The sensations arising from many impulses coming from the skin are grouped together under the name of the Sense of Touch. This special sense may be resolved into a number of specific sensations, each of which might be considered as a distinct kind of feeling, but is usually regarded as simply giving different qualities to the sensations excited by the skin. These sensations are: (1) Tactile Sensation, or sensation proper, by means of which we appreciate a very gentle contact, recognize the locality of stimulation, and judge of the position and form of bodies; (2) the sense of pressure; and (3) the sense of temperature.
The variety of perceptions derived from the cutaneous surface, and the large extent of surface capable of receiving impressions, make the skin the most indispensable of the special sense organs, though we value this source of our knowledge but little. If we could not place our hands as feelers on near objects to investigate their surfaces, etc., we should lose an important source of information that has contributed largely to our visual judgment. We think we know by the look of a thing what we originally learned by feeling it. If our conjunctiva did not feel, we should miss its prompt warning, and our voluntary movements could not protect our eyes from many unseen injuries that normally never trouble us. If the skin were senseless, it would require constant mental effort to hold a pen, and our power of standing and walking would be most seriously impaired. And how utterly cut off from the outer world should we be, were we incapable of feeling heat and cold.
Fig. 209. Drawing from a section of injected skin, showing three papillae, the central one containing a tactile corpuscle (a), which is connected with a medullated nerve, and those at each side are occupied by vessels. (Cadzat).