454 THE POPULAR SCIENCE MONTHLY 



said that almost all the blood passed from the right to the left side of 

 the heart across the septum of the heart, but Harvey, maintaining that 

 the septum was not porous, proved that all the blood, not merely some 

 of it, went round by the lungs. 



Of course, this pulmonary or "lesser" circulation was taught be- 

 fore his time, notably by Servetus and M. K. Columbus; but it was 

 Harvey who first showed that the valves of the heart and the valves of 

 the veins absolutely prevent any other direction of flow except from the 

 veins to the right heart and thence via the lungs to the left heart. This 

 doctrine of the porosity of the septum died hard, for we find Harvey, 

 towards the close of his life, attempting to convince an objector — Pro- 

 fessor Eiolanus — that if only he will pour water into the right heart 

 and tie all vessels to and from the lungs, not one drop will get into the 

 left ventricle. 



No one before Harvey had fully understood the venous valves. His 

 own professor at Padua — Fabricius — had talked a great deal of non- 

 sense about them in a treatise entirely devoted to them. Harvey said 

 that they were not primarily for supporting columns of blood, but for 

 preventing any back-flow towards the periphery, seeing that they were 

 present in the veins of the head in which the blood (under gravity) 

 flowed past them with the greatest ease: here, since they opened 

 towards the heart, they could not support any column of blood. 



In Chapter II. of his great book — the " De Motu " — his chief point 

 is, "the charge of blood is expelled by force," that is, the heart is dy- 

 namic for the circulation, a point by no means admitted before his time, 

 for M. R. Columbus denied the heart to be even muscular. Harvey is 

 absolutely clear on this point; he writes: 



It is in virtue of one and the same cause that all arteries of the body 

 pulsate, namely, the contraction of the left ventricle. 



Again in Chapter V. he writes : 



The one action of the heart is the transmission of blood and its distribution 

 by means of the arteries to the very extremities of the body. 



In Chapter VI. he gives a remarkably good account of the circula- 

 tion through the fetal heart, that is, before lungs are developed; it is 

 surprisingly accurate to have been done three hundred years ago. In 

 Chapter VII. he returns to the circulation through the lungs and clearly 

 arrives by induction at the existence of capillaries; the word of course 

 he does not use, he calls them "porosities of the flesh," but he under- 

 stands perfectly that arteries do not become veins without undergoing 

 some complete change in structure and nature. He says if arteries be- 

 came veins, there would be a pulse in the veins, marvellously good physi- 

 ology for 1628 ! 



Owing to his having no microscope sufficiently powerful, Harvey 

 could not see the capillaries even in those transparent animals which he 



