“…As regards the occurrence of an cestrus-producing substance in the male, it has been reported as present in the testis (1,3), the blood (4,6) and the urine (7,8,10). In most cases, however, vaginal cornification appears to have been the only criterion of cestrus used, and since this reaction is now known not to be entirely specific for cestrus (2) it seemed desirable to test extracts from male sources by at least one other criterion of cestrus.…”