Sense-delusions can be suggested in various ways. We tell a subject that he sees a bird, and he does. We can suggest the same thing by gesture - for example, by pretending to hold a bird in the hand - particularly after the subject has received some hypnotic training. The chief point is that the subject should understand what is intended by the gesture.

Naturally, several organs can be influenced by suggestion at the same time. I tell some one, "Here is a rose"; at once he not only sees, but feels and smells the rose. I pretend to give another subject a dozen oysters; he eats them without it being necessary for me to say a word. The suggestion here affects sight, feeling, and taste at the same time. In many cases the muscular sense is influenced in a striking manner by such suggestions. I give a subject a glass of wine to drink; he lifts the pretended glass to his lips, and leaves a space between hand and mouth as he would if he held a real glass. I am not obliged to define the delusion for each separate sense; the subject does that spontaneously for himself. The subject in this way completes most suggestions by a process resembling the indirect suggestion described on page 67. The results of the external suggestion naturally depend on the character of the subject. I remember a case of chronic alcoholism being brought to me for treatment by suggestion. The patient had been accustomed to consume enormous quantities of alcohol daily. On the first few occasions that I hypnotized him, he made frantic efforts to drink any glass of wine I suggested.

In the course of time, however, I not only succeeded in making him a total abstainer, but even created in him such an aversion to alcoholic drinks that his friends could not but laugh at his quaint behaviour. The change was also very noticeable during hypnosis. At first he drank every glass of wine suggested with avidity, but later on he would push the imaginary glass of wine away with a gesture of disgust, sometimes even attempting to dash it to the ground.

Besides which, the deception, if it is thorough, is clearly reflected in the subject's expression and gestures. No gourmand could wear a more delighted expression over some favourite dish than does a subject over a suggested delicacy. The fear depicted on the face of a subject when he believes he is about to be attacked by a tiger is most impressive. A subject will drink several glasses of wine by suggestion, will become red in the face, and then complain of his head. I give a piece of cork to a subject for an onion; he smells it and his eyes fill with tears.

By means of suggestion, we can place a subject in any situation we please, and from his behaviour draw conclusions as to what his conduct would be under analogous circumstances, and also as to his character (Morselli). But it is necessary to exercise great caution in drawing such conclusions, since the subject nearly always has some dim consciousness of his real surroundings, however completely he may seem to be transported into the imaginary ones.

Some authors (Dumontpallier, Berillon) have particularly directed attention to the suggestions which take effect on one side of the body only. For example, we can cause a bird to be seen on the right side, a dog on the left; but this appears to be only a matter of suggestion and training. The case mentioned by Magnin is connected with this: a person affected by weak sight of the left eye, of hysterical origin, believed that he saw with the right eye things which he really saw with the left, and so thought they were on his right side when they were really on his left (allochiria).

In contrast with the delusions of sense hitherto described, which are sometimes called positive, there are also negative delusions of sense. The older mesmerists (Deleuze, Bertrand, Charpignon) published many observations of them. When the delusion is positive the hypnotic believes he sees what does not exist; when it is negative he fails to recognize the presence of an object really placed before him. For example, Mr. X. is in hypnosis. Two other persons are present besides myself. I tell him: "From this moment you will only be able to see me; you can no longer see the other men, though they are still here." The experiment is successful; X. replies to every question addressed to him by these gentlemen, and can feel them, but he cannot see them. This is a negative hallucination of sight only. But a negative hallucination of several senses can be induced as readily as a positive one. I say to X.: "The two men have gone away; you and I are now alone." From this moment X. neither sees nor hears them, nor perceives them by means of any sense. When I ask him who is in the room he replies, "Only you and I." The whole or part of any object or person can be made invisible in the same way.

We can cause people to appear headless and armless, or make them disappear by putting on a particular hat, as in the story. of the Magic Cap. The situation may be varied in any way we please. Forel has pointed out that the insane often have these negative hallucinations. He has also shown that hypnotics complete, and even extend, negative hallucinations. Thus, I say to X, while A. is sitting on a chair: "A. has gone away; there is nobody on that chair." X. examines the chair, and as he feels something there, he imagines that a shawl has been laid upon it. We see here how a suggested negative hallucination gradually passes into an illusion, through the auto-suggestion of the hypnotic; this is very common. To be exact, we can regard every illusion as the sum of a positive and a negative hallucination, as in each illusion something present is not perceived and something not present is perceived.

Further, it is also possible to prevent recognition of certain colours, and to induce colour-blindness by suggestion. But we have here only to do with a defective perception of colours, and not with an alteration of the stimulus affecting the eye; the disturbance is purely mental (Schirmer). Cohn's assertion that, on the other hand, colour-blindness sometimes disappears in hypnosis has been contested by Konigshofer. At all events, this could only be a hysterical disturbance of the sense of colour, and not a disturbance founded on peripheral alterations.