4 NATURE OF LIVING BODIES. 



the things around them for the materials for their support ; 

 out the power of altering the nature of those materials, and 

 appropriating them to their own use, is peculiar to themselves. 

 Vhe functions of living systems are not only performed with 

 out the assistance of the physical powers of matter, but often 

 in direct opposition to them ; and the substances which are 

 introduced into them, lose their chemical relations, and are 

 combined according to new laws, and for new purposes. 



This power of insulation, possessed by living systems, is in 

 no instance more strikingly evinced, than in the possession 

 by animals of a certain degree of vital heat, which they pre- 

 serve under all circumstances, short of those which impair or 

 destroy the texture of their parts. This degree of heat 

 which in man is about 98 of Fahrenheit's thermometer 

 continues nearly the same, even when we are exposed to the 

 most intense cold, and is but little elevated, when we are sub- 

 jected to a heat above that of boiling water. In many coun- 

 tries, in which the degree of cold is for many months in the 

 year very much below the freezing point of mercury, men not 

 only exist, but enjoy all the comforts of life. In some high 

 latitudes, Europeans have been exposed to temperatures as 

 low as - 50 or even - 60 of Fahrenheit's thermometer, that 

 is, to a cold 180 below the natural standard of animal heat, 

 and have escaped every ill consequence. Very lately the 

 whole of two ships' crews wintered in about 75 ot north lat- 

 itude in perfect safety, where the temperature of the air was, 

 for many weeks together, almost constantly below 30, and 

 where they became so accustomed to severe cold, that the 

 atmospmere, when at zero, felt mild and comfortable. On 

 the other hand, in many countries men exist without difficulty 

 under a high degree of heat. In Sicily, during certain winds, 

 the thermometer has been observed at 112, in South Amer- 

 ica by Humbolt at 115, in Africa at 125. But, for a lim- 

 ited period, much higher degrees of artificial heat have been 

 borne without injury. Individuals have exposed themselves 

 voluntarily to the air of ovens at temperatures from 260 to 

 315 of Fahrenheit's thermometer, without any great incon- 

 venience, while water was boiling and meat baking in the 

 same atmosphere. These facts show a power of resisting the 

 operation of external causes, which is possessed by nr, sub 

 stances except such as are endowed with life, and is, proba- 

 bly, possessed in some degree by all that are. For, although 

 vegetables and the lower orders of animals are not capable 

 of resisting to the same extent the influence of heat <md cold, 



