90 MICRO-ORGANISMS AND FERMENTATION. 



7. BACTERIA EXERCISING AN INVERTING, DIASTATIC, 

 OR PEPTONISING ACTION. 



Bacteria play a great part in the formation of soluble 

 chemical ferments. This constitutes one of the chief means 

 by which these organisms produce such marked effects in the 

 economy of nature. 



According to HANSEN, many species of bacteria which 

 generally occur in beer secrete invertive ferments. Amongst 

 these species are a number of bacteria which exhibit an inver- 

 tive action on a pure cane-sugar solution, but lose this property 

 when yeast-water is added. 



FERMI and MONTESANO found that, e.g., Bac. megaterium, 

 Proteus vulgaris, and Bac. fluorescens liquefaciens invert this 

 sugar in neutral broth containing 4 per cent, of cane-sugar. 

 Several of these bacteria, however, lose their power of inversion 

 if the broth is rendered alkaline, whilst most of them are un- 

 injured in slightly acid broth. In broth without sugar and in 

 media containing no albumen such bacteria produce invertine ; 

 thus almost all the species that were examined formed invertine 

 in a nutritive salt solution containing glycerine. The invertine, 

 produced by these bacteria proves to be a soluble enzyme, 

 which is destroyed at temperatures differing according to 

 the species, but is always more resistant during its action 

 on cane-sugar than in a dissolved state ; it is very sensitive 

 to acids and alkalies, and especially to mineral acids and 

 potash. 1 



Similar properties to those discovered by HANSEN were 

 observed by WORTMANN in the case of bacteria which develop 

 diastatic ferments. He found these on putrefying beans and 

 potatoes, and grew the cultures in mixtures of nutritive salts 

 and wheat-starch. MARCANO also found a species which exer- 



1 According to ADR. J. BROWN, the Bacillus snbtilis (Hay bacillus), which 

 occurs everywhere, also belongs to this class of bacteria. He states that 

 this bacterium does not develop in beer or wort of normal acidity, even if 

 the latter is very low. In a neutral hay-infusion containing 5 per cent, 

 of dextrose it oxidises the sugar ; it also inverts cane-sugar and completely 

 oxidises it. 



