262 MICRO-ORGANISMS AND FERMENTATION. 



fermentation. The amount of alcohol, extract, the specific 

 gravity, attenuation, glycerine, nitrogen, reducing substance, 

 and degree of colour, were determined in the fermented worts. 

 The tables show palpable differences in the chemical reactions 

 brought about by the different species. The percentage of 

 alcohol varied within the limits of 4-34 and 6-02 by volume 

 (3-55 to 5-94 at the end of the primary fermentation), the 

 extract from 8-27 to 11-23 (8-49 to 11-61 at the end of the 

 primary fermentation), the attenuation from 36-7 to 53-3 

 (28-8 to 52-1 at the end of the primary fermentation) ; the 

 percentage of glycerine showed very striking differences, and 

 fluctuated between 0-08 and 0-15; likewise the amounts of 

 nitrogen, of reducing substance, and to some extent even the 

 colour intensity, showed considerable variations. 



Hiepe drew some interesting parallels between the behaviour 

 of a number of culture yeasts and wild yeasts with regard to 

 the sugars. For this purpose he instituted fermentations in 

 sugar solutions containing yeast decoction. He took out the 

 first sample five minutes after the fermentation has been 

 induced, and then fresh samples every day, till the fermenta- 

 tion had subsided. In each sample the amount of (1) inverted 

 sugar, (2) fermented extract, (3) fermented dextrose, and (4) 

 fermented laevulose was determined. In these four respects 

 well-marked, specific differences developed in the course of a 

 day. Thus, in five minutes an English high-fermentation 

 yeast had inverted 1-95 per cent, sugar, whilst a low-fermenta- 

 tion yeast from the author's collection had inverted 58-85 

 per cent. A complete inversion of the sugar with two low- 

 fermentation brewery yeasts took place in the course of about 

 twenty-four hours, whilst in the case of Sacch. exiguus this 

 reaction required eleven days ; for the other species the time 

 required lay between these two limits. The detailed tables, 

 given by Hiepe, show that the successive fermentation of the 

 total quantity of extract, as well as that of the two sugars, 

 takes place according to a scale peculiar to each individual 

 species. A glance at the numerous details of the experiments 

 further shows that the fermentation of dextrose, as a rule, 

 begins much more vigorously than that of laevulose ; but 

 whilst the fermentation of the former reaches its maximum 



