SEASONAL AND HORMONE INDUCED CHANGES IN

The general conclusions of the majority of those biologists who have experi-mented with the frog Rana pipiens pipiens (Schreber) indicate that the male frog is an excellent test animal for the early diagnosis of human pregnancy. Nevertheless there are some unanswered questions which affect the use of this test. One of these is the possibility of seasonal variation in sensitivity in the frog, a period of time when the test animal is less responsive to chorionic gonadotrophin than in other seasons. This period of lessened sensitivity occurs during the summer months. It is important to determine the reason for this seasonal sensitivity since during this time false negative results for pregnancy tests are most frequently reported. A histological study has been made of seasonal differences in the maturation and release of spermatozoa by R. pipiens after injections of concentrated pregnancy urine and injections of fresh anterior lobes of frog pituitary glands. The results are compared with the seasonal picture of testes of treated frogs. A study of the condition of the testes during the various seasons of the year has helped to answe