548 JOHJtf R. MURLIN 



laboratories for this purpose in hospitals or elsewhere will continue to 

 give more accurate results, as is true of x-ray and electrocardiographic 

 work and for the same reasons. 



III. Methods of Calculating the Heat Production 

 from the Respiratory Exchange 



Historically four distinct methods (LeFevre(<jr)) have been employed 

 for the calculation of the heat production from the chemical changes going 

 on in the body. In each case the method rests upon the fact established by 

 Lavoisier that the products of respiration are the products of combustion. 



1. Calculation from Heats of Combustion of Carbon and Hydrogen, 

 This method possesses only historical interest to-day, yet it should be pre- 

 sented briefly for the sake of the underlying principle involved. In 1783 

 Lavoisier published a celebrated work upon the respiratory metabolism and 

 calorimetry of the guinea pig. The chamber in which the animal was 

 contained was traversed by a current of air from which the carbon dioxid 

 was absorbed at the entrance and exit in potash bottles. The gain in 

 weight of the latter less the gain in weight of the former gave the carbon 

 dioxid produced by the animal. In ten hours a guinea pig gave off 3.33 

 gm. of carbon, which from previous experiments Lavoisier knew was 

 equivalent in heat value to 32G.T6 gm. of ice melted at 0. He proved 

 this by placing the pig in an ice calorimeter and found 341.08 grn. melted. 



In 1785 Lavoisier, applying his work to the human subject as well 

 as to the animal, established the fact that out of 100 parts of oxygen ab- 

 sorbed, 81 parts only reappeared as carbonic acid gas; and he concluded 

 that the other 19 parts were combined with hydrogen to form water (Gavar- 

 ret). Respiration was thus seen to be accompanied by double combustion 

 and Lavoisier proposed by quantitative studies of the respiration to deter- 

 mine the proportion in which oxygen is partitioned between carbon and 

 hydrogen of the materials in the blood to produce carbonic acid gas, water 

 and heat. 



But this is not all. With Seguin, Lavoisier (Lavoisier and Seguin(&)) 

 made a series of experiments upon the human subject and demonstrated 

 that carbon dioxid is produced and oxygen is absorbed in proportion to the 

 mechanical work effected by the organism. "By this new discovery 

 Lavoisier raised the theory of combustion to the level of a great generaliza- 

 tion and revealed for the first time the essential source of all animal 

 energy' ' ( LeFevr e ( g ) ) . 



A method devised by Dulong consisted simply in measuring directly 

 the CO 2 produced and indirectly the water by assigning to hydrogen all 

 the oxygen which was not recovered as CO 2 . Since, however, it is not cer- 

 tain that all of the oxygen which escapes combination with carbon serves 



