produced disease and those which produced ordinary putrefaction. Then came the experimental evidence of Davaine and Koch, who demonstrated the development of bacteria from spores. It is hardly necessary to discuss this theory further, but I may mention the labors of Panum and of Brieger, who deeply investigated the poisons produced by bacteria, to which are given the general titles of ptomaines and toxins. It would be unjust, however, did I not mention the name of Lister in connection with the inestimable benefit that has accrued to surgery from the practical application of the theory of infection to wounds,--a measure that brought about an entire revolution in surgery and surgical technique, and an entire reversal of the statistics of operations; where thousands formerly died, thousands now live, their lives being indirectly due to the labors of this one man and his following. I will add that it is necessary to realize the difference between life and death to appreciate the changes that have been brought about during the last score of years. Much that in former years was unjustifiable has become both justifiable and feasible; to-day patients, as a matter of course, live after operations which, so recently as when I was{262} a student, were considered impossible, or if performed exposed the operator to the charge of manslaughter. I have spoken of the impulse which came from Avenbrugger's invention of percussion, which was greatly extended through the translation of his work by Corvisart (1755-1821); the latter also excelled as a clinical teacher and pathological anatomist, and had much to do with the education of others of his _confrères_ whose names are lustrous in history. Among the most celebrated was Laënnec (1781-1826), who, though brought up among most trying surroundings, early manifested a zeal for medicine. He became a field-surgeon in the French army soon after the Reign of Terror, and pushed his classical and medical studies with restless zeal. In 1815 his first experiments were made with the stethoscope, the invention of which was due to accident: in order to hear the sounds of the heart more clearly, lie one day applied a cylindrical roll of paper, and then immediately constructed the whole form of the stethoscope upon the principle now everywhere resorted to. In 1819 he published his work on Mediate Auscultation,--a treatise on prognosis in disease of the lungs and heart, based principally upon this new aid to investigation. The treatise was speedily translated into all the languages of Europe. After enjoying a large practice Laënnec succumbed to ill health at the early age of forty-five. He seems to have had but slight appreciation of his own services to medicine, and to have prided himself rather on his skill in riding horseback. Honor and fame, however, followed closely upon the publication of his well-known work, and the manuals of physical diagnosis which now find frequent mention