"Dr. Goode thought that the cancers might have been caused artificially by X-rays or radium," I ventured.
Craig shook his head. "I have taken a piece of filter paper saturated with a solution of potassium iodide, starch paste, and ferrosulphate and laid it over a sample of blood, not four millimeters away. The whole I have kept in the dark.
"Now, we know that blood gives off peroxide of hydrogen. Peroxide of hydrogen is capable of attacking photographic plates. The paper can be permeated by a gas. No, that was not a case of photo-activity observed by Dr. Goode. It was the emission of gas from the blood that affected the plates."
"But suppose that is the case," objected Dr. Goode hastily. "There are the 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.