388 BACTERIAL ORIGIN OF GUMS OF ARABIN GROUP, 



bearing Acacia binervata, DC.,* it was noted that subjacent to 

 the hole in the bark through which a large globule of gum had 

 exuded there occurred a small quantity of fluid which was acid 

 and contained a tannin body. In the tissue saturated with this 

 fluid, slime-forming bacteria identical with the bacterium from 

 Acacia penninervis were obtained in pure culture. The occurrence 

 of tannin at the site of production of the gum suggested that it 

 might influence the production of gum. Accordingly experiments 

 were made with it, and from these it appeared that from 0*2 to 

 0'4% of tannin did influence the formation of slime. Smaller 

 proportions of tannin when added to saccharose-potato agar 

 seemed to produce a relatively greater quantity of bacteria and 

 less slime, while more tannin produced less bacteria and less slime. 

 With regard to the reaction of the medium, experiments made 

 with varying amounts of citric acid and of sodium carbonate 



* This was growing in a garden in Macpherson-street, Waverley, Sydney, 

 and my attention was drawn to it by Miss S. Hynes, of the Botanic Gardens. 



Maiden (Pharm. Jour. [3] xx., 980) gives the following description of 

 the gum : — 



"Acacia binervata, DC, B.F. ii., 390. 



Arabin 76' 57 



Metarabin 4'24 



Ligneous matter 1 '62 



Moisture - ... 16-01 



Ash -771 



99-211 



" A ' black wattle ' found in New South Wales and Queensland ; obtained 

 from old trees, Cambewarra, New South Wales ; diameter 8-12 inches. It 

 is obtained in pieces from the size of a pigeon's to that of a hen's egg, and is 

 of a waxy lustre. The freshly exuded gum is very pale brown; old gum is 

 often nearly black. Being in comparatively large masses, sorting for market 

 would be easy. It has a dull horny-looking fracture. 



It dissolves fairly well in water, leaving a quantity of gum in the form of 

 a flocculent deposit. The colour of the dissolved gum is rather dark owing 

 to the presence of included fragments of bark. This description of the effect 

 of cold water will apply equally well to A. dealhata and A. elata. Like other 

 wattle gums, its aqueous solution is distinctly acid to litmus paper." 



