. Within an area an inch square on the back of the
hand, several of these _cold spots_ can be found; and when the
exploration is carefully made, and the cold spots marked, they will be
found to give the same sensation every time. Substitute a metal point
a few {198} degrees warmer than the skin, and a few spots will be
found that give the sensation of warmth, these being the _warmth
spots_. Use a sharp point, like that of a needle or of a sharp
bristle, pressing it moderately against the skin, and you get at most
points simply the sensation of contact, but at quite a number of
points a small, sharp pain sensation arises. These are the _pain
spots_. Finally, if the skin is explored with a hair of proper length
and thickness, no sensation at all will be felt at most points,
because the hair bends so readily when one end of it is pressed
against the skin as not to exert sufficient force to arouse a
sensation; but a number of points are found where a definite sensation
of touch or contact is felt; these are the _touch spots_.

No other varieties of "spots" are found, and the four sensations of
touch, warmth, cold and pain are believed to be the only elementary
skin sensations. Itch, stinging and aching seem to be the same as
pain. Tickle is touch, usually light touch or a succession of light
touches. Smooth and rough are successions of touch sensations. Moist
is usually a compound of smooth and cold. Hard and soft combine touch
and the muscular sensation of resistance.

Hot and cold require more discussion. The elementary sensations are
warmth and coolness, rather than hot and cold. Hot and cold are
painful, and the fact is that strong temperature stimuli arouse the
pain spots as well as the warmth or cold spots. Hot, accordingly, is a
sensation compounded of warmth and pain, and cold a sensation composed
of coolness and pain. More than this, when a cold spot is touched with
a point heated well above the skin temperature (best to a little over
100 Fahrenheit), the curious fact is noted that the cold spot responds
with its normal sensation of cold. This is called the "paradoxical
cold sensation". From this fact it is probable that a hot object
excites the cold sensation, along with those of warmth and {199} pain;
so that the sensation of heat is a blend of the three. Another curious
fact is that a very cold object produces a burning sensation
indistinguishable from that of a hot object; so that the sensation of
great cold,