the filtrate from the lead treatment was put through a strong cation 

 exchange colunnn to remove the lead, andithe unadsorbed portion, or 

 filtrate, was tested, there was no positive response (No„ 268), 

 When the pH of this material was adjusted from about 3 to near 

 neutral, there was attraction (No, 269). When a further portion of 

 the unadsorbed material from the cation exchange column was put 

 through a strong anion exchange column and the adsorbed (eluate) 

 and the unadsorbed (filtrate) portions tested, there was no response 

 to either one (Nos, 26l and 262); the pH was unknown, but was pro- 

 bably basic. In a repeat experiment with the unadsorbed material 

 from the cation exchange column, adjustment to pH 7 gave a response 

 (No. 272), but adjustment to pH 2 gave no response (No. 277), There 

 was the possibility that loss of attraction was related to pH, 



In another series of experiments designed to check the 

 stage at which loss occurred and the effect of strong and weak ex- 

 changers, bigeye flesh after extraction with alcohol was again treat- 

 ed with lead acetate, filtered, treated with sodium chloride (fig, 13), 

 and divided into aliquots such that each test contained the treated ex- 

 tract from 400 g„ of flesh. One portion gave an excellent response 

 (No, 273) even after heating (see above), A second portion was 

 passed through a weakly acidic (Duolite C-3) cation exchanger and 

 the filtrate was tested, with a weak positive response (No, 278). 

 A third portion was passed through a strongly acidic (Amber lite 

 IR~120) cation exchanger and the filtrate was tested, with negative 

 results (No„ 274), Fourth and fifth portions were treated as above, 

 but the filtrate from the strong cation exchanger was passed through 

 a strongly basic (Amberlite IRA-400) anion exchanger (No, 275) and 

 through a weakly basic (Duolite A- 3) anion exchcinger (No, 276), and 

 the eluates tested, in each case with negative results. The only 

 noticeable reaction with materials fractionated with ion exchangers 

 was with the filtrate from the wecikly acidic column. Again, the neg- 

 ative results may have been due to the unresponsive condition of the 

 fish (although they reacted well in No. 273) or to the rather extreme 

 changes in pH which occurred in passage through the ion exchangers 

 --from about 7 to 3 with the cation exchangers and from about 3 to 

 12 with the anion exchangers. 



Another series, designed to check the stage at which 

 loss of the attractive substance occurred and the effect of pH, is 

 depicted in figure 14. Yellowfin flesh was extracted with alcohol, 

 the filtrate was acidified with hydrochloric acid to precipitate the 

 lead as lead chloride (rather than as sodium chloride, as before), 

 and filtered. One portion of the filtrate gave a good reaction when 

 tested (No, 280). A second portion of the filtrate was evaporated 

 to dryness over a water bath and dissolved in absolute ethyl alcohol, 



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