286 GENERAL ANATOMY. 



heart, this organ becomes a powerful agent of the movement 

 of the blood; it is thus, that by its own action the arterial cir- 

 culation, although continuous, is pulsatory; it is thus that the 

 circulation takes place in the sturgeon, although the aorta is 

 inclosed in a bony canal; in the same manner in man, the aorta 

 and its principal branches may be ossified without materially 

 impairing the regularity of the course of the blood. We must 

 hence conclude that both these powers (that of the heart and 

 that of the arteries,) contribute to the performance of the cir- 

 culation, and that one may in a measure supply the action of 

 the other. But the action of the heart on the blood gradually 

 diminishes, and that of the vessels augments, in proportion as 

 it is more distant from the centre of circulation. The vital 

 contraction of the arteries is also one of the causes of their 

 emptiness in the dead body.* 



424. The arterial circulation is accompanied with a move- 

 ment called pulse. At different times it was ascribed to the 

 alternate dilatation and contraction of the arteries; to the elon- 

 gation of these vessels, and to the motion which results from 

 it; to the pressure of the finger while feeling it, or to several 

 of these causes combined. The number of pulsations de- 

 pend solely upon that of the contraction of the heart. The 

 volume or fullness of the pulse is owing to the quantity of the 

 blood contained in the arteries; its duration, to that of the con- 

 tractions of the heart; its strength, to the quantity of the blood 

 propelled by the heart, to the power with which it is pushed, 

 to the quantity contained in the arteries, and to that which 

 passes through the capillary vessels. 



The feeling of the pulse has for its object the examination 

 of the state of the circulation, and of the powers which move 

 the blood, viz., the heart and vessels. 



* With all due deference for the opinion of our author, we beg to differ 

 with him on this point. We believe that the new experiments on endos- 

 mose and exosmose tend to prove the contrary position. We conceive that 

 the larger arteries have lost at this time all power of vital contract here 

 ascribed to them, when the blood is, by an action in the capillaries, as y t 

 not positively demonstrated, drawn from the larger arteries through the ca- 

 pillaries into the veins. 



