Chap. IX] VASCULAR SYSTEM 145 



Amoeboid movements. — One distinctive property of white 

 blood corpuscles is their power of making amoeboid movements, 

 which enables them to change their form and escape through the 

 walls of the blood capillaries into the surrounding tissues. This 

 property has earned for them the title of wandering cells, and the 

 process is spoken of as migration. It occurs under normal condi- 

 tions, but is vastly accelerated under pathological conditions. 



Function of the white corpuscles. — It is definitely known that 

 they act (1) as protective agents, (2) aid in the absorption of fats 

 and proteins from the intestines, and (3) assist in the coagulation 

 of the blood. 



Their function of protection is very important, and is accom- 

 plished in two ways : — 



(a) By forming certain substances called bacteriolysins, which 

 when imbibed by bacteria kills them ; (b) by virtue of their amoe- 

 boid movements they can creep around bacteria, envelop them 

 with their own substance, and so put them inside themselves. 

 This process is called phagocytosis, and has earned for them the 

 name of phagocytes. 



Opsonins. — This is a name given to chemical substances found 

 in blood plasma. The function of an opsonin ^ is to prepare certain 

 disease germs for destruction and absorption by the white cor- 

 puscles of the blood. The phagocytic properties of the leucocytes 

 become especially developed as the result of the action of opsonins. 



Inflammation. — When any of the tissues become inflamed 

 either as the result of injury or infection, the first effect is irritation, 

 followed by an increased supply of blood to the part. If the irri- 

 tation continues or is severe, the flow of blood begins to slacken, 

 and a condition of stasis or engorgement results. The white 

 corpuscles become particularly active and migrate into the infected 

 tissues in large numbers. Some of the blood plasma exudes, and a 

 small number of red corpuscles are forced through the capillary 

 walls.2 This general condition is described as inflammation, and 

 the symptoms of pain, heat, redness, and swelling are due, (1) to 

 the increased supply of blood, (2) to the engorgement of the blood- 

 vessels, and (3) to the collection of fluid in the tissues, which is 



1 From opso'no, I prepare food for. 



" This passive ability of red corpuscles to pass through the capillary walls is 

 called diapedesis. 



