Thomas Grant Jr., age 13, of Twin Falls, Idaho, for his question:

IS TOUCH AN IMPORTANT SENSE?

Touch is the sense which gives us notice of contact with an object. It is also called a tactile sense and it is definitely important to people. Touch was formerly considered one of the five special, or exterior, senses. Now, however, it is considered a common or general sense because the touch organs are found all over the body.

Touching an object can give rise to feelings of warmth, cold, pain and pressure. Free nerve endings in the tissue give the sense of pain. Touch, warmth, cold and pain are alos called cutaneous senses.

There are several kinds of touch organs, called tactile corpuscles, in the skin and mucous membranes. One kind is found near hair. another in hairless areas and still another kind in deeper tissues.

The sensation occurs when an object comes in contact with the sense organs and presses them out of shape, or touches a nearby hair Nerves from the organs then carry nerve impulses to the brain. Touch is more sensitive in some parts of the body than in othrs.

This difference is due to the fact that the end organs for touch are not scattered evenly over the body, but are arranged in clusters. The feeling of pressure is keenest where there are the greatest number of end organs. It is most highly developed on the tip of the tongue and is poorest on the back of the shoulders.

The tips of the fingers and the end of the nose are other sensitive areas.

Scientists can easily measure keenness of touch with the esthesiometer This instrument looks like a drawing compass with two needle points. The tip of the tongue can feel both points when they are only 1.1 millimeters apart    about one twenthy fifth of an inch.

Less sensitive areas feel only one point at this distance. The back of the shoulders feels the two points as a single one until they are 66 millimeters apart    about 2.6 inches.

The end organs for warmth, cold and pain are also distributed unevenly. A person can discover this for himself by running a pointed metal instrument over his skin. All of the instrument is colder than the skin, but it feels cold only at some points. At other points the instrument is simply felt as pressure.

Many objects act on several of the senses at once. As an example, a hot iron that touches a person's skin would cause the sensations of pain, heat and touch.

Scientists know there are several million points on the body that register either cold, heat, pain or touch It is possible to map these points for the four cutaneous senses on any area of skin.

Insects are much more highly sensitive to touch than we are. The touch organs consist of hairs and spines that cover all parts of an insect's body, even its eyes. Any kind of pressure moves the hairs, setting up a nerve reaction that goes to the brain. Some of the hairs are so sensitive that the gentlest air current can bend them.