Subjective Sensations and Illusions. 827 



ous or terrifying. A black stump becomes a prowling beast or a skulk- 

 ing assassin ; a white object is a ghost, &c. 



Sir Walter Scott relates a story of a gentleman, who one evening was 

 reading an account of the life of a poet who had recently died, and 

 with whom he had been well acquainted. His emotions were consider- 

 ably aroused as a result of his reading. After a time he laid down his 

 book and went into an adjoining hall, which was dimly lighted by the 

 moon. There he saw right before him in a standing posture, the exact 

 representation of his departed friend. He paused long enough to ob- 

 serve the details of dress, posture, &c. , which corresponded with his 

 memory of them, and then, sensible that it was all a delusion, he walked 

 up to it. As he did so the apparition resolved itself into the various 

 materials of which it was composed. " These were merely a screen oc- 

 cupied by great coats, shawls, plaids, and such other articles as usually 

 are found in a country entrance hall. " 



It is evident that in complete hallucination of vision (or an}*- other 

 sense), the centers of sensation must be stimulated to an extent equal to 

 that which usually arises when the stimulation comes by the ordinary 

 route of the sense organs, and yet not coming from any object in the 

 external environment. 



If the hallucination is of a simple sensation, as of a flash of light, it 

 might arise from a stimulation of the retina or of the optic nerve by a 

 blow, a lesion, or other abnormal cause. But if it is a revived image 

 of a former sensation, it must arise from the restimulation of the cere- 

 bral memory organs, the internal sense organs. 



But the halluciation at times consists of images newly made, like 

 dreams, from materials already in the memory, of course, but differently 

 associated, so that as a whole it is quite new. Such images are formed 

 as ideas of a complicated nature always are, by the powerful erethism 

 of parts of various memory organs; at the same time, such action result- 

 ing in the formation of new organs whose ordinary stimulation would 

 produce the sensation of a fancy, but whose extraordinary stimulation 

 might produce an illusion or hallucination. The hallucinations of the 

 insane are usually uncontradicted, and so take full sway of the patient, 

 causing him to adapt his actions to false conceptions of the condition of 

 his environment. The hallucinations of the sane are, sooner or later, 

 contradicted. Often the subject has in reserve, a sufficient number of 

 organs not involved in the production of the image in question, to set 

 up an idea inconsistent with the realty of the first one, and so he may 

 know at the time, that his vision is a hallucination. Or, after it has 

 passed off, and other ideas supervene, he becomes undeceived by them 

 as to the reality of the vision. 



While the hallucination endures, it is so complete, that the excite- 



