546 CIRCULATION OF BLOOD AND LYMPH. 



least, the electrical variation exhibits several phases, and the char- 

 acter of these phases, that is, whether the base or the apex first 

 shows a negative potential, has been used in discussions upon 

 the direction of the wave of contraction. In Fig. 227 is given 

 an illustration of a human electro-cardiogram obtained by con- 

 necting the right and left hands with the electrodes of a string 

 galvanometer. With such an arrangement or "lead" the elec- 

 trode in the right hand may be regarded as leading off from the 

 auricular end of the heart, while that in the left hand leads off 

 from the apex of the ventricle.* As the galvanometer is arranged, 

 a negativity (indicative of excitation) toward the auricular end 

 is shown by a movement above the horizontal base line, while 

 a negativity toward the apex is shown by a movement in the 

 opposite direction. Similar electrocardiograms, differing in certain 

 details, may be obtained by connecting the electrodes with other 

 parts of the body. In experimental as well as clinical work it has 

 become customary to use the three "leads" introduced by Ein- 

 thoven namely, lead I, the electrodes connected with the right and 

 left hands respectively; lead II, right hand and left foot; lead III, 

 left hand and left foot. The electrocardiogram taken from lead I 

 (Fig. 227) shows three positive waves, P, R, and T, and two nega- 

 tive waves, Q and S. The first positive wave, P, indicates an initial 

 development of negativity toward the base or auricular end of the 

 heart. All observers practically agree that this wave is due to the 

 contraction of the auricles. On the other hand, the waves Q, R, S, 

 and T occur during the systole of the ventricles. R and T are the 

 more prominent and constant of these waves. Q and S may be 

 absent or scarcely detectable in normal electrocardiograms. There 

 is much difference of opinion in regard to the exact significance of 

 these waves. As the galvanometer is arranged and connected with 

 the heart one can say that the negative wave Q indicates the exist- 

 ence of a negative potential in the apical portion of the heart. It 

 would, therefore, suggest that the excitation wave reaches first 

 some region of the heart toward the apex. The succeeding positive 

 wave, R, indicates, on the contrary, negativity and, therefore, an 

 excitation toward the base of the ventricle. Following this method 

 of interpretation the electrocardiogram has been used to trace out 

 the course of the wave of excitation and contraction in the ventricle, 

 but there has been little agreement in the conclusions reached by 

 various workers. If we can accept the description, given in the 

 preceding paragraph, of the course of the wave of excitation and 

 contraction in the ventricle it would seem that the whole of the 



* For a description of the Electrocardiogram and the literature consult, 

 James and Williams; "American Journal of the Medical Sciences," Nov., 1910, 

 or Kraus and Nicolai, "Das Elektrokardiogramm," Leipzig, 1910. 



