A NEW THEORY OF HEARING. 335 



presents the appearance of being torn and jagged and 

 portions of it may sometimes be seen attached to the 

 upper surface of the cells of Hensen : a portion so attached 

 was figured by Ketzius and is shown in the figure repro- 

 duced from his work in such text-books as Foster's 

 Physiology (fifth edition, p. 1351). It is highly probable 

 therefore that this membrane is attached at both edges 

 throughout the entire length, and that its frequent 

 separation is due to shrinkage under the action of reagents. 

 A similar shrinkage of the upper surface of their hair-cells 

 is prevented by the stiff unyielding reticular membrane, 

 and the tearing of the tectoria at its thinnest part when 

 exposed to reagents which cause shrinkage is precisely 

 what might be expected— it might even be said to be the 

 inevitable consequence. 



The tectoria when stretched in its natural condition 

 between the cells of Hensen and the lip of the spiral 

 lamina would rest just over the tips of the hairs of the 

 hair-cells. Between the tectoria and the reticular mem- 

 brane is then a thin layer of fluid which is somewhat 

 viscid and in which the stiff hairs project. The thickness 

 of this layer is about "004 mm. and in consequence of its 

 viscidity the friction involved in its movement would be 

 relatively great. The fluid in the wide scala media above 

 the tectoria is, however, much more free to move and the 

 tectoria would therefore move with the organ of Corti 

 almost as if it were rigidly bound to it. The passage of the 

 basilar wave would thus simply move the whole organ of 

 Corti, together with the tectorial membrane up and down 

 without disturbing the relative position of one to the other. 



This purely physical conclusion accords well with the 

 physiological observation that a single aerial wave im- 

 pinging upon the ear does not suffice to produce a 

 sensation of sound. 



