126 INTERNAL SECRETIONS OF THE OVARY 



appearance of changes characteristic of the post-ovulative phase. 

 Animals such as the rabbit and the ferret which remain on 

 oestrus indefinitely (in the absence of copulation) without show- 

 ing any other changes, lead one to suppose that prolonged 

 exertion of the oestrous stimulus does not cause changes 

 characteristic of the luteal phase. This supposition can be 

 confirmed experimentally — continued injection of oestrin results 

 in continued oestrus, probably with exaggerated symptoms, but 

 in nothing more. Analysis of the results produced in the 

 various accessory organs by prolonged administration of oestrin 

 fails to show the production of any changes characteristic of the 

 luteal phase. 



Changes tn the vagina. Cornification of the immature or 

 ovariectomized rodent vagina has been prolonged for nine days 

 by Frank, Kingery and Gustavson (224), thirteen days by 

 Parkes and Bellerby (505), two to three weeks by Zondek and 

 Aschheim (652), fifteen days by Mahnert and Siegmund (436), 

 and thirteen days by Tuisk (619), who concludes 'that we shall 

 always find a prolonged oestrus if in any way the threshold 

 concentration of the follicular hormone is maintained in the 

 blood.' Failure to secure persistent cornification in the normal 

 adult with the doses employed may be due to the cyclic activity 

 of the corpus luteum. The evidence is thus against the view 

 that continued injection of oestrin in the ovariectomized animal 

 will produce anything but prolonged cornification in the vagina, 

 which contrasts definitely with the disappearance of cornified 

 cells and the great infiltration of leucocytes which follow 

 ovulation in the normal animal. Continued action of oestrin 

 is therefore antagonistic to the vaginal changes characteristic of 

 the luteal phase. 



(Estrin and the post-ccstrous uterus. The growth of the uterus 

 in the non-pregnant animal may be divided into two phases, 

 namely that occurring at oestrus and that occurring after 

 ovulation, presumably as a preparation for the reception of a 

 fertilized ovum. In most animals these two phases are quite 

 distinct and the changes characteristic of oestrus pass off before 

 the onset of those correlated with the luteal phase of the cycle. 

 It is known quite definitely that the oestrous changes in the 

 uterus are brought about by the oestrus-producing hormone, and 



