MAMMARY GLANDS. 329 



grow to considerable size and are called colostrum corpuscles. Beneath 

 the alveolar epithelium there are basal or basket cells which have been 

 compared with the muscle fibers of sweat glands. A basement membrane 

 separates them from the connective tissue which contains many mono- 

 nuclear leucocytes and eosinophilic cells. 



After the birth of the child the gland cells become larger and are 

 filled with stainable secretory granules and fat droplets; the latter are 

 near the lumen and are often larger than the nucleus (Fig. 383). After 

 two days of lactation some of the gland cells are flat and empty of secre- 

 tion. Others are tall columnar, with a rounded border toward the lumen; 



Branch of an excretory duct. Connective tissue. 



itftlrt? 



^". V *'\ i/.*V* - - %'* 



-Tubule. 



Alveole- tubular 

 end piece. 



mA 



FIG. 382. SECTION OF A HUMAN MAMMARY GLAND AT THE PERIOD OP LACTATION X 50. 



often they contain two nuclei. The fat within them is not a degeneration 

 as in sebaceous glands, nor a secretion produced by the nucleus; it is a 

 product of protoplasmic activity, and may fill the cell several times before 

 it perishes. Transitions between the low empty cells and the columnar 

 forms occur, but mitoses are absent from the lactating gland. Mitotic 

 divisions are numerous during pregnancy. 



Milk consists of fat droplets, 2-5 p in diameter, floating in a clear 

 fluid containing nuclein derived from degenerating nuclei, and occasion- 

 ally a leucocyte or colostrum corpuscle. The interstitial connective tissue, 

 greatly reduced by the enlarged glands, also contains very few leucocytes 

 and eosinophilic cells. 



