CHAP. XI.] THE VASCULAR SYSTEM. 135 



ing application, the blushing or paling of the face from mental 

 emotion, the increased flow of blood to the mucous membranes 

 during digestion, being all instances of this kind. 



But the condition of the capillary walls themselves also exerts 

 an influence upon the capillary circulation. If some trans- 

 parent tissue, preferably the web of a frog's foot, be watched 

 under the microscope, it will be observed that in the small 

 capillaries the corpuscles are pressed through the channel in 

 single file, each corpuscle as it passes occupying the whole bore 

 of the capillary. In the larger capillaries and smaller arteries 

 and veins the red corpuscles run in the middle of the channel, 

 forming a coloured core, between which and the sides of the 

 vessels is a colourless layer containing no red corpuscles, and 

 called the "peripheral zone." In the peripheral zone are fre- 

 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 re- 

 main 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 



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." 



