"To determine exactly what was the poison used was an almost insurmountable task, for I had never met with the substance before; but, after working diligently all this time, I have found that by treating it with sulphuric acid it underwent no change, yet by adding a fragment of bichromate of potassium a series of blue, violet, purple, and red tints were produced, very similar to those seen in the tests for strychnia. The same results were brought about, also, by peroxide of lead and black oxide of manganese. I dried the skin of a frog and touched it with a drop of solution containing a single one of the tiny crystals, when strong tetantic convulsions ensued and the animal died in ten seconds. At last, however, after many other experiments, the idea occurred to me that it was an alkaloid of some plant unknown in modern toxicology. I was, of course, aware of the action of the calabar bean of the West Coast of Africa, the akazga, the datura seeds of India, and such-like poisons, but this was certainly none of these. It was a substance terribly deadly--the only substance that could strike death through the cuticle--utterly unknown to us, yet the most potent of all secret poisons." "And how did you determine it at last?" "By a reference I discovered in an ancient Latin treatise on poisons from the old monastery at Pavia, now in the British Museum. It gave me a clue which ultimately led me to establish it as the alkaloid of the vayana bean. This bean, it appears, was used in the tenth and eleventh centuries by a sect of the despotic Arab mystics called the Fatimites, who had made Cairo their capital, and held rule over Syria as well as the northern coast of Africa. The last Fatimite was, at a later date, dethroned by Saladin, conqueror of the Koords, and who opposed Richard the First of England. The poison, introduced from Egypt into Italy, was known to the old alchemists as the most secret means of ridding one of undesirable acquaintances. Its effect, it was stated, was the most curious of any known drug, because, for the time being, it completely altered the disposition of the individual and caused him to give way to all sorts of curious notions and delusions, while at the same time he would be entirely obedient to the will of any second person. Afterwards came fierce delirium, a sensation as though the lower limbs were frozen, complete loss of power, exhaustion, and death. But in modern toxicology even the name of the vayana was lost.