62 MOSTLY MAMMALS 



it would be the basal half which was white, and the 

 terminal half which retained its natural colouring — in other 

 words, precisely the reverse of the condition obtaining in 

 Sir John Richardson's lemming, thereby affording further 

 presumptive evidence as to the abnormal condition of the 

 change in that animal. 



As a matter of fact, however, those of us who have 

 reached an age when silver hairs have begun to make 

 their appearance among the brown can easily satisfy them- 

 selves that such hairs are white throughout their entire 

 length, and that a hair half white and half brown is quite 

 unknown. From this we infer that the change from brown 

 to white takes place in human beings by the gradual 

 shedding of the dark hairs and their replacement by new 

 ones from which pigment is entirely absent. So that 

 normally there is no such thing as bleaching of individual 

 hairs. The change is, indeed, precisely similar to the one 

 which takes place at the approach of winter in mammals 

 that habitually turn white at that season, with the exception 

 that, as a general rule, it is extremely slow and gradual, 

 instead of being comparatively rapid, and also that the white 

 hairs differ from their dark predecessors solely by the 

 absence of colouring-matter. Unfortunately, there is no 

 subsequent replacement of the white hairs by dark ones ! 



The fact that the change from brown to white in the 

 mountain hare {Lepus timidus) is really due to a change 

 of coat and not to bleaching was known at a very early 

 period to the English naturalist Pennant ; and the exist- 

 ence of this change was likewise recognised by Macgillivray. 

 It was not, however, till Dr. J. A. Allen, in a paper on 

 the colour-change in the North American variable hare 

 published in the Bulletin of the American Museum of Natural 

 History for 1894, demonstrated by actual experiment the 



