=How the Heart Does Its Work.=--The power back of blood distribution is the heart. It is an automatic pump, as it were, that sends blood to the lungs and through the arteries to all parts of the body. The heart is divided into four divisions: the left and right ventricles and the right and left auricles. The right auricle receives the blood from the upper half of the body through a large vein and the lower half of the body through another large vein, and the blood from both lungs empties into the left auricle through two left and two right pulmonary veins. The large arteries of the heart which carry the blood from the heart to the different organs arise from the ventricle. The blood always flows in the same direction. It goes into the auricle from the veins, and from this into the ventricle. It then passes into the arteries, then to the veins and then to the capillaries. The action of the heart is very much like a force pump; the dark blood flows into the right auricle, which contracts; when this is done, the blood is forced into the right ventricle; this in turn contracts and forces the blood into the lungs, where oxygen is taken on and carbonic acid gas and other impurities are thrown off. From the lungs the blood, now red and pure, passes into the left auricle and thence into the left ventricle, from which it is forced into the aorta to be distributed to all parts of the body. We now see the close connection existing between the digestive system and the circulatory system. The digested food in the intestines is gathered in by villi cells. The question can now be asked, What do these cells do with this nutriment or digested food? They pour it into the absorbent vessels or lymphs, as they are called; these in turn empty the assimilated stores of food into larger and still larger vessels, which continues until the whole of the nutritive fluid is collected into one great duct or tube, which pours its contents into the large veins at the base of the neck, from whence it is carried into the circulatory system, the very basis of which is the blood. RESPIRATION The dark and impure blood, after returning to the heart, is sent to the lungs. It is, when collected from the body, just before being sent to the lungs dark, dull and loaded with worn-out matter. It must now be sent to the lungs, where it may be spread over the delicate thin walls of millions of vesicles, to be exposed to the air, which is inhaled by the acts of breathing. The blood gives off the broken-down material and carbonic acid gas very readily. It is both unpleasant and disagreeable, and the blood cells find it very unattractive. The cells of the blood, however, have a great attraction for oxygen, consequently the cells absorb oxygen with greediness, so that when the blood returns to the heart it is fresh and bright and ready to take its journey back over the body again. This is done just about every three minutes. This endless round continues until stopped forever by death.