EAR AS AN ORGAN FOR SOUND SENSATIONS. 397 



conveyed to the brain as a nerve impulse. We should be capable of 

 perceiving, theoretically, as many distinct musical tones as there 

 are fibers in the basilar membrane, while a compound wave, by set- 

 ting a number of these mechanisms into action, gives a series of 

 sensations which are more or less fused in consciousness. The 

 peculiar quality or timbre of the tone of each instrument is refer- 

 able, therefore, immediately to the number and relative intensities 

 of the simple tone sensations that it arouses. The fusion of these 

 elementary tone sensations into compound ones of different qual- 

 ities is comparable, in a general way, to the fusion of simple color 

 sensations, with this exception, however, that in the compound 

 tone sensations we are capable of distinguishing more clearly the 

 fact that they are composed of simpler elements ; the constituent 

 tones may be recognized by the trained ear at least. The mechan- 

 ism by which the vibrations of the strings of the basilar mem- 

 brane are conveyed to the hair cells and through them to the nerve 

 fibers is a matter of speculation only, as are also the functions of the 

 remaining parts of the organ of Corti. It may be suggested, 

 perhaps, that the rods of Corti and Deiters's cells, together with 

 the reticulate membrane, with wliich they are both connected, 

 form not only a supporting apparatus for the hair cells, but also 

 a mechanism by which the vibrations of the strings are commu- 

 nicated to the hairs of the hair cells ; but the suggestion is unsatis- 

 factory, as the anatomical arrangement does not suffice to explain 

 how the vibrations of individual strings are transmitted to the 

 separate hair cells. The assumption has also been made that 

 the tectorial membrane acts as a damper to the vibrating hair cells 

 or the reticulate membrane. Its position as a pad lying over the 

 rods of Corti and the reticulate membrane justifies perhaps such an 

 assumption. Many physiologists, while accepting the general 

 principle that the cochlea analyzes the sound waves by a mechan- 

 ism for sympathetic vibrations, have been unwilling to admit 

 that the basilar membrane constitutes such a mechanism. They 

 point to the improbability or impossibility of fibers of only 0.36 

 mm. (or 0.5 mm. at the best) in length acting as efficient reso- 

 nators, especially as they are not entirely free and are surrounded 

 by liquid. Attempts have been made, therefore, to select other 

 structures in the cochlea as more likely to be affected by sympa- 

 thetic vibrations. Attention has been directed mainly to the 

 tectorial membrane or membrane of Corti. V. Ebner,* reviving 

 an older view of Hasse, has suggested that the tectorial membrane, 

 especially its free end, serves as the mechanism for sympathetic 

 vibration. This membrane increases in width from the base to 

 the apex of the cochlea and varies in thickness in its radial diam- 



* Kolliker, "Handbuch d. Gewebelehre," sixth edition, vol. iii, pt. ii, 

 p. 958, 1902; also Hardesty, "American Journal of Anatomy," 8, 109, 1908. 



