80 Profs. H. Marshall Ward and J. Keynolds Green. 



not manifested. The yeast was found to be capable of fermenting 

 both glucose and fructose (levulose), but to be more active in the pre- 

 sence than the absence of the latter. Only half the amount of alcohol 

 was formed when the fructose was excluded. The latter sugar was 

 more favourable also to the acid fermentation by the yeast. If we 

 compare Experiments II and III, we find that while the same quantity 

 of alcohol was formed in both cases, the proportion of both acetic and 

 succinic acids was about doubled in the presence of fructose. 



The bacterium, however, was responsible for the greater amount of 

 the acid formation. While it caused the production of both acetic and 

 succinic acids in greater proportion than the yeast, it yielded far more 

 relatively of the former. In the experiment with beer wort it produced 

 fifteen times as much acetic acid as the yeast ; it only gave rise to four 

 to five times as much succinic. With cane-sugar solution it formed 

 seventy times as much acetic and ten times as much succinic acid as 

 the yeast. The same result was obtained with cane-sugar and 

 fructose. 



With grape-sugar the bacterium, like the yeast, could do but little. 

 It produced about the same amount of acetic acid, but scarcely more 

 than one-third as much succinic. 



The experiments on the fermentations confirm the view expressed in 

 the early portion of the paper, that cane-sugar is the most favourable 

 medium for the bacterium, but before it is of use to it, it undergoes 

 inversion. 



The association of the. two organisms together introduced a some- 

 what curious feature of the fermentation. The yeast continued to 

 produce alcohol in the same proportion as when alone, but the acid 

 fermentations were modified considerably. Comparative experiments 

 were made with cane-sugar, dark brown sugar containing fructose, and 

 grape-sugar. In the first two cases the amount of both acetic and 

 succinic acids produced by the conjoint organism was distinctly less 

 than that which was formed by the bacterium alone. In the grape- 

 sugar fermentation the contrary was the case. 



The association of the two organisms into the jelly-like clumps was 

 not without its effect upon the progress of the fermentation, and this 

 effect again appeared in connection with the process of the acidification. 



With the dark brown sugar the conjoint organism produced twice as 

 much acetic acid as the two separate constituents working together, but 

 only one and a half times as much succinic. With grape-sugar there 

 was a diminution of the succinic acid, which fell to one-half the 

 quantity produced by the yeast and the bacterium, while not in such 

 close association. The acetic acid, on the other hand, increased. In the 

 first two cases again, the presence of the yeast was very considerably 

 inhibitory of the activity of the bacterium, the latter producing far 

 more acid of both kinds when it was alone in the fermenting liquid. 



