CHAPTER X. 



AGGLUTINATION. 



BACTERIAL AGGLUTININS. HEMAGGLUTININS. TRANSFUSION TESTS. 



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

 The Phe- m g a f ter an i n f ec tion, be mixed with a suspension of the bac- 

 oA ^lu ter * a w ki cn were i nvo l ve d m the production of said conditions, 

 tination a P ecu li ar phenomenon takes place. In the former dif- 

 fusely cloudy liquid, small granules and clumps appear which 

 sink to the bottom of the test-tube and leave a supernatant clear fluid. 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 with perhaps more flattering results when the 

 experiment is performed in a hanging drop. 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 serum or that of the convalescent patient, 

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

 agglutination likewise occurs. The reaction is, however, somewhat incom- 

 plete ; the clumps are smaller, and formed much more slowly. // a quantita- 

 tive 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. Nor- 

 mal 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. 



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