868 INFLUENCE OF THE NERVOUS SYSTEM 



either proceeding directly from the sympathetic ganglia, or through and 

 beyond these from some part of the cerebro-spinal system, the office of which 

 is to preside over the contraction of the vessels and calorification. A further 

 corroboration of this vieAV was obtained by experiments in which the lumbar 

 ganglia of the Sympathetic were destroyed, when the vascular changes and 

 the increase of temperature in the lower limb were observed without the 

 occurrence of any paralysis. Dr. Waller 1 has shown that some of the results 

 of irritation of the cervical portion of the sympathetic may be made apparent 

 during life by pressure of the point of the" finger behind the ramus of the 

 jaw, though they are associated with other phenomena proceeding from irri- 

 tation of the pneumogastric. The more important symptoms observed were 

 dyspno?a, cardiac and gastric disturbance, tingling and heat of the ear, last- 

 ing for upwards of half an hour, and in one instance dilatation followed by 

 contraction of the pupil. Dr. Waller 2 has also ingeniously shown the effects 

 of paralysis of the. vaso-motor nerves of the arm in the living body, by ap- 

 plying a freezing mixture to the ulnar nerve at the elbow; the effect in the 

 first instance being to produce a fall of temperature equal to about 0.5 C. 

 in the two inner fingers; but as the vaso-motor nerves became paralyzed, 

 the temperature gradually rose until it attained a height of from 5 to 6 

 C. above that of the outer fingers ; the difference between the outer and inner 

 fingers appeared to be partially attributable to a decrease in the temperature 

 of the former as well as to an increase in that of the latter, owing to the 

 diversion of part of the blood of the radial into the ulnar artery. The effects 

 of percutaneous excitation of the sympathetic.-; in man by means of electricity 

 are very slight, consisting only, according to MM. Eulenberg and Guttman, 3 

 of an almost inappreciable dilatation of the pupil, and a lowering of the 

 frequency of the pulse. As the smaller vessels contract, there is probably 

 an increase of pressure in the larger ones, but it must be remembered that it 

 is difficult to irritate the cervical Sympathetic without coincidentally ex- 

 citing the vagus-depressor nerve of Cyon, the laryngeal nerve, and desceudens 

 noni, which may materially influence the result. The vaso-motor nerves of 

 the upper extremity do not proceed from the spinal cord, in common with 

 the sensori-motor nerves forming the brachial plexus, but issue from it at a 

 much lower point, namely, between the third and seventh dorsal nerves. 

 The vaso-motor nerves for the lower extremities spring from the adjoining 

 dorsal roots, and not from those which form the sciatic plexus. The chief 

 vaso-motor of the body which supplies all the vessels distributed to the vis- 

 cera is the splanchnic nerve, and by reason of the large quantity of blood 

 these vessels can contain the splanchnic nerve plays the principal part in 

 the distribution of the blood generally in the body. 4 If it be irritated, the 

 blood is driven in large quantity into the vessels of the head and limbs, 

 whilst if it be paralyzed the blood accumulates in the viscera, and the head 

 and extremities are rendered amemic. Budge 5 maintains that the small arteries 

 throughout the body can be made to contract by electrical irritation of the 

 pedunculus cerebri, which, therefore, he regards' as the centre of the. vaso- 

 motor nerves, but there can now be no question that the principal vaso-motor 

 centre is, as already stated ( 254) situated in the medulla oblongata. 



716. It is very difficult to give a satisfactory explanation of the <!i/<ititti.ou 

 observed in the vessels of certain regions of the body when the nerves sup- 

 plying them are irritated. The most marked instances of such dilatation 



1 Proceedings of the Royal Society, vol. xi, p. 302. 



8 Ibid., p. 430. 



1 Dio Pathologic do* Sympathicns, 1873, p. 202. 



4 See Cyon, Electrothcrapie, is;:',, p. i>03. 



6 Pfluger'a Archiv, 13d. vi, 1872, p. 303. 



