110 BACTERIA AND FERMENTATION 



Bacillus acidi butyrici (Kedrowski's Butyric acid bacillus). Anaerobic. 

 Kedrowski (Z. 16. 3) has isolated from mixtures of sugar solution with bad cheese 

 or rancid cream-butter which has been placed in the incubator, two organisms 

 which only show small deviations from one another. (Gf. the B. saccharo-bulyricus 

 of Klencki from cheese). Kedrowski's B. acidi butyrici is a motile bacillus, which 

 towards one end produces ellipsoidal spores. The staining of the spores is readily 

 accomplished The colonies in gelatine show rays those in agar partly reticulated 

 and interlaced spurs. Liquefaction of gelatine is more or less marked. Milk is 

 coagulated with separation of serum on the surface (acid reaction). There is 

 gradual peptonisation and simultaneous gas development. 



Although, according to Pasteur's researches, the butyric acid 

 ferment performs its function anaerobically, many butyric organisms 

 can act in the presence of oxygen, and yield somewhat different 

 products. 



All of them, however, ferment most actively at a temperature at 

 or about blood-heat, and the spores are able to withstand boiling for 

 from three to twenty minutes (Fitz). It will be observed that as in 

 lactic acid fermentation so in butyric, the results are not due to one 

 species only. 



5. Ammoniacal Fermentation (see under Soil). 



From what has now been said, it is obvious that although we learn 

 many important facts by a study of these different forms of fermen- 

 tation, we may also learn on the one hand how to prevent or correct 

 those conditions constantly occurring in fermented beverages, which 

 are known as " diseases," and on the other, the opportunities which 

 occur in industrial processes for the application of fermentation. 

 We will first deal with the former. 



Diseases in Beer and Wines 



We have seen how the knowledge of fermentation has been com- 

 piled by a large number of workers. Spallanzani, Schwann, Pasteur, 

 and Hansen all contributed epoch-making researches. In the same 

 way the investigations of diseases in beers and wines were carried on 

 by many observers, and were, at all events in the early stage, closely 

 connected with those relating to spontaneous generation and mixed 

 cultures of bacteria, or of yeasts occurring in fermentation. These 

 so-called "diseases" are analogous to the taints occurring in milk. 

 It was in 1883 that Hansen demonstrated that the universally 

 dreaded yeast turbidity and the disagreeable changes in taste, odour, 

 or colour of beer were caused not by the water or malt or particular 

 method of brewing, as was commonly believed, but that these 

 diseases had their origin in micro-organisms or in the yeast itself.* 

 A clue had been given by Scheele and Appert, who had prevented 

 these diseased conditions by physical agents which had destroyed the 



* Practical Studies in Fermentation, E. C. Hansen, pp. 156-231. 



