Modification of mammalian sexual cycles ; Reactions of ferrets ( Putorius vulgaris ) of both sexes to electric light added after dark in November and December

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Abstract
Between Oct. 12 and Jan. 5, 3 [female] ferrets, subjected to 6-6[image] hrs. of electric light per night, of between 4.88 and 14.1 ft. candles intensity (as measured at backs and fronts of the cages), came on heat, copulated, and became pseudo-pregnant, with mammary gland activity. Controls underwent no change. Full estrus was induced in 38-64 days, with typical vulval swelling; successful coitus in 59-70 days, followed by the usual external changes of pseudopregnancy. In [male][male], subjected to like treatment, interstitial cells were greatly stimulated. This was accompanied by penis and epididymis enlargement to breeding condition, and by increased libido, leading to copulation in 59 days. Spermatogenesis was stimulated to secondary spermatocyte and rare spermatid formation; but no mature sperms were found, even at 71 days. While sexual cycles in [female] ferrets are conditioned largely, if not completely, by light rations in the visible part of the spectrum, [male][male] are much less so, and require some other conditioning factors for complete fertility. This situation in mammals differs from that in birds, where [male][male] are more responsive than [female][female]. In the light of parallel reactions of birds and mammals to changes in anterior lobe hypophysis, hormone concentration and balance, it is suspected that there is a common fundamental cause, and that light may act through modifying anterior lobe activity, or susceptibility to it. A fundamental genetic difference between birds and mammals, correlated with this difference in reaction to anterior lobe hormone and light ration changes, is pointed out.

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