250 BACTERIAL ORIGIN OF GUMS OF ARABIN GROUP, 



metarabinum on account of its property of remaining in clumps, 

 while Bact. acacice diffuses throughout the culture medium. The 

 finding of even one colony of Bact. metarahinum was therefore 

 quite sufficient, for there might have been, and probably were, 

 more original bacteria in the one colony of Bact. metarabinum 

 than in all the colonies of Bact. acacice. The impurity in the 

 original colony consisted of Bact. acacice and a form intermediate 

 between it and Bact. metarabinum, that is a transition form 

 between the two. Upon glucose gelatine the colonies of the 

 transition form grew first like Bact. acacice and then became 

 puckered like Bact. metarabinum. 



It has by this experiment been shown that the host plant can 

 alter the physiological function of Bact. acacice, and that so pro- 

 foundly that the acquired character is practically permanent. 

 In the case of the bacterium from Acacia penninervis, the forma- 

 tion of metarabin has been maintained for two years, during 

 which the organism was subcultivated in the laboratory. Since 

 both bacteria were found in the tissues of the tree, it is probable 

 that the exudate really did consist of a mixture of the gums, 

 and that taken from the wounds was really the metarabin residue. 

 The fact that a tree can alter the gum-forming function explains 

 how the gum from different species of trees are so constant in 

 their characters. 



The groivth of Bact. metarabinum. — Experiments were made 

 with Bact. metarabinum to determine the nutrients that favoured 

 the production of slime when the research with Bact. acacice was 

 Hearing completion. Like the preliminary experiments with the 

 latter, the first trials were abortive owing to the lengthened sub- 

 culture of the organism upon nutrient meat-agar. But after a 

 few rapid transfers upon saccharose-potato-agar* the bacteria 

 rapidly regained the power of forming slime. This was, however, 

 so insoluble that it could not be removed from the agar even 

 when made with 0-3% of tannin. As the gum is not readily 



* The saccharose-potato-agar which I now employ consists of potato- 

 extract 250 c.c, 50% solution of saccharose (autoclaved to free it from Bac. 

 levanij'ormcnu) 40 c.c, agar 20 grams, and water to 1000 c.c. 



