336 PHYSIOLOGY CHAP. 



rhythm is obtained, which does not appear after cutting the other 

 vagus (v. Bezold, Drechsfeld, Aubert and Koever, etc.). The 

 various pulmonary branches of the vagus were stimulated, accord- 

 ing to Hering, by insufflating the lungs with open thorax, 

 producing, acceleration of cardiac rhythm, which is absent with 

 division of the cervical vagi. The acceleration of pulse which 

 Sommerbrodt observed in man after screaming, singing, coughing, 

 inhaling of compressed air, is due to the same cause, i.e. to 

 abnormal rise of bronchial pressure. 



Central excitation of the superior laryngeal, as also stimulation 

 of the laryngeal inucosa above the vocal cords, produces arrest or 

 slowing of the heart-beat with intact vagi (Franc^ois-Franck). 

 This does not occur with centripetal excitation of the inferior 

 laryngeal, or on stimulation of the laryngeal mucosa below the 

 vocal cords. 



On exciting the, abdominal sympathetic by repeated taps of 

 moderate strength on the belly wall, slight inhibitory phenomena 

 are readily obtained on the frog (Goltz). 



The sensory branches of the posterior spinal roots have a double 

 reflex action on the heart, either a slowing (Cl. Bernard, Frangois- 

 Franck), or an acceleration of rhythm (Asp). Central excitation 

 of the sciatic plexus by mechanical stimuli provokes inhibition, by 

 electrical stimuli, acceleration. The muscular nerves also produce 

 opposite effects : the same thing produces inhibition with a strong 

 stimulus, acceleration with a weaker one. When chemically 

 excited (e.g. by inhalation of chloroform), the sensory fibres of the 

 trigeminus readily induce slowing and even arrest of the heart, and 

 syncope, which has a great practical significance. The nerves of 

 the special senses also act in this twofold way upon the heart. 



XII. The afferent nerves of the heart affect the efferent 

 through centres which determine the reflex effects. 



The centre of the diastolic nerves is in the bulb or medulla 

 oblongata (E. Weber, Budge). In the frog it extends from the 

 optic lobes to the tip of the calamus scrip torius. In the rabbit 

 it is apparently confined to the bulb (Frangois-Franck). In the 

 cat there is about half-way up the rhomboid sinus, a point at 

 which excitation by a needle produces arrest or slowing of the 

 heart (Laborde). 



The centre for the systolic nerves has up to the present not 

 been exactly located. The whole upper section of the cervical 

 cord reacts by acceleration of cardiac rhythm^ 



Although the paths are not yet exactly determined, it must 

 be remembered that the cardiac centres are in connection with 

 the cortical and subcortical centres of the brain. The influence 

 of psychical states upon the heart is undeniable ; some people 

 even have the faculty of voluntarily influencing their heart-beats. 



It is probable that under normal conditions the cardiac 



