834 COLD THE ONLY CAUSE OF LETHARGY. 



ceased entirely, that no change whatever could 

 be observed on placing them in vacuo, or the me- 

 phitic gases ; and that they no longer responded 

 to the stimulus of electricity. What then must 

 be the condition of such animals during winter 

 in the higher latitudes of Asia and America, where 

 the mercury falls from 40 to 70 lower than in 

 England and Italy ? How are the foregoing facts 

 to be reconciled with the assertions of Marshall 

 Hall, Dr. Edwards, and all those physiologists 

 who regard " the lethargy of animals during win- 

 ter as a condition of the system which differs 

 from ordinary sleep only in degree ?" 



That hybernation is owing to cold alone, would 

 appear from the fact, that neither in plants nor 

 animals does it ever occur in temperate latitudes 

 until the approach of winter, if we except the 

 torpor of the tenrec, the serpent, and some other 

 animals within the tropics, caused by excessive 

 drought, and the evaporation of their fluids, for 

 the same reason that grass and many other succu- 

 lent plants wither and die during summer in all 

 parts of the world. And as vegetation may be 

 kept up during winter by artificial warmth, so 

 has it been found, that the dormouse, squirrel, 

 and other hybernating animals, remain active 

 throughout the year, when kept in a temperature 

 above 65, as in climates of perpetual summer. 

 It has also been proved by the experiments of 

 Spallanzani and Pallas, that hybernation may be 



