506 



N. S. FERRY AND ARLYLE NOBLE 



cent salt solution plus 5 per cent formalin was added. The anti- 

 gens were then kept in the ice chest. 



Cross titrations. Cross titrations were made between the 

 several strains of B. hronchisepticus, the several strains of Perez' 

 Bacillus and between B. hronchisepticus and Perez' Bacillus. 



Each serum was tested against each of the seven antigens and 

 on the same day, all the tests being run parallel. 



Tables 4, 5 and 6 show the results of the complement fixation 

 tests. 



TABLE 4 



C. H. = Complete hemolysis. 



C. I. = Complete inhibition of hemolysis. 



SUMMARY OF COMPLEMENT FIXATION TESTS 



1. Sera of high complement-fixing titre were produced in rab- 

 bits by three intravenous injections of killed unheated suspensions 

 of B. hronchisepticus and Perez' Bacillus. 



2. The four strains of Perez' Bacillus gave identical complement 

 fixation reactions. 



