ABSENCE OF LIGHT AND THE REPRODUCTIVE CYCLE IN THE GUINEA PIG

Abstract

In 30 [male] guinea pigs confined in a completely darkened room, estrus, after the first period, ceased to be nocturnal. In 271 cases observed [under normal conditions] during the 2 mos. Oct. 15-Dec. 15, 1933, the mean point of estrus occurrence was 1 hr. 16 min. earlier than in 442 cases observed Feb. 15-May 15, 1933[long dash]a shift 6.2 times its probable error, and of the same order of magnitude and in the same direction as the change in the time of sunset, indicating that the change from daylight to darkness is the factor which is responsible for the more frequent occurrence of estrus between 6 P.M and 6 A.M. than between 6 A.M and 6 P.M. Animals kept away from light were normal in respect to length of reproductive cycles, duration of estrus, vaginal smears and fertility, indicating that exposure to light is not necessary for the existence or maintenance of the reproductive rhythm in at least one polyestrous species, the guinea pig.