for the propulsion of blood, he takes up in Chapters vi and vii the question of the conveyance of the blood from the right side of the heart to the left.  Galen had already insisted that some blood passed from the right ventricle to the lungs—­enough for their nutrition; but Harvey points out, with Colombo, that from the arrangement of the valves there could be no other view than that with each impulse of the heart blood passes from the right ventricle to the lungs and so to the left side of the heart.  How it passed through the lungs was a problem:  probably by a continuous transudation.  In Chapters VIII and ix he deals with the amount of blood passing through the heart from the veins to the arteries.  Let me quote here what he says, as it is of cardinal import: 

“But what remains to be said upon the quantity and source of the blood which thus passes, is of a character so novel and unheard of that I not only fear injury to myself from the envy of a few, but I tremble lest I have mankind at large for my enemies, so much doth wont and custom become a second nature.  Doctrine once sown strikes deeply its root, and respect for antiquity influences all men.  Still the die is cast, and my trust is in my love of truth, and the candour of cultivated minds."(28) Then he goes on to say: 

     (28) William Harvey:  Exercitatio Anatomica de Motu Cordis et
     Sanguinis in Animalibus, Francofurti, 1628, G. Moreton’s
     facsimile reprint and translation, Canterbury, 1894, p. 48.

“I began to think whether there might not be A movement, as it were, in A circle.  Now this I afterwards found to be true; and I finally saw that the blood, forced by the action of the left ventricle into the arteries, was distributed to the body at large, and its several parts, in the same manner as it is sent through the lungs, impelled by the right ventricle into the pulmonary artery, and that it then passed through the veins and along the vena cava, and so round to the left ventricle in the manner already indicated."(29)

     (29) Ibid. p. 49.

The experiments dealing with the transmission of blood in the veins are very accurate, and he uses the old experiment that Fabricius had employed to show the valves, to demonstrate that the blood in the veins flows towards the heart.  For the first time a proper explanation of the action of the valves is given.  Harvey had no appreciation of how the arteries and veins communicated with each other.  Galen, you may remember, recognized that there were anastomoses, but Harvey preferred the idea of filtration.