1880.] Experimental Researches : Heart of the Frog. 377 



If it is desired to investigate more minutely a part of the variation, 

 as for example, the changes which take place in the first four-tenths 

 of a second, a table is used in which the rheotome readings for twenty 

 periods ending respectively at 0"'02, 0"*04, 0"'06 and so on, after ex- 

 citation, are recorded. The following table exemplifies the kind of 

 result so obtained, the period of closure being 0"*1. 



Table II. 



Time after excitation 

 of opening of galvano- 



0-02 



0-04 



0-06 



0-08 



ii 



o-io 



a 



0-12 



0-14 



0-16 



ii 



0-18 



0'20 



0-22 



0-24 



ii 



U-26 



a 



U-28 



'30 &c. 





Deflections 



-0 



-1 



-12 



-31 



-42 



-46 



-40 



-32 



-12 



-7 



-4 















&c. 



These readings show that in the particular preparation investigated 

 (which may be taken as a representative one) the state of negativity 

 of the contact m did not last more than 0""06, and culminated before 

 a tenth of a second had elapsed after excitation. 



Whenever the surface of the ventricle is led off in the way above 

 described, i.e., by contacts of which one is close to the seat of excita- 

 tion, the other remote from it, the same results are obtained. We 

 are therefore justified, first, in repeating the statement contained in 

 our last paper, viz., that the electrical effect of excitation manifests 

 itself in two phases, an initial and a terminal one, which have 

 opposite signs ; and, secondly, in adding to our previous statement, 

 that the initial is separated from the terminal phase, by a relatively 

 prolonged state of equipotentiality of the two contacts. If we com- 

 pare this result with that of Professor Engelmann, observed in a 

 similar way, it will be at once seen that although the interpretation 

 may be different, our observations are in accordance with his, so far as 

 they relate to the same period. The whole of the phenomena recorded 

 by him belong to the beginning of the 1st second. The beginning 

 of the period of equipotentiality is regarded by him as the end of 

 the excitatory effect. To us the absence of galvanometric effect during 

 this period, which we designate the isoelectrical interval, is merely 

 the expression of the fact that both contacts are in the same degree of 

 excitation. 



2. Time-relations of the Variation in the partially zvarmed Ventricle. — 

 The proof that the period of equipotentiality is one of balanced ac- 

 tivities, not of quiescence, is readily obtained by subjecting the two 

 led-off surfaces, i.e., the base and apex of the heart, to different tem- 

 peratures. For this purpose the cylindrical support on which the 

 preparation rests is divided into two chambers through which water 

 Hows at different temperatures by a vertical non-conducting septum. 

 If, then, the ventricle is placed in such a position that its apex rests 



