III. AGGLUTININS 



The Agglutination Phenomenon. We have just 

 seen that pathogenic bacteria may be divided into 

 those which produce extracellular toxins in culture 

 media, and those which do not. Against the 

 former the organism defends itself by the production 

 of antitoxins ; against the latter it produces a variety 

 of antibodies: bacteriolysins, agglutinins, precipi- 

 tins, opsonins and possibly others. 



The agglutinins can be observed either in a test- 

 tube or in a microscopical preparation. For example, 

 if typhoid or cholera immune sera are added respec- 

 tively to a 24-hour culture of typhoid or cholera 

 bacilli, and the mixture placed in a thermostat, 

 the following phenomenon will be noticed: The 

 bacteria which previously clouded the bouillon 

 uniformly, clump together into little masses, settle 

 to the sides of the test-tube and gradually fall to 

 the bottom until the fluid is almost entirely clear. 

 In a control test, on the contrary, to which no active 

 serum is added, the fluid remains uniformly cloudy. 

 The reaction is completed in twenty-four hours 

 at the most. If the reaction is observed in a hang- 

 ing drop, it is seen that the addition of the active 



serum first produces an increased motility of the 



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