72 MICRO-ORGANISMS AND FERMENTATION. 



belonging to the ellipsoid group of this genus, and probably 

 originating from the ginger and brown sugar employed in 

 ordinary practice; the author has named it Saccharomyces 

 pyriformis. It inverts cane-sugar, actively ferments the 

 products, and forms a white pasty deposit at the bottom of 

 the flasks. It yields spores on gypsum blocks at 25 C. 

 in 40 to 50 hours ; it also forms spores on gelatine. 



In hopped wort it induces a not very vigorous fermen- 

 tation, and it forms a film on the surface ; the cells in this 

 film are usually pyriform or sausage-shaped. 



The other constant and essential form is a Schizomycete, 

 Bacterium vermiforme, which, according to Professor Ward, 

 originates from the ginger. It is a peculiarly vermiform 

 organism, enclosed in hyaline, 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 the sheaths, and with 

 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 also occurred as casual intruders. 



The author 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 of the same kind as 

 that obtained when the ordinary ginger-beer plant is em- 

 ployed. But it is only when both species develop together 

 in the liquid that they bring about this result, and the 

 author's experiments point to the view that the relations 

 between the yeast and the bacterium are those of true 



