108 THE THEORY OF IONS 



the contents of the test-tube are allowed to stand 

 for a few days, the decolorised fluid gradually regains 

 its blue colour from a recombination of Cu and SO 4 

 ions.) Neutral salts have an extremely feeble power 

 of destruction over the bacteria. But the disin- 

 fecting power of nitrate, sulphate or acetate of Hg 

 in aqueous solution is increased by the addition of 

 a halogen compound. This clearly shows the asso- 

 ciation between certain metallic ions and anions. 



2. The acids, both inorganic and organic, have a 

 destructive effect upon the bacteria which is pro- 

 portionate to the concentration of H ions in the 

 solution. Oxidising agents, e.g. nitric, chloric, per- 

 manganic acids, have their power increased by 

 addition of a halogen acid, as HC1 to permanganic 

 acid. 



3. The alkaline salts of K, Na, Li and NH 4 in 

 solution were also destructive to the bacteria in 

 proportion to the concentration of OH ions. H ions 

 are more destructive to anthrax spores and staphy- 

 lococcus than OH ions in equal concentrations. 



The direct application of ions as a therapeutical 

 agent has been put to practical use. In a paper 

 read by Professor Stephane Leduc an account was 

 given of such a mode of application. The facility 

 of introducing electrolytic substances through the 

 skin or surface of a wound increases the power of 

 medicine. The knowledge that the electric current 

 provokes an exchange of contents between the con- 

 stituents of two different electrolytes or between 

 two different cells has been taken advantage of in 

 therapeutics. Such an interchange can take place 

 at the surface between the skin and the electrodes. 



