§ 3. In its first form, the question is one between central and peripheral origin. Do hallucinations originate in the brain - in the central mechanism of perception? or in some immediate condition of the eye, or of the ear, or of other parts? or is there possibly some joint mode of origin?

For a long time the hypothesis of an exclusively central origin was much in the ascendant. But this was greatly because - as already noted - Esquirol and the older writers did not recognise the sensory element as truly and literally sensation, but regarded the whole experience as simply a very vivid idea or memory. If the central origin is to be established, it must be by something better than arbitrary psychological distinctions. Hibbert and Ferriar, going to the other extreme, contended that the memory was a retinal one; if a man sees what is not there, they held, it can only be by a direct recrudescence of past feeling in his retina. "But," urged Esquirol, "the blind can have hallucinations of vision; the deaf can have hallucinations of hearing; how can these originate in the peripheral organs? " The obvious answer, that this did not necessarily thrust the point of origin back as far as the cerebrum, does not seem to have been forthcoming; and the opposite party preferred to fall back on definite experiment. They pointed out, for instance, that visual hallucinations often vanish when the eyes are closed; or that they may be doubled by pressing one eyeball.

There was not enough here, however, to show that the external organs so much as participated in the process, much less that they originated it, even in these particular cases; while for other cases the observations did not hold. The fact that external objects are hidden from view by the interposition of our own eyelids or any other opaque obstacle, has become to us a piece of absolutely instinctive knowledge; and we should surely expect that an object which was but the spontaneous projection of a morbid brain, might still be suppressed by movements and sensations which had for a lifetime been intimately associated with the suppression of objects. And as for the doubling by pressure of one eyeball, it might fairly have been represented as telling against the theory of retinal origin. For the impression - not coming from without - would cover the same retinal spot after the displacement of the eyeball as before; and the natural hypothesis seems certainly to be that retinal identity would, in its mental effect, overpower the sensation of the moved eyeball's position.1

1The obliteration by closure of the eyes is certainly not invariable. See, e.g., Dr. Voisin, Lecons Cliniques sur les Maladies Mentales, p. 72. Sir J. F. W. Herschel, in his Familiar Lectures on Scientific Subjects, p. 406, has described some hallucinations of his own, of which "the impression was very strong - equally so with the eyes open or closed." As regards the failure of lateral pressure to double the image, I do not know whether any clear case has been recorded. Brewster, indeed, speaks of the ' immobility of the image when the eyeball is displaced; but he made no sufficient distinction between actual hallucinations and mental pictures; while he had an odd notion that even the latter were "painted" on the retina. (Letters on Natural Magic, 1868, p. 131).

An immense advance was made by Baillarger, who maintained the central origin by really scientific arguments. He pointed out (1) that the external organ may often be affected by local irritants - inflammation, blows, pressure, galvanism - without the production of any more pronounced form of hallucination than flashes, or hummings; that is to say, the peripheral stimulation sometimes fails to develop hallucination, even under the most favourable conditions; (2) that there is a frequent correspondence of hallucinations of different senses - a man who sees the devil also hears his voice, and smells sulphur - and that it is impossible to refer this correspondence to abnormalities of the eye, ear and nose, occurring by accident at the same moment; (3) that hallucinations often refer to dominant ideas - a religious monomaniac will see imaginary saints and angels, not imaginary trees and houses. Hence, argued Baillarger, "the point of departure of hallucinations" is always " the intelligence" - the imagination and memory - which sets the sensory machinery in motion.1 He naively admitted that how this action of an immaterial principle on the physical apparatus takes place passes all conception; but it might be forgiven to a medical man writing forty years ago, if he had not fully realised " brain as an organ of mind," and so did not see that what he took for a special puzzle in the theory of hallucinations, is simply the fundamental puzzle involved in every mental act.