70 Lectures on Bacteria. [f vii. 



juice of animals, convert albuminous bodies with absorption 

 of water into easily soluble peptones, peptonising enzymes. 



After what has now been said it scarcely requires to be 

 pointed out that every organism which sets up fermentation or de- 

 composition displays a specific activity in the directions indicated, 

 and it may be also a specific formation of enzymes. In the 

 same saccharine solution one species excites alcoholic fer- 

 mentation, another lactic acid or butyric acid fermentation, and 

 so on. Again, the same fermentation, according to the primary 

 products, may also be produced by dissimilar species under 

 otherwise similar conditions, though in unequal quantitative 

 amount. Alcoholic fermentation, for example, is excited in 

 saccharine solutions by several species of Saccharomyces, and 

 also by certain species of the group of Mucorini. The same 

 species can also set up different decompositions in different sub- 

 strata. The vinegar-bacterium oxidises the alcohol in a dilute 

 solution, and converts it into acetic acid and this into carbonic 

 acid and water when the alcohol is exhausted. The Saccharo- 

 myces of beer-yeast changes grape-sugar by fermentation 

 directly into carbonic acid and alcohol ; cane-sugar does not 

 ferment, but is first ' inverted ' by the above-mentioned enzyme, 

 and the ' invert-sugar ' formed of glucose and laevulose ferments 

 as it arises. 



The Bacillus of butyl-alcohol of Fitz (Bacillus Amylobacter, 

 see Lecture IX) vegetates in nutrient solutions of milk-sugar, 

 erythrite, ammonium tartrate, salts of lactic acid, malic acid, 

 tartaric acid, &c., without exciting characteristic fermentations 

 in them ; it produces fermentation in glycerine, mannite, and 

 cane-sugar, with carbonic acid, butyric acid, and butyl-alcohol 

 as the primary products, and small amounts of lactic and other 

 acids as secondary products, the quantities of the primary pro- 

 ducts varying much according to the nature of the substratum. 

 The relative quantities of butyric acid, for example, under similar 

 conditions of fermentation, are 17-4 in the case of glycerine, 

 35-4 in that of mannite, and 42-5 in that of cane-sugar. 



