ALCOHOLIC FERMENTS. 139 



obtained confirmation of this fermentation theory was by 

 examining the behaviour of HANSEN'S and other yeast species 

 towards the artificial sugar species, synthetically obtained by 

 FISCHER. They found, indeed, that the yeast species are quite 

 fastidious regarding the geometrical configuration of the sugar 

 molecule, whilst they often remain unaffected by other altera- 

 tions in its composition. 



Among the various synthetically prepared sugar species 

 examined by FISCHER with regard to their behaviour towards 

 yeasts, melibiose is especially mentioned. It is fermented by 

 brewers' common bottom-fermentation yeasts, but not by many 

 brewers' top-fermentation yeasts. In harmony with this, 

 FISCHER found that bottom-fermentation yeast contains an 

 enzyme capable of extraction from the dried yeast in aqueous 

 solution, which decomposes melibiose, converting it into glucose 

 and galactose ; but in a corresponding treatment of the brewers' 

 top-fermentation yeasts used no decomposition of this sugar 

 could be observed. As brewers' top-fermentation yeast con- 

 tains invertase, it follows that the ferment which splits up 

 melibiose cannot be identical with invertase. 



C. J. LINTNER and FISCHER showed, by methods devised by 

 the latter, that natural maltose, if acted upon by an aqueous 

 extract of dried yeast, is split up into glycose, and that there 

 is a marked difference between this enzyme and invertase 

 which decomposes cane-sugar. FISCHER terms the former 

 enzyme yeast-glycase or yeast-maltase. Its optimum tem- 

 perature is about 40 C., whilst that of invertase, according 

 to KJELDAHL, is 52- 5 3 C. 



PRIOR compared the fermentation energy of a number of 

 yeast-cells by accurately testing them under similar conditions 

 according to MEISSL'S method. He found marked differences, 

 as shown in the following examples. The numbers are cal- 

 culated on the weight of dried yeast. 



Carlsberg yeast, I., - 136-40 



II, 106-13 



Saccharomyces Pastorianus, I., - 153-48 



II, 280-72 



HI, 202-20 



,, ellipsoideus, I, - 28576 



II, - - 219-03 



