PHENOMENA AND 'CONOTTIONS' Otf 'Lltffi ' 43 



cold weather sets in. These animals hibernate during a period, 

 the extent of which varies with the different species, but there is 

 always noticeable a great decrease in metabolism. Eespiration 

 ceases, the actions of the heart are hardly perceptible, and 

 the body temperature of the sleepers, which otherwise about 

 equals that of man, almost falls .to freezing point. When the 

 mild weather returns vital activity gradually recommences, and 

 emaciated and exhausted the animals come out of their winter- 

 quarters. 



For many animals hibernation is a direct necessity. As their 

 food consists of insects or plants, and as they cannot, like some 

 birds, undertake long journeys to some more hospitable country, 

 they would die from hunger if they could not sleep the time 

 away. But as in hibernating animals metabolism is not entirely 

 suspended but only reduced, a certain quantity of substance is 

 naturally used up even during sleep. The animals live during 

 this time on the fat which they have accumulated during the 

 good season. If we examine a bat which we find hibernating in 

 a cellar or chimney, we notice that all organs, muscles, intes- 

 tines, &c., are surrounded with thick layers of fat. But in 

 spring, on re-awakening, the bat is thin and emaciated, having 

 lost about a quarter of its body-weight. 



Some of the hibernating animals make the period of hunger 

 easier to sustain by carrying together, in the autumn, stores of 

 food which they consume whenever a sunny winter day awakens 

 them. While most animals, when hibernating, are insensible 

 to almost every external stimulus, and most difficult to rouse, 

 others as, for instance, the bear awaken at the least suspicious 

 noise. 



To the decrease of vital activity corresponds a considerable 

 increase in insensibility to injuries. Wounds, to which these 

 animals would in the waking state succumb almost instan- 

 taneously, are frequently sustained for days. The heart of a 

 hibernating hedgehog beats for hours after the spinal cord has 

 been severed. 



We have so far seen that the withdrawal of water, variation of 

 air-pressure, and extreme cold and heat, will cause in animals tem- 

 porary torpor. But the same effect can also be produced by purely 



