THE CONTROL OF THE RESPIRATION 



363 



The exact time during which air enters is recorded by the small spirometer by means of 

 a grooved dial on the axis of the lid, on, which a thread works over a system of pulleys, 

 and any movement is accurately recorded by a writing point on the smoked paper of a 

 drum. The spirometers are connected so that the air current may be directed in the 

 three following ways: (1) through Cocks 1 and 2 outside; (2) directly through both 

 cocks into the large spirometer for the purpose of collecting a series of expirations; 

 and (3) through Cock 1 directly into the small spirometer for catching a single expira- 

 tion. In all experiments the first filling of the spirometer is rejected, so that the dead 

 space of the spirometers is filled with air of approximately the same composition as in 

 the succeeding expirations. The time is marked in seconds by a time clock. The respira- 

 tory movements are recorded by a pneumograph. (Fig. 128.) 



The subject is brought into respiratory equilibrium by having him breathe through 

 the valves for a period of time before the observation. The respiratory movements 

 during this time are recorded while the cocks are in Position 1. When the observation 

 is started, the cocks are turned into Position X during the time an inspiration is being- 



Fig. 128. Arrangement of meters and connections of Pearce's method for measurement of CO* 



of alveolar air in normal subjects. 



made, so that the expirations which follow may be collected in the large spirometer. 

 After about ten respirations (a counted number) have -been collected, the cocks are 

 turned to Position 3 during an inspiration, and a single deep expiration is collected 

 in the small spirometer. In order that the time of this may be the same as the normal 

 expiration, it is necessary to quicken it. This is more or less a chance procedure, but 

 with a little training, the operator can close the stopcock with sufficient accuracy to 

 interrupt the deep expiration, at the end of the normal expiratory time. Should 

 there be any gross variation from the normal expiratory time, the sample must be col- 

 lected again. Not infrequently the inspiration immediately preceding the expiration 

 into the small spirometer is varied involuntarily by the subject on account of his being 

 aware that the following expiration has to be deepened and quickened; this can be 

 partially overcome by giving him the signal to breathe out deeply after he has actually 

 begun to expire. 



Determinations are made of the average volume of the tidal air (c.c. air in large 

 spirometer divided by number of breaths), of the volume collected from the deep ex- 

 piration, and of the percentage composition of the tidal air and that of the deep 

 expiration. A criterion for determining whether or not the procedure has been carried 

 out correctly is the respiratory quotient (ratio of CO 2 excreted to O 2 absorbed). For 



