174 PHYSIOLOGY AND HEALTH. 



CHAPTER II. 



Law of Equilibrium of Heat different in Regard to living and dead 

 Matter. Animals maintain their own Temperature, and give 

 Heat to other Bodies. Animal Heat generated within. Warm 

 and cold blooded Animals. Power of sustaining Heat varies 

 with respiratory Apparatus. Fishes breathe by Gills, and have 

 little Heat. Whales breathe by Lungs, and have much Heat. 

 Animals have internal Apparatus for generating Heat. 



407. BESIDE this maintenance of its own warmth, the 

 living animal body is continually giving out heat to other 

 substances which are cooler than itself; and yet it does not 

 apparently lose its own heat ; at least its temperature remains 

 undiminished. If we hold a piece of ice in our hand, it is 

 melted, but the hand is not much cooled ; or, if cooled, it 

 soon regains its heat after being separated from the ice. But, 

 if we place the ice upon a piece of iron heated to the tem- 

 perature of the hand, the ice melts there, as in the other 

 case, and the iron is cooled down to a lower temperature, and 

 the waiter of the ice is raised to the same degree. The ice 

 cools the iron, and the iron warms the water of the ice ; and 

 then the temperature of both remains the same, until some 

 external influence changes it. 



408. Here, then, is a manifest difference in the law that 

 governs the heat of living and that of dead substances. One 

 class seems to have heat only in common with contiguous 

 and surrounding objects. If they are warm, the dead matter 

 becomes warm ; if they are cold, this is cooled to the same 

 degree. It neither warms itself nor cools itself, but depends 

 upon others for its heat. But the living body is neither 

 cooled nor heated materially by surrounding matters. Its 

 own heat seems to be independent of them. 



409. Our heat is not borrowed from external objects; 

 certainly not from the atmosphere, for we have seen that 

 the human bodies are warm when the air is extremely cold ; 

 nor from the sun or fire, for we are warm in the absence of 



