CUTANEOUS SENSATIONS (Fr. cutane, Port.. It. cutaneo, from Lat. cutis, skin). The sensations aroused by stimulation of skin and mucous membrane. The term 'cutaneous' is ap plied to all these sensations, although one of them, the sensation of pain, is derived not from the cutis proper, but from the epidermis. (See SKIN.) The skin has been credited, in one or another psychological system, with a large num ber of sensations: sensations of contact, pres two things will happen: either it will arouse a dull, vague, diffuse pressure sensation, or it will arouse a sharp, distinct pressure, the kind of sensation that one might suppose to come from the inward pressure of a little hard seed lodged in the eutis (Goldscheider). If the point be now applied lightly, we get either no sensation at all, or (at the place where the seed-pressure was before produced) a light, fine, rather ticklish pressure sensation. The seed-pressure and the ticklish pressure come from the organs of the pressure sense, the 'pressure spots,' as they are called. The dull pressure with intensive stimu lation is set up by the indirect affection of sev eral pressure spots; the stimulus makes an in dentation in the skin, and the dragging down of the tissue squeezes the pressure organs that lie about the point of application. The absence of sensation with light contact means that the experimenter has applied the stimulus at a point of the skin which has no pressure organ. We see, then, from this simple experiment, that the skin is not uniformly sensitive to pressure; it may rather be compared to a mosaic of tiny blocks, some of which are sensitive, while the rest are insensitive, to mechanical stimulation.
A careful exploration of the cutaneous sur face, undertaken with the object of mapping the pressure spots, has led to two definite results. (a) If the portion of the skin explored is hairy, the pressure spot lies always to windward of a hair-shaft, immediately above a hair-bulb. It follows that the nerve-skein which enfolds the bulb is the terminal organ of pressure, and that the hairs are as truly sense-apparatus in man as they are, e.g. in the cats. (h) if the region is
hairless, pressure spots, arranged in lines and groups, can still be identified. The organs in this case are the corpuscles of 'Meissner.
(2) Warmth and ('old.—If the blunt point of an ordinary lead-peneil he drawn slowly over the back of the hand, it will give rise, from time to time, to little flashes of cold; over the rest of its course, it will arouse nothing but pressure sensations. If the point be warmed, and drawn in the same way over the closed eyelid, it will give rise, from time to time, to little dots of warm sensation; at other points, it excites noth ing but pressure. There is, then, a mosaic of temperature organs as there is a mosaic of pres sure organs. INIoreover, if a small square or circle of skin is accurately marked, and explored twice over, once with a cooled and once with a warmed point of metal, it will be found that the cold and warm spots do not coincide. A 'cold spot' never gives a warm sensation; a 'warm spot' never responds to stimulation by a cold sensation. While, therefore, we are justified, physically, in speaking of 'degrees' of tempera ture, and in arranging 'warms' and 'colds' upon a single thermometric scale, we must recognize the fact that. psychologically regarded, warmth and cold are distinct things; there are two tem perature senses, each with its own distribution and its peculiar terminal organs. The organs of cold are more numerous than those of warmth. They are to be found, probably, in the end-bulbs of Krause, while the organs of warmth are the cylinders of flutfini (von Frey). All these cu taneous organs are of extremely simple struc ture, consisting of little more than a skein or tangle of nerve-fibrils, twined about a cluster of conneetive-tissue cells. All alike are readily fatigued; and all show differences of responsive ness of 'attunement,' some answering a given stimulus with an intensive, others with a weak sensation.