THE GONADOTROPIC HORMONES 



havior in mammals with yearly sexual cycles. Oestrus and 

 the conditions necessary for its production by artificial illumi- 

 nation have been repeatedly studied in the ferret.'-' Both the 

 "quantity" and the wave-length of light are important. Vari- 

 ations in duration, the quantity of light remaining unaltered, 

 do not influence the rate of acceleration of oestrus (Marshall 

 and Bowden). These authors also concluded that, whereas in- 

 frared rays had little effect, ultraviolet rays caused a pre- 

 mature appearance and abnormal persistence of oestrus. Bis- 

 sonnette found that the light and hair cycles of the ferret de- 

 pended upon an intact pituitary, Hypophysectomy pre- 

 vented both oestrus and its associated hair cycle even in ani- 

 mals artificially illuminated. Apparently the effect on hair- 

 growth may be due to the direct action of a pituitary hor- 

 mone, inasmuch as cyclic changes in hair-growth are not in- 

 fluenced by gonadectomy. Hill and Parkes were not able to 

 prevent or delay the onset of oestrus and gonad development 

 at the usual time of breeding by keeping animals in darkness. 

 Although the authors agreed that the effect of light on the 

 anterior pituitary probably explains how oestrus is initiated 

 in the anoestrous season by increased illumination, they de- 

 nied that the increasing length of daylight is responsible for 

 normal oestrus. Bissonnette stated that the latter may be de- 

 layed or made to persist by severing both optic nerves. Fer- 

 rets in precocious oestrus have been successfully bred by Bis- 

 sonnette and Bailey. 



In a preliminary report, Whitaker (1936) reported that 

 white-footed mice {Peromyscus leucopiis noveboracensis) went 

 into oestrus 6-8 weeks early if they were treated with a com- 

 mercial ultraviolet lamp. By the increase of the daily ration 

 of artificial illumination a similarly precocious oestrus with 

 pregnancy was produced in the raccoon {Procyon lotor) by 

 Bissonnette and Csech (1937). In the female rat, reversed 

 illumination (light by night, darkness by day), darkness, or 



'^ Late reports are those of Hill and Parkes (1934), Bissonnette (1935), Bisson- 

 nette and Bailey (1936), and Marshall and Bowden (1936). 



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