From this cavity the impure blood passes into the right ventricle from which it is conveyed through the pulmonary (lung) arteries to the lungs.  In the capillaries of the lungs it again becomes arterialized by the air that fills the lungs and is then carried to the left auricle by the pulmonary veins.  From this cavity it passes into that of the left ventricle, from which the cycle once more begins.  The heart, then, is a hollow muscular organ of a conical form, placed between the lungs and enclosed in the cavity of the pericardium.  It is placed obliquely in the chest.  The broad attached end or base is directed upwards, backwards and to the right and extends up to the right as high as the second rib and the center of the base lies near the surface underneath the breast bone.  The apex (point) is directed downwards, forward and to the left and corresponds to the space between the cartilage of the fifth and sixth ribs, three-fourths of an inch to the inner side, and one and one-half inches below the nipple, or about three and one-half inches from the middle line of the breast bone.  The heart is placed behind the lower two-thirds of the breast bone and extends from the median line three inches to the left half of the cavity of the chest and one and one-half inches to the right half of the cavity of the chest.

Size:  In adults it is five inches long, three and one-half inches in breadth at its broadest part and two and one-half inches in thickness.  Weight in the male ten to twelve ounces; in the female eight to ten.  It increases up to an advanced period of life.  The tricuspid valve (three segments) closes the opening between the right auricle and right ventricle.  Pulmonary semilunar valves guard the orifice of the pulmonary artery, keeping the blood from flowing back into the right ventricle.  The mitral valve guards the opening to the left ventricle from the left auricle.  The semilunar valves surround the opening from the left ventricle into the aorta and keep the blood from flowing back.  If any one of these valves becomes diseased it may not thoroughly close the opening it is placed to guard and then we have a train of important symptoms.

[Circulatory diseases 341]

Pericarditis.—­This is an inflammation of the pericardium, the sac containing the heart.

Primary or First Causes.—­They refer in this disease to a peculiar constitution.  Children that have a tuberculous constitution are more liable to this disease.  Acute rheumatism or tonsilitis are the causes and this trouble follows or goes with them.  Infectious diseases also cause it.

Symptoms.—­Slight pain in the heart region, fever moderate.  These subside or effusion may set in and this usually occurs with acute rheumatism, tuberculosis and septicemia.  Sometimes these symptoms are absent.

Treatment of Pericarditis.—­The patient must rest quietly in bed and a doctor should be in attendance.  An ice bag placed over the heart frequently gives relief and quiets the distress and pain.  There is apt to be liquid in the sac (pericardium) and to lessen the tendency to this there should not be much drink or liquid food taken.  There should be what is called a dry diet. (See Nursing Department for this.)