MAMMARY GLANDS. 145 



The walls of the alveoli consist of a basement-membrane, 

 covered, during the period when the gland is not active, by a single 

 layer of flat or cuboidal cells (Fig. 90) with one nucleus and 

 presenting a granular appearance. There are at this time no fat- 

 globules. When, however, the gland begins to take on an active 

 condition (Fig. 91) these cells become higher and project into the 

 interior of the alveoli, and the single nucleus divides, thus becom- 

 ing two. In the cytoplasm drops of fat appear, especially at the 

 ends of the cells nearest the interior of the alveoli, and at the 

 same time the nucleus which is nearer to this end of the cell 

 becomes fatty. This end of the cell then breaks down, and the 



FIG. 87. Arrangement of glandular tissue of breast, the fat having been removed 

 to show the ducts and acini (Astley Cooper). 



material forms the albuminous ingredients of the milk and the 

 lactose, while the drops of fat become the milk-globules. The 

 portion of the cell which remains forms new cytoplasm, and the 

 same process is repeated over and over again. The cells also 

 secrete water and the salts which are found in the milk. 



There is some difference of opinion as to the origin of the 

 corpuscles found in the colostrum, and which are known as 

 colostrum-corpuscles. One view is that they are epithelial cells 

 of the alveoli, which become rounded and in which fat is devel- 

 oped, and that in this condition they become detached and are 

 discharged into the cavity of the alveolus. Another view is that 

 10 



