80 MICRO-ORGANISMS AND FERMENTATION. 



into spherical spores, which form small red clusters, or else 

 a number of small rods become enclosed in a common mem- 

 brane, termed a cyst. With these may be associated the 

 remarkable slime-formation, packed with bacteria (Bacteroids), 

 which penetrate through the root-hairs into the nodules of 

 the leguminosse, and assimilate nitrogen from the atmosphere. 

 Lastly may be mentioned the remarkable " bacteria-bubbles " 

 (bacteriocysts) described by Miiller-Thurgau, which occur in 

 fruit wines containing tannic acid, especially in perry, and 

 more particularly in and upon the yeast which settles after 

 fermentation. These are zoogloea forms of lactic acid bacteria, 

 which surround themselves with a membrane, and thus re- 

 semble the cells of higher plants. Inside this membrane the 

 bacteria are embedded in a clear mobile liquid, and they 

 eventually collect in the lower part of the bubble. These 

 may gradually increase in size. There is a certain resemblance 

 between these and the remarkable forms described by Wino- 

 gradsky in 1888, the Amoebobacter (sulphur bacteria), which 

 also occur in cell families, the cells being bound together 

 with threads of plasma, and the whole family moving as a 

 slimy mass (amoeba?) in ever-varying forms. When these 

 reach the resting stage, a thin gelatinous skin separates out, 

 and is slowly transformed into a hard skin enclosing the whole 

 family, which eventually breaks away from its husk. 



Many bacteria contain blue, red, yellow, or green colouring 

 matter, which may cause intense coloration. In most bacteria 

 of this category the colouring matter is present in solution 

 in the nutritive liquid, whilst the bacteria appear to be colour- 

 less. In other cases, on the contrary, the colouring matter is 

 found in the cells, for instance, in the red sulphur-bacteria, 

 where the red colour plays the same part in the nutrition of 

 the bacteria that chlorophyll plays in the higher plants. One 

 of the commonest pigment bacteria is the Bacillus fluorescens 

 liquefaciens commonly occurring in water, which yields a 

 greenish-yellow, fluorescent colour, soluble in water. 



Phosphorescent bacteria are found more particularly in 

 sea water ; great numbers occur on dead animals and plants. 

 The phosphorescent phenomenon is connected with aeration, 

 for it ceases when air is excluded. 



