x VASCULAE MUSCLE AND NEEVES 361 



of the splanchnic nerve, partly to other dilator nerves, since, when 

 the splanchnics are divided, the depressor part is not entirely 

 abolished. It has, however, been established that the depressors 

 do not exert their reflex dilator action upon all the vascular regions, 

 and that the vessels of the ear, face, adjacent mucosae, and perhaps 

 of the skin in general, are constricted during stimulation of the 

 depressors (Dastre and Morat). 



The reflex pressor effects on excitation of the sensory nerves are 

 chiefly due to the vaso-constrictor fibres of the splanchnics, because 

 when these nerves are divided, they are much reduced. But even 

 in these cases vaso-constriction is not the only reflex effect, since 

 it can be shown that while the internal visceral vessels contract, 

 the cutaneous vessels dilate. This fact, which indicates a certain 

 antagonism between the deep and the superficial vessels of the 

 body, was demonstrated by Heidenhain in measurements of the 

 temperature of the skin and of the deep-lying portions of the body 

 during excitation of the sensory nerves. 



The antagonism between the cutaneous and visceral vessels 



O 



is even more apparent in the asphyxia produced by suspension of 

 artificial respiration in curarised animals. While the cutaneous 

 vessels of ear, face, and extremities dilate, those of the viscera 

 (intestine, spleen, kidneys, uterus) contract. The pressure effect 

 results from the predominance of vaso-constriction in the visceral 

 vessels over dilatation of the superficial vessels (Dastre and Morat). 

 It is highly probable, although definite experimental evidence 

 is wanting, that this dilatation is active, and not the passive effect 

 of the constriction of the deep vessels. 



AVe must not, however, take this supposed antagonism between 

 the deep and the superficial vessels in too absolute a sense, since 

 the fact that in vascular reflexes constriction of the one and 

 dilatation of the other occurs is not constant. Heidenhain, 

 indeed, observed with strong electrical excitation of the medulla 

 oblongata that there was a pressor effect greater than that of 

 asphyxia or any kind of reflex stimulation, which was determined 

 not merely by constriction of the internal vessels, but by that of 

 the cutaneous and muscular vessels also. 



VI. The vascular reflexes, i.e. the excitatory processes trans- 

 mitted from the centripetal or afferent to the centrifugal or 

 efferent nerves (the constrictors or dilators of the vessels), are 

 necessarily carried out by means of the centres in the cerebro- 

 spinal system, from which the vascular nerves arise. The capacity 

 of the peripheral ganglia of the sympathetic system to function 

 as centres for reflex processes (in so far as reflex is taken in 

 the restricted sense of a transformation of afferent into efferent 

 influences) has not yet been demonstrated, even if it cannot be 

 << priori excluded. 



We have seen that the greater part, if not the whole, of the 



