26 



RESPIRATION 



ately, since a few seconds were needed before the "apnoeic" blood 

 could affect the respiratory center. In Figure 6 the distention was 

 sufficiently prolonged for the "apnoeic" blood to affect the center 

 before the end of distention. The effect is therefore similar to 

 that in Figure 2. 



Figure 4. 



Figure 5. 



Figure 6. 



Effects of distention with pure air for increasing short 

 periods. Crosses show beginning and end of distention. To read 

 from left to right. Fig. 4 distention for i sec. ; Fig. 5 for 3 sees. ; 

 and Fig. 6 for 5 sees. 



The regularity of ordinary breathing is constantly being inter- 

 fered with in various ways, as for instance during talking or 

 singing; and the breath can if necessary be held for about a minute 

 by voluntary effort. The readiness with which these interruptions 

 occur has given rise to the popular idea that the supply of air to 

 the lungs is to a large extent under voluntary control, and can be 

 increased or diminished by proper training. In reality the mean 



