The Amide Nitrogen of Blood.

Certain chemical changes are known to occur in muscle during, and immediately following, short periods of exercise. With respect to the alteration in the acid-base equilibrium under such conditions, some facts are definitely established. It has been shown by Barr and Himwich (1) that within a few minutes after exercise very considerable, amounts of plasma bicarbonate are neutralized by acid, and the finding of simultaneous increases in blood lactic acid of more than 500 per cent leaves no doubt that lactic acid as it issues from the muscles where it was formed, combines with base, and thus accounts for the lowering of the alkaline reserve as measured in blood. Liljestrand and Wilson (2) have shown that at such times there is a marked increase in the urinary excretion of lactic acid, although the amounts so lost to the body constitute but a small fraction of all the lactic acid which must be disposed of within a short period following muscular exercise. Unquestionably, resynthesis of the lactic acid precursor occurs, and this disposition of a considerable quantity of lactic acid is a rapid affair. The high concentrations of lactic acid found in blood shortly after exercise are of short duration, and the return to a normal level of blood lactic acid is the net result of the simultaneous accumulation and removal of lactic acid. The two processes proceed at different rates and in different places. Lactic acid formed in the muscles of the leg is disposed of in resting muscles elsewhere in the body (3). The whole cycle of events may take from 10 to 50 minutes after short periods of muscular exercise (1).