452 STUDIES IN GENEKAL PHYSIOLOGY 



to twenty-four hours. They found that aqueous solutions 

 of HBr, HC1, HNO 3 , H 2 SO 4 , and KHSO 4 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 anioiis (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- 

 aleiit) or ^ 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 1o 

 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 HC1, 

 ^H 2 SO 4 , and HNO 3 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. 



