BACILLUS OF TYPHOID FEVER 419 



will not only definitely demonstrate the presence of bactericidal sub- 

 stances in the immune serum, but wiir furnish a reasonably accurate 

 quantitative estimation. (For these tests see p. 255.) 



Although normal human serum contains in small quantity substances 

 bactericidal to typhoid bacilli, moderate dilution, 1 : 10 or 1 : 20, of such 

 serum will usually suffice to eliminate any appreciable bactericidal action. 

 The bactericidal powers of immune serum, on the other hand, are often 

 active, according to Stem and Korte, in dilutions of over 1 : 4,000 and in 

 one case even of 1 : 4,000,000. The specificity of such reactions gives 

 them a considerable degree of practical value, both in the biological 

 identification of a suspected typhoid bacillus in known serum and in the 

 diagnosis of typhoid fever in the human patient by the action of the 

 patient's serum on known tj^phoid bacilli. In the publication of Stem 

 and Korte, quoted above, it was found that typhoid patients during the 

 second week often possess a bactericidal power exceeding 1 : 1,000, 

 whereas the blood of normal human beings was rarely active in dilu- 

 tions exceeding 1 : 50 or 1 : 100. While scientifically accurate, the prac- 

 tical application of bactericidal determinations for diagnosis presents 

 considerable technical difficulties, and gives way to the no less accurate 

 method of agglutination. 



Agglutinins. — Agglutinins are formed in animals and man inoculated 

 with typhoid bacilli, and in the course of typhoid fever. It was, in fact, 

 while studying the typhoid bacillus that the agglutinins were first dis- 

 covered by Gruber and Durham. 



In animals, by careful immunization, specific typhoid agglutinins 

 may easily be produced in sufficient quantity to be active in dilution 

 of 1 : 10,000, and occasionally even 1 : 50,000 or over. In the blood 

 of typhoid patients, the agglutinins may often be found in dilu- 

 tions of 1 : 100 and over. It is interesting to note that irrespec- 

 tive of the agglutinin contents of any given serum, there may 

 occasionally be noted differences in the agglutinability of various 

 typhoid cultures, a point which is practically important in the choice 

 of a typhoid culture for routine diagnosis work. Weeny ' has 

 called attention to the fact that bacilli which do not readily agglutinate 

 when directly cultivated from the body, may often be rendered more 

 sensitive to this reaction by several generations of cultivation upon 

 artificial media. Walker has noted ' a loss of agglutinability if the bacilli 



' Weeny, Brit. Med. Jour., 1889. 



' Walker, Jour, of Path, and Bact., 1892; Totsuka, Zeit. f. Hyg., xlv, 1903. 



