FROM TIME TO TIME, you stick me out and examine me in the mirror. You are not exactly sure what you're looking for. If you find anything unusual, you're almost certain to misinterpret it. That is about the end of your interest in me. After all, I'm only four inches long and weigh but two ounces, and I usually stay out of sight. I am your tongue.
Compared with the eyes and ears, I have had a bad press: my faculty of taste has been called the "poor cousin of the five senses." Unfair, I say! Just try to get along without me! Try extend me from your mouth; for instance, and clamp me lightly between your teeth, and then try to speak. What comes out is, hardly recognizable.
True, I don't have the virtuosity of some animal tongues. I can't flick out to catch insects the way a frog's tongue does, or "feel" the way through a dark cavern as a serpent's tongue can. Just the same, I have a large assortment of jobs: assist in mastication, rolling food around in the mouth so that it is evenly ground and made acceptable to the stomach. I am quite a serviceable toothpick-I like to keep my domain clean of debris of all sorts. I even express emotions: Children stick out their tongues indicate avertion or disgust.
One of my most important-and complex-tasks is to assist in swallowing. For this, my front part presses against the hard roof of the mouth. Then my rear portion humps up, catapulting food into the passage which leads to the esophagus. Though it sounds quite simple, it is actually a symphony of activity conducted by nerves and executed by intricate muscles. You knew how to swallow before you emerged from the womb-an indication of how critical the swallowing reflex is to life.
Speech is another matter. I had to be trained for this extraordinary neuromuscular feat. As a baby, you experimented with sounds for more than two years before you were able to form simple sentences. Today, I am a tireless gymnast, able to flex myself into a great variety of shapes for more complex expression. You can get some idea of my acrobatics by uttering a single sentence. As you speak, lets concentrate on my motions. You will be amazed at the activity.
Or, you can give thought to another matter. I live in constant proximity to a very real enemy-the teeth. They are capable of doing me real injury. But I am an extremely artful dodger; I keep out of their way and am rarely bitten.
Essentially, I am a slab of mucous membrane enclosing a complex array of muscles and nerves. My upper surface is studded with papillac-little nipples, some of which contain taste buds. Located in my taste buds are taste cells, which actively receive the sensation of taste. On my underside is a tiny cord, the frenulum. Let this cord be too short, restraining normal motion, and I am tongue-tied. Victims once went through life with garbled speech. Today, this defect can be corrected by surgery.
My taste buds look something like microscopic rosebuds. Their tasting action is a chemical process, like smell. Curiously enough, they are on my under as well as my upper side. Until recently, scientists thought that they had my taste buds completely mapped: I tasted salt with my tip, sweet in the middle, bitter in the rear and sour along my sides. (These are four of the basic tastes). And just as the primary colors red, blue and yellow blend into a thousand hues, so too do the basic taste's blend into thousands of taste sensations. But the researchers were wrong.
Taste buds are by no means confined to me, but are scattered around your oral cavity. The primary taster of sour and bitter are near the junction of the soft and hard palates in the roof of the mouth. If you ever wear dentures' that cover your palate, these buds will be covered up and things won't taste so good. Lemon pie will lose some of its sour tang; and tea and coffee may become less flavor some without their predominant bitterness. Most of the buds for salt and sweet are on the tongue although a few are else where; particularly in the upper throat.
Food must be liquefied before any taste emerges. This is true even of ice cream, which until it melts in the mouth, is quite tasteless. But once liquefied, it binds to the sweet-taste receptors of the buds; a minute electrochemical current is generated and passed by cranial nerves to the gustatory terminals in the brain. (Other impulses are transmitted for foods that taste sour, bitter or salty.) Like colors mixed on a palette, the messages are blended, and the brain hands down its verdict: the ice cream is delicious.
For a long time it was assumed that all foods tasted alike to all people. (It's a strange notion when you think about it-everyone knows that hearing and sight are subject to great variations.) Now it becomes clearer all the time that there are vast differences in taste sensitivity. To one person, spinach may be honestly delicious; to another bitter and horrid. It's the same with scores of other foods. Several pure chemicals point up variations in human taste response. Sodium benzoate, for example, is sweet to some, and to others sour, bitter, salty or tasteless. So there's no point in arguing if someone doesn't like the Roquefort cheese that you find delectable.
Indications are that taste follows regular inheritance patterns. Just the same, tongues do have a certain amount of adaptability, and you have learned to accept foods that you once found intolerable. Few babies like buttermilk; many adults do. It took time for me to learn to accept such things as curry, chili and strong cheese. And once I've learned I don't forget: unlike most other organs of the body, I hold up well with age. Your sight and hearing will diminish, but not your taste-bean soup has about the same flavor for someone at 90 as when he was ten.