304 Prof. R Muir and Mr. C. H. Browning. [Nov. 10, 



even with this combination, however, the amount taken up appeared 

 to diminish somewhat over night. 



The fact already stated that, when guinea-pig's corpuscles were used as the 

 indicator, additional doses of immune-body did not appear to lead to the taking-up 

 of additional amounts of complement, raised the question whether there might 

 not be two immune-bodies present, one of which acted with rabbit's complement, 

 and one with guinea-pig's complement. Evidence of this was sought for by 

 leaving the immune-serum in contact with the corpuscles for a time, then 

 separating by centrifugalisation, and thereafter testing the dose of the un- 

 combined immune-body with rabbit's and with guinea-pig's complement respec- 

 tively. It is evident that if two immune-bodies were present, and were taken up 

 by the corpuscles in different proportions, then the relative doses of the separated 

 fluid would become changed. Such an investigation is theoretically of simple 

 nature, but it is difficult to carry it out exactly ; owing to the fact that it is not 

 possible to remove completely the natural immune-body from the rabbit's serum, 

 i.e., to make this serum entirely devoid of hsemolytic action. In several experi- 

 ments, however, allowance being made for this circumstance, it appeared that the 

 relative doses with the two complements did alter in the way that the dose with 

 guinea-pig's complement became relatively still higher, i.e., after the contact with 

 the corpuscles there seemed to be immune-body molecules left, which acted 

 with rabbit's, but not with guinea-pig's complement. This may mean merely that 

 the molecules of immune-body vary in their combining affinities, and that those 

 with the weaker affinity act with the more powerful complement (rabbit's). The 

 question is one of great complexity, and we have not attempted a full solution, as 

 it did not appear necessary for the purposes of the present research. Everything 

 goes to show, however, that the great majority of the immune-body molecules act 

 both with rabbit's and with guinea-pig's complement ; and we found that the 

 presence of a small amount of guinea-pig's complement kept out of combination a 

 certain amount of rabbit's complement, and vice versa. 



(c) With Ox's Complement 



The ox's complement is not a very suitable one to employ in this 

 combination, as the natural serum of the ox has a very powerful 

 hsemolytic action in itself, and it is only possible to remove a small 

 proportion of the natural immune-body by contact experiments. 

 Nevertheless, we have found that the dose of ox's complement, along 

 with the immune-body to guinea-pig's corpuscles, is a small one, and 

 there is no doubt that guinea-pig's corpuscles are very sensitive to the 

 zymotoxic action of ox complement. 



When we come to investigate the combining affinities, we find that 

 multiple doses of immune-body have very little effect on the amount of 

 ox's complement taken up, the amount taken up by means of from four 

 to eight doses, for example, being very little more than that taken up 

 by means of one dose. This may be due to a true want of combining 

 affinity on the part of the complement, or it may be due to the 

 combination being a very loose one. It may be noted, however, that 

 there is practically no evidence of dissociation of complement in the 

 course of 12 hours. The following will serve as an example : 



