Here, then, is a comprehensive and reasonable way of regarding these multifarious hallucinations or sensory automatisms. They are phenomena which must neither be feared nor ignored, but rather controlled and interpreted. Nor will that interpretation be an easy matter. The interpretation of the symbols by which the retina represents the external world has been, whether for the race or for the individual, no short or simple process. Yet ocular vision is in my view a simple, easy, privileged case of vision generally; and the symbols which represent our internal percepts of an immaterial world are likely to be far more complex than any impressions from the material world on the retina. All inward visions are like symbols abridged from a picture-alphabet. In order to understand any one class of hallucinations we ought to have all classes before us. At the lower limit of the series, indeed, the analysis of the physician should precede that of the psychologist. We already know to some extent, and may hope soon to know more accurately, what sensory disturbance corresponds to what nervous lesion. Yet these violent disturbances of inward perception--the snakes of the drunkard, the scarlet fire of the epileptic, the jeering voices of the paranoiac--these are perhaps of too gross a kind to afford more than a kind of neurological introduction to the subtler points which arise when hallucination is unaccompanied by any observable defect or malady. It is, indeed, obvious enough that the more idiognomonic the hallucination is, the more isolated from any other disturbance of normality, the greater will be its psychological interest. _An apparently spontaneous modification of central percepts_--what phenomenon could promise to take us deeper into the mystery of the mind? Yet until quite recently--until, in short, Edmund Gurney took up the inquiry in 1882--this wide, important subject was treated, even in serious text-books, in a superficial and perfunctory way. Few statistics were collected; hardly anything was really known; rather there was a facile assumption that all hallucinations or sensory automatisms _must_ somehow be due to physical malady, even when there was no evidence whatever for such a connection. I must refer my readers to Gurney's résumé in his chapter on "Hallucinations" in _Phantasms of the Living_, if they would realise the gradual confused fashion in which men's minds had been prepared for the wider view soon to be opened, largely by Gurney's own statistical and analytical work. The wide collection of first-hand experiences of sensory automatisms of every kind which he initiated, and which the S.P.R. "Census of Hallucinations" continued after his death, has for the first time made it possible to treat these phenomena with some surety of hand.[103]