UNION OF COMPLEMENT 37 



two points to be borne in mind : the one is (which 

 we had not recognized till after the experiments were 

 first performed) that immune-body at 37 C. separates to a 

 certain extent into the surrounding fluid. It is thus possible 

 that a certain amount of immune-body may have become 

 free before the combination of complement was complete. 

 Even, however, on this supposition, we would expect the 

 amount of immune-body dissociated to be much diminished 

 by the fixation of complement. Then, again, we do not know 

 that every molecule of immune-body takes up a molecule 

 of complement, and theoretically it is possible that immune- 

 body attached to a receptor A of a corpuscle may not take 

 up complement, and thus be free to dissociate ; whereas it 

 may be active in haemolysis (that is, take up complement) 

 when attached to receptor B in the same or another 

 corpuscle. Study of this kind shows clearly that we can 

 regard neither the receptors, nor the molecules of immune- 

 body, nor the molecules of complement as being identical 

 in their respective classes it is not as if we were dealing 

 with the combination of three definite chemical substances. 

 We do not maintain that the results completely disprove 

 the theory that the immune-body acts as an amboceptor ; 

 but the experiments on the whole are against such a view, 

 and at least point strongly to the fact that ultimately the 

 molecule of complement becomes firmly attached to the 

 receptor of the corpuscle. It is to be noted that even, 

 however, if immune-body was no longer dissociable after the 

 union of complement, this in itself would not establish its 

 amboceptor constitution ; it would simply prove that its 

 union had become firmer after the union of complement. 



Another point bearing on this subject may be referred 

 to. If it is the case that immune-body can be dissociated 

 from the receptors of the red corpuscles after having led 

 to the union of complement, whereas the complement is 

 firmly fixed, then the following phenomenon should result. 



