organs; there is in each organ also a receiving nervous surface; there is from this surface, leading unto the man, a communicating nervous cord; and, at last, ending the communicating cord is a nervous centre, in ready communication with a congeries of nervous centres, for taking up the impression conveyed, for fixing it, and for bringing it into union with other impressions that have already been received, fixed, associated. Suppose all these parts at all times natural, at all times in harmony, then everything that seems unnatural would be fairly ascribed to the reception of actual outward manifestations that are not of the common denomination of nature. Suppose, on the other hand, that these parts are not always in harmonious working order, then the design unfolds itself that there may be impressions, made by or within the man, that are mysterious, unreal in so far as the true reading of the outer universe is concerned, and, in a word, hallucinatory.

And this is what physical science teaches, that each of the parts named as factors are, at times, disturbed or deranged in function. The collecting organ may be at fault; the receiving nervous surface may be at fault; the communicating cord may be at fault; the receiving centre may be at fault: and, in accordance with error of function in one or more of the parts, there will be aberration varying from that which is simply physical to that which is psychological in the most refined degree.

The simplest illustration of derangements of function are met with when there is perversion of action in the collecting organ, as in the eye, in instances of colour blindness or of muscæ volitantes-floating specks appearing in the field of vision. More complex, is a condition in which the reception of an impression on the receiving nervous surface of an organ of sense is too long retained, so that the impression remains when the first cause of it is gone.

Sir Isaac Newton, looking too intently at the sun, had left upon his vision a vivid picture of the sun, a phantom to some men, to him a phenomenon, painfully persistent, but understood by him as a pure physical fact. I knew once a gentleman who had a peculiar impression of an odour left on his olfactory surface, and for months it remained a source of constant discomfort, anxiety, and even timidity. In vision an aberration of function in the receiving surface may occur from mere strain to see in obscurity. Thus in looking at an object in partial darkness, as at night, when the stars are beclouded, an object, steadily and strainingly gazed at, seems to come and go, or, as is commonly said, to vanish and reappear.

There are various states of the nervous organization in which the conduction of external impressions from the organs of

sense to the sensorium is so perverted that modifications of external impressions are both induced and sustained. The delicate muscular mechanism by which the two great organs of the senses, the eye and the ear, have their various parts correctly adapted, are under refined nervous control, and easily loose their adaptations when the nervous control is either defective or changed from its natural use. The nervous atmosphere through which impressions vibrate from the receiving surface to the receiving centres is susceptible of change, and thus under various circumstances there is an easy step to perverted appreciation of external things. We have many known agents which exert their power by thus interfering with the healthy relations that should subsist between the organs of sense, the conducting way, and the mental centres to which all impressions are finally delivered. Alcohol taken in excess leads to such disturbance of balance of action, and therewith to false impressions of external objects-phantoms not made by the imagination, but constructed out of perverted sensual action. Opium, haschish, and some vapours and gases made to enter the body, induce the same perversions. So that objects that are really before the observer to the perverted sight appear far distant, or larger or smaller than they are. Slight sounds are exaggerated into tempestuous noises, and sensations of smell, taste, and touch, are either exalted into undue activity or lost altogether.

In connection with this subject I may observe that the tendency of recent physiological research is to the effect that in certain conditions of the body there are produced, within the body itself, some organic products which in the most potent manner affect the organs of the senses, and interfere with their function. In a recent investigation on the action of organic compounds of the sulphur series, I found that the most marked changes in the reception of impressions could be induced by certain of these bodies, together with symptoms of hysteria and of muscular debility singularly analogous to those states of the body in which debility of the motor organs is attended with what is called excessive nervous susceptibility and excitability. In certain diseased states these same organic products exhale from the body, or pass off by the secretions, as products derived from organic chemical changes progressing within the organism.

It would be an easy task to fill page upon page with illustrations of translations of external objects into mysterious manifestations under the mere influence of perverted functions of the senses and their dependent parts; but I must forbear, and content myself with one remark in reference to these phenomena. The remark is this: that the man, under any of the influences cited, is never supposed to be anything less than de

ceived. The man suffering from muscæ volitantes explains the
form of the shadowy things he sees with the utmost exactitude,
he may (I have known such a case) give to the appearances fanci-
ful names from their forms; yet it is not at any time supposed
that the seeings are realities: the man who tells you a red
object is colourless, or is of different colour to what all other
men call red, is considered, however persistent he may be in his
opinion, peculiar only and deluded: the man who explains that
he sees but the half of an object, or that he sees two objects
when there is but one before him, is at once accepted as in-
correct in his observation: the man who, under opium or
haschish, receives the impression of being in rooms of infinite
space, of grasping in one sweep of apprehension incalculable
intervals of history, is held to be for the time of disordered
mind: and the man who, under the poison of alcohol, turns the
simplest of objects into the likeness of the fiend, is credited
with obvious derangement so long as he thus misinterprets what
exists before him. Yet there are many persons who, recognis-
ing such everyday truths to the full, accept other hallucinatory
phenomena, of a similar origin, as actual external realities, and
who, once believing it, adhere to the opinion they have formed
more determinately than to any ordinary fact or business with
which they are hourly concerned. The story is an old one:-
"John Absolute believed he could not be deceived,
When to prove his own belief he took the pains;

So he vowed he'd seen a ghost, though he'd felt it was a post,
And his head had paid the forfeit for his brains."

The illusions depending upon changes of functions in the receiving nervous surface of an organ of sense, or in the conducting cord, are comparatively simple. It is when we come to consider the reception and the fixing of impressions in the brain that the profoundest difficulties arise. Here we pass, with ease, out of the domain of current physical science into what is but useless speculation, unless we are ever on our guard in thought. I shall touch, consequently, on but few subjects; on such as are nearest to the physical basis of research.

The brain receives and retains external impressions brought to it through the senses. In the exercise of this function it may become unduly impressionable, and may be the seat of illusion. Under these circumstances, one particular impression may so overrule every other impression that it shall persistently present itself. Sometimes a sudden impression is made upon the brain so potently that it is stamped, as it were, in persistent relief, coming forward at any time-but specially when the mind is unoccupied or is weakened—with all the force of a new reality. The distinguished French

physician, Andral, one of the most accurate of observers and least superstitious of men, affords an illustration of this illusion. When he was a pupil commencing his medical studies, he was terribly impressed at seeing, for the first time, a dead body on the lecture-table. Many years afterwards, during an attack of illness, he saw in his room a dead body stretched out before him, and it was not until some minutes had elapsed that he recalled the connection between this outward vision and the early impresIsion that had been made upon his brain. I know myself another instance, differing in detail, but belonging to the same order of phenomena. A youth, who had all his life been easily moved by any painful sight, entered the profession of medicine, and saw, as a first experience, an eminent surgeon perform the operation of amputation at the shoulder-joint. This was before the introduction of means for the abolition of pain, and the effect on the mind of this observer was terrible. He did not faint, as some of his neophyte comrades did, but stood resolutely transfixed in wonder and fear. In time he got over the dread, from that moment lost all dread at seeing operations, and, in fact, has himself many hundred times since taken part in surgical art. But this remains, that whenever he is present at any operation, the first operation that so impressed him is always present to him in its minutest details, as if it also were veritably in progress.

Connected with this form of hallucination is that of hearing sounds, with which the ear has been at one time very familiar, without external obvious cause. Dr. Samuel Johnson, in this. manner, heard, he believed, the sound of his mother's voice calling his name, Sam! when separated from him by the distance between Lichfield and Oxford.

In studying this class of illusion, it is necessary to observe that the illusion is not an act or effort of memory: i.e. it is not an effort called forth by any act of volition. It is akin to that singular sensation which they who have lost a limb occasionally experience, spontaneously, as if the limb were still in its place, and were endowed with sensibilities it once had, but which practically are forgotten. It is the source of that illusion of "pre-existence" which many have experienced, when a recognition seems to be felt of something already known, and which the memory is utterly unable, however severely it is taxed, to recall. In a word, it is illusion suns volition.

A number of mysterious manifestations are traceable to the simple fact of recurrence of impressions altogether independently of the will. There are others which are purely volitional, and these constitute a distinct class of hallucinatory phenomena. They are illusions produced by what I should call the faculty of projection of objects that have been received from

without, by the brain and fixed in it. We exercise this faculty, naturally, when at will we re-picture to ourselves, or project what we have seen, heard, felt, or otherwise received by the senses. We recall a landscape we have surveyed, a tune we have heard, and the like; and if the impression be correctly fixed in us, and we will it to return, it comes back correctly. In the act we project from us that which we recall, and look at it, or listen to it, as if it were again external to us. This faculty, exalted to unnatural degree, is a fruitful source of illusion. Wigan supplies a striking illustration of the kind in the case of an eminent portrait painter who followed Sir Joshua Reynolds. The painter in question once produced three hundred portraits from his own hand in one year. When asked on what this peculiar power of rapid work depended, he answered that when a sitter came to him, he looked at him attentively for half an hour, sketching from time to time on the canvas; then he put away the canvas and took another sitter. When he wished to resume the first portrait, he said, "I took the man and put him in the chair, where I saw him as distinctly as if he had been before me in his own proper person. When I looked at the chair I saw the man." After a while the painter began to fail to discover the difference between the real and the imaginary sitters, so that he became actually insane and remained in an asylum for thirty years. Then his mind was restored to him, and he resumed the use of the pencil; but the old evil threatened to return, and he once more forsook his art, soon afterwards to die.

Talma, the actor, had a faculty of mental projection equally singular with that possessed by the artist whose history Wigan has related. Talma could project before himself the form of a human skeleton with such perfection of detail that to him the form was a reality, and when he stood before the footlights he had in his presence, in the theatre, an audience of skeletons. Goethe, who conceived that if Shakespeare was the greatest of men who had lived he himself was the second, once projected his own figure and viewed it as if it had been another person.

I might prolong the record of these hallucinations, but to prove that they exist is all sufficient for the purpose I have in view. They are, the reader will see, nothing more than the results of an exaggeration of a natural faculty, which faculty, well possessed is a marvellous accomplishment, but over possessed is a disaster to the possessor.

There is another form of hallucination, having its seat in the brain, and which springs from what has been called the effect of the imagination. Imagination, brought to its true meaning, is the art of the will to combine into various groups the pictures or impressions that have been condensed in the brain through