A short period of incubation in oxygen increases the rate of anaerobic glycolysis in all the normal adult tissues that have been tested, with the exception of erythrocytes. 2. This stimulation does not occur in the six different tumours and in the two embryonic tissues that have been studied. 3. In rat liver and in chicken heart, stimulation is first seen at birth. 4. Stimulation in rat liver slices is decreased in the presence of some inhibitors of oxidative metabolism (cyanide, Amytal, dinitrophenol, malonate), but is not affected if the aerobic preincubation is carried out at 1 degrees . 5. The presence in the medium of some metabolites that are known to be important regulators of the glycolytic rate in living tissues has essentially no effect on stimulation. 6. The pretreatment of animals with inhibitors of oxidative metabolism and with antioxidants does not suppress stimulation; the observed effect of NN'-diphenyl-p-phenylenediamine is probably the consequence of the fall of the glycogen content in the liver. 7. The stimulation of anaerobic glycolysis by previous aerobiosis could not be demonstrated in liver homogenates.
