THE GENITAL GLANDS 17 



other may pour out a little milk, but this is due to 

 reflex contraction of the muscle about the ampullae 

 of the ducts. The only drug which increases the 

 flow of milk is pituitary extract, and we have not 

 yet found a way to utiHze this in the human subject. 



The physiological stimulus which starts the 

 lactation is an internal secretion derived from the 

 foetus. Injection of extracts of foetal animals into 

 a non-pregnant female of the same species brings 

 about hypertrophy and functional activity of the 

 mammary glands (Starling and Lane-Claypon) . The 

 statement that this hormone is derived from the 

 ovary can scarcely be true, because lactation is 

 normal after double oophorectomy. It is not un- 

 common for the rudimentary breasts, even of the 

 foetus, to be stimulated to a few days' activity 

 (" witch's milk "). One of a pair of conjoined 

 Siamese twins was recently delivered of a child, 

 and both commenced lactating. 



Once started, the secretion of milk is kept up by 

 suction. When this ceases, the glands return to the 

 quiescent state. 



THE OVUM. 



The epithehal and other cells of the adult are not 

 immortal, and require frequent renewal to repair 

 daily wear and tear. The cell-divisions bringing 

 this about are initiated by the division of a body 

 outside the nucleus, called the centrosome, which 

 forms the achromatic spindle. A skein appears in 

 the nucleus, which divides into V-shaped bodies 

 called chromosomes, which in man are twenty-four 



2 



