Leonor Michaelis

MICHAELIS, Leonor (born 1875), an eminent German physical chemist. All of Michaelis's works are devoted to the application of physical-chemical methods to the study of biological problems. The result of Michaelis's earlier works was his manual «Einführung in die Farbstoffchemie für Histologen» (Berlin, 1902). Later, Michaelis became interested in capillary phenomena («Dynamik der Oberflächen—eine Einführung in biologische Oberflächen-Studien», Dresden, 1909). However, the most important question that for many years riveted Michaelis's attention and brought him particularly great renown was the study of the biological significance of the hydrogen ion. Michaelis published a large number of studies on the isoelectric point of various amphoteric substances, in particular enzymes, as well as on the pH of various tissues and body fluids under normal and pathological conditions. Michaelis's book, representing a general summary on the significance of hydrogen ion concentration for biology and on the methods for measuring them («Die Wasserstoffionenkonzentration, ihre Bedeutung für die Biologie und die Methoden ihrer Messung», Berlin, 1914), gained wide circulation; of the second edition, only part 1 was published, devoted to general theoretical foundations (Berlin, 1922). Furthermore, Michaelis produced a number of precise experimental studies (published, like most of Michaelis's other works, mainly in the Biochemische Zeitschrift) on the question of the permeability of the cell membrane to ions. The result was a completed theory of ionic permeability, which received experimental confirmation from other researchers as well. As a result of studying oxidative processes by the method of measuring oxidation-reduction potentials, Michaelis compiled the monograph «Oxydations-Reduktions-Potentiale» (Berlin, 1929), which is a continuation of Michaelis's unfinished manual dedicated to hydrogen ions. Michaelis also authored a practical manual on physical chemistry («Praktikum der physikalischen Chemie, insbesondere der Kolloidchemie für Mediziner und Biologen», 3rd ed., 1926; Russian edition: Moscow-Leningrad, 1925) and a textbook of higher mathematics («Einführung in die Mathematik für Biologen und Chemiker», Berlin, 1912; 3rd ed., Berlin, 1927; Russian ed.: Moscow-Leningrad, 1928).