41. But as this is contrary to appearance, it may seem not to merit belief unless it be proved; and since it can be proved only by such things as man can apprehend by his bodily senses, by these it shall be proved. Man has five external senses, called touch, taste, smell, hearing and sight. The subject of touch is the skin by which man is enveloped, the very substance and form of the skin causing it to feel whatever is applied to it. The sense of touch is not in the things applied, but in the substance and form of the skin, which are the subject; the sense itself is nothing but an affecting of the subject by the things applied. It is the same with taste; this sense is only an affecting of the substance and form of the tongue; the tongue is the subject. It is the same with smell; it is well known that odor affects the nostrils, and that it is in the nostrils, and that the nostrils are affected by the odoriferous particles touching them. It is the same with hearing, which seems to be in the place where the sound originates; but the hearing is in the ear, and is an affecting of its substance and form; that the hearing is at a distance from the ear is an appearance. It is the same with sight. When a man sees objects at a distance, the seeing appears to be there; yet the seeing is in the eye, which is the subject, and is likewise an affecting of the subject. Distance is solely from the judgment concluding about space from things intermediate, or from the diminution and consequent indistinctness of the object, an image of which is produced interiorly in the eye according to the angle of incidence. From this it is evident that sight does not go out from the eye to the object, but that the image of the object enters the eye and affects its substance and form. Thus it is just the same with sight as with hearing; hearing does not go out from the ear to catch the sound, but the sound enters the ear and affects it. From all this it can be seen that the affecting of the substance and form which causes sense is not a something separate from the subject, but only causes a change in it, the subject remaining the subject then as before and afterwards. From this it follows that seeing, hearing, smell, taste, and touch, are not a something volatile flowing from their organs, but are the organs themselves, considered in their substance and form, and that when the organs are affected sense is produced.