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 THE PEECEPTION OF SPACE, (ill.) 331 the sensible quality of touch change under his hand, as sudden contact with something moist, or hairy in the dark, awoke a shock of disgust or fear which faded into calm recognition of some familiar object ? Even so small a thing as a crumb of potato on the table cloth, which we pick up, thinking it a crumb of bread, feels horrible for a few moments to our fancy, and different from what it is. Weight or muscular feeling is a sensation ; yet who has not heard the anecdote of Wollaston when Sir Humphrey Davy showed him the metal sodium which he had just discovered? " Bless me, how heavy it is," said Wollaston ; .showing that his idea of what metals as a class ought to be, had falsified the sensation he derived from a very light sub- stance. Smell is a sensation ; yet who does not know how a sus- picious odour about the house changes immediately its character the moment we have traced it to its perhaps small and insignificant source? When w r e have paid the faithless plumber for pretending to mend our drains, the intellect inhibits the nose from perceiving the same unaltered odour, until, perhaps, several days go by. As regards the ventilation or heating of rooms, we are apt to feel for some time as we think we ought to feel. If we believe the venti- lator is shut, we feel the room close. On discovering it open, the oppression disappears. 1 Taste is a sensation; yet there are but few people, in tast- ing wine, butter, oil, tea, meats, &c., who are not liable, temporarily at any rate, completely to misjudge the quality of what is in their mouth, through false expectation, or in con- 1 An extreme instance of the power of imagination over the sense of smell is given in the following extract : " A patient called at my office one day in a state of great excitement from the effects of an offensive odour in the horse-car she had come in, and which she declared had probably ema- nated from some very sick person who must have been just carried in it. There could be no doubt that something had affected her seriously, for she was very pale, with nausea, difficulty in breathing, and other evidences of bodily and mental distress. I succeeded, after some difficulty and time, in quieting her, and she left, protesting that the smell was unlike anything she had ever before experienced and was something dreadful. Leaving my office soon after, it so happened that I found her at the street corner, waiting for a car : we thus entered the car together. She immediately called my attention to the same sickening odour which she had experienced in the other car, and began to be affected the same as before, when I pointed out to her that the smell was simply that which always emanates from the straw which has been in stables/ She quickly recognised it as the same, when the unpleasant effects which arose while she was possessed with another perception of its character at once passed away." (C. F. Taylor, Sensation and Pain, p. 37 ; N. Y., 1882.)