550 CIRCULATION OF BLOOD AND LYMPH. 



fore, to attribute it to the vibration of these valves when suddenly 

 put under tension by the ventricular systole. Most authors, in- 

 deed, beheve that this factor is at least partially responsible for 

 the sound — that is, that the sound contains a valvular element. 

 But that this is not the sole cause is shown by the fact that the 

 bloodless beating heart still gives a sound at the time of the 

 ventricular systole. 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 auriculoventricular 

 valves, and a muscular element due to the vibration of the con- 

 tracting muscular mass. 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 the heart beat 

 with results such as are shown in Fig. 235. The figure shows 



Fig. 235. —To show the time relation of the heart sounds to the ventricular beat 

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

 low 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 begi' 

 ning of diastole. 



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 detailed study 

 of the time relations of the heart sounds has been made by Ein- 

 thoven 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. 236. 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-h) . Over the 

 base of the heart (second intercostal space) the first sound is heard 

 (h to c-d) just at the time when the semilunar valves are opened 

 (b') — that is, at the beginning of the period of emptying according 

 to the classification given on p. 546. The beginning of the second 



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

 1894. Einthoven, ibid., 1907, vol. 117. Fahr, "Heart," 4, 147, 1912. 



