402 



STRUCTURE OF THE MAMMA. 



During the first few days after delivery, the breasts secrete a small amount of 

 milk of greater consistence, and of a yellow colour the colostrum in which 



large cells filled with fatty granules occur 

 the colostrum-corpuscles. Sometimes a nucleus 

 is observable within them, and rarely they 

 exhibit amoeboid movements (Fig. 172, c, d, c). 

 The regular secretion of milk begins after 3-4 days. 

 It was formerly supposed that the cells of the 

 acini underwent a fatty degeneration, and thus 

 produced the fatty granules of the milk. It is 

 more probable, from the observations of Strieker, 

 Schwarz, Partsch and Heidenhain, that the cells 

 of the acini manufacture the fatty granules, and 

 their protoplasm eliminates them, at the same 

 time forming the clear fluid part of the milk. 



Fig. 171. 



Acini of the mammary gland 

 of a sheep during lactation 

 a, membrana propria ; b, 

 secretory epithelium. 



Changes during Secretion. Partsch and 

 Heidenhain found that the secretory cells 

 in the passive non-secreting gland (Fig. 172, I) were flat, polyhedral, 

 and uni-nucleated, whilst the secreting cells (Fig. II) often con- 



Fig. 172. 



I Inactive acinus of the mamma. II During the secretion of milk ; a, b, milk- 

 globules ; c, d, ?, colostrum-corpuscles ; f, pale cells (bitch). 



tained several nuclei, were more albuminous, higher, and cylindrical 

 in form. The edge of the cell directed towards the lumen of the 

 acinus undergoes characteristic changes during secretion. Fatty 

 granules are formed in this part of the cell, and are afterwards ex- 

 truded. The decomposed portion of the cell is dissolved in the milk, 

 and the fatty granules become free as milk-globules. (Fig. II, a). If 

 nuclei are present in that part of the cell which is broken up, they also 

 pass into the milk and give rise to the presence of nuclein in the 

 secretion. 



Besides the milk-globules and colostrum-corpuscles, Rauber has found leucocytes 

 undergoing fatty degeneration and single pale cells (/). Occasionally milk-globules 

 are found with traces of the cell-substance adhering to their surface (6). 



Formation Of Milk. Concerning the formation of the individual constituents 



