110 THE INFLUENCE OF INANIMATE SURROUNDINGS. 



nation or winter-sleep, and of resuscitation after being frozen 

 up, must be briefly examined. 



It is universally known that there are forms among the 

 Vertebrata, as well as the Invertebrata, which are distinguished 

 from all their congeners by the circumstance that they are 

 lulled to sleep by the falling temperature at the beginning of 

 winter; they sink into a state of rest of longer or shorter 

 continuance, during which their active life, if not totally sus- 

 pended, is reduced to a minimum. My two tame Prairie-dogs, 

 Hans and Gretel, feel the effect of a falling temperature, when the 

 thermometer is only down to 7-10 centigrade; the Amphibia 

 of our latitudes first perceive it when the temperature is very 

 little above the freezing-point of water, while in Cuba they 

 succumb at degrees lying between 7 and 24 ; the common 

 continental vineyard-snail, Helix Pomatia, does not throw off 

 the calcareous lid which protects it during its four-months 

 sleep till the temperature by day has reached about 10-12 centi- 

 grade. In tropical countries, various animals, as snakes, lizards, 

 &c., fall into a state of chill-coma, precisely resembling a 

 winter sleep, at a temperature far above that at which the hyber- 

 nating animals of northern latitudes 34 are still quite active 

 another proof of the truth of the statement that it is the depar- 

 ture from the optimum, not the absolute high or low tem- 

 perature, that affects animals. In the Philippine Islands I have 

 frequently found snakes under stones early in the morning, 

 that were quite stiff, though the temperature of the soil under 

 stones, or protected against radiation by the shade of forest 

 trees, was never below 16-18. It may perhaps be here ob- 

 jected that, for this very reason, the winter-sleep of our animals 

 cannot be directly compared to the chill-coma of those living 

 between the tropics ; but I think this objection ill-founded. 

 Certainly the temperature in tropical countries never remains 

 for any length of time, for days or even weeks, so low as to 

 induce an unbroken or prolonged chill-coma during such 

 periods. But it is obviously of small consequence whether the 

 effects produced by the lowered temperature are of long or 

 short continuance ; even among our hybernating animals the 

 duration of their sleep varies considerably, but the general 



