FORM OF THE PULSE. 257 



was simply a series of regular elevations and depressions. 

 A comparison of the traces obtained by these two observers 

 gives an idea of the defects which have been remedied by 

 Marey ; for it is evident that the dilatation and contraction of 



FIG. 5. 



Trace of Marey. Portions of four traces taken In different conditions of the pulse (Ibid.) 



the arteries cannot be as regular and simple as would be in- 

 ferred merely from the trace made by the instrument of 

 Yierordt. 



Analyzing the traces of Marey, we see that there is a 

 dilatation following the systole of the heart, marked by an 

 elevation of the lever, more or less sudden, as indicated by 

 the angle of the trace, and of greater or less amplitude. The 

 dilatation, having arrived at its maximum, is followed by 

 contraction ; which may be slow and regular, or may be, and 

 generally is, interrupted by a second and slighter upward 

 movement of the lever. This second impulse varies very 

 much in amplitude. In some rare instances it is nearly as 

 marked as the first, and may be appreciated by the finger, 

 giving the sensation of a double pulse following each con- 

 traction of the heart. This is called the dicrotic pulse. 



As a rule, the first dilatation of the vessel is sudden, and 

 indicated by an almost vertical line ; this is followed by a 

 slow reaction, indicated by a gradual descent of the trace, 

 which is not, however, absolutely regular, but marked by a 

 slight elevation indicating a second impulse. 



The amplitude of the trace, or the distance between the 

 highest and lowest points marked by the lever, depends upon 

 the amount of constant tension of the vessels. Marey has 

 found that the amplitude is in an inverse ratio to the tension ; 

 which is very easily understood, for when the arteries are little 

 distended, the force of the heart must be more marked in its 

 17 



