The variation which is encountered in the absolute and relative activities of endocrinologically active substances, according to the method of administration, has been the object of much study. An investigation into the activities of certain androgens having strong physiological activity other than androgenic brought to light instances in which the various activities of a substance seemed to be exerted to a different degree, not only according to the species of test animal, but also according to the route of administration. Changes of the latter type, in which the same test animal is considered, present peculiar difficulties. Unless relatively minor differences in action are sought, such as that between the response of the prostate and of the seminal vesicles in male rats, the various recognized tests for androgenic, progestational, and other activities are not, with the partial exception of those with the rat, adapted to an investigation of this kind. Thus,