We looked at each other, and the horror of the thing sank deep into our minds.  Woorali.  What was it?  There were many travellers in the room who had been in the Orient, home of poisons, and in South America.  Which one had run across the poison?

“Woorali, or curare,” said Craig slowly, “is the well-known poison with which the South American Indians of the upper Orinoco tip their arrows.  Its principal ingredient is derived from the Strychnos toxifera tree, which yields also the drug nux vomica.”

A great light dawned on me.  I turned quickly to where Vanderdyke was sitting next to Mrs. Ralston, and a little behind her.  His stony stare and laboured breathing told me that he had read the purport of Kennedy’s actions.

“For God’s sake, Craig,” I gasped.  “An emetic, quick—­Vanderdyke.”

A trace of a smile flitted over Vanderdyke’s features, as much as to say that he was beyond our interference.

“Vanderdyke,” said Craig, with what seemed to me a brutal calmness, “then it was you who were the visitor who last saw Laura Wainwright and John Templeton alive.  Whether you shot a dart at them I do not know.  But you are the murderer.”

Vanderdyke raised his hand as if to assent.  It fell back limp, and I noted the ring of the bluest lapis lazuli.

Mrs. Ralston threw herself toward him.  “Will you not do something?  Is there no antidote?  Don’t let him die!” she cried.

“You are the murderer,” repeated Kennedy, as if demanding a final answer.

Again the hand moved in confession, and he feebly moved the finger on which shone the ring.

Our attention was centred on Vanderdyke.  Mrs. Ralston, unobserved, went to the table and picked up the gourd.  Before O’Connor could stop her she had rubbed her tongue on the black substance inside.  It was only a little bit, for O’Connor quickly dashed it from her lips and threw the gourd through the window, smashing the glass.

“Kennedy,” he shouted frantically, “Mrs. Ralston has swallowed some of it.”

Kennedy seemed so intent on Vanderdyke that I had to repeat the remark.

Without looking up, he said:  “Oh, one can swallow it—­it’s strange, but it is comparatively inert if swallowed even in a pretty good-sized quantity.  I doubt if Mrs. Ralston ever heard of it before except by hearsay.  If she had, she’d have scratched herself with it instead of swallowing it.”

If Craig had been indifferent to the emergency of Vanderdyke before, he was all action now that the confession had been made.  In an instant Vanderdyke was stretched on the floor and Craig had taken out the apparatus I had seen during the afternoon.

“I am prepared for this,” he exclaimed quickly.  “Here is the apparatus for artificial respiration.  Nott, hold that rubber funnel over his nose, and start the oxygen from the tank.  Pull his tongue forward so it won’t fall down his throat and choke him.  I’ll work his arms.  Walter, make a tourniquet of your handkerchief and put it tightly on the muscles of his left arm.  That may keep some of the poison in his arm from spreading into the rest of his body.  This is the only antidote known—­artificial respiration.”