LEUCOCYTES. 145 



acteristic of the disease. Organisms similar to 

 the streptococcus and pneumococcus lead to the 

 formation of pus and fibrin, to the accumulation 

 of serum and of polymorphonuclear leucocytes 

 more than mononuclears, whereas the prolifera- 

 tion of fixed tissue elements is secondary. The 

 tetanus bacillus alone causes almost no local in- 

 flammatory change. 



2. The reaction is influenced by the virulence 

 of a particular strain. A streptococcus which 

 has lost its virulence is disposed of by the animal 

 tissues with a minimum tissue reaction, perhaps 

 no more than slight congestion and edema and 

 the wandering in of a few leucocytes ; one of high- 

 er virulence causes an intense reaction, mani- 

 fested by congestion, edema, hemorrhages, necro- 

 sis and pus formation; then streptococci of such 

 great virulence that they destroy life in the course 

 of a few hours are occasionally encountered in 

 wound infections and in peritonitis, having in the 

 meantime elicited a minimum inflammatory reac- 

 tion. 



3. It has a relation to the resistance or the nat- 

 ural immunity of the individual. Metchnikoff. 

 in particular, has shown that animals of high re- 

 sistance to a particular microbe destroy the germ 

 quickly by phagocytosis, while in susceptible ani- 

 mals the accumulation and activity of phagocytic 

 leucocytes are deficient. 



The occurrence of leucocytes in inflammatory Leucocytes. 

 conditions is so characteristic that one naturally 

 seeks to associate their presence with some in- 

 fluence which is exerted by the toxic substance or 

 the bacteria which cause the inflammation. It is 

 a long-known fact that some microbes attract one 



