CAUSES OF DISEASE. 27 



it is either antitoxic or bactericidal. Technically bacteri- 

 cidal antibodies are known as lysins, or bacteriolysins. 

 Antedating and also accompanying the 

 Agglutinins, formation of the solvent antibodies (bac- 

 teriolysins), there appears in the blood- 

 serum of infected animals and persons other antibodies 

 which have the property of drawing together in groups 

 or clumps the invading bacteria. This phenomenon 

 is called agglutination , the substances which excite 

 it, agglutinins. 



Agglutination, it is commonly accepted, has these 

 two advantages : It is a preliminary stage in the process 

 of immunity (it appears before the bacteriolytic sub- 

 stance); it facilitates the ingestion of the bacteria by 

 the phagocytes (phagocytosis). 



Bacteriolysins and agglutinins are specific substances, 

 just as antitoxins are, and therefore act only when 

 brought into relation with such bacteria as call them 

 forth. This knowledge of the specificity of the agglu- 

 tinins is made use of for the diagnosis of various 

 diseases, especially typhoid fever, the examination for 

 agglutination in the latter disease constituting the well- 

 known Widal reaction. 



In recovery or immunity from diseases 



Opsonins, due to the second class of bacteria, i.e., 



those which attack the body largely through 



multiplication, another antibody has lately come to 



the fore which bids fair to overshadow all others in 



