Harvey's Views on the Use of the Circulation of the Blood

by John Green Curtis

After more than twenty years of the comment and criticism, called forth by his treatise of 1628, he said to Riolanus:—

"As to whether the moving blood be attracted, or impelled, or move itself by virtue of its own intrinsic nature, enough has been said in my little book on the motion of the heart and blood."[258]

Yet about two years after the Exercises to Riolanus, Harvey, in writing a private letter, judged it necessary to accentuate, as follows, his denial that forces of attraction really play the part in physiology which the ancients had conceded to them. Speaking of the impulsion of the blood through the arteries, he says:—

"Indeed, the passage of the blood into the veins is brought about by that impulsion and not by any dilatation of the veins whereby, like bellows, they draw in the blood."[259]

But, despite the foregoing utterances and other such, his statements are sometimes vague and sometimes quite unexpected, regarding the nature of the movement of the blood in the veins. Indeed, in 1628 he speaks quite as a disciple of Aristotle. He says regarding the flow in the arteries:—

"For this distribution and movement of the blood there is need of impetus and violence and of an impeller such as the heart. Partly because the blood readily concentrates and gathers together of itself—toward its seat of origin, as it were,[260] or as a part to the whole, or as a drop of the water sprinkled upon a table to the mass thereof—as the blood habitually and very speedily does from slight causes, from cold, fear, horror, and other causes of this sort; partly, also, because the blood is pressed out of the capillary veins into the small branches and thence into the greater by the movements of the limbs and the compression of the muscles; the blood is more disposed and prone to move from the circumference on the center than the other way, even supposing no valves to be present as a hindrance. In order, therefore, to relinquish its seat of origin, and enter constricted and colder places, and move in opposition to its bent,[261] the blood has need not only of violence but of an impeller, such as is the heart alone, and after the fashion described already."[262]

This picture of the blood hesitating to leave its warm cardiac birthplace for the chill regions of the periphery, but very ready to return, has a tone far from hydraulic, but may so much the better prepare us for the view, made public by Harvey in his old age, that the blood is the primal seat of the soul itself. Except in the light of the foregoing passage the following words would be quite obscure. He says that the auricles

"are filled as being the storehouse and reservoir[263] of the blood, the blood turning of itself and compressed toward the center by the movement of the veins."[264]

With due allowance for the use of modes of expression no longer familiar we find Harvey in 1649 handling the venous flow with no very modern touch, in the following passage—a passage which also reminds us that not till twelve years later, four years after Harvey's death, did Malpighi announce his discovery of the capillary blood-vessels in the lung of the frog.[265] Harvey says to Riolanus:—

"The arteries are never depleted except into the veins or the porosities of the parts, but are continually stuffed full by the pulse of the heart; but in the vena cava and the circulatory vessels, into which the blood glides at a quick pace and hastens toward the heart, there would be the greatest scarcity of blood, did not all the parts incessantly pour out again the blood poured into them. Add, also, that the impetus of the blood which is urged and driven at every pulsation into all parts of the second and third regions, forces the blood contained therein from the porosities into the little veins and from the branches into the larger vessels; this being effected also by the motion and compression of the surrounding parts; for contents are squeezed out of whatever contains them, when it is compressed and narrowed. So by the movements of the muscles and limbs the venous branches which creep on between are pressed upon and narrowed, and push on the blood from the lesser toward the greater."[266]