414 ALFEED BINET : VISUAL HALLUCINATIONS IN HYPNOTISM. (3) Mechanical pressure of the eye doubles the hallucination (Brewster's experiment). (4) A prism placed before the more normal eye doubles the hallucinatory image and makes one of the images undergo a deviation in conformity to the laws of optics (Ch. Fere's experi- ment). Even when the subject is colour-blind with one eye the two images show the same tint (Parinaud's experiment). I have observed in the hysterical mad woman above-mentioned that the deviating hallucinatory image was surrounded by a band of prismatic colours ; the patient declared that she saw two Grippeaus (the name she gives to the individual who appears to her) and that one of them was surrounded by a rainbow. (5) A spy-glass removes or approximates the imaginary object, according as the object-glass or eye-piece of the instrument is placed before the patient's eye. This effect is only produced when the glass has been properly focussed for the sight of the subject, just as if a real object was to be looked at. A myopic and an eminetropic subject cannot make use of the same glass without accommodation to the sight of each. The glass which has not been focussed plays the part of a screen, and consequently suppresses the hallucination for certain patients, and leaves it as it was for others, according as the screen produces one or the other effect upon them. The experiment of the spy-glass may be varied in a thousand ways by employing instruments in all of which the action depends upon the refraction of light, as the magnifying glass, the prism, a double-refracting crystal, the microscope, &c. (6) A mirror reflects the hallucination and gives a symmetrical image of it. All that is necessary for this is to get a reflection of the point of space which is the seat of the hallucination. To bring out the symmetrical character of the reflected image, it is a good plan to give the subject the hallucination of a portrait on a sheet of paper ; suppose, for instance, that the profile of the imaginary portrait is turned to the left. When the sheet of paper is placed before the mirror, the subject sees the same portrait, but the profile appears to be turned to the right. If for the portrait written lines are substituted, the characters in the mirror appear reversed from right to left or from top to bottom, according to the position in which the paper is placed before the mirror. This last experiment is delicate and requires a certain practice. (7) The hypnotic hallucination of the somnambulist stage is complete ; in the absence of a suggestion to the contrary it en- gages all the senses. These experiments in hypnotism serve as an introduction to the study of mental pathology. It is interesting to try to repeat the same experiment on the spontaneous hallucinations of the insane. Unfortunately, it is rare to meet with visual hallucina- tions so persistent that ve can study them directly without being
