THE VASO-MOTOR NERVES 233 



vessels of the lower limbs is recovered in the course of a few days. 

 In this case the recovery is attributed to the ganglioiiic and nervous 

 structures which are intercalated between the spinal cord and the 

 muscular walls of the bloodvessels. There are thus three mechanisms 

 of control: the bulbar centre, influenced particularly by the visual, 

 auditory, and vestibular nerves ; the spinal centres ; and the peripheral 

 ganglionic structures. 



The vaso-motor centre is reflexly excited by the afferent nerves, 

 and its ever- varying tonic action is made up of the balance of the 



FIG. 124. SHOWING THE EFFECT OF A PLEASANT TASTE (+ ) AND OF AN UNPLEASANT 

 TASTE (- ) UPON (1) THE VOLUME OF THE ABDOMINAL ORGANS, (2) THE VOLUME 

 OF THE ARM, (3) THE RESPIRATION. 



pressor and depressor influences which thus reach it, and from the quality 

 of the blood which circulates through it. Pressor effects i.e., those 

 causing increased constriction and rise of arterial pressure may be 

 produced by stimulating the central end of almost any afferent 

 nerve, and especially that of a cutaneous nerve (see Fig. 84). 

 Depressor effects are always obtained by stimulating the depressor 

 nerve (Fig. 83), and may be obtained by stimulating the afferent 

 nerves under special conditions. There seems to be good evidence 

 that, after division of the vaso-constrictor nerves, dilatation of a limb 

 can be brought about reflexly by stimulating the depressor nerve, and 



