228 BACTERIAL ORIGIN OF GUMS OF ARABIX GROUP, 



obtained, although it would have perhaps been more striking 

 had only certain numbers been given, as, for example, the higher 

 of two duplicates upon the third day. Experiment No. 1 cannot 

 be compared with No. 2 because the experiments were made at a 

 time when the laboratory temperature differed considerably from 

 day to da}^; each experiment must be considered by itself. 



Considering the experiments broadly, it is clear that certain 

 tannins augment and that others diminish the yield of slime. 

 Purity appears to be a hindrance, from which it would appear that 

 the stimulative or the physical effect, whichever it be, is due to 

 the presence of an impurity. Tannin No. 3 arrived at the 

 laboratory in the same condition as the commercial lot with 

 which the other experiments were made; the passage through the 

 tropics had caused the powder or granules to fuse into hard 

 glistening dark lumps. They were probably the same. Nos. 1, 

 4 and 8 were fine buff-coloured powders, very similar in appear- 

 ance ; No. 10 was much the same, but coarser. Nos. 2 and 6 

 were granular and glistening, 2 being dark, 6 being light in colour. 

 No. 4 consisted of dull, light-coloured granules. Messrs. 

 Harrington Bros, informed me that Nos. 1, 2 and 3 were prepared 

 specially for dyers and were manufactured from sumach; Nos. 6, 

 7 and 8 for printers, and No. 10 (pure) were obtained from gall 

 nuts. 



At present I cannot explain the difference between 1, 2, 3 and 

 6, 7, 8, but it would seem that Bact. acacice can enable the 

 tannins to be separated into two groups. One group considerably 

 augments the yield of slime and includes the sumach tannins 

 used by dyers. The other group either is inactive or diminishes 

 the yield. It contains the kinds obtained from gall nuts, such as 

 the purer forms and those used by calico printers. Since Bact. 

 acacice can distinguish between certain of the tannins it is pos- 

 sible that it might form the basis of a biological method for their 

 recognition. 



The experiment with glycerine shows that this substance 

 assists the tannin, so that by their combined use any depressing 

 effect of one is annulled if sufficient time be allowed for the 

 complete growth of the slime. 



