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ON THE ELECTKICAL CHANGES IN THE HEAET. 
From the Physiological Laboratory of the South African College, 
(Preliminary Note.) 
By W. a. Jolly, D.Sc, Professor of Physiology. 
(Received August 25, 1913. Read September 17, 1913.) 
The interpretation of the electrocardiogram has remained doubtful, 
notwithstanding the very large amount of work that has been devoted 
to it in recent years, and very divergent views are entertained as to the 
significance of the features of the curve without conclusive evidence having 
been adduced. 
Since the electrocardiogram is now the most valuable means at the 
disposal of medical men for the diagnosis of heart conditions, it is of 
the utmost importance that the curves should be rightly interpreted. 
The following is the explanation which I have arrived at from experi- 
ments on the isolated tortoise heart, and especially from cases of systolic 
alternation in auricles and ventricle. 
The electrocardiogram of the ventricle when electrodes are applied 
(1) to base and apex, and (2) to symmetrical points on the right and 
left edges of the ventricle, and the connections made with the string 
galvanometer, as in Einthoven's work, represents the algebraic sum of 
two diphasic variations. 
In the case of base and apex leads the one variation is due to the trans- 
mission of excitation from the point between the leading off electrodes 
at which the stimulus reaches the ventricular muscle to the base of the 
ventricle. It consists of two phases, the first a brief positive deflection 
downwards and return to the zero line, the second a deflection upwards 
of much longer duration than the first phase, and exhibiting in its course 
a decline, subsequent slight rise, and ultimate fall to the zero line. 
The other diphasic variation is due to transmission of excitation from 
the point of entrance of the stimulus to the apex of the ventricle. Its 
