THE FUNCTION OF (ESTRIN 119 



anterior pituitary body. Zondek and Aschheim (659), however, 

 produced ovulation but not abortion by the same means. The 

 bulk of the evidence suggests most strongly that oestrus and 

 pregnancy are incompatible, and that the artificial production of 

 an oestrous phase during pregnancy will result in its termination. 

 The lactating animal. During lactation, when oestrus is in 

 abeyance in the rat, mouse, and guinea-pig (except for the 

 immediate post-partum period), injection of oestrin will result 

 in the appearance of oestrous symptoms in the accessory organs 

 (23, 505, 565). Parkes and Bellerby (505) came to the following 

 conclusions: 



[a) The amount of cestrin required to produce oestrous 

 changes is roughly proportional to the number of 

 young suckling. It is well known that if only one or 

 two young are suckling, spontaneous oestrus will appear 

 during lactation. With three or four suckling several 

 m.u. of oestrin are required, while with seven suckling 

 not less than 10-12 units will produce oestrus. This is 

 probably a corpus luteum effect (see p. 183). 



(h) The induction of oestrus does not materially affect the 

 efficiency of lactation, but a slight break in the growth 

 curve of the young was found following injection of the 

 mother. 



The senile animal. Slonaker (568), Steinach, Heinlein, and 

 Wiesner (594) and Laqueur, Hart, and de Jongh (345) report the 

 production of oestrous changes in the senile anoestrous mouse by 

 the injection of oestrin. The last authors obtained the result 

 with 2 m.u. Later, Steinach, Kun, and Hohlweg (596) report the 

 complete rejuvenation of the senile mouse by oestrin, including 

 the recommencement of follicular maturation and ovulation. 



Effect of oestrin on follicular maturation. Injection of the 

 immature animal has been described by Loeb (405) and Truffi 

 (616) as stimulating the development of the follicles, without, 

 however, causing ovulation. Frank, Kingery, and Gustavson 

 (224) originally claimed to have caused ovulation in the im- 

 mature rat, but their results were probably due to the use of 

 animals approaching the first oestrous period. All other 

 workers appear to agree that oestrin injection does not cause 



