HISTORY OF THE INVOLUNTARY NERVOUS SYSTEM 13 



were found to pass off into the membranes round the spinal cord 

 to supply the blood vessels : none entered into the spinal cord 

 itself. It was perfectly evident that the reciprocal connexion 

 between the two nervous systems did not exist, that in fact all 

 the characteristic sympathetic^ nerve fibres non-medullated 

 fibres wherever found are peripheral nerves ; and incidentally an 

 observation of Valentine " that stimulation of posterior roots 

 caused constriction of the blood vessels of the dura mater" was 

 explained. 



At the time when I made these observations, I was unaware 

 that Beck had published a paper in the " Philosophical Transac- 

 tions " in 1846, in which he gave evidence for the suggestion that 

 all the non-medullated fibres passing in towards the spinal cord 

 were peripheral fibres. 



Further, if there were two distinct nervous systems, animalic 

 and organic, the one forming a peripheral nervous system and 

 the other a central nervous system, there must be a separate 

 origin for these two systems. At about the same time Onodi 

 showed that each of the groups of cells, which form collectively the 

 main chain of the sympathetic system, had differentiated out from 

 a mass of cells close against the central nervous system, and that 

 the remainder of this mass formed the posterior root ganglion. 

 These observations of Onodi point to the conclusion that the 

 ganglia of the sympathetic chain do not arise independently, but 

 are originally a part of the central nervous system, and have 

 emigrated still further than the ganglia of the posterior roots. 



The observations of Onodi, of Beck, and myself gave the 

 death-blow to Bichat's conceptions of the independence of the 

 sympathetic nervous system, and proved that there is only one 

 system of communication between the organic and animalic 

 nervous systems, viz. the white rami communicantes. 



The next step was to trace the white rami communicantes 

 into the spinal cord. Sections of osmic preparations of the white 

 rami of the second thoracic nerve showed that its structure was 

 very different from that of ordinary nerves, in that it was com- 

 posed almost entirely of very small medullated fibres. On ex- 

 amining the roots of that nerve, masses of similar fine medullated 

 fibres were found in the anterior root. 



I then proceeded to cut sections of the anterior roots of all 

 the spinal nerves, and discovered that these masses of small 



