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A MANUAL OF BACTERIOLOGY 



electric charge borne by them, so that surface tension 

 becomes sufficiently powerful to cause them to aggregate 

 into masses. Evidence in favour of this explanation of 

 agglutination is given by the fact that the particles of 

 heat-coagulated protein may be deprived oi their electric 

 charges and be rendered isoelectric with the solution, and 

 when this has happened surface tension causes floccula- 

 tion. By the addition of electrolytes acids, alkalies 

 and certain salts the electric charge of the particles 



Agglutination of Meningococci suspended in Distilled 

 Water with Cerous Nitrate (twenty hours at 56 C.). 



may be increased so that the aggregated particles again 

 disperse. This kind of action is the explanation of the 

 zones of no reaction, already mentioned, which may 

 occur with an agglutinating serum. It may be completely 

 simulated by experiments with acids and salts which in 

 certain concentrations cause agglutination of bacteria 

 and reproduce the phenomena of agglutination with 

 agglutinin, and concentration both of the electrolyte (the 

 salt) and of the antigen (bacterium) affects the result, as 

 is seen in the above table. This illustrates the effect of 



