STIMULATION OF MUSCLE AND NERVE 115 



anode shall be next the muscle. Move the slider 

 near the positive post. Make and break the gal- 

 vanic current. If no contraction is secured, 

 move the slider to increase the current, and 

 repeat the experiment. 



The first contraction will take place on mak- 

 ing the current. Continue to increase the cur- 

 rent strength by moving the slider. 



A point will be reached at which contraction 

 will occur both on opening and closure. 



Increase the intensity of the current by add- 

 ing dry cells in series (zinc to carbon), testing 

 the effect after each addition by closing and 

 opening the current. 



An intensity will be reached at which opening 

 and not closure causes contraction. 



In a similar manner, work out the law of con- 

 traction for descending currents. (It may be 

 necessary to take a fresh nerve-muscle prepa- 

 ration.) 



Set down the results in a table. 



2. The remarkable nature of these results is 

 apparent on observing that contraction is easily 



