Royal Microscopical Society. 91 



inner ones. The numbers in the two series will, in that case, differ 

 by one only, and not be in the ratio of 2 to 3, as the author sup- 

 poses. The number of the rods is assumed by the author to be not 

 less than 5000, a number far greater than the differences of pitch 

 that the human ear can be required to appreciate. The cochlea 

 is furnished with a very large bundle of nerves ; so large indeed, 

 as probably to supply a fibre in relation with each one of the rods. 

 It is well known that the pitch of sounds depends on the length of 

 the waves of air by which they are transmitted — that those sepa- 

 rated by an octave, for instance, are in the proportion of 2 to 1, 

 and it is also easy to imagine that a sound of any particular pitch 

 is specially impressed upon some particular portion of this spiral 

 membrane — ^^just as in the case of two harps tuned in unison, the 

 sound produced by one will set in motion the corresponding string 

 of the other, and cause it to vibrate and to emit the same sound. 

 The transverse fibres of the spiral membrane may be considered to 

 act exactly as the harp, and, if this is the case, all that is wanting 

 is that each nerve-fibre should receive an impression from the cor- 

 responding fibre of the spiral membrane, and convey it to the brain, 

 to produce there the impression which we recognize as sound. This 

 may readily be effected by means of the rods, the inner of which 

 are surrounded by very delicate nerve-cells. This view of the func- 

 tion differs slightly from that of the author, but it may possibly be 

 more correct. 



This subject is one in which the writer has long taken a great 

 interest, and having been strongly impressed with the correctness of 

 the views above set forth has endeavoured, but hitherto without 

 success, to construct some mechanical illustration of the mode in 

 which a sound of any given pitch becomes impressed on the corre- 

 sponding portion of the spiral membrane ; but the very lucid de- 

 scription of the actual mechanism of the cochlea given by Dr. 

 Pritchard wUl probably conduce to the accomplishment of this object. 



AVith regard to sounds of very high pitch, the power of appre- 

 ciating them in different ears is very various. This fact was well 

 known to the celebrated Dr. WoUaston, who stated that he had two 

 small pipes of very high pitch, and between which there was (quoting 

 from recollection) an interval of a fifth, one of which he could hear 

 and the other he could not; and he met with some who could 

 hear the notes of both pipes, others could, like himself, hear only 

 one, and others could hear neither of them. There are individuals 

 (of whom the mother of the writer was an example) who cannot 

 hear tlie shrill chirp of a cricket. These differences in the range of 

 audition may be readily accounted for if it be the fact, as it is not 

 improbable, that the narrowest portion of the spiral lamina may 

 vary slightly in width in different cochleae. 



Immediately following the former is an important paper by Mr. 



H 2 



