594 



VITAL ACTIONS OF THE LOWER FUNGI. 



Influence of 

 various con- 

 ditions on the 

 quantitative 

 result. 



Amount of 

 sugar. 



Quantity of 

 yeast. 



Accumulation 

 of alcohol. 



Temperature. 



into the interior of the yeast cells, and that for this a 

 certain time is required ; for the same phenomenon is 

 observed when the yeast is implanted in a new solution 

 directly from a solution in active fermentation. 



The quantitative result of the fermentation undergoes 

 marked variations according to the composition of the 

 fermenting material, according to the quality of the 

 yeast, according to the length of time, and according to 

 various external influences. 



The amount of sugar in the solution must not exceed 

 35 per cent., for otherwise the yeast cells suffer for want 

 of the proper quantity of water ; the best proportion of 

 sugar seems to be 2 to 4 per cent., and then 20 

 to 25 per cent. (Wiesner), but this striking fact of 

 two optima requires confirmation. The quantity of 

 yeast added is, within certain limits, irrelevant for the 

 progress of the fermentations. Dumas found that one 

 gramme of sugar was completely broken up at 24 C. 

 by 20 grammes of yeast within twenty-four minutes ; 

 the addition of 100 grammes of yeast did not alter this 

 result in the slightest. Where a large amount of yeast 

 is added intense fermentation occurs, even in pure solu- 

 tions of sugar, which ultimately ceases, leaving behind 

 a yeast which is exhausted and poor in nitrogen ; if it 

 is desired to keep up a permanent fermentation with 

 relatively small quantities of yeast, the addition of other 

 nutrient materials, more especially of nitrogenous 

 materials, is necessary. Further, the continuation of 

 the fermentation is limited by the accumulation of the 

 alcohol ; the presence of 12 per cent, of alcohol hinders 

 the growth of the yeast, and when more than 14 per 

 cent, is present fermentation ceases entirely. In the 

 case of the mucor yeast this limit is much lower 

 about 34 to 4 per cent, (in the case of Mucor stolonifer 

 even 1*3 per cent.) ; this form of yeast is also much 

 more sensitive to great concentration of the sugar solu- 

 tion, for a satisfactory fermentation only occurs in 

 solutions containing less than 7 per cent, of sugar 

 (Fitz). Of the external influences the temperature is 

 of chief importance ; as a rule 25 C. seems to be 



