96 THE THEORY OF IONS 



Ostwald was the first to discover, in this semi- 

 permeability for ions, the cause of the electrical 

 phenomena observed in cells. Pauli admits it as a 

 very probable explanation ; and Bernstein has 

 applied the same idea to muscle and nerve. " If 

 we imagine the surface of the muscle fibril to be 

 more permeable for positive ions than for the nega- 

 tive ions contained within the muscle, then the 

 muscle must carry a positive charge externally and 

 a negative charge within." Stimulation of the nerve 

 brings about the well-known phenomena of negative 

 variation by altering the permeability for ions ; and 

 Bernstein's experiments have shown that the 

 muscle current follows very accurately the laws 

 governing ionic concentration chains. " The current 

 of rest is due to the semi-permeability of the mem- 

 branes for ions ; and when the permeability of the 

 membrane is altered through some agency which pre- 

 cipitates protein or causes it to go into solution, we 

 get variations in the current of rest."* 



The two chief laws of protein precipitation hold 

 good for the physiological effects of ions. We have 

 seen that protein forms the point of attack of many 

 salts in the organism, and that by them a change in 

 state is produced. This change of state consists of 

 precipitation or solution, and frequently a coincident 

 alteration in the state of the energy associated with 

 the molecule. In the case of salts of the alkali 

 metals and magnesium precipitation does not occur 

 until a fairly high concentration has been reached ; 



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

 p. 150. 



