Observations on the Œstrous cycle of the albino mouse

Cyclic changes in the female generative tract, correlated with ovulation, and constituting the uterine as compared with the ovarian cycle, have been described for the great majority of mammals. In the past, however, the difficulty of detecting the changes in the intact animal has retarded both the study of the phenomena themselves, as they normally occur, and the use of the cyclic changes as part of the technique for experimental work on the physiology of reproduction. In rodents, particularly, the outward and visible signs of the various stages of the œstrous cycle are almost negligible, and, in the absence of the male, it is notoriously difficult to detect the period of œstrus in the intact animal by superficial examination. One part of the reproductive tract—namely, the vagina—is, however, accessible for examination, and cyclic changes of the vaginal epithelium corresponding to changes in the uterus were described by Morau as early as 1889. No particular advantage, however, was taken of this fact until the important discovery by Stockard and Papanicolaou (7), in the guinea-pig, that desquamated epithelium could be removed periodically from the vagina, and that the nature of this epithelium varied with the stage of the œstrous cycle arrived at. The elaboration of this discovery into a technique for the detection of the œstrous cycle may be said to have originated the accurate study of the œstrous cycle in spontaneously ovulating rodents, and to have made possible the use of the uterine cycle as part of experimental technique.