INFLAMMATION. 107 



eliminated. Suppose the invading microbe belongs 

 to a species which causes suppuration. The next 

 stage in this form of inflammation would then be lique- 

 faction of the dead cells by ferments, and rupture of 

 the fluid contents through the skin. Gradual enlarge- 

 ment of the opening often permits a '^core^^ of dead 

 tissue not yet liquefied to be extruded. The material 

 escaping from such a lesion is pus, and consists chiefly 

 of large numbers of leucocytes suspended in serum and 

 liquefied tissues. In this discharge are also eliminated 

 bacteria and toxins. Leucocytes give pus its creamy 

 consistency and yellow color. The dead tissue having 

 thus been gotten rid of, healing goes on through growth 

 of connective tissue cells and contraction (cicatrization). 

 The above is a description of the formation and course 

 of an abscess. 



Suppuration under natural conditions is practically 

 always due to bacteria — a single exception among 

 animal infectious agents being the amoeba of dysen- 

 tery, which is known to cause abscess of the liver. 

 There are a number of bacteria which cause suppura- 

 tion; some habitually, some specifically, and others acci- 

 dentally. The common members of these three groups 

 are as follows: 



I. Pyogenic Bacteria. 

 Staphylococcus pyogenes aureus. 

 Staphylococcus pyogenes citreus. 

 Staphylococcus pyogenes albus. 



