1000 



PHYSIOLOGY 



degeneration of the nerve fibres to their peripheral terminations, the applica- 

 tion of croton or mustard oil, even to the delicate conjunctiva, is without 

 effect. The same results may be produced if the peripheral terminations of 

 the nerves be paralysed by the subcutaneous injection of local anesthetics. 

 We must assume that the axons of the peripheral sensory nerves branch, 

 some branches going to the surface, others to the muscle-cells of the cutaneous 

 arterioles, as indicated in the diagram (Fig. 467). 



Gaskell has drawn an analogy between the nerves distributed to the 

 blood-vessels and those going to the heart, which is indeed only a specialised 

 part of the general blood-tubes of the body. These nerves, according to 



sup. nerve plex. 



p.r.g. 



Sens. n. f. 



r 



skin 



art 



FIG. 467. Diagram to illustrate the production of vaso-dilatation in the area 



of distribution of a sensory nerve. 



prg, posterior root ganglion ; sens.nf, sensory nerve fibre, branching to supply 

 dilator fibres to the skin arteries, and sensory fibres to the skin. 



their action on the metabolic activity of the tissues supplied, are divided by 

 Gaskell into anabolic and catabolic nerves. The anabolic nerves, as indicated 

 by their name, cause a building up or regeneration of the contractile tissue. 

 They therefore act as inhibitory nerves. 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 both heart 

 and blood-vessels, from the viscera, from the muscles, and from the surface 



