CHEMICAL UEGULATOllS 399 



which is a sterile female calf, born with a normal male twin. Lillie 

 discovered in these instances that there was a fusion of the embryonic 

 circulations between the twins and that, since the male gonads develop 

 before those of the female, the male hormone appeared first in the 

 united fetal circulation and not only interfered with the growth of the 

 ovary to such an extent as to cause sterility, but even caused a tend- 

 ency toward the assumption of secondary male characters. 



Evidence relating to a second type of secretion associated with the 

 rhythmical recurrence of ovulation in the female of all vertebrates 

 leads to the belief that in mammals at least two ovarian hormones 

 occur, — one derived from the follicular cells surrounding the egg 

 before it escapes from the ovary, and the other from the mass of cells, 

 or corpus lutcum, that fills the follicle after rupture. 



The cells of the follicle secrete a hormone known as ocstrin into the 

 follicular fluid. This substance has the dual function of initiating 

 some changes in the female and completing other reactions. Ocstrin 

 is secreted by the ovaries of all vertebrates which have been studied so 

 far. It is a growth-promoting hormone which governs the develop- 

 ment of the secondary sexual characters, including the reproductive 

 tract of the female, while the corpus luteum, as known at present, is 

 really a mammalian gland w^hich has appeared in association with 

 lactation and viviparity. The corpus luteum hormone, progestin, 

 prepares the uterus for the reception of a fertilized egg, and if one 

 does not appear the corpus luteum involutes, the uterus returns to a 

 resting condition, and a new cycle is started. Progestin quiets the 

 uterus by inhibiting its rhythmic, spontaneous contractions. In the 

 strict sense the corpus luteum may be regarded as a gland of preg- 

 nancy. Several interesting experiments have been performed on 

 various mammals. It is well known that the mating instinct is lost 

 when a normal female is spayed (removal of ovaries). Allen and 

 Doisy were able to produce characteristic cychcal changes in the genital 

 tract of spayed rats and mice by the injection of the hormone from 

 the follicular fluid. 



The interstitial cells of the testes evidently yield hormones which 

 produce secondary sexual characters in a castrated male. Much 

 work still remains to be done on this point. 



The Master Gland or "Generalissimo," the Pituitary 



The pituitary gland, or hypophysis, might well be regarded as the 

 commander-in-chief of all the endocrine glands. Embryologically the 



