194 



THE CIRCULATION OF THE BLOOD 



significance in connection with their function of tightening the chorda 1 

 tendineae so as to prevenl any bulging of the flaps of the auriculoven- 

 tricular valve into the auricles when, at the beginning of the presphygmic 

 period, the high intraventricular pressure is brought to bear on their 

 under surfaces. After starting at this point in the ventricle, the con- 

 traction wave seems to spread farther through the ventricular muscle at 

 a fairly uniform rate. 



Investigation of this problem by means of the galvanometer has been 

 technically a very difficult matter, and the details of the researches by 

 Lewis and his pupils have not as yet been published in full. According 

 to the preliminary communications at hand, however, 3 ' 1 it appears that, 



Fig. 56. — Diagram of experiment by Lewis showing the times at which the excitation wave 

 appeared on the front of the heart relative to the upstroke of R in lead II. R.A., right appen- 

 dix; D.B.L., descending branch of left coronary artery. (From Thomas Lewis.) 



when nonpolarizable electrodes are placed at various parts of the outer 

 aspect of the ventricle, and comparison made of the moments at which 

 the cardiac impulse arrives, as judged by the appearance of the excita- 

 tion wave relative to R in a standard electrocardiogram, it has been 

 Pound that the time of arrival bears no relationship to the anatomic ar- 

 rangement of the muscle bundles of the ventricle. It arrives early and 

 simultaneously over an area of the surface near the anterior attachment 

 of the wall of the right ventricle. It arrives late at the base of the right 

 ventricle and in the part near the posterior intraventricular groove. 

 Histological examination lias shown that the branches of the right division 

 of the auriculoventricular bundle are most closelv connected with the 



