NERVOUS CONTROL OF THE BLOOD-VESSELS 1001 



of the body. The reflex effects produced by stimulation of the various 

 afferent nerves may be classified, according as they affect the general blood- 

 pressure or the circulation through restricted areas of the body, as general 

 and local. 



The afferent impulses affecting the general blood-pressure are distin- 

 guished as pressor and depressor, and these names are sometimes applied 



FIG. 468. Blood-pressure curve from carotid of dog. Between the arrows the 

 central end of a sensory nerve was stimulated. (HTJRTHLE'S manometer.) 



to the nerves which carry the impulses. A pressor reflex is one which 

 induces a rise of general blood-pressure by constriction of the blood-vessels, 

 especially in the splanchnic area (Fig. 468). Effects of this kind are pro- 

 duced by stimulation of nearly all the 

 sensory nerves of the skin. Practi- 

 cally all impulses which, if conscious- 

 ness were present, would be attended 

 with pain cause also a rise of general 

 blood-pressure. A rise of pressure 

 may be produced by the stimulation 

 of such nerves as the fifth, the central 

 end of the splanchnic nerves, or of 

 the nerves distributed to the surface 

 of the body. This rise occurs in all 

 animals under morphia and curare. 

 In the rabbit, when anaesthesia is 

 induced by means of chloral or 

 chloroform, stimulation of sensory 

 nerves may cause a fall of blood- 

 pressure. 



The chief example of a depressor 

 nerve we have already studied in 



dealing with the reflexes from the heart. The fall of pressure produced by 

 stimulation of this nerve is effected chiefly by dilatation of the splanchnic 

 area (Fig. 469), though, as Bayliss has shown, practically all the vessels of 

 the body partake in the relaxation. The lowering of blood-pressure produced 

 by stimulation of this nerve differs from that obtained on stimulating the 

 sensory nerves of the rabbit under chloral, in that its effect lasts as long as 



32* 



FIG. 469. Simultaneous tracing of arterial 

 blood-pressure and splenic volume from 

 a rabbit, showing the marked swelling of 

 the spleen associated with fall of general 

 blood-pressure on stimulation of the cen- 

 tral end of the depressor nerve. The nerve 

 was excited between a and 6. (BAYLISS.) 



