( fi5 ) 



pillars (showing no joint like the auditory bones) finds an explana- 

 tion. For a pressure wliich is always positive this is snfïicicnt, not 

 for a vibration. In the second place it explains the varying shapes 

 and aspects presented by the membrana basilaris iji the preparations. 

 These are very obscure when they concern an integrating part of the 

 organ, but are explained very easily if what we see in the prepa- 

 rations, is only a coagulated colloid or elastic mass. 



Finally our conception is by no means bound to the theory of 

 Helmholtz-Hensp^n. It is also acceptable to those who would exchange 

 this theory for that of Ewald. For Lord Rayleigh treats in his paper 

 also the case of a vibrating membrane : "but a membrane with a 

 flexible and extensible boundary capable of slipping along the surface, 

 provides for two dimensions. If the vibrations be equally distributed 

 in the plane, the force outward per unit length of contour will be 

 measured b^' one-half of the superficial density of the total energy". 



So the theory of the pressure of sound might also be applied 

 to a membrane such as is imagined by J. R. Ewald. But his mem- 

 brane does not answer the conditions mentioned by Rayleigh, so 

 that the C{uantitative relations are not so easily perceived as in the 

 above developed case. 



Finally, concerning the modern theories of hearing which I would 

 call the pulsatory ones, since they only take into account the bul- 

 gings of the membrana basilaris, caused by the piston movement of 

 the stapes, the hypolliesis of the pressure of sound cannot be applied. 

 For tliese theories purposely neglect tlie vibratory mo\ements of the 

 smallest parts and only take into account the mass-result. If however 

 we lose sight of what is the essential thing in a vibration, Ave also 

 lose the right of applying the properties of a vibration. In my 

 opinion there can then be no question of pressure of sound. 



The reader will have perceived that the starting-point of our reasoning 

 was the probability of the fact that the arcuate zone and the arches 

 vaulting over it remain perfectly at rest. On anatomical grounds this 

 is very probable. Should it appear later that this rest is not absolute 

 but only relative, the preceding reasoning is none the less valid. 



Only one objection could then be raised, namely the small amount 

 of the pressure of sound. This would then have to be placed 

 against another small value, that of the possible movement of the 

 hair-cells. Hence the question would be a quantitative one. But also 

 in this case the two forces, the pressing force and the thrusting 

 force, would by no means preclude each other. They would both luwe 

 to be present. For the present we prefer, by assuming immovability, 

 to neglect the thrusting force and only to retain the pressing force. 



