Microbes And Health

inflammation of the lungs. The lungs may be represented by a tree hanging with its top down. The body and limbs of the tree would represent the large and small air tubes. The body would represent the trachea or "windpipe," and the innumerable branches, their divisions and subdivisions would represent the smaller tubes, and three or more dilatations like a small hollow bead on the end of each twig would represent the air-cells. The air tubes open into the air cells, and both tubes and cells are lined with mucous membrane which is continuous from the mouth and throat. All are held together by a connective tissue frame work. This frame work is elastic, hence the power of the lungs to expand and contract. The heart and lungs are the only organs through which all the blood passes. In the heart it simply passes from one cavity to another, but in the lungs it must pass through the intricate network of thin-walled vessels called capillaries. The heart is a hollow muscular organ; a longitudinal septum or partition divides it into two lateral halves, which from their position are called right and left heart. A transverse septum; i. e., one extending from side to side, again divides the heart into four cavities, two upper and two lower. The right heart controls the circulation through the lungs only, the left heart control the general or systematic circulation. The dark venous blood from the whole system is received into the right heart, and sent through the lungs whe...