No. I.] THE VERTEBRATE EAR. 285 



sity of overcoming these changed conditions of pressure in the 

 ear by thus artificially increasing the intensity of the external 

 stimuli. 



The auditory impressions gain access to the sensory struc- 

 tures only by the propagation of the wave impulses through the 

 wall of the cochlear tube ; and since the membrana Reissneri is 

 much the thinner and less resistant of the two walls through 

 which it is possible for the stimuli to pass, it is probable that 

 it is upon the surface of this membrane only that the waves 

 impinge which are to give rise to auditory impressions. 



This is rendered all the more probable from the fact that the 

 auditory hairs are directed upwards, inwards, and backwards 

 (with reference to the axis of the cochlear tube), and are thus 

 disposed in positions very favorable for the reception of wave 

 motion progressing up the cochlear tube. 



The basilar membrane, owing to the fact that it is heavily 

 loaded on both sides and tensely drawn, does not in all proba- 

 bility vibrate under the influence of such delicate stimuli, i.e. 

 permit their passage into the endolymph. For the moment let 

 us admit for the sake of the older view that the basilar mem- 

 brane may vibrate. It is still just as true that the stimuli are 

 sent into the sensory apparatus from the wrong side, from 

 within and not without, as is the case with all other known 

 sense organs where the stimulation progresses from the sensory 

 hair or rod through the cell into the nerve. Again, the auditory 

 hairs of the cochlea, as I have proved them to exist, are incal- 

 culably more delicate agents for the picking up of and trans- 

 mission of mechanical stimuli such as audible undulations of the 

 endolymph from any source whatsoever. 



In order to determine the physical characteristics of the hair 

 band as a structure capable of sympathetic vibration, we tried 

 a series of experiments on the ears of the Pig and Cat. The 

 OS petrosum was removed from the skull immediately after 

 death and transferred to aqueous humor until it could be opened. 

 This was done in each case as soon as possible. The cochlear 

 eminence was removed from the petrous mass and the roofs of 

 the several spires removed, thus exposing the membranous 

 ductus cochlearis entire. The dorsal and outer walls were then 

 cut away, the lower cut being made along the outer edge of the 

 sulcus spiralis externus, and the upper cut along the insertion 



