This thesis is based on an examination by the writer of 323 children attending elementary schools in the City of Lincoln. The examination consisted of a physical examination and the application of the Stanford Revision of the Binet Simon tests. The ages of the children were from six to thirteen years. The social and economic problems of mental snbnormality have been discussed. In two hundred and twenty children information was obtained of their family history. Mental retardation, insanity, epilepsy and syphilis, abnormalities of pregnancy and labour, and tuberculosis, were noted. Each factor in the inheritance was considered first alone, then in combination with the other factors which are grouped under the heading "Other causative factors". Factors like epilepsy, insanity, tuberculosis, were not proved, when found alone, to affect the mental intelligence of the child, though when together or combined with factors like mental retardation they had an adverse effect. Mental retardation in the parents or grandparents was shown to he one of the most instrumental factors in the production of mentally subnormal children
