G26 TRANSACTIONS OP SECTION L. 



Between none of these grades does there appear to be any hard-and-fast line 

 of division. Whether we consider them from the standpoint of general intel- 

 lectual capacity, from the result of a more detailed psychological analysis, or 

 from the histological examination of the brain, it would seem as if the idiots 

 could hardly be regarded as a peculiar and separate class, for the differences pre- 

 sented by these various groups of mankind seem to be in their essence not 

 qualitative but merely quantitative ones. 



This being the case, what is the mental ' normal,' and how are we to define 

 what we mean by ' mental defect ' ? Where does the normal end and the ab- 

 normal begin? Indeed, in view of the fact that every living species naturally 

 varies within very wide limits, are we justified in saying that there is any 

 abnormal ; may not even the idiots be but the expression at one end of the scale 

 of normal mental variation, just as extreme brilliancy is its expression at the 

 other end ? 



The fact that the differences are quantitative, however, does not negative the 

 possibility of qualitative change, and there are reasons for thinking that a mere 

 diminution of brain development may give rise to a mind of a very different 

 order, to real differences in quality and nature. 



In order to arrive at a basis of differentiation between the normal and abnor- 

 mal we must go much deeper than ability to perform certain occupations ; we must 

 consider what are the essential qualities of mind. 



I consider the essential faculty of mind to be the capacity for self-preservation. 

 This results from the conscious adaptation of the individual to his environment, 

 and any person deficient in this fundamental capacity must be regarded as abnor- 

 mal and mentally deficient. I therefore define mental defect as a condition due 

 to arrested or imperfect development of the brain, in consequence of which the 

 individual is incapable of maintaining an independent existence. 



Let us now apply this criterion to the various grades of mankind, and see 

 where the line of division falls. With regard to the idiots, imbeciles, and feeble- 

 minded, the mere statement of their accepted definitions suffices to show their 

 incapacity for maintaining an independent existence, and consequently their 

 abnormality. 



With regard to the next group, the dull and backward, there is no authorita- 

 tive definition, but a large experience of this class has convinced me that they 

 are sharply differentiated from the feeble-minded in that they possess this 

 capacity for self-preservation, and I would define them as — those persons who are 

 below the average standard of intellectual ability, but are capable of managing 

 themselves and their affairs with sufficient prudence to maintain an independent 

 existence. 



Two other matters need a brief reference — i.e., curability and diagnosis. 



With regard to curability, it might be thought that, since the change is 

 fundamentally a quantitative one, it should be possible, by special methods, to 

 bring brain development up to the level of the normal standard. This is not 

 confirmed by experience, and a consideration of the conditions to which mental 

 defect is due shows the extreme unlikelihood of anything of the kind happening. 



The question of diagnosis practically resolves itself into the differentiation of 

 the feeble-minded from the dull and backward. The criterion which must be 

 borne in mind is not ability to acquire book-learning, but to profit by experience, 

 to adapt conduct to environment, and to maintain an independent existence. In 

 my experience the careful examination of the mental and physical status of the 

 child, with a consideration of his family and personal history, will usually enable 

 the expert to make a diagnosis without much difficulty. A few cases occur 

 where no definite opinion can be given until adolescence, but the occurrence of 

 these, which are relatively few, should not prevent us adopting measures for the 

 administrative cure of the majority, about whose condition there can be no doubt. 



(ii) Mental Tests for ' Backward ' Children. 

 By A. R. Abelson, B.Sc, D.-es-L. 



In late years increased attention has been given to the study of mental 

 deficiency. There is a growing feeling that the methods at present in vogue for 

 the recognition of mental defect are unsatisfactory. The diagnosis is often a 

 very difficult one. Bright-looking children are to be found among the most 



