BUTYRIC ACID BACTERIA. 125 



with the proper culture species, and amongst them Bac. 

 Hayducki and Bac. Buchneri. Bac. Lister i should also be 

 mentioned, which occurs in comparatively short rods and in 

 chains. Its optimum for acid formation is at 34 C. Bac. 

 Wortmanni has its optimum at 33- 40 C., and later at 

 25- 29 C. Lastly, three forms occur, Bac. Leichmanni 

 (I., II., and III.). When cultivated in mash they appear chiefly 

 as short rods linked in chains, with an optimum for acid 

 formation of 35-36-5 C. at first, and afterwards at consider- 

 ably lower temperatures. When pressed yeast turns soft, the 

 various kinds of lactic acid bacteria increase largely in numbers. 

 The lactic acid fermentation plays a very important part 

 in the means adopted in different countries for preserving 

 vegetable foods for both man and beast. Vegetables are 

 chopped up, in certain cases salt is added, and they are placed 

 in vessels or in hollows protected from access of air. A fer- 

 mentation sets in and lactic acid is produced as one of the 

 products. This acid protects the material from the attack 

 of other micro-organisms, and gives the peculiar character to 

 the preserved vegetables. The temperature usually rises 

 when fermentation begins, which allows of the partial develop- 

 ment of special therm ophilous bacteria. As a consequence 

 of the development of other micro-organisms, the amount of 

 acid is always reduced with prolonged fermentation. The 

 active species are described by Wehmer, Aderhold, Weiss, 

 Henneberg, and others. A rich flora of species occurs, how- 

 ever, in such ferments. In the same way such a souring is 

 used for the preservation of different feeding stuffs. The heat 

 evolved during the fermentation imparts a special character 

 to the fermenting mass, which varies according to the extent 

 to which the temperature rises. 



3. Butyric Acid Bacteria. 



When stale milk in which lactic acid bacteria have de- 

 veloped is neutralised by the addition of calcium carbonate, 

 so that calcium lactate is formed, it will, as a rule, undergo 

 a butyric fermentation. Pasteur showed in 1861 that this 

 fermentation is brought about by particular micro-organisms 



