Sir William Harvey initiated the modern science of physiology through his explanation of body processes in physical terms. His discovery of the circulation of the blood has few equals in the history of science.This English physician's knowledge of comparative anatomy of the heart and blood vessels was beyond that of any of his contemporaries. Indeed, the presentation of his theory of blood circulation is a marvel of conciseness reflecting patient observations and clear logic.Some of Harvey's discoveries include the following: There are no "pores" between the various parts of the heart-all blood makes a complete circulation.The same blood flows through veins and arteries, not different blood in each.Most of the blood in the arteries is not "used up," but flows into the veins.