|Portrait of Paracelsus, circle of Quentin Matsys,|
Probably a copy of a copy.
Books of secrets were popular across all social classes. They covered a wide range of subjects. Printers were eager to supply the hungry for new material, so not everything printed garnered a high level of scrutiny. To a critical eye, many of these books of secrets begged broad questions of credibility. Many publications were little more than unchecked compilations of folklore or exaggerated claims recorded in haste and hawked at the public squares by mountebanks. 
On the other end of the spectrum, careful, thought-out works such as Paracelsus' Great Surgery Book  vied for the attention of more sophisticated readers. He became controversial for challenging the establishment with iconoclastic ideas about medicine and science. Paracelsus was a one-time physician to miners  and sought to push medicine beyond the entrenched traditions of Galen and Hippocrates. He based his ideas more on experimentation and the observation of nature, less on supposition and dogma.
|Image of paracelsus that his biographer|
Charles Webster feels is more accurate.
Paracelsus coined the word "spagyric" in his book Liber Paragranum,  where he argues medicine should be based on the physical laws of nature alone. The word derives from two Greek terms: spao meaning to separate and ageiro meaning to combine. The underlying philosophy recurs throughout the history of alchemy. To enhance the special properties of a plant, break it down, to its separate constituents, then purify each and recombine them for a more potent product. Herein lay the bones of Neri’s empirical methodology; one built on the processes of reduction, purification and recombination. These methods appear throughout his glass recipes. Neri utilizes the technique with both plant and mineral ingredients, in the preparation of basic materials and pigments and throughout his medicinal work. He and his friend Emmanuel Ximenes discuss Paracelsus in their correspondence.  In 1608, Neri wrote to a friend that he had cured diseases using the "grandissima meraviglia" (wonderfully grand) methods of Paracelsus. 
Within months of his own death, Neri wrote a small tract titled Discorso. The full title translates to 'Discourse on Chemistry, what it is, and its Operations'.  In it, he "manifests right from the outset his adherence to the Paracelsian doctrine, which is not restricted to inorganic chemical operations involving the transmutation of metals, but has broader applicability to the field of medicine."  Neri begins:
The operations belonging to chemistry do not only, as some estimate, involve the transmutation of metals. It is a much more universal art, which in some ways also embraces medicine (or at least it comes very close in assisting) and it can be defined. It is an art, which resolves and reduces all ‘mixed bodies’ [corpi misti] into their primary elements, it searches out their nature and separates the pure from the impure and it makes use of the pure to perfect these bodies and even to transform one body into another. Neri’s philosophy is clear, he considers himself an alchemist and his art—the art of chemistry—embraces metallurgy, glassmaking and medicine.
 Montebanco; one who stand on a box or stage. Also called charlatans (ciarlatani), which means to chatter.
 Paracelsus (1493–1541), also Phillip von Hohenheim, Philippus Theophrastus Aureolus Bombastus von Hohenheim. See Paracelsus 1536; cf. Webster 2008, p. 17.
 Webster 2008, p. 9, 148.
 Neri 1612, p. vii.
 Neri 1612, pp. 40, 104, medicina; p. 9, dose and throughout.
 Neri 1612, p. 98 ana
Opus Paragranum, written in 1529/30 not published until 1565. Cf. Paracelsus 1565.
 Neri 1980, pp. xlii–xliii, lix. In his letters, Ximenes is careful about references to Paracelsus.
 Neri 1608; Zecchin 1987–89, p. 157. “… che già stava in casa il s.r. Zanobi Bartolini, che mostra gl’ effetti di mali da lui guariti secondo gli ordini Paracelsici di grandissima meraviglia…” [that previously when in the house s.r. Zanobi Bartolini showed the effects on sicknesses that he healed using the instructions of the great and marvelous Paracelsus ....].
 Discorso sopra la Chimica, che cosa sia, e sue Operazioni, Neri 1613.
 Grazzini 1983, p. 221.
 For the original Italian, see Grazzini 2012.