Between 1994 and 1997, William Newman published three articles in which, for the first time, a profound connection between Roger Bacon's doctrine and Ps.-Avicenna's alchemical De anima was pointed out. These studies were a major step in understanding Roger Bacon's elemental physics, alchemy, and alchemical medicine, as well as his prolongatio vitae theory. By a thorough study of the physical, alchemical, and medical doctrine of the Jābirian treatises via Ps.-Avicenna's De anima, in comparison with Bacon's texts, I will continue the work initiated by Newman and draw some new conclusions. I will specifically focus on some principal differences between Roger Bacon and his favorite alchemical source, which allow us to understand the originality and innovation of the Franciscan. In addition to the De anima, a specific aspect of the alchemy of the Ps.-Aristotelian Secretum secretorum will also be studied here, being another of Bacon's major sources.