Research on the production of H²S by various species of the majority of the genuses of heterotrophic bacteria was carried out using a liverspleen medium with the bismuth indicator lately proposed by authors. 2) All bacterium species submitted to test on this medium were found capable of decomposing the sulphur compounds in the culture medium with the production of H²S. 3) It was found that all the heterotrophic bacteria produce H²S. 4) there were variations in the amounts produced by different strains of the same species, by different species of the same genus and by different genuses, calculatedby the greater or lesser darkening of the bismuth indicator. 5) There were also differences between the specimens tested as to the time taken for the production of H²S. 6) The expression < sulphydrigenous power > is proposed to designate the propertie of H²S production by bacteria.