512 IRVING HARDESTY 



tory structure contained. In my paper of 1915 attention was 

 called to the fact that the spiral organ (of Corti) or the load 

 carried by the basilar membrane increases appreciably in both 

 width and thickness in passing from the base to the apex of the 

 cochlea. This increase in proportions is, however, by no means 

 so great as is the case with the tectorial membrane. The possi- 

 bility that wave energy imparted to the fluid in the cochlea may 

 also result in some vibration of the membranous spiral lamina, 

 or basilar membrane, as a whole is not denied. While it is a 

 flat tendon stretched with both edges attached instead of having 

 a free edge and lying limph^ passive, the fact that it is a little 

 wider at its apical end (averaging 1.4 times) and that its chief 

 load, the spiral organ, increases nearly two times in size in passing 

 to the apical end seem suggestive of an adaptation for vibratory 

 activity. But it must offer greater resistance to undulatory 

 movement than the tectorial membrane, being far less flexible 

 and of different proportions as well as of different structure 

 and position. It is possible that vibrations of low frequency and 

 high amplitude may throw both the tectorial and the basilar 

 membrane into vibration, while the lesser amplitudes may affect 

 the tectorial membrane only. If the two were equally affected 

 by given vibrations, then their undulations w^ould be parallel 

 and, the two remaining the same distance apart, the required 

 stimulation of the hair cells would not occur But, if the posi- 

 tion and greater flexibility of the tectorial membrane allow in it 

 vibrations of greater excursion than in the basilar membrane, 

 then the hair cells may be stimulated and with the frequency of 

 the wave motion imparted. It might be advanced that in case 

 of very violent stimulation, the undulation of both membranes 

 is a necessary and economical arrangement, for in such cases 

 injuriously forcible impingement of the tectorial membrane, 

 which alone stimulates the hair cells, may be avoided while yet 

 the tectorial membrane is kept within working distance of the 

 hairs. The increasing load (spiral organ) upon the basilar mem- 

 brane must act as suggested for that of the tectorial membrane, 

 making it possible, by its increasing resistance with the increas- 

 ing distance from the basis of the stapes, that varying extents 

 of it may be affected according to the intensity and vibration 



