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lipochromes (see p. 20).

The aqueous humour is lymph.^ In parts per 1000 it contains :
water, 986-87 ; solids, 13'13 ; proteids, 1-22 ; extractives, 4-21 ; inorganic
salts, 7'70 ; sodium chloride, 6-89.^ It does not clot spontaneously, 1)ut
does so on addition of serum. The proteids in it are fibrinogen, serum
globulin, and serum alljumin.'^- Kiihne ^ found a reducing substance
among the extractives. This is not sugar. Urea and sarcolactic acid
are also present in small quantities.^

The vitreous humour. — The memljranes of the vitreous humour

worked at especially by v. Jaksch. The following are references to the princi[ial papers
on the subject: — Miirner, loc. cit., also ibid., Bd. xii. S. 229; Nencki, Arch. f. cx'per.
Path. u. PharmaJcol., Leipzig, Bd. xxiv. S. 17, 27 ; Chem. Centr.-BL, Leipzig. 1888,
S. 587; Brandl and Pfeitfer, Ztschr. f. Biol.,^ Mtinchen, Bd. xxvi. S. 348; v. Jaksch,
Ztschr. f. 'phAjsiol. Chem., Strassbnrg, Bd. xiii. ; Aliel and Davis, Journ. Exfcr. Med..
Baltimore, 1896, No. 3, vol. i. ; Schniiedeberg, Arch. f. ed:i}er. Path. u. Pharmakol.,
Leipzig, 1897, Bd. xxxix. S. 1.

\ Untersuch. a. d. physiol. Inst. d. Univ. Heidelhercj, Bd. ii. S. 324.

- Delepine has even suggested that, in the case of the skin pigment, hfemoglobin is derived
from it {Proc. Phj^siol. Soc, London, Dec. 13, 1890, ]^. xxvii.). Abel and Davies (loc. cit.)
have recently studied the pigment of the negro's .skin. The granules contain inorganic
matter as well as pigment. The latter contains the merest trace of iron. They conclude
that it originates not from haemoglobin, but from the proteids of the tissue juice.

'^ Ztschr. f. 'physiol. Chem., Strassbnrg, Bd. xiii. S. 66.

'^ Hirschfeld, ibid., Bd. xiii. S. 407.

•' Chavvas, Arch. f. d. ges. Physiol., Bonn, Bd. xvi. S. 143.

'' Lohnieyer. See Gorup-Besanez, "Lehrbuch," 4th edition, 1878, S. 401.

'' Friend and Halliburton, Pi,cp). Brit. Ass. Adi\ S'c, London, 1889, p. 130.

^ Arch. f. d. ges. Physiol, Bonn, Bd. xii. S. 200.

" Griinhagen, ibid., Bd. xliii. S. 377; Pautz, Ztschr./. Biol., Mrlnchen, Bd. xxxi.



THE LENS.



123



yield gelatin. Its chief constituent is mucin, or mucinogen (Young),
called mucoid by C. T. Morner. According to the latter, this mucoid con-
tains 12-27 nitrogen, and 1"19 sulphur, per cent. There are also small
quantities of proteid. Eeferences to the papers of Young and Morner,
the most recent workers on this suljject, will be found on p. 62.

The lens. — The following are the results of Laptschinsky's ^
analyses : —



Water .


. 63-50 per cent.


Cliolesterin - .


0-22 per cent


Solids .


. 36-50 „


Fats


0-29 „


Proteids


. 34-93 „


Salts


0-82 „


Lecithin


. 0-23 „








Fig. 20. — Absorption spectra of retinal pigments. — 1, of visual purple ; 2, of visual yellow ;
3, of xanthophane in ether ; 4, of rliodophane in turpentine ; 5, of ehlorophane in
ether. This diagr'ainmatic way of representing absorption spectra indicates the thick-
ness of the absorption-bands in solutions of different strengths ; the top of each
spectrum shows the thickness of the bands in a dilute solution ; as the concentra-
tion of the solution increases, the bands become wider, as in the lower part of each
diagram. — After Kiihne.

The proteid matter is thus very abundant ; it is chiefly a globulin, to
which Berzelius gave the name of crystallin. It has also been the
subject of researches by Hoppe-Seyler, Laptschyisky, Kiihne, and C. T.
Morner.^ According to the last-named investigator, about 52 per cent,
of the proteid matter of the lens is insoluble in water and saline
solutions. The insoluble proteid residue is an albuminoid, and it is

1 Arch. f. d. ges. Physiol., Bonn, Bd. xiii. S. 6?.l.

- The cholestevin increases greatly in cataract (Cahn, Hoppe-Seylev's " Pliysiol. Chem,,"

'■^ Ztschr. f. physiol. Chem., Strassburg. Bd, xviii. S. 61.



124 THE CHEMISTRY OE THE TISSUES AND ORGANS.

most abundant in the inner denser portions of the lens. It yields
no nuclein on gastric digestion ; the small amount of phosphorus it
contains is due to inorganic phosphates. The soluble proteids of the
lens are also not nuclein compounds. About one per cent, of the
soluble proteid is albumin; the rest is globulin. The globulin is
precipitated by saturation with magnesium sidphate, but not with
sodium chloride ; in this it resembles vitellin. The globulin consists
of two proteids, a-crystallin and /S-crystallin.

a-Crystalhn is completely precipitable by saturation with magnesium
sulphate or with sodium sulphate at 30° C, by the addition of one and a
half times its volume of saturated ammonium sulphate solution, by a
stream of carbonic anhydride, and by very dilute acetic or hydrochloric
acids. It coagulates at 72° C. It contains : N, 16-68 ; S, 0-56 ; C, 52-83 ;
and H, 6-94 per cent. (a)„ = -46°-9.

/3-Crystallin differs from this in its coagulation temperature (64° C.)
and specific rotatory power (a)j,=-43°. It contains 17-04 nitrogen and
1-27 sulphur per cent.

a-Crystallin is more abundant in the outer, /3-crystallin in the inner,
portions of the lens; the allDumin is equally distributed. The lens
contains no keratin. The proportion between the four proteids in the
lens as a whole is as follows : —





Total Proteids.


Soluble Proteids.


In Fresh Lens.


Albuminoid .


48-0 per cent.




17-0 per cent.


a-Crystallin .


19-5


37 per cent.


6-8 „


)3-Crystallin .


32-0 ,,


62


11-0 „


Albumin


0-5




0-2 „



The Mammary Glands.

The chemical constituents of the mammary gland have not been
much studied. The principal proteid constituent of the cells is nucleo-
proteid, which swells with dilute alkali, and yields, by boiling with
mineral acid, a reducing substance. That a reducing substance (sugar)
can be obtained from the gland was first noted by Bert,^ and confirmed
by Landwehr,^ who considered its mother substance to be animal-gum ;
it is considered by Thierf elder ^ to Ije the mother-substance of lactose.
It is possil^le that the nucleo-proteid just mentioned may be the precursor
of caseinogen. The lactalbumin of milk is not identical with serum
albumin, so that its presence in milk cannot be explained by a simple
transudation from the blood.

The extractives of the mammary gland contain not unimportant
quantities of hypoxanthine ; * they have not been further investigated.



^ Gaz. hebd. de med., Paris, 1879, No. 2 ; Com]}t. rend. Acad. d. sc, Paris, tome xcviii.
" Arch. f. d. ges. Physiol., Bonn, Bd. xl. S. 21. Thierf'eldcr had previously (ibid., Bd.
xxxii. S. 619) recognised that the substance is not glycogen.
^ Loc. cit.
■* HaiuMKirsten, " Pliysiol. Clicni.," S. 378.



MILK. 125

Milk,

General properties and composition. — Milk consists of liuid (milk
plasma) in wliicli are suspended innumerable minute gloljules of fat.^ It
is therefore an emulsion, and its white colour is produced, as in other
emulsions, by reflection from the surface of the numerous globules.
The specific gravity of cow's and of human milk is about the same,
namely, 1028 to 1034.^ It is increased by the removal of the lightest
constituent, the cream. Among the milk globules are smaller particles
of proteid matter (caseinogen or nuclein X)?

The statement is still often made that each fat gioljule in milk is
surrounded by a thin membrane of caseinogen — the so-called haptogen
memljrane,'^ and it was considered that it was the rupture of these
membranes during the process of churning that enabled the fat globules
to run together to form butter. The evidence on which this idea has
rested is of a threefold nature : —

1. If the milk is filtered through a cell of porous earthenware, the
filtrate is free, not only from fat, but also from caseinogen.

2. The mass of milk globules, after having been well washed within
the filter, gives the reactions for caseinogen.^

3. If ether is added to the milk, without previous addition of
caustic potash or acetic acid (these were supposed to dissolve or
break up the proteid envelope), the fat is dissolved out with great
difficulty.

But it is now generally held with Quincke,^ who made experiments
with oil and mucilage, that each fat globule by molecular attraction
is surrounded \)j a more closely adherent layer of caseinogen solution
(or rather milk plasma), and not by a membrane. How then can
one explain the three facts just adduced in favour of the membrane
theory ?

1. If milk is filtered through porous earthenware, it is naturally free
from caseinogen ; blood serum filtered in the same way is proteid free.
The molecules of proteid are too big to go through the pores of the filter ;
there is no necessity, therefore, to suppose that the caseinogen is in a
solid condition in the milk.

2. For the same reason, no amount of washing would wash the
caseinogen through, and so naturally the milk globules would give the
reactions of the proteid with which they are contaminated. Further,
Hoppe-Seyler '^ has shown that cream yields the same percentage of
casein as the layers of milk below it.

3. The addition of reagents such as acetic acid (and rennet) enables
the fat to pass into solution more easily, not because they are solvents
of proteid, for they are not, but because they alter the relations
between the surface tensions of fat globules and milk plasma, and so

^ For tlie measurement and examination of the fat globules, see Fleisclimann, " Das
Molkereiwesen," Braunschweig, 1876-9, S. 206; F. W. Woll, "Wisconsin Exper. Stat.
Agric. Sc," 1892, vol. vi.

- For observations on the specific gravity of human milk, see Monti, Arch. f. Kmderh.,
Stuttgart, Bd. xiii.

'' Kehrer, Arch. f. Gynaek., Berlin, Bd. ii. S. 1 ; D. F. Harris, Proc. Roij. Soc. Edin.,
1896, p. 72.

•* Ascherson, Arch. f. Anat. u. Physiol., Leipzig, 1840, S. 53.

■' Radenhausen and Danilewsky, Forsch. a. d. Gcb. d. Vichhaltung, Bremen, 1880, Heft 9.

« Arch./, d. (jcs. Physiol., Bonn, 1879, Bd. xix. S. 129.

^ "Physiol. Chem.,"S. 728.



126 THE CHEMISTRY OF THE TISSUES AND ORGANS.

enable the ether to attack the fat more easily. Moreover, Hoppe-Seyler
states that it is not so difficult to remove the fat simply with ether ;
the fluid still remains cloudy, it is true, but solutions of caseinogen
are always opalescent, and this is increased by the presence in the
milk of particles of proteid or proteid-like substances, as described by
Kehrer.

The reaction of milk. — Milk readily turns sour from the fermentation
of lactose and formation of lactic acid. In carnivora fresh milk has an
acid reaction, but in most aihmals it gives either an alkaline or, more
frequently, an amphoteric reaction ; the acid phosphates in the milk
turn neutral litmus red, and the alkaline phosphates turn it blue. The
proportion between these salts varies very considerably in different
animals, in the same animal at different stages of lactation, and even
between the first and last portions of the same milking (Thorner/
Sebelien,^ Courant ^).

Courant estimated the alkaline constituent by titration with
decinormal sulphuric acid, with blue lackmoid as indicator, and the acid
constituent with decinormal soda with phenolphthaleiu as indicator.
He found as a mean for the first and last portions of the milking of
twenty cows, that the alkalinity of 100 c.c. of the milk was equal to
41 c.c, and the acidity equal to 19'5 c.c. of the respective solutions
used. In human milk the proportional alkalinity is higher ; the average
of the numbers was 10 '8 and 3 '6 c.c. respectively.

Constituents of milk. — These are water, three proteids (caseinogen,
lactalbumin, lacto-globulin), two carbohydrates (lactose, animal gum ?),
fats, extractives (traces of urea, creatine, creatinine, hypoxan thine,
lecithin, cholesterin, citric acid*), salts and gases. Most of these de-
mand separate discussion.

Effect of Ijoiling milk. — When milk is heated to, or near to, the
boiling point, a scum forms on the surface ; on the removal of this skin
it is rapidly renewed, and this can be repeated over and over again.
This is probably in part produced by the coagulation of the lact-
albumin ; this carries to the surface some caseinogen and fat.^ Contact
with air appears to be the chief influence in causing the solidification
which results in the formation of the scum ; evaporation is rapid from
the surface exposed to the atmosphere, and thus partial drying occurs
there.

The boihng of milk before it is used as a food is advantageous in
two ways — (1) all micro-organisms are destroyed ; (2) the gastric juice, in
virtue of its rennet, causes a flocculent and not a bulky precipitate.
These quite outweigh any slight diminution of digestibility alleged to
occur.^ The reason that boiled milk curdles with rennet with greater
difficulty than fresh milk appears to be that, by boiling, a part of the
dissolved calcium salt is precipitated as tricalcium phosphate.

As milk turns sour, it is possible to get a bulky heat coagulum Ijy
boiling.'''

1 Cheni. Zkj., Cothen, Bd. xvi. S. 1469. "■ Ihid., S. 597.

^ Inaug. Diss., Bonn, 1891 ; and Arch. f. d. gcs. Physiol., Bonn, Bd. 1.

^ Sdldner, Landiv. Versuchs. Stat., Berlin, Bd. xxxv.

•' Sfie D. F. Harris, Journ. Anat. and Physiol., London, 1894, vol. xxix. p. 188.

^ Raudnity,, Ztschr. f. physiol. Chcin., Strassbiirg, Bd. xiv. S. 1.

'' Recent work on this question will Le found in a paj^er by Cazeneuve and Haddon,
Comiot. rend. Acad. d. sc, Paris, 1895, tome cxx. p. 1272. Sec also influence of lioiling on
the proteids of cows' milk, Ccntralbl. f. d. med, Wissctiscli., Berlin, Bd. xxxiv. S. 145.



HUMAN MILK.



127



Under the iiiflueiice of extracts of the pancreas, the caseinogen,
before it is clotted hy the milk-curdling ferment of the gland, passes
through a stage in which it coagulates by heat. This was termed
the " metacasein " reaction by its discoverer, Sir William Koberts.^ It
does not appear to be due to the simultaneous development of acid
produced by the fat-splitting ferment of the pancreas, Ijut rather to
the action of trypsin. Edkins'-^ showed that Kiihne's purified trypsin
also produces " metacasein " in an early stage of its action, though it
does not produce coagulation of milk.

The composition of milk varies in different animals ; human milk
and cows' milk are those which have been most investigated. There
are also variations due to constitution, state of nutrition, and age.

Human milk. — The mammary glands of new-born animals of both
sexes often secrete a small quantity of milk for a few days. It is
popularly termed " witches milk." It is allsaline.^ Analyses by Schloss-
berger and Hauff,* Gubler and Quevenne,^ and Genser,*" show that the
milk of new-born children contains from 1'05 to 2-8 proteid, 0-82 to
1'46 fat, 0'9 to 64 sugar, and 0*8 salts per cent.

Colostrmn. — This liquid is yellower and more alkaline than fully-
formed milk. It contains colostrum corpuscles, rather more solids than
milk, and coagulates on heating. It contains little or no caseinogen,
but a mixture of lacto-globulin and lactalbumin.'^ The globulin is only
present in traces in fully-formed milk. The following analyses are by
Clemm,^ with the exception of the last, which is by Tidy.^



Coustitueuts.


Four "Weeks before
UeliverJ^


Seventeen

Days before

Delivery.


Nine Days

before
Delivery.


Twenty-
four Hours

after
Delivery.


Two Days

after
Delivery.




I.


11.


Water


94-52


85-2


85-17


85-85


84-38


86-79


84-08


SoHds .


5-48


14-8


14-83


14-15


15-62


13-21


15-92


Casein












2-18^




Albumin and


2-88


6-9


7-48


8-07




3-23


globulin














Fat .


0-71


4-1


3-02


2-35




4-86


5-78


Lactose


1-73


3-9


4-37


3-64




6-10


6-51


Salts .


0-44


0-44


0-45


0-54


0-51




0-34



1 Proc. Hoy. Soc. London, 1879, 1891.

" Journ. Physiol., Cambridge and Loudon, 1891, vol. xii. p. 203.

^ Witches' milk obtained from foals l;)y Amnion [Jahresh. u. d. Fortschr. ^. Thier-Chcm.,
Wiesbaden, 1876, S. 118) was acid, but this Avas probably due to fermentation having set in.

'^ An7i. d. Chem., Leipzig, Bd. xcvi. S. 68.

* Gaz. mM. de Pai'is, 1856, p. 15.

^Jahrb.f. Kinderh., Leipzig, N. F., Bd. ix. S. 60.

''J. Sebelien, Ztschr. f. physiol. Chem., Strassburg, Bd. xiii. S. 135.

^ Wagner's " Handwiirterbuch d. Physiol," Bd. ii. S. 464.

^ Land. Hosp. Ec}')., 1867-8, p. 77. See also Woodward {Journ. E^per. lied., Baltimore,
1897, vol. ii. p. 217), for recent analyses of human colostrum. Colostrum corpuscles are
not constantly present.



128 THE CHEMISTRY OF THE TISSUES AND ORGANS.



Normal human milk. — The following table gives some of the
principal analyses that have been pul^lished : —



Water.


Case-
inogen.


Albu-
min.


Fat.


Sugar.


Salts.


Remarks.


Observers.


88-58


3


69


3-53


4-3


0-17


9 days after delivery.


j-Clemni.


90-58


2-91


3-34


3-15


0-19


12 „ „


86-27


2-95


5-37


5-13


0-22




Tidy.


86-31
to \

88 -8 J




r2-6

- to
[5-4


5-8


0-23


1




1-68 to 3-15


to


to


\


Biel.i




6-6


0-34


J






1-28 i 0-34


2-56


5-6






TolmatscliefF.^


89-1


1-79


3-3


5-4


0-42




Gerber."*


87-24


1-9


4-3


5-9


0-28




Christenn.'*


89-29


1-6


3-2


5-8


0-16


Women 20-30years old


{Pfeiffer.5


89-06


1-72


2-9


6-0


0-2


„ 30-40


87-79


2-53


3-9


5-5


0-25




Mendus de Leon.''


i


1-8


0-7]












to


tol

1-7










Makris.''


4-8












97-6


1-52


3-28


6-50


0-27




Soldnor & Camerer.^


88-5


1-2 1 0-5


3-3


6-0


0-2




Lehmann & Hempel.^



The most constant feature in these analyses is the relatively low
percentage of proteids and high percentage of sugar.

Among other constituents of human milk are, 0-32 per cent, of
cholesterin (Tolinatscheff), 0-05 of citric acid/^ and 0-78 ^^ of unknown
extractives ; the last are more abundant in the colostrum, and less
abundant in cows' milk (Soldner and Camerer).

Variations in the composition of the milk occur with the stages of lactation,^^
in the milk from the two breasts and between the first and last portions of
the milking,^-^ Avith the complexion ^^ (Vernois and Becquerel — -questioned
by Tolmatscheff), Avith the age of the individual (Pfeiffer), and Avith menstrua-
tion (Vernois and Becquerel). The nature and quality of the food have a
considerable influence on the quality of the milk.^^

The salts of human milk are thus given by Bunge ^'^ in parts per 1000. —





A.


B.




A.


B.


K,0


. 0-780


0-703


Fe.,Oo .


. 0-004


0-006


]NTa.,0 .


. 0-232


0-257


P.P, .


. 0-473


0-469


CaO


. 0-328


0-343


CI.


. 0-438


0-445


MgO .


. 0-064


0-065









"^ Jalircsb. ii. d. Fortschr. d. Thier-Chem., Wiesbaden, 1874, S. 168.
" "Med. Chem. Untersueli.," Bd. ii. S. 272.

2 Bull. soc. chim., Paris, tome xxiii. •* Diss., Erlangen, 1877.

5 Jahrb. f. Kinderh., Leipzig, Bd. xx. ® Diss., Heidelberg, 1881.

■? Diss., Strassburg, 1876. » Ztsclir. f. Biol, Mlinclien, 1896, Bd. xxxiii. S. 43.

3 Arch. f. d. gcs. Physiol., Bonn, Bd. Ivi. S. 558.

1" The jn-esence of citric acid has also been noticed by Scheibe, Landw. Versuchs. Stat.,
Berlin, Bd. xxxix.

1^ J. Munk {Firchoiv's Archiv, Bd. cxxxiv. S. 501) gives the jiroportion of extractive
nitrogen to total nitrogen as 1:11 in human and 1:16 in cows' milk.

1- Pfeill'er, loc. cit. ; Vernois and Becquerel, Compt. rend. Acad. d. sc, Paris, tome xxxvi.
p. 188.

^^ Sourdat, ibid., tome Ixxi.; Brummer, Arch. f. d. gcs. Physiol., Bonn, Bd. vii.

" I'Heritier, "Traite de chim. pathoL," Paris, 1842.

15 Decaisne, Gaz. mid. dc Paris, 1871, p. 317. These are very interesting observations
made during the siege of Paris. Other Avork on the influence of food on milk is that by
Szubotin, Ccntralhl. f. d. vied. TFissensch., Berlin, 1866, S. 337, and by Commaille, quoted
by KiJnig, "Chem. d. menschl. Nahrungs. u. Gennssmittel," Bd. ii. S. 235. The question
oi' the influence of diseases and drugs Avill be found discussed in works on Therapeutics
and Pathology. -"^ Ztschr. f. Biol., Miinchen, Bd. x.



CO WS' MILK.



129



The gases of human milk. — In five experiments, 100 c.c. of mills
yielded 1-07 to 1-44 c.c. of oxygen, 2-35 to 2-87 c.c. of carbonic anhydride,
and 3-37 and 3-81 c.c. of nitrogen. The method of collecting the milk
could not have obviated admixture witli small quantities of air ; hence,
no doubt, the higher percentage of oxygen and nitrogen than previous
observers have found in the milk of lower animals.^

Cows' milk. — Colostrum. — This has a high specific gravity (1046-
1080). Its fat has a higher melting point than that of normal milk,
being poorer in the lower fatty acids.^ It contains more lecithin,
cholesterin, and proteid coagulable by heat than normal milk.^ The
following are some analyses that have been made : —



Water

Solids

Casein

Albumin and globulin

Fat .

Lactose

Salts ....


Fleischmann.-i


K6nig-.5


Vaiidin.B
Just after delivery.


Vaudin.6

Five days after

delivery.


78-7
21-3
7-3
7-5
4-0
1-5
1-0


74-7
25-3

4-041
13-6 /

3-6

2-7

1-6


77-6-72-7
22-4-27-4

14-9-20-1

2-42-6-3

1-02-2-86

1-1-1-2


85-63
14-37

4-35

5-18
4-07
0-16



Normal cows milk. — The following are averages of numerous
analyses, in the first column of those collected by Gorup-Besanez,'^ in the
second, by Hoppe-Seyler.^





I.


II.


Water .


84-28


85-86


SoHds .


15-72


15-18


Caseinogen


3-57


3-4


Albumin


0-75


0-3-0-5


Fat


6-47


4


Lactose .


4-34


4-5-5


Salts


0-63





Hammarsten^ gives the following tables (from Konig) of normal
milk and the averages of various preparations from milk as follows : —









Milk.


Skimmed Milk.


Cream.


Butter Milk.


Whey.


Water


87-17


90-66


65-51


90-27


93-24


Solids






12-83


9-34


34-49


9-73


6-76


Caseinogen
Albumin






3-021

0-53/


3-11


3-61


4-06


0-85


Fat .






3-69


0-74


26-75


0-93


0-23


Sugar .






4'88


4-75


3-52


3-73


4-7


Salts .






0-71


0-74


0-61


0-67


0-65


Lactic acid












0-34


0-33



Tatlock^*^ gives the average composition of skimmed milk as follows — (1)

1 E. Kiilz, Ztschr.f. Biol., Miinchen, 1895, Bd. xxxii. S. 180.
^ Nilson, Jaliresb. il. d. Fortschr. d. TMer-Chem., Wiesbaden, Bd. xvii. S. 169.
^ Ihid., Bd. xviii. S. 102.

'' "Das Molkereiwesen," S. 39. ^ "Chem. d. Menscli. Nahrungsmittel."

^ Journ. de pharm. et cMrn., Paris, 1894, Ser. 5, tome xxx. p. 337.
^ "Lehrbuch," 1878, S. 424. *^ "Physiol. Chem."

" "Physiol. Chem.," 3rd German edition, S. 388, 390.

^" "Produce of the Dairy," Glasgow, 1888. Numerous milk analyses will be found in
this book.

VOL. I. — 9



I30 THE CHEMISTRY OF THE TISSUES AND ORGANS.



By repose and skimming — fat, 1; proteid, 3*44; lactose, 5*1; ash, 0*75;
water, 89*67. (2) By separator — fat, 0*2; proteids, 3'4; lactose, 5*01; ash,
0-75 ; and water, 90-64.

The presence of citric acid in milk was first shown by Soxhlet. Yaudin ^
considers that this is not from the food, but produced in the mammary gland.

The variations in the milk with feeding, species of animal, time of day,
etc., are described by Struckmann and Bodeker,^ Fleischmann,-^ Tatlock,^
Kiihne and Fleischer,^ and others.



-Soldner ^ gives the following percentages :-
.■ . . 0-172

0-051

0-198

0-020

0-182
0-098



&alts of cows milk.-

K,0

m,o

CaO

MgO

P0O5 (after correction for pseudo-nuclein)
ci

Of the total phosphoric acid, from 36 to 56 per cent., and of the lime from
53 to 72 per cent., is not simply dissolved in the fluid, but is united more or
less firmly to the caseinogen. The excess of bases over mineral acids is united
to organic acids, such as citric. Bunge found 0-00035 per cent, of iron.

The gases of cows milk have been analysed by Setchenow^ and Pflliger.'^
There are small quantities of oxygen and nitrogen, and from 5 to 10 per
cent, of carbonic anhydride.

In comparing the composition of cows' milk with that of human .milk,
the main difference consists in the high percentage of proteids, fats, and
salts, and the low percentage of sugar in cows' milk as compared with
human milk. Qualitative differences will be noted under the headings
" Proteids " and " Fats."



Online LibraryE. A. (Edward Albert) Sharpey-SchäferText-book of physiology; (Volume v.1) → online text (page 18 of 147)