ACID AGGLUTINATION 229 



cerous nitrate in agglutinating meningococci suspended 

 in distilled water. The first column gives the concentra- 

 tion of the salt, and the three following columns the 

 agglutinating effect on the antigen (meningococcus sus- 

 pension) in three concentrations 1,000 parts, 500 parts 

 and 250 parts per million the extent of agglutination 

 being represented by the number of -f- signs. 



This table illustrates very well (1) the agglutination of 

 a bacterium by an inorganic salt, (2) the zones of no 

 reaction with particular concentrations of the salt, and 

 (3) variations of agglutination with the concentration of 

 the antigen. 1 



As indicated, various inorganic substances may cause 

 agglutination of bacteria, particularly acids. Michaelis 

 found that acid agglutination might be employed to some 

 extent for the differentiation of bacterial species, on the 

 basis that the hydrogen ion concentration at which 

 agglutination is maximal is characteristic for various 

 species of closely allied types. Mixtures of lactic acid and 

 sodium lactate have generally been used for this purpose. 



The vitality of agglutinated bacteria is not injured by 

 agglutination ; they will, in fact, grow and multiply in 

 an agglutinating serum. The amount of agglutination 

 does not bear any constant ratio to the intensity of an 

 infection, though, on the whole, if the patient is reacting 

 satisfactorily to an infection, the agglutination reaction 

 tends to be marked ; if not, it tends to be feeble or absent, 

 e.g. in severe typhoid infections with fatal issue. This, 

 while true for an aggregate of cases, is not necessarily 

 true for any particular case. Agglutinins are probably 

 formed in the polymorphonuclear leucocytes. 



In order to obtain reliable results by the agglutination method in 

 the diagnosis of disease, and particularly to compare the intensity 



1 See a good resume on agglutination by R. E. Buchanan in Journ. of 

 Bacteriology, vol. iv, 1919, No. 2, p. 73. 



