120 PHYSICAL CHEMISTRY 



Bernstein's theory. Furthermore, it is the only theory that will 

 account for all of the facts. 



According to Bernstein, the striated muscle fiber or cell is 

 surrounded by a membrane or surface (called the plasma mem- 

 brane since it is the superficial layer of the protoplasm), which 

 is more permeable to the cation than to the anion of some elec- 

 trolyte more concentrated in the interior than on the exterior of 

 the muscle cell. The cations passing through the plasma mem- 

 brane leave the interior negative, and form a positive outer 

 stratum of an electric double layer thus formed at the surface of 

 the cell. Many attempts to determine the electrolyte have been 

 indecisive, but it seems probable that the cation in question is 

 the. hydrogen ion, in which case the cell surface must be rela- 

 tively impermeable to all anions. This assumption has the ad- 

 vantage that it avoids the necessity of difference in osmotic 

 pressure on the two sides of the membrane. A diagram of this 



+ +*■+ -K+ + ++ + + + +++ j. 



+ +*+ -K -t- + + + 



— _Q, _® _ _ + 



*ar - + - + - + - + - + -+- + -H 

 «-Q+ -+ +-+-+-+-+-+ 



^ + _ + _ + 2s + T-h + _ + _ + lj+ 



- - ~B - -B -I- - -"* . 



^0 + +"+ + +~+ + + +++ + + * 



% 



Fig. 28. Scheme showing the plasma membrane of a cell torn open at 

 one end and liberating the excess of anions. The + and — indicate the 

 charge of ions and the arrows the direction of diffusion. Only + ions 

 can come out through the intact plasma membrane and hence there is an 

 excess of — ions on the interior. The tear causes a negative charge to 

 appear at the surface and give rise to the current of injury. 



idea is shown in Fig. 28, representing a muscle cell with one end 

 cut off to produce the current of injury. The ( — ) signs are 

 anions that can escape only at the cut end. The current of injury 

 is caused by the escape of the anions at the cut surface. What 

 these anions may be is immaterial, but presumably they include 

 proteids with negative charges and anions of carbonic and lactic 

 acids produced in the muscle fiber. 



The acidity within the cell necessary to produce such an emf 

 as in muscle need be only that of a molecular solution of C0 2 . 



