"It is as well that such poison is not generally known, or it would be used by many who wished to get rid of their friends," I remarked. The Professor laughed, and agreed, saying: "There are several poisons of the same type which are known only to toxicologists, and we are very careful not to allow the public sufficient knowledge of them. I must confess that I never dreamed when I commenced my investigations that I was in the presence of orosin. There is sufficient in this little tube"--and he held it to the light--"to kill a hundred persons. It certainly is one of the most dangerous of known compounds." "So it is evident that the man Despujol entered my room and placed the pins there intending that I should step upon one or other of them!" I gasped. "Without doubt. And it seems little short of a marvel that you escaped," said the Professor. "It certainly does," I remarked. "But I must tell the police of the fact you have established. The affair now assumes a new phase. The man was not in my room with the intention of robbery, but in order to encompass my death by secret means." "If you had not so fortunately avoided treading upon the pins you certainly would not be alive at the moment," remarked the Professor, again reflectively examining the yellow fluid in the tube. "What motive could the man have had in gaining access to your room and placing the pins there? I suppose he did not risk putting them there before you went to bed, as you might have picked one up on your boot, and that would have drawn your attention to them. By placing them there after you were in bed he hoped that, on getting out, your bare foot would come into contact with one of the impregnated points." "It was certainly a most fiendish plot!" I declared. "And I thank you, Professor, for taking all this trouble with your analysis and so establishing the truth. I will go to the police and inform them." "Yes. I wish you to do that, for the fellow is undoubtedly in possession of orosin, and intends to use it. Perhaps he has already killed people by the same subtle and secret means." "He must be arrested at all costs," I said. "Already the police all over Spain are watching for him, and special surveillance is being kept along all the railways and on the frontier." "Any person with orosin in his possession should be detained and examined," the Professor declared. "I wonder where he obtained it?" "Who knows?" I exclaimed, but I was reflecting whether, after all, my presence in Madrid was not known to De Gex. If so, was it possible that he had hired the notorious Despujol to attack me in secret!