EXCITABILITY OF MUSCLE AND NERVE. 203 



nerve, and then apply the same stimulus to the gastrocnemius 

 directly. It will be ineffectual. 



Approach the S coil until the stimulus is strong enough 

 and note the difference in strength required. 



From this experiment alone it is not permissible to conclude 

 that muscle itself is directly stimulable, the participation of 

 nerve endings in muscle not being excluded from the process. 



See the experiment with Curara later. 



Induction shocks have great power of overcoming 

 resistance. Place a nerve-muscle preparation in a muscle 

 chamber at one end of the room. Lay the nerve upon the 

 platinum electrodes and connect one of its poles by means 

 of a long wire to one of the terminals of the S coil of the 

 inductorium. The latter is to be placed on a table at the 

 furthest distance from the muscle-chamber which the room 

 will allow, and is to be insulated on inverted porcelain basins. 



Let your co-worker make and break the P circuit, or use 

 interrupter shocks the muscle does not contract the insula- 

 tion is sufficient to prevent the passage of the current. 



If he now touches the unconnected terminal of the S coil 

 with his finger the muscle will contract. His body by 

 bridging the gap in the S circuit between the floor and the 

 binding screw allows enough current to pass to stimulate 

 the nerve. 



This so-called unipolar stimulation is therefore due to 

 defective insulation and is the reason for which the S 

 circuit must always be provided with a shorting key, since 

 the insertion in this circuit of an open break key is not 

 enough to prevent induction currents from passing to the 

 preparation, and especially so when strong currents are in use. 



