92 THE POPULAR SCIENCE MONTHLY 



The following photographs show types of tests, used for making 

 mental diagnoses of children at Vineland, the Lincoln Institution in 

 Illinois, the University of Chicago, the Chicago Juvenile Court, Co- 

 lumbia University, University of Pennsylvania, University of Wash- 

 ington, University of Texas, and similar institutions (Figs. 4 to 14). 



The foregoing tests and experiments show that mentally defective 

 children offer excellent material for psychological investigation, since 

 they are a more or less isolated group with quite definite boundaries and 

 are dependent on others. They may be observed continuously during 

 their lifetime, they are incapable of being stimulated or enthused by 

 artificial reactions, they are not easily embarrassed or self-conscious; 

 some of their mental processes are slowed down, others almost elimi- 

 nated and some grossly exaggerated ; their motor reactions are usually 

 the direct result of their ideas with little inhibition, decision, choice or 

 judgment, and may therefore be considered fairly safe criteria of the 

 concomitant mental activities. The various stages of mental deficiencv 

 frequently parallel the stages of development of the normal mind and 

 since the defective mind may remain for a lifetime at a given level, it 

 may be studied in such a manner as to shed much light on the corre- 

 sponding stages of the developing mind of the normal child, which is so 

 fleeting in its passage to higher levels. 



Finally: 1. Defectives are worthy of careful study for their own 

 sake, for the welfare of society, and for the scientific insight they offer 

 into the mental processes of normal children and the problem of edu- 

 cation. 



2. They offer, where their ancestry may be traced, the best material 

 at present available for the study of human heredity on account of the 

 pronounced deviations which may be traced. 



3. They have so far contributed most to the scientific application of 

 " mental and physical tests " which dominates contemporary tenden- 

 cies in child psychology and its application to education. 



4. Mental defectives present tremendous sociological difficulties in 



