FERMENTATION 25 



impurity of their yeast, and the evil result on the 

 liquor. Always, he is the man with the microscope : 

 he understands the nature and the life-history of 

 each ferment : its range of action, its tricks and its 

 ways, what it likes, what it dislikes. For the diseases 

 of wines, his was the best opinion : there was none 

 so well able, from the look of a speck of yeast or a 

 film of sediment under the microscope, to give 

 a correct diagnosis and a correct prognosis. No 

 man has done more to raise brewing and wine- 

 making to their present standard of accuracy and 

 of purity. Not that he stands alone, or that no 

 further advance has been gained since his time : 

 there is the work of Hansen, Traube, Nageli, 

 Buchner, Jacobsen, and many more : there are 

 new methods, new safeguards, new forms of yeasts 

 identified and classified, new exercises of theory in 

 chemistry. The controversy, fifty years ago, between 

 Liebig and Pasteur between the older man of 

 science, who thought of fermentation in terms of 

 molecular physics, and the younger man of science, 

 who thought of it in terms of plant physiology 

 has been resolved by Buchner's work : who, in 1897, 

 extracted from yeast the very substance of its 

 ferment, the zymaze, separable from the yeast-cells, 

 yet formed within them, as ptyalin is formed within 

 the cells of the salivary glands. The action of 

 zymaze may be stated in terms of molecular physics : 



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