LABORATORY MANUAL OF PHYSIOLOGY 



This condition of change in a nerve or a muscle, since the muscle 

 itself reacts in the same manner as the nerve, is known as electro- 

 tonus. The condition of the nerve about the anode is called anelec- 

 trotonus; that about the kathode is called katelectrotonus. The 

 conditions of anelectrotonus and katelectrotonus are most marked 

 in the immediate vicinity of the anode and kathode. From these 

 poles they gradually diminish in the extrapolar and interpolar 

 regions, until, in the latter, a neutral point is reached about midway 

 between the two poles (see Fig. 17). 



When the kathode is near the muscle and the anode farther from 

 the muscle, the current is said to be descending. When these con- 

 ditions are reversed, that is, when the anode is near the muscle, the 

 current is said to be ascending. In the following experiments the 

 electrotonic conditions will be tested with the nerve, the muscle 

 twitch being used as a convenient indicator. 



i. Make a sciatic-gastrocnemius preparation. Save the whole 

 length of the nerve. Arrange moist chamber with non-polarizable 

 electrodes placed in circuit with one or more battery cells, rheo- 

 cord, and Pohl's commutator or current-changer. Place the nerve 

 upon the non-polarizable electrodes as shown in Fig. 17. Place 

 a pair of platinum electrodes from the secondary coil of an induc- 

 torium on the nerve at the anode of the constant current, and an- 

 other at the kathode of the constant current. Arrange as in Fig. 

 17, so that the nerve may be stimulated with the induced current 

 at either pole of the constant current. By means of the Pohl's 

 commutator, the constant current may be reversed in direc- 

 tion; i.e., it may be made either an ascending or a descending 

 current. 



Attach the tendon of the muscle to the writing lever of a myo- 

 graph. Let this record the contractions of the muscle on a drum 

 arranged to be revolved by hand. Send an ascending current 

 through the nerve. While the constant curfent is passing, stimu- 

 late the nerve in the anodic region with a medium strong single- 

 break shock from the inductorium. Mark result of muscular con- 

 traction, if any, on drum, as well as data needed to identify what 



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