BY R. GRBIG SMITH. 405 



in progress. Gum tragacanth will undoubtedly be shown to 

 have a bacterial origin. 



The various gums of the arabin group are not found upon 

 Acacias only. This, however, does not militate against the 

 bacterial origin of all these gums. Thus the gums exuded by 

 certain Rosaceae*, e.g., cherry, peach, plum, are very similar to 

 wattle gum, and are probably the work of bacteria such as Bad. 

 acacice and metarabiuum. These fruit tree gums are being 

 investigated. 



Bacterium metarabinum, n.sp. 



Shape, etc. — The organism is a stout, motile, short rod, with 

 rounded ends. The dried and imbedded bacteria when taken 

 from cultures on saccharose-potato agar appear as oval cells, 

 measuring 0-8 : 1-2 /z, and as rods measuring 1 : 2 /^t. On the oval 

 cells the flagella are generally terminal, but as the cell grows 

 longer many peritrichous flagella can be seen, up to seven have 

 been counted; but as the growths on agar are cohesive many more 

 may occur on the cells. Staining by Gram's method is negative, 

 and spores are not formed. 



Temperature, etc. — The optimum temperature is about 30°. At 

 37° the growth is less than at 22° or 15°. The bacterium is 

 aerobic, but grows slightly under anaerobic conditions. 



Nutrient agar plate. — The colonies are dirty-white, raised and 

 rough. When magnified they appear rounded, irregular or 

 lobular, with a smooth edge and convoluted, puckered or crinkled 

 centre. The deep colonies appear moruloid or very irregular, as 

 if several colonies had fused together at different parts. As the 

 colony increases in size the colour deepens to a yellowish-bnff. 



Glucose-gelatine plate. — The colonies are ivory-white, dry and 

 puckered, and have a very cohesive consistency; it is almost 



* The slime-flux or mucilage-flux and the gum-flux of certain trees have 

 been ascribed to the action of certain Ascomycetes by Ludwig and by 

 Beijerinck. In view of my research it is possible that in some cases at least 

 these ascomycetes have appeared in the flux at a period subsequent to its 

 formation by bacteria. 

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