292 Lieut-Colonel C. B. Heald and Major W. S. Tucker. 



consist of (reading from right to left) a small peak, followed immediately by 

 two considerably larger peaks, and then by two smaller and somewhat flatter 

 peaks. These peaks have been numbered 1 to 5 in the diagram. These five 

 peaks, since they are nearly always present in every curve, may be considered 

 as the essential elements of the normal recoil curve. In some of the heart 

 cycles in the figure other smaller peaks may be observed, and it is generally 

 these secondary peaks that tend to become exaggerated, or entirely absent, 

 from case to case. 



Fig. 5 shows also a simultaneous record taken over the carotid by means of 

 the special hot-wire microphone previously described. On this record, the 

 time relations of the various peaks of the recoil curve in relation to the 

 phenomena of a heart cycle have been purposely omitted. This has been done 

 to avoid confusion and error, as the peak of the " hot-wire " carotid curve, 

 which indicates the maximum of velocity, does not occur at the same time 

 as that on the ordinary carotid curve. It is, as shown previously, a curve out 

 of phase with the ordinary curves which record changes in pressure. When 

 the simultaneous records of figs. 5 and 6 were taken we had no comparator at 

 our disposal and therefore have not given an exact figure for the time 

 interval between the commencement of the first heart sound and the 

 •commencement of the carotid peak. 



In the heart-sound microphone, the deflections caused by the commence- 

 ment of the first and second sounds, corresponding, as they do, to the closure 

 of the auriculo-ventricular and semilunar valves, fix very definite points of 

 time in the heart cycle for comparative purposes on simultaneous tracings. 



As heart-sound records are free from the difficulty inherent in any 

 comparison between potential and kinetic energy curves, a simultaneous record 

 of recoil and heart sounds has been prepared, and this is shown in fig. 6, while 

 the relation of the two sounds has been more clearly defined by lines drawn 

 through their commencement to cut the recoil curve. 



As it is undesirable to introduce the recoil curve into the standard composite 

 diagram representing changes of pressure in auricles, ventricles, aorta and 

 •carotid, a special diagram, fig. 7, has been prepared, in which the kinetic 

 energy curves of body recoil and carotid are co-ordinated with heart sounds. 

 For the time relations of the various events in a heart cycle, the data given 

 by Lewis (10) have been used. 



From figs. 5 and 7 the commencement of the carotid curve is seen to 

 coincide with the beginning of the first or small peak of the recoil curve. 

 This peak (1) is, therefore, probably caused by the feetward movement of the 

 body corresponding to the headward movement of blood as it is projected 

 from the left ventricle shortly after the beginning of each systole. The 



