A healthy adult ordinarily breathes about eighteen times per minute, taking in each time about twenty inches of air. It is said that it takes at this rate sixteen respirations to completely renovate the air. This is probably true of our ordinary breathing, but the renovation of the air depends upon our manner of breathing. It is possible for us to breath so that at one expiration we almost displace the air from every portion of our lungs, and then by a full, deep, prolonged inspiration, (throwing forward the chest, throwing back the shoulder, and keeping the body erect,) fill the lungs fully with air and thus not only change the air in our lungs, but change in some degree the character of our blood so as to increase its purity. In order to test this let me ask anyone who is suffering from any slight indisposition, if it be headache, nausea, pains in different parts of the body, or any sickness, to try to breathe in this manner for half an hour, and observe if they do not feel better, being careful at the same time that the air breathed is good and pure. This point is of so much importance that I will refer to it again hereafter. The character of the respiration is an important diagnostic symptom and should always be noted. The rate of respiration varies as does that of the pulse, but the former is partly under the control of the will. The respirations are more rapid in women than in men, in children than in adults; it is modified also by position, exertion, excitement, and other conditions. We may count the respirations by observing the rise and fall of the chest, but it is well to put our hand on the stomach where the motions may be felt. Breathing is in man mostly abdominal, in woman mostly thoracic, but inflammation in the chest or abdomen will affect its character. DYSPNŒA, difficulty of breathing, arises when from any cause the amount of air entering the lungs does not correspond to the amount of blood sent by the heart for purification. The air may be unfit for its work, or disease in the lungs, or air passages may shut it out. Asphyxia results if the supply of air is in any way cut off. OF THE AIR. In this connection I will say to the nurse, give the patient pure air. Learn how indispensable this is to life, or health, or comfort; how indispensable to any person, and especially to the sick; how liable the air in the room is to be contaminated by the air breathed or expired by those in the room; by lights burning in the room; by exhalations from the bodies of the sick; by excreta left for a time in the room; by the inevitable floating dust from the floors and walls; from clothing, bedding, and furniture; and from the presence of organic matter in increased quantity, and of most deleterious quality in and around the sick.