THE CONQUEST OF THE DRY LAND 219 



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 gradually 

 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 

 similar 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 



