Physiology at the beginning of the 19th century was dominated by vitalistic theories, which postulated that life is governed by mysterious, nonquantifiable “vital forces.” In spite of the late 18th-century discovery of oxygen by Lavoisier, Priestly, and others, and of the essential role that oxygen plays in sustaining animal life, few efforts had been made to identify the laws that govern physiological behavior. Claude Bernard, a determinist who used the experimental method to identify and quantify physicochemical laws that operate in living animals, is generally viewed as one of the pioneers who built the foundation for modern physiology...