How The Blood Moves In The Veins

The principal cause of the mavement of the blood in the veins is what the jhysiologists refer to as "the pressure 'rom behind." By this is meant the capillary circulation or a movement of the blood caused by the constant pumpng action of the heart, which forces the current into and through the veins - that is, to prevent their becoming so illed with blood that their resistance would counterbalance the pressure !rom the arteries - each pulsation of the heart by emptying the right ven;ricle allows a part of the blood accumulated in the veins to be removed, [n this way the backward resistance in the veins is kept inferior to the pressure of the arterial circulation. The venous circulation is also greatly aided by the action of the voluntary muscles. It is a well-known fact that when a murcie contracts it thickens andi becomes diminished in length. The effect of this lateral swelling is to compress the veins lying between the muscles, thus forcing the blood forward. Another peculiarity is the half-moon shaped valves with which the veins are wll provided. These "semilunar" valves open duly toward the heart, making any backward movement of the blood into the venous system possible.-