404 BACTERIAL ORIGIN OF GUMS OF ARABIN GROUP, 



The gum yields gum acids which partly dissolve* and partly swell 

 up with water. These have the test tube reactions of gum 

 acacia and contain the arabinan-galactan complex. The gum 

 acids are similar to those of the natural gum of Acacia penni- 

 7iervis, and there can be no doubt that the natural gum is of 

 bacterial origin. Since Bad. acacice was found with Bad. 

 metarahinum the gum is probably produced by both bacteria, the 

 former producing the water-soluble portion, the latter the water- 

 insoluble portion. 



Since Bad. acacice was found in the only two instances which 

 were examined, it is possible that it is the only producer of all 

 sorts of soluble acacia gums. If this should prove to be the case, 

 the varieties of the gums will depend upon a number of factors 

 such as the host, plant, the juices of w^hich undoubtedly vary, and 

 thus influence the relative proportions of arabinan and galactan in 

 the gum complex. The situation will undoubtedly influence the 

 susceptibility of the tree towards the microbe. It is generally 

 recognised with all plant diseases that unhealthy surroundings 

 have much to do with the invasion by bacteria and other fungi. 

 But perhaps the most important factor will prove to be the 

 temperature. The slow growth at the higher temperatures (and 

 the appearances of the growths in test tube cultures indicated a 

 clearer slime at comparatively high temperatures; will, I think, 

 explain the better qualities of the gums produced in arid regions. 

 But on the other hand it is possible, and analogy supports this 

 contention, that there is a class of bacteria which produce the 

 soluble gums, each characteristic gum being formed by a different 

 species. Future research alone will settle the question. 



Since the arabin and the metarabinf gums are produced by 

 different bacteria it is extremely probable that the pararabin 

 <yums have also their particular microbe. This investigation is 



"" The partial solution may be accounted for by the treatment with acid in 

 the autoclave during the process of eliminating the bacteria. 



t Metarabin and pararabin are insoluble but swell up with water. The 

 former is soluble in dilute alkalies, the latter in dilute acids. 



