BY R. GREIG-SMITH. 



67 



noiinced ropiness with ((uantities of tannic acid up to 0.4 % and a slight ropiuoss 

 with 0.7%. On the 4tli and 9th days these contained a pure culture of B2. 



The experiment was repeated a fortnight later with a similarly prepared in- 

 fusion. It had a Sp. G. 1.023 at 21° and an acidity of +24° by Procter's 

 lime water test. A similar infusion made on the following- day at 21° had a Sp. Gr. 

 1.022. -|-22.5° by Procter's test and -|-7° to methyl-red. Procter's test seems to 

 indicate the acids other than tannic acid that are present, for tannic acid- in pur-i 

 solution is precipitated at once by the lime water. 



Table ix. — Bark infusion with Tannic Acid. 



AVe see that an infusion of wattle-bark having a Sp. G. of 1.023 is immune 

 to the phase Al and that the derived phase A2 is able to develop ropiness, but the 

 addition of a small quantity of tannic acid, 0.2 %, prevents the formation. A 

 .smaller quantity, 0.1 %, permits a slight ropiness to appear. Phase B2 is more 

 tolerant of tannic acid, the limiting amount of which lies between 0.4 % and 0.0 %. 



Larger amounts of tannic acid were used but these are omitted from the table. 

 The i^ortions containing- over 0.4 % showed cobwebby growths, doubtless consist- 

 ing of bacteria bound up with coagulated slime. 



As a bark liquor o'f Sp. G. 1.010 may contain 1.8 % of tannin and 0.5 % 

 to 0.7 % of e.xtractives (non-tannins), the infusion of Sp. G. 1.023 presumably 

 contained about 4 % of tannin. The experiments show that this reputed 4 % of 

 tannin had much the same effect in prohibiting- the formation of ropiness as 1.75 % 

 of pure tannic acid. 



A stronger infusion of wattle bark of Sp. G. 1.054 wh^n seeded with A2 

 and B2 did not develop ropiness, even when the infusion was streng:thened by 

 quantities of dextrose and ammonium sulphate rising- to 5% and 0.5% respect- 

 ively. This seems to indicate that the tannins are the iiroliibiting- agents, and when 

 they are present in sufficient amount, Ijacterial nutrients have little influence in 

 assisting- the development of ropiness . 



A few tests had been made in the earlier part of the research to see if the 

 quantity of sugar in synthetic media had any effect in increasing the formation ut 

 ropiness, Imt it was not definitely shown that the amount of ropiness was in-o- 

 portional to the sugar in the medium, or that any advantage would be gained by 

 increasing the quantity over the usual 2 %. It seemed possible, however, that 

 sugar miglit to some extent modify the action of tannic acid, and that an increase 



