TISSOT APPARATUS WITHOUT AUTOMATIC COUNTERPOISE. 225 



From the results of these comparisons it may be seen that with the 

 Tissot 200-liter spirometer, with a pressure on the air inside the bell 

 varying from +0.4 mm. to — 0.4 mm. of water, it is not necessary to 

 counterpoise the spirometer bell exactly and automatically by the use 

 of water in the counterpoise tube. These variations in pressure are 

 too small to affect the respiratory exchange. 



Table 42. — Variations of average results obtained xvithout automatic counterpoise from those 

 obtained with automatic counterpoise — Tissot apparatus. 



CAMONDKHIOCEJJMINCTCD 



8 9 10 I 



13 14 15 

 PER CENT OF VARIATION 



8 9 10 I I 12 13 14 15 



Fig. 74. — Probability curves for the series of comparison experiments with and without the 

 counterpoise on the Tissot spirometer. 

 The ordinates indicate the percentage of the total number of periods and the abscissae repre- 

 sent the percentage of variation from the average. 



