56 ROPINESS IX WATTLE BARK INFUSIONS 



contact for varying times, the infusions were filtered. Tlie following were the 

 Specific Gravities of the extracts : — 15 minutes, 1.010 ; 30 minutes, 1.013 ; 1 hour, 

 1.016; 2 hours, 1.020; 3 hours, 1.024; 4 hours, 1.027; 5 hours, 1.029; 1 day, 

 1.048; 3 days, 1.052. The infusions were portioned into tubes and seeded with 

 phases of the bacteria. 



Phase Al: no ropiness in any of the extracts. 

 A2: ropiness in all up to three hours. 

 B2: ropiness in all up to 24 hours. 



The experiment was repeated with new extracts i\\> to ti\e hours. 

 Phase Al : no ro]>iness in any of the extracts . 

 A2 : ropiness in al! extracts. 

 B2 : ropiness in all extracts . 



From the earlier tests with bark extract, it appeared pi'obable that tannin 

 when present in excess will prohibit the formation of the ropy substance. But 

 we are in doubt as to just hnw much will constitute an excess. Tannic acid 

 seemed to act differently t'nnn tlie tannin in bark extract, and it is possil)le that 

 ropiness occui's when there is a balance between the tannins and non-tannins of 

 the extracts. Several experiments were made with the idea of feeling the way 

 in this direction. 



A quantity of bark was infused for two days at 28° with twice the weight of 

 water. The infusion had a Sp. G. of 1.053. Portions were seeded with the 

 various phases of the bacteria and in no case was ropiness obtained. The extract 

 was probably too rich in tannin to permit the formation of the slime. It was 

 then jn'ogressively diluted down to one-tenth the strength and seeded with phases 

 A2 and B2. No ropiness became apparent. Bearing in mind the earlier ex- 

 periment with the tamed infusions of bark, in which the live hours' infusion having 

 a Sp. G. of 1.029 became ropy, it seems that this longer infusion, after dilution 

 to an approximate Sp. G. of 1,005, failed to produce ropiness because the tan- 

 nins overwhelmed tlie activity of the nutrients. 



In another experiment bark was treated for two hours with twice its weight 

 of water and filtered. A i|uantity of water equal to that removed was added 

 to the residual bark and allowed to remain in contact for 22 hours. The tivo 

 infusions were callei 

 of solids and 0.232 



The two infusions were mixed in descending and ascending proportions from 5 

 to and from to 5 and seeded with A2 and B2. The tests witli B2 did not 

 become ropy. 



Table ii. — Medium and Stronu- Infusion of Hark. 



