io8 IXTRODUCTIOX TO SEXUAL PHYSIOLOGY 



therefore, that the internal secretion of the persistent corpus 

 hiteum sensitises tlie uterine mucous membrane, thereby render- 

 ing it capable of reacting to mechanical stimulation in the rat, 

 just as it has been shown to do in the other animals experimented 

 upon. In the pregnant animal in which the corpus luteum also 

 persists the direct stimulus is produced by the fertilised ovum. 



It has been already mentioned that in polyoestrous animals 

 the corpus luteum spurium persists for only a short time. This, 

 to speak teleologically, is to admit of o\iilation and heat recurring 

 after a short interval, since these processes cannot normally 

 take place in the presence of a fully functional corpus luteum 

 in either ovary. It would appear that this organ dominates 

 the ovarian metabolism and inhibits the secretion which is a 

 normal factor in producing the prooestrum and oestrus. It also 

 arrests the ripening of the follicles. In monoestrous animals 

 like the dog, on the other hand, the corpus luteum persists during 

 a pseudo-pregnant period, since in such animals a new heat is 

 not in any case due until a prolonged interval after the previous 

 o\Tilation. 



Under certain abnormal conditions the corpus luteum of the 

 cow, and so possibly in other animals, may persist for a prolonged 

 period unaccompanied by pregnancy. Such a condition is usually 

 associated with some pathological affection of the uterus or 

 Fallopian tubes, but the affection by itself is often slight and 

 insufficient to cause sterility. The corpus luteum, however, 

 inhibits the occurrence of oestrus, for, as first shown by Zschokke 

 and now confirmed by many others, if the corpus luteum is squeezed 

 out and thereby destroyed (as can be done in the cow through 

 the rectum) oestrus will generally recur within a few days, and the 

 cow may be got to breed. Furthermore, Hammond has shown 

 that if the normal corpus luteum of a cow is pressed out some time 

 during the " dioestrous " interval, a new heat period will ensue 

 several days before the normal time for recurrence. So also with 

 regard to ovulation ; Leo Loeb found in the guinea-pig that if 

 the corpora lutea " spuria " are removed from the ovaries, the 

 ovulation interval may be reduced from the normal sixteen or 

 eighteen days to twelve or even six days. 



The Ovaries and Partuntio7i. — The study of .pseudo-pregnancy 

 in the bitch, the experimental rabbit, and the marsupial cat 

 throws some light on the factors responsible for parturition. 



