THE PROTEIN METABOLISM OF MANKIND 



69 



is that of the respiration calorimeter, in which the total heat 

 generated in the body under different conditions, the waste 

 products, work done, etc., are measured and expressed in terms 

 of heat. The amount of potential energy to be supplied in the 

 form of food in order to maintain body equilibrium can be 

 computed from the heat given off from the body under the 

 different experimental conditions. By means of certain known 

 factors this required energy can be expressed as so much protein, 

 carbohydrates, and fat. 



By means of these and other methods of statistical and ex- 

 perimental study a fairly accurate knowledge has been obtained 

 of the amounts of protein, carbohydrates, fat, and energy 

 ordinarily consumed by people of different classes and in different 

 countries. The knowledge thus derived has led to the general 

 acceptance of certain standards for the average food consumption 

 of different classes, and has brought out this fact : " That all 

 over the world people who can obtain such food as they desire 

 use liberal rather than small quantities ; and that the more active 

 or severe the work done, the larger the quantity of food eaten."* 



The standards that have been most widely accepted, such as 

 those of Voit, Atwater, Rubner, and others, all agree pretty 

 closely in the quantities of their constituents with the average 

 dietaries to which custom and instinct have guided mankind in 

 the formation of his dietetic habits. These standards have been 

 generally regarded as representing the minimum amount neces- 

 sary for the maintenance of the average man, under average 

 conditions, doing a moderate amount of work, in health and 

 strength. Some of these standards are 



It will be observed that there is a general consensus of opinion 

 that the protein element should amount to over 100 grammes a 

 day, and that the energy value should be over 3,000 calories. 



* Benedict, " The Nutritive Requirements of the Body," American Journal 

 of Physiology, 1906, xvi. 



