ELECTROCARDIOGRAMS 



271 



certaining to what extent the string moves when a current of known 

 voltage is sent through it and by altering the tension of the string so that 

 one millivolt of current causes an excursion of one centimeter of the 

 string shadow on the photographic plate. It would take us beyond the 

 confines of this volume to go in any greater detail into the technic in- 

 volved in taking electrocardiograms, but it may be said that this is by 

 no means difficult, provided the instructions which are supplied with 

 the instrument are carefully followed. In practice the taking of elec- 



Fig. 81. Klectrocardiographic apparatus as made by the Cambridge Scientific Materials Co. Con- 

 tact electrodes are shown, but the immersion electrodes described in the context are preferable. 



tro cardiograms is indeed quite a simple matter, and the extremely im- 

 portant information which they give us concerning the mechanism of 

 the heartbeat and the evidence of myocardial disease should make their 

 employment a universal practice in all cardiac clinics. Some of these 

 clinical applications are described elsewhere (page 278). 



Interpretation of Electrocardiograms by the Triangle Method 



In the analysis of the electrocardiographic tracing, much information has been 

 gained with regard to the relation which the various deflections bear to the electrical 

 changes occurring within the heart, by determining the average direction along 



