ELECTROCARDIOGRA M 



13 



no evidence in favor of such a diffused effect; on the contrary, the 

 argument based on the fact that in one instance we are dealing with a 

 single piece of muscle and in the other case with separate pieces of 

 muscle, though plausible, can be shown to be unsound. The experiment 

 of the bent piece of muscle can be performed on uninjured heart muscle. 

 It is accomplished as follows : Leading off contacts are placed on a dog's 

 chest wall (Fig. 3 A), the one on the right side, the other on the left, 

 and the right ventricle is stimulated first on its epicardial surface at 2, 

 and secondly on its endocardial surface at 1, the points stimulated 

 being in the same line as the leading off contacts. It will be obvious 

 that, when we stimulate at 2, the excitation wave will move in a general 

 direction in the body from right to left across the heart (from 2 toward 

 3). It will be equally obvious that if we stimulate at 1 the excitation 

 will at first move in a general direction from 1 toward 2, and that a 

 little later the general course from 2 toward 3 will be pursued. In the 





\ 



i \ 



1 ( 



S i S 



M 





Fig. 4. An example of the findings of four distinct experiments. The lead 

 was from the right chest wall (Z contact) to the left chest wall (C contact) and 

 the wall of the right ventricle was stimulated on its epicardial surface (right 

 hand record), and on its endocardial surface (left hand record). In the last 

 case a small pair of long insulated electrodes was introduced through a small 

 slit in the wall of the conus or through the jugular vein. The two points of 

 stimulation (inside and outside) lay no more than 0.5 cm. from each other. 

 The curves differ in one respect, the left hand curve begins with an initial 

 phase i directed downward, in the right hand curve this phase is directed 

 upward. These initial phases of the curves correspond to involvement of the 

 wall at the point stimulated (the involvement being in opposite directions in 

 the two circumstances). The main deflection m is similar in both curves; it 

 represents spread from right to left in the ventricles as a whole. Curves of 

 this kind are obtained most successfully if the lungs are well inflated so that 

 good contact is maintained between the sides of the heart and the chest wall. 

 The curves represent responses to rhythmic break shocks (single shocks give 

 similar effects). The stimulus is recorded electrically in the top line. The curves 

 are not distorted by the stimuli, as the time relations of stimulus and shock 

 show ; reversal of the direction in which the stimulus entered the heart did not 

 affect the form of the curves. 



