218 INFECTION AND IMMUNITY. 



The value of the agglutination reaction as a 

 clinical diagnostic aid will be considered later in 

 connection with the individual diseases. 

 Agglutination A consideration of agglutination would be in- 



of Red Blood , . . ,. ^ 



Corpuscles, complete it one did not mention the phenomenon 

 as it occurs with cells other than those of bacteria, 

 in particular the red blood cells. The serums of 

 many animals, as stated in a previous chapter, are 

 toxic for the erythrocytes of some other species. 

 In some instances, the corpuscles lose their hemo- 

 globin under the influence of the serum (hemoly- 

 sis) ; in other instances, or even with the same 

 serums if previously heated, the corpuscles are 

 thrown into clumps and settle to the bottom of the 

 test tube, leaving a clear overlying fluid. The 

 analogy with the bacterial agglutinins goes still 

 further, in view of the fact that the formation of 

 these tff hemagglutinins" may be induced artificially 

 in the body of an animal by the injection of 

 erj^throcytes from another species. An animal 

 does not form agglutinins for its own cells (auto- 

 agglutinins), but often does, however, for the cells 

 of another member of the same species (iso-agglu- 

 tinins). What is said in the next chapter con- 

 cerning the specificity of the bacterial agglutinins 

 also holds for the hemagglutinins. 



plant Hemagr- Certain plant toxins, true toxins with hapto- 

 phorous and toxophorous structures, agglutinate 

 red blood cells: ricin, abrin, crotin, etc. Some of 

 the earliest and most important work which 

 Ehrlich has done in the field of immunity was ac- 

 complished with thesp plant toxins. 



