FROM THE SMALL INTESTINE 629 



the voltage required to separate its charge from it. This voltage 

 when measured will also give the solution tension of the element, 

 that is, the tendency of the element to go into (solution and 

 acquire a charge. Solution tension will therefore be the re- 

 ciprocal of ionic potential. In other words, the greater the 

 solution tension of an ion, the less will be the ionic potential ; 

 the electrical stability of the ion will be greater, and the physio- 

 logical action less. Now Ag has a much lower solution tension 

 than Na, therefore it possesses a greater ionic potential and a 

 more powerful depressant action. In this way Mathews explains 

 the fact that AgCl depresses nerve whilst NaCl stimulates it. 

 Similarly for any other salt we may lay down the general pro- 

 position that the more stable the anion the less is the stimulant 

 action of the salt, and the greater the electrical stability of the 

 cation the less is the depressant power of the salt. Mathews has 

 shown that the physiological action of an ion is modified also by 

 its velocity, weight and volume in such a way that the faster it 

 moves the more powerful it is, and the heavier it is the, less is its 

 power. But these points cannot be discussed here. Mathews has 

 summed up this part of the subject as follows : Ions are minute, 

 freely movable electrodes, of different voltages. The physiological 

 action of any ion depends upon (1) its concentration, (2) the sign 

 of its electrical charge, and (3) its electrical stability or ionic 

 potential. The physiological action of an ion is therefore de- 

 pendent on electrical state and stability, and is independent of 

 chemical composition except in so far as this may influence the 

 velocity and weight of the ion. The physiological action of a salt 

 depends upon the sum of the physiological actions of its com- 

 ponent ions. 



Thus far we have seen that chemical stimulation is electrical 

 and independent of the chemical composition of the ions which 

 cause it. But this does not exclude the possibility that ions 

 might have a chemical as well as an electrical action. And that 

 they had, was thought to be shown most clearly by a considera- 

 tion of the toxic and antitoxic actions of salts. Ringer made the 

 original discovery that the action of K salts on the heart could 

 be antagonised by Ca salts. His observations have been extended 

 by Loeb, MacCallum and others, for other salts and for other 

 tissues and cells. Further, it has been shown that salts may 

 antagonise the action of drugs other than salts. For instance, the 



