"A certain use," the other replied cautiously. "Or, rather, it was not he, but an associate, called by him the Physician of Aleppo, who discovered it. This man was the pupil of the learned Rhazes, and the tutor of the equally learned Avicenna, the link, in fact, between them; but his name, for some reason, perhaps because he mixed with his practice a greater degree of mysticism than was approved by the Arabian schools of the next generation, has not come down to us. This man identified the product which had defied Ibn Jasher's tests with a substance even then considered by most to be fabulous, or to be extracted only from the horn of the unicorn if that animal existed. That it had some of the properties of the fabled substance, he proceeded to prove to the satisfaction of Ibn Jasher by curing of a certain incurable disease five persons."
"No more than five?"
"No."
"Why?"
"The substance was exhausted."
Blondel gasped. "Why did he not make more?" he cried. His voice was querulous, almost savage.
"The experiment," Basterga answered, "of which it was the product was costly."
Blondel's face turned purple. "Costly?" he cried. "Costly? When the lives of men hung in the balance."
"True," Basterga replied with a smile; "but I was about to say that, costly as it was, it was not its price which hindered the production of a further supply. The reason was more simple. He could not extract it."
"Could not? But he had made it once?"