Annette Roach, age 14, of Biloxi, Miss., for her question:

HOW DO WE TASTE THINGS?

Taste is one of five special senses in humans and other animals. With taste, four qualities of a substance are distinguished: sweetness, sourness, saltiness and bitterness. Taste is determined by receptors, called taste buds, that in human beings are located on the surface and sides of the tongue, the roof of the mouth and the entrance to the pharynx.

The mucous membrane lining parts of the mouth is invested with tiny projections of papillae, each of which is turn invested with 2,00 to 300 taste buds.

The papillae located at the back of the tongue are called circumvailate and are arranged to form a V with the angle pointing backward. They transmit the sensation of bitterness. Those at the tip of the tongue transmit sweetness, while saltiness and sourness are transmitted from the papillae on the sides of the tongue.

Each flask shaped taste bud contains an opening at the base through which nerve fibers enter. These fibers transmit impulses directly to the brain. In order for a substance to stimulate these impulses, however, it must be in solution, moistened by the salivary glands.

Sensations of taste are strongly interrelated with sensations of smell.