INFLAM.MATIUN. 



147 



Temporary contraction of arteries is the first result of the ap- 

 plication of an irritant. The cause of the constriction of the 

 arteries is a spasmodic contraction of the musculature of the 

 vessels. This is succeeded l)y a marked arterial dilatation. 



Dilatation of the arteries and arterioles. The response to 

 stimuli on the arteries is rapid and always active, in veins slow 

 and usually passive, in capillaries either rapid or slow Init al- 

 ways passive. Di4atation of vessels in an inflamed area is 

 caused by stimulation of the vaso-dilators or inhibition of the 



FiPT. SS. — Bluod \>-Sstl, sh'i\\-in;4 C«(rinisele.s otcuiAing central portinn m1 striani, 

 t^jiical of normal circulation. 



vaso-constrictors. An increase in the calibre of the arteries 

 results in an increased amount of blood flowing throug-h them 

 and into the capillaries. The increased amount of blood in the 

 capillaries mechanically increases their calibre and also in- 

 creases the amount of blood which enters the related veins and 

 results in a dilatation of them. By increasing the lumen of a 

 vessel the resistance to the flowing contents is correspondingly 

 diminished and this results in a temporarj- acceleration of the 

 rate of blood flow. 



Acceleration of the rate of flow of the blood. The cor- 

 puscles occupy the axial, or central part of the stream as in 

 the normal circulating blood. The arterial dilatation plus the 

 acceleration of the blood flow constitute the essential factors m 

 active hyperemia. 



