fifty-five, and that of
his wife twenty-six, and I may say that the marriage has been--well, by
no means a success. Now, within the last fortnight, my brother has been
attacked by a mysterious and extremely painful affection of the stomach,
to which his doctor seems unable to give a name. It has resisted all
treatment hitherto. Day by day the pain and distress increase, and I
feel that, unless something decisive is done, the end cannot be far
off."

"Is the pain worse after taking food?" inquired Thorndyke.

"That's just it!" exclaimed our visitor. "I see what is in your mind,
and it has been in mine, too; so much so that I have tried repeatedly to
obtain samples of the food that he is taking. And this morning I
succeeded." Here he took from his pocket a wide-mouthed bottle, which,
disengaging from its paper wrappings, he laid on the table. "When I
called, he was taking his breakfast of arrowroot, which he complained
had a gritty taste, supposed by his wife to be due to the sugar. Now I
had provided myself with this bottle, and, during the absence of his
wife, I managed unobserved to convey a portion of the arrowroot that he
had left into it, and I should be greatly obliged if you would examine
it and tell me if this arrowroot contains anything that it should not."

He pushed the bottle across to Thorndyke, who carried it to the window,
and, extracting a small quantity of the contents with a glass rod,
examined the pasty mass with the aid of a lens; then, lifting the
bell-glass cover from the microscope, which stood on its table by the
window, he smeared a small quantity of the suspected matter on to a
glass slip, and placed it on the stage of the instrument.

"I observe a number of crystalline particles in this," he said, after a
brief inspection, "which have the appearance of arsenious acid."

"Ah!" ejaculated Mr. Barton, "just what I feared. But are you certain?"

"No," replied Thorndyke; "but the matter is easily tested."

He pressed the button of the bell that communicated with the laboratory,
a summons that brought the laboratory assistant from his lair with
characteristic promptitude.

"Will you please prepare a Marsh's apparatus, Polton," said Thorndyke.

"I have a couple ready, sir," replied Polton.

"Then pour the acid into one and bring it to me, with a tile."

As his familiar vanished silently, Thorndyke turned to Mr. Barton.

"Supposing we find arsenic in this arrowroot, as we probably shall, wh