50 EXPERIMENTAL GENERAL PHYSIOLOGY 



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 simultaneously. 



Vary the experiment by using other combinations: silver and 

 steel, copper and steel, etc. Note briefly the original observations 

 of Galvani. Are the observations just made different in any essential 

 respect from the observation which led to the discovery of what we 

 call galvanic electricity? 



XI. ELECTRIC STIMULATION AND THE MYOGRAM. 



The simplest work in the field of electro-physiology is that which 

 involves the use of the induction shock as a stimulus and the use 

 of a myograph and kymograph to record the result of the stimulus. 



FIG. 29 



The inductorium. 



1. Appliances. Inductorium; myograph; kymograph; frog; oper- 

 ating case; glass hook; dry cell; contact key with three wires; shielded 

 electrode with two wires; normal saline solution. 



2. Apparatus, (a) The Frog-board Myograph. The frog-board 

 myograph is a new form of myograph, so constructed as to permit all 

 experiments usually performed on the gastrocnemius-sciatic prepara- 

 tion without exposing the active tissues to the atmosphere or dis- 

 turbing the blood supply. The instrument is constructed as follows : 

 An oaken base about one-fourth of an inch in thickness supports 

 a cork plate of equal thickness; the cork plate presents a surface 

 about 10 cm. by 25 cm. (Fig. 31). The lever holder at the end 

 of the plate is constructed of thin sheet steel and slips from side 

 to side in order to bring it opposite either leg of the frog. 



The distance from the axis of the elbow lever to the thread-eye 

 is the same as that to the weight; therefore, the weight lifted by the 



