32

        In (7) the exact conditions of sachs's experiment were imitated and his find-
ings were fully confirmed.

       Sachs explains his experiment by assuming that the normal amboceptors
circulating in the blood have a higher degree of affinity for complement than
artificial amboceptors, and that the union of normal amboceptor molecule and
complement molecule can occur in the test tube without previous union of the
amboceptor with a RBC.

       In his experiment A heated normal-rabbit-serum containing various ambocep-
tors is incubated with fresh guinea-pig serum. Then heated rabbit-antisheep-serum
and sheep RBCs are added. The sheep RBCs attach both the normal amboceptor
of the normal-rabbit-serum and the artificial amboceptor of the rabbit-antisheep-
serum. Lysis is effected by union of the complement with the attached normal
amboceptor, for which it has a greater affinity than for either the attached artificial
amboceptor or the free normal amboceptors of other kinds. In his experiment B
the same procedure is followed but the normal-rabbit-serum is first digested with
washed sheep RBCs which extract the normal sheep amboceptor from it. When
the antisheep serum and sheep RBCs are finally added the RBCs find no normal
amboceptor to fix, but only artificial amboceptor. The guinea-pig complement is
supposed to have a higher degree of affinity for the free normal amboceptors of
other kinds in the rabbit serum than for the artificial amboceptor attached to the
RBCs. The complement molecules consequently remain united to these free
amboceptors and do not combine with the artificially sensitized RBCs. Hence there
is no lysis. The free normal amboceptors, therefore, are supposed to act as
anticomplements and to deviate the complement.

      On this hypothesis in our experiment (3) the absence of prevention of lysis can
only be explained by assuming that goat complement has a greater affinity for goat
antisheep amboceptor in combination with sheep RBCs than it has for free normal
amboceptors, whereas the converse is the case with guinea-pig complement. This
is supported by our experiment (4).

     Sachs's interpretation involves the view that there can be union between
amboceptor and complement molecules without union of the former with RBCs,
which is by no means generally accepted (vide "Deviation," p. 28). It is
recognised that the reactions
       (1)RBC + Amboceptor=(RBC + Amboceptor)
 and (2)(RBC + Amboceptor) + complement = lysis
take an appreciable time,the length of which is related to the quantities
present and to the temperature

    If amboceptor and complement were already united in the fluid it would seem
probable that the reaction (C + A) + RBC = lysis would be more rapid than the
reaction RBC + A + C = lysis

     To put this to the test we took heated pony-antisheep-serum for amboceptor,
fresh guinea-pig serum for complement, and washed sheep RBCs. Two series, A
and B, were put up, and the degree of lysis in the tubes noted every three minutes.
In A, amboceptor and complement were incubated together for an hour before
adding the RBCs; in B, amboceptor, complement and RBCs were incubated
separately. The racks, pipettes and tubes used were all similarly incubated, and
the final mixtures were made with the utmost rapidity.

   No acceleration of lysis was observed in series A in which amboceptor and
complement had been given an opportunity of uniting before the addition
of the RBCs; so it must be concluded either that amboceptor and complement do
not unite in the absence of RBCs or that, if they do unite, the combination thus
formed does not produce lysis with greater velocity than when amboceptor and com-
plement meet the RBCs without previous combination.