376 Mr. ft. Moon on the Structure of the Human Ear. 



ened in such a manner as to draw out the stapes, whereby the 

 auditory apparatus, before the sonorous impressions became inci- 

 dent upon it, was placed in a state unfavourable for their reception. 

 By the action of the needle the tympanal membrane would be- 

 come stretched, thus allowing the stapes to assume its proper 

 position ; and this effect would continue until, by the gradual 

 but slow recovery by the membrane of its former status, in the 

 manner described by Dr. Brennan, the original obstacle to the 

 hearing of the patient would recur. 



VII. In conformity with the views which I have endeavoured 

 to explain, loud sounds may be expected to produce deafness 

 either (1) by rupture of the tympanal membrane, (2) by dis- 

 connexion of the chain of ossicles either from one another or 

 from the tympanal membrane, or (3) by sudden convulsive 

 action of the muscles of the tympanum, through which the stapes 

 becomes so firmly fixed in the fenestra ovalis as to be with diffi- 

 culty withdrawn. 



I conceive that deafness might result, in the manner last men- 

 tioned, even in cases where the sound which is the cause of it is 

 not exceptionally loud, provided that it was so sudden and unex- 

 pected as to cause alarm. 



Probably also there is a fourth mode in which, in the case of 

 loud sounds, deafness might result, namely where a great con- 

 cussion of the air occurs ; in which case the tympanal membrane 

 may become stretched by reason of the unusual pressure exerted 

 upon it by the condensed wave, in the manner in which Dr. 

 Brennan describes it as capable of being stretched by the conti- 

 nued action of a more moderate pressure. The same cause 

 which stretched the membrana tympani would force in the stapes, 

 and thus tend to produce the same kind of deafness as No. 3 

 just referred to. 



VIII. The mode in which deafness is sometimes relieved by 

 means of a loud sound falling upon the ear is readily explicable 

 upon the principles before set forth, if we suppose the deafness 

 to have resulted from the stapes having become too firmly im- 

 bedded in the fenestra ovalis, or from rigidity of the articula- 

 tions of the ossicles. 



IX. In accordance with the same principles, nervous deafness 

 may be expected to occur in either of two ways, viz, by paralysis 

 or torpor (I) of the auditory nerve proper, (2) of the motor 

 nerves connected with the muscles of the tympanum. 



I shall seek for another opportunity to point out the functions 

 of the membranous labyrinth and the semicircular canals*. 



6 New Square, Lincoln's Inn, 

 October 1, 1869. 



* In connexion with the explanation given in my former paper of the 



