EFFECT OF ACIDS ON TYPHOID AND COLON BACILLI 263 



transfer to fresh beef infusion, and those which entirely succumbed 

 to the action of the toxic substances. The wide difference between 

 the concentration of acid producing, respectively, injury, inhibition, 

 and death was one of the most interesting results of these experiments. 

 As in Stevens' work, it was apparent that the fungi are extremely 

 resistant to disinfectants, and it was necessary to use somewhat 

 concentrated solutions, from 0.008 to 0.287 normal acid, for killing. 

 It is perhaps partly for this reason that, as the author says, "in this 

 study no new evidence has been adduced supporting the theory that 

 the chemical activities of a substance are due wholly or chiefly to the 

 ionized portion." On the other hand, it was held that "in the case 

 of several acids, ionization lessens the chemical activities toward 

 the substances involved in the life-processes of the plant." This 

 conclusion is based on calculations of the specific toxicity of each ion 

 and molecule, obtained by comparing the effects of different com- 

 pounds varying from each other in one element or group. Thus, hy- 

 drochloric acid in the solutions used was over 90 per cent dissocia- 

 ted and since experiments with the similarly dissociated chloride of 

 potassium showed this salt to be practically non-toxic, it is evident that 

 its action was due to the combined effect of the hydrogen ion and the 

 undissociated molecule. Nitric acid, dissociated in the same proportion 

 was much more toxic. Since hydrogen ions are equal in the two cases 

 and since the NO 3 ion is harmless, as shown by experiments with 

 neutral salts, the increased effect must be due to the undissociated 

 part of the molecule of nitric acid. Clark calculates that the toxic 

 value of one molecule of undissociated HNO 3 is 7.7 times that of an 

 ion of hydrogen, so that the acid actually loses nearly seven-eighths 

 of its disinfectant power by becoming ionized. 



The effect of sulphuric acid was about the same as that of hydro- 

 chloric ; since it is less dissociated, the author attributes an appreciable 

 influence to the anion, HSO 4 . Acetic acid, at the strength used, is 

 only 2 per cent dissociated, so that its high toxic effect is due to the 

 un-ionized molecule. 



The results obtained in this series of experiments with hydro- 

 cyanic acid are also interesting. Kronig and Paul (1897) found 

 this acid almost without effect on anthrax spores, while Kahlenberg 

 and True (1896), on the other hand, record very strong toxic action 



