SEROLOGICAL METHODS IN THE STUDY OF PROTOZOA 435 



logically. Many of these immunity tests indicate a greater anti- 

 genic difference between the relapse variants of one strain of 

 trypanosomes than between what are generally recognized species 

 of trypanosomes. For example, Braun and Teichmann (1912) 

 found that mice immunized with T. cqnipcrdiim showed a group 

 immunity, i.e., were immune to T. brucei and T. evansi, although 

 they were not immune to a serum resistant (relapse) strain of 

 T. equiperduni. The same situation is evident in many of the 

 serological tests. Thus, a given trypanolysin may be reactive not 

 only against the original strain which stimulated its production 

 but against a number of related species (Leger and Ringenbach, 

 1912), whereas it may not be reactive against the trypanosomes 

 (relapse strain) reappearing in the body of the same animal in 

 which the trypanolysin was formed. 



FUNCTIONAL ROLE OF ANTIBODIES IN MODIFYING THE COURSE OF 



INFECTION AMONG THE PROTOZOA ; LYSIS, PHAGOCYTOSIS 



AND INHIBITION OF REPRODUCTION 



The reactions, which have been considered in vitro, can im- 

 doubtedly take place within the body under suitable conditions. 

 Thus, complement fixation is simply an expression of the fact 

 that complement may combine with a specific antibody and a 

 specific antigen or test antigen. Agglutination has been shovvm 

 by the work of Bull and others (see review by Bailey, 1928) 

 to be probably of functional importance in the natural and ac- 

 quired immunity of animals to bacteria. Little has been done on 

 this phase of the subject in protozoology. There are other reac- 

 tions, however, zns., lysis, phagocytosis and inhibition of reproduc- 

 tion, which have a direct effect on the parasites and which can be 

 shown to alter the course of infections in animals. It should be 

 emphasized that the consideration of complement fixation, agglu- 

 tination, precipitation, lysis, phagocytosis and inhibition of re- 

 production, as such, does not imply that there are so many different 

 antibodies. Many immunologists believe that the first five are 

 manifestations of the same antibody tested under diverse condi- 

 tions, while the last mentioned, according to available evidence, 

 is probably due to a separate one. 



The protozoa are preeminently fitted, because of their com- 

 paratively large size, for a study of the in vivo action of anti- 

 bodies and their functional role in influencing the course of in- 



