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, perhaps, that, when we say of any phenomenon, however strange, that it is singular and quite unlike anything else in the world, we are mistaken, 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 stimulation 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 circulation, 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 appear 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 obtain 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,