BY R. GREIG SMITH. 223 



Influence of the Quantity of Salt upon the Yield of Slime. 



Salt. 



Slime in grams from 100 c.c. of medium.*.--"?"^ 



^■} C A 7 ^ 



25 ,^Ov/-.,Ohi ... < 



2| Li L I !ir R A R Y 



26 V''^ "^^.^ '**' 

 24 



From the numbers as a whole we must conclude that succi- 

 nates and citrates in anything but small amount, viz. 0'1%, act 

 as depressants. B}^ the reversal of the yields, as compared with 

 the last experiment, the question is still undecided as to whether 

 citrate or succinate is the better; although when the results are 

 expressed in the graphic form the curves show that citrate is 

 rather better than succinate. 



The action of tannin. — Previous experience • had shown that 

 tannin increased the amount of slime, and at the same time 

 made it of such a nature that it could be removed from the 

 surface of the agar medium with the greatest ease. The very 

 early experiments had indicated that the optimum quantity of 

 tannin lay between 0*2 and 0*4%, and 0'3% was taken in making 

 the saccharose-potato media. That this is the best quantity is 

 open to doubt, and an experiment was arranged to find the 

 weights of slime produced by varying amounts of tannin in a 

 synthetic medium. Tannin is objectionable for two reasons. 

 Firstly, it tends to soften the medium during sterilisation. This 

 it probably does by reason of its acidity. Secondly, it passes 

 into the slime and darkens the gum which is ultimately obtained 

 unless the solutions are made decidedly acid, a condition which 

 somewhat hinders the precipitation of the gum by alcohol. If, 

 therefore, smaller quantities of tannin should be found to be as 

 good as larger for the purpose, a distinct advance would be made. 



Asparagine O'l, levulose 2, tannin 0*1, agar 2, water 100 grms. 



