BACTERLiL INFECTIONS 215 



vated by heating to 55° C, and are not dependent upon 

 the presence of complement for their action. It is 

 probable that the humoral bactericidal substances are 

 specific, each one acting against a certain microorgan- 

 ism, while the leucocytic substance is non-specific. 



Among the natural defences of the body also are 

 substances in the blood known as opsonins, which have 

 the property of preparing bacteria for phagocytosis 

 by the leucocytes. Whether these are distinct soluble 

 substances or only a property of the serum is not de- 

 termined; it is quite likely opsonins are a modified 

 form of the bactericidal substances in the blood-fluid. 



From the foregoing discussion and from previous 

 chapters, we see that the principal defences of the 

 body against the deleterious effects of bacterial infec- 

 tion include antitoxins, agglutinins, bacteriocidins 

 (bacteriolysins), opsonins and phagocytosis, each of 

 these playing a distinct part in the spontaneous 

 recovery of the organism from disease. By a knowl- 

 edge of the way in which different varieties of bac- 

 teria produce their deleterious effects, and the re- 

 sources present in the body for meeting the attack of 

 the different species, we are enabled to assist nature in 

 combating different forms of infection by artificial 

 stimulation of these natural resources. This is 

 brought about by the various general therapeutic 

 measures, and in a specific manner by bacterin therapy. 



