498 



CIRCULATION OF BLOOD AND LYMPH. 



will affect the electrodes at different times. This electrical varia- 

 tion of the contracting heart muscle may be shown easily by 

 means of the rheoscopic muscle-nerve preparation (see p. 99). If 

 the heart is exposed and the nerve of the preparation is laid over its 

 surface each ventricular systole is accompanied by a kick of the 

 muscle, since the nerve by connecting separated points acts as a 

 conducting wire for the current generated, and is stimulated, there- 

 fore, at each systole. Since the muscle-nerve preparation gives 

 only a simple contraction for each ventricular systole, we may 

 assume that this latter contraction is itself simple, that is, due 

 to a single stimulus. The electrical variation may be obtained also 

 by means of the capillary electrometer (p. 94), and since the move- 

 ment of the mercury in this instrument may be photographed the 



Fig. 209. Electrocardiogram obtained by photographing the movements of a sensitive 

 galvanometer. The upper figure shows the photographed curve, while the [lower one is a 

 diagram constructed from the photograph to make clearer the electrical changes in a single 

 cardiac cycle. To obtain this record the electrodes were connected with the right and left 

 hands. Waves with the apex upward indicate that the base of the heart (or the right ven- 

 tricle) is negative to the apex (or left ventricle). Waves with the apex downward have 

 the opposite significance. Wave P is due to the contraction of the auricle. Waves Q, 

 R, S, and T occur during the systole of the ventricle. The curve seems to show that the 

 contraction in the ventricles begins first toward the apex (or in the left ventricle), since 

 the negativity first appears toward that side (wave Q). (Einthoven). 



results can be studied in detail. Owing to the sensitiveness of the 

 instrument, the beat of the human heart may be registered in 

 this way (Waller) when the right hand, giving the potential changes 

 of the base of the heart, is connected with one electrode, and the 

 left hand (apex of heart) is connected with the other. The electro- 

 cardiograms thus obtained photographically show that, in the 

 ventricle at least, the electrical variation exhibits several phases, 

 and the character of these phases, that is, whether the base or the 

 apex first shows a negative potential, has been used in discussions 



