17time from pool acetate to expired C02 as 60 minutes which is slightly shorter than the half life from the carboxyl carbon of acetate to C02 obtained in this investigation of 76.5 minutes. This result following equilibration during an infusion period is probably a better figure than that obtained following a single injection. The longer half life (135 min) of conversion from the methyl carbon of acetate to pool C02 found when 2-C14 acetate was infused, emphasizes the difference in the pathway of oxidation of the methyl carbon and of the carboxyl carbon of acetate.The biological half lives, as calculated from the fall of specific activity of body pool bicarbonate and from expired C02, are in excellent agreement. Thus, blood data may be used for studying the oxidative rates of acetate, eliminating the turnover time of the bicarbonate pool which otherwise masks the picture of oxidation in the animal body.Summary. The rates of oxidation of acetate to COa were estimated by using l-C14 and 2-C14 labeled acetate and measuring both blood and expired C1402. Following 1-C14 labeled acetate infusion, the half life of blood and expired C140a was about 76 minutes indicating a mean turnover time of acetate carboxyl to pool C02 of about 110 minutes.The half lives of 2-C14 labeled acetate were 135 minutes and 195 minutes respectively. The half life of the pool acetate was 1.2 minutes; turnover time 1.7 minutes; turnover rate 3.4 meq per hour and pool size 6.0 meq per sheep.

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