BACTERIA. 67 



In the saccharine mashes of breweries, distilleries, and 

 pressed-yeast factories, some species of butyric acid bacteria 

 always occur, and if the mashes are maintained for a 

 lengthened period at certain temperatures, these bacteria 

 develop very rapidly and exercise a retarding influence on 

 the alcoholic ferments. If butyric acid occurs to any extent 

 in beer, it will acquire a very unpleasant taste. 



According to Pasteur's experiments, the butyric acid 

 ferment can perform its functions without access to the free 

 oxygen of the air. More recent investigations have shown, how- 

 ever, that many butyric acid bacteria exist which not only yield 

 different fermentation products, but also behave differently 

 with regard to free oxygen, in that some are not capable of 

 developing when the latter is present, so-called anaerobic 

 species, whilst others multiply and induce butyric acid fer- 

 mentation when they have access to oxygen, aerobic species. 



One of the first species which were minutely described is 

 Prazmowski's Clostridium butyricum (Bacillus butyricus) 

 (Fig. 13). It occurs in the form of short and long rods, 

 which may be either straight or somewhat curved. Before 

 the formation of spores in the rods, the latter swell and form, 

 as shown in the figure, peculiar spindle- and lemon-shaped, 

 elliptical, or club-like forms ; at the same time there is the 

 important fact that they are coloured blue by iodine. On 

 germination the spores burst their outer envelope, and the 

 germ filament grows in the same direction as the longitudinal 

 axis of the spore. Clostridium butyricum grows most readily 

 at a temperature of about 40 C., and is especially able to 

 predominate in a solution of sugar if the lactic acid ferment 

 has previously converted a portion of the sugar into lactic 

 acid. This species is decidedly anaerobic. 



Fitz has described a species belonging to the aerobic 

 forms. It is a bacillus of a short cylindrical form, which is 

 not coloured blue by iodine, is motile in a moderate degree, 

 and forms no spores. It ferments all carbohydrates, with the 

 exception of starch and cellulose. 



