1126 PHYSIOLOGY 



This class would include the vagus and the vaso-dilator fibres. The 

 catabolic nerves cause an increased activity of the contractile tissue, 

 and active contraction is associated with and derives its energy 

 from disintegration or catabolism of the muscular substance. An 

 ordinary motor nerve to a muscle is therefore a catabolic nerve. 

 This class would include the accelerator nerves to the heart, and the 

 vaso -constrictors. The course of these two sets of nerves bears out 

 this comparison, the path taken by the accelerator nerves being 

 identical at first with that of the vaso-constrictor fibres to the head and 

 neck. 



VASO-MOTOR REFLEXES 



The vaso-motor centre with its efferent tracts is constantly played 

 upon by impulses arriving at it from the vascular system, including 



FIG. 473. Blood-pressiire curve from carotid of dog. Between the arrows 

 the central end of a sensory nerve was stimulated. (HURTHLE'S 

 manometer.) 



both heart and blood-vessels, from the viscera, from the muscles, 

 and from the surface 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 dis- 

 tinguished as pressor and depressor, and these names are sometimes 

 applied 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. 473). Effects 

 of this kind are produced by stimulation of nearly all the sensory nerves 

 of the skin. Practically all impulses which, if consciousness 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 



