Marshall, F. H. A. 1940. The experimental modification of the oestrous cycle in the ferret by different intensities of light irradiations and other methods. Journal of Experimental Biology 17, 139-147.

With female ferrets subjected to different degrees of intensity of light irradiation as measured by placing them at different distances from a 1000 W. lamp, the acceleration of the oestrous cycle, generally speaking, was correlated with the degree of intensity. There were, however, individual exceptions. The distances between the ferrets and the lamp varied from 1 to 22 ft. Female ferrets subjected to ultra-violet irradiation usually remained on heat until much later in the year than those submitted to light irradiation. With male ferrets ultra-violet irradiation caused descent of the testes in December and the testes remained descended until the autumn.