THE HEART BEAT. 505 



sound. It is usually said, therefore, that the first heart sound is 

 caused by the combination of at least two factors, a valvular 

 element due to the vibration of the auriculo- ventricular valves, and 

 a muscular element due to the vibration of the contracting muscular 

 mass. Accepting this view, there is a further difficulty in explain- 

 ing the origin of the muscular element. According to some, it is 

 due to the fact that the contraction of the muscle fibers is not 

 simultaneous throughout the ventricle and the friction of the inter- 

 lacing fibers sets up vibration in the muscular mass; according to 

 others, the so-called muscular element is mainly a resonance tone of 

 the ear membrane of the auscultator, the shock of the contracting 

 heart sets the tympanic membrane to vibrating. It seems useless 

 to attempt a detailed discussion of these conflicting views, since no 

 convincing statements can be made. Practically, the time at which 

 the heart sounds occur is of great importance. A number of 

 observers have recorded the time upon a cardiographic tracing of 



Fig. 213. To show the time relation of the heart sounds to the ventricular beat 



iMarey) : V.D., Tracing of the ventricular pressure in the right ventricle of the horse. Be- 

 ow the two marks show, respectively, the time of the first and second sounds. The first 

 occurs immediately after the beginning of systole, the second immediately after the begin- 

 ning of diastole. 



the heart beat with results such as are shown in Fig. 213. The 

 figure shows clearly the general fact that the first sound is heard 

 very shortly after the beginning of systole and the second one 

 immediately after the end of systole. The first sound is therefore 

 systolic, and the second sound diastolic. A more exact and de- 

 tailed study of the time relations of the heart sounds has been made 

 by Einthoven and Geluk.* These authors obtained graphic records 

 of the heart sounds. The sounds received first by a microphone 

 were transmitted to a capillary electrometer and the movements 

 of the latter were photographed. As one result of their work they 

 give the schema shown in Fig. 214. It will be seen from this figure 

 that the first sound begins about 0.01 sec. before the cardiogram 

 shows the commencement of systole, and that for the first 0.06 sec. 

 the sound is heard only over the apex of the heart (a-6). Over the 



* Einthoven and Geluk, "Archiv f. d. gesammte Physiologic, " 57, 617, 

 1894. Einthoven, ibid., 1907, vol. 117. 



