SACCHAROMYCES. 357 



caused the Logos yeast to bring about inversion and to begin 

 fermentation more rapidly. It can also withstand larger quan- 

 tities of lactic acid than the other two species. In the presence 

 of lactic acid the formation of alcohol is reduced, but by the 

 addition of 0-125 per cent, the Logos yeast gives more acid than 

 usual. In general the production of acid is considerably 

 greater in the presence of lactic than in the presence of acetic 

 acid. In the presence of both acetic and lactic acid the for- 

 mation of volatile acids is considerably greater than that of 

 non-volatile. The fermentative energy (four days) is greater 

 in presence of acetic acid than in the absence of acid, but the 

 .addition of lactic acid considerably restricts it. 



According to Korff , non-volatile acids are formed in larger 

 quantities in aerated cultures ; on the other hand, more 

 volatile acids are formed when hydrogen is passed through 

 the solution. 



According to Bau, Logos yeast does not contain melibiase, 

 whereas Lindner arrived at the opposite result. Further 

 research has shown that both authors are right, for a similar 

 subdivision of the race takes place as in the case of Torula, 

 <colliculosa (see below). 



Saccharomyces thermantitonum Johnson 



is a yeast found on eucalyptus leaves, and was accidentally 

 grown in a flask which had been infected at a temperature of 

 84 C. The cells had not, however, been killed at this high 

 temperature. By subsequent repeated observations, it was 

 found that this species reacts best at high temperatures. 

 Johnson used a temperature of 50 C. as the pitching tempera- 

 ture for fermentations on the large scale. The wort need not, 

 therefore, be cooled so strongly as usual, and the yeast can be 

 applied in tropical countries where ice machines are not 

 available. Within seventeen hours it is said to furnish a 

 properly and completely fermented beer. It does not grow at 

 temperatures under 10 C., and its optimum temperature for 

 propagation and fermentation lies between 40 and 44 C. 

 The cells are small and oval. They agglutinate and form 

 clots, which sink rapidly and adhere closely to the bottom. 

 Consequently, the liquid clarifies very rapidly. 



