The lungs. Each lung is irregularly pyramidal or conical, with its base downwards, and one side (the inner) much flattened. The broad concave base is of a semi-lunar form, and rests upon the arch of the diaphragm. The apex is blunt, and reaches into the root of the neck, above the first rib, where it is separated from the first portion of the subclavian artery by the pleural membrane. The lungs vary much in size and weight, according to the quantity of blood and mucous or serous fluid they may happen to contain, which is greatly influenced by the circumstances immediately preceding death, as well as other causes. The weight of both lungs together, as generally stated, ranges from 30 to 48 ounces, the more prevalent weights being found between 36 and 42 ounces. The proportion borne by the right lung to the left is nearly 22 ounces to 20, taking the combined weight of the two at 42 ounces. The lungs are not only absolutely heavier in the male than in the female, but appear to be heavier in proportion to the weight of the body. The general ratio between the weight of the lungs and body in the adult fluctuates between one to thirty-five and one to fifty. The average weight in twenty-nine cases, male and female: Male. Female. Right lung, 24 ounces. 17 ounces. Left lung, 21   ,,    15   ,,    --------- --------- 45 ounces. 32 ounces. The proportionate weight of the lungs to the body is: Male. Female. 1 to 37 1 to 34 The substance of the lungs is of a light porous spongy texture, and when healthy is buoyant in water. Specific gravity, 0.126; deprived of air, 1.056. When pressed between the fingers, the lungs impart a crepitant sensation, which is accompanied by a peculiar noise, both effects being caused by the air contained in the tissue. On cutting the lung the same crepitation is heard. The pulmonary tissues are endowed with great elasticity, in consequence of which the lungs collapse to about one-third of their bulk when the thorax is opened. The root of each lung consists of bronchi, arteries, and veins, together with the nerves, lymphatic vessels, and glands, connected by areolar tissue, and inclosed in a sheath of the pleura. Respiration consists of an expiration and an inspiration. The air passes in through the nose or mouth, through the larynx, trachea, bronchi, into the lungs. Inspiration: By the contraction of certain muscles, the cavity of the thorax is enlarged; in consequence the pressure of the air within the lungs becomes less than that of the air outside the body, and this difference of pressure causes a rush of air through the trachea into the lungs until an equilibrium of pressure is established between the air inside and that outside the lungs. This constitutes inspiration.