In medical jurisprudence. A trick or deceit of the senses; a morbid error either of the sense of sight or that of hearing, or possibly of the other senses; a psychological 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 a voice or other sound when nothing strikes his ear. Hallucination does not by itself constitute insanity, though it may be evidence of it or a sign of its approach. It is to be distinguished from “delusion” in this, that the latter is a fixed and irrational belief in the existence of a fact or state of facts, not cognizable through 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 external object, perceptible by the senses, but having no real existence; or, in so far as a delusion 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. For example, if a man should believe that he saw his right hand in its proper place, after it had been amputated, it would be an hallucination; but if he believed that his right hand was 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, but their evidence is rejected by the mind on account of the existence of an irrational belief formed independently of them. They are further distinguished by the fact that hallucinations may be observed and studied by the subject himself and traced to their causes, or may be corrected by reasoning or argument, while a delusion is an unconscious error, but so fixed and unchangeable that the patient cannot be reasoned out of it. Hallucination is also to be distinguished from “illusion.” the latter term being appropriate to describe a perverted or distorted or wholly mistaken impression in the mind, 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, as above stated, there is no objective reality to correspond with the imagined perception.