The tactile sense not only makes known the size, shape and other properties of bodies, but it also differentiates the varieties of pain and temperature. Goldscheider believes there are two kinds of sensitive nerves of touch. The office of the tactile corpuscle, in the light of later investigations, appears to be to give greater mechanical protection to the nerve terminations. That the quality of touch can be educated to a surprising degree is demonstrated in the blind who, by their delicacy and expertness of touch, seem almost to supply a substitute for the loss of vision. The distribution of temperature sensation is very like that of common sensation and varies in different parts of the skin, but is not modified by the relative thickness of the skin to the same extent as general sensation.
Temperature perception was once thought to be a variety of general sensation. The experiments of Blix and Goldscheider not only tend to disprove this, but seem to show that there is a separate nerve mechanism for cold, for heat and for pressure. Experimenting independently of each other, these investigators found that the same irritant produced on some parts of the skin a sense of cold; on other parts heat; and on others, only the ordinary sense of pressure. It is well known that in some diseases attended with paralysis of ordinary sensation, sensitiveness to heat and cold may remain intact. The degree of temperature felt depends, in great measure, on the extent of surface exposed. For instance, one finger can be comfortably borne in hot water which would become painfully hot to the whole hand. The tip of the tongue, the fingers and face are most sensitive to temperature changes, one-half to one degree variation being readily appreciated by these parts.
The non-striated muscles of the arteries are well supplied with vasomotor nerves, and although these elements are not concerned in sensory function, they must be briefly mentioned. They control the constriction and dilatation of cutaneous vessels causing increased or diminished blood supply and hence affecting the temperature of a part. Many morbid conditions are directly affected by these actions which originate from the depression or stimulation of the nerve centers in the medulla or from a similar action exerted upon the peripheral nerve terminations. So little is known about the action of the so- called trophic nerves that, although there will be affections of the skin which will hereafter be referred to as trophoneuroses, it is impossible to give any detailed description of their working. For the most part the nutrition of the peripheral parts is influenced or controlled by the spinal cord.