PHYSIOLOGICAL EFFECT OF IONS 97 



and the precipitate redissolves when the mixture is 

 diluted. In other words, the action is reversible. 

 Certain laws govern these reactions. As already 

 shown, the effect of the salt is the algebraical sum of 

 the effects of its individual ions. Anions and cations 

 antagonise one another ; cations precipitate, anions 

 inhibit the precipitation * in proportion to their 

 power. 



All cations have certain physiological characters 

 in common. They precipitate protein. They more 

 or less increase the irritability of muscle and nerve ; 

 they excite intestinal activity and increase the blood 

 pressure. 



The anions have a solvent action on protein, or, 

 to speak more correctly, they inhibit the action of 

 cations in general. The physiological effect of the 

 anions and their solvent action upon proteins in- 

 creases through the scale, from sulphate to sulpho- 

 cyanate. The sulphates, citrates and tartrates are 

 protein-precipitators, because the anion is associated 

 with the over-balancing properties of the metallic 

 ions ; they are therefore cathartics. But in the 

 nitrates, bromides, iodides and sulphocyanates the 

 anion has the predominating influence, the charac- 

 teristic effect of which is sedative attended by a 

 decrease of blood pressure. 



The ions of salts of the alkaline earths and the 

 heavy metals have likewise been studied, and have 

 been shown to obey the above broad general rule, 

 although their action is attended by complicating 

 circumstances. 



It has long been recognised that there was a certain 



* Brit. Med. Jour., 1896, ii., 837. 



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