FOODS NUTRITION. 699 



slightly more than the theoretical quantity. The^e results are in harmony with 

 those obtained in earlier experiments. 



In the experiments reported the amount of oxygen consumed Avas calculated, and 

 the values obtained are used in a discussion of the respiratory quotient. The authors 

 believe that the carbon dioxid thermal quotient also serves as an index of changes 

 taking place in the body. Concerning this quotient they state that, "in comparing 

 the results of these experiments, it was found tliat the amounts of carbon dioxid and 

 heat produced varied so uniformly that it was believed the ratio of one to the other 

 would afford means of judging of changes which occur in the body. This ratio, which 

 we have called a carbon dioxid thermal quotient, is nearly uniform in experiments 

 with the same conditions of food and work, but changes notably wdth changes in diet, 

 which accords with the fact that, in the oxidation of the various nutrients of food 

 and the corresponding compounds in the body, the ratio of carbon dioxid to heat is 

 nearly uniform for different compounds of the same class and that the values are 

 sufficiently distinctive to characterize the class. 



" From the composition and heats of combustion of the different classes of nutrients 

 the ratios of carbon dioxid to heat produced by oxidation are easily computed. 

 Provided the amount of oxygen were measured, similar ratios could be computed 

 for carbon and heat and oxygen and heat, and would doubtless give useful data. 

 Such ratios might be designated carbon thermal quotient and oxygen thermal 

 quotient. ' ' 



Concerning the relative merits of fats and carbohydrates as sources of energy for 

 muscular work, the general conclusion drawn from the experiments reported is 

 that " the fats were slightly inferior to isodynamic amounts of carbohydrates as parts 

 of a ration for muscular work. But while the natural inference is that calorie for 

 calorie the carbohydrates were slightly superior to the fats as sources of muscular 

 energy, the difference observed was very small and may have been due to some 

 individual peculiarity of the subject with whom the more directly comparable 

 experiments were made rather than to any inherent difference in the capacity of the 

 materials to yield energy for external muscular work." 



The experiments reported also furnish information regarding the different nutri- 

 ents as sources of energy for muscular work. The conclusions drawn are that a con- 

 siderable amount of the energy of external muscular work in these experiments 

 must have come from material other than protein, and that "it is in the highest 

 degree probal)le that the larger part of the material which was broken down and 

 oxidized to supply the energy of external muscular work consisted of carbohydrates 

 and fats. 



"These conclusions agree fully with the general belief of physiologists, that all of 

 the nutrients of food, proteids, fats, and carbohydrates may supply energy for mus- 

 cular work, but that the chief source is in the carbohydrates and fats. They leave 

 no basis whatever for the theory that the proteids are the sole source of muscular 

 energy." 



As regards the efficiency of the body as a machine, the results obtained with the 

 different subjects varied somewhat under different experimental conditions. Con- 

 sidering the results of the different experiments the efficiency ranged from 13.3 to 

 20.2 per cent, and in the latest experiments the average was over 19 per cent in all 

 cases. It appeared that whatever the amount of work which the subject of the 

 experiments did with the muscles used in turning the wheel of the bicycle ergometer, 

 he transformed al)out 5 calories of energy in his body for every one which was util- 

 ized in the performance of mechanical work. 



"In all these cases the subjects were fairly efficient machines, as will be seen when 

 it is remembered that the ordinary steam engine transforms only al)Out 15 per cent 

 of the energy of the fuel into work. It is quite {)ossil)le that something more satis- 

 factory than tlie ergometer may be devised for utilizing the external muscular work 

 performed by the subject." 



