scrutinized with his simple lens, but he inferred the existence of capillaries without ever seeing them. There are at the Royal College of Physicians in London three large boards on which he has dissected out the blood-vessels of the human body to the extreme limits which his scalpel would allow him. There they are to this day, a testimony to his eagerness to find those vessels in which the arteries ended. But it was not to be: I sometimes call these "tabulæ Harveianæ," his "sorrow's crown of sorows," for his finest dissection could not reach the capillaries. Three years after his death, in 1660, the great Italian naturalist, Marcello Malpighi, at Bologna, was the first of all men to see the living capillaries in the lung of the frog; he saw the blood coursing through them exactly as Harvey had predicted. Systemic capillaries were first seen in 1688 by Anthony van Leeuwenhoek, the Dutchman, at Delft.
Chapter VIII. contains the epoch-making metaphor, "motion as it were in a circle," "motion of the blood we may be allowed to call circular." Chapter IX. contains the argument from quantity, one of the subtlest in the whole book. It is a matter of very simple calculation to show that in an hour or two the heart will eject far more blood than the body possesses unless the blood comes back again to the heart: Harvey showed that the body of a sheep does not contain much more than about four pounds of blood, but that in an hour quite seven pounds of blood have passed through the heart. Now the heart can not deal with more blood than the body possesses, therefore blood is continually returning to the heart. Harvey, believing that the blood carried the nourishment to all parts, applied this view to an actual case of pulsating tumor which he had to treat: he tied the artery so tight as to stop the blood-flow to the tumor which shortly dried up from lack of nourishment. He had the full courage of his convictions; he applied his scientific knowledge to a surgical case for the relief of a suffering man. Chapter XVI. has the most interesting application of all; the argument based on the general or systemic effects of local absorption. Harvey points out that poisoned wounds, what we should call local infections, can poison the whole body; certainly this could not be so unless there was a carrying of the poison round through all the body, but that is just another expression for circulation. Were it not for the circulation, food absorbed where it is digested could never be distributed over the whole body: the circulation accounts equally for the universal distribution of food, drugs and poisons. Not until this was understood could there be a rational basis for physiology or the healing art; Harvey divides the empirical from the rational, for ever. In this way we may say emphatically that the discovery of the circulation was epoch-making, it brought in the era of experiment in biology, for Harvey experimented; had to do so in order to see nature at work; he tied this vessel and that, he looked into the body for himself; he was done with what Aristotle or. Galen had said, done with library or arm-chair physiology.
