§ 5. But in any case, imaginary objects which are projected on a convenient flat surface form a very outlying class. For the common run of visual hallucinations, even of those seen in good light, we cannot assume the necessity of any objective points de repere, or any definite external stimulation of the retina.1 On the contrary, they have every appearance of being centrally initiated, as well as centrally constructed. For instance, it is quite as easy to make the patient see objects in free space - say, out in the middle of the room; and such is the common form of spontaneous hallucination, both of sane and insane persons, where human figures are seen. The eyes are then focussed, not on the real objects from which points de repere would have to be supplied, but on the figure itself; which may be much nearer than the wall behind it, and may thus require a very different adjustment of the eyes. For eyes adjusted to the imaginary object, the real objects behind, though in the line of sight, may be quite outside the range of clear vision; and we can scarcely suppose points de repere to excite a percept whose position is such that, for it to be visible, they themselves must cease to be so.

And the difficulty of regarding external points of excitation as a necessary condition becomes even greater when the hallucination is a moving one. I refer not to the cases where the imaginary figure follows the movements of the eye, owing to some morbid affection of that organ which acts as a real moving substratum for it, but to those where the eye follows the figure in its seemingly independent course. Here we should have to assume that the point de repere keeps changing; that is, as the imaginary figure passes along the side of the room, in front of a multitude of different objects - pictures, paper, furniture, etc. - the very various excitations from these several objects act in turn as the basis of the same delusive image. There seem no grounds for such an assumption. What is there to produce or to guide the selection of ever-new points de repere? To what external cause could we ascribe the perpetual substitution of one of them for another? On the view that the figure may be centrally initiated, no less than centrally constructed, none of these difficulties occur. Such a figure may just as well appear in the empty centre of the room as on a piece of cardboard, and may just as well move as stand still. Stronger still are cases where . the hallucination is not in the line of vision.

Dr. Charcot has noted a curious form of unilateral hallucination, which occurs sometimes to hysterical patients with normal eyes, on the side on which they are hemian-aesthetic - animals passing rapidly in a row from behind forwards, which usually disappear when the eyes are turned directly to them.1 Another type where the hallucination passes out of the range of direct vision is presented by Bayle's case, where a spider used first to appear life-size, and then gradually to expand till it filled the whole room.2 Sir J. F. W. Hers-chel describes an analogous experience of his own. The same sort of argument applies to hallucinations where a figure appears repeatedly, but only in one place, while still not an illusion due to any real feature in the place - as in the case of a patient of Morel's,3 who always saw a headless man at the bottom of the garden, or of an informant of my own whose phantasmal visitant confined itself to a particular bed; and also where the percipient is haunted by a figure which can be seen only in one direction, as in Baillarger's case of a doctor who could not turn without finding a little black cow at his side.4 The mind may locate its puppet according to its own vagaries; and this last experience is very like a sensory embodiment of the well-known delusion that somebody is always behind one.

1It should be observed that light may favour, and darkness hinder, the projection of a phantasm, owing to the different effect of the one and the other on the general physiological state. The presence of light might thus be a necessity, quite apart from any distinguishable points de repere; and this may apply not only to a crucial case - as, e.g., where Professor Bernheim made a hypnotic "subject" see a phantom-balloon in a cloudless blue sky - but to the common type of hallucinations which cease when the room is darkened. In the same way the presence of light is occasionally found to be a condition of auditory hallucinations. (Ball, Lecons sur les Maladies Mentales, p. 116.) See also the very interesting case given by Professor F. Jolly in the Archiv fur Psychiatrie, vol. iv., p. 495. His paper is on the production of auditory hallucinations by the application of an electric current in the neighbourhood of the ear. In one case, he shows good reason for attributing the hallucination, not to a stimulation of the auditory nerve, but to a transference to the auditory centre of the stimulus given to fibres of the fifth nerve.

For the subjective sounds did not, as in all the other cases, correspond in a regular way to the opening and closing of the current, but appeared under all conditions in which pain was produced. See also Koppe (Op. cit., p. 54) on the same subject.