KATABOLISM. . Ig 



the internal fires burn fiercely, and therefore the tem- 

 perature of the blood is high and independent of the 

 temperature of the exterior medium. In cold-blooded 

 animals, such as reptiles, amphibians, and fishes among 

 vertebrates, and in nearly all invertebrates, the fires 

 burn so low that the temperature of the blood fol- 

 lows somewhat closely that of the exterior medium. 

 Every stage of gradation, however, may be traced be- 

 tween them. 



2. The Purpose of the Combustion.— The pur- 

 pose of the combustion is threefold: (a) To remove 

 waste. The waste of tissues is highly poisonous and 

 must be quickly removed ; most of it is removed in res- 

 piration by burning it up and changing it into gaseous 

 CO s and H s O vapor, which are readily exhaled from the 

 lungs, (b) A still more fundamental and necessary pur- 

 pose of combustion is the generation of force. This, in- 

 deed, is the origin of the vital force, as it is that of the 

 force of the steam engine, (c) A third purpose is the 

 generation of heat — i. e., animal heat. This, however, is 

 of secondary importance. In the animal machine, as in 

 the steam engine, the real purpose is force, and the heat 

 is a necessary concomitant. In the animal body the heat 

 is sometimes a comfortable (in cold weather), sometimes 

 an indifferent, and sometimes a distressing (in hot 

 weather) concomitant. But we can not get the force 

 without the heat. It is worthy of note, however, that 

 from this point of view the animal body is a far more 

 efficient machine than any engine ever constructed — 

 i.e., of the heat of combustion, a far greater proportion 

 is converted into force. 



3. The Fuel. — Again, the fuel used in combustion 

 is of three general kinds — viz., the amyloids and fats, the 

 albuminoid excess, and the waste, (a) The amyloids and 

 fats consist only of C, H, and O, and therefore these 



