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vapours, rather than the vapours themselves. suppose all the air were taken away, and you were left standing with nothing around you but these vapours, what do you think would happen to you? You would be dead in less than three minutes, killed by their poisonous power. The vapours which are bred in decaying substances are poison-vapours.

You would like to know why it is, as these poisonvapours are poured out in such quantities from all decaying substances, that you do not see people dying all round from breathing them. Did I not tell you, in the case of the poison-vapours of the manure-heap, that you could breathe them because they were freely scattered into the fresh air? Now just come a few yards this You observe the smell of the manure grows less way. and less. Here you cannot any longer perceive it, although the wind is actually blowing over the manureheap towards us. The fact is, these poison-vapours cannot bear the presence of pure air. Pure air is the natural antidote or remedy for their poison. The instant it mingles with them it begins to destroy their hurtfulness, and in a few moments it has so thoroughly accomplished this good work that no single trace of mischievous power remains.

Has it ever occurred to you to ask yourself why the pleasant wind blows over hills and fields, and through lanes and streets? You know very well that the wind always is blowing, more or less. Go out when you will, you find it, if you turn the right way. It is the most uncommon thing in the world for the air to be altogether still. The fresh wind blows so constantly over hill and plain, because God sends it to sweep away and destroy the poison-vapours that steam out from decaying substances. The breeze is God's invisible antidote to the invisible poison. The pleasant wind blows in order that the air may be kept fresh and pure.

In the open air the fresh wind very soon scatters and destroys all poison-vapours. But civilized men do not

dwell always in the open air. The wind sometimes makes them feel cold, so they build themselves houses to shut out the wind. To-night, before you go to bed in your small sleeping room, you will close the windows and the door; and you will think, when you have done so, that you have shut out everything which could harm you, with the cold. But what will you say to me if I show you that after you have closed the windows and the door, poison-vapours are bred in great quantities in the room where you are lying? and that so long as you remain in it, they keep gathering more and more strength, and becoming more and more dangerous. Just come back with me to the cottage, and let us look at the room in which you were sleeping last night. The beds, you believe, are not yet made-never mind that. I often go into rooms under such circumstances, and perhaps upon this occasion it may be even better for the purpose I have in view, if I find the chamber in disorder. At any rate let us go upstairs and take our chance.

Sure enough you have been at great pains here to keep the cold from getting in. There is only one casement in this low small room, and that casement has not been unbarred since yesterday. I do not need to be told this. I make the discovery myself; for you have also kept something from getting out, which had better have been away. I feel at once this is not the same kind of air which we were breathing just now in the open garden. Indeed, I cannot remain in the room without opening the window. There; I throw open the casement, and in a few minutes the air will be as fresh here as it is outside of the house.

Now what do you think it was that made the air of this room so unpleasant? It was the poison-vapour with which it was laden, and which had steamed out of your body mixed with your breath during the night. Poison-vapours are bred in the bodies and in the blood of all living animals, just as they are in manure-heaps.

All the working organs of your frame being exhausted by use, undergo decay and are turned into vapour, and that vapour, being bred of decay, is poison-vapour, which must be got rid of out of the body as quickly as it is formed Living bodies are worn away into vapour by working just as mill-stones are worn away into dust by grinding. You would see them waste under work, if it were not that they are repaired by food. You wonder, then, that as this vapour is poisonous, living creatures do not destroy themselves by the poison they form in their blood? Occasionally human creatures do so destroy themselves. But the merciful Designer of the animal frame has furnished a means by which, in a general way, the poison is removed as fast as it is formed. Can you not guess what this means is?

LESSON 42.-POISON-VAPOURS AND THEIR DANGER.-Part 2.

GOD employs the same plan for driving away poisonvapours from the inside of living animal bodies, that He uses for the purification of the air in the open country. He causes a current of air to circulate through them. Notice how, while we are talking together, our chests heave up and down. You know this is what we term breathing. Now, when we breathe, we first make the insides of our chests larger by drawing their walls and floors further asunder. Then we make them smaller by drawing their walls and floors once more nearer together. When the chest is made larger, fresh air rushes in through the mouth and wind-pipe, and through the twig-like branches of this pipe, until it fills a quantity of little round chambers which form the ends of those branches. Look at this picture. It is a representation of one of these chambers, greatly magnified, in order

that its character may be readily seen. The wind-pipe branches out into several millions of fine twig-like tubes, and then each tube ends in a blind extremity, or chamber exactly like this.

Do you observe that the air-chamber in the picture is covered by a sort of net-work, stretched tightly over it? That net-work is formed of blood-vessels, through which the blood is constantly streaming, driven on by the action of the heart. This blood sucks air from the air-chambers into itself, and carries that air onwards to all parts of the living frame. But the blood-streams in the net-work of vessels also steam out into the airchambers poison-vapours, which are then driven out through the windpipe and the mouth. Thus the breath which goes into the mouth is fresh air; but the breath which comes out of the mouth is foul air. Air is spoiled, and, as it were, converted to poison, by being breathed; but the body is purified by the breathing, because it is its poison-vapours that are carried away, mingled with the spoiled air.

This, then, is why men breathe. Breathing is the blowing of a fresh wind through the living body for the cleansing away of its impurities. The purifying part of the air which is breathed actually circulates with the blood through all parts of the frame.

Exercise quickens and exalts the cleansing powers of the breathing and this is why it is of such great importance to the health. When you go and take a brisk walk in the open air, you increase the force of the internal breeze. The exertion makes your chest expand to a larger size, so that it can admit more fresh air, and it also causes your blood-streams to course along more rapidly, so that a greater abundance of the air is carried on through your frame.

A very large quantity of fresh air is spoiled and rendered foul by the act of breathing. You, yourself, spoil not less than a gallon every minute. In eight hours' breathing a full-grown man spoils as much fresh

air as seventeen three-bushel sacks could hold! If you were shut up in a room seven feet broad, seven feet long, and seven feet high, the door and windows fitting so tightly that no air could pass through, you would die, poisoned by your own breath in a very few hours; in twenty-four hours you would have spoiled all the air contained in the room, and have converted it into poison, provided you could have lived therein so long.

I will explain how all the mischief, which results from breathing foul air, may be prevented. Come down with me into the garden, and creatures that you believe to be of far inferior powers to yourself shall give you a lesson.

You keep bees. Here is a hive, I see, crowded with the busy insects. By the numbers that I observe clustering about the low arched door, and bustling out and in so incessantly, I learn that the industrious little fellows must be very closely packed together in their straw house. There must be many thousands of them dwelling together in a space that cannot, at the most, equal more than a couple of square feet; and there is not a single window in the straw wall; no opening of any kind but the low, and half-choked entrance. Really if those bees need to breathe, you who have furnished them with their dwelling must be nearly as bad as the cruel Nabob, who shut up his prisoners in the Indian Black Hole!

Those bees certainly do need to breathe every bit as much as men and women; and what is more, they manage to breathe ten times better than you do at night. Notwithstanding all the crowding there is within their close dwelling, the air never gets there into the poisonous state in which the air of your sleeping room is by the morning. The bees take care that it shall not do so. Just bend down your ear and listen near the hive for a minute. Do you hear that incessant low humming? That is the bees hard at work, making an artificial wind. It is the sound of a couple of score

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