556 THE PHYSIOLOGY OB' REPRODUCTION 



In the secretory cells of the lactating mammary gland an 

 active and a resting condition can be distinguished. In the 

 latter the lumina of the alveoli are wide, and the cells of the 

 lining epithelium form a single flat layer with centrally situated 

 nuclei. In the active condition the epithelial cells are long 

 and columnar, and project into the lumina, and some of them 

 have two nuclei. 



In these cells numbers of granules and globules accumulate, 



FIG. 135. Section of mammary gland of woman. (From Sehafer, 



after de Sinety.) 



a, lobule of gland ; b, acini lined by cubical epithelium ; c, duct; 

 t, connective tissue. 



the former being probably of a protein nature, and the latter of 

 a fatty composition. Gradually the alveoli become charged 

 with a fluid containing detached cells and fatty globules. The 

 detached cells are usually filled with granules, staining with 

 osmic acid and seemingly identical with the colostrum corpuscles 

 which have been observed to occur in milk in the first few days 

 after parturition, and occasionally also at other times. These 

 colostrum corpuscles have been seen to exhibit amoBboid move- 

 ments, and so are probably leucocytes which have wandered 

 into the lumina of the alveoli. 1 The secretory fluid also con- 



1 Schiifer, "The Mechanism of the Secretion of Milk," Text-book of 

 Physiology, vol. i., Edinburgh, 1898. 



