e deaths from cancer. How do you explain them? It is not a cancer
house, you say. Is it mere chance?"

"Anyone may be pardoned for believing that cancer houses or even cancer
districts exist," reiterated Craig. "Indeed some observations seem to
show it, as I have said, though the opponents of the theory claim to
have found other causes. Here, as you hint, five people, living in close
association, have died in five years."

He paused and drew from the satchel the little porcelain cone which he
had picked up between the Moreton and Goode houses.

"I have here," he resumed, "what is known as a Berkefeld filter. Its
meshes let through none of the germs that we can see with a microscope.
It is bacteria-proof. Only something smaller than these things can pass
through it, something that we cannot see, a clear watery fluid. That
something in this case is a filterable virus."

Kennedy paused again, then went on, "Although the filterable viruses
have only recently come to attention, it is known that they are of very
diverse character. Here we have opened up the world of the infinitely
little--the universe that lies beyond the range of the microscope. The
study of these tiny particles is now one of the greatest objects in
scientific medicine.

"Are they living? It seems so, for a very little of the virus gives rise
to growths from which many others start. It may, of course, be chemical,
but it looks as if it were organic, since it resists cold, although not
heat, and can be destroyed by phenol, toluol, and other antiseptics.
Perhaps the virus may be visible, but not by any means yet known. Still,
we do know that these things which no eye can see may cause some of the
commonest diseases."

Kennedy paused. As usual he had his little audience following him
breathlessly. Even Dr. Loeb forgot to glower.

"In recent experiments with cancer in chickens," continued Craig, "tumor
material ground fine and treated in various ways has been filtered
through these filters. Cancers have been caused by this agent which has
passed through the filter.

"On the inside of the filter which I picked up back of this very house,
near the boundary of Dr. Goode's, I have found the giant cells of
cancer. On the outside was something which I have been able to develop
into a virus, these micro-organisms that belong to the ultra-invisible.
I do not pretend to know just how this bacteriological dwarf has been
used. But I know enough to say that someone