TYPHOID BACILLUS 339 



Incubation of these infected tubes for one to two hours almost invari- 

 ably gives sufficient numbers of organisms to make a microscopic 

 agglutination. A confirmatory cultural diagnosis may be obtained' 

 by the inoculation of small tubes of semi-solid media and milk with 

 the remainder of the broth culture. This method differs from the one 

 usually employed merely in the small amount of broth used, which 

 requires less bacteria to produce turbidity, and in the fact that the 

 growth is practically continuous from the Endo medium to the tube, 

 the broth being warmed to the body temperature at the start. Taking 

 advantage of these factors cuts down the time required for diagnosis 

 nearly twentv-four hours. 



(6) SEROLOGICAL DIAGNOSIS. The blood serum of patients who 

 have recovered from a typical attack of typhoid fever contains elements 

 which give specific reactions with the typhoid bacillus or its products ; 

 of these, lysins, agglutinins, opsonins and precipitins have been 

 carefully studied. The method of fixation of complement and the 

 ophthalmo reaction have received less attention. 



The lysins, which appear early in the course of the disease, dissolve 

 typhoid bacilli, but not other bacteria, at least in the dilutions ordi- 

 narily used. It is probable that the lysins not only dissolve typhoid 

 bacilli in vitro, they destroy the organisms in the blood stream as 

 well, 1 liberating endotoxins which play a prominent part in the produc- 

 tion of the febrile reaction. 



Agglutinins are formed in the majority of cases, which will clump 

 typhoid bacilli. The significance of agglutinins in the typhoid complex 

 is not definitely established. 



The opsonic index of the serum of immunized animals and of clinical 

 cases of typhoid fever in man appears to be increased, but available 

 methods of measuring the opsonic index do not furnish information 

 consistent enough to warrant definite conclusions. 



The reaction of fixation of complement has been used diagnostically 

 in a limited number of cases. The technical skill required to elicit 

 satisfactory results has doubtless interfered with its general application. 



The agglutination reaction is by far the most commonly used anti- 

 body reaction employed in the diagnosis of typhoid fever. 



The Widal Reaction. Historical. Gruber and Durham appear 

 to have first demonstrated that the sera of animals immunized to 

 typhoid bacilli would agglutinate the typhoid bacilli, even if the 



1 Coleman and Buxton, Medical and Surgical Report of Bellevue and Allied Hospitals, 

 1909-10, iv, 46. 



