224 



BACTERIAL ORIGIN OF GUMS OF ARABIN GROUP, 



The slimes in the experiment were incubated at 13° and weighed 

 at the end of the third day. 



The Slime fkom Varying Amounts of Tannin. 



Tannin %. 



Grams of Slime from 100 cc. of medium.* 



The influence of the tannin in giving an easily removable slime 

 was again demonstrated, although the difference was not so 

 marked as in the earlier experiments, especially with saccharose- 

 potato-agar. The better nutrition of the bacterium, e.g.^ with 

 levulose, caused a greater slime-production, with a concomitant 

 greater ease in removal. The consistency of the plate containing 

 0*1% was firmer and the medium of a lighter colour. Both of 

 these appealed strongly in favour of the use of 0'1%. However, 

 I determined to repeat the experiment, especially as the test with 

 a new lot of tannin gave such a very low yield. In this experi- 

 ment which follows, the temperature of the laboratory varied 

 from 14° to 17° C. The old and new lots of tannin were powders; 

 the commercial sample consisted of dark-coloured lumps. 



The Effect of different Tannins. 



* Asparagine 0-1, levulose 2, potassium citrate 0-6, agar 2, water 100 grms. 

 t Asparagine 0-1, levulose 2, sodium succinate 0*5, agar 2, water 100 grms. 



