52 PROPERTIES OF H^MOLYTIC SERA 



plementoids, and differences are found in the two cases. 

 In five experiments in which rabbit's complementoid was 

 used, it was found that there was kept out of combination 

 a quantity of complement approximately equal to the amount 

 of complementoid used. In the case of the guinea-pig's 

 complement, on the other hand, the amount of complement 

 kept out was always distinctly less ; on the average, 0-6 c.c. 

 of C corresponded to 1 c.c. of complementoid. We may 

 therefore say that a molecule of rabbit's C gives rise to a 

 molecule of Cd, which has an affinity for the R + IB mole- 

 cules after lysis, practically equal to that of C; whereas, 

 with the guinea-pig's serum, in the process of heating either 

 some of the C becomes entirely destroyed, or the Cd formed 

 has a lower combining affinity and some of it can be dis- 

 placed by C. 



ON THE RELATIVE FIRMNESS OF UNION OF COMPLEMENT 

 AND COMPLEMENTOID RESPECTIVELY WITH R -f- IB 

 MOLECULES (SENSITIZED RECEPTORS) AFTER LYSIS 



To determine this, we have compared in the usual way 

 the amount of unaltered C which can be taken up with the 

 amount of a mixture of C and Cd in equal parts. If the C 

 and Cd molecules have the same combining power, it is 

 evident that the saturation of the R -{- IB molecules will 

 occur after the addition of the same amounts in the two 

 cases. After the saturation point has been reached, how- 

 ever, twice as much of the C + Cd mixture as of the undiluted 

 C would have to be added before a free dose of C would be 

 obtained. As a matter of fact, this is pretty much what 

 happens. 



The following may be taken as examples : 

 I. Two series of tubes, A and B, three doses (3 D) of IB 

 added to each tube, and lysis is produced in all by 1 D 

 of guinea-pig's C, M.H.D. = 0-05 c.c. C is then added in 

 increasing amounts. 



