Flexner, Simon

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Flexner, Simon

(b. Louisville, Kentucky, 25 March 1863; d. New York, N.Y., 2 May 1946)

pathology, bacteriology.

Flexner was the fourth child of Morris Flexner, member of an educated Jewish family in Czechoslovakia, who immigrated to Kentucky. Starting as a peddler, he became a successful wholesale merchant. Flexner’s mother, Esther Abraham, was born in Alsace. Flexner attended public schools in Louisville and was apprenticed to a druggist who sent him to the Louisville College of Pharmacy, from which he was graduated in 1882. He then worked in his eldest brother’s drugstore and studied medicine at the University of Louisville, receiving the M.D. degree in 1889. Although the medical school then provided little opportunity for laboratory study, Flexner acquired a microscope, with which he studied pathological tissues and made microscopic examinations for doctors who patronized the Flexner pharmacy.

In 1890, at the suggestion of another of his remarkable brothers, Abraham, Flexner went to Baltimore to study pathology and bacteriology at the Johns Hopkins Hospital with William H. Welch, who gave him a fellowship and in 1892, when the Jons Hopkins Medical School opened, made him his first assistant in the department of pathology. In 1893 Flexner visited Europe, working at Strasbourg with Friedrich von Recklinghausen and at Prague. On his return he became resident pathologist at the Johns Hopkins Hospital. By 1899 he reached full professorial rank. In that year, following the acquisition of the Philippine Islands by the United States, Flexner and two medical students spent several months in Manila studying health conditions. During this stay he isolated an organism that causes a prevalent form of dysentery. This Bacillus (now Shigella) dysenteriae is still commonly known as the “Flexner bacillus.”

Soon after his return to Baltimore, Flexner was appointed professor of pathology at the University of Pennsylvania, where he organized an excellent staff, planned a new laboratory building, and carried out important researches on experimental dysentery, on experimental pancreatitis, and on immunological problems, especially with regard to hemolysis and hemagglutination. One of his associates was the brilliant young Japanese physician Hideyo Noguchi, who came from Japan inexperienced and penniless and found in Flexner a lifelong friend and guide.

When bubonic plague broke out in California in 1901, the federal government sent Flexner to San Francisco to study the epidemic. Within a month he and a few associates confirmed the presence of the plague bacillus and made a report to health authorities that aided them in eradicating the disease.

In 1901 John D. Rockefeller and his son John D. Rockefeller, Jr., were planning the creation of the Rockefeller Institute for Medical Research in New York City. Flexner, who by this time, at the age of thirty-eight, was beginning to be nationally known, was appointed to the institute’s board of scientific directors, which was composed of seven eminent medical men and headed by his friend and mentor William H. Welch. In 1902 Flexner was chosen to lead a department of pathology and bacteriology in the institute, and soon he established himself as head of the whole enterprise. He brought together a strong group of investigators, including Hideyo Noguchi, S. J. Meltzer, P. A. T. Levene, Alexis Carrel, Jacques Loeb, Eugene Opie, Rufus I. Cole, and Peyton Rous. Flexner’s colleagues found him a man of exceedingly keen intelligence, with a reserved manner that concealed a sympathetic heart. He directed his staff with great skill, giving free rein to those who showed independent competence while guiding with a wise hand those who needed advice. His financial acumen impressed the astute patron of the institute, who showed his confidence by successive additions to its funds.

To combat an epidemic of cerebrospinal meningitis in 1906, Flexner produced a serum that remained the best treatment until the sulfa drugs were introduced. When in 1910 poliomyelitis was epidemic in New York, he and his assistants were the first to transfer the virus from monkey to monkey. This success enabled the investigators to keep the virus alive in the laboratory and thus ultimately, after development by others of a less expensive method of perpetuating it (by cultivation in hens’ eggs), led to the preparation, in the 1950’s, of protective vaccines.

The Rockefeller Institute, quite early in its history, came under strong attack from organizations opposed to the use of animals in experiments on the causes of disease. Flexner’s accomplishments in such work and his calm generalship made him a natural leader in the successful deterrence of these opponents.

In 1903 Flexner married Helen Whitall Thomas, member of a prominent Quaker family of Baltimore. She helped to expand his intellectual interests beyond the medical sciences, giving him an appreciation of literature and the arts. Of their two sons, William became a physicist and James Thomas a writer and historian of American culture.

Flexner’s medical and biological accomplishments led to public service in various health fields, as chairman of the Public Health Commission of New York State, as medical consultant of the U. S. Army during World War I, and as member of the China Medical Board of the Rockefeller Foundation. When in 1902 William H. Welch wearied of the editorship of the Journal of Experimental Medicine, Flexner took it over and for about fifteen years was its chief editor, giving the task much time and attention.

His executive competence was recognized by trusteeships of the Rockefeller Foundation, the Carnegie Foundation for the Advancement of Teaching, and the Johns Hopkins University. A little-known but very important public service was his leadership in establishing fellowships of the National Research Council, provided by the Rockefeller Foundation, for promising young medical scientists. Oxford University called him in 1937–1938 to its Eastman professorship, at a time when his counsel was needed in the organization of Lord Nuffield’s endowment of medical professorships. A book, The Evolution and Organization of the University Clinic (Oxford, 1939), resulted from this experience. Flexner was elected member of the American Philosophical Society in 1901, the National Academy of Sciences in 1908, and foreign member of the Royal Society in 1919.

During his long career Flexner published several hundred scientific papers, lectures, and essays. At the age of seventy-eight he published jointly with his son James a notable biography, William H. Welch and the Heroic Age of American Medicine (New York, 1941). He quietly resigned the directorship of the Rockefeller Institute in 1935.


Flexner’s papers are in the library of the American Philosophical Society, Philadelphia.

Secondary literature includes Stanhope Bayne-Jones, “Simon Flexner, 1863–1946,” in Year Book [for] 1946. American Philosophical Society (Philadelphia, 1947), pp. 284–297; George W. Corner, History of the Rockefeller Institute (New York, 1965), passim; Memorial Meeting for Simon Flexner (New York, 1946), a pamphlet issued by the Rockefeller Institute that contains personal characterizations by John D. Rockefeller, Jr., and others; and Peyton Rous, “Simon Flexner, 1863–1946,” in Obituary Notices of Fellows of the Royal Society of London, 6 (1948–1949), 409–445, with portrait and complete list of publications.

George W. Corner