690 PHYSIOLOGY 



data with regard to the respiratory exchange under various circum- 

 stances have therefore been obtained by one of the three following 

 methods : 



II. THE METHOD OF REGNAULT AND REISET. The prin- 

 ciple of this method consists in placing the animal that is to be the 

 subject of investigation in a closed chamber containing a given 

 volume of air. The carbon dioxide produced by the animal 

 is absorbed by means of caustic alkali, and the oxygen consumed 

 by the animal is made good by allowing oxygen to flow into the 



chamber from a gasometer. 

 The inflow of oxygen is 

 regulated so as to keep 

 the pressure of air in 

 the chamber constant. At 

 the end of the experi- 

 ment the alkali is titrated 

 and the amount of carbon 

 dioxide absorbed thus 

 determined. The air in the 

 chamber is also analysed 



FIG. 315. Air circuit in Benedict's respiration go ag to be certa m that it 

 apparatus. 



contains an excess neither 



of carbon dioxide nor of oxygen. The amount of oxygen absorbed 

 by the animal is known already, the oxygen which has been allowed 

 to flow in having been measured. 



A modification of this method has been devised by Benedict 

 and is especially applicable to clinical purposes. In this method 

 the individual who is the subject of the experiment breathes 

 through a nose-piece into a wide metal tube, the mouth being 

 kept closed. The metal tube forms part of a closed system through 

 which a current of air is maintained by means of a pump. In 

 the course of the current of air are interposed vessels for the 

 absorption of carbon dioxide and of water, and the volume of 

 gas in the system is maintained constant by admitting oxygen 

 to it in proportion as the oxygen of the system is used up 

 in respiration. In Fig. 315 is given a diagrammatic scheme of the 

 air ^circuit, and in Fig. 316 a diagram of the arrangement of the 

 whole respiration apparatus, showing the nose-piece for breathing, 

 the tension equaliser, the air-purifying apparatus, and the oxygen 

 cylinder. The tension equaliser, A, is attached to the ventilating 

 pipe near the point of entrance of the air into the lungs. It consists 

 of a pan with a rubber diaphragm (which may be conveniently made 

 from a lady's bathing-cap). As the air is drawn into the lungs 

 the rubber diaphragm sinks, to rise again with expiration. The 



