ACTION OF THE TECTORIAL MEMBRANE 507 



higher part of the range of the organ, notes of varying vibration 

 frequencies involve correspondingly varying extents of the 

 tectorial membrane and that sensations of pitch are determined 

 by the number of stmuli applied in a unit of time to a unit area 

 of hair cells might be so elaborated as to satisfy some of the 

 simpler requirements of the idea that analysis of sound is 

 accomplished in the cochlea or peripheral part of the auditory 

 apparatus. 



It is known that the natural vibration periods of strips of 

 material vary according to their proportions: that a thin, narrow 

 strip has a higher natural vibration frequency than a thick, 

 broad strip of the same length, and that a shorter strip has a 

 higher natural frequency than a longer one of the same thickness 

 and width. A load added to a strip lowers its natural vibration 

 frequency. Of the number of musical instruments constructed 

 on these principles, the xylophone may be preferably mentioned 

 here. However, there is no available information as to what 

 would be the behavior of a series of such varying strips joined 

 continuous with each other end to end in their natural sequence, 

 and especially if of a material soft and flexible as that of the 

 tectorial membrane. The tectorial membrane is not only soft 

 and very flexible but its vibrating part or outspanning zone is 

 attached all along one side, and thus its vibratory behavior 

 must necessarily be different from that of a metal or hard-wood 

 strip shaped in the same proportions and lying free as to both its 

 sides. Very possibly, being flexible and attached, the natural 

 vibration frequency of each segment comprising the whole would 

 be modified by that of the segments adjacent to it, that is, the 

 natural frequencies of adjacent regions would overlap into each 

 other as it were, and yet a given region of the whole membrane 

 would have a natural frequency differing from that of another 

 region. If such is possible, then a region would, in its center at 

 least, have a tendency to vibrate in resonance with imparted 

 vibration frequencies corresponding to its own natural frequency. 

 Thus it would be possible that, when the apparatus is subjected 

 to a given sound, a given region of the membrane may vibrate 

 with sufficient excursion to impinge upon the hairs of the hair 



