188 A MANUAL OF BACTERIOLOGY 



The agglutination reaction is made use of in bacterio- 

 logical tests and in clinical diagnosis. The " Bordet- 

 Durham " reaction consists in testing an unknown organism 

 with a specific anti- serum prepared by injecting an animal 

 with a known microbe ; if the organism tested becomes 

 agglutinated, it is regarded as being of the same species 

 as that with which the anti-serum was prepared. With 

 certain precautions the " Bordet-Durham " reaction is 

 one of the most delicate and certain for the recognition of 

 bacterial species. The converse of this is the agglutination 

 reaction proper (frequently termed the Widal reaction), 

 and consists in testing an unknown serum upon a 

 known microbe. It is especially used in the diagnosis of 

 microbial diseases ; for example, in typhoid fever the 

 blood of the typhoid patient powerfully agglutinates the 

 typhoid bacillus, that of Malta fever the Micrococcus 

 melitensis, that of bacillary dysentery the dysentery 

 bacillus, etc. 



A remarkable phenomenon observed in connection with 

 agglutination, which the writer has particularly noticed 

 in the case of Malta fever, is the occurrence of what may be 

 termed a zone of no reaction or of inhibition with some 

 particular dilution. Thus, dilutions of 1 in 10 and 1 in 20 

 may agglutinate strongly, a 1 in 30, however, may hardly 

 agglutinate at all, while dilutions of 1 in 40 and upwards 

 to 1 in 100 or more may agglutinate well. A similar 

 phenomenon has been observed with non-specific agglu- 

 tinating agents, and also in the action of coagulating agents 

 on colloid emulsions. Thus orthophosphoric acid agglu- 

 tinates a certain volume of a suspension of B. coli when 

 present to the extent of between 118 cgrm. and 4 cgrm., 

 and between 1-1 mgrm. and 0-001 mgrm., but not in 

 intermediate amounts between 40 and 1-1 mgrm. 



Anti-serum, prepared by injecting erythrocytes, also 

 agglutinates the red blood- corpuscles, and in certain 



