36 RESPIRATORY EXCHANGE OF ANIMALS AND MAN 



possible with this instrument to determine CO 2 with an accuracy of 

 0*0004 per cent, and perfectly reliable results can be obtained therefore 

 when the ventilation is so regulated that the percentage of carbon 

 dioxide in the outgoing air is allowed to rise to O'l per cent. only. 



For many experiments on man the Tigerstedt-Sonden apparatus 

 has been used without any ventilation whatever, but the air in the 

 chamber which is very large (100 cub. metres in the Stockholm ap- 

 paratus and 76 cub. metres in that at Helsingfors [Tigerstedt, 1906]) 

 has been mixed continually by an electric fan, and the increase in CO 2 

 per cent, measured by analyses in half-hour intervals. 



Benedict and Romans [1911] have constructed their respiration 

 apparatus for small animals (dogs of 5 kg.) on this latter principle 

 and without any provision for ventilation (fig. 2, p. 15). They point 

 out that for experiments of a preliminary nature such simple devices 

 are often very useful. 



In the Jaquet apparatus [1903] advantage is taken of the fact 

 that the CO 2 percentage of the inspired air can be allowed to rise to 

 at least I per cent, without causing the slightest inconvenience to the 

 subject. The only effect is a slight increase in the pulmonary ventila- 

 tion sufficient to maintain the alveolar CO 2 percentage at practically 

 the same level as before. With accurate gas analysis both oxygen 

 and carbon dioxide can be determined to about 0*01 per cent, and the 

 method consists therefore simply in passing a measured current of at- 

 mospheric air through the respiration chamber, taking an average 

 sample of the air leaving the chamber and analysing this accurately. 

 The most perfect and at the same time simple form of the Jaquet 

 apparatus is that described by Grafe [1910] (fig. n). The whole 

 upper part of the chamber is suspended from the ceiling of the room, 

 and can be lowered into a water (or oil) seal provided by a small 

 trough round the floor of the chamber. The chamber is provided 

 with an electric fan. Air is sucked through the chamber at a uniform 

 rate by means of a motor-driven gas meter, and by suitable transmis- 

 sion from the shaft of this meter mercury vessels can be lowered at a 

 uniform rate, thereby taking an average sample of the air leaving the 

 chamber during a certain time. 



As the air leaving the chamber is not always or even generally 

 saturated with moisture it will be apt to take up water from the gas 

 meter, the water level of which will thereby be lowered. It is neces- 

 sary therefore to saturate the air with water vapour in a suitable vessel 

 (Stahelin) or to maintain a constant level in the meter by having a 

 slow current of water through it 



