i82 INTERNAL SECRETIONS OF THE OVARY 



ligaments of the virgin guinea-pig in full cestrus. The smallest 

 amount that will do this is taken as a unit. Fifteen to twenty 

 of these units are required daily to inhibit oestrus in a rat. It 

 seems probable, however, that the most satisfactory way of 

 assaying the oestrus-inhibiting hormone will be to test it against 

 a known quantity of the oestrus-producing hormone, but this, 

 of course, would involve the accurate assay of the oestrus- 

 producing substance and it cannot be said at the moment that 

 such accuracy has been achieved. 



Scope of function. It has been found by Weichert (633) that 

 the oestrus-inhibiting hormone also performs the function of 

 sensitizing the uterus to mechanical stimulation (see p. 184), 

 and it is thus possible that the same hormone is responsible for 

 all functions of the corpus luteum. 



TJic ijiteyaction of ccstrus-producer and ccstnis-inhihitoy. The 

 work described above shows that results are being obtained which 

 indicate that the effects of luteal activity may be reproduced 

 by extracts. The oestrus-inhibiting action of the corpus luteum 

 would thus appear to be definitely endocrine in nature. In this 

 case the interaction of the oestrus-producing hormone and the 

 oestrus-inhibiting hormone affords a rich field for experimental 

 work. Preliminary research in this direction has been carried out 

 by a number of workers, who have injected the oestrus-producing 

 hormone during the time when the corpus luteum dominates 

 ovarian activity, as for instance, during pregnancy or pseudo- 

 pregnancy. In such experiments it has been shown that the 

 injection of the oestrus-producer in sufficient amounts will 

 override the inhibiting action of the persistent corpus luteum. 

 Smith (573), and Parkes and Bellerby (504) were able to override 

 the activity of the persistent corpora lutea of pregnancy in the 

 mouse by the injection of the oestrus-producing hormone, while 

 Engle and Mermod (179) produced the same result by injection 

 of the oestrus-stimulating extracts of anterior pituitary. Some 

 doubt exists as to whether the effects produced were due to 

 overriding the oestrus-inhibiting power of the corpus luteum of 

 pregnancy, or to local action on the uterus. It is hardly possible, 

 therefore, to claim these experiments as demonstrating the 

 interaction of the corpus luteum and the oestrus-producing 

 hormone. The ordinary dioestrous period of the rat and mouse 



