IMMUNOLOGY 877 



anatomical structure. The reactions have to be studied, however, to see 

 if, on the one hand, they vary too much within what is a generally recog- 

 nized species, or if, on the other hand, they do not differentiate suffi- 

 ciently among large groups. The extreme specificity within a species 

 may be exemplified by the diversification of a single cell strain of 

 trypanosomes, through the mediation of immune serums or drugs, into 

 a large number of strains which will remain immunologically distinct 

 for long periods. 



In a sense most of the work on the serology of parasites can be used 

 in classification. For example, an investigator, in attempting to dis- 

 cover a serological test for a given infection, generally considers at 

 once the specificity of the reaction by ascertaining to what extent group 

 reactions with other species exist. On the whole, however, the study of 

 the immunological relationships of organisms can best be attained by 

 using antiserums from artificially immunized laboratory animals. By 

 this method animals such as rabbits, in which antibodies are readily 

 produced, can be immunized until high titer antiserums are obtained. 



Immunological methods have been employed extensively to estab- 

 lish the identity or nonidentity of various proposed species of Leish- 

 tnan}a, which are morphologically identical, and their relationship to 

 certain insect and plant herpetomonads which resemble the cultural 

 forms of Le'ishmama. This work is fairly consistent in showing that the 

 members of the genus Lehhmama are a closely related group and are 

 entirely distinct from the genus Herpetomonas (Noguchi, 1926; Wage- 

 ner and Koch, 1926; Zdrodowski, 1931). 



Since trypanosomes, like the Leishmanias are frequently morphologi- 

 cally indistinguishable from one another, various immunological tests, 

 as well as biological criteria, have been employed to distinguish them. 

 The in vivo cross-immunity test has been most extensively used (Braun 

 and Teichmann, 1912; Laveran, 1917; Kroo, 1925, 1926; Schilling and 

 Neumann, 1932), but in vitro tests have also been used, such as com- 

 plement fixation by Robinson (1926), the phenomenon of "attachment" 

 by several authors (see Levaditi and Mutermilch, 1911) and in vitro 

 trypanolysis by Leger and Ringenbach (1912) and others. In evaluat- 

 ing the results of these methods, it appears that they need to be re- 

 worked, because of the advance in modern technique and because au- 



