SEC. 3. THE 



When the finger is placed on an artery, such as the radial, an 

 intermittent pressure on the finger, coming and going with the 

 beat of the heart, is felt. When a light lever such as that of the 

 sphygmograph is placed on the artery, the lever is raised at each 

 beat, falling between. The pressure on the finger, and the raising 

 of the lever, are expressions of the expansion of the elastic artery, 

 of the temporary additional distension which the artery undergoes 

 at each systole of the ventricle. This intermittent expansion is 

 called the pulse; it corresponds to the intermittent outflow of 

 blood from a severed artery, being present in the arteries only, 

 and except under particular circumstances, absent from the veins 

 and capillaries. The expansion is frequently visible to the eye, 

 and in some cases, as where an artery has a bend, may cause a 

 certain amount of locomotion of the vessel. 



All the more important phenomena of the pulse may be 

 witnessed on an artificial scheme. 



If two levers be placed on the arterial tubes of an artificial 1 

 scheme, one near to the pump, and the other near to the peripheral 

 resistance, with a considerable length of tubing between them, and 

 both levers be made to write on a recording surface, one im- 

 mediately below the other, so that their curves can be more easily 

 compared, the following facts may be observed, when the pump is 

 set to work regularly. 



1 By this is simply meant a system of tubes, along which fluid can be driven by a 

 pump worked at regular intervals. In the course of the tubes a (variable) resistance 

 is introduced in imitation of the peripheral resistance. The tubes on the proximal 

 side of the resistance consequently represent arteries; those on the distal side, veins. 



F. 11 



