In studying epilepsy we see and study symptoms only. The pathology of the disease is very obscure, and it is mainly from its clinical features that we are able to assume the presence of detrimental changes in the more highly specialised tissues of the cerebrum. These changes may be primary or developmental as in the idiopathic type; or they may be accidental, and due to toxic agencies or traumatic injury; or they may be senile, as seen in rare cases (not accidental) occurring in late adult life or old age. Whatever the origin, a condition of nervous instability is set up, which may vary in every possible degree, from simple molecular disarrangement, giving rise to perverted functional action for a brief period of time only, to more lasting effects which conduce to morbid energising of a permanent nature.