. Adventures in radioisotope research;. Radioactive tracers; Radiobiology. 420 ADVENTURES IN RADIOISOTOPE RESEARCH follow that the half life-time of saturated fatty acids is less than one day and that of unsaturated fatty acids about two days ; our data indicate practically the same result, and days, respectively. A closer coincidence is hardly to be expected in view of the fact that even when comparing fatty acid turnover in the liver of rats of the same race, age and weight, very appreciable fluctuations appear. Ame- iOO 50- 25- icorporation of ac'efate "Cinto saturorecl faffy a
. Adventures in radioisotope research;. Radioactive tracers; Radiobiology. 420 ADVENTURES IN RADIOISOTOPE RESEARCH follow that the half life-time of saturated fatty acids is less than one day and that of unsaturated fatty acids about two days ; our data indicate practically the same result, and days, respectively. A closer coincidence is hardly to be expected in view of the fact that even when comparing fatty acid turnover in the liver of rats of the same race, age and weight, very appreciable fluctuations appear. Ame- iOO 50- 25- icorporation of ac'efate "Cinto saturorecl faffy acids '>..^oss of "c by saturated fatty acids -V Fig. 1. Rate of incorpo- ration of acetate C^* (PiHL et al.) and rate of loss of 1*0 by saturated fatty acids extracted from rat liver. ("Rise curve" and "Decay curve".) 4 days 100 ncorporation of acetate '^C into unsarurated fatty acids. Less of'*Cby unsaturated fatty acids 4 days Fig. 2. Rate of incorpo- ration of acetate "C (PiHL et al.) and rate of loss of "C by unsaturated fatty acids extracted from rat liver. lioration of purification or measuring methods would hardly lead to more accurate mean renewal times, such could be obtained only by investi- gating an appreciably larger number of animals. The significance of the data obtained is restricted, as both the satu- rated and unsaturated fatty acids represent a mixture of components having different turnover rates, some components of the unsaturated fatty acid mixture as linoleic or linoleic acid are not synthesized in the animal organism, and thus are not labelled. While Pihl and Bloch [8] state that the linoleic acid content of the rat liver is almost negligable, these authors find neutral fatty acids to contain 16 per cent, phospha- tide fatty acids and 8 per cent of linoleic acid. From the fatty acids ex- tracted from the liver of rabbits Popjak and Beeckmans [10] found that when the acetate was given to the animals for 20 hr the spec
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