R. J. ANDERSON1 gave the name ‘mycolic acid’ to a high-molecular weight fatty acid (m.p. 58°), isolated from the H 37 strain of Mycobacterium tuberculosis var. hominis. The structural features of mycolic acid, as elucidated by him, are as follows: its probable formula is C88H176O4, with one—COOH, one—OH and one—OCH3 group ; pyrolysis at 300° in a vacuum gives a volatile distillate (m.p. 88°), identified as n-hexacosanoic acid, C26H52O2. Chromic acid oxidation breaks up mycolic acid into smaller fragments, among which the following could be identified: stearic acid, n-hexacosanoic acid and hexadecane, 1, 16-dicarboxylic acid2.