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

by John Green Curtis

Farther on in the same treatise Harvey says:—

"Moreover, the reason why the lungs have vessels so ample, both vein and artery, that the trunk of the venous artery exceeds in size the crural and jugular branches taken both together; and the reason why the lungs are so full of blood as we know them to be by experience and inspection (heeding Aristotle's warning,[22] and not deceived by the inspection of such lungs as we have removed from dissected animals from which all the blood had flowed out)—the reason is, that in the lungs and heart is the storehouse, the source, the treasury of the blood, the workshop of its perfection."[23]

So the great Englishman gropes for a moment or two by the light of ancient Greek doctrines and puts the question of respiration by. But this very attitude shows Harvey's thought to be in such contrast with the thought of to-day that in order to understand him we need to learn more fully his views of respiration; and we find with satisfaction that in his lecture notes of more than eleven years before he had not put this question by, for he had been called upon to lecture upon the uses of the lungs. We must seek in his lecture notes, therefore, for what he had thought those uses to be. These notes, however, we shall be unable to follow unless now, first of all, we shall give the floor for a while to the ancients; for from their doctrines Harvey necessarily took his cue, like the other thinkers of his time.

The momentous physiological facts that the living body of man, beast, or bird, is warm of itself and that its cooling means its death, must always have struck and impressed the human mind, whether trained or untrained. More than nineteen centuries before Harvey certain thoughts of Aristotle were recorded as follows:—

"In animals all the parts and the entire body possess a certain innate natural heat; wherefore they are sensibly warm when living, the reverse when making an end and parting with life. In the animals which have blood the origin of this heat is necessarily in the heart, in the bloodless kinds in the analogue thereof; for all work up and concoct the nourishment by means of the natural heat, the master part most of all. Life persists, therefore, when the other parts are chilled; but if what resides in this one be so affected total destruction ensues, because upon this part they all depend as the source of their heat, the soul being as it were afire within this part; that is, within the heart in the animals which have blood, in the bloodless kinds in the analogue thereof. Necessarily, therefore, the existence of life is coupled with the preservation of the heat aforesaid, and what is called death is the destruction thereof."[24]

This heat which is innate in all living animals was styled by Aristotle not only "innate" but "natural," "vital,"[25] and "physical,"[26] it being indispensable to life and to the working of the soul. He held the continued existence of the innate heat to depend upon conditions similar to those under which a fire is kept alive, viz.: protection both from burning out and from extinction due to external forces. Yet the true nature of combustion was not settled till more than a century after Harvey's death. The fact that air is necessary to fire must always have been a matter of common knowledge. Therefore, the views of the relations of air to fire maintained by Aristotle nearly twenty-one centuries before the discovery of oxygen did not seem naïve to Harvey, whatever they may seem to us. Aristotle held that air exerts upon fire a cooling influence which saves it from burning out too fast; and that the same influence is exerted upon the vital innate heat of animals by the air which they breathe in, or the water which bathes their gills.[27] Moreover, Aristotle says:—

"Why those animals breathe most which have lungs containing blood, is plain from this: that the warmer an animal is, the greater need it has of cooling, while at the same time the breath passes easily toward the source of warmth within the heart. But the way in which the heart is pierced through toward the lung must be studied from dissections and from the history of animals which I have written. In general terms, then, it is the nature of animals to need cooling on account of the firing of the soul within the heart."[28]

In the treatise styled the "History of Animals," to which he refers us, Aristotle says:—