THE LUNGS.

The color of the lungs at birth is a pinkish-white; in adult life a dark slate-color, mottled in patches; and as age advances this mottling assumes a black color. The coloring matter consists of granules of a carbonaceous substance deposited in the areolar tissue near the surface of the organ. It increases in quantity as age advances, and is more abundant in males than in females. The posterior border of the lung is usually darker than the anterior. 'I'he surface of the lung is smooth, shining, and marked out into numerous polyhedral spaces, indicating the lobules of the organ; the area of each of these spaces is crossed by numerous lighter lines. The substance of the lung is of a light, porous, spongy texture; it floats in water and crepitates when handled, owing to the presence of air in the tissue; it is also highly elastic; hence the collapsed state of these organs when they are removed from the closed cavity of the thorax. Structure.-The lungs are composed of an external serous coat, a subserous areolar tissue, and the pulmonary substance or parenchyma. The serous coat is derived from the pleura; it is thin, transparent, and invests the entire organ as far as the root. The subserous areolar tissue contains a large proportion of elastic fibres; it invests the entire surfa.ce of the lung, and extends inward between the lobules. 'I'he parenchyma is composed of lobules which, although closely connected together by an interlobular areolar tissue, are quite distinct from one another, and may be teased asunder without much difficulty in the fostus. The lobules vary in size; those on the surface are large, of pyramidal form, the base turned toward the surface; those in the interior, smaller and of various forms. Each lobule is composed of one of the ramifications of a bronchial tube and its terminal air-cells, and of the ramifications of the pulmonary and bronchial vessels, lymphatics, and nerves, all of these structures being connected together by areolar tissue.

The color of the lungs at birth is a pinkish-white; in adult life a dark

slate-color, mottled in patches; and as age advances this mottling assumes a black color. The coloring matter consists of granules of a carbonaceous substance deposited in the areolar tissue near the surface of the organ. It increases in quantity as age advances, and is more abundant in males than in females. The posterior border of the lung is usually darker than the anterior.

'I'he surface of the lung is smooth, shining, and marked out into numerous polyhedral spaces, indicating the lobules of the organ; the area of each of these spaces is crossed by numerous lighter lines.

The substance of the lung is of a light, porous, spongy texture; it floats in

water and crepitates when handled, owing to the presence of air in the tissue; it is also highly elastic; hence the collapsed state of these organs when they are removed from the closed cavity of the thorax.

Structure.-The lungs are composed of an external serous coat, a subserous

areolar tissue, and the pulmonary substance or parenchyma.

The serous coat is derived from the pleura; it is thin, transparent, and invests

the entire organ as far as the root.

The subserous areolar tissue contains a large proportion of elastic fibres; it

invests the entire surfa.ce of the lung, and extends inward between the lobules.

'I'he parenchyma is composed of lobules which, although closely connected together by an interlobular areolar tissue, are quite distinct from one another, and may be teased asunder without much difficulty in the fostus. The lobules vary in size; those on the surface are large, of pyramidal form, the base turned toward the surface; those in the interior, smaller and of various forms. Each lobule is composed of one of the ramifications of a bronchial tube and its terminal air-cells, and of the ramifications of the pulmonary and bronchial vessels, lymphatics, and nerves, all of these structures being connected together by areolar tissue.