182 GEOKGE RALPH MINES. 



alteration and the length of thiae it was allowed to act — but if the 

 membrane is treated with a faintly alkaline solution the effect of 

 the acid or the trivalent ion is removed at once. 



The parallel with the action of these same agencies on the heart is 

 sufficiently striking. And the parallel does not end here. 



Seeking to test further whether this potent action on the heart is 

 indeed a general property of trivalent ions, I employed solutions of 

 certain cobaltammines which yield complex trivalent ions in neutral 

 solution. The compound used most frequently was luteo-cobalt chloride 

 [Co(NH;,)6]Cl3, which yields the ion [Co(NH3)o] • ' '. Through the 

 generosity of Prof. Werner I was able to test also four other complex 

 trivalent ions. All agreed in showing very much weaker action on the 

 heart than the rare earth solutions. A concentration of the complex 

 ion of the order of 1000 times as great as of the simple ion is needed to 

 stop the perfused heart. A similar difference is shown in the action 

 of these ions on the gelatine membrane. Even large concentrations 

 have only a slight effect on the ionic permeability of a membrane of 

 this type. 



The influence of hydrogen ion eoncentration and of trivalent kations on 

 the heart is jmrcdleled in detail hy the action of these ions on the ionic i^er- 

 meahility of certain artificial membranes. 



The ionic permeability of a membrane can be shown, both theoretic- 

 ally and experimentally, to depend— other things being equal — on the 

 electric charge of the membrane. 



Now it can be demonstrated by a variety of methods that most 

 membranes in water, or in a solution like our " neutral saline," possess 

 a negative charge. This charge is reversed with great ease by acid or 

 by the rare earth solution. This can easily be shown, for instance, by 

 the use of dyes, which are themselves charged colloids. A piece of 

 gelatine soaked in " neutral saline " stains very feebly with eosin, 

 strongly witli methylene blue. But after treatment with acid or 

 rare earth it takes up eosin with great avidity and is hardly tinged 

 by methylene blue. Eosin consists of negatively charged particles, 

 methylene blue of positively charged particles. If the membrane has 

 a negative charge it can hold the latter, if a positive charge, the former. 

 This method also reveals the fact that the complex trivalent ions are 

 much less potent than the simple trivalent ions in altering the charge 

 of the gelatine membrane. 



In these membranes we^ are, of course, dealing with substances in 

 the colloidal state. If instead of using extended sheets of material we 

 turn our attention to colloidal solutions, where one phase of the 

 colloidal system consists of discrete particles floating freely in the 



