132 MICRO-ORGANISMS AND FERMENTATION. 



There is no doubt that butyric acid fermentation may 

 take place both in breweries, distilleries, and yeast factories, as 

 well as in the fermentation of wine, which is probably caused 

 by the activity of certain species. Thus butyric acid has been 

 detected in potato fusel oil and in cognac, as well as in the yeast 

 " goods " of the distillery, but more exact information is 

 lacking. 



If the preparation of the mash and wort goes on under 

 indifferent conditions, a good opportunity is afforded for the 

 development of such bacteria, and this applies also to the 

 higher temperatures at which top fermentation is carried on. 



A bacterium that produced butyric acid together with 

 other substances is Bac. lupuliperda, described by Behrens, 

 which occurs frequently on hops. The spontaneous heating 

 of hops has been shown by Behrens to be due to the development 

 of this and other organisms. It consists of motile cocci and 

 short bacilli which liquefy gelatine. In nutrients free from 

 saccharose it produces large quantities of ammonium com- 

 pounds, and, in particular, trimethylamine (the smell of rotten 

 herrings). In presence of saccharose the nutrient solution soon 

 turns sour, and butyric acid is formed. The species appears 

 to have its chief habitat in the earth, and bears much 

 resemblance to Bac. fluorescens putidits, described by Fliigge. 



The sulphuring of hops appears to protect them particularly 

 from moulds. To ensure that micro-organisms do not develop 

 on soured hops the amount of moisture must not exceed 8 to- 

 10 per cent., and they must be stored in a cold place. 



4. Bacteria Fermenting Cellulose. 



These bacteria are just as widely distributed in nature aa 

 butyric acid bacteria. These are the organisms that ferment 

 cellulose in plant residues present in the mud of rivers and 

 ponds, and thus give rise to the evolution of marsh gas. It 

 is only quite recently, however, that, thanks to the admirable 

 researches of Omelianski, we have obtained a clear conception 

 of what bacteria are responsible for this action. He sowed 

 horse dung and river mud on Swedish filter paper (pure cellu- 

 lose), with the addition of 1 gramme of chalk, 1 gramme of 



