252 COMPARISONS OF RESPIRATORY EXCHANGE. 



smoked surface of a kymograph. Care must be taken, however, to 

 make sure that there are no errors due to inertia and that the tambour 

 is calibrated so that the pressure can be read directly. 



Another test of the pressure may be made by noting the effect of 

 using the valves with a spirometer, a meter, or a bag. If the pressure 

 increases very largely under these conditions, it is doubtless too great ; 

 some means should therefore be taken to overcome it, either by weight- 

 ing the counterpoise of the spirometer or by a device producing a 

 slightly diminished pressure in the meter, such as that recommended by 

 Magnus-Levy 1 in connection with the sampling apparatus of the 

 Zuntz-Geppert method. 



The test for the efficiency of the valve, that is, for the quantitative 

 separation of inspired and expired air, may be made by means of 

 special apparatus. If a pair of valves is connected to the hand spi- 

 rometer 2 and a pointer writing upon a kymograph drum is attached to 

 the bell of the spirometer, the natural respirations of a man breathing 

 through the valves can be imitated and a direct record made of the total 

 ventilation as determined by the hand spirometer. The air can then 

 be collected in a large spirometer or passed through a meter and with 

 proper precautions as to temperature and saturation a calculation may 

 be made from the movements of the hand spirometer of the amount of 

 air which has passed through the valves, and from the meter or large 

 spirometer how much air has been received. The results of such a 

 calculation will show the efficiency of the valves for separating the 

 inspired and the expired air. Of course care must be taken that the 

 movements of the hand spirometer are at approximately the rate and 

 depth of normal breathing. 



While no complete study of the efficiency of different valves has been 

 made in this research, two series of experiments have been carried out 

 by this method, one with the Tissot valves and the other with the 

 Siebe-Gorman valves. In these experiments the Tissot valves gave 

 results which were superior to those obtained with the Siebe-Gorman 

 valves. The total efficiency of the Tissot valves was about 99 per cent, 

 while that of the Siebe-Gorman valves may fall as low as 75 per cent, 

 according to which valve is used for the inspiratory valve. It can be 

 seen from these experiments that this method affords a good test of 

 the efficiency of valves. Simultaneous with this efficiency test, a 

 graphic record of the cycle of pressure may be obtained by means of 

 a side tube in the manner previously described. 



BREATHING APPLIANCES. 



In the experiments here reported the different types of breathing 

 appliances which have been used are the glass and pneumatic nose- 

 pieces, the rubber mouthpiece, and the mask. The last permits breath- 

 ing either through the mouth or the nose, or both. 



'Magnus-Levy, Archiv f. d. ges. Physiol., 1894, 55, p. 1. 2 See p. 79. 



