290 AGGLUTININS 



serum gives no indication of the degree of immunity that exists. For 

 instance, relapses may occur in typhoid fever at a time when the agglu- 

 tinating power of the patient's blood is at its highest. 



At present agglutinins are regarded as playing a subsidiary role in 

 immunity, their presence being of diagnostic value, and an indication of 

 the presence of more important factors, and as an aid to bacteriolysis, 

 and phagocytosis.. 



As shown by Bull 1 experimentally, agglutination may occur in vivo, 

 and the power of the blood to cause agglutination determines, in large 

 measure, whether after their direct introduction in an experimental way 

 the bacteria are to be removed promptly from the circulation and bac- 

 teremia avoided, or whether they are to remain and produce bacteremia. 

 Microorganisms which are not agglutinated in the normal rabbit may 

 be made to do so by the intravenous injection of homologous immune 

 serum, and this probably explains the rapid disappearance of pneumo- 

 cocci from the blood following the intravenous injections of homologous 

 antipneumococcus serum. The bacterial clumps accumulate in the 

 organs in which they are phagocyted. In this way it appears that ag- 

 glutinins, opsonins, and phagocytosis are closely related and probably 

 exert an important role in resistance to. and recovery from, infection. 



PRACTICAL APPLICATIONS 



The agglutination reaction is used for the following purposes: 

 1. For the diagnosis of disease, by identifying the bacterial infection 

 from which the patient is suffering. To do this satisfactorily we must 

 have on hand stock cultures of bacteria, and test the patient's serum for 

 agglutinins for these bacteria. For instance, if a patient presents symp- 

 toms of typhoid fever, the serum is tested for typhoid agglutinins; if 

 the reaction is very weak or negative and continues so, the serum is 

 further tested for agglutinins for Bacillus paratyphosus A and B. 



In typhoid fever the Gruber-Widal reaction may be positive as early 

 as the third day; usually, however, the positive reaction is obtained 

 somewhat later about, the seventh or the eighth day. A day or so 

 earlier the bacilli used in making the test may be seen to lose their mo- 

 tility, and two or three may form a loose clump. This is the doubtful 

 reaction, and it is well to test every day or every other day until a de- 

 cisive reaction is obtained. 



According to Park, " about 20 per cent, of typhoid infections give 



i Jour. Exper. Med., 1915, 22, 484; ibid., 1916, 24, 25. 



