Praxis

Praxis (PROSE: The Book of the War) or praxsis (PROSE: The Caves of Androzani) was a chemical compound that created spontaneous and temporary mutations of the Spiral Politic. (PROSE: The Book of the War)

The Doctor was allergic to gases in the praxis range. (TV: The Caves of Androzani, AUDIO: Planet X, A Heart on Both Sides, COMIC: Nurse Who?) As celery turned purple in praxis gas, the Fifth Doctor kept a sprig on his lapel to identify its presence. (TV: The Caves of Androzani)

Origins
A powerful urban myth grew around the few genuine documented cases of praxis in Earth's history. Many misunderstood it as a drug that created subjective hallucinations, and it was often called "the Holy Grail of hallucinogenics", but it was actually a compound of several elements that defied subatomic analysis and were unknown in the Spiral Politic's periodic table.

The only known producer of the drug was the Pilots' Coterie, whose members used it to distort the continuum in their calculations of space-time events for piloting ships like the Bababadalgharaghtakamminarronnkonnbronntonnerronntuonnthunntrovarrhounawnskawntoohoohoordenenthurnuk. Their praxis took the form of a tasteless gelatinous biomass, and humanoids needed to ingest at least 10 times their own body weight before it had any useful effect. However, there were many more efficient sources beyond the frontier in time.

House Xianthellipse sponsored the ruling caste of a posthuman colony to produce praxis for them; Robert Scarratt became addicted to the drug during his time working there. Under its influence, he (reportedly) single-handedly defused a local uprising caused by native resentment at the rulers' high-handed attitudes. In reality, his native contacts undoubtedly played a major role. (PROSE: The Book of the War)

Instances
The Saragossa manuscript, recovered in the early 19th century by Count Potocki, recounted von Worden's experience of false consciousness. The Rivera Manuscript described a similar praxis fugue, this time forced on a renegade of the Great Houses by the enemy. A note on the latter manuscript, written in English by an alien hand, said, "Praxis is not a drug. Praxis is not a weapon. Praxis is not a training manual. Praxis is what we were meant to become." (PROSE: The Book of the War)

Avus fell into a pool of praxis in an alter-time realm and experienced a fugue. (PROSE: Cobweb and Ivory)

The Eighth Doctor had a reaction to praxis gas during the Last Great Time War. (AUDIO: A Heart on Both Sides)

Octavia Sutherland once sent a group of Cousins into a disintegrating praxis-liner to rescue "some trinket". (PROSE: Warring States)

Godmother Antigone of Faction Paradox sent Cousin Rupert to Bankside to investigate Haribeaux's Blue Praxis experiments; however, these claims were merely an excuse to ensnare Rupert into Father Christèmas' plan. (PROSE: Weapons Grade Snake Oil)

An alien bomb, which by Sontaran interference arrived in ancient Greece and travelled to the British Museum, was booby trapped with praxis gas. When the Tenth Doctor deactivated the bomb, he was poisoned by the gas, but Elizabeth Garrett Anderson saved him with natural Quercetin in food and tea. (COMIC: Nurse Who?)

By 2154, IMC trooper Jason Dommer's throat had been scarred by praxis gas, making his voice scratchy and grating. (PROSE: Lucifer Rising)

The flechette guns of the Already Dead soldiers used compressed praxis gas. (PROSE: The Undertaker's Gift)

Behind the scenes

 * In The Caves of Androzani, "gases in the Praxis range" was a joke about the allergenic gasses that came from Eric Saward's Praxis 35 typewriter.
 * With its role in posthuman piloting, praxis is very similar to the drug from 's 1965 science fiction novel . The brief summary of Robert Scarratt's defusing of an uprising on the sole planet where praxis was produced closely mirrors the plot of Dune.