Because their material was studied in institutions for the insane, the majority of writers on epilepsy have expressed the opinion that this disorder inevitably leads to mental deterioration. This view was challenged by one of us (H. A. P.)1 in 1932, in a study made on epileptic patients seen in private, extramural practice. In that study attention was directed to the fact that only 6.5 per cent of 304 such epileptic patients presented mental changes characteristic of epileptic deterioration after a suitable lapse of time. The remaining patients in this series retained normal mental health and suffered no impairment in their ability to work at their various vocations. We have become convinced that the disorder known as "idiopathic epilepsy" is of two types: In one variety mental deterioration occurs, and in the other it does not.
In addition to the mental status, certain differences between the mentally deteriorated and