Jared Diamond tells us more about rat by-product consumption in the Old West in Collapse:
In 1849, hungry gold miners crossing the Nevada desert noticed some glistening balls of a candy-like substance on a cliff, licked or ate the balls, and discovered them to be sweet-tasting, but then they developed nausea. Eventually it was realized that the balls were hardened deposits made by small rodents, called packrats. that protect themselves by building nests of sticks, plant fragments, and mammal dung gathered in the vicinity, plus food remains, discarded bones, and their own feces. Not being toilet-trained, the rats urinate in their nests, and sugar and other substances crystallize from their urine as it dries out, cementing the midden to a brick-like consistency. In effect, the hungry gold miners were eating dried rat urine laced with rat feces and rat garbage.
These middens are quite valuable to paleontologists interested in finding out about local vegetation in specific periods; they serve as rough-and-ready time capsules. Diamond seems to have an interest in rats as food sources; he also tells us in passing about recipes for laboratory rat that circulated among British scientists during the post-WW II period of food rationing.