of these cells, by-and-by.) The blood having given up a supply of nourishment, begins its return journey to the heart, taking with it the waste products, dead cells, broken-down tissue and other refuse of the system. It starts with the capillaries, but this return journey is not made through the arteries, but by a switch-off arrangement it is directed into the smaller veinlets of the venous system (or system of "veins"), from whence it passes to the larger veins and on to the heart. Before it reaches the arteries again, on a new trip, however, something happens to it. It goes to the crematory of the lungs, in order to have its waste matter and impurities burnt up and cast off. In another chapter we will tell you about this work of the lungs.
Before passing on, however, we must tell you that there exists another fluid which circulates through the system. This is called the Lymph, which closely resembles the blood in composition. It contains some of the ingredients of the blood which have exuded from the walls of the blood-vessels and some of the waste products of the system, which, after being cleansed and "made-over" by the lymphatic system, re-enter the blood, and are again used. The lymph circulates in thin vein-like canals, so small that they cannot be readily seen by the human eye, until they are injected with quicksilver. These canals empty into several of the large veins, and the lymph then mingles with the returning blood, on its way to the heart. The "Chyle," after leaving the small intestine (see last lesson) mingles with the lymph from the lower parts of the body, and gets into the blood in this way,
