and the slant. Under anaerobic conditions (as occur toward the bottom of the tube) some bacteria use thiosulfate as an electron acceptor and reduce it to hydrogen gas. This is not very soluble and may accumulate as bubbles along the inoculation track, between the agar and the glass, or in the fluid which accumulates at the bottom of the slant. Hydrogen production may lift the agar from the butt of the tube or fracture the agar (crack the agar). Carbon dioxide, if produced, may not show as bubbles because it is far more soluble in the medium. See also Cystine tryptic agar References Biochemistry detection reactions Microbiological media