One of these gases, named oxygen, might well be called "life-sustainer"; it forms about one-fifth of the air we breathe, and is that part of it which makes our fires burn and our lamps give light, and keeps us and all the animals alive. The other gas is called nitrogen; it is a dull gas, with no life in it, and remains behind when all the oxygen is taken out of the air. But this part of the air is very useful; it prevents the breathing of men and animals and the burning of fires and lamps, from going on too fast. If you had only the life-sustaining part of the air to breathe, you would soon die; and if the air was all made of that part which burns so well, one spark falling upon it would be enough to burn up the whole world, for no one could put the fire out. These two gases are mixed in nearly the same proportions in all climates so as to make the beautiful pure air which God has given us to live and go about in. There is another gas, called carbonic acid, made partly of oxygen and partly of carbon, or burnt wood, which might be called "life-destroyer," for it will put out light and make an end of life. It is one of the most deadly poisons, and forms the "choke-damp" which too often suffocates the miner; but what we call fresh air contains such a very small proportion of this dangerous gas that it is harmless. Still we must remember that every time anyone or any animal breathes, some of the air by which we live is taken away from that which surrounds us, and some of this poisonous air is thrown into it. If this is the case, should we not, by degrees, find the air becoming less and less pure and fit for us to breathe? Certainly it would be so, if God had not made a beautiful provision for keeping the air fresh, which I will try to explain to you. You may remember that the Lord Jesus, after He had made the five barley loaves and two small fishes prove enough for thousands of hungry men and women and little children, turned to His disciples, and said, "Gather up the fragments that remain, that nothing be lost." So, in the world around us, we may often see that God gives freely, but does not allow what He has freely given to be lost or wasted. Now when you take a long breath, and breathe in the air, you presently breathe it out again. But what you breathe out is not the same; the part of it by which you live is gone, and a poisonous air has taken its place. Then, if every person in the world, and even the smallest animal, is constantly using up the good part of the air, and breathing out that which has been spoilt for animals, and would kill them if they had nothing else to breathe--why are not all animals poisoned? What becomes of this air which has been spoilt for them? Is it good for anything? Ah! there is a wonderful, beautiful answer to these questions going on all day long, surely and silently, unseen by any of us.