HALLUCINATIONS OF THE SENSES. 703 



ne would recognize them instantly, and ever afterward the impression 

 which they produce on sight would be associated with the impression 

 which they produce on touch, and he would know them when he saw 

 them. That is the way in which the perception of a particular object 

 is formed by the association of all the sensations which it is adapted 

 to excite in our different senses, their combination in what we call an 

 idea. For example, in the idea of an orange are combined the sensa- 

 tions which we get by tasting it, by touching it, by smelling it, by 

 looking at it, by handling it, each sensation having been acquired by 

 its particular sense in the course of an education which has been going 

 on ever since we were born ; when we have got them in that way, they 

 combine to form the idea of the orange ; and it is by virtue of this idea, 

 which has been formed and registered in the mind, that we are able to 

 think of an orange, that is, to form a mental image of it, when it is not 

 present to any sense, and to recognize it instantly when it is. It is 

 plain, then, how large a part, by virtue of its past experience, the mind 

 contributes to each perception ; when we look at an orange it tacitly 

 supplies to the impression which it makes on sight all the information 

 about it which we have got at different times by our other senses, and 

 which sight does not in the least give us ; the visual impression is no 

 more in truth than a sign to which experience has taught us to give its 

 proper meaning, just as the written or spoken word in any language is 

 a sign which is meaningless until we have been taught what to mean 

 by it. So true it is that the eye only sees what it brings the faculty of 

 seeing, and that many persons have eyes, yet see not. 



This being so, it is clear that the idea in the mind will very much 

 affect the perception, and that if any one goes to look at something, 

 or to taste something, or to feel something, with a strongly-precon- 

 ceived idea of what it is, he will be likely, if it is not what he thinks 

 it, to have a mistaken perception to see, or feel, or touch, what he 

 thinks it is, not what it really is. This is, indeed, one of the most 

 common causes of erroneous observation, and one which the scientific 

 observer knows well he must always vigilantly guard against. If a 

 man has a foregone conclusion of what he will see, it is not safe to 

 trust his observation implicitly, either in science or in common life. 

 We witness the most striking examples of this dominion of the idea 

 over sense in persons who have been put into the so-called mesmeric 

 state. The operator gives them simple water to taste, telling them at 

 the same time that it is some nauseating and bitter mixture, and they 

 spit it out with grimaces of disgust when they attempt to drink it ; 

 when he tells them what he offers them is sweet and pleasant, though 

 it is as bitter as wormwood, they smack their lips as if they had tasted 

 something remarkably good ; if assured that a swarm of bees is buzz- 

 ing about them, they are in the greatest trepidation, and go through 

 violent antics to beat them off. Their senses are dominated by the 

 idea suggested, and they are very much in the position of an insane 



