HOW ARCTIC ANIMALS TURN WHITE 59 



weeks of the commencement of the experiment. In con- 

 sequence of the conditions under which it had been kept, 

 this lemming was still brown in midwinter, when it ought 

 to have been white. As the result of its first night's 

 exposure, the fur on the cheeks and a patch on each 

 shoulder became completely white, and by the end of the 

 first week the whole coat had turned white. On exami- 

 nation it was found that only the tips of some of the hairs 

 had become blanched, and that these white-tipped hairs 

 were longer than the rest of the coat, apparently owing 

 to a sudden growth on their part in the course of the 

 experiment. By clipping these long white-tipped hairs the 

 animal was restored to its original brown condition. 



Nothing is said with regard to any change of coat on 

 the part of this lemming previous to the experiment, but 

 it is probable that none occurred. It seems, however, to 

 be clearly demonstrated that the tips of the hairs lost their 

 colour by bleaching, induced by sudden exposure to the 

 intense cold, and that the hairs thus blanched increased 

 considerably in length in a very short period. 



In spite of the very obvious fact that these changes 

 occurred under extremely abnormal circumstances, it has 

 been argued that Arctic mammals which turn white in 

 winter do so normally by a similar blanching of the hair 

 of the summer coat, and that the greater length of the 

 winter, as compared with the summer dress of such white 

 animals, is due to a lengthening of the individual hairs of 

 the former.* Moreover, it has been inferred that the 

 colour-change is directly under the control of the animals 

 themselves. Quite apart from many other considerations, 

 one weak point in this argument is that the hairs in the 

 subject of the experiment were white only at their tips. 



* See E, B. Poulton, " The Colours of Animals," chap. vii. (1900). 



