THE HEAVY METALS 99 



smallest doses without influencing metabolism. The 

 excretion of sulphocyanate is decreased when iodine 

 is taken, and is completely stopped when iodine is 

 produced ; under such circumstances no sulpho- 

 cyanate is found in the saliva. 



Another factor is the relation between the 

 effects of iodides or sulphocyanates and the 

 effects of salts of the heavy metals or alkaline 

 earths. " It has been definitely established through 

 exact observation and experiment, that the 

 iodides favour and bring about the excretion of 

 ions of the heavy metals, e.g. lead and mercury, in 

 cases of chronic intoxication. The explanation of 

 this fact which has long been known therapeutically, 

 has been sought in the formation of soluble albu- 

 minates which the iodides have been supposed to 

 bring about."* In fact, the iodides not only inhibit 

 the precipitation of protein by the metallic ion, but 

 they dissolve already existing precipitates. 



The heavy metals Pb, Zn, Hg, etc., coagulate 

 proteins even in the weakest concentration. There 

 is at first a rapid increase in the power of precipita- 

 tion with an increase in the concentration, but this 

 falls to zero as concentration goes on. Still further 

 concentration will cause a second precipitate, which 

 is very heavy and again soluble. But the precipi- 

 tating power of these metals suffers a great change 

 in presence of the anions such as iodide and sulpho- 

 cyanate. " If the ions of the metal are present in 

 a low concentration the precipitation of protein is 

 prevented altogether ; if present in larger amount the 



* Pauli's "Physical Chemistry in the Service of Medicine," 

 p. 84. 



72 



