BIO-ELECrniC PHENOMENA 



153 



positi\e. The current, however, flows from the copper to the 

 zinc, outside the battery. The zinc is, therefore, said to form the 

 negative pole. Current of action. — When alterations of tension 

 or stress take place in a cell they are accompanied by alterations 

 in electric potential. The part under stress becomes as if injured, 

 i.e. electropositive or zincy to the normal or unstressed part. 

 This may be due to an increase in the permeability of the membrane 

 at the stressed part, so that the positive ion gains access to the 

 cell. The seat of stress does not, however, remain at its point of 



CAPILLAfiY ELfCTffpMETER. 



1^^ 



=-^VQ,= -:: 



■=-* 



" - -- 



km'mTOW.'.'.wmmwmm^'.'.'mft' 



ne.f(cuio'\ 



+ +▼ + + + + + + -!-▼+ + 



+++++++▼++ 



+ 

 + 

 + 

 + 

 + 

 - + 



+ H- + + + ++ + + + ++ + 

 RLSrill^ OKIfiTACT CCLL 



++++++++++ 



INJUKlb OR. COHTKfiCTING C£U.. 

 THE. SMOED PARJ U IHJUKP> 

 OR. 15 COHTRfiCTINQ 



Fig. 38. — To show the origin and method of measuring the current of action or of injury 

 in a living cell. In the resting cell (central figure) all points on the surface of the cell are at 

 the same potential. >;ote position of Hg in the capillary tube. Action or injury produces 

 contact with the interior of the cell at the part active or injured, so that a current Hows with 

 the effect shown. Compare with the zinc-copper galvanic cell. 



origin, but passes as a wave of increased stress over the whole cell 

 followed immediately by an electropositive wave (Fig. 43). 



MacDougal and Moravek (1927) have constructed a cell that 

 answers several of Sir Edward Sharpey-Schafer's requirements 

 (p. 150). Their cell membrane consisted of a Soxhlet thimble 

 (cellulose + calcium salts) impregnated with a solution of choles- 

 terol in lecithin, which mixture is incorporated in a hydrophilic 

 gel (gelatin-agar). Various mixtures, solutions, etc., may be put 

 inside the cell and the cell immersed in various solutions. For 

 example, when the cell contained 20 per cent, sugar solution, an 

 increasing endosmotic series in Na > K >> Ca is given, implying 

 decreasing permeability with this series of cations. Further 

 addition of any of these cations further decreases permeability. 

 The cell wall shows excellent buffering power (Chap. XXII, ) — i.e., 

 even when the hydrogen ion concentration of the external solution 

 varied as much as from pH 3-05 to ^H 8-2, the interior remained 



