LAW OF THE CONSERVATION OF ENERGY 



573 



which the Respiratory Quotient could be calculated. Deducting the 

 protein carbon from the total carbon output, and the oxygen required 

 to oxidize the protein from the total oxygen intake, the ratio of the 

 non-protein carbon dioxide to the residual oxygen intake, or the non- 

 protein respiratory quotient; afforded a measure of the proportion of 

 fat to carbohydrate actually consumed by the subject of the experi- 

 ment. Thus a non-protein respiratory quotient of 0.707 indicates the 



FIG. 49. General view of the respiration-calorimeter laboratory at Middletown, 

 Connecticut. The calorimeter-chamber is seen, with window open upon the right. 

 The principle of its construction is that of an ordinary refrigerator, namely, a chamber 

 surrounded by a series of confined air-spaces. The inner chamber is of copper. This is 

 succeeded by a wall of zinc and two walls of wood, each pair of walls being separated by 

 about three inches of air-space. Gain or loss of heat through the metallic walls of the 

 chamber is prevented by keeping the zinc wall at the sa.me temperature as the copper. 

 Any difference of temperature between these two walls is indicated by a thermocouple 

 and a galvanometer. Heat is supplied to the air-space surrounding the zinc wall by 

 passing an electrical current through coils of resistance-wire. Cooling is accomplished 

 by currents of water. The heat generated in the chamber is removed partly in the 

 form of the latent heat of vaporization of the water exhaled from the lungs and partly 

 by means of cold-water absorbers. The quantity of heat evolved is computed from the 

 amount of water passing through the heat-absorbers and its rise in temperature during 

 its passage. (After Benedict and Milner.) 



combustion of pure fat, a quotient of 1 .00 indicates the combustion of 

 pure carbohydrate (cf . Chapter XXII) and intermediate values repre- 

 sent the combustion of a mixture of these foodstuffs, the composition 

 of which can be estimated by a simple calculation. 



It now remained, in order to complete the demonstration of the 

 validity of the law of the conservation of energy in the animate world, 

 to investigate the source of the energy which is expended by an animal 

 in the performance of external work. In the experiments hitherto 



