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 
