766 THE POPULAR SCIENCE MONTHLY. 



and, without losing consciousness, she uttered a loud shriek, and pointed 

 at an object which she apparently saw near her. I at once discon- 

 tinued the pressure, when she informed me that she had seen an im- 

 mense negro rushing toward her with a club, and that as soon as I 

 had stopped pressing on her neck the figure had disappeared. I as- 

 sured her it was an hallucination, and induced her to let me repeat the 

 experiment. I now exerted moderate pressure, with the view of keep- 

 ing 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 fre- 

 quently give circumstantial accounts of incidents which they believe 

 have occurred to them, of voices they have heard, etc. It is often im- 

 possible 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 halluci- 

 nations, but without much result so far as any explanation of the pro- 

 cess 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 illu- 

 sions 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 docti-ine 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 elabo- 

 rate these impressions, and that, by means of the fibers of the corona 

 radiata, they transmit them to the cortex, to be still further perpetu- 

 ated by being converted into ideas. 



If there is no organ of sense, there can be no normal sensorial im- 

 pression ; if the optic nerve be divided, the sensation can not be trans- 

 mitted 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 le- 

 sions of the optic thalamus necessary to the production of a false sen- 

 sorial 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 



