CIRCULATION OF THE BLOOD. 135 



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 dis- 

 tant, is nevertheless 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 en- 

 tirely, 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 time when the thorax is laid open, and the lungs having 

 collapsed, all the respiratory motions have ceased ; here, never- 

 theless, for a little while you may perceive the left auricle con- 

 tracting and emptying itself, and becoming whiter ; but by and 

 by growing weaker and weaker, it begins to intermit, as does 

 the left ventricle also, and then it ceases to beat altogether, 

 and becomes quiescent. Along with this, and in the same 

 measure, does the stream of blood from the divided artery 

 grow less and less, the pulse of the vessel weaker and weaker, 

 until at last, the supply of blood and the impulse of the left 

 ventricle failing, nothing escapes from it. You may perform 

 the same experiment, tying the pulmonary veins, and so taking 

 away the pulse of the left auricle, or relaxing the ligature, and 

 restoring it at pleasure. In this experiment, too, you will 

 observe what happens in moribund animals, viz., that the left 



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



