I.— PHYSIOLOGY 197 



this quotient there is 10 -6 Cals. less heat given out and 2 -7 litres less O2 

 absorbed ; or 3 -93 Cals. per litre Oj. 



The following calculations have been made : 



CO 2 grams per hour ..... 



R.Q. o • 75 Cals. liberated per litre oxygen absorbed 

 „ 0-90 Cals. absorbed per litre oxygen liberated 



n ^ ' 95 '> '» " " " 



»» ^ *00 >) )) )) >> >» 



The figures for the Cals. per litre of oxygen are of the same order as the 

 theoretical figure 3-93, and the equations 3 and 4 for R.Qs. o -95 and i • 00, 

 where there is the largest amount of conversion, give the closest figures. 

 The other two equations 5 and 8 give at one point an impossible figure, 

 indicating absorption of heat when there should have been liberation, 

 and vice versa. But the figures are provisional. The R.Qs. chosen for 

 calculation are not the averages, or the medians of the R.Qs. in the 

 groups, and it appears now that determinations in diabetes should be 

 added. But considering that the figures represent the ratio of differences 

 between quantities ten times as large, and so are particularly liable to error 

 they do seem compatible with the conversion of carbohydrate and fat at 

 high and low quotients, and in this sense provide a quantitative proof. 



Food. — I have just said that the values for the COg-heat relation after 

 food fall into line with the basal metabolism results when grouped 

 according to the respiratory quotient. This has implications of interest, 

 because most results in the groups belonging to the higher quotients 

 were obtained after food, and particularly carbohydrate. Hence, con- 

 version into fat takes place within the first few hours after ingestion of 

 carbohydrate, and the resulting absorption of heat explains the well-known 

 small specific dynamic action of carbohydrate. After ingestion of fat the 

 specific dynamic action is also small, but this is because the values remain 

 at the basal level without alteration of quotient, presumably because fat 

 delays the emptying of the stomach. On the other hand, after protein 

 there is eventually increase both in the heat and the respiratory exchange 

 — hence the high specific dynamic action ; but in the first hour or two 

 there is often a rise of quotient and little if any increase of heat, which 

 makes it probable that any rate part of the protein is immediately con- 

 verted into fat, and in this case invalidates the usual method of calculating 

 non-protein metabolism. 



Muscular Work. 



Investigating the effect of diet on the respiratory exchange due to 

 muscular work, Krogh and Lindhard found that with carbohydrate more 

 CO2 was excreted and less Oj was absorbed than with a diet mainly of fat. 

 On the theory of the variable combustion ratio this meant that less heat 

 was produced with carbohydrate, so that the body worked more economi- 

 cally, Benedict and Milner^ have made the only systematic investigation 

 * U.S. Dept. of Agriculture. Office of Exp. Stations, Bull. 175, 1907. 



