THE ALCOHOLIC FERMENTATION 323 



(The enzyme system catalyzes the decarboxylation of pyruvic acid 

 to carbon dioxide and acetaldehyde.) They claim that the amount 

 of carbon dioxide produced in a microrespirometer or a fermentometer 

 by yeast suspended in a salt-glucose solution is directly proportional 

 to the amount of thiamin added. However, the compressed yeast 

 recommended for this assay purpose can also be stimulated to pro- 

 duce gas by the pyrimidine fraction of the thiamin molecule as 

 well as thiamin.^- See page 318 for the structure of thiamin. 



The use of yeast for assay of pyridoxine (vitamin Be) has also 

 been suggested by these two groups of workers.*- ^^ At the present 

 time, the method of assay for pyridoxine using yeast and measuring 

 the growth response turbidimetrically is the best available. It is 

 superior to the assay method employing lactobacilli as the test or- 

 ganism. 



Williams, Snell, and their associates have also described techniques 

 for the microbiological assay of pantothenic acid,^'' inositol,^^ and 

 biotin *^ employing yeasts as the test organisms and using the tur- 

 bidity method. 



THE ALCOHOLIC FERMENTATION 



The final establishment of the fact that fermentation, as it occurs 

 in nature, is caused by living cells comes from Pasteur's classical 

 experiments with yeasts. His views were vigorously opposed, espe- 

 cially by the chem'ist Liebig, who held that ferments were not living 

 cells but merely organic catalysts in a state of extreme disquietude, 

 this state being transferred to sugar molecules, which then changed 

 to forms more stable, alcohol and carbon dioxide. Pasteur's thesis 

 that fermentations occurring in nature are due to living cells has been 

 firmly established. However, his view that fermentation is a part 

 of the vital phenomenon which cannot be separated from the life of 

 the yeast cell, that fermentation is inseparable from the presence of 

 living cells, has been proved fallacious. Buchner found that cell- 

 free press juice, obtained by grinding yeast cells with sand and 

 subjecting the ground cells to hydraulic pressure, could carry out the 

 fermentation. From his studies, this investigator concluded that the 

 production of alcoholic fermentation does not require as complicated 

 an apparatus as the living yeast cell, and that the fermenting power 

 of yeast juice is due to an enzyme, zymase. Actually, zymase has 

 proved to be a battery of individual enzymes. Buchner's discovery 

 of enzymes in the cell-free press juice of yeast has provided a tech- 



