ORIGIN OF MILK FAT 423 



ORIGIN OF MILK FAT 



As the final subject of this section of our study of fat 

 metabolism, the origin of the fat in milk may be presented 

 for consideration. 71 In bringing this subject forward in 

 direct connection with the chapter upon the processes of 

 fatty change, a historical rather than a logical relation is 

 being followed. 



The older pathologists looked upon the origin of the milk 

 fat as an example of supposed conversion of protein into fat. 

 Virchow was fully convinced that both the fat globules and 

 the other constituents of milk arise from a fatty degeneration 

 and disintegration of the cells of the mammary gland. Then, 

 later, Haidenhain modified this view by supposing that only 

 that part of the gland cell next to the lumen sets free the fat 

 droplets as it undergoes disintegration. C. Voit, in connec- 

 tion with his above mentioned doctrines, advocated the idea 

 that protein breaks down in nursing animals in such manner 

 that its nitrogen is excreted as urea and the residue, rich in 

 carbon, is secreted as fat with the milk. That the doctrine 

 of the protein origin of the milk fat was firmly impressed by 

 the weight of the great and overpowering authority of these 

 men upon the minds of physiologists is, of course, not in the 

 least remarkable ; and it has required a great deal of labor to 

 evict it. Among others, the noted Heidelberg pathologist, 

 J. Arnold (to whom I refer as one of my teachers with special 

 appreciation), not long ago undertook to reinvestigate the 

 subject by a thorough histological study of the mammary 

 glands of women and female animals. He came to the con- 

 clusion that, contrary to the assumption of Virchow, even the 

 freest secretion of milk may take place without any degener- 

 ation of the cells of the mammary glands. The fat appears 

 in the interior of the cells, especially in the basal portion of 

 the cytoplasm, that away from the lumen of the gland, and 



"Literature upon Milk Fat: K. Basch, Ergebn. d. Physiol., 2', 366-373, 

 1903; R. W. Raudnitz, ibid., 259-264, 1903; A. Magnus-Levy and L. F. Meyer, 

 Hand. d. Biochem., 4', 468, 1909 ; L. Kalabaukoff, Biologic mdicale, Jan., 1909. 



