9 7 6 , ▁is ▁however ▁quite ▁complicated . ▁The ▁cor ne al ▁button ▁is ▁stored ▁in ▁an ▁inc ub ator ▁approximately ▁ 3 0 – 3 7   ° C ▁in ▁a ▁t issue ▁culture ▁medium ▁into ▁which ▁either ▁f etal ▁or ▁new - born ▁cal f ▁ser um , ▁ant ib iot ics ▁and ▁ant im yc ot ics ▁are ▁added . ▁The ▁cor ne al ▁cells ▁are ▁also ▁inject ed ▁with ▁de h yd rating ▁mac rom ole cules ▁to ▁maintain ▁hyd r ation , ▁this ▁causes ▁the ▁cor ne al ▁button ▁to ▁sw ell ▁to ▁approximately ▁twice ▁its ▁original ▁thick ness ▁during ▁storage . ▁During ▁storage , ▁the ▁medium ▁must ▁be ▁replaced ▁within ▁every ▁ 1 0 – 1 4 ▁days . ▁When ▁it ▁is ▁required ▁for ▁surg ery , ▁the ▁sw ol len ▁t issue ▁is ▁placed ▁in ▁a ▁de xt rin ▁containing ▁storage ▁medium ▁which ▁brings ▁down ▁the ▁sw elling ▁and ▁must ▁also ▁be ▁ins pected ▁under ▁strict ▁a se ptic ▁conditions . ▁ ▁Don or ▁selection ▁ ▁There ▁is ▁a ▁rig orous ▁criteria ▁for ▁don or ▁selection ▁as ▁it ▁is ▁essential ▁to ▁minim ise ▁possibility ▁of ▁disease ▁transmission . ▁This ▁criteria ▁focus es ▁on ▁med ial ▁medical ▁records ▁and ▁post - mort em ▁ser ological ▁tests ▁which ▁aim ▁not ▁to ▁eliminate ▁risk , ▁but ▁to ▁limit ▁risk ▁to ▁a ▁reasonable ▁level . ▁A ▁balance ▁between ▁safety ▁and ▁avail ability . ▁ ▁A ▁health ▁history ▁report ▁is ▁usually ▁used ▁however , ▁death ▁certificate ▁reports ▁and ▁data ▁from