The Phylogenetic Odyssey of the Erythrocyte. I. Hemoglobin: the Universal Respiratory Pigment

Hemoglobin is a molecular entity that is capable of reversibly binding and releasing oxygen in either extra- or intracellular milieus. It is present in scattered invertebrates in physical solution or in cellular sites while in vertebrates it is universally located in circulating erythrocytes. These cells serve as the vehicle for and otherwise foster the optimum utilization hemoglobin. Hemoglobin's variable sphere of respiratory activities can be viewed as reflecting the specific requirements for each organism in which it is observed. Once these concepts have been established and the advantages and limitations of its cytologic packaging recognized, the study of the erythrocyte as expressed in its dimensions, colligative aspects, geometry, internal morphology and pathologic variations can be approached in a purposeful manner.