THE NERVOUS SYSTEM. 141 



blance of the action of the nerves to the phenomena pro- 

 duced by the series of a galvanic apparatus and by the 

 common electrical machine,* in a living animal or in 

 parts not quite deprived of vitality. These phenomena 

 in fact long ago induced some physiologists to compare 

 the nervous to the electric fluid. The singular and 

 undeniable effects attributed to animal magnetism ,^ as 

 well as other phenomena which have given rise to the 

 belief of a kind of sentient atmosphere surrounding 

 the nerves,;]; agree very well with the same hypothesis. 



226. If we regard the oscillation of the nerves, not 

 as similar to that which occurs in tense chords, but of 

 such a description as may be conceived to occur in 

 the soft pulp of the brain, we shall find many phy- 

 siological phenomena exactly corresponding with the 

 supposition. 



It is demonstrated that hearing depends upon an 

 oscillation. 



In vision also it probably occurs, although not to 

 the extent imagined by Euler. 



The penetration of Hartley in following up the 

 conjectures of the Great Newton, || has rendered it so 

 probable that the action of the other senses is not very 



* Fr. Al. Von Humboldt, iiber die gereizte Mvskel und Nervenfafer. 

 Posen. 1797. ii vol. 8vo. 



J. W. Hitter, Beweis dass cin bestiindiger Galvanismits den Lebensprocess im 

 Thierreiche begleite. Vinar. 1798. 8vo. 



J- J. Heineken, Ideen u. Beobachtungen den thieriscken Afagnetismus betref- 

 fend. Brem. 1800. 8vo. 



J v. Humboldt and Heineken, 11. cc. 



Dav. Hartley, Observat. on Man, his Frame, his Duty, and his Expecta- 

 tions. Lond. 1749. 8vo. vol. i. p. 44. 



t) Queries at the end of his Optic*. Qii. 23. p. 355. Lond. 1789. 8vo. 



