EXPEKIMENTS ON GUM rUODUCTION IN JiOKDOI'AN 83 



The final product was nearly white and vesenililed h'"" •" appearance. From the I'lopcrties of 

 method of its separation described above it will be seen tluit tliis substance also resembled bacterial 

 gum in being soluble in water and insoluble in 75 per cent, alcohol. Levulose is readily i>roduct 

 soluble even in alcohol of a much higher strength, and any of this sugar which had been 

 unchanged by the bacteria would remain in solution when the product of bacterial action 

 was precipitated at first. The same is true of the other constituents of the original medium, 

 and", in addition to this, the amount of asparagin and potassium citi'ate used was so small 

 that the new substance could only be accounted for by having been derived from the 

 levulose, and perhaps to some extent from the glycerine, any products of a protein nature 

 being removed in the treatment of the original solution with acid and afterwards with 

 alcohol. 



The bacterial product did not reduce Fehling's solution, but on boiling a solution of the 



former in five per cent, sulphuric acid for twenty minutes and then neutralising this, a good 



reduction took place, showing another point of resemblance between this bacterial product 



and the gums exuded from tapped trees. Some of the ordinary gum tests were also tried, 



such as coagulation with basic lead acetate and ferric chloride, and these gave positive 



results. From the examination of this bacterial substance, therefore, we must assume that 



these bacteria, when grown in an artificial medium of suitable composition, produce, among 



other things, a substance of the same nature as the gum of the tree from which they have 



originally been isolated. The formation of gum from the sugars of the sap is thus, as 



Greig Smith pointed out, the result of pathological conditions. In the first place, exudation 



of gum does not take place from Hashcib trees in those districts where the rainfall is high 



compared with that met with in the gum-producing districts of Kordofan. In the latter case 



the tree as a whole is in a state of reduced vitality, and the tissues are therefore more 



susceptible to the effects of abnormal injuries. In those districts where the proportion of Effect of 



moisture in the soil is relativelv high, the injury produced when the tree is tapped is "is^<;hanicai 



"•'•''- ^^ injury to the 



repaired before the bacteria present have time to produce any appreciable amount of gum. ,rees 



The wounding of the tree through tapping causes a local weakness in the tissues next to 



the bark, and the cells of the tree are then unable to prevent the rapid increase of, and 



increased transformation of the sap by, the bacteria. This appears to go on until sufficient 



new bark has grown over the wound to form a protection for the exposed surface. In the 



case of a tree which was quite free from bacteria, it has already been shown how infection 



can readily be carried by means of ants or flies. 



Since my return from Taiara, I have confirmed my work there, both in obtaining pure 

 cultures of this bacterium from gum-bearing branches of hashdb trees, and also in 

 producing a substance of the nature of a gum by cultivating the bacteria on artificial 

 media containing sugar as the principal constituent. I regret, however, that I have been 

 unable up to the present to investigate the properties of these bacteria at all fully. 

 They grow equally well on glucose and levulose media, but not so well on maltose 

 and other sugars, and they do not appear to form a very adhesive slime. Greig 

 Smith found his bacteria to produce slime more readily in presence of tannin, but 

 the hashdh bacteria do not grow at all well in media containing tannin. 



Acting on a suggestion made by Dr. Beam, I obtained, through the kindness of 

 Mr. Tippetts, Inspector at Taiara, some gum-bearing branches of talk trees from 

 Sherkeila, and made cultures from small portions of these in the manner already j^^ij^dQ^ 

 described. It is of great interest to note that by far the largest nuiidier of colonies of the 

 obtained in this case also were those of the same bipolar bacteria isolated from caiacensic 



^ bacteria from 



hashdb branches. In this connection it is well to recall the fact that Greig Smith /■„//, trees 



