INFLUENCE OF THE NERVOUS SYSTEM. 167 



influence of these two nerves on respiration has induced 

 these authors to allow that the left pneumo-gastric nerve 

 acts especially on the lung.) 



Recent investigations by Schiff, however, appear to show 

 that some of the nervous fibres which accelerate the pulsation 

 of the heart, are contained, at least in the dog, in the pneumo 

 gastric nerve (Schiff, Lo Sperimentale^ Novembre, 1872.) 

 These fibres appear to come from the accessory nerve of 

 Willis (N. Spinalis), and to join the pneumo-gastric nerve 

 for an instant, quitting it with the superior laryngeal nerve, 

 and reaching the heart after following a most remarkable 

 course, not unlike Galen's anastomosis: (this anastomosis 

 unites the superior laryngeal nerve to the inferior, which also 

 furnishes a cardiac nerve of its own). 



Accelerating Nerves of the Heart. The influence which 

 the cord, by means of the great sympathetic nerve, exercises 

 on the heart, in increasing both the force and number of its 

 pulsations, has been variously explained, and the investiga- 

 tions made on this subject have resulted in the discovery of 

 a nerve whose functions are very peculiar. This is the nerve 

 of Cyan, a sensory nerve of the heart ; and by means of this 

 the heart produces a reflex action which causes the organs 

 of the peripheral circulation to dilate, and, consequently, 

 enables the heart to diminish the energy and number of its 

 efforts. We borrow from Cl. Bernard's recent lectures (May, 

 1872), and from his report to the Academy of Sciences on 

 Cyon's experiments, our account of this interesting question. 



Le Gallois first pointed out the influence of the spinal cord 

 on the pulsation of the heart. But Von Bezold, by his ex- 

 periments, in 1863, proved more particularly that section of 

 the cord between the occipital region and the atlas, produces 

 considerable diminution of the pressure of the blood in the 

 large arteries, as well as retardation in the pulsations of the 

 heart. He afterwards proved that excitation of the cord 

 behind this section restores both the pressure of the blood, 

 and the rapidity of the pulsation, thus showing that the 

 effect of the cord upon the heart is to modify the force and 

 number of pulsations. 



Ludwig and Thiry, however, having observed that excita- 

 tion of the cord, separated from the brain, always exerts its 

 influence on the pressure of the blood, even when the cardiac 

 nerves which unite the heart to the cord have been de- 

 stroyed, inferred from this that the cord has no real influ- 

 ence upon the heart itself but upon the peripheral circulating 



