HAZARDS OF MODERN DIAGNOSIS AND THERAPY—THE PRICE WE PAY FRANK BILLINGS MEMORIAL LECTURE David P. Barr, M.D., New York "First of all, be sure you do no harm:Primum non nocere."In all ages this admonition has been fundamental to the practice of medicine. It applied to the use of all the empirical drugs of ancient and medieval times. Failure to regard it inspired the scathing satires of Molière and was responsible for the research of Pierre Louis and the reforms of Oliver Wendell Holmes and Ignaz Semmelweis. The admonition applied in the age of nihilism, when most of the useless drugs of the past had been abandoned and when Osier could find only a dozen or so to recommend for detailed study by his students. Even then, the few great drugs were as well known for their toxic as for their therapeutic effects. Mercury, the recognized specific for syphilis,