BY R. GREIG SMITH. 399 



II. — The Insoluble (Metarabin) Wattle Gums. 

 (Bacterium metarahinum, n.sp.) 



While the natural gum of Acacia binervata was, in the absence 

 of particles of bark, entirely soluble in water, the gum of Acacia 

 penninervis was only partly so. The bacteria associated with the 

 gum of the former were entirely JJact. acacice, while from the 

 latter this organism and another were found. As separated from 

 my culture solutions the other bacterium was in the minority, 

 but on considering the matter this can be accounted for by its 

 method of growth. Bad. acacice in peptone saccharose fluid 

 grows as single cells, while the other bacterium has a tendency 

 to grow in aggregates^*, and thus in plate culture the aggregate 

 comes out as if it had been a single cell. 



I did not think that the plant would convert soluble gum to 

 the insoluble or meta modification, and expected that the 

 insolubility resulted from the further action of the organism, the 

 action of tannin, or that it was produced by quite another 

 bacterium. The first is unlikely, the second is quite possible, and 

 the last is most probable. Tannin is known to stiffen the gum, 

 and it would therefore be an easy thing to affirm that the 

 insolubility was entirely due to its action. But the gum of 

 Acacia binervata is formed in the presence of tannin bodies, and 

 although fragments of bark are imbedded in the solid exudate, 

 yet, when these are picked out, the gum is found to be entirely 

 soluble in w'ater. There is, therefore, strong reason to believe 

 that tannin has nothing to do with the production of the 

 insoluble portion of the gums. 



The second bacterium from Acacia pennhiervis forms, in suit- 

 able media, slime masses similar to Bad. acacice^ and while the 

 latter forms gummy colonies on gelatine media, the colonies of 

 the former are dry and cohesive, so that the colonies are removed 

 from the medium by the inoculating needle f:n masse. There is 



On this account the bacterium must be " plated " several times before a 

 pure culture is obtained. 



