CHAPTER XXI 



THE IMPORTANCE OF ANTIBODIES IN 

 DIAGNOSIS 



In the previous chapters antibodies have been defined and dis- 

 cussed and methods of measuring them have been suggested. 

 While there is some controversy over their importance in the body's 

 defense against infectious agents, there is general agreement that 

 they are frequently of great value in diagnosis. 



Discovery of Role of Ag-glutinins in Diagnosis. — The Widal 

 Test. — Gruber and Durham (1896) investigated the phenomenon 

 of bacterial clumping by immune serum and named it agglutina- 

 tion. Almost simultaneously Widal (1896) studied the blood of 

 typhoid fever patients and found that such bloods specifically 

 clumped suspensions of living or dead typhoid bacteria. Both 

 Widal and CI ruber recommended that the reaction be iLsed as an aid 

 in the diagnosis of typhoid fever. In honor of its discoverer, the 

 test has been known as the Widal or the Gruber-Widal reaction. 



Scope of Subsequent Investigations. — Since then the phenom- 

 enon of agglutination has been investigated to ascertain the prev- 

 alence of normal agglutinins, the effect of vaccination on ag- 

 glutinin titer, the time of their appearance and the titers at- 

 tained in both experimental infections and clinical cases due to a 

 variety of infectious agents. The agglutinin reaction has also 

 found wide application in the identification of bacteria isolated 

 from pathological lesions and other sources. When the test was 

 first introduced it was not realized that serological types exist 

 among the pneumococci, meningococci, streptococci and other bac- 

 teria. Perhaps this was because B. typhosus (Eherthella typhosa) 

 was until recently regarded as being represented by one uniform 

 type. While types are not as yet described for this organism, 

 Downis (1925) and White (1926) have reviewed the literature and 

 shown antigenic variation of practical importance. In preceding 

 chapters a more comprehensive discussion of antigenic factors and 

 variants now known to exist among bacteria have been discussed. 



Antigens Used in the Widal.- — At this point it is sufficient to 

 .say that Widal discovered that suspensions of living organisms 



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