Hallucinations. To realise in any proper way what memory is from the physiological point of view, we must assume that every impression on the senses is conducted by molecular movements through the nerves to the ultimate cells of the brain, which then undergo a certain molecular change that is revealed to consciousness as the qualities of the thing seen or heard or felt. By a process of instinctive reasoning the thing itself is thus instantly realised in the grown man, but not in the child. This molecular change in the cells may be evanescent, or it may be lasting. When lasting, the impression may be said to be 'registered,' so that it can come before consciousness again, and be 'remembered.' Each act of memory of the same impression in a healthy brain adds to the distinctness of the registration, and it is thus more and more easily recalled or suggested, either spontaneously or from without. The millions of brain-cells contain an inconceivable number of such registered impressions of things seen, heard, touched, smelt, and tasted, besides the impressions of past states of feeling, past trains of thought, and recombinations of them by means of the imagination. It is in no way thought a strange thing that we can recall all these in memory at any time, or that by unconscious processes of association they project themselves across the field of consciousness irrespective of our wills. It is not thought so very strange that, when we take a dose of opium or cocaine, the registered images lying in the brain-cells rise up and come across our consciousness so vividly that we cannot distinguish between them and real objects seen with the eyes. The same phenomenon often occurs in conditions of half sleep. In dreaming the impressions appear perfectly real to the half-consciousness existing at the time.
Now there are certain very sensitive people, who have an element of the morbid in their brain condition or heredity similar to the morbidness caused by a dose of cocaine. This being so, what is the difficulty in believing that those registered brain images should stand out, and seem to the consciousness as real as the original impression, and so produce a hallucination, or a subjective impression from an image already in the brain that is practically the same to the consciousness as the impression from a real object? This is in no way more remarkable than memory itself. It is simply more unusual. It is very questionable whether the original acts of memory of the young child are not all of the nature of hallucinations. The after recollections of things seen and of things imagined are certainly so real to some children that they confuse them with things seen or experienced. If a man can by using tests, and by the use of his reason, be made to know that the thing that appears to be seen and real is not so, and has no objective existence where he sees it, and that it is his brain that is playing him a trick, he has a sane hallucination. If he cannot be made to do so, and thinks it a real object, he is insane to this extent. The condition of hypnotism illustrates the origin of hallucinations better than almost anything else. Hypnotism (q.v.) is a modified, artificially-induced sleep, in which the consciousness is changed but not abolished, and the reasoning power much impaired. If a person hypnotised is told that a piece of ice is red-hot, he will not touch it, and if he is made to do so, he behaves as if he had touched hot iron. His whole mental condition is one of temporary hallucinations of every sort. Yet in the face of all these scientific facts and reasonable hypotheses and deductions we have persons calling in the aid of imaginary forces, 'telepathy,' 'spirits,' 'psychic force,' &c., to explain hallucinations, and associations formed for 'psychical research,' evidently on the theory that there can be a cause for hallucinations other than the registered images in the brain itself, together with altered conditions of consciousness. Many religious leaders and others in a state of intense brain excitement from religious or other causes have had hallucinations, after they had been sinning against nature's laws by depriving themselves of sleep and of exercise, and by exposing themselves to the contagion of morbid feeling interspersed by reason or common sense. Luther's seeing the devil, and throwing his ink-bottle at him, and Swedenborg's seeing spiritual beings among the ministers at the council board are certainly explicable on the theory of suggestion and a temporary morbidness of brain-working.
But, say the telepathists, 'two people have had the same hallucination at the same moment. How can that be explained on brain-cell principles?' If two people had been thinking of the same thing—for example, a dear friend or relative of both who was ill and supposed to be dying—and if both were sensitive persons, and their feelings were very excited at the time, what marvel is it if through a rare coincidence they had seen the form of the dying friend? And if this impression happened to be near the time when he died, is it remarkable in the unscientific state of most minds that they made out it was the same moment that they both saw their friend's form appear and walk out at the door? When such duplicate hallucinations are probed by hard scientific methods it is always found that the hour of seeing them by the two people was not quite the same, that one had previously made a suggestion to the other forgotten in the excitement of the moment, or that the figures seen by them had on different clothing, or had quite different beards. Without far more evidence than has been brought forward by the pseudo-scientific believers in ghosts and apparitions, an age of science will never admit a hallucination to be anything but a brain phenomenon, obscure perhaps, but no more obscure than many other correlated facts of brain and mind. Every advance that is made in our knowledge of the brain and its working in relation to mind renders the rational and scientific explanation of all the hallucinations of the same recorded by trustworthy, unbiased observers more easy and probable, and makes less excusable the calling in to explain the facts of new and unknown 'forces' or 'influences' in nature beyond those we know and can scientifically investigate. Hallucinations may be of all the senses, and may be of every degree of variety and complication, from flashes of light to armies of men, from hummings in the ear to strains of 'celestial music.' But it has never been proved, as ought certainly to have occurred if there was any reality in those occult forces, that anything has ever been seen or heard by any one which the person might not possibly have seen or imagined previously, so that its image might be lying registered in his brain-cells; and no new knowledge has ever come to humanity from such sources. Hallucinations were much more common among primitive peoples and in the early ages of the world than they are now. See INSANITY.