PHTSIOLOGT 43 



passage of ions this resistance may be overcome 

 under electric stress so that ions may be forced 

 through the surface of the protoplasm, although 

 they would not enter if the electric potential 

 were absent. In this case the measurement of 

 electrical conductivity would reveal changes in 

 resistance to the passage of ions brought about 

 by various conditions, but the passage of the 

 electric current would not mean that ions could 

 penetrate to an appreciable extent in the absence 

 of an applied potential. From this standpoint we 

 may say that the general conclusions derived 

 from electrical experiments would not be 

 changed except that the normal cell would not 

 be regarded as permeable to ions. The measure- 

 ment of changes in resistance to the passage of 

 ions brought about by abnormal conditions and 

 the conclusions drawn from these measurements 

 would still be valid. 



In the second place it is possible that the meas- 

 urements of conductivity do not indicate the 

 passage of ions through the protoplasm, as has 

 been supposed. If the cell acts as a condenser an 

 alternating current may pass without actual 



\^l LIBRARY 1? 



