Anatomy: Animals Inside

Circulatory System

Who first demonstrated that blood circulates?

English physician William Harvey (1578–1657) was the first person to demonstrate that blood circulates in the bodies of humans and other animals. Harvey’s hypothesis was that the heart is a pump for the circulatory system, with blood flowing in a closed circuit. Harvey conducted his research on live organisms as well as dissection of dead organisms to demonstrate that when the heart pumps, blood flows into the aorta. He observed that when an artery is slit, all the blood in the system empties. Finally, Harvey demonstrated that the valves in the veins serve to make sure blood returns to the heart.


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