INCOME AND OUTGO 329 



air in the chamber which have to be carried out, and there 

 are other details which we have not enumerated. 



The Energy of the Metabolism. We may look at the 

 income and outgo of the body from the standpoint of 

 energy as well as from that of matter. The food, looked 

 upon as fuel, represents a definite amount of potential 

 energy. The excreta represent very little. For any 

 discussion of the facts we must have a unit for the 

 measurement of energy and the one most used is the 

 large Calorie. This is primarily a heat unit but we know 

 that all forms of energy are convertible and we can make 

 the Calorie stand for work or for electricity if we choose. 

 The body generally disperses practically all its energy 

 in the form of heat and so the unit is evidently the best 

 possible. A large Calorie is the amount of heat required 

 to raise the temperature of a kilogram (1000 grams) of 

 water 1C. 



Oxidizable compounds of a uniform composition are 

 said to have definite fuel values. The fuel value of a 

 compound is expressed as the number of Calories set 

 free by completely oxidizing 1 gram of that compound. 

 One gram of sugar oxidized to carbon dioxid and water 

 without by-products gives nearly 4 Calories. Starch 

 has a value very slightly in excess of that of sugar. 

 One gram of fat gives much more, say 9.3 Calories. 

 The fuel value of alcohol is about 7 Calories. These 

 figures do not seem to vary whether the oxidation is a 

 literal burning or a physiologic decomposition in the 

 body cells. 



The case of protein is peculiar. One gram of protein 

 burned in the open with a full supply of oxygen gives 

 nearly 6 Calories. It contributes less than this quantity 

 of energy to the organism for it is less completely oxidized 

 in the life process than it can be by flame. Such products 

 as urea have a moderate fuel value and represent energy 

 which the body has failed to extract. They remind us 

 of the cinders left by a coal fire. The actual fuel value 



