THE SYMPATHETIC NERVES 689 



the relations of the spinal roots to the ganglia of the sympathetic system in 

 man. It will be observed that the main outflow of sympathetic fibers takes 

 place between the first thoracic and second lumbar roots. 



C. REGENERATION IN THE SYMPATHETIC NERVOUS SYSTEM 



Regeneration in the sympathetic system is of particular interest because it 

 is the only place in the entire nervous system where ganglion cells are found 

 interpolated in the direct course of definite nerve fibers. As we have already 

 seen (page 687) the fibers running in the cervical sympathetic which are inter- 

 rupted by the superior cervical ganglion are distributed to the different spinal 

 roots according to their destination. If now the cervical sympathetic is cut, 

 after a time regeneration takes place just as in all the nerves. But what is 

 specially remarkable in this case is this : that stimulation of the separate spinal 

 roots after regeneration produces in the main the same effects as before they 

 had been sectioned. Again, if the superior cervical ganglion be painted with 

 nicotine after regeneration, we get the same negative results as if the paint- 

 ing were done previous to sectioning. It follows that the regenerated nerve 

 fibers have reestablished their old connections, or have made new connections in 

 the same ganglion with cells of exactly the same kind. It would seem that the 

 growing nerve fibers must be guided by some chemotropic influence to the very 

 cells with w r hich they were formerly connected (Langley). 



By the same method Langley has found that postganglionic fibers likewise 

 regenerate and reestablish their old connections and that they also form new 

 ones. 



When the superior cervical ganglion is cut out, the cervical sympathetic 

 does not recover its functions possibly because the preganglionic fibers are not 

 capable of establishing functional connection with the peripheral tissues directly. 

 We may suppose that the nutritive influence of the ganglion cell does not extend 

 far enough to permit the fibers to grow farther than the interpolated ganglion. 

 It is likewise impossible to bring about a union of the true efferent cranial or 

 spinal nerve fibers with the postganglionic fibers, although union of these nerves 

 with preganglionic fibers has often been demonstrated. 



D. AFFERENT NERVES IN THE SYMPATHETIC 



The sympathetic contains afferent fibers, whose trophic centers are for the 

 most part in the spinal ganglia. The number of such fibers is much smaller 

 than that of the efferent fibers. Thus Langley has found by the method of 

 regeneration that only one-tenth of all the fibers in the hypogastric are afferent 

 in function; in the nervus erigens the number is one-third. 



Stimulation of any one of the white rami communicantes produces reflex 

 movements and variations in the blood pressure. Hence they must contain 

 afferent fibers. It appears that such fibers run almost exclusively to the thoracic 

 and abdominal viscera, and that they probably have the same distribution as 

 the corresponding efferent nerves. It is probable that they account for such 

 conscious sensations as " referred pains," so called because they are referred to 

 regions of the skin innervated from the same root as the diseased organ. Im- 

 pulses from the latter are therefore conveyed in some way, either by mediation 



