THE CESTRUS-PRODUCING HORMONE 93 



possibility. Under such conditions, however, frequent injec- 

 tions would be required to keep up the continuous action on 

 the reproductive organs which is necessary for a positive 

 result. 



{d) TEST-OBJECTS 



Any biological test of oestrus-producing activity must clearly 

 depend on the production of oestrous changes when they would 

 not otherwise occur. Immature, an oestrous, dioestrous, or 

 ovariectomized animals must therefore be used. Of these, all 

 except the last are unsuitable, though they have been used, 

 because it is impossible to eliminate entirely the possibility of 

 spontaneous ovarian activity. Ovariectomized animals are, 

 therefore, highly desirable and are generally used. The oestrous 

 changes which can be used as criteria of activity are various. 

 Changes in the vulva are very indefinite (except in the ferret 

 and certain Primates), while the oestrous growth of the 

 mammary gland is not yet known sufficiently to be of value. 

 In most animals the uterine changes are quite distinct, but 

 autopsy is required for every test. The two desirable conditions, 

 that the change shall be abrupt, and discernible in the intact 

 animal, are best satisfied by using the vaginal reaction of the 

 mouse, rat, or guinea-pig. 



Rabbit uterus. In seeking some means of testing the activity 

 of ovarian extracts on the accessory reproductive organs, 

 the early workers used immature animals, usually the rabbit, 

 as test animals, and considered hypertrophy of the uterus as a 

 positive result. Subsequently, ovariectomized animals were 

 used for the same purpose. As work on the extraction of 

 ovaries became concentrated on the oestrus-producing hormone, 

 hypertrophy of the uterus was considered as a sign of 

 oestrus-producing activity. This test, however, cannot be said 

 to be ideal because of (a) the uncertainty of the nature of 

 the reaction unless histological examination is made; (b) the 

 necessity for autopsy at every test; (c) the lack of an end- 

 point in a positive reaction; {d) the difficulty of arriving at time 

 relations; (e) the large amount of active material required; 

 (/) the unsuitability for quantitative work. Uhlmann (620) 

 gives some methods of assessing the intensity of the reaction. 



