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been correctly observed; that its function and that of the arteries were associated with hypothetical vital spirits, the existence of which no one doubted; and that the nourishment of the body was supposed to be derived only from the blood in the veins, moved alternately in a flux and reflux by the respiratory acts.
Harvey had to disabuse first his own, and then other men's minds of these errors, and replace them by sounder views. Accordingly, the subject of his great work is the movements of the heart as well as of the blood, and the proof of the circulation is made up of a series of propositions, successively demonstrated by plain and clear reasoning from the evidence of observation and experiment. Harvey's inference that the blood must pass from the arteries into the veins is a triumph of pure reasoning, for the visible evidence of this fact was not given till many years afterwards by the microscopes of Malpighi and Leeuwenhoek and the injections of Blancard and Ruysch.
The facts which formed the basis of Harvey's reasoning were mostly his own, and were drawn from all available sources. Nature was in his esti-
