250 HUMAN PHYSIOLOGY 



3rd. That upon the descent of the primary wave there are 

 one or more secondary waves. 



One of these is constant and is often very well marked. 

 It forms a second crest, and is hence called the dicrotic wave. 



Between the chief crest and this secondary crest, a smaller 

 crest is often manifest (Fig. 120, 3), and, from its position, it is 

 called the predicrotic wave. Sometimes other crests appear. 



Medium Pressure. 



Medium Pressure. 



Low Pressure. 



FlG. 120. Three Sphygmographic Tracings made from the radial artery of a 

 healthy man in the course of one hour without removing the Sphymograph. 

 1 was made immediately after muscular exercise ; 2 was made after sitting 

 still for half-an-hour ; and 3, after an hour. 



If the wave has only one crest it is called a one-crested or 

 monocrotic wave. If only the dicrotic crest is well marked 

 it is called dicrotic. If three crests are present, tricrotic ; 

 if several crests, polycrotic. 



To understand the various parts of the pulse wave it is 

 necessary to compare it with the intra-ventricular pres- 

 sure changes. This may be done by taking synchronously 

 tracings of the intra-ventricular pressure, and of the aortic 

 pressure (Fig. 121). 



