82 



Profs. H. Marshall Ward and J. Beynolds Green. 



It seemed possible that the bacterium might assist the latter by 

 fixing nitrogen from the air, as bacteria have been found to do in other 

 cases of symbiosis. Careful experiments showed, however, that neither 

 the conjoint organism nor the bacterium alone could grow in a culture 

 fluid which did not contain combined nitrogen. A quantitative esti- 

 mation of nitrogen was made of two fermentations of cane-sugar, one 

 by yeast alone, the other by the conjoint organism, a control of the 

 culture fluid alone being examined simultaneously. The nitrogen was 

 determined by Kjeldahl's process. The initial amount of nitrogen 

 present was 0*013 gram. Neither flask showed any variation from 

 this quantity at the end of the fermentation. 



The presence of the bacterium was seen consequently to be of no 

 service to the yeast, but on the other hand to be disadvantageous to 

 its growth. 



The yeast was, on the other hand, found to be of some value to the 

 bacterium. During the fermentations the former was found to excrete 

 a certain amount of various extractives into the liquid, which had a 

 distinctly nutritive value to the latter. The bacterium grew very 

 much better at the expense of these extractives than it did when sup- 

 plied with combined nitrogen in the form of ammonium tartrate, or 

 of asparagin. Comparative experiments made with the extractives 

 prepared from a fermentation showed that neither asparagin nor an 

 ammonium salt could minister to its development so readily as they 

 did. This view was also supported by the fact that yeast-water had 

 already been found to be the best form of supplying combined nitrogen 

 artificially to cultures of the isolated bacterium. 



The alcohol was of no nutritive value to the latter. When it was 

 cultivated in the presence of varying quantities of the spirit, it made 

 no use of it, and the original quantity of alcohol was found to be pre- 

 sent in the liquid at the conclusion of the experiment. 



The relationship between the two is not therefore one of symbiosis. 

 The bacterium appears to be a saprophyte, thriving at the expense of 

 the nitrogenous excreta of the yeast. It is not at all parasitic on its 

 neighbour, the yeast never being injured by its presence until sufficient 

 acid has been produced to cause a secondary inhibition. 



In the formation of the acetic acid this bacterium is peculiar. It 

 cannot be referred to the ordinary group of acetifying organisms,* as 

 it has not the power of affecting alcohol as they do. Its action on the 

 sugar seems to be a direct one, causing a formation of acid at the 

 expense of the latter, without setting up any preliminary fermenta- 

 tion. Bacterium aceti (Brown) has also this power in the presence of 

 oxygen, but it can oxidise alcohol in addition. 



The immediate antecedent of the acid appears to be fructose. 



* See Beijerinck, ' Cent. f. Bakt.,' vol. 4, 1898, for a summary of the kno$ra 

 acetic organisms. 



