nt of the perfected microscope, some three-quarters of a century
ago, that pathological anatomy began to have any proper claim to
scientific rank. Indeed, it was not until about the year 1865 that the
real clew was discovered which gave the same impetus to pathology that
the demonstration of the germ theory of disease gave at about the same
time to etiology, or the study of causes of disease. This clew consisted
of the final demonstration that all organic action is in the last resort
a question of cellular activities, and, specifically, that all abnormal
changes in any tissues of the body, due to whatever disease, can consist
of nothing more than the destruction, or the proliferation, or the
alteration of the cells that compose that tissue.

That seems a simple enough proposition nowadays, but it was at once
revolutionary and inspiring in the day of its original enunciation some
forty years ago. The man who had made the discovery was a young German
physician, professor in the University of Freiburg, by name Rudolph
Virchow. The discovery made him famous, and from that day to this the
name of Virchow has held somewhat the same position in the world
of pathology that the name of Pasteur occupied in the realm of
bacteriology. Virchow was called presently to a professorship in the
University of Berlin. In connection with this chair he established his
famous Institute of Pathology, which has been the Mecca of all students
of pathology ever since. He did a host of other notable things as well,
among others, entering the field of politics, and becoming a recognized
leader there no less than in science. Indeed, it seemed during the later
decades of his life as if one encountered Virchow in whatever direction
one turned in Berlin, and one feels that it was not without reason that
his compatriots spoke of him as "the man who knows everything." To the
end he retained all the alertness of intellect and the energy of body
that had made him what he was. One found him at an early hour in the
morning attending to the routine of his hospital duties, his lectures,
and clinical demonstrations. These finished, he rushed off, perhaps
to his parliamentary duties; thence to a meeting of the Academy of
Sciences, or to preside at the Academy of Medicine or at some other
scientific gathering. And in intervals of these diversified pursuits he
was besieged ever by a host of private callers, who sought his opinion,
his advice, his influence in some