along, the analogy between disease and fermentation must have been in Pasteur’s mind; and then came the suggestion, “What would be most desirable is to push those studies far enough to prepare the road for a serious research into the origin of various diseases.”  If the changes in lactic, alcoholic and butyric fermentations are due to minute living organisms, why should not the same tiny creatures make the changes which occur in the body in the putrid and suppurative diseases?  With an accurate training as a chemist, having been diverted in his studies upon fermentation into the realm of biology, and nourishing a strong conviction of the identity between putrefactive changes of the body and fermentation, Pasteur was well prepared to undertake investigations which had hitherto been confined to physicians alone.

So impressed was he with the analogy between fermentation and the infectious diseases that, in 1863, he assured the French Emperor of his ambition “to arrive at the knowledge of the causes of putrid and contagious diseases.”  After a study upon the diseases of wines, which has had most important practical bearings, an opportunity arose which changed the whole course of his career, and profoundly influenced the development of medical science.  A disease of the silkworm had, for some years, ruined one of the most important industries in France, and in 1865 the Government asked Pasteur to give up his laboratory work and teaching, and to devote his whole energies to the task of investigating it.  The story of the brilliant success which followed years of application to the problem will be read with deep interest by every student of science.  It was the first of his victories in the application of the experimental methods of a trained chemist to the problems of biology, and it placed his name high in the group of the most illustrious benefactors of practical industries.

In a series of studies on the diseases of beer, and on the mode of production of vinegar, he became more and more convinced that these studies on fermentation had given him the key to the nature of the infectious diseases.  It is a remarkable fact that the distinguished English philosopher of the seventeenth century, the man who more than anyone else of his century appreciated the importance of the experimental method, Robert Boyle, had said that he who could discover the nature of ferments and fermentation, would be more capable than anyone else of explaining the nature of certain diseases.

In 1876 there appeared in Cohn’s “Beitrage zur Morphologie der Pflanzen” (II, 277-310), a paper on the “AEtiology of Anthrax” by a German district physician in Wollstein, Robert Koch, which is memorable in our literature as the starting point of a new method of research into the causation of infectious diseases.  Koch demonstrated the constant presence of germs in the blood of animals dying from the disease.  Years before, those organisms had been seen by Pollender and Davaine, but the epoch-making