CHAPTER XXXVI. 

 BACTERIA IN THE ARTS AND INDUSTRIES. 



BACTERIA play an ever-increasing part in the arts and industries 

 and man is learning that the majority of them are his friends and not 

 his enemies. In addition to the processes considered in the preced- 

 ing pages bacteria play a leading role in many important industries, 

 a few of which are briefly considered below. 



Alcoholic Fermentation. The development of bacteriology as a 

 science is intimately associated with the history of fermentation. 

 Some of Pasteur's classic studies dealt with this subject and ever 

 since it has commanded considerable attention. 



Although from a commercial viewpoint the yeasts are of first 

 importance in alcoholic fermentation, yet there are many bacteria 

 which produce alcohol, for instance : 



B.fitzianus, ferments glycerin with the formation of ethyl alcohol. 



B. ethaceticus ferments glycerin, starch, sucrose, lactose, glucose, 

 mannite, and arabinose with the formation of ethyl alcohol and 

 acetic acid. 



A number of bacteria, chief among which are B. butylicus, B. 

 B. orthobutylicus, B. amylozyme, and Beijerinck's genus Granulo- 

 bacter, ferment carbohydrates with the production of butyric acid. 



Recently Northrop and coworkers have outlined a method of 

 producing acetone on a commercial scale, ethyl alcohol being a by- 

 product. The organism used is B. aceto-ethylicum which acts on a 

 solution of beet molasses. The fermentation yielded from 8 to 8.5 

 per cent, of the sugar as acetone and 20 to 21 per cent, as ethyl 

 alcohol. 



Milk usually undergoes lactic acid fermentation, yet Koumiss, 

 Matzoon, Keffir, and Leben all contain alcohol and bacteria play an 

 important role in their fermentation. 



Vinegar. Many species of bacteria have been described which 

 produce acetic acid. They are all closely related but differ slightly 

 in morphology and fermentative power. It is believed that the 

 oxidation of the alcohol is due to an intracellular enzyme. All of 

 the organisms are bacilli and a few of the most common species 

 are as follows: 



Bacterium pasteurianum non-motile rods, 1/z x 2^, that do not 

 form spores. Their optimum temperature is about 34 C. They 

 develop best in solutions not over 9.5 per cent, of alcohol and 

 produce under favorable conditions about 6 per cent, of acetic acid. 



