BACTERIA. 85 



the yeast cells in brain-like masses formed by its convolutions. 

 It is the swollen sheaths of this organism which constitute the 

 jelly-like matrix of the " plant." It also appears without the 

 sheaths, and in all the various growth-forms which we meet 

 with among the bacteria. It is a markedly anaerobic bacterium. 

 The gelatinous sheaths are only developed when the saccharine 

 liquid is acid, and free from oxygen. 



Of the other organisms which occur in the ginger-beer plant, 

 a Mycoderma species and Bacterium aceti were found in all the 

 specimens examined, and a variety of other bacteria and fungi 

 occurred as casual intruders. 



MARSHALL WARD has proved experimentally that SaccTiaro- 

 myces pyriformis and Bacterium vermiforme are the only two 

 essential species in the ginger-beer fermentation, since it was 

 only by inducing a fermentation with these two species that 

 he was was able to produce an effect similar to that obtained 

 when the ordinary ginger- beer plant is employed. But it is 

 only when both species develop together in the liquid that 

 they bring about this result, and his experiments indicate that 

 the relations between the yeast and the bacterium are those of 

 true symbiosis, so that the two species form a lichen-like com- 

 pound organism, which induces a " symbiotic fermentation" 



6. SLIME-FORMING BACTERIA. 



Among the various species of slime-forming bacteria there 

 are several which are of peculiar interest in the fermentation 

 industries, as they occur in wine and fermenting wort, causing 

 morbid changes. By analogy, this slime formation may be 

 regarded as a phenomenon closely related to the commonly 

 occurring zoogloea formation of certain bacteria. In the case 

 of some species the slime is, however, regarded as a product 

 of the decomposition of sugar, and not as a substance separated 

 from the organism itself. 



In the viscous fermentations examined by BECHAMP a kind 

 of gum termed viscose was formed together with carbon dioxide 

 and, frequently, mannite. 



In his "Etudes sur la biere " (Plate 1, Fig. 4) PASTEUR des- 

 cribes bead-like chains of spherical organisms, which render 



