56 PROPERTIES OF ELEMOLYTIC SERA 



got is much lengthened in series B, though it is not quite 

 doubled. If we take the tube in series B (mixture of C and 

 Cd added), which gives a third lysis in the added corpuscles, 

 we find that the corresponding tube in series A (C alone 

 added) gives about two-thirds lysis. We may thus conclude 

 that in this case also the firmness of union of Cd does not 

 differ greatly from that of C. 



ON THE UNION OF COMPLEMENTED WITH R + IB MOLECULES 

 BEFORE LYSIS 



As has been mentioned above, the addition of comple- 

 mentoid to red corpuscles treated with IB does not prevent 

 the subsequent action of complement and the production 

 of lysis. This may be due either (a) to complementoid 

 failing to combine with the R + IB molecules, or (b) to its 

 being displaced by complement after it has combined ; both 

 factors may be partly concerned. There are two methods 

 by which the question may be investigated, and we have 

 carried out both of them. 



In the first place, we may add a given amount of heated 

 serum (Cd) to red corpuscles treated with IB, allow time for 

 combination, then remove the fluid by centrifugalization, 

 and then test the amount of Cd present in the fluid by finding 

 how much C it will prevent from combining with R + IB 

 molecules after lysis. We shall call the Cd treated in this 

 way Cdx. A control is made with the same amount of 

 heated serum (Cd) which has not been in contact with red 

 corpuscles treated with IB. We have performed a number 

 of experiments of this kind, and the result has always been 

 to show that only a fraction of the Cd combines with the 

 R -f- IB molecules. In one experiment it was found that 

 the Cdx of the rabbit kept out two-thirds of the amount of 

 guinea-pig's C kept out by rabbit's Cd, i.e. only one-third 

 of the Cd molecules had combined with the intact red 



