the desires become less and one has not so much pleasure in eating unless by active labor or from some other cause the digestive organs are kept in a robust condition.
With the years the tastes change. We wonder how children can possibly eat such quantities in such combination. The food which fairly delighted us long ago has little or no attraction for us, and with many adults there is need for strong seasoning and condiments which children avoid.
The child clamors for sweets. The adult is inclined to check the child in eating that which would not digest in the adult's stomach. But Herbert Spencer won the hearty esteem of the youngster when he gave scientific argument showing that growing children need highly concentrated foods to meet the demands of nature, and they may be permitted, in fact encouraged, to eat freely of foods which are unsuited to mature people.
The tongue's special work is telling us whether a given substance is good for us. Like other senses it may be deceived and is not always to be relied upon. And when it has told us once correctly we may make a serious mistake in following its advice too extensively so as to learn that too much of a good thing is not all good.
Nearly all substances have taste. That is, the tongue has power to tell us something about almost every substance in nature. Water is about the only substance found in nature that has no taste. But we rarely find water that is pure enough to be entirely without taste. Nearly all solids that can be dissolved in water have taste. So have nearly all liquids. When we say that water tastes good we recognize the mineral in it, or some combination of minerals that the human body needs in its economy.
The substances that the taste recognizes most readily are common salt, vinegar, quinine, pepper, and alcohol. Those least exciting to the tongue are starch, white of egg, and gum.
The tongue does its work by means of three sorts of papillæ which cover its surface. There are many very fine ones all over the tongue, but these are most numerous near the tip. Some larger ones which are not so pointed in form are also more plentiful near the tip of the tongue. And there are from eight to fifteen much larger still that are arranged in rows like the letter V at the base of the tongue.
Bitter is tasted mainly at the back of the tongue. Sweet is tasted all along, but is most delightful at the base of the tongue, and it is by this cunning arrangement that nature gets the tongue to pass the sweet morsel along to the throat where it is seized and hurried downward by the act of swallowing.
These papillæ have within them capillary blood vessels and the filaments of nerves. They are the seat of the tongue's sensibility. Whatever is tasted must come into chemical action over these little points. Moderate pressure helps the sensation, so we smack our tongues sometimes when we are not in company. Cold deadens taste to some extent and heat acts in nearly the same way. Rinse the mouth with very warm or very cold water and then take in a solution of quinine at about forty degrees temperature and the bitter fluid will have almost no bitterness till the temperature of the mouth and its contents becomes somewhere near one hundred degrees.
Three things are necessary in a substance in order that it may be tasted, and it is curious to note how common are all three. First, it must be easily mixed with the saliva; second, it must easily spread itself about so that it may mingle with the mucus that always covers the papillæ; and third, it must be capable of acting chemically on the protoplasm of the end organs when once it gets into the taste bulb. All tasteless substances have one or more of these qualities lacking. Wipe the tongue dry and place a sugar crystal upon it. No taste will be experienced until the spot is moistened.
All substances do not taste alike to different tongues. We have noted the difference in appreciation of certain foods in infancy and in mature years. Water tastes differently to the fever patient and to the well man. As substances taste differently at different times to the same person, so they vary with individuals. One tongue is found on careful examination to have three times as many papillæ as another, one system is more susceptible to chemical action than another, and the nervous system varies enough in different subjects to make a considerable difference in the powers of taste.
One guest at table is delighted with a dish which appeals not at all to the palate of his neighbor. In fact there are cases where the power of taste has been temporarily or entirely lost. In such cases the patient goes on with his daily eating in a mechanical way, not because it tastes good, but because he must.
There seem to be different nerves for sweet, for bitter, for salty things, and for acids. Substances are known to chemistry which act differently on the nerves of the front and those of the back of the tongue. They very curiously taste sweet to the nerves of the tip of the tongue and at the same instant bitter to those at the base. If leaves of the Gymnema sylvestre be chewed, sweet and bitter things are tasteless for awhile although acids and salts are tasted as usual.
Let an electric current pass through the tongue from the tip to the root and a sour taste will be experienced at the tip. But no one has yet explained why when the same sort of current is passed through in the opposite direction the taste is alkaline.
Place a small piece of zinc under the tongue and a dime on top. The saliva which moistens them will cause them to form a small galvanic battery. As they are allowed to touch each other at the tip of the tongue a sour taste will be experienced and in the dark a spark will appear to the eyes.
There is a pretty microscopic formation on the sides of some of the papillæ. It consists of rows of small openings or sacs egg-shaped with very minute mouths at the surface. These are known to science as taste bulbs. They are so small that three hundred of them put together the long way will scarcely reach one inch. They are so numerous that 1,760 have been counted on one papilla of an ox's tongue. They are not entirely confined to the surface of the tongue, for they have been found in large numbers upon the soft palate and the uvula, and many have been discovered on the back side of the throat and down into the voice box, some of them even appearing upon the vocal cords. Their form is much like that of a long musk melon, but they are too small to be seen by the naked eye. The outer part or rind consists of rows of cells evidently formed to hold what is within. On the inside are from five to ten taste cells which are long enough to reach the whole length of the bulb and protrude slightly at the opening where they are finely pointed. They are attached at the other end and branch out as if to run to several extremely fine divisions of the nerves.
Birds and reptiles have no taste bulbs in their papillæ. Tadpoles and freshwater fishes have similar bulbs in their skin, and it is thought they enjoy the taste of things around them without the necessity of taking them in at the mouth.
We give the sense of taste more credit sometimes than it merits. What we regard as tastes are often flavors or only smells. What is taken in at the mouth gets to the nose by the back way if it is of the nature of most spices, and so by use of the nose and the imagination we taste things that do not affect the tongue at all. A cold in the head shows us we do not taste cinnamon, we merely experience its pungency as it smarts the tongue while its flavor we enjoy only with the nose.
With some substances we have a mixed experience that passes for taste, but it is really a combination of taste, smell, and touch. With the nostrils held one can scarcely distinguish between small quantities of pure water and the same with a very little essence of cloves. The difference is easily observed with the nostrils open or after swallowing, for the odor of the mixture gets readily into the nose from either direction.
It is curious to note that, although there are so many varieties of taste, man has but few words to describe them with. We know the taste of a thousand substances, and yet we are in nowise superior to the veriest savage in the matter of speaking about their flavors. We are obliged to speak in the same manner as the wild man of the forest and say that a given taste is like the taste of some other thing, only different.
One of the lowest forms of tongues is that of the gasteropod. All snails and slugs are gasteropods. They have instead of a regular tongue a strip
