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(1) The concentration of small-clumping (O) typhoid agglutinin in the serums of a group of recently inoculated persons was found to be, on an average, distinctly higher than that of a group of uninoculated persons.
Additional proof that this is the result of the inoculation is given by tracing the curve of production of “O” agglutinin in a healthy adult immediately after inoculation.
(2) The serums of healthy persons show a moderate but extremely variable power of clumping typhoid “O” suspensions. Expressed as a titre, the normal limit varies between 1 in 50 and 1 in 200, according to the sensitiveness of the suspension used. Expressed in standard units of “O” agglutinating power the normal limit is 10 standard “O” units.
(3) Methods of preparation of permanent suspensions for the estimation of “O” agglutinin are discussed and Felix's recommendation of the alcohol method is confirmed. The agglutinability standardisation of suspensions of this kind is described.
(4) Broth suspensions treated with 0·1 per cent, formalin, such as are used for the ordinary Widal reaction, are shown to be capable of detecting “O” agglutinin, but to be less suitable for its estimation than alcohol suspensions.
(5) The place of small-clumping “O” agglutination in the diagnosis of typhoid fever is discussed, and a method of performing the combined “H” and “O” test in inoculated persons is suggested, wherein a compromise is effected between the customary quantitative measurement and Felix's qualitative “one-dilution” method.
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