Huxley's account will perhaps give a clearer idea of Harvey's relation to his predecessors and contemporaries, and of the value of his services to mankind, than would a far longer biography of the great physician, physiologist, and anatomist. Many opinions have been held respecting the exact nature and value of Harvey's contributions to the elucidation of the fundamental problem of the physiology of the higher animals; from those which deny him any merit at all--indeed, roundly charge him with the demerit of plagiarism--to those which enthrone him in a position of supreme honor among great discoverers in science. Nor has there been less controversy as to the method by which Harvey obtained the results which have made his name famous. I think it is desirable that no obscurity should hang around these questions; and I add my mite to the store of disquisitions on Harvey, in the hope that it may help to throw light upon several points about which darkness has accumulated, partly by accident and partly by design. About the year B.C. 300 a great discovery, that of the valves of the heart, was made by Erasistratus. This anatomist found, around the opening by which the vena cava communicates with the right ventricle, three triangular membranous folds, disposed in such a manner as to allow any fluid contained in the vein to pass into the ventricle, but not back again. The opening of the vena arteriosa into the right ventricle is quite distinct from that of the vena cava; and Erasistratus observed that it is provided with three pouch-like, half-moon-shaped valves; the arrangement of which is such that a fluid can pass out of the ventricle into the vena arteriosa, but not back again. Three similar valves were found at the opening of the aorta into the left ventricle. The arteria venosa had a distinct opening into the same ventricle, and this was provided with triangular membranous valves, like those on the right side, but only two in number. Thus the ventricles had four openings, two for each; and there were altogether eleven valves, disposed in such a manner as to permit fluids to enter the ventricles from the vena cava and the arteria venosa respectively, and to pass out of the ventricles by the vena arteriosa and the aorta respectively, but not to go the other way. It followed from this capital discovery that, if the contents of the heart are fluid, and if they move at all, they can only move in one way; namely, from the vena cava, through the ventricle, and toward the lungs, by the vena arteriosa, on the right side; and, from the lungs, by way of the arteria venosa, through the ventricle, and out by the aorta for distribution in the body, on the left side.