An Intermediate Complex in Immune Hemolysis by Carp Complement Homologous to Mammalian EACl, 4*1

plement in the presence of Ca2+, but absenco of Mg2+, certain components (Cx') of complement combine with EA, while the other components (Cy') of complement are left in the fluid phase. In order to determine the complement components involved in EACx' and Cy', carp seru m was inactivated by carrageenin (Cn), ammonia (Am), hydrazine (Hd), zymosan (Z) and heat treatment (13), and each inactivated serum was combined with EACx'or (EA+Cy'). Consequently, the combinations of EACx'+Cn, EACx'+Am, and (EA+Cy')+Z resulted in hemolysis, while the other combinations were not hemolysed. This suggests that EACx' comprises two components which are destroyed by carrageenin and by ammonia, probably the Cl and C4 components, and that Cy' contains the compovents which are removed by zymosan. Furthermore, it was found that in the reaction between EA and Am, the first component combines with EA, with formation of EACl, and that this complex is hemolyzed by Cn. This confirms that the component inactivated by carrageenin corresponds to the Cl component of complement. From these data, it was concluded that the intermediate complex EACx'obtained in immune hemolysis by carp complement is a complex corresponding to mammalian EAC1, 4, and that Cy' is a mixture of the other components.