ALCOHOLIC FERMENTS. 153 



important character for the determination of the Saccharo- 

 mycetes. 



A new distinctive characteristic for the species has been 

 discovered by the same author in the different anatomical 

 structures of the spores. Both these characters and others, 

 which are described in the following pages (e.g., film-formation), 

 must necessarily be considered in a complete examination of a 

 Saccharomyces species. 



The method given below for the practical analysis of low 

 'brewery-yeast was based by HANSEN on certain observations 

 both of the temperature curves for the development of spores 

 and of the structure of spores. Thus it was found that at 

 certain temperatures the species employed in the brewery, the 

 so-called cultivated yeasts, develop their spores later than the 

 so-called wild yeasts, several species of which also occur as 

 disease germs in the brewery. HANSEN also found that the 

 structure of the spores in these two groups is generally different. 

 The young spore of cultivated yeast has a distinct wall or 

 membrane, the contents are not homogeneous, but are granular, 

 and exhibit vacuoles. In the case of wild yeast, on the other 

 hand, the wall of the young spore is most frequently indistinct, 

 the contents are homogeneous and strongly refract light. It 

 should also be added that the spores of cultivated yeasts are 

 usually larger than those of wild yeasts. 



1. For the continual, daily control of low brewery -yeast, as 

 regards contamination with wild yeast-species, the following 

 very convenient method is made use of : At the conclusion of 

 the primary fermentation, a small quantity of the liquid is 

 transferred from the fermenting-vessel to a sterilised flask ; 

 this is set aside for some hours until the yeast has settled to 

 the bottom, and the sediment is spread upon a gypsum block 

 in the manner described above. This is then introduced into 

 a thermostat maintained at a temperature of 25 C. or 15 C. 



It was shown that the species of cultivated yeasts employed 

 in low-fermentation breweries can be divided into two groups. 

 This has been subsequently confirmed by the elaborate inves- 

 tigations of HOLM and POULSEN. One group yields spores at a 

 later period than wild yeast, when a temperature of 25 C. is 

 maintained ; the other group, on the contrary, produces spores in 



