558 



JOHN K. MUKLIN 



footed up 528 grams. The thermal quotient therefore was 3.41 Cal. as 

 against a theoretical value of 3.45 calculated from the composition of the 

 diet. The error involved in the use of a thermal quotient of 3.43 Cal. per 

 gram for vegetarian as well as mixed diet would not be in excess of 0.5 

 per cent. 



The values thus far discussed were obtained upon the resting subject. 

 Would they apply equally to a subject engaged in heavy muscular work 

 where oxygen is utilized not merely for production of heat by combustion 

 but also for the transformation of the food's potential energy into mechan- 

 ical work? Lefevre(gr) has calculated the thermal quotients for many of 

 the work experiments found in Atwater's publications and has grouped 

 them as given in the table below. The amount of work reckoned on the 

 basis of 24 hours was from 120,000 to 190,000 kilogrammeters. 



TABLE 4 

 THEBMAL- QUOTIENTS OF 2 DURING MUSCULAR WORK (ATWATEB AND BENEDICT) 



It appears that the mechanical equivalent of oxygen when expressed 

 as heat is the same as the pure combustion equivalent. This is a very sig- 

 nificant fact for it means that the liberation of energy from combustible 

 substances is a constant function of the oxygen absorbed whether that en- 

 ergy take the form at once of free heat or pass first through the form of 

 mechanical work. 



It is clear that if the oxygen absorption of a subject is known the 

 amount of energy liberated in the body (not necessarily the amount of 

 heat) can be found with a high degree of accuracy by simply multiplying 

 the number of grams of oxygen by 3.43 Cal. or the number of liters at 

 and 760 by 4.90 Cal. or the number at 18 C. by 4.60 Cal. 



b. Thermal Quotient of Carbon Dioxid. Kesults not nearly so con- 

 stant are obtained when the carbon dioxid elimination is employed as the 

 basis of computing the heat production. For example, when tristearin is 

 completely oxidized the thermal quotient of CO 2 is 3.35 Cal. per gram. 

 When glucose is completely oxidized it is only 2.59 Cal. per gram (Table 

 2). Besides, it is possible to have CO 2 produced in large excess when glu- 

 cose is transformed into fat, and when the heat production is very low. Un- 

 der these circumstances the thermal quotient of CO 2 is given by Lefevre at 

 0.3 Cal. per gram. Finally, if fat is ever converted to glucose in the body 



