932 METABOLISM. 



V. THE NECESSITY OF FOOD BY MAN UNDER VARIOUS CONDITIONS. 



Various attempts have been made to determine the daily quantity of 

 organic food needed by man. Certain investigators have calculated 

 from the total consumption of food by a large number of similarly fed 

 individuals soldiers, sailors, laborers, etc. the average quantity of 

 foodstuffs required per head. Others have calculated the daily demand 

 for food from the quantity of carbon and nitrogen in the excreta, or cal- 

 culated it from the exchange of force of the persons experimented upon. 

 Others, again, have calculated the quantity of nutritive material in a 

 diet by which an equilibrium was maintained in the individual for one or 

 several days between the consumption and the elimination of carbon 

 and nitrogen. Lastly, still others have quantitatively determined, dur- 

 ing a period of several days, the organic foodstuffs daily consumed by 

 persons of various occupations who chose their own food, by which they 

 were well nourished and rendered fully capable of work. 



Among these methods a few are not quite free from objection, and 

 others have not as yet been tried on a sufficiently large scale. Neverthe- 

 less the experiments collected thus far serve, partly because of their 

 number and partly because the methods correct and control one another, 

 as a good starting-point in determining the diet of various classes and 

 similar questions. 



If the quantity of foodstuffs taken daily be converted into calories 

 produced during physiological combustion, we then obtain some idea of 

 the sum of the chemical energy which under varying conditions is intro- 

 duced into the body. It must not be forgotten that the food is never 

 completely absorbed, and that undigested or unabsorbed residues are 

 always expelled from the body with the feces. The gross results of calo- 

 ries calculated from the food taken must therefore, according to RUBNER, 

 be diminished by at least 8 per cent. This figure is true at least when 

 the human being partakes of, a mixed diet of about 60 per cent of the 

 proteins as animal, and about 40 per cent of the proteins as vegetable 

 foodstuffs. With more one-sided vegetable food, especially when this 

 is rich in undigestible cellulose, a much larger quantity must be sub- 

 tracted. 



The following summary contains a few examples of the quantity of 

 food which is consumed by individuals of various classes of people under 

 different conditions. In the last column we also find the quantity of 

 living force which corresponds to the quantity of food in question, calcu- 

 lated as calories, with the above-stated correction. The calories are 

 therefore net results, while the figures for the nutritive bodies are gross 

 results. 



