MODIFICATION OF MAMMALIAN SEXUAL CYCLES

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Abstract
From Nov. 10, 3 immature [female][female] were given constant 8i-hr. days till killed at 106, 125, and 149 days for histological study of gonads and epididymides; 3 others were given whole days + 6 hrs. of electric light each night till killed at 106, 210, and 211 days (June 9), for similar study. Mating reactions and potency were tested at intervals from Jan. 13 onward. Onset of sexual activity was delayed considerably in 2 "short day" ferrets, as compared with normals, only slightly in the 3rd. It was hastened in two "long day" animals, but was late in the 3rd. In both groups, interstitial cells came into activity more quickly than germ-cells, and, in 2 "long-day" animals, remained active longer after testis regression set in. Epididymal changes were more closely correlated with interstitial than with germ-cell changes. In "long day" animals, testis regression set in before June 8 (when ferrets on normal light cycles are completely active) in spite of increasing time and intensity of daily light. So that, while increasing light induces or hastens sexual activity in such young [male][male], regression sets in after a time in spite of it. Regression is related either to reactions within the animals, unrelated to light, or to increase of lighting above the optimum, or to both. Probably shortening days after June 21 hasten it.

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