85 Essays on Infinite Lifespans   Robert A. Freitas Jr. Our natural white cells – even when aided by antibiotics – can sometimes take weeks or months to completely clear bacteria from the bloodstream. By comparison, a single terabot dose of microbivores should be able to fully eliminate bloodborne pathogens in just minutes or hours, even in the case of locally dense infections. Microbivores would be up to ~1000 times faster  acting  than  natural  leukocytes.  They’d  digest  almost 100 times more microbial material than an equal volume of natural white cells could digest, in any given time period. Even  more  powerful  applications  –  most  importantly, involving cellular replacement or repair – are possible with medical nanorobotics. For example, most diseases involve a molecular malfunction at the cellular level, and cell function is significantly controlled by gene expression of proteins. As a result, many disease processes are driven either by defec- tive chromosomes or by defective gene expression. So in many cases it may be most efficient to extract the existing chromo- somes from a diseased cell and insert fresh new ones in their place.  This  procedure  is  called  “chromosome  replacement therapy”. During this procedure, your replacement chromosomes are first manufactured to order, outside of your body, in a clinical benchtop production device that includes a molecular assem- bly  line.  Your  individual  genome  is  used  as  the  blueprint. If the patient wants, acquired or inherited defective genes could be replaced with nondefective base-pair sequences during the chromosome manufacturing process, thus permanently elimi- nating any genetic disease – including conditions related to aging. Nanorobots called chromallocytes [18], each carrying a single copy of the revised chromosomes, are injected into the body and travel to the target tissue cells. Following powered cytopenetration and intracellular transit to the nucleus, the chromallocytes remove the existing chromosomes and then install the properly methylated replacement chromosomes in