Effect of Acids on Typhoid and Colon Bacilli 259 



then by the addition of potassium hyposulphite to permit fermenta- 

 tion without precipitating any of the mercury, simply by the 

 formation of the differently dissociated double salt. 



Scheurlen and Spiro (1897) confirmed the conclusions of Dreser 

 as to the correlation between dissociation and disinfectant action 

 among the mercury salts, and extended them to cover certain com- 

 pounds of iron. At the same time they maintained that in other 

 cases (the ethylchlorid and ethylsulphate of mercury) strong disin- 

 fectant action was apparently due, not to free ions, but to the 

 undissociated molecule. 



A number of phenomena which had long been empirically familiar 

 in bacteriology found an easy explanation on the electrolytic theor}' 

 of disinfection. The effect of temperature in increasing the activity 

 of disinfectants, for example, had been pointed out by Koch (18S1), 

 and later by Behring (iSgo) and Hejder (1892), and many others. 

 It was at once obvious that this might be due in some cases to the 

 increased dissociation at high temperatures. It would be well worth 

 while today to see how far the increased activity of disinfectant runs 

 quantitatively parallel to its dissociation. Again, Minervini (1898), 

 and other investigators, have shown that various antiseptic agents 

 (carbolic acid, chromic acid, mercuric chloride, and silver nitrate 

 in Minervini's experiments) are much less active in alcoholic than in 

 aqueous solutions. This fact, too, is easily explicable as due to the 

 diminished dissociation in such solvents. 



The relation between dissociation and toxicity was put upon a 

 sound quantitative basis by the work of Kronig and Paul, first pub- 

 lished in 1896 (Paul and Kronig, 1896), and in fuller detail in 

 the next year (Kronig and Paul, 1897). These authors carried out 

 an elaborate series of experiments on the disinfectant action of various 

 salts, bases, and acids in the light of the new conclusions of physical 

 chemistry. The details of the investigation were arranged with the 

 greatest care in order to secure comparable results. Spores of Bacillus 

 anthracis and vegetative cells of Micrococcus aureus were used, dried 

 on Bohemian garnets. By using a definite number of garnets of a 

 certain size shaken up with a suspension of an agar culture, after 

 filtering through paper, and carefully drying, it was found possible to 

 expose approximately the same number of cells in each experiment. 



