The Nature of the Tectorial Membrane 165 



walls of the cochlea, and (2) upon the breadth and thickness of the 

 membrane and thus upon the extent to which the wave energy is ex- 

 hausted in overcoming the inertia of the membrane itself. 



That notes of higher pitch or greater vibration frequency are more 

 apt to produce vibrations in the thin, narrow, basal coil of sufficient 

 amplitude to stimulate the auditory hairs than they are to produce such 

 vibrations in the apical coil is considered probable for the following 

 reasons : 



(1) The thin, basal end of the membrane lies nearer the fenestra 

 vestibuli (ovalis) or the point at which the waves are imparted to the 

 endolymph. Of sounds of equal intensity, or amplitude of vibration, 

 but of different pitch, those of higher pitch or greater vibration fre- 

 quency are sooner overcome by the resistance of the medium (do not 

 travel so far) as those of lower vibration frequency. In the atmosphere, 

 sound waves of high frequency are damped out before those of low 

 frequency and their speed of transmission continuously decreases as they 

 become fainter. This damping out must occur much more quickly in 

 a medium like the much more viscous endolymph. Therefore it is 

 possible that sound waves of the highest perceivable pitch may affect 

 only the end of the basal coil of the tectorial membrane and be damped 

 out wholly before reaching the upper coils, or at least to such an extent 

 as not to agitate the upper portions of the membrane sufficiently for 

 stimulation of the hair cells. 



(2) The natural vibration period of the thin, narrow strip is of 

 greater frequency than that of the thicker wider strip. It is possible to 

 subject a strip of material to vibrations of such frequency, either above 

 or below its natural vibration period, that it will not vibrate at all or 

 vibrate weakly or irregularly. It is probable that no portions of the 

 tectorial membrane, when subjected to sound waves transferred to the 

 endolymph, will undergo vibrations of sufficient excursion to impinge 

 upon the auditory hairs except those portions whose natural periods 

 correspond to the vibration frequencies of the waves affecting the 

 endolymph. Portions adjacent to these, having approximately the same 

 natural periods (thickness and width), would of course be also affected, 

 but to a degree decreasing as the distance from the portion most affected 

 increases. Or, again, the effect of loading a vibrating body is to lower 

 its vibration frequency or pitch. If the body be of uniform proportions 

 and the load be distributed uniformly, the vibration frequency of all its 

 components will be lowered; if the load be placed at one part of the 



