THE SYMPATHETIC NERVE. 449 



Thus, through these communicating branches, which have 

 been generally called roots or origins of the 'sympathetic nerve, 

 an interchange is effected between all the spinal nerves and 

 the sympathetic trunks ; all the ganglia, also, which are seated 

 on the cerebral nerves, have roots (as they are called) through 

 which filaments of the cerebral nerves are added to their own. 

 So that, probably, all sympathetic nerves contain some inter- 

 mingled cerebral or spinal nerve-fibres ; and all cerebral and 

 spinal nerves some filaments derived from the sympathetic 

 system or from ganglia. But the proportions in which these 

 filaments are mingled are not uniform. The nerves which 

 arise from the brain and spinal cord retain throughout their 

 course and distribution a preponderance of cerebro-spinal fibres, 

 while the nerves immediately arising from the so-called sym- 

 pathetic ganglia probably contain a majority of sympathetic 

 fibres. But inasmuch as there is no certainty that in struc- 

 ture the branches of cerebral or spinal nerves differ always 

 from those of the sympathetic system, it is impossible in the 

 present state of our knowledge to be sure of the source of 

 fibres which from their structure might lead the observer to 

 believe that they arose from the brain or spinal cord on the 

 one hand, or from the sympathetic ganglia on the other. In 

 other words, although the large white tubular fibres are espe- 

 cially characteristic of cerebro-spinal nerves, and the pale or 

 gelatinous fibres of a sympathetic nerve, in which they largely 

 preponderate, there is no certainty to be obtained in a doubt- 

 ful case, of whether the nerve-fibre is derived from one or the 

 other, from mere examination of its structure. It may be de- 

 rived from either source. 



With respect to the functions of the sympathetic nervous 

 system, it may be stated generally that the sympathetic nerve- 

 fibres are simple conductors of impressions, as those of the 

 cerebro-spinal system are, and that the ganglionic centres have 

 (each in its appropriate sphere) the like powers both of con- 

 ducting and of communicating impressions. Their power of 

 conducting impressions is sufficiently proved in ordinary dis- 

 eases, as when any of the viscera, usually unfelt, give rise to 

 sensations of pain, or when a part not commonly subject to 

 mental influence is excited or retarded in its actions by the 

 various conditions of the mind ; for in all these cases impres- 

 sions must be conducted to and fro through the whole distance 

 between the part and the spinal cord and brain. So, also, in 

 experiments, now more than sufficiently numerous, irritations 

 of the semiluuar ganglia, the splanchnic nerves, the thoracic, 

 hepatic, and other ganglia and nerves, have elicited expres- 



