o various indiscretions of food or drink, to unhygienic
surroundings, to material injuries, or to other forms of environmental
stress quite dissociated from the action of bacteria. It is true that
one would need to use extreme care nowadays in defining more exactly the
diseases that thus lie without the field of the bacteriologist, as that
prying individual seems prone to claim almost everything within sight,
and to justify his claim with the microscope; but after that instrument
has done its best or worst, there will still remain a fair contingent
of maladies that cannot fairly be brought within the domain of the
ever-present "germ." On the other hand, all germ diseases have of course
their particular effects upon the system, bringing their results within
the scope of the pathologist. Thus while the bacteriologist has no
concern directly with any disease that is not of bacterial origin, the
pathologist has a direct interest in every form of disease whatever;
in other words, bacteriology, properly considered, is only a special
department of pathology, just as pathology itself is only a special
department of general medicine.

Whichever way one turns in science, subjects are always found thus
dovetailing into one another and refusing to be sharply outlined.
Nevertheless, here as elsewhere, there are theoretical bounds that
suffice for purposes of definition, if not very rigidly lived up to in
practice; and we are justified in thinking of the pathologist (perhaps
I should say the pathological anatomist) as the investigator of disease
who is directly concerned with effects rather than with causes, who aims
directly at the diseased tissue itself and reasons only secondarily
to the causes. His problem is: given a certain disease (if I may be
permitted this personified form of expression), to find what tissues of
the body are changed by it from the normal and in what manner changed.

It requires but a moment's reflection to make it clear that a certain
crude insight into the solution of this problem, as regards all common
diseases, must have been the common knowledge of medical men since
the earliest times. Thus not even medical knowledge was needed to
demonstrate that the tissues of an in: flamed part become red and
swollen; and numerous other changes of diseased tissues are almost
equally patent. But this species of knowledge, based on microscopic
inspection, was very vague and untrustworthy, and it was only after the
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