438 NERVOUS SYSTEM. 



tion reduces the quantity of blood and diminishes the tem- 

 perature, it is reasonable to infer that the reflex action takes 

 place through the vaso-motor nerves. If we assume that 

 the impression is conveyed to the centres by the nerves of 

 general sensibility, and that the vessels- are modified in 

 their calibre and the heat is affected through the sympathetic 

 fibres, we have only to determine the situation of the cen- 

 tres which receive the impression and generate the stimulus. 

 These centres, as we have already seen, are not located in 

 the sympathetic ganglia, but in the cerebro-spinal axis. . 



In this connection, we may quote a curious observation 

 by Schiff, which he brings forward to illustrate the influence 

 of the brain in certain acts, probably operating through the 

 sympathetic system : " It is undisputed that psychical acts 

 are determined by the brain. If we bring a dog and a cat 

 together, their psychical irritation is manifested more espe 

 cially therein that the hair of the dog on his back, of the 

 cat on her tail, stands up. Now, if we destroy, in the cat, 

 the lumbar portion of the spinal cord, and bring her together 

 with, a strange dog, the hair of the tail will still rise. If we 

 leave the spinal nerves intact, the hair of the cat's tail will 

 remain smooth, even though she be attacked by a dog." l 



From all of these observations, and others of the same 

 kind which we have not thought it necessary to quote, the 

 existence of vaso-motor nerves and their connection with 

 centres in the cerebro-spinal axis are sufficiently well estab- 

 lished. It is certain, also, that centres presiding over par- 

 ticular functions may be located, as the genito-spinal centre, 

 in the spinal cord opposite the fourth lumbar vertebra, and 

 the cilio-spinal centre, in the cervical region of the cord, 

 both described by Budge. 2 A stimulus generated in these 



1 SCHIFF, The Independence of the Sympathetic. Journal of Psychological 

 Ifcdicine, Xew York, 1871, vol. v., p. 687. 



2 BuDfJE, Lehrbuch der specidhn Physiologic dcs Mcnschcn, Leipzig, 1862, 

 S. 510, 767. 



In a recent review of the theory proposed by Cyon ; viz., that the true ^aso- 

 motor centres are located in the encephalon, above the medulla oblongata and 



