in ELECTRICAL EXCITATION OF MUSCLE 259 



tinuous systolic contraction, the sole visible effects of electrical 

 excitation with the constant current would be local relaxation of 

 the muscular wall of the ventricle, appearing with closure at the 

 anode, but with opening at the kathode thus, as it were, forming 

 an antithesis to the response of the muscle relaxed in diastole. 

 It is difficult, and more or less incidental, to obtain a prolonged^ 

 systolic contraction in the frog's heart ; but, on the other hand, 

 this is easily produced in the cardiac muscle of many invertebrates, 

 e.g. snail's heart (35). We have already seen that a ventricle tied 

 to a canula will often, if the latter is suddenly filled with fluid 

 (snail's blood, 0*6 / NaCl), fall, after a longer or shorter series of 

 regular contractions, into a state of protracted, uniform contraction. 

 If during this time a current of 12 Dan. is led through it 

 by means of unpolarisable electrodes, by allowing the suitably- 

 moistened thread of the lower ligature of the apex of the heart 

 to dip into a vessel with salt solution, in which one of the elec- 

 trodes is already plunged, while the other pointed brush electrode 

 is placed above the second ligature at the boundary between 

 auricle and ventricle, an immediate relaxation of the ventricle 

 may be seen in every case with closure of the circuit, which 

 however it must be noted never occurs simultaneously at all 

 points of the area traversed, but begins without exception at the 

 end where current enters, i.e. at the anode. The relaxation 

 always progresses in the direction of the current from the positive 

 to the negative pole, and forms a more or less rapidly-transmitted 

 wave, always, however, visible to the eye. If the current is only 

 kept closed until the "wave of relaxation " has reached the kathodic 

 end of the preparation, and is then broken, the ventricle returns 

 as a rule at least in all cases where the tonus was ab initio 

 strongly developed to its original state of continuous contrac- 

 tion. It is only in cases where a less pronounced tonus prevails 

 from the beginning of the experiment, or where the preparation 

 is excited at a time when the pulsations have begun again spon- 

 taneously, that an unbroken series of regular, rhythmical contrac- 

 tions follow a single short closure of the constant current, in 

 which case they either persist indefinitely or give way after a time 

 to secondary tonic contraction. In many cases the ventricle 

 remains for several seconds, during the closure of the current, in 

 a state of diastolic relaxation, after which only it begins the rhyth- 

 mical peristaltic contractions. The anodic relaxation frequently 



