Page:Laboratory Manual of the Anatomy of the Rat (Hunt 1924).djvu/64



The vascular system conveys food materials and oxygen to the cells of the body, and carries away from these cells the waste products of metabolism. The food substances dissolved in the blood furnish energy for the cell's activities, and materials for replacing the protoplasm which has disintegrated during metabolism. The blood stream tends also to equalize the temperature throughout the body. Still another function is the conveyance of hormones from their sources to parts of the body whose activities the hormones accelerate or retard.

The vascular system carries two fluids—blood and lymph. The former consists of an almost colorless fluid, plasma, and of red (erythrocytes), and white (leucocytes) blood cells. When clotting occurs the plasma is resolved into the fluid serum, which is incapable of clotting under ordinary conditions, and the solid clot of fibrin. The capacity of blood to form a clot is of primary importance, since it greatly reduces the chance of death through the loss of blood following injury. The red blood cells contain hemoglobin, which has the power of combining with oxygen in the lungs, and carrying it to the tissues, where it is released. Hemoglobin gives the blood its reddish color when exposed to oxygen. There are several types of white blood cells.