88 LOCALIZED INFECTIONS OF PUS NATURE 



the pus occurs and cellulitis or phlegmon arises. The 

 next grade of severity would be septicemia or pyemia, 

 defined before, which arises when the active inflam- 

 mation enters and involves the bloodvessels. The 

 softening of tissue into pus is called suppuration, which 

 may be defined as the destruction of tissues and cells 

 by bacteria and their products. Pus under the micro- 

 scope is composed of white blood cells, particularly 

 the so-called polynuclear leukocytes, microorganisms, 

 some of which are free, others englobed by phagocytes, 

 partly or wholly destroyed tissue, and, at least early 

 in inflammation, a delicate mesh work of coagulum 

 called fibrin; the last is dissolved shortly as the sup- 

 puration proceeds. There is also some granular fluid. 

 The fluid and cells which appear in inflammation 

 are collectively called an exudate. This may be of 

 several forms; it may be true pus; it may be a thin, 

 watery fluid in which are floating shreds of a gray, 

 friable character, called lymph, in reality a coagulum, 

 such as is formed in blood clotting, but without red- 

 blood cells; it may be a tenacious covering of a surface, 

 called a false membrane, such as is seen on a diphtheritic 

 throat, more or less closely adherent to the surface 

 from which it arises; it may possess special characters, 

 such as hemorrhagic when much blood is admixed, 

 or mucoid when it resembles mucus. 



PUS-PRODUCING MICROORGANISMS. 



It has been stated that there is no particular germ 

 always responsible for pus, but some varieties of the 

 round bacteria are the commonest causes. Thev are 



