I.— PHYSIOLOGY 199 



Another method of calculation depends on using equation 7 in com- 

 paring Experiments 63 and 62. With carbohydrate there was excreted 

 361 -4 grms. CO2 more than on the mixed diet. If this resulted from 

 oxidation of a carbohydrate-fat mixture at R.Q. 0-802, the heat would 

 be by equation 7, 1097-4 Cals. Hence 14670 -i + 1097-4 — 144^4 "4 

 (= 1303 -i) Cals. must have been absorbed on changing to the carbo- 

 hydrate diet, owing to conversion. Since 44 grms. CO2 requires 32 grms. 

 O2 for its formation, the oxygen required to produce 361 -4 grms. COj 



at the R.Q. would have been 3^ ^ "4 X 3^ ^^ 327-7) grms. The oxygen 



44 X 0-002 

 that must have been absorbed on changing to the carbohydrate diet was 

 ^^217-2 + 327-7 — 4158 -6 (= 486 -3) grms. Hence the calories absorbed 



per grm. of oxygen was ^„^ = 2-679, or 2-679 -— - (= 3 "83) Cals. 



per litre. This value, 3-83, is very close to the theoretical value 3-93. 



Thus, there is every probability that carbohydrate is converted into 

 fat in muscular work on a carbohydrate diet. This may explain the 

 quotients above unity obtained by C. H. Best, K. Furusawa and J. R. 

 Ridout.^ A point of interest is that the amount of the conversion 

 increases with the muscular work and the total respiratory exchange, 

 which suggests that conversion and combustion are linked reactions. 



Teleologically, the value of a conversion of carbohydrate to fat may be 

 questioned, considering the enormous storage of fat in the body compared 

 to carbohydrate ; but these deposits of fat may not be readily available, 

 and anyhow a better way of looking at the conversion process is from the 

 point of view of a velocity reaction, the amount of conversion depending 

 on the concentration of carbohydrate in the reacting tissues, which is 

 increased on a high carbohydrate diet. The interesting conclusion may 

 be drawn that muscular work on any diet produces nearly the same 

 amount of heat ; if heat is absorbed in conversion from carbohydrate to 

 fat this must be provided by increased combustion of the standard carbo- 

 hydrate-fat mixture. 



A New Definition of Basal Metabolism. 



On the theory of indirect colorimetry, based on the constant combustion 

 ratio of carbohydrate and fat, the non-protein carbon dioxide results 

 entirely from the combustion of carbohydrate and fat, while the oxygen 

 is used partly for combustion and partly in conversion processes. If the 

 respiratory quotient is high, say 0-9, the heat, calculated on the assumption 

 that the oxygen is used entirely for combustion, is about 8 per cent, above 

 the heat actually found, because the heat due to combustion is diminished 

 by the heat absorbed in the conversion of carbohydrate towards fat (see 

 fig. 4). Since under basal conditions there are continual small variations 

 in the quotient, there will be continual additions to or subtractions 

 from the heat of combustion, according as the conversion of fat to 

 * Proc. Roy. Soc, B., 104, 119, 1929, 



