in ELECTRICAL EXCITATION OF MUSCLE 255 



It is evident that if the make excitation occurs only at the 

 point where current leaves the muscular integument (the latter 

 is hatched in the figure) the same could, and indeed must, be 

 the case in the proximity of the positive electrode also. " If the 

 branches of current drawn in the figure as proceeding from E -f 

 (the anode) are followed, it will be noticed that a part of theni_ 

 leave the muscle-substance at the points e f e" e f ". These points 

 (secondary kathodic points) lie in the immediate proximity of the 

 positive electrode, but are of course, with regard to the muscle- 

 substance, to be viewed as the negative pole (physiological kathode). 

 And here the closure excitation makes its appearance." That 

 this does not actually occur, is referred by Engelmann in part to 

 the differences in current density on the side turned towards, and 

 away from, the electrode, in part to the depression of excitability 

 and conductivity of the contractile substance in the region of the 



FIG. 91. 



positive electrode (infra). A much wider distribution of the lines 

 of current, and hence a richer development of secondary kathodic 

 points in the region of the anode, and conversely of secondary 

 anodic points in the region of the kathode, occurs, however, 

 invariably whenever the ureter is left in situ, or placed on a 

 moderately good conductor (Fig. 92). Conditions being favour- 

 able, excitation (contraction) will then occur on closure of the 

 current at innumerable places in the proximity of the anode (not 

 at the anode itself), and is either transmitted as an undulation 

 (ureter), or remains localised as a persistent contraction. Con- 

 versely, further diffusion of the closure excitation discharged 

 at the kathode proper is hindered by the vicinity of secondary 

 anodic points. 



It can hardly be necessary to point out that these considera- 

 tions are legitimate and valid in all the cases previously quoted, 

 where, as in the muscles of Holothuria and Echinidse, and also 

 the muscular integument of worms, and the intestine of verte- 



