372 PHYSIOLOGY CHAP. 



sympathetic to a limited extent, viz. for the visceral organs. The 

 remainder receive their afferent fibres direct from the spinal nerves 

 and not from the sympathetic by the grey rami. After section of 

 the grey raini Langley found that only one or two fibres, which 

 apparently terminated close to the vertebral column, degenerated 

 in the central end, and stimulation of the central end evoked no 

 reflex. So that if the walls of the blood-vessels in the skin and 

 limbs, or the plain muscle and cells, or the ducts of the glands 

 receive afferent fibres, these must run in the spinal nerves from 

 the periphery to the cord, without passing through the ganglion 

 chain of the sympathetic. The same is true of the head also, in 

 which the sympathetic sends its efferent nerves into the province 

 of the bulbar (autonomic) nerves ; and perhaps also for the lower 

 part of the gut, where in the same way it enters the region inner- 

 vated by the sacral system. 



The afferent innervation of the viscera is quite different. The 

 majority of the afferent fibres of the thoracic organs, as well as of 

 the stomach, intestine, mesentery, etc., electrical stimulation of 

 which causes pain, run in the sympathetic nerve trunks and not 

 in the vagus. It has long been known that excitation of the 

 vagus below the diaphragm produces little or no pain in animals. 



The afferent sympathetic fibres come from the same spinal 

 nerves as the efferent fibres, that is, in man from the first thoracic 

 to the second or third lumbar. Like the efferent fibres, they pass 

 through the white rami communicantes. Their peripheral course 

 is, however, quite different, for while the efferent paths are inter- 

 rupted in their passage through the ganglion, so that a pre- and a 

 post-ganglionic part can be distinguished in them, this, so far as 

 we know, is not the case for the afferent neurones. The latter, 

 both in their mode of origin and their subsequent peripheral 

 course, behave like the rest of the afferent neurones in the body, 

 ascending as medullated fibres to the intervertebral ganglia, where 

 they have their trophic centre, and from which they run in the 

 dorsal roots to the cord. 



There is obviously no reason to suppose that the afferent fibres 

 belonging to the cutaneous organs, which run with the spinal 

 nerves, without entering the ganglia of the sympathetic chain, 

 behave differently from other afferent fibres. And we have direct 

 experimental evidence that the sympathetic afferents which 

 supply the visceral organs for the most part have their trophic 

 centre in the intervertebral ganglia. The proof is that 

 section of the mixed spinal nerves, immediately below the 

 spinal ganglion, causes all or nearly all the fibres of the white 

 rami to degenerate, while, on the contrary, section of the lateral 

 strand of the sympathetic or of the two splanchnics produces no 

 degeneration of the fibres of the white rami. 



The same is true of the sacral nerves. In the cat, for instance, 



