The furocoumarins useful for inactivation are primarily illustrated by the class of compounds referred to as psoralens, which includes psoralens and substituted psoralens where the substituents will be: alkyl, particularly having from 1 to 3 carbon atoms, e.g., methyl; alkoxy, particularly having from 1 to 3 carbon atoms, e.g., methoxy; and substituted alkyl having from 1 to 6, more usually from 1