276 CIRCULATION. 



becomes rapidly diminished, being reduced in one experiment 

 about two-thirds ; the dicrotic impulse becomes very feeble or 

 even abolished ; but the constant flow is very much increased 

 in rapidity. This fact coincides with the ideas already ad- 

 vanced, with regard to the gradual conversion, by virtue of 

 the elasticity of the vessels, of the impulse of the heart into, 

 first, a remittent, and, in the very smallest arteries, a nearly 

 constant current. 



The rapidity of the flow in any artery must be subject to 

 constant modifications due to the condition of the arterioles 

 which are supplied by it. When these little vessels are di- 

 lated, the artery of course empties itself with greater facility, 

 and the rapidity is increased. Thus the rapidity bears a re- 

 lation to the arterial pressure ; as, independently of a dimi- 

 nution in the entire quantity of the circulating fluid, varia- 

 tions in the pressure depend chiefly on causes which facili- 

 tate or retard the flow of blood into the capillaries. A good 

 example of enlargement of the capillaries of a particular part, 

 is in mastication, when the salivary glands" are brought into 

 activity, and the quantity of blood which they receive is 

 greatly increased. Chauveau found an immense increase in 

 the rapidity of the flow in the carotid of a horse during mas- 

 tication. The enlargement of the vessels of the glands during 

 their function has been conclusively proven by the experi- 

 ments of Bernard. 



It must be remembered that in all parts of the arterial 

 system the rapidity of the current of blood is constantly liable 

 to increase from dilatation of the small vessels, and diminution 

 from their contraction. 



Arterial Murmurs. 



In the largest vessels, we can frequently hear with the 

 stethoscope the sounds conducted from the heart. In addi- 

 tion, we can hear, in all except the smallest vessels, a pecu- 

 liar blowing sound, called the l>ruit de sovffie, which is 



