828 Dynamic Theory. 



merit aroused in the cerebral organs overflows backwards along the optic 

 nerve to the retina, and from thence, to all appearance, it is projected 

 into space, forming an image which appears to occupy the same position 

 that a real object would have to occupy in order to produce the same 

 sensation in the brain. 



This position, or point of projection in space, is called by the French, 

 the point de repere. The hallucination is often initiated, or modified, 

 or influenced by some real object in the environment. Such object may 

 then occupy the point de repe're, and the details of the hallucinatory 

 image be constructed about it, as in the case mentioned by Walter Scott, 

 and quoted above. When such real object furnishes a nucleus for the 

 hallucination, and forms a part of its structure, if the eyes are turned 

 away from it, that much of the image is torn away, and so the image 

 usually falls to pieces. But when the image is wholly constructed 

 within, and projected without through the sense organ, the external pro- 

 jection appears to share in all respects the conditions of an incoming 

 stimulation from a real object. Thus it was observed by M Fere, that 

 a prism applied to one eye doubled the imaginary object. A magnify- 

 ing glass, placed in the line of the projection, increased the size of the 

 supposed object, while, if the glass were reversed, the object was dim- 

 inished. Equally remarkable, when a mirror is placed so as to reflect 

 the point de repere to the e} 7 e of the subject, the image of the imaginary 

 object may appear in the glass. 



In two spontaneous cases cited above, the image was said to have 

 been seen in a mirror. It is proper to state that the experiments 

 with prism, spy-glass, etc. , have been successful in some cases only, not 

 in all. 



Those hallucinations or illusions which persist when the eyes are 

 closed, are no doubt to be explained as the sensation of the restimula- 

 tion, or the first construction, of an internal sense organ merely. But 

 those cases in whicli the spectre is projected to the point de repere, and 

 especially the cases in which the looking glass, spy glass and prism are 

 found to influence the conditions of the vision, require a further explana- 

 tion. The possibility of working certain sorts of machinary backwards has 

 been pointed out. The retina and the internal sense organ stand to 

 each other in the same relationship as two electric dynamos, connected 

 by conducting wires. If power be applied to either of the dynamos, it 

 will pass to the other and cause it to revolve. There is good reason to 

 believe that there is the same reciprocity between the brain organ and 

 retina, and that the application of energy to either will set up motion in 

 the other. The two considered together constitute a single machine, 

 bound into one by the connecting nerves. If we suppose the dynamos 

 above to be driven by an overshot water-wheel, we might regard the 



