4 6 IMMUNE SERA 



a serum containing agglutinins against protoplasm 

 A, B, and C. By virtue of this the serum \vould exert 

 some agglutinating power also on colon bacilli. 



Absorption Method for Differentiating between 

 a Mixed and a Single Infection and for Identifying 

 Bacteria. In 1902 Castellani called attention to 

 a procedure which consists in saturating the diluted 

 immune serum with successive quantities of the 

 bacteria most strongly agglutinated until the agglu- 

 tinating power for these is zero. After centrifug- 

 ing, the clear fluid is tested on the second variety 

 of bacteria, and from this one learns whether mixed 

 or single infection was present. According to Castel- 

 lani, if the serum of an animal immunized against a 

 certain microorganism is saturated with that organ- 

 ism, the serum will lose its agglutinating power not 

 only for that organism, but also for all other varieties 

 that it formerly acted on. Saturated with the others, 

 its action upon the first is reduced little or none at all. 

 The serum of an animal immunized against two 

 microorganisms A and B. loses its agglutination 

 when saturated with A, only for A. Saturated with 

 A and B it loses agglutinating power for both. 



The absorption test is extensively used in the 

 identification of bacteria, but it must be used with 

 caution, as its interpretation is open to error. Refer- 

 ring to the figure illustrating specific and group 

 agglutinins, let us assume we have obtained a 

 specific typhoid serum by immunization with typhoid 

 bacilli. By virtue of the common agglutinin, this 



