42 



salt, although a much smaller one in general than have the cathions. 

 Furthermore, these vieAvs are in harmony with Loeb's idea that SO4 

 ions are more toxic than CI ions, because thej tend to precipitate 

 calcium from its proteid compounds. 



In other cases, however, addition of a salt which furnishes new 

 anions, bat not new cathions, to the mixture is effective in raising the 

 endurable limit of concentration for the more toxic salt. A striking 

 case is the elevation of the limit for magnesium sulphate eight times 

 by the addition of magnesium carbonate. Here it would appear that 

 the HCO3 anions alone can be the effective agenc}^ Sodium sulphate 

 slightly raises the limit of sodium carbonate, and a relatively unim- 

 portant increase of the -concentration of a calcium chloride solution 

 in which lupine roots can survive is obtained by addition of calcium 

 sulphate. But in these last two cases the eft'ect is so small as to be 

 almost negligible, and is perhaps entirely attributable to the forcing 

 back of the dissociation of the more toxic salt rather than to any 

 direct lAysiological action of the new anions. 



The superior efficacy of cathions over anions in neutralizing the 

 toxic effect of other cathions is illustrated by the discovery that 

 sodium is equally effective as an antidote to magnesium chloride, 

 whether it be added as sulphate (Na2S04) or as chloride (NaCl).^ A 

 much more striking illustration is afforded by the fact that calcium, 

 when added to a solution of magnesium sulphate or of sodium sul- 

 phate, is very much more ef&cacious when furnished as the relatively 

 insoluble sulphate than as the readily soluble chloride. In other 

 words, the presence of chlorine anions actually hinders the full exer- 

 tion of the ph3^siological effect of calcium cathions, unless we are to 

 believe that the superior efficacy of calcium sulphate is due merely to 

 its greater influence in retarding the dissociation of the sulphates of 

 magnesium and of sodium. 



If we turn now to the effect of mixtures in which two kinds of 

 cathions are present we find that these are almost invariably much 

 less poisonous than is the pure solution of the more toxic salt. Even 

 the addition of a sodium salt (sulphate or chloride) to one of magne- 

 sium (sulphate or chloride) raises the limit of endurance for the latter 

 three to six times. Still more remarkable is the effect of magnesium 

 carbonate as an antidote to salts of sodium (carbonate, sulphate, 

 chloride), raising their limits two to four times. But these effects are 

 trivial as compared with the extraordinary ef&cacj^ of calcium in 

 counteracting the toxic effects of other bases (magnesium, sodium). 



Even when added as the but slightly soluble carbonate, calcium 

 raises the limit of magnesium sulphate and of magnesium chloride 

 sixteen times, of sodium sulphate more than five times, and of sodium 



^ On the other hand, sodium chloride is twice as effective as sodium sulphate in 

 neutralizing magnesium sulphate. 



