“I have myself also very frequently seen these phantasms, but am now less liable to them than formerly. It has become my custom when I perceive such images, immediately to open my eyes, and direct them upon the wall or surrounding objects. The images are then still visible, but quickly fade. They are seen whichever way the head is turned, but I have not observed that they moved with the eyes. The answers to the inquiries which I make every year of the students attending my lectures as to whether they have experienced anything of the kind, have convinced me that it is a phenomenon known to comparatively few persons. For among a hundred students, two or three only, and sometimes only one, have observed it. This rarity of the phenomena is, however, more apparent than real. I am satisfied that many persons would perceive these spectres if they learned to observe their sensations at the proper times. There are, however, undoubtedly many individuals to whom they never appear, and in my own case they now sometimes fail to show themselves for several months at a time, although in my youth they occurred frequently. Jean Paul recommended the watching of the phantasms which appear to the closed eyes as a means of inducing sleep.” If such phenomena take place in persons of healthy brains, the greater liability of the insane to experience them will readily be admitted. The character of dreams, as Macario[102] remarks, varies according to the type of insanity to which the patient is subject. In melancholia they are ordinarily sad and depressing, and leave a deep and lasting impression; in expansive monomania they are gay and exciting; in mania they give evidence of the extraordinary mental excitement and activity of the subject, and in duration they are vague, fleeting, and occur but seldom. ESSENTIAL MORBID DREAMS.--Under this head are comprehended the various forms of frightful dreams which are ordinarily designated under the name of nightmare. It has been my good fortune to have had the opportunity of carefully studying the phenomena of this singular affection in several persons of intelligence, and I propose, therefore, detailing the results of my own experience, after a short historical retrospect, which I hope will not prove uninteresting. Nightmare is characterized by the existence during sleep of a condition of great uneasiness, the principal features of which are a sense of suffocation, a feeling of pain or of constriction in some part of the body, and a dream of a painful character. There are thus two essential elements of the affection--the bodily and the mental. At a very early period the phenomena of nightmare attracted the attention of physicians. Hippocrates[103] describes it in the following words: “I have often seen persons in their sleep utter groans and cries, appear as if suffocated, and throw themselves wildly about until they finally waked. Then they were in their right minds, but were, nevertheless, pale and weak.”