78 PROPERTIES OF KLEMOLYTIC SERA 



the chief complement present acts on both varieties, and 

 its union is a firm one ; 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 comple- 

 ment, 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 centrifugalization, and thereafter testing 

 the dose of the uncombined immune-body with rabbit's and with 

 guinea-pig's complement respectively. 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 experiments, how- 

 ever, 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 com- 

 plement kept out of combination a certain amount of rabbit's 

 complement, and vice versa. 



