290 THE OUTGO OF ENERGY 



through a short-circuiting key. Note the posi- 

 tion of the meniscus on the micrometer scale. 

 Open the short-circuiting key. 



The meniscus will move but little. It will not 

 move at all, provided the muscle has not been 

 injured ; but the difficulty of preparation is such 

 that some difference of potential will probably 

 appear. 



Close the key. Injure the muscle by drawing 

 a hot wire across one end. Open the key. 



A strong demarcation current will appear. 



Stimulation by Demarcation Current. 1. Make 

 a nerve-muscle preparation (sciatic nerve and 

 gastrocnemius muscle). Let the nerve near the 

 muscle touch a cross-section of the sartorius. 

 Now let the end of the nerve fall on the longi- 

 tudinal surface near the equator. 



The gastrocnemius will contract; the nerve 

 acts as a conductor between the positive longi- 

 tudinal surface and the negative cross-section. 



It should be pointed out that the conclusion 

 here drawn is not entirely free from criticism. 

 The muscle is a conductor as well as the nerve, 

 and may close the demarcation current of the 

 nerve, as the nerve may close that of the muscle. 

 Thus it is possible that the nerve is stimulated 

 by its own demarcation current. The former 

 explanation is the more probable. 



