1880.] Experimental Researches : Heart of the Frog. 375 



excitation, were recorded graphically in a curve of which the abscissae 

 express the times, the ordinates the deflections. This curve shows 

 that, in the 33 preparations, the first phase began 0"'06 after excita- 

 tion, and rapidly attained its maximum ; that the reversal of sign took 

 place at 0"*26, the contacts becoming finally equipotential at 0""5. In 

 10 similar experiments, in which the nearest contact was only 

 1 millim. from the seat of excitation, the interval of time between 

 the excitation and the beginning of the variation was much 

 shorter. (3) The phenomenon of the " Doppelschwankung " is 

 understood by Engelmann to mean that " each part of the muscular 

 substance of the ventricle becomes, for a moment during excitation, 

 negatively electromotive (vorubergeliencl negativ electromotor iscli wirk- 

 sam), and that this negativity is propagated from the seat of excitation 

 in all directions." The rate of propagation was estimated as probably 

 50 millims. per second. 



It is to be noticed that the researches of Engelmann refer exclusively 

 to the first half- second after excitation, and that he has taken no 

 account of the phenomena which occur later ; and, further, that his 

 observations are, as regards this first period, in the main in accordance 

 with the statements contained in our former paper. His interpretation 

 of them is however different, for phenomena to which we apply the 

 term initial are regarded by him as constituting the whole process. 



1. Time-relations of the Excitatory Variation in the Uninjured Heart. 

 — By the term excitatory variation we mean the succession of elec- 

 trical changes which manifest themselves galvanometrically as the 

 result of excitation, when the surface of the ventricle is led off at two 

 points. The method of observing these changes is as follows : — The 

 preparation rests on the carefully lacquered surface of the upper end 

 of a brass box of cylindrical form, the axis of which is vertical. 

 Through this box water flows at 10° C. Of the two contacts by which 

 the ventricle is led off, one (m) is close to the apex, the other (/) near 

 the base, on the ventral aspect. The two platinum wire electrodes, 

 by which the induction shocks pass for excitation, are insulated up to 

 their tips, which are 1 millim. apart. They are in contact with the 

 surface of the ventricle at the apex. The arrangement of the galvano- 



Fio. 1. 



