164 Circulation of the Blood 



because the arteries have to sustain no shock from the 

 impulse of the blood. 



An artery denuded and divided in the way I have 

 indicated, sustains no shock, and therefore does not 

 pulsate ; whence it clearly appears that the arteries have 

 no inherent pulsative power, and that neither do they 

 derive any from the heart ; but that they undergo their 

 diastole solely from the impulse of the blood; for in 

 the full stream, flowing to a distance, you may see the 

 systole and diastole, all the motions of the heart their 

 order, force, rhythm, &C., 1 as it were in a mirror, and 

 even perceive them by the touch. Precisely as in the 

 water that is forced aloft, through a leaden pipe, by 

 working the piston of a forcing-pump, each stroke of 

 which, though the jet be many feet distant, is neverthe- 

 less distinctly perceptible, the beginning, increasing 

 strength, and end of the impulse, as well as its amount, 

 and the regularity or irregularity with which it is given, 

 being indicated, the same precisely is the case from the 

 orifice of a divided artery ; whence, as in the instance 

 of the forcing engine quoted, you will perceive that the 

 efflux is uninterrupted, although the jet is alternately 

 greater and less. In the arteries, therefore, besides the 

 concussion or impulse of the blood, the pulse or beat 

 of the artery, which is not equally exhibited in all, 

 there is a perpetual flow and motion of the blood, 

 which returns in an unbroken stream to the point 

 from whence it commenced the right auricle of the 

 heart. 



All these points you may satisfy yourself upon, by 

 exposing one of the longer arteries, and having taken it 

 between your finger and thumb, dividing it on the side 

 remote from the heart. By the greater or less pressure 

 of your fingers, you can have the vessel pulsating less 

 or more, or losing the pulse entirely, and recovering it 

 at will. And as these things proceed thus when the 

 chest is uninjured, so also do they go on for a short 



1 Vide Chapter III, on the Motion of the Heart and Blood. 



