As early as the 17th century, William Harvey had already discerned the existence of the Ductus arteriosus and explained its relative function. Here he says, "...in embryos, whilst the lungs are in a state of inaction, performing no function, subject to no movement any more than if they had not been present, Nature uses the two ventricles of the heart as if they formed but one for the transmission of the blood." However, the apex of Harvey's work is probably the eighth chapter, in which he deals with the actual quantity of blood passing through the heart from the veins to the arteries. Coming into conflict with Galen's accepted view of the liver as the origin of venous blood, Harvey estimated the capacity of the heart, how much blood is expelled through each pump of the heart, and the number of times the heart beats in a half an hour. All of these estimates were purposefully low, so that people could see the vast amount of blood Galen's theory required the liver to produce. He estimated that the capacity of the heart was , and that every time the heart pumps, of that blood is expelled. This led to Harvey's estimate that about of blood went through the heart every time it pumped. The next estimate he used was that the heart beats 1,000 times every half an hour, which gave 10 pounds 6 ounces of blood in a half an hour, and when this number was multiplied by 48 half hours in a day he realised that the liver would have to produce 498 pounds of blood in a day, more than the weight of the whole body.