66 MAN, THE ANIMAL 



chemical bodies approximating in complexity pro- 

 toplasm itself. This is the second well-known 

 source of metabolic inefficiency. One more will 

 be mentioned. 



During oxidation and the utilization of nitro- 

 genous foods but a small proportion of the energy 

 in the food bodies from which the energy is sup- 

 posed to come is actually used. Some writers 

 place the chemical energy thus used between 25 

 per cent, and 30 per cent, of the total amount in 

 these food bodies. This is a starthng revelation 

 of inefficiency. 



In so far as the fundamental principles of 

 metabolism are concerned, they reveal that man is 

 certainly very inefficient in his ability to utilize the 

 available energy in his foods. It is doubtful if 

 15 per cent, of the total amount of energy in the 

 food as it enters the digestive tract actually con- 

 tributes to the life of man. Steam engines are 

 from 24-25 per cent, efficient; gasoline engines 

 20 per cent.; the Liberty Motor 23 per cent., 

 typical examples of mechanical efficiency. Line- 

 hart, 1920, concludes from his study of the bac- 

 terium, Azotobacter, that it is i per cent, efficient 

 in its ability to fix nitrogen in a solution of man- 

 nite. 



Enough has been presented concerning what 

 makes the body go to indicate that there is a 

 limited source for all of this energy and that it 



