202 EXCITABILITY OF NERVE FIBRES. 



it, iQiist cease to effect this important change ? Is it 

 not certain that in consequence the axis cylinder of a 

 nerve-fibre must be much changed, and especially at 

 the peripheral distribution of the fibres where they 

 are very delicate and ramify naked upon the muscular 

 tissue ? No vi^onder then that the muscles fail to 

 respond to the stimulus as before. This fact is 

 attributed to the nerve having lost its " excitability," 

 but is it not more probable that the true explanation 

 of the fact is, that in consequence of the change in 

 the constitution of the nerve-fibre, resulting from the 

 cessation of the currents of fluid through it con- 

 sequent upon the death of the bioplasm, it fails to 

 conduct the electrical current as it did when in a 

 state of integrity ? So far, therefore, from the above 

 fact being an argument against the idea that nerve 

 force is really electricity, it actually affords supjoort 

 to this viev?'. 



The power of causing the muscles to contract when 

 the nerve is irritated, is lost sooner if the nerve be 

 irritated than if it be left at rest. It is increased hy 

 heat and decreased by cold. When the nerve is 

 "irritated " the operation is such as would be certain 

 to alter any structure so delicate as the peripheral 

 ramifications of nerves and impair or destroy their 

 conducting power. Dr. Rutherford has remarked 

 that the nerves of a weak animal conduct faster than 

 those of a strong one. " The velocity is so great in 

 this case that it may be scarcely measurable," a fact 

 which, perhaps, may depend apon the circumstance 

 that the conducting tissue is more moist. In weak 

 animals the masses of bioplasm are much more 

 abundant than in strong ones and the tissues contain 

 a large quantity of fluid. The axis cylinder par- 

 ticipates in this change, and in this way the remark- 

 able irritability manifested may be accounted for. 



Again, it has been argued that because the irrita- 

 bility of a nerve can be destroyed by the electi^ical 



