7 02 THE POPULAR SCIENCE MONTHLY. 



false perceptions of the senses as I have given examples of and the 

 faithfully-serving senses of a person who is in good health of mind and 

 body. But here, as elsewhere, in Nature we find, when we look closely 

 into the matter, that there is no break ; we may be pretty sure, per- 

 haps, that, when we say of any phenomenon, however strange, that it 

 is singular and quite unlike anything else in the world, we are mis- 

 taken, and that we shall not fail to discover other things like it if we 

 search intelligently. Certainly we can trace gradational states between 

 the most extreme hallucinations and such temporary disorders of the 

 senses as healthy persons often have. Let any one stoop down with 

 his head hanging low for a minute, and when he raises it he will have, 

 besides a feeling of giddiness, a sound of singing or of ringing in his 

 ears, and may see a flash or two of light before his eyes ; and there are 

 some persons who, under such circumstances, see actual figures for the 

 moment. These sensations are hallucinations ; there is no light, nor 

 sound, nor figure, outside to cause them ; they are owing to the stimu- 

 lation of their respective nerve-centres by a congestion of blood in the 

 brain, which has been produced by the hanging down of the head. 

 Here, then, we have hallucinations that are consistent with the best 

 health ; they are due to temporary causes of disturbance of the circula- 

 tion, and disappear as they disappear. Going a step further, we may 

 watch at the beginning of a fever how gradually the hallucinations take 

 hold of the mind, until their true nature is not recognized. At first 

 the fever-patient is quite aware of his actual surroundings, knowing 

 the persons and objects about him, and when strange faces seem to ap- 

 pear among the familiar faces, as they do, he knows that they are not 

 real, and will talk of them as visions ; perhaps they occur at first only 

 when his eyes are shut, or when the room is dark, and vanish directly 

 he opens his eyes or the room is lit up. After a while they come more 

 often, and whether his eyes are shut or not ; he becomes uncertain 

 whether they are real or not, assenting when he is told that they are 

 phantoms, but falling back immediately into doubt and uncertainty. 

 At last they get entire mastery of him, he cannot distinguish in the 

 least between them and real figures, discourses with them as if they 

 were real is wildly delirious. 



If the nature of the process by which we perceive and know an 

 external object be considered, it will be seen that it is much easier to 

 have a false perception than might appear at first sight. When we 

 look at any familiar object say a cat or a dog we seem to see at 

 once its shape, its size, its smoothness of coat, and the other qualities 

 by which we know it to be a cat or a dog, but we don't actually see 

 anything of the kind. The proof is that, if a person blind from his 

 birth, who knew the cat and dog perfectly well by touch, were to ob- 

 tain sight by means of a surgical operation when he was thirty years 

 old, he would not know by sight alone either cat or dog, or be able to 

 tell which was which. But, if he were permitted to touch the animals, 



