I. INTRODUCTION When the respiration calorimeter of the Russell Sage Institute of Pathology was originally planned one of the main problems in view was the study of the rise and fall of the body temperature in fever. For the first time it became possible to measure in the clinic practically all the factors which would tell the story as to what was taking place within the body. The preliminary work that was done in typhoid fever, with its comparatively slow changes in body temperature, demonstrated the extraordinary difficulty of the technic. One case of malaria studied that same year gave warning of the troubles to be encountered when the temperature fluctuations were rapid. It was for this reason that the main study of malaria was postponed until the calorimeter staff had been drilled four years and the technic and apparatus so improved that the problem seemed capable of solution. The