22 LOUIS PASTEUR. 



numerous careful experiments along these various lines which he 

 devised in his laboratory, it required only four or five years for 

 him to undermine completely the chemical theory of Liebig, and 

 to put in its place (on a somewhat unstable basis at first, perhaps) 

 the theory that all types of fermentation are organic in their nature 

 and produced by the life of microscopic organisms. Even at this 

 early day we can see his recognition of the value of the practical 

 application of science, for among the very early pieces of work 

 which he performed was the study of the acetic acid fermentation 

 in the making of vinegar, and by a practical application of his 

 results to this industry he developed a vast improvement in the 

 manufacture of vinegar and a great cheapening of the process. 



Pasteur had thus made something his oimi, and at this date, in 

 the vicinity of i860, he became recognised as the exponent of the 

 biological theory of fermentation. From this time he progressed 

 rapidly. The fermentation of wine next claimed his attention. 

 Here was a second fermentative industry, in which unexplained 

 difficulties were constantly occurring. He soon found the cause 

 of the various failures of the vintner, by which were produced 

 many of the so-called "diseases of wine." These diseases, he 

 found, were all due to the presence of improper micro-organisms 

 during the fermentation instead of the pure fermenting yeasts, and 

 he quickly devised a remedy for them in a process that has subse- 

 quently been known by his name as the process of pasteurisation. 

 This method of preventing the evils, involving the heating of wine, 

 was received with great opposition, on the ground that the heating 

 injured the flavour. After a great deal of more or less violent 

 disputing on the matter, Pasteur arranged for a public test of the 

 question by getting together a large number of experts and con- 

 vincing them against their will, by ingeniously devised deceits, 

 that they were unable to distinguish between wines that had been 

 pasteurised by his process and wines that had not been subject to 

 heat. Having previously shown that the method of pasteurisation 

 was almost a sure remedy against the various diseases, this first 

 public demonstration was thus a brilliant success, and at once 

 obtained for his method the acceptance of the vintner. 



Meantime, he had been giving his attention to the vexed 

 problem of the last two or three centuries — namely, the ques- 



