The origin of disease has aroused remarkable human interest from the dawn of history. The most important findings in this field were the great microbial discoveries at the end of the 19th century, when recognition of pathogenic microbes seemed to be identical with the recognition of causes of the particular disease. Molecular events happen in living organisms, therefore the molecular mechanisms of disease turn from the environment to the organism, lending itself to the production of disease. Molecular disturbances as causes of disease usually are recognized in heritable diseases. Unfortunately, the general knowledge of living processes was, at that time, so unsatisfactory that it was impossible to establish a substantial theory about causes of disease. Correct views of the life processes did not occur prior to discovery of the molecular bases of heredity and knowledge of the mechanisms of protein biosynthesis and the function of protein molecules.