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In that wide field of psychopathic deficiency where Science has demarcated the diseases of epilepsy, hysteria and neurasthenia, we meet scattered observations concerning certain rare states of consciousness as to whose meaning authors are not yet agreed. These observations spring up sporadically in the literature on narcolepsy, lethargy, automatisme ambulatoire, periodic amnesia, double consciousness, somnambulism, pathological dreamy states, pathological lying, etc.
These states are sometimes attributed to epilepsy, sometimes to hysteria, sometimes to exhaustion of the nervous system or neurasthenia, sometimes they are allowed all the dignity of a disease sui generis. Patients occasionally work through a whole graduated scale of diagnoses, from epilepsy, through hysteria, up to simulation. In practice, on the one hand, these conditions can only be separated with great difficulty from the so-called neuroses, sometimes even are indistinguishable from them; on the other, certain features in the region of pathological deficiency present more than a mere analogical relationship not only with phenomena of normal psychology, but also with the psychology of the supernormal, of genius. Various as are the individual phenomena in this region, there is certainly no case that cannot be connected by some intermediate example with the other typical cases. This relationship in the pictures presented by hysteria and epilepsy is very close. Recently the view has even been maintained that there is no clean-cut frontier between epilepsy and hysteria, and that a difference is only to be noted in extreme cases. Steffens says, for example—"We are forced to the conclusion that in essence hysteria and epilepsy are not fundamentally different, that the cause of the disease is the same, but is manifest in a diverse form, in different intensity and permanence."
The demarcation of hysteria and certain borderline cases of epilepsy from congenital and acquired psychopathic mental deficiency likewise presents the greatest difficulties. The symptoms of one or other disease everywhere invade the neighbouring realm, so violence is done to the facts when they are split off and considered as belonging to one or other realm. The demarcation of psychopathic mental deficiency from the normal is an absolutely impossible task, the difference is everywhere only "more or less." The classification in the region of mental deficiency itself is confronted by the same difficulty. At best, certain classes can be separated off which crystallise round some well-marked nucleus through having peculiarly typical features. Turning away from the two large groups of intellectual and emotional deficiency, there remain those deficiencies coloured pre-eminently by hysteria or epilepsy (epileptoid) or neurasthenia, which are not notably deficiency of the intellect or of feeling. It is essentially in this region, insusceptible of any absolute classification, that the above-named conditions play their part. As is well known, they can appear as part manifestations of a typical epilepsy or hysteria, or can exist separately in the realm of psychopathic mental deficiency, where their qualifications of epileptic or hysterical are often due to the non-essential accessory features. It is thus the rule to place somnambulism among hysterical diseases, because it is occasionally a phenomenon of severe hysteria, or because mild so-called hysterical symptoms may accompany it. Binet says: "Il n'y a pas une somnambulisme, état nerveux toujours identique à lui-même, il y a des somnambulismes." As one of the manifestations of a severe hysteria, somnambulism is not an unknown phenomenon, but as a pathological entity, as a disease sui generis, it must be somewhat rare, to judge by its infrequency in German literature on the subject. So-called spontaneous somnambulism, resting upon a foundation of hysterically-tinged psychopathic deficiency, is not a very common occurrence and it is worth while to devote closer study to these cases, for they occasionally present a mass of interesting particulars.