HOW ARCTIC ANIMALS TURN WHITE 61 



is very striking indeed. On the other hand, the summer 

 coat is only donned for a comparatively short season, and 

 that at a time of year when it does not become much 

 damaged by" the effects of the weather. Consequently no 

 marked change is noticeable as the long winter hairs grow 

 up through it, and it has accordingly become a common 

 article of belief that, whether there is a change of colour 

 or not, the long winter coat is produced by a lengthening 

 of the summer dress. 



Apart from the evidence of animals like the roebuck 

 and many other deer as to the existence of an autumn 

 change of coat, as deduced from a difference in colour, 

 the fact of such a shedding of the fur is demonstrated 

 by the circumstance that in many species, as, for instance, 

 the mountain hare, the individual hairs themselves, as seen 

 under a microscope, differ appreciably in calibre at the two 

 opposite seasons of the year. In that species, for example, 

 the hairs of the winter coat are of a much finer character 

 than are those forming the short dress of summer, which 

 are comparatively coarse and thick. Moreover, in spite of 

 the natural tendency to believe in blanching on account 

 of the aforesaid abnormal instances of turning white in a 

 single night, there is abundant evidence to show that even 

 in human hair the change from dark to white as age 

 advances is brought about by the replacement of dark 

 hairs by white ones, and not by the bleaching of the 

 former. In this case, however, the change, instead of 

 being seasonal and sudden, is gradual and due to age. 

 If the change was due to blanching, we should, of course, 

 find some hairs which were partially white and partially 

 brown (or black, as the case may be). And here it 

 may be remarked that if such partially blanched hairs 

 were met with, we should naturally expect to find that 



