CH. XXI.] THE PULSE 287 



None of these methods, however, give the true time of the entire 

 circulation ; they give merely the shortest possible time in which any 

 particle of blood can travel through the shortest pathway. The 

 blood that travels in the axial current, or which takes a broad path- 

 way through wide capillaries, will arrive far more speedily at its 

 destination than that which creeps through tortuous or constricted 

 vessels. The direct observations of Tigerstedt on the output of the 

 left ventricle show that the circulation time of the whole blood is at 

 least five times as long as the period arrived at by the Hering 

 method. It is therefore fallacious to use the circulation times 

 arrived at by Bering's or Stewart's methods as a basis for calculating 

 the total amount of the blood in the body. 



The Pulse. 



This is the most characteristic feature of the arterial flow. It is 

 the response of the arterial wall to the changes in lateral pressure 

 caused by each heart-beat. 



A physician usually feels the pulse in the radial artery, since this 

 is near the surface, and supported by bone. It is a most valuable 



FIG. 286. Marey's Sphygmograph, modified by Mahomed. 



indication of the condition of the patient's heart and vessels. It is 

 necessary in feeling a pulse to note the following points : 



1. Its frequency ; that is the number of pulse-beats per minute. 



This gives the rate of the heart-beats. 



2. Its strength ; whether it is a strong, bounding pulse, or a feeble 



beat; this indicates the force with which the heart is 

 beating. 



