Method of Investigation. 15 



BESPIEATOBY PRODUCTS. 



For any study of the transformations of matter in the body, complete 

 knowledge of the respiratory products is of the greatest importance. In the 

 experiments here reported, determinations were made not only of the carbon 

 dioxide and of the water-vapor eliminated through the lungs and skin, but 

 likewise of the oxygen absorbed. The apparatus and methods have been 

 described in detail in a previous publication." 



Water. The determination of water, in brief, is as follows : The air-current 

 which leaves the respiration chamber and which contains the water-vapor is 

 caused to pass through a previously weighed vessel containing strong sulphuric 

 acid. The water is retained by the acid and the increase in weight of the 

 vessel indicates the amount of water absorbed during each experimental period, 

 which is usually of from two to three hours' duration. Since there may be 

 noticeable fluctuations in the amount of water in the residual air in the 

 chamber, absolute determinations of the amounts of moisture in this air are 

 made at the end of each period, the differences between the amounts at the 

 beginning and end of each period giving data for correcting the absolute water 

 elimination for that period. 



Carbon dioxide. The determinations of carbon dioxide are made by con- 

 ducting the air-current from the respiration chamber after it has been freed 

 from water, through vessels filled with soda lime. The carbon dioxide is 

 completely absorbed and provision is made for collecting and weighing the 

 quantity of water lost from the reagent as the dried air passes through it. 

 The soda-lime vessels, as well as the last sulphuric acid-containing vessel, are 

 weighed at the beginning and end of each period. Fluctuations in the quantity 

 of carbon dioxide residual in the air of the chamber are allowed for by analyses 

 immediately after the end of each period and thus the actual carbon dioxide 

 production can be computed accurately. 



Oxygen. The determination of oxygen is somewhat more complex. This 

 gas is inclosed in a highly compressed form in steel cylinders, from which it is 

 admitted to the ventilating air-current. The loss in weight of the cylinder at 

 the end of each period indicates the amount of oxygen admitted. Corrections 

 are made for the slight amounts of nitrogen present in the gas. In addition 

 to the amount of oxygen so admitted, however, there may be very marked 

 fluctuations in the oxygen in the volume of air residual in the chamber, and, 

 consequently, analyses of this residual air are also necessary to ascertain any 

 alterations in the oxygen content. Actual determinations of oxygen from ab- 

 sorption by potassium pyrogallate are made at the end of each day. A system 

 of computation which includes the determination of the apparent volume of 

 the air in the chamber at the end of the period, the amount of carbon dioxide in 



Carnegie Institution of Washington Publication No. 42 (1905). 



