▁guard ed ▁and ▁so ▁deliber ate ▁well ▁poison ing ▁may ▁have ▁happened . ▁Although ▁no ▁proof ▁of ▁such ▁poison ing ▁has ▁been ▁found , ▁some ▁histor ians ▁believe ▁the ▁decrease ▁of ▁the ▁population ▁correl ates ▁with ▁the ▁end ▁of ▁religious ▁orders ' ▁control ▁of ▁the ▁water . ▁ ▁In ▁the ▁centuries ▁that ▁followed , ▁accus ations ▁and ▁discuss ions ▁of ▁bi ological ▁war fare ▁were ▁common . ▁Well - document ed ▁accounts ▁of ▁inc idents ▁involving ▁both ▁thre ats ▁and ▁acts ▁of ▁deliber ate ▁in fection ▁are ▁very ▁rare , ▁but ▁may ▁have ▁occurred ▁more ▁frequently ▁than ▁sch ol ars ▁have ▁previously ▁acknowled ged . ▁Many ▁of ▁the ▁instances ▁likely ▁went ▁un report ed , ▁and ▁it ▁is ▁possible ▁that ▁documents ▁rel ating ▁to ▁such ▁acts ▁were ▁deliber ately ▁destroyed , ▁or ▁san it ized . ▁By ▁the ▁middle ▁of ▁the ▁ 1 8 th ▁century , ▁colon ists ▁had ▁the ▁knowledge ▁and ▁technology ▁to ▁attempt ▁bi ological ▁war fare ▁with ▁the ▁small po x ▁virus . ▁They ▁well ▁understood ▁the ▁concept ▁of ▁quar antine , ▁and ▁that ▁contact ▁with ▁the ▁sick ▁could ▁inf ect ▁the ▁health y ▁with ▁small po x , ▁and ▁those ▁who ▁surv ived ▁the ▁ill ness ▁would ▁not ▁be ▁inf ected ▁again . ▁Whether ▁the ▁thre ats ▁were ▁carried ▁out , ▁or ▁how ▁effective ▁individual ▁attempts ▁were , ▁is ▁uncertain . ▁ ▁One ▁such ▁threat ▁was ▁delivered ▁by ▁fur ▁tr ader ▁James ▁Mc D oug all , ▁who ▁is ▁quoted ▁as ▁saying ▁to ▁a ▁gather ing ▁of ▁local