266 GENERAL PHYSIOLOGY 



since the brilliant work of Arrhenius led to the great de- 

 velopment of this science, in all chemical processes a disturbance 

 of electric equilibrium takes place. In every chemical decom- 

 position positively and negatively electric atoms or groups of 

 atoms appear. If similar chemical processes take place at all 

 points of a physical system and to the same extent, no current 

 can be led off from it, for no tension exists between the leading- 

 off points, because both positive and negative groups of atoms 

 arise in equal quantity (Fig. 119, 2). But if in the system, such 

 as a liquid mass, different kinds of chemical transformations, 

 spatially separated, go on, so that there appear at one point 

 a larger number of groups of atoms positively charged, and at 

 another point a larger number negatively charged, an electric 

 tension develops between these two points ; and, so long as the 

 processes continue, a galvanic current can be led off from the 



/ // 



Pig. 119. — Schematic. /. A drop of liquid in whicli the chemical processes are alike at all points 

 is without a current. //. A drop of liquid in which at two different points chemical pro- 

 cesses of different kinds occur gives a cun-ent. The large circle is the drop 'of liquid, the 

 small one the multiplier with the magnetic needle ; the two are united by wires. 



points to the outside (Fig. 119, II). The conditions under which 

 a galvanic current can appear may be expressed, therefore, 

 as follows : A current can be led off to the outside from a physical 

 system when chemical processes take place in it that produce 

 differences in the electric charge at the two leading-ofif points. 



This proposition is valid for living as well as for lifeless 

 substance. The living substance of a cell is a drop of liquid 

 in which complex chemical transformations continually take place. 

 If these be alike at all points of the cell, no current can be led 

 off (Fig. 120, I); if, however, they be qualitatively or quanti- 

 tatively different at two different poles, so that differences in the 

 electric charge appear, a tension between the two poles results ; 

 and if these could be joined together by a conductor, a current 

 would be obtained in the closed circuit. Naturally, this experi- 

 ment cannot be performed upon a single cell on account of the 



