CIR CULA TION. 167 



wave passes over the heart, while the contrary effects are witnessed after the 

 excitation of the augmentor nerves. 



Various attempts have been made to prove a trophic action of the vagus on 

 the heart by cutting the nerve in animals kept alive until degenerative changes 

 in the heart-muscle should have had time to appear. The important distribu- 

 tion of the vagus nerve to many organs, and the consequently wide extent of 

 the loss of function following its section, makes it difficult to decide whether the 

 changes produced in the heart are not secondary to the alterations in other tis- 

 sues. The work of Fantino will serve for an example of these investigations. 

 Fantino cut a single vagus to avoid the paralysis of deglutition and the inani- 

 tion and occasional broncho-pneumonia that follow section of both nerves. 

 Young and perfectly healthy rabbits and guinea-pigs were selected. The opera- 

 tion was strictly aseptic, and all cases in which the wound suppurated were 

 excluded. A piece of the nerve about one centimeter long was cut out, so that 

 no reunion could be possible. After the operation the animals were as a rule 

 lively, ate well, and gained weight. Post-mortem examination of animals 

 killed two days or more after section of the vagus nerve disclosed no patho- 

 logical changes in the lungs, spleen, liver, and stomach. In the heart, areas 

 were found in which the nuclei and the striation of the muscle-cells had disap- 

 peared. Eighteen days after section the atrophy of the cardiac muscle in these 

 areas was observed to be extreme. The degenerations following section of the 

 right vagus were situated in a different part of the ventricular wall from those 

 following; section of the left nerve. 



The effects of stimulation of the vagus nerve in the new-born do not differ 

 essentially from those seen in the adult. 1 



The relation between the action of the vagus and (lie intracardiac pressure 

 has been recently studied by Stewart. He finds that an increase in the pressure 

 in the sinus or auricle makes it difficult to inhibit the heart through the vagus. 



The inhibitory action of the vagus diminishes as the temperature of the 

 heart falls. At a low limit the inhibitory power is lost, but may return when 

 the heart is warmed again. Even when the stimulation of the trunk of the 

 nerve has failed to affect the cooled heart, the direct stimulation of the sinus 

 can still cause distinct inhibition. The power of inhibiting the ventricle is 

 first lost. Loss of inhibitory power does not follow the raising of the heart 

 to high temperatures. The vagus remains active to the verge of heat arrest, 

 mid resumes it.^ power as soon ;is the temperature is lowered. 



The Augmentor Nerves. 

 v. Bezold observed in 1862 that stimulation of the cervical spinal cord 

 caused an increased frequency of heart-beat. This seemed to him to prove 

 the existence of special accelerating nerves. Ludwig and Thiry, however, 

 soon pointed out that stimulation of the spinal cord in the cervical region 

 excited many vaso-constrictor fibres, leading to the narrowing of many vessels 

 and a corresponding rise of blood-pressure. The acceleration of the heart-beal 

 'Meyer: A rehire* tie Phyaiolngie, 1893, p. 477. 



