cause a noci-association (chemical), and a specific reaction analogous
to that following the administration of Coley's toxins might be expected.
Bacterial noci-association probably operates through the same
law as that through which physical noci-association operates.
Natural selection is impartial, however. It must be supposed that it
acts impartially upon the microscopic invader and upon the host.
On this ground one must infer that, in accordance with the same law
of natural selection, the bacteria of acute infections have met
by natural selection each advance in the struggle of the host
for immunity. Hence the fast and furious struggle between man
and his microscopic enemies merely indicates to what extent natural
selection has developed the ATTACK and the DEFENSE respectively.
This struggle is analogous to the quick and decisive battles
of the carnivora when fighting among themselves or when contending
against their ancient enemies. But when phylogenetically strange
animals meet each other, they do not understand how to conduct a fight:
natural selection has not had the opportunity of teaching them.
The acute infections have the characteristics of being ancient enemies.
On this hypothesis one can understand the high mortality of measles
when it is introduced into a new country. By natural selection,
measles has become a powerful enemy of the human race, and a race
to which this infection is newly introduced has not had the advantage
of building up a defense against it by the law of natural selection.
May not the phenomena of anaphylaxis be studied on associational lines?
Then, too, there may be chemical noci-associations with enemies
now extinct, which, like the ticklish points, may still be active
on adequate stimulation. This brief reference to the possible
relation of the phenomena of the acute infections to the laws
of natural selection and of specific chemical noci-association has
been made as a suggestion. Since the doctrine of evolution explains