The question of the cause or causes of feeblemindedness is no nearer solution today than thirty years ago, despite the enormous amount of investigation that has been carried out pathologically and experimentally. The multiplicity of the clinical syndromes in the group of mental deficiencies attests to the variations that may be expected in undertaking a study of these conditions. After eliminating all accidental mental deficiencies due to infection or injury that robs normally born children of their intelligence, we may divide the remainder for the sake of convenience into two general classes: (1) feeblemindedness with no neurologic defects and (2) feeblemindedness with neurologic defects. There are also patients who show endocrine dysfunction, but their conditions may as a rule be classified in one of the two groups just mentioned. The entire group of mental deficiencies may be more scientifically classified from a clinical standpoint, as advocated by Potter,1 under