20 LOUIS PASTEUR. 



things of life the discoveries revealed to him by his microscope. 



The active part of Pasteur's life was so full of investigations in 

 many lines that it is impossible that they should, in a brief review, 

 receive the weight which they deserve. Only the most important 

 of them can be here mentioned, a selection being made of those 

 upon which his reputation has been chiefly built. Pasteur 

 received an early training as a chemist, and the first work of his 

 life was chemical. Until he had reached about the age of 32 the 

 work he had been doing had been mostly in the line of molecular 

 physics, and certain papers upon the structure of crystals appeared 

 from his pen, which even in those early years showed signs of 

 genius. He would probably have made his mark as a chemist 

 had not his attention been turned to a more fruitful field. In 1854 

 he was appointed Dean of the University of Lille, and it was at 

 this place that his attention was first turned in the direction which 

 subsequently made him famous. 



A simple incident led him to the study of fermentations in the 

 manufacture of certain chemicals. The crystallisation of tartrates 

 had earlier interested him, but now he noticed that tartrate of 

 lime had a tendency to ferment. This fact attracted his attention, 

 and led him into observations and experiments upon the nature of 

 the fermentation of tartrates. These experiments demonstrated 

 to his microscope the universal presence of living organisms in the 

 fermenting material. Finding these fermentations universally 

 accompanied by living organisms, it appeared to him as probable 

 that the fact must be part of some general law. It was not a pure 

 accident that living organisms were present, but in some way he 

 beUeved there was a connection between the fermentations and the 

 presence of the organisms. A general law he formulated, and 

 reached the inference that fermentations in general are produced 

 by living organisms, microscopical in size, but of very great 

 potency. This conclusion was, of course, a simple inference as 

 yet undemonstrated, but it was the inference which started Pasteur 

 along the line of his experiments in fermentation. It was the 

 guiding star of Pasteur's life. From the moment the inference 

 was drawn until his death, this law — that fermentations, putrefac- 

 tions, and all similar chemical changes were produced by the 

 growth of micro-organisms — was the basis of every Une of investi- 



