STANDARD AGGLUTINATION 433 



Thus if standard agglutination occurs in a dilution of 1 in 1,000 

 and the number on the label is 2-5, then - 1 .& fi -, i.e., 400, is the 

 number of Standard Agglutinin Units contained in 1 c.c. of the 

 serum examined. 



For uniformity and simplicity in recording results they should 

 be expressed in Standard Agglutinin Units. 



2. DIAGNOSIS. 



A. In non-inoculated persons who have not had typhoid 

 (or paratyphoid) fever, agglutination in a dilution of 1 in 25 

 justifies a strong suspicion of typhoid (or paratyphoid) infection. 

 But the test must be applied again in the course of a few days to 

 ascertain whether there is any change in the titre of agglutina- 

 tion. Marked agglutination in a dilution of 1 in 50 or more is 

 nearly always diagnostic of active typhoid (or paratyphoid) 

 infection. 



A non-inoculated " carrier " will normally show no important 

 change in the titre of this serum on repeated examination at 

 short intervals. 



B. Inoculated persons, if quite recently inoculated, will 

 usually show a high titre of specific agglutination. A rapid 

 rise in titre sets in within two to four days of inoculation. This 

 is followed by a fall, at first rapid, but subsequently becoming- 

 very slow, so that a relatively high titre is maintained for a 

 long period (even for years). During this period examinations 

 made at intervals of a few days give practically identical 

 readings. 



It follows that in the case of inoculated persons the diagnosis 

 of active typhoid (or paratyphoid) infection will require two or 

 more successive examinations of the serum. 



(a) If the individual is suffering from active typhoid infection 



his titre of typhoid agglutination will exhibit the usual 

 rise and subsequent regular fall seen in non-inoculated 

 subjects, but starting from and returning towards the 

 higher base line of inoculated persons. 



(b) If the individual is suffering from active paratyphoid 



infection one of three things may occur as regards his 

 typhoid agglutination titre, namely : 



1. No appreciable change may occur in the titre of 



typhoid agglutination. 

 M.B. 28 



