“…The injection of oestrin into the immature animal brings about the appearance of precocious oestrous symptoms, including opening of the vaginal orifice, and where such symptoms may be detected in the intact animal, as in the rat and mouse, this is a fairly convenient test for oestrusproducing activity. It suffers, however, from two disadvantages An entirely different method of assaying oestrous activity has been put forward by Frank and his coworkers (222), by Seckinger (555) and by Brouha and Simonnet (103), who have suggested that the effect of the oestrous hormone on the spontaneous contractions of the uterus (see p. 203) could be used as a criterion. Such a proceeding, however, has obvious disadvantages.…”