An Injector Pistol is the primary weapon of the Death Guard Plague Marines known as Biologus Putrifiers. Biologus Putrifiers take a very active role in spreading disease upon the field of battle, lobbing Blight Grenades or using their cursed Injector Pistols to spread their epidemics far and wide amongst the ranks of their foes as they receive the Plague God's virulent blessings. Yet to simply observe the effect of Nurgle's gifts is not their way; samples must be extracted, and tests must be run. This is when their Injector Pistols come into play. Striding into the midst of their reeling foe, the Putrifiers pick out the most intriguing entities to assail. Some look for the most resilient enemies upon the field of battle; others seek out the most easily infected, the bravest, the swiftest, or whatever other esoteric criteria they decide their test subjects must display.
With their victims selected, the Biologus Putrifiers strike. They fire their Injector Pistols into vulnerable spots such as exposed flesh, chinks in armour and eyelenses before squeezing a concentrated dose of foulness into the target's body. The results are rarely less than spectacular, with victims erupting in explosive boils, liquefying into screaming sludge, vomiting billowing clouds of flies, and countless other revolting -- and mercifully lethal -- symptoms. Those specimens whose deaths are especially fascinating are pierced with Injector Pistols once again, this time to extract whatever clotted foulness now passes for their blood, ready for later study.
- Codex Heretic Astartes - Death Guard (8th Edition), pp. 23, 34, 61, 79