GENERAL PHYSIOLOGY OF MUSCLE AND NERVE TISSUE 65 



and breaking of the descending current and on making and breaking 

 of the ascending current. 



It also shows in a marginal column the gradual increase of the 

 strength of the current through gradual increase of resistance in 

 the rheocord. 



(2) Make and break with weak ascending current. If the con- 

 ditions are typical the muscle will contract on making both ascend- 

 ing and descending current. 



(3) Increase gradually the strength of the electrode circuit record- 

 ing results. After a longer or shorter transitional period in which 

 the result will be characterized by a contraction on the make of 

 both the ascending and descending current, one comes to a strength 

 of current which causes a contraction on both make and break of 

 both descending and ascending current. This is the medium strength 

 for the preparation and the condition in question. 



(4) Let the current be increased still farther and by larger incre- 

 ments. After passing another transitional stage one finally reaches 

 a strength of current which causes a contraction on make of descend- 

 ing current and on break of ascending current. This is the "very 

 strong" current for the preparation under observation. 



It not infrequently happens that through overstimulation and 

 fatigue of muscle the whole experiment cannot be completed upon 

 one preparation except by increasing the current by larger incre- 

 ments. 



(5) Pfliiger's law of contraction may be expressed in the follow- 

 ing table: 



(6) But how shall we account for these results? 



Let us recall some of the laws which have been demonstrated. 



Law I. The make contraction starts at the cathode and the 

 break contraction starts at the anode. 



Law II. The make or cathodic stimulus of a constant current 

 is more irritating than the break or anodic stimulus. 



Law III. The passage of a constant current through a nerve 

 induces a condition of electrotonus, marked by an increased irri- 



5 



