METABOLISM 159 



carbon in the income and outgo, the remainder will indi- 

 cate the amount of carbon derived from the non-nitrogenous 

 fat and carbohydrates. We can thus determine how much 

 non-nitrogenous foodstuff is consumed in the body and 

 whether the body has increased or decreased in non-nitro- 

 genous substances. 



Determination of the inhaled oxygen is of importance in 

 understanding the metabolic processes, for in warm-blooded 

 animals the amount of inhaled oxygen is a measure of the 

 extent of combustion taking place in the body. From the 

 amount of oxygen consumed, it can also be calculated how 

 much hydrogen, besides the carbon, is oxidized in the body. 



In cold-blooded animals the estimation of oxygen is of little 

 value, as the oxygen inhaled is not directly used up, but is stored 

 up for a longer or shorter time, because these animals can live for 

 some time in an atmosphere free of oxygen. Warm-blooded 

 animals, on the contrary, do not store up oxygen to any great 

 extent and can therefore endure the lack of oxygen for but a few 

 minutes. An exception to this are the warm-blooded hibernating 

 animals, which appear to be able to store up, during the period of 

 activity, a considerable amount of oxygen. 



The respiratory quotient, or the proportion between the 

 volumes of the carbon dioxide exhaled and oxygen inhaled, 

 tells us how much of the inhaled oxygen is used to oxidize 

 carbon, forming the carbon dioxide exhaled by the lungs, 

 and how much of it is used in oxidizing other elements, 

 especially hydrogen. 



When pure carbon is oxidized to carbon dioxide, the resulting 

 carbon dioxide has the same volume as the oxygen consumed. 

 In such a case the respiratory quotient is one. But if, in addition 

 to carbon, hydrogen is also oxidized, then the resulting volume 

 of carbon dioxide is less than the oxygen used up, and the more 

 hydrogen is oxidized, the less is the volume of carbon dioxide. 

 In such a case the respiratory quotient is less than one. 



The value of the respiratory quotient with carbohydrate ( 

 combustion is i; with proteid combustion, 0.8; with fat] 

 combustion, 0.7. 



Carbohydrates contain sufficient oxygen to oxidize all the 



