▁to ▁the ▁other ▁t ube ▁to ▁allow ▁for ▁aer ob ic ▁conditions . ▁ ▁The ▁tub es ▁are ▁then ▁inc ub ated ▁for ▁ 2 4 – 4 8 ▁hours . ▁ ▁If ▁the ▁medium ▁in ▁the ▁an a er ob ic ▁t ube ▁turns ▁yellow , ▁then ▁the ▁b acter ia ▁are ▁fer ment ing ▁gl uc ose . ▁ ▁If ▁the ▁t ube ▁with ▁oil ▁doesn ' t ▁turn ▁yellow , ▁but ▁the ▁open ▁t ube ▁does ▁turn ▁yellow , ▁then ▁the ▁b acter ium ▁is ▁ox id izing ▁gl uc ose . ▁ ▁If ▁the ▁t ube ▁with ▁min eral ▁oil ▁doesn ' t ▁change , ▁and ▁the ▁open ▁t ube ▁turns ▁blue , ▁then ▁the ▁organ ism ▁neither ▁fer ments , ▁nor ▁ox id izes ▁gl uc ose . ▁ ▁Instead , ▁it ▁is ▁ox id izing ▁pe pt ones ▁which ▁liber ates ▁am mon ia , ▁turning ▁the ▁indicator ▁blue . ▁ ▁If ▁only ▁the ▁aer ob ic ▁t ube ▁has ▁turned ▁yellow ▁then ▁the ▁organ ism ▁is ▁able ▁to ▁ox id ase ▁gl uc ose ▁aer ob ically ▁(" O "). ▁ ▁By - products : ▁CO 2 ▁and ▁although ▁organ ic ▁ac ids ▁may ▁be ▁present ▁at ▁low ▁rates . ▁▁ ▁If ▁both ▁tub es ▁are ▁yellow ▁then ▁the ▁organ ism ▁is ▁capable ▁of ▁fer ment ation ▁(" F "). ▁▁ ▁If ▁there ▁is , ▁however , ▁growth ▁evident ▁on ▁the ▁aer ob ic ▁t ube ▁yet ▁the ▁medium ▁has ▁not ▁turned ▁yellow , ▁either ▁(