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the body, the motions of the heart shake its whole mass, and these qui- 

 verings, which may be observed externally, are most manifest when the 

 circulation is carried on with rapidity and force. In some head-jches, 

 the internal carotid arteries pulsate with such violence, tJutt nut only the 

 ear is sensible to the noise made by the column of blood striking- against 

 the curvature of the osseous canal, but the head is evidently moved and 

 raised, as it were, at each pulsation. If you look at your hand or foot, 

 when the upper or lower extremity is quiescent and pendulous, you will 

 observe in it, a slight motion corresponding to the beats of the heart. 

 This motion increases, and even makes the hand shake, when, from the 

 influence of the passions, or from violent exercise, the circulation is ac- 

 celerated; in every violent emotion, we feel, within ourselves, the effort 

 by which the blood, at each beat of the pulse, penetrates into our organs, 

 and fills every tissue. And it is, in a great measure, from this inward 

 tact, that we are conscious of existence. A consciousness the more lively 

 and distinct, as the effect of which we are speaking is more marked. It 

 is, likewise, from observing this phenomenon, that several physiologists 

 have been led to conceive the idea of a double motion, which dilates or 

 condenses, which contracts or expands, alternately, all organs endowed 

 with life ; they have observed, that dilatation prevails in youth, in inflam- 

 mation and erection, conditions of which all parts are capable, according 

 to their difference of structure. 



LIX. At the moment when the left ventricle contracts, to send the 

 blood into the aorta, the sigmoid valves of that artery rise, and apply 

 themselves to its parietes, without, nevertheless, closing the orifices of 

 the coronary arteries, which lie above the loose edges of the valves; so 

 that the blood is received into these vessels, at the same time as into the 

 others. When the contraction of the ventricle is over, the aorta acts on 

 the blood which it contains, and would send it back into the ventricle, if 

 the valves, by suddenly descending, did not present an insuperable obsta- 

 cle to the return of blood, and did not yield a point of resistance to the 

 action of the whole arterial system ; only the small quantity of blood be- 

 low the valves, at the moment of their descending, flows back towards 

 the heart, and returns into the ventricle, 



Though the rate at which the blood flows along the aorta, has been 

 estimated at only about eight inches in a second, a pulsation is felt in all 

 the arteries of a certain calibre, at the instant the ventricles are contract- 

 ing. The reason that the pulsations of the heart appear to take place, at 

 the same time as those of the arteries, is, that the columns of blood, in 

 these vessels, receive an impulse from that which is issuing from the* ven- 

 tricles, and this concussion is felt in an instant of time, too short to be' 

 measured, such as that which is felt by the hand applied to the end of a 

 piece of timber struck, at the other end, with a hammer. The blood 

 which fills the main trunk, supplies to each of the branches which arise 

 from it, columns proportionate to their calibre. This division of the 

 principal column is effected by a kind of projection at the mouth of each 

 artery. These internal projections detach from the main stream, the 

 lesser ones, and these flow the more readily into the branches, according 

 as these arise from the trunk, at a more acute angle, as the projection is 

 more prominent, and the deviation of the fluid less considerable. If the 

 branches are given off, at an almost right angle, the orifices of the arte- 

 ries scarcely project at all, and nothing but the effort of lateral pressure; 

 determines the flow of the blood into them. 



