In these easily reproducible experiments, prefaced by an important historical introduction, Pasteur demonstrated beyond dispute that fermentation is caused by the action of minute living organisms, and that if these are excluded or killed fermentation does not occur. The heating process which Pasteur recommended for sterilization was the earliest form of “pasteurization”. The above paper marks the downfall of the theory of spontaneous generation. Pasteur’s researches on fermentation led him to the discovery of the bacteria and yeasts and hence to the germ theory of disease; from this all modern bacteriology and immunology have developed.