Atypical behaviour of certain avian antisera in complement-fixation tests.

T HE COMPLEMENT-FIXATION test has been applied to only a very limited degree in the study and diagnosis of avian infection for two probable reasons, (a), that the technical difficulties and expense involved have made it a less attractive method from the economic stand-point than agglutination, and (b), that the results have not been too en-couraging on the whole, either due to certain inherent peculiarities in the complement-fixing behaviour of these sera or because the antigens used have not been adequate. Review of the literature would suggest that the second reason may have been the more important of the two. Complement-fixation has been used with variable results in the diagnosis of tuberculosis (1), (2), and pullorum disease in chickens (3). It has been applied more widely in detecting the presence of or past contact with psittacosis (ornithosis) virus in parrots (4) and pigeons (5), (6). Weak reactions with these viruses have been reported in turkeys, ducks (7) and various wild birds (8); the test has not been satisfactory however with chicken serum (9). The study of Newcastle disease in chickens has not been aided by complement-fixation. Further evidence of the failure of chicken serum to fix complement with homologous antigen has been obtained in birds immunized with influenza virus vaccine. Whereas these antisera in high dilution inhibited the agglutination of chicken red cells by influenza virus of the homologous type, they did not fix complement with this antigen (10). In brief, therefore, complement-fixation with avian serum appears to occur irregularly and frequently is of low degree. the complement-fixation with avian