234 INFECTION AND IMMUNITY 



pleteness with the quantities of agglutinin and agglutinogen, a fact 

 which makes it necessary, especially for clinical tests, to preserve a 

 certain uniformity in the quantity and density of the bacterial culture 

 or emulsion employed. 



Specificity. — From the very beginning, Gruber and Durham ' had 

 claimed specificity for the agglutination reaction, and in this sense it was 

 clinically utilized by Widal for the diagnosis of typhoid fever. It was 

 noticed, however, even by these earliest workers, that the serum of an 

 animal immunized against one microorganism would often agglutinate, 

 to a less potent degree, other closely related species. Thus, the serum 

 of a typhoid-immune animal may agglutinate the typhoid bacillus in 

 dilutions of 1 : 1,000, and the colon bacillus in dilutions as high as 1 : 200; 

 while the agglutinating power of normal serum for the colon bacillus 

 rarely exceeds 1 : 20. The specificity of the reaction for practical pur- 

 poses, thus, is not destroyed if proper dilution is carried out, the degree 

 of agglutinin formation being always far higher for the specific organism 

 used in immunization than it is for allied organisms. The specific 

 immune-agglutinin in such experiments is spoken of as the chief ag- 

 glutinin (hauptagglutinin) , and the agglutinins formed parallel with it, 

 as the partial agglutinin (metagglutinin) , terms introduced by Wasser- 

 mann. Hiss has spoken of these as major and minor agglutinins. The 

 relative quantities of the specific chief agglutinin and partial agglutinins 

 present in any immune serum depend upon the individual cultures used 

 for immunization, and the phenomenon is probably dependent upon 

 the fact that certain elements in the complicated bacterial cell-body 

 may be common to several species and find common receptors in the 

 animal body. Whenever an immune serum agglutinates a number of 

 members of the group related to the specific organism used for its produc- 

 tion, the reaction is spoken of "group agglutination." 



The partial agglutinins (metagglutinins) have been extensively 

 studied by Castellani ^ and others, by a method spoken of as the " ab- 

 sorption method." This consists in the separate addition of bacterial 

 emulsions (agglutinogens) of the various species concerned in a group ,. 

 agglutination, to the agglutinating serum. In this way, specific and par- 

 tial agglutinins can be separately removed from the immune serum by 

 absorption — each by its corresponding agglutinogen. In such experi- 

 ments all agglutinins will be removed by the organisms used for im- 



1 Gruber und Durham, loc. cit. 



2 CasUllani, Zeits. f. Hyg., xl, 1902. 



