7 ]6 PHYSIOLOGY 



during six hours amounted to 189-6 grm. ; during a rest experiment 

 with food the average output for a period of six hours was 230*4 grm. 

 of carbon dioxide. During work the average output in the same 

 individual during six hours rose to 705 grm. of carbon dioxide on a 

 carbohydrate diet, and to 634-8 grm. on a diet containing a large 

 amount of fat. The oxidation of carbon was therefore increased 

 more than threefold as a result of muscular work. If we compare 

 in the same way the protein metabolism of the same individual 

 during these experiments no such alteration is observed. Thus the 

 average output per day during rest and starvation corresponded 

 to 82 grm. of protein. During rest and with an approximately suffi- 

 cient amount of food the average amount of protein consumed was 

 98-8 grm. During a work day in which he received practically the same 

 amount of protein in the food and a somewhat insufficient amount 

 of carbohydrates and fats, his consumption of protein amounted 

 to 109-4 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. 



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 hydro- 

 gen 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 



C0 2 expired 



quotient of the animal, namely, -^- - . _, would be equal to unity. 



2 inspired 



In fats the amount of oxygen is only sufficient to combine with four 

 atoms of the hydrogen of the molecule. When fats undergo oxida- 

 tion, of the oxygen used only a portion is devoted to the formation 

 of carbon dioxide, the rest being employed in the oxidation of hydro- 

 gen 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 respiratory quotient would be less than unity. The respiratory 

 quotients for protein, fats, and carbohydrates are given in the 

 following Table (Atwater) : 



