It is indeed a true saying that to be successful in the treatment of disease clinical observation must be accompanied by biological and bio-chemical research. Yet the practice of medicine in times not so very remote was chiefly based on careful observation and common sense. In by far the majority of diseases the ætiology was not understood, and this was strikingly true of the acute forms of mental derangement. Still, devoted workers and searchers after truth continued their investigations on the dead and their experiments on the living. Gradually appliances were improved and new methods pursued, and with such brilliant results that at last the true cause of infective disease was discovered. One by one bacteria were isolated and studied, and thus a great world of medical research was opened out and results obtained which have already wrought untold blessings to humanity.