THE CIRCULATION OF THE BLOOD 455 



scrutinized with his simple lens, but he inferred the existence of capil- 

 laries 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 " tabulae Harveianse," 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, Mar- 

 cello 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 cir- 

 cular." 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 : Har- 

 vey 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 re- 

 turning 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 nourish- 

 ment. He had the full courage of his convictions ; he applied his scien- 

 tific 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 emphat- 

 ically 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 S\§\ 

 looked into the body for himself; he was done with what Aristotle or. >' ^.o 

 Galen had said, done with library or arm-chair physiology. / ° -^ > 



