PATHOGENIC BACTERIA 263 



duces an agglutinate of the bacteria. Agglutinins are pro- 

 duced under similar conditions to the antitoxins. They are 

 discharged chemical side chains. Agglutinoids may be pro- 

 duced by heating or adding certain chemicals to the agglu- 

 tinin, and anti-agglutinins may be produced by immuniza- 

 tion with agglutinin. The phenomenon of agglutination is 

 made use of in the so-called Gruber-Widal reaction for ty- 

 phoid fever and also in the diagnosis of glanders. 



Opsonins. In some infections (pyogenic, etc.) due to bac- 

 teria which produce endotoxins, bactericidal substances are 

 not always easily produced. Without doubt phagocytosis 

 by the polymorphonuclear and mononuclear leucocytes, and 

 other cells of the body is of great importance in combating 

 certain infections. There are present in normal serums 

 specific substances called opsonins. These opsonins are in- 

 creased during an infection and by the process of immuniza- 

 tion by vaccination. The phagocytes during an infection 

 can only ingest the etiological microorganism after they 

 have come in contact with the opsonins of the blood serum. 

 This has been positively demonstrated. The nature of the 

 reaction between the opsonin and the bacteria and other 

 infectious microorganisms is not known. The opsonins pre- 

 pare the bacteria for phagocytosis, or, to use the latest ter- 

 minology, the bacteria are " sensitized." The more opsonins 

 the more phagocytic action will take place, and therefore the 

 more infecting bacteria will be destroyed. The opsonins 

 have no direct effect on the leucocytes or other phagocytes. 



