The circulation of the blood through the heart is as follows: The blood, which in the veins of the body is flowing towards the heart, passes by two channels, which respectively receive the blood from the upper and lower part of the body, into the right auricle. When this becomes distended it contracts, forcing the blood into the right ventricle; the ventricle then contracts and sends the blood into the arteries of the lungs, the passage of blood into the auricle being prevented by valves which close the opening between auricle and ventricle when the latter contracts upon its contents. When the ventricle empties by its contraction the wall relaxes and the back flow from the artery is prevented by crescentic-shaped valves placed where the artery joins the ventricle. A similar arrangement of valves is on the left side of the heart. The pressure given the blood by the contraction of the right ventricle sends it through the lungs; from these, after it has been oxygenated, it passes into the left auricle, then into the left ventricle and from this into the great artery of the body, the aorta, which gives off branches supplying the capillaries of all parts of the body. Both of the auricles and both of the ventricles contract at the same, time, the ventricular contraction following closely upon the contraction of the auricles. Contraction or systole is followed by a pause or diastole during which the blood flows from the veins into the auricles. The work which the right ventricle accomplishes is very much less than that of the left, and the right ventricle has a correspondingly thinner wall. The size of the heart is influenced by the size and the occupation of the individual being larger in the large individual than in the small, and larger in the active and vigorous than in the inactive. Generally speaking, the heart is about as large as the closed fist of its possessor. Imperfections of the heart which interfere with its action may be the result of failure of development or disease. An imperfect heart which can, however, fully meet the limited demands made upon it in intra-uterine life, may be incapable of the work placed upon it in extra-uterine life. Children with imperfectly formed hearts may be otherwise perfect at birth, but they have a bluish color due to the imperfect supply of the blood with oxygen, and are known as blue babies. The condition becomes progressively worse due to the progressive demands made upon the heart, and death takes place after some days or months or years, the time depending upon the degree of the imperfection.