1.The skin，as we all know，is very sensitiveto the“touch”of outside objects.It is also sensitive to heat and cold，and to pain.All parts of the body are not equally sensitive to touch.The skin of the finger-tips is more sensitive than the skin of the knuckles，but not so sensitive as the skin of the forehead or of parts that are covered with hair.In order to show that this is true，touch with your finger-tip a knuckle of the clenched hand of a friend.You can touch it so lightly that he does not feel the touch upon the knuckle，while you can feel it quite distinctly upon the finger.The skin of the lips and face is as sensitive as that of the finger-tip，and the tongue is even more so.
2.Not only can you feel that an object has touched the skin，but you have learned by experience to know what part of the body has been touched.Shut your eyes，and tell a friend to touch different parts of your face，and you will be able to tell him what parts he hastouched.This power of locatinga touch is greater insome parts of the skin than in others，and is possessedin the highest degree by the skin of the finger-tips and of the tongue.
3.If you bandage a friend‘s eyes，and touch his finger-tips with the points of a pair of compasses，he will be able to distinguish each point until they are nearly close together-say one-tenth of an inch apart.When they are closer than this，he will think that he is being touched by a single point.Now touch the palm of the hand，and the points of the compasses must be a quarter of an inch or half an inch apart before the two points can be felt separately.On the back of the arm a touch is even more badly located，and the points of the compasses must be an inch or so apart before each is felt separately.
4.The roots of the hairs are very sensitive to touch，as you can readily observe；for if a hair on the back of the hand or head be disturbed ever so little，this disturbance will be felt.Many animals，such as dogs，cats，and rabbits，are provided with special hairs of touch，which spring from the sides of the mouth，and from the temple，eyebrows，and edges of the ears.These hairs are very long and stout.In the dark theywarn the animal of any obstaclein its path.
5.As we have already seen，the skin is sensitive to heat and cold，but it readily becomes accustomed to any change of temperature.If you put your hand intolukewarmwater，it feels warm at first，and then thewarm feeling passes away.If after keeping your hand in really hot water for half a minute，you plunge it into the lukewarm water，the latter feels quite cold.As in the one case the lukewarm water feels warm and in the other case cold，it is evident that the skin is not a judge of the actual temperature of things.It only informs us whether heat is coming to the skin，or whether heat is leaving the skin.Thus lukewarm water gives heat to the skin when the hand is cold，but it takes heat from the hand which has previously been heated by hot water.
6.A piece of iron and a piece of wood in the same room appear to the hand to have quite different temperatures.The iron appears to be much the colder.They are reallyof exactly the same temperature，as a thermometerwould show.The iron feels colder simply because it is a better carrier （or conductor）of heat than the wood，and so it draws the heat out more quickly from the hand.In a very hot room，where both the iron and the wood are hotter than the hand，the iron feels the hotter of the two，because it carries more heat to the hand than the wood does.
7.The nerves of heat and of cold do not pass to all parts of the skin.They are to be found only in certainlocalities called the “heat spots”and the “cold spots.”The latter are most easy to find，and we can map out their position in our own hands quite readily.Take a pin，dip its head in water to cool it，and draw the head slowly along the back of the hand.Suddenly here and there you will feel the cold of the pin.If you mark one of these spots with ink，you will find that whenever the pin is drawn over it the same feeling of cold is produced.You must not do it too quickly，or too often，however，or the pin will get warm，and the nerves of that spot will be exhausted and become less sensitive.