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      Usually their cytophile affinity is stronger than their complementophile affi-
nity, for they can combine with cells in the cold at a temperature of 0° Cent. at
which temperature they will not combine with complement.

      Amboceptors are as we have seen specific, they can enter into combination
with only one kind of cell, that is cells possessing like receptors. But ambo-
ceptor alone, although it may enter into combination, cannot effect any
definite change in the cell to which it becomes bound by its cytophile affinity
Its function then appears to be the linking up of a cell to complement or cytase'
in such a way that this latter body which has toxic or ferment-like properties,
can act and destroy the cell to which the amboceptor has united it.

      We have seen therefore that amboceptors are not in themselves toxic, because
they possess no " zymotoxic group," and cells plus amboceptor remain apparently
undamaged and capable of performing all their normal functions.

      We have also seen that amboceptor possesses such a strong affinity for cells
with suitable receptors that it will enter into combination with them at exceed-
ingly low temperatures.

Combination of red cells and amboceptor in vitro.

      (1) To a suspension of red cells in .8 per cent. salt solution, specific hæmolytic
serum previously heated for ½ hour at 55° Cent. is added and the mixture is
allowed to stand for a time. The red cells remain apparently unaltered, but on
the addition of a little normal serum, which can be shown to have no action
upon similar red cells without treatment, rapid hæmolysis ensues.

      (2) To a suspension of red cells, unheated specific serum, capable of producing
hæmolysis, is added and the mixture is maintained at a temperature of 0° Cent.
for a time. No hæmolysis occurs. The mixture is then centrifuged and the red
cells separated from the supernatant liquid. The red cells are apparently un-
altered, but, on the addition of a little normal serum, speedy hæmolysis takes
place. If the mixture of haemolytic serum with red cells has been made in suitable
amounts, the separated supernatant liquid will show, on further examination, that
all the amboceptor has combined and been removed with the red cells, but
that free complement still remains, its combination with the amboceptor having
been prevented by the low temperature, at which therefore no hæmolysis
occurred.

      By a series of experiments such as these Ehrlich was able to show that red
cells possess the power of combining with far more specific amboceptor than is
sufficient to cause hæmolysis in the presence of complement. The amount taken up
227 H. D.

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