Page:Language of the Eye.djvu/44

26 made upon the sentient extremity of the nerve which is appropriated to sensation, is not the direct effect of the external body, but results from the agency of some intervening medium. There is always a portion of the organ of sense interposed between the object and the nerve on which the impression is to be made. The object is never allowed to come in direct contact with the nerves; not even in the sense of touch, for there the organ is defended by the cuticle, through which the impression is made. This observation refers equally to taste and smell, the nerves of which are not only defended by the cuticle, but by secretion of mucous character, which averts any violent excitement. The two senses, which are more relative than others, are the sight and hearing, both which receive their impressions through the medium of the air.

We feel some hesitation on proceeding further on this interesting part of the subject,—viz., the comparison of the organs of sense and their respective physiological distinctions. If we were to go much deeper, we should soon find ourselves amidst those most interesting distinctions of sense, as delineated by the general animal kingdom—the touch of the ant, the sight of the fish, the hearing of the bird, the smell of the dog, &c. We would refer our readers to Buffon, Laurence, Hutin, Koget, and Walker, and conclude this part of our subject with but few observations.

Touch furnishes the relation of mechanical bodies; taste is adapted to chemical relations; smell also to chemical relations, but for the perception of substances in the aëriform state; hearing is for sound and its many modifications, tones which are produced by the internal vibration and motion of the particles of bodies and through the medium of air, &c. Our subject, the sense of sight, is adapted to light and its modifications, colour and shade,