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HUMAN MILK. 661
while among the solid fatty acids myristic and palmitic acids are found
to a greater extent than stearic acid.
The essential qualitative difference between woman’s and cow’s milk
seems to lie in the proteins or in the more accurately determined casein.
A number of both the earlier and more recent investigators ’ claim that
the casein from woman’s milk has other properties than that from cow’s
milk. The essential differences are the following: The casein from
woman’s milk is precipitated with greater difficulty with acids or salts.
It does not coagulate uniformly in the milk after the addition of rennet,
which depends, essentially, upon the low amount of lime-salts and casein
contained in the milk.2
It may be precipitated by gastric juice, but
dissolves completely and easily in an excess of gastric juice; the casein pre-
cipitate produced by an acid is more easily soluble in an excess of the acid;
and lastly, the clot formed from the casein of woman’s milk does not
appear in such large and coarse masses as in the casein from cow’s
milk, but is more loose and flocculent. This last-mentioned fact is of
great importance, since it explains the generally admitted fact of the
easy digestibility of the casein from woman’s milk.
The question as to whether the above-mentioned variations depend
on a decided difference in the two caseins, or only on an unequal relation
between the casein and the salts in the two kinds of milk, or upon other
circumstances, has not as yet been decided. According to Szontagh
and Zaitschek and also Wr6blewsky, the casein from human milk
does not yield any pseudonuclein on peptic digestion, and hence it cannot
be a nucleoalbumin. According to Kobrak, woman’s casein yields
some pseudonuclein, and with repeated solution in alkali and precipitation
by an acid it becomes more and more like cow’s casein. He therefore
suggests the possibility that woman’s casein is a compound between a
nucleoalbumin and a basic protein. Wroblewsky found the follow-
ing for the composition of casein from woman’s milk: C 52.24, H 7.32,
N 14.97, P 0.6S, S 1.117 per cent. Langstein and Bergell obtained
much lower figures for N, S and especially P, namely, 14.34, 0.85 and 0.27
per cent, respectively. According to Langstein and Edelstein the
phosphorus content is only 0.22-0.29 per cent. On hydrolysis Abder-
halden and Langstein 3 could not find any difference between cow
and human casein.
1
See Biedert, Untersuchungen iiber die chemischen Unterschiede der Menschen-
und Kuhmilch (Stuttgart), 1884; Langgaard, Virchow’s Arch., 64; Makris, Studien
iiber die Eiweisskorper der Frauen- und Kuhmilch. [naug.-Diss. Strassburg, 1876.
2
See among others Bienenfeld, Bioch. Zeitschr., 7, an 1 Full and Wohlgemuth,
ibid., 8.
s
Szontagh, Maly’s Jahresber., 22; Zaitschek, 1. c. ; Wr6blewsky, Beitrage zur
Kenntniss des Frauenkaseins, Inaug.-Diss. Bern. 1894, and Ein neuer eiweissartiger
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