He was working over a microscope, while by his side stood in racks, innumerable test-tubes of various liquids. On the table before him lay the lock of our door which he had cut out after he gave me the sleeping draught.
"What was it?" I asked. "I feel as if I had been on a bust, without the recollection of a thing."
He shook his head as if to discourage conversation, without taking his eyes off the microscope through which he was squinting. His lips were moving as if he were counting. I waited in impatient silence until he seemed to have finished.
Then, still without a word, he took up a test-tube and dropped into it a little liquid from a bottle on a shelf above the table. His face lighted up, and he regarded the reaction attentively for some time. Then he turned to me, still holding the tube.
"You have been on a bust," he said with a smile as if the remark of a few minutes before were still fresh. "Only it was a laughing gas jag—nitrous oxide."
"Nitrous oxide?" I repeated. "How—what do you mean?"
"I mean simply that a test of your blood shows that you were poisoned by nitrous oxide gas. You remember the sample of blood which I squeezed from your thumb? I took it because I knew that a gas—and it has proved to be nitrous oxide—is absorbed through the lungs into the circulation and its presence can be told for a considerable period after administration."
He paused a moment, then went on: "To be specific in this case I found by microscopic examination that the number of corpuscles in your blood was vastly above the normal, something like between seven and eight million to a drop that should have had somewhat more than only half that number. You were poisoned by gas that—"
"Yes," I interrupted, "but how, with all the doors locked?"
"I was coming to that," he said quietly, picking up the lock and looking at it thoughtfully.