230 A MANUAL OF BACTERIOLOGY 



of agglutination at different stages of an attack and in different 

 individuals, it is necessary to employ the same method, the same 

 dilutions, and cultures of the same agglutinability. In order to 

 standardise these factors, Dreyer * has introduced what is termed 

 the " Standard Agglutination Method " for the diagnosis and com- 

 parison of degree of agglutination in typhoid and paratyphoid 

 fevers and bacillary dysentery. " Standard " dead cultures of the 

 respective organisms are employed, and the test is a macroscopic 

 one done in small tubes (for method of carrying it out see section 

 on " Typhoid Fever "). 



The following details and terms are used in connection with it : 



1. Standard Agglutinable Cultures are prepared of definite 

 opacity and measured agglutinability from strains of the bacilli 

 concerned which have been specially selected for their high 

 specificity. In successive batches of standard agglutinable 

 culture the relative sensitiveness to agglutination of the bacilli 

 contained is indicated by a figure the so-called Reduction Factor 

 the original standard agglutinable cultures having been arbi- 

 trarily given the figure 2-5 as a reduction factor. The reason for 

 this will appear immediately in connection with the Standard 

 Agglutinin Unit. 



2. Standard Agglutination is the degree of agglutination present 

 in the highest serum dilution in which marked agglutination 

 without sedimentation can be seen by the naked eye. 



3. The Standard Agglutinin Unit is that amount of agglutinat- 

 ing serum which when made up to 1 c.c. with normal saline 

 solution causes standard agglutination on being mixed with 

 1-5 c.c. of the original standard agglutinable culture and main- 

 tained at 55 C. for two hours (in the case of dysentery agglutina- 

 tion four and a half hours) in a water-bath, followed by fifteen to 

 twenty minutes at the room temperature. 



4. The Reduction Factor. The total volume in which the re- 

 action occurs being 2-5 c.c. (1 c.c. of serum added to 1-5 c.c. of 

 standard culture), the original standard agglutinable culture was 

 given the reduction factor of 2-5 to express the sensitiveness to 

 agglutination of that particular culture. All subsequent batches 

 of culture have been given reduction factors calculated on this 



1 See Journ. Roy. Army Med. Corps, September, 1916 (Refs.) ; Lancet, 1917, 

 vol. i, pp. 365 and 568 (Refs.). 



