PREGNANCY-BLOCK IN FEMALE MICE PLACED IN BOXES SOILED BY MALES

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Abstract
Newly mated female mice were placed singly for periods of up to 3 days in boxes recently vacated by five males of a different strain (alien males). When the soiled boxes were renewed twice daily, the females showed pregnancy-block to the same extent as when placed in the proximity of alien males for similar periods. When the soiled boxes were renewed once daily, the incidence of pregnancy-block was much reduced. An equal amount of disturbance, caused by similarly transferring the females to clean cages, did not affect the incidence of pregnancy. These results support previous work in indicating that the smell of the alien male is the operative factor in pregnancy-block, and further suggest that the odorous substances involved arc highly evanescent.