Since July, 1925, the author has undertaken several sorts of experiments with respect to the oestrus and ovulation in the rabbit, the main purpose of which was to find the cyclic change of the oestrous phenomena by means of the vaginal smear.
The works have been carried out at the Animal Breeding Experimental Laboratory of the Tokyo Imperial University largely with the subvention from the Imperial Academy, for which the author wishes to express his heartiest thanks. The results obtained may be summarized as follows:
(1) As in other rodents the oestrous cycle exists in the rabbit. It can be observed by the vaginal smear method, though the indication of oestrus is rather obscure than that of other rodents.
(2) In the rabbit three different pictures are presented by the vaginal smear, but only the nucleated epitherial cells may be used as criterion for the heat stage.
(3) The occurrence of nucleated epithelial cells in the vaginal lumen well corresponds to the development of ovarian follicles.
(4) The duration of the oestrous cycle, presumed from the existence of this sort of cells, is about 7 days on an average, varying from 3 to 12 days.
(5) Cornified epithelial cells are rarely found in abundance in the vaginal smear of the rabbit. This fact can also be proved by the serial section of genital tracts.
(6) The appearance of leucocytes is not confined to the normal oestrous cycle, but a number of leucocytes is observable at irregular intervals during pregnancy and lactation or even before puberty.
(7) It is also possible to distinguish the difference between complete and incomplete ovariotomy by the vaginal smear method.
(8) Oestrus-like phenonena sometimes take place at pregnancy, at lactation, and even after spaying in some animals. But ovulation never occurs spontaneously at any reproductive period and in any indinidual.
(9) Ovulation occurs following copulation in the complete hysterectomized rabbit and vagina-anaesthetized.
(10) Ovulation occurs, though with low percentage, in the normal doe by the artificial insemination and by the transplantation or injection of fresh hypophysis from a rabbit.
(11) Testicular substance, injectd or transplanted, somewhat accelerates the growth of ovarian follicles.
(12) It is suggested that the cause of ovulation in the rabbit depends upon some humoral mechanism.
