USES OF THE PARTS IN THE EAR. 333 



solids and fluids are much better vehicles of sound 

 than the atmosphere ; that it is the rarity and 

 elasticity of the atmosphere which makes all that 

 exterior apparatus which we have been consider- 

 ing necessary. Accordingly, an exterior ear is 

 not wanted in the fish. If a man dive under 

 water and carry a stone in each hand and strike 

 the stones together, he is sensible of a stunning 

 sound, and indeed of an impression on the whole 

 surface of his body. In short, although it was 

 once doubted whether water were capable of pro- 

 pagating sound, a hundred instances can now be 

 brought forward to prove that it can receive or 

 propagate every degree of sound and tone. Again, 

 when we find that the solid parts of the head con- 

 vey sounds, we perceive that in the fish there is 

 no occasion even for an external opening, far less 

 an external ear. An apparatus of a totally differ- 

 ent kind is bestowed. Within a little sac of fluid 

 a bone or concretion is suspended, which, being 

 more solid than the surrounding fluid, receives the 

 vibration and moves, necessarily producing waves 

 or motion in the surrounding fluid, and conse- 

 quently an agitation of the extremities of the 

 nerve exposed to the fluid. A very simple but 

 curious experiment of Professor Camper illus- 

 trates the effect of this structure : A bladder con- 

 taining a marble and full of water being held in 

 the hand, the slightest motion of the hand was at- 

 tended with a vibration communicated from the 



