ELECTRICAL CHANGES IN TISSUES 



645 



except a very temporary one. Unequal rate of diffusion from their place of 

 origin is the cause of this temporary electrical state. 



Suppose that the ions, newly produced, are free to diffuse. As we have seen 



FIG. 204. 



DIAGRAM OF CIRCUIT USED IN ' BSERVATIONS AND MEASUREMENTS OF CHANGES 

 IN DIFFERENCE OF ELECTRICAL POTENTIAL. 



B, Half-discharged accumulator cell, sending constant current through the stretched wire P, from which various 

 fractions can be led off by the sliding contact. 



K, Key for this circuit. 



R, Reverser, or commutator, by which the direction of the electromotive force led off can be changed without 

 changing the connections of the battery. 



S, Standard cell, which can be put into the circuit by the key W. 



M, Spring key for momentary closure, in order not to take off any appreciable current from the standard cell. 



O, The instrument used for detecting the electrical disturbance, electrometer or galvanometer. It can be short- 

 circuited by turning the switch D into the position opposite to that shown. When the capillary electro- 

 meter is used, a key should be introduced which keeps the instrument always short-circuited except when 

 in use. 



E, Nonpolarisable electrodes, leading off from points on the muscle T. 



E and T together represent any source of potential difference, such as those in tissues or in a hydrogen electrode. 



(page 158), the more rapidly moving ions will proceed in advance of the slower ones, 

 giving rise to a potential difference in proportion to the difference of their 

 velocities. In the small spaces within cells through which this diffusion takes 

 place, any difference of concentration will equalise itself very rapidly, and, except 

 in the case of the hydrogen and hydroxyl ions, can never give rise to any 

 considerable electromotive force. The factor expressing this occurs in the formula 



