Approximately one third of the mass of a mammalian red blood cell is hemo globin. Its major function is to bind oxygen at the partial pressure prevailing in the lungs and to release it to the tissues where the partial pressure is lower. The process whereby hemoglobin performs this essential physiological role is characterized by a cooperative interaction among its constituent subunits. A great deal of research effort has been devoted to this interaction, going back at least as far as the fitst decade of this century. Moreover, cooperativity in hemo globin is probably not unique; it may well...