MODIFICATION OF THE OESTROUS CYCLE OF THE MOUSE BY EXTERNAL STIMULI ASSOCIATED WITH THE MALE

Abstract

SUMMARY 1. It has been demonstrated in three strains of mice, one heterozygous and two inbred, that the oestrous cycle, as determined by vaginal smears, was shorter in the presence of a male than when males were absent. 2. When female mice were removed from males during metoestrus the duration of the ensuing cycle was the same as that observed in the absence of males. This indicates that the effect of stimuli received during one cycle was not carried over to the next. 3. The cycle was shortened when a male was present for the 48 hr following the start of metoestrus. When the period of exposure was reduced or postponed for 24 hr after metoestrus the shortening observed was not significant. 4. When a male was placed in a basket within the female's cage pseudopregnancy was not observed, but the incidence of abnormal cycles was reduced. 5. The duration of pseudopregnancy was not altered by the presence of a male.