The Determination of Lactic Acid.*

As the result of some experience in the determination of lactic acid in blood, muscle, and solutions of sugar derivatives, we have introduced various modifications in the process by which it gains considerably in simplicity, speed, convenience, and reliability. The basis of the method is the oxidation of the lactic acid in boiling sulfuric acid solution to acetaldehyde by permanganate (l), aeration of the aldehyde into large excess of sodium bisulfite solution, and titration of the combined bisulfite as described by Clausen (2). The chief modifications which we introduce are: (1) the form of apparatus used for the oxidation and for the collection of the aldehyde, (2) the addition of manganous sulfate to catalyze the oxidation by permanganate, and (3) more accurately defining the conditions for the titration of the sulfurous acid bound by the aldehyde. We have tested separately the several stages of the method and have checked it on known amounts of lactic acid in pure solution and after addition to blood. A number of other substances have been tested as to the extent of their interference in the determination of lactic acid. By the procedure as herein described the yield of aldehyde is consistently 96 to 98 per cent of the theoretical; and routine results are, in our hands, not subject to the variability and uncertainty commonly experienced with lactic acid determinations by older methods. The process is also much shorter in time and