382 IMMUNOLOGY 



served that in preparations containing normal serum or saline, the 

 organisms remain motile and no clumps appear, while in prepara- 

 tions containing agglutinins the organisms lose their motility and 

 come together in definite clumps. 



It is also customary to test the patient's serum, in the same way, 

 to see whether it agglutinates suspensions of aS^. 'paratyplii A or 

 B* since these organisms produce clinical pictures that cannot be 

 differentiated by physical examination and histor;/ of onset, al- 

 though the course of each is usually milder and the duration 

 shorter than in typhoid fever. 



Controls are very necessary in carrying out the test, since it 

 is not impossible for the laboratory technician to get his cultures 

 contaminated and use a suspension of the contaminant for the 

 typhoid or paratyphoid suspension. Where the suspension is made 

 from a pure culture of E. fijphom or of the aS'. puratuphi A 

 and B* the tubes containing known positive serum will sliow defi- 

 nite agglutination. The normal serum and saline controls should be 

 negative to rule out spontaneous agglutination. When even pure 

 cultures are used, if they are made from rough colony types, espe- 

 cially of 8. pamtupM B* they quite often show spontaneous 

 agglutination. When this occurs, the normal scrum and saline con- 

 trol tubes should show perceptible agglutination. 



Aside from errors due to antigenic variation and technical pro- 

 cedure, there are others due to mistakes in the interpretation of the 

 results. The Widal is essentially a test to ascertain whether specific 

 agglutinins for E. typJiosa or one of the paratyphoid organisms 

 is present in the blood stream in sufficient amounts to give positive 

 agglutination at the diagnostic titer used. If infection is present, 

 the efificiency of the body tissues in the production of antibodies 

 will determine the time of appearance and amount in the blood 

 stream. 



Variation in Time of Appearance of Agglutinins. — Marked 

 variation is to be observed in different individuals; some respond 

 readily with early and abundant antibody production while others 

 are poor antibody producers, the antibodies appearing later or in 

 meager amounts. This accounts for the fact that the Widal may 

 be positive in some cases of typhoid as early as the fifth day, while 

 in others not until the third or fourth week. Gay (1918) feels 



♦S'. schottmiilleri. 



