84 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 93 



maintained under the direction of special nervous centers, which as 

 yet are known but very imperfectly but the existence and regulatory 

 function of which are necessary, and which are called the trophic cen- 

 ters. They are highly important parts of the central government of 

 each individual organism. They act upon the blood and lymph supply 

 and doubtless also in other effective ways. The tissues themselves 

 can have no architectonic individuality ; they are but so much living 

 material from which, under the strongly hereditarily fixed specific 

 influence of the nervous centers, there are built different structures. 

 Nor does the function of these centers end with the finish of the con- 

 struction, just as the function of the government of a city cannot end 

 with the completion of its streets and houses. There is a perpetual 

 guardianship under the continued power of heredity, and there are 

 perpetual changes, for heredity is not fully discharged or satisfied with 

 the completion of the structures — it is a lifetime factor. And here, 

 I feel, lies the clue to the problem that confronts us in our study of 

 ear exostoses. 



It may safely be regarded as axiomatic that as long as both the 

 heredity and the nervous apparatus that subserves it in connection 

 with any given part of the organism are normal, that part will, unless 

 in some way injured, remain normal. If in the absence of a chemical, 

 mechanical, or bacterial injury a part behaves abnormally, it is an un- 

 questionable proof that at that point and to that extent there is either 

 a weakening or derangement of the hereditary control, or of its proper 

 transmission. The something we call heredity must not be conceived 

 as any special power acting within and upon an organism — it can in 

 the end consist only of a specific organization within and between the 

 molecules of the cells of the nervous centers. Such organization is as 

 a rule deeply fixed and not readily influenced. It may however be 

 affected by deep-acting causes. Just what such causes are and how 

 they may act, except in case of destructive bacterial or other poisons, 

 is still but little known. 



What from the above discussion can help us toward an understand- 

 ing of the basic cause of ear exostoses? Can it be a weakened or 

 temporarily disturbed heredity, or does the cause lie in a faulty or 

 temporarily disturbed mechanism of nervous transmission of the 

 hereditary control ? 



Both the above conditions are possible, but the wide prevalence of 

 ear exostoses in the human family, and their manifestations as to 

 age, sex, and side, seem to speak against derangements of nerve 

 transmission. 



