TOUCH (OF, toucher, tochel, Fr. toucher, It. toccare, from Germ. "tukkon, OHG. zuckan, Ger. ziieken, to twitch; connected with 014G. ziohan, Ger. ziehen, Goth. tinhon, AS. teon, to draw). One of the five special senses; the tactile sense. The sense of touch is widely dis tributed, but it must be distinguished from the other varieties of common sensation—pain, and temperature perception. These are perceived through the same nerves—the sensory—but the nerve fibres which are identified with the sense of touch proper are provided with special end organs, and the sense, moreover, is only exercised in any degree of perfection in those parts where there is an abundance of special end organs. These are of two kinds: touch corpuscles, situ ated chiefly in the skin; and end bulbs. found mainly in the mucous membranes. The lips and genital organs, being on the border line of skin and mucous membrane, are possessed of both touch corpuscles' and end bulbs. The Parinian corpuscles are widely distributed, but their part in connection with the tactile sense is only par tially understood. They are numerous as the nerves of the palmar surface of the fingers, but, when found. are situated deeply in the skin or in the subcutaneous tissue. The acuteness of the sense of touch depends to some extent on the cutaneous circulation, and this is largely in fluenced by the surrounding temperature. The numbness produced by the application of cold to the surface of the body is thus explained.
The acuteness of the sense of touch is com monly measured by an instrument known as the vesthesiometer and consisting of two needle points in arms movable upon a graduated scale. A pair of compasses may be used in the same way. The nearer together the points can be separately perceived the greater the delicacy of touch. The distance at which these two points can be separately distinguished in various parts of the body is indicated in the following table: It will thus be seen that the point of greatest delicacy of touch is the tip of the tongue, and the seat of the least developed tactile sense is the skin over the spinal column. The sense of touch, like all other perceptions, can be sharpened by exercise. This improvement is not to be ex plained by an increased development of the termi nal organs, nor by a growth of new nerve fibres in the skin, but by a more exact limitation of the sensational areas in the brain. _Many artisans acquire a highly specialized sense of touch. The delicacy of the tactile sense in the blind is a well-known condition; these people are able to read fine raised letters, and to make various articles of delicate structure, in a manner im possible to individuals who can see. See PSY CHOLOGY ; SENSATION ; and SKIN.