544 BACTERIAL ORIGIN OF GUMS OF ARABIN GROUP, 



used there is obtained a smaller quantity of a thick white slime. 

 Whether the increase of gum is due to the acid reaction of the 

 medium or to the partial inversion of the saccharose is not clear; 

 but, since reducing sugars are present in potato extract, it is 

 probable that the natural acidity is the essential factor in 

 stimulating the bacteria to slime-production rather than to repro- 

 duction. 



The races of the organism. — Upon saccharose-potato-agar the 

 bacteria always produced slime — that is to sa}', if the bacteria 

 grew at all, slime was produced. Three races of the bacterium 

 had been isolated, and these differed chiefly in the temperatures 

 between which they grew. Race i., produced as much slime at 

 18° as at 24°; at 30° and 37° the slime was less. Race ii., grew 

 equally well at 18°, 24°, 30° and 37°. Raceiii., grew equally well 

 at 18°, 24° and 30°, but did not grow at 37°. Race i., produced 

 the largest quantity of slime, and it is this race which was used 

 in the work connected with the action of the organism. 



The slimes {i.e., carbohydrate together with the bacterial cells 

 and other products) which were produced by these races behaved 

 differently to certain chemical reagents. For example, the slime 

 of race i., was coagulated by copper sulphate, neutral lead acetate 

 and barium hydrate, while races ii. and iii. were not. The slimes 

 of all the races were coagulated by ferric chloride, aluminium 

 hydrate, basic lead acetate, and milk of lime. The coagulation of 

 the slime by many reagents is therefore not distinctive.* 



When the gum was separated from the bacterial cells and other 

 products and while in the soluble condition it behaved somewhat 

 differently with these reagents. Curdy precipitates were obtained 

 with alcohol, barium hydrate, basic lead acetate and ferric 

 chloride. Neutral lead acetate and copper sulphate gave no pre- 

 cipitate. Copper sulphate followed by sodium hj'drate gave a 

 light blue precipitate which contracted but did not darken upon 



* The slime of Bad. jjer.siae differed in its behaviour to coi^per sulphate 

 according to the temperature of incubation of the cultures. These Proceed- 

 ings, 1903, p. 839. 



