PROPERTIES OF COMPLEMENTOIDS 51 



ON THE AMOUNT OF COMPLEMENTOID DERIVED FROM 

 COMPLEMENT 



We have seen that the evidence for the existence of 

 complementoid is supplied by its preventing complement 

 from combining with certain molecules (R + IB and S + 

 anti-S respectively). The amount of complementoid present 

 may be measured by the amount of complement which is 

 thus kept out of combination. Accordingly, if each molecule 

 of complement gives rise to one molecule of complementoid, 

 then 0-1 c.c. of heated serum (Cd) should prevent the com- 

 bination of the complement in 0-1 c.c. of the same serum 

 unheated, provided, however, that the complement cannot 

 displace the complementoid after it has combined. Suppose 

 we wish to estimate how much complement will be kept out 

 by a given amount of complementoid, we proceed as follows. 

 Two series of tubes (A and B) containing 1 c.c. of a suspension 

 of red corpuscles are taken, and to each tube is added the 

 same amount of IB (say four doses) ; lysis is produced in all 

 the tubes by a dose of C. To each tube in series A a given 

 amount of Cd is added, and one hour at 37 C. is allowed for 

 combination. We then add increasing amounts of C to the 

 tubes in each series, and find, by the method described above, 

 how much C is taken up in the two series. The difference 

 between the amounts in the two series gives, of course, the 

 amount of C which has been prevented from combining by 

 the Cd used. We can in the same way compare the amount 

 of guinea-pig's C kept out by a given amount of rabbit's 

 C and Cd respectively, and the amount of rabbit's C kept 

 out by guinea-pig's C and Cd. Of course, in every experi- 

 ment of this kind, the Cd is a heated portion of the same 

 C as that used for comparison. 



A considerable number of experiments of this kind have 

 been performed both with rabbit's and guinea-pig's com- 



E2 



