Before embarking on any consideration of the mutations undergone by witchers, let alone researching them, one should be aware of the specific physiology and biochemistry of these individuals. The transformations they experience during the Trial of the Grasses, which are widely considered to be irreversible, cause witchers to become infertile, while significantly increasing their physical strength and sharpening their senses. The processes also deprive witchers of emotions and human reflexes.
Although information about the Trial of the Grasses and other transformations to which young adepts of the witcher craft are subjected is strictly protected by master witchers and witcher sorcerers, Ludovic Cèlestin of Ban Ard claims the albumen of gray scolopendromorphs, the strain of giant centipede more commonly known as Pale Widows, constituted the basis of witcher mutagens. However, all research confirming this theory has been lost (...).