182 



ELECTROTONUS. 



[CH. XVI. 



reverser lead wires to the binding screws of the rheochord ; from 

 these same screws of the rheochord the non-polarisable electrodes 

 lead to the nerve of a nerve-muscle preparation. The strength of the 



I. A 



2. A 



3- A- 



Fig. 192. Diagram illustrating the effects of a polarising current on the conductivity of a 

 nerve. A B represents the nerve, and the anode and kathode are indicated by + and 



include tne anodic region, a snows tne enect immediately alter tne remove 

 current ; the fall is then greatest in the post-anodic region. (After Stewart.) 



current is varied by the slider S. The nearer S is to the binding 

 screws the less is the resistance in the rheochord circuit, and the 

 less the current through the nerve. With a weak current, a 



Cell 



Fig. 193. Arrangement of apparatus for demonstrating Pfluger's law. 



contraction occurs at make only, but more readily, i.e. with a 

 weaker current when its direction is descending, i.e. towards the 

 muscle. With a stronger current (ascending or descending) con- 

 traction occurs both at make and break. With a very strong 

 current (six Groves), the contraction occurs only at make with 



