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 these exceptionally clever men was able to offer an entirely acceptable solution. Harvey alone, as will appear farther on in this account, solved the riddle once and for all.

The "spirit"—the purest part of the blood—is lodged, according to Galen, in the left ventricle; and, inasmuch as even the venous blood, if it is to fulfil in some degree the function of a nourishing fluid, must possess a certain proportion of "spirit," it is clear that the two ventricles should communicate the one with the other; for how otherwise—thought Galen—is it possible for a certain amount of "spirit" to commingle with the venous blood? The locality at which this communication was assumed to exist was the interventricular septum; and, as nobody was able to find anything like a foramen in this membrane, it was asserted that the communication is effected through an infinite number of pores. For over one thousand years physicians accepted this porous character of the interventricular septum as an established fact. In his commentaries on Mondino's "Anatomy" (1521), Berengarius of Carpi timidly ventured the statement that the openings of communication are not distinctly visible, and this apparently was the first feeble expression of doubt concerning the correctness of the prevailing doctrine. Vesalius, on the other hand, boldly denied their existence altogether.

According to Galen's teaching the liver is the source of origin of all the veins, just as the heart is the starting-*point of all the arteries. It is quite remarkable, says Flourens, that physicians who performed almost daily the operation of venesection should, during a long series of years, have failed to observe that this doctrine of blood flowing through the veins from the liver to the different parts of the body, could not possibly be true, inasmuch as at each such operation the vein always became distended with blood below (i.e., on the distal side of) the ligature which they applied to the part (arm, for example) before opening the vessel. This phenomenon, of course, indicated clearly that the blood in the veins flowed toward the heart, and not from any centrally located spot or organ ''toward the extremities''. And yet—he adds—even so bright and