T W O FIQURESThe recent observation of Wade and Doisy ('35) that vaginal smears characteristic of estrus could be obtained in castrated rats without the presence of the estrous hormone has led us to wonder if the sharp division of the estrous cycles into stages as described by Long and Evans ('22) is still warranted. Their classical paper and that of Stockard and Papanicolaou ('17) have been far reaching in the problem of sex physiology. These publications and many others dealing with the estrous cycles in mammals were based upon the cellular structure of the vaginal smear.Quite in contrast is the recent report of Wade and Doisy establishing beyond doubt that the frequency of the smear determined the histological picture in castrated rats. Three examinations a day with a cotton swab caused positive smears in 25 per cent of their rats. I n our colony we had never observed any smears whose positive nature we considered due t o the method of examination, but our observations (unpublished) were limited to two smears daily. The smears were made by lavaging the vaginal canal with a little saline by means of a medicine dropper. Accordingly, it occurred to us that quite different results might be obtained if the rats were examined four times a day. This we have done in castrated and normal rats using the pipette or lavage method of examination, as well as the cotton swab method. A comparison of these data are presented in this paper.
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