Powers, working on some marine fishes, arrived at the important conclusion that the ability of fishes to absorb oxygen at low pressures is more or less dependent upon the hydrogen ion concentration of the water. His method of research was briefly as follows: a fish was placed in a two-quart jar filled with water, which was closed airtight with a rubber stopper. The pH and the oxygen determinations were made immediately after all the movements of the fish had ceased. The amount of oxygen left at death represented, according to Powers, the pressure below which the fish at the particular pH could not extract any more oxygen from water. Powers did not control the amount of oxygen at the beginning of an experiment; he says, “it was always sufficiently high so that the fish did not at first suffer from oxygen want.”