CHAPTER X. 

 AGGLUTINATION. 



If the serum from an immunized animal or a patient convalesc- 

 The Pheno- m g after an infection, be mixed with a suspension of the bac- 



menon of teria which were involved in the production of said conditions, 

 Agglutination. a peculiar phenomenon takes place. In the formerly dif- 

 fusely cloudy liquid, small granules and clumps appear which 

 sink to the bottom of the test-tube and leave a supernant clear liquid. On 

 microscopic examination, the sediment presents bacteria (which have re- 

 mained alive as is demonstrable by making cultures of same). This same 

 observation can be made when the experiment is performed in a hanging 

 drop with perhaps more flattering results. The bacteria are seen to lose 

 their motility, adhere to each other, finally gravitate toward larger groups 

 and arrange themselves in clumps. The phenomenon thus described was 

 discovered by Gruber and Durham, and is called agglutination; while sub- 

 stances which cause this, agglutinins. 



If instead of the immune or that of the convalescent patient, normal 

 serum is employed, and the above test repeated, it will be seen that agglutina- 

 tion likewise occurs. The reaction here is, however, somewhat incom- 

 plete, the clumps smaller, and formed much more slowly. // a quantitative 

 determination with different dilutions of both sera is made, the power of 

 agglutination disappears with the normal serum at a low dilution, while the 

 immune serum remains perfectly active at even much greater dilutions. 

 Thus the main difference between the agglutinating normal and immune 

 serum is a quantitative one depending upon the amount of agglutinins 

 present. Whether any qualitative difference exists between the normal and 

 immune agglutinins is doubtful. It is, however, of no practical significance. 



If instead of homologous bacteria, different (heterologous) bacteria are 

 employed, e.g., cholera vibrio and typhoid serum, agglutination also takes 

 place, if the typhoid serum is used in concentrated or only slightly 

 diluted form; but in moderate or great dilutions, no agglutination occurs. 

 Normal serum will agglutinate the cholera vibrio in the same strength as the 

 immune typhoid serum. In other words the typhoid serum contains more 

 agglutinins for its homologous bacteria, than a normal serum, but it has only 

 the same titer of agglutination as a normal serum for heterologous bacteria. 



The agglutination reaction is specific in the respect that weak dilutions of 

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