CHAPTER XVI 

 AGGLUTININS 



As previously stated, given any infection, several antibodies of 

 different properties may be produced. If the infecting microorganism 

 produces characteristically an exogenous toxin, as, for example, that 

 produced by the diphtheria bacillus, an antitoxin is produced as the most 

 prominent of several antibodies. With other pathogenic bacteria that 

 produce mainly an endogenous toxin various antibodies are formed, and 

 one or more may play a prominent role in protecting the host, such as 

 opsonins, agglutinins, precipitins, bacteriolysins, etc. 



If typhoid immune serum from an immunized animal or a patient;, 

 suffering from typhoid fever is added to an emulsion of typhoid bacilli' 

 in a test-tube and the mixture placed in an incubator, the following 

 phenomenon will be observed: the bacteria, which previously formed a 

 uniform emulsion, clump together into little masses, settle at the sides 

 of the test-tube, and gradually fall to the bottom, the fluid becoming 

 almost clear. In a control test to which no active serum is added, the 

 fluid remains uniformly cloudy. If the reaction is observed microscopic- 

 ally in a hanging drop, it is noted that with the addition of the serum the 

 bacilli move nearer and nearer one another, this process being followed 

 by a gradual loss in motility and the formation of clumps. The sub- 

 stance in the serum causing this phenomenon 'is called agglutinin, and 

 the reaction is known as agglutination. 



Definition. Agglutinins are antibodies that possess the power of caus- 

 ing bacteria, red blood-corpuscles, and some protozoa (trypanosomes) sus- 

 pended in a fluid to adhere and form clumps. 



Historic. Although Metchnikoff, Charrin, and Roger had noticed 

 peculiarities in the growth of Bacillus pyocyaneus when cultivated in 

 immune serum which we now believe were due to agglutinins, Gruber 

 and Durham and Bordet (1894-1896) were the first to recognize that 

 the agglutination reaction was a separate function of immune serum. 

 While investigating the Pfeiffer phenomenon of bacteriolysis with Bacil- 

 lus coli and the cholera vibrio, these investigators found that if the 

 respective immune serums were added to bouillon cultures of these two 



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