MILK. 319 



for casein. Better founded is the statement that the casein origi- 

 nates from the protoplasm of the gland cells, which seem to consist 

 of casein or a substance related to it. The previously (page 300) 

 mentioned nucleoalbumin of the gland-cells appears to be related 

 to casein, and it may possibly form its mother substance. There 

 does not seem to be any doubt that the protoplasm of the cells 

 takes part in the secretion in such a manner that it becomes itself 

 a constituent of the secretion. According to HEIDENHAIN, the 

 alveoles contain a simple layer of cells, which, in the inactive gland, 

 are flat, polyhedrons, and with single nucleus, while in the active 

 gland they often have several neuclei, are rich in albumin, and are 

 high and cylindrical in form. In the inner part of the cell turned 

 towards the cavity of the acinus, single fat-granules are formed 

 during the secretion which are broken off with the edge of the cells. 

 The broken-off or destroyed cell-substance in the secretion dissolves 

 in the milk, filling the lumen of the acinus, while the cells take up 

 nutrition by their outer parts, and grow, and replace the inner parts 

 used in the secretion. This reminds us of the action of the pan- 

 creas-cells in the secretion of the pancreatic juice. The colostrum- 

 corpuscles are not, according to HEIDENHAIN, degenerated fat- 

 cells, but are contractile elements originating from the epithelium, 

 which take up finely-divided fat and thereby obtain their quantity 

 of fat-globules. 



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

 plasm, 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. A formation of fat from 

 carbohydrates in the animal organism is at the present day consid- 

 ered as positively proved, and it is also possible that the milk-glands 

 also produce fats from the carbohydrates brought to them by the 

 blood. It is a well-known fact that an animal gives off for a long 

 time, daily, considerably more fat in the milk than it receives as 

 food, and this proves that at least a part of the fat secreted by the 

 milk is produced from proteids or carbohydrates, or perhaps from 

 both. The question as to how far this fat is produced directly in 

 the milk-glands, or from other organs and tissues, and brought to 

 the gland by means of the blood, cannot be decided. 



