LECTURE IV. 



CONTENTS. 



Polar effects. Pfliiger's law. Illustrated by experiments on 



Man. 

 Electrolytic dissociation. Electrolytic counter-current. 

 Internal polarisation. 



Polarisable core-models. Extra-polar currents in core-models. 

 Extra-polar currents in frog's nerve and in mammalian nerve. 



Polar effects. — In studying the electrical effects 

 manifested by living matter, we shall repeatedly have 

 occasion to employ electrical stimuli. It is important 

 at the outset to avoid a perhaps natural confusion of 

 ideas, and to expressly distinguish between electricity 

 applied from without by way of what we shall desig- 

 nate as leading-in or exciting electrodes, and elec- 

 tricity arising within ox aroused within the living 

 animal or tissue, and conducted to the galvanometer 

 or other electrical indicator by way of what we shall 

 designate as leading-out electrodes. The latter alone 

 is animal electricity, the former is not, although it is 

 often used to arouse within living matter that chemico- 

 physical action of which the deflection of a galv^ano- 

 meter is an outward and visible sign. 



