 At that time, there was uncertainty between the substance of creosote – a chemical that had been used to treat wood used for railway ties and ships since it protected the wood from rotting – and carbolic acid.Upon hearing that creosote had been used for treating sewage, Lister began to test the efficacy of carbolic acid when applied directly to wounds.Therefore, Lister tested the results of spraying instruments, the surgical incisions, and dressings with a solution of carbolic acid.