INFLAMMATION. 169 



pus are mixtures of mucous and pus, and of serum and pus, 

 respectively. Putrid pus is a thin, ill-smelling fluid, the result 

 of putrefaction. 



Infection is the usual cause of suppuration. The following 

 is a brief description of the process. Pyogenic micro-organisms 

 gain entrance either by deposition upon or into a wound by 

 passing through the tissue or are carried and deposited by the 

 blood or lymph, and, finding conditions favorable, develop and 

 multiply. In their development, pyobacteria produce chemic 

 substances that are sufficiently irritating to establish an active 

 hyperemia and also to exert a positive chemotactic influence, 

 the latter attracting at first mononuclear leucocvtes and later 

 causing the migration of neutrophilic polymorphonuclear leuco- 

 cytes to the focus of infection. Multiplication of the pyobac- 

 teria and leucocytic immigration continue. Phagocytosis be- 

 comes evident in leucocytes and some other cells, e. g., endo- 

 thelial cells. Liberated ferments, produced by the pvobacteria, 

 leucocytes and other cells, cause degeneration, necrosis and, 

 finally, solution of the tissue involved. Continued pyobacterial 

 multiplication stimulates an increased leucocytic immigration, 

 and the tissues are thus densely packed with cells. There is a 

 marked accumulation of leucocvtes around the suppurative focus 

 apparenth' attempting to circumscribe the aft'ected area. Thus 

 the process continues, there being a progressive liquefying cen- 

 tral necrosis within and a marginal leucocytic accumulation 

 without. The condition is repeated until the resistant influences 

 of the animal body destroy the pyobacteria, or until the pyo- 

 bacteria have destroyed the involved tissue, or the entire ani- 

 mal. (Suppurative osteitis mav occur subperiosteal or in the 

 osseous tissue proper. Leucocytes invade the lacunae and pro- 

 duce solution of the mineral matter, and thus the bone becomes 

 porous. If this process continues the bone ultimately liquefies ; 

 this is termed caries.) 



Surface suppuration (purulent inflammation) is suppuration 

 of a surface tissue. Pus produced in surface suppuration con- 

 stitutes a purulent discharge, and a persistent purulent discharge 

 is termed pyorrhoea. Inflammation of a mucous membrane ac- 

 companied by a purulent discharge is purulent catarrh. In puru- 

 lent catarrh the surface epithelium is infiltrated with leucocytes 

 frequently to such an extent that the epithelial cells are disin- 

 tegrated, become loosened and exfoliate. The surface cells of 

 serous membranes and the skin are similarly affected in purulent 

 inflammation. In any purulent inflammation there is always 



