Such was the state of anatomical science and physiological belief on this particular point when Michael Servetus came upon the stage, and suggested the transit of the blood through the lungs from the right side of the heart to the left, with a view of meeting the difficulty which the undeniable solidity of the septum ventriculorum opposed to the presumed necessary admixture of the two kinds of blood. Servetus’s idea, consequently--if at the distance of three hundred years we may presume to follow the mental process that led to the penning of the remarkable and often-quoted passage which occurs in his works--appears to be nothing more than a suggestion or proposition as a means of meeting a difficulty; it is very much as though he had said: If you cannot go straight through, you must even go round about. To so much and to no more, do Servetus’s claims to be considered a discoverer, in the sense we would attach to that word, amount. The passage from the ‘Restitutio Christianismi’ of Servetus, 1553, if viewed from the point proposed, will not fail to set his title to be regarded as the discoverer of the lesser circulation in its true light--in a light under which it has not yet been seen. We translate so much of the passage as bears on the question under review. “The vital spirit has its origin in the left ventricle, the lungs assisting especially in its generation. It is a subtile spirit * * * It is engendered from the mixture that takes place in the lungs of the inspired air with the elaborated subtile blood which the right ventricle of the heart communicates to the left. But this communication takes place, not by the middle septum of the heart, as is commonly believed, but by a remarkable artifice; the subtile blood of the right side of the heart is agitated in a lengthened course through the lungs, whereby it is elaborated, from which it is thrown of a crimson colour, and from the vena arteriosa (pulmonary artery) is transfused into the arteria venosa (pulmonary veins); it is then mixed in the arteria venosa itself with the inspired air, and by the act of expiration is purified from fuliginous vapours, when, having become the fit recipient of the vital spirit, it is at length attracted by the diastole. Now, that the communication and preparation take place as stated through the lungs, is proclaimed by the various conjunctions and communications of the arterial vein with the venous artery. The remarkable size of the arterial vein (pulmonary artery) confirms this, a vessel which could neither have its actual constitution nor dimensions, nor transmit such a quantity of the purest blood direct from the heart itself, for the mere nourishment of the lungs. Neither would the heart supply the lungs in such proportion, (especially when we see the lungs in the embryo nourished from another source) by reason of those membranes or valves which remain unopened until the hour of birth, as Galen teaches. The blood, consequently, from the moment of birth, is