NERVE 701 



nerves (p. 813). When all allowance has been made for these 

 factors, the rapid and characteristic degeneration of the striated 

 muscles, after their connection with the central nervous system is 

 severed, is still inexplicable, except on the assumption that their 

 nutrition is specially related to the integrity of their efferent 

 nerves. In other words, it is necessary to suppose, not, indeed, 

 that distinct trophic nerves exist for the muscles, but that an 

 influence or impulses, which can be termed trophic or nutritive, 

 do normally pass out to them from the spinal cord along their 

 motor nerves. 



Section of the cervical sympathetic in young rabbits and dogs 

 increases the growth of the ear and of the hair on the same 

 side. But it is impossible to separate these consequences from 

 the vaso-motor paralysis ; and the same is true of the hyper- 

 trophy following section of the vaso-motor nerves of the cock's 

 comb and of the nerves of the bones. After section of the superior 

 laryngeal the vocal cord on the side of the section is at once 

 rendered motionless, and remains so, but the muscles, notwith- 

 standing their inaction, do not degenerate. And Mott and 

 Sherrington have found that, although section of the posterior 

 roots in monkeys is followed after a time (three weeks to three 

 months) by ulceration over certain portions of the foot, no corre- 

 sponding lesions occur in the hand. They believe, therefore, 

 that the lesions are not due to the withdrawal of a reflex trophic 

 tone, but are accidental injuries in positions specially exposed 

 to mechanical or microbic insults. 



One of the best examples of interference with the proper 

 nutrition of a part produced by a lesion in the nerves supplying 

 it is an eruption (herpes zoster), limited to the skin supplied by 

 the nerve-fibres coming from one or more spinal ganglia, and 

 depending on an (infectious) inflammatory change in the ganglia. 

 It has been suggested that the vesicles are formed either because 

 the passage of afferent impulses normally concerned in the 

 nutrition of the skin is interfered with, or because the skin is 

 bombarded by antidromic (p. 165) impulses discharged from the 

 inflamed ganglia. But an alternative hypothesis is that a toxine 

 spreads out along the nerves from the ganglia, just as in traumatic 

 tetanus the toxine is known to pass in the opposite direction 

 along the nerves from the seat of injury to the central nervous 

 system. 



Omitting the group of ' trophic ' nerves, and the even more 

 problematical ' thermogenic ' fibres (which some have sup- 

 posed to preside over the production of heat, and therefore to 

 assist in the regulation of the temperature of the body, but of 

 whose existence as distinct and specific nerve-fibres with no 



