98 AGGLUTINATION. 



serum will agglutinate only its homologous bacteria and leave the heterologous 

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

 strong 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 typhoid the question is to establish this absolutely. One 



Agglutination, 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 also 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 established 

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

 and information is wanted as to whether same are of a typhoid nature, 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 

 absent in the second, proves the typhoid character of the unknown bacteria. 

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

 antigen. 



The practical application of agglutination has been greatly made use of 

 in cases of typhoid fever. Here the production of agglutinins is very easily 

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

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

 main 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. 



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



jc mque > r^g accoun t s for its wide adoption. It may either be per- 



Agglutmation. . . . . 



formed macroscopically or microscopically (orientation test). 



The Macroscopic Agglutination Reaction. 



The necessary requirements for carrying out the reaction consist of: 



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 : 



a. Bouillon Culture. Many bacteria, like typhoid, paratyphoid, dysen- 



