Georg Ernst Stahl was a leading German medical scientist and chemist of his day. Stahl was appointed professor of medicine at the University of Halle in 1694, and from 1716 until his death he served as personal physician to Frederick William I of Prussia. His numerous medical writings had a strongly doctrinal tendency, which made them the source of lively, often bitter, controversy. His famous phlogiston theory, an erroneous explanation of the nature of combustion and calcination, was nonetheless, before Antoine Lavoisier's discoveries, instrumental in placing chemistry on a scientific basis. The same may be said of his studies concerning the properties and composition of acids, alkalis, and salts.

Led by his medical, rather than chemical, interests to philosophy, Stahl elaborated (particularly in his Theoria Medica Vera, 1707) a rigorous position of animism, affirming that the animal organism was formed, governed, and preserved by an...