294 AGGLUTININS 



The " group agglutinins" constitute a source of difficulty in making 

 the differentiation among the numerous members of a group of micro- 

 organisms, but if a highly potent agglutinating serum is used and the 

 test is carried to the point of determining the highest dilution that will 

 agglutinate the bacteria, it will in most cases be possible to differentiate 

 the variously allied microorganisms by this test. 



In conducting these reactions it is best to use a macroscopic method, 

 and the agglutinating serum used must have been previously titrated 

 against an easily agglutinable and known strain of the microorganism 

 in question 



In this connection it is well to remember that freshly isolated cultures 

 of a microorganism may be not at all or but very slightly agglutinable. 

 Thus colonies of typhoid bacilli found in feces or in an abscess may, if 

 picked from a plate, resist agglutination until subcultured several times 

 in artificial media. 



The agglutination test has great value as a mode of differentiating 

 among the members of the typhoid-colon group of bacilli. In the diag- 

 nosis of cholera, suspicious bacilli isolated from the feces may be tested 

 with a known cholera immune serum, and the bacteriologic diagnosis 

 thus be greatly facilitated. The test also has some value in making a 

 biologic differentiation between meningococci and gonococci, and also 

 between other groups of bacteria. 



3. Agglutination tests are of value in determining whether, in a case 

 in which more than one microorganism has been cultivated, the condi- 

 tion at hand is a single or a mixed infection. The absorption agglu- 

 tinin test is made with the patient's serum, and the cultures are isolated 

 from the patient. 



4. 'Agglutination tests are also of value for measuring the immuniz- 

 ing response that a patient is making to his infection or to artificial 

 immunization. Thus the test is of some value in determining the re- 

 sponse to inoculation with typhoid vaccine, although it is probable 

 that the agglutinin itself does not possess true antimicrobic properties. 



THE AGGLUTINATION REACTION 



The value of the agglutination test in the diagnosis of disease is 

 limited chiefly to typhoid and paratyphoid fevers ; and, in a less degree, 

 to cerebrospinal meningitis and bacillary dysentery. It is especially 

 useful as a practical test in the diagnosis of obscure and atypical cases of 

 typhoid fever and also in the diagnosis of " typhoid carriers." 



