ses 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.

The "De Motu Cordis" constitutes a unique piece of work in the history
of medicine. Nothing of the same type had appeared before. It is
a thoroughly sensible, scientific study of a definite problem, the
solution of which was arrived at through the combination of accurate
observation and ingenious experiment. Much misunderstandi