UA crystals and precipitates. UA tends to crystallize on the grid, often starting with viruses as crystallization origin. Crystals come in many varieties. Some are small (Fig. S14) and feathery or appear as long black needles. Others are flat, large sheets (Figs. S15 and S16). One also observes, albeit rarely, membranaceous precipitates around phage particles. Viruses within crystals often appear as brilliant white structures of abnormally large size (Fig. S17) .