Twenty nine of rabbits were divided into 3 groups; the first group for liver tissue incubation experiment, the second group for kidney incubation experiment and the third group for brain incubation experiment.
The same tissue slices obtained from each run of every group were subdivided, into 3 subgroups. Each subgroup was incubated for a period of 2 hours in the constant temperature water bath with incubation mixtures consisting of 10 cc of phosphate buffer and 20 cc of oxygen, to which were added Lactate-1- C^14 in the subgroup "a´, Lactate-2-C14 in the subgroup "b", Lactate-3-C^14 in the subgroup "c" respectively.
The gas samples and incubation medium obtained at the end of incubation period from each subgroup. were analysed for total C02 production rates; radio activities of CO2 produced and lactate disappearance rates.
Data obtained from each groups were summerized as follows.
1) The mean value of total C02 production rates were, 27.8±9.3 ?M/hr/gm in the first group, 43.6±7.8 in the second group and 45.3-6.7 in the third group. The fractions of C02 derived from C14-lactate to total C02 production were 23.9 % in the first group, 52.9 % in the second group and 63.9 % in the third group. These data explained that carbohydrate such-as lactate contribute a minor part for the release of their oxidative energy, in the liver tissues, however more than 50 % of oxidative energy were released by lactate in the kidney and brain tissues. .
2) In each subgroups of vrious. tissues, comparing the C14o2 production rates from each carbon of lactate, C1402 yielded from the subgroup "a" were generally larger than that from the subgroups "b and "c", This ´effect explaines that carboxyl carbon of lactate contribute larger part to produce the respiratory C02 from lactate in the various tissues. While, comparing the C1402 yielded from non carboxyl carbons of lactate in the subgroups "b" and "c" in each group, the C1402 derived yieled from ,carbon of lactate was larger than that from the carbon of lactate in the liver tissue. There were littledifference in C1402 yield ? from the and , carbon in the kidney tissue, but Ci402 yield from carbon. of lactate was larger than that from the carbon of lactate in the brain tissue. Possibe explanations, for these effects were briefly discussed.
3) The fractions of disappeared lactate from incubation medium into respiratory C02 which wered expressed by relative lactate disapperance (RLD) were 18.1 % in the first group, 43.5 % in the: second group and 43.2 % in the third-group.
Thus´ less than 20 % of disappeared lactate was oxidized into respiratory CO2 and remainder of lactate disappeared was incorporated into synthetic process in the liver tissue. More than 40´ %´ of lactate disappeared was, however, utilized to release of their oxidative energy in the kidney and brain tissues.
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