vin CONDUCTIVITY AXD EXCITABILITY OF NERVE 111 



mal processes be taken as proven. Neither Heidenhain nor Helm- 

 holtz, in spite of the great delicacy of their methods, was able to 

 determine a reaction in peripheral nerve-trunks analogous to that 

 of muscle; Schiff (69), however, recorded positive results. Here 

 again it is necessary to distinguish between the ganglionic 

 substance of the central organs and the nerve-fibres proper, and 

 differences of thermal reaction must be expected in correspondence 

 with the established differences of chemical reaction. 



In view of the total lack of facts as to metabolism in the nerve- 

 fibres, we are thrown back upon probabilities. The functional 

 metabolism must under all circumstances (save in the gray matter 

 of the centres) be very insignificant, as is proved inter alia by the 

 poor supply of blood, as well as by the extraordinary tenacity of life, 

 at least in medullated nerve-fibres. The same conclusion appears 

 from the investigations into fatigue and recovery of nerve. The 

 main difficulty here lies in the comparatively great fatiguability 

 of the terminal organs (muscles, ganglion-cells) in which alone the 

 capacity of reaction, or alteration, can be demonstrated. The 

 existence of fatigue in nerve was for a long time assumed on quite 

 insufficient analogies, since experiments on fatigue of brain, retina, 

 etc., prove nothing as to the reaction in nerve-fibres. Bernstein 

 (70) was the first who endeavoured to demonstrate fatigue of the 

 persistently excited nerve in a nerve-muscle preparation. 



In studying the effect of long -continued excitation of any 

 point of the nerve upon its excitability, it is evidently essential 

 to block off the stimulus, during the greater part of the excitation, 

 from the terminal organ (muscle). Bernstein succeeded in doing 

 this by sending a constant current through a part of the nerve 

 between the point of excitation and the muscle. As we shall 

 see, conductivity may be locally abolished without suffering 

 permanent injury. From the reaction of the muscle after 

 opening the insulating current, Bernstein formed conclusions as 

 to the state of the muscle excited by the induction current. If 

 the muscle no longer reacted to the constant stimulus at the free 

 end of the nerve, Bernstein assumed a local fatigue, and computed 

 its appearance at 515 min. Wedenski tried to obviate the 

 injurious effect of the long closure of the battery current by send- 

 ing in a strong ascending or descending constant current at the 

 outset for a short time, so that the tract of nerve involved became 

 incapable of conducting (70). Very weak currents then sufficed 



