This supposed imperfection of the mitral valve played an important part in Galen's system, for it was possible thereby for the lung to receive, not only some spirituous blood from the left ventricle of the heart, but also, and especially, the injurious fumes which Galen held to arise from combustion in the left ventricle, to escape into the venous artery past the imperfect mitral valve, and to be exhaled in expiration. When this valvular door was open, therefore, the left ventricle drew from the lungs into itself crude spirits, these to be returned in some part perhaps to the lungs as spirituous blood in company with the deleterious fumes, when the valvular door was only ajar. This imperfection of the valve of two segments, however, was but a constant and fortunate exaggeration of a condition shared to a slight degree by all the valves; for Galen held these, in the act of closing, to allow slight regurgitation of spirits, vapor, or even of blood; and to do so exceptionally even when closed, if the movement of the heart were of unusual force. He commonly, however, assumed the tricuspid, pulmonary, and aortic valves to be competent, especially if he could gain a polemical point by doing so.[146] More than thirteen centuries later Columbus, as we have learned, announced that blood from the right ventricle entered the left ventricle, not by pores of the septum, but exclusively by pores of the lungs, in passing through which latter it became spirituous blood, needing but little elaboration in the ventricle before entering the arteries for distribution to the body. Columbus denied and derided the passage of fumes from the left ventricle to the lungs, while he accepted the ancient doctrine of the cooling effect of respiration. His view of the meaning of the pulmonary transit is therefore a striking approximation to the truth--a closer one than that of Harvey, who questioned everything except the fumes given off in expiration, which fumes, of course, Harvey did not send along the Galenic path. As Columbus declared the spirituous blood to be made up in the lungs, and these, therefore, to need no supply thereof from the left ventricle; and as he also denied the passage of fumes through the venous artery; the flow through the latter became simplified, spirituous blood alone passing through it, and in the true direction from the lungs to the heart. Accordingly the mitral valve also was cured of its Galenic imperfection; to the latter Columbus does not even refer, but he simply describes all the four valves as competent.