156 MICRO-ORGANISMS AND FERMENTATION. 



violent interference with the vital process of the cells, and 

 that they do not occur so long as the development takes 

 place in the normal manner. 



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 the above-named function, and yet the power to 

 do so has always been persistently retained. 



(A) Gelatinous Formation secreted by the Budding- 

 fungi. Under certain but as yet undetermined conditions, 

 the colonies produced by the budding of yeast cells can unite 

 to irregular masses which sink to the bottom more quickly 

 than the single yeast cells (breaking and clarifying in the 

 brewery). This behaviour is undoubtedly related to a phase 

 in the development of yeast cells which Hansen discovered 

 in 1884. He discovered that not only the Saccharomycetes 

 but also other budding-fungi are able to secrete a gelatinous 

 netiuork, which can be seen as threads or plates, and in 

 which the cells lie imbedded (Fig. 33, A, B). If, for example, 

 some moderately thick brewery yeast is placed in a glass and 

 allowed to remain covered up in such a manner that it slowly 

 dries, and then a trace of this yeast mixed with water, the 

 network can be clearly seen (Fig. 33, A). The formation 

 also occurs in the gypsum block and gelatine cultures. I 

 have myself very frequently observed this remarkable for- 

 mation, after Hansen had called my attention to its nature, 

 in the yeast samples which are sent to my laboratory in filter- 

 paper enclosed in envelopes. 1 Hansen also found it in the 



1 This method of preserving a sample of yeast for some time is very 

 convenient. A small piece of filter-paper is rapidly passed through a 

 flame several times, a few drops of yeast are poured on to it, and it is 

 then folded up, and afterwards wrapped in several layers of paper which 

 have been similarly treated. 



