FROM PARACELSUS TO HARVEY 



truth of existing doctrines as to the phenomena of the 

 circulation. Galen had taught that "the arteries are 

 filled, like bellows, because they are expanded," but 

 Harvey thought that the action of spurting blood from 

 a severed vessel disproved this. For the spurting was 

 remittant, "now with greater, now with less impetus," 

 and its greater force always corresponded to the ex- 

 pansion (diastole) , not the contraction (systole) of the 

 vessel. Furthermore, it was evident that contraction 

 of the heart and the arteries was not simultaneous, 

 as was commonly taught, because in that case there 

 would be no marked propulsion of the blood in any 

 direction ; and there was no gainsaying the fact that the 

 blood was forcibly propelled in a definite direction, and 

 that direction away from the heart. 



Harvey's investigations led him to doubt also the 

 accepted theory that there was a porosity in the sep- 

 tum of tissue that divides the two ventricles of the heart. 

 It seemed unreasonable to suppose that a thick fluid 

 like the blood could find its way through pores so small 

 that they could not be demonstrated by any means 

 devised by man. In evidence that there could be no 

 such openings he pointed out that, since the two ven- 

 tricles contract at the same time, this process would 

 impede rather than facilitate such an intra-ventricular 

 passage of blood. But what seemed the most conclu- 

 sive proof of all was the fact that in the foetus there 

 existed a demonstrable opening between the two ven- 

 tricles, and yet this is closed in the fully developed 

 heart. Why should Nature, if she intended that blood 

 should pass between the two cavities, choose to close 

 this opening and substitute microscopic openings in 



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