688 SYMPATHETIC AND OTHER SYSTEMS OF NERVES. 



General distribution of afferent fibres of autonomic nerves. — In 

 the sympathetic every white ramus contains afferent fibres, for stimu- 

 lation of the central end of even the smallest, readily causes a reflex 

 body movement and change of blood pressure. The white rami form 

 the only definitely proved channel for afferent impulses passing by the 

 sympathetic. It is true that, as we have seen, there is histological 

 ground for believing that a few afferent fibres pass to the spinal cord 

 by way of the grey rami, but we may leave these out of account, since, 

 in the experiments made so far, no reflex of any kind has been obtained 

 by stimulating them. 



The afferent fibres of the white rami do not run to the head, nor to 

 any appreciable extent to the skin of the body. They run to the 

 thoracic and abdominal viscera. 



Such afferent autonomic fibres as run to the skin of the head and body 

 must pass to it direct by the cerebro-spinal nerves. The deeper autonomic 

 structures of the head probably receive afferent autonomic fibres from the 

 seventh and the ninth nerves. 



It is probable from the experimental evidence, so far as this goes, 

 that the peripheral distribution in the viscera of the afferent fibres of 

 each white ramus is essentially the same as that of the efferent fibres of 

 the ramus, so that the sensory connection of the various viscera with 

 the spinal nerves differs but little from the scheme given earlier for the 

 motor connection. 



At the same time, it must be borne in mind that the observations in 

 man with regard to the cutaneous areas of tenderness and pain, which 

 occur in disease of the several viscera (cf. p. 689), tend to show that the 

 afferent fibres for any one organ arise from fewer white rami than do 

 the efferent fibres. It is possible, however, that the referred tenderness 

 ordinarily occurs only in the areas of those nerves which send a con- 

 siderable number of afferent fibres to the affected organs, and that wider 

 connections of afferent fibres with the several organs may be found, as 

 clinical attention is more directed to the question. The results obtained 

 so far are not concordant, but it is fairly well established that afferent 

 fibres to the heart and lungs, the stomach, the liver, the intestine and 

 kidney, form successive and overlapping series. 



The peripheral distribution of the afferent and of the efferent sacral 

 autonomic nerves appears also to correspond. Thus, on section of the 

 pelvic nerve, degenerated fibres can be traced to the structures in which 

 effects are produced by stimulation of the nerve, but degenerated fibres 

 cannot be traced — according to the observations of Anderson and 

 myself 1 — to the uterus, which is unaffected by stimulation of the pelvic 

 nerve. 



Sensitiveness of the viscera. — It has been long known that the 

 thoracic and abdominal viscera are very insensitive to certain forms of 

 stimulation, such as handling and cutting, and this fact formed the basis 

 of the theory put forward by Eeil in 1811, that the sympathetic ganglia 

 serve to suppress sensory impulses, and were only partial conductors of 

 sensibility. Nevertheless, the splanchnic nerves, superior and inferior, 

 and the pelvic nerve, when pinched or stimulated electrically, are 

 apparently as sensitive as any nerve in the body, and we know that 

 certain diseases of the viscera give rise to exquisite pain. There is 



1 Journ. Physiol., Cambridge and London, 1895, vol. xix. p. 272. 



