People who regularly culture animal cells become so comfortable with standard techniques that novel approaches can seem contrived or even unnatural. However, the typical cycle of seeding cells at very low density in an excess of medium and harvesting (often quite aggressively) just before the point of medium exhaustion is quite an unphysiologic process. Popular culture systems often take cells that originally grew attached to a porous matrix at high densities, with little variability in nutrient and oxygen supply, and…