Ccliii. the Determination of Lactic Acid in Muscle

THE method generally employed for the determination of lactic acid consists in the removal of protein by tungstic acid or trichloroacetic acid, the subsequent removal of sugar by copper sulphate and lime, the oxidation of the lactic acid by permanganate to acetaldehyde which is distilled off and trapped in sodium bisulphite solution and finally the titration with iodine of the bound bisulphite. It is evident that the "lactic acid" will include any substance which escapes removal by the preliminary treatment and which is either itself volatile and capable of binding bisulphite or is oxidised to such a substance. The most obvious of possible interfering substances is methylglyoxal, which is volatile in steam, combines with bisulphite and has been found in muscle and other tissues by many workers. In fact, a simple experiment (Table I) shows