[Excerpt from a natural philosopher's notes]
For over a year, I've studied this cursed plague, collecting and dissecting rats by the thousands. Given their rapid gestation and maturation cycle, it's been possible to breed them for numerous generations.
The rodents themselves seem immune to the plague, but they pass it readily between members of their own species, perhaps through mites.
The bloods of the rats tells its own story, allowing me to gauge the number of generations that a given group of rats have lived with the plague. As such, a nagging question remains. The rats collected in the poorest parts of town, in the slums, exhibit the oldest strains of the plague. While those found near the docks - where the foreign, plague-bearing rats would presumably have entered our city - exhibit a younger strain of plague.
Could this mean that the rats were transported to the slums in some way that is not obvious?
I will continue my research. If nothing else, I am living proof that Sokolov's Elixir and Piero's Remedy are very effective at protecting against the plague, if one consumes enough of the stuff.