bones in us, of any kind. Some have begun to be a little solid, others have not. Where the bones afterwards are, we find a piece or lump of something which is nearly transparent, and more like jelly than bone. This in time ossifies, that is, becomes solid, and thus forms bone.

GROWTH OF THE TEETH.-The teeth, as well as the other bones, are at first mere pieces of jelly. They do not appear at birth, for they are in the jaw-bone. And what may seem strange to you, the lumps of jelly-like substance which make both sets of teeth, (those which are shed early, and also those which come afterwards in their place,) are there at the same time; the former near the edge of the jaw-bone, and the latter a little deeper within it.

It will greatly help you in understanding me, if you examine the following engraving. It shows the teeth as they appear in a child, before he has shed many of the first set. Near the roots of the regular teeth, you will see the beginning of some of the second growth.

When the soft pieces of jelly which form the teeth become bone, the process is as follows:-First, a hard speck commences in the centre of a tooth, which is deposited by the blood-vessels which nourish it; and this gradu ally grows larger, till all the jelly is absorbed and gone, and its place occupied by bone.

think a

The teeth, however, consist of something else besides solid bone. If they did not, they would very soon wear out. Do you piece of common bone put in the place of a tooth, would last us to chew with half a century or more? By no means, you will say. I will therefore now tell you of the

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STRUCTURE OF THE TEETH.-Each tooth consists of three parts-the crown, the neck, and the fang. The fang or root is the part which is set firmly in the jaw-bone, as if it were driven in like a nail. The neck is close to the edge of the jaw, where the skin or membrane which covers the jaw-bone joins to the tooth and adheres to it. It is this membrane which the dentist separates from the tooth with his lancet, when he is about to extract it. The tooth is a little smaller here, like a neck, or as if a cord had been tied tightly around, and indented it. The crown or body of the tooth is that part which we see above the gum. Every tooth has blood, and feeling in it; but of this I cannot tell you the particulars now. You will find more about it in another chapter.

Now to prevent the teeth from wearing out, as a piece of common bone would, this crown is coated all over with something much harder than any bone in the human body. It is called enamel.

USES OF THE TEETH.-Hard as it is, however, enamel will wear out in time. It

will wear out much sooner, if we pick the teeth, as many do, with pins and needles. These things are too hard, even for the hard enamel, and are apt to crumble it off. So is the wretched practice of cracking nuts with the teeth, or indeed the biting of any substance harder than the crust of good dry bread. If used to bite nothing harder than that, and if not injured in any other way-for there are a thousand ways of injuring the teeth-they may perhaps last all our lives. But if the enamel once gets broken away, so that air and other substances come to the softer bone under it, the tooth soon becomes hollow, or decays. Like any other part of this wonderful frame which God has given us, the teeth will, however, last the longer for being moderately used.

Those kinds of food and drink which injure the stomach, injure also the teeth, and cause the enamel to become soft, and break away. Why this is so, is a question which it would take too long to answer here; but you may believe the fact. In another place, I shall probably say more on this subject.

One thing more, however. The teeth must be kept perfectly clean. After eating

anything, always rinse them well. And if you rub them with a soft brush several times a day, it will do some good in the way of preserving them, and prove a means of saving you from the racking torments of the toothache.

BONES OF THE EAR.-Hardly any part of the wonderful machinery of the human body is more difficult to understand, than the structure and uses of the organ whose bony part I am about to describe. About three quarters of an inch or an inch within each of the two side doors of the cupola-the ears—is a film or membrane drawn tightly across the passage, like a drum head. This is called the membrane of the tympanum-tympanum being the Latin word for drum; and a cavity behind the membrane is called the tympanum.

In this latter cavity are four small bones, which are undoubtedly, in some way or other,