“I prefer those which were not practical,” confessed the doctor, with a smile. “Consider for example the _Tinctura Physicorum_, which neither Pope nor Emperor could buy with all his wealth. It was one of the greatest alchemical mysteries, and, though mentioned under the name of _The Red Lion_ in many occult works, was actually known to few before Paracelsus, except Hermes Trismegistus and Albertus Magnus. Its preparation was extremely difficult, for the presence was needed of two perfectly harmonious persons whose skill was equal. It was said to be a red ethereal fluid. The least wonderful of its many properties was its power to transmute all inferior metals into gold. There is an old church in the south of Bavaria where the tincture is said to be still buried in the ground. In the year 1698 some of it penetrated through the soil, and the phenomenon was witnessed by many people, who believed it to be a miracle. The church which was thereupon erected is still a well-known place for pilgrimage. Paracelsus concludes his directions for its manufacture with the words: _But if this be incomprehensible to you, remember that only he who desires with his whole heart will find, and to him only who knocks vehemently shall the door be opened_.” “I shall never try to make it,” smiled Arthur. “Then there was the _Electrum Magicum_, of which the wise made mirrors wherein they were able to see not only the events of the past and of the present, but the doings of men in daytime and at night. They might see anything that had been written or spoken, and the person who said it, and the causes that made him say it. But I like best the _Primum Ens Melissæ_. An elaborate prescription is given for its manufacture. It was a remedy to prolong life, and not only Paracelsus, but his predecessors Galen, Arnold of Villanova, and Raymond Lulli, had laboured studiously to discover it.” “Will it make me eighteen again?” cried Susie. “It is guaranteed to do so,” answered Dr Porhoët gravely. “Lesebren, a physician to Louis XIV, gives an account of certain experiments witnessed by himself. It appears that one of his friends prepared the remedy, and his curiosity would not let him rest until he had seen with his own eyes the effect of it.” “That is the true scientific attitude,” laughed Arthur.