HYBERNATION. 697 



This torpidity is produced by a deficiency of external excitants, usually by cold 

 and want of food, and, in the language of Brown, is a state of direct debility, 

 while our ordinary sleep is one of indirect debility, exhaustion. No struc- 

 tural peculiarity is discoverable, which enables certain animals to exist in the 

 torpid state. 



Such animals at all times produce less heat, and vary more with the surround- 

 ing medium, than others, so that Dr. Edwards in an hour cooled a dormouse 36 

 by surrounding it with a freezing mixture, which caused a reduction of not more 

 than 5 or 6 in adult birds and guinea-pigs exposed to it for even a longer time. 

 (1. c. p. 154. sq.) Some which do not hybernate resemble them in this inferior 

 power; mice, for example, which, therefore, at all ages and seasons make 

 themselves nests, (p. 259.) On the other hand, hybernating animals are not all 

 equally deficient in the power of resisting the influence of surrounding low tem- 

 peratures ; dormice are the most so, marmots the least ; so that animals which 

 preserve their own temperature in low media, and those which readily follow the 

 surrounding temperature, are not widely separated, but insensibly run into each 

 other, (1. c. p. 257. sq.) to say nothing of the inferior power of the newly-born 

 among many of the former, and among all if born before full time, and of the 

 various degrees of this power in different adults, and in all at different seasons of 

 the year. (See section on animal heat.) Cold produces sleep in all, and if the 

 sleep is indulged, death is the result in those which cannot hybernate. Those 

 which can, become more and more torpid, by the mere continuance of the same 

 degree of cold. A very intense degree of cold has been found actually to arouse 

 animals in a state of torpidity, but the excitement of the functions could not con- 

 tinue long, and death ensued, (p. 398.) It appeared necessary that respiration 

 should be suspended in an experiment of M. De Saissy, who, by mere cold, 

 could not produce torpor in a marmot till he closed the lid of the vessel in which 

 it was placed, (p. 154.) Hence, exposure to carbonic acid, hydrogen, &c., in 

 this state, was found by Spallanzini to have no ill effect upon a torpid marmot. 

 (Rapports de VAir, t. ii. p. 207.) Yet respiration has often seemed not to cease 

 entirely. (See Dr. Reeve, Essay on the Torpidity of Animals.) The blood has 

 been found in a certain degree coagulated in torpid bats. (Hunter, On the 

 Stood, p. 25.) Cold, at any time of the year, will produce the torpid state, but 

 want of food must greatly assist in lessening the power of maintaining temper- 

 ature. On the other hand, a continual good supply of food and warm temper- 

 ature increases their power of evolving heat, and enables them to resist the power 

 of cold, so that, by domestication, some cease to hybernate in the winter. (Dr. 

 Edwards, 1. c. p. 472.) Dr. Edwards found that the temperature of hybernating 

 animals sinks considerably during sleep, even in summer, (p. 473.) 



Fish, and other cold-blooded animals, will survive an intense torpidity. " The 

 fish froze," says Captain Franklin, " as fast as they were taken out of the nets, 



ceptibility. I conceive that the whole is but one fact : that animals which 

 retain their powers well under privations, must be those which require less 

 frequent and less abundant supplies of food, air, &c. ; and that respiration is 

 less in them from the less necessity of stimuli to support the system. 



