The little boats come to Lung Station and load up with oxygen about three times every minute, so you see how fast they travel. This freight is the thing that paints our cheeks a rosy color and gives us good health. When each little boat has unloaded its cargo in the far countries, the little cell men load them with a return cargo, which is made up of waste matter (carbon dioxide). This cargo is carried back to the Lung Station, and unloaded there. It is breathed out into the air, through the air tubes. [Illustration] If we breathe impure air, the little boats go back to the far countries with only a small cargo of oxygen. Then the cell men feel as if they are cheated and refuse to do good work for us. In fact, they grow weak and cannot do as good work as they could if the boats brought a full cargo of fresh air. There is another boat in the stream; just look at its queer shape, and, queerer still, this little boat is changing its shape. Is not that funny? Now the small end is toward us, now the large end, and now it is round like the little freight boats, only it is larger. I wonder what kind of a vessel it is. It is larger than the freight boat. There are not so many of these boats either, not half so many as there are freight boats. They are flying white flags, and belong to the White Squadron. I wonder if that means peace. No, they are war-vessels. Let us see what these white ships are doing. We will call them Dreadnoughts. Watch them as they move slowly down the stream; how powerful they look. They have their searchlights on, looking for any enemy that may appear upon the surface. Further on some germs or bacteria are coming up the stream; they may be pneumonia germs, or typhoid germs. These are the Captains of the Death Armada. The Dreadnoughts pull up along side. War is declared, a battle royal is on. The victory will go to the strongest. When the smoke clears away we may see the Dreadnought sailing calmly down stream. Where now are these mighty Goliaths, the typhoid or pneumonia germs? As the Dreadnoughts were in good fighting trim, we may find them on the inside of the engine-room of the Dreadnought. They are being used as fuel in its furnace. Sometimes the battle is in favor of the germs, and the Dreadnought is destroyed by the germs. This happens when the little round freight boats have not found a full cargo of fresh air and oxygen waiting for them in the Lung Station. All this happens in this wonderful stream. If we look further we would find that the muscle men in the muscle countries are busy making heat to keep our bodies warm. The little workmen in the gland country are making fluids to mix with the food we eat. The fluids change the starch, the sugar, and the meat we eat, so that the muscle men can use it to build us large and strong. The little workmen in the skin are pouring water out of it in order that we may keep clean and cool.