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 found 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, 



1 Odenius, Maly's Jahresber., 30; Mandel and Levene, Zeitschr. f. physiol. Chem., 

 46; Loebisch, Hofmeister's Beitrage, 8. 



'Mandel and Levene, Zeitschr. f. physiol. Chem., 45, Mandel, Bioch. Zeitschr., 23. 



643 



