THE CIRCULATION OF THE BLOOD AND LYMPH 93 



sense. The intermittence in the flow with which the pulse- 

 wave is necessarily associated is at its height at the beginning of 

 the aorta. In middle-sized arteries, such as the radial, it is still 

 well marked, but it dies away as the capillaries are reached, and 

 only under special conditions passes on into the veins, where, 

 however, as has just been mentioned, pulsatory phenomena of a 

 different origin may be detected. 



The pulse was well known to the Greek physicians, and used 

 by them to a certain extent as an indication in practical medicine. 

 Harvey demonstrated with some clearness the relation of the 

 pulse to the contraction of the heart, but Thomas Young was 

 the first to form a proper conception of it as the outward token 

 of a wave propagated from heart to periphery. 



When the finger is placed over a superficial artery like the 

 carotid, the radial or the temporal, a throb or beat is felt, which, 

 without measurement, 

 seems to be exactly 

 coincident with the 

 cardiac impulse. In 

 certain situations the 

 pulse can be seen as 

 a distinct rhythmical 

 rise and fall of the 

 Skin over the vessel. FlG " SI-SCHEME OF MAREV'S SPHYGMOGRAPH. 

 TU u uu' f -t-v^ A, toothed wheel connected with axle H, and 



The throbbing of the gearing into toothed upright B . c ivory pad 



carotid, especially which rests over bloodvessel' and is pressed on it 

 after exertion is by movm g G, a screw passing through the spring J ; 

 familiar tn ^vprvnnf* E ' writin g' lev er attached to axle H, and moved by 



laminar to everyone, its rotation . E writes on D> a travelling surface 

 and the beat of the moved by clockwork F. 

 ulnar artery can be 



easily rendered visible by extending the hand sharply on the wrist. 

 When the pulse is felt by the finger, it is not the expansion, 

 but the hardening of the wall of the vessel, due to the increase of 

 arterial pressure, that is perceived ; and even a superficial artery, 

 when embedded in soft tissues so that it cannot be compressed, 

 gives no token of its presence to the sense of touch. Sometimes 

 an artery is longitudinally extended by the pulse-wave, and this 

 extension may be far more conspicuous than the lateral dilata- 

 tion. This is particularly seen when one point of the vessel is 

 fixed and a more distal point offers some obstruction to the blood- 

 flow, as at a bifurcation or in an artery which has been ligatured 

 and divided. 



By means of the sphygmograph, the lateral movements of 

 the arterial wall, or, rather, in man, the movements of the skin 

 and other tissues lying over the bloodvessel, can be magnified 

 and recorded. 



