CHAPTER XIV. 

 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, 

 investigated by ODENIUS, contains as an average the following: 17.28 

 per cent N, 0.89 per cent S, and 0.277 per cent P. .MANDEL has made 

 an analysis of the hydrolytic cleavage products of the nucleoprotein of the 

 mammary glands, carefully prepared according to HAMMARSTEN'S method, 

 and finds the amino-acids in nearly the same quantitative proportions as 

 they occur in casein, as determined by FISCHER and ABDERHALDEN-and by 

 HART. 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 pen- 

 tose reactions and yielded abundance of levulinic acid. Besides this 

 nucleic acid, MANDEL and LEVENE 2 isolated from the glands a gluco- 

 thionic acid with 2.65 percent S and 4.38 per cent N. We cannot state 

 what relation these substances bear to that constituent of the gland 

 found by BERT, which on boiling with dilute mineral acids yielded a 

 reducing substance. A similar substance, which acts perhaps as a step 

 toward the formation of lactose, has also been observed by THIERFELDER. 

 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-glcbules. The extractive bodies of the 

 mammary glands have been little investigated, but among them are 

 found considerable amounts of punne bases. The mammary glands 



1 Odenius, Maly's Jahresber., 30; Mandel, Bioch. Zeitschr., 22; Mandel and Levene, 

 Zeitschr. f. physiol. Chem., 46; Loebisch, Hofmeister's Beitrage, 8. 



2 Zeitschr. f . physiol. Chem., 45. 



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