Page:Popular Science Monthly Volume 82.djvu/457

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HE discoverer of the circulation of the blood was a London doctor called William Harvey.

The discovery of the circulation of the blood is the foundation of modern medicine; it was epoch-making, for it made possible that marvelous epoch in which we have seen the laws of living matter discovered and the actual, physical causes of the most mysterious diseases revealed. Harvey closed the dark ages of the science of the living; physiologically he "allured to brighter worlds, and led the way." Until it could be known that the blood, the same blood, moved round and round the body under the force of the propulsion of the heart, and that it traversed heart and lungs and all body-vessels in its closed circuit, there could be no physiology, no pathology, no therapeutics, no rational medicine: no such procedure as transfusion of blood. To understand what it was that Harvey discovered, we need to know what was believed as regards the movement of the blood before his time.

The oldest idea of all was that only the veins contain blood, the arteries air. Galen had corrected this latter mistake by tying a cord above and one below a length of artery and cutting out the piece above and below the ligatures; blood, of course, and not air was found inside. It was thought that blood went up and down the veins like the ebb and flow of a tide, that "crude" blood was made in the liver and taken to the heart to be purified. The heat supposed to be produced in this process was believed to make it necessary to cool the heart by drawing in air in the act of breathing, and this was regarded as the function of respiration even as late as the time of Haller, that is, the middle of the eighteenth century. The pulse or opening up of the arteries was regarded as an active thing on their part, blood not being forced into them by the heart but drawn into them by their own suction like a bellows draws in air. But Harvey said the heart is the pump, and the arteries are filled by its forcing its blood into them.

Harvey advanced not one or two but more like a dozen proofs of the circulation. His contention is—the blood in the arteries moves towards the tissues, thence towards the veins, it is collected in the right auricle of the heart, whence it flows to the right ventricle, this on contracting drives it through the lungs, whence it flows to the left auricle, passes to left ventricle and so is ready to be sent to the body again. Galen had