392 BACTERIAL ORIGIN OF GUMS OF ARABIN GROUP, 



petri-dishes. The medium in the larger vessels was after congela- 

 tion infected with a suspension of the bacteria in 10 c.c. of normal 

 saline; the medium in the petri-dishes, by smearing with a loop 

 of the culture. The culture used for the purposes of infection 

 was obtained by growing the bacteria at 30° in potato-saccharose 

 agar prepared in the same way, but without tannin. The incuba- 

 tion at 30° on this medium gives a loose yellow growth with very 

 little slime; the culture therefore readily becomes distributed in 

 the normal saline. The plates were kept at the laboratory tem- 

 perature (about 15°) and the slime was removed with a rubber 

 spade on the third, fifth and seventh days. The slime is easily 

 removed, and there is no danger of agar being taken at the same 

 time. The first and second crops were preserved by the addition 

 of a few drops of dilute hydrochloric acid and of alcohol until all 

 the slime was obtained. The total slime was then treated with 

 an excess of strong spirit and worked up in the manner already 

 described. The difference in the amount of slime obtained by 

 adding tannin to the potato-saccharose agar is ver}'' marked. 

 Without tannin the growth is bright yellow and slightly gummy, 

 while with tannin it is pale buff, thick and slimy. 



A portion of the gummy solution free from sugars was pre- 

 cipitated with alcohol and the precipitate treated with nitric acid, 

 sp.g. 1*1 '2. A white, sandy powder, difficultly soluble in cold 

 water but readily soluble in boiling water, was obtained. It had 

 an indefinite melting point over 210° C, and had the same crys- 

 talline appearance, viz., colourless tables with a straight side, as 

 mucic acid obtained from commercial gum acacia. The mother 

 liquor contained oxalic acid. The oxidation products are thus 

 identical with those of gum acacia. 



So far the identity of the bacterial gum with the natural gum 

 has been proved by the test-tube reactions, the presence of pen- 

 tosans and the oxidation products. There remained the optical 

 activity and the determination of the constituents of the gum 

 acids. The former, viz., the optical activit}', is of little con- 

 sequence in view of the researches of other investigators. 



