NO. 



EAR EXOSTOSES HRDLICKA 83 



may be excited locally by different agencies, but which have their 

 seat in the trophic nervous centers that control the bony structures of 

 the external auditory canal. 



There remains to be considered the general cause of the neurocentric 

 derangement and insufficiency. It was seen that two possible agencies 

 suggested themselves in this connection. One of these is degeneracy, 

 the other incomplete or disturbed evolutionary adjustment. 



The disgenic character of the ear growths would seem to point to 

 a degenerative cause affecting the aural apparatus — ^they tend to lead 

 to loss of hearing, local troubles, and indirectly, in rare cases, even 

 to death. Another item that might conceivably support the view of a 

 degenerative cause of ear exostoses is the fact, long known in otology 

 (see Biirkner, 1883, P- 103), that " the disposition to ear troubles (in 

 general) rises from birth to the 40th year and thence diminishes with 

 age ", which might be viewed as evidence of a degenerative condition 

 regarding the ear and which bears a close relation to the age incidence 

 of the ear growths. The much greater prevalence of ear exostoses 

 in the males than in the females, in all the human groups known to 

 show the abnormalities, might be viewed as a further support for the 

 idea of a basic degenerative cause, for the males as the less stable or 

 conservative sex might be expected to make just such a showing. 



But there are serious difficulties in the way of the hypothesis of 

 degeneration. The most potent are : There is no evidence that the 

 human ear is falling into disuse and hence would be starting on the 

 way to degeneration and restriction or elimination ; ear exostoses affect 

 not the organ of hearing proper, but the relatively much less important 

 bony passage that leads to the hearing apparatus itself ; the exostoses 

 as a rule are not accompanied by congenital defects in the parts in- 

 volved ; they are associated with few and followed by very few, if 

 any, changes that could possibly be looked ujxjn as of degenerative 

 nature of either the ear as a whole or of the meatus ; once successfully 

 removed by the surgeon they generally leave a sound ear with normal 

 function and but rarely recur ; the process of the production of these 

 growths is in substance an excess of production rather than any ex- 

 pression of structural weakness or defective vitality such as usually 

 result from degenerative causes ; and although they may be transmitted 

 to the progeny, the ear exostoses recur as such and not, so far as 

 known, in the form of any congenital defects of the meatus. 



It appears from the above that there is more that speaks against 

 than for a degenerative cause in the background of ear exostoses. 



There remains to be considered the central neurotrophic maladjust- 

 ment. It is plain that all structures in the body must be formed and 



