IMPORTANCE OF ANTIBODIES IN DIAGNOSIS 393 



bacillary dysentery, Asiatic cholera, and the study of gram- 

 negative diplococei from suspected meningococcus carriers and 

 other conditions, it is often necessary to ascertain whether the 

 organism isolated and culturally identified is agglutinated by 

 known immune serum. If it is agglutinated by high dilutions of 

 the known antiserum, its identity is considered as established. 

 Thus if we isolate a motile gram-negative bacillus that is culturally 

 similar to E. typhosa, the next step will be to see whether a sus- 

 pension of the organism isolated is agglutinated by antityphoid 

 serum and at a titer at which the antiserum will agglutinate a 

 suspension of E. typhosa. In addition to this it has usually been 

 decreed that for final identification an immune serum must be 

 prepared against the new organism and this immune serum must 

 react with a suspension of E. typhosa by agglutination and ab- 

 sorption tests in exactly the same way that it does with its 

 homologous organism. This is the "mirror reaction." 



Bacterial Types. — Since cellular antigens and specificity are 

 discussed extensively in earlier chapters, it is sufficient to state at 

 this time that each species of bacteria is represented usually by a 

 number of types which can be differentiated from each other by 

 agglutination. There are four or more types of meningococci, 

 fifty-five specific types of pneumococci and an heterogeneous 

 group not yet subdivided, four or more types of dysentery bacilli 

 that also differ in some of their cultural reactions. The colon 

 group is antigenically so diverse that the agglutination test is of 

 no value in identification, hence one depends entirely upon 

 morphology, staining, and cultural reactions. In regard to the 

 staphylococci, only morphology, cell grouping and i)igment produc- 

 tion are used as a rule in identification. In the more recent work 

 on streptococci (Bliss, Gordon, Tunnicliff, Lancefield, and others) 

 it has been reported that hemolytic streptococci can be subdivided 

 into a number of groups and types by agglutination or precipita- 

 tion. Virulent organisms from human sources fall into Lancefield 's 

 group A. The green producing streptococci are more hetero- 

 geneous, i.e., show greater antigenic diversity. 



C. DiPHTHERiAE. — In Identifying C. diphtheriae, agglutination 

 Is not only of little value, but it is unnecessary since toxin produc- 

 tion and specific neutralization of toxin by diphtheria antitoxin are 

 excellent criteria for the final identification of the organism. All 



