THE REPRODUCTIVE ORGANS 85 



of experiments designed to test the theory that the cestrous 

 cycle is determined by an internal secretion on the part of the 

 ovary. Extracts were made from ovaries in a pro-cestrous or 

 cestrous condition and injected subcutaneously into a bitch 

 at a period as remote as possible from the cestrous one. In 

 some of these experiments a swelling of the vulva and other 

 slight signs of the cestrous condition were induced, but the 

 results were not decisive enough to warrant publication. 

 Since then, however, Marshall and Jolly have reported that 

 " heat," or a transient condition resembling it, can be produced 

 by the injection of extracts of cestrous ovaries. It is possible 

 that in some of these experiments the extracted ovaries con- 

 tained corpora lutea and that the effects observed (chiefly 

 consisting of hyperaemia of the external genitals) were due to 

 active substances derived from the yellow bodies. Recent 

 experiments have confirmed the fact that injection of extracts 

 of ovary cause hypersemia and swelling of the reproductive 

 organs. It is not clear from these experiments how far the 

 results are due to corpus luteum and how far to other parts 

 of the ovary. The changes induced do not seem to be tr,ue 

 cyclic growth processes, but simply transient circulatory 

 effects. Pearl and Surface have recently shown that the 

 desiccated fat free substance of the corpus luteum of the cow, 

 when injected in suspension into an actively laying fowl, 

 immediately inhibits ovulation. After the bird begins ovula- 

 ting again, the laying goes on as before. The substance 

 which produces the effect is rendered inactive by boiling. 



In future researches upon the pharmacodynamics of ovarian 

 extracts great attention should be paid to the chemistry of 

 the products obtained, and very careful control experiments 

 should be carried out. 



Prenant, in 1898, thought that the corpus luteum, through 

 an internal secretion, influences the general metabolism of 

 the body and prevents ovulation during pregnancy anpl between 

 the cestrous periods. As a result of the investigations of 

 Loeb and others, this theory seems now to be firmly established. 

 Loeb found in sixty-six guinea-pigs that spontaneous ovulation 

 rarely occurs within sixteen to eighteen days after a preceding 

 ovulation. In twenty -five animals all the yellow bodies were 

 removed and 92 per cent, of these all ovulated within 12- 

 days after coitus, showing a marked shortening of the 



