GINGER-BEER PLANT. 141 



size from that of a pin's head to that of a large plum. It 

 induces an alcoholic fermentation in the sugar solution, which 

 at the same time becomes viscous. Marshall Ward isolated 

 the numerous micro-organisms existing in these lumps, and 

 described a series of yeast-fungi, bacteria, and moulds, and of 

 these, two organisms proved to be essentially concerned in the 

 fermentation of ginger-beer. One is a Saccharomyces (bottom 

 yeast), belonging to the ellipsoidal group of this genus, and 

 probably originating from the ginger and brown sugar com- 

 monly used ; Ward named it Saccharomyces pyriformis. It 

 inverts cane-sugar, actively ferments the products, and forms 

 a pasty white deposit at the bottom of the vessel. It yields 

 spores on gypsum blocks in 40 to 50 hours at 25 C. ; it also 

 forms spores on gelatine. In hopped wort it induces a feeble 

 fermentation, and forms a film on the surface containing many 

 pear- and sausage-shaped cells. 



The other essential organism, which is always present, is a 

 Schizomycete, Bacterium vermiforme, which, according to Pro- 

 fessor Ward, emanates from ginger, and is active in the lactic 

 acid fermentation. It is a peculiarly vermiform organism, 

 enclosed in clear, swollen, gelatinous sheaths, and imprisoning 

 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 

 sheaths, and in a great variety of shapes. The gelatinous 

 sheaths are only developed when the saccharine liquid is acid, 

 and free from oxygen. 



A Mycoderma and a Bacterium aceti were also found. 



Marshall Ward has proved experimentally that Saccharo- 

 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 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, because the yeast ferments more vigorously 

 in presence of the bacterium than it does alone. 



