RESPIRATION 



135 



area from the glottis to the alveoli of the lungs. If impulses 

 from the lungs to the medulla are cut off by dividing the vagi, 

 the respirations become slower and deeper (Fig. 51, C) ; in the horse 

 they have been known to fall to five per minute ; the inspirations 

 particularly are deep and prolonged. If one vagus only be cut, 



Fig. 50. — Diagram to illustrate the Chiep Nervous Connections of the 

 Respiratory Centre (after Waller). 



the effect just described may not occur, or only be of a partial 

 character. From this it is evident there are impulses passing 

 up the vagus from the lungs to the medulla which maintain the 

 normal respiratory rhythm, and these are permanently lost by 



Fig. 51. — Respiratory Tracings : Dog (Stewart). 



A. Normal; B, effect of stimulation of the central end of vagus 

 section of both vagi. Time tracing, seconds. 



C, effect of 



section of the nerves. If the end of the divided vagus which 

 is in connection with the brain be stimulated below the origin 

 of the superior laryngeal nerve, there is arrest of respiration if 

 the stimulation be strong, Lut with moderate stimulation it is 

 quickened (Fig. 51, B). The strength of the stimulating current 



