Abstract
Recent improvements in the technique previously described 1 , 2 have been made by the addition of a special circuit 3 with 3 vacuum tubes between the electrodes and the galvanometer. This apparatus gives a known and desired amplification (5 to 30 times) of the heart voltage, without distortion. By its use, a new series of electrocardiograms of the chick embryo from the fourth day to the twentieth day was taken.
Five distinct waves are seen as early as the fourth day. These, like those of the adult mammalian heart, can be separated into 2 parts, the auricular complex and the ventricular complex. The auricular complex consists of the P-wave which is followed immediately by a wave of longer duration, Ta, which occupies the remainder of the P-R interval. The analogy may be drawn between this new wave (Ta) and the T-wave following the ventricular complex. The ventricular complex starts with a sharp summit R, and a dip S. There is no Q-wave in any record. The T-wave follows, always diphasic in type. The recorded voltages on the fourth day were read from the β lead and the circuit resistance was 4300 to 5400 ohms.
The average P-wave deflection was 0.015 millivolts, Ta-wave was 0.010 millivolts. The average R-wave was 0.070 millivolts, the S-wave 0.070 millivolts, and the T-wave took origin 0.017 millivolts negatively to the isoelectric and after becoming 0.018 millivolts negative went to a summit of 0.003 millivolts before returning to the base line.
In the a lead the α-wave is diphasic up to the tenth day inclusive, after which it is always negative. The Ta wave is positive to the eleventh day inclusive and then becomes negative. The R-wave is upright, the S-wave dips, and the T-wave always starts negatively to the isoelectric line and is invariably diphasic.
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