HOBER: THE MEMBRANE THEORY 385 



sides chloride, there are in the axoplasm small concentrations of phos- 

 phate, sulfate, and lactate, but rather large amounts of organic anions of 

 low mobility, possibly the anions of amino acids. These conditions are 

 roughly reproduced in model experiments of Labes^^ and Ebbecke.^^ A 

 membrane core-conductor is formed by a collodion tube, with pores wide 

 enough to allow cations and anions to pass the wall. The tube is filled 

 with a solution of potassium phosphate and is packed in gauze which has 

 been wetted with a solution of sodium chloride. One electrode is placed 

 inside, another outside. If direct current passes the membrane, a smaller 

 resistance is encountered, when the current goes from within outwards, 

 than when it goes in the opposite direction. The reason is that, with the 

 outgoing current, the faster potassium inside and chloride outside are 

 swept into the membrane and travel, there, with greater velocity than so- 

 dium outside and phosphate inside, being driven by an ingoing 

 current. If, instead of collodium, hydrophilic and negatively charged 

 colloids are the membrane constituents, as they actually are under most 

 physiological conditions, then additional swelling and increasing dis- 

 persion occur at the cathode, as well as shrinking at the anode. Con- 

 sequently, the polarizability of the membrane falls at the cathode and 

 rises at the anode. Swelling causes in natural objects, such as muscle 

 and nerve, greater excitability at the cathode, but as the current 

 strength rises more and more, the higher excitability turns over to 

 inexcitability, or, in other words, to cathodic depression. More spe- 

 cifically, according to Blinks,^* the membrane polarization of a giant 

 cell of the fresh water alga Nitella, comparable to nerve or muscle with 

 its thread-like shape, drops down to zero, if exposed to the swelling effect 

 of potassium chloride in sufficiently high concentration, and the cell 

 does not respond any more to otherwise effective stimuli. How- 

 ever, by applying, locally, an anode of rising strength to the depolarized 

 Nitella cell, above a certain threshold value, the polarizability is re- 

 stored, and a normal action potential can be elicited upon stimulation. 

 Alternatively, with respect to cation antagonism, after excitability of 

 a nerve has been suppressed by calcium, this stiffening effect is can- 

 celled by the softening influence of a cathode, as shown by Woronzow," 

 and more recently by Guttman and Cole.^^ 



We turn, now, to the discussion of natural changes of ion permeability 

 during action. It has been accepted, for more than 40 years, that 

 depolarization, which is brought about by injury, compares essentially 

 to depolarization accompanying excitation, as indicated by the "nega- 

 tive variation" of du Bois-Reymond. The negativity wave, therefore, 

 is interpreted as a "breakdown of the membrane," by which the selec- 



