ess,
and some even such ludicrous misfits as impurities in the chemical
reagents used, scrapings from the corks of bottles, dust from the air,
or even air-bubbles. These "discoveries" have ranged the whole realm of
unicellular life,--bacilli, bacteria, spirilla, yeasts, moulds,
protozoa,--yet the overwhelming judgment of broad-minded and reputable
experts the world over is the Scotch verdict of "not proven"; and we are
more and more coming to turn our attention to the other aspect of the
problem, the factors which cause or condition this isolation and
assumption of autonomy on the part of the cells.

This is not by any means to say that there is no causative organism, and
that this will not some day be discovered. Human knowledge is a blind
and short-sighted thing at best, and it may be that some invading cell,
which, from its very similarity to the body-cells, has escaped our
search, will one day be discovered. Nor will the investigators diminish
one whit of their vigor and enthusiasm on account of their failure thus
far.

The most strikingly suggestive proof of the native-born character of
cancer comes from two of its biologic characters. The first is that its
habit of beginning with a mass formation, rapidly deploying into columns
and driving its way into the tissues in a ghastly flying wedge, is
simply a perfect imitation and repetition of the method by which glands
are formed during the development of the body. The flat, or epithelial,
cells of the lining of the stomach, for instance, begin to pile up in a
little swarm, or mass, elongate into a column, push their way down into
the deeper tissue, and then hollow out in their interior to form a
tubular gland. The only thing that cancer lacks is the last step of
forming a tube, and thereby becoming a servant of the body instead of a
parasite upon it.

Nor is this process confined to our embryonic or prenatal existence.
Take any gland which has cause to increase in size during adult life,
as, for instance, the mammary gland, in preparation for lactation, and
you will find massing columns and nests of cells pushing out into the
surrounding tissue in all directions, in a way that is absolutely
undistinguishable in its earlier stages from the formation of cancer. It
is a fact of gruesome significance that the two organs--the mammary
gland and the uterus--in which this process habitually takes place in
adult life are the two most fatally liable to the attack of cancer.