144 BIOLOGICAL ASPECTS OF HUMAN PROBLEMS 



the creation of brain centers by practice is a mere 

 play of words a postulate from the facts of func- 

 tional experience, lacking in histological demon- 

 stration. It is what Professor Meyer aptly terms 

 "metaneurology." The centers grow by the force 

 of growth and then develop from use, but only where 

 the conditions are suitable. It is definitely wrong 

 to say that in word centers each word has its own new 

 cell, for a partial lesion always deprives people of 

 the more unusual words first, and not special sets. 



So much, then, for the disturbances of the mind 

 that depend upon definite and gross structural altera- 

 tions in the brain. Obviously such physical altera- 

 tions cause changes in the mental functions which 

 tend both to shorten life and to destroy efficiency and 

 happiness. But these definite lesions of the brain, 

 common and important as they are (especially as 

 the result of arterial disease), form only a small part 

 of the influences that operate detrimentally on the 

 human mind. There is, in addition, a literally im- 

 mense group of nervous and mental derangements, 

 some slight, some severe, which have a wholly dif- 

 ferent origin. It can be said, with the utmost 

 confidence, that most mental disorders and most 

 nervous derangements are not due to alterations in 

 the brain that can be detected either by naked eye 

 inspection or by the use of the microscope. Yet it 

 is true that every mental disorder rests on a disturb- 

 ance of cerebral function. Many of these disorders 

 are of so slight a grade that there is no question about 



