and, without losing consciousness, she uttered a loud shriek, and pointed at an object which she apparently saw near her. I at once discontinued the pressure, when she informed me that she had seen an immense negro rushing toward her with a club, and that as soon as I had stopped pressing on her neck the figure had disappeared. I assured her it was an hallucination, and induced her to let me repeat the experiment. I now exerted moderate pressure, with the view of keeping it up for some little time. In about half a minute she said that she saw the figure, but not very distinctly, and I found that I could make the figure appear distinct or indistinct by varying the degree of pressure.
Children are very liable to be subject to hallucinations, and frequently give circumstantial accounts of incidents which they believe have occurred to them, of voices they have heard, etc. It is often impossible for them to discriminate between the true and the false, and I am afraid they are often punished for lying by ignorant parents, when they have told nothing but what they have had the evidence of their senses for believing.
A great deal has been written relative to the physiology of hallucinations, but without much result so far as any explanation of the process is concerned. There is some evidence to show that the thalami optici are the centers for all real perceptions, and that hence they are the organs, which, through their disease, give rise to all centric illusions and hallucinations. Luys more than any other physiologist has elaborated this idea, and has adduced arguments in its support which it is difficult to overlook. His doctrine is that the optic thalami are reservoirs for all sensorial impressions coming from the periphery of the nervous system, and that, like other ganglionic masses, they elaborate these impressions, and that, by means of the fibers of the corona radiata, they transmit them to the cortex, to be still further perpetuated by being converted into ideas.
If there is no organ of sense, there can be no normal sensorial impression; if the optic nerve be divided, the sensation can not be transmitted to the optic thalamus; if there be a diseased optic thalamus, the sensorial impression will be perverted and there will be an illusion of centric origin; if the cortex be in a normal condition, this illusion will be corrected and understood as such erroneous perception; if, however, the cortex be diseased, the illusion will be accepted as true, and a false idea, or delusion, will be formed. Such an impression formed in the optic thalamus is an hallucination, and will be accepted for reality or not according as the cortex is healthy or diseased.
Such is, I think, the pathology of perceptional insanity. The lesions of the optic thalamus necessary to the production of a false sensorial impression may be of varied character. Congestion is probably that which most commonly exists, especially in the early stages, and in those cases which are not accompanied by derangements of the other
