86 : BOTANICAL GAZETTE [ aucust 
If a very dilute solution of sodium chloride differs from a 
dilute solution of hydrochloric acid only in that the former con- 
tains Na ions and the latter H ions, then the poisonous action of 
the latter is plainly due to the H ions present. In like manner 
comparing a very dilute solution of sodium nitrate with a similar 
solution of nitric acid, the poisonous nature of the latter would 
‘be due to the H ions present. In general, if the solution is suf- 
ficiently dilute so that the acid is completely dissociated and the 
acid radical is of such a nature that at this concentration its 
ions have practically no poisonous action, the toxic value of the 
acid solution is due only to the H ions present. Now strong 
acids are highly dissociated in aqueous solutions, thus rendering 
these relatively rich in H ions. Weaker acids are not as strongly 
dissociated, their solutions contain less H ions, and are comnse- 
quently less active. It must be borne in mind that the salt 
remaining undissociated is present in the solution as well as the 
ions. That these undissociated remainders and the anions of 
the acid radical also exert an effect is not to be denied, but im 
many cases, such as that of the Cl ions in hydrochloric acid 
solutions, the action is practically mi/ at the strength at which 
hydrochloric acid is still effective, since a solution of common 
salt containing as many Cl ions as the hydrochloric acid solution 
in question is ineffective. The same reasoning may be applied 
to nitrate of sodium and nitric acid, also to sodium hydroxide 
and common salt. In the latter case the solutions differ from 
each other in that the former contains OH ions, whereas the 
latter contains Cl ions. All solutions of bases (lyes) contaill : 
OH ions and their toxic action is due to these alone, provide i 
that the metal or radical forming the cathion is itself harmless 
at the concentration used. Thus it is evident that H ions and 
OH ions have toxic properties. That it is the ionic condition 
which brings this about is shown by the fact that in the case fs 
water where we have these constituents in practically an undis- 
sociated state, there is no toxic action. 
The poisonous property of a very dilute solution is then due 
to the ions it contains, and if at the particular concentration ae 
