The experiments to be reported were undertaken in order to study the effects of varying degrees of hypoxia on the metabolism of the brain. Since formation of lactic acid and decomposition of phosphocreatine are known to occur in cerebral tissue under conditions of oxygen lack,1 it seemed pertinent to find the critical oxygen levels at which these changes begin. Gas mixtures low in oxygen were administered to dogs for periods of fifteen to sixty minutes, and chemical studies of parts of the cerebral cortex were made by the technic of freezing the brain in situ with liquid air prior to removal of specimens for analysis. The freezing suddenly stops all metabolic processes in the tissue and prevents the occurrence of postmortem changes. The resultant chemical pattern gives an indication of the metabolic conditions within the tissue at the time of freezing.
The cerebral arteriovenous differences in oxygen and carbon dioxide