164 BACTERIA IN RELATION TO PLANT DISEASES. 



Chief characters: A low, or bottom-fermentation yeast, which inverts and ferments cane-sugar. 

 Ordinary cells ovoid or globoid, ranging from 5 to o,/* in diameter, though smaller and larger ones 

 occur. Ascospores formed in from 2 to 4 days, at 25 C. and lower. Aerobian forms, as films, of 

 pyriform, or sausage-shaped cells are developed in wort in 21 days. Occurs in " home-brewed ginger- 

 beer, " and is the predominant form in the so-called "Ginger-beer plant. " 



Whenever the fermentations were carried on or finished with access of air, a dense wrinkled 

 skin formed at the surface; and, since this occurred when the air had to filter through sterilized plugs 

 of cotton wool, there can be no doubt as to the origin of the fungus from the inoculating material. 

 This growth was identified as the very polymorphic M ycoderma cerevisiae of Desmazieres. It is not a 

 true Saccharomyces for it does not form ascospores, and differs in several respects from the true yeasts, 

 in the narrow sense. It is distinctly an aerobian form; is unable to invert cane-sugar or to bring 

 about its fermentation; it is apt to appear on lager beer even in cold cellars; cells are elongated, 

 less translucent than active Saccharomyces cells; average size, 6 to 8^ long, by 2 to 4^ broad. 



A pink or rosy yeast Cryptococcus glutinis Fres. ?, also occurred. This organism is not a necessary 

 part of the ginger-beer plant, and is not always present in cultures of this "plant." 



A small yeast, the cells of which are very nearly spherical, averaging about 2.3 to 3. 7m in diameter 

 [Yeast D) was frequently met with, but is not a normal constituent of the ginger-beer plant. Not 

 sufficient knowledge of its characters to warrant any specific name. 



The ordinary beer-yeast {Saccharomyces cerevisiae) and two other forms, not identified with cer- 

 tainty, one of which is probably S. apiculatus, were found occasionally. These are not concerned in 

 the formation of the ginger-beer plant. 



The new schizomyeete called Bacterium vermiforme is a peculiarly vermiform organism, enclosed 

 in hyalin, swollen, gelatinous sheaths, and imprisoning the yeast-cells of Saccharomyces pyriformis, 

 etc., in the brain-like masses formed by its convolutions. It is a constant and essential form essential 

 because the ginger-beer plant can not exist as such without it. It is the swollen sheaths of this 

 organism which constitute the jelly-like matrix of the "plant. " 



Fig. 41.* 



Various attempts were made to isolate this organism a difficult thing to do at first, because 

 then it was not known what relation the naked forms bore to the sheathed cocci, rodlets, filaments, 

 etc. Two distinct phases of this organism exist the vermiform, sheathed stage found in acid 

 saccharine media saturated with carbon dioxide, and the motile naked filaments, rodlets and cocci 

 met with in neutral bouillon and other incomplete nutritive media containing oxygen. It was neces- 

 sary to take the precaution of cultivating both forms side by side, under exactly similar conditions, 

 varied one by one similarly for each. In the presence of oxygen the bacteria promptly escape from 

 their sheaths. If these unsheathed rods are grown in the presence of yeasts, i.e., carbon dioxide pro- 

 ducers and oxygen consumers, the sheaths form again. 



When a small piece of the gelatinous form, i. e., the compacted coils of sheathed filaments, rod- 

 lets, etc., of Bad. vermiforme is put into a test-tube of suitable nutritive fluid (e.g., Pasteur-bouillon, 

 beet-solution, boullion +5 per cent of sugar, etc.) and kept at 15 to 18 C, the usual course of 

 events is as follows: 



The liquid becomes more and more turbid after 48 hours or so; then a whitish film begins to 

 form above, and a deposit at the edges of the level of the liquid, while a similarly whitish, granular or 

 cloudy looking deposit falls to the bottom. In from 7 to 14 days the rapidly increasing deposit 

 becomes more and more gelatinous, and at length assumes the consistency of a sort of jelly. This 

 gelatinous cushion at the base consists of the sheathed coils so often referred to; the film and ring 

 at the level of the liquid, and the turbidity throughout the body of the same, are chiefly due to the 

 free filaments and rodlets already described as escaping from the sheaths. The preliminary turbidity 

 of the liquid is due to the motile forms of these filaments and rodlets. Flagella could not be demon- 

 strated. The sheaths may grow end on (fig. 41) or sidewise (fig. 42). 



*Fig. 41. Two stages of Marshall Ward's Bacterium vermiforme in a hanging drop of Pasteur bouillon stiffened 

 with gelatin. I have omitted intermediate stages b and c. The stage d was drawn 21 hours later than a. After Ward. 



