THE DESTRUCTION OF BACTERIA 87 



protoplasm and exert a toxic action. Again, in other cases, a dif- 

 ference in tonicity between cell protoplasm and disinfectant may 

 tend to withdrawal of water from the bacterial cell and consequent 

 injury of the microorganism. 



Among the inorganic disinfectants the most important are the 

 metallic salts, acids, and bases, the halogens and their derivatives, 

 and certain oxidizing agents like peroxide of hydrogen and perman- 

 ganate of potassium. 



It has been shown by Scheuerlen and Spiro, 33 Kronig and Paul, 3 * 

 and others, that in the case of the salts, acids, and bases, there is 

 a distinct and demonstrable relationship between the disinfecting 

 power of these substances and their dissociation in solution. 



According to the theory of electrolytic dissociation, when bodies 

 of this class go into solution they are broken up or dissociated into 

 an electro-positive and an electro-negative ion. Thus, metallic salts 

 are broken up into the kation, or positive metal, and into the anion, 

 or negative acid radicle (AgN0 3 = Ag, + ion and N0 3 , -- ion). 

 In the case of the acids, ionization takes place into the hydrogen 

 ions and the acid radicles, while in the case of the bases the dissocia- 

 tion occurs into the metal, on the one hand, and the OH group on 

 the other. The degree of dissociation taking place depends upon 

 the nature of the substance in solution, its concentration, and the 

 nature of the solvent. Thus, in any such solution there appear three 

 substances, the undissociated compound as such, its electro-negative 

 ion, and its electro-positive ion, their relative concentrations depend- 

 ing upon an interrelationship calculable by definite laws. It goes 

 without saying, therefore, that any chemical or physical reaction, 

 taken part in by such a solution, may be participated in, not only 

 by the dissolved iindissociated residue as a whole, but by its separate 

 ions individually as well. In the case of many disinfectants, the 

 writers referred to above have been able to demonstrate a relation- 

 ship between the degree of dissociation and the bactericidal powers. 

 According to Kronig and Paul, double metallic salts, in which the 

 metal is a constituent of a complex ion and in which the concentration 

 of the dissociated metal-ions is consequently low, have very little 

 disinfecting power. Thus potassium-silver-cyanide, which is a com- 

 paratively weak disinfectant, dissociates into the kation K and the 



33 Scheuerlen und Spiro, Munch, med. Woch., 44, 1897. 

 84 Krdnig un<l Paul, Zeit. f . Hyg., xxv, 1897. 



