268 FORMATION OF SLIME OR GUM BY RHIZOBIUM LEGUMINOSARUM, 



The medium which I have used for growing large quantities of 

 the slime has been saccharose-potato-agar, but saccharose-bean- 

 agar is quite as good and it is easier to prepare. Saccharose, 

 maltose, dextrose or levulose are the most suitable sugars, but 

 the races vary with regard to their power of producing slime 

 from each of these. The chief fault of the saccharose is that it 

 always contains the very resistant spores of the slime-forming 

 Bac. levaniformans, and during the sterilisation of the media 

 some of the sugar may become inverted. It is only by careful 

 intermittent sterilisation that the inversion can be avoided. In 

 some cases, e.g., the Krai races, the presence of small quantities 

 of the hexoses produces a considerable reduction in the yield of 

 slime. 



Infection of the media is accomplished by smearing the moist 

 surfaces of recently prepared large plates with an actively grow- 

 ing slimy culture of the bacterium. The plates are incubated at 

 the optimum temperature, which is generally 22°C, for a week 

 and the slime is then carefully removed. 



The crude slime is principally a solution of gum, but contains 

 in suspension the bacterial cells and in solution small quantities 

 of nutrient matter derived from the medium, and possibly also 

 diffusible albuminoids from the bacteria. The process of partial 

 purification consists in eliminating the bulk of the saccharine 

 impurity by coagulating the slime with alcohol, then in heating 

 the emulsified coagulum in the autoclave (for 15 minutes at three 

 atmospheres) which treatment brings about a separation of the 

 slime into a solution of a gum and into a curdy precipitate, 

 presumably of albuminoids and bacterial cells. The gum is 

 purified by repeated precipitation from aqueous solution by 

 alcohol, the tendency to "milk " or emulsify being counteracted 

 by the addition of small quantities of a solution of 10 % potassium 

 chloride. All bacterial gums after this method of treatment 

 retain a small quantity of nitrogenous matter which may have 

 been originally dissolved in the slime, or which may have been 

 produced from the action of the acid in the slime upon the 

 bacterial cells during the treatment in the autoclave. The slimes 



