But the
pus was pretty certain to reaccumulate in course of time, and it
became necessary again and again to repeat the process. And unhappily
there was no absolute security of immunity from bad consequences.
However carefully the procedure was conducted, it sometimes happened,
even though the puncture seemed healing by first intention, that
feverish symptoms declared themselves in the course of the first or
second day, and, on inspecting the seat of the abscess, the skin was
perhaps seen to be red, implying the presence of some cause of
irritation, while a rapid reaccumulation of the fluid was found to
have occurred. Under these circumstances, it became necessary to open
the abscess by free incision, when a quantity, large in proportion to
the size of the abscess, say, for example, a quart, of pus escaped,
fetid from putrefaction. Now, how had this change been brought about?
Without the germ theory, I venture to say, no rational explanation of
it could have been given. It must have been caused by the
introduction of something from without. Inflammation of the punctured
wound, even supposing it to have occurred, would not explain the
phenomenon. For mere inflammation, whether acute or chronic, though
it occasions the formation of pus, does not induce Putrefaction. The
pus originally evacuated was perfectly sweet, and we know of nothing
to account for the alteration in its quality but the influence of
something derived from the external world. And what could that
something be? The dipping of the instrument in oil, and the
subsequent precautions, prevented the entrance of oxygen. Or even if
you allowed that a few atoms of the gas did enter, it would be an
extraordinary assumption to make that these could in so short a time
effect such changes in so large a mass of albuminous material.
Besides, the pyogenic membrane is abundantly supplied with capillary
vessels, through which arterial blood, rich in oxygen, is perpetually
flowing; and there can be little doubt that the pus, before it was
evacuated at all, was liable to any action which the element might be
disposed to exert upon it.

On the oxygen theory, then, the occurrence of putrefaction under these
circumstances is quite inexplicable. But if you admit the germ
theory, the difficulty vanishes at once. The canula and trocar having
been lying exposed to the air, dust will have been deposited upon
them, and will be present in the angle between the trocar and