THE EEACTION OF NORMAL AND ABNORMAL NERVE 145 



to, the term anelectrotonus signifies a depression and the term catelectrotonus an 

 excitation occurring during the passage of the constant current. 



(c) It is also essential to remember that the excitatory process developed at the 

 cathode is always stronger than that developed at the anode. 



It appears, therefore, that the wave of excitation constituting the 

 nerve impulse, is developed at the cathode on the make and at the 

 anode on the break of the current. This inference may be substan- 

 tiated with a nerve-muscle preparation by simply recording making 

 and breaking contractions when the anode is placed far away from the 

 muscle and the cathode near to it. It will then be noted that the 

 latent period of the making twitch is much shorter than that of the 

 breaking twitch. This must necessarily be so, because in the former 

 instance the nerve impulse arises at the cathode which is situated 

 in the immediate vicinity of the muscle; while in the latter case it is 

 produced at the anode which lies at some distance away from it. If 



Fia. 85. — Methods Used to Show Electkotonic Changes on Making and 

 Breaking of Galvanic Current. 

 K, key for making and breaking of current; P, pole changer for making either 

 jend of muscle (M) anodic or cathodic; D, clamp applied to muscle to destroy contraction 

 wave but not wave of excitation; W , weights attached to ends of muscle. These may 

 be displaced by writing levers. 



Ithe current is now reversed so that the anode comes to lie near the 

 muscle and the cathode far away from it, the latent period will show 

 a greater length on the making of the current. On the making, the 

 : cathode serves as the stimulus and this pole is situated in this case far 

 away from the muscle, while, on breaking, the excitation results at 

 [the anode which lies very near the muscle. 



The preceding statement may also be proved by the procedure of Engelmann 

 j(Fig. 85). The positive and negative poles of a battery are connected with the 

 [two ends of along muscle, such as the sartorius. (M). This muscle is then con- 

 stricted about midpoint between its poles by means of a clamp (D), the com- 

 pression being just sufficient to prevent the contraction of one-half from being 

 imparted to the other half without actually hindering the passage of the wave of 

 10 



