242 



COMPARISONS OF RESPIRATORY EXCHANGE. 



It was shown in the comparison between the Tissot and the Benedict 

 apparatus that the respiratory quotients with the Tissot apparatus were 

 more uniform than those secured with the Benedict method. 



The Tissot spirometer used for the collection of expired air is easily 

 manipulated in the way devised by the originator, as one has simply to 

 adjust the counterpoise correctly for any position in which the drum 

 stands, i. e., so that the weight of the counterpoise will keep the spi- 

 rometer bell in exact equilibrium, the siphon device automatically main- 

 taining the equilibrium thereafter. The siphon attachment operates 

 without difficulty if there is sufficient water-pressure to force the air bub- 

 bles out of the siphon. When water-pressure is not available, use may 



Table 43. — Results of consecutive experiments with Benedict and Tissot apparatus, showing 

 difference in uniformity of respiratory quotients with subject J. H. H. 



be made of a Mariotte flask, as described by Laulanie, 1 or of a tank 

 attached to the wall or some other support above the spirometer. 



The spirometer is exceedingly sensitive to changes in the pressure of 

 the air inside the bell, Tissot claiming it to be sensitive to 0.1 mm. 

 of water-pressure. While in our use of it we have not found so great 

 a degree of sensitiveness, yet it is certainly sensitive to less than 1 mm. 

 of water-pressure. The series of comparison experiments in which 

 a study was made of the effect of discarding the automatic device on 

 the counterpoise showed that it is not necessary to have the spirometer 

 so delicately counterpoised as Tissot has suggested, and, for all prac- 

 tical purposes, with normal subjects in measuring the respiratory 



1 Laulanie, Elements de physiologie, Paris, 1905, p. 344. 



