Passing him this, we may say that his treatment of the question entitles him to the credit of the second great discovery about hallucinations. He had already made clear their genuinely sensory quality; he now made equally clear the fact that the mind (or its physical correlate) is their creator - that they are brain-products projected from within outwards.

This is a most important truth; but it is very far from being the whole truth. Baillarger saw no via media between the theory which he rejected - that the nerves of sense convey to the brain impressions which are there perceived as the phantasmal object - and the theory which he propounded, that "the intelligence" (i.e., for us, the brain, as the seat of memories and images), of its own accord and without any impulse from the periphery, excites the sensory apparatus. It seems never to have struck him that there may be cases where the sense-organ supplies the excitant, though the brain supplies the construction - that irritation passing from without inwards may be a means of setting in motion the constructive activity. He took into account certain states of the organ - e.g., fatigue produced by previous exercise - as increasing the susceptibility to excitation from "the intelligence," and so as conditions favourable to hallucination; but he got no further.

The facts of hallucination absolutely refuse to lend themselves to this indiscriminate treatment. Following the path of experiment, we are almost immediately confronted with two classes of phenomena, and two modes of excitation. We need not go, indeed, beyond the elementary instances already mentioned. Fechner's experiment, where green was seen by an eye on which only white rays were falling, fairly illustrates Baillarger's doctrine - the green being produced not by an outer affection of the eye, but by an inner affection of the brain. But in the case of a person who has been staring at the sun, the "after-image" or hallucination can be clearly traced to a continuing local effect in that small area of the retina which has just been abnormally excited; and it will continue to present itself wherever the eye may turn, until rest has restored this area to its normal condition. A still simpler form of change in the external organ is a blow on the eye; and the resulting "sparks" are genuine though embryonic hallucinations.

1Baillarger, Des Hallucinations, pp. 426, 469, 470.

Such cases as these last are, however, hardly typical; for in them the brain is not truly creative; it merely gives the inevitable response to the stimuli that reach it from below. They are, moreover, normal experiences, in the sense that they would occur similarly to all persons with normal eyes. Let us then take another instance, where the mind's creative role is fully apparent, while at the same time the primary excitation is clearly not central. Certain hallucinations - as is well known - are unilateral, i.e., are perceived when (say) the right eye or ear is acting, but cease when that action is obstructed, though the left eye or ear is still free. Now this in itself could not be taken, as some take it,1 for a proof that the exciting cause was not central; it might be a lesion affecting one side of the brain. But very commonly, in these cases, a distinct lesion is found in the particular eye or ear on whose activity the hallucination depends.1 It is then natural to conclude that the hallucination was the result of the lesion, and that the one-sidedness of the one depended on the one-sidedness of the other; and the justice of the conclusion has been proved in many cases by the fact that the hallucination has ceased when the local lesion has been cured.

Other cases which strongly suggest a morbid condition of the external organ are those where the imaginary figure moves in accordance with the movements of the eye. The visual hallucinations of the blind, and the auditory hallucinations of the deaf, would also reasonably be referred to the same class - the seat of excitation being then, not necessarily the external organ itself, but some point on the nervous path from the organ to the brain. In the case, for instance, of a partly-atrophied nerve, the morbid excitation would be at the most external point where vital function continued.3 It should be noted, in passing, that a distinct lesion, e.g., atrophy of the globe, of one eye may give rise to hallucinations of the sound eye4 - the sight of which then receives, so to speak, the rebound of the central disturbance initiated by its fellow.

1Dr. Regis in L'Encephalc, 1881, p. 51; Prof. Ball in l'Encephale, 1882, p. 6.

2Dr. Regis in L'Encephale, 1881, p. 46; Dr. Voisin in the Bulletin General de Therapeutique, December 15, 1868, and Op. cit.t p. 68, etc.; Dr. Despine, Psychologie Naturelle, vol. ii., p. 29; Krafft-Ebing, Die Sinnesdelirien, p. 25; Dr. Koppe's paper on "Gehorsstorungen und Psychosen," in the Allgemeinc Zeitschrift fiir Psychiatrie, vol. xxiv., pp. 18-28 and 39-46.

3Delusions due to visceral disturbances are often quoted as cases of hallucination excited from parts below the brain. Thus a woman dying of peritonitis declares that an ecclesiastical conclave is being held inside her (Esquirol, Maladies Mentales, vol. i., p. 211). But here there is a prior and independent basis of distinct sensation; so that the experience would at most be an illusion. And it is hardly even that; for one cannot say that the false object is sensorially presented at all; no one knows what a conclave in such a locality would actually feel like; the conclave is merely a delire - an imagination suggested by sensation, but which does not itself take a sensory form.

4 Vienna Asylum Report, 1858, cited by Griesinger, Op. cit., p. 88.