Chap. XX.] FEMALE GENERATIVE ORGANS. 251 



The walls of the ducts and of the secreting recesses are 

 formed of a basement membrane lined by epithelium-cells. 

 During lactation the secreting cells become much enlarged, 

 and fatty globules are formed within them. The fatty glob- 

 ules appear to be set free by the breaking down of the inner 

 part of the cell, the protoplasm becoming dissolved also, and 

 forming the proteid substances of the milk. At the beginning 

 of lactation the cells are imperfectly broken up, so that numerous 

 cells containing comparatively large masses of fat (the colostrum 

 corpuscles) appear in the secretion. 



Human milk has a specific gravity of from 1028 to 1034, and 

 when quite fresh possesses a slightly alkaline reaction. Its 

 average composition in every 100 parts is : — 



Proteids 2 



Fats 2.75 



Sugar 5 



Salts 0.25 



Water 90 



100 



{Foster.) 



