242 MICRO-ORGANISMS AND FERMENTATION. 



consequently the quantity of yeast is only slightly increased. 

 Nageli says (p. 26), " The theory of Pasteur, that fermenta- 

 tion results from a lack of oxygen, forcing the yeast cells to 

 secure their requirements of oxygen from the fermenting 

 material, is opposed to all the facts brought to bear upon this 

 subject." 



This view is shared by A. J. Brown. He arranged a set 

 of experiments in which fermentation proceeded in presence 

 of full access of oxygen, and a parallel set in which oxygen 

 was excluded. In both series the same number of yeast ceUs 

 were used, and they were kept under such conditions that 

 it was impossible for them to multiply. Otherwise every 

 condition was the same. It proved, contrary to Pasteur's 

 theory, that the cells in the first case developed a higher 

 fermentative activity than when oxygen was excluded. 



ERieppe and his pupils have also rejected Pasteur's theory 

 of fermentation, and have brought forward examples of 

 ferment organisms " which are able to bring about the specific 

 fermentation much better, on the whole, in presence of atmo- 

 spheric oxygen." 



Similar experiments were undertaken by H. Buchner and 

 Rapp, with the object of ascertaining by exact quantitative 

 methods to what extent free access of air brings about the 

 replacement and suppression of the fermentative power of 

 yeast cells by their oxidising function. With this object in 

 view, they prepared pure surface cultures of yeast with the 

 greatest possible access of air, and carried out parallel experi- 

 ments with limited access. The first lot of cultures were 

 grown in large cylindrical vessels, the inner wall of which was 

 covered with a thin lining of wort-gelatine containing 10 per 

 cent, of grape sugar. This was infected with a coating of 

 pure yeast, and in each experiment a current of air was passed 

 through the vessel for five days. The carbon dioxide was 

 absorbed in caustic potash, and after each experiment the 

 amount of alcohol and the ratio between the yeast and the 

 fermented sugar were determined. Parallel experiments were 

 carried out, in which the same quantities of beer-wort and 

 grape sugar were allowed to ferment in Erlenmeyer flasks. 



As a consequence of the rapid and abundant growth of 



