Physiology and biochemistry in modern medicine . part of theventricular musculature to contract is therefore located near the ter-mination of these branches, at the papillary muscles. That these shouldcontract before the rest of the muscle of the ventricles, has an obvious 194 THE CIRCULATION OP TIIK MLOOD significance in connection with their function of tightening the chordaetendineae so as to prevent any bulging of the flaps of the auriculoven-tricular valve into the auricles when, at the beginning of the prcsphygmicperiod, the high intraventricular pressure is brought to bear on theirunder
Physiology and biochemistry in modern medicine . part of theventricular musculature to contract is therefore located near the ter-mination of these branches, at the papillary muscles. That these shouldcontract before the rest of the muscle of the ventricles, has an obvious 194 THE CIRCULATION OP TIIK MLOOD significance in connection with their function of tightening the chordaetendineae so as to prevent any bulging of the flaps of the auriculoven-tricular valve into the auricles when, at the beginning of the prcsphygmicperiod, the high intraventricular pressure is brought to bear on theirunder surfaces. After starting at this point in the ventricle, the con-traction wave seems to spread farther through the ventricular muscle ata fairly uniform rate. Investigation of this problem by means of the galvanometer has beentechnically a very difficult matter, and the details of the researches byLewis and his pupils have not as yet been published in full. Accordingto the preliminary communications at hand, however,3* it appears that, •0*6/. Fig. 56.—Diagram of experiment by Lewis showing the times at which the excitation waveappeared on the front of the heart relative to the upstroke of R in lead II. , right appen-dix; , descending branch of left coronary artery. (From Thomas Lewis.) when noupolarizable electrodes are placed at various parts of the outeraspect of the ventricle, and comparison made of the moments at whichthe cardiac impulse arrives, as judged by the appearance of the excita-tion wave relative to R in a standard electrocardiogram, it has beenfound that the time of arrival bears no relationship to the anatomic ar-rangement of the muscle bundles of the ventricle. It arrives early andsimultaneously over an area of the surface near the anterior attachmentof the wall of the right ventricle. It arrives late at the base of the rightventricle and in the part near the posterior intraventricular examination has shown that the branches of
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