74 BIOLOGY AND TECHNIQUE 



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

 oxidizing agents like peroxide of hydrogen and permanganate of potas- 

 sium. 



It has been shown by Scheuerlen and Spiro,' Kronig and Paul,^ 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 (AgNOg = Ag, 4- ion and NO3,— 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 dissociation occurs into 

 the metal, on the one hand, and the OH group on the other. The de- 

 gree of dissociation taking place depends upon the nature of the sub- 

 stance in solution, its concentration, and the nature of the solvent. 

 Thus, in any such solution there appear three substances, the undis- 

 sociated compound as such, its electro-negative ion, and its electro- 

 positive ion, their relative concentrations depending upon an interrela- 

 tionship 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 undissociated residue 

 as a whole, but by its separate ions individually as weU. In the case of 

 many disinfectants, the writers referred to above have been able to 

 demonstrate a relationship 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 comparatively weak disinfectant, dissociates into the kation K 

 and the complex anion Ag (GN) 2, this latter further dissociating to a very 

 slight degree only. The same writers conclude that the bactericidal 

 action of mercuric chloride and of halogen combinations with metals is 

 directly proportionate to the degree of dissociation. This considera- 

 tion, moreover, explains why aqueous solutions of such substances are 

 more active than are solutions in the alcohols or in ether, since it is well 



1 Scheuerlen und Spiro, Milnch. med. Wooh., 44, 1897. 



2 Kronig und Paul, Zeit. f. Hyg., xxv, 1897. 



