1-378.] 



on Rhythmical Motions of the Heart. 



411 



coincides with the maximum of the preceding ventricular systole, and 

 that their endings are synchronous. 



3. The Stannius'' Heart. — In a heart of which the rhythmical action 

 has been arrested by the application of a tight ligature round the line 

 of junction between the wall of the sinus and of the auricles (" Stan- 

 nius' ligature "), the duration of the ventricular contraction, determined 

 by electrical or mechanical excitation, is much longer than in the beating 

 heart. The contraction attains its maximum from 1"'4 to 1"'8 after the 

 commencement as above denned, the ventricle remaining in full con- 

 traction for from 0"'4 to 0"'5. Accordingly the moment at which the 

 sudden relaxation takes place varies between 1""8 and 2""0. 



4. Time interval between Excitation and Contraction. — When a con- 

 traction is produced in a heart ligatured as above described (which 

 may be referred to as a " Stannius' heart") by the passage through 

 any part of its substance of a single induction shock, a sensible delay 

 intervenes between the excitation and the commencement of the con- 

 traction. If the electrodes are in contact with two points of the 

 surface of the ventricle at a short distance (one millim.) from each 

 other, and currents of small intensity, i.e., such as are just sufficient to 

 produce an effect, are used, the delay may amount to three-tenths of a 

 second. In this case contraction of the auricle commences after that 

 of the ventricle, the time interval between them being from 0""4 to 

 0"'5. If the seat of excitation be the posterior surface of the left 

 auricle near the ligature, the auricle contracts after a delay of about 

 one-sixth of a second, but the ventricular contraction does not com- 

 mence until from 0"*4 to 0""6 later. It frequently happens that the 

 ventricular systole produced by excitation of the auricle is followed 

 after an interval of inaction of about 1"'3 by a second contraction of 

 the auricles. 



Section II. — Electrical Condition of the Surface of the Uninjured and of 

 the Injured Heart. 



5. The Uninjured Heart. — It was shown by Engelmann in 1873, 

 that the surface of the uninjured resting heart is isoelectric, and 

 further, that the slightest mechanical or chemical injury renders the 

 injured part negative. These facts we have confirmed in numerous 

 observations relating both to the heart of the toad and of the frog. 



Nature of the Injuries Investigated. — In order to investigate the 

 influence of a local injury on the condition of the surface of the heart, 

 its rhythmical motion must be suspended. This may be done either 

 by the passage of a rapid succession of induction shocks in opposite 

 directions through the inhibitory tract, by applying to the surface a 

 trace of a solution of muscarin, or by Stannius' ligature. A localized 

 injury of the surface may be produced either by the scratch of a needle, 

 bv touching it with hot wire (preferably a platinum wire heated elec- 



2 e 2 



