Prof. Osier's declaration that the world's best work was mainly done by young men was not well received, but no one knew better than he that this is the most salient fact in the history of medical progress. There is practically not a single great discovery in medicine that was not made by a young man under thirty-five. As a rule, indeed, the new departures in medicine came from men who were well under thirty, some of them in fact only at the beginning of their third decade of life. Morgagni's great germinal idea, which made him the father of modern pathology, came to him when he was a student scarcely more than twenty. He then began to take notes on all the morbid appearances that he found in bodies, recognizing very clearly that he must trace out not only the main cause of the disease, but also the subsidiary pathological factors that were at work in the production of the various symptoms of the special case as he had studied it clinically. This idea is so obvious now as to seem impossible to be missed; yet scarcely a century ago it constituted the foundation-stone of modern pathology. {15} Auenbrugger, who laid the foundation of modern physical diagnosis by his observations upon percussion, began the work when he was under twenty-five, at the Spanish Hospital in Vienna, and carried it out to a completely successful issue absolutely without any encouragement from the great masters of the Vienna school. As a matter of fact, they rather pooh-poohed the idea that this foolish drumming, as one of them is said to have termed it, could ever amount to anything in enabling physicians to recognize pathological conditions within the chest. For twenty-five years after the publication of his little book, Auenbrugger's discovery attracted no attention. Laennec, who followed Auenbrugger in the development of physical diagnosis, set himself the much harder problem of constructing a system of auscultation when he was in his early twenties, studied the subject for twelve years and then published the book on it when he was as yet scarcely thirty-five. He accomplished the revolution in medicine that is due to him, though he was never strong and died at the early age of forty-six.