Abstract
The construction and use of a large continuous-flow ion-chamber is described which makes possible the continuous measurement of tracer levels of C14 in the expired air of cattle with a sensitivity of 0.005 fig/minute. The studies of acetate-l-C14 oxidation confirm Kleiber''s data and indicate rapid equilibrium of injected acetate with the acetate of the body pool and the rapid metabolic turnover of this pool. The entrance of the carboxyl carbon of acetate into pathways not leading directly to oxidation is indicated by the effect of body movement on the oxidation of this C and by the amount of this C oxidized in 3 hr.