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). 
