THERAPEUTIC STUDIES ON IONS. 85 



can be constructed to give a graphic survey of these 

 relations. Such precipitation curves suffer a great change 

 upon the addition of iodides or sulphocyanates. If the 

 ions of the heavy metals are present in a low concentra- 

 tion, the precipitation of the protein is prevented alto- 

 gether ; if present in larger amounts, the protein precipita- 

 tion is markedly increased. In the case of, living animals 

 only the former possibility, that of the presence of but 

 a low concentration of poisonous ions, comes into con- 

 sideration. The iodides and still more the sulphocyanates 

 do in fact act under these circumstances as substances 

 which favor the formation of readily soluble protein 

 compounds, through which an elimination of the heavy 

 metals is greatly aided. Conditions in the test-tube and 

 in the animal body are here, in the main, identical. 



The relation of the metals calcium, barium, and stron- 

 tium to the proteins is somewhat different, a fact of 

 interest because of the important role of the calcium 

 ions in physiological and pathological questions. These 

 metals stand in many ways between the alkali metals 

 and the true heavy metals. They have, in common with 

 the former, a high precipitation limit; with the latter, the 

 fact that the combination between protein and metal is a 

 firm one, and once produced continues even upon the ad- 

 dition of water to the solution. The power of depressing 

 most markedly the precipitation limit of the earthy metals 

 is possessed to a slight degree by the Br ion, in greater 

 degree by the I ion, and most powerfully by the sulpho- 

 cyanate ion. In the presence of sulphocyanate ions, 

 calcium, strontium, and barium chloride will precipitate 

 protein when present in simple normal solution and even 

 below this, while under ordinary circumstances the two 



