Democratic Sentinel, Volume 5, Number 31, Rensselaer, Jasper County, 9 September 1881 — What Causes the Blood to Circulate? [ARTICLE]

What Causes the Blood to Circulate?

To what degree the heart is aided by other forces is yet a matter of investigation. Probably there are several forces assisting. The elasticity of the arteries increases their carrying capacity. They are firm, elastic tubes, which expand under the pressure from each heart-contraction, and then by their own elasticity contract and help the onward flow of the blood. In the smaller arteries the flow loses the intermittent character it possesses in the larger arteries, and becomes a steady stream. The elasticity of the arteries serves precisely the same purpose Us the air chamber of any force-pump, that of equaliz-, ing the flow, and so increasing the amount delivered. The whole force is derived from the heart; the arteries cause the force to- act continuously. The veins are lax tubes somewhat larger than tb e arteries, and capable of holding all the blood of the body. They convey the same amount of blood as tliq latter, but more sipwly. In the larger veins, however, near the auricles, the velocity may be 200 milimetres per second. They are provided with valves which effectually prevent the blood from flowing backward toward the heart. Any compression, produced by muscular contraction or otherwise, will therefore assist the forward flow of venous blood. This is one explanation why exercise hastens the circulation. The movement of the chest in breathing probably aids the pulmonary circulation, the blood, as well as the atmosphere, tending to fill the vacuum during inspiration. Physical capillary force is not generally regarded as an active force in the circulation. But there is an admitted force in the capillaries, resulting from the attraction of the tissues for the arterial blood, containing the required oxygen and nutriment. “The vital condition of the tissue becomes a factor in the maintenance of the circulation. ” It is this force, primarily, which adapts the amount of blood to the varying needs of any organ the nervous system regulates the supply by varying the caliber of the vessels. The force in the capillaries, or some other force, carries the blood after death, from the arteries, where the heart leaves it, into the veins. Finding the arteries empty after death gave rise to the idea that they conveyed air; whence the name. It was this belief which Harvey overthrew in 1620. —Popular Science Monthly.