ANIMALS UNDERGROUND 231 



water without feeling pain, so many of the mining 

 animals can endure the presence of dust and grit on 

 the eye without discomfort. Tame rats will allow dust 

 or fine sand to rest on the eyeball without trying to 

 remove it ; and it may be inferred that rabbits, mice, 

 voles and shrews can do the same. The mole's eyes 

 have become so atrophied, that when a mole is skinned 

 the eyes come off with the skin ; but this is probably not 

 because the mining hurts the eye, but because the mole, 

 having learnt to work by scent and touch, had little 

 further use for sight. 



Ventilation, or rather the want of it, must be another 

 difficulty in the underground life of almost all mammals. 

 The rabbit and the rat secure a current of air by form- 

 ing a bolt-hole in connection with their system of 

 passages ; but the fox, the badger, and many of the 

 field voles and mice seem indifferent to any such pre- 

 caution. There is no doubt that whatever gave the 

 first impulse to burrow, many animals look upon this, 

 to us, most unpleasant exertion as a form of actual 

 amusement. It also confers a right of property. 

 Prairie-dogs constantly set to work to dig holes merely 

 for the love of the thing. If they cannot have a suit- 

 able place to exercise their talent in, they will gnaw 

 into boxes or chests of drawers, and there burrow, to the 

 great detriment of the clothes therein contained. In an 

 enclosed prairie-dog c town ' they have been known to 





