"This, to be sure, is conceded by all after a fashion, it being gathered from the structure of the heart and the arrangement, position, and use of the valves. But they seem to waver blindly as though in a dark place, and they put together varied, incoherent, and more or less contradictory doctrines and, indeed, set forth much upon conjecture, as has been shown already. "There seems to me to have been one single principal cause of hesitation and error in this matter, viz.: the connection between the heart and the lung in man. The disappearance of the arterial vein in the lungs having been noted, and likewise that of the venous artery, great obscurity prevailed as to whence or how the right ventricle distributed the blood to the body, or the left ventricle drew blood from the vena cava. This is attested by the words of Galen when he inveighs against Erasistratus regarding the origin and use of the veins and the coction of the blood. 'You will answer,' Galen says, 'that the way of it is this: that the blood is prepared beforehand in the liver and is transferred thence to the heart to receive the rest of its proper character in complete perfection. Surely this does not seem devoid of reason; for no great and perfect work can be accomplished suddenly at one attempt and receive its entire polish from a single instrument. If then this be so, show us another vessel which leads the completely perfected blood forth from the heart, and distributes it to the whole body as the artery does the spirits.'[150] Behold Galen disapproving and putting aside a reasonable opinion because, besides not seeing the path of transit,[151] he cannot find a vessel to distribute the blood from the heart to the whole body! "But had there been anyone on the spot to take the part of Erasistratus or of that opinion which is now our own and is confessed by Galen himself to be reasonable in other respects; and had the person aforesaid pointed his finger at the great artery [aorta] as the distributer of the blood from the heart to the body at large,--I wonder what answer that divine man would have made, full of genius and of learning as he was! Had he said that the artery distributed spirits and not blood, he certainly would sufficiently have refuted Erasistratus, who believed that only spirits were contained in the arteries; but in so doing Galen would have contradicted himself and would shamefully have denied what he sharply contends to be true in a special book[152] which he wrote against that same Erasistratus. For he proves by many powerful arguments, and demonstrates by experiments, that blood, and not spirits, is naturally contained in the arteries.