lungs is, that it may meet the air which we take in every time we breathe, and which passes through vessels constructed for this purpose, into the lungs. A certain portion of this air only is taken into the blood, and air of another kind is given out by it. It would be too difficult a subject for you at present to understand, if I explained this more fully; only I must tell you that the blood in the veins is of a dark purple colour, but when it meets the air, it changes into a bright red.

Emily. Then are there holes in the blood-vessels, or how do they get the air out of the air-tubes?

Mamma. No, there are no holes which can be perceived, either in the arteries, or in the air-vessels, which run always parallel with them in the lungs ; but it is supposed that the blood absorbs, in some way unknown to us, that portion of the air which is called oxygen, and which gives the blood that red colour it becomes after this has happened.

Emily. Will you repeat to us again, mamma, what you have said about the way the blood goes: it is so difficult to remember?

Матта. The heart is composed of how many parts?

Emily. Of two.

Mamma. And what is there in each of these parts?

Frank. An auricle and a ventricle.

Mamma. Right: for what purpose is this division?

Emily. One auricle and ventricle has to circulate the blood through the lungs, and the others through the body.

Mamma. Right. This then is the process: The

blood goes first into the right auricle, and passes from thence into the right ventricle, which throws it into the artery, which carries it through the lungs; this is called the pulmonary artery, and this distributes the blood through smaller branches, which empty themselves into the pulmonary veins, and finally into the left auricle. This throws the blood into the left ventricle, which empties itself into the great aorta. From thence the blood is distributed by smaller arteries all over the body. These, as I explained to you, empty themselves into veins, which bring back the blood to the right auricle.

Frank. Then, mamma, has the blood, after it has been through the body, to pass into the lungs again? Mamma. Yes, every time it is brought back by the veins to the heart.

Emily. Then are there two actions of the heart; one to throw the blood into the body, and the other to throw it into the lungs?

Mamma. No, it is one and the same; so wonderfully is that astonishing machine taught to work.

Frank. But, mamma, there is one thing which puzzles me very much; did you not say that the blood in the veins was black, and in the arteries red?

Mamma. Yes.

Frank. And that when it had met the air it became red?

Mamma. Yes.

Frank. Then when the arteries take the blood over the body it is red, is it not?

Mamma. Yes.

Frank. Then how does it turn black again when it gets into the veins?

Mamma. The oxygen, or vital air, contained in the arterial blood, is supposed to be absorbed, as the blood passes through its course of circulation, so that when it has entered the veins, it is again of its original dark colour, and therefore requires to pass again through the lungs, to gain a fresh supply of oxygen.

Frank. Thank you, mamma, I understand it now, but I have one more difficulty. If there is fresh blood continually made, how is it that the body does not get too full of it?

Mamma. For this reason: there is a process continually going on within us, by which its particles are carried off or absorbed; and this is so wonderfully contrived, that the fresh supply in healthy persons is just equal to the portion wasted.

Frank. But where can the blood go to?

Mamma. I told you before that our bodies were covered with little holes or pores, and through these the watery particles of the blood are continually escaping.

Emily. Is there water mixed with the blood?

Mamma. Yes, it contains a large portion of watery matter, which separates entirely from the other particles, when blood is put in a vessel by itself. Now let us return to what we were speaking of before.

Frank. Will you tell us something about the lungs, and where they are placed?

Матта. The lungs are placed in the cavity which you will remember there is between the spine and the breast-bone, and are of a soft spongy texture. Frank. Is there more than one lung, mamma, as there is only one heart?

Mamma. Yes, two; one on the right, and one on the left of the chest, and they contain both air and blood vessels. That on the right side is divided into three parts or lobes; that on the left side is divided into two lobes, between which is a space where the point of the heart lies.

Emily. How are they separated from each other? Mamma. Each lung is contained in a strong membraneous bag, called the pleura, and the air-vessels which are connected with the wind-pipe, through which you know we breathe, run along between the blood-vessels in the lungs, and so give to them that quantity of air which is required to change the colour of the blood, as I have already told you, and to render it fit for circulation.

Frank. I want to know how it is, that when the blood is sent from the auricle into the ventricle, it does not run back again?

Mamma. There is a curious provision to prevent this, which is, that the one is separated from the other by valves.

Jane. What are those, mamma?

Mamma. The simplest idea I can give you of them is, that they are like little doors, which, if shut up by a force on one side, continue closed, and cannot be opened by any pressure on the opposite side. Jane. But are they made of wood?

Mamma. No, nor of one membrane, but of several. The valve remains open whilst the blood is passing through the right way, but if any were to flow back, it would lift the door from the side on which it was hanging, and shut up the passage entirely.

Frank. What a wise plan! How exactly it must answer the purpose!

Mamma.

It does so completely, and gives us one of the many proofs we everywhere meet with, of the wonderful care of God in our formation.

Emily. hurt?

Are the lungs then very liable to be

Mamma. They are; and it is for this reason they are so well protected. Can you conceive of any situation in the body where they could have been so safe, as in the hollow strong box, made by the spine, the breast-bone, and the ribs?

Emily. They are well taken care of, indeed.

Frank. I think every body who studies these things much, must love God exceedingly, and be very pious-are they not, mamma? They must see more of his wonders than any one else.

Mamma. It should be so, my dear, but 1 fear it is not always the case, for we know that no outward thing will change the heart: this must be the work of God's Holy Spirit,

Frank. I want to ask you one thing more, and that is, how the discovery was made of the circulation of the blood, and who made it?

Mamma. A very wise author seems to have known it, one whose works you have read.

Frank. I, mamma?

Mamma. Yes, a very wise man, who when he was asked whether he would be rich, or powerful, or wise, chose the latter, before all the others.

Emily. O, mamma means Solomon; but is there anything in the Bible about the circulation of the blood? I do not remember it.

Mamma. There is a passage in the Ecclesiastes, which is generally understood to refer to this subject.