172 MICRO-ORGANISMS AND FERMENTATION. 



In these four respects well-marked, specific differences mani- 

 fested themselves. Thus, in the course of five minutes an 

 English high-fermentation yeast had inverted 1*95 per cent, 

 sugar, whilst a low-fermentation yeast from the author's 

 collection had inverted 58'85 per cent. A complete inversion 

 of the cane-sugar, in two brewers' low-fermentation yeasts, took 

 place in the course of about 24 hours, whilst in the case of 

 Sacch. exiguus this reaction required 1 1 days ; with regard to 

 the other species the duration lay between these two limits. 

 The detailed tables given by HIEPE show that the fermenta- 

 tion of the entire amount of extract and also of the two 

 sugar species mentioned takes place successively according 

 to a scale peculiar to each individual species. A cursory 

 glance at the numerous particulars of the experiments further 

 shows that the fermentation of dextrose as a rule begins much 

 more vigorously than that of laevulose; but, whilst the fer- 

 mentation of the former sugar species reaches the maximum 

 on the second day, that of Isevulose does not evince its highest 

 activity till later, in some species even as late as the fifth 

 day ; by slow degrees the proportionate amounts of sugar 

 fermented approach each other, and finally the two sugar 

 species disappear simultaneously. 



With regard to the amount of acid produced in the nutrient 

 liquid, the yeast species also behave differently. Thus PRIOR 

 examined, from this point of view, the fermentation products 

 of a number of brewery yeasts and wild yeasts in hopped wort, 

 and found that the amounts of acid formed varied from 4'7 to 

 10 c.c. of decinormal caustic soda solution per 100 c.c. of 

 fermented wort; the fixed organic acids varied from 2'1 to 

 5-4 c.c., the volatile organic acids from 2'1 to 5 '8 c.c. The 

 evidence supplied by this work shows that, in culture yeasts, 

 the amounts of fixed organic acids usually exceed those of 

 volatile acids, whereas in HANSEN'S wild yeast species (Sacch. 

 Pastorianus /., //., and III., and S. ellipsoideus I. and //.) the 

 reverse is the case, the volatile acids surpassing the fixed ones, 

 very considerably in the case of Sacch. Pastorianus I. 



A large number of Saccliaromycetes occurring in must 

 absolutely pure cultures of which were prepared by HANSEN'S 

 method were investigated by MARX (1888), both from a 



