82 INTERNAL SECRETIONS OF THE OVARY 



oestrus-producing hormone (see p. 121) as the only ovarian 

 hormone. This view is based mainly on the fact that injection 

 of this substance will cause the immature uterus and vagina to 

 show oestrous symptoms, and on the comparative failure up 

 to the present to obtain extracts which will substitute the pre- 

 sence of the corpus luteum. 



Active extracts of luteal tissue are now, however, being 

 prepared, and it may be said with some confidence that at least 

 two ovarian hormones exist. Probably three, as originally 

 suggested by Marshall, will eventually be demonstrated. 



