THE FUNCTION OF (ESTRIN 127 



accordingly it seems highly improbable that a further set of 

 different changes can be produced by the same agency. In the 

 normal mouse and rat the injection of oestrin after copulation 

 leads to the return of oestrous symptoms, and to the failure of 

 the embryos to become implanted. There is sufficient evidence 

 to state, therefore, that in the rat and mouse the oestrus- 

 producing hormone is not concerned with the production of 

 post-oestrous changes; the experimental prolongation of its 

 activity is directly antagonistic to the changes of the luteal 

 phase. In the guinea-pig and the cow, as shown respectively by 

 Loeb and by Hammond, the antagonism between the folli- 

 cular phase and the post-oestrous phase has been well demon- 

 strated. These authors showed that removal of the corpora 

 lutea after ovulation led to a much earlier return of oestrus, and 

 in these animals, therefore, the action of the corpus luteum is 

 clearly directly opposed to that of the oestrus-producing 

 substance. Loeb (405J, too, has shown that the pre-decidual 

 changes in the guinea-pig uterus are inhibited by the injection 

 of oestrin, and further, that such treatment inhibits the uterine 

 sensitivity to mechanical irritation necessary for the formation 

 of deciduomata. In the rabbit uterus, the prolonged period of 

 oestrus leads to none of the changes w^hich are characteristic of 

 pseudo-pregnancy. Many workers have figured the rabbit 

 uterus after heavy or prolonged dosage w^th oestrin, and in no 

 case has any appearance of pseudo-pregnancy been produced. 

 Thus Fellner's early figures (192) and a very recent illustration 

 by Laqueur (357) both show the typical oestrous condition, 

 which, as pointed out before (p. 54), is so obviously distinguish- 

 able from that of pseudo-pregnancy. The same condition is 

 shown in Courrier's (145) illustrations. Long and Evans (425) 

 have found that the onset of the next oestrus is fatal to the exist- 

 ence of deciduomata, which are known to be directly under the 

 influence of the corpus luteum. Ovulation, therefore, does not 

 merely transfer the elaboration of the oestrus-producing hormone 

 from the follicle to the corpus luteum. 



The most obvious post-ovulation changes in the uterus are of 

 course found in Primates, and evidence is now beginning to 

 accumulate as to the effect of various experimental procedures 

 upon this pseudo-pregnant development. Allen (12) has 



