12 Prof. R Muir and Mr. C. H. Browning. [May 17, 



On tJie Amount of Complementoid derived from Complement. 

 We have seen that the evidence for the existence of complemented 

 is supplied by its preventing complement from combining with certain 

 molecules (K + IB and anti-C respectively). The amount of comple- 

 mentoid present may be measured by the amount of complement which 

 is thus kept out of combination. Thus, if each molecule of com- 

 plement gives rise to one molecule of complementoid, then 0*1 c.c. of 

 heated serum (Cd) should prevent the combination of the complement 

 in O'l 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) 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 1 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 experiment 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 per- 

 formed both with rabbit's and guinea-pig's complementoids, 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 molecules after lysis, practically equal to that of C ; whereas, 

 with the guinea-pig, 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 displaced by C. 



On the Relative Firmness of Union of C and Cd respectively with 



R + IB Molecules after Lysis. 



To determine this, we have compared in the usual way the amount 

 f unaltered C which can be taken up, with the amount of a mixture 



