142 ON NERVE-EXCITATION BY THE NERVE-CURRENT. 



The fact that sufficiently excitable nerves fall into persistent 

 excitation if an external closure of low resistance is offered to their 

 proper current, suggests that the above-described tetanic excitation 

 which supervenes in cooled frogs after section of the sciatic nerve 

 or plexus, is also simply due to the current which arises in con- 

 sequence of the section. It must be remembered that this current 

 exists in every single fibre, and that the sheath of each fibre, the 

 fluid present between the fibres, as well as the common sheath of 

 all the fibres, provide channels for external closure to each indi- 

 vidual current. Consequently so soon as the nerve-current is pro- 

 duced by the transverse section, all the fibres fall under the 

 influence of the nerve-current, the direction of which in the fibre 

 is descending, and must excite it at the points of exit. Just as a 

 weak battery-current excites tetanically any very excitable nerve, 

 so, in the same way apparently must the proper current of nerve 

 produce its excitation ; and just as the lasting action of a current 

 led in artificially is a gradually diminishing one, so the excita- 

 tory action of the nerve-current on the fibres of the nerve must 

 be of limited duration. Apparently, therefore, there is nothing 

 opposed to the assumption that the more or less prolonged tetanic or 

 clonic excitation of the muscles of cooled frogs consequent upon 

 section of their nerves, is due to the nerve-current which results from 

 section. 



That with this cause other causes participate, as regards the 

 results of nerve section, is not, however, excluded by the above 

 assumption. Just as any living substance can adapt itself to any 

 persistent stimulus, so the nervous substance also adapts itself to a 

 weak persistent current, whether this be an artificially applied one, 

 or its own proper current. Provisionally one might, in accord- 

 ance with custom, speak of this as ( fatigue.' In consequence of 

 this adaptation or fatigue, the closure tetanus, or, in our case, 

 the tetanus after nerve section comes to an end. A new ex- 

 ternal closure of the nerve-current effects, however, a sudden 

 redistribution of current in the nerve, and therewith a renewed 

 excitation. 



Since other mechanical, thermic, and chemical agents act just 

 like section in giving rise to the development of current in the 

 nerve, there are many considerations regarding the mode of action 

 of these stimuli and regarding the nature of nerve excitation which 

 are suggested by these phenomena. I will not, however, yield 

 to the temptation to enter upon theoretical considerations, just 



