"Before we add any acid," said he, "or introduce any fresh matter, we will adopt the simple preliminary measure of tasting the solution. The sugar is a disturbing factor, but some of the alkaloids and most mineral poisons excepting arsenic have a very characteristic taste."
He dipped a glass rod in the warm solution and applied it gingerly to his tongue.
"Ha!" he exclaimed, as he carefully wiped his mouth with his handkerchief, "simple methods are often very valuable. There isn't much doubt as to what is in that sugar. Let me recommend my learned brother to try the flavour. But be careful. A little of this will go a long way."
He took a fresh rod from the rack, and, dipping it in the solution, handed it to me. I cautiously applied it to the tip of my tongue and was immediately aware of a peculiar tingling sensation accompanied by a feeling of numbness.
"Well," said Thorndyke; "what is it?"
"Aconite," I replied without hesitation.
"Yes," he agreed; "aconite it is, or more probably aconitine. And that, I think, gives us all the information we want. We need not trouble now to make a complete analysis, though I shall have a quantitative examination made later. You note the intensity of the taste and you see what the strength of the solution is. Evidently that lump of sugar contained a very large dose of the poison. If the sugar had been dissolved in your tea, the quantity that you drank would have contained enough aconitine to lay you out within a few minutes; which would account for Mrs. Schallibaum's anxiety to get clear of the premises. She saw you drink from the cup, but I imagine she had not seen you turn the sugar out."
"No, I should say not, to judge by her expression. She looked terrified. She is not as hardened as her rascally companion."
"Which is fortunate for you, Jervis. If she had not been in such a fluster, she would have waited until you had poured out your tea, which was what she probably meant to do, or have dropped the sugar into the milk-jug. In either case you would have got a poisonous dose before you noticed anything amiss."
"They are a pretty pair, Thorndyke," I exclaimed. "A human life seems to be no more to them than the life of a fly or a beetle."