THE CONQUEST OF THE DRY LAND 219 



the heap we can revive the fire by stirring it 

 up to admit air. When we have added fresh 

 fuel and cleared away the ashes it will burn as 

 brightly as ever again. So with the winter 

 sleeper. When the first warm breath of spring 

 penetrates into the hedgehog's hole, he gradu- 

 ally awakens, stretches his stiffened limbs, and 

 creeps forth with a new lease of life. His 

 breathing quickens as his lungs fill with air, 

 oxygen is carried to every part of his body, the 

 heart beats more strongly and rapidly, and the 

 now hungry hedgehog begins to search eagerly 

 for the insects and worms on which he feeds. 



If we stir up our resting fire too suddenly and 

 let in too much air at once the glow will die 

 out, and no amount of fresh fuel will re-kindle 

 the heap without fresh fire. Something simi- 

 lar sometimes happens to the lighter sleepers 

 if they have been roused by a spell of mild 

 weather, and a hard frost sets in so suddenly 

 that they are nipped by it before they have had 

 time to settle down to sleep again. But, on the 

 whole, hibernation is a very successful device 

 for withstanding great changes of temperature. 



Another way of meeting the winter is by 

 putting on a white dress. The ptarmigan, 

 which is rather grouse-like in summer, with a 



