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BACTERIAL ORIGIN OF GUMS OF ARABIN GROUP, 



Experiment 3. 



The three experiments do not agree in details. The divergences 

 are partly due to the different temperatures of incubation, pos- 

 sibly also to a difference in the vitality of the bacterium at the 

 time of each experiment, for they were not made simultaneously, 

 but following each other. But the third experiment shows that 

 a reinfection of the media was necessary to enable the nutrients 

 in the absence of tannin to be utilised. It is clear that the 

 tannin does not act by reason of its acidity. It seems to act as 

 a stimulant, for the nutrients are quickly utilised, that is to say, 

 the slime is formed quickly. In its absence the gum is very 

 slowly produced, as can be seen by referring to the action of 

 potassium citrate and comparing it with that salt plus tannin. 

 Citric acid alone made the medium brittle, so that the infection 

 of the plate and the removal of the slime had to be done with 

 the greatest care to prevent angular pieces of the agar coming 

 away with the slime. In considering the experiments as a whole, 

 one sees that a pronounced acidity of the medium is not to be 

 recommended. The addition of tannin and citrate is advisable, 

 but in the presence of a suitable proportion of asparagine and 

 levulose the addition could almost be dispensed with. If after 

 adding citrate only the medium is reinfected with bacteria, the 

 maximum yield of slime can be obtained. 



With regard to the function of the tannin in the medium, I 

 am of the opinion that it is purely physical and causes the agar 

 jelly to be somewhat contractile. A splitting of the agar is a 



* Asparagine 0-1, levulose 2, agar 2, vater 100 grms. 



