A Sugar Bacterium. 



83 



Though the bacterium flourishes in solutions of cane-sugar, it does not 

 convert the latter immediately into the acids of the fermentation, but 

 hydrolysis takes place first. In one experiment 150 c.c. of a 10 per 

 cent, solution of cane-sugar, containing 15 c.c. of yeast water, were 

 infected in a sterile flask with a pure culture of the bacterium, and 

 fermentation was allowed to proceed for twelve days at the tempera- 

 ture of the laboratory. At the end of that time the acetic acid was 

 distilled off, and the residue poured into alcohol to precipitate another 

 constituent, which will be referred to below. The remainder of the 

 sugar was left in solution in the alcohol. After filtration the alcoholic 

 liquid was evaporated to a syrupy consistency, and the residue taken 

 up with water. • It was then divided into two equal portions, and one 

 of them was acidified with sulphuric acid till the concentration of the 

 latter was 2 per cent. It was then boiled on a water-bath for two 

 hours and carefully neutralised. An aliquot part of each was then 

 titrated with Fehling's solution, and the cupric oxide formed was 

 weighed. The weights of the two were almost identical, differing by 

 only 0*002 gram. The inversion of the cane-sugar by the organism 

 had consequently been practically complete. 



A few bacteria only have been found to secrete invertase. Fermi 

 and Montesano found that Bacillus megatherium, B. fluorescens lique- 

 faciens, the red Kiel bacillus, and Proteus vulgaris were capable of 

 producing it in bouillon to which cane-sugar had been added. Van* 

 Tieghem showed that it was secreted by Leuconostoc mesentenoides. To 

 these the bacterium under observation must now be added. The 

 following experiment shows that the inversion noticed in the last case 

 was due to an exoreteel enzyme. 



A good culture was made in cane-sugar solution, and, after a few 

 days, was filtered under pressure through a Chamberlandt's porcelain 

 tube. Three flasks were taken, and 15 c.c. of cane-sugar solution of ■ 

 2 per cent, concentration placed in each. They were then carefully 

 sterilised. To A and B, 2 c.c. of the filtrate from the culture were 

 added, the filtrate having been found free from organisms by careful 

 microscopic examination; B was then boiled and allowed to cool 

 slowly. They were all kept for a few days at the temperature of 

 22° C. in an incubator. On titration with Fehling's solution, C, the 

 control, gave no reduction, B a slight one, and A threw down a con- 

 siderable precipitate of cuprous oxide. The small reduction in B was 

 due no doubt to a trace of invert-sugar present in the culture fluid 

 added to the flask. The much greater reduction in A was due to 

 invertase which the bacteria had excreted. 



The experiments quoted in the early part of this paper show, how- 

 ever, that the inversion must take place gradually and the fructose 

 be supplied almost as it is wanted. In presence of fructose only, growth 

 is almost impossible. 



