106 AGGLUTINATION 



The agglutination reaction is specific in the respect that high dilutions of 

 serum will agglutinate only its homologous bacteria and leave the heterologous 

 ones uninfluenced. Agglutination becomes non-specific, when concentrated or 

 low dilutions of serum are employed. 



The relative specificity just described is of great clinical 



Diagnostic diagnostic value. For example, given a serum suspicious of 

 Value of Ag- typhoid, the question is to establish this absolutely. One 



glutination. immediately proceeds to make a suitable dilution of the 

 unknown serum and mixes with it known typhoid bacilli. 

 A similar dilution of normal serum is made as a control and mixed with 

 the same amount of typhoid bacilli. If agglutination occurs with the 

 unknown serum and not with the control serum, the former must have come 

 from a typhoid patient. If the bacteria are not agglutinated, the serum 

 was not of typhoid origin. 



In an equal manner can the identity of unknown bacteria be estab- 

 lished by the use of known sera. Thus, when certain bacteria have been 

 isolated and information is wanted as to whether they are typhoid, an 

 emulsion of these is made and mixed with a typhoid serum in suitable 

 dilution, and a similar amount of bacteria is mixed with a normal serum of 

 like dilution. Agglutination occurring in the first of these mixtures and 

 not in the second proves the typhoid character of the unknown bacteria. 

 In this manner the agglutination test can be used for identification of any 

 antigen. 



The practical application of agglutination has been greatly used 

 in cases of typhoid fever. Here agglutinins are very easily stimu- 

 lated in the course of the disease and generally they can be demon- 

 strated in the serum seven to ten days after infection. The agglutinins 

 remain not only during the active stage of the disease, but also during the 

 convalescing period. Widal, the Parisian clinician, was the first to adopt 

 this agglutination reaction for the serum diagnosis of typhoid. It is thus 

 commonly known as* the Widal reaction. 

 Technique of The technique of the reaction is as simple as its principle. 



Aggluti- This accounts for its wide adoption. It may either be per- 

 nation. formed macroscopically or microscopically (orientation test). 



The Macroscopic Agglutination Reaction. 



For this reaction it is necessary to have 



1. The immune serum and a normal control serum; 



2. A homogeneous bacterial emulsion. 



The production of a homogeneous bacterial emulsion offers slight 

 technical difficulties. 



It can be obtained in the following ways: 



