X 



VASCULAK MUSCLE AND NEEVES 



359 



most remote from the afferent nerves stimulated. The visceral 

 vessels innervated by the splanchnic readily respond to the reflex 

 action of any sensory nerve, for the most part by contracting, 

 sometimes by dilating, Stimulation of the sciatic also constricts 

 the vessels of the tongue (Vulpian) ; excitation of the brachial 

 nerve dilates the vessels of the ear (Loven). This last effect may 

 be seen on the rabbit, whatever the sensory nerve stimulated, but 

 the dilatation is usually preceded by vaso-constriction (Eckhard). 

 When the vascular reflexes are not confined to any circum- 

 scribed area, but extend to a wider region, they cause a general 



FIG. 160. Reflex lowering of arterial pressure, Iroia electrical excitation of depressor 

 nerve of rabbit, in period comprised between two vertical lines. (Tigerstedt.) 



modification in blood pressure, usually expressed in an abnormal 

 rise, sometimes in a fall of pressure. 



The reflex pressor effects of exciting the sensory nerves, already 

 noted by Magendie, were clearly worked out for the first time by 

 von Bezold (1863), and were subsequently extended by a number 

 of other experimenters. 



They follow particularly on the stimulation of the posterior 

 spinal roots, the vagus, the trigeminus, the sciatic, the greater and 

 lesser splanchnic, the cutaneous and muscular nerves, the nerves of 

 the special senses (Fig. 164). The rise of blood pressure varies with 

 the nerve excited, and also with the intensity and nature of the 

 stimulus. The state of the animal prior to stimulation also has 

 great influence on the intensity of the pressor effect. In the 

 normal animal, e.g., acoustic stimuli induce a considerable rise of 



