460 



SYMPATHETIC NERVE. 



stimulus applied to the filaments of the sym- 

 pathetic which pass to the heart, have the 

 effect of accelerating the pulsations of that 

 organ and of exciting it to renewed contrac- 

 tion after it has ceased beating. As move- 

 ments very frequently arise in organs supplied 

 by the sympathetic, especially in the intestines, 

 spontaneously, at least under the stimulus of 

 the atmospheric air, it is sometimes difficult 

 to determine whether the contractions which 

 follow the application of a stimulus to any of 

 the nerves be really caused by this, or whether 

 they may not belong to those just mentioned. 

 Frequently, however, the contraction follows 

 the irritation so regularly as to leave no doubt 

 that the two are connected ; if, moreover, the 

 abdominal muscles in the cat or rabbit be 

 removed, so that the thin and transparent 

 peritoneum alone remains over the viscera, 

 application of mechanical or chemical irritants 

 to the splanchnic nerves in the thorax may 

 still be observed to be followed, in many cases 

 at least, by contractions in the intestine. In 

 such experiments the air is prevented from 

 acting upon the viscera by the intervening 

 peritoneum, and in this way the fallacy above 

 mentioned is less liable to occur. 



It remains to consider the motor influence of 

 the sympathetic in reference to the different 

 muscular organs supplied by it. 



Heart. The heart, as has been already 

 stated, derives its nerves from the sympathetic 

 and pneumogastric. That the branches which 

 are supplied by the sympathetic exercise an 

 influence over the movements of the heart, is 

 shown by what has been already stated, that after 

 it has ceased to beat, irritation of the branches 

 which pass to it from the cervical ganglia will 

 again excite it to contraction. Similar results 

 frequently follow irritation of the ganglia them- 

 selves. When the galvanic stimulus is ap- 

 plied to the cardiac branches of an animal in 

 which the heart has not yet ceased pulsating, 

 the effect is to augment the number of beats, 

 and at the same time to increase their strength. 

 In a rabbit in which the heart's action had 

 ceased, Valentin * found that when the 

 wires of the magneto-electric apparatus were 

 applied, about A of a millimetre distant from 

 each other, upon the second thoracic ganglion 

 of the right side, a very powerful contraction 

 in the auricles immediately ensued : the ex- 

 periment was repeated several times, and with 

 the same result. This also took place when 

 the same stimulus was applied to the first 

 thoracic ganglion. When, on the other hand, 

 the wires were laid upon the aorta at the dis- 

 tance of ^-th of a millimetre from the heart, or 

 upon the surface of the right ventricle, no effect 

 was produced. He concludes, therefore, that 

 the stimulus when applied to the nerves was, 

 in this case, more effectual than when applied 

 to the muscular fibres themselves. As regards 

 the function of those filaments which are sent 

 by the pneumogastric to the heart, E. H. 

 Weber f believes that they exercise a re- 



* Loc. cit. p. 427. 



f Wagner's Handworterbuch der Physiologic, 

 band iii., Abtheilung ii. p. 45. 



straining influence over the movements of the 

 organ ; stimulus applied to the pneumogastric, 

 according to his experiments, having the effect 

 of retarding or altogether stopping its move- 

 ments. When the stimulus of the electro- 

 magnetic rotation apparatus was applied to 

 the bulbus arteriosus in the frog's heart, the 

 part of the organ around which the fibres 

 derived from the sympathetic are, according 

 to him, chiefly distributed, he found that the 

 pulsations were increased in number as well 

 as in strength. When, on the other hand, 

 the same stimulus was applied to the upper 

 portion of the inferior vena cava, where the 

 filaments of the pneumogastric are mainly dis- 

 tributed, the effect produced was not an ac- 

 celeration but a retardation or stoppage of 

 the heart's action. When a defined part of 

 the vagus has been stimulated for some time 

 continuously, the heart again begins to pulsate : 

 when a portion of the nerve above this point 

 is now stimulated, no effect is produced; 

 when, on the other hand, the stimulus is ap- 

 plied to a portion further down, nearer the 

 heartj a cessation of its movements is again 

 produced. The circumstance that the heart, 

 after the stimulus has been applied to the 

 pneumogastric for some time, again commences 

 to beat, is attributed by Weber to the part of 

 the nerve becoming exhausted, or losing its 

 restraining influence, when the heart, being 

 thus freed again, begins to pulsate. Budge*, 

 however, attributes the cessation of the 

 movements of the heart, produced by the 

 application of galvanic stimulus to the pneu- 

 mogastric, not to any restraining power ex- 

 ercised by that nerve, but rather to a 

 temporary exhaustion produced by the 

 strength of the stimulus. In support of this 

 view, he states that, although the movements 

 of the iris chiefly depend upon the oculo-motor 

 nerve, yet Weber found, when the wires of 

 the magneto-electric rotation apparatus were 

 applied to this nerve within the cranium, that 

 the pupil became dilated, remaining so for a 

 considerable time after stimulus had been 

 withdrawn, and then again slowly contracting. 

 The effects thus produced upon the iris are, 

 according to him, analogous to those pro- 

 duced upon the heart by application of the 

 galvanic stimulus to the pneumogastric. More- 

 over, the nerves which are sent to the heart 

 of the frog do not present the arrangement 

 which Weber has described. No other fila- 

 ments than those which pass from the vagus 

 are distributed to the heart of this animal, at 

 least no others have been demonstrated. The 

 vagus nerve becomes united with the sympa- 

 thetic in the ganglion, which is situated about 

 one line from the root of the pneumogastric ; 

 and from this ganglion, which contains fibres of 

 the vagus and sympathetic, springs, amongst 

 other branches, a slender filament which is 

 destined for the heart. This runs down- 

 wards on the inner aspect of the lungs, and 

 passes along the veins to the auricles and 

 ventricle, the former receiving the greater 

 number of the nerve fibres. The branch in 

 * Wagner's Handworterbuch, band iii. p. 415. 



