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CHAPTER XIII.
MILK.
The chemical constituents of the mammary glands have been little
studied. The cells are rich in protein and nucleoproteins. Among the
latter we have one that yields pentose and guanine, on boiling with dilute
mineral acids, but no other purine base. This compound protein, inves-
tigated by Odenius, contains as an average the following: 17.28 per
cent N, .0.89 per cent S, and 0.277 per cent P. Besides this compound
proteid we have at least one other, as Mandel and Levene and Loebisch l
have isolated a nucleic acid from the mammary gland, which, like the
thymonucleic acids, yielded adenine, guanine, thymine, and cytosine.
This nucleic acid also gave the pentose reactions and yielded an abundance
of levulinic acid. Besides this nucleic acid, Mandel and Levene isolated
from the glands a glucothionic acid with 2.65 per cent S and 4.38 per
cent N. Among the cleavage products of the nucleoprotein Mandel 2
obtained no glycocoll, and the products of hydrolysis show a great cor-
respondence with those of casein. We cannot state what relation the
above-mentioned nucleic acids and the glucothionic acid bear to the
not well-known constituent of the glands fcund by Bert and by Thier-
felder and which yields a reducing substance when boiled with dilute
acids.
It is to be expected that these bodies are steps in the formation of
milk-sugar; still we have no point of support for such an assumption,
and recent investigations seem to indicate that the milk-sugar is produced
in the glands by a transformation of the sugar of the blood. Fat seems,
at least in the secreting glands, to be a never-failing constituent of the
cells, and this fat may be observed in the protoplasm as large or small
globules similar to milk-globules. The extractive bodies of the mam-
mary glands have been little investigated, but among them are found
considerable amounts of purine bases. The mammary glands also
contain enzymes, among which we especially mention : catalase,
Odenius, Maly’s Jahresber., 30; Mandel and Levene, Zeitschr. f. physiol. Chem.,
46; Loebisch, Hofineister’sBeitriige, 8.
* Mandel and Levene, Zeitschr. f. physiol. Chem., 45, Mandel, Bioch. Zeitschr , 23
643
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