+--------------<---------------+ | | | | v | _Dead animal | protein_ | | | | | v | _Decomposition bacteria_ | | | | | | | v ^ | _H₂S_ | | | | | | | | v | | _Sulphur bacteria_ | | | | | | | | v | | _Free S_ | ^ | | | | | | v | | _Sulphur bacteria_ | | | | | | | | v | | _Sulphates | | in the | | soil_ | | | | | | | | v | | _Green plants_ ^ | | | | | | | v | | _Plant protein_----->_Dead plant | | protein_ | | | v | _Animals_ | | | | | +-------------->---------------+ FIG. 71.--Diagram to illustrate the circulation of sulphur through the agency of bacteria.]