Pugging

My church in Newton, MA is looking at HVAC upgrades, and had someone look at the state of insulation in the walls. Looking in two places, a carpenter found that there was a layer of plaster/lath in the middle of each bay. I found a description of another house with this sort of invisible wall, which one writer called "pugging" claiming it was a German building tradition. Pugging, according to a book from 1883, is rather putting plaster and horsehair between floors to dampen sound.