448 THE CIRCULATION OF THE BLOOD 



That, you will observe, makes a complete circuit ; and it 

 was precisely here that the originality of Harvey lay. 

 There never yet has been produced, and I do not believe there 

 can be produced, a tittle of evidence to show that, before his 

 time, any one had the slightest suspicion that a single drop 

 of blood, starting in the left ventricle of the heart, passes 

 through the whole arterial system, comes back through 

 the venous system, goes through the lungs, and comes 

 back to the place whence it started. But that is the 

 circulation of the blood, and it was exactly this which 

 Harvey was the first man to suspect, to discover, and to 

 demonstrate. 



But this was by no means the only thing Harvey did. 

 He was the first who discovered and who demonstrated the 

 true mechanism of the heart's action. No one, before his 

 time, conceived that the movement of the blood was entirely 

 due to the mechanical action of the heart as a pump. There 

 were all sorts of speculations about the matter, but nobody 

 had formed this conception, and nobody understood that the 

 so-called systole of the heart is a state of active contraction, 

 and the so-called diastole is a mere passive dilatation. Even 

 within our own age that matter had been discussed. Har- 

 vey is as clear as possible about it. He says the movement 

 of the blood is entirely due to the contractions of the walls of 

 the heart that it is the propelling apparatus and all 

 recent investigation tends to show that he was perfectly 

 right. And from this followed the true theory of the pulse. 

 Galen said, as I pointed out just now, that the arteries dilate 

 as bellows, which have an active power of dilatation and 

 contraction, and not as bags which are blown out and 

 collapse. Harvey said it was exactly the contrary the 

 arteries dilate as bags simply because the stroke of the heart 

 propels the blood into them ; and, when they relax again, 

 they relax as bags which are no longer stretched, simply 

 because the force of the blow of the heart is spent. Harvey 

 has been demonstrated to be absolutely right in this state- 

 ment of his ; and yet, so slow is the progress of truth, that, 

 within my time, the question of the active dilatation of the 

 arteries has been discussed. 



Thus Harvey's contributions to physiology may be 

 summed up as follows : In the first place, he was the first 

 person who ever imagined, and still more who demonstrated, 

 the true course of the circulation of the blood in the body ; 

 in the second place, he was the first person who ever under- 



