AGGLUTININS 



45 



differentiated by means of their agglutination. 

 Because of this lack of absolute specificity the serum 

 diagnosis of infection or the identification of bac- 

 teria by means of agglutination tests, has value 

 only when very carefully tested. We have said 

 above that while agglutinins are specific, a serum 

 which produces agglutination may be far from 

 being so. The reason for this is that the serum 

 may contain several agglutinins. In fact, when 

 immunizing an animal with a particular bacterium 

 both specific and group agglutinins are produced. 

 This will perhaps be made clearer by reference to 

 the following diagram. We assume that the typhoid 



A B C B ft E F 





Typhoid Bacillus 



Colon Bacillus 



Dysentery Bacillus 

 FIG. 5. 



bacillus possesses considerable protoplasm A, which 

 is specific for the typhoid bacillus; that it possesses 

 also certain protoplasm B, which is common to it, 

 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 



