382 Experimental Researches : Heart of the Frog. [May 13, 



which most of our experiments were made, namely, at 10° or 12° C. 

 This conclusion is, indeed, the only one which the facts admit of, 

 for, inasmuch as the total duration of the variation is over two 

 seconds, and the time occupied in the propagation of the excitatory 

 wave from apex to base is one-twentieth of a second at most, it is clear 

 that it must last, at the part furthest from the seat of excitation, as 

 long as 1"'9. 



When both contacts are at the same temperature, and in all other 

 respects under the same conditions, the local duration of the excitatory 

 state is the same at both, consequently, it begins and ends earlier at m 

 than at /, the initial and terminal differences expressing themselves in 

 the initial and terminal phases of the normal variation. 



When one contact is warmer than the other, the local duration of 

 the excitatory state is less in the warmed than in the un warmed 

 surface. Consequently the terminal interval, i.e., the time during 

 which the excitatory state at / overlaps that at m, is longer. The 

 terminal phase of the variation begins earlier, and its deflections are 

 larger. 



If the surface at m is slightly injured, the local duration at the 

 injured surface is diminished in the same way as when its temperature 

 is increased. The effects, indeed, are indistinguishable ; but if the 

 injury is of such intensity as to destroy the surface, its most prominent 

 effect is to diminish its electromotive activity. Consequently, the 

 activity of the contact / is unbalanced, and expresses itself in the large 

 deflections which are exemplified in Table III. 



In general, it is observed that in the injured ventricle the total 

 duration of the variation is less than in the same preparation before 

 injury. We are not as yet in a position to offer an explanation of 

 this fact. 



Appendix. 



Condition of the Surface of the Ventricle in the Resting Heart. — It has 

 already been repeatedly stated that the surface of the ventricle, so 

 long as it is absolutely uninjured and at the same temperature in all 

 parts, is isoelectrical. Any inequality as regards the mechanical, 

 chemical, or thermal conditions to which the surface is exposed, is 

 accompanied by corresponding electrical differences, which are of the 

 following nature : — 



If a platinum wire, warmed by the passage along it of a voltaic 

 current, is brought into the neighbourhood of a led-off surface, the 

 effect invariably produced is to render that surface positive to the 

 other. If the warming is continued for a few seconds only, the effect 

 promptly subsides. If it is continued, the needle also returns to zero, 

 but continues to move to the negative side. If, as soon as this 

 second effect has been produced, the wire is withdrawn, it also 



