CHAP.XXVlll.] THE FORCE OF THE HEART. 357 



The difference in the results obtained by Hales, as regards the 

 velocity with which certain fluids passed through the blood-vessels, 

 is referrible to the contractile power of the arteries. Thus, while 

 warm water, injected into the blood-vessels of a dog's bowels, 

 passed in fifty-two seconds, the same quantity of common brandy 

 took sixty-eight seconds ; cold water (fourteen degrees above freez- 

 ing) was eighty seconds longer in passing than the same quantity 

 of warm water just before. A strong decoction of bark took much 

 longer to pass through the vessels than the same quantity of warm 

 water. Sixteen pots, of equally warm decoction of bark, were suc- 

 cessively poured in, the first of which passed in seventy-two seconds ; 

 the sixteenth, " as the vessels grew more and more contracted by 

 the styptic quality of the decoction," was 224 seconds in passing.* 



This contractile power in the walls of arteries (their tone or pas- 

 sive contraction) is capable of modifying considerably the character 

 of the pulse. When it is feeble, the artery offers but slight resist- 

 ance to the entrance of the blood, and it therefore yields more 

 completely under the force of the heart. Hence fulness of pulse 

 and feebleness of muscular power or of tone in the wall of the 

 artery, are apt to go together. On the other hand, an exalted 

 muscular power of tone in the wall of the artery, by contracting 

 the arterial tube, and resisting the flow of blood, would cause a 

 small, hard, and even a wiry pulse ; or a similar effect might be 

 produced by an irritating fluid, as a diseased blood, passing through 

 the artery. Again, failure of the tonic property of the arterial wall 

 causes a compressible pulse; an excited or well-developed tonic 

 power, will cause an incompressible pulse. 



Of the Force of the Heart. The blood encounters considerable 

 obstacles to its passage through the vascular system, which tend to 

 bring it to a state of rest. The friction against the inner surface of 

 the vessels, and the resistance of the elastic and muscular elements 

 of their walls to distension, must be overcome by any force 

 capable of keeping up a continual renewal of the supply of blood to 

 the several organs. Moreover, a certain rate of movement must 

 be maintained in the blood's current. The attainment of these ob- 

 jects is clearly provided for, in the main, by the action of the heart, 

 and that living pump is doubtless endowed with energies sufficient 

 to drive into the blood-vessels renewed supplies of blood, with a 



recently dead pass into the state of rigor mortis, like that of other muscles, 

 which will last a certain time ; the proper period for anatomical injections is 

 either before the rigor mortis has come on, or after it has ceased. 

 * Hsemastaticks, p. 124, et seqq. 



