272 AGGLUTININS 



paratyphoids might contain one or more of these four agglutinogens, 

 and, therefore, the agglutinating power of the typhoid serum for a para- 

 typhoid bacillus, though not so great as on the typhoid bacillus, is still 

 considerable. Accordingly, in an infection with one microorganism 

 a specific agglutinin will be formed for that microorganism, and group 

 agglutinins for other more or less allied microorganisms, and conse- 

 quently the specificity of the agglutinating reaction depends upon the 

 principle of dilution, the specific agglutinin being present in largest 

 amount and operative in dilutions above the range of the group agglu- 

 tinins. 



Absorption Methods for Differentiating Between a Mixed and a 

 Single Infection. In 1902 Castellani discovered that if the serum of an 

 animal immunized against a certain microorganism contains that 

 microorganism in large numbers, the serum will lose its agglutinating 

 power not only for that microorganism, but also for all other varieties 

 on which it formerly acted. If, however, the serum contains the organ- 

 ism corresponding to the group agglutinins, the agglutinating power of 

 the serum for the homologous organism is reduced but little or not at all. 



In a mixed infection due to two or more varieties of bacteria there 

 iwill be specific agglutinins for each of the microorganisms, and group 

 agglutinins for each of them as well. If the immune serum is saturated 

 with one of these varieties its chief or major agglutinins and some or all 

 of the group agglutinins will be removed, but the major agglutinin of the 

 second species will remain. On the addition of the second bacterium to 

 the immune serum agglutination occurs and its agglutinin is absorbed. 

 Park, who has carefully investigated this subject, finds that the absorp- 

 tion method proves that when one variety of bacteria removes all agglu- 

 tinins for a second, the agglutinins in question were not produced by the 

 second variety. 



Hemagglutinins. Agglutination, like other immunity reactions, is a 

 mifestation of broad biologic laws and is not limited to bacteria. As 

 by the injection of an animal with red blood- 

 corpuscles from anotherspbeies, so agglutinins that agglutinate the red 

 blood-corpuscles may be developed at the same time. When a serum 

 containing hemagglutinin is added to a suspension of the corresponding 

 red blood-corpuscles contained in a test-tube, it causes these to collect 

 into clumps and flakes and sink to the bottom, just as a typhoid immune 

 serum agglutinates typhoid bacilli. These clumps are broken up with 

 some difficulty, and may interfere with hemolytic reactions. They are 

 especially to be observed in antihuman hemolytic serums when agglu- 



