BY R. GREIG SMITH. 



225 



The most notable result of the experiment is the finding that 

 different tannins produce different results. The smaller quantity, 

 viz., 0-1%, produced more slime than the larger percentage. 

 Plates containing 0*5% were also prepared, but the medium was 

 like starch paste ; its gelatinous property had been destroyed by 

 the acid. All the plates containing tannic and gallic acid yielded 

 slimes which were readily removed. The slime in the plate 

 without tannin was not homogeneous and apparently contained 

 zoogloea masses, but still it could be removed without taking 

 away particles of the medium. 



The function of the tannin. — One cannot say what the role of 

 the tannin in the synthetic medium may be. It is possible that 

 it acts by reason of its acidity, or it may form an unstable com- 

 pound with the levulose, and thus play the part of a catalyte. 

 Probably it does neither of these, but before discussing its func- 

 tion it would be advisable to record some experiments with 

 organic acids, and with salts and tannin. The acidity of 0-1 % of 

 tannin is approximately equal to 0-02% of citric or succinic acid, 

 so this quantity was used in order to compare the effect of the 

 free acids. 



The Effect of Acidity and of Tannin. 



Asparagine O'l, levnlose 2, agar 2, water 100 grms. 



