Katabolism and Heat Production. 50? 



The absorption of oxygen results in the combustion of carbon in the case of 

 glycogen assuming that the oxygen of the carbohydrate molecule combines 

 with the hydrogen/ and the combustion of carbon and organic hydrogen in the 

 case of fat and protein, and hence it would be expected that the oxygen thermal 

 quotient would vary with the proportions of protein, fat, and glycogen con- 

 sumed. Since the widest fluctuations in the relative proportions of these com- 

 pounds occur on the first day of the experiments, the oxygen thermal quotients 

 would be expected to be less regular on the first day than on other days of the 

 fasts. It will be noticed that the highest and lowest quotients were observed on 

 the third and fifth days of fasting. This fact is of importance in the subsequent 

 comparison of the heat production with the estimated energy of the material 

 oxidized in the body (see p. 514). When the relative proportions of protein, 

 fat, and carbohydrate become more nearly established as on the second and 

 subsequent days, the quotient should remain practically constant, although 

 the fact must not be lost sight of that there are relatively wide variations in 

 the proportions of glycogen and fat katabolized even on some of the later 

 fasting days. Making due allowance, however, for such deviations, it is clear 

 that marked variations in the oxygen thermal quotients in the later days of 

 fasting are due to one of two things, defective oxygen determinations or 

 defective heat measurements. A further discussion of the relation of oxygen 

 and heat production is given on page 515. 



The carbon dioxide thermal quotient, like that of the oxygen is determined 

 by the nature of the material burned. The larger the amount of glycogen, 

 the greater the amount of carbon dioxide produced per 100 calories of energy. 

 Consequently we would expect to find on the first day of fasting, where the 

 greater amount of glycogen is consumed, the larger carbon dioxide thermal 

 quotient. It is important to recognize that in comparing these quotients the 

 variations in the total 24 hours' heat production from experiment to experi- 

 ment are without significance. In general, the carbon dioxide thermal quotients 

 are greatest on the first day of the fast. After the relative proportions of 

 protein, glycogen, and fat katabolized in the body have attained a constancy, 

 the quotient has a tendency to remain constant, in general not far from 30.7. 

 The lowest carbon dioxide- thermal quotient observed in any of the experiments 

 is 29.45 on the second day of experiment No. 81 and the highest 34.70 on the 

 third day of food experiment No. 76. 



1 The assumption that the absorbed oxygen combines only with carbon is 

 obviously untenable. 



