THE CARDIAC NERVES. 



541 



some difference in their place or manner of ending in the muscular 

 tissue? Views differ upon this point and many physiologists have 

 suggested that the impulses vary in quality; that the inhibitory 

 nerve impulse differs in some unknown way from a motor impulse, 

 and therefore causes an opposite reaction in the muscle. This latter 

 view seems, however, to be entirely disproved by the results of 

 experiments. Langley has shown upon blood-vessels (p. 76) that 

 an inhibitory nerve made 

 to grow down a motor path 

 causes when stimulated 

 only motor effects and vice 

 versa. And in the case in 

 point Erlanger * has proved 

 that, when an ordinary spinal 

 nerve (fifth cervical) is su- 

 tured to the peripheral end 

 of the cut vagus, it will, 

 after time for regeneration 

 has been allowed, cause when 

 stimulated the usual stop- 

 page of the heart. So far as 

 our facts go, therefore, we 

 must assume that motor 

 and inhibitory fibers have 

 opposite effects upon the 

 muscular fibers in which 

 they end because they ter- 

 minate differently in these 

 fibers, f 



The Course of the Ac- 

 celerator Fiber s. T h e 

 heart receives efferent or 

 motor nerve fibers from the 

 sympathetic system in ad- 

 dition to those reaching it 

 by way of the vagus nerve. 

 Attention was first called to 

 these sympathetic fibers by 

 Legallois (1812), but our re- 

 cent knowledge dates from 

 the experiments made by von Bezold (1862), which were afterward 



* Erlanger, "American Journal of Physiology," 13, 372, 1905. 



t For a special theory of heart inhibition and acceleration see Howell, 



1 T,, ! ~C "DU,.-^!^.-., 1 OrA i'ir OQft nnr\ " Trvnmol r\f "PV-.iroirkli-.mr " 



Fig. 223. Schematic representation of the 

 course of the accelerator fibers to the dog's heart 

 right side. (Modified from Pawlow.) The sym- 

 pathetic nerve is represented in solid black. The 

 course of the accelerator fibers is indicated by ar- 

 rows. /, Cervical sympathetic combined in neck 

 with, 10, the vagus; //, ///, IV, rami communi- 

 cantes from the second, third, and fourth thoracic 

 spinal nerves, carrying most of the accelerator fi- 

 bers to the sympathetic chain ; 7, annulus of Vieus- 

 sens; 8, inferior cervical ganglion; 2, 3, 4, 5, 

 branches from vagus and vago-sym pathetic trunk 

 going to cardiac plexus (some of these 3, 5, 

 carry accelerator fibers; 9, the inferior laryngeal 

 nerve. 



" American Journal of Physiology, 

 1906, xxxv., 131. 



1906, xv., 280, and "Journal of Physiology/ 



