THE CARBON OF THE FOOD. 15 



Since no part of the oxygen taken into the sys- 

 tem is again given oiF in any other form but that 

 of a compound of carbon or hydrogen ; since fur- 

 ther, the carbon and hydrogen given off are re- 

 placed by carbon and hydrogen supplied in the 

 food, it is clear that the amount of nourishment 

 required by the animal body must be in a direct 

 ratio to the quantity of oxygen taken into the 

 system. 



Two animals, which in equal times take up by 

 means of the lungs and skin unequal quantities of 

 oxygen, consume quantities of the same nourish- 

 ment which are unequal in the same ratio. 



The consumption of oxygen in equal times may 

 be expressed by the number of respirations ; it is 

 clear that, in the same individual, the quantity of 

 nourishment required must vary with the force and 

 number of the respirations. 



A child, in whom the organs of respiration are 

 naturally very active, requires food oftener than an 

 adult, and bears hunger less easily. A bird, deprived 

 of food, dies on the third day, while a serpent, 

 with its sluggish respiration, can live without food 

 three months and longer. 



The number of respirations is smaller in a state 

 of rest than during exercise or work. The quan- 

 tity of food necessary in both conditions must vary 

 in the same ratio. 



An excess of food is incompatible with deficiency 

 in respii'ed oxygen, that is, with deficient exercise ; 



