PROPERTIES OF COMPLEMENTOIDS 61 



that they are held to apply only to the cases investigated, 

 viz. the immune-body for ox's corpuscles obtained from the 

 rabbit, used along with rabbit's and guinea-pig's comple- 

 ments and complementoids. Further observations will be 

 necessary to determine whether they obtain generally. 



1. The existence of complementoids in heated sera can 

 be shown in ordinary test-tube experiments, by their pre- 

 venting (a) the union of complement with a serum -j- its anti- 

 serum (formerly styled ' anti-complement ') ; (b) the union 

 of complement with R + IB molecules after lysis. 



2. The amount of complementoid derived from comple- 

 ment, as tested by the combining relationships, varies ; in the 

 case of the rabbit it is approximately equal to the original 

 amount of complement ; in the case of the guinea-pig it is 

 considerably less than that amount. 



3. The combining affinity of complementoid, both for 

 a serum -f anti-serum and for R -|- IB molecules after lysis, 

 is not much inferior to that of complement. 



4. On the other hand, complementoid has a feeble affinity 

 for R + IB molecules before lysis, i.e. for intact red cor- 

 puscles treated with immune-body ; of the complementoid 

 added only a small quantity enters into combination ; 

 hence complementoid does not prevent lysis by complement. 



5. When red corpuscles united with multiple doses of 

 immune-body are lysed by a single dose of complement, the 

 surplus R+IB molecules can be saturated with excess of 

 complementoid, so that almost no complement can subse- 

 quently be taken up. This result is obtained also with 

 rabbit's complementoid and guinea-pig's complement, and 

 with guinea-pig's complementoid and rabbit's complement. 



