66 LABOR A TOR Y G VIDE IN PH YSIOLOG Y. 



the coins with the tongue as indicated. Is there any 

 difference in the sensation which the tongue receives 

 in these two experiments ? Record results, account- 

 ing for phenomena. 



(2) While in the operation of making a gastrocnemius 

 preparation, after the sciatic nerve has been freed from 

 the other structures in the thigh, slip the glass nerve- 

 hook under it so that the handle of the nerve hook 

 will hold the nerve away from the other tissues. Press 

 the end of a copper wire against the muscles of the 

 thigh, touch the silver probe to the sciatic nerve, then 

 to the copper wire, first separately, then simultane- 

 ously. 



Vary the experiment by using other combinations: 

 Silver and steel, copper and steel, etc. Note briefly the 

 original observations of Galvini. Are the observations 

 just made different in any essential respect from the 

 observation which led to the discovery of what we call 

 galvanic electricity? 



(3) Complete the gastrocnemius preparation, mount the 

 muscle in the myograph, place the nerve across the 

 horizontal ends of the two wires, lift the beaker of 

 water and immerse the two pendant plates the cop 

 per wire and the piece of zinc. 



If the experiment is successful the muscle responds 

 vigorously. Is there any chemical action in this water 

 element? If so, describe it. Would oxidized or tar- 

 nished plates answer as well as bright ones? 



(4) Mount another gastrocnemius preparation, adjust 

 the Daniell cell for action, set up the electric apparatus 

 as shown in Plate II, Fig. 5, clamp the two exposed 

 poles (p.) in the middle clamp so that the ends are 

 exposed for about two centimeters. Place the nerve 

 across the poles. Adjust the kymograph for tracing 

 a myogram. 



