290 THE CIRCULATION IN THE BLOOD-VESSELS [CH. XXII. 



The second method used is even simpler, and gives practically the 

 same results; a solution of methylene blue is injected into a 

 vessel. The corresponding vessel on the opposite side is exposed, 

 placed upon a sheet of white paper, and strongly illuminated. The 

 time is noted between the injection and the moment when the blue 

 colour is seen to appear in the vessel under observation. Stewart 

 has applied these methods also for determining the time occupied 

 by the passage of blood through various districts of the circulation ; 

 the longest circulation times were found in the portal system and 

 the lower limbs. He calculates that the total circulation time in 

 man is about 15 seconds. 



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 Tigers ted t on the output of the 

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

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

 method. It is therefore fallacious to use the circulation times 

 arrived at by Hering'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 

 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. 



3. Its regularity or irregularity ; irregularity may occur owing to 



irregular cardiac action either in force or in rhythm. 



4. Its tension ; that is the force necessary to obliterate it. This 



gives an indication of the state of the arterial walls and the 

 peripheral resistance. 



In disease there are certain variations in the pulse, of which we 

 shall mention only two ; namely, the intermittent pulse, due to the 





