CHAP. X.] THE VASCULAR SYSTEM. 113 



quently seen white corpuscles, sometimes clinging to the walls 

 of the vessel, sometimes rolling slowly along, and in general 

 moving irregularly, stopping awhile, and then suddenly moving 

 on again. 



These are the phenomena of the normal circulation, but a 

 different state of things sets in when the condition of the blood- 

 vessels is altered in inflammation. 1 If an irritant, such as a 

 drop of chloroform, be applied to the portion of transparent 

 tissue under observation, the following changes may be seen to 

 occur: the arteries dilate, the blood flows in greater quantity 

 and with more rapidity, the capillaries become filled with cor- 

 puscles, and the veins appear enlarged and full. This condition 

 of distension may pass away, and the blood-vessels return to 

 their normal state, the effect of the irritant having merely pro- 

 duced a temporary redness. 



The irritant, however, usually produces a more decided 

 change. The white corpuscles begin to gather in the periph- 

 eral zones, and this takes place though the vessels still 

 remain dilated and the stream of blood still continues rapid, 

 though not so rapid as at first. Each white corpuscle exhibits 

 a tendency to stick to the sides of the vessels, and, driven away 

 from the arteries by the stronger arterial current, becomes 

 lodged in the veins. Since white corpuscles are continually 

 arriving on the scene, the inner surface of the veins and cap- 

 illaries soon become lined with a layer of these cells. Now, 

 though the vessels still remain dilated, the stream of blood 

 begins to slacken, and the white corpuscles lying in contact 

 with the walls of the vessels are seen to thrust themselves 

 through the distended walls into the lymph spaces outside. 

 This migration of the white cells is accomplished by means of 

 their amoeboid movements. They thrust elongated processes 

 through the walls, and then, as these processes increase in size, 

 the body of the cell passes through into the enlarged process 

 beyond, the perforation appearing to take place in the cement 

 substance between the pavement epithelial cells forming the 

 walls of the vessels. Through this migration, the lymph 

 spaces around the vessels in the inflamed area become crowded 



1 The following account of the changes occurring in inflammation does not 

 strictly belong to a text-book on physiology, but I have ventured to introduce it, 

 as especially interesting to nurses, out of " Foster's Physiology." 



