THE FEMALE REPRODUCTIVE ORGANS. 



239 



FIG. 276. 



tion advances, their granular protoplasm becomes broken up and 

 displaced by the accumulation of oil-globules within the cell ; these 

 minute oil-drops exist at first as minute separate particles, which 

 gradually increase in size, until finally they become confluent and 

 form a single large globule, which occupies the greater part of the 

 entire cell ; the nucleus in consequence is displaced towards the 

 periphery, next the basement- membrane, where it lies embedded 

 within the thin belt of protoplasm occupying the outer zone of the 

 cell. During secretion the acini possess a comparatively wide 

 lumen, since the epithelial layer forms but a narrow lining to the 

 irregular spherical or tubular spaces. The cells within a single acinus 

 often contain very unequal amounts of oil ; some of the elements 

 are so loaded that the entire cell is occupied by the oil-drop, while, 

 on the other hand, the neigh- 

 boring cells may contain so 

 little oil that the presence of 

 the fatty particles is masked 

 by the general protoplasm. 

 Between the extremes all gra- 

 dations may be found. Upon 

 reaching a certain tension, the 

 contained oil-globules, es- 

 caping in the direction of least 

 resistance, are discharged into 

 the cavity of the acinus, where 

 they, together with the gran- 

 ular debris of old epithelial 

 cells, are collected within an 

 albuminous fluid and consti- 

 tute the lactiferous secre- 

 tion. The assumed destruction of the epithelial cells following the 

 discharge of the oil-globules is improbable, since the cell then simply 

 enters upon a period of rest and repair, during which its powers of 

 secretion are recuperated. In the earliest stage of the activity of the 

 mammary gland, when the flow of milk is first established, the acini, 

 in many cases, still retain their primitive condition of solidity ; 

 while the cells at the periphery remain as the secreting elements, 

 those occupying the centre of the acinus undergo fatty degeneration, 

 some become disintegrated, while others are cast off as masses which 

 constitute the colostrum-corpuscles found in the milk during the 

 first few days. 



The secretion accumulated within the comparatively large alveoli 

 is carried off by the terminal branches of the ducts, whose walls 

 consist of a basement-membrane and a single layer of low colum- 



Section of human mammary gland, including sev- 

 eral acini (a ) engaged in sluggish secretion of milk ; 

 b, epithelial elements containing oil-droplets ; c, inter- 

 acinous connective tissue. 



