“We are taking it for granted that the sugar was prepared,” I remarked.

“Yes. Our explanation is entirely hypothetical and may be entirely wrong. But it all hangs together, and if we find any poisonous matter in the sugar, it will be reasonable to assume that we are right. The sugar is the Experimentum Crucis. If you will hand it over to me, we will go up to the laboratory and make a preliminary test or two.”

I took the lump of sugar from my pocket and gave it to him, and he carried it to the gas-burner, by the light of which he examined it with a lens.