6 Prof. K. Muir and Mr. C. H. Browning. [May 17, 



(vide supra), i.e., 4M.H.D. treated with 0-1 c.c. anti-C produces lysis. 

 The anti-C has thus a marked effect on guinea-pig's C as compared 

 with that on rabbit's C. One would conclude that while some of the 

 molecules in the rabbit's C and in the guinea-pig's C have the same 

 combining affinity, most of the molecules in the rabbit's C do not 

 combine with the anti-C, i.e., have a different haptophore group from 

 that of the molecules of guinea-pig's complement. 



2. How do the complements behave towards the same K + IB 

 molecules ? As is well known, ox's corpuscles, treated with IB from 

 the rabbit, are lysed on the addition either of guinea-pig's C or of 

 rabbit's C. This would point to the haptophore groups of the two 

 complements being the same. Ehrlich and Morgenroth have supposed 

 in the corresponding case of the IB to rabbit's corpuscles obtained 

 from the guinea-pig, that there are really two IB's present, one of 

 which combines with the rabbit's complement and one with the 

 guinea-pig's, and point out in favour of this view that when rabbit's 

 C is used, the M.H.D. of IB is about ten times greater than when 

 guinea-pig's C is used. We have accordingly investigated the case 

 of the immune-body obtained by injecting the rabbit with ox's 

 corpuscles. As both rabbit's and guinea-pig's complements are taken 

 up by ox's corpuscles combined with immune-body, the question comes 

 to be whether both complements combine with the same molecules. 

 Does the combination of guinea-pig's complement prevent the combina- 

 tion of rabbit's complement and vice versd 1 We have conducted a 

 large number of experiments of this nature, and the result has always 

 been to give an answer in the affirmative. The experiments are on 

 the same lines as those already described. Suppose we wish to test 

 how much guinea-pig's complement is kept from combination by the 

 previous combination of a given amount of rabbit's complement. To 

 one series (A) of tubes, each containing the test amount of corpuscles 

 combined with the same amount of IB (generally 34 D), we add 

 increasing amounts of guinea-pig's complement and test how much 

 the treated corpuscles will take up. In another series (B) of similar 

 tubes, we add a given amount of rabbit's C, allow combination to take 

 place for an hour at 37 C., and then test as before how much guinea- 

 pig's C will be taken up. (It is convenient in such experiments to 

 produce lysis first of all in all the tubes, in a case such as the present 

 by guinea-pig's C. The amount of C used, of course, is added to the 

 final result.) The excess in the amount of guinea-pig's C taken up 

 in series A over that taken up in series B gives the amount which has 

 been kept out by the amount of rabbit's C used. The following may 

 be cited as examples : 



1. No. 3. M.H.D. of guinea-pig's C = 05 c.c. ; M.H.D. of rabbit's C = 0'22 c.c. 

 About 3D of IB added to each of two series of tubes, each tube containing 1 c.c. 

 suspension of red corpuscles. 



