1900.] on Symbiosis and Symbiotic Fermentation. 273 



titles of yeast and bacteria were employed in each experiment so that 

 the results might be comparable. With grape-sugar the ratio was 

 117 to 112, which is a little in the opposite direction. When they 

 were conjoined symbiotijcally the amount of acid produced was 474 

 compared with 224 when they were together but free, a mixture of 

 cane and fruit sugars being the culture medium. With grape-sugar 

 the proportions were 196 to 112 ; with fruit-sugar alone they 

 produced when symbiotic about one-eighth as much acid as when 

 they were free and separate. 



Without entering upon the question of the advantages or dis- 

 advantages of the association, these figures show that the symbiotic 

 relation greatly modified the progress and the results of the fer- 

 mentation. The bacterium when in symbiosis with the yeast forms 

 its sheaths readily in the presence of 2 per cent, of alcohol. When 

 free it produced no sheaths in less than 5—8 per cent., and then 

 only in long standing under the spirit. In 2 per cent, or less it 

 only brought about the viscous sediment which has been described. 



But little information has been gained as to the influence of the 

 one on the other in the symbiosis. It is not one of the preparation 

 of a suitable nutrient material for each other. The action of the 

 bacterium being to form acid, if this were the case the yeast should 

 be found capable of flourishing in such acid as it produces. But the 

 reverse is the case. In the absence of the bacterium so small a 

 quantity as ■ 25 per cent, of acetic acid is distinctly deleterious to it. 



Conversely the alcohol which the yeast produces is not made use 

 of by the bacterium in the production of the acid. It is utterly 

 unlike Bacterium aceti, the so-called vinegar plant which oxidises 

 alcohol to acetic acid. If alcohol is added to a fermentation which 

 is conducted by the bacterium alone, that alcohol can be recovered 

 unchanged when the fermentation has ceased. The source of the 

 acid appears to be the sugar, and a preliminary alcoholic fermentation 

 takes no part in the transformation. 



There is presumably some physiological influence excited by the 

 one organism upon the other, as the products of the fermentation 

 are so different when the two are in the different relationships 

 described ; but what is the nature of that influence there is at present 

 no evidence to show. 



[J. E. G.] 



