The Yogi practices exercises by which he attains control of his body, and is enabled to send to any organ or part an increased flow of vital force or "prana," thereby strengthening and invigorating the part or organ. He knows all that his Western scientific brother knows about the physiological effect of correct breathing, but he also knows that the air contains more than oxygen and hydrogen and nitrogen, and that something more is accomplished than the mere oxygenating of the blood. He knows something about "prana," of which his Western brother is ignorant, and he is fully aware of the nature and manner of handling that great principle of energy, and is fully informed as to its effect upon the human body and mind. He knows that by rhythmical breathing one may bring himself into harmonious vibration with nature, and aid in the unfoldment of his latent powers. He knows that by controlled breathing he may not only cure disease in himself and others, but also practically do away with fear and worry and the baser emotions. To teach these things is the object of this work. We will give in a few chapters concise explanations and instructions, which might be extended into volumes. We hope to awaken the minds of the Western world to the value of the Yogi "Science of Breath." CHAPTER III. THE EXOTERIC THEORY OF BREATH. In this chapter we will give you briefly the theories of the Western scientific world regarding the functions of the respiratory organs, and the part in the human economy played by the breath. In subsequent chapters we will give the additional theories and ascertained facts of the Oriental school of thought and research. The Oriental accepts the theories and facts of his Western brothers (which have been known to him for centuries) and adds thereto much that the latter do not now accept, but which they will in due time "discover" and which, after renaming, they will present to the world as a great truth. Before taking up the Western idea, it will perhaps be better to give a hasty general idea of the Organs of Respiration. The Organs of Respiration consist of the lungs and the air passages leading to them. The lungs are two in number, and occupy the pleural chamber of the thorax, one en each side of the median line, being separated from each other by the heart, the greater blood vessels and the larger air tubes. Each lung is free in all directions, except at the root, which consists chiefly of the bronchi, arteries and veins connecting the lungs with the trachea and heart. The lungs are spongy and porous, and their tissues are very elastic. They are covered with a delicately constructed but strong sac, known as the pleural sac, one wall of which closely adheres to the lung, and the other to the inner wall of the chest, and which secretes a fluid which allows the inner surfaces of the walls to glide easily upon each other in the act of breathing.