ELECTROCARDIOGRAMS 277 



cycle Fahr has traced the manner of spread of the excitation wave over 

 the ventricles, and from the results considered along with our knowl- 

 edge of the course of the Purkinje system of conducting tissue, and the 

 rate of -conduction of the electrical disturbance through it and through 

 the muscle fibers, as well as the precise moment of onset of the first 

 sound and of the rise in intraventricular pressure, he has arrived at the 

 following conclusions: The excitation process begins in the Purkinje 

 system in the neighborhood of the papillary muscles, a little earlier in 

 the right than in the left ventricle and spreads to the apical region, 

 causing the Q wave. It is then conducted to the basal portions of the 

 system, causing the ascending limb of the R wave, and while this is go- 

 ing on at the base, the impulse is being conducted from the Purkinje 

 fibers into the muscle fibers at the apex. When as a result, the muscle 

 fibers have acquired sufficient negativity to neutralize the hitherto pre- 

 ponderating negativity in the Purkinje system at the base, the descend- 

 ing limb of R is formed, and S results. Soon thereafter the muscle fibers 

 are equally affected over the ventricle and S becomes obliterated and, 

 finally, the negativity dies out at first at the apex and later at the base, 

 thus causing the T wave. When one ventricle of the heart is hypertro- 

 phied the conduction path on this side becomes elongated so that the 

 other ventricle receives its negativity first and the electrocardiogram 

 becomes distorted. The position of lesions affecting one or other of the 

 main branches of the conducting system, can be determined by a study 

 of the electrocardiograms by the above methods. When the left branch 

 is affected R should be high in lead I and S deep in lead III, whereas in 

 those of the right branch S should be deep in lead I and R high in lead 

 III. 



