ical kind, the same
truth becomes still more conspicuous. Expose several persons to a
drenching storm; and while one will subsequently feel no appreciable
inconvenience, another will have a cough, another a catarrh, another an
attack of diarrhoea, another a fit of rheumatism. Vaccinate several
children of the same age with the same quantity of virus, applied to the
same part, and the symptoms will not be quite alike in any of them,
either in kind or intensity; and in some cases the differences will be
extreme. The quantity of alcohol which will send one man to sleep, will
render another unusually brilliant--will make this maudlin, and that
irritable. Opium will produce either drowsiness or wakefulness: so will
tobacco.

Now in all these cases--mechanical and other--some force is brought to
bear primarily on one part of an organism, and secondarily on the rest;
and, according to the doctrine of Cuvier, the rest ought to be affected
in a specific way. We find this to be by no means the case. The original
change produced in one part does not stand in any necessary correlation
with every one of the changes produced in the other parts; nor do these
stand in any necessary correlation with one another. The functional
alteration which the disturbing force causes in the organ directly acted
upon, does not involve some _particular set_ of functional alterations
in the other organs; but will be followed by some one out of various
sets. And it is a manifest corollary, that any _structural alteration_
which may eventually be produced in the one organ, will not be
accompanied by _some particular set of structural alterations_ in the
other organs. There will be no necessary correlation of forms.

Thus Paleontology must depend upon the empirical method. A fossil
species that was obliged to change its food or habits of life, did not
of necessity undergo the particular set of modifications exhibited; but,
under some slight change of predisposing causes--as of season or
latitude--might have undergone some other set of modifications: the
determining circumstance being one which, in the human sense, we call
fortuitous.

May we not say then, that the deductive method elucidates this vexed
question in physiology; while at the same time our argument collaterally
exhibits the limits within which the deductive method is applicable. For
while we see that this extremely _general_ question may be
satisfactorily dealt with deductively; the conclu