Abstract
A test for the potency of ,a testicular hormone preparation was made by injecting [image] cc. daily of an unknown sample of hormone into rats, beginning the day after castration, and then studying microscopically the prostate and seminal vesicles. The prostate responded to 0.15-1.5 bird units by high epithelium and the presence of light areas. The seminal vesicles responded to 0.4-7.0 bird units by the presence of secretion, high cells, and secretory granules with halos.