So far we presupposed that the central system itself was normal. No sharp separation line, however, lies between all these disturbances and the equally large group of psychophysical disabilities resulting from a defective constitution of the brain. The normal brain shades over by smallest differences into the abnormal one; yes, even the varieties of temperament and character and intellectual capacity and industry and energy represent, in the midst of our social surroundings, large deviations from the standard. That which might still pass as normal under certain conditions of life would be unadjusted and thus abnormal under other conditions. In the same way, we certainly cannot point out where the natural constitution of a brain ceases to be fit for its organic purposes and where the structural variations are ill-prepared for the struggle for existence. Just as we claimed that an entirely normal brain might be brought by an emotional overstrain to a state of exhaustion and disability, we may claim on the other side that a brain which nature has poorly provided may yet be protected against damage and injury. The inborn factor does not alone decide the fate. Psychophysical prophylaxis may secure steadiness of equilibrium to a system which inherited little resistance. Yet this large borderland region, where an ill-adjusted brain may be saved or lost in accordance with favorable or unfavorable circumstances, shades off again to the darker regions where the inner evolution leads by necessity to disaster even under favorable conditions.