184 NUTRITIONAL PHYSIOLOGY 



hydrate feeding.) The apparent heat value of the calcu- 

 lated metabolism will be as follows: 



100 grams of protein at 4.1 calories = 410 Calories. 

 223.6 grams of fat at 9.3 " = 2079 

 Total "2489 



This bit of reckoning is an instance of indirect calorimetry. 

 It is found in practice that direct and indirect calorimetry 

 lead to results so nearly identical as to make it certain that 

 the discrepancy between them is accidental. The two 

 figures differ in modern work by less than 1 per cent. 



The correspondence between the observed and the cal- 

 culated calories means this: that the animal displays no 

 powers of movement or heat production which cannot be 

 referred to the oxidation of organic compounds in its body, 

 and so eventually to the stores of chemical energy in its food. 

 It is an engine, a transformer, and not a creator of energy. 

 A glimpse of this conception came within the vision of the 

 brilliant Count Rumford more than one hundred years ago. 

 He had become convinced that heat must be a form of 

 energy rather than a substance. His conclusions had been 

 drawn in part from the observation that there seemed to be 

 no limit to the quantity of heat obtainable from small 

 masses of metal in the process of drilling. With a flash 

 of insight he looked at the horse which was walking in a 

 circle to move the drill, and queried whether the heat in the 

 iron turnings might not be a derivative of the muscular 

 work of the animal, and whether the same energy had not 

 in some sense pre-existed in the food given to it. The 

 verification of his induction was long deferred, but has at 

 length been made entirely conclusive. The credit for 

 this demonstration is shared by many workers, but most 

 conspicuously by Rubner, in Germany, and Atwater, in 

 this country. 



Let us return once more to our quantitative illustration. 

 If the day of the experiment had been one of ample feeding 

 instead of fasting, and the diet had consisted of protein 

 and carbohydrate, the metabolism might have been held 



