THEORY OF DISINFECTION 757 



preventing or inhibiting the development of bacteria, are 

 not necessarily germicidal. 



Many deodorants act largely mechanically, and although 

 often not germicidal, and hence not ideal disinfectants.; are 

 of some value in preventing the deleterious and depress- 

 ing effects of the emanations from decomposing organic 

 matter. Such are charcoal, ashes, dry mould, and peat 

 (peat has also a germicidal action). Other deodorants, 

 such as quicklime and chloride of lime, act chemically. 



The principal germicides and antiseptics are the halogen 

 elements, the mineral acids, a large number of metallic 

 salts, phenol and many coal-tar derivatives, and various 

 organic bodies and essential oils. 



Theory of chemical disinfection. The theory of chemical 

 disinfection is not yet fully understood. It is probable, 

 as suggested by Paul and Kronig, that the degree of 

 ionisation of a solution may have an important bearing on 

 its disinfecting efficiency. 



Paul and Kronig l made a number of experiments on 

 the M . pyogenes, and spores of anthrax, with a view of 

 determining the effects of various acids, bases, oxidising 

 agents, and metallic salts on bacteria. The salts of 

 mercury, gold and silver exert a marked germicidal 

 action, strongest in the case of mercury, while the platinum 

 salts are almost inactive. The efficiency of mercuric 

 chloride is markedly lessened by the presence of sodium 

 chloride or other chlorides. Of the oxidising agents, 

 nitric, chromic, chloric, and permanganic acids act in the 

 order stated ; chlorine has the most powerful action of 

 the halogens. Phenol acts better in a 5 per cent, solution 

 than in higher concentrations, and the efficiency is in- 

 creased by the addition of sodium chloride, but diminished 

 by the presence of alcohol, and under the most favourable 

 conditions it is not such a powerful germicide as mercuric 



1 Zeitschr. f. physikal. Chem., 1896, xxi, p. 414. 



