PHARMACODYNAMICS OF SALTS AND DRUGS 95 



toxic action. For example, suppose it was attempted to classify them in 

 the order of their ionic weights. It will be seen that no parallelism 

 exists between toxic action and ionic weight, since we have nickel, atomic 

 weight 58, lead, atomic weight 200, hydrogen, atomic weight i, and 

 copper atomic weight 32, following each other closely. Furthermore, 

 attention may be called to the enormous difference in toxicity, exist- 

 ing between the same atom when carrying two different quantities of 

 potential energy. Ferrous iron has as an ion very little potential energy 

 compared with ferric iron, and it is enormously less poisonous than the 

 latter. 



It will be noticed also that in each of these cases certain metals 

 come out of their proper order of toxicity and potential. In the case 

 of Fundulus eggs, cadmium is considerably out of its proper place, 

 whereas it follows the rule in the case of diastase ; for diastase, lead is 

 quite out of its position ; for bromelin, the great exception is barium, 

 which is very toxic. The causes of these special and sporadic excep- 

 tions will be taken up later. 



TABLE 4 . 



MINIMUM FATAL DOSE AND IONIC POTENTIAL OF ANIONS. 

 (Eggs of Fundulus heterocliius.') 



If now we turn to the negative ions, or anions, a similar parallelism 

 is shown to exist between toxicity and potential energy content. Thus 

 chlorine is in all cases far less toxic than iodine, which has twice as 

 much potential energy. The oxalates and cyanides and sulphites are 

 the more toxic, the greater their available energy content. Unfortu- 

 nately, our knowledge of the potentials of the anions is less exact than 

 our knowledge of the potentials of the cations, so that it is impossible 

 to follow the correspondence in detail; but sufficient is shown to prove 

 that the same correspondence between toxicity and potential energy 

 exists here as in the cations. 



c) The quantitative relationship between ionic potential and the 

 minimum fatal dose. It was shown at the outset that the amount of 



