1880.] Experimental Researches : Heart of the Frog. 379 



the surface in modifying the phenomena of the excitatory variation. 

 The rheotome has enabled ns to add very considerably to our knowledge 

 ,of these modifications. The effect of all injuries, whether chemical or 

 mechanical, in so far resemble each other, that in all cases the injured 

 surface tends during the whole of the excitatory period to become 

 positive to the uninjured. The degree in which this effect manifests 

 itself varies in the same direction with the degree of injury. If the 

 injury is very slight, such for example as is produced by touching the 

 surface with a camel-hair pencil, which has been dipped in 10 per cent, 

 solution of salt, and then drained with filter- paper, the change which 

 follows resembles that of slight warming. The end phase begins 

 earlier, and its deflections are increased. If it is produced by ap- 

 proaching the platinum loop a little too near, the effect is similar, but 

 begins earlier and lasts longer, so that the isoelectrical interval is 

 much reduced in duration. If the led-off surface (m) is completely 

 destroyed, as by touching it instantaneously with the hot wire after 

 having removed the electrode, and then renewing the contact, it is 

 found that the whole isoelectrical interval is, as it were, filled up, 

 large positive* deflections being obtained with the rheotome through- 

 out the whole excitatory period, with the exception of the first tenth. 

 This is well seen in the following table, in which we have given the 

 means of the deflections recorded when the galvanometric circuit was 

 closed for ten successive periods of two-tenths of a second. By com- 

 paring these numbers with those given in Table III, it will be seen 

 that whereas, in the partially warmed ventricle, the temporary effect 

 produced culminates early in the 2nd second, the more lasting effect 

 produced in the injured ventricle reaches its maximum about the 

 middle of the 1st second. 



Table IV. 



Time after excitation of 

 opening of galvanometer cir- 

 cuit, the period of closure 

 being 0"-18 



0-2 



0-4 



u 



0*6 



0-8 



1-0 



+ 68 -3 



1 -2 



1-4 



1-6 



1-8 



2-0 





+ 58-6 



+ 85-3 



+ 82-3 



+ 75-0 



+ 62-3 



+ 50-0 



+ 31-8 



+21 -3 



+ 4-1 



4. The Period of Diminished Excitability. — Since the researches of 

 M. Marey, j in 1876, it has been known that the excitability of the 

 ventricle is diminished during the period of systole, Marey showed 

 that if the ventricle is excited by an induction shock of just sufficient 

 strength to evoke a response, the excitation is followed by a period of 



* Whenever the words " positive " or " negative" are used absolutely, the state 

 of m in relation to/ is meant. 



f Marey, " Des Excitations Artificielles du Coeur." " Physiol. Experiment-ale," 

 II, 1876, p. 85. 



