CHEMISTRY OF MILK SECRETION. 635 



secreted by the milk are in quite different proportions from those in the 

 blood -serum. 



Little is known in regard to the formation and secretion of the specific 

 constituents of milk. The older theory, that the casein was produced 

 from the lactalbumin by the action of an enzyme, is incorrect, and prob- 

 ably originated from mistaking an alkali albuminate for casein. Better 

 founded is the theory that the casein originates from the protoplasm 

 of the gland -cells. There does not seem to be any doubt that the pro- 

 toplasm of the cells takes part in the secretion in such a manner that it 

 becomes itself a constituent of the secretion, and this also agrees with 

 HEIDENHAIN'S l views. According to BASCH'S researches, the casein 

 is formed in the mammary gland by the nucleic acid of the nucleus being 

 set free and uniting intra-alveolar with the transudated serum, thus form- 

 ing a nucleoalbumin, the casein. The untenableness of this view has 

 been shown by LOBISCH, and the investigations of HiLDEBRANDT 2 upon 

 the proteolytic enzyme of the mammary gland, and the autolysis of the 

 gland have not given any clue as to the mode of formation of casein. 

 There is no doubt that it is formed in the mammary glands by a synthesis. 

 The findings of MANDEL 3 .that the hydrolytic cleavage products of the 

 nucleoprotein from the mammary glands occur approximately quan- 

 tatively in the same proportions as in casein, are important in this 

 connection. 



That the milk-fat is produced by a formation of fat in the protoplasm, 

 and that the fat-globules are set free by their destruction, is a generally 

 admitted opinion, which, however, does not exclude the possibility that 

 the fat is in part taken up by the glands from the blood and eliminated 

 with its secretion. That the fats of the food can pass into the milk follows 

 from the investigations of WINTERNITZ, as he has been able to detect the 

 passage of iodized fats in the milk. JANTZEN has shown that after feeding 

 iodized casein, the milk-fat of goats contained a little iodine, which 

 indicates that the iodized milk-fat could also have a different origin. 

 As a contamination of the casein fed with iodized fat was not excluded 

 in these experiments, they do not seem to modify the proof of the investi- 

 gations of WINTERNITZ and others (CASPARI, PARASCHTSCHUK 4 ). The 

 abundant quantities of iodized fat which were eliminated with the milk 

 in these cases without doubt depend, at least in great part, upon the 

 iodized fat of the food, hence it cannot be said that all of the milk-fat 



1 Hermann's Handbuch, 5, Teil 1, 380. 



2 Basch, Jahrb. f. Kinderheilkunde, 1898; Hildebrandt, Hofmeister's Beitrage, 5; 

 Ldbisch, ibid., 8. 



3 Bioch. Zeitschr., 22. 



4 Winternitz, Zeitschr. f. physiol. Chem., 24; Jantzen, Centralbl. f. Physiol., 15 ; 

 Caspar!, Arch. f. (Anat. u.) Physiol., 1899, Supplbd. and Zeitschr. f. Biologic, 46; 

 Paraschtschuk, Chem. Centralbl., 1903, 1. 



