10 Metabolism of Healthy Max. 



research, and evidence is at present being accumulated on this most important 

 point. It is hoped that a report will be issued in the near future. Conse- 

 quently, in this discussion no attempt will be made to introduce the discussion 

 of the influence of the ingestion of food, the specific dynamic action of the 

 foodstuffs, or the so-called work of digestion. 



METHOD OF EXPERIMENTING. 



The experiments here reported were all made with the respiration calorimeter 

 formerly at Wesleyan University, Middletown, Connecticut. The apparatus 

 has been described in detail in a number of places. 1 Suffice it to say here that 

 the apparatus is a respiration chamber with calorimetric features. The cham- 

 ber is air-tight, with a cubical content of about 5 cubic meters, and the venti- 

 lating air-current is caused to pass through a series of purifiers by which the 

 water-vapor and carbon dioxide are removed. The air is then returned to 

 the chamber, the deficiency in oxygen being made up by admitting oxygen 

 from a cylinder of the highly compressed gas. By noting the increase in 

 weight of the absorbers for water-vapor and carbon dioxide and the loss in 

 weight of the oxygen cylinder, the carbon dioxide and water-vapor given off 

 and the oxygen absorbed can be determined with a certain amount of accuracy. 

 Finally, corrections are made for variations in the composition of the air 

 remaining in the chamber and the figures thus corrected are the true values 

 for the carbon-dioxide production, water-vapor elimination, and oxygen 

 absorption. 



As a calorimeter, the chamber is surrounded by walls which prevent the 

 radiation of heat. Special precautions are taken to maintain the outer walls 

 at the same temperature as the inside of the calorimeter by arbitrarily heating 

 or cooling the air adjacent to the outer metal wall. By so doing all passage 

 of heat into or out of the chamber through the walls is prevented. The major 

 portion of the heat eliminated by the subject is brought away by a current of 

 cold water passing through an absorber system inside the chamber. The 

 temperature of the water as it enters and leaves and the mass of water are 

 carefully recorded, and from these data the amount of heat brought away can 

 be accurately computed. To the heat brought away in this manner must be 

 added the heat required to vaporize the water from the skin and lungs of the 

 subject. Consequently, the total heat of vaporization must be known. Multi- 

 plying the total water vaporized by the factor 0.586, the heat required to 

 vaporize the water is computed, and this added to the heat brought away by 

 the water-current gives the true measure of the heat eliminated by the subject. 



For purposes of extreme accuracy the heat elimination is not satisfactory, 

 since there may be a considerable storage or loss of heat from the body by 



1 Atwater and associates, U. S. Dept. Agr., Office Expt. Stas. Buls. 63 and 136, 1899 

 and 1903; Benedict and Milner, ibid., Bui. 175, 1907; Atwater and Benedict, Carnegie 

 Institution of Washington Publication No. 42, 1905. 



