236 BACTERIAL ORIGIN OF GUMS OF ARABIN GROUP, 



its utilisation. With regard to the sugars, mannose, arabinose, 

 and xylose I cannot speak with certainty, as I did not have them 

 in the laboratory when the experiments were made. In view of 

 the fact, however, that levulose produced so much slime experi- 

 mentally, and that it is the chief wandering sugar,* there is no 

 reason for supposing that the celluloses contribute to the smallest 

 extent in the nutrition of the organism, even if by some means 

 they should become hydrolysed. Maltose, the other wandering 

 sugar, has been shown to be active in producing gum. 



The ideas regarding the cellulose origin of the gum have 

 doubtless arisen in part from the occasional finding of the gum 

 in pockets in the trees. Lutzf found gum-reservoirs in the bark 

 and pericycle of acacia. These consisted of lacunae caused by the 

 enormous swelling and ultimate deliquescence of the cell walls. 

 It is extremely probable that the solution of the cell walls was 

 caused by micro-organisms other than the gum-forming bacteria. 

 The gum formed in the otherwise healthy vessels would naturally 

 flow into these cavities already formed by moulds, where it might 

 possibly increase in quantity. I have found gum in cavities in 

 the fruits of the almond and the peach, when it had undoubted!}^ 

 been formed in the stem and branches. It must also be remembered 

 that a semi-soluble gum might increase locally in some of the 

 vessels and rupture the tissues mechanically. This is very com- 

 monly observed in Eucalyptus trees, in which the semi-solid gum 

 kino is formed. I have never found soluble wattle-gum in pockets 

 which did not show evidence of grub habitation, and the pheno- 

 menon must be rare if it does occur. 



The depressing action of galactose and dextrose. — In writing this 

 part of the paper it occurred to me that galactose, one of the 

 most common hydrolytic products of many of the celluloses such 

 as the pectins and hemicelluloses, might not only be useless as a 

 source of gum, but might also hinder or prevent the utilisation of 

 other sugars by the bacterium. Dextrose might also be capable 

 of preventing the formation of gum from maltose. These points 



* Brown and Morris, Journ. Chem. 8oc. 1893, Trans. 674. 

 t Reynolds Green, Soluble Ferments, 98. 



