In medical jurisprudence. A trick or deceit of the senses; a morbiderror either of the sense of sight or that of hearing, or possibly of the other senses; apsychological state, such as would be produced naturally by an act of sense-perception,attributed confidently, but mistakenly, to something which has no objective existence ;as, when the patient imagines that he sees an object when there is none, or hears avoice or other sound when nothing strikes his ear. See Staples v. Wellington, 58 Me.459; Foster v. Dickerson, 64 Vt 233, 24 Atl. 257; McNett v. Cooper (C. C.) 13 Fed. 590;People v. Krist 168 N. Y. 19, 60 N. E. 1057.Hallucination does not by itself constitute insanity, though it may be evidence of it ora sign of its approach. It is to be distinguished from “delusion” in this, that the latter isa fixed and irrational belief in the existence of a fact or state of facts, not cognizablethrough the senses, but to be determined by the faculties of reason, memory,judgment, and the like; while hallucination is a belief in the existence of an externalobject, perceptible by the senses, but having no real existence; or, in so far as adelusion may relate to an external object, it is an irrational belief as to the character,nature, or appearance of something which really exists and affects the senses. Forexample, if a man should believe that he saw his right hand in its proper place, after ithad been amputated, it would be an hallucination; but if he believed that his right handwas made of glass, it would be a delusion. In other words, in the case of hallucination,the senses betray the mind, while in the case of delusion, the senses act normally, buttheir evidence is rejected by the mind on account of the existence of an irrational beliefformed independently of them. They are further distinguished by the fact thathallucinations may be observed and studied by the subject himself and traced to theircauses, or may be corrected by reasoning or argument, while a delusion is anunconscious error, but so fixed and unchangeable that the patient cannot be reasonedout of it Hallucination is also to be distinguished from “illusion,” the latter term beingappropriate to describe a perverted or distorted or wholly mistaken impression in themind, derived from a true act of sense-perception, stimulated by a real external object,but modified by the imagination of the subject; while, in the case of hallucination, asabove stated, there is no objective reality to correspond with the imagined perception.

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