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the thymus and other organs. Details of these will be given mider the
heads of the various organs in question. In my own analyses, the
amount of phosphorus rarely has exceeded 1 per cent.

Xucleo-histon appears to be identical with the tissue fibrinogen of
Wooldridge, but this included a variable" amount of lecithin. Other
forms of the same substance have been called cytoglobin and preglobin by
A. Schmidt.- Wooldridge prepared his tissue fibrinogens from cellular
structures, such as thymus and testis. The gland is finely minced and
extracted Avith water for twenty-four hour.s. Weak acetic acid is then added
to the decanted extract, and after some hours the precipitated nucleo-proteid
falls to the bottom of the vessel. This is the method used by Lihenfeld in
the manufacture of nucleo-histon. Another method, which I have largely
used, is to grind up the finely minced organ with about an equal volume of
sodium chloride in a mortar. The resulting viscous mass (originally called
hyaline substance by Eovida) is poured into excess of distilled water. The
nucleo-proteid rises in strings to the surface of the water, where it may be
skimmed ofi".

Prepared by either method, the nucleo-proteid may be dissolved in 1 per
cent, sodium carbonate solution. This solution injected intravascularly in
small doses in dogs produces a hindering of the coagidation of the blood
(Wooldridge's negative jihase). In larger doses it produces intravascular
coagulation. -5

The lecithin found associated with AVooldridge's tissue fibrinogens is
variable in quantity, and does not appear to be organically united to them.
After its removal the nucleo-proteids continue to exercise their most distinctive
physiological characteristic, in producing intravascular clotting.*

In connection with nucleins and nucleo-proteids, it should be men-
tioned that many of them contain iron, and, according to Bunge,^ con-
stitute in foods the normal supply of iron to the body ; in this sense he
has called them hsematogens. The composition of hsematogen from egg-
yolk he gives in percentages, which may be compared with the com-
position of nuclein from yeast, as follows : —

C
H



s
p

Fe

^ Zisclrr. f. pliysiol. C'hem., Straisliurg, Bde. xviii. and xx.

- " Weitere Beitr. ■/.. Blutlehre," Wiesbaden, 1895.

' Details Avith reference to the influence of nucleo-proteids on hluod coagulation are
given in tlie article dealing with that subject.

^ Halliburton and Brodie, Journ. Physiol., Cambridge and London, 1894, vol.
xvii. ]). 1.3.5.

^ Ztschr.f. physiol Chem., Strassburg, 1884, Bd. ix. S. 49.



ematogen.


Nuclein fron


42-11


40-81


6-08


6-38


14-73


15-98


31-0.5


31-26


0-55


0-38


5-19


6-19


0-29





THE ALBUMINOIDS. 69

If the iron is, as it appears to be, in organic union, the nucleins that
contain it must be among the most complex of known organic compounds,
consisting of seven elements.

The exact method in which the iron is comljined is however, like the
constitution of nuclein, still unknown.

Zaleski ^ has succeeded in separating from the liver one of these iron-con-
taining nucleins, which he terms liepatin. The subject has been largely worked
by microcheniical methods for the detection of iron ; and the terms " firmly
combined" and "loosely combined" iron are often used, according as the com-
pounds which contain that element give the reactions with difficulty or ease.
Macallum - finds that the chromatin of nuclei contains iron ; he regards
it as the mother substance of hsemoglobin, both in embryological develop-
ment and during nutrition in extra-uterine life. He finds similar hsematogens
in plants, as did also Bunge.

Lecith - albumins. — Liebermann^ has given the name lecith-albu-
niins to certain compounds of lecithin and proteid which he obtained from
the kidney, gastric mucous membrane, lungs, spleen, and liver. The
lecithin is not removable from these compounds by simple extraction
with alcohol and ether. These, however, can hardly be considered to
be immediate constituents of the cells, as they are obtained after sub-
jecting them to a very severe process, namely, artificial gastric digestion.
They yield no phosphoric acid and no xanthme bases on decomposition.
According to their discoverer, they play an important part (in wtue of
the acidity which they possess in common with nuclein compounds) in
the separation of the hydrochloric acid of the gastric juice, and in decom-
posing the alkahne salts of the blood plasma, so as to }T^eld the acid
salts of the urine. Much more extended investigations are needed,
however, before important functions like these can be safely attributed
to them.

We have already seen that vitellin is a proteid which by some is
regarded as a globuhn, by others as a nucleo-proteid. Hoppe-Seyler '^ was
inclined to regard the phosphorus found in it as due to a combination
with lecithin, whereas Hammarsten looks upon some forms of ^dtellin as
phosxDho-gluco-proteids. No doubt, vitellin is a name wdiich covers a
number of different substances ; the substance Hoppe-Seyler worked
with contained as much as 25 per cent, of lecithin. In those cases
where the phosphorus is present as a nuclein, the nuclein obtained by
gastric digestion is of the pseudo-nuclein variety.

The Albuminoids.

The albuminoids form a heterogeneous group of substances allied to
the proteids, but differing from them by certain marked characteristics.
As a rule, they are found in skeletal and epidermal structures, and
usually they are remarkable for their resistance to reagents. They

1 Ztschr. f. physiol. C'hem., Strassburg, Bd. x. S. 453 ; xiv. S. 274 ; CUiem. Centr.-Bl.,
Leipzig, 1888, S. 759. See also Quincke, Beutsches Arch. f. klin. Med., Leipzig, Bd. xxv.
S. 567 ; xxvii. S. 202 ; xxxiii. S. 23 ; Peters, ihid., Bd. xxxii. S. 182.

^ Macallum's most receut papers are in Journ. Physiol., Cambridge and London, 1894,
voL xvi. p. 268 ; Proe. Poy. Soc. London, 1895, vol. Ivii. p. 261 ; 1. 277 ; Quart. Journ.
Mkr. Sc, London, 1896, vol. xxxviii. p. 175 ; Rep. Brit. Assoc. Adv. Sc, London, 1896.

" Arch. f. d. ges. Physiol., Bonn, Bde. 1. and liv.

■* "Med. chem. Untersnch.," 1868; Ztschr. f. phi/siol. C'hem., Strassburg. Bd. xiii. S.
479.



70 CHEMICAL CONSTITUE^^TS OF BODY AND FOOD.

include keratin, elastin, collagen, gelatin, reticulin, amyloid substance,
and a group of materials called skeletins.

Collagen. — Collagen is the mother substance of gelatin. It is the
material of which the white fibres of connective tissue are made, and is
the principal constituent of wliich the organic substratiun of bone is
composed: it is there called ossein. In cartilage the material called
choudrigen is collagen mixed with the muciuoid materials of the carti-
laginous matrix. Collagen has also been obtained from the flesh of
cephalopods.^

By boihng with water, especially if it is faintly acidified, collagen is
converted into gelatm; and gelatm is reconverted into collagen by
heating it to 130" C. Hence collagen is regarded as the anhydride of
gelatin ( Hofmeister) : - the reaction may be represented by the erpiation —

^102-til51-^^ 31^29 -'^2 -^ ^^ ^102-L'-149-^ 31^28

(gelatin) (collagen)

The above formulte, however, cannot be regarded as more than provisional,
for we are as ignorant of the molecular constitution of the alljuminoids
as of the proteids. Schiitzenberger attributes the formula C^gHij^Xs^O^g
to gelatin, and regards the sulphm- descrilDcd by other investigators as
due to admixture with proteid impurities. Hammarsten,- on the other
hand, regards the sulphur, of which there is 0'6 per cent., as an integral
part of collagen and gelatin.

Collagen is insoluljle in water, alcohol, salt solutions, and dilute acids,
and alkahs. It swells with dilute acids. Its decomposition products
are the same as those of gelatin.

Gelatin. — Gelatin is a colouidess, amorphous, and translucent sub-
stance ; it swells but does not dissolve in cold water ; it readily dissolves
m hot water, and on cooling the solution, if its concentration is greater
than 1 per cent., it sets into a jelly. It contains a considerable amount
of ash, the removal of which lessens its power of gelatinising.^

Gelatm is precipitated by satm'ating its solution with neutral salts,
like magnesiimi sulphate and ammoniiun sulphate.^ This is also true for
gelatin which has been altered by the action nf hot water so as to be no
longer or only partially gelatinisable.

Gelatin is not precipitated by acetic acid, nor Ijy acetic acid and ferro-
cyanide of potassium, nor by most of the heavy metaUic salts that precipi-
tate proteids. It gives a violet colour with copper sulphate and caustic
•potash ; it gives jMillon's reaction, but only a faint xanthoproteic reaction.®

It is precipitated by mercuric chloride, and also, as in the process of
tanning, by tannic acid. Gelatin is levorotatory.'^

Derivatives of gelatin. — The prolonged action (twenty-four hours) of
boiling water, or the shorter action of water heated above the l)oiling
point, destroys the gelatinising power of gelatin. Gelatin, in fact, under-
goes hydrolysis, being converted into the so-called gelatin peptones.
Similar substances are formed during digestion. Hofmeister distinguished

' Hoppe-Seyler, "Physiol. Cliem.," S. 97.

- Zlschr. f. 'pliysiol. Chem., Strassbiirg, Bd. ii. S. 315.

" "Physiol. Chem.,'' 3rd Geiman edition, S. 46. Analy.ses of gelatin were made in addi-
tion to those quoted above by Mulder, Ann. d. Chem., Leipzig, Bd. xlv. : Fremy. Jahresh.
il. Chem., 1854 : and Paa], Bcr. d. dentsch. chem. Gesellsch., Berlin, Bd. xxv. S. 1208.

•* Xasse and Krliger, Jahrcsi. il. d. Fortschr. d. Thier-Cliem., Wiesbaden, Bd. xix. S. 29.

'' Xasse, Arch. f. d. ges. Physiol., Bonn, Bd. xli. S. 504.

*^ Salkow.ski, Ztschr.f.physiol. Chem.. StrassVairg, Bd. xii. S. 215 ; Bcrl. klin. TFehnschr.,
1885, No. 2.

' Hoppe-Seyler gives(a)p= - 130''at 30'C. Nasseand Krugergive(a)p= - 136^to - 167 "5'.



THE ALBUMINOIDS.



7J



two of these substances, which he named semigkitin and hemicollin.
Chittenden and Solley ^ distinguish between proto- and deuterogelatose,
and true gelatin-peptone. Paal ^ has obtained similar substances by the
use of hydrochloric acid. By the use of Eaoult's method, he gives the
molecular weight of gelatin as 878 to 960, and of gelatin-peptone as 352.

Strong reagents like sulphuric acid, on putrefaction, decompose
gelatin with the formation of giycocine,^ leucine, various fatty acids,
glutaminic acid, carbon dioxide and ammonia. The absence of tyrosine
should be noted. Schlitzenberger,'* who has worked with gelatin by the
same methods as he used with proteids, considers that gelatin, like
proteid, is a compound of urea with certain amido-acids.

The importance of gelatin as a proteid-sparing food, though it will
not replace proteid entirely in a diet, will be considered under " Nutrition."

Chonclrin is the name given to the impure gelatin obtained from
cartilage (which see).

Elastin. — Elastin is a material yielded by the yellow fibres of con-
nective tissue. It offers great resistance to reagents, and may be pre-
pared from the ligamentum nuchse by extracting the finely divided
tissue successively with reagents in which it is insoluble, and in which
adherent fatty, collagenous, and proteid matters dissolve (boiling water,
1 per cent, potassium hydroxide, 5 per cent, hydrochloric acid, alcohol
and ether). By this means a substance free from sulphur is obtained.
Chittenden and Hart,^ in some of their preparations, omitted the
extraction with potash, and in these a small percentage of sulphur (0"3)
was obtained ; this may be due to proteid impurities, or it may be loosely
combined in the elastin molecule. Schwartz ^ has also prepared a sulphur-
containing elastin from the aorta.

The following table shows the results of elementary analyses in per-
centages : —





Muller.7


Tilanus.8


Horbaczewski.9


Chittenden
and Hart.


Schwartz.


c .


55-09-55-7


54-9-55-65


54-32


54-24


53-95


H .


7-n-7-67


7-25-7-41


6-99


7-27


7-03


N .


15 -71-16 -52


17-52-17-74


16-75


16-7


16-67


.


20-7-21 -15


19-5-20-33


21-94


21-69


21-97


s .








0-3


0-38



Derivatives of elastin. — Elastin is gradually and slowly dissolved by

^ Journ. Physiol., Cambridge and London, vol. xii. p. 25.

^ Ber. d. deutsch. che^n. Gesellsch., Berlin, Bd. xxv.

^ On the preparation and estimation of glycocine from gelatin, see C. S. Fischer, Ztschr.
f. 2^hysiol. Chevi., Strassburg, Bd. xix. S. 164 ; and Gonnermann, Arch. f. d. ges.
Physiol., Bonn, Bd. lix. S. 42.

■* Compt. rend. Acad. d. sc, Paris, tome cii. p. 1296. See also Bnchner and Curtius,
Per. d. deutsch. chem. Gesellsch., Berlin, Bd. xix. S. 850.

^Ztschr. f. Biol., Miinchen, Bd. xxv. S. 368 ; Stud. Lab. Physiol. Cliem., New Haven,
vol. iii. p. 19.

^ Ztschr. f. physiol. Chem., Strassburg, Bd. xviii.

'' Ztschr. f. rat. Med., Leipzig, Dritte Reihe, Bd. x. pt. 2.

« Gorup-Besanez, " PhysioL Clicm.," Aufl. 3, S. 148.

^ Ztschr. f. physiol. Chem., Strassburg, Bd. vi. S. 330.



. 72 CHEMICAL CONSTITUENTS OF BODY AND FOOD.

pepsin or trypsin.^ Horbaczewski named the two products of digestion he
obtained, hemielastin and elastin-peptone. Chittenden and Hart, using
Kiihne's methods and nomenclature, have shown that hemielastin is
protoelastose, and elastin-peptone is deuteroelastose.

On more complete decomposition elastin yields products very like those
obtained from proteids, except that glycocine is obtained, but no aspartic
or glutamic acid, and very little tyrosine.''^ Lysatinine but no lysine was
obtained.^ By fusing with potash, indol, skatol, phenol, benzene, but no
methylmercaptan, were yielded (Schwartz).

Beticulin. — The fibres of reticular tissue, though histologically not
distinguishable from those of areolar tissue, were first stated to be
chemically different from them by Mall.''^ He asserted that no gelatin
v^as obtainable from them, a statement corrected by E. A. Young,^
and subsequently by Siegfried.*^ Siegfried, however, confirmed Mall's
idea that the fibres contained something special, and separated from
them a material he called reticulin. Keticulin has the following per-
centage composition :—C, 52-88 ;H, 6-97; N, 15-63; S, 1-88; P, 0-34;
ash, 2-27. By decomposition it yields sulphuretted hydrogen, ammonia,
lysine, lysatinine, and amidovalerianic acid, but no tyrosine and no glu-
taminic acid. It gives the proteid reactions with the exception of Millon's.

Siegfried prepared reticulin from the mucous membrane of the
intestine by digestion with trypsin and alkali. The residue was washed
and extracted with ether, again subjected to tryptic digestion, and
extracted with alcohol and ether ; the collagen was removed by hot water.

If glutaminic acid is absent, as Siegfried states, from the decomposi-
tion products of reticulin, and it is certainly very abundant in the
decomposition products of collagen and gelatin, there is distinct evidence
that reticulin is a new material.

We are therefore confronted with the difficulty, that the fibres of
reticular tissue are anatomically continuous with and histologically
identical with the white fibres of connective tissue, and yet they con-
tain chemically this new material. The answer to the problem is pro-
bably that reticulin is not specially characteristic of reticular fibres,
but is present in all white connective tissue fibres.

Keratin. — Keratin is the horny material of which the horny layer of
the epidermis, hair, wool, nails, hoofs, horns, feathers, etc., are composed.

It is prepared by successively boiling the tissue with ether, alcohol,
water, and dilute acid ; the insoluble residue is keratin. A variety of
keratin called neurokeratin is found in neuroglia, and has also been
described in the medullary sheath of nerve fibres ; though here no doubt
some of the histological appearances described may be artificially pro-
duced by reagents. It resembles keratin in its general properties, but
is less easily soluble in boiling solutions of caustic potash.'^

1 Ktilme and Ewald, "Die Verdauuiig als histol. Methode," Verlmndl. d. naturh.-med.
Ver. zu Heidelberg, 1877, N. F., Bd. i. S. 451; Etzinger, Ztsclir. f. Biol., Munchen, Bd. x.
S. 84 ; Horbaczewski, loc. cU. ; Morochewetz, Jahresh. it. d. Fortsch.r. d. Thier-Chem., Wies-
baden, 1886, S. 271 ; Chittenden and Hart, loc. cit.

^ Drechsel, Ladenljurg's " Handwurtevbucli," Bd. iii. ; see also Horbaczewski, Monatsh.
d. C'hem., Wien, Bd. vi.

^ See, however, Hedin's recent work referred to on p. 33 of this article.

'^ Anat. Anz., Jena, 1888, Bd. iii. No. 14; Ahhandl. d. math.-jihys. CI. d. k. sdchs.
Gesellsch. d. Wissensch. , 1887, Bd. xiv. No. 3 ; xvii. No. 14.

•'' Journ. Physiol., Cambridge and London, vol. xiii. p. 332.

« "Habilitationschrift," Leii^ig, 1892.

''Ewald and Kiihne, Verhandl. d. naf/urh.-med. Fer. ::u Heidelberg, N. F., Bd. i.
Heft 5 ; Kiihne and Chittenden, Ztsclir. f. Biol., Miinclien, VA. xxvi. S. 291.



THE ALBUMINOIDS.



73



The following are some elementary analyses tliat have l^een made of
keratin from dift'erent som'ces : —



Tissue .


From Hair.


Nail.


Neurokeratin.


Horn.


Analyst


V. Laar.i


Mulder.2


Kiihne.3


Horbaczewski.*


c .


50-60


51-00


56-1-58-4


50-86


H .


6-36


6-94


7 •2-8-0


6-94


N .


17-14


17-51


11-5-14-3




.


20-85


21-75






s .


5-00


2-80


1-6-2-2


3-30



.The main featm^e in the above analyses is the high percentage of
sulphm%^ which is in part in loose combination, and can be removed by
alkalis or even by boiling water.

An albuminoid obtainable from tracheal cartilage by C. T. Morner,'^
and further investigated by Hedenius/ is included by Hammarsten *^
among the keratins, or as a substance intermediate between keratin and
coagulated proteid. It contains only 1 per cent, of sulphur. Keratin
gives the proteid reactions.

Derivatives of keratin. — Keratin is not digestible hj either gastric
or pancreatic juice. By heating with water to 150°-200° C. it dissolves,
forming a turbid solution. It dissolves more readily in alkahs ; the
solution contains alkaline sulphides, and substances of the proteose class,
called keratinoses by Krukenberg.^

The decomposition products of keratin obtamed by the use of acids
are like those of the proteids, and include leucine, a good deal of tyrosiue
(1-5 per cent.), aspartic acid,^*^ glutamuiic acid,^^ ammonia, and sul-
phm'etted hydrogen, lysine,^^ lysatinine,^^ and a sulphur-contauiing sub-
stance^^ which forms a compound with hydrochloric acid, with the
formula Ci4ll3gN40i2SCl4. Drechsel ^^ considers that some of the oxygen
of the keratin is united to sulphur, and a part to amido-acid radicles.

The close chemical relationship of keratm to proteid coincides with
what is known as to its formation within the protoplasm of cells, for
instance in the epidermis. The eleiclin granules of the stratum granidosurii
probably represent an intermediate stage in the transformation.

^ Ann. d. Chevi., Leipzig, Bd. xlv.

^ " Versucli. einer allgem. physiol. Chem.," Braunschweig, 1844-51.
^ Klihne and Chittenden, loc. cit.

"• See Drechsel, Ladenburg's "Handworterbnch," Bd. iii. Other analyses of horn have
been made by Tilanus, Hoppe-Seyler's "PhysioL Chem.," S. 90 ; Lindvall, Jahresh. it. d.
Fortschr. d. Thier-Chem. , AViesbaden, 1881.

^ A large number of estimations of sulphur in keratins from difterent sources will be
found in a paper by Mohr, Ztsclw. f. physiol. Chem., Strassburg, 1895, Bd. xx. S. 403.
The percentage varies from 2-6 to 5*3. During {Hid., 1896, Bd. xxii. S. 281) obtained very
similar results.

^ Jahresh. ii. d. Fortschr. d. Thier-Ohem. , Wiesbaden, Bd. xviii. S. 217.
'' Skandin. Arch. f. Physiol., Leipzig, Bd. iii.
^ "Physiol. Chem.," 3rd German edition. S. 44.
^ Sitzimgsb. d. Jenaiseh. Gesellsch. f. Med. u. Naturic, 1886.
^^ Kreusler, Journ. f. 'prakt. Che7n., Leipzig, Bd. cvii.
^^ Horbaczewski, Sitzungsb. d. k. Akad. d. JFissensch., "VVien, Bd. Ixxx.
^^ Hedin, Jahresh. ii. d, Fortschr. d. Thier-Chem., "Wiesbaden, 1893, Bil. xxii,
^^ Loc. cit.



74 CHEMICAL COXSTITUENTS OF BODY AND FOOD.

Amyloid Substance. — Tliis laaterial, also called lardacein, occurs in
disease in the form of degeneration, called waxy, albmniiioid, amyloid, or
lardaceous. It principally affects small blood vessels, but it may involve
the tissue elements of organs. The degeneration occm's specially in
cases of cln'onic pus formation, and is fi'equently a sequela of sypliilis.
The name amyloid was given to it, because the substance is colom'ed
brownish red by iodine, and was supposed by Yirchow to be of
carbohydrate natm-e. Friedrich and Kekule^ were the first to show
that it is nitrogenoiLS, and gave as its percentage composition, C, 53-6 ;
H, 7: N, 15; O, 24-4 It also contains 1-3 per cent, of sulphm'.^
On decomposition it yields leucine, tp'osme, and the other products
rLSually obtained from albimiinous matter, but no sugar or other
reducing substance. By boiling with alkali a chitin-Hke residue is left.^
It is slowly soluble in gastric juice.*

Skeletins. — This term is apphed by Kridsenberg^ to a number of
nitrogenous substances found in the skeletal tissues of invertebrates.
They are characterised by gTeat insolubihty, and are probably all
amido-derivatives of carbohydi'ates. Under the term are included
chitin, conchiolin, spongin, corneui, filirom, and sericin.

Chit in. — This substance forms the chief constituent of the ectodermal
skeletal tissues of inverteljrate animals, especially of arthropods.*" In
Crustacea it is often impregnated with calcareous matter, and in the
odontophore of molluscs with silica. According to Krawkow,'^ it is in
union with a proteid-like substance. Gibson,^ Winterstein,^ and
Escombe '^^ have fomid chitin instead of cellulose in several fungi.

It is prepared from the wmg-cases of beetles by boihng them with
caustic soda. The chitin remains insoluble ; it may be dissolved in cold
concentrated hydrochloric acid, and precipitated imchanged from tliis
solution by the addition of water. It is colourless, amorphous, insoluble
in water, alcohol, ether, acetic acid, dilute mineral acids, and concen-
trated solutions of the alkahs. It is soluble in concentrated mineral acids.

The formula and constitution of clntin are differently given by
different observers. Ledderhose ^^ gave it the formula CV=iH26N20io.
Berthelot ^^ stated that it yields a fermentable sugar on boihng with
sulphmic acid. Sundwik^^ gave it the formula CgoH^ooNgOgg + wHoO
(n varying from 1 to 4), and considered it to l3e an amine derivative of
a carbohydrate with the formula {O-^M-iS^k^j,. Krawkow ^^ considers

^ Virchovs's Archiv, Bd. xvi. S. 58. - Kuhne and RuduefF, ibid., Bd. xxxiii.

" Krawkow, Centralhl. f. d. inzd. JFissenscJi., Berlin, 1892. The resemblance to chitin is
supported onlj' hy its behavioiir to staining agents like iodine. There is no true chemical
I'esemblance between the two substances. Amyloid substance, for instance, jaelds no gluco-
samine (Colin, Ztsclir. f. physiol. Chcm.. Strassburg, 1896, Bd. xxii. S. 153).

•• Kostiurin, Wien. nied. Jahrb., 1886, S. 181. See also Tschermak, Ztschr. f.iilitjslol.
Chem., Strassburg, 1895, Bd. xx. S. 343.

^ Ztschr. f. Biol., Miinchen, Bd. xxii. S. 241; " Grundziige einer vergl. Physiol, d.
thier. GeriLstsubstanz," Heidelberg, 1885.

* Gamgee ("Physiol. Chem.." vol. i. p. 299) gives a list of the situations Avhere chitin
has been described or inferred to exist. To tliese must be added the pen of cuttle-fishes
(Krukenberg, Ber. d. dcutsch. cMm. Gesellsch., Berlin, Bd. xviii. S. 989) ; and the cartilages
and other mesoblastic sti-uctures of the sepia and king crab (Halliburton, Proc. Boy. Soc.
London, vol. xxxviii. p. 75).

" Ztschr. f. Biol., Miinchen, Bd. xxix. ^ C'ompt. rend. Acad. d. sc, Paris, tome cxx.

^ Ber. d. devJsch. chcm. Gesellsch., Berlin, 1894 and 1895.

^'> Ztschr. f. physiol. Chem., Strassburg, 1896, Bd. xxii. S. 288.

" Ibid., Bd. ii. S. 213 : iv. S. 139.

'- Compt. rend.. Acad. d. sc, Paris, tome xlvii. p. 227.

'^ Ztschr. f. physiol. Chem., Strassburg, Bd. v. ^'^ Loc. cit.



SKELETINS. 75

that there are a niiniber of cliitins, amine derivatives of different
carbohydrates (dextrose, glycogen, dextrin, etc.) ; they give different
colour reactions with iodine.^ Ledderhose^ was the first to show that
the reducing substance obtained by the action of mineral acids in
chitin is not sugar but glucosamine (see p. 9). The equation re-



Online LibraryE. A. (Edward Albert) Sharpey-SchäferText-book of physiology; (Volume v.1) → online text (page 11 of 147)