The Effect of Irradiation With Different Wave-Lengths on the Oestrous Cycle of the Ferret, With Remarks on the Factors Controlling Sexual Periodicity

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Abstract
The recurrence of oestrus in the female ferret is greatly accelerated by irradiation with light of various wave-lengths. Heat rays and the near infra-red (λ 7500) are comaratively inactive. The effect begins with the red radiation (λ 6500) and extends throughout the visible to the near ultra-violet (λ 3650). Over this range of the spectrum intensity appears to be more important than wave-lenth. None of the wave-lengths employed produced retardation in the recurrence of oestrus. Female ferrets subjected to incomplete darkness did not come on heat but individuals which had already begun to come on heat entered into full oestrus and remained in that state for a normal period. It is concluded that in the ferret and so probably in many other animals light radiations of particular wave-length and sufficient intensity are an efficient cause of reproductive activity, but that the recurrence of the oestrous cycle is conditioned also by other factors which in the absence of variation in the daily duration of light may play an important part.