ii8 INTERNAL SECRETIONS OF THE OVARY 



continued cestrin injection (see p. 126). Both Mahnert and 

 Siegmund (436) and Brouha and Simonnet (91) found that 

 continued injection of the normal animal leads to long periods of 

 cornification separated by short dioestrous intervals. Since the 

 ovarian cycle is disturbed only slightly, if at all, and since 

 persistent cornification is easily produced in the normal im- 

 mature animal, this result may be due to the cyclic development 

 of the corpus luteum. There can be little doubt that the 

 continuous injection of large doses would lead to persistent 

 cornification in the normal animal. 



The pregnant animal. Since oestrus is invariably absent 

 during pregnancy, the artificial induction of oestrus during 

 gestation would seem to promise results of interest. Striking 

 effects have actually been obtained. Allen, Francis, and Craig 

 (23) obtained a positive oestrus smear during early pregnancy 

 as the result of injection of oestrin, but Brouha and Simonnet 

 (91) failed to do so in the later stages. Smith (573) showed that 

 pregnancy in the rat could be interrupted in its early stages by 

 the injection of the oestrus-producing hormone, while Parkes 

 and Bellerby (504) found that pregnancy in the mouse could be 

 terminated at all stages by the administration of an adequate 

 dose. The amount required during the later stages was twice as 

 great as in the early stages. Loeb and Kountz (405) failed to 

 interrupt pregnancy in the guinea-pig by similar means, but this 

 was probably due to inadequate dosage. Fraenkel (212) also 

 failed to produce the effect in the rabbit. Zondek and Aschheim 

 (659) produced abortion in the mouse even in the last half of 

 pregnancy by using large doses (10 m.u.), and Eels (205) reports 

 the same result. The facts seem to be well authenticated as re- 

 gards rats and mice. The effect may be brought about by either 

 or both of two actions. In the earlystages of pregnancy the effort 

 of the uterus to assume an oestrous condition may result in the 

 failure of the embryos to become implanted, or, on the other 

 hand, the injection of cestrin, by overriding the action of the 

 persistent corpora lutea, may bring about a state analogous with 

 that produced by removal of the corpora lutea during pregnancy. 



Abortion has also been reported by Engle and Mermod (179) 

 as a result of the artificial production of oestrus during pregnancy 

 by the injection of the oestrus-stimulating preparations of the 



