494 THE LIFE-WORK OF A CHEMIST. 



themselves walked in these enticing and yet often bewildering paths 

 can fully appreciate, and by attention to minute detail as well as to 

 broad principles to an extent which none can surpass and few can equal. 

 A knowledge of the action of the mold in the changes it effects on 

 tartaric acid led Pasteur to investigate that bete noire of chemists, the 

 process of fermentation. The researches thus inaugurated in 1857, not 

 only threw a new and vivid light on these most complicated of chemical 

 changes and pointed the way to scientific improvements in brewing 

 and wine-making of the greatest possible value, but were the stepping- 

 stones to those higher generalizations which lie at the foundation of 

 the science of bacteriology, carrying in their train the revolutions in 

 in modern medicine and surgery to which I have referred. 



The history of the various theories from early times until our own 

 day which have been proposed to account for the fact of the change of 

 sugar into alcohol, or that of alcohol into vinegar, under certain condi- 

 tions, a fact known to the oldest and even the most uncivilized of races, 

 is one of the most interesting chapters in the whole range of chemical 

 literature, but however enticing, is one into which I can not now enter. 

 Suffice it here to say that it was Pasteur who brought light out of dark- 

 nesss by explaining conflicting facts and by overturning false hypoth- 

 eses. And this was done by careful experiment and by bringing to 

 bear on the subject an intelligence trained in exact methods and in 

 unerring observation, coupled with the employment of the microscope 

 and the other aids of modern research. 



What now did Pasteur accomplish ? In the first place he proved 

 that the changes occurring in each of the various processes of fermen- 

 tation are due to the presence and growth of a minute organism called 

 the ferment. Exclude all traces of these ferments and no change 

 occurs. Brewers' wort thus preserved remains for years unaltered. 

 Milk and other complex liquids do not turn sour even on exposure to 

 pure air, provided these infinitely small organisms are excluded. But 

 introduce even the smallest trace of these microscopic beings and the 

 peculiar changes which they alone can bring about at once begin. A 

 few cells of the yeast plant set up the vinous fermentation in a sugar 

 solution. This is clearly stated by Pasteur as follows : " My decided 

 opinion," he says, " on the nature of alcoholic fermentation is the fol- 

 lowing : The chemical act of fermentation is essentially a correlative 

 phenomenon of a vital act beginning and ending with it. I think that 

 there is never any alcoholic fermentation without there being at the 

 same time organization, development, multiplication of globules, or the 

 continued consecutive life of globules already formed." 



Add on a needle's point a trace of the peculiar growth which accom 

 panics the acetous fermentation and the sound beer or wine in a short 

 time becomes vinegar. Place ever so small a quantity of the organism 

 of the lactic fermentation in your sweet milk, which may have been 

 presery^(i fresU for ye^r§ ip ab§eooo Qt m^k ovgmim^^ ^u^ yoiir milk 



