NATURAL HISTORY STUDIES 



the habitat. Thus the Arctic fox does not usually 

 turn white in Iceland ; the mountain hare rarely 

 changes in Ireland ; and white stoats or ermines 

 are comparatively rare in England. The suggestion 

 is that the changes which bring about the white- 

 ness require a considerable degree of cold to pull the 

 trigger, as it were. It does not by any means follow 

 that the cold is the direct or mechanical cause of 

 the whiteness. 



To the question, What actually takes place when 

 the white dress is put on ? a fairly secure answer can 

 be given in some cases. But in other cases we have 

 not as yet sufficient data. It is well known that the 

 stoat or ermine, which is brownish-red in summer, 

 usually becomes a beautiful white in winter, all but 

 the black tip of the tail. How is this effected ? 

 In the main, the white hairs of winter are new hairs 

 that take the place of the coloured hairs of summer. 

 In the mountain hare, the white hairs of winter are 

 partly new growths and partly the coloured summer 

 hairs changed. The same is true for the American 

 hare. 



In a famous experiment made by Sir John Ross, a 

 Hudson's Bay lemming was kept in the cabin of the 

 ship through the winter and did not change colour. 

 But on the first of February it was exposed on deck 

 and it had several white patches next day. It 

 turned white in a week, and died a few days after- 

 wards. In this case the blanching must have been 

 due to a change in individual hairs, such as some- 

 times occurs very rapidly in man as the result of a 

 nervous shock. 



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