APPENDIX I. 131 



some chemical change, of the substance itself con- 

 tained in the nerve-tubes, spreading along the tubes, 

 according to the speaker's experiments, both ways 

 from any point where the equilibrium has been 

 disturbed; being capable of an almost infinite 

 number of variations or gradations, and of so 

 peculiar a character as to require the unimpaired 

 condition of the nervous structure. It would be out 

 of place on the present occasion to venture upon 

 any more definite statement regarding the nature 

 of the nervous agent, although the progress recently 

 made in this line, chiefly by the modern school of 

 German physiologists, already affords the means of 

 doing so, and of discussing the merits and defects 

 of several solutions proposed. It may not, however, 

 be inappropriate to remark, that although the 

 electric theory of the nervous agent, in the sense 

 just alluded to, cannot any longer be thought of (as 

 little, indeed, as with any degree of probability it 

 ever could), yet it would be rash, as the matter 

 stands, entirely to dismiss the notion of electricity 

 being concerned, and even playing a prominent 

 part, in the internal mechanism of the nerves. 

 The electric currents discovered in the nerves by 

 the speaker four-and-twenty years ago ; the remark- 

 able changes which these currents undergo when- 

 ever the nervous agent is called into action; the 

 wonderful phenomena of electric fish ; those of the 

 muscles and glands ; finally, the extreme sensitive- 

 ness of the nerves for electricity however applied, 

 and the beautiful and peculiar laws which govern 

 their reaction thereupon, all these are facts which 



