Chap, xxxin.] THE MAMMARY GLAND. 275 



enveloped in a delicate cuticle the albumin mem- 

 brane of Ascherson. This membrane they receive 

 from the cell protoplasm. 



According to the state of secretion, most epithelial 

 cells lining an alveolus may be in the condition of 

 forming oil globules, or only some of them; and 

 according to the rate in which milk globules are formed 

 and carried away, the alveoli differ in the number of 

 milk globules they contain. 



According to Schmid, the epithelial cells, after 

 having secreted milk globules for some time, finally 

 break up, and are replaced by new epithelial cells 

 derived by the division of the other still active 

 epithelial cells. 



366. The resting gland, i.e., the gland of a non- 

 pregnant or non-suckling individual, contains, compara- 

 tively speaking, few alveoli, but a great deal of fibrous 

 connective tissue ; the alveoli are all solid cylinders, 

 containing within the limiting membrana propria 

 masses of polyhedral granular-looking epithelial cells. 

 During pregnancy these solid alveoli undergo rapid 

 multiplication, elongation, and thickening, owing to 

 the rapid division of the epithelial cells. 



Finally, when milk secretion commences, the cells 

 occupying the central part of the alveolus undergo the 

 fatty degeneration just like the peripheral cells, but 

 they, i.e., the central cells, are eliminated, while the 

 peripheral ones remain. These central cells are the 

 colostrum corpuscles, and consequently they are found 

 in the milk of the first few days only. 



367. Ordinary milk contains no colostrum corpus- 

 cles, but only milk globules of many various sizes, from 

 the size of a granule to that of a globule several times 

 as big as an epithelial cell of an alveolus of the milk 

 gland. These large drops are produced by fusion of 

 small globules after having passed out of the alveoli 

 Each milk globule is an oil globule surrounded, as 



