INFLUENCE OF FOOD 503 



eaters, chewers, nitrogen economists, all bear witness to some 

 portion of truth, but believe in the way characteristic of people 

 with a mission that their little piece is the whole truth and nothing 

 but the truth. The same may be said of many of the exponents 

 of systems for muscular training. 



The personal equation can only be determined by experiments 

 carried out upon the individual himself ; instinct and experience 

 result therefrom, and are the natural and safest guides. The idea 

 that a man should determine his diet by its chemical composition 

 or caloric value is not only repugnant but also unscientific ; like- 

 wise it is impossible to lay down hard-and-fast rules for the amount 

 and nature of exercise to be taken. The personal equation is the 

 primary factor. 



Influence of Food upon the Respiratory Exchange. There is a 

 daily variation in the respiratory exchange, which in its main 

 features agrees with the variation in the temperature of the body ; 

 there is a rise during the day, the time of activity and work, and 

 a fall during the night, the time of rest and sleep. One of the 

 chief factors in the production of this cycle is muscular activity, 

 which has already been discussed ; the next important factor is 

 the intake, digestion, and assimilation of food. 



The general effect of food can be best demonstrated by a 

 comparison of the respiratory exchange of a fasting animal with 

 that of the same animal when it has been well fed. In addition 

 to the general effect, the special influence of the different classes 

 of food-stuffs, proteids, carbohydrates, and fats, must be con- 

 sidered. 



The earliest work upon the subject is that of Lavoisier, who 

 showed that in man food caused an increase in the output of 

 carbon dioxide and the intake of oxygen. It is, however, the 

 classical research of Kegnault and Reiset, which first clearly de- 

 monstrated the influence of fasting and feeding upon the respira- 

 tory exchange. These observers found that the respiratory quotient 

 varied from 0-62 to 1*04, according to the nature of the food con- 

 sumed by the animal ; during fasting the respiratory exchange 

 of a herbivorous animal resembled that of a carnivorous animal, 

 for it was living upon its own flesh ; an animal well fed with 

 corn often discharged, combined with carbon as carbon dioxide, a 

 greater quantity of oxygen than that absorbed by the lungs. 

 Lavoisier believed that the combustion in an animal's body 



