Lungs

in man, a pair of organs playing the principal part in breathing. They are inclosed in the chest, an air-tight chamber cut off from the abdomen by the diaphragm. One lung is situated on the right side of the heart; the other on the left. Air entering the nose or mouth enters the lungs by means of a gristly windpipe or trachea. The windpipe branches at its lower end. The lungs are very light in structure, weighing not to exceed one-thirtieth to one-fiftieth of the body. The lungs of an adult male weigh between forty and fifty ounces; those of a female from twenty-eight to thirty-five ounces. In structure, the lungs are composed chiefly of air cells, having thin walls in which blood capillaries are spread out. All the blood of the body passes through these capillaries many times during an hour. By action of the diaphragm, which converts the lungs into a sort of bellows, air is inhaled and exhaled. The walls of the capillary are so thin that oxygen passes from the air through them into the blood. The blood gives off carbon dioxide through the walls into the air spaces. The air thus vitiated is driven out of the lungs and is replaced by fresh air. The more deeply one breathes, the more complete the change of air in these sacs. For this reason physical exercises designed to expand the chest are helpful. The process of breathing and purifying the blood must be kept up night and day, sleeping or waking. One who is deprived of air is said to be smothered. The lungs of all air-breathing vertebrates are much alike. The butcher speaks of an animal's lungs as the lights. See Air; Blood; Diaphragm; Asthma; Consumption; Heating And Ventilating; Fish; Grasshopper

Nothing is more interesting than the body's methods of economy. For instance, in its work of taking in oxygen and throwing off carbondioxid, it needs space, surface. And so there has been evolved a method by which in the lungs the inhaled air reaches a surface of sixteen hundred square feet. The peculiar little openings, or vesicles, by which this economy of space is gained are six hundred millions in number. There passes into and out of the lungs in one day no less than four hundred cubic feet of air. Each outgoing breath contains two cubic inches of carbondioxid, and contaminates five thousand cubic inches, about half a barrel of air. The lungs exhale every day an amount of carbon that if caught and solidified would about equal a lump of coal weighing half a pound.

The air breathed out is moving at a speed of forty-three inches a second, and is inhaled at a speed of fifty-two inches a second. In a sudden intake of breath, as in a sob or gasp of surprise, the speed of the inhalation may be much greater, -ten or even twenty feet a second.

The external surface of the body has an area of about twenty square feet, and contains seven million minute openings, perspiratory glands, out through which the blood pushes certain of its poisonous ingredients.

The skin has a respiratory as well as a perspiratory function. Through a healthy skin we take in about one-sixth as much oxygen as through the lungs. Dr. Woods Hutchinson, What the Lungs Do, in Sunday Magazine.