“No, of course not.  But she probably did know that ammonia is good for just that sort of faintness which she must have experienced after taking the powder.  Perhaps she thought of sal volatile, I don’t know.  But most people know that ammonia in some form is good for faintness of this sort, even if they don’t know anything about cyanides and—­”

“Then it was cyanide?” interrupted Craig.

“Yes,” he replied slowly.  It was evident that he was suffering great physical and nervous anguish as the result of his too intimate acquaintance with the poisons in question.  “I will tell you precisely how is was, Professor Kennedy.  When I was called in to see Miss Lytton I found her on the bed.  I pried open her jaws and smelled the sweetish odor of the cyanogen gas.  I knew then what she had taken, and at the moment she was dead.  In the next room I heard some one moaning.  The maid said that it was Mrs. Boncour, and that she was deathly sick.  I ran into her room, and though she was beside herself with pain I managed to control her, though she struggled desperately against me.  I was rushing her to the bathroom, passing through Miss Lytton’s room.  ‘What’s wrong?’ I asked as I carried her along.  ‘I took some of that,’ she replied, pointing to the bottle, on the dressing-table.

“I put a small quantity of its crystal contents on my tongue.  Then I realized the most tragic truth of my life.  I had taken one of the deadliest poisons in the world.  The odor of the released gas of cyanogen was strong.  But more than that, the metallic taste and the horrible burning sensation told of the presence of some form of mercury, too.  In that terrible moment my brain worked with the incredible swiftness of light.  In a flash I knew that if I added malic acid to the mercury—­perchloride of mercury or corrosive sublimate—­I would have calomel or subchloride of mercury, the only thing that would switch the poison out of my system and Mrs. Boncour’s.

“Seizing her about the waist, I hurried into the dining-room.  On a sideboard was a dish of fruit.  I took two apples.  I made her eat one, core and all.  I ate the other.  The fruit contained the malic acid I needed to manufacture the calomel, and I made it right there in nature’s own laboratory.  But there was no time to stop.  I had to act just as quickly to neutralize that cyanide, too.  Remembering the ammonia, I rushed back with Mrs. Boncour, and we inhaled the fumes.  Then I found a bottle of peroxide of hydrogen.  I washed out her stomach with it, and then my own.  Then I injected some of the peroxide into various Parts of her body.  The peroxide of hydrogen and hydrocyanic acid, you know, make oxamide, which is a harmless compound.

“The maid put Mrs. Boncour to bed, saved.  I went to my house, a wreck.  Since then I have not left this bed.  With my legs paralyzed I lie here, expecting each hour to be my last.”

“Would you taste an unknown drug again to discover the nature of a probable poison?” asked Craig.