THE GINGER-BEER PLANT. 



165 



"It must, therefore, be concluded that this schizomycete is able to live and grow in an acid sac- 

 charine solution, with suitable minerals and nitrogenous materials, not only in an atmosphere totally 

 deprived of oxygen, but in one of vapor which is so attenuated that it is practically a vacuum so far 

 as permanent gases are concerned and that only forms its gelatinous sheaths if carbon dioxide is 

 present." (See figs. 43 and 44.) 



A ginger-bacillus (Schizomycete No. 2.) is frequently met with in fermentations to which lumps 

 of unsterilized ginger were added, but is not essential to the formation of the ginger-beer plant. 

 It occurs on ginger rhizomes. 



Cultures of Schizomycete No. 3 (Bacterium aceti Kiitz.), demonstrated not only that this bacte- 

 rium is not a normal or necessary constituent of the ginger-beer plant, but also that it can not be 

 induced to form a submerged commensal growth with any of the yeasts. 



SYNTHESIS OF THE GINGER-BEER PLANT FROM PURE CULTURES. 



The most conclusive proof of the accuracy of the foregoing studies is afforded by the re-consti- 

 tution of the ginger-beer plant as such, by bringing together pure cultures of the organisms com- 

 posing it, and showing that the specimens so produced act like the original specimens. The other 

 forms mentioned above were tried in various combinations, but only the two essential ones, Sac- 

 charomyccs pyrij'ormis and Bacterium vermiforme were successful. The relations between this yeast 





Fig. 42.* 



and bacterium are those of true symbiosis. The ginger-beer plant forms only in acid media and in 

 closed vessels, or in other conditions in which the free oxygen has been removed and carbon dioxide 

 substituted, e.g., under Mycoderma pellicles. The nutritive substance must also contain carbo- 

 hydrates. Cane-sugar is better than glucose; milk-sugar will not do ; sterilized ground rice may be 

 used in place of ginger the starch in the ginger being apparently the essential. The schizomycete 

 will grow in the absence of these substances but no sheaths form. 



The origin of the ginger-beer plant is involved in obscurity, but there is evidence to show that 

 the yeast is introduced from the grocer's shops attached to the ginger and brown sugar employed in 

 ordinary practice, while the bacterium is introduced with the ginger. 



*Fic. 42. Splitting of sheaths in Marshall Ward's Bacterium vermiforme: a, condition when fixed under the 

 microscope in a drop of ginger-gelatin; b, 6 hours later; c, 18 hours after b. The corresponding parts are designated 

 by x's. After Ward. 



fFiG. 43. The ginger-beer plant, a compact mass due to growth of Bacterium vermiforme with yeast in a suitable 

 saccharine medium. This figure shows appearance after 15 days in Pasteur-bouillon. "The filaments and rodlets 

 ensheath themselves as soon as the carbon dioxide is in excess, and entangle the well-developed yeast-cells in the coils 

 of the gelatinous matrix. The mass becomes denser and denser, and at last forms the hard, brain-like lumps of the 

 ginger-beer plants." After Ward. 



tFiG. 44. Bacterium vermiforme and Saccharomyces pyriformis grown in an unsuitable medium in which no 

 sheaths appear on bacteria and no symbiosis takes place. Drawing made after 15 days in ordinary bouillon. "The 

 yeast buds slowly and for a short time only. The Schizomycete grows out into filaments which rapidly break up into 

 very short rodlets (bacteria) and cocci." After Ward. 



