THE TOTAL EXCHANGES OF THE BODY 



663 



only carbon dioxide and water, and absorbs only oxygen during its stay in the chamber, 

 the loss of weight of the animal during its stay in the chamber, subtracted from the 

 total amount of carbon dioxide plus water it gives off, will represent the amount of 

 oxygen absorbed. 



The advantage of this apparatus is that it can be fitted up in any laboratory, and 

 is accurate for the purposes to which it is applied. It is not however appropriate 

 for long-continued experiments or for experiments on larger animals or on man 

 himself. Most of the data with regard to the respiratory exchange under various 

 circumstances have therefore been obtained by one of the following methods. 



II. THE METHOD OF REGNAULT AND REISET. The principle 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 experiment the alkali is titrated and the amount of carbon dioxide 

 absorbed thus determined. The- air in the chamber is also analysed so as to be certain 

 that it 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 

 n devised by Benedict and is espe- 

 cially 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 inter- 

 posed vessels for the absorption of 

 carbon dioxide and of water, and the 



C;U i 



bee 



Air circuit in Benedict's respiration 

 apparatus. 



volume of gas in the system is main- FIG. 328. 

 tained constant by admitting oxygen 

 to it in proportion as the oxygen of 



the system is used up in respiration. In Fig. 328 is given a diagrammatic 

 scheme of the air circuit, and in Fig. 329 a diagram of the arrangement of the whole 

 respiration apparatus, showing the nose-piece for breathing, the tension equaliser, 

 tlie 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 respiratory movements can thus proceed without 

 altering appreciably the pressure within the closed system of tubes. By the admission 

 of oxygen the supply of oxygen is adjusted so as to keep the bag from becoming either 

 too much distended or too much flattened. As the air leaves the lungs and passes 

 into the constantly moving current of air, it is carried along by the pump and flows 

 through two Wolff's bottles containing strong sulphuric acid and pumice for the removal 

 of water vapour. It then passes through a brass cylinder, c, filled with soda lime 

 for the absorption of carbon dioxide. From here it passes again through sulphuric 

 acid in a Kipp generator for the absorption of water given off by the soda lime. Since 

 the air so deprived of moisture would be uncomfortable to breathe, it is then carried 

 through another Kipp generator containing water with a trace of sodium carbonate 

 for the neutralisation of any acid fumes which may be given off by the sulphuric acid. 

 It then passes back to the tube from which the subject is breathing. In this way it is 

 possible to determine very accurately the amount of oxygen used up and the amount 



