182 MICRO-ORGANISMS AND FERMENTATION. 



with the vital process of the cells ; they do not occur so long 

 as development takes place in the normal manner. 



The variation of low- and high-fermentation yeast in breweries 

 has occupied the writer's attention for many years, and has 

 led to several researches. These have proved that a 

 " degeneration " of a brewery's yeast may be brought about by a 

 deviation from the normal of a large number of the individuals 

 of which the growth consists, their acquired properties 

 exercising a disturbing influence on the course of fermentation. 

 In such a case the yeast can be restored to its original con- 

 dition by selecting " non-degenerate" individuals from a sample 

 of the yeast used in the brewery. This is done in the 

 following manner : A sufficiently large number of cells are 

 isolated, absolutely pure cultures are developed from these 

 individuals, and a culture is selected which exhibits the 

 required properties. 



The variations which yeast undergoes during its use in the 

 factory were further employed by the author with the object 

 of systematically improving yeast. For this purpose samples 

 were taken from particularly good fermentations, and from this 

 yeast whole series of cells were isolated. Among the growths 

 descended from these, such were selected as were found to 

 possess the required properties in a marked degree. Methodical 

 work in this direction, carried on during several years with 

 one and the same type of yeast, has led to decidedly favourable 

 results. 



An example of the persistence with which Saccharomyces 

 cells retain, under normal conditions, the property of spore- 

 formation, is met with in breweries and distilleries. We have 

 here species of yeasts which have lived through hundreds of 

 years, and have developed an infinite number of generations 

 under conditions which, as a rule, have not permitted the 

 exercise of this function, and yet the power of forming spores 

 has been persistently retained. 



(Ji) Gelatinous Formation secreted by the Budding- 

 fungi. Under certain, as yet undetermined, conditions, the 

 colonies produced by the budding of yeast-cells can form 

 irregular agglomerations which sink to the bottom more 

 quickly than the single yeast-cells (breaking and clarifying 



