1906.] 



Special Excitable Substances in Cells. 



189 



think, fairly conclusive against the continuity theory put forward by JBethe ;* for if 

 conducting neuro-fibrils traversed the nerve cell, stimulation of the neuro-fibrils in the 

 cell either directly or indirectly must lead to nervous impulses being conducted in both 

 directions. And that the pre-ganglionic fibres can conduct in both directions is shown by 

 the axon reflex produced on electrical stimulation of the nerves. 



Nicotine, then, stimulates the nerve cells. Since curari in sufficient 

 amount prevents this action, curari also must act upon nerve cells, and we 

 may infer, as in the case of striated muscle, that neither act upon the nerve 

 endings. 



It may be noted that there is histological confirmation of the direct 

 action of nicotine on nerve cells, for, according to Cosmettatosf it produces 

 chromatolysis of the cells of the superior cervical ganglia of the rabbit, 

 a change which EveJ showed is not produced by protracted stimulation of 

 the cervical sympathetic. 



One piece of evidence is lacking in the case of nerve cells, viz., that they 

 retain their fundamental properties after nicotine or curari poisoning in the 

 way striated muscle does. The nerve cells cannot be stimulated apart from 

 the nerve-fibres these give off, so that it is only by analogy that I conclude 

 that the substance affected by the poisons is a special receptive substance 

 and not the fundamental substance of the cell. 



The experiments on sympathetic ganglia give, I think, good ground for 

 believing that in the central nervous system also, both the specific effect of 

 nicotine, strychnine, and other poisons, and the phenomena of fatigue must 

 be attributed to an action on nerve cells (either root cells or short fibred 

 commissural cells) and not to an action on nerve endings. They support the 

 view that the special functions of the central nervous system are carried on 

 in vertebrates by the nerve cells (including their dendrons), and not by 

 a neuro-fibrillar network outside the nerve cells. 



Nerve Endings in Unstriated Muscle and Glands. 



The nerves under this heading are post-ganglionic fibres arising from the 

 sympathetic and allied ganglia. 



The evidence centres round the action of adrenalin. Adrenalin was 

 discovered comparatively recently,§ and it does not stand on the same footing 

 as curari and nicotine, for from the first it has been a matter of discussion 

 whether it acts on nerve endings or on muscle. Since it has long been 



* Bethe, ' Allg. Anat. u. Physiol, d. Nervensystems ' (Leipzig), 1903. 



t Cosmettatos, 'Archives d'Ophthalmologie,' 1904. 



% Eve, ' Journ. of Physiol.,' vol. 20, p. 334, 1896. 



§ Oliver and Schafer, ' Journ. of Physiol.,' vol. 18, p. 230, 1895. 



