Immunity and Resistance 647 



hemolysis indicates that complement was fixed in the test reaction, since 

 there was none available for the hemolytic reaction. Absence of hemolysis 

 thus indicates that the test serum contains antibodies homologous for 

 the test antigen. On the other hand, the occurrence of hemolysis, indi- 

 cating that complement was not fixed in the test reaction and hence was 

 free to combine with the red corpuscles and hemolysin, demonstrates 

 that the test serum does not contain the homologous antibodies. In the 

 usual procedure, the test is checked with various control tubes containing 

 no test antigen, no test serum, neither test antigen nor test serum, or 

 only red corpuscles, as well as with complete systems containing known 

 positive and negative test sera. 



Complement-fixation has sometimes shown good correlation with other 

 methods for diagnosis of leishmaniasis. Using L. donovani antigen pre- 

 pared from spleens of infected hamsters, Hindle, Hou, and Patton (89) 

 obtained good results with sera from kala-azar patients. Comparable and 

 more significant results have been reported for antigens prepared from 

 cultures (6, 61, 77, 124). The test is positive in early cases and seems to 

 be highly specific (77). The usual procedure also has been reversed by 

 using antiserum from immunized rabbits to detect Leishmania antigens 

 in human blood (121). Complement-fixation has been useful in the 

 diagnosis of dourine because tests are positive at an early stage, and in 

 spite of group reactions with Trypanosoma evansi, seem to be reliable. 

 Complement-fixation also has been used extensively in the diagnosis of 

 Chagas' disease (122). With antigens prepared from cultures of T. criizi, 

 the test is dependable and apparently is not complicated by cross-reactions 

 with Wassermann sera (96). A polysaccharide fraction prepared from 

 T. cruzi also has proven effective as a test antigen (119a). 



Izar (91) and Scalas (146) apparently were the first to report success 

 with complement-fixation in amoebiasis. Subsequently, the results of 

 Craig (52, 53, 54) and later workers, with antigens prepared from cultures 

 of E. histolytica, indicated the practical value of this test in mild intestinal 

 amoebiasis. The important handicap to wider application seems to have 

 been the difficulty of preparing effective test antigens. Establishment of 

 E. histolytica in cultures with one strain of bacteria (136) and the current 

 availability of commercially prepared antigen should eliminate certain 

 variables caused by uncontrolled bacterial flora. However, one modifica- 

 tion of the test, carried out with commercially produced materials, seems 

 to be useful for diagnosis of hepatic but not intestinal amoebiasis (90a). 



Application of complement-fixation to diagnosis of malaria was not 

 successful at first because sensitivity of the tests was too low. More re- 

 cently, reasonably good results have been obtained with antigens prepared 

 from parasitized human or monkey blood (44, 45, 62, 67, 71, 83, 98, 111, 

 164, 165) and from chicken blood containing P. gallinaceum (83, 98). 

 Such tests also will detect malarial antigens, in the blood of the host. 



