BORDET-DURHAM REACTION 223 



two or more races of an organism, or even, to a limited 

 extent, heterologous organisms, but if the serum be 

 saturated with culture so that the agglutinin may be 

 absorbed and taken up, the absorption will usually be 

 complete only with the strictly homologous organism, 

 and in this way different races of an organism, e.g. the 

 meningococcus, may be distinguished. Absorption of 

 agglutinin is determined by saturating the agglutinating 

 serum with culture, centrifuging, and then testing whether 

 the supernatant fluid will agglutinate or not ; this is 

 known as the absorption, or saturation, test of Castellani. 



Under the name of the " Bordet-Durham reaction," 

 agglutination is employed to determine the species of an 

 organism that may have been isolated, e.g. presumed 

 paratyphoid, Gartner and dysentery bacilli and cholera 

 vibrio. For this purpose agglutinating sera of high titre 

 (i.e. possessing considerable agglutinating power) are 

 prepared with known strains of the organisms which are 

 to be determined, and the organism isolated is tested with 

 the appropriate serum. With necessary precautions and 

 controls, the Bordet-Durham reaction is one of the most 

 certain and specific for the recognition of species of bac- 

 teria, and becomes still more so if the saturation test be 

 employed in addition. 



For the diagnosis of disease, the agglutination reaction 

 is extensively employed in presumed typhoid, para- 

 typhoid and undulant (Malta) fever infections, in which 

 case it is frequently termed the " Widal reaction," the 

 agglutinating power of the patient's serum being deter- 

 mined upon a known culture of the organism in question. 



Different strains of an organism vary in some degree 

 as to their capacity for being agglutinated by the homo- 

 logous serum, so that for agglutination tests a specially 

 chosen and appropriate culture ought to be employed. 



The agglutination of organisms by anti-sera, though 



