Why is smoking injurious to the teeth? 226. What remark respecting the temporary teeth? 227. What remarks respecting the permanent teeth? Do those persons that extract teeth require skill as well as knowledge? 228. Why should not teeth be extracted at all times when they are painful? -=-=-=-=-=-=-=-=-=-=-=-= _Illustration._ Dr. H. M., of Belfast, Me., related to me that an individual in that vicinity had his teeth, (all of them sound,) on one side of the lower jaw, extracted by an ignoramus of a "tooth-puller," and this without any relief from pain. The disease was tic douloureux, which was relieved by Dr. M. 229. _The preservation of the teeth requires that they be frequently examined._ When a part of the enamel is removed, and a small portion of the body of the tooth has become carious, in many instances such teeth may be preserved from further decay by having them filled or "plugged" with _gold foil_. All amalgams, pastes, and cheap patent articles for filling, should be avoided, if you would preserve both the teeth and the general health. 230. The practice of cracking nuts with the teeth, or of lifting heavy bodies, and the constant habit of biting thread, should be avoided, as they finally destroy the enamel. 231. _All acidulated drinks and mineral waters, that "set the teeth on edge," are injurious._ All tooth-powders and washes that contain any article that is acid, corrosive, or grinding, should be banished from the toilet. Tobacco is not a preservative of the teeth. It contains "grit," which wears away the enamel; beside, when chewed, it debilitates the vessels of the gums, turns the teeth yellow, and renders the breath and the appearance of the mouth disagreeable. 232. Healthy persons have generally sound teeth, while feeble persons have decayed teeth. For this reason, we should try to learn and practise the few simple rules that promote health. -=-=-=-=-=-=-=-=-=-=-=-= Give an illustration of the removal of sound teeth. 229. How may decaying teeth be preserved? What should be avoided in the filling of teeth? 230. What practices should also be avoided? 231. What is said of acidulated drinks? What effect has the chewing of tobacco upon the teeth? 232. What is one reason for preserving health? -=-=-=-=-=-=-=-=-=-=-=-= CHAPTER XIII. THE DIGESTIVE ORGANS. 233. From the earliest existence of the human system to the last ray of life, change is impressed upon it by the Giver of this curious fabric. New atoms of matter are deposited, while the old and now useless particles are constantly removed. The material necessary to sustain the growth of the body in early life, and also to repair the waste that is unceasing to animal existence, is the food we eat. 234. Food, animal or vegetable, contains most of the elements of the different tissues of the system, yet it must undergo certain essential alterations before it can become a part of the body. The first change is effected by the action of the _Digestive Organs_.