62 IMMUNE SERA 



and to the colon bacillus; and some protoplasm 

 C, common perhaps to some other bacterium. In 

 the case of the colon bacillus, protoplasm D is 

 specific, i.e., possessed only by this bacillus, while 

 B is common to it and the typhoid bacillus, and E 

 common to colon and dysentery bacilli. By immu- 

 nization with the typhoid bacillus we would obtain 



A B 7/ C B D E F 



Dysentery Bacillus 



FIG. 5. 



a serum containing agglutinins against protoplasm 

 A, B, and C. By virtue of this the serum would 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- 



