PARATYPHOID INFECTIONS 437 



fermentation reactions of the paratyphoid bacilli are 

 given in the table on p. 450. 



As regards the agglutination reaction, the blood of the 

 paratyphoid fever patient either does not agglutinate 

 the typhoid bacillus or agglutinates it only in low dilution, 

 e.g. 1 in 5 to 25, while it agglutinates the corresponding 

 paratyphoid bacillus of the infection in higher dilution. 

 The agglutination titre of the serum in cases of para- 

 typhoid A infection is sometimes very low 1 in 25 or 

 even 1 in 10. In cases that have been inoculated with 

 typhoid vaccine, the agglutination titre of the serum 

 for the typhoid bacillus may be somewhat increased as 

 a result of paratyphoid infection. 



Cases of mixed infection with typhoid and paratyphoid 

 bacilli occasionally occur. 



The diagnosis of paratyphoid fever is determined by 

 (a) the agglutination reaction, as for typhoid fever (p. 430) ; 

 (6) the isolation of a paratyphoid bacillus by blood- 

 culture, as for the typhoid bacillus (p. 430), and its 

 differentiation by culture and by agglutination. The 

 recovery of the bacillus from the blood is sometimes not 

 practicable, as the bacillsemia of paratyphoid fever is 

 often very transient and cases are frequently not seen until 

 too late. The paratyphoid bacilli are present in the 

 fseces and urine, but frequently only during the height of 

 the disease, unless the carrier state is being established ; 

 the method of isolation and differentiation is given below. 

 Prophylactic vaccines for paratyphoid fever may be 

 prepared with paratyphoid bacilli in the same manner 

 as for typhoid fever, and Castellani introduced a mixed 

 typhoid-paratyphoid vaccine. This was extensively 

 used during the War under the name of T.A.B. 

 vaccine. It contains 1,000 millions of B. typhosus, 

 with 500-750 millions each of para A and para B per cubic 

 centimetre, 



