INTRODUCTION 



The publication in the Bibliotheque de Philosophie Scientifique 

 of a volume dealing with micro-organisms was entirely indicated, 

 for microbiology is taking every day a larger aijd larger place 

 in the realm of knowledge and philosophy. Although dis- 

 covered more than two hundred years ago, microbes were long 

 neglected, and it was only during the second half of last 

 century that their true role was ascertained. 



Ehrenberg in the middle of the nineteenth century had 

 already perceived the importance of microscopic organisms in 

 the evolution and life of our planet. The discovery of the 

 fossil remains of Diatoms and Foraminifera led him to appre- 

 ciate the great part these minute creatures have played in the 

 building up of the earth's crust. 



There were not lacking men of science disposed to attribute 

 to micro-organisms an important action in the phenomena of 

 fermentations and of disease, but it was only after the labours 

 of Pasteur that this truth was definitely established and became 

 part of our common heritage of knowledge. 



Relations had long been perceived between the animal 

 kingdom and the vegetable, animals furnishing carbonic acid 

 and nourishment to plants, while these, on their side, nourish 

 the animals with their organic matter and provide them with 

 oxygen. Later it was recognised that between these two 

 kingdoms there lies the domain of the microbes. It is the 



