640 



PHYSIOLOGY 



the same amount of protein in the food and a somewhat insufficient 

 amount of carbohydrates and fats, his consumption of protein amounted 

 to 1094 grm. Here, as against a three- to fourfold increase of the gaseous 

 metabolism of the body, we have only a 10 per cent, increase of the protein 

 metabolism. 



A still larger difference between the respiratory changes in the resting or 

 working condition is found when the exchanges are taken over shorter 

 intervals. The following Table represents the respiratory exchanges in a 

 trained muscular subject during complete rest and when doing moderate 

 or severe work, namely, riding a bicycle with a brake. Each observation 

 lasted from 10 to 15 minutes. 



These last figures represent a maximum since the subject worked with 

 great difficulty and was exhausted when he came off the machine. 



There is another method by which we can arrive at some idea of the nature 

 of the material which is furnishing by its oxidation the necessary energy 

 for the performance of muscular work. It is evident, if we compare the 

 formulae of a carbohydrate and a fat respectively, that it will require a 

 relatively larger amount of oxygen to oxidise the fat than is necessary in the 

 case of the carbohydrate. In the latter there is sufficient oxygen to combine 

 with all the hydrogen present and form water. The whole of the oxygen 

 therefore which is taken in is employed in the oxidation of the carbon, 

 and one volume of oxygen will produce one volume of carbon dioxide. Thus : 

 C 6 H 12 6 + 60 2 = 6H 2 + 6C0 2 . If the whole of the animal's energy 

 requirements were furnished by the oxidation of carbohydrates, the output 

 of carbon dioxide expired would be exactly equal in volume to the oxygen 



inspired, and the respiratory quotient of the animal, namely, 2 . . -, 



2 inspired 



would be equal to unity. In fats the amount of oxygen is only sufficient to 

 combine with four atoms of the hydrogen of the molecule. When fats 

 undergo oxidation, of the oxygen used only a portion is devoted to the 

 formation of carbon dioxide, the rest being employed in the oxidation of 

 hydrogen to water. In an animal using only fats the carbon dioxide output 

 of the body would be considerably less than the oxygen intake and its respira- 

 tory quotient would be less than unity. The respiratory quotients for pro- 

 tein, fats, and carbohydrates are given in the following Table (Atwater) : 



