when certain forms of bacteria are subjected to starvation they are rendered fit to penetrate contaminated media whose surfacial pores would otherwise be too small for their size. Reaching the undersurface, shrunk bacteria resuscitate and accomplish a task hitherto unthought of. They create a barrier between the contaminated stretches of the medium and the rest of it so that the pollutant does not diffuse further. This property of the bacteria to create a