100 INNERVATION. [CHAP. XVIII. 



is not very rare, as he met with several instances of persons not 

 aware of such a sound. 



Every one must be conscious that the sensation of sound fre- 

 quently lasts longer than the exciting cause of it, as the sensation 

 of light does. This has been demonstrated experimentally by 

 Savart, who found in his experiments upon toothed wheels that 

 the removal of one tooth did not produce any interruption of the 

 sound. Other proof of this is obtained from the noise which remains 

 in the ears after long travelling in a coach, or in a train upon a rail- 

 road. The subjective phenomena of hearing generally result from 

 some affection of the brain, or of that part of it in which the auditory 

 nerve is implanted. The most common of them are tinnitus aurium, 

 and the buzzing or rushing noise in the ears, which is generally in- 

 dicative of a deficiency rather than a redundancy of blood in the 

 brain; or it may be caused by some disturbance of local nutrition 

 of the brain giving rise to an irregular development of nervous 

 power. 



Upon the subjects discussed in this chapter, the reader may consult the 

 works of Scarpa and Soemmerring ; the excellent article on the organ of Hearing 

 by Mr. Wharton Jones in the Cyclop, of Anat.; Miiller's elaborate chapter 

 on Hearing in his Physiology ; Dr. Wollaston's paper on Sounds inaudible by 

 certain ears, Phil. Trans. 1820 ; the article Hearing, Cyclop. Anat. ; Dr. Elliot- 

 son's Physiology, where the ingenious views of Mr. Wheatstone are briefly 

 stated ; and a paper by the latter philosopher in the Journal of the Royal 

 Institution, for July 1827. 



