308 



VETERINARY PHYSIOLOGY 



have been cut, the connection of the centre with the upper 

 toain tracts is severed, the mode of action of the centre 



D/apk 



FIG. 140. Nervous Mechanism of Respiration. R.C., respiratory centre; Cut,, 

 cutaneous nerves; Ph., phrenics ; In.C., intercostal nerves; P., pul- 

 monary branches of vagus ; S.L., superior laryngeal branch of vagus ; 

 La., the larynx ; Cf.Ph., glossopharyngeal nerve ; Diaph., diaphragm. 



changes. Instead of discharging rhythmically it may dis- 

 charge irregularly. 



To investigate further this influence of the vagus it is 

 necessary to study the effect of stimulating the nerve. 



FIG. 141. Tracings of the Respirations Downstroke is Inspiration; Upstroke is 

 Expiration. At a one vagus nerve was cut ; at b the second was divided ; 

 at c the upper brain tracts also were cut off ; d and d' show the effect of 

 stimulating the glossopharyngeal nerve. 



Strong stimulation of the pulmonary branches of one vagus 

 (vagus below the origin of the superior laryngeal) causes the 

 respiration to become more and more rapid, the inspiratory 



