THE GLANDS OF THE SKIN. 



401 



lium, except near their termination in the nipple, where they are 

 lined by stratified pavement epithelium, and surrounded by a fibrous 

 tissue sheath. 



The epithelium of the alveoli differs according to the state of 

 functional activity. In a state of rest it consists of a single layer 

 of glandular cells of nearly cubical shape which stain deeply, the 

 internal surfaces now and then projecting slightly into the lumen. 

 At the beginning of secretion fat globules make their appearance in 

 the distal ends of the cells. At the same time a corresponding 



Alveolus. 



Duct and 

 alveoli. 



Adipose tissue. 



Fig. 325. From section of mammary gland of nullipara. (From Nagel's "Die 

 weiblichen Geschlechtsorgane," in " Handbuch der Anatomic des Menschen," 1896.) 



increase in size occurs throughout the entire alveolus. There are 

 as yet current two quite contradictory views as to the manner in which 

 the milk is secreted. According to certain observers, the free ends 

 of the cells, which contain the most fat globules, are constricted off", 

 after which the fat globules are freed in the lumen. The secretory 

 portion of the alveolus is then composed of low epithelial cells, in 

 which the process begins anew. The process of milk secretion 

 therefore consists in throwing off the inner halves of the cells con- 

 taining the fat globules, and in regeneration of the cells from the 

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