618 



PHYSIOLOGY 



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 



of carbon dioxide given off in the course 

 of an experiment lasting one to three hours 

 or longer. The oxygen consumption is 

 measured by weighing the cylinder of this 

 gas, chosen small for this purpose, before 

 and after the experiment. 



III. PETTENKOFER'S METHOD. In 

 the apparatus designed by Pettenkofer 

 the animal or man was placed in a 

 chamber through which a constant cur- 

 rent of fresh air was passed. The amount 

 of air passing through the chamber was 

 measured by means of a meter. Through- 

 out the experiment continuous samples 

 both of the air entering the chamber 

 and of the air leaving the chamber were 

 taken. The analyses of these samples 

 served to show the composition of the 

 whole air entering and leaving the cham- 

 ber, and therefore the changes in the air 

 caused by the presence of the animal. 

 The advantage of this apparatus is that 

 an adequate ventilation can be kept up, 

 and the apparatus can be built of any size. 

 In the apparatus of Tigerstedt built on 

 this plan the chamber had a capacity 

 of 100*6 cubic metres, and was, in fact, 

 a small room. A small respiratory 

 apparatus has been built by Atwater. 

 IV. ZUNTZ AND GEPPERT'S METHODS. For many purposes the methods 

 devised by Zuntz and Geppert present many advantages, especially when it is desired 

 to take the respiratory exchanges in man or any animal during a limited period of time. 

 The subject of the experiment has his nostrils clamped and breathes into and out of 

 a face-piece. This face-piece is provided with valves either of aluminium or of animal 

 membrane, which serve to separate the in -going from the out-going current of air, 

 In the course of the out-going current is placed a very delicate gas meter which presents 

 practically no resistance to the air current. A branch from the efflux tube passes to a 

 gas analysis apparatus. By an ingenious method it is arranged that an aliquot part 

 of the whole of the out-going air is drawn off into this apparatus, so that the experiment 

 can be interrupted at any time, and the analysis of this sample will give the average 

 composition of the expired air, and therefore, on multiplication by the total gas passing 

 through the gas meter, the total output of carbon dioxide during the course of the 

 observation. One advantage of this method is that the apparatus is portable, and can 

 be applied to the investigation of the respiratory exchanges of patients in hospitals 

 or of man or animals while they are walking about. It has been used, for instance, 

 by Zuntz and his pupils in an interesting series of researches on the gaseous metabolism 

 of men at high altitudes. 



FIG. 318. Arrangement of apparatus in 

 Benedict's method for determination of 

 respiratory exchange. 

 N, tubes inserted into nostrils of patient ; 

 A, tension equaliser ; c, cylinder contain- 

 ing soda lime for absorbing C0 2 . 



