30 RESPIRATORY EXCHANGE OF ANIMALS AND MAN 



from a rapid current of moist air e.g. in experiments involving 

 heavy muscular work. 



The oxygen supply has to maintain the inside pressure as near as 

 possible to the atmospheric in order to minimize the danger of leakage. 

 When it fulfils this purpose it will at the same time maintain the com- 

 position of the atmosphere in the apparatus sufficiently constant. 



FIG. 7. 



Various devices are in use. The simplest plan is undoubtedly to 

 arrange a volume recorder connected with the chamber which will at 

 a certain point close an electric circuit and admit oxygen from a 

 cylinder and reduction valve, or an oxygen generator through a meter 

 as shown in fig. 15. With a sensitive volume recorder the pressure 

 in the chamber can be kept equal to the atmospheric within less than 

 cri mm. of water. Leakage can then take place by diffusion only. 



