134 BACTERIA 



irregularly placed in the rod, and may cause considerable 

 variations in morphology. The culture gives off a strong 

 butyric acid odour. It grows most readily at a temperature 

 of about 40° C. 



Although, according to Pasteur's researches, the butyric 

 acid ferment performs its functions 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 temper- 

 ature 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). 



Diseases in Beer, We have seen how a knowledge of fer- 

 mentation has been compiled by a large number of workers. 

 Spallanzani, Schwann, Pasteur, and Hansen all made epoch- 

 making contributions. In the same way the investigations 

 of diseases in beers and wines were carried out by many ob- 

 servers, and were closely connected with those relating to 

 spontaneous generation and mixed cultures of bacteria in 

 fermentation. These so-called *' diseases *' are analogous 

 to the taints occurring in milk and due to fermentations. 

 Turning {tourne), turbidity, ropiness, bitterness, acidity, 

 mouldiness, are all terms used to describe these diseases. 

 They are chiefly brought about by four agencies : — 



1. Bacteria. 



2. Mixed yeasts. 



3. '' Wild*' yeasts. 



4. Moulds. 



To each species of wild yeast there belongs some taint- 

 producing power in the fermentations for which it is respon- 

 sible. Saccharomyces ellipsoideus IL and S, pastorianus L^ 

 IIL, are such yeasts; they only produce their diseases when 

 introduced at the commencement of the fermentation. 



