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the mischievous effects, it is not only foolish but wrong if, by our neglect, we go on breaking what He has thus shown to be one of His laws. Life is thrown away in the common course of events by the want of care in such small things, much faster than in great battles. We are very pitiful when we hear that three hundred men were killed at Inkerman; but we think nothing of it when the Registrar-General's Return shows that six hundred people died in London of preventible disease. "Let each one mend one," a wise woman once said, "and then we should get on faster."

If every person kept his own house clean and freshly aired, there is no telling how many dreadful diseases would be saved to the nation. So that we must remember that we are not only responsible for our own health, but for that of our neighbours too.

LESSON 41.-POISON-VAPOURS AND THEIR DANGER.-—Part 1.

How

JUST come out with me here, upon the road. pleasant and fresh the day is. Do you not feel the gentle breeze fanning your cheek as you turn up the lane? Yet you cannot see the breeze! What is it, then? Certainly it is something, for it touches and even presses against your skin. But it is something, too, which has weight and power of its own. Observe how it shakes the leaves of the trees as it sweeps past them. It is, as you know, the same unseen breeze which also drives round those great mill-sails yonder with such violence, and which grinds as much corn in that mill, as could be ground by the efforts of a dozen horses, kept up to their work by the whip. We have not had to move far, then, before we have come upon something which we cannot see; before we have proved to ourselves that we must not altogether depend upon our eye-sight for information, even concerning the exist ence of surrounding things.

But what is this? The breeze is not so fresh here as

it was just now at the end of the lane. There is some very disagreeable smell now floating upon it. Here again we can see nothing, any more than we could when we had only the fresh breeze blowing around us. But there must be some cause for the unpleasant odour. The smell gets stronger and stronger as we approach this bank. We climb over the bank, and we find on the other side, in the corner of a field, a manure-heap, from which the smell is evidently poured out. Now that smell is really a vapour, bred of decay in the manure, and then steaming up from it into the air. If our eyes were as sharp as our noses, we should be able to see a great host of little bodies rushing up from the manure, and scattering themselves through the air. It is because some of those little bodies strike upon the lining of our noses, as they are drawn in by our breathing, that we smell the unpleasant odour. The nose feels the touch of those bodies as a smell.

Wherever substances which have been alive, are dead and undergoing decay, vapours of this kind are bred and steamed forth. This is the way in which dead things are got rid of; they turn to vapour and crumble to dust. If we could see all the vapours that are being bred of decay, we should be sensible of a thick mist covering the entire face of the land and sea, and rising up from it continually. Some of these vapours have strong smells, like those which issue from the manure-heap; but some of them cannot even be smelt, any more than they can be seen.

But these invisible vapours bred of decay, were not intended to be breathed by living creatures; and, indeed, cannot be breathed by them without mischief. We are able to stand near the manure-heap for some time without taking any particular harm, because the vapours are scattered as fast as they are formed, and are mingled in small quantities with large quantities of pure air. We thus breathe air tainted with these

But

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 way. You observe the smell of the manure grows less 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.

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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

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