64 



EXPERIMENTAL GENERAL PHYSIOLOGY 



(c) Laws of Electrotonus. 



(a) The passage of a current through a nerve induces a condition 

 of electrotonus marked by increased irritability in the region of the 

 cathode (catelectrotonus) and decreased irritability in the region oj 

 the anode (anelectrotonus) . 



(b) During electrotonus induced by a strong current the conductivity 

 is decreased in the region of the anode. Further though not derived 

 from the foregoing experiment "at the instant that the polarizing 

 current is withdrawn the conducting power is suddenly restored in 

 the region of the anode and greatly lessened in the region of the cathode." 

 Lombard, in American Text-book of Physiology. 



XVII. THE LAW OF CONTRACTION. 



1. Appliances. The simple rheocord; four Daniell cells; frog- 

 board myograph, or myograph with moist chamber, simple key; 

 Du Bois-Reymond key; commutator; two N. P. electrodes. 



2. Preparation. Set up apparatus with four cells in series, simple 

 key as closing key. Commutator with cross-bars; short-circuiting 

 key; the two N. P. electrodes clamped in chamber of myograph or 

 mounted above the frog-board myograph (Fig. 39). 



FIG. 39 



3. Operation. Make and mount a gastrocnemius preparation. 



4. Observations. (1) Stimulate with make and break of the 

 very weakest descending current. The first response is elicited by 

 the very, weak descending current. A slightly stronger current is 

 required to elicit a response with the ascending current. 



Record results in such a table as suggested under (5) . This table 

 shows what response (contraction or rest) the muscle gives on making 



