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effective against the RBCs of some out of each these groups. Some of his
isolysins dissolved sheep RBCs, some did not. Again, some goats did not
develop an isolysin at all. His isolysins, however, were all tested directly and not
with the aid of guinea-pig complement.
The serum of a pony which we have injected with sheep blood for a year now
lyses goat RBCs readily, but it contains no isolysin for horse RBCs. It seems
clear that the RBCs of any one species contain some substances in common with
the RBCs of nearly allied species, so that the injection of the RBCs of that
species into an animal of another species gives rise to the formation of immune
bodies against each of those substances. Judging by the length of time required
for the formation of isolysins, comparatively speaking, the amount of these common
substances must be relatively small.
It is also clear that the RBCs of individuals are not of exactly similar com-
position, since isolysins are not uniformly active against the RBCs of all indi-
viduals. Indeed, if an isolysin is totally inactive against the RBCs of some one
individual, one can only assume that the structure of that individual's RBCs is
entirely different from the structure of the RBCs with which the animal providing
the isolysin was immunised. Todd and White found that by mixing their serums
they obtained an isolysin which was universally potent. Our Goat B, which has
been injected with the blood of a different sheep on each occasion during the three
years, has probably had a sample of most of the possible varieties of sheep RBCs.
It has not failed to lyse the RBCs of any goat which has been tested, except its
own, so that with the RBCs from a large number of different sheep it has prob-
ably also received most of the possible varieties of the substance common to sheep
and goat RBCs, and is, therefore, probably universally potent against goat
RBCs, though, as we demonstrated, not in equal degree in every case. Why
does this difference exist in the potency of isolysins against the RBCs of different
individuals when it has never been recorded that a specific heterolysin has failed
against the RBCs of any one individual ? Might it happen that the serum of a
horse immunised against sheep RBCs would fail against the RBCs of certain
sheep, if the blood used for immunisation on each occasion had been obtained from
the same sheep ; or without complete failure is there a recognisable difference in
the degree of lysis obtained with RBCs from various individuals ?
Answers to these questions cannot as yet be given, nor can a clear explanation
be put forward to account for the escape from autolysis of the RBCs of the animal
furnishing the isolysin, unless we postulate the simultaneous production of anti-
autolysin. In the cases of our Goat B and Todd and White's cattle the isolysins
were not able to be complemented except by guinea-pig serum. Ehrlich's isolytic
serums apparently sufficed in themselves without a heterogenous complement.
It is conceivable that the specificity of artificially produced lytic serums is
relative only. If one injects a goat with sheep RBCs, first a sheep heterolysin is
formed ; then gradually a goat isolysin, which increases its range over individual
goats as the number of individual sheep providing RB Cs for injection is multi-
plied. Thirdly, a horse heterolysin appears. Supposing that it were practicable
to inject a goat with RBCs from an infinite number of sheep, a sufficient variety
of substances, proceeding from an infinite number of varying RBCs, might be
injected to produce lysins for the RBCs of other less nearly allied animals, per-
haps for all orders.
5. Some Facts relating to Complement.
(I) Lability of complement.—Whether complement exists as such in the plasma
or is excreted by leucocytes either during their life or on their disintegration,
mechanical or otherwise, does not seem capable of demonstration by extracorporeal
experiment. Precisely the same degree of lysis appears to be given by serum
obtained by defibrination and centrifugation and by serum obtained from blood