METABOLISM 55 



it is to be burned. This takes place in 

 the candle, as in the simpler organisms, 

 by such processes as diffusion, capillary 

 action, assisted by convection currents. 



When combustion has ceased we find 

 certain substances left over which are 

 given off as gases or as solid particles 

 which constitute the smoke. These may 

 be compared with the excreta of the or- 

 ganism. With a few exceptions, the same 

 substances can be burned in the candle 

 as in the organism. If we introduced 

 into the candle bits of the food sub- 

 stances which can be burned by the or- 

 ganism, they would also be burned in the 

 candle and most of the substances which 

 the organism is unable to bum could not 

 be burned in the candle. 



The beginning and the end of the proc- 

 ess of combustion is the same in both 

 cases, though the intermediate steps dif- 

 fer. Thus we find that an ounce of 

 tallow ordinarily consumes the same 

 amount of oxygen, sets free the same 

 amount of heat, and produces the same 



