ALCOHOLIC FERMENTATION OF SUGAR 135 



Tyndall allowed the open ends of flasks containing boiled 

 fermentable solutions to communicate with a chamber whose 

 walls were coated with glycerine, and the air in which had 

 been allowed to be at rest for some time ; in this way all the 

 germs present settled and were fixed by the glycerine. That 

 the space was free from germs was proved by passing a 

 strong beam of light, as explained on p. 8. 



The researches of Pasteur and Tyndall corroborated one 

 another : no fermentation took place in Pasteur's boiled flasks 

 when the precaution was taken to prevent subsequent access 

 of germs ; similarly no fermentation took place in Tyndall's 

 flasks when the beam of hght showed the air above them to 

 be germ free. Pasteur, therefore, contended that no fermen- 

 tation took place without an organism, and he even went 

 further, and stated that for any given fermentation a specific 

 organism must be present. Liebig remained unconvinced ; 

 he found that while no fermentation occurred in a solution 

 seeded with yeast after filtration through a membrane, 

 yet an extract of meat similarly filtered became putrid. 

 Moreover, Liebig quoted his own experiments, in conjunction 

 with Wohler, on the decomposition of oil of bitter almonds 

 into benzaldehyde and grape sugar by a substance contained 

 in the almond, which we should now call an enzyme. He 

 considered that a substance of a like character must be 

 secreted by the yeast, and that the only connection between 

 the physiological development of the yeast and the phenomena 

 of fermentation is the production in the Uving cell of a substance 

 which, acting as a ferment or catalyst, effects the decom- 

 position of the sugar.i 



Liebig died in 1873 before the pubhcation of the recent 

 researches, which have provided an explanation of the apparent 

 contradiction between the purely vital or physiological 

 theories of Pasteur and his own purely chemical point of view. 



The development of enzyme chemistry has been to a large 

 ' Ann. Chem. Pharm., 153, 1870, p. 6. 



