Importance of the study of hallucinations - Definition of authors - Outline of the principal classifications - Character of the one presented by the author.

The psychological history of man does not offer a more curious question than that of hallucinations. To see what no eye perceives, to hear what no ear hears, to be convinced of the reality of sensations to which all are incredulous - does not this present matter for research full of interest?

Hallucination, recorded in the annals of every people, and in the lives of the greater number of celebrated persons, and existing as a creed through a long vista of ages, is, doubtless, restrained by the progress of science; but, such as it now appears, its study becomes a matter of high import, from the part it plays in a host of psychological phenomena, its intervention in many diseases, and particularly in mental affections.

What is hallucination? How can it be defined? Is it simple, or combined with other morbid conditions? Such are the different questions with which we shall commence our work.

Aristotle, Zeno, and Ghrysippus, among the ancients, were, in a degree, aware of a false perception, and endeavored to distinguish it from true perception; they described three sorts of hallucinations - those of the sight, of the hearing, and of smell; but they neither noted all the degrees nor all the conditions of its existence.

The definition of hallucination does not appear to trace to a period far back; Arnold is, we think, the first who gave it any completeness of form. "Ideal insanity," said he, "is the intellectual state of a person who believes he sees and hears what no other person sees or hears; who imagines he converses with spirits, perceives things impalpable to the senses, or that do not exist outwardly such as they appear to him; or who, when he sees external objects in their reality, has false and absurd ideas of his own form, and of the palpable qualities of objects."*

One cannot but see in this definition, certainly somewhat long, the distinction of hallucinations and illusions, as also errors of personality.

Al. Crichton, who wrote about the same time, defined hallucination or illusion, as a delusion of mind, in which fancies are mistaken for realities, and real objects become falsely represented, without any general derangement of the intellectual faculties.†

Sauvages, with Felix Plater, called hallucination a false perception caused by imperfection of the external senses; and included, under the vague term delirium, that the principle of which is in the brain itself. Amongst hallucinations, he placed vertigo, double-sight, tingling in the ear, hypochondria, and somnambulism. Darwin, in his Zoonomia, admits the opinion of the two preceding authors.

By the word hallucination, Ferriar understands all deceitful impressions, from the fly that flutters before the eye to the most frightful spectre.‡

According to Hibbert, hallucinations are merely ideas and recollections, so vivid as to surpass real impressions. §

Esquirol, the first in France who gave a precise sense to the word hallucination, has applied it to phenomena neither dependent on a local lesion of the senses, nor on a vicious association of ideas, nor on the effect of imagination, but solely on a particular, and, as yet, unknown lesion of the brain; he defines hallucination as a cerebral or psychical phenomenon, acting independently of the senses, and consisting in external sensations, that the patient believes he experiences, although no external agent acts materially on his senses. In another part of his book, he says: "The professed sensations of the hallucinated are images, and ideas, reproduced by memory, associated by imagination, and personified by habit."

* Arnold's Observations on the Nature, Kinds, Causes, and Prevention of Insanity; two vols. 8vo., 2d edition, t. 1, p. 55, London, 1806. First edition published in 1782.

† Alex. Crichton, An Inquiry into the Nature and Origin of Mental Derangement, t. 2, p. 342, London, 1798.

‡ An Essay towards a Theory of Apparitions, p. 95, London, 1813.

§ Samuel Hibbert, Sketches of the Philosophy of Apparitions, 2d edition, p. 1, London, 1825.

This second definition has been strongly attacked as being neither logical nor consonant with facts. We will not bring forward the criticism to which it has been subjected, but we consider it more brilliant than correct.

M. Fabret, in his Lectures upon Mental Diseases, published in the Gazette des Hopitaux for 1850, adopts Esquirol's opinions, though with some slight modifications.

Darwin, and subsequently M. Faville, considered hallucinations as a lesion of the organs of sense. On this hypothesis, a false perception, always the same, is assumed to exist; but it is impossible to adopt it for the hallucinations that are connected with the habitual ideas of the individual, or with those which are prevalent at certain historical epochs.

According to M. Calmeil, hallucinations are ideas that are converted into material impressions, and are carried into action on the external senses, although the nervous system of the periphery is passive. But this physician goes farther, since he admits that the peripheric nervous system may be the starting-point for the most varied, and probably the most numerous, hallucinations. M. Calmeil combines hallucinations and illusions.

Mons. Lelut considers hallucinations to be an intermediate phenomenon between sensation and conception. This phenomenon he regards as a spontaneous transformation of thought into sensations generally external.

M. Bland has attacked this definition, by remarking that hallucination cannot be a transformation of thought, because thought, immaterial in its nature, has no form, consequently cannot be transformed, nor become material like a sensation, viewed by the impulse which produces it.*