il l>y simply multiplying A by

the coefliciellt of extinction /

Spectrophot, •meters an- instruments by which the value «\ /
ab,,\e) and hence of E may be detennine<|. Those of Yierordt 6 and

i / bedbd -I-.M-IH. -i.-nt <>f ••\tinrtiuu. ' a term ininxlu. -•,! l.\ IJunacn and Kotcoe,
Pogp. Aini.il. 11.1. . i (IV.7). S

•( •»ii.-i-iitr:iti»ii ' i- tin- 1111111!.. r of grams of i ..Inuring sub«tance diwolred
in I r i- "( tluiil ( Vii-ronlt).

; Ciilli-.l tin- ' :il>t.ir|>ti>in r.c

4 Tin- ititriMliirtiuti »f tin- |pactr<i|ihotomftrir nicth.Hl in a r.-li.ilil.- f<«nn i
!•• N'i.-r.T.li. l.:i.-.-.l ii|.-.n tli«- |>li..t... li.-!ni.-:il roearche* of Mun-i-n ami I
\'i.T"plt. (i) " Anw.-ii-l. 'I S|M-.-tr;ilapparaU /.nr I'li.ii.iin.-trii- .1 A [Kjctren

11 /. .|ii.uii rlii-in An.il ." TiilHiiu'-n. IH"-'». and (ii) "Die quajit. S|>cctralaaal. in
ilir.T Anw.-ri.l auf l'liv.-i.,l. u. •> w ." Tubingen, 1876.

» loc.cit. (i). >

16

226 METH^MOGLOBIN.

Hiifner l have been most generally used for physiological purposes,
but there are many other forms.2 The value of A. has been deter-
mined by several observers for haemoglobin,8 oxy -haemoglobin,4 carbon-
monoxide haemoglobin 8 and methaemoglobin,6 for certain fixed parts
of the spectrum; as also its value for bile and urinary pigments.7 If
the value of A. has been determined for two substances in two differ-
ent parts of the spectrum, the amount of each substance in a mixture
of the two may be determined spectrophotometrically.8 This is a
possibility of considerable importance when working with blood in
which varying amounts of haemoglobin and oxy-haeinoglobin may
occur simultaneously.

6. Methsemoglobin. When blood or solutions of haemo-
globin which have been exposed to the air for some time are
examined with the spectroscope they are frequently found to
exhibit, in addition to the more or less persistent absorption
bands of oxy-hsemoglobin, a marked band of absorption between
C and D, closely resembling but differing slightly in position
from the band which hsematin shows in acid solution (see below).
This band may also frequently be observed in many pathological
fluids, such as those from ovarial cysts, etc., which are coloured
by blood, and in urine when similarly coloured.9 The substance
to which the band is due is known as niethsemoglobin.10 It may
be readily prepared in the laboratory by the action of many
reagents such as acids or alkalis, or more conveniently of certain
salts, on solutions of oxy-hsemoglobin. Of these salts those which
may perhaps on the whole be most advantageously employed to
obtain the spectrum of methsemoglobin are nitrites,11 potassium
ferricyanide, or potassium permanganate.12 With the two latter
salts the spectrum of methsemoglobin may be obtained as follows.
To 10 c.c. of a moderately strong solution of oxy-haamoglobin
add a few drops of a dilute ('5 — 1*0 p.c.) solution of either of the
salts and warm very gently. If on examination with a spectro-
scope the two bands of oxy-hsemoglobin are still strongly visible,

i Jn. f. prakt. Chem. N.F. Bd. xvi. (1877), S. 290. Cf. Otto, Pfltiger's Arch.
Bd. xxxvi. (1885), S. 12. Glazebrook has constructed a modification of Hiifner's
instrument. See Lea, Jl. of Physiol. Vol. v. (1883), p. 239.

'2 For all details of instruments and spectrophotometry in general see G. u. H.
Kriiss, Kolonm. u. quant. Spektralanal. 1891, Very complete details are given in
Neubauer u. Vogel, Analyse d. Hams, 1891, S. 411.

3 Hiifner, Zt.f. physiol. Chem. Bd. in. (1879), S. 7.

4 Hiifner, Ibid. Bde. i. (1878), S. 317, in. (1879), S. 4. Von Noorden, Ibid.
Bd. iv. S. 9. Otto, Ibid. Bd. vn. S. 62. Pfliiger's Arch. Bd xxxi. (1883), S. 244.
xxxvi. (1885), S. 12. Sczelkow, Ibid. Bd. XLI. (1887), S. 373.

5 Marshall, Zt. f. physiol. Chem. Bd. vn. (1882), S. 81.

6 Otto, Pfliiger's Arch. Bd. xxxi. (1883), S. 263.

7 See Vierordt, loc. cit. or G. u. H. Kriiss, loc. cit.

8 Vierordt, loc. cit.

9 Hoppe-Seyler, Zt. f. physiol. Chem. Bd. v. (1881), S. 6.

10 The name was first used by Hoppe-Seyler in 1865, Centralb. f. d. me.d. W/xs.
S. 65. But see also previously Ibid. 1864, S. 834, and Virchow's Arch. Bd. xxix.
(1864), Sn. 233, u. 597.

11 Gamgee, Phil. Trans. 1868, p. 589.

12 Jaderholm, Zt. f. Biol. Bd. xin. (1877), S. 193.

228 METH^MOGLOBIN.

let the mixture stand for a short time, and if the band character-
istic of methsemoglobin has not made its appearance, add one or
two drops more of the solution of the salt and proceed as before.
As soon as the bands of oxy-hsemoglobin have markedly disap-
peared, acidulate very faintly and examine again. The band
which should now be visible as characteristic of methsemoglobin
lies in the red part of the spectrum, between C and D, nearer to
the former line As already remarked, its position is closely sim-
ilar to that of hiematin in acid solution ; but comparison will
show that it lies nearer D than does the hsematin band, the
centre of the latter being situated at w. L. 640, while that of the
former is at w. L. 630 l (See Fig. 37, Nos. 4 and 5).

In addition to the reagents recommended above, an extensive series
of other substances are also found to effect the conversion of oxy-
hsemoglobin into methaemoglobin, such as potasssium chlorate, amyl-
nitrate, iodine dissolved in potassium iodide, bromine, osmic acid,
hydrochinon, pyrocatechin, &c.2 It may also be obtained as the
result of prolonged evacuation with a mercurial pump, of putrefactive
changes, or of the action of palladium saturated with hydrogen and
immersed in the solution of oxy-hsemoglobin.3

The absorption band which has so far been described is the one
which is to be regarded as characteristic of methcemoglobin, being
accompanied by a very marked absorption of the violet end of the
spectrum extending up to the D line. In addition to this band it
is stated that, working with a good spectroscope of low dispersive
power, three other bands may be additionally seen,4 two corre-
sponding closely with those of oxy-hsemoglobin but not identical,
their centres corresponding to w. L. 580 and 539, and the third in
the blue at w. L. 500 (?).5

In an alkaline solution the position of two of these bands
differs slightly from that just given, being stated by Jaderholm
to be at w. L. 602 and 578, while the third is unaltered at
539.

In the preparation of large quantities of crystallised oxy-
hsemoglobin from pig's blood, it was observed that during the
recrystallising essential to its purification a copious crop of
reddish-brown crystalline needles was obtained. These were
found on examination to be crystals of methsemoglobin.6 They

1 This method of localising the bands means that their centres occupy positions
in the spectrum where the wave-length of light is respectively 640 and 625
millionths of a millimeter. It should always be adopted for all absorption bands,
since it is independent of the varying dispersion and arbitrary scales of different
spectroscopes. For details see Gamgee, Bhysiol. Chem. Vol. i. p. 94.

2 For list of substances see Hayem, Compt. Rend. T. en. (1886), p. 698.

3 Hoppe-Seyler, Zt. f. pjiysiol. Chem. Bd. 11. (1878), S. 149.

* Jaderholm, Zt. /, Biol. Bd. xx. (1884), S. 419. Also Nord. Med. Arkiv.
Abst. in Maly's Jahresb. 1884, S. 113. But see also Araki, Zt. f. physiol. Chem.
Bd. xiv. (1890), S. 405.

5 For figure see Halliburton, Chem. Phi/siol. and Pathol. Fig. 59, Spect. 6, p. 277.

e Hufner u. Otto, Zt.f.physiol. Chem. Bd. vn. (1883), S. 65.

CHEMICAL BASIS OF THK ANIMAL BODY. 229

are mo<t • 'a-ily nl.tained if the oxy-hrcmoglobin is first converted

into metha-moglohin by the action of potassium ferric\anide (mi,,
or two minute crystals of tin- salt to half a litre of warm con-
centrated sulution of oxy-hii-nioglobin) ; the mixture i-. then
shaken until it lias a dark-brown colour and is cooled to 0
tin- addition of one quarter of its bulk of alcohol also cooled to
0°. They have also been obtained from the bl 1 of tin-
horse .- and other animals,3 and resemble in crystalline form the

crystals of Mnr-httmoglobin from the same sources. These crystals

arc doubly refracting, readily soluble in water, though less so than
oxy-luemoglobin, and the solution, unlike that of the latter sub-
stance, yields a precipitate with basic lead acetate in presence of
ammonia ; they are identical in percentage composition with those
of oxy-luemoglobin. The behaviour of metha-moglobin towards
reducing agents is interesting and also important as affording a
means of discrimination between this substance and hit-matin.
If some ammonium sulphide be added to an alkaline solution of
methcemoglobin, the mixture may be observed to yield the spectrum
of i reduced) ha-moglobin ; and on now shaking np with o
(air» it sln>w> tlie spectrum of OXV-hftmqglobilL "When a solution
of ha matin is similarly treated it yields the spectrum of ha mo-
chromogen (reduced hematin) in alkaline solution (see below).
"While the close relationship of methsemoglobin to oxy-ha-moglobin
is thus clearly shown, very great differences of opinion have ex-
isted as to the exact nature of that relationship. Three \
have been put forward. 1. That meth&emoglobin is more highly
oxjdised than OXY-hffimoglobilL -. That it is le»s highly oxidised.
."•. That it is united with exactly the same amount of oxygen as
is oxy-luemoglobin i only in a more stable combination. Th-
ins to have been based on the ready production of
nietha-moglobin by oxidising agents and on the statement that
when metha-moglohin is reduced it yields //,•*/ oxy-h;emoglobin
and then ha-moglohin. The second view iv-ted on the possibility
of obtaining metbttmoglobui by the prolonged action of a \acuum
or the -bolter action of palladium saturated with hydi
and on the statement that by reducin it passe

to ha-moglobin \\ithout tin- intermediate appearance of
ha-moglnbin. The third view, which now appears to be generally

ted, H derived fr-Ull obs,-r\ at j« 'US of the aillolint -

which can be pumjied out from a mixture of meth.emoglobin ami
oxy-ha-moglubin of known composition.1 and from the amount of

' IIufn.T. //././. Bd.Tm.(lM4),fl 'IMV .lu,!,.rl,..ln, / / IM XX. (1884),

> in

,n..t. .1 l.y Jii<lcrli<-]in, lor. ,

illilmrt-.ii. Quart. ./'/. .I/;. \\\m (isssi. j. i'ui (.iv... rapid

iiii-ih<><l fur inirr»srii]iii- pnrpoHoti ; <iml t'nthoJ p. 28O.

4 Tlif» liti-ratiip- i-f tin- .li-|,iiti' i* fully qt -»9 IT

I',.! \\\i >n. -.•»:• - mini: lii«-rntnre to

(18IU) has l.c.'n u'iv.-n /-i^,m in tli" ;ili<i\i- ;irr<>uiil "f this -tiih-'

230 H^MOCYANIK

oxygen which is displaced from a given weight of methsemoglobin
when it is treated with nitric oxide.1 We may probably say,
therefore, that under certain conditions, without our being able
to state exactly what has taken place, the oxygen loosely united
to hemoglobin as oxy-hsemoglobin becomes more stably combined,
and is now not removable by either a vacuum, or carbon-monoxide,
or a current of hydrogen, and further that the resulting substance
(methpemoglobin) has the same composition and crystalline forms
as oxy-haemoglobin, and may be reconverted into the latter body
by suitable means, such as reduction by ammonium sulphide and
subsequent oxidation.

7. Hsemocyanin.2 As previously stated (p. 217) the blood-
plasma of many invertebrates contains haemoglobin in solution ;
in a few cases this is united to special corpuscles in the blood.
But in the case of other invertebrates this respiratory pigment is
replaced by another to which, since it turns blue on exposure to
air (oxygen), the name hsemocyanin has been given. Hence the
arterial blood of those animals in which it occurs is blue, while the
venous is colourless.

Hcemocyanin is a proteid of the globulin class ; it is therefore
partially precipitated by a current of carbon-dioxide, by satura-
tion of its solutions with sorh'nm p.h1nr[rjp and completely by satu-
ration with magnesium sulphate.3 Unlike haemoglobin it has not
yet been crystallised ajid contains copper, presumably as a con-
stituent of its molecule, in place of the iron characteristic ^f
haemoglobin. It exhibits no absorption bands when examined
spectroscopically.

Another animal pigment is known, into whose composition copper
(5 — 8 p. c.) enters ; this is the substance called turacin.4 It gives
the characteristic colour to the plumage of certain African birds known
as Touracos or Plantain-eaters, whence the name turacin. It differs
entirely from hasmocyanin in its general properties, and is only men-
tioned here because it contains copper, as does the former pigment.
It is slightly soluble in water, readily soluble in dilute alkalis, the
solutions in either of these solvents showing two absorption bands be-
tween D and E very similar to, though not identical with, the bands
of oxy-haenioglobin and a third faint broad band at F. It is not how-
ever a respiratory pigment.

1 Hiifner u. Kiilz, Zt.f. phi/siol. Chem. Bd. vn. (1883), S. 366.

2 For literature see' Halliburton, Chem. Phi/sioi. and Pathol. 1891, p. 321.
Details of previous work to date (1880) are given by Krukenberg, Vergleich.-physiol.
Studien, in. Abth. (1881), S. 66.

3 Halliburtou, ,//. of Phi/siol. Vol. vi. (1884), p. 319.

* Church, Phil. Trans. Vol. CLIX. (1870), p. 627. Cf. Ber. d. d. chem. Gesell. Bd. IT.
(1869), S. 314; in. (1870), S. 459. See later Krukenberg, Veryl.-pht/siol. Stud.
v. Abth. (1881), S. 72; 2 Reihe, i. Abth. (1881), S. 151. The same work (2 Reihe,
Abth. n. n. in. 1882, Sn. 1 u. 128) contains elaborate observations on other pigments
from feathers.

CIIKMICAL BASIS OF THK ANIMAL l',«U>V.

8. Haemochromogen. C34H,,N4FeO, (?).

When (reduced) ha-moglobin is treated with acids, or, better
still, with alkalis in the entire absence of oxye.-n, it i.- d
posed into a proteid and a coloured sub-tan. .- t<. \\hi.-h
Euemochromogen P given by Hoppe-Seyler.1 When alkalis

an- u.-ed in its preparation, the solution obtained i> of a brilliant
purplish-red colour, ami is characterised by t\\<> marked al-s.-ij.-
tiuii band-, the stronger lying halfway between 1> ami /„', the
other ;;ml fainter between E and I. These are identical with
tin- l>aiuls of Stokes' reduced luematin in alkaline solutioi
Fit,'- 37, No. 3). When exposed to the air (oxygen ) tin- solution
rapidly loses its brilliant colour, becomes dichioio, vi/. : red in
thick, and greenish in thin layers (cf. xnh ha-matin) and now
yields an absorption spectrum, which exhibits one not
strongly marked hand in the yellow, to the red side of It ami
touching the latter line. This is the spectrum of ha matin in an
alkaline solution (see Fig. 37, Nos. 1 and 2). "When the de. « m
position of the haemoglobin is brought about by acids instead of
alkalis, the coloured product is similarly kuemochiomogeil, but in
this case, unless special precautions are taken, some of the ha nio-
chromo^en is itself further decomposed ami yields ha ma'
phyrin or iron-free ha-matin (see below). Tin- mixture thus
obtained probably accounts for the four-banded spectrum as thst
.lied by Hoppe-Seyler.2 When a solution of ha-matin in
alkali is reduced with Stokes' fluid (see sub oxy-hu/moglohin) or
ainiii'inium sulphide the solution obtained shows U\ •• absorption
bands identical with those already described as chara« -tei i-tie of
ha-nio.-hronio^en. l-'nun these fa<-t- it would at tiist si-lit . ;
that reduced ha-matin in alkaline solution and b.i-miK-hron
imilar solution are identical substances, and this is it
the view which has been most generally adopted. l-'mm a
Bpectroecopic ]>oint of view they do aj>])ear to be the same, but
Hoppe-Seyler maintain- that they are not.8 According to him
h&mochromogeu i- a simple product of the decomposition of
ha-nio^lubjii, while ha-matin is an oxidi»-d pioduct which dilleis
from true oxy-lia-mochrom-^en by he in;,' united to a smaller
amount of oxygen than is tin- former. lie has further
in obtaining imt only ha-mocln-omo^en in a crystalline form.4 but
a l-o a compound of h.i-moehromo^.-n with carbon-iiH»no\i,i
hibitinu' the al.-orption hand- of carbon-monoxide hemoglobin
ami containinu tlie same am.iunt of carb..n-monoxi.le unite.l to

i M,,I.-.-I,.,H Pi* < lift M fisrii. S :.4o 'in«e.

<•!„,„ v,,l. i ], us. See A!M later Hopper v«o/. Cktm.

Hih i

- 104,

•J. <'hrm. (1881), 8. 394.
9 t'. i>hv*i»l. i '!•• ••>. IM. MO

4 H\ the aetfon of itraag CMMtii -«!a»t 100° in tin- ••mire absence of oxrgea.

232 ILEMATIN.

each atom of iron as does that body, whereas haematin in alkaline
solution will not unite with carbon-monoxide. He therefore
considers that haemoglobin is a compound of a proteid with this
haemochromogen, to which it owes its colour, and that it is with
the haemochromogen group rather than with haemoglobin as a
whole that the gases are united in the formation of such com-
pounds as oxy-haemoglobin and carbon -monoxide haemoglobin.
Further investigation, more particularly of the crystalline haemo-
chromogen, is needed for the final establishment of these views.

9. Hsematin. C34H36N4Ee05.1

When oxy -haemoglobin is decomposed by either acids or alkalis
it yields a proteid and a coloured substance known as haematin.
This decomposition may take place in old blood-clots or extrav-
asations and is readily produced by the action of either gastric or
pancreatic juice on oxy-haemoglobin, so that haematin is frequently
found in the contents of the alimentary canal and in the faeces,
more especially with a flesh diet. It has also been found in urine
as the result of poisoning with sulphuric acid or arseniuretted
hydrogen.

Preparation. The following method slightly modified after Klihne 2
may be advantageously employed, and yields not only solutions which
show strikingly the spectroscopic appearances of haematin in acid and
alkaline solution, but also finally a fairly pure and typical specimen
of haematin itself. Defibrinated blood is made into a thin paste by
mixture with potassium carbonate, and is then evaporated to dryness
on a water-bath. The dry residue is powdered, placed in a flask, and
extracted with about four times its bulk of strong alcohol by boiling
on a water-bath. The deeply coloured extract thus obtained is poured
off and the residue again extracted as before with alcohol, the process
being repeated as long as any colouring matter is extracted. The ex-
tracts are mixed and filtered and form a strong solution (a) of haematin
in alkaline alcohol. A portion of this extract may be kept for spectro-
scopic examination. The remainder is strongly acidulated by the care-
ful addition of sulphuric acid, any precipitate which is formed is
removed by filtration, and the filtrate (b) provides a typical solution
of haematin in acid alcohol. A portion of this may as before be kept
for spectroscopic examination. The remainder is made alkaline by
the addition of an excess of ammonia and filtered; the filtrate (c) is,
as in the case of (a), a solution of haematin in alkaline alcohol, but
now the extraneous salts present are chiefly those of ammonium. The
filtrate (c) is finally evaporated to dryness on a water-bath, extracted
with several portions of boiling water, and the undissolved residue con-
sists of fairly pure haematin. This should finally be washed with
alcohol and ether and then dried for a prolonged period at 130-150° .

To obtain pure haematin it is probably better to prepare it from
haemin whose purity as a mother substance can be ensured at the out-

1 Hoppe-Seyler, Med.-chem. Untersuch. 1871, Hft. 4, S. 523.

2 Physiol. Chem. 1868, S. 202.

I'.ASIS OF TIM: ANIMAL r.nny.

set liy tin- fact that, unlike ha-matin, it is ivadily obtained in rrystala.
••elow.) Tin- ha-iiiiu crvtals sh,,uld !„• |i..ilr<l with strong acetic
acid, tlii-ii \\a-ht-il with water, ale. .hoi. ami ether, ;m«l dissolved in
dilute raustir potash. The solution is th«-n tillered, precipitated with
hydrochloric acid, and washt-d with boiling \\ater until tin- washings
an- >hown, a> tested by nitrate ••!' -il\er. \» l.e free from hydrochloric
arid. The residue is tinallv dried l>v prolonged heating to l.'lu —
150°. »

ordinary purposes hiematin is characterised chiefly by the
speetroseopie appearances of its solutions. When dissolved in an
alkali (ammonia, as in solution (c) above) it shows one absorp-
tion band in tin- yellow adjuiniiiLj D t<> the red side of this lin.-,
while at the same linn- th.-iv is ^reat absorption at tin- Idin- end
of the sjM-ctruni ( Fi^. 37, Nos. 1 and 2). On tivatnirnt with a
ivduriim a-. -nt, Stokes' fluid or annnoniuni sulphide, this band is
ri'plai-fd by two others in the green, of which the «>ne neaiv-t l>
is remarkably dense, the other less sharply defined. Very little
absorption of the red end is observed while that of the blue is as
bt-iore very marked (Fi<{. 37, No. 3). This is the spectrum of
Stokes' reduced ha-matin and is identical with that of Hoppe-
Seyler's ha-niochroiiH^en. The two substances have usually been

led as identical, but this is disputed by Hoppe-Seyl. -\
aliove). Alkaline solutions of ha-niatin are strongly dichr.'ie.
bein.i,' ruby-red in thick layers and greenish in thin 1
viewed by reflected li^ht.

The arid alcoholic solution of ha-niatin (solution (l>) above) is
characterised by <ni>- absolution band between r and />. adjoining
<', whose centre is situated at w. L. (140. This baiid is somewhat
similar to that of metha'moglobin, but it is le-s dense, and careful
observation shows that the centres (.f the re>p. •• -live bands do not
coincide ( Fiij. 37, Nos. 5 and 4). Acid solutions of ha-niatin are
monuclironiatic and of a dull reddish-brown colour. If blood or a
strong solution of o\y-ha-moul"bin be made strongly acid by tin-
addition of acetic acid the ha-moglobin is decomjM.se.l. ha-matin is
B6l free, and if the volution be shaken up with ether and all

ml, the ether li-es to the surface and is m. • coloured

owing to the presence of hiematin held in solution in the acid ether.
This acid ethereal solution shows, in addition to the one band al-
ready described as characteristic of ha-matin in an acid solution.
three other bands whose positions and relative inten.sitir- are siif-
liciently shown in Fi-. -"-T, N<

Bflematinafl prepared by the method bed above i- usu-

ally obtained Iv but not crvstalline mass of bhiish-black

colour and metallic lustre, strongly resembling iodine. When
finely powdered it appears d.uk or light-brown according to the

Ml />/,,, W.-/xi/A«/.-<-Vm. Amil. :> Ami l"-i S. 239. SPO al*.

/ \',Mr. in M:ilv-- C'Aiw.

I \\\u (1877), p. 485. .Ma.-.Mni.n. ./. tfPkgtb \»\. \i I8M. p. 22.

234 HISTOHyEMATINS.

fineness of the powder. It is a remarkably stable substance ;
may be heated to 180° without decomposition, but by stronger
heating is finally decomposed, liberates an odour of hydrocyanic
acid, and leaves a residue (12'5 p. c.) of pure oxide of iron. It is
quite insoluble in either water, alcohol, ether, chloroform, or ben-
zol. It is somewhat soluble in strong acetic acid, especially if
warm, also in alcohol (not water) to which some acid has been
added, and readily soluble in alkaline solutions or in alcohol con-
taining alkalis. It is not affected either by strong caustic alkalis
even when heated, or by hydrochloric or nitric acids. It may be
dissolved in strong sulphuric acid, but is now found to have un-
dergone a change during solution which results in the removal of
iron and the production of hsematoporphyrin or iron-free hsema-
tin J (see below).

If the decomposition of hsematin by sulphuric acid be brought about
in the absence of oxygen an iron-free insoluble substance is obtained
known as haematolin, to which the formula C68H78N807 is assigned.2

If potassium cyanide be added to an alkaline solution of hsematin,
this now shows one broad absorption band extending from D to E
(Hoppe-Seyler). By the action of reducing agents, this band is re-
placed by two other bands.3 The substance to which these appear-
ances are due is known as cyan-haematin, but all further information
is still wanting.

Some more recent observers (Nencki and Sieber) have assigned
to hsematin the formula CsoHsaN^FeO^ the validity of which as
against the views of Hoppe-Seyler is not as yet generally accepted.
It will be referred to again under haemin.

10. Histohaematins. This is the name assigned to a class of
pigments which are stated to be of wide-spread occurrence in the
tissues of both vertebrates and invertebrates, and to be related to
though quite distinct from haemoglobin and haematin. They are
regarded as respiratory pigments, playing towards the muscles or
other tissues in which they more particularly occur the same part
that haemoglobin does to the tissues generally. Our knowledge of
these pigments is however as yet limited to the spectroscopic ap-
pearances which they present either in situ in the mother-tissue
or in solutions obtained by the action of ether, while their respi
ratory function is assumed from the changes which they exhibit
under the influence of reducing agents and subsequent exposure
to oxygen. Of these histohsematins the one most fully de-
scribed is known as myohaematin from its characteristic presence
in muscles.

1 The haematoin of Preyer. See " Die Blutkrystalle," 1871, S. 178.

2 Hoppe-Seyler, Med.-chem. Unters. 1871, Hf. 4, S. 533. Cf. Nencki u. Sieber,
Bar. d. d. chem. Gesell. Bd. xvii. (1884), S. 2272.

3 See Gamgee, Physiol. Chem. Vol. i. p. 115.

CHEMICAL BASIS OF THK ANIMAL I'.oDV.

•1nr m<i tin.1 To observe the spectrum of this substance a
slice of tissue, such as that of the In-art, is sijuee/ed in a coin-
pressorium until sufficiently thin to transmit lk:ht. It i- then
examine. 1 with a mierospectroscope under strong illumination.
Or, on the other liand, the tissue may be treated with excess of
ether under whose intluciice an aqueous juice is extruded in
which tin- niyiiha-matin is in solution. Speaking generally, for
tin- appearances vary slightly according to the source ot tip
nn-nt. niyohii'iuatm yields a four-banded absorption spectrum.
Tin- first band lies close to 1), but towards the red end of the
spectrum. The next two bands are situated close together about
midway between D and E. The remaining band lies in tl
gion between E and b. Solutions of myohtematin an- when weak
of a ivddish-yellow colour, but if strong they an- pure red. I',\
tin- action of warm alcohol containing a little sulphuric acid a
spectrum is obtained closely similar to that of ha-matin in acid
solution, and by the use of concentrated sulphuric acid a sul>-
stauce is produced which in both acid and alkaline solutions shows
bands similar to those of haematoporphyrin in the same si-lvi-nts.
Under certain conditions myohaematin becomes ' modified ' and now
yields two bands similar to those of ha-rnochromogen, but situated
nearer the violet end of the spectrum.

The conclusions drawn from the above spectroscopic facts have,
been the subject of some controversy and adverse criticism, the
appearances being regarded as due not to a specific pigment, but
rather to haBmochromogen or mixtures of other products of the
decomposition of haemoglobin.2

11. Haemin. C^Hu^FeO, . HC1. (Haiinatin-hydrochloride,
or Teichmann's crystals.)

These crystals may be readily obtained for microscopic ex-
amination by heating a drop of fresh blood on a glass-slide under

FlO. 38. H.EM IN CRYSTALS FROM A DROP OF BLOOD. (Kuhn«.)

a cover-slip with a little glacial acetic arid.3 In the case of
blood which has been dried, as in an old blood-clot or stain, the

i MacMunn, Phil. Tram. It. i. 1886, p. 267, .rt. of Pkytiol. Vol. rill. (1887),

i. :.i

VT. '/A. f. i.f»,*nJ. ('/»<» 15.1 xiii (!--''). S lin II, ,,,,„- /. Bd.

Xiv. (is'.in) S UK, K,-r fi.lv »oe MacMunn. /'•/./. MII S »••:. \n :»28.
» Tei.liiniu.n. Xt. f. rat. Kd. IM. in ( l«:i). S. 375, Bd. Till. S. 141.

236

residue should be powdered as finely as possible with a minute
quantity (trace) of sodium chloride. A little of the powder is
then placed on a slide and covered with a slip under which some
glacial acetic acid is now run in. It is then warmed carefully to
a temperature just short of that which would cause the acid to
boil. If the operation has been successful, on cooling crystals of
haemin will be seen under a microscope, mixed in either case as in
Fig. 38 with a granular ddbris. If they are absent, warm again,
adding more acid if necessary. The crystals are dark-brown, fre-
quently almost black, elongated rhombic plates and prisms be-
longing to the triclinic system.1 In a purified specimen they are

FIG. 39. H.EMIN CRYSTALS. (After Preyer.)

arranged singly or in groups as shown in Fig. 39, and apart from
their form are characterised by being strongly doubly-refracting :
when examined under the microscope between crossed Nicol
prisms those crystals whose axes are suitably inclined to the in-
cident light stand out bright yellow or orange on the dark field.2
They are quite insoluble in either water, alcohol, ether, chloro-
form, or dilute acids : they may however be dissolved to some
extent in glacial acetic or hydrochloric acids, especially if
warmed, and are readily soluble in alkaline carbonates or dilute
caustic alkalis, being at the same time decomposed by the latter
solvent into haematin and a chloride of the alkali. This fact pro-
vides the best means for obtaining pure haematin (see above).

Although it is quite easy to obtain typical crystals under the
microscope from minute amounts of haemoglobin or haematin, their
preparation on a large scale is somewhat tedious ; several methods

1 Lahorio. Quoted by Schalfejew, Jn. d. rttss. phys.-chem. Gesell. 1885, S. 30.
See Abstr. in Ber. d. d. chem. Gesell. Bd. xvni. Ref., S. 232. Cf. Hogyes, Centralb.

/. d. med. Wiss. 1880, No. 16.

2 A. Ewald, Zt.f. Biol Bd. xxir. (1886), S. 474.

CHEMICAL BASIS OF THK ANIMAL lioDV.

have been t-iiiployed,1 of which the most recent, said to \ j. M
of crystals from ea'-h 1 litre of blood, is as follows.2 T.<
volume lit' defihrinat'-d ami -trained blood add f«uir volumes of
glacial acetic acid previously warmed to 80°. As soon as the
temperature of tin- mixture has fallen to 55 — 60°, it must be
auain warmed to 80°. On cooling ami standing for 1U — ll' hours
ils separate out; the supernatant liquid is then removed l.y
a syphon. the crystals are washed with water repeatedly i,v d--
cantation in a tall glass cylinder and are finally n.lleeted oil a
filter and washed with water, alcohol, and ether.

Tim successful preparation of hainin crystals from minute
quantities of ha-imi^lobiu or metlia-moglohin is of the gr-
importance for medico-legal purposes, since they suffice, even in
the absence of all other confirmatory evidence, to establish the
nature of the material used in their preparation. In the detection
of 1)1« md-stains it is usual first to examine with a spectroscope an
aqueous solution of the colouring matter if it can lie obtained, for
the characteristic absorption bands of oxy-memoglohin or nietli;em.i-
globin. In old stains the hemoglobin is frequently decomposed,
in which case it is insoluble in water, and alkaline extracts must
be made and examined for the spectra characteristic of ha-matin
The residues from the spectroscopic examination are lastly u-ed
to prepare hsemin crystals, in final confirmation of the evidence
previously obtained.3

has already been made (see p. 234) to some work on liii'inin
and huMiiatin which assigns to these substances a eompo>it imi and
relationship very different from those usually accepted, and further
puts the relationship of the colouring matter of blond to the hile-
pigmentfl in a new light.4 "With the preliminary rautinii that the>r
\ii-\vs are not as yet generally aecfjited and reijuire continuation, tln-y
may be briefly dealt with here. Using aniyl-ulcohol in the pri-para-
tioii of h.-emiii rrv>t;ds it is stated that the crystals have the following
.•onipo>iti.,n (CMH,oN4FeO, . HC1)«C6H,. OH. Th.- gr..uj. « II N,
it regarded as the true ha-min. Teiohnuuui^ oryttala ooniuting

of C88H$0N4Fe08. HC1. When thr crystals thus pivpaiv,! are d.-.-oin-
[...-. d by caustic alkalis as in the ordinary method for |.iv]iariiiKr h:«-ina
tin from tin-in, the heemin is Hii|.p.i>ed to take up one m-.b-i-uli- of
watrr and yi.'M ba-matin C,,HMN4FeOv I'.y treating this li:ematin
with strong sulphuric acid, it loses its iron and uniting with OS
yield- li:ematoj>or]iliyrin or iron-free luematin, Ca,HMN4Oj, \\lncli i-

M Gamgee, Physiol. Chun. Vol. i. p. 116, or H..p|M-Scyler, Pkytiol.
1 Anil :. I*-:?. S. -JH.

•:;ilfi-j.-w. .In. ,1. runs. ,>h Ht.-chftn. Getfll. 1885. See Ah«tr. in Her. d d
,h.m. H.srll. xvni. M.l (ls".-.i. K'.-f. S. 232.

•For detail* see Hoppe-Seyler. lor. fit. S. 529. Gamgee, /<*. c,t j. i'l..
\Iiiini, The gnectroscoiH! in medectne, 1883. pp. l:w— U-

ndd ii Sieber, Btr. <l .1 ••//. IM. xvn. (1«H4). S :•

, .

S. 392, Arch. f. txp. I>,,th. „. I'lm.m. IM. win (1884), & 4«>l. IM. XX. (1886), 8.
Bd. x\n (1888), S 4.'!0 NViu-ki n. l{..t-!i\ .'/ "><it»hf. f. Chem. '

also Hoppe-Sevl.T in advrrs- . ritic-imn. /;••.-. d.d.chem. GtMU. Bd XMII
(1885), S. 601, Zt.f. phytio). Chem. Bd. X (1886), S. 331.

238 ILEMATOPOKPHYKIK

however further regarded as derived by dehydration from a true hoema-
toporphyrin whose composition is Ci6H18N208. The latter is thus
identical in composition with bilirubin, whose formula is undoubtedly
C16H18N208. This is regarded as affording the desired chemical proof
of the genetic relationship of the bile- and blood-pigments, the deri-
vation of the former from haematin being represented as follows,
C82H82N4Fe04 + 2H20 — Fe = 2 (C16H18N203) .

12. Haematoporphyrin.1 C68H74N8012 (?). (Iron-free hsematin.)

If haematin is dissolved in concentrated sulphuric acid it yields
a solution which, after nitration through asbestos, is of a brilliant
purple-red colour. By the action of the acid, the iron is removed
from the haematin and haematoporphyrin is formed.2 If this solu-
tion is diluted with sulphuric acid it shows with a spectroscope
two absorption bands of which one adjoins D to the red side of
this line, while the other is very strongly marked and lies midway
between D and E. By the addition of water to the solution in
sulphuric acid the colouring matter is largely precipitated, especi-
ally if some alkali be carefully added to neutralise the acid. The
precipitate thus obtained is readily soluble in dilute alkalis, and
this solution is characterised by four absorption bands, one half-
way between C and D, two between D and E, and one conspicuous
band adjoining b and extending nearly to F.3 Haematin also yields
haamatoporphyrin by the action of strong hydrochloric acid at 130°
in sealed tubes.

Some interest attaches to this substance owing to its occasional
occurrence in urine in forms which show slightly different absorp-
tion spectra but are probably closely related if not identical.
Thus it occurs as urohasmatin or urohsematoporphyrin,4 or as
ordinary haematoporphyrin.5 It is also found in the integument
of some invertebrates 6 and in the egg-shells of certain birds.7 It
is further interesting to notice that in haematoporphyrin we have a
strongly coloured pigment derived from hsematin with removal of
the iron which the latter contains, a fact which facilitates our con-
ception of a possible derivation of the iron-free bile-pigments
from the iron-containing haemoglobin or haematin. This relation-
ship will be more fully discussed when the bile-pigments are
described.

1 Hoppe-Seyler, Med.-chem. Unters. Hft. 4. 1871, S. 528.

2 In the absence of oxygen a substance called by Hoppe-Seyler hcematolin is
obtained, C68H78F8O7.

3 These spectra are figured in Halliburton, Chem. Physiol. and Pathol. Fig. 59,
p. 277, Nos. 10 and 11.

* MacMunn, Proc. Roy. Soc. Vol. xxxi. 1880, p. 206, Jl. of Physiol. Vols. vi.
(1884), p. 36, x. (1889), p. 71, Clinical Chem. of Urine, 1889, p. 109,' Proc. Physiol.
Soc. No. iv. 1890. See Jl. of Physiol. Vol. xi. (1890), p. xiii.

5 E. Salkowski, Zt. f. physiol. Chem. Bd. xv. (1891), S. 286.

B MacMunn, Jl. of Physiol. Vols. vn. (1885), p. 240, vm. p. 384.

7 For literature see MacMunn, Jl. of Physiol. Vol. vu. p. 251.

CHEMICAL BASIS OF T1IK ANIMAL linDV.

13. Haematoidin.1 CuHuNaO,.

This substance is found as reddish or orange rhomboh-
crystals in old blood-clots as of cerebral haemorrhages,8 in corpora
lutea, iii the urine in cases of transfusion of blood 3 and in cases
of luematuria.4 There is no doubt that as occurring in the above
cases it is directly derived from some metamorphosis of haemo-
globin. Apart from the .similarity of crystalline form and colour
it was further found that ha-matoidin crystals readily ^ive the
characteristic (Umelin's; reaction for bilirubin by treatment with
nitric acid, and thus its identity with bilirubin was at once asserted
and supported by very convincing evidence.6 The identity was
however for some time disputed, notably by Stadeler, and by

*?/ 0 *

40. H.KMATOIUIV CRYSTALS. (Frey after Funke.)

others largely on the basis of inconclusive spectroscopic im
Cation of the two substances. There is however no doubt that
nfematoidin is really identical with bilirubin, so that imw the
nuinf is of interest rather from a historical point of vi.-\v and
physiuluu'iriiiiy aa indicating »lu- undoubted genetio reUtioDBbip
of the pigments of bile to those of blood.

I, ILK-PIGMENTS AND TIIKIK DERIVATIVES*

The bile is in all animals a characteristically .

secreti. >n. The colour of the fresh bile is as a general rale

i The litoratnre of this «ul>.«tance is very fully quoted in Hermann1! lldbch. d.

fully closrril.o.1 it -TS ol.taino.l frmn tins ..ource. ai
hamatoidin t.. indirat.- iti iind..nl.t«-d .lrriv.iti..n fr-.m the colouring matter o

\'in-h..w^ .I-/,. l',.|

ii ..;.;.. Eteyter, I'fln^or's .l/w,. B«i. \ -Mi.

i I <rA. Arch. f. Klin. M ' ' "'

6 See among others K. 'Salkowski, Hoppe-Seyh-r'n Mtd.-cktm. DM

| Qlvfi tt *l*lf*

I MeUh Malv it, H-nnam.-- I/'I'^h. ,1. /'Av».o'. Hd. r. Th. 2 J-l.
AN.. f..r hi«t..rv aud literature. Heyusiu* u. Campbell, Pfliiger • Arch.
8. 497.

240 BILIRUBIN.

red in man and carnivora, and more or less bright green in herbi-
vora. These colours are due to the presence of a pigment known
as bilirubin in the first case and biliverdin in the second ; but
since the latter pigment may be readily formed by simple oxida-
tion from the former, bile may frequently contain both these
colouring-matters and hence possess a colour intermediate to the
above though usually with a preponderance of either the golden-
red or green shade. In addition to these two pigments others
are occasionally present in bile, as evidenced by the fact that
while neither bilirubin nor biliverdin exhibits any absorption
bands when examined spectroscopically, fresh bile of herbivora 1
frequently does show bands, due to substances of which but little
is known beyond these spectroscopic appearances (see below). It
is possible that the bile-pigments of different animals may ulti-
mately be found to differ slightly but distinctly in their composi-
tion, much in the same way that the bile-acids as already stated
differ ; but as yet no such distinct differences have been made out,
and we may therefore treat of them as being identical from what-
ever source they have been obtained.

1. Bilirubin. C16H18N2Oa.3

It occurs chiefly and characteristically in the fresh bile of man
and carnivora, to which it imparts the well-known golden-red
colour. It frequently constitutes the larger part of some kinds
of gall-stones, more especially of the ox and pig, not as free bili-
rubin but as a compound with chalk, and amounting to some 40
p.c. of the concretions. (Maly.)3 It is also found in the urine
in icterus, also constantly in the serum from horses' blood, though
not from that of man or the ox,4 and frequently as crystals under
the name ' hsematoidin ' (see above) in old blood-clots (extrava-
sations) and fluids from ovarial and other cysts. Bile-pigments
are also stated to occur normally in the urine of dogs, more par-
ticularly in the summer.5

Bilirubin is insoluble in water and almost insoluble in either
ether or alcohol, though distinctly more soluble in alcohol than
in ether. It is on the other hand readily soluble in alkaline solu-
tions, hence its solution in bile, also in glycerin carbon-disulphide,

1 Bile of carnivora does not usually show bands until it has been treated with an
acid.

2 This is the generally accepted formula, assigned to this substance by Maly. ./».
f. prakt. Chem. Bd. civ. (1868), S. 28, confirming Staedeler. It is possible that the
formula is really twice the above, viz. C32H3~,N4O6, as required to represent the
formula of a well-defined tribromo-substitution product, C32H33Br3N406. This
doubling of the formula is also necessarv to express the derivation of hvdrobilirubin.
(C32H40N4O7) from bilirubin. Maly, Sitzb. d. k. Akad. d. Wiss. Wien. in. Abth.
Oct.-Hft. 1875. Liebig's Anna!. Bd* CLXXXI. (1876), S. 106.

3 See earlier Staedeler, Vierteljahrschr. d. naturforsch. Gesetl. Ziirich, Bd. viu-
1863, and Liebig's Annul. Bd. cxxxn. (1864), S. 323.

4 Hammarsten (Swedish). See Abstr. in Maly's Jahresb. 1878, S. 129.
8 Salkowski u. Leube, Die Lehre vom Harn, 1882, S. 246.

CHEMICAL BASIS OF TUK A MM A I. I'.oDY I'll

ami benzol, and above all in chloroform. Knun its solution in
the latter it may be separated out by extremely slow evaj-oratiou
of tin- solv.-nt in a crystalline form as rhombic plates or j.i
Tin- ;_reneral shape of these is shown above in Fig. 40 ; but as
obtained t'roiii solution in either carbon-disulphide or chloi
the crystal- usually exhibit somewhat blunt ends and slightly
e»nvex surfaces as first pointed out by Staedeler. A.s ordinarily

FIG. 41. BILIRDBIX CRYSTALLISED FROM CARBON-DISCLPHIDE. (Krukenberg.)

prepared it is an amorphous powder of the colour of sulphide of
antimony. It readily forms compounds with bases, e.g. sodium,
barium, and calcium, the latter providing a convenient means
i"i tin- separation of bilirubin from bile, urine, or other dilute

solution.

/-" i-i'tion. (i) When gall-stones are not available bile may
lie treated as follows.1 The bile is slightly diluted with water,
somw lime-water is added (avoiding excess) and after thorough
mixture, as by shaking, a current of carbon dioxide is passed to
convert all the excess lime into carbonate. The precipitate thus
formed contains the bilirubin as a calcium compound. This is
then collected on a filter, washed with water, and after suspe:
in a little water, decomposed by the addition of a slight excess of
acetic or hydrochloric acid. By this means the bilirubin is set

UK! may now be extracted by shaking with an excess of
chloroform. The chloroform solution is separated by decantation.
and evaporated to a small bulk; the bilirubin may then finally
be ] precipitated by an excess of alcohol. The amount thus ob-
tained is not «|uantitatively accurate, since all the bilirubin is not
precipitated by the lime at the outset and there is a further loss
during the subsequent operations, (ii) Since, as already stated,
the ^all-Mom '.s of the ox or pig may consist of nearly half their
weight of bilirubin combined with calcium, they provide the best

..M Iluppcrt. Arch. d. Ileill. IM. vm
S-vl.T. //./'..-A. ,/. i,li,i.<i.,:..r.,t/,. .-/,.,„. Awii. I *•*:», s. i>:,i> Cf Hilger, Artk. </.
I'fiarm. (3), Bd. vi. (1875). S. 385.

16

242 BILIKUBIN.

and simplest source for the preparation of this substance.1 The
stones are finely powdered, extracted with ether to remove any
cholesterin, then with water and treated with either strong acetic
acid or dilute hydrochloric acid. By -this means the bilirubin is
set free from its calcium compound, and after being washed with
water and alcohol is dissolved in chloroform, and finally separated
by precipitation with alcohol as already described. To obtain it
quite pure the dissolving in chloroform and precipitating by alco-
hol should be repeated several times. The final product is amor-
phous. Crystals are most readily obtained by slow evaporation
of the first and hence slightly impure solution in chloroform.

When carnivorous bile is exposed to the air it turns more or
less rapidly green ; this is due to its oxidational conversion into
biliverdin, the normal pigment of herbivorous bile. A similar
change is at once produced by an oxidising agent such as nitric
acid containing nitrous acid, but in this case the change of colour
does not stop short with green, but passes successively through
blue, violet, and red to a final yellow. These later colours are
due to products of the progressive oxidation of the first formed
biliverdin, but with the exception of the final substance (cholete-
lin) are as yet but imperfectly characterised. The play of colours
observed when either bilirubin or biliverdin is oxidised, consti-
tutes the well-known Gmelin's reaction.2 This is extremely
delicate and may be applied in either of the two following ways.
A few drops of the suspected solution are placed on a porcelain
slab and a drop of yellow fuming nitric acid is brought into con-
tact with it. A play of colours is observed at the junction of the
fluids if bile-pigments are present. Or on the other hand some
of the acid may be poured into the bottom of a test-tube and the
suspected fluid carefully added so as not to mix with the acid but
float on its surface. If bile-pigments are present coloured rings
(layers) appear at the junction of the two liquids, being yellow
nearest the acid and progressively red, violet, blue, and green
passing upwards. It is stated that this test will detect as little
as 1 part of bilirubin in 70,000 — 80,000 parts of solvent.

Other tests have been recommended, but they are perhaps un-
necessary in view of the extreme delicacy of Gmelin's reaction when
properly applied.3 The certain detection of minute amounts of bile-
pigments in urine is frequently of great clinical and physiological
importance. If any very appreciable quantity of the pigments are
present, Gmelin's reaction applied as above will \isually suffice to

1 The coloured residue from human gall-stones left after the extraction of
cholesterin (p. 131) may also be used for the preparation of bilirubin.

2 Tiedemann u. Gmelin. Die Verdauung nach ^7ersuchen, 1826, S. 80.

3 See more particularly Capranica, Gaz. chim. Ital. Vol. xi. (1881), p. 430.
Moleschott's Untersuch. z. Naturlehre, Bd. xin. (1882), S. 190. Ehrlich. Centralb.
f. klin. Med. 1884, No. 45, or Centralb. f. d. med. Wiss. 1884, S. 143. In the latter
case a solution of diazobenzosulphonic acid is employed, and is stated to discriminate
between bilirubin and other bile-pigments.

< 1IK.MICAL BASIS OF Till! ANIMAL BODY,

detect tin-in. If not they may be obtained in a more com-ei.-
residue, which has been largely freed by Hu|>]nTt's method from
other colouring matters which inti-rtn. with tin- test. The tluiil is
precipitated by lime-water and carbon dioxide. Tin- compound ..i"
lime and liilirnl.in is then collected .,n a tiller, \\a-hed and te-t,-d in
situ by the addition of fuming nitric acid; ,,r it may !>«• boiled in a
te>t-tube with a little alcohol acidulated with sulphuric acid; the pre-
cipitate l,.-.-- its colour and the •apernatant alcohol turns to a brilliant

-,'i-een. The following i- al-o a relialde tot as applied to urine.1 To
I'll ,.r .'!(» c.c. of urine add ."» to 1(1 c.c. of a •Oration ol xinr a
(!:.">). Tin- can-.-- a \ oliiminous precipitate of \, ile-pi<rmeiit>. espe-
cially if the acid reaction he >ome\\hat redu.-ed l>y tin- simultaneous
addition of a little sodium carbonate. The precipitate is co] ;
(.n a filter, washed with water, and dissolved in a little ammonia. If
bile-pigments are present tbe solution i- u-ually tliior.--c.-nt, and on
standing, if not at once, shows the absorption hands characteristic
of bilicyanin. (See below.) For further details (.f other methods
con-ult some special work.9

The accurate quantitative determination of bilirubin. as of
other bile. and also of urinary-pigments is only possible l.y
spectrophotometrio methods. These have l)ecn already brietly
described on p. 224. The requisite constants for the application
of the method in the case of each pigment are given in tin- litera-
tim • 1 1 noted below.3

r.ilirubin, while it exhibits no distinct absorption bands, is
< hara< tdisrd by u powerful absorption of the violet end of the
spectrum.

1'. Biliverdin. ('...H.^A-

This is, as aln-ady stated, the first product of the oxidation of

bilirubin. It gives the characteristic colour t<> tin- bile of lu-rbi-

vma. probably accounts for tbe colour of biliary vomit in caini-

\..ni iinaii), i- p<.--il>ly found in tin- urine in icterus, has l>een

stated to occur in the edges of the placenta in pregnant animals *

hitches , while on the other hand it occur- in m.-iv trace- in gall-

stones whether of man or other animals. It 1ms also M8D

•:l>ed as occurring in egg-shells6 and the integuinciits of

M invertebrates.0

Preparation. An impure product may be obtained a- follows
from herbivorous bile. After the removal of mucin (p. 76). barium

See Abst. in Malr's Jahretb. 1992, S. 226.

- N.-ul.aii.T ti. V. >£,.]. Amtl. <1. //<irnt, 1890, 8. 321 et teq.

• Vioronlt, !>>>• i/n"nt. SftetnUutalyM u. t. w. Tubingen, 1876, 8. 76. '/J. f.

13), S. |t,o. |M v (1S74). S. 21, 399. V<m\a», Arch. f. erp. Patkol.

M. xi. (is:

* Ktti. s,-«. MaU's ./<i/,/> s'.. 1871,8 MS, •

•'• l.i.-K.-rmaim. /'»-•. //. J. <•!„,„. '/.«//. I'.-l M. (l">l. S. f.Ol.
Vtrhnndi. ,1. /,/, i/.vil.-w. ,1. (1. It '>'. tu U .. \MI. (1883), a 109.

« Krukenbefg, Ctnlralb./. •!. »<"/ H'i«. 1883, 8. 785.

244 BILIVERDIN.

chloride is added ; this precipitates the pigment as a compound
with barium (?). The precipitate is then collected on a filter,
washed with water and alcohol, and decomposed with dilute
hydrochloric acid ; this liberates the biliverdin which is simultan-
eously precipitated as a fiocculent mass, and is then washed with
ether to remove all fat and dissolved in alcohol. The alcoholic
solution is finally filtered and by spontaneous evaporation yields
a dark-green glittering residue of impure biliverdin. To obtain
the pigment pure it must be prepared from bilirubiu. The con-
version may be effected in several ways.1 (i) Bilirubin is dissolved
in a dilute alkali and exposed for some time to the air in thin
layers, 'whereby it is slowly oxidised into biliverdin. When the
conversion is complete, the pigment is precipitated by the addition
of hydrochloric acid, thoroughly washed with water, dissolved in
absolute alcohol, and precipitated by an excess of water or by
spontaneous evaporation of the alcoholic solution, (ii) By en-
closing bilirubin solutions in tubes with glacial acetic acid and
heating to 100°. (iii) By the action of monochloracetic acid and
gentle heating at intervals for one or two days, (iv) Also by the
action of caustic potash on tribromobilirubiu.2

Apart from its colour biliverdin differs most characteristically
from bilirubin in its solubilities. It is (like bilirubin) soluble in
alkalis but insoluble in water and ether, whereas (unlike bilirubin)
it is insoluble in either chloroform, carbon bisulphide or benzol,
but readily soluble in alcohol and in glacial acetic acid. It has
further never been obtained in a crystalline form, and like bili-
rubin it shows no absorption bands but a somewhat strong absorp-
tion of the violet end of the spectrum. Treated with fuming
(yellow) nitric acid it gives Gmelin's reaction, starting now witli
a blue colour as a product of the first stage of its oxidation. It
also yields Huppert's reaction. (See above sub bilirubin.)

Like bilirubin the quantitative determination of biliverdin is
dependent upon spectrophotometric methods.3

The formula assigned above to biliverdin represents its forma-
tion from bilirubin by simple oxidation.4 This is undoubtedly
correct as against the older view of Staedeler that the change
consists not only in the assumption of oxygen but also of a mole-
cule of water.

Bilifuscin, bilihumin, and biliprasin ars the names given by Staede-
ler to ill-defined and probably impure products obtained during his
investigations on bile-pigments as obtained from gall-stones. Bili-
prasiu is apparently only impure biliverdin (Maly).

1 Maly, Sitzb. d. k. Akad. Wien, Bd. LXX. 3 Abth. 1874. Juli-Hft.

2 Maly, Ibid. Bd. LXXII. 3 Abth. 1875. Oct.-Hft.

3 See references sub bilirnbin.

4 Maly, loc. cit. Thudichum, Jl. Chem. Soc. July, 1876.

CHEMICAL BASIS OF THK ANIMAL i;«»DV. 245

3. Bilicyanin.1 (Cholecyanin, Choleverdin.)

Tliis is tin- sul istance which results from the oxidation of bili-
verdin and is the cause of the blue colour ..li-ened \vh.n l.jl<- is
treated with fuming (yellow) nitric acid as in (Imdin's n-u. -lion.
It has not as yet been isolated either in sufficient quantity, and
still less in a condition of suflieieiit purity, tn admit of such a
chemical investigation as would lead to the determination .
composition. But by analogy with the known relationship of
liiliverdin to bilirubin, and from the evidence afforded by the
composition of choletelin (see below ) into which hilicyanin may
idily converted by further oxidation, hilicyanin will probably
be found to differ from biliverdin -imply by the addition of oxygen
to the molecule of the latter.

Preparation. Bilirubin is dissolved in chloroform or suspended
in alcohol and slowly oxidised either by gradual addition (,f l.p.-
mine or fuming nitric acid; as soon as the mixture is of a bright
Line colour, the bilicyanin is precipitated by an BXCen ot' v

As thus ohtained it is insoluble in water, almost in.-oluhle in either
ether or chloroform, but soluble in alcohol and alkalis. In
ence of alkalis it is still almost insoluble in either ether or chloro-
form ; in presence of acids it is now scarcely soluble in water, but
soluble in ether and chloroform.

r.ilicyanin i- for practical purposes characterised solely by its
marked absorption spectrum. This consists of three Lands.— one
on cadi side of J), that to the red side of D liein^ the darkest, and
one between /< and /•'. The latter is probably identical with tin-
band seen in acid solutions of choletelin and due to the produc-
tion of this substance in small quantity during the oxidation of
bilirubin. The position of the hands varies somewhat according
to the solvent employed and as to whether the solution is acid or
alkaline.

Durinu' the application ..f Cm.-lin's test f..r l.ile-pi^ ..... nts tin- Mm-
due t.» liiliryuiiin is L.rdered l.y a \ i<det ci.l..ur and tin- l-y a n-«|. tin-
final and pennaiient c«d"iir l.einjj yellow. ( M" these three the first is
ii-.t as yet kn-.wn t«i In- definitely due 1.. ..nc s|..'.-ilic siil. stance; it is
ni..st |. rnl.al.lv the result «.f a n;i\tur« of the blue of Lilicyauiii \\itli
tin- red .,f the next pr..«Iurf. The r. d <-..!. ,ur i- ..n tl ..... tln-r hand
.siipp..seill\ due t<> a definite pi^uieiit s. mi. •linn- called l»ilipur|iurin.
..I' which li«. \ve\er IK. tiling definite i- a> yet kimwn. 'I'll.' yell-.w
iiiarks the final t'»nnat inn <>f cli.det.din.

I CholeteHn. (V.H.-NW

This is the final product ..f the oxidation of bile-pi^ment-
dily obtained l.y siis]M-ndinur l-iliruhin in alcohol .::

1 Hoynsins n. C.iin|.l.o]1, I'H.i-. :>26. x. lt«75, 3. «4«.

gives lilrraturv «.f this ami ..tlicr l.ili- ]>i-4iiients.

246 HYDROBILIRUBIN.

ing it by passing the fumes of nitrous acid into the mixture. As
soon as the play of colours is complete and the solution is of a
pure yellow colour, it is poured into a large excess of water, from
which on more or less prolonged standing choletelin separates out
as a flocculent mass, which if washed and dried yields a brown
powder.1 It is readily soluble in alkalis, as also in either alcohol,
chloroform, or ether, but least so in the two last solvents. None
of the solutions exhibit any fluorescence even after the addition
of zinc chloride. In this it differs markedly from urobilin, a well-
known yellow urinary pigment. The above statements scarcely
provide any certain means of identifying choletelin as a chemical
substance, and no specific test for it has as yet been described.
Neither is it quite certainly characterised by its absorption spec-
trum, so far at least as any specific bauds are concerned. Indeed
there has been very great difference of opinion as to whether it
ever gives any band at all, and if it does, where this baud is situ-
ated. With our existing knowledge it seems safe to say that in
alkaline solutions choletelin shows no absorption band, and that
in acid solutions a band may be, and frequently is seen, lying be-
tween b and F. The uncertainty as to its spectroscopic properties
led some of the older observers 2 to regard choletelin as identical
with hydrobilirubin (urobilin). This view is however quite un-
tenable both as the result of purely chemical investigations 3 and
of spectrophotometric determinations of the optical properties of
the two substances.4

5. Hydrobilirubin. C32H40N407.

When bilirubiu is dissolved in dilute caustic potash or soda or
suspended in water and treated with sodium-amalgam in succes-
sive portions, air being at the same time carefully excluded, it is
observed that at first no hydrogen is evolved ; the dark-coloured
solution becomes gradually lighter in colour and more transparent,
until at the end of two or three days it is bright yellow or brown-
ish-yellow, and now hydrogen begins to come off from the mixture.
At this stage the supernatant fluid should be poured off from the
metallic mercury which has accumulated, and if it is now acidu-
lated strongly with either hydrochloric or acetic acid, it yields a
more or less copious flocculent precipitate of a dark reddish-brown
colour. This precipitate is impure hydrobilirubin. It is purified
by being redissolved in ammonia, reprecipitated from this solution
by the addition of acid, and finally washed with water. At first

1 Maly, Siiz. d. L Akad. d. Wiss. Wien, Bd. LVII. (1868), 2 Abth. Feb.-Hft. LIX.
(1869), 2 Abth. Ap.-Hft.

2 Heynsius u. Campbell, foe. cit. Stokvis, Centralb.f. d. med. Wiss. 1873, S. 211,
449.

3 Maly, Ibid. S. 321, and more particularly Liebermann, Pfliiger's Arch. Bd.
XI. (1875), S. 181.

* Vierordt, Zt.f. Biol. Bd. x. (1874), S. 399.

CHEMICAL BASIS OF THE ANIMAL liom

during the washing a considerable amount of the sub-tan' e passes
into solution. Inn as tin- merely adherent salt-
it becomes !.--> and less soluble in water until at la-t it is almost
insoluble When dried it takes tin- form of a dark ivddish-bro\vn
amorphous j.owdt-r, which is ivadily >'«lublc in alcohol andchl«>i"
form, and but sparingly soluble in pun- ether. It is also
soluble in alkaline solutions, to which it impart- a yellow colour
a- <if normal urine: when acidulated the >.. Unions turn red.1

The acid solutions of hydrobilirubin show a marked absorption
band between // and /-'which becomes fainter if ammonia i- added
until the reaction is alkaline. But on the subsequent addition of
a few drops of a solution of zinc chloride, the band reappear-
with usually increased intensity, though shifted slightly towards
the violet end of the spectrum.2 This alkaline solution to which
the /inc salt has been added also shows, in marked distinction
to the acid solutions, a brilliant fluorescence which is most ob
teristic of the substance, being of a bright rosy-red colour by
transmitted, and bright ureeii by reflected light.

Previously to the discovery of hydrobilirubin by Maly, a well-
cliaracterised urinary pigment had been isolated and described by
under the name of urobilin (see below), while about the
same time that Maly's work was carried on, a pigment had
obtained from teces and described, under the name of stercobilin,
as identical with urobilin.3 Careful comparison by Maly of his
hydrobilirubin with urobilin led him to assert the complete iden-
tity of the two substances. This view has been n rally

adopted, and is probably correct as a broad statement
There are on the other hand several observers who have expi
themselves against the exact identity of these subsln Their

views are however based on comparatively slight and inooodnUTQ
spectroscopic differences between the natural and artiticialh
pared substances and on other differences, such as of the intensity
of their fluorescent activity, which are still less conclusive. For the
:it the evidence of close relationship if not of absolute iden-
tity sullices fully as a basis for our belief in the genetic relation-
ship of the bile and urinary pigments and of the ultimata
derivation of these from the colouring-matter of the blood

I Miring his earlier researches on the pigments of bl«" :
Seyler described a product resulting fn-m the reduction of li
tin in acid solution by the action of zinc and hydrochl.>ri

' Maly, Cntralb.f. d. med. Wiu. 1871, 8. 849. A**al. d. rh,m IM 163 (187*)

- Vi,.r..r.Jt. /.! t\ /Hoi. Bd. ix. (1873), S. 160. Sec lator 'Quantitative Spectral-
aiialv.-e.' ls;r,, S. 99.

3 Vanlair a. Maria*, Centralb.f d. mrd. \\'i»». 1871, 8. 369. Cf. J»ff<?. /
M5

« See MacMnnn, Clinical Chrmittr,, of I'nn*. |K«'J. p. 105, or J!
Vol. x. H-- ill ii.--«'f«:irv r-furence*. But M Afatost DitqM

see also Malv. I'tiiiger'n An-l,. \',<\ \\ .(31.

248 ORIGIN OF BILE-PIGMENTS.

characterised by one absorption band between b and F and, as he
then said, two other bands.1 After the appearance of Maly's work
he was led to suspect that the substance he had previously de-
scribed was in reality identical with hydrobilirubin and therefore
with urobilin, a conclusion which he verified by a careful repeti-
tion of his earlier experiments.2

More recently Nencki and Sieber have prepared a similar pigment
by the action of hydrochloric acid and zinc on their haematoporphyrin,
to which latter substance, as was stated above, they assigned a formula
identical with that of bilirubin. They state however that the pigment
(urobilin) is not quite identical as obtained on the one band by the
action of nascent hydrogen on bilirubiu, and on the other hand on their
hsematoporphyrin. 3

Assuming then the identity of these substances we have in
Hoppe-Seyler's work the best and most direct chemical evidence
of the relationship between the colouring-matters of the blood
and bile. For if one and the same substance, viz. urobilin, can
be prepared by the same means, namely reduction (hydrogena-
tion) from both haematin (haemoglobin) and bilirubin, these two
substances must be themselves closely related. It has not how-
ever as yet been found possible to produce a bile-pigment directly
from haemoglobin or haematin by any artificial process outside the
animal body. The derivation of the urinary pigments (urobilin)
from those of bile presents no difficulty when it is remembered
that a not inconsiderable quantity of hydrogen is present in the
gases of the intestine (§ 282) which may be accounted for by
(butyric) fermentative processes (p. 105), and that this hydrogen
might in its nascent state readily produce the simple change
which is known to occur when bilirubin is converted into
hydrobilirubin or urobilin. And here it is interesting to note
that hydrobilirubin is readily absorbed and excreted in the
urine either when placed in the alimentary canal or injected
subcutaneously.

The question of pigmentary relationships to which reference
has just been made suggest the present as a convenient place to
enter into further details on the now undoubted but once dis-
puted derivation of the bile-pigments from the colouring-matter
of blood (see § 477).

The starting point for this view was the discovery and descrip-
tion of haematoidin crystals by Virchow (see p. 239) as occurring
411 old blood-clots in parts of the body remote from the liver and
in which it was inconceivable that they could have arisen by any
process other than a gradual formation from the pigment of the

1 Med.-chem. Untersuch. Hft. 4, 1871, S. 536.

2 Ber. d. d. chem. Gesell. Bd. vn. (1874), S. 1065.

3 Monatsh. f. Chem. Bd. ix. (1888), S. 115; Arch. f. exp. Path. u. Pharmakd. Bd.
xxiv. (1888), S. 430.

CHEMICAL BASIS OF THK ANIMAL I'.nhY.

red corpuscles, followed as this was by proofs of the iiK-nt;
lia-matoidin and hilirubin. This was followed l by experiments
on the injection of bile-salts into the blood and an accompanying
output of bile-pigments in the urine, to which the true signifi-
cance was subsequently attached by Kiihne, namely that the
pigments arose from a conversion of hieuioglobin set free from

"i-puscles under the solvent action of the bile-salt?. This
he continued by injections of lueinoglobin in solution.2 These
views were however opposed on the basis of similar experiments
in which it was stated that either no bile-pigments appeared in
the urine as the result of injections of haemoglobin into the vas-
cular system, or that if they did, they were due merely to an ac-
cumulation of that small amount which is frequently present in
the urine of dogs.3 But the careful subsequent experiments of
Tarchanoil', in which he endeavoured to avoid many obvious
sources of error present in those of Naunyn and Steiner, are
more usually regarded as having afforded detinite and conclusive
confirmation of the earlier views.4 This observer further found
a considerably increased amount of bile-pigments in the bile col-
lected during the experiments, and came to the conclusion that
the conversion of blood- into bile-pigments takes plan- in the
blood-vessels, a part being excreted in the urine, while the. !
part passes "lit in the bile. He showed in confirmation of earlier
experiments 5 that the liver is extremely active in excreting bili-
rubin injected into the blood-vessels; practically the whole of it

s out in the bile.6 The relationships thus indicated receive
further confirmation from the observation that in many patho-
logical conditions .>!' the horse, bile-pigments ate « Mpmi-ly found
in it- tissues and transudations. accompanied by blood-pigments.
and that solutions of hamoMlohiu when injected into the snh-
eutanei.us tissue of this animal become after a t> \\ tially

<•. ni verted in situ into granules and flakes whirl i are of a yellow

jange colour and yield an intense (imelin's reaction."

Finally by the action of phenylhydra/.in on ha matin and on
bilirnbin products are obtained which in each case exhibit a
similar and marked play of colours under the action of fuming
(yellow) nitric acid.8

1 Froriclis n. Stno.lHrr, Miillor'* Ardi. .lahrir 1-

- Vir.-i...w's Arck. r.

• • 1 •,. f. Annt. u. Pkfltiol. .!:.!. •

S. ir.O. Contain full rff.-n-iK-i-s tu all tli"ii i-xi-tiiiL' literatim-
« 1 Id. IX. (!-:»). Sn. -VI, 329.

| \..MitU. AT*.

''l,,,rm<dnl. IM. M (181

l.-hiiaiin. /•••'•/ l'"l KT. (188J "» «M <he

next r.-f.-rc-n.-r! 1M Jtxvn

T Lat»chenberg( !'.-!. I. (1886). - r H*nat*. /. CKtm.

U<\. iv

* Fil.-l.iio. V.rhnwl. d. Congreuei f. IHM. .'/../ H • • U- f "i Ctntralb. /
klin. M,,l.

250 ORIGIN OF BILE-PIGMENTS.

One point still remains for discussion. It has been seen that
bile-pigments can be formed from those of the blood in outlying
parts of the body without the intervention of the liver. Are we
therefore to suppose that the liver is similarly inoperative in that
increased formation and excretion of bile-pigments, both in the
urine and bile, which result from the intravascular injection of
haemoglobin ? Opinions have differed on this point. It is on the
whole more probable that the liver is in all cases the chief factor
in the conversion. The normal production of bile-pigments is
entirely due to hepatic activity, for no pigments are accumulated
in the body after extirpation of the liver in frogs or its exclusion
from the circulation in birds.1 This accords with the fact that
apparently the larger part of the pigments resulting from the in-
jection of haemoglobin pass out in the bile while but little goes
into the urine. If this is so, how shall we account for the excre-
tion of the latter and smaller portion by the kidneys ? It is
known that the liver is peculiarly liable under the influence of
but slight operative and other influences to pass some of its pro-
ducts over into its lymphatics whence they make their way into
the blood-vessels and may hence be excreted by the kidneys.
Very slight obstruction of the bile-duct suffices to produce this
result, and it has been observed that the bile formed after injec-
tions of haemoglobin is unusually viscid. The views here put
forward (see also § 477) are further in complete accord with the
facts that hsematin (haemochromogen) readily loses iron and
yields hsematoporphyrin C32H32N405 which differs but slightly in
composition from bilirubin (Ci6Hi8N203)2, and that it is precisely
in bile and very largely in the liver that we meet with consider-
able quantities of iron in some as yet not well-known form.2
The possible function of the spleen as an organ in which a con-
siderable disintegration of red corpuscles takes place, in providing
the material requisite for the formation of bile-pigments by the
liver has been already discussed 3 (§ 478).

As already stated herbivorous bile, as of ox and sheep, frequently
shows absorption bands even when fresh. These are regarded by
MacMunn as due to a substance to which he has given the name
cholo-hsematm since it occurs in bile and, as the action of sodium-
amalgam shows, is related to hsematin. The bands more usually seen
are three, two near D and one near £J.*

1 Stern, Arch. f. exp. Path. u. Pharm. Bd. xix. (1885), S. 39. Minkowski u.
Naunyn, Ibid. Bd.'xxi. (1886), S. 1.

2 Zaleski, Zt. f. physiol. Chem. Bd. x. (1886), S. 453. See also Virchow's Arch.
Bd. civ. (1886), S. 91.

3 According to Schafer, Proc. Physiol. Soc.. 1890, No. 3 (see Jl. of Physiol. Vol.
XL), there is no evidence of any discharge of haemoglobin from the spleen in the
blood of the vein of this organ.

* Jl. of Physiol. Vol. vi. (1884), p. 24.

CHEMICAL BASIS til' TIIK ANIMAL UuDV.

THE PICMKNTS 01 1 KINK1

When fresh normal urines are examined Bpectrophotometrically
it is found that the extinction c..ettiei.-nt> (ao
given portion of the spectrum of the several thuds d.. n..t 1
constant ratio each to the other. If the urines contained duly
one colouriiig-suKstance, then no matter how much -lute

value of the extinction coefficients varied for diilm-m regions of
tin- spectrum, their ratios would be constant for any given region.
From this it appears probable at the outset that even n.
urine is coloured by at least two if not more pigment-.- < MM
knowledge of these pigments is at present impeiteet and n!
limited to that of one substance, namely urobilin, and even with
respect to this one, considerable difference of opinion exists as to
its nature and relationships to the other laments of the body
fr<>m which it is supposed to be ultimately derived. The reasons
for this are simple. It is extremely probable that normal urine
is often coloured by some chromogenic mother-substance (cf. /.y-
mogens) rather than by the fully formed pigment. In the n.-\t
place, since the colouring-matters are normally present in but
very small amount, and since they are not known to In- eiy-t.il-
lisahle or to form definite compounds with well-known precipi-
tant s. they have not as yet, with the exception perhai
uroliilin, been obtained either with any guarantee of their purity
or in quantities sufficient to admit of ultimate analy-i II
our knowledge of them is chiefly based upon their spectrose«j 'it-
properties. They are further most probably far from stable sub-
stances, so that they may undergo some considerable < 1
either by mere exposure to the air (oxygen) or as the result of
the various and often different methods of extraction and pi.
tinn employed by various authors. This, together with the fact
that the position of the absorption band ..mewhat

with the reaction of the solution and the nature of the solvent,
counts with but little doubt not only for th- extremely nu-
merous and insufficiently characterised pigments which h.-
one tini" or another been obtained from urine, but also for much
of the rontliet and confusion of opinion which exists as to t;
ture and relationships of those pigments of which we
with most confidence.

1. Urobilin. CMH40N407. (?)

This, the best known and most definitely characterised ot
urinary pigments, was first described by Jaffa* who regarded it as

r rffi-ronc-os to tlm |.rinci|i.il earlier works on urinary pigment* we TMn<
,7/vM"/. C/i'm. H.I. xi. (I**7).S. 537, and for all detail* ..>n«itlt N,-n>

\nt1 i \ l«90.
ii-rordt, Die i/unntit. $i»rtmlanalytc, 1876, 8. 78.

252 UKOBILIN.

the chief colouring-substance of normal urine, while present in
much larger amounts in the urine of fever.1 He also obtained it
occasionally from bile, the name urobilin thus indicating its double
source. In fresh normal urine the amount was frequently ex-
tremely small, but was observed to increase on standing exposed
to the air (oxygen), a result due to the probable presence in the
urine of some chromogen or mother-substance (urobilinogen)2 of
the urobilin. The amount of this pigment in urine is too small
to provide adequate material for an elementary analysis, so that it
was at first characterised by its solubilities in various fluids, by
the strongly-marked fluorescence of certain of these solutions
and more particularly by the absorption-spectrum it exhibited.
The subsequent preparation of hydrobilirubin from bilirubin, and
the establishment of its identity with urobilin (p. 246) provided
for the first time a mass of the substance sufficient to admit of
analysis, and upon this the formula given above for urobilin is
based. It must not however be forgotten that the identity of
the two pigments is disputed by several observers, although the
balance of belief seems as yet to support it. It will conduce to
clearness if we incline for the present to this belief and describe
the preparation and properties of urobilin as given by Jaff'^, on
the assumption that it is identical with hydrobilirubin, and then
subsequently give a short account of the opposing views.

Preparation from urine. Several methods may be adopted ; of
these only the broader facts can here be given, but they suffice
to provide solutions which exhibit the characteristic spectra,
(i) When urine contained much urobilin Jaffe' precipitated it by
the addition of chloride of zinc in presence of an excess of am-
monia ; if but little, then by the addition of basic lead acetate.
These precipitates were then worked up by processes which do
not admit of a suitably brief description.3 (ii) Precipitate the
urine completely by the addition first of normal lead acetate, then
of the basic acetate. Wash the precipitates, dry at low tempera-
ture, and extract with absolute alcohol (not methylated spirit)
acidulated with 1 — 2 p.c. of sulphuric acid. This extract may
be then diluted with water and the pigment extracted by shaking
up with chloroform, in which it is readily soluble.4 (iii) The
urine is acidulated with 0*2 p.c. of sulphuric acid and then satu-
rated with neutral ammonium sulphate. The precipitate thus
obtained is then collected on a filter, washed with an acidulated
saturated solution of the ammonium salt, freed by pressure from
adhering fluid, and dissolved by gentle warming in absolute alcohol

1 Centralb. f. d. med. Wiss. 1868, S. 243; 1869, S. 177. Virchow's Arch. Bd.
XLVII. (1869), S. 405.

2 For further references see Xeubauer u. Vogel, Anal. d. Harris. 1890, Sn. 331,
336.

3 For details see Neubauer u. Vogel, he. cit. S. 334.

4 Mac Munn, Proc. Roy. Soc. pp. 26, 206. Jl. ofPhysiol. Vol. x. (1889), p. 71.

( 11L.MICAL BASIS OF THK ANIMAL BODY.

t<> which if nei.'e»>ary ;i few drops of ammonia have been ad
(iv Kiv4iiriit.lv from normal urine, the in- ly if that he

highly coloured. a solution of urobilin may In- obtained by -imple
agitation with chloroform, or by gently shaking it up with half its
volume <>f fare ether free from all traces of alcohol. Th«- »-th«-r
is then removed l.y a separating I'mimd. «-\ ;ip,, rated at ordinary
temperatures, and the residue dissolved in a small quanti1
absolute alcohol.3

If the alcoholic or chloroformic solutions above descril»-<i
evaporated to drvness at a low teni]>erature, the urobilin remain*
as a yellowish-brown amorphous pigment, which i- pra« tieally
insolulde in water except in presence of small amounts of neutral
salts, very slightly soluble in either ether or ben/ol. readily soluble
in alcohol and in chloroform. The neutral alcoholic solutions if
dilute are yellow with a rosy tint, and if strong show a ;_
tluore>crnee. The acid solutions are reddi>h-yello\v, or if dilute
bright rose-coloured and do not fluoresce. Alkaline (alcoholic)
solutions are yellow or yellowish green according to the concen-
tration and usually show a marked fluorescence, which is much
increa>rd on tin- addition of a solution of x.inc chloride, ap|*-ai-
ing now rose-coloured by transmitted light and brilliant green
by reflected.

S/»rf,-" of urobilin. Neutral or alkaline alcoholic solutions
show one absorption band between b and /'. In alkaline solution
the band i< frequently very faint, but is more strongly m
after the addition of zinc chloride, so much so that it can
only hi- distinctly seen after the addition of this salt In
solutions a similar band is seen, situated however in this case
iitly more toward-* the violet end of tin- spectrum.

The methods given above for the preparation of urobilin, indi-
mfficiently the procedure requisite f,,r its d.-tection in sol u-
tioii*. A^ already stated (p. 246) the ].ositi«m «»f the abeorption
band of urobilin is very similarly situated to that of choletelin
un.l.-r d-rtain i-omliti.ins. The conflict of opinion as to the identity
of the two substances has been dealt with above.

It now remains to -jive a short account of the more recent views
on urobilin and its relationship to other pigmentary substances to
which ivferenee has already been made.8

Mac Miinn di<tingui-hes between two forms ef urobilin
normal and febrile or pathological. They are both obtained from
mine by the same method (see above) and differ as follow*

i M. 1m. ./..urn. d. pharm. el >l' rhim. T. xsvm 159. ThU method b

go<xl, aa avoiding to a considerable extent any alteration of the pigmttB

1,1-. "•••-< finii'ive.

Salkowski, 7* f. phvuiol. Ch,m. Bd. iv. (1880), S
• u- Munn. Clinical t&m. nft'rw. 1«89, p. 104. Gires all nectary
For spectra see Jl. ofPhyiiot. Vol. x. (1889), p. 116.

254 UEOBILIK

(i) Normal urobilin. In acid alcoholic solution it shows one
absorption band, close to and enclosing F: this band disappears
when the solution is neutralised by alkalis. If treated with zinc
chloride in presence of ammonia this band is replaced by one
narrower and nearer the red end of the spectrum, while at the
same time a green fluorescence is observed, but much less marked
than in the case of febrile urobilin. (ii) Febrile urobilin. The
solubilities of this substance are the same as of the preceding
form. On the other hand the band at F is broader and darker
than is that of normal urobilin, and further in an ethereal acid
solution two other bands may be seen, one adjoining D towards
the red, the other mid-way between D and E. These last two
bands are invisible in urine. By prolonged .action of sodium
amalgam on an alcoholic solution of normal urobilin, fibrile urobi-
lin is obtained. The spectrum of normal urobilin is the same as
that of choletelin, but the substances differ with respect to the
greater ease with which choletelin may be reduced to febrile
urobilin. Normal urobilin is regarded as differing from hydro-
bilirubin, the evidence being deduced from spectroscopic obser-
vations. Febrile urobilin on the other hand is identical with
stercobilin and is apparently the pigment to which the absorption
spectra of the bile of some animals is due.1

In concluding this account of urobilin and allied substances it
may be well once more to draw attention to the fact that the
differences of opinion among the various observers is based almost
entirely on spectroscopic appearances. These are far from conclu-
sive for there is no guarantee that in any given case the solution
under examination contains only one pigment. It may contain at
most a preponderance of this one but frequently mixed with other
pigments which are derived either from the fluid originally oper-
ated upon, or are decomposition products resulting from the action
of the reagents employed.2 The final solution of the questions
raised above will only be supplied by a purely chemical investiga-
tion of the several substances under discussion ; such an investi-
gation would however be one of extreme difficulty.

Thudichum considered that normal urine contains only one pigment,
which he called urochrome.8 Maly regarded this as the same as urobi-
lin.4 More recently Thudichum has upheld his former views.6

1 Mac Munn, The Spectroscope in Med. 1880, p. 156. A tabular conspect of the
above statements is given by Halliburton, Chem. Physiol. and Pathol. 1891, p. 752.

2 Thus Vierordt has shown that if the urinary pigments are precipitated by the
acetates of lead and extracted from this by absolute alcohol acidulated with oxalic
acid, the coloured solution thus obtained possesses optical properties quite different
from those of the original urine ; a result which indicates that the pigments have
been considerably changed during extraction. Die quantitat. Spectraianalijse, 1876,
S. 96.

8 Brit. Med. Jl. No. 201, 1864, p. 509.

4 Liebig's Ann. Bd. CLXIII. (1872), S. 90.

6 Jl. Chem. Soc. Ser. 2, Vol. xm. (1875), pp. 397, 401.

CHEMICAL BASIS OF Till-; ANIMAL BODY. 255

_. Uroerythrin.

This is a pigment of which but little is known. It i- r. _
as ih.- colouring-substance of certain bright-mi (pink) ui
deposits and as possibly occurring in the highly coloured urine's
of rheumatism, \-c. It appears to be an amorphoiu reddish sub-
stance, with an acid reaction, slowly soluble in either water,
alcohol, or ether.1 Treated with caustic alkalis it turns green',
more particularly when in the solid form. In alcoholic solution
obtained by boiling pink unites with alcohol it shows two ill-
d;-tined absorption bands between D and /'.-

3. Urohaematoporphyrin.

This pigment was first described by Mac Munn (under tin- iiame
of orohaematin) as occasionally occurring in certain pathol.
urines as of acute rheumatism, Addison's disease, &c. and to it he
Lrave the present name from certain resemblances of its spectra to
those of ha matoporphyrin.3 It is obtained from urine by the
method employed for the separation of urobilin, or artificially by
the action of reducing agents on ha?matin, this being tin- suj
source of its origin in the body. It is soluble in either ale«.h..l.
cthtT, benzol, or chloroform. In acid alcoholic solution it shows
thn-c absorption bands, one narrow adjoining D on the red side of
this line, one half way between D and E, and one between I and
/' clo>el\- resembling the band of urobilin. There is also occa-
sionally a fourth very faint band between the first two bands
described above. In alcoholic solution made alkaline by ammonia
it yields a spectrum closely resembling that of ha>matoporphyrin
(see above p. 238). But unlike the latter substance its solutions
show a very faint green fluorescence on the addition of xine
chloride and ammonia. The oeeurrence. of ha-matoporjihyrin in
urine has been frequently recorded4 and from the >].ectro>c.ipie
appearances described above, some observers are inclined to the
view that urohrematoporphyrin is not a single substance but a
mixture of luematoporplm in with some pigment closely resem-
bling urobilin.

Uroh»matoporphyriD is perhaps closely rrlat<-,l t.» t\\.» ;
known as m-Mn!l.r..lia-m:itin and urofusc'>ha-mat in obtained from a
case of leprosy* (Mac Munn).

' Hi-IW. ill Ins .\rrhlv. (2) K.I. If]

- M:i.- Mum.. / •! UXT. (1883), pp. 13S, 870.

» .//. ../ /'/,,/>"-''. V..N. N i. (1HH4), p. 3fi ; X. (IH- •

Sdkowdd, Zt. /: /./,.,>„.:. <•/„„, \\,\ xv. (1M1).& 2M.
in tin- caaea examined some evidence tli..i tin- ... .ur- <-rn»U>-

in tho urine was perhaps not unconnected with tin* a<iminurtration of

.

niKt.irk. I\T. d. ,1. rh.m. <;, *• /.' I'.! MI (1874), ^ ii:<» l(tliig«r'« Arc*.
1M. i\ ( 1>74). S. 568. Cf. Hoppe-Seyler, Phytiol. Ckem. 1879, 8. 875.

256 HUMUS PIGMENTS. UKINAKY MELANIN.

4. Humus pigments.

When carbohydrates are treated with acids or alkalis, among
the numerous products which arise are certain pigmentary bodies
of a more or less dark -brown colour. A similar colouration is
well known as occurring in fruits when bruised or exposed to
the air,1 and generally in decaying vegetable tissues. These sub-
stances are known under the name of ' humus.' When urine is
treated with acids in presence of oxygen it acquires a markedly
darker colour, and since carbohydrates in small amount are prob-
ably present in all urines,2 there is at once a possibility that some
at least of the observed colouration is due to the production of
humus-pigmented substances by the action of the acids on the
carbohydrates. In accordance with this view certain so-called
humus pigments have been prepared from urine, but our knowl-
edge of them is as yet very incomplete. They are stated to be
practically insoluble in any solvents other than amyl-alcohol,
strong ammonia, and caustic alkalis : the solutions show no
absorption bands when examined spectroscopically. They are
further said to account for the usually dark colour of normal
herbivorous urine and of urine after the cutaneous absorption
of carbolic acid and several other aromatic compounds.3

It is very probable that several dark-coloured pigments such as the
uromelanius of Flosz and Thudichum obtained by the action of acids
on urinary pigments or chromogens are allied to if not identical with
these humus substances.

5. Urinary melanin.4

Certain tumours are not infrequently observed which from
their extremely dark pigmentation are spoken of as ' melanotic,'
the colouring-substance being known as melanin.5 The urine of
patients suffering from these tumours is either dark-brown or
black when voided, or speedily assumes this colour after brief
exposure to the air or by the action of nitric acid or other oxidis-
ing agents, the pigment to which the colour is due being ap-
parently identical with that present in the tumour. This action
of oxidising agents indicates that here also, as in the case of
other urinary pigments, there is primarily some chromogenic
forerunner (melanogen) of the actual pigment. This chromogen

1 Hoppe-Seyler, Zt. f. phi/siol. Chem. Bd. xin. (1889), S. 66.

2 SeeWedenski, Ibid. S/122. E. Salkowski, Ibid. S. 270.

8 Udranszky, Ibid. Bde. xi. (1887), S. 537, xn. (1888), S. 33. Contains very full
references to other works.

* Morner, Zt. f. physiol. Chem. Bde. xr. (1887), S. 66, xn. (1888), S. 229. Gives
list of literature to date. See also Zeller, Langenbeck's Arch. Bd. xxix. (1884), S. 2,
and later Brandl u. Pfeiffer, Zeitsch.f. Biol. Bd. xxvi. (1890), S. 348.

5 The name melanin is more usually applied as a generic title for the dark-
brown or black pigments such as occur in the hair, epidermis, retinal epithelium,
choroid, &c.

CHEMICAL BASIS OF THE ANIMAL l,«»I)i

may be partially precipitated from the urine by baryta water ;uul
completely by normal lead acetate. When tin- latter pre< ipitate
•j. ended in water and decomposed by sulphuretted hydrogen,
•Ids a colourless solution \vhii-h when evaporated to di\
9 a dark amorphous residue insoluble in water, ether, cold
alcohol. acetic acid, and dilute mineral acids. The fully formed
pigment may, like its chromogenic forerunner, be partially pre-
cipitated by baryta water, the remainder being pivcipitable by tin*
subsequent addition of normal lead acetate. The baryta precipi-
tate contains the larger amount of the pigment, and bom it the
colouring-matter may be more easily obtained than from the
precipitate with the lead salt, since the latter carries down other
urinary pigments at the same time. The isolation of the urinary
melanin in a pure form from the baryta compound admits nf no
suitably concise description ; it must suffice here to state that an
impure product is obtained by decomposing the compound with
sodium carbonate assisted by gentle warmth and precipitating the
pigment from the resulting solution by a slight excess of sul-
phuric acid. The product when purified is partly insoluble,
partly soluble in acetic acid of 50 — 75 p. c. Of these portions
the former when dried is a brownish-black amorphous powder,
insoluble in either water, alcohol, ether, chloroform, or dilute
(mineral) acids, but readily soluble in alkalis. The lattei
obtained in too small amounts to admit of complete investigation.
(in analyst the pigment was found to contain iron (*2 p. <•.)
and a considerable amount of sulphur (9 p. c.) and not to
show any absorption bands when its solutions were examined
spectroscopically.

Tliis pigment appears to be identical with one previously il.-rribed

under tin- name of phymatorhusin as obtained from nu-laiiotic tum-.ui>,
and el.'>ely allied to hyppoiuelauin obtained from similar tumours of
tin- horse'.1

When melanotic urines are treated with solutions of ferric
chloride, they yield, according to the concentration of t!
agent, either a dark-brown cloudiness or else a black precipitate
soluble in excess of the precipitant: this test is both delicate and
characteristic. Further when to these urines a dilute solution of
sodium nitroprusside and some caustic potash is added tli°
(pientlx show a pink or red colouration which turns blue on tin-
addition of acids, owing to the formation of Prussian him-. The
latter reaction is not due to the melanotic pigment but to some
other substance simultaneously excreted.*

1 IS.-r.l.-/. n. NVn.-ki. Arch. f. crf>. I'.ith.J. u. rharmaicol. B.I. xx. (l*«6), S. 346.
\«MI< -ki u. si, !„ r. II,!,!. H.I. xxiv. (1888), 8. 17. See alao Minra, Virchow'i Arck.

H.I. < vii (\^i\. s. -.'50.

- v. Jaks. h, /A. f. i>hvsiol. Chem. Bd. xm. (1889), S. 385.

17

258 INDOXYL-PIGMENTS. SKATOXYL-PIGME^TS.

6. Indoxyl-pigments.

Of the total indol formed in the alimentary canal, a portion is
excreted with the faces, while the remainder is absorbed and re-
appears in the urine united with potassium as ethereal compounds
of indoxyl with either glycuronic acid (p. 107) or sulphuric acid
(p. 199), the latter being known as urinary indican. When
warmed with hydrochloric acid these compounds are decomposed,
yielding indoxyl and the potassium salt of the corresponding acid.
If the decomposition is effected in the absence of oxygen, the in-
doxyl may be in part gradually changed into an amorphous red-
dish substance, indigo-red, which is insoluble in water, but yields
a red solution when dissolved in alcohol, ether, or chloroform.1
These solutions show no certainly characteristic absorption bands.
In presence of oxygen and with most certainty by the action of
an oxidising agent, the indoxyl is readily converted into indigo-
blue, whose properties and solubilities have been already suffi-
ciently described. Dilute solutions of indigo-blue exhibit in thin
layers one absorption band in the red lying between a and B 25
C ; if the thickness of the solution be increased this band widens
out towards D and at the same time a second faint band makes
its appearance in the green lying between D 50 E and D 77 E?

The numbers just given refer to the method (Vierordt's) frequently
used for indicating the position of an absorption band. In this the
distance between any two of the fixed lines of the solar spectrum is re-
garded as being divided into 100 equal parts and the extent of the
band is given by reference to these divisions. Thus if a band is de-
scribed as lying between D 50 E and D 77 E it implies that the band
begins half way (-fifa of the distance) between D and E and extends
to -j7^ of the distance between the same two lines.8 (See also above,
note I, p. 228.)

Variable accounts of the above pigments may be obtained from
urines during their spontaneous decomposition or when treated
with hydrochloric acid or oxidising agents, the amount being
greatest in herbivorous urine and especially great in certain
pathological urines (see p. 199). They have also been met
with in urinary sediments and calculi.4

7. Skatoxyl-pigments.

The skatol formed in the alimentary canal gives rise, like in-
dol, to compounds of skatoxyl with either sulphuric acid or glycu-

1 Cf. Nencki, Ber. d. d. chem. Gesell. Bd. ix. (1876), S. 299, and see MacMunn,
Proc. Roy. Soc. Vol. xxxv. (1883), p. 370.

2 Vierordt, Zt.f. Biol. Bde x. (1874), S. 27, xi. (1875), S. 192.

8 A table for the conversion of these data into wave-length limits is given by G.
n. H. Kriiss, Kolorimetrie u. quant. Spe.ktra/ana/yse, 1891, S. 290.

* Ord, Berl. klin. Wochensch. 1878, S. 365. Chiari, Prager med. Wochensch.
1888, S. 541.

CHEMICAL HAMS oF THK ANIMAL BOD1

ronic acid (see p. 202). These compounds when d- 1 by

hydrochloric acid or oxidising agei:- . ;i eolou:

ter which is more or less red and may exlui um-t and

strong purple tint.1 Tin- pigment is inaolnbk in water, I. ut solu-
ble in either alcohol or chloroform, also when freshly prepai
ether 1'iit less so if it has been kept some time. A'lcoholi,
lions are ut' a reddish-violet colour ; etheieal solutions may
a x1"''*'1' fluorescence, which on exposure to tin- air takes on a
reddish tinge. It is also soluble in hydro* -hlori, • ;in,l sulphuric
BCidB, giving bright iv.l or pink solutions, and in alkalis \ield-
ing yellow solutions. No absorption band* for this
have as yet been described and the whole subjeet n-.juii
investigation.

A considerable number of red or reddish-purple pigment.- have
at different times been obtained and described urnl*
names as derived either from pathological urines when
voided, or from the spontaneous decompositions of or action of
mineral acids on different urines. The remarks which hav-
made on the indoxyl and skatoxyl pigments indicate a possibility
that they may all have a common origin and thus be closely re-
lated it' nut in many cases identical. In the absence of any
antee of the purity of the several coloured product their

not having undergone some change during the operations in-
volved in their preparation, no authoritative statement »\\ this
point can as yet be made. Indeed the whole subject of the
origin, nature, and relationships of urinary pigments is at pres-
ent in a state of considerable confu-imi and uncertaii.-

The urinary pigments so far dealt with may be regarded as
either normal or pathological, or as resulting from the spontaneous
or artificial decomposition of urinary constituents which an- at the
outset colourless. In addition to these, other colouring substances
are not. infrequently observed, or colour-reactions obtained, in
urines passed after the admini.-tration of certain drugs or the
consumption of certain vegetable tissues. They are in many cases
not unimportant as leading at first sight to possibly •
conclusions as to the presence in urine of pathologically iin]K»rtant
pigments, e.g. of bile or blood. After the administration of rhu-
barb or senna, the urine may be yellow :i-h-\.-llo\v. d

the presence of chrysophanic acid [<',,!! ( II I (OH)
similarly after the use of santonin « ',.11,. <>.,). In such ( uses if
the urine is strongly alkaline it may be of a red colour; tl
changed to yellow on the addition of hydrochloric acid, and if it

1 ntt,,, pfliignr's Arch, Bel. xxxili. (1884), S. f.l f, '/J. f. pkyiiol.

H.I. MI (1888), s i.-in

r further litorature of these rod pigment* Me Mmtr Abo

lifrl. «&• /

klin. Meil. ISXH, -tokvis (Piit.-M. .\i~' in Maly'i litrlcht. 1W»9. 8. 468.

260 KETINAL PIGMENTS.

is initially acid, it turns red on the addition of an excess of
alkali.1 After the internal administration of copaiba, the urine
turns pink or rose-coloured on the addition of hydrochloric acid
and shows three absorption bands, one (narrow) in the orange to
the red side of D, one broad band in the green between D and E,
similar to that of fuchsin, and one in the blue.2 Tannin leads to
the appearance in urine of gallic acid [C6H2. (OH)8 . COOH], which
is hence sometimes found normally in the urine of herbivora
(horse).3 In such cases the urine if made alkaline with caustic
potash turns brown, and bluish-black on the addition of ferric
chloride. It also yields a pink colouration with Millon's reagent,
similar to that given by proteids or tyrosin. After doses of anti-
pyrin [C9H6N20 (CH3)2] the urine may be dark-coloured and gives
a brownish-red colour on the addition of ferric chloride.4 Fuchsin
(hydrochloride of rosaniline C20H19N3 . HC1) reappears partly un-
changed in the urine, to which it imparts a reddish tinge. It is
detected by making the urine alkaline with ammonia and shaking
with an equal volume of ether : the latter extracts the colouring
matter and into the solution thus obtained a thread of white wool
is dipped and allowed to dry spontaneously. If fuchsin is present
the wool is stained red. Salicylic acid (ortho-oxybenzoic acid,
OH . C6H4 . COOH) is excreted partly in an unaltered form, partly
as salicyluric acid, OH . C6H4 . CONH . CH2 . COOH. These may
be detected by the intense violet colour they yield on the addition
of ferric chloride. Finally after the absorption of carbolic acid
(phenol) and many other aromatic compounds such as pyrocate-
chin, hydrochinon, &c., the urine turns greenish-brown and finally
dark-brown on exposure to air.

KETINAL PIGMENTS.5

The pigments which have to be considered under this heading
are numerous. There is in the first place the extremely stable
dark-brown colouring-matter of the retinal epithelium, belonging
to that general class of pigments known as melanins (see p. 256)
and called in this case fuscin. In addition to this the retinal
epithelium of some animals contains a not inconsiderable amount
of fat globules whose yellow colour is due to lipochrin, a pigment

1 For discrimination of these see Munk, Virchow's Arch. Bd. LXXII. (1878),
S. 136.

2 Quincke, Arch. f. exp. Path. u. Pharm. Bd. xvn. (1883), S. 273.

3 Baumann, Zt. f. physiol. Chem. Bd. vi. (1882), S. 193.

* Umbach, Arch.f. exp. Path. u. Pharm. Bd. xxi. (1886), S. 161.

6 The following account of these pigments is based upon Kiihne's article in
Hermann's Hdbch. d. Physiol. Bd. in. Thl. 1. 1879, and on the original papers in
Kiihne's Untersuch. a. d. physiol. Inst. zu Heidelberg, 1878 — 1882, in which the
literature is fully quoted.

CHEMICAL BASIS OF THK ANIMAL I:<>1>\

closely allied to that of other fata of the body ami ku<>\vn under
tin- ^eiienc name of lipochromes or luteins. Pas- the

epithelium tn tin- ivtina proper we lind in tin- outer end of the
inner liiul> iif the cones highly coloured fat globules from \vlii«-h
three distinct pigments known as chroniophanes. also belon^in^'
to the u'eneral class of lipochromes, may be obtained
names rli'H/ojifniiif, chlorophanf,;(\\<\ •'• nthujihn,"
in correspondence with their ivsp«-ctive red, ^n-i-n. ami yellow
colours. In addition to the above the outer limits ot tin
the inner limbs or either the inner or outer limits of the .
after the retina has lieen shielded for some time from the ;i< tion
of liidit, are found to present a distinct reddish-purple colour
which is very marked when the retina is examined as a \\li.-le.
This colour1 is due to an exceedingly unstable- pigment <-alled by
Kuhne ' visual-jturple' or rhodopsin. The staltility of the.
piiMuents other than visual-purple is merely relative not al. solute,
since they are all sooner or later destroyed 1. leached l.y suffi-
ciently prolonged exposure to li^'ht. The powibilitii

sted of a photochemical exjtlanation of retinal excil
have however as yet thrown no real lij:ht on the nature of the
process. It may be that the impulses result from the changes
which these pigments undergo, and it is p»silile that the col
^loltules of the cones play a part in the whole proce-«. not merely
I iy the instability of their colours but also l.y acting as eoloun-d
tlioui.'li traiisj.arent screens, and thus at the same time determin-
ing the advent to the photochemical apparatu-

leii-th only. Such speculations are interesting luit f«ir the
devoid of any decisive exjK-rimental Mipport >; 7

1. Fuscin (Retinal melanin).3

This- ].iLriiient is found as minute granules iml.edded in the cell-
sulistance and jirocesses of the retinal epithelium (see §
Th'--e -ninnies niav lie either irr.-i.Mi la r. as they always are in the
ehoroid, or may, especially as in turds, possess an elongated form
with sharply pointed ends distinctly su^'u'«->-tiv • illine

structure. It is obtained by «-\t ra.-t in-j l! • vsith boiling

alcohol, eth.-r, and water, and then di- MIC time with

tryp-in. The residue is fr ..... 1 from nin-I.-iiis by di--o Ivin^ the
latter in caugtk alkalis. and from neiiiokerat in (p. S7i bv
tion an<l straining through fine The pigment v\h'

pivpar.'d is practically insoluble in all ordinal
partially dissolved if'boiled for some time with stioi;
alkalis 'or sulphuric acid. I'.v prolonged tieatment with dilut«-

i First ..hsri-voil id tin- n-tina «( * • •: ' II \\<>'.'1- : < t«*od

l>v I.i-\ <\\£ in I -

iiiM.-it.ili! . IN t.. liiilif w:v« t:

8 The- j.i.i:iii.-:it-; ..f :!,. i- :n.:il r|iitli«-limn :nnl <-tioroid «r« mppamitly ulontlcal.

262 LIPOCHRIN.

nitric acid it becomes soluble in alkalis, yielding yellow solutions.
It becomes similarly soluble by prolonged exposure to light with
free access of air (oxygen) and may be again precipitated from
these solutions by the addition of an acid. It is remarkable that
notwithstanding its extreme insolubility and resistance to the
action of most reagents fuscin is gradually bleached by exposure
to light, a result due to some oxidational change since it only
occurs in presence of oxygen. The product to which the above
description refers contains much nitrogen, and leaves on incinera-
tion a slight ash-residue containing traces of iron.

Later investigations of the pigment (from the choroid and iris) con-
firm the above statements of its insolubility in most reagents, and
further show that it contains neither sulphur nor iron. The black
pigment from hairs is stated to contain less nitrogen and a not incon-
siderable amount of sulphur but no iron, and to be readily soluble in
alkalis.1 When the several substances described under the general
term melanins are compared each with the other it is found that they
are by no means identical, but in the absence of any guarantee of the
purity of each product or of the absence of change during its prepara-
tion, all specific statements of differences must be received with caution.
Possibly they are all closely allied and probably in some cases, as in
the melamemia of the malarial fever 2 or the melanuria (and melanotic
pigmentation) accompanying certain kinds of tumours (p. 256), they
are derived from the colouring-matter of the blood. The divergence
in views as to their derivation from haemoglobin has apparently turned
in many cases on the presence or absence of iron in the pigments un-
der examination. Some of the melanins may contain iron, some none,
but whether they do or do not is not a decisive test of their derivation.
If they do it makes the connection more probable, if they do not they
may still take their origin from blood-pigments, as in the case of the
highly coloured but iron-free haematoporphyrin.

2. Lipochrin.

The fat globules in the retinal epithelium from which this pig-
ment is obtained are more especially abundant in the frog. It is
soluble in chloroform, ether, benzol, carbon bisulphide, &c. When
dissolved in ether it gives two absorption bands between F and G ;
in carbon bisulphide two bands, one each side of F? The pigment
of the body-fat of frogs gives similar absorption spectra when
dissolved in the same solvents. Solutions of lipochrin are slowly
bleached by exposure to a strong light. The pigment is probably
closely allied to the yellow colouring-matter of many other animal
fats. (See below sublutein.)

1 Sieber, Arch.f. exp. Path. u. Pharm. Bd. xx. (1886), S. 362.

2 For references see Gamgee, Physiol. Chem. Vol. i. (1880), p. 162.

3 See Kiihne and Ayres, Jl. of Physiol. Vol. i. (1878), p. 109.

CHKM;< LSIfl <»F THK ANIMAL i;<>;

3. Chromophanes.

Tli-- •'•«! above, tin- colou! M of th-

»lohule> which iM-eiir betwern the outer and inner limbs of th,.
r-tinal conea They are prepa: . .-t chiefly from tin- e\

l.inl>, a> follow. The retinas an- dehydrated with al... li.il and
extracted with ether. The ethereal -olution of the f:,ts is then
evaporated tit dryness. tin- residue dissolved in hut alcohol :,iid
saponified witli raustir soda. Tlu- haul ,.ij,> thus

ol,tain.-.l a iv tlii-ii extract. -d in sii.-.-.->sion with j^tml.-uin
(see note p. 156), ether, and henxol. of these solv.-nt^ th-

out the vellowish-«;reen chloroj.hane. th i tlie

yellow xanthoi.hane, and the third the ivd-eolouivd

(i) ('lil<>f'i>li'iif Solul.lr in jM-tri.lelllii ether, ether,
hisulphide. and in alcohol. When dissolved in tin- tii
th'--e solvents it shows t\\o al.soijition hands K-tween /'and C ,
in solution in tin- latter, tin- t\\o band> lie one each sidr of /'

(ii) A'<'iit/t'>/i/i»M. Soluble in ether, carbon bisulphide, and in
alcohol. In ethereal solution it shows only on,- absorption band.
near /•', towards the blue end of the s]>ectruin. In carbon bi-
sulphide it shows similarly one band near, and to the blur, side
It is thus distinguished from the yellow pigment (lipochrin)
of the retinal epithelium previously deserihed.

iii Ji'liii</»j>liti,ii\ Soluble in turpentine, beniol, and in •lodfaol,

In ben/olic solution it shows one band close to, but on the red
side of./'; in solution in turpentine the band i- similarly
but now on the blue side of. /•'

Solutions of tbe chmniophanes ;nv slowly bleached by the ac-
tion of liu'ht. - chlorophane losing its colour fairly rapidly, xantho-
phane inoi-e slowly, and rhodojthane only alter prolonged exp>
In the. 1«.-^ pure form in which the chroniopli t ob-

tained by Kuhne, they ^ave the reactions which characterise the
lil'ochroines or lutein. \\/,. : (i) A tran-ient violet, foil-
bright blue, when treated with »••.//.-.////•///.'/ sulj-huric acid .
tran-ient bluMi-^n-eii under the intluei; •n^ (yell. .\\ i nitric

arid, (iii) An initial uieen colour, passing into bluisli-^r«-«-u. by the
action of a dilute iT. p. c. solution of iodine in dibit.
iodide of pota.-siuni.'-' In the jmrei form in which they \\ere sub-
sequently prejtared, Kiihiie found that they all t: • th«-

tir>t of the abo\e ivartions, while Hone of then; I'.uied by

the iotline solution, and in the cast- of rhodophane the second
reaction with nitric acid was scarcely marked

......... \vrr-i. ' ' ' aii'l

views a* to the i.l.-ntitv ..f thf-n- fattv ].i^ni.'iits \Mth Intcin. j.ir > thu

H K , -.:.. / -. ,-. ,/. </. i>h>i»ii>l. Imttt. Hfxlrlf,. \M. iv. (1H«2). S. 169.

264 VISUAL-PURPLE.

4. Visual-purple (Rhodopsin).

This extremely unstable pigment may be stated to occur gen-
erally (some few exceptions have been observed) in the retinae of
all vertebrates. It does not appear as yet to have been found
in the eye of invertebrates.1 It is confined entirely to the outer
limbs of the rods, but while occurring in the majority of the rods
it is not found in all of them ; thus, it is absent in those situated
in the immediate neighbourhood of the ora serrata, and (in man
at least) it is wanting in the scantily disposed rods in the imme-
diate neighbourhood of the fovea centralis. It is entirely absent
from the cones, and hence is not found either in the fovea cen-
tralis of the human retina, or in the rod-free retina of reptiles.

Preparation in solution. The most suitable material is afforded
by the retinae of frogs which have been kept in the dark for two
or three hours ; since in these animals not only is the visual-pur-
ple very marked and somewhat persistent under the action of light,
but further, the retina can be separated from the adjacent epithelium
with great ease and is free from blood. The necessary operation
for the removal of the retinse, as also all subsequent manipula-
tions, must be carried on in a feeble light from a sodium flame
to avoid bleaching. The retinas (20 — 30 suffice) are then extracted
for an hour in the dark with about 1 c.c. of a freshly prepared
2 — 5 p. c. solution of bile salts from ox-bile, which is finally fil-
tered. If brought into daylight and examined, the solution is
seen to possess a brilliant pinkish-purple colour, which rapidly
becomes red, yellow, and finally colourless, under the action of
light. A similar initial colour is observed in the retina in situ,
followed by the same change of colour when exposed to light,
the yellow being regarded as due to a ' visual-yellow ' (xanthopsin)
and perhaps the final colourless stage, since it admits of regenera-
tion in the dark into visual-purple if the retina is fresh and in
contact with its epithelium (see § 773), may be spoken of as a
' visual-white ' (leukopsin).

Spectroscopic properties. Neither visual-purple nor visual-yel-
low gives any distinct absorption band ; there is a general absorp-
tion of the central parts of the spectrum easily seen between E and
G in the case of visual-purple, which changes into a general absorp-
tion of the violet end of the spectrum from F onwards as the
purple changes into yellow and finally disappears altogether.

Action of light. White light, as also that from an electric
lamp or magnesium flame, bleaches visual-purple with extreme
rapidity, dependency upon the intensity of the illumination:
direct sunlight destroys the colour almost instantaneously.

is dne

1 The red colour of the retina of Cephalopods, first described by Krohn ill 1 839,,
lue to other pigments which are very resistent to the action of light.

CHEMICAL BASIS 01 1111. ANIMAL BODY

When monochromatic light (of the spe< •trum) is used,
found that tin- yellowish-green, i. e. the region most str
absorbed by the pigment, is most, active, followed seriati:.

., blue, greenish-yellow, yellow, violet, orange, and red: the
ultra-iv.l r.iys have no such bleaching power. At low tem-
peratures the effect of light is less, increases with rise of
ature. and at 75° the colour is destroyed even without
to light.

A' fun i of reagents. The colour is at once destroy, -d by tin-
action of caustic alkalis, most acids, alcohols, chloroform, and
ether: it is on the other hand persistent in presence of ami:
solutions of ordinary alum, of sodium chloride, carbonates of the
alkalis, and a large number of other salts. One of the most im-
portant factors in determining the bleachii ual-purple l»y
either light or heat is the presence or absence «,f water. If the
entire retina be dried in vacuo over sulphuric acid, or if a solution
of the lenient be similarly evaporated to d: he visual
jairple is comparatively resistent to the action of light, although
bleached by a sufficiently prolonged exposure.

LIPOCHROMES OR LI I KINS

r the rupture of the ovarian follicle which accompanies the
discharge "f nu ovum, the cavity of the follicle becomes tilled
with a" mass of cells, traversed by ingrowth- of connecti\e \
from tbe neighboring stroma. and frequently contains
re-lilting from ha-morrhage at the time of rupture $ '.'.".4 Thi-
is followed, most strikingly if impregnation of tl
ovum takes place, by a fatty degeneration of the contained
resulting in the formation «-f a bright jugmentrd n. bril-

liant yell..w or orange colour, while at the same time the coluur-
inu'-matter ,if the blood may be converted into tl; linn-

substance already described under the name ha matoidin (p. 'J

being identical with bilirubin The structure which i
from the al.ove rhaiii."-- i< km-wn as a 'mrpus biteiim. I

(1868) examination o! n.i..nred extract* of tl

l.-d to erroneous -tateni.-iit- of the identity of the pi-mei/
t. ,ined from them with h;i-mat..idin. a \ie\v \\hi.-h \\a- ilfflOl
immediately mntrM-d, — while the cul.iuring matt- • •! the

nan f ha molutcin. A renewed inve-tigat imi of tl.

Thudichum ' to charactefwe n u

highly coloured fatty COnatitttenti as of butter

and of some vegetable tissues, and to give it the name lutcin. under

t Centralb.f. d. med. W>tt 18*9,B. I.

266 LUTEINS.

which designation as a class-name these fatty pigments have
usually been known. Since, however, as we have already seen
in the case of the chromophanes, and as will appear subsequently
in the case of the pigments of egg -yolk, and of the substance
tetronerythrin, we have to deal with pigments which, while they
give the reactions characteristic of the group, exhibit colours
other than yellow, it is perhaps advisable now to use the term
' lipochrome ' as generic, and to retain lutein as specific for certain
yellow pigments only. The lipochromes are characterised by
exhibiting absorption bands which, though varying somewhat in
position according to the solvent employed, are usually situated
towards the violet end of the spectrum. From a chemical point
of view the reactions already described on p. 263 may be regarded
as characteristic of the whole class.

1. Lutein.1

This pigment may be obtained from corpora lutea by extraction
with chloroform. If the orange-coloured solution thus obtained
be allowed to evaporate spontaneously, a fatty residue is left in
which the lutein is found in a crystalline form, as minute either
rhombic prisms or plates, which are pleochromatic (see p. 216).
They are insoluble in water, but readily soluble in alcohol, ether,
chloroform, and benzol. These exhibit two absorption bands, one
inclosing F, the other about half way between F and G.

If egg-yolk be extracted with a little alcohol and much ether,
the solution shows two bands similar to those already described
for lipochrin or frog's fat (p. 262), while sometimes a third faint
band near G may be seen, especially if the residue from the
ethereal extract be dissolved in carbon bisulphide and examined.
If the residues from the ethereal extracts of egg-yolk and corpora
lutea be saponified and extracted with carbon bisulphide, the
solutions yield identical absorption spectra.2

Maly,3 operating on the bright red eggs of a sea-spider (Maja
Squinado) considered that lutein (assuming its identity in this
case with that from ordinary egg-yolk) consists of two pigments,
vitellolutein (yellow) and vitellorubin (red). For further details
see the original paper. Lutein is more or less rapidly bleached
by the action of light.

2. Serum lutein.

The serum from the blood of almost all animals is usually of
a more or less yellow colour ; it is specially marked in the case
of the horse and ox, is also marked in the case of sheep and man,
and is but slightly present under normal conditions in the serum

1 See Capranica, loc. cit. on p. 263.

2 Kiihne and Ayres, Jl. qfPhi/siol. Vol. i. (1878), p. 127. Gives spectra.

3 Monatshefle f. Chem. Bd. n. (1881), S. 18. Gives literature to date. See
recently Bein," Be'r. d. d. chem. Gesell. Bd. xxm. (1890), S. 421

CHEMICAL BASIS OF THK ANIMAL l:«»i»\

of the doe/, rabbit. «>r rat. Tin- colour has l.y ditier.-nt "b- |
been ascribed to different pigments. In -onie cases it in
iluc. at lea-t partl\. to tin- presence of bile-pigmentfl or their
derivatives,1 tin-si- bein,u much increased in en tain d
as: jaundice. I'.ut in addition to these it appears that tin- colour
of all pi-jmcnted scrums is due to a specitic pigment. \\ln. h. while
it may differ (?) slightly as obtained from the l.li.nd o| dit:
animals, belongs in each case to the general class .
known as lipochromes. This view was originally put forward b\
Thudichum.- who ascribed the colour to the pigment lutein, \\hi<h
has been already described. This view is probably e(, rivet. inde-
pendently of the possibility that the colour may be in some cases
due partly to the simultaneous pieseii'-e of bile-pigments or their
derivatives. Thus it is found" that by shaking serum with «-th\ 1
or amyl alcohol a coloured extract is obtained which cont;:
fatty pigment, evidently belon^in^ t<> the <• lass of lipoohromet, as
judged liy tin- fact that it is soluble in alcohol, ether. < hloio-
t'orm, ben/ol, carbon bisulphide, &c., shows the two ,in t:
birds only one) bands in the blue part of the sjn'ctruin, and
the chemical reactions (p. 263) with nitric acid and sulphuri<
eharacteri>tic of these substances. It is in many cases identical
with the pigment which can be extracted from the fat of the
animal from whose blood the serum was obtained. Serum-lutein
is bleached by the action of light.

3. Tetronerythrin

This name wa> liist given to a substance ;loro-

form from the red exCTOSCencefl over the . :n biid.-4

It was siibsiMjuently investigated by H<>pp< - • Horn tin-

same source), and described later as occurring in some -j-nnges*
fishes,6 and feathci-.-.7 More recently it ha> been f"iiiid M a pig-
mentary constituent of the blood of crusta. , a .s The pigment is
readily soluble in alcohol, ether, chloroform, ben/ol. and . ail.oii
bisulj.hide. i> readily bli-ached by li-ht. \iel.U the chemical reac-
tions with siil]ihuri'- acid, nitric acid, and iodine, \\hi--l.

itic of the lipochioines (see p. :.'»'•."•). like theM shot)
al»orption band near F somewhat similar to that of \anthoj.hanc

i Flai.ni,:, > !-''» (Hilinil.in in

senini ..f li..i>.- Imt n..t .-f ..x ..r m;r

(IIy.lr..».ilinil.in). M:i.- Mm. Soc V..1 \\\i. (1880). p. 331 (Choletdia).

fro/6. /: '/. ///../. M'/».

,/. ./,„„. • Nahmeiu. 1RM Hnllit.urton.

1 \Vur.n, ZLf.vii X'-i IM \\M

R
Krnk« nix rsr, 1 >'""/• l H"ihn. Al.ih. 4. l^1*!. v

• Knik.-nlH.rj;, Ibid. Al.tli. :.. S ST. I M 8« •**> ^

,./ T \. in. (IH81). j>. loan. Mn< Min.n. Proe. Roy. S-
\\\\ (1888), IM. I .-.-'. -iro

- Ilallihurtun../. ../ ' Phytinl Vol. VI. (1884). p. 324.

LV>8 PYOCYAXIX.

and rhodophane (p. 263), and is slowly bleached by the action of
light.

The pigments of the animal body which have been so far dealt
with admit of a certain amount of classification with reference
either to the secretions or organs in which they occur, to their
genetic relationships each with the other, or in some cases (lipo-
chromes) to their probable chemical similarities. But in addition
to these an extremely numerous mass of pigments has been at dif-
ferent times described under various names, as obtained from the
brightly -coloured parts of invertebrates and of vertebrates, such as
the feathers, &c. Our knowledge of them is quite incomplete and
limited in most cases to statements of their solubilities and the
absorption spectra which some of them yield. In most cases nothing
is known of their chemical nature or their relationships (if any)
to each other, and any description of them even if it were profit-
able, is impossible within any reasonable limits.

For details and references to the literature of the several pigments
see Gamgee, Physiological Chemistry, Vol. i. 1880, p. 305, and parti-
cularly Krukenberg, Vergleichend-physiol. Studien, Heidelberg, 1881-
1888 and Vergleich. physiol. Vortrage, Bd. i. 1886, Nr. 3.

In conclusion it must suffice to describe two pigments which do
not naturally fall under any of the above groups into which these
substances have been divided.

Pyocyanin.1 Pus, which ordinarily presents a more or less
bright yellow colour, is frequently greenish and sometimes blue.
The blue colour is due to a pigment (pyocyanin) which is ap-
parently formed in the pus by the action of specific organisms.
It is obtained either from pus or the bandages into which it has
been absorbed by extraction with dilute alcohol or with water to
which a trace of ammonia has been added. The alcoholic extract
is then evaporated to a small bulk and the residue extracted with
chloroform, or it may be extracted at once from the aqueous solu-
tion by shaking with chloroform. It may be obtained in a crys-
talline form by slow evaporation of the chloroformic solutions, the
crystals being readily soluble in water and alcohol, but only slightly
in ether. Acids change the blue colour to red, and alkalis restore
the original blue. None of the solutions show any distinct ab-
sorption bands. When kept the crystals turn greenish, due to a
decomposition which takes place most readily in alkaline solu-
tions exposed to the air and light, and results in the formation of
a yellow pigment, pyoxanthose. The latter is, unlike pyocyanin,

1 Fordos, Compt. Rend. T. LI. (1860), p. 215; Ibid. LVI. (1863), p. 1128. Liicke,
Arch. f. Uin. Chirurg. Bd. in. (1863), S. 135. Girard, Deutsch. Zeit. f. Chirurg.
Bd. vii. (1876), S. 389. Fitz, Ber.d. d. chem. Gesell. Bd. xi. (1878), Sn. 54, 1893.
Kunz, Monatsh.f. Chem. Bd. ix. (1888), S. 361.

rilKMK AL BASIS OF THF. ANIMAL BOO

only .slightly soluble. in water, but readily soluble in .
which property tin- two pigments ailiuit of being sepai

uithose is crystalline, soluble in alcohol ami oEloxofonil, is
coloured red l»y acids and violet liy alkalis. Since pyoxan;
appears to In- a product of tin- decomposition of pyocyanin, both
pigments may oceur simultaneously in pus. in which cast- the
fluid is green. According to some more r.-c.-nt dboen
eyanin, as judged of by its reactions with tin- chlorides ot
jilatiniun and with other alkaloidal jin-i-ijiitants, as also from tin-
t'onnatioii of crystalline compounds with acids, is closely ivhu
tin- alkaloids.

Sweat is also occasionally coloured blue, in some cases by in-
dii:<>-blue (p. 200) as in urine, and it may be (?) by a pigment
similar to pyocyanin.

i if (I,,- suprarenal bodies. A suprarenal body when a
11 is made through it is found to consist of an outer »i
eal portion, of a yellow colour, which constitutes the chief jKirt »i

: rnetuiv, and an inner, medullary part of a darker colour.
When the latter is acted upon by ferric chloride it assuu
dark bluish- or greenish-black colour, and if an aqueous ev
ot' its substance (or the tissue itself) be treated with an o\idi>ing
a-ent it turns red (§ 498). It appears therefore that the >upru-
ivnals contain some form of chromogen or pigment-forerunner
which gives rise under appropriate conditions to a pigment
cording to some observers extracts of the cortex show a spectrum
similar to that of the histohaematins (p. 234) while the medulla
gives one resembling hivmochromogen.2 The pigment obtainable
from the suprarenals has been investigated by Erokenbeig.1 By
a method for which the original paper must be consulted. 1
lated a brownish-red substance with an acid reaction, soluble in
water and alcohol, whose reactions were the same as those oi

s of the suprareuals. None of the solutions showed any dis-
tinct absorption bands. The whole subject requires fuither

-libation, which mi.uht be of interest in connection with the
origin and causation of the incivacsd pigmentation of the skin ob-

•d when the suprarenals are diseased.

-«ard, Comitt. fond. T. xnv. (1882), j.

1C MIIIIII. /' / IH84 (Jl. ofPftyiiol. Vol. T. p. \

Artk. IM. < i (1886), > 54a.

INDEX.

' Absorption ratio, ' 225, notf
Acetamid'-, formation of, 160

. 116
,117
\ Irxtrin, preparation of, 93

Munido-capnic, 147

ac..ti.-, 116, 124

allauturic, 170

amiilo-acetic, 140

amido-caprnic, 1 17

aiiiMo-t-tliylsiilphonic, HI

amido-lonim-, 139

•mido-pjro-tertuie, 152

ainid'i-Micciiiaiiiic, 153
ainMo-succinic, 1.02
ainidn-siilpliolactic (cystin), 150
ainido.vali-rijiim-, 85

-puragiiiic, 152
, 186

hutyri.-. 11-, 121
capric, 118
, 118

caprylic, 118
•:iii'-, !."•!

carbolic or phi-nvlir, 193
diolalic .>r rlmli. .
flmli'i

ctliylt-ii.-la.'tii', 129
Bthylidene-Uctic, !-."•

fdlir.

iir, 11.;, i-j.j

,
erinphoephorie, 135

glycocholic, -jlo

Mtii"1. 107
liil'l'iui.-, 186
livl .uitoi.', 170

liloric, percentage of in gas-
tri.' juice, 61
livilnixy-liutyrir. 130
liyilr<>\y-|ir«'pi»nir, 121
! -sulphuric, 199
ii-, 141
rii', 118

ric, 195
kynurenic, 192

Acid, Inctic, 124

lauri.- or lauttwtemric, 119
' lithii-,1 166
margaric, 119

nirthyl-^uaiiiiliii .1
iiiftliyl-liy.lantoii-, 141
niyri>tii-. 119

oteie,

oxalic, 130
oxaluri. , 171

n.xyi liiii..liii.<-arboxylic, 192
palmitic, 119
para ban ic, 169
paralartic, 126
phi-nylic, !'.':(
]'licii\ 1-siilphuric, 194
propioiiii-. 1 17, 121
sacch.i:i . 1"7
sarcoliK tic, i •_'.;. 128
skatoxyl-sulplmn
. 11:'

succiii!

Milpho-i vaiiic, 163
Milp)iuii<-, 53
tuurn-rarlmtiiic, 143
Uurwliolic, 211
uric, 164

valeric or vulcrianic, 118
\ilnitiiin. !:•
., its I.IUMH to alkali-albumin.

18
Acids of the acetic wrif». 115

,, aromatic arrie*, 185
glycolic wriea, 124

!ir) •rriec, 120
• • \alic wric*, 130
115
n, 121

the, 120

rotfidj, 8

. 119
cutii. 4

in,

95-90

Albumin, iu decompodtioo by add* and
enzymes, 40

272

INDEX.

Albumins, derived and native, 9
,, chemistry of, 11, 15
,, preparation of, 12, 16
Albuminates, 15
' Allmminose,' 37
Albumoses and peptones, 10

,, ,, chemistry of, 36

,, ,, preparation of, 42

Alcohols of the human body, 116
Aldehydes, their possible presence in

plants, 52, 115, note
,, their relations to the ketones, 117
Aleurone-grains of plants, 26, 36
Alkali-albumin, 9, 18

,, chemistry of, 18

,, preparation of, 19

,, rotatory power of, 19

,, its relations to casein, 22

Alkaloids, certain vegetable, their rela-
tion to the xanthins, 173,
174
vegetable, their resemblance

to ptomaines, 204, 205
Allantoin series, 170
,, sources of, 172
,, preparation, 173
Allanturic acid, 170
Alloxau series, 169
Amides and amido-acids, 139
Amido-acids of the acetic series, 139
„ ,, lactic series, 150

,, ,, oxalic series, 151

Amido-acetic acid, 140
a-amido-caproic acid, 147
Amido-ethylsulphonic acid, 141
Amido-formic acid, 139
Amido-pyro-tartaric acid, 152
Amido-succinamic acid, 153
Amido-succinic acid, 152
Amido-sulpholactic acid (cystin) 150
Aniido-valerianic acid, 85
Amines, composition of, 204, note
Ammonium carbonate, its relations to

urea, 161, 163
Amphikreatinin, 207
Amphopeptoue, 46
Amylodextrin, 92

Animal body, chemical basis of the, 3
' Animal gum,' Landwehr's, 79, 84, 95
Antialbumate, 40

,, characters of, 41

Antialbumose, 40

„ characters of, 42

Antipeptone, 39 and note, 40

,, preparation of, 45

Apoglutin, 82, note
Aromatic series, the, 185
Ascidians, tunicin prepared from mantle

of, 101

Ash of egg-albumin, 5
,, of proteids, 6
,, of casein, 20-21
,, of fibrin, 34
Asparagin, 153

Asparagin, its function in vegetable me-
tabolism, 52-53, 153, 154
Aspartic or asparaginic acid, 152

Bananas, presence of isobutyric acid in,

118
Barfoed's reagent, composition of, 112,

note

Beans, preparation of inosit from, 108
Benzoic acid, 186

„ its relations to hippuric

acid, 186

,, vegetable sources of, 188

Benzol-glycin, 186
Bile-acids, the, 207

,, variations in, according to

source, 209

,, Pettenkofer's reaction for, 213
Bile, the inucin of, 77
,, and tree fatty acids, emulsifying

power of, 123

Bile-pigments and their derivatives, 239
,, their relation to blood-

pigments, 248, 249
Bilicyanin, 245
Bilirubin, its identity with hsematoidin,

239

,, sources of, 240
,, preparation of, 241
Biliverdin, 243

,, preparation of, 243

Blood and bile, relationship between col-
ouring matters of, 237, 247, 249
,, dextrose a constituent of, 102
,, presence of sarcolactic acid in,

126
Blood-corpuscles, red, proteid constituent

of, 28
,, ,, „ colouring matter of,

215

,, ,, white, their connection
with fibrin for-
mation, 67-69
,, ,, ,, glycogen present

in, 96

,, ,, nucleated, nuclein pre-
pared from, 88
Blood-plasma, fibrinogen a constituent

of, 29

,, paraglobulin a constitu-

ent of, 27

Blood-stains, detection of, 237
Body, colouring matters of the, 215
Brain-substance, neurokeratin obtained

from, 87
,, ethyl-alcohol obtained

from, 116

,, inosit present in, 108

,, a sugar obtained from,

106-107
,, preparation of cerebrin

from, 138

„ pro tngon obtained from,

137

m>

Briicke's reagent for proteida, 8
Bunsen method, the, of estimating urea,
158

Bush-tea, alkaloid il juin -iple of, 185
Buttt-r, t'uts ]>!« .-,,'iit in, IL"_'
Butyric acid, 1 1s

,, fermentation, 105

Cadaverin, 206

1 at ions to xanthiu, 173,
174, 184-185
,, an excretionary product of

plants, 185
Calcium lactate, 126
,, oxalate, 130
,, salts, their action in clotting of

casein, 22

,, sarcolactate, 126, 127
Calculi, cystic, 150
,, niullvrry, 130
••-sugar, digestive changes in, 59, 110
,, <>se formed from, 105 N

' inversion ' of, 106, 110
Cane-sugar group, the, 110
Capric (rutic) add, 118
Capmii' arid, 118
vlic arid, 118
miic acid, 151
Carbamide, 1."..'.
Carbohydrates, 91-115

,, in what form assimilated,

59, 98, 103, 111, 114-115
>lic acid, 193

ii-dioxidi- h.rinoglobin, 222
>n -monoxide haemoglobin, 221
Carica Papaya, peptoni/ing enzyme. in

the juice of, 61
Carnin, preparation of, 178

nature of bile-acid of, 210
n, 9

,, cheinUti-y and preparation of, 20
,, action of rcniiiu on, -J-J
,, its relations to nucluin, 90
Caseinogen, 20

"

I ii liars, formic acid in the secretion
of certain, 116

ence of vitellin in, 26
(Vll-gl.ilMilins, 28
Cell-protoplasm, presence of nucleo-

alliuiiiin in, 90

Cell-walls, vegetable, lignification of, 99
Cells, chemical composition of nuclei of,

88
,, hepatic, their glycogen-con verting

action, 98

rvilulose of starch grains, 91
,, chemistry of, 99
„ digestion of, 99, 100

ti.-ulosa, presence of skatol in,
203

Oerebrin, 138
Cerebrose, 106
Cetyl alcohol, 116

Cbarcot's crystals, 139

Cheese, curxi of, produced only by reman

65

Chitin, preparation of, 87
Chloroform, discrimination between en.

••nts by means of, 56
Chloi i, 263

Chlorophyll, starch formed under the

influence .
Cholalic or cholic add.

Cholec van in or choleverdiu, 246
Choleic acid, 209
Cholesteru,

„ -us of, 133

Choletdii,
Choliu, 135
Cholo-hwuiatin, 250
Chondrigen, 83
Choudrin, preparation and reactions of,

83

Chondromucoid, 85
Chromogeus, 251, 25' :
Chromophanes of the letiua, 261, 263

,, 'ii of light on the, 26»

Chrysokreatinin.
Chyle, presence of globulins in, 28, 29

„ dextrose a constituent of, 102
Clotting of caaei:

of blood, 29. 67, 69
,, of muscle plasma, 30, 70
,, of milk, heat phenomena of, 75
Collagen, 80

,, its in to gelatin, 80

Copper, its presence in animal pigments,
•JO

is hit. inn, pigment of the, 266
Corpuscles, see Blood-corpuscles

lin, chemistry and preparation of,
25
Crystals, Charcot's, 139

:ig, 6

,, Teiehniaiin's, 286
Cyanogen c<>m|><>iiiids, t!n-ir possible

"film -tinii in metabolism, 62, 162
Cyst in, 150

DeuteroalbnmoK-
Deuterogelatose, 82

us, i!i.-. preparation of, 93
Dextrose (glucose, grape-sugar), 102-106
,,
,, discrimination of from BsJtOM,

111

Diabetes, chemical clung™ in. 117. 130
Diastase, formation of maltose by, 1 1 1
DigsstkM • •! protd i-. prodn, i •. •
„ 1. 68-59, 63, 64

gastric, 60

of cellulose. 99, 100
Diseasea. ptomainr-formation by

, !. .,'.,.. .;;:•..:.

Dysalbumose, 44

1-

274

INDEX.

Dyslysin, 210

Dyspeptone, Meissner's, 37, 42

Egg-albumin, chemistry of, 11, 89
,, preparation, 12

,, crystalline form of, 12

Egg-yolk, the proteid constituents of, 26
„ nuclein of, 88, 90
,, pigment of, 265, 266
Elastin, preparation of, 85
Elastoses, 86
Embryo, presence of glycogen in tissues

of, 96
Enzymes, 53-76

characteristics of, 53-56
discrimination of from organ-
ized ferments, 56
of the pancreas, 57
of gastric juice, 59
of muscle tissue, 70
mode of action, 72-74
heat phenomena accompany-
ing their action, 75
,, their products inhibitory to

their action, 94
,, their action on cane-sugar,

110, 111
Epidermal structures, keratin the chief

constituent of, 86
Erythrodextrin, 93
Ethane, 124
Ethyl, 124
Ethyl-alcohol, presence of, in animal

tissues, 116
Ethyl-glycol, 124
Ethylene-lactic acid, 129
Ethylidene-lactic acid, 125
Extract of meat, preparation of sarcolactic

acid from, 126-127
,, ,, preparation of carnin

from, 178

,, ,, presence of hypoxanthin
in, 179

Fats, their derivatives and allies, 115
„ the neutral, 120
,, complex nitrogenous, 133
Fattening, sources of fat deposited dur-
ing, 122
Fehling's fluid, composition of, 112,

note

Fellic acid, 209
Ferment, restriction of the term, 53,

note
Ferments, their probable mode of action,

72, 73
„ organized, discrimination of

from enzymes, 56
Fermentations of dextrose, 105

„ lactic, of souring milk,

114
Fibrin, 32

,, varying forms of, 33
„ ash of, 33

Fibrin, its action on hydrogen dioxide, 35

Fibrin-ferment, 67, 68

Fibrinogen, 29, 30, 69

Fibrino-plastin, 27, note

Fishes, presence of kreatinin in muscles

of, 145

Food, the three classes of, 4
Foot-mucin of Helix pomatia, 78
Formic acid, secreted by ants and certain

caterpillars, 116
Formica rufa, formic acid excreted by,

116

Fruits, presence of laevulose in, 106
Fuscin, 261, 262

Galactose, or cerebrose, reactions of, 106

,, a product of lactose, 113
Gall-stones, cholesterin a constituent of,

132
„ bilirubin prepared from, 240,

241

Gallois' test for inosit, 109
Gastric glands, pepsinogen in the cells

of, 61
Gastric juice, earlier experiments with,

37
,, the proteolytic enzyme of,

59
,, percentage of hydrochloric

acid in, 61
Gelatin or glutin, 80

,, liquefaction of, by growth of

micro-organisms, 82
Gelatin-peptones, preparation of, 81, 82
Gelatoses, the, 82
Gland, submaxillary, mucin of, 77
Globin, 32
Globulin of the crystalline lens, 25

„ as compared with myosin and

h'brin, 35
Globulins, the, 25-32

,, their conversion into acid-
albumin, 16

,, their relations to fibrin, 34
Glucose, 102
Glue, 80, note

Glutamic or glutaminic acid, 152
Glutin, or gelatin, 80
Glutoses, the, 82

Glycerin (glycerol), the chemistry of, 123
Glycerin phosphoric acid, 135
Glycin, glycocoll, or glycociue, 140
,, preparation of, 140
,, a product of gelatin decomposi-
tion, 81

Glycocholic acid, preparation of, 210
Glycogen, hepatic, its conversion into

sugar, 58, 98
, , the animal analogue of starch,

95
,, its presence in various tissues,

and in molluscs, 95-96
,, preparation of, 96
„ reactions of, 97, 98

END

•uiuution of, in muscles dur-
Glyculi

Glycuronic iu-iJ, ih«-nii>try •
(lin'-liii'.-. r--actii.il tor l>ilr pijjmi'ir.

'..•cumulation of uri<- acid salts in,
164

-sugar, chemistry of, 102
Guanidin in "ii «( \>i«:

,, its cnniiection with krcutin,

l-»

,, ., ,, with urea, 17 1

chemistry of, 184
s of, 184
Guuiiiu, connexions of, with uric acid,

171

,, preparation of, 182
,, its ccniver-ion into xanthin, 183
mica's rractiniis for, 183
: ition nf u : .

bom,

,, prciiaratii.il of guami! from, 182
:i.i, alkaloidal principle of, 184-185

..it in, preparation of, _

troscopy of, 233

•-••porphyrm (iron-free ha;matin),

Haemin (hematin-hydrochloride), '235

-l'i, 231
Haemoey.ini;

,, in the plasma of inverte-

brates, 217

II

voloM piv»ent in, 104

,, nitric-oxi-l.

,, carljon-di

1

!• i nun. i* inn ol,

Helix pomatia, nmcin in excretion of, 76
,, the twi ii mcinit of, 78

buinose, 39, 40
,, characters of, 42

prepiiratimi c,f, 43
,, :n> of, 43

. 40
,, how ohtainc.l, 46

•'•', 41

>n iif ci-lluliise by the,
99, 100
„ prc.l'.MiiM MI •(• of stearin in

fat of, 1-J2
,, sources of hippuric acid in

the, 188
pi^'in-nt of the bile of th> .

1 1

Heteroxanthin, 171, 177
Hi[' 186

reactions 186-187

sources of, in the hcrbirora, 188

t r » ilh

_

Hydrochinn:

• um of, in

ISO
i 1 inuiin, 174

:m. nation of from
xanthin.
sour

• .a to carnin,
178
,,

180, 181

Ichthin an.l ichthidin.

Ilex 1'ai. i'_'u in UM

lea-. 185

In. li.-. in, urinary, 199, 258
Indigo seri,-s, tli. ,
Inilii;o-blne, foi : 'J(X)

Imlixo-cannine. 200

Indol, its c i.niMination with glycuronic
. Io7

.

'. 198

•t', in til- body, 258
yl I'lL'in. n:,, 258
Indoxyl-Milphuric acid, 199
. pre|nration of, 108
., i

11. ill, li\.i M'«r of

variable f iu con-

, 63
.1 '!

,110
Inversion • .106

: <-jine-augar, 11"
Invertebrate, chit in in th< cxnOceletoiu

tiini' in in the tzoakeletooa

101
,. hcmoglnbin in blood-pU*-

I. raw uiiti in blood*

:

• «wnc« in hemoglobin, SSI

Isethionio acid. 141
•law. 80, not*

MU.ua

IsooMnam, pbytical or
Itopbeayl-ethylamiD, 209

276

INDEX.

Jaffe's test for indican, 200

,, ,, skatoxyl, 203
Jellies, their use in train ing diets, 83

Kephir, preparation of from mare's milk,

114

Keratin, composition of, 86
Keratinose, 86

Ketones, characteristics of the, 117
Kola-nuts, alkaloid principle of, 185
Kreatin, 143

,, its relation to kreatinin, 143

,, preparation of, 144

,, its relation to urea, 162
Kreatinin, 145

,, preparation of, 146
,, reactions of, 146-147
Kresol, 195

„ reactions of, 196
Kresylsulphuric acid, 195
Kumys, preparation of from mare's milk,

114
Kynureuic acid, 192

Lactalbumin, 23
Lactic acid series, the, 124-130
Lactic (hydroxypropionic) acid, 124
,, its presence in the body, 125
Lactic fermentation of dextrose, 105
Lactide, how formed, 128
Lactoprotein, 24

Lactose, preparation and reactions of, 113
,, lactic fermentation of, 114
,, its incapability of assimilation,

114
Lsevulose, synthesis of, 101-102

,, chemistry of, 106
Lardacein, or amyloid substance, 10
,, chemistry of, 48

,, preparation of, 49

Laurie or laurostearic acid, 1 19
Lecithin, 133

,, a constituent of egg-yolk, 26
,, preparation of, 134
,, constitution of, 135
Lens, crystalline, globulin of the, 25
Leprosy, pigments occurring in, 255
Leucin, 147

„ preparation of, 148
,, a result of decomposition of pro-
teids, 40, 50, 79, 81, 84, 85,
86, 147

I/eucomaines, 207
Leukopsin, 264

Liebig's Extract of meat, 127, 178, 179
Light, its bleaching action on chloro-

phanes, 262, 264
Lignin, 99
Ligroin, 156, note
Lipochrin in certain retinal epithelia,

260, 262

Lipochromes or luteins, 265
' Liquor pancreaticus,' its amylolytic
power, 58

' Lithates,' 166

'Lithic acid,' 166

Liver, formation of glycogen in the, 59

" conversion of glycogeii into sugar
in the, 98

,, its work in the formation of urea,
163, 171

,, ,, in the formation of bile-

pigments, 249
Liver-sugar, its apparent identity with

dextrose, 98
Lobster, chitin obtained from the exo-

skeleton of, 87

Lupins, xanthin found in, 175
Lutein, source of, 266
Luteins, the, 265

Lymph, dextrose a constituent of, 102
' Lysatin,' 51, 161

Malt-seedlings, xanthin present in, 175

Maltodextiiu, 94

Maltose, its conversion into dextrose, 57,

59, 112

,, formation of, 111
Mantle of Tunicata, tunicin prepared

from, 101

Mantle-mucin of Helix pomatia, 78
Margaric acid, 119

Marrow of bones, hemialbumin in, 43
Marsh -gas fermentation of cellulose, 100
Mate, alkaloidal principle of, 184-185
Meissner, ' parapeptone ' of, 36

,, his researches on the products

of digestion, 37, 38
Melanin, urinary, 256
Melanins, probable differences of, 262
Melanogen, 256
Metalbumin, 14
Metapeptone, Meissner's, 37
Methffimoglobin, preparation of, 22G
,, spectroscopy of, 227
,, its relation to oxyhsemoglobin, 229
Methyl-glycin, 141
Methyl-guanidinacetic acid, 143
Methyl-hydantoic acid, 141
Methyl-indol, 201
Methylphenol, 196
Micrococcus urese, 158
Micro-organisms, their appearance in

urine, 70, 71, 158
,, conversion of dextrose by

means of, 105

,, hydration of urea by, 158

Milk, preparation of casein from, 20
clotting of, 23

human, and of cows compared, 24
conversion of lactose into lactic

acid in, 105

varying amounts of lactose in, 113
alcoholic fermentation of, 114
Milk-sugar, 113

Millon's reagent for proteids, 7, 76
Mucin, reactions of, 76
„ chief sources of, 77

I.M.

Murexid test for uric acid, 167
Muscle, ethyl-ul.-oliol obtained from, 116
It-ad, cause of acid reaction of, 128
living, causes of acidi:
Mu.-elt-s, I'l.-Mcuce. of glycojjen in thi-,

95-96
,, ,, of inosit in the, 108

icid in the,
125
,, ,, of sarcolactic acid in

the, 1.-;

,, „ of hypoxanthin, 1 79

le-enzyme, 70

-plasma, clotting of, 80, 70
• Myeliu forms' of lecithin, 134
. .bulin, 31

::i.itin, 235
in, chemistry of, 30
,, preparation of, 31

:il-fermrlit, 70

uogen, 31
Myristic acid, 119

, meilullated, neurokeratin ob-
tained from, 87
Nvmin, 136
Xeurukeratin, 87

,, mor|>hological interest of, 87

. I'.'u

ixide haemoglobin, --2-1
Nitrogen, its forms in proteid matter, 52
,, its presence in chomlrin, 84
,, in the Inhly, asparagin a pos-
sible source of, 1 ."• t
,, inurin.-, in.-tho.l of di-termina-

lion, 159
„ its moile of exit from the

muscles, 160

Nitrogenous bo.li.-s allied to proteids, 76
,, holism lessened by gel-

atin as food, 82-83
Xn.-lein, ]>n-fi.u.i!ion an<l ]no[>erties of,

88
Xu.-l.-o-alhumins, reactions of, 89

Olctinc.s, relation of nl,-j,- :i.-j.i, t., •
Oleic acid, a constituent of human fat,

rjn (tri-o].-in), preparation of, 1'22
< >rthoilioxylx-n/i)l, 196
Osazones, !:.••, lui

„ formation of the, 102

i, 80

M-ries, the, 130
,, allliilo-ari.ls of the, 151

"\iluric acid, 169, 171

• xilic ai-i-l,
• •nioglobin. ]in-|Niratioh, 217

• • in .-ryst:iK "f from
iliU'.-r. II- -onrce«, 218
„ spectra of, 21'.'
Oyster, presence of glycngon in the, 96

Palm-oil, palmitin obtained from, 121

Palmitic acid. 11

Palmitin (tri-palmitm), 1 Jl

Pancreas, the *in> lolytic - uzyme of the,

57, 61
Pancreatic juice, its action oo starch.

Ill, ii-j
Papaiu, 61

,, elastiu <li«solved by, 86
Parabanic acid, 169, 170
Paradioxy benzol, 197
Paraglobulin ( serum-globulin ),cheiatolit

of, 27

Paramyoainogeii, 31
Para peptone, 36, 37
Paraxantln:

.. • r of theobromin, 177

Penicillium, etfcct of iu growth on g»U*

tin.
result- of its growth in ethy-

li'l'-ii' i, 128

Pepsin, preparation of, 59, 60

,, its possible combination with

hydriM-hli'i

Pepsinogen, an antecedent of i*psin, 61
Peptones, 10, 36

,, retrospect of history •

„ preparation <•'

,, their ulisorption and fate in

the body, 46

Petroleum-ether, 156, note, 186
Pettenkofer's reaction for bile-acids, SIS
Phenol.

,, reactions of, 195
Phenylir-aeid, 193
I'lu-nyl-glucoaazoue, 104
riiriivMiy.il. i. :n, an reagent for the

sugars, 101

,, in formation of osuones, 108
,, its action on malio**-, 1 TJ
Ph'-nyl-lactosazone, 114
I'll. livl-maltosazone, |.r>-|xir.itinn of, 112
I'lu -nyl-sulphuric acid, 194
I'i;" i icsrnre in casein, SO

..
..

PhyrnatorhiiMii. its i<ti ntity with BMla-
iiin.

i. 64

Pigments of the animal body, SIS
„ humus, 256
in.l

• • •

Piria'srear 191

Pl.ili!-. 01 •::;•:.•••• '• • ,147

i

•MIIJ;, 69

103

278

INDEX.

Propeptone, 43
Propionic acid, 117, 124
Protagou, 137
Protallmmose, 44
Proteids, 6-53

composition of, 5, 50-51
crystalline, 6
ash of, 6

general reactions of, 7
classification of, 9
coagulated, 10, 35
digestive changes of, 37, 38
duplexity of molecule of, 38
their decomposition by acids,

40, 50
,, products of decomposition of,

49
,, theories of the constitution of,

51

' Protein ' described by Mulder, 19
Protogelatose, 82
Pseudoxati thin, 207
Ptomaines, the, 204-207

,, their similarity to vegetable

alkaloids, 204, 205
Ptyalin, preparations of, 56

,, its action on starch, 57
Purple, visual-, 261, 264
Pus-cells, nuclein prepared from, 88
Pus-corpuscles, presence of glycogen in,

96

Putrefactive organisms, action on cellu-
lose of, 100
Putrescin, 206
Pyocyanin, 268
Pyoxanthose, 268
Pyrocatechin, 196

Kennet, use of, in cheese-making, 65
Kennin, its clotting action on milk, 22,

66

„ its enzymic nature, 65
Renninogen, 66

Retina, pigments of the, 260-265
Rhodophane, 261, 263
Rhodopsin, 261, 264
Rotation of light, mode of measurement
of, 103

Saccharic acid, its connection with gly-
cnronic acid, 107

Saccharose, 110

Saliva, ptyalin a constituent of, 57
„ mucin a constituent of, 76
,, its action on starch-paste, 111
,, presence of sulpho-cyanates in,
163

Salkowski-Ludwig method, estimation of
uric acid by the, 167

Sarcolactic, or paralactic acid, 126, 127

Sarkin, 180

Sarkosin, 140

Scherer's test for nosit, 109

SchifFs reaction for uric acid, 167

Schultze's reagent for cellulose, 100,

note
Schweizer's reagent, preparation of, 99,

note

Seidel's reaction for inosit, 110
Serum albumin, chemistry of, 12

,, preparation of, 14

Serum-casein, 27, note
Serum-globulin, 27
Serum-lutein, 266
Skatol, its combination with glycuronic

acid, 107

,, preparations of, 201
,, reactions of, 202
,, occurrence of, in a vegetable tis-
sue, 203

,, compounds of, 258
Skatoxyl-pigments, 259
Skatoxyl-sulphuric acid, 202
Snake's eggs, elastin-like substance in, 86
Soaps, formation of, with stearic and

palmitic acids, 119
,, composition of, 124
Soda, sulphindigotate of, 200
Soluble starch, preparation of, 92
Spectrophotometers, 225
Spectrophotometry, 224
Spermaceti, cetvl-alcohol obtained from,

116

Spermin, 139

Spleen, presence of inosit in the, 108
„ disintegration of red corpuscles in

the, 250

Starch, hydrolysis of, by ptyalin, 57
,, ,, by pancreatic secre-

tion, 57

-, sources of, 91
,, molecule of, 92
„ soluble, 92

,, digestion of, artificial and nor-
mal, 94
,, its conversion into sugar in the

body, 94-95

Starch group of the carbohydrates, 91
Starch -paste, action of saliva on, 111
Stearic acid, 119

Stearin (tri-stearin), preparation of, 121
Strecker's test for xanthin, 176
Strom a of red blood-corpuscles, proteid

constituent of, 28

Sub-maxillary gland, mucin of the, 77
Succinic acid, 131
Sugar in blood, determination of, 8
,, conversion of hepatic glycogen in-
to, 58, 98
,, diabetic, 98
Sugars, the, chemistry of, 101
„ artificial, 102
,, discrimination of, 102
Sulphindigotate of soda, 200
Sulpho-cyanic acid, its formation in the

body, 163

Sulphur, a constituent of fibrin, 34
,, its presence in lardacein, 48

INI-

Sulphur, its presence in keratin, 88

a constituent of cystin, 151
Bnlphuri

Suprarenal bodies, pigment of, 269
. presence of ur.

tl llui'l. nueleo-albiimiiis probably
at in, 90

Syntonin, chemistry of, 16
„ preparation of. 17
,, definition of, 36, note

Taurin, 142

Tauro-curliamic acid, 143
Taurocholic acid, preparation of, 211

,, precipitation of proteids by

means of, 212

Tea, traces of xanthin present in, 175
,, hypoxanthin present in, 179

:u. inn's crystals (liiumin), 235
Tendons, inucin of the, 78
Tetronerythrin, sources of, 267

, its relations to xanthin, 174, 184
Thfobroma cacao, its alkaloidal constit-
uent, 184
Theobromin, its relations to xantliin.

174, 184

,, isomerof paraxanthin, 177

,, an excretiouary product of

plants, 185
Theophyllin, its relations to xanthin,

174, 178, 184
Timml meat-. iH>ssible development of

nines in, 205
Tomla urea, enzyme developed by, 70

), presence of copper in plumage

.

• iivl vinyl -ammonium hydroxide,
}:;<;

TrojKeolins, classification of acid- and
alkali-albumin by means of the, 18

.11 on lil>i in, 34
,, its action on proteids, 36, 38

preparations oi.

logcn. tin- zymogen of trypsin, 64
Tanldn, 101
Tnracin
Tvr.-in, formation of, in clot ting of casein,

result of decomposition of

proteids, 40
,, a product of decomposition of

mucin, 79

,, constitution of, 189
,, preparation of, 190

II >lfinann'8 traction for, 191

rmhili.-.tl r,,r.|, mucin ..f the, 79
Urea, 155-164

average daily excretion of, 165
;i of, 158

synthe*M of. }'.<•
n'itrat- <>f. I.".-:
oxalatc of, l.'-7

l&S

Urea, det<

„ it-s proba

180-162

„ its relation

!'!• '.-:• nnsnt, h
I'rcas, sub.-,::- .-
Uric acid, 164-169
„ salts of, 188

lietnical constitution of. 188
„ synthesis of, 169
„ its relations to urea, 169-171
Urinary in
Urine, fermentative changes i

„ i«athological changVs in, 71, 10J,
108, 130, 208, note, 206, 268.

„ presence of kn-atinin in, 143

,, urea the chief nitrogenous con*

stitiient of, 155

,, deterinim: ^n in. 159

,, sulpho-cyanates present in, 183

phi-nyl-sulphuric n.-i.i in, 194
,, pyrocatechm in, 198
,, pistil- n!- oi, -j;,i-
Urobilin, it-, identity with li\dn>l>iliru-

bin,

,, prejNiration of,
s|».-.-tra of, 253
n."
„

..iv mMatt • t
Urochromi.
Uroerythrin.
Uroha-matin, 255
Uroha»mato|Mirpliyrin, 255

Val» i 118

Van't Hoff-Le Bel hypothesis of

ism.
Vegetable alkaloids, their analogy Mitli

ptomaines, 204, 205
tissues, ai: ud in. 172

-.11 found in.

,, ,. occurrence of jru» n in :

, . urr. :i .'...•

Visual.purple.2til

action of light and rrsgrnts

.
Vitrllin, chemistry and preparation of, 28

\Y • • ; •

•.'•-•

tiofsolabl*

r'.»r xsntluti
rkr.-atii.il.. 117

•i pnnip. thr. 173-186

i>80 INDEX.

Xanthin, preparatior of, 175 Yeast-cells, nuclein prepared from, 88
„ reactions for, 176

„ derivatives of, 184 Zinc lactate, 126

,, physiological action of, 185 ,, sarcolactate, 127

Xanthokreatinin, 207 Zymogen, an antecedent of the enzymes,

Xanthophane, 261, 263 56

Xauthoproteic reaction for proteids, 7 ,, of pepsin, 61

Xanthopsin, 264 ,, of trypsin, 64

Zymolysis, 53, note

Yeast-cells, early observations on, 72, „ phenomena of, 75

73 ,, heat phenomena of, 75

LIST OF AUTHORITIES QUOTED.

Those mentioned in the text are distinguished by an asterisk.

Abel, Ladenburgu., 139

Aliiu'-n, 195

Aii-ln-, Berthelot et, 76

:., v-.ii, \V«-yl u., 222
Araki, 228
Argutinsky, 155
Astaschewsky, 129
Ayres, Kiihne and, 263, 266

Baas, 189

i, 136, 201

Bagin>ky, 117, 179, 181
Barbieri, Schulze u., 131, 154, 172, 188

•I'.nth, 55
Murth, 71

i-, 81, 84
, 187

•IJ.uiiiiann, 53, 194, 199
Bumnaiin, 141. i:.o. 151, 189, 191, 193,

I'.'J, 196, 197, 198, 260
Ramiiiinn u. Brii-x«T. 196, 198, 200, 202

MIHIIII, Cliristiani u., 195
Baiuiiiuni, Gol-lm.-uin u., 150
:i;uin u. Herter, 194, 196
Bamiianu u. Boppe-Seyler, 141

'•',• riiiu'. 1 II
i .inn u. Preusse, 196, 197

: lilll, 200

11:11111, r-li.ni/-ky U., 204

./sky u., 150, 209, 207
Baumstark, 137, 255

•Beaumont, 37

• Mip, 26, 51, 161
ml u. Roosen, 168
K- in, 266

•-Jones, 39, 43
r.'iisch, 105

I, Turin and, 1 1

B.'ilin.-rlilaii, 136
"l!.Ti,:ii.l, 59, 65, 95
. ir-1. 1M. 111
-l-.t. Ml
lot. 73, 88
: lii-lot i-t Andiv. 78

Berzelius, 74

Beran, CTOM and, 09. 100

Bidder u. Schmidt, 61

Biedert, J4

Biel, 24, 114

Bimmerroaun, 59, 112

Bizio, 96

Bizzozero, 69
•Blnnkt.-iihorn, 1:17

Hli-ii<lfnn.inii. .

BU-unard, 86

Boaa.66

Bockluch, 206

Bodlander u. Traube, 9

Boedeker, 108

Boehm, 97, 136
•Boehra u. Hoffmann, 97

Boehm u. II .triuann, 96

Itohr, -J-J.', 238

Bohr u. Torup, 220

B6kay. 89
•

Boknrny. i

Boll, 261
•B»lton, ciiittt-ndcn and, 19

Borntraxi-r. Kul/ u.. M

140, 154, ITS, 189

Bou

Bouchut. Wiirt/ ct. 61

Bourgwiv rgtr «t, 81

r •. M». iu

luclot. I)Mtrr «t, 59
Bower, 100
Brandl u. I
•
Briager, 1S7. 191, 192. 199, 194. 19«.

Bricger, Bautoann u., 196, 196, 200,

Brirgcr, SUdtbagto u . 207
•Brown o:

Brown ai. : «, 59. 91. Ill

Brown and Morri«. J»^ 93. 94, 99, 107

^. 88. 69, 60, 67, M

282

INDEX.

Briicke, 34, 56

I '.minis, 89, 181

Bruntou, 88

Bruylants, 164
'Buchanan, 67, 68

Biitschli, 87

Bufalini, 154

Buligiusky, 194
*Bunge, 7, 189

Bunge, 88, 90, 100, 161, 171
•Buusen, 159

Buusen and Roscoe, 225

Burchard, 133

Cahours, Dumas et, 26

Camerer, 167

( umpbell, Heynsius u., 239, 245, 246

Capraniea, 145, 242, 263, 266

Cash, 63

Cazeneuve, 233

Cazeneuve et Livon, 70

Chaniewski, 122
*Charcot, 139

Chevalier, 87

Chiari, 258

Chittenden, 181
*Chittendeu and Bolton, 12

Chittenden and Goodwin, 32

Chittenden and Hart, 85, 86

Chittenden and Hartwell, 6, 26, 52
*Chittenden, Kuhne u., 5, 32, 44, 46

Chittenden, Kuhne u., 39, 42, 44, 47,

60, 87
*Chittenden and Painter, 25

Chittenden and Solley, 47, 82

Chittenden and Whitehouse, 7

Christian! u. Baumann, 195

Church, 230

Church, Johnston and, 185

Claus, 173
*Cloetta, 108

Cohn, 191
*Cohnheim, 57

Cohnheim, 55

Colasanti, 147

Colasanti and Moscatelli, 126

Commaille, Millon u. , 21

Coppola, 162
*Corin and Berard, 11
*Cornil, 48
*Corvisart, 37

Cramer, 97

Cross and Bevan, 99, 100

*Danilewsky, 18, 58, 62

Danilewsky, P, 17, 31, 47, 56, 63

Danilewsky u. Radenhausen, 21

Dastre, 59, 98, 114

Dastre et Bourquelot, 59

Davidson and Dieterich, 61

Demant, 31
*Demarcay, 207, 208
*Denis, 14, 30, 33

Denis, 27

Desmazieres, 72

Dessaignes, 144
*Diakouo\v, 137

Diakonow, 136

Dickinson, 47

Dieterich, Davidson and, 61

Disque, 247

Donath, 71
*Drechsel, 5, 6, 7, 50, 152, 161, 162, 210

Drechsel, 5, 9, 43, 51, 144, 151, 181,

213

*Duboscq, 224
*Dubrunt'aut, 111

Dubrunfaut, 73
. Duggan, Haycraft and, 11

Dumas et Cahours, 26

Dunstan, 203

Ebert, 120

Ebstein, 239

Ebstein u. Griitzner, 61

Ebstein u. Miiller, 196

Edkins, Langley and, 61

Edlefsen, 28

Ehrlich, 242

Eiclnvald, Kuhne u., 12

Emich, 81, 82, 21,3

Emich, Maly u., 213

Emmerling, 56

Erlenmeyer, 66, 142

Erlenmeyer u. Lipp, 189

Erlenmeyer u. Schoffer, 85

Erxleben, 72

Esclier, Hermann u., 83

Etti, 243

Etzinger, 80, 83

Eugling, 23

Eves, 59, 98

Eves, Langley and, 57, 63

Ewald, 80

Ewald, A., 216, 218, 236

Ewald u. Krukenberg, 182

Ewald, Kuhne u., 80, 87

*Fano, 68

Fano, 47, 69

Feltz et Ritter, 249

Fick, 110

Filehne, 249

Fileti, 201

*Fischer, Emil, 101, 104, 168, 170, 177,
178

Fischer, Emil, 175, 177, 179, 184, 202

Fischer u. Passmore, 102

Fischer u. Piloty, 107, 108

Fitz, 268

Flechsig, 100

Flechsig, Schulze u., 101

Fleischer, 43

Fleischl, E. von, 224

Fordos, 268

Franchimont, 101

Fredericq, 133
*Fremy, 26

INI-

_> :

Frerichs u. Staedeler, 249

Iberg, 66

u. K'-kule, 48

Fri'-nd, H;illi'>nrtoii ami, 90
Ful'ini, Mul.^.-hott u., 88
Fudakow>ki, 106
Fuhry-Sii«-thlage, 28
Funke, 133, 164

!, I'J

tgens, 81
Gagli.

-ee, 67, 86, 137, 270

»,«7, 117.127, 133,138,
t, 237, 262
•Kautliii-r, v., 13
•Gautier, A., 11, 204, 205, 207
:. A.. 17.'.

Ge.s

•(JilK-rt, I .awes and, ll'2
. l:U
i, 268

«i;ni.-lin, -Jos, 210

:n, 5

(iiii.-lin, Tifdemann u., 242
::;i.i,ni. 150
Onodwin, Chittrndrn and, 312

:.'.'Z, V., 113, 189

-

-. 68
Green, Lea and, 68

•Grimaux, .''1
(liiin.mx, 17'.
i HIM, 69
<:r;. ilu» U., 58, 111

I

•/IHT, 65

in u., 61
•

. 163
. 117
*Giu ! ,*8O, 204

^'en, 193

'

rniaiiii, Hlasuvt't/ U., 149, 190

enrorden,

•H:illi).in-t.)ii, i:». 11, 20, 28, 68
li

7, 218, 228,
•J67

Halliborton and Frii-nd, 90
•Haniliiir^T, 44
Hiuiiburijer, 43

•Ha.mnu-.t-,,. II. 2 1 . 23, 28, 29, 80, $8,
•:•!, 69, 78

-'4. 27,

29, 80, 33. 42, «5, «5, 6«, 77, 81, 90,
13,218, 2-

TK u. IM

>ud, 85, M
itden and, 0, 26, 52

1 1 . : N . . ' • I

H»ycrafi

Hay craft and Doggan, 1 1

;. 64
II :i, M, 61, 63, 64, 129

1.65, 119

••«, 61, 66

>tobnunn, 101

•HI i.

n, 95
aaliri, 83, 129

Bl

-cher, 83

•Heron, Brown and, 112
Heron, Brown and, 58, 60, 91, 111
Herrmann. 34, 71
Herter, Bauiuann u., 194, 196
,, 44, 45

I! . Ill

,1, 48
Hesse, 131, 195

:. 68
1!

u. Campbell, 239, 245, 24«
: , 86
r. II, inn. -'U

. 46
•Hlasiwrti, 50

.«••:.- u. ilabermann, 149, 190
1 1 ,-yes, 2S6

189
48

inn u., 97
. ll<>. Inn ii., M

K. H., Ultzmann u.. 133. 164
Hot, IS, 46,60, 80, 81, 100.

in. i.M. i :.-.'. 192
Hohl

,. 137.

234.

-Srylrr. 6, 7, 8, 9, 20, 21. 24, 2«.

96, 1 •'.. HI. 137

ItS, I .. . 11, IM

HoPr*-Srrlrr, O., 194, 199, «OJ

.iimann u.. 1 U
1. 84. 85, 86, 14
168. 171
r. 65. 68. 2M

284

INDEX.

Hufner, 54, 71, 149, 217, 218, 220, 226,

229

Hufner u. Kiilz, 230
Hufner u. Otto, 228
Hundeshagen, 134
Hiippe, 54
Huppert, 143, 241
Husemann, 205

Jaarsveld u. Stockvis, 189
Jacquemiu, 196

Jaderholm, 222, 226, 228, 229, 231
•Jatfe, 200, 247, 252
Jafle, 189, 192, 193, 199, 200
Jatie, Meyer u., 163
Jaksch, von, 70, 117, 158, 196, 257
Jaquet, 7
Jeanneret, 81
Jernstrom, 79
Johusou, 16

Johnston and Church, 185
Jolin, 220, 222
Jong, S. de, 114
Jonge, D. de, 116

Katayama, 222

Rekule, Friedreich u., 48

Rieseritzky, 18

Ristiakowsky, 34
*Rjeldahl, 159

Kjeldahl, 71

Klemptner, 70

Rlug, 47, 82

Knieriem, v., 153, 154

Robert, 185

Kochs, 195

Roebner, 111

Ronig, 113, 131

Roster, 22
*Rossel, 45, 89, 178, 181, 182

Rossel, 88, 89, 90, 176, 177, 179, 181,
182, 184

Rostjurin, 49

Roukol-Yasnopolsky, 198

Rrannhals, 114

Rratschmer, Seegen u., 59

Rratter, 120

Rrause, 180

Rrawkow, 55, 57

Rretschy, 193

Kreusler, Ritthausen u., 153

Rrohn, 264

Kriiger, A., 6, 68

Kniger, M., 181
*Rrukenberg, 4, 48, 147, 268, 269

Rrukenberg, 7, 84, 86, 87, 145, 147,
195, 230, 243, 267

Krukenberg, Ewald u., 182

Rvnkenberg u. Wagner, 178

Rriiss, G. u. H., 224, 226, 258

Rugler, 70

*Riihne, 17, 37, 38, 39, 40, 41, 42, 48,
55, 62, 86, 109, 217, 232, 249, 261, 263

Riihne, 8, 17, 21, 27, 28, 30, 34, 36, 39

44, 45, 47, 53, 55, 57, 63, 64, 74, 96,

198, 215, 262, 263
Riihne and Ayres, 263, 266
*Ruhue u. Chittenden, 5, 32, 44, 46
Riihne u. Chittenden, 39, 42, 44, 47,

60, 87

Riihne u. Eichwald, 12
Riihne u. Ewald, 80, 87
Riihne u. Rudneff, 49
Ruhne u. Sewall, 182
*Rulz, 97, 130

Ruiz, 59, 97, 98, 108, 111, 150, 218, 221
Ruiz u. Borntrager, 98
Ruiz, Hufner u., 230
Riissner, 191
Runkel, 75, 222
Runz, 268

Ladenburg, 206

Ladenburg u. Abel, 139

Lahorio, 236

Lailler, 71

Laker, 69

Lambling, 224

Landolt, 103, 195
•Landwehr, 79, 95, 97

Landwehr, 14, 30, 77, 95, 97

Langendorff, 98

Langgaard, 24

Langley, 57, 61, 66, 76

Langley and Edkins, 61

Langley and Eves, 57, 63

Laptschinsky, 11, 25

Latchenberger, 249

Latschinoff, 209
*Latour, Cagniard de, 72
*Lawes and Gilbert, 122

Lea, 63, 71, 95, 148, 153, 158

Lea and Green, 68

Le Bel, 128

Ledderhose, 87

Legal, 198

Lehmann, 28, 36, 37, 83, 120

Lepine, 75
*Leube, 127

Leube, 70, 110, 111

Leube, Salkowski u., 43, 155, 171, 188,

194, 240
*Leuwenhoek, 72

Levy, 235

Lewkowitsch, 129, 149

Leydig, 261
*Lieberkiihn, 19

Liebermann, 79, 89, 243, 248
*Liebig, 16, 72, 73, 75, 128, 129, 159,
192

Liebig, 73, 127, 131
*Liebreich, 137

Liebreich, 137

Lirubourg, 34

Limpricht, 98
*Lindberger, 64

Lindberger, 63, 213

Lindet, 94

1M'

880

•Liudwall, 87
Limlwall, 86
Lipp,

Lij.p, Kil'-nmfvr u., 189
I,ipj>in;uiii. 1 1'.', I'.'l

Li\ ive et, 70

LobUrli, 78
•l.-.w, 45, 51, 55
1-nw, . 71,88, 161, 181

•i. r.okoii.

i. i'>..k"Mr.

*L>\\
L6wil

', von, 131, 154
si. .">!
Lessen, 161

•litxer, 58
*Lub.ivin.
Lubavin, 90

-"J, 69, 152, 167, 171
Ltteki
Lundberg, 2'2, 23

M Kendrick, 134
. von, 181

Miinn, 2/iO, 253, 255
.Mt.M:in:; ;7, 238, 247,

•267, 269

M.ij.-rt u. Schmidt, 139
M.ikris, 25

^••/, -J-JI
•M.ily, 45, 61, 75, 125, 126, 240, 244,

••"., 211, 239, 240, 244,

nii.'h. '213
, , 68

•M.I IU-IHII-, IDS

Mi: 1 63

M .HIM'. •/ i , 135
M. u in.'-. 108
M ii p-ii HIM. 105

-'26
•>, ';1

M IMU-, Viinlair u., 247
ii-u et Urbain, 133
khner, ir.», I'.l, 191
i'l.i, 140
., 9S
r, A. I., 7J

, A. I., ''-I, 66, 71, 75
M VJ17

•Medico*, 168

M.-llM.

:. lor;, in

MIT. 122

7, 88, 39, 41, 42, 43
shopard, 189
M.T-jkow>'
•M'-ritii;, vnii, >• \

M-: •*, 84, 107, 111, 115

M'-ring, von, Baumann u., 141

Menng, TOO. Miuculus a., M, 59. 96,

98, 111. 11-

. '

Meyer u. Jafle, 163

M^.:. M . -•..-.. , : -.

107

•Mnli,.. ::. :,,
M

..•her, 88

Miller, VI, 103. 115, 128
Millon u. •
Minkowski, 126, 163

Mink in) u, 250

Mi u:

*M..ni.-r,
Mtirii.-r. 17. 1». -•, 256

• u. Fiibini, 83
howetz, 84

Morris, Brown and, 92, 93, 94, 99, 107
Mo- .-ianti aod, 124

Mono, Goareachi e, 204
•MuM.-r, 19, 37

MullT. H

•Mull. i. \V.. 108, 138
Mull.-r. \V
Miill.-r, Fr., 199
Mull.-r. KUt.-ii, u.. 196
Munk. 1 •_".'. 163, 260
MunU, 56

ulus. 71

Mnaculnx, 158
Miuoulua u. CrulH-t. ."-. Ill
. 106
MutwuliiH .„« 58, 59, 90, 99,

111, 11-J
'
Mylin-.. •-'"••

•Naaae, 32
Naaw, 50, 59, 96, 97

•Naunyn. 249
Naunyn, 96, 249

u. Minkowaki u., 250

18, 199. 201,258

oaa, 196
M-hjr, 237

Ncncki. S. hult/rn u.. 191

. 234. »;. *£7
Newler. 66

&], 159

286

INDEX.

Ni-ubauer u. Vogel, 104, 107, 113, 117,
130, 146, 155, 171, 172, 173, 194, 200,
206, 215, 226, 243, 251, 252

Neumann, 69
*Neumeister, 26

Ncuineister, 24, 34, 44, 47

Niggeler, 193

Nikoljukin, 25

Noorden, von, 226

Nussbaum, 223

Obolensky, 14, 77
( Ideraatt, 193

• >rd, 258
Ortweiler, 199
*O'Sullivan, 94, 111
Otto, 34, 46, 47, 203, 205, 206, 217,

•J-Jti, 229, 259
Otto, Hiifner u., 228

*Paijkull, 77

Paijkull, 77, 90
*Painter, Chittenden and, 25

Palm, 24

Panormow, 97, 98
•Panum, 206

Panum, 27

Parcus, 138

Parke, 212
*Paschutiu, 58, 65

Paschutin, 111

Passmore, Fischer u., 102
*Pasteur, 72

Pasteur, 70, 123, 158

Pecile, 182

Pekelharing, 47

Pelouze, 224

Petit, 61

Petri, 84
*Pettenkofer, 214

Pteiffer, 20

Pteiffer, Brandl u., 256
•PHiiger, 52, 159, 162

Philips, 59, 112

Piloty, Fischer u., 107, 108

Piria, 154

Piutti, 154
*P16sz, 256

Plosz, 14, 32, 34, 88, 90

Plugge, 195

Podolinski, 64

Podwyssozky, 61

Poehl, 139

Poggiale, 29

Pohl, 89

Polak, 61

Pollitzer, 47

Popoff, 100

Pouchet, 178

Poulton, 116

Preusse, 196, 197

Preusse, Baumann u., 196, 197
*Preyer, 32

Preyer, 96, 221, 234

Quincke, 260
Quinquaud, 224

Radenhausen, Danilewski u., 21

Radziejewski, 197

Radziejewski u. Salkowski, 152

Rajewski, 116

Kauke, 129
*Raoult, 92
*Rauschenbach, 68

Rauschenbach, 69
*Reaunmr, 37

Rechenberg, 76
*Reinke, 4

Reissert, 157

Reymond, Du Bois, 128

Rindfleisch, 69

Ringer, 22, 66

Risler, Schlitzenberger et, 224
*Ritter, 51, 161

Ritter, Feltz et, 249

Ritthausen u. Kreusler, 153
*Roberts, 58, 66

Robin, 135

Rodewald u. Tollens, 113

Rohmann, 44, 154, 191
*Rollett, 14

Rollett, 15
*Roosen, Behrend u., 168

Roscoe, Bunsen and, 225

Rosenberg, 18

Rossbuch, 185

Roster, 163

Rotschy, Nencki u., 237

Rubner, 76, 122

Rudneff, Kiihne u., 49

Sachsse, 92
*Salkowski, E., 43, 127, 162

Salkowski, E., 34, 42, 54, 71, 131, 141,
143, 145, 147, 148, 171, 172, 179, 188,
194, 195, 198, 203, 222, 238, 239, 253,
256

Salkowski, E. u. H., 188, 191, 201, 203

Salkowski u. Leube, 43, 155, 171, 188,
194, 240

Salkowski, Radziejewski u., 152

Salomon, G., 176, 177, 178, 179, 180,
181, 182

Salomon, W., 163, 189

Samson-Himmelstjerna, 68

Sander, 17
*Schafer, 14

Schafer, 101, 250

Schalfejew, 236, 237

Schefier, 61

Schenk, 213
*Scherer, 14, 108
*Schiff, 38

Schiff, 158

Schiffer, 141

Schimmelbusch, 69

Schindler, 89, 181

Schmidt, Albr., Majert u., 139

IM'

: It, Alexander, 14, 28, 30, 34, 67,
6S.

Schmidt, Alexander, U
133

.i.lt, Aug., 55
St-liiiii.lt, I'., 48
Srlin i.ler u., 61

3chmidt-Mulheinj, 36, 4-2, 46, 47, 63,

!>.-r^, 1 'I-', 189

Schiiii.-.l.-U-ix, IS1.', I'.'O, 197, 204
S.-!K. .. ll:irn;iuk, 136

• rg u. Sdi'.

Solun: r, 107

.., 85
191, 209
HIT, 139

163
von, 171

S.-hnl

. 204

. 149, 154, 190, 191
Srhiil/.' u. Karhi.-ri, 131, 154, K

i.ard, 149, 154, 172, 182
hsig, 101
•/.•ii, 1 II
. 141

i. Xencki, 191
S.-luilt/'-n, Si-hiuu-.leberg u., 192

39, 41, 50
. 51

: et Bourgeois, si, 84
Schutzenlwrger et Risler,

. 72

, 82
Sczelkow.

J01 .

Seegen, 8, 59, 98
Seegen u. Kratachmer, 59

., -il
•
S.-lini, -Jl

. 200
"Setschenow.

•nil, n-J

. KuliiH- u., 182
Sin-] -T u., 189

ki u.t 248

Sieber, N\-n. ki »., J16, 234, 287.
Siegfried, 51, 129

Smith, H. K.. 87

i-n and, 47, 82
Si.tnit- h.'xvsky, 135
•Sox hi.

Soxhht, 19, ''.6, 103, 10«, 111,

111', 113

Soyka, 16. 18. 19
.11 tin i, 37

i«*nn, 130

Imann, 61. 168, S49
181

>' • I' :. - .'

240

, u, r.'. la. H

•nigge, 87

Jl»

iiann, 76

ucU-rg u., 101

..ir>vi-ld u., 189

-i», 228
'-, 44

135, 208
Strecker,

1 u., 122

Struv.-. •_•!, 114
Sui.lii, Mauthuer u., 140
•Sun.n--rK', 60
Siin.Uik, 87
Szabu, 63

Tap|*in.r, :,|, 100, 161, 188
•Tarchanotf, 249

TaUrinotr, •

:.-l«li-r, 107
. 181

•Thu.li.-hum, 106, 254, 2M
Thu.lirhuin, 17;

Tieghem, ran, 70, 100, 158
Tiemann, Bauroann u., 200

:«. 91, 104

Tollrn*. Kodewald u , 118
Tolm.itH.hnr. 132, 188
Torup, 238
Tonip, Bohr u., 220
Trauba, 74
Traubr. Ikxllandrr a., 9

IM

•

191,195, 196, 198,21

•r . : .

Uilraniiky u. IWumano, 160, 206, 207

UlUmann <• K II II .ftn.nn. 188. 161

1'SS

INDEX.

Umbach, 260

Urbain, Mathieu et, 133

•Valenciennes, 26

Vanlair n. Masius, 247
*Vairt Hotr, 128

Van't Hotf-Le Bel, 128

Velden, v. d., 63

V.-lla, 59, 111
»Vierordt, 225

Vierordt, 225, 226, 243, 246, 247, 251,
254, 258

Vines, 6, 36, 153
•Virchow, 248

Virchow, 36, 48, 151, 182, 239
*Vogel, Neubauer u., 159

Vogel, Neubauer u., 104, 107, 113, 117,
130, 146, 155, 171, 172, 173, 194,
200, 206, 215, 226, 243, 251, 252

Vohl, 108, 109
*Voit, 83, 122, 154

Voit, 83, 122, 143, 145, 154, 185

Volhard, 143, 168

Vossius, 243, 249

Walcbli, 79, 85, 199
Wagner, Krukenberg u., 178
Warren, 129
Wasilewski, 61
Wedenski, 95, 256
Weidel, 178

Weiske, 80, 81, 101, 154, 188
*\Veiske and Wildt, 154
Weiss, 64

Welzel, 222

Wenz, 8, 45

Werigo, 14

Werther, 129

Weyl, 6, 26, 31, 32, 48, 81, 154, 191,
198, 199

Weyl u. von Anrep, 222

Weyl u. Zeitler, 129

Whitehouse, Chittenden and, 7
* Wildt, Weiske and, 154

Wislicenus, 127, 129
•Wittich, von, 58

Wittich, von, 55, 74
*Wohler, 156, 186

Wohl, 95, 110

Woltfberg, 223

Wooldridge, 28, 29
*Wooldridge, 69

Womi-Miiller, 88, 89, 147

Wurm, 267

Wurster, 191
*Wurtz, 55, 136

Wurtz, 61, 75

Wurtz et Bouchut, 61

Zahn, 23
Zaleski, 223, 250
Zeitler, Weyl u., 129
Zeller, 256
Zenker, 138
Zillner, 120
Ziuoffsky, 217, 218
Zuntz, 133, 221
Zweifel, 66

TEXT-BOOK OF EMBRYOLOGY: MAN AND MAMMALS.

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Professor Lang has here successfully carried out the very difficult
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and of combining them with great judgment. Besides this he has, more
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always to give the phylogenetic significance of ontogenetic facts. Lastly,
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which precede the anatomical account of each race, further facili-
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