1. Methylene blue injected intravenously in white rats is hyperthermizing or hypothermizing according to the environmental temperature.
2. It causes an increase in metabolism at 28°C. or above. At lower temperature it does not affect, or rather depresses, metabolism.
3. It does not seem likely that its hypermetabolic action is due to catalysis of cell oxidations.
4. In animals exposed to an atmosphere with a high partial pressure of oxygen, methylene blue causes pulmonary edema, much more rapidly than does oxygen alone.