78 RESEARCHES ON YEASTS. 



the maximum and minimum temperatures, afford definite 

 characteristics. It was also found that there were differences 

 in the behaviour of the species towards different media at 

 various temperatures; for instance, it was shown that the 

 species when heated in distilled water perished at different 

 temperatures. Differences were also found with respect to 

 bud-formation, fermentative activity, film-formation, &c. 



When yeasts are cultivated under identical conditions, 

 the forms of the cells may afford characters for their division 

 into groups, and sometimes also species ; this applies both 

 to sedimentary growths and to film-forms, and not only to 

 cultures grown in liquid media, but likewise to cultures on 

 solid substrata. It is true that almost all Sdccharomycetes 

 can assume the same forms, and that at least most, if not 

 all species can in the course of their development assume 

 all the forms mentioned by Reess as characterising different 

 species. Nevertheless, the same forms do not occur under 

 the same conditions in the case of the different species. 

 Therefore the character does not rest merely with the form 

 alone, as assumed by Reess and his followers, bttt is at the 

 same time dependent iipon external circumstances. 



There are also distinct differences in the behaviour of 

 the yeasts towards the carbohydrates, especially towards 

 maltose, and in the chemical changes which they bring 

 about in nutrient liquids. In connection with this, the fact 

 may be mentioned that whilst some species can be made 

 use of in the fermentation industry, others cannot, and some 

 others even produce diseases in beer. 



Differences, although only of a slight nature, were also 

 found when different stainings were applied. 



Of greater importance, at any rate as regards the practical 

 analysis, is the difference which, under certain conditions of 

 culture, is noticeable in the contents of the plasma of the 

 spores of culture yeasts as compared with that of the spores 

 of wild yeasts. If we confine ourselves merely to the micro- 



