Nanomedicine offers the prospect of powerful new tools for the treatment of human diseases and the improvement of human biological systems using molecular nanotechnology. This paper presents a theoretical nanorobot scaling study for artificial mechanical phagocytes of microscopic size; called "microbivores;" whose primary function is to destroy microbiological pathogens found in the human bloodstream using a digest and discharge protocol. The microbivore is an oblate spheroidal nanomedical device measuring 3.4 microns in diameter along its major axis and 2.0 microns in (...) diameter along its minor axis; consisting of 610 billion precisely arranged structural atoms in a gross geometric volume of 12.1 micron3. The device may consume up to 200 pW of continuous power while completely digesting trapped microbes at a maximum throughput of 2 micron3 of organic material per 30-second cycle. Microbivores are up to ~1000 times faster-acting than either natural or antibiotic-assisted biological phagocytic defenses; and are ~80 times more efficient as phagocytic agents than macrophages; in terms of volume/sec digested per unit volume of phagocytic agent. (shrink)