288 INFECTION AND IMMUNITY 



quantitative relations exist between the agglutinin-stimulating sub- 

 stances and the agglutinins. Every agglutination reaction, there- 

 fore, will vary in its degree of completeness with the quantities of 

 agglutinin and agglutinogeii, a fact which makes it necessary, es- 

 pecially 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 29 

 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 re- 

 lated 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 purposes, thus, is not 

 destroyed if proper dilutions 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 agglutinin 

 (hauptagglutinrn), and the agglutinins formed parallel with it, as 

 the partial agglutinin (metagglutinin), terms introduced by Was- 

 sermann. 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 com- 

 mon 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 production, the reaction is spoken of 

 " group agglutination. ' ' 



The partial agglutinins (met agglutinins) have been extensively 

 studied by Castellani 30 and others, by a method spoken of as the 

 " absorption method." This consists in the separate addition of 

 bacterial emulsions (agglutinogens) of the various species concerned 



29 Gruber und Durham, loc. cit. r 



80 Castellani, Zeits. f. Hyg., xl, 1902. 



