122 MORPHOLOGY AND LIFE-HISTORY OF YEASTS. 



at 6° to 7° 0., about 2 to 3 months. N"o formation of film 

 occurred above 34° 0. or below 5° C. 



These limits of temperature, which also apply to all the 

 other species examined, are therefore more restricted than those 

 wherein the yeast is able to bud and incite fermentation. Film 

 formation is therefore precluded in the fermentin^^ cellars of 

 bottom -fermentation breweries, the temperature here being, 

 wherever possible, maintained between 0° and 2° C. It has 

 already been shown by Hansen, and confirmed by H. Will 

 (VIII.), R. Aderhold (I.), and other workers, that the time 

 elapsing before the film makes its appearance, and the dimen- 



FiG. i33.-Sacch. Past. II. Hansen. Fig. 134.— Sacch. Past. III. Hansen. 



Cells of film grown on beer wort at 20° to 28° C. Magn. 1000. (After Hansen.) 



sions attained by the film, are very greatly dependent on the 

 conditions of cultivation (composition of the nutrient solution, 

 and also in a high degree on the method of sterilisation, supply 

 of air, (fee). 



In some cases morphological peculiarities in the film cells 

 afford a means for differentiating the species. With Sarch. 

 Past. II. and Sacch. Past. III. this can be recognised in a 

 beautiful manner, and at the same time a fresh in.stance is 

 afforded of the dependence of cell form on temperature. The 

 first-named, weak, harmless, top-fermentation species was 

 isolated by Hansen from the air of the Carlsberg brewery. 

 The other, which is of decidedly top-fermentation character, 

 was obtained as a pure culture from a Copenhagen lager-beer 

 suffering fi-om haze, and was recognised as the cause of the 

 malady. It is difiicult to distinguish between them by the form 

 of the cells present in the sedimental yeast, both being very 

 similar to Sacch. Past. I. (see Fig. 129). The same also applies 

 to the component members of their films grown at 20° to 28° 0. 

 and illustrated in Figs. 133 and 134. The case is, however, 



