MOUNTAIN MAMMALS 63 



In spring there is an opposite change, the white hairs 

 moulting off and new red ones taking their place. 

 While this is the true explanation, it does not exclude 

 the possibility that some individual hairs may turn 

 rapidly from brown to white. Indeed, Professor 

 MacGillivray thought that "sometimes the brown 

 hairs themselves, on the application of intense cold, 

 become whitened." We know that a man's hair may 

 turn white in a short time under great nervous strain, 

 and that this is due to a rapid change in the colour- 

 ing-matter in the hairs. The whiteness is due 'nega- 

 tively to a removal of or a change in the brown or 

 otherwise coloured pigment; it is due positively to 

 the formation of numerous microscopic bubbles of 

 gas. For the whiteness of white hair or of white 

 feathers is the same as the whiteness of foam ! When 

 the blanching of hair is gradual there is, as the great 

 Russian naturalist Metchnikoff showed, an interest- 

 ing activity on the part of the phagocytes, or wander- 

 ing amoeboid cells, of the body. They behave like 

 sappers and miners, entering the hair and creeping 

 out again with a microscopic burden of colouring- 

 matter. This is what goes on when particular hairs 

 turn white slowly, but in most cases what happens in 

 man is that the fresh growth of hair that is always 

 going on is unaccompanied by the formation of pig- 

 ment and is accompanied by the formation of gas 

 vacuoles. 



The Mountain Hare (Lepus variabilis), called by 

 many other names Alpine, Blue, Irish, and Variable 

 is first cousin of the Common Hare (Lepus euro- 

 pceus\ and is a distinctively northern mammal. Its 

 range extends from Ireland to Japan, but it does not 



