Studies in the biochemistry of micro-organisms LVII. Fumigatin (3-hydroxy-4-methoxy-2 : 5-toluquinone) and spinulosin (3 : 6-dihydroxy-4-methoxy-2 : 5-toluquinone), metabolic products respectively of Aspergillus fumigatus Fresenius and Penicillium spinulosum Thom