A. T. CAMERON AND M. S. HOLLENBERG 421 



for the lesser iodide is less toxic. This sudden decrease in degree of 

 toxicity with greater dilution seems to be in agreement with the non- 

 observance of distinct toxic effects after administration of small 

 doses of iodide to mammals. There would appear to be a similar 

 abnormal decrease for still smaller iodate concentrations, as contrasted 

 with nitrate-chloride mixtures (Fig. 2). Nevertheless, even very- 

 slight traces of any of the foreign ions that we have tested exhibit 

 a distinct toxicity, when compared with pure chloride-Locke solution. 

 For Locke solutions in which more then 5 per cent of chloride is 

 replaced by the corresponding molecular concentration of the foreign 

 ion, the toxicity is in descending order 



F > IO3 > I > NO3 > CIO3 > Br > CI 



This is in agreement with the effectiveness in producing rhythmic 

 contractions in muscle (Loeb); the inverse order is that found by 

 Biedermann for effectiveness as coenzymes of amylases. 

 When less than 2 per cent of the chloride is replaced the order is 



IO3 > NO3 > I > Br > CI 



These results can almost certainly be considered to hold for body 

 fluids circulating normally and containing these foreign ions. 



The much greater relative toxicity of fluoride solution under all 

 conditions is in agreement with the marked biochemical differences 

 of fluoride and the other halide ions. 



m/7.8 chlorate-Locke solution produced a regular series of rhythmic 

 contractions (about 35 per minute) in muscle, m/7.8 iodide-Locke 

 solution produced a similar effect; the rate was somewhat faster. 

 Fluoride produced a continuous fibrillation. The chlorate and iodide 

 effects were not observed with muscle of curarized frogs, though the 

 fluoride fibrillation persisted. No such effects were observed with 

 the other anions studied. 



This research fonns part of a series relating to the biochemistry 

 of iodine. Part of the expenses were defrayed by a grant from The 

 Chemical Society (of London) to whom wo tender our thanks. 



