family in Glasgow was poisoned without knowing it by the escape of this
gas. A little over one per cent of it in the atmosphere is fatal,
if breathed for any length of time. You know, it is a product of
combustion, and is very deadly--it is the much-dreaded white damp or
afterdamp of a mine explosion.

"I'm going to tell you a secret which I have not given out to the press
yet. I tried an experiment in a closed room today, lighting the brazier.
Some distance from it I placed a cat confined in a cage so it could not
escape. In an hour and a half the cat was asphyxiated."

The coroner concluded with an air of triumph that quite squelched the
district attorney.

Kennedy was all attention. "Have you preserved samples of the blood of
Mr. Templeton and Miss Wainwright?" he asked.

"Certainly. I have them in my office."

The coroner, who was also a local physician, led us back into his
private office.

"And the cat?" added Craig.

Doctor Nott produced it in a covered basket.

Quickly Kennedy drew off a little of the blood of the cat and held it up
to the light along with the human samples. The difference was apparent.

"You see," he explained, "carbon monoxide combines firmly with the
blood, destroying the red colouring matter of the red corpuscles. No,
Doctor, I'm afraid it wasn't carbonic oxide that killed the lovers,
although it certainly killed the cat."

Doctor Nott was crestfallen, but still unconvinced. "If my whole medical
reputation were at stake," he repeated, "I should still be compelled to
swear to asphyxia. I've seen it too often, to make a mistake. Carbonic
oxide or not, Templeton and Miss Wainwright were asphyxiated."

It was now Whitney's chance to air his theory.

"I have always inclined toward the cyanide-of-potassium theory, either
that it was administered in a drink or perhaps injected by a needle," he
said. "One of the chemists has reported that there was a possibility of
slight traces of cyanide in the mouths."

"If it had been cyanide," replied Craig, looking reflectively at the two
jars before him on the table, "these blood specimens would be blue in
colour and clotted. But they are not. Then, too, there is a substance
in the saliva which is used in the process of digestion. It gives a
reaction which might very easily be mistaken for a slight trace of
cyanide. I think that explains what the chemist discovered; no more, no
less. The cyanide theory does not fit."

"One chemist hinted at