452 STUDIES IN GENERAL PHYSIOLOGY 
to twenty-four hours. They found that aqueous solutions 
of HBr, HCl, HNO,, H,SO,, and KHSO, which contained 
the same number of hydrogen ions in the unit volume were 
equally toxic; that, in other words, the toxic exect of these 
acids was determined solely by the hydrogen ions and not 
by the anions (nor by the molecules which, at the dilution 
employed, were all dissociated electrolytically). They could 
show in a similar way that the toxic effects of salt solutions 
employed in their observations were determined by their ions. 
I do not doubt the correctness of the principal conclusions 
of Kahlenberg and True. But I do not believe that these 
authors determined the limit of the poisonous action sharply 
enough. They found, for example, that the acids mentioned 
above were no longer toxic when 1 gram-molecule (in univ- 
alent) or 4 gram-molecule (in bivalent acids) was dissolved 
in 6,400 liters, but that when this amount was dissolved 
in 3,200 liters they were poisonous; that is to say, the 
germinating lupines cease to grow in them after from sixteen 
to twenty-four hours. More accurate determinations than 
this they did not make. If someone should say that the 
acids studied in these experiments acted, not according to 
the number of hydrogen ions, but according to the percentage 
of acid, such a criticism could not be overcome by the figures 
of Kahlenberg and True. These concentrations for HCl, 
4H,SO,, and HNO, behaved, for example, as 36.5:49:63; 
they lie therefore between the values 1:2. Kahlenberg and 
True have chosen for these purposes a very unsatisfactory 
physiological reaction. The exact time at which growth 
ceases cannot be determined accurately; and when, in addi- 
tion, experiments must be continued through the night, the 
determination of the exact time becomes so uncertain that, 
according to my idea, the method is a questionable one for 
the quantitative determination of the toxicity of different 
solutions. 
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