Historical Perspective: Harvey's epoch-making discovery of the Circulation, its historical antecedents, and some initial consequences on medical practice.

In Harvey's Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus of 1628, we see the mechanisms of the Circulation worked out more or less in full from the results of experimental demonstration, virtually complete but for the direct visual evidence of a link between the minute final terminations and initial branches of the arterial and venous systems, respectively. This would become available only when the capillaries could be seen under the microscope, by Malpighi. Harvey's amazingly modern order of magnitude analysis of volumetric circulatory flow and appreciation of the principle of continuity (mass conservation), his adroit investigational uses of ligatures of varying tightness in elegant flow experiments, and his insightful deductions truly explain the movement of the blood in animals. His end was accomplished. So radical was his discovery that early in the 18th century, the illustrious Hermann Boerhaave, professor of medicine at Leyden, declared that nothing that had been written before Harvey was worthy of consideration any more. The conclusions of De Motu Cordis are unassailable and beautiful in their simplicity. Harvey's genius and tireless determination have served physiology and medicine well.