HIBERNATION OF MAMMALS — MATTHEWS 413 



Although hibernating warm-blooded animals are generally unable 

 to withstand being frozen, recent work on the subject has shown that 

 some species at least can be cooled to temperatures a few degrees below 

 freezing point. When this process is carried out under the correct 

 conditions a state of supercooling is attained in which the temperature 

 is below 0° C, and the animal can be brought back to life on raising its 

 temperature with suitable precautions, although it cannot revive spon- 

 taneously. But great care has to be taken not to disturb tlie super- 

 cooled state, for even a slight shock causes immediate crystalization of 

 ice to begin throughout the body, and when that has happened com- 

 pletely there is no return. Cooling to spectacular subnormal tem- 

 peratures, though not to anything approaching freezing, has recently 

 been used as a form of anesthesia for the performance of surgical 

 operations ^ — a technique that appears to be fraught with the greatest 

 dangers in view of our present very inadequate knowledge of this 

 new subject. 



In warm-blooded animals the approach of the cold-blooded state 

 of hibernation makes itself felt some time before its actual onset, and 

 the animals react by making provision accordingly. Terrestrial mam- 

 mals prepare a winter den or burrow of some sort, usually lining it 

 with dry vegetation to form a snug nest; and even among the bats 

 many species leave their summer haunts and withdraw to special 

 hibernating retreats which they do not inhabit during the rest of the 

 year. But hibernation is often interrupted — the dormouse, tlie mar- 

 mot, and others, lay up stores of food in or near the nest which are, 

 presumably, eaten when these animals, like the bats, awake at intervals. 

 The onset, too, of winter torpidity is very irregular in many species ; 

 in the hedgehog sleep may last for only a few days at a time, with 

 intervals of activity, mitil the winter is well advanced. 



THE LONG LIFE OF HIBERNATORS 



In the dormouse, and even more in the bats, normal summer sleep 

 passes some way toward the torpid state chaiacteristic of hibernation, 

 as in the hummingbirds and possibly some others. So great is the 

 difference between the active and resting metabolism in a bat that 1 

 hour of activity uses up as much food or fat stores as is used in more 

 than 12 hours at the torpid rate. When bats are active their ap- 

 petites are voracious, and were they active all the time they would, 

 like shrews, need to eat their own weight of food daily. But the long 

 periods of sleep spare them tliis necessity, and allow for the expendi- 

 ture of the energy needed during flight, for most insectivorous bats 

 are active for only a few hours at dusk and dawn. And there is a 



* This technique is described in Chapman Pincher's article in Discovery, vol. 15, 

 No. 10, pp. 443-446, 1954. 



