The epileptiform attacks that occur in the midst of these intoxications are quite as likely to be accompanied by various forms of mental disturbance as are attacks of true {257} epilepsy. Only one feature with regard to them is more favourable, and that is that the ultimate prognosis is not bad. The neutralisation of existing poison in the system, and the prevention of further ingestion of the toxic material, puts an end to the tendency to epileptiform convulsions, as a rule, and also to the mental symptoms associated with them. Epilepsy remains, notwithstanding all the advance in modern nervous pathology, quite as mysterious a disease as it has ever been. It matters not what its cause, or how slight it may be, sooner or later it is almost sure to be followed by mental disturbance and deterioration of intellectual and will power. At times there are periodic attacks of mental perturbation that may become true insanity. Even the mild form of epilepsy known as Jacksonian epilepsy, and consisting not of general convulsive movements, but of convulsive movements in only one member or one side of the body, are, if allowed to continue, followed by some mental disturbance. It would seem as if the explosion of nerve force in the brain centres,--which, physiologically speaking, an attack of epilepsy evidently is,--causes eventual deterioration of the physical basis of mind and will, so that mental operations can no longer be performed with their wonted expertness or accuracy, nor decisions made as rationally as before. In general, it is well understood that the more serious the epilepsy the more liability there is of the development of permanent mental disturbance. The earlier in life the epilepsy declares itself, too, the more unfavourable is the prognosis as to the enduring retention of complete mental sanity. In people in whom the epilepsy commences late in life, the process of mental deterioration does not begin to be noticeable so soon as when it occurs in younger years, and besides, it practically never runs a rapid course. Epilepsy, however, developing late in life, unless for some special cause, as injury or the development of syphilitic tumours in the brain, is an extremely rare affection. Idiopathic epilepsy, that is, epilepsy for which no definite cause can be discovered, is usually dependent on hereditary instability of the nervous system and is typically a disease of early years, of childhood {258} and adolescence. According to the best authorities, about one-fourth of the cases of epilepsy make their appearance before the age of 7 years. Over 50 per centum of all cases develop before puberty. About one-third of all the cases develop between 14 and 20. And even of the remaining, less than 20 per centum, over 12 per centum develop between 20 and 25, leaving scarcely more than 5 per centum for all the remaining years of life.