ELECTROLYTIC SOLUTIONS 35 



concentrated in the highly dissociated solution HgCl 2 , less 

 concentrated in the less ionized solution HgBr 2 , and exceed- 

 ingly dilute in the HgCy 2 . which is hardly ionized at all. 



What is true of the bactericidal action of the salts of 

 mercury is equally true of their therapeutic effect. It is a great 

 mistake to estimate the medicinal activity of a solution of a 

 salt of mercury, or indeed of any electrolytic solution, simply 

 by its degree of molecular concentration. The important 

 point is the degree of dissociation, which is the only true 

 measure of its activity. In the intramuscular injection of 

 mercury salts it is by no means a matter of indifference what 

 salt we employ. A salt should be used such as the bichloride 

 or the biniodide, which is easily dissociated. Other salts are 

 often employed because they occasion less pain at the site of 

 injection; hut the pain is a sign of the degree of activity of 

 the preparation. The pain, it is true, may he avoided bv 

 using a salt which is less easily dissociated, or in which the 

 mercury is bound up in a complex ion, but bv so doing we 

 diminish the efficacy of the remedy. It is moreover quite easy 

 to diminish, or even entirely to suppress, the pain, by usino- a 

 very dilute solution of an active ionized salt. A one-half per 

 cent, or even one-quarter per cent, solution of the bichloride 

 or biniodide of mercury may be injected very slowly in 

 sufficient quantity without producing the slightest discomfort. 

 Local action depends entirely on ionic concentration. One 

 drop of pure sulphuric acid will destroy the skin, whereas the 

 same amount if diluted in a tumblerful of water will furnish 

 a refreshing drink. 



