296 THE OUTGO OF ENERGY 



0.025 volt, as against about 0.060 volt in 

 muscle. The demarcation current of muscle is 

 maintained in force for a long time, whereas that 

 of nerve diminishes rapidly. The nerve current 

 is restored on making a fresh cross-section. 



The demarcation current from the cut branches 

 of a nerve may reach electrodes placed on the 

 main trunk, and thus confuse the electrometer 

 measurements. To this same cause must be 

 ascribed the increased irritability observed in the 

 main trunk in the neighborhood of branches; 

 the irritability is raised by the demarcation cur- 

 rent of the severed branch. 



Nerve may be stimulated by its own Demarca- 

 tion Current. On a glass plate make a U shaped 

 wall of normal saline clay, each limb about 1 cm. 

 long and 3 or 4 mm. wide. Carefully remove the 

 moisture between the clay walls with filter paper. 

 Lay the longitudinal surface of the nerve of a nerve- 

 muscle preparation on one limb of the U, and with a 

 glass rod let the cross-section fall on the other limb. 



When the circuit between the cross-section and 

 the longitudinal surface is completed by contact 

 with the clay, the demarcation current will 

 stimulate the nerve, and the resulting nerve im- 

 pulse will cause the muscle to contract. 



Other Examples. The dropping of the central 

 end of the severed vagus nerve into the wound 

 from which it was lifted has caused the slowing 



