SEROLOGICAL METHODS IN THE STUDY OF PROTOZOA 433 



SEROLOGICAL TESTS USED IN CLASSIFICATION 



In the foregoing sections, the specific nature of the various sero- 

 logical reactions has been emphasized. This specificity is not 

 absolute, however. It generally shows quantitative differences 

 closely paralleling zoological and botanical classifications (which 

 are based on anatomical criteria) so that in general the more 

 closely two species are related the stronger the group reaction 

 between them. Consequently, serological tests have been used for 

 many years to check and amplify other biological classifications. 

 Since much higher titres as a rule may be attained with immunized 

 than with infected animals, most of this work, and especially the 

 more recent work, has been carried out with immunized animals, 

 and in particular with immunized rabbits. 



Cross serological tests have been used among the Lcishumnia 

 infections (L. donovani of kala-azar, the similar infections of dogs, 

 L. infantum of infantile kala-azar,^ L. tropica of oriental sore 

 and L. brasilicnsis of American leishmaniasis), because they 

 cannot be dift'erentiated morphologically. They have also been 

 used in studying the relationship of the Lcishmania to various 

 insect and plant herpetomonads which bear a great resemblance 

 to the cultural forms. 



Some early work by Bandi (1913) with the agglutination test 

 and by di Cristina and Caronia (1913) with the agglutination 

 and complement fixation tests indicated the identity of L. infantum 

 and the parasite of the canine infection. Noguchi (1924) dis- 

 tinguished three varieties of Lcishmania (L. donovani, L. tropica 

 and L. brasilicnsis) by cross agglutination tests. He obtained 

 titres of i :io and i :ioo with immunized rabbits and living cul- 

 tures. Kligler (1925) confirmed this work in the main. Using the 

 same test but with standardized test antigens of killed organisms 

 Wagener and Koch (1926) found differences not only between 

 the three varieties just mentioned but also between them and L. 

 infantum. Moreover, none showed any relationship to Hcrpc- 

 tomonas ctcnoccpJiali. They obtained titres with homologous anti- 

 serums of 1:80 up to 1:600. In the same year, Noguchi (1926), 

 by means of agglutination and complement fixation reactions, ob- 

 tained no indication of a relationship between the various Lcish- 



^ The three visceral infections, i.e., kala-azar, infantile kala-azar and the 

 canine disease, are probably caused by the one parasite, L. donovani. 



