MEMBR.\NE CHANGES DURING STLMULATION 357 



finds that frogs' muscle gives olT inorganic phosphate 

 to the medium during contraction but not during rest, 

 and he regards this fact as further evidence of an increase 

 of permeabiHty during stimulation.' 



In nerve evidence of increased permeability during 

 stimulation is seen in a characteristic decrease in the 

 electrical polarizabiHty of the tissue. \\ hi-n a current 

 from a battery is passed by non-polarizable electrodes 

 through any living tissue, a counter electromoti\c force 

 is immediately set up in the tissue, so that when the latter 

 is connected with a galvanometer (preferably through 

 a double key w^hich simultaneously breaks the polarizing 

 circuit and opens the circuit through the galvanometer) 

 a temporary current is observed flowing in the reverse 

 direction. This current, the polarization current, has 

 its source within the tissue at the regions of entrance and 

 exit of the original or polarizing current. Apj^arently 

 the characteristically high resistance of living cells and 

 tissues to the electric current is largely or mainly a result 

 of this polarization, since the resistance to rapidly 

 alternating currents (which cause little or no polarization) 

 is found to be much less than to direct currents. The 

 indications are that the semi-permeable membranes of 

 the living cells are the chief seat of the polarization; 

 when semi-permeability is lost, as at death, polarizability 

 is greatly diminished or disappears. Some fifty years 

 ago Griinhagen and Hermann observed that batters- 

 currents flowing through a nerve underwent an increase 

 when the nerve was stimulated; and the most j^robable' 



^ Embden, Berichte iihcr d. ges. Physiol., II (1920), 159. 



' Cf . Hermann, "Das galvanische Vcrhaltcn cincr durch ' n 



Nervenstrecke wahrend der Erregung," Arch. ^f5. Physiol., \i v- , -;), 

 560; cf. also ibid., X (1875), 215- 



