ABSORPTION OF AGGLUTININS 427 



typhoid A fever, in contrast to the persistence of the specific agglutinin which 

 follows enteric fever (Firth). 



Moreover, Grattan and Wood l record that " In some cases the limits of 

 co-agglutination for the typhoid bacillus exceeded the limits of specific 

 agglutination : and that in other cases again, at one period of the disease the 

 limits of co-agglutination for the typhoid bacillus exceeded the limits of 

 specific agglutination, and at another period the limits of specific agglutination 

 exceeded the limits of co-agglutination." 



These observers find that " antityphoid inoculation seldom if ever pro- 

 duces co-agglutinins for the paratyphoid A bacillus. Hence in a typhoid- 

 vaccinated individual a serum reaction against the paratyphoid A bacillus 

 in a dilution of 1-20 is strong evidence of paratyphoid A fever. " And in 

 inoculated persons an attack of paratyphoid A fever raises the titre of 

 agglutination for the typhoid bacillus about the 8th day, while the agglutinins 

 for the paratyphoid A bacillus do not appear much before the 12th day." 



6. Absorption tests. 



To explain the phenomena just described it is necessary to assume the 

 presence of group agglutinins, or, in those cases where co -agglutination is 

 very marked, the existence of a double infection. 



Castellani's method of absorption of agglutinins may be used for diagnostic 

 purposes when the results of the agglutination tests are doubtful. 



Let us take the case of a serum which has but little agglutinating action on the 

 typhoid bacillus but agglutinates the paratyphoid A bacillus in higher dilution 

 (140 to 1100). To such a serum add paratyphoid A bacilli in sufficient quantity 

 to remove the whole of the paratyphoid A agglutinins and centrifuge. Then test 

 the agglutinating action of the clear supernatant fluid on both the typhoid and 

 paratyphoid A bacilli (to ascertain that the agglutinins for the paratyphoid A 

 bacillus have been removed). If the typhoid bacillus be agglutinated it may be 

 assumed that agglutinins were present in the serum for both the typhoid and para- 

 typhoid A bacilli ; but if on the other hand the typhoid bacillus is not agglutinated, 

 then the original action of the serum on the typhoid bacillus was due to the presence 

 in it of a co-agglutinin. But in cases of paratyphoid A fever, when the serum agglu- 

 tinates both the typhoid and paratyphoid A bacilli, absorption with the paratyphoid 

 A bacillus removes all agglutinins both specific and group ; while absorption with 

 the typhoid bacillus removes merely the co-agglutinin for the typhoid bacillus, 

 leaving the specific agglutinin for the paratyphoid A bacillus intact even though 

 it mav in the first instance have only been demonstrable in a dilution of 1-20 (Harvey 

 and Wood). 



If a person inoculated against enteric fever and whose serum agglutinates 

 the typhoid bacillus become infected with a paratyphoid A infection, absorp- 

 tion of the serum with the paratyphoid A bacillus only reduces the titre and 

 does not entirely remove the agglutinins specific for the typhoid bacillus 

 (Harvey and Wood). 



If in a case of paratyphoid A fever the serum agglutinate the typhoid 

 bacillus but not the paratyphoid A bacillus, absorption with the latter will 

 remove the whole of the agglutinin (co-agglutinin) for the former, whereas 

 the agglutinins for the typhoid bacillus in cases of enteric fever are not 

 removed by absorption with the paratyphoid A bacillus (Harvey and Wood). 



Another difference between the specific and group agglutinins for the 

 paratyphoid A bacillus is that when the serum-emulsion mixture is put up 

 in sedimentation tubes the specific agglutination appears almost immediately 

 while the co-agglutination does not appear for some hours (Harvey and Wood). 



To sum up : The serum of persons suffering from paratyphoid A fever usually 



1 Journal of the Royal Army Medical Corps. 



