then comes along a particle of blood, loaded with salts of lime, or some necessary ingredient, which it deposits, and which remains in its place; thus proceeding, little by little, till the whole osseous structure is complete.

These particles, which are thus conveyed to form bone in the place of gelatine, are most of them lime, or phosphate of lime, or at least something which makes lime, before it can become bone; though other earthy matters are slightly mixed with them. Who directs the little particles of lime to the places where they are wanted? Who tells them to stop at the bones, and not before? The same beneficent Creator, who arranges all the other wonderful things contained in our bodies.

The power of the system to take out from the blood what is wanted for its growth and support, is aptly, though quaintly, shown by Dr. Edwards. Speaking of the wonderful distribution of the blood, in the little arteries, to every part of the body, he thus adds:

Along, on the lines of these tubes or canals, (the arteries,) through which the blood, with all its treasures flows, God has provided a vast multitude of little organs or waiters, whose office is, each one, to take out of the blood as it comes along, that kind and quantity of nourishment which it needs for its own support, and also for the support of that part of the body which is committed to its care. And, although exceedingly minute and delicate, they are endowed by their Creator with the wonderful power of doing this, and also of abstaining from, or of expelling and throwing back into the common mass, what is unsuitable, or what they do not want, to be carried to some other place, where it may be needed; or, if it is not needed anywhere, and is good for nothing, to be thrown out of the body as a nuisance.

'For instance, the organs placed at the ends of the fingers, when the blood comes there, take out of it what they need for their support, and also what is requisite to make finger-nails; while they will cautiously abstain from, and repel, that which will only make hair, and let it go on to the head. And the organs on the head carefully take out that which they need for their support, and also that which will make hair, or, in common language, cause it to grow; while they will cautiously abstain from taking that which is good for nothing except to make eyeballs, and let it go to the eyes, and will even help it on. And the organs about the eyes will take that, and work it up into eyes, or cause them to grow. And so throughout the whole.'

By this it is plainly seen, that there must be a constant waste in every part of the system. It is impossible but that the friction-the 'wear and tear' of hundreds of muscles and tendons, and thousands of rapid streams should gradually produce decay, let the parts be ever so hard; a continual dropping will wear away a rock.

Now the blood not only carries out little atoms of particles, to cause all parts of the body to grow, and to replace the atoms that were worn off by friction, but it also takes away the worn-out and good-for-nothing particles, and carries them clean out of the body. It is true that they are taken up by the absorbents in the first place; but then the absorbents carry them to the blood, and empty them into it, which amounts to the same thing. In this way, as you may easily see, the blood is liable to lose its purity and excellence, since it is constantly giving out good particles, and receiving bad ones.*

* The manner in which the bad or waste particles are removed from the system is very curious. Take the kidneys, for instance, which seem

Motion of the Heart.-The heart is kept in motion, we know not how; nor can the wisest anatomist or physiologist in the world tell us. have something to do in the a-going, we can form some idea of what keeps it in action; but after all, the real cause of the continual

We know that the lungs

case; and when once set

motion of either the heart or the lungs, is a great mystery, and will probably remain so for ever.

You are aware that the motion of the heart can be

to be a sort of sieve or filter; with this difference, however, that while a sieve only permits the finest and best parts to pass through it, the kidneys filter out the worse or coarser parts. These are carried in two pipes, called ureters, to the bladder, whence they are conveyed immediately out of the system.

felt, when a hand is placed on the left side, near the middle of the ribs. This important organ-not much larger than a man's fist, and strong and muscular— is situated slanting, or obliquely, as you see in the above engraving. It is represented nearly in the position in which my heart would appear, if you could stand before me this moment, and see it just as it now is, in full motion. I mean, its position is just what it would then be. In other respects, it would appear differently, especially in its connexions; for the vessels which go to it and come from it are here represented as partially removed.

This engraving represents the heart with its principal vessels divested of their covering, called in technical language the pericardium, or, familiarly, the heart-purse, which closely envelopes the entire heart, and the commencement of the great vessels connected with it. This is one of the strongest membranes of the body, and, like all other parts, is supplied with arteries, veins, and nerves. In the view now represented, this heart-purse is cut away, and the heart itself exposed to view. I mentioned a little about the heart in a former chapter, but, as I am now about to explain its functions, it will be necessary, for the elucidation of the subject, to go a little more into detail.

The heart, then, is a hollow muscle, and, in persons of the ordinary standard, is about a pound in weight, varying, however, in this respect; its shape is conical, and it is placed in the chest, under the cartilages of the ribs and the breast-bone. The base, which is much the broadest part, and where the great apertures are placed, is turned obliquely upwards and backwards, almost facing the spine, while the point or narrow end projects

forwards and towards the left side. The heart contains within it four distinct chambers or cavities, two on the right side and two on the left; an auricle and a ventricle on each side, one of which, on the upper and right side of this viscus, is called, for the sake of distinction, the right auricle, and which receives the terminations of the two great veins of the body, the venæ cavæ. The next chamber is the right ventricle, a cavity much larger and thicker than the last, and lined with strong muscular projections. The orifice between these cavities is encircled by a tendinous ring, which gives attachment to a valve, and from the circumstance of its having three divisions in its substance, is called the tricuspid valve, and which is fixed to the strong muscular columns just mentioned, by several thin tendinous cords.

From the upper and left side of the right ventricle, emerges the pulmonary artery, which has also valves at its entrance, called semilunar valves. This artery is of considerable size, and passes behind the breast-bone, dividing into two branches, corresponding to the right and left lobes of the lungs; and these again, ramifying in still smaller divisions, gradually become more minute, throughout the entire substance of the important organ they supply.

At the extreme ends of the smallest branches of the pulmonary artery, commence in a series of corresponding minuteness, the pulmonary veins; these, gradually uniting, form four great trunks, which find their termination in the left auricle of the heart. The left auricle is in appearance and size very similar to its companion on the other side, excepting that it is much stronger in its texture. Adjoining to it, and towards the front of the body, is situated the left ventricle, separated from the last chamber by a valve, which, from its supposed re