THE SENSE OF HEARING. 167 



waves of souud from tho walls of a lofty apartment.) Numerous investigations 

 have been instituted by the most ingenious experimentalis'ts to throw light upon 

 these subtle inquiries, but the results have been so scanty and uncertain that we 

 abstain from the discussion of the different conjectures advanced, especially as 

 the possibility of making them suiBciently intelligible must be doubted. It has 

 also been a question, and one which has long been the subject of lively scientific 

 discussion, to what end serve the different arrangements observed in the exten- 

 sion of the terminal portions of tlip nerves, first in the saccules of the vestibule 

 and semicircular canals, in which the brush-shaped ramifications of the nerve 

 extremities are struck simultaneously by advancing particles of the fluid ; sec- 

 ondly, in the cochlea, in which these nerve extremities are so arrang(?d behind 

 one another that the waves must strik<^ them successively one after the other; 

 or, more generally, what special design have the cochlea, the vestibule, the semi- 

 circular canals ? We might fill pages with the enumeration and criticism of 

 the conjectures in which a solution has been sought, and would only see that 

 most of them were destitute of proof, some even absurd. It has been supposed, 

 for example, that the semicircular canals serve fur a knowledge of the direction 

 from which the wavfs of sound proceed. As if the perception of the direction 

 could at all be the object of an impression of the sense ; as if a wave of the fluid 

 could telegraph to the mind, through the nerve which is struck, the point of the 

 compass from which the excitation is directed ; as if a differeot direction of the 

 fluid-waves within the labyrinth could be the herald of a different direction of 

 the air- waves without! We hope to explain presently in what manner we ob- 

 tain an idea of the position in space of the external sources of sound. In regard 

 to the cochlea, the opinion has long obtained favor that it is intended to conduct 

 to the nerves contained in it the waves of sound directly communicated from 

 the air to the bones of the head and propagated through these, while the, vesti- 

 bule is destined only for the reception of the vibrations transmitted through the 

 auditory canal, the tympanum, and the ossicles. This assumption rests on the 

 early but erroneous opinion that the nerve filaments of the cochlea terminated 

 between the bony plates of the laminar partition. Since it is known, however, 

 that they issue from these and terminate free in the fluid of the cochlear canal, 

 this hypothesis has become untenable, for air-waves (and it is these almost 

 alone which convey a sound to the human ear) are transmitted with so much 

 difliculty and so much enfeebled to the bones of the cranium, and again with 

 such difficulty and feebleness from these to a fluid (the cochlea fluid,) that it is 

 scarcely conceivable that in this way a sound producing vibration could reach 

 the nerves of the cochlea with a strength sufficient for their excitation. In short, 

 the unpalatable but honest confession of ignorance is the only answer which can 

 properly be given to the above questions. 



We have finished our explanation of the progress of the auditory excitation 

 in our organ of hearing ; we have followed the sound-producing movement from 

 its origin in the outward object (the vibrating string) through the external air, 

 the external ear, the auditory canal, the tympanum, the movable bones, and the 

 fluid of the labyrinth, to the nerves. We come now to the pith of the subject, 

 the problem which it is the part of acoustical physiology to solve, to the ques- 

 tion, how does this movement operate upon the nerves when it has reached 

 them ? How does it release in them the so-called " nerve current," which, pro- 

 ceeding through their fibres to the brain, there, by a certain apparatus, so works 

 upon the soul that the latter instantaneously conceives a sensation of sound ? 

 We need not combat anew the irrational idea that the sound-movement, as such, 

 is propagated in the nerves ; that a sound wave, transmitted from particle to 

 particle, operates as such upon the perceptive apparatus in the brain. We have 

 in earlier articles sufficiently established the fact that tlni pi-ocess itself in the 

 nerve fibres is totally different from the external irritant of th^' sense which pro- 

 duces it ; that it is a specific movement of the nerve molecules of a yet unex- 



