§ 10. I have throughout tried to express what I have called the centrifugal theory in such terms that it might be accepted even by those who locate the sensory centres themselves not below, but in, the cortex. According to these physiologists, the whole double transformation, of physical impressions into visual or auditory sensations, and of these sensations into complete perceptions and mnemonic images, would be practically referred to one place. It must be admitted that this view seems at times connected with the want of a due psychological distinction between sensation and perception. But even supposing a specific centre of sensation to be thus equally the seat of psychic functions higher than sensation, it would still be none the less liable to be stimulated by parts of the cortex external to itself; and the nature of many hallucinations would still indicate that they depend on this stimulation, and not on a mere spontaneous quickening of morbid activity in the centre itself. For instance, a girl is violently distressed by seeing her home in flames, and for days afterwards sees fire wherever she looks.2 One must surely trace the hallucination to the distress, and so to an "escape of current" from the seat of ideas and images other than visual ones.

Again, in the conditions described above, where the hallucinations faithfully reflect the changes of the whole moral and intellectual bias, the local excitement in the sensory centre would still be traceable to an abnormally strong irradiation from the regions where the highest co-ordinations take place - these regions being themselves, ex hypothesi, already in a state of pathological activity. The other hypothesis would be that the mere hyper-excitability at the centre itself made it impossible for images to arise without getting hurried on, so to speak, into sensations by the violence of the nervous vibrations.1 But then, what should cause images belonging to one particular order of ideas - the order which happens to be diseased - to be picked out for thi3 fate in preference to any others? The hyper-excitable centre in itself, as an arena of images, could have no ground for such a partial selection among the crowd of them which emerge during every hour of waking life. Among the endless and multiform vibrations involved, why should the excessive amplitude that corresponds to sensation be confined to a particular set? A reason must exist.

The unique agreement between the sensory hallucinations and the more general moral and intellectual disorder must have its particular physical counterpart; and for this " a strong downward escape of current" is at any rate a sufficiently comprehensible metaphor.

1The view has been maintained that this process consists merely in the removal of an inhibition normally exercised on the sensory centres from above. (See, e.g., Kandinsky in the Archiv fur Psychiatrie for 1881.) But this seems to ignore the whole of the facts which support the theory of "ideational excitation".

2Griesinger, Op. cit., p. 99. For an auditory case, see the account, in the Lyon Medical, vol. xxxv., p. 437, of a young Frenchman who was rendered insane by the German invasion, and who was then haunted by the sound of guns firing.

1 This seems to be what Wundt has in view when he speaks of hallucinations as originating, not in an actual irritation, but in a heightened irritability, of the sensory centres (Op. cit., vol. ii., p. 357); and such a state may doubtless contribute to the effect, even where the disturbance is plainly propagated from above. There are even special cases of "ideational excitation" of which an abnormal strain or instability at the lower place seems a more prominent condition than an abnormal pressure at the higher. We might thus explain the echoing hallucinations, where a person finds that what he is reading to himself repeats itself audibly - the occasion for the discharge being here no doubt the slight reverberation which the mere idea of words may be supposed to set up at the auditory centre. (See Kraepelin, Op. cit., p. 356.) Very comparable are the hallucinations which present themselves only when a certain amount of external stimulation is supplied. For example, a man finds an old hallucination of hearing recur when people are talking in his neighbourhood, though able at the same time to distinguish what they are saying (Kahlbaum, Op. cit., pp. 7, 8, 27), another is troubled by insulting voices at night only when the patients in adjoining rooms are audibly speaking or moving (Koppe, Op. tit., p. 49). And with these may perhaps be classed the hallucinations, primarily due to lesions of the eye, which are found to be greatly favoured by a multiplication of external impressions, as by a visit to a busy city (Voisin, Op. cit., p. 71).