PERIPHERAL REGULATION OF THE FLOW OF BLOOD 



209 



quantity of blood. The other secondary waves are probably due to the os- 

 cillations in the elastic recoil of the arteries, though some of them at least 

 may be due to the inertia of the instruments used. 



In the use of the sphygmograph care must be taken in the regulation of 

 the pressure of the spring. If the pressure be too great, the characters of 



23456 7 



B 



FIG. 200. A, Normal Pulse- Tracing from Radial of Healthy Adult Obtained by the Sphyg- 

 mometer; B, from same artery, with the same extra-arterial pressure, taken during acute nasal 

 catarrh. 



the pulse may be almost entirely obscured, or the artery may be completely 

 obstructed and no tracing is obtained. On the other hand, if the pressure is 

 too slight, a very small part of the characters may be represented on the tracing. 



THE PERIPHERAL REGULATION OF THE FLOW OF BLOOD. 



The flow of blood through the circulatory system depends on the inter- 

 action of several factors which have already been mentioned in another con- 

 nection: The rate and volume of the heart-beat, the elasticity of the blood- 

 vessels, the resistance of the microscopic peripheral vessels, and the volume 

 of blood in the body. We have already learned, page 179, that both the 

 rate and the volume of the contractions of the heart are under very minute 

 and intimate regulation and control through the cardiac nervous mechanism. 

 Also we have found that there is intimate coordination between the activity 

 of the circulatory and the activity of all other parts of the body, a coordina- 

 tion accomplished through the, nervous system. All regulation which affects 

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