2 8
RBCs in the proportions of IO and IOO of serum to I of RBCs. The homo-
genous serums were used as complement, but no lysis occurred with either
IO to I or IOO to I sensitization, even when 84 per cent. complement was present
in the tube, except in the case of the guinea-pig RBCs; and even with them
only slightly more lysis was given by the IOO to I sensitization than by the
IO to I. It is evident that the amboceptor had not been fixed, and the conclu-
sion arrived at is that mere increase of the quantity of a normal serum, up to
practically infinity, does not cause foreign RBCs, which are strongly lysed by that
serum when unheated, to fix enough amboceptor to enable them to be lysed by large
doses of their homogenous complement. The presence or absence of added isotonic
NaCl in the sensitizing fluid has no effect on the fixation of amboceptor.
That a certain quantity of amboceptor, and occasionally the greater portion,
can be fixed in a normal serum by foreign RBCs is easily demonstrated, also
that complement cannot be withdrawn from a normal serum by its homogenous
RBCs. In one experiment it was found that treatment of rabbit serum by heated
rabbit RBCs did not lessen the lytic power of that rabbit serum against sheep
RBCs, so no complement had been withdrawn. It was also found that if heated
rabbit RBCs were sensitized in heated dog serum and then digested with
unheated rabbit serum, enough complement was withdrawn from the latter to
prevent it giving any lysis with sheep RBCs.
7. Deviation of Complement.
For specific precipitation to occur it is necessary that the molecules of
precipitinogen should fix a certain number of molecules of precipitin. If the
precipitinogen is in excess in the first place, the molecules of precipitin are so
distributed amongst them that no precipitinogen molecule can fix sufficient preci-
pitin to enable a precipitate to be formed. If the precipitinogen is not in excess
to begin with, a precipitate is formed and is not re-dissolved on the addition of
more precipitinogen.
For lysis to occur it is necessary that the RBCs should fix a certain number
of molecules of complement. This they cannot do at all until sensitized.
If the sensitizing molecules are insufficient, sufficient complement cannot be
fixed. If the sensitizing molecules are sufficient, enough complement is fixed for
complete lysis. If the sensitizing molecules are in excess, they may be attached
nevertheless to the RBCs, but since the complement is in defect, the proportion
of the two which is necessary for the optimum degree of lysis is not appropriate
and “ deviation” appears.
It is probable that the proportion of amboceptor to complement required for
the optimum degree of lysis varies with the RBC and with the sensitizer, and
that the range of combination which results in the optimum degree of lysis also
varies widely, so that in some cases a slight excess of sensitizer shows deviation
and in others almost an infinite quantity is required to demonstrate it. RBCs
probably lose their affinity for sensitizer in proportion to the amount of it that has
been fixed.
It is quite possible that in certain cases RBCs may be unable to fix a much
larger number of sensitizing molecules than is absolutely required for the optimum
combination. Deviation of complement can then be demonstrated with difficulty
or not at all. Deviation can only be demonstrated clearly when RBCs can fix
sensitizing molecules in notable excess of the actual requirements for the optimum
combination. The complement molecules are in this case divided up amongst the
attached sensitizing molecules, but not necessarily equally amongst the RBCs
present, and so many RBCs do not get enough to permit them to be lysed. If the
excess of sensitizer is great there may be only “ slight ” lysis or “ trace ” lysis,
or conceivably none at all.