212 SPECIAL SENSES. 



are wanting to show the exact relations of these different 

 conditions of the ossicles and of the membrane to the physi- 

 ology of audition. One very important physical point, how- 

 ever, which has been the subject of much discussion, is set- 

 tled. The chain of bones acts as a single solid body in con- 

 ducting vibrations to the labyrinth. 1 It is a matter of physi- 

 cal demonstration that vibrations of the bones themselves 

 would be infinitely rapid as compared with the highest tones 

 which can be appreciated by the ear, if it were possible to in- 

 duce in these bones regular vibrations. Practically, then, the 

 ossicles have no independent vibrations that we can appreci- 

 ate. This being the fact, the ossicles simply conduct to the 

 labyrinth the vibrations induced in the membrana tympani 

 by sound-waves ; and their arrangement is such that these 

 vibrations lose very little in intensity. "While it has been 

 shown experimentally, by Politzer and others, that the ampli- 

 tude of vibration in the membrana tympani and the ossicles 

 diminishes with the tension of the membrane, 3 it would seem 

 that, when the tensor tympani contracts, it must render the 

 conduction of sound-waves to the labyrinth more delicate 

 than when the auditory apparatus is in a relaxed condition, 

 which we may compare with the " indolent " condition of the 

 apparatus of accommodation of the eye. "When the mem- 

 brana tympani is relaxed and the cog-like articulation be- 

 tween the malleus and the incus is loosened, the vibrations 

 of the membrane and of the malleus may have a greater am- 

 plitude ; but, when the malleo-incudal joint is tightened and 

 the stapes is pressed against the f enestra ovalis, the loss of 

 intensity of vibration in conduction through the bones to the 

 labyrinth must be reduced to the minimum. "With this view, 

 the tensor-tympani muscle, while it contracts to secure for 



1 HELMHOLTZ (op. cit.) demonstrated the mechanism of the malleo-incudal 

 joint, and showed how the bones conduct vibrations as a single solid lever ; but 

 he gives full credit to Weber (p. 8), who first proposed this theory, though it was de- 

 fective from his want of knowledge of the exact mode of articulation of the bones. 



2 POLITZER, Untersuchungen uber Schallfortpflanzung und Schalllcltung im 

 Gehorgant. Archiv fur Ohrenheilkunde,W\iYzlQUY& 1864, Bd. i., S. 68, et seq. 



