124 BACTERIA AND THE CARBON DIOXIDE CYCLE 



ferments pectine substances prepared from linseed, pears, or turnips. 

 Cellulose and gum arabic are not attacked, but the power of breaking up 

 other carbohydrates is greatly increased if peptone be supplied instead of 

 ammonia. As to the products of pectine fermentation nothing is known, 

 but they are probably, as in other cases, CO 2 and fatty acids. The old idea 

 that the process was one of cellulose fermentation is certainly wrong. 



In the manufacture of indigo bacteria are considered to play an im- 

 portant part (98). The indigo plant (Indigofera tinctoria] contains a gluco- 

 side Indican which by anaerobic fermentation at 25-35 C. is converted 

 in from eight to fifteen hours into a sugar (Indigoglucin) and indigo-white. 

 The fermentation is carried on in large vats, the liquid in which becomes blue 

 on the surface where it is exposed to the air. By agitation the whole mass 

 is brought into contact with air, and becomes blue throughout. The micro- 

 organism which ferments the indican is a short capsulated bacillus, $. indigo- 

 genus. If the fluid be sterilized and the bacteria killed, no pigment is 

 formed. The process has not yet been followed in detail. 



The preparation of tobacco involves, to a considerable extent, the work 

 of bacteria (99). The dried leaves of the plant are damped and laid in 

 great heaps to ' ferment.' By this process various carbohydrates, nicotine, 

 and vegetable acids are converted into CO 2 , butyric acid, succinic acid, and 

 certain ' aromatic bodies,' whose nature is not precisely known. The 

 proteids are said not to be attacked. Various species of bacteria have 

 been isolated from the tobacco leaves. The ' Havannah ' bacteria are 

 said to differ from those of the German weed, and the inoculation of the 

 latter with Havannah bacteria has been to some extent successful. The 

 process is comparable to the improvement of wines by the inoculation of 

 the grape juice with specific pure yeasts. It is, however, doubtful whether 

 the real aroma of Havannah tobacco can be transferred in this way, since 

 the aromatic compounds of the plant itself have to be considered, not 

 merely those produced zymogenically. 



In the beet juice of sugar factories, and also in refineries (100), the 

 ' frog-spawn bacterium ' (Leuconostoc mcsenteroidcs) is sometimes a great pest 

 (Fig. 7, b d}. It is a mucigenous bacterium, and the chemical changes it 

 sets up have been designated as dextrane fermentation, because the mucilage 

 that appears in such profusion is supposed to be similar to a carbohydrate 

 of the beetroot, dextrane. The matter requires further investigation, however. 

 At the optimum temperature (3o-35) the micro-organism grows with 

 extraordinary rapidity, and whole vats may be filled with it in the course 

 of a single night *. Besides mucilage, the bacteria produce lactic acid and 

 CO 2 . The molecules of the fermentable substances are not so completely 



* In one case a vat of 49 hectolitres molasses, containing 10 per cent, sugar, was filled in twenty- 

 four hours with the spawn-like masses. 



