238 OUTLINES OF BACTERIOLOGY 



hue, is blue. By violently stirring the whole mass, and thus intro- 

 ducing oxygen, the liquid becomes blue throughout. The colouring 

 matter which gives its hue to the whole mass is called indigo blue. 

 That the production of this dye is due to bacteria, is shown by the fact 

 that its formation does not take place if the leaves are sterilised. The 

 microbe in question has been isolated. It is a short bacillus, which is 

 enveloped by a clearly visible mucilage layer. 



§8. TEA AND COCOA. 



Tea is prepared from the young leaves of Thea cMnensis, which 

 grows wild in Assam, and possibly also in China, but is now cultivated 

 in many parts of the globe. So far as the preparation of green teas 

 is concerned, fermentation does not come into play, because the leaves 

 are roasted immediately after being cut. In the preparation of black 

 teas, however, the cut leaves are exposed to the sun, in order to enable 

 a fermentation to be set up. The changes that take place during 

 fermentation are very little understood, but one change is the con- 

 version of a good part of the tannin that is in the leaves into tannic acid 

 and sugar. The planter knows by experience the exact moment to 

 stop the fermentation. The leaves are then removed to ovens, and 

 roasted. It is probable that oxidising enzymes are present, and that 

 they are largely concerned in the preparation of the leaves. It is 

 unknown whether bacteria come into play in the formation of the 

 alkaloid theine, the presence of which in tea forms the sole excuse for 

 its consumption. 



Cocoa is prepared from the seeds of Theobroma cacoa. The seeds 

 are mixed with plantain leaves and placed in barrels, the latter being 

 then hermetically sealed. Anaerobic fermentation sets in, which is 

 allowed to proceed for from four to seven days. The seeds are then 

 taken out, spread on trays, covered with red earth, and left for another 

 day to complete the fermentation. It is probable that the organisms 

 responsible for the fermentation are of a bacterial nature, and that 

 these are normally present in or on the plantain leaves. We have no 

 information as to the changes that take place during this fermentation. 



