ACTION OF ELECTRICAL STIMULI ON THE HEART. 107 



ventricle (Hildebrand). Even when strong tetanising induction-shocks are applied 

 to the heart, they do not produce tetanus of the entire cardiac musculature, or as it 

 is said, "the heart knows no tetanus" (Kronecker and Stirling). Small white local 

 weal-like elevations such as occur when the intestinal musculature is stimulated 

 appear between the electrodes. They may last several minutes. A frog's heart, 

 which yields weak and irregular contractions, may be made to execute regular 

 rhythmical contractions isochronous with the stimuli, if electrical stimuli are used 

 (Bowditch). In this case the weakest stimuli (which are still active) behave like 

 the stronger stimuli even with the weak stimulus the heart always gives the 

 strongest contraction possible. Hence this minimal electrical stimulus is as 

 effective as a "maximal" stimulus (Kronecker and Stirling). 



V. Ziemssen found that he could not alter the heart-beats of the Imman heart (Frau 

 Serafin, p.74,3), even with strong induction currents. The ventricular diastole seemed 

 to be less complete, and there were irregularities in its contraction. By opening and 

 closing, or by reversing a strong constant current applied to the heart, the number 

 of beats was increased, and the increase corresponded with the number of electrical 

 stimuli; thus, when the electrical stimuli were 120, 140, 180, the number of heart- 

 beats was the same, the pulse beforehand being SO. When ISO shocks per minute 

 were applied the action of the heart assumed the characters of the pulsus alternans 

 (p. 143). Minimal stimuli were also found to act like maximal stimuli. The 

 normal pulse-rate of SO was reduced to 60 and 50, when the number of shocks was 

 reduced in the same ratio. The rhythm became at the same time somewhat 

 irregular. In these experiments a strong current is required, and v. Basch found 

 that the same was true for the frog's heart. Even in healthy persons, v. Ziemssen 

 ascertained that the energy and rhythm of the heart could be modified by passing 

 an electrical current through the uninjured chest-wall. 



[Method. The apparatus (Fig. 32.) is also well adapted for studying the effect 

 of electrical currents upon the heart. Bowditch, Kronecker and Stirling, and 

 other observers, used the " heart-apex," as it does not contract spontaneously 

 for some time after the ligature is applied. One electrode is attached to the 

 canuula, and the other is placed in the fluid in which the heart is bathed.] 



[Opening induction shocks, if of sufficient strength, cause the heart to con- 

 tract, while weak stimuli have no effect; on the other hand, moderate stimuli, 

 when they do cause the heart to contract, always cause a maximal contrac- 

 tion, so that a minimal stimulus acts at the same time like a maximal stimulus. 

 The heart either contracts or it does not contract, and when it contracts the 

 result is always a "maximal" contraction. Bowditch found, that the excit- 

 ability of the heart was increased by its own movements, so that after a heart 

 had once contracted, the strength of the stimulus required to excite the next 

 contraction may be greatly diminished, and yet the stimulus be effectual. Usually 

 the amplitude of the first beat so produced is not so great as the second beat, and 

 the second is less than the third, so that a " staircase " (" Treppe ") of beats 

 of successively greater extent are produced (Fig. 34. ) This staircase arrangement 

 occurs even when the strength of the stimulus is kept constant, so that the produc- 

 tion of one contraction facilitates the occurrence of the succeeding one. A staircase 

 arrangement of the pulsations is also seen in Luciani's groups (p. 104). The ques- 

 tion, whether a stimulus will cause a contraction, depends upon what 

 particular phase the heart is iu, when the shock is applied. Even comparatively 

 weak stimuli will cause a heart to contract, provided the stimuli are applied at 

 the proper moment and in the proper tempo i.e. to say, they become what 

 are called "infallible." If stimuli are applied to the heart, at intervals which 

 are longer than the time the heart takes to execute its contraction, they are 

 effectual or "adequate," but if they are applied before the period of pulsation 

 comes to an end, then they are ineffectual (Kronecker). It is quite clear, there- 



