260 ELECTRO-PHYSIOLOGY CHAP. 



occurs more readily at one than at the other end of the pre- 

 paration, and as a rule the base of the ventricle appears most 

 favourable in this respect. This is probably related to the fact 

 stated above, that the mechanical stimulus of the ligature often 

 produces a pronounced local contraction at the apex of the heart, 

 which, as was also pointed out, opposes much greater resistance 

 to the action of the anode than the tonic contraction produced 

 by the state of wall-tension. 



If the electrodes are placed at opposite ends of the transverse 

 axis of the ventricle, relaxation will begin, on closing the current, 

 at the side of the anode, and accordingly the heart bulges out on 

 the same side. 



The intensity of current at which these phenomena 

 appear is essentially dependent upon the strength of the exist- 

 ing " tonus." We have frequently obtained marked effects on 

 using a Daniell cell, with rheochord resistance from a wire of 

 5 crn., and it may be taken as a general rule that with experi- 

 mental conditions as described above, anodic relaxation rarely 

 fails with a resistance of 100 cm. wire. If only minimal 

 currents are employed, the relaxation is always confined to the 

 close proximity of the point where the current enters. It appears 

 at closure, and gradually disappears, even if the exciting current 

 remains closed. In other cases it spreads, according to the 

 direction of the current, over one or the other half of the 

 ventricle. With moderate currents, and great excitability of the 

 preparation, the propagation of the anodic wave over the cnfi-rt' 

 ventricle is independent of whether the current is broken imme- 

 diately after the effect appears, or whether it remains closed for a 

 longer period. In the last case, however, the rhythmical contrac- 

 tions continue during the whole period of closure, and it should 

 be noted that with each new diastole, relaxation invariably begins 

 at the anode, and progresses from that point peristaltically. 

 Hence, by merely watching the pulsations of a snail's heart, under 

 the influence of the constant current, the direction of the current 

 may be accurately determined. 



The systolic contraction of the ventricle follows so much more 

 rapidly that mere inspection will not suffice to determine whether 

 under these conditions it also proceeds peristaltically (starting 

 from the kathode), or not. 



As previously stated, the rate of propagation of the anodic 



