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deviation, so as to give a regularly rising and falling line. No 
eT er. 
Fig. 1. 
difference between the different beats could be observed. The maximal 
P.D amounts to about 20-—30 microvolts. 
On the 8' day we get a curve which is perfectly differentiated. 
Instead of a series of continuous simple, nearly sinusoidal deviations 
we get deviations which may be grouped in series of 3 each, each 
group belonging to one heart beat. In each group the first and 
second deviation have the same polarity and are followed by a 
third peak of opposite polarity. The first peak seems to be somewhat 
higher than the others. I suppose that we may consider these three 
deviations as identical with the summits P, R, and T in thenormal 
human electrocardiogram. The largest potential difference, that of the 
Rare 
Fig. 2. 
P-deviation, amounts to some 50 or 60 microvolt. The duration of 
P is of the order of 0.07 second. The R-peak has a shorter duration. 
In a few records I believe I have also found slight indications of a 
Q and an S-peak. The electrical activity represented by the T-peak 
extends over 0.15—0.18 second. 
I am not yet prepared to speak about the extremely important 
question as to how the differentiated electrocardiogran: of the 8th day 
develops from the undifferentiated curves derived before the 6 day. 
After the 8 day, as the foetal heart grows stronger, the electro- 
cardiogram also grows stronger. It shows more markedly all the 
points generally visible in the electrocardiogram of the full-grown 
embryo and in that of the new-born chicken. This latter shows 
some similarity to the mammalian or human electrocardiogram. 
On the 12% and 14° day electrocardiograms with higher potential 
oscillations, up to 0,5 millivolt, can easily be recorded. After that 
Mat ne 
Fig. 3: 
time the maximal PD rises very slowly till the chicken is fully 
