28 THE MILK QUESTION 



which flows the milk from all the little alveoli to the 

 nipple. 



The alveoli are the true functional structures of the 

 gland — that is, the part where the milk is secreted. The 

 alveoli are lined with epithelial cells which, in a state of 

 rest, consist of a single layer of cells, nearly cubic in shape. 

 When the gland is ready to secrete milk the fat globules 

 make their appearance in the distal ends of the cells: at the 

 same time a corresponding increase in size occurs through- 

 out the entire alveolus. 



The exact manner in which the milk is secreted is not 

 definitely known. There are, as yet, current two quite con- 

 tradictory views as to the manner in which milk is formed. 

 According to certain observers the free ends of the cells 

 which contain the most fat globules are constricted off, 

 which sets the fat globules free in the lumen. The secretory 

 portion of the alveolus is then composed of low epithelial 

 cells in which the process begins anew. According to this 

 view the process of milk secretion, therefore, consists in 

 throwing off the inner halves of the cells containing the fat 

 globules. After this occurs, the cells regenerate themselves 

 from the nucleated remains of the glandular epithelium. 

 There is some doubt whether the nucleus divides or not 

 during this process, and of course there is no way of know- 

 ing how often the process of regeneration may be repeated 

 in a single cell. It is certain, -however, that entire cells are 

 destroyed, to be replaced later by new ones. Other ob- 

 servers regard the secretion of milk as occurring without 

 partial or total destruction of the secretory cells, but after 

 the manner of the secretion of other glands. This latter 

 view seems more in accord with recent observations. 



Although the exact mechanism of the production of milk 

 is not known, certain facts are perfectly clear: The milk 

 is formed from the blood. It is the epithelial cell in the 

 alveolus which takes the materials from the blood and trans- 

 forms them into milk. The little epithelial cell is a very 



