THE CIRCULATION OF THE BLOOD. 



241 



THE PULSE. 



Naturally' the intermittent action of the heart gives rise to 

 corresponding phenomena in the elastic tubes into which it 

 may he said to be continued, for it is very desirable to keep in 

 mind the complete continuity of the vascular system. 



The following phenomena are easy of observation : When 

 a fuiger-tip is laid on any artery, an interrupted pressure is felt; 

 if the vessel be laid bare (or observed in an old man), it may 

 be seen to be moved in its bed forward and upward ; the press- 

 ure is less the farther the artery from the heart ; if the vessel 

 be opened, blood flows from it continuously, but in spurts ; if 

 one finger be laid on the carotid and another on a distant ves- 

 sel, as one of the arteries of the foot, it may be observed (though 

 it is not easy from difficulty in attending to two events hap- 

 pening so very close together) that the beat in the nearer ves- 

 sel precedes by a slight interval that in the more distant. 



Investigating the latter phenomenon with instruments, it is 

 found that an appreciable interval, depending on the distance 

 apart of the points observed, intervenes. 



What is the explanation of these facts ? 



The student may get at this by a few additional observa- 

 tions that can be easily made. 



Fig. 205.— Marey'B apparatus for showing the mode in which the pulse is propagated 

 in the arteries. 5, a rubber pump, with valves to prevent regurgitation. The 

 working of the apparatus will be apparent from the inspection of the figure. 



If water be sent through a long elastic tube (so coiled that 

 points near and remote may be felt at the same time) by a bulb 

 16 



