The common impatience to get rid of the first set of teeth leads to the working at them when they may be a little loose. It is a bad practice. They should be left undisturbed until they are ready to be cast on the absorption of their slight roots, a process which is not complete until the new and permanent teeth are ready to make their appearance above the gum. They may then, at the last moment, when their hold is of the slightest, be aided by the gentle effort which will only be required to detach them.

The permanent teeth, that they may be worthy of their name, must be treated with the utmost care. They should be cleaned at least twice a day-on rising from and going to bed-and it would be well, also, to rinse out the mouth after each meal. A soft brush only should be used, and nothing but pure water will be necessary besides, if the cleansing of the teeth is habitual and frequent. When from neglect they have been allowed to become dirty, a little of the finest soap may be employed. All fancy powders and washes should be avoided, for, however good their immediate effect may seem, their habitual use will probably destroy the enamel of the teeth. This enamel, which covers the upper part or crown of the tooth, as

it is called, is certainly a very hard substance, but even it will yield to constant friction of hard or application of acid substances. It also is apt to be chipped off by being brought suddenly and violently into contact with any hard material, whether it be hickory-nuts or musket-balls; and if it should be chipped off or otherwise destroyed, the decay of the tooth will be sure to follow.

The shock, moreover, which the tooth receives from cracking nuts, or attempting to crush any excessively hard substance, will loosen it from its socket in the gum, which will become, in consequence, detached from its connection with the crown of the tooth, which is there protected by its coat of enamel, and, shrinking, expose the root of the tooth, which, being unguarded, will soon yield to decay.

Questions. What is mastication? How do birds masticate their food? Why is mastication necessary? How many teeth compose the first set? How many are the permanent teeth? How are the first teeth to be treated? How are the permanent teeth to be treated?

CHAPTER XIX.

Saliva. Use and Abuse of Taste.-Swallowing.-Its Dangers. Mr. Brunel's Escape. - Remedies for Choking.

It is not enough for the food to be cut up, which is done by the front teeth, called the incisors, or cutters, and ground by the back ones, termed molars, or grinders. It has to be moistened, particularly if the morsel eaten be very dry, for otherwise it could not, however finely cut or ground, be readily swallowed. While the masticating or chewing, then, is going on, if this important operation be properly performed, the food becomes mixed with the saliva, or spittle, supplied by little glands inside of the mouth. This is a fluid principally composed of water, but it has also a small quantity of albumen, which is the same substance as the white of egg, and some soda. These have not only the effect of smoothing and making the chewed and moistened food slippery, that it may be more easily swallowed, but also dissolve it to some extent, and thus assist in preparing it for the uses of the body.

The saliva is therefore of great service, and should neither be wasted nor abused. The habit of throwing it from the mouth on every occasion, or polluting it with tobaccojuice or anything else, is not only nasty, but harmful.

It is during the chewing of the food that the pleasure of eating is chiefly felt. By this active process the morsel is turned round and round in the mouth, and, being thus brought into close contact with the tongue and the palate, where there are nerves especially provided, is fully tasted and its flavor extracted. We are not, however, endowed with this taste merely for the gratification of sense, but it is given to us both as a motive to take food, and as a means of judging of the proper kind.

The tongue and palate, therefore, not only administer to our pleasure, but watch over our safety. They are ordinarily faithful servants and protectors, if not spoiled by over-indulgence, or rendered indifferent to their duty by brutal treatment. The taste is easily corrupted, and young people are accordingly warned against every abuse of their tongues and palates. They must check their excessive fondness for sucking sweets, their great proneness to imitate old

er fools in chewing and smoking tobacco, and their own frequent practice of exercising their jaws and powers of suction upon the tough india-rubber, the flinty rattan, and other substitutes for the sickening quid and cigar.

The morsel of food being well chewed, softened, smoothed, and tasted, is now, if acceptable, swallowed at the will of the eater. The process of swallowing is performed apparently so easily and ordinarily so carelessly that it is usually regarded as an operation entirely free from danger. There is, however, at the very beginning a certain risk, of which it is well to be aware.

There are two long passages which lead from the mouth into the interior of the body. These are the windpipe and the gullet. Through the former the air passes in and out of the lungs, and through the latter the food enters the stomach. They both open at the back part of the mouth close to each other, the windpipe just in front of the gullet.

There is a lid attached to the entrance of the former, over which all food must pass to get into the latter. This lid is ordinarily closed during the act of swallowing, and the food passes readily over its smooth surface into the opening of its proper passage, the