BY R. GREIG SMITH. 219 



potassium phosphate, citrate or asparaginate when peptone was 

 used. Furthermore, citric acid is the chief organic acid in 

 potato-juice, a fact which was brought out during the investiga- 

 tion of the acids formed by the bacteria. 



Like the previous experiment the slime-production was scanty, 

 but the results showed broadly that no slime was formed in the 

 presence of chloride or phosphate. Slime was produced on the 

 media containing citrate or citrate and chloride. A mixture of 

 citrate and phosphate prevented slime-formation. It was made 

 evident that a good salt to employ in the synthetic medium 

 would be potassium citrate. 



After finding that tannin and citrate were useful for a slime- 

 producing medium, the next step which was taken was the 

 influence of different carbohydrates. From 0-5-1 grm. of carbo- 

 hydrate was dissolved in 20 c.c. portions of a medium containing 

 peptone, citrate and agar; and with these plates were prepared, 

 and the surfaces smeared with Bact. acacice. At the same time 

 another set was made; these differed in containing asparagine in 

 place of peptone. The results showed that levulose was the chief 

 sugar from Avhich the organism formed its slime, and that aspara- 

 gine was much better than peptone. 



Experimental methods. — Hitherto the quantity of slime pro- 

 duced by a particular combination of nutrients had been roughly 

 estimated. But after making many experiments, it became 

 apparent that some definite method would have to be adopted to 

 distinguish small differences, and the use of the balance suggested 

 itself. Before proceeding to consider the next experiment, perhaps 

 it would be advisable to describe the method employed in obtaining 

 a certain weight of slime. In preparing the medium the agar 

 was first dissolved in about half the required quantity of water. 

 The remainder of the nutrients, etc., were dissolved in rather 

 less than half, which was heated and added to the solution of 

 agar upon its removal from the autoclave. The incomplete 

 medium was then put into wide (6x1 inch) numbered test tubes 

 by means of a 200 c.c. burette graduated in cubic centimetres. 

 Each tube contained 20 c.c. of medium. The nutrient under 



