DEGRADATION OF METHAEMOGLOBIN BY HYDROGEN PEROXIDE 669 in the form of methaemoglobin, but was apparently accounted for as carboxyhaemoglobin after the addition of carbon monoxide and dithionite. 4. The green pigment is distinct from choleglobin, and its formation is not prevented by carbon monoxide, showing that oxyhaemoglobin is not an intermediate in the reaction. We wish to thank Mr B. A. Collett for technical assistance during a part of the work.