IX 



THE SKIN AND CUTANEOUS GLANDS 



511 



case of all the other secretions. This does not preclude the multi- 

 plication of cells during the active secretory work of the mammary 

 gland to an extent in excess of the normal, but at present we 

 know nothing as to the exact manner in which this is accomplished. 

 According to Steinhaus (1892) there is frequent mitotic division 

 of the cell nuclei without subsequent cellular division, accom- 

 panied by transformation of the nuclear substance into fat which 

 would explain the origin of the fat of milk. Szabo (1896), on the 



Pio. 141. Section of lobule of mammary gland of guinea-pig during lactation. (Szymonowicz.) 

 olv, lumen of alveolus ; mp, membrana propria ; ep. olv, alveolar epithelium, tangential 

 section ; <jl, gr, fat drops stained o.srnic acid. 



contrary, observed no mitosis during lactation, but an a-mitosic 

 multiplication of nuclei, so that each cell contained two or three. 

 He also found a great accumulation of protein granules in the 

 cell protoplasm, which gradually pass into the secretion and 

 become dissolved. 



In all probability these granules are the nucleo-gluco-protein 

 which Hammarsten (1894) found in the protoplasm of the 

 mammary gland, and which probably represents the mother 

 substance of the caseinogen and lactose. In fact, Thierfelder 

 (1883) saw that on grinding up fresh mammary gland in physio- 

 logical saline, and leaving it to digest for some time at body 



