a) The addiction of liver-spleen extract to the medium with bismuth seems to have favored greatly the increase of the production of H²S by anaerobic clostridia. b) Bismuth added to the medium with liver-spleen extract showed greater sensibility to H²S than Spray’s medium with iron. c) The employment of the liver-spleen-cystine medium, with bismuth carbonate as indicator, revealed an markedely production of the H²S by all the anaerobi submitted to the H²S production test, which was not the case when iron was used as indicator of the test. d) Some species of clostridia have an earlier and more intense sulphidrigenous capacity than others. e) There are individual variations among anaerobes in their capacity for early production of hydrogen sulphide.