To understand this, we must learn what processes are going on in the body, by means of which food is converted into tissue, into heat and energy. These processes we find are chemical, and may be likened to the combustion of wood or coal in the furnace. We know that fire must have air in order to burn. Burning is the process of oxidation or combustion of oxygen with the atoms of fuel and the formation of a new substance thereby. Coal, we are told, consists of carbon and nitrogen, both of which readily combine with oxygen, and in the process of uniting heat is liberated, and waste compounds thus formed pass off through the smokestack or chimney. We may not understand this scientifically, but we know that if we want the fire to burn well we must give it draft or air. Our bodies are living engines, and use food and air instead of coal and air. Food in the body without air is like the coal in an engine without air; and air is useful only because it brings oxygen to unite chemically with the food. This process is going on all over the body. Each little microscopical cell is a furnace in which oxidation is taking place; and not only is energy liberated, but reconstructive processes are going on, new tissues are being formed, and old tissues removed. But how can the oxygen get to the cells in all parts of the body? We can readily see how it gets to the air-cells of the lungs, but it would do little good if it stopped there. It must be carried in some way to all the minutest cells of all the tissues. This is done through the breathing. The blood goes to the lungs, and there it gives out the waste material it has collected in its journey through the body and takes up oxygen. The blood goes to the lungs dark in color from its load of waste. It is changed to a bright red by taking up oxygen. Each red blood-corpuscle takes a load of oxygen, carries it to its destination, and gives it to some tissue to be used up in the chemical process of oxidation, upon which depends our life and energy. During the hours of rest the tissues are busy in this process, and during exercise the energy stored up in the tissue-cells is liberated and waste created. So we see that the process is a continual round of taking food and air, using them in rebuilding tissue, then using up the tissue by exercise and casting out the waste products. And now we can begin to understand that we live in proportion as we breathe. Dr. Holbrook says: "The activity of the child is in close relation to the strength of its lungs; so, too, is the calmness, dignity and power of a man in proportion to the depth and tranquility of his respiration. If the lungs are strong and active, there is courage and boldness; if feeble, there is cowardice and debility. To be out of spirits is to be out of breath. To be animated and joyous is to be full of breath." "Breathing," writes Dr. von der Deeken, "is an actual vivifying act, and the need of breath as felt is a real life-hunger and a proof that