666 PATHOGENIC MICROORGANISMS 



been observed in cases of jaundice and of tuberculosis, and these condi- 

 tions must occasionally be considered, though their importance was 

 formerly exaggerated. 



The method of making the Widal test from a drop of whole blood 

 dried upon a slide, is not to be recommended' since accuracy in dilution 

 by this method is practically impossible. 



As stated above, the agglutinin reaction rarely appears in typhoid 

 fever before the beginning of the second week. It may continue during 

 convalescence for as long as six to eight weeks and occasionally, in cases 

 where there is a chronic infection of the gall-bladder, a Widal reaction 

 may be present for years after an attack. 



For very exact work, even in clinical cases, the microscopic agglu- 

 tination method may be replaced by macroscopic agglutination, accord- 

 ing to the technique described in another section (page 303.) 



In order to avoid both the necessity of keeping alive typhoid cul- 

 tures for routine agglutination tests and also to preclude the danger of 

 infection by the use of living culture, Ficker 68 has recommended typhoid 

 bacilli killed by formalin. This method has no advantages for practical 

 purposes and in scientific bacteriological work it is, of course, not to 

 be considered in comparison with the more exact methods. 



The more recently introduced general practice of vaccination in 

 typhoid fever has added a complicating factor to diagnostic agglutina- 

 tion. Individuals so vaccinated develop agglutinins in consequence 

 of the inoculations, which may persist for six months or more, and even 

 after they have disappeared from the blood stream, various non-typhoid 

 febrile conditions may induce their appearance in the circulation for 

 reasons not well understood. In consequence of this, it is necessary, 

 before drawing conclusions concerning the meaning of a Widal reac- 

 tion, to be thoroughly informed concerning the vaccination history of 

 the patient and the time which has elapsed since the vaccination was 

 done. A certain amount of reliable information may be obtained even 

 in such cases by the study of the quantitative changes in the agglutinins 

 in the patient's blood by the comparative method of Dreyer as in use 

 in the United States Army. 



This method, however, is, in our opinion, not sufficiently useful or 

 simple to be recommended for ordinary clinical use. In the Dreyer 

 method, standardized suspensions of Bacillus typhosus or the para- 

 typhoid types are used. To obtain these, cultures of the bacilli are 

 grown for about two weeks by daily transplant in broth, a procedure 



68 Picker, Berl. klin. Woch., xlvii. 1903. 



