INTERNAL SECRETIONS loi 



development of the secondary sexual characters has also been 

 referred to the interstitial cells, and, as we shall see later, the 

 early sex differences even in the ffjetal stage of develo])ment 

 are sometimes accounted for by reference to an embryonic inter- 

 stitial gland. 



The Cause of Heat. — Recent experimental and observational 

 evidence points to the conclusion that " heat " in mammals is 

 directly correlated with the secretory activity of the epithelial 

 cells of the ripe Graafian follicle. Thus Robinson states that in 

 the ferret oestrus is experienced only when the follicles are in a 

 state of ripeness which he calls the pre-enseminal stage, and that 

 this stage may be very prolonged if copulation does not occur. 

 Hammond has made observations on the rabbit, showing that an 

 extended heat period is associated with an oestrus of indefinite 

 length. Moreover, in the dog it has been found that if the 

 follicles approaching maturity are destroyed experimentally, 

 heat does not supervene at the expected time, but may recur 

 subsequently in association with a new batch of ripe follicles 

 (Marshall and Wood). Furthermore, Allen and D'Oisy state 

 that they can induce heat in rats after the removal of the ovaries 

 by injecting specially prepared alcoholic extracts of liquor folliculi, 

 and this has been confirmed by Courrier on the guinea-pig and 

 hedgehog. There is, moreover, some evidence that where there 

 is persistent oestrus (nymphomania) associated with the presence 

 of ovarian cysts, as with cows and occasionally with women, 

 this abnormal condition is correlated with hyperactivity on the 

 part of the epithelial elements of the ovary. 



The Functions of the Corpus Luteum. — The main part played 

 by the corpus luteum is now beyond the reach of controversy. 

 Broadly speaking, this organ is responsible for the changes which 

 take place in the accessory female generative organs and mammary 

 glands during pregnancy and pseudo-pregnancy. 



To Fraenkel belongs the credit of assigning to this organ a 

 definite role as an internally secreting organ, and basing his 

 view on experimental evidence. According to this investigator, 

 the corpus luteum had the function of elaborating a hormone 

 which in some way assisted in the attachment of the fertilised 

 ovum to the uterine mucous membrane, and in the maintenance 

 of its nutrition in the first part of pregnancy. The evidence, 

 which has been repeatedly confirmed, was derived mainly from 



