258 LACTIC ACID BACTERIA IN DISTILLING, ETC. 



being then left to stand uncovered. The liquid soon begins to 

 ferment briskly, is bottled at the end of twenty-four hours, and 

 consumed within the next two days. The so-called ginger-beer 

 yeast was more closely examined by H. M. WARD (II.). It 

 consists of whitish translucent masses about the size of a hazel- 

 nut, and is a mixture (Fig. 52) of a yeast, Sacckaromyces 

 pyriformis, and a fission fungus. The cell-walls of the latter 

 organism are gelatinised in a manner with which we shall be- 

 come acquainted later on, more particularly in the case of certain 

 filamentous bacteria : the greatly swollen outer layers of the cell- 

 membrane becoming detached, but only so far as to constitute 

 an independent outer case or sheath enveloping the cells. This 

 jacket either surrounds the cell along its entire length or else 

 only along one side thereof, and is in some cases absent alto- 

 gether. The breadth of the cell itself measures about 0.5 ja, and 

 the length varies between 0.5 and 50/01. The thickness of the 

 sheath is often ten times greater than the diameter of the cell. 

 When examined under the microscope, this thick envelope with 

 its comparatively thin enclosure resembles a worm, and it is on 

 this account that the name Bacterium vermiforme has been given 

 to the fungus. 



The bacterium is shown in Fig. 53. It stands in symbiotic 

 relation with the Saccharomyces pyriformis, so that the develop- 

 ment of the one is facilitated by the presence and vital activity of 

 the other. Ward also succeeded in artificially constructing the 

 ginger-beer plant from its two components. The chief products 

 of this fermentation are carbonic acid and lactic acid, in addition 

 to traces of alcohol and acetic acid. The lumps of the plant are 

 kept in a state of saltatory motion by means of the carbonic acid 

 gas, and increase considerably in size during the fermentation. 

 They are able to withstand desiccation, and shrink up on drying 

 to form a horny mass, in which condition they are stored for future 

 use. The origin of the ginger-beer plant is unknown. 



