426 



THE PARATYPHOID A. BACILLUS 



5. Agglutination. 



The serum of vaccinated animals and of persons suffering from paratyphoid 

 A fever will agglutinate the paratyphoid A bacillus. The serum-diagnosis 

 of paratyphoid A fever however requires considerable skill and care on the 

 part of the observer. 



Agglutination with the serum of immunized animals. The serum of animals 

 highly immunized against the paratyphoid A bacillus contains both specific 

 agglutinins and group agglutinins. Not only does such a serum agglutinate 

 the paratyphoid A bacillus but it agglutinates also the typhoid bacillus and 

 other related bacilli ; but if the limits of agglutination be determined it will 

 be found that the serum agglutinates the paratyphoid A bacillus in a much 

 higher dilution than it agglutinates the typhoid or any other related bacillus. 



Thus an anti-paratyphoid A serum agglutinates all strains of the para- 

 typhoid A bacillus in dilutions of 1-1,000, 1-5,000 and even 1-40,000. On 

 the other hand it has very little agglutinating action on strains of the para- 

 typhoid B bacillus, on the gaertner bacillus, or on the aertrycke bacillus 

 and only agglutinates the typhoid bacillus in dilutions of 1-200, 1-100 

 or 1-20. 



The following table l illustrates this : 



Agglutination limits after incubation for 2 hours at 42 C. Macroscopic method. 

 In all cases control tubes showed no agglutination. 



Conversely, experimental typhoid serums have little action on strains 

 of the paratyphoid A bacillus and only agglutinate them in low dilution. 



A similar statement is justifiable for paratyphoid B, aertrycke and gaertner 

 serums. 



To sum up : By means of the agglutination reaction with an experimental 

 serum the paratyphoid A bacillus can with certainty be identified, being clearly 

 differentiated from the typhoid, paratyphoid B, gaertner and aertrycke bacilli. 



Agglutination reaction with human serum. The conditions are somewhat 

 different when working with an human serum. 



The experience in cases of paratyphoid fever in India is as follows : The 

 agglutination titre is usually low (1-20 to 1-40) and the reaction commonly 

 transient : it may be quite as high for the typhoid bacillus as during an ordinary 

 attack of enteric fever and the co-agglutinin for this bacillus may remain after 

 the specific agglutinin has vanished. Rarely, the specific agglutinin alone is 

 present ; and sometimes both it and the co-agglutinin for the typhoid bacillus 

 are present in so small an amount and for so short a time as to be easily over- 

 looked. Finally it is possible in undoubted cases of paratyphoid A fever 

 for the serum to contain co-agglutinins for the typhoid and paratyphoid B 

 bacilli but no specific agglutinin (Firth). 2 



The group agglutinin for the typhoid bacillus quickly disappears in para- 



1 Bainbridge, F. A., Journal of Pathology and Bacteriology, xiii. p. 341. 



2 Journal of the Royal Army Medical Corps. 



