▁To ▁this ▁end , ▁the ▁ 3 R ▁( Rep lacement , ▁Re fin ement , ▁and ▁Red u ction ▁of ▁Anim als ▁in ▁Research ) ▁principle ▁proposed ▁by ▁Russell ▁and ▁B urch ▁in ▁ 1 9 5 9 ▁was ▁adopted . ▁ ▁By ▁using ▁animals ▁under ▁strict ▁quality ▁control ▁and ▁cont rolling ▁the ▁environment ▁so ▁that ▁the ▁animals ▁are ▁not ▁subject ed ▁to ▁stress , ▁it ▁is ▁possible ▁to ▁reduce ▁the ▁number ▁of ▁animals ▁used ▁in ▁experiments ▁( R edu ction ▁among ▁the ▁ 3 R s ). ▁ ▁It ▁is ▁also ▁possible ▁to ▁prevent ▁in fe ctions ▁such ▁as ▁mouse ▁he pat itis ▁or ▁Send ai ▁virus ▁through ▁periodic ▁monitoring ▁of ▁the ▁micro bi ological ▁status ▁of ▁animals ▁for ▁early ▁diagn osis ▁and ▁quality ▁ass urance ▁and ▁to ▁minim ize ▁dis com fort ▁of ▁the ▁animals ▁( Re fin ement ). ▁ ▁These ▁policies ▁are ▁intended ▁to ▁maintain ▁the ▁animals ▁in ▁a ▁normal ▁state ▁by ▁minim izing ▁stress . ▁ ▁If ▁the ▁animals ▁are ▁not ▁maintained ▁in ▁a ▁normal ▁state , ▁reprodu ci b ility ▁of ▁results ▁of ▁experiments ▁on ▁animals ▁as ▁" l iving ▁meas uring ▁instruments " ▁cannot ▁be ▁assured . ▁ ▁A ▁system ▁has ▁been ▁established ▁in ▁which ▁m ice ▁with ▁the ▁human ▁pol io ▁virus ▁re ceptor ▁introduced ▁( pol io ▁m ice ) ▁replace ▁mon keys , ▁which ▁are ▁closest ▁to ▁humans , ▁used ▁in ▁ne uro vir ul ence ▁testing ▁of ▁live ▁pol io ▁v acc ine ▁( Rep lacement ). ▁The ▁number ▁of ▁animals