622 SYMPATHETIC AND OTHER SYSTEMS OF NERVES. 



these endings are paralysed by nicotin, just 'as nicotin in rather larger 

 doses paralyses motor nerve-endings in skeletal muscle. 



Occasionally, the cervical sympathetic has a slight effect on the 

 nictitating membrane and eyelid, after application of nicotin to the 

 superior cervical ganglion. In such cases it is found that there are 

 groups of nerve cells in the trunk of the nerve at or centrally of the 

 point stimulated. In fact a few of the nerve cells of the superior cervical 

 ganglion occasionally occur in the trunk of the nerve. 



The fibres of the cervical sympathetic, as we have seen, pass through 

 one or more of the upper thoracic sympathetic ganglia, and the inferior 

 cervical ganglion, but the cautious application of nicotin to all of these 

 ganglia does not prevent any one of the cervical sympathetic actions 

 from being obtained by stimulation of the spinal nerve. It follows from 

 this result that no appreciable number of any kind of nerve fibre present 

 in the cervical sympathetic has a relay station in any of the upper 

 thoracic ganglia, or in the inferior cervical ganglion ; and one may fairly 

 conclude and the conclusion is supported by other facts that all the 

 fibres which pass to the cervical sympathetic from the spinal cord reach 

 the nerve without having nerve cells on their course. 



A further question is, whether the nerve fibres given off by the 

 superior cervical ganglion run direct to the various peripheral structures, 

 or end in connection with the cells of some other ganglia. In order to 

 determine this, nicotin is injected into a blood vessel. The injection 

 paralyses the cervical sympathetic, just as application of nicotin to the 

 superior cervical ganglion paralyses it, and with the same occasional 

 restriction we have mentioned above. But, on stimulating the several 

 branches given off by the ganglion, all the normal effects can be pro- 

 duced, and to a maximal degree ; that is, the nerve-endings of the fibres 

 given off by the ganglionic nerve cells are not paralysed, and in con- 

 sequence we conclude that they do not run to other sympathetic nerve 

 cells, but proceed straight to the tissue. 



Conclusions similar to these deduced from the action of nicotin 

 may be legitimately deduced from the results of degenerative section 

 of the cervical sympathetic and of the branches of the superior cervical 

 ganglion. 1 Waller and Budge found that on section of the sympathetic 

 in the neck, the part in connection with the superior cervical ganglion 

 showed the microscopical signs of degeneration, but that the part still 

 in connection with the spinal cord and the part beyond the ganglion 

 remained unaltered. They found also that stimulation of the part 

 attached to the superior cervical ganglion no longer caused dilatation 

 of the pupil, but stimulation of the ganglion itself promptly caused 

 dilatation. The microscopical observations have been confirmed, and the 

 experimental results extended to other classes of nerve fibres. Waller 

 observed, further, that on degenerative 2 section of the internal carotid 

 branches of the ganglia, degenerated fibres could be traced to the 



1 Of. Papers by Waller and by Waller and Budge in Compt. rend. Acad. d. sc., Paris, 

 1851-1853; Ztschr. f. ivissensch. ZooL, Leipzig, 1851, Bd. iii. S. 347 ; Waller, " Nouvelle 

 methode anat., etc.," Bonn, 1852 ; Budge, Arch. f. physiol. Heilk., Stuttgart, 1852, S. 

 773 ; Langley, Journ. PhysioL, Cambridge and London, 1885, vol. vi. p. 87 ; 1896, vol. 

 xx. p. 70; 1897, vol. xxii. p. 228; Bradford, ibid., 1888, vol. ix. p. 302; Langley and 

 Sherrington, ibid., 1891, vol. xii. p. 278. 



2 I use the term "degenerative section" for the cases in which a nerve is cut, but the 

 animal is not killed until degeneration is sufficiently advanced to stop the passage of 

 nervous impulses. 



