Hales, Stephen, 1677–1761, English physiologist and clergyman. From 1709 he was perpetual curate of Teddington. His experimental studies in animal and plant physiology contributed greatly to the progress of science. In his investigations of circulation he made the first measurements of blood pressure by inserting a tube in a horse's artery. Plant physiology was given impetus by his work on transpiration, root pressure, circulation of sap, and the relationship between green plants and air. His inventions included apparatus for ventilating buildings. Some of his studies are described in his Vegetable Staticks (1727), Haemostaticks (1733), and A Description of Ventilation (1743).
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