TIME RELATIONS IN THE PREGNANCY-BLOCK INDUCED IN MICE BY STRANGE MALES

Abstract

Summary. (1) The time relations of the olfactory block to pregnancy in the mouse have been examined. (2) The female is most vulnerable within 48 hr of coitus (80% pregnancies blocked) and the reaction rapidly disappears after the start of implantation. (3) Exposure of at least 48 hr duration is necessary to elicit the maximum number of blocked pregnancies but, during the period of maximum vulnerability, the reaction occurs in some females with exposure lasting only 12 hr. (4) Over 90% of females in which pregnancy is blocked return to oestrus within 4 days of the beginning of exposure, with a peak (56%) on the third day.