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Portrait of the English physician John Mayow, 1641-1679. He published a book in 1674 in which he gives a theory of combustion similar to Hooke's but supported by new experiments. He concluded that air consists of at least two parts; one supports combustion and respiration, while the other part is inert. He held that it was the combustive principle in air which turned dark venous blood to bright arterial blood. In experiments with an air-pump he found that venous blood under the pump effervesced only gently, but arterial blood bubbled freely if fresh.
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