The baby had finished her first quarter year. A few days before, as we have seen, she had looked for a person out of sight; and now, just at the end of the third month, she showed that she could bring together the testimony of sight and hearing, by turning to look in the direction of a sound. Here seems evidence that by this time (whether she had done so before or not) she “externalized” her impressions more or less: that is, when waves of sound struck on her tympanum, or of light on her retina, she did not simply _feel_ the resulting sensation, but threw it back, so to speak, along the line of the wave, and seemed to herself to perceive something outside there, away from her. For when she looked around, seeking what she did not yet see, expecting sight sensations and hearing sensations to come from the same source, it is impossible to think she did not have a feeling of something really there, outside herself. Step by step with the sense of outsideness there must have come a sense of insideness, of self, for the two are only opposite sides of one feeling--that is, the feeling of _difference_ between oneself and the outer world. We must not suppose that before the baby externalized her impressions she felt everything as happening inside her: she must have just felt things, with no inside or outside about it. This may seem impossible, but really the sense of insideness and outsideness is not hard to upset, even at our time of life. Dizziness or mental shock will do it. Sometimes on waking from deep sleep we find our sense of a separate bodily self gone, and gather it slowly back. We may almost lose ourselves by lying idly, without thought or care, in some great, continuous sound, like the roar of a cataract, till we do not know which is ourself and which is the outward sound. Mystics and ecstatics have made an art of changing the bodily feelings by fasting and other means, till the usual marks of difference among impressions, by which we externalize some and refer others to our own bodies, are lost; and with them the sense of being in the body, surrounded by an outer world.