BY R. GREIG SiMITH. 



227 



common phenomenon when large plates are infected. A contrac- 

 tile jelly would slowly supply the bacteria with fluid containing 

 the nutrients. As the slime contains about 97% of water, from 

 20 to 24 grams of water are taken from every 100 grams of agar 

 medium. The agar without tannin has probably as great an 

 affinity for this water as has the slime, in which case the slime 

 would not be able to get the necessary amount. But the tannin, 

 by slightly contracting the agar or lessening its affinity for water, 

 enables the bacteria to get the moisture slowly and in quantity 

 sufficient for a maximum formation of slime. 



The action of various tannins. — The experiments with different 

 tannins showed that they varied in their effects; some increased 

 while others diminished the yield of slime. With the object of 

 determining the action of known tannins, I obtained samples 

 from Messrs. Harrington Bros., of London and Cork, and sub- 

 jected these to experiment. The results are expressed in the 

 following table. 



The Influence of different Tannins. 



For some reason the duplicate tests did not agree so closely 

 as could have been wished, and as they differed in some 

 cases by 2 or 3 units, I have given the numbers as they were 



* Levulose 2, (tannin O'l), potassium citrate O'l, asparagine O'l, agar 2, water 100. 



tLevulose 2, glycerine 1, (tannin 0-2), potassium citrate O'l, asparagine 0-1, agar 2, 

 water 100. 



