THE VAGUS NERVE AND RESPIRATION 315 



the heart possesses ganglionic centers in its own substance from 

 which it is supplied directly with nerve force. This rhythmic 

 and apparently independent action is regulated by the inhibiting 

 or restraining influence of the vagus nerve upon the cardiac nerves. 

 When from any cause the heart is over-stimulated the vagus 

 fibers of the cardiac plexus slow it down, thus guarding it from the 

 exhaustion which follows overwork. The vagus also inhibits 

 over-action of the vaso-constrictors preventing excessively high 

 blood pressure. Therefore, it is an important agent for preserving 

 the balance of force to be exerted between the heart and blood- 

 vessels. 



The vagus and the process of respiration. This process is 

 modified by the vagus nerve, probably through its influence upon 

 the respiratory center in the brain. The digestive organs (from 

 pharynx down) contain vagus fibers; their function is not perfectly 

 understood, they are probably sensory. 



