RESEARCHES ON YEASTS. 97 



as the first cultures in wort. This is a new proof showing 

 that little value can be attached to the microscopic examina- 

 tion alone when it is a question of the analysis of a sample of 

 yeast. (Both in breweries, in yeast factories, and distilleries, 

 too much weight is still attached to the microscopic appear- 

 ance of the yeast cells.) The new experiments further show 

 that if we wish to avail ourselves of the behaviour of the 

 cells under external influences for the purpose of character- 

 ising species, we must never depend exclusively on the 

 behaviour of the single cell, but we must take the collective 

 behaviour of a number of them. Other low-fermentation yeasts 

 give similar results under the conditions mentioned. 



The following experiment may be taken as another illus- 

 tration of the problem mentioned : When making plate- 

 cultures with wort-gelatine, it is frequently seen that two or 

 more cells lie so close together that on budding they will soon 

 grow together and form a single colony ; such a colony cannot, 

 of course, be made use of for the preparation of a pure culture. 

 If, however, as in this case, we have started with a pure culture, 

 it is evident that colonies like those mentioned contain pure 

 cultures, just as those which have grown from a single cell, 

 and that, in fact, all the colonies will consist of one species, 

 provided that no foreign organisms have gained admission. 

 If we confine ourselves to the colonies which have grown from 

 several cells, we shall often find a number of them which 

 appear very similar under the microscope, since they all 

 consist of a mixture of oval and sausage-shaped cells ; but if 

 we inoculate a corresponding number of flasks, each from one 

 colony, we may, however, obtain two series of fairly different 

 growths, one containing a preponderance of Pastorianus cells 

 and the other of cerevisia forms. Since we know that each of 

 the colonies sown from was originally formed from several 

 cells, the most probable explanation is that the two cell forms 

 were present in different proportions in the portion introduced 

 into the flasks, or if this were not the case, that during the 



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