Some New Observations on the Vaginal Smear of the Rat *

One of the landmarks in the history of the physiology of reproduction is the discovery by Stockard and Papanicolaou7 that the progress of the sexual cycle of mammals, conditioned by ovarian changes, is reflected in a spectacular rhythm of changes in the cell content of the vaginal lumen. Those changes could, it was discovered, readily be recognized by examination of a specimen from the vagina. The simplicity and reliability of the "vaginal smear" technic at once recommended itself as a most convenient tool for the determination of the stages (ovulation, for example) of the estrous cycle. The stimulus of this new method to research in reproductive phenomena is hard to over-estimate. In 1923 the vaginal smear method found an important application in the hands of Edgar Allen and E. A. Doisy5 in their development of what is known today as the "Allen-Doisy test," which consists of the vaginal response of the ovariectomized mouse to the injection of "estrogenic" hormones. The establishment of this method of assay led to the final discovery, in 1930, of the chemical constitution of estrone ("theelin" of Allen and Doisy). The writer of these lines is gratified to present herewith a small contribution in the field in which the man we wish to honor has pioneered. This laboratory's renewed interest in problems relating to the vaginal cycle may be said to be due to the cooperative study of Dr. Ines de Allende and the writer at the Carnegie Laboratory of Embryology, Baltimore, and of Dr. Ephraim Shorr at the New York Hospital. Dr. de Allende's task was to make a comparative study of the vaginal cyde of the monkey and of women. In the course of this study, a certain cell type (termed "Shorr" cell in the present paper) attracted our attention (type II of de Allende, Shorr, and Hartman6). With the aid of students (especially R. C. Melick) the writer has, during the past two years, as occasion offered, investigated the occurrence of this and other cell types in numerous species