HEART DISEASES.

(Also see Anatomy of Organs of Circulation.)

Life rests upon a tripod, the brain, the lungs, and the heart. These are equally important to its wellbeing and continuance.
In substance, the human heart is a bundle of muscles, so put together as to bear the greatest possible amount of work. In size, shape, and look, it is much like the heart of the hog. I wish it never had a likeness to it in its moral nature.
The heart is enclosed in a case or sac, called the pericardium. It lies between the two lungs, a little to the left side of the chest. Its point is under the sixth rib on the left side, and its lower surface rests on the diaphragm, a horizontal partition between the chest and belly.
The heart is double. It has four cavities, two for receiving the blood, which are called auricles, and two for driving it out, called ventricles.
The venous, or dark blood, is brought from all parts below, and emptied into the right auricle through the ascending vena cava, and from all parts from above, and pour into the same cavity through the descending vena cava. From this it passes into the right ventricle, which contracts, and forces it through the pulmonary artery into the lungs, where it becomes red, and passes into the left auricle through the pulmonary vein, thence into the left ventricle, which contracts, and throws it out through the great aorta to all parts of the body. Fig. 95 gives a good idea of the circulation through the heart and lungs.
The heart is divided into two sides, which are separated from each other by a muscular partition, each side having an auricle and a ventricle.
The auricles have comparatively thin walls, as they are only used for reservoirs. The walls of the ventricles are much thicker, being used, particularly that of the left side, for forcing the blood over a large surface.
Between the auricle and ventricle on the right side, axe three folds of triangular membrane, called the tricuspid valves. Between the auricle and ventricle on the left side, are three valves, called mitral.
At the beginning of the pulmonary artery, and the aorta, are three half moon shaped folds of membrane, called semi lunar valves.
The office of all these valves is, to close after the blood has gone through, and prevent its flowing back while the cavity is being again filled. They do the same duty, in fact, as the valves of a pump.
Through this heart, thus constructed, all the blood in the body, about twenty eight pounds, passes once in about one minute and a half. This is rapid work; and when we consider that the heart works in t his way through the whole life, resting not, day or night, we cannot wonder that it gets out of order.

The whole heart is seldom affected. The left side is more liable to disease than the right.