ELECTRICAL CHANGES IN TISSUES 



643 



another by a pendulum is frequently indispensable, and the most convenient way of doing this 

 is by the instrument described by Keith Lucas (1908, 2). 



10cm 



FIG. 202. CAPILLARY ELECTROMETER. Keith Lucas' pattern. End elevation. The 

 projecting microscope is supposed to be perpendicular to the plane of the paper. 



A, Heavy base. 



R, Casting on levelling screws Q. 



S, Screw for lateral adjustment. 



T and U, Upright rods, supporting ebonite plate V. 



X, Screw for vertical adjustment. 



Y, Screw for moving capillary at right angles to plane of paper. 



/, Block of ebonite, attached to R by bolts // and ///. 



/ K, Notch cut out to contain acid, closed at the sides by cover-glasses K, cemented by hot 



gutta-percha. 

 V and VI, Two holes, meeting at the bottom, containing mercury, into which dips the 



platinum wire VII. 



(Keith Lucas, 1909, 2, p. 212.) 



ORIGIN OF POTENTIAL DIFFERENCES IN TISSUES 



That the electrical phenomena observed in the activity of cells are due to 

 changes of potential, and not merely to changes of resistance, is evident, not only 

 from the fact that they are shown by instruments, electrometers, which do not 

 respond to changes of current only, but also in the ordinary way of demonstrating 



