The first part of the program demonstrates the isolation of mitochondria in a sample of minced homogenized liver from a freshly-killed rat. The experiment demonstrates the crucial conditions of homogenization and the subjection of the homogenate to several stages of increasing centrifugation; the result is the separation of successively lighter organelles and debris. The second part of the experiment is devoted to measuring the uptake of oxygen. The reaction vessel contains a reaction medium, mitochondria, a substrate such as succinic acid, and ADP. All air above the medium is excluded by means of a perspex stopper. As the oxygen in the solution is consumed by the reactions in the mitochondria, the fall in the oxygen concentration is recorded on the chart-recorder. As other substances are introduced via a small hole in the perspex stopper, their effects on the reactions are recorded. (15 minutes)