GENERAL PHYSIOLOGY. 77 



b. Myograpkic record of anelectrotonus and of katelectrotonus. 



1. Appliances. 3 or 4 Daniell cells; 3 Du Bois- 

 Reymond keys; contact key; 2 commutators; induc- 

 tcrium; 2 N-P electrodes; 18 wires; kymograph; 

 myograph with moist chamber; 2 pairs of platinum 

 wire electrodes to use with induction currrent. 



2. Preparation. Arrange apparatus according to plan 

 shown in PI. II., Fig. 9. Note that the cross bars 

 are absent from the commutator in the induction cir- 

 cuit. This enables one to stimulate the nerve at the 

 central end (c) or at the segment between the polar- 

 izing electrodes and the muscle (m), by simply revers- 

 ing the bridge of the commutator (B). 



j. Operation. Make and mount a gastrocnemius prepa 

 ration in moist chamber myograph; adjust drum for 

 tracing myogram. Adjust electrodes as shown in 

 diagram. 



Test apparatus and preparation by sending single 

 make (or break) induction shocks through nerve at c 

 or at m. Let there be a typical response at both 

 places. The secondary coil should be removed to a 

 distance that gives a little more than the minimum 

 stimulus required to cause a contraction of the muscle. 



To close the constant current "polarizes" the nerve 

 or, better, induces electrotonus. 



That segment of the nerve between the anode and 

 kathode is called the intra-polar region. 



Those segments centrally and distally located are 

 called extra- polar. 



The induced current is called the stimulating cur 

 rent. 

 4. Observations . 



(1) Adjust for descending, polarizing current. Stimulate 

 at c, i. e. in the region of anode. Note trace ex- 



