Page:The Harveian oration, 1875 (IA b22314611).pdf/37

 greater into the lesser veins;” thus favouring its motion from the lesser to the larger branches; and furnishing a conclusive argument for a circulation.

By applying a bandage above the elbow, as in bleeding from the arm, Harvey shows the site of the valves, and by the pressure of the finger, and “streaking” the blood in one direction and the other, demonstrates their action, and the movement of the blood from smaller veins to larger, always in the direction that leads to the heart. And here reverting to his favourite argument, based on figures, Harvey bids us select some length of vein, assume it to be able to hold some given quantity of blood, empty it by “ streaking;” suppose this process repeated for, say a thousand times, and then judge for ourselves what quantity of blood must be always passing towards the heart, and what sure evidence its passage affords of a circulation.

We who come to the study of the circulation with minds prepared to accept the evidence of facts, and the force of arguments, can scarcely appreciate the difficulty Harvey had in convincing some of his contemporaries, whose minds were pre-occupied by certain prevailing errors. I will mention four of them.