=Hygiene of the Lungs and Its Relation to the General Health.=—Two conditions are essential for the preservation of the health and prevention of diseases of the lungs—good chest and lung development, and a continuous supply of fresh air for the proper ventilation of the lungs. Fully one-third of the whole volume of blood is always circulating in the lungs, and each corpuscle passes through them 8000 times in the twenty-four hours. In other words, the lungs are the vitualizing stations of the corpuscles which unceasingly go hurrying by. If these carbonic-acid-laden corpuscles arrive in the lungs, and do not find the requisite amount of oxygen awaiting them, they return to the tissues, carrying part of their carbonic acid back to them instead of a fresh supply of oxygen, and so the tissues are weakened instead of being nourished, while the corpuscles themselves suffer from lack of proper nourishment and deteriorate in form and color. Imperfect ventilation of the lungs is the most frequent cause of anemia or thinness of the blood. It must not be overlooked that the air may be fresh and pure, and yet not able to penetrate all parts of the lungs because of superficial and improper breathing. =Relation of Respiration to Body Heat.=—The heat of the body is generated by the oxidation of the tissues. The chilliness experienced by persons engaged in sedentary occupations is by no means always caused by the low temperature of the room, as will be proved by the thermometer, but by the close air of the room and superficial respiration, which causes internal overheating with imperfect combustion. The correctness of this statement may be proved if the woman will throw the windows wide open and take deep breathing exercises for five minutes. She will then go back to her work thoroughly comfortable. In other words, she has breathed herself warm. =The Respiratory Function of the Abdominal Muscles.=—Well-developed abdominal muscles play an important part in expiration, hence, in emptying the lungs of their impurities. Under normal conditions the pressure in the abdominal cavity is greater than that of the atmosphere; hence in the elastic recoil following inspiration, the abdominal viscera constitute a buffer, so to speak, and drive the diaphragm upward. The chief causes of flabby abdominal muscles, with its consequent low intra-abdominal pressure, are a sedentary life, the wearing of corsets which prevent the free play of the abdominal muscles, and the overdistention of the abdominal walls by repeated pregnancies and by the accumulations of fat. As a result of lax abdominal walls, there is very frequently an enteroptosis or a falling of the abdominal contents far below their normal position; this includes the liver, spleen, pancreas, the intestines and stomach, and is the most frequent cause of floating kidney. Further, the accelerating influence of the diaphragmatic movements on the circulation is seriously interfered with.