782 OF THE ORGANS OF THE SENSES, AND THEIR FUNCTIONS. 



thrown into powerful vibration, but the higher harmonics are scarcely pro- 

 duced. With ?', as with u, it is difficult to pronounce it loudly enough to 

 excite vibrations in any but the fundamental note; the 2d and 3d harmonics, 

 however, appear to aid in determining the clear character of the note, and 

 slight vibrations may be observed in the 5th harmonic. The wires of the 

 piano in these instances may be said to analyze the vocal sound iuto its 

 secondary elements or partial notes; and Helmholtz has shown that the 

 same result may be attained by placing in connection with the ear a series 

 of glass vessels, producing by their vibration harmonic notes, and ascer- 

 taining with which note or kind of note they resonate most powerfully. In 

 another series of experiments, instead of analyzing the vocal sounds as above 

 mentioned, Helmholtz endeavored to produce them synthetically, by accom- 

 panying a given fundamental note with its several harmonics. This \vas 

 accomplished by a system of tuning-forks, arranged in harmonic series, which 

 could be thrown into vibration at will in various order. Thus the funda- 

 mental note of the first tuning-fork, resembling the vowel u, the vowel sound 

 or musical color o was produced if the harmonics 2 were powerfully, and 3 

 and 4 were weakly sounded ; e was produced by the 3d octave resonating 

 powerfully with the fundamental note, the 2 harmonic note moderately, and 

 the 4 and 5 harmonics feebly, and so on for the other vowel sounds. The 

 power which we possess of distinguishing the characters belonging to similar 

 notes produced by different instruments, appears, therefore, to be due to a 

 kind of analysis being performed by the ear, similar to that effected by the 

 wires of the piano; and we shall see that it is not unreasonable to attribute 

 this function especially to the branches of the auditory nerve distributed 

 upon the lamina spiral is of the cochlea. It may be said, indeed, to have 

 received direct confirmation from the observations of Hensen 1 upon the 

 auditory hairs on the free surface of a Decapod Crustacean (Mysis). These 

 were seen under the microscope to vibrate in certain groups corresponding 

 with the special note sounded in their vicinity. In the case of the human 

 ear very effective "damping apparatus" must exist, since through the greater 

 part of the musical scale a trill of ten alternate notes in the second can be 

 distinctly differentiated, which would be confused if the sensation of each 

 note persisted much longer than the sound itself. 



641. The essential part of an Organ of Hearing is obviously a nerve 

 endowed with the peculiar property of receiving sonorous undulations, and 

 of transmitting their effects to the Sensorium. This nerve is spread out 

 over the surface of a delicate membrane which lines the Vestibule and its 

 prolongations; and this membrane incloses a fluid, which is the medium 

 whereby the sonorous vibrations received through the external ear are com- 

 municated to the nerve. We learn from an examination of the compara- 

 tive structure of the auditory apparatus in the lower animals, and from the 

 study of its development in the higher, that the part which, being most con- 

 stantly present, and being also the earliest in its development, may be con- 

 sidered as the most essential, is the simple Vestibular cavity ; which exists 

 where there are no vestiges either of Semicircular Canals, or Cochlea, or of 

 Tympanic apparatus. Such a condition presents itself in some of the higher 

 Invertebrata and in the lowest Fishes ; but as we ascend the Vertebrated 

 series, \ve find the semicircular canals growing out (as it were) of the Vesti- 

 bule in Fishes, a Tympanitic apparatus superadded in Reptiles, and a 

 Cochlea first acquiring a more than rudimentary development in the class 

 of Birds, although only presenting in Mammalia that characteristic form 



1 Zeits. f. wiss. Zoologic, Bd. xiii, and Kioler Institut, 1809. 



