GENERAL PHYSIOLOGY OF MUSCLE AND NERVE TISSUE 71 



(B) Electromotive Force Detected by the Electrometer. 



1. Appliances. A large frog; non-polarizable electrodes; capillary 

 electrometer. 



2. Preparation. Pith the frog; prepare electrodes, using kaolin 

 wet with normal saline solution for the tips. Join the electrodes 

 to the binding posts of the electrometer. Make a muscle-nerve 

 preparation, lay it upon a glass plate, and prepare to stimulate with 

 induction shocks as in the case of muscle I above. 



3. Observations. (1) Place the electrode which is joined to the 

 capillary upon the tendon of the muscle; the other electrode upon 

 the belly of the muscle. Adjust the meniscus in the middle of the 

 field of the microscope. Open the short-circuiting key of the elec- 

 trometer while watching the meniscus. It will be displaced. Its 

 displacement suggests a difference of electric potential between the 

 tendon and the belly of the muscle. Such a difference of potential 

 is usually to be observed, and it is called the "demarcation current." 

 It is believed to be due to the injury to the muscle tissue incident 

 to its preparation. It is also called the current of injury. 



(2) After the meniscus has come to rest stimulate the muscle with 

 a single induction shock. The meniscus will move quickly, but in 

 the direction opposite to that of its first motion. That is, its current 

 of action is greater than its current of injury, and in an opposite 

 direction. Describe phenomena in notes. 



(3) Bring the muscle into action through other stimuli than 

 electricity and note results. 



