NORMAL PEOCESSES OF ENERGY METABOLISM 591 



Brezina and Kolmer likewise noted that the height of the initial respiratory 

 quotients during periods of muscular work varied with the intensity of 

 the work performed. When ^1.6 calories per minute was the rate of 

 metabolism the R. Q. was 0.83; but when the rate rose to 10 calories 

 per minute the quotient was 0.99. Lusk, who quotes this experiment, ex- 

 plains the higher quotients as due in part to the formation of acid with 

 consequent liberation of CO 2 from the plasma more rapidly than it was 

 formed. Other factors, he states, are the increased ventilation of the 

 lungs and carbohydrate utilization; for acid formation accelerates the con- 

 version of glycogen to glucose. In very extreme work, especially in short 

 spurts, it is quite possible also that oxygen absorption does not quite keep 

 )ace with CO 2 elimination from the lungs. Hence the purplish color' of 

 the face in muscular exhaustion as contrasted with the lighter but healthier 

 color of moderate exercise. After exercise when the oxygen absorption 

 is gaining on the CO 2 elimination the tendency would be for the R. Q. to 

 be depressed. That there is a real and not an imaginary mobilization 

 of carbohydrate during work Benedict and Cathcart infer from the fact 

 that following carbohydrate-rich diets the quotient rises somewhat more 

 in work than it does following carbohydrate-poor diets. 



As regards the mechanical efficiency upon different diets Zuntz was 

 convinced that there was nothing to choose between carbohydrate and fat. 

 He cites experiments performed by his students, especially Frentzel and 

 Reach and also of Atwater and his colleagues, which show that the absorp- 

 tion of oxygen is essentially the same whether carbohydrate .or fat is burned 

 (see Table 14). Benedict and Cathcart support this view with their 

 findings that the energy quotient (total calories produced per calorie of 

 effective work performed) was the same on days following a carbohydrate- 

 rich diet as on days following a diet poor in this foodstuff whether the 

 amount of work was large or small. Anderson and Lusk performed ex- 

 periments upon a 9 kilo dog while running upon a treadmill inside the 

 calorimeter both before and after feeding with large amounts of glucose 

 and noted a distinct difference in efficiency after the carbohydrate ingestion. 

 When the dog had been without food for 18 hours and the average re- 

 spiratory quotient was 0.78 it required 0.580 kilogrammeter of work to 

 move 1 kilo of the body weight 1 meter on the horizontal. In the first 

 hours after carbohydrate when the average quotient was 0.95 the same 

 work was done at an expenditure of 0.550 kilogrammeter, a saving of 

 5 per cent. Krogh and Lindhard point out that if the metabolism per 

 unit of work is assumed to be a straight line function of the quotient the 



