CH. XXVI.] 



NERVOUS FACTOR IN RESPIRATION 



377 



smaller waves upon these are due to its activity in reference to the 

 heart.* 



In fig. 300 B, a condition of apncea was produced so that the dog 

 did not breathe for a certain time. The vagogram therefore shows 

 no respiratory waves; and the variations due to cardiac action are 

 the only waves seen. 



During normal respiration, then, it seems that the inspiratory 

 centre alone is active, and that after the inspiration has reached a 



B 



Fio. 300. A, Upper line (E) is the electro-vagogram ; the middle tracing K is that of the respiratory 

 movements; the lowermost line (H) is a tracing of the heart-beats. In B, apnoea was produced, 

 and the electro-vagogram shows only the electrical variations in the vagus, which are due to 

 cardiac action. (Einthoven.) 



certain point, it is checked by an impulse (inhibitory) coming from 

 the lung along the vagus, 



A theoretical question arises at this point: Supposing no 

 inhibitory impulse came up the vagus, would the inspiration ever 

 cease of itself ? In answer to this question we may say at once that 

 when both vagi are divided, the respirations become much slower 

 and deeper, but they do not entirely cease. If this were the whole 

 case, we should conclude that the respiratory centre had a slow 



* Einthoven regards these as mainly due to afferent (depressor) impulses ; 

 whether this is so or not is immaterial to the main question discussed above. 



