34 THE MECHANISM OF LIFE 



Since all chemical, toxic, and therapeutic actions are ionic, 



they are proportional to the degree of ionic concentration, i.e. 



to the number of ions in a given volume. The only point of 



importance, that which determines their activity, whether 



chemical or therapeutic, is the degree of ionization or dissocia- 



+ 

 tion. For example, all acids have the same cation H. Thev 



have all identical properties, but they differ widely in the 



intensity of their action. There are weak acids such as 



acetic acid, and strong acids like sulphuric acid. The 



stronger acids are those which are more thoroughly dissociated. 



+ 

 and in which the ion H is very concentrated ; whereas the 



+ 

 feeble acids are but slightly dissociated, so that the ion H is 



less concentrated. 



Paul and Krdnig have shown that the bactericidal action 

 of different salts also varies with their degree of dissociation, 

 i.e. with the concentration of the active ions. They made a 

 series of observations on the bactericidal action of various 

 salts of mercury, the bichloride, the bibromide, and the 

 bicvanide, on the spores of Bacillus anthracis. The following 

 results were obtained from a comparison of solutions con- 

 taining 1 gramme-molecule of the salt in (>!• litres of water. 

 W'itli the bichloride solution, after exposure to the solution 

 for twenty minutes, only 7 colonies of the bacillus were 

 developed. After exposure to a similar solution of the 

 bibromide the number of colonies was 34. The antiseptic 

 action of the bichloride was therefore five times as great as 

 that of the bibromide. The bicyanide of mercury, however, 

 even when four times as concentrated, permitted the growth 

 of an enormous number of colonies, showing that it had no 

 appreciable antiseptic action whatever. Nevertheless, the 

 proportion of Hg is the same in all the solutions, and if there 

 were any difference one would naturally expect that the 



ion Cy would be more toxic than CI or Br. The real 

 condition which varies in these solutions and determines their 

 activity is the degree of dissociation. The whole of the 



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 antiseptic property resides in the ion Ilg. This ion is very 



