MEMBRANE CHANGES DURING STIMULATION 357 



finds that frogs' muscle gives off inorganic phosphate 

 to the medium during contraction but not during rest, 

 and he regards this fact as further evidence of an increase 

 of permeability during stimulation/ 



In nerve evidence of increased permeability during 



stimulation is seen in a characteristic decrease in the 



electrical polarizability of the tissue. When a current 



from a battery is passed by non-polarizable electrodes 



through any living tissue, a counter electromotive force 



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



is connected with a galvanometer (preferably through 



a double key which 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. Apparently 



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 battery 



currents flowing through a nerve underwent an increase 



when the nerve was stimulated; and the most probable^ 



» Embden, Berichte fiber d. ges. Physiol., II (1920), 159. 



^Cf. Hermann, "Das galvanische Verbal ten einer durchflossenen 

 Nervenstrecke wahrend der Erregung," Arch. ges. Physiol., VI (1872), 

 560; cf. also ihid.i X (1875), 215. 



