THE PuHysioLoGicaL EFrrects oF Ions 479 
NO, and the SO, ion does not come into consideration. I 
shall return to this point as soon as I have made further 
experiments. 
Tt is self-evident, of course, that so close a relation as 
proportionality between the velocity of migration and the 
relative toxicity of the ions ts to be expected only in those 
tons which belong to the same narrow group; a group in 
which the remaining characteristics of the ions are almost 
identical and in which important differences exist only with 
reference to atomic weight and velocity of migration. What 
has been said thus far holds only for the members of the Li 
series or the Be series among themselves; it would be wrong 
to judge the relative toxicity of K and Ca on the basis of 
the velocities of migration of their ions, because in doing 
this new differences come into consideration; for example, 
the difference in their valencies. It would be entirely 
absurd to judge the toxicity of the alkaloids by the velocity 
of the ions. 
This further fact is to be considered in judging toxicity, 
that all our evidence is of a negative character—the cessa- 
tion of life or of individual functions, especially irritability. 
The most widely differing circumstances may, however, 
bring about this result. One poison may act by rendering 
impossible processes of oxidation (for example, HCN, 
according to Geppert); another may bring about molecular 
changes which influence the transformations of energy in 
the cell, etc. It is to be expected that different groups of 
poisons bring about their toxic effects in different ways. 
This is a further warning against a too sweeping generaliza- 
tion of the relation between velocity of migration and 
toxicity. We must finally not overlook the apparent ine- 
quality in the permeability of the protoplasm for different 
ions, a subject concerning which special experiments are yet 
to be made. 
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